Processing solvent extraction

Miscellaneous Pharmaceutical Processes. Solvent extraction is used for the preparation of many products that ate either isolated from naturally occurring materials or purified during synthesis. Among these are sulfa dmgs, methaqualone [72-44-6] phenobarbital [50-06-6] antihistamines, cortisone [53-06-5] estrogens and other hormones (qv), and reserpine [50-55-5] and alkaloids (qv). Common solvents for these appHcations are chloroform, isoamyl alcohol, diethyl ether, and methylene chloride. Distribution coefficient data for dmg species are important for the design of solvent extraction procedures. These can be determined with a laboratory continuous extraction system (AKUEVE) (244). 

Other Organic Processes. Solvent extraction has found appHcation in the coal-tar industry for many years, as for example in the recovery of phenols from coal-tar distillates by washing with caustic soda solution. Solvent extraction of fatty and resimic acid from tall oil has been reported (250). Dissociation extraction is used to separate y -cresol fromT -cresol (251) and 2,4-x5lenol from 2,5-x5lenol (252). Solvent extraction can play a role in the direct manufacture of chemicals from coal (253) (see Eeedstocks, coal chemicals). 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

Solvent Extraction. Solvent extraction has widespread appHcation for uranium recovery from ores. In contrast to ion exchange, which is a batch process, solvent extraction can be operated in a continuous countercurrent-fiow manner. However, solvent extraction has a large disadvantage, owing to incomplete phase separation because of solubihty and the formation of emulsions. These effects, as well as solvent losses, result in financial losses and a potential pollution problem inherent in the disposal of spent leach solutions. For leach solutions with a concentration greater than 1 g U/L, solvent extraction is preferred. For low grade solutions with <1 g U/L and carbonate leach solutions, ion exchange is preferred (23). Solvent extraction has not proven economically useful for carbonate solutions. 

A great number of separation processes are based on solvent extraction, especially since this is also a concentration technique. For these reasons, solvent extraction will be considered, both from the point of view of the sampling process and from that of the general analytical process. Solvent extraction is ultimately a process of partitioning between two immiscible solvents, and for its optimization it is necessary to know first of all the operational parameters of the system. 

The use of solvent extraction also represents a potentially feasible process. Solvent extraction is an engineering unit operation that is adapted effectively to continuous processing. It has been used with success for the isolation of nonpolar compounds of bp >100 °C (58). Solvent extraction (continuous liquid-liquid extraction) may represent a useful process for routinely concentrating 50-100 L of water. The major problem with solvent extraction is the evaporation and recovery for reuse of large volumes of the organic solvent. Other problem areas that must be considered are purification of sufficient solvent and minimization of artifact formation by heat. 

The SETFICS process (Solvent Extraction for Trivalent /-elements Intragroup Separation in CMPO-Complexant System) was initially proposed by research teams of the former Japan Nuclear Cycle Development Institute (JNC, today JAEA) to separate An(III) from PUREX raffinates. It uses a TRUEX solvent (composed of CMPO and TBP, respectively dissolved at 0.2 and 1.2 M in -dodecane) to coextract trivalent actinides and lanthanides, and a sodium nitrate concentrated solution (4 M NaN03) containing DTPA (0.05 M) to selectively strip the TPEs at pH 2 and keep the Ln(III) extracted by the TRUEX solvent (239). However, the DFs for heavy Ln(III) are rather poor. An optimized version of the SETFICS process has recently been proposed as an alternative process to extraction chromatography for the recovery of Am(III) and Cm(III) in the New Extraction System for TRU Recovery (NEXT) process. NEXT basically consists of a front-end crystallization of uranium, a simplified PUREX process using TBP for the recovery of U, Np, and Pu, and a back-end Am(III) + Cm(III) recovery step (240, 241). 

Law, J.D., Herbst, R.S., Peterman, D.R., Todd, T.A., Romanovskiy, V.N., Babain, V.A., Smirnov, I.V., Esimantovskiy, V.N. 2005. Development of a regenerable strip reagent for treatment of acidic, radioactive waste with the Universal solvent extraction process. Solvent Extraction and Ion Exchange 23(1) 59-83. 

Nilsson, M., Nash, K.L. 2007. Review article A review of the development and operational characteristics of the TALSPEAK process. Solvent Extraction and Ion Exchange 25(6) 665-701. 

The alternative approaches to separation fall into a number of general categories such as differentiation between species based on size or charge/size effects chromatographic processes solvent extraction and selective chemical reactions. These topics have all been discussed in preceding sections. 

Solute Process" Solvent" (extractant/diluent) Contactor type" Literature... 

Because of special safety considerations, the solvent extraction process is constructed in a separate facility from the seed preparation process. The solvent extraction process consists of five closely interrelated unit processes solvent extraction, meal desolventizing, meal drying and cooling, miscella distillation, and solvent recovery. 

Classification and Source of High-Level Wastes. Hanford high-level wastes can be broadly categorized, as Smith has done (4), into high-heat wastes and low-heat wastes. The former consists primarily of Purex and Redox process solvent extraction wastes from fuels processing (Table I). 

The second important difference between classical and modem technology is the method used to separate the large amount of sodium ions. The old method used a calcium tungstate precipitation and subsequent hydrochloric acid treatment for that purpose, while in the modem process solvent extraction or ion exchange converts sodium into ammonium isopolytungstate solution. 

A number of methods exist for the extraction of CNSL, but most industries follow the CNSL bath process. Solvent extraction processes are also used at a limited scale. 

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