A clean route of biodiesel production using red mud-based potassium catalyst

In our work, a low-cost and high-efficiency red mud-based potassium composite (KRM) was successfully synthesized via solid-state method using red mud (RM) and potassium carbonate (K 2 CO 3 ) as material, and then was applied to produce castor oil biodiesel through transesterification . The preparation conditions of red mud-based potassium composite were optimized. The synthesized catalysts were characterized by X-Ray diffractometer (XRD), Scanning electron microscopy (SEM), Hammett method and Brunauer-Emmett-Teller (BET). The maximum conversion from castor oil to biodiesel (94.52%) was acquired with methanol to oil molar ratio 18:1, catalyst dosage 5 wt%, reaction temperature 65 °C and reaction time 2.5 h. According to the thermo-kinetic results, the castor oil transesterification catalyzed by KRM catalyst was a first-order kinetics reaction and was not an exothermic and spontaneous reaction pathway. Particularly, the characterization results indicated that the brightly textural properties (small particle size, high basicity , high surface area and pore volume) were favorable factors for the high catalytic activity of KRM catalyst. The KRM catalyst showed excellent reusability after four cycles. Besides, turnover frequency ( TOF ), green parameter of transesterification process and cost analysis demonstrated that the transesterification process catalyzed by the high-efficiency KRM catalyst possessed green reaction pathway and the composite catalyst of KRM could effectively reduce the cost of biodiesel production.