JPS6021143B2 - Lactam purification method - Google Patents

Description

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

Much research has been done on the purification of crude lactams, such as caprolactam, obtained by Beckmann 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 of treatment with ion exchange koji resin, etc., methods of recrystallization, and methods of simply oxidizing and purifying with 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 po-IJ lactam.

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

In view of the above circumstances, the present inventors have previously treated an aqueous solution of crude lactam with a cation exchange resin, and then treated it with an oxidizing agent in order to purify the recovered crude lactam with a simple operation and obtain a high-quality lactam. We proposed a method of purifying the product by distilling it in the presence of an alkali after treatment. However, if polycapramide contains a large amount of additives, dyes, or other copolymer components other than polycapramide, the crude lactam obtained by thermal depolymerization will contain a large amount of impurities caused by these. However, the refining is insufficient. This tendency becomes particularly noticeable when dyes are included. Therefore, the inventors of the present invention conducted intensive studies to further improve the quality and reduce the amount of by-products, and as a result, they completed the following method. That is, in the present invention, when purifying a crude lactam obtained by thermally depolymerizing polycapramide in the presence of a phosphoric acid catalyst or an alkaline catalyst, an aqueous solution of the crude lactam is treated with a cation exchange resin, and then oxidized with ozone. After that, it is distilled in the presence of an alkali.

The cation exchange resin used in the present invention includes:
Usually commercially available resins having a functional group such as -S03day, 1COOday, etc. as a cation exchange group can be used as they are, but strongly acid type resins are preferable.

However, there are no particular limitations on the exchange capacity, shape, density, etc. of the resin. The cation exchange treatment converts the recovered crude lactam into
It is carried out in an 85% by weight aqueous solution, preferably from 30 to 75% by weight. The treatment method may be a continuous method in which the above aqueous solution is passed through a column filled with cation exchange resin, or a suitable amount of exchange resin may be supplied into the aqueous solution and the exchange resin may be passed through a column filled with cation exchange resin. A batch method of separation may also be used. Note that the aqueous solution supplied to the cation exchange treatment is preferably set at a temperature in the range of room temperature to 8,000 °C. Next, in the ozone oxidation treatment, the lactam aqueous solution that has undergone the above cation exchange treatment has an ozone absorption amount of 0.05 to 0.5% by weight, preferably 0.05 to 0.25% by weight, based on the lactam contained therein. %, contact and absorb.

If the amount absorbed is too small, the oxidation of impurities will be insufficient, and if it is too large, side reactions such as oxidation of lactam will occur in addition to the oxidation of impurities, which is not preferable. The treatment method may be a continuous method in which the lactam aqueous solution is continuously supplied from the upper part of the oxidation tower, some number of flows are brought into contact with it while ozone is blown from the bottom, and the treated liquid is extracted.
Alternatively, a batch method may be used. The time required for the ozone oxidation treatment varies depending on the amount of ozone brought into contact with the lactam aqueous solution and the temperature of the lactam aqueous solution, but is from 0.2 to
2 hours is enough.

In addition, if the temperature of the lactam aqueous solution during oxidation treatment is too high, side reactions such as oxidation of lactam are likely to occur in addition to oxidation of impurities, while if it is too low, oxidation of impurities will be slow and the oxidation treatment will require a long time. Since this results in an undesirable result, it is preferable to carry out the treatment in a range of 10 to 50 qo. The aqueous lactam solution that has undergone the oxidation treatment is then distilled in the presence of an alkali, but if the aqueous solution that has undergone the oxidation treatment is already alkaline, there is no need to add a new alkali. On the other hand, when adding an alkali, the desired high-purity lactam can be obtained by adding a basic substance such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, or potassium carbonate and distilling it according to a conventional method. can get. The amount of alkali added at this time is 0.0 with respect to the lactam in the lactam aqueous solution.
1-1. It is preferable to select the weight percentage of . As described above, the crude lactam purification method of the present invention combines three operations: cationic resin treatment, ozone oxidation treatment, and distillation in the presence of an alkali. A step of passing it through an anion exchange resin may also be added.

In this case, as the anion exchange resin, any commercially available strong base type resin that has a functional group such as an anion exchange group can be used as is, and the resin exchange capacity, shape, density, etc. Not limited.

In anion exchange treatment, the oxidized crude lactam is
% by weight, preferably from 30 to 7% by weight. The treatment can be carried out in the same manner as the cation exchange treatment, and the aqueous solution is heated at room temperature to 50oC.
It is preferable to set it within the range of o. The method of the present invention having the above configuration is the most effective method for purifying recovered lactams and obtaining highly pure lactams that can be used in the production of polylactams.

That is, the lactam obtained by the above method is completely comparable to commercially available lactams, as shown in the Examples. Furthermore, the purification method of the present invention is an extremely simple operation, does not require large and complicated purification equipment, and the ion exchange resin has a long life, so it is economically advantageous to purify crude lactams. can do.

As described above, the present invention provides a method for economically obtaining lactam with higher purity than recovered crude lactam, and is extremely practical and has high utility value.

The present invention will be specifically explained below based on Examples, but the present invention is not necessarily limited to these. In the examples, the amount of volatile base (hereinafter referred to as VB), the amount of free base (hereinafter referred to as FB), and the potassium permanganate value (hereinafter referred to as PZ), which represent the quality of the lactam, were measured by the following methods.

FB: The amount of a 1'50N hydrochloric acid aqueous solution required to dissolve 50% of lactam in 50% of distilled water at pH 6 and return the solution to pH 6, expressed in meg/k9 units. VB;
Dissolve 50% of the lactam in 100% of 20% sodium hydroxide, perform steam distillation according to a conventional method, and extract 10% of the lactam into a 10% aqueous solution of 5-specified sulfuric acid to obtain a solution of 250%.

Next, this aqueous solution is titrated with a 1'5 normal sodium hydroxide aqueous solution, and the same operation is carried out with distilled water, taking into account a blank, and expressed in skin units in terms of ammonia.

PZ: Add 1/10 normal potassium permanganate aqueous solution to 1% lactam aqueous solution, and the color will be the same as that of the standard solution (
The time required for the solution to become the same color as a solution obtained by dissolving three parts of cobalt chloride/hexahydrate and two parts of steel sulfate/pentahydrate in distilled water is expressed in terms of the number of sands.

Example 1 Polycapramide yarn dyed with an acid dye was prepared by adding 100 g of phosphoric acid and blowing superheated steam into it.
A depolymerization reaction was carried out at 00°C for 3 hours to distill off the crude lactam.

The resulting crude lactam aqueous solution (lactam concentration 23.8%, lactam silk yield 95.2%) was approximately 3200
(lactam concentration 59.5%), and then this concentrated crude lactam aqueous solution was passed through a column with a diameter of 25 mm filled with cation exchange resin (Amberlite IR-12, H type) 1002. The lactam remaining in the column was further pushed out with water to obtain the desired lactam aqueous solution 3600 (lactam concentration 52.8%).
Next, put 400 parts of the obtained treatment liquid into a gas absorption bottle with a diameter of 7 cm, and use an ozone generator to generate 40 parts of ozone.
Blow at a rate of 3 minutes (ozonator air; 2.0 units/minute)
Oxidized for 3 minutes at 0 qo (ozone absorption of crude lactam aqueous solution 200.6 o, absorption rate for lactam 0.0
95% by weight).

After oxidation, a 20% aqueous sodium hydroxide solution of about 1.0% was added to the treated solution to adjust the pH of the solution to 12, then the water was evaporated and the lactam was distilled at a distillation temperature of 99 to 100 degrees and a vacuum degree of 2. Obtained. The quality of the lactam obtained by the above method is PZ3600 seconds VB4. Koga FBO. 003heq/
K9 and the quality of the commonly commercially available lactam is PZ1.
600 seconds or more, VB2.5-4. Nomasu F800.01~
Although it is 0.02 heq/k9, it is a highly pure lactam that is comparable in purity.

The amount of ozone generated and absorbed was determined by the method of absorbing ozone into an aqueous potassium iodide solution and titrating the liberated iodine with sodium thiosulfate. Example 2 A crude lactam aqueous solution subjected to depolymerization, concentration, and ion exchange treatment under the same conditions as in Example 1 was prepared into a 300 mm tube with a diameter of 3 ribs and a length of 10 mm.
The column was equipped with a liquid inlet, a gas outlet, a gas supply port, and an exhaust port of 0.000000000000000000000000000000000000000000 from the side, and were supplied from the side of the top at a rate of 10°/min, and continuously while blowing ozone at 200/min from the bottom. oxidized (average oxidation time of 6 times for crude lactam aqueous solution, ozone absorption rate relative to lactam 0.155% by weight).

The quality of the lactam obtained by distilling this oxidized solution according to Example 1 was PZ 3500 seconds, VB 4.0 feet, FBO
．． 004 meq/k9, and as in Example 1, a very highly purified lactam was obtained. Comparative Example 1 A crude lactam aqueous solution depolymerized and concentrated under the same conditions as in Example 1 was not subjected to cation exchange treatment, but simply ozone was blown in at a rate of 40 o/min and oxidized at 30 q○ for 30 minutes. The quality of the lactam obtained by distillation is PZ2.
000 seconds, 25.0 VBs, FBO. 7 mountains heq/k9
However, only very high VB and FB were obtained.

Comparative Examples 2 to 4 Of the crude lactam water obtained by the cation exchange treatment in Example 1, 1200% of the lactam water was separated into 3 parts of 400% each, and each part was treated with potassium permanganate, hydrogen peroxide, and sodium hypochlorite. oxidized with.

After each of the treated solutions was prepared in a vessel 12 (in the case of potassium permanganate oxidation, the manganese dioxide produced was separated in advance), and distilled according to Example 1 to obtain a lactam.
The oxidation conditions at this time and the quality results of the obtained lactam are shown in Table 1. As is clear from Table 1, oxidation with hydrogen peroxide and sodium hypochlorite does not sufficiently oxidize impurities, resulting in a significantly poor PZ. It can be seen that oxidation with potassium permanganate yields lactams of relatively high purity, but is worse than ozone oxidation. In addition, since manganese dioxide is created, it is necessary to concentrate and separate it, resulting in a large amount of waste. Table 1 Examples 3 to 4 and Comparative Examples 5 to 6 Of the crude lactam water obtained by the cation exchange treatment of Example 1, 1,600' of the crude lactam water was separated into four parts of 400 parts each, and each of them was divided into four parts of Example 1. After oxidizing at 30q0* for a predetermined time using the same equipment as in Example 1, the mixture was oxidized to pHI and distilled according to Example 1 to obtain a lactam.

The ozone absorption rate during oxidation and the quality results of the obtained lactam are shown in Table 2. Table 2 Absorption rate for lactam (weight association) From Table 2, it can be seen that if the oxidation time is insufficient and the amount of ozone absorbed is too small, the PZ will be bad, and if the oxidation is too much, the VB will be bad.

Claims (1)

[Claims] 1. When purifying the crude lactam obtained by thermally depolymerizing polycapramide in the presence of a phosphoric acid catalyst or an alkaline catalyst, the aqueous solution of the crude lactam is treated with a cation exchange resin, then oxidized with ozone, and then A method for purifying a lactam, which comprises distilling it in the presence of an alkali.