Synthesis Of NaA Zeolite Membranes By Dip-Spin Coating Method For O₂/N₂ Gas Seperation

NaA molecular sieve membranes are a kind of microporous material,which have regular three dimensionalpore structure, smaller aperture pore size(~0.41 nm) and strong hydrophilic property, thus NaA zeolite membranes can be used in many separating processes.In this paper, the seeds were prepared by hydrothermal synthsis method in the absence of template agent, at first, the seed layer is formed on the substates, at last, NaA zeolite membranes are made by secondary growth. Then the compactness of molecular sieve membranes were tested by one-component gas penetration and the membranes are used to separation performance of nitrogen and oxygen gas. The effect of the parameters such as the water content, aging time, crystallization temperature and crystallization time on the size of the seeds were investigated. The effect of different coating method such as ultrasonic oscillation method、hot dip- coating method and dip- spin coating method on the quality of seed layers were studied. The effect of synthesis mixture of molar composition, aging time, crystallization temperature and crystallization time on the microstructure of NaA zeolite membranes were investigated. XRD and SEM are used to characterize the materials as synthesized, the main contents are as follows:(1) The size of seeds were regulated by adjusting the water content of synthesis mixture, crystallization temperature and time, aging time by hydrothermal synthsis method in the absence of template agent, the uniform and sub-micron NaA zeolite were obtained with the synthesis mixture of molar composition of Na2O:SiO2:Al2O3:H2O =4:2:1:280, under the conditions of aging 2 d at room temperature, crystallizing 12 h at 90 °C(2) The different coating method including ultrasonic oscillation method、hot dip- coating method and dip- spin coating method were introduced to form the seed layers, in which the seed layer prepared by dip- spin coating method is most efficient in preparing high quality seed layers.(3) The seed layers grew to be NaA zeolite membranes by secondary growth, the effect of the composition synthesis mixture, crystallization temperature, crystallization time and aging time on microstructure of membranes were studied. The results show that the membrane was intergrown and highly compact, which was obtained with the synthesis mixture of molar composition of Na2O:SiO2:Al2O3:H2O =4:2:1:280, under the conditions of the aging time of 3d, the crystallization temperature of 90 °C and the crystallization time of 24 h.(4) the highest quality zeolite membrane was used to the separate oxygen and nitrogen experiments, the separation factor of oxygen and nitrogen was 1.45, with the O2 permeances of 8.14×10-7 mol/(m2·s·Pa) and the N2 permeances of 5.62×10-7 mol/(m2·s·Pa), when the separation was operated at 293 k and the 0.25 MPa, which showed the membrane have the potencial use in the oxygen-enriched air combustion.