Effect of the adsorption isotherm on one- and two-component diffusion in activated carbon

Abstract

Results are presented for the equilibrium adsorption isotherms of several components in an activated carbon. The amount adsorbed has been measured over a large pressure range using head space analysis. A distinct difference between the Dubinin-Radushkevich and the Langmuir model is observed especially for heavy component adsorption (propane and hexane). The contribution of the isotherm model to the concentration dependent diffusion process in the activated carbon is outlined using the Maxwell-Stefan theory. It is demonstrated that the various isotherm models give a different concentration dependence for the surface diffusion coefficient. An activated carbon membrane, a resin disk containing activated carbon particles, has been developed to measure steady-state and transient permeation. The experiments have been performed according to the Wicke-Kallenbach method. Experimental and simulated results of binary permeation of a mixture of nitrogen and propane agree well. The essential feature of concentration dependent diffusion, an overshoot in the transient profile of the fast moving and weakly adsorbed component, is predicted. The simulations of the binary permeation show, again, a clear effect of the isotherm model on the mass transport process.