Activity and osmotic coefficients in electrolyte solutions at elevated temperatures

Abstract

In this article, a numerical procedure is proposed for prediction of activity and osmotic coefficients at elevated temperatures based on the vapor pressure lowering of electrolyte splutions available at room and intermediate temperatures.The vapor pressure lowering of electrolyte solutions can be correlated over a wide temperature range by equation, In AP=A+B/T+C(ln T-T/2TC), where A, B and C are adjustable parameters and T, is the critical temperature of pure water. The procedure is illustrated in the cases of KCI, CaCl, and especially LiCl solutions. An analytical expression for osmotic coefficients in the Meissner approach is derived by an integration of the Bjerrum equation.Thermodynamic properties of aqueous solutions of strong electrolytes at high temperatures are of considerable importance in many areas of chemical industry, in geochemistry, in desalination and steam power generation. However, with few exceptions, the available experimental data are confined to temperatures which are not far from room temperatures. In recent years, our knowledge about activity and osmotic coefficients comes mainly from isopiestic measurements performed at elevated temperatures by the Holmes and Mesmer group. Unfortunately, these measurements constitute only a small part of industrially important electrolyte-water systems and therefore procedures for prediction of activity and osmotic coefficients must be considered. Since in the case of electrolyte solutions, a linear temperature dependence of the coefficients is rarely observed, ordinary interpolation and extrapolation techniques have rather limited value. For example, if one molal solution is considered, osmotic coefficients as a function of temperature in the 273-573 K range have a distinct maximum for NaCI, KCl and CsC1, they decrease monotonically for LiCl and for CaCl, remain practically constant up to about temperature of 373 K but after they decrease with temperature increasing (Lindsay and Liu, 1971 ;Holmes et al., 1978;Holmes and Mesmer, 1981).In our previous works on the subject, estimation procedures were proposed for activity and osmotic coefficients at elevated temperatures based on data at one or two temperatures (Apelblat et al., 1988) and on the application of the Moriyama rule (Apelblat et al., 1987). In this work, it is considered a new extrapolation technique to predict activity and osmotic coefficients which is based on plentiful data available at room and . intermediate temperatures (for example, Robinson and Stokes, 1965;Hamer and Wu, 1972;Goldberg, 1981; Lob0 and Quaresma, 1989). The proposed numerical procedure is illustrated in the cases of KCI, CaCl, and especially LiCl solutions (lithium chloride is very soluble in water).. Representation of Osmotic and Activity Coefficients as a Function of Temperature and Concentration

Vapor Pressure and Dissolution Enthalpy Measurements in Ternary {H2O + NaCl + Na2SO4} System between 298 K and 363 K

“…For each composition, experimental results can be regressed using the Appelblatt relation, given by where T is absolute temperature in K, T c is the critical temperature of water ( T c = 647.14 K), and A , B , and C are adjustable parameters depending on liquid composition. Values of these parameters were regressed on our experimental values of pressure for each ternary composition studied and are reported in the Table .…”

“…We made vapor pressure measurements in the ternary {NaCl (1) + Na 2 SO 4 (2) + H 2 O (3)} system between (298 and 363) K with different molality ratios m 1 / m 2 = 1/10 and m 1 / m 2 = 1/1. Data obtained at constant composition could be easily used for determining coefficients of Appelblatt's correlation …”

Vapor Pressures and Osmotic Coefficients of Aqueous LiOH Solutions at Temperatures Ranging from 298.15 to 363.15 K

“…For comparison with the values given by Holmes and Mesmer, our results are regressed for different compositions using the empirical relation given by Apelblat . This expression can be used to extrapolate the pressure lowering to high temperatures with a good precision for nondilute solutions: where Δ p = p * − p , T c is the critical temperature of pure water ( T c = 647.096 K), T is the temperature in Kelvin, and A , B , and C are adjustable parameters.…”

“…For comparison with the values given by Holmes and Mesmer, 4 our results are regressed for different compositions using the empirical relation given by Apelblat. 24 This expression can be used to extrapolate the pressure lowering to high temperatures with a good precision for nondilute solutions:…”

Vapor Pressure Measurements with a Nonisothermal Static Method between 293.15 and 363.15 K for Electrolyte Solutions. Application to the H2O + NaCl System

“…The osmotic coefficient, , defined on the molality scale is given by = (1000/vMwm) In aw (8) where Mw is the molar mass of water (Mw = 18.015 34 g) and v is the number of ions generated on complete dissociation (v = 2 for NaCl). For each composition, experimental results were regressed using the empirical relation given by Apelblat (1993). This expression can be extrapolated to high temperature with a good precision for nondilute solution:…”