Absorption Performance and Mechanism of CO2 in Aqueous Solutions of Amine-Based Ionic Liquids

Several amine-based ionic liquids (ILs) were synthesized via a one-step method using low-priced organic amines and inorganic acids, and they were mixed with water to form new CO 2 absorbents. The effects of the ionic structure, IL concentration, temperature, and pressure on the CO 2 absorption performance were investigated. The absorption performance of ILs was closely related to the ionic structure, and the CO 2 molar absorption capacity in ILs with the same cation followed the order of [NO 3 ] > [BF 4 ] > [SO 4 ] or [HSO 4 ], whereas that with the same anion ranked in the following order: multiple amine > diamine > monoamine. The IL [TETA][NO 3 ] with 40 wt % concentration showed the best capacity for CO 2 absorption. Moreover, low temperature and high pressure favored CO 2 absorption. The reaction mechanism of the amine group with CO 2 in aqueous solutions of [TETA][NO 3 ], primary amine, and secondary amine was studied via in situ infrared (IR) spectrophotometry. The results showed that the primary and secondary amines first reacted with CO 2 to form carbamate, which decomposed further into bicarbonate with the continuous addition of CO 2 . However, carbamate generated from the reaction of [TETA][NO 3 ] with CO 2 did not decompose further.