Equilibrium behaviour of fluids in the critical region from the fourth-order virial expansion: Supercritical fluid extraction of solids

The fourth-order virial expansion enables an exact and accurate description of the equilibrium behaviour of pure fluids and mixtures at temperatures close to and densities up to twice the critical values, provided all the virial coefficients are known with good accuracy. The paper deals with the determination of the virial coefficients for molecular fluids whose molecules interact via Kihara generalised plus electrostatic pair potentials. Virial expansions for the compressibility factor and chemical potential are used to determine solubilities of naphthalene in carbon dioxide and in carbon dioxide plus acetone (cosolvent). Dependence of solubilities on the values of dipole moment (or quadrupole moment) of the cosolvent is studied.