摘要
在综述甲苯择形烷基化机理并分析产生“反向效应”的原因的基础上,提出了克制“反向效应”的设想。以Sb_2O_3,TiCl_4,SiCl_4,H_3PO_4,Mg(AC)_2等化合物对分子筛进行改性,测定改性前后分子筛的表面酸性与孔结构,关联乙基化反应结果,证实中强酸中心在乙基化反应中的重要作用,认为保持孔道的畅通是解决“反向效应”的关键。并采用了K-Mg改性,制备出对甲苯乙基化具有高初活性和高对位选择性的催化剂。
The 'opposite effect' problem of toluene alkylation on ZSM-5 catalyst was studied systematically. The diffusion speed of p-xylene was 103 times more than that of m-xylene in the channel of ZSM-5 zeolite. The dynamic results of toluene alkylation with methanol showed that HZSM-5 zeolite exhibited more than 96 % p-selectivity under very short contact time.The pore system of ZSM-5 zeolite was favour for toluene shape-al-kylation to produce p-dialkylbenzene. The properties of zeolites modified with SiCl4, TiCl4, Sb2O3, P2O5, and MgO and their activity for ethylation confirmed this conclusion. It also showed that the surface acid sites were isomerization sites and the middle-strong acid sites were active sites for ethylation. The deposition of modified compounds in the channel could further enhance the shape selectivity of zeolite, but it also led to the decrease of reaction activity at the same time. This was the main reason for 'opposite effect'. A practical way was proposed to modify the ZSM-5 zeolite ethylation catalyst to increase the activity and p-selectivity, i.e. the vapour deposition of TiClr and K-Mg combined modification.
基金
国家自然科学基金
中山大学科学基金
关键词
ZSM-5分子筛
甲苯
乙基化
反向效应
K-Mg modification,ZSM-5 zeolite,toluene alkylation,opposite effect
