Countercurrent multiplication mechanism

Industrial applications usually are based on the most efficient methods that involve the countercurrent flow of two liquids across multiple stages. A variety of mechanical devices are available that can be used to achieve such mixing and separate the resulting extract and raffinate and so achieve the desire separation. Once the extraction is complete, almost always both the extract and raffinate need to be treated to recover solvent residuals as well as the desired products. 

Bubble columns (BCs) belong to a family of pneumatic bioreactors. These bioreactors do not have any mechanical or otherwise moving parts. Compressed air, which is used for mixing purposes, is injected into the base of a cylindrical vessel. This approach provides a cheap and simple method to contact and mix different phases (Diaz et al., 2008). The liquid phase is delivered in batch or continuous mode, which can be either countercurrent or cocurrent. The batch BC is the more common form, but the cocurrent version, shown in Figure 7.1, is also encountered. Countercurrent liquid flow is rarely used in industry as it provides minor, if any, advantages and multiple complications (Deckwer, 1992), with separation by evaporation being one of the few exceptions (Ribeiro Jr. and Lage, 2005). 

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