Phase separation behaviors and mechanisms of triazole-functionalized ionic liquid absorbents for energy-efficient CO₂ capture

Excessive carbon dioxide (CO₂) emissions have triggered global warming and frequent extreme weather, highlighting the urgency of advancing carbon capture technologies. Although phase change absorbents offer notable benefits for efficient CO₂ capture owing to low-energy regeneration volume enabled by phase separation, rational screening of high-performance ones remains challenging. In this work, three triazole-functionalized ionic liquids (TFILs) were synthesized and blended with organic solvents (as physical solvents or phase-separation agents) to develop novel TFIL absorbents for CO₂ capture. When the mass ratio of the TFIL [Emmim][Triz] to DMSO was 6 : 4, the absorbent showed a CO₂ capacity of 0.121 g CO₂ (g absorbent)⁻¹ at 40 ℃ and 1 bar, with the CO₂-rich phase accounting for 98.5% of the total CO₂ capacity and 53.85% of the total volume, and its regeneration energy consumption was only 1.12 GJ (t CO₂)⁻¹—70% lower than that of the conventional 30 wt% MEA solution. Mechanistic studies revealed that [Emmim][Triz] reacts with CO₂ to form highly polar carbamate, and strong intermolecular hydrogen bonding between carbamate molecules lowers their solubility in the solvent, causing self-aggregation into a rich phase, while the DMSO distributes to the upper lean phase. Based on the polarity-driven phase separation mechanism, a phase change criterion for CO₂ absorption by IL absorbents was proposed: phase change occurs when the dipole moment difference between the product and the phase-separating agent exceeds 12.41 D, which provides a quantitative basis for predicting phase separation behaviors in IL systems. This study developed a TFIL absorbent with excellent comprehensive performance for CO₂ capture and presented a strategy for regulating phase separation behaviors of the absorbents.