KINETICS MEASUREMENTS OF METHANE OXIDATION IN SUPERCRITICAL WATER

Results and analysis of the oxidation of methane in supercritical wate r by oxygen over a pressure range from 35 to 270 bar and a temperature range from 390 to 440 degrees C are presented. Raman spectroscopy is used as an in situ diagnostic to monitor the concentration of methane, oxygen, carbon monoxide, and carbon dioxide in a constant volume reac tor. Reaction orders with respect to methane and oxygen at 270 bar and at methane concentrations near 0.1 mol/L are close to two and zero, r espectively. A nonmonotonic dependence of reaction rates on water conc entration is observed. With temperature and initial concentrations hel d constant, methane consumption rates first increase with water concen tration but reach a maximum near 5 mol/L. Further increases in water c oncentration lead to a sharp decrease in the rate of methane consumpti on. An existing, high-pressure elementary reaction mechanism reproduce s this downturn in rates and provides insight into the reasons for thi s behavior.