Optimizing production of ethyl esters of grease using 95% ethanol by response surface methodology

Previous research suggested that ethyl esters derived from recycled restaur ant grease might be a potential source of biodiesel. Accordingly, response surface methodology (RSM) was employed to optimize reaction parameters-temp erature, time, level of lipase, mole ratio of reactants-in the PS-30 lipase -catalyzed transesterification reaction of grease to ethyl esters using 95% ethanol. The regression equation obtained by a modified central composite design of RSM predicted optimal reaction conditions of 38.4 degrees C, 2.47 h, 13.7 wt% lipase (PS-30), and a mole ratio of grease to ethanol of 1:6.6 . Under these conditions the predicted optimal percentage ethyl ester yield was 85.4%. Subsequent experiments using the predicted parameter combinatio ns indicated a trend where experimental percentage yields of ethyl ester we re consistently lower than predicted values. In an effort to improve the ex perimental yield of esters, a second portion of PS-30 lipase was added with out success; however, the addition of 5% SP435 one hour after the start of the initial reaction increased the yield of eaters to >96%. Neither lipase PS-30 nor lipase SP435 alone, however, gave the RSM-predicted yield of ethy l esters.