A fully analytical virial framework for predicting thermodynamic properties of the CH₄–CO₂ binary gas mixture

In this study, our previously developed analytical model based on the virial equation of state with Morse potential has been successfully applied to the binary gas mixture of CH 4 and CO 2 using an appropriate parameter combining method from the literature specific to the Morse intermolecular interaction potential, for the first time. Thermodynamic properties of specific heat capacities at constant pressure and volume, Joule–Thomson coefficient, isoentropic expansion coefficient, isothermal compressibility, thermal expansion coefficient, speed of sound, density, compressibility factor and fugacity coefficient for the like interactions of CH₄–CH₄ and CO₂–CO₂ were obtained, as well as for the unlike CH₄–CO₂ interactions for the binary gas mixture. The comparison results for the SVCs of like and unlike interactions, speed of sound, heat capacities, Joule–Thomson coefficient, density, compressibility factor, isothermal compressibility, thermal expansion and fugacity coefficients demonstrate good consistency with the literature for both low and moderate gas densities. This study also provides a comprehensive table of temperature-dependent Second Virial Coefficients (SVCs) and cross-SVCs, along with the terms including their first two derivatives, for CH₄, CO₂ and CH₄–CO₂ binary gas mixtures. The obtained data can be used directly to evaluate thermodynamic properties of both like and unlike interactions without the need to re-establish the analytical model’s computational code. The calculation results indicate that percent errors exceeding 6% occur in both density and the compressibility factor at 300 K for pressures higher than 4 MPa for the CO₂–CH₄ binary mixture at the elevated CO₂ mole fraction of 0.90112, which can be attributed to the proximity of carbon dioxide to its critical point (304.13 K and 7.38 MPa) since the system is highly CO₂-rich.