Counter-current batch extraction

Fig. 4.4. Counter-current batch extraction (a) limited number of batdies (b) infinite series of tatches.

In a counter-current batch process, portions of aqueous phase containing the solute are extracted with successive portions of organic solvent phase in such a manner that the fresh solvent always extracts from the weakest aqueous phase, and the most concentrated solvent extracts from the solute-rich aqueous feed. Similarly, the aqueous solutions of intermediate solute concentration are extracted by organic solvent which already has a moderate solute concentration. The situation is illustrated by Fig. 4.4(a). A stream of solvent portions passes from right to left with respect to a stream of initially solute-rich aqueous portions. At each contact of two new portions, it is necessary to mix throughly to allow solute to pass from one phase to the other and then to settle and separate again, into their separate phases. 

Separating funnels for batch extraction special glass apparatus for continuous extraction automatic shakers used for discontinuous counter-current distribution. 

A flavouring essence is a traditional flavouring product prepared by washing a selected oil blend (predominately citrus oils) with an aqueous alcoholic solvent mixture (e.g. 60% ethanol/40% water). It is an extraction process in which the aqueous extract phase becomes the flavouring. The process is earned out under cool temperatures, for example, 5-10°C, either batch-wise or by counter-current extraction. The soluble oxygenated flavouring constituents present in the essential oil blend (e.g. citral in lemon oil) are effectively partitioned between the two phases of the mixture. The low temperatures employed ensure that the transfer of any oil into the hydro-alcoholic phase is minimised as a poorly processed essence will tend to cloud when used in the drink formulation. 

Modolo, G., Asp, H., Vijgen H., Malmbeck, R., Magnusson, D., Sorel, C. 2007. Demonstration of a TODGA-based continuous counter-current extraction process for the partitioning of actinides from a PUREX raffinate. Part I batch extraction optimization studies and stability tests. Solvent Extr. Ion Exch. 25 703-721. 

The countercurrent DBBP z 1hn extraction process was operated on a plant-scale for about six years. During that time, it provided excellent recovery ( vl00%) of soluble plutonium in the feed and adequate decontamination of 21flAm from plutonium and other metallic impurities. The Am/Pu ratio in the WS-1 Column (Am strip column) product was 2.5/1 compared to only 1/1 for the batch extraction process americium product. Concentrations of calcium, aluminum, and other metallic impurities in the counter-current Am product stream were also much lower than in the Am product from the batch extraction process. 

This patent is another one on extraction of caffeine from aqueous solution. The examples cover extraction of caffeine from. solutions of tea, coffee, and neat caffeine. Batch autoclave extraction, batch-continuous extraction, and continuous counter current extraction are described. The patent gives a large table of decaffeination results, and some of the results are reproduced low. Distribution coefficients given in the last column are calculated from batch-continuous extraction mathematics using the relation DC R = In Cj/Cf. The decaffeination values accented with an a are achieved with a CO2 density of... 

We were anxious to evaluate the use of supercritical carbon dioxide (scCOj) to remediate an urban soil. A two-stage approach was prompted by our efiforts to make the process continuous. SCCO2 extraction of particulate media is inherently a batch process. Pressure within the extractor is maintained with a capillary restrictor (in our case a 50 pm diameter silica tube) that is prone to fouling. The non-polar organic Section of an aqueous (surfactant) extract can be removed continuously (either on site or off site) with scCOj in a counter current liquid-liquid like process. The heavy metal contaminants remain with the water fraction for subsequent treatment. The organics fraction is the subject of this short review on SCCO2 processing. 

Despite the success of the counter-current process in comparison with single batch or crosscurrent processes, a DFl value of 10 is modest in view of the hundredfold difference between and. Better decontamination can be achieved if a washing or scrub section is incorporated in the process. This involves contacting the loaded organic product stream with an aqueous phase having a low or zero Ln concentration. The raffinate from this section is then combined with the aqueous feed to the extraction section, as illustrated in Figure 31. The mass fraction, of... 

Generally, one has a choice of three methods of extraction batch extraction, continuous extraction, and counter-current extraction. The choice is generally determined by the distribution coefficient of the substance extracted and, in the case where separation is desired, by the closeness of the various distribution coefficients involved. Because of the speed and simplicity of batch extraction, this method is preferred when applicable. 

In addition to such important factors as the choice of organic solvent, the avoidance of emulsions, and the actual method of extraction—batch, continuous, or counter-current—there are other important and easily controlled experimental variables. In... 

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