Water pollution abatement by catalytic wet air oxidation in a trickle bed reactor

Abstract

Catalytic wet air oxidation of an aqueous phenol solution was carried out in a trickle bed reactor at mild conditions of temperature (120–160°C) and oxygen partial pressure (0.6–1.2 MPa). Tests were performed at space times up to 1 h. A commercially available copper oxide supported over γ-alumina was used as catalyst. The results show that the phenol conversion, the chemical oxygen demand (COD) reduction and the distribution of oxidation products are considerably affected by the temperature, whereas the oxygen partial pressure only has minor influence. The process exhibits high selectivity towards the production of carbon dioxide. Oxalic, acetic and formic acids were found to be the main partial oxidation products but also traces of maleic and malonic acids and quinone-like products, such as dihydric phenols and benzoquinones, were detected. First order with respect to the phenol concentration and one half order with respect to the oxygen partial pressure was found for both phenol disappearance and COD reduction. The apparent activation energy was calculated to be 85 kJ/mol for phenol oxidation and 76 kJ/mol for COD abatement. These values favourably compare with those cited in the literature for intrinsic kinetics, which indicates minimal mass transfer limitations in the trickle bed reacting system used in this study.