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

Abstract

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 (K2CO3) 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.