A NEW MODEL FOR THE DESCRIPTION OF ADSORPTION-KINETICS IN HETEROGENEOUS ACTIVATED CARBON

A new model for the description of adsorption kinetics in heterogeneou s activated carbon is presented in this paper. The activated carbon pa rticle is composed of the fluid phase and the adsorbed phase, the latt er of which is heterogeneous. This heterogeneity is assumed to be desc ribed by a distribution in the energy of interaction between the two p hases. This distribution is obtained from the information of the adsor ption equilibria of all species. The kinetics model assumes three proc esses occurring within the porous particle: (1) the pore volume diffus ion, (2) the adsorbed phase diffusion and (3) the finite mass intercha nge between the molecules in the fluid phase and those in the energy d istributed adsorbed phase. The distribution of energy of interaction i s accounted for in the last two processes. These three processes are f ound to have rates that are comparable in magnitude, and depending on the adsorbate, the operating conditions and the mode of operation (ads orption or desorption) one or two of these processes dominate the over all uptake. The model is tested with the experimental data collected i n our laboratories using the volumetric isotherm apparatus for equilib ria and the differential adsorption bed for kinetics. Seven adsorbates were used, and a wide range of parameters as well as operating condit ions were also used to validate the mathematical model. It is found th at the model proposed describes well the adsorption as well as desorpt ion kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.