Thermodynamics of the carbon dioxide plus nitrogen plus methane (CO₂ + N2 + CH₄) system: Measurements of vapor-liquid equilibrium data at temperatures from 223 to 298 K and verification of EOS-CG-2019 equation of state

Vapor-liquid equilibria (VLE) data of the ternary mixture of CO₂ + N2 + CH₄ were measured at the isotherms 223 K, 253 K, 273 K, 283 K, and 298 K and for pressures in the range of 0.8 MPa–9.3 MPa. The 62 experimental dew or bubble point data points have been measured using an analytical technique. For each temperature, the ratio between N2 and CH₄ mole fraction in the total composition has been close to constant, enabling the data to be visualized as quasi phase envelopes. Estimated standard measurement uncertainties (k = 1) better than 14 mK in temperature, 1.5 kPa in pressure, and 0.06 mol% in composition are reported, yielding a total uncertainty in terms of composition better than 0.07 mol%. The experimental data were compared to the EOS-CG-2019 model, which is a state-of-the-art Helmholtz energy-based equation of state for the mixture of CO₂ + N2 + CH₄. All deviations between model and experimental data points are below 0.5 mol% for liquid compositions and 1.0 mol% for vapor compositions. The deviations between model and experimental points in the ternary mixture of CO₂ + N2 + CH₄ follow the same trends seen in earlier reports between model and experimental data for the binary mixtures of CO₂ + N2 and CO₂ + CH₄. In addition, the model was analysed with respect to other thermophysical properties available in the literature. To a large extent, the results presented in this work validate the assumption that the thermodynamic properties of the multicomponent system CO₂ + N2 + CH₄ can be described purely based on the pure component and binary mixture contributions.