Catalytic conversion of residual raw material into biodiesel using a superior magnetic solid acid catalyst based on Zn–Fe ferrite: thermodynamic and kinetic studies

Abstract

This study investigates the potential and applicability of a novel solid magnetic catalyst constructed by incorporating molybdenum oxide (MoO₃) into zinc ferrite (ZnFe₂O₄) to biodiesel production using Waste Frying Oil (WFO) as the residual raw material. The molybdenum amounts (5, 15, 25, 35 and 45%) present in the catalyst were studied and the catalyst demonstrated great characteristics and high acid properties, as well as superior magnetic and catalytic attributes. The one variable at time (OVAT) optimization method revealed that the application of the MoO₃/ZnFe₂O₄ catalyst resulted in obtaining a biodiesel with 97.6% ± 0.727 conversion to fatty acid methyl esters (FAME) under the following optimized reaction conditions: temperature of 165 °C, methanol : WFO molar ratio of 40 : 1, catalyst amount of 6 wt% and reaction time of 3 h. In addition, the catalyst showed high reusability after six reaction cycles, with conversion to esters above 90%. Besides, the activation energy (E_a) calculated in the kinetic study was 25.3 kJ mol⁻¹. Moreover, the properties of the synthesized biodiesel met the standards set by the ASTM D6751 and EN 14214, which indicates the high MoO₃/ZnFe₂O₄ potential for industrial application with low energy consumption as well as minimal negative environmental impact.