Reviewing and screening ionic liquids and deep eutectic solvents for effective CO2 capture

Abstract

CO2 capture is essential for both mitigating CO2 emissions and purifying/conditioning gases for fuel and chemical production. To further improve the process performance with low environmental impacts, different strategies have been proposed, where developing liquid green absorbent for capturing CO2 is one of the effective options. Ionic liquids (IL)/deep eutectic solvents (DES) have recently emerged as green absorbents with unique properties, especially DESs also benefit from facile synthesis, low toxicity, and high biodegradability. To promote their development, this work summarized the recent research progress on ILs/DESs developed for CO2 capture from the aspects of those physical- and chemical-based, and COSMO-RS was combined to predict the properties that are unavailable from published articles in order to evaluate their performance based on the key properties for different IL/DES-based technologies. Finally, top 10 ILs/DESs were listed based on the corresponding criteria. The shared information will provide insight into screening and further developing IL/DES-based technologies for CO2 capture.

COSMO-RS Exploration of Highly CO2-Selective Hydrogen-Bonded Binary Liquid Absorbents under Humid Conditions: Role of Trace Ionic Species

“…Considering the CO 2 /CH 4 selectivity, it was clarified that mixtures including ionic species (choline acetate, betaine hydrochloride, and choline chloride; ChCl) would be more effective than those composed of non-ionic species (Figure b). These data are consistent with the experimental results. − Practically, a small amount of water is often added to reduce the viscosity of DESs; however, the effect of water addition on CO 2 absorption capacity is not clear. ,, Among the narrowed 17,681 mixtures, 438 were predicted to maintain satisfactory CO 2 absorption capacities even under humid conditions (Figure c). Further analyzing the role of ionic species, it was found that more effective absorbents would be obtained when ionic species act as an HBD (blue in Figure c).…”

“…They are obtained as mixtures of hydrogen-bonding donors and acceptors (HBDs and HBAs), − are suitable for reducing production costs, and impose fewer adverse environmental effects. Exploring the physicochemical properties of DESs corresponds with green chemistry and engineering objectives. − However, controlling physicochemical properties is less straightforward in DESs than in ILs, as it is impossible to predict the role of molecules (i.e., whether the molecule works as an HBA or HBD) in hydrogen-bonded mixtures solely from their chemical structures.…”

Comprehensive COSMO-RS Exploration of Highly CO2 Selective Hydrogen-bonding Binary Absorbents even under Humid Conditions

“…Here we could see that ionic ChCl-based 48 mixtures listed in Table 1 have higher CO2/CH4 selectivity than non-ionic mixtures, as in the previous reports. [19][20][21] The hydrogen-bonding capacity for ChCl was θChCl = tan -1 (0.0985/3.8047) = 1.4830°, which indicates that ChCl has strong HBA capacities, as reported previously. Additionally, θChCl > 0 indicates that ChCl exhibits weak HBD capacities.…”

“…Notably, exploring the physicochemical properties of DESs corresponds with green chemistry and engineering objectives. [19][20][21][22] However, DES design is not straightforward because it is impossible to determine which of the vast arrays of hydrogen-bonded organic molecules will act as the HBD or HBA based solely on the chemical structure. Thus, the microscopic solution chemistry governing their macroscopic properties is unclear when organic molecules with both HBD and HBA groups are mixed.…”

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

“…Li et al demonstrated that 1-methylimidazole is a phase separator that induces phase separation and an absorption promoter that increases the absorption rate [37]. 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].…”