From CO2 Solubility to the Carbon Capture Process: Thermodynamic Modeling, Electrolyte Speciation, Phase Behavior, Solidification, and Regeneration Energy in the CO2-NH3-H2O System.

This study investigates and validates a thermodynamic model for aqueous ammonia (NH3) in postcombustion CO2 capture, focusing on both vapor-liquid equilibrium (VLE) and NH4HCO3 precipitation. Experimental VLE data at 4-8 wt % NH3 (40-80 °C) and existing literature data sets were used to refine an electrolyte nonrandom two-liquid (e-NRTL) model. The results highlight that lower NH3 concentrations (under 7 wt %) eliminate solid precipitation (solidification) risk but may raise regeneration energy, while higher concentrations provide reduced circulation flow rates yet risk solid formation at high CO2 loadings. By applying a simplified regeneration energy analysis, we illustrate how stripper temperature, stripper pressure, and NH3 concentration influence the components of regeneration energy: reaction heat, sensible heat, and latent heat. For a 10 wt % NH3 solution, an optimal stripper temperature of about 130.0 °C and total pressure of 800 kPa are identified to minimize the total reboiler duty (2.90 GJ/tCO2). However, a further pressure increase reduces reaction and latent heat but simultaneously boosts lean loading, raising the sensible heat requirement. Overall, the thermodynamic model and parametric study provide operational strategies to reduce CO2 capture costs, highlighting temperature control and NH3 concentration as dominant factors.