Compensation effect in transesterification kinetics of croton megalocarpus oil using heterogeneous alkaline earth catalysts

Abstract

Reaction kinetics of transesterification of croton megalocarpus oil with methanol to produce fatty acid methyl ester was studied at 70oC, using homogeneous and heterogeneous catalysts through conventional heating and microwave irradiation. NaOH was used as a homogenous catalyst, and alkaline earth metal oxides, BaO, SrO, CaO, MgO and BeO, were the heterogeneous catalysts. Reaction rate constant k; and Arrhenius equation parameters, pre-exponential factor A and activation energy E were estimated from kinetic data, using the overall reaction. By considering the magnitudes of k, NaOH was the most active catalyst, followed by BaO, SrO, CaO, MgO and BeO. However, no specific order was observed in the estimated values of A and E. Activation energy was not found to be a direct measure of catalyst activity for heterogeneous catalysts. This was explained by the complex nature of the three-phase reaction system where twenty one reactions were likely to be taking place simultaneously, and the observed kinetic parameters were the overall apparent values. Cremer Constable scatter plot showed the data points roughly following a straight line. It was concluded that the discrepancies in A and E values were due to oversimplification of kinetic model, rather than being a physical phenomena.