Immiscibility gap

Here Xg is the composition at the critical point. Let us now calculate the immiscibility gap and the spinodal line for a regular solution A-B ... 

Both the binodal line, defining the immiscibility gap, and the spinodal line are for a regular solution symmetrical about xA = xB = 0.5. This is shown in Figure 5.7(a), where theoretical predictions of the miscibility gaps in selected semiconductor systems are given [15],... 

For the niobium-copper system different phase diagrams of the simple eutectic type (with the eutectic point very close to Cu) have been proposed, either with an S-shaped near horizontal liquidus line or with a monotectic equilibrium. It was stated that the presence of about 0.3 at.% O can induce the monotectic reaction to occur, whereas if a lesser amount of oxygen is present no immiscibility gap is observed in the liquid. 

Generally in cycloalkanes, solubility is very similar to that in alkanes. The solubility of imidazolium IL, l-ethyl-3-methylimidazolium tosylate, [C2Cilm][TOS] in cyclohexane and cycloheptane displays a very large miscibility gap in the liquid phase (close to its melting temperature) [101,102]. Ammonium IL, [(Ci)2C4HOC2N]Br, has shown lower solubility in cyclohexane than in heptane and the immiscibility gap was from Xjl = 0.02 to 0.90 [53]. 

Changing the solvent from an aliphatic hydrocarbon to an aromahc hydrocarbon demonstrates that the interaction is most likely due to n-n interactions between the oxygen atom of the IL and the benzene ring. Solid at room temperature ILs present usually much lower immiscibility gap in benzene than in alkanes or cycloalkanes. For example, [(C4H90CH2)2lm][BL4] shows... 

The separation of acetonitrile from acetonitrile by extractive distillation with water can be done in a more efficient two-column heat integrated setup. The separation of acrylonitrile from water, which is hindered by the existence of an azeotrope, can actually take advantage of the large immiscibility gap. Valuable byproducts, such as HCN and acetonitrile can be efficiently separated. Chemical conversion can solve the separation of difficult impurities, such as acroleine. 

FIGURE 16.39 Schematic of a phase diagram for a ceramic B and a metal A without any solubility of the solid ceramic A in the liquid A. When both A and B are liquid we have an immiscibility gap. 

The phase diagram of the Fe-0 binary system at ambient pressure exhibits a large liquid immiscibility gap (Baker, 1992 Figure 5(b)). 

This behavior of the mixtures of ionic liquids with molecular solvents was recently studied, experimentally and by molecular simulation, by Del Popolo et al. [45], for mixtures of [C4C1im][PF6] with naphthalene over the entire composition range. As in the previously discussed mixtures of ionic liquids with aromatics, naphthalene is able to cleave some interionic contacts, but not all of them. With compositions in which the ionic liquid is more dilute, the ionic network subsists in the shape of filaments of continuous cation-anion contacts in a medium composed mostly of the molecular fluid. If dilution is increased, then disjoint ionic clusters, down to ion pairs, will form. Some aromatic compounds are not sufficiently good solvents to the ionic liquids and cannot disrupt the ionic network, leading to an immiscibility gap (as is the case with benzene and toluene, for example, at mole fractions around 0.7-0.8 [46, 47],... 

Another experiment was carried out by quenching the 50/50 blend from the initial temperature of 127°C (i.e., the single phase) to a temperature of 11°C that lies underneath the liquidus line and the UCST spinodal. The same set of parameters for the iPP/EPDM blend was employed except for the thermodynamic parameter/g = 0.8 to account for the buried UCST immiscibility gap and the kinetic... 

The phenomenon of liquid immiscibility in silicate melts has been studied both theoretically and experimentally. The results of the theoretical analysis suggest that a criterion can be developed for the prediction of liquid immiscibility in silicate melts several examples of liquid immiscibility gaps were observed in an experimental investigation. ... 

Water and 1-butanol form a heterogeneous azeotrope and an immiscibility gap over a limited region of ternary compositions exists. The stability of the stationary points of the system and the distillation line map modeled by UNIQUAC are shown on Figure 3a. One distillation boundary, miming from methanol (unstable node) to the binary heteroazeotrope (saddle) divides the composition space in two regions. The system belongs to Serafimov s topological class 1.0-2 (Hilmen, 2002). 

The heavier elements sodium to cesium are miscible with one another in all proportions in the liquid state, and only in the case of mixtures with lithium does immiscibility arise. Lithium-sodium mixtures are miscible in all proportions above 305°C, but below this temperature the mixture separates into two separate phases. At 171°C, the immiscibility gap extends from 10.1 to 97.0 at.% of lithium. Liquid lithium is even less miscible with the heavier alkali metals. When liquid lithium and liquid potassium are mixed, two immiscible liquid phases are formed at 300°C the lithium phase contains 0.43 at.% of potassium, and the potassium phase contains only 0.024 at.% of lithium. The miscibility of lithium with rubidium and cesium is negligible. 

Fig. 1, Ce-Li-Ge, isothermal section at 470 K. The dashed line indicates the liquid immiscibility gap region.

---