Thermodynamics of the Phase Equilibria of Non Polar Gases and Brines. Example in the H2S–H2O–NaCl System

In this work we propose a thermodynamic model for the mixing of gases in water and in aqueous salt solutions valid to high pressures, high temperatures and high ionic strength solutions below the critical temperature of water (674 ° K), pressures up to 5 kbar and in brines with ionic strength equal to or less than 6 molal NaCl. Our model couples the Law of Henry with the Soave–Redlich–Kwong equation of state to reproduce experimental data in the aqueous liquid and vapor region. In our work, the chemical potential of the solute in the brine is related to the chemical potential of the solute in pure water through salting-out coefficients. The model reproduces all crucial phenomena of binary (gas–water) and pseudo-binary (gas–water–salt) vapor–liquid mixtures. We applied the model to reproduce the phase behavior of hydrogen sulfide in NaCl brines. The comparison of the calculated results with the experimental data of Lee and Mather (1977), shows that predictions are within experimental uncertainty.