Pseudobinary mixture

Figure A2.5.30. Left-hand side Eight hypothetical phase diagrams (A through H) for ternary mixtures of d-and /-enantiomers with an optically inactive third component. Note the syimnetry about a line corresponding to a racemic mixture. Right-hand side Four T, x diagrams ((a) tlirough (d)) for pseudobinary mixtures of a racemic mixture of enantiomers with an optically inactive third component. Reproduced from [37] 1984 Phase Transitions and Critical Phenomena ed C Domb and J Lebowitz, vol 9, eh 2, Knobler C M and Scott R L Multicritical points in fluid mixtures. Experimental studies pp 213-14, (Copyright 1984) by pennission of the publisher Academic Press.

Density and Specific Gravity For binary or pseudobinary mixtures of hquids or gases or a solution of a solid or gas in a solvent, the density is a funcrion of the composition at a given temperature and pressure. Specific gravity is the ratio of the density of a noncompress-ible substance to the density of water at the same physical conditions. For nonideal solutions, empirical calibration will give the relationship between density and composition. Several types of measuring devices are described below. 

Most columns handle multicomponent feeds. But many can be approximated by binary or pseudobinary mixtures. For this example, however, we will make several additional assumptions and idealizations that are sometimes valid but more frequently are only cmde approximations. 

Figure 5.51 A shows in greater detail how the stability field of biotite (phlogo-pite-annite pseudobinary mixture) is affected by /o2" conditions for a bulk pres-...

The compositions and quantities of the equilibrium gas and liquid are computed in the usual manner. Then the liquid is equated to a pseudobinary mixture consisting of the lightest component of the liquid and a hypothetical heavy component. 

Minimum reflux for binary or pseudobinary mixtures is given by the following when separation is esentially complete (xD — 1) and D/F is the ratio of overhead product and feed rates ... 

Strictly speaking, the convergence pressure of a binary mixture equals the critical pressure of the mixture only if the system temperature coincides with the mixture critical temperature. For multi-component mixtures, furthermore, the convergence pressure depends on both the temperature and the liquid composition of mixture. For convenience, a multicomponent mixture is treated as a pseudobinary mixture in this K-value approach. The pseudobinary mixture consists of a light component, which is the lightest component present in not less than 0.001 mol fraction in the liquid, and a pseudoheavy... 

The diffusional molar flux of component A is expressed via Pick s law in terms of the concentration gradient of A, only. Coupling between the diffusional mass flux of one species and all the independent mass fractions in the liquid phase is avoided by modeling this multicomponent diffusion problem as if it were a pseudobinary mixture. 

However, traditional chemical thermodynamics is based on mole fractions of discrete components. Thus, when it is applied to polydisperse systems it has been usual to spht the continuous distribution function into an arbitrary number of pseudo-components. In many cases dealing, for example, with a solution of a polydisperse homopolymer in a solvent (the pseudobinary mixture), only two pseudo-components were chosen (reproducing number and mass averages of molar mass of the polymer) which, indeed, are able to describe some main features of the liquid-liquid equilibrium in the polydisperse mixture [1-3]. In systems with random copolymers the mass average of the chemical distribution is usually chosen as an additional parameter for the description of the pseudo-components. However, the pseudo-component method is a crude and arbitrary procedure for polydisperse systems. 

In a true moving bed process, the solid phase (adsorbent) and the fluid phase (eluent) are moved in countercurrent directions. Free adsorbent is fed at the top of the column and the mobile phase is pumped in an upward direction. The adsorbent slides downward and selectively adsorbs compounds from the feed, which is introduced into the system at the middle part of the column. At the lower part of the column, the loaded adsorbent is racked off Compounds without affinity for the adsorbent will travel upward with the mobile phase and can be harvested at the top of the column. TMB can separate a mixture into two different components therefore, the system is capable of separating only binary and pseudobinary mixtures. 

The formation of IL/O microemulsions in mixtures of [bmim][BFJ (IL) and cyclohexane, stabilized by the nonionic surfactant, TX-lOO has been proved [30]. Three-component mixtures could form IL/O microemulsions of well-defined droplet size determined by fixing the water content (mole ratio of IL to TX-lOO) [30,48,49]. An upper critical point (T) was observed in the mixture [([bmim][BFJ/ TX-lOO)-I-cyclohexane] with fixed water content (mole ratio of [bmim][BFJ to TX-lOO) [50]. The mixture separated into two microemulsion phases of different composition but with the same composition below as occurred in other systems [48]. The microemulsion system, [bmim][BF ]/TX-100 +cyclohexane, could be regarded as a pseudobinary mixture of [bmim][BF ]/TX-100 IL droplets dispersed in the cyclohexane continuous phase. Therefore, the phase behavior could be depicted in a two-dimensional diagram with concentration of droplets along the abscissa and temperature along the ordinate. A coexistence curve of temperature (T) against a concentration variable, such as volume fraction ( ), could then be drawn in the same way as it was done for pseudobinary mixtures in AOT/water/decane micro-emulsions [48]. 

Titrating a binary or a pseudobinary mixture with the third component... 

Schiebel and Montross (Ref. 13) developed a method for making multicomponent design calculations on the basis of a pseudobinary mixture. A modification of this method by Bailey and Coates (Ref, 1) will be reviewed. 

Minimum reflux for binary or pseudobinary mixtures is given by the following when separation... 

There is one imphcit condition, not part of the design specifications, that needs to be considered in the bottom-up design. Because the flash unit separates a pseudobinary mixture (A/C and B/D), its temperature and pressure cannot be independently specified. Thus, either Tp or Pp, but not both, can be controlled. 

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