CO2 absorption characteristics of amino group functionalized imidazolium-based amino acid ionic liquids

Abstract

In this study, dual amino group functionalized imidazolium amino acid ionic liquids (AAILs) were synthesized from imidazole, bromoalkylamine, and amino acids. 1-(3-aminopropyl)-3-(2-aminoethyl)imidazolium hydroxide ([Apaeim][OH]), 1-propyl-3-(2-aminoethyl)imidazolium hydroxide ([Paeim][OH]), and 1-ethyl-3-(2-aminoethyl)imidazolium hydroxide ([Eaeim][OH]) were synthesized in two-steps, while [Apaeim][amino acid], [Paeim][amino acid], and [Eaeim][amino acid] were synthesized in three-steps. The structures of the synthesized AAILs were confirmed by 1H NMR analysis. Moreover, the CO2 absorption mechanism of [Apaeim][OH] was confirmed by FT-IR and 13C NMR analyses. Subsequently, CO2 absorption-desorption tests were conducted under at 15 vol% CO2, 313 K and atmospheric pressure. The cation and anion effects on the ionic liquid absorbents were also investigated. Among the tested ionic liquid solutions, 30 wt% [Apaeim][OH] and 30 wt% 1-(3-aminopropyl)-3-(2-aminoethyl)imidazolium alaninate ([Apaeim][ala]) displayed the best performances. Thus, both presented CO2 cyclic capacities 2.2-fold higher than that of the benchmark CO2 absorbent 30 wt% monoethanolamine (MEA), while their viscosities were comparable to that of 30 wt% MEA. Notably, 30 wt% [Apaeim][ala] show great potential as a CO2 absorbent due to its high CO2 cyclic capacity and low viscosity.