Carbon molecular sieve membranes permeance

Sofer et al. ° is one of the earliest works in this topic. These membranes are important due to the improved trade-off upper limit between permeabiUty and selectivity compared with their polymer precursor membranes. Singh-Ghosal and Koros reported the Robeson s plot (Oj/Nj selectivity versus O2 permeability) for some carbon membranes and corresponding polymer membranes (Fig. 10.2). It is obvious that the performance of carbon membranes is much better than that of corresponding polymer membranes. Moreover, the permeance of the carbon membranes depends on the surface characteristics and the interactions between pores and gas molecules rather than on the bulk properties as for the polymer membranes. When carbon membranes separate molecules based on the molecular-sieving mechanism, the molecules have to overcome an energetic barrier created by the differences between pore dimension and gas molecules. 

Although carbon membranes are still in their infant stage, and have some serious challenges such as weak mechanical strength for unsupported membranes and bad controllability and reproducibihty of the fabrication for supported membranes, they are believed to be promising candidates for porous membrane based membrane reactors because of their ease of fabrication, low cost of both fabrication and raw materials, molecular-sieve separation effect and high permeance. 

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