Generalized Interaction Parameter for the Modified Nonrandom Two-Liquid (NRTL) Activity Coefficient Model

Abstract

Activity coefficients are used in phase equilibria calculations to account for the nonideal behavior of liquids in a mixture. In our previous work, we proposed a modification to the widely used nonrandom two liquid (NRTL) activity coefficient model that reduced the number of parameters from two to one. The current work is an extension to the previous work, and it focuses on generalizing the parameter of the modified NRTL (mNRTL1) model using a theory-framed quantitative structure–property relationship (QSPR) modeling approach, where the mNRTL1 model was used as a theoretical framework to develop the behavior model, and QSPR was used to generalize the substance-specific parameter of the model. In this work, a VLE database consisting of 916 binary systems with a wide range of functional-group interactions was assembled. Data regression analyses were performed to determine the parameter of the mNRTL1 model. The structural descriptors of the molecules were used as inputs in the QSPR model to predict the regressed parameter. The generalized QSPR model produced equilibrium property predictions within two times the errors obtained through regression of the experimental data. The newly developed QSPR model resulted in comparable phase equilibria predictions to that of the group-contribution method, UNIFAC. In comparison, the QSPR model has less than 10% of the number of parameters used by UNIFAC and is applicable to a wider range of systems.