Comparative study on lipase-catalyzed transformation of soybean oil for biodiesel production with different acyl acceptors

Methyl acetate, a novel acyl acceptor for biodiesel production has been developed, and a comparative study on Novozym 435-catalyzed transesterification of soybean oil for biodiesel production with different acyl acceptors was conducted and reported in this paper. Methanol has a serious negative effect on enzymatic activity. A molar ratio of methanol to oil of above 1:1 leads to serious inactivation of the enzyme. However, when methyl acetate was used as the acyl acceptor, a yield of 92% of methyl ester could be obtained with a molar ratio of methyl acetate to oil of 12:1, and methyl acetate showed no negative effect on enzymatic activity. Additionally, with crude soybean oil as the oil source and methanol as acyl acceptor, a much lower methyl ester yield was obtained than that with refined soybean oil, while with methyl acetate as acyl acceptor, an equally high yield of methyl ester (92%) was achieved for both soybean oils. Lipase loses its activity very rapidly during repeated experiments with methanol as the acyl acceptor, while there is almost no detected loss in lipase activity, even after being continuously used for 100 batches, when methyl acetate was used for biodiesel production. Moreover, the by-product triacetylglycerol is an important chemical with a higher value than glycerol, and this novel acyl acceptor seems very promising for lipase-catalyzed large-scale production of biodiesel.