DE1132554B - Process for the production of the purest acrylic acid nitrile - Google Patents

Description

Process for the production of the purest acrylonitrile Acrylonitrile is difficult to obtain in a perfectly pure state. All known display methods initially provide a more or less impure nitrile. Depending on how the Acrylic acid nitrile is the impurities z. B. to polymers of Acetylene to acetaldehyde or ketones. There are numerous ways to remove these admixtures Suggestions have been made. Nevertheless, these processes can be used to purify the acrylonitrile cannot yet be described as satisfactory, as it has not yet been possible to to remove the last remnants of foreign compounds from the nitrile.

German Patent 851 341 proposes acrylonitrile to be cleaned by introducing chlorine. However, acidic acrylonitrile is always used and the use of chlorine results in inconsistent, chlorinated ones Connections which are very difficult to remove and whose presence is evident the properties of the polymers and copolymers obtained from the acrylonitrile has a detrimental effect.

Even when using nitrosyl chloride (see the German Auslegeschrift 1003 207) interfering chlorination products of acrylonitrile are formed.

Other methods of cleaning, e.g. B. the partial hydrogenation lead also not to completely pure acrylonitrile, as they attack this.

Also the treatment of optionally prepurified acrylonitrile with mercury chloride or copper halides or with resorcinol and sulfuric acid does not lead to a nitrile, which z. B. with sulfuric acid after a long time at all not discolored.

There has now been a process for the production of the purest acrylonitrile found, which is characterized in that prepurified acrylonitrile, which is as free as possible of vinyl methyl ketone, with about 1 to 10'0 / c acetic anhydride and about 0.1 to 0.5% anhydrous ferric chloride for about 0.5 to 5 hours heated under reflux and then immediately distilled off the acrylonitrile.

Preferably, 5% acetic anhydride and 0.3 0.3% are used anhydrous iron (III) chloride with a heating time of 3 hours.

It is known that acetic anhydride reacts with carbonyl groups under the catalytic action of anhydrous iron chloride to form diacetates of the general formula.

However, it was not to be expected that this reaction would also take place when the aldehyde is present in very great dilution, in amounts from 0.1 to 0.010 / o and acetic anhydride as well as anhydrous ferric chloride are also only very high diluted in the acrylonitrile.

However, it is completely surprising that acrylonitrile, which obtained by the addition of hydrogen cyanide to acetylene, by heating with Acetic anhydride can be purified in the presence of anhydrous ferric chloride; because this acrylonitrile contains polymers of acetylene as an impurity, their reactivity with acetic anhydride and anhydrous ferric chloride is not is easy to explain. Acrylonitrile of this origin is used, however also cleaned to the greatest extent by the treatment mentioned.

The process of the invention produces a purer acrylonitrile obtained than is possible with the previously known cleaning methods. However must the acrylonitrile z. B. by repeated distillation or by others known cleaning methods pre-cleaned and as free as possible from vinyl methyl ketone be.

The process of the invention continues to work with very high yields, as by treatment with acetic anhydride and anhydrous ferric chloride only very little acrylonitrile is lost. Another advantage of this cleaning process is that no water is brought into the acrylonitrile, whereby the formation of an azeotropic mixture is prevented.

With the process of the invention, an acrylonitrile is obtained, which z. B. after adding 3 percent by weight of concentrated sulfuric acid even not discolored in any way after three months.

The colorlessness was determined by measuring the extinction at 4000 Å. In the case of the acrylonitrile purified by the process of the invention, a Absorbance at said wavelength can be observed while acrylonitrile before the final cleaning at this wavelength after the addition of sulfuric acid shows quite a considerable extinction (see Fig. 1). All other cleaning methods, with which the pre-cleaned acrylonitrile is treated, result after Addition of 3 O / o sulfuric acid already after 3 days clear extinctions at 4000 Å, which are between 0.023 and 0.800 and are clearly brownish in color are recognizable.

Fig. 2 shows the absorption curves in the ultraviolet over the effect various cleaning processes on pre-cleaned acrylonitrile. at The recordings of the ultraviolet spectrogram were taken with a concentration of 15.2 Mol per liter worked and measured at layer thicknesses of 3.88, 0.88 and 0.13 cm. It means curve 1: starting acrylonitrile.

Curve 2: starting acrylonitrile treated with HgCl2 and HgCl (Chemical Abstracts, vol. 51, 1957, column 9212c).

Curve 3: Starting acrylonitrile treated with Cu Cl and NU4 CM at PH2 (Cemical Abstracts, vol. 52, 1958, column 1207d).

Curve 4: starting acrylonitrile treated with resorcinol and sulfuric acid (German patent specification 881 651).

Curve 5: starting acrylic acid nitrile treated with CuCl and CuCN (Chemical Abstracts, vol. 52, 1958, column 1207d).

Curve 6: starting acrylonitrile treated with CuCl2 and Cu2Cl2 (Chemical Abstracts, vol. 52, 1958, column 1207e).

Curve 7: Starting acrylonitrile treated according to the process of the invention.

The acrylonitrile treated by the process of the invention So it has the highest degree of purity.

Example 1 Acrylonitrile is produced by the addition of hydrocyanic acid Acetylene produced and purified to the extent that its Impurities are less than 1% (see Fig. 3, curve a).

A solution of 10 parts of this prepurified acrylonitrile and 1 part acetic anhydride and 0.02 part anhydrous ferric chloride 4th Heated to boiling on the reflux condenser for hours.

The acrylonitrile is then distilled off at a transition temperature of 760.degree. 9.6 parts of highly purified acrylonitrile are obtained in a yield of 96%. That The ultraviolet spectogram of this acrylonitrile is shown in Fig. 3, curve b.

The acetic anhydride can be obtained from the distillation residue of the acrylonitrile can be recovered in high yield.

Example 2 10 parts of acrylonitrile purified by multiple distillation (see. Fig.4, curve a) with 0.5 part of acetic anhydride and 0.03 part of anhydrous Ferric chloride added. The solution is refluxed for 2 hours. the end this is 9.65 parts of more highly purified acrylonitrile (see Fig. 4, Kurveb) and 0.45 parts of acetic anhydride obtained by distillation.

Example 3 Acrylonitrile is acetylated by thermal cleavage Lactic acid nitrile obtained from acetaldehyde, hydrocyanic acid and acetic anhydride has been received. 10 parts of this acrylonitrile, purified as far as possible by distillation, which still contains about 0.3 o / o acetaldehyde are mixed with 0.3 parts of acetic anhydride and 0.04 parts of anhydrous ferric chloride were added. The solution is on for 3 hours The reflux condenser is heated to the boil. This becomes 9.4 parts by distillation Acrylic acid nitrile with a boiling point of 760 C in 940 / above yield, along with 0.28 parts of acetic anhydride won. The ultraviolet spectrograms are shown in Fig. 5. The curve a denotes the aldehyde-containing nitrile, curve b denotes the purified acrylonitrile.

Claims (1)

PATENT CLAIM. Process for the production of the purest acrylonitrile, thereby characterized in that one pre-purified acrylonitrile, which is as free as possible from Vinyl methyl ketone, with about 1 to 10 0 / o acetic anhydride and about 0.1 to 0.5 ovo anhydrous iron (III) chloride heated under reflux for about 0.5 to 5 hours and then the acrylonitrile is immediately distilled off. ~~~~~~~~ Considered Printed publications: German Auslegeschrift No. 1003207; German patents No. 851 341, 881 651, 927 927, 944012; U.S. Patent Nos. 2,382,383, 2,770 645, 2,784,216, 2,784,217, 2,784,218, 2,792,415, 2,799,630; French patent specification No. 1,129,075; Japanese Patent Application SHo 32/7318 (published 9.9.1957); Chemical Abstracts, vol. 51, 1957, column 9212c; Vol. 52, 1958, column 1207 e.