Extractants phase splitting

Exchange heat Extract/phase split Extrude Ferment (kinetic)... 

Reaction step quench Distillation azeotropic solvent drying Aqueous extraction phase splits... 

Transfer Aqueous Phase (Batch Extraction / Phase Split Dispose Organic [Transfer Out)... 

The phenomenon of TPF is a disturbing one to be avoided for an application of liquid-liquid extraction. For the PUREX process, the conditions of TPF as functions of concentrations of HN03, U(VI), U(IV), and Pu(IV) diluent and temperature were investigated thoroughly (86-88). The conditions are commonly expressed in terms of LOC. The scientific elucidation, however, of the TPF, dealing with compo-sitions/speciation and structure of the phases, causes of the phase splitting and its mechanism, thermodynamic features of TPF, reasons for difference of the LOCs with respect to metals and acids, had been deficient. 

The term Third-Phase Formation in solvent extraction refers to a phenomenon in which the organic phase splits into two phases (126). One of the two phases is diluent rich, whereas the other is rich in extractant and also contains the metal solvate. Third-... 

Another method for obtaining the extension domain of the organic extractant phase before third-phase formation is to prepare a solution under the conditions of formation of a third phase, and allow it to equilibrate. Chemical analysis of the third phase and the dilute organic phase in equilibrium with the aqueous phase identifies tie-lines in the phase diagrams (Figure 7.5) (a tie-line joins the composition of the two phases (dilute and concentrated) in equilibrium after the splitting of the organic phase into two phases). 

Three main effects are universal and do not depend on the system studied. The favorable effect of a cation on third-phase formation is measured by the slope of the energy of attraction between the reverse micelles plotted versus the cation concentration in the organic phase or the total nitrate concentration for different salt. Whatever the nature of the extracted cations, third-phase formation is observed when the energy of attraction is near 2kBT. Finally, the tendency toward phase splitting correlates well with the hydration enthalpy of the cations. 

Mossbauer spectroscopy has been quite successful in identifying catalyst components. Mossbauer spectroscopy provides quantitative site populations, easily discriminating between various metal oxidation states and anion coordinations, and it can lead to phase compositions or distributions between phases of the isotope under investigation. It also gives quantitative population distributions of local distortion environments and local chemical environments, via extracted quadrupolar splitting distributions. 

Sometimes the mutual solubility of a solvent pair of interest can easily be decreased by adding a third component. For example, it is common practice to add water to a solvent system containing a water-miscible organic solvent (the polar phase) and a hydrophobic organic solvent (the nonpolar phase). A typical example is the solvent system (methanol + water) + dichloromethane. An anhydrous mixture of methanol and dichloromethane is completely miscible, but adding water causes phase splitting. Adjusting the amount of water added to the polar phase also may be used to alter the K values for the extraction, density difference, and interfacial tension. Table 15-5 lists some common examples of solvent systems of this type. These systems are common candidates for fractional extractions. 

A reflux arrangement is now added at the lower end of the column. The extract is sent to a solvent removal unit, and the solvent-free extract is split into an extract product and an extract reflux which is sent back to the bottom of the column. Without the solvent, the extract reflux is now composed of the raffinate component and the solute (components R and E), so that this reflux is actually on the raffinate side of the equilibrium curve (Section 11.2 and Figure 11.2) flowing countercurrent to the extract phase. The extract phase is thus interacting with a raffinate phase which is richer in the solute than the feed. As a result, the extract enrichment with the solute is greater than it would be if the extract were interacting directly with the external feed in the absence of the extractor section below the feed. A higher-purity extract product can therefore be expected. 

In the case of an ABC extractant there is room for another H bonding. HA present in the system, instead of HX, may bind to RpNH.T-pX . Several observations indicate that formation of R NH,t- .X HA takes place. In amine -I- apolar diluent + HX -I- water systems the organic phase splits into two, on reaching a certain level of loading, due to the low... 

With increasing content of solute B, the states of raffinate and extract approach each other and, finally, coincide at the critical point. In consequence, density difference Ap and interfacial tension cr approach zero as shown in Fig. 6.1-2. Low values of Ap and cr make the phase splitting more difficult or even impossible. Therefore, the region near the critical point cannot be utilized in solvent extraction processes. 

One of the most cmcial problems of extraction processes is the splitting of the phases after completion of the inteifacial mass transfer. Phase splitting is very diffi-... 

Solution behavior of polymers and proteins, salting out, precipitation, extraction, chromatography, resin swelling, phase splitting etc. General relevance for DSP... 

Another option is extractive crystallisation. Here, the tendency of particular aqueous-solvent mixtures such as water-propanol, water-amines, water-micelles, water-polar polymers to split into two liquid phases upon small variations in temperature is used to dehydrate solutions of crystallisable solutes. At low temperatures, these systems form homogeneous mixtures, whereas at high temperatures, a solvent rich phase is created. The aqueous solute becomes concentrated in a smaller volume and consequently crystallises, whereas the pure solvent is recycled. Also, alternative schemes may be used depending on the exact phase behaviour of the component. For instance, a solute such as amino acids and peptides may crystallise from an aqueous solution upon introducing a fully miscible component, such as in water-ethanol mixtures. In a second stage, after the separation of the crystals, the conditions may be altered to induce an L - L phase split that allows easy recovery of the auxiliary component. Maurer and co-workers [25] described the use of high pressure CO2 in water-alkanol systems. At low pres-... 

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