Energy-efficient biphasic solvents for industrial CO2 capture: Absorption mechanism and stability characteristics

The traditional CO2 capture process represented by monoethanolamine has excessive energy consumption, serious oxidative degradation and metal corrosion, which limits its potential for large-scale industrial applications. This study produced a highly effective biphasic 3-amino-1-propanol (MPA)-polyethylene glycol dimethyl ether (NHD)-H2O absorbent with easy modulation of phase separation and low levels of oxidative degradation and metal corrosion. The principal absorbent was MPA, and NHD served as the phase separation solvent. NHD's solvent effect decreased the energy barrier preventing MPA from forming zwitterions (MPA+COO-) and carbamate, thus promoting chemical absorption. The large polarity difference between the reaction products and NHD triggered phase separation, producing a low-polarity CO2-lean phase and a high-polarity CO2-rich phase; 97.41% of the absorbed CO2 accumulated in 43.7% of the CO2-rich phase solution. The sensible heat and latent heat of the MPA-NHD-H2O absorbent were relatively low because of the low saturation vapor pressure, high vaporization enthalpy, and excellent phase separation performance of NHD. The regeneration energy was as low as 2.66 GJ/t CO2, which was 30% less than that for monoethanolamine. Additionally, the oxidative degradation rate for the proposed absorbent was only 10.7% of that for monoethanolamine. This study provides a theoretical reference for application of the MPA-NHD-H2O biphasic absorbent.