96results 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 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.

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).

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 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 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 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 a method for purifying ethylene carbonate from a crude ethylene carbonate composition comprising the steps of: a) subjecting a crude composition containing ethylene carbonate to at least one distillation step so as to obtain a pre-purified composition containing 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 so as to obtain a purified ethylene carbonate composition, wherein in step a) as the distillation column, if step a) comprises one distillation step, or as the first distillation column, if step a) comprises two or more distillation steps, a bottom dividing-wall distillation column is used, which comprises a dividing wall being connected with and extending from the bottom of the bottom dividing-wall distillation column upwards over a part of the height of the bottom dividing-wall distillation column thereby subdividing the bottom section of the dividing-wall distillation column, seen in cross-section of the dividing-wall distillation column, into a first bottom subsection and into a second bottom subsection.

The invention relates to the technical field of caprolactam purification, and discloses a purification method of caprolactam heavy residual liquid. The purification method comprises the following steps: (1) distilling the caprolactam heavy residual liquid to obtain a caprolactam product; and (2) carrying out drying treatment on the distillation residual liquid after distillation to obtain crude caprolactam, returning to the step (1), and continuing distillation. The purification method disclosed by the invention can be used for carrying out efficient impurity removal treatment on the heavy raffinate in the caprolactam production process and recovering valuable caprolactam components in the heavy raffinate, and has the advantages of low ton treatment cost, high caprolactam recovery rate, good finished product quality and the like; and through a series of physical and chemical separation operations, the impurity content in the waste liquid is reduced, and the dual purposes of resource recycling and environment-friendly emission are achieved.

The present invention relates to a process for preparing ethylene oxide or propylene oxide comprising (b) reacting hydrogen with carbon oxides to form methanol, (c) converting the methanol from step (b) to ethene and / or propene, (d) reacting the ethene and / or propene from step (c) with oxygen or an oxidizing agent to form ethylene oxide and / or propylene oxide, wherein the carbon dioxide in step (b) is at least in part captured from industrial flue gases or from air or from ocean water or other natural waters or obtained from biological processes, for example from fermentation processes from waste or biomass, and / or wherein the hydrogen in step (b) is obtained at least in part by water splitting, the water splitting preferably using energy generated at least in part from non-fossil resources; a process for preparing ethanolamines, a process for preparing alkoxylated compounds, a process for making alkoxylated di-, oligo- and polyamines or alkoxylated polyethylenimine, a process for making alkoxylated polyethylenimine, a process for making surfactant, each process based on said process for preparing ethylene oxide or propylene oxide; polyethylenimines, ethanolamines, alkoxylated compounds, surfactants, alkoxylated di-, oligo- and polyamines, and alkoxylated polyethylenimines obtainable by the abovementioned processes; the use of the poly-ethylenimines, ethanolamines, alkoxylated compounds, surfactants, alkoxylated di-, oligo- and polyamines, and alkoxylated polyethylenimines; a composition being a laundry detergent, a cleaning composition or a fabric and home care product, containing at least alkoxylated di-, oligo- and polyamines or alkoxylated polyethylenimine, or a surfactant; the polyethylenimines, ethanolamines, alkoxylated, surfactants, alkoxylated di-, oligo- and polyamines, and alkoxylated polyethylenimines with a reduced amount of fossil-based hydrogen-content having thus an overall reduced cradle to gate product carbon footprint.

To provide a method for producing ε-caprolactam from a polyamide 6 resin composition, the method achieving both circulation utilization of fossil resources and reduction in global warming gas emissions, and therefore being green and energy-saving. The present invention is a method for producing ε-caprolactam, including bringing a resin composition (A) containing at least polyamide 6 and a polyamide 6 oligomer aqueous solution (C) heated to 290°C or higher and 350°C or lower into contact with each other, or bringing a resin composition (A) containing at least polyamide 6, a polyamide 6 oligomer aqueous solution (C) heated to 290°C or higher and 350°C or lower, and further water (B) heated to 290°C or higher and 350°C or lower into contact with each other.

The application provides a hole disc type liquid phase separator for cyclohexanone oxime liquid phase rearrangement product, which is arranged in the middle of a phase separation tower for liquid phase separation and comprises a liquid distribution disc and a liquid guide pipe, wherein the liquid guide pipe is composed of a support pipe and a phase separation structure which are connected with each other, and the liquid guide pipe is arranged perpendicularly to the liquid distribution disc. The phase separator can strengthen mass transfer and efficiently mix the liquid through the special liquid guide pipe. The space of each stage of the liquid distribution disc forms a uniform phase separation space, so that the purpose of multi-stage extraction is achieved, and the separation work such as single extraction, back extraction and ion exchange can be completed by a single extraction tower. Meanwhile, the phase separator can improve the mixing efficiency and mass transfer performance of the liquid, has the advantages of smaller occupied space, convenient installation and easy adjustment of the horizontal degree.

The invention provides a caprolactam purification method and application thereof. The purification method of caprolactam comprises the following steps: S1, carrying out alkali washing on a raw material benzene-hexane solution by using alkali liquor to obtain an alkali-washed benzene-hexane solution; s2, the benzene-hexane liquid obtained after alkali washing in the S1 is subjected to distillation and preliminary debenzolization, and benzene-hexane liquid obtained after preliminary debenzolization is obtained; s3, rectifying the benzene-hexane solution subjected to primary debenzolization obtained in the step S2 to obtain a caprolactam crude product rectified solution; and S4, recrystallizing the caprolactam crude product rectification liquid obtained in S3 to obtain caprolactam crystals. The caprolactam purification method is an efficient and green caprolactam rectification and crystallization purification method, can be used in a caprolactam-hexamethylenediamine process and can replace superior caprolactam, the cost is reduced, and the benefit is improved.

The present invention relates to: processes for producing vinyl acetate on the basis of methanol having a deuterium content of less than 90 ppm, comprising a step of reacting acetic acid with ethylene to obtain vinyl acetate; and processes for producing vinyl acetate based on methanol having a deuterium content of less than 90 ppm, comprising the steps of reacting acetic anhydride with acetaldehyde to form ethylidene diacetate, and reacting ethylidene diacetate to obtain vinyl acetate by thermal elimination of acetic acid; and vinyl acetate having a deuterium content of less than 90 ppm based on the total hydrogen content. The invention further relates to vinyl acetate of carbon-14 with natural abundance from non-fossil resources, preferably from biomass, and to the use thereof. The invention also relates to a process for the preparation of an alkoxylated compound comprising ethylene oxide units and / or propylene oxide units, comprising the steps of (a) reacting hydrogen with carbon dioxide to form methanol, (b) converting the methanol from step (a) to ethylene and / or propylene, (c) reacting the ethylene and / or propylene from step (b) with oxygen or an oxidizing agent to form ethylene oxide and / or propylene oxide, and (d) reacting the ethylene oxide and / or propylene oxide with at least one starter unit having Zerewitinoff-active hydrogen atoms to form the alkoxylated compound, wherein the carbon dioxide in step (a) is at least partially captured from industrial flue gas or from air or from seawater or other natural water or is obtained from a biological process; and an alkoxylated compound obtainable by the process. The invention further relates to graft polymers based on ethylene oxide-containing main chains grafted with ethylenically polymerizable monomers, preferably vinyl monomers, more preferably vinyl lactams, a) vinyl esters or b) vinyl lactams wherein such graft polymers are based at least in part on hydrogen from non-fossil-based sources, wherein the molar fraction of deuterium in such a graft polymer is lower than the molar fraction of deuterium in the same compound when only derived from fossil-based sources.

The invention discloses a preparation method of a catalyst suitable for caprolactam hydrofining, the caprolactam hydrofining catalyst prepared by the method, and a caprolactam hydrofining method adopting the catalyst. According to the present invention, after the surface treatment of the catalyst, the hydration reaction between the water molecules and the carrier (alumina) can be effectively inhibited so as to substantially improve the stability of the carrier pore structure in the water phase, such that the long-time storage of the catalyst under the deoxygenated water sealing condition is achieved, and the reduction state and deoxygenated water sealing supply form becomes possible.

The invention relates to the field of petrifaction, and discloses a green refining method of crude caprolactam, which comprises the following steps: S1, mixing crude caprolactam with a crystallization solvent, carrying out primary crystallization, carrying out solvent removal, heavy component removal and light component removal on a primary mother solution obtained by separation, mixing the recovered solvent and caprolactam with crude caprolactam, and recrystallizing; or removing the solvent from the primary mother liquor, recovering, concentrating, performing secondary crystallization, and separating to obtain secondary crystals and secondary mother liquor; carrying out solvent removal, heavy component removal and light component removal on the secondary mother liquor, mixing the recycled caprolactam with the primary mother liquor for secondary crystallization, separating to obtain secondary recycled crystals, mixing the secondary recycled crystals with secondary crystals and crude caprolactam, and then carrying out primary crystallization again; and S2, adsorption refining. According to the method disclosed by the invention, efficient and green refining of the crude caprolactam can be realized, the finally obtained caprolactam has high purity, low chroma and high yield, and the method has obvious advantages in production of high-end caprolactam products with extremely high chroma requirements.

To provide a collection method capable of collecting ε-caprolactam and a polyamide 6 oligomer in high yield only by depolymerization using a small amount of water and solid-liquid separation with a small energy consumption. This disclosure is a method of collecting ε-caprolactam and a polyamide 6 oligomer, including adding a resin composition (A) containing at least polyamide 6 and 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 make contact with each other to obtain a reaction mixture (C) containing at least ε-caprolactam, a polyamide 6 oligomer, and water, and subjecting the reaction mixture (C) to a solid-liquid separation (I) in a temperature range not higher than a boiling point of water at an operation pressure to separate and collect a polyamide 6 oligomer in a solid phase, and an ε-caprolactam aqueous solution in a liquid phase.