JPH07179419A - Production of high purity caprolactam - Google Patents

Abstract

PURPOSE:To effectively and continuously produce high purity caprolactam without accumulating impurities in the reaction system by separating the high purity caprolactam, extracting off the impurities from the crystallization mother liquid with a water-insoluble solvent, and subsequently recycling the purified mother liquid. CONSTITUTION:A method for producing high purity caprolactam comprises crystallizing caprolactam from a solution comprising melted crude caprolactam and water or a water-insoluble solvent (suitably cyclohexane) in a crystallization device, recovering the crystals, adding water and, if necessary, the water-insoluble solvent to the crystallization mother liquid to give a water concentration of 1-50wt.%, preferably 10-30wt.%, and a water-insoluble solvent concentration of 10-90wt.%, preferably 30-80 wt.%, fractionating the water-insoluble solvent layer from the water layer, separating impurities from the fractionated water-insoluble solvent layer by a distillation method, etc., recycling the purified water-insoluble solvent layer, separating the water and the caprolactam from the water layer by a distillation method, etc., and subsequently partially or wholly recycling the water and the caprolactam into the crystallization device. The method is especially effective for crude caprolactam obtained by the catalytic rearrangement of cyclohexanone oxime in the presence of a solid acid catalyst in a gaseous phase.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity caprolactam.

[0002]

2. Description of the Related Art Epsilon-caprolactam (hereinafter referred to as "caprolactam") is usually produced by the Beckmann rearrangement reaction of cyclohexanone oxime. As the Beckmann rearrangement reaction, a liquid phase reaction using a strong acid such as concentrated sulfuric acid or fuming sulfuric acid is industrially adopted at present. However, in such a method, it is usually necessary to neutralize sulfuric acid with ammonia in order to separate caprolactam, and there is a problem that a large amount of ammonium sulfate is produced as a by-product.

Therefore, various studies have been conducted on the Beckmann rearrangement reaction which does not use sulfuric acid. As a promising method, a method of carrying out the Beckmann rearrangement reaction in the presence of a solid acid catalyst in the gas phase has been proposed (JP-A-62-123).
167, JP-A-4-316558, etc.).

[0004]

However, in the method for producing caprolactam by the gas phase rearrangement method using these solid acid catalysts, in the crude caprolactam after rearrangement, cyclohexanone, 2-cyclohexenone, hexanenitrile, 5 -There are by-products such as hexene nitrile and methyl pyridine that are unique to the gas phase rearrangement method. Further, impurities such as aniline and orthohydrophenazine (hereinafter referred to as “OHP”) are also present in a significantly larger amount than in the existing method. These impurities significantly deteriorate the quality of caprolactam as a product. With crude caprolactam containing many impurities as described above, OH
Some impurities such as P cannot be removed sufficiently. On the other hand, it is possible to obtain considerably high-purity caprolactam by crystallizing and refining crude caprolactam, but some impurities such as OHP accumulate in the crystallizing mother liquor, so that continuous purification cannot be performed efficiently and industrially. Implementation was difficult.

[0005]

Means for Solving the Problems The present inventor has conducted extensive studies to solve the above-mentioned problems, and as a result, by adding water and, if necessary, a water-insoluble solvent to the crystallization mother liquor of crude caprolactam, The inventors have found that impurities such as OHP can be efficiently extracted from the crystallization mother liquor, and have completed the present invention.

That is, the gist of the present invention is to crystallize caprolactam from a solution consisting of molten crude caprolactam and water in a crystallizer to recover the crystals, while water and, if necessary, crystallization mother liquor. A non-water-soluble solvent is added and mixed, followed by liquid separation, and a method for producing high-purity caprolactam, which comprises separating caprolactam from the aqueous layer, and a solution consisting of molten crude caprolactam and a non-water-soluble solvent,
Caprolactam is crystallized in a crystallizer, and the crystals are recovered. On the other hand, water and optionally a non-water-soluble solvent are added to the crystallization mother liquor, and the mixture is separated to separate caprolactam from the aqueous layer. And a method for producing high-purity caprolactam.

The present invention will be described in detail below. The crude caprolactam as a raw material to be purified is not particularly limited, but is usually a crude caprolactam obtained by catalytic rearrangement of cyclohexanone oxime and a solid acid catalyst containing a large amount of impurities such as OHP in the gas phase. It is especially effective when applied.

As the crystallization method, generally the following two methods are performed. The first method is as follows. Crude caprolactam is melted and water is usually added in an amount of 0.5 to 20% by weight,
Preferably in the coexistence of 1 to 8% by weight, usually 20 to 70 ° C,
Caprolactam is crystallized in a crystallizer, preferably at 30-65 ° C. This crystallization operation is usually carried out under atmospheric pressure, but it may be carried out under reduced pressure or under pressure. Water may be mixed with caprolactam in advance and supplied to the crystallizer, or may be directly supplied to the crystallizer. The crystallized high-purity caprolactam is recovered from the slurry at a slurry concentration of usually 10 to 70% by weight, preferably 15 to 50% by weight. As a method of collecting, a conventionally known filtration method, for example, a continuous vacuum filtration method can be exemplified.

The second method is as follows. Crude caprolactam is melted and the water-insoluble solvent is usually added to 10 to 90
%, Preferably 15 to 80% by weight, usually 2
Caprolactam is crystallized in a crystallizer at 0-70 ° C, preferably 30-65 ° C. As the water-insoluble solvent,
Aliphatic or aromatic hydrocarbons such as cyclohexane, hexane, cyclopentane, pentane, octane, benzene, toluene and xylene, and mixtures of these hydrocarbons can be exemplified, and among them, cyclohexane is preferable. This crystallization operation is usually carried out under atmospheric pressure, but it may be carried out under reduced pressure or under pressure. The water-insoluble solvent may be mixed with caprolactam in advance and supplied to the crystallizer, or may be directly supplied to the crystallizer. The crystallized high-purity caprolactam is recovered from the slurry at a slurry concentration of usually 10 to 70% by weight, preferably 15 to 50% by weight. As a method of collecting, a conventionally known filtration method, for example, a continuous vacuum filtration method can be exemplified.

The crystallization mother liquor is usually molten caprolactam and a small amount of water in the case of the first crystallization method, and molten caprolactam and a water-insoluble solvent in the case of the second crystallization method.
A feature of the present invention is that impurities such as OHP are extracted and removed from the crystallization mother liquor and recycled to prevent accumulation of impurities in the system. Is shown.

Water is added to the crystallization mother liquor to adjust the water concentration to 1
-50% by weight, preferably 10-30% by weight. If necessary, a non-water-soluble solvent is added so that the concentration of the non-water-soluble solvent is usually 10 to 90% by weight, preferably 30 to 85% by weight. It is usually 20 to 80 ° C., but preferably 30
Extraction is carried out at ˜70 ° C., and the water layer and the non-water-soluble solvent layer are separated. Water or a water-insoluble solvent may be mixed with the crystallization mother liquor in advance and supplied to the extractor, or may be directly supplied to the extractor. Examples of the extraction method include a conventionally known extraction method, for example, a continuous countercurrent extraction method. As the non-water-soluble solvent, the same solvents as mentioned above can be exemplified, and cyclohexane is particularly preferable. In the second method, a water-insoluble solvent different from the water-insoluble solvent used in crystallization may be added at the time of extraction, but it is preferable to use the same water-insoluble solvent from the viewpoint of recycling, Especially preferred is cyclohexane. The non-water-soluble solvent layer containing impurities such as OHP separated is separated by O
After separating impurities such as HP, the water-insoluble solvent is recycled. In addition, the water layer is separated from water and caprolactam by distillation or the like, and then both are partially or wholly recycled.

If impurities such as OHP cannot be sufficiently removed by the above-described one-step crystallization and one-step extraction operation,
These may be performed in multiple stages. At this time, either one may be multistaged or both may be multistaged. In addition,
Usually, part or all of the crystallization mother liquor is subjected to the extraction operation, but if necessary, it may be recycled without performing the extraction operation or may be purged out of the system. The high-purity caprolactam crystal obtained by crystallization is usually dried or further purified by distillation or the like to obtain a product.

[0013]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the examples as long as the gist thereof is not exceeded. Example 1 (Crystallization Method 1) 2.0 g of water was added to 100 g of caprolactam containing 2000 ppm of OHP, and the mixture was heated and melted with stirring. This was kept at 58 ° C. under atmospheric pressure to crystallize caprolactam. When the crystal slurry concentration reached 19% by weight, the slurry was suction filtered to recover high-purity caprolactam. At this time, the OHP concentration in the high-purity caprolactam was 28 ppm, and the OH in the mother liquor was
The P concentration was 2466 ppm (vs. caprolactam in the mother liquor).

(Extraction Method 1) 39 g of water and 81 g of cyclohexane were added to the crystallization mother liquor obtained by the crystallization method 1 to obtain 25
After shaking at 0 ° C for 10 minutes, the mixture was allowed to stand for 5 minutes to separate into two layers. At this time, the distribution rates of the upper layer liquid (cyclohexane) / lower layer liquid (water) of caprolactam and OHP (the component concentration of the upper layer liquid / the component concentration of the lower layer liquid) were 0.011 and 1.28, respectively. The selectivity of OHP (OHP distribution ratio / caprolactam distribution ratio) was 116.4.

Example 2 (Crystallization Method 2) 5.3 g of water was added to 100 g of caprolactam containing 2000 ppm of OHP and heated and melted with stirring. This was kept at 47 ° C. under atmospheric pressure to crystallize caprolactam. Crystal slurry concentration is 18% by weight
At that point, the slurry was suction filtered to recover high-purity caprolactam. At this time, the OHP content of high-purity caprolactam was 29 ppm, and OHP in the mother liquor was high.
Concentration is 2438ppm (ε-caprolactam in mother liquor)
Met.

(Extraction method 2) 36 g of water and 82 g of cyclohexane were added to the crystallization mother liquor obtained in (crystallization method 2),
After shaking at 25 ° C for 10 minutes, the mixture was allowed to stand for 5 minutes to separate into two layers. At this time, the distribution ratios of the upper layer liquid / lower layer liquid of caprolactam and OHP were 0.011 and 1.28, respectively. The selectivity of OHP was 116.4.

Example 3 (Crystallization Method 3) To 100 g of caprolactam containing 2000 ppm of OHP, 300 g of cyclohexane was added and dissolved by heating. This was kept at 41 ° C. under atmospheric pressure to crystallize caprolactam. Crystal slurry concentration is 19% by weight
At that point, the slurry was suction filtered to recover high-purity caprolactam. At this time, the OHP content of high-purity caprolactam was 25 ppm, and the OHP content in the mother liquor was high.
Concentration is 7650ppm (ε-caprolactam in mother liquor)
Met.

(Extraction method 3) 49 g of water was added to the crystallization mother liquor obtained in (crystallization method 3), the mixture was shaken at 25 ° C. for 10 minutes and then allowed to stand for 5 minutes to separate into two layers. At this time,
The distribution ratios of the upper / lower layers of caprolactam and OHP were 0.011 and 1.28, respectively. The selectivity of OHP was 116.4.

[0019]

INDUSTRIAL APPLICABILITY According to the present invention, crude caprolactam containing impurities such as OHP is crystallized to separate high-purity caprolactam, and the crystallization mother liquor is treated with impurities such as OHP using a water-insoluble solvent. By extracting and removing and then recycling, high-purity caprolactam can be efficiently and continuously produced without accumulating impurities such as OHP in the system.

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[Procedure amendment]

[Submission date] February 10, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

[0004]

However, in the method for producing caprolactam by the gas phase rearrangement method using these solid acid catalysts, in the crude caprolactam after rearrangement, cyclohexanone, 2-cyclohexenone, hexanenitrile, 5 -There are by-products such as hexene nitrile and methyl pyridine that are unique to the gas phase rearrangement method. In addition, aniline, oh
Impurities such as Kuta Hidorofenajin (hereinafter referred to as "OHP") are also remarkably large amount of presence than the current law. These impurities significantly deteriorate the quality of caprolactam as a product. With crude caprolactam containing many impurities as described above, OH
Some impurities such as P cannot be removed sufficiently. On the other hand, it is possible to obtain considerably high-purity caprolactam by crystallizing and refining crude caprolactam, but some impurities such as OHP accumulate in the crystallizing mother liquor, so that continuous purification cannot be performed efficiently and industrially. Implementation was difficult.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Water is added to the crystallization mother liquor to adjust the water concentration to 1
-50% by weight, preferably 10-30% by weight. If necessary, a non-water-soluble solvent is added so that the concentration of the non-water-soluble solvent is usually 10 to 90% by weight, preferably 30 to 85% by weight. It is usually 20 to 80 ° C., but preferably 30
Extraction is carried out at ˜70 ° C., and the water layer and the non-water-soluble solvent layer are separated. Water or a water-insoluble solvent may be mixed with the crystallization mother liquor in advance and supplied to the extractor, or may be directly supplied to the extractor. Examples of the extraction method include a conventionally known extraction method, for example, a continuous countercurrent extraction method. Examples of the non-water-soluble solvent include the same solvents as above, and cyclohexane is particularly preferable. In the second method, it may be added to non-aqueous solvent that is different from the non-aqueous solvent used in the crystallization at the time of extraction, but rather to prefer to use the same water-insoluble solvent in terms of recycling Especially preferred is cyclohexane. In the separated water-insoluble solvent layer containing impurities such as OHP, impurities such as OHP are separated by distillation or the like, and then the water-insoluble solvent is recycled. In addition, the water layer is separated from water and caprolactam by distillation or the like, and then both are partially or wholly recycled.

Claims (8)

[Claims] 1. A caprolactam is crystallized in a crystallizer from a solution consisting of molten crude caprolactam and water, and the crystals are recovered, while water and optionally a water-insoluble solvent are added to a crystallization mother liquor. A method for producing high-purity caprolactam, which comprises adding, mixing, and separating to separate caprolactam from the aqueous layer. 2. The method for producing high-purity caprolactam according to claim 1, wherein the water-insoluble solvent is cyclohexane. 3. The caprolactam separated from the aqueous layer is circulated to the crystallizer, according to claim 1 or 2.
The method for producing high-purity caprolactam according to 1. 4. The method for producing high-purity caprolactam according to claim 1, wherein the crude caprolactam is obtained by subjecting cyclohexanone oxime to a gas phase rearrangement reaction. 5. A crystallizer is used to crystallize caprolactam from a solution consisting of molten crude caprolactam and a water-insoluble solvent, and the crystals are recovered, while water and optionally water-insoluble in a crystallization mother liquor. A method for producing high-purity caprolactam, which comprises adding an organic solvent, mixing, separating, and separating caprolactam from the aqueous layer. 6. The method for producing high-purity caprolactam according to claim 5, wherein the water-insoluble solvent is cyclohexane. 7. The caprolactam separated from the water layer is circulated to the crystallizer.
The method for producing high-purity caprolactam according to 1. 8. The method for producing high-purity caprolactam according to claim 5, wherein the crude caprolactam is obtained by subjecting cyclohexanone oxime to a gas phase rearrangement reaction.