Studies On The Properties Of Room Temperature Ionic Liquids And Its Aqueous Solutions

Ionic liquids (ILs) or room temperature ionic liquids (RTILs) are viewed as a novel class of green benign solvents, which promise wide-spread application in industry, possibly replacing currently used organic solvents due to unique properties such as negligible vapor pressures, broad liquid temperature ranges, and high specific solvent abilities. In particular, after IL EMIBF₄ was synthesized at 1992, many new air- and water-stable IL were reported, and have recently received increased attention from both industrial and academic communities. In spite of their importance and interest, accurate values for many fundamental physical-chemical properties of this class ILs are either scarce or even absent.First, this paper reports measurements of surface tension of ionic liquid EMIES (1-ethyl-3-methylimidazolium ethyl sulfate) using the forced bubble method at 278.15 to 323.15 K and densities of EMIES using Westphal balance at 278.15 to 338.15 K . For pure IL the interstice theory was put forward and according to the new theory, the expression of average volume of the interstices, v , was derived. The interstice volume fraction calculated by the expression is 0.12 for IL EMIES and it is in good agreement with that of majority of materials which exhibit 10¹5% volume expansion in processes from the solid to liquid state. It is considered that the thermalexpansion coefficient, α₀ , of ionic liquids is only dependent on the thermalexpansion of the interstices, and the value of α₀ calculated by the theory is in goodagreement with experimental value.Second, this paper reports measurements of densities of EMIES aqueous solutions at 278.15 to 333.15 K, with the concentration range from EMIES molality 0.2224 to 3.044 mol/kg. This paper reports volumetric properties of aqueous solution of ionic liquid EMIES. The values of Pitzer's parameter for volumetric properties,β_MX^(0)V,β_MX^(1)V, C_MX^V in the temperature range from 278.15 to 333.15 K and apparentmolar expansibility of EMIES, *E, and the coefficient of thermal expansion of the solutions, a, were obtained.Third, this paper reports measurements of surface tension of ionic liquid EMIES concentrated aqueous solutions at 278.15 to 323.15 K and densities of EMIES concentrated aqueous solutions at 278.15 to 338.15 K, with the concentration range from EMIES mole fraction 0.06 to 0.94. For EMIES aqueous solutions apparent molar volumes were calculated and the latter were treated by Pitzer-Simomson theory and Clegg-Pitzer theory, respectively. The values of Pitzer-Simomson parameters and Clegg-Pitzer parameters were obtained by fitting experimental data.The standard potential of the (Ag-AgCl) electrode, Eo, the standard second ionization constant of sulfuric acid, K2, and the standard association constant of theion pair [MgSOA]°, Kms, in the mixed solvent 15 mass % ethanol-water were determined from precise e.m.f. measurements of different cells without liquid junction. The dependence of pKaxx on temperature T is expressed by the empiricalequations: pKaxs =a, +a2(K/DT). The other thermodynamic functions of theassociation process were also calculated and showed that the driving force for the process of the ion pair is the entropy of association. Combining Owen's definition about medium effect with Pitzer's equation, the values of Pitzer's parameters of interaction between ions and ethanol can be obtained by fitting the experimental data.