Crystal Phase Evolution of High Temperature Annealed Fe3O4‐CaO Catalysts for Biodiesel Production

Biodiesel (BD) is an alternative transportation fuel that has been commercialized. Most CaO‐based heterogeneous catalysts that are applied for BD production become strongly deactivated after not more than five cycles of reuse. Predominantly CaO and Ca(OH)2 active phases in eggshell were mixed with Fe3O4 by ball milling for 3 h followed by annealing at different temperatures (200–1000 °C) for 2 h to produce a magnetic catalyst. The catalyst was deployed to synthesize BD using a transesterification reaction with methanol. The catalyst characterization results from X‐ray diffraction and Raman analysis revealed the phase evolution of the catalysts with increasing annealing temperature, which facilitated the oxidation of the Fe3O4 to the maghemite (Fe2O3) phase. Increasing temperature led to a decrease in the catalyst surface area due to increased rigidity and loss of pores; however, the basicity increased due to the conversion of calcium carbonates mainly to CaO. Under optimal conditions of 65 °C, methanol/oil molar ratio of 12:1, and 4 wt% catalyst loading, BD yield of 95.33% could be achieved under 120 min reaction time. The catalyst could be reused seven times with minimal loss in catalytic activity. The synthesized BD showed a calorific value of 39.99 MJkg‐1, a density of 0.9 gcm‐3, a viscosity of 4.92 mm2s‐1, which satisfactorily complied with the international standards of ASTM‐D‐6751 and EN‐14214.