Peculiarities of Carbamide Hydrolysis and Oxidation in a Water–Oxygen Fluid

The transformations of carbamide in a water–oxygen fluid (at a carbamide concentration of 0.29–0.39 mol/L, oxygen excess coefficient OR = 0.98–1.25, mole fraction of water 70.0–91.3%) are studied in a batch reactor when heated to 873 K at a rate of 1 K/min. It is shown that the transformations proceed via the mechanism of parallel and sequential reactions, including carbamide hydrolysis, formation and decomposition of cyanuric acid, oxidation of ammonia and products of the decomposition of cyanuric acid. From the analysis of the time dependencies of temperature and pressure, it follows that the oxidation of carbamide occurs predominantly heterogeneously on the surfaces of the reactor wall and the Pt–Rh/Pt-thermocouple inserted into the center of the reaction volume. It is established that excess oxygen (OR = 1.25) or the addition of NaOH leads to an increase in the fraction of nitrogen converted into N2 and prevents the formation of cyanuric acid. The influence of the concentration of reagents on the ratio of carbamide conversion pathways and the dynamics of heat release is discussed.