New criteria combined of efficiency, greenness, and economy for screening ionic liquids for CO2 capture

• New criteria were proposed for CO2 capture by ionic liquids.
• The capacity–toxicity ratio was proposed as green criterion.
• The capacity–price ratio was proposed as an economical criterion.
• Composite criteria combined of efficiency, greenness and economy were proposed.

Ionic liquids (ILs) are deemed as promising solvents for CO2 capture in the near future, however, some of them have very low sorption capacity, some of them are toxic, and most of them are expensive. These characters make the application of ILs not so efficient, green, and economic. Criteria were proposed to evaluate the utility of CO2 capture by ILs in this study. The sorption capacity (C) is an absolute criterion to characterize the efficiency of the CO2 capture. Besides capacity, the toxicity (T) and the price (P) of the ILs are also important for the industrial application of ILs. Thus, the capacity–toxicity ratio (Rg = C/T), the capacity–price ratio (Re = C/P), and the capacity–toxicity–price ratio (Rge = C/TP), were proposed as relative criteria for assessing the greenness, the economy, and the green-economy for CO2 capture by ILs, respectively. More practically, composite criteria Ri|C>0.5, which mean Ri with a threshold capacity greater than 0.5 expressed with the relative value, including composite greenness criterion, composite economy criterion, and composite greenness-economy criterion, were proposed with considering both the absolute and relative values for CO2 capture by ILs. These criteria combine the efficient, green, and economical of CO2 capture together. They were used to review the utility of pervious results for CO2 capture by ILs. The design of green and economical ILs in the future might also be favorable by taking the hint from these criteria.