Effective transesterification of castor oil to biodiesel catalyzed by novel carbon-based calcium composite

A novel carbon-based calcium catalyst was prepared through impregnation-calcination method, and was successfully applied as an effective catalyst for transesterification of castor oil to produce biodiesel. The catalyst prepared through the calcination at 500 °C for 3 h (Ca/C-500–3) exhibited the optimal performance. The prepared carbon-based calcium catalyst had excellent crystallinity and morphology, high basicity and surface area according to the characterization analysis results. Based on the XPS analysis, the combination of CaO and C in Ca/C-500–3 could improve the oxygen ion donating ability, which was beneficial for the reaction of triglycerides with methanol. The optimum composite of carbon-based calcium catalyst (Ca/C-500–3) displayed the excellent catalytic activity in castor oil transesterification, and 95.44 % of biodiesel conversion was obtained with the following conditions: methanol to oil molar ratio of 18:1, catalyst dosage of 5 wt%, reaction temperature of 65 °C and reaction time of 3 h. The TOF indicated that Ca/C-500–3 was an efficiency catalyst. Meanwhile, the calculation results of E-factor and PMI manifested that the transesterification of castor oil to biodiesel catalyzed by Ca/C-500–3 was a green reaction. Ca/C-500–3 could retain its high catalytic activity after five reaction cycles. The LCC cost analysis results suggested that, using Ca/C-500–3 as catalyst, biodiesel production from castor oil as feedstock had lower production cost compared to other biodiesel productions. The various factors affecting the cost of producing biodiesel were investigated using sensitivity analysis. Finally, the possible mechanism of catalytic transesterification reaction using carbon-based calcium composites was revealed.