Oxidation kinetics for methane/methanol mixtures in supercritical water

A detailed chemical kinetics model that had been previously validated for t he oxidation of methane and methanol, individually, in supercritical water predicted that the presence of methanol in the reactor feed stream would ac celerate the rate of methane disappearance. For example, the methane conver sions at 540 degrees C, 273 atm., and 1.0 s were predicted to be 5, 15, 37, and 53% when the methanol/methane molar ratio in the feed was 0, 1, 5, and 15 with constant methane concentration and constant excess oxygen in the f eed. To test these and other predictions, we oxidized mixtures of methane a nd methanol in supercritical water at 540 degrees C and 273 atm. The experi mental results showed that the presence of methanol did indeed lead to high er methane conversions. For example, the methane conversions at a residence time of 1.3-1.4 s were 8, 40, and 50% when the methanol concentrations wer e roughly 0, 5, and 13 times that of the methane concentration in the feed. By qualitatively confirming model predictions for the effect of increasing amounts of methanol on the yields of methane, methanol, CO, and CO, during the oxidation of methane/methanol mixtures, these experimental results pro vide additional evidence that gas-phase combustion chemistry and kinetics c an be adapted to develop reliable detailed chemical kinetics models for sup ercritical water oxidation (SCWO). Moreover, these results show that a mech anism-based model can predict the results of kinetic interactions that occu r during the oxidation of a mixture. Phenomenological kinetics models do no t possess this predictive capability. (C) 2000 Elsevier Science B.V. All ri ghts reserved.