Preparation and Characterization of Sulfonated Poly (Ether Sulfone) (SPES)/Phosphotungstic Acid (PWA) Hybrid Membranes for Biodiesel Production

Abstract

A new kind of organic–inorganic hybrid membrane based on sulfonated poly (ether sulfone) (SPES) with different degree of sulfonation (DS) embedded phosphotungstic acid (PWA) was prepared as a heterogeneous acid catalyst for biodiesel production. Three kinds of hybrid membranes with the DS of SPES 9.7, 20.3 and 39.1 % were obtained. The interactions between SPES and PWA in SPES/PWA hybrid membrane were characterized by Fourier transform infrared (FTIR), thermogravimetric analysis and X-ray diffraction (XRD). The band shift of FTIR spectrum showed that the PWA particles interacted primarily with sulfonic acid groups on the polymer backbone. Compared to pure SPES membrane, the thermal stability of SPES/PWA hybrid membrane was enhanced. The XRD results suggested that the PWA particles were incorporated inside membrane pores and adhered on the walls outside the pores which were due to the interaction between PWA and SPES polymer matrix. The catalytic properties of SPES/PWA membranes were tested by the esterification of the acidified oil with methanol. The reaction conditions were optimized by response surface model and the optimum conditions were obtained as: methanol/oil mass ratio of 1:1, hybrid membrane loading of 1.66 meq/g and reaction time 6 h with the free fatty acids conversion of 95.3 %. The hybrid membrane with SPES/PWA mass ratio of 2:1 and the membrane thicknesses of 0.06 mm were optimal for the esterification. The SPES/PWA membrane of DS 20.3 % exhibited the best catalytic stabilities among the three kinds of hybrid membranes with different DS with a stable conversion of above 90 % in all times.