Gas Separation by Carbon Membranes

School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 

Zeolite and other membranes are of particular interest for gas separation due to their potentially excellent separation efficiency and stability. Carbon membranes have the greatest potential of these nontraditional materials because of the relative ease of their formation. 

Several reviews of carbon molecular sieve (CMS) membranes have been presented (Ismail and David, 2001 Saufi and Ismail, 2004). This chapter is a broad overview and considers the modes of transport in carbon membranes, the formation processes used for fabrication, and the separation performance of several membranes, in particular membranes produced in the last 10 years. In addition, emerging efforts to produce industrial-scale carbon membranes will also be reviewed. 

The most common technique used to form carbon membranes is thermal decomposition of polymer precursors. When a polymer is thermally decomposed, it can either form coke or char. Coke can be heated further to form a graphitic stmcture while char remains in 

Advanced Membrane Technology and Applications. W. S. Winston Ho, and T. Matsuura Copyright 2008 John Wiley Sons, Inc. 

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Sircar, S. Rao, M.B. Nanoporous carbon membranes for gas separation. In Recent Advances on Gas Separation by Microporous Membranes Kanellopoulos, N., Ed. Elsevier Amsterdam, The Netherlands, 2000 473 96. 

Wang L-J and Chau-Nan Hong F. Carbon-based molecular sieve membranes for gas separation by inductively-coupled-plasma chemical vapor deposition. Micropor. Mesopor. Mat. 2005 77 167-174. 

The pure gas tests are normally used to indicate the ideal separation performance for carbon membranes. However, the separation properties will be affected by the presence of other penetrants in a gas mixture. Since the transport for gas mixture will be much different from that in pure gas, especially in the presence of strong adsorbable gas like CO2, the adsorption of gas molecules in carbon membranes matrix will significantly affect the penetration of other less or... 

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. 

The gas permeability of membranes can be measured by means of a two-chamber cell, as shown in Fig. 6.9. The two chambers have different pressures of up to 10 bar, and are separated by a membrane sample, which is supported by porous carbon or metallic mesh and sealed by, e.g., Viton gaskets [29]. 

PFA was rrsed exterrsively as a precnrsor dnring the preparation of nanoporons carbon (NPC) merrtbrane for gas separation by Foley and co-workers [52-58]. An early work had rmcovered the rrse of a spray-coating techniqne in order to prodnce a thinlayer of NPC inthe pororrs snrface of a stainless steel disk snpport [51,54]. Selectivity for O2/N2 separation of np to 4 was achieved for the snpported membrane carborrized at 600°C in flowing helitrm [54]. Later Foley arrd co-workers improved their preparation techrrique by using an ultrasonic deposition system which conld rrrriformly distribute the polymeric solution on to the support [52, 53, 57], They have fabricated a number of thin film supported nonporous carbon membranes... 

SO /CH ) are common industrii gas separations that utilize membrane technology. MMMs have been developed for gas separation processes in which different types of polymers and rigid filler materials such as zeolite were used for the preparation [68-70]. Here, selectivity is achieved by a combination of permeation rates of the desired gas through the polymer and the filler material [67]. Molecular sieves were initially incorporated by dispersion of zeolites in rubber polymer [71]. Furthermore, the dispersion of zeolite in glassy polymers has been studied [72,73]. Carbon nanotubes have recently been used as dispersed materials in the production of MMMs for gas separation [73-76]. 

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