The mechanism of methyl hydrazine degradation by supercritical water oxidation using ReaxFF simulation

Abstract

Methyl hydrazine (MMH) is a key ingredient in rocket fuel as well as an important intermediate and solvent in organic synthesis. However, any remaining MMH in environment could be harmful to both people and the environment. In this work, we proposed a method for treating MMH pollution by supercritical water oxidation (SCWO) technology. Reactive molecular dynamics were used to reveal the microscopic mechanism of the oxidation decomposition of MMH. The results showed that the principle of SCWO is that the OH radicals are formed by the reaction between H2O and O2. It can effectively capture the H both in MMH and its decomposition fragments, thus speeding up the decomposition. At low temperature and low oxygen content, the initial decomposition of MMH has two main pathways: (1) CH3NHNH2 → CH3NH + NH2 (R1), and (2) CH3NHNH2 + OH → CH3NNH2 + H2O (R7). N2, CO2, and H2O are the final products. At high temperatures, the intermediate NH3 can be converted to N2. The activation energy of MMH decomposition with excess oxygen was also obtained by the Arrhenius equation as 29.3 kcal/mol.