Evaluation of Reaction Mechanisms and Kinetic Parameters for the Transesterification of Castor Oil by Liquid Enzymes

The use of liquid enzymes for the production of biodiesel as an alternative to chemical catalysts requires significant investigation due to the lack of experimental data for the various feedstock and catalyst combinations. In this paper, reaction rates and kinetic modeling of the transesterification of castor oil with methanol using the enzyme Eversa Transform as the catalyst were investigated. Reactions were carried out for 8 h at 35 degrees C with an alcohol-to-oil molar ratio equal to 6:1, a 5 wt % of liquid enzyme solution, and addition of 5 wt % of water by weight of castor oil. From the concentration data, four different reaction mechanistic models were compared to determine the mechanism that best fitted the experimental data. Mechanisms where the methanolysis and hydrolysis reactions occurred simultaneously in the system were best at describing the concentration profiles. The high methanolysis rates of glycerides that were obtained indicated that transesterification dominates over hydrolysis. The mechanism among the four models proposed that gave the best fit could be simplified, eliminating the kinetic parameters with negligible effects on the reaction rates. This model was able to fit the experimental data at different reaction temperatures.