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

Abstract

A methodology, based on the Gibbs-Duhem equation, is developed to study thethermodynamic consistency of liquid–liquid equilibrium (LLE) data. The methodproposes evaluating the experimental data in two ways: (a) integral-form, veri-fying dependences among variables in the same phase, both for temperatures:bTj¼κTε0T,j Tj,exp Tj,cal, and compositions:bxJ1,j¼κxε0xJ1,j xJ1,j,exp xJ1,j,cal, and(b) differential-form, which validates relationships between the compositions of eachphase bybζj¼κζε0ζ,j ζj,exp ζj,cal. A coverage factorκis introduced in bothapproaches to define the degree of confidence of the evaluation using a database(T,xI1,xII1) of 50 binary systems to define the limits of inconsistency. Withκ=3, morethan 60% of the set is accepted (κ>3 falls to 38%) providing a guarantee of qualityfor 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 LLEgives the model a limited sensitivity to systematic errors