Scott–van Konynenburg phase diagram of carbon dioxide + alkylimidazolium-based ionic liquids

As part of an IUPAC task force, this study was initiated in collaboration with a number of different laboratories throughout the world to help understand the reasons for the discrepancies observed in ionic liquid properties published in literature and to establish an acceptable data bank for the investigated properties of one representative ionic liquid. This study presents experimental high-pressure solubility data of carbon dioxide in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide within the temperature range of 280–370 K and pressures up to 14 MPa. The data are compared with those obtained in other laboratories and the differences are not alarming. In addition, a discussion is presented on the carbon dioxide + ionic liquid phase behavior according to the classifications of Scott and van Konynenburg. Such an understanding can greatly help to predict what kinds of phase phenomena may be expected of such systems in regions outside those measured experimentally and can be a very valuable map when designing and optimizing processes involving gases and ionic liquids.

Figure optionsDownload as PowerPoint slideResearch highlights▶ The majority of binary mixtures of CO2 + ionic liquids most probably have type III phase behavior according to the classifications of Scott-van Konynenburg. ▶ Mixtures of polar gases with ionic liquids may exhibit Type V of Scott-van Konynenburg behavior. ▶ The experimental differences in CO2 solubility in [cnmim][Tf2N] ionic liquids most probably have more to do with the method of experimentation than the impurities of the ionic liquid.