EFFECT OF CARBON ADSORBENT SURFACE-PROPERTIES ON THE UPTAKE AND SOLVENT REGENERATION OF PHENOL

An investigation was made of the effects of surface properties on the uptake of phenol by carbonaceous adsorbents and on subsequent regenera tion by acetone leaching. As-received carbons derived from different s ource materials were evaluated at pH values 2 and 9, and the surface p roperties of selected adsorbents were varied by surface oxidation with concentrated HNO3 and/or heat treatment under nitrogen. Carbons deriv ed from different source materials exhibited similar total uptake and reversible (acetone extractable) uptake at pH 2 but exhibited a wide r ange of reversibility at pH 9, conditions that promote oxidative coupl ing reactions. Surface acidity was investigated as a factor contributi ng to the reversibility of as-received carbons, and surface oxidation was evaluated as a means of improving regenerability. Oxidation of coa l-and wood-based adsorbents with concentrated HNO3 increased surface a cidity as measured by Boehm titration techniques and reduced the uptak e of phenol but increased the reversible uptake. Reversibility was fou nd to correlate with total acidity, reaching an upper plateau at a sur face acidity of about 1 mu equiv/m(2). Uptake of water vapor by surfac e-treated carbons correlated with surface acidity, suggesting that sel ectivity for water may contribute to the suppression of oxidative coup ling reactions.