Superbase‐Added Choline Chloride‐Based Deep Eutectic Solvents for CO₂ Capture and Sequestration

Abstract

Deep eutectic solvents (DESs) have emerged as inexpensive and environmentally‐benign liquid media for potential usage in chemical sciences. CO2 capture and sequestration by various substances is an active area of research in green chemistry. CO2 capture ability of DES‐based systems composed of salt choline chloride mixed with hydrogen bond donors urea (named reline), ethylene glycol (named ethaline), and monoethanolamine (named MEACC), are assessed in the absence and presence of three superbases: 1,5‐diazabicyclo[4.3.0]‐non‐5‐ene (DBN), 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), and 1,5,7‐triazabicyclo[4.4.0]‐dec‐5‐ene (TBD), respectively. Addition of superbase is found to significantly increase the CO2 capture ability of the DESs reline and ethaline; for the DES MEACC, the CO2 capture ability is not changed much as monoethanolamine and MEACC on their own exhibit appreciable CO2 capture efficiency. It is found that the overall efficiency of CO2 capture is the best with superbase DBN as compared to DBU or TBD due to the lower steric hindrance around the imine structure. Presence of glycerol in the superbase‐added DESs results in decrease in CO2 capture ability due to significantly lower solubility of CO2 in glycerol. 13C NMR, FTIR and Raman spectroscopic measurements reveal that major part of the captured CO2 binds covalently to the electron‐rich functionalities present on the components of the DES with superbase assisting this association. The reversibility of the captured CO2 is assessed by introducing N2 gas into the CO2 captured superbase‐added DES system; it is found that only 21–25% CO2 by weight could be removed from the system through five cycles. Heating the CO2 captured superbase‐added DES system to 60 °C and 100 °C results in loss of only 23% and 35% CO2 by weight, respectively. Intramolecular excimer intensity of 1,10‐bis(1‐pyrenyl)decane and steady‐state fluorescence anisotropy of rhodamine 6G fluorescence probes effectively monitor the CO2 capture process as viscosity of the superbase‐added DES increases as more‐and‐more CO2 is captured. Efficiency, effectiveness, and robustness of superbase‐added DES‐based systems towards CO2 capture and sequestration is amply highlighted.

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

“…DESs have been investigated for CO 2 capture, as they can absorb CO 2 through the entropic voids within the liquid, similar to nonreactive ILs. , A DES is a mixture for which the melting point is significantly lower than either of the parent compounds: a hydrogen bond acceptor (HBA), usually a halide salt, and a hydrogen bond donor (HBD), such as EG. Recent studies showed that DESs and DES-like mixtures with superbase additives, superbase HBAs, or superbases as the tertiary component have CO 2 capacities ranging from 3.6 to 17.34 wt % at 1 bar of CO 2 with typical absorption temperatures of 45–60 °C. The highest gravimetric CO 2 capacity at 33.7 wt % is reported for a mixture of monoethanolammonium chloride, [MEA.Cl], and ethlyenediamine at 1 bar of CO 2 and 30 °C .…”

Distinct Solvation Structures of CO2 and SO2 in Reline and Ethaline Deep Eutectic Solvents Revealed by AIMD Simulations

“…Sulfur dioxide (SO 2 ), another greenhouse gas, is one of the main constituents responsible for acid deposition, which has adverse effects on materials, natural resources, and human health . In the past, in order to mitigate the emission of CO 2 and SO 2 gases, researchers have put forth enormous effort for the development of various technologies to capture them. − The most efficient and commonly used industrial technique to capture CO 2 is amine-based postcombustion CO 2 capture. , However, this technique has several drawbacks like amine degradation, equipment corrosion, and environmental issues. − Similarly, to mitigate SO 2 emission, most industrial processes use the wet limestone flue gas desulfurization technique. , However, this method is irreversible and leads to unwanted byproducts. , Therefore, the search for a superior method to overcome the drawbacks of conventional methods − led the researchers toward the use of novel materials such ionic liquids (ILs). − Owing to their unique properties, − ILs exhibited significant gas separation propensity. , Although gas absorption by ILs is a reversible process , with no side products, ILs are barely used in industries for gas capturing on a large scale because of their high production cost and low absorption capacity. , Recently, deep eutectic solvents (DESs) have emerged as alternative media for capturing gases − because of their biodegradable nature, ease of preparation, and lower cost of the starting materials. − DESs are commonly referred to as IL analogs because they share similar properties such as tunable character, high thermal stability, and low vapor pressure along with some new improved properties like biodegradability and low toxicity. − ...…”

“…Because of their numerous favorable properties, the role of DESs in the field of gas capture was explored through a series of experimental works. − Li et al highlighted the effect of temperature and pressure on the solubility of CO 2 at different compositions of choline–chloride ([Ch]­[Cl]) and urea . The authors showed that the solubility of CO 2 increased with increasing CO 2 pressure and decreased with increasing temperature.…”

“…Leron et al used a eutectic mixture of [Ch]­[Cl]/ethylene glycol (in molar ratio 1:2), called ethaline, to study the solubility of CO 2 at various temperatures and pressures, and the reported values of solubility were in the typical range as also found in ILs . Pandey and co-workers highlighted the effectiveness of superbases when added to [Ch]­[Cl]-based DESs for CO 2 sequestration . The authors showed that the CO 2 capture efficiency of reline and ethaline DESs increased with the addition of superbase.…”

The Influence of Hydrogen Bond Donors on the CO2 Absorption Mechanism by the Bio-Phenol-Based Deep Eutectic Solvents

“…A lot of DESs have been prepared as CO 2 absorbents so far. Among them, amine-based DESs [ 12 , 13 , 14 , 15 , 16 ], anion-functionalized DESs [ 17 , 18 ], and superbase-based DESs [ 19 , 20 , 21 , 22 ] showed attractive CO 2 capacities through the reaction between CO 2 and active sites in the components at ambient pressure, suggesting that adjusting the structures of the components in the DESs can be an effective strategy to meet the particular demands. Moreover, the interactions between CO 2 and the functionalized DESs were also reported in the literatures.…”