Monte Carlo simulation of solubilities of aromatic compounds in supercritical carbon dioxide by a group contribution site model

The Monte Carlo method was applied to calculate the solubilities of phenol, xylenol isomers, naphthol isomers, and dimethylnaphthalene isomers in supercritical carbon dioxide. These systems are binary mixtures under gas-solid equilibrium conditions. Carbon dioxide was treated as a single-site molecule, and aromatic compounds were treated as multisite molecules. For the aromatic compounds, a benzene ring, a methyl group, and a hydroxyl group were adopted as sites (groups). The Lennard-Jones (12-6) potential was used as the site-site potential, and the Lorentz-Berthelot mixing rules were adopted for unlike pair sites. A modified test particle method was adopted to calculate the residual chemical potentials of aromatic compounds in supercritical carbon dioxide based on the canonical (NVT) ensemble. The calculated solubilities were in good agreement with the experimental data by using common potential parameters determined. The solubilities of isomers can be quantitatively distinguished by the group contribution site model without any binary interaction parameters. Moreover, the microscopic structures of supercritical carbon dioxide around aromatic isomers were studied. The structures of supercritical carbon dioxide around aromatic isomers were found to be different because of the screen effect of substituents.