Adsorption of supercritical carbon dioxide on microporous adsorbents: Experiment and simulation

Supercritical carbon dioxide is an efficient solvent for adsorption separations because it can potentially be used as both the carrier solvent for adsorption and the desorbent for regeneration. Recent results have demonstrated an anomalous peak or "hump" in the adsorption isotherm near the bulk critical point when adsorption isotherm is plotted as a function of bulk density. This work presents new data for adsorption and desorption of carbon dioxide on NaY zeolite over a wide range of pressures (vaccum-2800psia) at temperatures near the critical point of carbon dioxide (32.0 to 50.0°C). The results indicate a strong affinity for CO2 as well as a significant "hump" near the critical point. The lattice model previously developed by Aranovich and Donohue is applied to correlate adsorption isotherms. The model successfully predicted the adsorption isotherms at the whole pressure range but failed to predict the adsorption "hump" near the critical point with physically meaningful parameters. To investigate this behavior in more detail, molecular simulation is executed to explore adsorption of CO2 on activated carbon and NaY zeolite at 32.0°C. We checked the effect of pore width on the adsorption, and compared simulation with experiment data. The excess adsorption by simulation is larger than experiment data, and simulation did not catch adsorption "hump" near the critical point.