Engineering aspects of aqueous biphasic catalysis

Abstract

Reaction engineering aspects of aqueous multiphase catalysis were investigated in a discontinuously stirred batch reactor as well as in a continuously driven loop reactor. The regioselective hydrogenation of αmβ-unsaturated aldehydes to the corresponding unsaturated alcohols with a water-soluble and highly active Ru(II)-TPPTS complex catalyst was chosen as model reaction system. Theoretical and experimental analysis of the mass transport rates at the G/L- and L/L-interphase in the batch reactor ensured that the reaction was limited by kinetics. Recycling experiments with different substrates then revealed that the catalyst phase stability is a function of the water solubility of the reaction products. Taking these aspects into account, kinetic modelling of the reaction rate was performed at elevated hydrogen partial pressure and reaction temperature. Additional experiments in a loop reactor where a significant mass transport limitation was observed allowed us to investigate the interplay between hydrodynamics and mass transport rates as a function of mixer geometry, the ratio of the volume hold-up of the phases and the flow rate of the catalyst phase. From further kinetic studies on the influence of substrate and catalyst concentrations on the overall reaction rate, the Hatta number was estimated to be 0.3-3, based on film theory. © 2006 Springer-Verlag Berlin Heidelberg.