Reverse solvent extraction

However, in general, solvent recovery is an important step in the overall solvent extraction process. Solvent recovery from the raffinate (i.e., water phase) may be accomplished by stripping, distillation, or adsorption. The extract, or solute-laden solvent stream, may also be processed to recover solvent via removal of the solute. The solute removal and solvent recovery step may include reverse solvent extraction, distillation, or some other process. For example, an extraction with caustic extracts phenol from light oil, which was used as the solvent in dephenolizing coke plant wastewaters (4). The caustic changes the affinity of the solute (phenol) for the solvent (light oil) in comparison to water as will be explained in the equilibrium conditions section. Distillation is more common if there are no azeotropes. 

Two similar methods for phosphate ion which involve an amplification reaction, solvent extraction, and reverse solvent extraction were described at about the same time by Umland and Wiinsch (29) and Djurkin, Kirkbright and West (10, 30). An acidic solution containing the phosphate ion is treated with an excess of molybdate ion to form the phosphomolybdic acid, which is extracted into a water-immiscible solvent to free it of excess molybdate ion. The phosphomolybdic acid is then broken down and re-extracted by an aqueous basic solution and the molybdate ion determined colorimetrically through the use of 2-amino-4-chlorobenzenethiol or thiocyanate ion. The effective molar absorptiv-ities of the reagents are 359,000 at 710 m/x. for 2-amino-4-chlorobenzene-thiol and 150,600 at 470 m/x. for thiocyanate, which represent multiplication factors of 10 and 12, respectively, caused by phosphate molybdate ratio in the extracted phosphomolybdic acid. 

Perez de Ortiz, E.S., Dias Lay, M. De L., Gruentges, K., Aluminium and iron extraction by DNNSA and DNNSA-DEHPA reverse micelles, Int. Solvent Extraction Conf. (ISEC 96) Value adding through solvent extraction, Ed. Shallcross, D.C., Paimin, R. Prvcic, L.M., Melbourne, Australia, pp.409-411, 1996. 

Dionex Corporation - Manufacturers of liquid chromatography systems (IC and HPLC), chromatography software data systems, reversed-phase and ion-exchange columns, and accelerated solvent extraction systems... http //www.dionex.com. 

Cyclodextrins can solubilize hydrophobic molecules in aqueous media through complex formation (5-8). A nonpolar species prefers the protective environment of the CDx cavity to the hulk aqueous solvent. In addition, cyclodextrins create a degree of structural rigidity and molecular organization for the included species. As a result of these characteristics, these macrocycles are used in studies of fluorescence and phosphorescence enhancement (9-11), stereoselective catalysis (.12,13), and reverse-phase chromatographic separations of structurally similar molecules (14,15). These same complexing abilities make cyclodextrins useful in solvent extraction. 

An excellent and comprehensive review has covered HPLC analysis of AOs and light stabilisers up to 1990 [576]. Normal vs. reversed-phase and isocratic vs. gradient-elution HPLC separation of synthetic mixtures of additives and of solvent extracts from polymers were discussed. 

Steam stripping Air stripping Biological nitrification Chemical oxidation Ion exchange Solvent extraction Biological oxidation (aerobic) Wet oxidation Activated carbon Chemical oxidation Chemical precipitation Ion exchange Adsorption Nano-filtration Reverse osmosis Electrodialysis... 

The disadvantages described above in terms of the irreversibility of the polyion response stimulated further research efforts in the area of polyion-selective sensors. Recently, a new detection technique was proposed utilizing electrochemically controlled, reversible ion extraction into polymeric membranes in an alternating galvanostatic/potentiostatic mode [51]. The solvent polymeric membrane of this novel class of sensors contained a highly lipophilic electrolyte and, therefore, did not possess ion exchange properties in contrast to potentiometric polyion electrodes. Indeed, the process of ion extraction was here induced electrochemically by applying a constant current pulse. 

Reverse osmosis Solvent extraction Ionizing radiation Adsorption Incineration Freezing Distillation Electrolysis Fungal treatment... 

Font N, Hernandez F, Hogendoorn EA, Baumann RA, van Zoonen P. Microwave-assisted solvent extraction and reversed-phase liquid chromatography-UV detection for screening soils for sulfonylurea herbicides. J. Chromatogr. A 1998 798 179-186. 

Recently however, it has been recognized that liquid extraction is a potential method in the primary recovery of fermentation cell culture products, such as proteins and amino acids. The separation problem, however, is difficult because the product mixtures are often complex, including cell debris and enzymes. Proteins are not suitable for conventional solvent extraction because of incompatibility with organic solvents, but can be handled in aqueous two-phase systems or by extraction in reverse micellar systems (Chapter 15). 

Purification and separation—solvent extraction, ion exchange, cementation, adsorption, liquid membranes, reverse osmosis, etc. 

The Winsor II microemulsion is the configuration that has attracted most attention in solvent extraction from aqueous feeds, as it does not affect the structure of the aqueous phase the organic extracting phase, on the other hand, is now a W/0 microemulsion instead of a single phase. The main reason for the interest in W/0 microemulsions is that the presence of the aqueous microphase in the extracting phase may enhance the extraction of hydrophilic solutes by solubilizing them in the reverse micellar cores. However, this is not always the case and it seems to vary with the characteristics of the system and the type of solute. Furthermore, in many instances the mechanism of extraction enhancement is not simply solubilization into the reverse micellar cores. Four solubilization sites are possible in a reverse micelle, as illustrated in Fig. 15.6 [19]. An important point is that the term solubilization does not apply only to solute transfer into the reverse micelle cores, but also to insertion into the micellar boundary region called the palisade. The problem faced by researchers is that the exact location of the solute in the microemulsion phase is difficult to determine with most of the available analytical tools, and thus it has to be inferred. 

Raw material recovery can be achieved through solvent extraction, steam-stripping, and distillation operations. Dilute streams can be concentrated in evaporators and then recovered. Recently, with the advent of membrane technology, reverse osmosis (RO) and ultrafiltration (UF) can be used to recover and concentrate active ingredients [14]. 

The fermentation broth typically contains 20-30 mg/L of antibiotics, which is to say 30 parts per billion, and must be extracted into concentrated form using solvent extraction. The solvent extraction method was developed by Shell Oil and by Podbielniack and is based on the principle that penicillin is hydrolyzed in aqueous medium to H+ and RCOO ions. Thus, equilibrium in an acidic medium (i.e., one with low pH or high H+ concentration) is favored by the neutral RCOOH form, whereas equilibrium in an alkaline medium (i.e., one with high pH or low H+ concentration) is favored by the RCOO ionic form. The neutral form is more soluble in an organic medium, and the ionic form is more soluble in an aqueous medium. Thus, with amyl acetate as the organic solvent the partition coefficient of penicillin between solvent and water is about 100 at pH 3 and about 1 at pH 6. In the industrial process, the aqueous broth was acidified to pH 3 for the extraction into the organic solvent, and alkalized to a pH 6 for reverse extraction back into an aqueous medium. 

Reverse osmosis is essentially the same process as ultrafiltration with low salt rejection. Kopfler and co-workers (12) used reverse osmosis in combination with solvent extraction and XAD adsorption. Solvent extraction with pentane and methylene chloride was used to remove organics from the reverse-osmosis concentrate (i.e., for desalting), and XAD was used for adsorption of the intractables from the extracted... 

In either approach, the selection of isolation (e.g., solvent extraction, adsorption on carbon and synthetic resins) and concentration (e.g., lyophilization, vacuum distillation, reverse osmosis, ultrafiltration) methods is of paramount importance in properly assessing the potential toxicity of waterborne organics. A comprehensive literature review on the development and application of these and other methods to biological testing has recently been published by Jolley (3). 

Within the realm of analytical separation systems, by far the most fruitful approach has been the use of solid sorbent techniques. Although other approaches have been studied (reverse osmosis, solvent extraction,... 

Table I. Experimental Results Testing Reverse Order Mechanism in Solvent Extraction of Coal8...

Synthetic dyes may be isolated, purified, or concentrated from foods or from extracts by wool-dyeing procedures column chromatography with polyamide ion-pair or solvent extraction reverse-phase cartridges or ion-exchange resins (157,159,168). These techniques are discussed next. 

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