DE1593691C3 - Process for the production of polymerizable butadiene - Google Patents

Description

To reduce solvent so far that polymerization of the butadiene can be avoided. In the case of acetonitrile, the addition of water aims to increase the selectivity.

The disadvantage here is that the presence of water leads to a strong reduction in all cases the solvency of the solvent and a relatively low capacity of the technical Plant leads. In addition, the addition of water requires special technical measures Procedure and leads, if appropriate, to solvent losses as a result of reaction with the solvent as well as corrosion problems.

The object of the present invention was to avoid the deficiencies outlined above and to provide a method to develop that allows a polymerizable butadiene in one process step below simultaneous separation of the more volatile and less volatile hydrocarbons than butadiene to win.

This object is achieved by a process for the recovery of polymerizable butadiene from C ₄ fractions containing this by gas-liquid scrubbing with dimethylformamide in that, according to the invention, the gas-liquid scrubbing is carried out in an absorption zone and containing less than 1 percent by weight of water containing dimethylformamide In a subsequent desorption zone, the gas-saturated solvent obtained during absorption is driven out of the hydrocarbons, which are more volatile than butadiene, in the lower region of the absorption zone by means of a butadiene stream and discharged together with the non-dissolved volatile components at the upper end of the absorption zone and that the hydrocarbons, which are less volatile than butadiene, are concentrated in the lower region of the desorption zone and this mixture, which contains only small amounts of butadiene, is continuously discharged, while the pure butadiene from the upper end of the des orption zone is derived.

The butadiene stream used for the expulsion of the lighter than butadiene volatile hydrocarbons from the gas-saturated solvent can either by partial desorption of the solvent by heating at 60 to 14O ⁰ C, preferably at 115 to 130 ⁰ C in the lower section of the absorption zone produces (F i g. 1) or removed as a substream from the pure butadiene emerging at the upper end of the desorption zone and returned to the lower region of the absorption zone (FIG. 2).

It is particularly advantageous to use a dimethylformamide with a water content of 0.1 to 0.3 percent by weight to use.

The use of practically anhydrous dimethylformamide is particularly advantageous because at the boiling point of this solvent under normal pressure (153 ^° C.) the undesired polymerization of butadiene can be avoided during desorption and the addition of water, which in the case of comparatively higher boiling solvents for the purpose of lowering the boiling point is required, can be dispensed with.

Another advantage of the proposed method is that when used according to the invention of practically anhydrous dimethylformamide compared to known solvents very much high solvency can be fully exploited.

To explain this, the following table compares the solubilities of the components of a C ₄ fraction that are characteristic for gas separation in anhydrous dimethylformamide at normal pressure with the solubilities in some known solvents:

Nl I-at

at 20 ⁰ C.

N-methylpyrrolidone

+ 5% H ₂ O

Acetonitrile

+ 5% H ₂ O

%
Dimethylformamide

cis-butene-2

38
49

1,3-butadiene

48

63
86

Vinyl acetylene

265

307
421

The selectivity of dimethylformamide that can be achieved without the addition of water is essential for the required separation process completely adequate.

Another advantage of using the dimethylformamide as a solvent results from its low vapor pressure, which is 2 Torr ^{at a temperature of 20 ° C.} The evaporation losses can thereby be kept extremely low.

Furthermore, an additional separation effect is achieved through the forced exchange of substances, which is carried out to displace the components that are more volatile than butadiene from the solvent either indirectly, by partially heating the solvent, or directly, by introducing purified and separated butadiene into the lower part of the absorption column will. The components, which are less volatile than butadiene, are separated off by a backwashing effect in the desorption column, i.e. these hydrocarbons are washed out of the desorbed gas mixture in the upper part of the desorption column by means of the cold, condensed solvent vapor from the butadiene stream and pressed into the lower part of the column .
Finally, it is possible to carry out the discharge of the gas stream, which is heavily enriched with hydrocarbons, which are less volatile than butadiene, without interference from polymer formation or without the use of additional solvents.

The method should be based on the F i g. 1 and 2 are explained in more detail.

The absorption column 1 is fed via line 2 approximately in the middle with a gaseous C ₄ fraction under atmospheric pressure. The via line 3 to the absorber at temperatures from 20 to 5O ⁰ C, preferably at 30 influent to 40 ⁰ C, the working top of the column 1 solvent washed from the oncoming flow of gas in addition to a small amount of lighter compared to butadiene-volatile hydrocarbons, the Butadiene and, compared to butadiene, the less volatile components and is in the lower half of the column either by means of the heater 4 a temperature increase to 60 to 140 ⁰ C, preferably 115 to

130 ° C, for the selective desorption of the dissolved butenes and a part of the butadiene is exposed (Fig. 1), or it is at the same temperatures as in the upper part the absorption column a butadiene stream originating from the top of the desorption column 7 via line 14 returned to the lower part of the absorption column (FIG. 2), the return gas ratio in relation to the amount of butadiene used is 8 to 20, preferably 12 to 15. In doing so, as a result the higher selectivity of the solvent towards butadiene displaces the butenes from the solvent. Compared to butadiene, the more volatile components leave the absorption column via the Line 5.

The gas-saturated solvent reaches the middle of the desorption column 7 via line 6 , the lower part of which is kept at 153 ° C. by means of the heater 8. As a result of the temperature gradient along the column, there is a concentration gradient corresponding to the different solubility of the solvent in relation to the dissolved components, so that highly purified butadiene collects in the upper part of the column 7 and is passed on via line 10 after passing through the cooler 9.

The gas mixture containing the components that are less volatile than butadiene and a very small part of the butadiene is passed at a suitable point from the lower part of the column 7 at a temperature of 115 to 145 ^° C. via line 11 to cooler 12 and via line 13 discharged, while the regenerated solvent is fed back to the circuit via line 3 after intermediate cooling.

example 1

A packed high efficiency absorption column having a length of 10 m and a

ίο had a clear width of 40 mm, was charged at a height of 6 m with 200 l / h of a gaseous C ₄ fraction of gasoline pyrolysis of composition A (see Table 1). 6 l / h of dimethylformamide containing 0.1 percent by weight of water were introduced into the top of the column as a solvent at a temperature of 30 ° C. under atmospheric pressure. 155 l / h of a gas of composition B (see Table 1) containing predominantly butenes were withdrawn at the top of the column.

The heated at the bottom to 125 ⁰ C, part of the absorption column accumulated gas-saturated dimethylformamide was in mid-height in a packed stripping column containing of 4 m in length and 40 mm internal diameter, the lower part

as was ^{heated to 153 0} C, initiated. At the top of this column, 44 l / h of butadiene of composition C (see Table 1) and in the lower part of a side stream at a temperature of 135 ° C. 0.6 l / h of a gas mixture of composition D (see Table 1) were added via a cooling system. Table 1).

Table 1

A.
(Volume percentage)

B.
(Volume percentage)

(Volume percentage)

(Volume percentage)

Propene ......

Propane ......

Isobutane
n-butane

Butene-1

Isobutene

trans-butene-2
cis-butene-2 ..

Butadiene

Isoprene

Pentenes

Ethyl acetylene
Vinyl acetylene

0.1 percent by volume

0.5 percent by volume

4.2 percent by volume

9.6 percent by volume

18.9 percent by volume

24.8 percent by volume

11.0 percent by volume

8.1 percent by volume

22.6 percent by volume

> 850 ppm

500 ppm
600 ppm

0.1 percent by volume

0.6 percent by volume

5.4 percent by volume

12.4 percent by volume

24.4 percent by volume

31.9 percent by volume

14.1 percent by volume

10.3 percent by volume

0.7 percent by volume

> 0.1 percent by volume

> 0.1 percent by volume
99.66 percent by volume
50 ppm

> 50 ppm

43 percent by volume f 16 percent by volume \ 8 percent by volume ( 15 percent by volume \ 18 percent by volume

Example 2

An absorption column according to Example 1 was charged with 200 l / h of a gaseous C ₄ fraction from gasoline pyrolysis with the composition A (see Table 2). 6 l / h of dimethylformamide containing 0.2 percent by weight of water were introduced into the top of the column at a temperature of 30 ^° C. under atmospheric pressure. At the lower end of the column, 600 l / h of butadiene of composition C (see Table 2) were fed from the top of the desorption column.

At the top of the absorption column, 116 l / h of a gas predominantly containing butenes were obtained Composition B (see Table 2) taken.

The accumulated in the lower part of the absorption column Gas-saturated dimethylformamide was in the middle of that described in Example 1 Desorption column fed. At the top of this column, 684 l / h of butadiene were added via a cooling system of composition C (see Table 2) and in the lower part via a side stream 1 l / h of one Gas mixture of composition D (see Table 2) obtained.

Table 2

A (volume percentage)

(Volume percentage)

(Volume percentage)

(Volume percentage)

Propene

propane

Isobutane

η-butane

Butene-1

Isobutene trans-butene-2 cis-butene-2 ..

Butadiene

Isoprene

Pentenes

Ethylacetylene Vinylacetylene

2.8 0.3 3.4 5.2 9.8

20.2 9.2 6.4

42.3

0.16 0.24

4.8

0.5

5.9

9.0

16.8

34.8

15.9

10.9

1.4

0.1 percent by volume 0.1 percent by volume

0.1 volume percent 99.7 volume percent

<55 ppm
<50 ppm

38%

From the examples it can be seen that the butadiene obtained in this way corresponds to its high Degree of purity not only for polymerizations, but also for oligomerization and cyclooligomerization can be used.

For this purpose 2 sheets of drawings

509 634/261

Claims (3)

1 2 the purity requirements for polymerisation claims: processes. It is also known to the solvent 1. Process for obtaining polymeriza- increasing the selectivity of the separation process to add water capable of butadiene from this containing 5, which, however, as will be explained later on Q-fractions by gas-liquid scrubbing, has considerable disadvantages.
It is also known, characterized by gas-liquid scrubbing, that the gas-liquid scrubbing with dimethylformamide with recycling of already scrubbing with less than 1 weight percent separated butadiene of this with a purity water containing dimethylformamide in a io degrees of 98% and more to be won.
Absorption zone and one adjoining it- The butadiene obtained in this way contains the desorption zone, but impurities that are less volatile than the gas-saturated butadiene obtained during absorption, such as acetylenes and solvents, which are lighter than butadiene 1,2-dienes (allenes), and small proportions of C ₅ -volatile hydrocarbons in the lower 15 olefins and diolefins, such as pentenes and isoprene, area of the absorption zone by means of a butadiene and therefore requires special post-treatment, drives out and together For example, acetylene compounds, such as iron-dissolved volatile fractions at the top. the polymerisation process of butadiene, which is less volatile than butadiene.
Hydrocarbons in the lower range of the desorption zone are known to accumulate the undesired acetylenes and to remove only small amounts of this generally first continuously from the gas mixtures by means of a mixture containing butadiene, to remove selective hydrogenation. However, this is associated with considerable butadiene losses during the pure butadiene from the upper end. the desorption zone is derived. 25 It is also known that butadiene, acetylenes 2. The method according to claim 1, characterized in that the allenes initially collectively from the C ₄ fraction that the to expel the in comparison tion to be separated and then the butadiene from butadiene more volatile hydrocarbons these mixtures, for example with ammonia from the gas-saturated solvent Lischer used copper salt solution or with selectively acting, butadiene stream either by partial desorption of the 30 preferably water-based solvents, such as. B. to extract solvents by heating to 60 to 140 ° C, lactones, pyrrolidones, dialkylformamides, fur preferably to 115 to 130 ° C, in the lower furol, acetonitrile or dimethyl sulfoxide, generated area of the absorption zone or as a partial with different operating at higher pressures current to be applied at the top of the desorption process process. For example, emerging pure butadiene has been removed and is known in 35 that vinyl acetylene is initially distilled back through a lower pressure region of the absorption zone as an azeotropic mixture with butene-2. or as a side stream of a fractionation of an over- 3. The method according to claim 1 and 2, characterized in that the mixture containing butadiene is indicated, that you enrich a dimethylformamide and then the vinylacetylene-rich fraction with a water content of 0.1 to 0.3 wt. 40 an extractive distillation with aqueous furfural percent used. to undergo. It is also known, in the absence of diolefins, to use alkynes of alkenes with the aid of gas-liquid scrubbing using dimethylformamide 45 as a solvent at higher pressures and depths Separate temperatures. However, all of these procedures are relatively complex, since the separation of the interfering components in an additional stage must be carried out. 50 It is also known, butadiene from acetylenes It is known to carry out an active, water-containing solvent extraction by means of dimethylformamide for enrichment or separation and alkenes practically at atmospheric pressure by means of butadiene, for example when working up a fractional desorption from a selective fractions of the catalytic butane dehydrogenation. separate and enriched with acetylenes and allenes. Atmospheric pressure as the solvent and the pressures N-methylpyrrolidone, acetonitrile and the use of inert gases such as nitrogen or carbon furfural with more than 5 percent by weight of water dioxide are used to recover the enriched or saturated water.
Butadiene from the solvent. Finally, it is known to produce a vinyl acetylene It is also known to use such separations as liquid 60 the dehydrogenation of highly saturated hydrocarbons Execute liquid extraction and with an increased high-percentage butadiene stream coming through Pressures and low temperatures to work. A fractional desorption using However, such a procedure requires a relatively selective acting solvent, such as. B. N-Memäßig high technical effort. thylpyrrolidone, acetonitrile, furfural or dimethyl It is also known that butadiene can be separated off by gas formamide and aqueous solutions thereof. Liquid washing in countercurrent with dimethyl- The presence of water is in the case of the to isolate formamide from gas mixtures. That required on N-methylpyrrolidone and furfurols Butadiene obtained in this way does not meet the boiling point of the butadiene in the desorption of the butadiene