High Molecular Permeance in a Poreless Ceramic Membrane

Gu, Yu; Oyama, S. Ted

doi:10.1002/adma.200602637

Cited by 101 publications

(79 citation statements)

References 37 publications

(41 reference statements)

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“…The activation energy can be determined by interactions between permeating molecules and the pore wall, based on the Lennard-Jones potential using the size (membrane pore size, molecular size of permeating molecules) and the interaction parameters. 35,36 Recently, Oyama et al 43,44 applied a different type of permeation equation, which was originally proposed by Barrer and Vaughan, 45 to the analysis of gaseous permeance through microporous silica membranes prepared by the CVD technique. Although the physical meaning of this permeation equation is clear, at least three parameters are required.…”

Section: Resultsmentioning

confidence: 99%

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

et al. 2011

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Silica and cobalt-doped silica membranes that showed a high permeance of 1.8 Â 10 À7 mol m À2 s À1 Pa À1 and a H 2 /N 2 permeance ratio of $730, with excellent hydrothermal stability under steam pressure of 300 kPa, were successfully prepared. The permeation mechanism of gas molecules, focusing particularly on hydrogen and water vapor, was investigated in the 300-500 C range and is discussed based on the activation energy of permeation and the selectivity of gaseous molecules. The activation energy of H 2 permeation correlated well with the permeance ratio of He/H 2 for porous silica membranes prepared by sol-gel processing, chemical vapor deposition (CVD), and vitreous glasses, indicating that similar amorphous silica network structures were formed. The permeance ratios of H 2 /H 2 O were found to range from 5 to 40, that is, hydrogen (kinetic diameter: 0.289 nm) was always more permeable than water (0.265 nm).

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Section: Resultsmentioning

confidence: 99%

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

et al. 2011

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“…The second is a membrane in which a thin, amorphous silica film is deposited on top of the first membrane, and thus, in which the γ-alumina portion servers as an intermediate layer, which will be called Membrane II. The synthesis of both membranes followed the procedures described by Gu and Oyama 29), 30) and is presented in the appendix. Briefly, Membrane I utilized a commercial α-alumina support with outer pore size of nominal size 5 nm.…”

Section: Application Of Membrane Theory In the Study Of Membranes Formentioning

confidence: 99%

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Oyama

Yamada

Sugawara

et al. 2011

J. Jpn. Petrol. Inst.

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The major mechanisms of gas permeation through solid membranes are described and the applicable equations describing the permeance are presented. The mechanisms depend on the relative size of the permeating molecules and the diameter of the pores. As pore size decreases the operable mechanisms are Hagen-Pouiselle flow, Knudsen diffusion, surface diffusion, gas-translation, and finally solid-state diffusion. The Hagen-Pouiselle mechanism involves flow through large pores, while the Knudsen mechanism involves collision of molecules with the walls of pores of intermediate size. Surface diffusion deals with movement of molecules trapped in the potential field of the walls of pores of relatively small size, while gas-translation involves molecules that can escape the field, but are constrained by the small pores. Finally, solid-state transport comprises dissolution and transport by diffusion within the solid. These mechanisms are illustrated for hydrogen permeance with the use of two membranes, an alumina membrane with intermediate sized pores and a silica on alumina membrane of dense structure. KeywordsPermeation mechanism, Inorganic membrane, Silica membrane, Solid-state diffusion, Glassy membranes mechanism, Hydrogen However, oftentimes the actual selectivity can deviate strongly from that defined above because of interactions between the species with each other or with the walls of the membranes. For example, the preferred adsorption or absorption of one species in the pores of a membrane can block the passage of other species. Thus, single-gas selectivities should be taken as a limiting case approximation.A fundamental expression for transport in membranes is derived from Fick's First Law, which relates the flux of species i to the concentration gradient. The gradient in turn can be related to the concentration in the inlet, cio and outlet, ciL, of a membrane of thickness L:The diffusivity in Fick's first law is the ordinary molecular diffusivity, Di(c) [m 2 ・s-1 ], which may have a concentration dependence. In the case of membranes an effective diffusivity, De,i is used, where the porosity ε and tortuosity τ of the membrane are included. The tortuosity is a factor that accounts for the increased length of a pore by the presence of twists and turns. For example, if a single straight pore is replaced by one having a single 90° turn, the tortuosity would be 2 or 1.4. In an early treatment the relative diameters of the diffusing molecules, dm, and pores, dP, was taken into account through a restrictive factor KrFor many membranes dm/dp is small, so Kr is unity. There have been many proposed mechanisms with a variety of materials based on various interaction and diffusion processes. These mechanisms are in broad terms distinguished by the ratio of pore diameter dp to kinetic diameter dm of the gas molecule. As the pore diameter becomes smaller, that is with increasing value of dm/dp, the interactions between the molecule and the surface become larger in proportion to the ratio of the area of the surface potential fi...

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“…Ultra-thin silica layers (20-30 nm) were deposited by CVD on alumina graded structures derived from size controlled boehmite sols in the studies of Gu and Oyama [3,25]. The size of the boehmite crystallites were in the 30-950 nm range and was controlled by changing the peptization conditions by using acetic, nitric and hydrochloric acid with H ?…”

Section: Introductionmentioning

confidence: 99%

Sol–gel derived mesoporous and microporous alumina membranes

Topuz

Çiftçioğlu

2010

J Sol-Gel Sci Technol

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Stable polymeric and colloidal boehmite sols were prepared by sol-gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12-25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600-800°C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800°C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values.

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High Molecular Permeance in a Poreless Ceramic Membrane

Cited by 101 publications

References 37 publications

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Permeation properties of hydrogen and water vapor through porous silica membranes at high temperatures

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Sol–gel derived mesoporous and microporous alumina membranes

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