Untitled

Oyama, S. Ted; Lee, D.; Sugiyama, Sho; Fukui, Ken–ichi; Iwasawa, Yasuhiro

doi:10.1023/a:1012450029714

Cited by 19 publications

(6 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For the sample with one layer of 40 nm sol, the formation of a silica layer was not complete and there were many visible pinhole defects (Figure 5c), with those at the center of the picture being especially conspicuous. For the sample with successive layers of 80 and 40 nm sols, the surface was formed from continuous rounded structures, which is characteristic of a CVD-derived silica layer (Figure 5d) [59]. In addition, its cross-sectional image revealed that the thickness of the silica layer was about 30-40 nm (Figure 5e), which was similar to that in the previous study.…”

Section: Morphology and Structure Of The Membranessupporting

confidence: 84%

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

et al. 2020

View full text Add to dashboard Cite

Silica-based membranes prepared by chemical vapor deposition of tetraethylorthosilicate (TEOS) on γ-alumina overlayers are known to be effective for hydrogen separation and are attractive for membrane reactor applications for hydrogen-producing reactions. In this study, the synthesis of the membranes was improved by simplifying the deposition of the intermediate γ-alumina layers and by using the precursor, dimethyldimethoxysilane (DMDMOS). In the placement of the γ-alumina layers, earlier work in our laboratory employed four to five dipping-calcining cycles of boehmite sol precursors to produce high H2 selectivities, but this took considerable time. In the present study, only two cycles were needed, even for a macro-porous support, through the use of finer boehmite precursor particle sizes. Using the simplified fabrication process, silica-alumina composite membranes with H2 permeance > 10−7 mol m−2 s−1 Pa−1 and H2/N2 selectivity >100 were successfully synthesized. In addition, the use of the silica precursor, DMDMOS, further improved the H2 permeance without compromising the H2/N2 selectivity. Pure DMDMOS membranes proved to be unstable against hydrothermal conditions, but the addition of aluminum tri-sec-butoxide (ATSB) improved the stability just like for conventional TEOS membranes.

show abstract

Section: Morphology and Structure Of The Membranessupporting

confidence: 84%

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

et al. 2020

View full text Add to dashboard Cite

show abstract

“…3). For the jump distance, d 0.8 nm 36) was used. The vibrational frequency, ν , of each gas species, the activation energy for solid-state permeation, ΔESS, and the number of solubility sites, NS, available for each gas species were calculated.…”

Section: Permeation In the Silica Layermentioning

confidence: 99%

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Oyama

Yamada

Sugawara

et al. 2011

J. Jpn. Petrol. Inst.

View full text Add to dashboard Cite

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...

show abstract

“…30 As the permeance of a membrane is inversely proportional to its thickness, 31 several atomistically thin porous structures aimed for gas separation have been proposed, for example functionalized porous graphene, [32][33][34][35] multilayer carbon-based membranes, [36][37][38] or nanoporous silica. [39][40][41] The effective pore size of graphdiyne can be determined by taking by the van der Waals diameter of the acetylene carbon links, resulting in a triangular pore with a length of $3.8…”

Section: Introductionmentioning

confidence: 99%

Selective hydrogen purification through graphdiyne under ambient temperature and pressure

2012

View full text Add to dashboard Cite

Graphdiyne, a recently synthesized one-atom-thick carbon allotrope, is atomistically porous - characterized by a regular "nanomesh"- and suggests application as a separation membrane for hydrogen purification. Here we report a full atomistic reactive molecular dynamics investigation to determine the selective diffusion properties of hydrogen (H(2)) amongst carbon monoxide (CO) and methane (CH(4)), a mixture otherwise known as syngas, a product of the gasification of renewable biomass (such as animal wastes). Under constant temperature simulations, we find the mass flux of hydrogen molecules through a graphdiyne membrane to be on the order of 7 to 10 g cm(-2) s(-1) (between 300 K and 500 K), with carbon monoxide and methane remaining isolated. Using a simple Arrhenius relation, we determine the energy required for permeation on the order of 0.11 ± 0.03 eV for single H(2) molecules. We find that addition of marginal applied force (approximately 1 to 2 pN per molecule, representing a controlled pressure gradient, ΔP, on the order of 100 to 500 kPa) can successfully enhance the separation of hydrogen gas. Addition of larger driving forces (50 to 100 pN per molecule) is required to selectively filter carbon monoxide or methane, suggesting that, under near-atmospheric conditions, only hydrogen gas will pass such a membrane. Graphdiyne provides a unique, chemically inert and mechanically stable platform facilitating selective gas separation at nominal pressures using a homogeneous material system, without a need for chemical functionalization or the explicit introduction of molecular pores.

show abstract

Untitled

Cited by 19 publications

References 23 publications

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

Synthesis of Silica Membranes by Chemical Vapor Deposition Using a Dimethyldimethoxysilane Precursor

Review on Mechanisms of Gas Permeation through Inorganic Membranes

Selective hydrogen purification through graphdiyne under ambient temperature and pressure

Contact Info

Product

Resources

About