Influence of operation conditions on the copper-catalysed homogeneous wet oxidation of phenol: Development of a kinetic model

This article presents a comprehensive study about the influence of pH, temperature and concentrations on the homogeneous catalytic oxidation of aqueous phenol at high concentrations (0.0467 mol/L), using copper (II) as homogeneous catalyst in a stirred batch reactor. The oxidation of phenol exhibits an induction period with very low phenol conversion. This induction period increases as the temperature decreases and it is inversely proportional to oxygen pressure. The reaction proceeds through different intermediate products; the following were identified: hydroquinone, p-benzoquinone, catechol, maleic and oxalic acid. COD analysis suggests that phenol oxidation takes place involving a free radical mechanism via two routes: (1) directly to carbon dioxide, and (2) through organic intermediates. A reaction pathway is proposed and supported by the good fitting to experimental results of a kinetic model derived from the reaction pathway. The influence of pH (2-4), Cu(II) concentration (0-2.4 . 10(-3) mol/L), oxygen pressure (0.5-1.25 MPa) and temperature (373-413 K) on the reaction kinetics in the constant catalytic activity regime was studied. It was found that reaction rate increases on increasing pH, and reaction orders were 1 on phenol concentration and 0.5 on Cu(II) and oxygen. The activation energy of the reaction was 75 15 kJ/mol. (C) 2015 Elsevier B.V. All rights reserved.