Ionic liquids (ILs) have the potential to outperform traditional solvents for CO2 capture, with a great many ILs having been studied to date. In this contribution we present a new approach for their evaluation, and identify which physical properties most infl uence their technical and economic performance. This work highlights a range of potential challenges that ionic liquids will face before they can be applied at process scale, and identifi es some key research opportunities. 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 properties, 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 property, 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.

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Efforts to reduce the cost of CO2captureviathe development of new sorbents have primarily focused on increasing CO2working capacity. Here we show that improved transport properties should be the primary focus.