Calculations of thermodynamic derivative properties from the NRTL and UNIQUAC models

The local composition models NRTL and UNIQUAC with temperature-dependent parameters have been employed to calculate the surfaces of excess heat capacity, C-p(E), excess enthalpy, h(E) and thermodynamic factor, Gamma for binary liquid mixtures. These thermodynamic properties represent the derivatives of the models with respect to temperature, C-p(E), h(E) and composition, Gamma. The parameters used in evaluating C-p(E) and h(E) are directly obtained from separate C-p(E) and h(E) data at different isotherms. Experimental g(E) and h(E) data at more than one different isotherm are used simultaneously to estimate the parameters in the evaluation of Gamma. The following mixtures are considered: methanol(1)-methyl acetate(2); 2-propanol(2)-n-heptane(2); methanol(1)-water(2); benzene(1)-n-heptane(2) and ethanol(1)-water(2). These mixtures show close deviations between experimental and calculated values obtained from both models and also include associating mixtures. Performances of the models based on different types of experimental data have been compared. The models show considerable regional discrepancies of the same thermodynamic property over the entire composition and temperature ranges for the mixtures that show small overall deviations between the calculated and experimental data. (C) 1997 Elsevier Science B.V.