Improving some thermodynamic consistency tests for VLE data evaluation

Abstract

The fundamental Gibbs-Duhem equation is the most widely referenced condition for consistency of the experimental VLE data, leading to a variety of thermodynamic consistency tests (TC tests). TC tests should be applied rigorously because deviations between the test results and VLE experimental data are usually attributed to the doubtful quality of the experimental data. Nevertheless, in many instances are the rough approximations involved in the applications of such TC tests the responsible of the bad results provided by a given experimental data set. In the present paper a method is suggested to calculate the term depending on the excess enthalpy (HE) that is rarely available and impedes rigorous calculation of the area test and the point (or differential) test in isobaric conditions. A relevant example of this problem is that the NIST algorithm uses the area test with the empirical Herington equation to estimate the term depending of HE, despite having been invalidated, and the point test is exclusively applied to isothermal and not to isobaric conditions. The comparison of the method proposed in this work with the standard procedures and data theoretically calculated demonstrates its capacity and validates experimental data sets otherwise improperly questioned.