A novel two-step transesterification process catalyzed by homogeneous base catalyst in the first step and heterogeneous acid catalyst in the second step

The utilization of base catalyst for two-step transesterification prompts soap formation and yield loss in biodiesel production. In order to overcome this difficulty, the two-step transesterification process was performed with homogeneous base catalyst and heterogeneous acid catalyst was performed in the batch reactor and the high-pressure apparatus. As per response surface methodology, optimum condition for the first step is determined. The ester content of 85% is obtained with the molar ratio of methanol to oil of 5.48:1, 0.32 wt% of CH3ONa catalyst, 40 min and at 55 degrees C. Final biodiesel production with ester content of 98% is produced from the second step under optimum condition (methanol/oil molar ratio of 10, Amberlyst 15 catalyst content of 12 wt%, 9 h and 115 degrees C). The soap content was 50% and amount of base catalyst used was 33% as compared to one-step transesterification process.