Highly efficient CaO–ZSM-5 zeolite/Fe3O4 as a magnetic acid–base catalyst upon biodiesel production from used cooking oil

Abstract

A magnetic acid–base catalyst, namely CaO–ZSM-5 zeolite/Fe3O4, was successfully synthesized from waste chicken eggshell and rice husk. This study covered the potential of the synthesized catalyst in direct transesterification of used cooking oil (UCO) containing high free fatty acid (FFA) value. The presence of ZSM-5 zeolite support in CaO is advantageous in enlarging the surface area and providing an acidity–basicity characteristic of the catalyst. Further incorporation of Fe3O4 component gives magnetic properties to catalysts and thus helps to improve the catalyst separation. Results revealed that the catalytic activity of CaO–ZSM-5 zeolite/Fe3O4 showed a high biodiesel yield of 91% with low leached Ca2+ concentration of 3.87 ppm. It was due to the high surface area and bifunctional acid–base properties of the catalyst, where the surface area, acidity and basicity strength of CaO–ZSM-5 zeolite/Fe3O4 catalyst were recorded to be 135.31 m2/g, 1.4340 mmol/g, and 1.8789 mmol/g, respectively. The saturation magnetization value of the CaO–ZSM-5 zeolite/Fe3O4 catalyst was 31.759 emu/g, indicating that the catalyst can be easily recovered by an external magnet due to its ferromagnetic feature. Furthermore, the catalyst showed a remarkable recyclability up to four consecutive cycles with yield over 85%. Thus, the CaO–ZSM-5 zeolite/Fe3O4 catalyst was regarded as a highly efficient, stable, and magnetically recoverable catalyst for the production of biodiesel from UCO.