Preparation, Characterization And Properties Of Thermostable Zeolite Membrane

Based on its unique properties, zeolite membrane, the important component of the inorganic membrane, has been paid much attention by immensity scientific researchers. As the application range expanding constantly, it is increasing outstanding that the disadvantage of thermostability is easy to form crack. Because of the closed relationship between the crack and support, especially the opposite coefficient of thermal expansion, it is maybe a good idea to reduce the coefficient of thermal expansion and increase the chemical compatibility at the same time to solve the problem. In the thesis, the mordenite (MOR) powder, synthesized from diatomite, is used as raw material for the porous support with secondary structure of MOR and low coefficient of thermal expansion by the cold isostatic pressing-calcination technology. The porous support is also used to prepare the MOR and ZSM-5 membranes for the study of thermostability. The N2 permeation, porosity, pore size and distribution, cross-bending strength, thermal expansion coefficient, Raman spectrum, XRD and SEM are used to characterize the properties and to study the best preparation technology of porous support. The single gas permeation, binary gas mixture separation, XRD and SEM are used to characterize the separation properties, thermalstability and study the growth mechanism of MOR and ZSM-5 membrane. The main results are as following:(1) The size and distribution, mixing methods, green body molding technology, calcination technology of raw material has important effect to the properties of porous support. The secondary structure of MOR aims to increase the chemial compatibility is kept in the porous support by the low calcination temperature, and also decrease the preparation cost at the same time. The porous support has low coefficient of thermal expansion and enough mechanical strength to the potential industry application.(2) The MOR membrane (i-MOR) was prepared by template-free in-situ hydrothermal synthesis on the porous support with secondary structure of MOR. The best crystallization conditions are 170℃,12 h and the composition of crystallization gel is 1 Na2O:2 SiO2:285 H2O. It can be decreased the preparation cost by stirring the crystallization gel and reusing the crystallization waste. The membrane layer is formed by the crystals, growing from the support and increasing the binding force, and which one, nucleating and growing in the liquid phase. The former also connects the membrane layer and support to an organic integer, which increases the strength between membrane and support, and makes the membrane system possessing good integrity, thermostability and thermal cycling resistance.(3) The MOR membrane (s-MOR) with good thermostability and reproducibility was prepared by template-free seed hydrothermal synthesis. The seed provides the more aluminum source and nucleation, decreases the crystallization time and membrane layer thickness, but doesn’t change the original hydrothermal growth mechanism. The s-MOR membrane also has good integrity, thermostability and reproducibility.(4) The ZSM-5 membrane was prepared by template-free seed hydrothermal synthesis. The composition of crystallization gel is abtained by orthogonal experiment, and the crystallization temperature at 180℃ and longer crystallization time are beneficial for the ZSM-5 membrane growth. The ZSM-5 membrane also has similar growth mechanism and membrane structure with MOR membrane, which make the membrane possessing good integrity and thermostability.