Thermodynamic Studies of Ionic Interactions in Aqueous Solutions of Imidazolium-Based Ionic Liquids [Emim][Br] and [Bmim][Cl]

Abstract

Experimental measurements of density at different temperatures ranging from 293.15 to 313.15 K, the speed of sound and osmotic coefficients at 298.15 K for aqueous solution of 1-ethyl-3-methylimidazolium bromide ([Emim][Br]), and osmotic coefficients at 298.15 K for aqueous solutions of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) in the dilute concentration region are taken. The data are used to obtain compressibilities, expansivity, apparent and limiting molar properties, internal pressure, activity, and activity coefficients for [Emim][Br] in aqueous solutions. Experimental activity coefficient data are compared with that obtained from Debye-Hückel and Pitzer models. The activity data are further used to obtain the hydration number and the osmotic second virial coefficients of ionic liquids. Partial molar entropies of [Bmim][Cl] are also obtained using the free-energy and enthalpy data. The distance of the closest approach of ions is estimated using the activity data for ILs in aqueous solutions and is compared with that of X-ray data analysis in the solid phase. The measured data show that the concentration dependence for aqueous solutions of [Emim][Br] can be accounted for in terms of the hydrophobic hydration of ions and that this IL exhibits Coulombic interactions as well as hydrophobic hydration for both the cations and anions. The small hydration numbers for the studied ILs indicate that the low charge density of cations and their hydrophobic nature is responsible for the formation of the water-structure-enforced ion pairs.

An improved model for the phase equilibrium of methane hydrate inhibition in the presence of ionic liquids

“…The IL ionizes to form ions in the presence of water resulting in a change of water activity in the liquid phase [34]. The activity of water a w ¼ x L w g w À Á in IL aqueous solution is calculated as shown in Eq.…”

Association of ionic liquids in solution: a combined dielectric and conductivity study of [bmim][Cl] in water and in acetonitrile

“…16 Also, various theoretical and experimental investigations on [bmim][Cl] and related 1-alkyl-3-methylimidazolium chloride + (water or AN) systems have been published recently, which provide useful background information. 15,[25][26][27][28][29][30][31][32] The second aim of the present investigation is to determine reliable transport properties, especially the limiting ionic conductivities, l N + , of the [bmim] + cation as a function of temperature. Almost nothing is known about the temperature dependence of such quantities despite their importance as one of the two reference states (in addition to the pure RTIL) in mixture studies.…”

Measurement and modeling of osmotic coefficients of aqueous solution of ionic liquids using vapor pressure osmometry method

“…[28,29]. Some thermodynamic properties such as activity and osmotic coefficients have been measured for aqueous solutions of [C n MIm]Cl [30][31][32]. Recently, the osmotic coefficients of aqueous solutions of ionic liquids based on 1-alkyl-3-methylimidazolium halide have been reported in our previous papers at different temperatures [33,34].…”