Method for refining cyclohexanone-oxime gas-phase rearrangement product

Abstract

The invention relates to the field of caprolactam production, and discloses a cyclohexanone-oxime gas-phase rearrangement product refining method which comprises the following steps: desolventizing a cyclohexanone-oxime gas-phase rearrangement product to obtain a caprolactam crude product; the method comprises the following steps: dissolving a caprolactam crude product in an organic solvent I, washing with water to remove water-soluble impurities, and concentrating to obtain a primary refined product; dissolving the preliminary refined product in water, and washing with an organic solvent II to remove oil-soluble impurities so as to obtain a crude caprolactam aqueous solution; performing adsorption and impurity removal on the crude caprolactam aqueous solution by using nitric acid modified activated carbon, and dehydrating to obtain a caprolactam refined product. By adopting the method disclosed by the invention, a relatively high refining yield can be realized, and the obtained caprolactam refined product has relatively high purity and relatively low platinum-cobalt chromaticity, extinction value and potassium permanganate value.

Description

Technical Field

[0001] The present invention relates to the field of caprolactam production, and in particular to a method for refining a product of gas-phase rearrangement of cyclohexanone oxime. Background Art

[0002] Caprolactam is an important organic chemical raw material and a key monomer in the synthesis of nylon-6 (PA6). It can be used to produce nylon-6 fiber and nylon-6 engineering plastics. The existing mature industrial production method for caprolactam is to produce caprolactam through a liquid-phase Beckmann rearrangement reaction of cyclohexanone oxime under the catalysis of fuming sulfuric acid. However, this liquid-phase rearrangement method produces a large amount of low-value-added ammonium sulfate as a by-product, and fuming sulfuric acid requires high equipment requirements and pollutes the environment. Currently, a newer production process is to produce caprolactam through a vapor-phase Beckmann rearrangement reaction of cyclohexanone oxime under the catalysis of solid acid.

[0003] Caprolactam vapor-phase rearrangement products contain a high concentration of impurities and typically undergo refinement and impurity removal processes such as distillation, crystallization, hydrogenation, and distillation to obtain premium caprolactam that meets polymerization requirements. Patents CN104024221B and CN1332158A utilize desolvation, dehydration, light and heavy removal, crystallization, hydrogenation, and distillation to obtain caprolactam. However, the light and heavy removal processes increase the risk of caprolactam deterioration, resulting in low refining yields. Summary of the Invention

[0004] To address the technical problem of a high risk of caprolactam deterioration in existing methods for refining cyclohexanone oxime vapor-phase rearrangement products, resulting in low refining yields, the present invention provides a method for refining cyclohexanone oxime vapor-phase rearrangement products. This method achieves a high refining yield, and the resulting refined caprolactam product exhibits high purity and low platinum-cobalt color, extinction value, and potassium permanganate value.

[0005] The specific technical solutions of the present invention are: A method for refining a product of cyclohexanone oxime gas phase rearrangement comprises the following steps: S1: desolvating the gas-phase rearrangement product of cyclohexanone oxime to obtain crude caprolactam; S2: dissolving the crude caprolactam in organic solvent I, washing with water to remove water-soluble impurities, and concentrating to obtain a preliminary refined product; S3: dissolving the preliminary refined product in water and washing with organic solvent II to remove oil-soluble impurities to obtain a crude caprolactam aqueous solution; S4: The crude caprolactam aqueous solution is adsorbed and impurities removed by nitric acid-modified activated carbon, and then dehydrated to obtain a refined caprolactam product.

[0006] During the vapor-phase Beckmann rearrangement of cyclohexanone oxime to produce caprolactam, complex side reactions occur. These include hydrolysis, hydrogenation, dehydration, condensation, cracking, and alcoholysis of the raw cyclohexanone oxime; hydrolysis, oxidation, hydrogenation, alkylation, and isomerization of the caprolactam product; and further reactions between impurities generated by these side reactions to form new impurities. These complex side reactions result in a wide variety of impurities in the vapor-phase rearrangement product of cyclohexanone oxime, making its purification and removal extremely challenging.

[0007] In view of the impurities contained in the gas-phase rearrangement product of cyclohexanone oxime, the present invention has designed a special purification method, the specific mechanism of which is as follows: in step S1, the reaction solvent used in the gas-phase rearrangement reaction of cyclohexanone oxime can be removed by a desolvation process; in step S2, the crude caprolactam is dissolved in an organic solvent I and then washed with water to remove water-soluble impurities including oxime, alcohol, lower aliphatic amine, amide, imidazole, and some slightly soluble impurities including ketones; in step S3, the crude caprolactam is dissolved in water and then washed with water to remove water-soluble impurities including oxime, alcohol, lower aliphatic amine, amide, imidazole, and some slightly soluble impurities including ketones; Washing with organic solvent II can remove oil-soluble impurities including benzene, nitriles, ketones, aromatic amines, amides, polycyclic benzenes, phenazines, and carbazoles. In step S4, after the activated carbon is modified with nitric acid, the content of acidic oxygen-containing functional groups therein is increased, and the hydrophilicity and affinity for polar organic matter are enhanced. The crude caprolactam aqueous solution is adsorbed by the nitric acid-modified activated carbon, which can further remove residual organic polar impurities containing O, N elements and unsaturated bonds, including aromatic amines, phenazines, and carbazoles.

[0008] In the above process, the present invention adopts the order of washing with water first and then washing with organic solvent II (in steps S2 and S3). After completing the washing with organic solvent II, a crude caprolactam aqueous solution is obtained, and nitric acid-modified activated carbon can be directly added to achieve a better adsorption and impurity removal effect. However, if steps S2 and S3 are swapped and the order of washing with organic solvent II first and then washing with water is adopted, a crude caprolactam organic solution is obtained after completing the water washing, and the effect of nitric acid-modified activated carbon on removing polar impurities therein by adsorption is poor.

[0009] By the above-mentioned manner, the method of the present invention can achieve a good removal effect on the impurities in the cyclohexanone oxime gas phase rearrangement product, and the whole refining process (desolventizing, washing, washing with organic solvent II, adsorption and impurity removal) in the present invention can be carried out under mild conditions, without the need to remove light and heavy substances by distillation or rectification, avoiding the deterioration problem caused by the further reaction between the caprolactam and the impurities, or between the impurities, caused by high temperature in the distillation or rectification process of the crude product, thereby avoiding the deterioration of the caprolactam causing the further improvement of the refining difficulty, and enabling the caprolactam finally obtained to have a higher purity, while achieving a higher refining yield. In addition, adopting the method of the present invention, organic impurities (such as aromatic amines, phenazines, carbazoles) containing O and N elements and conjugated large π bonds in the cyclohexanone oxime gas phase rearrangement product, as well as organic impurities containing unsaturated bonds, can be preferably removed, thereby obtaining a high-quality caprolactam refined product with low platinum-cobalt color and low potassium permanganate value, which can better meet the polymerization spinning processing requirements.

[0010] Preferably, in step S4, the nitric acid-modified activated carbon has a mesh size of 8 to 60 meshes and a specific surface area of not less than 900 m 2 / g, the proportion of mesopore volume is not less than 40%, the average pore diameter is not less than 2nm, the iodine value is higher than 1000mg / g, and the methylene blue value is higher than 15mL / 0.1g.

[0011] Furthermore, the mesh size of the nitric acid-modified activated carbon is 12 to 40 meshes, the mesopore volume accounts for more than 50%, the iodine value is more than 1100 mg / g, and the methylene blue value is more than 16.5 mL / 0.1 g.

[0012] The mesh size, specific surface area, pore structure, iodine value and methylene blue value of nitric acid modified activated carbon will affect its removal effect on organic polar impurities containing O, N elements and unsaturated bonds in the gas phase rearrangement product of cyclohexanone oxime. After a large number of screening, experiments and machine learning, the present invention team found that when the nitric acid modified activated carbon meets the mesh size of 8 to 60 and the specific surface area of not less than 900m 2 / g, mesopore volume ratio not less than 40%, average pore diameter not less than 2nm, iodine value higher than 1000mg / g, methylene blue value higher than 15mL / 0.1g, the removal effect of organic polar impurities containing O, N elements and unsaturated bonds in the gas phase rearrangement product of cyclohexanone oxime is better, and further preferred are mesh size 12-40 mesh, mesopore volume ratio higher than 50%, iodine value higher than 1100mg / g, and methylene blue value higher than 16.5mL / 0.1g.

[0013] Preferably, in step S4, the preparation step of the nitric acid-modified activated carbon comprises: soaking the activated carbon in a 1-5 mol / L nitric acid solution for 1-12 hours, and separating the product to obtain the nitric acid-modified activated carbon.

[0014] Preferably, in step S4, the activated carbon is at least one of powdered carbon, granular carbon and columnar carbon.

[0015] Furthermore, the granular carbon is at least one of wood charcoal, coal-based charcoal, coconut shell charcoal and fruit shell charcoal.

[0016] Preferably, in step S4, the adsorption impurity removal is carried out in a multi-stage adsorption impurity removal manner, with the temperature of each stage being 30-60° C. and the duration being 0.5-4 h.

[0017] Preferably, in steps S2 and S3, the organic solvent I and the organic solvent II are independently selected from at least one of aromatic hydrocarbons and halogenated hydrocarbons.

[0018] Furthermore, the aromatic hydrocarbon is at least one of benzene, toluene and xylene, and the halogenated hydrocarbon is at least one of dichloromethane, chloroform and 1,2-dichloroethane.

[0019] Preferably, in step S2, the water washing method is a two-stage continuous washing method, the volume ratio of the organic solution to water in the first stage is 2.5-15:1, the volume ratio of the organic solution to water in the second stage is 15-40:1, the equilibrium time in each stage is 10-60 minutes, and the temperature is 25-30°C; after the crude caprolactam is dissolved in the organic solvent I, the concentration of the crude caprolactam in the obtained organic solution is 10-30wt%.

[0020] The above-mentioned "two-stage continuous washing" means that after the crude caprolactam is dissolved in the organic solvent I, water is added to perform the first-stage washing, and water is further added to the obtained organic phase to perform the second-stage washing.

[0021] Furthermore, in step S2, during the water washing process, the volume ratio of the organic solution to water in the first stage is 5 to 10:1, the volume ratio of the organic solution to water in the second stage is 15 to 30:1, the equilibrium time in each stage is 20 to 30 minutes, and the temperature is 25 to 30°C; after the crude caprolactam is dissolved in the organic solvent I, the concentration of the crude caprolactam in the obtained organic solution is 20 to 30 wt%.

[0022] Preferably, in step S2, after washing with water to remove water-soluble impurities, the caprolactam in the aqueous phase is extracted and recovered by using organic solvent III, and the extracted caprolactam is combined with the organic phase obtained after washing with water to remove water-soluble impurities, and then the concentration is performed.

[0023] Furthermore, in the process of recovering caprolactam in the aqueous phase, the organic solvent III is an aromatic hydrocarbon and / or a halogenated hydrocarbon, and the volume ratio of the organic solvent III to the aqueous phase is 2 to 10:1, more preferably 2 to 5:1.

[0024] Preferably, in step S3, the washing method of the organic solvent II is three-stage continuous washing, the volume ratio of the aqueous solution to the organic solvent II in the first and second stages is 15-30:1, the volume ratio of the aqueous solution to the organic solvent II in the third stage is 30-50:1, the equilibrium time in each stage is 10-60 minutes, and the temperature is 25-30°C; after the preliminary refined product is dissolved in water, the concentration of the preliminary refined product in the obtained aqueous solution is 10-50wt%.

[0025] The above-mentioned "three-stage continuous washing" means: after the preliminary refined product is dissolved in water, organic solvent II is added for the first stage washing, organic solvent II is added to the obtained aqueous phase for the second stage washing, and organic solvent II is added to the aqueous phase obtained after the second stage washing for the third stage washing.

[0026] Furthermore, in step S3, during the washing process of the organic solvent II, the volume ratio of the aqueous solution to the organic solvent II in the first stage is 15 to 20:1, the volume ratio of the aqueous solution to the organic solvent II in the second stage is 20 to 30:1, and the volume ratio of the aqueous solution to the organic solvent II in the third stage is 40 to 50:1. The equilibrium time in each stage is 20 to 30 minutes, and the temperature is 25 to 30°C; after the preliminary refined product is dissolved in water, the concentration of the preliminary refined product in the obtained aqueous solution is 20 to 30 wt%.

[0027] Preferably, in step S3, after washing with organic solvent II to remove oil-soluble impurities, caprolactam in the organic phase is recovered by water extraction and combined with the aqueous phase obtained after washing with organic solvent II to remove oil-soluble impurities.

[0028] Furthermore, in the process of recovering caprolactam in the organic phase, the volume ratio of water to the organic phase is 5 to 20:1, more preferably 5 to 10:1.

[0029] Furthermore, in steps S2 and S3, the water washing and organic solvent washing are performed using a sieve plate extraction tower or a centrifugal extraction tower.

[0030] Preferably, in step S1, the desolvation conditions are: first desolvation at 70-80°C and -0.05-0.1 MPa until no obvious solvent evaporates, and then desolvation at 130-150°C and -0.05-0.1 MPa until caprolactam flows out.

[0031] Preferably, in step S4, the dehydration conditions are: temperature 70-80°C, air pressure -50--100 kPa.

[0032] Compared with the prior art, the present invention has the following advantages: (1) The method of the present invention can effectively remove impurities in the gas-phase rearrangement product of cyclohexanone oxime, and the risk of caprolactam deterioration during the refining process is low, and a higher refining yield can be achieved. The obtained caprolactam refined product has high purity, low platinum-cobalt chromaticity, extinction value and potassium permanganate value, and can better meet the requirements of polymerization spinning processing.

[0033] (2) The method of the present invention does not require high-temperature rectification, high-temperature distillation or fractional crystallization, the entire refining process is relatively streamlined, and the energy consumption of the equipment is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FTIR spectra of activated carbon (AC), hypochlorous acid modified activated carbon (AC-1M HClO) and nitric acid modified activated carbon (AC-1MHNO3). DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the embodiments.

[0036] Overall embodiment A method for refining a product of cyclohexanone oxime gas phase rearrangement comprises the following steps: S1: desolvating the gas-phase rearrangement product of cyclohexanone oxime to obtain crude caprolactam; S2: dissolving the crude caprolactam in organic solvent I, washing with water to remove water-soluble impurities, and concentrating to obtain a preliminary refined product; S3: dissolving the preliminary refined product in water and washing with organic solvent II to remove oil-soluble impurities to obtain a crude caprolactam aqueous solution; S4: The crude caprolactam aqueous solution is adsorbed and impurities removed by nitric acid-modified activated carbon, and then dehydrated to obtain a refined caprolactam product.

[0037] In some specific embodiments, in step S1, the desolvation conditions are: first desolvation at 70-80°C and -0.05-0.1 MPa until no obvious solvent evaporates, and then desolvation at 130-150°C and -0.05-0.1 MPa until caprolactam flows out.

[0038] In some specific embodiments, in steps S2 and S3, the organic solvent I and the organic solvent II are independently selected from at least one of aromatic hydrocarbons and halogenated hydrocarbons; the aromatic hydrocarbon is at least one of benzene, toluene and xylene, and the halogenated hydrocarbon is at least one of dichloromethane, chloroform and 1,2-dichloroethane.

[0039] In some specific embodiments, in step S2, the water washing method is a two-stage continuous washing method, the volume ratio of the organic solution to water in the first stage is 2.5 to 15:1, the volume ratio of the organic solution to water in the second stage is 15 to 40:1, the equilibrium time in each stage is 10 to 60 minutes, and the temperature is 25 to 30°C; after the crude caprolactam is dissolved in the organic solvent I, the concentration of the crude caprolactam in the obtained organic solution is 10 to 30 wt%.

[0040] In some specific embodiments, in step S2, after washing with water to remove water-soluble impurities, the caprolactam in the aqueous phase is extracted and recovered by an organic solvent III, and the extracted product is combined with the organic phase obtained after washing with water to remove water-soluble impurities, and then the concentration is performed; in the process of recovering the caprolactam in the aqueous phase, the organic solvent III is an aromatic hydrocarbon and / or a halogenated hydrocarbon, and the volume ratio of the organic solvent III to the aqueous phase is 2 to 10:1, more preferably 2 to 5:1.

[0041] In some specific embodiments, in step S3, the washing method of the organic solvent II is three-stage continuous washing, the volume ratio of the aqueous solution to the organic solvent II in the first and second stages is 15-30:1, the volume ratio of the aqueous solution to the organic solvent II in the third stage is 30-50:1, the equilibrium time in each stage is 10-60 minutes, and the temperature is 25-30°C; after the preliminary refined product is dissolved in water, the concentration of the preliminary refined product in the obtained aqueous solution is 10-50wt%.

[0042] In some specific embodiments, in step S3, after washing with organic solvent II to remove oil-soluble impurities, caprolactam in the organic phase is recovered by water extraction and combined with the aqueous phase obtained after washing with organic solvent II to remove oil-soluble impurities; in the process of recovering caprolactam in the organic phase, the volume ratio of water to organic phase is 5 to 20:1, more preferably 5 to 10:1.

[0043] In some specific embodiments, in step S4, the step of preparing the nitric acid-modified activated carbon includes: soaking the activated carbon in a 1-5 mol / L nitric acid solution for 1-12 hours, and separating the product to obtain the nitric acid-modified activated carbon.

[0044] In some specific embodiments, in step S4, the activated carbon is at least one of powdered carbon, granular carbon and columnar carbon; and the granular carbon is at least one of wood charcoal, coal-based charcoal, coconut shell charcoal and fruit shell charcoal.

[0045] In some embodiments, in step S4, the mesh size of the nitric acid-modified activated carbon is 8 to 60 meshes, and the specific surface area is not less than 900 m 2 / g, the proportion of mesopore volume is not less than 40%, the average pore diameter is not less than 2nm, the iodine value is higher than 1000mg / g, and the methylene blue value is higher than 15mL / 0.1g.

[0046] In some specific embodiments, in step S4, the adsorption removal is performed in a multi-stage adsorption manner, with the temperature of each stage being 30-60° C. and the duration being 0.5-4 h.

[0047] In some specific embodiments, in step S4, the dehydration conditions are: temperature 70-80° C., air pressure -50--100 kPa. Specific embodiments The present invention is described below by way of specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, any changes and advantages that can be imagined by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used herein are conventional in the art and can be obtained from conventional commercial sources. The methods used herein are conventional in the art, unless otherwise specified.

[0050] Example 1 The nitric acid-modified activated carbon used in this example was prepared according to the following steps: (1) After washing the fruit shell activated carbon with water until there is no powdered carbon, it is dried in an oven at 110°C to constant weight, and then the fruit shell activated carbon with mesh size of 12 to 40 is sieved out and immersed in 25 times the equivalent of 1 mol / L nitric acid solution, stirred at 25°C for 4 h, filtered, washed with water until neutral, and dried in an oven at 120°C to constant weight to obtain nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40, specific surface area of 1680 m 2 / g, the mesopore volume accounts for 79.2%, the average pore diameter is 3.42nm, the iodine value is 1310mg / g, and the methylene blue value is 18.5mL / 0.1g).

[0051] (2) After washing the coconut shell activated carbon with water until there is no powdered carbon, it is dried in an oven at 110°C to constant weight, and then 12-40 mesh coconut shell activated carbon is sieved out and immersed in 25 times the equivalent of 1 mol / L nitric acid solution, stirred at 25°C for 4 h, filtered, washed with water until neutral, and dried in an oven at 120°C to constant weight to obtain nitric acid-modified coconut shell activated carbon (mesh size of 12-40 mesh, specific surface area of 1118 m 2 / g, the mesopore volume accounts for 73.9%, the average pore diameter is 3.30nm, the iodine value is 1260mg / g, and the methylene blue value is 16.5mL / 0.1g).

[0052] (3) After washing the coconut shell activated carbon with water until there is no powdered carbon, it is dried in an oven at 110°C to constant weight, and then 12-40 mesh coconut shell activated carbon is sieved out and immersed in 25 times the equivalent of 1 mol / L nitric acid solution, stirred at 25°C for 4 h, filtered, washed with water until neutral, and dried in an oven at 120°C to constant weight to obtain nitric acid-modified coconut shell activated carbon (mesh size of 12-40 mesh, specific surface area of 1050 m 2 / g, the mesoporous volume accounts for 54.2%, the average pore size is 2.10nm, the iodine value is 1161mg / g, the methylene blue value is 18mL / 0.1g), and its Fourier transform infrared spectrum (FTIR) is shown in Figure 1 ( Figure 1 (In the table: "AC" refers to coconut shell activated carbon before nitric acid modification according to this step; "AC-1M HClO" refers to hypochlorous acid-modified coconut shell activated carbon obtained by replacing the 1 mol / L nitric acid solution in this step with a 1 mol / L hypochlorous acid solution.) Figure 1 It shows that nitric acid modification can effectively increase the content of carboxylate functional groups in activated carbon, and the effect is significantly better than hypochlorous acid modification.

[0053] In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated. The ethanol was then continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain a crude caprolactam product. The composition of the crude caprolactam was measured to be: 94.5 wt% caprolactam, 0.7 wt% water and ethanol, and 4.8 wt% impurities.

[0054] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution having a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water in a volume ratio of 7.5:1, allowed to stand for 20 minutes at 30°C, and the aqueous phase and the organic phase are separated, which are recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water in a volume ratio of 20:1, allowed to stand for 30 minutes at 30°C, and the aqueous phase and the organic phase are separated, which are recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane in a volume ratio of 1:5, allowed to stand for 15 minutes at 30°C, and the aqueous phase is separated from the organic phase. After mixing the obtained organic phase with the secondary organic solution, the mixture is concentrated to dryness by rotary evaporation at 40° and 200mbar to obtain a preliminary refined product.

[0055] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0056] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, mesoporous pore volume accounted for 54.2%, average pore diameter was 2.10nm, iodine value was 1161mg / g, methylene blue value was 18mL / 0.1g), and residence time was 40min. The three-stage cascade adsorption adopted a bottom-in, top-out method at a temperature of 30°C. After completion of the above three-stage adsorption, a caprolactam aqueous solution was obtained.

[0057] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0058] Example 2 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0059] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 30wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 30°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, and the obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0060] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0061] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0062] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0063] Example 3 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0064] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 25°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, the obtained organic phase is mixed with the secondary organic solution, and concentrated to obtain a preliminary refined product.

[0065] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 25°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 25°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 25°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0066] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0067] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0068] Example 4 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0069] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water in a volume ratio of 10:1, allowed to stand and equilibrate at 30°C for 20 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water in a volume ratio of 30:1, allowed to stand and equilibrate at 30°C for 30 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane in a volume ratio of 1:5, allowed to stand and equilibrate at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, the obtained organic phase is mixed with the secondary organic solution, and concentrated to obtain a preliminary refined product.

[0070] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0071] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0072] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0073] Example 5 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0074] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 30°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, and the obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0075] S3: The preliminary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the preliminary refined product. The solution was then mixed with dichloromethane at a volume ratio of 20:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 50:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0076] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0077] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0078] Example 6 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0079] S2: The crude caprolactam is mixed with benzene to prepare an organic solution having a crude caprolactam concentration (content) of 25 wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, allowed to stand and equilibrate at 30°C for 20 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, allowed to stand and equilibrate at 30°C for 30 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the secondary aqueous phase and the secondary organic solution, respectively. The primary aqueous phase and the secondary aqueous phase are combined, mixed with benzene at a volume ratio of 1:5, allowed to stand and equilibrate at 30°C for 15 minutes, and the aqueous phase and the organic phase are separated. The obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0080] S3: The preliminary refined product is mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the preliminary refined product. The solution is then mixed with benzene at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution is mixed with benzene at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution is mixed with benzene at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases are separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases are combined and mixed with water at a volume ratio of 1:7.5 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and the resulting aqueous phase is mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0081] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0082] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0083] Example 7 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0084] S2: The crude caprolactam is mixed with toluene to prepare an organic solution having a crude caprolactam concentration (content) of 25 wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, allowed to stand and equilibrate at 30°C for 20 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, allowed to stand and equilibrate at 30°C for 30 minutes, and the aqueous phase and the organic phase are separated, which are recorded as the secondary aqueous phase and the secondary organic solution, respectively. The primary aqueous phase and the secondary aqueous phase are combined, mixed with toluene at a volume ratio of 1:5, allowed to stand and equilibrate at 30°C for 15 minutes, and the aqueous phase and the organic phase are separated. The obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0085] S3: The primary refined product is mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution is then mixed with toluene at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution is mixed with toluene at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution is mixed with toluene at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases are separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases are combined and mixed with water at a volume ratio of 1:7.5 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases are separated and the resulting aqueous phase is mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0086] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0087] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0088] Example 8 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0089] S2: The crude caprolactam is mixed with 1,2-dichloroethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 30°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with 1,2-dichloroethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, the obtained organic phase is mixed with the secondary organic solution, and concentrated to obtain a preliminary refined product.

[0090] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with 1,2-dichloroethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with 1,2-dichloroethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with 1,2-dichloroethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0091] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0092] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0093] Example 9 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0094] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 30°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, and the obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0095] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0096] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 2h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 2h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 30°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0097] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0098] Example 10 In this example, the product of caprolactam prepared by vapor-phase Beckmann rearrangement of cyclohexanone oxime (containing 30 wt % of caprolactam, 66 wt % of ethanol, 0.8 wt % of water, and 3.2 wt % of impurities) was purified according to the following steps: S1: The cyclohexanone oxime gas phase rearrangement product was subjected to rotary evaporation to remove ethanol at 75°C and -0.1 MPa until no obvious ethanol was evaporated, and then the ethanol was continued to be removed at 130°C and -0.1 MPa until caprolactam flowed out to obtain crude caprolactam.

[0099] S2: The crude caprolactam is mixed with dichloromethane to prepare an organic solution with a crude caprolactam concentration (content) of 25wt% and a temperature of 30°C. The organic solution is mixed with water at a volume ratio of 7.5:1, and allowed to stand at 30°C for 20 minutes. The aqueous phase and the organic phase are separated and recorded as the primary aqueous phase and the primary organic solution, respectively. The primary organic solution is mixed with water at a volume ratio of 20:1, and allowed to stand at 30°C for 30 minutes. The aqueous phase and the organic phase are separated and recorded as the secondary aqueous phase and the secondary organic solution, respectively. After combining the primary aqueous phase and the secondary aqueous phase, they are mixed with dichloromethane at a volume ratio of 1:5, allowed to stand at 30°C for 15 minutes, the aqueous phase and the organic phase are separated, and the obtained organic phase is mixed with the secondary organic solution and concentrated to obtain a preliminary refined product.

[0100] S3: The primary refined product was mixed with water to prepare an aqueous solution with a concentration (content) of 20 wt% of the primary refined product. The solution was then mixed with dichloromethane at a volume ratio of 15:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the primary aqueous solution and primary organic phase, respectively. The primary aqueous solution was mixed with dichloromethane at a volume ratio of 30:1 and allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and recorded as the secondary aqueous solution and secondary organic phase, respectively. The secondary aqueous solution was mixed with dichloromethane at a volume ratio of 40:1 and allowed to equilibrate at 30°C for 30 minutes. The aqueous and organic phases were separated and recorded as the tertiary aqueous solution and tertiary organic phase, respectively. The primary, secondary, and tertiary organic phases were combined and mixed with water at a volume ratio of 1:7.5. The solution was allowed to equilibrate at 30°C for 20 minutes. The aqueous and organic phases were separated and the resulting aqueous phase was mixed with the tertiary aqueous solution to obtain a crude caprolactam aqueous solution.

[0101] S4: The crude caprolactam aqueous solution is transported to the adsorption tower for three-stage adsorption and impurity removal. The adsorbent used in the first stage of adsorption is nitric acid-modified fruit shell activated carbon (mesh size of 12 to 40 mesh, specific surface area of 1680m 2 / g, the mesopore volume accounts for 79.2%, the average pore size is 3.42nm, the iodine value is 1310mg / g, the methylene blue value is 18.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the second stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1118m 2 / g, the mesopore volume accounts for 73.9%, the average pore size is 3.30nm, the iodine value is 1260mg / g, the methylene blue value is 16.5mL / 0.1g, the preparation method is the same as that in Example 1), and the residence time is 1h; the adsorbent used in the third stage adsorption is nitric acid modified coconut shell activated carbon (mesh size is 12-40 mesh, specific surface area is 1050m 2 / g, the mesopore volume accounts for 54.2%, the average pore diameter is 2.10 nm, the iodine value is 1161 mg / g, and the methylene blue value is 18 mL / 0.1 g. The preparation method is the same as in Example 1), and the residence time is 40 min. The three-stage series adsorption adopts a bottom-in, top-out method, and the temperature is 50°C. After completing the above three-stage adsorption, a caprolactam aqueous solution is obtained.

[0102] S5: The caprolactam aqueous solution is transported to an evaporation tower for dehydration. The tower pressure is set to -80 kPa, the tower bottom temperature is set to 75° C., and the tower top temperature is set to 50° C. to obtain a refined caprolactam product.

[0103] Comparative Example 1 The only difference between this comparative example and Example 1 is that during the preparation of nitric acid-modified activated carbon, the concentration of the nitric acid solution in steps (1) to (3) was changed from 1 mol / L to 0.1 mol / L, and the stirring time was changed from 4 h to 24 h. The remaining steps were the same as in Example 1.

[0104] Comparative Example 2 The only difference between this comparative example and Example 1 is that during the preparation of nitric acid-modified activated carbon, the 1 mol / L nitric acid solution in steps (1) to (3) was replaced with a 1 mol / L hydrogen peroxide solution. The remaining steps were the same as in Example 1.

[0105] Comparative Example 3 The only difference between this comparative example and Example 1 is that step S2 is not performed, and the crude caprolactam obtained in step S1 is directly subjected to step S3. The remaining steps are the same as those in Example 1.

[0106] Comparative Example 4 This comparative example differs from Example 1 only in that, in step S4, the adsorbent used in the first-stage adsorption was replaced with LX-160 ion exchange resin instead of nitric acid-modified fruit shell activated carbon; the adsorbent used in the second-stage adsorption was replaced with LX-925 ion exchange resin instead of nitric acid-modified coconut shell activated carbon; and the adsorbent used in the third-stage adsorption was replaced with SAD502 ion exchange resin instead of nitric acid-modified coconut shell activated carbon. The residence time for each stage was 1 hour. The remaining steps were the same as in Example 1.

[0107] Comparative Example 5 The difference between this comparative example and Example 1 is that in step S4, the adsorbent used in the three-stage adsorption is nitric acid-modified fruit shell activated carbon with a mesh size of 12 to 40 and a specific surface area of 858 m 2 / g, the mesopore volume accounts for 13.5%, the average pore size is 1.4nm, the iodine value is 978mg / g, and the methylene blue value is 11.62mL / 0.1g; the preparation method of the nitric acid-modified fruit shell activated carbon is carried out according to step (1) in Example 1, except that the specifications of the fruit shell activated carbon used are changed.

[0108] Comparative Example 6 The only difference between this comparative example and Example 1 is that in step S4, the adsorbent used in the three-stage adsorption is nitric acid-modified fruit shell activated carbon with a mesh size of 12 to 40 and a specific surface area of 1194 m 2 / g, the mesopore volume accounts for 44.1%, the average pore size is 1.4nm, the iodine value is 868mg / g, and the methylene blue value is 13.35mL / 0.1g; the preparation method of the nitric acid-modified fruit shell activated carbon is carried out according to step (1) in Example 1, except that the specifications of the fruit shell activated carbon used are changed.

[0109] Test Case According to the refining method in each embodiment and comparative example, after continuous production for 240 hours, the quality of the obtained caprolactam refined product was evaluated and the refining yield was calculated as follows: (1) Purity: The purity of the caprolactam purified product was analyzed by Agilent gas chromatography 7890GC using HP-INNOWax (60m×320μm×0.5μm) as the chromatographic column with a minimum detection limit of 1μg / g.

[0110] (2) Platinum-cobalt chromaticity: Add 50 g of the sample to a 300 mL conical flask, add 50 mL of deionized water, shake until the sample is completely dissolved, and let stand until bubbles disappear to obtain a 50 wt % aqueous solution of purified caprolactam. Measure the color of the 50 wt % aqueous solution of purified caprolactam relative to deionized water using a spectrophotometer at a wavelength of 390 nm.

[0111] (3) Extinction value: Add 50 g of the sample to a 300 mL conical flask, add 50 mL of deionized water, shake until the sample is completely dissolved, and let stand until bubbles disappear to obtain a 50 wt % aqueous solution of purified caprolactam. Measure the color of the 50 wt % aqueous solution of purified caprolactam relative to deionized water using a spectrophotometer at a wavelength of 290 nm.

[0112] (4) Potassium permanganate value: Weigh 3g of sample into a dry 100mL colorimetric tube. Dilute to the mark with deionized water and shake well. Place the tube in a constant temperature water bath at 25±0.5°C for at least 15 minutes. Use a pipette to add 2mL of 0.01mol / L potassium permanganate standard solution, immediately start a stopwatch, shake well, and return the tube to the water bath. After 10 minutes ± 10 seconds, measure the potassium permanganate value relative to deionized water using a spectrophotometer at a wavelength of 420nm.

[0113] (5) Yield: The yield is calculated according to the following formula: The quality evaluation results and the purification yields of the purified caprolactam products in the examples and comparative examples are shown in Table 1.

[0114] Table 1 Analyzing the test results in Table 1, we can see that: (1) Compared with Example 1, the chromaticity and potassium permanganate value of the caprolactam refined products obtained in Comparative Examples 1, 2 and 4 are larger. The reasons are analyzed as follows: Impurities that affect color are primarily organic impurities containing O and N elements and conjugated large π bonds, such as aromatic amines, phenazines, and carbazoles. These impurities are typically polar organic impurities. Impurities that affect potassium permanganate values are primarily organic impurities containing unsaturated bonds.

[0115] In Example 1, activated carbon was modified with nitric acid for impurity adsorption and removal. Nitric acid modification increases the content of acidic oxygen-containing functional groups in the activated carbon, improving its hydrophilicity and affinity for polar organic compounds. Consequently, it effectively removes organic polar impurities containing O and N elements and unsaturated bonds, including aromatic amines, phenazines, and carbazoles. However, the low-concentration nitric acid solution in Comparative Example 1 and the hydrogen peroxide solution in Comparative Example 2 provide relatively mild modifications to the activated carbon, resulting in weaker adsorption of these impurities. The ion exchange resin used in Comparative Example 4, suitable for removing organic and inorganic ions, also exhibits weaker adsorption of these impurities. Consequently, the refined caprolactam products obtained in these Comparative Examples exhibit higher chroma and potassium permanganate values.

[0116] (2) Compared with Example 1, the chromaticity and potassium permanganate value of the caprolactam refined product obtained in Comparative Example 3 are larger. The reasons are analyzed as follows: In Example 1, by dissolving the crude caprolactam in an organic solvent and then washing with water, water-soluble impurities including oximes, alcohols, lower aliphatic amines, amides, and imidazoles, as well as slightly soluble impurities including ketones, were removed. In Comparative Example 3, although some water-soluble impurities were removed during the adsorption removal process, the effect was limited.

[0117] (3) Compared with Example 1, the chromaticity, extinction value and potassium permanganate value of the caprolactam refined products obtained in Comparative Examples 5 and 6 are larger. The reasons are analyzed as follows: In the present invention, adsorption removal can remove residual organic polar impurities containing O and N elements and unsaturated bonds, including aromatic amines, phenazines, and carbazoles. The mesh size, specific surface area, pore structure, iodine value, and methylene blue value of the nitric acid-modified activated carbon used in this process can affect the removal of these impurities.

[0118] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for refining a product of cyclohexanone oxime gas phase rearrangement, characterized in that: The following steps are involved: S1: desolvating the gas-phase rearrangement product of cyclohexanone oxime to obtain crude caprolactam; S2: dissolving the crude caprolactam in organic solvent I, washing with water to remove water-soluble impurities, and concentrating to obtain a preliminary refined product; S3: dissolving the preliminary refined product in water and washing with organic solvent II to remove oil-soluble impurities to obtain a crude caprolactam aqueous solution; S4: The crude caprolactam aqueous solution is adsorbed and impurities removed by nitric acid-modified activated carbon, and then dehydrated to obtain a refined caprolactam product.

2. The product purification method according to claim 1, characterized in that In step S4, the mesh size of the acid-modified activated carbon is 8 to 60 meshes, and the specific surface area is not less than 900 m 2 / g, the proportion of mesopore volume is not less than 40%, the average pore diameter is not less than 2 nm, the iodine value is higher than 1000 mg / g, and the methylene blue value is higher than 15 mL / 0.1 g.

3. The product purification method according to claim 1 or 2, characterized in that In step S4, the preparation step of the nitric acid-modified activated carbon includes: soaking the activated carbon in a 1-5 mol / L nitric acid solution for 1-12 hours, separating the product, and obtaining the nitric acid-modified activated carbon.

4. The product purification method according to claim 1 or 2, characterized in that: In step S4, the adsorption impurity removal method is multi-stage adsorption impurity removal, the temperature of each stage is 30-60° C., and the duration is 0.5-4 h.

5. The product purification method according to claim 1, characterized in that In steps S2 and S3, the organic solvent I and the organic solvent II are independently selected from at least one of aromatic hydrocarbons and halogenated hydrocarbons.

6. The product purification method according to claim 1, characterized in that In step S2, the water washing method is a two-stage continuous washing method, the volume ratio of the organic solution to water in the first stage is 2.5~15:1, the volume ratio of the organic solution to water in the second stage is 15~40:1, the equilibrium time in each stage is 10~60 min, and the temperature is 25~30°C; after the crude caprolactam is dissolved in the organic solvent I, the concentration of the crude caprolactam in the obtained organic solution is 10~30wt%.

7. The product purification method according to claim 1, characterized in that In step S2, after washing with water to remove water-soluble impurities, the caprolactam in the aqueous phase is extracted and recovered by using an organic solvent III, and the extracted caprolactam is combined with the organic phase obtained after washing with water to remove water-soluble impurities, and then concentrated.

8. The product purification method according to claim 1, characterized in that: In step S3, the washing method of the organic solvent II is three-stage continuous washing, the volume ratio of the aqueous solution to the organic solvent II in the first and second stages is 15-30:1, the volume ratio of the aqueous solution to the organic solvent II in the third stage is 30-50:1, the equilibrium time in each stage is 10-60 min, and the temperature is 25-30°C; after the preliminary refined product is dissolved in water, the concentration of the preliminary refined product in the obtained aqueous solution is 10-50wt%.

9. The product purification method according to claim 1, characterized in that: In step S3, after washing with organic solvent II to remove oil-soluble impurities, caprolactam in the organic phase is recovered by water extraction and combined with the aqueous phase obtained after washing with organic solvent II to remove oil-soluble impurities.

10. The product purification method according to claim 1, characterized in that: In step S1, the desolventizing conditions are: first desolventizing at 70-80°C and -0.05-0.1 MPa until no obvious solvent evaporates, and then desolventizing at 130-150°C and -0.05-0.1 MPa until caprolactam flows out; in step S4, the dehydration conditions are: temperature 70-80°C, air pressure -50-100 kPa.

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