Synthesis,Characterization And Separation Properties Of Ultramicroporous Zeolite Membranes

As a new highly efficient separation technology,membrane separation technology is widely used in chemical industry,food,biological technology and separation etc.Zeolites are a kind of crystalline materials with regular pore structures.Benefited by diverse pore structure,adjustable acidity and alkalinity,good thermal stability and chemical stability,zeolites has been widely used in different areas such as gas adsorption,catalysis,ion exchange,photoelectric materials,and membrane materials etc.In this thesis,we have designed and prepared various types of zeolite membranes with small pores to examine their application in gas and liquid separation.The main work includes the following contents:1.We prepared the AlPO₄-18 membrane by a seed growth method on the stainless steel-net substrate.The high-quality membrane showed an outstanding seawater desalination performance in terms of excellent ion rejection and record water flux.This is due to small pore size of the zeolite,and hydrated salt ions with larger dynamic diameters were rejected and did not pass the membrane freely.The water flux was as high as 2.14-3.37 kg·m^-1·h^-1,which exceeded the previous zeolite membranes for seawater desalination.Combination with theoretical calculation and experimental data,we concluded that the higher water flux cound be affected by the high water solubility and higher effective diffusion coefficient synergistically.In addition,the zeolite membrane showed higher stablitiy for water desalination.2.The prepared AlPO₄-18 membrane was also used for the separation of Kr/Xe gas mixture.The separation factor is 4.0 for the mixture and the permeability is 4×10^-8mol·m^-2·s^-1·Pa^-1 for Kr.The seving effect and the stronger adsorption of Xe than Kr accounted for the selectivity for Kr over Xe on the zeolite membrane.3.We exteneded the preparations of NaA and Silicalite-1 zeolite membranes by the seeding method,and employed pervaporation techniques to investigate the differences on seawater desalination efficiency among AlPO₄-18?NaA and Silicalite-1 zeolite membranes.All of the three type zeolite membranes exhibited good rejection higher than 99.4%.Essential influence factor of membrane materials on seawater desalination efficiency was identified.This work provides an experimental and theoretical basis of the molecular sieves in the application of seawater desalination.4.The SAPO-34 zeolite membranes were prepared using the same method of seeded growth on stainless-steel-mesh substrates,and then were used for the separation of C₂H₆/C₂H₄gas mixture.The separation factor for the C₂H₆/C₂H₄ is about 2.0 and just higher than the kundsen diffusion coefficient,which demonstrates that the prepared SAPO-34 zeolite membranes were continuous.