Carbon dioxide capture by new DBU ‐based DES : The relationship between ionicity and absorptive capacity

Efficient Absorption of CO2 by Protic-Ionic-Liquid Based Deep Eutectic Solvents

Carbon capture, utilization, and storage (CCUS) are among the key technologies to achieve large-scale carbon emission reduction globally. Deep eutectic solvents (DESs) are considered as designable solvents, which has attracted intensive attention for CO2 capture. Here, a series of binary DESs are synthesized through one-step mixing with the starting materials of protic ionic liquid (PIL) and amine. The eutectic behavior was investigated by measuring the melting point of PILs and amine. The saturated vapor of these DESs and industrial MDEA solution were measured and compared. These DESs are investigated to have high absorption capacity (0.1 g ⋅ g-1 at 1.0 bar and 25 °C), superior apparent absorption rate constant (0.381 min-1 vs 0.012 min-1 of 70 wt.% MDEA), moderate interaction with CO2 (the enthalpy change is as low as -34.8 kJ ⋅ mol-1). The absorption mechanism is also investigated by NMR analysis. Eight absorption/desorption regeneration experiments are carried out to show their reversibility. Considering the advantages, including convenience of synthesis, large absorption capacity, fast absorption rate, and moderate interaction energy as well as good regeneration, these DESs are believed to be as potential CO2 absorbent in practical applications.

Refractive Index of 48 Neat Deep Eutectic Solvents and of Selected Mixtures: Effect of Temperature, Hydrogen-Bonding Donors, Hydrogen-Bonding Acceptors, Mole Ratio, and Water

The refractive index (RI) is an important physiochemical property of deep eutectic solvents (DESs) for application in the optical identification of specific substances or measuring the concentration of solutes in solutions. However, the available data on the RI of DESs is limited. Here, a systematic investigation on the RI of 48 typical DESs and 30 mixtures with water was conducted under atmospheric pressure. The effect of temperature in the range 293.15-338.15 K, hydrogen-bonding donors (HBDs), and hydrogen-bonding acceptors (HBAs) on RI was investigated. Furthermore, the RI of DESs as a function of mass percentage in the range of 20-80% water was also studied. It was found that the RI of DESs and its aqueous binary mixtures decreases linearly with the increase of temperature. HBDs and HBAs had a significant influence on the RI of DESs. Among them, the RI of choline chloride (ChCl)/phenol and ChCl/o-cresol were obviously higher than those of other DESs. It was also found that the addition of water would decrease the RI of DESs, and the RI of DES content in percentage (wt %) of water binary mixtures increases linearly as a function of mass percentage of DESs for 20 DESs. However, for the other 10 DESs, there is no linear relationship between the RI and the DES content.

Acidity Scale in a Choline Chloride- and Ethylene Glycol-Based Deep Eutectic Solvent and Its Implication on Carbon Dioxide Absorption

An equilibrium acidity (pK_a) scale that comprises 16 Brönsted organic acids, including phenols, carboxylic acids, azoles, and phenylmalononitriles, was established in a choline chloride/EG-based deep eutectic solvent (DES) ([Ch][Cl]:2EG) by ultraviolet-visible (UV-Vis) spectroscopic methods. The established acidity scale spans about 6 pK units in the DES, which is similar to that for these acids in water. The acidity comparisons and linear correlations between the DES and other solvents show that the solvent property of [Ch][Cl]:2EG is quite different from those of amphiphilic protic and dipolar aprotic molecular solvents. The carbon dioxide absorption capabilities as well as apparent absorption kinetics for a series of anion-functionalized DESs ([Ch][X]:2EG) were measured, and the results show that the basicity of comprising anion [X] of choline salt is essential for the maximum carbon dioxide absorption capacity, i.e., a stronger basicity leads to a greater absorption capacity. The possible absorption mechanisms for carbon dioxide absorption in these DESs were also discussed based on the spectroscopic evidence.

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

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.