Biodiesel Production Catalyzed by a Methanol-Tolerant Lipase A from Candida antarctica in the Presence of Excess Water

[Image: see text] In this article, biodiesel was prepared using a novel free liquid lipase A from Candida antarctica (CALA) as a catalyst in the presence of excess water. The methanol tolerance of CALA was investigated. The effect of reaction conditions, including the molar ratio of soybean oil to methanol, water load, CALA load, reaction temperature, and reaction time, was evaluated. Reaction thermodynamics and kinetics were also analyzed. Results showed that free liquid lipase CALA showed excellent methanol tolerance in the reaction system using one-step addition of methanol and can be used to prepare biodiesel with water load of 12–14%. The influence of three transesterification variables on biodiesel yield was water load > temperature > time. The transesterification conditions were optimized by response surface methodology as follows: CALA load 5%, substrate molar ratio (soybean oil/methanol) 1:7, water load 14%, reaction time 26 h, and temperature 38 °C. The maximum biodiesel yield (92.4 ± 0.8%) was obtained under optimal conditions. The activation energy for biodiesel formation was 52.58 kJ/mol. Kinetic parameters K(m)(′) and V(max) were 4.84 × 10(–1) mol/L and 6.85 × 10(–2) mol/(L·min), respectively. The mechanism of CALA-catalyzed transesterification was also proposed.