硝酸胶溶剂对MCM-22分子筛催化剂性能的影响

Effect of nitric acid peptizator on the performance of a MCM-22 zeolite catalyst

以硝酸为胶溶剂,采用挤条成型工艺制备了一系列MCM-22分子筛催化剂,并采用颗粒强度仪、热重天平以及氮吸附脱附-压汞方法等手段对其物理化学性质进行表征,系统考察了硝酸用量对MCM-22分子筛颗粒强度、总酸量和孔道结构等性质的影响。表征结果表明,分子筛颗粒强度随成型过程中硝酸用量的增加呈现先增大后减小的趋势,最高颗粒强度对应的硝酸用量质量分数约为10%;随硝酸胶溶剂用量的增加,分子筛总酸量增加,比表面积逐渐增大,孔容先增后减。以苯和丙烯烷基化合成异丙苯为模型反应,分别采用气-液半连续和液-液连续两种操作方式对所制备分子筛的催化性能进行了实验评价。评价结果表明,当硝酸质量分数小于20%时,分子筛催化剂的活性随成型过程硝酸用量的增加而增加,当硝酸质量分数为10%时,异丙苯的选择性最大。

A series of MCM-22 zeolite catalyst samples have been prepared with nitric acid as peptizator using an extrusion molding method. The zeolites were characterized by means of particle strength tests, TG-DTA, N2 adsorption-desorption measurements, and mercury intrusion porosimetry. The effects of varying the amount of the peptizator on the physical properties of MCM-22 catalyst were investigated. The results showed that with increasing nitric acid dosage, the mechanical strength of the zeolite catalyst increased at first and then decreased, with the maximum catalyst strength being obtained at a dosage of 10 mass percent nitric acid. The specific surface area and total acid were enhanced by adding the appropriate amount of nitric acid. Taking the alkylation of benzene with propylene as a model reaction, the catalytic performances of the MCM-22 zeolite catalysts prepared in this work were evaluated by means of a semi-continuous gas-liquid reactor and a liquid-liquid continuous reactor. The experimental results showed that when the nitric acid dosage was less than 20 mass percent, the activity of MCM-22 zeolite increased with increasing nitric acid dosage. The selectivity to cumene reached a maximum value when the nitric acid dosage was 10 mass percent.