Alcohols ternary azeotropes with

Allyl alcohol forms an azeotropic mixture with water, and the mixture is a homogeneous liquid. Therefore, to obtain dry allyl alcohol, ternary azeotropic distillation and dehydration are required. 

Isopropyl alcohol [67-63-0] (2-propanol, isopropanol) is a colorless liquid that is miscible in all proportions with water and with commonly used organic solvents. It forms binary and ternary azeotropes with water and many organic solvents. 

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

ISOPROPYL ALCOHOL FORMS TERNARY AZEOTROPES WITH ... 

Surface tension at 20 C 23.6 dynes per cm ISOAMYL ALCOHOL FORMS TERNARY AZEOTROPES WITH ... 

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 and thermodynamic properties of benzene are shown in Table 1 (2). Azeotrope data for benzene with selected compounds are shown in Table 2 (3). Benzene forms minimum-boiling azeotropes with many alcohols and hydrocarbons. Benzene also forms ternary azeotropes. 

Esters of medium volatility are capable of removing the water formed by distillation. Examples are propyl, butyl, and amyl formates, ethyl, propyl, butyl, and amyl acetates, and the methyl and ethyl esters of propionic, butyric, and valeric acids. In some cases, ternary azeotropic mixtures of alcohol, ester, and water are formed. This group is capable of further subdivision with ethyl acetate, all of the ester is removed as a vapor mixture with alcohol and part of the water, while the balance of the water accumulates in the system. With butyl acetate, on the other hand, all of the water formed is removed overhead with part of the ester and alcohol, and the balance of the ester accumulates as a high boiler in the system. 

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. 

Like ethyl alcohol, the absolute (99 %) grade is made by forming a ternary azeotrope. In this case, DIPE (di-isopropyl ether) is used to form the ternary with water and IPA. But the idea is exactly the same. 

Because ethyl alcohol forms an azeotrope with water that is a constant boiling mixture, i.e. both the ethyl alcohol and the water, in a ratio of 95/5, boil together at a temperature different than either separately. Other examples in this chapter are the ternary azeotrope, ethyl alcohol - water -benzene and DIPE - isopropyl alcohol - water. An azeotrope mentioned earlier is MEK - water - toluene rafFmate used for toluene extraction. 

Allyl alcohol is a colorless liquid having a pungent odor its vapor may cause severe irritation and injury to eyes, nose, throat, and lungs. It is also corrosive. Allyl alcohol is freely miscible with water and miscible with many polar organic solvents and aromatic hydrocarbons, but is not miscible with n-hexane. It forms an azeotropic mixture with water and a ternary azeotropic mixture with water and organic solvents. Allyl alcohol lias both bacterial and fungicidal effects. Properties of allyl alcohol are shown in Tabic 1. 

Ethyl Acetate. The production of ethyl acetate by continuous esterification is an excellent example of the use of azeotropic principles to obtain a high yield of ester (2). The acetic acid, concentrated sulfuric acid, and an excess of 95% ethyl alcohol are mixed in reaction tanks provided with agitators. After esterification equilibrium is reached in the mixture, it is pumped into a receiving tank and through a preheater into the upper section of a bubblecap plate column (Fig. 5). The temperature at the top of this column is maintained at ca 80°C and its vapor (alcohol with the ester formed and ca 10% water) is passed to a condenser. The first recovery column is operated with a top temperature of 70°C, producing a ternary azeotrope of 83% ester, 9% alcohol, and 8% water. The ternary mixture is fed to a static mixer where water is added in order to form two layers and allowed to separate in a decanter. The upper layer contains ca 93% ethyl acetate, 5% water, and 2% alcohol, and is sent to a second recovery or ester-drying column. The overhead from this column is 95—100% ethyl acetate which is sent to a cooler and then to a storage tank. This process also applies to methyl butyrate. 

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. 

The esterification with propanols raises the problem of breaking the azeotrope that the alcohol forms with water. The solution of this problem passes by the use of an entrainer forming a heterogeneous ternary azeotrope. Suitable entrainers are hydrocarbons and oxygenated species, as esters and ethers. The solution is in principle similar for u-propanol with the notable difference that the reaction rate is much slower for the last when using the same catalyst. 

Not all liquids form ideal solutions and conform to Raoult s law. Ethanol and water are such liquids. Because of molecular interaction, a mixture of 95.5% (by weight) of ethanol and 4.5% of water boils below (78.15°C) the boiling point of pure ethanol (78.3°C). Thus, no matter how efficient the distilling apparatus, 100% ethanol cannot be obtained by distillation of a mixture of, say, 75% water and 25% ethanol. A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition is called an azeotrope 95% ethanol is such an azeotrope. The boiling point-composition curve for the ethanol-water mixture is seen in Fig. 4. To prepare 100% ethanol the water can be removed chemically (reaction with calcium oxide) or by removal of the water as an azeotrope (with still another liquid). An azeotropic mixture of 32.4% ethanol and 67.6% benzene (bp 80.1 °C) boils at 68.2°C. A ternary azeotrope (bp 64.9°C) contains 74.1% benzene, 18.5% ethanol, and 7.4% water. Absolute alcohol (100% ethanol) is made by addition of benzene to 95% alcohol and removal of the water in the volatile benzene-water-alcohol azeotrope. 

Water is probably the easiest product to separate, because it is immiscible with many organic solvents and may often be removed from the reaction mixture as an azeotrope. As a typical example, consider the formation of an ethyl ester. The acid, somewhat more than an equivalent amount of ethyl alcohol, and about three times the volume of benzene are placed in a flask equipped with a Dean-Stark water trap (Fig. 5-21). The solution is heated to reflux, and the ternary azeotrope (7.4 per cent water, 18.5 per cent alcohol, and 74.1 per cent benzene, bp 65°) is vaporized and transferred to the trap. The liquid upon cooling separates into two layers— the lower, a solution of ethanol in water, and the upper, a solution of ethanol in benzene. The upper layer returns to the flask to be recycled, and the amount of water may be noted in the graduated lower part of the trap. As this fills up, the water may be withdrawn. The completion of the reaction is taken as the point at which water no longer collects in the trap. In order to ensure completion of the reaction, a small additional amount of ethanol may be added to the reaction flask and the heating continued. If water still does not collect in the trap, the reaction is complete, and an essentially quantitative yield of product should be obtained. 

Any higher alcohols that may have formed in the process from traces of higher olefins present in the propylene feed are absorbed from the azeotrope into mineral oil, in which isopropanol is insoluble. Pure isopropanol is obtained by ternary distillation of the cleaned water azeotrope with the appropriate proportion of added di-isopropyl ether. The ternary azeotrope (Table 19.2) is the top product from the column, and pure isopropanol is removed from the bottom (see Section 16.4 for related information). 

Azeotropic distillation involves either an embedded azeotrope, present in the feed mixture, or a contrived azeotrope, formed by the addition of an extraneous component called an entrainer. Benzene-water may be separated into high-purity benzene and the benzene-water azeotrope this is frequently practiced to remove water from benzene when very dry benzene is needed for chemical processing. More commonly encountered are distillation separations that are enhanced through the addition of an entrainer to form an azeotrope. Perhaps the best known separation of this type is the production of anhydrous ethanol from the ethanol-water azeotrope. Here, benzene is added as the entrainer, with the result that a low-boiling ternary azeotrope is formed between benzene, ethanol, and water. This permits the higher-boiling ethanol to be taken from the bottom of the column. The distillate condenses to a heterogeneous mixture of benzene and alcohol-water phases. 

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. 

As can be readily seen from the above, the manufacture of ethyl acetate becomes a matter of distillation. With proper adjustments of rates of addition and distillation, the esterification can be carried out as a continuous process. ActuaUy, the liquor containing acetic acid and the proper amount of sulfuric acid is fed into the column at the proper plate where it meets the alcohol. Esterification takes place on the plates in the nolumn, and the ternary azeotrope of ester, alcohol, and water comes out at the top continuously. The distillate is washed with water and the ester passed to another column. The dilute alcohol obtained by washing the ternary azeotrope goes to a still for the recovery of the alcohol, which is returned to make more ester. 

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