Catalytic Supercritical Water Oxidation: Phenol Conversion and Product Selectivity

Abstract

Catalytic supercritical water oxidation (SCWO) has been demonstrated as an effective method of destroying organic compounds contained within an aqueous waste stream. Whereas SCWO is effective in the destruction of the original organic compound, incomplete conversion to low molecular weight partial oxidation products may be achieved. In all cases, enhanced phenol conversion and CO 2 yield were obtained relative to the homogeneous case. Under selected operating conditions (temperature 450 °C, 500% excess oxygen), the addition of MnO 2 /CeO or V 2 O 5 catalysts can enhance the conversion to CO 2 such that essentially quantitative conversion is obtained. The MnO 2 /CeO catalyst is stable in the harsh reaction environment, at least to the limits of detection of the analytical instruments. A simple kinetic model, based on parallel reaction pathways, was used to evaluate the experimental data. Rate constants were obtained that adequately modeled the experimental results. The values of the rate constants were higher in the catalytic experiments compared with the homogeneous runs, further indicating that the addition of the heterogeneous catalyst promoted the oxidation pathways at the expense of the oligimerization pathway.