ACTIVATED CARBON FOR GAS SEPARATION AND STORAGE

Activated carbons offer a large spectrum of pore structures and surfac e chemistry for adsorption of gases, which are being used to design pr actical pressure swing and thermal swing adsorption processes for sepa ration and purification of gas mixtures. The activated carbons are oft en preferred over the zeolitic adsorbents in a gas separation process because of their relatively moderate strengths of adsorption for gases , which facilitate the desorption process. Three commercial applicatio ns of activated carbons, (a) trace impurity removal from a contaminate d gas, (b) production of hydrogen from a steam-methane reformer off ga s, and (c) production of nitrogen from air, are reviewed. Four novel a pplications of activated carbons for gas separation and purification a re also described. They include, (a) separation of hydrogen-hydrocarbo n mixtures by selective surface flow of larger hydrocarbon molecules t hrough a nanoporous carbon membrane produced by carbonization of a pol ymer matrix, (b) gas drying by pressure swing adsorption using a water selective microporous carbon adsorbent produced by surface oxidation of a hydrophobic carbon, (c) removal by selective adsorption and in-si tu oxidation of trace volatile organic compounds from air by using a c arbon adsorbent-catalyst composite, and (d) storage of compressed natu ral gas on high surface area carbons.