High CO₂ absorption capacity by chemisorption at cations and anions in choline-based ionic liquids

Abstract

The effect of CO absorption on the aromaticity and hydrogen bonding in ionic liquids is investigated. Five different ionic liquids with choline based cations and aprotic N-heterocyclic anions were synthesized. Purity and structures of the synthesized ionic liquids were characterized by H andC NMR spectroscopy. CO capture performance was studied at 20 °C and 40 °C under three different pressures (1, 3, 6 bar). The IL [N][4-Triz] showed the highest CO capture capacity (28.6 wt%, 1.57 mol of CO per mol of the IL, 6.48 mol of CO per kg of the ionic liquid) at 20 °C and 1 bar. The high CO capture capacity of the [N][4-Triz] IL is due to the formation of carbonic acid (-OCOH) together with carbamate by participation of the -OH group of the [N] cation in the CO capture process. The structure of the adduct formed by CO reaction with the IL [N][4-Triz] was probed by using IR, C NMR andH-C HMBC NMR experiments utilizing C labeled CO gas. H andC PFG NMR studies were performed before and after CO absorption to explore the effect of cation-anion structures on the microscopic ion dynamics in ILs. The ionic mobility was significantly increased after CO reaction due to lowering of aromaticity in the case of ILs with aromatic N-heterocyclic anions.

Correspondence on “Preorganization and Cooperation for Highly Efficient and Reversible Capture of Low‐Concentration CO2 by Ionic Liquids”

“…The further shifts to δ =182.0, 159.2, and 30.4 ppm observed after absorption of another 1.25 mol of CO 2 was attributed to the cooperative N–CO 2 –O interactions . A signal at δ =158–162 ppm in the 13 C NMR spectra of ILs containing basic anions is usually observed in the presence of CO 2 and is generally assigned to the carbonate‐ or carbamate‐type carbonyl groups, formed by the “strong” interaction of the N‐ and/or O‐containing anions with CO 2 (Scheme S1) …”

“…Zanatta containing basic anions is usually observed in the presence of CO 2 and is generally assigned to the carbonate-or carbamatetype carbonyl groups,f ormed by the "strong" interaction of the N-and/or O-containing anions with CO 2 (Scheme S1). [5][6][7][8][9][10][11][12][13][14][15][16][17] At this point, we would like to note that ashift of around 159 ppm is also the chemical shift ( 13 C{ 1 H} NMR spectra) of ILs associated with bicarbonate anions [12,18,19] or ILs containing dissolved bicarbonate. [20] Moreover,i th as already been demonstrated that the formation of bicarbonate, [21] resulting from the reaction of CO 2 with the confined water in imidazolium ILs associated with basic imidazolate and acetate anions, [22] or wet amino acid containing ILs, [12] is responsible for ar esonance observed around d = 159 ppm in the 13 Cs pectrum.…”

CO2 Absorption Mechanism by Diamino Protic Ionic Liquids (DPILs) Containing Azolide Anions

“…During the past decade, ionic liquids have been widely studied for CO 2 capture because of their attractive properties [4], such as negligible vapor pressure, high thermal stability, and tunable structures [5,6]. Among the ILs used for CO 2 absorption, aprotic ILs [7][8][9], such as azolide-based [10] and hydroxypyridine-based ILs [11], exhibit high CO 2 capacity. However, tedious procedures are needed to synthesize these aprotic ILs, resulting in high costs.…”

Understanding the Interaction of Boric Acid and CO2 with Ionic Liquids in Aqueous Medium by Multinuclear NMR Spectroscopy

“…Over the past decade, ILs and their mixtures with different solvents have been investigated as potential sorbents for CO 2 gas, bearing in mind their outstanding properties of high CO 2 solubility and selectivity due to the combined chemisorption/physisorption processes . Unlike conventional liquid sorbents such as aqueous ethanolamine solutions, the use of ILs as CO 2 sorbents is very promising for industrial applications. − Amino acid-based ILs are considered the most efficient ILs for CO 2 absorption due to their fast reactivity toward CO 2 and their relatively low toxicity. ,,− ILs containing functionalized choline-based cations and various amino acid-based anions, which have low toxicity and high biodegradability, have also been demonstrated as effective CO 2 absorbents …”