Development and characterization of a microfiltration membrane catalyst containing sulfonated polystyrene grafts

Polymeric catalytic membrane reactors (CMRs) containing sulfonated polystyrene grafts can serve as an alternative to traditional strong acid catalysts such as sulfuric acid and strong acid ion-exchange resins (IERs) for esterification and alkylation reactions. This material offers advantages over conventional catalysts in terms of corrosivity, attrition, pressure drop, mass transfer limitations, and catalyst separation. The membrane reactors are functionalized membranes created by cationic polymerization of styrene in the pores of a porous matrix of polyethersulfone (PES). Sulfonation of the formed polystyrene grafts with sulfuric acid creates easily accessible sulfonic acid groups (∼2 meq/g) for catalysis. Diffusional limitations encountered in ion-exchange resins are minimized because transport through the membrane pore takes place by convection. Consequently, the membrane activation is accomplished with lower concentration acid. The activated membrane shows no loss of functionalized polymer during activation, demonstrating excellent material stability. Finally, the catalytic activity was verified for a simple esterification reaction between acetic acid and ethanol.