Carbon molecular sieve high-temperature

Carbon molecular sieve membranes Resistant to contaminants Intermediate hydrogen flux and selectivity Intermediate hydrogen flux and selectivity High water permeability Pilot-scale testing in low temperature WGS membrane reactor application Need demonstration of long-term stability and durability in practical applications... 

More promising for reactive separations involving gas phase reactions appears to be the development and use in such applications of microporous zeolite and carbon molecular sieve (Itoh and Haraya [2.25] Strano and Foley [2.26]) membranes. Zeolites are crystalline microporous aluminosilicate materials, with a regular three-dimensional pore structure, which are relatively stable to high temperatures, and are currently used as catalysts or catalyst supports for a number of high temperature reactions. One of the earliest mentions of the preparation of zeolite membranes is by Mobil workers (Haag and Tsikoyiannis... 

Tenax GC sorbent has a known upper temperature limit of350 °C. It is a commonly used adsobent because of its high upper temperature limit and low background on desorption. Tenax is a porous polymer of 2,6-diphenyl phenol and has a packed density of approximately 0.22 g/mL (60/80 mesh). Chromosorb 106 is a cross-linked polystyrene porous polymer. It has a published upper temperature limit of 250 °C and a packed density of approximately 0.39 g/mL (60/80 mesh). Porapak N sorbent is a styrene/divinyl benzene porous polymer in wich vinyl pyrollidone is added to increase its polarity. The published upper temperature limit of Porapak N is 190 °C. Porapak N has a packed density of approximately 0.42 g/mL (60/80 mesh). Carbosieve B sorbent is a synthetic carbon molecular sieve and is one of the most retentive solid adsorbents available. It has an upper temperature limit of at least 400 °C and a packed density of approximately 0.22 g/mL (60/80 mesh). 

A suitable polymer material for preparation of carbon membranes should not cause pore holes or any defects after the carbonization. Up to now, various precursor materials such as polyimide, polyacrylonitrile (PAN), poly(phthalazinone ether sulfone ketone) and poly(phenylene oxide) have been used for the fabrication of carbon molecular sieve membranes. Likewise, aromatic polyimide and its derivatives have been extensively used as precursor for carbon membranes due to their rigid structure and high carbon yields. The membrane morphology of polyimide could be well maintained during the high temperature carbonization process. A commercially available and cheap polymeric material is cellulose acetate (CA, MW 100 000, DS = 2.45) this was also used as the precursor material for preparation of carbon membranes by He et al They reported that cellulose acetate can be easily dissolved in many solvents to form the dope solution for spinning the hollow fibers, and the hollow fiber carbon membranes prepared showed good separation performances. 

Carbon molecular sieves are prepared by the controlled pyrolysis of poly(vinylidene chloride) or sulfonated polymers (Carboxen ). They consist of very small graphite crystallites cross-linked to yield a disordered cavity-aperture structure. Carbon molecular sieves are microporous and of high surface area, 200-1200 m g . They are used primarily for the separation of inorganic gases, C1-C3 hydrocarbons, and for the separation of small polar molecules such as water, formaldehyde, and hydrogen sulfide. Less volatile compounds cannot be desorbed efficiently at acceptable temperatures. 

A zeolite and carbon molecular sieves (CMS) have been examined for N2/CH4 separation. A process using 4A zeolite for this separation was developed by Habgood (1958), but this process was limited to low temperatures (—79 to 0°C) and a high-methane feed content (>90%). Ackley and Yang (1990) have demonstrated the use of carbon molecular sieve (CMS) for separation of N2/CH4 mixtures in pressure swing adsorption (PSA) processes but have also shown that the potential for CMS to achieve the desired pipeline quality (90% methane) is doubtful. The only two promising sorbents are clinoptilolites and titanosilicates, as discussed below. 

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]. 

Petersen J, Matsuda M, Haraya K (1997) Capillary carbon molecular sieve membranes derived from kapton for high temperature gas separation. J Membr Sci 131 (1-2) 85-94 Linkov VM, Sanderson RD, Jacobs EP (1994) Highly asymmetrical carbon membranes. J Membr Sci 95 (1) 93-99... 

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