GERMAN DEMOCRATIC REPUBLIC

OFFICE FOR INVENTIONS AND PATENTS

PATENT 133561

[SEAL] Economic Patent

Granted pursuant to §5 subs. 1 of

the amending law to the Patent Act

Published in the version submitted by the applicant

Int. Cl.²

(11) 133 561 (44) January 10, 1979 2(51) C 07 C 121/32

(21) WP C 07 C / 202 134 (22) November 18, 1977

(71) See (72)

(72) Dobberstein, Lutz; Marschner, Rolf, Grad.Eng.;

Mittenhuber, Karl, Grad.Chem.; Schaller, Wolfgang, Grad.Chem., DD

(73) See (72)

(74) Eberhard Wille, VEB Petrolchemisches Kombinat Schwedt,

Research and Development Management Division,

Industrial Property Rights Division, 133 Schwedt

(54) Method for the Production of Acrylonitrile

(57) The invention relates to an improved method for the production of acrylonitrile through the use of a new polymerization inhibitor during purification of the product. The object of the invention is to prevent acrolein-induced polymerization in the columns of the distillative purification steps, in conjunction with low acrylonitrile and hydrogen cyanide losses. Furthermore, the inhibitor shall combine such properties as low production costs, simple metering and high volatility under distillation conditions. It has been found that an o-, m- or p-cresol or a mixture thereof in concentrations ranging from 0.01 to 0.05%, based on the volume of the head reflux, is injected in a manner that is well-known on the upper-most plates of the columns that are used during distillative purification of acrylonitrile.

Field of Application of the Invention:

The invention relates to an improved method for the production of acrylonitrile through the use of a new polymerization inhibitor during distillative purification of the product.

Characteristics of the Prior Art Solutions:

There exist a plurality of acrylonitrile polymerization inhibitors, which have satisfied the specific requirements in conformity with the state of the development of the acrylonitrile [ACN] process over that time. With the development of new catalysts and improved process engineering, qualitatively new parameters have evolved in terms of both the starting mixture of the reactor and the technology. Hence, from the viewpoint of applied engineering these polymerization inhibitors can no longer stand up to the new parameters in terms of technology and thrift.

For example, the use of new multi-component catalysts is associated with not only a high yield but also an increased formation of acrolein.

With hydrogen cyanide, acrylonitrile, acetonitrile and ammonia, acrolein constitutes an extremely reactive compound.

The secondary reactions, which are introduced especially through acrolein, result in a loss of hydrogen cyanide and acrylonitrile, both of which can be fed, as high polymers, only to a cost intensive combustion or pressure oxidation. Furthermore, the clogging of the equipment causes problems. In the case of the polymerization inhibitors that have been used to date - like nitroso compounds (DT-OS 1543209) or nitroxides (DT-OS 2149670) -, no specific effect on acrolein or pure mixtures has been detectable.

Therefore, they are not suitable for use in modern ACN facilities. In addition, the complicated structure of such inhibitors incurs additional production costs as well as problems due to uncontrolled secondary reactions. Furthermore, these inhibitors, such as hydroquinone, tend to crystallize at lower temperatures, a feature that necessitates additional technological complexity during the metering process.

Object of the Invention:

The object of the invention is to develop an improved method for the production of acrylonitrile through the use of a new polymerization inhibitor during distillative preparation of an ACN-containing product stream.

According to this method, the simplified molecular structure of the inhibitor shall significantly reduce the production costs and prevent an acrolein induced polymerization in conjunction with low losses of acrylonitrile, hydrogen cyanide and acetonitrile. Furthermore, the object is to achieve a simplified metering while at the same time maintaining a good distribution in the column cross section by means of the high fluidity of the new inhibitor.

Presentation of the Essence of the Invention:

It has been found surprisingly that the polymerization of a ACN-containing mixture, which is subjected to a distillative treatment, is prevented if cresol is used as the polymerization inhibitor.

In this case, the industrially produced m-, p-, o-cresol or a mixture thereof can be used without any special purity requirements.

The volatility of the cresol in the distillative mixture and the feeding of the inhibitor into the heads of the columns guarantee a high degree of distribution in the columns under distillation conditions. Owing to the high efficiency of the inhibitor only a concentration ranging from 0.01 to 0.05 %, based on the volume of the head reflux, is necessary.

Therefore, a notable reduction in the polymers, which can be decomposed only with difficulty, in the waste water as well as a lower loss of acrylonitrile and hydrogen cyanide must be recorded. In addition, the cresol stays pumpable and meterable without the addition of a solvent or concomitant heating of the fittings during winter operation.

Embodiment:

Example 1

Acrylonitrile samples were treated with a variety of different inhibitors and subjected to a polymerization test (heated under O₂ atmosphere in a bomb).

In this case the following results were obtained:

a) ACN with 40 ppm of hydroquinone

polymerization (breaking point) after 4 to 6 hours

b) ACN with 40 ppm of hydroquinone methyl ether

Polymerization varied; the breaking point fluctuated between 5 and 8 hours

c) ACN with 40 ppm of cresol (mixture of m- and p-cresol with low amounts of o-cresol)

No polymerization after 12 hours, thereafter the tests were terminated.

Example 2

Cresol is injected onto the heads of the columns, which are employed during the recovery of acrylonitrile as the distillative purification steps. During a long term test of four months, a decrease in the carbon content in the waste water stream could be determined by analysis.

The decrease ranged on average from 1 to 2%.

Furthermore, owing to the simplified metering (no restriction due to low outside temperatures, metering without solvent) significant techno-economical advantages are achieved.

In addition, since cresol exhibits a higher volatility as compared to other inhibitors, better inhibition in the ACN vapor stage is achieved.

Hence, at the same time it was possible to significantly reduce the metering of the stabilizer hydroquinone mono methyl ether at the head of the production column, thus further improving the economical results.

Patent Claim

Method for the production of acrylonitrile when using a polymerization inhibitor in the distillative purification steps, characterized in that an o-, p- or m-cresol or a mixture thereof in concentrations ranging from 0.01 to 0.05%, based on the volume of the outer reflux, is injected in a manner that is well-known onto the head of the columns that are used during distillative purification of acrylonitrile.