Extractants amphiphilic properties

EXTRACTANT SOLUTIONS ARE COMPLEX FLUIDS 7.2.1 Amphiphilic Properties of Extractant... 

Delmau et al. (129) studied the self-association of fluorinated alcohols used as diluent modifiers for the selective extraction of cesium from caustic media by calixarene-crown ethers. They found that the salt distribution ratio is enhanced by the modifiers and explained this by a solubilization effect of the modifier due to its amphiphilic properties. 

A water-ln-oll mlcroemulslon Is an Interfaclal system of aqueous droplets In a continuous oil phase. By Including water soluble or amphiphilic reagents In this system, the components can be concentrated at will In the different phases of the mlcroemulslon. By selecting an electron donor or electron acceptor that alters Its amphiphilic properties upon oxidation or reduction, one of the photoproducts can be extracted Into the continuous organic phase and so the separation of the photoproducts In two distinct phases Is achieved. 

Another demonstration of a continuous flow operation is the psi-shaped microreactor that was used for lipase-catalyzed synthesis of isoamyl acetate in the 1-butyl-3-methylpyridinium dicyanamide/n-heptane two-phase system [144]. The chosen solvent system with dissolved Candida antarctica lipase B, which was attached to the ionic liquid/n-heptane interfacial area because of its amphiphilic properties, was shown to be highly efficient and enabled simultaneous esterification and product removal. The system allowed for simultaneous esterification and product recovery showed a threefold reaction rate increase when compared to the conventional batch. This was mainly a consequence of efficient reaction-diffusion dynamics in the microchannel system, where the developed flow pattern comprising intense emulsification provided a large interfacial area for the reaction and simultaneous product extraction. Another lipase-catalyzed isoamyl acetate synthesis in a continuously operated pressure-driven microreactor was reported by the same authors [145]. The esterification of isoamyl alcohol and acetic acid occurred at the interface between n-hexane and an aqueous phase with dissolved lipase B from Candida antarctica. Controlling flow rates of both phases reestablished a parallel laminar flow with liquid-liquid boundary in the middle of the microchannel and a separation of phases was achieved at the y-shaped exit of the microreactor (Figure 10.25). The microreactor approach demonstrated 35% conversion at residence time 36.5 s at 45 °C and at 0.5 M acetic acid and isoamyl alcohol inlet concentrations and has proven more effective and outperformed the batch operation, which could be attributed to the favorable mass and heat transfer characteristics. 

Desulfurization processes are absolutely necessary for producing clean fuels. Possible strategies to realize ultradeep suffiirization currently include adsorption, extraction, oxidation, and bioprocesses. Oxidative desulfurization (ODS) combined with extraction is considered one of the most promising of these processes [13]. Ultradeep desulfurization of diesel by selective oxidation with amphiphilic catalyst assembled in emulsion droplets has given results where the sulfur level of desulfurized diesel can be lowered from 500 ppm to about 0.1 ppm without changing the properties of the diesel [12]. 

An interesting twist to the story is provided by studies on N. brasiliensis, which secretes three distinct isoforms of AChE, designated A, B and C (Ogilvie et al, 1973). These enzymes can be easily separated by nondenaturing electrophoresis due to their distinct pis, and this is illustrated in Fig. 11.1, which also shows the distinct electrophoretic properties of the amphiphilic enzyme (arrowed) found only in somatic extracts and therefore presumably associated with neuromuscular function. The overall amount of AChE produced by this parasite increases dramatically following establishment in the jejunum, and a switch in isoform expression occurs,... 

Danes , P. R. Proc. ISEC 86, Munich DECHEMA, 1986 527-535 pp. Pabby, A. K. Sastre, A-M. Ion Exchange and Solvent Extraction, Marcus, Y. and Sengupta, A. K. Eds., Marcel Dekker New York, 2002 vol. 15, 331 69. Winsor, P. A. Solvent Properties of Amphiphilic Compounds, Butterworth Scientific London, 1954. 

Residues and extractives from different environmental matrices exhibit similar physical and chemical properties and can be classified as lipophilic, hydrophilic, or amphiphilic (exhibiting a dual nature). 

Blochet, J. E., A. J. P. Kaboulou, and D. Marion. 1991. Amphiphilic protein from wheat flour specific extraction, structure and lipid binding properties. In Gluten proteins 1990, ed. W. Bushuk and R. Tkachuk, 314-325. St. Paul, MN American Association of Cereal Chemists. 

The segregated core-shell microstmctures, consisting of a hydrophobic core surrounded by a hydrophilic shell, are of great praaical interest as their mechanical properties are mainly influenced by the core polymer and the chemical properties and solubility mainly by the shell monomer units. These materials have attracted increased attention because they not only maintain the funaions of both the core and shell components but also exhibit additional excellent optical, electrical, and magnetic properties. Polymeric core-shell microstmctures can be obtained through phase separation, which is realized by inductive polymerization," solvent extraction and evaporation,"" self-assembly of amphiphilic block copolymers,"" or sequential predpitation,"" which is intrinsically a self-assembly and phase-separation process. However, these methodologies are usually complicated and tedious. 

In the first case, transfer consists simply of a desolvation-resolvation process of the solute at the interface between two homogeneous phases. In the second case, the solute is solubilized in the organic phase by an extractant E added to a diluent generally the extractant has amphiphilic, surface active, properties that enhance its extracting properties, and the solute is not soluble in the diluent. In both cases the species is generally in an electrically neutral form in the organic phase, in most cases where the latter has a low dielectric permittivity. Therefore, if the species is an ion, it will either be complexed by the extractant in its ionized form or associate with a counterion taken from the aqueous phase. 

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