Enzymatic epoxidation of biodiesel optimized by response surface methodology

Abstract

During the enzymatic epoxidation of biodiesel, stearic acid was selected as oxygen carrier. Enzyme screening and the load of stearic acid were investigated. The effects of four main reaction conditions including reaction time, temperature, enzyme load, and mole ratio of H₂O₂/C=C-bonds on the epoxy oxygen group content (EOC) of epoxidized biodiesel were analyzed. Response surface methodology (RSM) was employed to study and optimize the reaction variables in the enzymatic epoxidation of biodiesel. A second-order model satisfactorily fitted the data (R² = 0.9893), with non-significant lack of fit. A higher EOC (6.40 ± 0.20%) of epoxidized biodiesel was obtained at the optimum conditions of 55.4°C, 3.91% enzyme load (relative to the weight of biodiesel), 2.93:1 mole ratio of H₂O₂/C=C-bonds, and 7.3 h. The relationship between initial reaction rate and temperature was also established, and the activation energy (Ea) of the enzymatic epoxidation is 16.03 KJ/mol.

Key words: Epoxidation, biodiesel, novozym 435, stearic acid, response surface methodology.