Aqueous polyamine-based deep eutectic solvent: balancing stability, CO2 absorption/desorption performance, and post-absorption viscosity

Deep eutectic solvents (DESs) have gained significant attention as potential absorbents for CO₂ capture due to their tunable physicochemical properties and environmental sustainability. However, achieving a balance of thermal stability, absorption/desorption performance, and viscosity remains a critical challenge for industrial applications. To address this, a novel aqueous polyamine-based DES system was developed using an ionic liquid with high stability–PzCl (piperazine chloride, P), as a hydrogen bond acceptor (HBA); a polyamine with multiple active sites, DETA (diethylenetriamine, D), as a hydrogen bond donor (HBD), and H₂O as co-solvent. By systematically optimizing the molar ratio of PzCl to DETA, [PzCl][DETA] (PD) with a 1:5 molar ratio was identified as the optimal one based on the absorption capacity/rate, thermal stability, post-absorption viscosity, and desorption efficiency of its aqueous solution. Further investigation into the water content revealed that 30 wt% [PzCl][DETA] (1:5) effectively balanced the CO₂ absorption capacity (0.168 g-CO₂/g-absorbent) and desorption efficiency (54%), more outstanding than those of 30 wt% MEA (0.126 g-CO₂/g-absorbent and 47%, respectively), and provided acceptable post-absorption viscosity (8.11 mPa·s), which was slightly higher than that of 30 wt% MEA (3.77 mPa·s) but lower than 10 mPa·s. These findings provide a scalable framework for designing sustainable absorbents that harmonize high performance with operational viability. This work bridges the gap between laboratory-scale innovations and industrial implementation in carbon capture technologies.