JPH0558625B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides 11- The present invention relates to a method for recovering cyanoundecanoic acid ammonium salt.

[Conventional technology]

A known method for obtaining 11-cyanoundecanoic acid, which is useful as a raw material intermediate for nylon 12, is to thermally decompose PXA. i.e. British Patent No.
No. 1198422 describes a method of thermally decomposing PXA at high temperatures of 300 to 1000℃, and Japanese Patent Publication No. 49-31969
The product is sprayed in small droplets in an inert gas atmosphere such as heated steam maintained at 250-1000℃.
A method for heating PXA is described. However, in addition to 11-cyanoundecanoic acid, the PXA thermal decomposition reaction product contains a considerable amount of byproducts such as ε-caprolactam, cyclohexanone, saturated and unsaturated carboxylic acids and nitriles, and cyclic imides. This thermal decomposition reaction product is usually colored brown to blackish brown.

Therefore, it contains a wide variety of by-products.
There has been a need for a method for recovering useful 11-cyanoundecanoic acid from PXA thermal decomposition products in a relatively simple process and in high yield. For example, Tokuko Sho 60
-26385, the thermal decomposition reaction product of PXA is dissolved in a mixed solvent of benzene, toluene, or xylene and water, and an aqueous layer containing ε-caprolactam and 11-
A method is described that includes the steps of separating the oil layer into an oil layer containing cyanoundecanoic acid, extracting the oil layer with ammonia, and crystallizing and separating ammonium salt of 11-cyanoundecanoic acid from this extract.

However, in the above method of crystallizing 11-cyanoundecanoic acid ammonium salt from the extract obtained by extracting the oil layer with ammonia, it is difficult to perform the crystallization efficiently and it is difficult to obtain highly pure 11-
There was a problem that it was difficult to obtain cyanoundecanoate.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for efficiently recovering highly pure 11-cyanoundecanoate from a thermal decomposition product of PXA through a relatively simple process.

[Means for solving problems]

The above objects of the present invention are to (a) pyrolyze PXA at high temperature and immediately quench it to produce pyrolysis products mainly containing 11-cyanoundecanoic acid, cyclohexanone and ε-caprolactam; Adjust the PH value of the decomposition product to 4 or less, (c) Extract the pyrolysis product to be adjusted with water and prepare ε-
Extract of water-soluble components including caprolactam and 11
- Separate into an oil layer containing cyanoundecanoic acid, (d) add ammonia water to the oil layer, and from the oil layer, cyclohexanone and hexanenitrile,
Impurities are extracted and removed from the oil layer using an extraction solvent that can extract and remove impurities containing hexenenitrile, and then (e) containing 11-cyanoundecanoic acid ammonium salt from which impurities have been removed by extraction. This is achieved by a method for producing 11-cyanoundecanoate, which is characterized by precipitating 11-cyanoundecanoate from an aqueous solution.

Hereinafter, the method for producing 11-cyanoundecanoate of the present invention will be explained step by step with reference to the flow sheet of the attached drawings. The figure shows the process for obtaining 11-cyanoundecanoate from PXA according to the method of the invention.

PXA1 is heated to a high temperature, preferably about 400 to 800°C, in the pyrolysis tower 3 to undergo pyrolysis. In one advantageous pyrolysis method, PXA is sprayed from the top of the pyrolysis tower with a heated inert gas, preferably heated steam 2, and heated steam 2 is blown into the top of the pyrolysis tower to inject the PXA. A thermal decomposition reaction is achieved instantaneously in the gas phase by maintaining a predetermined temperature.

By immediately quenching the thermal decomposition reaction system, the 11-cyanoundecanoic acid contained therein,
Components such as cyclohexanone and ε-caprolactam are condensed and recovered. That is, the cooling water 23 is directly poured into the thermal decomposition product obtained in the thermal decomposition process to rapidly cool it to a temperature of about 250° C. or lower. Preferably, cooling water 23 is sprayed into the tower from a spray nozzle provided at the bottom of the pyrolysis tower 3 to condense the pyrolysis reaction product, and the condensed pyrolysis containing 11-cyanoundecanoic acid is released from the bottom of the tower. Take out the liquid. The cooling water 23 used is one below 60°C, and the amount of water supplied is such that the thermal decomposition reaction system is immediately heated to below about 250°C, preferably about 130°C.
The temperature should be sufficient to allow rapid cooling to below ℃.

For the cooling water 23, from the viewpoint of economic efficiency, it is desirable that a part of the water extract taken out from the water extraction tower 4, which will be described later, be recycled.

The pyrolysis oil (condensate of pyrolysis products) taken out from the bottom of the pyrolysis tower is led to a PH adjustment tank 9, where an acid such as dilute sulfuric acid is added to adjust the PH value to 4 or less, preferably 2 to 2. Make it 3. This pH adjustment is effective in completely preventing flooding within the water extraction tower 4.

The pyrolysis oil with adjusted pH is supplied to the water extraction column 4. In the water extraction tower 4, the pyrolysis oil is extracted with water 11 and separated into an aqueous layer 12 containing ε-caprolactam and an oil layer 15 containing 11-cyanoundecanoic acid.
The amount of extracted water 11 is determined by the weight ratio of water layer 12 and oil layer 15.
It is preferable to select from 0.5 to 5, especially from 1 to 4.

The oil layer 15 is taken out from the top of the water extraction tower 4, mixed with a solution 18 containing ammonia and water, and then introduced into the organic solvent extraction tower 5. Solution 1 containing ammonia water
8, it is desirable to recycle and use a solution containing ammonia and water recovered from the mother liquor taken out from the crystallization tank 6. In the oil layer 15, in addition to 11-cyanoundecanoic acid, its isomers (for example, 7-
11-cyanoundecanoic acid and 2-butyl-7-cyanoheptanoic acid), but 11-cyanoundecanoic acid and its isomers become ammonium salts by reaction with ammonia, and are extracted into an aqueous layer 17 by extraction with an organic solvent 13. move inside. The concentration and amount of ammonia water are such that the concentration of 11-cyanoundecanoic acid ammonium salt in the water layer 17 is 10 to 30% by weight,
It is preferable to adjust the concentration of free ammonia to 1 to 20% by weight. Extraction operation is performed at a temperature of 30~
Preferably, the temperature is 70°C. On the other hand, the entrained cyclohexanone and ε-caprolactam are recovered from the extracted aqueous solution 12 taken out from the bottom of the water extraction tower 4.

At the bottom of the organic solvent extraction tower 5, an organic solvent for extraction,
Preferably, toluene is supplied to extract and remove cyclohexanone and other impurities (for example, hexanenitrile, hexenenitrile) from the mixture of the oil layer 15 and aqueous ammonia. The amount of toluene supplied is 0.1 to 2 times that of the oil layer 15 (weight ratio). The toluene extract 16 is taken out from the top of the extraction column 5, led to a cyclohexanone and toluene recovery step (not shown), and separated by distillation.

On the other hand, an aqueous solution 17 containing ammonium salts of 11-cyanoundecanoic acid and ammonium salts of its isomers is taken out from the bottom of the extraction tower 5, fed to the crude 11-cyanoundecanoic acid crystallization tank 6, and purified by crystallization. do. Although it is possible to perform crystallization in one step,
It is preferable to carry out the process in two stages as follows.

In the crystallization tank 6, the crude aqueous solution of ammonium 11-cyanoundecanoate is cooled to 0 to 20°C, particularly 5 to 15°C, to precipitate crystals of ammonium 11-cyanoundecanoate. Ammonium salts such as 7-cyanoundecanoic acid and 2-butyl-7-cyanoheptanoic acid contained as impurities have high solubility and therefore remain in the mother liquor side. This mother liquor is taken out from the crystallization tank 6 and introduced into the distiller 24. It is preferable that the solution 18 containing ammonia and water is recovered from the distiller 24, mixed with the oil layer 15 taken out from the water extraction column 4, and circulated to the organic solvent extraction column 5. The remaining mother liquor 19 containing ammonium salts such as 7-cyanoundecanoic acid and 2-butyl-7-cyanoheptanoic acid is purged from the distiller 24 to the outside of the system.

Note that a centrifuge may be used, for example, to separate the mother liquor and the crystals of ammonium 11-cyanoundecanoate salt.

The crystals 20 of 11-cyanoundecanoic acid ammonium salt precipitated in the crystallization tank 6 are led to the dissolution tank 7, and dissolved in the mother liquor 23 taken out from the next purified 11-cyanoundecanoic acid ammonium salt crystallization tank 8. The solution 21 is taken out from the solution tank 7 and sent to the purified 11-cyanoundecanoic acid ammonium salt crystallization tank 8. The solution is heated in the second crystallization tank 8 at a temperature of about 0 to 30°C, especially at 5°C.
Crystallize and purify again by cooling to ~20°C,
White crystals 22 of purified ammonium salt of 11-cyanoundecanoic acid with high purity are obtained.

〔Example〕

The present invention will be specifically described below with reference to Examples.

Example 1 PXA using an apparatus having the arrangement shown in Figure 1
11-cyanoundecanoic acid was produced from.

A toluene solution (PXA oil) containing 75% by weight of 1,1'-peroxycydichlorohexylamine at 30°C was injected at a rate of 800 kg/h from a spray nozzle installed at the top of the pyrolysis tower 3 at a rate of 500°C. It was sprayed together with superheated steam 2. Immediately after spraying, superheated steam 2 at 750°C is blown in to lower the temperature inside the pyrolysis tower.
The temperature was maintained at 480°C, and the thermal decomposition reaction was carried out instantaneously in the gas phase. The total feed rate of superheated steam was 2.8t/H. Immediately thereafter, cooling water 23 was sprayed at a rate of 6 m ³ /H from a number of spray nozzles provided at the bottom of the tower to rapidly cool the thermal decomposition reaction system to a temperature of 130° C. or lower. As this cooling water 23, a part of the water extract taken out from the water extraction tower 4 was recycled and used.

The pyrolysis oil taken out from the bottom of the pyrolysis tower was led to a pH adjustment tank 9, the pH of which was adjusted to 2.5 with dilute sulfuric acid, and sent to the water extraction tower 4. At the top of the water extraction tower 4, extracted water is
It was introduced at a rate of 3600Kg/H. By-product valuables (ε-caprolactam) in the pyrolysis oil are extracted and removed in the water extraction tower 4, and 1500 kg/11-cyanoundecanoic acid oil is extracted.
I got H. The composition of this 11-cyanoundecanoic acid oil is shown in Table 1.

Table-1 Concentration of components of 11-cyanoundecanoic acid oil (wt%) 11-cyanoundecanoic acid 20 cyclohexanone 12 7-cyanoundecanoic acid 1.3 2-butyl-7-cyanoic acid heptanoic acid 0.6 Hexanenitrile 0.5 Hexenenitrile 0.1 Others 5.5 In addition, the extracted aqueous solution 1 taken out from the water extraction tower 4
2 is led to an evaporator (not shown), and ε-caprolactam can be recovered from the bottom of the evaporator.

The 11-cyanoundecanoic acid oil is mixed with 1900 kg/H of mother liquor (containing 6% by weight of ammonia) taken out from the crystallization tank 6 in the next crystallization step, and then supplied to the upper part of the organic solvent extraction column 5. To the bottom of the extraction tower
700Kg/H of toluene 13 was supplied. Cyclohexanone and other impurities in the 11-cyanoundecanoic acid oil were extracted and removed. The composition of the toluene extract is shown in Table 2.

Table 2 Component concentration (wt%) of toluene extract Cyclohexanone 10 11-cyanoundecanoic acid 0.04 Hexanenitrile 0.40 Hexenenitrile 0.10 Other impurities 7.5 Toluene 81.96 Toluene extract 16 was taken out from the top of the extraction column, and cyclohexanone and toluene was sent to a recovery process (not shown).

The aqueous solution 17 containing ammonium 11-cyanoundecanoate taken out from the extraction column 5 is sent to the crude ammonium 11-cyanoundecanoate crystallization tank 6.
The mixture was cooled to 8° C. in a crystallization tank 6 to precipitate crystals of 11-cyanoundecanoic acid ammonium salt. The mother liquor is taken out from the crystallization tank 6, and the 7-
The ammonium salt of cyanoundecanoic acid and 2-butyl-7-cyanoheptanoic acid was purged, and the solution 18 containing about 6% by weight of ammonia, water and toluene recovered by distillation from the mother liquor was circulated to the organic solvent extraction column 5. . The precipitated crystals of 11-cyanoundecanoic acid ammonium salt were introduced into a dissolving tank 7, and mixed with the mother liquor 23 taken out from the next second crystallization tank 8 to be dissolved therein. The obtained solution is sent to the second crystallization tank (purified 11-cyanoundecanoic acid ammonium salt) 8, cooled to 12°C in the same tank, and crystallized again to obtain highly purified purified 11-cyanoundecanoic acid ammonium salt. 400 kg/h of white salt crystals were obtained. The resulting purification 11
-The composition of the cyanoundecanoic acid ammonium salt crystals is shown in Table 3.

Table-3 Composition of purified 11-cyanoundecanoic acid ammonium salt crystals Component composition (wt%) Ammonium 11-cyanoundecanoate 75 Ammonia 0.5 Water 24.5 7-cyanoundecanoic acid + 2-butyl-7-cyanoheptanoic acid 0.0 ε- Caprolactam 0.0 Cyclohexanone 0.0 Hexanenitrile 0.0 Hexenenitrile 0.0 [Effects of the Invention] According to the present invention, highly pure 11-cyanoundecanoic acid can be efficiently produced from PXA. In particular, according to the manufacturing method of the present invention,
In comparison with the method described in No. 26385, a step of adjusting the pH of the PXA pyrolysis product to 4 or less before extraction with water is provided, and the method 11-
Instead of sending the cyanoundecanoic acid solution directly to the crystallization separation process, we decided to extract and remove cyclohexanone and other impurities with an organic solvent such as mono-toluene before sending it to the crystallization separation process of ammonium 11-cyanoundecanoate. Therefore, the crystallization is performed very efficiently, and a product with high purity can be produced in high yield.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing a process for producing 11-cyanoundecanoic acid from PXA in accordance with the present invention. 1: PXA oil, 2: Superheated steam, 3: Thermal decomposition tower, 4: Water extraction tower, 5: Organic solvent extraction tower, 6: Crude
11-Ammonium cyanoundecanoate crystallization tank,
7: Dissolution tank, 8: Purification 11-cyanoundecanoic acid ammonium crystallization tank, 9: PH adjustment tank, 10: Acid, 1
1: Extract water, 12: Extract aqueous solution, 13: Extract organic solvent, 15: Oil layer, 16: Organic solvent extract, 1
7: Aqueous solution containing 11-cyanoundecanoic acid ammonium salt, 18: Solution containing ammonia and water from crystallization layer 6, 19: Mother liquor to be purged, 20: 11-cyanoundecanoic acid ammonium salt crystal to be crystallized, 21: Solution of the same crystal, 22: Purified 11-cyanoundecanoic acid ammonium salt crystal, 23: Mother liquor from crystallization tank 8, 24: Distillation column.

Claims (1)

[Scope of Claims] 1 (a) 1,1'-Peroxycyclohexylamine is thermally decomposed at a high temperature and then immediately rapidly cooled to produce a thermal decomposition product mainly consisting of 11-cyanoundecanoic acid, cyclohexanone and ε-caprolactam. (b) Adjust the PH value of the pyrolysis product to 4 or less; (c) Extract the pyrolysis product to be PH adjusted with water to
- Separate into an aqueous layer containing caprolactam and an oil layer containing 11-cyanoundecanoic acid, (d) After adding aqueous ammonia to the oil layer, cyclohexanone and hexanenitrile,
Extract and remove impurities from the oil layer with an extraction solvent capable of extracting and removing impurities containing hexenenitrile, and then (e) containing 11-cyanoundecanoic acid ammonium salt from which impurities have been removed by extraction. 1. A method for producing 11-cyanoundecanoate, which comprises precipitating 11-cyanoundecanoic acid ammonium salt from an aqueous solution.