Zeolite/Polyelectrolyte Multilayer Pervaporation Membranes for Enhanced Reaction Yield

Multilayer membranes were prepared by alternating adsorption of a cationic polyelectrolyte, chitosan, and an anionic polyelectrolyte, poly(4-styrene sulfonate), onto zeolite A films formed on porous supports in sheet and tube form. The multilayer membranes are shown to exhibit the high selectivity for water over alcohols associated with zeolite A but to be considerably more stable under acidic conditions than a pure zeolite A membrane. The membranes were successfully applied to the selective removal of water by pervaporation in the esterification of lactic acid with ethanol, catalyzed by p-toluenesulfonic acid. For esterification at 70 °C, yields of about 60% without the membrane were increased to >80% with pervaporation, and for esterification at 100 °C, yields of about 70% without the membrane were increased to >90% with pervaporation.