A novel magnetic CaO-based catalyst synthesis and characterization: Enhancing the catalytic activity and stability of CaO for biodiesel production

Calcium oxide (CaO) is recognized as a promising heterogeneous alkaline for transesterification. Nevertheless, equivalent catalytic activity to that of homogeneous alkaline and catalyst stability, especially, the Ca2+ leaching are still great challenges for CaO used in biodiesel production. To address these problems, in this study, a typical metal organic framework, MIL-100(Fe) and calcium acetate are employed to synthesize the high effective, stable, and magnetic CaO-based catalyst. The preparation factors including calcium acetate addition and activation temperature are investigated to acquire the optimal conditions. Also, effects of transesterification parameters on oil conversion are concerned and the optimized parameters are further used for reusability test. In the meantime, extensive characterizations of TG/DTG/DSC, XRD, Raman spectroscopy, Hammett indicator titration, XPS, N-2 adsorption and desorption, SEM, TEM, VSM are conducted to elucidate the catalytic activity behavior. The as-synthesized catalyst (CAM750) with strong magnetism (112 emu/g) exhibits excellent catalytic activity of 95.09% with catalyst amount of 4 wt% and molar ratio of methanol to oil of 9 at 65 degrees C for 2 h, which could be easily separated from reaction system by a magnet. More importantly, Ca2+ leaching is almost prohibited during the repeated cycle, where the leached Ca2+ in biodiesel at the fourth cycle (1.4 mg/kg) is much less than the limit of EN 14214 standard. Furthermore, crystalline phase and magnetic property of the recovered catalyst are basically in accordance with the fresh catalyst. Therefore, this synthesis method is feasible to enhance and stabilize the catalytic activity of CaO for transesterification.