Thermodynamic Properties of C₂H₆–CH₄ Mixtures via Pressure Expansion of the Virial Equation Using Empirical Correlations for Second and Third Virial Coefficients

An empirical-correlation-based method is employed to calculate the thermodynamic properties of C₂H₆, CH₄, and their binary mixtures using literature correlations for the second and third virial coefficients (SVC and TVC). The corresponding first- and second-order temperature derivative terms of the SVCs and TVCs are formulated and incorporated into the thermodynamic equations to calculate properties associated with both like and unlike interactions. The method is applied to pure C₂H₆ and the C₂H₆–CH₄ binary mixture for the calculation of isobaric and isochoric heat capacities, Joule–Thomson coefficient, isentropic expansion coefficient, thermal expansion coefficient, isothermal compressibility, density, speed of sound, fugacity coefficient, and compressibility factor. The calculated properties show good agreement with available experimental literature data, with low average absolute percent errors for the investigated properties. In addition, the calculated cross-SVCs and pure and cross-TVCs are consistent with the corresponding literature data. These results demonstrate that the empirical-correlation-based method, together with the appropriate binary interaction parameter, provides a convenient and reliable means of estimating a wide range of thermodynamic properties of the C₂H₆–CH₄ gas mixture and is also applicable to pure nonpolar gases and their binary mixtures. The Shomate coefficients for the ideal-gas heat capacity of C₂H₆ were also obtained by fitting experimental literature data and used in the thermodynamic calculations.