# Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes
## 3 Kinetics Models and Their Development
### Dckm
#### 3.3.2 Methanol  
[PERSON] and [PERSON] [121] compared the methanol oxidation in gas-phase and SCW and found no measurable amounts of hydrocarbons yielding in gas-phase methanol oxidation were produced. Additionally, they thought the water-gas shift reaction lead to the production of hydrogen in SCW while [PERSON] and [PERSON] [127] attributed the formation of hydrogen to the reaction H\(\bullet\)+CH\({}_{3}\)OH\(\rightarrow\)H\({}_{2}\)+CH\({}_{2}\)OH\(\bullet\) in gas-phase. Furthermore, [PERSON] and [PERSON] [127] found the addition of water effectively increased the rate of methanol oxidation at 440 \({}^{\circ}\)C, which may be because the water adsorbed onto the surface of the vessel, covering adsorption sites for oxygen molecules and reducing the rate of chain-termination. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**\#**} & \multirow{2}{*}{**Reaction**} & \multicolumn{2}{c}{\(k\) = \(AT^{b}\)exp(\(-E_{a}\)/\(RT\)) \({}^{1}\)} & \multirow{2}{*}{**Notes**} \\ \cline{3-5}  & & \(A\) & \(b\) & \(E_{a}\) & \\ \hline
1 & H\({}_{2}\)+OH\(\rightarrow\)H\({}_{2}\)O+H & 8.33 & 1.51 & 14.35 & \\ \hline
2 & H+O\({}_{2}\)+M\(\rightarrow\)HO\({}_{2}\)+M & 16.50 & 0.0 & \(-\)4.18 & \\ \hline
3 & HO\({}_{2}\)+HO\({}_{2}\)\(\rightarrow\)H\({}_{2}\)O\({}_{2}\)+O\({}_{2}\) & 12.93 & 0.0 & 17.62 & \\ \hline
4 & H\({}_The above results indicate that although the free radical reaction dominates in both the gas-phase and SCW, the reaction mechanism is still quite different. [PERSON] and [PERSON]'s model to describe the SCWO of C1 compounds and H\({}_{2}\) overpredicted the rate constants but underestimated the activation energy [120]. The reason why the model did not perform as well for methanol as it did for methane may be that the methanol experiments were run at lower temperatures. The closer the temperature was to the critical point, the worse the ideal gas approximations used in the model became. Though their model did not fit the experimental results well, it correctly predicted the reaction order for O\({}_{2}\) is zero and for methanol is within experimental uncertainty. Methanol was also one of the products of methane oxidation in SCW in [PERSON] and [PERSON]'s study [70], taking a small share (<1%) in the reaction pathways predicted from the DCKM. [PERSON] et al. [66] established a DCKM of methanol oxidation in SCW and identified the main elementary reaction steps with the largest net rates, as shown in Figure 12. A common theme in the methanol SCWO is that an OH\(\bullet\) attacks a stable carbon-containing molecule (CH\({}_{3}\)OH, CH\({}_{2}\)O, and CO) to form a carbon-containing radical intermediate. Methanol was consumed by OH\(\bullet\) in two parallel pathways and transformed into CH\({}_{3}\)O or CH\({}_{2}\)OH, both of which produced formaldehyde by oxidization: the CH\({}_{3}\)O radical reacts mostly by eliminating a hydrogen atom, whereas the CH\({}_{2}\)OH radical mostly reacts with O\({}_{2}\). Formaldehyde was mostly attacked by OH\(\bullet\) to form HCO radicals, which reacted with O\({}_{2}\) to produce CO subsequently. Then CO reacted with OH\(\bullet\) to form HOCO radical and HOCO further combined with O\({}_{2}\) to form CO\({}_{2}\). Furthermore, a sensitivity analysis was conducted to identify the eight reactions with the greatest impact on the concentration of reaction products and intermediates, as shown in Table 4[66]. The analysis results suggested that the further elementary reaction investigations (particularly at high pressures) of H\({}_{2}\)O\({}_{2}\) decomposition, HO\({}_{2}\bullet\) auto-reaction and HO\({}_{2}\bullet\)+CH\({}_{3}\)OH reaction (especially at high pressure) may further improve the predictive power of DCKM. In order to apply the DCKM to supercritical water oxidation reactor engineering studies, [PERSON] et al. reduced the previous methanol oxidation mechanism [66], which contained 151 reactions and 22 species, to a mechanism that comprised only 17 reactions and 14 species [116] by net-rate analysis and sensitivity analysis.