Thermodynamic description of H2S–H2O–NaCl solutions at temperatures to 573 K and pressures to 40 MPa

Abstract Reliable experimental results were selected from the literature (using over 700 data) to develop a thermodynamic model for calculating the solubility of hydrogen sulfide (H 2 S) in pure water and in aqueous NaCl solutions between 283 and 573 K, 0.1–40 MPa and m s 0–6 mol·kg − 1 . Thermodynamic properties of the pure components were calculated using highly accurate multiparametric equations of state for H 2 S (Lemmon and Span, 2006) and for H 2 O (Wagner and Pruss, 2002). Thermodynamic properties of H 2 S(aq) at infinite dilution were based on the Henry's law constants generated from the SOCW model (Sedlbauer et al., 2000) and reported by Majer et al. (2008). The determined activity coefficients of H 2 S in pure water and in NaCl solutions were treated using the Pitzer interaction model. The Pitzer parameters for H 2 S in binary and ternary solutions were newly determined while those for NaCl(aq) in the H 2 S-free system were adopted from the review of Archer (1992). The experimental solubilities selected for correlation are reproduced by the model with mean relative deviations of 5.2% and 6.1% for the H 2 S–H 2 O and for H 2 S–H 2 O–NaCl systems, respectively. These values are comparable to the experimental uncertainty of the solubility data. The new model allows a thermodynamically consistent description of numerous other properties of the liquid phase in the ternary H 2 S–H 2 O–NaCl system, including the activity coefficients of H 2 S and NaCl, the osmotic coefficients, the Setchenow constants, and the molar volume and density of the bulk liquid. These properties can be calculated for any H 2 S and NaCl concentrations up to halite saturation. The model is available as a computer code that is freely distributed.