Abstract: Coupled transport phenomena across a gas/liquid interface, relevant for distillation, were studied by nonequilibrium molecular dynamics simulations. The simulations were set in the context of bulk irreversible thermodynamics. It was then shown that mole fraction profiles in the liquid phase and the gas phase of ideal isotope mixtures are linear. For nonideal mixtures, Fick's law cannot be applied in the interface region, because the activity coefficients change dramatically across the interface. Fourier's law has a constant heat conductivity for both types of liquid mixtures but not for gas mixtures. The coupling between heat and mass transfer becomes negligible for distillation in the special case of ideal mixtures with constant molal overflow. In all other cases, the heat of transfer contributes significantly to the heat flux and causes deviations from Fourier's law in the gas phase. This all means that coupled flux equations are needed to describe distillation and that the properties of the surface are...

Abstract: For ternary systems, we present a method for using measured values of the four ternary diffusion coefficients and the Onsager reciprocal relations to extract derivatives of solute chemical potentials with respect to solute molar concentrations. The method is applicable to systems in which the molar concentration of one solute is very small compared to that of the other, and also small enough that an inverse concentration dependence dominates certain activity coefficient derivatives. These conditions apply to a large number of aqueous systems involving macromolecules of biological interest. Unlike other techniques, the present method can be used to study undersaturated and supersaturated solutions. The approach is illustrated for the lysozyme chloride - NaCl-H2O system at 25 °C, using data reported here for pH 6.0 at 0.60 mM (8.6 mg/mL) lysozyme chloride and 0.25, 0.50, 0.65, 0.90, and 1.30 M (1.4, 2.8, 3.7, 5.1, and 7.2 wt %) NaCl concentrations, and our earlier data for pH 4.5 at the same concentrations. We use these solute chemical potential derivatives to compute the protein cation charge approximately, and to construct a function approximating the derivative of the lysozyme chloride chemical potential with respect to NaCl concentration, which we integrate over a range of NaCl concentrations. This provides the change of the lysozyme chloride chemical potential with NaCl concentration well into the supersaturated region, and hence provides the driving force for nucleation and crystal growth of lysozyme chloride as a function of the extent of supersaturation. We also compute the diffusion Onsager coefficients (Lij)0 for each composition at pH 4.5 and 6.0. Binary diffusion coefficients of aqueous lysozyme chloride at 0.89 mM (12.7 mg/mL) for pH values from 4.0 to 6.0, and at pH 6.0 for concentrations from 0.25 to 1.95 mM (3.6-27.9 mg/mL) are also reported.

Abstract: New equations that describe the thermodynamic properties of the NaNO3+H2O system were obtained from previously published measurements for this system. The measured values included in the fitted equations spanned the range of temperatures of approximately 236–425 K for NaNO3(aq) and 16–548 K for NaNO3(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of NaNO3(cr) from 0 K to near the lambda transition, 548.6 K, (2) the change in chemical potential for both NaNO3 and H2O in NaNO3(aq) as a function of temperature, and molality, valid from 236 to 425 K, and the molality range of 0 mol⋅kg−1 to the lesser of the saturation molality or 25 mol⋅kg−1, and (3) standard-state properties for the aqueous solution process.

Abstract: Vapor−liquid equilibria are reported for the following five systems: phenol + styrene; ethyl mercaptan + n-butane; tert-butyl mercaptan + propane; dimethyl ether + propane; trifluoroacetic acid + hydrogen chloride. The system pressure and temperature were measured at several charge compositions along two isotherms for each system. Equilibrium vapor- and liquid-phase compositions were derived from the PTx data using the Soave equation of state to represent the vapor phase and the Wilson or NRTL activity coefficient model to represent the liquid phase. Liquid−liquid equilibrium studies were performed on the dimethyl carbonate + water system at two temperatures by analyzing samples taken from each liquid phase. The solubility of hydrogen in α-methyl benzyl alcohol was measured at three pressures at each of three temperatures.

Abstract: This work extends the previously published aqueous electrolyte equation of state (AEEOS) to predict liquid–liquid equilibria (LLE) of mixed-solvent electrolyte systems. Interaction parameters between ions and organic solvents, and cations and anions were determined by fitting the experimental vapor-pressure data of binary methanol + halide electrolyte mixtures, and then correlated to the cationic Stokes and anionic Pauling diameters. The focus is on the ionic standard/reference state and the standard Gibbs energy for transferring salts from one solvent to another. The methods applied to predict LLE of several ternary water + organic solvent + salt system are to select: 1. the hypothetical ideal gas at unit mol fraction, the system temperature, and 1 bar as the ionic standard state; 2. the infinite dilution in the solvent mixture as the ionic reference state, whose activity coefficients were converted to those at the infinite dilution in pure water by the ionic standard Gibbs energy of transfer. The predicted LLE results agree well with the measured data without any adjusted parameters in fitting the ternary experimental data. The extended AEEOS is comparable to the model of Zerres and Prausnitz, but the latter requires two adjusted parameters in fitting the ternary experimental data for each ternary system.

Abstract: A technique is developed for univalent salts that allows calculation of activity coefficients at very high ionic strengths using solubility data. Pitzer parameters for binary solutions are extended...

Abstract: A hard sphere system, using Kelvin tetrakaidekahedron cells, coupled with the mean spherical approximation (MSA), accurately correlates the mean ionic activity, and the individual activities of ions, in aqueous solutions of single 1:1 electrolytes. For the mean ionic activity coefficients, the diameter of the anion is fixed at the Pauling value and the cation diameter is a function of composition. Hydrated diameters of cations are realistic in comparison with Pauling values, and the like and unlike ionic pair correlation functions at contact value are positive in the whole concentration range. The use of a simpler version of the MSA has little effect on the results and dramatically reduces the computation time. The results obtained from the Kelvin mean spherical approximation, K-MSA model, compare favorably with those of other models. The correlation of individual ionic activity coefficients requires composition-dependent diameters for the cation and anion.

Abstract: The isopiestic osmotic coefficients, densities, and speeds of sound of aqueous mixtures of NaCl with guanidinium chloride (GnCl) have been measured at different ionic strengths with varying compositions at 298.15 K with a view to determine the ionic interactions. The excess free energy, ΔmGE, volume, ΔmVE, and compressibility of mixing, ΔmKE, of the NaCl−GnCl mixtures at constant ionic strength show interesting features with changing ionic strength fractions of the electrolytes. These excess properties of mixing with both negative and positive signs can be attributed to the mixing of hydrophilic and hydrophobic ions. It is shown that the binary and ternary interaction terms play an important role in the accurate representation of the osmotic coefficients, activity coefficients, volumes, and compressibilities of the mixtures. Measurements on the surface tension and viscosity of the NaCl−GnCl mixtures have also been reported. A simple equation incorporating like charge interactions has been employed to corr...

Abstract: Enthalpograms recorded using a titration microcalorimeter are reported for mixtures of surfactants hexadecyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) in aqueous solutions at 298.2 K. The enthalpograms for each mixture show that the micellar phase comprises a mixture of the surfactants rather than separate domains comprising single surfactants. The enthalpograms are satisfactorily accounted for using the pseudo-phase model taking account of the non-ideal properties of the mixed micellar phase and of the mixed aqueous surfactant solutions. A quantitative treatment is described for the analysis of titration calorimetric results for mixed ionic surfactant systems. For the micellar phase a key parameter determining the critical micellar concentration (c.m.c.) is a generalised rational activity coefficient for the micellar phase. For the systems described here this parameter is less than unity indicating that surfactant–surfactant interactions stabilise the micellar phase, whereas a generalised Gibbs energy surfactant–surfactant interaction parameter for the aqueous phase is positive, opposing Debye–Huckel ionic-atmosphere stabilising effects although the corresponding enthalpic parameter is exothermic. As the total concentration of surfactant in the sample cell of the calorimeter increases during a given experiment, the calculated c.m.c. changes as a consequence of these interactions which are a function of composition. In general terms the c.m.c. and enthalpy of mixed micelle formation for the CTAB–TTAB mixture change smoothly between the corresponding properties of the two pure surfactants.

Abstract: Component solubility in HClLiClH2O, HClMgCl2H2O and LiClMgCl2H2O systems of high ionic strength at 0°C and 20°C are calculated by using the Pitzer's ion-interaction model and parameters derived from a least-squares optimization procedure which couples activity coefficient with solubility data. Excellent agreement with experimental solubility for ternary mixtures indicates that the model can be successfully used to predict the component solubility of salt lake brine systems that contain high concentration of LiCl. For all of the systems containing a high concentration of HCl, measurements of the activities of the complex compounds are not available, hence the evaluation of the values for the mixing parameters θMN and ΨMNX relied on solubility data in subsystems. The prediction also indicates that the parameters used do not vary linearly with the temperature, thus the algorithm used in order to calculate the parameters of LiCl at different temperatures is presented here. Based on the predictions of the solubility, the solubility curves of six ternary systems are constructed.