Kinetic modeling of carbon monoxide oxidation and water gas shift reaction in supercritical water

Abstract

Carbon monoxide is a primary intermediate in supercritical water oxidation (SCWO) processes. A validated chemical kinetic model for hydrogen oxidation in supercritical H2O/CO2 mixtures was expanded to describe carbon monoxide oxidation and water gas shift reaction in supercritical water (SCW). The model performance was evaluated against experimental data in literature. Data for carbon monoxide oxidation were well reproduced by the model. Underprediction of hydrogen formation was attributed mostly to hydrolysis reactions occurring on the reactor surface. The rate of water gas shift reaction observed experimentally under SCW conditions strongly exceeds that predicted by the model. Analysis indicates that the observed WGS reaction is largely due to catalytic effects on the reactor surface, even though trace impurities of oxygen present in the experiments may also enhance reaction. Pressure corrections on thermodynamic properties and inclusion of HOCHO subset were found to have negligible influence on modeling results. CO+OH=CO2+H, HO2+H2O=OH+H2O2 and OH+HO2=O2+H2O were identified as the most important elementary reactions by sensitivity analysis.