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We study ion dissociation in four aqueous 1-alkyl-3-methyl-imidazolium chloride ([amim][Cl]) (where a = alkyl) ionic liquids (ILs) focusing on the effects of microstructure formation. We calculate ion dissociation using precise density, viscosity, and ionic conductivity measurements taken in this work as well as values reported by Rogac et al. (M. Bešter-Rogač, M. V. Fedotova, S.E. Kruchinin, and M. Klähn, Mobility and association of ions in aqueous solutions: The case of imidazolium based ionic liquids, Phys. Chem. Chem. Phys. 18, 28594–28605 (2016); R. Toma, A. Tot, J. Kuhar, and M. Be, Interactions in aqueous solutions of imidazolium chloride ionic liquids [C n mim][Cl] (n=0, 1, 2, 4, 6, 8) from volumetric properties, viscosity B-coefficients and molecular dynamics simulations, 254, 267–271 (2018)) in conjunction with our estimation framework presented previously (O. Nordness, L.D. Simoni, M.A. Stadtherr, and J.F. Brennecke, Characterization of Aqueous 1-Ethyl-3-Methylimidazolium Ionic Liquids for Calculation of Ion Dissociation, J. Phys. Chem. B 123, 1348–1358 (2019); L.D. Simoni, Predictive Modeling of Fluid Phase Equilibria for Systems Containing Ionic Liquids (University of Notre Dame, Notre Dame, IN, 2009)). We first consider ion dissociation at dilute IL concentrations below the critical aggregate concentrations (cac). We introduce a combined Stokes radii term calculated from limiting molar conductivity data, which more accurately estimates ion dissociation in dilute IL systems than radii estimated from a group contribution method. Incorporating the new radii term in the existing model, we study ion dissociation across a wide IL concentration range. Even if prior knowledge of aggregation were not available, as is the case for aqueous [amim][Cl] systems, aggregation is apparent from this analysis because the increased viscous forces of microstructure formation lead to unrealistic estimates of ion dissociation. [ABSTRACT FROM AUTHOR]

High pressure carbon dioxide was dissolved in ionic liquid + toluene mixtures to obtain the conditions of pressure and composition where a liquid-liquid phase split occurs at constant temperature. Ionic liquids (ILs) with four different cations paired with the bis(trifluoromethylsulfonyl)imide ([Tf2N]−) anion were selected: 1-hexyl-3-methylimidazolium ([hmim]+), 1-hexyl-3-methylpyridinium ([hmpy]+), triethyloctylphosphonium ([P2228]+), and tetradecyltrihexylphosphonium ([P66614]+). The solubility of CO2 was measured in the liquid mixtures at temperatures between 298 and 333 K and at pressures up to 8 MPa, or until the second liquid phase appeared, for initial liquid phase compositions of 0.30, 0.50, and 0.70 mole fraction of IL. Ternary isotherms were compared with the binary solubility of CO2 in each IL and pure toluene. The lowest pressure for separating toluene in a second liquid phase was achieved by decreasing the temperature of the system, increasing the amount of toluene in the initial liquid mixture and using [hmim][Tf2N]. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2968-2976, 2015 [ABSTRACT FROM AUTHOR]

Recommendations are given for reporting in the primary scientific literature of measurements involving phase equilibrium. The focus is on documentation issues, and many of the recommendations may also be applied to the more general fields of thermodynamic and transport properties. The historical context of the work and specific plans for implementation of the recommendations are discussed. [ABSTRACT FROM AUTHOR]

A new approach for modeling liquid−liquid equilibrium in electrolyte/mixed-solvent systems is presented, with particular focus on systems involving a dilute aqueous solution of an ionic liquid (IL). This new approach involves an asymmetric framework in which different phases have different degrees of electrolyte dissociation, and are thus represented by different Gibbs free energy models. As a first case, we consider the situation in which the electrolyte is either completely dissociated or completely paired (molecular), with its state depending on the dielectric constant of the mixed solvent and on the concentration of the salt in the phase in question. The theory underlying this asymmetric framework is developed, and a rigorous approach for phase stability analysis is presented. It is explained how to formulate and solve the parameter estimation problem for determining model parameters from binary data, and this process is demonstrated using examples. An immediate goal is to use this approach to predict liquid−liquid equilibrium for ternary IL/solvent/water systems, using parameters obtained from binary and pure component data only. [ABSTRACT FROM AUTHOR]

For the computation of chemical and phase equilibrium at constant temperature and pressure, there have been proposed a wide variety of problem formulations and numerical solution procedures, involving both direct minimization of the Gibbs energy and the solution of equivalent nonlinear equation systems. Still, with very few exceptions, these methodologies may fail to solve the chemical and phase equilibrium problem correctly. Nevertheless, there are many existing solution methods that are extremely reliable in general and fail only occasionally. To take good advantage of this wealth of available techniques, we demonstrate here an approach in which such techniques can be combined with procedures that have the power to validate results that are correct, and to identify results that are incorrect. Furthermore, in the latter case, corrective feedback can be provided until a result that can be validated as correct is found. The validation procedure is deterministic, and provides a mathematical and computational guarantee that the global minimum in the Gibbs energy has been found. To demonstrate this validated computing approach to the chemical and phase equilibrium problem, we present several examples involving reactive and nonreactive components at high pressure, using cubic equation-of-state models. [Copyright &y& Elsevier]

Abstract: A method based on interval analysis is presented for determining parameter values from mutual solubility data in two-parameter activity coefficient models for liquid–liquid equilibrium. The method is mathematically and computationally guaranteed to locate all sets of parameter values corresponding to stable phase equilibria. The technique is demonstrated with examples using the NRTL and electrolyte-NRTL (eNRTL) models. In two of the NRTL examples, results are found that contradict previous work. In the eNRTL examples, binary systems of an ionic liquid and an alcohol are considered. This appears to be the first time that a method for parameter estimation in the eNRTL model from binary LLE data (mutual solubility) has been presented. [Copyright &y& Elsevier]

Themolecular interactions between the ionic liquid trimethylbutylammomiumbis(trifluoromethylsulfonyl)imide, [N1114][Tf2N], and three common solvents, including short chain alcohols (ethanoland 1-propanol) and an aprotic solvent (N,N-dimethylformamideor DMF) were investigated through experimental properties. The excessenthalpies were measured by calorimetry at temperatures from 308.15K to 323.15 K over the whole composition range and excess volumeswere calculated from density measurements. The vapor–liquidequilibrium (VLE) measurements of the [N1114][Tf2N] + DMF mixture were obtained using a headspace gas chromatographyinstrument. It was determined that hydrogen bonds between the alcoholmolecules contribute to the positive excess enthalpies, while thefavorable interactions between DMF and [N1114][Tf2N] might be explained by electrostatic interactions between the ionicliquid and the zwitterionic resonance structure of DMF. The nonrandomtwo liquid (NRTL) equation was successfully used to correlate theexcess enthalpy and VLE results. [ABSTRACT FROM AUTHOR]

Abstract: Ionic liquids (ILs) have been suggested as potential “green” solvents to replace volatile organic compounds in reaction and separation processes due to their negligible vapor pressure. In order to develop ILs for these applications, it is important to understand the factors that control their phase behavior with other liquids. In this work, we continue our study of the effect of different factors on the phase behavior of imidazolium-based ionic liquids with alcohols, focusing on ILs with somewhat longer alkyl chains (hexyl and octyl) on the cation. All systems exhibit upper critical solution temperatures (UCSTs), with low solubility of the IL in the alcohol and high solubility of the alcohol in the IL. Increasing the alkyl chain length on the alcohol causes an increase in the UCST of the system. By contrast, increasing the alkyl chain length on the cation results in a decrease in the UCST of the system. Decreasing hydrogen bonding opportunities with the cation by replacing a hydrogen atom with a methyl group at the C2 position on the imidazolium ring results in an increase in the UCST. The degree to which the anion affects the UCST diminishes with increasing length of the cation alkyl chain. [Copyright &y& Elsevier]