Synthesis of biodiesel from rapeseed oil catalyzed by Ca/Al solid base

Ca/Al solid basic catalysts were prepared by co-precipitation method and used in the synthesis of biodiesel from rapeseed oil; the effect of preparation conditions such as precipitant selection, mole ratio of calcium to aluminum, precipitation temperature, pH value, aging temperature and time, and calcination temperature on their catalytic activity were investigated. Through orthogonal tests, the optimal conditions to prepare catalyst precursor are obtained as Ca/Al = 3, NaOH as precipitant, precipitation temperature of 60 ℃, pH value of 10, and aging at 90 ℃ for 18 h. Under the optimal conditions, the catalyst precursor obtained is in the form of Ca₄Al₂O₆(NO₃)₂·10H₂O crystal. After calcination at 300 ℃ for 2 h in N₂ atmosphere, Ca/Al mixed oxide is then highly dispersed on the catalyst surface with a pH value of above 26.5. The catalyst exhibits excellent activity in transesterification of rapeseed oil with methanol; the conversion of rapeseed oil and selectivity to fatty acid methyl ester reach 95% and 95.9%, respectively.