Achievement of a Homogeneous Phase in Ternary Ionic Liquid/Carbon Dioxide/Organic Systems

A few years ago, it was found that carbon dioxide (CO2) is able to induce in ternary ionic liquid (IL) + organic systems, a “two-phase (L + V)−three-phase (L1 + L2 + V)−two-phase (L1 + L2)” transition by pressure increase. In the two liquid phase region (L1 + L2), one of the phases did not contain any IL. Therefore, the organic compound could be separated from the IL at increased CO2 pressure without any IL contamination. However, the occurrence of a homogeneous phase by further pressure increase, a so-called L1 + L2 → L transition, in the same systems was never observed before. Here, we demonstrate that in addition a third phase transition is possible upon further CO2 pressure increase, where the two liquid phases (L1 + L2) can be forced to form one homogeneous liquid phase (L). This phenomenon has promising implications for reactions and separations in systems using ILs.