Molecular-Dynamics Simulation of a Methane–Oxygen Mixture: Prediction of P–V–T Data and Evaluation of Effective Pair Potential Models

Abstract

Abstract The results of a molecular-dynamics simulation using various isotropic pair potential functions for pure methane, oxygen, and their binary mixtures in the temperature range of 200 to 600 K and densities up to about 1.5 times their critical density is presented. The models studied in this work were: 1) Lennard–Jones (12–6) potential functions with different parameters, which have been proposed for methane and oxygen in the literature, 2) various types of Mie(n–m) potential with different values of n and m, for both methane and oxygen molecules, and 3) a potential function introduced by Dymond, Rigby, and Smith (DRS model). A Kihara–Mie(20–6) potential with the best value for the Kihara parameter, “γ” and optimized σ and ε is proposed for an oxygen molecule. Considering the predicting capability of the mentioned potential functions for pure methane and oxygen, two of them were selected for investigating methane–oxygen binary mixtures. The CH4–CH4 and O2–O2 center-of-mass radial distribution function, calculated with selected potentials, predicts the positions and peak height for g(r)CH4–CH4 and g(r)O2–O2 in good agreement with experimental data. The Deiters equation of state was used for PVT data production of pure methane and oxygen and their mixtures via imposing an intuitive mixing rule for the equation-of-state parameters. The results show good agreement between the LJ(12–6) and DRS potential models and the Deiters equation of state at densities of up to 0.25 g mL−1 at all temperatures, the deviations increasing by increasing the density. Furthermore, in the case of a methane–oxygen binary mixture, the Peng–Robinson equation of state was applied. The results reveal a strong influence of the binary interaction parameter, over the predicting ability of the Peng–Robinson equation of state for the mixture under study.