Preparation of calcium modified Zn-Ce/Al2O3 heterogeneous catalyst for biodiesel production through transesterification of palm oil with methanol optimized by response surface methodology

Abstract

The calcium modified Zn-Ce/Al2O3 heterogeneous base catalysts are synthesized by the hydrothermal method, impregnation method and co-precipitation method, respectively. Further, they are applied to catalyze transesterification of palm oil with methanol for the biodiesel production. The hydrothermal method with the Ca: Zn: Ce: Al molar ratio of 5: 4: 1: 1 is preferred to synthesize the catalyst due to the best catalytic performance. The catalyst shows strong reusability, where the biodiesel yield of 87.37% is obtained for the fifth reused cycle and the weakened catalytic capability is mainly ascribed to the leaching out of the active sites. The response surface methodology with the central composite design (RSM-CCD) is employed to optimize thetransesterification parameters and predict the biodiesel yield. The predicted maximum biodiesel yield of 99.44% is achieved at the reaction temperature of 66.12 °C, methanol to oil molar ratio of 18.53 and catalyst amount of 8.19 wt.% with 3 h, which is consistent with the experimental result of 99.41%. Also, the physical properties of the produced biodiesel meet the ASTM D 6751 standard. This study reveals the Ca-Ce-Zn/Al2O3 catalyst gains a good application prospect in the biodiesel production and the response surface methodology is effective in optimizing the transesterification parameters and predicting the optimal values.