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This paper explores the thermodynamic behavior of aqueous solutions of four ionic liquids (ILs), namely 1-butyl-1-methylpyrrolidinium dicyanamide [BMPYR][DCA], 1-butyl-3-methylimidazolium dicyanamide [BMIM][DCA], 1-butyl-1-methylpyrrolidinium 1,1,2,2-tetrafluoroethanesulfonate [BMPYR][TFES], and 1-butyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate [BMIM][TFES]. The ionic liquids with [TFES] – anion (tetraflates) have been scarcely researched so far and therefore were characterized here with 1 H NMR spectroscopy and DSC calorimetry. In all four systems studied, water activity was systematically measured, the determinations being carried out in the whole composition range and at seven temperatures in the range from 288.15 K to 318.15 K. In addition, the mixing enthalpies in the IL dilute region for (water + DCA IL) systems and the solid-liquid equilibria for (water + TFES IL) systems were experimentally determined. The dependences of activity coefficients on temperature and composition were correlated ( i ) separately with appropriate flexible equations and ( ii ) simultaneously with an extended NRTL model. Both correlation approaches provide adequate description of mixture energetics and, as documented by comparisons with other relevant data, allow extrapolations of activity coefficients to both higher and lower temperatures as well as good predictions of excess enthalpy. Furthermore, the volumetric and viscosity behavior of highly dilute solutions of the ILs was explored. The concentration dependences of the apparent volume and viscosity were fitted well by the respective classical Redlich-Meyer and Jones-Dole equations. The values of partial molar volumes at infinite dilution were found to perfectly obey the ion additivity and correlate well with the intrinsic volume of IL molecule. Thermodynamic behavior of studied systems was compared to each other and discussed with respect to molecular interactions and nanostructure as well as to how involved ions affect it. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the ionic liquids 1,2-diethylpyridinium ethylsulfate, EEpyESO4; 1-methylpyridinium methylsulfate, MpyMSO4; 1,3-dimethylpyridinium methylsulfate, MMpyMSO4; and 2-ethyl-1-methylpyridinium methylsulfate, EMpyMSO4; were synthesized in our laboratory, and their experimental densities, speeds of sound, dynamic viscosities, and refractive indices were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, molar volume, and molar refraction of these ionic liquids were calculated from the experimental density and refractive index values. [ABSTRACT FROM AUTHOR]

Abstract: The (Na+K+S) system is of primary importance for the combustion of black liquor in the kraft recovery boilers in pulp and paper mills. A thermodynamic evaluation and optimization for the (Na+K+S) system has been made. All available data for the system have been critically evaluated to obtain optimized parameters of thermodynamic models for all phases. The liquid model is the quasichemical model in the quadruplet approximation, which evaluates 1st- and 2nd-nearest-neighbour short-range-order. In this model, cations (Na+ and K+) are assumed to mix on a cationic sublattice, while anions are assumed to mix on an anionic sublattice. The thermodynamic data of the liquid polysulphide components M2S1+n (M=Na, K and n =1–7) are fitted to ΔG = A(n)+ B(n)· T for the reaction M2S(l)+ nS(l)=M2S n+1(l). The solid phases are the alkali alloys, alkali sulphides, several different alkali polysulphides and sulphur. The solid solutions (Na,K), (Na,K)2S and (Na,K)2S2 are modelled using the compound energy formalism. The models can be used to predict the thermodynamic properties and phase equilibria in the multicomponent heterogeneous system. The experimental data are reproduced within experimental error limits for equilibria between solid, liquid and gas. The ternary phase diagram of the system (Na2S+K2S+S) has been predicted as no experimental determinations of the phase diagram have been made previously. [Copyright &y& Elsevier]