JPH05310706A - Purification of caprolactam - Google Patents

Abstract

PURPOSE:To easily obtain caprolactam having high quality in high yield by an extremely simple operation comprising the crystallization of caprolactam from a liquid-liquid double-layer mixture of a hydrocarbon and crude caprolactam obtained by the catalytic rearrangement of cyclohexanone oxime. CONSTITUTION:A liquid-liquid double-layer mixture composed of crude caprolactam obtained by the catalytic rearrangement of cyclohexanone oxime and at least one kind of hydrocarbon selected from aliphatic hydrocarbons and alicyclic hydrocarbons is stirred preferably under heating to form a liquid- liquid heterogeneous layer. Caprolactam is crystallized by cooling the heterogeneous layer under stirring. The impurities in the crude caprolactam are almost completely extracted in the hydrocarbon layer. The crystal is separated by filtration, etc. As necessary, the crystal is washed with the above hydrocarbon and dried to obtain high-quality caprolactam free from octahydrophenazine, etc. The process can remarkably decrease the amount of solvent, reduce the size of the apparatus and save the energy and, accordingly, it has industrial advantages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying caprolactam, more specifically, at least crude caprolactam produced by catalytic rearrangement of cyclohexanone oxime under stirring, and at least one selected from aliphatic hydrocarbons and alicyclic hydrocarbons. The present invention relates to a method for purifying caprolactam, which comprises crystallizing caprolactam from a liquid-liquid two-layer system mixed liquid with one kind of hydrocarbon.

[0002]

2. Description of the Related Art Caprolactam is a high-purity material used as a raw material for polyamide fibers and polyamide resins. It is also well known that crude caprolactam obtained by neutralizing with ammonia water, extracting with an aromatic solvent such as benzene, and distilling off the solvent is purified by precision distillation to produce (industrial organic chemistry, page 244 ( 1989, Tokyo Kagaku Dojin))). However, in the case of catalytic rearrangement of cyclohexanone oxime using a solid acid instead of sulfuric acid, there was a problem that purification by precision distillation could not give a satisfactory quality, probably because the by-products were different. In particular, octahydrophenazine, which adversely affects the quality specification UV value of caprolactam, can hardly be removed by distillation.

On the other hand, as a method for purifying crude caprolactam by catalytic rearrangement of cyclohexanone oxime, a method in which potassium permanganate is allowed to act and then dissolved in toluene for crystallization (JP-A-53-37687), dimethylformamide A method of crystallization by dissolving in a polar solvent such as
-54389 issue) is known. However, there was a problem that the loss to the mother liquor was large and the yield of caprolactam was low.

Further, after forming a liquid-liquid two-layer system of crude caprolactam and an aliphatic hydrocarbon such as isooctane, the caprolactam layer in which the by-product is concentrated is separated and removed, and thereafter the hydrocarbon layer is removed. Method for crystallization (JP-A-46-523)
(Gazette No. 1) is also known. However, since the caprolactam layer is separated and removed, there are problems that the yield of caprolactam is low and the operation is complicated, and that a large amount of solvent, which is 3 to 6 wt times that of crude caprolactam, is required.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to find out a better purification method of crude caprolactam by catalytic rearrangement of cyclohexanone oxime. As a result, the crude caprolactam, aliphatic hydrocarbons and fats Crystallization from a liquid-liquid two-layer mixture with at least one hydrocarbon selected from cyclic hydrocarbons not only makes it possible to obtain high-quality caprolactam easily and also in a high yield, but also uses a solvent. The present invention has been completed by finding out that the usage amount of can be reduced, and further conducting various studies.

That is, the present invention provides a liquid-liquid mixture of a crude caprolactam produced by catalytic rearrangement of cyclohexanone oxime with stirring and at least one hydrocarbon selected from aliphatic hydrocarbons and alicyclic hydrocarbons. It is intended to provide an industrially excellent method for purifying caprolactam, which comprises crystallizing caprolactam from a layer mixture.

The present invention will be described in detail below. The present invention uses a crude caprolactam produced by the catalytic rearrangement of cyclohexanone oxime. For example, a boric acid catalyst (JP-A-53-37686), silica.
Alumina-based catalysts (UK Patent No. 831,927), solid phosphoric acid catalysts (UK Patent No. 881,926), zeolite-based catalysts (JP-A-62-123167), such as crude caprolactam catalytically rearranged by solid acid catalysts, etc. Used. The present invention is
It is particularly effective for crude caprolactam which has undergone catalytic rearrangement in the gas phase. As the crude caprolactam, the reaction solution subjected to catalytic rearrangement can be used as it is, but it is used after removing by-products such as high boiling substances by-produced and additives added to the reaction system by distillation or the like. Preferably.

The aliphatic hydrocarbon used in the present invention,
Examples of the alicyclic hydrocarbon include hydrocarbons having 6 to 12 carbon atoms such as cyclohexane, n-heptane, isooctane and n-decane. These may be used as a mixture of two or more. The boiling point of the hydrocarbon is preferably equal to or higher than the melting point of the crude caprolactam, in which case the present invention can be carried out under normal pressure.

The amount of the hydrocarbon used may be such that the hydrocarbon and caprolactam form a liquid-liquid heterogeneous layer above the melting point of caprolactam, and usually 5 to 200 per 100 wt parts of crude caprolactam. wt part, preferably 10
~ 100 wt part.

In carrying out the present invention, for example,
A liquid-liquid heterogeneous layer of crude caprolactam and the above hydrocarbon is formed under heating, and this is cooled under stirring to crystallize caprolactam. At this time, most of the impurities contained in the crude caprolactam are extracted into the hydrocarbon layer. Then, the crystals are separated by means such as filtration, and if necessary, washed with the above hydrocarbon and dried to obtain high-quality caprolactam containing no octahydrophenazine and the like. This product can be purified by a purification means such as vacuum distillation to produce caprolactam of higher purity.

[0011]

According to the present invention, crude caprolactam and
High-quality caprolactam can be easily produced in a high yield by an extremely simple operation of crystallization from a liquid-liquid two-layer mixture with a hydrocarbon. In addition, the amount of the solvent used can be drastically reduced, and the apparatus can be downsized and the energy can be saved. Therefore, the present invention is advantageous as an industrial purification method.

[0012]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 60 g of crude caprolactam (caprolactam: 94.2%, octahydrophenazine: 1200 ppm) produced by catalytic rearrangement of cyclohexanone oxime using a zeolite catalyst.
And 30 g of isooctane were placed in a flask equipped with a stirrer at 80 ° C.
The temperature was raised to. When the stirring was stopped, it separated into two layers, a molten caprolactam layer (lower layer) and an isooctane layer (upper layer). While rotating the stirrer at 400 rpm, the mixture was gradually cooled to 25 ° C. to precipitate crystals, which was then filtered and dried to obtain 57 g of caprolactam. The crystal purity was 99.6% as determined by gas chromatography, and octahydrophenazine was below the detection limit. Almost no adhesion of crystals to the wall surface of the flask or the stirrer was observed, and the obtained crystals were granular crystals with a uniform particle size, and were easy to filter.

Examples 2, 3 and Comparative Example 1 The procedure of Example 1 was repeated, except that the solvent shown in Table 2 was used instead of isooctane. The results are shown in Table 1. All of the octahydrophenazine in the crystals were below the detection limit.

Table 1 Caprolactam Example Solvent Status (80 ° C.) Recovery (g) Purity (%) Example 2 Cyclohexane Liquid-Liquid Two-layer System 53 99.4 Example 3 n-decane Liquid-liquid Two-layer System 54 99.3 Comparative Example 1 Toluene homogeneous system 32 99.5

Comparative Example 2 The procedure of Example 1 was repeated except that 300 g of isooctane was used to obtain 38 g of caprolactam. The crystal purity was 99.5%, and octahydrophenazine was below the detection limit. Incidentally, when the temperature was raised to 80 ° C., all the caprolactam was dissolved in isooctane, and a uniform solution was obtained. Crystallization showed that crystals adhered to the wall surface of the flask, and the obtained crystals were irregular plate crystals, which required a long time for filtration.

Comparative Example 3 50 g of the same crude caprolactam used in Example 1 was distilled.
By fractional distillation using (actual number of 20 stages) under the conditions of 5 mmHg and a reflux ratio of 5, 32 g of a caprolactam fraction was obtained.
The purity was 99.7%, but octahydrophenazine was 80%.
It contained 0 ppm.

Reference Example 1 Comparative Example 1 except that the caprolactam obtained in Example 1 was used in place of the crude caprolactam in Comparative Example 3.
Was carried out according to the above procedure to obtain 36 g of a caprolactam fraction.
The purity was 99.97%, and octahydrophenazine was below the detection limit.

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[Procedure amendment]

[Submission date] July 13, 1993

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[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying caprolactam, and more specifically, it is selected from crude caprolactam produced by catalytic rearrangement of cyclohexanone okikim under stirring and aliphatic hydrocarbons and alicyclic hydrocarbons. The present invention relates to a method for purifying caprolactam, which comprises crystallizing caprolactam from a liquid-liquid two-layer mixture with at least one hydrocarbon.

[Procedure 3]

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[0002]

2. Description of the Related Art Caprolactam is a high-purity material used as a raw material for polyamide fibers and polyamide resins. After caprolactam is produced by rearranging cyclohexanone oxime in a sulfuric acid medium, It is also well known that crude caprolactam obtained by neutralizing with ammonia water, extracting with an aromatic solvent such as benzene, and distilling off the solvent is refined and produced by precision distillation (Industrial Organic Chemistry, page 244 ( (1989, Tokyo Kagaku Dojin)
). However, when cyclohexanone oxime was catalytically rearranged using a solid acid instead of sulfuric acid, there was a problem in that purification by precision distillation could not give a satisfactory quality, probably because the by-products were different . In particular , octahydrophenazine, which adversely affects the quality specification UV value of caprolactam, can hardly be removed by distillation.

[Procedure amendment 4]

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[Correction method] Change

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That is, the present invention provides a liquid-liquid mixture of crude caprolactam produced by catalytic rearrangement of cyclohexanone okikim and at least one hydrocarbon selected from aliphatic hydrocarbons and alicyclic hydrocarbons under stirring. The present invention provides an industrially excellent method for purifying caprolactam, which comprises crystallizing caprolactam from a two-layer mixture.

[Procedure Amendment 5]

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Examples 2, 3 and Comparative Example 1 The procedure of Example 1 was repeated except that the solvent shown in Table 1 was used instead of isooctane. The results are shown in Table 1. All of the octahydrophenazine in the crystals were below the detection limit.

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Comparative Example 3 50 g of the same crude caprolactam as used in Example 1 was fractionally distilled using a distillation column (20 actual stages) under the conditions of 5 mmHg and a reflux ratio of 5 to obtain 32 g of a caprolactam fraction. It was. The purity was 99.7%, but it contained 800 ppm of octahydrophenazine.

[Procedure Amendment 7]

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Reference Example 1 Comparative Example 3 except that the caprolactam obtained in Example 1 was used in place of the crude caprolactam in Comparative Example 3.
The procedure was carried out in accordance with to obtain 36 g of a caprolactam fraction. The purity was 99.97%, and octahydrophenazine was below the detection limit.

Claims (2)

[Claims] 1. A liquid-liquid two-layer mixture of crude caprolactam produced by catalytic rearrangement of cyclohexanone oxime with stirring and at least one hydrocarbon selected from aliphatic hydrocarbons and alicyclic hydrocarbons. A method for purifying caprolactam, which comprises crystallizing caprolactam. 2. The method according to claim 1, wherein the hydrocarbon has 6 to 12 carbon atoms.