MONTE-CARLO SIMULATION OF N-PARAFFINS AND HIGHER ALCOHOLS IN SUPERCRITICAL CARBON-DIOXIDE

Monte Carlo simulation has been applied to calculate the static proper ties of n-paraffins; octacosane (C28H58) and triacontane (C30H62) and higher alcohols, cetyl alcohol (C16H33OH), stearyl alcohol (C18H37OH) and arachidyl alcohol (C20H41OH) in supercritical carbon dioxide at 30 8.2 K. Carbon dioxide was treated as single site molecule for simplifi cation, while chain molecules (n-paraffins and higher alcohols) were a pproximated as many sites molecules. The residual chemical potential w as calculated by the isothermal-isobaric Kirkwood method. It was shown that the solubilities (solid-gas equilibria) of n-paraffins and highe r alcohols in supercritical carbon dioxide can be calculated quantitat ively by introducing only one intermolecular parameter between unlike sites. The calculated results of mean-square end-to-end separations of n-paraffins increases with the pressure both in supercritical carbon dioxide and in supercritical ethane. The mean-square end-to-end separa tions of n-paraffins in supercritical carbon dioxide are shorter than those in supercritical ethane. Furthermore, the first peaks of the rad ial distribution functions of carbon dioxide for n-paraffins are lower than those of ethane for n-paraffins. These facts mean that supercrit ical carbon dioxide acts to n-paraffins as a poor solvent compared wit h supercritical ethane. The radial distribution functions of carbon di oxide for higher alcohols imply that carbon dioxide tends to cluster a round hydroxyl group.