Agitated extractors

HOLDUP - Transient Holdup Profiles in an Agitated Extractor... 

Transient Holdup Profiles in an Agitated Extractor 459 Homogeneous Free-Radical Polymerisation 310 Batch Reactor Hydrolysis of Acetic Anhydride 247 Continuous Bioreactor with Inhibitory Substrate 543 Dynamic Oxygen Electrode 462... 

Figure 11 Agitated extractors. Left to right RDC, Karr, Oldshue-Rushton, Scheibel, Kuhni extraction columns. 

Additives are usually amphiphilic in nature, and thus are either ionic or neutral surfactants or even polymers. The role of surfactants in solvent extraction is ambiguous. Usually, they should be avoided as they lower the interfacial tension, which may lead to emulsion formation in an agitated extractor. However, every metal-loaded ion exchanger is amphiphilic, and can adsorb at the interface or aggregate in the bulk phase. This occurrence is well known with sodium or other metals [17], and above a critical surfactant concentration (cmc, critical micelle concentration) micellar aggregates are formed. A dimensionless geometric parameter is decisive for the structure of the associates, according to Fig. 10.6 ... 

Perforated-plate (sieve-plate) towers B. Mechanically agitated extractors 1. Towers with rotating stirrers 2. Pulsed towers... 

As with other agitated extractors, the fin design of a commercial-scale Karr column is based on pilot test data. The column vendor should be consulted for specific information. The following general procedure is recommended ... 

Sieve-tray towers are very effective, both with respect to liquid-handling capacity and extraction efficiency, particularly for systems of low interfacial tension which do not require mechanical agitation for good dispersion. The general assembly of plates and downspouts is much the same as for gas-liquid contact except that a weir is not required. Towers packed with the same random packing used for gas-liquid contact have also been used for liquid extractors however, mass-transfer rates are poor. It is recommended instead that sieve-tray towers be used for systems of low interfacial tension and mechanically agitated extractors for those of high interfacial tension (Treybal, 1980). 

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