Stability, activity and selectivity study of a zinc aluminate heterogeneous catalyst for the transesterification of vegetable oil in batch reactor

The transesterification reaction of rapeseed oil by methanol was thoroughly studied using a zinc aluminate catalyst. Extra-attention was paid to the catalyst stability as it is a key property in the development of an industrial process. Zinc leaching was very low amounting to no more than 4 ppm by weight in the ester phase after 6 h of contact time. The transesterification reaction of rapeseed oil by methanol was studied using a zinc aluminate catalyst in order to develop an alternative to the currently used homogeneous processes. At first, the reaction parameters such as catalyst particle size, stirring rate and amount of catalyst required to perform the transesterification reaction under a kinetically controlled-regime were determined. Thorough study of the catalyst stability was performed, in particular leaching of active species. A peculiar activity of the reactor walls was observed and XPS analysis allowed to determine that it stemmed from adsorption on the reactor walls of zinc species coming from catalysts prone to leaching. A method was therefore proposed to free oneself from this phenomenon. The zinc aluminate catalyst was found to be particularly stable as compared to ZnO catalyst. Optimization of the reaction parameters for achieving high yields and obtaining high quality products was performed. Indeed the influence on the activity, stability and selectivity of the temperature, the reactants ratio, and the presence of water in the reactants, was studied. Finally a pseudo-homogeneous kinetic model was validated and used to determine the kinetic parameters of the reaction.