Physical properties of binary mixtures : ionic liquids + alcohols

Information on the interactions between ionic liquids and molecular solvents are essential for the understanding of the function of ionic liquids in related procedures, and excess properties are sensitive probe for studying these interactions. In this paper, physical properties such as densities and speeds of sound of the binary systems containing 1–propyl–4– methylpyridiniumbis(trifluoromethylsulfonil)imide and 1propyl–4–methylpyridiniumbis(trifluoromethylsulfonil)imide, ethanol and propanol, over the whole composition range were measured at T=(298.15, 308.15, 318.15) K and at atmospheric. These data were used to calculate the corresponding derived properties such as excess molar volumes and excess molar isentropic compressions, which were fitted with the RedlichKister equation. For the studied systems, the excess molar volume values show a sinusoidal behaviour with a minimum at high concentrations of alcohol due to changes from negative to positive values when the alcohol ́s alkyl chain length increases. The excess molar isentropic compression values are negative over the whole composition range and presenting also a minimum at high concentrations of alcohol. It is possible observed that an increase of the temperature causes that the negative excess molar volume and excess molar isentropic compression values for the alcoholic mixtures deviate more from ideality. INTRODUCTION The need to replace the volatile organic compounds has led to an increase the study of alternative solvents, such as ionic liquids, and of their properties which make them a versatility compounds to use on many different process like organic synthesis, chemical processing, liquid-liquid separations. Because of their importance and interest, detailed knowledge of the thermodynamic behavior of the mixtures of ionic liquids with organic solvents, is very important for using them in different processes [1]. The density and speed of sound data can be used to calculating the excess molar volumes and excess molar isentropic compressions, which are useful for the understanding of intermolecular interactions in the systems. In this work, density and speed of sound were measured for the binary mixtures (ionic liquid + alcohol) for 1-Propyl-4MethylpyridiniumBis(trifluoromethylsulfonil)imide [PMpy][NTf2] and 1-Propyl-3-Methylpyridinium Bis(trifluoromethylsulfonil)imide [PMpy][NTf2] with ethanol and 1-propanol.at T=(298.15, 308.15, 318.15) K. from these experimental results, excess molar volumes and excess molar isentropic compressions were calculated and fitted to a RedlichKister type equation. EXPERIMENTAL Ethanol and 1-propanol were purchased from Sigma– Aldrich with mass fraction purity higher than 0.999. They were degassed ultrasonically and dried over molecular sieves type 4.10-8 cm, supplied by Aldrich, and kept in bottles under inert atmosphere. The ionic liquid used in this work was acquired at IoLiTec with mass fraction purity higher than 0.99. This compound was dried under vacuum (p = 0.2 Pa) with stirring at moderate temperature (T = 343 K) for at least 48 h, to reduce the water content and volatile compounds to negligible values. All chemicals were always manipulated inside a glove box under an argon atmosphere to avoid water absorption. The purity of the solvents was checked by comparing the experimental density and refractive indices obtained with the data found in the literature [2-4] (Table 1). All binary mixtures were prepared by weighing using a Mettler AX-205 Delta Range balance with an uncertainty of ±3 10-4 g. Special care was taken to avoid variations in composition due to evaporation of solvent or pickup of water by the ionic liquid. For this, all samples were prepared immediately prior to measurements into stoppered bottles inside a glove box, which is under argon atmosphere. APPARATUS AND PROCEDURE Densities and speeds of sound of the pure ionic liquid were measured using an Anton Paar DSA-5000 digital vibrating-tube densimeter. The repeatability and uncertainty in experimental measurements have been found to be lower than ±(2 . 10-6 and 3 .10-5 ) g cm-3 for the density and ±(0.01 and 0.3) m s-1 for the speed of sound, respectively. This equipment has a temperature controller that keeps the samples at working temperature with an uncertainty of ±0.01 K. Moreover, the equipment automatically detects the presence of bubbles in the cell. The apparatus was calibrated by measuring the density of Millipore quality water and ambient air according to the manual instructions. The calibration was checked with known density and speed of sound of pure organic compounds. 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics