The Preparation Of ZSM-5 Zeolite Membrane For The Dehydration Of Organic/Water Mixtures

Membrane separation technology has important application requirements in organic dehydration system.The theoretical Si/Al ratio of ZSM-5 zeolite membrane is>2.5,so the Si/Al ratio adjustable space is wide,linear and sinusoidal pore diameter of ZSM-5 membrane is 0.53×0.56 nm and 0.51×0.55 nm respectively,which is similar to the dynamic diameter of many organic matter,and suitable for application in the dehydration of organic matter.This paper aims to prepare ZSM-5 zeolite membrane with high quality and low Si/Al ratio.Firstly,the best synthesis scheme of ZSM-5 zeolite membrane by hydrothermal method was explored.Then,ZSM-5 zeolite membrane was innovatively prepared by wet gel conversion method to explore its sensitive factors and optimize the synthesis conditions.Finally,the time and temperature dependence of ZSM-5 zeolite membrane in isopropyl alcohol/water system,ethanol/water system and ethyl acetate/water system were investigated,which realized the preparation of ZSM-5 zeolite membrane with high flux and high stability.The main contents are as follows:（1）ZSM-5 zeolite membrane was prepared by traditional hydrothermal method.The sensitive factors of ZSM-5 zeolite membrane prepared by hydrothermal method were investigated by examining the seeding conditions,crystallization temperature,crystallization time,small seed species and the influence of Na F,When the molar ratio of the synthetic gel is1 SiO₂:0.20 Na₂O:0.05 Al₂O₃:52 H₂O:0.99 Na F,the flux of the prepared membrane for 90wt.%isopropanol/water solution at 75℃is 3.10 kg·m^-2·h^-1,the separation factor is 9991,and the surface Si/Al ratio is 10.8.The membrane was also used to test the time dependence of isopropanol/water system.After 104 h of test,the permeation flux of ZSM-5 membrane was finally stabilized at 2.81 kg·m^-2·h^-1,with the separation factor stable at about 8173.（2）ZSM-5 zeolite membrane was innovatively prepared by wet gel conversion method.The amount of gel used to prepare one ZSM-5 zeolite membrane by wet gel conversion method was one thirty-fourth of that by traditional hydrothermal method,which greatly improved the gel utilization rate and made it more environmentally friendly and economic.The effects of crystallization temperature,crystallization time,silicon source dissolution time and Na F on the preparation of ZSM-5 zeolite membrane by wet gel conversion method were systematically investigated,and the sensitive factors for the preparation of ZSM-5 zeolite membrane were explored.（3）When the molar ratio of the synthetic gel is 1 SiO₂:0.20 Na₂O:0.05 Al₂O₃:52 H₂O:0.99 Na F,crystallization temperature is 175℃,crystallization duration is 72 h,dissolution time of silicon source is 20 h,the ZSM-5 zeolite membrane prepared by wet gel conversion method has the best performance and good repeatability.The high quality membrane has a surface Si/Al ratio of 8.8,a permeation flux of 3.20 kg·m^-2·h^-1 for 90 wt.%isopropanol solution at 75℃,with a separation factor of higher than 10000.（4）The high quality ZSM-5 zeolite membrane was used in the dehydration of isopropanol,ethanol and ethyl acetate to investigate the time dependence.The permeation flux of the membrane was stable at 2.96,0.91 and 2.05 kg·m^-2·h^-1,respectively,the separation factors were>10000,6420 and>10000,respectively.At the same time,the temperature dependence test of these three systems was also performed,and the fluxes of zeolite membranes increased with the increase of the temperature of the feed liquid.