Counter-current extraction

The results of Williams (Figure 10.15) show that for PE/PS mixtures (1 1) more gas and less liquid are produced than by the pyrolysis of the individual polymers at 700°C. This is in contradiction to Koo s results (Figure 10.14). For pure PS, the results are quite similar. The main differences are found for pure PE in the in proportions of gas and liquid phases (Figures 10.14 and 10.15). The contradiction in these results could be explained by the fact that the experimental conditions are quite different (3 g, 25 K/min for Williams and 20 g, 48 K/min for Koo) and that PE is more sensitive to the experimental conditions (see Figures 10.2 and 10.3). Indeed, the hot gas and oils are rapidly extracted co-cnrrently from the reactor with the nitrogen flow [16] in the experiments of Williams whereas they are extracted counter-currently and remain longer in the hot zone of the reactor, being partially cracked into smaller entities, in Koo s experiments [51], For the other binary mixtures of plastics, there is less deviation from additivity. 

Keywords. Magnetic extraction. Electrophoretic extraction. Aqueous two-phase extraction. Multistage extraction, Counter-current distribution... 

When mixtures of bile acids are hydrolyzed at an early stage of the analytical procedure, the free bile acids formed may have to be further purified. Extraction, counter-current distribution, reversed phase partition, and paper chromatography have been described (Section III.A) and these methods can also be used for free bile acids. 

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

Zirconium and hafnium have very similar chemical properties, exhibit the same valences, and have similar ionic radii, ie, 0.074 mm for, 0.075 mm for (see Hafniumand hafnium compounds). Because of these similarities, their separation was difficult (37—40). Today, the separation of zirconium and hafnium by multistage counter-current Hquid—Hquid extraction is routine (41) (see Extraction, liquid—liquid). 

A beryUium concentrate is produced from the leach solution by the counter-current solvent extraction process (10). Kerosene [8008-20-6] containing di(2-ethylhexyl)phosphate [298-07-7] is the water-immiscible beryUium extractant. The slow extraction of beryUium at room temperature is accelerated by warming. The raffinate from the solvent extraction contains most of the aluminum and aU of the magnesium contained in the leach solution. 

The hydrolysis of fats is improved by running in a counter-current extraction column (Donders et al., Proc. 4th Europ. Symp. Chem. React. Eng., Pergamon, 1968, pp. 159-168). 

Solids may be processed continuously or semicontinuously by pumping slurries or by using lock hoppers. An example is the separation of insoluble polymers by floatation with a variable-density SCF. For liquid feeds, multistage separation may be achieved by continuous counter-current extraction, much like conventional liquid-hquid extraction. The final produces may be recovered from the extract phase by a depressurization, a temperature change, or by conventional distillation. 

Trichloroethane and 1,1,1,2-tetrachloroethane can be removed by counter-current extraction with EtOH/water. 

Sodium chlorite [7758-19-2] M 90.4, m 180°(dec). Crystd from hot water and stored in a cool place. Has also been crystd from MeOH by counter-current extraction with liquid ammonia [Curti and Locchi Anal Chem 29 534 1957]. Major impurity is chloride ion can be recrystallised from O.OOIM NaOH. 

Counter-current rinsing and rinse-water reuse are useful tips for reducing usage. Counter-current contact systems are more efficient in promoting heat and mass exchanges, which are important to gas absorption, extraction, and many types of chemical reactions. 

Most of the chiral membrane-assisted applications can be considered as a modality of liquid-liquid extraction, and will be discussed in the next section. However, it is worth mentioning here a device developed by Keurentjes et al., in which two miscible chiral liquids with opposing enantiomers of the chiral selector flow counter-currently through a column, separated by a nonmiscible liquid membrane [179]. In this case the selector molecules are located out of the liquid membrane and both enantiomers are needed. The system allows recovery of the two enantiomers of the racemic mixture to be separated. Thus, using dihexyltartrate and poly(lactic acid), the authors described the resolution of different drugs, such as norephedrine, salbu-tamol, terbutaline, ibuprofen or propranolol. 

In the extraction process, the LPG from the prewash tower enters the bottom of an extractor column. The extractor is a liquid/liquid contactor in which the LPG is counter-currently contacted by a caustic solution. Another option is the use of a fiber film contacting device. The mercaptans dissolve in the caustic (Equation 1-14). The treated LPG leaves the top of the extractor and goes on to a settler, where entrained caustic is separated. 

Fig. 121. Diagram of multistage counter-current liquid-liquid extraction.

Multistage counter-current liquid-liquid extraction is a typical continuous process. Fig. 121 shows a schematic diagram of the process. The slope of the line depends on the volumetric ratio of the aqueous and organic phases. The aqueous and organic phases move through the system as two counter currents. The raffinate from a specific extraction stage moves on to the next stage, to be mixed with a relatively fresh portion of the extract, i.e. extractant that was previously mixed with a low-concentration aqueous solution. 

Multistage counter-current liquid-liquid extraction is characterized by a high production capacity and economic efficiency. 

Fig. 122. General scheme of liquid-liquid extraction process using the multistage counter-current method. The three main steps are extraction, washing and stripping.

Layered-type structure, 92-100 Lewis acidity, 15 Liquid - liquid extraction collective, 276-277 counter-current scheme, 272 equipment, 273 extractants, 279-281 mechanism, 274-276 multistage counter-current, 271 multistage cross-current, 270 one-stage process, 270 principals, 267-269 process performance, 282-283 process schemes, 277,278, selective, 277-278 with 2-octanol, 284-291... 

Counter-current extraction columns are used. Figure 7.12 shows the counter-current extraction column with a ternary diagram for material balance and equilibrium curve. 

In addition, some plutonium is also lost to the salt as PuCl3. A two-step counter-current extraction is used to minimize the amount of salt used in the MSE process, reduce plutonium losses... 

For a multi-stage counter-current extraction operated in true equilibrium without side reactions, the partitioning of a solute into the metal phase (fm) and the salt phase (fs) is defined as follows ... 

Present production processes use two stage counter-current extraction to remove americium from molten plutonium with magnesium chloride based salts. Both 35 mole % NaCl - 35 mole % KC1 - 3D mole % MgCl2 and 50 mole % NaCl-26 mole % CaCl2 - 24 mole % Mg Cl 2 are used for americium extraction. Figures 4 and 5 show the ternary phase diagrams for these salt systemsU0). 

The above salt fluxes will extract 90% of the americium present when a salt-to-metal mass-ratio of 0.06 is used in a two stage counter-current extraction. 

Figure 8. Yield Curves for Salt-To-Pu Ratio vs Concentration of MgC12 for Extraction of Americium From NaCi-CaCl2-MgCl2 Salt Using 2-Stage Counter-Current Extraction...

Figure 10. Yield Contours for Americium Extraction vs s/m Ratio for 1, 2, and 3-Stage Counter-Current Extraction. Salt Composition 30 m/o MgCl2, 35 m/o NaCl,...

The basic process outline is depicted in Figure 5.2 moist un-roasted coffee beans and CO2 are fed counter-currently into the extractor under supercritical conditions. Caffeine is selectively extracted into the CO2 and this stream is led to a water-wash column to remove caffeine at a reduced pressure, the CO2 being recycled back to the extraction column. Extraction of the caffeine into water is necessary to avoid dropping the CO2 pressure too low, since compression is energy-intensive. There is now the problem of separating the caffeine (which is used in soft drinks and pharmaceu-... 

High performance liquid chromatography (HPLC) has been by far the most important method for separating chlorophylls. Open column chromatography and thin layer chromatography are still used for clean-up procedures to isolate and separate carotenoids and other lipids from chlorophylls and for preparative applications, but both are losing importance for analytical purposes due to their low resolution and have been replaced by more effective techniques like solid phase, supercritical fluid extraction and counter current chromatography. The whole analysis should be as brief as possible, since each additional step is a potential source of epimers and allomers. 

Wei, Y. et ah. Application of analytical and preparative high-speed counter-current chromatography for separation of lycopene from crude extract of tomato paste, J. Chromatogr. A, 929, 169, 2001. 

Counter-current flow is the most efficient method and the most commonly used. It will give the greatest concentration of the solute in the extract, and the least use of solvent. 

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