ZSM-5 Zeolite Synthesized By Coal Kaolin And Its Catalytic Performance For MTG

In order to alleviate the supply pressure caused by the shortage of petroleum resources and make full use of excess methanol,it is significant for us to vigorously develop the process of converting methanol to methanol?MTG?in our country.As the main catalyst of MTG process,it is really critical for ZSM-5 zeolite to reduce its synthesis cost,increase the methanol conversion rate and gasoline selectivity in MTG reaction,and extend the service life of the catalyst.In this paper,coal-based kaolin is used as the main raw material for the synthesis of ZSM-5 zeolites.After calcining and activating,it is supplemented with an appropriate silicon source so that the ratio of silica to alumina can be increased to become a raw material for the preparation of ZSM-5 zeolite.ZSM-5 zeolites were successfully synthesized by the hydrothermal synthesis method.The comprehensive analysis of the synthesized ZSM-5 zeolites weretested by XRD,NH₃-TPD,SEM,FT-IR and other modern analytical techniques.The synthesized zeolites were also characterized by the catalytic performance of MTG,and the optimum conditions for preparation of ZSM-5 zeolite by kaolin were determined.The effects of different types of silicon source on the synthesis of ZSM-5 zeolites were studied.It was found that the ZSM-5 zeolites synthesized by different silicon sources have great differences in structure and properties.The results show that the ZSM-5 zeolite synthesized with silicic acid has the best crystallinity and specific surface area,has three acid sites with different acid strengths,and its MTG catalytic performance is much better than others.And also studied the influence of reaction conditions on the structure and properties of ZSM-5 zeolite.It was found that the synthesized ZSM-5 with Si/Al=25,TPAOH/Si=0.2,crystallization time of 60 h and crystallization temperature of 170?was the bestreaction condition.The specific surface of thezeolite was 422.15 cm²/g,and the volume of micropore was 0.15 cm³/g.In the MTG catalytic reaction,The selectivity of gasoline could reach 39.88%and the catalytic life of zeolite before deactivation could reach 44 hours.Generally,there are two methods to synthesize ZSM-5 zeolitefrom metakaolin?Silicon supplementation and acid dealumination?.In order to explore the advantages and disadvantages of structure and MTG catalytic performance of ZSM-5zeolite,a part of aluminum atoms in kaolin were removed by hydrochloric acid,and two kinds of zeolite were synthesized with the same reaction conditions?Si Al ratio,template ratio,crystallization time and crystallization temperature?.The structures of the two zeolites were characterized by modern analytical and testing techniques,such as XRD,NH₃-TPD,SEM,BET.The catalytic properties of the two catalysts were evaluated by the catalytic reaction of MTG.The results showed that the ZSM-5zeolite synthesized by silicon supplementation method was superior to that synthesized by acid dealumination method in the aspects of crystallinity,specific surface area and catalytic performance of MTG.In the NH₃-TPD test,the NH₃absorption peak of the ZSM-5 zeolite synthesized by adding silicon at 220?to 420?or 620?appears obvious,while the zeolite synthesized by acid dealumination method has almost no peak near 620?,which indicates that the zeolite has almost no strong acid potential.This may be one of the main reasons that its structure and MTG catalytic performance are inferior to that of ZSM-5 zeolite synthesized by silicon supplement method.