Sustainable technologies applied to energy-related applications should develop a pivotal role in the next decades. In particular, carbon dioxide capture from flue gases emitted by fossil-fueled power plants should play a pivotal role in controlling and reducing the greenhouse effect. Therefore, the development of new materials for carbon capture purposes has merged as central research line, for which many alternatives have been proposed. Ionic liquids (ILs) have emerged as one of the most promising choices for carbon capture, but in spite of their promising properties, some serious drawbacks have also appeared. Deep eutectic solvents (DESs) have recently been considered as alternatives to ILs that maintain most of their relevant properties, such as task-specific character, and at the same time avoid some of their problems, mainly from economic and environmental viewpoints. DES production from low-cost and natural sources, together with their almost null toxicity and total biodegradability, makes these solvents a suitable platform for developing gas separation agents within the green chemistry framework. Therefore, because of the promising characteristics of DESs as CO2 absorbents and in general as gas separating agents, the state of the art on physicochemical properties of DESs in relationship to their influence on gas separation mechanisms and on the studies of gas solubility in DESs are discussed. The objective of this review work is to analyze the current knowledge on gas separation using DESs, comparing the capturing abilities and properties of DESs with those of ILs, inferring the weaknesses and strengths of DESs, and proposing future research directions on this subject.

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Choline chloride + levulinic acid deep eutectic solvent is studied as a suitable material for CO2 capturing purposes. The most relevant physicochemical properties of this solvent are reported together with the CO2 solubility as a function of temperature. The corrosivity of this solvent is studied showing better performance than amine-based solvents. A theoretical study using both density functional theory and molecular dynamics approaches is carried out to analyze the properties of this fluid from the nanoscopic viewpoint, and their relationship with the macroscopic behavior of the system and its ability for CO2 capturing. The behavior of the liquid-gas interface is also studied and its role on the CO2 absorption mechanism is analyzed. The reported combined experimental and theoretical approach leads to a complete picture of the behavior of this new sorbent with regard to CO2, which together with its low cost, and the suitable environmental and toxicological properties of this solvent, lead to a promising candidate for CO2 capturing technological applications.

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Natural deep eutectic solvent (NADES) produced herein this work by mixing betaine and alanine with lactic acid and malic acid with 1:1 molar mixing ratios. Thermophysical properties including water content, thermal stability, density and gas solubility of CO 2 and N 2 were experimented at different isotherms for wide pressures range up to 50 bars. Moreover, detailed rheological experiments were conducted on the studied materials to obtain viscosity and deduce the dynamic flow behavior. A pressure driven physisorption mechanism was observed for the studied systems. Betaine based NADES materials showed superior carbon dioxide and nitrogen solubility when they are mixed with lactic acid. On the other hand, the rheological experimental results show shear-thinning effect in which the η is decreasing with shear rate at all temperatures. Low viscosity profiles NADES assure the less mass transfer resistance for lactic acid based NADES systems and it also confirmed that the high CO 2 and N 2 solubility for lactic acid based NADES samples.

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A potential of natural deep eutectic solvent (NADES) produced with the mixture of choline chloride with lactic acid, malic acid, citric acid and fructose is studied in this work. Experimental techniques are used to collect thermophysical property data including water content, thermal strength, density and gas solubility of CO2 and N2 data at pressures up to 50 bars. Detailed rheological measurements and various models have been studied to describe the dynamic flow behavior. Moreover, a density functional theory (DFT) and classical molecular dynamics (MD) methods have been used for investigating the physicochemical properties, structuring, dynamics and interfacial behavior of the studied NADES from the nanoscopic point of view to infer its viability for extensive usage. The rheological experimental results show usual shear‐thinning effect in which the η is decreasing with shear rate at all temperatures. A trend of studied NADES viscosity profiles were found as very similar to that of common ionic liquids that were previously, where the viscosities of all studied NADES decreased with increasing temperature. DFT simulations yielded with an accurate quantification of short‐range interaction but liquid state is also characterized by middle and long‐range interaction together with volumetric effects. Molecular orientations were quantified by radial distribution functions and the developed interactions are topologically characterized.