Commonly used solvents for separation of aromatics from aliphatics using liquid−liquid extraction are reviewed in terms of their physical properties and separation performance. The experimental liquid− liquid measurements for conventional solvents are contrasted with the phase behavior when using an ionic liquid as the extracting component. For comparison purposes, ternary systems of heptane + toluene + extraction solvent are used as representative mixtures, where sulfolane is the main organic extraction solvent discussed. Since ionic liquid properties are drastically changed by changing the anion, comparisons are performed for 1ethyl-3-methylimidazolium based ionic liquids using different anions. Ionic liquids containing cyano-substituted and bis(trifluoromethylsulfonyl)imide anions provide good selectivities and distribution ratios. On the basis of the phase behavior and capacities, as well as their relatively low viscosities, they appear to be competitive alternatives to organic solvents.

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The solubility of carbon dioxide in nine ionic liquids (ILs), at 298 K, 313 K, and 333 K and pressures up to 9 MPa, is presented. The solubility of CO2 in the selected ILs increases with increasing pressure and decreases with increasing temperature, as expected. The effect of several different anions on the solubility of CO2 with a common 1-ethyl-3-methyl­imidazolium cation is studied in this work. The anions compared were hydrogen sulfate ([emim][HSO4]), methylsulfate ([emim][MeSO4]), methane sulfonate ([emim][MeSO3]), thiocyanate ([emim][SCN]), and diethylphosphate ([emim][DEP]). The results for 1-ethyl-3-methyl­imidazolium hydrogen sulfate are particularly interesting and can be explained based on the stronger attractive interactions between the IL and CO2, which is supported by quantum calculations. Other ILs investigated were ethyl(tributyl)phosphonium diethylphosphate ([P2444][DEP]), 1-hexyl-3-methyl­imidazolium trifluoromethane sulfonate ([hmim][OTf]), 1-(2-hydroxyethyl)-3-methyl­imidazolium trifluoroacetate ([OHemim][TFA]), and trihexyl tetradecyl­phosphonium bis(trifluoro­methyl­sulfonyl)imide ([P66614][Tf2N]). Using the new data for the [emim]+ ILs, in concert with data from the literature, these ILs were selected primarily to study the effect on the solubility of changing the cation. Of particular note is the high solubility of CO2 in the trihexyltetra­decyl­phosphonium based IL compared with its imidazolium equivalent. A brief discussion is presented to explain the observed solubility results.

Deep eutectic solvents (DES) have emerged as promising 'green' solvents, but their successful industrial application requires relatively low viscosity. DES prepared from choline chloride and glycols offer such possibility. Viscosity and density are reported for a number of DES obtained by mixing choline chloride and a glycol (ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol). The measurements were performed at 101.3 kPa, at temperatures between 293.15 K and 333.15 K, and for different mole ratios of the glycol and choline chloride. The viscosity was measured with a capillary viscometer, while the density was measured by means of a vibrating U-tube densimeter. The density and viscosity data have expanded relative uncertainties of 0.2% and 2.0%, respectively, with a coverage factor of 2. The viscosity of pure glycols was modeled using the extended hard-sphere (EHS) model that has its basis in kinetic theory and the molecular description of the fluid. Each DES was treated as a binary mixture, and the EHS model was used, with a mole average mixing rule, to calculate its viscosity. The measured DES viscosity data were represented with the average absolute deviation of 1.4% and a maximum deviation of 7%.

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