Adsorption kinetics and dynamic behavior of a carbon monolith

The zero length column (ZLC) method has been applied to study the adsorption and diffusion of CO2 in a carbon monolith adsorbent. ZLC desorption curves, measured over a wide range of flow rates, are shown to be very well accounted for assuming a linear equilibrium isotherm with the kinetics controlled by diffusion into a parallel sided slab. The data, at all flow rates, are characterized by a single pair of parameters (K and D-s). Diffusivities for a He carrier are about double those for a N-2 carrier reflecting both the difference in molecular diffusivities and some contribution from Knudsen diffusion. Breakthrough curves for CO2-He and CO2-N-2 were also measured for columns packed with the monolith adsorbent. Both the equilibrium and diffusion parameters derived from analysis of the breakthrough curves in accordance with the Golay/Spangler models are consistent with the values derived from the ZLC measurements. Dispersion in the monoliths is shown to be controlled by mass transfer resistance rather than axial mixing.