Production method of ε-caprolactam

Abstract

The present invention relates to the field of caprolactam production, and discloses a method for producing high-purity ε-caprolactam. The method comprises the following steps: (1) subjecting cyclohexanone oxime to a gas-phase Beckmann rearrangement reaction; (2) successively performing gas-liquid separation, solvent removal, and light impurity removal on the reaction product obtained in step (1) to obtain crude caprolactam; (3) crystallizing the crude caprolactam to obtain a crystalline product and a crystallization mother liquor; (4) crystallizing the crystallization mother liquor to obtain a crystal slurry; and returning at least part of the crystal slurry to step (2) and / or step (3). The purification method of the present invention can obtain high-purity caprolactam without reducing the overall yield of caprolactam only through one crystallization and one crystallization of the mother liquor. In addition, the method provided by the present invention can effectively solve the problem of product quality fluctuation.

Description

Technical Field

[0001] The present invention relates to the field of caprolactam production, and particularly to a method for producing high-purity ε-caprolactam. Background Art

[0002] Caprolactam is one of the important raw materials for synthetic fibers and synthetic resins, and is mainly used for manufacturing polyamide fibers (nylon 6), resins, films, etc. Known methods for producing caprolactam include the liquid-phase Beckmann rearrangement method of cyclohexanone oxime using fuming sulfuric acid as a catalyst, the gas-phase Beckmann rearrangement method of cyclohexanone oxime using solid zeolite as a catalyst, and the depolymerization of waste polymers. The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime on a solid acid catalyst is a new process for realizing sulfur-free ammonium caprolactam production, which has no problems such as equipment corrosion and environmental pollution, and the separation and purification of products will also be greatly simplified. Therefore, the new process of the sulfur-free ammonium gas-phase Beckmann rearrangement reaction has received great attention from the industry.

[0003] However, the caprolactam obtained by these methods contains various impurities. As is well known, caprolactam is a raw material used to prepare polyamides, and it is required that the caprolactam products used to prepare polyamides and further manufacture synthetic fibers and synthetic resins have very high quality. Impurities at the μg / g level will affect the subsequent polymerization reaction of caprolactam and are not easy to form filaments. Therefore, various separation and purification methods are required to obtain crude caprolactam, and then various refining methods are used to finally obtain high-purity caprolactam, so that high-purity caprolactam can be used to manufacture products such as synthetic fibers, synthetic resins, and films. Known purification methods for the gas-phase rearrangement product caprolactam include distillation, crystallization, hydrogenation, etc.

[0004] CN109721520A and CN109721537A disclose a method for separating and recovering caprolactam from a crude caprolactam product. After the crude caprolactam product after solvent removal is dehydrated and light by-products are removed, it is directly crystallized, and the crystallized product is subjected to a hydrogenation reaction, and finally high-quality caprolactam with qualified quality can be obtained. This method removes the heavy impurity removal tower with high energy consumption, shortens the process, and further improves the economy.

[0005] Although the above methods have good effects on the production of high-purity caprolactam, in actual industrial applications, they all face the problems of how to improve the caprolactam yield of the entire gas-phase rearrangement process while obtaining high-purity ε-caprolactam, and how to improve the adaptability of the refining system to the reaction system. Summary of the Invention

[0006] The object of the present invention is to overcome the problems existing in the prior art, namely, the unstable quality of caprolactam products and the low yield of caprolactam in the production process, and to provide a method for producing high-purity ε-caprolactam. The method provided by the present invention can effectively solve the problem of product quality fluctuation and obtain high-purity caprolactam without reducing the overall yield of caprolactam.

[0007] To achieve the above object, the present invention provides a method for producing high-purity ε-caprolactam, which comprises the following steps:

[0008] (1) Performing a gas-phase Beckmann rearrangement reaction on cyclohexanone oxime;

[0009] (2) Separating the reaction product obtained in step (1) by gas-liquid separation, removing the solvent, and removing light impurities to obtain crude caprolactam;

[0010] (3) Crystallizing the crude caprolactam to obtain a crystalline product and a crystallization mother liquor;

[0011] (4) Crystallizing the crystallization mother liquor to obtain a crystal slurry;

[0012] Return at least part of the crystal slurry to step (2) and / or step (3).

[0013] The purification method of the present invention can obtain high-purity caprolactam without reducing the overall yield of caprolactam only through one crystallization and one crystallization of the mother liquor. In addition, the method provided by the present invention can effectively solve the problem of product quality fluctuation. Description of the Drawings

[0014] Figure 1 is a schematic diagram of a valve provided in a scrubber according to a specific embodiment of the method provided by the present invention;

[0015] Figure 2 is a schematic diagram of a partition provided in a scrubber according to a specific embodiment of the method provided by the present invention.

[0016] Description of the Reference Numerals

[0017] a--------Crystal slurry inlet b--------Washing solvent inlet

[0018] c--------Mother liquor outlet d--------Caprolactam (water) solution outlet

[0019] e--------Circulating water inlet f--------Heating tube

[0020] g--------Valve h--------Partition Detailed Embodiments

[0021] The endpoints and any values disclosed in this text for ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this text.

[0022] In the present invention, the pressure refers to the gauge pressure.

[0023] In the present invention, "the dilute-phase bed of caprolactam crystals" and "the dilute-phase bed" can be interchanged, "the dense-phase bed of caprolactam crystals" and "the dense-phase bed" can be interchanged, "the crystal slurry containing caprolactam crystals and crystallization mother liquor" and "the crystal slurry" can be interchanged, and "caprolactam crystals" and "crystals" can be interchanged.

[0024] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, "inner" and "outer" refer to the inside and outside relative to the contour of each component itself.

[0025] In the present invention, the "purity of caprolactam" refers to the percentage content of caprolactam in the sum of the weights of caprolactam and impurities, where the impurities do not include the washing solvent and the crystallization solvent in the mother liquor.

[0026] The high purity described in the present invention means that the purity of ε-caprolactam is not less than 99.99%.

[0027] In the present invention, the "particle density" refers to the bulk density of crystal particles, specifically the weight of caprolactam crystals per unit volume.

[0028] The present invention provides a method for producing high-purity ε-caprolactam, and the method includes the following steps:

[0029] (1) Performing a gas-phase Beckmann rearrangement reaction on cyclohexanone oxime;

[0030] (2) Sequentially performing gas-liquid separation, solvent removal, and light impurity removal on the reaction product obtained in step (1) to obtain crude caprolactam;

[0031] (3) Crystallizing the crude caprolactam to obtain a crystallization product and a crystallization mother liquor;

[0032] (4) Crystallizing the crystallization mother liquor to obtain a crystal slurry;

[0033] Return at least part of the crystal slurry to step (2) and / or step (3).

[0034] The gas-phase Beckmann rearrangement reaction described in step (1) of the present invention can be carried out by conventional means in the art, and the present invention has no special limitation in this regard. For better illustration of the present invention, the specific situation of the gas-phase Beckmann rearrangement reaction is described below by way of example.

[0035] According to the present invention, preferably, step (1) includes carrying out the gas-phase Beckmann rearrangement reaction of cyclohexanone oxime in an environment where a solvent and a carrier gas are present.

[0036] According to the present invention, preferably, the weight ratio of the solvent to cyclohexanone oxime is 1:1 - 3:1.

[0037] According to the present invention, preferably, the solvent described in step (1) is selected from C1-C6 aliphatic alcohols, preferably at least one of methanol, ethanol, and propanol.

[0038] According to the present invention, the carrier gas can be various gases that do not react with cyclohexanone oxime and the solvent under the conditions of the gas-phase Beckmann rearrangement reaction. Preferably, the carrier gas described in step (1) is selected from at least one of nitrogen, hydrogen, argon, ammonia, saturated hydrocarbons with a boiling point not higher than 180°C (such as methanol, ethanol, hexane, cyclohexane), and halogenated hydrocarbons (such as 1-chloropropane, 2-chloropropane, chlorobutane, 2-chlorobutane).

[0039] According to the present invention, the gas-phase Beckmann rearrangement reaction can be carried out according to conventional techniques in the art, and the present invention has no special limitation in this regard. Preferably, the conditions of the gas-phase Beckmann rearrangement reaction include: the temperature is 320 - 450°C, preferably 330 - 400°C; the pressure is 0.05 - 1.0 MPa, preferably 0.2 - 0.5 MPa; the weight hourly space velocity of cyclohexanone oxime is 0.1 - 5 h -1 .

[0040] According to the present invention, the catalyst used in the process of the gas-phase Beckmann rearrangement reaction can be a commonly used catalyst in the art. However, in order to improve the yield of crude caprolactam, preferably, the cyclohexanone oxime described in step (1) reacts on a solid acid catalyst, and the solid acid catalyst contains titanium silicalite, all-silica molecular sieve, or a molecular sieve with an MFI structure.

[0041] According to the present invention, in order to improve the purity of crude caprolactam, preferably, step (2) further includes removing heavy impurities after removing light impurities.

[0042] According to the present invention, the conditions for gas-liquid separation, solvent removal, light impurity removal, and heavy impurity removal in step (2) can be selected within a relatively wide range. The present invention does not particularly limit the conditions for gas-liquid separation, as long as the purpose of gas-liquid separation can be achieved. The solvent removal is to remove the solvent used in the gas-phase Beckmann rearrangement reaction. Those skilled in the art can select appropriate solvent removal methods and conditions according to the specific type of solvent, and the present invention will not elaborate herein.

[0043] The light impurity removal in the present invention refers to the removal of impurities with a boiling point lower than that of caprolactam, and specifically, a vacuum distillation method can be used. The heavy impurity removal in the present invention refers to the removal of impurities with a boiling point higher than that of caprolactam.

[0044] Preferably, the conditions for gas-liquid separation, solvent removal, light impurity removal, and heavy impurity removal in step (2) can make the purity of the obtained crude caprolactam be 98.8 - 99.7%.

[0045] According to the present invention, the conditions for crystallizing the crude caprolactam in step (3) can be selected within a relatively wide range. Preferably, the conditions for crystallizing the crude caprolactam include: a crystallization temperature of 10 - 60 °C and a crystallization pressure of 0.1 - 1.5 bar (absolute pressure).

[0046] According to the present invention, the conditions for crystallizing the crystallization mother liquor in step (4) can be the commonly used conditions in the art, as long as crystals can precipitate from the mother liquor to form a crystal slurry. Preferably, the crystallization conditions for the crystallization mother liquor include: a crystallization temperature of 10 - 60 °C and a crystallization pressure of 0.1 - 1.5 bar (absolute pressure). More preferably, the crystallization conditions for the crystallization mother liquor make the mass content of caprolactam in the crystal slurry be 10 - 90%, more preferably 20 - 70%.

[0047] According to the present invention, there is no particular limitation on the crystallizer used for crystallizing the crude caprolactam in step (3) and the crystallizer used for crystallizing the crystallization mother liquor in step (4). It can be a cooling crystallizer, an evaporative crystallizer, a vacuum crystallizer, and can include at least one of a forced outer circulation type crystallizer, an Oslo type crystallizer, an FC type crystallizer, a DTB type crystallizer, a DP type crystallizer, and a Messo turbulent crystallizer.

[0048] According to the present invention, preferably, at least part of the crystal slurry is returned to step (2) for solvent removal.

[0049] According to the present invention, the amount of the crystal slurry returned to step (2) and / or step (3) can be selected within a relatively wide range. To improve the yield of ε-caprolactam while ensuring the purity of ε-caprolactam, preferably, the weight percentage of the crystal slurry returned to step (2) and / or step (3) in the crude caprolactam is 2 - 50%, preferably 5 - 30%.

[0050] According to the present invention, preferably, the method further includes subjecting the crystal slurry to countercurrent washing, then subjecting the caprolactam crystals and the solvent obtained from the washing to aqueous phase dissolution and stratification to obtain an aqueous caprolactam solution, then returning the aqueous caprolactam solution to step (2) for dehydration after gas-liquid separation and desolvation, and then performing the removal of light impurities. Adopting this preferred embodiment is more conducive to improving the yield of caprolactam in the entire process while obtaining high-purity ε-caprolactam.

[0051] According to the present invention, the aqueous phase dissolution and stratification can be carried out by conventional technical means in the art. Preferably, the amount of the aqueous phase is 0.05 - 5 times, preferably 0.1 - 1 times, the mass of the caprolactam crystals obtained from the washing.

[0052] According to the present invention, preferably, the aqueous phase dissolution and stratification is dissolution at room temperature or heating dissolution. The temperature for dissolution at room temperature is 10 - 30 °C, and the temperature for heating dissolution is 30 - 110 °C.

[0053] According to the present invention, preferably, the method further includes subjecting the crystal slurry to countercurrent washing, then subjecting the caprolactam crystals and the solvent obtained from the washing to heating dissolution (the heating dissolution temperature is 50 - 110 °C) to obtain a caprolactam solution, and then returning the caprolactam solution to step (3) for crystallization. Adopting this preferred embodiment is more conducive to improving the yield of caprolactam in the entire process while obtaining high-purity ε-caprolactam.

[0054] According to the present invention, preferably, the countercurrent washing includes: making the crystal slurry and the washing solvent contact countercurrently in a washer, wherein the crystal slurry is fed into the washer from the upper part of the washer, and the washing solvent is fed into the washer from the lower part of the washer;

[0055] Wherein, a dense phase bed of caprolactam crystals and a dilute phase bed of caprolactam crystals are sequentially arranged in the washer from top to bottom.

[0056] In the present invention, "countercurrent contact" means that the crystal slurry enters the washer from the crystal slurry inlet, and the precipitated crystals move downward under the action of gravity to form a dilute (dense) phase bed of caprolactam crystals in the washer; at the same time, the washing solvent enters the washer from the washing solvent inlet, a part of the washing solvent flows upward through the dilute (dense) phase bed of caprolactam crystals to displace the crystallization mother liquor, and this part of the washing solvent and the crystallization mother liquor are discharged together from the mother liquor outlet, and the remaining washing solvent is carried out together with the crystals. Figure 1To further explain the "countercurrent contact" of the present invention, the scrubber includes a magma inlet a, a washing solvent inlet b, a mother liquor outlet c, a caprolactam (water) solution outlet d, a circulating water inlet e, a heating tube f, and a valve g. The magma enters the scrubber through the magma inlet a, and the washing solvent enters the scrubber through the washing solvent inlet b. The magma and the washing solvent are in countercurrent washing in the scrubber. The mother liquor in the magma flows out from the mother liquor outlet c, and the precipitated crystals move downward under the action of gravity to form a dense phase bed of caprolactam crystals above the valve g and a dilute phase bed of caprolactam crystals below the valve g. The circulating water introduced through the circulating water inlet e is dissolved under the action of the heating tube f to obtain a caprolactam solution, and the caprolactam solution is discharged from the caprolactam (water) solution outlet d.

[0057] In the present invention, in order to describe the positions where the magma and the washing solvent enter the scrubber, the descriptions of "upper part" and "lower part" are introduced. The "upper part" and "lower part" are relative and do not refer to specific position points or regions. For example, the top of the scrubber can be called the "upper part" of the bottom of the scrubber. On the contrary, the bottom of the scrubber can be called the "lower part" of the top of the scrubber. For another example, the position at the mid-height of the scrubber can be called the "lower part" of the top of the scrubber and can also be called the "upper part" of the bottom of the scrubber. At the same time, the "upper part" and "lower part" can be adjacent regions. For example, the region between the top of the scrubber and the mid-height of the scrubber can be called the "upper part" of the region between the bottom of the scrubber and the mid-height of the scrubber. On the contrary, the region between the bottom of the scrubber and the mid-height of the scrubber can be called the "lower part" of the region between the top of the scrubber and the mid-height of the scrubber. The "upper part" and "lower part" can also be non-adjacent regions. For example, the region between the top of the scrubber and one-third of the height of the scrubber can be called the "upper part" of the region between the bottom of the scrubber and the mid-height of the scrubber. On the contrary, the region between the bottom of the scrubber and the mid-height of the scrubber can be called the "lower part" of the region between the top of the scrubber and one-third of the height of the scrubber. In the present invention, it is usually said that the dense phase bed of caprolactam crystals is located above the dilute phase bed of caprolactam crystals. Correspondingly, the dilute phase bed of caprolactam crystals is located below the dense phase bed of caprolactam crystals.

[0058] According to the present invention, preferably, the bed particle density of the dense phase bed of caprolactam crystals is 400 - 1000 kg / m 3 ³, preferably 500 - 900 kg / m 3 ³.

[0059] According to the present invention, preferably, the bed particle density of the dilute phase bed of caprolactam crystals is 100 - 500 kg / m 3 ³, preferably 100 - 400 kg / m 3。

[0060] According to the present invention, the feeding rate of the crystals can be selected within a relatively wide range. Preferably, as long as the bed particle density of the dense phase bed and / or the dilute phase bed can meet the above range.

[0061] In the present invention, there is no particular limitation on the formation manner of the dilute phase bed of caprolactam crystals and the dense phase bed of caprolactam crystals in the scrubber. As long as the above characteristics can be satisfied, the object of the present invention can be achieved. For example, before startup, caprolactam crystals can be loaded into the scrubber to form a dilute phase bed of caprolactam crystals or a dense phase bed of caprolactam crystals; it can also be formed during the operation of the method. Specifically, crystal slurry can be directly added from the upper part of the scrubber, and the washing solvent can be directly added from the lower part of the scrubber, so that the crystal slurry and the washing solvent are in countercurrent contact during the washing process to precipitate crystals, and then by controlling the feeding rate of the crystals in the scrubber, a dilute phase bed and a dense phase bed can be formed in the scrubber.

[0062] According to the present invention, preferably, a partition plate (as shown in Figure 2 the figure) or a valve is arranged inside the scrubber, and the partition plate or the valve is used to reduce the flow cross-sectional area of caprolactam to form the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals. The present invention has no particular limitation on the setting manner of the partition plate or the valve, as long as the above object can be achieved. Preferably, the partition plate or the valve is located on the demarcation line between the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals in the scrubber.

[0063] According to the present invention, preferably, based on the total height of the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals, the height of the dense phase bed of caprolactam crystals is 50 - 80%, and the height of the dilute phase bed of caprolactam crystals is 20 - 50%; more preferably, based on the total height of the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals, the height of the dense phase bed of caprolactam crystals is 50 - 70%, and the height of the dilute phase bed of caprolactam crystals is 30 - 50%.

[0064] According to the present invention, preferably, the purity of the caprolactam crystals in the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals is independently 98.0 - 99.9%.

[0065] According to the present invention, preferably, the feeding rate of the washing solvent is 0.001 - 0.2 m / s, and further preferably 0.005 - 0.15 m / s; adopting this preferred embodiment is more conducive to cleaning the crystal surface, and the upward flowing washing solvent entangles as few crystals as possible.

[0066] According to the present invention, the amount of the washing solvent can be selected within a relatively wide range. However, in order to reduce the discharge amount of waste liquid and lower the production cost while ensuring the washing effect, preferably, the amount of the washing solvent is 0.1 - 10 times, preferably 0.2 - 5 times, and more preferably 0.2 - 2 times the mass of the caprolactam crystals in the crystal slurry.

[0067] According to the present invention, the residence time of the caprolactam crystals inside the washer has a relatively wide selection range. However, in the preferred case, considering comprehensively the purity, yield of the crystals and the amount of the washing solvent, preferably, the residence time of the caprolactam crystals inside the washer is 400 - 600 s.

[0068] According to the present invention, the washing solvent can be a solvent commonly used for caprolactam crystallization. However, in order to further improve the purity of the caprolactam crystals, the washing efficiency and the yield of caprolactam, preferably, the washing solvent is selected from at least one of halogenated hydrocarbons, ethers and alkanes with 6 - 12 carbon atoms; more preferably, the halogenated hydrocarbon is at least one of 1 - chloropropane, 2 - chloropropane, n - butyl chloride, 2 - chlorobutane, isobutyl chloride, tert - butyl chloride, n - propyl bromide, isopropyl bromide, 1 - bromobutane and 2 - bromobutane; the ether is at least one of methyl ethyl ether, diethyl ether, n - propyl ether, isopropyl ether, n - butyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, vinyl ether, methyl tert - butyl ether and ethyl tert - butyl ether; the boiling point of the alkanes with 6 - 12 carbon atoms is 60 - 180 °C (for example, n - heptane, n - hexane, isopentane, n - octane, n - nonane, methylhexane, isohexane, neohexane, isoheptane, isooctane, isononane), preferably 60 - 130 °C (for example, n - pentane, n - hexane, isopentane).

[0069] According to the present invention, preferably, the method further includes agitating the dense phase bed of the caprolactam crystals; adopting this preferred implementation mode is more conducive to the movement of the crystal bed on the one hand, and can more effectively wash the crystal surface on the other hand.

[0070] According to the present invention, preferably, a motor is used to drive a paddle or a baffle to agitate the dense phase bed of the caprolactam crystals.

[0071] According to the present invention, preferably, an overflow port is provided at the upper part of the washer, and the washing mother liquor flows out of the washer from the overflow port. Among them, a part of the upward - flowing washing solvent also flows out from the overflow port.

[0072] In the following examples, the following test methods are used to evaluate the quality of the prepared caprolactam product:

[0073] (1) Purity of caprolactam

[0074] Using a capillary column Innowax 60m and a gas chromatograph 7890GC to analyze the purity and impurity content of caprolactam, with the lowest detection limit of the chromatograph being 1 μg / g.

[0075] (2) Potassium permanganate absorption value of ε-caprolactam

[0076] Pour 3.000 grams of caprolactam into a 100 ml volumetric flask, dilute to the mark with distilled water, shake well, place it in a constant temperature water bath at 20 °C. Add 1 ml of 0.01N potassium permanganate solution to the volumetric flask, shake immediately, and start the stopwatch at the same time. Stop the stopwatch when the color of the sample solution in the volumetric flask is the same as that of the standard colorimetric solution (dissolve 3 grams of primary standard Co(NO3)·6H2O and 12 mg of primary standard K2Cr2O7 in water, dilute to 1 liter, and shake well). Record the time consumed (in seconds), which is the potassium permanganate absorption value.

[0077] (3) Volatile base (V.B)

[0078] In an alkaline medium, distill out the alkaline low-molecular impurities in the sample, absorb them with a known amount of hydrochloric acid solution, and titrate the excess hydrochloric acid with a standard sodium hydroxide solution. The determination value of the volatile base is the number of moles of acid consumption per kilogram of the sample. The calculation formula is as follows:

[0079] V.B (mmol / kg) = [(V0 - V) × C NaOH / M] × 1000

[0080] Where: V0 is the volume of the standard sodium hydroxide solution consumed in the blank test, in ml;

[0081] V is the volume of the standard sodium hydroxide solution consumed by the sample, in ml;

[0082] C NaOH is the accurate concentration of the standard sodium hydroxide solution, in mol / L;

[0083] M is the mass of the sample, in g.

[0084] (4) Extinction value E (at a wavelength of 290 nm)

[0085] Weigh 50 grams of the sample in a 300 ml conical flask, add 50 ml of distilled water, shake well to completely dissolve the sample, and let it stand for 10 minutes. Use a spectrophotometer to detect the extinction value of the 50% sample relative to distilled water at a wavelength of 290 nm.

[0086] (5) Yield of caprolactam product = mass of the crystalline product obtained in step (3) ÷ mass of caprolactam in the reaction product of step (2) × 100%.

[0087] The present invention will be described in detail below with reference to embodiments.

[0088] Embodiment 1

[0089] (1) The gas-phase Beckmann rearrangement reaction of cyclohexanone oxime is carried out in the presence of nitrogen, solvent methanol and all-silica molecular sieve. Among them, the weight ratio of the solvent to cyclohexanone oxime is 2:1. The conditions of the gas-phase Beckmann rearrangement reaction include: the temperature is 350 °C, the pressure is 0.4 MPa, and the weight hourly space velocity of cyclohexanone oxime is 2 h -1 .

[0090] (2) After the product of the gas-phase Beckmann rearrangement reaction is cooled, gas-liquid separation is carried out. The gas phase is compressed and recycled to the reaction system, and the liquid phase is subjected to methanol separation, light impurity separation and heavy impurity removal to obtain crude caprolactam with a purity of 99.6%.

[0091] (3) Crystallization is carried out on the crude caprolactam to obtain a crystalline product and a crystallization mother liquor. The conditions for crystallization include: the crystallization temperature is 35 °C and the crystallization pressure is 1 bar (absolute pressure). The crystalline product is washed and post-treated to obtain a caprolactam product.

[0092] (4) The crystallization mother liquor is crystallized to obtain a crystal slurry. The conditions for crystallization include: the crystallization temperature is 30 °C and the crystallization pressure is 1 bar (absolute pressure), and the mass content of caprolactam in the crystal slurry is 35%. All the obtained crystal slurries enter the scrubber for countercurrent washing, and then at 30 °C, the caprolactam crystals and the solvent obtained by washing are dissolved and layered in the aqueous phase (the amount of the aqueous phase is 0.2 times the mass of the caprolactam crystals obtained by washing) to obtain an aqueous caprolactam solution, and then the aqueous caprolactam solution is returned to step (2) for dehydration after gas-liquid separation and solvent removal, and then the light impurity removal is carried out, and the subsequent steps are carried out. At the same time, the ratio of the amount of crude caprolactam to the amount of the crystal slurry returned to step (2) is controlled to be 100:20.

[0093] Among them, the process of countercurrent washing includes: slowly feeding the crystal slurry into the scrubber from the upper part of the scrubber by a pump, feeding the washing solvent isopropyl ether (the amount used is 0.5 times the weight of the crystal slurry) into the scrubber from the lower part of the scrubber, and the feeding rate of the washing solvent is 0.02 m / s, so that the crystal slurry and the washing solvent are in countercurrent contact in the scrubber to wash the caprolactam crystals. The feeding speed of the crystals generated during the washing process is controlled by a valve to form a dense phase bed of caprolactam crystals in the upper part of the scrubber and a dilute phase bed of caprolactam crystals in the lower part of the scrubber. A partition plate is arranged between the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals, and the height ratio of the dense phase bed to the dilute phase bed is 5:5. The height of the dilute phase bed is 50% of the height of the scrubber, and the particle density in the dense phase bed is 850 kg / m 3 , and the particle density in the dilute phase bed is 400 kg / m 3, while controlling the residence time of the caprolactam crystals inside the scrubber to be 480 s.

[0094] In step (3), the yield of the caprolactam product obtained is 99.0%, the purity is 99.997% (mass fraction), the extinction value is 0.02, the volatile base value is 0.05, the PM value is 38000 s, the chromaticity is not greater than 1, and the product indicators are all superior to the national standard first-class product standard.

[0095] Example 2

[0096] (1) Carry out a gas-phase Beckmann rearrangement reaction of cyclohexanone oxime in the presence of nitrogen, solvent methanol, and all-silica molecular sieve. Among them, the weight ratio of the solvent to cyclohexanone oxime is 2:1. The conditions for the gas-phase Beckmann rearrangement reaction include: the temperature is 350 °C, the pressure is 0.4 MPa, and the weight hourly space velocity of cyclohexanone oxime is 2 h -1 .

[0097] (2) After the product of the gas-phase Beckmann rearrangement reaction is cooled, gas-liquid separation is carried out. The gas phase is compressed and recycled to the reaction system, and the liquid phase is subjected to methanol separation and light impurity separation to obtain crude caprolactam with a purity of 99%.

[0098] (3) Crystallize the crude caprolactam to obtain a crystalline product and a crystallization mother liquor. The crystallization conditions include: the crystallization temperature is 35 °C, and the crystallization pressure is 1 bar (absolute pressure). The crystalline product is washed and post-treated to obtain a caprolactam product.

[0099] (4) The crystallization mother liquor is crystallized to obtain a crystal slurry. The crystallization conditions include: the crystallization temperature is 30 °C, the crystallization pressure is 1 bar (absolute pressure), and the mass content of caprolactam in the crystal slurry is 40%. All the obtained crystal slurry enters the scrubber for countercurrent washing, and then the caprolactam crystals and the solvent obtained by washing are heated and dissolved (the heating and dissolving temperature is 70 °C) to obtain a caprolactam solution, and then the caprolactam solution is returned to step (3) for crystallization. At the same time, control the ratio of the amount of crude caprolactam to the amount of the crystal slurry returned to step (2) to be 100:30.

[0100] Among them, the process of countercurrent washing includes: slowly feeding the crystal slurry into the scrubber from the upper part of the scrubber by a pump, feeding the washing solvent isopropyl ether (the dosage is 0.6 times the weight of the crystal slurry) into the scrubber from the lower part of the scrubber, and the feeding rate of the washing solvent is 0.01 m / s, so that the crystal slurry and the washing solvent are in countercurrent contact in the scrubber to wash the caprolactam crystals. Control the feeding speed of the crystals generated during the washing process through a valve to form a dense phase bed layer of caprolactam crystals at the upper part of the scrubber and a dilute phase bed layer of caprolactam crystals at the lower part of the scrubber. A partition is provided between the dense phase bed layer and the dilute phase bed layer of caprolactam crystals. The height ratio of the dense phase bed layer to the dilute phase bed layer is 6:4, the height of the dilute phase bed layer is 40% of the height of the scrubber, and the particle density in the dense phase bed layer is 820 kg / m3 , the particle density in the dilute-phase bed is 380 kg / m 3 , and at the same time, the residence time of the caprolactam crystals inside the scrubber is controlled to be 480 s.

[0101] The yield of the caprolactam product obtained in step (3) is 99.2%, the purity is 99.995% (mass fraction), the extinction value is 0.03, the volatile base value is 0.1, the PM value is 30000 s, the chromaticity is not greater than 1, and the product indexes are all superior to the national standard excellent product standard.

[0102] It can be seen from Examples 1-2 that using the method of the present invention to produce caprolactam can improve the yield of the caprolactam product while ensuring the quality of the caprolactam product.

[0103] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A production method of high-purity ε-caprolactam, the method comprising the following steps: (1) performing a gas-phase Beckmann rearrangement reaction on cyclohexanone oxime; (2) successively performing gas-liquid separation, solvent removal, and light impurity removal on the reaction product obtained in step (1) to obtain crude caprolactam; (3) crystallizing the crude caprolactam to obtain a crystalline product and a crystallization mother liquor; (4) crystallizing the crystallization mother liquor to obtain a crystal slurry; returning at least part of the crystal slurry to steps (2) and (3); wherein the amount of the crystal slurry returned to step (2) accounts for 5-30% by weight of the crude caprolactam; wherein the purity of ε-caprolactam is not less than 99.99%; the method further comprises counter-currently washing the crystal slurry, then dissolving and layering the caprolactam crystals and the solvent obtained by washing in an aqueous phase to obtain an aqueous caprolactam solution, then returning the aqueous caprolactam solution to dehydration after gas-liquid separation and solvent removal in step (2), and then performing the light impurity removal; alternatively, the method further comprises counter-currently washing the crystal slurry, then heating and dissolving the caprolactam crystals and the solvent obtained by washing to obtain a caprolactam solution, and then returning the caprolactam solution to step (3) for crystallization; the counter-current washing comprises: making the crystal slurry and a washing solvent contact counter-currently in a washer, wherein the crystal slurry is fed into the washer from the upper part of the washer, and the washing solvent is fed into the washer from the lower part of the washer; a dense phase bed of caprolactam crystals and a dilute phase bed of caprolactam crystals are successively arranged in the washer from top to bottom; The bed particle density of the caprolactam crystal dense phase bed is 500-900 kg / m 3 ; The bed particle density of the dilute-phase bed of caprolactam crystals is 100 - 400 kg / m 3 .

2. The production method according to claim 1, wherein, returning at least part of the crystal slurry to step (2) for solvent removal.

3. The production method according to claim 1, wherein, the amount of the aqueous phase is 0.05-5 times the mass of the caprolactam crystals obtained by washing.

4. The production method according to claim 3, wherein, the amount of the aqueous phase is 0.1-1 times the mass of the caprolactam crystals obtained by washing.

5. The production method according to claim 1, wherein, the aqueous phase dissolution and layering is normal temperature dissolution or heating dissolution, the temperature of the normal temperature dissolution is 10-30°C, and the temperature of the heating dissolution is 30-110°C.

6. The production method according to claim 1, wherein, Based on the total height of the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals, the height of the dense phase bed of caprolactam crystals is 50-80%, and the height of the dilute phase bed of caprolactam crystals is 20-50%.

7. The production method according to claim 6, wherein, Based on the total height of the dense phase bed of caprolactam crystals and the dilute phase bed of caprolactam crystals, the height of the dense phase bed of caprolactam crystals is 50-70%, and the height of the dilute phase bed of caprolactam crystals is 30-50%.

8. The production method according to claim 1, wherein, The feeding rate of the washing solvent is 0.001-0.2 m / s.

9. The production method according to claim 8, wherein The feeding rate of the washing solvent is 0.005-0.15 m / s.

10. The production method according to claim 1, wherein, the amount of the washing solvent is 0.1-10 times the mass of the caprolactam crystals in the crystal slurry.

11. The production method according to claim 10, wherein, The dosage of the washing solvent is 0.2 - 5 times the mass of the caprolactam crystals in the crystal slurry.

12. According to the production method described in claim 11, wherein, The dosage of the washing solvent is 0.2 - 2 times the mass of the caprolactam crystals in the crystal slurry.

13. According to the production method described in claim 1, wherein, The washing solvent is selected from at least one of halogenated hydrocarbons, ethers, and alkanes with 6 - 12 carbon atoms.

14. According to the production method described in claim 13, wherein, The halogenated hydrocarbon is at least one of 1 - chloropropane, 2 - chloropropane, n - butyl chloride, 2 - chlorobutane, isobutyl chloride, tert - butyl chloride, n - propyl bromide, isopropyl bromide, 1 - bromobutane, and 2 - bromobutane; the ether is at least one of methyl ethyl ether, diethyl ether, n - propyl ether, isopropyl ether, n - butyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, vinyl ether, methyl tert - butyl ether, and ethyl tert - butyl ether; the boiling point of the alkane with 6 - 12 carbon atoms is 60 - 180 °C.

15. The production method according to any one of claims 1-14, wherein, Step (1) includes carrying out the gas - phase Beckmann rearrangement reaction of cyclohexanone oxime in an environment with a solvent and a carrier gas present.

16. According to the production method described in any one of claims 1 - 14, wherein, The cyclohexanone oxime in step (1) reacts on a solid acid catalyst, and the solid acid catalyst contains titanium - silicon molecular sieve, all - silicon molecular sieve, or a molecular sieve with an MFI structure.

17. According to the production method described in claim 15, wherein, The solvent in step (1) is selected from C1 - C6 fatty alcohols.

18. According to the production method described in claim 17, wherein, The solvent in step (1) is selected from at least one of methanol, ethanol, and propanol.

19. According to the production method described in claim 15, wherein, The carrier gas in step (1) is selected from at least one of nitrogen, hydrogen, argon, ammonia, saturated hydrocarbons with a boiling point not higher than 180 °C, and halogenated hydrocarbons.

20. The production method according to any one of claims 1-14, wherein, Step (2) further includes removing heavy impurities after removing light impurities.

Images