Molecular dynamics simulations and cubic equations of state of high-pressure CO2-hydrocarbon mixtures: compressibility factor and fugacity coefficient

ABSTRACT Molecular dynamics (MD) simulations were performed to investigate high-pressure thermodynamic properties of CO₂-hydrocarbon binary mixtures using different force-field strategies ‒ united atom, all atom, and hybrid combinations. Simulations were carried out in the isothermal-isobaric (NPT) ensemble to obtain molar volumes as a function of pressure and composition. As a preliminary step, four cubic equations of state were tested against available compressibility factor data, and Peng-Robinson (PR) was selected as the reference cubic framework for the subsequent analyses. MD-derived molar volumes were then coupled to PR in a hybrid workflow: compressibility factors were computed and benchmarked against experimental data, and PR-based fugacity coefficients were evaluated using either PR-predicted or MD-derived molar volumes to quantify the sensitivity of ϕ to the volume source under identical ( P,T , y ) conditions. The results show that force-field choice significantly affects high-pressure volumetric predictions, with TraPPE-based descriptions providing the closest agreement with experimental compressibility factors for CO 2 + CH 4 over the investigated conditions. Finally, effective PR mixture parameters were inferred by nonlinear least-squares fitting of the molar-volume form of PR to volumetric datasets, demonstrating that MD-generated V m ( P,T , y ) data can serve as an independent input for cubic-EoS parameter inference when experimental information or calibrated mixture parameters are limited.