Applications of an Association Activity Coefficient Model, NRTL-PA, to Alcohol-Containing Mixtures

A new activity coefficient method for associating systems, NRTL Plus Association (NRTL-PA), is developed and evaluated for alcohol + hydrocarbon systems. The method combines Wertheim’s perturbation theory using the PC-SAFT form of the association strength with Flory’s theory and a residual contribution represented with NRTL. The model is capable of accurate representation of simultaneous VLE, LLE, and excess enthalpy with the same set of parameters. The association contribution is fixed using literature values during regression to provide focus on the capabilities of combining Wertheim statistical mechanics with a residual activity model. The model is shown to be superior to the traditional NRTL model and represents accurately the increase in excess enthalpy as temperature increases. The NRTL-PA model is publicly available as an Aspen Plus user model.