AKUFVE

Figure 4.19 shows the extraction of Ga(III) by acetylacetone into benzene at various concentrations of total acetylacetone, [HA]t, and constant ionic strength, using the AKUFVE technique (see section 4.15.3). By comparing with Fig. 4.3, one may guess that hydroxy complexes are formed (diagram c). 

A different approach to solvent extraction experimentation, referred to as the AKUFVE principle, was developed in the 1960s [80a-d], The AKUFVE is... 

Fig. 4. 33 The AKUFVE solvent extraction apparatus Efficient mixing is achieved in the separate mixing vessel, from which the mixture flows down into the continuous liquid flow centrifugal separator (the H-centrifuge, hold-up time <1 s). (From Refs. 83a,b.) The outflow from the centrifuge consists of two pure phases, which pass on-line detectors, AMXs, for on-line detectors or continuous sampling. (From Refs. 80a-80d, 81.)...

Albinsson, Y. Development of the AKUFVE-LISOL Technique. Solvent Extraction Studies of Lanthanide Acetylacetonates. Diss. Chalmers Univ. Techn., Gothenburg (1988). 

In part also this is because better equilibrium data are now available through the use of equipment such as AKUFVE, which has brought the realization that it is not sufficient to view the isotherm as fixed. Quite small changes in aqueous composition or in phase ratio can change the isotherms and cause dramatic effects on the performance of a countercurrent cascade. Even relatively crude models for the isotherms, such as Eq. 8.3, can demonstrate these effects in cascades. 

Laboratory Extractors. Pilot-Scale Testing, and Scale-Up. Several laboratory units arc useful in analysis, process control, and process studies. The AKUFVE contactor incorporates a separate mixer and centrifugal separator. It is an efficient instrument for rapid and accurate measurement of partition coefficients, as well as for obtaining reaction kinetic data. Miniature mixer-settler assemblies set up as continuous, bench-scale, multistage, countercurrent, liquid-liquid contactors are particularly useful Tor the preliminary laboratory work associated with flow-sheet development and optimization because these give a known number of theoretical stages. 

The SISAK (Short-lived Isotopes Studied by the AKUFVE-technique, where AKUFVE is s Swedish acronym for an arrangement of continuous investigations of distribution ratios in liquid extraction) system performs continuous liquid-liquid extractions using small-volume separator centrifuges [66]. Activities are delivered to the apparatus with an aerosol... 

Davis, S.S., Elson, G., Tomlinson, E., Harrison, G., Dearden, J.C. (1976) The rapid determination of partition coefficient data using a continuous solvent extraction system. (AKUFVE). Chem. Ind. (London), 16, 677-683. de Kreuk, J.F., Hanstveit, A.O. (1981) Determination of the biodegradabUity of the organic fraction of chemical wastes. Chemosphere 10, 561-575. 

Some solvent-extraction techniques are relatively difficult to effect using conventional laboratory apparatus. For example, the classical penicillin G extraction in which acidified broth is contacted with a water-immiscible solvent can only be operated effectively using continuous-flow methods because of the poor stability of the product at low pH values. This extraction can be reproduced on the bench scale using the AKUFVE apparatus, which was designed for extraction studies in the nuclear industry (12,13). Selective extraction may involve the use of a solvent in which the product has a poor partition coefficient. Countercurrent extractors are mostly process scale devices but the smallest four-stage extractor produced by Robatel could be considered a bench scale. It has a throughput of 50-100 mL/min. 

To sum up, a lot of experience is needed to determine log P values by the classical shake flask method. Alternatives have been developed and compared with each other, e.g. filter probe methods [219, 220], the AKUFVE method [221], and different centrifugal partition chromatographic techniques (which correspond to true partitioning because only two immiscible liquid phases and no solid support are involved) [222-225]. As the scope and limitations of most of these techniques have been reviewed [173, 217, 218, 225], they shall not be discussed here in detail. 

Rate measurements with well-stined vessels may be continuous or batch. An example of the latter is simply a stirred flask. The former include the AKUFVE apparatus and bench-scale models of mixer-settler contactors. Because the interfacial area and mass transfer conditions in these systems are not known, th generally do not yield intrinsic heterogeneous rate data for metal-extraction systems. Nevertheless, th are useful for screening relative rates and identifying cases where slow kinetics may be a problem. 

There is another problem with man-made chemical elements, namely that their isotopes are short lived too. This, together with the need for their identification, calls for fast separation methods. The Automated Rapid Chemistry Apparatus (ARCA) II S) tem and the Short-lived Isotopes Studied by the AKUFVE-technique (SISAK) equipment (both described in Sect. 59.2.2 of Chap. 59, Vol. 6, on Solvent Extraction and Ion Exchange in Radiochemistry ) are able to handle radionuclides with half-lives of -10 s and 1 s, respectively. 

E reaction. The first method involved a series of solvent extractions performed continuously with the centrifuge system SISAK (Short-lived Isotopes Studied by the AKUFVE Technique) (Skarnemark et al. 1980) and the second one involved the ion-exchange separation apparatus ARCA (Automated Rapid Chemistry Apparatus) (Schadel et al. 1989). In the case of... 

AKUFVE extraction curve for the system americium in 1 M NaCI04 with varying concentration of ct-D-isosaccharinic acid//TBP (from Allard et al. 2008)... 

AKUFVE Apparatus for continuous determination of distribution ratios in solvent extraction... 

SISAK Short-lived Isotopes Studied by the AKufve technique... 

Liquid-liquid distribution data for which the volume ration V is given as one of the ap values— that is, V is given for each experimental point. For Typ = 1 or 2 the volume ratio is given a constant value for each group of data. These input data are suitable for distribution data collected by the AKUFVE technique [63,64]. 

Category 1 includes the Lewis cell [12] and its modifications (e.g. the Armollex cell [13] and the Nitsch cell [14] ) the highly stirred tanks (e.g. the AKUFVE apparatus [15]) and the moving drop technique [16]. 

Solvent extraction, in combination with the use of a radioactive tracer, is an excellent tool for the determination of stabihty constants in systems where low solubihty or hydrolysis at low pH is an issue. Nevertheless, there still may be limitations since an extractant must be found that extracts the metal of interest but also binds with a strength that is suitable in comparison with the stabihty constant to be determined. Controlling experimental factors such as temperature and pH may be difficult since the extraction itself may affect, for example, the pH of the solution where, for hydrolysis reactions, the free hydrogen ion concentration is the parameter of importance. Consequently, an online system such as the AKUFVE system is likely to have clear advantages. 

Albinsson, Y. (1988) Development of the AKUFVE-LISOL techniques. Solvent extraction studies of lanthanide acety-lacetonates. PhD dissertation. Chalmers University of Technology, Sweden. 

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