Functional ionic liquid as phase separation trigger in biphasic absorption of CO2

Abstract

An amino acid based ionic liquid ([N1111][Ala]) was employed as a trigger to start the phase separation of 2-(2-aminoethylamino) ethanol (AEEA) and 1-ethylimidazole (Eim) solutions (AEH) and to enhance CO2 capture. Due to the accompanying phase change, the CO2 load of AEEA-Eim-H2O-[N1111][Ala] (AEHI) is 1.47 times higher than that of AEH. The interaction mechanism between AEHI and CO2 was elucidated by spectroscopic analysis and molecular simulation. The water-shell layer around [Ala]–CO2 and hydrogen-bonding were first proposed and demonstrated to be the key reasons for the phase separation. The formation of the water-shell layer expelled Eim from the rich phase and thus facilitated the proton transfer process, which not only accelerated the phase separation process but also reduced the regeneration energy consumption. After successive absorption–desorption cycles, the CO2 uptake decreased slightly. The innovative mechanism provides important guidance for the design of excellent biphasic absorbents with good performance and low energy consumption.