JPH05301858A - Production of caprolactam - Google Patents

Abstract

PURPOSE:To obtain the subject compound having high quality and useful as a raw material for nylon by reacting cyclohexanone with a hydroxylamine mineral acid salt under specific condition and subjecting the reaction product to Beckmann rearrangement. CONSTITUTION:Cyclohexanone produced by the oxidation of cyclohexane is made to react with a hydroxylamine mineral acid salt in the presence of a platinum catalyst at 20-80 deg.C and pH 3-5. The obtained cyclohexanone oxime is subjected to Beckmann rearrangement by conventional method using a reactor such as a stirring tank or a pipe-line mixer in the presence of fuming sulfuric acid at 70-120 deg.C to obtain the objective caprolactam. Cyclohexanone having a hexahydrobenzaldehyde content of <=30ppm is used as the intermediate raw material of the above process.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing high quality caprolactam.

[0002]

BACKGROUND ART Caprolactam, a raw material for nylon, is usually produced by reacting cyclohexanone obtained by oxidizing cyclohexane with hydroxylamine mineral acid salt to synthesize cyclohexanone oxime, and then subjecting this to Beckmann rearrangement. ing. Of the above steps, in the step of oxidizing cyclohexane to synthesize cyclohexanone, a large number of by-products are produced in addition to cyclohexanone and cyclohexanol. Of these, cyclohexanol is converted to cyclohexanone by the dehydrogenation step.
Main products produced as the by-products include oxygen-containing compounds such as carboxylic acids, aldehydes, ketones, esters, ethers and alcohols, and hydrocarbons. Among these impurities, carboxylic acids, esters, alcohols and the like can be removed by saponification with an alkaline aqueous solution and then extraction with water. The distillation process then also removes many of the other by-products, but without saponification,
A small amount of by-product remains, which has a boiling point close to that of cyclohexanone (156.5 ° C.).

Purified cyclohexanone is reacted with hydroxylamine mineral acid salt to cyclohexanone oxime. Beckmann rearrangement is carried out by a method such as contacting cyclohexanone oxime with sulfuric acid or fuming sulfuric acid to produce caprolactam. The crude caprolactam obtained by Beckmann rearrangement is purified by distillation. Since the boiling point of caprolactam was 139 ° C. under a reduced pressure of 12 mHg, and the boiling point was different from that of cyclohexanone, it was thought that most of the residual trace by-products during the production of cyclohexanone could be removed.

[0004]

In recent years, it has been required to further improve the quality of caprolactam as a nylon raw material. As means for achieving this high quality, it is considered that increasing the reaction efficiency of Beckmann rearrangement and improving the purification method of the produced caprolactam are particularly effective. However, even though these methods have been studied for many years, there existed problems in quality of caprolactam that could not be sufficiently solved.

[0005]

Means for Solving the Problems The inventors of the present invention have been investigating the above-mentioned problems. Surprisingly, hexahydrobenzaldehyde, which is one of the trace impurities in cyclohexanone described above, is reacted. It was found that the compound remained in the process and became hexahydrobenzamide upon Beckmann rearrangement, which was one of the factors that deteriorate the quality of the product caprolactam. Specifically, it was confirmed that the amount of volatile base in the product caprolactam (hereinafter referred to as "VB amount") is increased by the remaining hexahydrobenzamide, which affects the appearance, strength, etc. of the fiber product made from caprolactam. did.

The gist of the present invention is to synthesize cyclohexanone oxime by reacting cyclohexanone produced by the oxidation of cyclohexane with hydroxylamine mineral acid salt,
Then, when producing caprolactam by subjecting this to Beckmann rearrangement, there exists a process for producing caprolactam, characterized in that as an intermediate raw material, cyclohexanone having a hexahydrobenzaldehyde content of 30 ppm or less is used.

The present invention will be described in detail below. In the present invention, it is essential to control the amount of hexahydrobenzaldehyde contained in the intermediate raw material cyclohexanone to 30 ppm or less, preferably 10 ppm or less, and particularly preferably 3 ppm or less. If the content of hexahydrobenzaldehyde is higher than the above value, a high quality caprolactam with improved VB cannot be stably obtained. The target VB amount of caprolactam products is usually 10 ppm or less, preferably 5 ppm or less. Hexahydrobenzaldehyde is converted to hexahydrobenzamide when the oxime is contacted with sulfuric acid or fuming sulfuric acid for Beckmann rearrangement. Further, hexahydrobenzamide has a small vapor pressure difference with caprolactam, and thus it is difficult to separate it by distillation of caprolactam.

Therefore, in the present invention, it is necessary to remove hexahydrobenzaldehyde, which causes hexahydrobenzamide, to a specific value or less before Beckmann rearrangement. The removing method is not particularly limited, but as a simple method, a method of subjecting cyclohexanone described below to alkali treatment to decompose and remove hexahydrobenzaldehyde is preferable.

The process from cyclohexane to caprolactam of the present invention will be described below. First, cyclohexane is mixed with molecular oxygen to obtain a mixture containing cyclohexanol and cyclohexanone in the presence of a boric acid compound or a cobalt catalyst. When the oxidation reaction is carried out in the presence of a boric acid compound, the mixture is hydrolyzed after the completion of the oxidation reaction, and then the aqueous phase containing the boric acid compound is separated into liquids. The main components of this mixture are unreacted cyclohexane and the target products cyclohexanol and cyclohexanone, as well as by-products such as esters and carboxylic acids. The content ratio of these is usually 85 to 95% by weight of unreacted cyclohexane,
The target product is 4 to 13% by weight and the by-product is 1 to 2% by weight.

As the treatment method after the reaction, the following method is usually adopted. First, as the first step, the above-mentioned oxidation reaction mixture containing cyclohexanol and cyclohexanone is mixed with an alkaline aqueous solution, and a primary alkali treatment is performed. This step allows impurities in the oxidation reaction mixture,
For example, it is for saponifying esters, extracting carboxylic acids with an alkali salt, and extracting these into an aqueous phase.

The alkali compound used in the alkaline aqueous solution is usually a caustic alkali such as caustic soda and potassium hydroxide, but an alkali carbonate such as sodium carbonate and potassium carbonate may be used in combination. It is also possible to carry out a multi-step treatment in which the first step is a treatment with an alkali carbonate aqueous solution and the second step is a treatment with a caustic alkaline aqueous solution. The alkali concentration in the aqueous alkali solution is usually 0.1 to 40% by weight,
It is preferably 1 to 30% by weight. The amount of the caustic aqueous solution used is usually 0.5 to 10 of the ester component in the oil phase.
It is selected in the range of weight times, preferably 1 to 5 times. The condition for the primary alkali treatment is usually 50
To 95 ° C, preferably 70 to 90 ° C, usually 0.1 to 2
The time is preferably 0.2 to 0.5 hours. When the treatment temperature is low, the saponification reaction becomes slow, and when the treatment temperature is high, a part of the target product, cyclohexanone, is lost due to the condensation reaction. It is desirable to select the conditions.

In the second step, the mixture subjected to the primary alkali treatment is separated into an oil phase and an aqueous phase. Since the alkaline component remains on the aqueous phase side and a small amount of the oil phase component is mixed in, the aqueous phase can be reused for the primary alkaline treatment in the first step. Further, since some water-soluble impurities remain on the oil phase side as well, it is preferable to completely remove the water-soluble impurities by further mixing and washing the oil phase with pure water for liquid separation.

When such water washing is carried out, the alkali concentration of the oil phase after liquid separation usually remains at only a few ppm or less. In the third step, usually 20 to 5000 ppm of an alkali compound is added to the oil phase separated in the second step, and the secondary alkali treatment is usually performed at a temperature of 60 to 150 ° C. .. By the secondary alkali treatment, hexahydrobenzaldehyde, which is a by-product that could not be sufficiently removed by the primary alkali treatment, is decomposed by a condensation reaction or the like, and as a result, hexahydrobenzaldehyde in cyclohexanone can be almost completely removed. ..

As the method of the secondary alkali treatment, the same alkaline compound as that used in the primary alkali treatment is used as it is or in the form of a solution, in the oil phase, usually 20 to 5000 ppm relative to the oil phase, Preferably 100-2000
It is added at a concentration of ppm, and usually heat treated at 60 to 150 ° C., preferably 100 to 130 ° C. for usually 0.2 to 4 hours, preferably 0.5 to 3 hours. When the temperature of the heat treatment or the alkali concentration is higher than the above range, a decrease in yield due to the condensation reaction of cyclohexanone becomes a problem, while
When they are lower than the above range, the progress of decomposition of hexahydrobenzaldehyde is delayed, which is not preferable.

The above-mentioned secondary alkali treatment may be carried out while distilling and separating unreacted cyclohexane contained in the oil phase. Specifically, an oil phase is introduced into the bottom of the distillation column, a predetermined amount of an alkali compound is added, the column bottom temperature is usually set to a range of 60 to 150 ° C., and the boiling point is lower than that of cyclohexanone and cyclohexanol. The cyclohexane and low-boiling-point by-product may be distilled off. When adopting such a method, the total amount of alkali compounds to be added is
Although it is an amount corresponding to 20 to 2000 ppm with respect to the oil phase before distillation, the alkali compound may be added during the distillation in consideration of the heat treatment time.

In the fourth step, cyclohexanone is separated and recovered by distillation by a known method. As a known distillation method, components such as unreacted cyclohexane having a lower boiling point than cyclohexanone are distilled off in the first distillation column, while the bottom liquid is supplied to the second distillation column for distillation. A general method is to distill out most of cyclohexanone in the second distillation column and separate and recover it. The bottom liquid of the second distillation column is supplied to the third distillation column and further distilled to distill cyclohexanol and the remaining cyclohexanone, and cyclohexanol in the distillate is dehydrogenated to give cyclohexanone. To
It can be circulated to the first distillation column.

Regarding the above operating conditions of distillation, the column top pressure is usually 20 to 500 Torr, and preferably the pressure is successively lowered in the order of the first, second and third. The column top temperature is usually controlled in the range of 50 to 150 ° C. according to the column top pressure. Further, as described above, when the method of performing the secondary alkali treatment of the fourth step while distilling off cyclohexane by distillation is performed, the separation of cyclohexane in the first distillation column described above in the fourth step is omitted. Will be.

Further, in the above-mentioned third step, unreacted cyclohexane contained in the oil phase may be separated by distillation under the same conditions as the above-mentioned distillation conditions for separating cyclohexane. In this case, as the fourth step, the remaining oil phase from which cyclohexane was separated is usually added to the oil phase by 10 times.
~ 2000 ppm, preferably 50-1000 ppm
The alkaline compound is added and the secondary alkali treatment is carried out at a temperature of 60 to 150 ° C., preferably 100 to 130 ° C., usually 0.2 to 4 hours, preferably 0.5 to 3 hours. Then, as a fifth step, distillation is carried out from the oil phase subjected to the secondary alkali treatment under the same conditions as the above-mentioned distillation conditions for separating cyclohexanone to recover cyclohexanone.

The cyclohexanone having a hexahydrobenzaldehyde content of 30 ppm or less thus obtained is then converted into cyclohexanone oxime by a known method.
An example of the method for producing cyclohexanone oxime is a method in which cyclohexanone and a hydroxylamine mineral acid are reacted in the presence of a platinum catalyst under conditions of usually 20 to 80 ° C. and pH 3 to 5. As the hydroxylamine mineral acid salt, a sulfate salt is usually used.

Then, caprolactam is produced from cyclohexanone oxime by Beckmann rearrangement. The Beckmann rearrangement is carried out according to a known method by using cyclohexanone oxime in a single stage or multiple stages in a reactor such as a stirring tank or a pipeline mixer in the presence of fuming sulfuric acid, and usually an acidity of 50.
-60%, temperature 70-120 ° C., and atmospheric pressure.

The mixture obtained by the Beckmann rearrangement is neutralized with ammonia, the precipitated by-product ammonium sulfate (ammonium sulfate) is separated, and then purified by distillation. If necessary,
Before distillation, high boiling substances such as oligomers may be extracted and removed with an extractant such as benzene.

[0022]

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. Hereinafter, “parts” in the examples mean “parts by weight”. Example 1 350 parts / hr of cyclohexane and 15 parts of air were placed in a stirring tank.
Parts / hr, in the presence of boric acid catalyst, 160-17
The oxidation of cyclohexane was carried out at 0 ° C. with an average residence time of 30 minutes.

Next, 6 parts of demineralized water was added to 150 parts of the cyclohexane oxidation reaction liquid to hydrolyze and remove the boric acid catalyst. After removing the boric acid catalyst, cyclohexane oxidation reaction liquid 15
A saponification reaction was carried out by adding 10% by weight and 20 parts of a caustic soda aqueous solution to 0 parts. After completion of the saponification reaction, the oil phase and the aqueous phase were separated, and the oil phase was washed with 4 parts of demineralized water.

Next, after adding 25% by weight and 0.03 part of a caustic soda aqueous solution to 150 parts of the oil phase, the mixture was supplied to the first distillation column to distill off cyclohexane (first distillation column condition: bottom temperature). 120 ° C, tower top temperature 60 ° C, tower top pressure 400T
orr). Next, the bottom liquid was supplied to the second distillation column, and purified cyclohexanone was separated by distillation from the top of the column. (Second distillation column conditions: column bottom temperature 110 ° C., column top temperature 70 ° C., column top pressure 50 Torr). When the purified cyclohexanone was analyzed by gas chromatography, the purity was 99.9% and the amount of hexahydrobenzaldehyde was 1 ppm or less (below the detection limit).

Next, the purified cyclohexanone was treated at a temperature of 70.
It was oxime-ized by reacting with hydroxylamine sulfate at 0 ° C and pH 4.0. The obtained cyclohexanone oxime was subjected to Beckmann rearrangement in the presence of fuming sulfuric acid at a temperature of 80 ° C. and an acidity of 56%. The reaction solution was neutralized with 24N aqueous ammonia, extracted with benzene, and caprolactam was recovered by distillation. Amount of VB determined by titration method of the obtained caprolactam (amount of volatile base, amount of ammonia conversion)
Was 5 ppm. Comparative Example 1 Same as Example 1 except that an aqueous sodium hydroxide solution was not added when distilling off unreacted cyclohexane from the cyclohexane oxidation reaction liquid. The amount of hexahydrobenzaldehyde in the recovered purified cyclohexanone was 100.
The VB amount of the obtained caprolactam was 15 ppm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ari Kanda 1-1, Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu, Fukuoka Prefecture Mitsubishi Kasei Co., Ltd. Kurosaki Plant

Claims (2)

[Claims] 1. A cyclohexanone oxime is produced by reacting cyclohexanone produced by the oxidation of cyclohexane with a hydroxylamine mineral acid salt, and is then subjected to Beckmann rearrangement to produce caprolactam.
A process for producing caprolactam, characterized in that the content of hexahydrobenzaldehyde in the cyclohexanone is 30 ppm or less. 2. The amount of volatile base in caprolactam is 1
The method for producing caprolactam according to claim 1, wherein the content is 0 ppm or less.