Liquid phase separation

The significance of these phenomena to thermodynamic studies has been demonstrated many times over the past decade, -with especial importance attaching to the two loci which can be expressed in closed form by equating to zero the Gibbs determinants, viz  

In contrast, the cloud point curve, the ratio (r) of volumes of dilute to concentrated phases and the distribution of polymer species between phases after separation, which in principle contain much more information, require numerical solutions to the set of simultaneous equations which characterize equilibrium between the two phases namely the equality of chemical potential in both phases for each species in the solution. 

Craubner claims - that the perturbation calculus which he has devised is the most successful means of dealing with such phase phenomena thus far. Multiphase Separation. Separation of polymer solutions into more than two liquid phases which coexist in equililnium is known and was predicted by Tompa on the basis of Flory-Huggins theory (see next section). It is one of the success stories in solution thermodynamics that a 3-phase region, so small as to be difficult to find experimentally by chance, was predicted for a polyethylene/ diphenylether system and subsequently confirmed experimentally.  

Chermin has reviewed the mechanisms of liquid 3-phase separation and shown that there is only one which can occur in Flory-Huggins theory. Furthermore, separation of a Flory-Huggins solution into more than 3 liquid phases caimot occur. Chermin also gives the general conditions for a multicritical point. Sole has numerically studied cloud point curves for hypothetical systems in 3- and 4-phase equilibria. 

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Figure A2.5.5. Phase diagrams for two-eomponent systems with deviations from ideal behaviour (temperature T versus mole fraetion v at eonstant pressure). Liquid-gas phase diagrams with maximum (a) and minimum (b) boiling mixtures (azeotropes), (e) Liquid-liquid phase separation, with a eoexistenee eurve and a eritieal point.

A third kind of phase diagram in a two-eomponent system (as shown in figure A2.5.5(e) is one showing liquid-liquid phase separation below a oritieal-solution point, again at a fixed pressure. (On aT,x diagram, the eritieal point is always an extremum of tire two-phase eoexistenee eurve, but not always a maximum. 

A2.5.4.1 LIQUID-LIQUID PHASE SEPARATION IN A SIMPLE BINARY MIXTURE... 

In the absence of special syimnetry, the phase mle requires a minimum of tliree components for a tricritical point to occur. Synnnetrical tricritical points do have such syimnetry, but it is easiest to illustrate such phenomena with a tme ternary system with the necessary syimnetry. A ternary system comprised of a pair of enantiomers (optically active d- and /-isomers) together with a third optically inert substance could satisfy this condition. While liquid-liquid phase separation between enantiomers has not yet been found, ternary phase diagrams like those shown in figure A2.5.30 can be imagined in these diagrams there is a necessary syimnetry around a horizontal axis that represents equal amounts of the two enantiomers. 

Fa]ula F and Plee D 1994 Applioation of moleoular sieves in view of oleaner teohnology. Gas and liquid phase separations Stud. Surf. Sc/. Catai. 85 633-51... 

R. L. Barton ( Sizing Liquid-Liquid Phase Separators Empirically, Chemical Engineering, July 8, 1974, Copyright (1974) McGraw-Hill, Inc., used with permission) provides the following quick method for sizing liquid-liquid phase sepai ators empirically. 

Barton, R. L., Sizing Liquid-Liquid Phase Separators Empirically, Chemical Engineering, July 8, 1974. 

P19 Other Liquid Phase Separation 4 = 1 part per billion to 1 part per million... 

PI 9 Other Liquid Phase Separation mass) for solids and liquids cubic centimeters/cubic meter ... 

We have seen above in two instances, those of liquid-liquid phase separation and polymer devolatilization that computation of the phase equilibria involved is essentially a problem of mathematical formulation of the chemical potential (or activity) of each component in the solution. 

If there are included among the diluents mixed with the crystalline polymer some which are sufficiently poor solvents, the phase diagram may then exhibit liquid-liquid phase separation, in addition to the liquid-crystal boundary curve. Examples are shown in Figs. 133... 

Recalling the previous assertion that efficient fractionation requires liquid-liquid phase separation, we conclude that nitrobenzene and amyl acetate should be satisfactory solvents from which to fractionate polyethylene by successively lowering the temperature and that the better solvent xylene should be avoided for this purpose. The character of the phase diagram may, in fact, be used as a criterion of the efficacy of a given solvent for fractionation (see Chap. VIII, p. 344). If the curve representing the precipitation temperature plotted against concentration rises monotonically, crystalline separation is clearly indicated if it passes through a maximum at a low concentration, liquid-liquid separation is virtually assured, and the solvent may be assumed to be a satisfactory one to use for fractionation. 

The improved method guarantees that the EoS will calculate the correct VLE not only at the experimental data but also at any other point that belongs to the same isotherm. The question that arises is what happens at temperatures different than the experimental. As seen in Figure 14.10 the minima of the stability function increase monotonically with respect to temperature. Hence, it is safe to assume that at any temperature between the lowest and the highest one, the EoS predicts the correct behavior of the system. However, below the minimum experimental temperature, it is likely that the EoS will predict erroneous liquid phase separation. 

MJ. Wilcox, Abstracts 22nd Inti Symposium on High Performance Liquid Phase Separations and Related Techniques (HPLC 98), St Louis, MO (1998). 

Principles and Characteristics The main reasons for hyphenating MS to CE are the almost universal nature of the detector, its sensitivity and the structural information obtainable, including assessment of peak purity and identity. As CE is a liquid-phase separation technique, coupling to the mass spectrometer can be achieved by means of (modified) LC-MS interfaces. Because of the low flow-rates applied in CE, i.e. typically below lOOnLmin-1, a special coupling device is required to couple CE and the LC-MS interface. Three such devices have been developed, namely a... 

R. L. Barton6 provides the following quick method for sizing liquid-liquid phase separators empirically. 

Figure 12.30 Heterogeneous distillation with liquid phases separated after distillation.

When introducing an entrainer, it will need to have a significant effect on the relative volatility between the azeotropic components to be separated, and it must be possible to separate the entrainer relatively easily. One way of making sure the entrainer can be easily separated is to choose a component that will introduce a two-liquid phase separation. Such entrainers typically introduce additional distillation boundaries, but the overall separation can be efficient if the two-liquid separation produces mixtures with compositions in the different distillation regions10. 

Hamler, R. L. Zhu, K. Buchanan, N. S. Kreunin, P. Kachman, M. T. Miller, F. R. Lubman, D. M. A two-dimensional liquid-phase separation method coupled with mass spectrometry for proteomic studies of breast cancer and biomarker identification. Proteomics 2004,4, 562-577. 

Wall, D. B. Kachman, M. T. Gong, S. Hinderer, R. Paras, S. Misek, D. E. Hanash, S. M. Lubman, D. M. Isoelectric focusing nonporous RP HPLC A two-dimensional liquid-phase separation method for mapping of cellular proteins with identification using MALDI-TOF mass spectrometry. Anal. Chem. 2000, 72, 1099-1111. 

TABLE 5.1 Classification and Examples of Two-Dimensional Liquid-Phase Separation Techniques... 

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