Adsorption of Gases on Carbon Molecular Sieves Used for Air Separation

Carbon molecular sieves are used in the separation and purification of mixtures of gases, a typical application being the industrial separation of air into oxygen and nitrogen by pressure swing adsorption (PSA). The PSA technique is based on the kinetics of adsorption of O₂ being much faster than N₂ despite their equilibrium adsorption capacities being similar. It has been proposed that the difference in adsorption kinetics is related to molecular size and to investigate this a series of noble gases were selected as probes for the selective porosity responsible for the molecular sieving characteristics in the CMS. The adsorption kinetics were studied as a function of temperature and pressure in order to determine the activation energies and preexponential factors for adsorption in relation to atom size.