Second through fifth virial coefficients for model methane-ethane mixtures

We report the virial coefficients for model methane-ethane mixtures up to the fifth order from 190K to 320K. United-atom models with modified Buckingham exp-6 sites are used for both methane and ethane. Comparison of computed second- and third-order coefficients to experimental values from the literature reveals some shortcomings in the molecular models, showing differences of order 5-10% for B₂, and 20-30% for B₃. We use the virial equation of state (VEOS) to obtain spinodal curves and critical points as a function of mole fraction. Despite the inaccuracies in the models' virial coefficients, we find that the VEOS provides accurate critical points for the methane-ethane mixture, in comparison to experiment.