Effects of ion concentration and solvent composition on the properties of water-methanol solutions of NaCl. NPT molecular dynamics computer simulation results

Abstract

Isothermal-isobaric molecular dynamics simulations are used to examine the microscopic structure and other properties of a model solution consisting of NaCl salt dissolved in water-methanol mixture. The SPC/E water model and the united atom model for methanol are combined with the force field for ions by Dang [J. Amer. Chem. Soc., 1995, 117, 6954] to describe the entire system. Our principal focus is to study the effects of two variables, namely, the solvent composition and ion concentrations on the solution's density, on the structural properties, self-diffusion coefficients of the species and the dielectric constant. Moreover, we performed a detailed analysis of the first coordination numbers of the species. Trends of the behaviour of the average number of hydrogen bonds between solvent molecules are evaluated.

Activity Coefficients and Solubilities of NaCl in Water–Methanol Solutions from Molecular Dynamics Simulations

“…Furthermore, Jörgensen and co-workers recommended the use of geometric combining rules in determining intra- and intermolecular cross interactions rather than the Lorentz–Berthelot (LB) rules. However, several prior studies ,,,, utilized the LB rules in simulations of water + methanol binary systems. As will be explained in the next section, it is important to use the geometric combining rule recommended by Jörgensen et al for the unlike interactions between OPLS-AA and SPC/E water Lennard-Jones (LJ) sites.…”

“…Ternary solutions of salt + water + an alcohol are of particular interest in many technological applications including crystallization, liquid–liquid extraction, and hydrometallurgical process, to name a few. A prominent such example is the NaCl + water + methanol ternary system which is frequently present in separation processes . The experimental ternary phase diagram (Shi et al) shows a sharp decline in solubility when moving from pure water to pure methanol as solvent.…”

“…Furthermore, there is a downward shift in the corresponding MIACs where the Debye–Hückel limiting slope falls much more sharply at higher methanol contents. There are a few prior studies of the NaCl + water + methanol system using molecular dynamics (MD) simulations. − ,, However, these studies have been limited to structural and some transport properties, such as pair correlation functions, coordination numbers, and self-diffusion coefficients. None of these reported MIACs and salt solubilities, which are the focus of the current work.…”

“…A prominent such example is the NaCl + water + methanol ternary system which is frequently present in separation processes. 52 The experimental ternary phase diagram (Shi et al 43 ) shows a sharp decline in solubility when moving from pure water to pure methanol as solvent. Furthermore, there is a downward shift in the corresponding MIACs where the Debye−Huckel limiting slope falls much more sharply at higher methanol contents.…”

On the properties of methanolic NaCl solution by molecular dynamics simulations

“…Recently, in [60], we explored the properties of NaCl solutions with water-methanol mixed solvent using the SPC/E water [38], united atom methanol [51] and NaCl force field due to Dang [61]. However, the limit of methanolic NaCl solution has not been explored profoundly.…”