Scalable and Ultra-Selective Carbon Molecular Sieve (CMS) Membranes for Challenging Gas Separations

Scalable and Ultra-Selective Carbon Molecular Sieve (CMS) Membranes for Challenging Gas Separations

Chen Zhang, William J. Koros

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

Carbon molecular sieve (CMS) membranes have received increasing attention in the past years for advanced gas separations. CMS membranes can be formed into asymmetric hollow fibers, by controlled pyrolysis of polymeric precursor hollow fiber membranes, and are capable of delivering simultaneously attractive productivity and separation efficiency without compromising scalability. Pyrolysis temperature is among the parameters that control CMS membrane's ultramicropore size distribution and therefore, gas separation performance. In general, more densely packed sp²-hybridized graphene-like sheets with lower permeability and higher selectivity are obtained with increasing pyrolysis temperature. For example, previous studies¹ showed that CO₂/CH₄ selectivity of Matrimid^®-derived CMS membranes was enhanced by 200% as pyrolysis temperature increased from 650 ^oC to 800 ^oC.

Nevertheless, formation of CMS membranes at pyrolysis temperatures above 800 ^oC has been rarely reported. This was partially due to challenges involved with processing brittle CMS dense films. We have discovered that this challenge can be successfully overcome by using hollow fiber precursors instead of dense film precursors. This talk will present CMS hollow fiber membranes formed at pyrolysis temperatures above 800 ^oC. Gas permeation measurements suggested that these CMS hollow fiber membranes were capable of delivering superior selectivities that are well-above the polymer upper bound.

References:

1.            (a) Bhuwania, N.; Labreche, Y.; Achoundong, C. S. K.; Baltazar, J.; Burgess, S. K.; Karwa, S.; Xu, L.; Henderson, C. L.; Williams, P. J.; Koros, W. J., Engineering substructure morphology of asymmetric carbon molecular sieve hollow fiber membranes. Carbon 2014, 76 (0), 417-434; (b) Ning, X.; Koros, W. J., Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation. Carbon 2014, 66 (0), 511-522.