Preparation Of Ultra-thin B-oriented MFI Zeolite Membranes And Their Application In N-/i-butane Separation

Ultra thin oriented crystalline film/membrane materials are the research frontier in the field of crystalline materials.They have a wide range of applications in separation,chemical sensors,catalysis,optical materials,corrosion resistance coatings.The MFI zeolite film/membrane has a three-dimensional channel network,and its pore structure is composed of straight channels and sinusoidal channels,and the diameter of the pore is 0.56×0.53 nm and 0.55×0.51 nm,respectively,and it has become an excellent membrane material for the separation of important organic systems in the industry.MFI zeolite has straight channels in the b-axis direction,short diffusion channels and low penetration resistance;The oriented membrane is conducive to the reduction of zeolite channel tortuosity.The accurate regulation of b orientation is the key microstructure factor to improve the gas permeance of MFI zeolite membrane,and the nanoscale thickness is another key factor to determine the permeance of MFI membrane.However,the preparation of b-oriented MFI zeolite with nanoscale thickness is still a great challenge.MFI zeolite nanosheets are promising building blocks to construct ultrathin and b-oriented MFI film/membrane.Therefore,the preparation of b-oriented MFI zeolite film/membrane using nanosheets as the construction unit is expected to break through the thickness limit of conventional MFI zeolite film/membrane.This thesis mainly focuses on the preparation of MFI zeolite nanosheets and the construction of ultra-thin b-oriented MFI zeolite film/membrane,and the main content mainly includes the following three aspects:（1）Two-dimensional MFI zeolite nanosheets were prepared by the bottom-up method,the obtained MFI nanosheets have typical diamond shape,high aspect-ratio and crystallinity.The a/c axis direction is about 1～2μm and the b-axis direction is about 5 nm.These characteristics are conducive to subsequent ultra-thin oriented zeolite film/membrane preparation.（2）The preparation of ultra-thin b-oriented film/membrane by SDA free method:b-oriented MFI zeolite nanosheet layer is prepared by slip coating method on a glass support andα-Al₂O₃ support,and the thickness is 95 nm and 130 nm,respectively.The SDA（structure directing agent）free secondary growth of MFI nanosheet layer was conducted to effectively seal the interlayer and nanoscale gap among the nanosheet layer.The SDA free secondary growth effectively preserve the b-orientation of the MFI film while maintaining the minimal thickness.The effects of synthesis conditions on zeolite film were investigated on glass support.A continuous and dense b-oriented MFI zeolite film with a thickness of about 220 nm was prepared under the optimized molar ratio of 1 Si O₂:（0.02～0.04）Na₂O:1.3 C₂H₅OH:0.89 H₂O with a crystallization time and temperature of 48 h and 180℃,respectively.Then,the optimal conditions are used to try to transfer the membrane preparation process to porousα-Al₂O₃support and applied to n-/i-butane gas separation,but no continuous and dense MFI zeolite membrane was prepared,which still needs further research.（3）The preparation of ultra thin b-oriented film/membrane by secondary hydrothermal growth method with crystallization regulator:the strategy of hydrothermal pretreatment of synthesis solution and the introduction of crystallization regulator catechol（C₆H₆O₂）was adopted.The effect of C₆H₆O₂/Si O₂ molar ratio was investigated on glass support.It was found that when the molar ratio of synthesis solution was 1TEOS:0.15TPAOH:135H₂O:0.3C₆H₆O₂,hydrothermal pretreatment conditions were 90℃and 6 h,and secondary growth conditions were 100℃and 24 h,a continuous and dense b-oriented MFI zeolite film with a thickness of about 310 nm was obtained.Then,the effects of C₆H₆O₂/Si O₂ molar ratio,crystallization time and crystallization temperature onα-Al₂O₃ support were investigated.When the molar ratio of C₆H₆O₂/Si O₂ is 0.05 and other conditions are the same,the MFI zeolite membrane has the best separation performance of n-/i-butane mixture gas,the permeance of n-butane is 4.2×10^-7mol·m^-2·s^-1·Pa^-1 and the separation factor is 19.3.