Visualization of Type-J counter current chromatography: Hydrodynamic behavior in a helical column

In counter-current chromatography (CCC), the hydrodynamic motion of a two-phase solvent system in the column/coil is very important. There are some previous visualization studies on CCC using stroboscopic photography. As CCC separation is a continuous liquid-liquid extraction process, observing the distribution and movement of the solvent system on-line will be helpful to understand the hydrodynamic behavior during the whole CCC separation process. In the present study, a high-speed imaging camera was employed to take videos of a running CCC bobbin (visualized continuously on-line). The dynamic motion and phase distribution of conventional quaternary solvent system hexane/ethyl acetate/methanol/water (HEMWat) and ternary solvent system dichloromethane/methanol/water were both investigated. Wave-like mixing was observed in the area where the centrifugal force is minimum in different diameter columns. When the coil rotated, the mixing zone was "fixed" at the minimum centrifugal force position. Several photographs of the rotating coiled tube were taken which revealed that the phase dispersion hardly changes once equilibrium is established. Finally, the sample dispersion process was also recorded. These results will help us to understand the separation process in a CCC column/coil and also present some more interesting questions related to separation efficiency which are shown in discussion part of this paper.