Majid Mohadesi

In this study, CaO/SiO2 was used as a catalyst of biodiesel production process. This catalyst was synthesized by the sol–gel method, which showed a high performance. Transesterification was carried out with corn oil, methanol to oil molar ratio 16:1 and 6 wt% catalysts (based on oil) mixture, at 60 C and 600 rpm during 8 h. Catalyst synthesis variables (catalyst loading, calcination temperature and acid to water ratio) were optimized. For optimizing, the Box–Behnken experimental design method was used. The results of experimental design method showed that the purity and conversion of the produced biodiesel at the catalyst loading 70 % (CaO based on SiO2) have maximum values. Also, by increasing calcination temperature from 650 to 850C, the purity and conversion were reduced. At a ratio of acid to water of 0.5, the best purity and conversion of biodiesel were shown. So the highest purity and conversion of biodiesel 98.5 and 85.6 % were obtained at the catalyst loading of 70 %, calcination temperature of 650C and acid to water ratio of 0.5. The catalyst synthesized at optimal values of parameters was reused five times. The purity and conversion of produced biodiesel during each reusing of catalyst are reduced due to CaO extraction by methanol during the reaction. However, the amount of CaO extraction by methanol is lower in comparison with the other method of catalyst preparation. Finally, the kinetics of the transesterification reaction was investigated. The results show that transesterification of corn oil in the presence of CaO/SiO2 catalyst obey a pseudo-first order rate equation.