A colleague at the Technical University of Denmark has often stated: “Life is too short for electrolytes”. Another well-known scientist in the field of molecular simulation has recently said during ...an international Thermodynamics conference: “All my life I have tried to keep myself away from water and electrolytes”. Sadly, what these statements correctly imply is that there are far too many unclear questions and concepts in electrolyte thermodynamics, and associated difficulties in modeling electrolyte solutions. In this work, we attempt to shed some light on some important concepts and misconceptions in electrolyte thermodynamics associated with the development of electrolyte equations of state, with emphasis on those based on the Debye-Hückel theory. Detailed mathematics is needed for some of the derivations but for brevity and in order to emphasize the principles rather than the derivations, the latter are omitted. We first discuss the peculiarities of electrolyte thermodynamics and associated modeling and continue with a literature review of equations of state for electrolyte solutions. Next we will provide a modern derivation of the Debye-Hückel and Born equations and discuss their assumptions in detail to answer some of the confusion that exists in current literature on the applicability ranges and show how the different versions of the Debye-Hückel and Born models are related. A discussion and outlook section conclude this review. Several of the statements in this work challenge “accepted beliefs” in electrolyte thermodynamics and, while we believe that this challenge is justified, we hope that a useful debate can result in improved and predictive thermodynamic models for electrolyte solutions.
The CPA equation of state is applied to model binary, ternary, and multicomponent mixtures that contain CO2 with polyethylene glycols or compounds relevant to biodiesel production, such as glycerol ...and various triglycerides. Effort has been made to evaluate the model performance on correlating both the liquid and the vapor phase compositions, which is a demanding task, revealing the model’s and parameters’ limitations, due to the rather low concentrations of heavy compounds in the vapor phase. Initially the model’s binary parameters, which in all cases were temperature independent, were estimated using experimental data for binary systems. Those parameters were used to predict the phase behavior of supercritical CO2 containing ternary and multicomponent mixtures. Since no parameter was adjusted to ternary or multicomponent systems’ data, the reported CPA results for such mixtures are considered as pure predictions. This is the final part of a series of studies Tsivintzelis et al. Fluid Phase Equilibria 430 (2016) 75–92 and 504 (2020) 112337 that complete the parameterization of the CPA equation of state for systems relevant to the biodiesel production, which allows the application of the model to multicomponent mixtures of the relevant processes.
Abstract
Ionic liquids (ILs) have received much attention in both academia and industries due to their superior performance in many applications. Efficient recovery/recycling of ILs from their dilute ...aqueous solutions is essential for the acceptance and implementation of many IL‐based technologies by industry. In this work, a practical and cost‐effective hybrid process design method that combines aqueous two‐phase extraction, membrane separation, and distillation operating at their highest efficiencies is proposed for the recovery of hydrophilic ILs from dilute aqueous solutions. The application of this hybrid process design method is illustrated through case studies of recovering two hydrophilic ILs, n‐butylpyridinium trifluoromethanesulfonate (C
4
PyTfO) (CAS number: 390423‐43‐5) and 1‐butyl‐3‐methylimidazolium chloride (C
4
mImCl) (CAS number: 79917‐90‐1), from their dilute aqueous solutions. For the recovery of 10 wt.% C
4
PyTfO from aqueous solution, the hybrid process using (NH
4
)
2
SO
4
as the salting‐out agent could reduce the total annual cost (TAC) and energy consumption by 57% and 91%, respectively, compared with the pure distillation processes. In the case of recovering 10 wt.% C
4
mImCl from aqueous solution, the reduction in TAC and energy savings of the hybrid process with salting‐out agent (NH
4
)
2
SO
3
could reach 49% and 87%, respectively, compared with the pure distillation process. Furthermore, uncertainty analysis through Monte Carlo simulations show that the proposed hybrid process design is more robust to uncertainties in energy prices and other material (e.g., equipment and solvent) costs.
The eCPA equation of state has been shown to be a promising electrolyte model, for which several applications have been demonstrated. The model at its current status is, however, limited by the use ...of salt-specific parameters for the interactions between salts and water. Having salt-specific parameters limit the applicability to simple systems of ions, as it can only be applied when a common ion is found between the salts in the solution. For more complex systems of multiple ions/salts this may not work well. In this work the main goal is to eliminate this limitation by parametrizing the model with an ion-specific parameter set. The ion-specific parameters are estimated by a simultaneous fitting of parameters for 17 ions, consisting of 10 cations and 7 anions, and with data for 55 salts. The parameters are fitted to osmotic coefficient and mean ionic activity coefficient data in a wide temperature range from 273.15 K to above 500 K and up to an ionic strength of 6 molal. The parameters are found to yield similar deviations as the salt-specific parameters, however, for a few salts cation-anion interaction parameters were needed in order to obtain reasonable accuracy.
The parameters are applied to a series of systems, which include mixed salt osmotic coefficients, solid-liquid equilibrium and vapor-liquid equilibrium of water-methanol-salt, illustrating the applicability of the ion-specific parameters. Modelling of mixed salt osmotic coefficients illustrate that the parameters work well in salt mixtures, while the phase equilibria alsv o illustrate the extension to mixed solvent systems.
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