The solubility parameters of carbon dioxide and ionic liquids: Are they an enigma?

In a recent article entitled "Solubility Parameter of Carbon Dioxide-an Enigma"[1], Marcus reported the literature values for the solubility parameter of liquid carbon dioxide (CO2) at 298 K with discrepancies as large as 200%. An analogous article on ionic liquids has also been published [2], entitled: "Chameleonic Behavior of Ionic Liquids and Its Impact on the Estimation of Solubility Parameter". Marcus [1] attempted to resolve this "enigma" for the total solubility parameter of liquid CO2, but much remains to be clarified. Similarly, much remains to be clarified in the second article on ionic liquids [2]. In the present work, the very concept of the solubility parameter is critically examined via a simple and consistent equation-of-state approach. It is demonstrated that the solubility parameter "enigma" can be resolved with such an approach and the potential sources of discrepancies in its estimation can be identified. The implications of this approach on a multitude of practical and theoretical applications are discussed. (C) 2020 Elsevier B.V. All rights reserved.