Azeotropic Distillation Apparatus

Method 5031 describes an azeotropic distillation technique for the determination of nonpurgeable, water-soluble VOCs that are present in aqueous environmental samples. The sample is distilled in an azeotropic distillation apparatus, followed by direct aqueous injection of the distillate into a GC or GC MS system. The method is not amenable to automation. The distillation is time-consuming and is limited to a small number of samples. 

Introduction Reactive distillation is a unit operation in which chemical reaction and distiUative separation are carried out simultaneously within a fractional distillation apparatus. Reactive distillation may be advantageous for liqiiid-phase reaction systems when the reaction must be carried out with a large excess of one or more of the reactants, when a reaction can be driven to completion by removal of one or more of the products as they are formed, or when the product recoveiy or by-product recycle scheme is complicated or macfe infeasible by azeotrope formation. 

Gillespie equilibrium still analychem A recirculating equilibrium distillation apparatus used to establish azeotropic properties of liquid mixtures. ga Ies-pe, e-kw3 llbre-om, stil ... 

The reaction from an enamine is initiated by the addition of a trace of a strong acid, e.g. /7-toluenesulfonic acid (TsOH, 4-methylbenzene-sulfonic acid), to the ketone and pyrrolidine in a solvent such as toluene. When the mixture is at reflux in a Dean-Stark apparatus, water is liberated and is removed through azeotropic distillation, leaving the enamine in the reaction vessel. After a follow-up reaction between the enamine and a suitable electrophile, an iminium salt is produced that liberates both the a-substituted ketone and pyrrolidine when it is treated with aqueous acid (Scheme 6.20). 

Apparatus—Conhnued automatic water trap for azeotropic distillation, 23, 38, 25, 42, 46 bain marie ware, 25, 72, 97 Claisen flask modified with column, 22, 11... 

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. 

The water content is determined by azeotropic distillation in the Dean-Stark apparatus. ... 

Apparatus for azeotropic distillation singlenecked round-bottomed flasks, condenser, distillation head, thermometer, and adapter... 

One of the first reactions carried out in perfluorinated solvents was the transesterification described by Zhu in 1993 [10]. He used the perfluorinated solvent FC-77 (mainly perfluoro-2-butyltetrahydrofuran) for an azeotropic distillation of the formed methanol or propanol in the transesterification of methyl- or pro-pylesters 1 with different alcohols 2 using a Dean-Stark apparatus Eq. (1). 

Washing and extraction steps are made easier or even suppressed. In the case of equilibrated reactions leading to light polar molecules (MeOH, EtOH or H2O), equilibrium can be easily shifted by a simple heating just above the boiUng points or under reduced pressure. With the usual procedure this operation is impeded by the presence of solvent necessitating an azeotropic distillation using a Dean-Stark apparatus [Eq. (2)]. 

Figure E4-2. Apparatus for a laboratoiy-scale azeotropic distillation.

Continuous removal of the product water by azeotropic distillation after addition of a carrier such as benzene, toluene, xylene, or a halogenated aliphatic solvent leads to rapid esterification ( azeotropic esterification ) and usually also to high yields. The course of the reaction can be followed directly from the amount of water liberated the apparatus used for this purpose (a water separator) is well known. 

Let us consider azeotropic distillation first. If a homogeneous azeotrope is produced, no changes in the normal apparatus for countercurrent distillation are required. When a heterogeneous azeotrope results the whole azeotrope is not returned to the column as reflux, but only the phase rich in additive. For this purpose an azeotropic column head is employed, as shown in Fig. 232, which allows either the heavy or the light phase to be used as reflux. The reflux is preferably returned to the column at some distance below the head. In continuous operation, if a honu eneous azeotrope is formed, the additive is mixed with the feed if the azeotrope is heterogeneous it is... 

Moisture and water content are important parameters in the processing and sale of materials from foodstuffs to petroleum based fuels. Azeotropic distillation is commonly used to determine water content using apparatus developed by Dean and Stark and an immiscible liquid such as toluene as the codistillate. 

The advantages of the coulometric method are its simplicity of operation, its increased sensitivity, and the fact that it does not require a standardized reagent, such as water saturated 1-octanol, to calculate the water content but only to assess the accuracy of the instrument. The advantage of the volumetric method is that it permits the use of a wider range of very polar solvents as well as nonpolar solvents for dissolving the sample in the titration vessel. Furthermore, the volumetric titration vessel can be heated to enhance the dissolution of slightly soluble samples. Either the volumetric or the coulometric titration instrument can be joined with an oven (evaporation) or a distillation apparatus (azeotropic distillation). In this configuration, the moisture that is volatilized from the sample can be transported to the titrator with a dry gas and the evaporated water measured either coulometrically or volumetrically. The recent... 

The dehydration of 34 to 29 is a reversible process that is driven to completion by removing the water from the reaction mixture. This is conveniently done by using toluene as the solvent for the reaction. Water and toluene form an azeotrope (Sec. 4.4), so azeotropic distillation allows the continuous separation of water as dehydration occurs. To minimize the amount of solvent that is required for distillations of this type, a Dean-Stark trap (Fig. 18.15) is commonly used. Because such traps are often not available in the undergraduate laboratory, an operational equivalent may be devised by assembling the apparatus in a way such that water, but not toluene, can be prevented from returning to the reaction flask (Fig. 18.16). 

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