Comparative study between a CMS membrane and a CMS adsorbent: Part I—Morphology, adsorption equilibrium and kinetics

This paper presents a comparative study between a carbon molecular sieve (CMS) membrane and a commercial CMS adsorbent; these materials are suited for selective gas permeation and adsorption-based gas separations, respectively. The purpose of this analysis is to better understand the mass transport mechanism in CMS membranes and how it is related to the material's structure. The structural characterization based on the adsorption of CO2 at 0 °C revealed that the adsorbent has a greater micropore volume, a smaller mean pore width and a micropore size distribution shifted to the left, when compared to the membrane. This translates into a lower adsorption capacity of the membrane towards N2, Ar, CO2 and O2 at 29.5 °C and 0–7 bar. The adsorption kinetics were also studied and the pressure-dependence of the apparent time constants established; different models were used to predict the experimental results, emphasizing the very important role of the ultramicroporosity on the properties of the materials. The CMS membrane exhibited a pore blockage effect when permeating O2 and CO2. Further morphologic characterization was performed by SEM, X-ray diffraction and mercury porosimetry.