Regulating Phase Separation Behavior of a DEEA-TETA Biphasic Solvent Using Sulfolane for Energy-Saving CO₂ Capture

Biphasic solvents containing mixed amines have a phase separation behavior and energy-efficient regeneration for CO₂ capture. However, the trade-off between the CO₂ absorption capacity and the volume ratio of the CO₂-rich phase presents a critical challenge to the reducing potential in regeneration energy consumption. In this study, sulfolane was proposed to regulate the phase separation behavior of a N,N-diethylethanolamine (DEEA)-triethylenetetramine (TETA) biphasic absorbent by simultaneously decreasing the volume ratio and increasing the CO₂ loading of the rich phase, without sacrificing the high CO₂ capacity. In the DEEA-TETA-sulfolane biphasic absorbent, sulfolane acted as a phase splitter and physical activator. The replacement of a part of H₂O by hydrophobic sulfolane contributed to a substantial decrease in the volume ratio of the rich phase from 83 to 39% and an increase in CO₂ loading of the rich phase from 3.10 to 4.92 mol/L. The regeneration heat decreased to 1.81 GJ/t CO₂, 26.4% less than DEEA-TETA, and 54.6% less than the 5 M monoethanolamine system. Moreover, by promoting the mass transfer coefficient of CO₂ in DEEA-TETA-sulfolane to 1.8 times the original DEEA-TETA system, sulfolane was validated as a physical activator. Our study provides a promising strategy for regulating the phase separation behavior of biphasic solvents and enhancing the regeneration energy efficiency for CO₂ capture.