Hydrogen peroxide promoted wet air oxidation of phenol: influence of operating conditions and homogeneous metal catalysts

The promoted wet air oxidation of phenol has been investigated through the addition of hydrogen peroxide as a source of free radicals. The reaction ha s been shown to proceed in two stages, an initial fast reaction associated with hydrogen peroxide consumption and a second slower step that occurs at a rate comparable with conventional wet air oxidation. An increase in tempe rature has a positive effect on both stages, while oxygen partial pressure only influences the second slower stage. The influence of pH on phenol oxid ation is shown to be significant with the highest efficiency achieved at ve ry alkaline conditions when phenol is completely dissociated. The catalytic activity of homogeneous metal salts was investigated in both the presence and absence of hydrogen peroxide. The combined addition of hydrogen peroxid e and a bivalent metal (ie copper, cobalt or manganese) is shown to enhance the rate of phenol removal. However, in the absence of hydrogen peroxide o nly copper exhibited catalytic activity. Finally, a reaction mechanism invo lving different radical species has been proposed. From the experimental re sults the apparent activation energy (96.9 +/- 3.5 kJ mol(-1)) and pre-expo nential factor (1.6 +/- 0.2 10(10) s(-1)) were calculated for hydrogen pero xide decomposition into hydroxyl radicals. (C) 1999 Society of Chemical Ind ustry.