Most of the established biodiesel production lines are based on chemical methods. The catalysts used are acid catalyst, such as H2 SO4, or alkaline catalysts, such as NaOH and sodium methoxide. The alkaline method is better than acid catalysis due to the high FAME yield and short reaction times. Generally, large molar ratio of methanol to oil is needed for alkaline catalysis process to achieve high yield, and a distillation process will be needed for methanol recovery and biodiesel refining. Chemical methods give high conversion of triacylglycerols (TAG) to methyl esters (biodiesel) in relatively short times (4-10 h). However, they have drawbacks such as high energy consumption, difficulty in recovering the glycerol, and significant amount of alkaline wastewater. The fatty acid alkaline salts (soaps) are by-products which have to be removed by washing with water. The chemical catalysis process is still the most popular method for industrial scale use due to the high cost of lipase (Tan et al. 2010).

To overcome the disadvantages of chemical catalyst, biocatalyst especially enzy­matic transesterification can be the solution for the production of biodiesel. Table 8.2 presented the comparison between enzymatic technology and chemical method using alkaline and acid process.

In contrast to chemical transesterification, enzyme-catalyzed processes are promising due to high selectivity of enzyme in reaction under mild operating con­ditions (Salis et al. 2003, 2004; Jaeger and Eggert 2002; Schimd et al. 2002). Furthermore, recovery of FAME is simple to accomplish (Fukuda et al. 2001). When compared to base catalysis, FFA concentration in the oil is not critical to enzymatic transesterification because fats containing triglycerides and FFA can be enzymatically converted to biodiesel in a one-step process. Lipases are able to catalyze both transesterification and esterification reactions (Szczesna Antczak et al. 2009). Production of cheaper an. robust lipase preparations together with system development that favors for long-term, iterative use of biocatalyst can give

rise to the replacement of chemical processes with enzymatic route (Gerpen 2005; Meher et al. 2006; Ma and Hanna 1999; Ranganathan et al. 2007; De Greyt 2004; Marchetti et al. 2007; Akoh et al. 2007).

Though at present, the high cost of enzyme production may be a major obstacle for commercialization of enzyme-catalyzed processes, recent advances in enzyme technology, such as the use of solvent-tolerant lipases and immobilized lipases, making catalyst reutilization possible, have been made to develop cost-effective systems (Oliveira et al. 2006; Rosa et al. 2008). In addition, if the lipase is immobi­lized, then it becomes an independent phase within the reaction system, which may easily be retained in the reactor with concomitant advantages in preventing con­tamination of the products and extending its useful active life. Further, increasing the temperature generally increases the rate of lipase-catalyzed reaction per unit amount of active enzyme; however, increasing the temperature also leads to a higher thermal deactivation rate of the lipase itself, thus yielding decreasing amounts of active enzyme. Because immobilization provides a more rigid external backbone for lipase molecule, temperature optima are expected to increase, which results in a faster reaction rate (Al-Zuhair et al. 2006).