Effect of fuel molecules on properties and activity of KOH/calcium aluminate nanocatalyst for biodiesel production

Abstract

New technologies such as microwaves have gained a large deal of attention from scientists and industries who sought increased rate of production processes. In this study, microwave irradiation was utilized to produce a novel KOH/Ca12Al14O33 nanocatalyst used for biodiesel production. As support, calcium aluminate was prepared by microwave combustion method using different fuels including urea, glycine, sorbitol, and citric acid. The samples were then impregnated by KOH to improve their catalytic activities for microwave-enhanced transesterification of canola oil for biodiesel production. Results of XRD, BET, FTIR, TG, EDX, and FE-SEM analyses showed differences in physicochemical properties of the samples when using different fuels with different flame characteristics and combustion temperatures. Only the urea-fueled sample showed the crystalline structure of monocalcium aluminate (CaAl2O4), with the other samples exhibiting amorphous structure of CaO–Al2O3. However, all samples, except for that prepared by citric acid, transformed to crystalline structure of Ca12Al14O33 by calcination during KOH impregnation. Among the samples, the KOH/Ca12Al14O33 nanocatalyst prepared by sorbitol showed the highest activity in microwave-enhanced biodiesel production because of its large surface area, pore size, and basicity, converting 93.4% of canola oil to biodiesel at a methanol-to-oil molar ratio of 18, catalyst concentration of 4 wt%, and microwave output power of 450 W in 60 min of reaction time. Moreover, the sample showed well-distributed particle sizes without any agglomeration, so that it could easily maintain its level of activity for several rounds of use.