Binary Mixtures Containing Solids

Can binary mixtures coexist as three liquid phases Such behavior is not prevented by the phase rule, but very unusual intermolecular forces would be required. As far as we are aware, binary LLLE occurs only when the components react to form either a physical or a chemical compound, so the mixture effectively becomes a ternary. An example is n-butyl chloral hydrate in water [17,18]. 

But not all solid-phase equilibria are simple complications may occur due to (i) partial immiscibility of solid phases, (ii) the presence of more than one crystalline structure (polymorphism) of a solid phase, and (iii) reaction of pure compounds to form solid intermolecular compounds. When any of these occur, the phase diagrams are complex but fortunately, those diagrams can be generally understood as superpositions of simpler diagrams. 

In addition, miscible liquid-solid systems can display phase behavior more complex than vapor-liquid systems. For example, mixtures of carbon tetrachloride and cyclohexanone form a compound from one molecule of each pure this compound (xj = 0.5) melts at -39.6°C. Below this temperature, the compound exhibits two minimum melting temperatures so the melting curve for this binary has three extrema, two minima and a maximum, and all three lie below the melting points of the pure components. Compound formation in a solid phase can also cause constant-composition melting without an extremum in temperature. This occurs in mixtures of bromine and iodine. At 40°C the compound IBr melts at constant composition, although this temperature lies between the melting points of pure iodine and pure bromine. Phase diagrams for these kinds of solid systems can be found in the book by Walas [5]. 

This procedure has been a traditional experimental method for locating the solidus and liquidus on LSE phase diagrams. To avoid effects of metastabUities, the solidus is 

Supercooling can also cause the spontaneous appearance of new phases, accompanied by large latent heat effects and a temporary increase in temperature. Since liquids can be so easily supercooled, cooling curves often fail to locate the solidus reliably cooling curves typically yield values of the solidus temperature that are too low. Therefore, once the liquid phase has completely solidified, the solidus is often determined by reversing the process and heating the solid back to the solidus [20]. To locate 

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The liquid membrane (thickness 0.2 cm) was separated from the aqueous solutions by two vertical cellophane films.The electrode compartments were filled with 0.05 M sulfuric acid solutions and were separated by the solid anion-exchange membranes MA-40. Binary mixtures contained, as a mle, 0.04 M Cu(II) and 0.018 M Pt(IV) in 0.01 M HCl. 0.1 M HCl was used usually as the strip solution. 

J. B. Ott and J. R. Goates. "(Solid + Liquid) Phase Equilibria in Binary Mixtures Containing Benzene, a Cycloalkane, an rc-Alkane. or Tetrachloromethane. An equation for Representing (Solid + Liquid) Phase Equilibria", J. Chem. Thermodyn., 15. 267-278 (1983). 

The calculation of the liquid-fluid equilibria with the group contribution method has been presented elsewhere [4], The matrix of the parameters of group interaction (Table 1) contains values readjusted relative to the matrix obtained considering only liquid-fluid equilibria [4], These parameters are Ai5, A35, A45 and A59. The introduction of supplementary increments for the form of the molecules (a3 and P3.5) enables good results to be obtained for the calculation of solid-fluid equilibria and does not essentially modify the representation of liquid-fluid equilibria. The average relative deviation 5r(x) for the experimental data as a whole is 16 7% for the group contribution method and 13.3% for the model with E12 adjusted. The experimental data concern 40 isotherms (P,x) for 11 binary mixtures of solid aromatic hydrocarbon with supercritical C02. 

The possible formation of carbon using a particular fuel can be determined by the simultaneous solution of the above equations using their equilibrium coefficients." No solid graphitic carbon exists at low temperatures (-600 °C) in binary mixtures containing at least 2 atoms of oxygen or 4 atoms of hydrogen per atom of carbon (14). 

The crystallization temperature depends on the composition of the mixture to be treated. The cooling diagram shows that a eutectic exists between p-xylene and each of the other components of the mixture. In the case of the m, p-xyiene binary system, the eutectic contains 13 per cent p-xylene and melts at —52 C (Fig. 4.10). It separates two iiquidus curves ME in equilibrium with solid m-xylene, PE in equilibrium with solid p-xylene. Provided that the initial mixture contains more than 13 per cent p-xyleoe. crystals of pure p-xylene are obtained by cooling to — 52 and a mother liquor, whose composition is that of the eutectic. However, it qan be noticed (bat the existence of the eutectic leads to limited recovery, and that this recovery requires beat exchanges at low temperature. 

Let us consider vapor-liquid (or vapor-solid) equilibria for binary mixtures. For the sake of simplicity it will be assumed that all gases are ideal. In addition to the vapors of each component of the condensed phase, the gas will be assumed to contain a completely insoluble constituent, the partial pressure p of which may be adjusted so that the total pressure of the system, p, assumes a prescribed value. Therefore, C = 3, P = 2, and, according to equation (51), F = 3. Let us study the dependence of the equilibrium vapor pressures of the two soluble species p and P2 on their respective mass fractions in the condensed phase X and X2 at constant temperature and at constant total pressure. Since it is thus agreed that T and p are fixed, only one remaining variable [say X ( = l — "2)] is at our disposal p, P2 and the total vapor pressure p = p + p2 will depend only on X. ... 

Solid-Solution Mixture In this system, a binary mixture is cooled but neither component solidihes without containing some of the other component Both components are deposited simultaneously, and the deposited sohd phase is a solid-solution. Only two phases can exist in such a system a homogeneous liquid-solution and a solid-solution. The equilibrium phase diagram is shown in... 

The results for the carbon dioxide and propane binary system, shown as dashed lines in Figure 4.2.2, on the other hand are not as good. When compared with the performance of the IPVDW model (solid lines in Figure 4.2.2), the use of the same parameters for all isotherms leads to inferior results at higher temperatures despite the use of an extra parameter in the Huron-Vidal model. This indicates that, for the mixtures containing supercritical components, the HVO mixing rule, when combined... 

By deuterium NMR, we have ascertained that the limit of solubility of 8a in the crystal-B phase is in fact somewhat less than 1.0 mol%. Under the conditions of our flash photolysis experiments, 8a is distributed between both a ketone-rich nematic phase and a ketone-depleted smectic phase at temperatures between 53-35°C. At 35°, the ketone-rich phase is transformed into a "p-phase" in which the ketone exhibits isotropic H and C NMR behavior, and which eventually crystallizes (though not under these conditions) to form a stable binary smectic or solid modification consisting of 8-10 mol% ketone and CCH-4. Thermal microscopy experiments with mixtures containing 1-3... 

Using the proposed procedure in conjunction with literature values for the density (11) and vapor pressure (12) of solid carbon dioxide, the solid-formation conditions have been determined for a number of mixtures containing carbon dioxide as the solid-forming component. The binary interaction parameters used in Equation 14 were the same as those used previously for two-phase vapor-liquid equilibrium systems (6). The value for methane-carbon dioxide was 0.110 and that for ethane-carbon dioxide was 0.130. Excellent agreement has been obtained between the calculated results and the experimental data found in the literature. As shown in Figure 2, the predicted SLV locus for the methane-carbon... 

The drying of MEK and pyridine is among commonly used applications of salting-out for binary mixtures of solvent and water. The MEK/water azeotrope is just single phase at ambient temperature and the addition of a salt produces two liquid phases and a solid/salt phase. The aqueous phase contains 4% MEK and is seldom worth recovering. The MEK-rich phase is easily split into the azeotrope and a dry MEK fraction. 

In a continuously operated production plant batchwise operation is a drawback. Principally speaking, the separation of a binary mixture with the components a and b can be carried out in a true moving bed (Seidel-Morgenstem et al. 2008). In Fig. 9.8-8 the principle of a countercurrent chromatography column is illustrated. The solid phase is moving downward whereas the mobile fluid phase is introduced at the bottom of the column. The feed of the components a and b is separated with the result that a raffinate containing a less adsorbable component a and an extract with the strong adsorbable component b are withdrawn as side streams. Therefore, the total column is subdivided into four zones ... 

The separation of a mixture containing sublimable components is carried out by fractional sublimation in countercurrent columns. The finely distributed solid phase trickles down the column countercurrently to the upflowing sublimate vapor (Fig. 7-43). For the treatment of binary mixtures, the lighter sublimable component is withdrawn from the top and the heavier sublimable component is withdrawn from the bottom of the column. Some of the lighter sublimable component is used as solid reflux at the top of the column [7.55]. 

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