Novozym 435-catalysed transesterification of crude soya bean oils for biodiesel production in a solvent-free medium.

When crude soya-bean oil was used as the source for biodiesel production, the yield of methyl ester was significantly lower than that from refined soya-bean oil. The major difference between refined and crude soya-bean oils was found to be due to the contents of phospholipids, free acid and water, which have varied influences on biodiesel production. Phospholipid content was the most influential factor; the higher the phospholipid content in the oil, the lower is the methyl ester yield. The optimal water activity was found to be in the range 0.12-0.44, and free acid included in crude soya-bean oils showed no negative effect on enzymic transesterification. During our study of three-step methanolysis of crude soya-bean oils for biodiesel production, we noted that the second-step methanolysis was much faster than the first-step reaction. On the basis of this finding, the proposal that immersing pretreatment of lipase in oils contributes to improvement in enzyme activity has been put forward. In addition, it has been demonstrated that immersing pretreatment of lipase in oils could improve both the reaction rate and methyl ester yield significantly. A methyl ester yield of 94% could be achieved by immersing lipase in crude oils for 120 h and this was just as high as the yield for refined oils.