Ethanol To Butadiene Second World

Separation Acetone From Water

WATER TO PURIF! CATION

Figure 6-1 Separation of a mixture containing acetone and methyl alcohol by azeotropic and extractive distillation. [W. C. Hopkins and J. J. Fritsch, Chem. Eng. 51(8):361 (1955), by courtesy McGraw-Hill Book Company.]

WATER TO PURIF! CATION

Figure 6-1 Separation of a mixture containing acetone and methyl alcohol by azeotropic and extractive distillation. [W. C. Hopkins and J. J. Fritsch, Chem. Eng. 51(8):361 (1955), by courtesy McGraw-Hill Book Company.]

water water

Figure 6-2 Purification of methyl ethyl keytone by azeotropic and extractive distillation. [W. C. Hopkins and J. J. Fritsch. Chem. Eng. 51(8):361 (1955), by courtesy McGraw-Hill Book Company.]

from a stream which also contained methyl-tetrahydrofuran, formais, acetals, and oxide impurities. The sequence of steps is shown in Fig. 6-2. All but a small portion of the oxide impurities are removed by azeotropic distillation. The azeo-trope is taken overhead at 65°C. In the second column, the solvent is separated from the remaining components by water extraction. The remaining impurities are separated from the methyl ethyl ketone by a water extractive distillation with a water concentration on the trays of approximately 60 percent by weight. The polar solvent, water, reduces the volatilities of the acetals, and the azeotrope of methyl ketone and water is removed overhead.26 The overhead, methyl ethyl ketone and water, is then dried bypentane extraction.

Separation of Ethanol and Water

An early application of azeotropic distillation was proposed by Guinot and Clark11 for the separation of ethanol and water by the use of benzene as the solvent. This process is based on the fact that benzene forms a ternary azeotrope with ethanol and water, which has a higher ratio of water to ethanol than does the ethanol-water azeotrope. In the first column, shown in Fig. 6-3, an azeotropic distillation is carried out. A two-phase liquid separation at 20°C in the decanter is used to concentrate the benzene in the reflux to the first column. The solvent benzene is recovered in the second column and water is removed in the third column.

Ethanol Butadiene Second World War

Figure 6-3 Azeotropic separation of ethanol and water by use of a benzene solyfcmSfH. Guinot ai W. Clark, Trans. Inst. Chem. Eng. (London) 16:187 (1938), by courtesy Thf * Engineers (London).]

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Figure 6-3 Azeotropic separation of ethanol and water by use of a benzene solyfcmSfH. Guinot ai W. Clark, Trans. Inst. Chem. Eng. (London) 16:187 (1938), by courtesy Thf * Engineers (London).]

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Solvents for Hydrocarbon Separations

The high demand for relatively pure butadiene and toluene at the outbreak of World War II was met through the use of azeotropic distillation. Nitration grade toluene was needed for the production of explosives and butadiene was needed for the production of synthetic rubber. As a result of the need for these chemicals, azeotropic and extractive distillation became large-scale industrial processes.

An enumeration of some of the specifications which must be met by an efficient solvent follows. Obviously, the solvent should be noncorrosive to the equipment and should not react with the feed to form undesired products. It should produce a sufficient change in the volatilities of the components to be separated so that these components may be separated with a reasonable number of plates at an economical reflux ratio. The solvent should have an appropriate boiling point relative to the components of the feed to be separated. An azeotropic solvent should have a volatility near the major component desired in the overhead product and an extractive solvent should have a volatility lower than the major component to be withdrawn in the bottom product. The solvent should not be toxic, and it should be available in sufficient quantities at a reasonable price.

Azeotropic Separation of Butadiene from a Mixture of the C4 Hydrocarbons by Use of Ammonia

One of the first processes employed to separate butadiene from a C4 hydrocarbon stream was an azeotropic distillation which used liquid ammonia as the solvent. A description of this process has been presented by Poffenberger et al.,24 who also gave a typical analysis of the C4 stream together with the boiling points of hydrocarbons and their azeotropes. Other solvents such as furfural and acetonitrile are presently employed to effect this separation.12

Other Extractive and Azeotropic Separations

Many solvents have been investigated for the separation of toluene and other aromatics from paraffinic mixtures. Dunn et al.,6 among others, have presented lists of possible solvents. The use of phenol for the extraction of toluene has been described by Dunn et al.6 A solvent-to-feed ratio of approximately 3 to 1 was used. The first commercial plant for the recovery of nitration grade toluene by phenol extraction was constructed and put into operation in 1940 at the Houston Refinery of ShelÉOil Company, Inc.6 Because of the emergencies which existed at that time, it wp necessary to go directly from the laboratory to the full-scale plant.

The production of butadiene from a butane feed generally requires a feed purification process which involves the separation of the butenes from the butanes. Atkins and Boyer1 have described a process in which the separation of the butenes from the butanes was carried out by use of extractive distillation with a mixture of 85 percent acetone and 15 percent water as the solvent. A solvent-to-feed ratio of 0.85 was used.

Separation of Azeotropes by Fractionation

The formation of azeotropes in azeotropic distillation calls for a discussion of some of the techniques which may be employed in the separation of such mixtures. If the azeotropic composition is sensitive to the variation of the total pressure, homogeneous azeotropes may be separated by use of a two-column fractionation scheme as described by Van Winkle,29 among others.

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