Study On The Effect Of Hydrothermal Treatment On The Acidity And Hexene Aromatization Of Zn/ZSM-5

ZSM-5 molecular sieve plays an important role in the production of low olefin and high aromatic gasoline from FCC F-T synthetic oil intermediate products.However,due to the high temperature hydrothermal environment in the regeneration process,the dealumination of molecular sieve skeleton will lead to the reduction of B acid centers.Therefore,the research on the effects of hydrothermal treatment on the aromatization performance of ZSM-5 and how to improve its hydrothermal stability is a topic of great concern in the field of aromatization catalysts.In this paper,the aromatization performance of ZSM-5 is analyzed by 1-hexene reaction evaluation,and the active centers are analyzed by NH₃-TPD,Py-IR,²⁷Al MAS NMR,XPS and other characterization methods.In this paper,Zn ZSM-5 is treated at different hydrothermal temperature and different hydrothermal time to study the aromatization performance and active centers inactivation.The results show that the higher the hydrothermal temperature,the fewer the active centers and the worse the aromatization performance of ZSM-5;while increasing the hydrothermal treatment time has little effect on the reactivity.In addition,the conversion rate of 1-hexene and the yield of aromatic hydrocarbon are relatively high under suitable conditions,at which time the weak acid B/L is 0.25?0.68 and the strong acid B/L is 0.27?0.98.Therefore,the hydrothermal conditions for subsequent experiments are determined to be 500?and 2 h.The inactivation of active centers are studied by the aromatization reaction of different Si O₂/Al₂O₃?25,48,126,101,137?Zn ZSM-5 samples before and after hydrothermal treatment.The results show that the Si O₂/Al₂O₃ is about 50,the Zn ZSM-5aromatization performance is best.In addition,when the Si O₂/Al₂O₃ increases,the B acid centers decrease.The inactivation behavior of B acid centers and L acid centers are studied by different active centers ZSM-5 before and after hydrothermal treatment.The results show that the Zn ZSM-5 with B acid centers and Zn-L acid centers has the best reactivity.The aromatic hydrocarbons produced by the reaction of hydrogen transfer and dehydrogenation of aromatic precursors.In addition,the hydrothermal environment has a significant effect on the B acid centers and has a limited effect on Zn-L acid centers.The inactivation behavior of the B acid centers and the Zn-L acid centers are proposed in the study.P,La,Ag are added to Zn ZSM-5 by equal volume impregnation method,and these samples are hydrothermally treated to study the hydrothermal stability of the additives to Zn ZSM-5.The results show that P,La,Ag can protect the framework aluminum,and P has the best protection effect on B acid centers.The polyphosphate or pyrophosphate associated with Al protect the framework aluminum.