Ionic Liquids have been extensively investigated as promising materials for several gas separation
processes, including CO
2
capture. They have the potential to outperform traditional solvents, in
terms of their capacity, selectivity, regenerability and stability. In fact, hundreds of ionic liquids
have been investigated as potential sorbents for CO
2
capture. However, most studies focus on
enhancing equilibrium capacity, and neglect to consider other properties, such as transport prop-
erties, and hence ignore the effect that the overall set of properties have on process performance,
and therefore on cost. In this study, we propose a new methodology for their evaluation using a
range of monetised and non-monetised process performance indices. Our results demonstrate
that whilst most research effort is focused on improving CO
2
solubility, viscosity, a transport prop-
erty, and heat capacity, a thermochemical property, might preclude the use of ionic liquids, even
those which are highly CO
2
-philic, and therefore increased effort on addressing the challenges
associated with heat capacity and viscosity is an urgent necessity. This work highlights a range
of potential challenges that ionic liquids will face before they can be applied at process scale, and
identifies some key research opportunities.