An Overview of Enzyme-Catalyzed Reactions and Alternative Feedstock for Biodiesel Production

Abstract

There is an increasing interest in biodiesel production because of the environmental and economic advantages of this biofuel over traditional fuels derived from non-renewable resources (Akoh et al., 2007). Biodiesel is a renewable, non-toxic and biodegradable fuel (Van Gerpen et al., 2004) defined as the mono alkyl esters of long chain fatty acids derived from vegetable or animal fats, for use in compression-ignition (diesel) engines (American Society for Testing and Material [ASTM], 1989). This fuel can be used pure or in a blend with petroleum-based diesel (Van Gerpen et al., 2004). Currently, large-scale biodiesel production has been done by means of alcoholysis reactions of fats and oils (Reaney et al., 2005). The choice of the suitable alcohol for this process will depend on factors like its cost, availability, toxicity, easy of recovering and recycling, and the amount of alcohol needed for the reaction. Commercially, biodiesel has been produced using methanol as alkyl donor due to advantages like easy recovering and low cost (Van Gerpen et al., 2004). Anhydrous ethanol has also a great potential for biodiesel production in Brazil, one of the largest world ethanol producers (Schuchardt et al., 1998). Renewable sources from both vegetable (Reaney et al., 2005) and animal (Lee et al., 2002) origin can be used as raw materials for biodiesel production. Microalgal oils have also received much attention as substrate for esters formation (Miao & Wu, 2006). Many agroindustrial processing operations generate a significant amount of lipids as by-products, such as chicken fat, beef tallow and fish oil. This feedstock, usually applied in livestock feeding, is a viable resource to produce biodiesel, and this use is a way for adding value to this material (Feltes et al. 2009). The conversion of used cooking oils and restaurant grease into alkyl esters is another proposal of particular interest in the field of alternative fuels (Lee et al., 2002). The use of biomass as feedstock is an attractive alternative for biodiesel production in tropical countries such as Brazil. The agricultural and farming industries are activities of great importance in many parts of this country. Also, government policies and legislative action may rapidly increase biodiesel production in such region (Ferrari et al., 2005; Meneghetti et al., 2006). Chemical catalysis is a well established process for biodiesel production (Bournay et al., 2005). The homogeneous alkali-catalyzed transesterification process has been extensively