JP2002012585A - METHOD FOR PURIFYING epsi-CAPROLACTAM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying a lactam by hydrogenation method for controlling an increase in VB and acidification. SOLUTION: This method for purifying ε-caprolactam comprises reducing an oxygen concentration in a hydrogen gas or a hydrogen-containing gas to <=1,000 volume ppm in bringing crude ε-caprolactam into contact with the gas in the presence of a hydrogenation catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying ε-caprolactam (hereinafter sometimes referred to as “lactam”). More specifically, the present invention relates to a method for purifying a lactam by subjecting a crude lactam containing impurities to a hydrogenation treatment.

[0002]

2. Description of the Related Art ε-caprolactam is mainly made of nylon-
Organic product used as a raw material of No. 6 and is industrially produced by a Beckmann rearrangement reaction of cyclohexanone oxime (hereinafter sometimes referred to as "oxime"). Product lactams have several types of quality standards that are generally common between manufacturers and users (for example, Ul
lmann's Encyclopedia of Industrial Chemistry 5
Version A5, p. 46) In order to satisfy these quality standards, lactam purification methods such as liquid-liquid distribution, distillation, crystallization, hydrogenation treatment, ion exchange, and activated carbon treatment have been studied and adopted. ing. Among these purification methods,
The hydrogenation method is effective for reducing the PM value (quality standard relating to the content of impurities oxidized by potassium permanganate), and various methods have been reported. For example, Japanese Patent Publication No. 32-6358 discloses a method of treating a crude lactam as an aqueous solution.
No. 743 discloses a method for treating a crude lactam in an aromatic hydrocarbon solvent in the presence of an organic amine.
No. 35958 describes a method of continuously treating an aqueous solution of a crude lactam by upflow under heating and pressurizing.

[0003]

SUMMARY OF THE INVENTION The present inventors have found that tetrahydroazepin-2-ones (1,3,3)
There are four types: 4,5-form, 1,3,4,7-form, 1,3,6,7-form and 1,5,6,7-form; hereinafter, referred to as "caprenolactams" In some cases, caprenol lactams were converted to lactams by hydrogenation to reduce the PM value, but VB ( However, it may cause an increase in the quality standard for volatile bases) or acidification, which is not always sufficient. An object of the present invention is to solve the above problems and to provide a method for purifying a lactam by a hydrogenation method in which an increase in VB and acidification are suppressed.

[0004]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that in the hydrogenation treatment of crude lactam, if a small amount of oxygen is present or mixed in the hydrogen gas to be brought into contact with the crude lactam, it can be reduced under reduced conditions. Nevertheless, lactams are oxidized and adipic imide (hereinafter sometimes referred to as “ADI”) is produced as a by-product.
And the degree of acidification tended to be large. Then, it was found that by reducing the oxygen concentration in the hydrogen gas to a specific amount or less, the by-product of ADI was suppressed, and the increase and acidification of VB were suppressed, and the present invention was completed. That is, the present invention relates to a method for purifying ε-caprolactam in which, when crude ε-caprolactam is brought into contact with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst, the oxygen concentration in the gas is 1,000 vol ppm or less. It is related.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, as the crude lactam, those obtained by various reactions producing lactam can be used,
Examples of the reaction include a Beckmann rearrangement reaction of an oxime, a cyclization reaction of a 6-aminocaproic acid ester such as methyl 6-aminocaproate, and a hydrolytic cyclization reaction of 6-aminocapronitrile. In particular, the method of the present invention can be suitably used for a crude lactam obtained by a Beckmann rearrangement reaction of an oxime.

[0006] The Beckmann rearrangement reaction of oxime includes:
For example, using an acid such as sulfuric acid, fuming sulfuric acid, phosphoric acid, hydrochloric acid, etc. under liquid phase conditions, boric acid catalyst, silica / alumina catalyst, solid phosphoric acid catalyst, composite metal oxide catalyst, metallosilicate And under a gas phase condition using a zeolite catalyst such as silica or silicalite. The method of the present invention can be applied to any crude lactam obtained by any Beckmann rearrangement reaction.

As the crude lactam obtained by the Beckmann rearrangement reaction under the liquid phase condition of oxime, an oil phase obtained by mixing a reaction solution with a base such as ammonia and water and separating the mixture into oil and water can be used. A lactam is extracted from the mixture or the oil phase with an organic solvent such as benzene, and a concentrate obtained by concentrating the extract may be used, or the oil phase or the concentrate may be obtained by distillation. Distillate may be used.

As the crude lactam obtained by the Beckmann rearrangement reaction of the oxime under gas phase conditions, a condensate of a reaction gas may be used, or a concentrate obtained by condensing the condensate may be used. A distillate obtained by distilling the condensate or the concentrate may be used.

The impurities contained in the crude lactam include:
Depending on the preparation method, for example, the remaining raw materials oxime, caprenolactams, 1,2,3,4,6,7,
8,9-octahydrophenazine (hereinafter may be referred to as “OHP”), 1-methyl-4,5,6,7-tetrahydrobenzimidazole (hereinafter may be referred to as “MTHI”) and the like. In the method of the present invention, the caprenol lactam of the impurity can be converted to the lactam of the target substance by the hydrogenation treatment. Therefore, the crude lactam contains caprenol lactam as the impurity in a relatively large amount, for example, 30 ppm or more. Even those can be suitably used.

On the other hand, an oxime, OHP,
The content of impurities other than caprenolactam such as MTHI should be as low as possible, for example, 10 ppm of oxime.
Below, OHP is 10 ppm or less, MTHI is 25 ppm
It is preferred that: Therefore, it is preferable to use a crude lactam that has been purified by crystallization or the like before the hydrogenation treatment. When crystallization is carried out using a solvent, examples of the solvent include aliphatic hydrocarbon solvents such as n-heptane and cyclohexane, and a mixed solvent can be used if necessary. If the solvent used for crystallization is susceptible to hydrogenation, it is preferable to remove it as much as possible before subjecting it to hydrogenation treatment. Can be subjected to hydrogenation treatment while the solvent is contained.

The hydrogenation treatment of the crude lactam can be carried out by bringing the crude lactam into contact with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst (hereinafter sometimes referred to as “catalyst”). Examples of the catalyst include a Group VIII transition metal such as nickel, palladium, platinum, ruthenium, and rhodium. If necessary, two or more of them can be used. The catalyst is preferably used as a supported catalyst supported on a suitable carrier, and examples of the carrier include activated carbon, alumina, silica, titania and the like. Among them, from the viewpoints of catalytic activity and catalyst life, those in which palladium is supported on the surface of activated carbon and those in which platinum and ruthenium are co-supported are preferable, and an egg shell type catalyst is particularly preferable. When a catalyst in which palladium is supported on activated carbon is used, the amount of palladium supported is usually 0.1 to 20% by weight, preferably 0.5 to 5% by weight, based on the entire supported catalyst.
% By weight. When a catalyst further supporting platinum or ruthenium is used, the amount of the catalyst is usually 2% by weight or less based on the whole supported catalyst. The life of the catalyst varies depending on the crude lactam used and the conditions of the hydrogenation treatment. However, according to the method of the present invention, it can be as long as one year or longer.

In the present invention, the oxygen concentration in the hydrogen gas or hydrogen-containing gas to be brought into contact with the crude lactam is 1000
ppm (vol / vol, hereinafter the same) or less, preferably 500 ppm or less, more preferably 5 ppm or less.
It is 0 ppm or less. The higher the oxygen concentration, the greater the amount of by-product ADI, and the greater the degree of VB and acidification tend to be. An example of the relationship between the oxygen concentration and the by-product rate of ADI is as follows.
Under the conditions of ° C., a reaction time of 1 h, and a hydrogen pressure of 0.3 MPa, the result showed that the generation rate of ADI was almost proportional to the logarithm of the oxygen concentration.

In order to keep the oxygen concentration below a predetermined value, a sufficiently purified hydrogen gas should be used, and the oxygen concentration should not exceed the predetermined value if air or the like is mixed into the reaction system. Need to be managed. When a supported catalyst is used, it is preferable to pretreat the supported catalyst with an inert gas or hydrogen gas in advance to remove oxygen adsorbed and retained in the pores of the carrier.

In the hydrogenation treatment, an organic solvent such as alcohol or water can be used as a solvent, if necessary. The hydrogenation treatment may be performed in a batch format or a distribution format. When carried out in a flow format, the crude lactam or a solution thereof may be flowed upflow or downflow with hydrogen gas through the layer filled with the catalyst, or may be flowed downflow, or the crude lactam or the solution thereof may be mixed with hydrogen. The gas may be allowed to flow in countercurrent.
Alternatively, the reaction may be carried out by a thin-layer flow method in which the catalyst layer is filled with hydrogen gas, and the reaction is carried out while a droplet of a crude lactam or a solution thereof is allowed to flow from above the catalyst layer. By keeping the pressure in the bed constant and replenishing the consumed hydrogen, the amount of hydrogen gas used can be suppressed and the problem of the drift of the hydrogen gas can be avoided. It is preferable that the catalyst be pretreated in advance with hydrogen gas in both the batch format and the flow format.

The amount of hydrogen gas used is usually 0.0001 mol or more, preferably 0.001 to 0.1 mol, per mol of lactam in the crude lactam. When caprenolactams are contained in the crude lactam, hydrogen gas of at least equimolar to the caprenolactams is required.
When the reaction is carried out in a flow system, the hydrogen gas discharged without being used can be purified and reused as necessary.

When no solvent is used, the temperature of the hydrogenation treatment must be higher than the temperature at which the crude lactam melts, and is preferably in the range of 70 to 150 ° C. When a solvent is used, the temperature can be lowered to a temperature at which the lactam does not precipitate from the solution. Further, in the case of carrying out in a flow-through manner, since the catalyst activity gradually decreases as time passes, it is preferable to increase the temperature as the activity decreases and maintain the catalyst activity at a constant level. Therefore, it is preferable to start at a relatively low temperature of 80 ° C. or lower at the beginning and gradually increase the temperature.

The pressure of the hydrogenation treatment is usually 0.05 to 1
0 MPa, preferably in the range of 0.1 to 1 MPa.
The time of the hydrogenation treatment is usually in the range of 10 minutes to 2 hours in the case of the batch type, and the WHS
V (feed rate of crude lactam per kg of catalyst (kg / kg)
h)) is usually 0.5 to 100 h ^-1 , preferably 1
-10 h ^-1 .

If the lactam after the hydrogenation treatment contains a solvent, the solvent can be removed by simple distillation. Further, even in the case where no solvent is contained, it is preferable to carry out simple distillation in order to remove foreign substances and the like derived from the catalyst. As a result of the hydrogenation treatment, the content of caprenolactams is usually 30 ppm or less, preferably 2 ppm or less.
5 ppm or less, the PM value is usually 10 or less, preferably 7 or less, and the ADI content is usually 15 pp
m, preferably 10 ppm or less of purified lactam can be obtained.

The method of the present invention can be employed as a lactam purification method in various lactam production methods. By including the step of purifying the lactam by the method of the present invention, a high-quality lactam can be produced.

[0020]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples. GC analysis and quality standard analysis were performed by the following methods. <GC Analysis> Column: DB-WAX, temperature: 80 ° C. → 230 ° C., detection: analysis under the conditions of FID, and the area percentage excluding the solvent was calculated. The detection limit for impurities is about 3 ppm. <UV Absorbance> A 50% aqueous solution of lactam was placed in a 1 cm cell, water was used as a blank, and ultraviolet transmittance (%) at a wavelength of 290 nm was measured. <Potassium permanganate value (PM value)> 1 g of lactam was dissolved in distilled water to make 100 ml, and 0.01N was added to the aqueous solution.
2 ml of an aqueous potassium permanganate solution was added and stirred. After adding the aqueous solution of potassium permanganate, add 250
After a lapse of seconds, the absorbance of light having a wavelength of 420 nm was measured at 25 ° C. (solution temperature). On the other hand, distilled water 1
To 0.01 ml of a 0.01 N aqueous solution of potassium permanganate 2
After 250 seconds had elapsed from the addition of the aqueous potassium permanganate solution, the absorbance of light having a wavelength of 420 nm was measured at 25 ° C (solution temperature). The absorbance of the latter was subtracted from the absorbance of the former, and the value obtained by multiplying the value by 100 was defined as the potassium permanganate value (PM value). <Free basicity (FB)> About 2.5 g of lactam was added to 10 ml of water adjusted to pH 5.7 by adding 0.01 N sulfuric acid or aqueous sodium hydroxide solution to distilled water, followed by stirring. The pH of the resulting solution is measured, and if the pH value is greater than 5.7, 0.01 N sulfuric acid is added to the solution at a pH of 5.7.
Until it became. Usage amount of added 0.01 N sulfuric acid v (ml), factor (f), weight of lactam used w
From (g), the free base (FB; meq / k)
g) was calculated. FB = 0.01 × v × f × 1000 / w <Volatile basicity (VB)> 5 g of lactam in a distillation flask
And 8 ml of a 20% aqueous sodium hydroxide solution were added thereto, followed by steam distillation, and the distillate was introduced into 5 ml of a 0.01 N aqueous sulfuric acid solution. Steam distillation was completed when the amount of distillate was 150 ml. The obtained solution was titrated with a 0.01 N aqueous sodium hydroxide solution using a methyl red-methylene blue mixed indicator. Titration B (ml), titration A (ml) in blank test without lactam, 0.0
The volatile basicity (VB; ppm) was calculated from the factor (f ') of the 1N aqueous sodium hydroxide solution and the weight lactam w' (g) used by the following equation. VB = [0.17 × (BA) × f ′ × 1000] /
w '<Chromaticity (APHA)> 5 cm of 50% aqueous solution of lactam
Was used as a blank, water was used as a blank, the absorbance of light at 370 nm was measured, and converted to chromaticity using a calibration curve prepared in advance with a Hazen standard color solution.

Reference Example 1 Oxime: 496 ppm, MTHI: 181 ppm, caprenolactams: 430 ppm, and OHP: 242
lactam with a purity of 99.20% containing 73 ppm
At 300 parts by weight per unit time and a solvent [n-heptane / cyclohexane = 3/1 (W / W)]
Was adjusted to 5.5 ° C., and 550 parts by weight per unit time was poured into a crystallization tank having an outer jacket at 56 ° C. for crystallization.
With stirring, the slurry was continuously introduced with an average residence time of 34 minutes into a centrifugal decanter kept at 56 ° C. to perform solid-liquid separation, and the solid phase was subjected to the solvent (120 parts by weight per unit time) at 50 ° C. Washed. As a result, 207 parts by weight of lactam per unit time were obtained as crystals. As a result of analysis, the solvent content was 1.7% by weight [n-heptane / cyclohexane =
1.75 (W / W)]. As a result of GC analysis (area percentage excluding solvent), lactam: 99.98%, oxime: 6 ppm, caprenolactams: 172 ppm, and MTHI, OHP and ADI Was not detected.

Reference Example 2 A lactam prepared in the same manner as in Reference Example 1 was concentrated under reduced pressure. As a result of analyzing the obtained lactam, the solvent content was 0.1% by weight or less, and as a result of GC analysis (area percentage excluding the solvent), lactam: 99.9858%, caprenolactams: 129 ppm, Oxime, M
THI, OHP and ADI were not detected.

Example 1 The lactam obtained in Reference Example 1 was 207 parts by weight per unit time and hydrogen having an oxygen concentration of 0.1 ppm was 0.0207 parts by weight per unit time. −20 mesh) was continuously supplied at 95 ° C. at a WHSV of 2.6 h ⁻¹ . The obtained reaction mass was concentrated and distilled under reduced pressure to obtain a lactam as a fraction. As a result of GC analysis of this lactam, it was found that lactam: 99.99% or more, caprenolactams: 1 ppm
And oxime, MTHI, OHP and ADI were not detected. The lactam quality standard analysis values were as follows: UV absorbance: 92.0%, PM value: 1.1, APH
A: 0.5, VB: 2.7, FB: 0.03.

Example 2 In a 200 ml SUS autoclave, 2% Pd / C
1.8 g of the catalyst was added, the inside of the system was replaced with hydrogen having an oxygen concentration of 0.1 ppm, the mixture was stirred at 120 ° C. for 1 hour at 100 rpm, and then cooled. After the replacement with nitrogen, 9 g of water and 90 g of the lactam obtained in Reference Example 2 were added thereto, and the oxygen concentration was 0.1%.
After replacing the inside of the system with 3 ppm of hydrogen,
g / cm ² (0.3 MPa) and at 120 ° C.
Stir at 1000 rpm for hours. The reaction solution was filtered under pressure under a nitrogen atmosphere to obtain a filtrate. The filtrate was subjected to GC analysis (area percentage excluding the solvent), and as a result, lactam: 99.9
981%, caprenolactams: 8 ppm, oxime, MTHI, OHP and ADI were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain a lactam as a fraction. As a result of quality standard analysis of this lactam, UV absorbance: 99.2%, PM value: 0.25, AP
HA: 0.65, VB: 3.0 ppm, FB: 0.04
It was 5.

Comparative Example 1 In Example 2, instead of hydrogen having an oxygen concentration of 0.1 ppm, a nitrogen concentration of 3900 ppm and an oxygen concentration of 1050 were used.
A filtrate was obtained by performing the same operation as in the previous step of Example 2 except that ppm of hydrogen was used. The filtrate was subjected to GC analysis (area percentage excluding the solvent), and as a result, lactam: 99.99
50%, caprenolactams: 8 ppm, ADI: 17
ppm, and no oxime, MTHI and OHP were detected. The filtrate was concentrated and distilled under reduced pressure to obtain a lactam as a fraction. As a result of quality standard analysis of this lactam, UV absorbance: 98.6%, PM value: 1.4.
3, APHA: 0.97, VB: 7.9, FB was less than 5.7 and could not be measured.

Example 3 In Example 2, instead of hydrogen having an oxygen concentration of 0.1 ppm, a nitrogen concentration of 1780 ppm and an oxygen concentration of 480 p
A filtrate was obtained by performing the same operation as in the previous step of Example 2 except that pm of hydrogen was used. The filtrate was subjected to GC analysis (area percentage excluding the solvent), and as a result, lactam: 99.992
6%, caprenolactams: 15 ppm, ADI: 8p
pm, oxime, MTHI and OHP were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain a lactam as a fraction. As a result of quality standard analysis of this lactam, UV absorbance: 98.9%, PM value: 0.7
7, APHA: 1.02, VB: 5.6, FB: 0.0
It was 13.

Example 4 In Example 2, instead of hydrogen having an oxygen concentration of 0.1 ppm, a nitrogen concentration of 160 ppm and an oxygen concentration of 50 ppm were used.
The same operation as in the previous stage of Example 2 was performed, except that hydrogen was used, to obtain a filtrate. The filtrate was subjected to GC analysis (area percentage excluding the solvent), and as a result, lactam: 99.9964
%, Caprenolactams: 9 ppm, ADI: 7 ppm
Oxime, MTHI and OHP were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain a lactam as a fraction. As a result of quality standard analysis of this lactam, UV absorbance: 98.7%, PM value: 0.56, A
PHA: 1.1, VB: 3.3, FB: 0.052.

[0028]

According to the present invention, the hydrogenation treatment can be performed under the condition that the increase of VB and the acidification are suppressed,
A lactam having a reduced M value can be obtained.

Claims (6)

[Claims] When the crude ε-caprolactam is brought into contact with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst,
A method for purifying ε-caprolactam, wherein the oxygen concentration in the gas is 1000 vol ppm or less. 2. The method according to claim 1, wherein the crude ε-caprolactam contains tetrahydroazepin-2-ones. 3. The method according to claim 1, wherein the crude ε-caprolactam is obtained by a Beckmann rearrangement reaction of cyclohexanone oxime. 4. The purification method according to claim 1, wherein the crude ε-caprolactam has been purified by crystallization in advance. 5. The purified ε-caprolactam has an adipic imide content of 15 ppm or less.
4. The purification method according to any one of 4. 6. A method for producing ε-caprolactam, comprising a step of purifying ε-caprolactam by the purification method according to any one of claims 1 to 5.