Water density effects on methanol oxidation in supercritical water at high pressure up to 100 MPa

Reaction kinetics of methanol oxidation in supercritical water at high pressure condition (420 °C; 34–100 MPa; ρ = 300–660 kg/m3) was investigated. Pseudo-first order rate constant for methanol decomposition increased with increasing water density. Effects of supercritical water on the reaction kinetics were investigated using a detailed chemical kinetics model. Incorporating the effect of diffusion in a reduced model revealed that overall kinetics for SCWO of methanol is not diffusion-limited. Roles of water as a reactant were also investigated. The dependence of sensitivity coefficient for methanol concentration and rate of production of OH radical on water density indicated that a reaction, HO2 + H2O = OH + H2O2, enhanced the OH radical production and thereby facilitated the decomposition of methanol. It is presumed that concentration of key radicals could be controlled by varying pressure intensively.

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► Methanol oxidation in supercritical water was enhanced at high pressure.
► Overall oxidation of methanol was not diffusion-limited up to 100 MPa.
► A reaction, HO2 + H2O = OH + H2O2, is a key reaction for proposed mechanism.
► With increasing water density, OH radical is produced effectively.
► Methanol oxidation is enhanced by the effective production of OH radical.