GE model independent application of the Gibbs-Helmholtz validation method to P-x data

摘要

Gibbs-Helmholtz (G-H) data validation for P-T-x/z (pressure-temperature-liquid mole fraction/overall mole fraction) binary VLE data sets, involves comparing calculated excess enthalpies (H-E) from model derivation to experimental excess enthalpy data obtained independently from calorimetry. The usual methods have generally been applied to data at low pressures (usually 1-3 bars) and are dependent on the model selected for the activity coefficient (G(E) model), however measurements of this nature, where the vapour phase is not determined analytically, can also be conducted at moderate pressures (up to 15 bars) and can be modelled in a similar manner. It's proposed in this work that the G-H validation procedure can also be applied in these ranges if a modification is made for the description of the vapour phase non-idealities through a cubic equation of state. Furthermore, the dependence of the procedure on the activity coefficient model selected in the correlation of the VLE data is investigated. Additionally, a G(E) model independent method for Gibbs-Helmholtz validation of binary VLE systems at moderate pressures is proposed and tested, that involves the integration of the coexistence equation, using a cubic equation of state to describe vapour-phase non-idealities. It was found that the G(E) model independent validation procedure generally provides a superior prediction of the temperature trends and magnitude of H-E than the model dependent method, and thus is a more reliable procedure for comparison to calorimetrically measured H-E data. (C) 2019 Elsevier B.V. All rights reserved.