Diesel fuel as a solvent for the lipase-catalyzed alcoholysis of triglycerides and phosphatidylcholine

The abilities of three commercially available lipases-lipozyme IM 20, Amano PS-30, and Amano CE-to synthesize fatty acid ethyl esters via the alcoholysis of soy triglycerides (TG) and phosphatidylcholine (PC) in grade No. 2 diesel fuel were investigated. All three enzyme preparations were active in water-saturated diesel fuel, synthesizing fatty acid esters from both TC and PC. Response surface methodology, based on a Modified Central Composite design, was employed to examine the coordinate effects of lipid, water, and ethanol concentrations on enzyme activities and to identify conditions yielding maximum alcoholysis. For all three enzymes, optimal activities toward TG occurred al added water concentrations of less than 0.3 M. With PC as substrate, optimal enzyme activities occurred at added water concentrations as much as tenfold greater than this, and the amount of water required for maximum activity was proportional to the substrate concentration. For both substrates the enzyme activities were generally reduced as ethanol concentrations rose. The exceptions to this were the Lipozyme-TG combination, where activity increased with increasing ethanol concentrations, and the PS-30-PC combination, where activity was roughly constant across the range of water and ethanol concentrations examined. Hydrolytic activities of the enzymes in aqueous reactions were poor predictors of transesterification activity in organic solvent: the aqueous hydrolytic activities of CE and PS-30 toward TG were roughly comparable, and 25 to 50 times greater than that of IM 20. However, in the alcoholysis of TG in diesel fuel the order of activities was PS-30 > IM 20 > CE. The activities of Lipozyme and CE toward PC were similar to one another, and PS-30 was considerably less active on this substrate. CE lipase was more active toward PC than toward TG. Lipozyme displayed comparable activity toward the two substrates. PS-30 was considerably more active on TG than on PC: Degrees of conversion were consistent with the transesterification of only one fatty acid of TG, and slightly greater than one fatty acid for PC. Preliminary studies indicated that for CE and PS-30, but not for Lipozyme IM 20, the degree of conversion of TC, but not PC, could be significantly increased by the further provision of ethanol. Expansion of this work could lead to a method for the production of simple fatty acid esters, which are suitable as diesel fuels, from multicomponent agricultural materials containing TC and PC.