CaO/Mg-Al-O固体碱的制备、表征及其催化活性

Preparation,Characterization and Catalytic Activity of CaO/Mg-Al-O Solid Base

采用共沉淀法制备了Ca O/Mg-Al-O固体碱催化剂;通过正交实验考察了催化剂制备条件对Ca O/Mg-Al-O固体碱催化剂催化蓖麻油与甲醇酯交换反应性能的影响。得到催化剂的优化制备条件为：浸渍液质量分数25%、焙烧温度800℃、焙烧时间2 h。以优化条件下制备的Ca O/Mg-Al-O固体碱为催化剂,在n（甲醇）∶n（蓖麻油）=9、m（催化剂）∶m（蓖麻油）=0.03、搅拌转速400 r/min、反应温度70℃、反应时间4 h的条件下,蓖麻油转化率稳定在95%~99%之间。采用TG-DTA,BET,XRD,SEM等技术对Ca O/Mg-Al-O固体碱催化剂进行了表征。Ca O/Mg-Al-O固体碱催化剂的BET比表面积为99.5 m^2/g,BJH脱附累积孔体积为0.24 cm^3/g,BJH脱附平均孔半径为4.5 nm;Ca O以无定形或微晶的形式分散于镁铝复合氧化物表面上,催化剂表面形貌为蜂窝状。采用Hammett指示剂法表征催化剂,其最大碱强度在11.2~15.6之间,蓖麻油转化率总体上随催化剂总碱量的增加而增大。

CaO/Mg-AI-O solid base catalysts were prepared through coprecipitation and characterized by means of TG-DTA, BET, XRD, SEM and Hammett indicator method. Their BET specific surfaces, BJH desorption cumulative pore volumes and BJH desorption average pore radiuses are 99.5 m^2/g, 0.24 cm^3/g and 4.5 nm, respectively. CaO was dispersed on the surface of Mg-A1-O in the amorphous or microcrystalline form, and the surface topography of the catalysts was honeycomb. The maximum base strength of the catalysts was in the range of 11.2-1 5.6. The effects of preparation conditions on the catalytic activities of the catalysts in the transesterification of castor oil with methanol were investigated by orthogonal experiments. The optimized preparation conditions for the catalyst were obtained as follows： impregnating solution mass fraction of 25%, calcination temperature of 800 ℃ and calcination time of 2 h. The castor oil conversion was stable in the range of 95%-99% under the reaction conditions of temperature of 70 ℃, time of 4 h, n （methanol） ： n （castor oil） of 9, m （catalyst） ： m （castor oil） of 0.03, stirring speed of 400 r/min and CaO/Mg-A1-O prepared under the optimized conditions as the catalyst. It was showed that the castor oil conversion increased with increasing the total basicity of the catalysts.