PHASE-EQUILIBRIA FOR BINARY N-ALKANENITRILE-N-ALKANE MIXTURES - IV - LIQUID-LIQUID PHASE-EQUILIBRIA FOR PROPANENITRILE WITH C-5-C-8 AND C-10 N-ALKANES

The orthobaric liquid-liquid phase diagrams for the five binary mixtur es of propanenitrile with the n-alkanes C-5-C-8, and C-10, have been d etermined by visual observation of the separation temperatures of mixt ures of known mass composition. The results have been fitted to a conv entional modern expression incorporating where needed Wegner extended- scaling terms. Various aspects of coexistence curve symmetry have been explored, particularly symmetry of the critical composition, i.e., wh ether it falls close to 0.5, and symmetry of the diameter, i.e., wheth er it falls parallel to the temperature axis. Neither mole fraction no r volume fraction fully meets either requirement. A new variable tau b ased on a forced fit to tau(c),= 0.5 reveals both kinds of symmetry an d the data for all five mixtures when expressed in terms of a reduced temperature T/T-c, as a function of tau fall on a universal curve. The implications of this for the coexistence curves for bihomologous mixt ures are briefly discussed. (C) 1997 Elsevier Science B.V.