Water influence on the kinetics of transesterification using CaO catalyst to produce biodiesel

Abstract

This research investigated the water influence on biodiesel production via transesterification, and especially on their kinetic parameters. The initial rate of transesterification was increased with increasing amount of water (0–5 wt%). On the contrary, the initial rate was significantly reduced for the water concentration of 8–15 wt%. Moreover, when the biodiesel yield reached the maximum value of 30–40%, saponification as a side reaction became more significant with the presence of the emulsion phase, resulting in a remarkable decrease in biodiesel yield. The simple kinetic model including the rate constant and apparent activation energy revealed that transesterification containing 5 wt% water gave the higher rate constant compared to the case with the absence of water. However, the simple model could not describe the case with high water content. The water effect should be accounted for in the reaction rate in the adsorption term. The modified Langmuir-Hinshelwood kinetic model including the effects of water contamination was originally proposed. Our finding suggested that despite the small amount of water content in transesterification using CaO catalyst giving rise in the initial rate, the water contamination in feedstocks for biodiesel production should be avoided because of the notable presence of saponification.