Catalysis for Glycerol Production and Its Applications

*Anele Sibeko, Lethiwe D. Mthembu, Rishi Gupta and Nirmala Deenadayalu*

#### **Abstract**

Globally, there is a climate change due to greenhouse gases, hence the production processes for chemicals should comply with green chemistry principles to decrease the impact it has on the climate. This book chapter focuses on the catalytic production of glycerol, which is a platform chemical that is widely used in the manufacture of various industrially important chemicals and derivatives, namely 2,3-dihydroxypropanal, glycerol ether, glycerol ester, acrolein, 1,2-propanediol and glycidol. The literature reviewed compares the production of glycerol using homogeneous and heterogeneous catalysts, to determine efficient and environmentally benign glycerol catalysts and to study glycerol as a platform chemical and its value in application.

**Keywords:** catalysis, homogenous catalysts, heterogeneous catalysts, value-added compounds, glycerol production

#### **1. Introduction**

The enormous growth in demand for fuels, along with growing environmental concerns and limited raw oil sources has increased the use of renewable energy. Biodiesel is one of the potential alternatives, and renewable fuels, has gained popularity in recent years, and their production capacity have grown significantly.

It is produced through various methods such as the transesterification of nonedible and waste vegetable oils with methanol and efforts are also being made to utilise the glycerol by-product to compensate the production cost of biodiesel to make it commercially viable, yielding quite significant percentage of a glycerol by-product which lowers the production cost and makes it commercially available. For every 4 litres of biodiesel generated [1].

Around 500 grams of glycerol is made, this equates to approximately 11,500 tons of 99.9% pure glycerine produced by a plant with a capacity of 113,562,354 million litres per year. The resulting oversupply of raw glycerol from biodiesel production can influence the purified glycerol market significantly as glycerol is a high-value and commercial chemical with thousands of applications [2].

Although extensive research has been carried out on the use of glycerol for various industrial applications, however, a compilation review on different approaches of glycerol production using homogenous and heterogeneous catalysts is scarce. The present chapter focuses on compiling different state-of-the-art in glycerol manufacturing techniques with a special emphasis on homogeneous and heterogeneous catalysis approaches. Moreover, an attempt has also been made to review the application of glycerol in the production of various platform chemicals preferably using microbial pathways. A section has been dedicated on reviewing the application of glycerol in animal feed.

## **2. Glycerol production**

Glycerol can be manufactured using a variety of chemical synthesis feedstocks. It can be produced, for example, by propylene synthesis by several methods [3], such as oil hydrolysis, or transesterification of fatty acids or oils. The following sections describe briefly about different glycerol production processes.

#### **2.1 Glycerol production by propylene**

As previously stated, several methods for producing glycerol from propylene can be used [4, 5]. In **Figure 1**, one of the major processes is shown, which includes the use of chlorination (Cl2) [6].

#### *2.1.1 Glycerol production via chlorination process*

Propylene chlorination (**Figures 1** and **2**) produces allyl chloride at a temperature of 510°C in the presence of hypochlorous acid at 38°C. Glycerine dichlorohydrin is formed when allyl chloride reacts. The glycerol dichlorohydrin is then hydrolysed by sodium carbon oxide in a 6% sodium carbonate solution at 96°C or directly to glycerine, the epichlorohydrin being removed as an overhead in a stripping column. Finally, the epichlorohydrin is hydrated to glycerine using sodium hydroxide [4], resulting in a final glycerol yield of around 90% [6].

#### **Figure 1.** *Flow diagram illustrating the production of glycerol from propylene [6].*

*Catalysis for Glycerol Production and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.109553*

#### **Figure 2.**

*Reaction of the propylene chlorination process.*

#### *2.1.2 Glycerol production via oxygenation process*

**Figure 3** illustrates two paths to produce glycerol from propylene via oxygenation. Oxygen (O2) reacts with propylene to produce acrolein, adding an aldehyde (HC=O). Acrolein can be converted to allyl alcohol with a reducing agent sodium borohydride (NaBH4) in a presence of isopropanol as a solvent; peroxide is added to allyl alcohol to produce glycerol. In the other reactions, peroxide is added to acrolein which results in the formation of glyceraldehyde; the glyceraldehyde reacts with hydrogen to produce glycerol.

#### **2.2 Saponification**

In this reaction, sodium hydroxide (base) reacts with triglyceride as an ester to form glycerol and soap molecules. This method has been employed since 2800, and the first industrial factory was developed in 1860 [7]. As demonstrated in **Figure 4**, this reaction occurs between triglyceride and sodium hydroxide (caustic soda), producing glycerol and soap [6, 8].

**Figure 3.** *Production of glycerol from propylene oxygenation reaction.*

#### **Figure 4.**

*Illustrates the saponification reaction between triglyceride and sodium hydroxide (caustic soda) for the glycerol production [6].*

#### **2.3 Transesterification of the beaver oil**

The transesterification reaction of beaver oil with ethanol to produce glycerol was carried out in 1864 [9, 10]. **Figure 5** shows the reaction in which methyl-esters from triglycerides (oils) and methanol (alcohol) combine to form glycerol and fatty esters (or biodiesel) [5, 6, 11, 12].

**Figure 5.**

*Glycerol production by a transesterification reaction [6].*


*Catalysis for Glycerol Production and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.109553*


#### **Table 1.**

*Different glycerol streams depending on initial feedstocks and production reactions.*

Interestingly, the glycerol yield from transesterification was not only found to be dependent on different types of processes but also on the different type of oil feedstocks (**Table 1**) [13–18].

#### **3. Glycerol catalysis**

Transesterification of oil is accomplished using both homogenous as well as heterogeneous catalysts. **Table 2** depicts glycerol production advantages and disadvantages of using different type of catalysts.

Moreover, depending on the type of catalyst used, the transesterification process can be categorised as homogeneous and heterogeneous catalysis to make biodiesel and subsequently glycerol.


#### **Table 2.**

*Advantages and disadvantages of glycerol catalysts [19].*

#### **3.1 Homogeneous catalysis**

During homogenous catalysis, the first stage comprises the reaction of vegetable oils with methanol in the presence of a catalyst, and then the separation of glycerol from the resultant mixture using a settler unit follows. The remaining flow is sent to a chamber that uses mineral acids to remove the catalytic component, resulting in two paths: a glycerol recovery chamber and an evaporator that separates biodiesel from the other products. The unit for purifying comprises three output units: the first with 80–95% glycerol; the second one with water, dissolved salts and unreacted methanol (it is then recycled back to the reactor); and one with fatty esters [12]. **Figure 6** depicts the glycerol manufacturing process employing homogeneous catalysts (namely, sodium hydroxide or sodium methylate) [6, 20, 21].

#### **3.2 Heterogeneous catalysis**

This type of catalysis procedure envisions two reaction phases to improve vegetable oil conversion; reactor 1 is supplied by vegetable oil and methanol. The product stream is sent through a heat exchanger to evaporate some of the residual methanol, and the remaining stream is directed to a decanter to separate polar and non-polar components such as glycerol and mainly vegetable oil and biodiesel, respectively. While, in reactor 2, the non-polar stream is reacted for the second time to boost biodiesel synthesis and recover methanol. The product stream travels through the heat exchanger, which takes out all unreacted methanol, and the decanter, which separates the biodiesel from polar components.

The polar streams from the first and second polar decanters are directed to another heat exchanger to recover the remaining methanol in the mixture, while the leftover fraction is delivered to a final decanter to separate vegetable oil and residual glycerol. **Figure 7** is a flowchart of triglyceride transesterification using heterogeneous catalysts such as aluminium and zinc oxide [6].

#### **Figure 6.**

*The production plant for biodiesel is based on a homogenous catalyst.*

*Catalysis for Glycerol Production and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.109553*

#### **Figure 7.**

*A heterogeneous catalysis-based production plant flowchart [6].*

#### **4. Glycerol: a platform chemical**

Synthesis of glycerol following microbial route has been known for over a century, however, new improvements in the biodiesel business have resulted in the production of large amounts of glycerol. During the biodiesel production process, approximately

**Figure 8.**

*Glycerol as a platform chemical.*

10% of glycerol is produced, accounting for about 90% of total glycerol produced [22]. Glycerol has gathered substantial interest in its conversion to higher value-added compounds due to its availability and potential to operate as a key building block in a biorefinery (**Figure 8**) [23].

Glycerol oxidation produces a wide range of compounds, such as glyceric acid dihydroxyacetone, glyceraldehyde, hydroxy-pyruvic acid, glycolic acid and others. Controlling reaction selectivity is a critical challenge in obtaining the desired molecules.

For example, glyceric acid is a crucial intermediary for more extensively oxidised compounds such as tartronic acid and mesoxalic acid. The catalytic aerobic oxidation of glycerol in a basic media has been extensively studied using monometallic or bimetallic catalysts such as Au, Pt and Pd.

**Table 3** lists some of the most prominent catalysts used in this field [24–27, 30, 38–40]. Another approach for producing value-added compounds from glycerol is the reduction process. Lactic acid is produced by a reduction of glycerol in the presence of hydroxide bases [41]. This reaction is frequently carried out at medium to high pressures and temperatures ranging from 100 to 240°C using Cu- and Zn-based catalysts enhanced by sulphide Ru [28].

Glycerol carbonate is another derivative of glycerol that is formed by reaction between glycerol and urea, ethylene or propylene carbonate [22] or carbon dioxide [42]. It is also used in the commercial manufacture of epichlorohydrin. Epichlorohydrin is produced in a similar manner by Solvay and Dow Chemical Company [43]. When the principal hydroxyl groups in glycerol are selectively oxidised, the economically valuable chemicals glyceraldehyde [44], glyceric acid [45] and tartronic acid [46] are formed. Dihydroxyacetone (DHA) is produced by oxidation of the secondary hydroxyl group, whereas ketomalonic acid is produced by oxidation of all three hydroxyl groups [47].

Another glycerol derivative, glycidol, offers immense potential for the synthesis of industrially useful compounds such as epoxy resins, polyurethanes and polyglycerol esters. A bio-based technique for producing glycidol from glycerol was recently published [48]. The manufacture of acrolein from glycerol is an innovative, eco-friendly technology that has several advantages, such as less oil extraction and a minimal environmental impact [31]. In general, acrolein is synthesised from glycerol by acidcatalysed dehydrogenation over synthetic aluminium phosphate (AlPO4), zeolites with varied channel configurations (HY and H-ZSM-5) and SiO2/Al2O3 ratio [31, 49].

A novel synthetic approach for the synthesis of chlorohydrin was proposed, which involved reacting a polyhydroxy aliphatic hydrocarbon with a chlorination agent. Vitiello et al. [33] focused on the activity and selectivity of homologous chlorinated series of catalysts for glycerol halogenation, such as acetic acid, monochloro, dichloro and trichloroacetic acid.

**Table 3** also includes information on one of the most significant glycerol conversion processes, esterification with acetic acid, which produces monoacylglycerol, diacylglycerol and glycerol carbonate. These materials are often used in cryogenics, biodegradable polyester and cosmetics [35, 36]. Sulphated-based superacids, heteropoly acid-based catalysts, tin chloride, zeolite, ZrO2-based solid acids and other significant acid catalysts can be used for glycerol esterification [35–37, 50–52].

Finally, pyrolysis of glycerol to produce syngas is another method of converting glycerol. The pyrolysis of biomass has been extensively studied in the specialist literature, although in most cases, only metal-based catalysts have been used. The microwave-assisted pyrolysis of glycerol over a carbonaceous catalyst is a unique approach


#### *Catalysis for Glycerol Production and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.109553*

#### **Table 3.**

*Compounds derived from traditional glycerol conversion under similar operating conditions.*

for syngas generation in which the heating method and operating temperature (between 400 and 900°C) can impact the catalytic action of the activated carbons to optimise syngas production [37]. **Table 3** outlines some of the products derived from glycerol that may be transformed into other compounds with high added value.

### **5. Value-added products from glycerol via biological conversions**

From 2004 to 2008, the global production of crude glycerol from biodiesel conversion increased from 200 thousand tonnes to 1.224 million tonnes [2, 19]. Meanwhile,

in 2005, the global market for purified glycerol was anticipated to be over 900,000 tonnes [53]. This provided a chance for scientists to discover new uses for refined and crude glycerol. Multiple publications on the direct use of crude glycerol from biodiesel synthesis have been published.

#### **5.1 1,3-Propanediol**

The most promising alternative for the biological conversion of glycerol in anaerobic fermentative production is 1,3-propanediol [54], which indicates that crude glycerol could be employed directly for the manufacture of 1,3-propanediol in fedbatch cultures of *pneumoniae*.

Raw glycerol composition had less influence on the biological conversion and, therefore, a low fermentation cost could be predicted. However, using a response surface approach, the generation of 1,3-propanediol by *Klebsiella pneumoniae* was optimised. The highest concentration of 1,3-propanediol produced However, statistical optimisation along with genetic engineering approaches may be utilised to improve the 1,3-propanediol production [14, 55]. *K. pneumoniae* ATCC 15380 recently improved the synthesis of 1,3-propanediol from crude glycerol from Jatropha biodiesel. The yield, purity and recovery of 1,3-propanediol obtained were 56 g/L, 99.7% and 34%, respectively [14]. In addition, a hollow fibre membrane was used to produce an integrated bioprocess that linked biodiesel generation by lipase with microbial production of 1,3-propanediol by *K. pneumoniae* [56].

#### **5.2 Citric acid**

Citric acid synthesis by *Yarrowia lipolytica* ACA-DC 50109 from raw glycerol was not only comparable to that obtained from sugar-based standard media [57] but also single-cell oil and citric acid were produced simultaneously [58, 59]. When acetate-negative mutants of the *Y. lipolytica* Wratislavia AWG7 strain were employed in a fed-batch fermentation to ferment crude glycerol, the final concentration of citric acid was 131.5 g/L, which was similar to that produced from pure glycerol (139 g/L). Similarly, *Y. lipolytica* LGAM S(7)1 has also shown the ability to convert crude glycerol to citric acid [60]. Interestingly, another strain *Y. lipolytica* N15 could produce large levels of citric acid, namely up to 98 g/L of citric acid and 71 g/L of citric acid from pure glycerol medium and crude glycerol medium, respectively [61].

#### **5.3 Hydrogen and other lower molecule fuels**

The photo-fermentative conversion of crude glycerol to hydrogen is one of the most fascinating approach to utilise glycerol. Both crude glycerol and pure glycerol can produce up to 6 moles of H2 per mole of glycerol, representing 75% of the theoretical value. However, significant technological challenges, such as increasing the efficiency of light use by organisms and building effective photobioreactors, must be overcome before a viable method can be developed [62]. When *Enterobacter aerogenes* HU-101 was used, hydrogen and ethanol were synthesised at high yields and rates. However, in order to improve the rate of glycerol use, the crude glycerol should be diluted with a synthetic medium [63]. While Jitrwung and Yargeau [64] modified several media compositions of the *E. aerogenes* ATCC 35029 fermented crude glycerol procedure to maximise hydrogen generation.

#### **5.4 Polyhydroxyalkanoates (PHB)**

As an estimate, a biodiesel facility with a capacity of 10 million gallons per year could produce 20.9 tons of PHB [65]. The feasibility of using crude glycerol for PHB manufacture was investigated using *Paracoccus denitrificans* and *Cupriavidus necator* JMP134, and the resultant polymers were shown to be remarkably comparable to those generated from glucose. However, a high osmotic (sodium chloride-contaminated) crude glycerol was found to have harmful impact on PHB synthesis and needs to be taken care of. One way to handle the issue is combining crude glycerol from various producers to reduce the harmful effect of NaCl contamination [66]. In addition, for a large-scale PHB synthesis, a technique based on the *C. necator* DSM 545 fermentation of crude glycerol was developed [67]. Following this in the presence of NaCl, *Zobellella denitrificans* MW1 could use crude glycerol for growth and PHB synthesis at high concentrations. As a result, it was recommended as an appealing alternative for large-scale PHB manufacturing using crude glycerol [68]. Furthermore, when mixed microbial consortia (MMC) were utilised to produce PHA from crude glycerol, it was shown that methanol in the crude glycerol was converted to PHB by MMC.

#### **5.5 Lipids as the sole carbon source**

Crude glycerol might be used to manufacture lipids, which could be utilised to make a sustainable biodiesel feedstock. For example, raw glycerol might be used to culture *Schizochytrium limacinum* SR21 and *Cryptococcus curvatus*. However, the glycerol


#### **Table 4.**

*Biological conversion of crude glycerol.*


**Table 5.**

*Conventional catalytic conversions of crude glycerol.*

content over a certain threshold may prevent the rapid reproduction of cells. The best glycerol content for batch culturing of crude glycerol obtained from yellow grease were 25 and 35 g/L for untreated and treated crude glycerol, respectively, which may subsequently lead to cellular lipid content of approximately 75%. Methanol residues in crude glycerol may cause damage to the development of *S. limacinum* SR21 [69].

For lipid synthesis in *C. curvatus* yeast, fed-batch was preferable to batch; however, the addition of ammonium sulphate and Tween 20 improved the accumulation of lipids and carotenoids Saenge et al. [70] demonstrated that the oleaginous red yeast *Rhodotorula glutinis* TISTR 5159 generated lipids and carotenoids when grown on crude glycerol. *Chlorella protothecoides* was also capable of converting crude glycerol to lipids.

The lipid yield was 0.31 g lipids/g substrate [71]. Similarly, using *C. protothecoides* and crude glycerol (62% purity), Furthermore, Chatzifragkou et al. [72] did research, to investigate the ability of 15 eukaryotic micro-organisms to change crude glycerol to metabolic products. The results showed that yeast accumulated limited lipids (up to 22 wt.% in the case of Rhodotorula), whereas fungi collected greater levels of lipids in their mycelia (range between 18.1 and 42.6 wt.% of dry biomass). Interestingly, Chen and Walker [73] found that a fed-batch operation yielded a maximum lipid productivity of 3 g/L per day, which was greater than that generated by a batch procedure.

**Tables 4** and **5** outline an overview of the conversions of crude glycerol to potential chemical through biological and catalytic conversions.

#### **6. Application of crude glycerol in animal feedstock**

Glycerol has been used as an animal feed additive since the 1970s [82]. However, the availability of glycerol has limited its application in diets [83], because of the rising corn prices and the oversupply of crude glycerol, the possibility of using crude glycerol from biodiesel in feeds has recently been examined.

#### **6.1 Crude glycerol in non-ruminant diets**

Crude glycerol is an excellent energy source due to its high absorption rates for non-ruminants such as broilers. Once ingested, the enzyme glycerol kinase converts it to glucose for energy generation in the liver of mammals [83]. Its samples from various biodiesel manufacturers were tested as energy sources. The digestible energy (DE) values for 85% of the crude glycerol samples ranged from 14.9 to 15.3 MJ/kg,

with metabolisable energy (ME) values ranging from 13.9 to 14.7 MJ/kg [84]. Overall, the use of crude glycerol derived from biodiesel process as an animal feed component offers significant potential for replacing maize in diets and is gaining popularity. However, the existence of potentially dangerous contaminants in biodiesel crude glycerol needs to be taken into consideration [85].

#### **6.2 Crude glycerol in ruminant diets**

Besides, the non-ruminants, crude glycerol may play a very significant role in the diets of ruminant animals as well. However, to improve its edibility, more emphasis should be placed on the crude glycerol produced by small-scale biodiesel plants that employ basic batch distillation or evaporation processes. There are several reports where use of crude glycerol has shown significant improvement in the overall performance of ruminants. Crude glycerol, at up to 15% dry matter in finishing lamb diets, might increase feedlot performance, particularly during the first 14 days, but had little influence on carcass attributes [86]. Diets for meat goats containing up to 5% crude glycerol were shown to be superior to medium-quality hay [87]. Nursing dairy cows can also be fed up to 15% of their dry matter diet without affecting feed intake, milk output or yield [88, 89]. When crude glycerol was added at 8% or less of dry matter in cow-finishing diets, its weight growth and feed efficiency were increased [90].

#### **7. Summary and conclusions**

Glycerol may be produced using various techniques and feedstocks, such as propylene synthesis by various routes, hydrolysis of fatty acid triglycerides, or transesterification of fatty acids or oils. The efficient use of crude glycerol is critical to the commercialisation and advancement of biodiesel synthesis. In the long run, using biomass-derived glycerol will not only help to reduce society's reliance on non-renewable resources, but it will also encourage the development of integrated biorefineries. This review focuses on the valueadded prospects for crude glycerol derived from biodiesel production, primarily as a feed ingredient for animal feed and as a feedstock for chemicals.

For example, crude glycerol can be converted into 1,3-propanediol, citric acid, poly(hydroxyalkanoates), butanol, hydrogen, docosahexaenoic acid-rich algae, monoglycerides, lipids and syngas. Though many of the processes discussed have already been employed by the industries, they require additional research to minimise the manufacturing cost and be operationally practical for inclusion into biorefineries.

Furthermore, contaminants in crude glycerol can have a noticeable impact on the conversion of glycerol into other products. Pollutants in crude glycerol hinder cell and fungi's rapid reproduction, resulting in less production rates and product yields in many biological conversion processes (compared with pure or commercial glycerol under the same culture conditions). Contaminants, on the other hand, poison the catalysts in traditional catalytic conversions, boosting char generation and affecting product yield.

Many technologies need to be better understood and refined, such as optimising reaction parameters, production yields and fermentation conditions; generating mutant strains and efficient bioreactors for stable cultures and enhancing the activity and selectivity of catalysts.

Researchers have also obtained promising results on utilisation of crude glycerol as animal feed, particularly with non-ruminant animals such as pigs, laying hens and broilers. But various precautions must be taken before this biomass-derived chemical may be used on a large scale in animal diets. To begin with, animal producers must exercise caution when deciding to incorporate crude glycerol as a component of animal feed diets, since the chemical composition of crude glycerol varies greatly depending on the processes and feedstocks used to manufacture biodiesel. Secondly, contaminants in crude glycerol affect feed performance to some extent. Finally, the amount of crude glycerol in feed formulations must be considered. It is advised that a crude glycerol feed standard be established so that it would be uniform for all producers, the resulting "standard" crude glycerol would have greater value.

There is a need to develop improved processes as well as other important valueadded products. For example, among other renewable and bio-derived sources, glycerol has come up as an appealing possibility since it represents a relevant and alternative solution for producing hydrogen via reforming processes that may be carried out in both traditional and novel reactors.

Besides, catalytic process, though it is not yet introduced, the transesterification reaction using supercritical fluids has also gained noticeable attention. As one or two reaction stages are possible in a single-step supercritical fluid transesterification, the reaction occurs only once reactants are heated to critical temperatures and pressures with triglycerides [20, 21]. Triglycerides are initially transformed to free fatty acids and by-products in the hydrolysis reaction during the two-step subcritical-supercritical fluid transesterification. The acquired free fatty acids undergo esterification reaction, yielding fatty acid methyl esters in a supercritical fluid process [91, 92].

#### **Conflict of interest**

The authors declare no conflict of interest.

### **Author details**

Anele Sibeko1 , Lethiwe D. Mthembu1 \*, Rishi Gupta<sup>2</sup> and Nirmala Deenadayalu1

1 Department of Chemistry, Durban University of Technology, Berea, Durban, South Africa

2 Anton Paar India Pvt. Ltd., Gurugram, Haryana, India

\*Address all correspondence to: lethiwem@dut.ac.za

© 2023 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.

*Catalysis for Glycerol Production and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.109553*

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## **Chapter 3** Bioethanol Production

*Chakali Ayyanna, Kuppusamy Sujatha, Sujit Kumar Mohanthy, Jayaraman Rajangam, B. Naga Sudha and H.G. Raghavendra*

#### **Abstract**

In recent decades, usage of biofuels as fossil fuel substitutes has increased. One method for lowering both crude oil use and environmental pollution is the production of ethanol (bioethanol) from biomass. This report offers an examination of the existing state of affairs and future prospects for biomass-to-ethanol. We examine different conversion routes from a technological, economic, and environmental standpoint. The main focus of this study is on the yield of ethanol from molasses in relation to the dilution ratio and the quantity of yeast used for fermentation while maintaining a constant fermentation temperature and time. In this investigation, the feedstock is sugarcane molasses. A thick by-product of turning sugar cane into sugar is sugarcane molasses. Consequently, sugarcane molasses and other agricultural byproducts are desirable feedstock for the manufacture of bioethanol. Agricultural wastes are cheap, abundant, and renewable. The least expensive strain for the conversion of biomass substrate is *Saccharomyces cerevisiae*. As a conclusion, it was found that the ethanol yield increased with an increase in yeast quantity, reaching an optimal yeast quantity before ethanol yield started to drop. The ideal ratio of molasses to water was found to be 1:2. The amount of fermentable sugars contained in the biomass has a significant impact on the output of ethanol.

**Keywords:** bioethanol, fermentation, feedstock, *Saccharomyces cerevisiae*, sugarcane molasses

#### **1. Introduction**

The research for alternative energy sources is stimulated by the growth in the nation's renewable sources and the gradual depletion of oil resources [1]. Particularly, biomass is a renewable resource that is currently researched for the utilization of bioethanol as an additive or replacement with gasoline has been driven by concerns about global warming and the need to lower greenhouse gas emissions [2]. Bioethanol can also be used as a raw material in the manufacture of various chemicals, resulting in fully renewable chemical industry. Bioethanol is created by fermenting sugars derived from biomass. Sucrose (e.g., sugarcane, sugar beet) or starch (e.g., corn, wheat), or lignocellulosic material can be used as bioethanol feedstock (e.g., sugarcane bagasse, wood, and straw). The main ethanol producers in the world, the US and Brazil, employ corn and sugarcane as their respective feedstocks. The use of fossil fuels during the processing of sugarcane is far lower than that of corn, making it the most

effective raw material for the manufacturing of bioethanol to date [3]. Additionally, there is still room for improvement in the sugarcane-based bioethanol manufacturing process, and large energy savings are conceivable.

Brazil, one of the world's top ethanol producers, has been using sugarcane as a primary input for the production of huge amounts of bioethanol for more than 30 years [4]. Large amounts of sugarcane bagasse are often created during the sugarcane processing (about 240 kg of bagasse with 50% humidity per ton of sugarcane), and this bagasse are presently burned in boilers to produce steam and power. It is now possible to have a surplus of bagasse thanks to improved cogeneration and optimization techniques for the bioethanol production process [5], which can be used as a fuel source for power production or as a raw material for making bioethanol and other biobased products [6]. Although sugarcane bagasse and other lignocellulosic materials have been the subject of intense research over the past few decades, it is still not economically feasible to produce bioethanol on an industrial scale [2]. To make hydrolysis a competitive technique, more research that takes into account process integration, increased fermentation yields, and integration of unit operations is still required [7, 8]. Hemicellulose, a mixture of polysaccharides primarily made of glucose, mannose, xylose, arabinose, lignin, and cellulose makes up the majority of lignocellulosic materials [1]. Sugarcane bagasse needs to be treated to produce fermentable sugars in order to be used as a raw material for bioethanol production [9]. To improve cellulose hydrolysis, lignin and hemicellulose must be separated from cellulose, cellulose crystallinity must be reduced, and the bagasse's porosity must be increased [10]. The Organogold procedure with diluted acid hydrolysis is one approach that might be used to accomplish that [11].

#### **2. Bioethanol production**

A gasoline substitute known as bioethanol (grain alcohol; C2H5OH (EtOH)) was used for transportation [12]. Globally, the amount of bioethanol produced has drastically increased [13]. Worldwide production of bioethanol climbed to 51,3 billion liters in 2006 from 45,98 billion liters in 2005 [2, 12]. Biomass-derived ethanol has been shown to be competitive with other liquid fuels on a large scale. The production method was refined and made practical by cellulose's enzymatic hydrolysis [9]. The creation of bioethanol from biomass was one method for lowering oil consumption and environmental contamination [12].

The production use of bioethanol is relevant to major national concerns like permanence, global climate change, biodegradability, municipal contamination, coal sequestration, national security, and the farm economy. It was obvious that production should be assessed in terms of economic factors, including farm-gate prices for biomass, logistic costs (transport and storage of biomass), the direct economic value of feedstocks taking into account byproducts, employment creation or maintenance, water requirements, and water availability [2, 12].

The comparison of the feedstocks for a given production line took into account a number of factors, including the chemical makeup of the biomass, cultivation methods, land availability and land use practices, resource use, energy balance, emission of greenhouse gases, acidifying gases, and ozone-depleting gases, mineral absorption into water and soil, pesticide injection, soil erosion, contribution to biodiversity, and landscape value losses [12]. Agricultural leftovers (such as corn stover and wheat straw), wood, and energy crops were all desirable raw materials

#### *Bioethanol Production DOI: http://dx.doi.org/10.5772/intechopen.109097*

for the synthesis of bioethanol [12]. The total amount of bioethanol that might be produced from such biomass was nearly 16 times greater than what is currently produced globally [14].

Arable agricultural starch and sugars were mostly used to make ethanol. Because it was pricey, the quest for other materials that would work for this purpose started [15]. Different processes were utilized depending on the type of biomass used to produce the bioethanol. It was difficult to bio-convert lignocellulosic biomass into fermentable sugars. The bioconversion of starch to sugars for the creation of bioethanol was more efficient and popular [16].

Through the hydrolysis and fermentation of sugars, biomass can be transformed into ethanol. Biomass wastes contain a complex mixture of cellulose, hemicellulose, and lignin, three carbohydrate polymers found in plant cell walls. In order to get sugars from the biomass, the biomass is first pre-treated with acids or enzymes to reduce the size of the feedstock and to open up the plant structure. Enzymes or weak acids hydrolyze the cellulose and hemicellulose components to produce sucrose sugar, which is subsequently fermented to produce ethanol. The biomass, which also contains lignin, is typically burned in the boilers of ethanol manufacturing facilities. The three main techniques for extracting sugars from biomass are as follows.

#### **3. Method of intense acid treatment**

The biomass needs to first be dried to a moisture level of 10% before the Alkanol process can begin, which involves adding 70–77% sulfuric acid. The temperature is kept at 50°C and the acid is added at a ratio of 1.25 acid to 1 biomass. The mixture is then heated to 100°C for another hour after the water is added to dilute the acid to 20–30%. The gel that results from this combination is then compressed to produce an acid-sugar mixture, which is purified to use a chromatographic column.

#### **3.1 Acid hydrolysis in dilutes**

One of the earliest, simplest, and most effective processes for generating ethanol from biomass is dilute acid hydrolysis. The biomass is hydrolyzed to produce sugar using diluted acid. The hemicellulose included in the biomass is hydrolyzed in the first step using 0.7% sulfuric acid at 190°C. An improved second stage results in a more

robust cellulose fraction. By utilizing 0.4% sulfuric acid at 215°C, this is accomplished. Following neutralization, the liquid hydrolases are recovered from the process.

#### **3.2 Enzymatic Hydrolysis**

We can similarly break down the biomass using enzymes as opposed to utilizing acid to hydrolyze it into sugar. However, this procedure is still being developed and is highly expensive.

#### **3.3 Wet milling processes**

Corn can be processed into ethanol using either the dry milling or the wet milling method. The wet milling procedure involves soaking the maize kernel in warm water. This aids in the breakdown of the corn's proteins, the release of its starch, and softening of the kernel in preparation for milling. Then, the ground maize is used to make products with starch, fiber, and germ. A gluten-wet cake is made from the starch fraction after it has been centrifuged and saccharified; maize oil is then made by removing the germ. The next step is to extract the ethanol using the distillation process. The wet milling method is commonly applied in businesses that generate several hundred million gallons of ethanol annually.

#### **3.4 Dry milling process**

Using a hammer mill, the maize kernel is cleaned and reduced to tiny pieces for dry milling. This results in a powder with a consistency similar to a coarse flour. Maize germ, starch, and fiber make up the powder. The combination is hydrolyzed, or changed into sucrose sugars, using enzymes or a moderate acid to create a sugar solution. After cooling, adding yeast causes the mixture to ferment into ethanol. In facilities that annually produce fewer than 50 million gallons of ethanol, dry milling is frequently employed.

#### **3.5 Sugar fermentation process**

The cellulose component of biomass or corn is broken down during the hydrolysis process into sugar solutions, which can subsequently be fermented to produce ethanol. The mixture is heated after adding the yeast. Invertase, an enzyme found in yeast, serves as a catalyst and aids in the breakdown of sucrose carbohydrates into glucose and fructose (both C6H12O6).

The chemical reaction is shown below


 A second enzyme called zymase, which is also present in yeast, then reacts with the fructose and glucose carbohydrates to create ethanol and carbon dioxide.

The chemical reaction is shown below:


 Between 250°C and 300°C, the fermentation process is carried out over the course of around 3 days.

#### **3.6 Fractional distillation process**

 The fermentation process results in the production of ethanol, but there is still a sizable amount of water present that needs to be removed. Utilizing the fractional distillation method, this is accomplished. The mixture of water and ethanol is heated during the distillation process. The fact that ethanol has a lower boiling point than water (78.3 vs. 100°C) means that it can be separated and condensed before water does.

#### **4. The possibility of using bioethanol**

 The performance of the vehicle would not be affected if bioethanol were used as a pure fuel or in a blend with other fuels in sufficient quantities to replace conventional motor fuels [ 17 ]. Without any adjustments, the mixture might be burned in a conventional combustion process. Gasohol was the most popular bioethanol-petrol mixture

(E10). 10% bioethanol and 90% gasoline were combined to create gasohol. Most contemporary automobiles with internal combustion engines (ICEs) were capable of burning E10 [12, 17]. The fuel blend E85, which is composed of 15% gasoline and 85% bioethanol, may also contain bioethanol [18]. About 5% of the ethanol created biologically was water. This blend was azeotropic. Because of this, ordinary distillation was insufficient to clean it. Gasoline and diesel fuel were not entirely blended with hydrated ethanol.

Bioethanol and diesel could be blended together by employing the right emulsifiers. Diesohol is a mixture of hydrated alcohol with diesel oil with an emulsifier. Diesel, hydrated ethanol, and a 0.5 percent emulsifier were used to make diesohol [17]. Ethanol was used as gasohol or clean fuel in Brazil (24% bioethanol and 76% gasoline) [12, 19]. The EN228 standard allows for the use of bioethanol as a 5% blend of gasoline in the European Union [12, 20]. Bioethanol was an oxygenated fuel with 35% oxygen content. Lowering the amount of nitrogen oxide (NOx) and particle pollutants produced during combustion. Utilizing a bioethanol-fuel combination allowed for the decrease in greenhouse gas (GHG) output and oil consumption [12]. It was possible to increase the fuel's oxygen content by adding bioethanol to conventional gasoline, which increased fuel combustion and reduced exhaust pollutants such CO and unburned hydrocarbons [12, 16]. Bioethanol was added to gasoline to reduce environmental pollution and the use of fossil fuels. Because 1 liter of bioethanol could substitute for 0.72 liters of gasoline, using it as a gasoline substitute proved very costeffective [14].

#### **5. Conclusion**

Bioethanol can be employed as a fuel source. Studies are now being done to advance biofuel producing technologies. Bioethanol manufacturing could be carried out using biomass as a raw source. The investigation mainly concentrated on the usage of biomass wastes. With the help of starch and lignocellulosic biomass, bioethanol was formed. Starch was transformed into bioethanol via three sequential steps: hydrolysis, fermentation, and product purification. Hydrolysis, fermentation, pretreatment, and purification were the four steps that were followed in order to produce bioethanol from lignocellulosic biomass. Pretreatment can be done physically, physiochemically, chemically and biologically. Each of these approaches has benefits and drawbacks. It played a crucial role in choosing the best pretreatment strategy. It was crucial to focus on the creation and application of suitable pretreatment techniques in addition to other phases of the synthesis of bioethanol.

### **Author details**

Chakali Ayyanna1 \*, Kuppusamy Sujatha2 , Sujit Kumar Mohanthy3 , Jayaraman Rajangam4 , B. Naga Sudha5 and H.G. Raghavendra1

1 Department of Pharmacology, CES College of Pharmacy, Kurnool, India

2 Department of Pharmaceutical Chemistry, Sri Ramachandra Institute of Higher Education and Research, Chennai, India

3 Department of Pharmaceutical Chemistry, Shri Vishnu College of Pharmacy, Bhimavaram, India

4 Department of Pharmacology, AMITY Institute of Pharmacy, AMITY University, Lucknow, India

5 Department of Pharmaceutical Chemistry, CES College of Pharmacy, Kurnool, India

\*Address all correspondence to: ayyannac5@gmail.com

© 2023 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.

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Section 2
