The concept of eutectic solvents as a platform technology for a variety of applications including gas separation has become a popular approach. To date, the number of known deep eutectic solvents (DESs) is limited mainly to halide salts easily interacting with a hydrogen-bond donor (HBD) and resulting in the formation of a liquid phase. Actually, the DESs properties may be tuned by selecting the appropriate HBD, while the structure of the anion is not a decisive factor. However, the presence of other anions may be favorable for certain applications; therefore, expanding the range of deep eutectic solvents seems a relevant issue of chemistry and material science. In this study, we report the high absorption properties of the DES based on 1-butyl-3-methyl imidazolium methanesulfonate–urea toward ammonia. The structure features investigations have revealed the major contribution of C(2)-H to hydrogen bonding. To assess the possibility of selective separation, the solubility of ammonia and two acidic gases (H2S and CO2) in the absorbent has been measured. A superior gas sorption capacity was observed for ammonia, for which the Henry’s law constant was equal to 1.52 bar. The obtained results exceeded the solubility data reported in the literature for various ILs containing hydrogen-donating groups. The DESs demonstrated lower yet acceptable solubility toward hydrogen sulfide, whereas the solubility of CO2 was relatively poor. The thermostimulated desorption has demonstrated that the ability of gases to bind with DES molecules can be ranked as follows: NH3 > H2S > CO2. The physical sorption mechanism of ammonia, hydrogen sulfide, and carbon dioxide in the DES was proven by FTIR and thermal desorption analysis. The absorption was totally reversible, and the solubility of gases remains almost unchanged after three cycles.

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO2 carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such membranes may be appropriate for better understanding of various factors affecting the separation performance and the selection of the optimal operating conditions. In this work, we have tested CH4, CO2 and H2S permeability across the supported ionic liquid membranes impregnated by 1-butyl-3-methylimidazolium acetate (bmim[OAc]) with the following determination of the ideal selectivity in order to compare the facilitated transport membrane performance with the supported ionic liquid membrane (SILM) that provides solution-diffusion mechanism, namely, containing 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]). Both SILMs have showed modest individual gases permeability and ideal selectivity of CO2/CH4 and H2S/CH4 separation that achieves values up to 15 and 32, respectively. The effect of the feed gas mixture composition on the permeability of acidic gases and permeselectivity of the gas pair was investigated. It turned out that the permeation behavior for the bmim[OAc]-based SILM toward the binary CO2/CH4, H2S/CH4 and ternary CO2/H2S/CH4 mixtures was featured with high acidic gases selectivity due to the relatively low methane penetration through the liquid phase saturated by acidic gases.

To properly design ionic liquids (ILs) adopted for gases separation uses, a knowledge of ILs thermodynamic properties as well their solubilities with the gases is essential. In the present article, solubilities of CO2 and H2S in bis(2-Ethylhexyl)sulfosuccinate based ILs were predicted using the conductor like screening model for real solvents COSMO-RS. According to COSMO-RS calculations, the influence of the cation change was extensively analyzed. The obtained data are used for the prediction of adequate solvent candidates. Moreover, to understand the intrinsic behavior of gases solubility the free volume of the chosen ILs and their molecular interactions with respectively CO2 and H2S were computed. The results suggest that hydrogen bonding interactions in ILs and between ILs and the gases have a pivotal influence on the solubility.