Study On The Performance Of Post-treatment Modified HZSM-5 In The Methane Dehydroaromatization

In recent years,with the continuous rise of international petroleum prices and the continuous increase of my country’s crude oil imports,it has become increasingly urgent to find non-petroleum-based raw materials to produce fuels and chemicals,and natural gas can undoubtedly be used as an alternative raw material.It is the most abundant and cleanest energy source,so it has the advantages of low price and less pollution.The main component of natural gas is methane.Compared with the indirect conversion method,the direct conversion of methane has attracted much attention.Among them,the anaerobic aromatization of methane has a good development prospect.During the reaction process,methane can be converted into benzene,toluene,naphthalene and other aromatic compounds in one step,and also generate hydrogen.However,since the reaction is carried out under high temperature and oxygen-free conditions,the coke deposition of the catalyst is unavoidable,and the consequence of the coke deposition is that the catalyst loses its activity rapidly in a short time.Therefore,the study of catalysts is crucial to the whole reaction.In this paper,the modification of HZSM-5 molecular sieve,which is commonly used in this reaction,is studied.The main research results are as follows:The HZSM-5 molecular sieve was subjected to secondary hydrothermal treatment with an aqueous solution of aluminum nitrate,and the effects of liquid-solid ratio,secondary hydrothermal treatment temperature,secondary treatment time and other conditions on the modification effect were investigated respectively.The secondary hydrothermal treatment in the aqueous solution of aluminum nitrate will promote the recrystallization of HZSM-5molecular sieve.The crystallinity of the molecular sieve becomes higher.In addition,the acid site distribution of the molecular sieve is more suitable,and the modified catalyst is applied to the MDA reaction,the stability is better than that of the unmodified HZSM-5.The deactivation rate of the catalyst was significantly slowed down.A combination of silanization and alkali treatment was used to modify the acid sites and control the pores of HZSM-5 molecular sieve.Factors such as the deposition amount and deposition time of ethyl orthosilicate during silanization were investigated,and the silicon-rich zeolite was determined.The optimal conditions for the treatment,and then alkali treatment is carried out on this basis to obtain the final modified catalyst.The corresponding characterization results and reaction results show that the silylation-alkali treatment combined with the modification successfully passivated the outside of the catalyst.At the same time,some mesopores were etched.The improvement in these two aspects enhanced the anti-carbon deposition ability of the catalyst.The modified catalyst was applied to the MDA reaction.After the reaction for 120 minutes,the methane conversion rate was still 15%,and the aromatics selectivity was still 15%.There was no significant decline.