Application of perturbation theory to VLE calculation for dipolar/quadrupolar fluids

Abstract

Thermodynamic perturbation theory has been applied to calculate vapour-liquid equilibria (VLE) of pure dipolar/quadrupolar hard sphere fluids. Effective model parameters for axial and nonaxial quadrupole potentials were determined from low temperature saturation properties. Then, VLE calculations were extrapolated up to the critical point to obtain vapour pressure and coexisting density curves. To improve the description in the critical region a perturbed chain model (PDQC) was introduced and the parameters fitted to reproduce T c. Results of the VLE calculation and critical point values are compared with experimental data for quadrupolar, dipolar and H-bonded fluids. They were used to discuss the success and the limitations of these theoretical models.