CO2 Absorption Mechanism by the Deep Eutectic Solvents Formed by Monoethanolamine-Based Protic Ionic Liquid and Ethylene Glycol

Abstract

Deep eutectic solvents (DESs) have been widely used to capture CO2 in recent years. Understanding CO2 mechanisms by DESs is crucial to the design of efficient DESs for carbon capture. In this work, we studied the CO2 absorption mechanism by DESs based on ethylene glycol (EG) and protic ionic liquid ([MEAH][Im]), formed by monoethanolamine (MEA) with imidazole (Im). The interactions between CO2 and DESs [MEAH][Im]-EG (1:3) are investigated thoroughly by applying 1H and 13 C nuclear magnetic resonance (NMR), 2-D NMR, and Fourier-transform infrared (FTIR) techniques. Surprisingly, the results indicate that CO2 not only binds to the amine group of MEA but also reacts with the deprotonated EG, yielding carbamate and carbonate species, respectively. The reaction mechanism between CO2 and DESs is proposed, which includes two pathways. One pathway is the deprotonation of the [MEAH]+ cation by the [Im]− anion, resulting in the formation of neutral molecule MEA, which then reacts with CO2 to form a carbamate species. In the other pathway, EG is deprotonated by the [Im]−, and then the deprotonated EG, HO-CH2-CH2-O−, binds with CO2 to form a carbonate species. The absorption mechanism found by this work is different from those of other DESs formed by protic ionic liquids and EG, and we believe the new insights into the interactions between CO2 and DESs will be beneficial to the design and applications of DESs for carbon capture in the future.

Deep eutectic solvents as a versatile platform toward CO2 capture and utilization

“…4c and d) are often mixed with superbases to form corresponding strong basic conjugate anions, thereby achieving equimolar CO 2 uptake. 24 A “switchable solvent” composed of DBU and an alcohol was developed to capture CO 2 . 103 DES formed by DBN and 2-imidazolidone (EU) exhibits a high absorption capacity of 1.75 mol CO 2 per mol DES (23.02 wt%) at 45 °C and 0.1 MPa, attributed to strong multiple-site interactions between EU and CO 2 .…”

“…6c) and CO 3 2− /HCO 3 − , respectively, which is consistent with Cheng's work. 24 In the superbase environment, EG is easily deprotonated, resulting in efficient CO 2 capture through carbonate formation (Fig. 6d).…”

“…20,21 As for chemical absorption, the interactions between DESs and CO 2 are significantly stronger than the physical absorption, thereby leading to a noticeable enhancement in absorption capacity as well as absorption enthalpy. The commonly used DESs for chemical absorption include ILs, amines, and alkanolamines, as well as superbases as HBA, 22–24 with absorption pathways involving N–C, 25,26 O–C, 26,27 and C–C 28–31 bond formations.…”

Aqueous 2-Ethyl-4-methylimidazole Solution for Efficient CO2 Separation and Purification

“…Moreover, imidazole ionic liquids show good CO 2 absorption capacity [38]. Cheng et al studied the CO 2 absorption mechanism by deep eutectic solvents based on ethylene glycol and protic ionic liquid ([MEAH][Im]), formed by monoethanolamine with imidazole [39]. Considering that imidazole-based compounds have low saturated vapor pressure and viscosity [40,41], excellent thermal and antioxidant stability [42][43][44], and low reaction heat [31], they should have potential for efficient and low-cost CO 2 capture.…”

Influence of Metal Salts Addition on Physical and Electrochemical Properties of Ethyl and Propylammonium Nitrate

“…These applications are only a small sample of the potential of these materials and the importance of research in future applications. As for the environmental field, materials capable of eliminating insecticides [13], filtering and purifying water [14], capturing carbon dioxide [15][16][17] or recovering metals [18] have been developed.…”