Assessment of CO₂ Capture into EfficientEAE/NHD Water Lean Solvent: CO₂ Capture Performance, PhaseChange Behavior, and Mechanism Analysis

Water lean solvents have received growing attention for CO₂ capture due to their low solvent evaporation and potential for energy saving. The previous study mainly focused on the organic diluent selection and paid less efforts on the amine effect. In this study, 11 types of amines with representative structures were selected to explore the effect of amine on CO₂ loading and CO₂ distribution with poly­(ethylene glycol) dimethyl ether (NHD) as organic diluent. Based on the cyclic loading and reaction heat comparison, <i>N</i>-ethylethanolamine (EAE) was selected and the EAE/NHD water lean solvent was constructed. The liquid–liquid phase separation was found in the EAE/NHD/H₂O system with more than 95% CO₂ concentrated in the lower phase, which yielded high cyclic loading and benefited regeneration energy consumption. The water content effect was further investigated in terms of CO₂ cyclic loading and phase separation behaviors, suggesting that EAE/NHD/H₂O with a mass ratio of 3:6:1 exhibited the excellent performance of 3.03 mol·kg^–1 cyclic loading and 2.27 GJ·t^–1 CO₂ regeneration energy consumption. ¹³C NMR and quantum chemistry calculations were conducted to explain the reaction route and phase change mechanism. The large difference between the ion–dipole interaction of ion–H₂O and the molecule–molecular interaction of ion-NHD was regarded as the main reason for phase separation. The long-term tests indicated the cycling stability and low corrosivity of EAE/NHD/H₂O, as exhibited by the stable CO₂ cyclic loading during 8 runs of absorption–desorption and lower corrosivity rate of carbon steel than 30 wt % MEA aqueous solution.