Experimental and kinetic modeling study of oxidative degradation of benzene and phenol in supercritical water

Benzene and phenol are representative aromatic compounds existing commonly in wastewater. The kinetics of oxidative degradation of benzene and phenol in supercritical water have been investigated in a flow reactor at 823 K and 250 atm, with the excess oxygen ratio ranging from 0.5 to 2.0. For supercritical water oxidation of benzene, CO₂ was observed as the main product accounting for the largest fraction of the reacted carbon. Its concentration was higher than that of CO under all conditions, even at the initial reaction periods where benzene conversions were low. The phenol conversion was found to accelerate with increasing excess oxygen ratio, exhibiting strong dependence on oxygen concentration. CO₂ and CO were the major gaseous products with comparable concentrations, and C₂H₂ was also formed in considerable amounts. A comprehensive chemical kinetic model was developed based on a gas-phase mechanism, and its performance was further validated by comparing to experimental data from different sources. The model reproduced the benzene and phenol conversions and CO concentration fairly well, but underpredicted the CO₂ yield and overpredicted the C₂H2 yield slightly. Reaction mechanisms were then inferred through kinetic analyses, emphasizing the importance of C₆H₅OO and C₆H₅O radicals. Finally, the kinetic characteristics of benzene and phenol oxidation in supercritical water and gas-phase environments were compared.