Ca-Mg-Zn-O催化剂的制备、表征及其蓖麻油醇解的催化活性评价

Preparation and Characterization of the Ca-Mg-Zn-O Catalyst,and Its Catalytic Activity Evaluation for Castor Oil Alcoholysis

采用共沉淀及焙烧的方法制备了Ca-Mg-Zn-O固体碱催化剂。采用正交试验考察了制备条件对Ca-Mg-Zn-O固体碱油脂醇解催化活性的影响,得到的优化条件为:n(Ca):n(Mg):n(Zn)=1:1:2、焙烧温度800℃、焙烧时间5 h。以优化条件下制备的Ca-Mg-Zn-O固体碱为催化剂,在醇/油摩尔比9:1、催化剂/油质量比0.04:1、搅拌速率550 r/min、反应温度65℃、反应时间3 h的条件下,蓖麻油转化率达到96.3%。采用TG-DTA、FTIR、XRD、BET技术及Hammett指示剂法对催化剂及其前驱体进行了表征,结果为:Ca-Mg-Zn碱式碳酸盐TG曲线有3个失重台阶,分别出现在200~350℃、450~550℃及680~750℃温区;Ca-Mg-Zn-O固体碱催化剂由ZnO、MgO及CaO 3种晶体构成,其BET、比表面积为5.91m^2/g,BJH脱附累积孔容为0.009 8 cm^3·g^(-1),BJH脱附平均孔半径为3.50 nm,碱强度在7.2~11.2之间。

Ca- Mg- Zn -O solid base catalyst was prepared by using coprecipitation and calcination. Influences of preparation conditions on the catalytic activity of the Ca - Mg - Zn - O solid base in oil alcoholysis were investigated through orthogonal tests. The optimized conditions obtained were as follows：n（ Ca）： n（ Mg）： n（Zn） = 1： 1：2, calcina- tion temperature of 800 ℃, calcination time of 5 h. When the transesterification of castor oil and methanol was carried out at 65 ℃ for 3 h with alcohol/oil molar ratio of 9 ： 1, catalyst/oil mass ratio of 0.04 ： 1, stirring speed of 550 r · min^-1 ,castor oil conversion reached 96.3% in the presence of Ca - Mg - Zn - O catalyst prepared under the opti- mum conditions. The catalyst and its precursor were characterized utilizing TG - DTA, XRD, BET technique and Hammett indicator method. It was concluded that TG curve of Ca - Mg - Zn basic carbonate had three weightlessness steps,emerging respectively in 200 - 350 ℃ ,450 - 550 ℃ and 680 - 750 ℃ Ca - Mg - Zn - O solid base catalyst was made up of ZnO, MgO and CaO three crystals, and that BET surface area of Ca - Mg - Zn - O solid base was 5.91 m2 · g^- 1, BJH desorption cumulative volume of pores was 0. 009 8 cm3 · g^- 1 , BJH desorption average pore radi- us was 3.50 nm,and the base strength was within the range from 7.2 to 11.2.