Perturbation theory of polar Kihara molecule mixtures applied to supercritical fluid extraction systems

Perturbation theory of non-spherical polar molecule systems is applied to characterize the carbon dioxide/6-caprolactam system at conditions of supercritical fluid extraction (SFE). Two aspects of the application of the perturbation theory on the SFE systems is discussed: self-consistency of the hard convex body equations of state (in the colloidal limit), and the way of determining the electrostatic contributions to the Helmholtz energy of molecules of non-spherical convex shape with embedded permanent multipole moments. The perturbation method is applied to determine phase equilibria in the system carbon dioxide/6-caprolactam at temperatures T = 307, 314 and 324 K. The dependence of the mole fraction of solute on pressure at the mentioned temperatures is compared with experimental data and with the correlation results obtained by applying the Peng-Robinson equation of state. A fair agreement of theoretical characteristics with experimental data is found.