Presence of Immiscible Phases

TABLE 4.4 Minimisation of the Schlieren Effect by Dual-Wavelength Spectrophotometry. Data Refer to Analytical Signals, in Arbitrary Units. Dye Solutions [Buffered Bromocresol Green (BCG) Solutions] Inserted into the Buffer Carrier Stream of a Single line Flow Injection Manifold. For Experimental Details, see Ref. [28],  

Although very effective for compensating the influence of the Schlieren effect, Eq. 4.7 holds only when the intensity of the Schlieren effect is not wavelength dependent, otherwise, correction factors should be added. As the transient mirrors established between fluid elements of different refractive indices are not ideal and the incident light is also partially refracted, the refraction angle is strongly wavelength dependent (Eq. 4.15). Hence, the use of Eq. 4.7 for Schlieren compensation may be subject to restrictions. Moreover, it cannot be directly applied for Schlieren compensation in flow systems with turbidimetric or nephelometric detection. 

Finally, Schlieren effect minimisation is inherent to most strategies already proposed for multivariate analyses relying on spectral exploitation. In fact, the calibration models are usually built after data decorrelation. As the Schlieren noise superimposed on every data point leads to an enhancement of the data correlation matrix, procedures for data decorrelation implicitly lead to Schlieren minimisation. This aspect has been demonstrated in relation to the partial least squares algorithm [120]. 

The sample zone may contain immiscible elements (e.gair, gas, solvent bubbles and suspended particulate matter) in close contact with each other, which may impair analyte detection. The most important 

The presence of air bubbles in some modes of flow analysis, e.g., segmented, mono-segmented and multi-commuted flow analysis, is beneficial, but some limitations should be mentioned [122]  

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Some emulsions are undesirable when they occur. In process industries chemical demulsification is commonly used to separate water from oil in order to produce a fluid suitable for further processing. The specific kind of emulsion treatment required can be highly variable, even within the same industry. The first step in systematic emulsion breaking is to characterize the emulsion in terms of its nature (O/W, W/O, or multiple emulsion), the number and nature of immiscible phases, the presence of a protective interfacial film around the droplets, and the sensitivity of the emulsifiers [295,408,451], Demulsification then involves two steps. First, there must be agglomeration or coagulation of droplets. Then, the agglomerated droplets must coalesce. Only after these two steps can complete phase separation occur. It should be realized that either step can be rate determining for the demulsification process. 

Because the separation of immiscible phases takes place only in the presence of gravity, it would not be... 

Most polymer blends are immiscible. Their flow is complex not only due to the presence of several phases having different rheological properties (as it will be demonstrated later, even in blends of two polymers the third phase, the interphase, must be taken into account), but also due to strain sensitivity of blend morphology. Such complexity of flow behavior can be best put in perspective by comparing it to flow of better understood systems, suspensions, emulsions, and block copolymers. 

The presence of immiscible aqueous and hydrocarbon phases in the S/AA solution was also investigated (19). On the basis of spectral analysis of... 

The broad variety of methods suitable for spectroscopy at surfaces and other kinds of surface analysis has been touched upon already in the preceding chapter. The term surface referred mostly to solids being exposed to a vacuum or even ultra high vacuum environment. Few methods can be used under ambient conditions and at atmospheric pressure or even in the presence of condensed phases as encountered in electrochemical systems because of the strong interactions between several probes and signals with particles in condensed phases or in the gas phase at ambient temperature and pressure. The same line of argument applies to the interface between immiscible liquids. 

Most polymer blends are immiscible. Their flow is complex not only due to the presence of several phases having different rheological properties (as it will be... 

Ultrasonic cavitation has particularly important effects on biphasic systems, emulsification of immiscible liquid-liquids, particle breakage and dispersion, and surface cleaning in liquid-solid mixtures. These mechanical effects, even if sometimes oversimplified, appear to be understandable and predictable by nonexperts in the field, who exploited them in a variety of heterogeneous reactions. Sonochemistry of biphasic systems then developed rapidly, and synthetic applications were reviewed in recent articles. In many cases, the presence of a phase transfer catalyst becomes unnecessary, and sonication can be considered as a "physical substitute to PTC", according to the expression of Ando. a... 

The interfacial technique (20), which is a heterophase process where two fast-reacting reactants are dissolved in a pair of immiscible solvents, one of which is usually water. The aqueous phase contains a diol or a diamine the organic phase contains a diacid chloride dissolved in a solvent such as dichloromethane, toluene, or diethyl ether. Condensation occurs at the water/organic solvent interface often in the presence of a phase transfer catalyst. 

However, this three-phase equilibrium L,-L2-G was found in ternary mixtures. It was especially clear in case of H2O - K2SO4 - KLiS04 system, where the liquid immiscibility in a presence of vapor phase (with and without equilibrium... 

The relative amounts of the two types of polymers are determined by reaction conditions. Hydrolysis with water alone yields 50—80% linear polydimethyl-siloxane-a,co-diols and 50—20% polydimethylcyclosiloxanes. Hydrolysis with 50—85% sulphuric acid gives mostly high molecular weight linear polymers with only small amounts of cyclosiloxanes. Conversely, the hydrolysis of dimethyl-dichlorosilane with water in the presence of immiscible solvents (e.g., toluene, xylene and diethyl ether) results in the preferential formation of lower polycyclosiloxanes. Such solvents, in which the organochlorosilane is readily soluble, lead to a reduction in concentration of dimethyldichlorosilane in the aqueous phase and thus intramolecular condensation is favoured over inter-molecular condensation. Further, the hydrolysis products are also soluble in the organic solvent and the cyclic compounds are protected from the action of the aqueous acid. (See later.)... 

The interaction parameters suggested by Sun et al. [38] were obtained using viscosity data to determine the miscibility. The ultrasonic velocity of the blend solutions as a function of PVP content is shown in Figure 8.4. For PS/PVP blends, there was an almost insignificant effect of the blend ratio on ultrasonic velocity, which indicated the presence of only one phase. In contrast, the PMMA/PVP blends showed a nonlinearity that indicated the presence of two phases. In the case of the blend system of cellulose acetate/PMMA [39], the nonlinear behavior of ultrasonic velocity with blend composition was due to the blend s immiscible nature. Singh and Singh [40] also attributed the linear variation of the ultrasonic velocity of PMMA/poly(vinyl acetate) with blend composition to the miscible nature of the blend. Singh et al. [41] noted that both the ultrasonic velocity and density with blend composition were linear for miscible blends but nonlinear (S-shaped) for immiscible blends, respectively. 

Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

In the previous sections, we indicated how, under certain conditions, pressure may be used to induce immiscibility in liquid and gaseous binary mixtures which at normal pressures are completely miscible. We now want to consider how the introduction of a third component can bring about immiscibility in a binary liquid that is completely miscible in the absence of the third component. Specifically, we are concerned with the case where the added component is a gas in this case, elevated pressures are required in order to dissolve an appreciable amount of the added component in the binary liquid solvent. For the situation to be discussed, it should be clear that phase instability is not a consequence of the effect of pressure on the chemical potentials, as was the case in the previous sections, but results instead from the presence of an additional component which affects the chemical potentials of the components to be separated. High pressure enters into our discussion only indirectly, because we want to use a highly volatile substance for the additional component. 

The concept of extractive reaction, which was conceived over 40 years ago, has connections with acid hydrolysis of pentosans in an aqueous medium to give furfural, which readily polymerizes in the presence of an acid. The use of a water-immiscible solvent, such as tetralin allows the labile furfural to be extracted and thus prevents polymerization, increases the yield, and improves the recovery procedures. In the recent past an interesting and useful method has been suggested by Rivalier et al. (1995) for acid-catalysed dehydration of hexoses to 5-hydroxy methyl furfural. Here, a new solid-liquid-liquid extractor reactor has been suggested with zeolites in protonic form like H-Y-faujasite, H-mordenite, H-beta, and H-ZSM-5, in suspension in the aqueous phase and with simultaneous extraction of the intermediate product with a solvent, like methyl Aobutyl ketone, circulating countercurrently. 

Liquid surfaces and liquid-liquid interfaces are very common and have tremendous significance in the real world. Especially important are the interfaces between two immiscible liquid electrolyte solutions (acronym ITIES), which occur in tissues and cells of all living organisms. The usual presence of aqueous electrolyte solution as one phase of ITIES is the main reason for the electrochemical nature of such interfaces. 

The above equation allows the calculation of Galvani potentials at the interfaces of immiscible electrolyte solutions in the presence of any number of ions with any valence, also including the cases of association or complexing in one of the phases. Makrlik [26] described the cases of association and formation of complexes with participation of one of the ions but in both phases. In a later work [27] Le Hung extended his approach and also considered any mutual interaction of ions and molecules present in both phases. Buck and Vanysek performed the detailed analysis of various practical cases, including membrane equilibria, of multi-ion distribution potential equations [28,29]. 

The investigations of interfacial phenomena of immiscible electrolyte solutions are very important from the theoretical point of view. They provide convenient approaches to the determination of various physciochemical parameters, such as transfer and solvation energy of ions, partition and diffusion coefficients, as well as interfacial potentials [1-7,12-17]. Of course, it should be remembered that at equilibrium, either in the presence or absence of an electrolyte, the solvents forming the discussed system are saturated in each other. Therefore, these two phases, in a sense, constitute two mixed solvents. 

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