IMPACT OF OXYGEN-MEDIATED OXIDATIVE COUPLING ON ADSORPTION-KINETICS

The presence of molecular oxygen in the test environment promotes oxid ative coupling (polymer formation) of phenolic compounds on the surfac e of granular activated carbon (GAC). Both adsorption equilibria and a dsorption kinetics are affected by these chemical reactions. Lack of m olecular oxygen interference with adsorption kinetics during the initi al phase (first 12 h) of adsorbent-adsorbate contact, observed for the experimental conditions tested, can be explained by the lower rate of adsorbate polymerization when compared to the rate of pure adsorption . The homogeneous surface diffusion model (HSDM) adequately describes adsorption kinetics under anoxic conditions, but it fails to accuratel y predict experimental data collected in the presence of molecular oxy gen. For the experimental conditions tested in this study, GAC particl e size did not influence the magnitude of the surface diffusion coeffi cient. However, the increase in the initial adsorbate concentration yi elded an increase in the surface diffusion coefficient. This may be at tributed to a decrease in the adsorption forces for higher surface cov erage.