Microporous carbon membranes

Despite these failures, microporous carbon membranes continue to be a subject of research by a number of groups [67-70], The selectivities obtained are often very good, even for simple gas mixtures such as oxygen/nitrogen or carbon dioxide/methane. However long-term, it is difficult to imagine carbon membranes... 

R. Ash, R.M. Barrer and P. Sharma, Sorption and Flow of Carbon Dioxide and Some Hydrocarbons in a Microporous Carbon Membrane, J. Membr. Sci. 1, 17 (1976). 

Gibon J and Soffer A. Knudsen diffusion in microporous carbon membranes with molecular sieving character. J. Membr. Sci. 2002 209 339-352. 

Katsaros FK, Steriotis TA, Stubos AK, Mitropoulos A, Kanellopoulos NK, and Tennison S. High pressure gas pemieabiUty of microporous carbon membranes. Microporous Mater. 1997 8(3 ) 171-176. 

Microporous carbon membranes have been developed [59] but their possibilities in high temperature hydrogen separation are still unclear, although it is believed that there are opportunities. Scaling-up of these membranes seems possible from a technical point of view. All these membrane types are potentially suitable for application in the WGS membrane reactor concept, provided their endurance is sufficient. 

Microporous Carbon Membranes for Gas Separations. Brite Euram Project BREU-CT92-0568. Partners BP Research and Eng. Centre (England), NRC Democritos (Greece), SCT (France) and Imperial College (England). 

Microporous carbon membranes with molecular sieving performance were successfully developed through detailed studies on carbonization of polyfimide) films [103-105]. In Fig. 31 are shown the amounts of gas molecules with diflferent sizes adsorbed on carbon films heat-treated at different temperatures. Ethane, with a size of 0.40 nm, permeates in a large... 

Figure 5.5 Schematic models for (a) parallel transport and (b) resistance in series transport [27], Reprinted from Journal of Membrane Science, 209, j. Gilron and /4. Soffer, Knudsen diffusion in microporous carbon membranes with molecular sieving character, 339-352, Copyright (2002), with permission from Elsevier...

Morooka, S., Kusakabe, K., Kusuki, Y., and Tanihara, N. (2000). Microporous carbon membranes, Recent Advances in Gas Separation by Microporous Ceramic Membranes, pp. 323-334, Kanellopoulos, N. K., ed., Amsterdam Elsevier. 

Chen YD, Yang RT (1994) Preparation of carbon molecular sieve membrane and diffusion of binary mixtures in the membrane. Ind Eng Chem Res 33 (12) 3146-3153 Moaddeb M, Koros WJ (1997) Gas transport properties of thin polymeric membranes in the presence of silicon dioxide particles. J Membr Sci 125 (1) 143-163 Ash R, Barrer RM, Lowson RT (1973) Transport of single gases and of binary gas mixtures in a microporous carbon membrane. J Chem Soc Faraday Trans I 69 (12) 2166-2178 Bird AJ, Trimm DL (1983) Carbon molecular sieves used in gas separation membranes. Carbon 21 (3) 177-163... 

Microporous carbon membranes have been prepared [26] by carbonization and activation of an asymmetric phenolic resin stmcture comprised of a dertse resol layer, and supported on a highly permeable macroporous novolak resin tube. 

Ash R, Barter RM, Lowson RT (1973) Transport of single gases and of binary gas mixtures in a microporous carbon membrane. J Chem Soc Faraday Trans I 69 (12) 2166-2178 Bird AJ, Trimm DL (1983) Carbon molecular sieves used in gas separation membranes. Carbon 21 (3) 177-180... 

Sakata Y, Muto A, Uddin MA, Suga H (1999) Preparation of porous carbon membrane plates for pervaporation separation applications. Sep Purif Technol 17 (2) 97-100 Clint JH, Lear AM, Oliver LF, Tennison SR (1992) Membranes. EP Patent 0,474,424 Katsaros FK, Steriotis TA, Stubos AK, Mitropoulos A, Kanellopoulos NK, Tennison S (1997) Fligh pressure gas permeability of microporous carbon membranes. Microporous Mater 8 (3) 171-176... 

Nguyen C, Do DD, Haraya K, Wang K (2003) The structural characterization of carbon molecular sieve membrane (CMSM) via gas adsorption. J Membr Sci 220 (1-2) 177-182 Nguyen C, Do DD (1999) Adsorption of supercritical gases in porous media Determination of micropore size distribution. J Phys Chem B 103 (33) 6900-6908 Katsaros FK, Steriotis TA, Ramanos GE, Konstantakou M, Stubos AK, Kanellopoulos NK (2007) Preparation and characterization of gas selective microporous carbon membranes. Microporous Mesoporous Mater 99 (1-2) 181-189... 

Calculate the values of the surface diffusion coefficient Dis for argon through the two different microporous carbon membranes. 

Consider two gases A and B being separated through a microporous carbon membrane. The gas transport may be described as that by Knudsen diffusion through the microporous membrane as well as by surface diffusion of the adsorbed gtis layer on the pore surface (3.4.112). 

Other methods to prepare porous membranes include pyrolysis for carbon membranes, heat treatment and leaching for mesoporous glass membranes, and anodization for alumina membranes. The microporous carbon membranes are prepared by coating a polymeric precursor such as polyfurfuril alcohol and polycarbosilane on porous substrates, followed by controlled pyrolysis under N2 atmosphere [15]. The carbon membrane structure is determined by the fabrication variables, including the polymeric solution concentration, solvent extraction, heating rate, and pyrolysis temperature [16]. 

The phenomenon of surface diffusion, demonstrated by Barter and Strachan (1955) may be used to advantage for the separation of some hydrogen-hydrocarbon mixtures (Sircar, 1993b). Thus, thin microporous carbon membranes (<5 pm), supported by macroporous sheets of graphite assembled into a plate and frame membrane module, were able to separate H2 at 63% recovery from a refinery waste gas. The feed was passed at high pressure over the membrane unit which preferentially adsorbed the hydrocarbons and facilitated surface diffusion of these species through the membrane to the low pressure side of the module. Adsorption, accompanied by surface diffusion through a thin microporous membrane, thus offers possible future applications. 

---