Vapor–liquid equilibria of binary and ternary mixtures containing nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and ethane (C2H6) are studied by molecular simulation using two-center Lennard-Jones plus point quadrupole models. Pure-component models are taken from recent work. Mixtures are described using the Lorentz-Berthelot combining rules. Predictions of vapor–liquid equilibria from pure-component data alone agree well with experimental data, for example, the azeotropic behavior of the carbon dioxide + ethane system is predicted correctly. Further improvements are achieved by adjusting one parameter in the energetic term of the combining rule to binary data. For this purpose, a simple and efficient procedure is proposed. Excellent agreement between the molecular models and experimental data for vapor-liquid equilibria, saturated densities, and enthalpies of vaporization is observed for the five binary systems studied in the present work (N2+O2, CO2+C2H6, O2+CO2, N2+CO2, N2+C2H6). Vapor–liquid equilibria of two ternary mixtures (N2+O2+CO2, N2+CO2+C2H6) are predicted well without any further adjustment of model parameters. Results from molecular simulation are compared to those from the Peng-Robinson equation of state, the PC-SAFT equation of state, and the BACKONE equation of state using the same data to determine model parameters. The quality of correlations with system-specific binary interaction parameters from molecular simulation and equations of state is similar, and the predictive power of molecular simulation is clearly superior.
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