| As one type of inorganic membranes, zeolite NaA membranes are not only of high solvent-resistant properties, high temperature stability and free of swelling, but also have unique pore structures and are extremely hydrophilic, thus zeolite NaA membranes are widely studied as pervaporation membranes for dehydration of alcohols or other solvents. Majority of the zeolite NaA membranes are synthesized on alumina and stainless steel tubes (O.D.>10mm) or discs by the seeded growth method, recently, α-Al2O3hollow fibers as supports for zeolite NaA membranes have been reported. Many seeding methods have been reported, such as dip-coating, rub-coating and vacuum method. However, none of them is a perfect method for synthesizing zeolite membranes with high pervaporation performance, because it is difficult to form a uniform seed distribution on the support surface. Moreover, the preparation method is complicated being involved in multi-step synthesis, and the reproducibility is not very high.In our laboratory, we have reported a new type of supports for synthesizing zeolite membranes, NaA/polymer composite hollow fibers (CHF), which have uniform zeolite crystals on the surface and can avoid the seeding step. Thus, zeolite membranes with high separation performance can be synthesized on these CHF supports by a simple hydrothermal synthesis with high reproducibility.CHF supports are fabricated from the dope slurry of NaA zeolite, N-methyl-2-pyrrolidone (NMP) and polyethersulfone (PES) using a dry-wet spinning process. Then the supports are used for synthesizing high performance zeolite NaA membranes. The influences of the spinning condition, the zeolite loading and particle size on the properties of the CHF supports and zeolite NaA membranes are investigated in detail. The main experimental results and conclusions are summarized as follows:At first, CHF supports fabricated under different pressure of N2and air-gap are obtained by dry-wet spinning. Then, zeolite NaA membranes are synthesized on the supports. The supports and membranes were characterized by SEM, bending strength tests and water/ethanol pervaporation separation tests. The experimental results indicate that the pressure of N2and air-gap have no significant influence on the seed distribution on support surface, and dense membranes with the separation factor>10,000are all obtained on the supports. The porosity of the support increase with the increase of the air-gap, but decrease with the increase of the N2pressure, which result that the water flux of supports and flux of zeolite membrane both increase with the increase of the air-gap, but decrease with the increase of the N2pressure. A linear relationship between the flux of zeolite NaA membranes and the support porosity was observed.In order to investigate the influences of the zeolite loading and particle size on the properties of the CHF supports and zeolite NaA membranes, CHF supports with two different zeolites (NaAl:4.0μm and NaA2:1.5μm) and different zeolite loadings (70%,75%and85%) were fabricated. Then, zeolite NaA membranes are synthesized on the supports for2-5h. Dense membranes with the separation factor>10,000were obtained on the Z1(4.0μm)-85(85wt%NaA) and Z2(1.5μm)-75supports after the synthesis of5h, while the zeolite membranes obtained on the Z1-70and Zl-75supports had pinholes. A dense membrane with the separation factor>10,000was obtained on the Z2-85support after the synthesis of4h. The results indicate that the CHF supports with smaller zeolite particles were better as the supports for zeolite NaA membranes. The flux of the zeolite membrane on the CHF support increased with the zeolite loading because the increase of the zeolite loading resulted in the increase of the support porosity. However, the increase of the zeolite loading can reduce the mechanical strength of the supports. |
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