Solvent extraction differential extractors

A wide variety of extraction column forms are used in solvent extraction applications and many of these, such as rotary-disc contactors (RDC), Oldshue-Rushton columns, and sieve-plate column extractors, have rather distinct compartments and a geometry, which lends itself to an analysis of column performance in terms of a stagewise model. As the compositions of the phases do not come to equilibrium at any stage, however, the behaviour of the column is therefore basically differential in nature. 

A single-stage extraction using the same total volume of solvent achieves only 92% extraction, and the extract concentration is only 0.23, vs. nearly 0.25 for the cross-flow extraction. The use of four cross-flow extraction stages is clearly preferable to a single extraction. Equally, of course, the use of more than four extraction stages, each with a proportionately smaller volume, would improve the performance. In the limit, one would seek a differential contacting process similar to the Soxhlet extractor employed for extraction from solid phases, but such a contactor has not found use in solvent extraction. 

One application for such differentially functionalized nanotubes is as smart nanophase extractors to remove specific molecules from solution. Nanotubes with hydrophUic chemistry on their outer surfaces and hydrophobic chemistry on their inner surfaces are ideal for extracting hpophihc molecules from an aqueous solution. The hydrophobic molecule 7,8-benzoquinoline (BQ), which has an octanol/water partition coefficient of 10 [3,8] was used as a model compound for such nanophase solvent extraction experiments. Figure 24.4A shows the UV-Vis spectmm of control solution containing 10 M aqueous BQ. A 5 mg of the silica-outer/Cig-inner nanotubes were suspended into 5 mL of 1.0 x 10 M aqueous BQ. The suspension was stirred for... 

If a deep bed u used in a reflux extractor the exlractur can be analyzed tike fixed-bed extractors operating with dtiwnftow and yj0 0. In such a case V = Ee. However, if the bed is Hooded and consequently part of the reflux bypasses the bed. V should be based on an Eh that barely results in bed saturation rather than the actual Efe. If the refluxed solvent b not passed throngh a bed but is edded 10 a well-mixed batch of extract and solid and the rate of extract discharge is E . the extractor can be treated like a diflcrtmriel extractor. Reflux extractors in which very short beds are used can also be treated like differential extractors as a mesonablc approximation. 

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