Molecular dynamics study with COMPASS II forcefield on nucleation and growth mechanism of sodium chloride in supercritical water

Abstract

Supercritical water gasification (SCWG) is a promising technology for converting and utilizing high-salt organic waste, while salt deposition problems seriously hinder its industrial application. In this work, the formation and evolution of sodium chloride (NaCl) clusters in supercritical water (SCW) at the range of (0.1–0.3) g·cm⁻³ and (673–1073) K are investigated using molecular dynamics simulations. The findings demonstrate that the nucleation and growth process can be divided into three stages: ion pairs, small ionic clusters, and large clusters. Nucleation processes are completed within the initial 20 ps, with the nucleation rate of NaCl in SCW reaching magnitudes of 10³⁶ m⁻³·s⁻¹, exhibiting an increasing trend with temperature and density. Lower densities and higher temperatures facilitate NaCl nucleation, and clusters grown at lower densities exhibit a more compact structure.