Solubility miscible pairs

For systems of type II, if the mutual binary solubility (LLE) data are known for the two partially miscible pairs, and if reasonable vapor-liquid equilibrium (VLE) data are known for the miscible pair, it is relatively simple to predict the ternary equilibria. For systems of type I, which has a plait point, reliable calculations are much more difficult. However, sometimes useful quantitative predictions can be obtained for type I systems with binary data alone provided that... 

For all calculations reported here, binary parameters from VLE data were obtained using the principle of maximum likelihood as discussed in Chapter 6, Binary parameters for partially miscible pairs were obtained from mutual-solubility data alone. 

Since in this mixture design problem we have to identify a mixture whose constituents perform different functions, i.e., the solvent needs to have high solubility for the solute while the anti-solvent needs to reduce the solubility, we have to solve two different single compound design problems (involving subproblem 1M, 2m and 3M) to identify the candidate solvents and anti-solvents. The mutually miscible pairs are identified in sub-problem 4M and the final optimisation problem is solved in sub-problem 5M. 

For ternary mixtures of Type I, we require mutual-solubility data for the partially miscible puir and vapor-liquid equilibrium data for the two completely-miscible pairs, For ternary mixtures of Type 1, calculated results are strongly sensitive to the choice of binary parameters obtained from bienry vapor-liquid equilibria. 

Solvent is chosen such that the compound of interest is neither excessively soluble nor insoluble. The common solvents include water, the short-chain alcohols (methanol to hexanol), halogenated solvents (chloroform and carbon tetrachloride), ketones such as acetone and methyl-isobutylketone, pyridine, 1,4-dioxane, ethyl acetate, diethyl ether, petroleum ether, hexane, and toluene. Solubility vanes tremendously with solvent. The solubility of naphthalene, for example, is approximately doubled going from methanol to ethanol, while the addition of water to either drastically reduces solubility (9). Thus, solvent selection is important, and solvent mixtures provide a convenient way of tailoring solubility to a required level. Any miscible pair of solvents is worth investigating, especially if compound solubility differs significantly between the two. 

Although the terms solubility and miscibility are related in meaning, it is important to understand that there is one essential difference. There can be different degrees of solubility, such as slightly, partially, very, and so on. Unlike solubility, miscibility does not have any degrees—a pair of liquids is either miscible or it is not. 

If the substance is found to be far too soluble in one solvent and much too insoluble in another solvent to allow of satisfactory recrystallisation, mixed solvents or solvent pairs may frequently be used with excellent results. The two solvents must, of course, be completely miscible. Recrystallisation from mixed solvents is carried out near the boiling point of the solvent. The compound is dissolved in the solvent in which it is very soluble, and the hot solvent, in which the substance is only sparingly soluble, is added cautiously until a slight turbidity is produced. The turbidity is then just cleared by the addition of a small quantity of the first solvent and the mixture is allowed to cool to room temperature crystals will separate. Pairs of liquids which may be used include alcohol and water alcohol and benzene benzene and petroleum ether acetone and petroleum ether glacial acetic acid and water. 

In general, pyridazine can be compared with pyridine. It is completely miscible with water and alcohols, as the lone electron pairs on nitrogen atoms are involved in formation of hydrogen bonds with hydroxylic solvents, benzene and ether. Pyridazine is insoluble in ligroin and cyclohexane. The solubility of pyridazine derivatives containing OH, SH and NH2 groups decreases, while alkyl groups increase the solubility. Table 1 lists some physical properties of pyridazine. 

Mixed Solvents. Where a substance is too soluble in one solvent and too insoluble in another, for either to be used for recrystallisation, it is often possible (provided they are miscible) to use them as a mixed solvent. (In general, however, it is preferable to use a single solvent if this is practicable.) Table 8 contains many of the common pairs of miscible solvents. 

The small size of lithium frequently confers special properties on its compounds and for this reason the element is sometimes termed anomalous . For example, it is miscible with Na only above 380° and is immiscible with molten K, Rb and Cs, whereas all other pairs of alkali metals are miscible with each other in all proportions. (The ternary alloy containing 12% Na, 47% K and 41% Cs has the lowest known mp, —78°C, of any metallic system.) Li shows many similarities to Mg. This so-called diagonal relationship stems from the similarity in ionic size of the two elements / (Li ) 76pm, / (Mg ) 72pm, compared with / (Na ) 102pm. Thus, as first noted by Arfvedson in establishing lithium as a new element, LiOH and LiiCOs are much less soluble than the corresponding... 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

Really soluble or miscible liquid pairs are no good for extraction and washing. When you mix them, they will not form two layers In fact, they ll mix in all proportions. A good example of this is acetone and water. What kinds of problems can this cause Well, for one, you cannot perform any extraction with two liquids that are miscible. 

The structural constraints used in the first case study namely, Eqn s 27,28 and 29 are used again. The melting point, boiling point and flash point, are used as constraints for both solvent and anti-solvent. Since the solvent needs to have high solubility for solute and the anti-solvent needs to have low solubility for the solute limits of 17 <8 < 19 and 5 > 30 (Eqn s. 33 and 37) are placed on the solubility parameters of solvent and anti-solvents respectively. Eqn.38 gives the necessary condition for phase stability (Bernard et al., 1967), which needs to be satisfied for the solvent-anti solvent pairs to be miscible with each other. Eqn. 39 gives the solid-liquid equilibrium constraint. 

The temperature also affects the composition of the two phases at equilibrium, but the effect is not equivalent in all systems. In the example shown in Figure 2.6, raising the temperature increases the solubility of the two phases and this is what is usually observed. The diagram shows that by heating the system, more of A dissolves in B and vice versa. However, other solvent pairs become less miscible with raised temperature, for example, water and ethylamine. In the case of these liquid pairs, the temperature-composition diagram is essentially reversed, as shown in Figure 2.7. 

For the two-component, two-phase liquid system, the question arises as to how much of each of the pure liquid components dissolves in the other at equilibrium. Indeed, some pairs of liquids are so soluble in each other that they become completely miscible with each other when mixed at any proportions. Such pairs, for example, are water and 1-propanol or benzene and carbon tetrachloride. Other pairs of liquids are practically insoluble in each other, as, for example, water and carbon tetrachloride. Finally, there are pairs of liquids that are completely miscible at certain temperatures, but not at others. For example, water and triethylamine are miscible below 18°C, but not above. Such pairs of liquids are said to have a critical solution temperature, For some pairs of liquids, there is a lower (LOST), as in the water-tiiethylamine pair, but the more common behavior is for pairs of liquids to have an upper (UCST), (Fig. 2.2) and some may even have a closed mutual solubility loop [3]. Such instances are rare in solvent extraction practice, but have been exploited in some systems, where separations have been affected by changes in the temperature. 

A method similar to the above was proposed recently by Kuhn, which uses a pair of solvents immiscible at a lower temperature but becoming miscible with elevating temperature5. To the present authors this method seems more easily applicable and perhaps more promising than the counter-current distribution, since no special instrumentation is necessary for the former. At any rate, it is obvious that these three methods do not allow fractionation of copolymers only by the composition without interference of the molecular weight, because they all are based on the solubility difference among constituent species. 

Table 10 summarizes the glass transition behavior of these polyimide blends and demonstrates that there is only one Tg for each blend. Similar results have been confirmed by Koros of the University of Texas [29], This data confirms that as long as the dianhydride is the same in the composition, the change of 6F diamine from 3,3 to 4,4 does not alter solubility significantly, and the pairs are miscible. The relationship between the Tg and the Fox equation is discussed by MacKnight et al. work [17]. 

When two (or more) metals are melted together and the melt is allowed to solidify, the product is called an alloy. (Sometimes alloys contain nonmetals such as carbon.) Since metals are more widely used as alloys than in pure condition, the nature of alloys has been the subject of much study. It has been found that some metals are miscible in all proportions, while with other pairs there is a definite limit to solubility. When a melted mixture cools, there may crystallize out (1) pure metal, (2) a solid solution, (3) a definite compound, (4) or a mixture of any of these. In the simplest case, one or the other pure metal (components) crystallizes as the temperature falls until the lowest melting point of... 

Many hundred CST could be added for pairs of liquids marked miscible or oo in handbooks. These could be listed with CST <20, etc. Likewise many more given as insoluble or slightly soluble could be listed as CST >20. The data of (15, 17,106, 121, 211, 372) and some of those of (85, 296, 340, 341) are of this type and are referred to only in groups. The table thus furnishes an index for these compilations. 

On a ternary equilibrium diagram like that of Figure 14.1, the limits of mutual solubilities are marked by the binodal curve and the compositions of phases in equilibrium by tielines. The region within the dome is two-phase and that outside is one-phase. The most common systems are those with one pair (Type I, Fig. 14.1) and two pairs (Type II. Fig. 14.4) of partially miscible substances. For instance, of the approximately 1000 sets of data collected and analyzed by Sorensen and Arlt (1979), 75% are Type I and 20% are Type II. The remaining small percentage of systems exhibit a considerable variety of behaviors, a few of which appear in Figure 14.4. As some of these examples show, the effect of temperature on phase behavior of liquids often is very pronounced. 

When sodium chloride is dissolved in water at ordinary temperatures, it is practically completely dissociated into sodium and chloride ions which, under the action of an external field, move in opposite directions and independently of each other subject to coulombic interactions. If, however, sodium chloride is dissolved in a solvent of lower dielectric constant, and if the solution is sufficiently dilute, there is an equilibrium between ions and a coulombic compound of the two ions which are commonly termed 4 ion pairs. This equilibrium conforms to the law of mass action when the interaction of the ions with the surrounding ion atmosphere is taken into account. In solvents of very low dielectric constant, such as the hydrocarbons, sodium chloride is not soluble however, many quaternary ammonium salts are quite soluble, and their conductance has been measured. Here at very low concentrations, there also is an equilibrium between ions and ion pairs which conforms to the law of mass action but at higher concentration, in the neighborhood of 1 X 10 W, or below, a minimum occurs in the conductance. Thereafter, it may be shown that the conductance increases continuously up to the molten electrolyte, provided that a suitable electrolyte and solvent are employed which are miscible above the melting point of the electrolyte. 

The formation of mixed crystals results from limited solubility or insolubility of one solid metal in the other. Lead and tin and lead and antimony are examples of pairs of metals that form alloys consisting of intimate mixtures of tiny pure crystals of each metal. The formation of solid solutions results when the liquid metals are miscible in all proportions and are capable of solidification to compositions that are essentially the same as those of the melts. Many of the most common and useful alloys consist of homogeneous solid solutions of one metal in the other (e.g., alloys of copper and zinc, gold and silver, nickel and... 

In the study of miscibility of partially miscible liquid pairs, the external pressure is kept constant and, therefore, the vapour phase is ignored. The mutual solubilities are represented by means of temperature-composition diagram. 

If miscibility is not restricted to the vapours, the case in which only one substance takes up the other may be distinguished from that in which each dissolves the other to a certain extent the first is familiar, being the case of a solid and a liquid in contact the second that of a pair of liquids. We will distinguish them as simple and mutual solubility. 

Whilst the various types of physical mixture have been dealt with above, from complete immiscibility to complete miscibility, two special cases may now be taken, the first of which is that of benzoic acid and water. Here we are essentially concerned with the fact that in the same pair of bodies, immiscibility may be gradually transformed into simple, then mutual solubility, and finally into complete miscibility. In the previous cases the transformation is effected by rise of temperature below the cryohydric temperature ice and benzoic acid are practically without action on one another on fusion of the ice, one-sided solution of the benzoic acid begins later, on fusion of the acid, mutual solubility occurs, changing eventually to complete miscibility. AlexejefTs investigations on this point have settled that benzoic acid, after an increase of solubility with rise of temperature has shown itself, melts at 90°, i.e. 31-4° under the usual melting point This is, therefore,... 

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