Biodiesel Production: Technologies, Challenges, and Future Prospects

The produced biodiesel is tested to determine fuel characteristics based on ASTM and European Union (EN) Biodiesel Fuel Quality Assurance Standard Tests. Biodiesel produced from various methods should be in its limits. The biodiesel and other biorefinery products such as bioethanol have similar characteristics like petroleum diesel. The performance and emission features of compression ignition engines depend on the inner nozzle flow and spray performance. Because of differences in the physical properties of biodiesel and petro-diesel, the inner nozzle flow and spray structure are expected to be significantly altered and consequently the performance and emission features of the diesel engine. One of the major technical advantages of biodiesel over petro-diesel is lubricity. Biodiesel fuel composition varies depending on the feedstock used in fuel production. EN 590166 and ASTM D975167 fuel specifications for petroleum-based diesel fuels permit blending with biofuel content of up to 5% and 20%, respectively.

This chapter looks into the various technical aspects of biodiesel that qualify it to be an alternative fuel and the physicochemical properties of biodiesel in greater detail. It also explains the cause and sometimes the need for variation in the biofuel and its effect on engine performance, the effect of such a change in the fuel characteristics on various quantifiable outputs, and examines the overall performance and potential of biofuels in comparison to conventional mineral oil. Depending upon the difference in their physicochemical properties, biodiesel has a number of variations and therefore is denoted by different names. A number of standards exist for biodiesel quality, based on some unique specifications. The European standard EN 14214, ASTM International D6751 of the United States, and the National Standard of Canada CAN/CGSB-3.524 are all comparable standards, although they are known by different nomenclatures in these different countries.

Several technologies have been developed to produce biodiesel, including pyrolysis, microemulsions, and transesterification. This chapter addresses biodiesel production by transesterification. It discusses parameters affecting transesterification. The chapter reviews the new technologies and their applications in transesterification. Transesterification is known as the most popular approach for biodiesel manufacture. It uses oil and/or fat to produce fatty acid methyl esters and glycerol by reacting with alcohols. Among all alcohols, methanol is preferable because of cost considerations. Catalyst type, alcohol type, oil type, alcohol to oil ratio, and assistance technology addition are significant parameters of transesterification. The general transesterification is to convert oil and/or fat to biodiesel. Directly transferring oil-bearing substance to biodiesel without the step of oil separation and/or extraction from the substance has been studied. The process is also called in situ transesterification. The technology becomes promising because it avoids oil extraction, which is a high-energy and high-cost process.

This chapter reviews enzyme-catalyzed biodiesel production, focusing on lipase as biocatalysts, factors affecting lipase-catalyzed transesterification, advancements in immobilization techniques, and development of bioreactors for competent transesterification with economic considerations for developed technology. To obtain high biodiesel yield, the transesterification process and rate of reaction can be affected by different parameters, such as chain length of alcohol, alcohol to substrate molar ratio, use of solvents, reaction temperature, water content, and catalyst concentration. For commercialization of enzyme-based biodiesel production, the enzymatic transesterification reaction should be performed at the reactor level. The most commonly used reactors for enzyme-based biodiesel production are stirred tank reactors, packed-bed reactors, and fluidized-bed reactors. Economic evaluation of any process technology is a key driving force for successful implementation at the commercial level. The major cost factor for industrial biodiesel production is the cost of feedstock, which adds up to 70% to 95% of the total production cost.

Biodiesel production from vegetable oils can be achieved by any of four methods: blending, pyrolysis, microemulsion, and transesterification. The most common method for conversion of triacylglycerides from vegetable oils to biodiesel is the reversible transesterification reaction. This method also overcomes the problem of high-viscosity oil. Many factors affect transesterification reaction and ester yield, such as type of alcohol, molar ratio of alcohol to oil, type and amount of catalyst, reaction time, temperature and pressure, moisture content, and free fatty acid content in oils. Transesterification reaction can take place in the presence or absence of a catalyst. Transesterification reactions can be categorized into homogeneously catalyzed or heterogeneously catalyzed, based on the catalyst solubility in a reaction mixture. The major contributor to cost in biodiesel production is feedstock, and in the case of plant oil, price increases caused by high demand.

This chapter is designed in a way to cover all possible aspects of animal fat biodiesel. It provides the sources of animal fats and the factors affecting rendering techniques and other chemical parameters. Biodiesel made from tallow and fats has a higher cetane number (CN) as compared with soy oil. The CN according to American Society for Testing and Materials D6751 and European Standard 14214 biodiesel standards has been determined as 47 and 51 minutes, respectively. The chapter also provides comparative studies of the free fatty acids from various animal fat sources to get an estimation of maximum saturated and unsaturated fatty acid production. Simultaneously, it describes the presence of various metals in animal fat and techniques for using natural resources to convert biodiesel. The chapter also describes economic impacts as well as the pros and cons of using animal fats for biodiesel production.

Waste cooking oil (WCO) is a promising alternative to vegetable oil for biodiesel production because it is much less expensive than virgin vegetable oil (VVO). This chapter discusses the sources of WCO, factors affecting WCO, methods for preparation of biodiesel from WCO, fuel characterization, comparison of WCO and VVO for biodiesel production, and economic assessment for biodiesel production from WCO. Both WCO and VVO biodiesels have the same cold filter plugging point (CFPP) value of 8°C, which is in excess compared to the standard. This excess may be caused by the higher content of saturated fatty acid methyl esters. Therefore, it is necessary to add antifreeze to improve low-temperature properties of both biodiesels. Additionally, WCO and VVO biodiesels show moderate density, kinematic viscosity, iodine value, and high ester content, which completely satisfy the biodiesel standard.

This chapter reviews oleaginous microalgae that are suitable for biodiesel production and the main lipid composition of these microalgae. It discusses the microalgae cultivation mode, factors affecting productivity of microalgae biomass and lipid, harvesting methods, the drying process, lipid extraction approaches, and transesterification. The major factors affecting oil accumulation in microalgae are strains, cultivation mode, and cultivation conditions. Harvesting as the step following microalgae cultivation plays an important role in biodiesel production from microalgae because the harvesting method directly influences biodiesel quality and cost. Centrifugation is efficient but expensive; flotation is cheap but not well developed; gravity sedimentation is simple but inefficient; filtration might be a wise choice currently for microalgae harvesting in practice, even though it could cause pollution on microalgae biomass. The chapter also addresses the current problems and future aspects of microalgae for biodiesel production.

Single cell oil (SCO), or microbial oil, is the most promising source of feedstock oil for the biodiesel industry. The inherent advantages associated with SCO and its method of cultivation make it a standout technology for food, feed, and fuel. This chapter focuses on the basic characteristics of SCO and discusses the basic elements of microbial oil production, such as oleaginous organisms, substrates usually available for economic production of SCO, and basic physiochemical factors for the production of SCO. It also discusses the various mechanisms and underlying biochemical pathways for SCO production and its consumption. In the discussion about the costs and economics of SCO, the chapter elucidates the bottlenecks of SCO production process development and future targets to be achieved. Intensive research is going on to realize the production of SCO at scales competitive to conventional vegetable oil for second-generation biodiesel production.

Organic wastes from agriculture, other industries, and residential areas are rich in carbon and/or nutrients, often available for free or at low cost, and thus, have been used as raw materials for culturing oleaginous microorganisms. This chapter overviews the sources and properties of these organic wastes, their use for growing oleaginous microorganisms, their bioconversion to biodiesel with related technologies and processes, as well as the parameters that affect lipid accumulation. Compared to agriculture wastes, industrial and residential wastes are a more suitable substrate and/or nutrients for oleaginous microbe production because they generally can be directly used without pretreatment. Enhancing lipid productivity is another way of reducing biodiesel production cost. By controlling cultivation conditions, including pH, dissolved oxygen, carbon to nitrogen ratio, temperature, trace elements, and fermentation modes, one can improve lipid productivity.

Sludge generated in wastewater treatment plants has been used as feedstock for biodiesel production. This chapter overviews the methods of sludge disposal, sludge characterization, different methods for oil extraction from sludge, properties of oil extracted from sludge, technoeconomic studies, and developments in the field. Pyrolysis is the thermal decomposition of organic substances under anaerobic circumstances. Catalytic pyrolysis studies indicated a decrease in yield when the catalyst is used in the pyrolysis system. This decrease is caused by the increase in catalytic cracking reactions of tar, leading to the formation of secondary products. For obtaining a high oil yield from pyrolysis reactions, primary sludge should be used at optimum temperature, gas residence time, and solid feed rate. In all the studies conducted, temperature was the most influential factor in deciding oil yield and oil composition.

This chapter focuses on the use of wastewater sludge as a substrate for lipid production during microbial fermentation. The microbial lipids accumulated inside the cells can be extracted and converted into biodiesel/fatty acid methyl ester (FAME) through transesterification reaction. The chapter overviews the feasibility of using wastewater sludge as a raw material to produce lipids and their subsequent conversion into biodiesel, along with sludge characteristics, challenges to use sludge as feedstock at a commercial level, and future perspectives. Use of sewage sludge as a raw material for biodiesel production for the commercial level poses many challenges, including variability of sludge characteristics, soap formation and product separation, screenings of oleaginous microbes, and impurities present in sludge. Biodiesel production methods and downstream processing are expensive for sludge-derived FAME. Hence, extensive research work is required for optimizing downstream processes to make wastewater sludge a more profitable candidate compared to other sources.

This chapter overviews lipid production studies using oleaginous microbes, metabolism of glycerol usage by oleaginous microbes, effects of impurities in crude glycerol on lipid production, the optimization of fermentation parameters for enhanced lipid production, and kinetic studies for lipid production by different microbes. Biodiesel and lipids manufactured using oleaginous microbes are sustainable and biodegradable compared to conventional biodiesel processes. Several successful laboratory-scale studies have been conducted on using crude glycerol as a substrate for lipid production. Studies include selection of strains using crude glycerol, fermentation cultivation mode, optimization of carbon/nitrogen ratio, media components and fermentation parameters, pretreatment of crude glycerol, and coculture systems for lipid production. These studies have mentioned the use of different oleaginous microorganisms and cultivation modes that resulted in high lipid productivity and content. The chapter compares fermentation parameters used in laboratory-scale studies that showed best results after optimization of media components and operating parameters.

Lignocellulosic materials are a substantial renewable substrate for biofuel applications. The most common lignocellulosic biomass used for biofuel generation is agro-residues, agro- and food-processing industrial waste, forestry waste, and municipal waste. This chapter overviews lipid production from different lignocellulosic biomass using single-cell organisms. It discusses advancement in the lignocellulosic biomass pretreatment and hydrolysis method, followed by in-depth descriptions about different microbes reported to grow and produce lipid from lignocellulose hydrolyzate, cofermentation, simultaneous hydrolysis and lipid production, and tolerance against different fermentation inhibitors. Two types of fermentation techniques are practiced to accumulate lipid-solid state and liquid state fermentation. Considering growth, recovery, and other economic factors, submerged fermentation is identified as the economically feasible method for oil fermentation. The pretreatment liquor is used as a carbon source for other fermentations, such as production of amino acid organic acids.

Biodiesel is converted from oils or fats contained in plants seeds, microorganisms, or animals. Therefore, extraction of the oils and fats from oil-bearing materials is an essential step of biodiesel production. This chapter reviews the technologies of oil extraction and discusses their advantages and disadvantages. Physical extraction breaks the cells to release the lipid by providing force, whereas chemical extraction uses solvent to pull lipids out of cells. Each of the methods has its advantages and disadvantages. Physical methods are clean but have low lipid extraction efficiency and high energy consumption. Chemical extraction has a high possibility of contamination of the lipid because of the presence of residual solvents when toxic organic compounds are used. The pressure generated by the driving force is the main factor in extraction efficiency because it is the main cause of cell disruption.

Oleaginous microorganisms have proved to be promising candidates for biodiesel production because they have high lipid productivity. The mass transfer of lipids from inside oleaginous microbes to outside of the microbes is an important area of future investigation for understanding and enhancing the extraction efficiency of lipids. This chapter discusses potential microbes for lipid production and various milking methods for their extraction. Milking is one of the best possibilities for this process; it was introduced by J. Frenz and collaborators in 1989 for extraction of hydrocarbons from Botryococcus braunii (green algae) by exposing cells to hexane for a short time. Various extraction processes are potentially applicable for milking microorganisms, including the use of biocompatible organic solvents, pulsed electric fields, spontaneous oozing, and membrane transport proteins. Hence, if milking comes to the commercial level, it would be more economical and environmentally friendly.

This chapter reviews implementation of nanotechnology at various process steps of biodiesel production, such as cultivation of microbes, lipid extraction, purification of hydrocarbons from oil, and transesterification. It discusses advantages and disadvantages of using nanotechnology at various process steps. Considerable research has been conducted at the transesterification stage with nanomaterial immobilized catalysts because they have advantages over traditional base-catalyzed transesterification, such as the lack of formation of soapy substances, high reaction rates, high enzymatic stability, activity, and reusability. Studies incorporating the use of nanotechnology in transesterification and selective extraction of value-added products from oil should be conducted on a large scale. But challenges like the high fabrication cost of nanomaterials, reliability, and nonuniformity of nanoparticles need to be addressed. As nanotechnology application in biodiesel production develops, biodiesel production using oleaginous microbes will be more sustainable than the current biodiesel production methods.

This chapter introduces the required gene editing tools for developing a genetically modified strain. It discusses the various strategies adopted to improve the overall biodiesel production process and the accompanying challenges in different oleaginous microorganisms, including yeast, algae, and bacteria. Transformation of the chromosomal genome is one of the most efficient methods to bring about any desired metabolic alteration in an organism. Microalgae have been the primary target of many metabolic modifications that researchers have been studying to improve single cell oil (SCO) production. Geneticists target different aspects of the microbial oil synthesis process to enhance SCO production. Broadly, their efforts have been directed to facilitating downstream extraction of microbial lipid bodies and increasing lipid quantity, lipid quality, and in situ biodiesel production. To achieve high lipid accumulation, researchers propose to incorporate, delete, suppress, overexpress, and replace various responsible genes related to lipid metabolism.

The primary objective of crude biodiesel purification is to achieve the purity and quality of biodiesel as per the standards set by EN 14214 and ASTM D6751 for diesel engine use. Purification of crude biodiesel is a main requirement for its commercial production and use. This chapter overviews the techniques and methods that are used for the separation and purification of biodiesel. It discusses the traditional method (gravitational settling) and new techniques (centrifugation and coalescing technologies) of biodiesel separation. After that, the chapter elucidates biodiesel purification techniques, including conventional biodiesel purification techniques and modern evolving technology. It also discusses the analytical techniques used for characterization of biodiesel and the factors that should be considered to prolong the stability of biodiesel. Finally, the chapter describes the challenges and future perspectives of the new approaches to developing robust and economical purification technology.

This chapter overviews studies reported on applications of ion-exchange resins and adsorbents in biodiesel purification. It explores ion-exchange resins, commercial adsorbents, agricultural and industrial wastes in biodiesel purification, advantages and disadvantages of each, process parameters, comparison with wet-washing techniques, and improvements that can be made for biodiesel purification using resins. A comparative study has been reported for the use of ion-exchange resins and adsorbents in biodiesel purification, and the results obtained were compared with the wet-washing method. In another study, biodiesel purification was done using three different procedures: washing with distilled water; dry-washing with Magnesol; and ion-exchange resins, and results were compared. Ion-exchange resin was most effective in removing impurities from biodiesel, but the purification ability of Magnesol was comparable to that of ion-exchange resins. However, toxic waste produced from filtered Magnesol requires further treatment, which would increase the process costs. Biodiesel purified using ion-exchange resin met the ASTM standards.

This chapter discusses the management of coproducts produced during biodiesel production and covers a wide array of coproducts from biodiesel production and the state of knowledge and its management. The cultivation of food and cash crops produces a huge amount of biomass, which is an issue of management. Around 200 billion tons of organic matter per year are produced globally through the photosynthetic process. Most of this organic matter is not edible by higher animals and is the cause of environmental problems. Organic matter, including straw, cobs, and leaves, is general waste produced during harvest. Oil cakes, algal biomass residues, microbial biomass, and other wastes are generated during oil extraction. In general, these wastes can be treated biotechnologically for value-added products. The production of bioenergy and chemicals from biomass can be defined as biorefinery by the integration of bioprocessing and appropriate low-impact environmental chemical technologies in a cost-effective and environmentally sustainable manner.

Knowledge of economic competence of developed technologies can only be supplemented with honest and genuine technoeconomic analysis. This chapter examines the technoeconomic studies performed with vegetable oil, algal oil, and single cell oil and reveals the technological aspects that affect the economy of the process of biodiesel production. After all the analysis and technoeconomic studies, the part of the results that intrigue or interest a nonresearcher the most is economic feasibility. In fact, people have long been indirectly trying to answer questions about whether a proposed process is economically feasible. Policy makers and industry in real life understand different languages; they look at processes using different visions, but they all stress profits and revenues. This chapter elaborates how people summarize the whole field of technoeconomic study using different parameters of economic feasibility and evaluates which variant of the process is economically better.

The biodiesel industry needs to pursue more interdisciplinary research to assess complex global environmental and health concerns. This chapter addresses scientific and industrial information on the effects of the biodiesel industry on biodiesel-related topics, such as water resources, emission, soil pollution, land use, biodiversity, greenhouse gases, and human well-being. Increased biodiesel crops require large amounts of water, and thus there will be an increase in the pressure on natural water resources. Water quality issues are likely to increase because of biodiesel manufacturing, as well as the contamination of water resources from biodiesel crops. Increases in irrigation, use of fertilizers, pesticides, and soil erosion caused by land activities are future challenges for maintaining the productivity and quality of the soil. Deforestation and conversion of food agricultural lands into fuel crops are likely to occur in biodiesel-producing countries.

This chapter looks into some of the issues beyond technology in the realms of economics, politics, and sociology and into the ideology of different sovereign countries and their take on biodiesel technologies, the international fora, and their mulling over proliferation of biodiesel technology, the oil sector, and its humongous power. It discusses the social and environmental developments occurring in biodiesel development, and most importantly, the implications for a common person and for a community as the consumer, producer, and observer of the biodiesel production phenomenon. Governments around the world have been promoting biofuel feedstock production hoping to fight climate change, to invigorate the rural economy by providing employment, and to nurture an alternative energy resource that is no longer limited by thoughts of nonavailability of crude oil in the near future, either by natural or political constraints. However, perpetuating this change has caused a domino effect and brought about other changes too.