Preparation of magnetic core-shell CaO-MgO@CoFe₂O₄ solid base and its catalytic performance in the transesterification of soybean oil to biodiesel

A magnetic core-shell CaO-MgO@CoFe₂O₄ solid base was prepared with oxalates as the precursor through a two-step method, which was used as the catalyst for the transesterification of soybean oil to biodiesel with methanol. The CaO-MgO@CoFe₂O₄ catalyst was characterized by magnetic hysteresis loop, X-ray diffraction (XRD), CO₂-TPD and transmission electron microscopy (TEM); the effects of core-shell molar ratio, catalyst calcination temperature, reaction temperature, reaction time, methanol/oil molar ratio and catalyst amount on the yield of biodiesel were investigated. The results indicated that over the CaO-MgO@CoFe₂O₄ catalyst with a core-shell molar ratio of 1:6 and calcined at 700 ℃, the biodiesel yield reaches 97.1% after conducting the transesterification reaction at 65 ℃ for 3 h, when the methanol/oil mol ratio is 12 and the amount of catalyst is 1.0% by mass. The catalyst exhibits excellent reusability; the biodiesel yield remains above 90% after reusing for four cycles.