Alcohol-water binary azeotropes

Absolute (100%) ethanol is often made by adding benzene to the ethanol -water binary azeotrope (two components), to make a ternary azeotrope (three components). This ternary alcohol-water-benzene (18.5 7.4 74.1) azeotrope comes over until all the water is gone, followed by a benzene-ethanol mixture. Finally, absolute ethanol gets its chance to appear, marred only slightly by traces of benzene. 

Sometimes the new azeotrope which is formed contains all three constituents. The dehydration of ethanol-water mixture with benzene as added substance is an example. Dilute ethanol-water solutions can be continuously rectified to give at best mixtures containing 89.4 mole percent ethanol at atmospheric pressure, since this is the composition of the minimum-boiling azeotrope in the binary system. By introducing benzene into the top of a column fed with an ethanol-water mixture, the ternary azeotrope containing benzene (53.9 mol %), water (23.3 mol %), ethanol (22.8 mol %), boiling at 64.9°C, is readily separated from the ethanol (bp — 78.4 C), which leaves as a residue product. In this case also the azeotropic overhead product separates into two liquid layers, one rich in benzene which is returned to the top of the column as reflux, the other rich in water which is withdrawn. Since the latter contains appreciable quantities of both benzene and ethanol, it must be rectified separately. The ternary azeotrope contains nearly equal molar proportions of ethanol and water, and consequently dilute ethanol-water solutions must be given a preliminary rectification to produce substantially the alcohol-rich binary azeotrope which is used as a feed. 

Isoprene [78-79-5] (2-methyl-1,3-butadiene) is a colorless, volatile Hquid that is soluble in most hydrocarbons but is practically insoluble in water. Isoprene forms binary azeotropes with water, methanol, methylamine, acetonitrile, methyl formate, bromoethane, ethyl alcohol, methyl sulfide, acetone, propylene oxide, ethyl formate, isopropyl nitrate, methyla1 (dimethoxymethane), ethyl ether, and / -pentane. Ternary azeotropes form with water—acetone, water—acetonitrile, and methyl formate—ethyl bromide (8). Typical properties of isoprene are Hsted in Table 1. 

The physical piopeities of ethyl chloiide aie hsted in Table 1. At 0°C, 100 g ethyl chloride dissolve 0.07 g water and 100 g water dissolve 0.447 g ethyl chloride. The solubihty of water in ethyl chloride increases sharply with temperature to 0.36 g/100 g at 50°C. Ethyl chloride dissolves many organic substances, such as fats, oils, resins, and waxes, and it is also a solvent for sulfur and phosphoms. It is miscible with methyl and ethyl alcohols, diethyl ether, ethyl acetate, methylene chloride, chloroform, carbon tetrachloride, and benzene. Butane, ethyl nitrite, and 2-methylbutane each have been reported to form a binary azeotrope with ethyl chloride, but the accuracy of this data is uncertain (1). 

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 answer is like fighting fire with fire—another azeotrope is formed. When benzene is added to ethyl alcohol and water a ternary azeotrope, a mixture of three compounds that boil at a single temperature, is formed. The ternary azeotrope has the composition of 68% benzene, 24% ethyl alcohol, and 6% water, and it boils at a temperature lower than the binary ethyl alcohol/water azeotrope. So, when a little benzene is added to the ethyl alcohol/water mixture and then put through a distillation column, the ternary azeotrope, in a 68-24-6 composition will come off the top, talcing with it all the benzene, all the water, but just some of the ethyl alcohol. Out the bottom comes whats left, the rest of the ethyl alcohol in nearly pure form. Slick. None of this, by the way, is shown in Figure 13—2. 

Vapor-liquid equilibrium data at atmospheric pressure (690-700 mmHg) for the systems consisting of ethyl alcohol-water saturated with copper(II) chloride, strontium chloride, and nickel(II) chloride are presented. Also provided are the solubilities of each of these salts in the liquid binary mixture at the boiling point. Copper(II) chloride and nickel(II) chloride completely break the azeotrope, while strontium chloride moves the azeotrope up to richer compositions in ethyl alcohol. The equilibrium data are correlated by two separate methods, one based on modified mole fractions, and the other on deviations from Raoult s Law. 

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. 

Figure 3.9 highlights the key feature of a RCM by means of the mixture isopropanol, n-propanol, water, in which two binary azeotropes of water-alcohol occur ... 

Give minimum boiler ternary heterogeneous azeotrope with alcohol and water, or most preferably binary heterogeneous azeotrope with water. The entrainer must form also a minimum binary azeotrope with the alcohol. 

Summary 99% ethyl alcohol is obtained by treating 95% ethyl alcohol with metallic sodium. The metallic sodium reacts with the water in the binary azeotrope, freeing the alcohol. Once the water has been neutralized (forming sodium hydroxide and sodium ethoxide), the mixture is distilled to recover the anhydrous ethyl alcohol. 

Except for alcoholic beverages, nearly all the ethyl alcohol used is a mixture of 95% alcohol and 5% water, known simply as P5% alcohol. What is so special about the concentration of 95% Whatever the method of preparation, ethyl alcohol is obtained first mixed with water this mixture is then concentrated by fractional distillation. But it happens that the component of lowest boiling point is not ethyl alcohol (b.p. 78.3°) but a binary azeotrope containing 95% alcohol and 5% water (b.p. 78.15°). As an azeotrope, it of course gives a vapor of the same composition, and hence cannot be further concentrated by distillation no matter how efficient the fractionating column used. 

An example of azeotropic distillation is the use of benzene to permit the complete separation of ethanol and water, which forms a minimum-boiling azeotrope with 95.6 weight percent alcohol. The alcohol-water mixture with about 95 percent alcohol is fed to the azeotropic distillation column with a benzene-rich stream added at the top. The bottom product is nearly pure alcohol, and the overhead vapor is a ternary azeotrope. The overhead vapor is condensed and separated into two phases. The organic layer is refluxed, and the water layer is sent to a benzene recovery column. All the benzene and some alcohol is taken overhead and sent back to the first column, and the bottoms stream is distilled in a third column to give pure water and some of the binary azeotrope. 

When the water has been eliminated, there follows at 68.3°C a binary azeotrope containing 32.4% of ethanol and 67.6% of benzene, and finally at 78.4°C alcohol of about 99.8% purity distils over. On an industrial scale the preparation takes place continuously, but in the laboratory it is often more convenient to operate in batch and work up the two layers of the ternary azeotrope and the binary azeotrope in portions. 

Figure 2.13b shows a structure of concentration space of mixture benzene (entrainer) (1) -isopropyl alcohol(2)-water(3). The mixture has a ternary azeotrope and three binary azeotropes. 

Due to the entrainer and the decanter, it is possible to separate binary azeotropic mixture Xf into products xb (almost pure isopropyl alcohol) andx/) (contaminated water), which may be purified easily in the second column. Point xd Fes not on the distillation trajectory but on the liquid-liquid tie line (xd=xi2). 

In fact, isopropanol and water form a binary azeotrope (entry 791 in Ref. 3, Table A 2-2, 87.7 % alcohol). 

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. 

C, 45% alcohol) into two immiscible azeotropic liquid phases on contact with water The phases are water and isobutyl acetate (87.5°C, 80.5% acetate), and water and isobutyl alcohol (79.9°C, 88.3% alcohol) Both immiscible azeotropic phases are more volatile than the original anhydrous binary azeotrope Ra between the binary azeotrope and water is 15 MPa . 

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