Molecular Dynamics Study of CO2-Induced Transfer of Crude Oil Components: Roles of Molecular Structure, Cohesion, and Mixture Composition.

Molecular dynamics simulations examined the roles of molecular structure, thermodynamic compatibility, intermolecular association, and mixture composition in the supercritical CO2 extraction of ten crude oil components at 363.15 K and 15 MPa. Single-component extraction ratios ranged from 80.70% for n-hexane to 5.85% for 2-naphthol. Compounds of similar size differed widely, indicating that topology, aromaticity, and polar functional groups were more informative than molecular size alone. CO2 solubility parameters obtained from MD agreed with estimates derived from NIST data, and δCO2 = 7.28ρr captured their reduced density dependence over 303.15-363.15 K. Extraction generally decreased with increasing oil-CO2 solubility parameter difference. In binary systems evaluated using oil boundaries determined by the half density criterion, higher fractions of nonpolar partners were associated with increased total extraction ratios, whereas higher fractions of polar partners were associated with decreases. Multicomponent systems showed redistribution that depended on the overall composition, and relative diffusion coefficients qualitatively reflected mobility differences. The gas-oil interaction competition factor, Rcomp, decreased from 1.985 to 0.087 in the same order as the extraction ratios. Both the thermodynamic and energetic correspondences persisted after excluding 2-naphthol. Configurations and radial distribution functions showed that association in nonpolar hydrocarbons was dominated by dispersion interactions, whereas polar and aromatic components exhibited additional hydrogen bonding, aromatic stacking, and dipolar or electrostatic organization. Local CO2 enrichment near polar sites alone did not explain overall extraction. Overall, the selective transfer of individual components was consistent with a balance between local CO2-oil association and collective oil-oil cohesion that depended on mixture composition, while molecular organization may regulate the accessibility of favorable CO2 contact sites.