Preparation Of Hierarchical ZSM-5 Zeolite And Its Methanol Aromatization Performance

As one of the most important basic organic chemical materials,aromatic hydrocarbons are synthesized from petroleum.However,with the gradual depletion of petroleum resources,aromatics are in short supply.Due to the mature production technology of methanol and its wide source of raw materials,the methanol aromatization process has gradually become a research hotspot in the production of aromatic hydrocarbons by non-petroleum route in recent years.At present,ZSM-5 zeolite is widely used in this process.However,ZSM-5 zeolite has a certain diffusion resistance due to its small pore size,which limits its application in catalytic reactions.Therefore,the researchers tried to introduce the mesoporous structure into the microporous zeolite to obtain a hierarchical zeolite,which combines the good catalytic performance of the microporous zeolite with the excellent mass transfer performance of the mesoporous material.Thus,in this disseration,hierarchical ZSM-5 zeolite was synthesized by acid modification,alkali modification and silanization.The effect of experimental conditions on the molecular sieve structure and acidity was studied.Acid modification was used to dealuminize ZSM-5 zeolite,so that the acid content of the zeolite was significantly reduced,the pore structure of the zeolite was not significantly changed,and the content of aromatic hydrocarbons in the product was significantly increased.However,the desilication of ZSM-5 zeolite by alkali modification method not only resulted in the formation of a large number of mesoporous structures,but also reduced the acid content of the zeolite to different degrees.The amount of Br?nsted acid of the zeolite modified with 0.5 mol/L sodium acetate solution was reduced from 5.37 to 1.31,and the pore size of the zeolite was between 1-3.5 nm.The introduction of mesopores is conducive to the diffusion of products and shortens the residence time of products in the pore channels,resulting in an increase in the service life of molecular sieves from 20 h to 74 h.Compared with the post-processing method,hierarchical ZSM-5 zeolite synthesized by adding methyl triethoxysilane(MTES)has a well-connected mesoporous structure.By optimizing the synthesis conditions of the hierarchical ZSM-5 zeolite,it is concluded that when the amount of MTES added is 1 mL and the precrystallization temperature is 90°C,the pore volume and specific surface area of the zeolite are large,and the amount of acid is appropriate,which makes the zeolite's life and product yield has increased significantly.