PREDICTION OF VAPOR-LIQUID-EQUILIBRIA OF NONAQUEOUS SYSTEMS IN THE SUBCRITICAL RANGE BY USING THE NRTL EQUATION

A method is proposed for using the NRTL equation to predict vapor-liqu id equilibria of non-aqueous mixtures in the subcritical range. For cl asses of mixtures having similar properties, the sum of the two charac teristic energy differences g(ii) - g(ij) and g(jj) - g(ij), which app ear in the NRTL equation, is simply related to the difference between the Hildebrand solubility parameters, delta(i) - delta(j), where i and j stand for the compounds in the mixture. The following subdivision d efines classes of binary solutions which obey the above rule: mixtures with a miscibility gap; polar/non-polar mixtures; polar/polar mixture s; nearly ideal mixtures; mixtures with negative deviations from Raoul t's law. The asymmetry of the NRTL equation is also determined from pu re-component properties. The proposed procedure is applied to over 60 binary solutions which are representative of various degrees of non-id eality, including highly asymmetric systems. A comparison is made with a previous predictive method based on the application of a multiconst ant equation of state (EOS).