Inorganic carbon-based membranes for gas separation comprise materials that are fabricated through pyrolysis of a precursor material (often a synthetic polymer), and the more recently discovered carbon nanotubes. Fabrication, assembly into different architectures, and mechanism of operation are summarized for precursor-based carbon membranes, with a focus on selective surface flow and molecular sieving. Only preliminary work on carbon nanotube-based membranes for gas separation has been published. Their unusual transport properties, however, promise their use in gas separation in the future. In light of this application, structural properties and results relating to flow through these tubular structures are summarized.

Dense metal membranes are a well-developed technology for the production of high-purity hydrogen. The physical mechanism of hydrogen transport across metal films—dissociation of molecular hydrogen, diffusion of interstitial atomic hydrogen, and subsequent recombinative desorption of molecular hydrogen—means that metal membranes can have extremely high selectivities for hydrogen transport relative to other gases. We describe current experimental and theoretical trends in the development of metal alloy membranes for hydrogen purification in practical, chemically robust processes.