Thermodynamics of Ideal and Non-Ideal Solutions for Monoethanolamine and 2-Amino-2-methyl-1-propanol Blends in Shipboard Carbon Capture Scenarios: Model Comparison and Regeneration-Energy Window

Reducing shipping carbon emissions requires absorbents that combine low regeneration energy with practical onboard applicability. However, for blended monoethanolamine and 2-amino-2-methyl-1-propanol solvents, effects of liquid-phase non-ideality on carbon dioxide loading, regeneration energy, and feasible operating windows have not been quantified systematically. In this study, a non-ideal electrolyte thermodynamic model was developed for the aqueous monoethanolamine-2-amino-2-methyl-1-propanol-carbon dioxide-water system by coupling gas-liquid partitioning, temperature-dependent chemical equilibria, ionic speciation, and activity coefficients. The model was calibrated and validated against literature data, reproducing carbon dioxide loading with a symmetric mean absolute percentage error of 8.3042%, a root mean square error of 0.0489, and a coefficient of determination of 0.94605. Within a unified thermodynamic framework, the regeneration energy was decomposed into sensible heat, water-vaporization heat, and reaction heat. Sensible heat was the dominant contribution, accounting for about 55-80% of the total regeneration energy over the investigated range, whereas the water-vaporization contribution increased markedly at higher regeneration temperatures. Relative to ideal-solution calculations, neglecting liquid-phase non-ideality led to a systematic underestimation of regeneration energy. This penalty was governed primarily by solvent composition, became most pronounced in monoethanolamine-rich blends, and was further amplified at relatively high regeneration temperatures, where the deviation reached 150-200 kJ per mole of carbon dioxide. The results identify monoethanolamine-lean, 2-amino-2-methyl-1-propanol-rich blends as the most favorable region, with a recommended monoethanolamine content of 0-10 wt% and a regeneration temperature of 410-425 K. The novelty of this work lies in explicitly quantifying non-ideality penalties and translating them into composition-temperature operating windows for shipboard carbon capture.