Hydrodynamic features of centrifugal contactor separators: Experimental studies on liquid hold-up, residence time distribution, phase behavior and drop size distributions

The liquid hold-up, residence time distributions (RTD), drop size distributions and continuous/dispersed phase for a typical centrifugal contactor separator (CCS) of the type CINC V02 were determined experimentally for various L-L systems. The hold-up ratio of the different solvents was mainly a function of the selected weir. Most of the liquids reside in the centrifuge, whereas the annular zone is only partly filled as was determined for four water–organic (heptane, toluene, 1-octanol and dichloroethane) systems. The macro-mixing pattern of both liquid phases was determined experimentally using step responses for several aqueous–organic solvent combinations. Fitting the experimental curves to a standard tanks-in-series model without dead zone yielded large errors, very good fits were obtained for typically seven (continuous phase) or more (dispersed phase) tanks in series with a dead zone of typically about 20 mL. Drop size distribution measurements using a FBRM probe for various solvent combinations showed that the Sauter mean drop sizes of the dispersed phase were between 30 and 600 μ. The small drops indicate a very high specific interfacial area in the annular zone of up to 10 times the specific interfacial area in stirred tanks. Phase inversion was observed for several solvent combinations (e.g. water–1-octanol, water–dichloromethane and water–dichloroethane) and was found to be perfectly reversible.