Prediction of H2S solubility in aqueous NaCl solutions by molecular simulation

Journal of Petroleum Science and Engineering(2017)

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Abstract
The solubility of hydrogen sulfide in aqueous NaCl solutions has been investigated by calculation of Henry constants through Monte Carlo simulations and using a nonpolarizable force field. The Lorentz-Berthelot combining rules appeared the most appropriate to simulate this system compared to other usual rules. The physical behavior and the trends experimentally observed are qualitatively well reproduced by this purely predictive approach for the binary system H2S + H2O as well as for the salted system H2S + H2O + NaCl: as experimentally expected, the simulations indicate a maximum in the Henry constant curve with temperature and an increase of the Henry constant with the salt concentration (salting-out effect). From a quantitative point of view, Henry constants are systematically overestimated, and more specifically for high temperatures. By introducing an empirical temperature-independent binary interaction coefficient between water and hydrogen sulfide, it is possible to obtain a good agreement between experiments and calculated Henry constants for both salt-free and salted systems, over a large temperature range (290–590 K) and salinity ranging from 0 to 6 mol/kg. For temperatures less than 400 K, the deviations are smaller and within the experimental uncertainties. At higher temperatures, deviations are higher but only few experimental data are available to confirm this result. Considering statistical and experimental uncertainties, this approach can thus provide a reasonable estimation of H2S solubility in NaCl aqueous solution in conditions encountered in geological formations. For a given temperature, the variation of the Henry constant with salt concentration is not exactly the same as the variation experimentally observed, and the salting-out effect is overestimated. This suggests for future works that additional forces such as polarization have to be taken into account for modeling high salt concentration systems.
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Key words
Hydrogen sulfide,NaCl,Solubility,Henry constant,Monte Carlo simulation
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