An electrolyte equation of state based on a hydrogen-bonding nonrandom lattice fluid model for concentrated electrolyte solutions

Abstract

Equations of state that are based on lattice fluids have been in use for nonelectrolyte components and their mixtures with somewhat different characteristics from hard-sphere chain-based equations of state or cubic equations. In the present study, an electrolyte equation of state was developed, based on a hydrogen-bonding nonrandom lattice fluid theory, by adding the long-range contribution that is due to the mean spherical approximation. Hydrogen bonding of solvent molecules and solvation between solvent molecules and cations were explicitly included by association contribution to extend the applicability to highly concentrated electrolyte solutions. Segment numbers of ions were obtained from the Pauling diameter, using the previously developed relationship between lattice and off-lattice fluids. The remaining electrolyte parameters-namely, interaction energy between electrolyte and solvent, hydrated ionic diameter, and hydration energy between cation and solvent molecule-were fitted to osmotic coefficients and mean activity coefficients at 298.15 K and 1 bar. Good agreements were obtained between the experimental and calculated results over the wide range of compositions, up to a molality of 20, with average absolute deviations (AADs) of 1.0%, 1.1%, and 1.6% for the osmotic coefficients, the mean activity coefficients, and the densities of 94 aqueous electrolyte solutions, respectively. The equation of state was determined to be applicable to sodium chloride solutions in the temperature range of 273-373 K when these properties were calculated using a temperature-dependent binary interaction parameter. Examples were presented for 1: 1 electrolytes to show that parameters of monovalent ions, rather than electrolyte parameters, can be used.