Abstract: Lipase from Penicillium expansum was immobilized by physical adsorption. An inexpensive resin D4020 was selected as the support after screening 20 kinds of supports from different sources for the better immobilization performance. The effects of immobilization conditions on the immobilization efficiency and transesterification activity of the immobilized lipase were systematically studied. The results showed that the optimal enzyme amount, pH, and adsorption time were 0.7 g/g, 9.4, and 4 h, respectively. The transesterification activity of the immobilized lipase could be improved by using 0.5% galactose as a lyoprotectant. Under optimal conditions, the transesterification activity of the immobilized enzyme was 404.4 U/g, whereas the free enzyme did not exhibit transesterification activity. Subsequently, transesterification of corn oil to biodiesel catalyzed by the immobilized lipase was explored. Tert-amyl alcohol was found to be the most suitable reaction medium with a favorable amount of 0.5 ml/g. The optimum enzyme amount, water added, and reaction temperature were 60.6 U/g, 1.2%, and 35 ℃, respectively. A three-step methanolysis protocol was used and one molar equivalent of methanol was added at a reaction time of 0, 2, and 6 h, respectively, by which a methyl ester yield of 85.0% was obtained after reaction for 24 h. Good operational stability was achieved after the enzyme was immobilized, and 62.8% of its original activity was retained after repeated use for 10 batches. The transesterification activity and operational stability of the Penicillium expansum lipase were enhanced remarkably by immobilization.

Key words: Penicillium expansum lipase, immobilization, biodiesel, corn oil, methanol, transesterification