Concentrated Brines in Aqueous Methanolic Solutions in Supercritical Conditions: Effect of Concentration and Composition from Molecular Dynamics Simulations

Abstract We have performed constant pressure constant temperature classical molecular dynamics simulations to study the effects of salt concentration and solvent composition of sodium chloride solutions at supercritical conditions. Structural properties of sodium chloride in water-methanol binary mixtures in supercritical conditions were determined in terms of potentials of mean force, radial distribution functions and hydrogen bonding. Potentials of mean force of Na+-Cl− ion-pairs in the binary mixtures showed the presence of contact ion pairs and solvent shared ion pairs and the depth of both the configurations increased with methanol content in the mixture and decreasing salt concentration. In a solution of low salt concentration, all the ions were found to be present as one single cluster whereas in higher salt concentration, smaller clusters of variable sizes were formed. The cluster size distribution shows strong dependence on salt concentration and less pronounced effect on the solvent composition.