Mixed Solvent Electrolyte Solutions: A Review and Calculations with the eSAFT-VR Mie Equation of State

In this work, mixed-solvent mean ionic activity coefficients(MIAC),vapor-liquid equilibrium (VLE), and liquid-liquid equilibrium(LLE) of electrolyte solutions have been addressed. An extended literaturereview of existing electrolyte activity coefficient models (eG(E)) and electrolyte equations of state (eEoS) for modeling mixedsolvent electrolyte systems is first presented, focusing on the detailsof the models in terms of physical and electrolyte terms, relativestatic permittivity, and parameterization. The analysis of this literaturereveals that the property predictions can be ranked, from the easiestto the most difficult, in the following order: VLE, MIAC, and LLE.We have then used our previously developed eSAFT-VR Mie model to predictMIAC, VLE, and LLE in mixed solvents without fitting any new adjustableparameters. The model was parameterized on MIAC of aqueous electrolytesolutions and successfully extended to nonaqueous, single solventelectrolyte solutions without any new adjustable parameters by usinga salt-dependent expression for the relative static permittivity.Our approach yields excellent results for MIAC and VLE of mixed solventelectrolyte solutions, while being fully predictive. LLE is significantlymore challenging, and an accurate model for the salt-free solutionis crucial for accurate calculations. When the compositions of thetwo phases in the binary salt-free system are accurately captured,then the electrolyte extension of our model shows a lot of potentialand is currently among the best eEoS for LLE prediction in the literature.

Automated summary

This study focuses on the mixed-solvent electrolyte solutions and addresses the mean ionic activity coefficients, vapor-liquid equilibrium, and liquid-liquid equilibrium. The existing models and equations of state for electrolyte systems are reviewed, with emphasis on physical and electrolyte terms, relative static permittivity, and parameterization. A predictive model, eSAFT-VR Mie, is used to predict the activity coefficients, vapor-liquid equilibrium, and liquid-liquid equilibrium without any new adjustable parameters. The model shows excellent performance in predicting the activity coefficients and vapor-liquid equilibrium, while the prediction for liquid-liquid equilibrium is more challenging but has potential with accurate composition capturing.