Process for recovering epsilon-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane

Abstract

The invention provides a method for recovering epsilon-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane in a plant, wherein the plant comprises a separation section [B], a depolymerization section [C], a recovery section [D] and a purification section [E].

Description

Technical Field

[0001] The present invention relates to a method for recovering ε-caprolactam from a material comprising nylon 6 and polyether polyurethane. More particularly, the present invention relates to a method for recovering both purified ε-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane on an industrial scale. Background Art

[0002] In 1938, Paul Schlack invented nylon 6 (CAS No. 25038-54-4), also known as polyamide 6, PA6, N6, polycaprolactam, poly(hexane-6-lactam), poly(6-aminocaproic acid), poly(hexamethylene adipamide), or poly[imino(1-oxohexane-1,6-diyl)].

[0003] Typically, nylon 6 is synthesized by ring-opening polymerization of ε-caprolactam at a temperature of about 260°C in an inert atmosphere:

[0004]

[0005] As is well known, ε-caprolactam can be prepared by the liquid-phase Beckmann rearrangement of cyclohexanone oxime in the presence of oleum, i.e., a mixture of sulfuric acid and SO₃, or by the gas-phase Beckmann rearrangement of cyclohexanone oxime in the presence of a solid catalyst. This type of ε-caprolactam is generally referred to as "virgin ε-caprolactam." The cyclohexanone oxime required to form (virgin) ε-caprolactam can be prepared from cyclohexanone, which is primarily produced from benzene. This benzene is largely derived from non-renewable fossil resources such as petroleum and coal.

[0006] Methods for producing native ε-caprolactam are described, for example, in the chapter “Caprolactam” in Ullmann's Encyclopedia of Industrial Chemistry (May 25, 2018), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, which is available electronically at https: / / doi.org / 10.1002 / 14356007.a05_031.pub3.

[0007] Processes for producing nylon 6 are described, for example, in the chapter “Polyamides” in Ullmann’s Encyclopedia of Industrial Chemistry (January 15, 2013), Wiley-VCH Verlag GmbH, Weinheim, Germany, which is available electronically at https: / / doi.org / 10.1002 / 14356007.a21_179.pub3.

[0008] Initially, pure nylon 6 was used to produce textiles, including stockings. Later, in order to improve the properties of the fabric, various blended fabrics were developed and produced. In particular, polyether polyurethane has been widely used in various nylon 6-based clothing. The benefits of polyether polyurethane are its significant strength and elasticity, as well as its ability to recover its original shape after stretching and its faster drying speed than ordinary fabrics. The improved elasticity of the fabric is usually obtained by applying a blended yarn made by blending nylon 6 fibers and polyurethane fibers. Examples of clothing containing fabric blends of nylon 6 and polyether polyurethane include stretchable stockings, underwear and sportswear. The moisture permeability and waterproofness of the fabric can be obtained by treating (e.g., coating) the surface of nylon 6 fibers with a polyurethane resin. These surface-treated yarns are usually used to make, for example, raincoats, clothes suitable for cold weather and ski suits. The polyether polyurethane used to produce clothing is also commonly referred to as spandex, lycra or elastane.

[0009] The recycling of nylon 6 enables the conservation of fossil resources and can add value to the circular economy. The mechanical recycling of waste nylon 6 comprises the process of converting waste nylon 6 into secondary raw materials or into products in which (preferably) the chemical structure of the material has undergone only minimal changes. The conversion of nylon 6 and the depolymerization of nylon 6 are two forms of chemical recycling of nylon 6. In the conversion recycling process, nylon 6 is broken down into raw materials similar to petroleum or natural gas, which can replace newly extracted fossil raw materials. The resulting products can be used to produce chemicals including the monomer ε-caprolactam. In the depolymerization recycling process, nylon 6 is broken down into its monomer building block ε-caprolactam. The depolymerization of nylon 6 to ε-caprolactam is the reverse reaction of the ring-opening polymerization of ε-caprolactam:

[0010]

[0011] Typically, prior art chemical regeneration or recycling processes for depolymerizing substantially pure nylon 6 to epsilon-caprolactam monomer include a hydrolytic degradation step at elevated temperature in the presence of water and a step of recovering the monomer formed by steam distillation.

[0012] The depolymerization and recycling process for nylon 6 was developed entirely for clean and relatively pure waste nylon 6 material. Mechanical recycling always results in downgraded recycling, and therefore the properties of products made from mechanically recycled nylon 6 are always inferior to those of products made from virgin nylon 6. However, chemical recycling of waste nylon 6-containing material may also allow the production of high-purity ε-caprolactam with properties similar to those of virgin ε-caprolactam, which can then be converted into high-grade nylon 6. Unfortunately, chemical recycling of waste nylon 6-containing material is often hampered by the presence of impurities in the waste nylon 6 material. Typically, due to the presence of these impurities, the quality of the ε-caprolactam produced is inferior to that of virgin ε-caprolactam.

[0013] Compared to the depolymerization of relatively pure nylon 6, the depolymerization of blends of nylon 6 and polyether polyurethane has numerous disadvantages. These disadvantages include, among other things, clogging of pipes and other equipment parts by the polyether polyurethane and its decomposition products, a poorer quality of the produced ε-caprolactam due to the presence of the polyether polyurethane decomposition products, a (significantly) reduced ε-caprolactam recovery rate, poisoning of the depolymerization catalyst, and, consequently, higher depolymerization catalyst consumption. Another disadvantage of adding the blend of nylon 6 and polyether polyurethane to the depolymerization reactor is the destruction of the polyether polyurethane. Consequently, recycling of the polyether polyurethane, which is more valuable than nylon 6, is not possible.

[0014] Virgin spandex is produced by a dry or wet spinning process starting with a spandex spinning solution consisting of polyurethane in a suitable solvent such as dimethylacetamide or dimethylformamide.

[0015] Direct recycling of normal (pure) elastane waste fibers, for example from yarn production, by dissolving them in the spinning solvent employed has proven unsuccessful due to the high viscosity which prevents further processing.

[0016] US Pat. No. 6,830,715 B1 describes a method for producing spandex yarn from a spinning solution using recycled spandex material, which overcomes the viscosity problem by adding a secondary aliphatic amine to a mixture of (cut) spandex and spinning solvent. Dissolution of the (cut) spandex is achieved at a temperature of 60° C. to 150° C.

[0017] In the past, several attempts to recycle blends of nylon 6 and polyether polyurethane have been described.

[0018] JP2011088943A describes a pretreatment method for separating polyether polyurethane from a nylon 6 product containing polyether polyurethane, followed by depolymerization of the residual nylon 6. The pretreatment involves heating the nylon 6 product containing polyether polyurethane with a solvent containing a cyclic amide at a temperature between 80°C and the boiling point of the solvent. JP2011088943A states that the amount of cyclic amide compound in the cyclic amide compound solvent is preferably 50% by weight or more, more preferably 85% by weight or more. JP2011088943A further states that the cyclic amide compound solvent may contain components other than the cyclic amide compound, such as water and an organic solvent, and that water is particularly preferred from the perspective of operability. The experiments described in the patent were conducted at a temperature of 110°C over a period of 2 hours using aqueous solutions containing 50 and 85% by weight of N-methylpyrrolidone, 85% by weight of 2-pyrrolidone, or 85% by weight of 2-piperidine as solvents. As a result of this treatment, the polyether polyurethane partially decomposed and dissolved in the solvent. Thus, the resulting nylon 6 product is depolymerized, the polyether polyurethane is removed from the product, and the product is separated from the solution by filtration. However, JP2011088943A does not mention the recovery of the partially decomposed polyether polyurethane. Nor does it describe the fate of the solvent used.

[0019] WO 2013032408 A1 describes a method for recycling polyamide fibers, including polyamide 6 and polyamide 6,6, which includes polyamide and spandex. The spandex fibers are removed from elastomeric fabrics by a process comprising controlled thermal degradation of the spandex, a controlled wash treatment using a suitable and sustainable solvent (preferably ethanol) to remove the spandex or its degradation products from the high-purity polyamide, and a final step to remove excess solvent from the polyamide fibers. The temperature used during the heat treatment of the polyamide fibers (including polyamide 6 fibers) is in the range of 150°C to 220°C, preferably 190°C to 216°C, and preferably for a period of 0.5 to 4 hours. Thereafter, the heat-treated fabric is washed, preferably with ethanol, at a temperature in the range of 5°C to 78°C to remove the spandex and its degradation components. WO 2013032408 A1 does not mention recovery of the spandex and its degradation components from the wash solvent.

[0020] Given the above, to date, there are no methods for recovering purified ε-caprolactam and polyether polyurethane from materials including nylon 6 and polyether polyurethane on an industrial scale. The lack of industrial-scale recycling methods for recovering purified ε-caprolactam and polyether polyurethane from materials including nylon 6 and polyether polyurethane is due to the fact that all methods for bringing elastic fibers into solution require high solution temperatures, typically well above 100°C. However, at these temperatures, the elastic fibers begin to degrade, and only low-quality materials are obtained after recovery. Consequently, the fate of the recovered elastic fibers is often limited to incineration and landfill. Another disadvantage of high-temperature dissolution processes is the formation of degradation products of the solvents used, which can hinder the recovery of nylon 6 and polyether polyurethane and the recycling of the solvents used.

[0021] Environmental issues surrounding the production and use of these materials, including nylon 6 and polyether polyurethanes, relate to the waste generated during and after consumption. These issues can be alleviated by recycling individual components (such as nylon 6 and polyether polyurethanes) from materials including nylon 6 and polyether polyurethanes that are no longer used or disposed of. Materials including nylon 6 and polyether polyurethanes are a particularly relevant source of waste as textiles. These typically contain large amounts of nylon 6 and polyether polyurethanes. Therefore, if there were a feasible method for recovering nylon 6 and polyether polyurethanes from these composite wastes, this would not only benefit the environment but also provide an economically valuable new source of nylon 6 and polyether polyurethanes.

[0022] From the perspective of reducing carbon dioxide emissions, recycling materials including nylon 6 and polyether polyurethane to recover purified ε-caprolactam and polyether polyurethane is of great significance.

[0023] There is also a need to provide high purity grades of ε-caprolactam and polyether polyurethanes from materials including nylon 6 and polyether polyurethanes, with a carbon footprint significantly lower than that produced by processes using virgin ε-caprolactam obtained by new synthesis (e.g., by Beckmann rearrangement of cyclohexanone oxime) and polyether polyurethanes produced by de novo synthesis of polyether polyurethanes.

[0024] The raw material price of virgin polyether polyurethane is high, often even more than twice the price of virgin nylon 6. Therefore, there is a strong economic incentive to recover and reuse (recycle) waste polyether polyurethane and nylon 6.

[0025] A problem with the prior art methods is that they consume a large amount of energy to recover the dissolved elastic fibers from the solution, since the dissolved elastic fibers are usually obtained by removing the solvent by evaporation.

[0026] There is also a need to purify crude ε-caprolactam obtained by depolymerization of polyether polyurethane from materials including nylon 6 and polyether polyurethane without using oxidants such as potassium permanganate (KMnO4) or adsorbents such as (activated) carbon and diatomaceous earth. Technologies based on these oxidants and adsorbents are quite laborious and generate solid waste.

[0027] Another shortcoming of the prior art is that no suitable recovery and reuse (recycling) strategy is provided or known for recovering and reusing (recycling) the solvents of polyether polyurethane and nylon 6 from materials comprising nylon 6 and polyether polyurethane.

[0028] Currently, despite a pressing need for methods for recovering high-purity ε-caprolactam from materials including nylon 6 and polyether polyurethanes, no such methods are available. Specifically, there is a pressing need for high-purity ε-caprolactam recovery methods that can replace virgin ε-caprolactam grades for demanding applications such as high-speed melt spinning during textile fiber production.

[0029] Finally, there is a need for a process that allows for the recovery of pure ε-caprolactam and polyether polyurethanes from materials comprising nylon 6 and polyether polyurethanes on an industrial scale in order to deal with the large amounts of materials comprising nylon 6 and polyether polyurethanes that are wasted every year. Summary of the Invention

[0030] It is an object of the present invention to meet one or more of the above needs and to overcome or alleviate the disadvantages associated with prior art approaches.

[0031] In particular, it is an object of the present invention to provide a process for recovering ε-caprolactam from a material comprising nylon 6 and polyether polyurethane. Another object of the present invention is to provide a process for recovering both purified ε-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane.

[0032] A further object of the present invention is to provide a process for recovering both purified ε-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane on an industrial scale.

[0033] It is also an object of the present invention to provide a process for recovering both purified ε-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane in an economical and efficient manner. In this respect, in particular, it is an object of the present invention to provide a process that is suitable for recovering both purified ε-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane and that does not exceed the production costs of virgin high-purity ε-caprolactam and polyether polyurethane.

[0034] The object of the present invention is also to provide a process for purifying crude ε-caprolactam obtained by depolymerizing a material comprising nylon 6 and polyether polyurethane, said process not generating solid waste.

[0035] A further object of the present invention is to provide a process for recovering both purified ε-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane, said process being characterized by a significantly lower carbon footprint than processes for producing virgin polyether polyurethane, for example, by the reaction of polyether polyols and diisocyanate monomers, and for producing ε-caprolactam by novel syntheses, for example by the Beckmann rearrangement of cyclohexanone oxime.

[0036] It is also an object of the present invention to provide a process for recovering high-purity ε-caprolactam from materials comprising nylon 6 and polyether polyurethane, which high-purity ε-caprolactam can replace high-purity virgin ε-caprolactam for all applications, including high-speed melt spinning of nylon 6 for the production of thin textile fibers.

[0037] Therefore, the present invention also aims to provide a method for reducing the environmental burden of discarded materials comprising nylon 6 and polyether polyurethane.

[0038] One or more additional objects may become apparent from the remainder of the specification.

[0039] All or at least some of the above objects are solved or at least alleviated to a large extent by the method of claim 1 , the plant of claim 13 and the products of claims 14 and 15 .

[0040] The present invention provides a method for recovering ε-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane in a plant, wherein the plant comprises

[0041] - separation section [B],

[0042] - depolymerization section [C],

[0043] - Recovery Segment [D], and

[0044] - purification segment [E],

[0045] And wherein the method comprises the following steps:

[0046] a) loading the material comprising nylon 6 and polyether polyurethane into the separation section [B];

[0047] b) separating the material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream in the separation section [B] by selectively dissolving the polyether polyurethane in an organic solvent at a temperature below 100°C, preferably at a temperature in the range of 0°C to 100°C, more preferably at a temperature in the range of 10°C to 90°C, even more preferably at a temperature in the range of 10°C to 80°C and most preferably at a temperature in the range of 20°C to 75°C, wherein the polyether polyurethane-rich stream is a solution comprising the organic solvent and the polyether polyurethane;

[0048] c.1) discharging the nylon 6-rich stream from separation section [B] and feeding the nylon 6-rich stream to a depolymerization section [C], wherein the nylon 6-rich stream has a nylon 6 content of at least 85 wt% on a dry weight basis;

[0049] c.2) depolymerizing said nylon 6 in said nylon 6-rich stream at a temperature in the range of 180° C. to 400° C., preferably 200° C. to 350° C., more preferably 220° C. to 340° C., and most preferably 240° C. to 325° C. in said depolymerization section [C], such that a stream comprising ε-caprolactam is obtained, and discharging the obtained stream comprising ε-caprolactam from said depolymerization section [C];

[0050] c.3) recovering crude ε-caprolactam from the stream comprising ε-caprolactam in the recovery section [D];

[0051] c.4) purifying the crude ε-caprolactam obtained in the recovery section [D] in the purification section [E] to obtain purified ε-caprolactam, wherein the purification comprises the following steps:

[0052] (i) extracting the crude ε-caprolactam with an organic solvent so as to obtain an aqueous phase and an organic phase, and wherein the organic phase comprises the organic solvent, the ε-caprolactam and impurities, and preferably the organic solvent is selected from the group consisting of cyclohexane, benzene, toluene, dichloromethane, chloroform, trichloroethane, 4-methyl-2-pentanol, 1-octanol, 2-ethylhexanol and mixtures thereof; and

[0053] optionally washing the obtained organic phase with water or with an alkaline aqueous solution;

[0054] (ii) optionally, switching the solvent by at least partially replacing the organic solvent with water or an aqueous solution, thereby obtaining an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam, and wherein the solvent switching is selected from a process based on back extraction with water and a process based on solvent exchange distillation, wherein the organic solvent is distilled off and water is charged; and

[0055] (iii) optionally, removing impurities having a boiling point lower or higher than that of ε-caprolactam by distillation to obtain purified ε-caprolactam;

[0056] (iv) obtaining purified ε-caprolactam by crystallizing ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10° C. to 95° C.;

[0057] d.1) recovering polyether polyurethane from the polyether polyurethane-rich stream in the separation section [B]; and

[0058] d.2) discharging the recovered polyether polyurethane from the separation section [B], wherein the polyether polyurethane content of the discharged stream is at least 85% by weight, based on the dry weight.

[0059] Surprisingly, the specific sequence of processing steps and process conditions according to the present invention, namely the aforementioned sequence of separation, depolymerization, recovery, and purification steps, allows for the recovery of ε-caprolactam from materials comprising nylon 6 and polyether polyurethane in high yields and in a straightforward, economically sound manner. The process of the present invention is economically sound and advantageous from several perspectives. First, the process of the present invention is applicable to a variety of materials derived from materials comprising nylon 6 and polyether polyurethane, which may differ, for example, in their overall composition and / or their polyether polyurethane content and / or their nylon 6 content. Second, the process of the present invention allows for the efficient separation of nylon 6 from polyether polyurethane compounds, thereby obtaining high-grade nylon 6. Third, the process of the present invention is highly efficient, making it possible to obtain ε-caprolactam in high yields. Fourth, the process of the present invention allows for the recovery of polyether polyurethane, which can be reused to replace polyether polyurethanes produced by de novo synthesis, for example, by the reaction of polyether polyols and diisocyanate monomers. Fifth, the process of the present invention allows for efficient separation of ε-caprolactam from non-ε-caprolactam compounds, making it possible to obtain high-purity grades of ε-caprolactam that can replace high-purity virgin ε-caprolactam for all applications, including high-speed melt spinning of nylon 6 for the production of thin textile fibers. Finally, the process of the present invention allows for the production of ε-caprolactam with a significantly lower carbon footprint compared to ε-caprolactam produced by de novo synthesis of ε-caprolactam (e.g., by Beckmann rearrangement of cyclohexanone oxime). The process of the present invention allows for efficient processing of materials including nylon 6 and polyether polyurethanes and reduces the environmental burden of the products. Specifically, the process of the present invention allows for the production of polyether polyurethanes with a carbon footprint of less than 1 kg CO2 / kg polyether polyurethane, which is a significant improvement over the 4.8 kg CO2 / kg polyether polyurethane associated with the production of "virgin" polyether polyurethanes obtained by chemical synthesis. In particular, the process of the present invention allows the production of purified ε-caprolactam with a carbon footprint of less than 3 kg CO2 / kg purified ε-caprolactam, which is a significant improvement compared to the 6.4 to 7.5 kg CO2 / kg ε-caprolactam associated with the production of "virgin" ε-caprolactam obtained from the Beckmann rearrangement of cyclohexanone oxime.

[0060] In addition to the process of the present invention, the present invention also provides a plant for producing purified ε-caprolactam and polyether polyurethane from materials comprising nylon 6 and polyether polyurethane, wherein the plant comprises:

[0061] - optionally, a pre-treatment section [A],

[0062] - separation section [B],

[0063] - Nylon 6 depolymerization segment [C],

[0064] -ε-caprolactam recovery section [D],

[0065] -ε-caprolactam purification section [E], and

[0066] The chemical plant is configured to carry out the method of the present invention.

[0067] The present invention also provides purified ε-caprolactam obtained by separation from a material comprising nylon 6 and polyether polyurethane according to the process of the present invention, wherein the product carbon footprint of the ε-caprolactam is less than 3.0 kg CO2 / kg purified ε-caprolactam.

[0068] The present invention also provides a polyether polyurethane obtained by separation from a material comprising nylon 6 and polyether polyurethane according to the method of the present invention, wherein the product carbon footprint of the polyether polyurethane is less than 1.0 kg CO2 equivalent / kg recovered polyether polyurethane.

[0069] Advantageous embodiments of the invention are indicated in the dependent claims and are explained in more detail below. DETAILED DESCRIPTION

[0070] Materials including nylon 6 and polyether polyurethane

[0071] The method of the present invention uses a material comprising nylon 6 and polyether polyurethane as a starting material. The material comprising nylon 6 and polyether polyurethane can be a (used) product comprising nylon 6 and polyether polyurethane or a material derived therefrom. The material comprising nylon 6 and polyether polyurethane can be a material comprising nylon 6 and polyether polyurethane, i.e., a plurality of materials comprising nylon 6 and polyether polyurethane or a mixture thereof. Typically, the material comprising nylon 6 and polyether polyurethane is a solid material, specifically a fiber, a yarn (i.e., a fiber strand spun together) or a fiber-based fabric, wherein the fiber is a blend of nylon 6 fiber and polyurethane fiber, or wherein the fiber is obtained by coating the surface of nylon 6 fiber with a polyether polyurethane resin.

[0072] The material comprising nylon 6 and polyether polyurethane can be of pre-consumer and post-consumer origin. The material comprising nylon 6 and polyether polyurethane can be a mixture of different materials comprising nylon 6 and polyether polyurethane, or a mixture of one or more materials comprising nylon 6 and polyether polyurethane with one or more different materials.

[0073] The material comprising nylon 6 and polyether polyurethane can include additional components. Such components can be added, for example, during or after polymerization, fiber formation, to achieve desired property changes. These compounds include, for example, brighteners, hardeners, antistatic lubricants, colorants, brighteners, spin finishes, surface smoothing agents, antioxidants, UV stabilizers, etc. The amount of these additional components depends on the application of the material comprising nylon 6 and polyether polyurethane.

[0074] The weight ratio of nylon 6 to polyether polyurethane in the material comprising nylon 6 and polyether polyurethane can vary. Preferably, the weight ratio of nylon 6 to polyether polyurethane ranges from about 1:1 to about 100:1, most preferably from about 3:1 to about 20:1.

[0075] Polyurethanes are produced by reacting an isocyanate containing two or more isocyanate groups per molecule with a polyol containing an average of two or more hydroxyl groups per molecule in the presence of a catalyst or by activation with ultraviolet light. The main ingredients for preparing polyurethanes are diisocyanates, triisocyanates, and polyols. The diisocyanate monomer methylene diphenyl diisocyanate (MDI) is the most commonly used isocyanate in the production of polyurethanes for apparel applications.

[0076] Polyether polyurethanes are produced by reacting isocyanates with polyether polyols. Polyether polyols are typically prepared by polymerizing a cyclic ether compound onto an initiator compound. The most commonly used cyclic ethers in polyether polyol production are ethylene oxide, propylene oxide, and 1,4-butylene oxide or tetrahydrofuran (for the production of poly(butylene oxide) polyols). Poly(butylene oxide) polyols are primarily used in applications requiring highly hydrophobic properties.

[0077] The term "about" or "approximately" is used in conjunction with the numerical values ​​herein to indicate that the numerical values ​​may be subject to measurement errors, which typically cause the numerical values ​​to vary by no more than ±5%. The numerical values ​​disclosed herein with the term "about" or "approximately" are also intended to be so, i.e., disclosed without the term "about". Further, the numerical ranges described herein are intended to include and disclose each value within the range. All upper and lower endpoints of the ranges of the same parameter disclosed herein are combinable with each other. All ranges of different parameters disclosed herein are combinable with each other. Specifically, ranges of different or identical "preference levels" are specifically compatible with each other. As used in the present disclosure and claims, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include plural forms, particularly in the sense of "one or more".

[0078] Possible preprocessing steps

[0079] Before being subjected to step a) of the method of the present invention, the material comprising nylon 6 and polyether polyurethane may be pretreated in a pretreatment section [A], specifically size reduction in a mechanical size reduction section [λ] and / or cleaning in a cleaning section [ω]. The pretreatment may be carried out in a location different from the location where the separation section [B] is located. However, preferably, the method of the present invention is carried out in a plant further comprising a pretreatment section [A], and wherein the material comprising nylon 6 and polyether polyurethane is subjected to pretreatment in the pretreatment section [A], specifically cleaning in a cleaning section [ω] and / or mechanical size reduction in a mechanical size reduction section [λ], prior to step a). This has the advantage that the material comprising nylon 6 and polyether polyurethane fed to the separation section [B] is less contaminated with foreign materials, which improves the yield and purity of the ε-caprolactam and polyether polyurethane produced in the plant of the present invention configured to carry out the method of the present invention. Another advantage is that the size-reduced material comprising nylon 6 and polyether polyurethane can be more easily processed.

[0080] The material comprising nylon 6 and polyether polyurethane is preferably or is derived from used or discarded material comprising nylon 6 and polyether polyurethane. The size and shape of the material depends to a great extent on the exact application of its source. The range of materials comprising nylon 6 and polyether polyurethane that can be used according to the present invention is from separated fibers and yarns that are optionally present in the form of spools to woven fabrics and garments. Preferably, the material comprising nylon 6 and polyether polyurethane is discarded or used material comprising nylon 6 and polyether polyurethane.

[0081] In particular, discarded or used materials including nylon 6 and polyether polyurethanes may be contaminated with various types of soil (eg, with dirt, oil, paint, or grease).

[0082] (Waste) materials including nylon 6 and polyether polyurethane can be mixed with a range of other materials such as rock, glass, metallic materials, organic waste and other polymer waste (e.g. polyamide 6,6, polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE)).

[0083] Preferably, the material comprising nylon 6 and polyether polyurethane is broken into fragments before separation in separation section [B] in step b). This mechanical pretreatment of the material comprising nylon 6 and polyether polyurethane, i.e., mechanical comminution or crushing, can be achieved, for example, by cutting, punching, chopping, grinding, crushing, and / or chipping. In a preferred embodiment, the material comprising nylon 6 and polyether polyurethane is charged to separation section [B] of step a) in the form of broken fragments. Using broken fragments has the advantage that the fragments can be more easily handled and / or cleaned by washing with a solvent. In a preferred embodiment, the fragments have an average length along the longest axis of the fragments of 1 mm to 100 m, preferably 3 mm to 1 m, and most preferably 1 cm to 50 cm. The average length along the longest axis of the fragments employed can be readily determined by a skilled person by first obtaining a representative sample of the fragments, then measuring the length of the longest axis of each of these fragments (e.g., 50 fragments), and finally calculating the average of all these individual measurements. Preferred particle sizes can also be described in terms of average particle weight. Preferably, the average particle weight of the fragments of the material comprising nylon 6 and polyether polyurethane is from 0.01 g to 25 kg, preferably from 0.05 g to 1 kg, and most preferably from 0.1 g to 100 g. Experiments have shown that fragments of the material comprising nylon 6 and polyether polyurethane having the above-mentioned size or weight dimensions are particularly suitable for treatment in the method of the present invention and / or cleaning by washing with a solvent.

[0084] Optionally, prior to mechanical comminution or crushing of the material comprising nylon 6 and polyether polyurethane, large metal fragments, rocks, and other interfering materials that cause significant wear on the equipment used for the mechanical comminution or crushing are removed. Preferably, foreign materials, including but not limited to polyethylene, polypropylene, and polyamide 6,6, are also removed prior to mechanical comminution or crushing of the material comprising nylon 6 and polyether polyurethane. Removal of foreign materials can be performed mechanically or manually. The advantage of removing these interfering materials is that maintenance costs for the equipment used for mechanical comminution or crushing can be significantly reduced. Furthermore, the nylon 6 and polyether polyurethane content of the material obtained after mechanical comminution or crushing is higher than in the absence of removal of interfering materials. Removal of polyamide 6,6 is particularly advantageous because it interferes with the depolymerization of nylon 6, reduces the recovery of ε-caprolactam, and interferes with the subsequent purification of the recovered ε-caprolactam. As used herein, the term "foreign materials" refers to non-nylon 6 and non-polyether polyurethane materials or compounds.

[0085] Optionally, the foreign material is separated from the material comprising nylon 6 and polyether polyurethane that has been mechanically crushed or broken. To this end, various separation methods can be applied, including but not limited to density separation and magnetic separation. In density separation, materials of different densities are placed in a medium-density liquid, wherein the lower-density material floats and is separated from the higher-density sinking material. In practice, density separation is typically accomplished through a series of density separation stages. For example, in one stage, high-density materials such as rock, sand, and metal (including iron and lead) are separated, while in another stage, low-density materials such as polyolefins, polypropylene, and polyethylene are separated. Magnetic separation is a method of separating the components of a mixture by using a magnet to attract a magnetic material. The method preferably used for magnetic separation separates non-magnetic materials from the magnetic material. Removing foreign materials from the crushed or broken material comprising nylon 6 and polyether polyurethane is advantageous because such materials can interfere with the separation of nylon 6 and polyether polyurethane, the depolymerization of nylon 6, reduce the recovery rate of ε-caprolactam, and / or interfere with the subsequent purification of the recovered ε-caprolactam.

[0086] Optionally, in particular in the above-mentioned pretreatment step, the material comprising nylon 6 and polyether polyurethane is cleaned by washing with a solvent (preferably at least water) before being loaded into the separation section [B]. The solvent used herein can be a single solvent or a mixture of different solvents. Preferably, a detergent in a concentration range of 0 to 20 wt % relative to the solvent is added to the solvent to improve the washing efficiency. NaOH is a preferred detergent. Even more preferably, an aqueous solution containing 0 to 10 wt % NaOH is used in the washing step, still more preferably 0 to 5 wt % NaOH. The enhanced washing effect of NaOH is likely caused by the enhanced hydrolysis of molecules (including biopolymers and non-biopolymers). Preferably, the washing solvent is heated to further enhance the washing process. In another preferred embodiment, the washing process includes a final rinse step with a detergent-free (clean) washing solvent to remove detergent residues and existing dirt adhering to the material comprising nylon 6 and polyether polyurethane.

[0087] Washing is preferably carried out under friction.Different types of washing systems for industrial friction applications are available on the market, such as rotary plastics washers and (high-speed) friction washers.

[0088] Washing the material comprising nylon 6 and polyether polyurethane, in particular mechanically comminuted or crushed material comprising nylon 6 and polyether polyurethane, is advantageous because any (adherent) dirt is removed and thus does not interfere with the following steps of the method of the invention.

[0089] Optionally, the material comprising nylon 6 and polyether polyurethane is dried after the cleaning step and before being fed into the separation section [B]. This has the advantage that the weight of the cleaned material comprising nylon 6 and polyether polyurethane is reduced and the next step is not affected by dilution or contamination by the washing solvent.

[0090] The location where the pretreatment of the material comprising nylon 6 and polyether polyurethane is performed and the location where the separation section [B] is located may be the same. However, preferably, one or more of the pretreatment steps are performed at a location different from the location of the separation section [B], for example, near a plant where (used or waste) the material comprising nylon 6 and polyether polyurethane is collected and / or at a location dedicated to the pretreatment of the material comprising nylon 6 and polyether polyurethane. A nylon 6-rich stream can then be obtained from the pretreated material comprising nylon 6 and polyether polyurethane in the separation section [B].

[0091] The location where the separation of the material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream is carried out and the location where the depolymerization section [C] is located may be the same. However, preferably, the separation of the material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream is carried out at a location different from the location of the depolymerization section [C], for example, near a plant for producing virgin polyether polyurethane and / or at a location dedicated to processing and / or distilling organic solvents.

[0092] The location where the pretreatment of the material comprising nylon 6 and polyether polyurethane is carried out and the location where the depolymerization section [C] is located may be the same. However, preferably, one or more of the pretreatment steps are carried out at a location different from the location of the depolymerization section [C], for example, near a factory where waste materials comprising nylon 6 and polyether polyurethane are collected and / or at a location dedicated to the pretreatment of materials comprising nylon 6 and polyether polyurethane.

[0093] Loading step a)

[0094] In step a) of the process of the present invention, the material comprising nylon 6 and polyether polyurethane, which has optionally been pretreated in pretreatment section [A], is fed to separation section [B].

[0095] In one embodiment, the material comprising nylon 6 and polyether polyurethane is mechanically compressed into a smaller volume before being loaded into the separation section [B]. This has the advantage that a smaller volume is required for intermediate storage and transportation, and can also facilitate administration to the separation section [B].

[0096] In another preferred embodiment, the material comprising nylon 6 and polyether polyurethane is dried before being charged to separation section [B], in particular after the nylon 6 and polyether polyurethane material has been subjected to a cleaning step. This has the advantage that little or no solvent is introduced into separation section [B] along with the material. Solvents, in particular water, introduced into separation section [B] may negatively impact the separation process (e.g., the rate of dissolution of polyether polyurethane from the material comprising nylon 6 and polyether polyurethane in the organic solvent is reduced).

[0097] The materials comprising nylon 6 and polyether polyurethane are preferably fed in solid phase to the dissolution section [α], in particular to the corresponding dissolution vessels contained therein.

[0098] Feeding the material comprising nylon 6 and polyether polyurethane to the separation section [B] (eg, to the polyether polyurethane dissolution section) may be achieved by continuously or intermittently dosing the material comprising nylon 6 and polyether polyurethane.

[0099] Separation step b)

[0100] In separation section [B], the material comprising nylon 6 and polyether polyurethane is separated to form a nylon 6 rich stream and a polyether polyurethane rich stream.

[0101] Preferably, the process of the present invention employs a separation section [B] comprising a dissolution section [α], a washing section [β], a precipitation section [γ] and a solvent distillation section [δ], and comprises the following steps in the separation section:

[0102] b.1) charging an organic solvent and a material comprising nylon 6 and polyether polyurethane into the dissolving section [α];

[0103] b.2) dissolving polyether polyurethane from the material comprising nylon 6 and polyether polyurethane in an organic solvent in the dissolution section [α], so that a polyether polyurethane-rich stream comprising organic solvent and dissolved polyether polyurethane and a stream comprising undissolved nylon 6 are obtained, and discharging the obtained stream from the dissolution section [α];

[0104] b.3) feeding a second solvent and the polyether polyurethane-rich stream comprising the organic solvent and the dissolved polyether polyurethane to the precipitation section [γ], so that the polyether polyurethane is precipitated from the mixture comprising the organic solvent and the second solvent;

[0105] b.4) recovering the precipitated polyether polyurethane from the mixture comprising the organic solvent and the second solvent, and discharging the precipitated polyether polyurethane from the precipitation section [γ];

[0106] b.5) ​​discharging the mixture comprising the organic solvent and the second solvent, from which the precipitated polyether polyurethane has been recovered in step b.4), from the precipitation section [γ] and charging the mixture to the solvent distillation section [δ];

[0107] b.6) charging a third solvent and the stream comprising undissolved nylon 6 to the washing section [β];

[0108] b.7) washing the stream comprising undissolved nylon 6 with the third solvent in the washing section [β], so as to obtain a stream rich in nylon 6 and a mixture comprising the organic solvent and the third solvent;

[0109] b.8) discharging the nylon 6-rich stream from the washing section [β];

[0110] b.9) discharging the mixture comprising the organic solvent and the third solvent obtained in step b.7) from the washing section [β] and charging the mixture partially or completely to the solvent distillation section [δ];

[0111] b.10) separating the organic solvent from the second solvent and the third solvent by distillation in the solvent distillation section [δ], and discharging the second solvent, the third solvent and the separated organic solvent from the solvent distillation section [δ].

[0112] Optionally, the second solvent (see step b.3)) may partly or completely be a mixture comprising an organic solvent and a third solvent obtained in step b.7) from the washing section [β].

[0113] Preferably, the separation section [B] employed in the process of the present invention comprises a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ]. Such a separation section [B] is particularly suitable for carrying out the process of the present invention to separate a material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream. Surprisingly, when process steps b.1) to b.10) are carried out in a separation section [B] comprising a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ], the separation of the material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream is particularly effective. Steps b.1) to b.10) carried out in the preferred separation section [B] are explained further below. Steps b.1) to b.10) can replace process steps a) and b) in the process of the present invention. Step b.1) thus corresponds to step a).

[0114] As used herein, a "stream enriched in..." refers to a stream that contains a greater amount of an enriched component than another stream obtained in the same process step. A nylon 6-rich stream thus contains more nylon 6 than a polyether polyurethane-rich stream. In contrast, a polyether polyurethane-rich stream contains more polyether polyurethane than a nylon 6-rich stream.

[0115] Specifically, the nylon 6-rich stream has a weight ratio of nylon 6 to polyether polyurethane that is higher than the weight ratio of nylon 6 to polyether polyurethane of the material comprising nylon 6 and polyether polyurethane.

[0116] Preferably, the nylon 6-rich stream has a weight ratio of polyether polyurethane to nylon 6 that is at most one-half, more preferably at most one-third, the weight ratio of polyether polyurethane to nylon 6 of the material comprising nylon 6 and polyether polyurethane.

[0117] The polyether polyurethane-rich stream has a polyether polyurethane to nylon 6 weight ratio that is higher than the polyether polyurethane to nylon 6 weight ratio of the material comprising nylon 6 and polyether polyurethane.

[0118] Preferably, the polyether polyurethane-rich stream has a weight ratio of polyether polyurethane to nylon 6 that is at least twice, more preferably at least three times, the weight ratio of polyether polyurethane to nylon 6 of the material comprising nylon 6 and polyether polyurethane.

[0119] Loading separation segment step (step b.1)):

[0120] In the separation section [B], the organic solvent and the material including nylon 6 and polyether polyurethane are charged into the dissolution section [α].

[0121] Charging the material comprising nylon 6 and polyether polyurethane into the dissolving section [α] is charging of the material comprising nylon 6 and polyether polyurethane optionally pretreated in the pretreatment section [A] as mentioned in step a) of the present invention.

[0122] The organic solvent charged to the dissolution zone [α] can be any organic solvent in which the polyether polyurethane can be dissolved, in particular at a temperature below 100°C and in particular in less than 24 hours or less than 6 hours. As used herein, the organic solvent can also refer to a mixture of organic solvents or a liquid composition comprising more than 60 vol.%, preferably more than 70 vol.%, 80 vol.% or 90 vol.% of an organic solvent, wherein the mixture is capable of dissolving the polyether polyurethane at a temperature below 100°C, preferably in the range of 0°C to 100°C, more preferably in the range of 10°C to 90°C, even more preferably in the range of 10°C to 80°C, and most preferably in the range of 20°C to 75°C. Preferably, the organic solvent combines good, in particular very good, solubility for the polyether polyurethane with poor, in particular very poor, solubility for nylon 6. These properties can be tested in a simple dissolution test using a material comprising nylon 6 and the polyether polyurethane or a mixture of nylon 6 and the polyether polyurethane. According to a preferred embodiment, the organic solvent includes or is selected from N,N-dimethylformamide (DMF, (CH3)2NC(=O)H), dimethylacetamide (DMAc, CH3C(=O)N(CH3)2), 1,4-dioxane (dioxane, C4H8O2), N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone (NMP, C5H9NO), tetrahydrofuran (THF; also known as oxolane, C4H8O), and combinations thereof. Even more preferably, the organic solvent is selected from N,N-dimethylformamide and dimethylacetamide. Most preferably, the organic solvent is dimethylacetamide.

[0123] The organic solvent charged to the dissolution section [α] may be a separated organic solvent (i.e. a recycled organic solvent or an organic solvent from within the process which has been recovered in the solvent distillation section), a fresh organic solvent (i.e. a solvent from outside the process) or a combination of separated and fresh organic solvents.

[0124] The organic solvent charged to dissolution section [α] preferably has a low water content. Even more preferably, the organic solvent is dried (preferably by distillation or using a drying agent, such as an inorganic salt such as Na2SO4, zeolite, silica, and alumina) before being charged to dissolution section [α]. Drying does not necessarily have to be complete. Generally, after drying the organic solvent, it is acceptable for less than 1 wt.%, preferably less than 0.1 wt.%, and more preferably less than 0.02 wt.% of water to remain.

[0125] Dissolution step (step b.2)):

[0126] In the dissolution section [α], polyether polyurethane is dissolved from the material comprising nylon 6 and polyether polyurethane in the organic solvent charged to the dissolution section [α] in step b.1). A polyether polyurethane-rich stream comprising the organic solvent and dissolved polyether polyurethane and a stream comprising undissolved nylon 6 are thus obtained, which are discharged from the dissolution section [α].

[0127] Preferably, dissolution of the polyether polyurethane will be complete within 0.1 hour to 24 hours, more preferably within 0.5 hour to 6 hours. Complete means that the dissolution has reached a plateau and no substantial further dissolution occurs at a later time point.

[0128] The temperature in the dissolution zone [α] can vary and is preferably below 120°C, more preferably below 110°C, even more preferably below 100°C, and most preferably below 80°C. Preferably, the temperature in the dissolution zone [α] can be in the range of 0°C to 100°C, more preferably 10°C to 90°C, even more preferably 10°C to 80°C, and most preferably 20°C to 75°C. Experiments have shown that these temperature ranges result in particularly complete dissolution of the polyether polyurethane while maintaining its integrity in the organic solvent. This has the advantage that the polyether polyurethane present in the material comprising nylon 6 and the polyether polyurethane can be dissolved while maintaining its integrity.

[0129] The amount of solvent (expressed by weight, specifically expressed in tons) in the dissolution section [α] can vary and can be 0.5 to 100 times, preferably 1 to 60 times, more preferably 2 to 20 times, and most preferably 3 to 10 times the amount of polyether polyurethane (expressed by weight, specifically expressed in tons) in the dissolution section [α]. Small amounts of solvent reduce the dissolution rate of the polyether polyurethane and may result in too slow or incomplete dissolution of the polyether polyurethane. Large amounts of solvent give the polyether polyurethane a high dissolution rate, but recycling the used organic solvent requires more energy and cost. A skilled person can determine the optimal ratio of solvent to polyether polyurethane or a material comprising nylon 6 and polyether polyurethane by routine testing.

[0130] The dissolution section [α] may comprise one or more dissolution vessels operated in series or in parallel. Preferably, these vessels are equipped with additional devices that increase friction, such as stirrers, mixers or agitators, which reduce the dissolution time.

[0131] Precipitation step (step b.3)):

[0132] The polyether polyurethane-rich stream comprising the organic solvent and dissolved polyether polyurethane discharged from the dissolution section [α] and the second solvent are fed to a precipitation section [γ] where they are mixed so that the polyether polyurethane is precipitated from the mixture comprising the organic solvent and the second solvent.

[0133] Preferably, the second solvent is a non-solvent (also known as an anti-solvent) for the polyether polyurethane, i.e., a liquid in which the polyether polyurethane is insoluble and causes the polyether polyurethane to precipitate. The addition of the second solvent reduces the solubility of the polyether polyurethane dissolved in the solution, which results in the precipitation of the precipitated polyether polyurethane particles. The second solvent can be any solvent. Preferably, the second solvent is an aqueous solution or water, which has the advantage of being an environmentally friendly solvent.

[0134] In a preferred embodiment, the second solvent consists of or is a portion of the mixture comprising an organic solvent and a third solvent obtained from the washing section [β] in step b.7). As used herein, "a portion of or is a mixture" is defined as any fraction between 1 and 100 wt.%, preferably between 10 and 100 wt.%, more preferably between 25 and 100 wt.%, and even more preferably between 75 and 100 wt.%. This has the advantage that less fresh solvent is required for the precipitation of the polyether polyurethane. Another advantage is that less solvent needs to be distilled in the solvent distillation section [δ], which results in lower energy costs, smaller equipment size, lower investment costs, and a more environmentally friendly process.

[0135] The temperature in the precipitation section [γ] can vary and may be in the range of 0° C. to 150° C., preferably 10° C. to 100° C., more preferably 15° C. to 80° C., and most preferably 20° C. to 60° C. Experiments have shown that these temperature ranges allow particularly complete precipitation of the dissolved polyether polyurethane.

[0136] The amount of second solvent charged to precipitation section [γ] can vary and can be in the range of 0.1 wt.% to 500 wt.%, preferably 0.2 wt.% to 100 wt.%, more preferably 0.5 wt.% to 50 wt.% and most preferably 1 wt.% to 25 wt.% compared to the organic solvent charged to precipitation section [γ].

[0137] Small amounts of the second solvent reduce the degree of precipitation of the polyether polyurethane. Large amounts of the second solvent complicate the recovery of the precipitated polyether polyurethane and organic solvent. Large amounts of the second solvent also require more energy and cost to recover the precipitated polyether polyurethane and organic solvent. A skilled artisan will be able to find the optimal ratio of the second solvent to the polyether polyurethane-rich stream for the specific solvent and equipment used by performing simple precipitation experiments.

[0138] Polyether polyurethane recovery step (step b.4):

[0139] In the polyether polyurethane recovery step, the precipitated polyether polyurethane is recovered from the mixture comprising an organic solvent and a second solvent, and the precipitated polyether polyurethane is discharged from the precipitation section [γ]. There are several suitable methods for recovering the polyether polyurethane precipitate, including but not limited to filtration, centrifugation and decantation. Preferably, filtration is used to recover the polyether polyurethane. For filtration, a solution containing the precipitate is loaded into a filter so that the precipitate is expected to remain on the filter when the liquid passes through the filter. When centrifugation is used as a recovery method, the solution containing the precipitate is rapidly rotated, causing the solid precipitate to settle (assuming that the density of the solid precipitate is higher than the density of the liquid). A compacted precipitate can also be obtained by pouring out the liquid. In decantation, the liquid layer is poured out or sucked out of the precipitate.

[0140] Optionally, the recovered precipitate is washed with a solvent before being discharged from the precipitation section [γ]. Preferably, the solvent used for washing the recovered precipitate is the organic solvent of step b.1) or the second solvent.

[0141] Optionally, the recovered precipitate, which has optionally been washed with a solvent, is dried before being discharged from precipitation section [γ]. Advantageously, it has been found that the precipitate and the recovered polyether polyurethane discharged from precipitation section [γ] in step b.4) of the process according to the invention are of high quality and can be reused in the production of textiles, optionally in combination with fresh polyether polyurethane, which is a preferred embodiment of the present invention.

[0142] Step of draining off the solvent mixture (step b.5)):

[0143] The mixture comprising the organic solvent and the second solvent, from which the precipitated polyether polyurethane has been recovered in step b.4), is discharged from precipitation section [γ] and fed to solvent distillation section [δ]. Optionally, the solvent resulting from washing the recovered precipitate is also discharged from precipitation section [γ] and fed to solvent distillation section [δ].

[0144] Load the wash step (step b.6):

[0145] In separation section [B], the third liquid solvent and the stream comprising undissolved nylon 6 are fed to washing section [β]. In addition to undissolved nylon 6, the stream comprising undissolved nylon 6 fed to washing section [β] may also comprise an organic solvent. The purpose of washing section [β] is to recover the organic solvent present in the stream comprising undissolved nylon 6, thereby obtaining a stream rich in nylon 6 that contains less organic solvent than the stream comprising undissolved nylon 6.

[0146] Preferably, the third solvent has good solubility in organic solvents but poor solubility in nylon 6. The third solvent can be any solvent. Preferably, the second solvent is water or an aqueous solution. The advantage of water as the third solvent is that it is an environmentally friendly solvent. The third solvent and the second solvent can have the same composition, which has the advantage of simplifying the process by reducing the amount of different components required.

[0147] The amount of third solvent charged to wash section [β] may vary and may be in the range of 10 wt.% to 1000 wt.%, preferably 20 wt.% to 500 wt.%, more preferably 50 wt.% to 400 wt.%, and most preferably 100 wt.% to 250 wt.% compared to the stream comprising undissolved nylon 6 charged to wash section [β].

[0148] Washing step (step b.7)):

[0149] In the washing section [β], the stream comprising undissolved nylon 6 is washed with a third solvent, so that a stream rich in nylon 6 and comprising a mixture of the organic solvent and the third solvent is obtained.

[0150] The temperature in the washing section [β] can vary and may be in the range of 0° C. to 150° C., preferably 10° C. to 100° C., more preferably 15° C. to 80° C., and most preferably 20° C. to 60° C. Experiments have shown that these temperature ranges result in particularly complete recovery of the organic solvent from a stream comprising undissolved nylon 6.

[0151] The skilled artisan can determine by routine experimentation the amount of third solvent and the optimal temperature required to effectively wash a stream comprising undissolved nylon 6.

[0152] Washing the stream comprising undissolved nylon 6 with the third solvent can be carried out in various apparatuses, all of which are known to the skilled person.

[0153] Step of discharging a stream rich in nylon 6 (step b.8)):

[0154] A nylon 6-rich stream is discharged from the wash section [β]. The nylon 6-rich stream comprises a third solvent and, optionally, an organic solvent. Preferably, the nylon 6-rich stream has an organic solvent content of less than 25 wt.%, preferably less than 10 wt.%, more preferably less than 2 wt.%, and most preferably less than 0.2 wt.%, relative to the total weight of the nylon 6-rich stream. Optionally, the nylon 6-rich stream is dried prior to discharge.

[0155] Typically, the resulting nylon 6-rich stream comprises a solid nylon 6-rich material. In this context, the term "solid" refers to the state of the material at room temperature (20° C.). At higher temperatures, the nylon 6-rich material may also be present as a melt. The nylon 6-rich material is stable and can be stored before being charged to the depolymerization section in step c.1) of the process of the present invention or transported to a depolymerization section at a different location for this purpose.

[0156] Preferably, the nylon 6 content in the resulting nylon 6-rich stream from washing section [β] is at least 85 wt%, more preferably at least 90 wt%, and most preferably at least 95 wt% on a dry weight basis.

[0157] Preferably, the polyamide 6 content of the resulting polyamide 6-rich stream from separation section [B] is at least 85 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-%, and most preferably at least 98 wt.-%, based on dry weight.

[0158] The determination of the nylon 6 content is a routine activity and can be carried out by various methods, all of which are known to the skilled person. Preferably, the polyamide 6 content in the nylon 6-rich stream is determined by thermogravimetric analysis (TGA) and / or by differential scanning calorimetry (DSC) (e.g., by method ISO 11357-3).

[0159] As used herein, "dry weight basis" refers to the amount of an ingredient expressed as a percentage relative to the total dry weight of the composition, wherein "dry weight" is the weight of a substance after removing water and / or other liquids from the substance by drying until the weight is constant.

[0160] Step of discharging the mixture comprising the organic solvent and the third solvent (step b.9)):

[0161] A mixture comprising an organic solvent and a third solvent is discharged from the washing section [β]. Typically, the organic solvent and / or the third solvent are valuable compounds, and recycling and reuse have significant economic and environmental advantages. In a preferred embodiment of the present invention, the mixture comprising an organic solvent and a third solvent is therefore fed to the solvent distillation section [δ]. Optionally, the mixture comprising an organic solvent and a third solvent is first fed to another section and used therein, in particular as a second solvent in a precipitation section, and then fed to the solvent distillation section [δ]. In a preferred embodiment, the mixture comprising an organic solvent and a third solvent is first partially or completely fed to the precipitation section [γ] and used as the second solvent. This provides for particularly efficient use and reuse of the solvent in the process of the present invention.

[0162] Solvent separation step (step b.10)):

[0163] In the solvent distillation section [δ], the various solvents used in the process of the present invention are separated and recovered. This allows them to be advantageously reused. Specifically, in the solvent distillation section [δ], the mixture comprising the organic solvent and the second solvent, from which the precipitated polyether polyurethane has been recovered, and the mixture comprising the organic solvent and the third solvent discharged from the washing section [β] are separated by distillation. Thereafter, the mixture comprising the organic solvent and the second solvent, from which the precipitated polyether polyurethane has been recovered, and the mixture comprising the organic solvent and the third solvent discharged from the washing section [β] are referred to as the combined feed to the solvent distillation section [δ].

[0164] The separated organic solvent, the second solvent, and the third solvent, as well as the residue, are discharged from solvent distillation section [δ]. In a preferred embodiment, the separated organic solvent discharged from solvent distillation section [δ] in step b.10) is fed to dissolution section [α] in step b.1). In another preferred embodiment, the second solvent and the third solvent discharged from solvent distillation section [δ] are optionally reused in precipitation section [γ] and / or washing section [β] after separation from each other.

[0165] Separation by distillation is used to separate liquids from non-volatile solids and to separate liquids having different boiling points.Distillation is a conventional activity and can be carried out in a variety of apparatuses, all of which are known to the skilled person.

[0166] The mixture comprising the organic solvent and the second solvent from which the precipitated polyether polyurethane has been recovered optionally further contains (dissolved) polyether polyurethane, (dissolved) nylon 6, colorant, additives, degradation products of the organic solvent and / or the second solvent. The mixture comprising the organic solvent and the third solvent optionally further contains (dissolved) polyether polyurethane, (dissolved) nylon 6, and degradation products of the organic solvent and / or the third solvent.

[0167] Generally speaking, separating three different liquids by distillation is more complex, requires more energy, and requires more equipment than separating two different liquids by distillation. Therefore, the ability to limit the number of different solvents in the method of the present invention to two by using the same solvent as the second solvent and the third solvent is particularly advantageous. In a preferred embodiment of the present invention, the second solvent and the third solvent are the same solvent. In a more preferred embodiment, the second solvent and the third solvent are water or an aqueous solution. Using water as the solvent is advantageous because it is inexpensive, available in large quantities, non-explosive, and environmentally friendly.

[0168] In a preferred embodiment of the present invention, the organic solvent is selected from N,N-dimethylformamide (DMF, (CH3)2NC(=O)H), N,N-dimethylacetamide (DMAc, CH3C(=O)N(CH3)2), 1,4-dioxane (dioxane, C4H8O2), N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone (NMP, C5H9NO), tetrahydrofuran (THF; also known as oxolane, C4H8O). In a more preferred embodiment, the organic solvent is N,N-dimethylacetamide (DMAc, CH3C(=O)N(CH3)2).

[0169] In another preferred embodiment, the organic solvent is selected from N,N-dimethylformamide (DMF, (CH3)2NC(=O)H), N,N-dimethylacetamide (DMAc, CH3C(=O)N(CH3)2), 1,4-dioxane (dioxane, C4H8O2), N-alkyl-2-pyrrolidone such as N-methyl-2-pyrrolidone (NMP, C5H9NO), tetrahydrofuran (THF; also known as oxolane, C4H8O), and the second solvent and the third solvent are both water. In a more preferred embodiment of the present invention, the organic solvent is N,N-dimethylacetamide (DMAc, CH3C(=O)N(CH3)2), and the second solvent and the third solvent are both water. N,N-dimethylacetamide (DMAc) has a boiling point of approximately 165°C at atmospheric pressure. Water has a boiling point of 100°C at atmospheric pressure.

[0170] When only DMAc and water are present in the combined feed to solvent distillation section [δ], the volatility difference between the two is significant, and separation by distillation is found to be relatively easy. In such cases, continuous separation of the combined feed to solvent distillation section [δ] can be achieved in a single distillation column operated in a continuous mode. In such a distillation column, water is distilled from the top of the column in a vaporous state, and DMAc is removed from the bottom of the column in a liquid state. When non-volatile compounds (such as polyether polyurethane and nylon 6) are present in addition to DMAc and water in the combined feed to solvent distillation section [δ], the solvent distillation layout required for continuous separation into DMAc, water, and non-volatile compounds is even more extensive. This type of direct layout for separation by distillation comprises two distillation columns operated in series. A feed consisting of DMAc, water, and non-volatile compounds (in liquid form) is fed to a first distillation column. Water is distilled from the top of the first distillation column in a vaporous state, and a mixture of DMAc and non-volatile compounds (in liquid or slurry form) is removed from the bottom of the first distillation column. The bottoms stream from the first column is fed to a second distillation column. DMAc is distilled in a gaseous state from the top of the second distillation column, and non-volatile compounds are discharged from the bottom of the second distillation column. In practice, a mixture of DMAc and non-volatile compounds can be discharged from the bottom of the second distillation column to reduce the risk of plugging the second distillation column. An extrusion unit can be added to recover DMAc from the bottom stream of the second distillation column to increase the overall recovery rate of DMAc.

[0171] As an alternative to separation by distillation in two distillation columns operated in series, a single distillation column with a side draw, operated in continuous mode, can be selected. In such a distillation column, water is distilled in the gaseous state from the top of the distillation column, DMAc is removed as a liquid side stream, and non-volatile compounds are removed from the bottom of the second distillation column. Optionally, the bottom stream is fed to an extrusion unit.

[0172] As an alternative to charging the distillation column in liquid form, the feed to the first distillation column can be carried out in gaseous form. In this case, the combined feed to the solvent distillation section [δ], excluding non-volatile compounds, is evaporated in a feed evaporator before being charged to the first distillation column. Non-volatile compounds are discharged from the feed evaporator. This alternative has the advantage of less fouling in the distillation column. Optionally, a squeeze column can be combined with the feed evaporator. Typically, process streams containing DMAc contain a certain amount of acetic acid and dimethylamine, for example due to degradation of DMAc. This also applies to the combined feed to the solvent distillation section [δ].

[0173] The boiling point of pure dimethylamine at atmospheric pressure is about 7° C. Dimethylamine is well soluble in water.

[0174] The boiling point of pure acetic acid at atmospheric pressure is approximately 118°C.

[0175] However, acetic acid and DMAc form a high-boiling azeotrope (composition of approximately 21 wt.% acetic acid and approximately 79 wt.% N,N-dimethylacetamide at atmospheric pressure) and have an atmospheric boiling point of approximately 171°C, which is only slightly higher than the atmospheric boiling point of N,N-dimethylacetamide. A high-boiling azeotrope (or constant-boiling mixture) is a mixture of two liquids that has a boiling point higher than the boiling points of the two individual liquids (in pure form).

[0176] If the pressure is reduced, the azeotropic point of the mixture of acetic acid and N,N-dimethylacetamide shifts to a higher concentration of the low-boiling-point component, which is acetic acid.

[0177] At 6.7 kPa, a high-boiling azeotrope consisting of about 30 wt.% acetic acid and about 70 wt.% N,N-dimethylacetamide is formed, and the boiling point of the high-boiling azeotrope is about 93°C.

[0178] At 1.3 kPa, a high-boiling azeotrope consisting of approximately 42 wt.% acetic acid and approximately 58 wt.% N,N-dimethylacetamide is formed, with a boiling point of approximately 75°C. Preferably, the degradation products are removed from the solvent that is reused in the process. This has the advantage of preventing the accumulation of degradation products. In a preferred embodiment, the degradation products of the organic solvent are removed before the separated organic solvent discharged from the solvent distillation section [δ] in step b.10) is fed to the dissolution section [α] in step b.1). However, due to the formation of a maximum azeotrope, DMAc and acetic acid cannot be separated by simple distillation.

[0179] Several techniques for breaking azeotropes in distillation are known to those skilled in the art.

[0180] One group of techniques is based on the addition of another compound that modifies the molecular interactions and eliminates the highest azeotrope of N,N-dimethylacetamide and acetic acid. Chlorobenzene, toluene, ethylbenzene, and xylene are examples of compounds that break this highest azeotrope. Adding one of these compounds to a mixture of N,N-dimethylacetamide and acetic acid results in the formation of a new azeotrope of this compound and acetic acid, which can be removed by evaporation. The resulting mixture of this compound and acetic acid is then separated.

[0181] Another group of technologies, often referred to as pressure swing distillation, is based on the fact that the highest azeotrope is pressure-dependent. In this type of system, two distillation columns are operated at different pressure levels. A feed mixture of N,N-dimethylacetamide and acetic acid is fed to a first distillation column operated at a certain pressure. The bottoms stream from this first distillation column is fed to a second distillation column. The bottoms stream from the second distillation column is fed to the first distillation column. High-purity N,N-dimethylacetamide and acetic acid are obtained as overhead products from the distillation columns. The main advantage of pressure swing distillation is the absence of foreign compounds.

[0182] Finally, there is a group of technologies that convert acetic acid into another component (eg, salt formation due to addition of caustic) or selectively adsorb acetic acid from a mixture of N,N-dimethylacetamide and acetic acid.

[0183] When, in addition to N,N-dimethylacetamide (DMAc), water and non-volatile compounds such as polyether polyurethane and polyamide 6, acetic acid and dimethylamine are also present in the combined feed to the solvent distillation section [δ], the required solvent distillation layout for the continuous separation into DMAc, water, non-volatile compounds, acetic acid and dimethylamine is even more extensive.

[0184] The optimum layout depends largely on the composition and volume flow of the combined feeds to the solvent distillation section [δ]. The layout may contain a combination of the various separation solutions described above.

[0185] If the fraction of acetic acid in the combined feed to solvent distillation section [δ] is relatively low, solvent distillation section [δ] can comprise two distillation columns operated in series, followed by a neutralizer evaporation step. A feed consisting of DMAc, water, non-volatile compounds, acetic acid, and dimethylamine is fed to a first distillation column. Water and dimethylamine are distilled in a gaseous state from the top of the first distillation column, and a mixture of DMAc, acetic acid, and non-volatile compounds (in liquid or slurry form) is removed from the bottom of the first distillation column. The water vapor from the top of the first distillation column is condensed. The resulting liquid phase contains water and dissolved dimethylamine. Dimethylamine can be removed from this liquid phase in a dimethylamine stripping unit, thereby obtaining (almost) dimethylamine-free water. The bottom stream of the first column is fed to a second distillation column. DMAc is distilled in a gaseous state from the top of the second distillation column, and a mixture of DMAc, acetic acid, and non-volatile compounds is removed from the bottom of the second distillation column. The bottom stream of the second column is fed to a neutralizer evaporation unit. A base, such as an aqueous NaOH solution, is charged to the neutralizer evaporation unit to neutralize the acetic acid. As a result of evaporation, gaseous DMAc is discharged from the neutralizer evaporation unit. Water, if present, also evaporates. A mixture of neutralized acetic acid (including salts of acetic acid) and non-volatile compounds is discharged from the bottom of the neutralizer evaporation unit. In practice, the mixture of DMAc, neutralized acetic acid (including salts of acetic acid), and non-volatile compounds can be discharged from the bottom of the neutralizer evaporation unit to reduce the risk of clogging of the neutralizer evaporation unit.

[0186] The DMAc recovered by distillation is discharged from the solvent distillation section [δ] and charged to the dissolution section [α].

[0187] Preferably, the water recovered in the solvent distillation section [δ] is reused in the process according to the invention, optionally after removal of dimethylamine. Preferably, water is used as the second solvent and / or as the third solvent.

[0188] Load step c.1)

[0189] In step c.1) of the present invention, the resulting nylon 6-rich stream is fed to a depolymerization section [C], wherein the nylon 6-rich stream has a nylon 6 content of at least 85% by weight, preferably at least 90% by weight, on a dry weight basis. This has the advantage that the nylon 6-rich stream fed to the depolymerization section [C] is less contaminated with foreign materials, which improves the yield and purity of ε-caprolactam produced in a plant of the present invention configured to carry out the process of the present invention. Further advantages are that the nylon 6-rich stream requires less depolymerization agent in the depolymerization section [C], generates less waste, and requires less energy. Finally, the nylon 6-rich stream is less susceptible to operational problems, such as fouling and clogging of equipment. The depolymerization section [C] comprises one or more depolymerization reactors operated in series and / or in parallel.

[0190] Optionally, the nylon 6-rich stream is mechanically compressed into a smaller volume before being fed into the depolymerization section [C]. This has the advantage that a smaller volume is required for intermediate storage and transport and can also facilitate dosing into the depolymerization section [C].

[0191] Optionally, the nylon 6-rich stream is compressed into pellets of increased density before being fed to the depolymerization section [C]. This can be achieved, for example, by mechanical compaction or by extruding the molten material through a die, followed by cooling and cutting to size. Compressing the nylon 6-rich stream into pellets offers the advantage of increased bulk density, which reduces intermediate storage and transportation costs. In addition to increased density, pelletization offers other benefits, such as a uniform shape and structure, which facilitates (automatic) feeding to the depolymerization section [C].

[0192] Optionally, the nylon 6-rich stream is fed into a furnace (e.g., an extruder). In the furnace, the nylon 6-rich stream is melted. Preferably, the resulting polymer melt is filtered. This has the advantage of removing solid impurities. The melted and optionally filtered polymer melt is cooled and then fed into a pelletizer to obtain pellets. These pellets are fed into the depolymerization section [C].

[0193] The size and shape of the pellets (also referred to as granules) can be selected within a wide range. Typically, the pellets are cylindrical in shape (derived from shredded strands). However, other shapes, such as (imperfect) spheres, are also possible. The size of the pellets can be selected within a wide range. The diameter of the pellets can range from 1 to 10 mm, preferably from 2 to 5 mm, and more preferably from 3 to 5 mm. In a preferred embodiment, the length of the pellets ranges from 1 to 50 mm, preferably from 2 to 25 mm, and more preferably from 5 to 15 mm.

[0194] Optionally, the nylon 6-rich stream discharged from separation section [B] is dried before being fed to depolymerization section [C]. This has the advantage that less or no solvent is introduced into depolymerization section [C]. Solvent introduced into depolymerization section [C] can negatively affect the depolymerization process (e.g., leading to a reduced depolymerization reaction rate, higher catalyst consumption, higher energy consumption, and the vapor stream comprising ε-caprolactam and water obtained in depolymerization section [C] may contain more impurities).

[0195] The nylon 6-rich stream is preferably fed to the depolymerization reactor in the solid phase or in the form of a melt. Preferably, the nylon 6-rich stream is fed in the form of a melt. Feeding in the form of a melt can be achieved by using an extruder, a gear pump, or other means known to those skilled in the art.

[0196] Feeding the nylon 6-rich stream to the depolymerization reactor can be achieved by continuously or intermittently dosing the nylon 6-rich stream.

[0197] Disaggregation step c.2)

[0198] In the depolymerization section [C], the nylon 6-rich stream is depolymerized to form ε-caprolactam. The ε-caprolactam formed is discharged from the depolymerization section [C] as a stream comprising ε-caprolactam.

[0199] Depolymerization of the nylon 6-rich stream is achieved by increasing the temperature of the nylon 6-rich stream to a temperature of at least 180° C. but not higher than 400° C. in the depolymerization zone [C]. The preferred temperature range for the depolymerization reaction is 200° C. to 350° C., more preferably 220° C. to 340° C., and most preferably 240° C. to 325° C. Experiments have shown that within these temperature ranges, depolymerization is particularly effective and that side reactions and impurity reactions of polyamide 6 and ε-caprolactam occur less frequently.

[0200] Generally, the rate of ε-caprolactam formation increases at elevated temperatures. Temperatures below 400°C are preferred because, at temperatures above 400°C, side reactions and impurity reactions of nylon 6 occur more frequently, resulting in the formation of a wider variety of impurities. A portion of these impurities will ultimately enter the ε-caprolactam-containing product stream exiting the depolymerization reactor section [C]. In a preferred embodiment of the present invention, the depolymerization of the nylon 6-rich stream is carried out at a temperature ranging from 220°C to 340°C or from 240°C to 325°C. This temperature range allows for the production of particularly pure ε-caprolactam.

[0201] The pressure in the depolymerization zone [C] can vary and may be in the range of 1 kPa to 100 MPa, preferably 10 kPa to 5 MPa, more preferably 25 kPa to 2 MPa, most preferably 50 kPa to 1 MPa. This pressure range allows the production of particularly pure ε-caprolactam.

[0202] The depolymerization of the nylon 6-rich stream can be achieved in the presence or absence of a solvent. Preferably, the depolymerization of the nylon 6-rich stream is achieved in the presence of water as a solvent. In this case, the water is preferably in the form of steam, in particular superheated steam.

[0203] Preferably, the depolymerization will be complete within 0.1 hour to 24 hours, more preferably within 0.5 hour to 6 hours.

[0204] Feeding water in the form of steam to the depolymerization reactor allows for obtaining a vapor stream comprising ε-caprolactam and water, optionally without further heating. The weight ratio of ε-caprolactam to water in this vapor stream can be adjusted by varying the amount of steam fed to the nylon 6-rich stream in the depolymerization section [C]. In a preferred embodiment, the depolymerization in step c.2) is carried out in the presence of water, whereby the ε-caprolactam-containing stream is a vapor stream comprising ε-caprolactam and water in a weight ratio of 1:1 to 1:50, preferably 1:2 to 1:15, more preferably 1:2 to 1:10, and most preferably 1:3 to 1:8. Within these ranges, a particularly cost-effective process can be performed.

[0205] Preferably, the ε-caprolactam in the vapor stream comprising ε-caprolactam and water has a partial pressure of 0.1 kPa to 1 MPa, more preferably 0.3 kPa to 0.5 MPa, and most preferably 1 kPa to 0.1 MPa.

[0206] During the depolymerization reaction, decomposition products may form, including oligomers of ε-caprolactam. Furthermore, the feed stream derived from a multicomponent material comprising nylon 6 may also contain other components, i.e., impurities, such as non-nylon 6 compounds that remain stable, react, or decompose under the depolymerization conditions, and residues of the solvent used in the pretreatment. Thus, when water is used as the solvent, the vapor stream removed from the depolymerization zone [C] includes not only water and ε-caprolactam, but also impurities.

[0207] Preferably, superheated steam having a temperature between 100°C and 600°C is fed to the depolymerization reactor. Preferably, the temperature of the superheated steam fed to the depolymerization reactor is at least the melting temperature of nylon 6. Preferably, the energy content of the superheated steam fed to the depolymerization reactor is sufficiently high that no additional heat input is required to carry out the depolymerization reaction and evaporate the ε-caprolactam formed. In another preferred embodiment, the depolymerization section [C] is fed with superheated steam having a temperature in the range of 220°C to 575°C. In an even more preferred embodiment, the depolymerization section [C] is fed with superheated steam having a temperature in the range of 275°C to 500°C. In another preferred embodiment, a portion of the heat input required to carry out the depolymerization reaction and evaporate the ε-caprolactam formed is introduced through the wall of the depolymerization reactor.

[0208] Typically, the mass of the vapor stream removed from the depolymerization section [C] is less than the mass of the total feed to the depolymerization section. The total feed to the depolymerization section [C] comprises a nylon 6-rich stream and, optionally, solvent, catalyst, additional reagents, and / or depolymerizing agent. Consequently, without any further measures, there will be an accumulation of material (often referred to as 'residual material') in the depolymerization section [C]. Preferably, a further stream is discharged from the depolymerization section [C]. This has the advantage of reducing or avoiding the accumulation of material in the depolymerization section [C]. The further stream may comprise impurities present in the nylon 6-rich stream, undepolymerized nylon 6, unevaporated ε-caprolactam, catalyst, and compounds formed under the depolymerization conditions, such as monoammonium phosphate, diammonium phosphate, and / or triammonium phosphate, when phosphoric acid is used as the depolymerization catalyst. In a preferred embodiment, a stream comprising monoammonium phosphate, diammonium phosphate, and / or triammonium phosphate is discharged from the depolymerization section [C]. Even more preferably, the stream discharged intermittently or continuously from the depolymerization section [C] comprises a weight fraction of monoammonium phosphate, diammonium phosphate and / or triammonium phosphate of 0.01 to 50% by weight, preferably 0.1 to 25% by weight, more preferably 0.5 to 10% by weight, most preferably 0.5 to 5% by weight.

[0209] The depolymerization of the nylon 6-rich stream in the presence of steam can be carried out in the presence of another depolymerizing agent, such as ammonia. The concentration of ammonia in the depolymerization zone [C] can vary. Thus, in the presence of ammonia in the depolymerization zone [C], the vapor stream removed from the depolymerization zone [C] includes not only ε-caprolactam and impurities, but also ammonia.

[0210] 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 can specifically be selected from the group consisting of orthophosphoric acid, p-toluenesulfonic acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids (including 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 can, for example, be selected from the group consisting of alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides and alkaline earth metal salts, organic bases and solid bases, and combinations thereof. Preferably, orthophosphoric acid, boric acid, organic acids, alkali metal hydroxides, and alkali metal salts are used as catalysts. More preferably, orthophosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate are used as catalysts. Still more preferably, orthophosphoric acid, p-toluenesulfonic acid, boric acid, and sodium hydroxide are used as catalysts. In a particularly preferred embodiment, orthophosphoric acid is used as the catalyst for the depolymerization, in another embodiment p-toluenesulfonic acid is used.

[0211] However, in another preferred embodiment, no catalyst is used for the depolymerization of the nylon 6-rich stream. This has the advantage of lower costs (for the disposal of the catalyst and catalyst waste). However, higher temperatures (and pressures) are generally required compared to depolymerization of nylon 6-rich streams carried out in the presence of a catalyst.

[0212] The advantage of using a catalyst (especially orthophosphoric acid) is that the depolymerization reaction starts at a relatively low temperature and can be carried out under atmospheric conditions. The appropriate concentration of the catalyst for depolymerizing nylon 6 to ε-caprolactam is known to those skilled in the art and can be easily determined by routine experiments. If the concentration of the catalyst used is too low, the reaction rate is slow. On the contrary, if the concentration of the catalyst used is too high, the reaction is very fast, but side reactions will also increase. In addition, the catalyst cost increases, which is economically disadvantageous. Preferably, the catalyst content is 0.01 to 100% by weight relative to the nylon 6 contained in the depolymerization reactor. Even more preferably, the catalyst content is 0.1 to 50% by weight. The optimal catalyst concentration depends on the type of catalyst used for the depolymerization of nylon 6. For the catalyst orthophosphoric acid, the preferred content is 0.1 to 25% by weight, and more preferably 1 to 20% by weight. The preferred content of the catalyst p-toluenesulfonic acid is 10 to 35% by weight, and more preferably 15 to 30% by weight.

[0213] The depolymerization of nylon 6 can be carried out in a batch mode, a semi-continuous mode or a continuous mode, all of which are known to those skilled in the art. As used herein, the terms "batch mode", "semi-continuous mode" and "continuous mode" refer to a mode in which a nylon 6-containing feedstock (i.e., a nylon 6-rich stream) and an optional catalyst are charged to a depolymerization reactor, and a mode in which residual material is discharged from the depolymerization reactor.

[0214] In a preferred embodiment, the depolymerization of nylon 6 is carried out in batch mode. In batch mode, the feedstock, i.e., the material derived from the multicomponent material comprising nylon 6, and optionally the catalyst, are initially charged to the depolymerization reactor. Subsequently, superheated steam is fed to the depolymerization reactor, and ε-caprolactam is removed from the depolymerization reactor as a steam stream comprising ε-caprolactam and water. Next, the feedstock to the depolymerization reactor is interrupted. After optionally removing residual material from the depolymerization reactor, a new cycle is started by charging the feedstock (and optionally the catalyst) to the depolymerization reactor. In a preferred embodiment, residual material is not removed between each cycle.

[0215] In a particularly advantageous embodiment, the depolymerization of nylon 6 is carried out in a continuous mode. In the continuous mode, a nylon 6-containing feedstock (and optionally a catalyst) is continuously charged to a depolymerization reactor. Simultaneously, superheated steam is continuously fed to the depolymerization reactor, and ε-caprolactam is continuously removed from the depolymerization reactor as a vapor stream comprising ε-caprolactam and water. Optionally, a catalyst is continuously or intermittently fed to the depolymerization reactor. Additionally, residual material is continuously removed from the depolymerization reactor. Preferably, the nylon 6-rich stream is fed as a melt. Preferably, the catalyst is fed as a melt, slurry, or solution.

[0216] In another preferred embodiment, the depolymerization of nylon 6 is carried out in a semi-continuous mode. In the semi-continuous mode, a feedstock containing nylon 6 (and optionally a catalyst) is intermittently charged to a depolymerization reactor, while superheated steam is continuously fed to the depolymerization reactor, and ε-caprolactam is continuously removed from the depolymerization reactor as a steam stream comprising ε-caprolactam and water. In the semi-continuous mode of nylon 6 depolymerization, residual material is intermittently removed from the depolymerization reactor.

[0217] Recovery step c.3)

[0218] In the recovery section [D], ε-caprolactam is recovered from the stream comprising ε-caprolactam discharged from the depolymerization section [C]. This stream comprises ε-caprolactam and impurities. Preferably, the recovery is carried out by (partial) condensation of the stream comprising ε-caprolactam.

[0219] Preferably, the ε-caprolactam obtained by condensation is dissolved in water without charging a solvent into the depolymerization section [C], thereby obtaining a phase rich in ε-caprolactam. This phase rich in ε-caprolactam also comprises impurities.

[0220] Preferably, when water is charged as solvent to the depolymerization section [C], the stream comprising ε-caprolactam discharged from the depolymerization section [C] comprises ε-caprolactam, water, and impurities. The water can be charged in liquid or vaporous form. Preferably, the water is charged in vaporous form. ε-caprolactam can be separated from the stream comprising ε-caprolactam discharged from the depolymerization section [C] by passing this vaporous or gaseous stream from the depolymerization reactor (preferably the top) to a (preferably partial) condenser to obtain a condensate containing ε-caprolactam. Preferably, the ε-caprolactam is separated from the remaining components of the vaporous stream by passing the product stream from the depolymerization reactor (preferably the top) to a distillation column, from which a water-rich phase is obtained as an overhead product and an ε-caprolactam-rich phase is obtained as a bottom product.

[0221] The ε-caprolactam recovered in the recovery section [D] is crude, since it contains impurities such as nylon 6 decomposition products or other impurities resulting from (decomposition products of) non-nylon 6 components of the material derived from the nylon 6-rich stream fed to the depolymerization section [C]. The crude ε-caprolactam recovered in step c.3) comprises water and ε-caprolactam, preferably the crude ε-caprolactam is an aqueous solution comprising ε-caprolactam. Therefore, the crude ε-caprolactam recovered in the recovery section [D] requires additional purification to produce high-purity ε-caprolactam. Therefore, "crude" as used herein can be defined as being of lower purity, i.e. containing more impurities, than the purified ε-caprolactam obtained as a product of the process of the present invention.

[0222] Preferably, the crude ε-caprolactam comprises in the range of 6 to 95 wt%, more preferably 20 to 90 wt%, and most preferably 35 to 80 wt% ε-caprolactam. The remainder is mainly water.

[0223] Purification step c.4)

[0224] In step c.4), the crude ε-caprolactam obtained in the recovery section [D] is purified in a purification section [E] to obtain high-purity ε-caprolactam.

[0225] Optionally, the crude ε-caprolactam is filtered before being charged to the purification section [E]. Filtration ensures the removal of undissolved impurities which might otherwise hamper further purification processes.

[0226] Optionally, oil is separated from the crude ε-caprolactam before charging to the purification section [D]. The separation of the oil ensures the removal of impurities that might otherwise hinder further purification processes.

[0227] Preferably, the purified ε-caprolactam is obtained by purifying the crude ε-caprolactam obtained in the recovery section [D] by crystallizing the ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10 to 95°C, more preferably at a temperature of 20 to 85°C.

[0228] The process of the present invention is carried out in a plant, wherein the plant comprises a purification section [E], wherein the purification comprises the following steps:

[0229] c.4) (iv) obtaining purified ε-caprolactam by crystallizing ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10°C to 95°C.

[0230] Preferably, the process of the present invention is performed in a plant, wherein the plant comprises a purification section [E], wherein the purification further comprises the following steps:

[0231] c.4) (i) extracting the crude ε-caprolactam with an organic solvent to obtain an aqueous phase and an organic phase, wherein the organic phase comprises the organic solvent, the ε-caprolactam and impurities;

[0232] c.4) (ii) optionally, switching the solvent by at least partially replacing the organic solvent with water, thereby obtaining an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam, and wherein the solvent switching step (ii) is selected from a process based on back extraction with water and a process based on solvent exchange distillation, wherein the organic solvent is distilled off and water is charged; and

[0233] c.4) (iii) removing impurities having a boiling point lower or higher than that of ε-caprolactam by distillation to obtain purified ε-caprolactam.

[0234] Preferably, after this:

[0235] c.4) (iv) obtaining purified ε-caprolactam by crystallizing ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10°C to 95°C.

[0236] High-purity ε-caprolactam is obtained from crude ε-caprolactam by first extracting the crude ε-caprolactam with an organic solvent in step c.4)(i), thereby obtaining an aqueous phase and an organic phase comprising the organic solvent, ε-caprolactam and impurities. The organic solvent used for extracting the crude ε-caprolactam is preferably an aromatic hydrocarbon, a halogenated hydrocarbon and / or a C4-C 10 Aliphatic or C4-C 10 Cycloaliphatic alcohol. Optionally, the organic solvent used to extract the crude ε-caprolactam is preferably a mixed extractant, i.e. it can be composed of one or more organic solvents and optionally another diluent. Preferably, the one or more organic solvents are independently selected from aromatic hydrocarbons, halogenated hydrocarbons and / or C4-C 10Aliphatic or cycloaliphatic alcohols, and C5-C8 alkanes or C5-C8 cycloalkanes. Particularly good purification results are achieved if the organic solvent used to extract the crude ε-caprolactam is selected from the group consisting of cyclohexane, benzene, toluene, dichloromethane, 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 used to extract the crude ε-caprolactam is selected from the group consisting of benzene, toluene, cyclohexane, alcohols, and mixtures thereof. Still more preferably, the organic solvent used to extract the crude ε-caprolactam is selected from the group consisting of toluene, cyclohexane, 1-octanol, 2-ethylhexanol, and mixtures thereof. Preferably, the weight ratio of organic solvent to ε-caprolactam is from 0.01:1 to 50:1, preferably from 0.05:1 to 20:1, more preferably from 0.1:1 to 10:1, and most preferably from 0.1:1 to 5:1.

[0237] In another embodiment, the extraction with the organic solvent in step c.4)(i) is carried out in an extraction column operated in countercurrent, whereby the crude ε-caprolactam to be purified is introduced at the top of the column and the organic solvent is introduced at the bottom of the column. The extraction produces an aqueous phase and an organic phase comprising the organic solvent, ε-caprolactam and impurities.

[0238] Optionally, the organic phase comprising the organic solvent, ε-caprolactam, and impurities is washed with water or an alkaline aqueous solution before entering step c.4)(ii). If washing is performed with an alkaline aqueous solution, the alkaline solution is preferably an aqueous solution comprising an alkali metal hydroxide and / or an alkali metal carbonate, preferably sodium hydroxide or potassium hydroxide. The alkali metal hydroxide solution preferably comprises 0.5 to 2.0 wt.% of sodium hydroxide or potassium hydroxide.

[0239] The amount of water or alkaline aqueous solution required for efficient washing of the organic phase comprising the organic solvent, ε-caprolactam and impurities can be determined by a skilled person through routine experiments. Preferably, the amount is between 0.1 vol.% and 5 vol.% relative to the amount of organic solvent in the organic phase to be washed.

[0240] In another preferred embodiment, washing the organic phase comprising the organic solvent, ε-caprolactam, and impurities with water or an alkaline aqueous solution is carried out in a countercurrent-operated wash column, whereby the organic phase comprising the organic solvent, ε-caprolactam, and impurities is introduced at the bottom of the column, and water or an alkaline aqueous solution is introduced at the top of the column. Washing produces a washed organic phase comprising the organic solvent, ε-caprolactam, and impurities, and a phase comprising a residue. The residue phase then contains water, impurities, and ε-caprolactam.

[0241] In a preferred embodiment, the optionally washed organic phase comprising the organic solvent, ε-caprolactam, and impurities is then extracted with water to obtain an ε-caprolactam-water phase. Preferably, the ε-caprolactam-water phase is then stripped and / or distilled to remove residual solvent. While the amount of water used to recover the ε-caprolactam can vary, the amount of water used is 0.5 to 20 times, preferably 0.75 to 10 times, and more preferably 1 to 5 times, by weight, the amount of ε-caprolactam recovered.

[0242] In another preferred embodiment, the extraction with water is carried out in a countercurrent extraction column, with the ε-caprolactam-containing phase to be purified introduced at the bottom of the column and the water introduced at the top. The extraction produces an ε-caprolactam-water phase and a solvent phase containing impurities. Typically, the solvent phase containing impurities is reused, optionally after purification (preferably by distillation).

[0243] The ε-caprolactam-aqueous phase, optionally stripped and / or distilled to remove residual solvents, is concentrated by evaporating the water, so that a concentrated ε-caprolactam-aqueous phase is obtained. The ε-caprolactam content of this concentrated ε-caprolactam-aqueous phase is generally between 60 and 99.9 wt.% relative to the total phase.

[0244] In another preferred embodiment, the organic solvent is evaporated from an organic phase comprising the organic solvent, ε-caprolactam, and impurities, which has been optionally washed rather than extracted with water. Any suitable evaporation vessel, such as a column, may 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 evaporates as an azeotropic mixture. The evaporation produces an ε-caprolactam product. Preferably, the ε-caprolactam product is an aqueous ε-caprolactam phase. The ε-caprolactam content of the aqueous ε-caprolactam phase, relative to the total phase, is typically between 40% and 99.9% by weight.

[0245] In another preferred embodiment, an oxidizing agent, such as potassium permanganate, sodium permanganate and / or hydrogen peroxide, is added to the ε-caprolactam-water phase prior to the distillative removal in step c.4)(iii) of the process of the present invention. Most preferably, potassium permanganate is used as the oxidizing agent.

[0246] Preferably, the oxidizing agent is added to the ε-caprolactam-water phase in the form of a solid, slurry, or aqueous solution, so that a dilute aqueous solution is obtained during the purification process by oxidation. A skilled person can determine the amount of oxidizing agent required for efficient oxidation of the ε-caprolactam-water phase by routine experimentation. The exact amount of oxidizing agent depends, inter alia, on the composition of the polyamide 6-rich stream fed to the depolymerization section of the process according to the 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.

[0247] The temperature used for oxidizing 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., prior to the distillative removal in step c.4)(iii), wherein the oxidizing agent is selected from the group consisting of potassium permanganate, sodium permanganate and hydrogen peroxide and combinations thereof, in particular potassium permanganate.

[0248] The length of time for the oxidation with the oxidizing agent can vary. Preferably, in the process of the present invention, the oxidation of the ε-caprolactam-water phase with the oxidizing agent is carried out for 1 minute to 24 hours, more preferably 2 minutes to 6 hours, and most preferably 5 minutes to 2 hours, prior to the distillative removal in step c.4)(iii).

[0249] The concentration of ε-caprolactam in the ε-caprolactam-water phase used for oxidation with the oxidizing agent can vary. Preferably, the aqueous solution used for oxidation comprises an ε-caprolactam to water weight ratio of 5:1 to 1:5, more preferably 3:1 to 1:3, and most preferably 2:1 to 1:2. Optionally, the ε-caprolactam to water weight ratio is adjusted prior to adding the oxidizing agent to the aqueous phase. Preferably, the ε-caprolactam to water weight ratio is adjusted by adding or removing water.

[0250] When potassium permanganate and / or sodium permanganate are used as oxidizing agents, solid manganese (IV) oxide (MnO2) particles are formed as a reaction product. The optimal solid-liquid filtration procedure for efficiently removing the solid manganese (IV) oxide particles from the aqueous phase after oxidation can be determined by a skilled artisan through routine experimentation. In this regard, it is common practice to enhance the filtration procedure using filter aids such as activated carbon or diatomaceous earth particles.

[0251] Optionally the aqueous ε-caprolactam phase is hydrogenated and, if hydrogenated, preferably in the presence of a hydrogenation catalyst known per se. The hydrogenation can be carried out as described, for example, in EP635487.

[0252] In a preferred embodiment of the present invention, prior to crystallization in step c.4) (iv), an aqueous solution comprising water, ε-caprolactam and impurities is hydrogenated in the presence of a hydrogenation catalyst. The hydrogenation catalyst can be any known heterogeneous hydrogenation catalyst. Examples of such catalysts are ruthenium on alumina, rhodium on alumina, platinum on carbon, palladium on carbon, Raney nickel, nickel on silica and nickel on alumina. Preferably, a catalyst made of nickel is used. Suitable nickel catalysts typically have a nickel content between 5 and 80 wt.% relative to the metal and the support. In addition to nickel, the catalyst may also contain some activators, such as Zr, Mn, Cu or Cr. The activator content is typically between 1 and 20 wt.%. If a palladium-containing heterogeneous catalyst is used, the palladium content will typically be between 0.01 and 10 wt.%.

[0253] The heterogeneous catalyst can be contacted with the hydrogen-containing reaction mixture in various ways. The hydrogenation can be carried out, for example, in a stirred tank reactor, wherein the catalyst particles are suspended in the mixture to be purified (slurry phase process). In another embodiment, the hydrogenation is carried out in a fixed bed reactor, wherein the catalyst is fixed in the reactor.

[0254] The hydrogenation can be carried out in a three-phase system (gas, liquid, solid) comprising an aqueous ε-caprolactam mixture, gaseous hydrogen, and a heterogeneous hydrogenation catalyst. Alternatively, the hydrogenation can be carried out in a two-phase system (liquid, solid) comprising an aqueous ε-caprolactam mixture fully or partially saturated with hydrogen and a heterogeneous hydrogenation catalyst. The dissolution of hydrogen in the water-ε-caprolactam mixture to obtain a mixture fully or partially saturated with hydrogen can be carried out by any method known to those skilled in the art.

[0255] The hydrogenation temperature is typically between 20° C. and 160° C. The hydrogenation pressure is typically between 0.1 and 15 MPa.

[0256] The hydrogenation of the water-ε-caprolactam mixture is intended to hydrogenate the unsaturated compounds present in the impure ε-caprolactam. The presence of these unsaturated compounds is disadvantageous because they can impair the physical and mechanical properties of nylon 6 produced by polymerizing ε-caprolactam. The saturated compounds formed by hydrogenation do not adversely affect these physical and mechanical properties of nylon 6, and these compounds can be more easily removed, for example, in a distillation step and / or crystallization step following the hydrogenation step.

[0257] Preferably, water is evaporated from the optionally hydrogenated aqueous ε-caprolactam phase.After hydrogenation and / or evaporation of water, the aqueous ε-caprolactam phase is distilled to recover high-purity ε-caprolactam and a distillation residue.

[0258] In step c.4)(iii) of the process of the present invention, the optionally washed organic phase comprising organic solvent, ε-caprolactam and impurities is subsequently distilled. Preferably, the distillation of the optionally washed organic phase comprising organic solvent, ε-caprolactam and impurities is carried out under reduced pressure. In one embodiment, the distillation is carried out at a pressure of less than 350 kPa, preferably less than 50 kPa, more preferably less than 20 kPa and most preferably less than 10 kPa. Preferably, the distillation temperature at the bottom of the distillation column is between 100° C. and 200° C. and more preferably between 110° C. and 180° C. The distillation comprises the separation of low-boiling organic impurities (with a boiling point lower than ε-caprolactam) and / or the separation of high-boiling organic impurities (with a boiling point higher than ε-caprolactam) from ε-caprolactam.

[0259] In a preferred embodiment, an alkali metal hydroxide, preferably NaOH, is added to the phase comprising ε-caprolactam prior to the distillative removal in step c.4)(iii). Preferably, the amount of NaOH added is in the range of 0.5 to 100 mmol / kg ε-caprolactam, and more preferably 2 to 80 mmol / kg ε-caprolactam. Experiments have shown that the addition of an alkali metal hydroxide, particularly NaOH, is particularly effective for the distillative removal of impurities having a boiling point both below and above that of ε-caprolactam.

[0260] In another preferred embodiment, in addition to the crude ε-caprolactam recovered in the recovery section, crude ε-caprolactam obtained from the Beckmann rearrangement of cyclohexanone oxime is also purified in the purification section [E]. This has the advantage that the carbon footprint of a plant for the de novo production of ε-caprolactam by the Beckmann rearrangement of cyclohexanone oxime can be reduced by introducing the recycled ε-caprolactam according to the invention.

[0261] In step c.4) (iv) of the process of the present invention, the solution comprising ε-caprolactam and impurities is crystallized at a temperature of 10 to 95°C to obtain purified ε-caprolactam.

[0262] Preferably, the solution comprising ε-caprolactam and impurities which is crystallized in step c.4)(iv) is the crude ε-caprolactam obtained in the recovery section [D].

[0263] More preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step c.4)(iv) is the organic phase comprising organic solvent, ε-caprolactam and impurities obtained by extraction in step c.4)(i), said organic phase being optionally washed with water or with an alkaline aqueous solution.

[0264] Even more preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step c.4)(iv) is an aqueous phase comprising water, ε-caprolactam and impurities having a lower or higher boiling point than ε-caprolactam obtained by solvent switching in step c.4)(ii).

[0265] Most preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step c.4)(iv) is the phase comprising ε-caprolactam and impurities obtained by distillation under vacuum conditions in step c.4)(iii).

[0266] Preferably, the ε-caprolactam crystallization process in step c.4) (iv) comprises the following steps:

[0267] 1. Feeding a solution comprising ε-caprolactam and impurities into a crystallizer;

[0268] 2. setting conditions in the crystallizer so that ε-caprolactam crystals and mother liquor are formed;

[0269] 3. Separation of ε-caprolactam crystals and mother liquor;

[0270] 4. Recirculate the mother liquor.

[0271] Crystallization can be applied to the production of ε-caprolactam. It is primarily used for its purification potential and / or product recovery to increase yield. All crystallization processes are based on the formation of a solid crystalline phase from a liquid. In a preferred embodiment, the crystallization in step c.4) (iv) is performed by solution crystallization or melt crystallization.

[0272] Optionally, according to step c.4)(iii) of the process of the invention, impurities having a boiling point lower or higher than ε-caprolactam are removed by distillation under vacuum conditions before the crystallization in step c.4)(iv), thereby obtaining a phase comprising ε-caprolactam and impurities.

[0273] Therefore, according to a particularly advantageous embodiment of the present invention, the purification in step c.4) further comprises c.4)(iii) a step of distilling under vacuum conditions to remove impurities having a boiling point lower or higher than ε-caprolactam before the crystallization in step c.4)(iv).

[0274] Optionally, according to step c.4)(iii) of the process of the invention, impurities having a boiling point lower or higher than ε-caprolactam are removed by distillation under vacuum conditions after the crystallization in step c.4)(iv), thereby obtaining a phase comprising ε-caprolactam and impurities.

[0275] Therefore, according to a particularly advantageous embodiment of the present invention, after the crystallization in step c.4)(iv), the purification in step c.4) further comprises the step c.4)(iii) of distilling under vacuum conditions to remove impurities having a boiling point lower or higher than that of ε-lactam.

[0276] Optionally, according to step c.4)(iii) of the process of the invention, impurities with boiling points lower or higher than ε-caprolactam are removed by distillation under vacuum conditions before and after the crystallization in step c.4)(iv), thereby obtaining a phase comprising ε-caprolactam and impurities.

[0277] Therefore, according to a particularly advantageous embodiment of the present invention, the purification in step c.4) further comprises, before and after the crystallization in step c.4)(iv), a step c.4)(iii) of distilling under vacuum conditions to remove impurities having a boiling point lower or higher than ε-caprolactam.

[0278] The term solution crystallization is used to crystallize a compound from a solution comprising the (impure) compound and to which an auxiliary solvent is added. The auxiliary solvent is water or a non-aqueous solvent. If the auxiliary solvent is water, the amount of water in the solution can be selected within a wide range, preferably the amount of water is in the range of 0.5 to 25 wt.%, more preferably 1 to 9 wt.%. The crystallization temperature can be selected within a wide range, preferably the crystallization temperature range is 10°C to 95°C, more preferably 20°C to 85°C, even more preferably the crystallization temperature range is 20°C to 70°C, most preferably 30°C to 65°C. Crystallized purified ε-caprolactam is recovered from a slurry having a slurry concentration preferably in the range of 5 to 75 wt.%, more preferably in the range of 10 to 70 wt.%, most preferably in the range of 15 to 50 wt.%. If the auxiliary solvent is a non-aqueous solvent, the amount of non-aqueous solvent in the solution can be selected within a wide range, preferably the amount of non-aqueous solvent ranges from 5 to 95 wt.%, more preferably 10 to 90 wt.%, most preferably 30 to 70 wt.%. The crystallization temperature can be selected within a wide range, preferably in the range of 10°C to 95°C, more preferably in the range of 20°C to 85°C, even more preferably in the range of 20°C to 70°C, and most preferably in the range of 30°C to 65°C. The crystallized purified ε-caprolactam is recovered from the slurry at a slurry concentration of preferably 5 to 75 wt.%, more preferably 10 to 70 wt.%, and most preferably 15 to 50 wt.%. Examples of non-aqueous solvents include alkanes (such as n-hexane, n-heptane, isooctane, cyclohexane), alcohols (such as methanol, ethanol, n-propanol, n-butanol), aromatic hydrocarbons (such as benzene, toluene, o-xylene, m-xylene, p-xylene), ammonia, chlorinated hydrocarbons (such as carbon tetrachloride, chloroform or ethyl chloride), ketones (such as acetone or methyl ethyl ketone) and esters (such as ethyl acetate), as well as mixtures of these solvents. Cyclohexane is preferred.

[0279] Solution crystallization is usually carried out at atmospheric pressure, but can also be carried out under reduced or pressurized conditions. In the case of solution crystallization, the product is crystallized by evaporative crystallization in which the solvent evaporates, or by cooling crystallization in which cooling is achieved by direct cooling, indirect cooling or vacuum cooling, or by a combination of these methods. After the crystallization step, the formed crystals and mother liquor are separated by, for example, sedimentation, filtration and / or centrifugation. Optionally, the resulting crystals are washed with, for example, a solvent or a solvent mixture with a low impurity content. Optionally, the crystallization-separation sequence is repeated several times. The product is obtained in the form of crystals.

[0280] The narrow definition of the term melt crystallization is to crystallize a compound from a solution comprising the (impure) compound without using an auxiliary solvent. In the broader definition of the term, melt crystallization is also applicable to crystallization from a solution containing a low solvent concentration. Preferably, the solvent concentration in the solution is less than 25wt.%, more preferably less than 10wt.%, and most preferably less than 5wt.%. Here, unless otherwise explicitly mentioned, the broader definition of melt crystallization will be used. The compound crystals obtained by melt crystallization are separated from the mother liquor and optionally washed with the melt of pure compound material. The purification efficiency can be further improved by, for example, sweating (also known as partial melting), that is, gently heating the crystal layer to near its melting temperature, thereby discharging the trapped and adhered impure mother liquor. Optionally, the crystallization-separation sequence is repeated several times. Finally, the optionally washed crystals are melted and discharged or mechanically removed in the form of a melt.

[0281] Preferably, the solvent is present in the mixture in the crystallizer, but crystallization can also be carried out in the absence of a solvent. Many solvents for ε-caprolactam are suitable. Examples of suitable solvents are water, alkanes (such as n-hexane, n-heptane, isooctane, cyclohexane), alcohols (such as methanol, ethanol, n-propyl alcohol, n-butanol), aromatic hydrocarbons (such as benzene, toluene, o-xylene, m-xylene, p-xylene), ammonia, chlorinated hydrocarbons (such as carbon tetrachloride, chloroform or ethyl chloride), ketones (such as acetone or methyl ethyl ketone) and esters (such as ethyl acetate). Preferably, water and aromatic hydrocarbons are used as solvents because these solvents produce large crystals. As solvent, most preferably water. The solvent will serve as a freezing point depressant for the melt in the crystallizer.

[0282] In general, melt crystallization requires less energy than solution crystallization, however, it can be more challenging to operate on an industrial scale.

[0283] Melt crystallization as used herein specifically refers to layer melt crystallization or suspension melt crystallization. The two types of melt crystallization technology methods are characterized by (1) forming a crystal layer on the heat exchanger wall (layer melt crystallization) and (2) crystals grown in suspension (suspension melt crystallization). In general, the operation of the method for growing a crystal layer on the heat exchanger wall is called layer melt crystallization. First, the melt is charged into the crystallizer, and then the crystal layer is grown on the cooled heat exchanger surface. Next, the remaining melt containing impurities discharged from the growing crystals is discharged from the crystallizer, and then the crystal layer is melted and the purified product is recovered. The purification efficiency can be further improved by, for example, sweating (also known as partial melting), that is, gently heating the crystal layer to close to its melting temperature, thereby discharging trapped and adhered impure mother liquor. The layer melt crystallization method is operated in batch mode. Well-known examples of methods based on layer melt crystallization are BEFS Prokem's ProABD method and the Sulzer Chemtech method.

[0284] Layer melt crystallization can be carried out in static or dynamic mode. In static crystallization mode, crystals grow from a stagnant melt onto a cooling surface. In static mode, the desired compound is crystallized in batches on the heat exchanger wall from a stagnant melt in a closed container. This type of crystallization is characterized by a low growth rate of the crystals and the long residence (or batch) time caused thereby. Preferably, the crystallization time ranges from 1 hour to 75 hours, more preferably from 2 hours to 50 hours, and most preferably from 4 hours to 24 hours. After the crystallization step, the remaining melt is discharged. Then, a sweating phase is optionally introduced to remove impurities adhering to or trapped in the crystals. Finally, the crystals are completely melted and discharged or mechanically removed.

[0285] Generally speaking, dynamic crystallization is carried out in a shell and tube heat exchanger, whereby the melt circulates downward along a cooling surface where the compound crystallizes. Generally speaking, the melt is pumped through the tubes, and crystals grow inside the tubes while the cooling medium flows outside the tubes. The thickness of the crystal layer increases over time. After a certain period of time, the circulation of the melt is stopped and the remaining melt is discharged. Like stagnant layer crystallization, dynamic layer crystallization is also carried out in batch mode. Compared with stagnant mode, the crystal growth rate in dynamic mode is higher, and therefore the crystallization time is shorter. Preferably, the crystallization time ranges from 0.05 hours to 12 hours, more preferably from 0.1 hours to 6 hours, and most preferably from 0.3 hours to 3 hours. Then, a sweating phase is optionally introduced to remove impurities adhering to the crystals or trapped in the crystals. Finally, the crystals are completely melted and discharged or mechanically removed.

[0286] Suspension melt crystallization can be carried out in batch mode or in continuous mode. In the case of suspension melt crystallization, the melt is cooled to below its saturation temperature, and crystals begin to grow (optionally, after adding nuclei). The growth rate of the crystal is controlled by the supersaturation temperature of the melt. Suspension melt crystallization can be carried out in any exchanger type or container type crystallizer that allows cooling of the melt. Preferably, suspension melt crystallization is carried out in a scraped surface crystallizer. Optionally, after crystallization, the mixture of the crystal obtained and the mother liquor is separated by filtration. Optionally, after crystallization, the mixture of the crystal of the desired compound obtained and the mother liquor is loaded into a so-called washing tower. In the washing tower, the mother liquor is filtered or discharged from the crystal, and then the crystal is usually washed with a purified compound material.

[0287] After the ε-caprolactam crystallization step, a mother liquor is obtained which contains ε-caprolactam in addition to impurities. Methods for recovering ε-caprolactam from such mother liquors are well known to those skilled in the art. And due to these recovery methods, almost all of the ε-caprolactam present in the mother liquor can be recovered and converted into high-purity ε-caprolactam. In the case of multi-stage crystallization, a possible solution is to recycle the mother liquor in a countercurrent manner, that is, the mother liquor obtained in the nth crystallization stage is charged into the feed of the (n-1)th crystallization stage. Generally speaking, the mother liquor obtained from the 1st crystallization stage is charged into an upstream (purification) unit or a dedicated mother liquor processing unit (e.g., based on distillation or crystallization) of the method. After the ε-caprolactam crystallization, it may be necessary to purify the obtained mother liquor (or a portion thereof) by, for example, recycling it to any previous stage in the method. Alternatively, the mother liquor can be purified, for example, by distillation, before being recharged into the ε-caprolactam crystallization step.

[0288] The high-purity ε-caprolactam obtained according to the process of the present invention can be used to prepare nylon 6 using methods well known to those skilled in the art. This nylon 6 can then be used in all known materials, including engineering materials, fibers, and membranes. The nylon 6 produced according to the present invention from a material comprising nylon 6 and polyether polyurethane is particularly suitable for high-speed spinning applications, including garments containing polyether polyurethane (also known as spandex).

[0289] factory

[0290] The present invention also provides a plant configured to carry out the above-described method of the present invention, namely a chemical plant, comprising a separation section [B], a depolymerization section [C], a recovery section [D], and a purification section [E]. All plant features specifically described in conjunction with the above-described method also apply to the plant of the present invention described below, and vice versa. Thus, the plant is suitable for carrying out the method of the present invention, and it should be understood that what has been described in conjunction with the method of the present invention applies equally to the plant embodiment.

[0291] The plant can be a laboratory setting as in the examples. However, preferably, the plant is an industrial-scale plant. "Industrial-scale" means that if it were to be operated, the plant would have an ε-caprolactam production capacity (i.e. the amount of ε-caprolactam that it could in principle produce) of at least 500 tonnes per year.

[0292] The plant of the present invention is suitable for producing purified ε-caprolactam from materials including nylon 6 and polyether polyurethane, and comprises at least the following four sections: a separation section [B], a depolymerization section [C], a recovery section [D], and a purification section [E]. These sections, and therefore the plant, are configured to carry out the above-described process of the present invention.

[0293] Optionally, the plant of the present invention may include a pretreatment section [A], which may include a mechanical size reduction section [λ] for crushing the material comprising nylon 6 and polyether polyurethane into fragments and / or a cleaning section [ω] for washing the material comprising nylon 6 and polyether polyurethane or the crushed fragments obtained therefrom. Cleaning comprises washing the material comprising nylon 6 and polyether polyurethane and separating foreign materials from said material. The separation of foreign materials can be performed manually (hand sorting) and mechanically (e.g. density separation and magnetic separation). Manual and mechanical devices, such as brushes, can assist the washing in the cleaning section [ω]. Washing is preferably performed by additional friction. Different types of industrial washing systems are available on the market, such as rotary plastic washers and (high-speed) friction washers. The mechanical size reduction section [λ] includes equipment for mechanically crushing the material comprising nylon 6 and polyether polyurethane into fragments. Non-limiting examples of such crushing equipment are cutters, punches, shredders, mills, grinders or chippers.

[0294] The separation section [B] may comprise the following four sections: a dissolution section [α], a washing section [β], a precipitation section [γ] and a solvent distillation section [δ]. These sections and therefore the plant are configured to carry out the above-described method of the invention.

[0295] The dissolution section [α] comprises one or more dissolution units, operated in series and / or in parallel, and one or more separation units, operated in series and / or in parallel. The optionally cleaned and / or shredded fragments of the material comprising nylon 6 and polyether polyurethane are fed to the dissolution unit in solid or melt form, preferably in solid form. The optionally cleaned and / or shredded fragments of the material comprising nylon 6 and polyether polyurethane are optionally dried before being fed to the dissolution section [α]. The dissolution unit is equipped with an inlet for charging the separated organic solvent and fresh organic solvent. The dissolution unit is equipped with one or more outlets for discharging the mixture obtained in the dissolution unit. The mixture comprises undissolved nylon 6 and the organic solvent in which the polyether polyurethane is dissolved. Preferably, the dissolution unit is closed. This has the advantage of reducing the emission of organic solvent into the environment. Preferably, the dissolution unit is equipped with a device for controlling the temperature in the unit (e.g., a steam coil, steam tracing, electric tracing). Optionally, the temperature of the separated organic solvent and fresh organic solvent is adjusted (e.g., in a heat exchanger) before being fed to the dissolution section [α].

[0296] Good contact between the organic solvent and the materials including nylon 6 and polyether polyurethane is essential for efficient operation. Such contact can be achieved by various means known in the art. Improved contact can be achieved by mechanical friction. Mechanical friction can then be achieved, for example, by stirring with a combination of rotating paddles and static fins.

[0297] Suitable dissolution units for dissolving polymers in organic solvents are known to the person skilled in the art. A stirred vessel is an example of such a dissolution unit.

[0298] In the separation unit, the mixture discharged from the dissolution unit is separated into a polyether polyurethane-rich stream comprising an organic solvent and dissolved polyether polyurethane and a stream comprising undissolved nylon 6. The polyether polyurethane-rich stream comprising an organic solvent and dissolved polyether polyurethane is discharged via a discharge line and fed to a precipitation section [γ]. The stream comprising undissolved nylon 6 is discharged via a discharge line and fed to a washing section [β]. Advantageously, the amount of organic solvent in the stream comprising undissolved nylon 6 is low to facilitate washing in the washing section [β].

[0299] Suitable separation units for separating (undissolved) polymer and organic solvent are known to the person skilled in the art. Centrifuges and filters are examples of such separation units.

[0300] Preferably, the dissolution unit and the separation unit are combined in one piece of equipment. This allows for process intensification.

[0301] Washing section [β] comprises a device for washing the stream comprising undissolved nylon 6 with a third solvent to obtain a stream rich in nylon 6 and a mixture of an organic solvent and a third solvent. The purpose of washing section [β] is to remove the organic solvent to a large extent. Optionally, washing section [β] comprises a device for drying the stream rich in nylon 6. The mixture comprising the organic solvent and the third solvent is discharged from washing section [β] and charged to solvent distillation section [δ]. In this context, "charging to solvent distillation section [δ]" also includes indirect means, i.e., additional steps / sections in the middle. Preferably, the mixture comprising the organic solvent and the third solvent discharged from washing section [β] is completely or partially charged to precipitation section [γ] before being charged to solvent distillation section [δ].

[0302] Optionally, after drying, a nylon 6-rich stream is withdrawn from the washing section [β] and fed to the depolymerization section [C].

[0303] Good contact between the third solvent and the nylon 6-rich stream is essential for efficient operation. This contact can be achieved by various means known to the skilled person. One means is a (continuous) centrifuge into which the nylon 6-rich stream is fed and into which the third solvent is charged as a wash solvent.

[0304] The distillation section [δ] comprises one or more distillation columns operated in series and / or parallel. The distillation columns can be operated in batch, semi-continuous, or continuous modes. The choice between these modes of operation depends largely on the scale of operation. Generally speaking, batch operation of distillation columns is more suitable for processing small-volume feed streams. Continuous operation of distillation columns is more suitable for processing large-volume feed streams.

[0305] The exact layout of the distillation section [δ] also depends on the nature of the organic solvent, the second solvent and the third solvent.

[0306] The mixture comprising the organic solvent and the second solvent from which the precipitated polyether polyurethane has been recovered, and the mixture comprising the organic solvent and the third solvent discharged from the washing section [β] are charged to the distillation section [δ]. The separated organic solvent is discharged from the distillation section [δ] and charged to the dissolution section [α]. The second solvent and the third solvent are discharged from the distillation section [δ] and optionally charged to the precipitation section [γ] and the washing section [β], respectively. The residue is discharged from the distillation section [δ]. Optionally, the residue is incinerated to recover energy. Finally, degradation products of the used solvent are discharged from the distillation section [δ]. Acetic acid and dimethylamine are examples of degradation products of the organic solvent DMAc.

[0307] The depolymerization section [C] comprises one or more depolymerization reactors operated in series and / or in parallel. The nylon 6-rich stream is fed into the reactor in the form of a solid or melt, preferably a melt. This feeding can be achieved by using an extruder, a gear pump, or other means known in the art.

[0308] During production, the depolymerization reactor is at least partially filled with a feedstock containing nylon 6, residual material, ε-caprolactam (and optionally a catalyst). The depolymerization reactor can have any desired form. Preferred reactor types are stirred and unstirred bubble column reactors, stirred reactors, and extruder-type reactors.

[0309] The depolymerization reactor must be equipped with means for feeding a stream rich in nylon 6, optionally superheated steam and optionally a catalyst. In addition, the depolymerization reactor is equipped with means for discharging a stream comprising ε-caprolactam and residual materials.

[0310] Good contact between the steam and the reactor contents is essential for efficient operation. This contact can be achieved by various means known to those skilled in the art. As an example, multiple inlets can be used, such as by using a steam distributor to spray steam through the material. Further improved contact can be achieved by incorporating mechanical agitation into the reactor, such as by using a combination of rotating paddles and static fins.

[0311] Preferably, depolymerization will be complete within 0.5 to 6 hours.

[0312] If high-temperature superheated steam is not available at the production location, superheated steam must be produced intentionally by superheating the steam available in the boiler in a so-called superheater.

[0313] The recovery section [D] may comprise one or more (preferably partial) condensers, to which the stream comprising ε-caprolactam is fed in the form of a vapor stream comprising ε-caprolactam and water. Such (partial) condensers may have any desired form. Preferably, the condenser is a distillation column, from which a water-rich phase is obtained as top product and crude ε-caprolactam is obtained as bottom product.

[0314] The purification section [E] may comprise one or more extraction apparatuses, one or more solvent switch apparatuses, an oxidation section, a hydrogenation section, one or more distillation apparatuses and a crystallization section, into which crude ε-caprolactam is fed and from which high-purity ε-caprolactam is discharged.

[0315] The crude ε-caprolactam and the organic solvent are charged into the extraction device, and the organic phase comprising the organic solvent, ε-caprolactam and impurities and the aqueous phase comprising water and impurities are discharged. The extraction device is selected from a mixer-settler extractor, an extraction column, a centrifugal extractor and a combination thereof. Preferably, the extraction device is a static or stirred extraction column, such as tower, towers, rotating disc contactors (RDC), pulse towers, sieve plate (static) towers, random packing (static) towers, and structured packing (SMVP) (static) towers.

[0316] The solvent switching device is charged with water and an organic phase comprising an organic solvent, ε-caprolactam and impurities, and the solvent phase comprising impurities and the ε-caprolactam-water phase comprising water, ε-caprolactam and impurities are discharged. The solvent switching device used in the stripping method is selected from a mixer-settler extractor, an extraction column, a centrifugal extractor and a combination thereof. Preferably, the device used for stripping is a static or stirred extraction column, such as tower, towers, rotating disc contactors (RDC), pulse towers, sieve tray (static) towers, random packing (static) towers, and structured packing (static) towers.

[0317] The solvent switching apparatus used in the solvent exchange distillation method is selected from a sieve tray distillation column, a random packing distillation column, and a structured packing distillation column. Preferably, the distillation column is equipped with a reboiler, a condenser, and a reflux device. The distillation column can be operated at atmospheric, subatmospheric, or superatmospheric pressure. Preferably, water is introduced into the upper portion of the distillation column, and the aqueous phase, comprising water, ε-caprolactam, and impurities having a boiling point lower or higher than that of ε-caprolactam, is discharged from the lower portion of the distillation column.

[0318] The optional oxidation section comprises one or more oxidation reactors operated in series and / or in parallel. An oxidant and an ε-caprolactam-water phase comprising water, ε-caprolactam, and impurities are charged to the oxidation section. Typically, the oxidant is charged in the form of a solid, a slurry, or an aqueous solution. When potassium permanganate or sodium permanganate is used as the oxidant, the oxidation section also includes a filtration section. The oxidation reactor may have any desired form. Preferred reactor types are stirred and unstirred reactors and packed column reactors. The oxidation reactor must be equipped with a means for feeding an aqueous phase comprising water, ε-caprolactam, and impurities having a boiling point lower or higher than that of ε-caprolactam, as well as the oxidant. Furthermore, the oxidation reactor must be equipped with a means for discharging the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam, and impurities, as well as any solid manganese(IV) oxide (MnO2) particles formed. Preferably, the oxidation is carried out at a temperature and atmospheric conditions ranging from 20°C to 85°C.

[0319] The solid manganese (IV) oxide (MnO 2 ) particles that are optionally present can be removed by sedimentation or by solid-liquid filtration, preferably by solid-liquid filtration. It is common practice to use filter aids such as activated carbon particles or diatomaceous earth to improve the filtration process. Filtration systems suitable for separating solid manganese (IV) oxide particles are known to the skilled person. Into this filtration system, a suspension of an oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities and solid manganese (IV) oxide particles is loaded, and the filtered oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities is discharged. Typically, the solid manganese (IV) oxide particles remain in the filtration system. Preferably, this filtration system is operated in a semi-continuous mode, whereby the suspension and the filtered phase are continuously loaded and continuously discharged, while the separated solids are collected in the filtration system. The loading of the suspension is interrupted from time to time, and the collected solids are removed from the filtration system.

[0320] Purification of the crude ε-caprolactam to obtain purified ε-caprolactam in step c.4) optionally comprises hydrogenation using a heterogeneous catalyst, in which case the plant will comprise a hydrogenation section. Preferably, the catalyst comprises nickel or palladium.

[0321] The hydrogenation section includes one or more hydrogenation reactors operated in series and / or in parallel. Hydrogenation can be carried out in a three-phase system (gas, liquid, solid), which includes an ε-caprolactam aqueous mixture, gaseous hydrogen and a heterogeneous hydrogenation catalyst. Alternatively, hydrogenation can be carried out in a two-phase system (liquid, solid), which includes an ε-caprolactam aqueous mixture that is completely or partially saturated with hydrogen and a heterogeneous hydrogenation catalyst. The dissolution of hydrogen in the water-ε-caprolactam mixture can be carried out by any method known to those skilled in the art. Preferably, the mixture is contacted with hydrogen in an absorber or mixer, wherein a constant hydrogen pressure is maintained. Close contact between hydrogen and the mixture will ensure that hydrogen dissolves in the mixture. This process is preferably carried out continuously. Subsequently, the hydrogen-containing mixture is contacted with a hydrogenation catalyst, for example in a separate reactor.

[0322] Heterogeneous catalysts can be contacted with the hydrogen-containing reaction mixture in various ways. Hydrogenation can be carried out, for example, in a stirred tank reactor, where catalyst particles are suspended in the mixture to be hydrogenated (slurry phase method). In this slurry phase method, the catalyst particles and the purified mixture must be separated in another method step after the hydrogenation reaction, for example by filtration separation. Preferably, the catalyst comprises palladium or nickel.

[0323] Alternatively, the hydrogenation can be carried out in a fixed bed reactor, wherein the catalyst is fixed in the reactor, so that an additional step for separating the catalyst and the reaction mixture can be omitted. Preferably, the fixed bed consists of a supported palladium or nickel catalyst.

[0324] The hydrogenation temperature is typically between 20° C. and 160° C. The hydrogenation pressure is typically between 0.1 and 15 MPa.

[0325] The distillation apparatus is charged with an optionally stripped and / or concentrated and / or optionally oxidized and / or hydrogenated ε-caprolactam-water phase comprising water, ε-caprolactam and impurities, and high-purity ε-caprolactam, water and impurities (i.e., low-boiling organic impurities (having a lower boiling point than ε-caprolactam) and high-boiling organic impurities (having a higher boiling point than ε-caprolactam)) are discharged. The distillation apparatus is selected from the group consisting of sieve tray distillation columns, random packing distillation columns, structured packing distillation columns, and horizontal and vertical (falling and rising) film evaporators. Preferably, the distillation column is equipped with a reboiler, a condenser and a reflux device. The distillation apparatus can be operated at atmospheric pressure, subatmospheric pressure or superatmospheric pressure, preferably at subatmospheric pressure.

[0326] Preferably, the distillation comprises separating water, low-boiling organic impurities (having a lower boiling point than ε-caprolactam), and / or high-boiling organic impurities (having a higher boiling point than ε-caprolactam) from ε-caprolactam. Preferably, the distillation comprises: in a first step, separating water as an overhead product, and producing low-boiling impurities containing ε-caprolactam and high-boiling impurities as a bottom product. In a second step, separating the low-boiling impurities as an overhead product, and obtaining high-boiling impurities containing ε-caprolactam as a bottom product. In a third step, separating high-purity ε-caprolactam as an overhead product, and producing a distillation residue comprising ε-caprolactam and high-boiling impurities as a bottom product. Optionally, the first and second steps are combined.

[0327] Preferably, an alkali metal hydroxide, preferably NaOH, is added to the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam, and impurities before distillative removal of water and impurities. The amount of NaOH added is preferably in the range of 0.5 to 100 mmol / kg ε-caprolactam, and more preferably 2 to 80 mmol / kg ε-caprolactam. This allows for particularly efficient distillative removal of impurities with lower and higher boiling points than ε-caprolactam in the subsequent distillation.

[0328] The crystallization section comprises one or more crystallizers operated in series and / or in parallel. Typically, the crystallization section also comprises several containers for storing (intermediate) product streams and / or fresh and used wash liquors. The crystallization of ε-caprolactam can be carried out by solution crystallization or melt crystallization as described above.

[0329] In the case of solution crystallization, ε-caprolactam is recovered by evaporative crystallization, in which the solvent evaporates, or by cooling crystallization, in which cooling is achieved by direct cooling, indirect cooling, or vacuum cooling, or by a combination of these methods. After the crystallization step in the crystallizer, the formed crystals and the mother liquor are separated, for example, by settling in a settler, filtration in a filter, and / or centrifugation in a centrifuge. Optionally, the crystallizer is equipped with a stirrer and / or one or more baffles.

[0330] Optionally, the resulting crystals are washed with, for example, a cleaning solvent. Optionally, the crystallization-isolation sequence is repeated several times. The product is obtained in the form of crystals.

[0331] The auxiliary solvent is water or a non-aqueous solvent. Examples of non-aqueous solvents include alkanes (such as n-hexane, n-heptane, isooctane, cyclohexane), alcohols (such as methanol, ethanol, n-propyl alcohol, n-butanol), aromatic hydrocarbons (such as benzene, toluene, o-xylene, m-xylene, p-xylene), ammonia, chlorinated hydrocarbons (such as carbon tetrachloride, chloroform or ethyl chloride), ketones (such as acetone or methyl ethyl ketone) and esters (such as ethyl acetate), and mixtures of these solvents. In general, the auxiliary solvent is reclaimed and reused in the crystallization process.

[0332] Solution crystallization is usually carried out at atmospheric pressure, but can also be carried out under reduced or increased pressure conditions.

[0333] The melt crystallization of ε-caprolactam can be achieved by layer melt crystallization, in which a layer of crystals containing ε-caprolactam forms on the heat exchanger wall, or by suspension melt crystallization, in which crystals containing ε-caprolactam grow in suspension.

[0334] Preferably, solvent is present in the mixture in the melt crystallizer, but melt crystallization can also be carried out when there is no solvent.Many solvents for ε-caprolactam are suitable.The example of suitable solvent is water, alkane (such as n-hexane, n-heptane, isooctane, cyclohexane), alcohol (such as methanol, ethanol, n-propyl alcohol, n-butanol), aromatic hydrocarbon (such as benzene, toluene, o-xylene, m-xylene, p-xylene), ammonia, chlorinated hydrocarbon (such as carbon tetrachloride, chloroform or ethyl chloride), ketone (such as acetone or methyl ethyl ketone) and ester (such as ethyl acetate).Preferably use water and aromatic hydrocarbon as solvent, because these solvents produce large crystals.As solvent, most preferably water.Solvent will serve as the freezing point depressant of the melt in the crystallizer.

[0335] Layer melt crystallization:

[0336] First, the melt is charged into a crystallizer, and then a crystal layer is grown on a cooled heat exchanger surface. Next, the remaining melt containing impurities discharged from the growing crystals is discharged from the crystallizer, and then the crystal layer is melted and the purified product is recovered. The purification efficiency can be further improved by, for example, sweating (also known as partial melting), that is, gently heating the crystal layer to near its melting temperature, thereby discharging trapped and adhering impure mother liquor. The layer melt crystallization process is operated in batch mode. Well-known examples of methods based on layer melt crystallization are the ProABD method of BEFS Prokem and the SulzerChemtech method.

[0337] Layer melt crystallization can be carried out in static or dynamic mode. In static crystallization mode, crystals grow from a stagnant melt onto a cooling surface. In static mode, the desired compound is crystallized in batches on the heat exchanger wall from a stagnant melt in a closed container. This type of crystallization is characterized by a low growth rate of the crystals, which results in a longer residence (or batch) time. Preferably, the crystallization time ranges from 1 hour to 75 hours, more preferably from 2 hours to 50 hours, and most preferably from 4 hours to 24 hours. After the crystallization step, the remaining melt is discharged. Then, a sweating phase is optionally introduced to remove impurities adhering to the crystals or trapped in the crystals. Finally, the crystals are completely melted and discharged or mechanically removed.

[0338] Suspension melt crystallization:

[0339] The suspension melt crystallization of ε-caprolactam can be carried out in batch mode or in a continuous mode. In the case of suspension melt crystallization, the melt is cooled to below its saturation temperature, and the ε-caprolactam crystals begin to grow (optionally, after adding nuclei). The growth rate of the crystal is controlled by the supersaturation temperature of the melt. Suspension melt crystallization can be carried out in any exchanger type or container type crystallizer that allows cooling of the melt. Preferably, suspension melt crystallization is carried out in a scraped surface crystallizer. Optionally, after crystallization, the mixture of the crystals and the mother liquor obtained is separated by filtration. Optionally, after crystallization, the mixture of the ε-caprolactam crystals and the mother liquor obtained is loaded into a so-called wash tower. In the wash tower, the mother liquor is discharged from the ε-caprolactam crystals, and then the ε-caprolactam crystals are optionally washed with purified ε-caprolactam.

[0340] The process of the present invention can be operated in a continuous, semi-continuous, or batch mode. Thus, the plant of the present invention can also be configured to allow for one or more of these operating modes. In a preferred embodiment, the plant is configured to operate 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 need not include all of the sections described herein in a single location. Specifically, the pretreatment section [A] can be located at a first location, while the separation section [B], depolymerization section [C], recovery section [D], and purification section [E] are located at a second location. Similarly, the mechanical size reduction section [λ], which is part of the pretreatment section [A], can also be located at a first location, while the cleaning section [ω], which is part of the pretreatment section [A], can be located at a second location, while the separation section [B], depolymerization section [C], recovery section [D], and purification section [E] are located at a third location. Optionally, the cleaning section [ω] is divided into two or more sections, with the two or more sections optionally all located at different locations. For example, the first section of the cleaning section [ω] as part of the pretreatment section [A] may be located at a first position, the mechanical size reduction section [λ] as part of the pretreatment section [A] may be located at a second position, and the second section of the cleaning section [ω] as part of the pretreatment section [A] may be located at a third position, while the separation section [B], the depolymerization section [C], the recovery section [D], and the purification section [E] are located at a fourth position. Optionally, the cleaning section [ω] as part of the pretreatment section [A] is divided into two or more sections, and the two or more sections are optionally all located at different positions. Optionally, the cleaning section [ω] as part of the pretreatment section [A] is located at the same position as the separation section [B]. Optionally, the separation section [B], the depolymerization section [C], and the recovery section [D] are located at different positions from the pretreatment section [A] and the purification section [E]. Optionally, the depolymerization section [C] and the recovery section [D] are located at a different position than the pretreatment section [A] and the separation section [B].

[0341] product

[0342] The process of the present invention provides ε-caprolactam and polyether polyurethane obtained by depolymerization of a material comprising nylon 6 and polyether polyurethane according to the process of the present invention as new products that meet specifications for demanding applications. At the same time, the process is particularly environmentally friendly due to its reduced product carbon footprint and the use of waste as starting materials. The ε-caprolactam obtained by the process of the present invention is particularly advantageous in that the product carbon footprint is less than 3 kg CO₂ / kg of purified ε-caprolactam. The ε-caprolactam obtained according to the present invention may also be referred to as "purified ε-caprolactam." As used herein, "purified" means that the ε-caprolactam is produced according to the process of the present invention from a material comprising nylon 6 and polyether polyurethane, resulting in it being obtained in a purified form. In this sense, the ε-caprolactam is obtained and purified from the material comprising nylon 6 and polyether polyurethane.

[0343] The process of the present invention allows the production of high-purity and therefore high-quality ε-caprolactam that meets the specifications for demanding applications and, at the same time, is particularly economical due to its reduced product carbon footprint and the use of waste as starting materials. In a preferred embodiment, the ε-caprolactam obtained by the process of the present invention meets one or more of the following specifications, wherein the parameters and measurement methods are defined in the Examples section below:

[0344] PAN: Maximum 5

[0345] E290: Maximum value 0.05

[0346] VB: Maximum value 0.5mmol / kg

[0347] Alkalinity: Maximum value 0.1mmol / kg

[0348] Acidity: Maximum value 0.1mmol / kg.

[0349] The ε-caprolactam produced by the process of the present invention is also particularly economical and environmentally friendly. This is evident because the carbon footprint of the ε-caprolactam produced by the process of the present invention is much lower than that of conventionally produced ε-caprolactam (e.g., by Beckmann rearrangement of cyclohexanone oxime).

[0350] The environmental impact of a product is often expressed as its 'product carbon footprint'. A product's carbon footprint is defined as the total emissions resulting from the production of the product, expressed in tons of CO2 equivalent per ton of product. A product's carbon footprint depends, among other things, on raw materials, auxiliary materials, energy consumption, energy sources, production methods, and process efficiency. Quantification of a product's carbon footprint can be performed, for example, as described in the European standard EN ISO 14040:2006 ("Environmental management - Life cycle assessment - Principles and framework").

[0351] The product carbon footprint calculation can be performed internally or by an external (preferably) certified organization. These organizations verify and certify product carbon footprint calculations based on, for example, the LCA standard ISO 14040.

[0352] J. Hong and X. Xu (“Environmental impact assessment of caprolactam production–a case study in China”; J. of Cleaner Production 27 (2012) 103-108; DOI: 10.1016 / j.jclepro.2011.12.037) reported that the global warming potential of “virgin” ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime in the context of coal-based electricity and steam generation is 7.5 tonnes of CO2 equivalent per tonne of ε-caprolactam (which is equivalent to 7.5 kg CO2 equivalent per kg of ε-caprolactam). In the case involving natural gas based electricity and steam generation, the global warming potential of the ε-caprolactam production process of virgin ε-caprolactam would drop to 6.4 tonnes CO2 equivalent per tonne ε-caprolactam (which is equivalent to 6.4 kg CO2 equivalent per kg ε-caprolactam).

[0353] The product carbon footprint of the ε-caprolactam obtained according to the process of the present invention is much lower than that of de novo synthesized or "virgin" ε-caprolactam. The product carbon footprint of the ε-caprolactam obtained in the process of the present invention is less than 4 kg, more preferably less than 3 kg, and most preferably equal to or less than 3.0 kg CO2 equivalent / kg ε-caprolactam.

[0354] The polyether polyurethanes produced by the process of the present invention are also particularly economical and environmentally friendly. Again, this is evident because the carbon footprint of the polyether polyurethanes produced by the process of the present invention is much lower than that of conventionally produced polyether polyurethanes (e.g., by reacting polyether polyols and diisocyanate monomers).

[0355] NM van der Velden, MK Patel and JG (Table 7 below: “LCA benchmarking study on textiles made of cotton, polyester, nylon, acryl, or elastane,” Int J Life Cycle Assess (2014) 19:331–356; DOI: 10.1007 / s11367-013-0626-9) reports that the global warming potential of virgin elastane production is equivalent to 4.836 kg CO2 equivalent / kg elastane.

[0356] The product carbon footprint of the polyether polyurethane obtained according to the process of the present invention is much lower than that of de novo synthesized or "virgin" polyether polyurethane. The product carbon footprint of the polyether polyurethane obtained according to the process of the present invention is less than 3.0 kg, preferably less than 2.0 kg CO2, and most preferably less than 1.0 kg CO2 equivalent per kg of polyether polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0357] Hereinafter, the present invention is described with reference to the accompanying drawings, which illustrate certain embodiments of the invention. However, the invention is defined in the claims and generally described herein. It should not be limited to the embodiments shown for illustrative purposes in the following drawings.

[0358] Figure 1 is a schematic diagram of a process of the present invention for recovering purified ε-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane, the process comprising treatment steps carried out in an optional pretreatment section [A], a separation section [B], a depolymerization section [C], a recovery section [D], and a purification section [E].

[0359] FIG2 shows two embodiments of a pretreatment section [A], wherein the material comprising nylon 6 and polyether polyurethane is cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent and is crushed in a mechanical size reduction section [λ] to obtain cleaned and crushed fragments of the material comprising nylon 6 and polyether polyurethane.

[0360] Figure 2A An embodiment of a pretreatment section [A] is depicted, wherein a material comprising nylon 6 and polyether polyurethane is first cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent and then fragmented in a mechanical size reduction section [λ] to obtain cleaned and fragmented fragments of the material comprising nylon 6 and polyether polyurethane.

[0361] Figure 2B An embodiment of a pretreatment section [A] is depicted, wherein the material comprising nylon 6 and polyether polyurethane is first fragmented in a mechanical size reduction section [λ] and then cleaned in a cleaning section [ω] by removing foreign material and washing with a solvent to obtain clean and fragmented fragments of the material comprising nylon 6 and polyether polyurethane.

[0362] Figure 3 An example of a separation section [B] is shown in which a material comprising nylon 6 and polyether polyurethane is separated to obtain a nylon 6-rich stream and recovered polyether polyurethane. The plant used in this example comprises a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ].

[0363] Figure 4 shows two examples of a purification section [E], wherein crude ε-caprolactam is purified to obtain high-purity ε-caprolactam.

[0364] Figure 4A An embodiment of a purification section [E] of the process of the present invention is depicted, comprising an extraction section [K], an optional washing section [L], an optional back-extraction section [M], an optional stripping and concentration section [N], an optional distillation section [O], and a crystallization section [P].

[0365] Figure 4B An embodiment of a purification section [E] of the process of the present invention is depicted, comprising an extraction section [K], an optional wash section [L], an optional solvent exchange distillation section [R], an optional stripping and concentration section [N], an optional distillation section [O], and a crystallization section [P].

[0366] Detailed description with accompanying drawings

[0367] The method of the present invention is Figure 1 The process is carried out in the following plant sections: optional pre-treatment section [A], separation section [B], depolymerization section [C], recovery section [D] and purification section [E].

[0368] In the optional pre-treatment section [A], the material comprising nylon 6 and polyether polyurethane

[301] is cleaned and / or crushed by mechanical size reduction to obtain discharged cleaned and / or crushed fragments of material comprising nylon 6 and polyether polyurethane

[304] . Optionally, in the pre-treatment section [A] in which the material comprising nylon 6 and polyether polyurethane

[301] is cleaned by removing foreign material and / or by washing with a washing solvent

[302] , discharged foreign material and contaminated washing solvent

[303] are obtained. Removal of foreign material may be performed before and / or after washing with the washing solvent

[302] . Cleaning may be performed before and / or after crushing the material comprising nylon 6 and polyether polyurethane

[301] . Optionally, the cleaned and / or crushed fragments of material comprising nylon 6 and polyether polyurethane

[304] are dried before being charged into the separation section [B]. Optionally, the cleaned and / or shredded chips of material comprising nylon 6 and polyether polyurethane are densified before being charged to separation section [B].

[0369] In the separation section [B], the fragments

[304] of the material comprising nylon 6 and polyether polyurethane, which are optionally cleaned and / or crushed, are separated to obtain a nylon 6-rich stream

[311] and recovered polyether polyurethane

[308] which are discharged from the separation section [B]. The nylon 6-rich stream

[311] is fed to the depolymerization section [C]. Optionally, the nylon 6-rich stream

[311] and / or the recovered polyether polyurethane

[308] are dried before being discharged from the separation section [B]. Optionally, the nylon 6-rich stream

[311] is densified before being depolymerized to ε-caprolactam in the depolymerization section [C]. The separation section [B] comprises the following sections: a dissolution section [α], a washing section [β], a precipitation section [γ] and a solvent distillation section [δ] ( Figure 1

[0065] is charged into the separation section [B] to dissolve the polyether polyurethane. The second solvent

[306] is charged into the separation section [B] to precipitate the dissolved polyether polyurethane. The third solvent

[307] is charged into the separation section [B] to wash the undissolved nylon 6. After distillation separation, the second solvent and the third solvent

[309] and the residue

[310] are discharged from the separation section [B].

[0370] The nylon 6-rich stream

[311] , which is optionally dried and / or densified, is depolymerized to ε-caprolactam in a depolymerization section [C]. A stream

[315] comprising ε-caprolactam is discharged from the depolymerization section [C]. In addition, residual material

[314] is discharged. Optionally, superheated steam

[312] and a catalyst

[313] are fed to the depolymerization section [C].

[0371] Crude ε-caprolactam

[317] is recovered from the stream

[315] comprising ε-caprolactam discharged from the depolymerization section [C]. The crude ε-caprolactam

[317] is discharged from the recovery section [D] and fed to the purification section [E]. In addition, water or superheated steam

[312] is fed to the depolymerization section [C] or ( Figure 1 In the case where water is charged to the recovery section [D] (not shown), the aqueous phase

[316] is discharged from the recovery section [D].

[0372] The crude ε-caprolactam

[317] discharged from the recovery section [D] is purified in the purification section [E] to produce high purity ε-caprolactam

[319] . Water and impurities

[318] are also discharged from the purification section [E].

[0373] Figure 2A An embodiment of a pretreatment section [A] (area surrounded by a dotted line) is depicted wherein the material comprising nylon 6 and polyether polyurethane

[31] is first cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent

[32] , thereby obtaining foreign material and contaminated washing solvent

[33] and cleaned material comprising nylon 6 and polyether polyurethane

[34] . Subsequently, the cleaned material comprising nylon 6 and polyether polyurethane

[34] is crushed in a mechanical size reduction section [λ] to obtain cleaned and crushed material comprising nylon 6 and polyether polyurethane

[35] . The cleaned and crushed material comprising nylon 6 and polyether polyurethane

[35] is then discharged. Optionally, the fragments of the cleaned and crushed material comprising nylon 6 and polyether polyurethane

[35] are densified ( Figure 2A not shown).

[0374] Figure 2B An embodiment of a pretreatment section [A] (area surrounded by a dotted line) is depicted in which the material comprising nylon 6 and polyether polyurethane

[41] is first crushed in a mechanical size reduction section [λ] to obtain crushed fragments of material comprising nylon 6 and polyether polyurethane

[42] . Subsequently, the crushed fragments of material comprising nylon 6 and polyether polyurethane

[42] are cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent

[43] to obtain foreign material and contaminated washing solvent

[44] and cleaned and crushed fragments of material comprising nylon 6 and polyether polyurethane

[45] . The cleaned and crushed fragments of material comprising nylon 6 and polyether polyurethane

[45] are then discharged. Optionally, the cleaned and crushed fragments of material comprising nylon 6 and polyether polyurethane

[45] are densified ( Figure 2B not shown).

[0375] Figure 3 An example of a separation section [B] (area surrounded by a dashed line) is shown, in which a material comprising nylon 6 and polyether polyurethane is separated to obtain a nylon 6-rich stream and recovered polyether polyurethane. This example includes the following sections: a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ].

[0376] In the dissolution section [α], polyether polyurethane is dissolved in an organic solvent from the optionally cleaned and / or crushed fragments

[101] of the material comprising polyamide 6 and polyether polyurethane to obtain a polyether polyurethane-rich stream

[104] comprising organic solvent and dissolved polyether polyurethane and a stream

[105] comprising undissolved nylon 6. These are discharged from the dissolution section [α]. The organic solvent is the separated organic solvent

[102] to which fresh organic solvent

[103] is optionally added.

[0377] In the precipitation section [γ], the second solvent

[106] and the polyether polyurethane-rich stream

[104] comprising the organic solvent and the dissolved polyether polyurethane are mixed so that the polyether polyurethane is precipitated from the mixture comprising the organic solvent and the second solvent. The precipitated polyether polyurethane is recovered from the mixture comprising the organic solvent and the second solvent (e.g., by filtration or centrifugation). The recovered precipitated polyether polyurethane is discharged from the precipitation section [γ] as recovered polyether polyurethane

[107] . Optionally, the recovered polyether polyurethane

[107] is dried after the recovery step and before being discharged from the precipitation section [γ]. The mixture comprising the organic solvent and the second solvent

[108] from which the precipitated polyether polyurethane has been recovered is discharged from the precipitation section [γ] and charged to the solvent distillation section [δ].

[0378] In the washing section [β], the stream

[105] comprising undissolved nylon 6 is washed with a third solvent

[109] to obtain a stream

[110] rich in nylon 6 and a mixture

[111] comprising an organic solvent and a third solvent. The stream

[110] rich in nylon 6 is discharged from the washing section [β]. Optionally, the stream

[110] rich in nylon 6 is dried after the washing step and before being discharged from the washing section [β]. Optionally, the stream

[110] rich in nylon 6 is densified before being depolymerized to ε-caprolactam in the depolymerization section [C] (not shown in 3). The mixture

[111] comprising an organic solvent and a third solvent is discharged from the washing section [β] and optionally charged to a solvent distillation section [δ].

[0379] In the solvent distillation section [δ], the mixture

[108] comprising the organic solvent and the second solvent, and optionally the mixture

[111] comprising the organic solvent and the third solvent, from which the precipitated polyether polyurethane has been recovered, is distilled to obtain a separated organic solvent

[102] , a second solvent and a third solvent

[112] , and a residue

[113] . Optionally, the second solvent and the third solvent are both water, in which case the separated organic solvent

[102] is a dried organic solvent. The separated organic solvent

[102] is charged into the dissolution section [α].

[0380] Figure 4A An example of a purification section [E] (area surrounded by dashed lines) is depicted, comprising the following sections:

[0381] In the extraction section [K], the crude ε-caprolactam

[201] is extracted with an organic solvent

[202] to obtain an aqueous phase

[203] comprising water and impurities and an organic phase

[204] comprising the organic solvent, ε-caprolactam and impurities. Both phases are discharged from the extraction section [K].

[0382] In the optional washing section [L], the organic phase

[204] comprising the organic solvent, ε-caprolactam and impurities is washed with water or an alkaline aqueous solution

[205] to obtain an aqueous phase

[206] comprising the residue and a washed organic phase

[207] comprising the organic solvent, ε-caprolactam and impurities. Both phases are discharged from the washing section [L].

[0383] In the optional stripping section [M], the optionally washed organic phase

[207] comprising the organic solvent, ε-caprolactam and impurities is stripped with water

[208] to obtain an organic solvent phase

[209] comprising impurities and an aqueous phase

[210] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than that of ε-caprolactam. Both phases are discharged from the stripping section [M].

[0384] In the optional stripping and concentration section [N], residual organic solvent and water are removed from the aqueous phase

[210] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam by stripping and / or distillation to obtain residual organic solvent and water

[211] and a stripped and concentrated aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam

[212] . Both phases are discharged from the stripping and concentration section [N].

[0385] Optionally, an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam, from which optional residual organic solvent and water have been removed by stripping and / or distillation, is oxidized with an oxidizing agent

[210] to obtain an oxidized ε-caprolactam-aqueous phase comprising water, ε-caprolactam and impurities ( Figure 4A not shown).

[0386] Optionally, the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities is filtered to remove solid manganese (IV) oxide particles ( Figure 4A not shown).

[0387] In the optional hydrogenation section, the stripped and concentrated aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam

[212] is hydrogenated with hydrogen in the presence of a heterogeneous catalyst before being fed to the next section to obtain a hydrogenated ε-caprolactam-water phase comprising water, ε-caprolactam and impurities ( Figure 4A not shown).

[0388] In the optional distillation section [O], the stripped and concentrated aqueous phase

[212] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam is distilled to remove impurities having a boiling point lower or higher than ε-caprolactam

[214] and optional organic solvent or water ( Figure 4A ) to obtain a distilled ε-caprolactam phase

[215] . All distillation products are discharged from the distillation section [O]. The distilled ε-caprolactam phase

[215] is charged to the crystallization section [P]. Optionally, before the distillation in the distillation section [O], an alkali metal hydroxide

[213] is added to the stripped and concentrated aqueous phase

[212] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than that of ε-caprolactam.

[0389] In the crystallization section [P], the optionally distilled ε-caprolactam phase

[215] is crystallized at a temperature of 10° C. to 95° C. to remove impurities

[217] from the ε-caprolactam, thereby obtaining high-purity ε-caprolactam

[218] . All crystallized product is discharged from the crystallization section [P]. Optionally, a solvent

[216] is charged to the crystallization section [P] before crystallization.

[0390] Figure 4B An example of a purification section [E] (area surrounded by dashed lines) is depicted, comprising the following sections:

[0391] In the extraction section [K], the crude ε-caprolactam

[401] is extracted with an organic solvent

[402] to obtain an aqueous phase

[403] comprising water and impurities and an organic phase

[404] comprising the organic solvent, ε-caprolactam and impurities. Both phases are discharged from the extraction section [K].

[0392] In the optional washing section [L], the organic phase

[404] comprising the organic solvent, ε-caprolactam and impurities is washed with water or an alkaline aqueous solution

[405] to obtain an aqueous phase

[406] comprising the residue and a washed organic phase

[407] comprising the organic solvent, ε-caprolactam and impurities. Both phases are discharged from the washing section [L].

[0393] In the optional solvent exchange distillation section [R], the optionally washed organic phase

[407] comprising organic solvent, ε-caprolactam and impurities is subjected to solvent exchange distillation by adding water

[408] to obtain a stream

[409] comprising organic solvent and an aqueous phase

[410] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than that of ε-caprolactam. Both products are discharged from the solvent exchange distillation section [R].

[0394] In the optional stripping and concentration section [N], residual organic solvent and water are removed from the aqueous phase

[410] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam by stripping and / or distillation to obtain residual organic solvent and water

[411] and a stripped and concentrated aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam

[412] . Both phases are discharged from the stripping and concentration section [N].

[0395] Optionally, oxidizing an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam, from which optional residual organic solvent and water have been removed by stripping and / or distillation, with an oxidizing agent

[410] , to obtain an oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities ( Figure 4B not shown).

[0396] Optionally, the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities is filtered to remove solid manganese (IV) oxide particles ( Figure 4B not shown).

[0397] In the optional hydrogenation section, the stripped and concentrated aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam is hydrogenated with hydrogen in the presence of a heterogeneous catalyst before being fed to the next section to obtain a hydrogenated ε-caprolactam-water phase comprising water, ε-caprolactam and impurities ( Figure 4B not shown).

[0398] In the optional distillation section [O], the stripped and concentrated aqueous phase

[412] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam is distilled to remove impurities having a boiling point lower or higher than ε-caprolactam

[414] and optional organic solvent or water ( Figure 4B) to obtain a distilled ε-caprolactam phase

[415] . All distillation products are discharged from the distillation section [O]. The distilled ε-caprolactam phase

[415] is charged to the crystallization section [P]. Optionally, before the distillation in the distillation section [O], an alkali metal hydroxide

[413] is added to the stripped and concentrated aqueous phase

[412] comprising water, ε-caprolactam and impurities having a boiling point lower or higher than that of ε-caprolactam.

[0399] In the crystallization section [P], the optionally distilled ε-caprolactam phase

[415] is crystallized at a temperature of 10° C. to 95° C. to remove impurities

[417] from the ε-caprolactam, thereby obtaining high-purity ε-caprolactam

[418] . All crystallized product is discharged from the crystallization section [P]. Optionally, a solvent

[416] is charged to the crystallization section [P] before crystallization.

[0400] Examples

[0401] The following examples are provided to explain the present invention in more detail, particularly with respect to certain forms of the present invention. However, the examples are not intended to limit the present disclosure.

[0402] ε-Caprolactam, which can be used in all major nylon 6 polymerization applications without dilution with purer qualities of ε-caprolactam, meets all of the following specifications:

[0403] PAN: Maximum 5

[0404] E290: Maximum value 0.05

[0405] VB: Maximum value 0.5mmol / kg

[0406] Alkalinity: Maximum value 0.1mmol / kg

[0407] Acidity: Maximum 0.1mmol / kg

[0408] The parameters and measurement methods are defined as follows:

[0409] PAN: ISO DIS 8660 - Plastics - Determination of the permanganate index of caprolactam - Spectrometric method, revision of the first edition of ISO 8660; 1988,

[0410] E290: ISO 7059 - Caprolactam for industrial use - Determination of absorbance at a wavelength of 290 nm,

[0411] Volatile base (VB) ISO 8661 - Caprolactam for industrial use - Determination of volatile base content - Titration after distillation.

[0412] Basicity of ε-caprolactam product: measured by using Tashiro indicator at 0.1wt. / v at 25℃ 乙醇 % Methylene blue: 0.1wt. / v 乙醇 Basicity is determined by a 1:2 ratio titration with 0.01N H2SO4 (if the solution is alkaline) or 0.01N NaOH (if the solution is acidic). The flask containing the water and indicator is first titrated to a gray color, then X grams of an aqueous ε-caprolactam solution containing Y wt.% ε-caprolactam (as determined by the refractive index) is added and the solution is titrated back to a gray color using 0.01N H2SO4 solution (if the solution is alkaline) or 0.01N NaOH solution (if the solution is acidic).

[0413] The alkalinity is then given by:

[0414] Alkalinity (mmol / kg ε-caprolactam) = v*t*1000 / (X*Y)

[0415] in:

[0416] v = volume of H2SO4 solution added (ml)

[0417] t = Normality of H2SO4 solution (=0.01N)

[0418] X = sample weight (g)

[0419] Y = concentration of ε-caprolactam (wt.%)

[0420] The acidity is then given by:

[0421] Acidity (mmol / kg ε-caprolactam) = v*t*1000 / (X*Y)

[0422] in:

[0423] v = volume of NaOH solution added (ml)

[0424] t = molar concentration of NaOH solution (=0.01N)

[0425] X = sample weight (g)

[0426] Y = concentration of ε-caprolactam (wt.%)

[0427] Example 1

[0428] Pretreatment and separation of nylon 6 and polyether polyurethane.

[0429] The polyether polyurethane content of the used nylon 6 waste fabric containing polyether polyurethane was 20.2 + / - 0.4 wt.% (as measured by Differential Scanning Calorimetry (DSC) ISO 11357-3, -130°C to 300°C, 10°C / min, dt 1.00 sec). The color of the used nylon 6 waste fabric containing polyether polyurethane (spandex) was purple.

[0430] Cut the nylon 6 waste fabric containing polyether polyurethane into small pieces, each small piece is 5 to 20 cm 2 150.4 g of this cut material was dissolved in 800 g of DMAc at 70°C with stirring for 1 hour. The resulting solution was vacuum filtered through a heated double-walled Buchner funnel at 70°C to obtain Filtrate 1. The remaining undissolved material was further treated three times with 400 g of DMAc each time and stirred at 70°C for 1 hour to obtain Filtrates 2 to 4.

[0431] The undissolved material on the Buchner funnel was washed with 325 g of water at 65°C to obtain Filtrate 5, and the undissolved material was then dried and weighed. The five filtrates were combined to obtain a precipitate and a clear solution. The precipitate was filtered out, washed with 200 g of water, dried, and weighed. The total weight of the dried precipitate and the dried undissolved material was almost equal to the weight of the starting material.

[0432] Analysis by differential scanning calorimetry (DSC) revealed that the dry precipitate had a polyether polyurethane content of approximately 100 wt.% (no polyamide 6 detected). The dried, undissolved material had a nylon 6 content of approximately 100 wt.% (no polyether polyurethane detected) based on DSC analysis.

[0433] The recycled polyether polyurethane precipitate can be reused as such or in combination with virgin polyether polyurethane in the production of textiles.

[0434] This example demonstrates that polyether polyurethane and nylon 6 can be separated from nylon 6 waste fabric containing polyether polyurethane by selective extraction, precipitation of the dissolved polyether polyurethane, and washing of the undissolved nylon 6. After drying, the recovered precipitate consisted of almost pure polyether polyurethane, and the dried undissolved material had a nylon 6 content of almost 100 wt.%.

[0435] Example 2

[0436] Pretreatment and separation of nylon 6 and polyether polyurethane.

[0437] The polyether polyurethane content of the used nylon 6 scrap fabric containing polyether polyurethane was 8.15 + / - 0.05 wt.% (as measured by Differential Scanning Calorimetry (DSC) ISO 11357-3, -130°C to 300°C, 10°C / min, dt 1.00 sec). The color of the used nylon 6 scrap fabric containing polyether polyurethane (spandex) was salmon pink.

[0438] The procedure of Example 1 was followed, except that 254.1 g of nylon 6 waste fabric containing polyether polyurethane was dissolved in 1200 g of DMAc and, after filtration, the remaining undissolved material on the Buchner funnel was washed with 475 g of DMAc and 350 g of water. The precipitate was filtered out, washed with 200 g of water, and subsequently dried. The undissolved material on the Buchner funnel was washed with 1000 g of water, then also dried and weighed. The weight fraction of the dried precipitate was 8 wt.% of the total weight of the dried precipitate and the dried undissolved material, which was approximately equal to the weight of the starting material.

[0439] Analysis by differential scanning calorimetry (DSC) revealed that the polyether polyurethane content of the dry precipitate was approximately 100 wt.% (no nylon 6 was detected). The nylon 6 content and polyether polyurethane content of the dried undissolved material were approximately 99 wt.% and less than 1 wt.%, respectively (DSC analysis).

[0440] The recycled polyether polyurethane precipitate can be reused as such or in combination with virgin polyether polyurethane in the production of textiles.

[0441] This example demonstrates that polyether polyurethane and nylon 6 can be separated from polyether polyurethane-containing nylon 6 waste fabric by selective extraction, precipitation of dissolved polyether polyurethane, and washing of undissolved nylon 6. After drying, the recovered precipitate consists of nearly pure polyether polyurethane, and the undissolved material has a polyether polyurethane content far lower than that of the starting material, polyether polyurethane-containing nylon 6 waste fabric. The obtained polyether polyurethane is of high quality and can be used as such or in combination with virgin polyether polyurethane for demanding subsequent applications, including spinning.

[0442] Example 3

[0443] Depolymerization of nylon 6 and recovery of ε-caprolactam.

[0444] Before loading the dried, undissolved material obtained in Example 1 into the depolymerization reactor, it was first densified. The dried, undissolved material was melted at 237°C under nitrogen and forced through a perforated metal plate. The resulting strands were cooled to room temperature and cut into pellets. The resulting pellets had a diameter and length of 3 mm and 1 cm, respectively.

[0445] 33.6 grams of these nylon 6 pellets and 9.5 grams of 20 wt.% phosphoric acid were charged to a Premex autoclave. The reactor contents were first heated under nitrogen, followed by continuous injection of superheated steam at a rate of 2.7 grams per minute over a 120-minute reaction period. 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 withdrawn from the reactor and cooled to approximately 20°C, yielding a condensate comprising ε-caprolactam and water.

[0446] The condensate, consisting of 25.7 g of ε-caprolactam (most of the remainder was water), was concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature approximately 65°C) to an ε-caprolactam concentration of 57.3 wt.%. (This mixture is the crude ε-caprolactam, the mixture to be purified.)

[0447] The specifications of crude ε-caprolactam are:

[0448] PAN: 353

[0449] E290:2.91

[0450] This example shows that crude ε-caprolactam can be obtained in good yield and without operational problems by depolymerization of nylon 6 obtained by extractive separation from nylon 6 waste fabric containing polyether polyurethane.

[0451] Example 4

[0452] Depolymerization of nylon 6 and recovery of ε-caprolactam.

[0453] The procedure of Example 3 was followed, except that now 48 grams of pellets made from the dried, undissolved material obtained in Example 2 and 14 grams of 20 wt. % phosphoric acid were charged to the Premex autoclave.

[0454] The condensate, consisting of 41 g of ε-caprolactam (most of the remainder being water), was concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature approximately 65°C) to an ε-caprolactam concentration of 63.1 wt.%. (This mixture is the crude ε-caprolactam, the mixture to be purified.)

[0455] The specifications of crude ε-caprolactam are:

[0456] PAN: 274

[0457] E290:2.70

[0458] This example shows that crude ε-caprolactam can be obtained in good yield and without operational problems by depolymerization of nylon 6 obtained by extractive separation from nylon 6 waste fabric containing polyether polyurethane.

[0459] Comparative Experiment 1

[0460] Depolymerization of nylon 6 and polyether polyurethane.

[0461] The procedure of Example 3 was followed except that now 37.6 grams of polyether polyurethane fibers (the same material contained in the waste fabric used in Example 1) and 14 grams of 20 wt. % phosphoric acid were charged to the Premex autoclave.

[0462] 10 minutes after the start of the superheated steam injection, the experiment had to be stopped because the line for discharging the vapor stream comprising ε-caprolactam and water became clogged with insoluble material.

[0463] From this comparative experiment it can be concluded that depolymerization of nylon 6 waste fabric containing polyether polyurethane creates operational problems if the polyether polyurethane is not removed prior to depolymerization.

[0464] Comparative Experiment 2

[0465] Depolymerization of nylon 6 waste fabric containing polyether polyurethane and recovery of ε-caprolactam.

[0466] The procedure of Example 3 was followed, except that now 48 grams of pellets made from nylon 6 waste fabric containing polyether polyurethane with a polyether polyurethane content of 20.2 + / - 0.4 wt.% (the same raw material used in Example 1) and 14 grams of 20 wt.% phosphoric acid were charged to the Premex autoclave.

[0467] The condensate, consisting of 26 g of ε-caprolactam (most of the remainder was water), was concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature approximately 65°C) to an ε-caprolactam concentration of 47.0 wt.%. (This mixture is the crude ε-caprolactam, the mixture to be purified.)

[0468] The specifications of crude ε-caprolactam are:

[0469] PAN: 352

[0470] E290:3.60

[0471] Observations:

[0472] The condensate obtained before concentration does contain an unknown precipitate

[0473] ●After the depolymerization experiment, the inner wall of the Premex autoclave was found to be fouled.

[0474] This comparative experiment again demonstrates the operational problems associated with depolymerization of nylon 6 waste fabric containing polyether polyurethane without removing the polyether polyurethane prior to depolymerization. Another observation is that the ε-caprolactam yield in this comparative experiment, defined as the ratio of the weight of ε-caprolactam in the condensate to the weight of nylon 6 in the feed to the Premex autoclave, was much lower than that in Example 3 (which used pretreated nylon 6 waste fabric containing polyether polyurethane as feed).

[0475] Comparative Experiment 3

[0476] Purification by distillation.

[0477] 75 mmol of aqueous sodium hydroxide solution per kg of ε-caprolactam was then added to the crude ε-caprolactam obtained in Comparative Experiment 2. The mixture was then distilled by reducing the pressure in steps. ε-caprolactam was distilled at 300 Pa.

[0478] The specifications of distilled ε-caprolactam are:

[0479] PAN: 31

[0480] E290:3.08

[0481] VB: 2.45mmol / kg

[0482] Alkalinity: 3.13mmol / kg.

[0483] This comparative experiment shows that the quality of the ε-caprolactam obtained by depolymerization of nylon 6 waste fabric containing polyether polyurethane (without pretreatment in a separation section in which the material comprising nylon 6 and polyether polyurethane is separated into a nylon 6-rich stream and a polyether polyurethane-rich stream) and subsequent concentration and purification by distillation is very poor, as it does not meet any of the specifications required for major polymerization applications.

[0484] Comparative Experiment 4

[0485] Depolymerization of nylon 6 waste fabric containing polyether polyurethane and recovery of ε-caprolactam by permanganate treatment Purification by treatment and distillation.

[0486] In this comparative experiment, nylon 6 waste fabric containing polyether polyurethane having a polyether polyurethane content of 8.15 + / - 0.05 wt. % (the same raw material as used in Example 2) was used.

[0487] The pretreatment and separation procedures of nylon 6 and polyether polyurethane were followed as in Example 1. The recovered polyether polyurethane precipitate could be reused in the production of textiles as such or in combination with virgin polyether polyurethane. The depolymerization and recovery procedures of Example 3 were followed.

[0488] The crude ε-caprolactam obtained was treated with 0.2 wt. % KMnO4, relative to ε-caprolactam, at 50° C. for 2 hours. The solid formed was then removed from the oxidized reaction product by filtration.

[0489] The ε-caprolactam in the oxidized reaction product was further purified by distillation as described in Comparative Example 3 after addition of 75 mmol of aqueous sodium hydroxide solution per kg of ε-caprolactam.

[0490] The specifications of distilled ε-caprolactam are:

[0491] PAN: 3

[0492] E290: 0.12

[0493] VB: 1.45mmol / kg

[0494] Alkalinity: 1.96mmol / kg

[0495] From this comparative experiment it can be concluded that purification of crude ε-caprolactam by permanganate treatment followed by distillation is not sufficient to meet all the specifications required for the main polymerisation applications as quantified above.

[0496] Example 5

[0497] Depolymerization of nylon 6 waste fabric containing polyether polyurethane and recovery of ε-caprolactam by extraction and stripping Purification by extraction, distillation and crystallization.

[0498] In this example, a nylon 6 waste fabric containing polyether polyurethane having a polyether polyurethane content of 8.15 + / - 0.05 wt. % (the same raw material as used in Example 2) was used.

[0499] The pretreatment and separation procedures of nylon 6 and polyether polyurethane were followed as in Example 1. The recovered polyether polyurethane precipitate could be reused in the production of textiles as such or in combination with virgin polyether polyurethane. The depolymerization and recovery procedures of Example 3 were followed.

[0500] 76 g of the crude ε-caprolactam obtained were extracted once with 100 g of a 50 wt.% 4-methyl-2-pentanol / 50 wt.% solvent mixture at 25°C and nine times with 50 g of this solvent mixture. The ten resulting ε-caprolactam phases, comprising the solvent mixture, were combined and subsequently concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature approximately 65°C) to an ε-caprolactam concentration of approximately 40 wt.%, followed by addition of fresh cyclohexane. The resulting mixture had an ε-caprolactam concentration of approximately 25 wt.%, and the weight ratio of the 4-methyl-2-pentanol / cyclohexane solvent mixture was 50 wt.%:50 wt.%. The concentrated ε-caprolactam solvent mixture was then extracted eight times with 50 g of water at 25°C. The eight resulting aqueous ε-caprolactam phases were combined. The combined aqueous phases were concentrated by evaporation in a rotary evaporator (rotavap) operated under vacuum (9.5 kPa; water bath temperature of about 65° C.) to an ε-caprolactam concentration of 47.1 wt.%. The specifications of the concentrated ε-caprolactam aqueous solution obtained were:

[0501] PAN: 108

[0502] E290:1.58

[0503] 75 mmol of an aqueous sodium hydroxide solution / kg of ε-caprolactam was added to the obtained concentrated ε-caprolactam aqueous solution.

[0504] Subsequently, water and impurities with a lower boiling point than ε-caprolactam are removed as top products by distillation under reduced pressure in a batch-operated distillation apparatus. Finally, at 300 Pa, the distilled ε-caprolactam is recovered as the top product, while impurities with a higher boiling point than ε-caprolactam remain in the distillation apparatus as the bottom product.

[0505] Distilled water was then added to the distilled ε-caprolactam to obtain a mixture with an ε-caprolactam concentration of 91.4 wt.%. This aqueous ε-caprolactam was introduced into a crystallization apparatus at a temperature of 52°C. The aqueous ε-caprolactam was cooled to 40°C, and 0.016 g of seed crystals were added to the mixture. The mixture was then further cooled to 30°C and held for 30 minutes. The crystallized ε-caprolactam was recovered by filtration and washed with an 85 wt.% aqueous ε-caprolactam solution. The specifications of the purified ε-caprolactam obtained were:

[0506] PAN: 2

[0507] E290: 0.02

[0508] VB: <0.01mmol / kg

[0509] Alkalinity: 0.03mmol / kg

[0510] From this experiment it can be concluded that purified ε-caprolactam meeting all specifications required for major polymerization applications can be obtained from the depolymerization of nylon 6 derived from nylon 6 waste fabric containing polyether polyurethane and purified by extraction, stripping, distillation and crystallization.

[0511] All of the above examples demonstrate that the present invention is capable of producing good products from coloured raw materials, particularly coloured raw materials derived from waste textiles as presented.

[0512] Example 6

[0513] Pretreatment and separation of nylon 6 and polyether polyurethane, depolymerization of nylon 6 and recovery of ε-caprolactam, Purification by extraction, back extraction, distillation and crystallization.

[0514] The pretreatment and separation procedures of nylon 6 and polyether polyurethane were followed as in Example 1. The recovered polyether polyurethane precipitate could be reused in the production of textiles as such or in combination with virgin polyether polyurethane. The depolymerization and recovery procedures of Example 3 were followed.

[0515] The 36 g of crude ε-caprolactam obtained was extracted once with 68 g of benzene and four times with 50 g of benzene at 25°C. The organic extracts were combined and concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature approximately 65°C) to an ε-caprolactam concentration of approximately 25 wt.%. This mixture was extracted twice in batches with 25 g of water at approximately 25°C. The specifications of the aqueous ε-caprolactam solution after stripping were:

[0516] PAN: 132

[0517] E290:1.55

[0518] 75 mmol of aqueous sodium hydroxide solution per kg of ε-caprolactam is then added to the concentrated ε-caprolactam solution. Water and impurities with a lower boiling point than ε-caprolactam are then removed as overhead products by distillation under reduced pressure in a batch-operated distillation apparatus. Finally, at 300 Pa, the distilled ε-caprolactam is recovered as the overhead product, while impurities with higher boiling points than ε-caprolactam remain in the distillation apparatus as the bottoms product.

[0519] Distilled water is then added to the distilled ε-caprolactam to obtain a mixture with an ε-caprolactam concentration of 91.4 wt.%. This aqueous ε-caprolactam is introduced into a crystallization apparatus at a temperature of 52°C. The aqueous ε-caprolactam is cooled to 40°C, and seed crystals are added to the mixture. The mixture is then further cooled to 30°C and held for 30 minutes. The crystallized ε-caprolactam is recovered by filtration and washed with an 85 wt.% aqueous ε-caprolactam solution. The specifications of the purified ε-caprolactam obtained meet all of the requirements for primary polymerization applications.

[0520] This example demonstrates that polyether polyurethane and nylon 6 can be separated from polyether polyurethane-containing nylon 6 waste fabric by selective extraction, precipitation of the dissolved polyether polyurethane, and washing of the undissolved nylon 6. Furthermore, from this experiment, it can be concluded that purified ε-caprolactam meeting all specifications required for major polymerization applications can be obtained by depolymerization of nylon 6 derived from discarded polyether polyurethane-containing nylon 6 waste fabric and purified by extraction, stripping, distillation, and crystallization.

[0521] Experiment 7

[0522] Calculation of the carbon footprint of purified ε-caprolactam and polyether polyurethane.

[0523] A continuous process for producing purified ε-caprolactam and polyether polyurethane from polyether polyurethane-containing nylon 6 waste fabrics according to the present invention was simulated. The polyether polyurethane content of these polyether polyurethane-containing nylon 6 waste fabrics was 20 wt.%, and the remainder was mainly nylon 6.

[0524] The method comprises:

[0525] - cutting nylon 6 waste fabric containing polyether polyurethane into small pieces;

[0526] - Selective extraction of polyether polyurethane with DMAc;

[0527] - separation of undissolved nylon 6 and a polyether polyurethane-rich stream by centrifugation;

[0528] - Washing undissolved nylon 6 with water;

[0529] - Separating the washed undissolved nylon 6 and aqueous extract by centrifugation;

[0530] - precipitation of the polyether polyurethane from the polyether polyurethane-rich stream by adding the aqueous extract obtained above;

[0531] - separating the precipitated polyether polyurethane from the DMAc-water mixture by filtration;

[0532] - recovering DMAc and water from the DMAc-water mixture obtained above;

[0533] - Dry filtered polyether polyurethane;

[0534] - Drying of washed undissolved nylon 6;

[0535] - melting and pelletizing the washed undissolved nylon 6;

[0536] - Depolymerization of nylon 6 under the action of H3PO4 and superheated steam;

[0537] - recovery of crude ε-caprolactam (80 wt.% ε-caprolactam) by partial condensation of the vapors exiting the depolymerization reactor;

[0538] - Extract the concentrated crude ε-caprolactam with toluene countercurrent;

[0539] - washing the organic extract with a dilute caustic solution;

[0540] - counter-extracting the washed organic extract with water;

[0541] - Concentrating the aqueous extract by evaporation;

[0542] - Add caustic soda;

[0543] - Removal of lights and heavies by vacuum distillation; and

[0544] - Recovery of pure ε-caprolactam by melt crystallization at a temperature of 61°C.

[0545] The carbon footprint of the purified ε-caprolactam and polyether polyurethane was calculated based on raw material consumption data, and the above-mentioned method was used based on data from ecoinvent version 3.7.1. The environmental impact distribution between the purified ε-caprolactam and polyether polyurethane products in the pretreatment section and the separation section was based on the weight ratio of these products.

[0546] The results revealed that the product carbon footprint of purified ε-caprolactam obtained from polyamide 6 waste fabric containing polyether polyurethane was less than 3.0 ton CO2 equivalent / ton ε-caprolactam and less than 1.0 ton CO2 equivalent / ton polyether polyurethane (location: Europe).

[0547] While the invention has been described with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention, including (semi)continuous operation and scaling up to commercial scale.

Claims

1. A method for recovering ε-caprolactam and polyether polyurethane from a material comprising nylon 6 and polyether polyurethane in a plant, wherein the plant comprises - separation section [B], - depolymerization section [C], - Recovery Sector [D], and - purification segment [E], And wherein the method comprises the following steps: a) loading the material comprising nylon 6 and polyether polyurethane into the separation section [B]; b) in the separation section [B], by, at a temperature below 100° C., selectively dissolving the polyether polyurethane in an organic solvent, preferably at a temperature in the range of 0°C to 100°C, more preferably at a temperature in the range of 10°C to 90°C, even more preferably at a temperature in the range of 10°C to 80°C and most preferably at a temperature in the range of 20°C to 75°C, separating the material comprising nylon 6 and polyether polyurethane into a nylon 6-rich stream and a polyether polyurethane-rich stream, wherein the polyether polyurethane-rich stream is a solution comprising the organic solvent and the polyether polyurethane; c.1) discharging the nylon 6-rich stream from separation section [B] and feeding the nylon 6-rich stream to a depolymerization section [C], wherein the nylon 6-rich stream has a nylon 6 content of at least 85% by weight on a dry weight basis; c.2) depolymerizing said nylon 6 in said nylon 6-rich stream at a temperature ranging 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 in said depolymerization section [C], such that a stream comprising ε-caprolactam is obtained, and discharging the obtained stream comprising ε-caprolactam from said depolymerization section [C]; c.3) recovering crude ε-caprolactam from the stream comprising ε-caprolactam in the recovery section [D]; c.4) purifying the crude ε-caprolactam obtained in the recovery section [D] in the purification section [E] to obtain purified ε-caprolactam, wherein the purification comprises the following steps: (i) extracting the crude ε-caprolactam with an organic solvent so as to obtain an aqueous phase and an organic phase, and wherein the organic phase comprises the organic solvent, ε-caprolactam and impurities, and preferably the organic solvent is selected from the group consisting of: Cyclohexane, benzene, toluene, methylene chloride, chloroform, trichloroethane, 4-methyl-2-pentanol, 1-octanol, 2-ethylhexanol, and mixtures thereof; and optionally washing the obtained organic phase with water or with an alkaline aqueous solution; (ii) switching the solvent by at least partially replacing the organic solvent with water or an aqueous solution, thereby obtaining an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam, and wherein the solvent switch is selected from a process based on back extraction with water and a process based on solvent exchange distillation, wherein the organic solvent is distilled off and water is charged; and (iii) removing impurities having a boiling point lower or higher than that of ε-caprolactam by distillation to obtain purified ε-caprolactam; (iv) obtaining purified ε-caprolactam by crystallizing ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10° C. to 95° C.; d.1) recovering polyether polyurethane from the polyether polyurethane-rich stream in the separation section [B]; and d.2) discharging the recovered polyether polyurethane from the separation section [B], wherein the polyether polyurethane content of the discharged stream is at least 85% by weight, based on the dry weight.

2. The method according to claim 1, wherein the separation section [B] comprises: - dissolution segment [α], - washing section [β], - precipitation section [γ], and - solvent distillation section [δ], and wherein the method comprises the following steps in the separation section [B]: b.1) charging an organic solvent and a material comprising nylon 6 and polyether polyurethane into the dissolving section [α]; b.2) dissolving the polyether polyurethane from the material comprising nylon 6 and polyether polyurethane in an organic solvent in the dissolving section [α], so that a polyether polyurethane-rich stream comprising the organic solvent and the dissolved polyether polyurethane and a stream comprising undissolved nylon 6 are obtained, and the obtained stream is discharged from the dissolving section [α]; b.3) feeding a second solvent and the polyether polyurethane-rich stream comprising the organic solvent and the dissolved polyether polyurethane into the precipitation section [γ], so that the polyether polyurethane is precipitated from the mixture comprising the organic solvent and the second solvent; b.4) recovering the precipitated polyether polyurethane from the mixture comprising the organic solvent and the second solvent, and discharging the precipitated polyether polyurethane from the precipitation section [γ]; b.5) ​​discharging the mixture comprising the organic solvent and the second solvent, from which the precipitated polyether polyurethane has been recovered in step b.4), from the precipitation section [γ] and charging the mixture to the solvent distillation section [δ]; b.6) charging a third solvent and the stream comprising undissolved nylon 6 into the washing section [β]; b.7) washing the stream comprising undissolved nylon 6 with the third solvent in the washing section [β], so as to obtain a stream rich in nylon 6 and a mixture comprising an organic solvent and a third solvent; b.8) discharging the nylon 6-rich stream from the washing section [β]; b.9) discharging the mixture comprising the organic solvent and the third solvent obtained in step b.7) from the washing section [β] and charging the mixture partially or completely to the solvent distillation section [δ]; b.10) separating the organic solvent from the second solvent and the third solvent by distillation in the solvent distillation section [δ], and discharging the second solvent, the third solvent and the separated organic solvent from the solvent distillation section [δ].

3. The process according to claim 2, wherein the separated organic solvent discharged from the solvent distillation section [δ] in step b.10) is fed to the dissolution section [α] in step b.1).

4. The method according to any one of claims 1 to 3, wherein (i) the nylon 6-rich stream discharged from the separation section [B] is dried and / or densified before being fed to the depolymerization section [C]; and / or (ii) the depolymerization in step c.2) is carried out in the presence of water, so that the stream comprising ε-caprolactam is a vapor stream comprising ε-caprolactam and water in a weight ratio of 1:1 to 1:50, specifically 1:2 to 1:15, 1:2 to 1:10 or 1:3 to 1:8; and / or (iii) charging the depolymerization section [C] with superheated steam having a temperature ranging from 220° C. to 575° C., specifically from 275° C. to 500° C., (iv) the depolymerization in step c.2) is carried out in the absence or presence of a catalyst, preferably in the absence or presence of orthophosphoric acid, wherein the catalyst is selected from acid and base catalysts, the acid catalyst being selected from the group consisting of: Orthophosphoric acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids, solid acids, salts of the above acids, Al2O3 and SiO2 and combinations thereof, in particular orthophosphoric acid, and the base catalyst is selected from the group consisting of alkali metal hydroxides, alkali metal salts, alkaline earth metal hydroxides and alkaline earth metal salts, organic bases and solid bases and combinations thereof, in particular sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

5. The process according to any one of claims 2 to 4, wherein the recovered polyether polyurethane discharged from the precipitation section [γ] in step b.4) is reused in the production of textile products.

6. The method according to any one of claims 1 to 5, wherein the plant further comprises - Pre-processing section [A], And wherein prior to step a), the material comprising nylon 6 and polyether polyurethane is subjected to a pretreatment in the pretreatment section [A], specifically to cleaning in a cleaning section [ω] and / or to mechanical size reduction in a mechanical size reduction section [λ].

7. The process according to any one of claims 1 to 6, wherein the organic solvent is dimethylacetamide, and optionally, wherein the second solvent and the third solvent are the same solvent, preferably an aqueous solution or water.

8. The process according to any one of claims 1 to 7, wherein the second solvent in step b.3) is partly or completely the mixture comprising an organic solvent and a third solvent obtained from the washing section [β] in step b.7).

9. The process according to any one of claims 1 to 8, wherein the second solvent and the third solvent discharged from the solvent distillation section [δ] are reused in the precipitation section [γ] and / or the washing section [β], optionally after being separated from each other.

10. The process according to any one of claims 3 to 9, wherein before the separated organic solvent discharged from the solvent distillation section [δ] in step b.10) is fed to the dissolution section [α] in step b.1), degradation products of the organic solvent are removed.

11. The process according to any one of claims 1 to 10, wherein the solution comprising ε-caprolactam and impurities from which ε-caprolactam is crystallized in step c.4)(iv) further comprises water, preferably more than 1 wt.% water.

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