Preparation of High Performance Zeolite T Membrane and Pervaporation Application
Author:Luo Yi Wei
Supervisor:yang jian hua
Dehydration of organic solution under acid environment is essential for industial demanding,and developing the high performance separation membrane with high acid resistance is very important in membrane research field.Zeolite membranes with high mechanical,thermal stability,organic resistance and selectivity show great potential for industrial separation under harsh conditions.T type zeolite with Si/Al ratio 3～4 and pore size 0.36 nm×0.51 nm possess good acid-resistance while remaining hydrophilic,which promote the industralization of zeolite T membranes.In this work,in order to solve the problem that NaA zeolite membrane is unbearable in acid conditions,the preparation and dehydration performance of zeolite T membranes were studied based on the controlling of zeolite T membrane microstructure.High performance zeolite T membranes were prepared through epitaxial growth mechanism,and the influences of zeolite T seeds layer microstrucre on the performance of zeolite T membranes were investigated.Moreover,the hydrothermal stability and acid resistance of the as-prepared zeolite T membranes were tested and explored.The research contents and results were listed as below.(1)Zeolite T membranes are generally synthesized by secondary growth method,and the key factor of influences on zeolite T membrane performance is the seeds layer microstrure.Here,the crystallizaiton time and temperature,the ratio of hydroxide,different heating ways,way of preparing synthesis gel etc.were investigated to understand the crystal growth process.Finally,different sizes and shape zeolite T crstals were synthesized.(2)The concentration of different ingredients in synthesis gel will affect the formation of zeolite membranes,thus the optimization of synthesis gel composition is very important.The water ratio,alkalinity and silica concentration effects on the performance of zeolite T membranes under high crystallization temperature were investigated.The optimized synthesis gel was obtained as 1 SiO2:0.05 Al2O3:0.26 Na2O:0.09 K2O:35 H2O at 150 ℃ crystallization for 4 h.(3)Tracking the membrane growth process at various synthesis time revealed that the dense zeolite T membrane formed via epitaxial growth of seeds in a-and b-planes with closure of voids between the seeds.The crystallization temperature,seeds size and shape on the performance of zeolite T membranes were investigated.The investigation of crystallization temperature 100～150 ℃ effects on the formation of zeolite T membranes showed that the membrane growth rate was different for different crystallization temperature while displayed the same growth mechanism.The investigation of seeds size of 0.4～3 pm and spherical shape effects on the formation of zeolite T membranes showed that the membranes formation is governed by epitaxial growth,not affected by the seed size and morphology.The dense membranes can be obtained by smaller crystal size seeds.(4)In order to overcome the difficulties of seeding on the hollow fibre support,the varying-pressure vacuum seeding method was proposed.High performance oriented zeolite T membranes were prepared by epitaxial growth,through the controlling of nuclei formation and crystal growth rate on hollow fibber support.The permeation fluxes and separation factors of zeolite T membranes on hollow fibber were as high as 9.8 kg·m-2·h-1 and 3790 for the dehydration of 90 wt.%isopropanol/10 wt.%water mixtures at 75 ℃.Besides,high performance oriented zeolite T membranes were prepared by epitaxial growth through the controlling of nuclei formation and crystal growth rate on Al2O3 support,and the same method is also successfully applied on mullite support.The prepared zeolite T membranes on both supports displayed high pervaporation performance with flux>5.8 kg·m-2·h-1 and separation factors>10000 for 90 wt.%isopropanol/10 wt.%water mixtures at 75 ℃.(5)The time-dependent dehydration of as-synthsized zeolite T membranes for organic/water mixtures(such as isopropanol/water,ethyl acetate/water)was explored,which showed good hydrothermal stabilities.The vapor permeation of zeolite T membranes showed stable separation performance compared to the flux decreasing of pervaporation,which probably due to the less water adsorption in zeolite pores and fast diffusion under high temperature vapor phase sepration.The time-dependent separation performance of as-synthesized zeolite T membranes in acid environmental,such as medium acid intensity of isopropanol/acetic acid/water mixture and strong acid intensity of tetrahydrofuran/hydrochloric acid/water mixture,was also investigated.The membranes displayed good acid resistance,and the acid content were not found in the permeate side,which will promote the industrialization and broad commercialization of zeolite T membranes.