Deep Eutectic Solvent Formed by Imidazolium Cyanopyrrolide and Ethylene Glycol for Reactive CO₂ Separations

Abstract

Solvents made from a reactive ionic liquid, with an imidazolium cation and pyrrolide anion, and ethylene glycol at a wide compositional range were studied for separations of CO 2 at low partial pressures (≪0.1 bar up to 1 bar). Thermal analysis and measurements of viscosity and density show compacting of the liquid upon mixing with enhanced stability achieved by hydrogen bonding. A detailed mechanistic study was performed by IR, quantitative NMR, and ab initio calculations that show significant CO 2 absorption capacity below 5000 ppm of CO 2 in N 2 . Three reversible routes are found that yield carbonate (major product), carboxylate (moderate), and carbamate (minor) species. With CO 2 at 100% RH, bicarbonate along with carbonate species form. The CO 2 -ethlyene glycol reaction complex, the carbonate anion, is stabilized by the hydrogen bonding and Coulombic interactions, thus preventing evaporation of the solvent during regeneration. This study demonstrates a promising approach to designer green solvents for CO 2 separations in open systems such as direct air capture.

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

“…The 1 H- 13 C HMBC suggested that the carbon C-4 should be the carbonyl carbon of the carbonate formed by CO 2 and EG. The carbons at 60.7 (C-2) and 65.9 (C-3) ppm are the -CH 2 -carbons of HO-CH 2 -CH 2 -OCOO − [20,21]. Similar carbon peaks could also be found in the Mukesh and co-authors' paper [22].…”

“…The peak at 1635 cm −1 is associated with the combined C=O stretching band of carbonate and carbamate species, and the peak at 1573 cm −1 corresponds to COO − asymmetric stretching of carbamate -NHCOO − . The new peak at 1296 cm −1 is ascribed to the stretching band of RO-COO − [21]. The FTIR results suggested again that both carbonate and carbamate species are formed after CO 2 capture.…”

“…Zeng et al investigated the reaction pathway between CO2 and DESs composed of protic IL 1,8-diazabicyclo [0,4,5]undec-7-ene imidazolate ([DBUH][Im]) and EG [20] and it was found that CO reacted both with the anion [Im] − and EG. Another reaction mechanism between CO2 and DESs consisting of ionic liquid 1-ethyl-3-methylimidazolium 2-cyanopyrrolide ([Emim][2-CNpyr]) and EG was reported by Gurkan and co-authors [21], and the results revealed that CO2 was attached to the anion [2-CNpyr]-, the imidazolium cation and EG by forming carbamate, carboxylate and carbonate species, respectively.…”

New Solvents for CO2 and H2S Removal from Gaseous Streams

“…However, some special DESs able to react with CO 2 also exist. An example is the [EMIM][2-CNpyr]: EG (1:0.5-1.10) solvent studied by Lee and coworkers [145]. The authors carried out a detailed reaction mechanism investigation, pointing out that carbonate formation is the dominant reaction while carbamate formation is minimal.…”

Deep eutectic solvents composed of bio-phenol-derived superbase ionic liquids and ethylene glycol for CO2 capture

“…The band at 1639 cm À1 relates to the CQO stretching of the EG-based carbonate, 33,36 and the band at 1282 cm À1 is from the O-C-O stretch. 29 Nevertheless, the CQO stretching band of the phenol-based carbonates cannot be observed in the FTIR spectra of [DBUH][Car] : EG (1 : 2) after absorption, which falls around 1615 cm À1 . 34,35 Therefore, the FTIR results confirm again that CO 2 is attached to EG, not to the [Car] À anion.…”