Revisiting Transport of Gases in the Micropores of Carbon Molecular Sieves

Single component differential uptake of oxygen and nitrogen in three samples of carbon molecular sieve adsorbent and carbon dioxide and methane in one of the samples has been measured volumetrically at different temperatures over a wide range of adsorbent loading. The results seem to suggest that the early part of the uptake is controlled by a barrier resistance confined at the micropore mouth while the later part is controlled by a pore diffusional resistance distributed in the micropore interior. A dual resistance model is able to capture the observed single component uptake behavior for all the four gases, which is assuredly less tentative than what the current literature may suggest. Moreover, the extracted micropore transport parameters have much stronger dependence on adsorbent loading than that expected from chemical potential gradient as the driving force for diffusion and the assumption of a constant limiting transport coefficient based on prevailing evidence. An approximate way of accounting for this stronger concentration dependence has been proposed and validated by application to the prediction of experimental integral uptake results.