A new force field for H2S and its binary and ternary mixtures with CO2 and CH4

We present a new force field for H2S, based on an exponential-6 functional form for the repulsion–dispersion interactions and a charge distribution. This force field is used in a series of Expanded Wang–Landau (EWL) simulations, which allow to obtain an accurate estimate for the partition function and thus provides access to all thermodynamic properties of the system. The simulation results show that this new force field yields accurate values for the VLE properties of pure H2S. For binary mixtures of H2S with CH4, EWL results, obtained with this force field and the standard combining rules, are in excellent agreement with the experimental data. In line with previous work, no combining rules were found to perform well for the H2S–CO2 binary mixture and parameters for the interactions between unlike sites were optimized to obtain an excellent agreement for this mixture. We finally extend the EWL simulation method to simulate phase equilibria for ternary mixtures of H2S with CH4 and CO2 and show that the parameters obtained in this work model accurately the vapor–liquid coexistence in these ternary mixtures.