K_(2)O/MgFe_(2)O_(4)磁性固体碱催化剂的制备、表征及催化酯交换制备碳酸甘油酯

Preparation,characterisation and catalytic transesterification for the preparation of glycerol carbonate of magnetic solid base catalyst K_(2)O/MgFe_(2)O_(2)

为了解决生物柴油制备过程中副产物甘油过剩、碳酸甘油酯产率低和催化剂回收困难的问题,以聚乙二醇600(PEG-600)为模板和分散剂,采用溶胶凝胶法制备镁铁氧体(MgFe_(2)O_(4)),以其为载体,KNO3为活性组分前驱体,采用浸渍法制备K_(2)O/MgFe_(2)O_(4)磁性固体碱催化剂。通过X射线衍射、X射线光电子能谱、扫描电镜、CO_(2)程序升温脱附(CO_(2)-TPD)和磁性分析对催化剂进行表征,并将催化剂用于甘油与碳酸二甲酯酯交换制备碳酸甘油酯的反应中,考察其催化性能。结果表明:制备的K_(2)O/MgFe_(2)O_(4)形成了K-Fe-Mg键,K_(2)O/MgFe_(2)O_(4)表面呈霉菌状,具有较多的中强碱位点和强碱位点,且具有较好的磁性;在PEG-600加入量10 g(硝酸镁1.5 g、硝酸铁4.71 g)、反应温度105℃、反应时间2 h、催化剂用量3%、甘油与碳酸二甲酯物质的量比1∶2的条件下,甘油转化率可达到99.53%,碳酸甘油酯产率可达到96.36%,且制备的催化剂重复使用性能良好,在重复使用5次后,碳酸甘油酯产率仍可达80.14%。综上,所制备的催化剂具有高甘油转化率、高碳酸甘油酯产率、重复使用性能高(通过外部磁场即可回收)等优点,有望实现工业化。

In order to solve the problems of glycerol excess as a by-product in the production process of biodiesel,low yield of glycerol carbonate and difficult recovery of catalyst,with polyethylene glycol 600(PEG-600)as templet and dispersant,magnesium ferrite(MgFe_(2)O_(4))was prepared by sol-gel method and magnetic solid base catalyst K_(2)O/MgFe_(2)O_(4) was prepared by impregnation method using MgFe_(2)O_(4) as the carrier and KNO3 as the precursor of the active component.The catalyst was characterised by X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,CO_(2) procedure temperature rise desorption and magneometer,and the catalytic performance was investigated by using the catalysts in the reaction of transesterification of glycerol with dimethyl carbonate to produce glycerol carbonate.The results showed that the prepared K_(2)O/MgFe_(2)O_(4) formed K-Fe-Mg bonds,the surface of K_(2)O/MgFe_(2)O_(4) was mould-like with more medium-strong base sites and strong base sites,and it had good magnetic properties.Under the conditions of PEG-600 addition amount 10 g(Mg(NO3)21.5 g,Fe(NO3)34.71 g),reaction temperature 105℃,reaction time 2 h,catalyst dosage 3%,and the molar ratio of glycerol to dimethyl carbonate 1∶2,the conversion rate of glycerol could reach 99.53%,and the yield of glycerol carbonate could reach 96.36%.The prepared catalyst had good reusability,and the yield of glycerol carbonate was still as high as 80.14%after 5 times of reuse.In conclusion,the prepared catalyst has the advantages of high glycerol conversion,high glycerol carbonate yield,and high reusability(easier recovery through an external magnetic field),which is expected to achieve industrialisation.