Assessment of liquid–liquid equilibrium data by solving the Gibbs-Duhem equation

A methodology, based on the Gibbs-Duhem equation, is developed to study the thermodynamic consistency of liquid–liquid equilibrium (LLE) data. The method proposes evaluating the experimental data in two ways: (a) integral-form, verifying dependences among variables in the same phase, both for temperatures: (Formula presented.), and compositions: (Formula presented.), and (b) differential-form, which validates relationships between the compositions of each phase by (Formula presented.). A coverage factor κ is introduced in both approaches to define the degree of confidence of the evaluation using a database (T, (Formula presented.)) of 50 binary systems to define the limits of inconsistency. With κ = 3, more than 60% of the set is accepted (κ > 3 falls to 38%) providing a guarantee of quality for LLE data. The results show that the consistency test can detect errors in the set {data + model} under study, although the absence of a reference state for the LLE gives the model a limited sensitivity to systematic errors.