JP6003755B2 - Lactam purification method - Google Patents

Description

  The present invention relates to a method for purifying a lactam containing an unsaturated lactam. More specifically, the present invention relates to a method for purifying a lactam that obtains a high-quality and high-efficiency lactam by first isomerizing an unsaturated lactam contained in a crude lactam, followed by crystallization and hydrogenation.

  Lactam is widely used as a nylon raw material, and various production methods are known. However, the crude lactam obtained by these methods contains various impurities such as unsaturated lactam. Along with the improvement in product quality, lactam quality is also required to have a high purity, and various purification methods have been known.

  As one of the purification methods, crystallization is known, a technique for crystallizing high-purity lactam by cooling a mixture of a crude lactam solution and water under reduced pressure (Patent Document 1), and hydrogenation after crystallization. Thus, a technique for removing by-products and refining to high-quality lactam (Patent Document 2) is known. In addition, in order to reduce lactam loss due to lactam that cannot be recovered in the above crystallization, the cooled solvent is added to the crude lactam heated and melted at the time of crystallization, and direct cooling is used to suppress scaling on the heat transfer surface, thereby reducing lactam loss. A technique for reducing (Patent Document 3) is known. However, in the above technique, the unsaturated lactam contained in the crude lactam remains a lactam eutectic and easily moves to the mother liquor side, so that the purity of the mother liquor is lowered and the crystallization operation conditions are deteriorated. If not collected, it leads to lactam loss, and it is difficult to sufficiently reduce lactam loss. Furthermore, as a method for reducing lactam loss by distillation, a technique (Patent Document 4) in which unsaturated lactam as a byproduct is separated from other impurities by distillation and then hydrogenated (Patent Document 4) is known. However, in the above technique, in order to hydrogenate the unsaturated lactam, distillation is performed to separate the unsaturated lactam from other impurities, resulting in a decrease in productivity.

JP-A-1-261363 Japanese Patent No. 4239339 JP 2011-201865 A JP 2005-510562 A

  Accordingly, an object of the present invention is to provide a lactam purification method with high efficiency and high yield.

In order to solve the problem,
1. In the invention according to claim 1, the eutectic unsaturated lactam contained in the crude lactam is isomerized into the solid solution unsaturated lactam, the crude lactam is crystallized, and then the lactam obtained by the crystallization. A method for purifying a lactam characterized by hydrogenating the crystal,
2. In the invention according to claim 2, the lactam purification method according to claim 1, wherein the lactam has 6 to 12 carbon atoms,
3. In the invention according to claim 3, the lactam purification method according to claim 1, wherein an alkali is added during the isomerization reaction,
4). In the invention according to claim 4, in the isomerization, alkali is added so that the ratio of the crude lactam solution is 0.012 mol / L or more and 0.035 mol / L or less based on the hydroxyl group. The method for purifying lactam according to any one of 3,
5. In the invention according to claim 5, the lactam purification method according to any one of claims 1 to 4, wherein the temperature during the isomerization reaction is performed at 100 ° C or more and 200 ° C or less,
6). In the invention according to claim 6, the lactam purification method according to any one of claims 1 to 5, wherein the isomerization reaction time is 10 minutes to 360 minutes,
7). In the invention according to claim 7, the lactam purification method according to any one of claims 1 to 6, wherein the crystallization is performed in the presence of a solvent.
8). The invention according to claim 8 is the lactam purification method according to claim 7, wherein the solvent is water.

  As described above, according to the method of the present invention described above, the unsaturated lactam contained in the crude lactam is isomerized and then subjected to a combination of simple steps of crystallization and hydrogenation, thereby achieving high efficiency and high yield. Lactam can be obtained. The method of the present invention is excellent in product yield by utilizing unsaturated lactam, and gives the effect of efficiently performing crystallization by improving the purity of the mother liquor of crystallization.

FIG. 1 is a diagram showing process steps of a lactam purification method according to the present invention. FIG. 2 is a diagram showing a chromatogram obtained by gas chromatography of a crude lactam.

  The crude lactam in the present invention is a lactam containing impurities of 100 ppm or more and 20 wt% or less such as unsaturated lactam or chlorlactam. The lactam is a lactam having 6 to 12 carbon atoms, such as caprolactam (carbon number 6), undecane lactam (carbon number 11), and lauryl lactam (carbon number 12).

  When the lactam is caprolactam (6 carbon atoms), the impurities contained in the crude lactam include unsaturated lactam, chlorlactam, aniline, octahydrophenazine (OHP), bicyclolactam (BCL), phenol, chloraniline and the like. It is done.

  Lactams are generally produced by rearranging oximes, but recently they have also been industrialized in a method of synthesis by vapor phase Beckmann rearrangement without using ammonium sulfate. Conventionally known methods for producing oxime include a method for producing cyclohexanone oxime in the production of caprolactam and a method for producing cyclododecanone oxime in the production of laurolactam. And as a manufacturing method of the said cyclohexanone oxime, the direct oxidation method which adds the hydroxylamine synthesize | combined from ammonia to cyclohexanone obtained by carrying out the air oxidation of cyclohexane, or the cyclohexane is made to react with nitrosyl chloride by a photochemical reaction. The photo-Nitrosation of Cyclohexane (PNC) method is mentioned. The method for producing the crude lactam used in the present invention is not particularly limited.

  In the PNC method, first, hydrocarbon is charged into a reaction vessel. The hydrocarbon itself does not need to be radicalized by light, and any substance that can be radicalized by a radicalizing agent may be used. Cycloalkanes such as cyclohexane and cyclododecane, straight chain hydrocarbons, unsaturated hydrocarbons, and aromatic hydrocarbons may be used, but cycloalkanes, particularly cyclohexane are more preferable.

  A radicalizing agent is added to the hydrocarbon. The radicalizing agent may be added as either a liquid or a gas. Preferred radicalizing agents are, for example, nitrosating agents, and nitrosyl chloride is particularly preferred because of its low radicalization energy. A preferred addition form of nitrosyl chloride is a form in which the nitrosyl chloride is dissolved into a solution by blowing it into a gaseous hydrocarbon liquid.

  Hereinafter, a case where caprolactam having 6 carbon atoms is produced by the PNC method will be described as an example.

  When caprolactam is produced by the PNC method, the raw material cyclohexane is charged into a reaction vessel and light is irradiated using a high-pressure sodium lamp or light-emitting diode while blowing a mixed gas of nitrosyl chloride and hydrogen chloride to produce photonitrosation. The reaction produces cyclohexanone oxime. If there is corrosion resistance, the lamp of the light source is immersed in the reaction solution charged in the reaction vessel in order to use light energy without loss. Also, nitrosyl chloride is photodissociated at a wavelength of 759 nm or less exceeding its binding energy of 38 kcal / mol to produce cyclohexanone oxime.

Since the produced cyclohexanone oxime does not dissolve in the raw material cyclohexane, it can be separated by specific gravity. A crude lactam can be obtained by Beckmann rearrangement of the separated cyclohexanone oxime. Any known method may be used for the Beckmann rearrangement. Examples include those using concentrated sulfuric acid, those using a solid catalyst, and those using N, N-dimethylformamide (DMF). Preferably, the reaction is carried out by adding a sulfuric acid catalyst. More preferably, the rearrangement reaction is performed using fuming sulfuric acid as a catalyst. The reason why fuming sulfuric acid is preferably used is that fuming sulfuric acid containing free SO ₃ is used because lactam generated by rearrangement is hydrolyzed by water contained in a small amount in cyclohexaneoxime, which may reduce the yield of lactam. If so, water contained in a trace amount can react with free SO ₃ to become sulfuric acid, thereby preventing a decrease in lactam yield in rearrangement. The reaction conditions are known per se. For example, the reaction temperature is 50 ° C. or more and 150 ° C. or less, and the amount of catalyst added is 1 mol or more and 5 mol or less per mol of oxime.

  The produced crude lactam contains various impurities, resulting in a reduction in product quality.

  One of the impurities contained is unsaturated lactam. Unsaturated lactam is produced from chlorocyclohexane. Chlorcyclohexane is produced as a by-product when a certain amount of cyclohexanone oxime is produced. This by-produced chlorocyclohexane becomes chlorocyclohexanone oxime by the photonitrosation reaction and becomes chlorlactam in the rearrangement step. There are three types of chlorlactam, α, β, and γ depending on where chlor is added. Of these, α and β are easily decomposed by heat at 80 ° C. to 90 ° C., dechlorinated, This produces unsaturated lactam. γ-Chloractam is very stable, but dechlorinated to produce bicyclolactam (BCL). α-Chloractam has a structure represented by the following formula (a), β-chlorlactam has the following formula (b), γ-chlorlactam has the following formula (c), and BCL has the following formula (d).

  Unsaturated lactams have isomers (U1, U2) depending on the position of the double bond. U1 is an isomer having a structure represented by the following formula (1), and U2 is a structure represented by the following formula (2). Both isomers behave differently in the crystallization process. Specifically, U1 is a lactam solid solution and is therefore easily incorporated into lactam crystals, whereas U2 is a lactam eutectic and is therefore easily incorporated into the mother liquor side.

  The purity and impurity content of the crude lactam, the purity of the lactam crystal, and the impurity content can be determined, for example, by gas chromatography. FIG. 2 shows a chromatogram of the crude lactam before the isomerization step as an example. In the chromatogram, the peak (1) of U1 and the peak (2) of U2 are shown. Since U2 is a lactam eutectic, much of it is taken into the mother liquor during crystallization, not only lowering the purity of the mother liquor and deteriorating the crystallization operating conditions, but also recovering U2 from the mother liquor. It leads to Lactam Ross. On the other hand, since U1 is a lactam solid solution, most of it is taken into the lactam crystal side during crystallization. For this reason, U1 can be made into a lactam by further providing a hydrogenation step in the subsequent step without lowering the purity of the mother liquor, leading to an increase in lactam yield.

  Therefore, in the present invention, paying attention to the fact that most of the unsaturated lactams contained in the crude lactam are present in the U2 state, isomerizing U2 to U1, and then performing crystallization and hydrogenation, By incorporating more of the unsaturated lactam into the lactam crystal side during crystallization and then converting the unsaturated lactam to lactam by hydrogenation, the lactam can be purified with high yield and high efficiency.

  FIG. 1 shows process steps of a lactam purification method according to the present invention. In this process, first, an unsaturated lactam is isomerized from an eutectic with a lactam to a solid solution (isomerization step) and then crystallized (crystallization step), and then the obtained lactam crystal is hydrogenated ( By performing the hydrogenation step), lactam can be recovered in high yield, and the purity of the mother liquor at the time of crystallization is increased, so that crystallization can be carried out efficiently.

(Isomerization process)
In the present invention, first, isomerization is performed from U2 to U1 in an isomerization step. The isomer of the crude lactam is carried out in the form of a molten crude lactam or a crude lactam solution dissolved in water or the like. The three conditions of alkali addition amount, temperature, and reaction time affect the progress of isomerization. The alkali addition amount / temperature is within the following range, and it is preferable to proceed with the isomerization over the following reaction time required in the isomerization step. The isomerization step may be performed in any form, You may implement by a batch type or a continuous type.

  The alkali addition amount needs to be 0.01 mol / L or more and 0.05 mol / L or less based on the hydroxyl group with respect to the crude lactam solution. When alkali is added exceeding the above range, it leads to the start of lactam low polymerization. On the other hand, when it is less than the above range, isomerization does not proceed. More preferably, it is desirable to add 0.012 mol / L or more and 0.05 mol / L or less of alkali to the crude lactam solution based on the hydroxyl group. More preferably, it is desirable to add 0.016 mol / L or more and 0.035 mol / L or less of alkali to the crude lactam solution based on the hydroxyl group. Here, the crude lactam liquid means a melted crude lactam or a crude lactam solution.

  When adding an alkali, in the case of a batch system, it is preferable to stir so that it is uniformly added. Even if it is a continuous type, it is preferable to stir if alkali is not uniformly added.

  Moreover, the alkali to add is not specifically limited, Caustic soda, ammonia, potassium hydroxide, calcium hydroxide, sodium carbonate, etc. are mentioned. More preferably, caustic soda is used.

  In order to promote isomerization, it is preferable to set the reaction temperature within an appropriate range in addition to the alkali addition amount. As temperature conditions, it is preferable that they are 100 degreeC or more and 200 degrees C or less. By setting the temperature to 100 ° C. or higher, isomerization can proceed more efficiently. On the other hand, it is possible to reduce the low polymerization of lactam by adjusting the temperature to 200 ° C. or lower. More preferably, it is 140 degreeC or more and 170 degrees C or less.

  Moreover, in order to advance isomerization, it is preferable to make reaction time into an appropriate range. A preferable reaction time for the progress of the isomerization reaction is 10 minutes or more and 360 minutes or less. By setting the reaction time to 10 minutes or more, isomerization can proceed more efficiently. On the other hand, low polymerization of lactam can be reduced by setting it to 360 minutes or less. More preferably, 180 minutes or more and 360 minutes or less are desirable.

(Distillation process)
Although the isomerized crude lactam is crystallized in the crystallization step, distillation may be performed before the crystallization step. By carrying out distillation, most of the impurities such as aniline and phenol which are lower boiling impurities than lactam, and chlorlactam which is higher boiling impurities than lactam can be removed. By carrying out the distillation, it is possible to reduce the load in the crystallization step and to obtain a higher quality lactam.

(Crystallization process)
After isomerizing U2 to U1 as described above, crystallization is performed in the crystallization step.

  At the time of crystallization, it may be carried out in a molten state with no solvent, or in the presence of a solvent. In the case of crystallization in the presence of a solvent, the solvent is not particularly limited, aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as hexane, heptane and cyclohexane, propanol, butanol, etc. At least one of chlorohydrocarbons such as alcohol, perchloroethylene, trichlene and water can be used. It is preferable to use water as a solvent because it is possible to crystallize crystals having a large particle size that can be easily separated, and the desolvation work after crystallization is unnecessary.

  Hereinafter, a case where a solvent is used during crystallization will be described. A specific amount of solvent is added to molten caprolactam to prepare a mixture of the two, the mixture is led to a crystallizer, cooled under reduced pressure under a specific pressure, and supersaturation is generated by evaporating the solvent from the lactam solution. By concentration, lactam crystals are precipitated.

  The temperature in the crystallizer is preferably 30 ° C. or higher and 50 ° C. or lower where operational maintenance such as clogging is relatively easy.

  The solvent concentration during crystallization is preferably 12% by weight to 13% by weight.

  Furthermore, it is preferable to implement the pressure in the crystallizer at a reduced pressure of 5 to 30 torr.

  By crystallization, most of impurities such as OHP and chloraniline contained in the crude lactam are discharged into the solvent. Further, by crystallization, most of U1 is taken into lactam crystals, and most of U2 is discharged to the mother liquor side. Crystallization may be performed once but may be performed a plurality of times.

  After crystallization, the lactam crystal containing U1 and the mother liquor are separated. The method for separating the lactam crystals and the mother liquor is not particularly limited, and examples thereof include centrifugation. The separated lactam crystals are subjected to the hydrogenation step of the next step.

(Hydrogenation process)
Finally, hydrogenation is performed on a lactam crystal containing more U1 produced by crystallization. By carrying out hydrogenation, hydrogen can be added to the unsaturated lactam and converted to lactam. Furthermore, dechlorination can be promoted also in γ-chlorolactam contained in a trace amount in the lactam crystal. In addition, since BCL produced by dechlorination of γ-chlorolactam is also hydrogenated, it can be converted to lactam. It does not limit about the method of hydrogenation, It can implement by a well-known method.

  The hydrogenation may be performed in a molten state without solvent or in the presence of a solvent. The solvent used for hydrogenation is not particularly limited, and water and organic solvents such as alcohols can be used. A small amount of solvent used in the crystallization process remains in the lactam crystal obtained in the crystallization process, but this solvent may or may not be separated before hydrogenation. When a solvent is used at the time of hydrogenation, it is preferable to separate the solvent when recovering the lactam.

  When the solvent is not used, the temperature at the time of hydrogenation needs to melt the lactam. Therefore, the temperature may be any temperature that is not lower than the melting point of the lactam and does not thermally deteriorate, and preferably 70 ° C. or higher and 150 ° C. or lower. When using a solvent, it may be at or above the temperature at which the lactam dissolves. Regardless of the use or non-use of a solvent, it is more preferable to carry out at 130 ° C. or higher and 140 ° C. or lower.

  The method of the hydrogenation reaction may be performed in a continuous tank flow format or in a batch format.

  As a catalyst for accelerating the hydrogenation reaction, a supported catalyst (catalyst layer) using activated carbon, alumina, silica, titania or the like as a carrier and supporting a Group VIII transition metal such as palladium, platinum, ruthenium or rhodium is used. it can. Preferably, a Raney alloy of nickel and aluminum having a very large surface area and high catalytic ability is used as the catalyst.

  The mechanism of the reactor for the hydrogenation reaction is not particularly limited, but it is preferable to use a gas-liquid cocurrent flow type fixed bed reaction column packed with a catalyst that requires a short residence time into a fixed bed. . If the fixed bed hydrogenation reaction method is used, the unsaturated lactam is completely hydrogenated within a reaction residence time of 10 minutes or less, so that the residence time of the lactam can be suppressed and thermal degradation can be avoided.

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

Crude lactam purity and impurity content:
The purity of the crude lactam and the content of impurities and the purity of the lactam crystals after crystallization and the content of impurities were determined by gas chromatography. Take a sample in a plastic container containing water, prepare a 50 wt% aqueous solution sample, then take 2 g of the 50 wt% sample into a 10 ml volumetric flask, and inject a sample with a constant volume in acetone into the gas chromatography. Asked. The detection limit of impurities is about 100 ppm.

Example 1
Cyclohexanone oxime was produced by photonitrosation using a 50 kW high-pressure sodium lamp by blowing a mixed gas of nitrosyl chloride and hydrogen chloride into a photoreactor filled with cyclohexane. The cyclohexanone oxime separated from unreacted cyclohexane by standing was subjected to Beckmann rearrangement using fuming sulfuric acid as a catalyst to produce a crude lactam, neutralized with ammonia, and then extracted with trichlorethylene as the extractant. As a result, a crude lactam containing an unsaturated lactam was obtained (the pH value at this time was 7.7, and U2 / U1 was 4.5).

  Subsequently, in order to isomerize the unsaturated lactam contained in the crude lactam, a caustic soda was used to add a crude lactam solution ratio of 0.016 mol / L on the basis of hydroxyl group, and then the mixture was held at a temperature of 145 ° C. for 60 minutes. U2 / U1 contained in the crude lactam after isomerization was 2.1.

  Thereafter, 12 wt% of water was added to the above-mentioned crude lactam, and the mixture was supersaturated by evaporating water from the aqueous lactam solution under vacuum (20 torr) to obtain a slurry containing lactam crystals. In this crystallization operation, U1 is incorporated in the lactam crystal structure because it is a solid solution of lactam, whereas U2 moves to the mother liquor side because it is a lactam eutectic. The sum of unsaturated lactam concentrations (U1 + U2) contained in the lactam crystals obtained by centrifuging the slurry was 3760 ppm.

  Finally, in order to convert the unsaturated lactam to lactam, water is added to the lactam crystal to make an 87.5% aqueous solution, and then hydrogenation is performed by hydrogen pressure and high temperature. Hydrogenation is carried out as follows. A Raney alloy which is a lactam crystal and a catalyst is charged into an autoclave, and after the inside of the autoclave is purged with nitrogen, it is filled with hydrogen and kept at 490 kPa. The unsaturated lactam hydrogenation rate at this time is 100%.

  It shows in Table 1 about the evaluation result of the obtained high quality lactam solution.

(Example 2)
The same procedure as in Example 1 was performed except that the retention time during isomerization in Example 1 was 180 minutes. The results are shown in Table 1.

(Example 3)
The same procedure as in Example 1 was performed except that the retention time during isomerization in Example 1 was 20 minutes. The results are shown in Table 1.

Example 4
Example 1 was carried out in the same manner as Example 1 except that caustic soda was added in a crude lactam solution ratio of 0.027 mol / L based on hydroxyl group. The results are shown in Table 1.

(Example 5)
The same procedure as in Example 1 was performed except that the temperature during isomerization in Example 1 was 160 ° C. The results are shown in Table 1.

(Example 6)
Example 1 was carried out in the same manner as Example 1 except that caustic soda was used and a crude lactam solution ratio of 0.011 mol / L was added on the basis of hydroxyl group. The results are shown in Table 1.

(Example 7)
The same operation as in Example 1 was performed except that the retention time during isomerization in Example 1 was 420 minutes. The results are shown in Table 1. A polymer was formed.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that caustic soda was not added in Example 1. The results are shown in Table 1.

  In Examples 1 to 7, a part of U2 becomes U1 by isomerization. By carrying out crystallization, it is taken into lactam crystals and can be converted to lactam by hydrogenation.

  In Comparative Example 1, since the isomerization step is not performed, since much of U2 remains in the mother liquor, the lactam yield is deteriorated and the mother liquor purity is lowered.

Claims (8)

The eutectic unsaturated lactam contained in the crude lactam is isomerized into the solid solution unsaturated lactam, the crude lactam is crystallized, and then the lactam crystals obtained by the crystallization are hydrogenated. To purify lactam. The lactam purification method according to claim 1, wherein the lactam has 6 to 12 carbon atoms. The method for purifying a lactam according to claim 1 or 2, wherein an alkali is added during the isomerization reaction. The lactam according to any one of claims 1 to 3, wherein an alkali is added so that the ratio of the crude lactam solution is 0.012 mol / L or more and 0.035 mol / L or less based on the hydroxyl group in the isomerization. Purification method. The method for purifying a lactam according to any one of claims 1 to 4, wherein the temperature during the isomerization reaction is 100 ° C or higher and 200 ° C or lower. The method for purifying a lactam according to any one of claims 1 to 5, wherein a reaction time of the isomerization is 10 minutes or more and 360 minutes or less. The method for purifying a lactam according to any one of claims 1 to 6, wherein the crystallization is carried out in the presence of a solvent. The method for purifying lactam according to claim 7, wherein the solvent is water.

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