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

Hu, Pengcheng, Zhang, Rui, Liu, Zhichang, Liu, Haiyan, Xu, Chunming, Meng, Xianghai, Liang, Meng, Liang, Shuangshuang
Energy & Fuels 2015 v.29 no.9 pp. 6019-6024
absorbents, absorption, aqueous solutions, bicarbonates, carbon dioxide, cations, inorganic acids, ionic liquids, secondary amines, spectroscopy, sulfates, temperature
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 in situ 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.