Synthesis Of Biodiesel From Transesterification Of Rapeseed Oil And Methanol Over Solid Base

Biodiesel, an alternative diesel fuel, is made from renewal biological sources such as vegetable oils and animal fats,and has become more attractive recently because of its environmental benefits and safety in use. Transesterification is one of the most important methods for biodiesel systhesis, and the reaction rate can be accelerated by acid and base. Biodiesel can be synthesized from transesterification catalyzed by high active solid base under mild reaction conditions, and the high active solid base catalyst shows a good prospect in avoidance the difficulty of products separation and purification and the problem of environmental pollution from the transesterification catalyzed by homogeneous base. So, the study on synthesis of biodiesel from transesterification over solid base has an important significant both in theoretic and practical aspects.Supported solid bases and metal oxide catalysts were prepared successfully by isochoric impregnation and the co-precipitation method, and were used for synthesis of biodiesel from transesterification of rapeseed oil and methanol. The high active solid base catalysts: KF/Al2O3, ZnO/La2O3 and La2O3 were found in this paper. The influence of reaction temperature, reaction time, catalyst dosage and other factors on the transesterification were investigated. The results show that the optimum reaction conditions are: molar ratio of methanol to oil 12:1, the amount of KF/Al2O3(35wt%) 5wt%, reaction temperature 50℃,reaction time 6.0 h, yield of biodiesel reaches 96.7%; while the amount of ZnO/La2O3(nZnO/nLa2O3=1.0) 3wt%, reaction temperature 65℃and reaction time 6.0 h, yield of biodiesel reaches 96.8%; under the same conditions, the amount of La2O3 3wt%, yield of biodiesel reaches 98.2%.The structures of the different catalysts were characterized by scanning electron microscopy(SEM), X-ray powder diffraction(XRD), XPS and BET method. The results showed that improvement of the KF/Al2O3 catalyst activity was closely related to formation of new crystal phase due to interaction of KF and Al2O3 during calcination,while the higher activity of metal oxide catalysts are mainly decided by hyperfine La2O3 particle.The transesterification of rapeseed oil and methanol forms a relatively stable self-emulsified reaction system. And the particle size of the emulsion was investigated with laser particle size analysis. On the base of two experimental phenomenons, the emulsion was discussed and analyzed. The transesterification mainly carried out inside micelle,and the mixing importance to the transesterification will be decrease, once the reaction was started.The different reaction mechanism was analyzed and advanced. And the intermediates from transesterification of ethyl acetate and methanol is applied to the simulation of the intermediates from transesterification of rapeseed oil and methanol. By means of the density functional theory (DFT) method, the geometries of the two species of different intermediates were optimized at the B3LYP/6-31g(d) level. The results of the theoretical study indicate that the zwitterions energy is 242.99kJ/mol higher than that of the other one. Obviously, the new reaction mechanism of transesterification is reasonable.