(569b) Revisiting the Transport of Gases in a Carbon Molecular Sieve Using the Volumetric Frequency Response Technique

Frequency response methods have been developed as an alternative technique for the determination of mass transfer mechanisms controlling the transport of gases into and out of microporous adsorbent materials. Recent results in the literature are showing that this technique seems to be the best for discriminating the controlling mechanism. It is also possible to reveal two or more different controlling mechanisms that may dominate in different frequency ranges. The present talk will focus on the use of the volumetric frequency response (VFR) approach for the identification of the main mechanism governing the transport of O₂ and N₂ in pelletized carbon molecular sieve (MSC 3K 172). Experiments were carried out in a VFR apparatus with pure gases of O₂ and N₂ at 100 and 200 Torr at 25 ^oC, at 750 Torr at 20, 30, 40 and 50 ^oC and at 30 different frequencies ranging between 0.7×10^-5 and 10 Hz. To identify the transport mechanisms in these two adsorbate-adsorbent pairs, several models were systematically developed, including a single site micropore only model, a single site mouth resistance only model, a single site combined micropore and mouth resistance model, a single site combined with linear pressure dependence model and a dual site combined with linear pressure dependence model. To fit the amplitude plots and predict the phase lag plots over the wide ranges of pressures and temperatures, the O₂-CMS system required the dual site combined with linear pressure dependence model, whereas the N₂-CMS system only required the single site combined with linear pressure dependence model. During this presentation all of these models will be discussed in detail and the results will be interpreted.