Modification Of HZSM-5 Zeolite For Methanol To Aromatics(MTA) Reaction

Methanol to aromatics(MTA)has great significance for increasing the additional values of down-stream product of methanol and relieving the shortage of aromatics,and attracted more and more attention recently.However,the acidity of HZSM-5 zeolite without modification is very strong,which can cause the methanol to crack into light alkanes.Therefore,modification of it is necessary.Up to now,the studies of modification of MTA catalyst by monometallic loading,bimetallic loading,silanizing mode,and the coke deposition over MTA catalyst are rarely reported.In this study,monometallic Zn,bimetallic Zn-Ce and tetraethyl orthosilicate(TEOS)were used to modify HZSM-5 zeolite.Meanwhile,the loading amount and loading mode of metallic components,the amount and adding ways of TEOS,and coke deposition over MTA catalyst were also studied.First of all,Zn,Ag,La,Cu and Cd were used separately to modify HZSM-5 zeolite,and it was found that Zn/HZSM-5 had the best performance in MTA process.Futhermore,in order to deeply understand the functional mechanism of Zn,the study was focused on the low loading range of 1~2.25 wt.%,and loading mode was studied as well.The result indicated that,2.0 wt.% Zn/HZSM-5 catalyst modified by impregnation method had the best catalytic performance.Second,considering the weaknessess of low aromatics yield and easy coke deactivation of HZSM-5 modified by Zn,Ce was selected to modify HZSM-5 zeolite together with Zn,and the effects of loadings of bimetal Zn and Ce and the MTA reaction conditions on catalytic performance were also studied.The results showed that,1.0 wt.%Zn-1.0 wt.%Ce/HZSM-5 had the best aromatization performance at the optimal conditions of 420? and low WHSV.Third,The influence of MTA reaction conditions(i.e.WHSV and temperature)on amount of coke formed on the catalyst was studied using catalyst 1.0 wt.%Zn-1.0 wt.%Ce/HZSM-5.The coke species were characterized by FT-IR,UV-Vis and TEM.The result showed that,the higher the WHSV and temperature,the more and faster rate the coke formation.Besides,bicycle and polycycle aromatics were the main species in the coke.Finally,TEOS was used to improve the performance of HZSM-5 zeolite,and the effects of TEOS amount and adding mode on catalyst performance were also investigated.The results indicated that,the amount of 0.1 m L TEOS/gcat added by continuous addition made catalyst the good performance,and bimetal modification first and then silanization of HZSM-5 zeolite would lead to better result.