Preparation And Separation Performance Study Of Small Pore Size Zeolite Membranes

Small pore zeolite membranes with small pore size,strong stability,good shape-specific catalysis,and selected permeance ability are of great application in many fields,such as membrane reactors,sensors,gas separation,and liquid separation.This paper,guided by the preparation of high-performance small pore zeolite membranes,zeolite T membranes,and CHA zeolite membrane,was investigated.Firstly,zeolite T membranes were prepared under the condition of the fluoride-free system by seeding microstructure regulation,and the influencing factors and repeatability of zeolite T membranes were investigated.Secondly,innovatively proposed a method called hetero-seed epitaxial growth to prepare CHA zeolite membrane,and similarly,its influencing factors and repeatability were examined.Finally,the pervaporation hydrothermal stability of two small pore zeolites was examined concerning their stability performance under acidic conditions.1.The molar ratio of SiO₂:Al₂O₃:Na₂O:K₂O:TMAOH:H₂O=1:x:0.23:0.0824:y（x=0.035 and 0.055;y=0.05 and 0.10）,two kinds of zeolite T with different sizes and morphologies were produced by adjusting the silicon to aluminum ratio of the precursor solution as well as the content of the templating agent:the rice grain type（2μm,400 nm）and sphere type（750 nm,250 nm）.2.Zeolite T membrane was prepared by using T seeds with different microstructures under the fluoride-free system.It was found that the direction of the long axis of crystals on the surface of the membrane prepared by spherical seeds was nearly parallel to the support,and the crystal radius perpendicular to the long axis direction was similar to the corresponding size of the half diameter of spherical seeds.Zeolite T membranes obtained from spherical seeds preparation are superior to rice grain type seeds.Subsequently,the influences of crystallization temperature,a silica source,and feed silicon aluminum ratio were investigated,and the optimized flux and separation factor of zeolite T membrane for the dehydration of 90 wt.%IPA/H₂O at 75°C was achieved with an optimal flux of 3.66 kg·m^-2·h^-1,corresponding to a separation factor of>10000.3.The preparation of CHA zeolite membrane by hetero-seed epitaxial growth was innovatively proposed.The effect of hetero-seed microstructure on the preparation of CHA zeolite membrane by hetero-seed epitaxial growth was investigated.The critical role of heterogeneous seed crystals was demonstrated by comparing the in situ growth and secondary growth methods under the same conditions.The effects of silicon source,water to silicon ratio,and crystallization time on the preparation of CHA zeolite membrane by hetero-seed epitaxial growth were examined.The optimized CHA membrane achieved the best flux of 4.71kg·m^-2·h^-1 for 75°C 90 wt.%IPA/H₂O membrane separation with separation factor more than10000 and excellent repeatability.4.Based on the above preparation of the resulting zeolite T membrane and CHA zeolite membrane,the separation process of the as-prepared zeolite membrane at 75°C in 90 wt.%isopropanol/water and studied its acid resistance stability at p H=5.The results showed that the zeolite T membrane prepared by the fluoride-free method and CHA zeolite membrane prepared by hetero-seed epitaxial growth had good hydrothermal stability and acid resistance stability.