Multi-Site Polylysine Ionic Liquid for CO ₂ Capture: Synergistic Regulation of Absorption and Corrosion

The trade-off between absorption performance and equipment corrosion poses significant challenges for carbon dioxide absorption. Herein, an abundant amine functional site polylysine-based protic ionic liquid [Chol][PLys] was synthesized using polylysine as the anion and combined with ethylene glycol. Owing to its abundant amine functional sites, the ionic liquid enables efficient chemical interaction with CO2, resulting in high absorption capacity. The concentration of [Chol][PLys], the absorption temperature, and the gas flow rate were optimized. The results showed that the absorption loading of [Chol][PLys]–EG was 5.18 mol CO2/mol PILs (50 °C, 100 mL/min). Even under simulated gas containing 15 wt % CO2, the absorption capacity reached 3.59 mol of CO2/mol of PILs, which was much higher than that of 30% industrial absorbent MEA, and the regeneration efficiency was maintained at 83.2% after the fifth regeneration cycle. The corrosion rate of the [Chol][PLys]–EG relative to 20# carbon steel was only 0.0042 mm/a, which is 14.23% of the rate of the saturated 30% MEA solution. Primary and secondary amines react with CO2 to form carbamates, which further convert to alkyl carbamates with ethylene glycol, suppressing hydrolysis and alleviating corrosion according to 13C NMR. Combined molecular dynamics simulations and experimental results indicate that higher absorption requires a synergistic effect between hydrogen bonding and interaction energy. Overall, the proposed absorbents indicated a promising potential in CO2 capture applications.