Abstract: Diacylglycerol (DG) was prepared through lipase-catalyzed reaction between soybean oil and glycerol in the supercritical system with carbon dioxide as the fluid. Three kinds of immobilized lipases such as Lipozyme RMIM, Novozyme 435 and Lipozyme TLIM were screened. The optimal esterification conditions for three kinds of immobilized lipases were achieved through single-factor tests. The results showed that the optimal preparation process parameters for three kinds of lipases were the addition amounts of 2.5%, 3% and 8% for Lipozyme RMIM, Novozyme 435 and Lipozyme TLIM, reaction temperatures of 65, 70 ℃ and 65 ℃ for three lipases, reaction time of 7, 8 h and 9 h for three lipases, and substrate ratio of 2:1. The yields of DG for three lipases were 68.6%, 67.7% and 64.8%, respectively, under their optimal reaction conditions. A two-step distillation technology was used to purify DG in the supercritical system. After the purification, the yield of DG was up to 60% and the purity of DG was improved to 90.4% from 68.6%. According to the comprehensive consideration, Lipozyme RMIM is recommended as lipase for the preparation of DG in industrial production.

Key words: CO2 supercritical system, lipase, glycerolysis, diacylglycerol, distillation