Synthesis and Catalysis of Mixed Oxides on Mesoporous Mayenite for Biodiesel Production from Castor Oil (Ricinus communis)

Abstract

Environmental concern has been driving the search for substitutes to the fossil based energy sources and has been pushing forward research for bolstering second generation biodiesel production processes. However, various challenges emerge from the use of such feedstocks, eg. in transesterification processes. The high content of free fatty acids and moisture in the precursor triglycerides are the major restraints for the transesterification reaction. For instance, Ricinus oil can be exploited by the use of a heterogeneous catalyst capable of maintaining high activity. This study shows the development of lithium and tin oxides catalysts supported on mayenite (Ca 12 Al 14 O 33 ) for the transesterification of Ricinus oil with methanol (CH 3 OH). A basic characterization procedure was carried out to establish the quality of the obtained ricinus oil. Once the ricinus oil properties were assessed it was used for the transesterification reaction by catalysts synthesized with mixtures of Li 2 O, CaO, and SnO 2 in different mass ratios. The best performance for the binary mixtures was obtained with 70/30 and 90/10% wt of CaO/SnO 2 mass ratios at a temperature of 60°C with a methanol to oil molar ratio of 12:1 and a catalyst load of 5% wt in respect to oil. Furthermore, catalysts with Li 2 O and SnO 2 were synthesized in mass ratios from 50/0 to 0/50% wt on a mesoporous mayenite. The synthesized catalysts were analysed by surface characterization techniques, such as N 2 -physisorption, NH 3 -desorption, and scanning electron microscopy (SEM). Furthermore, a central composite design with a response surface methodology was used to optimize the yield. The response surface methodology led to a maximum biodiesel yield of 85% with bare SnO 2 on mayenite with 6% wt of a catalyst load in respect to oil, 60°C of a temperature, and 4:1 of a methanol to oil molar ratio. X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA) were used to determine the state of the catalysts after carrying out the aging test of the catalysts in CH 3 OH.