Energy-efficient CO₂ capture using a biphasic tertiary-amine ionic liquid with reversible phase behavior

In this study, 2-dibutylaminoethanol imidazole ([DBAE][Im]) was developed as a novel ionic liquid for energy-efficient CO₂ capture to address key challenges, such as high energy consumption and elevated regeneration temperatures, associated with conventional amine-based absorbents. The self-extractable behavior of [DBAE][Im] facilitated reversible liquid–liquid phase separation during CO₂ absorption and desorption. The CO 2 absorption loading of the [DBAE][Im] solution (0.5 mol·L −1 ) reached 0.82 mol·mol −1 at 313.15 K, and the regeneration efficiency remained high at 87 % even after five consecutive regeneration cycles at 371.15 K. The reaction and self-extraction mechanisms were determined using carbon nuclear magnetic resonance spectroscopy and quantum chemical calculations. These analyses revealed that the significant polarity difference and weak hydrogen bonding between [DBAE][Im] and water (H₂O) induced a phase transition before CO 2 absorption. During absorption, CO 2 reacted with [DBAE][Im] to form carbamate/bicarbonate (HCO₃ − /CO₃ 2− ) species, which resulted in a homogeneous solution due to the decreased polarity of CO₂ products and the strong hydrogen bonds formed between the products and H₂O. Following thermal desorption, [DBAE][Im] separated into the upper phase, restoring its high polarity and reducing intermolecular hydrogen bonding with H₂O. Owing to its self-extraction capability, the regeneration rate of [DBAE][Im] improved significantly at 371.15 K, while the regeneration heat duty was reduced by 47 % compared to monoethanolamine. The results demonstrate that the novel aqueous [DBAE][Im] absorbent offers substantial energy savings for CO₂ capture, presenting a promising approach for advancing carbon capture technologies.