Recovery by Extraction

O Data from KRUPP INDUSTRIETECHNIK. n Data from W. V. Brown [54]. 

The same disadvantages of crud accumulation and thermal decomposition apply to extracting the carboxylic acids with a mixture of a high-boiling amine (ALAMINE 336 produced by HENKEL) and a high-boiling hydrocarbon fraction (SHELLSOL produced by SHELL). 

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Since no special ligand design is usually required to dissolve transition metal complexes in ionic liquids, the application of ionic ligands can be an extremely useful tool with which to immobilize the catalyst in the ionic medium. In applications in which the ionic catalyst layer is intensively extracted with a non-miscible solvent (i.e., under the conditions of biphasic catalysis or during product recovery by extraction) it is important to ensure that the amount of catalyst washed from the ionic liquid is extremely low. Full immobilization of the (often quite expensive) transition metal catalyst, combined with the possibility of recycling it, is usually a crucial criterion for the large-scale use of homogeneous catalysis (for more details see Section 5.3.5). 

Purex [Plutonium and uranium recovery by extraction] A process for the solvent extraction of plutonium from solutions of uranium and fission products, obtained by dissolving spent nuclear fuel elements in nitric acid. The solvent is tri-n-butyl phosphate (TBP) in... 

Siebold, M., Frieling, V.P, Joppien, R., Rindfleisch, D., Schiigerl, K., and Roper, H. 1995. Comparison of the production of lactic acid by three different lactobacilli and its recovery by extraction... 

Purex [Plutonium and uranium recovery by extraction] A process for the solvent extraction of plutonium from solutions of uranium and fission products, obtained by dissolving spent nuclear fuel elements in nitric acid. The solvent is tri- -butyl phosphate (TBP) in kerosene. First operated by the U.S. Atomic Energy Commission at its Savannah River plant, SC, in 1954 and at Hanford, WA, in 1956. Now in operation, with modifications, in several countries. Sites include Savannah River (SC), Cap de la Hague (France), Marcoule (France), Sellafield (England), Karlsruhe (Germany), and Trombay (India). See also Recuplex. 

If the acid concentration is too low for conventional recovery by extraction, and if recovery of water is of interest as well, an elegant industrially proven solution of the problem is a multieffect azeotropic distillation. This process was developed by the BASF in Ludwigs-hafen/Germany [58]. 

The outgoing acid concentration is increased by a factor of 4, thereby greatly reducing the specific steam consumption for an acid recovery by extraction. 

The essential functions of the reprocessing of spent fuel elements is to separate uranium and plutonium from one another and both of them from the radioactive fission products. For this purpose, the PUREX process (Plutonium and Uranium Recovery by Extraction), based on extractive separation, has become accepted worldwide. It is currently u,sed in all modern reprocessing plants. 

It is used in the mining industry to recover metals such as copper and nickel. Parasite plants, based on solvent extraction, are used in the phosphate industry to recover by-product uranium from crude phosphoric acid. The uranium concentration in phosphoric acid is very low but, because of the high volume of phosphoric acid that is produced to meet agricultural needs, considerable uranium can be recovered using solvent extraction. In the nuclear industry [5], solvent extraction is used to purify uranium and plutonium [using the plutonium and uranium recovery by extraction (PUREX) process], zirconium from hafnium, and for many other applications. It is also used in environmental applications to clean soil, say, to remove polychlorinated biphenyls (PCBs), dioxins, pesticides, and other hazardous pollutants. 

There are two breeder reactor fuel cycles. One involves the irradiation of U/ Pu oxide fuel with fast neutrons and is at the prototype stage of development. The other involves the irradiation of Th/ U oxide fuel with thermal neutrons and is at the experimental stage. Fuel from the U/ Pu cycle may be reprocessed using Purex technology adapted to accommodate the significant proportion of plutonium present in the fuel. Increased americium and neptunium levels will also arise compared with thermal reactor fuel. The Th/ U fuel may also be reprocessed using solvent extraction with TBP in the Thorex (Thorium Recovery by Extraction) process. In this case the extraction chemistry must also take account of the presence of Pa arising as shown in Scheme 2. 

Solvent recovery by extraction While most processes use distillation or evaporation to recover the solvent from the product solutions of liquid extraction, it is not uncommon to recover solvent by liquid extraction. A typical example is the recovery of penicillin from the acidified fermentation broth in which it occurs by extraction with amyl acetate as solvent, followed by stripping of the penicillin from the solvent by extracting it into an aqueous buffer solution. The amyl acetate is then returned to the first extraction. The calculations of such solvent-recovery operations are made in the same manner as those for the first extraction. 

Frenz, J., C. Largeau, and E. Casadevall Hydrocarbon recovery by extraction with a biocompatible solvent from free and immobilized cultures of Botryococcus braunii. Enzyme Microb. Technol. 11, 717 (1989). 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

Karcher P et al (2005) Microbial production of butanol product recovery by extraction. In Satyanarayana T, Johri BN (eds) Microbial diversity. Current perspectives and potential applications. I.K. International, New Delhi... 

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