Preparation of Biodiesel by Transesterification over Mg-Al Hydrolcite Supported Catalyst

A carbonate pillared magnesium aluminum hydrotalcite is synthesized via co-precipitation method. The hydrotalcite is used as support to load K₂CO₃ to prepare a series supported catalysts for synthesis biodiesel by the transesterification of rapeseed oil and methanol. The catalytic activity of the unsupported hydrotalcite catalysts before and after calcination and the supported hydrotalcite catalysts containing different K₂CO₃ contents is studied. Moreover, the crystal structure of the hydrotalcite and catalysts is characterized by X- ray diffraction (XRD). It is shown that the increased basic property and catalytic activity of the hydrotalcite supported catalysts are attributed to the new K-O-Al and Mg-O-K species produced by the interaction between support and K₂CO₃. Effects of K₂CO₃ loadings and transesterification conditions are also investigated. It is found that the catalyst loaded with 25%(wt) K₂CO₃ has high activity and the conversion rate of rapeseed oil can reach 99% under the conditions of catalyst amount 2%(wt), methanol/oil molar ratio 12:1, reaction temperature 60℃ and reaction time 1.5 h.