Study On Modified HZSM-5 Methanol Aromatization Catalyst

HZSM-5 zeolite is widely used in methanol aromatization,mainly because of its adjustable acidity,unique pore structure and relatively stable skeleton structure.However,the activity,BTX selectivity and lifetime of the catalyst in the methanol aromatization reaction need to be further improved.HZSM-5 can be modified to change its pore structure to make microporous-mesoporous structure,accelerate the diffusion of reactants and products,and slow down the accumulation rate of carbon deposits.It is also possible to change the acidity of HZSM-5.Reducing acid strength and acidity helps retard coking and increase BTX selectivity.In this paper,HZSM-5 was modified by hydrothermal treatment for different hydrothermal temperature and hydrothermal time,and characterized by various means.At the same time,the modified HZSM-5 catalyst was evaluated for methanol aromatization performance.X-ray fluorescence characterization showed that the HZSM-5 silica-alumina ratio after hydrothermal treatment became larger and the aluminum content decreased,which may be due to the phenomenon of dealumination after hydrothermal treatment.It is seen from the pore size distribution map that there is mesopores,which may be caused by the dealuminization of hydrothermal treatment and effective pore cleaning.The appearance of mesopores reduces the diffusion resistance of the reaction system,making the molecular diffusion path smooth,thus making carbon deposits.The precursor and aromatic products are able to diffuse out of the pores quickly.From the NH₃-TPD characterization,the content of strong acid and weak acid is reduced,which slows the formation rate of carbon deposit and prolongs the life of the catalyst.The performance of the catalyst was evaluated in a methanol aromatization reaction.It was found that the BTX selectivity of HZSM-5 at 16 h was40.00%and the lifetime was 28 h.It was found that the catalyst had the best effect when the hydrothermal treatment was carried out for 12 h and 100?,and the lifespan was longer than HZSM-5 for 108 h.When the catalyst was used for 16 h,the selectivity of BTX was increased by 18.00%.Glucose hydrothermal treatment of HZSM-5 can catalyze the production of levulinic acid from glucose,which in turn undergoes acid treatment of the molecular sieve during the slow formation process.The modified HZSM-5molecular sieve was characterized,and the modified HZSM-5 molecular sieve was evaluated on a methanol aromatization reactor.It was found that the skeletal structure of HZSM-5 was intact after glucose hydrothermal treatment.The infrared characterization of pyridine showed that the acidity and acid strength of HZSM-5 zeolite after modification were decreased.The decrease of B acid amount could inhibit the occurrence of side reactions and reduce the product.The deposition of carbon extends the life of the catalyst.Glucose hydrothermal treatment in methanol aromatization showed higher BTX selectivity and longer lifetime than hydrothermal treatment of HZSM-5.The ratio of B/L becomes larger.The selectivity of BTX increased by 9.00%and the lifetime was extended by 84 h to reach 174 h.