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 (H2S) in pure water and in aqueous NaCl solutions between 283 and 573K, 0.1–40MPa and ms 0–6mol·kg−1. Thermodynamic properties of the pure components were calculated using highly accurate multiparametric equations of state for H2S (Lemmon and Span, 2006) and for H2O (Wagner and Pruss, 2002). Thermodynamic properties of H2S(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 H2S in pure water and in NaCl solutions were treated using the Pitzer interaction model. The Pitzer parameters for H2S in binary and ternary solutions were newly determined while those for NaCl(aq) in the H2S-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 H2S–H2O and for H2S–H2O–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 H2S–H2O–NaCl system, including the activity coefficients of H2S 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 H2S and NaCl concentrations up to halite saturation. The model is available as a computer code that is freely distributed.