Abstract

Catalytic transesterification of triglycerides and esterification of free fatty acids underpins sustainable biodiesel production, wherein efficient heterogeneous catalysts are sought to replace mineral acids. A robust, magnetic core-shell SO4/Mg-Al-Fe3O4 catalyst was synthesised by stepwise co-precipitation, encapsulation, and surface functionalisation. The resulting magnetically-separable catalyst has a surface area of 123m2 g−1, uniform 6.5 nm mesopores, and a high total acid site loading of 2.35 mmol g-1. Optimum conditions for the (trans) esterification of waste cooking oil (WCO) over the sulfated solid acid catalyst were 95 °C, a methanol:WCO molar ratio of 9:1, and 300 min reaction to achieve 98.5% FAME yield. Esterification of oleic acid to methyl oleate resulted in an 88% yield after 150 min under the same reaction conditions. The magnetic solid acid catalyst exhibited good thermal and chemical stability and enabled facile catalyst separation post-reaction and the production of high quality biodiesel.