Three years later, the first commercial biodiesel production was started in America. By , the Commodity Credit Corporation started subsidizing value-added agriculture towards biodiesel production. The past decade to witnessed an unprecedented production of biodiesel. Incentives from policy makers such as tax exemptions, tax credits and renewable fuel standards aided the biodiesel growth.
However, some properties of biodiesel also contributed to the unprecedented growth we are witnessing in the biodiesel industry [ 16 - 18 ]. The increasing interests on biodiesel is fueled by the need to find a sustainable diesel fuel alternative. This is mainly because of environmental issues, apprehensions over energy independence and skyrocketing prices. Several processing options are available for the biodiesel production. The various feedstocks and processing conditions provide several processing technologies.
The choice of a particular technology is dependent on catalyst and the source, type and quality of feedstock. Others include postproduction steps such as product separation and purification and catalyst and alcohol recovery. It is therefore essential to utilize cheap feedstock to reduce the overall production costs.
In the same regards, some technologies are designed to handle variety of feedstocks. Non-fossil fuel alternatives are favored because of their common availability, renewability, sustainability, biodegrablability, job creation, regional development and reduced environmental impacts.
Table 1 summarizes some of the major successes of biodiesel. Numerous feedstocks have been experimented in biodiesel production. Advancements from such experimentations led to establishment of waste-to-wealth biodiesel production. Cheap and readily available raw materials such as used cooking oil and yellow grease are used for producing biodiesel.
These efforts helped in reducing the environmental impacts associated with dumping in landfills as well as saves the cost of paying for such dumping. The fact that it can be cultivated almost anywhere with minimal irrigation and less intensive care, made it suitable for peasant farmers. Sustained high yields were obtained throughout its average life cycle of 30—50 years.
Castor plantation are also intercropped with jatropha to improve the econmic viability of jatropha within the first 2 to 3 years [ 19 ]. Another oil crop that is used to improve soil quality is the nitrogen-fixing Pongamia pinnata. It produces seeds with significant oil contents. Biodiesel is one of the most thoroughly tested alternative fuel in the market today. Studies by many researchers have confirmed similar engine performance of biodiesel to petroleum diesel.
Transesterification produce oil with similar brake power as obtained with diesel fuel. Minimal carbon deposits were noticed inside the engine except the intake valve deposits which were slightly higher.
The level of injector coking was also reduced significantly lower than that observed with D2 fuel [ 7 , 17 ]. The process can be small in physical size and it utilizes heterogeneous catalysts to produce biodiesel within 4 s [ 20 , 21 ]. The easy fatty acid removal or EFAR system ensures that no wastes are produced from the process. It eliminates post production costs such as the washing and neutralization steps.
Energy efficiency is also achieved through heat transfer mechanism; in-coming cold reactants are preheated by the out-going hot products [ 20 , 21 ]. Process flow diafram of a biodiesel plant based on the Mcgyan proces[ 21 ].
Major achievements of biodiesel [ 16 , 23 - 27 ]. Departments of Agriculture and Energy with biodiesel usage. Essentially, biodiesel is non-aromatic and sulphur-free as compared with petrodiesel which contains 20 to 40 wt. Also, sulfates and oxides of sulfur major constituents of acid rain are essentially eliminated from the exhaust emissions compared to petrodiesel.
These help in curbing the increasing global warming problems. Average decrease of Human life expectancy is thereby enhanced because of improved air quality. Biodiesel reduces the excessive reliance on fossil fuels. This enhances the global energy security [ 17 ].
It also has the potential to replace oil importation since it is produced domestically, thereby providing additional market for agricultural products. It supports the rural communities where it is cultivated by protecting and generating jobs.
Approximately, for every unit of fossil energy used in biodiesel production, 4. Moreover, lesser energy is required for biodiesel production than the energy derived from the final product [ 16 ]. More than oil-bearing crops have been identified as potential sources for producing biodiesel. However, only palm, jatropha, rapeseed, soybean, sunflower, cottonseed, safflower, and peanut oils are considered as viable feedstocks for commercial production [ 28 ].
Depending on availability, different edible oils are utilized as feedstocks for biodiesel production by different countries. Palm oil and coconut oil are commonly used in Malaysia and Indonesia. Soybean oil is majorly used in U. In order to reduce production costs and to avoid the food-for-fuel conflict, inedible oils are used as the major sources for biodiesel production. Compared to edible oils, inedible oils are affordable and readily available.
They are obtained from Jatropha curcas jatropha or ratanjyote or seemaikattamankku , Pongamia pinnata karanja or honge , Calophyllum inophyllum nagchampa , Hevca brasiliensis rubber seed tree , Azadirachta indica neem , Madhuca indica and Madhuca longifolia mahua , Ceiba pentandra silk cotton tree , Simmondsia chinensis jojoba , Euphorbia tirucalli, babassu tree, microalgae, etc.
Many European countries utilize rapeseed [ 29 ]. During World War II, oil from Jatropha seeds was used as blends with and substituted for diesel [ 33 , 34 ]. It has been reported that biodiesel produced from palm and Jatropha have physical properties in the right balance; conferring it with adequate oxidation stability and cold performance [ 35 ]. Most of the strict requirements set by the American and European biodiesel standards for biodiesel have been achieved [ 36 ].
The major oils used for producing biodiesel are presented in Table 2. Major oil species for biodiesel production [ 37 ]. Currently, algae-based biodiesel is the focus of many research interests because they have the potential to provide sufficient oil for global consumption. Besides their high lipid contents and fast growth rate, microalgae have the potential to mitigate the competitions for land-use and food-for-fuel conflicts.
Microalgae can be cultivated in habitats which are not favorable for energy crops. Compared with oilseeds, the harvesting and transportation costs of microalgae are relatively low. Nannochloropsis , members of the marine green algae are considered the most suitable candidates for biodiesel production. These strains have shown high lipid content and biomass productivity. However, research in this area especially algal oil extraction is still limited and in early stages. Their low costs and availability make them suitable for reducing the production costs of biodiesel.
To achieve this however, the problems associated with high FFA which are common to these feedstocks, particularly when alkaline catalysts are employed need attention. Solid acid catalysts are currently receiving great attention because they are suitable for feedstocks containing FFAs [ 39 - 41 ]. Another process that has the potential of processing these feedstocks is supercritical transesterification. The pretreatment step, soap and catalyst removal common to alkaline catalysis are eliminated since the process requires no catalyst [ 42 , 43 ].
The process has fast reaction rate which significantly reduces the reaction time [ 44 ]. The process is insensitive to water and FFAs [ 43 , 45 ]. However, this method is not economical because it requires high reaction temperature, pressure and higher molar ratio of alcohol to feedstock [ 42 , 43 , 46 ]. Another interesting feedstock is Salicornia bigelovii Halophytessuch. It can produce equal biodiesel yields obtained from soybeans and other oilseeds. They grow in saltwater of coastal areas unsuitable for energy crops.
Estimated oil content, yields and land requirement for various biodiesel feedstocks. The three common methods used in extracting oil are: i Mechanical extraction, ii solvent extraction and iii enzymatic extraction.
However, most of the mechanical presses are designed for particular seeds which affect yields with other seeds. Also, extra treatments such as degumming and filtration are required for oil extracted by this technique. The commonly used chemical methods are: 1 soxhlet extraction, 2 Ultrasonication technique and 3 hot water extraction [ 48 , 49 ]. Yields are affected by particle size, solvent type and concentration, temperature and agitation. To increase the exposure of the oil to the solvent, the oilseeds are usually flaked.
After extraction, the oil-solvent mixture or miscella , is filtered while heat is used to vaporize the solvent from the miscella. Steam is injected to remove any solvent remaining from the oil. The immiscibility of the solvent and steam vapors is used to separate them in a settling tank after condensation.
The highest oil yields are obtained with n-hexane. However, the process requires higher energy and longer time compared to other methods. Furthermore, the human health and environmental impacts associated with toxic solvents, waste water generation and emissions of volatile organic compounds are challenges facing this method. Oilseeds are reduced to small particles and the oil is extracted by suitable enzymes. Volatile organic compounds are not produced by this method which makes it environmentally friendly when compared to the other methods.
However, it has the disadvantage of long processing time and high cost of purchasing enzymes [ 51 ]. Several researches were carried out to overcome or minimize the problems associated with producing biodiesel. The methods that have been used for minimizing the viscosity of vegetable oils for practical application in internal combustion engines include: pyrolysis, microemulsification, blending diluting and transesterification.
Dilution and microemulsification are not production processes and are therefore not discussed in this chapter. A summary of vegetable oils and animal fats and the major biodiesel production technologies are presented in Table 4. Pyrolysis is the heating of organic matter in the absence of air to produce gas, a liquid and a solid [ 52 ]. Heat or a combination of heat and catalyst is used to break vegetable oils or animal fats into smaller constituents.
Studies on effects of rapeseed particle size showed that the product yield is independent of the oilseed particle size [ 52 ]. Rapid devolatilization of cellulose and hemicellulose occur at this temperature. Heating rate and temperature have significant effects on bio-oil yields, char and gas released from olive [ 55 ]. The viscosity, flash and pour points and equivalent calorific values of the oil are lower than diesel fuel. Though the pyrolyzate has increased cetane number, it is however lower than that of diesel oil.
Apart from reducing the viscosity of the vegetable oil, pyrolysis enables de-coupling of the unit operation equipment in shorter time, place and scale. It produces clean liquids which needs no additional washing, drying or filtering. Product of pyrolysis consists of heterogeneous molecules such as water, particulate matter, sulfur, alkanes, alkenes and carboxylic acids [ 39 , 56 ]. Consequently, it is difficult to characterize fuel obtained from pyrolysis [ 52 ].
This process is energy consuming and needs expensive distillation unit. Moreover, the sulfur and ash contents make it less eco-friendly [ 57 ]. Transesterification is the most widely employed process for commercial production of biodiesel.
It involves heating the oil to a designated temperature with alcohol and a catalyst, thereby restructuring its chemical structure. This conversion reduces the high viscosity of the oils and fats. For the transesterification of triglyceride TG molecule, three consecutive reactions are needed. One mole of glycerol and three moles of alkyl esters are produced for each mole of TG converted at the completion of the net reaction.
These separate into three layers, with glycerol at the bottom, a middle layer of soapy substance, and biodiesel on top [ 57 ]. Transesterification is a reversible reaction.
To obtain reasonable conversion rates therefore, it requires a catalyst. The reaction conditions, feedstock compositional limits and post-separation requirements are predetermined by the nature of the catalyst. Table 5 presents a genaral overview of the several transesterification techniques for biodiesel production.
Alkali catalysts such as NaOH and KOH were preferred over other catalysts because of their ability to enhance faster reaction rates [ 63 ]. This is because they are readily available at affordable prices and enable fast reaction rates [ 24 ]. Detailed review on base-catalyzed transesterification of vegetable oils can be found in ref [ 64 ]. However, homogeneous catalysis has been faced with the been faced with the problems saponification, highly sensitive to FFAs, expensive separation requirement, waste water generation and high energy consumption.
Though the performance of this method is not strongly affected by FFAs in the feedstock, the process is not as popular as the base-catalyzed process.
This is because the use of strong acids such as H 2 SO 4 [ 65 , 66 ], HCl, BF 3 , H 3 PO 4 , and organic sulfonic acids [ 67 ], is associated with higher costs and environmental impacts. Moreover, the technique is about times slower than the homogeneous base-catalyzed reaction.
The mechanism of the acid-catalyzed transesterification can be found in ref [ 68 ]. Solid acid can simultaneously catalyze the esterification and transesterification without the need for pretreating feedstocks with high FFAs. Thus, this technique has the potential of reducing the high cost of biodiesel production by directly producing biodiesel from readily available and low-cost feedstocks [ 67 ].
Some of the problems associated with homogeneous catalysts such as expensive product separation, wastewater generation, and the presence of side reactions are avoided with enzymatic transesterification [ 69 ]. Enzyme immobilization is usually done to enhance the product quality, increase the number of times the catalyst is reused and to reduce cost [ 28 , 70 ].
However, several technical difficulties such as high cost of purchasing enzymes, product contamination, and residual enzymatic activity are limiting the applicability of this technique.
Unlike the conventional transesterification of two heterogeneous liquid phases involving alcohol polar molecule and non-polar molecules TGs , supercritical transesterification is done in single homogeneous phase. Subjecting solvents containing hydroxyl groups such as water and alcohol to conditions in excess of their critical points make them to act as superacids.
Under supercritical conditions, alcohol serves a dual purpose of acid catalyst and a reactant [ 46 , 71 ]. The absence of interphase solves the mass transfer limitations which gives the possibility of completing the reaction in minutes rather than several hours. However, this process is not economical especially for commercial production as it requires expensive reacting equipment due to high temperature and pressure [ 72 ].
Studies are currently being undertaken in order to reduce these high reacting conditions. The microwave irradiation as energy stimulant has been attracting the attention of many researchers. This is because the reaction process fast within minutes , it employs a lower alcohol-oil ratio and it reduces by-products quantities. It uses a continuously changing electrical and magnetic fields to activate the smallest degree of variance of the reacting molecules.
These rapidly rotating charged ions interact easily with minimal diffusion limitation [ 73 ]. However, this process also has commercial scale-up problem because of high operating conditions and safety aspects [ 74 ]. An even more daunting challenge is in increasing the irradiation penetration depth beyond a few centimeters into the reacting molecules.
This process utilizes sound energy at a frequency beyond human hearing. It stretches and compresses the reacting molecules in an alternating manner. Application of high negative pressure gradient beyond the critical molecular distance forms cavitation bubbles.
Some of the bubbles expand suddenly to unstable sizes and collapse violently. This causes emulsification and fast reaction rates with high yields since the phase boundary has been disrupted [ 75 - 77 ].
Merits and challenges surrounding transesterification processes [ 78 ]. In order to make biodiesel profitable, several technical challenges need to be resolved. The most important challenge is in reducing the high cost of feedstock. Low-cost feedstocks such as algal oils, used cooking oils and animal fats are utilized to increase biodiesel profitability. However, presence of higher amounts of water and FFAs in these feedstocks poses the problems of saponification and extra pretreatment and purification costs with alkali catalysts.
The challenge facing researchers currently is developing efficient heterogeneous acid catalysts that would alleviate these problems. Also, diversifying the by-product of biodiesel production processes is critical to ensuring its economic, social and environmental sustainability. Currently, biodiesel production costs are higher than those of petroleum diesel. Subsidies such as tax exempt and excise duty reductions are essential to make biodiesel price-competitive.
It is not certain whether these political supports will be sustained in the future. It is therefore crucial for the biofuel industry to establish readily available and affordable feedstocks and efficient production systems to sustain its market growth.
What is Biodiesel Why Biodiesel? Why Biodiesel? Biodiesel Basics. What Is Biodiesel? A Technical Definition Fuel-grade biodiesel must be produced to strict industry specifications in order to ensure proper performance. The technical definition of biodiesel is as follows: Biodiesel, n - a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B, and meeting the requirements of ASTM D Producing Biodiesel Biodiesel is made through a chemical process called transesterification whereby the glycerin is separated from the fat or vegetable oil.
Current Production Biodiesel production spans across the US and has grown to more than plants with the capacity to produce 3 billion gallons. Biodiesel Availability Biodiesel is available nationwide and blends over 4 percent are required to be labeled at the pump. Sustainability New land is not required for biodiesel production. Biodiesel has several environmental benefits when compared to petroleum-based diesel fuel: Reduces lifecycle greenhouse gases by 86 percent Lowers particulate matter by 47 percent, reduces smog and makes our air healthier to breathe Reduces hydrocarbon emissions by 67 percent For every unit of fossil energy it takes to produce biodiesel, 3.
For additional information on biodiesel see our Biodiesel Fact Sheets. Approximately pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol usually methanol in the presence of a catalyst usually sodium hydroxide [NaOH] or potassium hydroxide [KOH] to form pounds of biodiesel and 10 pounds of glycerin or glycerol.
Glycerin, a co-product, is a sugar commonly used in the manufacture of pharmaceuticals and cosmetics. Raw or refined plant oil, or recycled greases that have not been processed into biodiesel, are not biodiesel and should not be used as vehicle fuel. Fats and oils triglycerides are much more viscous than biodiesel, and low-level vegetable oil blends can cause long-term engine deposits, ring sticking, lube-oil gelling, and other maintenance problems that can reduce engine life.
Research is being conducted on developing algae as a potential biodiesel feedstock. It is expected to produce high yields from a smaller area of land than vegetable oils.
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