A rigorous thermodynamic model in Aspen Plush was developed to predict the thermodynamic properties of PZ-AMP-CO2-H2O over a wide range of conditions using the electrolyte non-random two liquid activity coefficient (e-NRTL) model. The sequential regression methodology was applied. This model is based on the piperazine (PZ) model developed by Frailie, in which PZ was treated as a Henry's component. Vapor-liquid equilibrium (VLE), heat capacity, and excess enthalpy data for the binary aqueous 2-amino-2-methyl-propanol (AMP) system were used to get the e-NRTL interaction parameters for AMP-H2O. Unavailable standard state properties of protonated amines were regressed from pK(a) data. VLE data for AMP-CO2-H2O were used to determine the e-NRTL interaction parameters for the molecule-electrolyte binaries. Finally, the thermodynamic model for PZ-AMP-CO2-H2O was obtained by regressing the VLE and heat capacity data for PZ-AMP-H2O and VLE data for PZ-AMP-C-2-H2O in two steps. The model succeeds in predicting CO2 solubility, NMR speciation, and heat of CO2 absorption for PZ-AMP blends with variable loading and temperature. The thermodynamic model can be used for the simulation and design of the CO2 capture process. (C) 2014 Elsevier Ltd. All rights reserved.