Esterification of oleic acid and ethanol in plug flow (packed bed) reactor under supercritical conditions: Investigation of kinetics

Abstract

The present work provided the reaction kinetic data, required to predict the performance of packed-bed plug flow bioreactor operating under supercritical conditions. It investigated the kinetics of esterification of oleic acid and ethanol. Biocatalyst Lypozyme™ IM60, which is lipase from Rhizomucor miehei immobilised on Duolite (an ion exchange resin), was employed to synthesise ethyl oleate. Experimentally, esterification was carried out using a range of oleic acid- and ethanol concentrations, respectively. The effect of water concentration on the enzyme activity was also investigated. Analytically, the reaction mechanism was investigated by a series of kinetic analysis using the Direct Linear, the Primary and the Burke–Lineweaver (double reciprocal) plots. The reaction was modelled by the Henri–Michaelis–Menten equation and the reaction constants, namely K m and V max, were evaluated. It was found that the initial water concentration in the system effected the enzyme initial activity in a bell-like manner, giving an optimum (enzyme activity,and water concentration) value for each alcohol concentration. Furthermore, it was found that under higher alcohol concentrations, the reaction experienced substrate inhibition. The latter was identified to be competitive inhibition under moderate alcohol concentrations and non-competitive inhibitions under high alcohol concentrations. Hence, reaction inhibition constant value K i was calculated.