(88a) Influence Of Carbon Dioxide Concentration On The Complete Miscibility Of Ionic Liquid – Organic – CO2 Ternary Mixtures

The use of ionic liquids and carbon dioxide as combined solvents for reactions and extractions has attracted increasing attention in the last few years. Not only they are able to efficiently replace common volatile organic solvents, but they are also suitable candidates for green chemistry. As it is known, ionic liquids have vanishingly low vapor pressures; they can be designed to be non-flammable, non-toxic, and cations and anions can be selected for a specific application. On the other hand, carbon dioxide is cheap, readily available, non-toxic, non-flammable and has mild critical pressure and temperature. Moreover, ionic liquids have negligible solubility in carbon dioxide, which means that supercritical CO2 can be used to extract compounds from the ionic liquid with a final product free of any solvent contamination. The combination of these two solvents for industrial purposes seems to be, therefore, a perfect solution for the increasing concern with the environment and for the new, more rigid governmental regulations. In the design of any operational unit, details from the behavior of the system are extremely important. Based on the phase behavior of the substances involved, reactions and separations can be efficiently performed. Therefore, phase diagrams are the core of any successful production process. Despite its importance, so far very little has been published on the phase behavior of mixtures with ionic liquids, especially regarding ternary systems. In one of these studies it has been discovered that carbon dioxide can be used to tune the miscibility of ionic liquid-organic mixtures [1], a phenomenon called miscibility switch. By changing the miscibility of the system, reactions can be performed in one homogeneous phase and a split into phases allows separations to be carried out more efficiently. In order to demonstrate the miscibility switch in ternary systems ionic liquid - organic - CO2, we present in this work the phase diagrams of ternary systems based on the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), carbon dioxide and different organic solutes. The location of the three-phase region L1L2V is shown, and the effect of CO2 concentration in the location of the L1L2->L boundary is studied.

[1] Scurto, A. M.; Aki, S. N. V. K.; Brennecke, J. F. (2002). CO2 as a separation switch for Ionic Liquid/Organic Mixtures. J. Am. Chem. Soc., 124(35), 10276.