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.