Salts phase equilibrium

Gordon JE (1965) Fused organic salts. IV. Characterization of low-melting quaternary ammonium salts. Phase equilibrium for salt-salt and salt-nonelectrolyte systems. Proptuties of the liquid salt medium. J Am Chem Soc 87 4347-4358... 

Electrodes such as Cu VCu which are reversible with respect to the ions of the metal phase, are referred to as electrodes of the first kind, whereas electrodes such as Ag/AgCl, Cl" that are based on a sparingly soluble salt in equilibrium with its saturated solution are referred to as electrodes of the second kind. All reference electrodes must have reproducible potentials that are defined by the activity of the species involved in the equilibrium and the potential must remain constant during, and subsequent to, the passage of small quantities of charge during the measurement of another potential. 

For a multi-stage counter-current extraction operated in true equilibrium without side reactions, the partitioning of a solute into the metal phase (fm) and the salt phase (fs) is defined as follows ... 

This PUCI3 also acts as a salt-phase buffer to prevent dissolution of trace impurities in the metal feed by forcing the anode equilibrium to favor production (retention) of trace impurities as metals, instead of permitting oxidation of the impurities to ions. Metallic impurities in the feed fall into two classes, those more electropositive and those less electropositive than plutonium. Since the cell is operated at temperatures above the melting point of all the feed components, and both the liquid anode and salt are well mixed by a mechanical stirrer, chemical equlibrium is established between all impurities and the plutonium in the salt even before current is applied to the cell. Thus, impurities more electropositive than the liquid plutonium anode will be oxidized by Pu+3 and be taken up by the salt phase, while impurities in the electrolyte salt less electropositive than plutonium will be reduced by plutonium metal and be collected in the anode. 

Equilibrium constants calculated from the composition of saturated solutions are dependent on the accuracy of the thermodynamic model for the aqueous solution. The thermodynamics of single salt solutions of KC1 or KBr are very well known and have been modeled using the virial approach of Pitzer (13-15). The thermodynamics of aqueous mixtures of KC1 and KBr have also been well studied (16-17) and may be reliably modeled using the Pitzer equations. The Pitzer equations used here to calculate the solid phase equilibrium constants from the compositions of saturated aqueous solutions are given elsewhere (13-15, 18, 19). The Pitzer model parameters applicable to KCl-KBr-l O solutions are summarized in Table II. 

EXAMPLE 8.1 Reaction Equilibrium and Phase Equilibrium Models of Micellization. Research in which the CMC of an ionic surfactant M+ S is studied as a function of added salt, say M+X, ... 

An accurate representation of the phase equilibrium behavior is required to design or simulate any separation process. Equilibrium data for salt-free systems are usually correlated by one of a number of possible equations, such as those of Wilson, Van Laar, Margules, Redlich-Kister, etc. These correlations can then be used in the appropriate process model. It has become common to utilize parameters from such correlations to obtain insight into the fundamentals underlying the behavior of solutions and to predict the behavior of other solutions. This has been particularly true of the Wilson equation, which is shown below for a binary system. 

Two approaches have been used in correlating the phase equilibrium behavior of complex mixtures involving a non-volatile salt dissolved in a binary solvent mixture. Johnson and Furter (i) developed what appears to be the most popular approach by correlating the ratio of relative volatilities of the solvents as a function of salt concentration. Meranda and Furter (2) review this approach and present experimental determinations of the necessary parameters as a function of mole fraction of one of the solvents. 

Phase equilibrium was accomplished by weighing suitable quantities of the sodium form of the zeolite into 125 ml polycarbonate bottles which contained 50 ml of the salt solution. 

As more salt is added, excess salt is present in the solid phase and the solution composition is invariant. Therefore, the pH is constant and the product of the cation and anion activities equals the solubility product, as deLned in Equation 15.5, in the absence of cation or anion from other sources including molecular complex forms (Amis, 1983). At this point, more salt will not dissolve, and the salt concentration represents the solubility of the drug in the speciLc salt form. To conLrm that the salt solubility has been reached, it should be veriLed (Anderson and Conradi, 1985) that the solid salt phase in equilibrium with the solution has not been contaminated with the uncharged form precipitate. 

When the equilibrium mixture is permitted to cool rapidly, the heavier salt phase settles and solidifies, thus leaving the lighter metal phase on top as a liquid. Inasmuch as calcium metal starts to precipitate and settle before the solidification point of the salt phase is reached, some of the calcium is trapped in the salt phase and, together with the calcium which is dissolved by the molten salt, is not recovered in the following synthesis. Once the sodium chloride-calcium chloride layer has solidified, however, the precipitating calcium remains trapped in the metal layer. When the metal layer freezes, its composition consists of calcium crystals embedded in a sodium matrix which may be removed by preferential reaction with a lower alcohol.9... 

Wt of solute in salt phase Wt of solute in metal phase Kd = distribution coefficient (as defined above) s/m = salt to metal ratio by weight F = fraction of equilibrium attained 0 = effects of side reactions... 

Popello, LA., Suchkov, V.V., Grinberg, V.Ya., and Tolstoguzov, V.B. (1990). Liquid/Uquid phase equilibrium in globuUn/salt/water systems. Legumin. J. Sci. Food Agric., 51, 345-353. 

These led to matrix studies of the structure of ion pairs and triple ions, such as the thorough studies by Devlin and coworkers on matrix isolated alkali nitrate (21), chlorate (22) and perchlorate ion pairs (23 ). For relatively simple salts, such as the alkali halides, investigations were conducted into the structure of the dimeric salt species (6, 7, ), which is present in a gas phase equilibrium with the monomeric salt species. These dimers have been found to be very strongly bound in a cyclic structure. 

The thermodynamics of corrosive alkali salt-oxide interaction is not well established. In an assessment of research needs for materials in coal conversion, the need for carbonate-silicate melt studies, including activity and phase equilibrium measurements, was stressed (31 ). The lack of thermodynamic data for fused salts, and their reactions with oxides and alloys leading to models of hot corrosion, was also indicated. 

As mentioned above, the time-integral of the dissipation function takes on the value of the extensive generalised entropy production, 2, over a period, t under suitable circumstances. The main requirement is that the dynamics satisfies the condition know as the adiabatic incompressibility of phase space . In this case, 2, = —JtFefiV, where is the dissipative flux caused by the field, F, p = IKk T) where T is the temperature of the corresponding initial system and V is the volume of the system. An example where such a relation can be applied is if a molten salt at equilibrium was exposed to a constant electric field. In that case the entropy production would be directly proportional to the current induced, and the FR would describe the probability that it would be observed to flow in the + ve or — ve... 

Impurity enhancement techniques such as fraction collection and phase equilibrium purification can be used to provide enriched samples for use in the method development process.23 When using the fraction collection approach, one or more cuts (fractions) of the chromatographic separation of a bulk lot or mother liquor are isolated. The excess solvent in these fractions is then evaporated to achieve the desired concentration enhancement. These fractions typically contain extraneous peaks because of the presence of salts in the mobile phase or sample degradation during the concentration step. The salts can be removed by extraction and/or a LC cleanup step. To insure that these extraneous peaks/artifacts are not identified as key peaks for separation, the original bulk lot or mother liquor should be included in the method development sample set. The same holds true for phase-equilibrium-purification supernatants. 

Of particular interest to those in the natural gas industry is the phase diagram of hydrate systems in the presence of inhibitors. Fig. 3 shows the phase diagram for methane hydrates in the presence of methanol and a NaCl and KCl mixture. The solid line is the three-phase equilibrium curve for methane in pure water. As seen from Fig. 3, forming hydrates in the presence of either an alcohol or salt increases the pressure required for gas hydrate formation, at a given temperature. 

Of the above-mentioned techniques, thermodynamic inhibitors, which include alcohols, salts, and glycols, are by far the most prevalent. For example, adding methanol to a natural gas will shift the equilibrium conditions so that a higher pressure is required to form hydrates, at a given temperature, as illustrated for methane in Fig. 3. Methods for estimating the saturation water content of natural gases and amounts of methanol or glycol required to suppress hydrate formation are discussed by Katz, Sloan,and Campbell. Current practice for the estimations is to use computer software based on phase equilibrium calculations. ... 

Elgin, J. C., and J. J. Weinstock. 1959. Phase equilibrium at elevated pressures in ternary systems of ethylene and water with organic liquids Salting out with a supercritical gas. J. Chem. Eng. Data 4 3. 

Consider the system consisting of Glauber s salt in equilibrium with solution and vapour. If these three phases are analysed, the composition of the solid wilLhe.. expressed by loH O that of the... 

This brief survey of applied phase-equilibrium thermodynamics can do no mote than summarize the main ideas that constitute ihe present state of ibe art. Attentina is restricted to relatively simple mixtures as encountered in the patrolenm. natural gas. and petmchemical industries unfortunately, limited space does not allow discussion of other important systems such as polymer mixtures, electrolyte solutions, metallic alloys, molien salts, refractories (such as ceramics), or aqueous solutions of biologically impurlant solutes, However, it is not only lack of space that is responsible for these omissions because, at present, thermodynamic knowledge is severely limited for lhese more complex systems,... 

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