Mass transfer and kinetic study on BEA zeolite-catalysed oil hydroesterification

In the present study, we have assessed the effect of mass transfer on the both steps of the zeolite catalysed oil hydroesterification to produce biodiesel (hydrolysis of the feed soybean oil producing free fatty acid and free fatty acid esterification). Both reactions were conducted over BEA zeolite in a batch reactor. Experimental results indicate the absence of internal and external mass transfer limitations on the overall rate of either reaction. A reversible, second order reaction was invoked in order to estimate the reaction rate constant, pre-exponential factor and activation energy of the esterification and hydrolysis reactions. Activation energy of 25.9 kJ/mol (soybean oil hydrolysis), 38.5 kJ/mol (ethyl acetate hydrolysis), 24.8 kJ/mol (oleic acid esterification) and 46.7 kJ/mol (acetic acid esterification) were calculated over H-BEA zeolite, illustrating the importance of reactant size and the fact that reactions take place on the pour mouth of the mesopouros zeolite in a case of large molecules reaction. Experimental results suggested that the relative hydrophobicity of the catalyst is a key parameter, which influences whether the reaction is under kinetic or diffusion control.