Mixed Solvent Electrolyte Systems Research Articles

Use of an electrolyte equation of state for the calculation of vapor–liquid equilibria and mean activity coefficients in mixed solvent electrolyte systems

In a previous paper [W. Fürst, H. Renon, AIChE J. 39 (1993) 335–343], a new electrolyte equation of state has been developed and applied to aqueous strong electrolyte solutions. One of the original features of this equation was that all ionic parameters could be determined using correlations related to experimental solvation properties which leads to a predictive model. Later, Zuo and Fürst [Y.-X. Zuo, W. Fürst, Fluid Phase Equilibria 138 (1997) 87–104.] extended it to predict vapor pressures and mean ionic activity coefficients for various non-aqueous electrolyte systems. In this work, the model has been extended to mixed-solvent electrolyte systems. This has been done by deducing most of the ionic parameters from experimental solvation properties and by developing mixing rules to represent preferential solvations in mixed-solvents, the aim being to minimize the number of adjustable parameters. Vapor–liquid equilibrium data relative to 26 water–alcohol–salt systems and mean ionic activity coefficients relative to eight water–alcohol–salt systems have been represented using only 18 parameters. The deviations for VLE are similar to those obtained by other authors, but with less adjustable parameters. Furthermore, it could represent mean ionic activity coefficients as well. Finally, the model has been used to predict VLE for 12 other mixed-solvent electrolyte systems with satisfactory results.

Representation of liquid-liquid equilibrium of mixed-solvent electrolyte systems using the extended electrolyte NRTL model

The three-contribution electrolyte NRTL model [1] with an additional term of Brønsted-Guggenheim type is applied to represent the liquid-liquid equilibrium (LLE) in mixed-solvent electrolyte systems. The Brønsted-Guggenheim term compensates for the inadequacies of the Debye-Hückel and Born equations when they are extended to mixed-solvent electrolyte systems. Attention is given to the definition of reference and standard states. The importance of the electrolyte solution chemistry is emphasized. The extended electrolyte NRTL model is compared with the Zerres-Prausnitz model [2] on correlation of LLE data for four ternary aqueous-organic solvent electrolyte systems.

Effect of Calcium Nitrate on the Vapor-Liquid Equilibria of Ethanol + Water and 2-Propanol + Water

The effect of calcium nitrate on the vapor-liquid equilibria of ethanol + water and 2-propanol + water was studied using a Swietoslawski ebulliometer. The measurements were performed for two constant salt molalities (1 and 2 mol[center dot]kg[sup [minus]1]) under isobaric conditions at 50.66 kPa. Strong salting-out of the alcohol was observed in all cases, leading to a complete elimination of the azeotropic point at relatively low salt concentrations. The results were correlated using an extension of the NRTL equation for mixed solvent electrolyte systems proposed by Mock, Evans, and Chen.

A gE model for single and mixed solvent electrolyte systems

Polka, H.-M., Li, J. and Gmehling, J., 1994. A gE model for single and mixed solvent electrolyte systems. 2. Results and comparison with other models. Fluid Phase Equilibria, 94: 115-127. A new gE model describing the behaviour of single and mixed solvent electrolyte systems is used to calculate vapour-liquid equilibria of 185 ternary systems (two solvents one salt), and vapour pressure, osmotic coefficients and activity coefficients of 362 binary systems (one solvent one salt). The results are compared with the models of Sander, Macedo, Pitzer, Bromley and Chen. For the large data base used, the new model improves the results not only for the description of single solvent data but also for the calculation of VLE for mixed solvent systems. Despite the relative improvement compared to other models, in certain cases serious deviations are obtained.

A gE model for single and mixed solvent electrolyte systems

Li, J., Polka, H.-M. and Gmehling, J., 1994. A gE model for single and mixed solvent electrolyte systems. 1. Model and results for strong electrolytes. Fluid Phase Equilibria, 94: 89-114. A gE model for electrolyte systems has been developed which is based on results from statistical thermodynamics and takes into account the interactions between all species present in the electrolyte solution. In this model the electrolyte solution is treated as a nonelectrolyte solution plus charge interactions, and it is assumed that the charge interactions show two effects, direct and indirect. The indirect effect differs not only from the long-range electrostatic interaction but also from the short-range interaction for nonelectrolyte solutions. With the help of a large data base the required parameters (164 in number) have been fitted for 10 solvents, 18 cations and 10 anions. The model parameters have been used to calculate the VLE behavior, osmotic coefficients and mean ion activity coefficients for a large number of systems with high accuracy.

Thermodynamic behavior of electrolyte solutions: Part I. Activity coefficients and osmotic coefficients of binary systems

Lin, C.-L., Lee, L.-S. and Tseng, H.-C., 1993. Thermodynamic behavior of electrolyte solutions. Part I. Activity coefficients and osmotic coefficients of binary systems. Fluid Phase Equilibria 90: 57-79. A predictive model with three parameters for the calculation of activity coefficients and osmotic coefficients of strong electrolytes in binary solutions is developed. In this development, the Poisson-Boltzmann equation was employed to account for the long-range, ion-ion interactions, and the concept of solvation was employed to account for the short-range, ion-molecule interactions. All three parameters included in the proposed model are expressed clearly with physical explanations. They are (1) the closest distance of approach, ã, (2) the equivalent dielectric constant. D̄ e, and (3) the solvation parameter, S. In the first part of this paper, experimental data obtained from the literature are fitted to the present model. These three parameters are also obtained for 144 aqueous electrolyte solutions and 16 non-aqueous electrolyte solutions. It is found that ã is independent of temperature and solvent, while S is temperature independent only. It is shown that the proposed model can be applied conveniently to systems other than those at 298.15 K and to non-aqueous electrolyte solutions. In the second part, this model is extended to predict vapor-liquid equilibria of mixed-solvent electrolyte systems.

Thermodynamic behavior of electrolyte solutions: Part II. Prediction of vapor-liquid equilibria for mixed-solvent electrolyte systems

Lin, C.-L., Lee, L.-S. and Tseng, H.-C., 1993. Thermodynamic behavior of electrolyte solutions. Part II. Prediction of vapor-liquid equilibria for mixed-solvent electrolyte systems. Fluid Phase Equilibria 90: 81-98. A predictive model for vapor-liquid equilibria of ternary systems, composed of two solvents and one electrolyte, is developed. The parameters for ternary systems are calculated from those for the constituent pairs of binary systems with simple mixing rules. Two isothermal and three isobaric sets of experimental data obtained from the literature and from our laboratory are compared with those calculated by this proposed model. The results are quite satisfactory, with average absolute error of vapor phase mole fractions of less than 0.0193.

Vapor-liquid equilibria of mixed-solvent electrolyte solutions: ion-size effects based on the MSA theory

Abstract Wu R.-S. and Lee L.L., 1992. Vapor-liquid equilibria of mixed-solvent electrolyte solutions: ion-size effects based on the MSA theory. Fluid Phase Equilibria, 78: 1-24. We present a new method for calculating the vapor-liquid equilibria of mixed-solvent electrolyte systems. We use the water-methahol-lithium chloride system as an example to demonstrate the approach. In this approach, a statistical mechanical theory, the mean spherical approximation (MSA), is used together with the Gibbs-Duhem relation of thermodynamics and Furter's linear volatility theory of solvation to form a complete theory of phase equilibria. The MSA theory gives the salt activity coefficients In γ±. The Gibbs-Duhem relation gives a relation between the activities of the solvent a, the cosolvent b and the salt s. A third equation that relates the relative affinity of the solvents for the salt completes the conditions needed for calculating the vapor-liquid equilibria of ternary systems. The MSA formulas are sensitive to ion-size variations: a requirement for modeling “salting-out” behavior. We have shown that up to 20% variations in in γ± could be caused by ion-size changes in some sample systems. We show that to achieve “complete” scale conversion for properties from the McMillan-Mayer scale to the Lewis-Randall scale, one must have a good theory of solvation. The solvent-ion and solvent-solvent correlations enter the conversion in a non-trivial way. The sample system water-methanol-LiCl can be predicted to within 0.01 in mole fractions and 5 mmHg in pressures over the concentration ranges 10–15 molal. This method introduces molecular theory into the formulation without postulating an excess free energy. It represents an alternative to the conventional excess free energy models.