Section 3 Biodiesel Catalysts

## **Chapter 4**

## Recent Developments in Catalysts for Biodiesel Production Applications

*Teketel Alemu and Anshebo Getachew Alemu*

## **Abstract**

The world's most urgent problem today is the quick depletion of energy resources, which necessitates research into alternative energy sources in order to meet the world's explosive growth in energy demand. Among other renewable energy sources, biodiesel holds promise for meeting energy demand at a low cost through a variety of processes. In the biodiesel industry, sophisticated catalysts have recently grown in popularity for their ability to activate esterification and transesterification processes. The goal of this chapter is to give a general overview of catalyst developments, including their benefits and drawbacks in the biodiesel production process. In particular, we present a comparison of various homogeneous and heterogeneous catalysts. We found that nanocatalysts hold the most promise for the production of biodiesel.

**Keywords:** biodiesel, homogenous, heterogeneous, nanocatalysts, biodiesel production

## **1. Introduction**

The increased global energy demand and the pursuit of environmentally friendly technology drive researchers toward alternative energy sources [1]. Currently, crude oil (35%), coal (29%), natural gas (24%), nuclear energy (7%), and renewable energy (5%) account for the majority of global energy consumption from fossil fuels [2]. This increased use of fossil fuels contributes to the global collapse of fossil fuels, air pollution, and global warming. Furthermore, it is predicted that all fossil fuel sources will be depleted by 2050 [3]. As a result, scholars have been motivated to find out renewable energy sources as clean energy alternatives, such as solar, wind, tidal, and geothermal energy, as well as biomass derived energy, to overcome these energy limitation [4]. Numerous innovative ideas can improve renewable energy technologies and provide sustainable methods to meet rising energy demand in a clean environment. In this regard, biodiesel is a potential fuel with a lower use of fossil fuels [5].

Furthermore, biodiesel offers the same performance as engine stability as petroleum diesel fuel, is nonflammable and nontoxic, reduces tailpipe emissions, visible smoke, and noxious fumes, and is safe for use in all conventional diesel engines [6]. It is produced from mono-alkyl esters of long-chain fatty acids through transesterification of vegetable oil by using catalysts as shown in **Figure 1**. It is renewable, nontoxic, biodegradable, and environmentally friendly and can be used in

 **Figure 1.**

 *Transesterification reactions of glycerides with alcohol to get methyl esters [ 7 , 8 ].* 

 **Figure 2.**  *Different feedstocks for biodiesel production.* 

*Recent Developments in Catalysts for Biodiesel Production Applications DOI: http://dx.doi.org/10.5772/intechopen.109483*

compression-ignition (diesel) engines with little or no modification due to its adjustable physical and chemical properties. It is a renewable energy source made from various oil sources, such as animal fat, canola, mustard, soybean, and sunflower, waste oils, such as waste edible or nonedible oil, waste cooking oil, and microbial oil.

**Figure 2** shows various sources of feedstock for biodiesel production. Furthermore, essential microorganisms in biodiesel production are classified into four types: bacteria, fungi, microalgae, and yeasts [7]. Yeasts include *Rhodotorula graminis* [8], *Candida tropicalis*, and *Yarrowia lipolytica* [9]. Fungi also include *Coniochaeta hoffmannii*, [10] *Alternaria alternata*, *Cladosporium cladosporioides*, *Epicoccum nigrum*, *Ffusarium oxysporum*, *Aspergillus parasiticus*, and *Emericella nidulans* [11]. *Chlorella minutissima* [12], *Scenedesmus obliquus*, and *Desmodesmus* spp. [13] are among the microalgae. Furthermore, bacteria such as *Serratia* sp. and *Bacillus* sp. were used [14–17]. Additionally, biodiesel is an ethyl ester derived from plant oil, microbial oil, animal oil, and the disposal of edible oil [16, 18].

## **2. Biodiesel production methods**

Generally, there are many ways for biodiesel production. Recently, the most commonly used methods are esterification and transesterification. According to recent reports, esterification stands for the reaction of FFAs and alcohol to make FAAEs, and water is released, whereas transesterification stands for the reaction of triglycerides or triacylglycerols (TAGs) with alcohol to make FAAE and glycerol is produced as a by-product [16, 18]. In terms of reaction rate, esterification process is faster than transesterification process, for the reason that of it is short step reaction as shown in **Figure 1** [19, 20].

## **3. Catalysts for biodiesel production**

Recently, catalysts have drawn a lot of attention for their applications in a range of fields, including materials science, bioremediation, food, photonic crystals, cosmetics, medication delivery, and food [19]. Nanomaterial-based catalysts have enormous promise for reducing biodiesel production costs and hastening transesterification processes [21]. The transesterification process is researched mostly through the employment of various types of nanocatalysts. The core, the surface, and the shell are the three layers that make up a nanoparticle, which is not a straightforward molecule. The NP's central region is known as the core, and its surface layer is made up of small molecules [8, 20, 22].

This chapter aims to overview recent developments in catalyst research and the types used in this process and their application to the production of biodiesel. Then, we point out the limitations of nanocatalysts in the production of biodiesel.

#### **3.1 Biocatalysts (Enzyme)**

Generally, either catalytic or non-catalytic processes are employed in the production of biodiesel. Among catalytic techniques, biocatalysts can be a successful way to make biodiesel in a sustainable way. Biocatalytic technologies for making biodiesel are in urgent demand to mitigate greenhouse gas emissions from conventional diesel or fossil fuels. The transesterification process in the production of biodiesel is usually catalyzed by lipases with superior biochemical and physiological features. In total,

70–95% of ethanol and methanol are produced by bacterial and fungal lipases [22]. Biodiesel is typically made of fatty acid alkyl esters, which are either mono-alkyl esters of fatty acid methyl esters or fatty acid ethyl esters, depending on the alcohol employed in the synthesis as shown in **Figures 1** and **3**.

Furthermore, the problems brought on by alkali and acid-catalyzed procedures are minimized by the biocatalytic biodiesel synthesis process. Since enzymes can esterify low-quality feedstock with a high concentration of free fatty acids, using enzyme catalysts has a number of economic and environmental advantages, such as the production of pure and highly valuable glycerol, the generation of the least amount of wastewater, the use of mild reaction conditions, and the absence of soap formation (FFA). Because they are simple to separate from the reaction mixture and have a generally lower chance of contamination, this production process is uncomplicated and has a low energy consumption [23, 24]. Recent developments in biomaterial catalysts, including cellulose, cellobiose, glucosidase, laccase, and xylanase, increase the effectiveness and durability of catalytic processes. Since nano biocatalysts may easily be reused and recovered by a continuous and large-scale process, using biocatalysts makes biocatalyst recovery and reusability easy (**Figure 4**) [24, 25].

## **3.2 Homogeneous catalysts**

The most common biodiesel productions process, such as esterification, ester hydrolysis, and transesterification, have all been studied by using both acid and base homogeneous catalysts. A chemical in a like phase of the reaction structure catalyzes a series of reactions in production kinetics. The homogeneous catalyst is the most popular catalyst used because it is easy to react, good conversion rate, and very fast to complete the reaction in the synthesis of biodiesel. In order to dissolve homogeneous

*Recent Developments in Catalysts for Biodiesel Production Applications DOI: http://dx.doi.org/10.5772/intechopen.109483*

#### **Figure 4.**

 *The various types of catalysts.* 

catalysts, the solvent is normally in the same phase as all of the reactants. However, the fundamental limitation it is problematic for reuse, and sometimes recycling this catalyst is very expensive [ 25 , 26 ].

#### *3.2.1 Homogeneous alkaline (base) catalysts*

 These catalysts are mostly alkaline liquids with high activity in transesterification reaction of low free fatty acid (FFA) [ 25 , 26 ]. The extensively used catalysts, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), potassium methoxide (CH 3 OK), and carbonates ( **Table 1** ) [ 27 – 43 ]. The conservative method for producing biodiesel from pure vegetable oils is the transesterification process using alkaline catalysts. For example, three moles of alcohol and one mole of triglyceride undergo this reaction, producing one mole of glycerol and three moles of fatty esters. The best alcohol-to-triglyceride ratio was a six-to-one give-up, which was 98%. Alkali metal methoxides are more energetic than alkali metal hydroxides, for the production of biodiesel, but its drawback is the significant amount of FFA remains as soap, it requests an extra catalyst and the catalyst is lost to the soap [ 44 , 45 ]. In addition, deactivation, slow reaction rates, and saponification are the main drawback of alkaline catalysts, difficult to discern the product from biodiesel in the reaction system have greater than 2.5% FFA concentration result unwanted saponification, leads to a loss in enzymatic activity and requires extra energy to solve various technical issues [ 46 , 47 ].

#### *3.2.2 Homogeneous acid catalyst*

 The homogenous acid catalysts, such as hydrochloric acid (HCl), sulfonic(R-SO 3H), and sulfuric acids (H 2 SO4), as well as Brønsted acids are commonly used catalysts for both the esterification and transesterification process ( **Table 1** ). These catalysts increase the yield of alkyl esters and lesser the cost of the feedstock, making the process more cost-effective. However, the process is less appealing since it requires high temperatures, operates more slowly, causes corrosion, and has higher purifying and separation expenses. Less rate reactions are involved in the transesterification processes catalyzed by acids. However, due to the slower reaction rates compared to alkali-catalyzed reactions and the higher energy demands, the procedure is economically difficult [ 48 , 49 ].


#### **Table 1.**

*Various nanocatalysts are used for biodiesel production from different sources [27–43].*

Therefore, homogeneous acid catalysis is applicable for both transesterification and esterification reaction processes [50, 51]. For example, p-toluene sulphonic acid catalyst and the Amberlyst-35 sulphonic acid catalyst were employed in series at 5% concentration in a specific application to extract the ester from vegetable refining waste. There are various alcohols, such ethanol, butanol, and methanol, for esterification reactions producing >90% biodiesel [52].

### **3.3 Heterogeneous catalysts**

These groups of catalysts are involved in a different state of product and reactants and also, they are noncorrosive, as well as easily separable from the products. These catalysts offer certain exceptional qualities. Furthermore, heterogeneous catalysts (solid) have empathetic nature with little harm to the environment. It is crucial to develop some suitable heterogeneous catalysts for the manufacture of biodiesel from affordable feedstocks. These heterogeneous catalysts are further subdivided into basic and acidic catalysts [51, 52].

### *3.3.1 Heterogeneous base catalysts*

Heterogeneous base catalysts overcome a number of obstacles, including saponification, which prevents glycerol from separating from the methyl ester layer. Heterogeneous base catalysts overcome a number of obstacles, including saponification, which prevents glycerol from separating from the methyl ester surface. In contrast, these catalysts have promising advantages such as environmental friendliness, reduced waste material harm, non-corrosiveness, selectivity, tolerance of high

### *Recent Developments in Catalysts for Biodiesel Production Applications DOI: http://dx.doi.org/10.5772/intechopen.109483*

FFA and moisture contents, promoting simple recovery, reusability, low cost, and green process. They can also be modified to increase activity, selectivity, and catalyst lifetime [53, 54]. Base alkali earth metal oxides, such as BeO, MgO, CaO, SrO, BaO, and RaO [55, 56], transition metal oxides [57], mixed metal oxides, such as CaTiO3, CaMnO3, Ca2Fe2O5, CaZrO3, and CaO-CeO2, ion exchange resins, and alkali metal compounds based on alumina are the most useful [58–61]. These solid-base catalysts, including CaO, MgO, SrO, KNO3/Al2O3, K2CO3/Al2O3, KF/Al2O3, Li/CaO, and KF/ZnO, applicable for transesterification [62, 63]. The basic hydrotalcite of Mg/Al, Li/Al, anion exchange resins, base zeolites, hydrotalcite, calcium carbonate rock, Li/ CaO, MgO/KOH, and Na/NaOH/-Al2O3 [64–67]. The oxide catalysts exhibit high yields and stability in the transesterification process [68, 69].

#### *3.3.2 Heterogeneous acid catalysts*

These catalysts are less toxic, corrosive, and cause less environmental issues [70]. They have a variety of acidic sites with varying levels of Lewis acidity. Despite offering encouraging results under modest reaction circumstances, they react much more slowly than solid base catalysts. These kinds of catalysts have further conditions like a high catalyst loading, high temperature, and prolonged reaction time [71]. Additionally, solid acid catalysts support the simultaneous transesterification and esterification of oils with high FFA contents to produce biodiesel. For example, solid-acid catalysts with organo-sulfonic groups, such as Nafion and Amberlyst, are used to speed up the esterification of fatty acids. In the transesterification reaction, another mesostructured catalyst modified by sulphonic acid is employed, leading to conversion rates as high as 100% [56, 72–74].

#### *3.3.3 Heterogeneous nanocatalysts*

These catalysts are known to improve the rate of transesterification reaction by removing unwanted processes and unnecessary reaction yield. These catalysts advance simple recovery, reusability, and a cost-effective friendly process [75]. In addition, these catalysts exhibit a number of advantages, such as enduring high FFA and moisture content, essential in certain insensitive high temperature and pressure. The cost-effective heterogeneous catalysts help out to diminish the overall cost of biodiesel production. These catalysts may be made to have a maximum yield of a reaction product by altering the number of atoms, surface functionality, and elemental composition, and they also have an efficient surface area, high stability, and higher resistance to saponification [76–80]. There are variety of techniques, including vacuum deposition, self-propagating high-temperature synthesis, evaporation, coprecipitation, electrochemical deposition, microwave combustion, hydrothermal, solvothermal, impregnation, and sol–gel technology [56, 81]. These catalysts are formed from nanoparticles with less than 100 nm variety of sizes and morphologies. They demonstrate critical advantages for both heterogeneous and homogeneous catalysts in terms of activity, selectivity, efficiency, and reusability [82, 83]. Here, biodiesel nanocatalysts are divided into magnetic and nonmagnetic categories.

### *3.3.3.1 Magnetic nanocatalysts*

These catalysts can aid in the reaction without the need for centrifugation or ultra-filtration. It is a powerful tool for the rapid separation of catalysts from reaction systems, offering an alternative to time-consuming, solvent-intensive,

and energy-intensive separation procedures while sustaining catalytic activity for successive cycles. They are suitable for inexpensive feedstocks [84, 85]. Among the number of magnetic catalyst Fe3O4, Cao/Fe3O4,Ca(OH)2/Fe3O4,Cs/Al/ Fe3O4,KF/CaO-Fe3O4,Fe3O4@SiO2,MgO/MgFe2O4, and Ca/Fe3O4@SiO2 are few of the magnetic catalyst that have recently been developed and used to make biodiesel [86–89]. For example, A. Ali et al. reported the use of the CaO-Fe3O4 magnetic catalyst in the generation of biodiesel from palm seed oil. In addition, cadmium oxide and tin oxide magnetic nanocatalysts have been employed for esterification, transesterification, and hydrolysis reactions of soybean oil [90]. Furthermore, more active catalysts Fe3O4 and Fe3O4@SiO2 (MNPs) have been used as fundamental recyclable catalysts achieving 96% yield production. The catalyst ZnO/BiFeO3 was also a promising catalyst for the generation of biodiesel from canola oil and yields of 95.43 and 95.02% in the first and second cycles, respectively [90, 91]. Another example, SnO produces 84% yield of esterification without loss, at 200°C after 1 h reaction. Therefore, magnetic catalyst show fast, clean, superior stability, and recyclability.

#### *3.3.3.2 Nonmagnetic nanocatalysts*

The ability to reuse the catalysts allows for lower-cost biodiesel production in a fixed-bed reactor. There are number of nonmagnetic nanocatalysts, such as hydrotalcite, metal oxides, sulfated oxides, zeolites, and zirconia, which are frequently employed in the manufacture of biodiesel [44, 77, 92–95]. Molina also used ZnO nanorods to produce biodiesel from olive oil and realized that their catalytic performance yield of 94.8% was slightly higher than the regular ZnO yield of 91.4% [81, 96]. Borah et al. reported a maximum production of 98.03% at a methanol/oil ratio of 9 at 60°C for 3 hours with 2.5 wt% Co/ZnO catalysts for biodiesel [34]. Zhang et al. improved by using the surface modification of the NaAlO2/c-Al2O3 with the M/O of 20.79:1, 10.89 wt% catalysts, and at 64.72°C to achieve the highest biodiesel production, which was 97.65% [97]. Alkaline earth metal compounds, in particular, Ca-enclose nanomaterials, have the potential to be nonmagnetic catalysts for the transesterification of biodiesel. The most widely used nonmagnetic catalysts include MgO/TiO2 [98], Mg-Al hydrotalcite [99], KF/ CaO [100], Mg/Al [101], Li/CaO [102], MgO [40], metal–organic frameworks (MOFs) [97, 103], Nanozeolites al. [104], potassium-doped zeolite [27], and hydrotalcite. The implementation of nanocatalysts gets much attention due to vast surface area strong catalytic performance, and appropriate charge transport channel.

## **4. Advantages and disadvantages of different catalysts**

Finally, **Table 2** highlights the advantages and disadvantages of various catalysts. From this point of view, a homogeneous catalyst has been thoroughly examined, and drawbacks have been discussed in the literature. However, there is currently a lot of study being done in the relatively new field of heterogeneous catalysts. The literature has noted a number of benefits and drawbacks for catalysts, as summarized in **Table 2**.


## *Recent Developments in Catalysts for Biodiesel Production Applications DOI: http://dx.doi.org/10.5772/intechopen.109483*


**Table 2.**

*Different group of catalysts for biodiesel production.*

## **5. Conclusion**

The development of various catalysts has recently received a lot of attention due to their high operating catalytic effectiveness. Numerous catalysts have been studied for their ability to improve biodiesel production performance. Among the various catalysts, homogeneous and heterogeneous are the better choices for biodiesel production, and their reaction is primarily dependent on catalytic systems. As a result, heterogeneous catalysts surpass homogeneous catalysts in terms of ease of separation, simplicity, and reusability. To overcome limitations such as stability, recyclability, durability, and aggregation, the production of highly efficient catalysts necessitates additional innovative strategies. The development of extremely active and selective catalysts, as well as their economic viability for industrial use, is an issue that must be addressed. The development of extremely active and selective catalysts that are also economically viable for use in biodiesel production is priority must be addressed.

## **Acknowledgements**

The authors acknowledge Intech open access for the invitation and constructive comments.

## **Conflict of interest**

The authors declare no conflict of interest.

*Recent Developments in Catalysts for Biodiesel Production Applications DOI: http://dx.doi.org/10.5772/intechopen.109483*

## **Author details**

Teketel Alemu1 and Anshebo Getachew Alemu<sup>2</sup> \*

1 College of Engineering and Technology, Wachemo University, Department of Chemical Engineering, Ethiopia

2 Facultyof Natural and Computational Science, Department of Physics, Samara University, Ethiopia

\*Address all correspondence to: agetachew2013alemu@yahoo.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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## **Chapter 5**

## Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review

*R. Dayana, P. Bharathi and G.M. Shanthini*

## **Abstract**

Petroleum-based fuels are widely utilized and pose a threat to the environment, necessitating an urge to bring up an equally effective substitute. Globally, research is focused on biofuel production from various sources which is renewable, highly affordable, and has lesser carbon emission. Biomass is used as raw material to produce biodiesel to achieve clean, green, and renewable fuel. Edible and nonedible raw materials are utilized for the production of biodiesel. Biodiesel from lipid sources produced through the transesterification process serves as an effective alternative for the production of renewable fuel with reduced carbon emissions and greenhouse gases. The cost of biodiesel is dependent on raw materials and catalysts. The acidic and basic homogeneous catalysis reaction has a corrosive effect during synthesis and poses a risk in scalability. The heterogeneous reaction is costlier and has poor performance in the transesterification of lipids. Raw material contributes to 70–80% of the overall production cost. Municipal sewage sludge (MSS) is rich in lipid content and serves as promising raw material for biodiesel production. Nanocatalyst has superior activity in producing pure products with fewer side reactions. This paper reviews the lipid extraction techniques and biodiesel production from MSS using various nanocatalysts.

**Keywords:** biodiesel, municipal sewage sludge, nanocatalyst, transesterification, lipid extraction

## **1. Introduction**

Petroleum-based fuels contribute a significant impact on the business economy in developing countries toward various applications such that the transport of goods from industries and agricultural products, in operating diesel tractors and pump sets in the agricultural lands. Economic growth is associated with the rate of transportation. The energy demand is always incorporated with the industrialized world and domestic sector. Due to high energy demand, the fossil fuel necessity also increases which leads to a large amount of pollution, hence it is necessary to develop renewable energy sources. Therefore, it is a stipulated time to focus on alternative sources. Mainly focus on alternative fuels should have technically economically feasible, smaller environmental impact, and be readily available [1]. The MSS is one of the high lipid sources, it is obtained mostly from the domestic sector which includes

long-chain fatty acids, grease, and fats, and an interesting factor is the microorganisms contain phospholipids present in their cell membranes, and during cell lysis, some of the byproducts and their metabolites acted as a major lipid source in MSS. This could be substantiated by the research work that has indicated that the lipid content in the sewage could be a conceivable feedstock for biodiesel production [2].

Biodiesel could be one of the solutions to overcome the issues of petroleum-based fuels, as, it is a fresh and renewed form of energy and it could own the worldwide markets due to its non-toxicity, biodegradability, environmentally beneficial, and similar ignition characteristics to fossil fuels [3]. Lower emissions of carbon monoxide, sulfur, and other hydrocarbons make biodiesel a carbon-neutral fuel [4]. It is a sustainable energy source used to reduce global warming [5]. Studies and recent research works revealed that using biodiesel can minimize CO2 release to 78% which helps to prevent nature from pollution [6]. With the help of non-edible feedstocks, India produces 10–250,000 tons of biodiesel per year. According to the survey of 2014, the overall consumption of biodiesel is 1000 barrels/day. The usage of biodiesel economically supports the growth of India's early \$1.47 billion foreign currency. Rapid growth in Industrial sectors and transport sectors are causes of polluting environment. Renewable energy sources are the best way to overcome this environmental crisis. Biodiesel production is one of them which supports technically and economically to the society.

## **2. Why biodiesel?**

India's growing economy, multiplying population, and rapid urbanization result in increasing energy demand. Accordance to the report from International Energy Agency (IEA), the energy requirement is more due to the high depletion of energy in the past few decades. The IEA report says that a 6 million barrels a day increase in oil consumption results in major energy demand in India. The rise in energy demand is mainly due to the increase in individual vehicle ownership. The planning commission's 2002 statement is that "The primary commercial energy demand has grown at the rate of 6% between the years 1981-2001". On the other hand, India is facing a coal shortage of 23.96 million tons in the past few decades due to the depletion of energy sources and an increase in energy demand. For a decade of years, the demand for natural gas is increasing at the rate of about 6.5%. Renewable energy sources offer an alternate supply of energy to face the energy crisis. India is the highest potential for renewable energy sources. The significant renewable energy sources are wind energy, small hydrothermal energy, solar energy, and biomass. Though India produces more renewable forms of energy, the energy dependence is expected to increase further by 8% to achieve the gross domestic product growth rate of the tenth five-year plan. To solve this issue Government of India has agreed on a high priority for the energy sector and renewable energy resources. Tamil Nadu is a pioneer state in promoting the production of renewable energy resources. At the Indian level, Tamil Nadu contributes 27% (29989.21 MW) of total renewable energy via renewable energy sources. There is a steady increase in non-conventional energy sources in the past 10 years. The main contributors of non-conventional energy sources are wind energy (61%), biomass (35%), and other renewable forms of energy contributing to the remaining energy sources. Tamil Nadu is facing a major power crisis as Tangedco (The state power utility) is running short of coal. Tangedco imported 1.4 million tons of coal by the year 2018. Due to climatic changes and cyclonic storms in the Arabian Sea, there is a drop in wind energy generation on the south side of Tamil Nadu. Therefore, there is a high demand for energy supply in the state as coal and non-conventional energy sources are kept on depleted.

*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

## **3. Municipal sewage sludge (MSS) as a promised raw material**

Sewage is untreated municipal waste generated by domestic, industrial, and commercial sources. The level of wastewater production is increased rapidly due to the population, economic development, urbanization, and improving living conditions. Central Pollution Control Board (CPCB) surveys depict that "There are a total of 269 sewage treatment plants in India of which 213 are in proper working condition. In urban centers of the nation, the total sewage generated per day is about 38 billion liters a day but the total sewage treatment plant capacity is around 12 billion liters a day". The Ministry of New and Renewable Energy (MNRE) suggests that there is a probability to produce nearly 226 MW of energy from sewage sludge of treated and untreated sewage sludge sources. Sewage sludge is the waste generated in huge amounts in the waste treatment processes after primary and secondary treatment processes [7]. Also, the sludge is rich in lipid content as the surface of the sludge is proficient enough to adsorb different forms of lipids [8].

## **4. Treatment methodologies of MSS**

In the sewage treatment plant, there are mainly 4 steps involved in the treatment of sewage sludge (**Figure 1**). The main 4 steps are

a.Pretreatment and grit removal

b.Primary treatment

c.Secondary treatment

d.Tertiary treatment

In the pretreatment process, easily removable materials like waste material, liters from trees, and large-sized materials will be removed from the raw sewage. The influent is passed into the bar screen where larger objects like plastic packets, liters, and cansticks present in the sludge were removed. Grit is composed of sand, gravel, heavy materials, organic material, fine solid particles, etc. The grit removal is done for the treatment of equipment with closely machined metal surfaces such as commuters, fine screens, centrifuges, heat exchangers, and high-pressure pumps. A grit removal system is present in sewage treatment plants for reasons which include; reducing the necessity for frequent cleaning of digester due to the accumulation of grit and lessening the settling of grit in the treatment tanks and passage pipes. The removal of grit also protects the digesters and clarifiers from wear and abrasion. The sewage flows through large tanks called "pre-settling basins" in primary sedimentation. This leads to a rise in the level of grease and oil on the surface of these tanks due to the continuous agitation of the sludge. The primary settling tanks have a scrapper and agitation tank and they continuously direct the collected sludge toward the sludge treatment facilities. After the primary clarification, the primary sludge is collected. The primary sludge is the combined form of free-floating grease and settled solid matter [9]. The secondary treatment involves the degradation of the biological content which could be human/food waste, and the removal of the organic content and the suspended solids which passes the primary treatment. In the secondary treatment, the settled


#### **Figure 1.**

*Overall view of sewage treatment plant.*

sewage liquor is treated with an aerobic biological process. The secondary treatment methods use filtration and aerobic treatments to separate and break down the content received in the secondary treatment unit [10]. The secondary sludge primarily encompasses microbial biomass and settled solids produced during the aerobic biological treatment of primary treated wastewater. Thus, the secondary sludge comprises the lipids from the lysed cell with lesser free fatty acids compared to the primary sludge [11]. The final stage of treatment is tertiary treatment. It is also known as effluent polishing. It is done to improve the quality of effluent when discharged into environments such as the sea, rivers, and lakes. The eradication of chemical pollutants obtained from pharmaceutical industries, particles present in household chemicals, chemical effluents for small-scale industry, and agricultural pesticides is quite difficult in the conventional sludge treatment procedures hence these waste/ effluents might pollute the water bodies in the disposal areas. In spite of the lesser concentration of the disposal, these pollutants are sufficient enough to be toxic to aquatic life. Also, pharmaceutical disposals that could induce genotoxicity and microbial resistance are considered to be toxicologically relevant pharmaceutical pollutants. The reduction of the fourth stage of treatment is being followed in many countries recently. Additional to this odor control, biological nutrient removal, phosphorous removal, nitrogen removal, and disinfectants were also added before disposal.

## **5. Production methodology of biodiesel from MSS**

The primary sludge flocs and secondary sludge has utilized as efficient raw materials for biodiesel production via the transesterification process. Initially, the lipids are extracted using various solvents. The stagewise extraction process was used to separation of lipid content from MSS. The efficiency of lipid extraction depends

*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

on the types of solvents or mixed solvents and the number of stages. Bharathi and Pennarasi [12] reported that using various solvents and their extraction efficiency of lipids from MSS (**Table 1**).

Lipids extraction is followed by the transesterification process for the production of biodiesel It is a chemically Fatty Acid Methyl Ester (FAME), formed by the transesterification reaction (**Figure 2**). Transesterification is a process that involves the swapping of the R (alkyl) group of triglyceride's esters with the R´ (alkyl) group of the alcohol compound [1].

The transesterification reaction may be a catalytic or non-catalytic process. Among these, the noncatalytic reactions are very slow and result in lesser yield compared to catalytic reactions. Hence, the transesterification reaction is manifested with the help of the catalysts and is a high-yielding process. Briefly, the complete transesterification process includes:

i. conversion of triglycerides to diglycerides,

ii. conversion of diglycerides to mono-glycerides and ultimately,

iii. conversion of mono-glycerides to glycerol along with the formation of biodiesel

## **6. Prominent status of nanotechnology**

Nanotechnology is a wide field in which nano-sized materials are used for various applications. Nano-sized materials are in the size of 10−9 nm. Such particles are said to be nanoparticles. The nanoscale ranges from 1 to 100 nm (**Figure 3**). The advantage of nanoparticles is the reactive area gets increased as the size reduces from bulk size. This has been used in the past few decades in the form of silver and gold glittering paints in the church, palaces, etc. Such old technology has been tuned even better to increase the application in all the emerging fields. There are various things in nature in nano size, apart from that; mankind played a major role in creating new nanomaterials for their relevant applications.

There are a lot of industries and researchers concentrated on nanotechnology and its applications (**Figure 4**). They explore the technology in various fields like improvement in energy efficiency, telecommunication fields, cosmetics, textile industry, foods, medicines, etc. The efficiency of fuel production is considerably improved using nanotechnology. One of the fuel production methods is from natural materials and low-grade


#### **Table 1.**

*Quantity of lipids extracted from MSS [12].*

#### **Figure 2.**

*General equation of transesterification of triglycerides [12].*

#### **Figure 3.**

*Natural and artificially produced nano-sized things (https://philebersole.files.wordpress.com/2012/04/ nanotechnology.jpg).*

crude oil by improving catalysis. Through nanotechnology, the fuel efficiency in vehicles and power plants is improved through friction, which increases efficiency and reduces combustion. Nanotechnology plays a vital role in telecommunication transceivers. The nanoscale-based transceivers reduce the system complexity and improve the Quality of Service (QoS). Faster and more power-efficient electronic devices are constructed using nanoscale transistors and diodes. Nowadays, nanoscale type memory devices are used to equip supercomputers eg. Magnetic Random Access Memory (MRAM), which enabled tunnel junctions of magnetic nanoparticles, which quickly and effectively saves the data during a system shutdown or crash. Such nano-based chronic devices are used in aircraft communication as well as the resumption of play and used for the collection of accident data vehicles. Advancements in various cosmetic products like lotions, dermatological creams, shampoos, sunscreen lotions, and specialized makeup products are prepared by superimposed nanomaterials. In the cosmetic field, nanomaterials provide greater clarity and good coverage in cleansing, absorption, customization, antioxidant, and anti-microbial. Nanotechnology not only plays the role in the cosmetic industry but also in the food industry. Nano-engineered nanocomposite materials support food packaging in the food industry. Food packaging reduces the escape of carbon dioxide from the

*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

#### **Figure 4.**

*Applications of nanotechnology (https://www.researchgate.net/profile/Karolina\_Niska/publication/317719241/ figure/fig 2/AS:555489508900864@1509450427466/Applications-of-nanotechnology.png).*

soda and reduces the amount of oxygen, humidity, or the growth of bacteria to keep fresh and safest food for a longer period. Nanosensors embedded in plastic containers warn of spoiled food and are currently being developed nanosensors for the detection of pesticides and other contaminants in food before packaging and distribution. The use of nanotechnology in the medical field has vast appliances. It is used to stimulate the neurological systems and their growth. Nano-sensors are used to predict the damage to spinal and brain tissues. One of the methods supports structured nano gel filling the space between existing cells and encouraging new cells' growth. Quantum dots are semiconductor nanocrystals that can improve biological imaging for medical diagnosis. Researchers are developing customized nanoparticles that can deliver drugs directly to diseased cells in the body. When it is perfected, this method greatly reduces the damage during the treatment (eg: chemotherapy) done to the patient's healthy cells. Marvelous support of nanotechnology to the environment is to meet the need for clean drinking water which is affordable through low-cost rapid detection of impurities, purification, and water treatment systems. For example, researchers have discovered unexpected magnetic interactions between the very small spots that can help in the removal of arsenic or carbon tetrachloride from water and are currently being developed filters that can remove virus cells from nanostructured water and they were investigating how the ionization electrode using nano-sized fibers reduce the energy requirements and costs of removing salts from water. It is also used to degrade solid waste with less time when compared to the naturally occurring degrading process. It is also helpful in the process of conversion of waste sources to renewable energy available for use. Manufacturing the fabric with nanoparticles allows the introduction of upgraded fabric properties without a substantial increase in weight, thickness, or stiffness, unlike the other modification techniques. The photocatalytic activity of the nano TiO2 in the fabric treated with Nano TiO2 could impart an anti-bacterial effect and might reduce the staining. Nanoparticles are primarily used in the catalysis of chemical reactions. Hence, the usage of nanoparticles possibly reduces the need for additional catalysts that are necessary to achieve the desired results, with lesser capital and pollutants. The main applications involved in the field of oil refining, catalytic converters in cars, and catalytic reactions in renewable bioenergy production. The functional nanomaterials with antimicrobial properties can be

used to build high-performance systems on a small-scale or point of use to increase the robustness of the network water supply and water networks that are not connected to the center and the emergency response network after catastrophic events. Nanotechnology can also be applied in the detection of even the minute quantity of gas and vapors with the highest sensitivity. Nanomaterials, such as quantum dots, carbon nanostructures, metal-based nanomaterials, and metal oxide semiconducting nanomaterials can be used as the gas sensing elements in the nanosensors. The nanoscale dimension of these nanomaterials helps in sensing the lesser level of the gas molecules that are adequate enough to tune the electrical properties of the detecting element, allowing the detection of the tiny concentration of gas vapors when nanoparticles are used. Nanotechnology can enhance the catalyst performance in transforming the vapor released from automobiles or industrial plants into harmless gasses as nanoparticles have a larger surface area which improves the interaction with the reacting chemicals compared to traditional catalysts. In addition, the larger surface area allows more chemicals to interact with the catalyst, making them ideal for sensing with higher sensitivity.

## **7. Role of nanocatalysts in various fields**

The nanocatalysts have their own property which was usually targeted for specific applications. The four major properties are


Nanocatalysts have placed their impact on almost all fields due to their multiple properties and uses toward the problem, thereby creating the best solution for the problems. Nanoscience contributes to the reduction in the size of devices and technologies with upgraded properties. The key applications of nanotechnology include, water purification, energy storage devices, biodiesel production, medical applications, dye reduction, fuel cell, carbon nanotubes, etc. [13].

Nanocatalysts are widely used in the following fields for a huge number of applications as follows:


*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*


Nanocatalyst is used against environmental pollution like wastewater treatment, soil remediation, waste degradation, chemical pesticide degradation etc. Nanoparticles are used as a catalyst in biodiesel production and plays the main role in photodegradation of methylene blue. Nanoparticles have applications in soil-plant systems in many ways like the delivery of pesticides and biopesticides, pesticide degradation, nanosensors for plant-pathogen detection, and also in fertilizer-controlled delivery [14]. Nanoparticles are employed in the delivery of genetic materials, in plant protection and nutrition like soil remediation, slow release of fertilizers, pesticide degradation, and in seed treatments [15]. The main important application of nanoparticles in agriculture was nanofertilizers. Nanofertilizers improve crop growth, yield, quality, and reduce fertilizer usage and cost for cultivation. It increases plant growth mainly by increasing the photosynthesis rate and also prevents plants from abiotic and biotic stress [16]. Applications of nanotechnology in precision agriculture are nano biosensors, early detection of viral disease in plants, nanoparticles serving as micronutrients for plants, nano herbicides, nano fungicides, and in insect pest management [17].

## **8. Nanocatalyzed transesterification process**

Nanotechnology has an increasing impact in the fields of biotechnology, pharmaceutical technology, and pure technological applications. Nanotechnology places its main role in the conversion of biomass to bio-energy in various renewable resources. Implementing nanotechnology in the bioenergy production process gives a high impact on bio-energy research. Four categories of nanoscale area units are investigated as useful materials for water purification which are metal-containing nanoparticles, carbon nanostructures, zeolites, and dendrimers [18]. Nanotechnology reveals good results than the other techniques used in water treatment as they exhibit higher interaction with high surface area (surface/volume ratio) [19]. The present

investigation of the potential applications of nanotechnology in water and wastewater treatments are adsorption, membrane processes, photocatalysis, antimicrobial efficiency, sensing, and monitoring [20]. Copper-doped zinc oxide nanocomposite (CZO) comes under heterogeneous catalyst as it contains both copper and zinc oxide nanoparticles in it. It shows a positive sign in the field of emerging catalysts as they are non-corrosive and can be easily separated from the product mixture. Doping is significantly used in enhancing the optical and electrical properties of semiconductors. Doping with transition metals leads to improving the interesting properties of zinc oxide [1]. CZO nanocomposite comes under heterogeneous nanoparticles, it can also be recycled and reused. CZO nanocomposite is a bifunctional heterogeneous catalyst. They gain attention because they carry out transesterification and esterification processes for both acid and base-containing reactions. The use of nanoparticles/ nanocomposites as catalysts provides higher catalytic activity and selectivity due to its nano-dimension and morphological structure. Thus, the CZO nanocomposite can be used as a catalyst for the transesterification of lipids obtained from municipal primary sewage sludge. It increases the yield of biodiesel and can be recovered, recycled, and reused [21]. After the transesterification process, the mixture was separated and the byproducts are separated. The biodiesel had to be subjected to washing subsequent to the transesterification process to eliminate excess catalysts, methanol, glycerol, and soap. After washing, the biodiesel sample must be heated to evaporate solvents and water present in the mixture [22]. Gas chromatography-mass spectrometry (GC-MS combines the features of gas chromatography and mass spectroscopy to identify the different substances present in the test sample. Applications of GC-MS include drug discovery, fire investigation, environmental check, explosives examination, and documentation of unknown samples. In addition, it can help in the identification of the trace elements in the samples which were earlier assumed to have disintegrated beyond identification. GC-MS is broadly used in the analysis of the compounds such as esters, fatty acids, alcohols, aldehydes, terpenes, etc. The below process flow chart clearly shows the production of biodiesel from MSS via the nanocatalyst transesterification process (**Figure 5**).

**Figure 5.** *Process flow chart of biodiesel production from MSS.*

*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

## **9. Quality standards of biodiesel**

Quality is meant for long time goals, exactly successful use, without any technical problems of biofuel. It can be depending on many factors: mainly, the quality of the raw material chosen, lipid content composition. The physicochemical properties of biodiesel were the most significant parameters to speak about the quality of biodiesel. Some of the important physical and chemical properties are listed in **Table 2** with their ASTM standards (ASTM D6751-06).

These quality standards of biodiesel on the market are affected by various factors, which vary from place to place, and country to country. Mainly, it compares the characteristics of the existing diesel fuel standards, types of diesel engines commonly used in practice region and their emissions, and climatic properties around the regions. Therefore, the quality standards of biodiesel are varied on country/region. Not surprising that there are some considerable differences between the regional standards. **Table 3** shows a worldwide important biodiesel quality standard.

Notable properties of biodiesel

i.Cetane number (CN)

It is used to measure the combustion properties of diesel fuel. It is a measurement of the quality of fuel. Modern highway diesel engines require a CN ranging from 45 to


#### **Table 2.**

*Physical and chemical properties of biodiesel compared with ASTM standards (ASTM D6751-06).*


#### **Table 3.**

*Biodiesel standards [23].*

55. The higher CN, the more fuel burns better within the engine. And also, it is associated with ignition delay time, engine knock, carbon monoxide emissions, combustion efficiency, smoothness, and hydrocarbon and nitrous oxide emissions [24, 25]. The length of the hydrocarbon chain increases with increasing CN, which leads to a decrease in the saturation state in the carbon chain of the Fames. The estimation of the CN formula was given below for individual fatty acids. These models were developed using a combination of [26, 27].

CN = 1.068 Σ (CNimi) – 6.747

Where CNi – Cetane number, mi – The mass percentage of FAME

#### ii.Viscosity

It is the predominant parameter with an impact on the fuel quality, since it plays a vital role in the fuel atomization process. High viscosity can lead to the coking process, and affect the combustion and emission rates from the engine. Generally, viscosity decreases as temperature decreases which leads to fuel components being saturated and causing precipitate problems. This may arise from clogging the fuel lines, pumps, and filters [25, 26]. As per the EN14214 guidelines, the specification for viscosity is 3.5–5 mm2 s −1 for 40°C. The degree of saturation of compounds depends on the viscosity of the fuel [28].

Allen et al. [29] proposed a mixture model for the estimation of viscosity,

$$
\begin{array}{c}
\mathbf{n} \\
\begin{array}{c}
\mathbf{\hat{n}} \\
\mathbf{\hat{n}}
\end{array}
\end{array}
\begin{array}{c}
\mathbf{\hat{n}} \\
\mathbf{\hat{n}}
\end{array}
$$

where μm is the viscosity of the mixture and Yi and μi mole fraction and viscosity of individual component I respectively.

iii.Oxidation properties

It is a difficult parameter to understand properly not unlike other properties such as cetane number since it is dependent on the bulk composition of the fuel. The double bonds present in the Fames are prone to autoxidation, which leads to deterioration

#### *Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

problems in the fuel system [28]. It is used to measure the fuel resists oxidative degradation property which determines the fatty acids occurrence with double bonds in feedstocks. A non-linear relationship between oxidation rate increases with an increasing double bond in a Fame. Minor components provide disproportionate effects on oxidative stability inhibiting oxidation. Therefore, to change the oxidative stability, any of the other properties to be improved by additives.

#### iv.Density

It is a significant parameter, with an impact on fuel quality. The density of biodiesel usually varies between 0.86 and 0.90 g/cm3 [30]. The non-edible biodiesel densities are also in the range of 800–965 kg/cm3 [31]. Generally, molecular weight is one of the important factors that contribute to fuel density. Densities are calculated with respect to various temperatures, instead of the standard value at 15°C, available at EN 14214. The ASTM standard procedures are also available at 15°C, required by D1298 [31]. The liquid densities are calculated by following the formula using the relationship between the molecular weight and molar volume.

$$\rho = \Sigma \,\mathbf{x\_i} \,\mathbf{M} \mathbf{V} \mathbf{V}\_i / \Sigma \mathbf{x\_i} \,\mathbf{V}\_i.$$

where xi is the molar fraction of the component and Vi is the molar volume of a liquid [32].

#### v.Flashpoint

It is the lesser temperature at which the liquid gives off its vapor, the lower the flash point the easier to ignite the material. Mostly the flash point of the combustible liquid is 104°C. It is used to analyze the hazards of fuels, which are less than 37.8°C are called flammable, whereas above that temperature are called combustible. Each biodiesel has its own flash point. Moreover, the flash point is affected by many factors including the number of double bonds, the number of carbon atoms, the chemical composition of the biodiesel, pressure, oxidant, and apparatus sheltering [33]. Different test methods are available to determine the flash point of biodiesel which includes the EN test method and the ASTM test method. In addition to the observation that both boiling point and flashpoint decrease with decreasing pressure, the literature, and the ATSM standard D6751 recommend a flash point of biodiesel is 130°C except for non-edible biodiesel.

#### vi.Cloud point and pour point

It is the minimum temperature at which the first nuclei crystal formation takes place. The pour point is the minimum temperature below which a liquid loses its flow characteristics. Comparatively, the cloud point is of a high value with high temperature and a low value with low temperature. Generally, biodiesel has higher cloud and pour points than conventional fuel [34]. Specifically, the standard ASTM D2500 and D97 test methods are available to measure the cloud and pour point. Generally, most biodiesel properties are matched with diesel fuel except cloud and pour point. These are low-temperature properties. Much literature indicated that the cloud point of pure biodiesel is around 13°C, and for pure biodiesel is 0°C. Cloud points may be achieved by adding liquid additives. It has a very low solidifying temperature and is highly soluble in biodiesel.

## **10. Economic impact of biodiesel**

Energy consumption is of great concern globally due to its availability. Also, global energy consumption is increasing day by day. To IEO 2016 projection, over the years 2010 to 2040, the total energy consumption is expected to increase by 50% compared to previous decades. The major part of the energy is being utilized by the developed countries due to their richness in economy and population. Apart from energy sources like coal, natural gas, and crude oil; petroleum-based fuels are in great demand. These fossil fuels are scarce and impose a negative impact such as the production of greenhouse gases and causes air pollution. Also, the excessive utilization of these fossil fuels is heading toward the global depletion of natural resources, demanding an equal and effective alternative, giving birth to renewable energy resources such as biodiesel. Biodiesel is generally produced by trans-esterifying fat-based feedstocks like waste cooking oil, oil-based industrial effluents, vegetable oil, and animal fat, waste sludge. The cost of the final product (biodiesel) will vary according to the kind of feedstock. Shifting fossil fuel to biodiesel is not easier due to less yield and high production cost. Researchers continued exploring the various options of biodiesel synthesis to reduce production costs, as it poses a major challenge in the extensive utilization of biodiesel.

Considering the traditional biodiesel etproduction technique, the most important costs in the production of biodiesel are capital investment costs and operating costs. The costs covered under capital investment are equipment and plant establishment costs. The plant establishment includes the cost of installation of equipment, instrumentation, pipelines, electrical lines, and a few other auxiliary developments. The operation costs include feedstock, catalyst, utility, labor charge, maintenance, and repair of equipment [35, 36]. Among these expenses, the feedstock significantly impacts biodiesel's economy, imparting more than 75% of the total production cost [35]. To reduce the feedstock cost, the poor quality of feedstock or reuse of feedstock is much preferred. These will influence the excessive release of free fatty acids (FFA) and increase the water content. The presence of excess FFA and water content in turn reduces the yield and quality of biodiesel [37]. To improve the yield and quality, additional processing steps should be carried out which in turn increases the production cost. A better and good quality of feedstock without compromising the food demand and environmental impact and which could reduce the final cost is much preferred and being in trials by many researchers and scientists. The choice of feedstock varies country-wise by their utilization of crops. Argentina prefers soybean as a feedstock owing to its less cost. While China does not choose soybean as a biodiesel feedstock as soybean oil is a staple demand in Chinese foods [38]. Jatropha and castor oil-based feedstocks are favorites in India [39]. Waste cooking oil and animal fats are ideal in countries like Japan, Canada, and Australia [40].

Waste cooking oil is one of the better preferences of feedstock in producing biodiesel. By utilizing waste cooking oil, roughly 1.5 ratios of energy output to input, can be obtained and approximately two times income can be obtained compared to the total expenses [41]. A study on biodiesel production from *Calophyllum inophyllum* oil gave an idea of the economic performance of heterogeneous catalyst-based production of biodiesel. The influence of the cost of feedstock on the net present value and payback time was investigated in detail. The cost of the feedstock is in the range of 0.2–0.5 \$/kg. In the case of a lesser feedstock price of 0.2 \$/kg, the net present value is about 31 million dollars, with a payback time of 0.41 years. While the feedstock purchase cost of 0.5 \$/kg and above poses a negative impact on net present value

## *Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

with the payback period being the time past the project completion time. Apart from lesser feedstock cost, the recovery and utilization of methanol and heterogeneous nanocatalyst could greatly reduce the cost of biodiesel [42]. The non-edible source of feedstock like microalgae is used to reduce the exploitation of food crops and oils in the production of biofuels. Microalgae as a feedstock are advantageous concerning their higher production rate, lesser environmental impact, and lesser requirement of land for setting up a biodiesel plant, which could in turn reduce the cost of biodiesel. In recent years, microalgae have been one of the most promising feedstock choices to produce biofuel which could replace approximately 50% of the fossil fuel demand as the mass cultivation of microalgae and its availability could greatly bring down the production price of biodiesel [43].

In addition, the cost of biodiesel varies greatly, in accordance with the type of catalyst used, which can be either homogeneous or heterogeneous. A heterogeneous catalyst has the limitations like deprived interaction as there might be restricted diffusion of the catalyst when it exists in different phases of reagents. In the case of a homogeneous catalyst, the separation and reuse of the catalyst are quite tedious. The behavior of nanocatalysts lies in between homogeneous and heterogeneous catalysts, with notable advantages like good selectivity, sensitivity, separation, and reuse of catalyst [44, 45]. The careful selection of catalyst reduces the number of processing steps and favors the reusability of the catalyst, which in turn supports minimizing the total production cost of biodiesel [46]. The magnetic nanomaterial-based catalyst is proven to be very effective in biodiesel production compared to the conventional catalyst, owing to its availability, size, surface area, high surface-to-volume ratio, stability to different reaction conditions, resistance to saponification, reusability, and wide synthesis options [46]. Also, the higher surface-to-volume ratio of the nanocatalyst favors simultaneous reactions to take place at the same time which in turn accelerates the process [47]. The acceleration of the reaction process contributes to minimizing the production cost. In addition, magnetically separable nanomaterials can easily eliminate the separation protocol for the recovery of catalysts [23, 48]. Bharathi and Pennarasi [12] estimated the cost of sludge biodiesel (**Table 4**). The overall production cost is 3.11 USD per gallon, but they did not include the byproduct (glycerol) sale cost. Surely it will reduce the overall biodiesel production cost as well.


#### **Table 4.**

*Cost estimation for sludge biodiesel [39].*

## **11. Summary**

Biodiesel has several benefits over diesel fuel. The production cost only is a major problem compared to petro-diesel. And also, vegetable oil and animal fats are the raw materials for biodiesel production causing the cost of biodiesel to increase. MSS is a waste and lipid source readily available for the extraction of lipids for biodiesel production. MSS treatment for biodiesel production may be used in a waste treatment facility with limited expenditure on raw materials. Also, municipal waste might not contribute to the landfill issue and renewable sewage waste can be considered for biodiesel production instead of depending on edible sources of raw material. But there are some disputes with MSS. The pre-treatment process includes collection, dewatering, drying, etc. The lipid extraction steps also need more amount of organic solvents which will increase the production cost. However, the amount of lipids depends on the type of sludge. Sludge-to-solvent ratio, extraction time, and solvent recovery are the factors that affect the efficiency of lipid extraction and cost. Optimization is only one solution to reduce the cost concerning the above factors. The role of catalyst for biodiesel production is also the most important. Acid and alkali transesterifications are high-cost and slow processes. Comparatively nanocatalyst transesterification is less costly and fast. Factors such as the choice of nanocatalyst based on its properties and type of feedstock will be highly favorable in improving the transesterification reaction. Based on the demand of the biodiesel market, the designing of these factors can be modified and improved. The nanocatalysts which are being developed in the recent past are highly preferred for the heterogeneous catalysis reaction as they are highly suitable for improving the efficiency of the transesterification process. Nanocatalysts can play a major role in improving the yield of biodiesel as they possess good surface area which could favor the catalytic efficiency and trigger the overall catalytic reaction. In spite of all these advantages, extensive research work is necessary to get optimization for biodiesel production from MSS and to study the toxicity levels of nanocatalysts before utilizing them in biofuel production and making a good profit from any source of raw material. Nanocatalysts could serve as efficient catalysts as they are recyclable, have less production cost, and possess a good life which could greatly influence the overall production cost of biodiesel. It is observed that the primary energy demand is set to double by 2040, therefore the use of alternative fuels such as biodiesel is bound to grow as well. In the meantime, it is observed that the percentage of MSS also increased due to the high population. This review insists on the methodology available for the production of biodiesel from MSS. It strongly helps future research thereby there is one forward step to save the environment and increase the global economy values.

*Nanocatalyst Mediated Biodiesel Production from Waste Lipid as Feedstock: A Review DOI: http://dx.doi.org/10.5772/intechopen.109481*

## **Author details**


\*Address all correspondence to: bharathipurush@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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## **Chapter 6**

## Bifunctional Heterogeneous Catalysts for Biodiesel Production Using Low-Cost Feedstocks: A Future Perspective

*Welela Meka Kedir*

## **Abstract**

Biodiesel can be produced using domestic resources like straight vegetable oil, animal fats, and waste cooking oil. Its use, instead of conventional diesel, contributes to the reduction of CO2 emissions. The production of biodiesel through transesterification (TE) reactions requires adequate catalysts to speed up the reactions. The classical methods of biodiesel production were conducted using homogeneous catalysts, which have drawbacks such as high flammability, toxicity, corrosion, byproducts like soap and glycerol, and a high wastewater output. Recently, various types of heterogeneous catalysts and continuous reactors have been invented for the production of biodiesel. As a result, the initial choice of catalysts is crucial. However, it is also affected by the amount of free fatty acids in a given sample of oil. In addition, most of the catalysts are not suitable for large-scale industrial applications due to their high cost. Bifunctional heterogeneous catalysts are widely applicable and have a rich history of facilitating energy-efficient, selective molecular transformations, and contributing to chemical manufacturing processes like biodiesel. This chapter underlines the use of bifunctional heterogeneous catalysts for biodiesel production using low-cost feedstock. Furthermore, it examines the sustainability of catalysts and low-cost feedstock for large-scale biodiesel production. Finally, the chapter indicates a further perspective of biodiesel as an alternative fuel using low-cost feedstock and recommends a sustainable bifunctional heterogeneous catalyst for biodiesel production.

**Keywords:** energy, biodiesel, bifunctional heterogeneous catalysts, transesterification, low-cost feedstock

## **1. Introduction**

Because of the energy and global warming crisis, the development of renewable energy has been focused on worldwide [1]. Fossil fuel is the single largest energy source, representing 88% of all total world energy consumption [2]. The U.S. energy information administration, in its international energy outlook 2016 report, indicated that the world's total energy consumption is significantly increasing [3]. However,

numerous studies showed that the combustion of non-renewable fossil fuels contributes approximately 52% of CO2 emissions, which is the major source of greenhouse gases [4]. Nowadays, various renewable resources such as wind, geothermal, solar, wave energy, and biofuel are considered as alternative fossil fuels [5, 6]. Among these alternative fuels, biodiesel is being promoted as a supplementary fuel for diesel engines. The major benefits of biodiesel are its renewability, biodegradability, and ability to blend with other energy sources compared to other alternative fuels [7]. Even though biodiesel is a good alternative to petroleum diesel in various aspects, it is always jeopardized by the high cost of feedstock and the absence of economically and technically viable technology for its efficient production from feedstock [8, 9]. Biodiesel is also known as fatty acid methyl ester and is obtained by the transesterification reaction of methanol and vegetable oil in the presence of a suitable homogeneous or heterogeneous catalyst [10, 11]. Nowadays, various heterogeneous alkali catalysts such as zeolite, alkali earth metal oxides, KF/Al2O3, sodium aluminate etc. were developed for biodiesel production [9]. However, due to the expensive cost of catalyst synthesis, only selective heterogeneous catalysts were utilized in the industry [12].

Bifunctional catalysts facilitate the esterification of free fatty acids (FFAs) into alkyl esters alongside the transesterification (TE) reaction, which allows for the use of waste vegetable oils with high water and FFA contents for biodiesel production [13]. Under ideal reaction circumstances, acid-base bifunctional mixed-metal oxide catalysts produced biodiesel with a conversion rate of almost 100% [14]. For sustainable biomass upgrading, bifunctional heterogenous catalysts have the advantage of combining multiple catalytic processes in a single vessel. Additionally, a catalyst with an acid and base active phase will convert high FFA (>3%) feedstock in a single-step reaction through a simultaneous TE and esterification reaction process [15]. Mesoporous morphology dramatically enhanced the number of active sites, which helps to increase overall biodiesel production. Additionally, it is readily recyclable by straightforward washing and drying to remove adsorbed materials, sustaining activity for numerous cycles without showing any signs of metal leaching [16]. In order to employ waste vegetable oils with higher moisture and FFA levels for biodiesel generation, bifunctional solid catalysts enable the esterification of free fatty acids (FFA) into alkyl esters through the TE reaction [17]. Bifunctional heterogeneous catalysis is based on the fundamental idea that two different kinds of active sites cooperate to carry out a surface-catalyzed reaction [18]. Such two kinds of locations are frequently anticipated to catalyze several fundamental steps inside an overall reaction [19, 20]. Bifunctional materials could be recycled repeatedly, with only a slight deactivation that was attributed to the leaching of the various active metals during TE and poisoning by strongly adsorbed organics [8]. Before discussing the usage of comparable types of materials in biomass refining reactions, we highlight two important types of materials that are utilized as bifunctional catalysts in this section [21, 22]. Because they have enough acid sites on the surfaces with different strengths of Lewis acidity, Nafion-NR50, WO3-ZrO2, and SO4-ZrO2 are used for TE instead of other strong acid catalysts like hydrochloric, sulfuric, or phosphoric acid, hetero-poly acid inseminated on various supports (zirconia, silica, activated carbon, and alumina), and hydrochloric, sulfuric, or phosphoric acid [21]. Vegetable oil derived from edible plants, including palm, soybean, and sunflower oil are common feedstock in biodiesel production [23]. Currently, biodiesel production using edible vegetable oil as a raw material was the main cause of increased global food market prices [9]. Another issue related to edible oil bioenergy is the potential depletion of biomass resources as a result of intensive agricultural practices used in crop cultivation [4]. Numerous

*Bifunctional Heterogeneous Catalysts for Biodiesel Production Using Low-Cost Feedstocks:… DOI: http://dx.doi.org/10.5772/intechopen.109482*

studies identified feedstock prices as the most important factor influencing the economic viability of the biodiesel market, accounting for up to 70–95% of total biodiesel production costs [15]. As a result, in order supply marketable biodiesel, the cost of the raw materials must be a key parameter [24]. The prominent alternate solution were using non-edible, low-cost feed stocks resource as a row material to investigate biodiesel [24–26]. Even though numerous study conducted on the production of biodiesel. The processing technologies are not yet commercially available, however, its predicted to enter the market within the next few years [27].

## **2. Biodiesel as alternative fuel**

Biodiesel is extremely biodegradable and has a low toxicity level [23]. It emits nearly no aromatic chemicals or other chemical pollutants that are harmful to the environment [28]. When the entire life-cycle is evaluated (including cultivation, oil production, and oil conversion to biodiesel), it has a modest net contribution of carbon dioxide; and its production may be decentralized, it has tremendous potential for improving rural economies [29]. In comparison to diesel fuel, biodiesel emits no sulfur, less carbon monoxide, fewer particulates, less smoke and hydrocarbons, and more oxygen. More free oxygen results in complete combustion and lower emissions [30]. Currently, many countries use renewable energy like biodiesel (**Figure 1**).

**Figure 1.** *Global biodiesel Trend (a) and worldwide use of vegetable oil (b) for biodiesel production [31, 32].*

## **3. Production of biodiesel from different feedstocks**

One of the advantages of producing biodiesel as an alternative fuel lies in its wide range of available feedstock [33]. The feedstock for biodiesel can be different from one country to another depending on their geographical locations and agricultural practices [30, 33]. The best feedstock must be chosen to guarantee minimal manufacturing costs. The ideal characteristics of a biodiesel feedstock include high oil content, ideal FFA composition, affordable agricultural resources, predictable growth and harvesting seasons, constant seed maturation rates, and a potential market for agricultural byproducts [30, 34]. Currently, both edible and non-edible oils are used to produce biodiesel; however, using edible oils on a large scale poses a significant risk to the world [32, 35]. The use of biodiesel feedstock varies from country to country since it depends on the availability and the cost of biodiesel production were depicted in **Figure 2**.

**Figure 2.**

*Production of biodiesel around the world from different raw materials [34].*

## **4. Transesterification (TE)**

A chemical process called TE turns TG and alcohol into alkyl esters and glycerol. It is a useful method for converting oil and fat feedstock, which chemically mimics petroleum diesel, into biodiesel. This method converts oils (TG) to low-viscosity alkyl esters, which are similar to diesel fuel [36]. This material can, therefore, be used in current petroleum-based diesel engines without needing to be modified because it has properties similar to those of petroleum-based diesel fuel. Reactants are frequently combined in TE, a reversible reaction when they are heated. But if a catalyst is added, the reaction will proceed more quickly [15]. The simplest chemical reaction for TE of TG is presented in **Figure 3**.

TE of oil and animal fats with a sufficient catalyst is a useful procedure for biodiesel production [37]. Several chemical catalysts are being utilized for TE of oil.

**Figure 3.** *Production of biodiesel from methanol and vegetable oil or animal fat.*

*Bifunctional Heterogeneous Catalysts for Biodiesel Production Using Low-Cost Feedstocks:… DOI: http://dx.doi.org/10.5772/intechopen.109482*

However, these chemicals are expensive, scarce, poisonous, and ineffective. TE is typically catalyzed chemically, as in base catalyzed TE and acid-catalyzed TE, or via enzyme catalysts, as in lipase-catalyzed TEs [38]. When alcohol, often methanol, is used in non-catalyzed TE, there is no need for a catalyst because the alcohol is used in supercritical conditions, when the alcohol is at a temperature and pressure above its critical point and there is no separation between the liquid and gas phases [39]. In the supercritical state, the dielectric constant of alcohol is decreased so that the two-phase formation of vegetable oil/alcohol mixture is not encountered and only a single phase is found favoring the reaction [40]. Each TE process necessitates a unique feedstock. Some esterification procedures are more advantageous than others, at least in terms of manufacturing costs, waste creation, productivity, and so on [40, 41].

## **5. Catalyst for transesterification**

The transesterification of oil can be catalytic, non-catalytic, or enzymatic. Catalytic transesterification of TG to fatty acid methyl ester was a major strategy for increasing biodiesel yield because the catalyst accelerates the rate at which the chemical reaction approaches equilibrium without becoming permanently involved [7]. Even when only a small amount of a catalyst is used, it affect the transesterification rate. The selectivity of catalysts, which are not consumed and many applications have been developed [42].

#### **5.1 Classification of catalyst**

Catalysts may be classified generally according to their physical state, their chemical nature, or the nature of the reaction that they catalyze (**Figure 4**). Catalysts used for biodiesel production are categorized into two types: heterogeneous catalysts and homogenous catalysts.

#### **Figure 4.**

*Classification of catalysts, feedstock oils, and solvents used for biodiesel production via TE/esterification reactions [17].*

#### *5.1.1 Heterogeneous catalyst*

In the heterogeneous TE reaction [8], a glyceride combines with an alcohol in the presence of a heterogeneous catalyst to produce fatty acid alkyl esters (biodiesel) and glycerol. The oxides of base supported on a large surface area, such as calcium oxide (CaO), magnesium oxide (MgO), and titanium dioxide, are commonly employed as heterogeneous catalysts in TE reactions [43, 44]. CaO is preferred as a catalyst because of its high activity, longer lifespan, and lack of consumption during the reaction [35]. Heterogeneous catalysts are understood to enhance the TE process by avoiding the extra processing costs associated with homogeneous catalysis and minimizing pollutant production (**Table 1**). Heterogeneous catalysts facilitate facile recovery, reusability, and a low-cost green process [15]. Efficient and low-cost heterogeneous catalysts help to reduce overall biodiesel production costs [25]. Heterogeneous catalysts are essential in difficult environments such as high temperatures and pressures. Such catalysts are easy to recover from the reaction mixture, can tolerate aqueous treatment stages, and can be modified to provide high activity, selectivity, and longer catalyst lifetimes. Several recent studies have focused on the technological and economic viability of producing biodiesel by heterogeneous acid-catalyzed TE [76]. As a result, the acidic catalytic reaction is very appealing for biodiesel production; however, acid catalysts exhibit lower catalytic performance in TE processes compared to basic catalysts, and heterogeneous solid catalysts were easily removed from the products in laboratory conditions. The water-washing and neutralizing processes were restricted [8].

#### *5.1.2 Homogenous catalyst*

Homogeneous chemical catalysts have good selectivity, high turnover frequency, high reaction rate, and easy activity adjustment [26]. Homogeneous chemical catalysts such as NaOH, CH3ONa, and KOH were the most commonly used alkali catalysts (**Table 1**). Because of its high quality and low cost, homogeneous catalysts such as NaOH was used in transesterification; additionally, a small amount is required compared to KOH [42]. Currently, most of the heterogynous catalyst are not effective for the production of biodiesel which leads to hydrolysis or saponification of the fay acid methyl ester [7]. The resulting soap decreases the biodiesel yield and complexes the separation process. As a result, a two-step TE with acid first and alkali second was proposed [77]. The initial acid-based esterification efficiently reduces the oil's FFA content and prepares the oil for alkali catalysis.

### **5.2 Heterogeneous catalyst for biodiesel production**

Many investigations have been conducted into the synthesis of heterogeneous catalysts in order to alleviate the issues associated with homogeneous catalysts in biodiesel synthesis. The literature has numerous reports on heterogeneous catalysts (acidic, basic, and enzymatic) for biodiesel synthesis. Alkali metal oxides and derivatives, as well as alkaline earth metal oxides [78], derived waste material-based heterogeneous catalysts [44], are examples of these ion exchange resins and sulfated oxides.

#### **5.3 Heterogeneous catalyst from solid waste**

Heterogynous catalysts synthesized from waste material play a crucial role to reduce organic pollutant elimination. Conversion of waste biomasses to catalysts helps



**Table 1.**

*Comparison of various solid catalysts for transesterification reaction.*

to improve environmental sustainability and renewable energy production such as biodiesel. CaO derived from seashells, chicken egg shells, and crab shells has been identified as an effective heterogeneous catalyst for biodiesel production (**Tables 1** and **2**). Those certain shells were reached in calcium carbonate (95%), with the rest being organic materials and other substances like MgCO3, phosphate, and trace metals [81]. Activated catalysts derived from calcined mud crab shells and waste cockle shells reacted with a 3 h reaction rate using palm oil, yielding 98.2% and 99% biodiesel, respectively [37]. Moreover, 98.5% FAME was derived in the TE reactions of palm oil using river snail shells as catalysts (>800°C). With 90% producing biodiesel, CaO leaching is also revealed to be the primary cause of catalytic activity. The CaO impregnated in deionized KF produces 85% biodiesel yield from soybean oil in 4 h with a catalyst concentration of 3.5% wt., with 1:6 oil-to-methanol molar ratio and a reaction temperature of 60°C [82].

## **5.4 Acid-catalyzed transesterification**

Heterogeneous acid catalysts are less corrosive and harmful than homogeneous acid catalysts and cause fewer environmental problems [83]. These catalysts have a wide range of acidic sites (**Figure 5**) with varying degrees of Brønsted or Lewis acidity. While these catalysts show promising performance under mild reaction conditions, they react much more slowly than solid-base catalysts [19]. Furthermore, this type of catalyst requires a large catalytic loading, high temperature, and a long reaction time.

### **5.5 Base-catalyzed transesterification**

The most widely utilized approach in the industry is the employment of alkaline catalysts in the TE of waste cooking oil. Because of their lower cost, metallic hydroxides are commonly utilized as catalysts (**Figure 6**). However, they have less activity than alkoxide [35]. According to reports, the pace of a base-catalyzed reaction is 4000 times faster than that of an acid-catalyzed reaction [83]. The most widely employed catalysts are potassium hydroxide (KOH) and sodium hydroxide (NaOH), both of which are highly sensitive to the quality of the reaction being impacted by the presence of water and free fatty acids [9]. In an alkaline environment, the presence of water may undergo saponification rather than esterification. Furthermore, the free fatty acids can react with the alkaline catalyst to produce soap and water [40].



#### **Table 2.**

*Benefits and drawbacks of various types of catalysts used for biodiesel production [79, 80].*

**Figure 6.** *The mechanism of the base-catalyzed TE of vegetable oils [84, 85].*

Saponification not only depletes the catalyst but also results in the production of emulsions that impede biodiesel separation, recovery, and purification.

## **6. Bifunctional heterogeneous catalyst**

Bifunctional heterogeneous catalysts are highly preferred by the chemical industry for both financial and environmental reasons, provided that they are available in the required quantity at a reasonable price and exhibit notable operational advantages over the corresponding homogeneous system [18]. Only a few examples of the use of

### *Bifunctional Heterogeneous Catalysts for Biodiesel Production Using Low-Cost Feedstocks:… DOI: http://dx.doi.org/10.5772/intechopen.109482*

heterogeneous multifunctional catalysts have been documented, and the majority of them, especially those containing transition metals, have issues with product contamination and limited reusability [20]. Additionally, they frequently require excessive amounts of expensive reagents or other additives, making them unsuitable for the mass production of extensive organic compounds [86]. Bifunctional catalysts that contain both supported acid and metal sites may encourage the transesterification reaction (**Table 1**). There are two types of bifunctional heterogeneous catalysts. i. Bimetallic: One of the most popular methods of regulating the catalytic performance of supported metal catalysts is to control the composition of bimetallic catalysts [21]. The intention of adding one metal to another is frequently to change the activity of the original metal rather than to establish a new catalytic function. The assumption that the modifying metal is absent from the surface layer limits its ability to directly produce a bifunctional effect in many of the situations where it is dominant [87]. Studies of these bifunctional (or "cooperative") catalysts have attracted a lot of attention in the scientific community [11]. There was a significant amount of interest in biodiesel production based on numerous reports in the literature on bifunctional heterogeneous catalysts. However, efficient and effective resources should be used to synthesize those catalysts. Furthermore, for large-scale industrial applications, optimization parameters such as reaction rate and effective transesterification should be required. In addition to focusing on efficient oil-to-biodiesel conversion, waste material utilization as a bifunctional heterogynous catalyst should be required to address the current associated problem of environmental pollution. As a result, there has been a lot of research done on bifunctional heterogeneous catalysts. In general, the use of bifunctional (or multifunctional) catalysts is a big step in the right direction for catalysis, especially for reactions that necessitate various kinds of intermediates as part of an overall reaction (**Table 1**).

## **7. Current status and future research direction**

The main source of greenhouse gases is CO2 emissions, which account for around 52% of emissions. Therefore, in order to reduce the greenhouse effect, alternative energy sources or technology must be developed. Alternative fossil fuels include a variety of renewable resources like wind, geothermal, solar, wave energy, and biofuel. Low efficiency and a high initial maintenance cost are a few downsides. Given the different difficulties of using renewable energy, biodiesel is a possible replacement for diesel made from petroleum. Due to its superior performance, biodegradability, nontoxic nature, lack of hazards, carbon neutrality, low pollution, environmental friendliness, low flammability, superior transportation, longer storage time, and low CO production, biodiesel is significant. On the other hand, it is crucial to produce biodiesel from non-edible sources as well as from edible sources. For the manufacturing of biodiesel, it is best practice to transesterify vegetable oil and animal fats using the appropriate catalyst. Currently, the TE of oil uses numerous chemical catalysts. However, those substances are expensive, scarce, hazardous, and ineffective. To address the current difficulties, it is therefore very important to produce alternative energy sources (biodiesel) from deep-frying oil and heterogeneous catalysts from solid waste. The bifunctional heterogynous catalyst has been the subject of numerous investigations and optimizations. To create an effective and efficient biodiesel yield, the bifunctional heterogynous catalyst must still be produced and studied. Additionally, intensification reactors will call for kinetics studies, optimization parameters, and

cost-effective TE in the presence of a bifunctional heterogynous catalyst, which may result in the creation of a workable replacement process for current industrial units. Furthermore, for efficient biodiesel synthesis and the minimization of harmful environmental consequences connected with waste materials, bifunctional heterogynous catalysts made from a variety of environmentally favorable materials would be needed. Therefore, more research should be conducted to produce biodiesel from lowcost feedstock using effective bifunctional heterogeneous catalysts. This requires particularly extensive research to demonstrate their potential for use in the synthesis of industrial biodiesel.

## **8. Conclusion**

Currently, there are numerous types of catalysts that have been investigated for transesterification. However, most of them are expansive, ineffective, and produce a lower yield of biodiesel. To overcome these problems, a bifunctional heterogynous catalyst was a viable alternative for producing high biodiesel yields. As a result, numerous studies on bifunctional heterogeneous catalysts should be conducted in order to improve biodiesel yields and reduce environmental pollution. A bifunctional heterogeneous catalyst can simultaneously esterify free fatty acids and transesterify triglycerides in oil. Using edible oil as a feedstock is not economical and is a major concern for biodiesel production. Therefore, research should be conducted on biomass waste as an alternative feedstock for the production of biodiesel. The chapter summarizes recent research advances in the development of bifunctional heterogynous catalysts for cost-effective biodiesel production. To prepare a better yield of biodiesel, future researchers should be focused on low-grade feedstock and bifunctional heterogeneous catalysts as an effective new route to replacing diesel fuel as a viable energy source in the near future.

## **Author details**

Welela Meka Kedir Department of Chemistry, College of Natural and Computational Science, Mattu University, Mattu, Ethiopia

\*Address all correspondence to: welelameka008@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.

*Bifunctional Heterogeneous Catalysts for Biodiesel Production Using Low-Cost Feedstocks:… DOI: http://dx.doi.org/10.5772/intechopen.109482*

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Section 4
