Extraction processes agitated devices

The direct expenditure of energy in the separation process of solvent extraction is due to the pumping costs and costs of agitation/dispersion in conventional solvent extraction devices (membrane solvent extraction devices do not have dispersion only pumping costs are relevant). Let us ignore the small amount of energy required for these steps. Instead, focus on the extract stream from which the extracted product and the solvent have to be separated to reuse the solvent and recover the product. Usually this is achieved by distillation. This cost must be less than that required to separate the product from the feed solution being subjected to extraction by distillation. This is the reason to choose solvent extraction to start with, unless the thermal stability of the product is in question, as is true for many pharmaceutical molecules. Solvent extraction is a necessity in such cases, e.g. penicillins. A small amount of extraction solvent will also be present in the raffinate. This solvent should be removed and recovered also (usually by distillation) (NuU, 1980). 

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