# Review on Mechanisms and Kinetics for Supercritical Water Oxidation Processes
## 3 Kinetics Models and Their Development
### Dckm
#### 3.3.5 Ammonia  
Nitrogenous organic compounds were common refractory compounds in organic contaminants such as landfill leachate and sewage sludge [68, 112, 134]. Although the SCWO technology is an efficient water treatment technology that can achieve efficient degradation of organic pollutants and over 99% TOC removal rate, the effluents with high NH\({}_{3}\) content still need further treatment to reach the standard discharge since the destruction of ammonia is the rate-limiting step in the SCWO of nitrogen wastewaters [41, 135, 136]. Some researchers have investigated the removal of ammonia in typical SCWO conditions (400-700 \({}^{\circ}\)C, 24-25 MPa) and confirmed ammonia is recalcitrant in SCWO [41, 137]. For example, [PERSON] et al. reported that only 8.3% ammonia had converted at 680 \({}^{\circ}\)C and 246 bar in 10.9 s when the ratio of oxygen and ammonia was 1.266 [41]. To achieve efficient degradation of NH\({}_{3}\), alcohols such as methanol [38; 41; 138], ethanol [125; 139; 140] and IPA [138; 141; 142; 143] were used in the SCWO treatment of ammonia and the degradation of ammonia could be drastically enhanced by controlling coexisting materials. Some researchers have developed detailed chemical kinetic models to clarify the effects of alcohols co-oxidation on the SCWO of ammonia and elucidate the reaction mechanisms in detail [124; 125]. [PERSON] et al. [125] constructed the initial ammonia-ethanol co-oxidation on the basis of the developed MPA-ethanol co-oxidation mechanism [126] composed of ammonia submechanism and ethanol submechanism. Although the initial model underpredicted the conversion of ammonia significantly and predicted the N\({}_{2}\)O yields poorly, it is accurate enough to provide a starting point for improvements. Figure 14 shows the predominant reaction pathways in the initial ammonia-ethanol mechanism. The reaction NO\({}_{2}\bullet\)+NH\({}_{2}\bullet\)=N\({}_{2}\)O+H\({}_{2}\)O is the dominant pathway forming N\({}_{2}\)O and the NO\({}_{\rm x}\) submechanism is in a dominant position under co-oxidation conditions. Since H\({}_{2}\)NNO\({}_{\rm x}\) adducts are more likely to be collision stabilized at high pressures, they were focused on improving the model predictions for ammonia conversion and N\({}_{2}\)O yield as the intermediate species of the NO\({}_{\rm x}\)+NH\({}_{2}\bullet\) reactions. The reaction surface and rearrangement products for the H\({}_{2}\)NNO\({}_{2}\) adduct and H\({}_{2}\)NNO adduct were calculated using Gaussian [144] software with the CBS-Q method [145] in the updated ammonia-ethanol co-oxidation model. The addition of the H\({}_{2}\)NNO\({}_{\rm x}\) adduct species have clearly improved the prediction of N\({}_{2}\)O yields, and the major reaction pathways for the revised ammonia-ethanol co-oxidation model are shown in Figure 15. However, the updated co-oxidation model cannot correctly reproduce the ammonia conversion trends as a function of temperature in experiments. Further studies of transient species are needed since the formation of the H\({}_{2}\)NNO\({}_{\rm x}\) and H\({}_{2}\)NONO adducts strongly affect the ammonia conversion trends and N\({}_{2}\)O production profiles. Figure 13: Revised major oxidation pathways of benzene in SCWO [123]. [PERSON] et al. [124] expounded the effects of methanol co-oxidation on SCWO of ammonia in detail based on the newly-developed elementary reaction model which combined the methylamine oxidation model [146] and ethanol/methanol oxidation model [147]. In the model simulations, the ammonia conversion increased with the increase in initial methanol concentration and the decomposition of methanol and the oxidation of CO mmol/L finished faster when NH\({}_{3}\) existed, which reproduced the phenomenological findings in the experiments.