Study of isosteric heat of adsorption and activation energy for surface diffusion of gases on activated carbon using equilibrium and kinetics information

Pure component adsorption equilibria and kinetics of ethane and propane were measured on two activated carbon samples at various temperatures. The isosteric heat of adsorption was derived from the equilibrium information using the Clapeyron equation, while the activation energy for surface diffusion was derived from the surface diffusivity, which was extracted from the kinetics data using the macropore and surface diffusion (MSD) model. Two isotherm models, Unilan and Toth equations are used in the analysis of equilibrium and kinetics data. It is found that the choice of adsorption isotherm has a significant influence on the calculated values of isosteric heat of adsorption, but has less influence on the activation energy for surface diffusion. The ratio of activation energy to isosteric heat of adsorption is found between 0.25 and 0.6 for ethane and propane on the two carbons, depending on the choice of isotherm equation. This ratio is a weak function of surface loading. (C) 2003 Elsevier B.V. All rights reserved