NaA zeolite membranes were prepared by secondary growth method on the outer surface of α-Al2O3 hollow fiber supports. Vacuum seeding method was used for planting zeolite seeds on the support surfaces. Hydrothermal crystallization was then carried out in a synthesis solution with molar ratio of Al2O3:Si O2:Na2O:H2O =1:2:2:120 at 100 °C for 4 h. Effects of seeding conditions on preparation of hollow fiber Na A zeolite membranes were extensively investigated. Moreover, hollow fiber membrane modules with packing membrane areas of ca.0.1 and 0.2 m2 were fabricated to separate ethanol/water mixture. It is found that the thickness of seed layer is obviously affected by seed suspension concentration, coating time and vacuum degree. Close-packing seed layer is required to obtain high-quality membranes. The optimized seeding conditions(seed suspension mass concentration of 0.5%–0.7%, coating time of 5 s and vacuum degree of 10 k Pa) lead to dense Na A zeolite layer with a thickness of 6–8 μm. Typically, an as-synthesized hollow fiber Na A zeolite membrane exhibits good pervaporation performance with a permeation flux of 7.02 kg·m-2·h-1and separation factor N 10000 for separation of 90%(by mass) ethanol/water mixture at 75 °C. High reproducibility has been achieved for batch-scale production of hollow fiber Na A zeolite membranes by the hydrothermal synthesis approach.
This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concentration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle.Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.
