Fluid Phase Equilibria 238 (2005) 220–228 The influence of Na 2 SO 4 on the CO 2 solubility in water at high pressure M.D. Bermejo a , A. Mart´ ın a , L.J. Florusse b , C.J. Peters b,∗ , M.J. Cocero a a Department of Chemical Engineering and Environmental Technology, University of Valladolid, Prado de la Magdalena s/n, 47011 Valladolid, Spain b Physical Chemistry and Molecular Thermodynamics, Department of Chemical Technology, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands Received 23 March 2004; received in revised form 5 October 2005; accepted 6 October 2005 Abstract Supercritical water oxidation (SCWO) is a very efficient process for the destruction of organic wastes. In this type of processes, conversions higher than 99% can be achieved with residence times shorter than a minute. The effluent of this process is a mixture of water, CO 2 and inorganic salts. For modeling this process, it is necessary to have reliable experimental data of the system water–carbon dioxide–inorganic salts. These data are scarce in literature, especially at high pressures. The solubility of CO 2 in water and aqueous solutions of Na 2 SO 4 was determined in the temperature range between 288 and 368 K, pressures up to 14 MPa were applied, Na 2 SO 4 concentrations of 0.25, 0.5 and 1 mol Na 2 SO 4 /kg water were used, and the CO 2 molar fractions were 0.0075, 0.01 and 0.0125. As expected, the data obtained showed that equilibrium pressure increases with temperature and CO 2 concentration. A salting out effect is observed. The experimental data were compared to available literature data and the CO 2 –water data were consistent with literature data, but for the equilibrium pressure of the bubble points in a solution of 1 mol Na 2 SO 4 /kg water, a systematic overpressure of approximately about 1 MPa with respect to some of literature data is found. The system CO 2 –H 2 O–Na 2 SO 4 was modeled using the Anderko–Pitzer EOS, specially developed for water–salt systems at high temperatures and pressures. Experimental data were used for obtaining parameters in the range of pressure and temperature of the data. In this range they differ with an average deviation of %P = 4.64% in total pressure from the experimental results. However, extrapolated results from the Anderko–Pitzer EOS are poor. In order to extend the region of applicability of the EOS, it will be necessary to adjust the parameters in the appropriate range of temperature and concentration. © 2005 Elsevier B.V. All rights reserved. Keywords: CO 2 solubility; Electrolyte solution; LV equilibrium; Sodium sulphate; Anderko–Pitzer EOS; SCWO 1. Introduction Supercritical water oxidation (SCWO) is the process that comprises the oxidation of organic solutes in an aqueous medium at temperatures and pressures above the critical point of water (647.3 K and 22.12 MPa). Its main application is destruction of organic waste. Conversions higher than 99% can be achieved with residence times shorter than a minute. High conversions can be explained by the sharp change in the thermo-physical properties of water near its critical point. The dielectric constant ∗ Corresponding author. E-mail addresses: Cor.Peters@tnw.tudelft.nl (C.J. Peters), mjcocero@iq.uva.es (M.J. Cocero). of water decreases sharply in the near critical region, so SCW behaves then as a non-polar solvent, i.e., non-polar compounds are completely soluble in SCW, while salts become insoluble in water at supercritical conditions. Supercritical water also shows complete miscibility with “permanent gases” as oxygen and nitrogen [1]. The combination of solvation properties and other physical properties makes SCW a very suitable medium for the oxidation of organic wastes. Products of hydrocarbon oxidation in SCWO are carbon dioxide and water. Hetero-atomic groups are converted into inorganic compounds, usually acids, salts, or oxides in high oxidation states [2]. The study of the system CO 2 –water–inorganic salts is impor- tant in the SCWO process, as the effluent of the SCWO reactor mainly consists of these components. But this is not the only field where this system plays an important role. Solubility data 0378-3812/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2005.10.006