Study On Synthesis Of Hollow ZSM-5 Zeolite And Its Catalytic Methanol To Aromatics

Based on the ground of the encouragement for the efficient and clean use of coal in China,coal-to-methanol industry has been developed rapidly.The development of high value-added methanol downstream products is of great significance for the rational use of energy in China due to a severe excess of methanol capacity.Recently,with the development of the related chemical industry,the demand for aromatics in the market has continued to increase,and traditional petroleum route has been unable to meet market demand.Therefore,methanol to aromatics?MTA?has been attracted widespread attention for replacing traditional petroleum routes.However,lower aromatic selectivity and higher deactivation rate for MTA catalysts have impeded its further application in industry.Therefore,the development of the catalysts with high aromatic selectivity and high stability is essential to the industrialization of MTA technology.In this thesis,based on the successful preparation of microporous ZSM-5 zeolites by hydrothermal method,studied on the effect of catalyst pore structure on MTA reaction performance.Then,the effects of alkali types and aluminum source types on the preparation and catalytic performance of hollow catalysts were studied.The hollow ZSM-5 had been modified with Zn,and the effects of modification methods and Zn content on the MTA reaction performance were studied.Meanwhile,the effects of weight hourly space velocity?WHSV?and reaction temperature on the selectivity of light aromatics?benzene,toluene,xylene,BTX?were investigated,and obtained the optimal reaction conditions.Conclusions are as follows:1.The results of the effect of the catalyst pore structure on the MTA reaction performance showed that the hollow structure was more conducive for MTA reaction at optimal reaction conditions(reaction temperature is 450 ^oC,WHSV=1.5 h^-1).2.Hollow structure had been formed by treating ZSM-5 with different kinds of alkalis.After alkali treatment,the number of strong acid and weak acid of all catalysts had increased,and the highest amount of strong acid was obtained by the catalyst treated with NaOH.Hollow ZSM-5 catalysts showed higher BTX selectivity than parent ZSM-5 in MTA reaction,and the hollow ZSM-5 treated with NaOH exhibited the highest BTX selectivity.3.The framework aluminum distribution of hollow ZSM-5 zeolites prepared with different aluminum sources was significantly different,which resulting in different hollow structures,and the acidity and pore structure of the catalysts also changed.The MTA reaction results showed that the hollow catalyst synthesized with aluminum isopropoxide exhibited the thinnest shell thickness,the most number Br?nsted acid sites,and obtained the highest BTX selectivity.In addition,the hollow ZSM-5 synthesized with aluminum isopropoxide displayed the lowest average coke formation rate and the highest stability.4.Zn was introduced into hollow catalysts with different modification methods,which changed the pore structure and acidity of the catalyst.The MTA reaction results showed that the Zn modified catalyst prepared by the vacuum equal volume impregnation method had higher selectivity to BTX,but the catalytic life was reduced.However,the Zn modified catalyst prepared by directly adding the process Zn during the alkali treatment exhibited a longer lifetime and a lower BTX selectivity.Then,the effect of Zn content on its catalytic performance was further investigated,it was found that Zn content of 3 wt%,the highest BTX selectivity was obtained over the Zn-modified hollow catalyst.