Experimental study of CO 2 absorption in aqueous cholinium-based ionic liquids

CO 2 removal (or separation) is the key step for biogas upgrading. This research aims to investigate aqueous solutions of amino acid ionic liquids to achieve effective CO 2 separation. In this work, three cholinium-based amino acid ionic liquids ([Cho][AA]s) (i.e. cholinium glycinate ([Cho][Gly]), cholinium alaninate ([Cho][Ala]) and cholinium prolinate ([Cho][Pro])) were synthesized and characterized. The effect of water on the viscosity, CO 2 absorption loading ( m and α ) and apparent absorption rate constant was systematically studied. The CO 2 absorption mechanism in the aqueous solution of [Cho][Gly] was explored by 13 C Nuclear Magnetic Resonance (NMR). The results demonstrate that the absorption loading ( m ) and viscosity increase with increasing IL concentration, while the apparent absorption rate constant decreases. The absorption loading decreased with increasing temperature. The CO 2 absorption mechanism in the aqueous [Cho][Gly] solution started with the chemical reaction to form carbamate at low absorption loading ( α ), and followed by the hydrolysis of carbamate and CO 2 hydration reaction at high absorption loading ( α ). Moreover, the aqueous solution with 5 wt % [Cho][Gly] showed the highest regeneration efficiency, and the absorption and regeneration performance of the aqueous solution of [Cho][Gly] was compared with commercial CO 2 absorbents with promising results.