Refluxed Extractors

Assume the feed contains two main components to be separated, designated as R, the raffinate component, and E, the extract component or solute. If it is not feasible to separate these components by distillation, an extraction process may be considered. A solvent stream containing mainly solvent component S enters at the top of the column, extracts a certain amount of component E from the rising raffinate phase to produce the raffinate product as column overhead, containing mostly component R. The solvent, forming the extract phase, flows down the column, extracting the solute E from the raffinate phase, and exits as the extract phase in the column bottoms, containing mostly components 5 and E. The solvent is chosen such that its removal from the raffinate and extract components can be readily accomplished, for example, by distillation. 

With this configuration the separation process is accomplished with no refluxes The overhead contains mostly the raffinate component, and the bottoms contains mostly the solute and solvent, from which the solvent can be easily removed. In the absence of refluxes, this arrangement is the same as a single-section extractor. In the section below the feed there is only one phase, the extract phase. It is flowing down the column, with no change in its composition. 

Refluxing part of the raffinate, on the other hand, does not increase the removal of 

The manner in which reflux influences an extractor performance and the extent of its effect depend on the equilibrium characteristics of the particular system. Also, the ranges of reflux and other operating conditions must be restricted to the two-phase region where separation is feasible, both thermodynamically and physically. 

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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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