Thermodynamic modeling of piperazine/2-aminomethylpropanol/CO2/water

• The e-NRTL model accurately represents the thermodynamics of AMP/PZ/CO2/water.
• The model represents CO2 solubility from 20 to 160 °C.
• Data is regressed for amine volatility, heat capacity, heat of mixing, NMR, and pKa.

A rigorous thermodynamic model in Aspen Plus® 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 pKa 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–CO2–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.