Extraction in Stages

These extraction stages are in the sequence petrol ether, chloroform, ether, acetone, methanol they are carried out in either a percolation tube or a Soxhlet apparatus. After removing fat with petrol ether, the chloroform extract contains chiefly compounds of group A, e. g., daphnoretin [218], lichen components, fully methylated flavones, many furocoumarins etc. Ether then extracts all the agly-cones and some glycosides (rhamnosides). Most of the glycosides are then to be found in the acetone and methanol extracts. 

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From examining the extract phenol concentrations in Table 15-9, it is clear that for 5 or more stages, they varied little with number of st es, as is expected since nearly all the phenol contained in the wastewater feed was extracted in stages 1 through 4. As a result, the extract will contain 1.3 wt % phenol, 5.2% water, and 93.5% MIBK. 

The commonest procedures are separations into hydrophilic and lipophilic compounds, followed by extraction in stages of the neutral and acid materials from suitably buffered aqueous solution using ether, chloroform or ethyl acetate [3, 55, 66, 67, 79]. 

Sometimes, however, the extractions in staged cascades are much less effective than expected even when the mass transfer is fast. In other words, the Murphree efficiencies are much less than one even when the quantity KyaVjGA) is expected to be much greater than one. Such poor performance is often due to backflow of either the raffinate or the extract. Such backflow may occur because of entrained liquid. While the cause varies, the effect is the same a lower apparent stage efficiency. We explore these ideas in the example that follows. 

Fig. 31. AOX formation in chlorination (C) and extraction (E) stages for 30 kappa softwood kraft pulp chlorinated at 4% consistency in mixer, using...

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

For vanadium solvent extraction, Hon powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent Hon to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH, and an oxyvanadium cation is extracted in four countercurrent stages of mixer—settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH, steam, and sodium chlorate to the strip Hquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip Hquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

The optimum conditions of heavy metals extraction from ordinary chernozem in different solvents are selected both at determination of the mobile forms of elements, and at an estimation of their gross contents. It is established, that the stage of elements extraction in the greater measure depends on time of action and intensity of ultrasonic, nature of selected solvents and determinated elements. It is shown, that for all type of soils the time of low frequency ultrasonic action does not exceed 10 minutes, and the intensity ranges in an interval of 3-4 W/cm. ... 

Parsons realized that he could, by using multiple rings of turbine blades on the same shaft, allow the steam to expand in stages through the turbine, and therefore extract energy more efficiently from the... 

In both cases, the extraction process includes washing (scrubbing) of the extract, a stage that is not shown separately. The organic phase that results from the stripping process is returned to the beginning of the extraction process for reuse as an extractant. 

The medium is most often acidihed with hydrochloric acid (0.1% vNY but it should be noted that in light of the work of Revilla et al., the hydrochloric acid concentration should not exceed 0.12 mole/liter to prevent risks of anthocyanidin hydrolysis. Formic acid (2% v/v), with a greater volatility than hydrochloric acid, is preferred because it prevents risks of hydrolysis during the extract concentration stage. ... 

After extraction, an extract purification stage is generally reconunended. This is most often done by liquid-solid exchange using resins such as Sephadex, Amber-lite XAD-7, or Cjg mini-columns. ° All the polar compounds are first trapped on the resin, and then in succession the sugars, acids, and other polar compounds (excluding polyphenolic compounds), polyphenolic compounds (excluding anthocyanidins), and anthocyanidins are respectively eluted with acidified water (HCl 0.01% v/v), ethyl acetate, and acidified methanol (HCl 0.01% v/v). 

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