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Multiple stage countercurrent extraction

The most effective mode of operation of extraction processes is depicted in Fig. 6.2-5. The raffinate R and the extract. E are in countercurrent contact in a cascade of n (here 4) equilibrium stages. The concentration of the feed decreases from Xp to x (n = 4). The transfer component B eruiches from to yj. An overall mass balance delivers the mixing point of the system  [Pg.357]

From a balance around the lower section of the cascade follows [Pg.357]

the difference of the states of the streams between neighboring stages is constant. This difference is called pole n. With E = R,  [Pg.357]

This equations state that the pole ti is collinear with the states of raffinate E and extract E between any neighboring stages of the separation cascade. [Pg.357]

Typically, the pole is located outside the triangular concentration space at the left-hand or the right-hand side. All states of the coexisting E and E phases can be determined graphically  [Pg.357]


Of these methods, multiple-stage countercurrent extraction enables the highest efficiencies and lowest ratios of leaching solution to solid, thereby... [Pg.127]

The holdups of the two phases are very small, which is advantageous in certain applications. As the phases are in the co-current flow, they can attain equilibrium. Therefore, the extractor is at best one equilibrium stage. However, multiple units can be configured to form a multi-stage countercurrent extraction unit. There is a need to evaluate the relative merits of the multiple units configuration vis vis the Podbielniak extractor, which offers 4 to 6 stages in a single unit. [Pg.140]

Systems that exhibit behavior of the type illustrated in Fig. 4 cannot be purified in a single crystallization stage. They represent situations in which multiple stages or continuous-contacting devices may be useful. The principles of such operations are analogous to those of other countercurrent contacting operations—for example, distillation, absorption, and extraction. [Pg.198]

Now consider a multiple-stage process with countercurrent flow of the raffinate and extract phases. Fig. 2B. Countercurrent is the most efficient multistage configuration. One can write a mass balance around the nth stage, as indicated by envelope 1, using the following units for a continuous flowing process ... [Pg.592]

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. [Pg.710]

Batchwise Extraction, Multiple Stage. This operation, usually a laboratory procedure, can be carried out in two ways. The immiscible solvents may be continuously pumped through the various stages in countercurrent flow, and the batch of mixture to be separated may be suddenly introduced near the center of the cascade. The result is an unsteady-state operation, the solutes leaving the opposite ends of the cascade in ratios different from that in the feed and in amounts varying with time. Such an operation has been considered in some detail by Martin and Synge (13) and Cornish et al. (4). [Pg.221]

The design and power requirements of baffled agitators or mixers have been discussed in detail in Section 3.4. In Fig. 12.6-la a typical mixer-settler is shown, where the mixer or agitator is entirely separate from the settler. The feed of aqueous phase and organic phase are mixed in the mixer, and then the mixed phases are separated in the settler. In Fig. 12.6-lb a combined mixer-settler is shown, which is sometimes used in extraction of uranium salts or copper salts from aqueous solutions. Both types of mixer-settlers can be used in series for countercurrent or multiple-stage extraction. [Pg.715]

It is proposed to reduce the concentration of acetaldehyde in aqueous solution from 50 per cent to 5 per cent by mass, by extraction with solvent S at 293 K. If a countercurrent multiple-contact process is adopted and 0.025 kg/s of the solution is treated with an equal quantity of solvent, determine the number of theoretical stages required and the mass flowrate and concentration of the extract from the first stage. [Pg.189]

Solvent leaving this equilibrium contactor is capable of extracting more of the metallic component from additional aqueous feed, because the feed concentration z is greater than the concentration x in the aqueous phase with which this solvent is in equilibrium. It is therefore possible to reduce the amount of solvent needed for a given fraction extracted by using multiple contact between solvents and aqueous phases in a countercurrent cascade, as illustrated in Fig. 4.2. As the number of stages is increased indefinitely, the organic extract approaches equilibrium with the aqueous feed, so that in the limit... [Pg.161]

Countercurrent multiple contact. This method involves the use of a cascade of stages, extracting solvent and solution to be extracted entering at opposite ends of the cascade. Extracts and raffinates flow counter-currently. The operation is more analogous to gas absorption than to any distillation practice. It is necessarily continuous but may be simulated in batch fashion, in the laboratory for example, as pseudo countercurrent multiple contact. ... [Pg.129]

Countercurrent multiple contact with reflux. This is a continuous operation an d()g()ll to fractional distillation. A cascade of stages is employed, with feed solution to be separated customarily entering somewhere in the middle of the cascade and extracting solvent at one end. Extract and raffinate phases flow countercurrently, with reflux provided at both ends of the cascade. Alternatively, reflux may be used only at one end of the cascade, corresponding to the enriching or stripping practices of distillation. [Pg.129]


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