New Insights into CO₂ Absorption Mechanisms with Amino‐Acid Ionic Liquids

Abstract

The last decade saw an explosion of interest in using amine-functionalized materials for CO2 capture and conversion, and it is of great importance to elucidate the relationship between the molecular structure of amine-functionalized materials and their CO2 capacity. In this work, based on a new quantitative analysis method for the CO2 absorption mechanism of amino-acid ionic liquids (ILs) and quantum chemical calculations, we show that the small difference in the local structure of amine groups in ILs could lead to much different CO2 absorption mechanisms, which provides an opportunity for achieving higher CO2 capacity by structure design. This work revealed that the actual CO2 absorption mechanism by amino-acid ILs goes beyond the apparent CO2 /amine stoichiometry; a rigid ring structure around the amine group in ILs creates a unique electrostatic environment that inhibits the deprotonation of carbamic acid and enables actually equimolar CO2 /amine absorption.

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.…”

Protein‐Rich Biomass Waste as a Resource for Future Biorefineries: State of the Art, Challenges, and Opportunities

“…However, glutamate‐ and aspartate‐based ionic liquids generally have higher glass transition temperatures, melting temperatures, and viscosities. These ionic liquids have potential applications in catalysis, chiral separations, gas separation and purification, CO 2 absorption, oil purification, coal and biomass pretreatment, as biolubricants, and as solvents for organic syntheses, such as Cu‐free Sonogashira coupling reactions or peptide synthesis …”

CO2 Absorption by DBU-Based Protic Ionic Liquids: Basicity of Anion Dictates the Absorption Capacity and Mechanism

“…Although a high absorption capacity of CO 2 has been realized in ILs, the fundamental rules that govern the absorption mechanism and performances are still not clear, which may hamper a rational design and development of ILs in this respect. In addition, currently the rationales for the catalytic performance of PILs on CO 2 absorption were almost entirely based on the acidity data determined in molecular solvents, such as water or DMSO (Wang et al, 2010; Yang et al, 2016). It is known from both experimental results and theoretical calculations that the acidity obtained in molecular solvents may not explain acid/base behavior in ILs satisfactorily (Mihichuk et al, 2011).…”