When decomposing using a radical reaction in hydrothermal treatment, higher temperature conditions are required than in the case of hydrolysis in Q.11.
For example, when decomposing harmful substances, oxygen is added to supercritical water.
There is also lightening and gasification using radical reactions in supercritical water without using oxygen.

In SuperCriticla Water Oxidation (SCWO), supercritical water mixes with oxygen and the oil to be decomposed, making the reaction extremely easy. Utilizing this, persistent organic chlorine compounds such as PCBs and dioxins are almost completely decomposed. Applying this, Namhae Chemical Co., Ltd. of South Korea started operation of a plant that treats waste liquid in the explosive (DNT / MNT) manufacturing process at 2 m³/hour (waste liquid COD 50000 to 40ppm, total nitrogen 20000 to 60ppm).

The following operating plants have been put into operation in Japan as well.

Pilot plant for sewage sludge treatment (moisture content of 90% or more): 1.1 m³ / hour, 27 MPa, ~ 600 ° C [Kobe City, Hyogo Prefecture (1999)]

Semiconductor manufacturing waste liquid treatment: 25MPa, ~ 600 ℃ [Tateyama City, Chiba Prefecture (1998)]
→ The decomposition rate of TMAH, ammonia, and TOC is 99.9% or more. This can be reused as water used in the factory.

In the example of lightening and gasification, when polypropylene (PP) is treated with supercritical water for 30 minutes, the decomposition rate is reported to be 30% at 400 ° C, 70% at 415 ° C, and 95% at 430 ° C. When the processing time is 60 minutes, the decomposition rate is almost 100%. According to this report, PP becomes molten at high temperatures, and the polymer backbone undergoes thermal decomposition at random positions in the molten phase, initiating a radical reaction. Furthermore, decomposition products of a certain molecular size or smaller are diffused and dissolved in supercritical water, and reactions such as backbone cleavage, hydrogen abstraction, isomerization, cyclization, and radical-to-radical recombination proceed. The product that has been decomposed to the extent of an oligomer remains as an oil phase component. When the main chain end or side chain of PP is cut and further decomposed, it becomes a gas component.
When hexane, which is the main component of naphtha, was used as a raw material and treated with supercritical water at 25 MPa, 380 ° C, and a water addition rate of 0.67, the recovery rate of methane was 78 mol% or more.