Studies On Synthesis Of Zeolite A Membranes And Adhensive-free Shaped Material

Synthesis and application of A-type zeolite membranes have attracted much attention because of their unique characteristics, especially their water-selective permeating property. Most works are still on the lab-scale all over the world except Japan, which has commercial products. Technology of preparation of NaA membranes must be grasped in order to fill the space. In view of these challenge in the field of zeolite membranes, the main works of this thesis are to synthesize NaA membranes on porous α-Al2O3 supports via the method of seeding plus secondary hydrothermal or VPT crystallization and on self-bonded NaA supports prepared by gel-casting method. Their pervaporation properties for dehydration of water/ethanol mixtures are examined. The seeding layers, which were formed by dip-coating, in-situ aging, and negative pressure adsorption methods, have the crucial effects on the preparation of NaA membranes. Surface seeding can not only accelerate the formation of A-type zeolite on the support surface, but also inhibit the transformation of A-type zeolite into other types of zeolite.The synthesis conditions of NaA membranes via hydrothermal methods have been studied. In the reaction sol of 2Na2O:1Al2O3:2SiO2:240H2O, performance of pervaporation showed that the NaA membranes had a selectivity of exceed 300 at 70℃ with 10wt% initial water concentration and a flux of 0.19kg/(m2·h). In addition, studies performed for various temperatures and concentration of ethanol in the pervaporation were also conducted.The synthesis condition for NaA membranes by VPT methods required more accurately control. In this work, the batch composition, crystallizing temperature, crystallizing time and amount of water have been studied, the optimal process condition have been decided. The high-quality NaA membranes can be got from the batch of 3.165Na2O:1Al2O3:1.926SiO2:256H2O at 90℃ with 3 hours' reaction.Self-bonded NaA structures with designed shapes were fabricated by gel-casting method. The crushing strength, adsorption capacity of water and ethanol were superior to the values reported in literature. NaA membranes can be synthesized on the shaped NaA supports and show certain selectivity for the separation of water from ethanol by PV.