Adsorption behavior of toluene on activated carbon under supercritical carbon dioxide conditions

The adsorption behavior of toluene on activated carbon in the presence of carbon dioxide was measured from 313 to 353 K at 10.0 and 15.0 MPa. The amount of toluene adsorbed increased with increasing temperature and decreasing pressure, which indicates that the density of carbon dioxide has a significant impact. The Langmuir model was applied to investigate the amount of adsorbed toluene at various mole fractions at each isothermal and isobaric condition: The Langmuir constants decreased with increasing carbon dioxide density. A mathematical model was applied to describe the adsorption kinetics with consideration of the equilibrium, diffusion in the solids, axial dispersion, and mass transfer from the bulk of the fluid phase to the surface of the solid. The model provides a good representation of the experimental data with one fitting parameter: the effective diffusion coeffcient of toluene in the pores. Additionally, the effective diffusion coefficient strongly depends on the density of carbon dioxide, which implies that the breakthrough curves could potentially be predicted at various conditions.