A method for recovering epsilon-caprolactam from multicomponent materials containing nylon 6.

Abstract

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).

Description

[Technical field]

[0001] The present invention relates to a method for recovering ε-caprolactam from multicomponent materials, in particular multilayer films, containing nylon 6. Furthermore, the present invention relates to a plant adapted to carry out the method of the present invention, and to the recovered ε-caprolactam obtained by the method of the present invention. [Background technology]

[0002] In 1938, Paul Schlack invented nylon 6 (CAS number: 25038-54-4), also known as polyamide 6, poly(caprolactam), poly(hexano-6-lactam), poly(6-aminohexanoic acid), poly(hexamethylene adipamide) or poly[imino(1-oxohexane-1,6-diyl)].

[0003] Generally, nylon 6 is prepared by the ring-opening polymerization of ε-caprolactam at a temperature of about 260° C. under an inert atmosphere: [ka] It is synthesized by:

[0004] A method for producing virgin ε-caprolactam is described, for example, in “Ullmann's Encyclopedia of Industrial Chemistry”, (Germany), Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim, May 25, 2018, Chapter 25 “Caprolactam” (electronic version available at https: / / doi.org / 10.1002 / 14356007.a05_031.pub3).

[0005] The production method of nylon 6 is described, for example, in “Ullmann's Encyclopedia of Industrial Chemistry”, (Germany), Wiley-VCH Verlag 30 GmbH and Co. KGaA, Weinheim, January 15, 2013, Chapter “Polyamides” (electronic version available at https: / / doi.org / 10.1002 / 14356007.a21_179.pub3).

[0006] Currently, nylon 6 is the most widely produced synthetic polyamide in the world, and it has a variety of favorable properties for industrial applications, such as high mechanical strength, especially stiffness, hardness and toughness, good electrical insulation, good dyeability, good processability, good UV light protection, good fatigue resistance, and good barrier properties against gases, aromas, hydrocarbon solvents and low polarity aroma compounds from food. Due to this set of favorable properties, nylon 6 is used in a great number of completely different industries, such as building and construction, consumer goods, electronics and electrical products, transportation and packaging. However, the disadvantage of using nylon 6 is that it is more expensive than the polyolefins polyethylene and polypropylene. On the other hand, polyolefins have the disadvantage that their industrial applicability is more limited due to their poor gas barrier properties, low temperature resistance and difficult to bond nature.

[0007] As a result, nylon 6 is widely used as a component in multicomponent materials, most often in combination with polyolefins. Multicomponent materials containing nylon 6 that are of particular concern are, for example, flexible modified or controlled atmosphere packaging films that are used to maintain a constant atmosphere to improve the shelf life of the packaged product, usually inside food-containing packages. The majority of packaging films today are multilayer films, typically having 2 to 15 layers, but can have many more. An example of an 11-layer coextruded cast film is the following: nylon 6 / TIE / PE(1) / TIE / nylon 6 / EVOH / PA / TIE / PE(2) / PE(3) / PE(4), where TIE is a tie layer, EVOH is ethylene vinyl alcohol, PA is a polyamide other than nylon 6, and PE(1), PE(2), PE(3) and PE(4) are different grades of polyethylene. The typical purpose of using nylon 6 in such multicomponent materials is to impart mechanical strength properties and puncture resistance, and / or barrier properties to limit gas exchange and aroma loss. Multilayer films containing nylon 6 in particular make it possible to maintain an optimized modified atmosphere inside the package, in particular a constant oxygen concentration, which is important for example to keep perishables fresh for longer periods of time. The use of multilayer films can allow for cost reductions, since more expensive polymers such as nylon 6 can be partially replaced by cheaper polymers. Nylon 6 is also a good alternative to aluminum and other metallic films.

[0008] Multicomponent materials, which contain two or more (polymer) components, are attractive for industrial applications, for example because the alternating layering of two (or more) different components is a way to obtain composite materials with new properties compared to the pure components. Combining several layers of different materials can improve, for example, the mechanical and physical properties of the film, including puncture resistance, tear resistance and heat resistance, as well as the barrier properties to moisture and gases (especially oxygen). It is possible to continuously observe how the properties of the multicomponent material change when changing the components used and the thickness of the component layers used, so that new composite materials with desired properties can be developed relatively easily. In multicomponent materials, especially multilayer films, polyolefin layers are often combined with layers made of polar polymers such as nylon 6, nylon 66, EVOH (ethylene vinyl alcohol) or PVDC (polyvinylidene chloride). In addition, a tie layer containing special adhesive polymers or binding resins (e.g. polyurethanes and acid / anhydride grafted polyolefins) is generally required as an intermediate layer between two dissimilar components that do not adhere well. As explained above, the use of nylon 6 in multicomponent materials has become very popular to improve the mechanical and gas barrier properties of such materials. Another important reason why nylon 6 is often combined with other materials is to save on the cost of nylon 6, which is quite expensive.

[0009] Environmental concerns regarding the production and use of the multicomponent nylon 6-containing materials mentioned above relate to the waste generated during manufacturing and after use. These concerns could be alleviated by recycling individual components, such as nylon 6, from multicomponent materials that are no longer in use or are otherwise disposed of. As packaging materials, nylon 6-containing multilayer films are a particularly problematic source of waste. These films often contain large amounts of nylon 6. Thus, if there were a feasible method for the recovery of nylon 6 from these composite waste materials, it would not only benefit the environment, but would also represent a new economically valuable source of nylon 6.

[0010] The same is true for the process waste that occurs during nylon 6 processes, particularly film production. For a limited number of applications, these waste materials can be recovered and reused as regrind. However, the optical and mechanical properties of the material are adversely affected by the regrind, and further degradation occurs with each repeated cycle of reuse and processing. As a result, the cycle of reuse and processing cannot be repeated as many times as would be desirable.

[0011] In addition, nylon 6 recycled by currently existing methods is generally not considered a "food-grade plastic," severely limiting its range of applications.

[0012] Mechanical recycling (also known as material recycling or back-to-plastics recycling or regrinding) refers to the recovery of plastics through mechanical processing (crushing, washing, separating, drying, regranulating and compounding) with the goal of producing recycled material that can be converted into plastic products to replace virgin plastics. Currently, most virgin plastics are produced from petrochemical feedstocks that have never been used or processed before, such as natural gas, coal or crude oil. In the mechanical recycling process, the polymer chains remain largely intact. Mechanical recycling is a type of waste down-recycling, as the recycled material is of lower quality and functionality than the original material.

[0013] Depolymerization or chemical recycling is a technique that converts a polymer into its monomeric components (ε-caprolactam in the case of nylon 6). Depending on the properties of the recovered monomers, they can either be substituted for virgin monomers in all applications or only in limited applications. Virgin monomers are produced from petrochemical feedstocks that have never been used or processed before, such as natural gas, coal, or crude oil.

[0014] Following the regrind of materials containing nylon 6, processes have been developed to depolymerize nylon 6 to its useful monomer, ε-caprolactam, which typically use as starting material nylon 6 plastic articles produced, for example, by injection molding, extrusion, spinning or other processing steps.

[0015] The depolymerization of nylon 6 to ε-caprolactam is the reverse reaction of the ring-opening polymerization of ε-caprolactam: [ka] It is.

[0016] Methods for the depolymerization of nylon 6 are known. Such processes may be carried out in a batchwise mode of operation, semi-continuously (typically involving batchwise (re)charging of nylon 6 to the depolymerization reactor), or continuously. LA Dmitrieva, AA Speranskii, SA Krasavin and YN Bychkov, "Regeneration of ε-Caprolactam From Wastes In the Manufacture of Polycaproamide Fibres and Yarns", Fibre Chemistry, (Germany), March 1986, pp. 229-241, (translated from Khimicheskie Volokna, (Russia), July-August 1985, No. 4, pp. 5-12) is a literature review that describes methods for the depolymerization of nylon 6 with and without the use of catalysts.

[0017] AA Ogale, "Depolymerization of Nylon 6: Some Kinetic Modeling Aspects", Journal of Applied Polymer Science, (USA), 1984, vol. 29, pp. 3947-3954 (available online at https: / / doi.org / 10.1002 / app.1984.070291227) is a paper that describes the depolymerization kinetics of nylon 6.

[0018] Generally, prior art processes for chemical regeneration or recycling of essentially pure nylon 6 by depolymerization to ε-caprolactam monomer include a hydrolysis step at high temperature in the presence of water and a recycling step of the formed monomer by steam distillation. The hydrolysis step can be carried out both in the presence and absence of a catalyst. Both acidic compounds, such as phosphoric acid and boric acid, and basic compounds, such as potassium carbonate and sodium hydroxide, can be used as catalysts.

[0019] US Patent No. 5,929,234 describes a method for recovering ε-caprolactam from waste materials containing polycaprolactam. Depolymerization is carried out in the absence of added catalyst using superheated steam at a temperature of about 250° C. to about 400° C. and a pressure in the range of about 1 atm to about 100 atm, which is significantly lower than the saturated vapor pressure of water at the temperature at which a vapor stream containing ε-caprolactam is formed.

[0020] The reuse of ε-caprolactam from essentially pure nylon 6 by recovery of the extracts of nylon 6 polymerization plants, recycling nylon 6 scrap (i.e. nylon 6 polymer containing little non-nylon 6 material) or products made of almost pure nylon 6 (e.g. fishing nets) has been known for a long time.

[0021] For example, DE 4211609 A1 discloses a method for recovering ε-caprolactam by thermal cleavage of polyamide 6 at 250-320° C. in the presence of a small amount of potassium carbonate, and a method for purifying the recovered ε-caprolactam. DE 4211609 A1 describes that the method is applicable not only to pure polyamide 6 products, but also to polyamide 6 products containing glass fibers and polyamide 6 products containing extenders, as well as to products containing impact modifiers. The term “polyamide 6” as used in DE 4211609 A1 refers to pure polyamide 6, and preferably to polyamides with more than 80% by weight of polyamide 6.

[0022] China Patent Publication No. 103467378 discloses a method for producing ε-caprolactam by using recycled waste chinlon silk and surplus products, in which phosphoric acid is used as the catalyst for depolymerization. Superheated steam is injected into the reaction system during the depolymerization process.

[0023] US Patent No. 5,869,654 discloses a method for recovering ε-caprolactam from polycaprolactam processing waste, where the polycaprolactam can be selected from scrap nylon 6 polymeric and / or oligomeric materials, such as yarn waste, chip waste, or extruder slag, etc. The method comprises contacting the polycaprolactam waste, in the absence of added catalyst, with superheated steam at a temperature of about 250° C. to about 400° C. and a pressure in the range of about 1.5 atm to about 100 atm, substantially below the saturation vapor pressure of water, at which a vapor stream containing ε-caprolactam is formed.

[0024] Japanese Patent Application Laid-Open No. 2000038471 discloses a method for depolymerizing nylon 6 resin derived from a molded body in order to obtain ε-caprolactam, in particular a method for depolymerizing automotive resin parts in which nylon 6 accounts for 90% by weight or more of the total organic compounds in the molded body, such as nylon 6 fastener parts, electrical parts, body mechanism parts and exterior parts.

[0025] Although methods have been developed to depolymerize nearly pure waste nylon 6 into its useful monomer, ε-caprolactam, recovery of ε-caprolactam from nylon 6-containing multicomponent materials, especially those with a medium to high nylon 6 content (e.g., 40% to 80% by weight), remains a major challenge. Recovery of ε-caprolactam from nylon 6-containing multicomponent materials with low nylon 6 content (e.g., less than 40% by weight) is even more difficult. An example of a nylon 6-containing product with a medium to high nylon 6 content is carpet. High-quality carpets typically contain face fibers containing up to 55% by weight of nylon 6. The remainder is the backing (support) material.

[0026] Reclaiming ε-caprolactam from nylon 6-containing materials, both low and medium to high nylon 6 content, has not been commercially viable or successful based on existing processes.

[0027] The most frequently reported problem associated with the recovery of ε-caprolactam from nylon 6-containing materials with a medium to high nylon 6 content is the low recovery rate, which is due, on the one hand, to the difficulty of separating the formed ε-caprolactam from the non-nylon 6 material, and, on the other hand, to the decomposition reactions leading to the production of ammonia and to the inhomogeneity of the depolymerization mixture, whose high viscosity prevents effective mixing, resulting in localized overheating and an increased consumption of expensive superheated steam (used as a discharging agent).

[0028] By introducing a mechanical pretreatment step (e.g. scraping or grinding of surface fibers from the carpet backing followed by density separation such as float-sink separation and air sorting), it is possible to produce a treated carpet material feed containing more than 90% by weight of nylon 6, which can be used in the prior art depolymerization process described above. However, this mechanical pretreatment is mainly applied to off-spec material (pre-consumer waste) within the production facilities of carpet and other nylon 6-containing textile products. Furthermore, this pretreatment cannot be transferred to other non-carpet nylon 6-containing multicomponent materials.

[0029] Currently, methods are not available for recovering high purity ε-caprolactam from multicomponent materials containing nylon 6 in an economically reasonable manner, despite the urgent need for such methods. In particular, there is an urgent need for ε-caprolactam recovery methods that handle more demanding nylon 6-containing multicomponent materials, such as those with low to moderate nylon 6 content (e.g., 1% to 35% by weight), and for the recovery of ε-caprolactam from complex nylon 6-containing multicomponent products that cannot be pre-concentrated by a simple mechanical pretreatment step (such as scraping or grinding followed by density separation). Finally, there is a need for methods that allow the recovery of ε-caprolactam from nylon 6-containing multicomponent materials, such as multilayer films, where the nylon 6 layers are often sandwiched between non-nylon 6 components and therefore cannot be accessed from the outer surface of the material.

[0030] Taken together, the prior art processes for recovering ε-caprolactam from nylon 6-containing multicomponent materials do not allow the production of high quality grades of ε-caprolactam that can be used to replace virgin grades of ε-caprolactam for demanding applications.

[0031] Currently, no methods are available for recovering high purity ε-caprolactam from nylon 6-containing multicomponent materials, despite the urgent need for such methods, particularly for recovering high purity ε-caprolactam that can replace virgin grade ε-caprolactam for demanding applications such as high speed melt spinning in textile fiber production.

[0032] Furthermore, there is a need for a process that allows for the recovery of high purity ε-caprolactam in an economically reasonable manner from multicomponent materials containing nylon 6. The production costs of the recovered high purity ε-caprolactam should be comparable to or lower than the production costs of high purity virgin ε-caprolactam.

[0033] There is also a need to purify the crude ε-caprolactam obtained by depolymerization of nylon 6-containing multicomponent materials without using oxidizing agents such as potassium permanganate (KMnO4) or adsorbents such as (activated) carbon and diatomaceous earth. These oxidizing and adsorbent-based techniques are very time-consuming and labor-intensive and generate solid waste.

[0034] Further, there is a need to provide high purity grades of ε-caprolactam derived from nylon 6-containing multicomponent materials that have a significantly lower carbon footprint than ε-caprolactam obtained by new syntheses, such as Beckmann rearrangement of virgin cyclohexanone oxime.

[0035] Finally, in order to process the enormous amounts of nylon 6-containing multicomponent materials that are discarded each year, a process is needed that allows for the recovery of ε-caprolactam from nylon 6-containing multicomponent materials on an industrial scale. Summary of the Invention

[0036] It is an object of the present invention to fulfill one or more of the above needs and to overcome the shortcomings associated with prior art methods.

[0037] In particular, the present invention aims to provide a method for recovering high purity ε-caprolactam in an economically reliable manner and with a high recovery rate from multicomponent waste materials containing nylon 6. In particular, the present invention aims to provide a method suitable for recovering ε-caprolactam from nylon 6-containing multicomponent waste materials having a nylon 6 content of up to 35% by weight, and from complex nylon 6-containing multicomponent materials, in particular nylon 6-containing multilayer films.

[0038] It is a further object of the present invention to provide a method for recovering high purity ε-caprolactam from nylon 6-containing multicomponent materials, which can replace high purity virgin ε-caprolactam for all applications including high speed melt spinning of nylon 6 to produce fine textile fibers.

[0039] It is a further object of the present invention to provide a process for the recovery of high purity grade ε-caprolactam from nylon 6-containing multicomponent waste materials, characterized by a significantly lower carbon footprint than neo-syntheses, such as processes for producing ε-caprolactam by Beckmann rearrangement of cyclohexanone oxime.

[0040] It is therefore a further object of the present invention to provide a method for reducing the environmental impact of multi-component waste materials containing nylon 6 and products made therefrom. The above mentioned objects are solved in whole or at least in part by the methods of claims 1 and 15, the plant of claim 13 and / or the product of claim 14.

[0041] Surprisingly, it has been found that it is possible to obtain high-purity grade ε-caprolactam in high yield from a nylon 6-containing multicomponent material by the following process of the present invention. The process of the present invention uses a plant comprising (A) a nylon 6 preconcentration section, (B) a depolymerization section, (C) a recovery section, and (D) a purification section. The process of the present invention comprises:

[0042] a) extracting the nylon 6-containing multicomponent material with one or more organic solvents in a nylon 6 pre-concentration section to obtain a solid pre-concentrated nylon 6-containing material enriched in nylon 6 relative to the nylon 6-containing multicomponent material; b) depolymerizing the pre-concentrated nylon 6-containing material in the presence of water in a depolymerization section to obtain a vapor stream comprising water and ε-caprolactam in a weight-to-weight ratio of 2:1 to 15:1; c) recovering crude ε-caprolactam from the vapor stream in a recovery section; d) purifying the crude ε-caprolactam in a purification section to obtain purified ε-caprolactam; Includes.

[0043] It was surprising that the combination of the special sequence of process steps and process conditions according to the invention, i.e. the sequence of nylon 6 preconcentration, depolymerization, recovery and purification steps defined above, allows for the recovery of high grade ε-caprolactam from nylon 6-containing multicomponent materials in high yield and in a straightforward and economically rational manner. The process of the invention is economically rational and advantageous from several points of view. First, the process of the invention is suitable for a wide variety of nylon 6-containing multicomponent materials that may differ, for example, in their overall composition, nylon 6 content and / or nylon 6 distribution within the material. Second, the process of the invention allows for an effective separation of nylon 6 from non-nylon 6 compounds so that a high purity grade of ε-caprolactam can be obtained. Third, the extraction of nylon 6 from nylon 6-containing multicomponent materials by the process of the invention is so effective that a high yield of ε-caprolactam can be obtained. Finally, the method of the invention allows the production of ε-caprolactam with a significantly lower carbon footprint compared to ε-caprolactam produced by de novo synthesis of ε-caprolactam, for example by Beckmann rearrangement of cyclohexanone oxime. The method of the invention allows the efficient processing of waste nylon 6-containing multicomponent materials and the reduction of the environmental impact of said products. In particular, the method of the invention allows the production of purified ε-caprolactam with a carbon footprint of less than 2.5 kg CO2 equivalent per kg purified ε-caprolactam, which is a significant improvement compared to the 7.5-6.5 kg CO2 equivalent per kg ε-caprolactam (based on data from Ecoinvent version 3.7.1 (region: Europe)) traditionally associated with the production of "virgin" ε-caprolactam obtained from the Beckmann rearrangement of cyclohexanone oxime. Product carbon footprint values ​​reported herein are based on Eco Invent version 3.7.1 and European region data, unless otherwise stated.

[0044] Next to the process of the present invention, the present invention further provides a chemical plant suitable for producing purified ε-caprolactam from a nylon 6-containing multicomponent material, comprising at least (A) a nylon 6 preconcentration section, (B) a depolymerization section, (C) a recovery section, and (D) a purification section, said plant and in particular said four sections are adapted to carry out the process of the present invention.

[0045] The invention further provides purified ε-caprolactam obtainable by the process of the invention and having a product carbon footprint of less than 2.5 kg CO2 equivalent per kg (based on Eco Invent version 3.7.1 (region: Europe) data).Finally, the invention provides the use of ε-caprolactam recovered from nylon 6-containing multicomponent materials for reducing the carbon footprint of an ε-caprolactam production plant, which also produces ε-caprolactam from the Beckmann rearrangement of at least cyclohexanone oxime. Advantageous embodiments of the invention are set out in the dependent claims and are explained in more detail below.

[0046] <Nylon 6-containing multi-component material> The process of the present invention uses as a starting material a nylon 6-containing multicomponent material. The nylon 6-containing multicomponent material is typically a solid, particularly a solid body, net, sheet or film material.

[0047] Multicomponent materials include two or more components. Multicomponent materials are often used as a means to combine the properties of different components into a single material. As used herein, the term "component" refers to a chemical entity. In a preferred embodiment, the nylon 6-containing multicomponent material includes nylon 6 and at least one non-nylon 6 polymer as components. The two or more components can be present as separate domains in the multicomponent material (e.g., in a sheath / core, sea-island, side-by-side, multilayer, or other structure). Alternatively or additionally, the multicomponent material can include a mixture of different components (e.g., in the form of a polymer blend). Mixtures of these two embodiments are also possible, such as in the case of a multilayer film that includes a layer of a single polymer and an additional layer of a polymer blend or polymer matrix filled with polymer filler particles. Typically, nylon 6 is present in the nylon 6-containing multicomponent material as a separate domain and / or as a mixture with at least one non-nylon 6 polymer.

[0048] Preferably, the components of the multicomponent material are at least two different polymers, one of which is or comprises nylon 6. In one embodiment, at least two components of the multicomponent material comprise or consist of polymers. In this embodiment, the multicomponent material may comprise additional non-polymeric components. However, preferably, more than 80% by weight of the multicomponent material is composed of polymers. The term "polymer" as used herein refers to the ordinary meaning of the term, i.e., a large molecule (e.g., an oligomer) or macromolecule made of repeating subunits. Polymers, as used herein, may be of synthetic origin, such as plastics including polypropylene, nylon 6, and polystyrene, or of natural origin, such as starch or proteins. The term "polymer" as used herein further includes homopolymers, copolymers, and polymer blends. Natural and synthetic polymers are created by the polymerization of many small molecules known as monomers. Homopolymers are prepared from only one type of monomer. Copolymers are prepared from different types of monomers and may be random or block structured. As used herein, "polymer blend" or "blend" refers to a composition of two or more polymers, usually obtained by extrusion. A blend may or may not be miscible and may or may not be phase separated.

[0049] In one embodiment, at least one component of the multicomponent material comprises or consists of nylon 6, and at least one other component of the multicomponent material comprises or consists of a polymer different from nylon 6. The polymer different from nylon 6 can be selected from the group consisting of polyolefins (especially polyethylene and polypropylene), polyethylene oxide, polypropylene oxide, polycaprolactone, polyamides (other than polyamide 6), polyesters, polyvinylidene fluoride, polyvinylidene chloride, polystyrene, polycarbonate, polymethyl methacrylate, ethylene acrylic acid copolymers, polyoxymethylene, ethylene vinyl alcohol, polyurethanes, and combinations thereof, in particular blends thereof. Particularly good results in terms of purity and yield of the ε-caprolactam obtained can be achieved when the polymer different from nylon 6 is selected from the group consisting of polyolefins (especially polyethylene and polypropylene), polyamides (other than polyamide 6, in particular polyamide 6,6, polyamide 4,6, polyamide 6,10, polyamide 12), and combinations thereof.

[0050] The multicomponent material used in the process of the present invention comprises nylon 6. The term "nylon 6" as used herein refers to polycaprolactam. The term "nylon 6-containing multicomponent material" as used herein refers to a multicomponent material comprising two or more components, one of which is or comprises nylon 6. The weight fraction of nylon 6 in the nylon 6-containing multicomponent material used in the process of the present invention is not critical for carrying out the present invention and may vary from 0.5% to 99% by weight. However, it is a particular advantage of the process of the present invention that it also works very well for multicomponent materials that contain a low nylon 6 content compared to the nylon 6 content of more than 80% by weight required for the successful application of the prior art methods in practice. Thus, according to a particular advantageous embodiment, the weight fraction of nylon 6 in the nylon 6-containing multicomponent material used in the process of the present invention is between 1% and 75% by weight, more preferably between 1% and 60% by weight, even more preferably between 2% and 35% by weight, and most preferably between 3% and 25% by weight. Unless otherwise specified, all weight percentages stated herein are always based on the total weight of the nylon 6-containing multicomponent material.

[0051] The nylon 6-containing multicomponent material can have any shape, such as (multifilament) yarn, chip, film or any molded form. The shape of the nylon 6-containing multicomponent material used in the method of the present invention is not critical.

[0052] Preferably, the nylon 6-containing multicomponent material used in the method of the present invention is a multilayer material in which at least one layer comprises or consists of nylon 6. As used herein, the term "multilayer material" refers to a material constructed of different layers. These layers can differ in their relative position, thickness and / or composition. These layers can be of the same type or different types. Preferably, the multilayer material includes at least one nylon 6-free layer. In a further preferred embodiment, the multilayer material comprises two skin layers as outermost layers on both sides of the multilayer material, neither skin layer comprises nylon 6, but nylon 6 is thus contained in one of the layers sandwiched between the skin layers. Non-limiting examples of suitable polymers that can be used for the skin layers include polypropylene, polyethylene, polyethylene oxide, polycaprolactone, polyamides (other than nylon 6), polyesters, polyvinylidene fluoride, polyvinylidene chloride, polystyrene, polycarbonate, ethylene vinyl alcohol, polymethyl methacrylate, ethylene acrylic acid copolymers, polyoxymethylene, and blends of two or more thereof. A particular advantage of the method of the present invention is that it works with multi-layer materials where nylon 6 does not need to be exposed or accessible at the surface of the material.

[0053] The multi-layer material may include a barrier layer as a skin layer or intermediate layer containing non-nylon 6. The barrier layer may be formed from any material with barrier properties. The barrier layer may include or consist of organic materials such as carbon; inorganic materials such as metals, ceramics, oxides; polymeric materials, or combinations thereof. Non-limiting examples of suitable polymers other than nylon 6 that may be used in or as a barrier layer include: polyethylene terephthalate, ethylene vinyl alcohol, polyvinylidene chloride copolymers, polyamides (non-nylon 6), polyketones, blends of two or more of these; and blends of one or more of these with other polymers.

[0054] The multi-layer material may include a cling or adhesive layer that connects at least one nylon 6-containing layer with other layers in the multi-layer material. Non-limiting examples of suitable polymers that can be used as cling or adhesive layers include: olefin block copolymers, such as propylene-based block copolymers sold under the trade name INTUNE™ (The Dow Chemical Company) and ethylene-based block copolymers sold under the trade name INFUSE™ (The Dow Chemical Company); polar ethylene copolymers, such as copolymers with vinyl acetate, acrylic acid, methyl acrylate, and ethyl acrylate; ionomers; maleic anhydride grafted ethylene polymers and copolymers; polyurethane adhesives; blends of two or more of these; and blends of one or more of these with other polymers.

[0055] In a preferred embodiment, the term "layer" as used herein refers to a "film". Even more preferably, the nylon 6-containing multicomponent material used in the method of the present invention is itself a film, i.e. a multilayer film comprising at least one layer comprising or consisting of nylon 6. Preferably, the multilayer film comprises at least one layer comprising or consisting of nylon 6 and at least one layer not comprising nylon 6. The multilayer film can be produced by any film lamination technique and / or coextrusion technique. The term "film" as used herein is defined as a thin sheet with a thickness of less than 1 mm. The "layers" in a film may be very thin, as in the case of nanolayers. The term "film" as used herein may be in a shape such as a profile, parison, tube, etc., that is not necessarily "flat" in the sense of planar. In a preferred embodiment, the term "film" as used herein means a film consisting of polymeric material or containing more than 80% by weight of polymeric material. The use of multilayer films in the method of the present invention is advantageous since multilayer films are a common waste product. The majority of packaging films today are multilayer films. According to an embodiment of particular practical importance, a "multilayer film" as used herein is a packaging film, particularly a modified atmosphere packaging film, both of which are described in the Background section above.

[0056] Due to the close connection between the film layers, before the present invention, it was very difficult to recover high grade ε-caprolactam from a multilayer film containing nylon 6, especially when the nylon 6 content is less than 80% by weight as mentioned above, and / or when at least one nylon 6-containing layer is sandwiched between two non-nylon 6-containing layers in the multilayer film, which may be, but need not be, skin layers, and therefore is not easily accessible. Thus, multilayer films of the above kind represent a particularly advantageous embodiment of the present invention when used as a nylon 6-containing multicomponent material in step a). Thus, in particular, the nylon 6-containing multicomponent material used in the method of the present invention can be a multilayer film comprising at least one layer comprising or consisting of nylon 6, sandwiched (i.e. embedded) between two or more layers not containing nylon 6. The multilayer film can of course comprise further layers, with or without nylon 6, anywhere between, above or below the above layers.

[0057] The method of the present invention has the advantage that, unlike the prior art methods, which are limited to fibers containing nylon 6 obtained from carpets, which need to be subjected to a mechanical pretreatment step, the method of the present invention is not so limited and can be very well applied, especially for multilayer films. In a particular embodiment, the nylon 6-containing multicomponent material used in the method of the present invention is not a carpet or a material derived from a carpet. In another embodiment, the nylon 6-containing multicomponent material is not a textile or a material derived from a textile. In another embodiment, the nylon 6-containing multicomponent material does not contain nylon 6 fibers.

[0058] <Possible pre-processing steps> The nylon 6-containing multicomponent-derived material used in step a) has been obtained by extracting the nylon 6-containing multicomponent material with one or more solvents to obtain a solid pre-concentrated nylon 6-containing material enriched in nylon 6 compared to the nylon 6-containing multicomponent material, as described in more detail below. Before or after this pretreatment, it may be advantageous to subject the material to a further pretreatment step, which is described below.

[0059] Prior to being subjected to the process step a) of the present invention, the nylon 6-containing multicomponent material preferably undergoes a pretreatment, in particular a mechanical crushing step and / or a washing step. Thus, a mechanical crushing section and / or a washing section may be provided prior to the nylon 6 preconcentration section in the process of the present invention. Preferably, the nylon 6-containing multicomponent material is fragmented into small pieces before being extracted with one or more organic solvents in the nylon 6 preconcentration section of step a). This mechanical pretreatment, i.e., mechanical comminution or fragmentation of the nylon 6-containing multicomponent material, can be achieved, for example, by cutting, chopping, grinding, milling, chipping. In a preferred embodiment, the nylon 6-containing multicomponent material is introduced into step a) in the form of small pieces having an average length along its longest axis of 0.01 to 100 cm, preferably 0.05 to 10 cm, most preferably 0.1 to 5 cm. A person skilled in the art can easily measure the average length along the longest axis of the particles used by first taking a representative sample of the particles, then measuring the length of the longest axis of each of these particles (e.g. 50 pieces), and finally calculating the average of all these individual measurements. The preferred dimensions of the particles can also be stated in terms of an average particle weight. Preferably, the particles of the nylon 6-containing multicomponent material have an average particle weight of 0.1 milligrams to 100 kilograms, preferably 1 milligrams to 10 kilograms, more preferably 10 milligrams to 1 kilogram, and most preferably 10 milligrams to 100 grams. The use of nylon 6-containing multicomponent material particles having the aforementioned dimensions has the advantage of a larger surface area and / or easier handling of the particles and / or mixing with the organic solvent added for extraction in the nylon 6 preconcentration section.

[0060] Optionally, the nylon 6-containing multicomponent material is cleaned before preconcentration of nylon 6 is carried out. This is advantageous since any (adherent) dirt that is removed will not consequently interfere with the next step of the method of the invention.

[0061] As used herein, the term "cleaning" is defined as any process that removes non-nylon 6 materials that are attached to or intermingled with a nylon 6-containing multicomponent material. Cleaning is advantageous because any non-nylon 6 materials that are removed will not result in interference with the next steps of the method of the present invention.

[0062] Optionally, the nylon 6-containing multicomponent material is cleaned by washing with a solvent, preferably water, before being fed into the nylon 6 preconcentration section. This is advantageous since any (adhering) dirt is removed, which does not consequently interfere with the next step of the method of the present invention. Preferably, a detergent in a concentration range of 0-30% by weight of the solvent is added to the solvent to improve the washing efficiency. In another preferred embodiment, the washing process includes a final rinse step with a detergent-free (clean) washing solvent to remove any residues of detergent and any existing dirt adhering to the nylon 6-containing multicomponent material. Preferably, the washing solvent is heated to further enhance the washing process. Optionally, the nylon 6-containing multicomponent material is dried after the cleaning step and before being fed into the nylon 6 preconcentration section. This has the advantage that the solvent added for extraction in the preconcentration section is not diluted or contaminated by the washing solvent. The washing is preferably carried out under friction. Various types of industrial washing systems are commercially available, such as rotary plastic washers and (high-speed) friction washers. Optionally, mechanical crushing and washing of the nylon 6-containing multicomponent material is combined, for example in a so-called wet crushing device.

[0063] Optionally, prior to mechanical comminution or fragmentation of the nylon 6-containing multicomponent material, metal chips, rocks and other obstructions that cause heavy wear of the equipment used for mechanical comminution or fragmentation are removed. Preferably, non-nylon 6-containing materials, such as polyethylene, polypropylene and nylon 6,6-containing materials, are removed prior to mechanical comminution or fragmentation of the nylon 6-containing multicomponent material or thereafter as described below. The removal of the foreign objects may be performed mechanically or manually. The removal of the obstructions has the advantage that the maintenance costs of the equipment used for mechanical comminution or fragmentation can be significantly reduced. In addition, the nylon 6 content of the material obtained after mechanical comminution or fragmentation is higher than if the removal of the obstructions is not performed. Optionally, the foreign objects are separated from the nylon 6-containing multicomponent material that has been mechanically comminuted or fragmented. For this purpose, various separation processes can be applied, such as, but not limited to, density separation and magnetic separation. In density separation, materials of different densities are placed in a liquid of intermediate density, in which the lower density materials float and separate from the higher density sinking materials. In practice, density separation is often performed by a series of density separation stages. For example, in one stage, high density materials such as rocks, sand and metals (including iron and lead) are separated and removed, while in another stage, low density materials such as polyolefins, polypropylene and polyethylene are separated and removed. Magnetic separation is a process of separating components of a mixture by using magnets to attract magnetic materials. A process typically used for magnetic separation separates magnetic materials from non-magnetic materials. Removal of foreign matter in the comminuted or fragmented nylon 6-containing multicomponent material is advantageous, since such materials may interfere with subsequent steps of the method of the present invention. Optionally, the nylon 6-containing multicomponent material, which has preferably been washed and crushed, is densified. Preferably, the densification of the nylon 6-containing multicomponent material is carried out by feeding it into a melting furnace (eg an extruder) or by compacting it in a (mechanical) compactor or agglomerator.Densification of the preferably cleaned and / or crushed nylon 6-containing multicomponent material has the advantage of increased bulk density, which reduces intermediate storage and transportation costs when pre-processing is carried out at a different location (see below).

[0064] In the melting furnace the nylon 6-containing multicomponent material is melted. Preferably the resulting polymer melt is filtered. This has the advantage that solid impurities are removed. The melted and optionally filtered polymer melt is then cooled and preferably fed to a pelletizer. The pelletizer cuts the product into pellets. The size and shape of the pellets (often called granules) can be chosen within wide limits. Generally, the pellets are cylindrical (resulting in thin strands chopped into small pieces). However, other shapes such as (not perfect) spheres are also possible. The size of the pellets can be chosen within wide limits. Usually the pellets have a diameter in the range of 1 to 10 mm, preferably 2 to 7 mm, more preferably 3 to 5 mm. In a preferred embodiment, the pellets have a length in the range of 1 to 50 mm, preferably 2 to 25 mm, more preferably 3 to 15 mm.

[0065] Pelletization of the preferably cleaned and crushed nylon 6-containing multicomponent material has the advantage of an increased bulk density, which reduces the costs of intermediate storage and transportation when pretreatment is carried out at different locations (see below). Apart from the increased density, pelletization also provides other benefits, such as a homogeneous shape and structure of the material to be processed, which is convenient for (automatic) feeding into equipment applied for nylon 6 preconcentration by extraction with solvents.

[0066] The site where the pretreatment of the nylon 6-containing multicomponent material is carried out and the site where the nylon 6 preconcentration by extraction with a solvent is located can be the same. However, preferably, one or more of the pretreatment steps are carried out at different sites, for example at a site dedicated to the pretreatment of waste polymeric materials and in particular nylon 6-containing multicomponent materials. The nylon 6-containing multicomponent materials pretreated at different sites can then be transported to the site where the nylon 6 preconcentration by extraction with a solvent is located.

[0067] Thus, according to a particularly advantageous embodiment of the present invention, prior to step a), the material comprising the nylon 6-containing multicomponent material is subjected to a pretreatment and preconcentration in a pretreatment section [A], in particular purification in a purification section and / or mechanical crushing in a mechanical crushing section and / or a densification section and extraction section, in order to obtain a material derived from the nylon 6-containing multicomponent material.

[0068] <Nylon 6 preconcentration step a)> In step a) of the method of the present invention, the nylon 6-containing multicomponent material is extracted with one or more organic solvents in the nylon 6 preconcentration section to obtain a solid preconcentrated nylon 6-containing material enriched in nylon 6 compared to the nylon 6-containing multicomponent material. This is a key step of the method of the present invention, which ensures a high yield and high quality of ε-caprolactam that can be obtained using the present invention. This step is particularly important when a multilayer film is used as the starting material, especially when the nylon 6-containing layer is sandwiched between other polymer layers and therefore cannot be directly contacted for depolymerization. Preconcentration of the nylon 6-containing multicomponent material is further particularly important when a multicomponent material comprising nylon 6 and at least one non-nylon 6 polymer is used as the starting material, especially when nylon 6 is present in the nylon 6-containing multicomponent material as a separate domain and / or as a mixture with at least one non-nylon 6 polymer and therefore cannot be directly contacted for depolymerization.

[0069] The extraction in the nylon 6 preconcentration section according to the present invention is typically carried out as follows: (i) adding one or more organic solvents to a nylon 6-containing multicomponent material; (ii) performing a phase separation to obtain a liquid extract phase comprising the solvent and dissolved components from the nylon 6-containing multicomponent material, and an at least partially solid phase comprising undissolved components of the nylon 6-containing multicomponent material and optionally the solvent; (iii) removing the solvent from the liquid extraction phase and, if present, from at least a partially solid phase to obtain two solid phases, one of which is a pre-concentrated nylon 6-containing material enriched in nylon 6 compared to the nylon 6-containing multicomponent material used as starting material; Includes.

[0070] Step (i) of course also includes treatment with a solvent, i.e. the solvent and the nylon 6-containing multicomponent material are brought into contact for a time and under conditions sufficient to dissolve the components to be extracted from the nylon 6-containing multicomponent material. The phase separation in step (ii) can be carried out by any suitable means known for solid / liquid phase separation. Suitable phase separation means are, for example, filters, centrifuges, cyclones. The solvent removal in step (iii) is advantageously carried out by evaporation of the solvent, which gives the dissolved components extracted from the nylon 6-containing multicomponent material as a residual solid precipitate. However, various techniques exist and can be used that allow the recovery of the solvent from the dissolved compounds. These techniques are well known to those skilled in the art and include cooling, evaporation, distillation, precipitation by addition of a precipitant (a solvent for precipitating the dissolved polymer) and combinations thereof.

[0071] The terms "extraction", "extracted" and "extracting", as used herein, refer to a physical or chemical method of removing one or more components from a substrate by a solvent followed by solvent removal and recovery of the extracted components. In the method of the present invention, one or more solvents may be used to extract nylon 6, in which case a pre-concentrated nylon 6-containing material is obtained as the remaining solid residue after removal of one or more solvents from an extraction phase containing a liquid solvent, and / or may be used to extract non-nylon 6 compounds from a nylon 6-containing multicomponent material, in which case the remaining undissolved nylon 6-containing multicomponent material, optionally after removal of adhering solvent, is the pre-concentrated nylon 6-containing material referred to herein.

[0072] The term "preconcentrated" as used herein refers to the extraction of a nylon 6-containing multicomponent material with one or more solvents and subsequent solvent removal to obtain a material enriched in nylon 6 compared to the nylon 6-containing multicomponent material used as starting material. "Enriched in nylon 6" means enriched compared to the nylon 6-containing multicomponent material used as starting material. The enrichment of nylon 6 is defined as the content of nylon 6 in weight percent based on the total weight of polymer in the solid nylon 6-containing material obtained after extraction compared to the content of nylon 6 in weight percent based on the total weight of polymer in the nylon 6-containing multicomponent material used as starting material. This enrichment depends very much on the proportion of non-nylon 6 compounds that are removed. The degree of enrichment in the preconcentrated nylon 6-containing material is advantageously 1.1-50, in particular 1.2-30, more particularly 1.5-10. If the starting material has a nylon 6 content of 20 wt. % based on the total polymer content, and the pretreated nylon 6-containing phase has a nylon 6 content of 80 wt. % based on the total polymer content, the degree of nylon 6 enrichment is (80% weight divided by 20% weight =) 4.

[0073] The solvent used for extraction in the nylon 6 preconcentration section can be an organic solvent or an inorganic solvent. Preferably, the solvent is an organic solvent. Extraction of nylon 6-containing multicomponent material with an organic solvent has the advantage that it is possible to separate the various components, in particular the various polymers, from each other and in particular from the nylon 6 to be enriched due to their different solubilities in certain solvents.

[0074] Extraction typically involves (i) contacting the nylon 6-containing multicomponent material with one or more solvents, resulting in a liquid extraction phase comprising the solvent and dissolved compounds from the nylon 6-containing multicomponent material, and a typically solid or partially solid second phase consisting of undissolved nylon 6-containing multicomponent material, followed by (ii) phase separation, and (iii) solvent removal to obtain a pre-concentrated nylon 6-containing material.

[0075] As explained above, depending on whether a solvent that dissolves (1) nylon 6 or (2) non-nylon 6 is used, a preconcentrated nylon 6-containing material will be obtained (1) after removal of the solvent from the liquid extraction phase containing dissolved nylon 6, or (2) from the solid or partially solid second phase of nylon 6-containing multicomponent material remaining undissolved. It is also possible to combine two or more different, especially complementary, extractions.

[0076] In the case of two or more solvents, the treatment can be carried out simultaneously or sequentially. When two or more solvents are used, the solvents should be distinguished by their nylon 6 dissolving ability. In a particular advantageous embodiment of the invention, step a) comprises at least a two-stage procedure in which (i) a first extraction is carried out on the nylon 6-containing multicomponent material with a solvent capable of dissolving the non-nylon 6 components, followed by (ii) a treatment and extraction of the remaining undissolved nylon 6-containing multicomponent material from the first extraction with a solvent capable of dissolving nylon 6, so that after phase separation, a pre-concentrated nylon 6-containing material is obtained after solvent removal from the liquid extraction phase containing dissolved nylon 6 resulting from this second extraction. Proceeding in this way is particularly advantageous when a multilayer film is used as starting material, in particular when the nylon 6-containing layer is covered, in particular sandwiched between other polymer layers, and therefore cannot be in direct contact with the solvent that dissolves nylon 6.

[0077] The choice of solvent and processing conditions (e.g. temperature, processing time, and amount of solvent relative to the amount of nylon 6-containing multicomponent material) can affect the effectiveness of the extraction. Depending on the solvent used, the extraction in step a) can be of the following types: - a preconcentration step, in which non-nylon 6 compounds are preferentially extracted from the nylon 6-containing multicomponent material (so that the resulting preconcentrated nylon 6-containing material is the unextracted nylon 6-containing multicomponent material, optionally after removal of the adhering solvent); - a preconcentration step, in which nylon 6 compounds are preferentially extracted from the nylon 6-containing multicomponent material (whereby the preconcentrated nylon 6-containing material is obtained after removing the solvent from the liquid extraction phase comprising the solvent and dissolved nylon 6); and - Nylon 6 and non-nylon 6 compounds are preferentially extracted from nylon 6-containing multicomponent materials in a sequential manner, i.e. extractions are performed in combination with extractions for non-nylon 6 compounds and nylon 6 in succession. It could be.

[0078] Extraction in which non-nylon 6 compounds are preferentially extracted from a nylon 6-containing multicomponent material can be carried out using a suitable solvent as a selective extractant for non-nylon 6 compounds. This is a solvent that readily dissolves non-nylon 6 compounds while dissolving nylon 6 to a limited extent. The solvent must have high selectivity for dissolving non-nylon 6 compounds. Apart from the choice of solvent, the temperature at which the extraction is carried out, the treatment time, and the amount of solvent relative to the amount of nylon 6-containing multicomponent material can also have a significant effect on the extraction selectivity. Thus, the choice of these parameters depends on the type of non-nylon 6-containing component to be selectively removed. A person skilled in the art can easily determine, by simple trial dissolution experiments, which solvent is effective for extracting the non-nylon 6-containing component of interest in a given nylon 6-containing multicomponent material. Any one or more of the organic solvents described below with respect to the specific non-nylon 6 compounds can be used as the solvent in the process of the present invention.

[0079] For dissolving polyolefins (e.g. LD, LLD and HD polyethylenes, and polypropylenes), solvents selected from the group consisting of, for example, aliphatic, naphthenic, aromatic hydrocarbons and mixtures thereof, are particularly useful. These are obtained as boiling fractions in petroleum refining to produce fuels such as gasoline and diesel. The aforementioned boiling fractions include paraffin wax, petroleum wax and white spirits, each of which may be used as a solvent in accordance with the present invention. Pure solvents such as isomeric mixtures of xylenes or toluene are also known to dissolve polyolefins. Chlorinated hydrocarbons such as tetrachloroethane may also be used to dissolve polyolefins.

[0080] A wide variety of solvents can be used to dissolve the polystyrene-based polymer, including aromatic organic solvents. Preferably, benzene, toluene, xylene and mixtures thereof are used as solvents to dissolve the polystyrene-based polymer. Most preferably, xylene is used to dissolve the polystyrene-based polymer.

[0081] To dissolve polyvinyl chloride, solvents such as tetrahydrofuran, cyclohexane, dioxane and methyl ethyl ketone (MEK) and mixtures thereof are preferably used.

[0082] Solvents that can be used to dissolve other polymeric non-nylon 6 compounds are known to those skilled in the art or can be easily identified by conducting pilot dissolution experiments. Due to the versatility of the method of the present invention, other factors can also be taken into consideration when selecting a solvent for extraction in the nylon 6 preconcentration section, such as the stable commercial availability, ease of handling, health aspects and cost of the solvent, among others.

[0083] After extraction, in which the non-nylon 6 compounds are preferably extracted with a solvent, the undissolved compounds are removed by phase separation from the mixture obtained in the nylon 6 preconcentration section. The extraction should be carried out in such a way that the largest proportion by weight of the undissolved compounds is nylon 6 upon extraction with a solvent that preferentially dissolves the non-nylon 6 compounds. This undissolved material then represents the nylon 6-rich preconcentrated nylon 6-containing material, possibly after removal of the entrained solvent. The used solvent is usually recovered from the extraction phase and reused in the nylon 6 preconcentration section.

[0084] In some cases, the extraction is carried out more than once, in which the non-nylon 6 compounds are preferentially extracted. By choosing a different solvent and / or other processing conditions (e.g., a different extraction temperature), the non-nylon 6 compounds that were not removed in the previous extraction can be removed in additional extractions. After every extraction, a pre-processed, usually solid or partially solid, nylon 6-containing phase is obtained that is richer in nylon 6 than the pre-concentrated nylon 6-containing material resulting from the previous extraction. With each extraction, more and more non-nylon 6 compounds are gradually extracted from the nylon 6-containing multicomponent material.

[0085] Alternatively, or as a complementary extraction to the above extraction with a solvent that dissolves non-nylon 6, extraction in which nylon 6 is preferentially extracted from a nylon 6-containing multicomponent material can be carried out using a suitable solvent as an extractant selective for nylon 6. To preferentially extract nylon 6, a solvent is used that dissolves nylon 6 but has limited dissolution of non-nylon 6. In other words, a solvent with high selectivity for dissolving nylon 6 should be used. As with the selective dissolution of non-nylon 6 compounds, the selective dissolution of nylon 6 compounds can also be affected by the choice of solvent, the temperature at which the extraction is carried out, the processing time, and the amount of solvent relative to the amount of nylon 6-containing multicomponent material.

[0086] Solvents known from prior art methods for extracting polyamides can be used in this nylon 6 specific extraction step. For example, EP 603434 A1 discloses suitable solvents for dissolving polyamides, including nylon 6. Such solvents include concentrated inorganic acids, formic acid, chloroacetic acid, phenol, cresol, alcoholic solutions of alkaline earth halides, aromatic alcohols such as phenylethanol and benzyl alcohol, as well as glycols, lactams and lactones. US Patent No. 5,840,773 describes aliphatic alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, pentanol, hexanol, 2-ethylbutanol, 4-methylpentanol, 1-heptanol, 2-heptanol, 4-heptanol, 2,4-dimethylpentanol, 1-octanol, 2-octanol, 2-ethylhexanol, 1-nonanol, 2-nonanol, n-decanol, n-undecanol, n-dodecanol, n-tridecanol, n-tetradecanol, n-pentadecanol, n-hexadecanol, n-octadecanol, and the like, as well as substituted monohydric and dihydric alcohols, such as 2-methoxy-1-ethanol and methylene glycol, as solvents for dissolving polyamides, such as nylon 6. In a preferred embodiment of U.S. Pat. No. 5,840,773, C1-C 12 Alcohols are used. In particular, methanol and ethanol are preferably used as the extractant. It is also conceivable that the extractant is a mixture of an aliphatic alcohol and water. US5840773 further discloses that an extraction time of 60 minutes has been found to be suitable for methanol extraction of polyamide-6, and that the extraction is preferably carried out in an autoclave at a temperature of about 135°C to about 140°C. Along these lines, US5840773 states that polyamide-6,6 is preferentially dissolved in methanol at a temperature of at least about 140°C. In Example IV of US5840773, an extraction temperature for polyamide-6,6 of about 160°C is applied.

[0087] In some cases, the extraction in which nylon 6 is preferentially extracted is carried out two or more times. After each extraction, a pre-concentrated nylon 6-containing material is obtained that is richer in nylon 6 than the pre-concentrated nylon 6-containing material resulting from the previous extraction. This is believed to be due to the fact that each extraction gradually reduces the amount of impurities in the pre-concentrated nylon 6-containing material, which typically includes non-nylon 6 compounds.

[0088] After extraction, in which nylon 6 compounds are preferentially extracted with the solvent, the solvent is recovered. In doing so, first, the undissolved materials are removed from the liquid extraction phase containing the solvent and nylon 6, for example by filtration or centrifugation. The extraction should be carried out in such a way that the maximum proportion by weight of the undissolved compounds are non-nylon 6 compounds. Second, the solvent is recovered from the nylon 6-containing liquid extraction phase to obtain a preconcentrated solid nylon 6-containing material enriched in nylon 6. Any of the above-mentioned solvent removal techniques, such as cooling, evaporation, distillation, precipitation by adding a precipitant (a solvent for precipitating the dissolved polymer), and combinations thereof, can be carried out to separate the dissolved nylon 6-containing material from the solvent.

[0089] The extraction may further be a combination of sequential extractions with a solvent that preferentially extracts non-nylon 6 compounds and a solvent that preferentially extracts nylon 6. Such a combination of sequential extractions results in a nylon 6-containing phase that is more enriched in nylon 6 than a nylon 6-containing phase that has been pretreated only once.

[0090] In an embodiment of the present invention, the nylon 6-containing multicomponent material is first extracted in a first nylon 6 pre-concentration section with a solvent that preferentially extracts non-nylon 6 compounds from the nylon 6-containing multicomponent material to obtain a nylon 6-rich pre-concentrated nylon 6-containing material. In a second extraction, the nylon 6-rich pre-concentrated nylon 6-containing material is treated with a solvent that preferentially extracts nylon 6 compounds from the nylon 6-rich pre-concentrated nylon 6-containing material to obtain a nylon 6-rich pre-concentrated nylon 6-containing material, which can then be used in step b). For example, in the first extraction, the non-nylon 6 compound LD polyethylene is removed from the nylon 6-containing multicomponent material by extraction with white spirit. In the second extraction, the nylon 6-rich pre-concentrated nylon 6-containing material is further extracted with methanol or aqueous methanol (e.g., water and MeOH in a weight ratio of 1:19) to obtain a further pre-concentrated solid nylon 6-containing material after removal of the solvent (methanol, water).

[0091] According to another advantageous embodiment of the present invention, the nylon 6-containing multicomponent material is first treated in a first nylon 6 preconcentration section with a solvent that preferentially extracts nylon 6 compounds from the nylon 6-containing multicomponent material to obtain a nylon 6-rich preconcentrated nylon 6-containing material. In a second extraction, the nylon 6-rich preconcentrated nylon 6-containing material is treated with a solvent that preferentially extracts non-nylon 6 compounds from the nylon 6-rich preconcentrated nylon 6-containing material to obtain a nylon 6-rich preconcentrated nylon 6-containing material. For example, in the first extraction, nylon 6 is extracted from the nylon 6-containing multicomponent material with ethanol to form a nylon 6-rich nylon 6-containing phase after recovery of the ethanol. In the second extraction, non-nylon 6 components are further extracted from the nylon 6-rich preconcentrated nylon 6-containing material with toluene to obtain a nylon 6-rich nylon 6-containing phase.

[0092] The extraction with the solvent in the nylon 6 preconcentration section is carried out at a temperature of 0° C. to 350° C. (above this temperature nylon 6 decomposes), more preferably 20° C. to 210° C., and most preferably 50° C. to 190° C. This temperature range enhances the selective extraction of most solvents.

[0093] The time required for extraction in the extraction section, i.e., extraction with a solvent, can be easily determined by a person skilled in the art through routine experimentation. The time allowed for extraction should preferably take into consideration the type of nylon 6-containing multicomponent material, as well as the amount of nylon 6 contained therein and its accessibility. The time required for extraction can range from a few seconds to a few hours. Preferably, the time required for extraction is longer than 5 seconds and shorter than 6 hours. More preferably, the time required for extraction is longer than 15 seconds and shorter than 2 hours.

[0094] As a result of the extraction in the nylon 6 preconcentration section, a solid preconcentrated nylon 6-containing material rich in nylon 6 is obtained. The term "solid" in this case refers to the state of the material at room temperature (20°C). At higher temperatures, the preconcentrated nylon 6-containing material may also exist as a melt. The preconcentrated nylon 6-containing material is stable and may be stored for later use in step b) of the method of the invention or may be transported to a depolymerization section at a separate location for this purpose. Thus, similar to the above description of the other pretreatment steps, the site where the nylon 6 preconcentration by extraction with a solvent is carried out and the site where steps a) to d) of the method of the invention are carried out may be the same or different. Preferably, one or more of the pretreatment step and the preconcentration step are carried out at different locations, for example at a site dedicated to the pretreatment of waste polymeric materials and in particular nylon 6-containing multicomponent materials. The nylon 6-containing multicomponent materials pretreated and preconcentrated at various locations may then be transported to the site where one or more of steps a) to d) of the method of the invention are carried out.

[0095] <Depolymerization step b)> In step b) of the present invention, the preconcentrated nylon 6-containing material rich in nylon 6 obtained in the nylon 6 preconcentration section is fed into the depolymerization section and depolymerized to form ε-caprolactam. The formed ε-caprolactam is discharged from the depolymerization section as an ε-caprolactam-containing stream. The depolymerization section comprises one or more depolymerization reactors operated in series and / or parallel.

[0096] In some cases, the pre-concentrated nylon 6-containing material is mechanically compressed to a smaller volume before being introduced into the depolymerization section. In particular, the pre-concentrated nylon 6-containing material can be compressed into dense particles before being introduced into the depolymerization section, for example, by mechanical compaction, or by extrusion of the molten material followed by cooling and cutting to size, or by forming droplets of the molten material which are then solidified by cooling. Such compression has the advantage that a smaller volume is required for intermediate storage and transportation, and injection into the depolymerization section may be easier.

[0097] Optionally, the pre-concentrated nylon 6-containing material is dried before being fed into the depolymerization section, which has the advantage that less or no solvent is carried into the depolymerization section, which may have a detrimental effect on the depolymerization process (e.g., slower depolymerization reaction rate, higher catalyst consumption, the resulting vapor stream containing ε-caprolactam and water in the depolymerization section may contain more impurities, etc.).

[0098] The pre-concentrated nylon 6-containing material is preferably fed to the depolymerization reactor as a solid phase or as a melt, which can be accomplished by using an extruder, gear pump, or other means known to those skilled in the art. Feeding the pre-concentrated nylon 6-containing material to the depolymerization reactor can be accomplished by continuous or intermittent injection of the pre-concentrated nylon 6-containing material enriched in nylon 6.

[0099] In the depolymerization section, the preconcentrated nylon 6-containing material is depolymerized to form ε-caprolactam. This is achieved by contacting the preconcentrated nylon 6-containing material with water, preferably in the steam state. By feeding water as steam to the depolymerization reactor, a vapor stream containing ε-caprolactam and water, which are desired as products of step b) according to the present invention, can be obtained, optionally without further heating. The weight-to-weight ratio of water to ε-caprolactam of 2:1 to 15:1, which is also desired in this vapor stream, can be obtained by adjusting the ratio of steam and preconcentrated nylon 6-containing material fed to the depolymerization section. During the depolymerization reaction, decomposition products can be formed, including linear oligomers of ε-caprolactam and cyclic oligomers of ε-caprolactam. In addition, the feed stream of preconcentrated nylon 6-containing material rich in nylon 6 can also contain other components, namely impurities such as non-nylon 6 compounds and residues of solvents used in the nylon 6 preconcentration section, which remain stable, react or decompose under the depolymerization conditions. Thus, the vapor stream withdrawn from the depolymerization section contains not only water and ε-caprolactam but also impurities.

[0100] The depolymerization reaction is preferably carried out at a temperature of at least 180°C but not exceeding 400°C. The preferred temperature range for the depolymerization reaction is 200°C to 350°C, more preferably 220°C to 340°C, most preferably 240°C to 325°C. In general, the rate of formation of ε-caprolactam increases at higher temperatures. Temperatures below 400°C are preferred, since at temperatures above 400°C side reactions of nylon 6 and reactions of impurities occur more frequently, leading to the formation of a more diverse and / or more abundant group of impurities. Some of these impurities will end up in the product stream comprising ε-caprolactam discharged from the depolymerization reactor. In a preferred embodiment of the invention, the depolymerization of the preconcentrated nylon 6-containing material is carried out at a temperature in the range of 220°C to 340°C or 240°C to 325°C. This temperature range has the result that after purification of the obtained crude product, ε-caprolactam of particularly high purity can be obtained. The depolymerization of nylon 6 is accomplished under wet conditions, i.e., in the presence of water, preferably in the steam form, especially superheated steam.

[0101] Preferably, superheated steam having a temperature between 100°C and 600°C is fed to the depolymerization reactor. Preferably, the superheated steam fed to the depolymerization reactor has a temperature which is at least the melting temperature of nylon 6. Preferably, the energy content of the superheated steam fed to the depolymerization reactor is high enough so that no additional heat input is required to carry out the depolymerization reaction and evaporate the ε-caprolactam formed. In a preferred embodiment of the invention, the depolymerization section is fed with superheated steam having a temperature in the range of 220°C to 575°C. In an even more preferred embodiment of the invention, the depolymerization section is fed with superheated steam having a temperature in the range of 275°C to 500°C.

[0102] The depolymerization of the pre-concentrated nylon 6-containing material in the presence of water vapor can be carried out in the presence of an additional depolymerization agent such as ammonia, an amine, or an alcohol, such as methanol and ethanol.

[0103] Most preferably, the depolymerization is carried out in the presence of a catalyst. Preferably, the catalyst used is a (Lewis or Bronsted) acid or base. The acid catalyst may in particular be selected from the group consisting of orthophosphoric acid, p-toluenesulfonic acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids such as xylenesulfonic acid, 4-sulfoisophthalic acid and other sulfonated aromatic hydrocarbons, solid acids, salts of the aforementioned acids, Al2O3 and SiO2, and combinations thereof. The base catalyst may for example be selected from the group consisting of alkalis such as alkali hydroxides, alkali salts, alkaline earth hydroxides and earth salts, organic bases and solid bases, and combinations thereof. Preferably, orthophosphoric acid, boric acid, organic acids, alkali hydroxides and alkali salts are used as catalysts. More preferably, orthophosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate are used. More preferably, orthophosphoric acid, p-toluenesulfonic acid, boric acid and sodium hydroxide are used. In one particularly preferred embodiment, orthophosphoric acid is used as the depolymerization catalyst, and in another embodiment, p-toluenesulfonic acid is used.

[0104] Although the aforementioned (Lewis or Bronsted) acids or bases are called "catalysts", it is known that some of them are consumed during the depolymerization reaction, resulting in the formation of by-products. For example, it is known that phosphoric acid is consumed during the depolymerization of nylon 6 with steam, resulting in the production of phosphorus-containing by-products. Generally, these phosphorus-containing by-products are ineffective as catalysts and represent a loss of effective catalytic activity. Moreover, some catalysts, such as H3PO4, have a tendency to polymerize and (partially) lose their catalytic activity, especially at higher temperatures.

[0105] However, in another preferred embodiment of the present invention, no catalyst is used to depolymerize the pre-concentrated nylon 6-containing material. This has the advantage of being less costly (both for catalyst and catalyst waste disposal), but higher temperatures (and pressures) are typically required.

[0106] The advantage of the catalyst (particularly orthophosphoric acid) is that the depolymerization reaction starts at a low temperature and can be carried out under atmospheric conditions. The appropriate concentration of catalyst used for the depolymerization of nylon 6 to ε-caprolactam is known to those skilled in the art and can be easily determined by routine experimental work. If the catalyst concentration used is too low, the reaction rate is slow. On the other hand, if the catalyst concentration used is too high, the reaction is fast but the side reactions also increase. Furthermore, the cost of the catalyst increases, which is economically disadvantageous. Typically, the catalyst content is 0.01-100% by weight based on the nylon 6 contained in the depolymerization reactor. Preferably, the catalyst content is 0.1-50% by weight. The optimum catalyst concentration varies depending on the type of catalyst applied for the depolymerization of nylon 6. For orthophosphoric acid catalyst, the preferred content is 0.1-25% by weight, more preferably 1-20% by weight. For p-toluenesulfonic acid catalyst, the preferred content is 10-35% by weight.

[0107] The depolymerization of nylon 6 can be carried out in a batch, semi-continuous, or continuous manner, all of which are well known to those skilled in the art. The terms "batch," "semi-continuous," and "continuous," as used herein, refer to a manner in which a nylon 6-containing feedstock, i.e., a pre-concentrated nylon 6-containing material rich in nylon 6 (and optionally a catalyst), is charged to a depolymerization reactor, and a residue is discharged from the depolymerization reactor. Typically, the residue includes non-nylon 6 compounds, non-depolymerized nylon 6, ε-caprolactam, catalyst, and decomposition products of these components.

[0108] In a preferred embodiment, the depolymerization of nylon 6 is carried out in a batch mode. In the batch mode, the feedstock, i.e., the pre-concentrated nylon 6-containing material enriched in nylon 6, and optionally a catalyst, are first charged to the depolymerization reactor. Superheated steam is then charged to the depolymerization reactor, and ε-caprolactam is discharged from the depolymerization reactor as a vapor stream comprising ε-caprolactam and water. The charging of superheated steam to the depolymerization reactor is then discontinued. After removing the residue from the depolymerization reactor, a new cycle is started by charging the feedstock (and optionally a catalyst) to the depolymerization reactor. In a preferred embodiment, the residue is not necessarily removed every cycle.

[0109] In a particularly advantageous embodiment, the depolymerization of nylon 6 is carried out in a continuous mode. In a continuous mode, the nylon 6-containing feedstock (and optionally the catalyst) is continuously fed to the depolymerization reactor. At the same time, superheated steam is continuously fed to the depolymerization reactor such that ε-caprolactam is continuously discharged from the depolymerization reactor as a vapor stream comprising ε-caprolactam and water. In addition, residue is continuously discharged from the depolymerization reactor. Preferably, the nylon 6-containing feedstock (and optionally the catalyst) is fed as a melt, solid pieces, a slurry or a solution. More preferably, the nylon 6-containing feedstock (and optionally the catalyst) is fed as a melt, a slurry or a solution.

[0110] In a preferred embodiment, the depolymerization of nylon 6 is carried out in a semi-continuous mode. In a semi-continuous mode, a nylon 6-containing feedstock (and optionally a catalyst) is intermittently charged to the depolymerization reactor while superheated steam is continuously charged to the depolymerization reactor and ε-caprolactam is continuously discharged from the depolymerization reactor as a vapor stream comprising ε-caprolactam and water. Residue is intermittently discharged from the depolymerization reactor in the semi-continuous mode of nylon 6 depolymerization.

[0111] The ε-caprolactam leaves the depolymerization section in the form of a vapor stream comprising water and ε-caprolactam in a weight to weight ratio of 1:1 to 50:1, preferably 2:1 to 10:1, more preferably 3:1 to 8:1. Preferably, the pressure of the ε-caprolactam in the vapor stream is 0.02 to 10 MPa, more preferably 0.08 to 1.5 MPa, most preferably 0.1 to 0.5 MPa.

[0112] <Recovery step c)> In the recovery section, ε-caprolactam is recovered from the ε-caprolactam-containing vapor stream discharged from the depolymerization section, preferably by (partial) condensation of the vapor stream.

[0113] The ε-caprolactam-containing vapor stream discharged from the depolymerization section contains ε-caprolactam, water and impurities. The ε-caprolactam can be separated from the remaining components of the vapor stream by passing the vapor stream from the depolymerization reactor, usually to a condenser (preferably a partial condenser), to obtain a condensate containing ε-caprolactam. Preferably, the ε-caprolactam is separated from the remaining components of the vapor stream by passing the product stream from the depolymerization reactor, preferably to a distillation column, to obtain a water-rich phase as an overhead product and an ε-caprolactam-rich phase as a bottom product.

[0114] The ε-caprolactam recovered in the recovery section is in a crude state since it contains impurities such as nylon 6 decomposition products and other impurities originating from the non-nylon 6 components of the multi-component starting material. The crude ε-caprolactam recovered in step c) comprises water and ε-caprolactam, preferably an aqueous solution comprising ε-caprolactam. Thus, the crude ε-caprolactam recovered in the recovery section requires additional purification to produce ε-caprolactam of high purity. Therefore, "crude" as used herein can be defined as having a lower purity than the purified ε-caprolactam obtained as the product of the process of the present invention.

[0115] Preferably, the crude ε-caprolactam contains in the range of 6% to 95% by weight, more preferably 20% to 90% by weight, and most preferably 40% to 75% by weight of ε-caprolactam. The remainder is primarily water.

[0116] Purification step d) In step d), the crude ε-caprolactam obtained in the recovery section [C] is purified in the purification section [D] to produce high purity ε-caprolactam. Optionally, the crude ε-caprolactam is filtered before being fed to the purification section, which ensures the removal of undissolved impurities that may interfere with further purification steps.

[0117] Purified ε-caprolactam is obtained from the crude ε-caprolactam by first extracting the crude ε-caprolactam with an organic solvent in step (i) which gives an aqueous phase and an organic phase containing the organic solvent, ε-caprolactam and impurities. The organic solvent used for the extraction of the crude ε-caprolactam is preferably an aromatic hydrocarbon, an aliphatic hydrocarbon, a cycloaliphatic hydrocarbon, a halogenated hydrocarbon and / or a C4-C 10 Optionally, the organic solvent used for the extraction of the crude ε-caprolactam is preferably an aromatic hydrocarbon, an aliphatic hydrocarbon, an alicyclic hydrocarbon, a halogenated hydrocarbon and / or a C4-C 10and a C5-C8 alkane or C5-C8 cycloalkane. Particularly good results are achieved when the organic solvent for the extraction of crude ε-caprolactam is selected from the group consisting of cyclohexane, benzene, toluene, methylene chloride, chloroform, trichloroethane, 4-methyl-2-pentanol (also known as MIBC, methyl isobutyl carbinol), 1-octanol, 2-ethylhexanol, and mixtures thereof. More preferably, the organic solvent for the extraction of crude ε-caprolactam is selected from the group consisting of benzene, toluene, alcohol, and mixtures thereof. Even more preferably, the organic solvent for the extraction of crude ε-caprolactam is selected from the group consisting of toluene, 1-octanol, 4-methyl-2-pentanol, 2-ethylhexanol, and mixtures thereof. Typically, the weight ratio of the organic solvent to ε-caprolactam is from 0.01:1 to 40:1, preferably from 0.01:1 to 20:1, more preferably from 0.05:1 to 10:1, and most preferably from 0.1:1 to 5:1.

[0118] Optionally, the organic solvent for the extraction of crude ε-caprolactam is alkane C m H 2m+2 (m is 5 to 8), cycloalkane or C m H 2m (m is 5 to 8) to form a mixed extractant. Particularly good results are achieved when the alkane or cycloalkane is present in the mixed extractant in a weight ratio in the range of 5 to 90%, preferably 25 to 75%, based on the total weight of the mixed extractant.

[0119] In an embodiment of the invention in which the organic solvent is less dense than the crude ε-caprolactam, the extraction with the organic solvent in step d)(i) is carried out in an extraction column operated in countercurrent, into which the crude ε-caprolactam to be purified is introduced at the top and the organic solvent at the bottom. The extraction results in an aqueous phase and an organic phase containing the organic solvent, ε-caprolactam and impurities, the weight ratio of impurities to ε-caprolactam in the organic phase being reduced compared to the weight ratio of impurities to ε-caprolactam in the crude ε-caprolactam. Thus, the extraction results in an ε-caprolactam that is purer than before the extraction.

[0120] In another preferred embodiment of the present invention, in which the organic solvent is denser than the crude ε-caprolactam, the extraction with the organic solvent in step d(i) is carried out in an extraction column operated in countercurrent, into which the crude ε-caprolactam to be purified is introduced in the lower part of the column and the organic solvent in the upper part. The extraction results in an aqueous phase containing water and impurities and an organic phase containing the organic solvent, ε-caprolactam and impurities, the weight ratio of impurities to ε-caprolactam in the organic phase being reduced compared to the weight ratio of impurities to ε-caprolactam in the crude ε-caprolactam. Thus, as a result of this extraction, the ε-caprolactam is purer than before the extraction.

[0121] Optionally, the organic phase containing the organic solvent, ε-caprolactam and impurities is washed with water or an aqueous alkaline solution before entering step d(iii). If washing is carried out with an aqueous alkaline solution, the alkaline solution is preferably an aqueous solution containing an alkali metal hydroxide and / or an alkali metal carbonate, preferably sodium hydroxide or potassium hydroxide. The alkali metal hydroxide solution preferably contains 0.5-2.0 wt. % sodium hydroxide or potassium hydroxide.

[0122] The person skilled in the art can determine by routine experimental work the amount of water or aqueous alkaline solution required for efficient washing of the organic phase containing the organic solvent, ε-caprolactam and impurities. Typically, this amount is 0.1-5% by weight, based on the amount of organic solvent, excluding ε-caprolactam, dissolved in the organic phase to be washed. Preferably, washing of the organic phase containing the organic solvent, ε-caprolactam and impurities with water or aqueous alkaline solution is carried out in a wash column operated in countercurrent, into which the organic phase containing the organic solvent, ε-caprolactam and impurities is introduced at the bottom of the column and water or aqueous alkaline solution at the top of the column. As a result of washing, a washed organic phase containing the organic solvent, ε-caprolactam and impurities and a phase containing the residue are obtained. Usually, the phase containing the residue contains water and ε-caprolactam and only small amounts of impurities. As a result of washing, the impurity content of the washed organic phase is reduced compared to the impurity content of the organic phase before washing.

[0123] Optionally, step d(iii) of the inventive process, in which purified ε-caprolactam is obtained by distillative removal of impurities having a lower or higher boiling point than ε-caprolactam, is preceded by one or more treatment steps in order to reduce the energy usage of purification step d) of the inventive process, to increase the quality of the purified ε-caprolactam and / or to simplify the distillative removal of impurities having a lower or higher boiling point than ε-caprolactam.

[0124] Optionally, according to step d)(ii) of the process of the present invention, the obtained organic phase comprising the organic solvent, ε-caprolactam and impurities, optionally washed with water or an aqueous alkaline solution, is subjected to a solvent switching process in which the organic solvent in the organic phase comprising the organic solvent, ε-caprolactam and impurities is replaced by water to obtain an aqueous phase comprising water, ε-caprolactam and impurities with a lower or higher boiling point than ε-caprolactam, the solvent switching process being selected from a process based on back extraction (also known as re-extraction) with water and a process based on solvent exchange distillation in which the organic solvent is distilled off and water is introduced. The term "replaced" as used herein means that at least 60%, preferably at least 80%, most preferably at least 90, 95 or 98% by weight of the organic solvent present in the organic phase comprising the organic solvent, ε-caprolactam and impurities is replaced by water.

[0125] Two solvent switching options are discussed below. Solvent Switching: First Choice: The optionally washed ε-caprolactam-solvent phase is then re-extracted with water, thereby obtaining an ε-caprolactam-aqueous phase. This ε-caprolactam-aqueous phase is then preferably subjected to stripping and / or distillation to remove the residual solvent. The amount of water used to recover ε-caprolactam is not critical, but the amount of water used is usually 0.5 to 20 times by weight relative to the ε-caprolactam recovered. Preferably, the amount of water used is 0.75 to 10 times by weight, more preferably 1 to 5 times by weight.

[0126] The re-extraction with water can be advantageously carried out in an extraction column operated in countercurrent, into which the ε-caprolactam-solvent phase to be purified is introduced at the bottom and water at the top. The re-extraction results in an ε-caprolactam-water phase and an impurity-containing solvent phase. Usually, the impurity-containing solvent phase is reused, possibly after purification, preferably by distillation.

[0127] In another preferred embodiment, where the organic phase, optionally washed, containing the organic solvent, ε-caprolactam and impurities is less dense than water, the organic phase is introduced at the lower part of the extraction column and the water at the upper part of the extraction column. The stripping results in an organic solvent phase containing impurities and an aqueous phase containing water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam, the weight ratio of impurities to ε-caprolactam being reduced compared to the weight ratio of impurities to ε-caprolactam in the organic phase containing the organic solvent, ε-caprolactam and impurities before stripping. Stripping thus results in a purer ε-caprolactam. Preferably, the organic solvent phase containing impurities is reused, optionally after purification (preferably by distillation).

[0128] In another preferred embodiment, where the organic phase containing the organic solvent, ε-caprolactam and impurities is denser than water, the organic phase is introduced at the upper part of the extraction column and the water at the lower part of the extraction column. The stripping results in an organic solvent phase containing impurities and an aqueous phase containing water, ε-caprolactam and impurities with lower or higher boiling points than ε-caprolactam, the weight ratio of impurities to ε-caprolactam being reduced compared to the weight ratio of impurities to ε-caprolactam in the organic phase containing the organic solvent, ε-caprolactam and impurities before stripping. Thus, after stripping, the ε-caprolactam is purer than before stripping. Preferably, the organic solvent phase containing impurities is reused, optionally after purification (preferably by distillation).

[0129] The resulting ε-caprolactam-water phase, which may have been stripped and / or distilled to remove the residual solvent, is concentrated by evaporation of the water, thus giving a concentrated aqueous ε-caprolactam phase, the ε-caprolactam content of which is usually between 50 and 99.9% by weight, based on the total phase.

[0130] Solvent Switching: 2nd Option: Optionally, instead of re-extraction with water, the organic solvent is evaporated from the optionally washed ε-caprolactam-solvent phase. Any suitable evaporation vessel, for example a column, can be used. Preferably, the evaporation is carried out in the presence of water. More preferably, the evaporation is carried out as an azeotropic distillation, in which case the organic solvent is evaporated as an azeotrope. The evaporation results in an ε-caprolactam product. Typically, the ε-caprolactam product is an aqueous ε-caprolactam phase. The ε-caprolactam content of this aqueous ε-caprolactam phase is usually between 50 and 99.9% by weight based on the total phase.

[0131] The solvent switching step may be a step based on solvent exchange distillation, where the organic solvent is distilled off and water is introduced. In a preferred embodiment, the solvent switching step is a step based on solvent exchange distillation carried out as a one-step step, where the organic solvent is distilled off from the organic phase comprising the organic solvent, ε-caprolactam and impurities, and water is introduced. More preferably, the solvent switching is carried out as an azeotropic distillation with the addition of water, where the organic solvent is evaporated as an azeotropic mixture comprising the organic solvent and water. The aim of the azeotropic distillation is to remove the organic solvent and add water. Preferably, almost all the organic solvent is removed. "Almost all" in this context means that at least 90%, preferably at least 95%, most preferably at least 98 or 99% by weight of the organic solvent present in the organic phase comprising the organic solvent, ε-caprolactam and impurities is removed. Preferably, the water is added as a liquid. More preferably, the water is added in liquid form as a reflux liquid to the upper part of the distillation column. Even more preferably, part of the water added as a reflux liquid is obtained by condensation of the azeotropic mixture distilled off in the distillation column. Any suitable vessel, such as a column, preferably a distillation column operated in a continuous manner, can be used for the solvent switching process. The distillation column can include a tray column, a packed column, or a combination thereof. In another preferred embodiment, the solvent exchange distillation is carried out as a two-stage process: the first stage is a pre-concentration stage and the second stage is the actual solvent exchange distillation.

[0132] The organic phase containing the organic solvent, ε-caprolactam and impurities is introduced into the first stage. In the first stage, a first fraction of the organic solvent is removed by distillation from the organic phase containing the organic solvent, ε-caprolactam and impurities in the upper part of the distillation column. Preferably, this distillation is carried out under reflux. Under reflux means that the organic solvent is introduced into the upper part of the distillation column in liquid phase. More preferably, a part of the organic solvent removed by distillation in the upper part of the distillation column is introduced into the upper part of the distillation column as a liquid after condensation. The remaining organic phase containing the organic solvent, ε-caprolactam and impurities is discharged from the first stage and introduced into the second stage. Due to the distillation in the first stage, the chemical composition of the remaining organic phase containing the organic solvent, ε-caprolactam and impurities is different from the organic phase containing the organic solvent, ε-caprolactam and impurities introduced into the first stage. Generally, compared to the organic phase containing the organic solvent, ε-caprolactam and impurities charged in the first stage, the remaining organic phase containing the organic solvent, ε-caprolactam and impurities has a higher weight percent content of ε-caprolactam and compounds with boiling points higher than ε-caprolactam, and a lower weight percent of compounds with boiling points lower than ε-caprolactam.

[0133] In a second step, the remaining organic solvent is distilled off from the remaining organic phase containing the organic solvent, ε-caprolactam and impurities, and water is introduced. More preferably, in the second step, the solvent switch is carried out as an azeotropic distillation with the addition of water, in which case the organic solvent is evaporated as an azeotropic mixture comprising the organic solvent and water.

[0134] Any suitable vessel, such as a column, preferably a distillation column operated in a continuous manner, can be used for each stage of the solvent switching. The distillation column can include a tray column, a packed column, or a combination thereof.

[0135] The solvent exchange distillation (carried out either as a one-step process or as a two-step process) results in an aqueous phase containing water, ε-caprolactam, impurities with lower or higher boiling points than ε-caprolactam, and optionally residual organic solvent. Preferably, the ε-caprolactam content of this aqueous phase is 25-99.9%, preferably 50-99.5%, most preferably 85-99% by weight of the total aqueous phase.

[0136] Thus, according to a particularly advantageous embodiment of the invention, after extraction of the crude ε-caprolactam in step d) (i), the purification in step d) also comprises a step of (ii) solvent switching based on solvent exchange distillation.

[0137] Optionally, the aqueous ε-caprolactam phase obtained according to the first or second solvent switching option step is subsequently subjected to oxidation and / or treatment with an ion exchange resin and / or hydrogenation.

[0138] In a preferred embodiment, an oxidizing agent, such as potassium permanganate, sodium permanganate, and / or hydrogen peroxide, is added to the aqueous ε-caprolactam phase. Most preferably, potassium permanganate is used as the oxidizing agent.

[0139] Preferably, the oxidizing agent is added to the aqueous ε-caprolactam phase in the form of an aqueous solution, so that a dilute aqueous solution is obtained during purification by oxidation. The oxidizing agent may be added as a solid. The oxidizing agent may be added as a slurry. The skilled person can determine the amount of oxidizing agent required for efficient oxidation of the aqueous ε-caprolactam phase by routine experimental work. The exact amount of oxidizing agent depends, among other things, on the composition of the nylon 6 stream fed to the depolymerization section in the process of the present invention. Preferably, the amount of oxidizing agent is between 0.01 and 5% by weight relative to the amount of ε-caprolactam dissolved in the aqueous phase to be oxidized.

[0140] The temperature used for the oxidation of the aqueous solution in the process of the present invention may vary. Preferably, the oxidation of the aqueous solution with an oxidizing agent is carried out at a temperature in the range of 20° C. to 85° C., more preferably in the range of 30° C. to 80° C., the oxidizing agent being selected from the group consisting of potassium permanganate, sodium permanganate and hydrogen peroxide and combinations thereof, in particular potassium permanganate.

[0141] The length of time for oxidation with the oxidizing agent may vary. Preferably, in the process of the present invention, the oxidation of the aqueous ε-caprolactam phase with the oxidizing agent is carried out for a period of from 1 minute to 24 hours, more preferably from 2 minutes to 6 hours, and most preferably from 5 minutes to 2 hours.

[0142] The concentration of ε-caprolactam in the aqueous ε-caprolactam phase used for oxidation with the oxidizing agent may vary. Preferably, the aqueous solution used for oxidation comprises ε-caprolactam and water in a weight to weight ratio of 5:1 to 1:5, more preferably 3:1 to 1:3, most preferably 2:1 to 1:2. Optionally, the weight to weight ratio of ε-caprolactam and water is adjusted before the addition of the oxidizing agent to the aqueous phase. Preferably, the weight to weight ratio of ε-caprolactam and water is adjusted either by adding water or by removing water.

[0143] When potassium permanganate and / or sodium permanganate are used as the oxidizing agent, solid manganese(IV) oxide (MnO2) particles are formed as a reaction product. Those skilled in the art can determine, by routine experimentation, the optimal solid-liquid filtration procedure for efficiently removing the solid manganese(IV) oxide particles from the aqueous phase after oxidation. The use of filter aids such as activated carbon particles or diatomaceous earth to improve the filtration procedure is common in this regard.

[0144] In another preferred embodiment, the aqueous ε-caprolactam phase is treated with an ion exchange resin. Optionally, the aqueous ε-caprolactam phase is first treated with an acidic cation exchange resin, followed by a basic anion exchange resin. Optionally, the aqueous ε-caprolactam phase is first treated with a basic anion exchange resin, followed by an acidic cation exchange resin. Preferably, the cation exchange resin is a sulfonated polystyrene or a styrene-divinylbenzene copolymer, and the anion exchange resin is a polystyrene containing quaternary ammonium groups, or an exchange resin having secondary or tertiary amino groups. The treatment temperature of the aqueous ε-caprolactam solution may be preferably 15° C. to 100° C., more preferably 35° C. to 70° C. In order to efficiently perform the adsorption and separation of impurities on the cation exchange resin and the anion exchange resin, the concentration of the aqueous ε-caprolactam solution to be treated may be preferably 5 to 90%, more preferably 5 to 70%.

[0145] A person skilled in the art can determine by routine experimentation the optimum (combination of) ion exchange resins and amounts of ion exchange resins for efficient removal of impurities from the aqueous ε-caprolactam phase and regeneration of the loaded ion exchange resin.

[0146] In another preferred embodiment, the aqueous ε-caprolactam phase is hydrogenated in the presence of a hydrogenation catalyst known per se. The hydrogenation can be advantageously carried out, for example, as described in EP-A-635487.

[0147] The hydrogenation temperature is generally between 20°C and 160°C. Generally, a temperature that is not too low is selected, because at low temperatures the reaction time is longer. Generally, the temperature is not too high, because high temperatures have a negative effect on the quality of ε-caprolactam. Therefore, the temperature is preferably between 70°C and 130°C, most preferably between 80°C and 100°C.

[0148] The hydrogenation pressure may be between 0.1 MPa and 15 MPa. High pressure is advantageous since it allows dissolving a large amount of hydrogen in the water-ε-caprolactam mixture. Excessively high pressure is not necessary since the impurity content is usually not high enough to require a large amount of hydrogen. Ultra-high pressure also has the disadvantage that expensive processing equipment is required. Thus, the pressure is generally between 0.3 MPa and 5 MPa.

[0149] The hydrogenation catalyst may be any known heterogeneous hydrogenation catalyst. Examples of such catalysts are ruthenium-aluminum oxide, rhodium-aluminum oxide, platinum on carbon, palladium on carbon, Raney nickel, nickel-silica and nickel-aluminum oxide. Preferably, a nickel-containing catalyst is used.

[0150] Suitable nickel catalysts generally have a nickel content of 5-80% by weight based on the metal and the support. Besides nickel, the catalyst may contain some activators such as Zr, Mn, Cu or Cr. The activator content is generally 1-20% by weight. If a heterogeneous catalyst containing palladium is used, the palladium content will generally be 0.01-10% by weight.

[0151] From the aqueous ε-caprolactam phase, which has optionally been subjected to oxidation and / or treatment with an ion exchange resin and / or hydrogenation, water is optionally evaporated. Following oxidation and / or hydrogenation and / or evaporation of water, the aqueous ε-caprolactam phase is distilled to recover high-purity ε-caprolactam and a distillation residue.

[0152] In a preferred embodiment of the process of the present invention, the aqueous phase comprising water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam prior to the distillative removal of step d)(iii) is A solvent replacement step, at least partially replacing the organic solvent with water, selected from a process based on re-extraction with water and a process based on solvent replacement distillation, in which the organic solvent is distilled off and water is introduced; and Optionally followed by oxidation with an oxidizing agent selected from potassium permanganate, sodium permanganate and hydrogen peroxide; and / or Optionally subsequent treatment with an acidic cation exchange resin and / or a basic anion exchange resin; and / or Optionally followed by hydrogenation in the presence of a hydrogenation catalyst selected from Raney nickel, nickel-silica, nickel-aluminum oxide, ruthenium-aluminum oxide, rhodium-aluminum oxide, platinum on carbon and palladium on carbon. is obtained by

[0153] In step d)(iii) of the process of the present invention, purified ε-caprolactam is obtained by distillative removal of impurities having a boiling point lower or higher than ε-caprolactam. Typically, the distillation of the optionally washed organic phase comprising the organic solvent, ε-caprolactam and impurities is carried out under reduced pressure. In an embodiment of the present invention, the distillation is carried out at a pressure of less than 50 kPa, preferably less than 20 kPa, more preferably less than 10 kPa. Preferably, the distillation temperature at the bottom of the distillation column is between 100° C. and 200° C., more preferably between 110° C. and 180° C. The distillation comprises separating low boiling organic impurities (having a boiling point lower than ε-caprolactam) and / or separating high boiling organic impurities (having a boiling point higher than ε-caprolactam) from ε-caprolactam.

[0154] In a preferred embodiment of the present invention, an alkali metal hydroxide, preferably NaOH, is added to the organic phase prior to the distillative removal in step d)(ii). Preferably, the amount of NaOH added ranges from 0.5 to 150 mmol per kg of ε-caprolactam, more preferably and most preferably from 2 to 80 mmol per kg of ε-caprolactam. This results in a particularly effective distillative removal of impurities with lower and higher boiling points than ε-caprolactam in the subsequent distillation.

[0155] The purification of crude ε-caprolactam in the purification section according to the invention typically comprises the following steps: (i) obtaining an aqueous phase and an organic phase by extracting crude ε-caprolactam with an organic solvent, the organic phase comprising the organic solvent, ε-caprolactam and impurities; (ii) optionally a step of switching the solvent, at least partially replacing the organic solvent with water to obtain an aqueous phase comprising water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam, said solvent switching step (ii) being selected from a process based on back extraction with water and a process based on solvent exchange distillation, in which the organic solvent is distilled off and water is introduced; and (iii) obtaining purified ε-caprolactam by distillative removal of impurities having a boiling point lower or higher than that of ε-caprolactam; Includes.

[0156] In a preferred embodiment of the present invention, the crude ε-caprolactam obtained from the Beckmann rearrangement of cyclohexanone oxime is also purified in the purification section separately from the crude ε-caprolactam recovered in the recovery section, which has the advantage that the carbon footprint of the plant producing ε-caprolactam de novo from the Beckmann rearrangement of cyclohexanone oxime can be reduced by introducing the recycled ε-caprolactam according to the present invention.

[0157] The high purity ε-caprolactam obtained by the process of the present invention can be used to make nylon 6 using methods well known to those skilled in the art. This nylon 6 can then be used in any known material, including engineering materials, fibers and films.

[0158] <Plant> The invention further provides a plant capable of carrying out the above-mentioned method of the invention. All apparatus features specifically described below with respect to the plant also apply to specific embodiments of the method of the invention and vice versa, i.e. the plant is suitable for carrying out the method of the invention. It should therefore be understood that what has been described with respect to the method of the invention applies equally to the embodiment of the plant.

[0159] The plant may correspond to a laboratory installation as in the examples. Preferably, however, the plant is an industrial-scale plant. By "industrial-scale" is meant that the plant has a production capacity (i.e. can in principle produce) of at least 500 tonnes / year of ε-caprolactam when operated full-time.

[0160] The plant of the present invention is suitable for producing purified ε-caprolactam from a nylon 6-containing multicomponent material and comprises at least four sections: (A) a nylon 6 preconcentration section, (B) a depolymerization section, (C) a recovery section, and (D) a purification section. These sections, and therefore the plant, are adapted to carry out the process of the present invention as described above.

[0161] In addition, the plant may include a mechanical crushing section [O] for fragmenting the nylon 6-containing multicomponent material into small pieces, and / or a washing section [W] for washing the nylon 6-containing multicomponent material. The mechanical crushing section [O] includes equipment for mechanically fragmenting the nylon 6-containing multicomponent material into small pieces. Non-limiting examples of the fragmenting equipment are a cutter, a shredder, a grinder, a pulverizer, or a chipper.

[0162] The nylon 6 pre-concentration section [A] comprises an extraction device in which the nylon 6-containing multicomponent material is extracted with one or more organic solvents. The extraction device can have any desired form, such as a mixer-settler extractor, an extraction column and / or a centrifugal extraction device, and is optionally operated under pressure. The nylon 6-containing multicomponent material particles are preferably mixed with the organic solvent in the nylon 6 pre-concentration section by means of an agitator. The nylon 6 pre-concentration section can comprise further units, in particular units allowing the storage, recovery and purification of one or more organic solvents used in this section, as well as units allowing the collection and intermediate storage of the obtained mainly non-nylon 6-containing by-products formed in this section and the desired pre-concentrated nylon 6-containing material.

[0163] The depolymerization section [B] comprises one or more depolymerization reactors operated in series and / or parallel. The nylon 6-containing multicomponent material is fed to the reactors as a solid or melt, preferably as a melt. This feeding can be accomplished by using an extruder, gear pump, or other means known in the art.

[0164] During production, the depolymerization reactor is at least partially filled with nylon 6-containing feed, residual material, ε-caprolactam (and optionally catalyst). The depolymerization reactor can have any desired configuration. Preferred reactor types are stirred and unstirred bubble column reactors, stirred reactors, and extruder type reactors.

[0165] The depolymerization reactor must be equipped with a facility for feeding the nylon 6-containing multicomponent material, superheated steam, and optionally a catalyst. In addition, the depolymerization reactor must be equipped with a facility for discharging a vapor stream containing ε-caprolactam and water, and residual materials.

[0166] Adequate contact between the steam and the reactor contents is essential for effective operation. Such contact can be achieved by a variety of means commonly known in the art. For example, multiple inlets can be used to distribute the steam throughout the material, for example using a steam distributor. Improved contact can be achieved by incorporating mechanical agitation into the reactor, for example using a combination of rotating paddles and stationary fins.

[0167] Depolymerization is usually complete in 0.5 to 6 hours. If hot superheated steam is not available at the production site, it must be systematically produced by superheating the steam available from the boiler in a so-called superheater.

[0168] The stripping section [C] comprises one or more condensers (preferably partial condensers) into which the vapour stream comprising ε-caprolactam and water is introduced. Such a condenser (partial condenser) can have any desired form. Preferably, the condenser is a distillation column which obtains a water-rich phase as overhead product and an ε-caprolactam-rich phase as bottom product.

[0169] The purification section [D] comprises one or more extraction units, optionally one or more solvent switching units, an optional oxidation section, an optional hydrogenation section, and one or more distillation units, into which crude ε-caprolactam is input and from which high purity ε-caprolactam is discharged.

[0170] The extraction equipment is fed with crude ε-caprolactam and an organic solvent, and discharges an organic phase containing organic solvent, ε-caprolactam and impurities, and an aqueous phase containing water and impurities. The extraction equipment is selected from mixer-settler extractors, extraction columns, centrifugal extractors, and combinations thereof. Preferably, the extraction equipment is a static or stirred extraction column, such as a KARR column, a SCHEIBEL column, a rotating disk contactor (RDC), a pulsed column, a sieve tray (static) column, a randomly packed (static) column, and a structured packed (SMVP) (static) column.

[0171] The solvent switching device is charged with water and an organic phase containing the organic solvent, ε-caprolactam and impurities, and discharged with an organic solvent and an ε-caprolactam-aqueous phase containing water, ε-caprolactam and impurities. The solvent switching device for the re-extraction based process is selected from mixer-settler extractors, extraction columns, centrifugal extractors, and combinations thereof. Preferably, the device for re-extraction is a static or stirred extraction column, such as a KARR® column, a SCHEIBEL® column, a rotating disk contactor (RDC), a pulsed column, a sieve tray (static) column, a randomly packed (static) column, and a structured packed (static) column.

[0172] The solvent switching equipment for the process based on solvent exchange distillation is preferably selected from sieve tray type distillation column, random packing distillation column and structured packing distillation column. Preferably, the distillation column is equipped with equipment for reboiler, condenser and reflux. The distillation column can be operated at atmospheric pressure, subatmospheric pressure or superatmospheric pressure. Preferably, water is charged to the upper part of the distillation column and an aqueous phase containing water, ε-caprolactam and impurities with lower or higher boiling points than ε-caprolactam is discharged from the lower part of the distillation column.

[0173] The oxidation section comprises one or more oxidation reactors operated in series and / or parallel. The oxidation agent and the ε-caprolactam-aqueous phase containing water, ε-caprolactam and impurities are fed to the oxidation section. Usually, the oxidizing agent is fed as an aqueous solution or as a solid. When potassium permanganate or sodium permanganate is used as the oxidizing agent, the oxidation section further comprises a filtration section. The oxidation reactor can have any desired form. Preferred reactor types are stirred and unstirred reactors and packed tower reactors. The oxidation reactor must be equipped to feed the aqueous phase containing water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam, and the oxidizing agent. In addition, the oxidation reactor must be equipped to discharge the oxidized ε-caprolactam-aqueous phase containing water, ε-caprolactam and impurities, and optionally the solid manganese(IV) oxide (MnO2) particles formed. Preferably, the oxidation is carried out at a temperature in the range of 20° C. to 85° C. and under atmospheric conditions.

[0174] Possibly present solid manganese(IV) oxide (MnO2) particles can be removed by precipitation or solid-liquid filtration, preferably by solid-liquid filtration. The use of filter aids such as activated carbon particles to improve the filtration procedure is common. Filter systems suitable for the separation of solid manganese(IV) oxide particles are known to the skilled artisan. Such a filter system is fed with a suspension of ε-caprolactam oxide-aqueous phase containing water, ε-caprolactam and impurities and solid manganese(IV) oxide particles, and discharges a filtered ε-caprolactam oxide-aqueous phase containing water, ε-caprolactam and impurities. In general, the solid manganese(IV) oxide particles are retained in the filter system. Preferably, such a filter system is operated in a semi-continuous manner, where the suspension and the filtered phase are continuously fed and discharged, while the separated solids are collected in the filter system. From time to time, the feeding of the suspension is interrupted and the collected solids are removed from the filter system.

[0175] The hydrogenation section comprises one or more hydrogenation reactors operated in series and / or parallel. All types of reactors can be used in which the hydrogenation is carried out in the presence of a solid catalyst. Preferably, the hydrogenation reactor is a stirred tank reactor or a fixed bed reactor.

[0176] A gas stream containing hydrogen and an ε-caprolactam-water phase containing water, ε-caprolactam and impurities are fed to the hydrogenation section. A hydrogenated ε-caprolactam-water phase containing water, ε-caprolactam and impurities and, optionally, a purge gas stream containing hydrogen are discharged from the hydrogenation section. Under normal operating conditions, the hydrogenation catalyst remains in the hydrogenation reactor and is replaced only after deactivation.

[0177] The distillation apparatus is charged with an ε-caprolactam-water phase containing water, ε-caprolactam and impurities and discharges high-purity ε-caprolactam, water and impurities, i.e. low-boiling organic impurities (having a boiling point lower than ε-caprolactam) and high-boiling organic impurities (having a boiling point higher than ε-caprolactam). The distillation apparatus is selected from sieve tray distillation columns, randomly packed distillation columns, structured packed distillation columns and horizontal and vertical (falling and rising) film evaporators. Preferably, the distillation column is equipped with equipment for a reboiler, a condenser and reflux. The distillation apparatus can be operated at atmospheric pressure, subatmospheric pressure or superatmospheric pressure, preferably subatmospheric pressure.

[0178] Preferably, the distillation comprises the separation of water, low-boiling organic impurities (having a boiling point lower than that of ε-caprolactam) and / or high-boiling organic impurities (having a boiling point higher than that of ε-caprolactam) from ε-caprolactam. Preferably, the distillation comprises in a first step the separation of water as an overhead product and the production of ε-caprolactam containing low-boiling and high-boiling impurities as a bottom product. In a second step, the low-boiling impurities are separated as an overhead product and ε-caprolactam containing high-boiling impurities is obtained as a bottom product. In a third step, high-purity ε-caprolactam is separated as an overhead product and a distillation residue containing ε-caprolactam and high-boiling impurities is produced as a bottom product. Optionally, the first and second steps are combined.

[0179] Preferably, prior to the distillative removal of water and impurities, an alkali metal hydroxide, preferably NaOH, is added to the oxidized ε-caprolactam-water phase containing water, ε-caprolactam and impurities. Preferably, the amount of NaOH added ranges from 0.5 to 100 mmol per kg ε-caprolactam, more preferably from 2 to 80 mmol per kg ε-caprolactam. This results in a particularly effective distillative removal of impurities with lower and higher boiling points than ε-caprolactam in the subsequent distillation.

[0180] The process of the present invention can be carried out in a continuous, semi-continuous or batch mode. Thus, the plant of the present invention can also be configured to allow one or more of these operating modes. In a preferred embodiment, the plant is configured to carry out the process of the present invention in a continuous or semi-continuous mode. However, discontinuous processes are also possible. For example, the plant of the present invention does not have to have all the sections described herein located in one place. In particular, it is possible that the nylon 6 preconcentration section is located in a first location, while the depolymerization section, the recovery section and the purification section are located in a second location. Similarly, the mechanical crushing section can be located in different locations.

[0181] In a particularly advantageous embodiment of the invention, the plant can comprise a purification section shared with a plant for the de novo synthesis of ε-caprolactam, which purification section is normally or actually used to purify crude ε-caprolactam produced by other processes, such as by Beckmann rearrangement of cyclohexanone oxime. The invention thus provides for the use of ε-caprolactam recovered from multilayer materials containing nylon 6 to reduce the carbon footprint of an ε-caprolactam production plant. Proceeding in this way also has the advantage that highly sophisticated purification sections of existing plants producing ε-caprolactam by the Beckmann rearrangement reaction can be used in the process of the invention. This is cost-effective since it is not necessary to build a separate purification section for the process and plant of the invention. It is surprising that recovered ε-caprolactam obtained by depolymerization of nylon 6 produced from nylon 6-containing multicomponent materials can be mixed and co-purified with crude ε-caprolactam produced by other processes, such as Beckmann rearrangement of cyclohexanone oxime, without compromising the quality of the crude ε-caprolactam. In the applicant's opinion, this is only possible by the special combination of nylon 6 preconcentration, depolymerization and recovery steps of the present invention, which results in an ε-caprolactam product of exceptional purity that can be mixed and co-purified with ε-caprolactam produced by other processes, such as Beckmann rearrangement, without any disadvantages in terms of the quality of the resulting product.

[0182] <product> The process of the invention makes it possible to produce a high purity and therefore high quality ε-caprolactam which meets the characteristic information for demanding applications while at the same time having a low product carbon footprint and being particularly economical due to the use of waste materials as starting material. In a preferred embodiment, the ε-caprolactam obtained by the process of the invention meets the following characteristic information: PAN: up to 5 E290: max 0.05 VB: max 0.5mmol / kg Alkalinity: Max 0.1mmol / kg Acidity: up to 0.1mmol / kg and the parameters and measurement methods are defined in the Examples section herein below.

[0183] The ε-caprolactam produced by the process of the invention is particularly economical and environmentally friendly, as evidenced by its much lower carbon footprint compared to conventionally produced ε-caprolactam (e.g. by Beckmann rearrangement of cyclohexanone oxime).

[0184] The environmental impact of a product is commonly expressed as the "product carbon footprint". The carbon footprint of a product is defined as the total emissions caused by the formation of that product, expressed in tonnes of carbon dioxide equivalent per tonne of product. The carbon footprint of a product varies depending on, among other things, the feed materials, auxiliary materials, energy consumption, energy source, production process and process efficiency. Quantification of the carbon footprint of a product can be done, for example, as described in the European standard EN ISO 14040:2006 ("Environmental management - Life cycle assessment - Principles and framework").

[0185] The product carbon footprint calculation may be performed either in-house or by an external (preferably) certified body that verifies and certifies the product carbon footprint calculation, for example according to the LCA standard ISO 14040.

[0186] J. Hong and X. Xu ("Environmental impact assessment of caprolactam production - a case study in China"; J. of Cleaner production 27, (Netherlands), 2012, 103-108; DOI: 10.1016 / j.jclepro.2011.12.037) report that the global warming potential of "virgin" ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime is 7.5 tons of CO2 equivalent per ton of ε-caprolactam when accompanied by coal-based electricity and steam generation. When accompanied by natural gas-based electricity and steam generation, the global warming potential of virgin ε-caprolactam from this ε-caprolactam production process is reduced to 6.4 tons of CO2 equivalent per ton of ε-caprolactam.

[0187] The product carbon footprint of the ε-caprolactam obtained by the process of the present invention is much lower than that of de novo synthesized, i.e. "virgin", ε-caprolactam. Preferably, the product carbon footprint of the ε-caprolactam obtained by the process of the present invention is less than 4 tons of CO2 equivalent per ton of ε-caprolactam, more preferably less than 3 tons of CO2 equivalent per ton of ε-caprolactam, even more preferably less than 2.5 tons of CO2 equivalent per ton of ε-caprolactam, and most preferably less than 2 tons of CO2 equivalent per ton of ε-caprolactam (based on Eco Invent version 3.7.1 (region: Europe) data). [Brief description of the drawings]

[0188] The invention will now be described with reference to the drawings, which show certain embodiments of the invention. The invention, however, as defined in the claims and generally as described herein, should not be limited to the embodiments shown by way of example in the following figures.

[0189] [Figure 1] 1 is a schematic diagram of the process of the present invention including the processing steps carried out in the nylon 6 preconcentration section, the depolymerization section, the recovery section and the purification section. [Diagram 2] FIG. 2 illustrates three embodiments of the nylon 6 preconcentration step a) of the method of the invention, in which a nylon 6-containing multicomponent material is extracted with an organic solvent to obtain a pretreated nylon 6-containing phase enriched in nylon 6. [Figure 2a] FIG. 2 illustrates an embodiment of nylon 6 pre-concentration step a) of the method of the present invention, which preferentially extracts non-nylon 6 compounds from a nylon 6-containing multicomponent material to obtain a pre-concentrated nylon 6-containing material enriched in nylon 6. [Figure 2b] FIG. 2 illustrates an embodiment of nylon 6 pre-concentration step a) of the process of the present invention, which preferentially extracts nylon 6 from a nylon 6-containing multicomponent material to obtain a pre-concentrated nylon 6-containing material enriched in nylon 6. [Figure 2c] FIG. 1 shows an embodiment of nylon 6 preconcentration step a) of the process of the invention, in which extraction of non-nylon 6 compounds from a nylon 6-containing multicomponent material is combined with extraction of nylon 6 from the resulting nylon 6-rich nylon 6-containing phase to obtain a nylon 6-containing phase that is even more enriched in nylon 6.

[0190] [Detailed description of the drawings] The method of the present invention is shown diagrammatically in Figure 1. The method comprises the following parts: - a nylon 6 pre-concentration part [A], in which a nylon 6-containing multicomponent material [1] is treated with an (organic) solvent [2] to obtain a pre-concentrated nylon 6-containing material [3] enriched in nylon 6 and a second phase [4] containing non-nylon 6 compounds; - Depolymerization section [B], where pretreated nylon 6 rich nylon 6 [3] is depolymerized to ε-caprolactam which is discharged as a product vapor stream [5] containing ε-caprolactam. In addition, residual materials [6] are also discharged. Superheated steam [7] and optionally a catalyst [8] are introduced into the depolymerization section [B]; - a recovery section [C] for recovering crude ε-caprolactam [9] from the ε-caprolactam-containing product vapor stream [5] discharged from the depolymerization section [B]; and - Refining section [D] which purifies the crude ε-caprolactam [9] discharged from the recovery section [C] to produce high-purity ε-caprolactam

[10] . Equipped with:

[0191] FIG. 2a shows an embodiment of the extraction in a nylon 6 pre-concentration section [A'], in which a nylon 6-containing multicomponent material [1'] is treated with a solvent [2'] that preferentially extracts non-nylon 6 compounds from the nylon 6-containing multicomponent material [1'] to obtain a pre-concentrated nylon 6-containing material [3'] enriched in nylon 6 and a second phase [4'] enriched in non-nylon 6 compounds.

[0192] FIG. 2b shows an embodiment of the extraction in a nylon 6 pre-concentration section [A″], where a nylon 6-containing multicomponent material [1″] is treated with a solvent [2″] that preferentially extracts nylon 6 from the nylon 6-containing multicomponent material [1″] to obtain a pre-concentrated nylon 6-containing material [3″] enriched in nylon 6 and a second phase [4″] enriched in non-nylon 6 compounds.

[0193] FIG. 2c shows an embodiment of extraction in a first nylon 6 pre-concentration section [A'''] in which a nylon 6-containing multicomponent material [1'''] is treated with a solvent [2'''] that preferentially extracts non-nylon 6 compounds from the nylon 6-containing multicomponent material [1'''] to obtain a pre-concentrated nylon 6-containing phase [3'''] enriched in nylon 6 and a second phase [4'''] enriched in non-nylon 6 compounds. In a second nylon 6 pre-concentration section [A''''], a pre-concentrated nylon 6-containing material [3'''] enriched in nylon 6 is treated with a second solvent [2''''] that preferentially extracts nylon 6 from the pre-concentrated nylon 6-containing material [3'''] enriched in nylon 6 to obtain a pre-treated nylon 6-containing phase [3''''] further enriched in nylon 6 and a further phase [4''''] enriched in non-nylon 6 compounds. EXAMPLES

[0194] The present invention is illustrated by the following examples, which are not intended to be limiting.

[0195] The starting material used in Examples 1, 2 and 4 and the Comparative Example was a multi-layer packaging film waste containing layers of polyethylene and nylon 6. The nylon 6 layer is buried in this used multi-layer packaging film waste, i.e. sandwiched between other layers, and therefore cannot be in full contact.

[0196] The nylon 6 preconcentration step a) of the multi-layer packaging film waste can be carried out as described in EP 0849312 or DE 102016015198, where polyethylene is selectively dissolved in an organic solvent, such as white spirit (Sigma-Aldrich; CAS number 68551-17-7) or methylcyclohexane, at high temperature, so that the resulting mixture contains undissolved nylon 6 and an organic solution containing the organic solvent and dissolved polyethylene. The undissolved nylon 6 material is obtained after separating the organic solution from the resulting mixture. The resulting undissolved nylon 6 material can be dried and optionally densified by melting under nitrogen and subsequently converted into solid particles enriched in nylon 6 compared to the nylon 6-containing multi-component starting material.

[0197] To determine the quality of the ε-caprolactam obtained, the following parameters were measured: the permanganate absorption number of ε-caprolactam was measured (PAN: ISO 8660 - Plastics - Determination of the permanganate absorption number of caprolactam - Spectroscopic analysis, 2nd edition ISO 8660; 2002). In addition, the absorbance at a wavelength of 290 nm was measured (E290: ISO 7059 - Caprolactam for technical purposes - Determination of the absorbance at a wavelength of 290 nm; 1982). In addition, the volatile base content was measured (Volatile Base (VB): ISO 8661 - Caprolactam for technical purposes - Determination of the volatile base content - Titration method after distillation, 1988). Finally, the alkalinity or acidity was measured to a level of 0.1% (weight / volume). エタノール) Methylene blue: 0.1% (weight / volume エタノール ) Methyl red is measured by titration (end point is grey) at 25°C using a 1:2 ratio of Tashiro indicator. A flask containing water and indicator is first titrated to grey, then X grams of an aqueous solution of ε-caprolactam containing Y weight percent ε-caprolactam (measured by refractive index) is added and the solution is titrated back to grey using 0.01N H2SO4 solution (if the solution is alkaline) or 0.01N NaOH solution (if the solution is acidic).

[0198] The alkalinity was then calculated using the following formula: Alkalinity(mmol / kg(ε-caprolactam))=v*t*1000 / (X*Y) (In the above formula: v = volume of H2SO4 solution added (ml) t = normality of H2SO4 solution (=0.01N) X = weight of sample (g) Y = concentration of ε-caprolactam (wt%) Obtained by.

[0199] The acidity was then calculated according to the following formula: Acidity(mmol / kg(ε-caprolactam))=v*t*1000 / (X*Y) (In the above formula: v = volume of NaOH solution added (ml) t = normality of NaOH solution (=0.01N) X = weight of sample (g) Y = concentration of ε-caprolactam (wt%) Obtained by.

[0200] A purer quality of ε-caprolactam that can be used undiluted for all major polymerization applications has the following properties: PAN: up to 5 E290: max 0.05 VB: max 0.5mmol / kg Alkalinity: Max 0.1mmol / kg Acidity: up to 0.1mmol / kg Satisfy all of the above.

[0201] [Example 1] <Depolymerization of nylon 6 and recovery of ε-caprolactam> The material used for depolymerization and further processing steps described below can be any nylon 6-containing multicomponent material or derivative thereof. The particular material used in the examples below was enriched in nylon 6 compared to the nylon 6-containing multicomponent starting material and was prepared as described above from multilayer packaging film waste.

[0202] This nylon 6-rich starting material was formed into pearl-like solid particles (diameter: 3-4 mm). The polyethylene content of this undissolved nylon 6 material was approximately 1 wt.% as measured by TGA (thermogravimetric analysis).

[0203] In step b), 33.6 g of pearl-shaped solid particles and 9.8 g of 20 wt.% phosphoric acid were charged into a Premex high-pressure autoclave. The reactor contents were first heated under nitrogen, and then superheated steam was continuously injected at a rate of 4 g / min during the 120 min reaction. The temperature and pressure in the reactor were maintained at 260° C. and 0.11 MPa, respectively. During the reaction, a steam stream was continuously discharged from the reactor.

[0204] In step c) the resulting vapor was cooled to 20° C. in order to recover crude ε-caprolactam from it. The condensate, containing an average of 28.3 grams of ε-caprolactam and the remainder mostly water, was concentrated by evaporation in a rotavap (rotary evaporator) operated under vacuum (9.5 kPa; water bath temperature approximately 65° C.) to an average ε-caprolactam concentration of 49.6% by weight. (The resulting mixture, crude ε-caprolactam, is the mixture to be purified.) Steps b) and c) were repeated five times. The solution obtained by combining the five mixtures was used as the stock solution in the following examples and comparative experiments.

[0205] This example shows that it is possible to obtain crude ε-caprolactam by depolymerization of nylon 6 derived from unwanted nylon 6 multilayer packaging film waste in good yield and without operational problems.

[0206] [Example 2] <Refining by extraction, caustic washing, re-extraction, oxidation and distillation> In step d)(i), 70 grams of crude ε-caprolactam obtained in Example 1 were extracted once with 100 grams and nine times with 50 grams of the solvent mixture MIBC / cyclohexane (50% by weight:50% by weight) at 25° C. The resulting ε-caprolactam phases containing the solvent mixture were combined in ten portions and washed with 7 grams of aqueous caustic solution (2% by weight). The washed ε-caprolactam containing solvent mixture was then extracted six times with 50 grams of water at 25° C. The resulting six portions of aqueous ε-caprolactam phase were combined. Water and the remaining solvent mixture were distilled off from the aqueous ε-caprolactam phase to obtain a concentrated ε-caprolactam solution with a water content of 50% by weight. The resulting mixture was treated with 0.2% by weight KMnO4 relative to ε-caprolactam at 50° C. for 2 hours. The solids formed were then removed from the oxidation reaction product by filtration. Then, 75 mmol of aqueous sodium hydroxide per kg of ε-caprolactam was added to the resulting aqueous ε-caprolactam solution.

[0207] In step d)(ii) the distillative removal of water and impurities with lower or higher boiling points than ε-caprolactam was carried out. Subsequently, water and impurities with lower boiling points than ε-caprolactam were removed as overhead product by vacuum distillation in a distillation plant operated batchwise. Finally, purified ε-caprolactam was recovered as overhead product at 300 Pa, while impurities with higher boiling points compared to ε-caprolactam were left as bottom product in the distillation plant. The characteristic information of this purified ε-caprolactam is: PAN: 5 E290: 0.023 VB: 0.167 Alkalinity: 0.044 It was.

[0208] From this example it can be concluded that purified ε-caprolactam meeting the required property information for major polymerization applications can be obtained from depolymerized waste multilayer packaging film pieces by removing the polyethylene by extraction and purifying by extraction with organic solvents, oxidation and distillation.

[0209] [Comparative experiment 1] <Purification by distillation> To 35 grams of crude ε-caprolactam obtained in Example 1, 0.75 mmol of aqueous sodium hydroxide per kg of ε-caprolactam was added. This mixture was then distilled according to the procedure described in Example 2. The characteristic information of the purified ε-caprolactam was: PAN: 73.5 E290: 0.531 VB: 0.718 Acidity: 7.643 It was.

[0210] This comparative experiment shows that the quality of ε-caprolactam obtained by depolymerization of small pieces of waste multilayer packaging film, followed by removal of polyethylene by extraction and purification by distillation, is very poor since it does not meet any of the required property information for the main polymerization applications.

[0211] [Comparative experiment 2] <Refining by oxidation and distillation> 35 grams of crude ε-caprolactam obtained in Example 1 was treated with 0.2% by weight of KMnO4 relative to ε-caprolactam at 50° C. for 2 hours. The solids formed were then removed from the oxidation reaction product by filtration. Then, 0.75 mmol of aqueous sodium hydroxide per kg of ε-caprolactam was added to the resulting aqueous ε-caprolactam solution. This mixture was then distilled according to the procedure described in Example 2. The properties of the purified ε-caprolactam are: PAN: 11.7 E290: 0.324 VB: 0.657 Acidity: 2.991 It was.

[0212] This comparative experiment shows that the quality of the ε-caprolactam obtained by depolymerization of small pieces of waste multilayer packaging film, removing the polyethylene therefrom by extraction and purifying it by oxidation and distillation is very poor since it does not meet any of the property information required for the main polymerization applications.

[0213] [Comparative experiment 3] <Purification by extraction, caustic washing, and re-extraction> 70 grams of crude ε-caprolactam obtained in Example 1 were extracted once with 100 grams and nine times with 50 grams of the solvent mixture MIBC / cyclohexane (50% by weight:50% by weight) at 50° C. The resulting ε-caprolactam phases containing the solvent mixture were combined in ten portions and washed with 7 grams of aqueous caustic solution (2% by weight). The washed ε-caprolactam containing solvent mixture was then re-extracted six times with 50 g of water at 25° C. The resulting six portions of aqueous ε-caprolactam phase were combined. Water and the remaining solvent mixture were distilled off from the aqueous ε-caprolactam phase to obtain a concentrated ε-caprolactam solution with an ε-caprolactam content of 50.4% by weight. The characteristic information of the purified ε-caprolactam is: PAN: 82 E290: 1.2 It was.

[0214] This comparative experiment shows that the quality of the ε-caprolactam obtained by depolymerization of small pieces of waste multilayer packaging film, followed by removal of the polyethylene by extraction therefrom and purification by extraction and re-extraction is very poor since it does not meet all the required property information for the main polymerization applications.

[0215] [Comparative experiment 4] <Refining by extraction, caustic washing, re-extraction and oxidation> The concentrated ε-caprolactam solution obtained in Comparative Experiment 3, with an ε-caprolactam content of 50.4% by weight, was treated with 0.04% by weight KMnO4 relative to ε-caprolactam at 50° C. for 2 hours. The solids formed were then removed from the oxidation reaction product by filtration. The characteristic information of the purified ε-caprolactam was: PAN: 83 E290: 3.01 It was.

[0216] This comparative experiment shows that the quality of the ε-caprolactam obtained by depolymerization of small pieces of waste multilayer packaging film, removing the polyethylene therefrom by extraction, re-extraction and purification by oxidation is very poor since it does not meet all the required property information for the main polymerization applications.

[0217] [Example 3] <Calculation of product carbon footprint of refined ε-caprolactam> A continuous process according to the present invention for producing purified ε-caprolactam from a multi-layer packaging film waste comprising a polyethylene layer and a nylon 6 layer was simulated. The nylon 6 content of the multi-layer packaging film waste comprising a polyethylene layer and a nylon 6 layer was 20 wt %.

[0218] The method includes: - cutting multi-layer packaging film waste, including a polyethylene layer and a nylon 6 layer, into small pieces; - washing a multi-layer packaging film waste piece comprising a polyethylene layer and a nylon 6 layer with water; - drying the washed pieces of multi-layer packaging film waste comprising a polyethylene layer and a nylon 6 layer by centrifugation; - Extraction of polyethylene using volatile oil; - Separation of the undissolved solid preconcentrated nylon 6-containing material by centrifugation; - washing the undissolved solid pre-concentrated nylon 6-containing material with water; - Separation of the washed undissolved solid preconcentrated nylon 6-containing material and the aqueous extract by centrifugation; - decolorization of volatile oil solutions containing polyethylene by treatment with activated carbon; - recovery of polyethylene from a polyethylene-containing volatile oil solution by cooling and partial evaporation of the volatile oil; - Melting and pelletizing of recycled polyethylene; - Melting and pelletizing of pre-concentrated nylon 6-containing material of washed undissolved solids; - Depolymerization of nylon 6 in pelletized nylon 6-containing materials under the influence of H3PO4 and superheated steam; - Recovery of crude ε-caprolactam by partial condensation of the vapors released from the depolymerization reactor; - Evaporative concentration of crude ε-caprolactam to 80% by weight ε-caprolactam; - Countercurrent extraction of concentrated crude ε-caprolactam with benzene; - washing of organic extracts with dilute caustic solutions; - Countercurrent extraction of the washed organic extract with water; - Evaporative concentration of the aqueous extract; - oxidation of the concentrated extract with KMnO4 followed by filtration of the oxidation product to remove the solids formed; - Caustic agent addition; - Recovery of pure ε-caprolactam by vacuum distillation Includes.

[0219] The main products of this process are polyethylene and pure ε-caprolactam. The recovery rate of pure ε-caprolactam is about 0.8 kg of pure ε-caprolactam per kg of nylon 6 in multi-layer packaging film waste containing a polyethylene layer and a nylon 6 layer. The resulting by-product is incinerated for energy recovery.

[0220] The product carbon footprint of refined ε-caprolactam was calculated based on the raw material consumption, while the utility of the above method is based on the data of Eco-Invent version 3.7.1. The allocation of the environmental impact of the products refined ε-caprolactam and polyethylene in the nylon 6 preconcentration section was based on the weight ratio of these products.

[0221] The results show that the product carbon footprint of purified ε-caprolactam obtained from multilayer packaging film containing a polyethylene layer and a nylon 6 layer is less than 2 tonnes of CO2 equivalent per tonne of ε-caprolactam (region: Europe).

[0222] [Example 4] <Depolymerization of nylon 6 and recovery of ε-caprolactam> The material used for depolymerization and further processing steps as described below was enriched in nylon 6 compared to the nylon 6-containing multicomponent starting material and was prepared as described above from multilayer packaging film waste. The nylon 6-rich starting material was formed into pearl-shaped solid particles (diameter: 3-4 mm). The polyethylene content of this undissolved nylon 6 material was about 1 wt% as measured by TGA (thermogravimetric analysis).

[0223] In step b), 33.6 g of pearl-shaped solid particles and 9.8 g of 20 wt.% phosphoric acid were charged into a Premex high-pressure autoclave. The reactor contents were first heated under nitrogen, then superheated steam was continuously injected at a rate of 2.7 g / min during the 135 min reaction. The temperature and pressure in the reactor were maintained at 260° C. and 0.11 MPa, respectively. During the reaction, a steam flow was continuously discharged from the reactor.

[0224] In step c), in order to recover crude ε-caprolactam from the resulting vapor, the vapor was cooled to 20° C. The condensate consisted of 26.1 grams of ε-caprolactam, with the remainder being mostly water.

[0225] Steps b) and c) were repeated following the same procedure, but this time 9.7 grams of 20% by weight phosphoric acid were charged into the Premex high-pressure autoclave and the resulting condensate consisted of 26.9 grams of ε-caprolactam.

[0226] The two ε-caprolactam-containing condensates were concentrated by evaporation in a rotavap (rotary evaporator) operated under vacuum (9.5 kPa; water bath temperature approximately 65° C.) and then combined to an ε-caprolactam concentration of 79.6% by weight. The resulting stock solution or crude ε-caprolactam is the mixture to be purified (see Example 5).

[0227] The properties of this crude ε-caprolactam are: PAN: 280 E290: 2.14 It was.

[0228] This example shows that it is possible to obtain crude ε-caprolactam by depolymerization of nylon 6 derived from unwanted nylon 6 multilayer packaging film waste in good yield and without operational problems.

[0229] [Example 5] <Purification by extraction, re-extraction, oxidation and distillation> In step d)(i), 43.4 grams of crude ε-caprolactam obtained in Example 4 were diluted to 68.9% by weight by adding 6.7 g of water and the resulting solution was extracted once with 77.5 grams of benzene and four times with 50 grams of benzene at 25° C. The resulting organic extracts were combined and concentrated by evaporation in a rotavap operated under vacuum (9.5 kPa; water bath temperature approximately 65° C.) to an ε-caprolactam concentration of about 24.5% by weight. The concentrated extract containing ε-caprolactam was then extracted three times in batches with 25 grams of water at a temperature of approximately 25° C. The resulting three aqueous ε-caprolactam phases were combined. The water and the remaining solvent mixture were distilled off from this aqueous ε-caprolactam phase to obtain a concentrated ε-caprolactam solution with a water content of 49.5% by weight. The characteristic information of the aqueous ε-caprolactam solution after re-extraction is: PAN: 83 E290: 1.15 It was.

[0230] The resulting mixture was treated with 0.2 wt. % KMnO4 relative to ε-caprolactam at 50° C. for 2 hours. The solids formed were then removed from the oxidation reaction product by filtration. After that, 75 mmol of aqueous sodium hydroxide per kg of ε-caprolactam was added to the aqueous ε-caprolactam solution after oxidation. The mixture was then distilled according to the procedure described in Example 2. The characteristic information of the purified ε-caprolactam was: PAN: <5 E290: <0.05 VB: <0.5mmol / kg Alkalinity: <0.1mmol / kg Acidity: <0.1mmol / kg It was.

[0231] From this example it can be concluded that purified ε-caprolactam meeting the required property information for major polymerization applications can be obtained from depolymerized waste multilayer packaging film pieces by extraction to remove polyethylene and purification by extraction with benzene, re-extraction with water, oxidation and distillation.

[0232] While the present invention has been illustrated with certain preferred embodiments, those skilled in the art will recognize that modifications, variations, including conversion to a continuous mode of operation, and improvements can be made while remaining within the scope and spirit of the invention. Accordingly, it is not intended that the invention be limited except as set forth in the appended claims.

Claims

1. 1. A process for recovering purified ε-caprolactam from a nylon 6-containing multicomponent material in a plant, the plant comprising: - nylon 6 depolymerization section, - Collection department, and - Refining department Equipped with And the method comprises: a) providing a pre-concentrated nylon 6-containing material obtained by extracting the nylon 6-containing multicomponent material with one or more organic solvents to obtain a solid pre-concentrated nylon 6-containing material enriched in nylon 6 relative to the nylon 6-containing multicomponent material; b) depolymerizing the pre-concentrated nylon 6-containing material in the presence of water in a depolymerization section to obtain a vapor stream comprising water and ε-caprolactam in a weight-to-weight ratio of 2:1 to 15:1; c) recovering crude ε-caprolactam from the vapor stream in a recovery section; d) purifying the crude ε-caprolactam in a purification section to obtain purified ε-caprolactam; A method comprising:

2. d) Purification: (i) obtaining an aqueous phase and an organic phase by extracting crude ε-caprolactam with an organic solvent, the organic phase comprising the organic solvent, ε-caprolactam and impurities; (ii) optionally a step of switching the solvent, at least partially replacing the organic solvent with water to obtain an aqueous phase comprising water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam, said solvent switching step (ii) being selected from a process based on back extraction with water and a process based on solvent exchange distillation, in which the organic solvent is distilled off and water is introduced; and (iii) obtaining purified ε-caprolactam by distillative removal of impurities having a boiling point lower or higher than that of ε-caprolactam. The method of claim 1 , comprising:

3. 3. The method according to claim 1 or 2, wherein the nylon 6-containing multicomponent material is a multilayer film containing at least one layer containing or consisting of nylon 6 and at least one layer not containing nylon 6, in particular, the at least one layer containing or consisting of nylon 6 is sandwiched between two or more layers not containing nylon 6.

4. 4. The method of any one of claims 1 to 3, wherein the nylon 6-containing multicomponent material comprises nylon 6 and at least one non-nylon 6 polymer, and wherein the nylon 6 is present in the nylon 6-containing multicomponent material as separate domains and / or as a mixture with at least one non-nylon 6 polymer.

5. 5. The method according to any one of claims 1 to 4, wherein the weight fraction of nylon 6 in the nylon 6 containing multicomponent material ranges from 1 wt% to 75 wt%, more preferably from 1 wt% to 60 wt%, even more preferably from 2 wt% to 35 wt%, and most preferably from 3 wt% to 25 wt%, based on the total weight of the nylon 6 containing multicomponent material.

6. The extraction in step a) comprises: (i) adding one or more organic solvents to a nylon 6-containing multicomponent material; (ii) performing a phase separation to obtain a liquid extract phase comprising the solvent and dissolved components from the nylon 6-containing multicomponent material, and an at least partially solid phase comprising undissolved components of the nylon 6-containing multicomponent material and optionally the solvent; (iii) removing the solvent from the liquid extraction phase and, if present, from at least a partially solid phase to obtain two solid phases, one of which is a pre-concentrated nylon 6-containing material enriched in nylon 6 compared to the nylon 6-containing multicomponent material used as starting material; The method according to any one of claims 1 to 5, comprising:

7. 7. The method according to any one of claims 1 to 6, wherein for the extraction in step a) an organic solvent is used which preferentially dissolves non-nylon 6 compounds from the nylon 6-containing multicomponent material and / or wherein in step a) an organic solvent is used which preferentially dissolves nylon 6 from the nylon 6-containing multicomponent material.

8. (i) prior to the extraction in step a), the nylon 6-containing multicomponent material has undergone a pretreatment, in particular a washing step and / or a mechanical disruption step; and / or (ii) the depolymerization of the pre-concentrated nylon 6-containing material in step b) is carried out at a temperature in the range of from 180° C. to 400° C., preferably from 200° C. to 350° C., more preferably from 220° C. to 340° C., and most preferably from 240° C. to 325° C.; and / or (iii) the water present in step b) is in the form of steam, which is preferably introduced into the depolymerization section in step b) as superheated steam at a temperature in the range of 220° C. to 575° C., preferably 275° C. to 500° C.; The method according to any one of claims 1 to 7.

9. The depolymerization of the pre-concentrated nylon 6-containing material in step b) is carried out in the absence or presence of a catalyst, the catalyst being selected from acid catalysts and base catalysts, the acid catalyst being orthophosphoric acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids, salts of the aforementioned acids, Al ２ O ３ and SiO ２ and combinations thereof, in particular selected from orthophosphoric acid, and the base catalyst is selected from the group consisting of alkali hydroxides, alkali salts, alkaline earth hydroxides and alkaline earth salts, organic bases and solid bases, and combinations thereof, in particular selected from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

10. - after step d)(i), washing the organic phase obtained in step d)(i) with water or an aqueous alkaline solution, and / or - adding an alkali metal hydroxide, preferably NaOH, prior to the distillative removal in step d)(iii); The method according to any one of claims 2 to 9.

11. Prior to the distillative removal in step d)(ii), the aqueous phase comprising water, ε-caprolactam and impurities with a boiling point lower or higher than that of ε-caprolactam is - a solvent replacement step, at least partially replacing the organic solvent with water, selected from processes based on re-extraction with water and processes based on solvent replacement distillation, in which the organic solvent is distilled off and water is introduced; and - optionally followed by oxidation with an oxidizing agent selected from potassium permanganate, sodium permanganate and hydrogen peroxide; and / or - optionally followed by treatment with an acidic cation exchange resin and / or a basic anion exchange resin; and / or - optionally followed by hydrogenation in the presence of a hydrogenation catalyst selected from Raney nickel, nickel-silica, nickel-aluminium oxide, ruthenium-aluminium oxide, rhodium-aluminium oxide, platinum on carbon and palladium on carbon. The method according to any one of claims 1 to 10, wherein the compound is obtained by

12. 12. The process according to claim 1, wherein in the purification section used in step d), the crude ε-caprolactam obtained from the Beckmann rearrangement of cyclohexanone oxime is also purified together with the crude ε-caprolactam recovered in step c).

13. 1. A chemical plant for the production of purified ε-caprolactam from a nylon 6-containing multicomponent material, comprising: A. Nylon 6 preconcentration section; B. depolymerization part, C. Recovery Division; and D. Refining department and A plant configured to carry out the method defined in any one of claims 1 to 12.

14. Purified ε-caprolactam obtained by depolymerization of nylon 6, produced from a nylon 6-containing multicomponent material according to the process defined in any one of claims 1 to 12, comprising a concentration of 100% CO per kg. ２ Refined ε-caprolactam having an equivalent product carbon footprint of less than 2.5 kg.

15. Use of ε-caprolactam recovered from a nylon 6-containing multicomponent material to reduce the carbon footprint of an ε-caprolactam production plant that also produces ε-caprolactam from the Beckmann rearrangement of at least cyclohexanone oxime.

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