Plait point in ternary system with a miscibility gap: Analysis of the procedures involved in its determination and development of novel procedures

Ternary miscibility data, usually reported in the Roozeboom triangular diagram, have been analyzed in Cartesian coordinates defined by X = (xi − xj)/3 and Y = xk where xi, xj, and xk are the mole fractions of the two solvents and of the solute, respectively. This has allowed for an easy analytical representation of all the elements which are characteristic of the system: binodal curve, tie lines, plait point. Three novel methods for determining the plait point composition have been proposed based only on its fundamental properties. The results have been presented by applying the methods to some systems described in the literature. Differences between the values obtained with the proposed methods and those obtainable with the NRTL and UNIQUAC models have been found and are discussed.