Binary distillation azeotropic mixtures

The breaking up of azeotropic mixtures. The behaviour of constant boiling point mixtures simulates that of a pure compound, because the composition of the liquid phase is identical with that of the vapour phase. The composition, however, depends upon the pressure at which the distillation is conducted and also rarely corresponds to stoichiometric proportions. The methods adopted in practice will of necessity depend upon the nature of the components of the binary azeotropic mixture, and include —... 

The first binary mixture quantitatively studied was the water-thiazole system, thiazole being a very hygroscopic compound (104), Determining the purity of thiazole sample obtained by distillation, Metzger and Distel-dorf (287) observed the existence of a stable azeotropic mixture, the characteristics of which are the following ... 

Minimum Boiling Azeotropes. AH extractive distillations of binary minimum boiling azeotropic mixtures are represented by the residue curve map and column sequence shown in Figure 6b. Typical tray-by-tray composition profiles are shown in Figure 7. 

Esters of low volatility are accesible via several types of esterification. In the case of esters of butyl and amyl alcohols, water is removed as a binary azeotropic mixture with the alcohol. To produce esters of the lower alcohols (methyl, ethyl, propyl), it may be necessary to add a hydrocarbon such as benzene or toluene to increase the amount of distilled water. With high boiling alcohols, ie, benzyl, furfuryl, and P-phenylethyl, an accessory azeotroping Hquid is useful to eliminate the water by distillation. 

The azeotrope in the ethanol-water binary system has a composition of 89 mole per cent of ethanol(14). Starting with a mixture containing a lower proportion of ethanol, it is not possible to obtain a product richer in ethanol than this by normal binary distillation. Near azeotropic conditions exist at points marked in Figure 11.44. The addition of the relatively non-polar benzene entrainer serves to volatilise water, a highly polar molecule,... 

Data of Azeotropes. The choice of azeotropic entrainer for a desired separation is much more restricted than that of solvents for extractive distillation, although many azeotropic data are known. The most extensive compilation is that of Ogorodnikov, Lesteva, and Kogan (Handbook of Azeotropic Mixtures (in Russian), 1971). It contains data of 21,069 systems, of which 1274 are ternary, 60 multicomponent, and the rest binary. Another compilation Handbook of Chemistry and Physics, 60th ed., CRC Press, Boca Raton, FL, 1979) has data of 685 binary and 119 ternary azeotropes. Shorter lists with grouping according to the major substances also are available in Lange s Handbook of Chemistry... 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

Nitromethane shows the simplest residue curve map with one unstable curved separatrix dividing the triangle in two basic distillation regions. Methanol and acetonitrile give rise two binary azeotropic mixtures and three distillation regions that are bounded by two unstable curved separatrices. Water shows the most complicated residue curve maps, due to the presence of a ternary azeotrope and a miscibility gap with both the n-hexane and the ethyl acetate component. In all four cases, the heteroazeotrope (binary or ternary) has the lowest boiling temperature of the system. As it can be seen in Table 3, all entrainers except water provide the n-hexane-rich phase Zw as distillate product with a purity better than 0.91. Water is not a desirable entrainer because of the existence of ternary azeotrope whose n-hexane-rich phase has a water purity much lower (0.70). Considering in Table 3 the split... 

Figure 9.20(b) illustrates the use of pervaporation with two distillation columns to break a binary azeotrope such as benzene/cyclohexane. The feed is supplied at the azeotropic composition and is split into two streams by the pervaporation unit. The residue stream, rich in cyclohexane, is fed to a distillation column that produces a pure bottom product and an azeotropic top stream, which is recycled to the pervaporation unit. Similarly, the other distillation column treats the benzene-rich stream to produce a pure benzene product and an azeotropic mixture that is returned to the pervaporation unit. 

Azeotrope mixtures reach a point at which liquid and vapor compositions become the same at a certain temperature and pressure. Some azeotropes show a maximum boiling temperature, while others show a minimum boiling temperature. Table 1.8 shows some examples of binary and ternary azeotropes. Azeotrope mixtures cannot be separated into their pure species by a single distillation column. 

By far, the most common prejudice (sometimes completely overlooking the other alternative) is to propose the most volatile composition (low-boiling node) as distillate (Fig. 28). In this region containing the decant aqueous layer, the lightest composition is the ternary azeotrope. With enough stages, all of the azeotropic composition in the decant aqueous layer may be recovered, and the underflow will contain only a binary ethanol-water mixture. If the distillate of... 

The high boiling reactant is fed as feed 1 and the low boiling reactant as feed 2. Between the two feeds, there is the reaction zone. As a special application, feed 1 can serve as an extractive agent, e.g. in the case of the production of methyl acetate, acetic acid serves as an entrainer for the binary azeotropic mixture methanol and methylacetate. The ensemble is then a reactive extractive distillation column. 

Binary azeotropic mixtures cannot be separated by fractional distillation. A mixture of two components which form maximumboiling or minimum-boiling mixtures may be separated into portions of different compositions, but cannot be separated into pure... 

Figure 9.4 displays RCMs for some typical azeotropic mixtures. Figure 9.4a presents the mixture acetone (56.2 °C) / benzene (80.1 °C) / heptane (98.4 °C). Acetone and heptane form a minimum boiling azeotrope with nbp of 55.1 °C, which is the lowest boiler. It may be observed that the residue curves emanate from the azeotropic point, take the direction to the benzene/heptane edge, and then deflect to the heptane vertex. Binary azeotrope and heptane are unstable and stable nodes, respectively. Acetone and benzene are saddles. In this case there is a single distillation region, as for zeotropic mixtures, but the shape of the residue curves is peculiar. 

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