Kinetics of the catalytic hydrogenation of D-fructose over a CuO-ZnO catalyst

Kinetics Of D-fructose hydrogenation over a copper catalyst (61 wt% CuO and 39 wt% ZnO) in aqueous solutions was studied. The hydrogenation experiments were carried out batchwise in a three-phase laboratory-scale reactor (300 ml, Parr Co.), operating at 35-65 bar and between 90 and 130 degrees C. The main hydrogenation products were mannitol and its epimer, sorbitol. Also, a minor isomerization of fructose to glucose was observed. In the operating regime studied, the reaction rate showed a second order dependency with respect to the hydrogen pressure. Mannitol selectivity at the experimental range varied from 60 to 68%. The selectivity values improved slightly, as the hydrogen pressure increased or the reaction temperature decreased. The effect of catalyst loading and catalyst deactivation during consecutive hydrogenation batches was also studied. Catalyst characterization studies (nitrogen adsorption BET, XPS, SEM and particle size analysis) were carried out for a better understanding of the catalyst deactivation and reduction processes. The fitting of the experimental data to the kinetic model was carried out by Modest software using a combined Simplex-Levenberg-Marquardt method. The proposed kinetic model was able to predict the experimental concentrations of fructose and mannitol as well as the by-products sorbitol and glucose with a better than 95% degree of explanation. (c) 2005 Elsevier B.V. All rights reserved.