Miscibility binary systems

Adrian et al. (2000) have reported a novel high-pressure liquid-liquid extraction process with reference to processing in biotechnology the example of cardiac glycosides (digitoxin and digoxin) is cited. A completely miscible, binary system of water and a hydrophobic organic solvent like ethanol can split into two liquid phases when a near-critical gas (e.g. CO2) is added. The near-critical C02/water/l-propanol system is reported, for which possibilities for industrial exploitation exist. 

Movements in the plane of the interface result from local variations of interfacial tension during the course of mass transfer. These variations may be produced by local variations of any quantity which affects the interfacial tension. Interfaeial motions have been ascribed to variations in interfacial concentration (H6, P6, S33), temperature (A9, P6), and electrical properties (AlO, B19). In ternary systems, variations in concentration are the major factor causing interfacial motion in partially miscible binary systems, interfacial temperature variations due to heat of solution effects are usually the cause. 

FIGURE A.l. Vapor pressures versus condensed-phase composition for completely miscible binary systems. 

With that in mind the author and co-workers have been carrying out experiments with many hquid-liquid systems and in this paper the results obtained in recent years are summarised. Sections 2 and 3 include theory and the definition of interfacial convection, which give the background for the analysis of the experimental results shown later. Section 4 describes the experimental equipment and methods used to obtain the results presented in Section 5, for hquid-hquid partially miscible binary systems with and without surfactants Section 6, for the same systems under microgravity conditions and Section 7, for ternary systems with and without surfactants. Section 8 covers work previously done on stability criteria to predict Marangoni convection in hquid-hquid systems. In Section 9 some of the results presented in the previous sections are discussed. Relevant results obtained in the field of Biotechnology by the author and co-workers are mentioned in Section 10. Conclusions and future work follow in Section 11. 

Most of the fundamental work is being conducted on the transfer of a single solute between two immiscible solvents and there is a number of such systems specially recommended for such investigations by the European Federation of Chemical Engineering (1). Partially miscible binary systems may also be used for this purpose as examj)les of mixtures with low interfacial tension. In practice, however, partially miscible multicomponent systems are often encountered, e.g. in the removal of aromatics from lubricating oil. This represents an area which is not particularly well researched and documented. 

K,a and K a, unless partially miscible binary systems are ei foyed. iSe fundamentals of mass transfer are therefore often studied in equipment of constant interfacial area such as the stirred cells of Lewis (28), Austin (30-31), Prochazka (32) or Nitsch (32-35) or the drop-forming device of Goltz (36, 37). The correlation of Davies (38) seems to give best result for horizontal interfaces in stirred cells. 

The diagram refers to the enthalpy relationships of a completely miscible binary system at a constant pressure of 1 atm. The mole fraction of component B is plotted horizontally from left to right and the enthalpy of the mixture, relative to the pure components in chosen reference states, is plotted vertically. Curve CD represents the enthalpy of the liquid phase, at its boiling-point, as a fimction of composition. Curve EF represents the enthalpy of the vapour above the boiling liquid as a function of its own composition. (Thus CE and DF are the enthalpies of vaporization of A and B respectively.) OH and IJ are typical tie-lines, i.e. a boiling liquid of composition ( is in equilibrium with vapour of composition H,... 

Show that if the isothermal P-x curve for a miscible binary system passes through a maximum, there is an azeotrope at the point of maximum. 

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... 

Using the ternary tie-line data and the binary VLE data for the miscible binary pairs, the optimum binary parameters are obtained for each ternary of the type 1-2-i for i = 3. .. m. This results in multiple sets of the parameters for the 1-2 binary, since this binary occurs in each of the ternaries containing two liquid phases. To determine a single set of parameters to represent the 1-2 binary system, the values obtained from initial data reduction of each of the ternary systems are plotted with their approximate confidence ellipses. We choose a single optimum set from the intersection of the confidence ellipses. Finally, with the parameters for the 1-2 binary set at their optimum value, the parameters are adjusted for the remaining miscible binary in each ternary, i.e. the parameters for the 2-i binary system in each ternary of the type 1-2-i for i = 3. .. m. This adjustment is made, again, using the ternary tie-line data and binary VLE data. 

Alloys. GaUium has complete miscibility in the hquid state with aluminum, indium, tin, and zinc. No compounds are formed. However, these binary systems form simple eutectics having the following properties ... 

Wilson s [77] equation has been found to be quite accurate in predicting the vapor-liquid relationships and activity coefficients for miscible liquid systems. The results can be expanded to as many components in a multicomponent system as may be needed without any additional data other than for a binary system. This makes Wilson s and... 

Partial mutual solubility in the solid state. Fig. 2.9 shows different examples of binary systems for which there is still a complete miscibility in the liquid state, but only a limited mutual solubility in the solid state, depending on the temperature. The Ni-Au system, for instance, still has complete mutual solid solubility but only at high temperature, that is, by decreasing the temperature, de-mixing... 

All the phase diagrams reported above show a complete mutual solubility in the liquid state. The formation of a single phase in the liquid state corresponds to behaviour frequently observed in intermetallic (binary and complex) systems. Examples, however, of a degree of immiscibility in the liquid state are also found in selected intermetallic systems. Fig. 2.16 shows a few binary systems in which such immiscibility can be observed (existence of miscibility gaps in the liquid state). All the three... 

To our knowledge, direct experimental data on amphibole mixtures have been obtained only for the (pseudo)binary system actinolite-cummingtonite (Cameron, 1975) at Ptotai = -Phjo = 2 kbar and for the (pseudo)binary system tremolite-pargasite at Ptotai = PhjO = 1 kbar (Oba, 1980). In both cases, an extended miscibility gap (or solvus field in the second case), is evident at low T(i.e., 600 to 800 °C), which is indicative of strong positive interactions in the solid mixtures. Unmixing of other compositional terms is also evident in microprobe investigations (see Ghose, 1982 for an appropriate discussion). 

Figure 7.2 G-X and T-X plots for a binary system with a molten phase with complete miscibility of components at all T conditions and a solid phase in which components are totally immiscible at all proportions (mechanical mixture, 7 = 7 + V )-...

Phosphorus and sulphur are only sparingly soluble in the liquid, but sulphur monochloride is miscible.10 The binary systems formed by liquid sulphur dioxide with the tetrachlorides of carbon, tin and titanium, and with the tetrabromide of tin, have been investigated. The liquids are only partly miscible at lower temperatures and compound... 

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