Monte Carlo calculation of solubilities of aromatic compounds in supercritical carbon dioxide

Monte Carlo method has been applied to calculate the solubilities (gas-solid equilibria) of naphthalene, dimethylnaphthalene isomers, and xylenol isomers in supercritical carbon dioxide. Carbon dioxide was treated as single-site molecule and naphthalene, dimethylnaphthalenes, and xylenols were treated as two-site (two benzene-ring groups), four-site (two benzene-ring and two methyl group), four-site (one benzene-ring, one hydroxyl, and two methyl groups) molecules, respectively. The Lennard-Jones (12-6) potential was used as the site-site potential and the Lorentz-Berthelot mixing rules were adopted for unlike site pairs. A modified test particle method was used to calculate the residual chemical potentials of aromatic compounds in supercritical carbon dioxide based on the NVT canonical ensemble. The calculated results of solubilities show good agreement with the experimental values. The solubilities of isomers can be distinguished by the site model. The residual chemical potentials of xylenol isomers calculated by the site model are affected by the position of methyl group. This fact suggests the screen action of methyl group against hydroxyl group. The site model is very useful to explain the screen action.