Miscible system

An adequate prediction of multicomponent vapor-liquid equilibria requires an accurate description of the phase equilibria for the binary systems. We have reduced a large body of binary data including a variety of systems containing, for example, alcohols, ethers, ketones, organic acids, water, and hydrocarbons with the UNIQUAC equation. Experience has shown it to do as well as any of the other common models. V7hen all types of mixtures are considered, including partially miscible systems, the... 

There are many simple two-parameter equations for Hquid mixture constituents, including the Wilson (25), Margules (2,3,18), van Laar (3,26), nonrandom two-Hquid (NRTI.v) (27), and universal quasichemical (UNIQUAC) (28) equations. In the case of the NRTL model, one of the three adjustable parameters has been found to be relatively constant within some homologous series, so NRTL is essentially a two-parameter equation. The third parameter is usually treated as a constant which is set according to the type of chemical system (27). A third parameter for Wilson s equation has also been suggested for use with partially miscible systems (29,30,31). These equations all require experimental data to fit the adjustable constants. Simple equations of this type have the additional attraction of being useful for hand calculations. 

Renon s [58] technique for predicting vapor-liquid relationships is applicable to partially miscible systems as well as those with complete miscibility. This is described in the reference above and in Reference 54. 

Since Ag is a function of pressure, it follows that, under certain conditions, a change in pressure may produce immiscibility in a completely miscible system, or, conversely, such a change may produce complete miscibility in a partially immiscible system. The effect of pressure on miscibility in binary liquid mixtures is closely connected with the volume change on mixing, as indicated by the exact relation... 

When a reversible transition from one monolayer phase to another can be observed in the 11/A isotherm (usually evidenced by a sharp discontinuity or plateau in the phase diagram), a two-dimensional version of the Gibbs phase rule (Gibbs, 1948) may be applied. The transition pressure for a phase change in one or both of the film components can be monitored as a function of film composition, with an ideally miscible system following the relation (12). A completely immiscible system will not follow this ideal law, but will... 

A rams, D. S., and J. M. Prausnitz, "Statistical Thermodynamics of Liquid Mixtures A New Expression for the Excess Gibbs Energy of Partly or Completely Miscible Systems," AIChE J., 1975, 21, 116. 

Note 3 A miscible system can be thermodynamically stable or metastable (see Note 4 in Definition 1.2). 

Note 1 Use of the term compatibility to describe miscible systems is discouraged. 

Note 3 The miscible system can be thermodynamically stable or metastable. 

Abrams, D.S. and Prausnitz, J.M., Statistical thermodynamics of liquid mixtures a new expression for the excess Gibbs energy of partly or completely miscible systems, A. I. Chem. E. /., 21 (1975) 116-128. 

As an alternative to distillation, extraetion with a eo-solvent that is poorly mis-eible with the ionie liquid has often been used. There are many solvents that can be used to extract product from the ionic liquid phase, whether from a monophase reaction or from a partially miscible system. Typical solvents are alkanes and ethers (15). Supercritical CO2 (SCCO2) was recently shown to be a potential alternative solvent for extraction of organics from ionic liquids (22). CO2 has a remarkably high solubility in ionic liquids. The SCCO2 dissolves quite well in ionic liquids to facilitate extraction, but there is no appreciable ionic liquid solubilization in the CO2 phase in the supercritical state. As a result, pure products can be recovered. For example, about 0.5 mol fraction of CO2 was dissolved at 40°C and 50 bar pressure in [BMIMJPFe, but the total volume was only swelled by 10%. Therefore, supercritical CO2 may be applied to extract a wide variety of solutes from ionic liquids, without product contamination by the ionic liquid (29). 

In the same book, on p 462 is described "Colorimetric Method for Determining Trace Quantities of Hydroxy Compounds . This method developed by V.W. Reid R.K. Trulove and described in Analyst 77, 325(1952) uses ceric ammonium reagent and is applicable to determination of small quantities of alcohol in aqueous or water miscible systems [Compare with J. Lamond, Analyst 74, 560—61 (1949), listed here as Ref 5, under "Ethanol, Etber, Acetone and Water Determinations in Solvents Used in Manufacture of Smokeless Propellants, as Described in the Literature ]... 

A New Approach to the Calculation of Liquid-Vapor Equilibrium Data for Partially Miscible Systems Containing Salts at Saturation... 

The problems of smoothing are most acute with partially miscible systems, and it is with these that the present paper deals. 

Azeotropic and Partially Miscible Systems. Azeotropic mixtures are those whose vapor and liquid equilibrium compositions are identical. Their x-y lines cross or touch the diagonal. Partially miscible substances form a vapor phase of constant composition over the entire range of two-phase liquid compositions usually the horizontal portion of the x-y plot intersects the diagonal, but those of a few mixtures do not, notably those of mixtures of methylethylketone and phenol with water. Separation of azeotropic mixtures sometimes can be effected in several towers at different pressures, as illustrated by Example 13.6 for ethanol-water mixtures. Partially miscible constant boiling mixtures usually can be separated with two towers and a condensate phase separator, as done in Example 13.7 for n-butanol and water. 

Figure 13.28. Vapor-liquid equilibria of some azeotropic and partially miscible liquids, (a) Effect of pressure on vapor-liquid equilibria of a typical homogeneous azeotropic mixture, acetone and water, (b) Uncommon behavior of the partially miscible system of methylethylketone and water whose two-phase boundary does not extend byond the y = x line, (c) x-y diagram of a partially miscible system represented by the Margules equation with the given parameters and vapor pressures Pj = 3, = 1 atm the broken line is not physically significant but is...

Miscible systems invariably form a single phase and are transparent. Their physical properties are directly related to the properties of the individual components and the mole fractions of these in the mixture, the glass temperature (Tg) composition diagram of such mixtures is Unear between the two Tg of the individual components. Since, however, the majority of would be interesting polymer combinations are immiscible, they separate into two phases and become practically uninteresting because of the relatively weak adhesion between the two phases. 

In partially miscible systems with y typically in the range 20 to 200, appreciable dissolution of water in the chemical phase may occur, thus the vapor pressure Ps is not that of the pure chemical but of the somewhat diluted chemical phase. 

Although some miscible systems exhibit Tg-composition dependencies as defined by these simple equations, many blends cannot be correlated by them or any of the other well known expressions such as the Kelly-Bueche, Gordon-Taly-lor or the Gibbs-Dimarzio relationships [126-128]. However, the existence of thermodynamic miscibility has not been proven for epoxy-polyimide systems. 

As shown in a previous section, fluorinated nadimides exhibit the best thermo-oxidative behavior. NR 150 linear polymers are prepared by reaction of HFDE and a mixture of para- and raefa-phenylenediamine. A semi-IPN was prepared by addition of a 150 °C staged PMR-15 to a solution of the NR 150 precursor. The solution was used for the composite manufacture. After curing at 250 °C, the DSC diagram showed two peaks in agreement with a non-miscible system. After curing, the Glc of the blend is higher than that of pure PMR-15 (Table 8) [119]. 

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