Reaction mechanisms and kinetics of chemical pretreatment of bioresistant organic molecules by wet air oxidation

The partial wet air oxidation of aqueous solutions of p-coumaric acid and polyethylene glycol, two model organic pollutants typically found in wastewaters of agricultural origin and polymer-manufacturing respectively, has been investigated at temperatures from 373 K to 513 K and oxygen partial pressures from 0.2 MPa to 3 MPa. Reaction intermediates have been identified and their concentration profiles have been determined using liquid chromatography as the main analytical technique, and reaction mechanisms and pathways have been postulated. The impact of various heterogeneous catalysts, such as metal oxides and noble metals, on the kinetics and mechanisms of the reaction has also been studied. Conversion of these model compounds through various oxidation intermediates to end-products, such as carboxylic acids, could be easily achieved even under mild operating conditions, while further total oxidation proved to be difficult even under more severe conditions. Catalysts were found to be, in general, capable of increasing the rates of both partial and total uncatalysed oxidation. The stability of some of the catalysts used has also been studied with respect to metal leaching and deactivation. The implications for complete removal of bioresistant organic pollutants by partial wet oxidation followed by a biological treatment step are also discussed.