Ion-Pair Association Constant for LiOH in Supercritical Water

Abstract

The equilibrium ion-pair association constant for LiOH in supercritical water is determined by means of molecular dynamics (MD) simulations via the potential of mean force calculation. Simulations are performed along three supercritical isotherms of (673.15, 773.15, and 873.15) K, covering a density range from (0.05 to 0.8) g·cm–3. Over the examined temperature and density range, the obtained association constant increases with increasing temperature and decreasing density. A significant increase in the association constant is observed upon transition into the low density (ρ < ρc) supercritical region. The obtained results are compared with the available experimental data at the corresponding states. To determine the corresponding states, an accurate reference equation of state for the simulated water model is used. An analytical expression for the association constant of LiOH in aqueous solution over the examined thermodynamic range is given. The results are of practical interest for chemistry control in the supercritical water-cooled nuclear reactor heat transport system.