Centrifugal contactors mixing

Solvents were pretreated with scrub solution in experiments 1 and 2 the contact was achieved in a centrifugal contactor (mixing time 4 seconds), while in experiments 3 and 4, it was achieved during 5 min in a separatory funnel. 

The annular centrifugal contactor is designed so that each stage achieves the required mixing and subsequent separation. Besides the conditions specified above, at least five additional factors must be considered. First, to allow the dispersion to flow by gravity from the mixing zone into the rotor, stationary radial vanes under the rotor must dissipate the rotational velocity of the dispersion. Second, the rotor inlet (RI) must be small... 

FIGURE 10.2 Mixing zone of a 2-cm annular centrifugal contactor. (Figure 10.2b Reprinted from Leonard, R. A., D. B. Chamberlain, and C. Conner., Sep. Sci. Technol. 32(1-4), 193-210, 1997. With permission of Taylor Francis Ltd., http //www.tandf.co.uk/journals.)... 

FIG U RE 10.12 Variations in the mixing zone with time at constant operating conditions for a 12-cm annular centrifugal contactor. 

Wardle, K. E., T. R. Allen, and M. H. Anderson. 2008. Free Surface Flow in the Mixing Zone of an Annular Centrifugal Contactor. AIChE J. 54, 74—84. 

This development could eventually replace the settlers now used for the separation of the organic phase from the aqueous phase after the mixing step. The high cost of centrifugal contactors makes their use for the recovery of large-tonnage, low-cost metal very uneconomical. 

Typical extraction curves obtained in our laboratory scale apparatus show that Murphree s efficiency ( E ) varies with the nature of the solvent and with mixing time figure 7 . From the linear dependence of E/l-E on mixing time, it may be concluded that our centrifugal contactor can be assimilated to a perfectly stirred continuous reactor of which the characteristic equation is (19)... 

Centrifugal contactor Works at low density differences between two fluids Less solvent volume required for extraction Rapid mixing and separation can enhance product recovery and cost Difficult to scale up Mechanical complexity and high maintenance cost... 

Continuous liquid-liquid extraction is carried out in a centrifugal contactor at low rotor speeds to achieve 90% efficiency. Mixing and disengaging times range from 10 to 30 s, respectively. Efficient two-phase mixing is achieved in the annulus between the spinning rotor and fixed housing. 

Liibbert (1994) were among the first to find the unsteadiness of gas-liquid flows by means of a mixed Eulerian-Lagrangian code developed in-house the papers by Sokolichin and Eigenberger (1994) and Sokolichin et al (1997) illustrated this once more. More recent simulations of dispersed bubbly flows by Deen et al (2001), BombardeUi et al (2004), Zhang et al (2006), Dhotre et al (2009), and Niceno et al (2009) all exhibit the chaotic behavior of the bubbly plume and the liquid bulk. Wardle (2011) reported similar chaotic structures in the liquid-liquid mixture in an annular centrifugal contactor. 

If separation is difficult in a mixer-settler unit, a centrifugal extractor may be used in which the mixing and the separation stages are contained in the same unit which operates as a differential contactor. 

Many modifications and elaborations on these systems are possible, such as the use of motor-driven contactors for mixing the stocks, centrifuges for separating the stocks, filters for removing traces of solids, and various sequences of contacting, settling, washing, etc., as illustrated in the pressure-distillate treater of Fig. 10-8. 

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