Preparation And Hydrophobic Modification Of Silicalite-2 Zeolite Membrane And Study On Its Separation Properties Of Ethanol/Water

Zeolite membranes are widely studied and used for their excellent thermal,chemical and mechanical stability.Silicalite-2 zeolite membrane can be used as potential excellent zeolite membrane material because of special straight channels and strong hydrophobic property due to the absence of Al element in the framework.Hydrophobic modification of membrane materials is an effective way to improve the separation performance for ethanol/water mixtures.The objective of this thesis is to prepare silicalite-2 zeolite membrane with good hydrophobicity and to improve its pervaporation performance of ethanol/water mixture,as a result,promoting resolution of intermittent production problem in fermentation for ethanol production.In this dissertation,the growth law of silicalite-2 zeolite molecular sieve was explored firstly,and then nano silicalite-2 zeolite was successfully prepared.Silicalite-2 zeolite membranes were synthesized on macroporous alumina support by secondary growth method.On this basis,the strategies to enhance the hydrophobic properties of zeolite membranes by loading of silica and modifying by trimethylchlorosilane were explored for the first time.The prepared zeolite membranes were applied to the separation of ethanol/water mixtures.(1)The growth law of silicalite-2 zeolite was found by adjusting the dosage of template,water content,alkalinity,crystallization temperature and crystallization time.At last,homogeneous and pure phase nano silicalite-2 zeolite seeds were synthesized from a clear solution of 1TEOS: 0.35TBAOH:12H2O: 0.01 NaOH at 120? for 72 h.(2)1?m and <100 nm silicalite-2 crystals were used as large and small seeds.With a varying temperature hot dip-cocating seeding method,cheap macroporous alumina tubes were coated with silicalite-2 crystals.Then the silicalite-2 zeolite membrane was prepared by secondary growth method.The effects of crystallization temperature,water content and crystallization time were examined in detail.The pervaporation performances of silicalite-2 zeolite membranes for 5% ethanol/water mixture were investigated at 60?.The results revealed that silicalite-2 zeolite membranes were synthesized at 175? for only 24 h which was shortened by 2-3 times compared with that of literatures.The membrane exhibited a high permeation flux of 7.78 kg·m-2·h-1 and a separation factor of 5.63.(3)A simple and effective zeolite membrane hydrophobic modification technique was designed to improve the hydrophobicity of silicalite-2 zeolite membrane.With this technique,a layer of silica particles were pre loaded on the surface of the zeolite membranes,and then trimethylchlorosilane was used to modify the membranes to enhance their hydrophobicity.The effects of preparation conditions of silica sol and modification reaction conditions of trimethylchlorosilane were investigated in detail.The structural properties of silicalite-2 zeolite membranes were characterized by X-ray diffraction,scanning electron microscope,FT-IR,contact angle measurements and pervaporation.The results showed that the new technique of silica supported and using TMCS surface modification significantly improved hydrophobicity of zeolite membrane.The water contact angle of the zeolite membrane modified under the optimum conditions reached 127.5°,which is higher than that of modified by using only TMCS.In addition,the zeolite membranes were smoother,denser and less defects after the loading of silica.The modified zeolite membrane exhibit a high pervaporation performance with the permeation flux of 3.67 kg·m-2·h-1and ethanol/water separation factor of 31.4.