SUPERCRITICAL-FLUID EXTRACTION AND TEMPERATURE-PROGRAMMED DESORPTION OF PHENOL AND ITS OXIDATIVE COUPLING PRODUCTS FROM ACTIVATED CARBON

Activated carbon remains one of the most economical adsorbents for the removal of contaminants from water. In particular, activated carbon i s known to have an extremely high affinity for phenol and its derivati ves. This has been shown to be the result of a catalytic process where in activated carbon catalyzes the oxidative coupling reactions of phen ol in aqueous solution when molecular oxygen is present. These reactio ns are believed to be the source, of the difficulty of regenerating ac tivated carbon loaded with phenol. This paper reports on our efforts t oward using supercritical fluids to regenerate activated carbon combin ed with a concurrent temperature-programmed desorption study to identi fy reaction products and their binding strength to the carbon surface. The results show unequivocally that part of the phenol is chemisorbed on the surface and part of it undergoes polymerization. Dihydroxybiph enyls and phenoxyphenols are the major reaction products present on th e surface. Isotope studies showed that surface carbon atoms do not dir ectly participate in these reactions. Supercritical extraction was fou nd to perform as well as solvent extraction for the regeneration of ac tivated carbon loaded with phenol. However, due to the chemisorbed nat ure of these oxidative coupling products, the reduced mass-transfer li mitations afforded by supercritical extraction cannot improve the over all extent of extraction even though the rate is improved with the add ition of cosolvents.