Synthesis And Characterization Of NaA Zeolite Membrane On Porous α-Al₂O₃ Ceramic

NaA Zeolite membranes formed by microcrystalline zeolite which continually grow in the homogeneous body ofα-Al2O3 support, which combine the physical and chemical performance of inorganic films with zeolites. Therefore, it can be widely used in dehydration of biomass fuels, environmental protection, and chemical industry and so on. However, those applicable fields are confined because some problems such as defects and low intensity of combination in zeolite membranes exist easily, which seriously impact on its separation performance. So it is of paramount importance to study the preparation and performance of NaA zeolite membranes.Important factors influencing formation and performances of NaA zeolite membranes prepared by secondary synthesis are thoroughly studied in this thesis. The following researches were made on pretreatment of the support, preparation and coating of seeds, membranes synthesized with the dynamic hydrothermal synthesis, the effect parameters on synthesis of membranes, and the relationship between film microstructure and properties.The seeds were synthesized by hydrothermal treatment. The influences of synthesis conditions including gel composition, temperature and time were discussed. It was indicated that seeds were gained from the starting materials in a molar ratio of Na2O:SiO2:Al2O3:H2O=3:2:1:300, under 90℃for 3h combined with stirring-assisted by 120r/min. Moreover, the seed-coating methods were tried by dip-coating, ultrasonic vibration and hot dip-coating. The result showed that the effect of seed layer on the preparation of NaA membranes was crucial, and that the hot dip-coating method was the most beneficial to the membranes.Taking into account of its influences on the generation of zeolite membranes, the support was pretreated. In our experiments, the support was polished first, and then immersed in the NaOH solution of lmol/L NaOH for 1h. On the basis of pretreatments mentioned above, the silica-sol was coated to modify the support in order to prevent some little zeolite seeds from permeating into the holes of support, and to improve the continuity of membranes and the bonding strength between membrane and support.The technical conditions preparing zeolite membrane were explored. The high-quality NaA zeolite membranes onα-Al2O3 plates were synthesized by the following steps. The seeds were coated by hot dip-coating; then immersed in the solution of Na2O:SiO2:Al2O3:H2O=6:2:1:600 (a molar ratio), under 90℃for 3h combined with stirring-assisted by 80-90r/min. The characterization of membrane so-prepared showed that the membrane’s crystalline was excellent with 10μm thickness and uniform in size. It was proved that the flux and the separation factor of the membrane on the ethanol/water solution of 95wt% were 1.75 Kg/m2·h and 266, respectively.The growth mechnism of zeolite crystals on the support in the dynamic synthetic system and in the static one was studied by means of XRD, FT-IR and SEM. It was found that the dynamic hydrothermal condition was more beneficial to the formation of a single-phase NaA zeolite membrane with an excellent continuity and a uniform thickness.