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.
对Na Y分子筛进行Ce4+交换改性,获得Ce Na Y载体,继而负载Au制备一系列Au/Ce Na Y催化剂。采用电感耦合等离子光谱分析仪(ICP-OES)、N2物理吸附仪、X线衍射仪(XRD)、高分辨透射电子显微镜(HRTEM)和H2程序升温还原(H2-TPR)等方法对负载纳米Au催化剂进行表征,并考察催化剂的水汽变换反应活性。结果表明:随着载体中Ce4+含量增加,催化剂的Au负载量逐渐提高,比表面积和孔容显著下降,且纳米Au颗粒均匀地分散于分子筛载体上。Au/Ce Na Y比Au/Na Y具有更高的水汽变换反应活性,且Au/Ce Na Y催化剂的反应活性随载体中的Ce4+含量的增加而提高。在350℃时,Au/Na Y的反应活性为2.6 mol/(mol·h),而Au/Ce Na Y的反应活性高达33.2 mol/(mol·h)。
A hollow-fiber-supported stable Au/FAU catalytic membrane was successfully synthesized through a polydopamine coating modification-removal strategy and used as a flow-through catalytic membrane reactor for preferential oxidation of CO.Small Au nanoparticles can be efficiently isolated by dopamine and the dopamine-derived carbon shells.The interactions between Au nanoparticles and zeolite layer support are enhanced during annealing at high temperature under an inert atmosphere.A zeolite membrane supported Au nanoparticle catalyst was obtained after the removal of carbon shells,which showed high catalytic activity and stability for the removal of CO from hydrogen.
Li PengLimin WangFeng ZhuJinyun LiuWenfu YanXuehong Gu
