Modified flow geometry for higher extraction performance with a liquid–liquid centrifugal contactor with Taylor vortices

Extraction with multiple theoretical stages by a single contactor is possible when a liquid–liquid countercurrent centrifugal contactor with Taylor vortices (TVs) is used. A series of TVs inside the flow region between the coaxial inner rotor and static outer wall can sustain stable concentration gradients, thereby improving the extraction performance. In the TVs, an axial force driving the dispersed organic phase arises from the different specific weights of the organic and aqueous phases. In this study, the geometry of the flow region was modified using (1) different aspect ratios and (2) tapered and (3) eccentric geometries for better extraction performance. The flows were observed experimentally and simulated numerically using the volume-of-fluid method to understand the flow inside the TVs. Changing the geometry greatly affected the size of the TVs, the flow stability, and the emulsification behavior. In continuous-extraction experiments involving zinc ions with bis(2-ethylhexyl)phosphoric acid, the tapered geometry showed the highest number of theoretical stages because of its simultaneous vigorous agitation, stable TV arrangement, and phase separation.