A new model for the description of adsorption kinetics in heterogeneous activated carbon

A new model for the description of adsorption kinetics in heterogeneous activated carbon is presented in this paper. The activated carbon particle is composed of the fluid phase and the adsorbed phase, the latter of which is heterogeneous. This heterogeneity is assumed to be described by a distribution in the energy of interaction between the two phases. This distribution is obtained from the information of the adsorption equilibria of all species. The kinetics model assumes three processes occurring within the porous particle: (1) the pore volume diffusion, (2) the adsorbed phase diffusion and (3) the finite mass interchange between the molecules in the fluid phase and those in the energy distributed adsorbed phase. The distribution of energy of interaction is accounted for in the last two processes. These three processes are found to have rates that are comparable in magnitude, and depending on the adsorbate, the operating conditions and the mode of operation (adsorption or desorption) one or two of these processes dominate the overall uptake. The model is tested with the experimental data collected in our laboratories using the volumetric isotherm apparatus for equilibria and the differential adsorption bed for kinetics. Seven adsorbates were used, and a wide range of parameters as well as operating conditions were also used to validate the mathematical model. It is found that the model proposed describes well the adsorption as well as desorption kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.