Transport solvent extraction

A growing-drop method has been reported [53] for measuring interfacial liquid-liquid reactions, in which mass transport to the growing drop was considered to be well-defined and calculable. This approach was applied to study the kinetics of the solvent extraction of cupric ions by complexing ligands. 

A significant advance was made in this field by Watarai and Freiser [58], who developed a high-speed automatic system for solvent extraction kinetic studies. The extraction vessel was a 200 mL Morton flask fitted with a high speed stirrer (0-20,000 rpm) and a teflon phase separator. The mass transport rates generated with this approach were considered to be sufficiently high to effectively outrun the kinetics of the chemical processes of interest. With the aid of the separator, the bulk organic phase was cleanly separated from a fine dispersion of the two phases in the flask, circulated through a spectrophotometric flow cell, and returned to the reaction vessel. 

Lee, S. S. Yoon, I. Park, K.-M. Jung, J. H. Lindoy, L. F. Nezhadali, A. Rounaghi, G. Competitive bulk membrane transport and solvent extraction of transition and post transition metal ions using mixed-donor acyclic ligands as ionophores. J. Chem. Soc.-Dalton Trans. 2002, 2180-2184. 

Solvent extraction procedures involve collection of sample by an appropriate device and subsequent immediate placement into a borosilicate glass vessel, which contains a known quantity of ultrapure methanol. The bottle is then transported to the laboratory at 4°C, and the methanol fraction analyzed by purge-and-trap gas chromatography (or a similar procedure). 

The driving force of the transport of salts, proteins, etc., through the cell membrane from the nuclens to the body fluids, and vice versa, is a complicated biochemical process. As far as is known, this field has not been explored by traditional solution chemists, although a detailed analysis of these transfer processes indicates many similarities with solvent extraction processes (equilibrium as well as kinetics). It is possible that studies of such simpler model systems could contribute to the understanding of the more complicated biochemical processes. 

Solvent extraction deals with the transport of chemical substances from one phase into another one, the chemical kinetics of this process, and the final equilibrium distribution of the substances between the two phases. Such transport and distribution processes are the motors that make life in biological systems possible. Fundamental studies of such solvent extraction processes contribute to the better understanding of all processes in nature. Here, only the lack of imagination stands in the way of important new scientific discoveries. 

The centrifugal separator of the AKUEVE system is also used for phase separation in the SISAK technique [84]. SISAK is a multistage solvent extraction system that is used for studies of properties of short-lived radionuclides, e.g., the chemical properties of the heaviest elements, and solvent extraction behavior of compounds with exotic chemical states. In a typical SISAK experiment, Fig. 4.34, radionuclides are continuously transported from a production... 

When one or more of the chemical reactions is sufficiently slow in comparison with the rate of diffusion to and away from the interface of the various species taking part in an extraction reaction, such that diffusion can be considered instantaneous, the solvent extraction kinetics occur in a kinetic regime. In this case, the extraction rate can be entirely described in terms of chemical reactions. This situation may occur either when the system is very efficiently stirred and when one or more of the chemical reactions proceeds slowly, or when the chemical reactions are moderately fast, but the diffusion coefficients of the transported species are very high and the thickness of the two diffusion films is close to zero. In practice the latter situation never occurs, as diffusion coefficients in liquids generally do not exceed 10 cm s, and the depth of the diffusion films apparently is never less than 10 cm. 

The use of liquid membranes in analytical applications has increased in the last 20 years. As is described extensively elsewhere (Chapter 15), a liquid membrane consists of a water-immiscible organic solvent that includes a solvent extraction extractant, often with a diluent and phase modifier, impregnated in a microporous hydrophobic polymeric support and placed between two aqueous phases. One of these aqueous phases (donor phase) contains the analyte to be transported through the membrane to the second (acceptor) phase. The possibility of incorporating different specific reagents in the liquid membranes allows the separation of the analyte from the matrix to be improved and thus to achieve higher selectivity. 

Mixed donor macrocycles have been employed in a number of applications involving the separation or analysis of manganesetll). These include examples of use of such a ligand as the extractant in solvent extraction processes " and as the ionophore in membrane transport studies. 

The Terra-Kleen solvent extraction technology is an on-site, batch-process system that uses a proprietary solvent to remove hazardous organic constituents from soils. The treatment system uses a solvent regeneration system that concentrates the extracted contaminants and then recycles the extraction solvent. The treated soil can often be returned to the site. The concentrated contaminants are usually transported off-site for disposal. 

Extensive studies have been carried out concerning ion transfers, electron transfers and combinations of ion and electron transfers at liquid-liquid interfaces. Po-larography and voltammetry at liquid-liquid interfaces are of analytical importance, because they are applicable to ionic species that are neither reducible nor oxidizable at conventional electrodes. They are also usefid in studying charge-transfer processes at liquid-liquid interfaces or at membranes solvent extractions, phase transfer catalyses, ion transport at biological membranes, etc. are included among such processes. 

It has been reported that vitamin Kj and several of the vitamin K2 homologues are capable of restoring electron transport in solvent-extracted or irradiated bacterial and mitochondrial preparations. Other reports suggest that vitamin K is concerned with the phosphorylation reactions accompanying oxidative phosphorylation The capacity of these compounds to exist m several forms, e.g., quinone, quinol. chromanol, etc., appears to strengthen the proposal that links them to oxidative phosphorylation. Information has suggested that vitamin K acts to induce prothrombin synthesis. Since prothrombin has been shown to be synthesized only by liver parenchymal cells m the dog, it would appear that the proposed role for vitamin K is not specific for only prothrombin synthesis, but applicable to other proteins. 

Patil, C.B. Mohapatra, P.K. Singh, R.R. Gurba, P.B. Janardan, P. Changrani, R.D. Manchanda, V.K. Transport of uranium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor, Radiochim. Acta 94 (2006) 331-334. 

HOST-GUEST COMPLEXATION AS A TOOL FOR SOLVENT EXTRACTION AND MEMBRANE TRANSPORT OF (BIO)ORGANIC COMPOUNDS Igor V. Pletnev and Yuri A. Zolotov... 

Carrier facilitated transport processes often achieve spectacular separations between closely related species because of the selectivity of the carriers. However, no coupled transport process has advanced to the commercial stage despite a steady stream of papers in the academic literature. The instability of the membranes is a major technical hurdle, but another issue has been the marginal improvements in economics offered by coupled transport processes over conventional technology such as solvent extraction or ion exchange. Major breakthroughs in performance are required to make coupled transport technology commercially competitive. 

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