Deactivation and Rejuvenation of Pellet MgO/SiO2 Catalysts for Transesterification of Soybean Oil with Methanol to Biodiesel: Roles of MgO Morphology Change in Catalysis

Abstract

Pellet MgO/SiO2 catalysts with pore diameters of 30 and 40 nm were prepared by incorporating Mg(NO3)2 on granular SiO2 followed with calcination at 500 °C. These pellet catalysts and MgO powder were tested and compared by using transesterification of soybean oil with methanol. Combined results of the test reaction, FT-IR, XRPD, and pore-size distribution suggested that the reaction is catalyzed by both Bronsted and Lewis base sites and is limited by mass transfer. The observation of Mg2+ in the reaction products and gum formed on the catalysts further indicated that the catalysts are deactivated by carbonaceous deposition and MgO leaching. Thus, the deactivated catalysts were rejuvenated by an ethanol wash followed with makeup MgO. However, inferred from synchrotron XRPD results, we suggested that the rejuvenation process cannot recover the morphological change of MgO that took place in the reaction and rejuvenation, leading to a decrease in product selectivity for FAME.