Preparation And Stability Study Of Zeolite T Membrane

Pervaporation is an efficient and energy-saving high-tech,and is widely used in organics dehydration process.Zeolite membranes,which have excellent chemical stability,mechanical strength,corrosion resistance and many other advantages,become the preferred membrane material for pervaporation technology.In the industry,dehydration of organics usually occur under the acidic conditions,in which zeolite NaA membranes with high hydrophilicity are extremely unstable,and the permeation flux decreases rapidly.Though the hydrophilicity of zeolite T membranes is slightly less than zeolite NaA membranes,zeolite T membranes have good acid resistance.Therefore,more and more authors pay attention to the research of zeolite T membranes.The discovery of high-performance zeolite T membranes has become a research hotspot.This work focused on the synthesis of high-performance zeolite T membranes,and explored its hydrothermal stability and acid resistance stability.The main results are showed as follows:?1?The self-synthesized zeolite T with different sizes was used as seeds to modify the surface defects of the support and induce crystal to form into the membrane.The high-quality seed layer was prepared on the macroporous?-Al₂O₃ tubes.And the influence of Si/Al molar ratio under the condition without fluorine on the separation performance of zeolite T membranes was investigated.When the molar ratio of n?SiO₂?/n?Al₂O₃?was 20:1,the permeation flux reached 2.78 kg·m^-2·h^-1 and the separation factor was more than 1000 for separating 90wt.%IPA/H₂O at 348K.?2?High-performance zeolite T membranes were synthesized by adding fluoride salts in the clear solution.The effects of species and content of fluoride salt on the zeolite T membrane have been investigated.Zeolite T membranes synthesized under the condition of n?3NaF:1KF?/nSiO₂=0.25 had good pervaporation performance.Typically,water permeation flux of 4.06 kg·m^-2·h^-1 and 2.30 kg·m^-2·h^-1 with separation factor of 10591 and 3539 was obtained for pervaporation?PV?dehydration of 90wt.%IPA/H₂O and 90wt.%EtOH/H₂O at348K,respectively.And the zeolite T membrane synthesized under this condition has good repeatability.?3?The growth pattern of zeolite T membranes was explored.After hydrothermal synthesis for 1h,zeolite T seeds were arranged neatly on the surface of the support and there was no obvious growth.With increasing in crystallization time to 2 h,the crystal began to grow epitaxially and the crystal dissolved mutually.After 3 h,the crystal grew rapidly with epitaxial growth of the crystal into the rod-like structure.When the time was 4 h,the crystal has grown to be a uniform and dense membrane.And the crystal growth rate in fluoride is faster than without fluorine.?4?The effects of Si/Al ratio on the separation performance of zeolite T membranes were investigated in detail.The results showed that,when zeolite T membrane synthesized in fluoride media was used to separate 90wt.%IPA/H₂O at 348 K,the separation performance was good that the i-propanol/water separation factor was higher than 2000,and the flux was higher than 3.50 kg·m^-2·h^-1.?5?Based on the above exploration,hydrothermal and acidic stability of high-performance zeolite T membranes were studied.Zeolite T membrane synthesized under the condition of n?3NaF:1KF?/n SiO₂=0.25 had good hydrothermal and acid stability in long-term pervaporation test.