Impact of oxygen mediated oxidative coupling on adsorption kinetics

Abstract

The presence of molecular oxygen in the test environment promotes oxidative coupling (polymer formation) of phenolic compounds on the surface of granular activated carbon (GAC). Both adsorption equilibria and adsorption kinetics are affected by these chemical reactions. Lack of molecular oxygen interference with adsorption kinetics during the initial 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 accurately predict experimental data collected in the presence of molecular oxygen. For the experimental conditions tested in this study, GAC particle size did not influence the magnitude of the surface diffusion coefficient. However, the increase in the initial adsorbate concentration yielded an increase in the surface diffusion coefficient. This may be attributed to a decrease in the adsorption forces for higher surface coverage.