132results about "Lactams separation/purification" patented technology

The invention relates to the field of caprolactam production, and discloses a green and efficient production process and device. The process comprises the following steps: continuously oximating cyclohexanone and hydroxylamine in a microreactor under the catalysis of mesoporous silica solid acid; carrying out gas phase rearrangement on cyclohexanone-oxime in the presence of a ZSM-5 molecular sieve under the assistance of microwaves; coupling, rectifying and purifying the crude product through a four-stage molecular sieve membrane; and performing catalytic cracking on the by-product to obtain N2 / H2O and recycling. The device comprises a micro-reaction unit, a microwave-radial reactor, a membrane coupling rectifying tower group and a tail gas cracking unit. Zero emission of ammonium sulfate is achieved, the product purity is larger than or equal to 99.95%, and energy consumption is reduced by 45%.

The invention discloses a hydroxylamine sulfate preparation method, which comprises: S1, carrying out analysis on caprolactam sulfate with water or a hydroxylamine sulfate aqueous solution to obtain a caprolactam sulfuric acid aqueous solution; extracting and separating the caprolactam sulfuric acid aqueous solution by using an extracting agent, conveying an extraction phase caprolactam organic solution to a caprolactam device for treatment, and entering a step S2 into a raffinate phase sulfuric acid aqueous solution or hydroxylamine sulfate and sulfuric acid aqueous solution; s2, adding ketoxime and a sulfuric acid aqueous solution or hydroxylamine sulfate and the sulfuric acid aqueous solution to generate a hydrolysis reaction to generate a hydroxylamine sulfate aqueous solution and ketone, and after ketone separation, sending the ketoxime to a ketoxime preparation device; s3, carrying out steam stripping separation on the hydroxylamine sulfate aqueous solution, sending unreacted ketoxime to the step S2 to participate in a hydrolysis reaction, and carrying out concentration crystallization, centrifugal filtration and drying dehydration on the hydroxylamine sulfate aqueous solution to obtain hydroxylamine sulfate; and S4, returning part of hydroxylamine sulfate raffinate subjected to centrifugal filtration to the step S1 for resolving caprolactam sulfate, and carrying out oximation reaction treatment on the residual hydroxylamine sulfate raffinate and ketone.

A process for preparing a liquid high-purity ε-caprolactam stream ST, comprising preparing a liquid stream SC comprising ε-caprolactam, said preparing comprising depolymerizing a material M comprising polyamide 6, said liquid stream SC further comprising one or more oxidizable organic impurity compounds X, wherein the stream SC has an ε-caprolactam purity ΩGC(SC) of at least 99 %; providing a stream SO comprising at least one permanganate; preparing an oxidation reaction educt mixture MOE from the stream SC and the stream SO, and subjecting the mixture MOE to oxidation reaction conditions, obtaining an oxidation reaction product stream SP comprising ε-caprolactam, further comprising one or more oxidation products Y obtained from the oxidation of at least a part of the one or more compounds X, and optionally further comprising a part of the one or more organic compounds X; separating at least a part of the one or more oxidation products Y and optionally at least a part of organic compound X from the stream SP, obtaining the stream ST exhibiting an ε-caprolactam purity ΩGC(ST) of at least 99.5 % with ΩGC(ST) > ΩGC(SC), and an APHA value ΩGC(ST) of at most 10.

The present invention relates to the chemical industry field, and particularly relates to a method for synthesizing valerolactam. The steps are as follows: cyclopentanone and the reaction auxiliary cyclohexanone are mixed in a certain proportion, and then through ammoximation reaction, Beckmann rearrangement reaction, hydrolysis and neutralization reaction, and then through separation, valerolactam is obtained. The method of the present invention has a high atom utilization rate and a high product extraction rate, and has the prospect of actual industrial production.

The invention relates to the technical field of caprolactam production, in particular to a fixed bed hydrogenation catalyst and a preparation method thereof.The fixed bed hydrogenation catalyst at least comprises an activated carbon-based carrier and a nickel salt solution, the specific surface area of the activated carbon-based carrier is larger than or equal to 400 m < 2 > / g, the pore volume of the activated carbon-based carrier is larger than or equal to 0.3 mL / g, and the strength of the activated carbon-based carrier is larger than or equal to 90%; activated carbon is selected as a carrier, the carrier is shaped into an amorphous shape, a cylindrical shape, a clover shape and the like, the carrier with high strength and high specific surface area is obtained, and the acid-resistant, alkali-resistant and water-resistant fixed bed hydrogenation catalyst is obtained by carrying out load modification, drying and activation on the carrier. And the application requirement of unsaturated hydrocarbon hydrogenation reaction of the crude caprolactam aqueous solution in a caprolactam device is met.

The present application belongs to the technical field of recycling of waste textiles, and particularly relates to a method for recycling waste nylon textiles, comprising: mechanically crushing the waste nylon textiles to obtain nylon fragments; mixing the nylon fragments, polyacrylic acid, metal or its compound, and then, under inert atmosphere and stirring, heating to 60-120 DEG C for 0.5-2 hours, and then, continuously heating to 220-300 DEG C, and catalytically depolymerizing under 1-5 MPa to obtain depolymerate; wherein the metal element of the metal or its compound is a metal having coordination ability with carbonyl; purifying the depolymerate to obtain caprolactam. The present application uses one-step mixing and two-step heating process, and the catalyst exists in the form of coexistence of metal coordination sites and carboxyl, so that the catalyst simultaneously plays the metal coordination activation role and the amide bond breaking and exchange reaction participated by carboxylic acid in the depolymerization process, forming a synergistically promoted efficient depolymerization mechanism, and effectively improving the efficiency of catalytic depolymerization.

The invention relates to the technical field of chemical engineering, and discloses an amide oil separation and ammonium sulfate crystallization integrated device. Comprising a neutralization reactor, a settling separation tank, a pre-crystallization solution tank, a DTB crystallizer, a centrifugal machine, a settling separator, a dryer, a mother liquor tank, a condensate water tank, an amide oil decanter, an ammoximation tert-butyl alcohol tower reboiler, a mother liquor heater set, a condenser, a vacuumizing condensing unit, a stirrer set and a reactor circulating pump. The invention further comprises a process for preparing the large-particle ammonium sulfate crystal from the saturated amide oil solution, rearrangement liquid from a lactam rearrangement system and gas ammonia are added into a neutralization reactor through an external circulation pipeline, and the large-particle ammonium sulfate crystal is prepared by fully utilizing heat in the gas ammonia dissolution and neutralization reaction and crystallization process. By combining the compound additive, the seed crystal and the continuous crystallization technology, the generation of large-particle ammonium sulfate crystals is promoted, meanwhile, the crystallization process is optimized, an efficient amide oil separation and continuous crystallization mode is realized, the energy consumption is saved, and the production efficiency is improved.

A system for preventing ammonium sulfate blockage in caprolactam production comprises an elutriator and an amide oil storage tank, the elutriator is communicated with the upper portion of the amide oil storage tank through a second delivery pump, and the amide oil storage tank is communicated with a benzene extraction tower through a middle lower discharge pipeline connected with a fourth delivery pump. The lower part of the amide oil storage tank is communicated with the crystallizer through a third delivery pump, and the treatment system is characterized in that the treatment system comprises a first benzene injection pipe arranged between the elutriator and the second delivery pump and / or a second benzene injection pipe arranged between the second delivery pump and the amide oil storage tank; and benzene enters the second delivery pump through the first benzene injection pipe and / or benzene enters the amide oil storage tank through the second injection pipe. The utility model has the advantage that the problem that the pipeline is blocked due to ammonium sulfate crystallization precipitation when the amide oil is extracted can be solved.

The present invention provides an improved process for recovering ε-caprolactam from multicomponent materials, in particular multilayer films, comprising nylon 6. Furthermore, the present invention provides a plant adapted to carry out the process of the present invention, and recovered ε-caprolactam obtainable by the process of the present invention, having a product carbon footprint of less than 2.5 kg CO2 equivalent per kg purified ε-caprolactam (based on Eco Invent version 3.7.1 (region: Europe) data).

The utility model discloses equipment for recovering caprolactam in benzene residual liquid. The equipment comprises a crude benzene feeding assembly, the feeding end of the benzene distillation assembly is connected with the discharging end of the crude benzene feeding assembly, the benzene distillation assembly is used for distilling crude benzene, and the benzene distillation assembly comprises a first benzene distillation tower and a second benzene distillation tower; the benzene raffinate extraction assembly comprises a benzene raffinate extraction tower feeding cooler, the feeding end of the benzene raffinate extraction tower feeding cooler is connected with the discharging end of the benzene distillation tower II, and the benzene raffinate extraction tower feeding cooler is used for cooling benzene raffinate generated by the benzene distillation assembly; the feeding end of the benzene raffinate extraction tower is connected with the discharging end of the benzene raffinate extraction tower feeding cooler, and the benzene raffinate extraction tower is used for extracting the cooled benzene raffinate. The device is reasonable in design, the recovery rate of caprolactam in the benzene raffinate can reach 90% or above by additionally arranging the benzene raffinate extraction assembly, energy expenses such as steam and electricity are not generated, material consumption is reduced, and sewage treatment pressure can be reduced.

A continuous process for separating one or more organic compounds X from an aqueous liquid stream SL0 comprising monomeric ε-caprolactam and said one or more compounds X, the process comprising (i) providing the stream SL0; (ii) providing a non-aqueous stripping gas stream SG0 comprising at least one inert gas G; (iii) producing in a stripping unit US1 from the stream SL0 an aqueous gas stream SV1 and a liquid stream SL1; (iv) producing in a separation unit US2 from the stream SV1 an aqueous gas stream SV2 and a liquid stream SL2.

The present invention relates to a process for recovering epsilon-caprolactam from a nylon 6-containing multi-component material. The present invention provides an improved process for the recovery of epsilon-caprolactam from nylon 6-containing multi-component materials, in particular multilayer films. Furthermore, the invention provides: a plant configured to carry out the method of the invention; and the recovered [epsilon]-caprolactam obtainable by the process of the invention having a product carbon footprint of less than 2.5 kg CO2 equivalents per kg of purified [epsilon]-caprolactam.

The utility model provides an energy-saving caprolactam production device which comprises an extraction tower, the extraction tower is connected with a buffer tank through a pipeline, one side of the buffer tank is connected with a benzene-hexyl buffer tank through a pipeline, the benzene-hexyl buffer tank is connected with a reverse extraction tower through a pipeline, the reverse extraction tower is connected with a heat exchanger through a pipeline, and the heat exchanger is connected with a heat exchanger through a pipeline. The heat exchanger is connected with a heater through a pipeline, the heater is respectively connected with a first already-water preheater and a debenzolization tower through pipelines, and the debenzolization tower is respectively connected with an already-water buffer tank and a condensate tank through pipelines. According to the caprolactam energy-saving production device provided by the utility model, the use amount of low-pressure steam (t / h) can be saved by recovering the heat of the steam condensate for preheating a hexane solution, and the use amount of the low-pressure steam (t / h) can be saved by repeatedly utilizing the MVR evaporation secondary steam condensate for heat exchange and preheating the MVR evaporation secondary steam condensate with the residual liquid of the hexane extraction tower.

The application provides a purification process method and device of a lactam, wherein an oxime is subjected to a rearrangement reaction with a catalyst, the obtained lactam is purified after the rearrangement reaction, and the method comprises the following steps: extracting the lactam by using an extraction solvent to obtain a lactam solution from which the catalyst is separated, performing alkali washing and water washing on the obtained lactam solution to obtain a lactam solution after alkali washing and water washing, performing hydrogenation reaction on the obtained lactam solution again, performing crystallization separation on the lactam solution after hydrogenation to obtain a lactam product crystal, and then performing treatment on the obtained lactam product crystal by means of solvent washing, rectification, distillation or crystallization to obtain the lactam with a purity of greater than or equal to 99.9%.

The invention provides a caprolactam flash evaporation system and a flash evaporation process. The caprolactam flash evaporation system comprises a separation kettle and a flash evaporation tank which are sequentially communicated, a liquid phase outlet pipe of the flash evaporation tank is communicated with a buffer tank, a gas phase outlet pipe of the flash evaporation tank is communicated with a mixer, an outlet pipe of the mixer is communicated with a condenser, and the condenser is provided with a vacuum pump for keeping an internal vacuum state. The method has the beneficial effects that by improving a current vacuum flash evaporation system and abandoning an ejector with great water consumption, efficient utilization of steam and condensate is realized, energy conservation and improvement of environmental protection benefits are greatly promoted, and by reducing the generation amount of the steam condensate, the burden of subsequent wastewater treatment is relieved, and the production cost is reduced. The potential environmental pollution risk is reduced from the source, the green production and sustainable development goals of enterprises are favorably realized, and greater economic benefits are created for the enterprises.

This invention belongs to the field of pharmaceutical chemistry technology, specifically relating to a monopravir-caprolactam cocrystal, its preparation method, and its applications. The monopravir-caprolactam cocrystal is composed of monopravir and caprolactam in a molar ratio of 1:1.9-2.1. X-ray powder diffraction was performed using Cu-Kα radiation, with angles expressed as 2θ±1, at 6.91, 7.09, 8.38, 11.24, 12.52, 13.26, 13.87, 14.24, 15.22, 16.82, 17.31, and 1... Characteristic peaks are observed at 9.73, 20.22, 20.53, 20.84, 21.90, 22.28, 22.52, 22.95, 23.51, 23.75, 24.00, 24.31, 24.86, 25.35, 26.44, 27.41, 28.02, 28.69, 29.22, 29.84, and 30.33. Monopravir-caprolactam cocrystals can be successfully prepared by grinding and / or solution methods, and grinding and / or melting methods. The preparation process is simple, and the obtained product has high purity. Characterization has confirmed it to be a new cocrystal. Powder flowability and tableting tests revealed that the monopravir-caprolactam cocrystals provided by this invention have better flowability and tableting properties compared to monopravir crystal form I, meeting the requirements of formulation and manufacturing processes.

The present invention provides a caprolactam hydrorefining catalyst, a preparation method, and a caprolactam hydrorefining method. The caprolactam hydrorefining catalyst comprises a catalyst support and an active ingredient, Ni, supported on the catalyst support. The catalyst support comprises rare earth oxide-modified alumina, a structural additive, a binder, and a lubricant. The mass ratio of the alumina to the rare earth metal elements contained in the rare earth oxide is 15 to 50:1. A portion (40% to 70%) of the rare earth oxide-modified support is subjected to high-temperature calcination to significantly increase the support pore size, while the remaining portion (30% to 60%) serves as a binder for subsequent forming. The resulting catalyst has a large pore size and a narrow pore size distribution. When used in a fixed-bed hydrogenation reactor, the catalyst can withstand long-term corrosion from weakly acidic or weakly alkaline aqueous caprolactam solutions, maintains stable particle strength, and exhibits excellent hydrogenation performance.

The present invention provides an improved process for the recovery of ε-caprolactam from Nylon 6 comprising multi-component material, in particular multi-layered film. Further, the invention provides a plant configured to carry out the process of the invention, and the recovered e-caprolactam obtainable by the process of the invention that has a product carbon footprint of less than 2.5 kg CO2 equivalent per kg purified e-caprolactam (based on data originating from ecoinvent version 3.7.1; location: Europe).

The method comprises the following steps: (a) enabling the caprolactam aqueous solution to sequentially pass through an oximation reaction liquid heat exchanger, a primary rearrangement reaction liquid heat exchanger and a secondary rearrangement reaction liquid heat exchanger, heating the caprolactam aqueous solution by utilizing the heat of the cyclohexanone oximation reaction liquid, the primary rearrangement reaction liquid and the secondary rearrangement reaction liquid; (b) introducing the heated caprolactam aqueous solution into a second inlet of the distillation tower for connection, and separating and removing part of water through vacuum distillation to obtain a concentrated caprolactam solution; part of the concentrated solution is circulated and combined with the low-concentration caprolactam aqueous solution, and the rest of the concentrated solution is extracted to a downstream process; and (c) refluxing the water phase part extracted from the tower top of the distillation tower to the distillation tower, and extracting the other part to a downstream process for use. Through comprehensive utilization of waste heat and integrated innovation of the system, the system has remarkable advantages in the aspects of energy conservation, consumption reduction, cost control and environmental protection performance.

The invention relates to a method for purifying ethylene carbonate from a crude ethylene carbonate composition, comprising the following steps: a) subjecting a crude composition comprising ethylene carbonate to at least one distillation step to obtain a pre-purified composition comprising at least 99.5% by weight of ethylene carbonate, and b) subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition wherein in step a) a bottom divided wall distillation column is used as a distillation column (if step a) comprises one distillation step) or as a first distillation column (if step a) comprises two or more distillation steps), and a bottom partition distillation column comprising a partition wall connected to the bottom of the bottom partition distillation column and extending upward from the bottom of the bottom partition distillation column by a portion of the height of the bottom partition distillation column, whereby a bottom section of the divided wall distillation column is subdivided into a first bottom sub-section and a second bottom sub-section as viewed from a cross-section of the divided wall distillation column.

The present invention provides a method and a plant for recovering purified ε-caprolactam from fishing nets containing polyamide 6, said plant comprising a depolymerization section [B], a recovery section [C] and a purification section [D]. The present invention also provides purified ε-caprolactam obtained via depolymerization of polyamide 6 from fishing nets, having a particularly low product carbon footprint.

The present invention relates to a purification method for laurolactam, and more particularly, to a purification method capable of obtaining high-purity laurolactam substantially free of impurities. The present invention provides a purification method for laurolactam from a reaction product of a laurolactam synthesis process, the production method including: (S1) obtaining a first mixed solid by separating and removing low-boiling point materials through distillation of the reaction product; (S2) removing impurities suspended in a first mixed solution obtained by dissolving the first mixed solid in a good solvent; (S3) obtaining a second mixed solid precipitated by adding a poor solvent to the first mixed solution from which the impurities are removed; and (S4) evaporating a melt obtained by heating and melting the second mixed solid to obtain laurolactam in a gas phase and performing crystallization.

The present invention relates to a process for purifying ethylene carbonate from a crude ethylene carbonate composition, said process comprising the steps of: a) subjecting a crude composition comprising ethylene carbonate to at least one distillation step to obtain a pre-purified composition comprising at least 99.5% by weight of ethylene carbonate; and b) subjecting the pre-purified composition obtained in step a) to at least one melt crystallization step to obtain a purified ethylene carbonate composition wherein the process is carried out in a plant comprising at least one distillation column, one vessel, at least one crystallizer and a feed line for a crude composition containing ethylene carbonate, wherein, if the apparatus comprises one distillation column, the distillation column, or, if the apparatus comprises two or more distillation columns, the first distillation column, comprising a top outlet line, a bottom outlet line and a side outlet line, wherein the at least one crystallizer comprises an inlet line for the pre-purification of the composition and an outlet line for the purification of the ethylene carbonate composition, and wherein the side outlet line of the distillation column is directly or indirectly connected to the inlet line of the at least one crystallizer for the pre-purification of the composition, wherein i) or the vessel is connected to the feed line for the crude composition containing ethylene carbonate and to an inlet line, where the inlet line is connected to a gas outlet of a first reboiler, where the first reboiler is further connected to a bottom outlet line of the distillation column, where the vessel further comprises an outlet line, where the outlet line is connected to a gas outlet of a second reboiler, where the first reboiler is further connected to a bottom outlet line of the distillation column. The outlet line leads to the inlet line of the distillation column via a second reboiler, in which a bottom fraction of the distillation column withdrawn from the distillation column via the bottom outlet line is partially evaporated in the first reboiler to obtain a gas fraction and a liquid fraction, or ii) the feed line for the crude composition containing ethylene carbonate is introduced into the distillation column, where the bottom outlet line of the distillation column leads to the vessel via a first reboiler, where the vessel comprises a gas outlet connected to the inlet line of the distillation column, where the bottom outlet line of the distillation column leads to the vessel via a second reboiler, where the gas outlet is connected to the inlet line of the distillation column. And the container comprises a liquid outlet which is connected with a pipeline leading into a second reboiler, the second reboiler comprises a gas outlet which is connected with an inlet pipeline of the distillation column, and the gas outlet is connected with a gas outlet of the distillation column. Wherein a bottom fraction of the distillation column withdrawn from the distillation column via the bottom outlet line is partially evaporated in the first reboiler, and wherein at least a portion of a gas fraction obtained in the first reboiler is recycled to the distillation column via the inlet line.

The utility model provides a pretreatment device for caprolactam refining raffinate, which is characterized in that a raffinate tank is communicated with the middle part of a solvent recovery tower through a raffinate tank discharge pump by a pipeline, the top of the solvent recovery tower is communicated with a solvent recovery tower top condenser and a solvent recovery tower reflux tank through pipelines, and the solvent recovery tower reflux pump is circularly communicated with the upper part of the solvent recovery tower; the bottom of the solvent recovery tower is communicated with the middle of the concentration tower through a solvent recovery tower kettle pump by a pipeline; the top of the concentration tower is circularly communicated with a concentration tower top condenser, a concentration tower reflux tank, a concentration tower reflux pump and the upper part of the concentration tower through pipelines; the bottom of the concentration tower is communicated with the upper part of the benzene extraction tower through a concentration tower kettle pump through a pipeline. The caprolactam refining raffinate recycling device solves the problem of high energy consumption caused by the fact that a large amount of caprolactam refining raffinate returns to an ammonium sulfate crystallization process, greatly reduces the circulation volume of the caprolactam refining raffinate, and greatly reduces accumulation of impurities in the device as the impurities and sewage are discharged to the sewage treatment device.

Provided is a method for recovering a highly pure fibrous filler and ε-caprolactam from a polyamide 6 resin composition, which contains the fibrous filler, only by solid-liquid separation. The present invention pertains to a method for recovering a fibrous filler and ε-caprolactam, said method comprising adding and contacting a polyamide 6 resin composition (A) containing at least the fibrous filler (D) with water (B) heated to 290-350°C inclusive and / or an aqueous polyamide 6 oligomer solution (B1) heated to 290-350°C inclusive to give a mixture (C) and then recovering the fibrous filler and ε-caprolactam from the mixture (C), characterized in that the following steps (a) to (c) are performed in this order. (a) A step for preparing the mixture (C) under such condition that, when the mass ratio of water to polyamide 6, etc. is X:1 and the reaction temperature is Y°C, then the product of X and Y is 2,000 or less. (b) A step for performing solid-liquid separation (I). (c) A step for washing the material on the filter.

The present invention provides an improved process for the recovery of epsilon-caprolactam from a multi-component material, in particular a multi-layer film, containing nylon 6. Furthermore, the present invention provides: a plant configured to carry out the process of the present invention; and the recovered epsilon-caprolactam obtainable by the process of the present invention having a product carbon footprint of less than 2.5 kg CO2 equivalent per kg of purified epsilon-caprolactam (based on data from ecoinvent version 3.7.1 ; location: Europe).

The utility model relates to the technical field of caprolactam, in particular to a device for reducing ammonium sulfate content in amide oil, which comprises a static mixer, the static mixer is provided with an amide oil feed pipe and a benzene feed pipe, a discharge port of the static mixer is connected to a decanter after passing through a decanter feed pump and a heat exchanger, the decanter is provided with a heavy phase discharge port and a light phase discharge port, and the heavy phase discharge port is connected with the light phase discharge port. A light-phase discharge port is conveyed to a cyclone membrane filter through a decanter discharge pump, a heavy-phase outlet of the cyclone membrane filter and a heavy-phase discharge port of the decanter are converged and connected to an ammonium sulfate mother liquor tank, and a light-phase outlet of the cyclone membrane filter is connected to a subsequent amide oil purification process. The device is provided with the links of benzene dissolving and crystallization, filtration, cooling, decanting, refiltration, cyclone separation, membrane filtration and the like, ammonium sulfate mother liquor and free ammonium sulfate particles in the amide oil are removed, the quality of the amide oil is improved, and the content of ammonium sulfate in the amide oil can be reduced to 0.5 wt% or below.

A method of producing a thermoplastic resin includes obtaining ε-caprolactam by steps (a) and (b) using a waste (A) of a resin molded body containing at least polyamide 6 as a raw material, and polymerizing a raw material containing the ε-caprolactam: (a) adding at least one of water (B) heated to 290° C. or higher and 350° C. or lower and a polyamide 6 oligomer aqueous solution (B1) heated to 290° C. or higher and 350° C. or lower to the waste (A) of the resin molded body to make contact with each other; and (b) separating a reaction mixture obtained in step (a) into a solid and an aqueous solution containing ε-caprolactam by a solid-liquid separation (I).

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.

The utility model belongs to the technical field of caprolactam production, and particularly relates to a device for improving caprolactam back extraction hexane water concentration, which is characterized in that a hexane solution discharge port of a hexane extraction tower is connected with a hexane solution feed port of a hexane evaporation tower through a pipeline, and a hexane solution discharge port of the hexane evaporation tower is connected with a back extraction tower through a pipeline; a benzene steam pipeline is arranged at the top of the benzene-hexane evaporation tower, a hexane water pipeline is arranged at the bottom of the back extraction tower and is connected to the next working section, and a water inlet pipe and a liquid benzene pipeline are arranged at the middle upper part of the back extraction tower. The device has the beneficial effects that by increasing the concentration of the benzene-hexane solution, the concentration of hexane water can be increased during back extraction, so that the consumption of steam during evaporation of hexane water in a subsequent working section is reduced, the energy is saved, the productivity is improved, and meanwhile, the solvent benzene in the benzene-hexane solution is recovered and recycled.