Transesterification of Rice Bran Oil with Methanol Catalyzed by Mg(Al)La Hydrotalcites and Metal/MgAl Oxides

Abstract

Both MgAl and Mg(Al)La hydrotalcites were synthesized by an alkali-free coprecipitation method and calcined to their corresponding oxides. MgAl oxide was impregnated with different kinds of metals (M = Cs, Sr, Ba, and La). All materials were characterized by the XRD, FT-IR, BET, NH3 TPD, and SEM techniques. The catalytic activity order of the M/MgAl oxides in the transesterification of glyceryl tributyrate (a model triglyceride) with methanol was found to be Cs > Ba ≈ Sr > La. The Mg(Al)La hydrotalcite that was calcined and then rehydrated contains Brønsted base sites, exhibiting higher activity than the calcined sample with Lewis base sites. In the preparation of biodiesel from rice bran oil via a two-step catalyzed process, crude rice bran oil (11.14% FFAs) was first dewaxed/degummed and then esterified using silica-supported heteropolyacid H3PW12O40. FFAs were decreased to 0.98% at 70 °C in 4 h. This oil was then transesterified with methanol using the rehydrated Mg(Al)La hydrotalcites. At a temperature of 100 °C, a reaction time of 9 h, a methanol/oil molar ratio of 30:1, and a catalyst content of 7.5 wt %, biodiesel with 97% ester content and 78% product yield was obtained.