Preparation And Functional Modification Of Silicalite-1 Zeolite Membrane For Acetic Acid Dehydration

Acetic acid is an important chemical raw materials,widely used in medicine,dyes,pesticides,synthetic fibers and other industries.China is the world's largest acetic acid producing countries.Byproduct water is produced during the acetic acid production process.However,conventional distillation methods for acetic acid dehydration have higher energy consumption.Pervaporation is a new low-energy,high-efficiency separation technology,especially for the dehydration of the high concentrations of organic matter contain a small amount of water by the zeolite membrane pervaporation separation technology.Comparing to traditional distillation,pervaporation can reduce energy consumption by about 60%.NaA,T-type and other aluminum-containing zeolite membranes have excellent hydrophilicity and are widely used for the dehydration of organic solvents in neutral environments.However,these aluminum-containing zeolites have poor stability in acidic environments.Therefore,it is necessary to prepare a hydrophilic and acid resistant zeolite membrane.The dense silicalite-1 zeolite membrane was prepared on low cost tubular macroporous ?-Al₂O₃ support by secondary method from ultradilute solutions.The silicalite-1 zeolite membrane was modified by ionic liquid to increase the hydrophilicity of the zeolite membrane and improve the pervaporation performance of the zeolite membrane for acetic acid dehydration.The main conclusions of this thesis were as follows:?1?A hydrophilic silicalite-1 zeolite membrane was prepared in the synthesis solution with molar ration 1SiO₂:0.1TPABr:0.17TPAOH:650H₂O by crystallization at 175? for 4 h.Since the prepared zeolite membrane was not subjected to high temperature calcination,the surface and intercrystalline pores of the membrane retained a large amount of hydrophilic silicon hydroxyl groups,so that the intercrystalline pores had good permselectivity for water molecular.The total flux is higher than 0.03 kgm-2h-1 and the permeated side water content is more than 98.0wt%,for pervaporation dehydration of the 90wt% HAc/H₂ O solution at 75?.The Silicalite-1 zeolite membrane prepared in the fluorine-containing system has better hydrophilicity.?2?A high performance silicalite-1 zeolite membrane was prepared in the solution with molar ration 1SiO₂:0.1TPABr:0.17TPAOH:1000H₂O by crystallization at 175? for 24 h.The total flux and separation factor?ethanol/water?were 4.09 kg·m-2·h-1 and 47,respectively,for separating 5wt% ethanol/water at 60? by pervaporation.Results showed that the seed layer prepared with 0.4 ?m seeds had higher crystal nucleus density which could increase the amount of the nucleation site on the support surface,and thus resulted in a stronger induced effect for the growth of zeolite membrane.The low-concentration template and silicon source in ultradilute solution will decrease the growth rate of zeolite crystals,which can not only reduce the zeolite membrane thickness but also effectively inhibit the formation of intercrystalline defects.?3?Silicalite-1 zeolite membrane was functionally modified by ionic liquids to increase the hydrophilicity of surface of the membrane.The silicalite-1 zeolite membrane modified with N-methylimidazolium tetrafluoroborate was used for the pervaporation dehydration of 90 wt% HAc/H₂ O solution at 75?,the water content of the permeated side was increased from 6.0 wt% before modified to 75wt%,and the pervaporation performance of the modified membrane was stable during the continuous 96 h test,the total flux was always greater than 0.3 kgm-2 h-1,and the water concentration in the permeated side was higher than 75 wt%.