The Performance Study Of The Hierarchical Pore ZSM-5 Molecular Sieve Used To Catalyze The Aromatization Of Methanol

Establishing a new methanol conversion process with high efficiency and stability is an important developing direction for modern coal chemical industry.In order to solve the key problem of short catalyst life for methanol to aromatics?MTA?,combining the excellent diffusion properties of hierarchical zeolite for macromolecular compounds,this study intends to modify the commercial ZSM-5 by using NaOH and tetrapropylammonium hydroxide?TPAOH?.A series of ZSM-5 molecular sieves with hierarchical structure were prepared.The molecular sieve pore structure and acidity can be adjusted by changing the species and concentration of alkalis.The influence of pore structure and acidity of hierarchical ZSM-5towards coke amount and position were studied in MTA process.?1?MFI type molecular sieves with different pore structure and acidity were prepared by using different concentrations of NaOH to modify the commercial ZSM-5 molecular sieves through desiliconizing,dealuminizing or desiliconizing/dealuminizing.The acidity of the ZSM-5 was changed by NaOH treatment,and the mesoporous pore volume was increased.The pore structure and acidity are the two important factors affecting the methanol conversion process in MTA.The strong acid center is the active site for the conversion of olefins to aromatics.The reduction in the number of strong acid centers is beneficial to suppress the formation of carbon deposits.Mesoporous pore volume can influence the reactants diffusion,thereby affect the conversion process and carbon deposits.?2?Desilication treatment of ZSM-5 with TPAOH was carried out to analyze the influence of molecular sieve structure and acidity on the catalyst life in MTA reaction.The change of pore structure before and after treatment was tested by N₂ adsorption desorption technique.The acidity of modified ZSM-5 zeolite was analyzed by NH₃-TPD.The results showed that the desiliconization treatment can increase the mesoporous pore volume and decrease the strong acid density,thereby reducing the formation of coke and improving the stability of the catalyst.