A thermodynamic property model with new mixing rules using the Helmholtz free energy is presented for the binary mixture of methane and hydrogen sulfide based on experimental P ρ T x data, vapor-liquid equilibrium data, and critical-point properties. The binary mixture of methane and hydrogen sulfide shows vapor-liquid-liquid equilibria and a divergence of the critical curve. The model represents the existing experimental data accurately and describes the complicated behavior of the phase equilibria and the critical curve. The uncertainty in density calculations is estimated to be 2%. The uncertainty in vapor-liquid equilibrium calculations is 0.02 mole fraction in the liquid phase and 0.03 mole fraction in the vapor phase. The model also represents the critical points with an uncertainty of 2% in temperature and 3% in pressure. Graphical and statistical comparisons between experimental data and the available thermodynamic models are discussed.
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