Preparation and characterization of a novel bifunctional heterogeneous Sr–La/wollastonite catalyst for biodiesel production

The development of reusable heterogeneous catalysts with acid-base bifunctions employing low-cost oil as a raw material is critical for optimizing the biodiesel synthesis process. In the present study, Sr–La/wollastonite bifunctional catalysts with the different Sr/La atomic ratios are synthesized using a straightforward impregnation technique. The results show that the Sr7La3/wollastonite catalyst establishes a biodiesel yield of 95.35% upon initial use and 85.14% after the fifth cycle of reuse, under the transesterification conditions of a catalyst content of 8 wt%, methanol to oil molar ratio of 15, reaction duration of 3 h, and reaction temperature of 150 °C. The biodiesel yield of 91.62% is obtained even after the addition of 5 wt% oleic acid, and the catalyst maintains a high biodiesel yield (>80%) for three reused cycles, which illustrates the good resistance to free fatty acids (FFAs). Meanwhile, the process parameters for transesterification are optimized utilizing Response Surface Methodology combined with Box-Behnken Design (RSM-BBD). With a methanol to oil molar ratio of 17.7 and a catalyst content of 6.4 wt%, biodiesel yield is 96.08% at 149 °C for 3 h. This study revealed the enormous potential of the Sr–La/wollastonite bifunctional catalyst in biodiesel production.