A Model Incorporating Ion Dissociation, Solute Concentration, and Solution Density Effects To Describe the Thermodynamics of Aqueous Sodium Chloride Solutions in the Critical Region of Water

Abstract

A model, based on Helmholtz energy, describing the thermodynamics of NaCl solutions in the near-critical region of water has been developed and tested as a function of temperature (350-402 °C), pressure (18-41 MPa), and solute concentration (0-5 m) using literature heat of dilution (∆ dil H) data. This model is an extension of one developed by Anderko and Pitzer (Geochim.

The system H2O–NaCl. Part I: Correlation formulae for phase relations in temperature–pressure–composition space from 0 to 1000°C, 0 to 5000bar, and 0 to 1 XNaCl

“…A number of equation of state representations have been developed and suggested for this system (e.g., Haas, 1970;Rogers and Pitzer, 1982;Pitzer et al, 1984;Bischoff and Rosenbauer, 1985;Bodnar, 1985;Clarke and Glew, 1985;Pitzer and Pabalan, 1986;Pitzer and Schreiber, 1987;Gallagher and Levelt Sengers, 1988;Tanger and Pitzer, 1989;Hovey et al, 1990;Lvov and Wood, 1990;Archer, 1992a,b;Sterner et al, 1992;Anderko and Pitzer, 1993a,b;Pitzer and Sterner, 1993;Pitzer and Jiang, 1996;Povodyrev et al, 1997Povodyrev et al, , 1999Palliser and McKibbin, 1998a,b,c;Thiéry and Dubessy, 1998;Oscarson et al, 2001Oscarson et al, , 2004Sedlbauer and Wood, 2004;Liu et al, 2006). However, all of these are limited in their range of validity and frequently provide accurate data only for a limited number of properties.…”

The system H2O–NaCl. Part II: Correlations for molar volume, enthalpy, and isobaric heat capacity from 0 to 1000°C, 1 to 5000bar, and 0 to 1 XNaCl

“…Rather, as pointed out already by Oscarson et al (2001), the Anderko and Pitzer (1993) equation underpredicts the heats of dilution. More recently, studies by Oscarson and coworkers (Oscarson et al, 2001(Oscarson et al, , 2004Liu et al, 2006) extended the Anderko and Pitzer formalism by accounting for ionization, partly including results by Myers et al (2003). The latest of these models (Liu et al, 2006) reproduces experimental high temperature heats of dilution very well but shows some artifacts in the calculation of apparent molar volumes V NaCl / at low concentrations.…”

“…A number of authors have put major effort into the design of reliable equations of state for the system H 2 O-NaCl (e.g., Haas, 1970;Rogers and Pitzer, 1982;Pitzer et al, 1984;Bischoff and Rosenbauer, 1985;Clarke and Glew, 1985;Pitzer and Pabalan, 1986;Pitzer and Schreiber, 1987;Gallagher and Levelt Sengers, 1988;Tanger and Pitzer, 1989;Lvov and Wood, 1990;Archer, 1992;Anderko and Pitzer, 1993;Pitzer and Sterner, 1993;Pitzer and Jiang, 1996;Povodyrev et al, 1997;Palliser and McKibbin, 1998a,b,c;Thiéry and Dubessy, 1998;Anisimov and Sengers, 2000;Oscarson et al, 2001Oscarson et al, , 2004Myers et al, 2003;Sedlbauer and Wood, 2004;Liu et al, 2006), but the range of validity of most of these is too restricted to make them useful for flow simulations that investigate systems over wide ranges of temperature, pressure, composition, and phase state of the fluid. The only model that covers the whole T, P, and X NaCl range of interest (Palliser and McKibbin, 1998a,b,c) shows unphysical features in some parts of the phase diagram, including negative heat capacities of saline fluids near the critical temperature of water.…”

Improved Thermodynamic Model for Aqueous NaCl Solutions from 350 to 400 °C

“…The result is that small fluctuations in T, P, or molality (m) in the dilute region cause large changes in F, enthalpies (H), and degree of solute dissociation of the constituent ions of the solute. 20 As m increases, T c and P c also increase. 30 Hence, as m increases at constant T and P values near or above the water critical point, the solution becomes a subcritical fluid.…”

“…The discovery that oxidation of organic wastes in supercritical water is extremely rapid and efficient has led workers to propose supercritical water oxidation as an alternative to conventional methods of waste disposal. [3][4][5][6][7][8] Aqueous-solution chemistry under high T and P conditions has been studied using solubility measurements, 9,10 potentiometry, 11,12 electrical conductivity, [13][14][15] calorimetry, [16][17][18][19][20][21][22] isopiestic measurements, 23 spectroscopy, [24][25][26] and density (F) measurements. [27][28][29] Making experimental measurements and interpretation of results involving aqueous solutions at these T and P conditions are challenging.…”