Phase equilibria for binary n-alkanenitrile-n-alkane mixtures. III. Vapour-liquid phase equilibria for propanenitrile with C5C8 n-alkanes

Vapour-liquid phase equilibria at 313.15 K for the four mixtures of propanenitrile with n-pentane, n-hexane, n-heptane and n-octane have been determined by the measurement of the total vapour pressure in a static apparatus. All mixtures display azeotropy, with the alkane mole fraction of the azeotrope moving from 0.938 in the C5 mixture to 0.239 for the C8 mixture. The excess Gibbs functions calculated by the Barker method (Barker, 1953) are positive, large, symmetrical and, within the range studied, relatively independent of the alkane chain length; their value increases from 1331 J mol−1 for the C5 mixture to 1442 J mol−1 for the C8 mixture, a pattern consistent with what is already known about such mixtures. The results are tolerably well described by the Weimer-Prausnitz modification of the Scott-Hildebrand solubility-parameter version of the regular solution theory, with a Flory-Huggins entropy of mixing that gave a good account of the upper critical solution temperatures of these and other members of this series of mixtures.