Preparation Of Template-free Acid-resistant ZSM-5Zeolite Membrane And The Application In Pervaporation Dehydration

Pervaporation is a new environmental membrane separation technology with highefficiency, low energy consumption and low investment. It is a promising process forazeotropic separation because it is not limited by the vapor-liquid equilibrium. It iswidely used in the dehydration of organic matter, especially the dehydration of alcoholssolvent dehydration. With high thermal stability, acid resistance, and excellentselectivity, the ZSM-5zeolite membrane is ideal for pervaporation separation.Preparation of ZSM-5zeolite membranes with high quality through appropriate routehas become a hot spot on membrane research.In this paper, the secondary growth method was used to prepare ZSM-5zeolitemembranes on α-Al2O3supports without using templating agents. The pervaporationperformances of the membranes were evaluated in isopropanol/water system. Thesynthesis conditions were studied, such as the seed concentration, the number ofcrystallizations, the crystallization time, the molar ratio of Si/Al and the molar ratio ofF/Si. Finally, the ZSM-5zeolite membrane was successfully prepared with conditionsthat pre-seeding and crystallization twice, respectively, the molar ratio of Si/Al was0.7,the molar ratio of F/Si was0.9. The pervaporation performances of the membranes wereimproved by optimizing the synthesis conditions, such as the crystallization time, theseed concentration and the pre-seeding temperature. High-flux and high-selectivityZSM-5zeolite membrane was obtained and the flux and separation factor were1.106kg·m-2·h-1and24991, respectively.The hydrothermal stability and acid resistance of the prepared ZSM-5membraneswere studied. It was found that the separation factor of the membranes was kept above1×104, indicating that there was a high hydrothermal stability with the membranes. Inacidic solution with the pH of about5.8, the influences of operating temperature on thepervaporation performance were studied. The results showed that under conditions atthe operating temperature of70℃and the feed concentration of about97wt.%, the permeation flux is0.287kg·m-2·h-1and the separation factor is3790. After soaking for10d at a water/ethyl acetate solution with the pH of about5.8, the separation factor7894, indicating that there was a high acid resistance with the membranes.The as-synthesized ZSM-5membrane was applied to the dehydration ofisopropanol. When the operating temperature was70℃and the isopropanol was about80wt.%, after dehydration for48h, the concentrations of isopropanol was up to99.613wt.%and the water content of the permeate was always maintained above99wt.%. Theresults indicated that water and isopropanol can be efficiently separated by theas-synthesized ZSM-5membrane.