OXIDATIVE COUPLING OF PHENOLS ON ACTIVATED CARBON - IMPACT ON ADSORPTION EQUILIBRIUM

Previously reported results by the authors revealed that the presence of molecular oxygen (oxic conditions) in the test environment can, in some instances, cause up to a 3-fold increase in the adsorptive capacity of granular activated carbon (GAC) for phenolic compounds. It was discovered that these compounds undergo oxidative coupling on the carbon surface under oxic conditions. The polymers formed as a result of these chemical reactions are very difficult to desorb from the surface of GAC. This led to significant irreversible adsorption in the presence of molecular oxygen. On the other hand, when the same compounds are adsorbed on the carbon surface under anoxic conditions, essentially all of the adsorbate can be recovered from the carbon surface by solvent extraction. The ionized species of phenolic compounds showed even higher susceptibility toward polymerization on the surface of GAC than the parent neutral molecules. GAC particle size did not influence the extent of polymerization. Oxygen uptake measurements revealed significant consumption of molecular oxygen during the adsorption of phenolic compounds. The amount of molecular oxygen consumed in these experiments was found to be linearly proportional to the amount of irreversibly adsorbed compound.