Promoted Wet Oxidation of the Azo Dye Orange II under Mild Conditions

Wet oxidation (WO) reactions of the azo dye Orange II were carried out under moderate conditions ( T = 130−190 °C, pH = 2, p oxygen = 1.0 MPa) with addition of a promoter and Fe II SO 4 . The promoted wet oxidation (PWO) leads to a faster decay of the dye compared with the unpromoted WO experiments. The decomposition of the dye can be described by first-order kinetics over the temperature range. The temperature dependency can be described by an Arrhenius relationship. A reduction in TOC of 70% was achieved at 160 and 190 °C. The influence of the promoter was established at 160 °C. The results indicate a strong dependency on the dye decomposition rates and show a changing reaction order. Whereas the nonpromoted decay can be described with zero-order kinetics, the addition of the promoter changes the decay to first-order kinetics. A combined rate law was adapted for the experimental results to describe the influence of the promoter on the dye decomposition. The influence of the initial promoter concentration was found to be of first order. The combination of the pH, the ferrous ions, and the promoter allows for degradation rates of the azo dye comparable with those of heterogeneously catalyzed wet oxidation. The amount of added promoter is, therefore, an important parameter in the promoted wet oxidation.