Vapor–liquid equilibria of mixtures containing nitrogen, oxygen, carbon dioxide, and ethane

Abstract

AbstractVapor–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.