Inorganic solid supported polymer acid catalyst - Sulfonated polystyrene grafted silica gel in liquid phase esterification

Sulfonated polystyrene grafted silica gel particles were synthesized for use as an acid catalyst in the liquid phase esterification of acetic acid with ethanol at 313-353 K. The synthesis of the grafted silica gel particles consists of three steps: polymerization, grafting, and sulfonation. The synthesized catalyst is non-cross-linked, non-swelling, and mechanically as well as chemically stable. It contains 29% covalently-bound sulfonated polystyrene chains that give an acid capacity of 0.99 mmol g−1. The kinetics of the grafted silica gel is as rapid as that of a commercial ion-exchange resin. Since the acid capacity of the grafted silica gel is only 25% of the ion-exchange resin, the catalytic activity of acid groups in the grafted silica gel is higher than in the resin. A pseudohomogeneous kinetic model provides a satisfactory fit for both catalysts.