Solvent extraction backmixing

It would be of interest to find out the role (if any) of backmixing in nondispersive porous membrane based solvent extraction devices. Here, only the shell-side liquid phase can encounter backmixing, or, more correctly, bypassing and channeling. Simple countercurrent devices often display such flow behavior. However, the baffled construction with radial flow illustrated in Figure 8.1.35(f) is thought to be generally free of such flow distortions. 

The above model of settler flow behaviour, combined with entrainment backmixing was used by Aly (1972) to model the unsteady-state extraction of copper from aqueous solution, using Alamine 336 solvent. An identification procedure for the relevant flow parameters showed an excellent fit to the experimental data with very realistic entrainment backmixing factors, fL = fQ = 3.5 percent, the fraction of well-mixed flow in the settlers, (XX = ay = 5 percent and an overall mass transfer capacity coefficient, Ka = 25 s->. 

In this example of a five stage extraction column with backmixing, proportional plus integral control of the exit raffinate concentration is to be achieved by regulating solvent flowrate. 

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