油脂醇解固体碱催化剂的制备及表征

Preparation and characterization of solid base catalyst for oil methanolysis

以硝酸钙、硝酸锌、乙酸镁、乙酸铝为原料,碳酸钠为沉淀剂进行共沉淀反应,先制得钙、镁、锌碳酸盐及氢氧化铝混合沉淀,再经陈化、水洗、干燥、焙烧制得钙镁锌铝固体碱催化剂。将蓖麻油甲醇解反应中的蓖麻油转化率作为活性评价指标,采用正交试验考察了制备条件对催化剂活性的影响,得到制备催化剂的优化条件为:n(Ca)∶n(Mg)∶n(Zn)∶n(Al)=2∶0.5∶0.5∶1,混合溶液p H 8,焙烧温度850℃,焙烧时间7 h。将优化条件下制备的固体碱催化剂用于催化蓖麻油甲醇解反应,蓖麻油转化率达93.2%。采用热重分析、X射线衍射、N2吸附-脱附、扫描电镜及Hammett指示剂滴定法对催化剂及其前驱体进行了表征。结果显示:催化剂前驱体在700~800℃温区有1个明显的失重台阶,在800℃以后质量基本不随温度变化;固体碱催化剂主要由Ca O、Zn O及Mg O3种晶体构成,其比表面积为44.08 m^2/g、孔容为0.062 65 cm^3/g,特征为多孔连续型蜂窝状结构;固体碱催化剂的碱强度在7.2~15.0之间,总碱位量为14.895 mmol/g。

The precipitates of calcium, magnesium, zinc carbonate and aluminum hydroxide were pre- pared by coprecipitation with calcium nitrate, zinc nitrate, magnesium acetate and aluminum acetate as raw materials and sodium carbonate as precipitation agent, and then the calcium magnesium zinc alumi- num solid base catalyst was prepared by the aging, washing, drying and calcination. The effects of prepa- ration conditions on the catalytic activity were investigated by orthogonal experiment, with castor oil con- version rate in methanolysis reaction of castor oil as the activity evaluation index. The optimal conditions for the preparation of the catalyst were obtained as follows： n （Ca） ： n （Mg） ： n （Zn） ： n （ A1 ） = 2：0.5： 0. 5： 1, pH of the mixed solution 8, calcination temperature 850 ℃, and calcination time 7 h. With the solid base obtained under these conditions as catalyst in methanolysis reaction of castor oil, the castor oil conversion rate was up to 93.2%. The catalyst and its precursor were characterized by thermogravimetric analysis, X- ray diffraction, N2 adsorptiondesorption, scanning electron microscopy and Hammett indicator method. The results showed that the catalyst precursor had a significant weight loss step in the temperature range of 700- 800 ℃, and the mass did not change with catalyst was mainly constituted of three kinds of crystals CaO, temperature above 800 ℃. The solid base ZnO and MgO. The specific surface areaand pore volume of the catalyst were 44.08 m2/g and 0. 062 65 cm3/g respectively, and it was porous continuous honeycomb structure. The alka- li strength of the solid base catalyst was between 7.2 and 15.0, and the total alkali amount was 14. 895 mmol/g.