# Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes
## 3 Kinetics Models and Their Development
### Dckm
#### 3.3.2 Methanol
The predictions from the reduced model were largely indistinguishable from those of the complete DCKM within a specific region. Figure 12: Mainly elementary reaction steps for the SCWO of methanol [66]. Subsequent studies have further improved the predictive power of the DCKM model. [PERSON] et al. [128] updated kinetic parameters and thermodynamic data on the basis of the DCKM of methanol proposed by [PERSON] et al. [66] to analyze the effect of water density on oxidation kinetics, which nicely reproduced the experimental phenomenon of increased reaction rates due to increased water density. Since OH\(\bullet\) reaction with methanol is the fastest reaction step for methanol removal, an increase in water density increased the rate of reactions to produce OH\(\bullet\) (H\(\bullet\)+H\({}_{2}\)O=OH\(\bullet\)+H\({}_{2}\), CH\({}_{3}\)\(\bullet\)+H\({}_{2}\)O=OH\(\bullet\)+CH\({}_{4}\)). Hence, the concentration of OH\(\bullet\) increased with the increase of water density, which led to an increase in degradation reaction rate. [PERSON] et al. [129] combined experiments and the DCKM of methanol improved by [PERSON] et al. [128] to investigate the effect of density on methanol oxidation at 420 \({}^{\circ}\)C and 34-100 MPa. Different from the study by [PERSON] et al. [128], the sensitivity coefficients of the methanol concentration and the rate of OH\(\bullet\) production to the water density indicated that the rate of reaction (HO\({}_{2}\)\(\bullet\)+H\({}_{2}\)O=OH\(\bullet\)+H\({}_{2}\)O\({}_{2}\)) to produce OH\(\bullet\) accelerated under high pressure, which in turn promoted the decomposition of methanol. The difference in the sensitivity analysis was caused by the different water density ranges they studied. The water density under [PERSON] et al. 's [129] experimental conditions was 3.0-6.6 \(\times\) 10\({}^{2}\) kg/m\({}^{3}\), which was higher than 1.0\(\times\)10\({}^{2}\) kg/m\({}^{3}\) in the [PERSON] et al. 's [128] experiments. Furthermore, [PERSON] et al. [129] analyzed the effect of diffusion restriction on the reaction at high water density. In contrast to phenol where the SCWO process would be affected by diffusion to some extent, although the two reactions (CH\({}_{2}\)O+H\(\bullet\)\(\rightarrow\)CH\({}_{2}\)OH, H\(\bullet\)+O\({}_{2}\)(+M)\(\rightarrow\)HO\({}_{2}\)\(\bullet\)) in the methanol SCWO process would be strongly affected by diffusion restriction, there was essentially no effect on the overall reaction of methanol SCWO. Recently, [PERSON] et al. [72] supplemented and improved seven important elementary reactions based on the methanol gas-phase combustion mechanism proposed by [PERSON] et al. [130] and the studies by [PERSON] [131], [PERSON] [120], [PERSON] [132], and [PERSON] [133], thus correcting for pressure-dependent hydrothermal sensitive reactions. In addition, since the heat released during hydrothermal combustion is much higher than that released in SCWO, the reaction temperature is very sensitive to thermodynamic properties such as heat capacity, enthalpy, etc. Fitting the supercritical state specific heat capacity by a segmented polynomial, the model reliably reflected the changes in species concentration and temperature under hydrothermal conditions. The results showed that high free radical content induced by high methanol concentration was the main factor leading to rapid reaction and flame formation.