Reversible phase-change extraction process based on temperature-responsive solvent

Abstract

In this study, N-butylpyridinium tetrachloroferrate ([Bpy][FeCl4]), a temperature-responsive solvent, was applied to achieve reversible phase-change extraction with simultaneous solvent recycling for the ethanol/heptane and toluene/heptane systems. The distribution and selectivity coefficients were 7.87 and 0.862, respectively, for ethanol in the 60 mass% ethanol/heptane system; the corresponding values for toluene in the 20 mass% toluene/heptane system were 1.34 and 44.3, respectively, which are significantly better than those for existing conventional solvents. [BPy][FeCl4] was reused five times in each system, and the extraction efficiency remained stable at high values. The experimental results as a function of temperature and solvent:solute mass ratio showed that the reversible phase-change process by [BPy][FeCl4] could be achieved under a range of conditions. This process achieves switchable phase-change extraction and simultaneous solvent recovery, thus offering the possibility of saving energy, reducing equipment requirements, and simplifying operations.