Mechanism and experimental investigation of a novel non-aqueous functionalized ionic liquid biphasic absorbent with high absorption capacity and low energy consumption for CO2 capture

To address the trade-off effect between high CO 2 loading and low regeneration energy consumption, a novel functionalized ionic liquid (IL) non-aqueous biphasic absorbent composed of diethylenetriamine-4-hydroxypiperidine/ethylene glycol/diethylene glycol dimethyl ether ([DETAH][4-HP]/EG/DGDE) was proposed for CO 2 capture. The optimal absorbent achieved a maximum CO 2 capacity of 2.09 mol·mol −1 , which is significantly higher than that of other IL absorbents with an equivalent number of amine groups. The regeneration energy was only 1.94 GJ·t −1 CO 2 , which is approximately 51.38 % lower than that of the 30 wt% monoethanolamine (MEA) aqueous solution. Reaction mechanisms were elucidated via 13 C NMR characterization and quantum chemical calculation. CO 2 initially reacted with the amino groups of [DETAH] + to form zwitterions and subsequently carbamate through deprotonation, while it directly bound with the amine site of [4-HP] − to form carbamate. Additionally, part of the carbamate further reacted with EG to generate alkyl carbonate. Weak intermolecular interaction analysis results indicated that EG formed dimeric structures with rich-phase products, facilitating the absorption process. Quantum chemical calculation further confirmed that the polarity difference of CO 2 products between solvents was the primary driver for phase separation. Moreover, [DETAH][4-HP]/EG/DGDE exhibited no corrosivity toward 20# carbon steel before and after CO 2 absorption, along with high stability against degradation, demonstrating strong potential for industrial carbon capture applications.