Line, azeotropic critical

Exceptions to these general rules about behaviour in the critical region occur at special points on a binary mixture critical line - examples are extrema in pressure or temperature, points where azeotrope lines join critical lines, or double points (intersections of two critical lines). Moreover, in the special higher-order critical points ( tricritical points ) found in systems with a greater number of variables (three- and four-component fluid mixtures He + He), different exponents may be found. ... 

Fig. 15. Isobaric vapor—liquid—liquid (VLLE) phase diagrams for the ethanol—water—benzene system at 101.3 kPa (D-D) representHquid—Hquid tie-lines (A—A), the vapor line I, homogeneous azeotropes , heterogeneous azeotropes Horsley s azeotropes, (a) Calculated, where A is the end poiat of the vapor line and the numbers correspond to boiling temperatures ia °C of 1, 70.50 2, 68.55 3, 67.46 4, 66.88 5, 66.59 6, 66.46 7, 66.47, and 8, the critical poiat, 66.48. (b) Experimental, where A is the critical poiat at 64.90°C and the numbers correspond to boiling temperatures ia °C of 1, 67 2, 65.5 3, 65.0 ...

Figure 14.11 The critical locus for (xiQHp + x2C6F6), a system with a maximum boiling azeotrope. In (A), the circles represent the critical points (a and b) of pure components (1) and (2) the solid lines represent (vapor + liquid) equilibrium for the pure substances the dashed line is the critical locus, and the short-dashed line represents the azeotrope composition, which intersects the critical locus at point c. (B) shows the intersection of the (vapor + liquid) equilibrium lines with the critical locus.

As tire pressure increases, line C D becomes shorter and shorter (indicated in Fig. 14.17 by lines CD and C"D"), until at point M it dimiirishes to a differential length. For still Irigher pressures (P4) the temperature is above tire critical-solution temperature, and there is but a single hquid phase. The diagram then represents two-phase VLE, and it has the form of Fig. 10.9(d), exhibiting a minimum-boiling azeotrope. 

In general, the steps of this separations system synthesis method for nonideal mixtures involving azeotropes include examination of the RCM representation (overlaid with vapor-liquid equlibria (VLE) pinch information, liquid-liquid equlibria (LLE) binodal curves and tie lines, and. solid-liquid equlibria (SLE) phase diagrams if appropriate) determination of the critical thermodynamic features to be avoided (e.g., pinched regions), overcome (e.g., necessary distillation... 

If we consider a type V system, instead, as the temperature increases, an azeotrope appears. The binary system DMSO-COj is of type I and the presence of Cefonicid at 40 °C does not modify this characteristic. But when the temperature is increased at 60 °C, a type V situation is probably produced. It means that an azeotrope is formed the critical line is not continuous, but is formed by two lines, which start... 

In those cases, where rj and V2 both either less or greater than unity, the curves of Figure 8.2 cross the line Fj = fj. The points of interception represent the occurrence of azeotropic oopolymerization that is, polymerization proceeds without a change in the composition of either the feed or the copolymer. For azeotropic copolymerization the solution to Equation 8.5 with d[M[]/d[M2] = [Mi]/[M2] gives the critical composition. 

If we substitute (9.3.23) into (9.3.13), we find that critical points occur at extrema on isothermal Px and Py plots. Likewise if we substitute (9.3.23) into (9.3.16), we find that critical points occur at extrema on isobaric Tx and Ty plots. However, the converses of these statements are not true extrema on such plots are not necessarily critical points we have already seen that they could be azeotropes. Further, those extrema mean that the numerator and denominator in the triple product rule (9.3.18) are both zero however, that ratio need not be zero, so on PT diagrams, critical points rarely occur at extrema of constant-composition lines. 

Class A. These binaries never exhibit LLE and therefore have no critical end points, although many form azeotropes. However, most mixtures in class A would exhibit LLE with UCEPs, except that solidification occurs at temperatures above that at which a liquid-liquid split would occur. Although the mixture critical line is continuous, the mixture critical T and P may not be bounded by the pure-component critical points. In a few class A mixtures phase splits occur at temperatures above the critical points of both pures. This could hardly be called liquid-liquid equilibrium instead, such an immisdbility is called gas-gas equilibrium (GGE). Three kinds of gas-gas equilibria have been identified that in class A is called GGE of the third kind. 

Chang, R. E, Doiron, T. Pegg, I. L. (1986). Decay rate of critical fluctuations in ethane + carbon dioxide mixtures near the critical line including the critical azeotrope, /nt. J. Thermophys., 7,295—304. 

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