Liquid-Liquid Equilibria in Ionic Solvent Systems
Summary
Liquid–liquid equilibria in ionic solvent systems govern the mutual solubilities and phase separations when one or more immiscible or partially miscible liquid phases interact, a phenomenon of central importance for chemical separations, extractions and waste treatment. In ionic solvent systems, which often employ ionic liquids or deep eutectic solvents, tunable interactions between ions, polar solvents and solutes give rise to complex phase behaviour. Such systems can exhibit striking selectivity for target compounds, minimal vapour pressures and enhanced thermal stability compared with conventional molecular solvents. The phase diagrams of these mixtures reflect a balance between ion–dipole, hydrogen bonding and van der Waals forces, modulated by temperature, composition and solvent structure. Thermodynamic models that capture excess Gibbs energy, such as the non-random two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) approaches, remain indispensable for correlating and predicting equilibrium data. Recent years have also seen the integration of quantum-chemical screening methods, such as conductor-like screening models (COSMO), and machine-learning techniques, including physics-guided neural networks and matrix completion methods, to augment experimental campaigns and generate reliable activity-coefficient parameters over broad chemical spaces. These advances support the design of greener extraction processes for aromatics, pharmaceuticals and metal separations, offering pathways to reduced energy consumption and improved sustainability. Interdisciplinary efforts link experimental measurements with high-throughput computational screening to accelerate the development of ionic solvent systems tailored to specific separations, underpinning innovations in biorefining, gas separation and environmental remediation.
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Liquid-Liquid Equilibria in Ionic Solvent Systems publication trend
The graph below shows the total number of articles in liquid-liquid equilibria in ionic solvent systems across all publications each year (not limited to Nature Index journals).
Technical terms
Liquid–Liquid Equilibrium (LLE): A state in which two immiscible or partially miscible liquids coexist with fixed compositions at given temperature and pressure.
Ionic Liquid: A salt in the liquid state below 100 °C, composed of discrete cations and anions, known for negligible vapour pressure and tunable solvating properties.
Activity Coefficient: A factor expressing deviation from ideality in a solution, used to calculate chemical potentials in non-ideal mixtures.
Non-Random Two-Liquid (NRTL) Model: A thermodynamic model for correlating excess Gibbs energy of liquid mixtures, accounting for local composition effects.
UNIQUAC Model: A universal quasi-chemical model for excess Gibbs energy that separates combinatorial and residual contributions based on molecular size and interaction parameters.
COSMO/SAC: A quantum-chemical approach predicting solvation and phase behaviour by computing surface charge densities of molecules in a conductor-like environment.
References
- Separation of benzene from cyclohexane by liquid-liquid extraction for a pseudo-ternary system with (sulfolane + 2-propanol) solvent: An experimental and modeling study. Results in Engineering (2024).
- SPT-NRTL: A physics-guided machine learning model to predict thermodynamically consistent activity coefficients. Fluid Phase Equilibria (2023).
- Extractive Distillation with Ionic Liquids To Separate Benzene, Toluene, and Xylene from Pyrolysis Gasoline: Process Design and Techno-Economic Comparison with the Morphylane Process. Industrial & Engineering Chemistry Research (2022).
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