KF改性固体碱的制备、表征及在菜籽油醇解中的应用

Preparation and Characterization of KF Modified Solid Base and its Application in Rapeseed Oil Alcoholysis

将乙酸钙溶液、氟化钾溶液作为浸渍液,氧化铝作为载体,通过二次浸渍、二次焙烧制得KF-CaO/Al2O3固体碱催化剂。通过正交试验考察各制备因素对催化剂在菜籽油醇解中活性的影响。得出的最佳制备条件为:乙酸钙溶液质量分数20%,氟化钾溶液质量分数25%,一次焙烧温度950℃,一次焙烧时间5 h。最佳条件下制得的催化剂可使菜籽油转化率达到99.4%。采用热重分析、X射线衍射、N2吸附-脱附、扫描电镜及Hammett指示剂滴定法对最佳条件下制备的CaAc2/Al2O3、CaO/Al2O3及焙烧前后的KF-CaO/Al2O3进行了表征。结果显示:CaAc2/Al2O3在140、420、700℃附近有明显失重,焙烧前KF-CaO/Al2O3在200、570℃附近有明显失重。焙烧后KF-CaO/Al2O3固体碱催化剂由无定形Al2O3载体及负载于表面的以单层分散的CaO、KF及反应产物构成。其比表面积为29.72 m^2/g、孔体积为0.074 2 cm^3/g。催化剂为表面光滑的层状结构,其碱强度介于7.2~18.4。

KF-CaO/Al2O3 solid base catalyst was prepared through secondary impregnation and two calcinations with a calcium acetate solution and a potassium fluoride solution as an impregnation liquid and alumina as carrier.The orthogonal table was used to arrange experiments to investigate the effects of various preparation factors on the activity of the catalyst in the alcoholysis of rapeseed oil.The optimal preparation conditions are as follows:calcium acetate solution mass fraction was 20%,potassium fluoride solution mass fraction was 25%,primary calcination temperature was 950°C,and one roasting time was 5 h.The catalyst prepared under the optimum conditions could achieve a conversion rate of rapeseed oil of 99.4%.Thermogravimetric analysis,X-ray diffraction,N 2 adsorption-desorption,scanning electron microscopy and Hammett indicator titration were used to characterize CaAc 2/Al2O3,CaO/Al2O3 under optimal conditions and KF-CaO/Al2O3 before and after calcination.The results showed that CaAc 2/Al2O3 had significant weight loss near 140,420,and 700℃.KF-CaO/Al2O3 had significant weight loss near 200 and 570°C before calcination.After calcination,the KF-CaO/Al2O3 solid base catalyst is composed of an amorphous Al2O3 support and a monolayer-dispersed CaO,KF and a reaction product supported on the surface.Its specific surface area is 29.72 m^2/g,pore volume is 0.0742 cm^3/g.The catalyst is a layered structure with a smooth surface and an alkali strength of between 7.2 and 18.4.