The Production of Biodiesel and Related Fuel Additives E-Book
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- Herausgeber: Bentham Science Publishers
- Kategorie: Für Kinder und Jugendliche
- Serie: Recent Advances in Renewable Energy
- Sprache: Englisch
This volume is a review of recent developments, opportunities, and challenges in the conversion of biomass from different sources to biodiesel or related fuel additives. Key features of the book include fully referenced chapters edited by experts, a blend of basic and current information on biodiesel and a summary of sustainable use of biodiesel byproducts like glycerol.
The volume presents a comprehensive range of 13 topics related to biodiesel production and fuel additives. It begins with a historical overview of biodiesel and related additives, followed by detailed chapters on biodiesel production from various sources such as soybean oil, palm oil, and Jatropha curcas oil. Recent advancements in catalytic thermochemical conversions of biomass into biofuels are explored, alongside discussions on algal biocrude as a feedstock. The role of homogeneous and heterogeneous catalysis in biodiesel production is examined, along with innovative techniques such as microwave and ultrasound-assisted synthesis. The book also presents information about the utilization of waste cooking oil and waste-derived catalysts, concluding with insights into solketal synthesis and catalytic biodiesel production via simultaneous esterification and transesterification.
The book imparts the technical know-how on biodiesel and relevant fuel additives for engineering and sustainability students, professionals and apprentices. It also informs policymakers in the energy sector on the benefits of biodiesel as a renewable energy resource.
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Veröffentlichungsjahr: 2024
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PREFACE
Progress in fuel and energy has always been the subject of interest in the world economy, transportation, and fuel market. The interest is growing exponentially due to the limit of traditional fossil fuels, out of many renewable energies. Biofuels are just one source, but they still count as an important one.
This book “Recent Advances in the Production of Biodiesel and Related Fuel Additives” deals with the many new developments along with substantial limitations in the production as well as use on a global level. Besides the basic introductory part, the book covers current approaches and plausible future approaches to be addressed. This book contains 12 chapters providing a comprehensive and all-encompassing reference about biodiesels which will be helpful to students, teachers, researchers, and professionals. In this book, readers will find fundamental concepts of important biofuels and the current state-of-the-art technology for their production.
Chapter 1 gives basic information about biodiesel and related fuel additives. The history, availability, and viability of biodiesel, as well as its relevance, technical properties, and prospective replacement for diesel fuel in internal combustion engines along with the biodiesel fuel additives, are discussed in this chapter.
Chapter 2 deals with the utilization of soybean oil as a source of biodiesel. Soybean oil has been widely used for oil production and the leftover is commonly used as animal meal. The chapter includes a detailed discussion of the catalysts used for biodiesel production from soybean oil feedstock.
Chapter 3 shares the production of biodiesel from palm (Arecaceae) oil. Different types of catalysts developed for the transesterification of palm oil are well-audited in this chapter. Meanwhile, chapter 4 discusses the details of biodiesel production from Jatropha curcas oil. This chapter describes the Jatropha system, oil extraction, and catalytic conversion by traditional and modern processes, downstream processes, and final product characteristics.
Chapter 4 discusses the production of biodiesel from Jatropha curcas oil. Jatropha oil is found in a wide range of fatty acid methyl esters profile, and free fatty acids content. Consequently, the adjustments of upstream processes must be considered. Jatropha curcas biodiesel is basically focused on small or medium-scale production. This chapter describes the Jatropha system, oil extraction, and catalytic conversion by traditional and modern processes, downstream processes, and final product characteristics.
Chapter 5 focuses on catalytic pyrolysis of biomass to biodiesel. This chapter focuses on recent catalytic methods for the conversion of biomass to biofuels namely biodiesel along with the pros and cons of the methods.
Chapter 6 describes biodiesel biocrude production from algae as a feedstock. The algal biocrude produced using hydrothermal liquefaction is a drop-in kind of biocrude. It can be processed, independently or in combination with fossil- based crude, in existing refinery infrastructure to produce green biofuel.
Chapter 7 deals with the homogeneous and heterogeneous catalysis in biodiesel production. The efficiency, limitations, advantages of all kinds of catalysts, comparison of their properties, and suitability in the transesterification are also discussed.
Chapter 8 emphasizes microwave-assisted synthesis of biodiesel and related fuel additives. This book chapter covers a broad spectrum of scientific and instrumental aspects of microwave radiation methodology in chemical synthesis, the practical approach of the microwave reactor design, the production of different biofuels and additives using microwave techniques, along with the advantages and several limitations of this methodology.
Chapter 9 throws light on the ultrasound-assisted production of biodiesel. The use of ultrasounds in biodiesel production has a growing interest due to several advantages; as it significantly reduces the reaction time and avoids the use of heating, reaching similar or higher FAME yield. This chapter explores the basis of ultrasounds and their use in biodiesel production, its main features, and challenges.
Chapter 10 provides an in-depth analysis of several cooking oils as a biodiesel feedstock, including their salient qualities and most common pests.
Chapter 11 emphasizes the waste-derived catalysts for biodiesel production. This chapter gives brief knowledge about such heterogeneous catalysts derived from waste in particular.
Chapter 12 deals with the synthesis of solketal: a potent fuel additive from glycerol, a by-product of biodiesel industries. This chapter gives new insight into the researcher to find a new pathway to utilize the by-product in an environmentally friendly manner.
Chapter 13 provides a brief review of the catalytic production of biodiesel specifically the esterification and transesterification processes. The advantages of solid acid catalyst, its activity, performance, efficacy, and reusability are well discussed in this.
With the high spirits of hope, we are serving this book to society and our all stakeholders. But at the same time, we are open and thankful for the comments and suggestions that will be received from our readers towards the improvement of this book.
List of Contributors
Biodiesel and Related Fuel Additives: A Brief History
Supongsenla Ao1,Samuel L. Rokhum1,*Abstract
The discovery of the diesel engine by Rudolf Diesel in the mid-19th century is where the origin of what finally came to be known as “biodiesel” lies. Since then, numerous approaches have been suggested to utilize pure or blended, straight vegetable oils or their derivatives for the production of biodiesel. The availability and viability of biodiesel, as well as its relevance, history, technical properties, and prospective replacement for diesel fuel in internal combustion engines including various types of biodiesel fuel additives, are all discussed in this chapter.
1. INTRODUCTION
The demand for more ecologically friendly and sustainable means to power modern economies has recently been fueled by the rise in global energy consumption, as well as the depletion of fossil fuel supplies and increasing CO2 emissions [1, 2]. In light of this, the search for alternative renewable energy has been sparked by worries about the depletion of fossil fuels and the degradation of the environment. Researchers are interested in biodiesel as a potential alternative fuel among the contenders. The biofuel biodiesel, which emits less carbon monoxide (CO), sulfur dioxide (SO2), and unburned hydrocarbons (HC) than petroleum diesel and is non-toxic, has the potential to replace petroleum diesel as an alternative energy source at present [3]. Several countries now have laws and policies that promote the use of alternative fuels, such as biodiesel, by providing incentives and setting stringent limits on the usage of each fuel. Here, in this chapter, we will discuss about the insights into biodiesel, its properties, production techniques, and various types of fuel additives.
1.1. Background of Biodiesel and Related Fuel Additives
1.1.1. Biodiesel
Although the term “biodiesel” was first used in 1988, the practice of substituting vegetable oil for diesel as a fuel dates back to 1900. The invention of the diesel engine by Rudolf Diesel laid the foundation for what eventually came to be known as “biodiesel” [4]. In the year 1900, the Paris World Fair hosted the first diesel engine demonstration for those nations growing oil crops, especially those in Africa in the 1940s, knowing that vegetable oils could be used to power the diesel engine which gave them a sense of energy independence [5, 6]. This was particularly true during the years of World War II when cottonseed oil exports were outlawed even in Brazil so that it might be utilized as a diesel alternative. In China, kerosene and gasoline were produced using tung oil and other vegetable oils [7]. In addition, India and the USA also did research on the conversion of a range of vegetable oils to diesel in response to the lack of fuel during World War II [8]. A passenger bus that ran between Brussels and Louvain in 1938 used palm oil ethyl ester as fuel, and vegetable oil was used as fuel by many nations, including Brazil, Argentina, China, India, and Japan, during World War II (1939– 1945), when petroleum fuel supplies were disrupted. However, when the war was over and petroleum was once more accessible and affordable, vegetable oil fuel was forgotten. In Europe, commercial production of biodiesel began in 1992, with Germany being the biggest producer [4]. In Kansas City, Missouri, biodiesel was first produced commercially in the United States in 1991 [4]. Since then, the output of biodiesel increased globally from 1 billion liters in 2001 to 6 billion liters in 2006 [9]. One of the biggest non-governmental organizations for the development of standards, American Society for Testing and Materials (ASTM) International released ASTM Standard D6751 in 2001 as a biodiesel standard. This gave fleet owners and engine manufacturers confidence that biodiesel would meet their standards for quality.
1.1.2. Fuel Additives
With the exponential growth in biodiesel production, a significant amount of crude glycerol has been produced as a byproduct around the world. Glycerol could be a building block with many useful derivatives. For every 100 kg of biodiesel, glycerol accounts for 1 kg (w/w) or, 1.05 pounds of glycerol are created for every gallon of biodiesel produced [10]. This means that a factory producing 30 million gallons of glycerin annually will produce around 11,500 tonnes of 99.9% pure glycerin. In 2019, the market for glycerol was estimated to be worth USD 2.6 billion [11]. Additionally, from 2020 to 2027, it is predicted to rise at a compound annual growth rate of 4.0% [11, 12]. Therefore, finding new applications for both crude and refined glycerol is vital for researchers. Value-added chemicals such as solketal, glycerol carbonate, acetin, can increase sales for the existing biodiesel industry and improve the sustainability of the process [13, 14].
1.1.2.1. Solketal
The very first solketal production occurred in 1895 when glycerol and acetone were combined in a batch reactor under acidic circumstances with hydrogen chloride as a catalyst [15]. In the years that followed, fresh ideas for achieving greater output in less time were put forth. In the beginning, homogeneous catalysts and strong acids such as sulfuric, hydrochloric, hydrofluoric, and phosphoric acids were used in the process, while para-toluene sulphonic acid (pTSA) was also utilised by Newman and Renoll back in 1945 [16]. The issues with using homogeneous catalysts are well documented and include difficult product separation, equipment degradation, and significant worries regarding effluent disposal [17, 18]. The use of heterogeneous catalysts adheres to several of the Green Chemistry principles, including safer solvents, accident prevention through auxiliary, naturally safer chemistry, and less hazardous chemical synthesis [19]. Since then, many production techniques for the production of solketal in batch and continuous methods of operation have been proposed, with the majority of studies concentrating on batch techniques, particularly in relation to overcoming the thermodynamic limitation [20, 21].
1.1.2.2. Glycerol Carbonate
Another value-added glycerol derivative that is popular for industrial use is glycerol carbonate (GC). Glycerol 1,2-carbonate is a naturally occurring substance that is environmentally benign, harmful, and biodegradable. Its chemical name is 4-(hydroxymethyl)-1,3-dioxolane-2-one [22, 23]. Due to its two separate functional groups, hydroxyl and cyclic carbonate, it is a five-membered cyclic carbonate with distinctive chemical reactivity. Vieville et al. [24], reported the first study on the carboxylation of glycerol utilizing zeolites and ion exchange resins as catalysts in the presence of supercritical CO2. Zeolite Purosiv, zeolite 13X, and Amberlyst A26 were utilised as the catalysts, and they successfully accelerated the reaction of glycerol adsorption onto the solid catalyst and ethylene carbonate dissolution in a supercritical CO2 solution. Glycerol and supercritical CO2 are combined with methanol to achieve 100% solubility, which promotes a more homogenous process and increases yield [25]. Since then, considerable research on the carboxylation of glycerol utilising homogeneous and heterogeneous catalysts has been explored.
1.2. State of the Art in Biofuel Production
A vast variety of feedstocks have been and are still being investigated for the generation of biodiesel. They include animal fats, waste cooking oils, non-edible oils, edible plant oils, and algal oil [26, 27]. Yet, using the first of these results in the conversion of potential food for human consumption into fuel, creating a nexus between food and fuel. Inedible oils like Jatropha curcus oil [28], Pongamia glabra (karanja) [29], Pongamia pinnatta (Honge) [30], and palm fatty acid distillate (PFAD) [31] have therefore drawn increasing attention lately which is also categorized as second generation feedstocks. The focus of the study has shifted from edible oils to inedible oils to algal oil, which is recently known as third generation feedstock, due to the low activity of the catalyst caused by the presence of high free fatty acids (FFAs). The most quickly expanding photosynthesizing organisms are microalgae. Every several days, they can finish their entire growing cycle. Using diatom algae, 46 tonnes of oil may be generated per hectare each year [32]. Various types of algae produce varying amounts of oil. Some algae can produce up to 50% of their weight in oil. Some estimates place the yield of oil produced by algae (per acre) at nearly 200 times that of the best plant/vegetable oils [33, 34]. Although commercial-scale algae farming to gather oil for biodiesel has not been attempted, practicability studies have been carried out to reach the aforementioned figure.
The most practical and economical method for creating biodiesel has shown to be transesterification [35]. Transesterification merely reduces the viscosity of the oils produced from any feedstock. The three heating methods used to carry out the transesterification process over the years are conventional heating, supercritical heating, and microwave heating [3]. Table 1 compares and demonstrates the differences between them as well as their benefits and drawbacks.
In an attempt to reduce the overall cost of biofuel production, energy products made from biomass utilizing current conversion methods have been introduced. Biofuel production has been documented since the 19th century. Biomass sources, which are once again renewable energy sources, are used to make biofuels [3] as was previously indicated. The term “biomass” is used to describe all organic materials that can be converted into bioenergy, which primarily include forests, agricultural crops, and animal waste from agroforestry and livestock [50]. Up to 27% of the world's supply of liquid fuel is expected to come from biofuels. New manufacturing methods for biodiesel are being proposed as a result of the rising need for it in research. These approaches will produce high conversion yields while posing no environmental risks and remaining commercially viable. A total of 8.3 billion gallons of biodiesel can be produced annually from animal fats and vegetable oil, and that number is rising daily [51]. It is anticipated that by 2040, the demand for primary biomass energy will rise from 26.9 million barrels of oil equivalent per day to 35.5 million barrels per day [52]. By 2030, the Sustainable Development Scenario (SDS) estimates that 10% of the world's transportation fuel needs will be met by biofuels [53]. This framework as their main goals is the blending of biodiesel with diesel and the use of wastelands for the production of biofuels.
2. CATALYTIC BIODIESEL PRODUCTION
The employment of a catalyst to speed up the transesterification of vegetable oils and alcohol into biodiesel has caught the attention of a number of researchers. In general, biocatalysts, homogeneous and heterogeneous catalysts are the three categories into which the catalysts employed in chemical reactions are divided (Fig. 1). Catalytic processes could usually use both homogeneous and heterogeneous catalysts. In comparison to homogeneous catalysts, heterogeneous catalysts have various benefits, including easy glycerol recovery, easy catalyst recovery, easy product purification, and easy catalyst reuse [26, 54]. Accordingly, the production of inexpensive, active catalysts for efficient transesterification of catalysts that are economically viable is needed to generate biodiesel that is commercially viable.
Fig. (1)) Types of catalyst for biofuel production.2.1. Homogenous Catalyst
Homogeneous catalysts are mostly divided into two groups such as a) base catalyst and b) acid catalyst. As indicated in Table 2, numerous homogeneous base catalysts, including KOH, NaOH, and NaOCH3, have been used to generate FAME to date [3, 47]. The production of biodiesel using NaOH and KOH as catalysts has shown remarkable catalytic activity, such as the shortest reaction time and the highest biodiesel yield at room temperature and pressure. The output of biodiesel is decreased by the formation of water as a byproduct, which is one of the process' constraints [55]. Since water is not produced during these procedures, sodium methoxide and potassium methoxide perform better than KOH and NaOH in terms of biodiesel production [56].
Since basic catalysts are less expensive and more reactive than acid catalysts, they are typically preferred. However, base catalysts could interact with the FFA in the feedstock during transesterification, leading to the saponification of soap, which could deplete the catalyst and reduce its reactivity [57]. The transesterification or esterification of vegetable oils or fats with a high quantity of FFA (2 wt. %), however, produces superior results when using an acidic catalyst because it is neutral to the FFA [58, 59]. Typically, before transesterification using a base catalyst, acid catalysts are used to lower the FFA concentration in WCO and animal fats by esterification. The manufacturing of biodiesel using an acid catalyst has some significant drawbacks, although, a high molar substrate ration (alcohol: feedstock) is used, including a reaction rate that is 4,000 times slower than that of the base-catalyzed transesterification [60]. Similarly, it also promoted environmental and corrosive-related issues. Due to these drawbacks, acid-catalyzed biodiesel synthesis is not widely used and is not as extensively researched. In general terms, however, the current homogenous catalysts for biodiesel production with their associated merits and demerits are summarized in Table 2.
2.2. Heterogeneous Catalyst
The potential of heterogeneous catalysts to address the issues of homogenous catalysts has therefore assumed importance. If prepared straightforwardly from relatively easily sourced materials, these can offer to reduce environmental contamination while bringing greater cost-effectiveness largely through their simple isolation and recovery [61, 62]. In principle, heterogeneous catalysts can be recycled and reused multiple times, maintaining morphology, active site density, and activity and making biodiesel manufacture significantly more cost-effective [63, 64]. The characteristics of heterogeneous base catalysts and mineral acids (such as cation exchange resins, supported heteropoly acids, sulfonated solids, zeolites, metal oxides, etc.) that are moisture-resistant, have resistance against high FFA content, and can simultaneously carry out both transesterification and esterification reactions that have been combined to create heterogeneous acid catalysts. Fig. (2) shows us the different types of heterogenous catalysts used for biofuel production explored over the years.
Fig. (2)) Heterogeneous catalyst for biodiesel production.Transesterification was employed to produce biodiesel using a novel heterogeneous base catalyst based on barium aluminate (BaAl2O4) and vegetable oil [65]. According to the findings, a methyl ester conversion rate of 93.28% was attained during the transesterification reaction. One of the most researched heterogeneous base catalysts is CaO [66], which has received the greatest attention in studies on metal oxides and zeolites. These catalysts have demonstrated that they are effective at transesterifying oils with low FFA contents. Over the years, a study on the production of catalysts for biodiesel from waste biomass was introduced, where the catalytic capabilities of carbon-based catalysts produced from papaya seeds [67], orange peel [68], empty fruit bunches (EFBs) [69], and corncob biomass waste [70] were explored. It was predicted that catalytic production conditions, such as carbonization temperature (600–1000 °C), sulfonation time (0.5–2.5 h), and sulphate acid/activated carbon weight ratio (3:1–13:1), had animpact on the yield of fatty acid methyl esters (FAME) and the FFA conversion coefficient. Table 3 summarizes the types of heterogeneous catalysts and their synthesis over the years.
3. FUEL ADDITIVES
A fuel additive is a chemical substance that enhances the characteristics of fuel, cleans engine components, lowers consumption ratios, and/or reduces greenhouse gas (GHG) emissions to improve engine performance [71]. Some oxygenated chemicals are utilised as fuel additives to enhance particular fuel qualities (diesel, biodiesel, and gasoline). These additives could improve the octane-cetane rating and combustion behavior by increasing its oxygen content, decrease particle emissions, and produce less carbon monoxide. They could also decrease the density and viscosity of particular fuels [72]. Glycerol is the main result of the vast volume of waste produced by biodiesel synthesis. According to several publications, glycerol makes up 10-20% of the total amount of biodiesel produced. In other words, 10 kg of glycerol is generated for every 100 kg of biodiesel produced (Fig. 3) [10, 12].
Glycerol, which has been said to have a low commercial value due to its poor quality, will undoubtedly be in surplus due to the expanding biodiesel production [73]. When disposed of without proper treatment, there are also social and environmental issues to consider; as a result, a lot of research is concentrated on the conversion of glycerol into high-value and useful products (Fig. 4). Researchers and industrialists believe that this will improve the economics of biodiesel by reducing its production costs. Glycerol's usage in virtually all spheres of human activity has made it known how versatile it is [72, 74, 75]. Glycerol must be pure in order to be employed in the food, pharmaceutical, cosmetic, and other personal care industries. Therefore, it should be no surprise that using raw, partially treated glycerol in the creation of higher-value goods has recently attracted a lot of attention. This is anticipated to encourage integrated biodiesel and other chemicals’ production—a term now used to refer to biorefineries.
Fig. (3)) Biodiesel byproducts and fuel additives. Fig. (4)) Glycerol derivatives and their applications [17].3.1. Solketal
Certainly, one of the most favorable uses of glycerol is the synthesis of fuel additives like ketals and cyclic acetals from aldehydes and ketones, respectively [76]. A clean fuel additive called solketal, which is made from glycerol and acetone, does wonders in improving biodiesel to a greater extent [77, 78]. It is produced by ketalizing glycerol and acetone near a catalyst, which causes water to be released as a byproduct (Fig. 5) [79]. The reaction complies with a number of green chemistry principles because all reactants are derived from renewable resources, the reaction can be catalyzed by a heterogeneous catalyst and carried out under benign conditions, the chemicals used in the reaction are relatively non-toxic, and water is produced as a byproduct. In terms of the sustainability of the biodiesel sector, solketalization of bioglycerol stands out as a very successful method. It is an antiknocking ingredient that aids in the development of gum in biodiesel [80], improves stability to maintain octane number [20], and also lessens viscosity [10]. It also has industrial uses as a flexible solvent, plasticizer in the polymer sector, medicinal, flavouring ingredient, and surfactant [81, 82].
Fig. (5)) Synthesis of solketal from bioglycerol.Generally, the synthesis of solketal is proceeded via both homogeneous and heterogeneous catalysts, but heterogeneous catalysts are preferred due to their many advantages over homogeneous catalysts, such as their ability to recover catalyst more easily [82], their ability to prevent corrosion in the reaction systems [83], and their ability to address both economic and environmental concerns regarding the disposal of effluents [15, 20]. Numerous heterogeneous solid acid catalysts, including biomass-derived catalysts [75], metal oxides [84], amberlyst resins [16], transition metals as solid acid catalysts [85], niobia zirconia [86], magnetic nanoparticles [72], and sulfonic acid mesostructured silica [87], have been investigated for the glycerol acetalization.
The effectiveness of three types of heterogeneous catalysts (Amberlyst–15, 35, and 36) was compared by Da Silva et al. [88], also known as first-generation solketal. According to the study, Amberlyst-15 had the maximum conversion (95%) after only 15 minutes of reaction in a batch reactor operating at 373 K. Only after 40 minutes did zeolite beta and montmorillonite K-10 achieve conversions of up to 90%. Nanda et al. [16], reported second-generation catalyst research by employing ethanol as a solvent and Amberlyst-35 as a catalyst to produce a yield of more than 74% at a reaction temperature of 25–45 °C and a substrate ratio (mol) of glycerol to acetone at 2:1. They succeeded in reducing the process temperature by employing ethanol as a solvent. Moreover, the third generation [89] underwent an acetalization reaction of solvent-free glycerol utilising heterogeneous catalysts to produce desirable products (solketal) at a relatively high efficiency even without the requirement of a solvent. A review of recent research on the production of solketal from bioglycerol is discussed in Table 4.
3.2. Glycerol carbonate
Glycerol carbonate (GC), a five-membered cyclic carbonate having functional groups (hydroxyl and cyclic carbonate), has gained momentum in recent years for its physical and chemical properties [103] (Fig. 6). It is chemically stable, nonflammable, water-soluble and has a low volatility [104]. Because of its biodegradability, it has drawn our attention in terms of environmental balancing.
Fig. (6)) Synthetic scheme of GC through glycerol transesterification with DMC.The explosive growth of the biodiesel sector is ascribed to the threat posed by the depletion of petroleum over the past ten years. Glycerol is produced at a rate of 10% (w/w) of the entire amount of biodiesel produced, and the industry's rapid expansion has resulted in a glut of glycerol [12]. The paradigm shift has unavoidably drawn the attention of researchers, who are now looking into the potential for converting glycerol into chemicals with an added value, such as fuel, chemical intermediates, and chemicals, including 1,3-propanediol, epichlorohydrin, acrolein, fuel additive, glycerol carbonate (GC), and glycidol. According to reports, glycerol carbonate (GC) holds the most promise due to its prospective use as a green solvent, surfactant, fuel additive, and in skincare and cosmetics industries. It is a high-value product, with a market price of more than 8141 US dollars per ton. It is still not frequently employed in commercial applications because of the expensive cost. On the bright side, GC can be made from biogenic glycerol and has a great deal of potential for application as an alternative to petro-derived chemicals.
The most promising, efficient, and economically feasible method of producing GC is the transesterification of glycerol using DMC [105]. Even though glycerol is thermally stable, it needs the maximum threshold energy for breakage of the bond and to participate in the transesterification reaction. Therefore, the effective catalyst applied, which can suggest an eventual lower-activation-energy reaction pathway, is the key criterion to ensure a feasible glycerol transesterification. Numerous reports of catalytic transesterification using a broad range of catalysts with various property combinations have been published (Table 5) [106, 107]. However, homogeneous catalysts have certain downsides, including non-recyclability and complex and time-consuming product separation. Heterogeneous catalysts are considered the most important for transesterification reactions due to their capacity to immediately phase separate from reaction products. As they are easily separated from the products and reusable, they produce GC through glycerol valorization, which is both efficient and affordable. In order to produce GC from glycerol, a range of inorganic and organic catalysts are used, including enzymes [107], ionic liquids, hydrotalcites [108], mixed metal oxides [109, 110], metal supported on metal oxide [111, 112], and zeolites. Changmai et al. [113] reported on the efficiency of a solid basic catalyst made from Musa acuminata peel ash (MAPA) for the manufacture of GC, and more recently Das et al. [12] used Mangifera indica peel ash (MIPCA) as a catalyst for microwave-assisted glycerol transesterification. The principal active ingredient, K2O, is made up 65.9% of the content of the catalysts made from biomass waste MAPA, which also includes CaO (7.78%), MgO (2.42%), and SiO2 (10.86%). Comparably, MIPCA contains SiO2 (15.42%), CaO (26.2%), MgO (8.53%), and the main active ingredient K2O (37.9%), which is notable for its high basicity. Both the catalysts have been reported to display high glycerol conversion and GC selectivity above 90%.
Magnesium nickel-based mixed oxide (MgNiOx), a low-cost heterogeneous basic catalyst, was synthesized by Pradhan et al. [114] for GC production. The high turn-over frequency and low E-factor (0.074) implied the effectiveness and environmentally benign nature. Meanwhile, using biomass waste as a catalyst source solves the issue of waste disposal and manages the cost of GC production through transesterification, researchers are much more worried about using catalysts made from biowaste [23, 115] for GC synthesis. Calcium is found in abundance in the shell of crayfish, a crustacean cray fish that makes a suitable raw material for producing glycerol transesterification catalysts. Wang et al. [116], synthesized glycerol carbonate from discarded crayfish shell powder, which resulted in the development of a collection of solid base catalysts. Significant catalytic activity was demonstrated by the catalyst created by calcining crayfish shell at 800 °C. Under ideal reaction conditions (90 min, 1:6 glycerol to DMC molar ratio, 4 wt. % catalyst dosage, and 75 °C reaction temperature), this catalyst enabled 95.3% GC yield.
In a study by Zhang et al. [117], magnetic mesoporous CoFe2O4@(CaO-ZnO) showed good catalytic activity for the transesterification of GC with glycerol. A GC yield of 96.9% was generated by this chemical system. At room temperature, the magnetic properties of CoFe2O4 and CoFe2O4@(CaO-ZnO) were assessed using vibrating sample magnetometers (VSMs). CoFe2O4 had a saturation magnetization value of 82.7 emu/g and was ferromagnetic. Due to the encapsulation of CaO and ZnO, the saturation magnetization of CoFe2O4@(CaO-ZnO) decreased to 18.2 emu/g. This value, although, was still adequate for the catalyst's separation and recovery. In an attempt to go beyond, Naik et al., [118], created acidic, basic, and neutral ionic liquids in two phases. The findings demonstrated that basic ILs have more catalytic activity than acidic or neutral ILs in the transesterification reaction and are more potent than inorganic basic catalysts. Under additional optimization reaction conditions, a new basic ionic liquid, 1-methyl-3-butylimidazolium imidazolium ([Bmim]Im), led to 98.4% glycerol conversion and up to 100% GC selectivity.
4. SOCIO-ECONOMIC AND ENVIRONMENTAL IMPACT OF BIOFUEL PRODUCTION
The selection and execution of biofuel manufacture systems must ensure global socioeconomic and environmental benefits if humankind is to stop additional biodiversity losses and general environmental degradation while controlling global warming [124]. Systems that may meet socioeconomic goals such improving the welfare of local people and citizens in nations that produce biofuels as well as biofuel production goals based on their high production levels or the availability of feedstocks may be given preference over others (Fig. 7). Additionally, biofuel production methods with positive effects on the environment [125] could help to meet goals for carbon emission reduction, biodiversity preservation, and ecosystem services. These cover a wide variety of sustainable economic contributions, labour rights and conditions, health and safety, gender, land rights and conflicts, food security, and other environmental issues that could affect inhabitants in the area. These systems would need to avoid conflicting with agricultural lands [126], and reduce pollution [127], soil degradation [128], and the potential for invasiveness [124]. Furthermore, for the evaluation of the socioeconomic implications of biofuel production, a number of sustainability criteria and indicators were put forth that are further described below.
Fig. (7)) Socio-economic impact representation of biofuel production.A similar amount of focus is required on the socioeconomic difficulties related to the making and use of biofuels, even though the production of biofuels to satisfy global demand requires more affordable and high-throughput technologies. Risks to one's health as well as demands for water, land, employment, and equality are mostly covered here. The European Commission has created a number of binding directives for biofuels, biomass, and bioliquids, but they have not established any specific standards for social sustainability. Therefore, before widespread popular acceptance of biofuels, the social implications of biofuels need to be properly assessed.
The socio-economic effects of biofuel include its impact on food security, supply, and accessibility. The growth of energy crop plantations and the effects of the rising demand for liquid biofuels on food prices will impact at least two important aspects of food security: access and availability. Due to their great profitability, energy crop plantations may be created on high-quality fields, leaving subsistence crops on low-quality lands. Additionally, the production of biofuels may have a negative impact on the livestock industry, which is essential to the food security of rural households, by reducing the amount of land available for grazing and driving up the cost of fodder (as a result of the expanding use of agricultural products for the production of biofuels). Agriculture is also under risk from the probable loss of biodiversity and agro-biodiversity, which poses a severe challenge to rural livelihoods and long-term food security. The areas deemed favourable for the production of biofuels include those that are close to rivers or that rely on non-renewable subsurface water, which is used by small-scale farmers. Large-scale biofuel production will divert the majority of the water into their plantations, denying access to water to small-scale farmers. In the medium term, increasing agricultural commodity prices will negatively impact household food security on a large scale. Particularly in danger are poor urban consumers and poor rural net food buyers, who typically make up the majority of the rural poor. Establishing suitable safety nets is crucial to guarantee the poor and vulnerable have access to food.
Through contracting with the manufacturers that make liquid biofuels, new employment opportunities in rural regions have been considered as a method to boost revenue creation and rural development. The creation of new jobs, better energy services, and an increase in local health are all immediate direct effects of this development. These immediate repercussions, along with other repercussions, may have a favourable influence on a number of rural development factors, including enhanced rural infrastructure, knowledge and skills, productivity, and quality of life. Ultimately, all these modifications might lead to rural communities becoming more stable. Growing and harvesting biomass, moving and handling, and running plants all present new work prospects. They encompass equipment makers and maintenance workers as well. Given an additional source of income from energy byproducts, farmers may increase returns as marginal crops become profitable. Waste streams can be redirected to create electricity, and degraded woods can be revitalised.
Crops are the primary source of biofuels, and the development of biofuels can both investigate the industrial potential of agricultural goods and raise their added value. Economic expansion and the development of biofuels can interact according to experience. On the one hand, economic expansion will increase the need for energy in the country, which will affect the production of biofuels because they are becoming an increasingly important fuel source. On the other side, because the government has expanded its efforts to create biofuels, the biofuel chain (production, transportation, etc.) can offer numerous employment possibilities and raise people's income [129]. The socioeconomic benefits of biofuel production are extensive and include a wide range of stakeholders. Thus, we suggested a conceptual framework to address the issue of sustainability, roles, and duties of stakeholders.
CONCLUSION and FUTURE OUTLOOK
This history of biofuels introduction was written with the goal of enhancing the reader's understanding of earlier accomplishments that paved the way for the development of renewable biofuels in the twenty-first century. As a finite, non-renewable energy source with limitations, fossil fuels must be replaced because their combustion has negative consequences on the environment. The use of biofuels is anticipated to aid in the preservation of energy and the mitigation of global warming.
The adoption of more environmentally friendly biofuel production methods, such as those using native perennial crops, wastes sourced sustainably, and microalgal production methods grown on degraded or low-biodiversity lands, could lessen the severity of a number of socioeconomic and environmental effects, particularly in terms of lessening competition for food production and biodiversity. The commercialization and future growth of biodiesel production depend heavily on the efficient use of crude glycerol. Using glycerol made from biomass will, over time, not only help society become less reliant on nonrenewable resources but will also encourage the growth of integrated biorefineries. Researchers should consider before using this chemical generated from biomass on a large basis in animal diets as different feedstocks and technologies have different chemically composed glycerol.
It is necessary to produce extensive assessments that consider the social and environmental effects of biofuel production in order to inform decisions and implement more sustainable biofuel production alternatives. This could involve, for example, the development and standardization of environmental indicators, the development of standardized assessments on the environmental effects imposed by biofuel production systems, the development of in-depth case studies that consider a range of socioeconomic and environmental objectives, improved projections of potential biofuel production feasibility and yield, and the development of integrated assessments to comprehend the socioeconomic and environmental impacts of various biofuel production systems.
Finally, when the byproducts are transformed into goods with value added biodiesel, production will be economically feasible. By using extraction, transesterification, pyrolysis, gasification, combustion, and anaerobic digestion technologies, these three prospective biofuel plants can be successfully valorized. As a crucial component of the circular bioeconomy, a zero-waste strategy should be used. Therefore, it is important to thoroughly research the profitability and supply chain market of the promising biofuel plants, putting an emphasis on the ecological and socioeconomic sustainability.
