Zeolites vapor transport

Hgl2 is also a typical semiconductor material, and it is also easy to vaporize after thermal treatment. Therefore, Hgl2 may be loaded into various zeolites through a vapor-transportation approach. Because of the confinement of the zeolite framework, Hgl2 in zeolites may exhibit distinct quantum-size effects. The electronic transition absorption spectrum of Hgl2 loaded in AlPOs-5 single crystals shows an apparent blue-shift, and in... 

Polycrystalline zeolite membranes consist of inter-grown zeolite crystals with no apparent cracks or pinholes (Fig. lA). These films are composed of only zeolite (i.e., there are no non-zeolite components such as amorphous silica or polymer). They are normally supported on a substrate although free-standing films have also been synthesized. Membranes can be prepared on different substrates such as silicon wafer, quartz, porous alumina, carbon, glass, stainless steel (SS), gold, etc. Polycrystalline films are primarily prepared by hydrothermal synthesis methods including in situ crystallization, seeded growth,and vapor transport, " and have potential use in all of the applications discussed in this entry. 

The present review of zeolite membrane technology covers synthesis and characterization methods as well as the theoretical aspects of transport and separation mechanisms. Special attention is focused on the performance of zeolite membranes in a variety of applications including liquid-liquid, gas/vapor and reactive... 

Zhang, Y. W., Okubo, T. and Ogura, M. Synthesis of mesoporous aluminosilicate with zeolitic characteristics using vapor phase transport, Chem. Commun. 2005, 2719-2720. 

First results on n-complexation sorbents for desulfurization with Ag-Y and Cu(I)-Y zeolites have been reported recently [3,4]. In this work, we included the known commercial sorbents such as Na-Y, Na-ZSMS, H-USY, activated carbon and activated alumina (Alcoa Selexsorb) and made a direct comparison with Cu(l)-Y and Ag-Y which were the sorbents with n-complexation capability. Thiophene and benzene vapors were used as the model system for desulfurization. Although most of these studies can be applied directly to liquid phase problems, Cu-Y (auto-reduced) and Ag-Y zeolites were also used to separate liquid mixtures of thiophene/benzene, thiophene/n-octane, and thiophene/benzene/n-octane at room temperature and atmospheric pressure using fixed-bed adsorption/breakthrough techniques. These mixtures were chosen to understand the adsorption behavior of sulfur compounds present in hydrocarbon liquid mixtures and to study the performance of the adsorbents in the desulfurization of transportation fuels. Moreover, a technique for regeneration of the adsorbents was developed in this study [4]. 

In many studies the separation factor, which is indicative of the membrane s ability to separate two gases in a mixture, is predominantly governed by Knudsen diffusion. Knudsen diffusion is useful in gas separation mostly when two gases are significantly different in their molecular weights. In other cases, more effective uansport mechanisms are required. The pore size of the membrane needs to be smaller so that molecular sieving effects become operative. Some new membrane materials such as zeolites and other molecular sieve materials and membrane modifications by the sol-gel and chemical vapor deposition techniques are all in the horizon. Alternatively, it is desirable to tailor the gas-membrane interaction for promoting such transport mechanisms as surface diffusion or capillary condensation. 

To avoid pinholes and cracks, Matsukata et al. [46] optimized the density of the precursor phase by using a dry gel instead of a solution. This was achieved through the use of a slipcasting method. A dry porous alimina plate of 2.2 cm was dipped into a gel whereby the support surface was covered with an amorphous aluminosilicate phase. After drying, the sample was exposed to template vapor, triethylamine, ethylenediamine and steam (the Vapour-phase Transport Method). However, the zeolite layer (20 pm thick) consisted of a mkture of ZSM-5 and Ferrierite. Nitrogen and oxygen permeation were studied. 

Supported zeolite membranes have been prepared using numerous procedures [4] such as alignment of crystals in electrical fields, electroplating, self-assembly, growth on organic molecular layers, covalent linkages, hydrothermal synthesis (in situ and ex situ), hydrothermal method microwave heating assisted, dry gel method (vapor-phase transport method and steam-assisted crystallization), synthesis at the interface between two fluid phases, etc. 

The transport mechanisms through zeolite membranes depend on different variables such as operation conditions (especially temperature and pressure), membrane pore size distribution, characteristics of the pore surface of the zeohtic-channel network (hydrophilicity/hydrophobicity ratio), as well as the characteristics of the crystal boundaries and the characteristics of the permeating molecules (kinetic diameter, molecular weight, vapor pressure, heat of adsorption), and their interactions in the mixture. 

Matsufuji T, Nishiyama N, Matsukata M, and Uyama K. Separation of butane and xylene isomers with MFI-t5fpe zeolitic membrane synthesized by a vapor-phase transport method. J Membr Sci 2000 178 25-34. 

M.H. Kim, H.X. Li, and M.E. Davis, Synthesis of Zeolites by Water-Organic Vapor-phase Transport. Microporous Mater., 1993, 1, 191-200. 

N. Nishiyama, K. Ueyama, and M. Matsukata, Synthesis of Defect-free Zeolite-alumina Composite Membranes by a Vapor-phase Transport Method. Microporous Mater., 1996, 7, 299-308. 

Specifically for the preparation of zeolite films, zeolite nanoparticles could be used directly to form zeolite films by self-assembly. They could also be combined nicely with the seeded growth and vapor phase transport method to produce high quality polycrystalline zeolite films. There is clear evidence that small zeolite nanoparticles are preferred for producing compact continuous films. 

Nishiyama. N. Ueyama, K. Matsukata. M. Synthesis of defect-free zeolite-alumina composite membranes by a vapor—Phase transport method. Microporous Mat. 1996. 

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