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 HO2 and 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.