Absorption characteristics and rheological properties of quaternized polyamine-based deep eutectic solvents for high performance CO₂ capture

This study explores the synthesis and characterization of deep eutectic solvents (DES) for efficient CO₂ capture, focusing on the hydrogen bonding strength between hydrogen bond acceptors (HBA) and donors (HBD). Tetraethylenepentamine (TEPA) was quaternized with hydrochloric acid (HCl) to produce HBAs, which were then combined with various HBDs, including monoethanolamine (MEA), diethanolamine (DEA), N-methyldiethanolamine (MDEA), ethylenediamine (EDA), triethylenetetramine (TETA), and TEPA. The DES were synthesized and their structures confirmed using FT-IR for functional group analysis and DSC for thermal behavior assessment. The molecular structure of DES was further elucidated through 2D ¹H/¹H NOESY, revealing significant effects of the HBA accepting site on physicochemical properties. Our results indicate that DES exhibit two distinct behaviors when water is used as an additive, creating additional voids during semicrystalline transitions and enhancing CO₂ absorption efficiency. DES composed of MEA and EDA demonstrated superior absorption performance due to their lower viscosity. Polyamine-based DES showed increased CO₂ capacity per mole of DES but reduced efficiency per mole of amine, attributed to increased viscosity from carboxylate formation. This research provides a detailed analysis of the hydrogen-bond network within DES and its impact on CO₂ absorption. By optimizing the selection of HBA and HBD, we developed low-viscosity DES, suitable for applications in porous material impregnation, membrane impregnation, and porous liquids. This study provides new insights into the role of free volume and hydrogen bonding in enhancing gas diffusivity and reaction kinetics. The findings contribute significantly to the development of advanced DES for industrial applications, offering a promising solution for mitigating greenhouse gas emissions and promoting a sustainable, low-carbon future.