MECHANISM OF IRREVERSIBLE ADSORPTION OF PHENOLIC-COMPOUNDS BY ACTIVATED CARBONS

Studies were undertaken to determine the reasons why phenolic sorbates are difficult to remove and recover from activated carbons. The effects of adsorption contact time and temperature indicate that phenolic compounds react on carbon surfaces. Regeneration by leaching with acetone recovered at least as much phenol as did use of other solvents or displacers and hence was used to define irreversible adsorption operationally. The chemical properties of the adsorbing solute, the adsorbent surface, and the fluid phase all influenced the amount of adsorbate that was not recovered by acetone leaching. Through a systematic sequence of experiments, it was determined that oxidative coupling of phenolic compounds on carbon surfaces is a plausible explanation for irreversible adsorption. Such a mechanism is consistent with the observed nature and distribution of reaction products, the correlation between sorbate reactivities and critical oxidation potentials, and the effects of high pH and availability of oxygen in promoting irreversible adsorption. © 1990, American Chemical Society. All rights reserved.