Conversion enhancement for acetalization using a catalytically active membrane in a pervaporation membrane reactor

Abstract

Glycerol ketals are often considered as important bio-based diesel additives or perfume substances which could be synthesized from the acetalization of glycerol and cyclohexanone, however, acetalization is a typical example of reactions controlled by thermodynamic equilibrium. In this study, a catalytically active membrane was prepared by immersion phase inversion and was used for the conversion enhancement of present reaction by continuous removal of by-product water in a pervaporation membrane reactor. SEM images showed that a highly porous “sponge-like” catalytic layer immobilized with catalyst Zr(SO4)2·4H2O was uniformly coated on a polyvinyl alcohol/polyethersulfone pervaporation membrane. Synthesis performances in batch reactor, inert membrane reactor and catalytically active membrane reactor were compared, showing that no equilibrium limitation for glycerol conversion was observed in both the inert membrane reactor and catalytically active membrane reactor. The effect of various operational parameters on the synthesis performance in the catalytically active membrane reactor were investigated, showing that higher temperature and A/V ratio favored better enhancement in glycerol conversion since an acceleration of water removal rate was induced. Optimal catalyst loading and initial mole ratio was also determined for better synthesis performance. Under optimized conditions, the glycerol conversion reached 93% and a conversion enhancement of approximately 52% was achieved when compared to equilibrium conversion at 75°C.