Study On The Synthesis And Performance For Methanol Aromatization Of Nano ZSM-5 Zeolite With Double Templates

A series of nano multistage aperture ZSM-5 zeolites were synthesized by hydrothermal method with double templates.The properties of the prepared zeolites were researched through experimental evaluation of methanol aromatization combining with characterization of XRD,SEM,BET and NH3-TPD.The effects of synthesis conditions,metal ion modifiers and process conditions on physical-chemical properties and methanol aromatization properties of the prepared zeolites were investigated.The suitable synthesis and application conditions of ZSM-5 catalyst were determined.A series of ZSM-5 zeolites were synthesized using TPAOH and CTAB as double templates by means of hydrothermal method.The effects of templates ratio,Si/Al ratio,amount of ethanol additives,as well as crystallization temperature and time on physical-chemical properties of the prepared zeolites were studied.The results show that:(1)The molecular sieves synthesized within the experimental conditions are all nano ZSM-5,and they have multistage pore structure and three kinds of acids:weak acid,medium strong acid and strong acid.(2)The particle size decreases firstly and then increases with increasing the amount of TPAOH and TEOS.The addition of CTAB can slow down the aggregation of molecular sieve,but has little effect on particle size.The addition of appropriate amount of ethanol can decrease the particle size.The crystallization temperature and time have little effect on particle size.The crystallinity of the synthesized molecular sieve reduces with rising crystallization temperature and extending crystallization time.(3)Based on the stability of catalyst and molar yield of aromatic hydrocarbons,The relative optimum synthesis conditions finally determined are:TEOS:AIP:TPAOH:CTAB:C2H6O:H2O =58:1:18:1.5:172:4290,crystallization temperature 150 ?,crystallization time 24 h.Based on the ZSM-5 zeolites prepared with the appropriate synthesis conditions,the metal ions of Zn2+,Ag+ and Ga3+ were loaded by ultrasonic impregnation method and metal ion modification study was carried out.The results indicate that:The loading of metal ions can decrease the crystallinity of ZSM-5 and to a certain extent change the distribution of pore size,specific surface area and acid distribution,but has little effect on particle size.The better modified metal ion determined by the molar yield of aromatics was Zn2+ and the appropriate loading amount was 2.0%.Using the 2.0%Zn/ZSM-5 as model catalyst,the effect of temperature and operating space velocity on aromatization was studied by means of the Single-Factor method.The results show that:within a certain temperature range,higher temperature,higher molar yield of aromatics and shorter catalyst life;reducing space velocity,the catalyst life was prolonged,and the molar yield of aromatics was stable.The relative optimum process conditions finally determined are:atmospheric pressure,pure methanol feed,temperature 500 ?,and the methanol mass space velocity 1.49 h-1.