Zeolite NaA membrane: Preparation, single-gas permeation, and pervaporation and vapor permeation of water/organic liquid mixtures
Zeolite NaA membrane: Preparation, single-gas permeation, and pervaporation and vapor permeation of water/organic liquid mixtures
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DOI：
10.1021/ie0006007
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发表时间：
2001-01-10
影响因子：
4.2
通讯作者：
Kondo, M
中科院分区：
文献类型：
--
作者：
Okamoto, K;Kita, H;Kondo, M
采用Al2O3:SiO2:Na2O: H2O = 1:2:2:20 20（摩尔数）的凝胶，在多孔氧化铝支撑管中植入NaA沸石晶体，在373 K条件下一次性水热合成了NaA沸石膜，反应时间仅为3 h。外表面形成厚约30微米的致密交错生长的沸石晶体层。沸石NaA膜对水蒸气具有高度渗透性，但除非完全干燥，否则对任何气体都不渗透性。完全干燥的膜表现出由Knudsen扩散引起的气体渗透行为，表明沸石晶体颗粒之间存在间隙或非沸石孔隙。膜对水/有机液体混合物的渗透汽化（PV）和蒸汽渗透（VP）表现出优异的水/透选择性能。随着温度的升高，渗透通量Q和分离因子α均增大，且VP膜的性能明显优于PV膜。在378 K和10 wt %的给水VP下，水/乙醇、甲醇和二氧六环体系的Q值分别为4.5、3.5和7.8 kg/(m(2) h)， a值分别为>30000、5700和>9000。提出了一种基于沸石和非沸石孔隙中水的毛细凝结和其他分子进入孔隙的阻断作用的PV和VP机理。
Zeolite NaA membranes were prepared reproducibly by a one-time-only hydrothermal synthesis with a short reaction time of 3 h at 373 K using a gel with the composition Al2O3:SiO2:Na2O: H2O = 1:2:2:120 (in moles) and porous ex-alumina support tubes seeded with zeolite NaA crystals. A dense intergrown zeolite crystal layer of about 30 mum in thickness was formed on the outer surface. The zeolite NaA membranes were highly permeable to water vapor but impermeable to every gas unless dried completely. The completely dried membranes displayed gas permeation behavior attributed to Knudsen diffusion, indicating the presence of interstitial spaces between the zeolite crystal particles, or nonzeolitic pores. The membranes displayed excellent water/permselective performance in pervaporation (PV) and vapor permeation (VP) toward water/organic liquid mixtures. With an increase in temperature, both the permeation flux Q and the separation factor alpha increased, and the membrane performance was much better for VP than for PV. For VP at 378 K and 10 wt % of feedwater, Q values were 4.5, 3.5, and 7.8 kg/(m(2) h) and a values were >30000, 5700, and >9000 for the water/ethanol, /methanol and /dioxane systems, respectively. A mechanism of PV and VP based on the Capillary condensation of water in the zeolitic and nonzeolitic pores and the blocking of other molecules from entering the pores was proposed.