RESUMEN
The transesterification reaction conditions of lard with methyl acetate with combined use of immobilized lipases as catalysts were conducted. Initially, according to single factorial experiments, the studies on Lipozyme TL IM and Novozym 435 respectively catalyzed transesterification of lard showed that the optimal parameters of transesterification reaction were: the molar ratio of methyl acetate to oil of 14∶1, 40% enzyme added based on oil weight, temperature 50℃. Combined use of Lipozyme TL IM and Novozym 435 was proposed further to improve the catalytic performance by the response surface method (RSM). Herein, a 5-level-3-factor central composite rotated design was employed to evaluate the effects of lipase loading, the proportion of the two lipases and amount of methyl acetate. The optimum conditions were as followings: 40% lipase loading based on oil weight, 50%/50% the proportion of lipases (Novozym 435/Lipozyme TL IM), and the molar ratio of methyl acetate to oil of 14∶1. And under the optimal conditions, the highest biodiesel yield of 97.6% could be attained, which was higher than the biodiesel yield with each single one of the two lipases. The results suggested that the technics of combined use of certain immobilized lipases catalyzed transesterification reaction of lard for biodiesel production with methyl acetate as the acyl acceptor could raise the FAME yield and save the production cost.