Production of Biodiesel by Enzymatic Transesterification: using Waste Cooking Oil as feedstock and Candida Antarctica Lipase B as Biocatalyst.
The high cost of bio-diesel, compared to petroleum-based diesel, is a major barrier to its commercialization. It has been reported that 60-90% of bio-diesel cost arises from the cost of the feedstock oil (C.C. Lai et al., 2005). Studies showed the potential of waste-cooking oil (WCO) as a material for biodiesel production (Sulaiman Al-Zuhair, 2008). Therefore, the use of WCO should greatly reduce the cost of bio-diesel. In addition to the choice of lipase employed, factors which make the transesterification process feasible and ready for commercialization are: enzyme modification, the selection of feedstock and alcohol, use of common solvents, pretreatment of the lipase , alcohol to oil molar ratio, water activity/content and reaction temperature. Optimization of these parameters is necessary in order to reduce the cost of biodiesel production. Use of no/low cost waste materials such as the WCO will have double environmental benefits by reducing the environmental pollution potential of the wastes and producing an environmentally friendly fuel.
In addition, production of bio-diesel from WCO is considered an important step in reducing and recycling waste. A fresh vegetable oil and its waste differ significantly in water and free fatty acids (FFAs) contents, which are around 2000 ppm and 10-15%, respectively (C.C. Lai et al., 2005; Y. Zhang et al., 2003). Because of this the traditional alkaline-catalyzed biodiesel production is unsuitable (Zhang et al., 2003).
The use of the enzyme lipase as a biocatalyst for the transesterification reaction step in biodiesel production has been extensively investigated. Lipase is produced by all living organisms and can be used intracellularly or extracellularly. In order to design an economically and environmentally sustainable biodiesel production process, a proper understanding of the factors affecting the process and their relative importance of enzyme-catalyzed biodiesel production is necessary. A general equation for transesterification (where group R is a fatty acid, R’ is the length of the acyl acceptor and R” is the rest of the triglyercide molecule) is as follows:
Methanol is the most popular alcohol used in the transesterification process because of its relatively cheaper price compared to other alcohols. When methanol is used in the process, the reaction is known as methanolysis as shown in the following equation:
Lipases from microorganisms (bacterial and fungal) are the most used as biocatalysts in biotechnological applications and organic chemistry. Fungal – source lipases have been found to produce high yields of lipases compare to the animal and plants. Because their bulk production is easier, commercialization of microbial lipases and their involvement in enzymatic biodiesel production are more common than animal and plant ones (Hasan et al., 2006;Akoh et al., 2007; Antczak et al., 2009). The lipase to be employed as the biocatalyst is Candida Antarctica lipase B (Novozyme CABL L), one of the most common fungal lipase used for the production of biodiesel (Vasudevan and Briggs, 2008). Lipases are capable of converting all the triglycerides derive from the feed stocks into their respective fatty acids methyl esters (FAMEs). They act on the ester bonds of carboxylic acids allowing them to carry out their primary reaction of hydrolyzing fats (Joseph et al., 2008). Enzyme immobilization is an important approach that could be used as a tool to improve and optimize operation stability, activity and selectivity which allows the enzyme to study under harsher environmental condition and also provides their separation from the reaction mixture without filtration in case of packed bed reactor (Fernandez-Lafuente et al., 1998; Bhushan et al., 2009; Gao et al., 2006) and, hence, could lead to more...
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