JP2013151487A - METHOD FOR PRODUCING ε-CAPROLACTAM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high-quality ε-caprolactam by efficiently refining crude ε-caprolactam obtained by the Beckmann rearrangement of cyclohexanon oxime.SOLUTION: A method for producing high-quality ε-caprolactam includes: a step of crystallizing ε-caprolactam at a crystallization temperature from 10°C to a temperature less than a melting point of lactam from a mixed solution prepared by mixing crude ε-caprolactam, which is obtained by the Beckmann rearrangement of cyclohexanone oxime, with an organic solvent, and thereby obtaining a slurry liquid containing ε-caprolactam crystals; a step of separating the obtained slurry liquid into a liquid phase containing the organic solvent and a solid phase containing the ε-caprolactam crystals, and thereby obtaining the ε-caprolactam crystals; a step of subjecting the obtained ε-caprolactam crystals to repulp cleaning using an organic solvent at a temperature not less than the crystallization temperature but less than a melting point of ε-caprolactam, and thereby obtaining a slurry liquid containing ε-caprolactam crystals; and a step of separating the slurry liquid into a liquid phase containing the organic solvent and a solid phase containing the ε-caprolactam crystals, and thereby obtaining the high-quality ε-caprolactam.

Description

  The present invention relates to a method for producing ε-caprolactam, and more particularly to a method for efficiently purifying high-quality ε-caprolactam from crude ε-caprolactam containing impurities obtained by Beckmann rearrangement of cyclohexanone oxime.

 ε-Caprolactam is an important compound as a production intermediate of nylon-6, and various production methods are known. For example, it is produced in large quantities by subjecting cyclohexanone oxime to Beckmann rearrangement in the presence of an acidic medium such as fuming sulfuric acid. However, this method has a problem that a large amount of ammonium sulfate with a small added value is by-produced.

  As a method for improving this, a method for producing ε-caprolactam by a gas phase Beckmann rearrangement reaction using a solid catalyst is known. As the solid catalyst used in the gas phase Beckmann rearrangement reaction, a boric acid catalyst, a silica / alumina catalyst, a solid phosphoric acid catalyst, a composite metal oxide catalyst, a zeolite catalyst, and the like have been proposed. However, since ε-caprolactam obtained by this method contains various impurities, it is usually purified by various methods such as crystallization, extraction, distillation and hydrogenation.

  Patent Document 1 discloses a method for producing purified ε-caprolactam by solid-liquid separation by crystallizing ε-caprolactam by co-injecting molten crude ε-caprolactam and a cooled organic solvent. It is disclosed. Moreover, the effect of multistage crystallization is also mentioned as a method of improving quality.

JP 2002-3472 A

However, when the quality is improved by performing multi-stage crystallization, the latter crystallization tank needs to be set at a lower temperature than the preceding crystallization tank for crystallization. Therefore, in the subsequent crystallization tank, the adhesion (scaling) of crystals to the vessel wall becomes remarkable, which may cause a decrease in the crystal recovery rate and an obstacle to continuous operation.
Or, it is possible to improve the quality by washing by spraying an organic solvent toward the crystal, but in order to obtain extremely high quality ε-caprolactam, it is necessary to spray a large amount of organic solvent, Since a large amount of energy is required for solvent recovery and the like, the economic burden increases as the production scale increases.

  Therefore, there has been a demand for a method for purifying ε-caprolactam and obtaining high-quality ε-caprolactam by a method in which the amount of the organic solvent used is reduced without performing multistage crystallization.

  The present invention has been made in view of such circumstances, and can efficiently purify crude ε-caprolactam containing impurities obtained by the Beckmann rearrangement of cyclohexanone oxime, thereby obtaining high-quality ε-caprolactam. It aims at providing the manufacturing method of (epsilon) -caprolactam.

  In order to solve the above-mentioned problems, the present invention is based on a mixed solution obtained by mixing a crude ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime and an organic solvent at a crystallization temperature of 10 ° C. to less than the melting point of lactam. A crystallization step of crystallizing ε-caprolactam to obtain a slurry liquid containing ε-caprolactam crystals; a slurry liquid obtained in the crystallization step, a liquid phase containing an organic solvent; and a solid phase containing ε-caprolactam crystals. The first solid-liquid separation step for obtaining ε-caprolactam crystals separated into phases, and the ε-caprolactam crystals obtained by the first solid-liquid separation at a temperature equal to or higher than the crystallization temperature and lower than the melting point of ε-caprolactam And a repulp washing step of obtaining a slurry liquid containing ε-caprolactam crystals by repulp washing with an organic solvent, and a liquid phase containing an organic solvent. And a second solid-liquid separation step of obtaining a high-quality ε-caprolactam by separating it into a solid phase containing ε-caprolactam crystals, and a method for producing ε-caprolactam.

  In the present invention, it is desirable to further include recycling at least part of the liquid phase obtained in the second solid-liquid separation step as at least part of the organic solvent used for the repulp washing.

  In the present invention, the amount of the solvent used for the repulp washing is desirably 0.5 to 10 times the ε-caprolactam crystal obtained in the first solid-liquid separation step.

  In the present invention, it is desirable that the repulp washing is performed for 5 minutes or more and 60 minutes or less.

  In the present invention, the temperature at which the repulp washing is performed is preferably 45 ° C. or more and 60 ° C. or less.

  In the present invention, it is desirable to include continuously performing the repulp washing step and the second solid-liquid separation step.

  In the present invention, the crude ε-caprolactam is desirably obtained by gas phase Beckmann rearrangement using cyclohexanone oxime as a raw material and a solid catalyst.

  In the present invention, the crystallization is carried out in the form of liquid crude ε-caprolactam and cooled aliphatic hydrocarbons, or a small amount of organic solvent having higher polarity than the cooled aliphatic hydrocarbons and aliphatic hydrocarbons. It is desirable to carry out by mixing and mixing the mixed solvent in the container in a container at a temperature lower than that of the liquid crude ε-caprolactam.

  The “liquid crude ε-caprolactam” includes a melted crude ε-caprolactam (hereinafter sometimes referred to as a molten crude lactam) and a mixed solution of a molten crude lactam and an organic solvent.

  In the present invention, the liquid crude ε-caprolactam is molten crude ε-caprolactam, a mixed solution of molten crude ε-caprolactam and aliphatic hydrocarbons, or molten crude ε-caprolactam and aliphatic. It is desirable to be a mixed solution with a mixed solvent in which a small amount of an organic solvent having a higher polarity than hydrocarbons and aliphatic hydrocarbons is mixed.

  According to the present invention, the crude ε-caprolactam containing impurities obtained by the Beckmann rearrangement of cyclohexanone oxime can be efficiently purified by repulping the crystal obtained by crystallization, and high-quality ε- Caprolactam can be obtained.

It is a flowchart in the case of implementing the manufacturing method of this embodiment by a continuous process.

  The production method of ε-caprolactam according to this embodiment is performed at a crystallization temperature of 10 ° C. to less than the melting point of ε-lactam from a mixed solution of a crude ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime and an organic solvent. A crystallization step of crystallizing ε-caprolactam to obtain a slurry liquid containing ε-caprolactam crystals; a slurry liquid obtained in the crystallization step, a liquid phase containing an organic solvent; and a solid phase containing ε-caprolactam crystals. The first solid-liquid separation step for obtaining ε-caprolactam crystals separated into phases, and the ε-caprolactam crystals obtained by the first solid-liquid separation at a temperature equal to or higher than the crystallization temperature and lower than the melting point of ε-caprolactam A repulp washing step for obtaining a slurry liquid containing ε-caprolactam crystals by repulping with a solvent at a temperature of, and a liquid phase containing an organic solvent. Separating the solid phase containing ε- caprolactam crystal comprises a second solid-liquid separation to obtain a high quality ε- caprolactam, a.

In the present specification, “crude ε-caprolactam” means ε-caprolactam which is a target product obtained in the production process of ε-caprolactam, and impurities (reaction solvent, unreacted raw materials, side reaction products, etc.) And a reaction mixture. The following explanation uses a zeolite-based catalyst (solid catalyst) such as silica-alumina, metallosilicate, silicalite, etc. as crude ε-caprolactam (hereinafter sometimes abbreviated as “crude lactam”), and cyclohexanone oxime The reaction mixture obtained by vapor phase Beckmann rearrangement is exemplified, but the crude lactam to which the present invention can be applied is not limited thereto.
The “high-quality ε-caprolactam” is ε-caprolactam in which a basic compound such as cyclohexanone oxime, MTHI, or OHP contained is at a specific concentration or less. More specifically, the concentration of cyclohexanone oxime contained in ε-caprolactam is 0 ppm or more and less than 10 ppm with respect to ε-caprolactam; 1,2,3,4,6,7,8,9-octahydro It means ε-caprolactam in which the concentration of phenazine is 0 ppm or more and less than 10 ppm; the concentration of 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole is 0 ppm or more and less than 25 ppm.

FIG. 1 is a flowchart showing an example of the case where the manufacturing method of the present embodiment is carried out in a continuous process.
1 includes a crystallization tank 1, a separator 2, a crystallization tank 3, a solid-liquid separator 4, a crystal washing machine 5, a dissolution tank 6, a crystallization tank 7, a solid-liquid separator 8, A cooling facility 9, a solid-liquid separator 10, a crystal washer 11, and a repulp washing tank 12 are included. In the figure, the solid-liquid separation performed by the solid-liquid separator 10 corresponds to the “first solid-liquid separation” in the present invention, and the solid-liquid separation performed by the solid-liquid separator 4 is “second” in the present invention. Falls under “Solid-liquid separation”.
Hereinafter, it demonstrates in order.

First, in the dissolution tank 6, the molten crude lactam is mixed with an organic solvent, and a mixed solution (liquid crude ε-caprolactam) prepared by mixing the molten crude lactam and the organic solvent is prepared.
The crude lactam is not uniquely defined depending on the production method, but in addition to methanol and unreacted cyclohexanone oxime used as a solvent, cyclohexanone, cyclohexenone, n-hexonitrile, 5-hexonitrile, methyl lactam, 1,3,4, 5-tetrahydroazepin-2-one, 1,5,6,7-tetrahydroazepin-2-one, 1,2,3,4,6,7,8,9-octahydrophenazine (hereinafter abbreviated as OHP) May contain various by-products such as amines such as 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole (hereinafter sometimes abbreviated as MTHI). .

  For example, in the crude lactam obtained by the gas phase Beckmann rearrangement method, the concentration of cyclohexanone oxime is usually 10 ppm or more with respect to ε-caprolactam; 1,2,3,4,6,7,8,9-octa Hydrophenazine concentration of 10 ppm or more; 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole concentration of 25 ppm or more; and 1,3,4,5-tetrahydroazepin-2-one, 1,5 , 6,7-tetrahydroazepin-2-one, and their structural isomers (hereinafter abbreviated as caprenolactams) may be contained in concentrations of 25 ppm or more. Except for lenolactams, it can be removed and purified all at once by applying the crystallization method of the present invention.

  The crude lactam obtained by the gas phase Beckmann rearrangement reaction using a zeolite-based catalyst contains a solvent such as methanol, various low-boiling by-products, and various high-boiling by-products. Therefore, for the purpose of increasing the crystallization efficiency, it is preferable to carry out preliminary distillation or the like to remove some or all of these solvents and by-products as necessary before dissolution in the dissolution tank 6.

  As the organic solvent used in the dissolution tank 6, aliphatic hydrocarbons having low polarity are recommended so that a large amount of ε-caprolactam does not remain in the mixed solution after crystallization.

  Examples of such aliphatic hydrocarbons include linear aliphatic hydrocarbons having 6 to 12 carbon atoms, branched aliphatic hydrocarbons having 6 to 12 carbon atoms, and alicyclic compounds having 6 to 12 carbon atoms. And hydrocarbons. More specifically, linear aliphatic hydrocarbons such as n-hexane, n-heptane, n-octane, n-nonane and n-decane; branched aliphatic carbonization such as methylhexane, isooctane and neohexane Hydrogen: cyclic aliphatic hydrocarbons such as methylcyclopentane, cyclohexane, and methylcyclohexane; and mixtures of aliphatic hydrocarbons such as petroleum benzine (specified in JIS K 8594; mixtures of hexane, isohexane, etc.) It is done. Among them, aliphatic hydrocarbons having a boiling point not lower than the melting point (69 ° C.) of ε-caprolactam and lower than the boiling point (267 ° C.) of ε-caprolactam, such as n-heptane, isooctane, petroleum benzine, etc. are preferable, and the boiling point is ε-caprolactam. Aliphatic hydrocarbons (for example, cyclohexane, etc.) having a melting point of not lower than about 150 ° C. and lower are more preferable.

  These may be used alone or in combination of two or more or more polar organic solvents that can be mixed uniformly with these. That is, within the range in which impurities that are the object of the present invention can be removed, the above-mentioned aliphatic hydrocarbons include a small amount of aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as trichrene; propyl ether Ethers such as isopropyl ether; esters such as ethyl acetate and isopropyl acetate; alcohols such as ethanol and isopropanol are mixed, and a mixed solvent having a boiling point equal to or higher than the melting point of ε-caprolactam and lower than the boiling point of ε-caprolactam Preferably used as a mixed solvent having a boiling point not lower than the melting point of ε-caprolactam and not higher than about 150 ° C.

Of these solvents, combinations of solvents with low polarity and close boiling points are recommended. In this case, in continuous operation, even if there is a change in the solvent composition, the change in the solubility of lactam is small and the influence on the crystallization yield is small, so that the concentration control of the solvent becomes easy. As such a solvent combination, a straight chain aliphatic hydrocarbon having 6 to 12 carbon atoms and an alicyclic hydrocarbon having 6 to 12 carbon atoms are preferable, and a combination of n-heptane and cyclohexane is particularly preferable. .
Specifically, the mixing ratio (mass ratio) of n-heptane and cyclohexane is preferably 3: 1 to 2: 1.
The amount of the organic solvent used is preferably about 1/2 to about 5 times by mass, more preferably about 1 to about 4 times by mass with respect to the crude lactam.

  In addition, it is good also as performing crystallization of a back | latter stage only using a melt | fusion rough | crude lactam, without mixing a melt | fusion rough | crude lactam and an organic solvent in the dissolution tank 6 as mentioned above. However, it is preferable to perform crystallization using a mixed solution obtained by mixing molten crude lactam with an organic solvent in the dissolution tank 6 because ε-caprolactam having a low cyclohexanone oxime content can be obtained.

  The mixed solution adjusted in the dissolution tank 6 is supplied to the crystallization tank 1. In the crystallization tank 1, the mixed solution prepared in the dissolution tank 6 and the organic solvent (hereinafter sometimes referred to as a cold solvent) cooled in the cooling equipment 9 are supplied in parallel to form a crystal. Analyze.

  As the cold solvent, an organic solvent similar to the organic solvent used for mixing with the crude lactam in the dissolution tank 6 can be suitably used after being cooled. In addition, as long as the solubility of ε-caprolactam is not high (a solvent having high polarity), the organic solvent used for mixing with the crude lactam and the cold solvent may be different types.

  The amount and temperature of the cold solvent supplied to the crystallization tank 1 are defined in accordance with a crystallization temperature determined in advance in order to realize a target crystal recovery rate. That is, the cold solvent to be supplied includes the amount of heat of the difference between the temperature of the crude lactam (molten crude lactam or a mixed solution of molten crude lactam and an organic solvent) supplied to the crystallization tank 1 and the crystallization temperature, A heat removal capability capable of offsetting the heat of crystallization of the precipitated crystals is required. Accordingly, the amount and temperature of the cold solvent are defined such that the sensible heat of the cold solvent cancels out these amounts of heat.

  The amount of the solvent applied for crystallization is about 1/2 to about 5 times by mass, preferably about 1 to about 4 times by mass, with respect to the crude lactam used for purification. Even if it is used beyond the above range, a crystallization effect commensurate with the amount used cannot be obtained, and the cost required for solvent recovery increases. On the other hand, if the amount is small, it may not be possible to recover crystals of sufficient quality.

  The crystallization temperature is about 10 ° C. to less than the melting point of lactam (68 ° C.), preferably about 30 ° C. to about 60 ° C., more preferably about 40 ° C. to about 60 ° C. The crystallization temperature takes into account the lactam solubility of the liquid phase at the crystallization temperature in order to achieve both the target crystal recovery rate and the reduction of heat removal requirements (reduction of process operating energy). It is preferable to set the temperature close to the upper limit temperature at which a predetermined crystal recovery rate can be set. Further, such a crystallization temperature is preferable because impurities can be easily separated.

  Furthermore, the temperature of the outer wall of the crystallization tank is slightly lower than the temperature of the crystallization tank to the extent that the crystallization product is not excessively redissolved in order to prevent scaling of the outer wall of the crystallization tank. A high temperature is recommended. Specifically, by setting the temperature a few degrees higher than the crystallization temperature, more specifically, the crystallization temperature of lactam + about 5 ° C. or less, more preferably, the crystallization temperature of lactam + 1 ° C. or less, to the vessel wall. Generation of scaling can be suppressed. Alternatively, the outer wall of the crystallization tank may be a heat insulating structure.

  In the crystallization tank 1, liquid crude ε-caprolactam (molten crude lactam or a mixed solution of molten crude lactam and an organic solvent) is continuously mixed (mixed and mixed) at a constant rate together with a cold solvent to form crystal precipitation. With this, the crystallization temperature is maintained.

  In this case, even if the ratio of the crude lactam used for the crystallization is the same as that of the solvent, a part of the solvent used as the cold solvent as described above is added to the crude lactam in advance to form a diluted solution, and the solution is crystallized. A crystallization method is preferred in which cooling is performed in a range in which no precipitation occurs and crystallization treatment is performed by pouring together the remaining cold solvent. This makes it possible to reduce the content of specific impurities, particularly cyclohexanone oxime, remaining in the obtained crystal as compared with a method in which a dilute solution is not applied in advance.

  In the crystallization tank 1, the concentration of the slurry in which the crystallized crystals are dispersed can be stabilized by securing the time necessary for crystallization (that is, by providing the aging time). The time for stabilizing the slurry concentration is preferably 5 minutes to 60 minutes.

  In the case of adopting a continuous crystallization process in the crystallization tank 1, it is necessary to increase the capacity of the crystallization tank 1 in order to extend the average residence time of the crystallization tank 1. Therefore, an appropriate time is selected from the viewpoint of crystal quality and economy. Since the time required for stabilizing the concentration of the slurry is sufficient from 5 minutes to 60 minutes, it is preferably managed in such a range, and more preferably from 20 minutes to 40 minutes.

  The slurry containing ε-caprolactam crystals obtained in the crystallization tank 1 is separated from a part of the liquid phase by using a separator 2 such as a liquid cyclone, and then recrystallized from the remaining crystal slurry liquid. It is good as well. Specifically, the remaining crystal slurry liquid may be introduced into the crystallization tank 3, and a cold solvent may be poured again into the remaining portion to cool the remaining portion to crystallize the lactam. In this case, it is possible to increase the yield (precipitation amount) as compared with the case of collecting ε-caprolactam by crystallization only in the crystallization tank 1 without using the separator 2 and the crystallization tank 3. Become.

  In this case, since the yield in crystallization in the crystallization tank 1 can be lowered, the crystal obtained in the crystallization tank 1 can be made less likely to contain impurities. Further, since the cold solvent is added again in the crystallization tank 3, the impurity concentration of the solution to be crystallized can be reduced, which is effective in improving the quality of the ε-caprolactam crystals obtained in the crystallization tank 3. is there.

  In the separator 2, the amount of the organic solvent to be removed from the slurry is not particularly limited, but is usually 10% to 70% of the liquid phase, and the amount is determined by the crystal quality. The crystallization method in the crystallization tank 3 is the same as that of the crystallization tank 1, and for example, the crystallization tank may be kept warm and the cold solvent may be mixed and mixed. In addition, although the crystallization temperature in the crystallization tank 3 is implemented in the range of about 30 to 60 degreeC, it is set lower than the temperature conditions in the crystallization tank 1.

  Further, after separating a part of the liquid phase from the slurry liquid obtained in the crystallization tank 1 using the separator 2, the remaining crystal slurry liquid is returned to the original crystallization tank 1 again, or a solid liquid It is also possible to obtain the same effect by sending the liquid to the separator 4. By improving the ability of the solid-liquid separator 4 used to obtain the same crystallization yield by these methods, the latter case can reduce the number and capacity of the crystallization tanks, thereby improving efficiency. Is.

  The slurry liquid obtained in the crystallization tank 1 and the crystallization tank 3 is introduced into the solid-liquid separator 10. In the solid-liquid separator 10, the introduced slurry can be separated into a solid phase containing ε-caprolactam crystals and a liquid phase containing impurities (first solid-liquid separation). ). In this case, it is preferable that the process from the crystallization tank 1 to the solid-liquid separator 10 is kept warm so that the slurry temperature does not fall.

  Solid-liquid separation can be performed using a filter used for normal crystallization, such as vacuum filtration, pressure filtration, etc. In order to perform continuous filtration, centrifugal filtration, continuous scraping centrifugal A filter, a centrifugal decanter, or the like may be used. Especially in continuous scraping centrifugal filters and centrifugal decanters, crystals can be rinsed continuously, and the liquid phase containing impurities attached to the crystals can be washed to further improve the quality of the crystals. Is preferable.

  Crystals (solid phase) of ε-caprolactam separated by the solid-liquid separator 10 are supplied to the crystal washing machine 11 for washing the crystals, and washed (rinsed) by spraying an organic solvent toward the crystals. Thereby, impurities adhering to the crystal surface can be removed, and ε-caprolactam with higher purity can be obtained as compared with those not washed.

  The organic solvent used for rinsing is preferably one having a low solubility of ε-caprolactam, and the above-mentioned low-polarity hydrocarbons can be used.

  In the present embodiment, the solid-liquid separator 10 and the crystal washer 11 are described as separate devices, but the same device functions as the solid-liquid separator 10 and the crystal washer 11. It is good also as having (a solid-liquid separator has a crystal washing part).

  When the liquid phase containing the organic solvent separated by the solid-liquid separator 10 and the liquid phase containing the organic solvent discharged from the crystal washer 11 are preliminarily mixed with the molten crude lactam and the organic solvent in the dissolution tank 6, A part of the organic solvent may be used.

  Crystals of ε-caprolactam from which impurities on the surface have been removed in the crystal washer 11 are supplied to a repulp washing tank 12. In the repulp washing tank 12, the crystals supplied using the organic solvent are repulped (reslurry) to form a slurry. Thereby, the impurities adhering to the crystal are dissolved in the organic solvent of the slurry and removed from the crystal surface.

  In the above-described crystal washer 11, cleaning is performed by spraying an organic solvent toward the crystal, so that impurities adhering between crystal particles tend to remain. Although the remaining impurities are reduced by rinsing for a long time in the crystal washer 11, the processing efficiency is low and a large amount of organic solvent is required, resulting in a large process load.

  On the other hand, when repulp washing is performed in the repulp washing tank 12 as in this embodiment, impurities attached to the crystal surface can be reliably removed with a small amount of organic solvent.

  The amount of the organic solvent used for the repulp washing is preferably 0.5 mass times or more with respect to the ε-caprolactam crystals supplied to the repulp washing tank 12. In order to ensure repulp washing, it is more preferably 2 times by mass or more. The amount of the organic solvent used for repulp washing is preferably 10 times by mass or less, and more preferably 5 times by mass or less.

  The time for performing the repulp washing is preferably 5 minutes or more. In order to ensure repulp washing, it is more preferably 10 minutes or longer. Moreover, the time which performs repulp washing | cleaning is set in the range which does not reduce production efficiency, and it is preferable in it being 60 minutes or less.

  As the organic solvent used in the repulp washing tank 12, those having a low solubility of ε-caprolactam are preferable, and organic solvents similar to the above-described aliphatic hydrocarbons having low polarity can be used. Among these, it is preferable to use a mixed solvent of linear aliphatic hydrocarbons and alicyclic hydrocarbons. As such a mixed solvent, a mixed solvent of n-heptane and cyclohexane can be suitably used, and the mixing ratio is preferably n-heptane: cyclohexane = 3: 1 (mass ratio).

The temperature in the repulp washing tank 12 is preferably high from the viewpoint of promoting the removal of impurities adhering to the crystal and suppressing scaling, and on the other hand, it is possible to suppress dissolution of the crystal of ε-caprolactam. It is desirable that Therefore, the temperature in the repulp washing tank 12 is not less than the crystallization temperature in the crystallization tank 1 and less than the melting point of ε-caprolactam, preferably not less than the temperature of the crystallization tank 1 and not more than 60 ° C. (however 45 ° C. or more), more preferably crystallization. It is above the temperature of the tank 1 and below 58 ° C. (however, it is above 50 ° C.).
That is, the temperature in the repulp washing tank 12 is preferably from the temperature of the crystallization tank 1 to 60 ° C, and more preferably from the temperature of the crystallization tank 1 to 58 ° C.

  The slurry liquid obtained in the repulp washing tank 12 is introduced into the solid-liquid separator 4. In the solid-liquid separator 4, the introduced slurry is separated into solid and liquid (second solid-liquid separation step), and a liquid in which impurities on the crystal surface are dissolved by repulping and a solid phase containing ε-caprolactam crystals. Can be separated into phases.

  As the solid-liquid separator 4, a solid-liquid separator similar to the above-described solid-liquid separator 10 can be used. Moreover, the repulp in the repulp washing tank 12 and the solid-liquid separation in the solid-liquid separator 10 may be performed in a continuous manner or in a batch manner (batch manner). Since production efficiency can be improved, it is preferable to carry out by a continuous type.

  Crystals (solid phase) of ε-caprolactam separated by the solid-liquid separator 4 are supplied to the crystal washing machine 5 for washing the solid phase and washed using an organic solvent. As a result, impurities remaining slightly on the surface of the crystal after repulping can be removed, and ε-caprolactam with higher purity (high quality ε-caprolactam) can be obtained compared to ε-caprolactam crystals that are not washed. Can be obtained.

  The organic solvent used for the washing is preferably one having low solubility of ε-caprolactam, and the above-mentioned aliphatic hydrocarbons having low polarity can be used.

  In the present embodiment, the solid-liquid separator 4 and the crystal washer 5 are described as separate devices. However, like the solid-liquid separator 10 and the crystal washer 11, the same device is used as the solid-liquid separator 4 and the crystal washer 11. It is good also as having the function of the liquid separator 4 and the crystal washing machine 5 (a solid-liquid separator has a crystal washing part).

The liquid phase containing the organic solvent separated by the solid-liquid separator 4 and the liquid phase containing the organic solvent discharged from the crystal washer 5 are discharged from the solid-liquid separator 10 and the crystal washer 11 described above. Impurity concentration is low compared to the liquid phase. Therefore, if the liquid phase discharged from the solid-liquid separator 4 and the crystal washer 5 is circulated as an organic solvent used in the crystal washer 11 and the repulp washing tank 12, the cost for recovering the organic solvent is reduced. This is preferable. However, if a recirculated washing is used for repulp washing, quality deterioration is unavoidable, so it should be changed according to the required quality.
Of course, you may use partially as an organic solvent which melt | dissolves a crude lactam with the dissolution tank 6. FIG.

  Among the liquid phases discharged from the separator 2, the solid-liquid separator 10, the crystal washer 11, the solid-liquid separator 4, and the crystal washer 5, the liquid phase not used in the dissolution tank 6 or the like is ε− from the liquid phase. The yield can be easily increased by recovering the crystals by recrystallizing caprolactam. Of course, the crystals may be recovered by a combination of known methods such as distillation, extraction, chemical treatment, activated carbon treatment and the like other than crystallization. The recovered crystal can be efficiently recovered from the crude lactam by adopting a method of recycling the recovered crystal to the first solid-liquid separation step.

  More specifically, a liquid phase not used in the dissolution tank 6 or the like is introduced into the crystallization tank 7. As the crystallization method in the crystallization tank 7, various methods can be used. As a crystallization method at this point in which the solvent and ε-caprolactam are already mixed, evaporation crystallization which can be crystallized by concentrating at a constant temperature while heating the crystallization tank is advantageous in terms of preventing scaling. It is. Further, it is particularly effective from the viewpoint of energy saving to distill away the solvent to some extent using a multi-effect can etc. before evaporative crystallization.

  In the case of evaporation crystallization, the solvent is evaporated and separated, so the organic solvent discharged from the crystallization tank 7 is a purified organic solvent from which impurities have been removed. Therefore, although not shown, this can be reused as a cold solvent for the crystallization tank 1, a solvent used for the crystallization tank 3, a cleaning solvent applied to the crystal washing machine 5, or the like.

  The slurry after the crystallization treatment is introduced into a solid-liquid separator 8 and separated into ε-caprolactam crystals (recovered lactam) as a solid phase and a liquid phase in which impurities are concentrated. The recovered lactam discharged from the solid-liquid separator 8 is introduced into the dissolution tank 6 and reused.

  On the other hand, the liquid phase discharged from the solid-liquid separator 8 is distilled in a solvent recovery step (not shown) to recover the organic solvent and the impurities are separated as a residue. As a result, the concentrated impurities are discharged out of the system, avoiding the accumulation of impurities in the system, and enabling the long-term continuous operation of this manufacturing process.

  Note that, when mixed solvents having different boiling points are used, the composition of the recovered solvent is different. However, it is preferable to reuse the mixture after adjusting the concentration by mixing the recovered solvent including the solvent recovery step.

  The recovered solvent may be circulated as a solvent used in the crystallization tank 1 and the like, and the discharge from this process is only the residue in the solvent recovery step, resulting in a production process with very little waste.

  As described above, the degree of treatment of the crude lactam is preferably controlled so that basic compounds such as cyclohexanone oxime, MTHI, and OHP are not more than a specific concentration. More specifically, the concentration of cyclohexanone oxime contained in the obtained ε-caprolactam (high quality ε-caprolactam) is 0 ppm or more and less than 10 ppm with respect to ε-caprolactam, 1, 2, 3, 4, 6, 7 , 8,9-octahydrophenazine so that the concentration of 0 to 10 ppm and the concentration of 3-N-methyl-4,5,6,7-tetrahydrobenzimidazole is 0 to 25 ppm. It is preferable to manage the operating conditions of the crystal washer 11 and the crystal washer 5.

  The degree of treatment of the crude lactam is controlled by the above impurity content index. The degree of removal of impurities by the crystallization treatment can be adjusted by crystallization conditions such as the type of solvent used, the amount of solvent, and the crystallization temperature, and may be confirmed by preliminary experiments.

  Each crystallization treatment may be usually performed once, but a plurality of crystallizations may be performed in order to further refine the ε-caprolactam obtained by crystallization. In particular, when obtaining high-quality ε-caprolactam from crude lactam with many impurities, for example, the crystal obtained by crystallization in the crystallization tank 1 is supplied again to the dissolution tank 6 and subjected to a plurality of crystallization treatments. Recommended to do.

For caprenolactams that are difficult to remove by crystallization, the caprenolactams obtained by the crystal washer 5 are contacted with hydrogen in the presence of a hydrogenation catalyst, and then hydrogenated. It is possible to remove. Such treatment can usually reduce caprenolactams to less than 25 ppm.
The method for producing ε-caprolactam according to this embodiment is performed as described above.

  According to the method for producing ε-caprolactam having the above-described configuration, the crude ε-caprolactam containing impurities obtained by the Beckmann rearrangement of cyclohexanone oxime can be efficiently purified by repulping the crystal. Quality ε-caprolactam can be obtained.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

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

  In the examples, a reaction mixture (crude lactam) produced in a factory facility that produces ε-caprolactam by vapor phase Beckmann rearrangement of cyclohexanone oxime using a zeolite catalyst is sampled, and a change in OHP concentration is confirmed. Thus, the effect of the present invention was verified.

(Measurement of OHP concentration)
The OHP concentration was determined by liquid chromatographic analysis using a column (SUMIPAX ODS-A212, 15 ml × 6 mmφ, 5 μm), water-acetonitrile as a mobile phase, gradient analysis, and UV detection using an absolute calibration curve. Measured by the method. The detection limit of OHP in this method is about 0.1 ppm.

Example 1
The following operations were performed continuously. The flow rate of each substance in the following operation was shown by mass per hour.

  Using a high silica type zeolite catalyst, a gas phase Beckmann rearrangement reaction of cyclohexanone oxime was carried out at 380 ° C. in the presence of methanol to obtain a reaction product. As a result of analyzing the composition of the reaction product excluding the solvent, the concentration of ε-caprolactam in the reaction product was 99.448% (area percentage), and the OHP concentration in the reaction product was 226 ppm (area percentage). Met.

  The reaction product is melted to 75 ° C., 200 parts by mass of the melted reaction product, and a mixed solvent of 55 ° C. n-heptane: cyclohexane = 3: 1 (mass ratio) (hereinafter, a mixed solvent of the same composition is used). Crystallization was carried out by continuously pouring a mixed solution with 100 parts by mass (referred to simply as “mixed solvent”) and 300 parts by mass of the mixed solvent into a crystallization tank whose jacket was kept at 52 ° C. As the mixed solvent to be added, a solvent whose temperature was adjusted so that the crystallization temperature in the crystallization tank was 50 ° C. was used. The average residence time in the crystallization tank was about 30 minutes.

  600 parts by mass of the slurry obtained in the crystallization tank was fed from the crystallization tank to a heat-insulated centrifugal decanter for solid-liquid separation to obtain 150 parts by mass of a solid. Liquid phase mixture containing organic solvent separated by solid-liquid separator before repulp washing, kept at about 50 ° C., and liquid phase mixture containing organic solvent discharged from crystal washer (Circulating solvent 1) was sprayed at a ratio of 180 parts by mass and continuously rinsed.

  150 parts by mass of the solid after rinsing, a liquid phase containing an organic solvent separated by a solid-liquid separator after repulp washing, and a mixed solvent of a liquid phase containing an organic solvent discharged from a crystal washing machine (circulating solvent) 2) Along with 330 parts by mass and 71 parts by mass of the mixed solvent, the mixture was continuously poured into a repulp tank kept at 52 ° C. The average residence time in the repulp tank was 10 minutes.

  550 parts by mass of the slurry liquid in the repulp tank was sent to a centrifugal decanter kept at about 52 ° C. and subjected to solid-liquid separation to obtain 150 parts by mass of a solid. With respect to the obtained solid, the solid was continuously rinsed with 180 parts by mass of a mixed solvent kept at about 55 ° C. to obtain 150 parts by mass of purified crystals. In addition, the liquid phase obtained by solid-liquid separation was circulated and used as a mixed solvent poured into the above repulp tank.

  As a result of analyzing the composition of the crystal obtained by removing the solvent, the concentration of ε-caprolactam in the crystal was 99.974% (area percentage), and the OHP concentration in the crystal was 0.16 ppm (area percentage). there were. In Example 1, the amount of the mixed solvent used for the rinse cleaning and the repulp cleaning, excluding the circulating solvent 1 and the circulating solvent 2, was 251 parts by mass.

(Comparative Example 1)
In the same manner as in Example 1, a reaction product was obtained. As a result of analyzing the composition of the reaction product excluding the solvent, the concentration of ε-caprolactam in the reaction product was 99.682% (area percentage), and the OHP concentration in the reaction product was 214 ppm (area percentage). Met.

  Ε-Caprolactam was crystallized from the reaction product in the same manner as in Example 1. Thereafter, 600 parts by mass of the slurry liquid obtained in the crystallization tank was fed from the crystallization tank to a heated centrifugal decanter for solid-liquid separation to obtain 150 parts by mass of a solid. To the obtained solid, a mixed solvent kept at about 50 ° C. was sprayed at a ratio of 260 parts by mass and continuously rinsed to obtain 150 parts by mass of crystals.

  As a result of analyzing the composition of the obtained crystal excluding the solvent, the concentration of ε-caprolactam in the crystal was 99.974% (area percentage), and the OHP concentration in the crystal was 0.65 ppm (area percentage). there were. The amount of the mixed solvent used for the rinse cleaning in Comparative Example 1 is 260 parts by mass.

(Comparative Example 2)
A reaction product was obtained in the same manner as in Example 1. As a result of analyzing the composition of the reaction product excluding the solvent, the concentration of ε-caprolactam in the reaction product was 99.648% (area percentage), and the OHP concentration in the reaction product was 223 ppm (area percentage). Met. Ε-Caprolactam was crystallized from the reaction product in the same manner as in Example 1. Thereafter, 600 parts by mass of the slurry liquid obtained in the crystallization tank was fed from the crystallization tank to a heated centrifugal decanter for solid-liquid separation to obtain 150 parts by mass of a solid. Liquid phase mixture containing organic solvent separated by solid-liquid separator before repulp washing, kept at about 50 ° C., and liquid phase mixture containing organic solvent discharged from crystal washer (Circulating solvent 1) was sprayed at a ratio of 190 parts by mass and continuously rinsed.

  150 parts by mass of the solid after rinsing, a liquid phase containing an organic solvent separated by a solid-liquid separator after repulp washing, and a mixed solvent of a liquid phase containing an organic solvent discharged from a crystal washing machine (circulating solvent) 2) It poured continuously into the repulp tank kept at 52 degreeC with 320 mass parts. The average residence time in the repulp tank was 10 minutes.

  470 parts by mass of the slurry liquid in the repulp tank was sent to a centrifugal decanter kept at about 52 ° C. for solid-liquid separation to obtain 150 parts by mass of a solid. With respect to the obtained solid, the solid was continuously rinsed with 190 parts by mass of a mixed solvent kept at about 55 ° C. to obtain 150 parts by mass of purified crystals.

  As a result of analyzing the composition of the crystal obtained by removing the solvent, the concentration of ε-caprolactam in the crystal was 99.968% (area percentage), and the OHP concentration in the crystal was 0.54 ppm (area percentage). there were. In Comparative Example 2, the amount of the mixed solvent used for the rinse washing and the repulp washing excluding the circulating solvent 1 and the circulating solvent 2 was 190 parts by mass.

(Example 2)
A reaction product was obtained in the same manner as in Example 1. As a result of analyzing the composition of the reaction product excluding the solvent, the concentration of ε-caprolactam in the reaction product was 99.095% (area percentage), and the OHP concentration in the reaction product was 234 ppm (area percentage). Met. Ε-Caprolactam was crystallized from the reaction product in the same manner as in Example 1. Thereafter, 600 parts by mass of the slurry liquid obtained in the crystallization tank was fed from the crystallization tank to a heated centrifugal decanter for solid-liquid separation to obtain 150 parts by mass of a solid. Liquid phase mixture containing organic solvent separated by solid-liquid separator before repulp washing, kept at about 50 ° C., and liquid phase mixture containing organic solvent discharged from crystal washer (Circulating solvent 1) was sprayed at a ratio of 140 parts by mass and continuously rinsed.

  150 parts by mass of the solid after rinsing, a liquid phase containing an organic solvent separated by a solid-liquid separator after repulp washing, and a mixed solvent of a liquid phase containing an organic solvent discharged from a crystal washing machine (circulating solvent) 2) Both 300 parts by mass and 39 parts by mass of the mixed solvent were continuously poured into a repulp tank kept at 52 ° C. The average residence time in the repulp tank was 10 minutes.

  489 parts by mass of the slurry liquid in the repulp tank was sent to a centrifugal decanter kept at about 52 ° C. and subjected to solid-liquid separation to obtain 150 parts by mass of a solid. The solid was continuously rinsed with 130 parts by mass of a mixed solvent kept at about 55 ° C., and 150 parts by mass of purified crystals were obtained. As a result of analyzing the composition of the crystal obtained by removing the solvent, the concentration of ε-caprolactam in the crystal was 99.955% (area percentage), and the OHP concentration in the crystal was 0.48 ppm (area percentage). there were. In Example 2, the amount of the mixed solvent used for rinsing and repulp washing, excluding the circulating solvent 1 and the circulating solvent 2, was 169 parts by mass.

(Example 3)
A reaction product was obtained in the same manner as in Example 1. As a result of analyzing the composition of the reaction product excluding the solvent, the concentration of ε-caprolactam in the reaction product was 99.467% (area percentage), and the OHP concentration in the reaction product was 226 ppm (area percentage). Met. Ε-Caprolactam was crystallized from the reaction product in the same manner as in Example 1. Thereafter, 600 parts by mass of the slurry liquid obtained in the crystallization tank was fed from the crystallization tank to a heated centrifugal decanter for solid-liquid separation to obtain 150 parts by mass of a solid. Liquid phase mixture containing organic solvent separated by solid-liquid separator before repulp washing, kept at about 50 ° C., and liquid phase mixture containing organic solvent discharged from crystal washer (Circulating solvent 1) was sprayed at a ratio of 120 parts by mass and continuously rinsed.

  150 parts by mass of the solid after rinsing, a liquid phase containing an organic solvent separated by a solid-liquid separator after repulp washing, and a mixed solvent of a liquid phase containing an organic solvent discharged from a crystal washing machine (circulating solvent) 2) Both 250 parts by mass and 78 parts by mass of the mixed solvent were continuously poured into a repulp tank kept at 52 ° C. The average residence time in the repulp tank was 10 minutes.

  478 parts by mass of the slurry liquid in the repulp tank was sent to a centrifugal decanter kept at about 52 ° C. and subjected to solid-liquid separation to obtain 150 parts by mass of a solid. The solid was continuously rinsed with 130 parts by mass of a mixed solvent kept at about 55 ° C., and 120 parts by mass of purified crystals were obtained. As a result of analyzing the composition of the obtained crystal excluding the solvent, the concentration of ε-caprolactam in the crystal was 99.961% (area percentage), and the OHP concentration in the crystal was 0.24 ppm (area percentage). there were. In Example 3, the amount of the mixed solvent used for the rinse washing and the repulp washing, excluding the circulating solvent 1 and the circulating solvent 2, was 198 parts by mass.

  From the above results, the usefulness of the present invention was confirmed.

DESCRIPTION OF SYMBOLS 1 ... Crystallization tank, 2 ... Separator, 3 ... Crystallization tank, 4 ... Solid-liquid separator, 5 ... Crystal washing machine, 6 ... Dissolution tank, 7 ... Crystallization tank, 8 ... Solid-liquid separator, 9 ... Cooling equipment, 10 ... solid-liquid separator, 11 ... crystal washing machine, 12 ... repulp washing tank

Claims (9)

Ε-caprolactam crystallized from a mixed solution obtained by mixing the crude ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime with an organic solvent at a crystallization temperature of 10 ° C. to less than the melting point of lactam, A crystallization step of obtaining a slurry liquid containing
A first solid-liquid separation step in which the slurry liquid obtained in the crystallization step is separated into a liquid phase containing an organic solvent and a solid phase containing ε-caprolactam crystals to obtain ε-caprolactam crystals;
The ε-caprolactam crystals obtained by the first solid-liquid separation are repulp washed with an organic solvent at a temperature not lower than the crystallization temperature and lower than the melting point of ε-caprolactam to obtain a slurry liquid containing ε-caprolactam crystals. Obtaining a repulp washing step;
A second solid-liquid separation step of separating the slurry liquid into a liquid phase containing an organic solvent and a solid phase containing ε-caprolactam crystals to obtain high-quality ε-caprolactam, and a method for producing ε-caprolactam .   The production of ε-caprolactam according to claim 1, further comprising circulating at least a part of the liquid phase obtained in the second solid-liquid separation step as at least a part of the organic solvent used for the repulp washing. Method.   The amount of the solvent used for the repulp washing is 0.5 mass times or more and 10 mass times or less with respect to the ε-caprolactam crystal obtained in the first solid-liquid separation step. -Method for producing caprolactam.   The method for producing ε-caprolactam according to any one of claims 1 to 3, wherein the repulp washing is performed for 5 minutes to 60 minutes.   The method for producing ε-caprolactam according to any one of claims 1 to 4, wherein a temperature at which the repulp washing is performed is 45 ° C or more and 60 ° C or less.   The manufacturing method of the epsilon caprolactam of any one of Claim 1 to 5 including implementing the said repulp washing process and the said 2nd solid-liquid separation process continuously.   The method for producing ε-caprolactam according to any one of claims 1 to 6, wherein the crude ε-caprolactam is obtained by gas phase Beckmann rearrangement using cyclohexanone oxime as a raw material and a solid catalyst.   The crystallization is a mixture of the liquid crude ε-caprolactam and a cooled aliphatic hydrocarbon, or a cooled aliphatic hydrocarbon and a small amount of an organic solvent having a higher polarity than the aliphatic hydrocarbon. The method for producing ε-caprolactam according to any one of claims 1 to 7, wherein the solvent is mixed and mixed in a container at a temperature lower than that of the liquid crude ε-caprolactam.   The liquid crude ε-caprolactam is molten crude ε-caprolactam, a mixed solution of molten crude ε-caprolactam and aliphatic hydrocarbons, or molten crude ε-caprolactam and aliphatic hydrocarbons and The method for producing ε-caprolactam according to claim 8, which is a mixed solution with a mixed solvent obtained by mixing a small amount of an organic solvent having a polarity higher than that of the aliphatic hydrocarbon.

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