(297d) A Novel Class of Calcium Oxide Based Catalysts in Transesterification of Vegetable Oils with Methanol
Biodiesel is a mixture of fatty acid esters and can be produced from vegetable oils or animal fats with methanol. Conventional biodiesel production process generally employs homogeneous base catalysts such as NaOH. One disadvantage of such catalysts is that the waste catalysts are difficult to be removed after reaction. In this study, a new class of calcium-containing mixed oxide catalysts was prepared by a novel ammonia-ethanol-carbon dioxide precipitation method. Compared to the conventional homogeneous base catalysts, these solid base catalysts show higher activities. XRD, XPS, BET, FTIR, SEM, EDS, and Hammett indicator method were used to characterize the structure of catalysts and the nature of active sites. It was found that ammonia-ethanol-carbon dioxide precipitation method resulted in the highest BET specific surface area, base strength and base site concentration. Moreover, catalyst surface composition and basicity are a function of calcination temperature, precipitants, pH and molar ratio of Ca to La in precursor solution, and storage conditions. The effects of water and free fatty acids (FFA) levels in oil feedstock, water and CO2 in air, mass ratio of catalyst, molar ratio of oil to methanol, and reaction temperature on fatty acid methyl ester (FAME) yield were investigated. Under optimal conditions, FAME yields reached 94.3 % within 60 minutes at 58 oC. Mixed CaO-based catalyst showed a high tolerance to water and FFA, and could be used for converting pure or diluted unrefined/waste oils to biodiesel.