Absorption of CO2 by amino acid-functionalized and traditional dicationic ionic liquids: Properties, Henry’s law constants and mechanisms

Six dicationic ionic liquids (DILs) were synthesized, including four amino acid-functionalized DILs (AA-DILs) and two traditional DILs (T-DILs), and were found to be effective for CO2 capture as reversible absorbents. Their physical properties were measured, containing density, conductivity, thermal decomposition temperature, glass transition temperature and viscosity. Their CO2 absorption behaviors under different pressures and temperatures with various water contents were also investigated. The results showed that the CO2 absorption capacities of pure AA-DILs were enhanced heavily compared to other monocationic ionic liquids. Mixing AA-DIL and water could be combined in a more rapid and efficient manner for CO2 gas capture, superior to the use of pure DIL only, due to their visible decrease in viscosity. The effect of temperature on CO2 absorption by aqueous AA-DIL mixtures at ambient pressure was extremely obvious: when temperature rose from 30 to 50 °C, the capacity of the 60 wt% [Bis(mim)C4][Pro]2 solution decreased from 1.52 to 0.78 mol/mol; as the pressure rose up to 10.0 bar, the total maximal capacity also dropped by more than a half. On the other hand, the two traditional DILs also exhibited an excellent physical absorption compared to varieties of monocationic ionic liquids.

► Six novel dicationic ionic liquids (DILs) were synthesized and characterized.
► Henry’s law constants of CO2 in DILs were calculated for the first time.
► Different absorption rate curves accounted for 1.0 and 2.0 molar ratio.
► High temperature dissatisfied chemical absorption in AA-DIL solution.
► Mechanism was verified by NMR and FT-IR.