Modeling of Gas Solubility in Aqueous Electrolyte Solutions with the eSAFT-VR Mie Equation of State

In
this work, the eSAFT-VR Mie equation of state (EoS) is applied
to water–methane–salt and water–carbon dioxide–salt
mixtures. Initially, the EoS parameters for nonelectrolyte systems
are fitted, and temperature-dependent water–ion interaction
parameters are introduced to improve the behavior of the model at
high temperatures. Furthermore, a database of experimental methane
and carbon dioxide solubility in single-salt aqueous solutions was
compiled. Four different parameterization schemes regarding gas–ion
dispersion energy have been pursued in this work, namely, (a) setting
the gas–ion dispersion energy parameter to zero, (b) using
the SAFT-VR Mie combining rules without any binary interaction parameters,
(c) using the predictive Hudson–McCoubrey combining rules,
and last but not least (d) fitting to experimental solubility of gases
in aqueous solutions of single salts. The fitting approach yields
an average deviation from experimental data of about 10%, compared
to more than 25% for the other approaches. However, despite the great
overall deviations of the predictive methods, there are cases where
they yield excellent results, such as methane solubility in aqueous
NaCl solutions. The salting-out behavior predicted with the fitted
parameters is excellent at room temperature but deviates from experimental
data at higher temperatures. Finally, the model is applied to gas
solubility in mixed-salt solutions, without further adjustable parameters,
and the predictions are in excellent agreement with experiments. Overall,
eSAFT-VR Mie shows great potential for gas solubility calculations
under salinity.