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 CO₂ absorbents. The effects of the ionic structure, IL concentration, temperature, and pressure on the CO₂ absorption performance were investigated. The absorption performance of ILs was closely related to the ionic structure, and the CO₂ molar absorption capacity in ILs with the same cation followed the order of [NO₃] > [BF₄] > [SO₄] or [HSO₄], whereas that with the same anion ranked in the following order: multiple amine > diamine > monoamine. The IL [TETA]­[NO₃] with 40 wt % concentration showed the best capacity for CO₂ absorption. Moreover, low temperature and high pressure favored CO₂ absorption. The reaction mechanism of the amine group with CO₂ in aqueous solutions of [TETA]­[NO₃], primary amine, and secondary amine was studied via <i>in situ</i> infrared (IR) spectrophotometry. The results showed that the primary and secondary amines first reacted with CO₂ to form carbamate, which decomposed further into bicarbonate with the continuous addition of CO₂. However, carbamate generated from the reaction of [TETA]­[NO₃] with CO₂ did not decompose further