Permeation carbon molecular sieve

Advanced Materials Experimental membranes have shown remarkable separations between gas pairs such as O9/N9 whose kinetic dian ieters (see Table 22-23) are quite close. Most prominent is the carbon molecular sieve membrane, which operates by ultran iicro-porous molecular sieving (see Fig. 22-48c). Preparation of large-scale permeators based on ultran iicroporous membranes has proven to be a major challenge. 

Koresh, J. E. and A. Sofler. 1986. Mechanism of permeation through molecular-sieve carbon. J.C.S. Faraday I 82 2057-63. 

Mixed matrix membranes using carbon molecular sieves. II. Modeling permeation behavior./. Membr. Sd., 211 (2), 335-348. 

The hollow fiber membranes are the optimum choice for gas separation modules due to their very high packing density (up to 30,000 m /m may be attained [1]). Figure 4.21 shows alternative configurations for such modules [108]. Modifications of this configuration exist, where possibility for introduction of sweep gas on permeate side is included, or fibers may be arranged transversal to the flow in order to minimize concentration polarization [109,110]. The hollow fiber membranes are usually asymmetric polymers, but composites also exist. Carbon molecular sieve membranes may easily be prepared as hollow fibers by pyrolysis. 

H.-J. Lee, H. Suda, K. Haraya, and S.-H. Moon. Gas permeation properties of carbon molecular sieving membranes derived from the polymer blend... 

Another kind of membrane material is represented by a group of nanoporous, hydrogen-selective carbon molecular sieve membranes, which exhibit excellent permeation characteristics and hydrogen permeabilities competitive with metallic membranes (Harale et al., 2007). Furthermore, they are unaffected by CO or hydrogen sulfide (H2S) contamination. Nevertheless, their hydrothermal stability is not guaranteed at r > 623 K. 

Wang, K., Suda, H. Haraya, K. (2001). Permeation Time Lag and the Concentration Dependence of the Diffusion Coefficient ofCO in a Carbon Molecular Sieve Membrane. Industrial Engineering Chemistry Research, 40(13), 2942-2946. 

Koresh J, Soffer A (1981) Molecular sieve carbons. Part 3. Adsorpton kinetics according to a surface barrier model. J Chem Soc Faraday Trans 177 (12) 3005-3018 Koresh JE, Soffer A(1983) Molecular sieve carbon permselective membrane. Part I. Presentation of a new device for gas mixture separation. Sep Sci Technol 18 (8) 723-734 Koresh JE, Soffer A(1986) Mechanism of permeation through molecular-sieve carbon membrane. Part 1. The effect of adsorption and the dependence on pressure. J Chem Soc Faraday Trans 1 82 (7) 2057-2063... 

Carbon molecular sieve membranes suitable for gas separation have been prepared by pyrolyzing thermosetting polymers. CMSMs with pore diameter 3-5 A have ideal separation factors, ranging from 4 to more than 170 for various gas pairs [2]. The permeation characteristics of the molecular sieve carbon membrane can be varied by changing the high temperature treatment parameters [8]. 

Suda and Haraya [10] were successful in preparation of flat, asynunetric carbon molecular sieve membranes, which exhibited the highest gas permselectivities among those fabricated in the past research by pyrolysis of a Kapton type PI derived from pyromellitic dianhydride (PMDA) and 4,4 -oxydianiline (ODA). They used the permeation measurements and X-ray powder diffraction to relate the relationship between the gas permselectivity and microstucture of the CMSM. They proposed that the decrease of the interplanar spacing, amorphous portion and pores upon heating might be the origin of the molecular sieving effect . 

Suda H, Haraya K (1997) Gas permeation through micropores of carbon molecular sieve membranes derived from kapton polyimide. J Phys Chem B 101 (20) 3988-3994... 

Hayashi J, Yamamoto M, Kusakabe K, Morooka S (1997) Effect of oxidation on gas permeation of carbon molecular sieve membranes based on BPDA-pp ODA polyimide. Ind Eng Chem Res 36 (6) 2134-2140... 

Kusakabe K, Yamamoto M, Morooka S (1998) Gas permeation and micropore structure of carbon molecular sieving membranes modified by oxidation. J Membr Sci 149 (1) 59-67... 

Suda H, Haraya K (1997) Gas permeation through micropores of carbon molecular sieve membranes derived from kapton polyimide. J PhysChem B 101 (20) 3988-3994 TaniharaN, Shimazaki H, Hirayama Y, Nakanishi S, Yoshinaga T, Kusuki Y (1999) Gas permeation properties of asymmetric carbon hollow fiber membranes prepared from asymmetric hollow fiber. J Membr Sci 160 (2) 179-186... 

Although carbon molecular sieves (CMSs) and zeolites offer very attractive permeation properties and the selectivites are significantly higher than that of polymeric materials, processing challenges and high costs are still hindering their industrial applications. 

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