A Water-Lean [DBAPA][52AMP]-Ethanol‑H₂O Absorbent Enables Efficient CO₂ Capture with Low Regeneration Heat Duty

To address the challenges of high desorption temperatures and excessive regeneration energy consumption in conventional organic amine absorbents, a novel functionalized ionic liquid-based ternary water-lean absorbent, [DBAPA]-[52AMP]-Ethanol-H₂O, was proposed for efficient CO₂ capture. This novel absorbent not only demonstrated excellent absorption performance, achieving a CO₂ loading of 1.03 mol·mol^-1, but also could be regenerated at a low temperature of 371 K, with a regeneration efficiency of 94%. The heat duty was estimated as 2.12 GJ·t^-1 CO₂, representing a 43.8% reduction compared to the benchmark MEA solution. Mechanistic studies using ¹³C NMR revealed that the dominant reaction during absorption-desorption is the conversion of carbamate to ethyl carbonate in the presence of ethanol, with minimal hydrolysis due to the low water content. This reaction pathway facilitated easier desorption and reduced regeneration energy consumption. The proposed reaction mechanism involves the initial formation of a zwitterion between the cation and CO₂, followed by deprotonation of the cation, transferring the proton to the tertiary amine in the anion. Deprotonation was found to be the rate-limiting step, and its low activation energy barrier allows for efficient desorption at low temperature. This work offers valuable insights into the development of ionic liquid-based water-lean absorbents for industrial carbon capture, integrating low energy consumption, high efficiency, and excellent recyclability.