Biocatalytic esterification of palm oil fatty acids for biodiesel production using glycine-based cross-linked protein coated microcrystalline lipase

Conversion of feedstocks containing high free fatty acid contents to alkyl esters is limited by the currently used alkali-catalyzed biodiesel synthesis process. In this study, esterification of palm fatty acids to ethyl esters was studied using heterogeneous cross-linked protein coated microcrystalline (CL-PCMC) lipase. Optimization of biocatalyst synthesis by variation of matrix components and organic solvents showed that highly active CL-PCMCs could be prepared from Thermomyces lanuginosus lipase with glycine as the core matrix in acetone. The optimized reaction contained 20% (w/w) glycine-based CL-PCMC-lipase, a 1:4 fatty acid molar equivalence to ethanol in the presence of an equimolar amount of tert-butanol which led to production of 87.2% and 81.4% (mol/mol) of ethyl ester from palmitic acid and industrial palm fatty acid distillate (PFAD), respectively after incubation at 50 °C for 6 h. CL-PCMC-lipase is more catalytically efficient than protein coated microcrystalline (PCMC) lipase, Novozyme®435 and Lipolase 100T for both free fatty acids and palm fatty acid distillate. The CL-PCMC-lipase showed high operational stability with no significant loss in product yield after 8 consecutive batch cycles. The glycine-based microcrystalline lipase is thus a promising alternative economical biocatalyst for biodiesel production from inexpensive feedstocks with high free fatty acid contents.