Molecular Simulations of Dense Hydrothermal NaCl-H2O Solutions from Subcritical to Supercritical Conditions

This research has demonstrated that simple structural and potential models can qualitatively and quantitatively predict properties in dense hydrothermal solutions of sodium chloride and water using molecular dynamics simulation. The PTFxi behavior of simulated model systems at 250 bar and 21 wt % NaCl compared favorably to experimental data from ambient to near-critical temperatures as represented by the Anderko-Pitzer equation of state. The system internal energy, including both dispersion and electrostatic contributions, was computed for a range of temperatures from 177 to 727 °C at 250 bar and found to be realistic in terms of the known thermodynamic properties of water. Radial distribution functions indicate little change in water structure from ambient to near-critical temperatures but large changes in ion association consistent with experimental observation. We found that varying system pressure from 250 to 1000 bar does not noticeably affect solution structure or ion association at subcritical conditions.