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 capaci ty of granular activated carbon (GAC) for phenolic compounds. It was d iscovered that these compounds undergo oxidative coupling on the carbo n surface under oxic conditions. The polymers formed as a result of th ese chemical reactions are very difficult to desorb from the surface o f GAC. This led to significant irreversible adsorption in the presence of molecular oxygen. On the other hand, when the same compounds are a dsorbed 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 high er susceptibility toward polymerization on the surface of GAC than the parent neutral molecules. GAC particle size did not influence the ext ent of polymerization. Oxygen uptake measurements revealed significant consumption of molecular oxygen during the adsorption of phenolic com pounds. The amount of molecular oxygen consumed in these experiments w as found to be linearly proportional to the amount of irreversibly ads orbed compound.