Method for recovering standles and nylene 6 from materials comprising standles and nylene 6

Abstract

The present invention provides a process for recovering nylon 6 and Spandex elastomeric fibers from nylon 6 and Spandex elastomeric fiber products in a plant wherein the plant comprises a separation section [B] comprising a dissolution section [alpha] and a precipitation section [gamma].

Description

Technical Field

[0001] The present invention relates to a method for recovering spandex and nylon 6 from a material comprising spandex and nylon 6. More particularly, the present invention relates to a method for recovering spandex and nylon 6 from a material comprising spandex and nylon 6 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. Usually, this type of ε-caprolactam is called "native ε-caprolactam". The cyclohexanone oxime required to form (native) ε-caprolactam can be prepared from cyclohexanone, which is mainly produced from benzene. Most of this benzene comes 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 in electronic form 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, Weinheim, Germany, which is available in electronic form at https: / / doi.org / 10.1002 / 14356007.a21_179.pub3. In addition to nylon 6, other important types of nylon are nylon 4,6 and nylon 6,6.

[0008] In 1959, American textile chemist Joseph Shivers invented spandex fiber, also known as Lycra or elastane.

[0009] The US Federal Trade Commission defines spandex as a long-chain synthetic polymer comprising at least 85% segmented polyurethane. It is made by reacting a high molecular weight dihydroxy compound with an organic diisocyanate and a chain extender to form an elastomeric polymer. It is segmented because it consists of alternating soft and hard regions within the polymer structure. The hard segments act as physical crosslinks that connect the polymer chains together. The soft segments of the polymer chain consist of polymers containing long, curly segments that can be oriented when the material is stretched. Crosslinking prevents the polymer chains from passing each other significantly. After stretching, the linear soft segments return to a curly form, allowing the fiber to return to its original shape. The synthesis of spandex consists of the following initial steps: reacting macroethylene glycol with diisocyanate monomers to obtain a prepolymer. The typical ratio of ethylene glycol to diisocyanate is 1:2. The prepolymer formed is then further reacted with an equal amount of diamine. This reaction is called a chain extension reaction. Thus, spandex fibers are produced from polymer materials.

[0010] Polyurethane gets its name from ethyl carbamate, which is called urethane.

[0011] Spandex fibers are known for their extraordinary elasticity: they can be stretched to almost 500% of their length and then return to their original shape. The impressive stretch and recovery capabilities make them ideal for close-fitting garments worn by athletes, such as swimsuits, cycling or yoga pants, and sportswear. The form-fitting properties of spandex make it ideal for underwear. Therefore, it is used in girdles, leggings, stockings, bras and briefs. In addition, it is widely used in (tight-fitting) jeans, trousers, shirts, dresses, underwear and shoes.

[0012] There are two main types of polyurethane - polyester and polyether. Both are used in a variety of industrial applications. Both are urethane elastomers and both are used in different types of spandex.

[0013] The main properties of polyester polyurethanes are oil / solvent resistance, mild acid / alkali resistance, abrasion resistance, excellent mechanical properties, fungus resistance and excellent vibration damping. Polyester polyurethanes are not recommended for use in situations of high humidity or water exposure. Hydrolysis is a risk that can negatively affect the physical properties of polyurethanes.

[0014] In a preferred embodiment, throughout this disclosure, the term "spandex" may be replaced by polyether polyurethane, which is a preferred spandex or component present in spandex that may be used according to the present invention. The main properties of polyether polyurethane are low temperature flexibility, excellent hydrolytic stability, food grade application, temperature resistance, excellent mechanical properties and weathering (UV) resistance. Polyether polyurethane is recommended for applications that are expected to experience medium to high stresses. Typically, native polyether polyurethane is obtained by the reaction of polyether polyol and diisocyanate monomers.

[0015] Typically, spandex is not used alone, but rather it is mostly blended with other natural fibers such as cotton and / or man-made fibers such as nylon 6 and polyethylene terephthalate (PET). As a result, spandex typically only makes up a small portion of the final fabric, which thus retains much of the look and feel of the other fibers.

[0016] Initially, pure nylon 6 was used to produce textiles, including stockings. Later, in order to improve the properties of fabrics, various blended fabrics were developed and produced. In particular, spandex has been widely used in various nylon 6-based clothing. The benefits of spandex 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 blended from nylon 6 fibers and spandex fibers. Examples of clothing containing fabric blends of nylon 6 and spandex 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.

[0017] The recycling of nylon 6 enables the saving 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 a secondary raw material or into a product with (preferably) only minimal changes in the chemical structure of the material. Typically, mechanical recycling comprises a melting step, which is optionally followed by a filtering step and finally a solidification and / or molding step. A slightly expanded form of mechanical recycling comprises a solvent-based purification (dissolution) step prior to the melting step of waste nylon 6. In this form, the waste nylon 6 is first dissolved in a solvent, while non-nylon 6 impurities are (partially) not dissolved, followed by a separation step of dissolved nylon 6 and undissolved materials, and finally the solvent is recovered from the solution containing nylon 6.

[0018] The conversion of nylon 6 and the depolymerization of nylon 6 are two forms of nylon 6 chemical recycling (also called feedstock recycling). In the conversion recycling process (e.g., by cracking and gasification), nylon 6 is broken down into feedstocks like petroleum or natural gas that can replace newly extracted fossil feedstocks. 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:

[0019]

[0020] Typically, prior art chemical regeneration or recycling processes for depolymerizing substantially pure nylon 6 to epsilon-caprolactam monomers include a hydrolytic degradation step at elevated temperature in the presence of water and a step of recovering the monomers formed by steam distillation.

[0021] The depolymerization recycling process of nylon 6 was developed entirely for clean and fairly pure waste nylon 6 materials. Mechanical recycling always results in downgraded recycling, so 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 materials may also allow the production of high-purity ε-caprolactam with properties similar to those of virgin-prepared ε-caprolactam, which can then be converted into high-grade nylon 6. Unfortunately, the chemical recycling of waste nylon 6-containing products is often hampered by the presence of impurities in the waste nylon 6 products. Typically, due to the presence of these impurities, the quality of the produced ε-caprolactam is inferior to that of virgin ε-caprolactam.

[0022] The depolymerization of a material comprising nylon 6 and spandex has a number of disadvantages compared to the depolymerization of fairly pure nylon 6. These disadvantages include, among other things, clogging of pipes and other equipment parts by spandex and its decomposition products, a poorer quality of the produced ε-caprolactam due to the presence of spandex decomposition products, a (strongly) reduced ε-caprolactam recovery, poisoning of the depolymerization catalyst and, therefore, a higher consumption of the depolymerization catalyst. Another disadvantage of adding a material comprising nylon 6 and spandex to a depolymerization reactor is that the spandex is destroyed. Therefore, simultaneous recycling of spandex, which is more valuable than nylon 6, is not possible.

[0023] Virgin spandex fibers are produced by a dry or wet spinning process starting with a spandex spinning solution consisting of a polyurethane in a suitable solvent such as dimethylacetamide or dimethylformamide.

[0024] Directly recycling normal (pure) spandex waste fibers, for example from yarn production, by dissolving in the spinning solvent employed has proven unsuccessful due to the high viscosity which prevents further processing.

[0025] US6830715B1 describes a method for producing spandex yarn from a spinning solution using recycled spandex material, which overcomes the above-mentioned viscosity problem by adding a secondary aliphatic amine to the mixture of (cut) spandex fibers and the spinning solvent. The dissolution of the (cut) spandex fibers is achieved at a temperature of 60°C to 150°C.

[0026] In the past, several attempts to recycle blends of nylon 6 and polyether polyurethanes have been described.

[0027] JP2011088943A describes a pretreatment method for separating polyether polyurethane from a nylon 6 material containing polyether polyurethane, followed by depolymerization of the residual nylon 6. The pretreatment comprises heating the nylon 6 material containing polyether polyurethane together with a solvent containing cyclic amide at a temperature of 80°C to the boiling point of the solvent. JP2011088943A indicates that the amount of cyclic amide compound in the cyclic amide compound solvent is preferably 50% by weight or more, more preferably 85% by mass or more. JP2011088943A further indicates that the cyclic amide solvent may contain components other than the cyclic amide compound, such as water and an organic solvent, and water is particularly preferred from the viewpoint of operability. The experiment described in the patent was conducted at a temperature of 110°C with an aqueous solution containing 50 and 85% by weight of N-methylpyrrolidone, 85% by weight of 2-pyrrolidone or 85% by weight of 2-piperidine as a solvent over a period of 2 hours. As a result of this treatment, the polyether polyurethane was partially decomposed and dissolved in the solvent. Thus, the resulting nylon 6 material is depolymerized, the polyether polyurethane has been removed from the material and the material is separated from the solution by filtration. However, JP2011088943A does not mention the recovery of the partially decomposed polyether polyurethane. The fate of the used solvent is also not described.

[0028] WO 2013032408A1 describes a method for recycling polyamide fibers including polyamide 6 and polyamide 6,6 including polyamide and spandex. Spandex fibers are removed from spandex fabrics by a method comprising controlled thermal degradation of spandex, a controlled washing treatment to remove spandex or its degradation products from high purity polyamide by using a suitable and sustainable solvent, preferably ethanol, 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-220°C, preferably 190°C-216°C, and preferably during a time period of 0.5 to 4 hours. Thereafter, the heat treated fabric is washed with preferably ethanol at a temperature in the range of 5°C to 78°C to remove spandex and its degradation components. WO 2013032408A1 does not mention the recovery of spandex and its degraded components from the washing solvent.

[0029] In view of the above, there is no process for recovering both nylon 6 and spandex from materials comprising nylon 6 and spandex on an industrial scale to date. The reason may be that in the prior art methods for bringing spandex into solution, high solution temperatures need to be applied, usually well above 100° C. However, at these temperatures, spandex begins to degrade and only inferior materials are obtained after recovery. Therefore, the fate of the recovered spandex is often limited to incineration and land filling. Another disadvantage of the dissolution process at high temperatures is the formation of degradation products of the applied solvents, which may hinder the recovery of nylon 6 and spandex and the recycling of the applied solvents.

[0030] Environmental issues regarding the production and use of these materials including nylon 6 and spandex relate to the waste generated during and after consumption. These issues can be alleviated by recycling individual components (such as nylon 6 and spandex) from materials including nylon 6 and spandex that are no longer used or disposed of. Textiles made from materials including nylon 6 and spandex are a particularly relevant source of waste. These typically contain large amounts of nylon 6 and spandex. Therefore, if there is a feasible method to recover both nylon 6 and spandex from these composite wastes, this would not only benefit the environment, but also provide an economically valuable new source for nylon 6 and polyether polyurethanes.

[0031] From the perspective of reducing carbon dioxide emissions, recycling materials including nylon 6 and spandex, thereby recovering nylon 6 and spandex, is of great significance.

[0032] And there is a need to provide nylon 6 and spandex from materials that include nylon 6 and spandex with a carbon footprint that is significantly lower than nylon 6 produced by a process using virgin ε-caprolactam obtained by new synthesis (e.g., by Beckmann rearrangement of cyclohexanone oxime) and spandex produced by de novo synthesis of spandex.

[0033] A problem with prior art methods is that they consume a large amount of energy to recover the dissolved spandex from the solution since the dissolved spandex is typically obtained by removing the solvent by evaporation.

[0034] And there is a need to separate the nylon 6 from the spandex present in a material comprising nylon 6 and spandex to obtain a nylon 6 material that can be further upgraded by known mechanical or chemical nylon 6 recycling processes.

[0035] Another shortcoming of the prior art is that no suitable recovery and reuse (recycling) strategies are provided or known for recovering and reusing (recycling) spandex and nylon 6 solvents from materials including nylon 6 and spandex.

[0036] Finally, there is a need for a process that allows for the recovery of nylon 6 and spandex from materials comprising nylon 6 and spandex on an industrial scale in order to deal with the large amounts of materials comprising nylon 6 and spandex that are wasted each year. Summary of the invention

[0037] It is an object of the present invention to meet one or more of the above needs and to overcome or mitigate the disadvantages associated with prior art approaches.

[0038] In particular, it is an object of the present invention to provide a method for recovering spandex and nylon from a material comprising nylon and spandex.

[0039] It is a further object of the present invention to provide a process for recovering both nylon and spandex from a material comprising nylon and spandex on an industrial scale.

[0040] It is also an object of the present invention to provide a method for recovering both nylon and spandex from a material comprising nylon and spandex in a cost-effective manner. In this regard, in particular, it is an object of the present invention to provide a method that is suitable for recovering both nylon and spandex from a material comprising nylon and spandex and that does not exceed the production costs of virgin nylon and spandex.

[0041] It is also an object of the present invention to provide a method for recovering nylon from a material comprising nylon and spandex, said nylon being suitable for further upgrading by mechanical or chemical recycling.

[0042] It is a further object of the present invention to provide a process for recovering both nylon 6 and spandex from materials comprising nylon 6 and spandex, said process being characterized by a carbon footprint significantly lower than processes for producing virgin spandex, for example, by reaction of polyether polyols or polyester polyols and diisocyanate monomers and for producing ε-caprolactam by novel synthesis, for example, by Beckmann rearrangement of cyclohexanone oxime.

[0043] It is also an object of the present invention to provide a method for recovering nylon 6 from materials including nylon 6 and spandex, wherein the recovered nylon 6 can replace nylon 6 for certain applications where virgin nylon 6 is currently obtained from ε-caprolactam by novel synthesis, such as Beckmann rearrangement of cyclohexanone oxime.

[0044] Another object of the present invention is to provide a method for recovering nylon 6 from materials including nylon 6 and spandex, the recovered nylon 6 can be depolymerized to monomeric ε-caprolactam, which can be converted into high-purity ε-caprolactam by purification, and the high-purity ε-caprolactam can replace virgin ε-caprolactam for all applications currently using virgin ε-caprolactam obtained by novel synthesis, such as by Beckmann rearrangement of cyclohexanone oxime.

[0045] Therefore, the present invention is also directed to a method of reducing the environmental burden of discarded materials comprising nylon and spandex.

[0046] One or more additional objects may become apparent from the remainder of the specification.

[0047] 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.

[0048] The present invention provides a method for recovering nylon and spandex from a material comprising nylon and spandex in a plant, wherein the plant comprises

[0049] - separation section [B],

[0050] The separation section comprises

[0051] - dissolution segment [α], and

[0052] - precipitation section [γ],

[0053] And wherein the method comprises the following steps:

[0054] b.1) charging an organic solvent and the material comprising nylon and spandex into the dissolving zone [α];

[0055] b.2) selectively dissolving said spandex from said material comprising nylon and spandex in said organic solvent in said dissolving zone [α], 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, such that a spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon are obtained;

[0056] b.3) discharging the resulting spandex-rich stream from the dissolving zone [α];

[0057] b.4) feeding a second solvent and the spandex-rich stream into the precipitation zone [γ] such that spandex is precipitated from the mixture comprising the organic solvent and the second solvent;

[0058] b.5) ​​recovering the precipitated spandex from the mixture comprising the organic solvent and the second solvent and discharging the precipitated spandex from the precipitation zone [γ], wherein the discharged stream has a spandex content of at least 85 wt% on a dry weight basis, more preferably at least 90 wt% on a dry weight basis;

[0059] b.6) discharging from the precipitation section [γ] the mixture comprising the organic solvent and the second solvent from which the precipitated spandex has been recovered in step b.5); and

[0060] b.7) Discharging the stream comprising undissolved nylon obtained in step b.2) from dissolving section [α].

[0061] Surprisingly, the combination of a particular sequence of processing steps and process conditions according to the invention, i.e. a sequence of selective dissolution and precipitation steps as defined above, allows the recovery of nylon and spandex from a material comprising nylon and spandex in high yield and in a direct and economically sound manner. The process of the invention is economically sound and advantageous from several points of view. Firstly, the process of the invention is applicable to a variety of materials derived from a material comprising nylon and spandex, which may differ, for example, in their overall composition and / or their spandex content and / or their nylon content. Secondly, the process of the invention allows the efficient separation of nylon from spandex compounds, making it possible to obtain high-grade nylon. Thirdly, the process of the invention is very efficient, making it possible to obtain nylon in high yield. Fourthly, the process of the invention allows the recovery of spandex, which may be used again to replace spandex produced by de novo synthesis, for example by reaction of polyether polyols or polyester polyols and diisocyanate monomers. Fifth, the process of the present invention allows for efficient separation of nylon 6 from spandex compounds, so that after depolymerization and purification, high purity grades of ε-caprolactam can be obtained, which 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 nylon 6 with a significantly lower carbon footprint compared to nylon 6 produced by de novo synthesis of nylon 6 (e.g., by Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam, which is then polymerized). The process of the present invention allows for efficient processing of materials including nylon 6 and spandex, and reduces the environmental burden of the materials. Specifically, the process of the present invention allows for the production of spandex with a carbon footprint of less than 1 kg CO2 / kg spandex, which is a significant improvement over the 4.8 kg CO2 / kg polyether polyurethane associated with the production of "virgin" polyether polyurethane obtained by chemical synthesis. Specifically, the process of the present invention allows for the production of nylon 6 with a carbon footprint of less than 1 kg CO2 / kg nylon 6, which is a significant improvement over the 6.4 to 7.5 kg CO2 / kg nylon 6 associated with the production of "virgin" ε-caprolactam obtained by Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam and then polymerizing the ε-caprolactam.

[0062] In addition to the method of the present invention, the present invention also provides a plant for producing nylon and spandex from a material comprising nylon and spandex, wherein the plant comprises

[0063] - Optionally, a pre-treatment section [A],

[0064] - separation section [B],

[0065] -optionally, a nylon depolymerization zone [C],

[0066] -optionally, an ε-caprolactam recovery section [D],

[0067] - optionally, an ε-caprolactam purification section [E], and

[0068] Wherein the chemical plant is configured to carry out the method of the present invention.

[0069] The present invention also provides nylon obtained by separation from a material comprising nylon and polyether polyurethane according to the method of the present invention, wherein the product carbon footprint of the nylon is less than 1.0 kg CO2 equivalent / kg nylon.

[0070] The present invention also provides a polyether polyurethane obtained by the method of the present invention, wherein the product carbon footprint of the polyether polyurethane is less than 1.0 kg CO2 equivalent / kg recycled polyether polyurethane.

[0071] Advantageous embodiments of the invention are indicated in the dependent claims and are explained in more detail below. DETAILED DESCRIPTION

[0072] Materials including nylon and spandex

[0073] The method of the present invention uses a material comprising nylon and spandex as a starting material. The material comprising nylon and spandex may be a product comprising nylon and spandex (used) or a material derived therefrom. Typically, the material comprising nylon and spandex is a solid material, specifically a fiber, a yarn (i.e., fiber strands spun together) or a fiber-based fabric, wherein the fiber is a blend of nylon fiber and polyurethane fiber, or wherein the fiber is obtained by coating the surface of nylon fiber with a spandex resin. The term "nylon" as used herein refers to any type of polyamide. Preferably, the nylon is selected from the group consisting of: nylon 6; nylon 4,6; nylon 6,6; and mixtures thereof. Most preferably, the nylon is nylon 6. Hereinafter, the present invention will be exemplarily described with respect to nylon 6 as nylon. However, this shall not limit the scope of the present disclosure, and all embodiments described herein for nylon 6 are also meant to disclose corresponding embodiments, in which other polyamides, specifically nylon 4,6 and / or nylon 6,6, are used as nylon.

[0074] The material comprising nylon and spandex can be of pre-consumer and post-consumer origin. The material comprising nylon and spandex can be a mixture of different materials comprising nylon and spandex, or a mixture of one or more materials comprising nylon and spandex with one or more different materials.

[0075] Thus, the material comprising nylon and spandex may contain additional components. Such components may be added, for example, during polymerization, fiber formation, or thereafter, to achieve desired property changes. These additional compounds include, for example, brighteners, hardeners, antistatic lubricants, colorants, brighteners, spin finishes, surface smootheners, antioxidants, UV stabilizers, and the like. The amounts of these additional components depend on the application of the material comprising nylon and spandex.

[0076] In materials including nylon and spandex, the weight ratio of nylon to spandex can vary, but preferably ranges from about 1:1 to about 100:1, most preferably from about 3:1 to about 20:1.

[0077] Spandex is 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 making polyurethane 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.

[0078] The two main types of spandex are polyester polyurethane and polyether polyurethane.

[0079] Polyester polyurethane is made by the reaction of isocyanate and polyester polyol.

[0080] Polyether polyurethanes are made by reacting isocyanates with polyether polyols. Polyether polyols are usually made by polymerizing a cyclic ether compound onto an initiator compound. The most commonly used cyclic ethers in the production of polyether polyols 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 that require highly hydrophobic properties.

[0081] Preferably, in the method of the present invention, the spandex is a polyether polyurethane. In another preferred embodiment, the spandex is a polyester polyurethane.

[0082] 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 can be combined with each other. All ranges of different parameters disclosed herein can be combined with each other. Specifically, the 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 provides otherwise, the singular forms "one", "a kind of" and "the" include plural forms, particularly in the sense of "one or more".

[0083] Possible preprocessing steps

[0084] Before being subjected to step b.1) of the method of the present invention, the material comprising nylon 6 and spandex may be pretreated in a pretreatment section [A], in particular 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] in addition to the separation section [B], and wherein before step b.1), the material comprising nylon 6 and spandex is subjected to a pretreatment in the pretreatment section [A], in particular cleaning in a cleaning section [ω] and / or mechanical size reduction in a mechanical size reduction section [λ]. More preferably, the method of the present invention is carried out in a plant further comprising a pretreatment section [A] and / or a mechanical size reduction section [λ], said pretreatment section comprising a cleaning section [ω], and wherein said method comprises the following steps before step b.1):

[0085] a.1) loading a material comprising nylon 6 and spandex into the pretreatment section [A]; and

[0086] a.2) cleaning the material comprising nylon 6 and spandex in a cleaning section [ω]; and / or

[0087] a.3) mechanically reducing the material comprising nylon 6 and spandex in a mechanical size reduction section [λ]; and

[0088] a.4) Discharge the pretreated material comprising nylon 6 and spandex from pretreatment section [A].

[0089] Pre-treatment has the advantage that the material comprising nylon 6 and spandex fed to separation section [B] is less contaminated with non-spandex or nylon 6 material, which increases the yield and purity of ε-caprolactam and spandex produced in a plant of the invention configured to carry out the process of the invention. Another advantage is that the size-reduced material comprising nylon 6 and spandex can be processed more easily.

[0090] The material comprising nylon 6 and spandex is preferably or derived from used or waste material comprising nylon 6 and spandex. The size and shape of the material will depend largely on the exact application from which it is sourced. The materials comprising nylon 6 and spandex that may be used in accordance with the present invention range from separate fibers and yarns, optionally in spool form, to woven fabrics and garments.

[0091] In particular, discarded or used materials including nylon 6 and spandex may be contaminated with various types of dirt (e.g., with mud, oil, paint, or grease), or may be mixed with a range of other materials, such as rock, glass, metallic materials, organic waste, and other polymer waste (e.g., polyethylene terephthalate (PET), polypropylene (PP), or polyethylene (PE)).

[0092] Preferably, the material comprising nylon 6 and spandex is broken into fragments before separation in the separation section [B]. Such mechanical pretreatment of the material comprising nylon 6 and spandex, i.e. mechanical comminution or crushing, can be achieved, for example, by cutting, punching, chopping, grinding, crushing and / or cutting. In a preferred embodiment, the material comprising nylon 6 and spandex is charged to the separation section [B] of step b.1) in the form of broken fragments. The use of 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 employed fragments can be easily determined by a skilled person by first taking 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. The preferred particle size can also be described by the average particle weight. Preferably, the average particle weight of the fragments of the material comprising nylon 6 and spandex 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 spandex having the above size or weight dimensions are particularly suitable for treatment in the method of the present invention and / or cleaning by washing with a solvent.

[0093] Optionally, large metal fragments, rocks and other interfering materials that cause severe wear on the equipment used for mechanical comminution or crushing are removed before mechanical comminution or crushing of the material including nylon 6 and spandex. Preferably, foreign materials including but not limited to materials including polyethylene, polypropylene and polyamide 6,6 are also removed before mechanical comminution or crushing of the material including nylon 6 and spandex. The removal of foreign materials can be performed mechanically or manually. The advantage of removing these interfering materials is that the maintenance costs of the equipment used for mechanical comminution or crushing can be greatly reduced. In addition, the nylon 6 and spandex content of the material obtained after mechanical comminution or crushing is higher than when the interfering materials are not removed. In particular, the removal of polyamide 6,6 is advantageous because it interferes with the depolymerization of nylon 6, reduces the recovery rate of ε-caprolactam, and interferes with the subsequent purification of the recovered ε-caprolactam. The term "foreign materials" as used herein refers to non-nylon 6 and non-spandex materials or compounds.

[0094] Optionally, the foreign material is separated from the material including nylon 6 and spandex elastic fiber 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 liquid of medium density, wherein the lower density materials float and are separated from the higher density sinking materials. In practice, density separation is usually accomplished through a series of density separation stages. For example, in one stage, high density materials such as rocks, sand and metals (including iron and lead) are separated, 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 the magnetic material. The method preferably used for magnetic separation separates the magnetic material from the non-magnetic material. Removal of extraneous materials from the comminuted or crushed material comprising nylon 6 and spandex is advantageous because such materials may interfere with the separation of nylon 6 and spandex, the depolymerization of nylon 6, reduce the recovery of epsilon-caprolactam, and / or interfere with the subsequent purification of the recovered epsilon-caprolactam.

[0095] Optionally, in particular in the above-mentioned pretreatment step a.2), the material comprising nylon 6 and spandex is cleaned by washing with at least one solvent, preferably at least water, before being loaded into the separation section [B]. The solvent used herein may 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 most 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 comprises a final rinsing step with a detergent-free (clean) washing solvent to remove detergent residues and dirt present adhering to the material comprising nylon 6 and spandex.

[0096] Washing is preferably carried out under friction.Different types of industrial friction application washing systems are available on the market, like rotary plastics scrubbers and (high speed) friction scrubbers.

[0097] Washing the material comprising nylon 6 and spandex, in particular mechanically comminuted or crushed material comprising nylon 6 and spandex, is advantageous because any (adherent) dirt is removed and thus does not interfere with the following steps of the method of the invention.

[0098] Optionally, the material comprising nylon 6 and spandex is dried after the cleaning step and before being loaded into the separation section [B]. This has the advantage that the weight of the cleaned material comprising nylon 6 and spandex is reduced and the next step is not affected by dilution or contamination with washing solvents.

[0099] The location where the pretreatment of the material comprising nylon 6 and spandex is carried out and the location where the separation section [B] 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 separation section [B], for example, near a factory where the (used or waste) material comprising nylon 6 and spandex is collected and / or at a location dedicated to the pretreatment of the material comprising nylon 6 and spandex. A nylon 6-rich stream may then be obtained in the separation section [B] from the already pretreated material comprising nylon 6 and spandex.

[0100] The location where the material comprising nylon 6 and spandex is separated into a nylon 6-rich stream and the location where the nylon 6-rich stream is further processed by mechanical or chemical recycling can be the same or adjacent to each other. However, preferably, these steps are performed at different locations. In particular, the location where the separation of the material comprising nylon 6 and spandex into a nylon 6-rich stream and a spandex-rich stream is performed and the location where the depolymerization section [C] is located can be the same or different. Preferably, the separation of the material comprising nylon 6 and spandex into a nylon 6-rich stream and a spandex-rich stream is performed at a location different from the location of the depolymerization section [C], for example near a plant producing virgin spandex and / or at a location dedicated to the treatment and / or distillation of organic solvents.

[0101] Similarly, the location where the pretreatment of the material comprising nylon 6 and spandex is performed and the location where the depolymerization section [C] 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 depolymerization section [C], for example, near a factory where waste material comprising nylon 6 and spandex is collected and / or at a location dedicated to the pretreatment of the material comprising nylon 6 and spandex.

[0102] In separation section [B], the material comprising nylon 6 and spandex is separated to form a nylon 6-rich stream and a spandex-rich stream.

[0103] Preferably, the separation section [B] in the plant further comprises

[0104] - a washing section [β], and

[0105] - Solvent distillation section [δ].

[0106] In this case, the method according to the invention preferably comprises the following further steps:

[0107] c.1) charging a third solvent and the stream comprising undissolved nylon 6 obtained in step b.2) to the washing section [β];

[0108] c.2) washing the stream comprising undissolved nylon 6 with the third solvent in the washing section [β] so as to obtain a nylon 6-rich stream and a mixture comprising an organic solvent and a third solvent, wherein the nylon 6-rich stream has a nylon 6 content of at least 85 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-% and most preferably at least 99 wt.-% on a dry weight basis;

[0109] c.3) discharging the nylon 6-rich stream from the washing section [β];

[0110] c.4) discharging the mixture comprising the organic solvent and the third solvent obtained in step c.2) from the washing section [β];

[0111] d.1) charging the mixture comprising the organic solvent and the second solvent from which the precipitated spandex has been recovered in step b.5) and discharged from the precipitation section [γ] in step b.6) to the solvent distillation section [δ];

[0112] d.2) charging part or all of the mixture comprising the organic solvent and the third solvent obtained in step c.2) and discharged from the washing section [β] in step c.4) to the solvent distillation section [δ];

[0113] d.3) separating the organic solvent from the second solvent and the third solvent by distillation in the solvent distillation section [δ]; and

[0114] d.4) discharging the second solvent, the third solvent and the separated organic solvent from the solvent distillation section [δ].

[0115] Preferably, the separation section [B] employed in the process of the present invention comprises a dissolving 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 separation of a material comprising nylon 6 and spandex into a nylon 6-rich stream and a spandex-rich stream according to the process of the present invention. Surprisingly, when the process steps b.1) to b.7), c.1) to c.4) and d.1) to d.4) are carried out in a separation section [B] comprising a dissolving 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 spandex into a nylon 6-rich stream and a spandex-rich stream is particularly effective. Steps b.1) to b.7), c.1) to c.4) and d.1) to d.4) are further explained below.

[0116] 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. For example, when looking at step b.2), a stream enriched in nylon 6 contains more nylon 6 than a stream enriched in spandex. In contrast, a stream enriched in spandex contains more spandex than a stream enriched in nylon 6.

[0117] Specifically, the nylon 6-rich stream has a nylon 6 to spandex weight ratio that is higher than the nylon 6 to spandex weight ratio of the material comprising nylon 6 and spandex.

[0118] Preferably, the nylon 6-rich stream has a spandex to nylon 6 weight ratio that is at most one-half, more preferably at most one-third, the spandex to nylon 6 weight ratio of the material comprising nylon 6 and spandex.

[0119] The spandex-rich stream has a spandex to nylon 6 weight ratio that is higher than the spandex to nylon 6 weight ratio of the material comprising nylon 6 and spandex.

[0120] Preferably, the spandex-rich stream has a spandex to nylon 6 weight ratio that is at least twice, more preferably at least three times, the spandex to nylon 6 weight ratio of the material comprising nylon 6 and spandex.

[0121] Optionally, in the process according to the invention, the separated organic solvent discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1).

[0122] Preferably, in the method of the present invention, the organic solvent is dimethylacetamide. Preferably, the second solvent and the third solvent are the same solvent, specifically an aqueous solution or water.

[0123] Preferably, in the process of the invention, the second solvent in step b.4) is partly or completely a mixture comprising an organic solvent and a third solvent which is obtained in step c.2) and discharged from the washing section [β] in step c.4).

[0124] Preferably, in the process according to the invention, 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 separation from one another.

[0125] Preferably, in the process according to the invention, impurities, in particular degradation products of the organic solvent, are removed before the separated organic solvent discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1).

[0126] Preferably, the plant used in the method of the present invention further comprises

[0127] - depolymerization section [C],

[0128] - Recovery Sector [D], and

[0129] - Purification segment [E].

[0130] In this case, the method according to the invention preferably comprises the following further steps:

[0131] e.1) feeding the nylon 6-rich stream discharged from the washing section [β] in step c.3) to the depolymerization section [C];

[0132] e.2) depolymerizing the nylon 6 in the nylon 6-rich stream in the depolymerization section [C] such that a stream comprising ε-caprolactam is obtained, wherein the depolymerization is 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 and in the absence or presence of a catalyst (wherein the catalyst is selected from the group consisting of 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 being 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), preferably in the absence or presence of a catalyst or in the presence of orthophosphoric acid and

[0133] in the presence of water, preferably in the presence of water charged in the form of superheated steam having a temperature in the range of 220° C. to 575° C., specifically 275° C. to 500° C., so that the stream comprising ε-caprolactam is a steam 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;

[0134] e.3) discharging the obtained stream comprising ε-caprolactam from the depolymerization section [C];

[0135] e.4) recovering crude ε-caprolactam from the stream comprising ε-caprolactam in the recovery section [D];

[0136] e.5) 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 one or more techniques selected from the group consisting of: filtration, adsorption, extraction, washing, stripping, solvent exchange distillation, oxidation, hydrogenation, distillation and crystallization;

[0137] e.6) discharging the purified ε-caprolactam from the purification section [E].

[0138] Load step b.1)

[0139] In step b.1) of the present invention, an organic solvent and a material including nylon 6 and spandex are charged into a dissolving section [α].

[0140] The material comprising nylon 6 and spandex charged in step b.1) may optionally have been pretreated in a pretreatment section [A], in particular as specified in steps a.1), a.2), a.3) and a.4) of the present invention.

[0141] In one embodiment, the material comprising nylon 6 and spandex is mechanically compressed into a smaller volume before being loaded into the dissolving section [α]. This has the advantage that a smaller volume is required for intermediate storage and transportation, and can also facilitate administration into the dissolving section [α].

[0142] In another preferred embodiment, the material comprising nylon 6 and spandex is dried before being charged to the dissolving zone [α], in particular after subjecting the nylon 6 and spandex material to a cleaning step. This has the advantage that less or no solvent is introduced into the dissolving zone [α]. Solvents introduced into the dissolving zone [α], in particular water, may negatively affect the separation process (e.g. the dissolution rate of spandex from the material comprising nylon 6 and spandex in the organic solvent is reduced).

[0143] The material comprising nylon 6 and spandex is preferably fed in solid phase to the dissolution section [α], specifically the corresponding dissolution vessel contained therein.

[0144] Feeding the material including nylon 6 and spandex to the dissolving section [α] may be achieved by continuously or intermittently dosing the material including nylon 6 and spandex.

[0145] The organic solvent charged into the dissolving section [α] may be any organic solvent in which the spandex can be dissolved, in particular at a temperature below 100° C. and in particular in less than 24 hours or in less than 6 hours. The organic solvent as used herein may 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 spandex at a temperature below 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. Preferably, the organic solvent combines a good, in particular very good, solubility for spandex with a poor, in particular very poor, solubility for nylon 6. These properties can be tested in a simple dissolution test with a material comprising nylon 6 and spandex or a mixture of nylon 6 and spandex. 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 includes or is selected from N,N-dimethylformamide and dimethylacetamide. Most preferably, the organic solvent is dimethylacetamide.

[0146] 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 a separated organic solvent and a fresh organic solvent.

[0147] The organic solvent charged to the dissolution section [α] preferably has a low water content. Even more preferably, the organic solvent is dried (preferably by distillation or application of a drying agent, such as an inorganic salt such as Na2SO4, zeolite, silica and alumina) before being charged to the dissolution section [α]. Drying does not necessarily have to be performed to completion. Generally, it is acceptable for less than 1 wt.%, preferably less than 0.1 wt.%, more preferably less than 0.02 wt.% of water to remain after drying the organic solvent.

[0148] Feeding the organic solvent to the dissolution section [α] can be achieved by continuously or intermittently dosing the organic solvent.

[0149] Selective dissolution step (step b.2)):

[0150] In dissolving section [α], spandex is dissolved from the material comprising nylon 6 and spandex in the organic solvent charged to dissolving section [α] in step b.1). A spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon 6 are thereby obtained.

[0151] Preferably, dissolution of the spandex will be complete within 0.1 hour to 24 hours, more preferably within 0.5 hour to 6 hours. Complete means that dissolution has reached a plateau, with no substantial further dissolution occurring at later time points.

[0152] The temperature in the dissolution zone [α] may 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] may 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 cause the spandex to dissolve particularly completely while maintaining its integrity in the organic solvent. This has the advantage that the spandex present in the material comprising nylon 6 and spandex can be dissolved without or substantially without decomposition.

[0153] 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 spandex (expressed by weight, specifically expressed in tons) in the dissolution section [α]. Small amounts of solvent reduce the dissolution rate of spandex and may result in too low or incomplete dissolution of spandex. Large amounts of solvent give spandex a high dissolution rate, however, more energy and cost are required to recycle the used organic solvent. The skilled person can determine the optimal ratio of solvent to spandex or a material comprising nylon 6 and spandex by routine testing.

[0154] After the spandex is dissolved, the resulting mixture is separated into a spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon 6. There are several suitable methods for separating the mixture into a spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon 6, including but not limited to filtration, centrifugation, and sedimentation-decantation. A skilled artisan will be able to determine the best separation method. Good separation of the spandex-rich stream comprising organic solvent and dissolved spandex from the stream comprising undissolved nylon 6 is preferred because it improves the recovery of both spandex and nylon 6.

[0155] 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. In addition, the dissolution section [α] may comprise one or more units for separation, whereby a spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon 6 are obtained. These units may be operated in series or in parallel. Preferably, these separation units are selected from liquid-solid filters, centrifuges and / or vessels for sedimentation-decantation.

[0156] Discharge step (step b.3)):

[0157] A spandex-rich stream obtained in the dissolution section [α], comprising an organic solvent and dissolved spandex, is discharged from the dissolution section [α]. The spandex-rich stream comprises spandex and an organic solvent and optionally comprises a small portion of undissolved solid material. Preferably, the spandex-rich stream is a clear solution, optionally containing a small portion of undissolved solid material. Preferably, the fraction of undissolved solid material in the spandex-rich stream is less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 0.5 wt.%, and most preferably less than 0.1 wt.%, relative to the total weight of the spandex-rich stream 6. The discharge of such a stream is a conventional activity and can be performed by various methods, including pumping and displacement by gravity, all of which are known to the skilled person.

[0158] Precipitation step (step b.4)):

[0159] The spandex-rich stream comprising organic solvent and dissolved spandex discharged from dissolution section [α] and the second solvent are fed to precipitation section [γ] where they are mixed such that spandex is precipitated from the mixture comprising the organic solvent and the second solvent.

[0160] Preferably, the second solvent is a non-solvent for spandex (also called an anti-solvent), i.e., a liquid in which spandex is insoluble and causes the spandex to precipitate. The addition of the second solvent reduces the solubility of spandex dissolved in the solution including the organic solvent, which results in the precipitation of the spandex. The second solvent may be any solvent in which spandex is insoluble and causes the spandex to precipitate. Preferably, the second solvent is an aqueous solution or water, which has the advantage that it is an environmentally friendly solvent.

[0161] In a preferred embodiment, the second solvent consists of or is a portion of a mixture comprising an organic solvent and a third solvent obtained in step c.2) and discharged from the washing section [β] in step c.4). "A portion of a mixture or" as used herein is defined as any fraction between 1 and 100 wt.%, preferably between 10 and 100 wt.%, more preferably between 25 and 100 wt.%, even more preferably between 75 and 100 wt.%. This has the advantage that less fresh solvent is required for the precipitation of the spandex. 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.

[0162] The temperature in the precipitation section [γ] can vary and can 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 spandex.

[0163] The amount of the second solvent charged to precipitation section [γ] may vary and may 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.%, based on the spandex-rich stream containing the organic solvent charged to precipitation section [γ].

[0164] Small amounts of the second solvent reduce the extent of spandex precipitation. Large amounts of the second solvent complicate recovery of the precipitated spandex and organic solvent. Large amounts of the second solvent also require more energy and cost to recover the precipitated spandex and organic solvent. A skilled artisan will be able to find the optimum ratio of second solvent to spandex-rich stream for the particular solvent and equipment used by performing simple precipitation experiments.

[0165] Spandex recovery step (step b.5):

[0166] In the spandex recovery step, precipitated spandex is recovered from the mixture including the organic solvent and the second solvent, and the precipitated spandex is discharged from the precipitation section [γ]. There are several suitable methods for recovering the spandex precipitate, including but not limited to filtration, centrifugation, and decantation. Preferably, filtration is used to recover the spandex. For filtration, a solution containing the precipitate is charged to a filter, such that the precipitate is expected to be retained on the filter as 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 off the liquid. In decantation, the liquid layer is poured or sucked off from the precipitate.

[0167] Optionally, the recovered precipitate is washed with a solvent before being discharged from precipitation section [γ]. Preferably, the solvent used for washing the recovered precipitate is the organic solvent of step b.1) or the second solvent of step b.4).

[0168] Optionally, the recovered precipitate, optionally washed with a solvent, is dried before being discharged from precipitation section [γ]. The recovered spandex discharged from precipitation section [γ] in step b.5) of the process of the present invention is of high quality and can be reused as such or in combination with virgin polyether polyurethane in the production of textiles, which is a preferred embodiment of the present invention.

[0169] Step of discharging the solvent mixture (step b.6)):

[0170] The mixture including the organic solvent and the second solvent from which the precipitated spandex has been recovered in step b.5) is discharged from precipitation section [γ]. Optionally, it can then be charged to solvent distillation section [δ]. Optionally, the solvent resulting from washing the recovered precipitate is also discharged from precipitation section [γ] and charged to solvent distillation section [δ].

[0171] Step of discharging undissolved nylon 6 (step b.7)):

[0172] From the dissolution section [α] a stream comprising undissolved nylon 6 obtained in step b.2) is discharged.

[0173] The stream comprises undissolved solid nylon 6 and an organic solvent. In this regard, the term "solid" refers to the state of the material under operating conditions. Optionally, the stream also includes spandex elastic fiber in the form of undissolved material and / or dissolved in the organic solvent. Preferably, the organic solvent content of the stream is less than 75 wt.%, preferably less than 25 wt.%, more preferably less than 10 wt.%, and most preferably less than 2 wt.%, relative to the total weight of the stream. Preferably, the spandex elastic fiber content of the stream is less than 10 wt.%, preferably less than 5 wt.%, more preferably less than 2 wt.%, and most preferably less than 1 wt.%, relative to the total weight of the stream. The discharge of such streams is a conventional activity and can be carried out by various methods (including moving on a conveyor belt, pumping and shifting by gravity), all of which are known to the skilled person. The stream comprising undissolved nylon 6 is stable and can be stored before being loaded into downstream processing steps or transported to different locations for this purpose.

[0174] Load the wash step (step c.1)):

[0175] In the separation section [B], the third liquid solvent and the stream comprising undissolved nylon 6 obtained in step b.2) and discharged from the dissolving section [α] in step b.7) are fed to the washing section [β]. The stream comprising undissolved nylon 6 fed to the washing section [β] may also comprise, in addition to undissolved nylon 6, an organic solvent. The purpose of the washing section [β] is to recover the organic solvent present in the stream comprising undissolved nylon 6, thereby obtaining a stream enriched in nylon 6 containing less organic solvent than the stream comprising undissolved nylon 6. Another purpose of the washing section [β] is to recover the spandex present in the stream comprising undissolved nylon 6, thereby obtaining a stream enriched in nylon 6 containing less spandex than the stream comprising undissolved nylon 6.

[0176] Preferably, the third solvent has good solubility for organic solvents and poor solubility for nylon 6. The third solvent may be any solvent. Preferably, the second solvent is water or an aqueous solution. This has the advantage that it is an environmentally friendly solvent. The third solvent and the second solvent may have the same composition, which has the advantage of simplifying the process by reducing the amount of different components required.

[0177] The amount of the third solvent charged to washing 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 washing section [β].

[0178] Washing step (step c.2)):

[0179] 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 a mixture comprising the organic solvent and the third solvent is obtained.

[0180] 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%, even more preferably at least 95 wt% and most preferably at least 99 wt% on a dry weight basis.

[0181] Preferably, the nylon 6 content in the resulting nylon 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% on a dry weight basis.

[0182] 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).

[0183] 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.

[0184] The temperature in the washing section [β] can vary and can 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.

[0185] 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.

[0186] 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.

[0187] Step of discharging a stream rich in nylon 6 (step c.3)):

[0188] A nylon 6-rich stream is discharged from the washing 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.

[0189] Typically, the nylon 6-rich stream obtained comprises a solid nylon 6-rich material and a liquid third solvent and optionally an organic solvent. In this regard, 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.

[0190] The nylon 6-rich material is stable and can be stored prior to loading into downstream processing steps or transported to a different location for this purpose.

[0191] Optionally, the nylon 6-rich stream discharged from separation section [B] is dried, in particular so as to obtain a solid composition comprising nylon 6. This has the advantage that less or no solvent is introduced in the consecutive downstream steps.

[0192] Optionally, the nylon 6-rich stream discharged from separation section [B] is dried at a temperature above the melting point of nylon 6, in particular so as to obtain a liquid composition comprising nylon 6 and a vapor containing a solvent. This has the advantage that less or no solvent is introduced in the successive downstream steps. Melting wet nylon 6 is a conventional activity and can be carried out in various equipment (including degassing extruders), all of which are known to the skilled person.

[0193] Optionally, the nylon 6-rich stream discharged from separation section [B] is densified. This has the advantage that less volume is required for intermediate storage and / or transport of the nylon 6-rich stream. Another advantage of densification is that it facilitates processing in downstream steps.

[0194] Optionally, the nylon 6-rich stream or a solid composition comprising nylon 6 derived therefrom is fed, after discharge from separation section [B], to a nylon 6 mechanical recycling section in which nylon 6 from the nylon 6-rich stream is melted and then solidified again.

[0195] Optionally, the nylon 6-rich stream or the solid composition comprising nylon 6 derived therefrom, after being discharged from the separation section [B], is fed to a nylon 6 chemical recycling section, in which nylon 6 is depolymerized to obtain ε-caprolactam. It can then be used again for polymerization to nylon 6.

[0196] Preferably, the nylon 6-rich stream discharged from separation section [B] is dried and / or densified before being subjected to mechanical or chemical recycling. In this way, the nylon 6-rich stream is upgraded.

[0197] Step of discharging a mixture comprising an organic solvent and a third solvent (step c.4)):

[0198] The mixture comprising the organic solvent and the third solvent obtained in step c.2) is discharged from the washing section [β]. Usually, the organic solvent and / or the third solvent are valuable compounds, and recycling and reuse have great economic and environmental advantages. In a preferred embodiment of the present invention, the mixture comprising the organic solvent and the third solvent is therefore charged to the solvent distillation section [δ]. Optionally, the mixture comprising the organic solvent and the third solvent is first charged to another section and used in said another section, in particular as the second solvent in the precipitation step b.4, and then charged to the solvent distillation section [δ]. In a preferred embodiment, the mixture comprising the organic solvent and the third solvent is first partially or completely charged to the precipitation section [γ] and used as the second solvent. This provides a particularly efficient use and reuse of the solvent in the process according to the invention.

[0199] Step of charging a mixture comprising an organic solvent and a second solvent (step d.1)):

[0200] The mixture comprising the organic solvent and the second solvent, from which the precipitated spandex has been recovered in step b.5) and which was discharged from the precipitation section [γ] in step b.6), is fed to the solvent distillation section [δ].

[0201] Step of charging a mixture comprising an organic solvent and a third solvent (step d.2)):

[0202] The mixture comprising the organic solvent and the third solvent obtained in step c.2) and discharged from the washing section [β] in step c.4) is partially or completely charged to the solvent distillation section [δ]. In a preferred embodiment, the mixture comprising the organic solvent and the third solvent is first partially or completely charged to the precipitation section [γ] before being charged to the solvent distillation section [δ].

[0203] In a preferred embodiment of the process of the invention, the second solvent in step b.4) is partly or completely a mixture comprising an organic solvent and a third solvent which is obtained in step c.2) and discharged from the washing section [β] in step c.4).

[0204] Solvent separation step (step d.3)):

[0205] In the solvent distillation section [δ], the different solvents used in the method of the present invention are separated and recovered again. This enables them to be advantageously reused. Specifically, in the solvent distillation section [δ], the mixture including the organic solvent and the second solvent from which the precipitated spandex elastic fiber has been recovered discharged from the precipitation section [γ] and the mixture including the organic solvent and the third solvent discharged from the washing section [β] are separated by distillation. Thereafter, the mixture including the organic solvent and the second solvent from which the spandex elastic fiber has been recovered discharged from the precipitation section [γ] and the mixture including 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].

[0206] The separated organic solvent, the second solvent and the third solvent as well as the residue are discharged from the solvent distillation section [δ]. In a preferred embodiment, the separated organic solvent discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1). In another preferred embodiment, 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.

[0207] Separation by distillation is used to separate liquids from non-volatile solids and to separate liquids with 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.

[0208] The mixture comprising the organic solvent and the second solvent from which the precipitated spandex has been recovered optionally further comprises (dissolved) spandex, (dissolved) nylon 6 and degradation products of the organic solvent and / or the second solvent. The mixture comprising the organic solvent and the third solvent optionally further comprises (dissolved) spandex, (dissolved) nylon 6 and degradation products of the organic solvent and / or the third solvent.

[0209] In general, separation of three different liquids by distillation is more complicated than separation of two different liquids by distillation, requires more energy, and requires more equipment. Therefore, the ability to limit the number of different solvents in the method of the present invention to two by using a solvent identical to 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 identical solvents. In a more preferred embodiment, the second solvent and the third solvent are water or an aqueous solution. Using water as a solvent is advantageous because it is cheap, available in large quantities, non-explosive and environmentally friendly.

[0210] 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).

[0211] 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. The boiling point of N,N-dimethylacetamide (DMAc) at atmospheric pressure is about 165°C. The boiling point of water at atmospheric pressure is 100°C.

[0212] When only DMAc and water are present in the combined feed to the solvent distillation section [δ], the difference in volatility between the two is large, and it is found that separation by distillation will be quite easy. In such cases, the continuous separation of the combined feed to the 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 gaseous state, and DMAc is discharged from the bottom of the column in a liquid state. When non-volatile compounds (such as spandex and nylon 6) are present in the combined feed to the solvent distillation section [δ] in addition to DMAc and water, the solvent distillation layout required for continuous separation into DMAc, water and non-volatile compounds is more extensive. This type of direct layout for separation by distillation includes two distillation columns operated in series. A feed consisting of DMAc, water and non-volatile compounds (in liquid form) is charged to the first distillation column. Water is distilled from the top of the first distillation column in a gaseous state, and a mixture of DMAc and non-volatile compounds (in liquid or slurry form) is discharged from the bottom of the first distillation column. The bottom stream of the first column is fed to the 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 of the second distillation column. An extrusion (column) unit that recovers DMAc from the bottom stream of the second distillation column can be added to increase the overall recovery of DMAc.

[0213] As an alternative to separation by distillation of 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 discharged as a liquid side stream, and non-volatile compounds are discharged from the bottom of the second distillation column. Optionally, the bottom stream is fed to an extrusion (column) unit.

[0214] As an alternative to charging the feed in the distillation column in the liquid state, the charging into the first distillation column can be carried out in the gaseous state. In this case, the combined feed to the solvent distillation section [δ], except for the non-volatile compounds, is evaporated in the feed evaporator before being charged into the first distillation column. The non-volatile compounds are discharged from the feed evaporator. The advantage of this alternative is that less fouling occurs in the distillation column. Optionally, the squeeze column can be combined with the feed evaporator. Typically, process streams comprising DMAc contain a certain amount of acetic acid and dimethylamine due to, for example, the degradation of DMAc. This is also the case for the combined feed to the solvent distillation section [δ].

[0215] The boiling point of pure dimethylamine at atmospheric pressure is about 7° C. Dimethylamine is very soluble in water.

[0216] The boiling point of pure acetic acid at atmospheric pressure is approximately 118°C.

[0217] However, acetic acid and DMAc form a high boiling azeotrope (composition of about 21 wt.% acetic acid and about 79 wt.% DMAc at atmospheric pressure) and have an atmospheric boiling point of about 171°C, which is only slightly higher than the atmospheric boiling point of DMAc. 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).

[0218] If the pressure is reduced, the azeotropic point of the mixture of acetic acid and DMAc shifts to a higher concentration of the low-boiling component, which is acetic acid.

[0219] At 6.7 kPa, a high boiling azeotrope consisting of about 30 wt.% acetic acid and about 70 wt.% DMAc is formed, the boiling point of the high boiling azeotrope being about 93°C.

[0220] At 1.3 kPa, a high boiling azeotrope of composition of about 42 wt.% acetic acid and about 58 wt.% DMAc is formed, the boiling point of which is about 75°C. Preferably, the degradation products are removed from the solvent which is reused in the process. This has the advantage that the accumulation of degradation products is prevented. 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 d.4) is charged 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.

[0221] Several techniques for breaking azeotropes in distillation are known to those skilled in the art.

[0222] One group of techniques is based on adding another compound that changes the molecular interactions and eliminates the highest azeotrope of DMAc-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 DMAc and acetic acid results in the formation of a new azeotrope of this compound and acetic acid that can be removed by evaporation. Subsequently, the resulting mixture of this compound and acetic acid is separated.

[0223] Another group of technologies, generally referred to as pressure swing distillation, is based on the fact that the highest azeotrope is pressure-dependent. In such systems, two distillation columns are operated at different pressure levels. A feed mixture of DMAc and acetic acid is fed to a first distillation column operated at a certain pressure. The bottom stream of this first distillation column is fed to a second distillation column. The bottom stream of the second distillation column is fed to the first distillation column. As top products of the distillation columns, high-purity DMAc and acetic acid are obtained. The main advantage of pressure swing distillation is the absence of foreign compounds.

[0224] Finally, there is a group of techniques that convert acetic acid to another component (e.g., salt formation due to the addition of caustic) or selectively adsorb acetic acid from a mixture of DMAc and acetic acid.

[0225] When acetic acid and dimethylamine are present in the combined feed to the solvent distillation section [δ] in addition to DMAc, water and non-volatile compounds such as spandex and nylon 6, the solvent distillation layout required for the continuous separation into DMAc, water, non-volatile compounds, acetic acid and dimethylamine is even more extensive.

[0226] 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.

[0227] If the fraction of acetic acid in the combined feed to the solvent distillation section [δ] is rather low, the solvent distillation section [δ] may comprise two distillation columns operated in series, followed by a neutralizer evaporation step. A feed consisting of N,N-dimethylacetamide (DMAc), water, non-volatile compounds, acetic acid and dimethylamine is charged to a first distillation column. Water and dimethylamine are distilled in the 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 discharged 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. In a dimethylamine stripping unit, dimethylamine can be removed from this liquid phase, thereby obtaining (almost) dimethylamine-free water. The bottom stream of the first column is charged to a second distillation column. N,N-dimethylacetamide (DMAc) is distilled in the gaseous state from the top of the second distillation column, and a mixture of DMAc, acetic acid and non-volatile compounds is discharged from the bottom of the second distillation column. The bottom stream of the second column is charged to a neutralizer evaporation unit. A base, such as an aqueous NaOH solution, is charged into the neutralizer evaporation unit to neutralize the acetic acid. Due to evaporation, gaseous N,N-dimethylacetamide (DMAc) is discharged from the neutralizer evaporation unit. If present, water is also evaporated. 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.

[0228] 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.

[0229] Step of discharging the second solvent, the third solvent and the separated organic solvent (step d.4)):

[0230] The separated organic solvent, the second solvent and the third solvent and the residue are respectively discharged from the solvent distillation section [δ]. In a preferred embodiment, the separated organic solvent discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1). In another preferred embodiment, 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.

[0231] In a more preferred embodiment of the present invention, the organic solvent is DMAc. In such embodiments, the DMAc recovered by distillation is discharged from the solvent distillation section [δ] and charged to the dissolution section [α].

[0232] Load step e.1)

[0233] In step e.1) of the present invention, the resulting nylon 6-rich stream is fed to a depolymerization section [C]. The nylon 6 content in the nylon 6-rich stream is at least 80% by weight, preferably at least 85% by weight, more preferably at least 90% by weight, even more preferably at least 95% by weight, and most preferably at least 99% by weight, based on dry weight. This has the advantage that the nylon 6-rich stream fed to the depolymerization section [C] is less contaminated with foreign materials, which increases the yield and purity of ε-caprolactam produced in the plant of the present invention configured to carry out the process of the present invention. Other advantages are that the nylon 6-rich stream will require less depolymerization agent in the depolymerization section [C], will generate less waste, and will require less energy. And finally, the nylon 6-rich stream will reduce operating 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.

[0234] 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].

[0235] Optionally, the nylon 6-rich stream is compressed into granules of increased density before being fed into the depolymerization section [C]. This can be achieved, for example, by mechanical compaction or by extruding the molten material by means of a die, followed by cooling and cutting to size. Compressing the nylon 6-rich stream into granules has the advantage of increased bulk density, which reduces the costs of intermediate storage and transportation. In addition to the increased density, granulation also provides other benefits, such as a uniform shape and structure, which facilitates (automatic) feeding into the depolymerization section [C].

[0236] 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 a depolymerization section [C].

[0237] The size and shape of the pellets (also referred to as granules) can be selected within a wide range. In general, the shape of the pellets is cylindrical (derived from the strands cut into pieces). 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, 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.

[0238] Optionally, the nylon 6-rich stream discharged from the separation section [B] is dried before being fed to the depolymerization section [C]. This has the advantage that less or no solvent is introduced in the depolymerization section [C]. The solvent introduced in the depolymerization section [C] can have a negative impact on 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 the depolymerization section [C] may contain more impurities).

[0239] 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 charged 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 the skilled person.

[0240] Feeding the nylon 6-rich stream to the depolymerization reactor can be achieved by continuously or intermittently dosing the nylon 6-rich stream.

[0241] Depolymerization step e.2)

[0242] In step e.2) of the present invention, the nylon 6-rich stream is depolymerized in depolymerization section [C] to form ε-caprolactam. In step e.3) of the present invention, the ε-caprolactam formed is discharged from the depolymerization section [C] as a stream comprising ε-caprolactam.

[0243] 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 side reactions and impurity reactions of polyamide 6 and ε-caprolactam occur less frequently.

[0244] In general, the rate of formation of ε-caprolactam increases at elevated temperatures. Temperatures below 400°C are preferred because at temperatures above 400°C, side reactions of nylon 6 and impurity reactions occur more frequently, which will lead to the formation of a greater variety of impurities. A portion of these impurities will eventually enter the material stream comprising ε-caprolactam discharged from the depolymerization reactor section [C]. In a preferred embodiment of the invention, the depolymerization of the nylon 6-rich stream is carried out at a temperature in the range of 220°C to 340°C or 240°C to 325°C. This temperature range allows the production of particularly pure ε-caprolactam.

[0245] The pressure in the depolymerization section [C] may 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.

[0246] 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.

[0247] Preferably, the depolymerization will be complete within 0.1 hour to 24 hours, more preferably within 0.5 hour to 6 hours.

[0248] Feeding water in the form of steam to the depolymerization reactor allows obtaining a steam stream comprising ε-caprolactam and water, optionally without further heating. The weight ratio of ε-caprolactam to water in the steam 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 e.2) is carried out in the presence of water, whereby the stream comprising ε-caprolactam is a steam 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 economical and efficient process can be carried out.

[0249] 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.

[0250] During the depolymerization reaction, decomposition products may be formed, which decomposition products include oligomers of ε-caprolactam. In addition, the feed stream originating from the material of the multicomponent material including 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 applied in the pretreatment. Therefore, in the case of using water as solvent, the vapor stream removed from the depolymerization section [C] includes not only water and ε-caprolactam, but also impurities.

[0251] 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 further heat input is required for the depolymerization reaction and for the evaporation of 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 for the depolymerization reaction and for the evaporation of the ε-caprolactam formed is introduced through the wall of the depolymerization reactor.

[0252] 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 stream rich in nylon 6 and optionally solvents, catalysts, further reagents and / or depolymerizing agents. Therefore, without any further measures, there will be an accumulation of material (usually referred to as 'residual material') in the depolymerization section [C]. Preferably, another 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 include impurities present in the stream rich in nylon 6, undepolymerized nylon 6, unevaporated ε-caprolactam, catalysts and compounds formed under depolymerization conditions, such as monoammonium phosphate, diammonium phosphate and / or triammonium phosphate in the case where phosphoric acid is used as a 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 intermittently or continuously discharged from the depolymerization section [C] comprises a weight fraction of monoammonium phosphate, diammonium phosphate and / or triammonium phosphate of 0.01 to 50 wt.%, preferably 0.1 to 25 wt.%, more preferably 0.5 to 10 wt.%, most preferably 0.5 to 5 wt.%.

[0253] The depolymerization of the nylon 6-rich stream in the presence of steam can be carried out in the presence of an additional depolymerizing agent such as ammonia. The concentration of ammonia in the depolymerization section [C] can vary. Thus, in the presence of ammonia in the depolymerization section [C], the vapor stream removed from the depolymerization section [C] comprises not only ε-caprolactam and impurities, but also ammonia.

[0254] Most preferably, the depolymerization is carried out in the presence of a catalyst. Preferably, the catalyst used is a (Lewis or Bronsted) acid or base. The acid catalyst may be specifically 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 above acids, Al2O3 and SiO2 and combinations thereof. The base catalyst may, 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 catalyst for the depolymerization, in another embodiment p-toluenesulfonic acid is used.

[0255] 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 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.

[0256] The advantage of using a catalyst (especially orthophosphoric acid) is that the depolymerization reaction already starts at a relatively low temperature and can be carried out under atmospheric conditions. The suitable concentration of the catalyst for depolymerizing nylon 6 into ε-caprolactam is known to the technician 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.

[0257] The depolymerization of nylon 6 can be carried out in batch mode, semi-continuous mode or continuous mode, all of which are known to the skilled person. The terms "batch mode", "semi-continuous mode" and "continuous mode" as used herein 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 materials are discharged from the depolymerization reactor.

[0258] In a preferred embodiment, the depolymerization of nylon 6 is carried out in a batch mode. In the batch mode, the raw materials, i.e., the materials derived from the multi-component material including nylon 6 and the optional catalyst are initially charged into the depolymerization reactor. Subsequently, superheated steam is charged into the depolymerization reactor, and ε-caprolactam is discharged from the depolymerization reactor as a steam stream including ε-caprolactam and water. Next, the charging of superheated steam into the depolymerization reactor is interrupted. After optionally removing residual materials from the depolymerization reactor, a new cycle is started by charging the raw materials (and optional catalyst) into the depolymerization reactor. In a preferred embodiment, the residual materials are not removed between each cycle.

[0259] In a particularly advantageous embodiment, the depolymerization of nylon 6 is carried out in a continuous mode. In the continuous mode, a feedstock containing nylon 6 (and optionally a catalyst) is continuously charged into a depolymerization reactor. At the same time, superheated steam is continuously charged into the depolymerization reactor, and ε-caprolactam is continuously discharged from the depolymerization reactor as a steam stream comprising ε-caprolactam and water. Optionally, the catalyst is continuously or intermittently charged into the depolymerization reactor. In addition, residual material is continuously discharged from the depolymerization reactor. Preferably, the nylon 6-rich stream is charged in the form of a melt. Preferably, the catalyst is charged in the form of a melt, a slurry or a solution.

[0260] In another preferred embodiment, the depolymerization of nylon 6 is carried out in a semi-continuous mode. In the semi-continuous mode, the feedstock containing nylon 6 (and optional catalyst) is intermittently charged into the depolymerization reactor, while superheated steam is continuously charged into the depolymerization reactor, and ε-caprolactam is continuously discharged from the depolymerization reactor as a steam stream comprising ε-caprolactam and water. In the semi-continuous mode of nylon 6 depolymerization, the residual material is intermittently discharged from the depolymerization reactor.

[0261] Discharge step e.3)

[0262] In step e.3) of the invention, the ε-caprolactam formed is discharged from the depolymerization section [C] in a stream comprising ε-caprolactam.

[0263] Recycling step e.4)

[0264] In the recovery section [D], ε-caprolactam is recovered from the stream comprising ε-caprolactam discharged from the depolymerization section [C]. The stream comprises ε-caprolactam and impurities. Preferably, the recovery is carried out by (partial) condensation of the stream comprising ε-caprolactam. The recovered ε-caprolactam is discharged from the recovery section [D] as crude ε-caprolactam.

[0265] 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. The phase rich in ε-caprolactam also comprises impurities.

[0266] Preferably, in case 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 may be charged in the form of liquid or steam. Preferably, the water is charged in the form of steam. ε-caprolactam may be separated from the stream comprising ε-caprolactam discharged from the depolymerization section [C] by conveying this vapor or gaseous stream from the depolymerization reactor (preferably the top) to a (preferably partial) condenser to obtain a condensate containing ε-caprolactam. Preferably, ε-caprolactam is separated from the remaining components of the vapor stream by conveying the product stream from the depolymerization reactor (preferably the top) to a distillation column, from which a water-rich phase as top product and an ε-caprolactam-rich phase as bottom product are obtained.

[0267] 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 originating from the nylon 6-rich stream. The crude ε-caprolactam recovered in step e.4) 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 may be defined as being lower in purity, i.e. containing more impurities, than the purified ε-caprolactam obtained as the product of the purification step e.5) of the process of the present invention.

[0268] 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.

[0269] Purification step e.5)

[0270] In step e.5), the crude ε-caprolactam obtained in the recovery section [D] is purified in a purification section [E] to obtain high purity ε-caprolactam, wherein the purification comprises one or more techniques selected from the group consisting of: filtration, adsorption, extraction, washing, stripping, solvent exchange distillation, oxidation, hydrogenation, distillation and crystallization.

[0271] 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 the further purification process.

[0272] Preferably, purified ε-caprolactam is obtained by purifying crude ε-caprolactam obtained in recovery section [D] by crystallizing ε-caprolactam from a solution comprising ε-caprolactam and impurities at a temperature of 10 to 95°C in purification section [E].

[0273] In a preferred embodiment, the process of the present invention is carried out in a plant, wherein the plant comprises a purification section [E], wherein the purification comprises a step of extracting the crude ε-caprolactam with an organic solvent, thereby obtaining an aqueous phase and an organic phase, and wherein the organic phase comprises the organic solvent, ε-caprolactam and impurities.

[0274] High-purity ε-caprolactam is obtained from crude ε-caprolactam by first extracting the crude ε-caprolactam with an organic solvent in step e.5), 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-C10 Cycloaliphatic alcohol. Optionally, the organic solvent used for extracting the crude ε-caprolactam is preferably a mixed extractant, i.e. it may consist of one or more organic solvents and optionally an additional diluent. Preferably, the one or more organic solvents are independently selected from aromatic hydrocarbons, halogenated hydrocarbons and / or C4-C 10 Aliphatic or cycloaliphatic alcohols, and C5-C8 alkanes or C5-C8 cycloalkanes. Particularly good purification results can be obtained if the organic solvent used for extracting 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 for extracting 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 for extracting 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.

[0275] In another embodiment, the extraction with the organic solvent in step e.5) 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, the organic phase comprising the organic solvent, ε-caprolactam and impurities.

[0276] In another preferred embodiment, the purification further comprises a solvent switching step, in which the organic solvent from the organic phase comprising the organic solvent, ε-caprolactam and impurities obtained in the step of extracting the crude ε-caprolactam with the organic solvent is at least partially replaced with water, thereby obtaining an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower than or higher than ε-caprolactam, and wherein the solvent switching step is selected from a process based on back extraction with water and a process based on solvent exchange distillation, in which the organic solvent is distilled off and water is charged.

[0277] Optionally, the organic phase comprising the organic solvent, ε-caprolactam and impurities is washed with water or an alkaline aqueous solution before entering the solvent switching step. 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 wt.% to 2.0 wt.% of sodium hydroxide or potassium hydroxide.

[0278] The skilled person can determine by routine experiments the amount of water or alkaline aqueous solution required for efficient washing of the organic phase comprising organic solvent, ε-caprolactam and impurities. 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.

[0279] In another preferred embodiment, washing the organic phase comprising organic solvent, ε-caprolactam and impurities with water or an alkaline aqueous solution is carried out in a countercurrently operated washing column, whereby the organic phase comprising 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. The washing produces a washed organic phase comprising organic solvent, ε-caprolactam and impurities and a phase comprising the residue. The phase comprising the residue then contains water, impurities and ε-caprolactam.

[0280] In a preferred embodiment, the optionally washed organic phase comprising 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. Although the amount of water used to recover 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 of the ε-caprolactam recovered.

[0281] In another preferred embodiment, the extraction with water is carried out in an extraction column operated in countercurrent, the ε-caprolactam-containing phase to be purified is introduced at the bottom of the column, and water is introduced at the top of the column. The extraction produces an ε-caprolactam-water phase and a solvent phase comprising impurities. Typically, the solvent phase comprising impurities is reused, optionally after purification (preferably by distillation).

[0282] The ε-caprolactam-water phase, optionally stripped and / or distilled to remove residual solvents, is concentrated by evaporating water so that a concentrated ε-caprolactam-water phase is obtained. The ε-caprolactam content of the concentrated ε-caprolactam-water phase is generally between 60 and 99.9 wt.% relative to the entire phase.

[0283] In another preferred embodiment, the organic solvent is evaporated from an organic phase comprising the organic solvent, ε-caprolactam and impurities which is optionally washed rather than extracted with water. Any suitable evaporation vessel, such as a tower, can be used. Preferably, the evaporation is carried out in the presence of water. More preferably, the evaporation is carried out in the form of azeotropic distillation, in which case the organic solvent evaporates in the form of an azeotropic mixture. The evaporation produces an ε-caprolactam material. Preferably, the ε-caprolactam material is an ε-caprolactam aqueous phase. The ε-caprolactam content of the ε-caprolactam aqueous phase is typically between 40 wt.% and 99.9 wt.% relative to the entire phase.

[0284] 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. Most preferably, potassium permanganate is used as oxidizing agent.

[0285] Preferably, the oxidant is added to the ε-caprolactam-water phase in the form of a solid, a slurry or an aqueous solution, so that a dilute aqueous solution is obtained during the purification by oxidation. The skilled person can determine the amount of oxidant required for efficient oxidation of the ε-caprolactam-water phase by routine experiments. The exact amount of oxidant depends to a great extent on the composition of the polyamide 6-rich stream fed to the depolymerization section in the process according to the invention. Preferably, the amount of oxidant is between 0.01 and 5% by weight relative to the amount of ε-caprolactam dissolved in the aqueous phase to be oxidized.

[0286] 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, 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.

[0287] The length of time for oxidation with the oxidizing agent may vary. Preferably, in the process of the present invention, 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.

[0288] The concentration of ε-caprolactam in the ε-caprolactam-water phase used for oxidation with the oxidant can vary. Preferably, the aqueous solution used for oxidation comprises a weight ratio of ε-caprolactam to water of 5:1 to 1:5, more preferably 3:1 to 1:3, and most preferably 2:1 to 1:2. Optionally, the weight ratio of ε-caprolactam to water is adjusted before the oxidant is added to the aqueous phase. Preferably, the weight ratio of ε-caprolactam to water is adjusted by adding water or by removing water.

[0289] In the case of using potassium permanganate and / or sodium permanganate as oxidants, solid manganese (IV) oxide (MnO2) particles are formed as reaction products. The best solid-liquid filtration procedure for efficiently removing the solid manganese (IV) oxide particles from the aqueous phase after oxidation can be determined by the skilled person through routine experimentation. In this regard, it is common practice to use filter aids such as activated carbon or diatomaceous earth particles to improve the filtration procedure.

[0290] In a preferred embodiment of the process of the invention, the purification section [E] comprises a hydrogenation step in which the ε-caprolactam aqueous phase is hydrogenated, and if the ε-caprolactam aqueous phase is hydrogenated, it is preferably carried out in the presence of a hydrogenation catalyst known per se. The hydrogenation catalyst may 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 a nickel-containing catalyst is used. Suitable nickel catalysts generally have a nickel content of 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 generally between 1 and 20 wt.%. If a palladium-containing heterogeneous catalyst is used, the palladium content will generally be between 0.01 and 10 wt.%.

[0291] 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.

[0292] 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.

[0293] The hydrogenation temperature is typically between 20° C. and 160° C. The hydrogenation pressure is typically between 0.1 and 15 MPa.

[0294] The hydrogenation of the water-ε-caprolactam mixture is to hydrogenate the unsaturated compounds present in the impure ε-caprolactam. The presence of these unsaturated compounds is disadvantageous because they impair the physical and mechanical properties of nylon 6 prepared by polymerizing ε-caprolactam. The saturated compounds formed by hydrogenation do not have an adverse effect on these physical and mechanical properties of nylon 6, and these compounds are more easily removed in, for example, a distillation step and / or a crystallization step after the hydrogenation step.

[0295] The hydrogenation can be carried out as described, for example, in EP635487.

[0296] In a preferred embodiment of the process of the present invention, the purification section [E] comprises a distillation step, wherein low boiling organic impurities (with a boiling point lower than ε-caprolactam) and / or high boiling organic impurities (with a boiling point higher than ε-caprolactam) are separated from ε-caprolactam. Preferably, the distillation step is carried out under reduced pressure. In one embodiment, the distillation is carried out at a pressure lower than 350 kPa, preferably lower than 50 kPa, more preferably lower than 20 kPa and most preferably lower 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.

[0297] In a preferred embodiment, an alkali metal hydroxide, preferably NaOH, is added to the phase comprising ε-caprolactam before distilling off low-boiling organic impurities and / or high-boiling organic impurities. 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 alkali metal hydroxides, especially NaOH, is particularly effective in distilling off impurities having a boiling point lower and higher than that of ε-caprolactam.

[0298] In a preferred embodiment of the process of the present invention, the purification section [E] comprises a crystallization step, in which a solution comprising ε-caprolactam and impurities is crystallized to obtain purified ε-caprolactam. Preferably, the crystallization is carried out at a temperature in the range of 10°C to 95°C, more preferably at a temperature in the range of 20°C to 85°C.

[0299] Preferably, the solution comprising ε-caprolactam and impurities which is crystallized in step e.5) is the crude ε-caprolactam obtained in the recovery section [D].

[0300] More preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step e.5) is an organic phase comprising an organic solvent, ε-caprolactam and impurities obtained by extracting crude ε-caprolactam with an organic solvent, said organic phase being optionally washed with water or with an alkaline aqueous solution.

[0301] Even more preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step e.5) is an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than ε-caprolactam obtained by solvent switching.

[0302] Most preferably, the solution comprising ε-caprolactam and impurities from which purified ε-caprolactam is obtained by crystallization in step e.5) is a phase comprising ε-caprolactam and impurities obtained by distillation under vacuum conditions.

[0303] Preferably, the ε-caprolactam crystallization process in step e.5) comprises the following steps:

[0304] 1. Feeding a solution comprising ε-caprolactam and impurities into a crystallizer;

[0305] 2. setting conditions in the crystallizer so that ε-caprolactam crystals and mother liquor are formed;

[0306] 3. Separating ε-caprolactam crystals and mother liquor;

[0307] 4. Recirculate the mother liquor.

[0308] Crystallization can be applied to the production of ε-caprolactam. It is mainly 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 e.5) is carried out by solution crystallization or melt crystallization.

[0309] 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 in 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 in 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. Crystallization purified ε-caprolactam is recovered from a slurry preferably ranging from 5 to 75 wt.%, more preferably ranging from 10 to 70 wt.%, most preferably ranging from 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 in a wide range, preferably the amount of solvent ranges from 5 to 95 wt.%, more preferably 10 to 90 wt.%, most preferably 30 to 70 wt.%. Preferably, the crystallization temperature ranges from 20°C to 70°C, more preferably from 30°C to 65°C. Crystallized purified ε-caprolactam is recovered from a slurry having 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), and mixtures of these solvents. Cyclohexane is preferred.

[0310] 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 is evaporated or by cooling crystallization in which cooling is obtained 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 cleaning solvent. Optionally, the crystallization-separation sequence is repeated several times. The product is obtained in the form of crystals.

[0311] 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.%, 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 a melt of pure compound material. 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.

[0312] Preferably, the solvent is present in the mixture in the crystallizer, but crystallization can also be carried out without 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-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). Preferably water and aromatic hydrocarbons are used as solvents because these solvents produce large crystals. As solvent, water is most preferred. The solvent will serve as a freezing point depressant for the melt in the crystallizer.

[0313] In general, melt crystallization requires less energy than solution crystallization, however, it can be more challenging to operate on an industrial scale.

[0314] Melt crystallization used herein specifically refers to layer melt crystallization or suspension melt crystallization. The characteristics of these two types of melt crystallization technology methods are that (1) a crystal layer is formed on the heat exchanger wall (layer melt crystallization) and (2) crystals grown in a suspension (suspension melt crystallization). In general, the operation of the method for the crystal layer grown on the heat exchanger wall is called layer melt crystallization. First, the melt is loaded into a crystallizer, and then a crystal layer is grown on the cooled heat exchanger surface, followed by discharging the remaining melt containing impurities discharged from the growing crystals 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 the 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 the ProABD method of BEFS Prokem and the Sulzer Chemtech method.

[0315] 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.

[0316] In general, 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. In general, the melt is pumped through the tube, and the crystal grows inside the tube while the cooling medium flows outside the tube. 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 the stagnant mode, the crystal growth rate in the 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 crystal or trapped in the crystal. Finally, the crystal is completely melted and discharged or mechanically removed.

[0317] 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 below its saturation temperature, and the crystal begins 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 obtained crystal and mother liquor is separated by filtration. Optionally, after crystallization, the mixture of the obtained crystal and mother liquor of the desired compound is loaded into a so-called washing tower. In the washing tower, the mother liquor is filtered or discharged from the crystal, and the crystal is then usually washed with a purified compound material.

[0318] After the ε-caprolactam crystallization step, a mother liquor is obtained which includes 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. In general, 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 it by, for example, recycling the obtained mother liquor (or a portion thereof) 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.

[0319] 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 the skilled person. The nylon 6 can then be used in all known materials, including engineering materials, fibers and films. The nylon 6 produced from the material including nylon 6 and spandex is particularly suitable for high speed spinning applications, including garments containing spandex.

[0320] factory

[0321] The present invention also provides a plant configured to implement the above method of the present invention, i.e. a chemical plant, the plant comprising a separation section [B]. The separation section [B] comprises the following four sections: a dissolution section [α], a washing section [β], a precipitation section [γ] and a solvent distillation section [δ]. All plant features specifically described in conjunction with the above method are also applicable to the plant of the present invention described below, and vice versa. Therefore, the plant is suitable for implementing the method of the present invention, and it should be understood that the content that has been described in conjunction with the method of the present invention is equally applicable to the plant embodiment.

[0322] The plant may be a laboratory setting as in the examples. Preferably, however, the plant is an industrial scale plant. "Industrial scale" means that the ε-caprolactam production capacity (i.e. the amount of ε-caprolactam that can be produced in principle) of the plant, if it were operating, is at least 500 tonnes / year.

[0323] The plant of the present invention is suitable for producing spandex and nylon 6 from a material comprising nylon 6 and spandex, and comprises at least a separation section [B]. The separation section [B] comprises 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 present invention.

[0324] The dissolving section [α] comprises one or more dissolving units operating in series and / or in parallel, and one or more separating units operating in series and / or in parallel. The optionally cleaned and / or crushed fragments of the material comprising nylon 6 and spandex are fed to the dissolving unit in the form of a solid or a melt, preferably a solid. The optionally cleaned and / or crushed fragments of the material comprising nylon 6 and spandex are optionally dried before being fed to the dissolving section [α]. The dissolving unit is equipped with an inlet for charging the separated organic solvent and fresh organic solvent. The dissolving unit is equipped with one or more outlets for discharging the mixture obtained in the dissolving unit. The mixture comprises undissolved nylon 6 and the organic solvent in which spandex is dissolved. Preferably, the dissolving unit is closed. This has the advantage of reducing the emission of organic solvent to the environment. Preferably, the dissolving unit is equipped with means for controlling the temperature in the unit (e.g., steam coils, steam tracing, electric tracing). Optionally, the temperature of the separated organic solvent and the fresh organic solvent is adjusted (eg in a heat exchanger) before charging into the dissolution section [α].

[0325] Good contact between the organic solvent and the materials including nylon 6 and spandex 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, in turn, can be achieved, for example, by stirring with a combination of rotating paddles and static fins.

[0326] 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.

[0327] In the separation unit, the mixture discharged from the dissolution unit is separated into a spandex-rich stream comprising organic solvent and dissolved spandex and a stream comprising undissolved nylon 6. The spandex-rich stream comprising organic solvent and dissolved spandex is discharged through a discharge line and charged to a precipitation section [γ]. The stream comprising undissolved nylon 6 is discharged through a discharge line and charged 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].

[0328] 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.

[0329] Preferably, the dissolution unit and the separation unit are combined in one piece of equipment. This allows for process intensification.

[0330] The washing section [β] comprises a device for washing a stream comprising undissolved nylon 6 with a third solvent to obtain a stream rich in nylon 6 and a mixture comprising an organic solvent and a third solvent. The purpose of the washing section [β] is to remove the organic solvent to a large extent. Optionally, the 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 the washing section [β] and charged to the solvent distillation section [δ]. In this context, "charging to the 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 the washing section [β] is completely or partially charged to the precipitation section [γ] before being charged to the solvent distillation section [δ].

[0331] Optionally, after drying, a nylon 6-rich stream is discharged from the washing section [β] and fed to the depolymerization section [C].

[0332] Good contact between the third solvent and the nylon 6-rich stream is essential for efficient operation. Such 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.

[0333] The distillation section [δ] comprises one or more distillation columns operated in series and / or in parallel. The distillation columns can be operated in batch, semi-continuous or continuous mode. The choice between these operating modes depends largely on the scale of operation. In general, 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.

[0334] The exact layout of the distillation section [δ] also depends on the nature of the organic solvent, the second solvent and the third solvent.

[0335] The mixture including the organic solvent and the second solvent from which the precipitated spandex elastic fiber has been recovered and the mixture including the organic solvent and the third solvent discharged from the washing section [β] are charged into the distillation section [δ]. The separated organic solvent is discharged from the distillation section [δ] and charged into the dissolving section [α]. The second solvent and the third solvent are discharged from the distillation section [δ] and optionally charged into 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, the 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 N,N-dimethylacetamide (DMAc).

[0336] Furthermore, the plant of the present invention comprises, adjacent to the separation section [B], an optional pretreatment section [A], an optional depolymerization section [C], an optional recovery section [D] and an optional purification section [E], which are configured to carry out the above-described method of the present invention.

[0337] Preferably, the plant of the present invention comprises, adjacent to the separation section [B], a pretreatment section [A], a depolymerization section [C], a recovery section [D] and a purification section [E], said sections being configured to carry out the process of the present invention as described above. The plant of the present invention is suitable for producing spandex and purified ε-caprolactam from materials comprising nylon 6 and spandex.

[0338] In addition, the plant of the present invention may comprise a pretreatment section [A] which may comprise a mechanical size reduction section [λ] for breaking the material comprising nylon 6 and spandex into pieces and / or a cleaning section [ω] for washing the material comprising nylon 6 and spandex. Cleaning comprises washing the material comprising nylon 6 and spandex and separating foreign materials from said material. Separation of foreign materials may be performed manually (hand picking) and mechanically (e.g. density separation and magnetic separation). Manual and mechanical devices, such as brushes may assist washing in the cleaning section. Washing is preferably effected 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 comprises equipment for mechanically breaking the material comprising nylon 6 and spandex into pieces. Non-limiting examples of such breaking equipment are cutters, punches, shredders, mills, grinders or chippers.

[0339] In addition, the plant of the present invention may include a depolymerization section [C] comprising 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 a melt, preferably a melt. This feeding can be achieved by using an extruder, a gear pump or other means known in the art.

[0340] During production, the depolymerization reactor is at least partially filled with feedstock containing nylon 6, residual material, ε-caprolactam (and optionally a catalyst). The depolymerization reactor may have any desired form. Preferred reactor types are stirred and unstirred bubble column reactors, stirred reactors and extruder type reactors.

[0341] 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.

[0342] Preferably, the depolymerization reactor must be equipped with facilities for feeding a nylon 6-rich stream and a superheated steam stream and optionally a catalyst. Good contact between the steam and the reactor contents is essential for efficient operation. Such contact can be achieved by various means known to the skilled person. As an example, multiple inlets can be used, such as using a steam distributor to spray steam through the material. Even further improved contact can be achieved by including mechanical agitation in the reactor, such as using a combination of rotating paddles and static fins.

[0343] Preferably, depolymerization will be complete within 0.5 to 6 hours.

[0344] If high-temperature superheated steam is not available at the production location, superheated steam must be produced intentionally by superheating the available steam in the boiler in a so-called superheater.

[0345] In addition, the plant according to the invention may comprise a recovery section [D] which may comprise one or more (preferably partial) condensers into which a stream comprising ε-caprolactam is charged in the form of a vapour 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.

[0346] In addition, the plant of the present invention may comprise a purification section [E], which may comprise one or more extraction devices, one or more solvent switching devices, an oxidation section, a hydrogenation section, one or more distillation devices and a crystallization section, crude ε-caprolactam being charged into said device or said section and high-purity ε-caprolactam being discharged from said device or said section.

[0347] The crude ε-caprolactam and the organic solvent are charged into the extraction device, and the organic phase including the organic solvent, ε-caprolactam and impurities and the aqueous phase including 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 disk contactors (RDC), pulse towers, sieve plate (static) towers, random packing (static) towers, and structured packing (SMVP) (static) towers.

[0348] 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 for the method based on stripping is selected from a mixer-settler extractor, an extraction column, a centrifugal extractor and a combination thereof. Preferably, the device for stripping is a static or stirred extraction column, such as tower, towers, rotating disk contactors (RDC), pulse towers, sieve plate (static) towers, random packing (static) towers, and structured packing (static) towers.

[0349] The solvent switching device for the process based on solvent exchange distillation is selected from a sieve plate 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 device for reflux. The distillation column can be operated at atmospheric pressure, subatmospheric pressure or superatmospheric pressure. Preferably, water is charged to the upper part of the distillation column, and the aqueous phase comprising water, ε-caprolactam and impurities with a boiling point lower or higher than ε-caprolactam is discharged from the lower part of the distillation column.

[0350] The oxidation section optionally present comprises one or more oxidation reactors operated in series and / or in parallel. The oxidant and the ε-caprolactam-water phase comprising water, ε-caprolactam and impurities are charged into the oxidation section. Typically, the oxidant is charged in the form of a solid, a slurry or an aqueous solution. In the case of applying potassium permanganate or sodium permanganate as the oxidant, the oxidation section also comprises a filtration section. The oxidation reactor may have any desired form. Preferred reactor types are stirred and non-stirred reactors and packed tower reactors. The oxidation reactor must be equipped with facilities for feeding an aqueous phase comprising water, ε-caprolactam and impurities having a boiling point lower or higher than that of ε-caprolactam and an oxidant. In addition, the oxidation reactor must be equipped with facilities for discharging the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities and optionally formed solid manganese oxide (IV) (MnO2) particles. Preferably, the oxidation is carried out at a temperature and atmospheric conditions ranging from 20°C to 85°C.

[0351] The solid manganese (IV) oxide (MnO2) particles which are optionally present can be removed by sedimentation or by solid-liquid filtration, preferably by solid-liquid filtration. It is common practice to improve the filtration procedure using filter aids such as activated carbon particles or diatomaceous earth. Filtration systems suitable for separating solid manganese (IV) oxide particles are known to the skilled person. Into this filtration system is loaded a suspension of an oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities and solid manganese (IV) oxide particles, 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.

[0352] 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.

[0353] 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 and a heterogeneous hydrogenation catalyst that is completely or partially saturated with hydrogen. The dissolution of hydrogen in the water-ε-caprolactam mixture can be implemented by any method known to those skilled in the art. Preferably, the mixture is contacted with hydrogen in an absorber or a mixer, wherein a constant hydrogen pressure is maintained. Close contact between hydrogen and the mixture will ensure that hydrogen is dissolved in the mixture. This process is preferably implemented continuously. Subsequently, the mixture containing hydrogen is contacted with a hydrogenation catalyst, for example in a separate reactor.

[0354] 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 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 filtering. Preferably, the catalyst comprises palladium or nickel.

[0355] Alternatively, the hydrogenation can be carried out in a fixed bed reactor, in which 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.

[0356] The hydrogenation temperature is typically between 20° C. and 160° C. The hydrogenation pressure is typically between 0.1 and 15 MPa.

[0357] The distillation apparatus is charged with an ε-caprolactam-water phase comprising water, ε-caprolactam and impurities, which is optionally stripped and / or concentrated and / or optionally oxidized and / or hydrogenated, and high-purity ε-caprolactam, water and impurities (i.e. low-boiling organic impurities (with a boiling point lower than ε-caprolactam) and high-boiling organic impurities (with a boiling point higher than ε-caprolactam)) are discharged. The distillation apparatus is selected from a sieve plate distillation column, a random packing distillation column, a structured packing distillation column and a horizontal and vertical (descending and ascending) film evaporator. Preferably, the distillation column is equipped with a reboiler, a condenser and a device for reflux. The distillation apparatus can be operated at atmospheric pressure, subatmospheric pressure or superatmospheric pressure, preferably at subatmospheric pressure.

[0358] 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 out from water as a top product, and producing low-boiling impurities and high-boiling impurities containing ε-caprolactam as a bottom product. In a second step, separating out low-boiling impurities as a top product, and obtaining high-boiling impurities containing ε-caprolactam as a bottom product. In a third step, separating out high-purity ε-caprolactam as a top product, and producing a distillation residue comprising ε-caprolactam and high-boiling impurities as a bottom product. Optionally, the first step and the second step are combined.

[0359] Preferably, an alkali metal hydroxide, preferably NaOH, is added to the oxidized ε-caprolactam-water phase comprising water, ε-caprolactam and impurities before distilling off water and impurities. 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. This allows particularly efficient distillation removal of impurities having lower and higher boiling points than ε-caprolactam in the subsequent distillation.

[0360] In the purification step, distillation can be performed before, after, or before and after crystallization. Preferably, distillation is performed at least before crystallization.

[0361] Optionally, the distillation in the process of the present invention is a step wherein impurities having a boiling point lower or higher than ε-caprolactam are removed by distillation under vacuum conditions after crystallization has been carried out, thereby obtaining a phase comprising ε-caprolactam and impurities.

[0362] Therefore, according to a particularly advantageous embodiment of the invention, after the crystallization, the purification further comprises a step of distilling under vacuum conditions to remove impurities having a boiling point lower or higher than ε-caprolactam.

[0363] Optionally, impurities having a boiling point lower or higher than that of ε-caprolactam are removed by distillation under vacuum conditions before and after crystallization, thereby obtaining a phase comprising ε-caprolactam and impurities.

[0364] Therefore, according to a particularly advantageous embodiment of the invention, the purification step, before and after the crystallization, further comprises a step of distilling under vacuum conditions to remove impurities having a boiling point lower or higher than ε-caprolactam.

[0365] The crystallization section comprises one or more crystallizers operated in series and / or in parallel. In general, the crystallization section also comprises several containers for storing (intermediate) product streams and / or fresh and used washing liquids. The crystallization of ε-caprolactam can be carried out by solution crystallization or melt crystallization as described above.

[0366] In the case of solution crystallization, the ε-caprolactam is recovered by evaporative crystallization in which the solvent evaporates or by cooling crystallization in which cooling is obtained 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, filtering in a filter and / or centrifuging in a centrifuge. Optionally, the crystallizer is equipped with a stirrer and / or one or more baffles.

[0367] Optionally, the resulting crystals are washed, for example, with a cleaning solvent. Optionally, the crystallization-separation sequence is repeated several times. The product is obtained in the form of crystals.

[0368] 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-butyl alcohol), 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 recovered and reused in the crystallization process.

[0369] Solution crystallization is usually carried out at atmospheric pressure, but can also be carried out under reduced or increased pressure conditions.

[0370] The melt crystallization of ε-caprolactam can be achieved by layer melt crystallization, in which a layer of crystals containing ε-caprolactam is formed on the heat exchanger wall, or by suspension melt crystallization, in which crystals containing ε-caprolactam grow in suspension.

[0371] Preferably, the solvent is present in the mixture in the melt crystallizer, but melt 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-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). Preferably water and aromatic hydrocarbons are used as solvents because these solvents produce large crystals. As solvent, water is most preferred. The solvent will serve as a freezing point depressant for the melt in the crystallizer.

[0372] Layer melt crystallization:

[0373] First, the melt is charged into a crystallizer, then a crystal layer is grown on a cooled heat exchanger surface, the remaining melt containing impurities discharged from the growing crystals is subsequently discharged from the crystallizer, and the crystal layer is then melted and the purified product is recovered. The purification efficiency can be further improved by, for example, sweating (also known as partial melting), i.e., gently heating the crystal layer to close to 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 processes based on layer melt crystallization are the ProABD process of BEFS Prokem and the SulzerChemtech process.

[0374] 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 or trapped in the crystals. Finally, the crystals are completely melted and discharged or mechanically removed.

[0375] In general, 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. In general, the melt is pumped through the tube, and the crystal grows inside the tube while the cooling medium flows outside the tube. 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 the stagnant mode, the crystal growth rate in the 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 crystal or trapped in the crystal. Finally, the crystal is completely melted and discharged or mechanically removed.

[0376] Suspension melt crystallization:

[0377] The suspension melt crystallization of ε-caprolactam can be carried out in batches or in a continuous mode. In the case of suspension melt crystallization, the melt is cooled below its saturation temperature, and the ε-caprolactam crystals begin to grow (optionally, after adding nuclei). The growth rate of the crystals 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 obtained crystals and mother liquor is separated by filtration. Optionally, after crystallization, the mixture of the obtained ε-caprolactam crystals and mother liquor is loaded into a so-called washing tower. In the washing tower, the mother liquor is discharged from the ε-caprolactam crystals, and then the ε-caprolactam crystals are optionally washed with purified ε-caprolactam.

[0378] The method of the present invention can be operated in a continuous, semi-continuous or batch mode. Therefore, the plant of the present invention can also be configured to allow one or more of these operating modes. In a preferred embodiment, the plant is configured to operate the method of the present invention in a continuous or semi-continuous manner. However, a discontinuous method is also possible. For example, the plant of the present invention does not need to contain all the sections described herein in one position. Specifically, the pretreatment section [A] can be located at a first position, while the separation section [B], the depolymerization section [C], the recovery section [D] and the purification section [E] are located at a second position. Similarly, the mechanical size reduction section [λ] as part of the pretreatment section [A] can also be located at a first position, while the cleaning section [ω] as part of the pretreatment section [A] can be located at a second position, while the separation section [B], the depolymerization section [C], the recovery section [D] and the purification section [E] are located at a third position. Optionally, the cleaning section [ω] is divided into two or more sections, and the two or more sections are optionally all located at different positions. 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].

[0379] product

[0380] The present invention provides nylon 6 and spandex (in particular polyether polyurethane) obtained by separation of a material comprising nylon 6 and spandex according to the process of the present invention as new products, which meet the specifications of various applications and 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 advantageous feature of the nylon 6 obtained by the process of the present invention is in particular that the product carbon footprint is less than 1 kg CO2 / kg nylon 6. The nylon 6 obtained according to the present invention may also be referred to as "purified nylon 6". "Purified" as used herein means that the nylon 6 is produced from a product comprising nylon 6 and spandex according to the process of the present invention, which makes it obtained in a purified form. In this sense, nylon 6 is obtained and purified from a product comprising nylon 6 and spandex. The nylon 6 content in the purified nylon 6 is at least 85% by weight, more preferably at least 90% by weight, even more preferably at least 95% by weight, and most preferably at least 99% by weight on a dry weight basis of the purified nylon 6.

[0381] The nylon 6 produced by the process of the present invention is also particularly economical and environmentally friendly. This is evident because the carbon footprint of nylon 6 produced by the process of the present invention is much lower than that of conventionally produced nylon 6 (e.g., by Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam and then polymerization).

[0382] 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 the reaction of polyether polyols and diisocyanate monomers).

[0383] The environmental impact of a product is often expressed as the 'product carbon footprint'. The carbon footprint of a product is defined as the total emissions caused by the formation of the product, expressed in tonnes of CO2 equivalent / tonne of product (equivalent to kg CO2 equivalent / kg product). The carbon footprint of a product depends inter alia on raw materials, auxiliary materials, energy consumption, energy sources, production methods and process efficiency. The quantification of the product carbon footprint can be carried out as described in, for example, the European standard EN ISO 14040:2006 ("Environmental management - Life cycle assessment - Principles and framework").

[0384] 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.

[0385] PlasticsEurope, an association of plastics manufacturers, has published an environmental product declaration (EPD) for nylon 6 based on life cycle inventory (LCI) data from the PlasticsEurope eco-profile program entitled "Polyamide 6 (PA6), PlasticsEurope, February 2014, Eco-profiles and Environmental Product Declarations of the European Plastics Manufacturers" (available from https: / / plasticseurope.org / sustainability / circularity / life-cycle-thinking / eco-profiles-set / , evaluated on March 28, 2022). This EPD for nylon 6 was prepared according to the PlasticsEurope Eco-profiles and Environmental Declarations - LCI method and PCR for uncompounded polymer resins and reactive polymer precursors (PCR version 2.0, April 2011). The EPD describes the production of nylon 6 polymer from cradle to gate (from crude oil extraction to pellets or resin at the plant). The primary data source is data collected from European nylon 6 producers. PlasticsEurope reports that the global warming potential of "virgin" nylon 6, obtained by Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam and then polymerizing ε-caprolactam to nylon 6, is 6.7 tonnes CO2 equivalent / tonne nylon 6 (which is equal to 6.7 kg CO2 equivalent / kg nylon 6).

[0386] The product carbon footprint of nylon 6 obtained according to the process of the present invention is much lower than the product carbon footprint of nylon 6 produced by de novo synthesis or "virgin" nylon 6. The product carbon footprint of nylon 6 obtained in the process of the present invention is less than 2 kg, more preferably less than 1.5 kg CO2, and most preferably equal to or less than 1.0 kg CO2 equivalent / kg nylon 6.

[0387] 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.

[0388] The process of the 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 economically friendly 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 invention meets one or more of the following specifications, wherein the parameters and measurement methods are defined as in the Examples section below:

[0389] PAN: Maximum 5

[0390] E290: Maximum value 0.05

[0391] VB: Maximum value 0.5mmol / kg

[0392] Alkalinity: Maximum value 0.1mmol / kg

[0393] Acidity: Maximum value 0.1mmol / kg.

[0394] The ε-caprolactam obtainable from the depolymerization of purified nylon 6 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).

[0395] 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 / tonne of ε-caprolactam (which is equivalent to 7.5 kg CO2 equivalent / kg ε-caprolactam). In the case involving natural gas based electricity and steam generation, the potential impact of virgin ε-caprolactam on global warming for the ε-caprolactam production process would drop to 6.4 tonnes CO2 equivalent / tonne ε-caprolactam (which is equivalent to 6.4 kg CO2 equivalent / kg ε-caprolactam).

[0396] The product carbon footprint of the ε-caprolactam obtained according to the process of the present invention is much lower than the product carbon footprint of ε-caprolactam produced by de novo synthesis or "virgin" ε-caprolactam. The product carbon footprint of the ε-caprolactam obtained in the process of the present invention is less than 5 kg, more preferably less than 4 kg CO2, and most preferably equal to or less than 3.0 kg CO2 equivalent / kg ε-caprolactam.

[0397] The product carbon footprint of the spandex obtained according to the process of the present invention is much lower than the product carbon footprint of de novo synthesized or "virgin" spandex. The product carbon footprint of the spandex 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 / kg spandex.

[0398] The product carbon footprint of the polyether polyurethane obtained according to the method of the present invention is much lower than the product carbon footprint of de novo synthesized or "virgin" polyether polyurethane. The product carbon footprint of the polyether polyurethane obtained according to the method 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 / kg polyether polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0399] In the following, the present invention is described with reference to the accompanying drawings, which depict certain embodiments of the present invention. However, the present invention is defined in the claims and as generally described herein. It should not be limited to the embodiments shown in the following drawings for illustrative purposes.

[0400] Figure 1 An embodiment of a separation section [B] is shown, wherein a material comprising nylon 6 and spandex is separated to ultimately obtain a stream comprising undissolved nylon 6 and precipitated spandex. The embodiment consists of a dissolution section [α] and a precipitation section [γ].

[0401] FIG2 shows two embodiments of a separation section [B] in which a material comprising nylon 6 and spandex is separated to obtain a nylon 6-rich stream and recovered spandex. The embodiments consist of a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ].

[0402] Figure 2A An example of a separation section [B] is depicted, wherein an organic solvent is charged to a dissolution section [α], a second solvent is charged to a precipitation section [γ], and a third solvent is charged to a wash section [β].

[0403] Figure 2B An embodiment of a separation section [B] is depicted, wherein DMAc is charged to a dissolution section [α], water is charged to a wash section [β], and a mixture comprising DMAc and water discharged from the wash section [β] is charged to a precipitation section [γ].

[0404] FIG. 3 illustrates two embodiments of a pre-treatment section [A], wherein the material comprising nylon 6 and spandex is cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent and shredded in a mechanical size reduction section [λ] to obtain cleaned and shredded pieces of the material comprising nylon 6 and spandex.

[0405] Figure 3A An embodiment of a pre-treatment section [A] is depicted wherein a material comprising nylon 6 and spandex is first cleaned in a cleaning section [ω] by removing foreign material and washing with a washing solvent and then shredded in a mechanical size reduction section [λ] to obtain pieces of cleaned and shredded material comprising nylon 6 and spandex.

[0406] Figure 3B An embodiment of a pretreatment section [A] is depicted, wherein a material comprising nylon 6 and polyether polyurethane is first shredded 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 cleaned and shredded pieces of material comprising nylon 6 and spandex.

[0407] Figure 4is a schematic diagram of an embodiment of the process of the present invention, wherein a material comprising nylon 6 and spandex is separated to obtain a nylon 6-rich stream and recovered spandex. Thus, the nylon 6-rich stream is further processed into purified ε-caprolactam by depolymerization, recovery and purification. The embodiment consists of: a pretreatment section [A], a separation section [B], a depolymerization section [C], a recovery section [D] and a purification section [E].

[0408] Detailed description with drawings

[0409] Figure 1 An example of a separation section [B] (area surrounded by a dotted line) is shown, in which a material comprising nylon 6 and spandex is separated to obtain a stream comprising undissolved nylon 6 [3] and precipitated spandex [6]. The example consists of a dissolution section [α] and a precipitation section [γ].

[0410] The material [1] comprising nylon 6 and spandex and the organic solvent [2] are charged into the dissolving section [α]. The material [1] comprising nylon 6 and spandex is optionally cleaned and / or crushed before being charged into the dissolving section [α]. Figure 1 The organic solvent [2] is optionally fresh organic solvent, or an organic solvent recovered from a mixture [7] comprising an organic solvent and a second solvent from which the precipitated spandex has been recovered, or a mixture of fresh organic solvent and an organic solvent recovered from a mixture [7] comprising an organic solvent and a second solvent from which the precipitated spandex has been recovered. Figure 1 In the dissolving section [α], the spandex present in the material [1] comprising nylon 6 and spandex is dissolved in the organic solvent [2] to obtain, after separation (e.g., by filtration or centrifugation), a spandex-rich stream [4] comprising the organic solvent and the dissolved spandex and a stream [3] comprising undissolved nylon 6. The two obtained streams [3], [4] are discharged from the dissolving section [α]. Optionally, the stream [3] comprising undissolved nylon 6 is dried before being discharged from the separation section [B]. Figure 1 Optionally, the stream [3] comprising undissolved nylon 6 is densified ( Figure 1 Optionally, the stream [3] comprising undissolved nylon 6 is fed to a nylon 6 mechanical recycling section after being discharged from the separation section [B], in which the stream [3] comprising undissolved nylon 6 is melted and then solidified again ( Figure 1Optionally, the stream [3] comprising undissolved nylon 6 is fed to a nylon 6 chemical recycling section after being discharged from the separation section [B], wherein the stream [3] comprising undissolved nylon 6 or nylon 6 derived therefrom is depolymerized to obtain ε-caprolactam, which is then polymerized to nylon 6 ( Figure 1 not shown).

[0411] The second solvent [5] and the spandex-rich stream [4] comprising the organic solvent and the dissolved spandex are fed to a precipitation section [γ]. In the precipitation section [γ], the second solvent [5] and the spandex-rich stream [4] comprising the organic solvent and the dissolved spandex are mixed such that the spandex is precipitated from the mixture comprising the organic solvent and the second solvent. The precipitated spandex is recovered from the mixture comprising the organic solvent and the second solvent (e.g., by filtration or centrifugation). The recovered precipitated spandex is discharged from the precipitation section [γ] as recovered spandex [6]. Optionally, the recovered spandex [6] is dried ( Figure 1 The mixture comprising the organic solvent and the second solvent from which the precipitated spandex elastic fiber has been recovered is discharged from the precipitation section [γ]. Optionally, the organic solvent is recovered from the mixture comprising the organic solvent and the second solvent [7] from which the precipitated spandex elastic fiber has been recovered ( Figure 1 not shown).

[0412] Figure 2A An embodiment of a separation section [B] (area surrounded by dashed lines) is depicted wherein a material comprising nylon 6 and spandex is separated to obtain a nylon 6-rich stream

[110] and recovered spandex

[107] . The embodiment consists of a dissolution section [α], a wash section [β], a precipitation section [γ], and a solvent distillation section [δ].

[0413] The material

[101] comprising nylon 6 and spandex and the organic solvent

[103] and / or

[102] are charged into the dissolving section [α]. The material

[101] comprising nylon 6 and spandex is optionally cleaned and / or crushed before being charged into the dissolving section [α]. Figure 2AIn the dissolving section [α], the spandex present in the material comprising nylon 6 and spandex is dissolved in the organic solvent to obtain, after separation (e.g., by filtration or centrifugation), a spandex-rich stream

[104] comprising the organic solvent and the dissolved spandex and a stream

[105] comprising undissolved nylon 6. The two obtained streams are discharged from the dissolving section [α] to the precipitation section [γ] and the washing section [β], respectively. The organic solvent is the separated organic solvent

[102] (see below) to which a fresh organic solvent

[103] is optionally added.

[0414] The second solvent

[106] and the spandex-rich stream

[104] comprising the organic solvent and the dissolved spandex are fed to a precipitation section [γ]. In the precipitation section [γ], the second solvent

[106] and the spandex-rich stream

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

[107] . Optionally, the recovered spandex

[107] is dried ( Figure 2A ). A mixture

[108] including an organic solvent and a second solvent from which precipitated spandex has been recovered is discharged from precipitation section [γ] and fed to a solvent distillation section [δ].

[0415] The stream

[105] comprising undissolved nylon 6 and the third solvent

[109] are fed to a washing section [β]. In the washing section [β], the stream

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

[109] to obtain, after separation (e.g., by filtration or centrifugation), a stream

[110] rich in nylon 6 and a mixture

[111] comprising an organic solvent and the third solvent. The mixture

[111] comprising the organic solvent and the third solvent is discharged from the washing section [β] and fed to a solvent distillation section [δ]. 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 separation section [B] ( Figure 2A Optionally, the nylon 6-rich stream

[110] is densified ( Figure 2AOptionally, the nylon 6-rich stream

[110] , after being discharged from the separation section [B], is fed to a nylon 6 mechanical recycling section, in which the nylon 6-rich stream

[110] is melted and then solidified again ( Figure 2A Optionally, the nylon 6-rich stream

[110] , after being discharged from the separation section [B], is fed to a nylon 6 chemical recycling section, in which the nylon 6-rich stream

[110] is depolymerized to obtain ε-caprolactam, which is then polymerized to nylon 6 ( Figure 2A not shown).

[0416] In the solvent distillation section [δ], the mixture

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

[111] comprising the organic solvent and the third solvent from which the precipitated spandex has been recovered are distilled to obtain a separated organic solvent

[102] , a second solvent and a third solvent

[112] , and a residue

[113] . The separated organic solvent

[102] , the second solvent and the third solvent

[112] , and the residue

[113] are discharged from the solvent distillation section [δ]. Optionally, the second solvent and the third solvent are both water, in which case the separated organic solvent

[102] is a dried organic solvent.

[0417] Figure 2B An embodiment of a separation section [B] (area surrounded by dashed lines) is depicted wherein a material comprising nylon 6 and spandex is separated to obtain a nylon 6-rich stream

[210] and recovered spandex

[207] . The embodiment consists of a dissolution section [α], a wash section [β], a precipitation section [γ], and a solvent distillation section [δ].

[0418] The material

[201] comprising nylon 6 and spandex and DMAc (N,N-dimethylacetamide) are charged into the dissolution zone [α]. The material

[201] comprising nylon 6 and spandex is optionally cleaned and / or crushed before charging into the dissolution zone [α]. Figure 2B In the dissolving section [α], the spandex present in the material comprising nylon 6 and spandex is dissolved in DMAc to obtain, after separation (e.g., by filtration or centrifugation), a spandex-rich stream

[204] comprising DMAc and dissolved spandex and a stream

[205] comprising undissolved nylon 6. The two obtained streams are discharged from the dissolving section [α]. The DMAc is the separated DMAc

[202] (see below) to which fresh DMAc

[203] is optionally added.

[0419] A mixture comprising DMAc and water

[211] (see below) and a spandex-rich stream

[204] comprising DMAc and dissolved spandex are fed to a precipitation section [γ]. In precipitation section [γ], the mixture comprising DMAc and water

[211] and the spandex-rich stream

[204] comprising DMAc and dissolved spandex are mixed such that spandex is precipitated from the mixture comprising DMAc and water. The precipitated spandex is recovered from the mixture comprising DMAc and water (e.g., by filtration or centrifugation). The recovered precipitated spandex is discharged from precipitation section [γ] as recovered spandex

[207] . Optionally, the recovered spandex

[207] is dried ( Figure 2B ). A mixture

[208] comprising DMAc and water from which precipitated spandex has been recovered is discharged from precipitation section [γ] and fed to solvent distillation section [δ].

[0420] A stream

[205] comprising undissolved nylon 6 and water

[209] are charged to a washing section [β]. In the washing section [β], the stream

[205] comprising undissolved nylon 6 is washed with water

[209] to obtain, after separation (e.g., by filtration or centrifugation), a stream

[210] rich in nylon 6 and a mixture

[211] comprising DMAc and water. The mixture

[211] comprising DMAc and water is discharged from the washing section [β] and charged to a precipitation section [γ]. A stream

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

[210] rich in nylon 6 is dried after the washing step and before being discharged from the separation section [B] ( Figure 2B Optionally, the nylon 6-rich stream

[210] is densified ( Figure 2B Optionally, the nylon 6-rich stream

[210] , after being discharged from the separation section [B], is fed to a nylon 6 mechanical recycling section, in which the nylon 6-rich stream

[210] is melted and then solidified again ( Figure 2B Optionally, the nylon 6-rich stream

[210] , after being discharged from the separation section [B], is fed to a nylon 6 chemical recycling section, in which the nylon 6-rich stream

[210] is depolymerized to obtain ε-caprolactam, which is then polymerized to nylon 6 ( Figure 2B not shown).

[0421] In the solvent distillation section [δ], the mixture

[208] comprising DMAc and water from which the precipitated spandex elastic fiber has been recovered is distilled to obtain separated DMAc

[202] , water

[212] and residue

[213] . The separated DMAc

[202] , water

[212] and residue

[213] are discharged from the solvent distillation section [δ]. Optionally, the water

[212] obtained in the solvent distillation section [δ] is partially or completely charged to the washing section [β] to partially or completely replace the charging of water

[209] ( Figure 2B Optionally, the water

[212] obtained in the solvent distillation section [δ] is partially or completely charged to the precipitation section [γ] to partially or completely replace the charging of the mixture comprising DMAc and water

[211] , in which case the remaining part of the mixture comprising DMAc and water

[211] is directly charged to the solvent distillation section [δ] ( Figure 2B not shown).

[0422] Figure 3A An embodiment of a pre-treatment section [A] (area surrounded by dashed lines) is depicted, where the material comprising nylon 6 and spandex is first cleaned and then shredded. The embodiment consists of a cleaning section [ω] and a mechanical size reduction section [λ].

[0423] A material comprising nylon 6 and spandex

[31] and a washing solvent

[32] are charged into a cleaning section [ω]. In the cleaning section [ω], the material comprising nylon 6 and spandex

[31] is cleaned by removing foreign material and washing with a washing solvent

[32] , thereby obtaining foreign material and contaminated washing solvent and clean material comprising nylon 6 and spandex. The foreign material and contaminated washing solvent

[33] and clean material comprising nylon 6 and spandex

[34] are discharged from the cleaning section [ω]. The clean material comprising nylon 6 and spandex

[34] is charged into a mechanical size reduction section [λ], where the material is crushed to obtain clean and crushed fragments of the material comprising nylon 6 and spandex

[35] . The clean and crushed fragments of the material comprising nylon 6 and spandex

[35] are discharged from the mechanical size reduction section [λ]. Optionally, the cleaned and shredded nylon 6 and spandex-containing fragments

[35] are densified ( Figure 3A not shown).

[0424] Figure 3BAn embodiment of a pre-treatment section [A] (area surrounded by dashed lines) is depicted, where the material comprising nylon 6 and spandex is first shredded and then cleaned. The embodiment consists of a cleaning section [ω] and a mechanical size reduction section [λ].

[0425] A material comprising nylon 6 and spandex

[41] is fed into a mechanical size reduction section [λ], where the material is crushed to obtain crushed fragments of material comprising nylon 6 and spandex

[42] . The crushed fragments of material comprising nylon 6 and spandex

[42] are discharged from the mechanical size reduction section [λ]. The crushed fragments of material comprising nylon 6 and spandex

[42] and a washing solvent

[43] are fed into a cleaning section [ω]. In the cleaning section [ω], the crushed fragments of material comprising nylon 6 and spandex

[42] are cleaned by removing foreign materials and washing with a washing solvent

[43] , thereby obtaining foreign materials and contaminated washing solvent and cleaned and crushed fragments of material comprising nylon 6 and spandex. Foreign material and contaminated wash solvent

[44] and cleaned and shredded material comprising nylon 6 and spandex

[45] are discharged from the cleaning section [ω]. Optionally, the cleaned and shredded material comprising nylon 6 and spandex

[45] is densified ( Figure 3B not shown).

[0426] Figure 4 is a schematic diagram of the process of the present invention, wherein a material comprising nylon 6 and spandex is separated to obtain a nylon 6-rich stream and recovered spandex. Thus, the nylon 6-rich stream is further processed into purified ε-caprolactam by depolymerization, recovery and purification. The embodiment consists of: a pretreatment section [A], a separation section [B], a depolymerization section [C], a recovery section [D] and a purification section [E].

[0427] The material

[301] including nylon 6 and spandex and the washing solvent

[302] are loaded into the pretreatment section [A]. The pretreatment section [A] includes a cleaning section [ω] and a mechanical size reduction section [λ] ( Figure 4In the pretreatment section [A], the material comprising nylon 6 and spandex

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

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

[303] and pieces of cleaned and shredded material comprising nylon 6 and spandex

[304] . The foreign material and contaminated washing solvent

[303] and pieces of cleaned and shredded material comprising nylon 6 and spandex

[304] are discharged from the pretreatment section [A]. Optionally, the pieces of cleaned and shredded material comprising nylon 6 and spandex

[304] are densified ( Figure 4 not shown).

[0428] In the separation section [B], the cleaned and crushed fragments of the material including nylon 6 and spandex

[304] are separated to obtain a nylon 6-rich stream

[311] discharged from the separation section [B] and recovered spandex

[308] . The nylon 6-rich stream

[311] is fed to the depolymerization section [C]. The separation section [B] includes the following sections: a dissolution section [α], a washing section [β], a precipitation section [γ], and a solvent distillation section [δ] ( Figure 4 not shown).

[0429] Optionally, the nylon 6-rich stream

[311] and / or the recovered spandex

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

[311] is densified prior to being depolymerized to ε-caprolactam in depolymerization section [C]. An organic solvent

[305] is charged to separation section [B] to dissolve the spandex. A second solvent

[306] is charged to separation section [B] to precipitate the dissolved spandex. A third solvent

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

[309] and the residue

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

[0430] 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] and fed to a recovery section [D]. In addition, residual material

[314] is discharged. Optionally, superheated steam

[312] and a catalyst

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

[0431] In the recovery section [D], 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 charged to the purification section [E]. In addition, water ( Figure 4 (not shown) or superheated steam

[312] is fed into the depolymerization section [C] or water is fed into the recovery section [D] ( Figure 4 In the case where the aqueous phase

[316] is discharged from the recovery section [D] (not shown).

[0432] In the purification section [E], the crude ε-caprolactam

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

[319] . Water and impurities

[318] are also discharged from the purification section [E]. The purification section [E] may contain one or more purification techniques such as filtration, adsorption, extraction, washing, stripping, solvent exchange distillation, oxidation, hydrogenation, distillation and crystallization ( Figure 4 not shown).

[0433] Examples

[0434] The following examples are used 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.

[0435] 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:

[0436] PAN: Maximum 5

[0437] E290: 0.05 max.

[0438] VB: Maximum value 0.5mmol / kg

[0439] Alkalinity: Maximum value 0.1mmol / kg

[0440] Acidity: Maximum value 0.1mmol / kg

[0441] The parameters and measurement methods are defined as follows:

[0442] PAN: ISO DIS 8660 - Plastics - Determination of the permanganate index of caprolactam - Spectroscopic method, revision of the first edition of ISO 8660; 1988,

[0443] E290: ISO 7059 - Caprolactam for industrial use - Determination of absorbance at a wavelength of 290 nm,

[0444] Volatile base (VB) ISO 8661 - Caprolactam for industrial use - Determination of volatile base content - Titration after distillation.

[0445] Basicity of ε-caprolactam product: measured by using Tashiro indicator at 0.1wt. / v at 25°C 乙醇 % Methylene blue: 0.1wt. / v 乙醇 Basicity is determined by a 1:2 ratio titration with 0.01N H2SO4 solution (if the solution is alkaline) or 0.01N NaOH solution (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 solution of ε-caprolactam containing Y wt.% ε-caprolactam (as determined by refractive index) is added and the solution is titrated back to a gray color using a 0.01N H2SO4 solution (if the solution is alkaline) or a 0.01N NaOH solution (if the solution is acidic).

[0446] The alkalinity is then given by:

[0447] Alkalinity (mmol / kg ε-caprolactam) = v*t*1000 / (X*Y)

[0448] in:

[0449] v = volume of H2SO4 solution added (ml)

[0450] t = normal concentration of H2SO4 solution (= 0.01N)

[0451] X = sample weight (g)

[0452] Y = concentration of ε-caprolactam (wt.%)

[0453] The acidity is then given by:

[0454] Acidity (mmol / kg ε-caprolactam) = v*t*1000 / (X*Y)

[0455] in:

[0456] v = volume of NaOH solution added (ml)

[0457] t = molar concentration of NaOH solution (=0.01N)

[0458] X = sample weight (g)

[0459] Y = concentration of ε-caprolactam (wt.%)

[0460] Example 1

[0461] Pretreatment and separation of nylon 6 and polyether polyurethane.

[0462] The used nylon 6 waste fabric containing polyether polyurethane (spandex) had a polyether polyurethane content of 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.

[0463] 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. for 1 hour under stirring. 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.

[0464] At a temperature of 65°C, the undissolved material on the Buchner funnel was washed with 325 grams of water to obtain filtrate 5, and the undissolved material was then dried and then weighed. The five filtrates were combined to obtain a precipitate and a clear solution. The precipitate was filtered out and washed with 200 grams of water, and then dried and then weighed. The total weight of the dried precipitate and the dried undissolved material was almost equal to the weight of the starting material. Analysis by differential scanning calorimetry (DSC) revealed that the polyether polyurethane content of the dry precipitate was about 100 wt.% (polyamide 6 was not detected). Based on the DSC analysis, the nylon 6 content of the dried undissolved material was about 100 wt.% (polyether polyurethane was not detected).

[0465] The recycled polyether polyurethane precipitate can be reused in the production of textiles as such or in combination with virgin polyether polyurethane.

[0466] This example shows that polyether polyurethane and nylon 6 can be separated from nylon 6 waste fabric containing polyether polyurethane by selective extraction, precipitation of dissolved polyether polyurethane and washing of 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.%.

[0467] Example 2

[0468] Pretreatment and separation of nylon 6 and polyether polyurethane.

[0469] The used nylon 6 waste fabric containing polyether polyurethane had a polyether polyurethane content of 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 waste fabric containing polyether polyurethane (spandex) was salmon pink.

[0470] The procedure of Example 1 was followed, except that now 254.1 g of nylon 6 waste fabric containing polyether polyurethane was dissolved in 937 g of DMAc and 475 g of DMAc and 350 g of water were used to wash the remaining undissolved material on the Buchner funnel after filtration. The precipitate was filtered out and washed with 200 g of water and then dried. The undissolved material on the Buchner funnel was washed with 1000 g of water, then also dried, and then 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 almost equal to the weight of the starting material.

[0471] Analysis by differential scanning calorimetry (DSC) revealed that the polyether polyurethane content of the dry precipitate was about 100 wt.% (no nylon 6 detected). The nylon 6 content and polyether polyurethane content of the dried undissolved material were about 99 wt.% and less than 1 wt.%, respectively (DSC analysis).

[0472] The recycled polyether polyurethane precipitate can be reused in the production of textiles as such or in combination with virgin polyether polyurethane.

[0473] This example shows that polyether polyurethane and nylon 6 can be separated from nylon 6 waste fabric containing polyether polyurethane by selective extraction, precipitation of dissolved polyether polyurethane and washing of undissolved nylon 6. After drying, the recovered precipitate consists of almost pure polyether polyurethane, and the nylon 6 content of the dried undissolved material is almost 100 wt.%, which is much higher than that of the starting material nylon 6 waste fabric containing polyether polyurethane. 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.

[0474] Example 3

[0475] Depolymerization of nylon 6 and recovery of ε-caprolactam.

[0476] Before the dried undissolved material obtained in Example 1 was charged into the depolymerization reactor, the material was first densified. The dried undissolved material was melted at 237° C. under nitrogen and forced through a perforated metal plate. The obtained strands were cooled to room temperature and cut into pellets. The diameter and length of the obtained pellets were 3 mm and 1 cm, respectively.

[0477] 33.6 g of these nylon 6-containing pellets and 9.5 g of 20 wt.% phosphoric acid were charged into a Premex autoclave. First, the reactor contents were heated under nitrogen, and then superheated steam was continuously injected at a rate of 2.7 g per minute during a reaction period of 120 minutes. The temperature and pressure in the reactor were maintained at 260° C. and 0.11 MPa, respectively. During the reaction, a vapor stream was continuously discharged from the reactor and cooled to about 20° C., thereby obtaining a condensate including ε-caprolactam and water.

[0478] The condensate consisting of 25.7 g of ε-caprolactam (most of the remainder is water) is concentrated by evaporation in a rotary evaporator (rotary evaporator) operated under vacuum (9.5 kPa; water bath temperature is about 65° C.) to an ε-caprolactam concentration of 57.3 wt.%. (This mixture is crude ε-caprolactam, which is the mixture to be purified.)

[0479] The specifications of crude ε-caprolactam are:

[0480] PAN:353

[0481] E290:2.91

[0482] This example shows that crude ε-caprolactam can be obtained in good yield and without operating problems by depolymerization of nylon 6 obtained by extractive separation from nylon 6 waste fabric containing polyether polyurethane.

[0483] Example 4

[0484] Depolymerization of nylon 6 and recovery of ε-caprolactam.

[0485] 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.

[0486] The condensate consisting of 41 g of ε-caprolactam (most of the remainder is water) is concentrated by evaporation in a rotary evaporator (rotary evaporator) operated under vacuum (9.5 kPa; water bath temperature is about 65° C.) to an ε-caprolactam concentration of 63.1 wt.%. (This mixture is crude ε-caprolactam, which is the mixture to be purified.)

[0487] The specifications of crude ε-caprolactam are:

[0488] PAN: 274

[0489] E290: 2.70

[0490] This example shows that crude ε-caprolactam can be obtained in good yield and without operating problems by depolymerization of nylon 6 obtained by extractive separation from nylon 6 waste fabric containing polyether polyurethane.

[0491] Comparative Experiment 1

[0492] Depolymerization of nylon 6 and polyether polyurethane.

[0493] 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.

[0494] 10 minutes after the start of the injection of superheated steam, the experiment had to be stopped because the line for discharging the vapor stream comprising ε-caprolactam and water was clogged with insoluble material.

[0495] This comparative experiment shows that depolymerization of nylon 6 waste fabric containing polyether polyurethane can cause operational problems if the polyether polyurethane is not removed prior to depolymerization.

[0496] Comparative Experiment 2

[0497] Depolymerization of nylon 6 waste fabric containing polyether polyurethane and recovery of ε-caprolactam.

[0498] 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.

[0499] The condensate consisting of 26 g of ε-caprolactam (most of the remainder is water) is concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature is about 65° C.) to an ε-caprolactam concentration of 47.0 wt.%. (This mixture is crude ε-caprolactam, which is the mixture to be purified.)

[0500] The specifications of crude ε-caprolactam are:

[0501] PAN:352

[0502] E290: 3.60

[0503] Observations:

[0504] ●The condensate obtained before concentration does contain an unknown precipitate

[0505] ●After the depolymerization experiment, it was found that the inner wall of the Premex autoclave was fouled

[0506] This comparative experiment again shows that depolymerization of nylon 6 waste fabric containing polyether polyurethane without removing the polyether polyurethane prior to depolymerization can cause operational problems. Another observation is that the ε-caprolactam yield in this comparative experiment is much lower than the yield in Example 3 (pretreated nylon 6 waste fabric containing polyether polyurethane as feed), where the ε-caprolactam yield is defined as the ratio of the weight of ε-caprolactam in the condensate to the weight of nylon 6 in the feed charged to the Premex autoclave.

[0507] Comparative Experiment 3

[0508] Purification by distillation.

[0509] Then, 75 mmol of aqueous sodium hydroxide solution / kg of ε-caprolactam was 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.

[0510] The specifications of distilled ε-caprolactam are:

[0511] PAN: 31

[0512] E290: 3.08

[0513] VB: 2.45mmol / kg

[0514] Alkalinity: 3.13mmol / kg.

[0515] 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.

[0516] Comparative Experiment 4

[0517] Depolymerization of nylon 6 waste fabrics containing polyether polyurethane and recovery of ε-caprolactam by permanganate treatment Purification by treatment and distillation.

[0518] In this comparative experiment, 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.

[0519] The pretreatment and separation procedures of nylon 6 and polyether polyurethane of Example 1 were followed. The recovered polyether polyurethane precipitate can 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.

[0520] 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.

[0521] The ε-caprolactam in the oxidized reaction product was further purified by distillation as described in Comparative Example 3 after adding 75 mmol of aqueous sodium hydroxide solution / kg of ε-caprolactam.

[0522] The specifications of distilled ε-caprolactam are:

[0523] PAN: 3

[0524] E290: 0.12

[0525] VB: 1.45mmol / kg

[0526] Alkalinity: 1.96mmol / kg

[0527] 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 specifications required for the main polymerization applications as quantified above.

[0528] Example 5

[0529] Depolymerization of nylon 6 waste fabrics containing polyether polyurethane and recovery of ε-caprolactam by extraction and stripping Purification by extraction, distillation and crystallization.

[0530] 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.

[0531] The pretreatment and separation procedures of nylon 6 and polyether polyurethane of Example 1 were followed. The recovered polyether polyurethane precipitate can 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.

[0532] 76 grams of crude ε-caprolactam obtained were extracted once with 100 grams of a solvent mixture 4-methyl-2-pentanol (50 wt.%) / cyclohexane (50 wt.%) at 25° C. and nine times with 50 grams of the 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 of about 65° C.) to an ε-caprolactam concentration of about 40 wt.%, and fresh cyclohexane was then added. The ε-caprolactam concentration of the resulting mixture was about 25 wt.%, and the weight ratio of the solvent mixture 4-methyl-2-pentanol / cyclohexane was 50 wt.%:50 wt.%. Subsequently, the concentrated solvent mixture comprising ε-caprolactam was extracted eight times with 50 grams of water at 25° C. The eight resulting ε-caprolactam aqueous phases were combined. The combined aqueous phases were concentrated by evaporation in a rotary evaporator (rotavapor) 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:

[0533] PAN: 108

[0534] E290:1.58

[0535] 75 mmol of an aqueous sodium hydroxide solution / kg of ε-caprolactam was added to the obtained concentrated ε-caprolactam aqueous solution.

[0536] 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 top product, while impurities with a higher boiling point than ε-caprolactam remain in the distillation apparatus as bottom products.

[0537] Distilled water is then added to the distilled ε-caprolactam to obtain a mixture with an ε-caprolactam concentration of 91.4 wt.%. The 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 0.016 grams of seed crystals are added to the mixture. The mixture is then further cooled to 30°C and maintained for 30 minutes. The crystallized ε-caprolactam is recovered by filtration and washed with an 85 wt.% ε-caprolactam aqueous solution. The specifications of the purified ε-caprolactam obtained are:

[0538] PAN: 2

[0539] E290: 0.02

[0540] VB: <0.01mmol / kg

[0541] Alkalinity: 0.03mmol / kg

[0542] From this example 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.

[0543] 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.

[0544] Example 6

[0545] Pretreatment and separation of nylon 6 and polyether polyurethane, depolymerization of nylon 6 and recovery of ε-caprolactam, Purification by extraction, stripping, distillation and crystallization.

[0546] The pretreatment and separation procedures of nylon 6 and polyether polyurethane of Example 1 were followed. The recovered polyether polyurethane precipitate can 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.

[0547] The 36 g of crude ε-caprolactam obtained were extracted once with 68 g of benzene at 25° C. and four times with 50 g of benzene. The organic extracts obtained were combined and concentrated by evaporation in a rotary evaporator operated under vacuum (9.5 kPa; water bath temperature of about 65° C.) to an ε-caprolactam concentration of about 25 wt.%. The mixture was extracted twice in batches with 25 g of water at a temperature of about 25° C. The specifications of the ε-caprolactam aqueous solution after stripping were:

[0548] PAN: 132

[0549] E290:1.55

[0550] 75 mmol of aqueous sodium hydroxide solution / kg of ε-caprolactam is then added to the concentrated ε-caprolactam solution. 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 a top product, while impurities with a higher boiling point than ε-caprolactam remain in the distillation apparatus as a bottom product.

[0551] Distilled water is then added to the distilled ε-caprolactam to obtain a mixture with an ε-caprolactam concentration of 91.4 wt.%. The aqueous ε-caprolactam is introduced into a crystallization device at a temperature of 52°C. The aqueous ε-caprolactam is cooled to 40°C and some seed crystals are added to the mixture. The mixture is then further cooled to 30°C and kept for 30 minutes. The crystallized ε-caprolactam is recovered by filtration and washed with an 85 wt.% ε-caprolactam aqueous solution. The specifications of the purified ε-caprolactam obtained meet all of the specifications required for the main polymerization applications.

[0552] This example shows that polyether polyurethane and nylon 6 can be separated from nylon 6 waste fabric containing polyether polyurethane by selective extraction, precipitation of dissolved polyether polyurethane and washing of undissolved nylon 6. Further, it can be concluded from this example that purified ε-caprolactam meeting all specifications required for major polymerization applications can be obtained by depolymerization of nylon 6 derived from discarded nylon 6 waste fabric containing polyether polyurethane and purified by extraction, stripping, distillation and crystallization.

[0553] Example 7

[0554] Calculation of the carbon footprint of nylon 6 and polyether polyurethane.

[0555] A continuous process for producing nylon 6 and polyether polyurethane from nylon 6 waste fabrics containing polyether polyurethane according to the present invention was simulated. The polyether polyurethane content of these nylon 6 waste fabrics containing polyether polyurethane was 20 wt.%, and the remainder was mainly nylon 6.

[0556] The method comprises:

[0557] - cutting nylon 6 waste fabric containing polyether polyurethane into small pieces;

[0558] - Selective extraction of polyether polyurethane with DMAc;

[0559] - separation of undissolved nylon 6 and a polyether polyurethane-rich stream by centrifugation;

[0560] - Washing the undissolved nylon 6 with water;

[0561] - Separating the washed undissolved nylon 6 and aqueous extract by centrifugation;

[0562] - precipitating the polyether polyurethane from the polyether polyurethane-rich stream by adding the aqueous extract obtained above;

[0563] - separating the precipitated polyether polyurethane from the DMAc-water mixture by filtration;

[0564] - recovering DMAc and water from the DMAc-water mixture obtained above;

[0565] - Dry filtered polyether polyurethane;

[0566] - Drying of washed undissolved nylon 6;

[0567] - The washed undissolved nylon 6 is melted and pelletized.

[0568] The carbon footprint of nylon 6 and polyether polyurethane was calculated based on the consumption data of raw materials and the utility of the above method was based on data from ecoinvent version 3.7.1. The distribution of environmental impact between nylon 6 and polyether polyurethane products in the pretreatment section and separation section was based on the weight ratio of these products.

[0569] The results revealed that the product carbon footprint of nylon 6 obtained from nylon 6 waste fabric containing polyether polyurethane was less than 1.0 ton CO2 equivalent / ton nylon 6 and less than 1.0 ton CO2 equivalent / ton polyether polyurethane, respectively (location: Europe).

[0570] 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 may be made therein, including (semi)continuous operation and scaling up to commercial scale, without departing from the spirit and scope of the invention.

Claims

1. A method for recovering nylon 6 and spandex from a fabric comprising nylon 6 and polyether polyurethane in a plant, wherein the plant comprises - separation section [B], The separation section [B] comprises - dissolution segment [α], and - precipitation section [γ], And wherein the method comprises the following steps: b.1) loading dimethylacetamide and the fabric comprising nylon 6 and polyether polyurethane into the dissolving section [α]; b.2) selectively dissolving the polyether polyurethane from the fabric comprising nylon 6 and polyether polyurethane in the dimethylacetamide in the dissolving zone [α], 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, so that a polyether polyurethane-rich stream comprising dimethylacetamide and dissolved polyether polyurethane and a stream comprising undissolved nylon 6 are obtained; b.3) discharging the obtained polyether polyurethane-rich stream from the dissolution section [α]; b.4) feeding a second solvent and the polyether polyurethane-rich stream into the precipitation section [γ], so that the polyether polyurethane is precipitated from the mixture comprising dimethylacetamide and the second solvent; b.5) ​​recovering the precipitated polyether polyurethane from the mixture comprising dimethylacetamide and a second solvent and discharging the precipitated polyether polyurethane from the precipitation section [γ], wherein the polyether polyurethane content of the discharged stream is at least 85% by weight, based on dry weight, more preferably at least 90% by weight, based on dry weight; b.6) discharging from the precipitation section [γ] the mixture comprising dimethylacetamide and the second solvent from which the precipitated polyether polyurethane has been recovered in step b.5); and b.7) Discharging the stream comprising undissolved nylon 6 obtained in step b.2) from dissolving section [α].

2. The method according to claim 1, wherein the separation section [B] in the plant further comprises: - a washing section [β], and - solvent distillation section [δ], And wherein the method comprises the following additional steps: c.1) charging a third solvent and the stream comprising undissolved nylon 6 obtained in step b.2) to the washing section [β]; c.2) washing the stream comprising undissolved nylon 6 with the third solvent in the washing section [β] so as to obtain a nylon 6-rich stream and a mixture comprising dimethylacetamide and the third solvent, wherein the nylon 6-rich stream has a nylon 6 content of at least 85 wt.-%, more preferably at least 90 wt.-%, even more preferably at least 95 wt.-% and most preferably at least 99 wt.-% on a dry weight basis; c.3) discharging the nylon 6-rich stream from the washing section [β]; c.4) discharging the mixture comprising dimethylacetamide and the third solvent obtained in step c.2) from the washing section [β]; d.1) charging the mixture comprising dimethylacetamide and the second solvent, from which the precipitated polyether polyurethane has been recovered in step b.5) and which has been discharged from the precipitation section [γ] in step b.6), to the solvent distillation section [δ]; d.2) partially or completely charging the mixture comprising dimethylacetamide and the third solvent obtained in step c.2) and discharged from the washing section [β] in step c.4) to the solvent distillation section [δ]; d.3) separating dimethylacetamide from the second solvent and the third solvent by distillation in the solvent distillation section [δ]; and d.4) discharging the second solvent, the third solvent and the separated dimethylacetamide from the solvent distillation section [δ].

3. The process according to claim 2, wherein the separated dimethylacetamide discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1).

4. The process according to any one of claims 1 to 3, wherein the nylon 6-rich stream discharged from the separation section [B] is dried and / or densified before being subjected to mechanical or chemical recycling.

5. The process according to any one of claims 1 to 4, wherein the recovered polyether polyurethane discharged from the precipitation section [γ] in step b.5) 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], The pre-processing section [A] comprises - cleaning section [ω], and / or - Mechanical size reduction section [λ], And wherein the method comprises the following steps before step b.1): a.1) loading the fabric comprising nylon 6 and polyether polyurethane into the pretreatment section [A]; as well as a.2) cleaning the fabric comprising nylon 6 and polyether polyurethane in the cleaning section [ω]; and / or a.3) subjecting the fabric comprising nylon 6 and polyether polyurethane to mechanical size reduction in the mechanical size reduction section [λ]; and a.4) Discharge the pretreated fabric comprising nylon 6 and polyether polyurethane from the pretreatment section [A].

7. The method according to any one of claims 1 to 6, wherein optionally, 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.4) is partly or completely the mixture comprising dimethylacetamide and a third solvent obtained in step c.2) and discharged from the washing section [β] in step c.4).

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 separation from one another.

10. The process according to claim 3 , wherein before the separated dimethylacetamide discharged from the solvent distillation section [δ] in step d.4) is fed to the dissolution section [α] in step b.1), impurities, in particular degradation products of the off-gas dimethylacetamide, are removed.

11. The method according to any one of claims 2 to 10, wherein the plant further comprises - depolymerization section [C], - Recovery Sector [D], and - purification segment [E], And wherein the method comprises the following additional steps: e.1) feeding the nylon 6-rich stream discharged from the washing section [β] in step c.3) to the depolymerization section [C]; e.2) depolymerizing the nylon 6 in the nylon 6-rich stream in the depolymerization section [C] such that a stream comprising ε-caprolactam is obtained, wherein the depolymerization is carried out 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 and in the presence of water, preferably in the presence of water charged in the form of superheated steam having a temperature in the range of 220°C to 575°C, specifically 275°C to 500°C, such that the stream comprising ε-caprolactam is a steam 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; e.3) discharging the obtained stream comprising ε-caprolactam from the depolymerization section [C]; e.4) recovering crude ε-caprolactam from the stream comprising ε-caprolactam in the recovery section [D]; e.5) 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 one or more steps selected from the group consisting of: filtration, adsorption, extraction, washing, stripping, solvent exchange distillation, oxidation, hydrogenation, distillation and crystallization; e.6) discharging the purified ε-caprolactam from the purification section [E].

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