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

• Developed a novel aluminum supported Cs–Zr mixed oxide catalyst.
• The prepared catalyst was characterized for its chemical and physical properties.
• FAMEs were produced from cheap feed stock of waste cooking oil.

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 (1 w/w–5 w/w oil), and reaction time (1–5 h), on the catalyst performance were investigated. During 3 h reaction time 90%FAME content was produced at 65 °C with 20:1 methanol-to-WCO molar ratio and 3 wt.% 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 0.8 w.% water, without significant changes in the FAME content.

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