Study On Transesterification Of Soybean Oil And Methanol To Biodiesel On Solid Base Catalysts

Mg-Al composite oxide (MA) with different atomic ratios of Mg and Al were obtained from the calcinations of hydrotalcite precursor by precipitation. The property and the structure of MA were investigated using X-ray diffraction, thermogravimetry, differential thermal analysis and temperature-progammed desorption of carbon dioxide. The activity of MA in the transesterifiacation of soybean oil and methanol to biodiesel was measured in a batch reactor mounted with a stirrer. The influence of the conditions on the yield of biodiesel, such as catalyst pretreatment, reaction temperature and the composition of MA was studied. Additionally, potassium carbonate supported on MA was prepared by calcination of potassium acetate that was loaded on the surface of MA by dry impregnation method and their activity was also observed.The results showed that the Al ions were distributed in the lattice of MgO crystal in the system of MA and there existed abundant base sites of different strength. The strength of the corresponding base sites tended to increase with MgO content. In the transesterification reaction of the soybean oil with methanol, the base sites of low strength may take in a more important role than those of high strength. There was not clear influence of the refining process of soybean oil and the reaction temperature on the biodiesel yield on MA, however, the pretreatment of MA in N₂ could improve the activity greatly.Potassium carbonate produced after the calcinations of the supported potassium acetate on MA could be dispersed uniformly on the surface of MA and many base sites of high strength were formed in this catalyst system. The activity of the transesterification reaction was increased effectively after the loading of potassium carbonate on MA and the activity was also increased with the content of loading potassium acetate. However, the loss of potassium carbonate in the catalyst system could cause the decrease of the catalytic activity in the transesterification reaction process.