Biodiesel production from refined sunflower oil over Ca-Mg-Al catalysts: effect of the composition and the thermal treatment

Abstract

Different Ca–Mg–Al catalysts were prepared by the hydrotalcite route using co-precipitation and impregnation techniques. The effect of thermal treatment was studied and the obtained mixed oxides were characterized by X-ray diffraction, N2 adsorption-desorption and CO2-temperature programmed desorption. Catalysts were then tested in the transesterification of sunflower oil. The catalyst that showed the best catalytic performance was an uncalcined Mg4Al2 support impregnated with 40 wt% of calcium followed by a calcination at 600 °C (Ca600/Mg4Al2HT). Optimum conditions for biodiesel production over this catalyst were a reaction time of 6 h, a catalyst to oil ratio of 2.5 wt%, a 15:1 methanol to oil molar ratio, a stirring rate of 400 rpm and a temperature of 60 °C giving a final FAME yield of 95%.