The experimental data of viscosity and density for six binary mixtures of water (methanol or ethanol) with an ionic liquid, 1-butyl-3-methylimidazolium dimethylphosphate ([BMIM][DMP]) or 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM][DMP]), were measured in the temperature range of (293.15 to 333.15) K at atmospheric pressure using a viscometer and densimeter. The solution behavior of the mixtures is discussed in terms of the variation of the excess viscosity and excess volume with temperatures and compositions. It is found that both excess volume and viscosity of the mixtures studied show a negative deviation from the ideal solution behavior, and the viscosity of the mixtures decreases drastically with the increase of temperatures and mole fractions of solvents. The excess volume of the binary mixtures is quite low, in the range of (1.0 to 1.9) cm 3 3 mol À1 ; moreover, it shows a monotonic decrease with increasing temperature for the aqueous solution of ILs and a reverse trend for the IL solutions of methanol or ethanol at any concentrations. ' INTRODUCTIONIonic liquids (ILs), as a hybrid of neutral and ionic entities, show some unique properties, like negligible volatility, good conductivity and stability, and high solvating capacity for polar and nonpolar compounds, and are deemed as a potential greener solvent for many reactions and separation processes. For example, ILs might be applicable in the extractive desulfurization of fuel oils 1,2 and in extractive distillation of some mixtures with close boiling points or azeotropes 3,4 depending on the task and specific constituents of ILs. From the application point of view, it is necessary to know the physical and thermodynamic properties of ILs and their mixtures with other solvents, for example, density and viscosity, for the process design. From the academic point of view, the physical and thermodynamic data are also crucial in understanding the structureÀproperty relationship of ILs and the interaction between different ILs and solvents, in developing thermodynamic models, 5 and accordingly guiding the design of a task-specific ILs for different purposes.By far, many experimental data of density and viscosity of pure ILs have been reported and documented in some recent reviews; 6,7 however, the same property data for the IL-containing mixtures are quite scarce in comparison with the huge amount of IL species and possible combination approaches with different solvents. In our group, a series of vaporÀliquid equilibrium data have been measured for waterÀmethanolÀethanol systems containing an imidazolium-based ILs with a dialkylphosphate anion, for example, [MMIM][DMP], [EMIM][DEP], [BMIM][DBP], and [EEIM] [DEP], 8À10 aimed to find an appropriate entrainer for the efficient separation of ethanolÀwater solution. It is found that some of these ILs have a profound salting-out effect and can even break the azeotropic phenomena of the ethanolÀwater mixture at a specified IL-content and facilitate the distillation separation. To our understanding, these halog...

Surface tension data were measured by the Wilhelmy plate method for the binary mixtures containing an ionic liquid of the imidazolium dialkylphosphate family and water (methanol or ethanol) at 298.15 K and atmospheric pressure. The enthalpy of vaporization Δ1 g H m o and Hildebrand solubility parameter δH for the pure components are estimated from the experimental data, and a perfect correlation is found between surface tension and specific cohesive energy per unit surface area for the imidazolium dialkylphosphate series ionic liquids (ILs). The surface tension as well as the surface tension deviation against the solution composition shows a remarkable difference between the mixtures of an IL with water and with alcohols, which is interpreted qualitatively by the δH values of the corresponding pure components. Some ILs act as a surfactant in aqueous solution, but most of them more like a conventional nonelectrolyte component in the alcoholic solutions.

Densities were measured for the binary mixtures of water (methanol or ethanol) and an ionic liquid (IL) 1,3diethylimidazolium diethylphosphate [EEIM][DEP] or 1-n-butyl-3-ethylimidazolium diethylphosphate [BEIM][DEP] at 1 atm and (293.15 to 333.15) K using a vibrating-tube densimeter. The molecular volume, standard entropy, and lattice energy of the two ILs were estimated with the Glasser theory. The excess volumes are negative for all binary mixtures studied in the whole composition range, and reach to the maximum at the mole fraction of IL being around 0.3. Besides, they decrease with increasing temperature for the aqueous solution of ILs, whilst a reverse trend is found for the IL solutions of methanol or ethanol at any concentration. The excess molar volumes were correlated successfully by a fiveparameter polynomial equation as a function of temperature and mole fraction of IL with average absolute relative deviation (ARD) of density within 0.02%.