Thermodynamics of aqueous sodium chloride to 823 K and 1 kilobar (100 MPa)

Abstract

It is shown that a very simple semiempirical equation represents quite accurately the thermodynamic properties of aqueous sodium chloride from 373 to 823 K. The equation comprises one Margules term and a Debye-Huckel term. Just the one Margules parameter is freely adjustable because the Debye-Hfickel parameter is determined by the properties of water. The equation is valid from the saturation composition down to infinite dilution for solvent density above. 0.75 gcm-3 but at lower density only above a solute mole.fraction of about 0.1 on an ionized basis. Both solute and solvent activity coefficients are fitted from the lowest pressure of solution existence up to 1 kilobar (1 bar = 100 kPA). Derivation of enthalpy and other related functions is discussed.The thermodynamic properties at high temperature for aqueous NaCl are important for many industrial and geological systems and have theoretical interest. These properties are now quite well known to 573 K, and a comprehensive equation of state is now available to that temperature (1, 2). In extending the treatment of the thermodynamic properties of aqueous NaCl above 573 K, it is apparent that most of the experimental data are both less complete and less accurate. Thus, the vapor pressures and density measurements above 573 K have a precision on the order of 1% or a few percent, whereas the lower temperature data are more precise and are supplemented by heats of dilution and heat capacities. The most extensive and selfconsistent array of measurements are those of Urusova (3-5), and our treatment is based primarily on her data but with use of other measurements (6-13) where available and accurate. Urusova (14) made some calculations of the activity coefficients of water on the basis of her measurements, but these are given only for a single pressure at a given temperature. We consider the activity coefficient of NaCl as well as that for H20 and consider each as a function of pressure P and of temperature T.This effort toward an equation for the thermodynamic properties of NaCl/H20 at temperatures above 573 K was initiated by a study of dilute NaCl in steam (15) that used mass spectrometric data to calculate properties of individual ion hydrates. Next an equation for the dielectric constant of water (16) was developed that should yield valid predictions when extrapolated to high temperature.In this paper we show that the composition dependence of the properties of aqueous NaCl over the full range of solubility and from about 373 to 573 K conforms to a simple equation developed previously (17, 18) for systems continuously miscible to the fused salt. This form of equation should remain valid for NaCl/H20 to higher.temperatures, at least at liquid-like densities. Because the equation has only one empirical parameter, one can hope to complete its evaluation, as a function of T and P, from the sparse experimental data available. The resulting equation will then predict various properties over a wide range of conditions.It has been established (17,18) that syst...

Extraction of biofuels and biofeedstocks from aqueous solutions using ionic liquids

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Critical phenomena and thermodynamics of dilute aqueous sodium chloride to 823 K

“…Thus, for the NaCl, X2 = 2n2/(ni + 2n2). [1] It is convenient to extend this same system for the present range but recognizing ion pairing when necessary. With 6, the fraction of solute as ion pairs, one can define mole fractions offree ions xi (either + or -), of pairs xp, and of solvent (water) x, as follows:…”

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Pressure-volume-temperature relations of hydrothermal seawater; experimental determination, mathematical formulation, and calculation of thermochemical parameters

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