Preparation And Modification Of Mesoporous ZSM-5 Zeolite And Its Application In MTA Process

With the development of social economy,aromatics demand in China is increasing.Aromatics produced by petroleum reforming and coal thermal fractionation can not meet the demand.Methanol to aromatics(MTA)process can effectively alleviate the contradiction between insufficient supply of aromatics and serious excess capacity of methanol.Recently,it has become one of the hot topics in the field of coal chemical industry and the kernel is the preparation of catalytic materials.ZSM-5 zeolite is an excellent MTA catalyst due to its suitable pore structure,excellent shape selectivity,hydrothermal stability,and acidity.However,the narrow pore channel of ZSM-5 zeolite increases the diffusion resistance of molecules.Besides,sole acidic active sites can not meet the demand for dehydrogenation and result in a low yield.In the presented thesis,commercial ZSM-5 zeolite was used as a raw material to prepare mesoporous ZSM-5 zeolite by desilication and sequential desilication-dealumination using by NaOH and HCl,respectively.The effects of temperature,concentration,time and liquid-solid ratio on the pore structure and acid properties of zeolites were investigated.The optimum preparation conditions were selected according to the results of MTA reaction.In addition,zinc modified ZSM-5 samples were prepared and employed in the MTA reaction.The effects of the zinc load,reaction temperature,weight hourly space velocity of methanol and the flow rate of nitrogen on the reaction properties of the zeolite MTA were investigated.The results are as follows:(1)Compared with commercial microporous ZSM-5 zeolite,the mesoporous ZSM-5 zeolite prepared by alkali treatment can significantly improve the activity and life in MTA reaction.(2)Compared with the alkali treatment,the subsequent acid treatment can further improve the activity and increase life in MTA reaction of mesoporous ZSM-5 zeolite.(3)Compared with the mesoporous ZSM-5 zeolite prepared by the sequential alkali-acid treatment,zinc modified sample can significantly improve the activity with a shorten lifetime.