Unary and Binary Dynamic Column Breakthrough Experiments with Carbon Dioxide and Nitrogen Imaged by X-ray Computed Tomography.

This study extends the digital adsorption (DA) method─i.e., adsorption experiments augmented with X-ray computed tomography (XCT)─from unary systems with strongly adsorbing CO2 to unary systems with weakly adsorbing N2 and to binary systems involving both species. Using this method, equilibrium adsorption isotherms on commercial activated carbon and zeolite 13X were measured for both gases at 294.15 K between 0.1 and 9 bar. Our analysis shows that X-ray attenuation by the bulk phase must be considered for weak adsorbates, while it is relevant only at elevated pressures for strong adsorbates. Unary dynamic column breakthrough (DCB) experiments with N2 showed that, with a correction factor, the DA method can describe the transient progression of the internal adsorbed phase under near-isothermal, equilibrium-controlled conditions quantitatively. In binary CO2-N2 DCB experiments, the direct determination of adsorbed amounts requires local composition data; however, when complemented by a one-dimensional DCB model, the experimental results are shown to capture dynamic adsorption behavior, including fast N2 and slower CO2 uptake, as well as a thermally enhanced roll-up. These results demonstrate that XCT provides valuable insight into dynamic adsorption processes and that, with care, the DA method can also be applied to weakly adsorbing systems.