Performance and mechanism investigation of CO2 capture by novel ternary MEA/tertiary amine/sulfolane biphasic solvents

Chemical-physical biphasic absorbents significantly reduce CO2 capture energy consumption. In this study, four tertiary amines were combined with monoethanolamine (MEA) and sulfolane to form ternary MEA/co-absorbent/sulfolane biphasic solutions for CO2 capture. The co-absorbents used were N-methyldiethanolamine (MDEA), 1-Dimethylamino-2-propanol (DMIPA), 3-(Dimethylamino)-1,2-propanediol (DMAP), and 3-Diethylamino-1,2-propanediol (DEAP). The dynamic phase separation behavior and properties were examined, the absorption/desorption characteristics were analyzed, and the phase separation absorption mechanism was explored through C-13 Nuclear Magnetic Resonance (NMR) Spectroscopy. Results showed that all four ternary solvents performed excellently, achieving high CO2 loadings in the upper phases (3.09-3.41 mol/L), strong absorption and desorption efficiencies (over 92.5 % and 85 %, respectively), large cyclic loadings (above 2.67 mol/L), and reduced energy consumption (>45.81 % lower compared to 5 M MEA solution). The addition of tertiary amines improved the absorption performance of MEA/sulfolane solutions. Phase separation was influenced by amine solvent alkalinity and hydrophilicity, leading to the presence of sulfolane in both liquid phases and the selective distribution of MEA and tertiary amines. This research offers promising alternatives for efficient CO2 capture and provides theoretical guidance on liquid-liquid phase separation absorption mechanisms.