DE1568895B2 - PROCESS FOR OBTAINING ISOPRENE WITH HIGH PURITY - Google Patents

Description

To explain the invention, reference is made to the drawing Reference which shows a schematic flow diagram of the process according to the invention.

According to the drawing, the feedstock, namely a C ₅ fraction, which has a large amount of cyclopentadiene with a degree of saturation and chemical and physical properties comparable to those of isoprene and which is complicated during the distillation and makes it difficult to recover the isoprene, is first in treated a boiler H ₁ at 80 to 120 ^{0 C.} By this heating, the cyclopentadiene is easily dimerized to dicyclopentadiene with a higher boiling point (17O ⁰ C), whereby the following steps are greatly simplified. The treated C ₅ fraction is introduced into a separating column T ₁ for the higher-boiling components, in which the dimer and the _{components boiling higher than the C 5} fraction are drawn off at the bottom. The drawn off at the head mixture which consists of components having a boiling point of not more than 55 ⁰ C, is introduced into a column, separation column T _2, for the lower boiling Komponanten in which the lower boiling than isoprene components consisting mainly of isopentane , are distilled off at about 28 ⁰ C (atmospheric pressure) at the top.

This feed contains approximately 30% hydrocarbons

substances that boil lower than isoprene. It is possible, To distill off acetylenic hydrocarbons at temperatures which are lower than the boiling points of the pure substances, however, it is impossible to obtain all fractions with a lower boiling point than isoprene with practically no isoprene losses to distill off. Acetylene hydrocarbons can be almost completely distilled off, some of the monoolefin hydrocarbons remaining in the residue. The amount of on the head

The fraction withdrawn and the amount of isoprene lost depend directly on the number of trays in the fractionating column and the reflux ratio. When carrying out the invention, the loss of isoprene can be up to 5%, preferably up to 2%, based on the total isoprene content, while the amount of the fraction withdrawn at the top is up to 30%, preferably up to 25% on the total amount of the input material. The acetylenic hydrocarbons were analyzed; it was found to contain butyne-2, pentyne-1, isopropyl acetylene and isopropenyl acetylene. It is most advantageous to remove these substances at this point, as they act as inhibitors in the polymerization of isoprene. The fraction withdrawn at the bottom is a C ₅ fraction with a narrow boiling range and consists mainly of paraffinic, monoolefinic and diolefinic hydrocarbons.

Components of the Boil composition A A (Weight percent) Swamp- 44. 52. head head head swamp head head Q group Point corridor corridor from floor floor from from from from from from ⁰ C A from from head T ₂ from from T ₃ T ₁ T ₁ T. T ₃ T ₁ sentence- T ₁ T ₁ from T ₂ T ₂ Well B. C. Ά E. F. G H I. J K L. M. A. D.

Paraffin

Isopentane 27.9

n-pentane 36.1

Cyclopentane 49.3

Monoolefins
3-methylbutene-1 20.1
Pentene-1 30.0

2-methylbutene-l 31.2
Trans-pentene-2 36.4
Cis-pentene-2 36.9
2-methylbutene-2 38.6
Cyclopentene 44.2

Diolefins

Isoprene 34.1

Trans-piperylene 42.0

Cis-piperylene 44.1

Cyclopentadiene 41

Acetylenes

Butyne-2 27.2

Isopropyl 28

acetylene

Isopropenyl- 33
acetylene
α-acetylene

Higher than that
C ₅ fraction
boiling fraction

13.4

22.3

0.6

0.6
3.7
4.7
2.1
1.3
2.3
2.3

14.1
4.3
2.2

10.9

13.4

22.3

0.6

0.6 3.7 4.7 2.1 1.3 2.3 2.3

14.1 4.3 2.2 1.9

16.8

27.9

0.8

0.7 4.7 6.0 2.6 1.7 2.9 2.9

17.7 5.9 3.1 2.1

65.5 0.4

2.6

12.0

7.2

3.9

2.1 5.2 3.5 2.1 3.9 4.0

0.3 0.3 0.4 2.0 1.4 1.4 1.4 6.2

0.1 0.1 0.1 0.1 17.0

25.1

0.2

10.0
14.3
1.9
0.9
1.4
0.1

22.7
2.2
1.0
2.0

0.2 0.8

9.3

29.4

0.2

9.2
14.7
2.1
1.1
1.5
0.9

25.5
2.4

1.1
2.2

0.2

1.2
64.0

1.7

3.5
8.6
6.0
3.6
6.6
0.8

4.0

0.4

0.1
0.1
0.1
0.1
0.2
8.3

0.8

0.05
0.05
0.05
0.05
0.1

0.4 15.5

1.2

63.8

1.8

3.6 8.8 6.0 3.5 6.5 1.1

47.3 99.8 15.5

19.1 0.03 34.8

10.5 0.02 19.1

6.0 0.4

3.7 48.3

18.8

0.1

13.3 22.3 2.3 3.1 0.2 0.2

8.1

13.5

The C ₅ fraction thus obtained is then passed into a column T ₃ in which the diolefin hydrocarbons are separated off by extractive distillation. Acetone, acetonitrile, dimethylformamide, dimethylacetamide, furfural, etc., for example, can be used as the selective solvent at this stage; however, / 7-methoxypropionitrile is particularly preferred. It is possible to selectively separate the diolefins from the hydrocarbon mixtures with a narrow boiling range by distilling the mixture with such a solvent.

If a low-boiling solvent is used as the selective solvent, then part of the solvent is used contained in the top fraction of the distillation column in the form of an azeotropic mixture, and it is then necessary that the solvent be removed from the distillate. This method also has the disadvantage that you need colder cooling water or must work under pressure, since the The temperature at the top of the column is low, and that additional trays are required for the Hydrocarbons from the extract, that from a mixture of the solvent and the hydrocarbon consists of the column, to be separated.

If, on the other hand, a high-boiling solvent is used, the above-mentioned disadvantages become avoided; however, the solvent should be chemically resistant, since this step is necessary is carried out at high temperatures. Some of the well known high boiling solvents can be well suited as solvents because, for example, the relative volatilities are different Hydrocarbons are favorable to those of diolefins in these solvents, however, their chemical resistance at elevated temperatures is insufficient.

It was found that / 3-methoxypropionitrile meets all of the above requirements. A comparison of the relative volatilities of hydrocarbons and isoprene in this solvent and known solvents is given in Table II.

Table II

Influence of the solvent on the relative volatilities of hydrocarbons

Table III

Composition of the C ₅ fraction

composition
(Weight percent)

X YZ

Isopentane 15.2 23.4 8.11 n-pentane 23.6 40.0 Cyclopentane 0.75 0.4 0.91 Pentene-1 4.96 7.21 Cis-pentene-2 3.66 5.28 Trans-pentene-2 3.41 4.28 ¹⁵ 3-methylbutene-1 0.19 - 3.87 2-methylbutene-1 7.03 11.1 2-methylbutene-2 4.05 3.90 55.9 Cyclopentene 2.76 9.64 ²⁰ isoprene 17.9 19.3 Cis-piperylene 3.43 2.32 Trans-piperylene 6.70 Cyclopentadiene 0.94

solvent

n-pentane

2-methylbutene-2

No solvent 0.92 0.88 acetone 1.80 1.16 Acetonitrile 2.36 1.29 Dimethylformamide 2.44 1.30 / J-methoxypropionitrile 2.37 1.37

The feed used at this stage is obtained by _{subjecting a C 5} fraction from a cracked naphtha residue to a heat treatment in which the cyclopentadiene is removed; it has the composition given in column X of Table III. The ratio between solvent and hydrocarbons is 2: 1.

As already mentioned, the / 3-methoxypropionitrile is comparable with the solvents known hitherto with regard to its solvent properties and much more advantageous than the known solvents with regard to 2-methylbutene-2, which was previously difficult to separate. Furthermore, the ß- methoxypropionitrile has the advantage that the above-mentioned disadvantages of the low-boiling solvents are avoided and that it is chemically stable at high temperatures and easily accessible and cheap.

In the case of an extractive distillation, the acetylenic hydrocarbons in the feedstock accumulate at the bottom or in the bottom of the column together with the diolefins, even if their boiling points are lower than that of isoprene. In contrast, according to the process according to the invention, the acetylenic hydrocarbons are practically not contained in the diolefins, since they were removed beforehand in the column T _2. The amount of the selective solvent introduced into the distillation column is preferably one to five times the volume of the hydrocarbons introduced at the tray to which the solvent is directed. The diolefin fraction drawn off at the bottom of the column is then passed into a column T ₄ for recovery of the solvent, in which the solvent is completely separated off from this fraction.

The diolefin fraction treated in this way is then washed with water in a column T ₅ and passed into a fractionation _{column T 6} , in which the isoprene is separated off. The fraction consists of diolefins and a small amount of monoolefins, it does not contain a fraction lower than isoprene. Therefore, an isoprene of high purity can easily be obtained from this fraction.

The working steps indicated above can be carried out either at atmospheric pressure or at overpressure be performed; however, avoid using the temperature at a higher isoprene concentration Bring to more than 90 ° C in order to avoid the polymerization of the isoprene.

7 8

The following examples explain the invention nitrile at a point 100 mm below the head

manure. at a speed of 500 cm ³ / hour. initiated

B e i s σ i e 1 1 was. The extractive distillation was at a

Reflux ratio of 8.5 carried out, with a

A C ₅ fraction with that in column A of table I 5 diolefin-free fraction with that in column L of table I.

specified composition was in a specified composition at the top of the column

Autoclave heated to HO ⁰ C for 4 hours, a was obtained. A fraction that is the solvent

Product with that indicated in column B of Table I and which contained hydrocarbons was at the bottom

Composition was obtained. This product of the column at a velocity of 520 cm ³ /

was then subjected to direct distillation, withdrawn by 10 hours and then in the middle of a distillation

the low-boiling fractions with boiling points up to streaker with a diameter of 20 mm and one

to 55 ° C to remove. The distillate, whose total height of 500 mm was initiated. That way it was

Composition indicated in column C of Table I, a fraction which mainly contained diolefins and

was then at a rate of 150 cm ³ / hour. the composition given in column M of table I

in a packed column (T ₂ in the drawing) with 15 composition, at a speed of

an inner diameter of 20 mm, a packing 20 cm ³ / hour. received at the head of the column,

height of 1500 mm and a theoretical number of floors. .

initiated by 70 on 44th floor from above. The co-example 3

lonne was prepared at a reflux ratio of 25. A feed with that shown in column X of Table III

travel. 20 percent by weight of the carbon used - 20 specified composition was with a

Hydrogen mixture were at the top of the column speed of 50 cm ³ / hour. in the middle of a

withdrawn, while the remainder at the bottom of the column packed column with a diameter of 20 mm

was withdrawn. The temperature at the head was initiated while at and a height of 1200 mm

Atmospheric pressure 27 ⁰ C. The overhead distillate and the / 9-methoxypropionitrile at a point 100 mm below-

At the bottom, the half of the top of the column indicated in column D or E had a speed

composition. The acetylene hydrocarbons were 500 cm ³ / hour. was introduced into the column,

The column was operated at a reflux ratio of

Head of the column removed; they were in the lower part 8.5 (refluxing amount is about 280 cm ³ / hr.) and a

the column, d. H. from the 44th floor from the top, head temperature of 35 ° C drove. The distillate

table no longer available. In Table I show the 30 was at a rate of 33 cm ³ / hour. at the

Columns F and G removed the composition at the 44th and top of the column, respectively. Here was a

52. floor. About 5% isoprene goes in this operation with the diolefin-free fraction in column Y of Table III

lost. given composition obtained.

The bottom residue thus obtained was then washed with a fraction, the solvents and the coals at a rate of 120 cm ³ / hour. Contained in the middle 35 hydrogen, was at the bottom or bottom of a packed column (T ₃ in the drawing) with the column at a rate of 250 cm ³ / an internal diameter of 20 mm, one packed hour. And then in the middle of one Stripper height of 1300 mm and a theoretical number of plates with a diameter of 20 mm and a height of 60 initiated, while acetonitrile initiated with 2% water of 500 mm. Here, a fraction, at the 12th floor from the top at a rate of 40, which mainly contained diolefins, with that in column Z of 550 cm ³ / hour. was initiated. The column was operated on the composition indicated in Table III at a reflux ratio of 6. 55 Ge head of the column at a rate of weight percent of the C ₅ fraction used were 20 cm ³ / hour. obtain,
withdrawn at the top of the column, while the rest. .
was withdrawn at the bottom of the column. The temperature 45 B e 1 s ρ 1 e 1 4
temperature at the top was 32 ° C. The bottom fraction, This example shows the results of an experiment carried out at Überdie, mainly from a mixture of diolefins, pressure.
Acetonitrile and water consisted in a co- A C ₅ fraction with the lonne in column A of Table IV for recovery of the solvent (Γ ₄ in the specified composition was with one of the drawings) with an internal diameter of 50 residence time of 5.7 Hrs. Passed through the 20 mm tube H ₁ ^{kept at 110 °} C. and a packing height of 1000 mm, the C ₅ fraction being heated and passed, in which the hydrocarbons were dimerized by the acetonitrile. The oil so treated was then separated. The diolefins thus obtained were at a rate of 10.0 kg / hour. then washed into one of the with water and introduced into a filling distillation column T ₁ with 18 trays. The body column (Γ ₆ in the drawing) with an inner column was operated with a reflux ratio of diameter 20 mm and a packing height of 0.35. The C ₅ fraction was with a Ge-1500 mm and a theoretical number of plates of 80 speed of 7.82 kg / hour. distilled at the top of the column. Here, an isoprene was withdrawn with a to. The temperature at the top was 6O ⁰ C and polymerization of sufficient purity (column J of the pressure 2.2 ata.

Table I) obtained at the top of the column. 60 The parliamentary group from which the highly

. -19 boiling components were removed, the in

Example I Composition given in column C of Table IV.

The bottom fraction obtained according to Example 1 with the The fraction was then at a rate

in column E of Table I, the total of 7.82 kg / hour. in a rectification column with 130

reduction was the introduced at a rate of 50 ^cm3 / 65th The column was at a return

Hours driven in the middle of a packed column with a flow ratio of 18. The lower than that

Diameter of 20 mm and a packing height C ₅ fraction boiling fraction, which is mainly

of 1200 mm, while / contained 9-methoxypropio-isopentane, was at the top of the column with

ίο

a speed of 1.99 kg / hour. deducted. The acetylenic hydrocarbons contained in the feed were practically completely enriched in this fraction. A practically acetylene-free fraction with the composition given in column E of table IV was at the bottom of the column obtain. The temperature at the top was 58 ° C. and the pressure 2.8 ata.

The fraction obtained in the preliminary stage with the composition given in column E of Table IV was fed at a rate of 82 kg / hour. Introduced in the middle of a column T ₃ for extractive distillation with 94 plates and a reflux ratio of 5, while acetonitrile, which contained 5 percent by weight of water, at a rate of 39.5 kg / hour. was introduced into the column at the 10th tray from the top. The temperature at the head was 60 ° C. and the pressure was 2.66 ata.

The composition of the C ₅ fraction in the distillate withdrawn at the top is given in column H of Table IV. A mixture of acetonitrile and a C ₅ fraction, which consisted essentially of diolefins, was at the bottom of the column with a GeTable IV

speed of 41.0 kg / hour obtain. This mixture was then fed to a 20 tray solvent recovery column operated at a reflux ratio of 3.0. A diolefin fraction was obtained at the top of the column at a rate of 2.23 kg / hour. The temperature was 60 ^° C. and the pressure was 2.16 ata.

The thus obtained diolefin fraction was in one

ίο washing tower T _s washed with water to separate the solvent from the fraction. After the aqueous layer had been separated off, the fraction was returned to the rectification stage for the isoprene. This operation was carried out at a reflux ratio of 11 using a column T ₆ having 106 trays. At a rate of addition of the input material of 2.29 kg / hour. isoprene was fed at the top of the column at a purity of not less than 99.8% and at a rate of 1.05 kg / hour. obtain. The composition of the stream withdrawn at the bottom is given in column K of Table IV. The temperature at the top was 50 ° C. and the pressure 1.72 ata.

Components of the Q fraction Composition (weight percent) For this Entrance from T ₂ swamp from T ₂ E. Head of T ₃ Bottom of T, Charge B. H K A. 3.2 Lower than the Q faction 2.5 · boiling components 1.9 Paraffins 16.6 35.2 3.2 - Isopentane 13.0 26.2 0.1 58.2 - n-pentane 20.5 0.1 0.7 - 0.6 2,3-dimethylbutane 0.1 0.6 0.6 - 3.5 Cyclopentane 0.5 0.5 0.9 - 3.0 3-methylpentane 0.4 0.8 - 5.3 n-hexane 0.7 - Monoolefins 1.0 4.0 - - _: 3-methylbutene-1 0.8 5.2 7.7 6.6 - Pentene-1 4.0 6.8 3.8 12.7 - 2-methylbutene-1 5.3 2.9 2.4 6.4 - Trans-pentene-2 2.2 1.8 4.5 3.9 - Cis-pentene-2 1.4 3.0 3.2 7.3 0.1 2-methylbutene-2 2.6 2.4 - 15.0 Cyclopentene 1.8 21.2 Diolefins 16.6 7.4 1.7 9.4 Isoprene 13.6 5.5 4.0 - 34.5 Trans-piperylene 4.3 3.0 1.9 - 18.8 Cis-piperylene 2.4 1.4 - 8.7 Cyclopentadiene 10.8 - Acetylenes 0.4 - - - Butyne-2 0.3 1.7 0.2 - - α-acetylene 1.3 0.2 - 1.1 Higher than the C faction 11.5 1 sheet of drawings boiling components

Claims (25)

1 2 Hydrocarbon to the desired value Claim: bring what the pure hydrocarbon through Rectifying is obtained. Other procedures work Process for the production of isoprene with high similar. Purity from a hydrocarbon mixture that 5 becomes the C ₅ fractions of a thermal obtained by thermal cracking, cracking residue obtained from naphtha with a content of paraffins, monoolefins, separated by these known processes, see above Diolefins and acetylenes obtained by dimerization usually contain small amounts of isoprene of cyclopentadiene in the heat, separation of the amount of monoolefins, mainly 2-methyl- Dimers by fractional distillation, enriching io-butene-2, and acetylene compounds such as butene-2, tion of isoprene by extractive distillation and isopropyl acetylene and isopropenyl acetylene, while Fractionation of the isoprene-rich concentrate, the paraffinic hydrocarbons practically full characterized in that they are constantly separated from the isoprene, Isoprene-containing C ₅ -hydrocarbon fraction, which There have already been several methods of recovery contains about 30% hydrocarbons, which are lower than 15 from isoprene from complex C ₅ mixtures boil as isoprene and that by distillative stripping, by steam cracking or by other, separation of the cyclopentadiene dimer gives rise to hydrocarbons at high temperatures den is obtained prior to the extractive distillation of a substance conversion process. Some- subjected to fractional distillation and once a two-stage, extractive distillation separates lower boiling fraction than isoprene. 20 tion to remove the acetylene compounds. Furthermore, to remove the acetylene compounds, a combination of direct distillation and carried out an extractive distillation. After DT-PS 11 61 554 are the acetylenes only after one 25 dimerization of cyclopentadiene and after a Extraction distillation separated. These procedures In recent years, however, thermal cracking has not proven to be entirely satisfactory of petroleum, especially naphtha, has been proven to a large extent, since very small amounts of acetylene compounds Catch for the production of gaseous olefins, such as fertilizer remaining in isoprene. To the product Ethylene, propylene and the like. The at this 30 to an isoprene suitable for the polymerization Crack residue obtained from thermal cracking is an additional step to remove holds various C ₅ hydrocarbons with less impurities required. Through this different degrees of saturation. The typical together- the procedures are complicated and difficult, and settlement of the cracking residue and the boiling point the yield decreases. It is therefore difficult of these hydrocarbons, isoprene suitable for polymerization can be obtained in column A of Ta- 35, Belle I stated. Table I shows that this C ₅ fraction object of the invention is to provide a method for tion contains a large amount of isoprene, and it is very isoprene with one used for polymerization it is desirable to recover the isoprene and provide it to the appropriate degree of purity at which the use. Acetylene compounds before extractive distillation With the separation of the isoprene from a carbon 40 are removed, whereby the for the hitherto usual hydrogen mixture with this composition occur process characteristic disadvantages are eliminated however difficulties arise; for example one is den. small amount of acetylenic hydrocarbons, especially this object is achieved according to the invention by a special carbon process with a lower boiling point than isoprene for the production of isoprene with high levels of hydrogen, present in the crack residue, which is 45 purity from a hydrocarbon mixture, formed by the thermal cleavage of naphtha has been obtained by thermal cracking; Furthermore, there are components with and paraffins, monoolefins, diolefins and acetylenes boiling points close to the boiling point at which the cyclopentadiene in the heat is C ₅ diolefins in a mixture of C ₅ paraffins and dimerized, the dimer by fractional distillation -C ₅ -Monoolefinen etc. These substances behave 50 tion separates, the isoprene by extractive distillation is similar to isoprene, and it is difficult to separate isoprene and the isoprene-rich concentrate fractionated in high purity with good efficiency, the process being characterized win . is that the isoprene-containing Cs-hydrocarbon-There is already a process known in which the fraction, which contains about 30% hydrocarbons, crack residue with the help of a selective solution 55 which boil lower than isoprene and which by distillation medium, z. B. an ammoniacal copper (I) -acetat- tive separation of the cyclopentadiene dimer solution obtained from sulfolanes, etc. in groups with under- is separated before the extraction distillation of a fractional-different degree of saturation, the ned distillation is subject and a deeper than on the different saturation based isoprene separating the boiling fraction.
Differences in the chemical and physical properties are preferably exploited from a mixture of hydrocarbons, based on which it is assumed that the desired pure hydrocarbon was then obtained by thermal cracking from petroleum, in particular from naphtha. Rectifying is gained. Furthermore, an invention has now been found that, for. B. drive is known in which an extractive distillation from the Q-hydrocarbons given in Table I with a selective solvent is carried out 65 substance mix the acetylenes completely by direct; Here the different distillations can be distilled off at the same time after the degree of saturation and the different boiling points of cyclopentadiene have been dimerized; Utilized in this way to achieve the desired concentration, isoprene can be obtained with high purity.