MOLECULAR-SIEVES FOR AIR SEPARATION

Generally, the commercial separation of air is achieved by cryogenic distillation, pressure-swing adsorption (PSA) or over polymeric membranes. This chapter describes carbon molecular sieves and zeolites that are currently used as adsorbents for the production of nitrogen and oxygen from air by PSA techniques. Carbon molecular sieve (CMS) materials are contrasted with the use of zeolites as molecular sieves for air separation. CMS are amorphous, quasi-graphitic materials that exhibit a high equilibrium capacity for both oxygen and nitrogen, but they are able to discriminate on a kinetic basis for adsorption of these gases. These amorphous carbons are prepared in tonnage quantities with precise control of the pore size distribution in the 3-4-Angstrom region to within 0.2 Angstrom! The preparation and properties of these materials used for the separation of air are described.