DE2115858C3 - Process for stabilizing butadiene or isoprene and / or cyclopentadiene when they are obtained from hydrocarbon mixtures - Google Patents

Description

th. Suitable groups R are, for example, the methyl, jJ-Methoxyäthyl-, 0-Phenoxyäthyl-, j9-Dimethylaminoäthyi-, isopropyl, butyl, octyl, decyl, stearyl, cyclohexyl, cyclooctyl, cyclododecyl, methyloleyclohexyl, cyano-cyclohexyl and benzyl group.

The N-substituted N-nitroso-hydroxylamine _L , can be used as such and / or in the form of the salts as inhibitors. The transition metals, the metals of group 3a of the periodic table, the alkaline earth metals and in particular the alkali metals and the lanthanides are preferably used as cations (the transition metals and the metals of group 3a correspond to those in the periodic table according to the Handbook of Chemistry and Physics, 49th edition [1968 —1969] specified elements.) Suitable metals are z. B. sodium, potassium, magnesium, calcium, aluminum, lead, silver, copper, zinc, mercury, cerium, iron, nickel, cobalt. The ammonium cation and organic radicals such as lower alkyl or cycloalkyl groups, e.g. B. cyclohexyl substituted ammonium cations are suitable. Metals with complex-bound ligands, for example [Cu (NH ₃ ) ,,] + *, also come into consideration as cations. For practical reasons, the ammonium salts of the N-substituted N-nitroso-hydroxylamimes, which may be substituted by organic radicals, are preferred, since these inhibitors give a residue during the distillative regeneration of the solvents used in the separation processes described above, which can be incinerated without difficulty. Because of their easy accessibility: the alkali salts are also used with advantage.

The preparation of the inhibitors to be used according to the invention is known per se. For example, they can be prepared by reducing the corresponding nitro compound of the general formula RNO ₂ , in which R has the abovementioned meaning, to give the hydroxylamines and then nitrosating the hydroxylamines obtained.

As the salts of the N-substituted N-nitroso-hydroxylamine are usually more stable than the corresponding free compounds, are advantageous the salts of these compounds are used as polymerization inhibitors.

The polymerization inhibitors are advantageously used for those processes for stabilizing butadiene when it is obtained from hydrocarbon mixtures or isoprene and / or cyclopentadiene when it is obtained from Cs hydrocarbon mixtures at which elevated temperatures, e.g. B. temperatures of 50 to 180 ⁰ C or even higher temperatures are required. Suitable selective solvents for the decomposition of the hydrocarbons are, for example, dimethylformamide, dimethylacetamide, furfural, acetonitrile and in particular N-alkylpyrrolidones such as N-methylpyrrolidone. It can be advantageous to add a small amount of water, for example 5 to 15, preferably 5 to 10% by weight, to the selective solvents in order to increase the selectivity.

The use of the N-substituted N-nitrosohydroxylamines to be used according to the invention and or or their Sab: e takes place in a manner known per se, for example by adding them to the mixtures of the Hydrocarbons and / or added to the solvent. The polymerization inhibitors can be used here be added in substance or in the form of their solutions, whereby - depending on the point of addition - appropriate the hydrocarbons to be separated, the selective solvent used in the separation process or water can be used as a solvent.

^ Of course, you can use the invention to polymerization inhibitors used also as a solution in another optionally water-containing one Add organic solvent or solvent mixture. The concentration of the polymerization inhibitor based on the amount of selective solvent is usually very small and amounts to generally 1 wtppm to 10 wt%, preferably 1 wtppm to 0.1 wt%. in particular 10 to 100 weight sppm. It is true that larger concentrations of the polymerization inhibitor can also be used admit, however, there is generally no benefit.

To maintain a certain concentration of the polymerization inhibitors in the selective It can be advantageous to add such N-substituted N-nitrosohydroxylamines or their salts to solvents use that have only a relatively low solubility in the selective solvents used, the about the desired concentration of the polymerization inhibitor in the relevant seleküven solvent is equivalent to. Used a certain amount of these polymerization inhibitors with limited solubility in a suitable manner, for example in a filter basket, as a depot in the circuit of the selective solvent

If the separation process in question is incorporated, the desired concentration of the polymerization inhibitor can be kept constant over a relatively long period in a simple manner.

The N-substituted N-nitroso-hydroxylamines and

jt5 or their salts are very effective polymerization inhibitors to stabilize butadiene or isoprene and / or cyclopentadiene in their Extraction from hydrocarbon mixtures by means of selective solvents, with a compound or Mixtures of several of these polymerization inhibitors can be used. However, it can be advantageous, one or more of these polymerization inhibitors in combination with conventional ones Inhibitors such as mono- or polyphenols, e.g. B.

■ 4S tert-butylpyrocatechnine or hydroquinone, mcrcaptans, Phenothiazine, aromatic amines such as j3-naphthylamine, esters of phosphorous acid, Use methylene blue, aliphatic or aromatic aldehydes, sodium nitrile.

It can also be advantageous to add substances to the selective solvent with which a certain pH values, preferably values between 7.5 and 9, can be adhered to, such as buffer substances, z. B. salts of phosphoric acid, lower aliphatic

5S carboxylic acids, e.g. B. acetic acid, or alkali hydroxides or alkali carbonates, e.g. B. Sodium Hydroxide and Soda.

example 1

N-methylpyrrolidone (NMP) and the inhibitors listed in the table below are poured into a carefully cleaned autoclave with the exclusion of air. Sufficient butadiene is then added that at 140 ^° C. an overpressure of 15 atm is created. After 20 hours, the amounts of polymers formed are compared with one another. The following results are obtained:

Table 1

Inhibitor

concentration

in NMP Gewichlsppm effect

1. none

2. Ce III salt of N-nitrosooyclohLxylhyroxylamine 1000

3rd same 500

4. The same 100 5. Ca-salt of N-nitrosocyclohexylhydroxylamine 1000

6. The same "500

7. K. Salt of N-nitrosocyclohexylhydroxylamine 1000

8.NHvSaIz of N-nitrorocyclohexylhydroxylamine 500

9. AI salt of N-nitrosocyclohexylhydroxylamine 1000

10. NaNO ₂ 1000

11.NaNO ₂ 500

12. N-nitrosophenyl hydroxyamine 1000

13. The same. 500 I4.p-nitrobenzoic acid 500 15.Nitrobenzene 500 Lö.Nitrophenol 500 17.Nitroaniiline 500 18. Mixture of o-nitrophenol and NaNG ₂ 500 + I9.tert.-butylpyrocatechol 1000 20.N, N-diethylhydroxylamine 1000 21. Na salt of N-nitroso-n-octylhydroxylamine 1000 22. Na salt of N-nitroso-N-cyclodecylhydroxyl-1000

amine

23. Na salt of N-nitroso-N-cyclooctylhydroxylamine 1000

This table shows that the polymerization inhibitors to be used according to the invention in
N-methylpyrrolidone under elevated temperature and
Are better inhibitors than sodium nitrate,

very strong polymerization

no polymerization

few polymers (like 1000 ppm NaNO ₂ )

Polymers (such as 500 ppm NaNO ₂ )

very little polymers

few polymers (like 1000 ppm NaNO ₂ )

few polymers (less than with

1000 ppm NaNO3)

few polymers (like 1000 ppm NaNO ₂ )

few polymers (a little better than 10.)

few polymers (more than 7th, like 3rd)

Polymers

strong polymerization

very strong polymerization

more polymers than at 500 ppm NaNO ₂

more polymers than at 500 ppm NaNO ₂

more polymers than at 500 ppm NaNO ₂

more polymers than at 500 ppm NaNO ₂

worse than 1000 ppm NaNO ₂

very strong polymerization

few polymers, like 500 ppm NaNO ₂

few polymers (like 7.)

few polymers (like 1000 ppm NaNO ₂ )

few polymers

which in turn has the stabilizing effect of organic nitro compounds and other known polymerization inhibitors Exceeds (see. The comparative experiments Examples 10 to 20).

example

N-methylpyrrolidone,
which is 500 ppm by weight peroxide (calculated as H ₂ O ₂ ) 40
and those in Table 2 below
listed inhibitors filled. It will be so much
Butadiene added that at 140 ° C a pressure of
15 atm in the autoclave. After 20 hours

Table 2

the amounts of polymers obtained are compared with those amounts of polymer which are obtained when sodium nitrite is used as an inhibitor in peroxide-free NMP 1000 ppm by weight during the same time under the same test conditions.

Inhibitor

a) NMP with 500 ppm by weight peroxide

1. Cer-III salt of N-nitrosocyclohexylhydroxylamine

2. Ca-CaIz of N-nitrosocyclohexylhydroxylamine

3. the same

4. K salt of N-nitrosocyclohexylhydroxylamine

5. none

b) NMP without peroxides

6. Sodium nitrite

From Table 2 it can be seen that the salts of N-nitrosocyclohexylhydroxylamine even in peroxide-containing NMP are better polymerization inhibitors than sodium nitrite in peroxide-free NMP.

example

In a carefully cleaned autoclave for 6 seconds, an overpressure of 5 atm is created at 140 "C. After

with the exclusion of air N-methylpyrrolidone (NMP) and the 20 hours, the amounts of

inhibitors polymers mentioned in the table below compared with one another. There were the following

filled. Then enough isoprene is added, results are obtained:

concentration effect in NMP Weight ppm 1000 few polymers 1000 few polymers 1500 very little polymers 1000 few polymers - very strong polymerization 1000 few polymers (more than 1, 2 and 4.)

Table 3

Inhibitor

concentration
in NMP
(Wt .-%)

1. none -

2. Ce III salt of N-nitrosocyclohexylhydroxylamine 1000

3. Ca salt of N-nitrosocyclohexylhydroxylamine 1000

4. K salt of N-nitrosocyclohexylhydroxylamine 1000

5. NH t-salt of N-nitrosocyclohexylhydroxylamine 1000

6. NaNCh 1000

effect

very strong polymerization

few polymers

few polymers, a little more than

at 2.

few polymers, a little more than

at 2.

few polymers

Polymers

(more than 2nd, 3rd, 4th, 5th)

Example 4

Dimethylformamide (DM F) and the in the following table filled with inhibitors.

Table 4

Sufficient butadiene is then added that a pressure of 15 atm is established in the autoclave ^{at 140 ° C.} After 20 hours, the amounts of polymers obtained are compared with one another. The following results were obtained:

Inhibitor

1. none

2. Ce-IH salt of N-nitrosocyclohexylhydroxylamine

3. Ca salt of N-nitrosocyclohexylhydroxylamine

4. NI-U salts of N-nitrosocyclohexylhydroxylamine

5. NaNO ₂

concentration effect in the DMF Wt .-%) very strong polymerization 1000 no polymerization 1000 very little polymers 500 few polymers 1000 few polymers (more than 4.)

The usefulness of the results from the rapid test described in the previous examples was by comparison with the results when measuring factors for polymer deposition (fouling factors) in an experimental plant for the dismantling of Q-crack cuts with extractive distillation under Use of N-methylpyrrolidone as a selective solvent has been examined. An estimate of the Inhibitory effect of the inhibitors used in the examples when used in a technical Separation plant is possible by comparing it with the action of sodium nitrite, for precise measurements of There are fouling factors. The fouling factor has, for example, when using N-methylpyrrolidone as a selective solvent and a sodium nitrite concentration of 100 ppm approximately the value of 1 x 10- "per month.

Claims (1)

Claim: Process for stabilizing butadiene when it is obtained from C ₄ hydrocarbon mixtures or from isoprene and / or cyclopentadiene when it is obtained from C5 hydrocarbon mixtures at elevated temperature using selective solvents in the presence of polymerization inhibitors, characterized in that N-substituted N-nitrosohydroxylamines are used the general formula R -N -OH NO in which R is an aliphatic, cycloaliphatic or substituted by inert radicals means araliphatic hydrocarbon radical with up to 20 carbon atoms, and / or their Salts used as polymerization inhibitors. 25th Mixtures containing hydrocarbons containing unsaturated compounds are important starting materials for the extraction of valuable petrochemical preliminary products such as acetylene, butene, butadiene, isoprene, Cyclopentadiene and aromatics. For the large-scale production of these preliminary products are predominantly used today in pyrolysis processes, in dehydration processes and in the incomplete combustion of hydrocarbons Hydrocarbon mixtures obtained with oxygen are used, from which the said Pre-products using special separation processes, for example with the help of solvent absorption, countercurrent gas scrubbing, extractive distillation, liquid-liquid extraction or a combination these processes using selective solvents. In the with these Apparatus used for separation processes, such as columns, heat exchangers, pumps, can now go through the deposition of high molecular weight compounds that are sparingly soluble in the solvents used, Difficulties arise because the deposits can lead to clogging of the apparatus. One This makes it impossible to carry out the separation process continuously over extended periods of time. As the hydrocarbon mixtures used for the decomposition rubbed the main products a variety of various olefinically and / or acetylenically unsaturated compounds, it was previously despite, many studies not possible about the chemical mechanism of the formation and about the Get a clear picture of the nature of these deposits. For example, polymerization inhibitors are such as tertiary butyl catechol, which is commonly used for the fi.s Preventing the polymerization of monomers such as butadiene or styrene can be used for the Preventing polymer deposits without any effect. Conversely, however, it also holds that ζ. B. Sodium Niirite, which has a relatively good effect of preventing polymer deposits, as an inhibitor for the storage of monomers such as butadiene is completely unsuitable. Also show connections like that N-diethylhydroxylamine and salts of N-nitrosuphenylhydroxylamine, which are very effective inhibitors in preventing popcorn polymerization, almost No or extremely little effect in preventing polymer deposits. Apparently, in addition to polymerisation processes, oxidation processes also play a role in the formation of polymer deposits an important role. Without uneconomically large equipment expenditure, it can be in the In most cases it is impossible to avoid that - even if a technical system is operated at overpressure - but small amounts of oxygen enter such a system. The elemental analysis of the Deposits that occur in the technical implementation of one of the above-mentioned separation processes in the absence of polymer scale inhibitors have shown that these deposits are surprisingly high Quantities, e.g. B. up to 5 wt .-%, contain oxygen. An advantageous process has now been found for stabilizing butadiene when it is obtained from C ₄ hydrocarbon mixtures or from isoprene and / or cyclopentadiene when it is obtained from C5 hydrocarbon mixtures at elevated temperature using selective solvents in the presence of polymerization inhibitors, which is characterized by that one N-substituted N-nitrosohydroxylamines of the general formula N-OH NO in which R is an aliphatic, cycloaliphatic or substituted by inert radicals means araliphatic hydrocarbon radical with up to 20 carbon atoms, and / or their salts used as polymerization inhibitors. By using the polymerization inhibitors to be used according to the invention, it is possible to reduce the continuous decomposition of butadiene or of isoprene and / or cyclopentadiene-containing hydrocarbon mixtures can also be carried out over extended periods of time without interruption. In the N-substituted N-nitroso-hydroxylamines the general formula R N-OH NO R denotes an aliphatic, cycloaliphatic or substituted by inert radicals araliphatic hydrocarbon radical with up to 20, preferably up to 10 carbon atoms. the mentioned groups can also inert radicals such as halogen, hydroxy, lower hydroxy, Containing alkoxy, aroxy, carbonyl, carboxyl, amino, lower alkylamino, sulfo, nitro or cyano groups