Monte Carlo simulation of n-paraffins and higher alcohols in supercritical carbon dioxide

Abstract

Monte Carlo simulation has been applied to calculate the static properties of n-paraffins; octacosane (C 28H 58) and triacontane (C 30H 62) and higher alcohols; cetyl alcohol (C 16H 33OH), stearyl alcohol (C 18H 37OH) and arachidyl alcohol (C 20H 41OH) in supercritical carbon dioxide at 308.2 K. Carbon dioxide was treated as single site molecule for simplification, while chain molecules (n-paraffins and higher alcohols) were approximated as many sites molecules. The residual chemical potential was calculated by the isothermal-isobaric Kirkwood method. It was shown that the solubilities (solid-gas equilibria) of n-paraffins and higher alcohols in supercritical carbon dioxide can be calculated quantitatively 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 separations of n-paraffins in supercritical carbon dioxide are shorter than those in supercritical ethane. Furthermore, the first peaks of the radial distribution functions of carbon dioxide for n-paraffins are lower than those of ethane for n-paraffins. These facts mean that supercritical carbon dioxide acts to n-paraffins as a poor solvent compared with supercritical ethane. The radial distribution functions of carbon dioxide for higher alcohols imply that carbon dioxide tends to cluster around hydroxyl group.