Study on supercritical water partial oxidation mechanism of sulfur-containing compounds by ReaxFF molecular dynamics

Supercritical water partial oxidation (SCWPO) is a new type of highly efficient and clean energy conversion technology. This technology adds less oxidant than that required for complete oxidation in the supercritical water environment, altering the original reaction process. However, there is limited research on the role of oxidants and the migration of sulfur during the SCWPO process. Therefore, the conversion of sulfur-containing compounds during the SCWPO process were investigated by ReaxFF molecular dynamics simulation. The results indicated that the cleavage of C-S bonds was the key step in the decomposition of sulfur-containing compounds. Free radical reactions were the important part of the SCWPO process. The reactants provided the initial ·H radicals, which promoted the decomposition of water, generating ·OH radicals. The ·OH radicals attacked molecules and were converted into ·H radicals. O₂ mainly affected free radical reactions by increasing the number of ·OH radicals. However, excessive amount of ·OH radicals hindered the participation of O₂. Through the interconversion of free radicals, the SCWPO process achieved efficient conversion of reactants. The migration of sulfur was clearly driven by free radical reactions. HS·/HOS· radicals were very crucial sulfur radicals that could be oxidized or reduced to form H₂S or inorganic acids. The addition of O₂ promoted the oxidation of sulfur, thereby facilitating its conversion to cleaner inorganic ionic forms.