A dual-functional ionic liquid biphasic absorbent for efficient CO2 capture: Enhanced capacity and reduced regeneration energy

To overcome the limitations of conventional ionic liquid-based CO 2 absorbents—namely high regeneration energy consumption and low absorption capacity—a novel biphasic dual-functionalized ionic liquid system, [AEPH][Im]/NPA/H 2 O, was synthesized and evaluated. Initially homogeneous, the system undergoes spontaneous phase separation upon CO 2 absorption, forming distinct lean and rich phases. At saturation, the rich phase accounted for 53.00% of the total volume, with a viscosity of 15.75 mPa·s and a CO 2 loading capacity of 3.43 mol·L −1 . The system exhibited a high regeneration efficiency of 83.42% at 393.15 K, and the regenerated phases could be recombined into a uniform solution. After six absorption-desorption cycles, the absorbent retained 96.39% of its initial capacity, with only a 1.32% decline in desorption efficiency. The 13 C NMR analysis and DFT calculations revealed that CO 2 primarily reacts with [AEPH][Im] to form carbamate, carbonate, and bicarbonate species, which are predominantly concentrated in the rich phase, while only unreacted components remain in the lean phase. NPA facilitates the formation of alkyl carbonates via reaction with carbamates, and the high concentration of bicarbonate significantly enhanced desorption efficiency. The total regeneration energy consumption was calculated to be as low as 1.58 GJ·t −1 CO 2 —markedly lower than that of traditional MEA-based solvents. The [AEPH][Im]/NPA/H 2 O biphasic system demonstrates superior cyclic stability, high CO 2 capture capacity, and low energy demand, presenting a promising alternative for industrial-scale carbon capture applications.