不同硅铝比HZSM-12分子筛的酸性及其烷基化合成异丙基苯的催化性能

ACIDITY OF ZEOLITE HZSM-12 WITH DIFFERENT RATIOS OF Si/AI AND ITS CATALYTIC ACTIVITY FOR THE SYNTHESIS OF ISOPROPYL BENZENE BY ALKYLATION

本文研究了不同硅铝比HZSM-12催化剂的丙烯-苯气固相烷基化的催化性能。实验结果表明,随着硅铝比的降低,烷基化活性逐渐增加,老化速度减慢。应用TPD,IR和毗啶脉冲中毒等方法考察了HZSM-12的酸性与烷基化反应之间的关系。证实了烷基化反应是在HZSM-12分子筛上中等强度B酸中心上进行。这种酸中心数目越多,反应的活性越高,稳定性越好。用水蒸汽处理的方法,可减少HZSM-12催化剂上的强酸中心数,相对增加有利于烷基化反应的中等强度的酸中心数,因而可以减缓HZSM-12的失活速率,改善催化剂的稳定性能。

This article deals with the catalytic properties of HZSM-12 catalyst with different SiO_2/Al_2O_3 ratios for the alkylation of benzene with propene. The results show that with the decrease of SiO_2/Al_2O_3, the alkylation activity increases gradually, and the rate of ageing slows down. By means of TPD, IR and poisoning by pyridine pulses, the relationship between the acidity of HZSM-12 and the alkylation activity has been established. It is shown that the alkylation takes place on moderate B-acid sites. The greater the number of these sites, the higher will be the activity, and stability of the zeolite.When treated with water-vapor, the number of strong acid sites in HZSM-12 catalyst decreases, whereas the relative number of moderate acid sites favourable for alkylation increases consequently, the stability of the catalyst is improved.