Azeotropes of Ethanol

LYL ALCOHOL. FORMS TERNARY AZEOTROPES WITH 17, 5 Water 81.4 

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Wash with rectified spirits (azeotrope of Ethanol + water, also known as "grain alcohol") to dissolve the Safrole, leaving the Phellandrene behind. Of course, one should use only the amount of alcohol necessary to dissolve the expected yield of Safrole. 1 1 seems to work, but could be an excessive amount. 

A summary of physical properties of ethyl alcohol is presented ia Table 1. Detailed information on the vapor pressure, density, and viscosity of ethanol can be obtained from References 6—14. A listing of selected biaary and ternary azeotropes of ethanol is compiled ia Reference 15. 

Water and ethanol form a low boiling point azeotrope. So, water cannot be completely separated from ethanol by straight distillation. To produce absolute (100 per cent) ethanol it is necessary to add an entraining agent to break the azeotrope. Benzene is an effective entrainer and is used where the product is not required for food products. Three columns are used in the benzene process. Column 1. This column separates the ethanol from the water. The bottom product is essentially pure ethanol. The water in the feed is carried overhead as the ternary azeotrope of ethanol, benzene and water (24 per cent ethanol, 54 per cent benzene, 22 per cent water). The overhead vapour is condensed and the condensate separated in a decanter into, a benzene-rich phase (22 per cent ethanol, 74 per cent benzene, 4 per cent water) and a water-rich phase (35 per cent ethanol, 4 per cent benzene, 61 per cent water). The benzene-rich phase is recycled to the column as reflux. A benzene make-up stream is added to the reflux to make good any loss of benzene from the process. The water-rich phase is fed to the second column. 

Peivaporation, the separation of tw o peilectly mixed liquids (usually w here they cannot he separated by distillation, because they form an azeotropic, constant boiling mixture at a particular concentration ratio - most famously the azeotrope of ethanol and w ater), is easily achieved through a membrane, by virtue of the different diffusion rates of the tw o vapours. It is also used to treat riitse w aters that have become contaminated by VOCs (volatile organic compounds, hazardous to human health), such as solvents, degreasers and petroleum-based mixtures. In either case, 99% contaminant removal can be achieved. 

One may inquire about how "breaking" of binary azeotropes by soil components (such as water) — which does not happen — is distinct from disruption of binary azeotropes by tramp contaminants (such as water) — which does happen. The difference is in the outcome. The former presupposes that the binary azeotrope of cyclohexane and isopropanol liberates cyclohexane to dissolve oils and then the binary azeotrope is reconstituted when the oil is separated. The latter recognizes that the binary azeotrope of ethanol and toluene forms a stable ternary azeotrope of ethanol, toluene, and water or that ethanol, heptane, and water do the same, or that the binary azeotrope of isobutyl acetate and isobutyl alcohol upon contact with water is disrupted to form two separate and immiscible binary azeotropes. 

As stated in Chapter 7, the composition of an azeotrope varies with the distillation pressure. Thus, the azeotrope between ethanol and water contains 89.4 mol% ethanol at atmospheric pressure, 90.2 mol% ethanol at 380 mm Hg, and 92.0 mol% ethanol at 190 mm Hg absolute pressure [6]. Similarly, the azeotrope between methyl ethyl ketone and water contains 65.4 mol% MEKat atmospheric pressure, 70.0 mol% MEKat 350 mm Hg, and 72.2 mol% MEKat 200 mm Hg absolute pressure. Because MEK and water form two immiscible liquid phases upon condensation of the overhead, these two compounds can be separated by distilling each of these two phases separately. Because the azeotrope of ethanol and water is a single-phase liquid, separation of these two components can be achieved by distillation in two columns operating at different pressures in order to shift the azeotropic composition. 

A selection of industrial appHcations of extractive distillation includes (/) the separation of the / -butane—butadiene azeotrope in mixed C -hydrocarbon streams using furfural [98-01-17, as the solvent (36) (2) the dehydration of ethanol using ethylene glycol [107-21-1] (37—39) (J)... 

The first successful appHcation of heterogeneous azeotropic distillation was in 1902 (87) and involved using benzene to produce absolute alcohol from a binary mixture of ethanol and water. This batch process was patented in 1903 (88) and later converted to a continuous process (89). Good reviews of the early development and widespread appHcation of continuous azeotropic distillation in the prewar chemical industry are available (90). 

Fig. 18. Separation of ethanol from an ethanol—water—benzene mixture using benzene as the entrainer. (a) Schematic representation of the azeo-column (b) material balance lines where I denotes the homogeneous and the heterogeneous azeotropes D, the end points of the Hquid tie-line and A, the overhead vapor leaving the top of the column. The distillate regions, I, II, and III, and the boundaries are marked. Other terms are defined in text.

Fig. 19. Separation of ethanol and water from an ethanol—water—benzene mixture. Bottoms and are water, B is ethanol, (a) Kubierschky three-column sequence where columns 1, 2, and 3 represent the preconcentration, azeotropic, and entrainer recovery columns, respectively, (b) Material balance lines from the azeotropic and the entrainer recovery columns, A and E, respectively, where represents the overall vapor composition from the azeo-column, 2 1SP Hquid in equiUbrium with overhead vapor composition from the azeo-column, Xj, distillate composition from entrainer...

FIG. 13-108 Initial steady state for dynamic azeotropic distillation of ethanol-water with benzene. 

Volkov (1994) has given a state-of-the-art review on pervaporation. A number of industrial plants exist for dehydration of ethanol-water and (.vwpropanol-water azeotropes, dehydration of ethyl acetate, etc. There is considerable potential in removing dissolved water from benzene by pervaporation. The recovery of dis.solved organics like CH2CI2, CHCI3, CCI4, etc. from aqueous waste streams also lends itself for pervaporation and pilot plants already exist. 

Column 3. In this column the water is separated and sent to waste treatment. The overhead product consists of the azeotropic mixture of ethanol and water (89 per cent ethanol, 11 per cent water). The overheads are condensed and recycled to join the feed to the first column. The bottom product is essentially free of ethanol. 

Consider a second example involving the separation of a mixture of ethanol and water that forms an azeotrope at around a mole fraction of ethanol of 0.88. It is proposed to use ethylene glycol as entrainer. An overall mass balance for the separation is shown in Figure 12.22a. As with the... 

An equimolar mixture of ethanol and ethyl acetate is to be separated by distillation into relatively pure products. The mixture forms a minimum-boiling azeotrope, as detailed in Table 12.1. However, the composition of the azeotrope is... 

Enanthaldehyde, -METHYL-/3-OXO-, DIMETHYL ACETAL, 32, 79 Enanthic acid, e-oxo, 31, 3 Epichlorohydrin, 31, 1 Esterification, by azeotropic distillation with toluene, 30, 30, 31 of ethanol with phosphorus trichloride, 31, 111... 

Benzene forms an azeotrope with ethanol and water that is 7.5% water which boils at 64.9°C => allows removal of the water from 95% ethanol. 

The ethanol-water azeotrope (95%ethanol-5%water) is an example of a minimum boiling azeotrope. Its boiling point is lower than that of the components (Fig. 143). If you ve ever fermented anything and distilled the results in the hopes of obtaining 200 proof (100%) white lightning, you d have to content yourself with getting the azeotropic 190 proof mixture, instead. Fermentation usually stops when the yeast die in their own 15% ethanol solution. At room temperature, this is point A on our phase diagram. When you heat the... 

In some instances, it is desirable to remove lipids and other so-called extractives before proceeding with polysaccharide separation. This removal is generally accomplished through Soxhlet extraction with an azeotropic mixture of ethanol and benzene.26 2 27... 

If, for example, a mixture of ethanol and water is distilled, the concentration of the alcohol steadily increases until it reaches 96 per cent by mass, when the composition of the vapour equals that of the liquid, and no further enrichment occurs. This mixture is called an azeotrope, and it cannot be separated by straightforward distillation. Such a condition is shown in the y — x curves of Fig. 11.4 where it is seen that the equilibrium curve crosses the diagonal, indicating the existence of an azeotrope. A large number of azeotropic mixtures have been found, some of which are of great industrial importance, such as water-nitric acid, water-hydrochloric acid, and water-alcohols. The problem of non-ideality is discussed in Section 11.2.4 where the determination of the equilibrium data is considered. When the activity coefficient is greater than unity, giving a positive deviation from Raoult s law, the molecules of the components in the system repel each... 

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