Carbon Molecular Sieve Membranes: Structure and Gas Separation Applications

William Koros, Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, USA


Following the pioneering work by Koresh and Sofer on molecular sieve carbons in the early 1980’s, progress toward practical membranes for challenging separations has advanced steadily. Characterization beyond traditional microscopy, scattering and spectroscopy is needed to engineer the sub-angstrom discrimination between penetrants in carbon molecular sieve (CMS) membranes. A method based on molecular scale gas diffusion probes is described to assist in engineering relevant membrane properties. The method is also used to test hypotheses about the evolution of structure responsible for fundamental properties of CMS materials derived from a high performance CMS precursor polymer, 6FDA:BPDA-DAM. Linking hypotheses about structural changes likely to occur during pyrolysis with the probe data provides insights regarding transformation of the random coil polyimide into ultra-rigid CMS, with exquisite size and shape diffusion selectivity. The results provide a framework for understanding and tuning properties of this special class of materials with important technological advantages in energy-intensive gas separations.