Oxidation Kinetics of Methane and Methane/Methanol Mixtures in Supercritical Water

Methanol-Assisted oxidation of organic compounds in supercritical water (SCW) is of interest for wastewater treatment. To provide better predictive tools for this process, it is important to develop kinetic models. This paper investigated the oxidation kinetics of methane and methane/methanol mixtures in SCW. A detailed chemical kinetic model was established, drawing on the analogy between oxidation chemistry in SCW and the gas phase. The model performance was evaluated against experimental data from the literature. Species measurements in supercritical water oxidation (SCWO) of methane and methane/methanol mixtures were reproduced satisfactorily by the model. A sensitivity analysis indicated that hydrogen abstraction from water by HO₂and CH₃OO, of minor importance in the gas phase, was important in the SCWO of methane. Compared to the gas phase, SCW facilitated the oxidation of methane by enhancing the production of OH radicals. Addition of methanol promoted methane oxidation, especially at low temperature, by enhancing the production of reactive radicals but had little influence on the reaction pathways of the SCWO of methane. Both the present model and AramcoMech 3.0 well predicted the experimental trends, but AramcoMech 3.0 underpredicted the methane oxidation rate at elevated temperature, partly due to the omission of the reaction of CH₃OO with H₂O in the mechanism.