Synthesis Of Hierarchical ZSM-5 And Its Application In MTG

ZSM-5 molecular sieve has a wide range of applications in the petrochemical industry due to its uniform micro porous structure,good hydrothermal stability and excellent shape-selective catalytic performance.In view of the fact that ZSM-5 molecular sieves are restricted by the diffusion of macromolecules and are easy to accumulate carbon and lose activity,which affects the catalytic performance of the catalyst,the synthesis of hierarchical ZSM-5 molecular sieves and its application in methanol to gasoline(MTG)are carried out.First,in this paper,hierarchical ZSM-5 molecular sieve with a silicon-aluminum molar ratio of 40 was prepared by in-situ synthesis method,using polyethylene glycol-1000,cetyltrimethylammonium bromide,tetra propylammonium bromide,and polyether P123 as mesoporous template agents.At the same time,the synthetic ZSM-5 molecular sieve was subjected to alkaline treatment and hydrothermal treatment to prepared hierarchical ZSM-5,and comparative characterization of the synthesized molecular sieves was performed.The results show that the hierarchical ZSM-5 molecular sieve synthesized with different mesoporous template agents and post-treatment methods has a relative crystallinity greater than 93%,specific surface area above 320m2/g,and mesoporous specific surface area above 81 m2/g,which is larger than 55m2/g of ZSM-5 molecular sieve.Among them,the hierarchical ZSM-5 molecular sieve using poly ether P123 as mesoporous template has obviously mesoporous structure and retains the complete microporous structure.The specific surface area is 350m2/g,the mesoporous specific surface area is above 130m2/g,the pore volume of mesopores is 0.3 1cm3/g,and the pore size distribution is wide.Next,the catalytic performance of the synthesized hierarchical ZSM-5 molecular sieve during MTG catalytic reaction was evaluated,and the catalyst was screened.The optimal catalyst was optimized for the reaction process conditions.The results showthat the hierarchical ZSM-5 molecular sieve has a longer service life and catalytic activity,the hierarchical ZSM-5 molecular sieve with polyether P123 molecular sieve as the mesoporous template was screened out.The optimized process conditions are space velocity 0.8h-1,The temperature is 380℃ and the pressure is 1.5MPa.Under optimized conditions,compared to ZSM-5 molecular sieve,in the initial stage of the reaction,the oil yield of hierarchical ZSM-5 increased by 14%,and after 288h,the oil yield increased by 40%,Ron reached 97.4,and the single life was extended about 168h,and hierarchical ZSM-5 molecular sieve has better resistance to hydrothermal stability.Finally,hierarchical ZSM-5 molecular sieve using P123 as mesoporous template was synthesized by a 50-fold crystallization kettle,and applied to MTG pilot process.The results show that the synthesized molecular sieve still has similar physical and chemical properties,and the catalytic effect is basically equivalent.The hierarchical ZSM-5 molecular sieve can increase the yield,reduce the number of regenerations,enrich the basic theory of MTG.