Accurate modeling of thermodynamic properties of CO2 absorption in aqueous alkanolamine solutions is essential for simulation and design of such CO2 capture processes. In this study, we use the Electrolyte Nonrandom Two-liquid activity coefficient model in Aspen Plus to develop a rigorous and thermodynamically consistent representation for the MEA-H2O-CO2 system. Vapor-liquid equilibrium (VLE), heat capacity and excess enthalpy data for the binary aqueous amine system (MEA-H2O) are used to determine the NRTL interaction parameters for the MEA-H2O binary. VLE, enthalpy of absorption, heat capacity and NMR spectroscopic data for the MEA-H2O-CO2 ternary system are used to identify the electrolyte NRTL interaction parameters for the molecule-electrolyte binaries and the previously unavailable standard state properties of the amine ions, MEA protonate and carbamate. The predicted VLE, enthalpy of absorption, heat capacity and speciation for the MEA-H2O-CO2 system are compared favorably to experimental data. (C) 2011 Elsevier B.V. All rights reserved.