NaCl aggregation in water at elevated temperatures and pressures: Comparison of classical force fields

Area of Science:

• Physical Chemistry
• Chemical Engineering
• Materials Science

Background:

• Water properties change significantly with temperature and density, impacting its solvent capabilities.
• Supercritical water is a promising solvent for extraction and desalination due to tunable properties.
• Experimental challenges exist in obtaining data for salt-containing systems under supercritical conditions.

Purpose of the Study:

• To evaluate the accuracy of classical force fields for simulating salt solutions in supercritical water.
• To investigate the behavior of sodium chloride (NaCl) in water across a range of temperatures, pressures, and concentrations.
• To compare different water and salt models for their ability to predict structural properties.

Main Methods:

• Parametric study of NaCl in water using molecular simulations.
• Comparison of various salt and water force field models.
• Analysis of systems at 200-600 bar and 450-750 K with varying salt concentrations.

Main Results:

• All force fields reproduced liquid phase density trends and showed increased ion aggregation with decreasing density.
• Ion aggregation was more dependent on the salt force field than the water force field.
• A decrease in the static dielectric constant and reduced charge screening were observed with increasing NaCl concentration.

Conclusions:

• Classical force fields can qualitatively capture key trends in supercritical water-salt systems.
• Salt force field choice significantly impacts the prediction of ion aggregation and dielectric properties.
• Further refinement of force fields is needed for accurate quantitative predictions in supercritical solutions.