Investigation into the mechanics and feasibility of continuous counter-current extraction

Abstract

Continuous counter current extraction (CCCE) or dual flow counter current chromatography (DFCCC) is a promising technique where components can be separated continuously by two liquid phases that flow in opposite directions through a continuous length of coiled tubing. Specially designed end connectors and a coil planet centrifuge allow each respective phase to be pumped into each end of the tubing and the other phase to elute at each opposite end. In this thesis the feasibility and the mechanics of CCCE are investigated using stroboscopic photography on an experimental rig and a specially built pilot-scale CCCE centrifuge.

The mechanics of the hydrodynamics in the coil was investigated systematically by comparing the measured volumes with photographic images of the process. This investigation revealed that the phases are not distributed evenly throughout the coil, which was previously assumed, but that there is a transition area where the phases switch from mainly upper phase at the head end of the tubing to mainly lower phase at the tail end. This means that the sample encounter three different phase distribution zones in the coil. At the head the upper phase is the dominant phase with a small volume of lower phase running through. At the tail the reverse situation is found and lower phase is dominant. The third zone is a short segment of the coil where there is a transition between the dominant phase conditions that exist at each end. The position of the transition zone and the volume of the other two zones are profoundly affected by the relative flow rates of the two phases. This work indicates that the volume distribution in the coil is affected most by the upper phase flow rate.

The pilot-scale CCCE centrifuge was used to successfully separate industrially supplied samples. Crude reaction liquor was processed in both batch and continuous modes achieving the separation of the multi-component mixture into two groups. Changing the flow rate combinations changed the location of elution of some of the components in the mixture. Separation efficiency was maintained even when sample loading was increased. The separations were shown to be predictable with the dual flow theoretical model.