Catalytic Performance of MCM-22 Zeolite for Alkylation of Toluene with Methanol

摘要

The selective preparation of p-xylene by alkylation of toluene with methanol is an alternative route for the adsorption separation of xylene isomers arid toluene diproportionation. In general, methylation of toluene has been carried out over acidic zeolites, such as ZSM-5, Mordenite, Y-Zeolite and SAPO-11 etc. Toluene disproportionation to benzene and xylene, as a by-reaction, may also take place over acidic zeolites. The modification of acidity and structure of ZSM-5 zeolite have been widely investigated to reduce the by-reaction and improve the selectivity of methylation-of toluene to p-xylene. Zeolite MCM-22 has two different intracrystalline pore systems, one consisting of a two-dimensional (i. e., interconnected) system of 10-membered channels, the other one consisting of large intracrystalline cages which are accessible only by 10-membered ring windows. The MCM-22 catalyst in a new Mobile process for alkylation of benzene with propylene, gives the high yield of cumene with high purity. In this work, the effect of acidity and structure of MCM-22 zeolite on the alkylation of toluene with methanol, including toluene disproportionation, is investigated in detail. The modification of MCM-22 was also studied to improve the para-xylene selectivity of products.