Multistage countercurrent extraction cascade

For a high degree of extraction efficiency, it is usual to connect several continuous flow stages to form a countercurrent flow extraction cascade, as indicated in Fig. 3.36. 

In each stage, it is assumed that the two phases occupy well-mixed, constant volumes Vl and Vg- The phase volumes Vl and Vq can, however, vary from stage to stage along the cascade. This effect is easily included into any 

For any given stage, n, the component material balance equations for each phase are thus defined by 

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We wish to remove acetic acid from water using pure isopropyl ether as solvent. The operation is at 293 K and 1 atm (see Table 7.2). The feed is 45 wt% acetic acid and 55 wt% water. The feed flow rate is 2000 kg/h. A multistage countercurrent extraction cascade is used to produce a final extract that is 20 wt% acetic acid and a final raffinate that is also 20 wt% acetic acid. Calculate how much solvent and how many equilibrium stages are required. 

Dynantics of Heat Exchangers, Simple Batch Extraction, Multi-Solute Batch Extraction, Multistage Countercurrent Ctiscade, Extraction Cascade with Backmixing, Countercurrent Extraction Cascade with Reaction, Absorption with Chemical Reaction, Membrane Transfer Processes... 

Figure 8.1.37. (a) Continuous countercurrent multistage solvent extraction cascade of N stages (b) graphical determination of stage numbers in such a cascade of equilibrium extraction stages. 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Sec. 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the... 

The modelling approach to multistage countercurrent equilibrium extraction cascades, based on a mass transfer rate term as shown in Section 1.4, can therefore usefully be applied to such types of extractor column. The magnitude of the mass transfer capacity coefficient term, now used in the model equations, must however be a realistic value corresponding to the hydrodynamic conditions, actually existing within the column and, of course, will be substantially less than that leading to an equilibrium condition. 

Continuous Countercurrent Multistage Fractional Extraction. The industrial process utilizing the double-solvent principles is continuous and is carried out according to the flowsheet of Fig. 7.18 (2, 15). The feed, consisting principally of a mixture of B and C to be separated, is introduced into the central portion of a cascade of stages, 1 to 1. To facilitate... 

A countercurrent multistage extraction system is shown below, which is to be modelled as a cascade of equilibrium stages. 

With countercurrent processing, carried out using either a multistage cascade or an extraction column, the required solvent-to-feed ratio generally can be reduced by adding more and more stages or transfer units. As discussed in Minimum and)Maximum Solvent-to-Feed Ratios, the minimum practical solvent-to-feed ratio is approximated by... 

Extraction of a dilute solute between immiscible solvents in a continuous countercurrent multistage device/ cascade... 

Often solvent extraction is carried out continuously in a countercurrent multistage device/cascade. The sieve-plate tower is an example of one multistage device, whereas Figure 8.1.37(a) illustrates a multistage arrangement of N mixer-settler devices (one such device is studied in Section 6.4.1.2). First, we analyze a dilute solution of solute i in a feed-extract phase system assumed to be essentially insoluble in each other (Cussler, 1997). Then we will analyze extraction systems with some mutual solubility of the feed and the extraction solvent. 

Example 8.1.18 Equilibrium data of the ternary system water (A)-isopropyl ether (B)-acetic acid (C) have been provided in Table 8.1.7. The source of this data acquired at 20 °C is Treybal (1980). Using these data, solve the following problem. Pure isopropyl ether is being used in a countercurrent multistage cascade to extract acetic acid from a feed aqueous solution of 37 wt% acetic acid. The final raflinate product on a solvent-free basis should be 2wt% acetic acid. The feed solution flow rate is 2000 kg/hr. 

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