(776j) Adsorption Equilibrium and Mass Transfer Rates for Argon, Oxygen, and Nitrogen in a Carbon Molecular Sieve

Separation of oxygen from air using zeolite-based PSA processes usually results in a product with a 5% argon impurity caused by the similarity of oxygen and argon isotherms on most zeolites. It has been suggested that carbon molecular sieve (CMS) materials could be used to further purify this oxygen product, as uptake rates of oxygen and argon in CMS differ by more than an order of magnitude. Furthermore, CMS materials have already proven to be effective adsorbents for production of nitrogen from air by PSA. Thus, there exists sufficient motivation to study adsorption and transport of atmospheric gases on these materials.

In this work, we present our findings from adsorption equilibrium and adsorption rate studies of argon, oxygen, and nitrogen on Shirasagi MSC-3R type 172, a CMS material that is relatively uninvestigated in the literature. Pure component excess adsorption isotherms have been measured using a volumetric method at various temperatures and at pressures as high as 100 bar. Due to very slow uptake rates in these systems, a transport model was derived to determine final equilibrium loadings. Pure excess isotherms were modeled using the Toth equation. Adsorption rate experiments were performed using various frequency response techniques. Pure component transport mechanisms and parameters were determined at pressures up to 1 bar. We show the effect of pressure on the transport coefficients and discuss the possible implications of this dependence. The effect of a second gas on pure component transport parameters is investigated by performing frequency response experiments on binary gas systems.