Liquid-liquid extraction based on a new flow pattern: Two-fluid Taylor-Couette flow

The exploitation of flow instabilities that can occur in rotating flows is investigated as a new approach to liquid extraction. Two immiscible liquids are radially stratified by centrifugal force in the annulus between corotating coaxial cylinders. The inner cylinder is rotated above a critical speed to form Taylor vortices in one or both of the fluids. This flow pattern produces a relatively small amount interfacial surface area that is of highly active for interphase mass transfer. Continuous processing is also possible with the addition of countercurrent axial flow.; The present study includes: (1) A review of aqueous-aqueous and reversed micelle extraction techniques, the commercially available centrifugal extractors, and one fluid Taylor-Couette flow and its variations. (2) A theoretical analysis to predict the onset of the two-fluid Taylor-Couette instability in the presence of countercurrent axial flow. (3) Theoretical predictions for interphase mass transfer using penetration theory and computational fluid dynamics. (4) The demonstration of two-fluid Taylor-Couette flow with countercurrent axial flow in the laboratory, including: (1) fluid mechanics studies to determine the onset of vortices, and (2) mass transfer studies to characterize intraphase and interphase mass transfer. The agreement between the experiments and theory is good for both the fluid mechanics and the mass transfer. Furthermore, the extraction performance is quite promising with the mass transfer coefficient approximately proportional to the vortex strength. Even higher extraction efficiencies should be obtainable with even larger relative rotation rates or cylinder modification to promote vortex formation.; Besides two-fluid Taylor-Couette flow, other instabilities can also occur. With low viscosity fluids at low rotation rates, the “barber pole” pattern is observed experimentally and is believed to be a lingering gravitational effect. At high countercurrent axial flowrates, the linear stability analysis predicts a Kelvin-Helmholtz instability related to the countercurrent flow profile. If axial flow is not present, two computational fluid dynamics packages calculate that vortices paired across the interface can corotate with each other.