Esterification catalysis using functionalized membranes

Novel functionalized microfiltration membranes have been developed for use as a heterogeneous, solid-phase, flowthrough catalytic structure for the esterification reaction between ethanol and acetic acid. Catalytic sites are located on each repeat unit of sulfonated polystyrene chains grafted in the flow pathways of the membrane. Batch studies showed that the activity of the catalytic membrane was comparable to the standard ion-exchange resin (IER) for the same acid capacity. Significant improvement in reaction kinetics was observed in flowthrough studies; a residence time of 20 s gave the same conversion as 11 h in batch reaction. The activation energy in flowthrough reaction was at least 20% lower than for the conventional IER. Some loss of grafted polystyrene (∼25%) in the reaction permeate was observed during flowthrough experiments, resulting in partial loss of activity. However, an increase in the graft chain length reduced graft loss by 60%, and there was essentially no graft loss when the grafts were covalently bound.