Solubility and RESS Experiments of Solid Solution in Supercritical Carbon Dioxide

Abstract

An anthracene + phenanthrene mixture forms a solid-solution over the whole composition range. The solubility of anthracene + phenanthrene in supercritical carbon dioxide were measured for the mixture of pure solids and the solid solution at 35°C and between 10.6 and 24.6 MPa. The solubility data of the former were fitted by the Peng-Robinson equation of state (PR EOS), and those of the latter were correlated by the PR EOS and the Wilson equation for a solid phase.
RESS (Rapid expansion from supercritical solution) experiments for pure anthracene, pure phenanthrene and the anthracene + phenanthrene mixtures were performed to study the influence of the operating conditions on the solid formation with emphasis on separation as well as morphology. In the case of RESS for pure compounds, a decrease in the solute concentration brought about an increase in particle size. Operating conditions have scarcely any influence for the mixtures. The particles produced from the CO₂ solution containing anthracene and phenanthrene were all homogeneous crystals of the solid solution. It was confirmed on the based of observations by an optical microphotograph and an X-ray diffratometer. Most of the RESS experiments were carried out at an extraction temperature of 35°C and pressure of 17.0 MPa.