Liquid single-stage extraction

Consider a single stage extraction process, Eig. 2A, where a feed liquid (i.e., water) containing a solute (i.e., acetone) contacts an extraction solvent (i.e., chloroform). In this... 

Fig, 2,8 Depiction of a single-stage extraction in a triangle diagram 2.1.1.3.2 Multi-Stage Liquid-Liquid Extraction... 

By substitution of known values into this expression, the concentration is found to be 9 X 10 M. Thus, one extraction stage as described decreases the benzoic acid concentration in the effluent to just under one-half the original value. Similarly, by substituting this concentration value and Kp into Eq. 10.36, the concentration of benzoic acid obtained in the benzene extract is found to be 0.04 M, a ratio corresponding to the benzoic acid partition factor between these two liquids. The same equation may also be used to calculate the single-stage extraction parameters for any other solute of interest, provided that Kp for the system is known, or is determined experimentally. 

Batch extractors are used Tor single-stage extraction. In most of these tha solid-liquid mixture is agitated (e.g., by slowly turning, large-diameter propellers) to suspend the solids in the liquid. In other cases the solids settle and are resuspended by conveying mixers (e.g., Naula mixers). In other batch extractors a... 

Figure 9. Flow scheme of a screening unit for the extraction from solids (and single stage extraction from liquids) [1].

After a single-stage liquid-liquid contact the phase remaining from the feed sohition (raffinate) can be contacted with another quantity of fresh extraction solvent. This crosscurrent extraction scVieme (Fig. 15-4) is an excellent laboratoiy procedure because the extrac t and raffinate phases can be analyzed after each stage to generate equihbrium data. Also, the feasibility of solute removal to lowTevels can be demonstrated. 

In general, with a sufficiently large equilibrium constant (distribution ratio) and a rapid rate of attainment of equilibrium, quantitative transfer from one phase to another can be made in a single stage. For such highly favorable systems, batch liquid-liquid extractions can be used in which one phase is equilibrated with several successive fresh portions of a second phase. Such batch separations are most effective when one component remains quantitatively in one phase while another distributes itself between the two phases. 

We note that the liquid/liquid extraction step accomplishes separations across three relatively azeotropic compositions namely, that between acetone and pentane. that between methanol and pentane, and that between water and pentane. It should also be noted that, since the extractor does not have to perform sharp separations, it requires an overall optimization to determine how many stages should be used. In principle, a single stage or, in other words, a simple decanter should suffice to make the process feasible. 

A pure solvent 5 is used to remove component E from a binary liquid solution containing 30% mole E and 70% mole R. In a single-stage extractor how many kmol solvent per 100 kmol feed are required to bring the concentration of E in the raffinate to 3% mole What are the resulting rates and compositions of the raffinate and extract Use liquid-liquid equilibrium data from Figure 11.2. 

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