Systematic Screening of Deep Eutectic Solvents as Sustainable Separation Media Exemplified by the CO2 Capture Process

Although deep eutectic solvents (DESs) have attracted significant interest in various separation processes, rational methods guiding task-specific DES selection are still scarce. In this work, a systematic method for screening DESs as sustainable separation solvents is proposed and exemplified by the CO2 capture application. To achieve a large screening space, experimentally reported DESs are collected exhaustively from the literature; for most of the studied choline chloride (ChCl)-based DESs, a correlation between their freezing point depression and COSMO-RS molecular descriptors of their hydrogen bond donors (HBDs) is established, which is applied to search a huge number of novel combinations of ChCl and HBD candidates for potential DESs. From the extended database combining experimental and potential DESs, promising CO2 absorbents are screened by integrating (a) the freezing point constraint according to the operating requirement; (b) the estimation of environment, health, and safety (EHS) impacts using quantitative structure- activity relationships methods; and (c) the prediction of thermodynamic properties by COSMO-RS. The practical solvent performance of the top DES candidates is finally studied by experiments, identifying ChCl:ethylenecyanohydrin (at mole ratios of 1:2 and 1:3) as very attractive CO2 absorbents.