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

Abstract

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 PTFx i 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.

Ion Association in Hydrothermal Sodium Sulfate Solutions Studied by Modulated FT-IR-Raman Spectroscopy and Molecular Dynamics

“…A similar increase of the first maximum of the RDF has been reported by Reagan et al 37 in a study on cluster formation in dense NaCl solutions at hydrothermal conditions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 The RDF of the simulations at 300 °C and 320 °C furthermore exhibits a strong, broad second maximum at 0.625 nm, which suggests that larger clusters with a second coordination shell of ions exist.…”

Quantitative approaches for the description of solubilities of inorganic compounds in near-critical and supercritical water

“…Approaches using molecular dynamics have shown interesting insights in the fundamental ideas of supercritical water and systems containing supercritical water and inorganic compounds [14][15][16][17][18]. These studies are focused on the behavior of supercritical water and not on the quantitative description of the solubility of salts.…”

Guidelines for Phase Separations in High-Temperature and Supercritical Water Solutions: A Report on a Workshop Organized by the U.S. Army Research Office and the Forschungzentrum Karlsruhe, 7-9 July 1999

“…In the second area, the research focus has been on experimental characterization of phase boundaries and compositions in binary (single salt-water) and ternary (two salt-water) systems (e.g., Armellini and Tester, 1993;DiPippo et al, 1999) and on modeling of salt-water systems in general (Cui and Harris, 1995a,b;Reagan et al, 1999;Tester et al, 1998).…”

“…For example, various researchers (at MIT, NIST, ORNL, and elsewhere) are quantifying the PTXj behavior of the NaCl-Na 2 S0 4 -H 2 0 binary and ternary systems using the Anderko-Pitzer model and other theoretically based equations of state (see papers presented by Anderko and Simonson from this workshop for further details). In separate studies at MIT and ORNL, molecular simulations are being used to shed light on important phenomena in hydrothermal and supercritical salt solutions, such as local solvation and solution structure, hydrogen bonding, ion pairing, solid phase nucleation, phase coexistence, and spinodal decomposition (Reagan et al, 1999).…”