Ion-Pair Association in Ultrasupercritical Aqueous Environments: Successful Interplay among Conductance Experiments, Theory, and Molecular Simulations

Abstract

We discuss the interplay among theory, molecular simulations, and electric conductance experiments as an important tool for the extraction of ion-pair interaction potentials to make possible the bridging of the density gap between the lowest experimentally attainable conductance measurement and the theoretically acceptable zero-density limit of the ion-pair association constant. The density dependence of the Na + · · · Cl -pair association constant in ultrasupercritical (USC) steam environments is predicted by a constraint molecular dynamics simulation over state conditions relevant to the new generation of USC steam power plants. Finally, we draw attention to relevant modeling challenges associated with the behavior of these systems around the zero-density limit, discuss ways to overcome the drawbacks of traditional log K a -log F models, and illustrate the case with an explicit quartic (F) 1/2 -polynomial representation for log K a .

Toward the understanding of hydration phenomena in aqueous electrolytes from the interplay of theory, molecular simulation, and experiment

“…Moreover, while the second scenario provides a way to estimate the ion-pair association constant of electrolytes, something that has been achieved successfully for many relevant systems [224][225][226] , the first scenario might also be a viable approach to Figure 21a. These azimuthal angles can be taken as reference orientations since f = 0 represents the distributions in the plane perpendicular to the nitrate"s rigid geometry containing the N -O 1 bond (this distribution is identical to that defined by f = 120 due to molecular symmetry), while f = 60 defines the distribution on the plane bisecting the O 1 -N -O 2 angle and containing the N -O 3 bond, i.e., it describes a plane of symmetry.…”

Thermodynamics of Small Alkali Metal Halide Cluster Ions: Comparison of Classical Molecular Simulations with Experiment and Quantum Chemistry

“…6,7 Beyond specific applications, small vapor-phase cluster ions offer a unique window into the fundamental problem of single-ion solvation thermodynamics because, unlike ions in bulk liquid solutions, individual cluster properties can be studied experimentally using mass spectrometric methods based on equilibrium measurements 8−14 and collision-induced dissociation. 15−17 The experimental results have been used as anchoring points for the extrapolation of hydration properties to bulk conditions, 18,19 as well as for the development and validation of classical molecular force fields.…”

Limiting Conductivities and Ion Association Constants of Aqueous NaCl under Hydrothermal Conditions: Experimental Data and Correlations

“…3 As a result, sodium chloride has been used as a validity check for the calibration of conductivity high-temperature thermodynamic and transport property measurements 1, 4,5 and for theoretical studies of ionic transport and ion pairing under hydrothermal conditions. 6,7 The dependence of limiting equivalent conductivities Λ°on temperature and pressure for electrolytes has been described by a number of models. 8−17 All of these models are based on values for the conductivity of the chloride ion λ°(Cl − ) that were reported by Quist and Marshall in 1965.…”