JPS5943945B2 - ε↓−Method for purifying caprolactam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying crude lactam recovered by depolymerizing polycapramide with a phosphoric acid or alkali catalyst.

Much research has been done on the purification of crude lactams, such as ε-caprolactam, obtained by Beckman rearrangement of cyclic ketoxime, and various purification methods have been proposed.

For example, methods for purifying crude lactams by multistage distillation, methods for distilling in the presence of alkali or alkali metal peroxides, methods for extraction using organic solvents, activated carbon,
Methods such as treatment with an ion exchange resin, recrystallization, and simple oxidation purification using potassium permanganate, potassium dichromate, etc. are known.

On the other hand, recently, from a resource-saving and economic standpoint, emphasis has been placed on a method of recovering lactam by thermally depolymerizing polylactam.

In the above recovery method, thermally depolymerized crude lactam is recovered as a concentrated aqueous solution, but unlike the lactam obtained by the Beckman rearrangement of a cyclic ketoxime, this crude lactam is extremely difficult to purify. The quality of the lactam obtained is also considerably lower than that commercially available.

This is due to the fact that the thermal depolymerization of polycapramide is exposed to harsh reaction conditions at 280°C, which inevitably results in a large number of impurities, as well as the various additives contained in polycapramide or the dyeing process. This is thought to be because the dyes used tend to cause impurities. One of the conventional purification methods is to make the recovered crude lactam into an aqueous solution, oxidize it with potassium permanganate under neutral conditions, and separate the by-product manganese dioxide, and then immerse the filtrate in alkaline f. Distillation is said to be effective, but the quality of the lactam obtained by this method is not very high, and the volatile base content (hereinafter referred to as V
B) and free base content (hereinafter referred to as FB) are higher than those of commercially available lactams. Therefore, it is very difficult to produce high quality polycapramide suitable for fiber production using only the lactam obtained by the above method.

In view of the above circumstances, the inventors of the present invention have conducted intensive studies to purify the recovered crude lactam using simple operations and obtain high-quality lactam. I found out what can be achieved.

That is, the present invention provides crude ε-
A method for purifying ε-caprolactam, which comprises distilling an aqueous solution of the crude ε-caprolactam under acidic conditions of pH 2 to 6 and distilling it under alkalinity of pH 10 to 14 when purifying caprolatatum; An aqueous solution of crude ε-caprolactam is distilled under acidic conditions,
This is a method for purifying ε-caprolactam, which is characterized in that it is then treated with an oxidizing agent and then distilled under alkaline conditions.
In the present invention, an aqueous solution of crude ε-caprolactam is adjusted to pH
As the acidic substance used for distillation with 2 to 6 acidic acids, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, and monochloroacetic acid can be used. However, two or more types may be used in combination.

If the pH during the above distillation is 2 or less, the purification effect of the crude lactam is high and a highly pure lactam can be obtained, but the lactam is easily hydrolyzed during the distillation, so ε-amino-n-
A large amount of caproic acid is produced as a by-product, which results in a decrease in the yield of lactam after purification, which is not preferable. Also, increase the pH to 6
If it is more than that, the effect of purifying the crude lactam will be lowered, which is not preferable. The lactam that has undergone the above-mentioned distillation process under acidic conditions is made into an aqueous solution by adding condensed water or new water, and then distilled under alkaline conditions, or treated with an oxidizing agent and then distilled under alkaline conditions.

When carrying out the above oxidation treatment, the oxidizing agents used include alkali salts of permanganic acid such as potassium permanganate and sodium permanganate, sodium hypochlorite, potassium hypochlorite, sodium chlorite, and chlorine. Alkali salts of halogen acids such as potassium acid, hydrogen peroxide, sodium percarbonate, sodium perborate, ozone, and the like are used.

In the present invention, it is particularly preferable to use hydrogen peroxide or ozone, which produces fewer by-products after oxidation. For example, when hydrogen peroxide is used, the lactam aqueous solution that has passed through the acidic distillation step has a concentration of 0.001 to 0.5% relative to the lactam.
It is convenient to follow the usual method of adding oxidizing agent in an amount of % by weight, preferably 0.002 to 0.01% by weight, followed by stirring. Note that the amount of the above-mentioned oxidizing agent added or absorbed varies depending on other oxidation conditions and the amount of oxidizable impurities in the lactam aqueous solution to be purified. A sufficient time for hydrogen peroxide treatment is 0.2 to 2 hours.

Additionally, if the temperature of the lactam aqueous solution is too high during treatment, side reactions are likely to occur in addition to oxidizing impurities.
On the other hand, if the temperature is too low, the impurities will not be oxidized and an excessive amount of oxidizing agent will remain, which is undesirable, so care should be taken to keep the temperature as low as possible in the range of 20 to 60°C. In addition, when the above hydrogen peroxide treatment is performed at a pH of 10 to 14, preferably 11 to 13, stronger oxidizing power is exhibited.
It is desirable to add a basic substance such as sodium hydroxide or potassium hydroxide. In distillation under alkaline conditions, if the lactam aqueous solution that has undergone the oxidation treatment is already alkaline as described above, there is no need to add a new alkali. On the other hand, when adding alkali, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide,
By adding a basic substance such as sodium carbonate or potassium carbonate and distilling according to a conventional method, the desired high-purity lactam can be obtained. The amount of alkali added at this time is 0.01 to 1.0% to the lactam in the lactam aqueous solution.
It is preferable to select 0% by weight.

By adopting the present invention having the above configuration,
Amine-based impurities, which were difficult to remove using conventional methods, can be completely removed, and high-purity lactam, which is comparable to commercially available lanotam, can be obtained economically with simple operations.

The present invention will be specifically described below based on Examples, but the present invention is not necessarily limited to these Examples.

In addition, FB,. VBl potassium permanganate value (hereinafter referred to as PZ
) was measured by the following method.

FB: The amount of 1/50 normal hydrochloric acid aqueous solution required to dissolve lactam 507 in 50 ml of distilled water at pH 6 and return the solution to pH 6. Expressed in Meq/Kg.

VB: Lactam 50f 20% sodium hydroxide 10
Dissolve in 0ml and perform steam distillation according to the usual method to 1/50
It is distilled into 10 ml of normal sulfuric acid aqueous solution to give 250TI11.

Next, this aqueous solution is titrated with a 1/50N aqueous sodium hydroxide solution, and the same operation is performed with distilled water, taking into consideration a blank, and expressed in units of Ppm in terms of ammonia. P
Z: Add 1 ml of 1/100N potassium permanganate aqueous solution to 1% lactam aqueous solution, and the color changes from standard solution (cobalt chloride hexahydrate 3y and copper sulfate pentahydrate 27 dissolved in 11 distilled water) The time it takes for the color to become the same as that of the liquid (mixed liquid) is expressed in seconds. Example 1 50 y of phosphoric acid was added to 1000 y of scraps such as polycapramide threads and chips, and the mixture was heated for 300 y while blowing superheated steam.
A depolymerization reaction was carried out at C for 3 hours, and the crude lactam was distilled off.

Approximately 1,600 ml of the obtained crude lactam aqueous solution (lactam concentration 24.5%, lactam yield 98.0%) was
1 (lactam concentration about 60%), then 25.3 ml of 5 volume % sulfuric acid was added to this concentrated crude lactam aqueous solution to adjust the solution to pH 4, and then water was first distilled off, and then Distillation temperature 98-100℃, degree of vacuum 2m77! H
g to obtain lactam 9657, which was dissolved in the distilled water to make 1600 ml (distillation yield under acidic conditions: 98.5%). 20 ml of this lactam aqueous solution
The solution was adjusted to pH by adding 0.95ml of % sodium hydroxide.
l. After adjusting to 2, water is evaporated and the distillation temperature is 99-100.
The lactam was distilled off at a temperature of 2 mmHg. The quality of the obtained lactam is PZ;) 2500 seconds, VB; 3.0p
pm. FB: 0.003 meq/Kg, and the quality of normally commercially available lactams is PZ: 1600 seconds or more, V
B; 2.5 to 4.0 ppm,. FB: 0.01~0.0
Although it is 2meq/K9, it is comparable. Examples 2 to 4 The remaining 1200 ml of the lactam aqueous solution obtained by distillation under acidic conditions in Example 1 was separated into 400 ml portions, each of which was oxidized with potassium permanganate, hydrogen peroxide, and ozone.

After each of the treated solutions was adjusted to PHL2 (in the case of potassium permanganate oxidation, by-product manganese dioxide was separated by filtration in advance), the lactam was distilled out in the same manner as in Example 1. The oxidation conditions at this time and the quality results of the obtained lactam are shown in Table 1. From Table 1, it can be seen that PZ becomes even better through oxidation treatment.

Comparative Example 1 400 ml of a crude lactam aqueous solution depolymerized and concentrated in the same manner as in Example 1 was not distilled under acidic conditions, but simply 14.4 ml of 5% potassium permanganate (0.0 ml of 5% potassium permanganate (based on the amount of lactam added).
After oxidation at 40° C. for 30 minutes, the by-product manganese dioxide was separated, and then the lactam was distilled out in the same manner as in Example 1.

The quality of the obtained lactam is PZ: 2000 seconds, VB: 1
1.4 ppm FB; 0.45 meq/K9, which was considerably worse than in Example 1. Comparative Examples 2 and 3 A crude lactam aqueous solution depolymerized and concentrated in the same manner as in Example 1 was diluted with 5% sulfuric acid to PHL. After adjusting the pH to 5 and 6.5, distillation was performed under acidic conditions, and the resulting aqueous lactam solution was treated in the same manner as in Example 1 to distill off the lactam.

The quality of the lactam obtained and the lactam yield upon distillation under acidic conditions are shown in Table 2. From Table 2, when the pH during distillation under acidic conditions is 2 or less, the purification effect is good and highly pure lactam can be obtained, but the yield of lactam is low.

Claims (1)

[Scope of Claims] 1. When purifying crude ε-caprolactam obtained by thermally depolymerizing polycapramide in the presence of a phosphoric acid catalyst or an alkaline catalyst, an aqueous solution of the crude ε-caprolactam is purified to a pH of 2 to 6. Distillation process under acidic conditions and pH 10
A method for purifying ε-caprolactam, which comprises the steps of distilling under alkaline conditions. 2. When purifying crude ε-caprolactam obtained by thermally depolymerizing polycapramide in the presence of a phosphoric acid catalyst or an alkaline catalyst, an aqueous solution of the crude ε-caprolactam is distilled under acidic conditions of pH 2 to 6, A method for purifying ε-caprolactam, which comprises treating it with an oxidizing agent and then distilling it under alkaline conditions with a pH of 10 to 14.