JPH0899954A - Method for purifying lactams and lactams - Google Patents

Abstract

(57) Abstract: Ultraviolet absorbing impurities contained in lactams are removed to obtain high-purity lactams. A method for purifying a lactam, which comprises irradiating a lactam containing an ultraviolet-absorbing impurity with an ultraviolet ray, and a lactam having a reduced amount of an ultraviolet-absorbing impurity by irradiating with an ultraviolet ray.

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 lactams, and more particularly to lactam purification characterized by irradiating a lactam containing ultraviolet absorbing impurities with ultraviolet rays to decompose the ultraviolet absorbing impurities. It is about the method.

[0002]

BACKGROUND OF THE INVENTION Lactams are important industrial raw materials such as synthetic raw materials, polyamide fibers, and polyamide resins. Along with the improvement in quality of polyamide products, high-quality lactams are required. Many purification means are known for removing impurities from a crude lactam to obtain a purified lactam. It can be roughly classified into a physical treatment method such as extraction, distillation and recrystallization, and a chemical treatment method using potassium permanganate, sodium hypochlorite and the like. Generally, an appropriate combination of purification methods is selected depending on the type of impurities in the crude caprolactam.

For example, as a method for purifying caprolactam, there is a method in which cyclohexanone oxime is subjected to Beckmann rearrangement using fuming sulfuric acid, and then the reaction mixture is held at a temperature of 70 to 110 ° C. (Japanese Patent Laid-Open No. 63-156766). .

Further, Japanese Patent Laid-Open No. 6-1763 discloses that
A method of distilling in the presence of saturated aliphatic hydrocarbons having 10 to 18 carbon atoms for the purpose of removing octahydrophenazine in caprolactam is described.

[0005]

One of the quality characteristic values of lactam is the ultraviolet transmittance (UVT) of a 50 wt% aqueous solution of lactam at a wavelength of 290 nm, which is a measure of the amount of ultraviolet absorbing impurities contained in the lactam. Is used as. As the ultraviolet absorbing impurities, phenol, aniline, octahydrophenazine and the like are fried. Especially, octahydrophenazine has a large molecular absorption coefficient (λ _max : 290 nm, ε: 9,300 l / mol).
.Cm), and in order to obtain a high-quality purified lactam, the content thereof needs to be 1 ppm or less, and thus it is an impurity to be particularly noted in the purification of lactam.

Since octahydrophenazine is a chemically stable substance, it is difficult to selectively decompose octahydrophenazine without damaging the lactam, and no excellent method has been found yet.

In the method described in JP-A-63-156766, not only is the decomposition rate of octahydrophenazine insufficient, but there is also the risk of loss of thermal decomposition of caprolactam. Therefore, physical means such as distillation and recrystallization are exclusively used as means for removing octahydrophenazine. However, the relative volatility of octahydrophenazine with respect to caprolactam is as small as about 1.3, and an extremely high number of rectification columns is required to obtain a content of 1 ppm or less by the distillation method. The UVT of the purified caprolactam obtained by using the method disclosed in JP-A-6-1763 is not satisfactory. On the other hand, the recrystallization method is one of the excellent purification methods for removing octahydrophenazine, and in this case also, 1 pp of crude caprolactam having a content of several tens of ppm is used.
A multi-stage crystallization tank is required to reduce the volume to m or less. As described above, both the distillation method and the recrystallization method have economical difficulties such as high equipment costs.

[0008] Therefore, the inventors of the present invention have been keen on a method for easily and efficiently removing the ultraviolet absorbing impurities from the crude lactams containing the ultraviolet absorbing impurities represented by octahydrophenazine, at a low equipment cost. As a result of study, they have found that the ultraviolet absorbing impurities are decomposed by irradiating the crude lactams with ultraviolet rays without damaging the lactams, and arrived at the present invention. That is, the object of the present invention is to provide efficient removal of ultraviolet absorbing impurities in crude lactams by an economical and inexpensive method. Lactams can be obtained.

[0009]

That is, the present invention is a method for purifying lactams, which comprises irradiating ultraviolet rays to lactams containing ultraviolet absorbing impurities.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The lactams referred to in the present invention are ε
-Caprolactam, ω-laurolactam, valerolactam and the like. Preferably, ε-caprolactam, ω-
Used when purifying laurolactam and the like.

The history of the production method, the recovery method, etc. of the lactam containing the ultraviolet absorbing impurities which is the object of the present invention is not particularly limited. For example, ε-caprolactam is obtained by subjecting cyclohexanone oxime to Beckmann rearrangement in a liquid phase using a catalyst such as fuming sulfuric acid, or obtained by catalytic rearrangement in a gas phase using a solid acid catalyst such as zeolite. In addition to this, lactams recovered from polycaprolactam-extracted water, polycaprolactam, and recovered lactams obtained by depolymerizing oligomers and the like can also be used.

The term "UV-absorbing impurities" as used in the present invention mainly describes octahydrophenazine, but in addition to this, substances that affect the ultraviolet transmittance characteristic value of caprolactam, that is, lactams such as phenol and aniline Examples include UV absorbing impurities that are by-produced during the manufacturing, refining, and recovery processes.

The form of lactam irradiated with ultraviolet rays is gas,
It may be solid or liquid. Gaseous refers to those vaporized in a distillation column, products obtained by catalytic rearrangement in the gas phase, and solid refers to crystals obtained by crystallization, flakes obtained with flakers, and the like. Further, the liquid state refers to a molten state of lactam or a state of being dissolved in a solvent, and the solvent in this case is preferably one that does not absorb effective ultraviolet rays, and has a transmittance of UVB (ultraviolet rays having a wavelength of 280 to 315 nm). It is preferably 50% or more. Specifically, for example, water, methanol, ethanol, n-hexane, cyclohexane, chloroform, carbon tetrachloride, etc. are fried. These may be used in combination of two or more.

The decomposition rate of the ultraviolet absorbing impurities greatly changes depending on the pH of the lactam solution, and the alkaline <neutral <
It becomes larger in the order of acidity. Therefore, the more the pH is changed to the acidic side, the higher the decomposition rate of the ultraviolet absorbing impurities per unit time, but when it becomes strongly acidic, an undesirable side reaction such as hydrolysis of caprolactam occurs. Usually, it is preferably carried out in neutral or weak acidity. The preferred pH of the lactam solution is 1-13. More preferably, pH 2
8

When the lactam which is irradiated with ultraviolet rays contains a large amount of coloring impurities such as tar-like substances, effective ultraviolet rays are absorbed by the coloring impurities and the ultraviolet absorbing impurities to be decomposed are not absorbed. The light utilization rate decreases.
Therefore, when the lactam is markedly colored, it is preferable to remove the coloring impurities by means such as distillation before the ultraviolet irradiation treatment.

The ultraviolet light source used in the present invention is not particularly limited, and an artificial light source or a natural light source is used. The artificial light source may be one that is generally used in organic photochemical reactions and the like, and may be one that emits ultraviolet light together with visible light. For example, a low-pressure mercury lamp typified by a sterilization lamp, various fluorescent lamps in which a phosphor for ultraviolet rays is applied to the inner wall of the low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, and a metal halide lamp are lifted. It is economically advantageous to select a lamp having a high output ratio of ultraviolet rays to the lamp power.

The wavelength of ultraviolet rays effective in the present invention is 400 nm.
Considering that ε-caprolactam itself absorbs ultraviolet rays of 280 nm or less and the maximum absorption wavelength of octahydrophenazine is 290 nm,
A wavelength of 80 to 350 nm is preferable from the viewpoint of effective use of ultraviolet rays. Also, 280 absorbed by ε-caprolactam
Ultraviolet rays having a wavelength of nm or less are not preferable because ε-caprolactam itself may be decomposed by irradiation.

The ultraviolet transmittance (UVT) referred to in the present invention is the transmittance of 50 wt% lactam aqueous solution in a cell of quartz having a width of 10 mm, and the ultraviolet transmittance of 290 nm wavelength, which is measured by a spectrophotometer.

In the present invention, the amount of ultraviolet rays to be irradiated may be an amount sufficient to decompose ultraviolet absorbing impurities contained in lactams, but is preferably 10 joules or more per 1 kg of lactams. . The amount of ultraviolet rays to be applied (joule) can be calculated from the ultraviolet ray output (W) of a lamp as a light source and the irradiation time (seconds) by the following formula.

Amount of ultraviolet light (J) = UV light output of lamp (W) × irradiation time (sec) × light utilization ratio Here, the light utilization ratio is the output of light from the lamp that is actually irradiated to lactams. It is the ratio to the light emitted.

The temperature of the ultraviolet irradiation treatment varies depending on the form of the lactam to be handled, but it is preferably performed at 0 ° C. or higher and 200 ° C. or lower. Except for the case of irradiation treatment with gaseous lactams, it is preferably carried out at 90 ° C. or lower. In the case of a solid, the temperature is below the freezing point of lactams, and in the case of a molten lactam, the temperature is above the melting point to below 90 ° C,
In the case of a solution, it is preferably carried out at a temperature above the temperature at which the lactams dissolve and above 90 ° C. Even if the irradiation treatment temperature is raised more than necessary, the decomposition rate of the ultraviolet absorbing impurities does not change, and it is not preferable because of problems such as energy loss and deterioration of lactams.

The UV irradiation device also varies depending on the form of the lactam to be handled. In a gaseous state, it can be carried out by installing an ultraviolet lamp equipped with a protective cover in an apparatus in which gas is present, for example, in a distillation column. In the case of a solid state, there is a method of attaching an ultraviolet lamp to the upper part of a belt conveyor for external irradiation, a method of internally irradiating with a lamp installed in a fluidized bed of lactam powder, and the like. Most commonly, the irradiation is performed in a liquid state, but in this case, a general photoreaction device can be used as it is. For example, in addition to the internal irradiation type device such as a tank type in which a lamp is immersed and mounted in a normal tank, a double tube type in which a lamp is mounted in an inner tube,
It is also possible to externally irradiate from the liquid surface with a lamp mounted on the ceiling of the storage tank. Needless to say, it is preferable to use an outer tube (cover) of a lamp having a high ultraviolet transmittance such as ultraviolet-transparent glass or quartz. The ultraviolet irradiation treatment method may be either batch or continuous, but it is preferable to use an inert gas atmosphere such as nitrogen or argon in the apparatus system, and particularly when the treatment is carried out at a high temperature, oxidation of lactams is prevented. An inert gas atmosphere is preferred for the purpose. When lactams containing ultraviolet absorbing impurities such as octahydrophenazine are subjected to ultraviolet irradiation treatment, the treated lactam may be yellow due to a coloring component produced by decomposition of the ultraviolet absorbing impurities. This decomposition product can be easily removed as a distillation residue by, for example, simple distillation, and adsorption by activated carbon can also be adopted. Further, when the content of the ultraviolet absorbing impurities in the lactam before the treatment is small, the coloring of the caprolactam after the treatment can be ignored even if the ultraviolet absorbing impurities are completely decomposed. It can be directly supplied to the next purification step, or can be directly commercialized if there is no problem.

The distance from the light source to the lactams is preferably within 10 m in consideration of the light utilization rate.

The ultraviolet absorbing impurities absorb ultraviolet rays,
The following formula is considered to hold when it is decomposed or changed.

Light energy amount = k · impurity amount (k = constant) Therefore, when the light energy is small, the amount of impurities decomposed or reduced decreases, which is industrially undesirable.

Therefore, it is desirable to give a certain amount or more of light energy.

[0027]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

Example 1 Purified caprolactam was added to the reagent octahydrophenazine (OH
P) is added at 9.74 ppm and water is added to obtain a water content of 20 w.
A t% lactam aqueous solution was prepared and used as a test solution. The pH of the lactam aqueous solution was 6.8.

270 at the center of the cylindrical constant temperature water tank (20 ° C.)
A 20 mm diameter quartz glass test tube containing 40 g of the test solution was set at a position approximately 5 cm from the lamp in an external irradiation type ultraviolet irradiation device equipped with a W high-pressure mercury lamp (ultraviolet output 20 W). After lighting the lamp, the test solution is sampled at regular intervals and OHP is performed by liquid chromatography.
The content of the test solution was measured by the spectrophotometer to determine the ultraviolet transmittance (50w).
The transmittance of a t% lactam aqueous solution in a 10 mm cell at 290 nm (%, hereinafter referred to as UVT) was measured. Lamp irradiation time 1, 2, 3 hours later (UV irradiation amount per 1 kg of lactams is 90,000 joules, 18 hours, respectively)
OH of 10,000 Joules, 270,000 Joules)
P concentration is 0.94, 0.22, 0.06ppm respectively
Decreased to. UVT was 54.1% before irradiation, but was improved to 97.2% 3 hours after irradiation.

Comparative Example 1 In Example 1, except that water containing a fluorescent dye having a characteristic of absorbing ultraviolet rays was used as the cooling water for the lamp, ultraviolet rays of 400 nm or less were cut, and only visible light of 400 nm or more was irradiated. Was performed in the same manner as in Example 1. The OHP concentration after 3 hours of lamp irradiation was 9.73 ppm, and almost no decomposition of OHP occurred.

Example 2 35 mmΦ × 550 mm quartz inner tube and 80 mmΦ × 5
A 20 W fluorescent lamp (UV output 9 W) in a quartz tube of an UV irradiation device consisting of a double tube type internal irradiation tube (liquid phase thickness 45 mm) consisting of a 10 mm Pyrex outer tube, a circulation pump and a 2 l test solution temperature control tank. ) Was attached, and 1.8 l (lactam 1.5 kg) of the test solution used in Example 1 was charged into the test solution temperature control tank, and the gas phase part in the apparatus was replaced with nitrogen gas. The circulation pump was operated to circulate the test solution at a flow rate of 5 l / min, and then the lamp was turned on. The temperature of the test solution is 20 ℃
It was irradiated with a lamp for 60 minutes while being kept at a room temperature. 15, 30, and 60 minutes after the start of the lamp lighting (ultraviolet irradiation amount per 1 kg of lactams is 5,400 Joules, 11,
2,000 joules, 22,000 joules) test solution O
HP concentration is 2.10, 0.35, 0.10 pp, respectively
m, and the UVT after 60 minutes was 96.5%.

Example 3 The procedure of Example 2 was repeated, except that the pH of the test solution was changed to acidic and alkaline. When the pH of the test solution is 3.5 and 12.5, 15 minutes after lamp irradiation (UV irradiation amount per 1 kg of lactams is 5,40
0 joules) have OHP concentrations of 0.95 and 7.3, respectively.
It was 8 ppm. The decomposition rate of OHP was 2.2 times higher at pH 3.5 than at neutral (Example 2) and at pH 1
At 2.5, it increased 0.28 times.

Comparative Example 2 Example 2 was repeated except that the pH of the test solution was changed to 13.5. 15 minutes after lamp irradiation (UV irradiation amount per 1 kg of lactams is 5,400 joules), the OHP concentration is 9.59 ppm.
It was 0.06 times as high as the decomposition rate (Example 2).

Example 4 Example 4 was repeated except that the OHP concentration was changed to 100 ppm. Lamp irradiation time 1 hour later (UV irradiation amount per 1 kg of lactams is 2
The OHP concentration of 2,000 joules was 1.8 ppm. The test liquid after 1 hour had a pale yellow color, and the UVT was 25.8%. The UVT of caprolactam obtained by subjecting the test solution after 1 hour to dehydration and then subjecting it to simple distillation under reduced pressure was 8
It improved to 5.2%.

Example 5 Example 3 was repeated except that the UV lamp was replaced with a 30 W lamp (main wavelength 254 nm, UV output 7.5 W). 15,30 after starting the lamp
60 minutes later (UV irradiation amount per 1 kg of lactams is
4,500 joules, 9,000 joules, 1
8,000 joules) OHP concentration is 5.4 each
It was 2, 0.75 and 0.30 ppm.

Comparative Example 3 The procedure of Example 2 was repeated, except that the UV lamp was replaced with a 20 W lamp (main wavelength 540 nm, UV output 0.02 mW). 5 hours after starting the lamp (UV irradiation amount per 1 kg of lactams is 0.2
The OHP concentration of Joule) was 9.74 ppm.

Example 6 Example 6 was repeated except that the ultraviolet lamp was replaced by a 20 W fluorescent lamp (main wavelength 360 nm, ultraviolet light intensity 3 W). 15,3 after starting the lamp
After 0 and 60 minutes (the ultraviolet irradiation amount per 1 kg of lactams is 1,800 joules, 3,600 joules, and 7,200 joules, respectively), the OHP concentration is 8.
It was 72, 7.80 and 6.79 ppm.

Example 7 In Example 2, the test solution was prepared by melting molten lactam (anhydrous, OHP: 9.
The same procedure as in Example 2 was carried out except that the temperature of the test solution was changed to 80 ° C. 30 minutes after starting the lamp (UV irradiation amount per 1 kg of lactams is 9.00
The OHP concentration of 0 joule) was 0.30 ppm.

Example 8 Cyclohexanone oxime was subjected to Beckmann rearrangement with fuming sulfuric acid and then neutralized with ammonia to obtain crude caprolactam (O
HP content 50.4ppm), benzene extraction, simple distillation,
Then, crystallized to obtain caprolactam crystals (OHP content: 5.2 ppm).

30 g of this crystal was dispersed in a 150 mmΦ petri dish, and the same lamp as used in Example 2 was used.
External irradiation was performed at a distance of 40 cm from the light source covering the upper part to the lactam. After irradiation for 2 hours (ultraviolet irradiation amount per 1 kg of lactams was 38,000 joules), the OHP concentration was 0.51 ppm.

Example 9 Water was added to the caprolactam crystals obtained in Example 8 to prepare an aqueous lactam solution having a water content of 12.5%. Using this test solution, the same procedure as in Example 2 was performed except that the temperature was changed to 40 ° C. After irradiation for 30 minutes (UV irradiation amount per 1 kg of lactams is 10,000 joules), the OHP concentration decreased to 0.45 ppm. UVT is 67.9 before irradiation
% After irradiation to 94.8%.

Example 10 Phenol 25.3 ppm, aniline 25.0 ppm,
The same treatment as in Example 2 was carried out except that crude caprolactam (water content: 20%) containing 10.0 ppm of OHP was used as the test solution. After irradiation for 30 minutes (the ultraviolet irradiation amount per 1 kg of lactams was 11,000 joules), the concentrations of phenol, aniline and OHP in caprolactam were 2.5, 3.5 and 0.9 ppm, respectively.

Example 11 The procedure of Example 2 was repeated, except that a 50% methanol solution of crude laurolactam containing ultraviolet absorbing impurities was used as the test solution, and the lamp irradiation time was 180 minutes. After irradiation for 180 minutes (UV irradiation amount per 1 kg of lactams is 65,0
The UVT of (00 joules) was improved from 62.3% before irradiation to 80.3% after irradiation.

Comparative Example 4 In Example 2, the outer tube was changed to a cylindrical reactor of light-shielding metal having a diameter of 12 m and a height of 5 m, and an ultraviolet irradiation device was fixed to the center of the reactor, and the test solution was 150 liters / minute. The same procedure as in Example 2 was carried out except that the liquid was passed through and the inside of the reactor was stirred. The OHP concentration of the test solution 60 minutes after the lamp was started (UV irradiation amount per 1 kg of lactams was 3 joules) was
It was 9.52 ppm.

[0045]

INDUSTRIAL APPLICABILITY According to the present invention, by irradiating a lactam containing an ultraviolet absorbing substance with ultraviolet rays, a lactam with reduced ultraviolet absorbing impurities can be produced with high purity and industrially advantageously. .

Claims (14)

[Claims] 1. A method for purifying lactams, which comprises irradiating ultraviolet rays to lactams containing ultraviolet absorbing impurities. 2. The method for purifying a lactam according to claim 1, wherein the artificial or natural light source is used to irradiate the ultraviolet rays. 3. The wavelength of ultraviolet rays is 280 nm to 350 nm.
The method for purifying lactams according to claim 1 or 2, wherein 4. The ultraviolet ray of 10 joules or more is irradiated per 1 kg of lactams.
The method for purifying a lactam according to any one of 1. 5. The distance from the light source to the lactams is 10 m
The method for purifying a lactam according to any one of claims 2 to 4, wherein the content is within the range. 6. The method for purifying lactams according to claim 1, wherein the lactams in a molten state or the lactams dissolved in a solvent are irradiated with ultraviolet rays. 7. The method for purifying lactams according to claim 7, wherein the solvent has a UVB transmittance of 50% or more. 8. The pH of lactams dissolved in a solvent
The method for purifying lactams according to claim 6 or 7, wherein is 1 to 13. 9. The method for purifying a lactam according to claim 1, wherein the irradiation of ultraviolet rays is carried out at 0 ° C. or higher and 200 ° C. or lower. 10. The method for purifying a lactam according to any one of claims 1 to 9, wherein the coloring impurities contained in the lactam are removed in advance and then irradiated with ultraviolet rays. 11. The method for purifying a lactam according to claim 1, wherein the ultraviolet absorbing impurity is octahydrophenazine. 12. The method for purifying a lactam according to any one of claims 1 to 11, wherein the lactam is ε-caprolactam and / or ω-laurolactam. 13. Wavelength 290 of a 50% aqueous lactam solution.
A lactam having a UV transmittance of 95% or more. 14. The lactam is ε-caprolactam or ω-laurolactam.
The lactams according to 3.