Thermodynamic modeling of aqueous piperazine/N-(2-aminoethyl) piperazine for CO2 capture

Aqueous piperazine (PZ) blended with N-(2-aminoethyl) piperazine (AEP) is an attractive solvent for CO₂ capture from coal-fired power plants. A rigorous thermodynamic model was developed in Aspen Plus® to predict properties of PZ/AEP/H₂O/CO₂, using the electrolyte-Nonrandom Two-Liquid (eNRTL) activity coefficient model. A sequential regression was performed to represent CO₂ solubility, speciation, and amine volatility data over operationally significant loading and temperature ranges. The model predicts a CO₂ cyclic capacity of 0.86 mol/kg (PZ + AEP + water) for 5 m PZ/2 m AEP, compared to 0.50 mol/kg for 7 m MEA and 0.86 mol/kg for 8 m PZ. The predicted heat of absorption is 75 to 85 kJ/mol CO₂ in the operating loading range (0.288-0.380 mol CO₂/mol alkalinity). Speciation for PZ/AEP/H₂O at various CO₂ loading and temperature was also predicted, from which behavior of CO₂ in the amine system was proposed.