Enzymes are proteins that work as nature’s catalysts. They are specific in the reactions they catalyze and are very proficient in doing so. Enzymes consist of active sites where the substrates bind, in a favorable position and angle, and react. They lower the activation energies of reactions by large factors and, similar to mineral catalysts, they are not consumed in the process.

Typically, enzymes are named and classified according to the substrates they catalyze, or a word or phrase describing their activity. Accordingly, lipase would be the class of enzymes that hydrolyze triglycerides (or lipids) to produce fatty acids. However, lipases have also been found to display catalytic activity towards a large variety of alcohols and acids in ester synthesis reactions. Since the synthesis of methyl esters are of primary interest, lipase would be the appropriate enzyme to be used for biodiesel production. Lipase-catalyzed production of biodiesel has been proposed to overcome the drawbacks facing the conventional chemically catalyzed methods, and have shown promising results. Most importantly, glycerol can be easily recovered without any complex process, FFA contained in the oils can be completely converted to methyl esters and subsequent wastewater treatment is not required (Al-Zuhair, 2008). As shown in Fig. 6.2, the enzymatic process is less complicated and does not require as many upstream and downstream

(b)

6.2 Comparison between alkali (a) and enzymatic (b) processes.

operations, compared to conventional alkali-catalyzed processes. Furthermore, lipase-catalyzed transesterification is performed at low temperature and ambient pressure making it not only less energy intensive but also safer than chemically catalyzed reactions.