负载型镁铝水滑石催化酯交换合成生物柴油

采用共沉淀法合成了镁铝水滑石,以其为载体负载K2CO3制备了负载型镁铝水滑石催化剂,用于菜籽油酯交换合成生物柴油。研究了未负载活性组分时,镁铝水滑石和焙烧后得到的镁铝复合氧化物对酯交换反应的催化活性,以及负载K2CO3后,活性组分负载量对催化剂活性的影响,并利用X射线衍射表征了焙烧前后以及负载K2CO3前后催化剂物相结构的变化。实验发现,水滑石载体和K2CO3在高温焙烧后形成的钾铝和镁钾氧化物是催化剂碱性和活性提高的重要原因。进一步优化了活性组分负载量和酯交换反应条件,以镁铝水滑石为载体,负载25%的K2CO3作为催化剂,在催化剂用量2%,醇油摩尔比12∶1,反应温度60℃,反应时间1.5h时,油脂转化率高达99%。

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.