Highly active alumina-supported Cs–Zr mixed oxide catalysts for low-temperature transesterification of waste cooking oil

Abstract

An impregnation method was used to develop a reusable and highly active heterogeneous catalyst (CsxZry/Al2O3) with different Cs/Zr molar ratio (0.3≤x, y≤0.7). The catalyst activity was evaluated in the transesterification of waste cooking oil (WCO) with methanol for the synthesis of fatty acid methyl esters (FAMEs). A typical Cs0.6Zr0.4/Al2O3 catalyst was characterized for physical and chemical properties in terms of the amount of FAME produced. Brunauer–Emmett–Teller method, X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, basic strength analysis, scanning electron microscopy, and high-resolution transmission electron microscopy were utilized in the characterization of the catalysts. The effects of different process variables of transesterification reaction, such as methanol-to-WCO ratio (10:1–30:1), catalyst amount (1w/w–5w/w oil), and reaction time (1–5h), on the catalyst performance were investigated. During 3h reaction time 90%FAME content was produced at 65°C with 20:1 methanol-to-WCO molar ratio and 3wt.% catalyst loading. Results of the reusability tests indicated that the solid catalyst can be re-used for four batch cycles. Also, the catalyst exhibited good tolerance toward 0.8w.% water, without significant changes in the FAME content.