Base-catalyzed transesterification of microalgae oil is used most frequently and involves the presence of a base catalyst (hydroxides/carbonates) to precede the reaction (Meher et al., 2006; Vargha and Truter, 2005). In the reaction, the triglycerides are readily transesterified batchwise in the presence of the catalyst at an atmospheric pressure and tem­perature of 60-70 °C in the presence of excess methanol (Srivastava and Prasad, 2000). The main drawback with the process is the formation of soap at high free fatty acid concentrations (Furuta et al., 2004). Prior removal of free fatty acid and water from algae oils is a prerequisite for the reaction (Demirbas, 2008).

8.7.2 Enzyme-Catalyzed Transesterification

The reaction in an enzyme-catalyzed transesterification process is catalyzed by the enzyme lipase, whereby total triacylglycerides (both extracellular and intracellular) can be converted to biodiesel (Bisen et al., 2010). The conversion process requires complex processing instru­ments, and the costliness of the enzymes makes the process limiting. Immobilization was employed to overcome the limitations. However, the low feasibility of the process makes the reaction complex (Helwani et al., 2009; Watanabe et al., 2001).