Potassium and 12‐tungstophosphoric acid loaded alumina as heterogeneous catalyst for the esterification as well as transesterification of waste cooking oil in a single pot

Abstract

AbstractTo prepare the heterogeneous catalyst for the simultaneous transesterification and esterification of waste cooking oil (WO), 12‐tungustophosphoric acid (TPA) and K+ were loaded over alumina. The catalyst structure was confirmed by powder X‐ray diffraction analysis while the catalyst composition and the elemental oxidation state by X‐ray photoelectron spectroscopic study. The surface morphology of the catalyst was established by high‐resolution transmission electron microscopy. The temperature‐programmed desorption study supports the existence of basic and acidic sites over the catalyst surface owing to the presence of potassium oxide and TPA, respectively. Underneath the optimized conditions for reaction, that is, 10 wt% of catalyst with respect to oil, 9:1 methanol to oil molar ratio and 65°C reaction temperature, 97% fatty acid methyl ester (FAME) yield was obtained within 1.25 h of reaction time. The catalyst was recovered from the reaction mixture via centrifugation and reused in four consecutive runs. Moreover, the presence of high moisture (4 wt%) and free fatty acid (7.8 wt%) contents was not found to have any adverse effect on the catalyst activity. To demonstrate the catalyst stability, the metal content in the reaction mixture was analyzed, and total metal content was found to be less than 2 ppm to hold the catalyst stability. The kinetic study suggests that the reaction follows (pseudo) first‐order kinetic equation with the prepared catalyst.