Assessment of CO2 Capture into Efficient EAE/NHD Water Lean Solvent: CO2 Capture Performance, Phase Change 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, N-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.