**Biodiesel**



[35] Ballesteros M, Oliva JM, Negro MJ, Manzanares P, Ballesteros I. Ethanol from lignocel

**102**(2):1415-1424

90 Biofuels - State of Development

lulosic materials by a simultaneous saccharification and fermentation process (SFS) with *Kluyveromyces marxianus* CECT 10875. Process Biochemistry. 2003;**39**(12):1843-1848 [36] Redding AP, Wang Z, Keshwani DR, Cheng JJ. High temperature dilute acid pretreat

ment of coastal Bermuda grass for enzymatic hydrolysis. Bioresource Technology. 2011;

[37] Sun Y, Cheng JJ. Dilute acid pretreatment of rye straw and Bermuda grass for ethanol

production. Bioresource Technology. 2005;**96**:1599-1606

**Chapter 6**

**Provisional chapter**

**Review of Catalytic Transesterification Methods for**

**Review of Catalytic Transesterification Methods for** 

Attempts for improving the synthesis procedure of catalysts for fatty acid methyl ester production have been progressing for a considerable length of time. Biodiesel lessens net carbon dioxide emissions up to 78% with reference to conventional fuel. That is the reason for the improvement of new and operative solid catalysts necessary for inexhaustible and efficient fuel production. Homogenous base catalysts for transesterification is risky in light of the fact that its produces soap as byproduct, which makes difficult issues like product separation and not temperate for industrial application. In comparison, heterogeneous process gives higher quality FAME which can be effectively isolated and facilitate costly refining operations that are not required. A focus of this review article is to study and compare various biodiesel synthesis techniques that are being researched. The catalytic strength of numerous heterogeneous solid catalysts (acid and base), specially earth and transition metal oxides were also appraised. It was observed that catalytic proficiency relied upon a few factors, for example, specific surface area, pore size, volume and active site concentration at catalyst surface. This review article will give assistance in assortment of appropriate catalysts and the ideal conditions for biodiesel generation. **Keywords:** biodiesel, heterogeneous catalyst, fatty acid methyl ester, transition metals,

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Fatty acid methyl ester (FAME) commonly called biodiesel is a fuel derived from renewable sources suitable for use in conventional compress ion-ignition engines. The interest and

DOI: 10.5772/intechopen.75534

**Biodiesel Production**

**Biodiesel Production**

Ali Sadiq and Syed Danial Ali

**Abstract**

**1. Introduction**

Ali Sadiq and Syed Danial Ali

Sadia Nasreen, Muhammad Nafees,

Sadia Nasreen, Muhammad Nafees,

http://dx.doi.org/10.5772/intechopen.75534

vegetable oil, transesterification

Liaqat Ali Qureshi, Muhammad Shahbaz Asad,

Liaqat Ali Qureshi, Muhammad Shahbaz Asad,

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

#### **Review of Catalytic Transesterification Methods for Biodiesel Production Review of Catalytic Transesterification Methods for Biodiesel Production**

DOI: 10.5772/intechopen.75534

Sadia Nasreen, Muhammad Nafees, Liaqat Ali Qureshi, Muhammad Shahbaz Asad, Ali Sadiq and Syed Danial Ali Sadia Nasreen, Muhammad Nafees, Liaqat Ali Qureshi, Muhammad Shahbaz Asad, Ali Sadiq and Syed Danial Ali

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75534

#### **Abstract**

Attempts for improving the synthesis procedure of catalysts for fatty acid methyl ester production have been progressing for a considerable length of time. Biodiesel lessens net carbon dioxide emissions up to 78% with reference to conventional fuel. That is the reason for the improvement of new and operative solid catalysts necessary for inexhaustible and efficient fuel production. Homogenous base catalysts for transesterification is risky in light of the fact that its produces soap as byproduct, which makes difficult issues like product separation and not temperate for industrial application. In comparison, heterogeneous process gives higher quality FAME which can be effectively isolated and facilitate costly refining operations that are not required. A focus of this review article is to study and compare various biodiesel synthesis techniques that are being researched. The catalytic strength of numerous heterogeneous solid catalysts (acid and base), specially earth and transition metal oxides were also appraised. It was observed that catalytic proficiency relied upon a few factors, for example, specific surface area, pore size, volume and active site concentration at catalyst surface. This review article will give assistance in assortment of appropriate catalysts and the ideal conditions for biodiesel generation.

**Keywords:** biodiesel, heterogeneous catalyst, fatty acid methyl ester, transition metals, vegetable oil, transesterification

#### **1. Introduction**

Fatty acid methyl ester (FAME) commonly called biodiesel is a fuel derived from renewable sources suitable for use in conventional compress ion-ignition engines. The interest and

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

development of biofuels has grown exponentially over the last few years in response to the need to develop sustainable energy resources and to address climate change. Currently, biodiesel are the most successful fossil fuel supplements. Notwithstanding limited market share, biodiesel has several strong traits to make a considerable influence to energy portfolio propose that its usage will continue to raise in the forthcoming years. Many countries are promoting the use of biodiesel through government incentives and targets, and the production of biodiesel is increasing worldwide. Besides the obvious economic benefits, renewable fuels are also offering environmental benefits by reducing the greenhouse gas emission and increase the energy security of the country by plummeting necessity on foreign oil.

FAME is synthesized through the transesterification reaction of triglyceride and methanol. Transesterification is the process by which an ester is converted into another product over the exchange of the alkoxy moiety.

**3. Heterogeneousversus homogenous catalysis**

**Figure 2.** Biodiesel production path way by heterogeneous and homogeneous process.

partition and reuse [17].

**Figure 1.** Catalytic methods.

Catalyst fundamentally has a place with the classifications of homogeneous or heterogeneous. Homogeneous catalyst act in a soluble stage from the blend, while heterogeneous catalyst act in an alternate stage from the response blend. The outline of reactant process is given in **Figure 2**. Being in an alternate stage, heterogeneous impetuses have the upside of simple

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95

Heterogeneous catalyst is supplanting homogeneous catalyst because of hurdles in catalyst separation and waste disposal. [18]. The need for the neutralization step and subsequent disposal of neutralized salt in acid and base catalyzed reactions could be eliminated by replacing

Vegetable oils are attractive promising substitute to diesel fuel since they are inexhaustible in nature and can be produced locally and eco-friendly as well. All unsaturated fat sources, such as animal fats or plant lipids can be used in biodiesel production [1–5]. Edible vegetable oils like canola, soybean and corn have been utilized for biodiesel generation and observed to be great as a diesel substitute [6, 7]. The non-consumable vegetable oils such as *Madhuca indica*, *Jatropha curcas* and *Pongamia pinnata* are observed to be suitable for biodiesel synthesis under the test conditions researched. In perspective of the few focal points, vegetable oils have an incredible potential to supplant oil-based powers over the long haul [7–9].

#### **2. Transesterification methods**

Catalysis of transesterification can be done by catalytic, non-catalytic and enzymatic [8–11]. Non-catalytic transesterification mechanism takes place at supercritical conditions. These conditions entail a greater temperature and higher pressure, which is not an economically viable choice, for this reason catalytic transesterification approaches for biodiesel production are more commonly used and more vastly preferred [12]. Homogeneous catalysis may be basic, acidic or enzymatic in which basic catalysis of oils comprise alkaline, for example, potassium and sodium hydroxide, alkoxides summary of catalytic methods are given in **Figure 1**. At low temperature and pressure, basic catalysts have extraordinary activity rate in transesterification. Sulfuric, hydrochloric and sulfonic acids are the major acid catalysts [13, 14]; whereas homogeneous acids and bases have well-defined chemical properties; heterogeneous acid and bases exhibit a variety of sites; while heterogeneous catalysts can be categorized by the Bronsted or Lewis nature of sites, acid or base strength of sites and the texture of support [15, 16].

The base catalyzed transesterification process is primary viable heterogeneous process practiced now a days [11]. It has various mechanism which converts the triglycerides (TG) to FAME with the liberation of glycerol such as a byproduct [17, 18]. Specialists are seeking after new catalyst. Additionally, the limpidness of the required feedstock, reaction kinetics and postreaction processing is relying on the used catalyst [19].

Review of Catalytic Transesterification Methods for Biodiesel Production http://dx.doi.org/10.5772/intechopen.75534 95

**Figure 1.** Catalytic methods.

development of biofuels has grown exponentially over the last few years in response to the need to develop sustainable energy resources and to address climate change. Currently, biodiesel are the most successful fossil fuel supplements. Notwithstanding limited market share, biodiesel has several strong traits to make a considerable influence to energy portfolio propose that its usage will continue to raise in the forthcoming years. Many countries are promoting the use of biodiesel through government incentives and targets, and the production of biodiesel is increasing worldwide. Besides the obvious economic benefits, renewable fuels are also offering environmental benefits by reducing the greenhouse gas emission and increase

FAME is synthesized through the transesterification reaction of triglyceride and methanol. Transesterification is the process by which an ester is converted into another product over the

Vegetable oils are attractive promising substitute to diesel fuel since they are inexhaustible in nature and can be produced locally and eco-friendly as well. All unsaturated fat sources, such as animal fats or plant lipids can be used in biodiesel production [1–5]. Edible vegetable oils like canola, soybean and corn have been utilized for biodiesel generation and observed to be great as a diesel substitute [6, 7]. The non-consumable vegetable oils such as *Madhuca indica*, *Jatropha curcas* and *Pongamia pinnata* are observed to be suitable for biodiesel synthesis under the test conditions researched. In perspective of the few focal points, vegetable oils have an

Catalysis of transesterification can be done by catalytic, non-catalytic and enzymatic [8–11]. Non-catalytic transesterification mechanism takes place at supercritical conditions. These conditions entail a greater temperature and higher pressure, which is not an economically viable choice, for this reason catalytic transesterification approaches for biodiesel production are more commonly used and more vastly preferred [12]. Homogeneous catalysis may be basic, acidic or enzymatic in which basic catalysis of oils comprise alkaline, for example, potassium and sodium hydroxide, alkoxides summary of catalytic methods are given in **Figure 1**. At low temperature and pressure, basic catalysts have extraordinary activity rate in transesterification. Sulfuric, hydrochloric and sulfonic acids are the major acid catalysts [13, 14]; whereas homogeneous acids and bases have well-defined chemical properties; heterogeneous acid and bases exhibit a variety of sites; while heterogeneous catalysts can be categorized by the Bronsted or Lewis nature of sites, acid or base strength of sites and the

The base catalyzed transesterification process is primary viable heterogeneous process practiced now a days [11]. It has various mechanism which converts the triglycerides (TG) to FAME with the liberation of glycerol such as a byproduct [17, 18]. Specialists are seeking after new catalyst. Additionally, the limpidness of the required feedstock, reaction kinetics and

postreaction processing is relying on the used catalyst [19].

the energy security of the country by plummeting necessity on foreign oil.

incredible potential to supplant oil-based powers over the long haul [7–9].

exchange of the alkoxy moiety.

94 Biofuels - State of Development

**2. Transesterification methods**

texture of support [15, 16].

#### **3. Heterogeneousversus homogenous catalysis**

Catalyst fundamentally has a place with the classifications of homogeneous or heterogeneous. Homogeneous catalyst act in a soluble stage from the blend, while heterogeneous catalyst act in an alternate stage from the response blend. The outline of reactant process is given in **Figure 2**. Being in an alternate stage, heterogeneous impetuses have the upside of simple partition and reuse [17].

Heterogeneous catalyst is supplanting homogeneous catalyst because of hurdles in catalyst separation and waste disposal. [18]. The need for the neutralization step and subsequent disposal of neutralized salt in acid and base catalyzed reactions could be eliminated by replacing

**Figure 2.** Biodiesel production path way by heterogeneous and homogeneous process.

a homogeneous acid or base by a heterogeneous catalyst. This trend to switch homogeneous catalysts with heterogeneous catalysts is part of the drive toward green chemistry which in turn minimize waste and eliminate the need for harmful reactants. Comparison of catalysis for biodiesel production is given in **Table 1** which reveals that many industrial processes now operate with solid acid catalysts [19]. But fewer processes operate with solid bases, as solid bases are less prevalent than solid acids [20].

The homogeneous catalysts, commonly utilized for commercial processes, have some disadvantages, such as they cannot recycle, large amounts of waste water is being produced, produce low grade glycerol as byproduct. In other hand, the heterogeneous catalysis offers easy production and purification process with reference to economic and environment. Truth is told, a few scientists have announced the potential monetary focal points of the heteroge-

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Cost of biodiesel production by heterogeneous catalysts is 4–20% less then homogeneous catalysts. Preparation of new long-lasting heterogeneous catalysts with anticipated physical and chemical properties is one of the most important and eye-attracting emphases of the latest studies. This is the main reason for the production of new heterogeneous catalysts which are suitable for pure biodiesel from different type of fatty acids that have been produced and

However, numerous additional thought-provoking issues endure to be resolved until highly proficient solid catalysts can be industrialized. However, with a specific end goal to build up a superior comprehension of impetus outline for the transesterification procedure, distinctive heterogeneous incentive utilized for biodiesel generation has been considered and examined in this article. It can be concluded that each of these catalyst properties have remarkable effect on the transesterification reaction. The application of catalysts is for various kinds of oils, reaction parameters and there for stability of the catalysts are also incorporated in this discussion. It can be inferred that each of these catalyst properties have significant influences on the

**4. Biodiesel production with alkaline metal oxides and derivatives**

) and carboxylates (PbCH<sup>3</sup>

for biodiesel production from oil even if it have high concentration of FFA [13, 27, 28]. Several heterogeneous acids were also used and reported in literature (ion-exchange resin, metal oxides, heteropolyacids, etc.). However, three main drawbacks reported for the use of carboxylates catalyst are its work under high temperature and pressure (T > 190°C, P > 20 bar); purification of product is costly and not economical for industrial application. Supported sodium and potassium on larger surface area zeolite and alumina had given upto 85% conversion of

Presently, there are various alkali-based catalysts have been utilized as homogeneous and heterogeneous transesterification. Base catalyzed transesterification is substantially less time consuming with respect to acid catalyzed transesterification and it is regularly used technique for commercial purpose. Numerous solid alkali base metal oxides and there substrate have

COOH) have been used as catalyst

SO<sup>4</sup>

fame which is still lower as compare to solid base catalyst [6, 29, 30].

neous reactant process over the option homogeneous one [21–23].

appraised for FAME synthesis processes [24–26].

transesterification process.

**4.1. Acid catalyzed transesterification**

**4.2. Base catalyzed transesterification**

Homogeneous Lewis acid (H<sup>2</sup>


**Table 1.** Comparison of homogeneous, heterogeneous and enzymatic catalysis for biodiesel production.

The homogeneous catalysts, commonly utilized for commercial processes, have some disadvantages, such as they cannot recycle, large amounts of waste water is being produced, produce low grade glycerol as byproduct. In other hand, the heterogeneous catalysis offers easy production and purification process with reference to economic and environment. Truth is told, a few scientists have announced the potential monetary focal points of the heterogeneous reactant process over the option homogeneous one [21–23].

Cost of biodiesel production by heterogeneous catalysts is 4–20% less then homogeneous catalysts. Preparation of new long-lasting heterogeneous catalysts with anticipated physical and chemical properties is one of the most important and eye-attracting emphases of the latest studies. This is the main reason for the production of new heterogeneous catalysts which are suitable for pure biodiesel from different type of fatty acids that have been produced and appraised for FAME synthesis processes [24–26].

However, numerous additional thought-provoking issues endure to be resolved until highly proficient solid catalysts can be industrialized. However, with a specific end goal to build up a superior comprehension of impetus outline for the transesterification procedure, distinctive heterogeneous incentive utilized for biodiesel generation has been considered and examined in this article. It can be concluded that each of these catalyst properties have remarkable effect on the transesterification reaction. The application of catalysts is for various kinds of oils, reaction parameters and there for stability of the catalysts are also incorporated in this discussion. It can be inferred that each of these catalyst properties have significant influences on the transesterification process.

#### **4. Biodiesel production with alkaline metal oxides and derivatives**

#### **4.1. Acid catalyzed transesterification**

a homogeneous acid or base by a heterogeneous catalyst. This trend to switch homogeneous catalysts with heterogeneous catalysts is part of the drive toward green chemistry which in turn minimize waste and eliminate the need for harmful reactants. Comparison of catalysis for biodiesel production is given in **Table 1** which reveals that many industrial processes now operate with solid acid catalysts [19]. But fewer processes operate with solid bases, as solid

**Type Homogeneous catalysts Enzymatic catalysts Heterogeneous catalysts**

Very selective FFA are converted to

temperature, insensitive

Environmentally benign, noncorrosive, recyclable, fewer

Ease separation of products, higher selectivity, longer catalyst

simultaneously and insensitive to

Can be used in continuous fixed

Currently moderate conversion compare to high active basic

Mass transfer limitation due to the presence of three phase and

Basic catalysts require low FFA and anhydrous condition and pretreatments is required for high FFA feedstock

High alcohol to oil ratio required, high temperature and pressure Acidic catalysts: low acid site concentration, low microporosity, and high cost compared with basic types

disposal problems

Acid heterogeneous catalyze both esterification and transesterification

FFA and water Comparatively cheap

bed reactors

homogeneous

need well mixing

life

Higher yield than base

Can be implemented as homogeneous or heterogeneous catalysts

Enzyme is inhibited in the presence of methanol and may require additional supportive solvents to be used as a

Ease of separation products

biodiesel Low reaction

to water

catalysts

Expensive

medium

References [17, 24–27] [13, 17, 25, 28, 29] [13, 17, 24, 30–33]

**Table 1.** Comparison of homogeneous, heterogeneous and enzymatic catalysis for biodiesel production.

bases are less prevalent than solid acids [20].

96 Biofuels - State of Development

Advantage Modest operation conditions

Disadvantages Separation of waste problem after reaction

formation

reaction

Base catalyst give favourable kinetics: high activity and give high yield in short time Base catalysts are 4000 times faster reaction than acid catalyzed transesterification Basic methoxides are more effective than hydroxides Acid catalysts can be used for both esterification and transesterification simultaneously

Acid catalyst are preferred for low grade oils and are insensitive to FFA and water

Saponification, emulsion

Catalyst reuse not possible Limited to batch type of reactors Basic catalysts are sensitive to the presence of FFA and water High production cost compared with heterogeneous type Acid catalysts are corrosive and give very small reaction rate Acid catalysts require higher molar ratio of methanol to oil, higher temperature, concentration acid and more waste from neutralization

Homogeneous Lewis acid (H<sup>2</sup> SO<sup>4</sup> ) and carboxylates (PbCH<sup>3</sup> COOH) have been used as catalyst for biodiesel production from oil even if it have high concentration of FFA [13, 27, 28]. Several heterogeneous acids were also used and reported in literature (ion-exchange resin, metal oxides, heteropolyacids, etc.). However, three main drawbacks reported for the use of carboxylates catalyst are its work under high temperature and pressure (T > 190°C, P > 20 bar); purification of product is costly and not economical for industrial application. Supported sodium and potassium on larger surface area zeolite and alumina had given upto 85% conversion of fame which is still lower as compare to solid base catalyst [6, 29, 30].

#### **4.2. Base catalyzed transesterification**

Presently, there are various alkali-based catalysts have been utilized as homogeneous and heterogeneous transesterification. Base catalyzed transesterification is substantially less time consuming with respect to acid catalyzed transesterification and it is regularly used technique for commercial purpose. Numerous solid alkali base metal oxides and there substrate have


been used for homogeneous catalyzed transesterification (**Table 2**). The benefit of alkali base

**Catalyst Reaction time in hour Reaction temperature, °C Yield, % Reference** ZnO/Ba 1 65 95 [47] Na/hydrotalcite with pure oil 8 60 88 [90] Na/hydrotalcite with used oil 8 60 67 [90] KF/hydrotalcite 5 65 92 [76] KF/Ca–Al hydrotalcite 3 65 99 [77]

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Basic metal alkoxide, hydroxide and sodium and potassium carbonates are utilized as a part of alkali-based catalyzed transesterification process [31–37]. With virgin vegetable oil, basic catalyst typically show high performance. If oil have critical amount of unsaturated fats then these free unsaturated fats respond with the basic catalyst to produce soap that inhibit glycerol that restrain the division of biodiesel, glycerin and wash water [16, 38]. NaOH or KOH are generally utilized as catalyst for transesterification of triglycerides at atmospheric pressure and temperature. Evacuation of these catalyst is in fact troublesome and it adds additional cost to the final product [39, 40]. It was reported in may researches that alkaline metal are less expensive than metal alkoxides, however the action of alkaline metal alkoxides

ONa for the methanolysis) is more dynamic as catalyst, then soluble metal hydroxides

NaO, when alco-

NaO as catalyzed. While if we use homogeneous

(KOH and NaOH since the previous) give high yield in short time than the last mentioned.

of 333 K for 0.1 h. The reaction is very vigorous between a plant oil and CH<sup>3</sup>

that only 1% sodium hydroxide gives about 94% of FAME [41–45].

catalyst undergo fouling due to impurities in reaction mixture [48, 49].

Homogeneous base catalyst catalyzed transesterification of oil into FAME fast. Freedman et al. observed that only 1% sodium hydroxide gives 94% conversion of oil at the temperature

hol is being used as solvent. It takes 2–3 min for complete transesterification of triglycerides at

acid and base for transesterification, it takes 60–360 min at 303–338 K. Freedman et al. stated

However, water which is produced as byproduct caused during soap formation, as a result it becomes hard to recover catalyst and purification the products. Therefore, NaOH and KOH catalysts become slowly got replaced in coming eras by environmental friendly and long-lasting heterogeneous catalysts. However, these catalysts exhibit remarkable activity in esterification of FFA, but on the other hand they are not good in glycerides transesterification. Moreover a huge number of these catalysts get leached into product [46, 47]. In lot of cases,

Now a days, alkali oxides, alkaline oxide earth metals supported over large surface area are

catalysis requires a little amount in catalysis [8].

**Table 2.** Alkaline metal oxides catalysts used for the transesterification of oils.

room temperature (293–298 K) by using CH<sup>3</sup>

used for biodiesel production [50].

(CH<sup>3</sup>


**Table 2.** Alkaline metal oxides catalysts used for the transesterification of oils.

**Catalyst Reaction time in hour Reaction temperature, °C Yield, % Reference** Li/CaO 3 60 100 [87] Li-Al HTA 1 65 83 [88]

O<sup>2</sup> 1 60 91.6 [90]

O<sup>3</sup> 1 25–65 89 [85]

O<sup>3</sup> 2 60 65 [91]

O<sup>3</sup> 4 60 24.7 [90]

:NaOH 6 60 96.4 [39] NaOH 1 60 97 [79]

KOH/NaY 3 60 91.1 [64] Na/NaOH 1 60 70 [91]

NaO/NaX 1 65 28 [85] Ki/NaX 2 65 12.9 [6]

/Na/NaOH 2 60 83 [91] KI/SiO 8 70 90.9 [47]

O<sup>3</sup> 6 65 84 [26]

/MgO 2 70 99 [26]

KOH/MgO 7 100 99.4 [93]

doped in Li 2 min 120 100 [92]

O<sup>3</sup> 7 70 87 [47]

O<sup>3</sup> 3 60 96 [47]

O<sup>3</sup> 3 65 90 [66]

O<sup>3</sup> 2 60 91.1 [60]

O<sup>3</sup> 5 65 48 [47]

O<sup>3</sup> 5 65 84–87 [94]

O<sup>3</sup> 65 80.2 [47]

/KNO<sup>3</sup> 7 60 83 [47]

/KI 8 96 [16] ZnO/KF 9 65 87 [47]

KOH/NaX 60 82 [85] KX 60 82 [85] KI/ZnO 60 72.6 [47] Kf/ZnO 60 80 [47] Ki/ZrO 60 78.2 [47]

LiNO<sup>3</sup> /Al<sup>2</sup>

Na/NaOH/γ-Al<sup>2</sup>

98 Biofuels - State of Development

NaOH/Al<sup>2</sup>

NaNO<sup>3</sup> /Al<sup>2</sup>

Al<sup>2</sup> O3

KNO<sup>3</sup> /Al<sup>2</sup>

KAlSiO<sup>4</sup>

KNO<sup>3</sup> /Al<sup>2</sup>

KI/Al<sup>2</sup>

KF/Al<sup>2</sup>

KCO<sup>3</sup> /Al<sup>2</sup>

KNO<sup>3</sup> /Al<sup>2</sup>

Al<sup>2</sup> O3

Al<sup>2</sup> O3

KOH/Al<sup>2</sup>

KOH/Al<sup>2</sup>

K2 CO<sup>3</sup>

H2 SO<sup>4</sup>

> been used for homogeneous catalyzed transesterification (**Table 2**). The benefit of alkali base catalysis requires a little amount in catalysis [8].

> Basic metal alkoxide, hydroxide and sodium and potassium carbonates are utilized as a part of alkali-based catalyzed transesterification process [31–37]. With virgin vegetable oil, basic catalyst typically show high performance. If oil have critical amount of unsaturated fats then these free unsaturated fats respond with the basic catalyst to produce soap that inhibit glycerol that restrain the division of biodiesel, glycerin and wash water [16, 38]. NaOH or KOH are generally utilized as catalyst for transesterification of triglycerides at atmospheric pressure and temperature. Evacuation of these catalyst is in fact troublesome and it adds additional cost to the final product [39, 40]. It was reported in may researches that alkaline metal are less expensive than metal alkoxides, however the action of alkaline metal alkoxides (CH<sup>3</sup> ONa for the methanolysis) is more dynamic as catalyst, then soluble metal hydroxides (KOH and NaOH since the previous) give high yield in short time than the last mentioned.

> Homogeneous base catalyst catalyzed transesterification of oil into FAME fast. Freedman et al. observed that only 1% sodium hydroxide gives 94% conversion of oil at the temperature of 333 K for 0.1 h. The reaction is very vigorous between a plant oil and CH<sup>3</sup> NaO, when alcohol is being used as solvent. It takes 2–3 min for complete transesterification of triglycerides at room temperature (293–298 K) by using CH<sup>3</sup> NaO as catalyzed. While if we use homogeneous acid and base for transesterification, it takes 60–360 min at 303–338 K. Freedman et al. stated that only 1% sodium hydroxide gives about 94% of FAME [41–45].

> However, water which is produced as byproduct caused during soap formation, as a result it becomes hard to recover catalyst and purification the products. Therefore, NaOH and KOH catalysts become slowly got replaced in coming eras by environmental friendly and long-lasting heterogeneous catalysts. However, these catalysts exhibit remarkable activity in esterification of FFA, but on the other hand they are not good in glycerides transesterification. Moreover a huge number of these catalysts get leached into product [46, 47]. In lot of cases, catalyst undergo fouling due to impurities in reaction mixture [48, 49].

> Now a days, alkali oxides, alkaline oxide earth metals supported over large surface area are used for biodiesel production [50].

It was reported that alkaline metal are economical than metal alkoxides, but the activity of alkaline metal alkoxides (CH<sup>3</sup> ONa for the methanolysis) is higher then KOH and NaOH, since the former gives high yield in short reaction time than the latter. In industries, biodiesel is synthesized, now a days, by transesterification of oils in presence of solvent along with NaOH and NaOMe. The advantage of the homogeneously base catalyzed transesterification is that the reaction of transesterification is very fast and performed at room temperature. Glycerol and FAME are being separated by settling after catalyst neutralization followed by purification of crude glycerol and biodiesel [51].

and separation of product is costly and not economical. On the other hand use of heterogeneous acid catalyst can overcome this problems and could reduce economic issues and better

Hamed et al. reported the use of RSM response surface methodology as a statistic tool for study instruction among experimental variables and optimizing reaction condition [71]. Jeong et al. had reported 98% conversion of fame [54]. He used RSM to study animal fat transesterification at 65°C for 20 min, KOH (1.25 wt% 7.5:1 molar ratio of methanol and fat) [72].

According to literature, the production of methyl ester with extraordinary yield not only the choice of catalyst but also experimental conditions should be concerned, optimization of some reaction parameters and the application of those parameters are essential. Solid base catalyst synthesized by loading KNO3 aluminum oxide calcinated at 773 K for 5 h gives only 75% conversion by using 3.5% catalyst. While same method was used by Supper et al. in 2004 for

by using 1–3% w at 25–65°C and 1–3% w/w catalyst was found to attain conversion rate that

Heterogeneous catalysts possessing dual acidic and basic sites had been examined which could simultaneously esterify FFA and transesterify triglycerides (TG) to biodiesel [74]. Catalytic activity of Li/CaO has been stated by Watkins et al., where 100% FAME has been achieved 3 h at 60°C [75]. Shumaker et al. reported that Li-Al HTA was found to work efficiently and gives 65% yield only in 1 h reaction time [76]. Hernandez et al. used incorporated sodium hydrotalcite in Mg–Al mixed oxide. Sodium was incorporated as sodium acetate in Mg–Al mixed oxide calcite at 500°C for 8 h. He found that incorporation of sodium enhances the activity and it works at a low temperature (60°C) and with pure and used soybean oil. This

catalyst gives 88% conversion for pure soybean oil and 67% for used soybean oil [77].

**5. Biodiesel production with alkaline earth metals and metalloids**

Several attempts had been made in search for promising solid base alkali earth oxides catalyst such as CaO, SrO and BaO [78–81]. Magnesium oxide and salts based catalyst have been examined in past by different research. Early research has not showed satisfactory output, but far ahead on CaO and MgO were modified to acquire 99% yield and conversion of biodiesel. It was observed that preparation method, calcination and time of reaction and temperature and oil to methanol molar ratio have a great impact at biodiesel yield. Wang et al. used nanomagnesium oxide for transesterification of vegetable oil at 250°C reaction temperature for

MgO is very reactive at supercritical reaction condition giving upto 99% methyl ester. It was observed that reaction is finished in 10 min at 300°C by using methanol to oil molar ratio of

Venkat Reddy et al. used noncrystalline CaO for the conversion of poultry fat triglyceride into biodiesel. He observed 100% conversion of fame at 25°C with temperature with 1 mmol

catalyst. Supper et al. reported high conversion of soybean oil

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profitability of the biodiesel production process [68–70].

O3

was more then two orders of magnitude [73].

0.3 h reported biodiesel yield was 98% [82].

39.6:1. [83, 84].

preparing Na/NaOH/γ-Al<sup>2</sup>

However, during the transesterification reaction, certain amount of water is produced as byproduct which causes ester hydrolysis along with soap, as a result it become hard to purify product by separating the catalyst. Therefore, it is assumed that heterogeneous catalyst will replace conventional homogeneous catalysts. Homogeneous catalysts show good performances in FFA esterification, while their performance for glycerides transesterification is not suitable. Another drawback is that this catalyst leached into reaction mixture and showed rapid deactivation [66, 67]. Alkali salts supported on metal oxide such as KOH/Al<sup>2</sup> O3 KF/MgO exhibited good results for transesterification [52, 53].

Recently, numbers of heterogeneous catalysts such as ion-exchange resin CaO, alkylguanidines, KI/Al<sup>2</sup> O3 , Na/NaOH/Al<sup>2</sup> O3 , ionic liquid and lipase have been reported in literature for catalyzed transesterification of vegetable oils in presence of methanol [54–63].

Gao et al. prepared KF supported on hydro calcite by using co-precipitation techniques. It was observed that the formation of KMgF<sup>3</sup> and KAlF<sup>4</sup> enhance catalytic activity of catalyst. KF/hydro calcite gives 92% fame yield with 12:1 (alcohol to oil) molar ratio in 5 h reaction time at 65°C.

Gao et al. also study the percentage activity of KF supported at Ca–Al hydro calcite. He observed that catalytic activity is very satisfactory, about 99.7% yield can be obtained. It was assumed that this high output of 99.74% was due to the new crystal phases KCaF<sup>3</sup> , KCaCO<sup>3</sup> F and CaAl<sup>2</sup> F4 (OH) [64, 65]. KI loaded at mesoporous silica has been used as heterogeneous catalysis for conversion of TG in to FAME. It was observed that increase in reaction temperature and time enhances yield up to 90.09%. This highest yield ware obtained at 70°C, 15 wt.% of KI, within 8 h by using 5.0% by weight of the oil [34].

It was reported that biodiesel could be effectively produced by two-step process with ultrasonic radiation in less time. Xin deng in 2010 investigated two-step esterification and transesterification of jatropha oil in ultrasonic reactor. He used NaOH and H<sup>2</sup> SO<sup>4</sup> as catalyst at 60°C the reaction temperature. It was observed that 96.4% yield can be obtain just in 1.5 h by esterification of oil with H<sup>2</sup> SO<sup>4</sup> for 1 h and then subsequent transesterification by NaOH for 0.5 h [66].

Umer et al. used alkali catalyst for transesterification of sunflower oils to alkyl esters. They get 97.1% yield at 60.8°C by using 1%W catalyst. However, he observed that increase in catalyst concentration above 1 wt% has no effect at yield but it could add extra costs of production [67]. Sulfuric acid or hydrochloric acid used as homogeneous catalyst does not produce soap but the main problem in using these catalyst is corrosiveness and downstream purification and separation of product is costly and not economical. On the other hand use of heterogeneous acid catalyst can overcome this problems and could reduce economic issues and better profitability of the biodiesel production process [68–70].

It was reported that alkaline metal are economical than metal alkoxides, but the activity of

since the former gives high yield in short reaction time than the latter. In industries, biodiesel is synthesized, now a days, by transesterification of oils in presence of solvent along with NaOH and NaOMe. The advantage of the homogeneously base catalyzed transesterification is that the reaction of transesterification is very fast and performed at room temperature. Glycerol and FAME are being separated by settling after catalyst neutralization followed by

However, during the transesterification reaction, certain amount of water is produced as byproduct which causes ester hydrolysis along with soap, as a result it become hard to purify product by separating the catalyst. Therefore, it is assumed that heterogeneous catalyst will replace conventional homogeneous catalysts. Homogeneous catalysts show good performances in FFA esterification, while their performance for glycerides transesterification is not suitable. Another drawback is that this catalyst leached into reaction mixture and showed

Recently, numbers of heterogeneous catalysts such as ion-exchange resin CaO, alkylguani-

Gao et al. prepared KF supported on hydro calcite by using co-precipitation techniques. It

KF/hydro calcite gives 92% fame yield with 12:1 (alcohol to oil) molar ratio in 5 h reaction

Gao et al. also study the percentage activity of KF supported at Ca–Al hydro calcite. He observed that catalytic activity is very satisfactory, about 99.7% yield can be obtained. It was

catalysis for conversion of TG in to FAME. It was observed that increase in reaction temperature and time enhances yield up to 90.09%. This highest yield ware obtained at 70°C, 15 wt.%

It was reported that biodiesel could be effectively produced by two-step process with ultrasonic radiation in less time. Xin deng in 2010 investigated two-step esterification and trans-

60°C the reaction temperature. It was observed that 96.4% yield can be obtain just in 1.5 h by

Umer et al. used alkali catalyst for transesterification of sunflower oils to alkyl esters. They get 97.1% yield at 60.8°C by using 1%W catalyst. However, he observed that increase in catalyst concentration above 1 wt% has no effect at yield but it could add extra costs of production [67]. Sulfuric acid or hydrochloric acid used as homogeneous catalyst does not produce soap but the main problem in using these catalyst is corrosiveness and downstream purification

assumed that this high output of 99.74% was due to the new crystal phases KCaF<sup>3</sup>

esterification of jatropha oil in ultrasonic reactor. He used NaOH and H<sup>2</sup>

and KAlF<sup>4</sup>

(OH) [64, 65]. KI loaded at mesoporous silica has been used as heterogeneous

rapid deactivation [66, 67]. Alkali salts supported on metal oxide such as KOH/Al<sup>2</sup>

catalyzed transesterification of vegetable oils in presence of methanol [54–63].

ONa for the methanolysis) is higher then KOH and NaOH,

, ionic liquid and lipase have been reported in literature for

for 1 h and then subsequent transesterification by NaOH for

O3

enhance catalytic activity of catalyst.

SO<sup>4</sup>

KF/MgO

, KCaCO<sup>3</sup>

as catalyst at

F

alkaline metal alkoxides (CH<sup>3</sup>

100 Biofuels - State of Development

dines, KI/Al<sup>2</sup>

time at 65°C.

and CaAl<sup>2</sup>

0.5 h [66].

F4

esterification of oil with H<sup>2</sup>

O3

purification of crude glycerol and biodiesel [51].

exhibited good results for transesterification [52, 53].

of KI, within 8 h by using 5.0% by weight of the oil [34].

SO<sup>4</sup>

O3

, Na/NaOH/Al<sup>2</sup>

was observed that the formation of KMgF<sup>3</sup>

Hamed et al. reported the use of RSM response surface methodology as a statistic tool for study instruction among experimental variables and optimizing reaction condition [71]. Jeong et al. had reported 98% conversion of fame [54]. He used RSM to study animal fat transesterification at 65°C for 20 min, KOH (1.25 wt% 7.5:1 molar ratio of methanol and fat) [72].

According to literature, the production of methyl ester with extraordinary yield not only the choice of catalyst but also experimental conditions should be concerned, optimization of some reaction parameters and the application of those parameters are essential. Solid base catalyst synthesized by loading KNO3 aluminum oxide calcinated at 773 K for 5 h gives only 75% conversion by using 3.5% catalyst. While same method was used by Supper et al. in 2004 for preparing Na/NaOH/γ-Al<sup>2</sup> O3 catalyst. Supper et al. reported high conversion of soybean oil by using 1–3% w at 25–65°C and 1–3% w/w catalyst was found to attain conversion rate that was more then two orders of magnitude [73].

Heterogeneous catalysts possessing dual acidic and basic sites had been examined which could simultaneously esterify FFA and transesterify triglycerides (TG) to biodiesel [74]. Catalytic activity of Li/CaO has been stated by Watkins et al., where 100% FAME has been achieved 3 h at 60°C [75]. Shumaker et al. reported that Li-Al HTA was found to work efficiently and gives 65% yield only in 1 h reaction time [76]. Hernandez et al. used incorporated sodium hydrotalcite in Mg–Al mixed oxide. Sodium was incorporated as sodium acetate in Mg–Al mixed oxide calcite at 500°C for 8 h. He found that incorporation of sodium enhances the activity and it works at a low temperature (60°C) and with pure and used soybean oil. This catalyst gives 88% conversion for pure soybean oil and 67% for used soybean oil [77].

#### **5. Biodiesel production with alkaline earth metals and metalloids**

Several attempts had been made in search for promising solid base alkali earth oxides catalyst such as CaO, SrO and BaO [78–81]. Magnesium oxide and salts based catalyst have been examined in past by different research. Early research has not showed satisfactory output, but far ahead on CaO and MgO were modified to acquire 99% yield and conversion of biodiesel. It was observed that preparation method, calcination and time of reaction and temperature and oil to methanol molar ratio have a great impact at biodiesel yield. Wang et al. used nanomagnesium oxide for transesterification of vegetable oil at 250°C reaction temperature for 0.3 h reported biodiesel yield was 98% [82].

MgO is very reactive at supercritical reaction condition giving upto 99% methyl ester. It was observed that reaction is finished in 10 min at 300°C by using methanol to oil molar ratio of 39.6:1. [83, 84].

Venkat Reddy et al. used noncrystalline CaO for the conversion of poultry fat triglyceride into biodiesel. He observed 100% conversion of fame at 25°C with temperature with 1 mmol of 1 wt% catalyst). The reaction was performed for 7 h by using 70:1 molar ratio of methanol to triglyceride [85].

**Catalyst Reaction time in hour Reaction temperature, °C Yield, % Reference** Mgo 0.3 250 98 [99] Mgo/SiO<sup>2</sup> 5 220 96 [125]

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103

O<sup>4</sup> 10 65 57 [99]

O<sup>3</sup> 2.2 25 100 [104]

O<sup>3</sup> 3 180 92 [108]

O<sup>3</sup> 2 65 66 [108]

)<sup>2</sup> 3 60 99.9 [105]

)<sup>2</sup> 10 65 98 [115]

CaTiO<sup>3</sup> 10 60 79 [115] CaMnO<sup>3</sup> 10 60 92 [115]

CaCeO<sup>3</sup> 10 60 89 [115] SrO 0.5 65 95 [96]

CaO/ZnO 0.5 65 93.5 [105]

O<sup>5</sup> 10 60 92 [115] CaZrO<sup>3</sup> 10 60 88 [115]

O<sup>3</sup> 3 60 94.3 [39]

/ZnO 5 65 96 [119]

MgO/Cao 1 60 92 [108] Mgo-CaO 2 60 92 [114] CaO 1.5 75 91.1 [109] CaO 2 65 98 [110] Oyster shell 4 65 96 [111] Mud crab shell 2.5 65 98 [112] Egg shell 2 60 90 [113] Cao/SiO<sup>2</sup> 5 60 95 [114]

MgO-ZrO<sup>2</sup> 0.5 65 100 [103] MgO/CaO 1 60 92 [105] Mg-Al HTA 4 65 90.5 [125] Mg/Al/Zr 1.5 70 74 [91] Mg/Al HT 1 100 75 [91] Mg/Al 1 130 65 [91] MgO 1.5 75 12.1 [109] MgO-SBA-15 5 220 96 [125]

MgO-MgAl<sup>2</sup>

Mgo-La<sup>2</sup>

MgO/Al<sup>2</sup>

MgO/Al<sup>2</sup>

CaMg(CO<sup>3</sup>

Ca(OCH<sup>3</sup>

CaFe<sup>2</sup>

Ca(NO<sup>3</sup> ) 2 /Al<sup>2</sup>

Sr(NO<sup>3</sup> ) 2

Li et al. used MgO supported silica as a solid heterogeneous catalyst at 220°C for 5 h reaction time gives 96% biodiesel yield [80]. Additionally, magnesium oxide supported at high surface are metal like lanthinum, zirconium and aluminum have been screened for biodiesel production. Babu et al.l reported that magnesium oxide supported at zirconium oxide showed 100% yield in 30 min just at 65°C reaction temperature [86, 87].

Furthermore, Ngamcharussrivichai et al. used CaMg(CO<sup>3</sup> ) 2 as a catalyst for esterification of plant oil. They remarked that under 60°C in 3 h, the catalyst yielded optimum biodiesel yield of 99.9% [88, 116]. Takagaki et al. and Li et al. studied catalytic activity of magnesium- and aluminum-based metal oxides such as Mg-Al HTA, Mg/Al/Zr, Mg/Al HT, Mg/Al and MgO/ Al<sup>2</sup> O3 in the methanolysis of plant oil. Batch reactor was used for reaction for different combination at 65–130°C. The reaction time was from 1 to 4 h, resulting in yield of 65–90.5%. It was observed that Mg-Al HTA show high durability, ester product more than 90.5% and can be effectively used as heterogeneous base catalysts [89–91].

Serio et al. described the kinetics of MgO heterogeneously catalyzed methanolysis of soybean oil by using MgO/Al<sup>2</sup> O3 , MgO/Cao as catalyst. He observed 92% yield in the transesterification of soybean oil at 60°C within 2 h reaction time MgO/Cao catalyst [92]. Ochoa et al. and Liu at et al. used CaO as heterogeneous catalyst. It was observed that when CaO was calcination at 550°C temperature, 98% yield can be obtained at 60°C within reaction temperature and in 2 h reaction time [93, 94].

Nakatani et al. had used oyster shell as CaO source. He obtained 96% conversion of fame at 65°C for 4h reaction time. While Boey et al.l used mud crab shell as heterogeneous catalyst for transesterification of palm olein, the results showed 98% yield in 150 min at 65°C reflex temperature. Sarin et al. used seashell and eggshells as CaO source for TG conversion from different feed stocks. All this catalyst shows 98% FAME yield only in 60 min of reaction time [59, 95–97].

Albuquerque et al. used mesoporous silica supported by CaO as solid base catalyst for biodiesel production and gets 95% conversion in 5 h reaction at 60°C reaction temperature [98].

CaMg(CO<sup>3</sup> )2 and Ca(NO<sup>3</sup> )2 /Al<sup>2</sup> O3 were used as solid base catalyst by Ngamcharussrivichai et al., Benjapornkulaphong et al., for palm kernel oil transesterification at 60°C reaction temperature. They get 99.9 and 94% yield, respectively, after 3 h reaction time [26, 88]. Summary of alkaline earth metals and metalloids is given in **Table 3**.

Kouzu et al. [98] investigated the use of CaO as catalyst in a batch reactor at methanol reflux temperature for 2 h and achieved 93% biodiesel production. Kawashima et al. also discussed calcium oxide activity as catalyst along with its derivatives such as Ca(OCH3)<sup>2</sup> , CaTiO<sup>3</sup> , CaMnO<sup>3</sup> ,Ca<sup>2</sup> Fe<sup>2</sup> O5 , CaZrO<sup>3</sup> and CaO–CeO<sup>2</sup> for rapes oil transesterification of rapeseed oil. CaO were activated by methanol at 25°C for 1.5 h to increase basic strengths. The reaction mixture was refluxed for 10 h at 60°C. It was observed that Ca(OCH<sup>3</sup> )2 gives 98% yield among other derivatives the reason for highest yield of Ca(OCH<sup>3</sup> )2 is it had a remarkable basic strength in the range of 11.1–15.0 and these results demonstrated the reasons why Ca(OCH<sup>3</sup> )2


of 1 wt% catalyst). The reaction was performed for 7 h by using 70:1 molar ratio of methanol

Li et al. used MgO supported silica as a solid heterogeneous catalyst at 220°C for 5 h reaction time gives 96% biodiesel yield [80]. Additionally, magnesium oxide supported at high surface are metal like lanthinum, zirconium and aluminum have been screened for biodiesel production. Babu et al.l reported that magnesium oxide supported at zirconium oxide showed 100%

plant oil. They remarked that under 60°C in 3 h, the catalyst yielded optimum biodiesel yield of 99.9% [88, 116]. Takagaki et al. and Li et al. studied catalytic activity of magnesium- and aluminum-based metal oxides such as Mg-Al HTA, Mg/Al/Zr, Mg/Al HT, Mg/Al and MgO/

Serio et al. described the kinetics of MgO heterogeneously catalyzed methanolysis of soybean

tion of soybean oil at 60°C within 2 h reaction time MgO/Cao catalyst [92]. Ochoa et al. and Liu at et al. used CaO as heterogeneous catalyst. It was observed that when CaO was calcination at 550°C temperature, 98% yield can be obtained at 60°C within reaction temperature and

Nakatani et al. had used oyster shell as CaO source. He obtained 96% conversion of fame at 65°C for 4h reaction time. While Boey et al.l used mud crab shell as heterogeneous catalyst for transesterification of palm olein, the results showed 98% yield in 150 min at 65°C reflex temperature. Sarin et al. used seashell and eggshells as CaO source for TG conversion from different feed stocks. All this catalyst shows 98% FAME yield only in 60 min of reaction time

Albuquerque et al. used mesoporous silica supported by CaO as solid base catalyst for biodiesel production and gets 95% conversion in 5 h reaction at 60°C reaction temperature [98].

et al., Benjapornkulaphong et al., for palm kernel oil transesterification at 60°C reaction temperature. They get 99.9 and 94% yield, respectively, after 3 h reaction time [26, 88]. Summary

Kouzu et al. [98] investigated the use of CaO as catalyst in a batch reactor at methanol reflux temperature for 2 h and achieved 93% biodiesel production. Kawashima et al. also discussed

CaO were activated by methanol at 25°C for 1.5 h to increase basic strengths. The reaction

strength in the range of 11.1–15.0 and these results demonstrated the reasons why Ca(OCH<sup>3</sup>

calcium oxide activity as catalyst along with its derivatives such as Ca(OCH3)<sup>2</sup>

and CaO–CeO<sup>2</sup>

mixture was refluxed for 10 h at 60°C. It was observed that Ca(OCH<sup>3</sup>

other derivatives the reason for highest yield of Ca(OCH<sup>3</sup>

 in the methanolysis of plant oil. Batch reactor was used for reaction for different combination at 65–130°C. The reaction time was from 1 to 4 h, resulting in yield of 65–90.5%. It was observed that Mg-Al HTA show high durability, ester product more than 90.5% and can be

) 2

, MgO/Cao as catalyst. He observed 92% yield in the transesterifica-

were used as solid base catalyst by Ngamcharussrivichai

for rapes oil transesterification of rapeseed oil.

)2

)2

, CaTiO<sup>3</sup>

gives 98% yield among

is it had a remarkable basic

,

)2

as a catalyst for esterification of

yield in 30 min just at 65°C reaction temperature [86, 87].

Furthermore, Ngamcharussrivichai et al. used CaMg(CO<sup>3</sup>

effectively used as heterogeneous base catalysts [89–91].

O3

to triglyceride [85].

102 Biofuels - State of Development

oil by using MgO/Al<sup>2</sup>

[59, 95–97].

CaMg(CO<sup>3</sup>

CaMnO<sup>3</sup>

)2

,Ca<sup>2</sup> Fe<sup>2</sup> O5

and Ca(NO<sup>3</sup>

, CaZrO<sup>3</sup>

)2 /Al<sup>2</sup> O3

of alkaline earth metals and metalloids is given in **Table 3**.

in 2 h reaction time [93, 94].

Al<sup>2</sup> O3


temperature for 8 h, 67% conversion of fame ware reported at 9 h reaction time with methanol to oil ratio of 15:1. While Barakos reported 99% conversion of oil by using Mg–Al–CO<sup>3</sup>

perature for 6 h and methanol to oil molar ratio of reaction was 6:1 at 200°C reaction for 3 h

Transition metal oxides and chlorides are widely examined in several chemical reactions concerning their activity in plant oils transesterification. Transition metal complexes are also been

In literature, the best reported catalytic activity and strength were detected for the CaZrO<sup>3</sup>

alkene oxidation, alcohol dehydration and plant oils transesterification [16, 29, 112].

to 7th, and gave up to 80% yield in methyl esters were obtained within in 60 min reaction at 60°C by using 6:1 oil to methanol ratio. Possessing of variable Lewis acidity, metal oxidation state and ion radius size makes transition metal oxides and Oxo salts more suitable for transesterification catalysts. Due to their acidic properties, a lot of transaction metals like zinc, zirconium and titanium oxide are best among the transition metal oxides which are famous and broadly used for biodiesel synthesis. Past molybdenum- and tungsten-containing solids have been accounted in various reactions in which the acidity profile assumes essential parts in isomerization, cyclic

There have been a few research provided details regarding the utilization of sulfated zirconia as a strong catalyst for triglyceride conversion of various oils, because of its strong acidity it was discovered that the causticity is advanced when the surface of this zirconia metal contains anions of sulfate and tungstate. Catalytic activity of SO4 2-/ZrO2 was studied by Lam

area and active site number assume to be an essential part in the catalytic action.. Sulfated zirconia showed more activity in less time for conversion of oil into biodiesel than tungstated

Zinc(II) Shiff base complexes have been reported by martino as catalysts for biodiesel production from waste oil. He demonstrated that zinc(II) species can work in mild condition for catalyzing the triglyceride conversion of plant oil and activity could modified by a fine choice of the anions of the metals on the ancillary bidentate ligand. Homogeneous acid catalyst was widely studied in literature. Despite they have lower activity, yet strong acid catalyst have been utilized as a part of numerous modern commercial process since they contain a variety of acid sites with various quality of Bronsted or Lewis acridity. Nafion-NR50, tungstated, sulfated zirconia and zirconia possesses sufficient acid site and had been used in transesterification. Nafion were found to be the best, among these catalyst, because of their acid Nafion has hindrances of high cost and lower activity contrasted with liquid acids so it is

not exceptionally practical catalyst for commercial application [115–117].

was studied by Sunita. It was accounted for that the specific surface

heterogenized catalysts. It is found that Zr and Ce catalyst endured highly active up

**6. Biodiesel production from transition metals, lanthanide actinides** 

studied in literature as active materials for esterification reactions. [111].

hydrotalcite calcinated at 350°C tem-

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Review of Catalytic Transesterification Methods for Biodiesel Production

and

105

hydrotalcite as catalyst. He has calcinated Mg–Al–CO<sup>3</sup>

[6, 91, 107–110].

CaOCeO<sup>2</sup>

et al., and WO<sup>3</sup>

zirconia [113, 114].

/ZrO<sup>2</sup>

**and their derivatives**

**Table 3.** Alkaline earth metals and metalloids catalysts used for the transesterification of oils.

exhibited a greater catalytic activity than CaO and Ca(OH)<sup>2</sup> for others the resulting yield is from 79 – 90%. CaZrO<sup>3</sup> and CaO–CeO<sup>2</sup> exhibit high durability and it can be used in future as heterogeneous catalyst [99].

Application of strontium oxide- and nitrate-based catalyst is also reported in literature, there reported order of activity observed to be BaO > SrO > -CaO > MgO [100].

In past, the activity of MgO, CaO and SrO were are studied by different researcher for biodiesel productions and the observed conversion efficiency of followings ranging from 90 to 95% Liu et al. reported the use of SrO for transesterification of soybean oil. It is examined that SrO gives 95% yield in just 30 mins reaction time and at 65°C temperature as reported by Liu et al.[86, 101–103].

The catalytic efficiency of activated Sr(NO<sup>3</sup> )2 /ZnO was also examined by Yanz et al., the catalyst was prepared by using 2.5 mmol of strontium nitrate Sr(NO<sup>3</sup> ) 2 /g on ZnO by wet impregnation process followed by calcination at 600°C for 5 h. Transesterification of soybean oil was carried out in batch reactor at 65°C 12:1 methanol:oil molar ratio. Under this condition, reaction was complete in 5 h by giving 96% conversion of FAME [104].

Alkali metal hydrotalcite is another group catalyst which has been used extensively for triglyceride conversion into FAME. Hydrocalcite are important as their acidic and basic properties can be monitored by fluctuating their composition and hence can be used for fatty acid methyl ester production. Helwani et al. and Zabeti reported use of hydrotalcites as catalyst for the production of biodiesel. Magnesium-based hydrotalcite are common and mostly synthesized by co-precipitation method [24, 50, 105].

Most commonly hydrocalcite has three groups of basic sites, like weak basic site(OH), medium basic site (oxygen in metal oxide) and strong basic sites (O<sup>2</sup> anions) present in hydrocalcite [106].

Hydrocalcite possesses large pore than the normal metal oxides, the large pro size of this hydrocalcite results in higher catalytic then normal common metal oxides. Magnesium and aluminum-based hydrocalcite have been reported in literature. Mg-based hydrocalcite showed optimum activity from 350 to 600°C calcination temperature. Xie et al. reported Mg-Al-based hydrocalcite for transesterification of plant oil. It was observed that at high calcination temperature catalyst become deactivated. The hydrocalcite calcinated at 500°C temperature for 8 h, 67% conversion of fame ware reported at 9 h reaction time with methanol to oil ratio of 15:1. While Barakos reported 99% conversion of oil by using Mg–Al–CO<sup>3</sup> hydrotalcite as catalyst. He has calcinated Mg–Al–CO<sup>3</sup> hydrotalcite calcinated at 350°C temperature for 6 h and methanol to oil molar ratio of reaction was 6:1 at 200°C reaction for 3 h [6, 91, 107–110].

#### **6. Biodiesel production from transition metals, lanthanide actinides and their derivatives**

exhibited a greater catalytic activity than CaO and Ca(OH)<sup>2</sup> for others the resulting yield is

**Catalyst Reaction time in hour Reaction temperature, °C Yield, % Reference** Mg–Al hydrotalcite 9 65 67 [6]

Mg–Al hydrotalcites 4 65 90 [124] Mg–Al hydrotalcite 6 100 96 [124] Mg–Co–Al–La 5 200 97 [125]

hydrotalcite 3 180–200 99 [122]

Application of strontium oxide- and nitrate-based catalyst is also reported in literature, there

In past, the activity of MgO, CaO and SrO were are studied by different researcher for biodiesel productions and the observed conversion efficiency of followings ranging from 90 to 95% Liu et al. reported the use of SrO for transesterification of soybean oil. It is examined that SrO gives 95% yield in just 30 mins reaction time and at 65°C temperature as reported by Liu

)2

nation process followed by calcination at 600°C for 5 h. Transesterification of soybean oil was carried out in batch reactor at 65°C 12:1 methanol:oil molar ratio. Under this condition, reac-

Alkali metal hydrotalcite is another group catalyst which has been used extensively for triglyceride conversion into FAME. Hydrocalcite are important as their acidic and basic properties can be monitored by fluctuating their composition and hence can be used for fatty acid methyl ester production. Helwani et al. and Zabeti reported use of hydrotalcites as catalyst for the production of biodiesel. Magnesium-based hydrotalcite are common and mostly syn-

Most commonly hydrocalcite has three groups of basic sites, like weak basic site(OH),

Hydrocalcite possesses large pore than the normal metal oxides, the large pro size of this hydrocalcite results in higher catalytic then normal common metal oxides. Magnesium and aluminum-based hydrocalcite have been reported in literature. Mg-based hydrocalcite showed optimum activity from 350 to 600°C calcination temperature. Xie et al. reported Mg-Al-based hydrocalcite for transesterification of plant oil. It was observed that at high calcination temperature catalyst become deactivated. The hydrocalcite calcinated at 500°C

exhibit high durability and it can be used in future as

/ZnO was also examined by Yanz et al., the cata-

/g on ZnO by wet impreg-

anions) present in

) 2

and CaO–CeO<sup>2</sup>

reported order of activity observed to be BaO > SrO > -CaO > MgO [100].

**Table 3.** Alkaline earth metals and metalloids catalysts used for the transesterification of oils.

lyst was prepared by using 2.5 mmol of strontium nitrate Sr(NO<sup>3</sup>

tion was complete in 5 h by giving 96% conversion of FAME [104].

medium basic site (oxygen in metal oxide) and strong basic sites (O<sup>2</sup>

from 79 – 90%. CaZrO<sup>3</sup>

Mg–Al–CO<sup>3</sup>

104 Biofuels - State of Development

et al.[86, 101–103].

hydrocalcite [106].

The catalytic efficiency of activated Sr(NO<sup>3</sup>

thesized by co-precipitation method [24, 50, 105].

heterogeneous catalyst [99].

Transition metal oxides and chlorides are widely examined in several chemical reactions concerning their activity in plant oils transesterification. Transition metal complexes are also been studied in literature as active materials for esterification reactions. [111].

In literature, the best reported catalytic activity and strength were detected for the CaZrO<sup>3</sup> and CaOCeO<sup>2</sup> heterogenized catalysts. It is found that Zr and Ce catalyst endured highly active up to 7th, and gave up to 80% yield in methyl esters were obtained within in 60 min reaction at 60°C by using 6:1 oil to methanol ratio. Possessing of variable Lewis acidity, metal oxidation state and ion radius size makes transition metal oxides and Oxo salts more suitable for transesterification catalysts. Due to their acidic properties, a lot of transaction metals like zinc, zirconium and titanium oxide are best among the transition metal oxides which are famous and broadly used for biodiesel synthesis. Past molybdenum- and tungsten-containing solids have been accounted in various reactions in which the acidity profile assumes essential parts in isomerization, cyclic alkene oxidation, alcohol dehydration and plant oils transesterification [16, 29, 112].

There have been a few research provided details regarding the utilization of sulfated zirconia as a strong catalyst for triglyceride conversion of various oils, because of its strong acidity it was discovered that the causticity is advanced when the surface of this zirconia metal contains anions of sulfate and tungstate. Catalytic activity of SO4 2-/ZrO2 was studied by Lam et al., and WO<sup>3</sup> /ZrO<sup>2</sup> was studied by Sunita. It was accounted for that the specific surface area and active site number assume to be an essential part in the catalytic action.. Sulfated zirconia showed more activity in less time for conversion of oil into biodiesel than tungstated zirconia [113, 114].

Zinc(II) Shiff base complexes have been reported by martino as catalysts for biodiesel production from waste oil. He demonstrated that zinc(II) species can work in mild condition for catalyzing the triglyceride conversion of plant oil and activity could modified by a fine choice of the anions of the metals on the ancillary bidentate ligand. Homogeneous acid catalyst was widely studied in literature. Despite they have lower activity, yet strong acid catalyst have been utilized as a part of numerous modern commercial process since they contain a variety of acid sites with various quality of Bronsted or Lewis acridity. Nafion-NR50, tungstated, sulfated zirconia and zirconia possesses sufficient acid site and had been used in transesterification. Nafion were found to be the best, among these catalyst, because of their acid Nafion has hindrances of high cost and lower activity contrasted with liquid acids so it is not exceptionally practical catalyst for commercial application [115–117].

Most transition metal are expensive and heterogeneous catalyst of these metal need high temperature and pressure to achieve high conversion of oil. It was found that pure and mixed ZnO exhibits the conversion efficiency ranging from 90 to 95%. while strontium loaded at fly ash ZnO-La<sup>2</sup> O3 and zinc aluminate have been reported. WO<sup>3</sup> /ZrO<sup>2</sup> and Sr(NO<sup>3</sup> ) 2 /ZnO have been used for the canalization of plant activity of zirconium and tungsten oxide investigated by Lopez et al. had found that the calcination temperatures impact on synergist properties of catalyst, concluded that more strong catalyst could be acquired after calcination at 800°C (with the development of Bronsted acid sites centralization of 161 μmol/g). At 2.5 h reaction time at 200°C reaction temperature, the methyl ester yields within the sight of WO3/ZrO2/ MCM-41 were 85% [38, 111, 118–120].

effective for transesterification at 65°C and attain a remarkable yield exceeded 94.1% at a reaction time of 1 h [136, 137]. Summary of biodiesel production from transition metals, lantha-

tion. They had studied several reaction parameters carried out at optimal transesterification.

O<sup>3</sup> 0.5 200 99 [153, 154]

O<sup>4</sup> 8 60 90 [142]

O<sup>3</sup> 3 180 80 [128]

O<sup>3</sup> Continuous run 200 90 [158]

/MCM-41 2.5 200 85 [159]

O<sup>3</sup> Continuous run 250 97 [81]

/ZrO<sup>2</sup> 5 200 97 [129]

/ZrO<sup>2</sup> Continuous run 250 95 [16] MnCex 5 140 87 [157]

H3PW12O40/ZrO2 10 200 77 [130] H3PW12O40/Ta2O5 24 65 65 [160] Cs25H3PW12O40 1 65 96 [131] MnO-TiO 0.35 260 92 [161] Fe-Zn 5h 170 99 [150] CaMnO<sup>3</sup> 10 60 75 [75]

/PO4 3- 5 200 69 [162]

/CaO 1 60 94.3 [126]


/WO<sup>3</sup> 20 75 85 [163]

O 1 150 80 [15]

/La3+ 5 60 95 [128, 156]

ZnO/CaO 1 60 94.2 [105]

ZrO<sup>2</sup> 1 200 64.5 [131] SO4 2-/ZrO<sup>2</sup> 1 200 90 [128] SO4 2-/TiO<sup>2</sup> 1 20 40 [127] SO4 2-/SnO<sup>2</sup> 3 180 65 [155]


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107

**Reaction temperature, °C Yield, % Reference**


nide actinides is given in **Table 4**.

They concluded that CeO<sup>2</sup>

97% yield [138].

ZnO-Al<sup>2</sup>

SO4 2-/SnO<sup>2</sup>

SO4 2-/SnO<sup>2</sup>

SO4 2-/ZrO<sup>2</sup>

ZrO<sup>2</sup> /Al<sup>2</sup>

WO<sup>3</sup>

TiO<sup>2</sup>

WO<sup>3</sup> /ZrO<sup>2</sup> /Al<sup>2</sup>

WO<sup>3</sup> /ZrO<sup>2</sup>

Al<sup>2</sup> O3

Al<sup>2</sup> O3 /ZrO<sup>2</sup>

La<sup>3</sup> O3

CeO<sup>2</sup>

VOPO<sup>4</sup> ·2H<sup>2</sup> +Fe<sup>3</sup>

+Al<sup>2</sup>


Thitsartarn et al. examined the use of CeO<sup>2</sup>

**Catalyst Reaction time in** 

**hour**

A variety of transition metal-based solid acids SO<sup>4</sup> /ZrO<sup>2</sup> –Al<sup>2</sup> O3 SO<sup>4</sup> /ZrO<sup>2</sup> , WO3/ZrO<sup>2</sup> , SO<sup>4</sup> /TiO<sup>2</sup> , and Nafion had already been tested for esterification and their catalytic efficiency for esterification and transesterification of free fatty acid and triglycerides [112, 121–126].

According to the literature, microwave heating along with barium, alumina, silica, zinc aluminate and zirconium-based catalysts are good catalyst for biodiesel production (Portnoff et al., 2005; Bournay et al; Ondrey et al., 2004). By using different approach, utilization of sulfated transition metal oxides such as SO<sup>4</sup> /TiO<sup>2</sup> , SO<sup>4</sup> /ZrO<sup>2</sup> , SO<sup>4</sup> 2-/SnO<sup>2</sup> + Fe<sup>3</sup> O4 and SO<sup>4</sup> / SnO<sup>2</sup> is also reported in literature as a good catalyst [116]. Zhai et al. reported 90% activity of SO<sup>4</sup> 2-/SnO<sup>2</sup> + Fe<sup>3</sup> O4 catalyst at 60°C reaction temperature for 8 h reaction while Lam et al. reported 90% activity of SO4 2-/ZrO2 catalyst 200°C in 1 h reaction time [113, 127–129]. In acid catalyzed reaction, heteropoly tungstate was found as active catalysts for pure and waste oil. Zirconia (ZrO<sup>2</sup> ), silica (SiO<sup>2</sup> ) and alumina (Al<sup>2</sup> O3 ) support could be used to produce heterogeneous HPAs. HPAs supported at Cs+, NH4+ are also very active and useful as acid catalyst. Chai et al. who investigated the activity of Cs25H3PW12O40 has reported 96% conversion of FAME in 65°C reaction for 1 h [115, 116, 129–131]. In previous research, the activity of acids fall in CsHPW >20%WO<sup>3</sup> /ZrO<sup>2</sup> > 20%HPW/Al<sup>2</sup> O<sup>3</sup> > 20%HPW/ ZrO2 > 20%HPW/SiO2 order [47, 131–134].

Zirconium, hafnium and antimonium-based transition metal catalyst were also being studied by researchers in past for transesterification. Porous zirconia, titania and alumina microsphere stabilized chemically, thermally and mechanically have been investigated by Clayton et al. [30]. Yan et al. tested Fe–Zn catalyst methanolysis of vegetable oil (using 1:15 molar ration of methanol at 170°C, by using catalyst in amount of 3 wt.% showed TG conversion more than 99% within 5 h of reaction). It was assumed that the catalyst activity was endorsed due to the Lewis acid active sites of probably Zn2+ on the surface of catalyst [135].

Serio et al. studied solid acid vanadium phosphate catalyst for biodiesel synthesis, it was observed that the methyl ester yields reached 80% at 150°C within 60 min using 0.2 wt.% of the catalyst under and 1:1 of alcohol/oil molar ratio. However, the catalyst could be recycled after regeneration at high temperature [15].

Lee and Shiro used ZnO–La<sup>2</sup> O3 , which combines acid (ZnO) and base sites (La<sup>2</sup> O3 ) for transesterification of oil they got high conversion of 96% TG in 180 min. Yan el al. used calcium oxides modified with lanthanum (La<sup>3</sup> O3 /CaO) and observed that this catalyst is particularly effective for transesterification at 65°C and attain a remarkable yield exceeded 94.1% at a reaction time of 1 h [136, 137]. Summary of biodiesel production from transition metals, lanthanide actinides is given in **Table 4**.

Most transition metal are expensive and heterogeneous catalyst of these metal need high temperature and pressure to achieve high conversion of oil. It was found that pure and mixed ZnO exhibits the conversion efficiency ranging from 90 to 95%. while strontium loaded at fly

been used for the canalization of plant activity of zirconium and tungsten oxide investigated by Lopez et al. had found that the calcination temperatures impact on synergist properties of catalyst, concluded that more strong catalyst could be acquired after calcination at 800°C (with the development of Bronsted acid sites centralization of 161 μmol/g). At 2.5 h reaction time at 200°C reaction temperature, the methyl ester yields within the sight of WO3/ZrO2/

and Nafion had already been tested for esterification and their catalytic efficiency for esterifi-

According to the literature, microwave heating along with barium, alumina, silica, zinc aluminate and zirconium-based catalysts are good catalyst for biodiesel production (Portnoff et al., 2005; Bournay et al; Ondrey et al., 2004). By using different approach, utilization of

/TiO<sup>2</sup>

reported 90% activity of SO4 2-/ZrO2 catalyst 200°C in 1 h reaction time [113, 127–129]. In acid catalyzed reaction, heteropoly tungstate was found as active catalysts for pure and waste oil.

O3

neous HPAs. HPAs supported at Cs+, NH4+ are also very active and useful as acid catalyst. Chai et al. who investigated the activity of Cs25H3PW12O40 has reported 96% conversion of FAME in 65°C reaction for 1 h [115, 116, 129–131]. In previous research, the activity of acids

Zirconium, hafnium and antimonium-based transition metal catalyst were also being studied by researchers in past for transesterification. Porous zirconia, titania and alumina microsphere stabilized chemically, thermally and mechanically have been investigated by Clayton et al. [30]. Yan et al. tested Fe–Zn catalyst methanolysis of vegetable oil (using 1:15 molar ration of methanol at 170°C, by using catalyst in amount of 3 wt.% showed TG conversion more than 99% within 5 h of reaction). It was assumed that the catalyst activity was endorsed

Serio et al. studied solid acid vanadium phosphate catalyst for biodiesel synthesis, it was observed that the methyl ester yields reached 80% at 150°C within 60 min using 0.2 wt.% of the catalyst under and 1:1 of alcohol/oil molar ratio. However, the catalyst could be recycled

esterification of oil they got high conversion of 96% TG in 180 min. Yan el al. used calcium

, which combines acid (ZnO) and base sites (La<sup>2</sup>

/CaO) and observed that this catalyst is particularly

due to the Lewis acid active sites of probably Zn2+ on the surface of catalyst [135].

O3

is also reported in literature as a good catalyst [116]. Zhai et al. reported 90% activity

/ZrO<sup>2</sup>

, SO<sup>4</sup>

–Al<sup>2</sup> O3 SO<sup>4</sup>

/ZrO<sup>2</sup>

catalyst at 60°C reaction temperature for 8 h reaction while Lam et al.

, SO<sup>4</sup>

/ZrO<sup>2</sup>

/ZrO<sup>2</sup>

and Sr(NO<sup>3</sup>

, WO3/ZrO<sup>2</sup>

2-/SnO<sup>2</sup> + Fe<sup>3</sup>

) support could be used to produce heteroge-

O<sup>3</sup> > 20%HPW/ ZrO2 > 20%HPW/SiO2 order

)2

/ZnO have

, SO<sup>4</sup>

O4

O3

) for trans-

and SO<sup>4</sup>

/

/TiO<sup>2</sup> ,

and zinc aluminate have been reported. WO<sup>3</sup>

cation and transesterification of free fatty acid and triglycerides [112, 121–126].

) and alumina (Al<sup>2</sup>

/ZrO<sup>2</sup> > 20%HPW/Al<sup>2</sup>

ash ZnO-La<sup>2</sup>

106 Biofuels - State of Development

SnO<sup>2</sup>

of SO<sup>4</sup>

Zirconia (ZrO<sup>2</sup>

[47, 131–134].

2-/SnO<sup>2</sup> + Fe<sup>3</sup>

fall in CsHPW >20%WO<sup>3</sup>

O3

MCM-41 were 85% [38, 111, 118–120].

A variety of transition metal-based solid acids SO<sup>4</sup>

sulfated transition metal oxides such as SO<sup>4</sup>

O4

), silica (SiO<sup>2</sup>

after regeneration at high temperature [15].

oxides modified with lanthanum (La<sup>3</sup>

O3

Lee and Shiro used ZnO–La<sup>2</sup>

Thitsartarn et al. examined the use of CeO<sup>2</sup> -CaO mixed oxides as catalysts for biodiesel production. They had studied several reaction parameters carried out at optimal transesterification. They concluded that CeO<sup>2</sup> -CaO mixed oxides gives best catalytic activity at 85°C in 2 h with 97% yield [138].



It was investigated that recombinant DNA technology can be used to produced large quantities of lipases. Casimir et al. recommended that the utilization of immobilized lipase may diminish the general cost of biodiesel production and lower downstream preparing issues and this is ecologically suitable with respect to other conventional methods. Watanab et al. built up a three-advance methanolysis process for biodiesel synthesis by utilizing Candida antarctica lipase for persistent generation of biodiesel fuel from vegetable oil. It was observed that 95% yield can be gotten by utilizing 4% immobilized Candida lipase as a catalyst at 308°C reaction time in a 20-or 50-ml screw-topped vessel with The 1:2 molar amount of methanol against the aggregate unsaturated fats. Hideki et al. additionally reviewed utilization of enzymatic-catalyzed transesterification to reduce problems associated with homogeneous catalysis. The author revealed the use of immobilized antarctica lipase (Novozym-435) for

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109

Additionally, Shah et al. used lipase for synthesis of biodiesel from jatropha oil. He used solvent-free system for screening of pancreas porcine, C*andida rugosa* and Chromobacterium viscosum for the production of biodiesel. 0.5 g of jatropha seed oil in a vessel having 1:4 molar ratio of ethanol and 50 mg of enzyme was introduced and incubated at 40°C with constant stirring at 200 rpm. They observed 62–71% yield of ester by free-tuned enzyme of lipase

The generation and utilization of biodiesel have seen a quantum bounce in the current century because of advantages related to its capacity to relieve ozone depleting substance (GHG). There is a huge number of non-edible plants oil use for biodiesel synthesis through transesterification of fats, a stable catalysts in terms of, catalytic life, recyclability and lower cost are critical as these directly affect the general cost of the overall process. The different choices of heterogeneous strong catalysis were accounted for the particular research results of transesterification on heterogeneous catalysis majorly centered on examining the suitable oil source, methanol to oil molar proportion, and assessing the accessibility of catalyst. Unlike homogeneous, heterogeneous catalyst are cost effective and environmental friendly can easily be reused and recovered. As lower reaction rate and side reactions make the use of catalyst limited, solid acidic catalysts for biodiesel synthesis. Solid acid catalyst are very useful in term or their ability to work in one step and are able to convert oils with high amount of free fatty acids (FFA) into biodiesel. Presence of water in feedstock obstructed the activity of the basic heterogeneous catalyst. Be that as it may, strong base work quicker and gives higher TG conversion then an acid catalyst. Amendment of the catalyst by monitoring different aspects makes catalyst more suitable for transesterification and makes it more energy intensive. Mutual esterification and transesterification could be simultaneously done by using acid-base catalysts. On the other hand enzymatic catalysts are highly promising but enzymes carried out transesterification reaction in very slow rate. On the other hand heterogeneous catalyst work smoothly when

reaction temperature, pressure and molar ratio of alcohol to oil is considerably high.

high FFAs feed stock for biodiesel production [147].

**8. Conclusion**

(Chromobacterium viscosum) in a process time of 8 h at 40°C.

**Table 4.** Transition metals, lanthanide actinides based catalysts used for the transesterification of oils.

Bancquart et al. investigated the activity of La<sup>2</sup> O3 for glycerol transesterification to investigate the relationship between activity and basicity. It was reported that at high temperature of 200°C, the fame yield was 97.5% in 2 h. On the other hand, both these metals are very expensive and not economical for the production of biodiesel [139].

Li et al. studied the activity of a novel solid super base of Eu<sup>2</sup> O3 /Al<sup>2</sup> O3 complex for transesterification triglycerides with alcohols, he observed 63.2% yield of FAME in 8 h reaction at 195°C [140].

Currently, due to the believe that solid base catalyst are more environmental friendly and could replace acid catalyst, researches are focusing at the synthesis of novel, stable and economical solid acid catalysts for transesterification reaction [68].

#### **7. Bio catalyst**

The utilization of lipases (triacylglycerol acyl hydrolases) as biocatalyst for the production of biodiesel has become more appealing since the ease of glycerol recovery (byproduct) and purification of FAME [141]. Plethora of research reports demonstrated the used of lipase as a catalyst for production of biodiesel; however, this technology has not received much commercial attention due to the high cost of enzyme [141]. To overcome the drawback of free lipases, recent research efforts have been made toward the immobilization of lipases on solid support (such as zeolite, Celite, silica gel, inorganic nanoparticles, acrylic resin and textile membrane etc.) which not only reduce the cost in terms of reusability but also increases the number of available active sites [142]. Crosslinking, covalent bonding, adsorption and entrapment are the most common approaches that are involved in immobilization of lipase onto the solid support [143–145].

Casimir et al. stated that enzymes can be used as biocatalyst for transesterification reaction, for example, Candida antarctica lipase many enzyme like *Pseudomonas fluorescens* Rhizomucor miehei and Chromobacterium viscosum [146] and Rhizopus oryzae lipase [147] have been used as enzyme catalyzed transesterification reactions. Immobilized lipase have been used by Tan et al. for biodiesel synthesis covalent bonding, crosslinking, encapsulation, entrapment and adsorption have also being reported in literature to rise the stability of lipase in FAME synthesis.

It was investigated that recombinant DNA technology can be used to produced large quantities of lipases. Casimir et al. recommended that the utilization of immobilized lipase may diminish the general cost of biodiesel production and lower downstream preparing issues and this is ecologically suitable with respect to other conventional methods. Watanab et al. built up a three-advance methanolysis process for biodiesel synthesis by utilizing Candida antarctica lipase for persistent generation of biodiesel fuel from vegetable oil. It was observed that 95% yield can be gotten by utilizing 4% immobilized Candida lipase as a catalyst at 308°C reaction time in a 20-or 50-ml screw-topped vessel with The 1:2 molar amount of methanol against the aggregate unsaturated fats. Hideki et al. additionally reviewed utilization of enzymatic-catalyzed transesterification to reduce problems associated with homogeneous catalysis. The author revealed the use of immobilized antarctica lipase (Novozym-435) for high FFAs feed stock for biodiesel production [147].

Additionally, Shah et al. used lipase for synthesis of biodiesel from jatropha oil. He used solvent-free system for screening of pancreas porcine, C*andida rugosa* and Chromobacterium viscosum for the production of biodiesel. 0.5 g of jatropha seed oil in a vessel having 1:4 molar ratio of ethanol and 50 mg of enzyme was introduced and incubated at 40°C with constant stirring at 200 rpm. They observed 62–71% yield of ester by free-tuned enzyme of lipase (Chromobacterium viscosum) in a process time of 8 h at 40°C.

#### **8. Conclusion**

Bancquart et al. investigated the activity of La<sup>2</sup>

**Catalyst Reaction time in** 

at 195°C [140].

La<sup>2</sup>

108 Biofuels - State of Development

Eu<sup>2</sup> O3 /Al<sup>2</sup>

**7. Bio catalyst**

sive and not economical for the production of biodiesel [139].

**hour**

Li et al. studied the activity of a novel solid super base of Eu<sup>2</sup>

nomical solid acid catalysts for transesterification reaction [68].

O3

the relationship between activity and basicity. It was reported that at high temperature of 200°C, the fame yield was 97.5% in 2 h. On the other hand, both these metals are very expen-

O<sup>3</sup> 2 200 97.5 [165]

**Table 4.** Transition metals, lanthanide actinides based catalysts used for the transesterification of oils.

O<sup>3</sup> 8 70 63.2 [166] Sulphonated carbon 2.5 260 90 [167, 168] Sulphonic/SiO<sup>2</sup> 5 150 60 [169] Sulphonic acid/SBA-15 8 180 96 [170]

esterification triglycerides with alcohols, he observed 63.2% yield of FAME in 8 h reaction

Currently, due to the believe that solid base catalyst are more environmental friendly and could replace acid catalyst, researches are focusing at the synthesis of novel, stable and eco-

The utilization of lipases (triacylglycerol acyl hydrolases) as biocatalyst for the production of biodiesel has become more appealing since the ease of glycerol recovery (byproduct) and purification of FAME [141]. Plethora of research reports demonstrated the used of lipase as a catalyst for production of biodiesel; however, this technology has not received much commercial attention due to the high cost of enzyme [141]. To overcome the drawback of free lipases, recent research efforts have been made toward the immobilization of lipases on solid support (such as zeolite, Celite, silica gel, inorganic nanoparticles, acrylic resin and textile membrane etc.) which not only reduce the cost in terms of reusability but also increases the number of available active sites [142]. Crosslinking, covalent bonding, adsorption and entrapment are the most common approaches that are involved in immobilization of lipase onto the solid support [143–145].

Casimir et al. stated that enzymes can be used as biocatalyst for transesterification reaction, for example, Candida antarctica lipase many enzyme like *Pseudomonas fluorescens* Rhizomucor miehei and Chromobacterium viscosum [146] and Rhizopus oryzae lipase [147] have been used as enzyme catalyzed transesterification reactions. Immobilized lipase have been used by Tan et al. for biodiesel synthesis covalent bonding, crosslinking, encapsulation, entrapment and adsorption have also being reported in literature to rise the stability of lipase in FAME synthesis.

for glycerol transesterification to investigate

complex for trans-

O3 /Al<sup>2</sup> O3

**Reaction temperature, °C Yield, % Reference**

The generation and utilization of biodiesel have seen a quantum bounce in the current century because of advantages related to its capacity to relieve ozone depleting substance (GHG). There is a huge number of non-edible plants oil use for biodiesel synthesis through transesterification of fats, a stable catalysts in terms of, catalytic life, recyclability and lower cost are critical as these directly affect the general cost of the overall process. The different choices of heterogeneous strong catalysis were accounted for the particular research results of transesterification on heterogeneous catalysis majorly centered on examining the suitable oil source, methanol to oil molar proportion, and assessing the accessibility of catalyst. Unlike homogeneous, heterogeneous catalyst are cost effective and environmental friendly can easily be reused and recovered.

As lower reaction rate and side reactions make the use of catalyst limited, solid acidic catalysts for biodiesel synthesis. Solid acid catalyst are very useful in term or their ability to work in one step and are able to convert oils with high amount of free fatty acids (FFA) into biodiesel.

Presence of water in feedstock obstructed the activity of the basic heterogeneous catalyst. Be that as it may, strong base work quicker and gives higher TG conversion then an acid catalyst. Amendment of the catalyst by monitoring different aspects makes catalyst more suitable for transesterification and makes it more energy intensive. Mutual esterification and transesterification could be simultaneously done by using acid-base catalysts. On the other hand enzymatic catalysts are highly promising but enzymes carried out transesterification reaction in very slow rate. On the other hand heterogeneous catalyst work smoothly when reaction temperature, pressure and molar ratio of alcohol to oil is considerably high.

Efficiency of catalyst also depends upon calcination time and temperature. Calcination leads to alteration of the starting reactant into new compound possessing high catalytic activity then original compound. It is because calcination increases basicity, pore size and pore volume specific surface area and active site concentration could at catalyst.

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Only few researches specify the industrial level production of FAME by implementing the heterogeneous catalyst method. In past, a lot or researches were done to explore and exploit synthesis and use of novel heterogeneous catalysts in the production of FAME. Some of the reasons for the recent growth and development of heterogeneous catalysts include among others are biodiesel yield of 98 wt% and simplicity in catalyst separation process, high-purity byproducts, less cost of separation and low energy.

#### **Author details**

Sadia Nasreen\*, Muhammad Nafees, Liaqat Ali Qureshi , Muhammad Shahbaz Asad, Ali Sadiq and Syed Danial Ali

\*Address all correspondence to: sadia.nasreen@uettaxila.edu.pk

Department of Environmental Engineering, University of Engineering and Technology, Taxila, Pakistan

#### **References**


Efficiency of catalyst also depends upon calcination time and temperature. Calcination leads to alteration of the starting reactant into new compound possessing high catalytic activity then original compound. It is because calcination increases basicity, pore size and pore vol-

Only few researches specify the industrial level production of FAME by implementing the heterogeneous catalyst method. In past, a lot or researches were done to explore and exploit synthesis and use of novel heterogeneous catalysts in the production of FAME. Some of the reasons for the recent growth and development of heterogeneous catalysts include among others are biodiesel yield of 98 wt% and simplicity in catalyst separation process, high-purity

Sadia Nasreen\*, Muhammad Nafees, Liaqat Ali Qureshi , Muhammad Shahbaz Asad,

Department of Environmental Engineering, University of Engineering and Technology,

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TiO<sup>2</sup>


**Chapter 7**

Provisional chapter

**Ultrasound Methods for Biodiesel Production and**

DOI: 10.5772/intechopen.74303

Ultrasonic techniques have been widely used in biodiesel production, since the acoustic cavitation is a phenomenon capable of accelerating potentially the transesterification reactions. The equipment employed in such approach was simply equipment available in any regular laboratory of chemistry. Further developments introduced the ultrasound as an important tool to produce biodiesel. The main advantage is increasing the conversion of esters at reduced reaction times, with significantly lower production costs. As a method for characterization and analysis of materials, ultrasound has been used since several decades ago. However, ultrasonic analytical methods based on metrological principles are fairly recent investigated. Using ultrasound as physical principle to interrogate biodiesel is a promising field of research, with some remarkable outcomes produced so far. The aim of this chapter is to demonstrate advances of using ultrasonic techniques in production and characterization of biodiesel, as well as an appraisal of the current technology

Keywords: ultrasound, metrology, chemical kinetics, real-time reaction monitoring,

Biodiesel production has achieved increasing importance worldwide due to the potential depletion of oil reserves and the environmental impacts caused by gases of fossil fuel. Biodiesel is a renewable fuel composed of alkyl esters of fatty acids, which are derived from triglycerides (vegetable oils or animal fats). There are several routes for biodiesel production, but the most

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Ultrasound Methods for Biodiesel Production and

**Analysis**

Analysis

Rodrigo P.B. Costa-Félix

Rodrigo P.B. Costa-Félix

Abstract

biodiesel production

1. Introduction

Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and

Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and

Additional information is available at the end of the chapter

status, and provide insights into future developments.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74303

#### **Ultrasound Methods for Biodiesel Production and Analysis** Ultrasound Methods for Biodiesel Production and Analysis

DOI: 10.5772/intechopen.74303

Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and Rodrigo P.B. Costa-Félix Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and Rodrigo P.B. Costa-Félix

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74303

#### Abstract

Ultrasonic techniques have been widely used in biodiesel production, since the acoustic cavitation is a phenomenon capable of accelerating potentially the transesterification reactions. The equipment employed in such approach was simply equipment available in any regular laboratory of chemistry. Further developments introduced the ultrasound as an important tool to produce biodiesel. The main advantage is increasing the conversion of esters at reduced reaction times, with significantly lower production costs. As a method for characterization and analysis of materials, ultrasound has been used since several decades ago. However, ultrasonic analytical methods based on metrological principles are fairly recent investigated. Using ultrasound as physical principle to interrogate biodiesel is a promising field of research, with some remarkable outcomes produced so far. The aim of this chapter is to demonstrate advances of using ultrasonic techniques in production and characterization of biodiesel, as well as an appraisal of the current technology status, and provide insights into future developments.

Keywords: ultrasound, metrology, chemical kinetics, real-time reaction monitoring, biodiesel production

#### 1. Introduction

Biodiesel production has achieved increasing importance worldwide due to the potential depletion of oil reserves and the environmental impacts caused by gases of fossil fuel. Biodiesel is a renewable fuel composed of alkyl esters of fatty acids, which are derived from triglycerides (vegetable oils or animal fats). There are several routes for biodiesel production, but the most

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

common is the transesterification, which is the reaction between triglycerides and a short chain alcohol in the presence of a catalyst, producing esters and glycerol [1].

Propagation direction. Considering ultrasonic waves propagating through matter, energy is transferred from one location to another, but this energy is not associated with mass transfer. Based on the relation between the wave propagation direction and the motion direction of the particles constituting the medium, the waves can be divided in two propagation types: longitudinal and transverse. In the longitudinal propagation, the direction of displacement for the medium's particles is parallel to the direction of wave propagation (Figure 1, top). For the transverse propagation, the direction of displacement for the medium's particles is perpendicular to the direction of wave propagation (Figure 1, bottom). Despite that this basic division is frequently used in ultrasound, it is important to have in mind that there are also wave types for which the direction of motion for the medium's particles is not fixed relative to the wave propagation direction. In surface waves, for example, the angle between the two directions

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123

Wave front geometry. Another important classification is based on the wave front geometry. Using this approach, waves can be divided into planar, in which the wave front is located on a plane that propagates in space and spherical ones that propagates symmetrically around a reference point (Figure 2). However, in practice, intermediate type of waves can be found over the ultrasonic beam transmitted. Considering a disc-shaped transducer, planar wave characteristics are observed near the transducer particularly around its central region. However, as far as the propagation is from the transducer, the wave will have more and more spherical wave characteristics. Similarly, as the ratio between the transducer diameter and the wavelength is decreased, the same behavior is observed [11]. The general case is defined by Huygens' principle, in which

Figure 1. Example of longitudinal (top) and transverse (bottom) propagation.

Figure 2. Diagram representing planar (left) and spherical (right) waves.

changes continuously [11].

The 3:1 molar ratio of alcohol/triglycerides is required for the complete transesterification. However, an excess of alcohol is usually added to displace the equilibrium of the reaction, ensuring the ester formation completely. Besides the molar ratio, there are other reaction variables such as temperature, type and quantity of catalyst and type of agitation, among others, that will affect the equilibrium and biodiesel production.

The conventional biodiesel production method uses mechanical agitation and high temperatures to facilitate mass transfer between the immiscible reagents (triglycerides and alcohol). Alternative methods were developed with the aim of increasing ester conversion with the decreasing of the reaction time [2].

The use of ultrasound in biodiesel production has gained emphasis over the years [3–6], since ultrasound can promote homogenization between the reagents through acoustic cavitation. Acoustic cavitation is the growth and violent collapse of cavitation bubbles, which, when exploded, generate an increase in temperature in the reaction medium. This phenomenon is able to increase the speed of the reaction, reduce the amount of catalyst and reduce the reaction time from hours to minutes [7]. In most of the cases, the reactions use simple ultrasonic baths or ultrasonic probes operating in the frequency range between 20 and 50 kHz and high output power (typically over 200 W). New developments introduced biodiesel as an important tool in biodiesel production, using more economical equipment and demonstrating satisfactory conversion values using powers as low as 50 W or even lower [8].

Not just as a way to accelerate the transesterification, the ultrasound is being studied as a tool to monitor the biodiesel reaction [9]. The use of low-power ultrasound to determine the end of the reaction in an inline method cannot just save time and energy, but also it can potentially avoid waste.

As a method for material characterization and analysis, ultrasound has been used for several decades in several applications. However, ultrasonic analytical methods for biodiesel production are quite recent. The aim of this chapter is to demonstrate advances of using ultrasonic techniques for the production and the characterization of biodiesel, as well as an appraisal of the current technology status, and to provide insights into future developments.

#### 2. What is ultrasound?

#### 2.1. Ultrasound basic concepts

According to IEC 60050-802:2011 [10], ultrasound is defined as "acoustic oscillation whose frequency is above the high-frequency limit of audible sound (about 20 kHz)" and has no difference from sound concerning its physical properties, except in that humans cannot hear it. In large spectrum, ultrasound devices operate with frequencies from 20 kHz up to several gigahertz. The most relevant physical properties are summarized hereafter.

Propagation direction. Considering ultrasonic waves propagating through matter, energy is transferred from one location to another, but this energy is not associated with mass transfer. Based on the relation between the wave propagation direction and the motion direction of the particles constituting the medium, the waves can be divided in two propagation types: longitudinal and transverse. In the longitudinal propagation, the direction of displacement for the medium's particles is parallel to the direction of wave propagation (Figure 1, top). For the transverse propagation, the direction of displacement for the medium's particles is perpendicular to the direction of wave propagation (Figure 1, bottom). Despite that this basic division is frequently used in ultrasound, it is important to have in mind that there are also wave types for which the direction of motion for the medium's particles is not fixed relative to the wave propagation direction. In surface waves, for example, the angle between the two directions changes continuously [11].

common is the transesterification, which is the reaction between triglycerides and a short chain

The 3:1 molar ratio of alcohol/triglycerides is required for the complete transesterification. However, an excess of alcohol is usually added to displace the equilibrium of the reaction, ensuring the ester formation completely. Besides the molar ratio, there are other reaction variables such as temperature, type and quantity of catalyst and type of agitation, among others,

The conventional biodiesel production method uses mechanical agitation and high temperatures to facilitate mass transfer between the immiscible reagents (triglycerides and alcohol). Alternative methods were developed with the aim of increasing ester conversion with the

The use of ultrasound in biodiesel production has gained emphasis over the years [3–6], since ultrasound can promote homogenization between the reagents through acoustic cavitation. Acoustic cavitation is the growth and violent collapse of cavitation bubbles, which, when exploded, generate an increase in temperature in the reaction medium. This phenomenon is able to increase the speed of the reaction, reduce the amount of catalyst and reduce the reaction time from hours to minutes [7]. In most of the cases, the reactions use simple ultrasonic baths or ultrasonic probes operating in the frequency range between 20 and 50 kHz and high output power (typically over 200 W). New developments introduced biodiesel as an important tool in biodiesel production, using more economical equipment and demonstrating satisfactory con-

Not just as a way to accelerate the transesterification, the ultrasound is being studied as a tool to monitor the biodiesel reaction [9]. The use of low-power ultrasound to determine the end of the reaction in an inline method cannot just save time and energy, but also it can potentially

As a method for material characterization and analysis, ultrasound has been used for several decades in several applications. However, ultrasonic analytical methods for biodiesel production are quite recent. The aim of this chapter is to demonstrate advances of using ultrasonic techniques for the production and the characterization of biodiesel, as well as an appraisal of

According to IEC 60050-802:2011 [10], ultrasound is defined as "acoustic oscillation whose frequency is above the high-frequency limit of audible sound (about 20 kHz)" and has no difference from sound concerning its physical properties, except in that humans cannot hear it. In large spectrum, ultrasound devices operate with frequencies from 20 kHz up to several

the current technology status, and to provide insights into future developments.

gigahertz. The most relevant physical properties are summarized hereafter.

alcohol in the presence of a catalyst, producing esters and glycerol [1].

that will affect the equilibrium and biodiesel production.

version values using powers as low as 50 W or even lower [8].

decreasing of the reaction time [2].

122 Biofuels - State of Development

avoid waste.

2. What is ultrasound?

2.1. Ultrasound basic concepts

Wave front geometry. Another important classification is based on the wave front geometry. Using this approach, waves can be divided into planar, in which the wave front is located on a plane that propagates in space and spherical ones that propagates symmetrically around a reference point (Figure 2). However, in practice, intermediate type of waves can be found over the ultrasonic beam transmitted. Considering a disc-shaped transducer, planar wave characteristics are observed near the transducer particularly around its central region. However, as far as the propagation is from the transducer, the wave will have more and more spherical wave characteristics. Similarly, as the ratio between the transducer diameter and the wavelength is decreased, the same behavior is observed [11]. The general case is defined by Huygens' principle, in which

Figure 1. Example of longitudinal (top) and transverse (bottom) propagation.

Figure 2. Diagram representing planar (left) and spherical (right) waves.

any wave source (or wave front) can be considered as an infinite collection of spherical wave sources (Figure 3).

Diffraction. It is a phenomenon by which a sound wave is changed in direction by an obstacle or other heterogeneity in the medium. This phenomenon is enhanced for wavelengths that are relatively long relative to the geometry of the obstacle [11]. The diffraction phenomenon is illustrated in Figure 3.

Interference. An important phenomenon occurs when two waves encounter each other in a propagation medium. It is called interference. The interference can be constructive, when the amplitudes of two waves enhance each other, or destructive, and their amplitudes attenuate each other. After passing through each other, if nonlinear effects are negligible (see "Nonlinear Propagation" section), the two waves proceed as though nothing has happened. Summarizing, within interference zone the result amplitude is the sum of all the interacting wave amplitudes, which is defined as the "superposition principle" [11].

Characteristic impedance of a medium. Product of the equilibrium density (r) and speed of sound (v) in a medium, as represented in (1). It can be understood as a measure of the impediment caused by a medium to the movement induced by a pressure applied to it. It is noteworthy that for a plane acoustic wave propagating in a non-dissipative medium, the specific acoustic impedance (at a specified surface, quotient of sound pressure (P) by volume velocity (U) through the surface) relative to this wave is equal to the characteristic impedance of the medium [11]:

$$Z = v \cdot \rho = \frac{P}{U} \tag{1}$$

when the incidence at the interface of the media is perpendicular to the direction of wave

<sup>¼</sup> ð Þ <sup>Z</sup><sup>2</sup> � <sup>Z</sup><sup>1</sup>

ð Þ Z<sup>2</sup> þ Z<sup>1</sup>

<sup>¼</sup> ð Þ <sup>4</sup> � <sup>Z</sup><sup>2</sup> � <sup>Z</sup><sup>1</sup> ð Þ Z<sup>2</sup> þ Z<sup>1</sup>

Propagation velocity. The propagation velocity of the wave in a medium (v) is dependent on the density and modulus of elasticity of the medium and can also be represented by the product of

in which f is the frequency of the ultrasound, λ is the wavelength, K is the modulus of elasticity (rigidity) and r is the density of the propagation medium [11]. Propagation velocity is named as speed of sound as well. Depending on some medium and the sound characteristics, phase velocity and group velocity are quantities more usable to physically describe the waveform

Attenuation. In a planar wave propagating in a free field, the main causes of attenuation (loss of energy due to the distance traveled by the wave in a medium) of the ultrasound are scattering and absorption (mechanical energy conversion into thermal energy). Therefore, the attenua-

One of the most evident features in the shape of the ultrasonic beam generated by a piston, circular or not, is caused by the so-called edge effect [12]. This effect generates constructive and destructive interferences in a region known as near field, being observed in continuous waves. These interferences are not so evident in short-duration pulses [13, 14]. The edge effect is originated by the diffraction of the wave caused by the transducer because it has a finite

Each element of the transducer surface can be considered an infinitely smaller point source and as such can generate spherical acoustic waves that create field interferences. In Figure 4, point A is distant from the transducer surface by a distance r, and it is apart from the symmetry axis by a distance r'. The lines d1 and d2 represent the distances from point A to the nearest and the farthest edges, respectively. Analytical expressions for pressure at A are available in the literature [14] and are relatively simple to derive because of the axial symmetry of a pistonlike circular transducer. An even greater and possible simplification is the case where d1 = d2, i.e. the point A is on the symmetry axis of the transducer [15]. For this particular situation, Eq. 8.31b of Ref. [16], reproduced in (5), expresses the amplitude of the acoustic pressure as a

2

<sup>2</sup> (2)

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Ultrasound Methods for Biodiesel Production and Analysis

<sup>2</sup> (3)

¼ f � λ (4)

<sup>R</sup> <sup>¼</sup> IR II

<sup>T</sup> <sup>¼</sup> IT II

> <sup>v</sup> <sup>¼</sup> <sup>K</sup> r <sup>1</sup> 2

tion of the signal is influenced by the characteristics of the medium [11].

the ultrasonic frequency by wavelength as presented in (4):

propagation [11]:

displacement per unit of time.

2.2. Linear propagation

aperture in relation to ultrasound wavelength.

Reflection and transmission. Given an incident wave at the interface between two media with different acoustic impedances, part of its energy is reflected, and part is transmitted to the adjacent medium, with or without a change in direction. The proportions of reflected (ER) and transmitted (ET) energies, relative to energy of the incident wave (EI), can be estimated from the reflection (R) and transmission (T) coefficients. Eqs. (2) and (3) define these coefficients

Figure 3. Schematic demonstration of Huygens' principle (left). Demonstration of the diffraction phenomenon for a planar wave propagating from the bottom toward the top and passing through a slot (right).

when the incidence at the interface of the media is perpendicular to the direction of wave propagation [11]:

$$R = \frac{I\_R}{I\_I} = \frac{\left(Z\_2 - Z\_1\right)^2}{\left(Z\_2 + Z\_1\right)^2} \tag{2}$$

$$T = \frac{I\_T}{I\_I} = \frac{(4 \cdot Z\_2 \cdot Z\_1)}{\left(Z\_2 + Z\_1\right)^2} \tag{3}$$

Propagation velocity. The propagation velocity of the wave in a medium (v) is dependent on the density and modulus of elasticity of the medium and can also be represented by the product of the ultrasonic frequency by wavelength as presented in (4):

$$w = \left(\frac{K}{\rho}\right)^{\frac{1}{2}} = f \times \lambda \tag{4}$$

in which f is the frequency of the ultrasound, λ is the wavelength, K is the modulus of elasticity (rigidity) and r is the density of the propagation medium [11]. Propagation velocity is named as speed of sound as well. Depending on some medium and the sound characteristics, phase velocity and group velocity are quantities more usable to physically describe the waveform displacement per unit of time.

Attenuation. In a planar wave propagating in a free field, the main causes of attenuation (loss of energy due to the distance traveled by the wave in a medium) of the ultrasound are scattering and absorption (mechanical energy conversion into thermal energy). Therefore, the attenuation of the signal is influenced by the characteristics of the medium [11].

#### 2.2. Linear propagation

any wave source (or wave front) can be considered as an infinite collection of spherical wave

Diffraction. It is a phenomenon by which a sound wave is changed in direction by an obstacle or other heterogeneity in the medium. This phenomenon is enhanced for wavelengths that are relatively long relative to the geometry of the obstacle [11]. The diffraction phenomenon is

Interference. An important phenomenon occurs when two waves encounter each other in a propagation medium. It is called interference. The interference can be constructive, when the amplitudes of two waves enhance each other, or destructive, and their amplitudes attenuate each other. After passing through each other, if nonlinear effects are negligible (see "Nonlinear Propagation" section), the two waves proceed as though nothing has happened. Summarizing, within interference zone the result amplitude is the sum of all the interacting wave amplitudes,

Characteristic impedance of a medium. Product of the equilibrium density (r) and speed of sound (v) in a medium, as represented in (1). It can be understood as a measure of the impediment caused by a medium to the movement induced by a pressure applied to it. It is noteworthy that for a plane acoustic wave propagating in a non-dissipative medium, the specific acoustic impedance (at a specified surface, quotient of sound pressure (P) by volume velocity (U) through the surface) relative to this wave is equal to the characteristic impedance of the

<sup>Z</sup> <sup>¼</sup> <sup>v</sup> � <sup>r</sup> <sup>¼</sup> <sup>P</sup>

Reflection and transmission. Given an incident wave at the interface between two media with different acoustic impedances, part of its energy is reflected, and part is transmitted to the adjacent medium, with or without a change in direction. The proportions of reflected (ER) and transmitted (ET) energies, relative to energy of the incident wave (EI), can be estimated from the reflection (R) and transmission (T) coefficients. Eqs. (2) and (3) define these coefficients

Figure 3. Schematic demonstration of Huygens' principle (left). Demonstration of the diffraction phenomenon for a

planar wave propagating from the bottom toward the top and passing through a slot (right).

<sup>U</sup> (1)

sources (Figure 3).

124 Biofuels - State of Development

illustrated in Figure 3.

medium [11]:

which is defined as the "superposition principle" [11].

One of the most evident features in the shape of the ultrasonic beam generated by a piston, circular or not, is caused by the so-called edge effect [12]. This effect generates constructive and destructive interferences in a region known as near field, being observed in continuous waves. These interferences are not so evident in short-duration pulses [13, 14]. The edge effect is originated by the diffraction of the wave caused by the transducer because it has a finite aperture in relation to ultrasound wavelength.

Each element of the transducer surface can be considered an infinitely smaller point source and as such can generate spherical acoustic waves that create field interferences. In Figure 4, point A is distant from the transducer surface by a distance r, and it is apart from the symmetry axis by a distance r'. The lines d1 and d2 represent the distances from point A to the nearest and the farthest edges, respectively. Analytical expressions for pressure at A are available in the literature [14] and are relatively simple to derive because of the axial symmetry of a pistonlike circular transducer. An even greater and possible simplification is the case where d1 = d2, i.e. the point A is on the symmetry axis of the transducer [15]. For this particular situation, Eq. 8.31b of Ref. [16], reproduced in (5), expresses the amplitude of the acoustic pressure as a

Figure 4. Representation of a point A positioned in the acoustic field generated by a flat piston with radius a.

function of the distance to the center of the piston, being valid for continuous waves or long tone bursts.

$$p(r) = 2\rho\_0 c\_0 \mathcal{U}\_0 \left| \text{sen} \left\{ \frac{1}{2}kr \left[ \sqrt{1 + \left(\frac{a}{r}\right)^2} - 1 \right] \right\} \right| \tag{5}$$

In Eq. (5), p rð Þ is the pressure amplitude along the symmetry axis as function of the distance; r, r<sup>0</sup> and c<sup>0</sup> denote the density and the phase velocity of the medium, respectively; U<sup>0</sup> is the transducer's surface velocity in the direction perpendicular to its face; and <sup>k</sup> <sup>¼</sup> <sup>2</sup><sup>π</sup> <sup>λ</sup> is the circular wavenumber (<sup>λ</sup> <sup>¼</sup> <sup>c</sup><sup>0</sup> f 0 and <sup>f</sup> <sup>0</sup> is the frequency). Figure 2 shows the normalized amplitude p rð Þ 2r0c0U<sup>0</sup> plotted as a function of the normalized distance <sup>r</sup> <sup>a</sup> for the case in which <sup>a</sup> <sup>λ</sup> ¼ 4. The distance rMax, described in (6), is the position of the last maximum in the increasing direction of r. It is considered the point of separation between the near field and the distant (or remote or far) field, from which the pressure amplitude decays with increasing r. In the example of Figure 5, rMax ffi 4a:

$$r\_{\text{Max}} = \frac{a^2}{\lambda} - \frac{\lambda}{4} \tag{6}$$

propagation of the ultrasonic wave in fluid media cannot be arbitrarily neglected, under penalty of the theoretical model to present great discrepancies in relation to the realized measurements [17, 18], particularly in the ultrasonic fields generated by focused transducers [17, 19, 20]. Nonlinear effects can be observed even for small amplitudes [21, 22], from the propagation of only a few wavelengths [23, 24], in both water and other liquids [25, 26]. Essentially, the nonlinear propagation of the mono-frequency ultrasonic wave makes the power of the spectral component of the fundamental frequency to be gradually transferred to the higher harmonics, transforming an originally sine wave into a distorted or shock wave [27]. Despite that the shock wave profile is often compared to a sawtooth wave [22], in fact the negative peak of the wave is always smaller than the positive peak [17, 28], and the upward region of the wave has a curved and non-rectilinear profile (see Figure 6). The theory presented in [28] was used in the simulation of a distorted sine wave (burst) caused by the nonlinear propagation in water. The values of the relations between the harmonics, shown in the bottom graph of the figure, agree with [22] for a harmonic distortion parameter σ ffi 5.7, i.e. the wave of shock is completely developed—see Eq. (8). Figure 7 shows the evolution of the composition of the harmonics as a

continuous vertical line simulates the position of a hydrophone in the field generated by the piston. In the example, the

<sup>λ</sup> ¼ 4. The

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Figure 5. Pressure amplitude generated on the axis of symmetry of a plane circular piston-like transducer for <sup>a</sup>

hydrophone is positioned at r ¼ 2:5a, given a normalized pressure of 0.663.

Nonlinearity can be mathematically described by considering the higher-order terms in the resolution of the wave equation in which the wave propagation velocity becomes dependent on the velocity of the particle. During the compression (positive wave peak) the propagation velocity is higher than during rarefaction, and the waveform became distorted [22]. The shape of the beam is also changed, becoming more directional whilst the harmonics are being

An effect resulting from the transfer of energy to high frequencies, particularly evident in organic medium such as fuel and biofuel, is the increase of absorption, since this effect is

function of the propagation distance.

generated [29].

Another important position in the symmetry axis of a piston-like circular transducer is the last minimum, which Eq. (7) defines

$$r\_{\rm Min} = \frac{a^2 - \lambda^2}{2 \cdot \lambda} \tag{7}$$

According to [16], if r > 6:41 <sup>a</sup> <sup>λ</sup>, then (1) can be approximated to the far field equation p rð Þ¼ <sup>k</sup>r0c0U<sup>0</sup> <sup>2</sup><sup>r</sup> , ensuring an error of less than 1% with that approximation. In general, measurements are taken in the far field, except when the effects of the near field are of interest in the measurement.

#### 2.3. Nonlinear propagation

The theory adopted in the formulation of Eqs. (5) and (7) considers only the linear terms of the wave equation, so it is only an approximation of reality. The nonlinear effects of the

function of the distance to the center of the piston, being valid for continuous waves or long

1 2 kr

In Eq. (5), p rð Þ is the pressure amplitude along the symmetry axis as function of the distance; r, r<sup>0</sup> and c<sup>0</sup> denote the density and the phase velocity of the medium, respectively; U<sup>0</sup> is the

described in (6), is the position of the last maximum in the increasing direction of r. It is considered the point of separation between the near field and the distant (or remote or far) field, from which the pressure amplitude decays with increasing r. In the example of Figure 5,

rMax <sup>¼</sup> <sup>a</sup><sup>2</sup>

Another important position in the symmetry axis of a piston-like circular transducer is the last

rMin <sup>¼</sup> <sup>a</sup><sup>2</sup> � <sup>λ</sup><sup>2</sup>

ments are taken in the far field, except when the effects of the near field are of interest in the

The theory adopted in the formulation of Eqs. (5) and (7) considers only the linear terms of the wave equation, so it is only an approximation of reality. The nonlinear effects of the

<sup>λ</sup> � <sup>λ</sup>

<sup>2</sup><sup>r</sup> , ensuring an error of less than 1% with that approximation. In general, measure-

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ a r � �<sup>2</sup> <sup>r</sup>

and <sup>f</sup> <sup>0</sup> is the frequency). Figure 2 shows the normalized amplitude p rð Þ

<sup>a</sup> for the case in which <sup>a</sup>

� ( ) " # �

� 1

� � � � �

(5)

2r0c0U<sup>0</sup>

<sup>λ</sup> is the circular

<sup>λ</sup> ¼ 4. The distance rMax,

<sup>4</sup> (6)

<sup>2</sup> � <sup>λ</sup> (7)

<sup>λ</sup>, then (1) can be approximated to the far field equation

p rð Þ¼ 2r0c0U<sup>0</sup> sen

� � �

Figure 4. Representation of a point A positioned in the acoustic field generated by a flat piston with radius a.

transducer's surface velocity in the direction perpendicular to its face; and <sup>k</sup> <sup>¼</sup> <sup>2</sup><sup>π</sup>

tone bursts.

126 Biofuels - State of Development

wavenumber (<sup>λ</sup> <sup>¼</sup> <sup>c</sup><sup>0</sup>

rMax ffi 4a:

p rð Þ¼ <sup>k</sup>r0c0U<sup>0</sup>

measurement.

f 0

minimum, which Eq. (7) defines

According to [16], if r > 6:41 <sup>a</sup>

2.3. Nonlinear propagation

plotted as a function of the normalized distance <sup>r</sup>

Figure 5. Pressure amplitude generated on the axis of symmetry of a plane circular piston-like transducer for <sup>a</sup> <sup>λ</sup> ¼ 4. The continuous vertical line simulates the position of a hydrophone in the field generated by the piston. In the example, the hydrophone is positioned at r ¼ 2:5a, given a normalized pressure of 0.663.

propagation of the ultrasonic wave in fluid media cannot be arbitrarily neglected, under penalty of the theoretical model to present great discrepancies in relation to the realized measurements [17, 18], particularly in the ultrasonic fields generated by focused transducers [17, 19, 20]. Nonlinear effects can be observed even for small amplitudes [21, 22], from the propagation of only a few wavelengths [23, 24], in both water and other liquids [25, 26]. Essentially, the nonlinear propagation of the mono-frequency ultrasonic wave makes the power of the spectral component of the fundamental frequency to be gradually transferred to the higher harmonics, transforming an originally sine wave into a distorted or shock wave [27]. Despite that the shock wave profile is often compared to a sawtooth wave [22], in fact the negative peak of the wave is always smaller than the positive peak [17, 28], and the upward region of the wave has a curved and non-rectilinear profile (see Figure 6). The theory presented in [28] was used in the simulation of a distorted sine wave (burst) caused by the nonlinear propagation in water. The values of the relations between the harmonics, shown in the bottom graph of the figure, agree with [22] for a harmonic distortion parameter σ ffi 5.7, i.e. the wave of shock is completely developed—see Eq. (8). Figure 7 shows the evolution of the composition of the harmonics as a function of the propagation distance.

Nonlinearity can be mathematically described by considering the higher-order terms in the resolution of the wave equation in which the wave propagation velocity becomes dependent on the velocity of the particle. During the compression (positive wave peak) the propagation velocity is higher than during rarefaction, and the waveform became distorted [22]. The shape of the beam is also changed, becoming more directional whilst the harmonics are being generated [29].

An effect resulting from the transfer of energy to high frequencies, particularly evident in organic medium such as fuel and biofuel, is the increase of absorption, since this effect is

more difficult to obtain in the past [35]. The theoretical model on which most of experimental applications are based today is described by Blackstock [30], which can be found in formula-

A parameter used to describe the nonlinear deformation stage of the ultrasonic wave is called

In Eq. (8), β is a dimensionless parameter dependent on the propagation medium (for water at 20�C, β ¼ 3:5, according to [36]), P<sup>0</sup> is the effective pressure amplitude in the face of the generating transducer, Δt is the elapsed time since the waveform starts its propagation away

Ultrasound is used in many different fields, and different devices have been constructed to specific applications. The most common uses include detecting objects and measuring distances; ultrasound imaging is used in medicine for diagnostic and in non-destructive testing of products, materials and structures to detect invisible flaws for raw eyes. Industrial applica-

According to [37], sonicate is "to disrupt (something) by exposure to high-frequency sound waves", and sonication is "the act of applying sound energy to agitate particles in a sample, for various purposes". Hence, ultrasonication is a process in which ultrasonic frequencies are usually used to produce alternating low- and high-pressure waves in liquids, leading to the formation and violent collapse of small vacuum bubbles. This phenomenon is called cavitation and causes high-speed foist liquid jets and strong hydrodynamic shear forces. Ultrasonication proffers great potential in the processing of liquids, improving the mixing and chemical

P0f <sup>0</sup>Δt r0c<sup>2</sup> 0

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(8)

129

σ ¼ 2πβ

from the transducer, and the other parameters are the same described previously.

tions of ultrasound include cleaning, mixing and accelerating chemical processes.

tions of easy computational implementation [17, 22, 28].

Figure 7. Sine wave distortion as a function of propagation distance.

2.4. Ultrasound industrial applications

reactions in various industrial applications.

the degree of harmonic distortion σ, which for plane waves is defined as

Figure 6. Example of a sine wave distorted by nonlinear propagation. (a) Graph of the wave in the time domain, showing the ratio between the positive and negative peaks (P+/P-). (b) Graph in the frequency domain, showing the ratio between the powers of the harmonics 2–5 in relation to the fundamental, in dB, which is related to the degree of wave distortion. For the example of the figure, σ ffi 5:7.

directly proportional to the frequency. In other words, the higher the energy at high frequencies, the greater the attenuation caused by propagation at these frequencies.

Although the waveform distortion mechanism is physically complex, involving the generation of harmonics and diffraction, dissipation and dispersion phenomena during the propagation of the acoustic wave in the fluid medium [28], mathematical models are available and are able to portray fairly accurately experimental results [30–33]. Of course, appropriate equipment allows reliable measurements capable of corroborating theoretical models [34], which was

Figure 7. Sine wave distortion as a function of propagation distance.

more difficult to obtain in the past [35]. The theoretical model on which most of experimental applications are based today is described by Blackstock [30], which can be found in formulations of easy computational implementation [17, 22, 28].

A parameter used to describe the nonlinear deformation stage of the ultrasonic wave is called the degree of harmonic distortion σ, which for plane waves is defined as

$$
\sigma = 2\pi \beta \frac{P\_0 f\_0 \Delta t}{\rho\_0 c\_0^2} \tag{8}
$$

In Eq. (8), β is a dimensionless parameter dependent on the propagation medium (for water at 20�C, β ¼ 3:5, according to [36]), P<sup>0</sup> is the effective pressure amplitude in the face of the generating transducer, Δt is the elapsed time since the waveform starts its propagation away from the transducer, and the other parameters are the same described previously.

#### 2.4. Ultrasound industrial applications

directly proportional to the frequency. In other words, the higher the energy at high frequen-

Figure 6. Example of a sine wave distorted by nonlinear propagation. (a) Graph of the wave in the time domain, showing the ratio between the positive and negative peaks (P+/P-). (b) Graph in the frequency domain, showing the ratio between the powers of the harmonics 2–5 in relation to the fundamental, in dB, which is related to the degree of wave distortion.

Although the waveform distortion mechanism is physically complex, involving the generation of harmonics and diffraction, dissipation and dispersion phenomena during the propagation of the acoustic wave in the fluid medium [28], mathematical models are available and are able to portray fairly accurately experimental results [30–33]. Of course, appropriate equipment allows reliable measurements capable of corroborating theoretical models [34], which was

cies, the greater the attenuation caused by propagation at these frequencies.

For the example of the figure, σ ffi 5:7.

128 Biofuels - State of Development

Ultrasound is used in many different fields, and different devices have been constructed to specific applications. The most common uses include detecting objects and measuring distances; ultrasound imaging is used in medicine for diagnostic and in non-destructive testing of products, materials and structures to detect invisible flaws for raw eyes. Industrial applications of ultrasound include cleaning, mixing and accelerating chemical processes.

According to [37], sonicate is "to disrupt (something) by exposure to high-frequency sound waves", and sonication is "the act of applying sound energy to agitate particles in a sample, for various purposes". Hence, ultrasonication is a process in which ultrasonic frequencies are usually used to produce alternating low- and high-pressure waves in liquids, leading to the formation and violent collapse of small vacuum bubbles. This phenomenon is called cavitation and causes high-speed foist liquid jets and strong hydrodynamic shear forces. Ultrasonication proffers great potential in the processing of liquids, improving the mixing and chemical reactions in various industrial applications.

Industrial processes like the disintegration of cells or the mixing of reactants as well as the deagglomeration and milling of micrometer and nanometer-size materials are examples of ultrasonication application. Besides, chemical reactions benefit from the free radicals created by the cavitation, as well as from the energy input and the material transfer through boundary layers. For many processes, this sonochemical effect leads to a substantial reduction in the reaction time, like in the transesterification of oil into biodiesel.

The working frequency of an ultrasonic transducer is defined as the frequency of an ultrasonic signal based on the observation of the output of a hydrophone placed in an ultrasonic field at the position corresponding to the spatial-peak temporal-peak ultrasonic pressure [40]. The hydrophone is a transducer made from either polyvinylidene fluoride (PVDF) or piezoceramic (PZT) that produces electrical signals in response to surface input of ultrasonic signals [41]. Those signals are often measured using an oscilloscope, and the signal is analyzed using either

The ultrasonic properties of materials within the megahertz frequency range are determined using techniques commonly referred to as the through-transmission substitution technique [42, 43] and as pulse-echo technique [44]. Using those techniques, it is possible to measure speed of sound and attenuation coefficient of the material under text. In general lines, the time of flight (related to the speed of sound) and the amplitude (related to attenuation) of the ultrasonic signal are measured in a reference medium, normally water. In the sequence, the time of flight and the amplitude are measured over the material under test. As the speed of sound and attenuation coefficient in the water are well known, and accurately determined based on measured temperature, the properties of the material under test are determined

In more details, calculation of speed of sound is carried out by measuring the arrival time of the ultrasonic pulse both with (ts) and without (t0) the test sample in the ultrasonic beam. The difference in these times (t ¼ ts � t0) is the time-shift caused by the different speed of sound in

vs <sup>¼</sup> <sup>l</sup> � vw

in which vw is the speed of sound in water at the temperature of interest and l is the sample

The ultrasonic transmission loss (TL) can be determined by measuring the frequencydependent (f) change in amplitude of the electrical waveform through water (V0ð Þf ) and with the test sample in the ultrasonic beam (Vsð Þf ), which shall be positioned and aligned

V0ð Þf

TL dB ð Þ¼�20 � log <sup>10</sup>

incident wave at the interface between the water and the sample.

The attenuation coefficient of the test sample is obtained by dividing the TL by the sample thickness, after appropriately correcting for attenuation in water path and reflection of the

It is known that biodiesel is typically obtained by the transesterification of the triglycerides of oils and fats with an alcohol in the presence of an acid or alkaline catalyst [46]. This reaction is

vw � <sup>t</sup> <sup>þ</sup> <sup>l</sup> (10)

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Vsð Þ<sup>f</sup> (11)

the zero-crossing technique or a spectral analysis method [40].

relative to water [45].

thickness.

within the beam:

3. The past

the material (vs), which can be derived as [45]

In general, ultrasonic concepts of industrial processes are initially tested on laboratory scale to prove feasibility and establish the required operation ultrasonic parameters. The next step is to transfer the validated concept to a pilot scale for optimization and finally to an industrial scale. During the scale-up, it is important to guarantee that all exposure conditions (e.g. ultrasonic amplitude, working frequency, cavitation intensity, ultrasound exposure time, etc.) remain the same, in order to assure the final product quality, whilst the productivity is increased by a "scale-up factor".

#### 2.5. Ultrasound parameter measurement

Considering some industrial applications, high ultrasonic power is required for many processes. On the other hand, when ultrasound is used to analyze the quality of chemical inputs [38] or the behavior of chemical reactions, low-power ultrasound is used to avoid any alteration in the chemical product or any interference in the chemical reaction.

In this direction, ultrasound parameters shall be calibrated to guarantee the adequate use of ultrasound at each specific industrial application. Herein, some parameters will be highlighted and how they are measured, as the output power and the working frequency, which are related to the device that generates the ultrasonic waves, and the propagation velocity and the attenuation, which are intrinsically correlated to the properties of the medium in which the ultrasonic waves are traveling.

According to IEC 61161 [39], output ultrasonic power (OP) is defined as the "time-average ultrasonic power emitted by an ultrasonic transducer into an approximately free field under specified conditions in a specified medium, preferably water". The output power is expressed in watt (W). In general, ultrasonic power is measured in water, based on the measurement of the ultrasonic radiation force (F), which is the time-average force (expressed in N) acting on a target in an ultrasonic field and caused by the ultrasonic field. This force is typically measured using the radiation force balance that consists of a reflecting or absorbing target connected to a gravimetric microbalance. The ultrasonic beam is directed vertically upwards or downwards on the target, and the gravimetric balance measures the radiation force exerted by the ultrasonic beam. The radiation force component on the absorbing target in the propagation direction of the incident wave is related to the acoustic output power of the ultrasonic transducer as presented in (9):

$$O\_P = \upsilon \cdot F \tag{9}$$

The ultrasonic power shall be determined from the difference between the force measured with and without ultrasonic radiation. The great advantage of radiation force measurements is that a value for the total radiated power is obtained without the need to integrate field data over the cross section of the radiated ultrasound beam.

The working frequency of an ultrasonic transducer is defined as the frequency of an ultrasonic signal based on the observation of the output of a hydrophone placed in an ultrasonic field at the position corresponding to the spatial-peak temporal-peak ultrasonic pressure [40]. The hydrophone is a transducer made from either polyvinylidene fluoride (PVDF) or piezoceramic (PZT) that produces electrical signals in response to surface input of ultrasonic signals [41]. Those signals are often measured using an oscilloscope, and the signal is analyzed using either the zero-crossing technique or a spectral analysis method [40].

The ultrasonic properties of materials within the megahertz frequency range are determined using techniques commonly referred to as the through-transmission substitution technique [42, 43] and as pulse-echo technique [44]. Using those techniques, it is possible to measure speed of sound and attenuation coefficient of the material under text. In general lines, the time of flight (related to the speed of sound) and the amplitude (related to attenuation) of the ultrasonic signal are measured in a reference medium, normally water. In the sequence, the time of flight and the amplitude are measured over the material under test. As the speed of sound and attenuation coefficient in the water are well known, and accurately determined based on measured temperature, the properties of the material under test are determined relative to water [45].

In more details, calculation of speed of sound is carried out by measuring the arrival time of the ultrasonic pulse both with (ts) and without (t0) the test sample in the ultrasonic beam. The difference in these times (t ¼ ts � t0) is the time-shift caused by the different speed of sound in the material (vs), which can be derived as [45]

$$
\upsilon v\_s = \frac{l \cdot \upsilon\_w}{\upsilon\_w \cdot t + l} \tag{10}
$$

in which vw is the speed of sound in water at the temperature of interest and l is the sample thickness.

The ultrasonic transmission loss (TL) can be determined by measuring the frequencydependent (f) change in amplitude of the electrical waveform through water (V0ð Þf ) and with the test sample in the ultrasonic beam (Vsð Þf ), which shall be positioned and aligned within the beam:

$$\text{TL}(dB) = -20 \cdot \log\_{10} \frac{V\_0(f)}{V\_s(f)} \tag{11}$$

The attenuation coefficient of the test sample is obtained by dividing the TL by the sample thickness, after appropriately correcting for attenuation in water path and reflection of the incident wave at the interface between the water and the sample.

#### 3. The past

Industrial processes like the disintegration of cells or the mixing of reactants as well as the deagglomeration and milling of micrometer and nanometer-size materials are examples of ultrasonication application. Besides, chemical reactions benefit from the free radicals created by the cavitation, as well as from the energy input and the material transfer through boundary layers. For many processes, this sonochemical effect leads to a substantial reduction in the

In general, ultrasonic concepts of industrial processes are initially tested on laboratory scale to prove feasibility and establish the required operation ultrasonic parameters. The next step is to transfer the validated concept to a pilot scale for optimization and finally to an industrial scale. During the scale-up, it is important to guarantee that all exposure conditions (e.g. ultrasonic amplitude, working frequency, cavitation intensity, ultrasound exposure time, etc.) remain the same, in order to assure the final product quality, whilst the productivity is increased by a

Considering some industrial applications, high ultrasonic power is required for many processes. On the other hand, when ultrasound is used to analyze the quality of chemical inputs [38] or the behavior of chemical reactions, low-power ultrasound is used to avoid any alter-

In this direction, ultrasound parameters shall be calibrated to guarantee the adequate use of ultrasound at each specific industrial application. Herein, some parameters will be highlighted and how they are measured, as the output power and the working frequency, which are related to the device that generates the ultrasonic waves, and the propagation velocity and the attenuation, which are intrinsically correlated to the properties of the medium in which the

According to IEC 61161 [39], output ultrasonic power (OP) is defined as the "time-average ultrasonic power emitted by an ultrasonic transducer into an approximately free field under specified conditions in a specified medium, preferably water". The output power is expressed in watt (W). In general, ultrasonic power is measured in water, based on the measurement of the ultrasonic radiation force (F), which is the time-average force (expressed in N) acting on a target in an ultrasonic field and caused by the ultrasonic field. This force is typically measured using the radiation force balance that consists of a reflecting or absorbing target connected to a gravimetric microbalance. The ultrasonic beam is directed vertically upwards or downwards on the target, and the gravimetric balance measures the radiation force exerted by the ultrasonic beam. The radiation force component on the absorbing target in the propagation direction of the incident wave is related to the acoustic output power of the ultrasonic transducer as presented in (9):

The ultrasonic power shall be determined from the difference between the force measured with and without ultrasonic radiation. The great advantage of radiation force measurements is that a value for the total radiated power is obtained without the need to integrate field data

over the cross section of the radiated ultrasound beam.

OP ¼ v � F (9)

ation in the chemical product or any interference in the chemical reaction.

reaction time, like in the transesterification of oil into biodiesel.

"scale-up factor".

130 Biofuels - State of Development

2.5. Ultrasound parameter measurement

ultrasonic waves are traveling.

It is known that biodiesel is typically obtained by the transesterification of the triglycerides of oils and fats with an alcohol in the presence of an acid or alkaline catalyst [46]. This reaction is traditionally performed using mechanical stirring, but this process is limited by mass transfer between the different reactants. This limitation is normally overcome by increase stirring, temperature and reaction time to aid in solubility between the reactants.

Ultrasound methods for biodiesel production have developed continuously. Table 1 compiles several papers published in the last decade, whether by irradiation ultrasonic indirect (bath) or direct (probe and transducer), in the presence of acid or basic catalysts, using the most diverse

The main perspective in the past was the use of equipment available in any chemical labora-

The ultrasonic probe is a usual commercialized equipment that has high power output capability as it concentrates energy delivering. In this type of equipment, there is a distance (about 5 cm) between the transducer (responsible for irradiation) and the tip of the horn. The ultrasonic energy is provided to the liquid through the horn immersed in it, as shown in Figure 8. Many studies using this equipment for producing biodiesel are found in the literature [3–6]. In the study by Lifka et al. [3], an ultrasonic processor (24 kHz; 200 W) known as ultrasonic probe was used in the transesterification reaction of canola oil with ethanol. After 30 min of reaction, a conversion of 87% was obtained to a molar ratio of 6:1 and 0.5–1% of the sodium hydroxide. A study of the energy balance was carried out comparing the three methods of agitation: magnetic, mechanical and by ultrasound. It was concluded that using ultrasound obtains lower energy costs. Georgogianni et al. [4] also performed biodiesel production with ultrasonic probe at low frequency (24 kHz; 200 W). They used sunflower oil and methanol at a molar ratio alcohol/oil of 7:1 and 2% sodium hydroxide. In 20 min of reaction, it reached 95% yield. In the presence of ethanol, using the same reaction parameters, the ultrasound led to high ester

tory, with ultrasonic waves of low frequency (up to 500 kHz) and high power [51].

Catalyst type; (%)

Canola oil Methanol 6:1 NaOH; 0.5 20 kHz; 200 W 30 min; 87 [3] Sunflower oil Methanol 7:1 NaOH; 2 24 kHz; 200 W 20 min; 95 [4] Coconut oil Ethanol 6:1 KOH; 0.75 24 kHz; 200 W 7 min; 98 [5] Canola oil Methanol 5:1 KOH; 0.7 20 kHz; 2000 W 50 min; 99 [6] Synthetic oil Methanol 6:1 NaOH; 0.5 40 kHz; 840 W 20 min; 98 [52] Soybean oil Ethanol 10:1 NaOH; 0.3 40 kHz; 30 min; 91.8 [53] Oleic acid Ethanol 3:1 H2SO4; 5 40 kHz; 700 W 120 min; 90 [54] Fish oil Methanol 9:1 H2SO4; 2 40 kHz; 60 W 90 min; 98.2 [55]

Cottonseed oil Methanol 6:1 KOH; 1 40 kHz; 5 min; 96.0 [57] Palm acid Methanol 7:1 H2SO4; 5 22 kHz; 120 W 200 min; >90 [58]

Jatropha oil Methanol 7:1 H2SO4; 4 210 W 60 min; 96.4 [60]

Table 1. Compilation of studies with typical parameters in ultrasound-assisted transesterifications.

Frequency; power

Methanol 6:1 KOH; 1 20 kHz; 200 W 40 min; 89 [56]

Methanol 9:1 H2SO4; 3 40 kHz; 200 W 60 min; 99.9 [59]

Time(min); conversion

Refs.

(%)

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raw materials.

Feedstock Alcohol type; molar ratio

Waste cooking

Waste cooking

oil

oil

Originally, the ultrasound was used in transesterification reactions to homogenize the two immiscible phases (triglyceride and alcohol). This homogenization is caused by acoustic cavitation. This phenomenon releases large amounts of energy resulting in very high temperatures and pressures [47].

In addition, there is another application which consists of the use of non-destructive ultrasound for characterization and analysis of materials. Ultrasound has been used for this purpose for several decades in various industrial applications, including chemistry reactions. However, in the past, methods were not addressed for the characterization and analysis of materials focused in the production of biodiesel. There is a study [46] that uses ultrasound to characterize the by-product (glycerol) formed in the transesterification reaction. The objective was not the ester formation, but the analyses of glycerol deposition instead.

That said, a systematic review of the use of ultrasound in biodiesel production will be presented in this section. Taking into account the importance of technology, the review will include a discussion about the notorious advantages of the technique, interaction with other methods and method limitations.

#### 3.1. Ultrasound-assisted biodiesel production

According to [47], in 1927, Alfred L. Loomis was the first chemist to recognize the effect of intense sound waves propagating through the liquid, more known as sonochemical effect. Despite the discovery, research focused on the area started from 1980. In this context, since 2003, ultrasound has been a favorable tool in biodiesel production, due to the ability to eliminate the mass transfer resistance and for being an efficient and low-cost method.

WO2007/077302A1 [48] is the first patent that encompasses an ultrasound method and the production of biodiesel. This invention relates to equipment and process for producing biodiesel where ultrasound is used to destruct heated fat. The preheated fat is cracked in several tanks that are connected to each other in series or in parallel. The ultrasound device is situated inside the tank and uses ultrasonic frequency between 15 and 55 kHz.

Subsequently, two more patents were deposited. KR20100110678 [49] describes a reactor for biodiesel production, where the ultrasonic horn is exposed in the inside of the reactor. The reaction is performed under pressure from 100 to 350 bar, temperature between 35 and 60�C and ultrasonic power from 60 to 1.500 W. This invention aims to synthesize biodiesel with high reaction speed and high yield. The other invention US2012279111 [50] is a continuous process for producing biodiesel fuel. In this process, the reagents are fed into an ultrasonic cavitation reactor. After 5–30 s, the flow leaves the reactor and goes to an agitated-tank-type reactor. The mixture remains for about 1 h, which is the time needed to yield the final conversion of triglycerides of about 96%. The mechanical stirring is responsible for most of the reaction, and ultrasonic cavitation only assists the homogenization of the reagents.

Ultrasound methods for biodiesel production have developed continuously. Table 1 compiles several papers published in the last decade, whether by irradiation ultrasonic indirect (bath) or direct (probe and transducer), in the presence of acid or basic catalysts, using the most diverse raw materials.

traditionally performed using mechanical stirring, but this process is limited by mass transfer between the different reactants. This limitation is normally overcome by increase stirring,

Originally, the ultrasound was used in transesterification reactions to homogenize the two immiscible phases (triglyceride and alcohol). This homogenization is caused by acoustic cavitation. This phenomenon releases large amounts of energy resulting in very high temperatures

In addition, there is another application which consists of the use of non-destructive ultrasound for characterization and analysis of materials. Ultrasound has been used for this purpose for several decades in various industrial applications, including chemistry reactions. However, in the past, methods were not addressed for the characterization and analysis of materials focused in the production of biodiesel. There is a study [46] that uses ultrasound to characterize the by-product (glycerol) formed in the transesterification reaction. The objective

That said, a systematic review of the use of ultrasound in biodiesel production will be presented in this section. Taking into account the importance of technology, the review will include a discussion about the notorious advantages of the technique, interaction with other methods and

According to [47], in 1927, Alfred L. Loomis was the first chemist to recognize the effect of intense sound waves propagating through the liquid, more known as sonochemical effect. Despite the discovery, research focused on the area started from 1980. In this context, since 2003, ultrasound has been a favorable tool in biodiesel production, due to the ability to

WO2007/077302A1 [48] is the first patent that encompasses an ultrasound method and the production of biodiesel. This invention relates to equipment and process for producing biodiesel where ultrasound is used to destruct heated fat. The preheated fat is cracked in several tanks that are connected to each other in series or in parallel. The ultrasound device is situated

Subsequently, two more patents were deposited. KR20100110678 [49] describes a reactor for biodiesel production, where the ultrasonic horn is exposed in the inside of the reactor. The reaction is performed under pressure from 100 to 350 bar, temperature between 35 and 60�C and ultrasonic power from 60 to 1.500 W. This invention aims to synthesize biodiesel with high reaction speed and high yield. The other invention US2012279111 [50] is a continuous process for producing biodiesel fuel. In this process, the reagents are fed into an ultrasonic cavitation reactor. After 5–30 s, the flow leaves the reactor and goes to an agitated-tank-type reactor. The mixture remains for about 1 h, which is the time needed to yield the final conversion of triglycerides of about 96%. The mechanical stirring is responsible for most of the reaction, and

eliminate the mass transfer resistance and for being an efficient and low-cost method.

inside the tank and uses ultrasonic frequency between 15 and 55 kHz.

ultrasonic cavitation only assists the homogenization of the reagents.

temperature and reaction time to aid in solubility between the reactants.

was not the ester formation, but the analyses of glycerol deposition instead.

and pressures [47].

132 Biofuels - State of Development

method limitations.

3.1. Ultrasound-assisted biodiesel production

The main perspective in the past was the use of equipment available in any chemical laboratory, with ultrasonic waves of low frequency (up to 500 kHz) and high power [51].

The ultrasonic probe is a usual commercialized equipment that has high power output capability as it concentrates energy delivering. In this type of equipment, there is a distance (about 5 cm) between the transducer (responsible for irradiation) and the tip of the horn. The ultrasonic energy is provided to the liquid through the horn immersed in it, as shown in Figure 8.

Many studies using this equipment for producing biodiesel are found in the literature [3–6]. In the study by Lifka et al. [3], an ultrasonic processor (24 kHz; 200 W) known as ultrasonic probe was used in the transesterification reaction of canola oil with ethanol. After 30 min of reaction, a conversion of 87% was obtained to a molar ratio of 6:1 and 0.5–1% of the sodium hydroxide. A study of the energy balance was carried out comparing the three methods of agitation: magnetic, mechanical and by ultrasound. It was concluded that using ultrasound obtains lower energy costs. Georgogianni et al. [4] also performed biodiesel production with ultrasonic probe at low frequency (24 kHz; 200 W). They used sunflower oil and methanol at a molar ratio alcohol/oil of 7:1 and 2% sodium hydroxide. In 20 min of reaction, it reached 95% yield. In the presence of ethanol, using the same reaction parameters, the ultrasound led to high ester


Table 1. Compilation of studies with typical parameters in ultrasound-assisted transesterifications.

Figure 8. Schematic representation of the reaction using ultrasonic probe. Adapted from Sáez-Bastante et al. [7].

yields, about 98%. In only 40 min of reaction while using mechanical stirring it gave lower yields, about 88%, even after 4 h of reaction time.

Rodrigues et al. [53] also produced biodiesel in an ultrasonic bath with low-frequency waves (40 kHz), using soybean oil as raw material and ethanol. The author reports that after 30 min of reaction, the conversion (91.8%) was greater than the conversion obtained using the conventional process. Studies from other research groups too have confirmed the high conversion by using the ultrasonic bath. In study of Hanh et al. [54], the reaction was carried out in an ultrasonic bath operating at 40 kHz and 700 W. The conversion obtained was 90% after 120 min of reaction, using oleic acid and ethanol at an alcohol-to-oil molar ratio of 3:1. Santos et al. [55] also used ultrasonic bath, operating at 40 kHz and 60 W. The biodiesel was produced from reaction fish oil with methanol by an ultrasound-assisted method. The reaction was carried out with molar ratio alcohol/oil of 9:1 and a catalyst concentration of 2.0%. A higher methyl ester yield was achieved as compared to mechanical stirring. The yield was equal to

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Figure 9. Schematic representation of the reaction using ultrasonic bath.

It may be noted that using an ultrasonic bath, it is possible to achieve high conversions. The ultrasonic bath was designed for cleaning and degassing and does not allow directional irradiation in the reaction medium. Therefore, a possible explanation for their performance is that these reactions are always conducted with external heating between 40 and 70�C, and heating facilitates transesterification of triglycerides. Despite the favorable results, this equipment has as disadvantage the low cavitation efficiency and distribution of the dispersed and non-homogeneous acoustic intensity and usually requires mechanical agitation

In 2009, the use of ultrasonic transducer directly applied in the reaction media begins to be proposed. Different than the use of ultrasonic probe, in this application there is no separation between the transducer and the liquid surface; thus, the volume of wave propagation is more

Hingu et al. [56] synthesized biodiesel from waste cooking oil using a low-frequency ultrasonic reactor at 20 kHz with power of 200 W. The optimum conditions for the process have been molar ratio of alcohol to oil of 6:1, catalyst concentration of 1% and temperature of 45�C. The

98.2% in 90 min of reaction.

confined (see Figure 10).

[61].

Kumar et al. [5] used the same equipment as described in [3] in the transesterification of coconut oil to produce ethyl ester. A 98% conversion of the ethyl ester was obtained in 7 min of reaction at a molar ratio of 6:1. In these studies the ultrasonic probe was used as an alternative to the usual production process and resulted in high conversions. Thanh et al. [6] developed a pilot scale plant for biodiesel production from canola oil catalyzed by hydroxide potassium. An ultrasonic probe was used at low frequency (20 kHz). After 50 min of reaction, a maximum conversion of more than 99% was obtained with a methanol-to-oil molar ratio of 5:1, 0.7% catalyst concentration. The authors conclude that optimization of ultrasonic power and mode of delivery (pulsed ultrasound) can be carried out to minimize energy consumption while attaining high conversions.

Although it has been widely used, the ultrasonic probe has some disadvantages as it easily corrodes the horn tip [51] and presents low cavitation efficiency. In addition, the acoustic intensity is distributed in a concentrated and non-homogeneous fashion.

Another equipment commonly used in the production of biodiesel mainly because of its low cost and for being an equipment of easy acquisition is the ultrasonic bath. In this equipment, the ultrasonic transducers are positioned in the bottom or lateral position of the bath, and a reactor is fixed to the bottom, as shown in Figure 9.

There are several studies that performed transesterification reactions in ultrasonic baths. In these studies, the conversion results were greater than 90% [52–55]. Stavarache et al. [52] produced biodiesel using an ultrasonic bath with frequency of 40 kHz. The authors compared the profile of methyl esters of different vegetable oils produced under ultrasonic irradiation with conventional heating. The profile of methyl esters in the presence of potassium hydroxide was quite similar for both procedures. In the case of sodium hydroxide, the reaction with using ultrasound gave better results. In this study, the highest conversion obtained was 98% after 20 min of reaction at an alcohol-to-oil molar ratio of 6:1.

Figure 9. Schematic representation of the reaction using ultrasonic bath.

yields, about 98%. In only 40 min of reaction while using mechanical stirring it gave lower

Figure 8. Schematic representation of the reaction using ultrasonic probe. Adapted from Sáez-Bastante et al. [7].

Kumar et al. [5] used the same equipment as described in [3] in the transesterification of coconut oil to produce ethyl ester. A 98% conversion of the ethyl ester was obtained in 7 min of reaction at a molar ratio of 6:1. In these studies the ultrasonic probe was used as an alternative to the usual production process and resulted in high conversions. Thanh et al. [6] developed a pilot scale plant for biodiesel production from canola oil catalyzed by hydroxide potassium. An ultrasonic probe was used at low frequency (20 kHz). After 50 min of reaction, a maximum conversion of more than 99% was obtained with a methanol-to-oil molar ratio of 5:1, 0.7% catalyst concentration. The authors conclude that optimization of ultrasonic power and mode of delivery (pulsed ultrasound) can be carried out to minimize energy consumption

Although it has been widely used, the ultrasonic probe has some disadvantages as it easily corrodes the horn tip [51] and presents low cavitation efficiency. In addition, the acoustic

Another equipment commonly used in the production of biodiesel mainly because of its low cost and for being an equipment of easy acquisition is the ultrasonic bath. In this equipment, the ultrasonic transducers are positioned in the bottom or lateral position of the bath, and a

There are several studies that performed transesterification reactions in ultrasonic baths. In these studies, the conversion results were greater than 90% [52–55]. Stavarache et al. [52] produced biodiesel using an ultrasonic bath with frequency of 40 kHz. The authors compared the profile of methyl esters of different vegetable oils produced under ultrasonic irradiation with conventional heating. The profile of methyl esters in the presence of potassium hydroxide was quite similar for both procedures. In the case of sodium hydroxide, the reaction with using ultrasound gave better results. In this study, the highest conversion obtained was 98% after

intensity is distributed in a concentrated and non-homogeneous fashion.

yields, about 88%, even after 4 h of reaction time.

reactor is fixed to the bottom, as shown in Figure 9.

20 min of reaction at an alcohol-to-oil molar ratio of 6:1.

while attaining high conversions.

134 Biofuels - State of Development

Rodrigues et al. [53] also produced biodiesel in an ultrasonic bath with low-frequency waves (40 kHz), using soybean oil as raw material and ethanol. The author reports that after 30 min of reaction, the conversion (91.8%) was greater than the conversion obtained using the conventional process. Studies from other research groups too have confirmed the high conversion by using the ultrasonic bath. In study of Hanh et al. [54], the reaction was carried out in an ultrasonic bath operating at 40 kHz and 700 W. The conversion obtained was 90% after 120 min of reaction, using oleic acid and ethanol at an alcohol-to-oil molar ratio of 3:1. Santos et al. [55] also used ultrasonic bath, operating at 40 kHz and 60 W. The biodiesel was produced from reaction fish oil with methanol by an ultrasound-assisted method. The reaction was carried out with molar ratio alcohol/oil of 9:1 and a catalyst concentration of 2.0%. A higher methyl ester yield was achieved as compared to mechanical stirring. The yield was equal to 98.2% in 90 min of reaction.

It may be noted that using an ultrasonic bath, it is possible to achieve high conversions. The ultrasonic bath was designed for cleaning and degassing and does not allow directional irradiation in the reaction medium. Therefore, a possible explanation for their performance is that these reactions are always conducted with external heating between 40 and 70�C, and heating facilitates transesterification of triglycerides. Despite the favorable results, this equipment has as disadvantage the low cavitation efficiency and distribution of the dispersed and non-homogeneous acoustic intensity and usually requires mechanical agitation [61].

In 2009, the use of ultrasonic transducer directly applied in the reaction media begins to be proposed. Different than the use of ultrasonic probe, in this application there is no separation between the transducer and the liquid surface; thus, the volume of wave propagation is more confined (see Figure 10).

Hingu et al. [56] synthesized biodiesel from waste cooking oil using a low-frequency ultrasonic reactor at 20 kHz with power of 200 W. The optimum conditions for the process have been molar ratio of alcohol to oil of 6:1, catalyst concentration of 1% and temperature of 45�C. The

yield. This improvement made this technique to be one of the most studied for the biodiesel

Although the use of ultrasound to improve the biofuel production has been used for decades,

When the question is "can we make better for the environment?" or "can we think in a greener procedure?", the use of high-power ultrasound for biodiesel production, even as it already demands less energy than the usual method, makes us reflect about the real energy necessary to produce a biofuel with quality. Within this approach, the Laboratory of Ultrasound of the Brazilian National Metrology Institute (Inmetro) has been developing different ways to produce biodiesel. The first results published about this study [8] used an ultrasonic transducer with 9 W to produce soybean biodiesel with methanol and potassium hydroxide as a catalyst. Despite that the results were considered good (conversion around 95%), the method used to analyze the conversion in that paper is not so well described in the literature regarding the reproducibility. In this way, the researches continued regarding the use of a lower-power and high-frequency ultrasound in the biofuel field production. Promising results have been

The optimization of the parameters and experimental setup were not the only changes in the study as shown in Figure 11. The monitoring of the conversion using the nuclear magnetic

calibrated according to the international standard [39], and 9.06 W was the effective acoustic power. The 85% of conversion supports the idea that reducing the delivered ultrasound energy is possible to produce biodiesel with a good conversion rate. Furthermore, it shows that the increase of the alcohol/oil ratio to 8:1 decrease the necessary time to achieve the maximum

Figure 11. Soybean biodiesel by ultrasound using the 1 MHz transducer using an alcohol/oil ratio of 6:1 and 8:1.

H NMR) gives more reliability to this study. The output power was

Ultrasound Methods for Biodiesel Production and Analysis

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137

the literature about low-power ultrasound (less than 50 W), for this purpose, is rare.

obtained with the same equipment used in [8] (see Figure 11).

production.

resonance of hydrogen (1

conversion rate.

Figure 10. Schematic representation of the reaction using ultrasonic transducer.

power effect was studied, and the obtained conversion was around 66% at a power of 150 W. However, when the power was increased to 200 W, extent of conversion also increased to about 89%. On the other hand, an increase in the power dissipation from 200 to 250 W resulted in lower conversions. It was concluded that this can be attributed to the fact that at higher power levels, usually cushioning effect is observed which results in to decrease the transfer of energy into the system.

Fan et al. [57] used a transducer powered by a function generator to perform the transesterification of crude cottonseed oil with methanol in molar ratio of 6:1 in the presence of base catalyst. The reaction was conducted with low-frequency ultrasonic irradiation at room temperature. After 60 min of reaction, using the 40-kHz frequency waveform, a yield of approximately 90% yield was obtained. Four different frequencies were investigated: 400 Hz, 4 kHz, 40 kHz and 400 kHz. Significant difference in biodiesel yield among different frequencies was not observed. This suggests that there were no remarkable differences in the formation of the cavitation bubbles at the examined frequencies.

In the past, the use of ultrasound has proved to be an efficient technique to produce biodiesel. However, several ultrasonic parameters such as power, frequency and mode of operation can optimize the efficiency of this reaction. In this context, the development of new methods and equipment for ultrasound application must occur to make biodiesel production increasingly competitive.

#### 4. The present

For the last 7 years, several studies showed the effective system optimization regarding the use of high-power and low-frequency (typically up to 50 kHz) ultrasound in the biodiesel production [7, 62–66]. These studies investigate the best procedure or configuration to achieve a better yield. This improvement made this technique to be one of the most studied for the biodiesel production.

Although the use of ultrasound to improve the biofuel production has been used for decades, the literature about low-power ultrasound (less than 50 W), for this purpose, is rare.

When the question is "can we make better for the environment?" or "can we think in a greener procedure?", the use of high-power ultrasound for biodiesel production, even as it already demands less energy than the usual method, makes us reflect about the real energy necessary to produce a biofuel with quality. Within this approach, the Laboratory of Ultrasound of the Brazilian National Metrology Institute (Inmetro) has been developing different ways to produce biodiesel. The first results published about this study [8] used an ultrasonic transducer with 9 W to produce soybean biodiesel with methanol and potassium hydroxide as a catalyst. Despite that the results were considered good (conversion around 95%), the method used to analyze the conversion in that paper is not so well described in the literature regarding the reproducibility. In this way, the researches continued regarding the use of a lower-power and high-frequency ultrasound in the biofuel field production. Promising results have been obtained with the same equipment used in [8] (see Figure 11).

The optimization of the parameters and experimental setup were not the only changes in the study as shown in Figure 11. The monitoring of the conversion using the nuclear magnetic resonance of hydrogen (1 H NMR) gives more reliability to this study. The output power was calibrated according to the international standard [39], and 9.06 W was the effective acoustic power. The 85% of conversion supports the idea that reducing the delivered ultrasound energy is possible to produce biodiesel with a good conversion rate. Furthermore, it shows that the increase of the alcohol/oil ratio to 8:1 decrease the necessary time to achieve the maximum conversion rate.

power effect was studied, and the obtained conversion was around 66% at a power of 150 W. However, when the power was increased to 200 W, extent of conversion also increased to about 89%. On the other hand, an increase in the power dissipation from 200 to 250 W resulted in lower conversions. It was concluded that this can be attributed to the fact that at higher power levels, usually cushioning effect is observed which results in to decrease the transfer of

Fan et al. [57] used a transducer powered by a function generator to perform the transesterification of crude cottonseed oil with methanol in molar ratio of 6:1 in the presence of base catalyst. The reaction was conducted with low-frequency ultrasonic irradiation at room temperature. After 60 min of reaction, using the 40-kHz frequency waveform, a yield of approximately 90% yield was obtained. Four different frequencies were investigated: 400 Hz, 4 kHz, 40 kHz and 400 kHz. Significant difference in biodiesel yield among different frequencies was not observed. This suggests that there were no remarkable differences in the formation of the

In the past, the use of ultrasound has proved to be an efficient technique to produce biodiesel. However, several ultrasonic parameters such as power, frequency and mode of operation can optimize the efficiency of this reaction. In this context, the development of new methods and equipment for ultrasound application must occur to make biodiesel production increasingly

For the last 7 years, several studies showed the effective system optimization regarding the use of high-power and low-frequency (typically up to 50 kHz) ultrasound in the biodiesel production [7, 62–66]. These studies investigate the best procedure or configuration to achieve a better

energy into the system.

136 Biofuels - State of Development

competitive.

4. The present

cavitation bubbles at the examined frequencies.

Figure 10. Schematic representation of the reaction using ultrasonic transducer.

Figure 11. Soybean biodiesel by ultrasound using the 1 MHz transducer using an alcohol/oil ratio of 6:1 and 8:1.

The reactions described in Figure 11 achieve 43�C without necessity of a heating system. This leads an energy saving, when you think that the most expensive part of the reaction is the heating. These first results aim not just the optimization of the ultrasound use in the transesterification but the current concerns about energy wasting.

Considering the present worldwide biodiesel consumption, which increases every year, a new method for monitoring the production, helping to avoiding the waste of reagents, energy and time, is extremely necessary. The expensive and offline available methods can lead to accurate values but just in the end of each batch. This means that if something goes wrong during the process, the results would be noticed just after the end of the production. Thus, a low-cost and accurate technique, suitable to the process line, has been studied recently as a technological

Baesso et al. [9] disclose in their study that ultrasound can notice changes in the medium during transesterification reaction but can also monitor the kinetics behind the biodiesel production. That study analyzed four different reactions to produce biodiesel from commercial soybean oil. Methanol was the alcohol used, and potassium hydroxide was the catalyst. The changing of the catalyst concentration (0.2 or 1.5%) and the mechanical stirring (200 or 520 rpm) allowed the analyses of ultrasound capability to detect the real impact of changing these parameters. The study compared and related the oil consumption (CTAG), the biodiesel conversion rate (XTAG) and the propagation velocity. Both CTAG and XTAG were monitored

H NMR, as an offline method. Figures 12 and 13 show some results published in [9]. From the both figures reprinted from [9], it is possible to notice that ultrasound follows the

that for the four analyzed reactions, the ultrasound was capable to distinguish the end of

Figure 13. Variation of (a) TAG concentration, (b) propagation velocity and (c) TAG conversion for the reactions with

H NMR technique but in an inline mode. Baesso et al. [9] proved

Ultrasound Methods for Biodiesel Production and Analysis

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139

alternative way in the biodiesel industry.

520 rpm of rotation. Reprinted from Baêsso et al. [9].

by <sup>1</sup>

results obtained by the <sup>1</sup>

However, the use of ultrasound to produce biofuels is not the only application of this versatile technique. The use of very low-power and high-frequency ultrasound to monitor the liquid properties has been used in several fields for many years [46, 67–72]. One of the first studies was in 1995, when Sheen et al. [73] showed a non-invasive and inline system capable to measure the density and viscosity of Newtonian liquids using a 1 MHz transducer. The inline applicability of the ultrasound techniques boosted the development of these techniques in the biofuel field. In the last 6 years, studies to detect the adulteration in biofuels [74, 75], to quantify oil and grease contents in biofuel wastewater [76] and to monitor the biodiesel reactions [77] were carried out with good results. The ethanol adulteration analyzed by Figueiredo et al. [75] introduced the idea of the importance of the metrology in the biofuel system. Not just the possibility of the use of ultrasound was proved to be simple and accurate but its feasibility as an auxiliary tool that can be applied in the line process.

In this way, the constant search for the improvement in ultrasound measurements is developing the real possibility of an ultimate ultrasound system to monitor not just the biodiesel production but its quality as well.

Figure 12. Variation of (a) TAG concentration, (b) propagation velocity and (c) TAG conversion for the reactions with 200 rpm of rotation. Reprinted from Baêsso et al. [9].

Considering the present worldwide biodiesel consumption, which increases every year, a new method for monitoring the production, helping to avoiding the waste of reagents, energy and time, is extremely necessary. The expensive and offline available methods can lead to accurate values but just in the end of each batch. This means that if something goes wrong during the process, the results would be noticed just after the end of the production. Thus, a low-cost and accurate technique, suitable to the process line, has been studied recently as a technological alternative way in the biodiesel industry.

The reactions described in Figure 11 achieve 43�C without necessity of a heating system. This leads an energy saving, when you think that the most expensive part of the reaction is the heating. These first results aim not just the optimization of the ultrasound use in the transester-

However, the use of ultrasound to produce biofuels is not the only application of this versatile technique. The use of very low-power and high-frequency ultrasound to monitor the liquid properties has been used in several fields for many years [46, 67–72]. One of the first studies was in 1995, when Sheen et al. [73] showed a non-invasive and inline system capable to measure the density and viscosity of Newtonian liquids using a 1 MHz transducer. The inline applicability of the ultrasound techniques boosted the development of these techniques in the biofuel field. In the last 6 years, studies to detect the adulteration in biofuels [74, 75], to quantify oil and grease contents in biofuel wastewater [76] and to monitor the biodiesel reactions [77] were carried out with good results. The ethanol adulteration analyzed by Figueiredo et al. [75] introduced the idea of the importance of the metrology in the biofuel system. Not just the possibility of the use of ultrasound was proved to be simple and accurate but its

In this way, the constant search for the improvement in ultrasound measurements is developing the real possibility of an ultimate ultrasound system to monitor not just the biodiesel

Figure 12. Variation of (a) TAG concentration, (b) propagation velocity and (c) TAG conversion for the reactions with

ification but the current concerns about energy wasting.

feasibility as an auxiliary tool that can be applied in the line process.

production but its quality as well.

138 Biofuels - State of Development

200 rpm of rotation. Reprinted from Baêsso et al. [9].

Baesso et al. [9] disclose in their study that ultrasound can notice changes in the medium during transesterification reaction but can also monitor the kinetics behind the biodiesel production. That study analyzed four different reactions to produce biodiesel from commercial soybean oil. Methanol was the alcohol used, and potassium hydroxide was the catalyst. The changing of the catalyst concentration (0.2 or 1.5%) and the mechanical stirring (200 or 520 rpm) allowed the analyses of ultrasound capability to detect the real impact of changing these parameters. The study compared and related the oil consumption (CTAG), the biodiesel conversion rate (XTAG) and the propagation velocity. Both CTAG and XTAG were monitored by <sup>1</sup> H NMR, as an offline method. Figures 12 and 13 show some results published in [9].

From the both figures reprinted from [9], it is possible to notice that ultrasound follows the results obtained by the <sup>1</sup> H NMR technique but in an inline mode. Baesso et al. [9] proved that for the four analyzed reactions, the ultrasound was capable to distinguish the end of

Figure 13. Variation of (a) TAG concentration, (b) propagation velocity and (c) TAG conversion for the reactions with 520 rpm of rotation. Reprinted from Baêsso et al. [9].

each one without any sample pretreatment. The use of the ultrasound in this study would allow the industry save not just energy with the reducing time but with the expensive techniques to analyze the final product. Not just the idea of using this kind of technology in biodiesel industry is remarkable, but the use of the metrology gives more reliability for the current technologies that aim the biofuel production optimization.

#### 5. The future

Disclosing the future is not often considered science. Nevertheless, some clues can be gathered in the well-established state of the technique to point out some possible tracks to be followed. With respect to the use of ultrasound in biodiesel production and analysis, the future seems to be related to the use of broadband, frequency-modulated waveforms. Deconvolution techniques, both in time or frequency domains, are ready enough to be used in biodiesel analysis and production. Some recent achievement will be discussed in this section, and a sort of future prediction will be essayed.

delay is mathematically constructed based on the pseudo-inverted frequency spectrum, and the complex frequency spectrum is determined on sequence. Finally, the time-domain signal is constructed using the inverse Fourier transformation. Details of the processing can be found in the literature. The important concept here is that the system identification method developed as that has the intrinsic characteristic of putting apart any distortion caused by the system, including that one caused by nonlinear propagation. The distortion can even be evaluated separately, being the harmonics characterized or quantified individually. Such process has a completely unexploited capability to be used in fuel and biofuel analysis. It is our bet for the future of

Figure 14. CFM construction forms a predetermined system frequency response. Adapted from Costa-Felix et al. [84].

Ultrasound Methods for Biodiesel Production and Analysis

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141

Throughout this chapter, the past, the present and the future of biodiesel production and analyses using ultrasound methods were presented and discussed. The chapter was written aiming to let the not insider reader to be able to conquest the basis of ultrasound and biodiesel technical

The past was a remarkable assortment of attempts to make use of generic ultrasound systems to accelerate biodiesel production. The present brings several dedicated instruments, measurement systems and fabrications tools specially designed for the use of ultrasound in fuel and biofuel. In the future, who knows? The trend seems to be related to the use of digital signal processing for specially designed applications, using, for instance, online real-time signal design based on transfer function and system identification for manufacturing optimization.

Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and

Laboratory of Ultrasound, Directory of Scientific and Industrial Metrology, National Institute

ultrasound methods on fuel identification, quantification and quality control.

6. Final remarks

That is our best bet.

Author details

Rodrigo P.B. Costa-Félix\*

\*Address all correspondence to: rpfelix@inmetro.gov.br

of Metrology, Quality and Technology (Inmetro), Xerem, RJ, Brazil

relationship.

Quantitative ultrasound (QUS) is a measurement approach for quantifying ultrasonic parameters of a medium. In general, the ultrasonic quantities are derived from two basic measuring quantities: time of flight and amplitude. Those quantities vary as function of frequency and physical-chemical properties of the interrogated medium, including density, temperature, viscosity, the presence of scatters, discontinuities and other interleaved structures or intercurrent phenomena. The aforementioned quantities are extracted from a time- or frequency-domain ultrasonic signal.

For inspection in liquid media, the most important aspects are the ultrasonic phase velocity and the scattering pattern [42, 43, 45]. The behavior of those derived quantities as function of frequency is deeply related to density and viscosity. Many studies have been demonstrating the relationship between QUS and fuel [9, 75, 76, 78]. Another approach to the use of ultrasound in the industry of fuel and biofuel is its use for production [1, 8, 54, 63, 64]. Ultrasound has been demonstrated to be useful to cell culture treatment [79], as well. In all cases, a proper evaluation of ultrasonic parameters or transducer characteristics plays an important role, and some basic metrological procedures shall be followed, including uncertainty determination [80–83].

Ultrasound propagation has intrinsic capability of generating nonlinear distortion, depending of some factors such as frequency, power and propagation distance [17, 23, 30]. It could even be of great interest as a disaster for ultrasound analysis. Fortunately, there is relatively simple way to deal with nonlinear distorted fields, which is the use of compensated frequency-modulated signals to identify systems and perform ultrasound measurements [84, 85]. The method described in those papers can be generalized for virtually any system to be measured, for instance, fuel and biofuel, including contaminants. The basis consists in constructing a waveform in the time domain from information previously known or experimentally obtained about the system frequency response. Figure 14 was extracted and adapted from [84] and summarizes the signal construction method.

The system frequency response (FR) shall be previously determined or arbitrarily defined. After that, it is band-limited and pseudo-inverted, defining a bandwidth for the final signal. The group

Figure 14. CFM construction forms a predetermined system frequency response. Adapted from Costa-Felix et al. [84].

delay is mathematically constructed based on the pseudo-inverted frequency spectrum, and the complex frequency spectrum is determined on sequence. Finally, the time-domain signal is constructed using the inverse Fourier transformation. Details of the processing can be found in the literature. The important concept here is that the system identification method developed as that has the intrinsic characteristic of putting apart any distortion caused by the system, including that one caused by nonlinear propagation. The distortion can even be evaluated separately, being the harmonics characterized or quantified individually. Such process has a completely unexploited capability to be used in fuel and biofuel analysis. It is our bet for the future of ultrasound methods on fuel identification, quantification and quality control.

#### 6. Final remarks

each one without any sample pretreatment. The use of the ultrasound in this study would allow the industry save not just energy with the reducing time but with the expensive techniques to analyze the final product. Not just the idea of using this kind of technology in biodiesel industry is remarkable, but the use of the metrology gives more reliability for

Disclosing the future is not often considered science. Nevertheless, some clues can be gathered in the well-established state of the technique to point out some possible tracks to be followed. With respect to the use of ultrasound in biodiesel production and analysis, the future seems to be related to the use of broadband, frequency-modulated waveforms. Deconvolution techniques, both in time or frequency domains, are ready enough to be used in biodiesel analysis and production. Some recent achievement will be discussed in this section, and a sort of future

Quantitative ultrasound (QUS) is a measurement approach for quantifying ultrasonic parameters of a medium. In general, the ultrasonic quantities are derived from two basic measuring quantities: time of flight and amplitude. Those quantities vary as function of frequency and physical-chemical properties of the interrogated medium, including density, temperature, viscosity, the presence of scatters, discontinuities and other interleaved structures or intercurrent phenomena. The aforementioned quantities are extracted from a time- or frequency-domain

For inspection in liquid media, the most important aspects are the ultrasonic phase velocity and the scattering pattern [42, 43, 45]. The behavior of those derived quantities as function of frequency is deeply related to density and viscosity. Many studies have been demonstrating the relationship between QUS and fuel [9, 75, 76, 78]. Another approach to the use of ultrasound in the industry of fuel and biofuel is its use for production [1, 8, 54, 63, 64]. Ultrasound has been demonstrated to be useful to cell culture treatment [79], as well. In all cases, a proper evaluation of ultrasonic parameters or transducer characteristics plays an important role, and some basic

metrological procedures shall be followed, including uncertainty determination [80–83].

Ultrasound propagation has intrinsic capability of generating nonlinear distortion, depending of some factors such as frequency, power and propagation distance [17, 23, 30]. It could even be of great interest as a disaster for ultrasound analysis. Fortunately, there is relatively simple way to deal with nonlinear distorted fields, which is the use of compensated frequency-modulated signals to identify systems and perform ultrasound measurements [84, 85]. The method described in those papers can be generalized for virtually any system to be measured, for instance, fuel and biofuel, including contaminants. The basis consists in constructing a waveform in the time domain from information previously known or experimentally obtained about the system frequency response. Figure 14 was extracted and adapted from [84] and summarizes the signal construction method.

The system frequency response (FR) shall be previously determined or arbitrarily defined. After that, it is band-limited and pseudo-inverted, defining a bandwidth for the final signal. The group

the current technologies that aim the biofuel production optimization.

5. The future

140 Biofuels - State of Development

prediction will be essayed.

ultrasonic signal.

Throughout this chapter, the past, the present and the future of biodiesel production and analyses using ultrasound methods were presented and discussed. The chapter was written aiming to let the not insider reader to be able to conquest the basis of ultrasound and biodiesel technical relationship.

The past was a remarkable assortment of attempts to make use of generic ultrasound systems to accelerate biodiesel production. The present brings several dedicated instruments, measurement systems and fabrications tools specially designed for the use of ultrasound in fuel and biofuel. In the future, who knows? The trend seems to be related to the use of digital signal processing for specially designed applications, using, for instance, online real-time signal design based on transfer function and system identification for manufacturing optimization. That is our best bet.

#### Author details

Pâmella A. Oliveira, Raphaela M. Baesso, Gabriel C. Moraes, André V. Alvarenga and Rodrigo P.B. Costa-Félix\*

\*Address all correspondence to: rpfelix@inmetro.gov.br

Laboratory of Ultrasound, Directory of Scientific and Industrial Metrology, National Institute of Metrology, Quality and Technology (Inmetro), Xerem, RJ, Brazil

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**Chapter 8**

**Provisional chapter**

**Kinetics of Transesterification Processes for Biodiesel**

**Kinetics of Transesterification Processes for Biodiesel** 

Biodiesel is a renewable fuel mainly produced by transesterification of oils and fats that can be used as a transportation fuel, solvent and for energy generation with the potential

the kinetic behavior of triglycerides by different transesterification technologies is investigated through a critical review of the kinetic models reported in the study with the aim to establish a trend of the reaction mechanisms and the main variable effects and to further optimize the chemical process. The study of the transesterification reaction kinetics is performed for every type of transesterification, that is, homogeneous, heterogeneous, enzymatic and supercritical. The kinetic models are thus reviewed by describing the way they have evolved and how they can be used for process simulation and optimization. This chapter is divided in a study of the state of the art, an analysis and synthesis of research results, and an application for further optimization of the biodiesel production process.

Biodiesel is a renewable fuel of key importance to meet environmental and economic sustainability. It is produced by transesterification of vegetable oils or animal fats with an alcohol, such as methanol or ethanol, on an alkaline, acid or enzyme catalyst, and it is composed of a

, CO and HC, compared to fossil fuels. In this work,

, SO<sup>2</sup>

**Keywords:** biodiesel, kinetics, transesterification, optimization, modeling

mixture with at least 96 wt% of fatty acid methyl or ethyl esters (FAME or FAEE).

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.75927

**Production**

**Production**

Fernando Trejo-Zárraga,

Fernando Trejo-Zárraga,

Rogelio Sotelo-Boyás

Rogelio Sotelo-Boyás

**Abstract**

**1. Introduction**

Felipe de Jesús Hernández-Loyo,

Felipe de Jesús Hernández-Loyo,

http://dx.doi.org/10.5772/intechopen.75927

to reduce the emissions of CO<sup>2</sup>

Juan Carlos Chavarría-Hernández and

Juan Carlos Chavarría-Hernández and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

[85] Dantas TM, Costa-Felix RPB, Machado JC. Nonlinear frequency modulated excitation signal and modified compressing filter for improved range resolution and side lobe level of ultrasound echoes. Applied Acoustics. 2018;130:238-246. DOI: 10.1016/j.apacoust.2017.10.008

#### **Kinetics of Transesterification Processes for Biodiesel Production Kinetics of Transesterification Processes for Biodiesel Production**

DOI: 10.5772/intechopen.75927

Fernando Trejo-Zárraga, Felipe de Jesús Hernández-Loyo, Juan Carlos Chavarría-Hernández and Rogelio Sotelo-Boyás Fernando Trejo-Zárraga, Felipe de Jesús Hernández-Loyo, Juan Carlos Chavarría-Hernández and Rogelio Sotelo-Boyás

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75927

#### **Abstract**

[84] Costa-Felix RPB, Machado JC. Output bandwidth enhancement of a pulsed ultrasound system using a flat envelope and compensated frequency-modulated input signal: Theory and experimental applications. Measurement. 2015;69:146-154. DOI: https://doi.org/10.1016/

[85] Dantas TM, Costa-Felix RPB, Machado JC. Nonlinear frequency modulated excitation signal and modified compressing filter for improved range resolution and side lobe level of ultrasound echoes. Applied Acoustics. 2018;130:238-246. DOI: 10.1016/j.apacoust.2017.10.008

j.measurement.2015.03.019

148 Biofuels - State of Development

Biodiesel is a renewable fuel mainly produced by transesterification of oils and fats that can be used as a transportation fuel, solvent and for energy generation with the potential to reduce the emissions of CO<sup>2</sup> , SO<sup>2</sup> , CO and HC, compared to fossil fuels. In this work, the kinetic behavior of triglycerides by different transesterification technologies is investigated through a critical review of the kinetic models reported in the study with the aim to establish a trend of the reaction mechanisms and the main variable effects and to further optimize the chemical process. The study of the transesterification reaction kinetics is performed for every type of transesterification, that is, homogeneous, heterogeneous, enzymatic and supercritical. The kinetic models are thus reviewed by describing the way they have evolved and how they can be used for process simulation and optimization. This chapter is divided in a study of the state of the art, an analysis and synthesis of research results, and an application for further optimization of the biodiesel production process.

**Keywords:** biodiesel, kinetics, transesterification, optimization, modeling

#### **1. Introduction**

Biodiesel is a renewable fuel of key importance to meet environmental and economic sustainability. It is produced by transesterification of vegetable oils or animal fats with an alcohol, such as methanol or ethanol, on an alkaline, acid or enzyme catalyst, and it is composed of a mixture with at least 96 wt% of fatty acid methyl or ethyl esters (FAME or FAEE).

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A high percentage of the current investigations in the domain of biodiesel production is oriented toward the design of suitable solid catalysts, either with acid or with alkaline properties. Likewise, much emphasis is being placed on research on free or supported enzyme catalysts. Other transesterification methods that are under development include the application of supercritical conditions without the use of catalysts and the use of radiofrequency or ultrasonic assistance.

response and provide more detail on the composition and, therefore, on the quality of the products. Thus, a more robust model can be more useful; however, the number of kinetic parameters can increase significantly. The estimation of these parameters must be performed

Kinetics of Transesterification Processes for Biodiesel Production

http://dx.doi.org/10.5772/intechopen.75927

151

On the other hand, modeling of chemical reactors is very useful for the simulation and control of the process involved. This requires a previous selection of the kinetic model to be applied. Reactor modeling is used to determine concentration, temperature and pressure profiles, generating valuable information for the scaling-up of the process. The reactor model may include more or less the detail of the variables of interest, being possible to determine temperature and concentration profiles at intraparticle conditions, as in the case

The development of kinetic models of biodiesel production processes and their application to simulate and optimize these processes has been investigated and reported by a number of researchers. Portha et al. [1], for example, reduced the excess of ethanol used in the transesterification reaction of oils in a continuous process by using a two-stage continuous heterogeneous catalytic reactor. Their simulation results enabled them to determine that the overall performance of the system could be improved with the use of an inter-stage methanol addition as well as by changing the reaction temperature for the second reactor. In their experimentation with triolein as a model compound, the authors found converting the main part of triolein in the first reactor and converting diglyceride and monoglyceride in the second one to be useful. Their simulations also indicated that a higher temperature in the second reactor was advisable to enhance reaction rates at this stage. They also worked on the optimization of the inlet methanol-to-triolein molar ratio, finding that the use of a molar ratio larger than than 25:1 mol/mol had no further significant impact on the biodiesel yield. Furthermore, by introducing the kinetic model into a reactor model, the authors calculated internal concentration profiles and found that the internal diffusion of triglycerides (TG), diglycerides (DG) and monoglycerides (MG) was the limiting phenomena in the

A kinetic model can also be applied as a strategic tool for obtaining a better understanding of the rates of product formation and the inhibition patterns present in the transformation scheme [2]. A reaction scheme for the biodiesel production, for example, through enzymatic processes, can consider much more reaction steps and thus a higher number of reaction parameters. This certainly introduces an additional complication in the development of a kinetic model, but when this model is solved, it can be used to design a reactor based on

In the field of research and process development, the application of kinetic models that are able to accurately simulate the process at different reaction conditions is useful to provide the guidelines for further experimental work, helping in this way to discard potentially unproductive experimental trials. Models can also help to predict the effect of composition on the quality of the product. For example, a model could predict how the FFA or the water content in the feedstock can affect the reaction conversion and therefore the yield and quality

rigorously in order to generate reliable results.

of heterogeneous reactors.

overall transformation.

of biodiesel.

enzyme catalysis and ultimately to optimize the process.

The development and optimization of biodiesel production processes involve much experimental work, as well as the application of kinetic models that try to describe the process in a more comprehensive and realistic way. Some of the variables that are commonly studied in the development of kinetic models are the reaction temperature, the feedstock composition, including different contents of free fatty acids (FFAs), the alcohol-to-oil molar ratio, the mixing speed and the reaction time. The internal and external mass transfer limitations when using solid catalysts have also been studied.

This chapter deals with the main challenges in the development and application of kinetic models for the transesterification reaction, as well as representative results of current developments in this area.

#### **2. The importance of kinetic modeling for process optimization**

The development of kinetic models of chemical transformation processes for the production of higher added-value products is a powerful tool for reactor design. The kinetic model is also necessary for the optimization of the complete process, including the separation and heating steps. Thus, the kinetic model must be incorporated into the reactor model and then applied in the process simulation.

Regarding chemical or biochemical transformations in reactors or bioreactors, the kinetic models are of great help in the selection of the most favorable reaction conditions (e.g. temperature, pressure, mixing rate) to maximize the formation of desired products with the least investment of material and the use of economic resources. This also applies to the different biodiesel production processes, including homogeneous, heterogeneous, enzyme catalysis, and so on, which will be addressed in the next sections.

A well-planned experimental study and the subsequent development of a kinetic model are considered one of the most crucial steps in the chemical process development for industrial applications.

Kinetic models may offer different levels of detail and predictive capabilities, as they can take into account mass and heat transfer phenomena, as well as thermodynamic equilibrium. The level of theory for modeling the reactions can go from the use of quantum chemistry to the individual elementary steps up to a series of encompassed reaction steps between pseudo-components (lumped model). The catalyst deactivation, the presence of undesired side reactions, the consideration of inhibition processes and a detailed feedstock composition are among other factors that can be considered to derive more realistic kinetic models and with a higher predictive capacity. A more comprehensive model can give a more significant response and provide more detail on the composition and, therefore, on the quality of the products. Thus, a more robust model can be more useful; however, the number of kinetic parameters can increase significantly. The estimation of these parameters must be performed rigorously in order to generate reliable results.

A high percentage of the current investigations in the domain of biodiesel production is oriented toward the design of suitable solid catalysts, either with acid or with alkaline properties. Likewise, much emphasis is being placed on research on free or supported enzyme catalysts. Other transesterification methods that are under development include the application of supercritical condi-

The development and optimization of biodiesel production processes involve much experimental work, as well as the application of kinetic models that try to describe the process in a more comprehensive and realistic way. Some of the variables that are commonly studied in the development of kinetic models are the reaction temperature, the feedstock composition, including different contents of free fatty acids (FFAs), the alcohol-to-oil molar ratio, the mixing speed and the reaction time. The internal and external mass transfer limitations when

This chapter deals with the main challenges in the development and application of kinetic models for the transesterification reaction, as well as representative results of current devel-

The development of kinetic models of chemical transformation processes for the production of higher added-value products is a powerful tool for reactor design. The kinetic model is also necessary for the optimization of the complete process, including the separation and heating steps. Thus, the kinetic model must be incorporated into the reactor model and then applied

Regarding chemical or biochemical transformations in reactors or bioreactors, the kinetic models are of great help in the selection of the most favorable reaction conditions (e.g. temperature, pressure, mixing rate) to maximize the formation of desired products with the least investment of material and the use of economic resources. This also applies to the different biodiesel production processes, including homogeneous, heterogeneous, enzyme catalysis,

A well-planned experimental study and the subsequent development of a kinetic model are considered one of the most crucial steps in the chemical process development for industrial

Kinetic models may offer different levels of detail and predictive capabilities, as they can take into account mass and heat transfer phenomena, as well as thermodynamic equilibrium. The level of theory for modeling the reactions can go from the use of quantum chemistry to the individual elementary steps up to a series of encompassed reaction steps between pseudo-components (lumped model). The catalyst deactivation, the presence of undesired side reactions, the consideration of inhibition processes and a detailed feedstock composition are among other factors that can be considered to derive more realistic kinetic models and with a higher predictive capacity. A more comprehensive model can give a more significant

**2. The importance of kinetic modeling for process optimization**

tions without the use of catalysts and the use of radiofrequency or ultrasonic assistance.

using solid catalysts have also been studied.

and so on, which will be addressed in the next sections.

opments in this area.

150 Biofuels - State of Development

in the process simulation.

applications.

On the other hand, modeling of chemical reactors is very useful for the simulation and control of the process involved. This requires a previous selection of the kinetic model to be applied. Reactor modeling is used to determine concentration, temperature and pressure profiles, generating valuable information for the scaling-up of the process. The reactor model may include more or less the detail of the variables of interest, being possible to determine temperature and concentration profiles at intraparticle conditions, as in the case of heterogeneous reactors.

The development of kinetic models of biodiesel production processes and their application to simulate and optimize these processes has been investigated and reported by a number of researchers. Portha et al. [1], for example, reduced the excess of ethanol used in the transesterification reaction of oils in a continuous process by using a two-stage continuous heterogeneous catalytic reactor. Their simulation results enabled them to determine that the overall performance of the system could be improved with the use of an inter-stage methanol addition as well as by changing the reaction temperature for the second reactor. In their experimentation with triolein as a model compound, the authors found converting the main part of triolein in the first reactor and converting diglyceride and monoglyceride in the second one to be useful. Their simulations also indicated that a higher temperature in the second reactor was advisable to enhance reaction rates at this stage. They also worked on the optimization of the inlet methanol-to-triolein molar ratio, finding that the use of a molar ratio larger than than 25:1 mol/mol had no further significant impact on the biodiesel yield. Furthermore, by introducing the kinetic model into a reactor model, the authors calculated internal concentration profiles and found that the internal diffusion of triglycerides (TG), diglycerides (DG) and monoglycerides (MG) was the limiting phenomena in the overall transformation.

A kinetic model can also be applied as a strategic tool for obtaining a better understanding of the rates of product formation and the inhibition patterns present in the transformation scheme [2]. A reaction scheme for the biodiesel production, for example, through enzymatic processes, can consider much more reaction steps and thus a higher number of reaction parameters. This certainly introduces an additional complication in the development of a kinetic model, but when this model is solved, it can be used to design a reactor based on enzyme catalysis and ultimately to optimize the process.

In the field of research and process development, the application of kinetic models that are able to accurately simulate the process at different reaction conditions is useful to provide the guidelines for further experimental work, helping in this way to discard potentially unproductive experimental trials. Models can also help to predict the effect of composition on the quality of the product. For example, a model could predict how the FFA or the water content in the feedstock can affect the reaction conversion and therefore the yield and quality of biodiesel.

#### **3. Kinetic modeling for biodiesel production**

There is a consensus on the reaction steps involved in the transesterification process of triglycerides, which are indicated in **Figure 1**. These are the three consecutive and reversible reactions.

In the first reaction, triglyceride (TG) molecule reacts with an alcohol molecule, typically methanol (M) to produce diglyceride (DG) and a fatty acid methyl ester (ME). Then, in the second reaction, diglyceride reacts with alcohol to form monoglyceride (MG) and another molecule of fatty acid ester. In the third reaction, monoglyceride (MG) reacts with alcohol to produce glycerol (G) and a third molecule of fatty acid ester.

When the concentration of FFA present in the oil requires a previous (or simultaneous) stage of esterification, the following reaction that forms one molecule of methyl ester and one molecule of water (W) is considered in the model:

$$\text{FFA} + \text{M} \leftrightarrow \text{ME} + \text{W} \tag{1}$$

using a larger excess of alcohol. From their results with a butanol-to-soybean oil molar ratio of 30:1 mol/mol, they found that the forward reaction followed pseudo-first-order kinetics for both alkaline and acid catalysts, as expected. The kinetic coefficients for the first reaction shown in **Figure 1** are higher than those for the second and third reactions. This is valid for the forward and reverse reactions and is a general result reported by different authors for alkaline-catalyzed transesterification [5]. In the case of acid-catalyzed tests, the rate coefficients for the first reaction were lower than those for the second and third reactions for both forward and reverse reactions. This has also been reported by other authors [6]. The activation energies for all the alkaline- and acid-catalyzed transesterifications using both butanol and ethanol ranged from 8000 to 20,000 cal/mol. These results are also in agreement with the

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Other kinetic models like the one proposed by Gonzalez-Brambila et al. [7] consider the effects of mass transfer phenomena on the transesterification of soybean oil with methanol and NaOH in a batch reactor, using the experimental data from the study [8] and by proposing a mass transfer-kinetic dynamic model. Two liquid phases were considered: a non-polar TG-rich phase and a polar methanol-rich phase, and the reaction was considered to take place only in the interphase of the drops. Besides the six kinetic coefficients derived from **Figure 1**, the mass transfer coefficient between drops and alcohol phase was evaluated. In this way, the model can not only describe the evolution on time of TG, DG, MG, glycerine, methanol and ester composition but also estimate the reduction of drops' radii during the reaction, which

The use of heterogeneous catalysts presents several advantages over the use of homogeneous catalysts, among which the ones that have been most emphasized include the elimination of the washing section and huge amounts of waste water, reusable catalyst and easier disposal of the spent one, high purity of glycerol and the end product [9]. Hence, several conventional solid bases and acids (with and without promoters/dopants) have been investigated with this purpose. These included different solid acid catalysts such as sulphated zirconia [10], zeolites [11], heteropolyacids [12], ion-exchange resins [13] and sulphonated carbons [14]. Moreover, it has been reported that working under optimal conditions, heterogeneous transesterification can approximate the activity obtained with homogeneous catalysts. For example, Kim et al.

methanol-to-oil molar ratio of 9:1 mol/mol at an atmospheric pressure. These results are com-

Like homogeneous acid catalysis, when the oil to be fed has a concentration of FFA greater than 3 wt%, an acid solid catalyst that tolerates the presence of FFA and possess activity for both esterification and transesterification to convert FFA and oil to biodiesel should be used. Normally, the first option to carry out the scaling-up of a continuous heterogeneous transesterification process is the use of a fixed bed reactor (FBR), due to the simplicity of its design and the ease of its operation. However, the effect of the diffusive resistances must be consid-

parable to those obtained with the conventional homogeneous catalyst (NaOH).

ered in order to obtain a reactor design that meets the expected conversion levels.

O3

, reaching conversions of 95%, with a

are relevant data considering that reaction takes place on the drops' surface.

activation energies reported by other researchers [5, 6].

**3.2. Heterogeneous transesterification**

[15] used the heterogeneous catalyst Na/NaOH/γ-Al<sup>2</sup>

The development of kinetic equations is performed from the reactions taken into account for each particular case. The final form of the kinetic expressions is affected by the nature of the reacting mixture, homogeneous or heterogeneous, the selected alcohol, the alcohol-to-oil molar ratio and the influence of mass transfer effects, among other factors. In the following subsections, representative kinetic models for each type of reaction are discussed.

#### **3.1. Homogeneous transesterification**

Most of the work reported on the kinetics of transesterification of oils and fats has been derived from experiments with homogeneous catalysts and mainly with alkaline catalysts.

Freedman et al. [3] carried out the homogeneous transesterification of soybean oil using butanol and methanol and both alkali and acid catalysts, finding that alkaline-catalyzed reactions proceed at considerably faster rates than acid-catalyzed transesterification. The kinetic coefficients reported at 60°C for the former were two to four orders of magnitude higher than the latter. For this reason and because alkaline catalysts are less corrosive to industrial equipment than acid catalysts, most commercial biodiesel processes are conducted with alkaline catalysts. Sodium alkoxides are among the alkaline catalysts that have been used extensively for this reaction [4]. Freedman et al. [3] also found that the reaction with butanol follows a second-order reaction. These authors performed alkaline- and acid-catalyzed experiments


**Figure 1.** Consecutive reversible reaction steps considered in the formation of methyl esters from triglycerides.

using a larger excess of alcohol. From their results with a butanol-to-soybean oil molar ratio of 30:1 mol/mol, they found that the forward reaction followed pseudo-first-order kinetics for both alkaline and acid catalysts, as expected. The kinetic coefficients for the first reaction shown in **Figure 1** are higher than those for the second and third reactions. This is valid for the forward and reverse reactions and is a general result reported by different authors for alkaline-catalyzed transesterification [5]. In the case of acid-catalyzed tests, the rate coefficients for the first reaction were lower than those for the second and third reactions for both forward and reverse reactions. This has also been reported by other authors [6]. The activation energies for all the alkaline- and acid-catalyzed transesterifications using both butanol and ethanol ranged from 8000 to 20,000 cal/mol. These results are also in agreement with the activation energies reported by other researchers [5, 6].

Other kinetic models like the one proposed by Gonzalez-Brambila et al. [7] consider the effects of mass transfer phenomena on the transesterification of soybean oil with methanol and NaOH in a batch reactor, using the experimental data from the study [8] and by proposing a mass transfer-kinetic dynamic model. Two liquid phases were considered: a non-polar TG-rich phase and a polar methanol-rich phase, and the reaction was considered to take place only in the interphase of the drops. Besides the six kinetic coefficients derived from **Figure 1**, the mass transfer coefficient between drops and alcohol phase was evaluated. In this way, the model can not only describe the evolution on time of TG, DG, MG, glycerine, methanol and ester composition but also estimate the reduction of drops' radii during the reaction, which are relevant data considering that reaction takes place on the drops' surface.

#### **3.2. Heterogeneous transesterification**

**3. Kinetic modeling for biodiesel production**

152 Biofuels - State of Development

produce glycerol (G) and a third molecule of fatty acid ester.

ecule of water (W) is considered in the model:

**3.1. Homogeneous transesterification**

There is a consensus on the reaction steps involved in the transesterification process of triglycerides, which are indicated in **Figure 1**. These are the three consecutive and reversible reactions. In the first reaction, triglyceride (TG) molecule reacts with an alcohol molecule, typically methanol (M) to produce diglyceride (DG) and a fatty acid methyl ester (ME). Then, in the second reaction, diglyceride reacts with alcohol to form monoglyceride (MG) and another molecule of fatty acid ester. In the third reaction, monoglyceride (MG) reacts with alcohol to

When the concentration of FFA present in the oil requires a previous (or simultaneous) stage of esterification, the following reaction that forms one molecule of methyl ester and one mol-

FFA + M ↔ ME + W (1)

The development of kinetic equations is performed from the reactions taken into account for each particular case. The final form of the kinetic expressions is affected by the nature of the reacting mixture, homogeneous or heterogeneous, the selected alcohol, the alcohol-to-oil molar ratio and the influence of mass transfer effects, among other factors. In the following

Most of the work reported on the kinetics of transesterification of oils and fats has been derived from experiments with homogeneous catalysts and mainly with alkaline catalysts.

Freedman et al. [3] carried out the homogeneous transesterification of soybean oil using butanol and methanol and both alkali and acid catalysts, finding that alkaline-catalyzed reactions proceed at considerably faster rates than acid-catalyzed transesterification. The kinetic coefficients reported at 60°C for the former were two to four orders of magnitude higher than the latter. For this reason and because alkaline catalysts are less corrosive to industrial equipment than acid catalysts, most commercial biodiesel processes are conducted with alkaline catalysts. Sodium alkoxides are among the alkaline catalysts that have been used extensively for this reaction [4]. Freedman et al. [3] also found that the reaction with butanol follows a second-order reaction. These authors performed alkaline- and acid-catalyzed experiments

**Figure 1.** Consecutive reversible reaction steps considered in the formation of methyl esters from triglycerides.

subsections, representative kinetic models for each type of reaction are discussed.

The use of heterogeneous catalysts presents several advantages over the use of homogeneous catalysts, among which the ones that have been most emphasized include the elimination of the washing section and huge amounts of waste water, reusable catalyst and easier disposal of the spent one, high purity of glycerol and the end product [9]. Hence, several conventional solid bases and acids (with and without promoters/dopants) have been investigated with this purpose. These included different solid acid catalysts such as sulphated zirconia [10], zeolites [11], heteropolyacids [12], ion-exchange resins [13] and sulphonated carbons [14]. Moreover, it has been reported that working under optimal conditions, heterogeneous transesterification can approximate the activity obtained with homogeneous catalysts. For example, Kim et al. [15] used the heterogeneous catalyst Na/NaOH/γ-Al<sup>2</sup> O3 , reaching conversions of 95%, with a methanol-to-oil molar ratio of 9:1 mol/mol at an atmospheric pressure. These results are comparable to those obtained with the conventional homogeneous catalyst (NaOH).

Like homogeneous acid catalysis, when the oil to be fed has a concentration of FFA greater than 3 wt%, an acid solid catalyst that tolerates the presence of FFA and possess activity for both esterification and transesterification to convert FFA and oil to biodiesel should be used.

Normally, the first option to carry out the scaling-up of a continuous heterogeneous transesterification process is the use of a fixed bed reactor (FBR), due to the simplicity of its design and the ease of its operation. However, the effect of the diffusive resistances must be considered in order to obtain a reactor design that meets the expected conversion levels.

The transesterification reactions of oils in a fixed bed reactor (FBR) present different mass transport processes that affect the rate of production of biodiesel. The reaction system has two liquid (L) phases and one solid (S) phase represented by the catalyst. One of the liquid phases is rich in oil, while the other is rich in methanol, or any other alcohol. In this way, the external diffusive resistances associated with the transport of methanol and triglyceride toward the surface of the catalyst must be considered and the intraparticle diffusive resistances as well. The modeling of these complex processes involves the calculation of mass transfer coefficients of the components involved in the chemical reactions. Moreover, as reaction proceeds, the solubility of methanol in the oil-rich phase is increased due to a higher presence of esters, which act as co-solvents for methanol. The formation of monoglycerides and diglycerides increases the solubility of methanol in the oil-rich phase. As this solubility increases, the diffusive resistances at the L-L interface decrease [8], accelerating the transport of the reactants and therefore increasing the reaction rates. A similar effect is observed in the case of feedstock with a high FFA content, giving rise to a greater solubility and ease of transportation of the reactants in the L-L interface and thus allowing higher rates of biodiesel formation. This was confirmed by the results of Bhoi et al. [16], who reported that the rates observed for pure TG were significantly lower than those for a mixture of TG and FFA. They also estimated that for a mixture containing 20 wt% FFA, the rise in solubility was of the order of 1.35–1.5 times the solubility in pure TG. Similar results have also been reported by Singh et al. [17].

**Figure 1** indicated that the first reaction was the fastest, while the second and third reactions

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In an experimental study that considered the adsorption process, Dossin et al. [18] evaluated the intrinsic kinetics of the transesterification of ethyl acetate with methanol over an MgO catalyst. Among the evaluated models, the one that best fitted the experimental data corresponded to an Eley-Rideal (ER) type model, with the adsorption of methanol as the rate-limiting step.

Other promising transesterification methods for producing biodiesel that are gaining more

Among the main advantages of using enzymes (free or immobilized) is that they can process variable and low-quality feedstocks, as they are less sensitive to high FFA and water content. Then, enzymes can process FFA and TG in a single reaction step. Moreover, when using enzymes, there is no need for a subsequent washing step. On the other hand, lipases have the disadvantage of being sensitive to high concentrations of methanol, and their implementation is currently more expensive compared with other methods. The mechanism widely accepted for describing enzymatic transesterification corresponds to a double-displacement type or a ping-pong mechanism [19]. This reaction scheme presents a great complexity to be modeled, since the number of kinetic coefficients involved is high, and their experimental determination is a great challenge. Due to this complexity, simplified models are used, which generally do not describe the formation and transformation of di- and monoglycerides, as well as the influence of temperature on the enzyme deactivation and the conversion limits derived from equilibrium. The complexity of the process can further increase if the presence of multiple phases is taken into account when immobilized enzymes are employed. Moreover, stearic effects may have an important impact due to the large size of the glyceride molecules. To promote the fitting of experimental data to kinetic models of the process, simplified models such as the Michaelis-Menten type are used [20], although their predictive capacity is limited generally. Kinetic studies on the enzymatic production of biodiesel have been performed mainly with immobilized lipases, and most of these simplified models consider only irreversible reactions. Firdaus et al. [2] applied a simplification of the ping-pong model that resulted in the evaluation of about 30 rates coefficients, including those corresponding to the reversible steps. This model was later applied to describe the transformation of oil with a liquid lipase from *Thermomyces lanuginosus* in a 24-h reaction at 35°C. The authors analysed, among other aspects, the effect of water and FFA content and reported that the biodiesel obtained nearly complies with the

Catalytic and non-catalytic transesterification using an alcohol at supercritical conditions is another method under intensive investigation. This process has a high potential for both the transesterification of TG and for the esterification of FFA. Conversions reported are commonly greater than 90%, and reaction times are as short as 10 min or less [21]. The high temperatures and pressures required for the application of this technique represent, however, a limitation for its development and application, mainly due to the high energy costs of the process. In recent years, there have been an increasing number of reports in which this process is applied, either with the use of a catalyst or without it. In a recent work [22], the application

relevance as research progresses are enzyme catalysis and supercritical methanol.

were about one order of magnitude lower.

**3.3. Other transesterification methods**

quality standards.

The application of a model that considers the mentioned effects in the three consecutive reversible reaction steps shown in **Figure 1** is not an easy task, since it requires data on liquidliquid distribution for reactants and products and the relative proportion of each phase at different reaction conversions.

Bhoi et al. [16] developed a model that incorporates the effect of mass transfer resistances at both L-L and L-S interfaces for the transesterification reaction and simulated an FBR. Experimental data were obtained from two reactors, a spinning basket reactor (SBR) and an FBR and using a catalyst in pellets of a 6-mm diameter and an 8–10-mm length. Higher reaction rates in the reactor free of external diffusive resistances, that is, the SBR, were observed, concluding that the FBR is strongly hampered by external mass transfer resistances. The estimated kinetic parameters with the SBR were observed to be affected by internal diffusive resistances, which were corroborated by an estimated value of the activation energy of 25 kJ/mol, corresponding to the first reaction (forward) shown in **Figure 1**. Although this reaction was only considered in their kinetics for lower conversions, they were able to estimate the L-L and the L-S mass transfer coefficients. The latter was found to be four to eight times higher. Thus, they concluded that resistance in the L-L interface determined the overall rate of the process.

Bhoi et al. [1] developed a model for an FBR with axial dispersion considering mass transfer limitations in the catalyst as well as dynamic aspects. The reactor was considered to operate isothermally considering that transesterification reactions are almost athermic. The reaction stage consisted of two FBR connected in series and at 50 bar and 175°C. The simulations yielded a conversion of triolein (model feedstock) of 87% with a methanol:triolein ratio of 36:1 mol/mol, over a solid alkaline catalyst. It was found that the kinetic system behaves according to a second-order rate law. Adsorption terms were not included in the developed kinetic expressions. Similar to what has been reported for homogeneous-catalyzed transesterification of triglycerides, the calculation of the kinetic coefficients for the three reactions shown in **Figure 1** indicated that the first reaction was the fastest, while the second and third reactions were about one order of magnitude lower.

In an experimental study that considered the adsorption process, Dossin et al. [18] evaluated the intrinsic kinetics of the transesterification of ethyl acetate with methanol over an MgO catalyst. Among the evaluated models, the one that best fitted the experimental data corresponded to an Eley-Rideal (ER) type model, with the adsorption of methanol as the rate-limiting step.

#### **3.3. Other transesterification methods**

The transesterification reactions of oils in a fixed bed reactor (FBR) present different mass transport processes that affect the rate of production of biodiesel. The reaction system has two liquid (L) phases and one solid (S) phase represented by the catalyst. One of the liquid phases is rich in oil, while the other is rich in methanol, or any other alcohol. In this way, the external diffusive resistances associated with the transport of methanol and triglyceride toward the surface of the catalyst must be considered and the intraparticle diffusive resistances as well. The modeling of these complex processes involves the calculation of mass transfer coefficients of the components involved in the chemical reactions. Moreover, as reaction proceeds, the solubility of methanol in the oil-rich phase is increased due to a higher presence of esters, which act as co-solvents for methanol. The formation of monoglycerides and diglycerides increases the solubility of methanol in the oil-rich phase. As this solubility increases, the diffusive resistances at the L-L interface decrease [8], accelerating the transport of the reactants and therefore increasing the reaction rates. A similar effect is observed in the case of feedstock with a high FFA content, giving rise to a greater solubility and ease of transportation of the reactants in the L-L interface and thus allowing higher rates of biodiesel formation. This was confirmed by the results of Bhoi et al. [16], who reported that the rates observed for pure TG were significantly lower than those for a mixture of TG and FFA. They also estimated that for a mixture containing 20 wt% FFA, the rise in solubility was of the order of 1.35–1.5 times the

solubility in pure TG. Similar results have also been reported by Singh et al. [17].

different reaction conversions.

154 Biofuels - State of Development

interface determined the overall rate of the process.

The application of a model that considers the mentioned effects in the three consecutive reversible reaction steps shown in **Figure 1** is not an easy task, since it requires data on liquidliquid distribution for reactants and products and the relative proportion of each phase at

Bhoi et al. [16] developed a model that incorporates the effect of mass transfer resistances at both L-L and L-S interfaces for the transesterification reaction and simulated an FBR. Experimental data were obtained from two reactors, a spinning basket reactor (SBR) and an FBR and using a catalyst in pellets of a 6-mm diameter and an 8–10-mm length. Higher reaction rates in the reactor free of external diffusive resistances, that is, the SBR, were observed, concluding that the FBR is strongly hampered by external mass transfer resistances. The estimated kinetic parameters with the SBR were observed to be affected by internal diffusive resistances, which were corroborated by an estimated value of the activation energy of 25 kJ/mol, corresponding to the first reaction (forward) shown in **Figure 1**. Although this reaction was only considered in their kinetics for lower conversions, they were able to estimate the L-L and the L-S mass transfer coefficients. The latter was found to be four to eight times higher. Thus, they concluded that resistance in the L-L

Bhoi et al. [1] developed a model for an FBR with axial dispersion considering mass transfer limitations in the catalyst as well as dynamic aspects. The reactor was considered to operate isothermally considering that transesterification reactions are almost athermic. The reaction stage consisted of two FBR connected in series and at 50 bar and 175°C. The simulations yielded a conversion of triolein (model feedstock) of 87% with a methanol:triolein ratio of 36:1 mol/mol, over a solid alkaline catalyst. It was found that the kinetic system behaves according to a second-order rate law. Adsorption terms were not included in the developed kinetic expressions. Similar to what has been reported for homogeneous-catalyzed transesterification of triglycerides, the calculation of the kinetic coefficients for the three reactions shown in Other promising transesterification methods for producing biodiesel that are gaining more relevance as research progresses are enzyme catalysis and supercritical methanol.

Among the main advantages of using enzymes (free or immobilized) is that they can process variable and low-quality feedstocks, as they are less sensitive to high FFA and water content. Then, enzymes can process FFA and TG in a single reaction step. Moreover, when using enzymes, there is no need for a subsequent washing step. On the other hand, lipases have the disadvantage of being sensitive to high concentrations of methanol, and their implementation is currently more expensive compared with other methods. The mechanism widely accepted for describing enzymatic transesterification corresponds to a double-displacement type or a ping-pong mechanism [19]. This reaction scheme presents a great complexity to be modeled, since the number of kinetic coefficients involved is high, and their experimental determination is a great challenge. Due to this complexity, simplified models are used, which generally do not describe the formation and transformation of di- and monoglycerides, as well as the influence of temperature on the enzyme deactivation and the conversion limits derived from equilibrium. The complexity of the process can further increase if the presence of multiple phases is taken into account when immobilized enzymes are employed. Moreover, stearic effects may have an important impact due to the large size of the glyceride molecules. To promote the fitting of experimental data to kinetic models of the process, simplified models such as the Michaelis-Menten type are used [20], although their predictive capacity is limited generally. Kinetic studies on the enzymatic production of biodiesel have been performed mainly with immobilized lipases, and most of these simplified models consider only irreversible reactions. Firdaus et al. [2] applied a simplification of the ping-pong model that resulted in the evaluation of about 30 rates coefficients, including those corresponding to the reversible steps. This model was later applied to describe the transformation of oil with a liquid lipase from *Thermomyces lanuginosus* in a 24-h reaction at 35°C. The authors analysed, among other aspects, the effect of water and FFA content and reported that the biodiesel obtained nearly complies with the quality standards.

Catalytic and non-catalytic transesterification using an alcohol at supercritical conditions is another method under intensive investigation. This process has a high potential for both the transesterification of TG and for the esterification of FFA. Conversions reported are commonly greater than 90%, and reaction times are as short as 10 min or less [21]. The high temperatures and pressures required for the application of this technique represent, however, a limitation for its development and application, mainly due to the high energy costs of the process. In recent years, there have been an increasing number of reports in which this process is applied, either with the use of a catalyst or without it. In a recent work [22], the application of simplified kinetic models that describe only the formation of esters and disappearance of triglycerides as a function of conversion has been performed.

## **4. Analysis of general aspects affecting the kinetics of transesterification**

#### **4.1. Homogeneous catalysis**

Homogeneous catalysis is commonly used during transesterification reaction, and alkaline and acid catalysts are used. The most active catalysts have been reported to be alkaline ones [23].

#### *4.1.1. Reaction mechanisms*

Two mechanisms are involved in transesterification reaction depending on whether acid or basic catalysts are used.

#### *4.1.1.1. Basic catalysis*

In the case of alkaline catalysts, the reaction proceeds very fast, hydroxides, alkoxides, and sodium and potassium carbonate being the most commonly used catalysts (**Figure 2**). When an alkali is used, the first step is the formation of an alkoxide, which is a strong nucleophile that attacks the electrophilic carbon in a carbonyl group of the triglyceride. This attack turns the carbonyl into a tetrahedral intermediate as shown in the second step. Then, the tetrahedral carbon is separated from the intermediate to form an alkyl ester (third step). Deprotonation of catalyst regenerates the alkali, whereas the proton is attached to a diglyceride anion as shown (fourth step). Catalyst can react with another alcohol molecule and the mechanism is repeated until the catalyst reacts once again with an alcohol molecule to produce glycerol and alkyl esters [24].

#### *4.1.1.2. Acid catalysis*

When sulphuric or sulphonic acid is used, a very high yield of alkyl esters is obtained. In this case, the reaction mechanism is acid catalyzed. Early research [3] has reported that transesterification of soybean oil with methanol reached almost 100% after 50 h of reaction at 65°C using 1 mol% of sulphuric acid with an alcohol-to-oil molar ratio of 30:1 mol/mol, whereas using ethanol and 1-butanol as alcohols took 18 and 3 h, respectively; however, reaction temperature was higher (78 and 117°C, respectively). Inconvenience such as glycerol recovery due to alcohol in excess is to be expected by which the oil-to-alcohol molar ratio needs to be optimized [24].

To select the most suitable transesterification reaction pathway, either alkaline or acid, it is necessary to determine firstly the FFA content. This value must be lower than 3 wt% to proceed by the alkaline-catalyzed route without the significant formation of soap. This can lead to an emulsion that makes difficult the biodiesel and glycerol phases separation. Thus, oils with a high FFA content require a two-step process to be converted into biodiesel: (1) the FFAs are converted to fatty acid methyl esters as a pre-treatment with acid and (2) transesterification with basic catalyst is carried out [4, 25]. In this way, both the acid- and alkaline-catalyzed

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Since alcohol and triglycerides are immiscible at room temperature, stirring needs to be carried out to enhance the contact between phases so that a perfect mixing is achieved, avoiding

processes are efficiently used.

**Figure 2.** Alkali-catalyzed reaction mechanism.

*4.1.2. Mass transfer limitations and reactors for transesterification*

**Figure 3** shows a schematic reaction mechanism when an acid is used as catalyst, which is valid not only for a monoglyceride but also for di- and triglycerides. Protonation of the carbonyl group is the first stage (I). A carbocation (II) is then formed and undergoes a nucleophilic attack. Alcohol is attached to the tetrahedral intermediate (III), and a new ester (IV) is obtained by glycerol elimination and catalyst regeneration. The carbocation formed in step II is highly reactive by which water must be avoided during reaction because this molecule can act as a nucleophile and form carboxylic acids, which is a competitive reaction [24].

**Figure 2.** Alkali-catalyzed reaction mechanism.

of simplified kinetic models that describe only the formation of esters and disappearance of

Homogeneous catalysis is commonly used during transesterification reaction, and alkaline and acid catalysts are used. The most active catalysts have been reported to be alkaline ones [23].

Two mechanisms are involved in transesterification reaction depending on whether acid or

In the case of alkaline catalysts, the reaction proceeds very fast, hydroxides, alkoxides, and sodium and potassium carbonate being the most commonly used catalysts (**Figure 2**). When an alkali is used, the first step is the formation of an alkoxide, which is a strong nucleophile that attacks the electrophilic carbon in a carbonyl group of the triglyceride. This attack turns the carbonyl into a tetrahedral intermediate as shown in the second step. Then, the tetrahedral carbon is separated from the intermediate to form an alkyl ester (third step). Deprotonation of catalyst regenerates the alkali, whereas the proton is attached to a diglyceride anion as shown (fourth step). Catalyst can react with another alcohol molecule and the mechanism is repeated until the catalyst reacts once again with an alcohol molecule to produce glycerol and alkyl esters [24].

When sulphuric or sulphonic acid is used, a very high yield of alkyl esters is obtained. In this case, the reaction mechanism is acid catalyzed. Early research [3] has reported that transesterification of soybean oil with methanol reached almost 100% after 50 h of reaction at 65°C using 1 mol% of sulphuric acid with an alcohol-to-oil molar ratio of 30:1 mol/mol, whereas using ethanol and 1-butanol as alcohols took 18 and 3 h, respectively; however, reaction temperature was higher (78 and 117°C, respectively). Inconvenience such as glycerol recovery due to alcohol in excess is to be expected by which the oil-to-alcohol molar ratio needs to be optimized [24]. **Figure 3** shows a schematic reaction mechanism when an acid is used as catalyst, which is valid not only for a monoglyceride but also for di- and triglycerides. Protonation of the carbonyl group is the first stage (I). A carbocation (II) is then formed and undergoes a nucleophilic attack. Alcohol is attached to the tetrahedral intermediate (III), and a new ester (IV) is obtained by glycerol elimination and catalyst regeneration. The carbocation formed in step II is highly reactive by which water must be avoided during reaction because this molecule can

act as a nucleophile and form carboxylic acids, which is a competitive reaction [24].

triglycerides as a function of conversion has been performed.

**transesterification**

156 Biofuels - State of Development

**4.1. Homogeneous catalysis**

*4.1.1. Reaction mechanisms*

basic catalysts are used.

*4.1.1.1. Basic catalysis*

*4.1.1.2. Acid catalysis*

**4. Analysis of general aspects affecting the kinetics of** 

To select the most suitable transesterification reaction pathway, either alkaline or acid, it is necessary to determine firstly the FFA content. This value must be lower than 3 wt% to proceed by the alkaline-catalyzed route without the significant formation of soap. This can lead to an emulsion that makes difficult the biodiesel and glycerol phases separation. Thus, oils with a high FFA content require a two-step process to be converted into biodiesel: (1) the FFAs are converted to fatty acid methyl esters as a pre-treatment with acid and (2) transesterification with basic catalyst is carried out [4, 25]. In this way, both the acid- and alkaline-catalyzed processes are efficiently used.

#### *4.1.2. Mass transfer limitations and reactors for transesterification*

Since alcohol and triglycerides are immiscible at room temperature, stirring needs to be carried out to enhance the contact between phases so that a perfect mixing is achieved, avoiding

vortices, improving radial mixing and plug flow behavior [47]. Optimal baffle spacing has been previously calculated, and it was found that mass transfer rate depends on this spacing along with oscillation frequency and amplitude [48]. A better contact between phases is obtained with the use of static mixers consisting of motionless elements inside a pipe or a column to create radial mixing between immiscible liquids [49, 50]. A micro-channel reactor also improves the mass and heat transfer because of its high surface area/volume ratio which enhances the yield of methyl esters (above 90% in short reaction time) as reported elsewhere [51]. Cavitation-based reactors use acoustic energy to collapse cavities that increase local temperature and pressure. Cavitation intensifies the mass transfer rate creating local turbulence and reaching a high yield of FAME at room conditions [52]. Other studies have reported a FAME yield higher than 95% at 35°C, with an ultrasound frequency of 40 kHz at 1200 W of power using 1 wt% of KOH as

As mentioned earlier, if FFA or water content is high, then acid-catalyzed transesterification is preferred. In this case, sulphuric, phosphoric, hydrochloric, or sulphonic acids are the most

latter behaved better at 2.25 M [54]. Sulphuric acid at 0.87 M was used during transesterifica-

Alkaline catalysts such as sodium alkoxide are very active in short reaction times at low catalyst amount but anhydrous conditions are required. Instead, KOH and NaOH can be used in typical concentrations from 0.4 to 2% w/w of oil [4]. Earlier studies have reported that potassium carbonate (2–3%) as catalyst yielded a high content of methyl esters with minimal soap formation [56]. Encinar et al. [23] used KOH at 0.7% w/w of oil and obtained around 98% of methyl esters. The higher the catalyst concentration, the higher the reaction rate. However, catalyst in excess will turn the separation of products very difficult by which the amount of catalyst must be optimized.

When the methanol and sodium hydroxide solution are immiscible, mixing is necessary to promote the reaction [57]. The initial agitation improves the contact among phases and reduces the mass transfer limitations. Once reaction advances, methyl esters formed act as solvent for reactants and mixing needs to be continued for promoting the reaction rate. Mixing speed was studied by Encinar et al. [23] varying from 500 to 1100 rpm. The optimal mixing speed was stated at 700 rpm, and only a slight increase on the yield of methyl esters was observed above 95%.

Oil concentration in alcohol is low, particularly when methanol is used once transesterification reaction begins. As oil concentration increases in alcohol, the reaction rate is also increased and triglycerides are converted into diglycerides, which subsequently can react in the alcohol phase rather than being dispersed into the oil phase. As reaction progresses, a glycerol layer is separated. To reduce the mass transfer limitations, the use of nonreactive co-solvents to form a single phase is recommended [58]. Co-solvents such as tetrahydrofuran (THF), dimethyl

SO<sup>4</sup>

as catalyst was made elsewhere and the

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159

catalyst, a methanol-to-oil molar ratio of 6:1 mol/mol, for 25 min [53].

tion of Hevea br*a*siliensis at ca. 56°C and 240 min of reaction time [55].

*4.1.3. Effect of catalyst concentration*

*4.1.4. Effect of mixing speed*

*4.1.5. Effect of solvent/co-solvent*

used catalysts. A comparison among HCl and H<sup>2</sup>

**Figure 3.** Acid-catalyzed reaction mechanism.

mass transfer limitations and performing the reaction under an intrinsic kinetics. This is not so easy to achieve.

Mass transfer limitation studies have been reported and modeled in detail in a continuous tubular reactor at different reaction conditions [26, 27]. According to the authors, there are two steps that need to be addressed: (1) the reaction mixture passes through the mass transfer-determining region (heterogeneous system where methanol is the dispersed phase and the oil is the continuous phase) to (2) the kinetic-determining region (pseudo-homogeneous system in a single phase).

When using methanol, an emulsion is very quickly formed which is then broken down into two phases, that is, an upper phase constituted by methyl esters and a lower one formed by glycerol. When NaOH is used as catalyst, for example, it dissolves into the alcohol and then triglycerides diffuse through this mixture, and so the reaction is initially mass transfer controlled [4].

Transesterification by supercritical conditions is another reported process to reduce the mass transfer limitations. Several reports have discussed different supercritical conditions to carry out transesterification [28–45] ranging in the case of temperature from 270 to 350°C and pressure from 10 to 45 MPa to ensure only one reacting phase, which eliminate the mass transfer limitations; however, an increase in operation cost is to be expected, while high temperature and pressure could enhance the degradation of fatty acids or FAME, which is known to occur above 250°C. Reaction time has also been reported to vary from 4 to 110 min. The alcoholto-oil molar ratio is also quite high at these conditions, that is, from 20 to 40. At supercritical conditions, alcohol acts as an acid catalyst [29] and FFA and water present in the feed do not affect the transesterification conversion [46].

To further minimize the mass transfer limitations, reactors that enhance the contact between phases can be used. One of these reactors is the so-called oscillatory baffled reactor (OBR) composed of a tube containing equally spaced orifice plate baffles in which the oscillatory flow forms vortices, improving radial mixing and plug flow behavior [47]. Optimal baffle spacing has been previously calculated, and it was found that mass transfer rate depends on this spacing along with oscillation frequency and amplitude [48]. A better contact between phases is obtained with the use of static mixers consisting of motionless elements inside a pipe or a column to create radial mixing between immiscible liquids [49, 50]. A micro-channel reactor also improves the mass and heat transfer because of its high surface area/volume ratio which enhances the yield of methyl esters (above 90% in short reaction time) as reported elsewhere [51]. Cavitation-based reactors use acoustic energy to collapse cavities that increase local temperature and pressure. Cavitation intensifies the mass transfer rate creating local turbulence and reaching a high yield of FAME at room conditions [52]. Other studies have reported a FAME yield higher than 95% at 35°C, with an ultrasound frequency of 40 kHz at 1200 W of power using 1 wt% of KOH as catalyst, a methanol-to-oil molar ratio of 6:1 mol/mol, for 25 min [53].

#### *4.1.3. Effect of catalyst concentration*

As mentioned earlier, if FFA or water content is high, then acid-catalyzed transesterification is preferred. In this case, sulphuric, phosphoric, hydrochloric, or sulphonic acids are the most used catalysts. A comparison among HCl and H<sup>2</sup> SO<sup>4</sup> as catalyst was made elsewhere and the latter behaved better at 2.25 M [54]. Sulphuric acid at 0.87 M was used during transesterification of Hevea br*a*siliensis at ca. 56°C and 240 min of reaction time [55].

Alkaline catalysts such as sodium alkoxide are very active in short reaction times at low catalyst amount but anhydrous conditions are required. Instead, KOH and NaOH can be used in typical concentrations from 0.4 to 2% w/w of oil [4]. Earlier studies have reported that potassium carbonate (2–3%) as catalyst yielded a high content of methyl esters with minimal soap formation [56]. Encinar et al. [23] used KOH at 0.7% w/w of oil and obtained around 98% of methyl esters. The higher the catalyst concentration, the higher the reaction rate. However, catalyst in excess will turn the separation of products very difficult by which the amount of catalyst must be optimized.

#### *4.1.4. Effect of mixing speed*

mass transfer limitations and performing the reaction under an intrinsic kinetics. This is not

Mass transfer limitation studies have been reported and modeled in detail in a continuous tubular reactor at different reaction conditions [26, 27]. According to the authors, there are two steps that need to be addressed: (1) the reaction mixture passes through the mass transfer-determining region (heterogeneous system where methanol is the dispersed phase and the oil is the continuous phase) to (2) the kinetic-determining region (pseudo-homogeneous

When using methanol, an emulsion is very quickly formed which is then broken down into two phases, that is, an upper phase constituted by methyl esters and a lower one formed by glycerol. When NaOH is used as catalyst, for example, it dissolves into the alcohol and then triglycerides

Transesterification by supercritical conditions is another reported process to reduce the mass transfer limitations. Several reports have discussed different supercritical conditions to carry out transesterification [28–45] ranging in the case of temperature from 270 to 350°C and pressure from 10 to 45 MPa to ensure only one reacting phase, which eliminate the mass transfer limitations; however, an increase in operation cost is to be expected, while high temperature and pressure could enhance the degradation of fatty acids or FAME, which is known to occur above 250°C. Reaction time has also been reported to vary from 4 to 110 min. The alcoholto-oil molar ratio is also quite high at these conditions, that is, from 20 to 40. At supercritical conditions, alcohol acts as an acid catalyst [29] and FFA and water present in the feed do not

To further minimize the mass transfer limitations, reactors that enhance the contact between phases can be used. One of these reactors is the so-called oscillatory baffled reactor (OBR) composed of a tube containing equally spaced orifice plate baffles in which the oscillatory flow forms

diffuse through this mixture, and so the reaction is initially mass transfer controlled [4].

so easy to achieve.

158 Biofuels - State of Development

**Figure 3.** Acid-catalyzed reaction mechanism.

system in a single phase).

affect the transesterification conversion [46].

When the methanol and sodium hydroxide solution are immiscible, mixing is necessary to promote the reaction [57]. The initial agitation improves the contact among phases and reduces the mass transfer limitations. Once reaction advances, methyl esters formed act as solvent for reactants and mixing needs to be continued for promoting the reaction rate. Mixing speed was studied by Encinar et al. [23] varying from 500 to 1100 rpm. The optimal mixing speed was stated at 700 rpm, and only a slight increase on the yield of methyl esters was observed above 95%.

#### *4.1.5. Effect of solvent/co-solvent*

Oil concentration in alcohol is low, particularly when methanol is used once transesterification reaction begins. As oil concentration increases in alcohol, the reaction rate is also increased and triglycerides are converted into diglycerides, which subsequently can react in the alcohol phase rather than being dispersed into the oil phase. As reaction progresses, a glycerol layer is separated. To reduce the mass transfer limitations, the use of nonreactive co-solvents to form a single phase is recommended [58]. Co-solvents such as tetrahydrofuran (THF), dimethyl ether and methyl tert-butyl ether (MTBE) have been reported to improve miscibility among alcohol and oil. Previous reports [58] have stated that THF and MTBE behave as good cosolvents, THF being better than MTBE. Using a ratio of 1.25 vol/vol of methanol and keeping the methanol-to-oil molar ratio in 6:1 mol/mol at 23°C, the yield of methyl esters was 95% at 20 min. Other authors have studied the influence of methanol/co-solvent molar ratio in the range of 1:0.5–1:2 mol/mol and different co-solvents such as acetone, diethyl ether, dibutyl ether, methyl tert-butyl ether, diisopropyl ether and tetrahydrofuran [23]. Diethyl ether was the preferred co-solvent in a methanol/co-solvent molar ratio of 1:1 mol/mol.

[65]. In other cases, the optimal alcohol-to-oil molar ratio has been reported to be 9:1 mol/mol that yielded ~94% of methyl esters [23]. This molar ratio is also reported in previous reports [66]; however, depending on the type and quality of the oil, the methanol-to-oil molar ratio

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The conversion of triglycerides increases as the reaction time gets longer. In the case of alkaline catalysts, the reaction time is lower than 90 min to reach a maximum yield of methyl esters. As the alcohol and oil mixing starts, their immiscibility slows down the reaction within the first minutes; however, when reactants are well mixed, the reaction proceeds fast [63]. When acid catalysts are used, the reaction time is commonly increased up to several hours as reported before where sulphuric acid in the presence of soybean oil and methanol took 50 h to reach almost 100% of yield of methyl esters [3]. As in the case of methanol-to-oil molar ratio and temperature, the optimal values need to be found for each case depending on the catalyst type and the oil to be used.

The transesterification of triglycerides by heterogeneous catalysis is an alternative way to produce a biofuel that could help to reduce CO<sup>2</sup> emissions at reduced production costs, becoming thus competitive with petroleum-based diesel fuel [67–69]. There are still many areas of opportunity to improve the economy of the process. Heterogeneous transesterification has been shown to reduce the separation operations, the generation of waste and the use of large quantities of water [70]. One of the most difficult challenges is to find a catalyst with comparable activity to that of homogeneous catalysis, that is, at the same pressure and temperature

The kinetics of the transesterification reaction of oils and fats by heterogeneous catalysis is not so well understood as it is for homogeneous catalysis [72]. Most research works on heterogeneous catalysis have been focused on the synthesis and application of catalysts, and only a few deal with kinetic modeling. Among these, the efforts have been put on the use of small solid particles to obtain reaction conditions under an intrinsic kinetics and in which the

Thus, most heterogeneous vegetable oil transesterifications have found to follow a pseudofirst-order rate law. For example, Kaur and Ali [73], in their study with 15-Zr/CaO-700 catalyzed methanolysis and ethanolysis of Jatropha curcas L. oil, found that both reactions followed a pseudo-first-order rate law. The negligibility of the transport influences was demonstrated by the Koros-Nowak test. Lukić et al. [74] also found at optimal conditions for the transesterification of sunflower oil a first-order reversible rate law using a ZnO-alumina/ silica-supported catalyst and by evaluating both the effects of the calcination temperature and the effects of various supports. A number of kinetic modeling works of heterogeneous

phenomena of both intraparticle and external mass transfer are negligible.

must be optimized in each case as in catalyst concentration.

*4.1.8. Effect of reaction time*

**4.2. Heterogeneous catalysis**

*4.2.1. Kinetics*

and in which leaching is not present [71].

transesterification are presented in **Table 1**.

Acetone was used as co-solvent at 25 wt% using KOH as catalyst at 1 wt% and 4.5:1 mol/mol as methanol-to-oil molar ratio, and a yield of 98% of methyl esters was obtained at room temperature after 30 min [59]. Acetone at 20 wt% as co-solvent has also been reported elsewhere [60]. Other authors used dichlorobenzene and acetone at 10% (vol/vol) in methanol as co-solvents and reducing the reaction time by 60% [61]. THF was used as co-solvent in a methanol/co-solvent molar ratio of 1:1 mol/mol and 0.5 wt% of catalyst along with a methanol-to-oil molar ratio of 4:1 mol/ mol, and a yield of 98% of methyl esters was obtained after 10 min at 40°C and 200 rpm [62].

When selecting a suitable co-solvent, one has to take into account that at the end of reaction, it will be removed and if possible it will be reused. Thus, its boiling point needs to be maintained low.

#### *4.1.6. Effect of temperature*

Temperature influences on kinetics and equilibrium of reaction. It diminishes the viscosity of products and improves the mass transfer. At high temperature values, saponification is enhanced, lowering the yield of methyl esters. If methanol is used, the reaction temperature is commonly set at a value lower than its boiling point [63]. The effect of temperature on FAME yield has been studied from 20 to 40°C. If co-solvent is used, then temperature will be lower than its boiling point to avoid vaporization. The authors found that the yield of methyl esters at 30°C was optimal [23]. Some authors have reported temperature values ranging from 50 to 60°C [64]. The use of novel reactors as mentioned earlier is intended to reduce the reaction temperature at near room temperature.

#### *4.1.7. Effect of methanol-to-oil molar ratio*

Stoichiometrically, three moles of methanol are required by one mole of triglycerides. Since transesterification is a reversible reaction, the addition of methanol in excess displaces the equilibrium toward products in such a way that triglycerides will be converted into methyl esters, by which commonly methanol-to-triglycerides molar ratio is set to 6:1 mol/mol or higher. Nevertheless, methanol in excess increases the cost of biodiesel production, and therefore its recovery is one of the options used to improve the economy of the process. Some reports have studied the effect of methanol-to-oil molar ratio on FAME yield and have found an increase in the yield of methyl esters from 86 to 95% when increasing the molar ratio from 6:1 to 10:1 mol/mol [65]. When using waste cooking oil as feedstock, a higher methanol-tooil molar ratio of 16:1 mol/mol decreased the yield of FAME, probably because of a reduced catalyst concentration in the reacting mixture. Thus, the optimal molar ratio was 10:1 mol/mol [65]. In other cases, the optimal alcohol-to-oil molar ratio has been reported to be 9:1 mol/mol that yielded ~94% of methyl esters [23]. This molar ratio is also reported in previous reports [66]; however, depending on the type and quality of the oil, the methanol-to-oil molar ratio must be optimized in each case as in catalyst concentration.

#### *4.1.8. Effect of reaction time*

ether and methyl tert-butyl ether (MTBE) have been reported to improve miscibility among alcohol and oil. Previous reports [58] have stated that THF and MTBE behave as good cosolvents, THF being better than MTBE. Using a ratio of 1.25 vol/vol of methanol and keeping the methanol-to-oil molar ratio in 6:1 mol/mol at 23°C, the yield of methyl esters was 95% at 20 min. Other authors have studied the influence of methanol/co-solvent molar ratio in the range of 1:0.5–1:2 mol/mol and different co-solvents such as acetone, diethyl ether, dibutyl ether, methyl tert-butyl ether, diisopropyl ether and tetrahydrofuran [23]. Diethyl ether was

Acetone was used as co-solvent at 25 wt% using KOH as catalyst at 1 wt% and 4.5:1 mol/mol as methanol-to-oil molar ratio, and a yield of 98% of methyl esters was obtained at room temperature after 30 min [59]. Acetone at 20 wt% as co-solvent has also been reported elsewhere [60]. Other authors used dichlorobenzene and acetone at 10% (vol/vol) in methanol as co-solvents and reducing the reaction time by 60% [61]. THF was used as co-solvent in a methanol/co-solvent molar ratio of 1:1 mol/mol and 0.5 wt% of catalyst along with a methanol-to-oil molar ratio of 4:1 mol/ mol, and a yield of 98% of methyl esters was obtained after 10 min at 40°C and 200 rpm [62].

When selecting a suitable co-solvent, one has to take into account that at the end of reaction, it will be removed and if possible it will be reused. Thus, its boiling point needs to be maintained low.

Temperature influences on kinetics and equilibrium of reaction. It diminishes the viscosity of products and improves the mass transfer. At high temperature values, saponification is enhanced, lowering the yield of methyl esters. If methanol is used, the reaction temperature is commonly set at a value lower than its boiling point [63]. The effect of temperature on FAME yield has been studied from 20 to 40°C. If co-solvent is used, then temperature will be lower than its boiling point to avoid vaporization. The authors found that the yield of methyl esters at 30°C was optimal [23]. Some authors have reported temperature values ranging from 50 to 60°C [64]. The use of novel reactors as mentioned earlier is intended to reduce the reaction

Stoichiometrically, three moles of methanol are required by one mole of triglycerides. Since transesterification is a reversible reaction, the addition of methanol in excess displaces the equilibrium toward products in such a way that triglycerides will be converted into methyl esters, by which commonly methanol-to-triglycerides molar ratio is set to 6:1 mol/mol or higher. Nevertheless, methanol in excess increases the cost of biodiesel production, and therefore its recovery is one of the options used to improve the economy of the process. Some reports have studied the effect of methanol-to-oil molar ratio on FAME yield and have found an increase in the yield of methyl esters from 86 to 95% when increasing the molar ratio from 6:1 to 10:1 mol/mol [65]. When using waste cooking oil as feedstock, a higher methanol-tooil molar ratio of 16:1 mol/mol decreased the yield of FAME, probably because of a reduced catalyst concentration in the reacting mixture. Thus, the optimal molar ratio was 10:1 mol/mol

the preferred co-solvent in a methanol/co-solvent molar ratio of 1:1 mol/mol.

*4.1.6. Effect of temperature*

160 Biofuels - State of Development

temperature at near room temperature.

*4.1.7. Effect of methanol-to-oil molar ratio*

The conversion of triglycerides increases as the reaction time gets longer. In the case of alkaline catalysts, the reaction time is lower than 90 min to reach a maximum yield of methyl esters. As the alcohol and oil mixing starts, their immiscibility slows down the reaction within the first minutes; however, when reactants are well mixed, the reaction proceeds fast [63]. When acid catalysts are used, the reaction time is commonly increased up to several hours as reported before where sulphuric acid in the presence of soybean oil and methanol took 50 h to reach almost 100% of yield of methyl esters [3]. As in the case of methanol-to-oil molar ratio and temperature, the optimal values need to be found for each case depending on the catalyst type and the oil to be used.

#### **4.2. Heterogeneous catalysis**

The transesterification of triglycerides by heterogeneous catalysis is an alternative way to produce a biofuel that could help to reduce CO<sup>2</sup> emissions at reduced production costs, becoming thus competitive with petroleum-based diesel fuel [67–69]. There are still many areas of opportunity to improve the economy of the process. Heterogeneous transesterification has been shown to reduce the separation operations, the generation of waste and the use of large quantities of water [70]. One of the most difficult challenges is to find a catalyst with comparable activity to that of homogeneous catalysis, that is, at the same pressure and temperature and in which leaching is not present [71].

#### *4.2.1. Kinetics*

The kinetics of the transesterification reaction of oils and fats by heterogeneous catalysis is not so well understood as it is for homogeneous catalysis [72]. Most research works on heterogeneous catalysis have been focused on the synthesis and application of catalysts, and only a few deal with kinetic modeling. Among these, the efforts have been put on the use of small solid particles to obtain reaction conditions under an intrinsic kinetics and in which the phenomena of both intraparticle and external mass transfer are negligible.

Thus, most heterogeneous vegetable oil transesterifications have found to follow a pseudofirst-order rate law. For example, Kaur and Ali [73], in their study with 15-Zr/CaO-700 catalyzed methanolysis and ethanolysis of Jatropha curcas L. oil, found that both reactions followed a pseudo-first-order rate law. The negligibility of the transport influences was demonstrated by the Koros-Nowak test. Lukić et al. [74] also found at optimal conditions for the transesterification of sunflower oil a first-order reversible rate law using a ZnO-alumina/ silica-supported catalyst and by evaluating both the effects of the calcination temperature and the effects of various supports. A number of kinetic modeling works of heterogeneous transesterification are presented in **Table 1**.


**Oil source and catalyst Reaction conditions Kinetic model: rate constant (***k***)** 

Molar ratio 6:1 methanol:oil Temperature: 60 °C Agitation speed: 900 rpm

Molar ratio 16:1 ethanol: oil

Molar ratio 10:1 methanol:oil Agitation speed: 300 rpm Temperatures range: 60-96 °C

Reaction time: 5 h Temperature: 413-473 K

With sunflower oil Temperatures:

60 °C

70 °C

84 °C

96 °C

60 °C

84 °C

96 °C

50 °C 55 °C 60 °C 65 °C 70 °C

With waste cooking oil

Molar ratio 70:1 methanol:oil Agitation speed: 300 rpm Reaction time: 14 h Temperatures:

Sunflower oil Catalyst: CaO, 1, 2.5 and 10 wt %

Canola oil

HDL, 2 wt%

2 wt %

Catalyst: Mg-Co-Al-La

Sunflower and waste cooking oil Catalyst: CaO·ZnO

Waste cooking oil Catalysts: Heteropoly

acid, 10 wt % **and activation energy (***E<sup>a</sup>*

Kinetics of Transesterification Processes for Biodiesel Production

Kinetic model: First order

: 60.5 KJ/mol

*k* = 0.043 min−1; (*k*mt,TG)

*k* = 0.051 min−1; (*k*mt,TG)

*k* = 0.083 min−1; (*k*mt,TG)

*k* = 0.120 min−1; (*k*mt,TG)<sup>0</sup>

(*k*mt,TG)AVE = 0.170 min−1

*k* = 0.120 min−1; (*k*mt,TG)

*k* = 0.140 min−1; (*k*mt,TG)

(kmt,TG)AVE = 0.493 min−1 *k* = 0.170 min−1; (*k*mt,TG)

AVE = 0.311 min−1

AVE =1.664 min−1

Kinetic model: First order

= 53.99 KJ/mol

*k* = 0.059 min−1 *k* = 0.067 min−1 *k* = 0.091 min−1 *k* = 0.144 min−1 *k* = 0.1062 min−1

AVE = 0.012 min−1

AVE = 0.151 min−1

AVE = 0.244 min−1

(*k*mt,TG)

(*k*mt,TG)

(*k*mt,TG)

(*k*mt,TG)

(*k*mt,TG)

*Ea*

reaction *k* = 0.07 min−1

*Ea*

Kinetic model: Pseudo-first order

Kinetic model: Pseudo-first order Constant *k* and triglycerides (TG) mass transfer coefficient *kmtTG*

0

0

0

0

0

0

= 0.00021 min−1

= 0.00244 min−1

= 0.00285 min−1

= 0.140 min−1

= 0.0038 min−1

= 0.0033 min−1

= 0.0038 min−1

[81]

**)**

http://dx.doi.org/10.5772/intechopen.75927

**Ref.**

163

[78]

[79]

[80]


**Oil source and catalyst Reaction conditions Kinetic model: rate constant (***k***)** 

Molar ratio 10:1, methanol:oil with 5% oleic

acid and without acid Agitation speed: 550 rpm Temperature: 50°C

Agitation speed: 500 rpm

Molar ratio 15:1 methanol:oil Temperature: 65°C Ethanolysis Molar ratio 21:1 ethanol:oil Temperature: 75° C

Molar ratio 30:1 methanol:oil

Catalyst ZnO Al/Si ratio 3/1 Calcination 600 °C, 12 h Catalyst ZnO Al/Si ratio 3/1 Calcination 300 °C, 12 h Catalyst ZnO Al/Si ratio 1/0 Calcination 600°C, 12 h Catalyst ZnO Al/Si ratio 1/0 Calcination 300 °C, 12 h

Temperature: 200°C Pressure: 37 bar Reaction time: 4 h

Temperature: 60 °C Agitation speed: 900 rpm Molar ratio 6:1, methanol:oil Agitation speed: 900 rpm Molar ratio 6:1, methanol:oil Agitation speed: 300 rpm Molar ratio 10:1, methanol:oil

Molar ratio 6:1 methanol:oil

Reaction time: 5 h Temperature: 60 °C Agitation speed: 900 rpm

Methanolysis

Soybean oil

Catalyst: Amberlyst A26-OH basic ionexchange resin

162 Biofuels - State of Development

*Jatropha Curcas L.* oil Catalyst: Zr/CaO

Sunflower oil

silica, 2 wt %

Sunflower oil CaO, 1 wt % Ca(OH)<sup>2</sup>

Sunflower oil Catalyst: Ca(OH)<sup>2</sup>

weight

1-10 wt % based on oil

,

, 1 wt % CaO·ZnO, 2wt %

Catalyst: ZnO/alumina-

**and activation energy (***E<sup>a</sup>*

Kinetic model: Eley-Rideal *k* = 7.48x10−4 h−1 without FFA *k* = 1.94 h.1 with FFA

Kinetic model: Pseudo-first order

= 29.8 KJ mol−1; *k* = 0.062 min−1

= 42.5 KJ mol−1; *k* = 0.0123 min−1

Kinetic model: First-order, *k* model irreversible (for catalyst

with lower activity)

*k*-1 = 0.00140 min−1 *k* = 0.0027 min−1; *k*<sup>1</sup>

*k*-1 = 0.00170 min−1 *k* = 0.0036 min−1; *k*<sup>1</sup>

*k*-1 = 0.00082 min−1 *k* = 0.0064 min−1; *k*<sup>1</sup>

*k*-1 = 0.00014 min−1

*k* = 0.063 dm6

1.63mol dm−3 *k* = 0.025 dm6

0.539mol dm−3 *k* = 0.043 dm6

3.414mol dm−3

Kinetic model: Miladinovic model, *k* is an apparent reaction rate constant and *K* is a model parameter defining the TG affinity for the catalyst active sites.

mol−2min−1; *K* =

mol−2min−1; *K* =

mol−2min−1; *K* =

Kinetic model: Pseudo-first order. *k* = 0.07(1-exp(- *C*cat/2.86); min−1 Where *C*cat is the catalyst amount (in wt% based on the oil weight)

, *k*-1 model reversible *k* = 0.0138 min−1; *k*<sup>1</sup>

*Ea*

*Ea*

*k*1

**)**

= 0.0190 min−1

= 0.0054 min−1

= 0.0059 min−1

= 0.0068 min−1

**Ref.**

[72]

[73]

[74]

[75]

[77]


Miladinović et al. [76] also used a first-order reaction rate with respect to TG and FAMEs, respectively. Tasić et al. [75] also showed that the TG mass transfer limitation depends on the methanol-to-oil dispersion. When it is not fine enough, the available active surface is small. To reduce that effect, that is, to increase the TG-methanol miscibility, a co-solvent can be added. However, these authors found that FAME can act as a co-solvent, and therefore as it is formed,

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Stamenković et al. [77], studied the kinetics of the methanolysis of sunflower seed oil at 60°C,

They proposed a pseudo-first-order reaction kinetic model and related the TG mass transfer limitations to the limited available surface area that resulted from the high adsorbed methanol concentration in the first stage of the reaction. Mass transfer limitations were also important when small amounts of catalyst were used (1–2.5 wt%, oil based). When the catalyst was used in amounts greater than 10 wt%, the significant agglomeration of catalyst particles

Practically, the entire active surface of the porous granules is internal, and the reaction that takes place inside the pellet consumes reactants and induces internal gradients of concentration and temperature which may be of sufficient magnitude to cause a significant variation of the reaction rate. Thus, the size of the particles of the catalyst affects the mass transfer at both intraparticle and at the interface. A suitable size of particle can be found experimentally so that a reaction rate and the final conversion degree do not depend on it, which is fundamental in kinetic studies to

There are few studies on particle size in the production of biodiesel by heterogeneous catalysis. Veljković et al. [78] in their study on sunflower methanolysis with CaO showed that the intraparticle diffusion of reactants from the surface to the active sites was the rate-controlling step; however, when they used catalyst particles in between 3 and 15 μm, they found no influence of the average particle size on the reaction rate and the final conversion, which indicated

Li et al. [79] in their study on ethanolysis of canola oil using a lactate dehydrogenase (LDH)

greater than 1 mm and another being less than 100 μm, both at the same conditions. In both cases, a reduction in the conversion was found, indicating that there is a resistance to internal mass transfer and therefore an intraparticle diffusion control. However, for both cases, the rates were very similar in between 30 and 90 min, but with a delay of about 15 min for the larger particles. They concluded that the conversion rate was kinetically controlled rather than intra-

The stirring speed plays an important role in the evaluation of the limitations of external mass transfer, so to corroborate if there are external mass transfer limitations from the reactants to the particle surface, a study of the reaction rate is usually carried out at different agitation

CoAl) compared the reaction rates for two different particle sizes, one being

that the resistance due to intraparticle mass transfer was negligible in this size range.

catalyst.

165

the interfacial area gets larger, and hence the transfer limitations become smaller.

using a methanol-to-oil molar ratio of 6:1 mol/mol and different amounts of Ca(OH)<sup>2</sup>

occasioned the limitation of TG mass transfer.

*4.2.3. Effect of particle size*

obtain the intrinsic kinetics.

oxide catalyst (Mg2

particle diffusion.

*4.2.4. Effect of stirring speed*

**Table 1.** A review of kinetic models and reaction conditions of heterogeneous transesterification of vegetable oils.

#### *4.2.2. Reaction mechanisms*

The heterogeneous catalysis of vegetable oils takes place in a number of steps and in a threephase system consisting of a solid (heterogeneous catalyst) and two immiscible liquid phases (oil and alcohol, usually methanol or ethanol). To determine the rate-limiting step, a comparison of rates of the different elementary steps should be performed. This has been tried by several researchers by using either the Eley-Rideal (ER) or the Langmuir-Hinshelwood-Hougen-Watson (LHHW) methods.

Jamal et al. [72] have used both ER and LHHW in the transesterification of soybean oil on an Amberlyst A26-OH basic ion-exchange resin and in the presence and absence of free fatty acids. They proposed a four-step mechanism: (1) methanol adsorption by ion exchange on basic resin surface; (2) fatty acid (oleic acid) adsorption by ion exchange on basic resin surface; (3) hydrolysis of tri-, di- and monoglycerides from soybean oil; and (4) transesterification of glycerides (tri-, di- and mono-) with basic resin surface-bound methoxide. By considering the first step as the rate-limiting step, they showed that the ER model describes better the surface interactions occurring on the resin.

Some other authors have developed kinetic models based on first-order rate law. The following three cases show how sunflower methanolysis kinetics has been modeled within two stages, the first one being the initial TG mass transfer limitations and the second one the chemically controlled region.

Tasić et al. [75] have developed a reaction model for the methanolysis of sunflower oil on three calcium-based catalysts: CaO, Ca(OH)<sup>2</sup> and CaO·ZnO, by using the chemical kinetics reported by Miladinović et al. [76], in which it is assumed that the methoxide ions are first adsorbed on the active centers and then they react with the liquid phase TG that are close to the active centers. The mass transfer limitations of the methanol adsorption were found to be negligible. Miladinović et al. [76] also used a first-order reaction rate with respect to TG and FAMEs, respectively. Tasić et al. [75] also showed that the TG mass transfer limitation depends on the methanol-to-oil dispersion. When it is not fine enough, the available active surface is small. To reduce that effect, that is, to increase the TG-methanol miscibility, a co-solvent can be added. However, these authors found that FAME can act as a co-solvent, and therefore as it is formed, the interfacial area gets larger, and hence the transfer limitations become smaller.

Stamenković et al. [77], studied the kinetics of the methanolysis of sunflower seed oil at 60°C, using a methanol-to-oil molar ratio of 6:1 mol/mol and different amounts of Ca(OH)<sup>2</sup> catalyst. They proposed a pseudo-first-order reaction kinetic model and related the TG mass transfer limitations to the limited available surface area that resulted from the high adsorbed methanol concentration in the first stage of the reaction. Mass transfer limitations were also important when small amounts of catalyst were used (1–2.5 wt%, oil based). When the catalyst was used in amounts greater than 10 wt%, the significant agglomeration of catalyst particles occasioned the limitation of TG mass transfer.

#### *4.2.3. Effect of particle size*

*4.2.2. Reaction mechanisms*

Sunflower oil Catalyst: CaO, 1 wt %

164 Biofuels - State of Development

occurring on the resin.

chemically controlled region.

calcium-based catalysts: CaO, Ca(OH)<sup>2</sup>

Hougen-Watson (LHHW) methods.

The heterogeneous catalysis of vegetable oils takes place in a number of steps and in a threephase system consisting of a solid (heterogeneous catalyst) and two immiscible liquid phases (oil and alcohol, usually methanol or ethanol). To determine the rate-limiting step, a comparison of rates of the different elementary steps should be performed. This has been tried by several researchers by using either the Eley-Rideal (ER) or the Langmuir-Hinshelwood-

**Table 1.** A review of kinetic models and reaction conditions of heterogeneous transesterification of vegetable oils.

**Oil source and catalyst Reaction conditions Kinetic model: rate constant (***k***)** 

Molar ratio 6:1 methanol:oil Agitation speed: 200 rpm Pressure: 1-15 bars Temperature: 60-120 °C Reaction time: 1.5 h

Reaction time: 2.5 h

Reaction time: 3.5 h

Reaction time: 4.5 h

Reaction time: 5.5 h

Jamal et al. [72] have used both ER and LHHW in the transesterification of soybean oil on an Amberlyst A26-OH basic ion-exchange resin and in the presence and absence of free fatty acids. They proposed a four-step mechanism: (1) methanol adsorption by ion exchange on basic resin surface; (2) fatty acid (oleic acid) adsorption by ion exchange on basic resin surface; (3) hydrolysis of tri-, di- and monoglycerides from soybean oil; and (4) transesterification of glycerides (tri-, di- and mono-) with basic resin surface-bound methoxide. By considering the first step as the rate-limiting step, they showed that the ER model describes better the surface interactions

Some other authors have developed kinetic models based on first-order rate law. The following three cases show how sunflower methanolysis kinetics has been modeled within two stages, the first one being the initial TG mass transfer limitations and the second one the

Tasić et al. [75] have developed a reaction model for the methanolysis of sunflower oil on three

by Miladinović et al. [76], in which it is assumed that the methoxide ions are first adsorbed on the active centers and then they react with the liquid phase TG that are close to the active centers. The mass transfer limitations of the methanol adsorption were found to be negligible.

and CaO·ZnO, by using the chemical kinetics reported

**and activation energy (***E<sup>a</sup>*

restrictions at 80 °C *k* [=] (10−3 min−1)

Kinetic model: Pseudo-first order with significant diffusion

*k*(60°C) = 2.67, *k*(80°C) = 73.71, *k*(100°C) = 175.4, *k*(120°C) = 220.86 *k*(60°C) = 3.08, *k*(80°C) = 88.09, *k*(100°C) = 140.77, *k*(120°C) = 131.96 *k*(60°C) = 3.26, *k*(80°C) = 81.81, *k*(100°C) = 100.41, *k*(120°C) = 94.25 *k*(60°C) = 5.32, *k*(80°C) = 77.68, *k*(100°C) = 76.94, *k*(120°C) = 72.79 *k*(60°C) = 8.3, *k*(80°C) = 65.63, *k*(100°C) = 61, *k*(120°C) = 59.22

**)**

**Ref.**

[9]

Practically, the entire active surface of the porous granules is internal, and the reaction that takes place inside the pellet consumes reactants and induces internal gradients of concentration and temperature which may be of sufficient magnitude to cause a significant variation of the reaction rate. Thus, the size of the particles of the catalyst affects the mass transfer at both intraparticle and at the interface. A suitable size of particle can be found experimentally so that a reaction rate and the final conversion degree do not depend on it, which is fundamental in kinetic studies to obtain the intrinsic kinetics.

There are few studies on particle size in the production of biodiesel by heterogeneous catalysis. Veljković et al. [78] in their study on sunflower methanolysis with CaO showed that the intraparticle diffusion of reactants from the surface to the active sites was the rate-controlling step; however, when they used catalyst particles in between 3 and 15 μm, they found no influence of the average particle size on the reaction rate and the final conversion, which indicated that the resistance due to intraparticle mass transfer was negligible in this size range.

Li et al. [79] in their study on ethanolysis of canola oil using a lactate dehydrogenase (LDH) oxide catalyst (Mg2 CoAl) compared the reaction rates for two different particle sizes, one being greater than 1 mm and another being less than 100 μm, both at the same conditions. In both cases, a reduction in the conversion was found, indicating that there is a resistance to internal mass transfer and therefore an intraparticle diffusion control. However, for both cases, the rates were very similar in between 30 and 90 min, but with a delay of about 15 min for the larger particles. They concluded that the conversion rate was kinetically controlled rather than intraparticle diffusion.

#### *4.2.4. Effect of stirring speed*

The stirring speed plays an important role in the evaluation of the limitations of external mass transfer, so to corroborate if there are external mass transfer limitations from the reactants to the particle surface, a study of the reaction rate is usually carried out at different agitation speeds. Veljković et al. [78] carried out studies at agitation speeds of 700 and 900 rpm for a methanolysis reaction with 1 wt% catalyst and speeds of 900–1250 rpm with a 10 wt% catalyst, and by using the correlation of Dossin et al. [18], they found that the minimum stirring speed to carry out a perfect mixture and a complete suspension of catalyst particles was 430 rpm for the former and 740 rpm for the latter. They found that agitation speeds of 1250 rpm introduced air inside the reactant mixture. The experimental conditions and values of the kinetic constants are summarized in **Table 1** [78].

*4.2.7. Effect of reaction time*

reached after 5.5 and 2.5 h, respectively.

**5.1. Simulation of transesterification process**

represented by methyl oleate (C19H36O<sup>2</sup>

tion pre-treatment process, oleic acid (C18H34O<sup>2</sup>

Reaction time is very significant in the production of biodiesel by heterogeneous catalysis, since to obtain the same yields as those in homogeneous catalysis sometimes need up to more than five times the time that is carried by homogeneous catalysis. In the abovementioned work carried out by Vujicic et al. [9], the achieved activities at reaction temperatures of 80 and 100°C were significantly affected by the reaction run, and high steady-state conversions were

The economic evaluation of biodiesel production is based on general mass and energy balances that can be obtained from process simulation [82]. Among the most common process simulators used for the simulation of biodiesel production are Aspen Plus®, Aspen HYSIS, PRO/II, SuperPro Designer, and VMGsim. These programs can be used to design and optimize a large-scale biodiesel production. **Table 2** shows relevant data for different simulation

The typical process simulation procedure involves definition of the components, selection of the thermodynamic model, property estimation, drawing of the flowsheet, definition of

Most simulators do not contain all the components present in the transesterification reaction,

model compound of TG, mainly because it accounts for 40–75 wt% in most used oils for biodiesel production, such as olive, canola, palm and jatropha oils [83, 86], and hence biodiesel is

The most recent version of Aspen Plus® (ver. 10) includes most of the TG and methyl esters present in the transesterification reaction, including (tri)ricinoleine, which is the main component in castor oil. The properties of these components are estimated in the simulators. However, some important properties estimated for these components, for example, normal boiling points and vapor pressures, are somehow inconsistent with experimental data and databases, and therefore some researchers choose to update their values from either experimental data [87, 88],

The Non-Random Two Liquid (NRTL) or the Universal Quasi Chemical (UNIQUAC) models are the preferred thermodynamic models, mainly because of the presence of highly polar compounds, such as methanol and glycerol. In Aspen Plus, however, the binary NRTL coefficients usually need to be estimated, which is commonly carried out by the UNIFAC LLE model for liquid-liquid equilibrium and Peng-Robinson or SRK equations of state for vapor. The performance of NRTL has been shown to be better than UNIQUAC [90]. These mod-

) is regularly used as a

). When the oil contains FFA that requires an esterifica-

Kinetics of Transesterification Processes for Biodiesel Production

http://dx.doi.org/10.5772/intechopen.75927

167

) is used as a model compound.

**5. Simulation and optimization of biodiesel production**

studies. Complimentary numbers can be found elsewhere [83–85].

so that their properties cannot be estimated. Thus, triolein (C57H104O6

contribution methods [89] or from properties databanks such as NIST [83].

chemistry and kinetic models, and the input of units and operation conditions.

#### *4.2.5. Effect of temperature*

The effect of temperature on the reaction rate plays also a very important role since the rate constants are temperature-dependent. The temperature can influence transport phenomena in heterogeneous catalysis; Lukić et al. [80], for example, conducted the transesterification of sunflower and waste cooking oil using methanol at temperatures in a range between 60 and 96°C. As catalyst, they used CaOZnO with a methanol-to-oil molar ratio of 10:1 mol/mol. They showed that at relatively low temperatures of 60–70°C and at the start of the reaction for the production of esters, there is a resistance to the mass transfer, but with an increase in the production of methyl esters, the resistance to mass transfer reduced, so that the initial TG mass transfer limits the rate process, and eventually as biodiesel concentration increases, the chemical reaction is the rate-limiting step. For temperatures higher than 84 and 96°C, the resistance to mass transfer is almost negligible, and thus the conversion rate is controlled by the chemical reaction. The reaction rate was expressed by a pseudo-first-order model and corresponding values of the mass transfer coefficients.

In another study [81], a heteropoly acid catalyst was used to carry out the transesterification reaction of waste cooking oil with methanol temperatures in the range of 50–70°C to determine how temperature influences the conversion of TG. The conversion degree had a considerable increase when the temperature increased from 50 to 65°C, in the range of 40% (from 20 to 60%) at 50°C and 57.6% (from 31 to 88.6%) at 65°C. However, above 65°C, the conversion rate decreased, which was claimed to be due to the chemical reactions that occur during the cooking process, as these reactions can generate undesirable components such as free fatty acids that cause a decrease in the conversion of TG and therefore the production of biodiesel.

#### *4.2.6. Effect of alcohol-to-oil molar ratio*

Methanol is mostly used for transesterification of vegetable oils, mainly to avoid the formation of a stable emulsion between biodiesel and glycerol. In practice, it is better to perform a study at different molar ratios for each specific case of conditions and catalysts. Vujicic et al. [9], for example, used CaO as catalyst to transesterify sunflower oil. An excess of alcohol was observed to influence the reaction kinetics, and the overall reaction rate was found to follow strictly a fourth-order kinetics, since each TG molecule should be converted into glycerol by consecutive reactions, first becoming diglyceride, then monoglyceride and finally glycerol, but when carrying out the reaction with a large alcohol excess, the kinetics was observed to follow a pseudo-first order (**Table 1**).

#### *4.2.7. Effect of reaction time*

speeds. Veljković et al. [78] carried out studies at agitation speeds of 700 and 900 rpm for a methanolysis reaction with 1 wt% catalyst and speeds of 900–1250 rpm with a 10 wt% catalyst, and by using the correlation of Dossin et al. [18], they found that the minimum stirring speed to carry out a perfect mixture and a complete suspension of catalyst particles was 430 rpm for the former and 740 rpm for the latter. They found that agitation speeds of 1250 rpm introduced air inside the reactant mixture. The experimental conditions and values of the kinetic

The effect of temperature on the reaction rate plays also a very important role since the rate constants are temperature-dependent. The temperature can influence transport phenomena in heterogeneous catalysis; Lukić et al. [80], for example, conducted the transesterification of sunflower and waste cooking oil using methanol at temperatures in a range between 60 and 96°C. As catalyst, they used CaOZnO with a methanol-to-oil molar ratio of 10:1 mol/mol. They showed that at relatively low temperatures of 60–70°C and at the start of the reaction for the production of esters, there is a resistance to the mass transfer, but with an increase in the production of methyl esters, the resistance to mass transfer reduced, so that the initial TG mass transfer limits the rate process, and eventually as biodiesel concentration increases, the chemical reaction is the rate-limiting step. For temperatures higher than 84 and 96°C, the resistance to mass transfer is almost negligible, and thus the conversion rate is controlled by the chemical reaction. The reaction rate was expressed by a pseudo-first-order model and cor-

In another study [81], a heteropoly acid catalyst was used to carry out the transesterification reaction of waste cooking oil with methanol temperatures in the range of 50–70°C to determine how temperature influences the conversion of TG. The conversion degree had a considerable increase when the temperature increased from 50 to 65°C, in the range of 40% (from 20 to 60%) at 50°C and 57.6% (from 31 to 88.6%) at 65°C. However, above 65°C, the conversion rate decreased, which was claimed to be due to the chemical reactions that occur during the cooking process, as these reactions can generate undesirable components such as free fatty acids that cause a decrease in the conversion of TG and therefore the production

Methanol is mostly used for transesterification of vegetable oils, mainly to avoid the formation of a stable emulsion between biodiesel and glycerol. In practice, it is better to perform a study at different molar ratios for each specific case of conditions and catalysts. Vujicic et al. [9], for example, used CaO as catalyst to transesterify sunflower oil. An excess of alcohol was observed to influence the reaction kinetics, and the overall reaction rate was found to follow strictly a fourth-order kinetics, since each TG molecule should be converted into glycerol by consecutive reactions, first becoming diglyceride, then monoglyceride and finally glycerol, but when carrying out the reaction with a large alcohol excess, the kinetics was observed to

constants are summarized in **Table 1** [78].

responding values of the mass transfer coefficients.

*4.2.5. Effect of temperature*

166 Biofuels - State of Development

of biodiesel.

*4.2.6. Effect of alcohol-to-oil molar ratio*

follow a pseudo-first order (**Table 1**).

Reaction time is very significant in the production of biodiesel by heterogeneous catalysis, since to obtain the same yields as those in homogeneous catalysis sometimes need up to more than five times the time that is carried by homogeneous catalysis. In the abovementioned work carried out by Vujicic et al. [9], the achieved activities at reaction temperatures of 80 and 100°C were significantly affected by the reaction run, and high steady-state conversions were reached after 5.5 and 2.5 h, respectively.

#### **5. Simulation and optimization of biodiesel production**

#### **5.1. Simulation of transesterification process**

The economic evaluation of biodiesel production is based on general mass and energy balances that can be obtained from process simulation [82]. Among the most common process simulators used for the simulation of biodiesel production are Aspen Plus®, Aspen HYSIS, PRO/II, SuperPro Designer, and VMGsim. These programs can be used to design and optimize a large-scale biodiesel production. **Table 2** shows relevant data for different simulation studies. Complimentary numbers can be found elsewhere [83–85].

The typical process simulation procedure involves definition of the components, selection of the thermodynamic model, property estimation, drawing of the flowsheet, definition of chemistry and kinetic models, and the input of units and operation conditions.

Most simulators do not contain all the components present in the transesterification reaction, so that their properties cannot be estimated. Thus, triolein (C57H104O6 ) is regularly used as a model compound of TG, mainly because it accounts for 40–75 wt% in most used oils for biodiesel production, such as olive, canola, palm and jatropha oils [83, 86], and hence biodiesel is represented by methyl oleate (C19H36O<sup>2</sup> ). When the oil contains FFA that requires an esterification pre-treatment process, oleic acid (C18H34O<sup>2</sup> ) is used as a model compound.

The most recent version of Aspen Plus® (ver. 10) includes most of the TG and methyl esters present in the transesterification reaction, including (tri)ricinoleine, which is the main component in castor oil. The properties of these components are estimated in the simulators. However, some important properties estimated for these components, for example, normal boiling points and vapor pressures, are somehow inconsistent with experimental data and databases, and therefore some researchers choose to update their values from either experimental data [87, 88], contribution methods [89] or from properties databanks such as NIST [83].

The Non-Random Two Liquid (NRTL) or the Universal Quasi Chemical (UNIQUAC) models are the preferred thermodynamic models, mainly because of the presence of highly polar compounds, such as methanol and glycerol. In Aspen Plus, however, the binary NRTL coefficients usually need to be estimated, which is commonly carried out by the UNIFAC LLE model for liquid-liquid equilibrium and Peng-Robinson or SRK equations of state for vapor. The performance of NRTL has been shown to be better than UNIQUAC [90]. These mod-


**Table 2.** Key features of some simulation studies for biodiesel production. els present different characteristics that make them complimentary [91], and the use of both

Kinetics of Transesterification Processes for Biodiesel Production

http://dx.doi.org/10.5772/intechopen.75927

The Dortmund UNIFAC excess free energy model has also been used for the estimation of activity coefficients [84], as it has been found to provide good fit between estimated and measured methanol-biodiesel and methanol-glycerol vapor-liquid equilibrium data [92]. In this study performed by Kuramochi et al. [92], the Dortmund-UNIFAC was found to represent the best way to model the liquid-vapor equilibrium in the biodiesel process, while UNIFAC-LLE was found to be the best method to model the liquid–liquid equilib

rium with methanol, methyl oleate and glycerin mixture and methanol water system. The COSMO-SAC model, included in Aspen Plus, has also been used for VLE calculations in the esterification reactor [93]. The advantages of this method compared to NRTL are that its predictions are based on quantum chemistry, and the parameters required for its use are of molecular and electronic nature, and therefore they will not be affected by temperature

The selection of a kinetic model for both the transesterification and esterification reactions is very important for determining the product yield and performance of the equipment. Despite the multiple kinetic models found in the study, as shown in Section 3, a number of simulation studies do not include a detailed kinetic model to simulate the reactors. Instead, the simula

tion is performed by using a stoichiometric or an equilibrium reactor and using a specific value for the conversion or yield. Different studies for base-catalyzed reaction use a conver

sion value in between 95 and 99%. Some authors [100] argue that the various kinetics and mechanisms are not clear enough to design methods to follow and hence they prefer to simu

Similarly, since many kinetic models for transesterification reaction have been obtained for the entire mixture of TG and FFA, the use of triolein in the simulation does not entirely rep

resent the observed kinetic behavior in the reactor. In addition, most kinetic models found in the study have only been derived for one TG as a pseudocomponent. A detailed kinetic, and hence a more realistic simulation, should include triolein, tripalmitin, trilinolein and tristea

rin, as they account for more than 90 wt% of jatropha, palm, soybean, rapeseed and sunflower

Lee et al. [103] have developed a kinetic model based on three TGs, that is, for each compo

simulated the biodiesel production by considering a feedstock containing four TGs.

nent, kinetics parameters have been estimated. This model was used by Garcia et al. [90], who

Most simulation studies found in literature have been performed at a large-scale process; however, there seems to be a lack of data about industrial performances that are not totally realistic. A more comprehensive and close comparison between real plant operation and pro

Optimization is one of the most quantitative tools in the industrial decision-making process [91]. The purpose of biodiesel production optimization is to find the value of the variables


169








(UNIQUAC as referenced model) can achieve more reliable simulations.

changes along the process [93].

late the reactors as conversion reactors.

cess simulation could help to reduce this gap.

**5.2. Process optimization for biodiesel production**

oils [84, 102].

els present different characteristics that make them complimentary [91], and the use of both (UNIQUAC as referenced model) can achieve more reliable simulations.

The Dortmund UNIFAC excess free energy model has also been used for the estimation of activity coefficients [84], as it has been found to provide good fit between estimated and measured methanol-biodiesel and methanol-glycerol vapor-liquid equilibrium data [92]. In this study performed by Kuramochi et al. [92], the Dortmund-UNIFAC was found to represent the best way to model the liquid-vapor equilibrium in the biodiesel process, while UNIFAC-LLE was found to be the best method to model the liquid–liquid equilibrium with methanol, methyl oleate and glycerin mixture and methanol water system. The COSMO-SAC model, included in Aspen Plus, has also been used for VLE calculations in the esterification reactor [93]. The advantages of this method compared to NRTL are that its predictions are based on quantum chemistry, and the parameters required for its use are of molecular and electronic nature, and therefore they will not be affected by temperature changes along the process [93].

The selection of a kinetic model for both the transesterification and esterification reactions is very important for determining the product yield and performance of the equipment. Despite the multiple kinetic models found in the study, as shown in Section 3, a number of simulation studies do not include a detailed kinetic model to simulate the reactors. Instead, the simulation is performed by using a stoichiometric or an equilibrium reactor and using a specific value for the conversion or yield. Different studies for base-catalyzed reaction use a conversion value in between 95 and 99%. Some authors [100] argue that the various kinetics and mechanisms are not clear enough to design methods to follow and hence they prefer to simulate the reactors as conversion reactors.

Similarly, since many kinetic models for transesterification reaction have been obtained for the entire mixture of TG and FFA, the use of triolein in the simulation does not entirely represent the observed kinetic behavior in the reactor. In addition, most kinetic models found in the study have only been derived for one TG as a pseudocomponent. A detailed kinetic, and hence a more realistic simulation, should include triolein, tripalmitin, trilinolein and tristearin, as they account for more than 90 wt% of jatropha, palm, soybean, rapeseed and sunflower oils [84, 102].

Lee et al. [103] have developed a kinetic model based on three TGs, that is, for each component, kinetics parameters have been estimated. This model was used by Garcia et al. [90], who simulated the biodiesel production by considering a feedstock containing four TGs.

Most simulation studies found in literature have been performed at a large-scale process; however, there seems to be a lack of data about industrial performances that are not totally realistic. A more comprehensive and close comparison between real plant operation and process simulation could help to reduce this gap.

#### **5.2. Process optimization for biodiesel production**

**Materials** **Feedstock (Model** 

**Catalyst**

**compound)**

Rapeseed

MgO

Eley-Rideal

none

Bach and

UNIFAC

Aspen Plus

100000

[94]

168 Biofuels - State of Development

continuous

(slurry)

Pseudo second-order

reversible

(triolein)

Rapeseed

KOH/Enzyme

Yield model

None

Continuous

Dortmund

Aspen Plus

8000

[84]

UNIFAC

(CSTR)

(96 %)

(triolein)

Seven kinds of

NaOH

Second order

None

Batch

Dortmund

Aspen Plus

9125

[83]

UNIFAC

reversible

Second order

None

Continuous/Batch

Dortmund

Aspen HYSYS

562

[95]

(feed)

UNIFAC

irreversible

vegetable oils

Cottonseed

NaOH

> (pseudocomponents)

Soybean

Nb

O2 5

Pseudo homogeneous

Pseudo

Continuous (Pack

Dortmund

Non-commercial

2134

[96]

computational code

UNIFAC

bed reactor/RDC)

homogeneous

(hydrolysis) reversible

(triolein)

Soybean

Mg(OCH3

)2

Second order

None

Continuous

Dortmund

Aspen Plus

7542

[97]

UNIFAC

(CSTR/RD)

reversible

(heterogeneous)

(triolein)

Palm (triolein)

Soybean

NaOCH3

Conversion reactor

None

Continuous

NRTL

Aspen Plus

150000

[99]

UNIQUAC

(99%)

(trilinolein)

Jatropha (triolein)

Waste cooking oil

Tungsten on

Conversion reactor

Conversion

Membrane

NRTL

Aspen HYSYS

N/A

[101]

reactor

reactor

(92.34%)

alumina supported

(96.54%)

(WAI)

**Table 2.**

Key features of some simulation studies for biodiesel production.

NaOH

Conversion rector

None

Continuous

NRTL UNIFAC

Aspen HYSYS

8000

[100]

(CSTR)

(98.86%)

KOH or NaOH

Second-order

Second-order

Continuous

UNIFAC and

Aspen Plus

100000

[98]

NRTL

reversible

(CSTR)

reversible

**Reactor models**

**Transesterification**

**Esterification**

**Operation mode**

**Thermodynamic model**

**Program**

**Production size**

**Reference**

**Tonnes/year**

Optimization is one of the most quantitative tools in the industrial decision-making process [91]. The purpose of biodiesel production optimization is to find the value of the variables involved in the process that maximizes the profit, minimizes the cost of the process or maximizes the yield of biodiesel, so that the process becomes competitive in the fuel market. The optimization of biodiesel process should start from the optimization of the reaction conditions at a laboratory scale. This is usually performed by running a design of experiments and optimizing the conditions by the use of the surface response methodology (SRM). The model can later be validated at bench or pilot plant scale. Thus, the model can be used in the simulation process as a yield model.

**Author details**

Oaxaca, Mexico

**References**

Fernando Trejo-Zárraga<sup>1</sup>

Juan Carlos Chavarría-Hernández<sup>3</sup>

DOI: 10.1016/j.rser.2004.09.002

Química. 2014;**13**(1):311-322

\*Address all correspondence to: rsotelob@gmail.com

, Felipe de Jesús Hernández-Loyo<sup>2</sup>

1 Instituto Politécnico Nacional, CICATA-Legaria, Col. Irrigación, Mexico City, Mexico

2 Department of Petroleum Engineering, Tehuantepec, University of Istmo, Tehuantepec,

3 Renewable Energy Unit, Scientific Research Centre of Yucatán, Mérida, Yucatán, Mexico

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[7] González-Brambila MM, Montoya de la Fuente JA, González-Brambila O, López-Isunza F. A heterogeneous biodiesel production kinetic model. Revista Mexicana de Ingeniería

[8] Noureddini H, Zhu D. Kinetics of transesterification of soybean oil. Journal of the American Oil Chemists' Society. 1997;**74**:1457-1463. DOI: 10.1007/s11746-997-0254-2

4 Instituto Politécnico Nacional, ESIQIE, Col. Lindavista, Mexico City, Mexico

Engineering Journal. 2012;**207**:285-298. DOI: 10.1016/j.cej.2012.06.106

2006;**97**(12):1392-1397. DOI: 10.1016/j.biortech.2005.07.003

and Rogelio Sotelo-Boyás4

,

\*

Kinetics of Transesterification Processes for Biodiesel Production

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171

The use of a simulator can also be useful to add different factors that are not present at a laboratory scale, as well as to optimize the operation of the different equipment in the industrial plants by performing a sensitivity analysis. Several optimization studies have been reported in literature, mainly to perform an economic analysis [84, 88], to determine the optimal conditions to maximize the conversion of vegetable oils [104], to perform sensitivity analyst of design parameters and operating conditions to optimize the operation of each step [96], to study the excess methanol recovery in continuous production [105] and to evaluate new process intensification technologies [106], among others.

#### **6. Conclusions**

The goal in the development of heterogeneous catalysis seems to be the development of catalysts with high activity at low temperatures and pressures, being selective, being stable and should not be deactivated by water or leached. The kinetic modeling of the transesterification reaction should include more TG components; this, however, requires a more detailed characterization of both the feedstock and reaction products. These detailed kinetic models should also allow the simulation of TG mixtures or feedstocks such as waste cooking oil. By doing so, a more realistic simulation and optimization of the process could be obtained. As chemical process simulators have been incorporating most of the components in the biodiesel process, it is expected that the estimation of the properties becomes more reliable in these programs and provide more realistic simulated results. There is, however, a need for information on industrial data for the different biodiesel technologies, so that the biodiesel simulation studies can be compared and be validated with industrial data.

#### **Acknowledgements**

Rogelio Sotelo-Boyás and Fernando Trejo-Zárraga gratefully acknowledge the support of the Instituto Politécnico Nacional of Mexico for the development of institutional projects on biofuels research through SIP 20090379-20181723, whose results have contributed to write this chapter. Juan C. Chavarría acknowledges the support of the FSE-2014-01-254667 project for the realization of renewable energy studies, whose results have provided useful information for this work.

#### **Author details**

involved in the process that maximizes the profit, minimizes the cost of the process or maximizes the yield of biodiesel, so that the process becomes competitive in the fuel market. The optimization of biodiesel process should start from the optimization of the reaction conditions at a laboratory scale. This is usually performed by running a design of experiments and optimizing the conditions by the use of the surface response methodology (SRM). The model can later be validated at bench or pilot plant scale. Thus, the model can be used in the simulation

The use of a simulator can also be useful to add different factors that are not present at a laboratory scale, as well as to optimize the operation of the different equipment in the industrial plants by performing a sensitivity analysis. Several optimization studies have been reported in literature, mainly to perform an economic analysis [84, 88], to determine the optimal conditions to maximize the conversion of vegetable oils [104], to perform sensitivity analyst of design parameters and operating conditions to optimize the operation of each step [96], to study the excess methanol recovery in continuous production [105] and to evaluate new pro-

The goal in the development of heterogeneous catalysis seems to be the development of catalysts with high activity at low temperatures and pressures, being selective, being stable and should not be deactivated by water or leached. The kinetic modeling of the transesterification reaction should include more TG components; this, however, requires a more detailed characterization of both the feedstock and reaction products. These detailed kinetic models should also allow the simulation of TG mixtures or feedstocks such as waste cooking oil. By doing so, a more realistic simulation and optimization of the process could be obtained. As chemical process simulators have been incorporating most of the components in the biodiesel process, it is expected that the estimation of the properties becomes more reliable in these programs and provide more realistic simulated results. There is, however, a need for information on industrial data for the different biodiesel technologies, so that the biodiesel simulation studies

Rogelio Sotelo-Boyás and Fernando Trejo-Zárraga gratefully acknowledge the support of the Instituto Politécnico Nacional of Mexico for the development of institutional projects on biofuels research through SIP 20090379-20181723, whose results have contributed to write this chapter. Juan C. Chavarría acknowledges the support of the FSE-2014-01-254667 project for the realization of renewable energy studies, whose results have provided useful information

process as a yield model.

170 Biofuels - State of Development

**6. Conclusions**

**Acknowledgements**

for this work.

cess intensification technologies [106], among others.

can be compared and be validated with industrial data.

Fernando Trejo-Zárraga<sup>1</sup> , Felipe de Jesús Hernández-Loyo<sup>2</sup> , Juan Carlos Chavarría-Hernández<sup>3</sup> and Rogelio Sotelo-Boyás4 \*

\*Address all correspondence to: rsotelob@gmail.com

1 Instituto Politécnico Nacional, CICATA-Legaria, Col. Irrigación, Mexico City, Mexico

2 Department of Petroleum Engineering, Tehuantepec, University of Istmo, Tehuantepec, Oaxaca, Mexico

3 Renewable Energy Unit, Scientific Research Centre of Yucatán, Mérida, Yucatán, Mexico

4 Instituto Politécnico Nacional, ESIQIE, Col. Lindavista, Mexico City, Mexico

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[105] Dhar BR, Kirtania K. Excess methanol recovery in biodiesel production process using a distillation column: A simulation study. Chemical Engineering Research Bulletin.

[106] Wu L, Huang K, Wei T, Lin Z, Zou Y, Tong Z. Process intensification of NaOH-catalyzed transesterification for biodiesel production by the use of bentonite and co-solvent

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[87] Goodrum JW, Geller DP. Rapid thermogravimetric measurements of boiling points and vapor pressure of saturated medium-and long-chain triglycerides. Bioresource Technology.

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**Chapter 9**

Provisional chapter

**Study About Nitrogen Oxide Emissions and Fuel**

DOI: 10.5772/intechopen.74681

Study About Nitrogen Oxide Emissions and Fuel

**Consumption in Diesel Engines Fueled with B20**

The use of biodiesel is one of the alternatives to reduce oil dependence in the transport sector and to reduce greenhouse gas emissions. One of the most common engines in Europe was subjected to some tests, aiming to discover the efficiency effects and the emission characteristics when consuming a fuel containing 20% of biodiesel and 80% of diesel (B20), and comparing the results with the use of 100% diesel (B0). Using an engine test bench, several working points of the engine were chosen considering different engine rotation from idle speed to 3500 rpm and from residual torque to 120 Nm, covering the great majority of the normal running operation of this kind of engines when installed in light vehicles. The results revealed a non-proportional effect for fuel consumption for different engine regimes where the energetic differences were, in some operation regimes, totally compensated with efficiency increase. The NOx emission analysis allows to admit that the use of biodiesel in the fuel leads to a consequence on emissions increase that is not always obvious, since in some regimes that increase is noticeable, but for other regimes a

Consumption in Diesel Engines Fueled with B20

Luis Manuel Ventura Serrano and

Luis Manuel Ventura Serrano and

http://dx.doi.org/10.5772/intechopen.74681

Additional information is available at the end of the chapter

slight decrease or no significant change was detected.

Keywords: biodiesel, alternative fuel, energy, greenhouse gases, sustainability,

The use of oil as a source of energy was a key factor in the development of industry, economy and world's society. Actually, society is strongly addicted to this energetic source, revealing an enormous inability to free itself from this submission. The world is also subjugated to the

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Manuel Gameiro da Silva

Manuel Gameiro da Silva

Abstract

NOx emissions

1. Introduction

#### **Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20** Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

DOI: 10.5772/intechopen.74681

Luis Manuel Ventura Serrano and Manuel Gameiro da Silva Luis Manuel Ventura Serrano and Manuel Gameiro da Silva

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74681

#### Abstract

The use of biodiesel is one of the alternatives to reduce oil dependence in the transport sector and to reduce greenhouse gas emissions. One of the most common engines in Europe was subjected to some tests, aiming to discover the efficiency effects and the emission characteristics when consuming a fuel containing 20% of biodiesel and 80% of diesel (B20), and comparing the results with the use of 100% diesel (B0). Using an engine test bench, several working points of the engine were chosen considering different engine rotation from idle speed to 3500 rpm and from residual torque to 120 Nm, covering the great majority of the normal running operation of this kind of engines when installed in light vehicles. The results revealed a non-proportional effect for fuel consumption for different engine regimes where the energetic differences were, in some operation regimes, totally compensated with efficiency increase. The NOx emission analysis allows to admit that the use of biodiesel in the fuel leads to a consequence on emissions increase that is not always obvious, since in some regimes that increase is noticeable, but for other regimes a slight decrease or no significant change was detected.

Keywords: biodiesel, alternative fuel, energy, greenhouse gases, sustainability, NOx emissions

#### 1. Introduction

The use of oil as a source of energy was a key factor in the development of industry, economy and world's society. Actually, society is strongly addicted to this energetic source, revealing an enormous inability to free itself from this submission. The world is also subjugated to the

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

incessant desire to consume more energy, becoming increasingly degraded, subordinating all other aspects to be consumed almost exclusively in the control of privileged access to oil.

transport sector, which would reduce CO2 emissions per year by 2.1 gigatonnes (Gt) if a

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

http://dx.doi.org/10.5772/intechopen.74681

183

Considering the use of biodiesel, savings in terms of CO2 emissions can range from 36 to 83% when compared to conventional diesel [9]. However, for this fuel to be economically profitable, it will be necessary to use subsidies to balance the difference in the price of production and to

Given the lower amount of available energy per unit mass of biodiesel compared to diesel, to provide the same amount of energy required by the engine, it would be expected an increase in fuel consumption when biodiesel was used. However, biodiesel affects engine combustion and the consequent emissions [10] existing several conditions that contribute to this behavior. These conditions are higher density of biodiesel, because fuel supply control is made on a volume basis; the existence of oxygen in biodiesel that can affect the thermal yield and other properties such as viscosity; the cetane number among others that affects how the fuel mixes in the heated air inside the cylinder and influences the way energy is released. It is still necessary to consider the cumulative effect of these parameters with the different interactions promoted

Analyzing what is reported by various researchers, there is often an association between increased fuel consumption caused by the lower calorific value of biodiesel [11]. In concrete terms, the heat-based calorific value of biodiesel is 10–14% lower than that of diesel [12] [13]. In this way, it will be expected that the mass consumption of fuel will increase in the same proportion. However, as already mentioned, the fuel supply to the engine is made on a volumetric basis, so given the density differences, where biodiesel is denser between 3 and 4% [13], it would be expected that specific fuel consumption (g/kWh) would increase by 10– 14% and the volume (l/km) should increase by 5–10%. In the case of using a B20 blend, with 20% biodiesel and 80% of fossil diesel, it means that the difference in terms of amount of

Graboski and McCormick [14] explicitly state that regardless of whether the consumption of biodiesel is pure or mixed with diesel, a proportional fuel economy is revealed in the difference between the calorific value and there is no improvement or degradation of energy efficiency. In fact, the question is whether the use of biodiesel will promote an increase in energy efficiency. Deviations in this efficiency relative to diesel can be justified when considering other properties such as viscosity and density that promote changes in the type and shape of the spray and which affect the way the fuel is mixed in the air [15, 16] or when assessing the impact of the existence of oxygen on the molecular structure with biodiesel that modifies the way how combustion reaction is performed [15, 17–22]. It is explicitly referred by Demirbas [22] that despite the lower calorific value of biodiesel the oxygen content in this fuel promotes more complete combustion due to improved homogeneity in the local fuel mixture in the air.

Most of the authors report that the consumption of biodiesel in substitution of diesel fuel induces an increase in NOx emissions [11]. As possible causes for the variation in NOx

sustainable system was considered [8].

2. Literature review

account for the savings effects per tonne of CO2 not emitted.

by the use of diverse blends of biodiesel in diesel.

energy in that blend only implies a reduction of 2–3%.

In 2009, the European Commission unveiled its intentions of promoting the use of renewable energy sources. In the so-called Energy Policy Objectives, this commission defined sustainability criteria for the use of biofuels, making it mandatory for each of the member states of the European Community to define concrete objectives in such a way that, in general, it could be possible, to reach a quota up to 20% of the European Union's final energy consumption from renewable energy sources by the year 2020. In order to achieve this goal, each Member State should promote and encourage energy efficiency and energy savings [1].

In order to reduce energy dependency on oil and CO2 emissions, some measures have already been taken by the European Community [1] by setting targets for 10% of the energy used in the transport sector by 2020 to be obtained from biofuels. In the European Union, between 2005 and 2010, consumption of biofuels increased from 1.03 to 4.42% of total fuel consumption by the transport sector, but remained below the target set for 2010, with 5.75%. In parallel, there was a reduction in CO2 emissions from transport of 16.4 megatonnes (Mt) in 2008 and 26.6 Mt in 2009, with a total of 920.74 Mt of CO2 emissions [2].

The bet on biofuels is increasing and is an obvious alternative to the automotive sector, given the enormous amount of energy used by road vehicles, adding to the difficulty of finding alternative solutions to oil guaranteeing the essential energy mobility for this sector. In fact, the biggest problems in implementing solutions with lower environmental impact reside in the processes of distribution and storage of energy, making it accessible and allowing autonomy and reliability close to the existing solution. The European Community has determined the need to increase the production of commercially viable biofuels which are CO2-efficient and compatible with combustion engines for motor vehicles [1] and also intends to ensure the development of biofuels from sources other than food sources [3]. From the European point of view, the use of biofuels increases security of energy supply, reduces greenhouse gas emissions and increases the yield and employability of agricultural activity [4].

The most widely used biofuel in Europe is biodiesel, an ester produced from vegetable or animal oils, through a transesterification process. This renewable energy source accounted for 82% of total biofuels produced in Europe (27 members) in 2003 [4] and in 2007 a share of 84.7% of all biofuels consumed [5]. The European Union is the largest producer and consumer of biodiesel, with a production of 9164 million liters of biodiesel in 2008, about half of the world's biodiesel production [6]. The world average of biodiesel production in the years 2013–2015 was 31.1 billion liters, and it is expected to reach 37.9 billion liters by 2020 [7]. The consumption of vegetable oils to produce biodiesel has been increasing in the World, mainly due to its renewable nature and to the fact that it is less polluting when compared to petroleum-based diesel. Biodiesel is a renewable fuel which can alternatively be used in internal combustion engines of compression ignition, without having to make any changes, substituting part or all of the fuel of fossil origin. The efficient use of biodiesel in the transport sector brings some important environmental, economic and social benefits, resulting in job creation, reduction of pollutant emissions, reduction of the country's dependence on petroleum and reduction of CO2 emissions levels for the transport sector. The International Energy Agency believes that in 2050 it will be possible for biofuels to account for 27% of the total amount of fuels in the transport sector, which would reduce CO2 emissions per year by 2.1 gigatonnes (Gt) if a sustainable system was considered [8].

Considering the use of biodiesel, savings in terms of CO2 emissions can range from 36 to 83% when compared to conventional diesel [9]. However, for this fuel to be economically profitable, it will be necessary to use subsidies to balance the difference in the price of production and to account for the savings effects per tonne of CO2 not emitted.

#### 2. Literature review

incessant desire to consume more energy, becoming increasingly degraded, subordinating all other aspects to be consumed almost exclusively in the control of privileged access to oil.

In 2009, the European Commission unveiled its intentions of promoting the use of renewable energy sources. In the so-called Energy Policy Objectives, this commission defined sustainability criteria for the use of biofuels, making it mandatory for each of the member states of the European Community to define concrete objectives in such a way that, in general, it could be possible, to reach a quota up to 20% of the European Union's final energy consumption from renewable energy sources by the year 2020. In order to achieve this goal, each Member State

In order to reduce energy dependency on oil and CO2 emissions, some measures have already been taken by the European Community [1] by setting targets for 10% of the energy used in the transport sector by 2020 to be obtained from biofuels. In the European Union, between 2005 and 2010, consumption of biofuels increased from 1.03 to 4.42% of total fuel consumption by the transport sector, but remained below the target set for 2010, with 5.75%. In parallel, there was a reduction in CO2 emissions from transport of 16.4 megatonnes (Mt) in 2008 and 26.6 Mt

The bet on biofuels is increasing and is an obvious alternative to the automotive sector, given the enormous amount of energy used by road vehicles, adding to the difficulty of finding alternative solutions to oil guaranteeing the essential energy mobility for this sector. In fact, the biggest problems in implementing solutions with lower environmental impact reside in the processes of distribution and storage of energy, making it accessible and allowing autonomy and reliability close to the existing solution. The European Community has determined the need to increase the production of commercially viable biofuels which are CO2-efficient and compatible with combustion engines for motor vehicles [1] and also intends to ensure the development of biofuels from sources other than food sources [3]. From the European point of view, the use of biofuels increases security of energy supply, reduces greenhouse gas

The most widely used biofuel in Europe is biodiesel, an ester produced from vegetable or animal oils, through a transesterification process. This renewable energy source accounted for 82% of total biofuels produced in Europe (27 members) in 2003 [4] and in 2007 a share of 84.7% of all biofuels consumed [5]. The European Union is the largest producer and consumer of biodiesel, with a production of 9164 million liters of biodiesel in 2008, about half of the world's biodiesel production [6]. The world average of biodiesel production in the years 2013–2015 was 31.1 billion liters, and it is expected to reach 37.9 billion liters by 2020 [7]. The consumption of vegetable oils to produce biodiesel has been increasing in the World, mainly due to its renewable nature and to the fact that it is less polluting when compared to petroleum-based diesel. Biodiesel is a renewable fuel which can alternatively be used in internal combustion engines of compression ignition, without having to make any changes, substituting part or all of the fuel of fossil origin. The efficient use of biodiesel in the transport sector brings some important environmental, economic and social benefits, resulting in job creation, reduction of pollutant emissions, reduction of the country's dependence on petroleum and reduction of CO2 emissions levels for the transport sector. The International Energy Agency believes that in 2050 it will be possible for biofuels to account for 27% of the total amount of fuels in the

emissions and increases the yield and employability of agricultural activity [4].

should promote and encourage energy efficiency and energy savings [1].

in 2009, with a total of 920.74 Mt of CO2 emissions [2].

182 Biofuels - State of Development

Given the lower amount of available energy per unit mass of biodiesel compared to diesel, to provide the same amount of energy required by the engine, it would be expected an increase in fuel consumption when biodiesel was used. However, biodiesel affects engine combustion and the consequent emissions [10] existing several conditions that contribute to this behavior. These conditions are higher density of biodiesel, because fuel supply control is made on a volume basis; the existence of oxygen in biodiesel that can affect the thermal yield and other properties such as viscosity; the cetane number among others that affects how the fuel mixes in the heated air inside the cylinder and influences the way energy is released. It is still necessary to consider the cumulative effect of these parameters with the different interactions promoted by the use of diverse blends of biodiesel in diesel.

Analyzing what is reported by various researchers, there is often an association between increased fuel consumption caused by the lower calorific value of biodiesel [11]. In concrete terms, the heat-based calorific value of biodiesel is 10–14% lower than that of diesel [12] [13]. In this way, it will be expected that the mass consumption of fuel will increase in the same proportion. However, as already mentioned, the fuel supply to the engine is made on a volumetric basis, so given the density differences, where biodiesel is denser between 3 and 4% [13], it would be expected that specific fuel consumption (g/kWh) would increase by 10– 14% and the volume (l/km) should increase by 5–10%. In the case of using a B20 blend, with 20% biodiesel and 80% of fossil diesel, it means that the difference in terms of amount of energy in that blend only implies a reduction of 2–3%.

Graboski and McCormick [14] explicitly state that regardless of whether the consumption of biodiesel is pure or mixed with diesel, a proportional fuel economy is revealed in the difference between the calorific value and there is no improvement or degradation of energy efficiency. In fact, the question is whether the use of biodiesel will promote an increase in energy efficiency. Deviations in this efficiency relative to diesel can be justified when considering other properties such as viscosity and density that promote changes in the type and shape of the spray and which affect the way the fuel is mixed in the air [15, 16] or when assessing the impact of the existence of oxygen on the molecular structure with biodiesel that modifies the way how combustion reaction is performed [15, 17–22]. It is explicitly referred by Demirbas [22] that despite the lower calorific value of biodiesel the oxygen content in this fuel promotes more complete combustion due to improved homogeneity in the local fuel mixture in the air.

Most of the authors report that the consumption of biodiesel in substitution of diesel fuel induces an increase in NOx emissions [11]. As possible causes for the variation in NOx emissions due to the use of biodiesel, pointed out by Graboski and McCormick [14], are the increase of the flame temperature and the decrease of the radiate effect that promotes the increase of the temperature in the combustion chamber, since the heat transfer by radiation is carried out by particles. Since biodiesel has reduced particle emissions, it decreases this ability to radiate heat, resulting in higher temperatures and consequently higher NOx emissions. In fact, the increase in the in-cylinder temperature is the most relevant parameter that causes an increase in NOx emissions [23].

The engine regime and the way how fuel flow interacts in the injection process for each regime shows to some significant differences with respect to the energy efficiency of the combustion process for the different fuels [24–33]. It is expressed by several authors that the use of 20% biodiesel in a mixture with 80% of fossil diesel (B20) corresponds to the optimum mixture where the maximum value of thermal efficiency is revealed and logically a minimum value of specific consumption is expected [11–13, 31, 33]. The study performed by Suresh et al. revealed that the engine presents different heat release rate behaviors with partial load and full load for diesel when compared with B10, B20 and B30, where B20 presents the most significant results [34]. Also the goals imposed by the European Union point out that in the near future the amount of biodiesel incorporated in the commercial diesel is close to 20%. This lead to the analysis that was done in the present work considering the realization of tests with a B20 blend covering all the operation regime of the engine, finding how this fuel affects engine in terms of energetic efficiency and in terms of NOx emissions, that is the most controversial emission for diesel engines, after the introduction of diesel particles filters (DPF).

#### 3. Experimental methodology

Tests were completed using an engine test bench, equipped with a Schenk hydraulic dynamometer with a capacity to test engines up to 230 kW at a maximum engine rotation of 13,000 rpm and a torque limit of 600 Nm. It also has an AVL gravimetric fuel consumption measurement system and a Horiba gas analyzer. The schematic of the experimental setup is represented in Figure 1.

Tests were made using two different biodiesel blends (B0 and B20). The properties of the fuels, biodiesel and commercial diesel, are presented in Table 2. B0 is fully constituted by a petroleum-based fuel, and the B20 was made by mixing this base fuel with biodiesel constituting a blend in proportion 80 diesel – 20 biodiesel. This B20 blend was selected considering that the amount of petroleum diesel incorporated in diesel is of 5–7%, so it seems important to better characterize the expected blends in the next few years, considering that the use of 20%

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

http://dx.doi.org/10.5772/intechopen.74681

185

Since all engines are produced assuming that they will consume petroleum diesel fuel, it is important to define a specific methodology for this kind of studies, including the way how different fuels affect engine efficiency and performance. It is expected that the use of biodiesel, with different properties that interact differently with injection system and combustion process, will certainly produce effects on emissions and consumption [10]. Furthermore, there is a certain inadequacy of the regulated cycles for engine homologation to reflect the proper effects

In the first evaluations of the engine's operation, it was verified that there were some problems that conditioned the test's performance. The original idea was to carry out a detailed analysis of the entire motor parameter map. In this way, a series of tests were carried out in stabilized regimes to obtain the consumption and emissions of exhaust gases relative to the engine

of changing from petroleum diesel to biodiesel in a certain proportion.

biodiesel will be a highly plausible scenario.

Figure 1. Engine test bench.

A data acquisition system collects the engine data, the equipment measurements (fuel consumption, exhaust emissions, temperature and pressure sensors). The acquisition system is integrated with a control system that defines the parameters specified by the test cycle imposed, without the intervention of the technician, which allows a better accuracy and reliability of the obtained results [20].

The engine used for these tests was a VW 1.9 TDI with four cylinders in line and 1896cm3 , developing a maximum power of 66 kW, with EuroII exhaust emission technology. This engine equipped a large part of the VW group of vehicles with great success, such as the VW Passat, VW Golf, Audi A3, A4 and Seat Ibiza. The main characteristics of the engine are presented in Table 1, including that it is a direct injection supercharged engine with EGR. This engine is known to have high reliability, allowing having a maximum torque a relative low engine rotation (202 Nm at 1900 rpm).

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20 http://dx.doi.org/10.5772/intechopen.74681 185

Figure 1. Engine test bench.

emissions due to the use of biodiesel, pointed out by Graboski and McCormick [14], are the increase of the flame temperature and the decrease of the radiate effect that promotes the increase of the temperature in the combustion chamber, since the heat transfer by radiation is carried out by particles. Since biodiesel has reduced particle emissions, it decreases this ability to radiate heat, resulting in higher temperatures and consequently higher NOx emissions. In fact, the increase in the in-cylinder temperature is the most relevant parameter that causes an

The engine regime and the way how fuel flow interacts in the injection process for each regime shows to some significant differences with respect to the energy efficiency of the combustion process for the different fuels [24–33]. It is expressed by several authors that the use of 20% biodiesel in a mixture with 80% of fossil diesel (B20) corresponds to the optimum mixture where the maximum value of thermal efficiency is revealed and logically a minimum value of specific consumption is expected [11–13, 31, 33]. The study performed by Suresh et al. revealed that the engine presents different heat release rate behaviors with partial load and full load for diesel when compared with B10, B20 and B30, where B20 presents the most significant results [34]. Also the goals imposed by the European Union point out that in the near future the amount of biodiesel incorporated in the commercial diesel is close to 20%. This lead to the analysis that was done in the present work considering the realization of tests with a B20 blend covering all the operation regime of the engine, finding how this fuel affects engine in terms of energetic efficiency and in terms of NOx emissions, that is the most controversial emission for

Tests were completed using an engine test bench, equipped with a Schenk hydraulic dynamometer with a capacity to test engines up to 230 kW at a maximum engine rotation of 13,000 rpm and a torque limit of 600 Nm. It also has an AVL gravimetric fuel consumption measurement system and a Horiba gas analyzer. The schematic of the experimental setup is

A data acquisition system collects the engine data, the equipment measurements (fuel consumption, exhaust emissions, temperature and pressure sensors). The acquisition system is integrated with a control system that defines the parameters specified by the test cycle imposed, without the intervention of the technician, which allows a better accuracy and

The engine used for these tests was a VW 1.9 TDI with four cylinders in line and 1896cm3

developing a maximum power of 66 kW, with EuroII exhaust emission technology. This engine equipped a large part of the VW group of vehicles with great success, such as the VW Passat, VW Golf, Audi A3, A4 and Seat Ibiza. The main characteristics of the engine are presented in Table 1, including that it is a direct injection supercharged engine with EGR. This engine is known to have high reliability, allowing having a maximum torque a relative low engine

,

diesel engines, after the introduction of diesel particles filters (DPF).

increase in NOx emissions [23].

184 Biofuels - State of Development

3. Experimental methodology

reliability of the obtained results [20].

rotation (202 Nm at 1900 rpm).

represented in Figure 1.

Tests were made using two different biodiesel blends (B0 and B20). The properties of the fuels, biodiesel and commercial diesel, are presented in Table 2. B0 is fully constituted by a petroleum-based fuel, and the B20 was made by mixing this base fuel with biodiesel constituting a blend in proportion 80 diesel – 20 biodiesel. This B20 blend was selected considering that the amount of petroleum diesel incorporated in diesel is of 5–7%, so it seems important to better characterize the expected blends in the next few years, considering that the use of 20% biodiesel will be a highly plausible scenario.

Since all engines are produced assuming that they will consume petroleum diesel fuel, it is important to define a specific methodology for this kind of studies, including the way how different fuels affect engine efficiency and performance. It is expected that the use of biodiesel, with different properties that interact differently with injection system and combustion process, will certainly produce effects on emissions and consumption [10]. Furthermore, there is a certain inadequacy of the regulated cycles for engine homologation to reflect the proper effects of changing from petroleum diesel to biodiesel in a certain proportion.

In the first evaluations of the engine's operation, it was verified that there were some problems that conditioned the test's performance. The original idea was to carry out a detailed analysis of the entire motor parameter map. In this way, a series of tests were carried out in stabilized regimes to obtain the consumption and emissions of exhaust gases relative to the engine

the operability and reliability of the engine without damaging it, a 30-point table was chosen, shown in Figure 2. This distribution covers the major part of the engine operating regime

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

http://dx.doi.org/10.5772/intechopen.74681

187

The sequence of the tests was as follows: after ensuring the stabilized normal operating conditions of the engine on the test bench, the speed of rotation is set at 1250 rpm, with the brake torque at its minimum value, corresponding to the residual torque which is the sum of the energy losses due to friction and to the inertia that must be overcome in order to keep the

After reaching a stable operation, reading and acquiring the information about the performance of the motor at this operating point, the torque value is increased to 40 Nm, for the same rotation, waiting for the stabilization of the operation of the various parameters to make the data acquisition. This process is repeated in successive steps for various values of resistant torque until reaching the value of 120 Nm. At this point and after data collection, the rotation is increased to 2000 rpm. Following the stabilization at this rotation value, the cycle already performed is repeated, but successively decreasing the torque value by 20 Nm,

The process is repeated by maintaining the descending torque sequence until the throttle reaches the minimum position. When this operating point is properly characterized, the whole process will be repeated with the increase of rotation to 2500 rpm, followed by the addition in terms of torque to the value 120 Nm, doing the same in the downward direction, with successive increments of 500 rpm, repeating this sequence until the rotation reaches 3500 rpm. In the most demanding conditions, such as rotations above 3000 and 3500 rpm with torque

when in normal operation to drive a light vehicle.

with the corresponding lowering of the throttle position.

engine at the desired speed.

Figure 2. Operation points chosen for the tests.

Table 1. Main characteristics of the engine used in the bench tests.


Table 2. Biodiesel and fossil diesel properties.

operation from idle to 4000 rpm in successive increments of 500 rpm, and from 0% load up to 80% load, in increments of 20%.

However, it was found that in certain schemes engine operation became quite unstable due to several occurrences: the opening and closing of the exhaust gas recirculation "EGR" valve; the functioning of the turbocharger and the waste gate valve which adjusts its operating pressure, and the excessive heating of the engine in higher load conditions. Thus, after a few attempts to establish a procedure that would allow reliable data to be obtained and at the same time guarantee the operability and reliability of the engine without damaging it, a 30-point table was chosen, shown in Figure 2. This distribution covers the major part of the engine operating regime when in normal operation to drive a light vehicle.

The sequence of the tests was as follows: after ensuring the stabilized normal operating conditions of the engine on the test bench, the speed of rotation is set at 1250 rpm, with the brake torque at its minimum value, corresponding to the residual torque which is the sum of the energy losses due to friction and to the inertia that must be overcome in order to keep the engine at the desired speed.

After reaching a stable operation, reading and acquiring the information about the performance of the motor at this operating point, the torque value is increased to 40 Nm, for the same rotation, waiting for the stabilization of the operation of the various parameters to make the data acquisition. This process is repeated in successive steps for various values of resistant torque until reaching the value of 120 Nm. At this point and after data collection, the rotation is increased to 2000 rpm. Following the stabilization at this rotation value, the cycle already performed is repeated, but successively decreasing the torque value by 20 Nm, with the corresponding lowering of the throttle position.

The process is repeated by maintaining the descending torque sequence until the throttle reaches the minimum position. When this operating point is properly characterized, the whole process will be repeated with the increase of rotation to 2500 rpm, followed by the addition in terms of torque to the value 120 Nm, doing the same in the downward direction, with successive increments of 500 rpm, repeating this sequence until the rotation reaches 3500 rpm. In the most demanding conditions, such as rotations above 3000 and 3500 rpm with torque

Figure 2. Operation points chosen for the tests.

operation from idle to 4000 rpm in successive increments of 500 rpm, and from 0% load up to

Engine VW 1.9 TDI Engine code 1Z/AHU

Swapped volume

Exhaust emissions technology

(Soybean 86.5% + Palm 13.5%)

) 882 EN ISO 3675 840

/s] 4.15 EN ISO 3104 2.43

Ester Content [% (m/m)] 97.7 EN ISO 14103 —

Flash Point (�C) >120 EN ISO 3679 >55 Water Content (mg/kg) 216.8 EN ISO 12937 — Iodine Value (g iodine/100 g) 117 EN ISO 14111 — Sulfated ash content [% (m/m)] <0.02 ASTM D 874 — Cetane number 51 EN ISO 5165 >51 Higher heating value (HHV) [kJ/kg] 39,909 ASTM D 240 45,620 Oxidation stability, 110�C (hours) 6.3 EN 14112 —

Table 1. Main characteristics of the engine used in the bench tests.

Parameter/Unit Biodiesel (BD)

Compression ratio

Type 4 cylinders in line, 8 valv.

19.5:1

1896 cm3

controlled Supercharged Yes, with intercooler

Yes (Euro II)

Results Method Results

Power máx. 66 kW (89cv) @ 4000 rpm Torque máx. 202 Nm @ 1900 rpm

Ignition system Rotate pump with direct injection electronic

Fossil diesel (FD)

However, it was found that in certain schemes engine operation became quite unstable due to several occurrences: the opening and closing of the exhaust gas recirculation "EGR" valve; the functioning of the turbocharger and the waste gate valve which adjusts its operating pressure, and the excessive heating of the engine in higher load conditions. Thus, after a few attempts to establish a procedure that would allow reliable data to be obtained and at the same time guarantee

80% load, in increments of 20%.

Table 2. Biodiesel and fossil diesel properties.

Density at 15�C (kg/m<sup>3</sup>

186 Biofuels - State of Development

Kinematic Viscosity at 40�C [mm<sup>2</sup>

values above 80 Nm, it was found necessary to interrupt the sequential process to allow engine cooling. Thus, when the engine oil temperature was no longer stable, the cycle was interrupted so that some of the accumulated energy could be dissipated and the established process could continue.

amount of energy that fuel releases in an ideal combustion and that can be obtained in an

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

The graphical presentation of the results is based on the representation of the consumption values measured with the two types of fuel in the narrow bars, read on the vertical axis on the left and correspondent representation of the relative difference in the wide bars read on the vertical axis on the right. The value of the relative difference is calculated with reference to the case of consumption for B0. Thus, if the bar is above the red dashed line it translates into an increase of consumption, efficiency or emissions for biodiesel; if, on the other hand, the bar is

The analysis of the results obtained with this engine reveals that the mass fuel consumption shown graphically in Figure 3a and b does not exhibit a behavior proportional to the introduction of biodiesel and the corresponding slight decrease in energy associated with the use of this type of fuel. It is apparent that in certain regimes, usually associated with high torque values, specific consumption increases when using B20; however, the variations are very slight for torque values of 40 and 60 Nm. In this situation there is some variation in terms of specific fuel consumption, with a slight increase for low rotation (1250 rpm), as opposed to the slight reduction corresponding to 2000 rpm, with an increase of more than 5% to 40 Nm at 2500 rpm and a reduction of about 5% to 60 Nm. An abnormally high amount of consumption occurs at 3000 rpm with residual torque when using B20, however, given that this situation is quite unlikely to occur under normal vehicle use and that the engine has a somewhat unstable behavior at this rate, because of the rather oscillating operation of the turbocharger, a more

Overall, it cannot be stated in full that the use of biodiesel in a blend containing 20% biodiesel and 80% diesel results in a direct increase in specific fuel consumption, but there is a tendency for that increase to occur when the engine is subjected to high torque demanding situations in

If the evaluation of the results obtained account for the higher fuel density promoted by the incorporation of biodiesel, comparing the consumptions on a volumetric basis, it is possible to emphasize what was already pointed out in the mass analysis, that is, only in the situation of torque of 40 Nm at 2500 rpm and 60 Nm at 1250 rpm there is an increase in consumption, except for cases of higher torque (100 and 120 Nm). It may even be considered that in volumetric terms, the use of B20 promotes very few changes in the total fuel consumption. In the most normal conditions of engine operation when under normal road conditions, which correspond to low torque values and low and medium engine rotation, it may be possible to

The analysis of the energy conversion efficiency (ECE) results, shown in Figure 4, accentuates what has already been verified in the evaluation of consumption results, that is, for loads up to 80 Nm there is a similar efficiency of conversion of the existing energy in the B20 relative to the

<sup>3600</sup>∗<sup>1000</sup> <sup>∗</sup>HHV <sup>∗</sup><sup>100</sup> (1)

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189

ECE <sup>¼</sup> <sup>1</sup> sfc

below the red line it represents a decrease of the parameters in question.

in-depth study of this situation was not considered relevant.

high revs (3000 and 3500 rpm) and very low rotation (1250 rpm).

observe an overall slight reduction in volumetric fuel consumption.

laboratorial experience.

#### 4. Results

Each of the cycles defined in the methodology was repeated two times, according to a certain sequence that would allow analyzing possible degradations in the operation and in the performance of the motor. As such, two measurements were performed with B0, followed by three measurements with B20 and a new measurement with B0. The results obtained are the average of the three measurements whenever they do not differ by more than the standard deviation of the three measurements made. When this happens, the value that shows higher deviations from the average value is not considered, resulting in the final value considered from the average of the two values that meet the defined criteria.

Of all the information collected a large part served as a way of controlling the process in order to guarantee the comparability of the results and to verify the occurrence of some situations, as was verified for the control of the exhaust gas circulation and the turbocharger, for example.

The data presented are related to the two most relevant aspects of this work, fuel consumption and NOx emissions, which are more controversial about how the use of biodiesel affects the engine. The emissions of CO and HC are not the most problematic emissions for this type of motor and, considering the low resolution of the equipment in the measurement of CO, it was decided to devote more attention to the emissions of NOx, having not considered the emissions of CO and HC, although the data on these combustion products were collected.

#### 4.1. Fuel consumption

The results presented relate to the consumption on a mass basis, through the result of the specific consumption (g/kWh), taking into account that the measurement was carried out according to a gravimetric process to avoid problems with fuel density. Considering the importance of the efficiency process in the evaluation of the engines, the results in terms of energy conversion efficiency (ECE) are also presented, using the different energy values available in each of the fuels. This will allow evaluating the way how the engine can avail this energy at useful power from different available energy levels.

The energy conversion efficiency (ECE) is a very useful concept to compare different fuels since it allows having quantification about the way how the available energy in the fuel can be converted into work. This parameter can be determined with the mathematic expression (1) where: "sfc" (g/kWh) is the specific fuel consumption obtained through the gravimetric measurement of the fuel consumed in each operation point divided by the developed engine power at that same point; "PCS" is the higher heating value (HHV) of the fuel that characterizes the amount of energy that fuel releases in an ideal combustion and that can be obtained in an laboratorial experience.

values above 80 Nm, it was found necessary to interrupt the sequential process to allow engine cooling. Thus, when the engine oil temperature was no longer stable, the cycle was interrupted so that some of the accumulated energy could be dissipated and the established process could

Each of the cycles defined in the methodology was repeated two times, according to a certain sequence that would allow analyzing possible degradations in the operation and in the performance of the motor. As such, two measurements were performed with B0, followed by three measurements with B20 and a new measurement with B0. The results obtained are the average of the three measurements whenever they do not differ by more than the standard deviation of the three measurements made. When this happens, the value that shows higher deviations from the average value is not considered, resulting in the final value considered from the average of

Of all the information collected a large part served as a way of controlling the process in order to guarantee the comparability of the results and to verify the occurrence of some situations, as was verified for the control of the exhaust gas circulation and the turbocharger, for example. The data presented are related to the two most relevant aspects of this work, fuel consumption and NOx emissions, which are more controversial about how the use of biodiesel affects the engine. The emissions of CO and HC are not the most problematic emissions for this type of motor and, considering the low resolution of the equipment in the measurement of CO, it was decided to devote more attention to the emissions of NOx, having not considered the emis-

sions of CO and HC, although the data on these combustion products were collected.

The results presented relate to the consumption on a mass basis, through the result of the specific consumption (g/kWh), taking into account that the measurement was carried out according to a gravimetric process to avoid problems with fuel density. Considering the importance of the efficiency process in the evaluation of the engines, the results in terms of energy conversion efficiency (ECE) are also presented, using the different energy values available in each of the fuels. This will allow evaluating the way how the engine can avail this energy at useful power

The energy conversion efficiency (ECE) is a very useful concept to compare different fuels since it allows having quantification about the way how the available energy in the fuel can be converted into work. This parameter can be determined with the mathematic expression (1) where: "sfc" (g/kWh) is the specific fuel consumption obtained through the gravimetric measurement of the fuel consumed in each operation point divided by the developed engine power at that same point; "PCS" is the higher heating value (HHV) of the fuel that characterizes the

continue.

188 Biofuels - State of Development

4. Results

the two values that meet the defined criteria.

4.1. Fuel consumption

from different available energy levels.

$$ECE = \frac{1}{\frac{s\text{fc}}{3600 \ast 1000} \ast HHV} \ast 100 \tag{1}$$

The graphical presentation of the results is based on the representation of the consumption values measured with the two types of fuel in the narrow bars, read on the vertical axis on the left and correspondent representation of the relative difference in the wide bars read on the vertical axis on the right. The value of the relative difference is calculated with reference to the case of consumption for B0. Thus, if the bar is above the red dashed line it translates into an increase of consumption, efficiency or emissions for biodiesel; if, on the other hand, the bar is below the red line it represents a decrease of the parameters in question.

The analysis of the results obtained with this engine reveals that the mass fuel consumption shown graphically in Figure 3a and b does not exhibit a behavior proportional to the introduction of biodiesel and the corresponding slight decrease in energy associated with the use of this type of fuel. It is apparent that in certain regimes, usually associated with high torque values, specific consumption increases when using B20; however, the variations are very slight for torque values of 40 and 60 Nm. In this situation there is some variation in terms of specific fuel consumption, with a slight increase for low rotation (1250 rpm), as opposed to the slight reduction corresponding to 2000 rpm, with an increase of more than 5% to 40 Nm at 2500 rpm and a reduction of about 5% to 60 Nm. An abnormally high amount of consumption occurs at 3000 rpm with residual torque when using B20, however, given that this situation is quite unlikely to occur under normal vehicle use and that the engine has a somewhat unstable behavior at this rate, because of the rather oscillating operation of the turbocharger, a more in-depth study of this situation was not considered relevant.

Overall, it cannot be stated in full that the use of biodiesel in a blend containing 20% biodiesel and 80% diesel results in a direct increase in specific fuel consumption, but there is a tendency for that increase to occur when the engine is subjected to high torque demanding situations in high revs (3000 and 3500 rpm) and very low rotation (1250 rpm).

If the evaluation of the results obtained account for the higher fuel density promoted by the incorporation of biodiesel, comparing the consumptions on a volumetric basis, it is possible to emphasize what was already pointed out in the mass analysis, that is, only in the situation of torque of 40 Nm at 2500 rpm and 60 Nm at 1250 rpm there is an increase in consumption, except for cases of higher torque (100 and 120 Nm). It may even be considered that in volumetric terms, the use of B20 promotes very few changes in the total fuel consumption. In the most normal conditions of engine operation when under normal road conditions, which correspond to low torque values and low and medium engine rotation, it may be possible to observe an overall slight reduction in volumetric fuel consumption.

The analysis of the energy conversion efficiency (ECE) results, shown in Figure 4, accentuates what has already been verified in the evaluation of consumption results, that is, for loads up to 80 Nm there is a similar efficiency of conversion of the existing energy in the B20 relative to the

Figure 3. Results for specific fuel consumption (g/kWh) with B0 and B20.

B0. Although only slight, it is an aspect that needs to be analyzed in detail in order to enhance this energy gain. Considering that the maximum torque for this engine is obtained with 1900 rpm, it is interesting to observe that the results for 2000 rpm with biodiesel reveal an overall increase of ECE for all load conditions evaluated.

In the remaining points analyzed and considering the normal operating conditions of the engine, when installed in a vehicle subject to actual driving on the road, it can be stated that there are serious indications of the possibility of slight increases in engine efficiency when supplied with B20 compared to the consumption of B0, mainly when low and medium operating regimes are required, corresponding to the urban and extra-urban circuit operation. In a more demanding operating regime, such as high-slope or high-speed road traffic, where the required engine operation is supported at higher torque values, the use of B0 indicates a

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

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191

Analysis of fuel or energy consumption results reinforces the need to evaluate the behavior of the vehicle in real road situations so that it will become possible to see how this behavior will affect fuel consumption. An assessment can be made of these results and try to fit the type of

slight advantage over the B20 in energetic terms.

Figure 4. Results for energetic conversion efficiency (ECE) (%) with B0 and B20.

As indicated above, somewhat different values occur in terms of magnitude in cases of high rotation (3000 and 3500 rpm) under residual torque conditions, where the minimum required effort is to overcome the mechanical losses. In these circumstances which are very rare to occur in actual circulation, the engine exhibits an unstable behavior, in which the turbocharger exhibits some sudden deviations and the consumption is relatively low, allowing that small variations, due to the behavior of the engine in terms of control, become most noticeably in global terms.

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20 http://dx.doi.org/10.5772/intechopen.74681 191

Figure 4. Results for energetic conversion efficiency (ECE) (%) with B0 and B20.

B0. Although only slight, it is an aspect that needs to be analyzed in detail in order to enhance this energy gain. Considering that the maximum torque for this engine is obtained with 1900 rpm, it is interesting to observe that the results for 2000 rpm with biodiesel reveal an

As indicated above, somewhat different values occur in terms of magnitude in cases of high rotation (3000 and 3500 rpm) under residual torque conditions, where the minimum required effort is to overcome the mechanical losses. In these circumstances which are very rare to occur in actual circulation, the engine exhibits an unstable behavior, in which the turbocharger exhibits some sudden deviations and the consumption is relatively low, allowing that small variations, due to the behavior of the engine in terms of control, become most noticeably in global terms.

overall increase of ECE for all load conditions evaluated.

Figure 3. Results for specific fuel consumption (g/kWh) with B0 and B20.

190 Biofuels - State of Development

In the remaining points analyzed and considering the normal operating conditions of the engine, when installed in a vehicle subject to actual driving on the road, it can be stated that there are serious indications of the possibility of slight increases in engine efficiency when supplied with B20 compared to the consumption of B0, mainly when low and medium operating regimes are required, corresponding to the urban and extra-urban circuit operation. In a more demanding operating regime, such as high-slope or high-speed road traffic, where the required engine operation is supported at higher torque values, the use of B0 indicates a slight advantage over the B20 in energetic terms.

Analysis of fuel or energy consumption results reinforces the need to evaluate the behavior of the vehicle in real road situations so that it will become possible to see how this behavior will affect fuel consumption. An assessment can be made of these results and try to fit the type of behavior expected on the road for a light vehicle and realize the perspectives for overall results of consumption. In this way, it is possible to verify that the specific mass consumption presents small oscillations that were already expected, given the little significant difference in calorific value of the two evaluated fuels (B0 and B20). However, the differences became more significant only in the relative circumstances of higher rotation and high load, which may correspond to the typical high-speed freeway circulation, which implies a high engine speed and also high loads since the aerodynamic drag force becomes very relevant. For the other situations, corresponding to urban and extra-urban traffic, characterized by low and medium speeds and low and medium loads, the differences in consumption are minor, revealing a tendency to small decrease in fuel consumption when fueling the engine with B20, especially if a consumption analysis is made on a volumetric basis.

#### 4.2. NOx emissions

As mentioned above, the study on the impact on NOx emissions by the use of B20 compared to the use of B0 was established. The results below are the reflection of this study allowing evaluating the influence that the B20 consumption has on the NOx emissions when compared to the consumption of diesel, for the various selected engine operating regimes. In order to make the analyzed results more comparable, the value of the NOx volumetric percentage present in the exhaust gas was divided by the power obtained corresponding to each selected engine operating point, and the results of Figure 5 in (ppm/kWh) corresponding to specific NOx emissions.

The analysis of the specific NOx emission results presented in the graphs of Figure 5 reveals an interesting behavior and probably explains what has been the major focus of controversy regarding the use of biodiesel.

In fact, depending on the engine operating regime, there is typically an increase or a decrease in NOx emissions due to the use of biodiesel. The analysis of the graphs related to the representation of the NOx emission results allows to conclude that: when the engine operates at low RPM and high RPM, the use of biodiesel leads to a decrease in emissions; however, for average engine rotation regime (2000 and 2500 rpm), the use of B20 conducts into an increase in specific NOx emissions. It appears that there is not a discernible direct relation between the load and the differences in NOx emissions related to the two fuels considered, except in the case of the tests carried out at 2500 rpm where, as the load increases, there is an increase in NOx emissions caused by the use of B20.

What is clear from the present study is that it is not possible to directly express an increase or decrease in NOx emissions caused by the use of biodiesel, without it being possible to characterize the way in which the vehicle equipped with a given engine operates under normal operating conditions. However, variations in NOx are not significant either in terms of increase or decrease and, given that the results were obtained without the exhaust gas passing through any treatment system, it can be concluded that any negative connotation on the use of biodiesel associated with NOx emissions, considering that the small variations in the use of B20, whether positive or negative, are always below 10% and will therefore be practically canceled

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20

http://dx.doi.org/10.5772/intechopen.74681

193

The present work on NOx emissions allows clarifying the existing doubts on this subject with the existence of disparate results from different studies, evaluating the behavior of the engines at a given rotation or a given torque. In reality, only through a study like the one carried out in the present study, considering a large number of points of operation, it is possible to draw a

out by the use of an efficient exhaust treatment system.

Figure 5. Results for specific NOx emission [ppm/kWh] with B0 and B20.

The relative effect of NOx emissions may be associated with increased energy conversion efficiency, which will enhance an increase in the combustion temperature responsible for the eventual formation of NOx compounds via the thermal process (Zeldovich formation process). Nevertheless, the increase in energy conversion efficiency is not the only responsible for the fluctuations in NOx emissions.

In fact, the presence of oxygen in the fuel allows the combustion process to be carried out differently from the two fuels, creating a different evolution of the heat release to take place, which could enhance or reduce NOx formation. These differences are surely also justified by the formation of the fuel spray, driven by the different properties introduced with biodiesel and the different levels of saturation of the molecules that constitute it.

Study About Nitrogen Oxide Emissions and Fuel Consumption in Diesel Engines Fueled with B20 http://dx.doi.org/10.5772/intechopen.74681 193

Figure 5. Results for specific NOx emission [ppm/kWh] with B0 and B20.

behavior expected on the road for a light vehicle and realize the perspectives for overall results of consumption. In this way, it is possible to verify that the specific mass consumption presents small oscillations that were already expected, given the little significant difference in calorific value of the two evaluated fuels (B0 and B20). However, the differences became more significant only in the relative circumstances of higher rotation and high load, which may correspond to the typical high-speed freeway circulation, which implies a high engine speed and also high loads since the aerodynamic drag force becomes very relevant. For the other situations, corresponding to urban and extra-urban traffic, characterized by low and medium speeds and low and medium loads, the differences in consumption are minor, revealing a tendency to small decrease in fuel consumption when fueling the engine with B20, especially if a

As mentioned above, the study on the impact on NOx emissions by the use of B20 compared to the use of B0 was established. The results below are the reflection of this study allowing evaluating the influence that the B20 consumption has on the NOx emissions when compared to the consumption of diesel, for the various selected engine operating regimes. In order to make the analyzed results more comparable, the value of the NOx volumetric percentage present in the exhaust gas was divided by the power obtained corresponding to each selected engine operating point, and the results of Figure 5 in (ppm/kWh) corresponding to specific NOx emissions.

The analysis of the specific NOx emission results presented in the graphs of Figure 5 reveals an interesting behavior and probably explains what has been the major focus of controversy

In fact, depending on the engine operating regime, there is typically an increase or a decrease in NOx emissions due to the use of biodiesel. The analysis of the graphs related to the representation of the NOx emission results allows to conclude that: when the engine operates at low RPM and high RPM, the use of biodiesel leads to a decrease in emissions; however, for average engine rotation regime (2000 and 2500 rpm), the use of B20 conducts into an increase in specific NOx emissions. It appears that there is not a discernible direct relation between the load and the differences in NOx emissions related to the two fuels considered, except in the case of the tests carried out at 2500 rpm where, as the load increases, there is an increase in

The relative effect of NOx emissions may be associated with increased energy conversion efficiency, which will enhance an increase in the combustion temperature responsible for the eventual formation of NOx compounds via the thermal process (Zeldovich formation process). Nevertheless, the increase in energy conversion efficiency is not the only responsible for the

In fact, the presence of oxygen in the fuel allows the combustion process to be carried out differently from the two fuels, creating a different evolution of the heat release to take place, which could enhance or reduce NOx formation. These differences are surely also justified by the formation of the fuel spray, driven by the different properties introduced with biodiesel

and the different levels of saturation of the molecules that constitute it.

consumption analysis is made on a volumetric basis.

4.2. NOx emissions

192 Biofuels - State of Development

regarding the use of biodiesel.

NOx emissions caused by the use of B20.

fluctuations in NOx emissions.

What is clear from the present study is that it is not possible to directly express an increase or decrease in NOx emissions caused by the use of biodiesel, without it being possible to characterize the way in which the vehicle equipped with a given engine operates under normal operating conditions. However, variations in NOx are not significant either in terms of increase or decrease and, given that the results were obtained without the exhaust gas passing through any treatment system, it can be concluded that any negative connotation on the use of biodiesel associated with NOx emissions, considering that the small variations in the use of B20, whether positive or negative, are always below 10% and will therefore be practically canceled out by the use of an efficient exhaust treatment system.

The present work on NOx emissions allows clarifying the existing doubts on this subject with the existence of disparate results from different studies, evaluating the behavior of the engines at a given rotation or a given torque. In reality, only through a study like the one carried out in the present study, considering a large number of points of operation, it is possible to draw a real range of results that allow to cross with the typical characterization of an engine when installed in a vehicle, leading to authentic values of NOx emissions emitted by that engine into the atmosphere when fueled by biodiesel or other fuel.

greater energy availability. It is also clear, through the results obtained, that due to the behavior of engines when subjected to different types of requirement, corresponding to different types of route, a distinct evaluation in terms of consumption and NOx emissions occurs when

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It should be noted that currently engines are designed to use diesel, not considering the use of biodiesel at the outset. A step has already been taken by the European Union to ensure the mandatory incorporation of biodiesel into diesel and to ensure that the biodiesel used effectively corresponds to a reduction in greenhouse gas emissions. By guaranteeing the use of a sustained form of production of this energy source, it will also be important that the development of engines corresponds to the preferential use of a given amount of biodiesel incorpo-

Still, in relation to the obtaining results, as already recognized by the European community itself, it is not enough to have characterized a certain cycle of tests for approval of engines and use it in characterizing the behavior of these engines when fueled by fuels from different sources. It will be necessary to integrate the use of in-service vehicle tests under real traffic, road and environmental conditions, allowing for a more faithful and less standardized characterization in order to provide a more adequate response to the actual conditions in which the

1 School of Technology and Management, Polytechnic Institute of Leiria, Leiria, Portugal 2 ADAI–LAETA–Industrial Aerodynamics Development Association, Coimbra University,

[2] Cansino J, Pablo-Romero MDP, Román R, Yñiguez R. Promotion of biofuel consumption in the transport sector: An EU-27 perspective. Renewable and Sustainable Energy Reviews.

[4] Bozbas K. Biodiesel as an alternative motor fuel: Production and policies in the European Union. Renewable and Sustainable Energy Reviews–Elsevier Ltd. 2006;12:542-552 [5] Bloem H, Monforti-Ferrario F, Szabo M, Jäger-Waldau A. Renewable Energy Snapshots 2010. European Commission, DG Joint Research Centre, Institute for Energy, Renewable

the engine is supplied with a mixture of biodiesel in diesel.

rated in the diesel fuel, so that it can derive the maximum yield.

Luis Manuel Ventura Serrano1,2\* and Manuel Gameiro da Silva2

[1] Conselho e Parlamento Europeu, Diretiva 28/2009/CE, 2009

Energy Unit. EUR 24440 EN, June 2010, European Union; 2010

[3] E. C. EU, COM. 595 Final, Bruxelas; 2012. 2012

\*Address all correspondence to: luis.serrano@ipleiria.pt

vehicles will be used.

Author details

Portugal

References

2012;16:6013-6021

Comparing the results obtained with those of other researchers it is clear that only in similar situations, where a very wide set of engine operating points was considered, it was possible to register positive and negative oscillations in NOx emission values due to the use of [15, 35, 36]. Most of the works report an increase in NOx emissions, but it also becomes obvious that this situation reflects the testing in a narrow range of the normally operating engine.

As indicated by Yanowitz and McCormick [37] when averaging NOx emissions, masks the complex variability that occurs with the emission of these substances when using biodiesel in the engines, it is also important to remember what is reported by Hribernik and Kegl [38] confirming that the influence of biodiesel on combustion and emissions in an engine cannot be generalized, since they are engine-specific parameters. In fact, the engine type, circuit typology and driving mode completely change the way the engine operates when fueled with fuels containing biodiesel in different proportions. The different fuels offer different properties, namely in the presence of oxygen, density and viscosity, volatility, energy content and degree of saturation, being these factors responsible for the occurrence of different behaviors in the process of fuel injection. It is also important to note that the results obtained with singlecylinder engines, light-duty engines and engines of heavy vehicles lead to different conclusions, so it is necessary that the analyzes should also be different. This complexity is confirmed by the analysis performed on the results obtained by the present work, which helps to understand that the conclusions obtained by the work of other researchers in this area are, once again, emphasizing the need to evaluate the behavior of vehicles in circulation on the road, complementing those results with those obtained in the laboratory tests.

#### 5. Conclusions

The energy dependence of the transport sector is evident, being effectively minimized by the use of biodiesel. It may be argued that this energetic option will only be transitional and that in the near future some other solution will emerge with other potentialities, given that despite the decrease of greenhouse gas emissions impacts, this decrease is not as relevant as desired. However, in the current circumstances, this is effectively a real solution and already with some evidence given, arising with the ability to replace part of the diesel fuel consumed in the world.

The present work is a concrete evaluation of the effects that the use of biodiesel in substitution of diesel would bring in terms of fuel consumption and greenhouse gas emissions. It can be concluded that there is no significant impact due to the use of biodiesel, especially when considering the use of incorporations of up to 20% biodiesel in diesel. Contrary to what is stated in several publications, it is not absolutely clear that the use of biodiesel, because it has lower energy content per liter of fuel, translates this characteristic directly into an increase in consumption. There is a reason to believe that in certain situations there is an increase in energy efficiency, and it is possible that, even with the use of a fuel with less energy results greater energy availability. It is also clear, through the results obtained, that due to the behavior of engines when subjected to different types of requirement, corresponding to different types of route, a distinct evaluation in terms of consumption and NOx emissions occurs when the engine is supplied with a mixture of biodiesel in diesel.

It should be noted that currently engines are designed to use diesel, not considering the use of biodiesel at the outset. A step has already been taken by the European Union to ensure the mandatory incorporation of biodiesel into diesel and to ensure that the biodiesel used effectively corresponds to a reduction in greenhouse gas emissions. By guaranteeing the use of a sustained form of production of this energy source, it will also be important that the development of engines corresponds to the preferential use of a given amount of biodiesel incorporated in the diesel fuel, so that it can derive the maximum yield.

Still, in relation to the obtaining results, as already recognized by the European community itself, it is not enough to have characterized a certain cycle of tests for approval of engines and use it in characterizing the behavior of these engines when fueled by fuels from different sources. It will be necessary to integrate the use of in-service vehicle tests under real traffic, road and environmental conditions, allowing for a more faithful and less standardized characterization in order to provide a more adequate response to the actual conditions in which the vehicles will be used.

#### Author details

real range of results that allow to cross with the typical characterization of an engine when installed in a vehicle, leading to authentic values of NOx emissions emitted by that engine into

Comparing the results obtained with those of other researchers it is clear that only in similar situations, where a very wide set of engine operating points was considered, it was possible to register positive and negative oscillations in NOx emission values due to the use of [15, 35, 36]. Most of the works report an increase in NOx emissions, but it also becomes obvious that this

As indicated by Yanowitz and McCormick [37] when averaging NOx emissions, masks the complex variability that occurs with the emission of these substances when using biodiesel in the engines, it is also important to remember what is reported by Hribernik and Kegl [38] confirming that the influence of biodiesel on combustion and emissions in an engine cannot be generalized, since they are engine-specific parameters. In fact, the engine type, circuit typology and driving mode completely change the way the engine operates when fueled with fuels containing biodiesel in different proportions. The different fuels offer different properties, namely in the presence of oxygen, density and viscosity, volatility, energy content and degree of saturation, being these factors responsible for the occurrence of different behaviors in the process of fuel injection. It is also important to note that the results obtained with singlecylinder engines, light-duty engines and engines of heavy vehicles lead to different conclusions, so it is necessary that the analyzes should also be different. This complexity is confirmed by the analysis performed on the results obtained by the present work, which helps to understand that the conclusions obtained by the work of other researchers in this area are, once again, emphasizing the need to evaluate the behavior of vehicles in circulation on the road,

The energy dependence of the transport sector is evident, being effectively minimized by the use of biodiesel. It may be argued that this energetic option will only be transitional and that in the near future some other solution will emerge with other potentialities, given that despite the decrease of greenhouse gas emissions impacts, this decrease is not as relevant as desired. However, in the current circumstances, this is effectively a real solution and already with some evidence given, arising with the ability to replace part of the diesel fuel consumed

The present work is a concrete evaluation of the effects that the use of biodiesel in substitution of diesel would bring in terms of fuel consumption and greenhouse gas emissions. It can be concluded that there is no significant impact due to the use of biodiesel, especially when considering the use of incorporations of up to 20% biodiesel in diesel. Contrary to what is stated in several publications, it is not absolutely clear that the use of biodiesel, because it has lower energy content per liter of fuel, translates this characteristic directly into an increase in consumption. There is a reason to believe that in certain situations there is an increase in energy efficiency, and it is possible that, even with the use of a fuel with less energy results

situation reflects the testing in a narrow range of the normally operating engine.

complementing those results with those obtained in the laboratory tests.

5. Conclusions

194 Biofuels - State of Development

in the world.

the atmosphere when fueled by biodiesel or other fuel.

Luis Manuel Ventura Serrano1,2\* and Manuel Gameiro da Silva2

\*Address all correspondence to: luis.serrano@ipleiria.pt

1 School of Technology and Management, Polytechnic Institute of Leiria, Leiria, Portugal

2 ADAI–LAETA–Industrial Aerodynamics Development Association, Coimbra University, Portugal

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**Chapter 10**

**Provisional chapter**

**Cultivation Systems of Microalgae for the Production**

**Cultivation Systems of Microalgae for the Production** 

As reported in the study, the high-oil/ha-year productivity of microalgae has raised a lot of interest in their use as a source of raw materials for biofuels. However, the high costs of production and maintenance of closed culture systems (photobioreactor type) and the problems of contamination that lead to lower productivity of open systems (of the "open-pond" type) have become important limitations in evaluating the sustainability of producing biofuels from microalgae.In the view of the favorable prospects of employing microalgae as an economically viable source of raw materials for the production of biofuels, this chapter outlines the different ways microalgae are cultivated, the required nutritional conditions and the main procedures used for increasing their scale. Additionally, those more commonly used on a large scale are described and their advantages and disadvantages are pointed out. This analysis results in a proposal of a new type of photobioreactor, of the cylindrical container type, constructed of polyethylene, a nontransparent material that is cheaper and more durable than the ones that are commonly used (polycarbonate, glass or polymethyl methacrylate (PMMA)). Internal illumination of the photobioreactor is provided by a beam from plastic optical fibers that receive sun-

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.74957

**of Biofuels**

**of Biofuels**

Rosa C.V. de Paula

**Abstract**

Rosa C.V. de Paula

Yordanka Reyes Cruz, Donato A.G. Aranda, Peter R. Seidl, Gisel C. Diaz, Rene G. Carliz,

Yordanka Reyes Cruz, Donato A.G. Aranda, Peter R. Seidl, Gisel C. Diaz, Rene G. Carliz, Mariana M. Fortes, Deusa A.M.P. da Ponte and

Mariana M. Fortes, Deusa A.M.P. da Ponte and

Additional information is available at the end of the chapter

light focused at the extremity of the beam.

**Keywords:** cultivation systems, microalgae, biofuels, photobioreactor

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74957


#### **Cultivation Systems of Microalgae for the Production of Biofuels Cultivation Systems of Microalgae for the Production of Biofuels**

DOI: 10.5772/intechopen.74957

Yordanka Reyes Cruz, Donato A.G. Aranda, Yordanka Reyes Cruz, Donato A.G. Aranda,

[35] Yamane K, Kawasaki K, Sone K, Hara T, Prakoso T. Oxidation stability of biodiesel and its effects on diesel combustion and emission characteristics. International Journal of Engine

[36] Panwar N, Shrirame HY, Rathore N, Jindal S, Kurchania A. Performance evaluation of a diesel engine fueled with methyl ester of castor seed oil. Applied Thermal Engineering–

[37] Yanowitz J, McCormick R. Effects of biodiesel blends on north American heavy-duty diesel engine emissions. European Journal of Lipid Science and Technology–Wiley-Vch.

[38] Hribernik A, Kegl B. Influence of biodiesel fuel on the combustion and emission formation in a direct injection (DI) diesel engine. Energy & Fuels–American Chemical Society.

Research–Professional Engineering Publishing. 2007;8:307-319

Elsevier Ltd. 2010;30:245-249

2009;111:763-772

198 Biofuels - State of Development

2007;21:1760-1767

Peter R. Seidl, Gisel C. Diaz, Rene G. Carliz, Mariana M. Fortes, Deusa A.M.P. da Ponte and Rosa C.V. de Paula Peter R. Seidl, Gisel C. Diaz, Rene G. Carliz, Mariana M. Fortes, Deusa A.M.P. da Ponte and Rosa C.V. de Paula

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74957

#### **Abstract**

As reported in the study, the high-oil/ha-year productivity of microalgae has raised a lot of interest in their use as a source of raw materials for biofuels. However, the high costs of production and maintenance of closed culture systems (photobioreactor type) and the problems of contamination that lead to lower productivity of open systems (of the "open-pond" type) have become important limitations in evaluating the sustainability of producing biofuels from microalgae.In the view of the favorable prospects of employing microalgae as an economically viable source of raw materials for the production of biofuels, this chapter outlines the different ways microalgae are cultivated, the required nutritional conditions and the main procedures used for increasing their scale. Additionally, those more commonly used on a large scale are described and their advantages and disadvantages are pointed out. This analysis results in a proposal of a new type of photobioreactor, of the cylindrical container type, constructed of polyethylene, a nontransparent material that is cheaper and more durable than the ones that are commonly used (polycarbonate, glass or polymethyl methacrylate (PMMA)). Internal illumination of the photobioreactor is provided by a beam from plastic optical fibers that receive sunlight focused at the extremity of the beam.

**Keywords:** cultivation systems, microalgae, biofuels, photobioreactor

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **1. Introduction**

The progressive exhaustion of fossil-based fuels, the uncertainity in their respective prices and the growing control of their emissions in large cities have led to the generation of energy from renewable sources that reduce the dependence on petroleum and the problems associated with environmental pollution. In Brazil, 45% of the energy and 18% of the fuels are renewable while in the rest of the world 86% is produced from non-sustainable sources. A world leader in the use of biofuels, Brazil, has reached a position that is sought by many countries that try to develop renewable sources of energy as strategic alternatives to petroleum. Bioethanol is used as an automotive fuel since the early twentieth century and all new cars are "flex-fuel" (they run on either ethanol or a combination of around 25% of anhydrous ethanol in gasoline). In the case of biodiesel, it has been added to diesel fuel since 2005, starting with 2% in 2005 and reaching 8% in March 2017 [1].

From this experience, it was possible to determine that 80% of the final cost of the production of biodiesel can be attributed to raw materials. In general, the investigation of alternative and economically viable sources has been the main goal of research on the subject. Thus, ideal sources of biofuels are determined mainly by their availability and costs.

Biofuels can be produced from many different sources. For biodiesel, for example, the most common are soy, palm, sunflower and cotton and among other sources of vegetable oils, animal fats and residues from food preparation. However these sources are not limited to conventional raw materials, they also apply to microalgae. Recent studies have confirmed that the conditions in which they grow, their high productivity in terms of oil/ha/year, viability of genetic manipulation of metabolic pathways, multiplication of yields of biomass in short periods of time and the possibility of controlling these conditions give microalgae a very large advantage in the evaluation of alternative sources of biofuels. Here, we emphasize the cultivation systems that are employed in the production of biomass from microalgae [2, 3].

#### **2. Microalgae in the production of biofuels**

Oils found in microalgae have physic-chemical characteristics similar to those of vegetable oils [4, 5] and thus are considered potential raw materials for the production of biofuels. In conventional production systems, microalgae have a higher productivity of oil by hectare than palm, the commercial source of oil with the highest productivity (**Table 1**). Recent reports confirm that microalgae are capable of meeting global demands for combustible oils [6, 7].

.Microalgae can be considered a very good alternative source of lipids since they have content between 15 and 75% of their dry weight depending on the type and conditions under which they are cultivated (**Table 2**) [3]. In some cases, when this content reaches 75% of their weight relative to the dry mass, a reduction in cellular growth occurs as is the case of *Botryococcusbraunii*, for example. For other microalgae, with levels of oils between 20 and 50%, such as *Chlorella* sp.*, Dunaliella* sp.*, Isochrysis* sp.*, Nannochloris* sp.*, Nannochloropsis* sp. and *Tetraselmis* sp., higher growths are reported [8].

**3. Cultivation of microalgae**

**Table 2.** Lipid content of selected microalgae.

**Table 1.** Yields in oil/ha from selected sources of biomass.

The growth characteristics and composition of microalgae are significantly dependent on the type of cultivation—phototrophic, heterotrophic, mixotrophic and photoheterotrophic being the principal types used [9, 10]. Phototrophic cultures occur when the microalgae use light, for

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**Table 1.** Yields in oil/ha from selected sources of biomass.

**1. Introduction**

200 Biofuels - State of Development

2% in 2005 and reaching 8% in March 2017 [1].

**2. Microalgae in the production of biofuels**

*Tetraselmis* sp., higher growths are reported [8].

The progressive exhaustion of fossil-based fuels, the uncertainity in their respective prices and the growing control of their emissions in large cities have led to the generation of energy from renewable sources that reduce the dependence on petroleum and the problems associated with environmental pollution. In Brazil, 45% of the energy and 18% of the fuels are renewable while in the rest of the world 86% is produced from non-sustainable sources. A world leader in the use of biofuels, Brazil, has reached a position that is sought by many countries that try to develop renewable sources of energy as strategic alternatives to petroleum. Bioethanol is used as an automotive fuel since the early twentieth century and all new cars are "flex-fuel" (they run on either ethanol or a combination of around 25% of anhydrous ethanol in gasoline). In the case of biodiesel, it has been added to diesel fuel since 2005, starting with

From this experience, it was possible to determine that 80% of the final cost of the production of biodiesel can be attributed to raw materials. In general, the investigation of alternative and economically viable sources has been the main goal of research on the subject. Thus, ideal

Biofuels can be produced from many different sources. For biodiesel, for example, the most common are soy, palm, sunflower and cotton and among other sources of vegetable oils, animal fats and residues from food preparation. However these sources are not limited to conventional raw materials, they also apply to microalgae. Recent studies have confirmed that the conditions in which they grow, their high productivity in terms of oil/ha/year, viability of genetic manipulation of metabolic pathways, multiplication of yields of biomass in short periods of time and the possibility of controlling these conditions give microalgae a very large advantage in the evaluation of alternative sources of biofuels. Here, we emphasize the cultiva-

tion systems that are employed in the production of biomass from microalgae [2, 3].

that microalgae are capable of meeting global demands for combustible oils [6, 7].

Oils found in microalgae have physic-chemical characteristics similar to those of vegetable oils [4, 5] and thus are considered potential raw materials for the production of biofuels. In conventional production systems, microalgae have a higher productivity of oil by hectare than palm, the commercial source of oil with the highest productivity (**Table 1**). Recent reports confirm

.Microalgae can be considered a very good alternative source of lipids since they have content between 15 and 75% of their dry weight depending on the type and conditions under which they are cultivated (**Table 2**) [3]. In some cases, when this content reaches 75% of their weight relative to the dry mass, a reduction in cellular growth occurs as is the case of *Botryococcusbraunii*, for example. For other microalgae, with levels of oils between 20 and 50%, such as *Chlorella* sp.*, Dunaliella* sp.*, Isochrysis* sp.*, Nannochloris* sp.*, Nannochloropsis* sp. and

sources of biofuels are determined mainly by their availability and costs.


**Table 2.** Lipid content of selected microalgae.

#### **3. Cultivation of microalgae**

The growth characteristics and composition of microalgae are significantly dependent on the type of cultivation—phototrophic, heterotrophic, mixotrophic and photoheterotrophic being the principal types used [9, 10]. Phototrophic cultures occur when the microalgae use light, for example sunlight, as a source of energy, and CO<sup>2</sup> as a source of inorganic carbon, to produce chemical energy by photosynthesis [11].

This type of cultivation has an environmental advantage. Since atmospheric carbon dioxide, the principal contribution to the greenhouse effect, may be used in the production of microalgal biomass for biofuels, it results in a favorable energy balance. Mainly because of this, the phototrophic cultivation is most commonly used for the growth of microalgae [12].

Mata et al. [8] report that the lipid content of microalgae can vary from 5 to 60%, depending on the specie, when cultivated phototropically. However, light intensity and the insufficient supply of CO<sup>2</sup> are always problematic questions for this type of cultivation. In open cultivation systems the limitation is mostly relative to the photoperiod. Besides, the irregular distribution of light intensity affects the productivity in terms of biomass. Final concentrations of biomass of over 2 g.L−1 of Na are rarely reported in the study [13, 14].

Some authors suggest that supplementation with CO<sup>2</sup> could increase productivities of biomass and lipids, since its concentration in the atmosphere is low [15, 16]. However, it is important to construct systems that prevent the loss of excess CO<sup>2</sup> . Still, it must be taken into consideration that the accumulation of oxygen, formed in the process of photosynthesis, increases the production of O<sup>2</sup> that acts as an inhibitor of hydrogenases, the enzymes responsible for the production of hydrogen necessary for the production of lipids. With this, the increase in CO<sup>2</sup> could result in a reduction in the production of lipids [17].

Some species of microalgae can not only grow under phototrophic conditions but can also use organic carbon in the absence of light. In this case, in which algae use organic carbon both as a source of energy and carbon, the cultivation is referred to as heterotrophic [18, 19].

photoheterotrophic cultivation, the application of this type of cultivation for production of biodiesel is very rare, as is the case with mixotrophic cultivation. Both types of cultivation are limited by the risk of contamination and the presence of light may require a special large-scale

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The production of lipids and the concentrations of different fatty acids in microalgae are also influenced by the composition of culture media. Frequently the increase in the accumulation of fatty acids is described as a consequence of the effects of the limitation of nutrients and the

Under growth limiting conditions a drop in cellular division is verified in the photosynthetic rate of protein synthesis. The photosynthetic energy is deviated from the cellular division to the accumulation of carbohydrates and synthesis of lipids, also resulting in an increase in the

On the other hand, Huerlimann et al. [18] verified an increase in the content of some lipid classes in the exponential phase of *Rhodomonas* sp. and *Isochrisys* sp. cultivated, in K+ medium and under 250 μ moles photons.m−2.s−1. Usually, microalgae present a small production of lipids during the exponential phase, generally of polars polyunsaturates, with an increase in the synthesis when cultures reach the stationary phase of growth, the apolars predominating

photobioreactor, resulting in high costs of operation [17].

time of cultivation [8].

**Table 3.** Cultivation methods.

[25, 26].

**Table 3** summarizes the main characteristics of each type of cultivation.

**4. Nutritional conditions for the cultivation of microalgae**

synthesis of enzymes that are specific for the absorption of nutrients [23, 24].

Heterotrophic cultivation avoids problems associated with the limitation of light and has led to relevant results in the production of microalgal biomass, the yields being significantly superior to those from phototrophic cultivation [11].

Xu et al. [20] observed an increase of 40% in the lipid content when they altered the type of culture from phototrophic to heterotrophic for *Chlorella protothecoides.*

The choice of heterotrophic metabolism is questioned in the sense that it is necessary to add a source of organic carbon and may lead to high costs if it must be purchased, making the production of biofuels from microalgae unviable [21, 22].

In mixotrophic cultivation, the microalgae are submitted to photosynthesis and uses organic and inorganic (CO<sup>2</sup> ) compounds as a source of carbon for growth. Thus, microalgae are capable of living under both phototrophic as well as heterotrophic conditions As they use organic compounds, microalgae release CO<sup>2</sup> via respiration, being absorbed and utilized under phototrophic cultivation [8].

In photoheterotrophic cultivation, microalgae require light when they use organic compounds as a source of carbon. The principle difference between the mixotrophic and photoheterotrophic is that, for the former, only light is used as a source of energy. Besides, in photoheterotrophic systems, light and other organic sources are necessary at the same time. Although the production of some metabolites regulated by the intensity of light could be increased in


**Table 3.** Cultivation methods.

example sunlight, as a source of energy, and CO<sup>2</sup>

of over 2 g.L−1 of Na are rarely reported in the study [13, 14].

Some authors suggest that supplementation with CO<sup>2</sup>

to construct systems that prevent the loss of excess CO<sup>2</sup>

could result in a reduction in the production of lipids [17].

superior to those from phototrophic cultivation [11].

production of biofuels from microalgae unviable [21, 22].

organic compounds, microalgae release CO<sup>2</sup>

under phototrophic cultivation [8].

culture from phototrophic to heterotrophic for *Chlorella protothecoides.*

This type of cultivation has an environmental advantage. Since atmospheric carbon dioxide, the principal contribution to the greenhouse effect, may be used in the production of microalgal biomass for biofuels, it results in a favorable energy balance. Mainly because of this, the

Mata et al. [8] report that the lipid content of microalgae can vary from 5 to 60%, depending on the specie, when cultivated phototropically. However, light intensity and the insufficient sup-

systems the limitation is mostly relative to the photoperiod. Besides, the irregular distribution of light intensity affects the productivity in terms of biomass. Final concentrations of biomass

and lipids, since its concentration in the atmosphere is low [15, 16]. However, it is important

ation that the accumulation of oxygen, formed in the process of photosynthesis, increases the

production of hydrogen necessary for the production of lipids. With this, the increase in CO<sup>2</sup>

Some species of microalgae can not only grow under phototrophic conditions but can also use organic carbon in the absence of light. In this case, in which algae use organic carbon both as

Heterotrophic cultivation avoids problems associated with the limitation of light and has led to relevant results in the production of microalgal biomass, the yields being significantly

Xu et al. [20] observed an increase of 40% in the lipid content when they altered the type of

The choice of heterotrophic metabolism is questioned in the sense that it is necessary to add a source of organic carbon and may lead to high costs if it must be purchased, making the

In mixotrophic cultivation, the microalgae are submitted to photosynthesis and uses organic

capable of living under both phototrophic as well as heterotrophic conditions As they use

In photoheterotrophic cultivation, microalgae require light when they use organic compounds as a source of carbon. The principle difference between the mixotrophic and photoheterotrophic is that, for the former, only light is used as a source of energy. Besides, in photoheterotrophic systems, light and other organic sources are necessary at the same time. Although the production of some metabolites regulated by the intensity of light could be increased in

) compounds as a source of carbon for growth. Thus, microalgae are

via respiration, being absorbed and utilized

a source of energy and carbon, the cultivation is referred to as heterotrophic [18, 19].

are always problematic questions for this type of cultivation. In open cultivation

that acts as an inhibitor of hydrogenases, the enzymes responsible for the

phototrophic cultivation is most commonly used for the growth of microalgae [12].

chemical energy by photosynthesis [11].

ply of CO<sup>2</sup>

202 Biofuels - State of Development

production of O<sup>2</sup>

and inorganic (CO<sup>2</sup>

as a source of inorganic carbon, to produce

could increase productivities of biomass

. Still, it must be taken into consider-

photoheterotrophic cultivation, the application of this type of cultivation for production of biodiesel is very rare, as is the case with mixotrophic cultivation. Both types of cultivation are limited by the risk of contamination and the presence of light may require a special large-scale photobioreactor, resulting in high costs of operation [17].

**Table 3** summarizes the main characteristics of each type of cultivation.

#### **4. Nutritional conditions for the cultivation of microalgae**

The production of lipids and the concentrations of different fatty acids in microalgae are also influenced by the composition of culture media. Frequently the increase in the accumulation of fatty acids is described as a consequence of the effects of the limitation of nutrients and the time of cultivation [8].

Under growth limiting conditions a drop in cellular division is verified in the photosynthetic rate of protein synthesis. The photosynthetic energy is deviated from the cellular division to the accumulation of carbohydrates and synthesis of lipids, also resulting in an increase in the synthesis of enzymes that are specific for the absorption of nutrients [23, 24].

On the other hand, Huerlimann et al. [18] verified an increase in the content of some lipid classes in the exponential phase of *Rhodomonas* sp. and *Isochrisys* sp. cultivated, in K+ medium and under 250 μ moles photons.m−2.s−1. Usually, microalgae present a small production of lipids during the exponential phase, generally of polars polyunsaturates, with an increase in the synthesis when cultures reach the stationary phase of growth, the apolars predominating [25, 26].

In the composition of microalgae, besides carbon (C), at least 19 chemical elements are present. Some are necessary in concentrations in the order of milligrams per liter, such as H, N, O, P, S, K, Na, Ca and Mg. Others can be detected as trace elements or micronutrients and normally are required in concentrations of nanograms to micrograms per liter, such as Si, Fe, Mn, Mo, Cu, Co, Zn, B and Va. These micronutrients are incorporated in essential organic molecules as a variety of coenzymes (CoA, cobamamide, etc.) that participate in reactions that are primordial to the life of the cells [27].

In studies run with microalgae cultivated under low concentrations of nitrogen, Piorreck et al. [25] observed an increase in the lipid content of these microalgae without, however, altering the lipid and fatty acid profile. In *Chlorella*, cultures in which the cellular division ceased because of the lack of nitrogen in the culture medium, the lipid content of the cells increased from 28 to 70%, coinciding with a decrease in the protein content from 30 to 8% [32]. Most of the culture media used to facilitate accumulation of lipids in the microalgae are modified

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The cultivation of microalgae for the production of biofuels can be considered highly promising mainly because of the diverse advantages already mentioned in the study [2, 6, 35–39].

• They do not require arable land and can be cultivated in desert regions and on degraded soils since the demand for land is only utilized as a support for the cultivation system.

• Even growing in aqueous media, they consume less water than terrestrial plants and, depending on the process utilized in concentration of biomass, the residual water may be

• They have high productivity in biomass and rapidly accumulate lipids, between 15 and

• The nutrients for their cultivation can be obtained from residual waters and agroindustrial

• They efficiently fix atmospheric carbon, or even residues from industrial process, through

• They can produce a series of other valuable products besides lipids, such as proteins, carotenoids and carbohydrates that can be utilized as foods or fertilizers, fermented to produce

Besides the innumerous advantages previously cited, the production of oil from microalgae of approximately 60,000 liters/ha/year can surpass that of palm oil (5000 liters/ha/year) and of soya (450 liters/ha/year). More optimistic financial analyses affirm that oil from microalgae

, 10–20 times more

according to those that are known such as BG-11 [33] and BOLD 3 N [34].

reutilized in the process, reducing global consumption of fresh water.

• They are produced all year round and do not depend on seasons and crops.

• Their cultivation does not require the application of herbicides or pesticides.

photosynthesis (each ton of biomass produced consumes 1.7 tons of CO2

**5. Advantages of using microaIgae for biofuels**

• The do not compete with agriculture.

50% in dry mass in many species.

that is absorbed by cultures of oilseeds).

can be produced at a cost of US\$ 0.50/L [2, 3].

ethanol or other products with high added value.

wastes.

• They can produce more than half the oxygen in nature.

The macronutrients form the structural constituents of biomolecules, in the cytoplasmic membranes of the intracellular medium, and still take part in the energetic and metabolic regulation processes. The absence or insufficiency of these micronutrients can cause damage affecting some of the vital functions of these microorganisms [28].

Among the most important nutrients are phosphorus (P) and nitrogen (N) that exist in the aquatic environment in diverse forms. They may be dissolved, as particulates or in biotic form. However, only the dissolved form is directly available for growth of microalgae. Several species still require minute quantities of organic compounds for their growth, as is the case with vitamins [28].

Phosphorus is an important limiting factor for the growth of microalgae, since it is essential for cellular processes such as the transfer of energy (ATP) and the biosynthesis of nucleic acids, phospholipids, DNA, and so on, influencing the composition of biomass. Inorganic orthophosphate (PO4 −3) is the ionic form of phosphorus preferred by microalgae and its absorption depends on energy. Thus, this is the source of phosphorus most commonly used in culture media. Other sources of inorganic phosphorus exist that could be absorbed by microalgae, such as dyadic phosphate or dihydrogen phosphate (H<sup>2</sup> PO4 − ) which are species obtained from orthophosphoric acid (H3 PO4 ) [29].

Vitamins are essential organic compounds for the functioning of the metabolism and many can be found as cofactors of enzymes, carrying out the functions of coenzymes that have vital roles for the viability and growth as well as the accumulation of biomolecules in the cell. Among them, biotin stands out as the coenzyme that catalyzes activation and transfer of CO<sup>2</sup> reactions, cobalamine (B12), a coenzyme that catalyzes de-isomerization and transfer of methyl group reactions, and thymine (B1), the coenzyme that catalyzes activation and transfer of aldehyde reactions [30].

Some biotechnological processes with microalgae aim for high yields in biomass and, for this, must choose the adequate nutrients and physic-chemical parameters, taking into consideration the natural habitat of the species in order to determine the basic necessities for their growth. On the other hand, some biotechnological applications are directed to stress conditions to optimize the biosynthesis of specific bio-compounds, such as fatty acids. The most widely studied stress factors are the concentrations of certain nutrients, light intensity, temperature, salinity and pH. The limitation of nutrients in the cultures affects, in large proportions, the chemical composition of the algae, as well as their rate of growth [31].

In studies run with microalgae cultivated under low concentrations of nitrogen, Piorreck et al. [25] observed an increase in the lipid content of these microalgae without, however, altering the lipid and fatty acid profile. In *Chlorella*, cultures in which the cellular division ceased because of the lack of nitrogen in the culture medium, the lipid content of the cells increased from 28 to 70%, coinciding with a decrease in the protein content from 30 to 8% [32]. Most of the culture media used to facilitate accumulation of lipids in the microalgae are modified according to those that are known such as BG-11 [33] and BOLD 3 N [34].

## **5. Advantages of using microaIgae for biofuels**

The cultivation of microalgae for the production of biofuels can be considered highly promising mainly because of the diverse advantages already mentioned in the study [2, 6, 35–39].


In the composition of microalgae, besides carbon (C), at least 19 chemical elements are present. Some are necessary in concentrations in the order of milligrams per liter, such as H, N, O, P, S, K, Na, Ca and Mg. Others can be detected as trace elements or micronutrients and normally are required in concentrations of nanograms to micrograms per liter, such as Si, Fe, Mn, Mo, Cu, Co, Zn, B and Va. These micronutrients are incorporated in essential organic molecules as a variety of coenzymes (CoA, cobamamide, etc.) that participate in reactions that

The macronutrients form the structural constituents of biomolecules, in the cytoplasmic membranes of the intracellular medium, and still take part in the energetic and metabolic regulation processes. The absence or insufficiency of these micronutrients can cause damage

Among the most important nutrients are phosphorus (P) and nitrogen (N) that exist in the aquatic environment in diverse forms. They may be dissolved, as particulates or in biotic form. However, only the dissolved form is directly available for growth of microalgae. Several species still require minute quantities of organic compounds for their growth, as is the case

Phosphorus is an important limiting factor for the growth of microalgae, since it is essential for cellular processes such as the transfer of energy (ATP) and the biosynthesis of nucleic acids, phospholipids, DNA, and so on, influencing the composition of biomass. Inorganic ortho-

depends on energy. Thus, this is the source of phosphorus most commonly used in culture media. Other sources of inorganic phosphorus exist that could be absorbed by microalgae,

Vitamins are essential organic compounds for the functioning of the metabolism and many can be found as cofactors of enzymes, carrying out the functions of coenzymes that have vital roles for the viability and growth as well as the accumulation of biomolecules in the cell. Among them, biotin stands out as the coenzyme that catalyzes activation and transfer of

 reactions, cobalamine (B12), a coenzyme that catalyzes de-isomerization and transfer of methyl group reactions, and thymine (B1), the coenzyme that catalyzes activation and transfer

Some biotechnological processes with microalgae aim for high yields in biomass and, for this, must choose the adequate nutrients and physic-chemical parameters, taking into consideration the natural habitat of the species in order to determine the basic necessities for their growth. On the other hand, some biotechnological applications are directed to stress conditions to optimize the biosynthesis of specific bio-compounds, such as fatty acids. The most widely studied stress factors are the concentrations of certain nutrients, light intensity, temperature, salinity and pH. The limitation of nutrients in the cultures affects, in large proportions, the chemical composition of the algae, as well as their rate of

−3) is the ionic form of phosphorus preferred by microalgae and its absorption

PO4 −

) which are species obtained from

are primordial to the life of the cells [27].

with vitamins [28].

204 Biofuels - State of Development

phosphate (PO4

CO<sup>2</sup>

growth [31].

orthophosphoric acid (H3

of aldehyde reactions [30].

affecting some of the vital functions of these microorganisms [28].

such as dyadic phosphate or dihydrogen phosphate (H<sup>2</sup>

PO4 ) [29].


Besides the innumerous advantages previously cited, the production of oil from microalgae of approximately 60,000 liters/ha/year can surpass that of palm oil (5000 liters/ha/year) and of soya (450 liters/ha/year). More optimistic financial analyses affirm that oil from microalgae can be produced at a cost of US\$ 0.50/L [2, 3].

#### **6. Cultivation of microalgae on a lab scale**

The cultivation of microalgae requires a climatized space, with stable temperature, so that the thermal amplitude allows the activities that are necessary to the cell. The atmosphere must have controlled access to reduce the heat exchange and contamination. As the temperature affects the metabolic rate of the organisms, it must be chosen according to species that is studied and what the cultivation is for. The constancy of the temperature and the low variability (< 0.5°C) provide stability and predictability to the cultivation. Tropical species can be cultivated under temperatures between 20 and 25°C, such as, for example, Spirulina, Scenedesmus, Ankistrodermus, Monoraphidium, Chlorella and Chlamydomonas, among others. Generally, the choice is for a temperature of 23°C that is tolerated, although it may not favor optimum growth. Light intensity, its duration and wavelength influence growth of phytoplankton. Incandescent lamps better simulate the amplitude of wavelengths between 350 and 700 nm, necessary for photosynthesis but could heat the cultivation. Fluorescent lamps do not heat up since the wavelengths in the red region are not emitted, but they could lead to unsatisfactory growth. Sunlight, not in excess, could stimulate growth. The efficiency of solar collectors in the production of microalgae also is being studied [40]. Lamps of 40 and 20 W are more frequently utilized, a distance of 25–30 cm from the cultivation is being recommended to minimize the heat. The adequate photoperiod is important, the use of 12:12 hours (dark light) for maintenance of cultivations and continuous light for 18:6 hours being common for commercial purposes [28, 41].

**Figure 1.** *Scenedesmus* sp. inoculum, conserved (A) and incubator (B).

**Figure 3.** Microbial growth curve.

**Figure 2.** Flowchart of scale up for the cultivation of microalgae used by GreenTech.

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In the cultivation rooms the inoculums of microalgae are normally preserved in sterile glass tubes (**Figure 1A**) utilizing an incubator (**Figure 1B**). This preservation is conducted under controlled conditions (temperature between 20 and 25°C, light intensities of 40 μ moles.m−2. s−1, photoperiod of 12 h) and with manual agitation three times a week in order to not allow the cells to decant for too long.

#### **6.1. Scaling up the cultivation of microalgae from the lab**

The cultivation of microalgae from the lab is scaled up by successive transfers of algal cultures of systems of cultivation from smaller to larger followed by the addition of culture media. In most cases four transfers are made, namely culture from the preservation tube to the cultivation system of 250 mL; activation culture, from the activation culture to the system of 1 L, a pre-inoculum culture; from the pre-inoculum culture to a system of 20 L, to obtain the bottle cultivation; followed by the propagation from the bottle to various systems of 20 L, called propagation cultivations to obtain the volume of culture to be inoculated in the photo-bioreactors reaching, in this step, the cultivation of microalgae on a pilot scale (**Figure 2**). The four transfers, from the preservation step until the cultivation propagation, are run under sterile atmospheres and also utilize sterile materials.

The growth of cultures regarding microalgae, in each step of cultivation previously described, follows the growth phases given in **Figure 3**—*Lag or adaptation* (induction of growth), *Log* (exponential growth), *Transition (*reduction of growth), *stationary* and *decline/death*. The period of duration of each phase depends on the specie and the conditions of cultivation. For the construction of

**Figure 1.** *Scenedesmus* sp. inoculum, conserved (A) and incubator (B).

**6. Cultivation of microalgae on a lab scale**

206 Biofuels - State of Development

commercial purposes [28, 41].

the cells to decant for too long.

**6.1. Scaling up the cultivation of microalgae from the lab**

atmospheres and also utilize sterile materials.

The cultivation of microalgae requires a climatized space, with stable temperature, so that the thermal amplitude allows the activities that are necessary to the cell. The atmosphere must have controlled access to reduce the heat exchange and contamination. As the temperature affects the metabolic rate of the organisms, it must be chosen according to species that is studied and what the cultivation is for. The constancy of the temperature and the low variability (< 0.5°C) provide stability and predictability to the cultivation. Tropical species can be cultivated under temperatures between 20 and 25°C, such as, for example, Spirulina, Scenedesmus, Ankistrodermus, Monoraphidium, Chlorella and Chlamydomonas, among others. Generally, the choice is for a temperature of 23°C that is tolerated, although it may not favor optimum growth. Light intensity, its duration and wavelength influence growth of phytoplankton. Incandescent lamps better simulate the amplitude of wavelengths between 350 and 700 nm, necessary for photosynthesis but could heat the cultivation. Fluorescent lamps do not heat up since the wavelengths in the red region are not emitted, but they could lead to unsatisfactory growth. Sunlight, not in excess, could stimulate growth. The efficiency of solar collectors in the production of microalgae also is being studied [40]. Lamps of 40 and 20 W are more frequently utilized, a distance of 25–30 cm from the cultivation is being recommended to minimize the heat. The adequate photoperiod is important, the use of 12:12 hours (dark light) for maintenance of cultivations and continuous light for 18:6 hours being common for

In the cultivation rooms the inoculums of microalgae are normally preserved in sterile glass tubes (**Figure 1A**) utilizing an incubator (**Figure 1B**). This preservation is conducted under controlled conditions (temperature between 20 and 25°C, light intensities of 40 μ moles.m−2. s−1, photoperiod of 12 h) and with manual agitation three times a week in order to not allow

The cultivation of microalgae from the lab is scaled up by successive transfers of algal cultures of systems of cultivation from smaller to larger followed by the addition of culture media. In most cases four transfers are made, namely culture from the preservation tube to the cultivation system of 250 mL; activation culture, from the activation culture to the system of 1 L, a pre-inoculum culture; from the pre-inoculum culture to a system of 20 L, to obtain the bottle cultivation; followed by the propagation from the bottle to various systems of 20 L, called propagation cultivations to obtain the volume of culture to be inoculated in the photo-bioreactors reaching, in this step, the cultivation of microalgae on a pilot scale (**Figure 2**). The four transfers, from the preservation step until the cultivation propagation, are run under sterile

The growth of cultures regarding microalgae, in each step of cultivation previously described, follows the growth phases given in **Figure 3**—*Lag or adaptation* (induction of growth), *Log* (exponential growth), *Transition (*reduction of growth), *stationary* and *decline/death*. The period of duration of each phase depends on the specie and the conditions of cultivation. For the construction of

**Figure 2.** Flowchart of scale up for the cultivation of microalgae used by GreenTech.

**Figure 3.** Microbial growth curve.

kinetic profiles of each culture, necessary to monitor the biomass produced, samples are collected every day, and their analyses of cell count, dry weight and turbidity are run.

#### **7. Principal cultivation systems of microalgae on a large scale**

The large-scale systems of cultivation of microalgae were developed during the first decades of the twentieth century. These organisms can be cultivated in diverse systems of production. The systems of cultivation on a large scale commonly employ types like "*open ponds*", generally called "*raceways"*, where tanks of varied sizes are kept in the open air, exposed to natural conditions of illumination, temperature, evaporation and contamination. These tanks generally are shallow, constructed in concrete, fiberglass or polycarbonate, with an earth bottom or coated with plastic material, where the cultures are kept in constant circulation. The other well-known open system of cultivation is the cascade model or descending film, developed in the Czech Republic around the 1970s. Here, the culture is exposed to sunlight in a thin film, of about 1 cm, that promotes a cellular density of up to 10 g L−1. This system has a circuit with a base originally in glass, which made it very expensive, but with the evolution of models, the use of cheaper materials, plastics, cement or metals made the costs decrease. The system has some advantages, namely a thin film of culture leading to a high concentration of cells, an efficient transfer of gas liquids favoring the exposure of the culture to sunlight even more, a low cost compared to other closed reactors and the necessity of less area for its installation, when compared to the *raceway.* Although it is a system with good productivity, the possibility of contamination remains analogous to systems of *raceways*. There are some variations of this system where the tray on which the culture is exposed to sunlight presents undulations, allowing cycles of light and dark, that result in an increase in lipid content of the cell, in spite of the decrease in productivity [42, 43].

In the GreenTec/EQ/UFRJ pilot unit 30, vertical photobioreactors of the window type are distributed in 3 series of 10 arranged in parallel as can be visualized in **Figure 5**. Each series of

• polycarbonate structure (5 mm thickness) that is 1.2 m wide, 0.8 m in height and 11 cm thickness, containing internal baffles, top lid, two lower outlets and a connections for hoses.

• three refrigeration systems composed of three iced-water generators with temperature controllers; tubes with isolation; three temperature sensors; and three stainless steel serpen-

• an air injection system in each photobioreactor with stainless steel tubes, with outlets of

• a system to control the pH, composed of a control panel, three pH sensors and tubes

The recirculation of the culture along 10 photobioreactors of each series occurs through its passage from the first reactor to the second, from the second to the third and so successively, until reaching the tenth, from where it is pumped back to the first via tubes (**Figure 6**).

network through which cultures are injected when the pH limit is

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The series of photobioreactors of the pilot unit have the following characteristics:

tines, submerged in the culture of the first photobioreactor in each series;

• recirculation of the cultivation system with tubes and pumps.

bubbled air in the basal part of the reactor and valves to control the flow of air;

photobioreactors has a capacity of 1100 L of cultivation.

**Figure 4.** Thin-layer cascade cultivator installed at GreenTech.

connected to the CO<sup>2</sup>

passed;

An open photobioreactor of the descending film type was constructed in fiberglass at the Laboratory of GreenTechnologies, GreenTec/EQ/UFRJ, with the objective of producing biomass from microalgae to be utilized as a raw material in the development of technologies for the production of biofuels (**Figure 4**). Additionally, in this system of cultivation, it was possible to monitor the growth of lineages of microalgae that were cultivated and compare the results obtained from the growth of lineages in photobioreactors.

Today, 95% of the total production of microalgae is in open systems. The volume of around 20,000 tons of microalgae/year is considered incipient in terms of biofuels [44].

Other more sophisticated systems of cultivation of microalgae are the closed ones known as photobioreactors. These cultivators are usually constructed from transparent materials, glass or plastics, distributed in flat panels or in serpentines. There are diverse models of photobioreactors: bubble columns, windows, horizontal tubes, helicoidal, agitated tanks and so on [45]. In spite of the higher initial costs, photobioreactors have many advantages over open systems. In photobioreactors, it is possible to control the conditions of cultivation. This way the concentration of nutrients, temperature, light and pH can be adjusted to obtain higher yields of biomass in shorter times, reaching much higher productivities when compared to open systems.

**Figure 4.** Thin-layer cascade cultivator installed at GreenTech.

kinetic profiles of each culture, necessary to monitor the biomass produced, samples are collected

The large-scale systems of cultivation of microalgae were developed during the first decades of the twentieth century. These organisms can be cultivated in diverse systems of production. The systems of cultivation on a large scale commonly employ types like "*open ponds*", generally called "*raceways"*, where tanks of varied sizes are kept in the open air, exposed to natural conditions of illumination, temperature, evaporation and contamination. These tanks generally are shallow, constructed in concrete, fiberglass or polycarbonate, with an earth bottom or coated with plastic material, where the cultures are kept in constant circulation. The other well-known open system of cultivation is the cascade model or descending film, developed in the Czech Republic around the 1970s. Here, the culture is exposed to sunlight in a thin film, of about 1 cm, that promotes a cellular density of up to 10 g L−1. This system has a circuit with a base originally in glass, which made it very expensive, but with the evolution of models, the use of cheaper materials, plastics, cement or metals made the costs decrease. The system has some advantages, namely a thin film of culture leading to a high concentration of cells, an efficient transfer of gas liquids favoring the exposure of the culture to sunlight even more, a low cost compared to other closed reactors and the necessity of less area for its installation, when compared to the *raceway.* Although it is a system with good productivity, the possibility of contamination remains analogous to systems of *raceways*. There are some variations of this system where the tray on which the culture is exposed to sunlight presents undulations, allowing cycles of light and dark, that result in an increase in lipid content of

An open photobioreactor of the descending film type was constructed in fiberglass at the Laboratory of GreenTechnologies, GreenTec/EQ/UFRJ, with the objective of producing biomass from microalgae to be utilized as a raw material in the development of technologies for the production of biofuels (**Figure 4**). Additionally, in this system of cultivation, it was possible to monitor the growth of lineages of microalgae that were cultivated and compare the

Today, 95% of the total production of microalgae is in open systems. The volume of around

Other more sophisticated systems of cultivation of microalgae are the closed ones known as photobioreactors. These cultivators are usually constructed from transparent materials, glass or plastics, distributed in flat panels or in serpentines. There are diverse models of photobioreactors: bubble columns, windows, horizontal tubes, helicoidal, agitated tanks and so on [45]. In spite of the higher initial costs, photobioreactors have many advantages over open systems. In photobioreactors, it is possible to control the conditions of cultivation. This way the concentration of nutrients, temperature, light and pH can be adjusted to obtain higher yields of biomass in shorter times, reaching much higher productivities when compared to open systems.

every day, and their analyses of cell count, dry weight and turbidity are run.

208 Biofuels - State of Development

**7. Principal cultivation systems of microalgae on a large scale**

the cell, in spite of the decrease in productivity [42, 43].

results obtained from the growth of lineages in photobioreactors.

20,000 tons of microalgae/year is considered incipient in terms of biofuels [44].

In the GreenTec/EQ/UFRJ pilot unit 30, vertical photobioreactors of the window type are distributed in 3 series of 10 arranged in parallel as can be visualized in **Figure 5**. Each series of photobioreactors has a capacity of 1100 L of cultivation.

The series of photobioreactors of the pilot unit have the following characteristics:


The recirculation of the culture along 10 photobioreactors of each series occurs through its passage from the first reactor to the second, from the second to the third and so successively, until reaching the tenth, from where it is pumped back to the first via tubes (**Figure 6**).

**Figure 6.** Recirculation of cultivation system along the ten photobioreactors at GreenTech.

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**Figure 7.** Trajectory of cultivation system in photobioreactors during recirculation.

**Figure 5.** Photobioreactors at GreenTech.

The passage of the culture from one reactor to the other occurs by overflow through a small canal, situated between the reactors in the superior part. In each reactor, the culture follows a trajectory in a zigzag determined by the positioning of the internal baffles (**Figure 7**). The water utilized to make the cultures of microalgae developed in photobioreactors is treated through a hollow-fiber microfiltration system and activated pressurized charcoal that has a capacity of approximately 900 L/h.

In open systems, productions close to 180 tons per ha/year can be reached, competing naturally with the other microorganism in culture medium. The production in closed photobioreactors is more expressive, giving bigger volumes and, at times, over 1.500 tons/ha/year, since they can optimize the cultivation conditions, such as luminosity, temperature and pH that are favorable for the growth of populations of microalgae [40].

A study by Chisti [3] confirms the advantages of production of microalgae in photobioreactors in place of recirculation tanks. Taking as a basis the calculation of production of 100 tons of biomass for the two systems, with the same absorption of CO<sup>2</sup> , the volumetric productivity Cultivation Systems of Microalgae for the Production of Biofuels http://dx.doi.org/10.5772/intechopen.74957 211

**Figure 6.** Recirculation of cultivation system along the ten photobioreactors at GreenTech.

The passage of the culture from one reactor to the other occurs by overflow through a small canal, situated between the reactors in the superior part. In each reactor, the culture follows a trajectory in a zigzag determined by the positioning of the internal baffles (**Figure 7**). The water utilized to make the cultures of microalgae developed in photobioreactors is treated through a hollow-fiber microfiltration system and activated pressurized charcoal that has a

In open systems, productions close to 180 tons per ha/year can be reached, competing naturally with the other microorganism in culture medium. The production in closed photobioreactors is more expressive, giving bigger volumes and, at times, over 1.500 tons/ha/year, since they can optimize the cultivation conditions, such as luminosity, temperature and pH that are

A study by Chisti [3] confirms the advantages of production of microalgae in photobioreactors in place of recirculation tanks. Taking as a basis the calculation of production of 100 tons

, the volumetric productivity

capacity of approximately 900 L/h.

**Figure 5.** Photobioreactors at GreenTech.

210 Biofuels - State of Development

favorable for the growth of populations of microalgae [40].

of biomass for the two systems, with the same absorption of CO<sup>2</sup>

**Figure 7.** Trajectory of cultivation system in photobioreactors during recirculation.

of photobioreactors is 13 times larger than that of tanks. The area necessary also favors the photobioreactors, being approximately 30% inferior, assuming a similar productivity for the two systems of cultivation. The costs of separation are also an advantage of the photobioreactors, since the culture is 30 times more concentrated than in the recirculation tanks, and thus the separation of biomass from water is facilitated [46].

The estimated cost of production for each kilogram of biomass is, respectively, € 6.39 and € 3.80 for photobioreactors and recirculation tanks. These values do not take into account the costs of CO<sup>2</sup> , which could be obtained at cost zero. If the annual capacity of production of biomass could go over 10,000 tons, the costs of production for each kilogram are reduced to US\$ 4.11 and US\$ 1.17, for photobioreactors and recirculation tanks, respectively, because of economies of scale [47].

However, photobioreactors have several disadvantages that need to be considered and validated, such as difficulties with amplification, deterioration of the transparent material utilized, high cost of construction (investments including 10 times that of an open tank) and damage to the cells because of shearing stress [8, 48].

Based on advantages and disadvantages of systems of closed cultivation (photobioreactors), at GreenTec/EQ/UFRJ, a new model of photobioreactor of the cylindrical container type, of a volume similar to that described previously but occupying a smaller area because of the relative depth, was developed. The internal illumination of the photobioreactor is made by a beam of optical plastic fibers that receive sunlight from lenses focused on the extremities of the beam. These lenses are mounted on a solar tracking system that permits a more efficient use of light.

The great differential of this system of illumination is that it is possible to use non-transparent materials in the construction of photobioreactors that are much cheaper and durable, such as polypropylene, without incurring in additional energy costs.

**Figure 8.** Prototype: non-transparent photobioreactor with internal illumination by plastic optical fibers, coupled to

Cultivation Systems of Microalgae for the Production of Biofuels

http://dx.doi.org/10.5772/intechopen.74957

213

solar tracking.

**Figure 9.** Components of the prototype.

The proposed model will have the following advantages when compared to conventional photobioreactors: (a) systems with less entrance and exit of air, minimizing contamination; (b) occupies a small area; (c) uses materials that are not transparent, thus cheaper and more durable; (d) does not require the use of systems of heat exchangers to avoid the increase in temperature of the culture because of the use of isolation with polyurethane in the external part of the tank; (e) higher productivity of microalgae biomass relative to open systems; and (f) higher yields of lipids in the composition, fundamental aspects in the production of biodiesel.

In the pilot unit of GreenTec/EQ/UFRJ, a prototype of this new photobioreactor was mounted as can be visualized in **Figures 8** and **9** utilizing a polypropylene tank of 25 L capacity. An increase in the scale of this model is planned for a tank of similar characteristics and a volume of 1000 L.

After each cultivation is over, a culture of microalgae is directed to the concentration step. Diverse processes have been tested and continue being evaluated in this step, especially flocculation, microfiltration and centrifugation.

Two technologies flocculation followed by centrifugation and microfiltration followed by centrifugation are fundamentally utilized in the pilot unit of GreenTec/EQ/UFRJ. Biomass from microfiltration concentrated approximately 35 times is submitted to centrifugation at 10,000 rpm, 6°C, during 15 minutes, to obtain a cultivation concentrated over a 100 times (**Figure 10**).

Cultivation Systems of Microalgae for the Production of Biofuels http://dx.doi.org/10.5772/intechopen.74957 213

**Figure 8.** Prototype: non-transparent photobioreactor with internal illumination by plastic optical fibers, coupled to solar tracking.

**Figure 9.** Components of the prototype.

of photobioreactors is 13 times larger than that of tanks. The area necessary also favors the photobioreactors, being approximately 30% inferior, assuming a similar productivity for the two systems of cultivation. The costs of separation are also an advantage of the photobioreactors, since the culture is 30 times more concentrated than in the recirculation tanks, and thus

The estimated cost of production for each kilogram of biomass is, respectively, € 6.39 and € 3.80 for photobioreactors and recirculation tanks. These values do not take into account the costs of

However, photobioreactors have several disadvantages that need to be considered and validated, such as difficulties with amplification, deterioration of the transparent material utilized, high cost of construction (investments including 10 times that of an open tank) and damage to

Based on advantages and disadvantages of systems of closed cultivation (photobioreactors), at GreenTec/EQ/UFRJ, a new model of photobioreactor of the cylindrical container type, of a volume similar to that described previously but occupying a smaller area because of the relative depth, was developed. The internal illumination of the photobioreactor is made by a beam of optical plastic fibers that receive sunlight from lenses focused on the extremities of the beam. These lenses are mounted on a solar tracking system that permits a more efficient use of light. The great differential of this system of illumination is that it is possible to use non-transparent materials in the construction of photobioreactors that are much cheaper and durable, such as

The proposed model will have the following advantages when compared to conventional photobioreactors: (a) systems with less entrance and exit of air, minimizing contamination; (b) occupies a small area; (c) uses materials that are not transparent, thus cheaper and more durable; (d) does not require the use of systems of heat exchangers to avoid the increase in temperature of the culture because of the use of isolation with polyurethane in the external part of the tank; (e) higher productivity of microalgae biomass relative to open systems; and (f) higher yields of lipids in the composition, fundamental aspects in the production of biodiesel.

In the pilot unit of GreenTec/EQ/UFRJ, a prototype of this new photobioreactor was mounted as can be visualized in **Figures 8** and **9** utilizing a polypropylene tank of 25 L capacity. An increase in the scale of this model is planned for a tank of similar characteristics and a volume of 1000 L. After each cultivation is over, a culture of microalgae is directed to the concentration step. Diverse processes have been tested and continue being evaluated in this step, especially floc-

Two technologies flocculation followed by centrifugation and microfiltration followed by centrifugation are fundamentally utilized in the pilot unit of GreenTec/EQ/UFRJ. Biomass from microfiltration concentrated approximately 35 times is submitted to centrifugation at 10,000 rpm, 6°C, during 15 minutes, to obtain a cultivation concentrated over a 100 times

, which could be obtained at cost zero. If the annual capacity of production of biomass could go over 10,000 tons, the costs of production for each kilogram are reduced to US\$ 4.11 and US\$ 1.17, for photobioreactors and recirculation tanks, respectively, because of economies of scale [47].

the separation of biomass from water is facilitated [46].

polypropylene, without incurring in additional energy costs.

the cells because of shearing stress [8, 48].

culation, microfiltration and centrifugation.

(**Figure 10**).

CO<sup>2</sup>

212 Biofuels - State of Development

**Author details**

Janeiro, Brazil

**References**

Yordanka Reyes Cruz1,3, Donato A.G. Aranda1,2, Peter R. Seidl<sup>2</sup>

1 GreenTechnologies, Green Tec. Rio de Janeiro, Rio de Janeiro, Brazil

\*Address all correspondence to: pseidl@eq.ufrj.br

10.1016/j.biotechadv.2007.02.001

[6] Basu S, Roy AS, Mohanty K, Ghoshal AK. CO<sup>2</sup>

584-593. DOI: 10.1016/j.rser.2010.09.018

2014;**164**:323-330. DOI: 10.1016/j.biortech.2014.05.017

978925104059

10.1016/j.rser.2009.07.020

Rene G. Carliz1,2, Mariana M. Fortes1,2, Deusa A.M.P. da Ponte1,2 and Rosa C.V. de Paula1,2

2 School of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

www.anp.gov.br/wwwanp/biocombustiveis [Accessed: Sep 26, 2017]

Química da Universidade Federal do Rio de Janeiro, 2008

3 Department of Organic Processes, School of Chemistry, Federal University of Rio de

[1] Agência Nacional de Petróleo, Gás Natural e Biocombustíveis. Available from: http://

[2] Barbosa V.Produção de biodiesel a partir do cultivo de microalgas: Estimativa de custos e perspectivas para o Brasil. Dissertação de Mestrado apresentada ao Programa de Pós-Graduação em Planejamento Energético. da Universidade Federal do Rio de Janeiro: COPPE; 2012 [3] Chisti Y. Biodiesel from microalgal. Biotechnology Advances. 2007;**25**:294-306. DOI:

[4] Encarnação AP. Geração de biodiesel pelos processos de transesterificação e hidroesterificação, uma avaliação econômica. Dissertação de Mestrado apresentada ao Programa de Pós-graduação em Tecnologia de Processos Químicos e Bioquímicos, da Escola de

[5] FAO - Food and Agriculture Organization of the United Nations. Renewable Biological Systems for Alternative Sustainable Energy Production. Agricultura Services Bulletin – 128. In: Kazuhisa Miyamoto, editor. Osaka, Japan: Osaka University; 1997. 108 p. ISBN:

Scenedesmus obliquus SA1 cultivated in large scale open system. Bioresource Technology.

[7] Borowitzka MA. High-value products from microalgae – Their development and commercialisation. Journal of Applied Phycology. 2013;**25**:743-756. DOI: 10.1007/s10811-013-9983-9 [8] Mata TM, Martins AA, Caetano NS. Microalgae for biodiesel production and other applications: A review. Renewable and Sustainable Energy Reviews. 2010;**14**:217-232. DOI:

[9] Ahmad AL, Yasin NHM, Derek CJC, Lim JK. Microalgae as a sustainable energy source for biodiesel production: A review. Renewable and Sustainable Energy Reviews. 2011;**15**:

[10] Amaro HM, Guedes AC, Malcata FX.Advances and perspectives in using microalgae to produce biodiesel. Applied Energy. 2011;**88**:3402-3410. DOI: 10.1016/j.apenergy.2010.12.014

\*, Gisel C. Diaz1,2,

http://dx.doi.org/10.5772/intechopen.74957

215

Cultivation Systems of Microalgae for the Production of Biofuels

biofixation and carbonic anhydrase activity in

**Figure 10.** Concentrated microalgal biomass.

Filtered and centrifuged residual water is treated in a system of microfiltration with activated carbon and reutilized in cultures of photobioreactors.

#### **8. Main challenges in the production of biodiesel from microalgae**

The principal challenge in the use of microalgae as raw material for biodiesel is the selection of promising species with triacylglyrides in optimum conditions of cultivation, adaptation and growth of cultures (inocula), systems on a large scale and overall reduction of production costs [26].

The production of microalgae biomass requires basic inputs such as energy, water, CO<sup>2</sup> and mineral nutrients. In order to assure the viability of the cultivation of microalgae on the necessary scale, industrial effluents are presently discarded into the environment and use CO2 produced by several industries such as power plants cement factories and so on.

The refining of bio-oil extracted from microalgae is another of the current limitations in the production of international quality biodiesel. This fraction, in addition to being composed of triglycerides and fatty acids convertible into biodiesel, contains antioxidants and hydrocarbons that cannot be converted into biodiesel. The latter have polarity and degree of saturation similar to the compounds of interest for biodiesel, making it difficult to extract them.

It is also indispensible to invest in the development of processes that make full use of microalgae according to the biorefinery concept [49, 50].

However, in the last few years, the research related to this topic has been advanced, fundamentally in the cultivation stage, responsible for the higher costs of the productive process. With this objective, new and cheaper cultivation systems with higher productivity of biomass are being developed and proposed. In addition, studies are carried out to modify the composition of culture media, aiming at reducing the cost of the nutrients used as sources of nitrogen and phosphorus.

#### **Author details**

Yordanka Reyes Cruz1,3, Donato A.G. Aranda1,2, Peter R. Seidl<sup>2</sup> \*, Gisel C. Diaz1,2, Rene G. Carliz1,2, Mariana M. Fortes1,2, Deusa A.M.P. da Ponte1,2 and Rosa C.V. de Paula1,2

\*Address all correspondence to: pseidl@eq.ufrj.br

1 GreenTechnologies, Green Tec. Rio de Janeiro, Rio de Janeiro, Brazil

2 School of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil

3 Department of Organic Processes, School of Chemistry, Federal University of Rio de Janeiro, Brazil

#### **References**

and

Filtered and centrifuged residual water is treated in a system of microfiltration with activated

The principal challenge in the use of microalgae as raw material for biodiesel is the selection of promising species with triacylglyrides in optimum conditions of cultivation, adaptation and growth of cultures (inocula), systems on a large scale and overall reduction of production

The production of microalgae biomass requires basic inputs such as energy, water, CO<sup>2</sup>

produced by several industries such as power plants cement factories and so on.

mineral nutrients. In order to assure the viability of the cultivation of microalgae on the necessary scale, industrial effluents are presently discarded into the environment and use CO2

The refining of bio-oil extracted from microalgae is another of the current limitations in the production of international quality biodiesel. This fraction, in addition to being composed of triglycerides and fatty acids convertible into biodiesel, contains antioxidants and hydrocarbons that cannot be converted into biodiesel. The latter have polarity and degree of saturation similar to the compounds of interest for biodiesel, making it difficult to extract

It is also indispensible to invest in the development of processes that make full use of micro-

However, in the last few years, the research related to this topic has been advanced, fundamentally in the cultivation stage, responsible for the higher costs of the productive process. With this objective, new and cheaper cultivation systems with higher productivity of biomass are being developed and proposed. In addition, studies are carried out to modify the composition of culture media, aiming at reducing the cost of the nutrients used as sources of

**8. Main challenges in the production of biodiesel from microalgae**

carbon and reutilized in cultures of photobioreactors.

**Figure 10.** Concentrated microalgal biomass.

214 Biofuels - State of Development

algae according to the biorefinery concept [49, 50].

costs [26].

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**Chapter 11**

**Provisional chapter**

**Potential of Biofuel Usage in Turkey's Energy Supply**

Rapidly growing population and industrialization brought about the enormous need for energy, alongside the environmental problems. Since biofuel energy is inexhaustible, it is becoming increasingly important to address the energy problem. Today, it is possible to classify biomass energy into two classes: classical and modern. Classical biofuel utilization is the simple burning of wood obtained from tree cutting and animal wastes, where modern biofuel application consists of a variety of fuels produced from various sources. Turkey's potential for biofuels is estimated to be around 45 Mg. As a renewable energy, it's been under the Renewable Support Scheme by regulation for more than a decade now. By the end of 2016, installed biofuel electricity generation capacity had reached 468 MW with 2 billion kWh realized (~0.7% of national demand). The aim for 2023 is reaching at least 1000 MW (which will be around 1.3% by then). Many analysts believe that the potential for development is higher and realization therefore will surpass the official aims. Effective usage of biofuels for power generation may not be sizable but it's critical and will make multilayer contributions to energy supply and dependence as well as to meeting climate and sustainability targets

**Keywords:** energy policy, biofuel, agricultural and environmental interaction

The civilization tendencies toward modernization mainly progress through industrialization of societies. Combining the economic results of modernization, which are mainly increased public welfare, eased access to consumption, alongside the growth in population, leads to enormous increase in energy demand, where the upward acceleration persists for

**Potential of Biofuel Usage in Turkey's Energy Supply**

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.74604

Sirri Uyanik, Yavuz Sucu and Zeynep Zaimoglu

Sirri Uyanik, Yavuz Sucu and Zeynep Zaimoglu

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74604

**Abstract**

of the country.

**1. Introduction**

decades [1].

#### **Potential of Biofuel Usage in Turkey's Energy Supply Potential of Biofuel Usage in Turkey's Energy Supply**

DOI: 10.5772/intechopen.74604

Sirri Uyanik, Yavuz Sucu and Zeynep Zaimoglu Sirri Uyanik, Yavuz Sucu and Zeynep Zaimoglu

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74604

#### **Abstract**

Rapidly growing population and industrialization brought about the enormous need for energy, alongside the environmental problems. Since biofuel energy is inexhaustible, it is becoming increasingly important to address the energy problem. Today, it is possible to classify biomass energy into two classes: classical and modern. Classical biofuel utilization is the simple burning of wood obtained from tree cutting and animal wastes, where modern biofuel application consists of a variety of fuels produced from various sources. Turkey's potential for biofuels is estimated to be around 45 Mg. As a renewable energy, it's been under the Renewable Support Scheme by regulation for more than a decade now. By the end of 2016, installed biofuel electricity generation capacity had reached 468 MW with 2 billion kWh realized (~0.7% of national demand). The aim for 2023 is reaching at least 1000 MW (which will be around 1.3% by then). Many analysts believe that the potential for development is higher and realization therefore will surpass the official aims. Effective usage of biofuels for power generation may not be sizable but it's critical and will make multilayer contributions to energy supply and dependence as well as to meeting climate and sustainability targets of the country.

**Keywords:** energy policy, biofuel, agricultural and environmental interaction

#### **1. Introduction**

The civilization tendencies toward modernization mainly progress through industrialization of societies. Combining the economic results of modernization, which are mainly increased public welfare, eased access to consumption, alongside the growth in population, leads to enormous increase in energy demand, where the upward acceleration persists for decades [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


sources as a result of financial conditions accompanied by fossil-based technology infrastruc-

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 223

It is more widely accepted that the thread of global climate change is increasing, which is addressed to the greenhouse emissions from fossil fuel utilization. Thus, global debates on migration from carbon emitting resources are held in order to find a common international understanding [11]. In conjunction with environmental consequences of fossil fuel mining, the associated climate change projections predict some serious threads [10], including several negative impacts on human health along with the Earth's ecology [12]. Therefore, in order to overcome two detrimental challenges, namely energy crisis and environmental pollution, new alternative energy sources are required, which are essentially renewable, sustainable, environment friendly, efficient, and economically viable [12–14]. Many power generation alternatives are put forward to replace fossil fuels; the primarily listed and tested ones are wind, solar (thermal and photovoltaic [PV]), nuclear, geothermal, tidal, fuel cells and biofuels [15]. Among these alternatives, each has advantages and drawbacks against fossil fuels, where biofuels are found favorable over petroleum fuels because (1) they can be easily extracted from the biomass, (2) they are sustainable due to their biodegradability, (3) their combustion is based on carbon dioxide cycle, and (4) they are more environment friendly [3]. Further

In this study, definitions, applicability, and potentials of biofuels as an alternative energy source are investigated, with their current and probable future positions in the Turkish energy mix.

Although in the common and popular context biofuel is used to define liquids, scientifically,

• liquids (alcohols like bioethanol, biodiesel, vegetable oil, synthetic hydrocarbons, and their

Biofuels are commonly classified as primary and secondary according to the form of utilization. Primary biofuels are organic materials directly used to extract energy. Primary biofuels include wood, wood chips, pellet, animal wastes, forest and crop residuals, landfill gas, and so on from which energy is extracted traditionally without a conversion process. Secondary biofuel refers to chemically converted fuels [16] in solid, liquid, or gaseous forms, derived

Primary biofuel has relatively low efficiency and has limited utilization possibilities in terms of energy conversion and transportability, compared to the so-called secondary biofuel technologies, which are also classified further into generations. The first-generation fuels are bioethanol/butanol chemically produced from rape seed, soya bean, sunflower, date palm,

from organic material. **Figure 1** illustrates the common classification of biofuels.

ture and hence the pace to migrate from fossils to renewables remains low.

benefits in integrating biofuels to the fuel mix are summarized in **Table 1**.

the term "biofuel" refers to all fuels produced from biomass in forms of:

**2. Evolution of biofuels**

• and gases (biogas, syngas, and biohydrogen).

• solids (biochar),

mixtures),

**Table 1.** Major benefits of biofuels [37].

In the current situation, the leading primary energy sources used are fossil-based sources, having a contribution around 85% globally, where the largest consumer is power industry, utilizing 42% of the total primary sources, followed by industry and transport [1–3]. Despite global consensus on the need to shift primary energy sources to renewables, the situation is not expected to change drastically. Future scenario studies show only a slight decrease, down to 75% in 2040, on fossil fuel dependence [4], even with implementing new policy measures promoting to wane fossil fuels. Given the abundance of coal, oil, and natural gas globally, with new extraction technologies, potential reserves, and unconventional reserve exploitation (e.g. for natural gas), it is highly possible the fossil sources will be available for a considerable period at low costs [5–7]. Although supply reserve and financial scenarios demonstrate that fossil resources will continue dominating in the future for a number of decades, it is widely accepted that the current position has drawbacks.

Besides, fossil fuel is not sustainable by definition and many countries have concerns over fossil fuel dependence mainly connected to four conditions: (1) depleting fossil fuel stock [8], (2) price volatility of fossil resources [9], (3) greenhouse gas emissions in the atmosphere [10], and (4) geopolitical supply security [6, 7]. Even though each of these conditions is enough to convince conversion to renewables, a dilemma arises for countries being forced to use fossil sources as a result of financial conditions accompanied by fossil-based technology infrastructure and hence the pace to migrate from fossils to renewables remains low.

It is more widely accepted that the thread of global climate change is increasing, which is addressed to the greenhouse emissions from fossil fuel utilization. Thus, global debates on migration from carbon emitting resources are held in order to find a common international understanding [11]. In conjunction with environmental consequences of fossil fuel mining, the associated climate change projections predict some serious threads [10], including several negative impacts on human health along with the Earth's ecology [12]. Therefore, in order to overcome two detrimental challenges, namely energy crisis and environmental pollution, new alternative energy sources are required, which are essentially renewable, sustainable, environment friendly, efficient, and economically viable [12–14]. Many power generation alternatives are put forward to replace fossil fuels; the primarily listed and tested ones are wind, solar (thermal and photovoltaic [PV]), nuclear, geothermal, tidal, fuel cells and biofuels [15]. Among these alternatives, each has advantages and drawbacks against fossil fuels, where biofuels are found favorable over petroleum fuels because (1) they can be easily extracted from the biomass, (2) they are sustainable due to their biodegradability, (3) their combustion is based on carbon dioxide cycle, and (4) they are more environment friendly [3]. Further benefits in integrating biofuels to the fuel mix are summarized in **Table 1**.

In this study, definitions, applicability, and potentials of biofuels as an alternative energy source are investigated, with their current and probable future positions in the Turkish energy mix.

#### **2. Evolution of biofuels**

Although in the common and popular context biofuel is used to define liquids, scientifically, the term "biofuel" refers to all fuels produced from biomass in forms of:

• solids (biochar),

In the current situation, the leading primary energy sources used are fossil-based sources, having a contribution around 85% globally, where the largest consumer is power industry, utilizing 42% of the total primary sources, followed by industry and transport [1–3]. Despite global consensus on the need to shift primary energy sources to renewables, the situation is not expected to change drastically. Future scenario studies show only a slight decrease, down to 75% in 2040, on fossil fuel dependence [4], even with implementing new policy measures promoting to wane fossil fuels. Given the abundance of coal, oil, and natural gas globally, with new extraction technologies, potential reserves, and unconventional reserve exploitation (e.g. for natural gas), it is highly possible the fossil sources will be available for a considerable period at low costs [5–7]. Although supply reserve and financial scenarios demonstrate that fossil resources will continue dominating in the future for a number of decades, it is widely

Besides, fossil fuel is not sustainable by definition and many countries have concerns over fossil fuel dependence mainly connected to four conditions: (1) depleting fossil fuel stock [8], (2) price volatility of fossil resources [9], (3) greenhouse gas emissions in the atmosphere [10], and (4) geopolitical supply security [6, 7]. Even though each of these conditions is enough to convince conversion to renewables, a dilemma arises for countries being forced to use fossil

accepted that the current position has drawbacks.

Economic impacts Sustainability

222 Biofuels - State of Development

Environmental impacts Greenhouse gas reductions

Energy security Domestic targets

**Table 1.** Major benefits of biofuels [37].

Fuel diversity

Increased number of rural manufacturing jobs

Reducing the dependency on imported petroleum

Increased investments' innovation

Agricultural development International competitiveness

Reducing of air pollution

Higher combustion efficiency Improved land and water use

Biodegradability

Carbon sequestration

Reducing use of fossil fuels

Supply reliability

Ready availability Domestic distribution

Renewability


Biofuels are commonly classified as primary and secondary according to the form of utilization. Primary biofuels are organic materials directly used to extract energy. Primary biofuels include wood, wood chips, pellet, animal wastes, forest and crop residuals, landfill gas, and so on from which energy is extracted traditionally without a conversion process. Secondary biofuel refers to chemically converted fuels [16] in solid, liquid, or gaseous forms, derived from organic material. **Figure 1** illustrates the common classification of biofuels.

Primary biofuel has relatively low efficiency and has limited utilization possibilities in terms of energy conversion and transportability, compared to the so-called secondary biofuel technologies, which are also classified further into generations. The first-generation fuels are bioethanol/butanol chemically produced from rape seed, soya bean, sunflower, date palm,

**Figure 1.** Classification and sources of biofuels [17].

coconut, and animal oils, fermented from the starch of wheat, barley, corn, potato, sugar cane, and sugar beet [17]. The first-generation biofuels are well defined and have reached commercials level, especially in the US, EU, and Brazil [18]. First-generation biofuel production systems require large-scale land acquisition and have some environmental and economic limitations. Since they are mainly derived from food and oil crops, they directly compete with food for crops and agricultural land [5, 19]. There are many studies not only reporting the competition between food and fuel for land use, but also defining the dependence between a remarkable increase in food prices, mainly corn and soybean, with increased oil prices [20].

of familiarity in other applications, algae, commonly known as weeds, are referred within third-generation biofuel production, and for long years they are known as nutrient additive for animal feedstock. Due to the environmental concerns as well as the increase in oil prices, studies on biofuel sources have gained importance and algae have been considered as a promising sustainability and energy source. Because the first-generation biofuels are prone to creating environmental pollution during production process, whereas second-generation biofuels require expensive and complicated production technologies [5], far more innovative solutions—the fourth-generation biofuels or direct solar biofuels and synthetic biology technologies—are pertinently needed for replacement of all fossil fuels. Researchers are focused on third- and fourth-generation biofuels, collectively referred to as advanced biofuels, which

**Crop Seed oil (% oil by wt) Oil yield (L oil/ha yr) Land area use (m2**

Soybean 18 446–636 18

Camelia 42 915 12 Sunflower 40 952–1070 11

Canola 41 974–1190 12

Castor 48 1307–1413 9 Jatropha 20–60 1892 15

Oil palm 36 5366–5950 2

Microalgae 30–70 58,700–136,900 0.1–0.2

**1st generation**

**2nd generation**

**3rd generation**

Corn 44 172

Safflower 20 779

Peanut 70 1059

Polanga 65–75 2000 Coconut 65–75 2689

**Table 2.** Comparison of various biofuel sources [18].

 **yr./kg biodiesel)**

225

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604

Microalgae are a large and diverse group of simple, aquatic, and mostly microscopic unicellular organisms [24], which are capable of performing photosynthesis. These microalgae utilize

, water, and nutrients. While the percentages vary with the type, in general, nearly 15–77% of the microalgae cell is made up of oil. High oil content and growth efficiency compared to other plants make microalgae a promising and attractive source for biodiesel and biogas production. Generation of these fuels from microalgae would help to meet the increasing global demand in addition to contributing to the prevention of global warming by partially sequestering the excess amount

are promising in terms of conversion rates as shown in **Table 2**.

light and produce biomass from CO2

In order to overcome the competition between fuel and food crops over the limited agricultural land, second-generation biofuels, produced from mainly agricultural wastes, are used. Second-generation biofuels can be defined as bioethanol/biofuel generation from jatropha, cassava, miscanthus and bioethanol, biobutanol, or syndiesel production from lignocellulosic materials such as straw, wood, agricultural wastes, and grass [21, 22]. They are derived from biomass sources mainly agricultural residue, forest harvesting residue, wood processing, and non-edible parts of food crops. Thus, second-generation biofuels are not directly competing with agricultural lands and have lower environmental footprint than the first generation [18]. Limitation of second generation comes from its lower conversion rates (see **Table 2**). At this moment, with current conversion rates the process is not economically feasible [19]. The low conversion rates also require the second-generation biofuels to occupy large amount of lands, particularly arable lands for energy crop cultivation [23].

The third-generation biofuels are differentiated from the second-generation biofuels to the point where the utilized resource is modified via molecular biology technologies. Because


**Table 2.** Comparison of various biofuel sources [18].

coconut, and animal oils, fermented from the starch of wheat, barley, corn, potato, sugar cane, and sugar beet [17]. The first-generation biofuels are well defined and have reached commercials level, especially in the US, EU, and Brazil [18]. First-generation biofuel production systems require large-scale land acquisition and have some environmental and economic limitations. Since they are mainly derived from food and oil crops, they directly compete with food for crops and agricultural land [5, 19]. There are many studies not only reporting the competition between food and fuel for land use, but also defining the dependence between a remarkable increase in food prices, mainly corn and soybean, with increased oil prices [20]. In order to overcome the competition between fuel and food crops over the limited agricultural land, second-generation biofuels, produced from mainly agricultural wastes, are used. Second-generation biofuels can be defined as bioethanol/biofuel generation from jatropha, cassava, miscanthus and bioethanol, biobutanol, or syndiesel production from lignocellulosic materials such as straw, wood, agricultural wastes, and grass [21, 22]. They are derived from biomass sources mainly agricultural residue, forest harvesting residue, wood processing, and non-edible parts of food crops. Thus, second-generation biofuels are not directly competing with agricultural lands and have lower environmental footprint than the first generation [18]. Limitation of second generation comes from its lower conversion rates (see **Table 2**). At this moment, with current conversion rates the process is not economically feasible [19]. The low conversion rates also require the second-generation biofuels to occupy large amount of lands,

The third-generation biofuels are differentiated from the second-generation biofuels to the point where the utilized resource is modified via molecular biology technologies. Because

particularly arable lands for energy crop cultivation [23].

**Figure 1.** Classification and sources of biofuels [17].

224 Biofuels - State of Development

of familiarity in other applications, algae, commonly known as weeds, are referred within third-generation biofuel production, and for long years they are known as nutrient additive for animal feedstock. Due to the environmental concerns as well as the increase in oil prices, studies on biofuel sources have gained importance and algae have been considered as a promising sustainability and energy source. Because the first-generation biofuels are prone to creating environmental pollution during production process, whereas second-generation biofuels require expensive and complicated production technologies [5], far more innovative solutions—the fourth-generation biofuels or direct solar biofuels and synthetic biology technologies—are pertinently needed for replacement of all fossil fuels. Researchers are focused on third- and fourth-generation biofuels, collectively referred to as advanced biofuels, which are promising in terms of conversion rates as shown in **Table 2**.

Microalgae are a large and diverse group of simple, aquatic, and mostly microscopic unicellular organisms [24], which are capable of performing photosynthesis. These microalgae utilize light and produce biomass from CO2 , water, and nutrients.

While the percentages vary with the type, in general, nearly 15–77% of the microalgae cell is made up of oil. High oil content and growth efficiency compared to other plants make microalgae a promising and attractive source for biodiesel and biogas production. Generation of these fuels from microalgae would help to meet the increasing global demand in addition to contributing to the prevention of global warming by partially sequestering the excess amount of carbon dioxide via photosynthesis and converting it to new products. Due to rapid growth rate, contribution to reduce greenhouse gas and high oil generation capacity, microalgae are one of the most preferred third-generation biofuel sources. They can grow on areas unsuitable for agricultural purposes and on aquatic mediums and therefore do not compete with arable lands [25]. Besides, unlike the terrestrial plants, algae have reduced environmental risks on drinking water resources, and they are very efficient at removing nutrients like nitrogen and phosphorus from water. Many researchers consider microalgae as the unrivaled energy source and also emphasize the contribution to gaseous emissions. With very limited amount of water, microalgae can duplicate their population in 1 day by using solar energy. In fact, some types of algae require only few hours to reach such growth rates. This allows for production of millions of liters of biofuel per hectare per year, which is fairly high when compared with the palm oil (5950 L/ha) and makes algae one of the most desirable alternative sources of energy. Although not all types of algae are suitable for biodiesel production, some types are convenient for this purpose. The studies are concentrated particularly on fresh water algae (Chlorella) since it is easy to grow at laboratory conditions and is one of the best alternative algae for biodiesel production. The main processes to produce fuel from microalgae are listed in **Table 3**.

Studies on energy production including the use of a variety of algal species are generally lab-scaled, pilot, or small-scaled studies. Although these studies are successfully completed, desired efficiency is not achieved at large-scale production due to the failure in creating ideal conditions in full-scale systems.

#### **2.1. Biofuel generation from microalgae**

Microalgae can be found in natural water resources. More than 300,000 types of microalgae were determined. These organisms are very effective in converting the solar energy into biomass and contain more than 80% oil. Industrial life cycle and product line of algae are shown in **Figure 2**.

The growth phase requires setting up and operating a supporting medium in favor of algae. Under ideal conditions, in fact, it is hard to achieve in full-scale plants; they reproduce easily and grow very rapidly [27]. Ideal temperature range for the growth of microalgae is 20–30°C. They also require organic and inorganic elements (nitrogen, phosphorus, iron, and silicon in some cases) to grow up. In addition to trace elements, they can reproduce at domestic wastewaters, animal wastes, industrial wastewaters, and some aquatic environments in the case of carbon deficiency [28]. There are two main methods used to cultivate microalgae,

In addition, their growth rate is very fast. During the rapid growth period, doubling time of microalgae biomass is 3.5 h. For these reasons, larger quantities of microalgae can be produced at smaller areas with lower costs compared to the oil plants that are cultivated widely. The most popular algal species and microalgae are defined and their chemical compositions,

After the growth phase, algae should be harvested using various methods, which can be classified as chemical, mechanical, biological, and electrical methods. Among the processes of biofuel production from algae, one of the most costly steps is harvesting, summing up to

more effectively than the oil plants.

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 227

which are suspended cultures and immobilized cultures.

**Figure 2.** Industrial life cycle of microalgae [26].

During the production of oil, they use sunlight and CO2

properties, and cultivation techniques are mainly determined.


**Table 3.** Use of microalgae.

**Figure 2.** Industrial life cycle of microalgae [26].

of carbon dioxide via photosynthesis and converting it to new products. Due to rapid growth rate, contribution to reduce greenhouse gas and high oil generation capacity, microalgae are one of the most preferred third-generation biofuel sources. They can grow on areas unsuitable for agricultural purposes and on aquatic mediums and therefore do not compete with arable lands [25]. Besides, unlike the terrestrial plants, algae have reduced environmental risks on drinking water resources, and they are very efficient at removing nutrients like nitrogen and phosphorus from water. Many researchers consider microalgae as the unrivaled energy source and also emphasize the contribution to gaseous emissions. With very limited amount of water, microalgae can duplicate their population in 1 day by using solar energy. In fact, some types of algae require only few hours to reach such growth rates. This allows for production of millions of liters of biofuel per hectare per year, which is fairly high when compared with the palm oil (5950 L/ha) and makes algae one of the most desirable alternative sources of energy. Although not all types of algae are suitable for biodiesel production, some types are convenient for this purpose. The studies are concentrated particularly on fresh water algae (Chlorella) since it is easy to grow at laboratory conditions and is one of the best alternative algae for biodiesel production. The main processes to produce fuel from

Studies on energy production including the use of a variety of algal species are generally lab-scaled, pilot, or small-scaled studies. Although these studies are successfully completed, desired efficiency is not achieved at large-scale production due to the failure in creating ideal

Microalgae can be found in natural water resources. More than 300,000 types of microalgae were determined. These organisms are very effective in converting the solar energy into biomass and contain more than 80% oil. Industrial life cycle and product line of algae are shown

The growth phase requires setting up and operating a supporting medium in favor of algae. Under ideal conditions, in fact, it is hard to achieve in full-scale plants; they reproduce easily and grow very rapidly [27]. Ideal temperature range for the growth of microalgae is 20–30°C. They also require organic and inorganic elements (nitrogen, phosphorus, iron, and

microalgae are listed in **Table 3**.

226 Biofuels - State of Development

conditions in full-scale systems.

in **Figure 2**.

**2.1. Biofuel generation from microalgae**

**Final product Production process**

Methane Anaerobic fermentation of algae

Ethanol Fermentation

**Table 3.** Use of microalgae.

Biodiesel Extraction of oil from algae and transesterification

Heat and electricity Direct combustion of algae or gasification of biomass

silicon in some cases) to grow up. In addition to trace elements, they can reproduce at domestic wastewaters, animal wastes, industrial wastewaters, and some aquatic environments in the case of carbon deficiency [28]. There are two main methods used to cultivate microalgae, which are suspended cultures and immobilized cultures.

During the production of oil, they use sunlight and CO2 more effectively than the oil plants. In addition, their growth rate is very fast. During the rapid growth period, doubling time of microalgae biomass is 3.5 h. For these reasons, larger quantities of microalgae can be produced at smaller areas with lower costs compared to the oil plants that are cultivated widely. The most popular algal species and microalgae are defined and their chemical compositions, properties, and cultivation techniques are mainly determined.

After the growth phase, algae should be harvested using various methods, which can be classified as chemical, mechanical, biological, and electrical methods. Among the processes of biofuel production from algae, one of the most costly steps is harvesting, summing up to

**Figure 3.** Conversion process alternatives and their end products [30].

20–30% of total production costs [29]. Harvesting is accomplished in two separate steps—bulk harvesting (using e.g. flocculation, floatation, and sedimentation) followed by concentrating the biomass (via centrifugation or filtration). Subsequently, the biomass should be prepared for conversion process, where dehydration is essential. Many dehydration methods, like sun drying, low-pressure shelf drying, spraying, drum drying, fluidized bed drying, and freeze drying, may be used. The trade-off is between choosing low-cost, time-consuming sun drying and high-energy-consuming efficient methods. Conversion process alternatives and their end products are given in **Figure 3**.

#### **3. Renewable energy outlook**

#### **3.1. Global**

In recent years, several developments and trends clearly demonstrate a tendency and increased attention on renewable energy. The continuing comparatively low global fossil fuel prices, dramatic price reductions of several renewable energy technologies (especially solar PV and wind power), increase in energy storage, and increased appetite toward renewable technology and facility investments can easily be interpreted in favor of renewables.

Although it varies by country widely, global primary energy demand has grown by an annual average of around 1.8% in the last 5 years (**Figure 4**). Growth in primary energy demand has occurred largely in developing countries, whereas in developed countries it has slowed or even declined [31].

Looking into carbon emissions, when it is combined with increased renewable use, it is not surprising to see that, from 2013 to 2016, for the third consecutive year, global energy-related carbon dioxide emissions from fossil fuels and industries were nearly stabilized. The average increase of carbon dioxide emissions was 2.2% annually, in the previous decade [31], which cannot be connected directly to the economic recession. The breakdown of global renewable energy shares is given in **Figure 5** and share of renewables by sector is given in **Figure 6**.

As it can be seen from **Figure 5**, biomass-originated fuels became the fourth largest energy resource after coal, oil, and natural gas. Currently nearly 10% of global primary energy is sequestrated from biomass used for heating, cooking, transportation, and electric power generation. The utilization pathways are diverse through traditional use of primary fuel and biobased liquid fuels. Yet, for many countries setting targets on renewable energy, biomass is not the pointed focus, and the share in the energy mix is not expected to stack up in the future,

**Figure 4.** Growth in global renewable energy and total final energy consumption, 2005–2016 (data from [32]).

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 229

as **Figure 6** implies.

**Figure 5.** Global renewable energy share (data from [33]).

**Figure 4.** Growth in global renewable energy and total final energy consumption, 2005–2016 (data from [32]).

**Figure 5.** Global renewable energy share (data from [33]).

20–30% of total production costs [29]. Harvesting is accomplished in two separate steps—bulk harvesting (using e.g. flocculation, floatation, and sedimentation) followed by concentrating the biomass (via centrifugation or filtration). Subsequently, the biomass should be prepared for conversion process, where dehydration is essential. Many dehydration methods, like sun drying, low-pressure shelf drying, spraying, drum drying, fluidized bed drying, and freeze drying, may be used. The trade-off is between choosing low-cost, time-consuming sun drying and high-energy-consuming efficient methods. Conversion process alternatives and their end

In recent years, several developments and trends clearly demonstrate a tendency and increased attention on renewable energy. The continuing comparatively low global fossil fuel prices, dramatic price reductions of several renewable energy technologies (especially solar PV and wind power), increase in energy storage, and increased appetite toward renewable

Although it varies by country widely, global primary energy demand has grown by an annual average of around 1.8% in the last 5 years (**Figure 4**). Growth in primary energy demand has occurred largely in developing countries, whereas in developed countries it has slowed or

Looking into carbon emissions, when it is combined with increased renewable use, it is not surprising to see that, from 2013 to 2016, for the third consecutive year, global energy-related carbon dioxide emissions from fossil fuels and industries were nearly stabilized. The average increase of carbon dioxide emissions was 2.2% annually, in the previous decade [31], which cannot be connected directly to the economic recession. The breakdown of global renewable energy shares is given in **Figure 5** and share of renewables by sector is given in

technology and facility investments can easily be interpreted in favor of renewables.

products are given in **Figure 3**.

228 Biofuels - State of Development

**3.1. Global**

even declined [31].

**Figure 6**.

**3. Renewable energy outlook**

**Figure 3.** Conversion process alternatives and their end products [30].

As it can be seen from **Figure 5**, biomass-originated fuels became the fourth largest energy resource after coal, oil, and natural gas. Currently nearly 10% of global primary energy is sequestrated from biomass used for heating, cooking, transportation, and electric power generation. The utilization pathways are diverse through traditional use of primary fuel and biobased liquid fuels. Yet, for many countries setting targets on renewable energy, biomass is not the pointed focus, and the share in the energy mix is not expected to stack up in the future, as **Figure 6** implies.

also unsolved problems for biofuels to diffuse in the market, especially in distribution and lack of flex-fuel vehicles, as well as concerns on sustainability of first-generation biofuels. Nevertheless, developments like new biofuel plants and use of biofuels in commercial flights are still promising. Biojet fuels, with blends of up to 50% biofuel, have been used in more than

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 231

In addition to energy policies, biofuels are also connected to national economic policies, even to rural employment and rural development plans. Biofuel production line gets through agriculture, rural areas, producers and final consumers, creating multiple cross-industry effects. Thus subsidies towards biofuels are able to double their effects. Similar to any other renewable technology, biofuels have the ability to create new employment opportunities. Despite concerns on sustainability, some researchers argue that biofuels would perform better provided

Utilization of renewable energy, theoretically, backs up power generation by leading to three goals: (1) sustainable development, (2) decreasing energy import, thus relieving current account deficit, (3) and increasing energy security [38, 39]. Turkey has significant potential in terms of renewable energy. It is ranked 14th in the world with its geothermal energy capacity, 29th with its solar energy capacity and 16th with its wind energy capacity. For wind, the potential is estimated to be around 48 GW with a technically feasible capacity of 20–24 GW [40].

Historically, Turkish renewable energy generation was based on hydropower until privatization of the generation. From 2000s, renewable energy was put forward as one of the important issues on Turkey's energy agenda. Turkey's ambitious vision for 2023 envisages new and improved targets for the renewables, opening doors to other renewables other than hydropower [41]. Historical installed capacity of Turkey in terms of primary energy supply is given

In addition to energy security and economical requirements, Turkey also connects the renewable source utilization targets into the low-carbon economy transition. Turkish Intended Nationally Determined Contributions (INDCs) [43] includes increasing solar energy capacity to 10 GW and wind capacity to 16 GW, until 2030. Looking back to 2008, where renewable capacity (excluding hydro) was 212 MW [44], Turkey has demonstrated a vast improvement within 9 years, carrying the capacity over 7800 MW, as of 2016. It is certain that if the increase

The literature on the energy consumption-economic growth nexus has been widely researched (e.g. [45–47]); however, the renewable energy-based studies are still scarce [48]. It is well established that as a domestic natural resource, renewable energy source (RES) can make contributions to energy security. Some references [51] even proclaimed that RES could supply Turkey with full energy independence. It is clear that, even though it requires grid improvement and modular planning as well as grid operation, renewable energy supplies diversification into

Another focal point to be addressed is the dependency problem in terms of account deficit. **Figure 9** shows the imported energy bill of Turkey. It is notable that the decrease in the total

that barriers via regulations are removed and opened to the free market [37].

in **Figure 7**, and future projection of renewable capacity is given in **Figure 8**.

is kept in the upwards direction, the 2030 targets seem highly probable.

the grid, which in turn relieves energy dependence in the Turkish case.

2500 commercial flights [36].

**3.3. Turkey**

**Figure 6.** Projection of global primary energy consumption by fuel (MTOE) (data from [34]).

#### **3.2. Biofuels in energy policy**

Biofuels traditionally are attributed to transport because they are the only candidates used in vehicles, besides EV. Particularly, biofuels are options that do not require costly modifications to existing infrastructure and the vehicle fleet. Biofuel production is driven through blending mandates (e.g. Brazil and Indonesia, increasing their mandates in recent years), subsidies (e.g. the US), or a combination of both. In the EU, because of sustainability concerns, the trend is accelerating the transition to more advanced biofuels [35]. Currently, the EU set a 7% cap on conventional biofuels in final transport consumption while maintaining the 10% target for renewable sources in transport by 2020.

Even though biofuels have policy support for a number of years, the slow economic recovery and advances in conventional vehicle fuel economy have limited demand growth. There are also unsolved problems for biofuels to diffuse in the market, especially in distribution and lack of flex-fuel vehicles, as well as concerns on sustainability of first-generation biofuels. Nevertheless, developments like new biofuel plants and use of biofuels in commercial flights are still promising. Biojet fuels, with blends of up to 50% biofuel, have been used in more than 2500 commercial flights [36].

In addition to energy policies, biofuels are also connected to national economic policies, even to rural employment and rural development plans. Biofuel production line gets through agriculture, rural areas, producers and final consumers, creating multiple cross-industry effects. Thus subsidies towards biofuels are able to double their effects. Similar to any other renewable technology, biofuels have the ability to create new employment opportunities. Despite concerns on sustainability, some researchers argue that biofuels would perform better provided that barriers via regulations are removed and opened to the free market [37].

#### **3.3. Turkey**

**3.2. Biofuels in energy policy**

230 Biofuels - State of Development

renewable sources in transport by 2020.

Biofuels traditionally are attributed to transport because they are the only candidates used in vehicles, besides EV. Particularly, biofuels are options that do not require costly modifications to existing infrastructure and the vehicle fleet. Biofuel production is driven through blending mandates (e.g. Brazil and Indonesia, increasing their mandates in recent years), subsidies (e.g. the US), or a combination of both. In the EU, because of sustainability concerns, the trend is accelerating the transition to more advanced biofuels [35]. Currently, the EU set a 7% cap on conventional biofuels in final transport consumption while maintaining the 10% target for

**Figure 6.** Projection of global primary energy consumption by fuel (MTOE) (data from [34]).

Even though biofuels have policy support for a number of years, the slow economic recovery and advances in conventional vehicle fuel economy have limited demand growth. There are Utilization of renewable energy, theoretically, backs up power generation by leading to three goals: (1) sustainable development, (2) decreasing energy import, thus relieving current account deficit, (3) and increasing energy security [38, 39]. Turkey has significant potential in terms of renewable energy. It is ranked 14th in the world with its geothermal energy capacity, 29th with its solar energy capacity and 16th with its wind energy capacity. For wind, the potential is estimated to be around 48 GW with a technically feasible capacity of 20–24 GW [40].

Historically, Turkish renewable energy generation was based on hydropower until privatization of the generation. From 2000s, renewable energy was put forward as one of the important issues on Turkey's energy agenda. Turkey's ambitious vision for 2023 envisages new and improved targets for the renewables, opening doors to other renewables other than hydropower [41]. Historical installed capacity of Turkey in terms of primary energy supply is given in **Figure 7**, and future projection of renewable capacity is given in **Figure 8**.

In addition to energy security and economical requirements, Turkey also connects the renewable source utilization targets into the low-carbon economy transition. Turkish Intended Nationally Determined Contributions (INDCs) [43] includes increasing solar energy capacity to 10 GW and wind capacity to 16 GW, until 2030. Looking back to 2008, where renewable capacity (excluding hydro) was 212 MW [44], Turkey has demonstrated a vast improvement within 9 years, carrying the capacity over 7800 MW, as of 2016. It is certain that if the increase is kept in the upwards direction, the 2030 targets seem highly probable.

The literature on the energy consumption-economic growth nexus has been widely researched (e.g. [45–47]); however, the renewable energy-based studies are still scarce [48]. It is well established that as a domestic natural resource, renewable energy source (RES) can make contributions to energy security. Some references [51] even proclaimed that RES could supply Turkey with full energy independence. It is clear that, even though it requires grid improvement and modular planning as well as grid operation, renewable energy supplies diversification into the grid, which in turn relieves energy dependence in the Turkish case.

Another focal point to be addressed is the dependency problem in terms of account deficit. **Figure 9** shows the imported energy bill of Turkey. It is notable that the decrease in the total

**Figure 7.** Development of installed capacity in Turkey (data collected from [42] and interpreted).

been increasing fast. While the installed capacity was only 43 MW in 2007, within 10 years, by the end of 2016, the installed capacity has reached 496 MW—that is more than a tenfold

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 233

As of today (end of 2016), there are more than 70 biomass/biogas power plants in diverse sizes (from less than 1 to 34 MW) (see **Table 5**). These plants were able to generate 2.372 GWh annually (which is 0.86% of total energy generated), with their 496 MW of installed capacity

The ratio of generation to capacity shows that the capacity usage factor has been quite high in these plants, suggesting that they have functioned as reliable base-load plants as opposed to other intermittent (like wind and solar) RES, which are actually called variable renewable energy (VRE) and frequently referred to as one of the obstacles to full-fledged RES

Therefore, this is an important feature and an attractive point in relation to biomass-based

Although there is considerable potential (see **Figure 12**), other than traditional biomass and biogas, there is not yet any utilization of other types of biofuels in Turkey. Studies on microalgae are mainly conducted by the Faculties of Aquaculture at the larva bait production areas and at eutrophic marine and surface water sources. Although biomass production of algae has already been initiated at some universities, particularly at Aegean University, there are not enough studies and investigations focusing on energy generation from microalgae. Studies related with energy are concentrated on Izmir, Ankara, and Gebze. Studies on energy are generally lab-scaled, pilot, or small-scaled studies and completed successfully. However, desired efficiency is not achieved at large-scale production due to the failure in creating ideal conditions. General Directorate of Electricity Transmission Corporation states that the annual

power generation investment: base load, reliable, and stable power.

increase (**Figure 10**). The annual average growth rate is actually more than 30%.

in total (0.63% of Turkey) (see **Figure 11**).

**Figure 9.** Imported energy cost of Turkey (TÜİK, 2017).

development.

**Figure 8.** Installed renewable capacity projection in Turkey (data collected from [42] and interpreted).

import price results from the global energy sources (natural gas for the Turkish case), where imported energy sources have still been increasing and energy is the major expenditure in Turkey's national account.

#### **3.4. Biofuel potential and utilization in Turkey**

In line with the rapid growth (due to governmental support mechanism) of Renewable Energy Sources (RES) in power generation (see **Table 4**), the investment in biomass has also

**Figure 9.** Imported energy cost of Turkey (TÜİK, 2017).

import price results from the global energy sources (natural gas for the Turkish case), where imported energy sources have still been increasing and energy is the major expenditure in

**Figure 8.** Installed renewable capacity projection in Turkey (data collected from [42] and interpreted).

**Figure 7.** Development of installed capacity in Turkey (data collected from [42] and interpreted).

In line with the rapid growth (due to governmental support mechanism) of Renewable Energy Sources (RES) in power generation (see **Table 4**), the investment in biomass has also

Turkey's national account.

232 Biofuels - State of Development

**3.4. Biofuel potential and utilization in Turkey**

been increasing fast. While the installed capacity was only 43 MW in 2007, within 10 years, by the end of 2016, the installed capacity has reached 496 MW—that is more than a tenfold increase (**Figure 10**). The annual average growth rate is actually more than 30%.

As of today (end of 2016), there are more than 70 biomass/biogas power plants in diverse sizes (from less than 1 to 34 MW) (see **Table 5**). These plants were able to generate 2.372 GWh annually (which is 0.86% of total energy generated), with their 496 MW of installed capacity in total (0.63% of Turkey) (see **Figure 11**).

The ratio of generation to capacity shows that the capacity usage factor has been quite high in these plants, suggesting that they have functioned as reliable base-load plants as opposed to other intermittent (like wind and solar) RES, which are actually called variable renewable energy (VRE) and frequently referred to as one of the obstacles to full-fledged RES development.

Therefore, this is an important feature and an attractive point in relation to biomass-based power generation investment: base load, reliable, and stable power.

Although there is considerable potential (see **Figure 12**), other than traditional biomass and biogas, there is not yet any utilization of other types of biofuels in Turkey. Studies on microalgae are mainly conducted by the Faculties of Aquaculture at the larva bait production areas and at eutrophic marine and surface water sources. Although biomass production of algae has already been initiated at some universities, particularly at Aegean University, there are not enough studies and investigations focusing on energy generation from microalgae. Studies related with energy are concentrated on Izmir, Ankara, and Gebze. Studies on energy are generally lab-scaled, pilot, or small-scaled studies and completed successfully. However, desired efficiency is not achieved at large-scale production due to the failure in creating ideal conditions. General Directorate of Electricity Transmission Corporation states that the annual


**Power plant name City Company Installed capacity**

Balıkesir Mutlular Enerji 30.0 MW

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604 235

Ankara ITC Katı Atık Enerji 11.0 MW

Erzincan Prokom Madencilik 7.0 MW

Aksaray Sütaş Süt Enfaş Enerji 6.4 MW

Belediyesi

Kayseri Her Enerji 5.8 MW

Konya ITC Katı Atık Enerji 5.7 MW

Aydın Batısöke Söke Çimento 5.3 MW

6.0 MW

Mersin Mersin Büyükşehir

Odayeri Çöp Gazı Santrali İstanbul Ortadoğu Enerji 34.0 MW Toros Tarım Samsun Atık Isı Santrali Samsun Toros Tarım 31.0 MW

Mamak Çöplüğü Biyogaz Tesisi Ankara ITC Katı Atık Enerji 25.0 MW Çadırtepe Biyokütle Sanrali Ankara ITC Katı Atık Enerji 23.0 MW Sofulu Çöplüğü Biyogaz Santrali Adana ITC Katı Atık Enerji 16.0 MW Akçansa Çimento Atık Isı Santrali Çanakkale Enerjisa Elektrik 15.0 MW Kömürcüoda Çöplüğü Biyogaz Santrali İstanbul Ortadoğu Enerji 14.0 MW Eti Alüminyum Atık Isı Elektrik Santrali Konya Cengiz Enerji 13.0 MW Zeus Biyokütle Enerji Santrali Kırklareli Zeus Enerji 12.0 MW Eti Maden Bandırma Atık Isı Santrali Balıkesir Eti Maden 12.0 MW

Bağfaş Gübre Fabrikası Biyogaz Santrali Balıkesir Bağfaş Gübre Fabrikası 9.9 MW Hamitler Çöplüğü Biyogaz Santrali Bursa ITC Katı Atık Enerji 9.8 MW Çimsa Atık Isı Santrali Mersin Enerjisa Elektrik 9.6 MW Batıçim Atık Isı Santrali İzmir Batıçim Batı Anadolu 9.0 MW

Karacabey Biyogaz Tesisi Bursa Sütaş Süt Enfaş Enerji 6.4 MW Şanlıurfa Biyokütle Enerji Santrali Şanlıurfa Full Force Enerji 6.2 MW

Avdan Biyogaz Tesisi Samsun Avdan Enerji 6.0 MW Modern Biyokütle Enerji Santrali Tekirdağ Eren Enerji 6.0 MW Trakya Yenişehir Cam Atık Isı Santrali Bursa Trakya Yenişehir Cam 6.0 MW

Gaziantep Çöp Gazı Gaziantep CEV Enerji 5.7 MW

Kocaeli Çöplüğü Biyogaz Santrali Kocaeli Ortadoğu Enerji 5.1 MW

Mutlular Biyokütle (Orman Atığı) Enerji

ITC-KA Sincan Biyokütle Gazlaştırma

Prokom Pirolitik Yağ ve Pirolitik Gaz

Aksaray OSB Gübre Gazı Elektrik

Eman Enerji Mersin Biyokütle Enerji

Kayseri Çöplüğü Biyogaz Elektrik

Konya Aslım Çöplüğü Elektrik Üretim

Batısöke Söke Çimento Atık Isı Elektrik

Santrali

Tesisi

Tesisi

Santrali

Santrali

Santrali

Santrali

Santrali

**Table 4.** Development of installed power generation capacity (MW)—Turkey (2008–2016).

**Figure 10.** Development of biomass/biogas power generation capacity in Turkey (2007–2016).

sunshine average of Turkey is 2640 per hour; in other words, average amount of energy that can be generated is 3.6 kWh/m2 in a day. Although, there are 50 licensed biofuel facilities in Turkey, having a total installed production capacity of 1.5 million Mg, only few of these are in production due to the misplanned raw material production or lack of feasibility. Algae are one of the main alternative fuel sources, and the weather condition of the country is suitable for algae production. In addition to this, all nutrient elements required for their growth are abundantly available. Alternative agricultural production is improving with the help of biofuel projects. Biofuels brought the agricultural activities back to the agenda and have opened new horizons for the countries by encouraging them to introduce new regulations.


sunshine average of Turkey is 2640 per hour; in other words, average amount of energy that

**Installed capacity 2008 2009 2010 2011 2012 2013 2014 2015 2016**

Lignite 8,205 8,199 8,199 8,199 8,193 8,223 8,281 8,696 9,127

Natural Gas 15,526 16,963 18,628 19,955 20,997 25,191 26,094 25,489 26,115 Biofuels 60 87 107 126 169 235 299 370 496 Hydro 13,829 14,553 15,831 17,137 19,609 22,289 23,643 25,868 26,681 Geothermal 30 77 94 114 162 311 405 624 821 Wind 364 792 1,320 1,729 2,261 2,760 3,630 4,503 5,751 Solar 40 249 833 Total **41,817 44,761 49,524 52,911 57,059 64,008 69,520 73,147 78,497**

1,986 2,391 3,751 4,351 4,383 4,383 6,533 6,825 8,229

1,819 1,699 1,593 1,300 1,286 616 595 523 445

Turkey, having a total installed production capacity of 1.5 million Mg, only few of these are in production due to the misplanned raw material production or lack of feasibility. Algae are one of the main alternative fuel sources, and the weather condition of the country is suitable for algae production. In addition to this, all nutrient elements required for their growth are abundantly available. Alternative agricultural production is improving with the help of biofuel projects. Biofuels brought the agricultural activities back to the agenda and have opened

new horizons for the countries by encouraging them to introduce new regulations.

**Figure 10.** Development of biomass/biogas power generation capacity in Turkey (2007–2016).

**Table 4.** Development of installed power generation capacity (MW)—Turkey (2008–2016).

in a day. Although, there are 50 licensed biofuel facilities in

can be generated is 3.6 kWh/m2

Hard Coal + Imported Coal + Asphaltite

234 Biofuels - State of Development

Oil + Motorin + LPG + Nafta

Fuel


**3.5. The contribution of biomass in power generation to energy dependence, supply** 

Cargill Tarım Bursa Bioenerji Santrali Bursa Cargill Tarım 0.1 MW

**Power plant name City Company Installed capacity**

Uşak Çöpgazı enerji Santrali Uşak Uşak Belediyesi 1.2 MW

Ekim Grup Gübre Gazı Konya Ekim Grup Elektrik 1.2 MW Malatya 1 Çöp Gaz Elektrik Üretim Tesisi Malatya 1.2 MW Bolu Çöplüğü Biyogaz Santrali Bolu CEV Enerji 1.1 MW Kırıkkale Çöp Gazı Enerji Santrali Kırıkkale Mustafa Modoğlu Holding 1.0 MW Sigma Suluova Biyogaz Tesisi Amasya Sigma Elektrik Üretim 1.0 MW Kemerburgaz Çöplüğü Biyogaz Santrali İstanbul Ekolojik Enerji 1.0 MW Hayat Biyokütle Elektrik Üretim Santrali Kocaeli Hayat Enerji 1.0 MW

Adana Batı Atıksu Biyogaz Santrali Adana Adana Büyükşehir

Adana Doğu Atıksu Biyogaz Santrali Adana Adana Büyükşehir

Solaklar İzaydaş Çöp Gazı Kocaeli Kocaeli Büyükşehir

Beypazarı Biyogaz Tesisi Ankara Derin Enerji Üretim 0.8 MW Frito Lay Gıda Biyogaz Santrali Kocaeli Frito Lay Gıda 0.7 MW Frito Lay Gıda Kojenerasyon Santrali Mersin 0.7 MW Kumkısık Çöplüğü Biyogaz Santrali Denizli Bereket Enerji 0.6 MW Sezer Bio Enerji Antalya Kalemirler Enerji 0.5 MW

Mersin Mersin Büyükşehir

Amasya Boğazköy Enerji Elektrik Üretim

Belediyesi

Kahramanmaraş Eman Enerji 1.0 MW

Belediyesi

Belediyesi

Belediyesi

Belediyesi

Denizli Denizli Büyükşehir

1.2 MW

237

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604

1.2 MW

0.8 MW

0.8 MW

0.5 MW

0.3 MW

TOTAL 496.4 MW

It is well established that as a domestic natural resource, RES can make contributions to energy security. BNEF [49] and Hill [50] even proclaimed that RES could supply Turkey with full energy independence. It is clear thus that renewable energy supplies diversification into the grid which in turn relieves energy dependence in the Turkish case. One of the main promising

**security, and national economy**

**Table 5.** Biomass/biogas: full list of power plants in Turkey (2017).

Denizli Atıksu Arıtma Tesisi Biyogaz

Elektrik Üretim Santrali

Eman Enerji Silifke Biyokütle Enerji

Amasya Çöp Gazı Elektrik Üretim

Eman Enerji Karaman Biyokütle Enerji

Santrali

Santrali

Santrali


**Table 5.** Biomass/biogas: full list of power plants in Turkey (2017).

**Power plant name City Company Installed capacity**

Belediyesi

Belediyesi

Hatay Novtek Enerji 2.8 MW

Belediyesi

Belediyesi

Belediyesi

Belediyesi

Belediyesi

Enerji

Mersin Mersin Büyükşehir

Malatya Malatya Büyükşehir

4.0 MW

3.2 MW

2.4 MW

2.4 MW

2.0 MW

1.9 MW

1.7 MW

1.4 MW

Ovacık Biyogaz Enerji Santrali Kırklareli Işıt Biyokütle 4.8 MW Tire Biyogaz Tesisi İzmir Sütaş Süt Enfaş Enerji 4.3 MW Hatay Gökçegöz Çöp Santrali Hatay Atya Elektrik 4.2 MW

Afyon Biyogaz Enerji Santrali Afyonkarahisar Afyon Enerji 4.0 MW Gönen Biyogaz Tesisi Balıkesir Gönen Yenilenebilir Enerji 3.6 MW

Atlas İnşaat Osmaniye Çöp Gazı Santrali Osmaniye Atlas İnşaat 3.1 MW ITC-KA Elazığ Çöp Gazı Santrali Elazığ ITC-KA Enerji 2.8 MW

Trabzon Rize Çöp Gazı Santrali Trabzon Mustafa Modoğlu Holding 2.8 MW Sivas Biyokütle Elektrik Üretim Tesisi Sivas Novtek Enerji 2.8 MW

Arel Enerji Biyokütle Tesisi Afyonkarahisar Arel Enerji 2.4 MW Manavgat Çöp Gazı Santrali Antalya Arel Enerji 2.4 MW Senkron Efeler Biyogaz Santrali Aydın Senkron Grup 2.4 MW Mauri Maya Bandırma Biyogaz Santrali Balıkesir Mauri Maya 2.3 MW Tokat Çöpgazı Elektrik Üretim Santrali Tokat Tokat Belediyesi 2.3 MW Bandırma Edincik Biyogaz Santrali Balıkesir Telko Enerji 2.1 MW

Albe Biyogaz Santrali Ankara Era Grup 1.8 MW

Karma Gıda Biyogaz Santrali Sakarya Karma Gıda 1.5 MW Polatlı Biyogaz Tesisi Ankara Polres Elektrik Üretim 1.5 MW Aksaray Çöp Gazı Elektrik Santrali Aksaray ITC Katı Atık Enerji 1.4 MW

Pamukova Katı Atık Biyogaz Santrali Sakarya Biosun Pamukova 1.4 MW

Hasdal İstanbul İstanbul Büyükşehir

Belka Çöp Gazı Biyogaz Ankara Ankara Büyükşehir

Konya Atıksu Biyogaz Santrali Konya Konya Büyükşehir

Eses Enerji Biyogaz Santrali Eskişehir Eskişehir Büyükşehir

GASKİ Atıksu Biyogaz Elektrik Santrali Gaziantep Gaziantep Büyükşehir

Karaman Biyogaz Tesisi Karaman Karaman Yenilenebilir

İskenderun Çöp Gazı Elektrik Üretim

236 Biofuels - State of Development

Malatya BŞB Çöp Gazı Elektrik Üretim

Karaduvar Atıksu Arıtma Tesisi Biyogaz

Tesisi

Santrali

Santrali

#### **3.5. The contribution of biomass in power generation to energy dependence, supply security, and national economy**

It is well established that as a domestic natural resource, RES can make contributions to energy security. BNEF [49] and Hill [50] even proclaimed that RES could supply Turkey with full energy independence. It is clear thus that renewable energy supplies diversification into the grid which in turn relieves energy dependence in the Turkish case. One of the main promising

energy imports from fossil fuels (in our case we take gas, which is the most expensive and the

The cost of imported natural gas in each MWh of electricity produced can be calculated as about 38 USD (with an assumption efficiency of average 55% of a combined cycle gas turbine

For the year 2016, the monetary value of avoided (not imported or "substituted with biomass fuel") natural gas can be currently calculated as approximately 90 million USD: 38 USD ×

total gas import amount) has been avoided to be imported, only with the utilization biomass as a fuel of choice in power generation from the biomass power plants of a total installed

Taking the official aim of reaching 1 GW (1000 MW) installed capacity by 2023 (which is around 0.8% of total capacity then) into consideration and assuming the same efficiency and capacity usage factors as was realized in 2016, 4800 GWh of power is then calculated that can be generated (which could yield a generation percentage of around 1.1% in general totally). This amount is equivalent to approximately 920 million cubic meter of natural gas as a fuel source to be burnt for power generation, which could be avoided (not to be imported) with a

In this way, the imported energy bill would have been cut by about 182 million USD by 2023. If we consider the fact that the total amount of imported natural gas was around 46

an import price tag of 3.5 billion USD (which had yielded 88.271 GWh of electricity), the import fuel-saved electricity from biomass (calculated to be 4.890 GWh) would therefore be equivalent to ~5.4% of total electricity obtained from natural gas per annum. Although the amount 182 million USD (which was achieved by burning biomass instead of gas) as savings in a gas-for-electricity portion of ~3.5 billion USD and around total gas import bill of 9 billion USD and of total 27 billion USD energy import bill or 32.6 billion current account deficit seems small (though only annual) and negligible, one should also consider the fact that biomass is actually one of the many domestic and environmentally friendly renewable energy sources (several of which, like wind, hydro, and solar, are much more contributive than biomass), which has enormous potential altogether to reduce significantly energy-dependence ratio and the total energy import bill of Turkey (and consequently cur-

That is, the total value of RES potential for 2023 (the official government target year) is—with 38% of total generation—actually more than total for the "gas-for-electricity" amount (which is around 30%). In other words, with the total RES-generated electricity, which would have otherwise been generated from imported natural gas, more than 3.5 billion USD could be saved per annum by 2023. Thus, it can safely be said that together with other renewables, biomass has a role to play to reduce both energy-import dependence and import bill of Turkey

2.372 GWh (which is the total generated from biomass only in 2016) = 90.136 T. USD.

or ~195 USD/1000 m3

of natural gas (which is around 1% of the

Potential of Biofuel Usage in Turkey's Energy Supply http://dx.doi.org/10.5772/intechopen.74604

was consumed for power generation with

).

239

most used power-generation fuel) was actually substituted for 2016.

(CCGT) plant current BOTAŞ wholesale gas price as 704 TL/1000 m<sup>3</sup>

In other words, an amount of around 456 million m3

monetary value of approximately 182 million USD.

and out of this amount 17.5 billion m3

capacity of 496 MW in the year 2016.

billion m3

rent account deficit).

in a better way.

**Figure 11.** Development of power generation by sources (percentages) in Turkey (2008–2016).

**Figure 12.** Biomass potential of Turkey by fuel type.

sources within RES portfolio of Turkey is therefore biofuels (especially biomass and biogas, which could help substitute the import fossil fuels.

Another focal point to be addressed is therefore the dependency problem in terms of current account deficit. **Figure 9** shows the imported energy bill of Turkey. It is notable that the decrease in the total import price results basically from the decline in global energy prices (oil and gas), but still energy is the major item in Turkey's trade balance.

In the analysis below, in order to calculate the contribution of biomass to energy security as well as to the relief of current account deficit, we make a comparison in terms of how much of energy imports from fossil fuels (in our case we take gas, which is the most expensive and the most used power-generation fuel) was actually substituted for 2016.

The cost of imported natural gas in each MWh of electricity produced can be calculated as about 38 USD (with an assumption efficiency of average 55% of a combined cycle gas turbine (CCGT) plant current BOTAŞ wholesale gas price as 704 TL/1000 m<sup>3</sup> or ~195 USD/1000 m3 ). For the year 2016, the monetary value of avoided (not imported or "substituted with biomass fuel") natural gas can be currently calculated as approximately 90 million USD: 38 USD × 2.372 GWh (which is the total generated from biomass only in 2016) = 90.136 T. USD.

In other words, an amount of around 456 million m3 of natural gas (which is around 1% of the total gas import amount) has been avoided to be imported, only with the utilization biomass as a fuel of choice in power generation from the biomass power plants of a total installed capacity of 496 MW in the year 2016.

Taking the official aim of reaching 1 GW (1000 MW) installed capacity by 2023 (which is around 0.8% of total capacity then) into consideration and assuming the same efficiency and capacity usage factors as was realized in 2016, 4800 GWh of power is then calculated that can be generated (which could yield a generation percentage of around 1.1% in general totally). This amount is equivalent to approximately 920 million cubic meter of natural gas as a fuel source to be burnt for power generation, which could be avoided (not to be imported) with a monetary value of approximately 182 million USD.

In this way, the imported energy bill would have been cut by about 182 million USD by 2023. If we consider the fact that the total amount of imported natural gas was around 46 billion m3 and out of this amount 17.5 billion m3 was consumed for power generation with an import price tag of 3.5 billion USD (which had yielded 88.271 GWh of electricity), the import fuel-saved electricity from biomass (calculated to be 4.890 GWh) would therefore be equivalent to ~5.4% of total electricity obtained from natural gas per annum. Although the amount 182 million USD (which was achieved by burning biomass instead of gas) as savings in a gas-for-electricity portion of ~3.5 billion USD and around total gas import bill of 9 billion USD and of total 27 billion USD energy import bill or 32.6 billion current account deficit seems small (though only annual) and negligible, one should also consider the fact that biomass is actually one of the many domestic and environmentally friendly renewable energy sources (several of which, like wind, hydro, and solar, are much more contributive than biomass), which has enormous potential altogether to reduce significantly energy-dependence ratio and the total energy import bill of Turkey (and consequently current account deficit).

That is, the total value of RES potential for 2023 (the official government target year) is—with 38% of total generation—actually more than total for the "gas-for-electricity" amount (which is around 30%). In other words, with the total RES-generated electricity, which would have otherwise been generated from imported natural gas, more than 3.5 billion USD could be saved per annum by 2023. Thus, it can safely be said that together with other renewables, biomass has a role to play to reduce both energy-import dependence and import bill of Turkey in a better way.

sources within RES portfolio of Turkey is therefore biofuels (especially biomass and biogas,

Another focal point to be addressed is therefore the dependency problem in terms of current account deficit. **Figure 9** shows the imported energy bill of Turkey. It is notable that the decrease in the total import price results basically from the decline in global energy prices (oil

In the analysis below, in order to calculate the contribution of biomass to energy security as well as to the relief of current account deficit, we make a comparison in terms of how much of

which could help substitute the import fossil fuels.

**Figure 12.** Biomass potential of Turkey by fuel type.

238 Biofuels - State of Development

and gas), but still energy is the major item in Turkey's trade balance.

**Figure 11.** Development of power generation by sources (percentages) in Turkey (2008–2016).

#### **4. Conclusions**

It has been understood for some time now that the dependence of the world (especially in power generation) on fossil fuels is not sustainable. One of the identified solid alternatives therefore has been biofuels. As biofuels are regarded as carbon neutral (x ref), they are listed under the renewable category of energy sources and are thus "climate friendly," as opposed to fossil fuels; they are given priority and are supported globally by government policies, as is the case with generous subsidies (such as the highest off-take guarantees from biofuel power plants) in Turkey. The potential of biofuels (although not as huge as solar or wind) especially in power generation is considered to be significant due to the fact that it is not actually an intermittent source of power as is the case with other renewables such as wind- and solar- (as they are actually called "variable renewable energies") based generation. Thus, biofuels can easily substitute other fossil fuels as a reliable and base-load source of power generation with high availability, as opposed to the variability and intermittency of other sources. This has been actually demonstrated in Turkey in relation to the operational conditions (high availability and reliability) of existing biomass power plants.

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[9] Baffes J, Kshirsagar V. Sources of volatility during four oil price crashes. Applied

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[11] Ugarte DG, Walsh ME, Shapouri H, Slinsky P. The economic impacts of bioenergy crop production in US agriculture. USDA Agricultural Economic Report No. 816; 2003. p. 41

[12] Joshia G, Pandey JK, Rana S, Rawat DS. Challenges and opportunities for the application of biofuel. Renewable and Sustainable Energy Reviews. 2017;**79**(2017):850-866

[13] Alemán-Nava GS, Casiano-Flores VH, et al. Renewable energy research progress in Mexico: A review. Renewable and Sustainable Energy Reviews. 2014;**32**:140-153

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ities of biofuel in Indonesia: A review. Energy Reports. 2016;**2**:237-245

Another result of this study in terms of the reasons for utilization of biomass/biogas resources is (in addition to all abovementioned environmental benefits)the contribution (so far small but promising for the future) of them reducing energy import dependence and energy import bill of Turkey. As analyzed in the relevant section, the development of biomass/biogas plants has been very rapid and the generation reached the equivalent of more than 5% of power generation from natural gas. Thus, the gas imports were reduced by this amount, or according to unit-based calculation, 1 MW of power generated by local/domestic and renewable biomass/ biogas obviously meant "1 MW less of imported and fossil natural gas-based power". The total savings or avoided import value per year (for only the year 2016) is around 185 million USD. Considering the potential of biomass/biogas and the fast development in utilization of these resources lately, one could assume that this amount or value (also depending on the price of import gas) will increase and biomass will (along with other RES) play a meaningful role in terms of contributing to meeting national climate targets as well to reducing energy import bill of Turkey, thus enhancing energy security and independence of the country in the long run.

#### **Author details**

Sirri Uyanik1 , Yavuz Sucu2 and Zeynep Zaimoglu3 \*

\*Address all correspondence to: zeynepzaimoglu6@gmail.com

1 Energy Management Department, Faculty of Economics and Administrative Sciences, KTO Karatay University, Konya, Turkey

2 Environmental Engineering Department, Institute of Natural and Applied Sciences, Cukurova University, Adana, Turkey

3 Department of Environmental Engineering, Faculty of Engineering, Cukurova University, Adana, Turkey

#### **References**

**4. Conclusions**

240 Biofuels - State of Development

**Author details**

, Yavuz Sucu2

KTO Karatay University, Konya, Turkey

Cukurova University, Adana, Turkey

and Zeynep Zaimoglu3

1 Energy Management Department, Faculty of Economics and Administrative Sciences,

2 Environmental Engineering Department, Institute of Natural and Applied Sciences,

3 Department of Environmental Engineering, Faculty of Engineering, Cukurova University,

\*Address all correspondence to: zeynepzaimoglu6@gmail.com

\*

Sirri Uyanik1

Adana, Turkey

It has been understood for some time now that the dependence of the world (especially in power generation) on fossil fuels is not sustainable. One of the identified solid alternatives therefore has been biofuels. As biofuels are regarded as carbon neutral (x ref), they are listed under the renewable category of energy sources and are thus "climate friendly," as opposed to fossil fuels; they are given priority and are supported globally by government policies, as is the case with generous subsidies (such as the highest off-take guarantees from biofuel power plants) in Turkey. The potential of biofuels (although not as huge as solar or wind) especially in power generation is considered to be significant due to the fact that it is not actually an intermittent source of power as is the case with other renewables such as wind- and solar- (as they are actually called "variable renewable energies") based generation. Thus, biofuels can easily substitute other fossil fuels as a reliable and base-load source of power generation with high availability, as opposed to the variability and intermittency of other sources. This has been actually demonstrated in Turkey in relation to the operational conditions (high avail-

Another result of this study in terms of the reasons for utilization of biomass/biogas resources is (in addition to all abovementioned environmental benefits)the contribution (so far small but promising for the future) of them reducing energy import dependence and energy import bill of Turkey. As analyzed in the relevant section, the development of biomass/biogas plants has been very rapid and the generation reached the equivalent of more than 5% of power generation from natural gas. Thus, the gas imports were reduced by this amount, or according to unit-based calculation, 1 MW of power generated by local/domestic and renewable biomass/ biogas obviously meant "1 MW less of imported and fossil natural gas-based power". The total savings or avoided import value per year (for only the year 2016) is around 185 million USD. Considering the potential of biomass/biogas and the fast development in utilization of these resources lately, one could assume that this amount or value (also depending on the price of import gas) will increase and biomass will (along with other RES) play a meaningful role in terms of contributing to meeting national climate targets as well to reducing energy import bill of Turkey, thus enhancing energy security and independence of the country in the long run.

ability and reliability) of existing biomass power plants.


[16] Russo D, Dassisti M, Lawlor V, Olabi AG. State of the art of biofuels from pure plant oil. Renewable and Sustainable Energy Reviews. 2012;**16**(6):4056-4070. DOI: 10.1016/j. rser.2012.02.024. ISSN 1364-0321

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[40] Peker HS. Yenilenebilir Enerjide Teknik Kapasite, Teknik Yapılabilir Kapasite ve Ekonomik Yapılabilir Kapasite. 2015. http://hasansencerpeker.blogspot.com.tr/2015/04/

[41] Ozcan A, Strauss EJ. Ecological modernization on Turkey's energy policy and renewable energy cooperatives suggestions for Turkey from the USA policy perspective. In: Acer Y, Koval I, Icbay MA, Arslan H, editors. Recent Developments in Social Sciences: Political Sciences and International Relations. International Association of Social Science

[42] TEIAS. Turkish Energy Transmission Company Statistics. https://www.teias.gov.tr/tr/

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[44] Tamzok N. Türkiye'nin yenilenebilir hesabı tutar mı?. Enerji Günlüğü. 2015. http:// www.enerjigunlugu.net/icerik/12510/turkiyenin-yenilenebilir-hesabi-tutar-mi.html [45] Wolde-Rufael Y. Energy consumption and economic growth: The experience of African

[46] Costantini V, Martini C. The causality between energy consumption and economic growth: A multi-sectoral analysis using non-stationary cointegrated panel data. Energy


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[17] Mussatto SI, Dragone G, Guimarães PMR, Silva JPA, Carneiro LM, Roberto IC, Vicente A, Domingues L, Teixeira JA. Technological trends, global market, and challenges of bio-

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[28] Zhou W, Chen P, Min M, Ma X, Wang J, Griffith R, Hussain F, Peng P, Xie Q, Li Y, Shi J, Meng J, Ruan R. Environment-enhancing algal biofuel production using wastewaters.

[29] Demirbas A. Use of algae as biofuel sources. Energy Conversion and Management. 2010;

[30] Naik SN, Goud VV, Rout PK, Dalai AK. Production of first and second generation biofuels: A comprehensive review. Renewable and Sustainable Energy Reviews. 2010;

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[47] Bhattacharya M, Rafiq S, Bhattacharya S. The role of technology on the dynamics of coal consumption-economic growth: New evidence from China. Applied Energy. 2015; **154**:686-695

**Chapter 12**

**Provisional chapter**

**Prospective Biodegradable Plastics from Biomass**

**Prospective Biodegradable Plastics from Biomass** 

DOI: 10.5772/intechopen.75111

The biomass energy source has been a promising renewable alternative for fossil fuels and their inevitable environmental impacts on Earth's life, from which the greenhouse gas (GHG) emissions and the environment pollution followed by consequent ecosystem imbalance are major concerns. Biofuels and bioplastics are well-known examples of renewable products obtained from biomass that has shown increasing potential to succeed the conventional fuels and plastics. However, biofuels and especially bioplastics have faced their main hindrance in their uncompetitive costs. Furthermore, the "drop-in" plastics are the market leaders, which reduce the carbon footprint but continue to state the biodegradability concern attributed to most of plastic products, the packaging sector. This chapter outlines the common features and feedstocks of biofuels and bioplastics aiming to support their associated production set toward the bio-based and biodegradable poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs) as promising models with fast-growing production capacity forecasted for the next years and biodegradable

Nowadays, the world has faced the side effects from fossil fuel dependence such as environmental pollution, greenhouse gas (GHG) emissions, and ocean acidification. Besides the large utilization of oil, coal, and natural gas to generate energy, a variety of petrochemical derivatives have also accounted to the ecological imbalance worldwide. The petrochemical plastics

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

**Conversion Processes**

**Conversion Processes**

Jonas Contiero

Jonas Contiero

**Abstract**

**1. Introduction**

Fabrício C. de Paula, Carolina B.C. de Paula and

Fabrício C. de Paula, Carolina B.C. de Paula and

solution for short-lived and disposable plastic materials. **Keywords:** biofuel, bioplastic, biodegradable, PHA, PLA

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75111


#### **Prospective Biodegradable Plastics from Biomass Conversion Processes Prospective Biodegradable Plastics from Biomass Conversion Processes**

DOI: 10.5772/intechopen.75111

Fabrício C. de Paula, Carolina B.C. de Paula and Jonas Contiero Fabrício C. de Paula, Carolina B.C. de Paula and Jonas Contiero

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75111

#### **Abstract**

[47] Bhattacharya M, Rafiq S, Bhattacharya S. The role of technology on the dynamics of coal consumption-economic growth: New evidence from China. Applied Energy. 2015;

[48] Bhattacharya M, Paramati SR, Ozturk I, Bhattacharya S. The effect of renewable energy consumption on economic growth: Evidence from top 38 countries. Applied Energy.

[49] Bloomberg New Energy Finance (BNEF). Turkey's changing power markets. 2014. https://about.bnef.com/blog/turkeys-changing-power-markets/ [Accessed: 02.02.17] [50] Hill JS. Renewables could Supply Turkey with Energy Independence, Continues Trend. 2014. https://cleantechnica.com/2014/11/19/renewables-supply-turkey-energy-

**154**:686-695

244 Biofuels - State of Development

2016;**162**(2016):733-741

independence/ [Accessed: 02.02.2017]

The biomass energy source has been a promising renewable alternative for fossil fuels and their inevitable environmental impacts on Earth's life, from which the greenhouse gas (GHG) emissions and the environment pollution followed by consequent ecosystem imbalance are major concerns. Biofuels and bioplastics are well-known examples of renewable products obtained from biomass that has shown increasing potential to succeed the conventional fuels and plastics. However, biofuels and especially bioplastics have faced their main hindrance in their uncompetitive costs. Furthermore, the "drop-in" plastics are the market leaders, which reduce the carbon footprint but continue to state the biodegradability concern attributed to most of plastic products, the packaging sector. This chapter outlines the common features and feedstocks of biofuels and bioplastics aiming to support their associated production set toward the bio-based and biodegradable poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs) as promising models with fast-growing production capacity forecasted for the next years and biodegradable solution for short-lived and disposable plastic materials.

**Keywords:** biofuel, bioplastic, biodegradable, PHA, PLA

#### **1. Introduction**

Nowadays, the world has faced the side effects from fossil fuel dependence such as environmental pollution, greenhouse gas (GHG) emissions, and ocean acidification. Besides the large utilization of oil, coal, and natural gas to generate energy, a variety of petrochemical derivatives have also accounted to the ecological imbalance worldwide. The petrochemical plastics

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

are perfect examples of petroleum-based compounds, which imply a problematic ecological issue due to the high demand of their use for several applications, inappropriate discard, and environmental persistence [1, 2]. Conventional plastics take many decades to be decomposed in nature and produce toxins [3], particularly plastic additives (e.g., phthalates as plasticizers) and toxic monomer residues (e.g., vinyl chloride). Microplastics (particles less than 5 mm) in the oceans are seriously harmful to many aquatic organisms, and some of which inevitably end up in the human nutrition, the last consumer of this food chain [4].

a byproduct of biodiesel industry, has been a promising feedstock to obtain a high diversity of products from microbial cultivation, which may be mentioned as 1,3-propanediol, dihydroxyacetone, succinic acid, propionic acid, ethanol, citric acid, biosurfactants, and bioplastics [15–24]. Lignocellulose hydrolysates are not only a source of the second-generation ethanol but also a feedstock of a multitude of chemicals such as xylose, mannose, galactose, acetic acid, ethylene, propylene, butadiene, xylitol, phenols, glucaric acid, glutamic acid, aspartic

Prospective Biodegradable Plastics from Biomass Conversion Processes

http://dx.doi.org/10.5772/intechopen.75111

247

Aside the environmental concern on fossil fuels being burnt into atmosphere, its plastic derivative is another critical issue, whose 60% of the total solid waste is discarded in landfills for 100 years of environmental persistence [1, 2]. Bioplastics from renewable energy sources that exhibit biodegradable characteristics are good candidates to replace short-lived and disposable plastic products, which accounts 50% of the total plastic production and so contributing for a significant diminishing of their long-term ecosystem intake and consequent harmful effects [4, 34, 35]. A biorefinery concept comprising biofuel and bioplastic production is an alternative solution to aggregate value to both industries and to improve the feasibility of a production set partially or totally disassociated from petrochemical compounds [23]. This chapter outlines a brief review on biofuels and bioplastics, and some of their interchangeable features in order to support a biorefinery model for bio-based and either biodegradable plastics belonging to biofuel production sets. Further, a special focus is dedicated to the production of poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs) from biofuel feedstocks and byproducts as promising bio-based and biodegradable plastics with fast-growing devel-

Biofuel refers to solid, liquid, or gaseous fuel obtained from renewable feedstocks, from which bioethanol and biodiesel are the most produced transportation fuel as potential substitutes for gasoline and diesel fuel [9, 36, 37]. According to their production technology, biofuels are classified into the first-, second-, third-, and fourth-generation biofuels (**Figure 1**). The first-generation biofuels are produced from edible sources, such as grains, oil seeds, sugar and starch crops, and animal fats. Well-established examples of the first-generation biofuels are ethanol from sugarcane in Brazil, corn ethanol in the USA, biodiesel from rapeseed oil in Germany, and palm oil–based biodiesel in Malaysia. The second-generation biofuels are obtained from nonedible feedstock, such as lignocellulosic materials including cereal straw, forest and wood

The second-generation biofuels are an alternative to mitigate the main concern about the first-generation biofuels: food versus fuel. An additional advantage is the utilization of agricultural byproducts and municipal solid wastes and thus lowering costs and improving the urban waste management [37]. The former Directorate-General for Energy and Transport has proposed the third- and fourth-generation biofuels, which are classified as advanced biofuels. The third-generation biofuels are obtained using molecular biology techniques, such as low-lignin content trees and genetically modified microalgae. The fourth-generation biofuels are those that should provide carbon capture and storage (CCS) processes with improved

residues, sugarcane bagasse, short-rotation crops, and vegetative grasses [37].

acid, syringols, eugenol, toluene, xylene, styrene, and others [14, 25–33].

opment foreseen for the next years.

**2. Biofuels: an overview**

As a result of the twentieth century development based on petroleum, coal, and natural gas exploitation, which were cheaply available, fossil fuels and their derivatives (e.g., fine chemicals, pharmaceuticals, detergents, plastics, fertilizers, lubricants, solvent, asphalt, and waxes) have become a major global threat directly linked to increasing levels of CO2 in the atmosphere and consequent global warming. Since these fossil resources are not considered as sustainable and they are prejudicial from the ecological point of view [5], there have been rising concerns over their global impact, which has led to the development of technologies focused on the production of fuels and materials from renewable carbon sources, such as plant biomass [6]. Biomass has the potential to reduce GHG emissions by replacing fossil fuels. The combustion of biomass feedstock has been considered as carbon neutral or low-carbon fuel, since the plant crops assimilate carbon dioxide from the atmosphere during the growth. Accordingly, the socalled biofuels are a promising alternative to replace nonrenewable fuels [7, 8].

The main advantages of biofuels include their biodegradable and renewable properties; the generation of employment and technical development in rural areas; decentralized production from locally available domestic biomass; besides the combustion based on carbon dioxide cycle as mentioned above [8–10]. A global volume of more than 100 Bln L per year of conventional biofuels has been obtained, which is referred to as the first-generation biofuels including ethanol from sugar or starch crops and biodiesel from oils and fats. In addition, there have been many efforts focused on the second- and third-generation biofuels produced from a broad range of nonedible biomass feedstock [11].

Likewise, other chemicals and industrial products from fossil energy sources have been replaced by renewable ones. "Green" chemistry is a broad term referring to these compounds that support the sustainable development, from which the bioplastics can illustrate how the chemical industry is able to integrate sustainable innovation into a business model. On the other hand, the "green" chemistry companies must take into account efficient and less costly processes in order to make feasible their products commercialization [12]. Therefore, the economic viability of biofuel industry depends on facilities that integrate biomass conversion processes and equipment to produce value-added compounds, such as fuels, power, and chemicals. The larger the ability to derive value from biofuel, including byproducts and residues, the higher will be the feasibility of a bio-based industry from economic and environmental points of view [13].

A "green" biorefinery is a multifunctional and full-integrated system for biomass utilization. Besides the fuels obtained from "green" biomass, several products can be obtained from the "green" juice to the lignocellulosic materials, such as dyes, pigments, crude drugs, free amino acids, organic acids, enzymes, hormones, and minerals [5, 14]. Moreover, the biofuel byproducts have been a source of chemicals. Crude glycerol from transesterification of fats and oils, a byproduct of biodiesel industry, has been a promising feedstock to obtain a high diversity of products from microbial cultivation, which may be mentioned as 1,3-propanediol, dihydroxyacetone, succinic acid, propionic acid, ethanol, citric acid, biosurfactants, and bioplastics [15–24]. Lignocellulose hydrolysates are not only a source of the second-generation ethanol but also a feedstock of a multitude of chemicals such as xylose, mannose, galactose, acetic acid, ethylene, propylene, butadiene, xylitol, phenols, glucaric acid, glutamic acid, aspartic acid, syringols, eugenol, toluene, xylene, styrene, and others [14, 25–33].

Aside the environmental concern on fossil fuels being burnt into atmosphere, its plastic derivative is another critical issue, whose 60% of the total solid waste is discarded in landfills for 100 years of environmental persistence [1, 2]. Bioplastics from renewable energy sources that exhibit biodegradable characteristics are good candidates to replace short-lived and disposable plastic products, which accounts 50% of the total plastic production and so contributing for a significant diminishing of their long-term ecosystem intake and consequent harmful effects [4, 34, 35]. A biorefinery concept comprising biofuel and bioplastic production is an alternative solution to aggregate value to both industries and to improve the feasibility of a production set partially or totally disassociated from petrochemical compounds [23]. This chapter outlines a brief review on biofuels and bioplastics, and some of their interchangeable features in order to support a biorefinery model for bio-based and either biodegradable plastics belonging to biofuel production sets. Further, a special focus is dedicated to the production of poly(lactic acid) (PLA) and polyhydroxyalkanoates (PHAs) from biofuel feedstocks and byproducts as promising bio-based and biodegradable plastics with fast-growing development foreseen for the next years.

#### **2. Biofuels: an overview**

are perfect examples of petroleum-based compounds, which imply a problematic ecological issue due to the high demand of their use for several applications, inappropriate discard, and environmental persistence [1, 2]. Conventional plastics take many decades to be decomposed in nature and produce toxins [3], particularly plastic additives (e.g., phthalates as plasticizers) and toxic monomer residues (e.g., vinyl chloride). Microplastics (particles less than 5 mm) in the oceans are seriously harmful to many aquatic organisms, and some of which inevitably

As a result of the twentieth century development based on petroleum, coal, and natural gas exploitation, which were cheaply available, fossil fuels and their derivatives (e.g., fine chemicals, pharmaceuticals, detergents, plastics, fertilizers, lubricants, solvent, asphalt, and waxes)

and consequent global warming. Since these fossil resources are not considered as sustainable and they are prejudicial from the ecological point of view [5], there have been rising concerns over their global impact, which has led to the development of technologies focused on the production of fuels and materials from renewable carbon sources, such as plant biomass [6]. Biomass has the potential to reduce GHG emissions by replacing fossil fuels. The combustion of biomass feedstock has been considered as carbon neutral or low-carbon fuel, since the plant crops assimilate carbon dioxide from the atmosphere during the growth. Accordingly, the so-

The main advantages of biofuels include their biodegradable and renewable properties; the generation of employment and technical development in rural areas; decentralized production from locally available domestic biomass; besides the combustion based on carbon dioxide cycle as mentioned above [8–10]. A global volume of more than 100 Bln L per year of conventional biofuels has been obtained, which is referred to as the first-generation biofuels including ethanol from sugar or starch crops and biodiesel from oils and fats. In addition, there have been many efforts focused on the second- and third-generation biofuels produced from

Likewise, other chemicals and industrial products from fossil energy sources have been replaced by renewable ones. "Green" chemistry is a broad term referring to these compounds that support the sustainable development, from which the bioplastics can illustrate how the chemical industry is able to integrate sustainable innovation into a business model. On the other hand, the "green" chemistry companies must take into account efficient and less costly processes in order to make feasible their products commercialization [12]. Therefore, the economic viability of biofuel industry depends on facilities that integrate biomass conversion processes and equipment to produce value-added compounds, such as fuels, power, and chemicals. The larger the ability to derive value from biofuel, including byproducts and residues, the higher will be the feasibility of a bio-based industry from economic and environ-

A "green" biorefinery is a multifunctional and full-integrated system for biomass utilization. Besides the fuels obtained from "green" biomass, several products can be obtained from the "green" juice to the lignocellulosic materials, such as dyes, pigments, crude drugs, free amino acids, organic acids, enzymes, hormones, and minerals [5, 14]. Moreover, the biofuel byproducts have been a source of chemicals. Crude glycerol from transesterification of fats and oils,

in the atmosphere

end up in the human nutrition, the last consumer of this food chain [4].

have become a major global threat directly linked to increasing levels of CO2

called biofuels are a promising alternative to replace nonrenewable fuels [7, 8].

a broad range of nonedible biomass feedstock [11].

mental points of view [13].

246 Biofuels - State of Development

Biofuel refers to solid, liquid, or gaseous fuel obtained from renewable feedstocks, from which bioethanol and biodiesel are the most produced transportation fuel as potential substitutes for gasoline and diesel fuel [9, 36, 37]. According to their production technology, biofuels are classified into the first-, second-, third-, and fourth-generation biofuels (**Figure 1**). The first-generation biofuels are produced from edible sources, such as grains, oil seeds, sugar and starch crops, and animal fats. Well-established examples of the first-generation biofuels are ethanol from sugarcane in Brazil, corn ethanol in the USA, biodiesel from rapeseed oil in Germany, and palm oil–based biodiesel in Malaysia. The second-generation biofuels are obtained from nonedible feedstock, such as lignocellulosic materials including cereal straw, forest and wood residues, sugarcane bagasse, short-rotation crops, and vegetative grasses [37].

The second-generation biofuels are an alternative to mitigate the main concern about the first-generation biofuels: food versus fuel. An additional advantage is the utilization of agricultural byproducts and municipal solid wastes and thus lowering costs and improving the urban waste management [37]. The former Directorate-General for Energy and Transport has proposed the third- and fourth-generation biofuels, which are classified as advanced biofuels. The third-generation biofuels are obtained using molecular biology techniques, such as low-lignin content trees and genetically modified microalgae. The fourth-generation biofuels are those that should provide carbon capture and storage (CCS) processes with improved

**Figure 1.** The first-, second-, third-, and fourth-generation biofuels.

CO2 assimilation by genetically modified plants and CO<sup>2</sup> storage as geological formations by carbonation, crude oil, and gas headings [38].

The relative low increase in global oil production and rising prices of barrel between 2004 and 2009 were a boost to biofuel production [39]. Despite some previous experiences with biofuels such as in the 1970s with Brazilian National Alcohol Program [40] and in the 1990s with European biodiesel [41], only after 2003 major policy measures were legislated for promoting biofuel production in the EU and the USA followed by advancements in oil extraction technologies, which induced a global awareness about the requirement of alternative and ecological solutions regarding the depletion of petrochemical reserves and the environmental side effects from a century of its utilization. The International Energy Agency forecasts a percent global increase of transportation biofuels from 2% to up to 20% from 2012 to 2040, respectively [39, 42].

Nowadays, the USA, Brazil, and the EU have been the largest biofuel-producing countries whose the first-generation biofuels, bioethanol and biodiesel, are still the most well-established and current produced biofuels, which attend most of the commercial demand (**Figure 2**). However, there is still a big difference between the world ethanol and biodiesel production, while the first is predominant in the USA and Brazil accounting most of the biofuel production, the latter is mainly produced in the EU, which retains the largest biodiesel production [43, 44]. Bioethanol comprises more than 80% of liquid biofuels in the USA,

**Figure 2.** (A) Total biofuel production of main producing countries from 2011 to 2014. Regional distribution of world

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biofuel production in 2014: (B) bioethanol and (C) biodiesel [43].

**Figure 2.** (A) Total biofuel production of main producing countries from 2011 to 2014. Regional distribution of world biofuel production in 2014: (B) bioethanol and (C) biodiesel [43].

CO2

248 Biofuels - State of Development

assimilation by genetically modified plants and CO<sup>2</sup>

The relative low increase in global oil production and rising prices of barrel between 2004 and 2009 were a boost to biofuel production [39]. Despite some previous experiences with biofuels such as in the 1970s with Brazilian National Alcohol Program [40] and in the 1990s with European biodiesel [41], only after 2003 major policy measures were legislated for promoting biofuel production in the EU and the USA followed by advancements in oil extraction technologies, which induced a global awareness about the requirement of alternative and ecological solutions regarding the depletion of petrochemical reserves and the environmental side effects from a century of its utilization. The International Energy Agency forecasts a percent global increase of transportation biofuels from 2% to up to 20% from 2012 to 2040, respectively [39, 42]. Nowadays, the USA, Brazil, and the EU have been the largest biofuel-producing countries whose the first-generation biofuels, bioethanol and biodiesel, are still the most well-established and current produced biofuels, which attend most of the commercial demand (**Figure 2**).

carbonation, crude oil, and gas headings [38].

**Figure 1.** The first-, second-, third-, and fourth-generation biofuels.

storage as geological formations by

However, there is still a big difference between the world ethanol and biodiesel production, while the first is predominant in the USA and Brazil accounting most of the biofuel production, the latter is mainly produced in the EU, which retains the largest biodiesel production [43, 44]. Bioethanol comprises more than 80% of liquid biofuels in the USA, Brazil, Canada, Australia, and China, while the European biodiesel accounts for more than 60% of total biofuel produced in these countries [39].

Besides bioethanol and biodiesel fuels obtained from sugar fermentation and transesterification reaction of oils and fats, respectively, there are some alternatives consisting of liquid and gaseous biofuels, which are facing technological challenges of cost effectiveness and supporting structure for their economical viability. Pyrolysis is a high-temperature heating (300–900°C) of vegetative biomass in the absence of air resulting in three products: biochar, bio-oil, and syngas. Although this technique is relative old and was utilized in ancient China and by the indigenous Amazonians to generate biochar 100 years ago, the bio-oil is unstable, corrosive, and immiscible with hydrocarbon fuels and difficult to ignite, which needs a significant upgrading to be used

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Some liquid biofuels such as butanol, liquefied biomass, syngas complexes, and sugar hydrocarbons have been developed to meet the existing fossil fuel specifications and hence to minimize the infrastructure and engine compatibility issues. They are the "drop-in" biofuels. Nevertheless, many efforts must continue to be made for the economical viability and the establishment of the "drop-in" biofuels as a renewable alternative in the future [41, 47]. Biogas is a gaseous alternative to natural gas from anaerobic digestion of organic wastes, which is constituted of methane, carbon dioxide, and a small percentage of sulfur hydroxide, water vapor, and hydrogen [41, 48]. Despite the minor biogas utilization in the energy sector, there is an impressive global potential for anaerobic digestion from agricultural and domestic wastes that could supply one quarter of

Syngas is a gaseous fuel obtained from gasification or pyrolysis of vegetable sources and consists of carbon monoxide, hydrogen, carbon dioxide, and small percentages of methane, water vapor, sulfur hydroxide, carbon oxide sulfide, ammonia, and others. This product can be directly burned to generate electricity, or more commonly, it is purified for the synthesis of methanol, ethanol, methane, dimethyl ether, and other fuels. The hydrogen obtained from the syngas purification process can be used for electricity generation and as a vehicle fuel. The synthesis gas can also be processed to liquid hydrocarbons like diesel fuel via Fischer-Tropsch syn-

and water. The product distribution depends on different process parameters like temperature, pressure, and the catalyst material resulting in short- or long-chain hydrocarbons. However, the

Plastics are organic polymers with high molecular weight, which are synthetically produced. The expression bioplastics have commonly been used to make a distinction from petrochemical polymers, which is partially misleading, since a polymer derived from biomass is not necessarily biocompatible, biodegradable, and ecologically friendly [4]. Bioplastics fulfill at least one of these two characteristics: biomass derivative or biodegradability. Thus, a bioplastic must be bio-based, biodegradable, or both (**Figure 3**). Bioplastics exhibit the same or similar properties as conventional plastics with additional environmental benefits such as reduced carbon footprint, organic recycling, or both [51]. This is a broad and logical bioplastic defini-

purification process of syngas is still rather costly and energy consuming [10, 41, 50].

and CO into hydrocarbons

the current natural gas and cover 6% of the global primary energy demand [41, 49].

thesis, which is an exothermal polymerization process converting H2

**3. Bioplastics: bio-based and/or biodegradable plastics**

tion adopted by European Bioplastic Association [4, 51, 52].

as a petrol fuel alternative [41, 45, 46].

A sustainable alternative to petrochemical fuels and the environmental concern with such fuels have also drawn the attention of the international scientific community, which is reflected in the increasing number of biofuel-related publications. Approximately 50 additional papers were published every year regarding biofuels from 1990 to 2005. After 2005, this expanding rate increased to 550 biofuel-related papers. Most of publilshed papers on biofuels are still related to first-generation biofuels based on edible feedstocks, constituting 46% of biofuel publications from 1990 to 2014, while papers related to lignocellulosic biofuels total 40% of biofuel literature, from which remains 14% of published studies concerning algae third-generation biofuels [39].

Whereas bioethanol is the largest produced biofuel of the world, research studies on biodiesel production from vegetable oils constitute 60% of the literature on liquid biofuels. Jatropha and palm oil were the most widely studied feedstocks for biodiesel production followed by soybean and rapeseed oils. Among the most important lignocellulosic materials for the second-generation biofuel production are crop residues such as straw and bagasse; forest, municipal, and livestock wastes; and energy grasses. Finally, the algal feedstocks have received significant attention and have become one of the main biofuel categories. Therefore, the fast increase of biofuel-related publications can be considered as a direct result of research and development expenditure on biofuel science in the last years [39].

In 2015, several policies were finalized in favor of the biofuel market. In Brazil, the mandatory anhydrous ethanol blending ratio was increased from 25 to 27%. In the EU, the Renewable Energy Directive and the Fuel Quality Directive were reviewed in the transport sector by 2020, and the US Environmental Protection Agency proposed new mandates to increase the production levels of biofuels. Most of these political changes are driven by blending mandates and sustained fuel use to attend the demand of transportation sector. Future prospects report a modest expansion of the global ethanol production from 116 Bln L in 2015 to 128.4 Bln L by 2025, with half of this growth originating from Brazil, while a more prominent biodiesel production is expected for this period from 31 Bln L in 2015 to 41.4 Bln L by 2025 as a result of political incentives of the USA, Argentina, Brazil, Indonesia, and the EU [44].

Coarse grains and sugarcane are expected to remain the dominant feedstock for bioethanol production and vegetable oils to continue as the main biodiesel feedstock. Whereas the biodiesel production processes aiming at the utilization of nonagricultural biomass, waste oils, and animal fats are expected to develop in the EU and the USA, the second-generation ethanol from lignocellulosic materials is projected to share less than 1% of total ethanol production by 2025. According to these projections, biofuel production will consume 10.4% of coarse grains and 12% of vegetable oils. The ethanol industry will utilize 22% of global sugarcane crops to supply its production [44]. This prospect shows a continuous establishment of current technologies and evidences the need of developing competitive ones in order to make feasible the second-, third-, and fourth-generation biofuels, not only to spare petroleum reserves but also should replace this fossil fuel and, consequently, to diminish the environmental impacts attributed to its utilization with additional preservation of agricultural land intended for food crops.

Besides bioethanol and biodiesel fuels obtained from sugar fermentation and transesterification reaction of oils and fats, respectively, there are some alternatives consisting of liquid and gaseous biofuels, which are facing technological challenges of cost effectiveness and supporting structure for their economical viability. Pyrolysis is a high-temperature heating (300–900°C) of vegetative biomass in the absence of air resulting in three products: biochar, bio-oil, and syngas. Although this technique is relative old and was utilized in ancient China and by the indigenous Amazonians to generate biochar 100 years ago, the bio-oil is unstable, corrosive, and immiscible with hydrocarbon fuels and difficult to ignite, which needs a significant upgrading to be used as a petrol fuel alternative [41, 45, 46].

Brazil, Canada, Australia, and China, while the European biodiesel accounts for more than

A sustainable alternative to petrochemical fuels and the environmental concern with such fuels have also drawn the attention of the international scientific community, which is reflected in the increasing number of biofuel-related publications. Approximately 50 additional papers were published every year regarding biofuels from 1990 to 2005. After 2005, this expanding rate increased to 550 biofuel-related papers. Most of publilshed papers on biofuels are still related to first-generation biofuels based on edible feedstocks, constituting 46% of biofuel publications from 1990 to 2014, while papers related to lignocellulosic biofuels total 40% of biofuel literature, from which remains 14% of published studies concerning algae

Whereas bioethanol is the largest produced biofuel of the world, research studies on biodiesel production from vegetable oils constitute 60% of the literature on liquid biofuels. Jatropha and palm oil were the most widely studied feedstocks for biodiesel production followed by soybean and rapeseed oils. Among the most important lignocellulosic materials for the second-generation biofuel production are crop residues such as straw and bagasse; forest, municipal, and livestock wastes; and energy grasses. Finally, the algal feedstocks have received significant attention and have become one of the main biofuel categories. Therefore, the fast increase of biofuel-related publications can be considered as a direct result of research

In 2015, several policies were finalized in favor of the biofuel market. In Brazil, the mandatory anhydrous ethanol blending ratio was increased from 25 to 27%. In the EU, the Renewable Energy Directive and the Fuel Quality Directive were reviewed in the transport sector by 2020, and the US Environmental Protection Agency proposed new mandates to increase the production levels of biofuels. Most of these political changes are driven by blending mandates and sustained fuel use to attend the demand of transportation sector. Future prospects report a modest expansion of the global ethanol production from 116 Bln L in 2015 to 128.4 Bln L by 2025, with half of this growth originating from Brazil, while a more prominent biodiesel production is expected for this period from 31 Bln L in 2015 to 41.4 Bln L by 2025 as a result of

Coarse grains and sugarcane are expected to remain the dominant feedstock for bioethanol production and vegetable oils to continue as the main biodiesel feedstock. Whereas the biodiesel production processes aiming at the utilization of nonagricultural biomass, waste oils, and animal fats are expected to develop in the EU and the USA, the second-generation ethanol from lignocellulosic materials is projected to share less than 1% of total ethanol production by 2025. According to these projections, biofuel production will consume 10.4% of coarse grains and 12% of vegetable oils. The ethanol industry will utilize 22% of global sugarcane crops to supply its production [44]. This prospect shows a continuous establishment of current technologies and evidences the need of developing competitive ones in order to make feasible the second-, third-, and fourth-generation biofuels, not only to spare petroleum reserves but also should replace this fossil fuel and, consequently, to diminish the environmental impacts attributed to its utilization

and development expenditure on biofuel science in the last years [39].

political incentives of the USA, Argentina, Brazil, Indonesia, and the EU [44].

with additional preservation of agricultural land intended for food crops.

60% of total biofuel produced in these countries [39].

third-generation biofuels [39].

250 Biofuels - State of Development

Some liquid biofuels such as butanol, liquefied biomass, syngas complexes, and sugar hydrocarbons have been developed to meet the existing fossil fuel specifications and hence to minimize the infrastructure and engine compatibility issues. They are the "drop-in" biofuels. Nevertheless, many efforts must continue to be made for the economical viability and the establishment of the "drop-in" biofuels as a renewable alternative in the future [41, 47]. Biogas is a gaseous alternative to natural gas from anaerobic digestion of organic wastes, which is constituted of methane, carbon dioxide, and a small percentage of sulfur hydroxide, water vapor, and hydrogen [41, 48]. Despite the minor biogas utilization in the energy sector, there is an impressive global potential for anaerobic digestion from agricultural and domestic wastes that could supply one quarter of the current natural gas and cover 6% of the global primary energy demand [41, 49].

Syngas is a gaseous fuel obtained from gasification or pyrolysis of vegetable sources and consists of carbon monoxide, hydrogen, carbon dioxide, and small percentages of methane, water vapor, sulfur hydroxide, carbon oxide sulfide, ammonia, and others. This product can be directly burned to generate electricity, or more commonly, it is purified for the synthesis of methanol, ethanol, methane, dimethyl ether, and other fuels. The hydrogen obtained from the syngas purification process can be used for electricity generation and as a vehicle fuel. The synthesis gas can also be processed to liquid hydrocarbons like diesel fuel via Fischer-Tropsch synthesis, which is an exothermal polymerization process converting H2 and CO into hydrocarbons and water. The product distribution depends on different process parameters like temperature, pressure, and the catalyst material resulting in short- or long-chain hydrocarbons. However, the purification process of syngas is still rather costly and energy consuming [10, 41, 50].

#### **3. Bioplastics: bio-based and/or biodegradable plastics**

Plastics are organic polymers with high molecular weight, which are synthetically produced. The expression bioplastics have commonly been used to make a distinction from petrochemical polymers, which is partially misleading, since a polymer derived from biomass is not necessarily biocompatible, biodegradable, and ecologically friendly [4]. Bioplastics fulfill at least one of these two characteristics: biomass derivative or biodegradability. Thus, a bioplastic must be bio-based, biodegradable, or both (**Figure 3**). Bioplastics exhibit the same or similar properties as conventional plastics with additional environmental benefits such as reduced carbon footprint, organic recycling, or both [51]. This is a broad and logical bioplastic definition adopted by European Bioplastic Association [4, 51, 52].

compounds are current being developed. PBAT is produced from 1,4-butanediol (1,4-BDO), terephthalate, and adipic acid. The bio-based adipic acid is not available yet for commercialization, and thus, PBAT can theoretically be up to 50% bio-based. Likewise, PBS is produced from 1,4- BDO and succinic acid, which can also theoretically be 100% bio-based [56]. Therefore, in a near future, PBAT and PBS are expected to be into the family of bio-based and biodegradable plastics.

Since most of conventional plastics and fuels are made from petrochemical compounds, in the opposite way, bioproducts derived from biomass such as biofuels and bioplastics share several favorable characteristics. All the advantages concerning the biofuel and bioplastic utilization can be addressed to a sustainable process, which has mainly driven by energy saving and reduction of GHG emissions [4]. According to the Intergovernmental Panel on Climate

mum limit to avoid a global warning increase of 2°C, which means a reduction of 50% of GHG emissions by 2050 [10, 57]. One alternative to reducing GHG emissions is the use of low carbon fuels [10] and bio-based plastics [4]. Since they are obtained from plant biomass, the

The rural development with employment opportunities can be achieved from biomass utilization to produce bioproducts such as biofuels and biopolymers [4, 5, 10]. The job creation is a global priority, especially in developing countries with high unemployment levels [10]. Most of references regarding biofuels and bioplastics agree that these bioproducts reduce the oil dependence as a sustainable alternative from diversified feedstock [3–5, 9, 10]. Most of crude oil reserves are centralized and located within countries under political uncertainties [10]. Among the top 15 countries with the world's biggest crude oil reserves are Middle Eastern countries, Venezuela, Russia, Libya, Nigeria, Kazakhstan, China, and Brazil [58]. Therefore, biofuels and bioplastics exhibit an advantage regarding the security of energy supply sup-

The research reports and reviews have constantly warned about the depletion of fossil fuel reserves like petroleum, natural gas, and coal [9, 36]. On the other hand, 100 Bln tonnes of crude oil and natural gas have been discovered in the last 40 years; however, the consumption rate of these resources has also increased. The US alone consumes 25% of total oil supply, while having 1.6% of global oil reserves. According to some authors, at the current consumption rate of oil supplies, the fossil fuel reserves will be depleted within 40–70 years [1]. Regardless the period of time for oil reserves depletion, it is a true fact that they are finite, and despite the recent increase in their exploitation, the future of petrochemical sources remains uncertain [39].

The rising consumer consciousness and environmental awareness are the biggest drivers for biofuel and bioplastic production. The global society has become aware of environment concerns and has continuously improved its sustainability standards. Therefore, there is a global trend on using products from renewable sources even in the face of low oil prices [4, 10]. Several

concentration of 450 ppm within the global atmosphere is the maxi-

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consumption during photosynthesis,

**4. Biofuels and bioplastics in a circular economy**

can be at least minimized by plant CO2

ported by a local production from available domestic biomass [10].

reducing the carbon footprint in the global atmosphere [5].

Change (IPCC), the CO2

released CO2

**Figure 3.** Bioplastics: bio-based and nonbiodegradable (blue); fossil-based and biodegradable (yellow); bio-based and biodegradable (green).

One of the bioplastic families is bio-based (or partially bio-based) and nonbiodegradable plastics, such as polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET), also called as "drop-in" bioplastics, since they are the renewable alternative for petroleum-based plastics [53]. Polyvinyl chloride (PVC) is another commodity example of a nonbiodegradable, and in fact, one of the least environment-friendly synthetic plastics produced from renewable resources [4]. Bio-PE has been produced by Braskem (Brazil) on a large scale. A partially biobased PET has been used for beverage bottles. Other examples of bio-based and nonbiodegradable plastics include polyamides (PA); polyesters such as polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT); polyurethanes (PUR); and polyepoxides. Important examples of bio-based and biodegradable plastics are thermoplastic starch blends (TPS), cellulose-acetate plastics (CA), poly(lactic acid) (PLA), and polyhydroxyalkanoates (PHAs). They are primarily used for short-lived applications, such as packaging and disposable products [53]. They are recognized as ecologically friendly, and some of them have been used for medical applications due to their lower or zero toxicity and high biocompatibility [54].

The third group constituted by non-bio-based and biodegradable polymers from fossil resources is a small group used in combination with other bioplastics, such as starch blends or applications, in which their biodegradable and mechanical properties [53] are desired. Examples of biodegradable petrochemical-based plastics are polycaprolactone (PCL), polyglycolide (PGA), and polyvinyl alcohol (PVOH) [4, 55]. Poly(butylene adipate-*co*-terephthalate) (PBAT) and polybutylene succinate (PBS) are bioplastics in class transition, since partially bio-based versions of these compounds are current being developed. PBAT is produced from 1,4-butanediol (1,4-BDO), terephthalate, and adipic acid. The bio-based adipic acid is not available yet for commercialization, and thus, PBAT can theoretically be up to 50% bio-based. Likewise, PBS is produced from 1,4- BDO and succinic acid, which can also theoretically be 100% bio-based [56]. Therefore, in a near future, PBAT and PBS are expected to be into the family of bio-based and biodegradable plastics.

#### **4. Biofuels and bioplastics in a circular economy**

One of the bioplastic families is bio-based (or partially bio-based) and nonbiodegradable plastics, such as polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET), also called as "drop-in" bioplastics, since they are the renewable alternative for petroleum-based plastics [53]. Polyvinyl chloride (PVC) is another commodity example of a nonbiodegradable, and in fact, one of the least environment-friendly synthetic plastics produced from renewable resources [4]. Bio-PE has been produced by Braskem (Brazil) on a large scale. A partially biobased PET has been used for beverage bottles. Other examples of bio-based and nonbiodegradable plastics include polyamides (PA); polyesters such as polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT); polyurethanes (PUR); and polyepoxides. Important examples of bio-based and biodegradable plastics are thermoplastic starch blends (TPS), cellulose-acetate plastics (CA), poly(lactic acid) (PLA), and polyhydroxyalkanoates (PHAs). They are primarily used for short-lived applications, such as packaging and disposable products [53]. They are recognized as ecologically friendly, and some of them have been used for medi-

**Figure 3.** Bioplastics: bio-based and nonbiodegradable (blue); fossil-based and biodegradable (yellow); bio-based and

biodegradable (green).

252 Biofuels - State of Development

cal applications due to their lower or zero toxicity and high biocompatibility [54].

The third group constituted by non-bio-based and biodegradable polymers from fossil resources is a small group used in combination with other bioplastics, such as starch blends or applications, in which their biodegradable and mechanical properties [53] are desired. Examples of biodegradable petrochemical-based plastics are polycaprolactone (PCL), polyglycolide (PGA), and polyvinyl alcohol (PVOH) [4, 55]. Poly(butylene adipate-*co*-terephthalate) (PBAT) and polybutylene succinate (PBS) are bioplastics in class transition, since partially bio-based versions of these Since most of conventional plastics and fuels are made from petrochemical compounds, in the opposite way, bioproducts derived from biomass such as biofuels and bioplastics share several favorable characteristics. All the advantages concerning the biofuel and bioplastic utilization can be addressed to a sustainable process, which has mainly driven by energy saving and reduction of GHG emissions [4]. According to the Intergovernmental Panel on Climate Change (IPCC), the CO2 concentration of 450 ppm within the global atmosphere is the maximum limit to avoid a global warning increase of 2°C, which means a reduction of 50% of GHG emissions by 2050 [10, 57]. One alternative to reducing GHG emissions is the use of low carbon fuels [10] and bio-based plastics [4]. Since they are obtained from plant biomass, the released CO2 can be at least minimized by plant CO2 consumption during photosynthesis, reducing the carbon footprint in the global atmosphere [5].

The rural development with employment opportunities can be achieved from biomass utilization to produce bioproducts such as biofuels and biopolymers [4, 5, 10]. The job creation is a global priority, especially in developing countries with high unemployment levels [10]. Most of references regarding biofuels and bioplastics agree that these bioproducts reduce the oil dependence as a sustainable alternative from diversified feedstock [3–5, 9, 10]. Most of crude oil reserves are centralized and located within countries under political uncertainties [10]. Among the top 15 countries with the world's biggest crude oil reserves are Middle Eastern countries, Venezuela, Russia, Libya, Nigeria, Kazakhstan, China, and Brazil [58]. Therefore, biofuels and bioplastics exhibit an advantage regarding the security of energy supply supported by a local production from available domestic biomass [10].

The research reports and reviews have constantly warned about the depletion of fossil fuel reserves like petroleum, natural gas, and coal [9, 36]. On the other hand, 100 Bln tonnes of crude oil and natural gas have been discovered in the last 40 years; however, the consumption rate of these resources has also increased. The US alone consumes 25% of total oil supply, while having 1.6% of global oil reserves. According to some authors, at the current consumption rate of oil supplies, the fossil fuel reserves will be depleted within 40–70 years [1]. Regardless the period of time for oil reserves depletion, it is a true fact that they are finite, and despite the recent increase in their exploitation, the future of petrochemical sources remains uncertain [39].

The rising consumer consciousness and environmental awareness are the biggest drivers for biofuel and bioplastic production. The global society has become aware of environment concerns and has continuously improved its sustainability standards. Therefore, there is a global trend on using products from renewable sources even in the face of low oil prices [4, 10]. Several companies have followed this tendency and have associated their brand logos to renewable or biodegradable products as ecologically friendly companies with social and environment responsibility [4, 59]. Biodegradability and compostability are interesting properties of some products obtained from biomass, especially concerning short-lived or disposable plastic materials, which account 50% of the total plastic production [4, 34, 35]. In general, about 10% of municipal waste is consisted of plastics, primarily constituted of fossil-based PE, PET, PP, PS, and PVC [1]. Composting is other alternative solution for short-lived and disposable bioplastics, which can be disintegrated under microbial fermentation resulting in humus-rich soil. Therefore, composting is a good alternative for packaging materials, such as agricultural and horticulture films. Further, compostable plastics is an additional effort for waste stream management [51, 60].

#### **5. Bioplastic market and future prospects**

The bioplastic industry is a young and innovative sector [51]. The bio-based plastics share has increased from 1.4 to 2% of global polymer capacity, from 2011 to 2013 [56]. Thereafter, in recent years, this share has been stagnating, and the bioplastic growth rate has become the same of any plastic. While a prominent production capacity growth of 10% per year was observed from 2012 to 2014, this growth rate decelerated to 4% per year from 2015 onwards, which can be attributed to the lower oil prices, the unfavorable political support, a slower growth rate of the capacity utilization, and global debates about land and food crops use. However, the bio-based and biodegradable PHAs, the high-performance PA, and "drop-in" PET are exceptions that have shown fast increase rates of their production capacities [61].

In 2016, the bio-based plastic income was about \$ 15 billion worldwide [61] with more than 43% of total bioplastic produced in Asia. The USA, Latin America, and Asia have implemented measures to attract investment and promote market development to achieve their production goal. The European bioplastic market is still restricted by a lack of economical and political incentives for scaling-up its production capacity. As one can see in **Figure 4**, the worldwide production capacity is forecasted to increase from 4.2 million tonnes in 2016 to 6.1 million tonnes by 2021 [51]. If the bio-based thermosets such as epoxies, ethylene propylene diene monomer rubber (EPDM) and CA were included in this forecast, the increase values of bioplastic production capacities can be extrapolated to 6.6–8.5 million tonnes for the same period [61].

Currently, the bioplastic market is dominated by bio-based and nonbiodegradable plastics with highlights of bio-based PUR and "drop-in" PET. "Drop-in" plastics exhibit the same properties and are identical to their petrochemical counterparts and thus do not demand further adaptation for processing. Some bioplastics have lower material performance and end up being utilized for blending with petrochemical polymers. Therefore, creating highperformance biopolymers at a competitive cost is still a key concern [12]. PUR market share is expected to remain stable, whereas PET share is forecasted to grow from 22.8% in 2016 to 28.2% by 2021 [61]. One of the big investors of bio-based PET has been The Coca-Cola Company with its Plant Bottle technology [59]. Bio-based PE is another "drop-in" bioplastic, which has been obtained from sugarcane-derived ethylene by Braskem Company in Brazil [4]. Among the bio-based and biodegradable polymers, Starch blends and CA markets are

expected to continue steady, and PLA and PHA production capacities are expected to consid-

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**Figure 4.** Global production capacities of bioplastics by material type in 2016 (A) and expected for 2021 (B) [51, 61].

There are infinite possible applications for bioplastics including textiles, construction and building, electrics and electronics, consumer goods, agriculture and horticultures, and automotive, although their largest application field is still the packaging, which shared almost 40% of the total bioplastic market in 2016. This percentage is expected to increase to 42% by 2021 (**Figure 5**). In the automotive industry, bioplastics make cars lighter to save fuel and,

consecutively, make them to reduce their carbon exhaustion [51].

erably grow in the next years [61].

companies have followed this tendency and have associated their brand logos to renewable or biodegradable products as ecologically friendly companies with social and environment responsibility [4, 59]. Biodegradability and compostability are interesting properties of some products obtained from biomass, especially concerning short-lived or disposable plastic materials, which account 50% of the total plastic production [4, 34, 35]. In general, about 10% of municipal waste is consisted of plastics, primarily constituted of fossil-based PE, PET, PP, PS, and PVC [1]. Composting is other alternative solution for short-lived and disposable bioplastics, which can be disintegrated under microbial fermentation resulting in humus-rich soil. Therefore, composting is a good alternative for packaging materials, such as agricultural and horticulture films. Further, compostable plastics is an additional effort for waste stream management [51, 60].

The bioplastic industry is a young and innovative sector [51]. The bio-based plastics share has increased from 1.4 to 2% of global polymer capacity, from 2011 to 2013 [56]. Thereafter, in recent years, this share has been stagnating, and the bioplastic growth rate has become the same of any plastic. While a prominent production capacity growth of 10% per year was observed from 2012 to 2014, this growth rate decelerated to 4% per year from 2015 onwards, which can be attributed to the lower oil prices, the unfavorable political support, a slower growth rate of the capacity utilization, and global debates about land and food crops use. However, the bio-based and biodegradable PHAs, the high-performance PA, and "drop-in" PET are exceptions that have shown fast increase rates of their production capacities [61].

In 2016, the bio-based plastic income was about \$ 15 billion worldwide [61] with more than 43% of total bioplastic produced in Asia. The USA, Latin America, and Asia have implemented measures to attract investment and promote market development to achieve their production goal. The European bioplastic market is still restricted by a lack of economical and political incentives for scaling-up its production capacity. As one can see in **Figure 4**, the worldwide production capacity is forecasted to increase from 4.2 million tonnes in 2016 to 6.1 million tonnes by 2021 [51]. If the bio-based thermosets such as epoxies, ethylene propylene diene monomer rubber (EPDM) and CA were included in this forecast, the increase values of bioplastic production capacities can be extrapolated to 6.6–8.5 million tonnes for the same period [61]. Currently, the bioplastic market is dominated by bio-based and nonbiodegradable plastics with highlights of bio-based PUR and "drop-in" PET. "Drop-in" plastics exhibit the same properties and are identical to their petrochemical counterparts and thus do not demand further adaptation for processing. Some bioplastics have lower material performance and end up being utilized for blending with petrochemical polymers. Therefore, creating highperformance biopolymers at a competitive cost is still a key concern [12]. PUR market share is expected to remain stable, whereas PET share is forecasted to grow from 22.8% in 2016 to 28.2% by 2021 [61]. One of the big investors of bio-based PET has been The Coca-Cola Company with its Plant Bottle technology [59]. Bio-based PE is another "drop-in" bioplastic, which has been obtained from sugarcane-derived ethylene by Braskem Company in Brazil [4]. Among the bio-based and biodegradable polymers, Starch blends and CA markets are

**5. Bioplastic market and future prospects**

254 Biofuels - State of Development

**Figure 4.** Global production capacities of bioplastics by material type in 2016 (A) and expected for 2021 (B) [51, 61].

expected to continue steady, and PLA and PHA production capacities are expected to considerably grow in the next years [61].

There are infinite possible applications for bioplastics including textiles, construction and building, electrics and electronics, consumer goods, agriculture and horticultures, and automotive, although their largest application field is still the packaging, which shared almost 40% of the total bioplastic market in 2016. This percentage is expected to increase to 42% by 2021 (**Figure 5**). In the automotive industry, bioplastics make cars lighter to save fuel and, consecutively, make them to reduce their carbon exhaustion [51].

such as Italy and France have started to devote strong political support for biodegradable plastics, especially for the packaging sector, which is the biggest in the plastic market. The packaging industry has been interested in biodegradable plastics for short-lived and disposable applications. In agriculture, most of applications are limited to biodegradable plastics. Although the biodegradable polymers are not market leaders, they are expected to grow

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Among the aliphatic biodegradable polymers, the main population of degrading microorganisms in different ecosystems has followed the order: PHAs = PCL > PBS > PLA [55]. PCL is fossil-based [4], and currently, PBS and PBAT are not fully bio-based. PBS is constituted of 1,4-BDO and succinic acid that are primarily fossil-based, although they could theoretically be obtained from microbial cultivation. Bio-based 1,4-BDO entered the market only in 2016. BioPBS is produced exclusively in Asia by Public Company Limited and Mitsubishi Chemical Corporation (PTT MCC Biochem) in Thailand [62]. Additional projects are not expected for the next years due to low oil prices. PLA has attracted a growing interest and nowadays accounts 20% of biodegradable plastic market [4]. The most dynamic development is forecasted for PHAs, whose production capacity is still small. However, the PHA market is fore-

Poly(lactic acid) (PLA), also called polylactide, refers to polymers based on lactic acid molecules, which is abbreviated as PLA. Therefore, the starting compound of PLA is lactic acid, a monomer that can be L(+) lactic acid or D(−) lactic acid due to the presence of a chiral carbon atom. The cyclization of two lactic acid molecules results in a dimer called lactide. Accordingly, there are two homochiral lactide L,L and D,D and a heterochiral mesolactide L,D. *Lactococcus lactis* LL0018 and *Lactobacillus casei* produce L-lactic acid, while *Lactobacillus delbrueckii* LD0025 and *Sporolactobacillus inulinus* SI0073 produce D-lactic acid, with up to 99% purity. *Lactobacillus helveticus* LH0030 is able to produce a racemic lactic acid, containing almost an equal mixture of L-lactic acid and D-lactic acid. Thus, the final lactic acid content is directly dependent of the fermentation process. Thereafter, a major concern is the purification of culture broth in order to obtain pure lactic acid. The lactic acid polymerization methods provide high molar mass polymers with high chiral purity, which are primarily based on catalysts with Sn and Zn metal, resulting in polymers with molar

[63]. The most common route to obtain PLA is ring-opening polymeriza-

tion of the intermediate dilactide. Direct condensation of lactic acid generally results in

The PLA currently available is based on linear macromolecules and presents low melting temperature. Consequently, more research must be developed aiming to improve the physical properties of such PLA [63]. PLA is a thermoplastic and is converted to a variety of products by injection molding, blow molding, foaming film extrusion, and fiber extrusion. The PLA applications include geotextile, agricultural film, packaging, 3D printing, absorbable sutures, and prosthetic devices [64]. The PLA is 100% bio-based and biodegradable under certain conditions. Nature Works is a leader company of PLA production. Among new bio-based polymers, PLA is the most well-established, and its market is expected to grow annually at a rate

of 10% until 2021, with comparable prices to fossil-based plastics [61].

strongly supported by environmental concerns [61].

seen to grow almost three fold by 2021 [61].

**6.1. Poly(lactic acid) (PLA)**

masses up to 106

lower molecular mass [64].

**Figure 5.** Global production capacities of bioplastics by market segment in 2016 (A) and expected for 2021 (B) [51, 61].

#### **6. PLA and PHAs: promising bio-based and biodegradable plastics**

Several companies have introduced starch and polyethylene blends as degradable materials for a number of short-lived applications, such as mulch films, beverage bottles, food containers, and plastic bags. Whereas starch component can be degraded, the polyethylene residues remain in the ecosystems. Therefore, many companies have failed associating plant-based blends with misleading biodegradable properties. Thenceforth, in order to restore the credibility of the bioplastic industry, the standard organizations have been concerned with distinguishing degradable, biodegradable, and compostable plastics [12]. Further, some countries such as Italy and France have started to devote strong political support for biodegradable plastics, especially for the packaging sector, which is the biggest in the plastic market. The packaging industry has been interested in biodegradable plastics for short-lived and disposable applications. In agriculture, most of applications are limited to biodegradable plastics. Although the biodegradable polymers are not market leaders, they are expected to grow strongly supported by environmental concerns [61].

Among the aliphatic biodegradable polymers, the main population of degrading microorganisms in different ecosystems has followed the order: PHAs = PCL > PBS > PLA [55]. PCL is fossil-based [4], and currently, PBS and PBAT are not fully bio-based. PBS is constituted of 1,4-BDO and succinic acid that are primarily fossil-based, although they could theoretically be obtained from microbial cultivation. Bio-based 1,4-BDO entered the market only in 2016. BioPBS is produced exclusively in Asia by Public Company Limited and Mitsubishi Chemical Corporation (PTT MCC Biochem) in Thailand [62]. Additional projects are not expected for the next years due to low oil prices. PLA has attracted a growing interest and nowadays accounts 20% of biodegradable plastic market [4]. The most dynamic development is forecasted for PHAs, whose production capacity is still small. However, the PHA market is foreseen to grow almost three fold by 2021 [61].

#### **6.1. Poly(lactic acid) (PLA)**

**Figure 5.** Global production capacities of bioplastics by market segment in 2016 (A) and expected for 2021 (B) [51, 61].

Several companies have introduced starch and polyethylene blends as degradable materials for a number of short-lived applications, such as mulch films, beverage bottles, food containers, and plastic bags. Whereas starch component can be degraded, the polyethylene residues remain in the ecosystems. Therefore, many companies have failed associating plant-based blends with misleading biodegradable properties. Thenceforth, in order to restore the credibility of the bioplastic industry, the standard organizations have been concerned with distinguishing degradable, biodegradable, and compostable plastics [12]. Further, some countries

**6. PLA and PHAs: promising bio-based and biodegradable plastics**

256 Biofuels - State of Development

Poly(lactic acid) (PLA), also called polylactide, refers to polymers based on lactic acid molecules, which is abbreviated as PLA. Therefore, the starting compound of PLA is lactic acid, a monomer that can be L(+) lactic acid or D(−) lactic acid due to the presence of a chiral carbon atom. The cyclization of two lactic acid molecules results in a dimer called lactide. Accordingly, there are two homochiral lactide L,L and D,D and a heterochiral mesolactide L,D. *Lactococcus lactis* LL0018 and *Lactobacillus casei* produce L-lactic acid, while *Lactobacillus delbrueckii* LD0025 and *Sporolactobacillus inulinus* SI0073 produce D-lactic acid, with up to 99% purity. *Lactobacillus helveticus* LH0030 is able to produce a racemic lactic acid, containing almost an equal mixture of L-lactic acid and D-lactic acid. Thus, the final lactic acid content is directly dependent of the fermentation process. Thereafter, a major concern is the purification of culture broth in order to obtain pure lactic acid. The lactic acid polymerization methods provide high molar mass polymers with high chiral purity, which are primarily based on catalysts with Sn and Zn metal, resulting in polymers with molar masses up to 106 [63]. The most common route to obtain PLA is ring-opening polymerization of the intermediate dilactide. Direct condensation of lactic acid generally results in lower molecular mass [64].

The PLA currently available is based on linear macromolecules and presents low melting temperature. Consequently, more research must be developed aiming to improve the physical properties of such PLA [63]. PLA is a thermoplastic and is converted to a variety of products by injection molding, blow molding, foaming film extrusion, and fiber extrusion. The PLA applications include geotextile, agricultural film, packaging, 3D printing, absorbable sutures, and prosthetic devices [64]. The PLA is 100% bio-based and biodegradable under certain conditions. Nature Works is a leader company of PLA production. Among new bio-based polymers, PLA is the most well-established, and its market is expected to grow annually at a rate of 10% until 2021, with comparable prices to fossil-based plastics [61].

#### **6.2. Polyhydroxyalkanoates (PHAs)**

Polyhydroxyalkanoates (PHAs) are microbial aliphatic polyesters synthesized as intracellular granules under nutrient imbalance and excess carbon source by several bacteria [65]. PHAs are a family of polymers constituted of monomers ranging from 3 to over 14 carbon atoms with more than 150 different monomer composition [3, 52]. PHAs have been classified into short-, medium-, and long-chain length PHAs (PHASCL, PHAMCL, and PHALCL, respectively). PHASCL with monomers consisting of 3–5 carbon atoms exhibit thermoplastic properties, whereas PHAMCL are constituted of monomers ranging from 5 to 14 carbon atoms, which are elastomeric materials. Poly(3-hydroxybutyrate) (PHB) is the most common and studied PHA. The PHA constituents are directly related to the carbon sources utilized for bacterial cultivations and the metabolic role of PHA synthases [3]. Such variety permits utilize PHAs in a large number of applications, such as packaging materials, biocompatible implants, and controlled drug delivery system [66].

PHAs are fully biodegradable and biocompatible and so are attractive for medical uses. They also meet the standard specification for marine degradability, which can be a biodegradable alternative for plastic wastes that end up within the ocean and are fragmented as microplastics. Furthermore, PHAs are compostable and at the same time exhibit good resistance to grease and oils besides boiling water [4]. Several companies are involved in the PHA market, although it is still small, mainly attributed to their relative high cost of production. However, PHA producers are optimistic, and several sugar companies are investing in PHAs, which are expected to triple their production capacity by 2021 [61].

#### **7. Biofuel feedstocks for PLA and PHA production**

The fermentation routes represent the most active areas of biopolymer production, which are generally performed at biorefineries based on particular agricultural feedstocks. A future trend is the utilization of multiple feedstocks according to the available resources and economic conditions, in order to increase the feasibility of bioplastic production [12]. This is also applicable to biofuels that are dependent on specific biomass sources, which are mostly terrestrial plants [9]. As aforementioned, PLA and PHAs are typically obtained from microbial cultivation and so can be adapted to multiple feedstocks. Particularly, PHA-producing bacteria are naturally very versatile and produce these biopolymers from many carbon sources. Next, it is shown some examples of PLA and PHA production from biofuel feedstocks and related byproducts, which may support a biorefinery model comprising biofuels and these bio-based and biodegradable plastics. Further, **Figure 6** presents a flow chart describing possible routes involving biofuels, PLA, and PHA bioplastics.

properties, and most of them exhibit low lactic acid production. However, many groups explore the acid or enzyme hydrolysis of starch compounds, such as wheat, corn, cassava, rice, potato, barley, rye, and sorghum, with subsequent use of sugars for lactic acid fermentation [67]. In the same way, starch has been a suitable carbon source for PHA production, including corn [68], potato [69], and cassava starch [70]. PHAs and PLAs have also been blended with starch

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Molasses is a high sugar co-product generated from sugar manufacturing industries [72]. Sugarcane molasses have been utilized for ethanol production in Brazil, while beet molasses

materials, resulting in different physicochemical properties [4, 71].

**Figure 6.** Common pathways for biofuels, PLA, and PHA production.

**7.2. Molasses**

#### **7.1. Starch**

Starch is a mixture of glucans, and consequently, a source of glucose obtained from various plants [67]. Starch has widely been utilized for bioethanol production, especially in US, where it is mainly extracted from corn crops [11], and it is also a raw material for starch blends, an established sector of bioplastic market [61]. Only few lactic acid bacteria possess starch-degrading

**Figure 6.** Common pathways for biofuels, PLA, and PHA production.

properties, and most of them exhibit low lactic acid production. However, many groups explore the acid or enzyme hydrolysis of starch compounds, such as wheat, corn, cassava, rice, potato, barley, rye, and sorghum, with subsequent use of sugars for lactic acid fermentation [67]. In the same way, starch has been a suitable carbon source for PHA production, including corn [68], potato [69], and cassava starch [70]. PHAs and PLAs have also been blended with starch materials, resulting in different physicochemical properties [4, 71].

#### **7.2. Molasses**

**6.2. Polyhydroxyalkanoates (PHAs)**

258 Biofuels - State of Development

controlled drug delivery system [66].

expected to triple their production capacity by 2021 [61].

**7. Biofuel feedstocks for PLA and PHA production**

sible routes involving biofuels, PLA, and PHA bioplastics.

**7.1. Starch**

Polyhydroxyalkanoates (PHAs) are microbial aliphatic polyesters synthesized as intracellular granules under nutrient imbalance and excess carbon source by several bacteria [65]. PHAs are a family of polymers constituted of monomers ranging from 3 to over 14 carbon atoms with more than 150 different monomer composition [3, 52]. PHAs have been classified into short-, medium-, and long-chain length PHAs (PHASCL, PHAMCL, and PHALCL, respectively). PHASCL with monomers consisting of 3–5 carbon atoms exhibit thermoplastic properties, whereas PHAMCL are constituted of monomers ranging from 5 to 14 carbon atoms, which are elastomeric materials. Poly(3-hydroxybutyrate) (PHB) is the most common and studied PHA. The PHA constituents are directly related to the carbon sources utilized for bacterial cultivations and the metabolic role of PHA synthases [3]. Such variety permits utilize PHAs in a large number of applications, such as packaging materials, biocompatible implants, and

PHAs are fully biodegradable and biocompatible and so are attractive for medical uses. They also meet the standard specification for marine degradability, which can be a biodegradable alternative for plastic wastes that end up within the ocean and are fragmented as microplastics. Furthermore, PHAs are compostable and at the same time exhibit good resistance to grease and oils besides boiling water [4]. Several companies are involved in the PHA market, although it is still small, mainly attributed to their relative high cost of production. However, PHA producers are optimistic, and several sugar companies are investing in PHAs, which are

The fermentation routes represent the most active areas of biopolymer production, which are generally performed at biorefineries based on particular agricultural feedstocks. A future trend is the utilization of multiple feedstocks according to the available resources and economic conditions, in order to increase the feasibility of bioplastic production [12]. This is also applicable to biofuels that are dependent on specific biomass sources, which are mostly terrestrial plants [9]. As aforementioned, PLA and PHAs are typically obtained from microbial cultivation and so can be adapted to multiple feedstocks. Particularly, PHA-producing bacteria are naturally very versatile and produce these biopolymers from many carbon sources. Next, it is shown some examples of PLA and PHA production from biofuel feedstocks and related byproducts, which may support a biorefinery model comprising biofuels and these bio-based and biodegradable plastics. Further, **Figure 6** presents a flow chart describing pos-

Starch is a mixture of glucans, and consequently, a source of glucose obtained from various plants [67]. Starch has widely been utilized for bioethanol production, especially in US, where it is mainly extracted from corn crops [11], and it is also a raw material for starch blends, an established sector of bioplastic market [61]. Only few lactic acid bacteria possess starch-degrading

Molasses is a high sugar co-product generated from sugar manufacturing industries [72]. Sugarcane molasses have been utilized for ethanol production in Brazil, while beet molasses is more common in Southeastern Europe, North America, and Asia, where it is primarily used for sugar production [40]. *L. delbrueckii* has been generally a lactic acid–producing bacteria using this carbon source, whose most abundant sugar is sucrose [73]. PHB is the most common product from molasses, since the sucrose content can be converted to acetyl-CoA and after to 3-hydroxybutyryl-CoA, the building block utilized by PHA synthase for PHB polymerization [3]. *Azotobacter vinelandii* and *Bacillus megaterium* are examples of PHB-producing bacteria utilizing sugarcane molasses [74, 75]. PHAMCL production has also been reported from *Pseudomonas corrugata* from soybean molasses [76].

assimilate the sugars from enzymatic hydrolysis of wheat bran, in which it was utilized a

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Nowadays, the crude glycerol is mainly obtained as a byproduct from the transesterification process of oils and fats for biodiesel production, which generates about 10% glycerol [83]. Since purified glycerol is a high-value chemical, alternative solutions are required to crude glycerol refining and one of the possible keys for this issue is the glycerol utilization in its crude form as carbon source in microbial cultivations, in order to obtain value-added chemicals such as bioplastics [84]. A glucose-affected mutant of *Cupriavidus necator*, former *Ralstonia eutropha* and a traditional PHA-producing strain, is able to accumulate PHB from crude glycerol [85]. Additionally, new wild bacterial strains have been isolated from the environment such as *Pandoraea* sp., which is able not only to produce PHAs from crude glycerol but also from sugarcane molasses and waste cooking oil, although the best polymer yields were obtained from crude glycerol [24].

Biogas is a renewable gaseous fuel alternative to natural gas, which is generated from anaerobic digestion of organic wastes by numerous bacteria. The main component of biogas is methane [41]. Over 300 bacterial strains, including *Methylocystis paravus*, *Methylosinus sporium*, and *Methylocella tundra*, have shown the ability to synthesize PHB from methane [86]. Furthermore, the integration of PHA-rich biomass production into a municipal waste water treatment plant with sludge digestion has been proposed to support the biogas and PHA production [87]. Synthesis gas or syngas is another gaseous biofuel obtained from gasification or pyrolysis of biomass feedstock. Carbon monoxide, hydrogen, and carbon dioxide are the most abundant constituents of syngas [41]. The purple nonsulfur bacterium *Rhodospirillum rubrum* is able to utilize carbon monoxide and carbon dioxide and has also been a model

Microalgae, such as blue-green algae, dinoflagellates, and bacillariophyta, can have from 8 to 31% of their dry weight constituted of lipids. They have been revealed as the best potential source for oil extraction compared to common biofuel crops [9]. Cyanobacteria are a good candidate for bioplastic production, which present the ability to grow in a variety of environments. Genetically engineered cyanobacteria were transformed with the genes encoding PHB synthesis, and their metabolisms have been extremely investigated aiming to establish new routes for PHA synthesis. Additionally, PLA/algae blends can be prepared and employed in bone and cartilage tissue engineering due to their biodegradability and biocompatibility [89]. Therefore, microalgae are new

PHB production has been described in lactic acid bacteria for the genera *Lactobacillus*, *Lactococcus*, *Pediococcus*, and *Streptococcus*. *Cupriavidus necator*, *L. delbrueckii*, and *Propionibacterium* have been cultivated in a bacterial consortia, which resulted in a co-production of lactic acid and

organism for the synthesis of PHASCL and PHAMCL from syngas [88].

and promising branch not only for biofuels but also for bioplastics.

**7.8. Simultaneous production of PLA and PHAs and their polymer blends**

crude enzyme preparation from *Aspergillus oryzae* [82].

**7.5. Crude glycerol**

**7.6. Biogas and syngas**

**7.7. Microalgae**

#### **7.3. Vegetable oil**

Vegetable oils are feedstock for biofuels with biodiesel representing a well-known example, which is mostly obtained from soybean oil in US and Brazil and from rapeseed oil in Germany [37]. Intermediates from β-oxidation of alkanoic or fatty acids can provide hydroxyalkanoyl-CoA molecules for PHAMCL production by several bacteria such as *Pseudomonas* strains [3].

Some authors have reported PHAMCL production from waste cooking oil by *P. aeruginosa* [22]. *Aeromonas caviae* is also an additional example of bacterial strain that is able to synthesize the co-polymer poly(3-hydroxybutyrate-*co*-3-hydroxyhexanoate) [P(3HB-*co*-3HHx)] from vegetable oil [77]. For the second-generation biofuel, nonedible oilseeds have been considered to avoid the debate food versus fuel, e.g., green seeds canola, high erucic mustard, Indian beech, etc., of which the most reported has been Jatropha [5]. Biosynthesis of co-polymers poly(3-hydroxybutyrate-*co*-3-hydroxyvalerate) [P(3HB-*co*-3 HV)] and P(3HB-*co*-3HHx) from Jatropha oil has also been observed [78].

#### **7.4. Lignocellulosic materials**

The postharvest processing of food crops, forest, and wood residues generates large amounts of lignocellulosic materials, which consist of cellulose, hemicellulose, and lignin. Cellulose is a crystalline glucose polymer, while hemicellulose is amorphous and exhibits xylose and arabinose sugars. Lignin is a large complex of aromatic compounds. Lignocellulose materials can be converted to sugars by acid or enzymatic hydrolysis, which can further be used for ethanol production [5]. The bioethanol production from sugarcane bagasse in Brazil is a well-known example of the second-generation biofuel from lignocellulosic materials [40]. The bioconversion of lignocellulosic biomass by lactic acid bacteria is still limited, and a pretreatment including hydrolysis is necessary to convert these materials to sugars for lactic acid fermentation. Recombinant strategies involving heterologous expression can be a solution for this problem. Some authors have reported that a simple consortium of recombinant *L. plantarum* strains was able to produce cellulase and xylanase and thus showing potential for biomass conversion [67, 79].

*Saccharophagus degradans* is a natural PHA-producing bacteria from tequila bagasse [80]. However, the main focus on PHA production from lignocellulosic materials has been based on this substrate conversion into monomer sugars, which are used for microbial cultivation [72]. Sugarcane bagasse was submitted to acid hydrolysis, and then, it was utilized for PHB and P(3HB-*co*-3 HV) production by *Burkholderia* sp. The co-polymer was obtained after addition of levunic acid to the medium, a 3HV precursor that can also be obtained from the hydrolysis of lignocellulosic compounds [81]. On the other hand, *Halomonas boliviensis* was able to assimilate the sugars from enzymatic hydrolysis of wheat bran, in which it was utilized a crude enzyme preparation from *Aspergillus oryzae* [82].

#### **7.5. Crude glycerol**

is more common in Southeastern Europe, North America, and Asia, where it is primarily used for sugar production [40]. *L. delbrueckii* has been generally a lactic acid–producing bacteria using this carbon source, whose most abundant sugar is sucrose [73]. PHB is the most common product from molasses, since the sucrose content can be converted to acetyl-CoA and after to 3-hydroxybutyryl-CoA, the building block utilized by PHA synthase for PHB polymerization [3]. *Azotobacter vinelandii* and *Bacillus megaterium* are examples of PHB-producing bacteria utilizing sugarcane molasses [74, 75]. PHAMCL production has also been reported

Vegetable oils are feedstock for biofuels with biodiesel representing a well-known example, which is mostly obtained from soybean oil in US and Brazil and from rapeseed oil in Germany [37]. Intermediates from β-oxidation of alkanoic or fatty acids can provide hydroxyalkanoyl-CoA molecules for PHAMCL production by several bacteria such as *Pseudomonas* strains [3]. Some authors have reported PHAMCL production from waste cooking oil by *P. aeruginosa* [22]. *Aeromonas caviae* is also an additional example of bacterial strain that is able to synthesize the co-polymer poly(3-hydroxybutyrate-*co*-3-hydroxyhexanoate) [P(3HB-*co*-3HHx)] from vegetable oil [77]. For the second-generation biofuel, nonedible oilseeds have been considered to avoid the debate food versus fuel, e.g., green seeds canola, high erucic mustard, Indian beech, etc., of which the most reported has been Jatropha [5]. Biosynthesis of co-polymers poly(3-hydroxybutyrate-*co*-3-hydroxyvalerate) [P(3HB-*co*-3 HV)] and P(3HB-*co*-3HHx) from

The postharvest processing of food crops, forest, and wood residues generates large amounts of lignocellulosic materials, which consist of cellulose, hemicellulose, and lignin. Cellulose is a crystalline glucose polymer, while hemicellulose is amorphous and exhibits xylose and arabinose sugars. Lignin is a large complex of aromatic compounds. Lignocellulose materials can be converted to sugars by acid or enzymatic hydrolysis, which can further be used for ethanol production [5]. The bioethanol production from sugarcane bagasse in Brazil is a well-known example of the second-generation biofuel from lignocellulosic materials [40]. The bioconversion of lignocellulosic biomass by lactic acid bacteria is still limited, and a pretreatment including hydrolysis is necessary to convert these materials to sugars for lactic acid fermentation. Recombinant strategies involving heterologous expression can be a solution for this problem. Some authors have reported that a simple consortium of recombinant *L. plantarum* strains was able to produce cel-

*Saccharophagus degradans* is a natural PHA-producing bacteria from tequila bagasse [80]. However, the main focus on PHA production from lignocellulosic materials has been based on this substrate conversion into monomer sugars, which are used for microbial cultivation [72]. Sugarcane bagasse was submitted to acid hydrolysis, and then, it was utilized for PHB and P(3HB-*co*-3 HV) production by *Burkholderia* sp. The co-polymer was obtained after addition of levunic acid to the medium, a 3HV precursor that can also be obtained from the hydrolysis of lignocellulosic compounds [81]. On the other hand, *Halomonas boliviensis* was able to

lulase and xylanase and thus showing potential for biomass conversion [67, 79].

from *Pseudomonas corrugata* from soybean molasses [76].

Jatropha oil has also been observed [78].

**7.4. Lignocellulosic materials**

**7.3. Vegetable oil**

260 Biofuels - State of Development

Nowadays, the crude glycerol is mainly obtained as a byproduct from the transesterification process of oils and fats for biodiesel production, which generates about 10% glycerol [83]. Since purified glycerol is a high-value chemical, alternative solutions are required to crude glycerol refining and one of the possible keys for this issue is the glycerol utilization in its crude form as carbon source in microbial cultivations, in order to obtain value-added chemicals such as bioplastics [84]. A glucose-affected mutant of *Cupriavidus necator*, former *Ralstonia eutropha* and a traditional PHA-producing strain, is able to accumulate PHB from crude glycerol [85]. Additionally, new wild bacterial strains have been isolated from the environment such as *Pandoraea* sp., which is able not only to produce PHAs from crude glycerol but also from sugarcane molasses and waste cooking oil, although the best polymer yields were obtained from crude glycerol [24].

#### **7.6. Biogas and syngas**

Biogas is a renewable gaseous fuel alternative to natural gas, which is generated from anaerobic digestion of organic wastes by numerous bacteria. The main component of biogas is methane [41]. Over 300 bacterial strains, including *Methylocystis paravus*, *Methylosinus sporium*, and *Methylocella tundra*, have shown the ability to synthesize PHB from methane [86]. Furthermore, the integration of PHA-rich biomass production into a municipal waste water treatment plant with sludge digestion has been proposed to support the biogas and PHA production [87]. Synthesis gas or syngas is another gaseous biofuel obtained from gasification or pyrolysis of biomass feedstock. Carbon monoxide, hydrogen, and carbon dioxide are the most abundant constituents of syngas [41]. The purple nonsulfur bacterium *Rhodospirillum rubrum* is able to utilize carbon monoxide and carbon dioxide and has also been a model organism for the synthesis of PHASCL and PHAMCL from syngas [88].

#### **7.7. Microalgae**

Microalgae, such as blue-green algae, dinoflagellates, and bacillariophyta, can have from 8 to 31% of their dry weight constituted of lipids. They have been revealed as the best potential source for oil extraction compared to common biofuel crops [9]. Cyanobacteria are a good candidate for bioplastic production, which present the ability to grow in a variety of environments. Genetically engineered cyanobacteria were transformed with the genes encoding PHB synthesis, and their metabolisms have been extremely investigated aiming to establish new routes for PHA synthesis. Additionally, PLA/algae blends can be prepared and employed in bone and cartilage tissue engineering due to their biodegradability and biocompatibility [89]. Therefore, microalgae are new and promising branch not only for biofuels but also for bioplastics.

#### **7.8. Simultaneous production of PLA and PHAs and their polymer blends**

PHB production has been described in lactic acid bacteria for the genera *Lactobacillus*, *Lactococcus*, *Pediococcus*, and *Streptococcus*. *Cupriavidus necator*, *L. delbrueckii*, and *Propionibacterium* have been cultivated in a bacterial consortia, which resulted in a co-production of lactic acid and PHAs. The implementation of co-cultures brings the advantage of increasing the range of substrates that can possibly be converted into accessible sugars by at least one of the members of microbial consortia [67]. Since PLA and PHASCL exhibit similar properties, PHA/PLA blend is one of the most studied blends. PHASCL generally presents higher melting temperatures than PLA, and thus, their utilization results in polymer blends with different properties. The poor processability of PHB is a drawback for its industrial applications, and the PHB/PLA blends represent a good alternative, which also brings improved properties to PLA. Additionally, PLA is cheaper than PHAs [90]. Therefore, the production of PHA/PLA blends is very advantageous for PHAs reducing their production cost [3, 63, 71].

In 2014, the land area required to grow the total biomass ascribed to the global production capacities of bioplastics was approximately 680,000 ha. About 0.01% of the global agricultural area of 5 Bln ha would be enough to supply the current world's bioplastic production [51]. If it considered that the bioplastic industry is not yet well-established [4] summed to the land area demanded for biofuel production, the agricultural area utilized for a bio-industry can increase significantly, which necessarily leads to an over production of agricultural commodities [10]. Therefore, the increasing of the efficiency of feedstock and agricultural technology is mandatory to compensate the future increase of land use for biofuels and bioplastics [51]. On the other hand, only 1.25% of the entire land biomass is used for food crops, thus the expansion of agricultural lands is other possible solution to attend biofuel and bioplastic demands [5]. Accordingly, the sustainability initiatives should implement development schemes, which must be adapted to protect the land, communities and biodiversity [9]. Whereas bioenergy and biofuels have received political support during commercial production such as quotas, tax incentives, market introduction programs, the bio-based chemicals and plastics have suffered the effects of still weak policies and underinvestment by the private sector. Therefore, a strong political support from the whole society and government is imperative for the establishment

Prospective Biodegradable Plastics from Biomass Conversion Processes

http://dx.doi.org/10.5772/intechopen.75111

263

Biofuels and bioplastics are certainly a present and especially a future trend, whose promising perspectives have faced its main delay in the low crude oil prices and the lack of cost effective technologies. Bioethanol and biodiesel are expected to continue growing in the next year as well-established first-generation biofuels, according to the current political incentives for blending mandates. The lignocellulosic fuels are forecasted to still share a small percentage of bioethanol production, while biogas, syngas from biomass pyrolysis, algae-derived, and other advanced fuels are in their infant stage, which reflects the need of technological upgrades toward cost-effective processes. The bioplastic market has also found in the "drop-in" plastics an economically feasible alternative to associate the biobased polymers with an ecologically friendly image, which is partially misleading, since bio-based plastics can help to reduce the carbon footprint, though the market leaders such as bio-PET, PE, and PUR are not biodegradable. Most of the plastic wastes are constituted of short term and disposable products; hence, the establishment of not only bio-based but also biodegradable plastic market is mandatory to minimize the strong persistence of conventional plastics in the environment and their inevitable damage to ecosystems. PLA is a biobased and biodegradable plastic with a well-established and continuous growing market, while PHAs are the versatile alternative, which can be obtained from a variety of biomass sources and are expected to triple their production capacity for the next years. A biorefinery model comprising biofuels and bioplastics is one of the possible solutions to add value and support a bio-based industry, since both products have found common feedstocks into biomass. Despite the challenges faced by the bio-based industry, the environment concerns and the increasing global sense of social and environmental sustainability will continuously

of the bioplastic industry [61].

be the engine for biofuels and bioplastics.

**9. Conclusions**

#### **7.9. PLA and PHA as sources for fuels**

Hydroxyalkanoate methyl ester, a product from PHA esterification reaction with methanol, produces combustion heats similar to ethanol. The esterified PHA could be used as fuel additive for gasoline and diesel, with good properties of viscosity, flash point, and oxygen content. The implementation of PHAs as biofuels does not require highly purified PHAs, which can be obtained from activated sludge or waste water [91]. Lactic acid bacteria have been considered good candidates for biofuel production, such as ethanol and butanol. Other interesting compound that could be obtained from lactic acid bacteria is formate, which is a precursor substrate for hydrogen production by fermentation processes [67].

#### **8. Challenges to be overcome by biofuels and bioplastics**

Despite numerous advantages regarding the production of biofuels and bioplastics such as renewability and /or biodegradability, there are many concerns about bioproducts derived from biomass. Nowadays, the biggest economical challenges are still fossil fuel dependence and cost effectiveness. The oscillating oil prices and the current technology, the existing fuel supply, and infrastructure make conventional fossil sources and "drop-in" solutions the best economical choice for fuel and plastic markets [4, 41]. The concept of bioplastics as a "green" alternative for petrochemical plastics is a complex matter, and their environmental impact must be better evaluated. Composting and recycling properties are key concerns that should be taken into account for a case-by-case life cycle assessment [4].

Other environmental and economical concern on biofuels is the debate fuel versus food, which can also be applied to bioplastics. Currently, most of biofuels and bioplastics are made from agro-based resources and lignocellulosic materials [5, 51]. The food crops such as corn and sugarcane with high carbohydrates content are up to now the most efficient and profitable option for biofuel and bioplastic industries. Further, these plants are adapted to produce high yields resisting to pests and weather conditions [51]. The renewable energy has also been recovered from lignocellulosic materials as residues of food crops or short rotation of nonedible plants, organic wastes by anaerobic digestion, animal manures, algae biomass, and an endless variety of alternative biomass sources. However, these technologies for biofuel and bioplastic production are still in their infant stage, which needs many upgrades to become economically feasible in face of the conventional fuels and plastics [4, 41].

In 2014, the land area required to grow the total biomass ascribed to the global production capacities of bioplastics was approximately 680,000 ha. About 0.01% of the global agricultural area of 5 Bln ha would be enough to supply the current world's bioplastic production [51]. If it considered that the bioplastic industry is not yet well-established [4] summed to the land area demanded for biofuel production, the agricultural area utilized for a bio-industry can increase significantly, which necessarily leads to an over production of agricultural commodities [10]. Therefore, the increasing of the efficiency of feedstock and agricultural technology is mandatory to compensate the future increase of land use for biofuels and bioplastics [51]. On the other hand, only 1.25% of the entire land biomass is used for food crops, thus the expansion of agricultural lands is other possible solution to attend biofuel and bioplastic demands [5]. Accordingly, the sustainability initiatives should implement development schemes, which must be adapted to protect the land, communities and biodiversity [9]. Whereas bioenergy and biofuels have received political support during commercial production such as quotas, tax incentives, market introduction programs, the bio-based chemicals and plastics have suffered the effects of still weak policies and underinvestment by the private sector. Therefore, a strong political support from the whole society and government is imperative for the establishment of the bioplastic industry [61].

#### **9. Conclusions**

PHAs. The implementation of co-cultures brings the advantage of increasing the range of substrates that can possibly be converted into accessible sugars by at least one of the members of microbial consortia [67]. Since PLA and PHASCL exhibit similar properties, PHA/PLA blend is one of the most studied blends. PHASCL generally presents higher melting temperatures than PLA, and thus, their utilization results in polymer blends with different properties. The poor processability of PHB is a drawback for its industrial applications, and the PHB/PLA blends represent a good alternative, which also brings improved properties to PLA. Additionally, PLA is cheaper than PHAs [90]. Therefore, the production of PHA/PLA blends is very advan-

Hydroxyalkanoate methyl ester, a product from PHA esterification reaction with methanol, produces combustion heats similar to ethanol. The esterified PHA could be used as fuel additive for gasoline and diesel, with good properties of viscosity, flash point, and oxygen content. The implementation of PHAs as biofuels does not require highly purified PHAs, which can be obtained from activated sludge or waste water [91]. Lactic acid bacteria have been considered good candidates for biofuel production, such as ethanol and butanol. Other interesting compound that could be obtained from lactic acid bacteria is formate, which is a precursor

Despite numerous advantages regarding the production of biofuels and bioplastics such as renewability and /or biodegradability, there are many concerns about bioproducts derived from biomass. Nowadays, the biggest economical challenges are still fossil fuel dependence and cost effectiveness. The oscillating oil prices and the current technology, the existing fuel supply, and infrastructure make conventional fossil sources and "drop-in" solutions the best economical choice for fuel and plastic markets [4, 41]. The concept of bioplastics as a "green" alternative for petrochemical plastics is a complex matter, and their environmental impact must be better evaluated. Composting and recycling properties are key concerns that should

Other environmental and economical concern on biofuels is the debate fuel versus food, which can also be applied to bioplastics. Currently, most of biofuels and bioplastics are made from agro-based resources and lignocellulosic materials [5, 51]. The food crops such as corn and sugarcane with high carbohydrates content are up to now the most efficient and profitable option for biofuel and bioplastic industries. Further, these plants are adapted to produce high yields resisting to pests and weather conditions [51]. The renewable energy has also been recovered from lignocellulosic materials as residues of food crops or short rotation of nonedible plants, organic wastes by anaerobic digestion, animal manures, algae biomass, and an endless variety of alternative biomass sources. However, these technologies for biofuel and bioplastic production are still in their infant stage, which needs many upgrades to become

tageous for PHAs reducing their production cost [3, 63, 71].

substrate for hydrogen production by fermentation processes [67].

be taken into account for a case-by-case life cycle assessment [4].

economically feasible in face of the conventional fuels and plastics [4, 41].

**8. Challenges to be overcome by biofuels and bioplastics**

**7.9. PLA and PHA as sources for fuels**

262 Biofuels - State of Development

Biofuels and bioplastics are certainly a present and especially a future trend, whose promising perspectives have faced its main delay in the low crude oil prices and the lack of cost effective technologies. Bioethanol and biodiesel are expected to continue growing in the next year as well-established first-generation biofuels, according to the current political incentives for blending mandates. The lignocellulosic fuels are forecasted to still share a small percentage of bioethanol production, while biogas, syngas from biomass pyrolysis, algae-derived, and other advanced fuels are in their infant stage, which reflects the need of technological upgrades toward cost-effective processes. The bioplastic market has also found in the "drop-in" plastics an economically feasible alternative to associate the biobased polymers with an ecologically friendly image, which is partially misleading, since bio-based plastics can help to reduce the carbon footprint, though the market leaders such as bio-PET, PE, and PUR are not biodegradable. Most of the plastic wastes are constituted of short term and disposable products; hence, the establishment of not only bio-based but also biodegradable plastic market is mandatory to minimize the strong persistence of conventional plastics in the environment and their inevitable damage to ecosystems. PLA is a biobased and biodegradable plastic with a well-established and continuous growing market, while PHAs are the versatile alternative, which can be obtained from a variety of biomass sources and are expected to triple their production capacity for the next years. A biorefinery model comprising biofuels and bioplastics is one of the possible solutions to add value and support a bio-based industry, since both products have found common feedstocks into biomass. Despite the challenges faced by the bio-based industry, the environment concerns and the increasing global sense of social and environmental sustainability will continuously be the engine for biofuels and bioplastics.

#### **Author details**

Fabrício C. de Paula1 \*, Carolina B.C. de Paula2 and Jonas Contiero1,2

\*Address all correspondence to: fcpbarretos@gmail.com


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Fabrício C. de Paula1

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270 Biofuels - State of Development


**Chapter 13**

Provisional chapter

**Syngas Production Using Natural Gas from the**

DOI: 10.5772/intechopen.74605

The search for clean and low-cost fuels as alternative for petroleum is a popular research focus in the energy field. The demand of natural gas as an energy source has increased steadily. The high H:C ratio and the absence of heteroatoms make natural gas an attractive feedstock for synthetic fuels and chemicals that can replace those that are typically petroleum-derived. The search for efficient routes to convert methane to other higher added-value products is a challenge for the scientific community. In addition, new fields of oil and gas contain associated CO2 (8–18%), and, in some specific fields, the associated gas encloses a higher CO2 content (79%). In this context, the tri-reforming process combines two of the most problematic greenhouse gases (CH4 and CO2) to generate syngas for the synthesis of clean liquid fuels and valuable chemicals. Developments in tri-reforming

processes, which include the new catalysts, are presented in this chapter.

Keywords: tri-reforming, syngas, catalysts, carbon dioxide, hydrogen production

Significant efforts are being directed nowadays towards finding alternatives that could restrain the climate change. The consistent rise of CO2 concentration in the atmosphere is known to be significantly detrimental to the environment. Thus, mitigating CO2 is becoming an urgent need. Current methods involving CO2 mitigation can be broadly divided into two major categories, which involve (1) CO2 capture and sequestration (CCS) and (2) CO2 capture and utilization (CCU). Since the production of fuels/chemicals is an added feature along with mitigation in

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Syngas Production Using Natural Gas from the

**Environmental Point of View**

Environmental Point of View

Rita M. de B. Alves, Reinaldo Giudici and

Rita M. de B. Alves, Reinaldo Giudici and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Karina Tamião de Campos Roseno,

Karina Tamião de Campos Roseno,

http://dx.doi.org/10.5772/intechopen.74605

Martin Schmal

Abstract

1. Introduction

Martin Schmal

#### **Syngas Production Using Natural Gas from the Environmental Point of View** Syngas Production Using Natural Gas from the Environmental Point of View

DOI: 10.5772/intechopen.74605

Karina Tamião de Campos Roseno, Rita M. de B. Alves, Reinaldo Giudici and Martin Schmal Karina Tamião de Campos Roseno, Rita M. de B. Alves, Reinaldo Giudici and Martin Schmal

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74605

#### Abstract

The search for clean and low-cost fuels as alternative for petroleum is a popular research focus in the energy field. The demand of natural gas as an energy source has increased steadily. The high H:C ratio and the absence of heteroatoms make natural gas an attractive feedstock for synthetic fuels and chemicals that can replace those that are typically petroleum-derived. The search for efficient routes to convert methane to other higher added-value products is a challenge for the scientific community. In addition, new fields of oil and gas contain associated CO2 (8–18%), and, in some specific fields, the associated gas encloses a higher CO2 content (79%). In this context, the tri-reforming process combines two of the most problematic greenhouse gases (CH4 and CO2) to generate syngas for the synthesis of clean liquid fuels and valuable chemicals. Developments in tri-reforming processes, which include the new catalysts, are presented in this chapter.

Keywords: tri-reforming, syngas, catalysts, carbon dioxide, hydrogen production

#### 1. Introduction

Significant efforts are being directed nowadays towards finding alternatives that could restrain the climate change. The consistent rise of CO2 concentration in the atmosphere is known to be significantly detrimental to the environment. Thus, mitigating CO2 is becoming an urgent need.

Current methods involving CO2 mitigation can be broadly divided into two major categories, which involve (1) CO2 capture and sequestration (CCS) and (2) CO2 capture and utilization (CCU). Since the production of fuels/chemicals is an added feature along with mitigation in

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

CO2 valorization-based methods, they could be economically favorable. An energy-intensive CO2 capture step is a common drawback of most CO2 valorization methods that aim to mitigate CO2 from major CO2 emission sources (such as industrial flue gases).

In particular, natural gas processes increase the options for the production of high addedvalue chemicals and energy demand. The Fischer-Tropsch (FT) technology is the main technology for the production of liquid fuels, named GTL process, but this technology is yet very expensive, due to the high costs of syngas production using steam reforming of methane (SRM) [7]. The tri-reforming process (TRM), introduced by Song et al. [10], allows to use flue gas and methane to produce syngas, which can be converted to methanol and higher hydrocarbons. This new process is a synergic combination of the endothermic CO2 and steam-reforming reactions with the exothermic oxidation of methane, as shown in

<sup>298</sup><sup>K</sup> <sup>¼</sup> <sup>206</sup>:3kJ:mol�<sup>1</sup> (1)

http://dx.doi.org/10.5772/intechopen.74605

275

Syngas Production Using Natural Gas from the Environmental Point of View

<sup>298</sup><sup>K</sup> <sup>¼</sup> <sup>247</sup>:3kJ:mol�<sup>1</sup> (2)

<sup>298</sup><sup>K</sup> ¼ �35:6kJ:mol�<sup>1</sup> (3)

<sup>298</sup><sup>K</sup> ¼ �880kJ:mol�<sup>1</sup> (4)

<sup>298</sup><sup>K</sup> <sup>¼</sup> <sup>75</sup>kJ:mol�<sup>1</sup> (5)

<sup>298</sup><sup>K</sup> ¼ �172kJ:mol�<sup>1</sup> (6)

<sup>298</sup><sup>K</sup> ¼ �393:7kJ:mol�<sup>1</sup> (8)

<sup>298</sup><sup>K</sup> ¼ �41kJ:mol�<sup>1</sup> (7)

Eqs. (1)–(4) [11], which are carried out in a single reactor.

CH<sup>4</sup> þ 1 2

reactions (Eq. (8)) occur simultaneously [12].

<sup>H</sup>2<sup>O</sup> <sup>þ</sup> CH<sup>4</sup> ! CO <sup>þ</sup> <sup>3</sup>H2; <sup>Δ</sup>H<sup>0</sup>

CO<sup>2</sup> <sup>þ</sup> CH<sup>4</sup> ! <sup>2</sup>CO <sup>þ</sup> <sup>2</sup>H2; <sup>Δ</sup>H<sup>0</sup>

CH<sup>4</sup> <sup>þ</sup> <sup>2</sup>O<sup>2</sup> ! CO<sup>2</sup> <sup>þ</sup> <sup>2</sup>H2O; <sup>Δ</sup>H<sup>0</sup>

CH<sup>4</sup> ! <sup>C</sup> <sup>þ</sup> <sup>2</sup>H2; <sup>Δ</sup>H<sup>0</sup>

<sup>2</sup>CO ! <sup>C</sup> <sup>þ</sup> CO2; <sup>Δ</sup>H<sup>0</sup>

CO <sup>þ</sup> <sup>H</sup>2<sup>O</sup> <sup>¼</sup> CO<sup>2</sup> <sup>þ</sup> <sup>H</sup>2; <sup>Δ</sup>H<sup>0</sup>

<sup>C</sup> <sup>þ</sup> <sup>O</sup><sup>2</sup> <sup>¼</sup> CO2; <sup>Δ</sup>H<sup>0</sup>

<sup>O</sup><sup>2</sup> ! CO <sup>þ</sup> <sup>2</sup>H2; <sup>Δ</sup>H<sup>0</sup>

In addition, during the tri-reforming process, methane cracking (Eq. (5)), CO disproportionation or Boudouard (Eq. (6)), water-gas shift (Eq. (7)) and complete oxidation of carbon

The heat released during the POM reaction is used to supply the heat needed for the SRM and DRM reaction, and therefore the TRM reaction is energetically more efficient [13]. In addition, TRM offers several advantages for syngas production compared to the single reactions [14]. TRM does not require pure CO2 supply in the reaction. This implies that the flue gas from the combustion processes of power plants or the coke oven gas (COG) from iron-making industries can be used directly as a CO2 source for TRM process [15–17]. TRM can also be used to upgrade the syngas quality produced from biomass or coal gasification [18, 19]. The H2/CO ratio in syngas produced from tri-reforming can be adjusted varying the amounts of reactants to satisfy the requirement for further processes, such as methanol and Fischer-Tropsch synthesis [20, 21]. In addition, integrating steam reforming and partial oxidation with CO2 reforming could dramatically reduce or eliminate carbon formation on a reforming catalyst, thus increasing the catalyst life and process efficiency [14] due to the addition of O2 in the feed, which also generates heat that increases the energy efficiency. Therefore, the tri-reforming has the advantage of using natural gas and flue gases from power plants. The syngas from tri-reforming is used for the production of chemicals (such as MeOH and dimethyl ether by oxo-synthesis), fuels (for the Fischer-Tropsch synthesis) and electricity in fuel cells, as shown in Figure 1 [14].

Different methane-rich gas streams can be found, both of natural and of anthropogenic origin. A decrease in fossil fuels and environmental concerns across the globe enforced researchers to work on energy resources like methane, which is the most abundant natural gas on earth [1].

Therefore, it is of utmost importance to seek for technologies that could convert two of the main product gases responsible for the greenhouse effect, methane and carbon dioxide, avoiding their massive release into the atmosphere.

Reforming of methane is one of the most important industrial processes, which convert natural gas into synthesis gas. Syngas is an intermediate feedstock for the production of hydrocarbons and hydrogen for fuel cells. Synthesis gas is produced from natural gas via catalytic processes based on dry reforming of methane (DRM), steam reforming of methane (SRM) and partial oxidation of methane (POM) [2]. In fact, the available natural gas can be exploited for the production of chemicals and fuels.

The reforming processes are classified based on the energetic demand of the process and the type of reforming agent. Steam reforming of methane (SRM) produces a high ratio of syngas (H2/CO = 3), suitable for the production of ammonia. This process is endothermic and requires high investments. The partial oxidation of methane, an exothermic reaction, is an alternative process with reduced capital and operation costs. However, the partial oxidation of methane (POM) needs oxygen, and the cost of its production is about 50% of the investment of the whole process. There is a high risk of explosion at an elevated temperature [3]. On the other hand, the dry reforming of methane (DRM) is a valuable reaction for biogas utilization and transformation of greenhouse gases (CH4 and CO2) in high-valued products. DRM produces a low syngas ratio (H2/CO = 1), which is suitable for the syntheses of oxygenates [4–6].

Tri-reforming of methane (TRM) is nowadays of great interest, because it combines the steam and dry reforming and partial oxidation of methane (CH4 + O2 + CO2 + H2O) processes; however, it holds the main advantages and disadvantages of all processes, to some extent [7].

It is well known that the major limitation of methane-reforming processes is the rapid deactivation of the catalyst, which has been commonly attributed to coke deposition and catalyst sintering.

The tri-reforming of methane may drastically reduce the carbon deposition. Furthermore, the presence of O2 in the feed allows the generation of energy in situ, due to the exothermal oxidation of methane, which increases the energy efficiency of the process. Besides, the possibility of changing the reactants' compositions, allows for a versatile synthesis of gas composition, which can be suitable for different applications of synthesis gas [8, 9].

#### 2. Tri-reforming process

Energy is the most important issue to modern economies, and it is predicted that a fastrising energy demand will require US \$45 trillion for new infrastructure investment by 2030. In particular, natural gas processes increase the options for the production of high addedvalue chemicals and energy demand. The Fischer-Tropsch (FT) technology is the main technology for the production of liquid fuels, named GTL process, but this technology is yet very expensive, due to the high costs of syngas production using steam reforming of methane (SRM) [7]. The tri-reforming process (TRM), introduced by Song et al. [10], allows to use flue gas and methane to produce syngas, which can be converted to methanol and higher hydrocarbons. This new process is a synergic combination of the endothermic CO2 and steam-reforming reactions with the exothermic oxidation of methane, as shown in Eqs. (1)–(4) [11], which are carried out in a single reactor.

CO2 valorization-based methods, they could be economically favorable. An energy-intensive CO2 capture step is a common drawback of most CO2 valorization methods that aim to

Different methane-rich gas streams can be found, both of natural and of anthropogenic origin. A decrease in fossil fuels and environmental concerns across the globe enforced researchers to work on energy resources like methane, which is the most abundant natural gas on earth [1]. Therefore, it is of utmost importance to seek for technologies that could convert two of the main product gases responsible for the greenhouse effect, methane and carbon dioxide,

Reforming of methane is one of the most important industrial processes, which convert natural gas into synthesis gas. Syngas is an intermediate feedstock for the production of hydrocarbons and hydrogen for fuel cells. Synthesis gas is produced from natural gas via catalytic processes based on dry reforming of methane (DRM), steam reforming of methane (SRM) and partial oxidation of methane (POM) [2]. In fact, the available natural gas can be exploited for the

The reforming processes are classified based on the energetic demand of the process and the type of reforming agent. Steam reforming of methane (SRM) produces a high ratio of syngas (H2/CO = 3), suitable for the production of ammonia. This process is endothermic and requires high investments. The partial oxidation of methane, an exothermic reaction, is an alternative process with reduced capital and operation costs. However, the partial oxidation of methane (POM) needs oxygen, and the cost of its production is about 50% of the investment of the whole process. There is a high risk of explosion at an elevated temperature [3]. On the other hand, the dry reforming of methane (DRM) is a valuable reaction for biogas utilization and transformation of greenhouse gases (CH4 and CO2) in high-valued products. DRM produces a

low syngas ratio (H2/CO = 1), which is suitable for the syntheses of oxygenates [4–6].

Tri-reforming of methane (TRM) is nowadays of great interest, because it combines the steam and dry reforming and partial oxidation of methane (CH4 + O2 + CO2 + H2O) processes; however, it holds the main advantages and disadvantages of all processes, to some extent [7]. It is well known that the major limitation of methane-reforming processes is the rapid deactivation of the catalyst, which has been commonly attributed to coke deposition and catalyst sintering.

The tri-reforming of methane may drastically reduce the carbon deposition. Furthermore, the presence of O2 in the feed allows the generation of energy in situ, due to the exothermal oxidation of methane, which increases the energy efficiency of the process. Besides, the possibility of changing the reactants' compositions, allows for a versatile synthesis of gas composi-

Energy is the most important issue to modern economies, and it is predicted that a fastrising energy demand will require US \$45 trillion for new infrastructure investment by 2030.

tion, which can be suitable for different applications of synthesis gas [8, 9].

mitigate CO2 from major CO2 emission sources (such as industrial flue gases).

avoiding their massive release into the atmosphere.

production of chemicals and fuels.

274 Biofuels - State of Development

2. Tri-reforming process

$$\mathrm{CH\_2O + CH\_4 \to CO + 3H\_2; \Delta H\_{298K}^0 = 206.3 \mathrm{kJ.mol^{-1}}}\tag{1}$$

$$2\text{ CO}\_2 + \text{CH}\_4 \rightarrow 2\text{CO} + 2\text{H}\_2; \Delta\text{H}\_{298\text{K}}^0 = 247.3 \text{kJ} \cdot \text{mol}^{-1} \tag{2}$$

$$2\,\text{CH}\_4 + \frac{1}{2}\text{O}\_2 \to \text{CO} + 2\,\text{H}\_2\text{:}\,\Delta H\_{298\text{K}}^0 = -35.6\,\text{kJ}\,\text{mol}^{-1} \tag{3}$$

$$\text{CH}\_4 + 2\text{O}\_2 \rightarrow \text{CO}\_2 + 2\text{H}\_2\text{O}; \Delta H^0\_{298\text{K}} = -880 \text{kJ} \cdot \text{mol}^{-1} \tag{4}$$

In addition, during the tri-reforming process, methane cracking (Eq. (5)), CO disproportionation or Boudouard (Eq. (6)), water-gas shift (Eq. (7)) and complete oxidation of carbon reactions (Eq. (8)) occur simultaneously [12].

$$\text{CH}\_4 \rightarrow \text{C} + 2\text{H}\_2\text{:}\,\Delta H\_{298\text{K}}^0 = 75\text{kJ}.mol^{-1} \tag{5}$$

$$2\text{CO} \rightarrow \text{C} + \text{CO}\_2; \Delta H^0\_{298\text{K}} = -172 \text{kJ}.mol^{-1} \tag{6}$$

$$\text{CO} + \text{H}\_2\text{O} = \text{CO}\_2 + \text{H}\_2; \Delta H\_{298\text{K}}^0 = -41 \text{kJ}. \text{mol}^{-1} \tag{7}$$

$$\text{C} + \text{O}\_2 = \text{CO}\_2; \Delta H\_{298\text{K}}^0 = -393.7 \text{kJ} \cdot \text{mol}^{-1} \tag{8}$$

The heat released during the POM reaction is used to supply the heat needed for the SRM and DRM reaction, and therefore the TRM reaction is energetically more efficient [13]. In addition, TRM offers several advantages for syngas production compared to the single reactions [14]. TRM does not require pure CO2 supply in the reaction. This implies that the flue gas from the combustion processes of power plants or the coke oven gas (COG) from iron-making industries can be used directly as a CO2 source for TRM process [15–17]. TRM can also be used to upgrade the syngas quality produced from biomass or coal gasification [18, 19]. The H2/CO ratio in syngas produced from tri-reforming can be adjusted varying the amounts of reactants to satisfy the requirement for further processes, such as methanol and Fischer-Tropsch synthesis [20, 21]. In addition, integrating steam reforming and partial oxidation with CO2 reforming could dramatically reduce or eliminate carbon formation on a reforming catalyst, thus increasing the catalyst life and process efficiency [14] due to the addition of O2 in the feed, which also generates heat that increases the energy efficiency. Therefore, the tri-reforming has the advantage of using natural gas and flue gases from power plants. The syngas from tri-reforming is used for the production of chemicals (such as MeOH and dimethyl ether by oxo-synthesis), fuels (for the Fischer-Tropsch synthesis) and electricity in fuel cells, as shown in Figure 1 [14].

Table 1 shows the advantages and disadvantages of tri-reforming compared to other reforming technologies [7, 18, 22].

3. Catalysts for methane-reforming reactions

are the main obstacles for industrial applications [31, 32].

metals but not totally eliminate the carbon deposition.

high reforming temperatures.

BaO, CaO, SrO, MgO and ZrO2 [37, 38].

3.1. Promising catalysts

reforming of methane [48].

The drawback of methane-reforming processes is mainly the severe tendency to carbon formation that deactivates the catalysts [23–25]. Noble metal-based catalysts (Rh, Ru, Pt, Pd and Ir) presented a high activity and stability against coke formation [26, 27]. However, their costs are still highly prohibitive for feasible application in this process. In fact, nickel-based catalysts are more preferable in the CH4 reforming, due to their availability and lower costs [28–30]. However, the stability of the nickel catalysts at elevated temperatures and the coke formation

Syngas Production Using Natural Gas from the Environmental Point of View

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277

The addition of promoters to Ni-containing catalysts led to the reduction of coke deposition, better metal dispersion or smaller particle size, and the synergic effect between Ni and the promoter [33–36]. In fact, bimetallic catalyst exhibits a higher activity compared to noble

The metal dispersion influences the coke deposition, since this process is structure-sensitive. The build-up of carbon involves quite large active metal particles, which are usually formed at

Alumina-based supports have been investigated mainly due to the high specific surface area, increasing the metal dispersion [37]. Nevertheless, the alumina supports easily deactivate due to the coke deposition and sintering. The formation of coke has been associated with the dehydration, cracking and polymerization reactions, occurring on the acid sites, while

Additional improvement can be achieved using well-developed supports. An effort to overcome these problems is to search for basic additives or promoters, such as CeO2, SiO2, La2O3,

Sintering of metal clusters can be prevented with supports having a strong interaction with the active component. In fact, ceria-based catalysts can minimize sintering and coke formation [39] compared to MgO, TiO2, Al2O3, SiO2 and ZrO2 supports [40–46]. On the contrary, these supports facilitate sintering when submitted to higher temperatures. Moreover, ceria-based catalysts present good redox properties and high oxygen mobility, and as reported in the study, without noticeable oxygen mobility, the deactivation of the catalyst occurs very fast [47]. On the other hand, the thermal stability of pure ceria under the typical reforming conditions is quite poor.

Although tri-reforming has not yet been implemented commercially, similar to steam or to dry reforming, Ni catalysts supported on a wide range of different supported materials, such as Al2O3, ZrO2, MgO, TiO2, CeO2, TiO2, CeZrO and SiO2, are the most popular catalysts for tri-

Song et al. [14] suggested that the supports should have a high oxygen storage capacity that promotes CO2 adsorption. They proposed a simplified mechanism for the CO2 reforming

sintering is due to the transition of crystalline phase during reaction [37].

However, due to the inherent problems of the reforming processes, there is a need to improve catalysts for optimizing the TRM process, improving the oxygen tolerance, resistance to coke formation and sintering of the metal-active sites at a high temperature.

Figure 1. Tri-reforming of natural gas using flue gas from fossil fuel-based power plants.


Table 1. Advantages and disadvantages of tri-reforming [7, 18, 22].

#### 3. Catalysts for methane-reforming reactions

Table 1 shows the advantages and disadvantages of tri-reforming compared to other

However, due to the inherent problems of the reforming processes, there is a need to improve catalysts for optimizing the TRM process, improving the oxygen tolerance, resistance to coke

formation and sintering of the metal-active sites at a high temperature.

Figure 1. Tri-reforming of natural gas using flue gas from fossil fuel-based power plants.

Advantages Disadvantages

Direct use of flue gases Usually requires oxygen plant High methane conversion No existing industrial process Elimination of CO2 separation No existing commercial catalysts Different H2/CO ratios Would require high GHSV Minimization of coke formation Heat management Use of waste H2O/O2 Mass management

reforming technologies [7, 18, 22].

276 Biofuels - State of Development

Simplifying the processing system

Table 1. Advantages and disadvantages of tri-reforming [7, 18, 22].

The drawback of methane-reforming processes is mainly the severe tendency to carbon formation that deactivates the catalysts [23–25]. Noble metal-based catalysts (Rh, Ru, Pt, Pd and Ir) presented a high activity and stability against coke formation [26, 27]. However, their costs are still highly prohibitive for feasible application in this process. In fact, nickel-based catalysts are more preferable in the CH4 reforming, due to their availability and lower costs [28–30]. However, the stability of the nickel catalysts at elevated temperatures and the coke formation are the main obstacles for industrial applications [31, 32].

The addition of promoters to Ni-containing catalysts led to the reduction of coke deposition, better metal dispersion or smaller particle size, and the synergic effect between Ni and the promoter [33–36]. In fact, bimetallic catalyst exhibits a higher activity compared to noble metals but not totally eliminate the carbon deposition.

The metal dispersion influences the coke deposition, since this process is structure-sensitive. The build-up of carbon involves quite large active metal particles, which are usually formed at high reforming temperatures.

Alumina-based supports have been investigated mainly due to the high specific surface area, increasing the metal dispersion [37]. Nevertheless, the alumina supports easily deactivate due to the coke deposition and sintering. The formation of coke has been associated with the dehydration, cracking and polymerization reactions, occurring on the acid sites, while sintering is due to the transition of crystalline phase during reaction [37].

Additional improvement can be achieved using well-developed supports. An effort to overcome these problems is to search for basic additives or promoters, such as CeO2, SiO2, La2O3, BaO, CaO, SrO, MgO and ZrO2 [37, 38].

Sintering of metal clusters can be prevented with supports having a strong interaction with the active component. In fact, ceria-based catalysts can minimize sintering and coke formation [39] compared to MgO, TiO2, Al2O3, SiO2 and ZrO2 supports [40–46]. On the contrary, these supports facilitate sintering when submitted to higher temperatures. Moreover, ceria-based catalysts present good redox properties and high oxygen mobility, and as reported in the study, without noticeable oxygen mobility, the deactivation of the catalyst occurs very fast [47]. On the other hand, the thermal stability of pure ceria under the typical reforming conditions is quite poor.

#### 3.1. Promising catalysts

Although tri-reforming has not yet been implemented commercially, similar to steam or to dry reforming, Ni catalysts supported on a wide range of different supported materials, such as Al2O3, ZrO2, MgO, TiO2, CeO2, TiO2, CeZrO and SiO2, are the most popular catalysts for trireforming of methane [48].

Song et al. [14] suggested that the supports should have a high oxygen storage capacity that promotes CO2 adsorption. They proposed a simplified mechanism for the CO2 reforming reaction. The first step occurs with the activation of methane, followed by the surface reaction and the adsorbed surface CO2 species or adsorbed oxygen atoms (Eq. (9)); CO2 is more acidic, and basic supports may preferentially interact with CO2. Therefore, the CO2 adsorption at the surface facilitates the reaction with CH4 producing CO and H2. Moreover, supports with a high oxygen storage capacity may also facilitate the dissociative adsorption of CO2 into CO and adsorbed oxygen, according to Eq. (9) [14]

$$\text{'}\,\text{CO}\_2 + \Box = \text{CO} + \text{O}^{\Box} \tag{9}$$

oxidation at 950C. However, the LaFeO3 presented negligible structural modifications. The stability of the perovskites occurs during repeated reaction cycles of generation-regeneration.

Syngas Production Using Natural Gas from the Environmental Point of View

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279

The LaFeO3, La0.8Sr0.2FeO3 and La0.8Sr0.2Fe0.9Co0.1O3 perovskite-type oxides were investigated in a continuous flow and sequential redox reaction [67] for the partial oxidation of methane in the absence of gaseous oxygen. The authors observed that methane reacted with sub-surface oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability is attributed to the continuous oxygen supply in the redox reaction, which evidences an excellent structural stability of the perovskite materials. Other perovskites were employed for the DRM, SRM and POM reactions [68–72]. The effect of replacing cobalt by iron in LaCo1xFexO3 (x = 0.0, 0.5 and 1.0) perovskite-type oxides over its physical properties and catalytic performance in the partial oxidation of methane (POM) was investigated. The product distribution varying with space time and with perovskite-type catalyst employed is found to be remarkable. For lower W/F values, the major product was H2 for the LaCoO3 (55.8%) and LaCo0.5Fe0.5O3 (59.2%), with similar ratios H2/CO (1.8–1.9) and

We studied the combined dry and partial oxidation reaction on LaCrO3 and perovskites, fed with CH4:CO2:O2 = 1:1:0.5 and using a GSVH 60,000 h<sup>1</sup> at 700C for 4 h. The conversions were 17% CH4 and 94% O2, respectively, and no conversion of CO2. Results showed an increasing formation of CO2 and a H2/CO ratio equal to 2.7, which suggests that the partial and total oxidation of methane initially takes place, producing CO, CO2 and H2O, and subsequently the steam and dry reforming occur to produce syngas. In fact, the water-gas shift

Steam reforming of methane is the only large-scale industrial process currently available for the production of synthesis gas, producing high-purity hydrogen with a H2/CO ratio equal to 3. The partial oxidation of methane produces synthesis gas with a H2/CO ratio of 2, as required for methanol synthesis. However, the POM reaction is exothermic, and the control of the temperature of this process is difficult. Tri-reforming of methane is energetically favorable compared to the steam reforming of methane and partial oxidation of methane. The process is energetically thermal neutral. Compared to the SRM and POM reactions, the tri-reforming

Singha et al. [74] found the optimum feed ratio and the effect of O2 and H2O concentration (mole ratio) conditions for the reaction, by monitoring the feed mixture and keeping the methane to CO2 mole ratio constant. The addition of oxygen in the feed helps to attain a thermal-neutral balance and compensate the heat necessary for the endothermic reactions occurring during the whole process [75]. A high oxygen concentration in the reaction feed inhibits the CO2 reforming and lowers the CO2 conversion [13] because the reaction between oxygen and methane is thermodynamically favored over the reaction between methane and CO2. The higher concentration of oxygen in the feed allows a maximum methane consumption, and the available methane for the dry and steam reforming is very low [76]. Table 2 shows the effect of O2 concentration

a low CO2 formation [73].

reaction also takes place due to the high H2:CO ratio.

process has the advantage to produce different H2/CO ratios.

3.2. Effect of O2 and H2O concentration

where □ denotes an active site.

Perovskite-type oxides have attracted significant interest as promising catalytic materials with applications in a wide range of reactions, including total oxidation and partial oxidation of hydrocarbons, carbon monoxide oxidation, alkenes hydrogenation, alkanes hydrogenolysis, alcohol synthesis, dry reforming and water-gas shift reaction [49–51]. The perovskites contain metallic and non-metallic elements, with a well-defined crystal structure. In general, the molecular formula is represented by ABO3, where A refers to an alkali metal, an alkaline earth metal or a lanthanide and B to a transition metal. These solids exhibit interesting properties such as superconductivity, ferromagnetism, appreciable thermal stability and conductivity and finally a high catalytic activity. The intrinsic properties of each perovskite are dependent on the type of inserted element and principally on the preparation method. In fact, perovskites as catalysts showed a reductive capacity under appropriate conditions. The metal particles are highly dispersed in the oxide matrix (AOX), inhibiting sintering of metal particles and carbon deposition. In fact, the high thermal stability makes the perovskites promising catalysts for the reforming of methane. Therefore, they are attractive alternatives to classic catalysts traditionally used in these reactions such as supported nickel and noble metals.

Various perovskites, including LaFeO3, LaNixFe1-xO3, LaNiO3 or La1-xCexFe0.7Ni0.3O3, have been found to exhibit a high activity in the steam reforming of methane with a minimal coke deposition under low steam-to-carbon ratios [52–67]. However, the need for high-operating temperatures (e.g. T ≥ 600�C) of methane-reforming reactions provokes irreversible structural changes, including structural collapse and dissolution of (reactive or inactive) metal particles from the perovskite lattice [57–60, 63, 64].

Choudhary et al. [63] verified that the oxygen from the La1-xSrxFeO3 perovskite-type oxides surface was responsible for the complete oxidation of CH4–CO2 and H2O, while the bulk lattice oxygen was responsible for the deep reduction of Fe3+–Fe2+, and this was suitable for the partial oxidation of CH4–H2 and CO. The La1-xSrxFeO3 has had good repeatability in the catalytic performance, and no significant deactivation was observed over five redox cycles.

The LaCrO3 and LaFeO3 oxides doped with alkaline earth (AE = Ba, Ca, Mg and Sr) metals were prepared and studied on how the atomic oxygen influences the partial oxidation of methane to syngas [66]. A-site doping with AE metals generally increases the mobility of lattice oxygen ions and thus decreases the temperature for the hydrogen and CO production, when compared with the non-doped LaCrO3 and LaFeO3 oxides. There are minor structural changes during the partial oxidation of methane of LaCrO3, which can be regenerated by oxidation at 950C. However, the LaFeO3 presented negligible structural modifications. The stability of the perovskites occurs during repeated reaction cycles of generation-regeneration.

The LaFeO3, La0.8Sr0.2FeO3 and La0.8Sr0.2Fe0.9Co0.1O3 perovskite-type oxides were investigated in a continuous flow and sequential redox reaction [67] for the partial oxidation of methane in the absence of gaseous oxygen. The authors observed that methane reacted with sub-surface oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability is attributed to the continuous oxygen supply in the redox reaction, which evidences an excellent structural stability of the perovskite materials.

Other perovskites were employed for the DRM, SRM and POM reactions [68–72]. The effect of replacing cobalt by iron in LaCo1xFexO3 (x = 0.0, 0.5 and 1.0) perovskite-type oxides over its physical properties and catalytic performance in the partial oxidation of methane (POM) was investigated. The product distribution varying with space time and with perovskite-type catalyst employed is found to be remarkable. For lower W/F values, the major product was H2 for the LaCoO3 (55.8%) and LaCo0.5Fe0.5O3 (59.2%), with similar ratios H2/CO (1.8–1.9) and a low CO2 formation [73].

We studied the combined dry and partial oxidation reaction on LaCrO3 and perovskites, fed with CH4:CO2:O2 = 1:1:0.5 and using a GSVH 60,000 h<sup>1</sup> at 700C for 4 h. The conversions were 17% CH4 and 94% O2, respectively, and no conversion of CO2. Results showed an increasing formation of CO2 and a H2/CO ratio equal to 2.7, which suggests that the partial and total oxidation of methane initially takes place, producing CO, CO2 and H2O, and subsequently the steam and dry reforming occur to produce syngas. In fact, the water-gas shift reaction also takes place due to the high H2:CO ratio.

#### 3.2. Effect of O2 and H2O concentration

reaction. The first step occurs with the activation of methane, followed by the surface reaction and the adsorbed surface CO2 species or adsorbed oxygen atoms (Eq. (9)); CO2 is more acidic, and basic supports may preferentially interact with CO2. Therefore, the CO2 adsorption at the surface facilitates the reaction with CH4 producing CO and H2. Moreover, supports with a high oxygen storage capacity may also facilitate the dissociative adsorption of CO2 into CO

Perovskite-type oxides have attracted significant interest as promising catalytic materials with applications in a wide range of reactions, including total oxidation and partial oxidation of hydrocarbons, carbon monoxide oxidation, alkenes hydrogenation, alkanes hydrogenolysis, alcohol synthesis, dry reforming and water-gas shift reaction [49–51]. The perovskites contain metallic and non-metallic elements, with a well-defined crystal structure. In general, the molecular formula is represented by ABO3, where A refers to an alkali metal, an alkaline earth metal or a lanthanide and B to a transition metal. These solids exhibit interesting properties such as superconductivity, ferromagnetism, appreciable thermal stability and conductivity and finally a high catalytic activity. The intrinsic properties of each perovskite are dependent on the type of inserted element and principally on the preparation method. In fact, perovskites as catalysts showed a reductive capacity under appropriate conditions. The metal particles are highly dispersed in the oxide matrix (AOX), inhibiting sintering of metal particles and carbon deposition. In fact, the high thermal stability makes the perovskites promising catalysts for the reforming of methane. Therefore, they are attractive alternatives to classic catalysts tradition-

Various perovskites, including LaFeO3, LaNixFe1-xO3, LaNiO3 or La1-xCexFe0.7Ni0.3O3, have been found to exhibit a high activity in the steam reforming of methane with a minimal coke deposition under low steam-to-carbon ratios [52–67]. However, the need for high-operating temperatures (e.g. T ≥ 600�C) of methane-reforming reactions provokes irreversible structural changes, including structural collapse and dissolution of (reactive or inactive) metal particles

Choudhary et al. [63] verified that the oxygen from the La1-xSrxFeO3 perovskite-type oxides surface was responsible for the complete oxidation of CH4–CO2 and H2O, while the bulk lattice oxygen was responsible for the deep reduction of Fe3+–Fe2+, and this was suitable for the partial oxidation of CH4–H2 and CO. The La1-xSrxFeO3 has had good repeatability in the catalytic performance, and no significant deactivation was observed over five redox cycles.

The LaCrO3 and LaFeO3 oxides doped with alkaline earth (AE = Ba, Ca, Mg and Sr) metals were prepared and studied on how the atomic oxygen influences the partial oxidation of methane to syngas [66]. A-site doping with AE metals generally increases the mobility of lattice oxygen ions and thus decreases the temperature for the hydrogen and CO production, when compared with the non-doped LaCrO3 and LaFeO3 oxides. There are minor structural changes during the partial oxidation of methane of LaCrO3, which can be regenerated by

ally used in these reactions such as supported nickel and noble metals.

from the perovskite lattice [57–60, 63, 64].

CO<sup>2</sup> <sup>þ</sup> □ <sup>¼</sup> CO <sup>þ</sup> <sup>O</sup>□ (9)

and adsorbed oxygen, according to Eq. (9) [14]

where □ denotes an active site.

278 Biofuels - State of Development

Steam reforming of methane is the only large-scale industrial process currently available for the production of synthesis gas, producing high-purity hydrogen with a H2/CO ratio equal to 3. The partial oxidation of methane produces synthesis gas with a H2/CO ratio of 2, as required for methanol synthesis. However, the POM reaction is exothermic, and the control of the temperature of this process is difficult. Tri-reforming of methane is energetically favorable compared to the steam reforming of methane and partial oxidation of methane. The process is energetically thermal neutral. Compared to the SRM and POM reactions, the tri-reforming process has the advantage to produce different H2/CO ratios.

Singha et al. [74] found the optimum feed ratio and the effect of O2 and H2O concentration (mole ratio) conditions for the reaction, by monitoring the feed mixture and keeping the methane to CO2 mole ratio constant. The addition of oxygen in the feed helps to attain a thermal-neutral balance and compensate the heat necessary for the endothermic reactions occurring during the whole process [75]. A high oxygen concentration in the reaction feed inhibits the CO2 reforming and lowers the CO2 conversion [13] because the reaction between oxygen and methane is thermodynamically favored over the reaction between methane and CO2. The higher concentration of oxygen in the feed allows a maximum methane consumption, and the available methane for the dry and steam reforming is very low [76]. Table 2 shows the effect of O2 concentration


Table 2. The effect of O2 concentration (mole ratio) on the reactant conversions verified by reference [74].

over methane, CO2 and H2O conversions and H2/CO ratios [74]. The effect of concentration of O2 over the reactant conversion was mainly due to the heat generated by the partial oxidation and complete oxidation of methane and the enhanced coke removal process [76, 77]. Increasing O2 concentration, the total oxidation of methane also increases, due to the exothermic reaction, and the amount of energy is released. The heat generated is useful for the steam- and dry-reforming reactions, which are endothermic, minimizing the required temperature to obtain a higher CH4 conversion [78] and external energy. On the opposite, lower O2 concentrations led to lower conversion; however, increasing the temperature, H2O and CO2 react with methane to produce synthesis gas [77]. The higher H2/CO ratio was attributed to the steam reforming of methane, producing a H2/CO ratio of 3, attributed to the water-gas shift reaction, which produces only hydrogen, without the production of CO [79]. On the other hand, with increasing temperature, one observes that the RWGS (reverse water-gas shift) reaction outweighs other reactions [77].

#### 3.3. Effect of space velocity and methane/oxygen ratio

The effect of replacing cobalt by iron in LaCo1-xFexO3 (x = 0.0, 0.5 and 1.0) perovskite-type oxides on its catalytic performance in the partial oxidation of methane (POM) process was investigated, varying the space velocity and methane/oxygen ratio. The inlet methane to oxygen proportion was fixed at 2:1. The methane conversion increased with the space time and the maximum conversion was 31% at 0.67 kg.s.mol�<sup>1</sup> for the LF perovskite. In terms of product selectivity, the catalysts produced mainly H2 and CO, CO2, C2H4 and/or C2H6, as shown in Table 3. The product distribution varying with space time and perovskite type catalyst is found to be remarkable. The H2 production decreased by about a half and the CO decreased four times for both LC and LCF catalysts. However, the CO2 formation increased by a factor of about 10, and the H2/CO ratio also increased by a factor of 2. Different was the product distribution of the LF perovskite presenting low H2 and CO formations and a high production of CO2, but a significant higher formation of C2 hydrocarbons compared to the other samples as W/F increases [73].

ethane could be oxidized to CO2. This last hypothesis is reinforced due to the increasing CO2 concentration at higher temperatures, most likely due to the oxidation of part of C2H6 (which leads to H2O and CO2), according to the following reactions, suggesting different reaction

Table 4. Conversions and selectivities over LF and LCF perovskites. Experimental conditions: P = 1 atm, inlet molar CH4/

) Catalysts X CH4 (%) H2/CO Selectivity (%)

0.16 LC 13.7 1.8 55.8 31.5 5.50 7.10

0.40 LC 22.0 2.8 22.2 7.90 1.50 68.4

0.67 LC 28.6 3.5 25.7 7.30 0.70 66.3

Table 3. Conversions and selectivity results over perovskites. Experimental conditions: P = 1 atm, inlet molar CH4/O2

2 LF 31.0 3.2 8.30 2.60 5.30 83.8

4 LF 15.5 0.0 0 2.70 10.5 86.8

LCF 28.7 4.4 22.2 5.10 0.80 72.0

LCF 15.5 2.0 5.00 3.60 0.80 90.6

ratio = 2/1, space time of reactants = 0.16, 0.40 and 0.67 kg s mol�<sup>1</sup> and temperature of 700�C [73].

CH4:O2 Catalysts X CH4 (%) H2/CO Selectivity (%)

LF 19.2 1.6 46.0 28.0 4.10 22.0 LCF 17.1 1.9 59.2 30.9 3.80 6.10

LF 28.1 2.2 16.6 7.50 3.10 72.8 LCF 27.7 3.2 20.5 6.50 0.90 70.2

LF 31.0 3.2 8.30 2.60 5.30 83.8 LCF 28.7 4.4 22.2 5.10 0.80 72.0

H2 CO C2 CO2

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Syngas Production Using Natural Gas from the Environmental Point of View

H2 CO C2 CO2

, and temperature of 700�C [73].

Different reactions may occur in the whole process; the formation of the desired product with maximum selectivity depends on the input feed mixture. Steam increases the methane reforming and the water-gas shift (Eq. (7)) (WGS) reaction. It also helps to reduce the carbon deposition, which occurs during the dry reforming of methane [75]. Therefore, the addition of H2O is thermodynamically more favorable for the methane reforming than for the dry reforming [13]. For a lower H2O concentration, the methane conversion was lower than the CO2 conversion, which is assigned to the competition between H2O and CO2 molecules with methane. Increasing the H2O concentration input, the CO2 conversion decreases. Both WGS and steam reforming are equally important at a temperature below 650�C; however, with

paths: C2H6 + 1/2O2 ! C2H4 + H2O and C2H6 ! C2H4+ H2.

O2 ratio = 2/1 and 4/1, space time of reactants = 0.67 kg s mol�<sup>1</sup>

4. Discussion

W/F (kg.s.mol�<sup>1</sup>

Catalytic tests with the LF and LCF perovskites were also performed with a methane/oxygen ratio of 4 (W/F = 0.67 kg.s.mol�<sup>1</sup> ). Table 4 shows that increasing the CH4/O2 ratio to 4, the methane conversion was halved, compared to the previous condition at a CH4/O2 ratio of 2 [73].

The formations of ethane and ethylene are attributed to secondary reactions. In particular, the oxidative coupling of methane reaction takes place, which increased the C2H4 and C2H6 to C2H4 at high temperatures (2CH4 + 1/2O2 ! H2O + 1/2C2H6). Parallel reactions of oxidative or non-oxidative dehydrogenation of ethane would occur, converting also C2H6 to C2H4 and then


Table 3. Conversions and selectivity results over perovskites. Experimental conditions: P = 1 atm, inlet molar CH4/O2 ratio = 2/1, space time of reactants = 0.16, 0.40 and 0.67 kg s mol�<sup>1</sup> and temperature of 700�C [73].


Table 4. Conversions and selectivities over LF and LCF perovskites. Experimental conditions: P = 1 atm, inlet molar CH4/ O2 ratio = 2/1 and 4/1, space time of reactants = 0.67 kg s mol�<sup>1</sup> , and temperature of 700�C [73].

ethane could be oxidized to CO2. This last hypothesis is reinforced due to the increasing CO2 concentration at higher temperatures, most likely due to the oxidation of part of C2H6 (which leads to H2O and CO2), according to the following reactions, suggesting different reaction paths: C2H6 + 1/2O2 ! C2H4 + H2O and C2H6 ! C2H4+ H2.

#### 4. Discussion

over methane, CO2 and H2O conversions and H2/CO ratios [74]. The effect of concentration of O2 over the reactant conversion was mainly due to the heat generated by the partial oxidation and complete oxidation of methane and the enhanced coke removal process [76, 77]. Increasing O2 concentration, the total oxidation of methane also increases, due to the exothermic reaction, and the amount of energy is released. The heat generated is useful for the steam- and dry-reforming reactions, which are endothermic, minimizing the required temperature to obtain a higher CH4 conversion [78] and external energy. On the opposite, lower O2 concentrations led to lower conversion; however, increasing the temperature, H2O and CO2 react with methane to produce synthesis gas [77]. The higher H2/CO ratio was attributed to the steam reforming of methane, producing a H2/CO ratio of 3, attributed to the water-gas shift reaction, which produces only hydrogen, without the production of CO [79]. On the other hand, with increasing temperature, one observes that the RWGS (reverse water-gas shift) reaction outweighs other reactions [77].

4.8NiZrO2 80,000 0.75:1:2.1:5:18 60 50 55 2.3

Table 2. The effect of O2 concentration (mole ratio) on the reactant conversions verified by reference [74].

CH4 conv. (%)

1:1:2.1:5:18 83 81 82 2.0 1.25:1:2.1:5:18 90 38 89 3.0

CO2 conv. (%)

H2O conv. (%)

H2/CO ratio

Feed ratio, O2:CO2:H2O:CH4:

The effect of replacing cobalt by iron in LaCo1-xFexO3 (x = 0.0, 0.5 and 1.0) perovskite-type oxides on its catalytic performance in the partial oxidation of methane (POM) process was investigated, varying the space velocity and methane/oxygen ratio. The inlet methane to oxygen proportion was fixed at 2:1. The methane conversion increased with the space time and the maximum conversion was 31% at 0.67 kg.s.mol�<sup>1</sup> for the LF perovskite. In terms of product selectivity, the catalysts produced mainly H2 and CO, CO2, C2H4 and/or C2H6, as shown in Table 3. The product distribution varying with space time and perovskite type catalyst is found to be remarkable. The H2 production decreased by about a half and the CO decreased four times for both LC and LCF catalysts. However, the CO2 formation increased by a factor of about 10, and the H2/CO ratio also increased by a factor of 2. Different was the product distribution of the LF perovskite presenting low H2 and CO formations and a high production of CO2, but a significant higher formation of C2 hydrocarbons compared to the

Catalytic tests with the LF and LCF perovskites were also performed with a methane/oxygen

the methane conversion was halved, compared to the previous condition at a CH4/O2 ratio

The formations of ethane and ethylene are attributed to secondary reactions. In particular, the oxidative coupling of methane reaction takes place, which increased the C2H4 and C2H6 to C2H4 at high temperatures (2CH4 + 1/2O2 ! H2O + 1/2C2H6). Parallel reactions of oxidative or non-oxidative dehydrogenation of ethane would occur, converting also C2H6 to C2H4 and then

). Table 4 shows that increasing the CH4/O2 ratio to 4,

3.3. Effect of space velocity and methane/oxygen ratio

other samples as W/F increases [73].

Catalyst GHSV (ml.g�<sup>1</sup>

280 Biofuels - State of Development

h�<sup>1</sup> ) .

He

ratio of 4 (W/F = 0.67 kg.s.mol�<sup>1</sup>

of 2 [73].

Different reactions may occur in the whole process; the formation of the desired product with maximum selectivity depends on the input feed mixture. Steam increases the methane reforming and the water-gas shift (Eq. (7)) (WGS) reaction. It also helps to reduce the carbon deposition, which occurs during the dry reforming of methane [75]. Therefore, the addition of H2O is thermodynamically more favorable for the methane reforming than for the dry reforming [13]. For a lower H2O concentration, the methane conversion was lower than the CO2 conversion, which is assigned to the competition between H2O and CO2 molecules with methane. Increasing the H2O concentration input, the CO2 conversion decreases. Both WGS and steam reforming are equally important at a temperature below 650�C; however, with increasing temperature, the H2O conversion increases. Above 650�C, the RWGS reaction prevailed, producing less H2 and decreasing the H2/CO ratio [77, 80].

The reaction mechanisms are yet unknown for oxide catalysts and in particular for perovskite structures, which apparently are the most promising catalysts for the tri-reforming, based on the combined SRM, DRM and POM reactions. One explanation is that these materials present defects which promote the modification of electronic effects. Indeed, electronic effects may arise in the presence of ions with different charges of those belonging to the ions of the network, or as a consequence of the transition energy levels of electrons normally filled (usually the valence band) to empty levels (the conduction band). In all cases, when an electron is missing, that is, when there is an electron deficiency, this is usually called electronic holes. In the absence of an electric field, the ionic networks of the oxide structures tend to be electronically neutral, which requires that charge defects are compensated by the presence of other filler defects in order to obtain the condition of electro-neutrality, making the structure more stable. This means that charge defects are always present as a combination of two or more types of failures [55].

A reaction mechanism on mixed oxides can be suggested, assuming that CH4 is activated by the metal at the surface, forming carbon and H2. The carbon atoms adsorbed at the surface can react directly with oxygen, forming CO and H2. These intermediate species may react with the adsorbed CO2 species or dissociated steam. Song et al. [14] claim that the different extent of interaction between CO2 and catalysts could be responsible for this mechanism. They assumed that the interaction between CO2 and the catalyst could change the CH4 conversion rate, based on a simplified Langmuir-Hinshelwood (L-H) mechanism (Eqs. (10)–(12)).

$$\text{CH}\_4 + \Box \to \text{CH}\_4^\ominus \tag{10}$$

of CO2 to a high-valued product could provide the necessary economic incentive towards both CO2 mitigation and fuel generation. The study reported new strategies of CO2 valorization. The tri-reforming produces directly synthesis gas from flue gases using methane as a co-feed. The utilization of CO2 without pre-separation from its sources saves energy, since a substantial energy input is required for CO2 separation from its concentrated sources [81]. Tri-reforming of methane can be carried out by using CO2, H2O and O2 as a co-feed with natural gas or methane, and flue gas can be a very good source of highly concentrated feed for the tri-reforming process. New catalysts have been suggested with suitable promoters, mixed oxides and different supports, resistant to coke formation and sintering of the metal-active sites and stable at an elevated temperature. Stable and active catalysts for industrial application are under development, and researches are expected to bridge the gaps in science and technology for the tri-reforming

Syngas Production Using Natural Gas from the Environmental Point of View

http://dx.doi.org/10.5772/intechopen.74605

283

The authors would like to thank FAPESP and Shell for supporting the "Research Centre for Gas Innovation—RCGI" (FAPESP Proc. 2014/50279-4), hosted by the University of São Paulo.

Karina Tamião de Campos Roseno\*, Rita M. de B. Alves, Reinaldo Giudici and Martin Schmal

[1] Zhu Q, Zhao X, Deng Y. Advances in the partial oxidation of methane to synthesis gas.

[2] Hanbo Z, Shengzhou C, Jiangnan H, Zhaohui Z. Effect of impregnation sequence on the catalytic performance of NiMo carbides for the tri-reforming of methane. International Journal of Hydrogen Energy. 2017;42:20401-20409. DOI: 10.1016/j.ijhydene.2017.06.203 [3] Kleinert A, Feldhoff A, Schiestel T, Caro J. Novel hollow fibre membrane reactor for the partial oxidation of methane. Catalysis Today. 2016;118:44-51. DOI: 10.1016/j.cattod.2005.11.097 [4] Kohn MP, Castaldi MJ, Farrauto RJ. Biogas reforming for syngas production: The effect of methylchloride. Applied Catalysis. B, Environmental. 2014;144:353-361. DOI: 10.1016/j.

Department of Chemical Engineering of Polytechnic School, University of São Paulo,

process, providing further improvements and economically feasible.

\*Address all correspondence to: ktamiao@gmail.com

Journal of Natural Gas Chemistry. 2004;13:191-203

Acknowledgements

Author details

São Paulo, SP, Brazil

apcatb.2013.07.031

References

$$\text{CO}\_2 + \Box \to \text{CO}\_2^{\triangle} \tag{11}$$

$$\rm{CH\_4^{\ominus} + CO\_2^{\ominus} \to 2CO + H\_2 + 2^{\ominus}}\tag{12}$$

where □ are the metallic surface sites.

They observed that the reaction order of CH4 on Ni/MgO is strongly compared to the adsorption of CO2 over Ni/MgO/CeZrO which is close to zero. This suggests that the CH4 conversion rate almost does not change with the partial pressure of CO2. However, it was found that Ni/ MgO/CeZrO has even more stronger interaction with CO2 than Ni/MgO. In fact, the sites for a strong CO2 adsorption over Ni/MgO/CeZrO are probably not the same as for CH4 adsorption. It is important to note that the metal is itself believed to be able to activate CH4, as suggested by Rostrup-Nielsen [47], while the types of supports, like MgO, facilitate the adsorption of CO2. Hence, the locations of the interfaces between Ni and supports are fundamental, where the adsorption and reaction take place.

#### 5. Conclusion

The energy crisis is a problem which will get exacerbated with depleting crude oil reserves around the world. There is an urgent need for alternative fuels around the world. The conversion of CO2 to a high-valued product could provide the necessary economic incentive towards both CO2 mitigation and fuel generation. The study reported new strategies of CO2 valorization. The tri-reforming produces directly synthesis gas from flue gases using methane as a co-feed. The utilization of CO2 without pre-separation from its sources saves energy, since a substantial energy input is required for CO2 separation from its concentrated sources [81]. Tri-reforming of methane can be carried out by using CO2, H2O and O2 as a co-feed with natural gas or methane, and flue gas can be a very good source of highly concentrated feed for the tri-reforming process. New catalysts have been suggested with suitable promoters, mixed oxides and different supports, resistant to coke formation and sintering of the metal-active sites and stable at an elevated temperature. Stable and active catalysts for industrial application are under development, and researches are expected to bridge the gaps in science and technology for the tri-reforming process, providing further improvements and economically feasible.

#### Acknowledgements

increasing temperature, the H2O conversion increases. Above 650�C, the RWGS reaction

The reaction mechanisms are yet unknown for oxide catalysts and in particular for perovskite structures, which apparently are the most promising catalysts for the tri-reforming, based on the combined SRM, DRM and POM reactions. One explanation is that these materials present defects which promote the modification of electronic effects. Indeed, electronic effects may arise in the presence of ions with different charges of those belonging to the ions of the network, or as a consequence of the transition energy levels of electrons normally filled (usually the valence band) to empty levels (the conduction band). In all cases, when an electron is missing, that is, when there is an electron deficiency, this is usually called electronic holes. In the absence of an electric field, the ionic networks of the oxide structures tend to be electronically neutral, which requires that charge defects are compensated by the presence of other filler defects in order to obtain the condition of electro-neutrality, making the structure more stable. This means that

charge defects are always present as a combination of two or more types of failures [55].

on a simplified Langmuir-Hinshelwood (L-H) mechanism (Eqs. (10)–(12)).

CH□

where □ are the metallic surface sites.

the adsorption and reaction take place.

5. Conclusion

<sup>4</sup> <sup>þ</sup> CO□

A reaction mechanism on mixed oxides can be suggested, assuming that CH4 is activated by the metal at the surface, forming carbon and H2. The carbon atoms adsorbed at the surface can react directly with oxygen, forming CO and H2. These intermediate species may react with the adsorbed CO2 species or dissociated steam. Song et al. [14] claim that the different extent of interaction between CO2 and catalysts could be responsible for this mechanism. They assumed that the interaction between CO2 and the catalyst could change the CH4 conversion rate, based

CH<sup>4</sup> <sup>þ</sup> □ ! CH□

CO<sup>2</sup> <sup>þ</sup> □ ! CO□

They observed that the reaction order of CH4 on Ni/MgO is strongly compared to the adsorption of CO2 over Ni/MgO/CeZrO which is close to zero. This suggests that the CH4 conversion rate almost does not change with the partial pressure of CO2. However, it was found that Ni/ MgO/CeZrO has even more stronger interaction with CO2 than Ni/MgO. In fact, the sites for a strong CO2 adsorption over Ni/MgO/CeZrO are probably not the same as for CH4 adsorption. It is important to note that the metal is itself believed to be able to activate CH4, as suggested by Rostrup-Nielsen [47], while the types of supports, like MgO, facilitate the adsorption of CO2. Hence, the locations of the interfaces between Ni and supports are fundamental, where

The energy crisis is a problem which will get exacerbated with depleting crude oil reserves around the world. There is an urgent need for alternative fuels around the world. The conversion

<sup>4</sup> (10)

<sup>2</sup> (11)

<sup>2</sup> ! <sup>2</sup>CO <sup>þ</sup> <sup>H</sup><sup>2</sup> <sup>þ</sup> <sup>2</sup>□ (12)

prevailed, producing less H2 and decreasing the H2/CO ratio [77, 80].

282 Biofuels - State of Development

The authors would like to thank FAPESP and Shell for supporting the "Research Centre for Gas Innovation—RCGI" (FAPESP Proc. 2014/50279-4), hosted by the University of São Paulo.

#### Author details

Karina Tamião de Campos Roseno\*, Rita M. de B. Alves, Reinaldo Giudici and Martin Schmal

\*Address all correspondence to: ktamiao@gmail.com

Department of Chemical Engineering of Polytechnic School, University of São Paulo, São Paulo, SP, Brazil

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apenergy.2015.12.100

## *Edited by Krzysztof Biernat*

This book offers the current state of knowledge in the field of biofuels, presented by selected research centers from around the world. Biogas from waste production process and areas of application of biomethane were characterized. Also, possibilities of applications of wastes from fruit bunch of oil palm tree and high biomass/bagasse from sorghum and Bermuda grass for second-generation bioethanol were presented. Processes and mechanisms of biodiesel production, including the review of catalytic transesterification process, and careful analysis of kinetics, including bioreactor system for algae breeding, were widely analyzed. Problem of emissivity of NOx from engines fueled by B20 fuel was characterized. The closing chapters deal with the assessment of the potential of biofuels in Turkey, the components of refinery systems for production of biodegradable plastics from biomass. Also, a chapter concerning the environmental conditions of synthesis gas production as a universal raw material for the production of alternative fuels was also added.

Published in London, UK © 2018 IntechOpen © MosayMay / iStock

Biofuels - State of Development

Biofuels

State of Development