Stagewise contacting countercurrent

Caustic Washing. A flowsheet of the type of Fig. 11.3 may be used, involving stagewise contacting. In the first extractor H2S is removed by a prewash of caustic, as outlined above. The next three stages are used for countercurrent extraction of the mercaptans from the gasoline with aqueous sodium hydroxide, and the treated gasoline is water-washed to remove... 

The next topics of interest are the operating line for the countercurrent adsorption device and the height of the device or the number of stages needed for the device to achieve a given separation. The device may be of continuous contact type or stagewise contact type. For continuous contact type devices, the approach will follow that in Section 8.1.2.3 employed for gas absorption from a concentrated gas stream. We focus on one particular species i (= A) which is being adsorbed, say, from a gas stream j = g, here the inert (solute-free) gas stream mass flow rate... 

Figure 6.5 Three-stage countercurrent stagewise contacting.

Mass transfer processes involving two fluid streams are frequently carried out in a column countercurrent flow is usually employed although co-current flow may be advantageous in some circumstances. There are two principal ways in which the two streams may be brought into contact in a continuous process so as to permit mass transfer to take place between them, and these are termed stagewise processes and continuous differential contact processes. 

Consider the countercurrent extraction of solute A from solution in B using pure solvent C. The operatioo is performed in the column shown in Fig. 7.3-1, which may be either continuous-contact (packed) or stagewise. 

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