Absorption of CO 2 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 CO 2 capture as reversible absorbents. Their physical properties were measured, containing density, conductivity, thermal decomposition temperature, glass transition temperature and viscosity. Their CO 2 absorption behaviors under different pressures and temperatures with various water contents were also investigated. The results showed that the CO 2 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 CO 2 gas capture, superior to the use of pure DIL only, due to their visible decrease in viscosity. The effect of temperature on CO 2 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)C 4 ][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.