Supercritical water co-oxidation behavior in the different monohydric alcohol-ammonia reaction environment

Abstract

The degradation of ammonia is a key rate-limiting step during the supercritical water oxidation of nitrogen-containing organics. This paper studied the co-oxidation behavior between different ammonia-alcohol environments, including the influence of reaction parameters and the co-oxidation mechanism. The results showed that increasing temperature, oxidation coefficient, residence time, and alcohol concentration significantly promoted the degradation of NH3–N and TOC, while rising the ammonia concentration enhanced the NH3–N destruction but inhibited the TOC degradation. Alcohols were oxidized first in the co-oxidation system to produce more OH* and HO2* radicals. Ethanol generated the highest concentration of HO2* in the shortest time, leading to more significant ammonia removal than isopropanol and methanol; however, the produced intermediate products like aldehydes and ketones reacted with residual ammonia to generate a small amount of organics at lower temperatures, inhibiting the degradation of alcohols slightly, and combined catalyst or nitrate in the batch reactor or used continuous supercritical water oxidation or supercritical hydrothermal combustion system without controlling the exotherm of fuels could improve this.