470170 Hydrodynamics of Two-Phase Ionic Liquid Solvent Systems in Countercurrent Chromatography
In this work, the application of ionic liquid biphasic solvent systems in a custom-designed CCC device has been investigated for the potential separation and recovery of valuable and intrinsically important metals, such as uranium, thorium, lanthanides and noble metals. Due to their dual nature and unique physiochemical properties, ionic liquids have gained increasing attention in recent years as potentially suitable candidates for replacement of volatile organic solvents in liquid-liquid extractions. Some of their most favourable features include their negligible vapour pressure, chemical and thermal stability, nonflammability and their adjustable miscibility and polarity. The unique combination of the two technologies, ionic liquids and CCC, represents a new and exciting philosophy to liquid-liquid separations. It overcomes the problems associated with the extractive process related to the use of organic solvents (flammability, volatility) and to the performance of the equipment (large inventories, long residence times) and will result in safer, more environmentally friendly approaches.
The viscosity of ionic liquids is often higher than that of common molecular solvents and can pose significant problems for traditional CCC devices, which are mostly low pressure. As a result, to date, their application to CCC has been very limited and greater insight into the hydyrodynamics that govern or control the extraction process is required. To investigate the hydrodynamic behaviour of the ionic liquid biphasic solvent system, visual observations have been carried out on a transparent 2-D spiral CCC column at different angles around the central axis of rotation using a high-speed camera. The images acquired have revealed the phase distribution and the mixing and settling areas within the column undergoing planetary motion, as well as the interfacial characteristics that can promote mass transfer (such as waves). A necessary condition to separate solutes using the CCC technique is that the column retains some of the stationary phase. Therefore, the influence of several operational parameters on the volume fraction of stationary phase retained was also studied including mobile phase flow rate, mobile phase pumping direction (Head --> Tail or Tail --> Head), rotational speed and direction of rotation. The settling and mixing characteristics of the two-phase mixture, and phase retention within the coils have been related to the densities, viscosities and interfacial tension of the ionic liquid solvent systems employed.
The project was funded by the UK Engineering and Physical Science Research Council (EPSRC) (Project title: Application of ionic liquid-liquid chromatography (ILLC) to extraction of metals), in collaboration with QUILL Research Centre at The Queen's University of Belfast, Northern Ireland, U.K.