VLE and LLE of perfluoroalkane plus alkane mixtures

Vapour-liquid equilibria (VLE) of binary mixtures of n-perfluorohexane plus a n-alkane (C-5-C-8) and of n-hexane plus a n-perfluoroalkane (C-5-C-8) were determined using a head-space gas-chromatographic technique. Excess molar Gibbs energies, G(E), for the systems investigated have been obtained by a least-square treatment of equilibrium data. Liquid-liquid equilibria (LLE) were determined by turbidimetry for n-perfluorohexane + n-CnH2n+2 (n = 6-8) mixtures and the observed T-x curves compared with those predicted by the temperature dependence of activity coefficients. All mixtures show strong positive deviations from ideality, which increase with the size of the second component. Solute-solvent and solute-solute interactions have been examined by calculating and discussing solvation Gibbs energies and Kirkwood-Buff integrals. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes. (C) 2002 Elsevier Science B.V. All rights reserved.