Maximum boiling azeotrope

Vinyl acetate-ethyl acetate Propane-propylene Ethanol-isopropanol Hydrochloric acid-water Nitric acid-water Close-boiling Close-boihng Close-boihng Maximum-boiling azeotrope Maximum-boiling azeotrope Phenol, aromatics Acrylonitrile Methyl benzoate Sulfuric acid, calcium chloride for salt process Sulfuric acid, magnesium nitrate for salt process Alternative to simple distillation Alternative to simple distillation, adsorption Alternative to simple distillation Sulfuric acid process rehes heavily on boundary curvature Sulfuric acid process rehes heavily on boundary curvature... 

Minimum-Boiling Azeotropes Maximum-Boiling Azeotropes Azeotropes on Purpose... 

Two types of azeotrope, maximum boiling point (Figure 3.9(a)) and minimum boiling point (Figure 3.9(b)), can be represented on this type of diagram. 

Figure 9.16 Different types of liquid-vapor phase diagrams for a binary liquid mixture of component A and B as functions of the mole fraction of the component with the higher boiling temperature, (a) The phase diagram for a system with a low-boiling azeotrope (minimum boiling point) and (b) the phase diagram for a system with a high-boiling azeotrope (maximum boiling point). The arrows show how the paths for various distillation processes depend upon the position of the initial composition relative to the azeotrope.

Figure 3.9a shows the temperature-composition diagram for a maximum-boiling azeotrope that is sensitive to changes in pressure. Again, this can be separated using two columns operating at different pressures, as shown in Fig. 3.96. Feed with, say, rpA = 0.8 is fed to the high-pressure column. This produces relatively pure A in the overheads and an azeotrope with xba = 0.2, Xbb = 0.8 in the bottoms. This azeotrope is then fed to a low-pressure column, which produces relatively pure B in the overhead and an azeotrope with 3 ba = 0.5, BB = 0.5 in the bottoms. This azeotrope is added to the feed to the high-pressure column.

Figure 3.9 Separation of a maximum boiling azeotrope by pressure change. (From Holland, Gallun, and Lockett, Chemical Engineering, March 23, 1981, 88 185-200 reproduced by permission.)...

Examples of azeotropic mixtures of maximum boiling point are tabulated below these are not as numerous as those of minimum boiling point. 

Generally more favorable for maximum boiling azeotrope because the recycles between columns are bottoms streams, pure products are distillates recycle not as energy-intensive, products distilled once. 

Fig. 5. Boiling poiat (a) and phase diagram (b) for a maximum boiling biaary azeotropic system at coastant pressure. B and C, D are representative...

All extractive distillations correspond to one of three possible residue curve maps one for mixtures containing minimum boiling azeotropes, one for mixtures containing maximum boiling azeotropes, and one for nonazeotropic mixtures. Thus extractive distillations can be divided into these three categories. 

Fig. 10. Residue curve map for separating a maximum boiling azeotrope using a high boiling solvent where (-----------------) represents the distillation boundary and...

I represents the maximum boiling azeotrope and (b), column sequence (67). 

FIG. 13-12 Liq iiid boiling points and vapor condensation temperatures for maximum-boiling azeotrope mixtures of chloroform and acetone at 101.3 kPa (1 atm) total pressure. 

FIG. 13-57 (Continued) Schematic isoharic-phase diagrams for binary azeotropic mixtures, (b) Homogeneous maximum-boiling azeotrope. 

Schematic DRD shown in Fig. 13-59 are particularly useful in determining the imphcations of possibly unknown ternary saddle azeotropes by postulating position 7 at interior positions in the temperature profile. It should also be noted that some combinations of binary azeotropes require the existence of a ternaiy saddle azeotrope. As an example, consider the system acetone (56.4°C), chloroform (61.2°C), and methanol (64.7°C). Methanol forms minimum-boiling azeotropes with both acetone (54.6°C) and chloroform (53.5°C), and acetone-chloroform forms a maximum-boiling azeotrope (64.5°C). Experimentally there are no data for maximum or minimum-boiling ternaiy azeotropes. The temperature profile for this system is 461325, which from Table 13-16 is consistent with DRD 040 and DRD 042. However, Table 13-16 also indicates that the pure component and binary azeotrope data are consistent with three temperature profiles involving a ternaiy saddle azeotrope, namely 4671325, 4617325, and 4613725. All three of these temperature profiles correspond to DRD 107. Experimental residue cui ve trajectories for the acetone-...

Hydrochloric acid-water Maximum boiling azeotrope Sulfuric acid Alternative to salt extractive... 

HBSA + HBSA HBSA-1- HBAD HBSA-1- HBA HBAD -1- HBAD HBAD + HBA Usually positive deviations some give maximum-boiling azeotropes H-bonds broken and formed... 

This example clearly shows good distribution because of a negative deviation from Raonlt s lawin the extract layer. The activity coefficient of acetone is less than 1.0 in the chloroform layer. However, there is another problem because acetone and chloroform reach a maximum-boiling-point azeotrope composition and cannot be separated completely by distillation at atmospheric pressure. 

An important system in distillation is an azeotropic mixture. An azeotrope is a liquid mixture which when vaporized, produces the same composition as the liquid. The VLE plots illustrated in Figure 11 show two different azeotropic systems one with a minimum boiling point and one with a maximum boiling point. In both plots, the equilibrium curves cross the diagonal lines. 

Figure 17.5 Liquid/gas phase equilibria for the systems HF/H2O and HCI/H2O showing the formation of maximum boiling azeotropes as described in the text.

For maximum boiling azeotropes the partial pressures will be less than predicted by Raoult s Law and the activity coefficients will be less than 1.0. 

Figure 8-9. Acetone (1)-chloroform (2) system at 760 mm Hg. Maximum boiling azeotrope formed by negative deviations from Raoult s Law (dashed lines). Used by permission, Smith, B.D., Design of EquiUbnum Stage Processes, McGraw-Hill, New York, (1963), all rights reserved.

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