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 th e alcoholysis of soy triglycerides (TG) and phosphatidylcholine (PC) i n grade No. 2 diesel fuel were investigated. All three enzyme preparat ions were active in water-saturated diesel fuel, synthesizing fatty ac id esters from both TC and PC. Response surface methodology, based on a Modified Central Composite design, was employed to examine the coord inate effects of lipid, water, and ethanol concentrations on enzyme ac tivities and to identify conditions yielding maximum alcoholysis. For all three enzymes, optimal activities toward TG occurred al added wate r concentrations of less than 0.3 M. With PC as substrate, optimal enz yme activities occurred at added water concentrations as much as tenfo ld greater than this, and the amount of water required for maximum act ivity was proportional to the substrate concentration. For both substr ates the enzyme activities were generally reduced as ethanol concentra tions rose. The exceptions to this were the Lipozyme-TG combination, w here activity increased with increasing ethanol concentrations, and th e PS-30-PC combination, where activity was roughly constant across the range of water and ethanol concentrations examined. Hydrolytic activi ties of the enzymes in aqueous reactions were poor predictors of trans esterification activity in organic solvent: the aqueous hydrolytic act ivities of CE and PS-30 toward TG were roughly comparable, and 25 to 5 0 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 act ivities of Lipozyme and CE toward PC were similar to one another, and PS-30 was considerably less active on this substrate. CE lipase was mo re active toward PC than toward TG. Lipozyme displayed comparable acti vity toward the two substrates. PS-30 was considerably more active on TG than on PC: Degrees of conversion were consistent with the transest erification of only one fatty acid of TG, and slightly greater than on e 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 no t PC, could be significantly increased by the further provision of eth anol. 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.