Study On Methane Dehydroaromatization

As the proved reserves of natural/shale gas local and abroad continue to rise,the conversion of methane(CH4)gradually shows great application prospects.Converting CH4 into high value-added chemical products can not only make full use of natural resources,but also bring huge economic value.Methane dehydroaromatization(MDA)is one of the effective ways to utilize CH4,and the Mo/HZSM-5 catalyst is one of the catalyst systems with the best performance.However,products in MDA contains large molecules of polycyclic aromatic hydrocarbons such as naphthalene,which leads to blockage of HZSM-5 channels and coverage of active sites,resulting in rapider deactivation.Therefore,reducing coke and increasing catalyst life have become the focus of research.Based on the Mo/HZSM-5 catalyst,this article explored the effect of the active component loading method,the role of additives,and the catalyst synthesis conditions on the catalyst performance firstly,then explored the effects of coupling reaction conditions,such as the types of alkylating reagents,space velocity(SV),methanol intake.It was found that the 8Mo/1Mg/HZSM-5 catalyst calcined at 400? for 6 h had higher activity.Subsequently,by introducing methanol as the alkylating agent into the reaction under 1500 mL/(gcat·h),MDA and aromatic alkylation reactions are coupled,which can effectively improve the stability of the MDA.In contrast,in the conventional MDA,the catalyst showed obvious deactivation within 7 h.Through the analysis of the reaction products,the selectivity of toluene has also been improved to a certain extent,indicating that methanol participates in the alkylation of benzene,reducing the production of naphthalene and other condensed aromatic hydrocarbons.As a result,the stability of the catalyst had been improved.Besides,this paper also explores the physical mixed catalysts.Apply 1:1 physical mixing of Mo/HZSM-5 and Zn/HZSM-5 or Mg/HZSM-5 to the reaction.The results show that the relatively large silica-aluminum HZSM-5 support and high Zn or Mg loading are not suitable for the coupling reaction.Additions,the Zn source and the Mg source also have a certain effect on the reaction.ZnO and Mg(NO3)2 as precursors are more conducive to improve the performance of the catalyst,but the activity of both are weaker than the 8Mo/1Mg/HZSM-5 catalyst prepared by co-impregnation.