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

Jinyu Cheng,Congyi Wu,Haoyuan Li,Dezhong Yang,Yanlong Ma,Weiji Gao,Shiyu Liu

doi:10.3390/ijms23031893

Jinyu Cheng, Congyi Wu + Show 5 more

Open Access

https://doi.org/10.3390/ijms23031893

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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.

Highlights

Deep eutectic solvents have attracted much attention because of their unique properties, including a negligible vapor pressure, non-flammability, ease of synthesis, and tailorable polarity, which make them a promising alternative to traditional organic solvents [1,2]
The absorption mechanism found by this work is different from those of other Deep eutectic solvents (DESs) formed by protic ionic liquids and ethylene glycol (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
We found that CO2 was attached to ethylene glycol (EG) with the formation of a carbonate species when CO2 was captured by DESs consisting of azolide-based ionic liquid (IL) and EG [18]

Summary

Introduction

Deep eutectic solvents have attracted much attention because of their unique properties, including a negligible vapor pressure, non-flammability, ease of synthesis, and tailorable polarity, which make them a promising alternative to traditional organic solvents [1,2]. It was found that 2 reacted both with the revealed that was attached to the anion [2-CNpyr]-, the imidazolium cation anion [Im] and EG Another reaction mechanism between CO2 and DESs consisting of and EG by forming carbamate, carboxylate and2-cyanopyrrolide carbonate species, respectively. On the basis of the NMR and FTIR results, they believed that CO2 was monoethanolamine (MEA) with imidazole (Im) These DESs showed a high absorption bonded for to the groupalso of polyamines or MEA, and EG or CO anion [Im]− did not reac capacity. The absorption mechanism found by this work example, CO2 reacted both with the anion [Im] and EG, but did not react with the cation is different from those of other DESs formed by protic ionic liquids and EG.

Results and Discussion

H-13 C

Materials and Characterizations

Conclusions