High pressure excess isotherms for adsorption of oxygen and argon in a carbon molecular sieve

Adsorption equilibrium data for oxygen and argon are needed for design of adsorptive separation processes to produce pure oxygen from air and also for adsorptive gas storage applications. Carbon molecular sieves may be used to accomplish a rate-based separation of oxygen and argon and, as we show, may also be useful for gas storage. Given the limited data available, particularly at high pressures, volumetric methods are applied in this paper to measure surface excess isotherms of oxygen and argon on a carbon molecular sieve, Shirasagi MSC-3R Type 172. Temperatures are considered from 25 to 100 °C with pressures as high as 100 bar. Isotherms are compared at 25 °C, including new data measured for nitrogen. Adsorbed-phase excess loadings are high, approaching 10 mol/kg at 100 bar. The oxygen capacity of the carbon molecular sieve at high pressure is comparable to that of a superactivated carbon on a mass basis, and it is higher on a volumetric basis. The excess adsorption isotherms are modeled using a multi-temperature Toth equation, which provides an excellent description. A carbon molecular sieve is shown to be a promising adsorbent for oxygen storage.