Method for recycling and regenerating waste colored nylon

Abstract

The present application belongs to the technical field of polymer material recycling and reuse, and particularly relates to a waste colored polyamide fiber recycling method, which adopts a depolymerization agent to depolymerize waste colored polyamide fiber to obtain crude polyamide 6-co-polyester oligomer; wherein the depolymerization agent is a carboxyl-terminated polyester synthesized by esterification reaction of a dicarboxylic acid or anhydride and a dihydric alcohol; the crude polyamide 6-co-polyester oligomer is purified and distilled, and then subjected to melt polycondensation to obtain a polyamide 6-co-polyester copolymer. The carboxyl at the end of the depolymerization agent and the acidic system can strengthen the catalytic cleavage effect of organic acid on the amide bond of polyamide 6, realize one-step leap of waste polyamide 6 from recycling to upgrading and reconstruction, and avoid the high energy consumption step of monomer purification and repolymerization. The method is particularly suitable for waste polyamide fiber textiles with complex components, pigments and various additives, and excellent regenerated copolymer materials can be obtained through integrated efficient purification steps.

Description

Technical Field

[0001] This invention belongs to the field of polymer material recycling and reuse technology, specifically relating to a method for recycling and regenerating waste colored nylon. Background Technology

[0002] Polyamide 6, or PA6 for short, is widely used in clothing, carpets, nylon fabrics, fishing nets, and various textiles due to its excellent mechanical properties, abrasion resistance, and chemical resistance. This results in a massive amount of waste. This waste often contains complex organic / inorganic impurities due to dyes, additives, oil contamination, and environmental aging, and its molecular chains undergo degradation or cross-linking. This leads to a darker color, significantly reduced mechanical properties, and poor quality in physically recycled and melt-regenerated products, making high-value reuse difficult. Therefore, developing efficient and environmentally friendly PA6 recycling technologies has significant practical application value.

[0003] Currently, the main recycling methods for waste PA6 include physical melting recycling and chemical depolymerization for caprolactam recovery. Physical methods struggle to remove blended impurities and colored components, while chemical recycling is the only recycling method that can close the plastic manufacturing cycle and is also a sustainable recycling model. Chemical recycling degrades PA6 into monomers or oligomers through depolymerization reactions, which are then repolymerized to prepare high-quality recycled materials, and is considered an effective way to achieve high-value recycling of PA6. However, traditional chemical recycling methods such as hydrolysis, alcoholysis, and ammonolysis have problems such as harsh reaction conditions, high energy consumption, and low product purity. Especially for waste colored PA6 textiles containing impurities such as dyes and additives, the depolymerization efficiency and product quality often fail to meet the requirements for recycling.

[0004] In the chemical recycling of waste PA6, there is a one-step process that directly mixes depolymerization precursors (such as diacids and diols) with PA6 raw materials. In this reaction system, small molecule acids, alcohols and PA6 macromolecular chains coexist, resulting in multiple competing reaction pathways occurring simultaneously, including esterification of diacids and diols, random acidolysis of PA6 by small molecule acids, and alcohololysis of PA6. This chaotic reaction system not only significantly reduces the efficiency of directional amide bond breaking and increases energy consumption, but also results in depolymerization products that are a mixture with a very wide molecular weight distribution and disordered sequence structure, which brings great difficulties to subsequent purification and repolymerization.

[0005] In recent years, acid hydrolysis has attracted attention as a highly efficient chemical recovery method for PA6. Compared with solvent systems such as pure water, methanol, or ammonia, the introduction of organic acids such as formic acid can significantly reduce the reaction energy barrier of the PA6 depolymerization step, and the molecular mechanism of synergistically catalyzing the cleavage of amide bonds changes the rate-determining step of the reaction, thereby improving the efficiency of the entire recovery process.

[0006] However, current technologies that directly use small-molecule organic acids (such as acetic acid) for PA6 depolymerization often face problems such as difficulty in acid recovery, equipment corrosion, and complex product post-processing. In addition, although simple depolymerization to monomers (such as ε-caprolactam) can achieve closed-loop recovery, the process still consumes a lot of energy, and for waste PA6 containing complex impurities (such as dyes and metal ions), impurity removal and product purification during the depolymerization process is a major challenge. Summary of the Invention

[0007] Based on the aforementioned shortcomings and deficiencies in the existing technology, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the existing technology. In other words, one of the objectives of this invention is to provide a method for recycling and regenerating waste colored nylon that meets one or more of the aforementioned requirements. This method utilizes carboxyl-terminated polyester oligomers synthesized from dicarboxylic acids / anhydrides and diols as highly efficient depolymerizing agents to achieve chemical depolymerization of waste colored nylon under mild conditions, while simultaneously achieving deep removal of impurities. Finally, high-performance PA6-co-polyester copolymers are directly prepared through melt polycondensation.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for recycling and regenerating waste colored nylon involves using a depolymerizing agent to depolymerize the waste colored nylon to obtain crude polyamide 6-co-polyester oligomers; wherein the depolymerizing agent is a carboxyl-terminated polyester synthesized by esterification reaction of dicarboxylic acid or acid anhydride with diol.

[0010] The crude polyamide 6-co-polyester oligomer was purified and distilled, and then subjected to melt polycondensation to obtain the polyamide 6-co-polyester copolymer.

[0011] As a preferred option, the method for recycling and regenerating waste colored nylon includes the following steps:

[0012] (1) The waste colored nylon is crushed and impurities are removed to obtain PA6 powder; the PA6 powder is mixed with the depolymerizing agent described in the above scheme or the depolymerizing agent prepared by the preparation method described in any of the above schemes, and the depolymerization reaction is carried out at 180-280℃ for 5-20 hours under stirring conditions to obtain crude PA6-co-polyester oligomer.

[0013] (2) The crude PA6-co-polyester oligomer was dissolved in an organic solvent and purified and distilled to obtain the refined PA6-co-polyester oligomer.

[0014] (3) The refined PA6-co-polyester oligomer was subjected to melt polycondensation reaction at 180-280℃ and 0.001-500Pa pressure for 4-30 hours to obtain PA6-co-polyester copolymer.

[0015] As a preferred embodiment, in step (1), the mass ratio of PA6 powder to depolymerizing agent is (0.1-10):1.

[0016] As a preferred embodiment, in step (2), the organic solvent is at least one of dichloromethane, chloroform, cyclohexanone, formic acid, acetic acid, methanol, ethanol, isopropanol, m-cresol, choline ion solution, dimethyl sulfoxide, and carbon tetrachloride.

[0017] The purification includes molecular enrichment purification and ion screening purification;

[0018] The enrichment medium used in the molecular enrichment purification is selected from at least one or more of activated carbon, silica gel, adsorption resin, bentonite, and diatomaceous earth.

[0019] The ion screening and purification process involves purification using ion exchange resin.

[0020] As a preferred embodiment, in step (2), distillation includes separation of low-boiling components and separation of reboiling components;

[0021] The conditions for separating the low-boiling components are: temperature of 120-180℃, pressure of 1-60kPa, and residence time of less than 60 minutes.

[0022] The conditions for separating the reboiling components are: temperature 150-240℃, pressure 0.1-3kPa, and residence time less than 60 minutes.

[0023] As a preferred embodiment, the waste colored nylon is selected from at least one of PA6 textiles such as clothing, carpets, nylon fabrics, and fishing nets.

[0024] As a preferred option, the method for recycling and regenerating waste colored nylon also includes the following steps:

[0025] PA6-co-polyester copolymer is subjected to devolatilization treatment at 130-250℃ and pressure below 1000Pa for 30-180 minutes, and then filtered through a melt filter to obtain PA6-co-polyester melt.

[0026] As a preferred embodiment, the preparation process of the depolymerizing agent includes: mixing dicarboxylic acid or anhydride, diol and catalyst under inert gas protection, and carrying out an esterification reaction at 180-260°C for 5-24 hours under stirring conditions;

[0027] The molar ratio of dicarboxylic acid or anhydride to diol is (1.01-3):1.

[0028] As a preferred embodiment, the dicarboxylic acid or anhydride is selected from at least one of succinic acid, adipic acid, glutaric acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, phthalic acid, isophthalic acid, terephthalic acid, malonic acid, succinic anhydride, phthalic anhydride, and adipic anhydride.

[0029] The diol is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,9-nonanediol, hydroquinone, terephthalic acid diethanol, and 2,5-furandiol.

[0030] As a preferred embodiment, the amount of catalyst added is 0.01-5% of the total mass of dicarboxylic acid or anhydride and diol;

[0031] The catalyst is selected from at least one of tetrabutyl titanate, antimony acetate, zinc acetate, germanium dioxide, zinc oxide, antimony trioxide, antimony glycolate, p-benzenesulfonic acid, zinc, magnesium acetate, magnesium succinate, and magnesium.

[0032] Compared with the prior art, the beneficial effects of this invention are:

[0033] (1) Significant upgrade effect: The molecular weight of the polymer is increased through the highly active reaction of the carboxyl-amide bond, and the mechanical properties are significantly improved;

[0034] (2) Thorough color removal: Solvent and molecular enrichment purification methods can treat waste PA6 of various colors and obtain near-original color;

[0035] (3) Performance can be designed: By selecting different combinations of dicarboxylic acids and diols, the performance of the final product can be customized;

[0036] (4) Wide range of applications: It can process waste PA6 from various sources, including textiles, engineering plastics, etc. Attached Figure Description

[0037] Figure 1 The PES synthesized in Example 1 of this invention 1 H NMR spectrum;

[0038] Figure 2 PA6-co-PES synthesized in Example 1 of this invention 1 H NMR spectrum. Detailed Implementation

[0039] The following provides a detailed description of the waste colored nylon recycling method of the present invention.

[0040] This invention synthesizes carboxyl-terminated polyester oligomers as depolymerizing agents for the chemical depolymerization of PA6 in waste colored nylon. The depolymerizing agent is a low-molecular-weight polyester synthesized from dicarboxylic acids or anhydrides and diols via esterification. Its terminal carboxyl groups and its ability to synergistically enhance the catalytic cleavage of PA6 amide bonds by organic acids in acidic systems enable efficient depolymerization under mild conditions. Simultaneously, the depolymerizing agent becomes part of the polymer chain after the reaction. Through copolymerization with the PA6 oligomers generated by depolymerization, PA6-co-polyester oligomers are obtained. Deep decolorization can be achieved through selective dissolution-precipitation using a solvent method. Further polycondensation is then used to prepare PA6-co-polyester copolymers, achieving a one-step leap from recycling to remanufacturing. This avoids the energy-intensive steps of monomer purification and repolymerization. This method is particularly suitable for waste PA6 textiles with complex compositions containing pigments and various additives. By integrating efficient purification steps, high-performance recycled copolymer materials can be obtained.

[0041] The method for preparing the depolymerizing agent for polyamide 6 of the present invention includes the following process: under the protection of an inert gas (such as nitrogen, argon or helium) and at normal pressure, a dicarboxylic acid or anhydride and a diol are mixed in a reactor in the presence of a catalyst, and an esterification reaction is carried out at a stirring speed of 100-500 r / min and at 180-260°C for 5-24 hours to synthesize a series of carboxyl-terminated polyester oligomers with different chain lengths, flexibility and reactivity as depolymerizing agents.

[0042] In one or more embodiments, the molar ratio of dicarboxylic acid or anhydride to diol is (1.01-3):1, and the specific molar ratio can be determined according to the actual application requirements.

[0043] In one or more embodiments, the dicarboxylic acid or anhydride is selected from at least one of succinic acid, adipic acid, glutaric acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, phthalic acid, isophthalic acid, terephthalic acid, malonic acid, succinic anhydride, phthalic anhydride, and adipic anhydride, and can be selected according to actual application requirements;

[0044] In one or more embodiments, the diol is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,9-nonanediol, terephthalic acid diethanol, and 2,5-furandiol, and can be specifically selected according to actual application requirements;

[0045] In one or more embodiments, the amount of catalyst added is 0.01-5% of the total mass of dicarboxylic acid or anhydride and diol, and the specific percentage can be determined according to the actual application requirements; wherein, the catalyst is selected from at least one of tetrabutyl titanate, antimony acetate, zinc acetate, germanium dioxide, zinc oxide, antimony trioxide, antimony glycolate, p-benzenesulfonic acid, zinc, magnesium acetate, magnesium succinate, and magnesium, and the specific selection can be made according to the actual application requirements.

[0046] The structural formula of the carboxyl-terminated polyester oligomer prepared by the above method is as follows:

[0047] ;

[0048] Wherein, R1 is selected from dicarboxylic acid or acid anhydride units, R2 is selected from diol units, and n is an integer from 5 to 20, which can be determined according to the actual application requirements.

[0049] The method for recycling and regenerating waste colored nylon of the present invention includes the following steps:

[0050] (1) Pre-treatment of waste colored nylon for recycling;

[0051] The recycled waste nylon textiles (such as clothing, carpets, nylon fabrics, PA6 textiles from fishing nets, etc.) are initially screened to separate the PA6 component. They are then mechanically crushed into fine powder by cutting machines, crushers or grinding mills. Soluble impurities (such as oil stains and some dyes) are removed using industrial detergents. Finally, they are dried at 80-120℃ for 5-12 hours to obtain clean PA6 powder raw materials.

[0052] (2) Depolymerization of waste PA6;

[0053] The PA6 powder obtained in step (1) is mixed with the above depolymerizing agent at a mass ratio of (0.1-10):1, added to the depolymerization reactor, and reacted for 5-20 hours under inert gas protection at a stirring speed of 200-400 r / min and a temperature of 180-280℃. During this process, the carboxyl group at the end of the depolymerizing agent attacks the amide bond in the PA6 chain, following the acid hydrolysis mechanism, involving coordinated proton transfer and nucleophilic attack: the depolymerizing agent attacks the amide nitrogen atom in the PA6 chain through its carboxyl proton H⁺, forming an amide bond protonation intermediate, which enhances the polarity of the C–N bond and makes it easier to break; the two carboxyl groups of the depolymerizing agent can interact with different PA6 segments or different sites of the same segment to form a multicenter hydrogen bond network, further stabilizing the transition state, reducing the reaction energy barrier, breaking the PA6 macromolecular chain, and generating crude PA6-co-polyester oligomer containing PA6 segments and polyester segments;

[0054] (3) Purification of depolymerization products;

[0055] The crude PA6-co-polyester oligomer was purified in multiple stages to completely remove metal ions, small molecule impurities, low-boiling substances, high-boiling substances, and color.

[0056] a) Molecular enrichment and purification: Crude PA6-co-polyester oligomers are dissolved in an organic solvent (selected from at least one or a mixture of dichloromethane, chloroform, cyclohexanone, formic acid, acetic acid, methanol, ethanol, isopropanol, m-cresol, choline ion solution, dimethyl sulfoxide, and carbon tetrachloride), transferred to a purification reactor, and treated by medium adsorption at atmospheric pressure; Waste PA6 textiles contain dyes, which are physically dispersed in the PA6 matrix as fine particles, without chemical bonds to the polymer chain, but are tightly wrapped, or can react chemically with the amino or carboxyl groups at the end of the PA6 molecular chain to form chemical bonds, or are firmly bound by strong hydrogen bonds and van der Waals forces, and the dyes are treated by medium adsorption;

[0057] The above-mentioned medium has a large specific surface area and porous structure, providing a large number of adsorption and enrichment sites, and has a strong adsorption capacity to remove dye impurities.

[0058] The above-mentioned media are selected from one or more of activated carbon, silica gel, adsorption resin, bentonite, and diatomaceous earth;

[0059] b) Ion screening and purification: The liquid after molecular enrichment and purification is treated with ion exchange resin at normal pressure and 60-90℃ to deeply remove metal ions and small molecule electrolyte impurities. In the process of preparing the depolymerizing agent, at least one catalyst is inevitably required. Based on the electrostatic attraction and chemical bonding between ions, the ion exchange resin is composed of polymers and has charged sites on its surface. It can exchange with ions in the solution to screen and remove metal ions and small molecule electrolyte impurities generated in the depolymerization reaction.

[0060] c) Separation of low-boiling components: The product purified by the above ion screening is subjected to 120-180℃, 1-60kPa and residence time <60 minutes to remove low-boiling substances; the PA6-co-polyester oligomer obtained by depolymerization is separated from other impurities by the difference in boiling point and the difference in molecular mean free path under different pressures, and the low-boiling components are vaporized and escape from the liquid surface.

[0061] d) Reboiling component separation: The product from the above low-boiling component separation is subjected to high-boiling components at 150-240℃, 0.1-3kPa, and residence time <60 minutes. The same principle is used to remove the high-boiling components, and finally refined PA6-co-polyester oligomer is obtained.

[0062] (4) Melt polycondensation;

[0063] The refined PA6-co-polyester oligomer was placed in a reactor and subjected to melt polycondensation reaction for 4-30 hours at 180-280℃ and vacuum degree of 0.001-500Pa. During this process, the functional groups such as amino, carboxyl, and hydroxyl groups at the end of the oligomer molecules further underwent condensation reaction, and the molecular weight increased to obtain PA6-co-polyester copolymer.

[0064] Main reactions: carboxyl-amide exchange reaction and esterification reaction.

[0065] In addition, the PA6-co-polyester copolymer obtained above can be further devolatilized: the PA6-co-polyester copolymer is devolatilized at 130-250°C and a pressure below 1000Pa for 30-180 minutes to remove residual volatile small molecules; then it is filtered through a melt filter to obtain a pure PA6-co-polyester melt that can be directly used for spinning or molding.

[0066] This invention employs a two-step method. Essentially, it first prepares well-defined PA6-co-polyester block oligomer building blocks. During the subsequent melt polycondensation process, these block oligomers, rich in terminal active functional groups (-NH2, -COOH), primarily undergo end-chain condensation reactions, effectively growing into high-molecular-weight multi-block copolymers. The PA6 segments form hard micro-regions providing strength, while the polyester soft segments impart toughness to the material. By precisely designing the chain length (n value) and chemical composition (R1, R2) of the depolymerizing agent, the properties of the final copolymer can be controlled, truly realizing the upgrading and remanufacturing of waste materials into high-performance materials.

[0067] PA6-co-polyester oligomers, with significantly reduced molecular weight and improved solubility, offer advantages in their oligomer state. This allows for the release of impurities, such as dyes, that exist in physically encapsulated forms, while also enabling the separation of small molecule impurities like metal ions. Therefore, subsequent molecular enrichment adsorption, ion exchange, and distillation purification steps can be performed efficiently and thoroughly. In contrast, one-step methods result in complex mixtures with extremely wide molecular weight distributions, where impurities are encapsulated in chain segments of varying lengths. The lack of effective selective purification methods leads to products with dark colors and low quality, failing to meet the requirements of high-value applications.

[0068] In comparison, the two-step process employed in this invention offers significant advantages in molecular design. First, a well-defined carboxyl-terminated polyester oligomer is pre-synthesized under controlled conditions. This oligomer acts as a macromolecular depolymerizing agent; its terminal carboxyl groups exhibit catalytic activity similar to that of small-molecule acids, while its polyester segments demonstrate good affinity and compatibility with the PA6 matrix. In the second depolymerization step, this prepolymer efficiently penetrates and acts on the PA6 chain. Its carboxyl groups can attack the amide bonds with high concentration and high selectivity, following a concerted proton transfer mechanism, enabling the depolymerization reaction to proceed efficiently under milder conditions.

[0069] The following specific embodiments and comparative examples further explain the waste colored nylon recycling method of the present invention.

[0070] Example 1:

[0071] The waste colored nylon recycling method in this embodiment adopts a depolymerization system of succinic acid and ethylene glycol;

[0072] Raw materials: Waste non-colored PA6 fishing nets;

[0073] Recycling pretreatment: Take the recycled waste colored PA6 fishing nets, crush them into fine powder using a shredder, remove soluble impurities using industrial detergent, and dry them in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0074] Synthesis of depolymerizing agent: 1.67 kg of succinic acid, 0.87 kg of ethylene glycol and 0.01 kg of antimony acetate in an acid-to-alcohol molar ratio of 1.01:1 were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 230 °C with a stirring speed of 300 r / min and the esterification reaction was carried out for 7 hours to obtain oligomers of poly(ethylene succinate) as depolymerizing agent PES.

[0075] Depolymerization of waste PA6: Waste colored PA6 powder and depolymerizing agent PES are mixed at a mass ratio of 0.21:1 and added to a depolymerization reactor. The mixture is stirred at 300 r / min and reacted at 230°C for 6 hours to obtain crude PA6-co-PES oligomer.

[0076] Purification of depolymerization products: The crude PA6-co-PES oligomers were dissolved in formic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by activated carbon and anion and cation exchange resins. Insoluble matter was removed by filtration. The low-boiling and high-boiling components were then separated by separation at 170℃ and 2000Pa for 20 min and by separation at 160℃ and 500Pa for 30 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6-co-PES oligomers.

[0077] Melt polycondensation: The above-mentioned refined PA6-co-PES oligomer was added to a polycondensation reactor and reacted for 8 hours at a pressure below 100 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 240 °C to obtain PA6-co-PES copolymer.

[0078] like Figure 1 As shown, this is the depolymerizing agent PES. 1 The H NMR spectrum, with its characteristic peaks assigned as follows:

[0079] δ=4.28ppm: The hydrogen in the methylene group –CH2– of –O–CH2–CH2–O– comes from the ethylene glycol unit;

[0080] δ=2.65ppm: The hydrogen in the methylene group –CH2–CO–CH2–CO– comes from the succinic anhydride unit;

[0081] δ=7.26ppm (sharp single peak): This is a solvent peak (usually residual CHCl3 in deuterated chloroform CDCl3).

[0082] The successful synthesis of PES was further demonstrated by calculating the optimal feed ratio based on peak area.

[0083] like Figure 2 As shown, this is a PA6-co-PES copolymer. 1 The H NMR spectrum, with characteristic peaks assigned as follows:

[0084] δ=4.40ppm: –O–CH2–CH2–O– from the PES segment, originating from the ethylene glycol fragment;

[0085] δ=2.82ppm: Hydrogen from the corresponding methylene –CH2– in the PES segment –CO–CH2–CH2–CO–, originating from the succinic anhydride unit;

[0086] δ=3.45ppm: corresponds to the hydrogen of the alkylene group in the PA6 segment –NH–CH2–;

[0087] δ=2.61ppm: corresponds to the hydrogen in the –CO–CH2– alkylene group in PA6 segment;

[0088] δ=1.73ppm: corresponds to hydrogen in the –CH2– segment of PA6;

[0089] δ=1.41ppm: corresponds to the hydrogen in the long-chain methylene group in the PA6 segment;

[0090] The peak area calculation is consistent with the feed ratio, further demonstrating the successful synthesis of PA6-co-PES copolymer.

[0091] Example 2:

[0092] The waste colored nylon recycling method in this embodiment uses a depolymerization system of adipic acid and 1,4-butanediol;

[0093] Raw material: Waste colored PA6 nylon fabric;

[0094] Recycling pretreatment: Take the recycled waste colored PA6 nylon fabric, crush it into fine powder using a shredder, treat it with industrial detergent to remove soluble impurities and oxides in the waste, and then dry it in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0095] Synthesis of depolymerizing agent: 2.48 kg adipic acid, 1.02 kg 1,4-butanediol and 0.01 kg zinc acetate were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 210 °C with stirring at 300 r / min for 6 hours to obtain oligomers of polybutylene adipate as depolymerizing agent PBA.

[0096] Depolymerization of waste PA6: PA6 powder and depolymerizing agent PBA were mixed at a mass ratio of 0.2:1 and added to the depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 230°C for 6 hours to obtain crude PA6-co-PBA oligomer.

[0097] Purification of depolymerization products: The crude PA6-co-PBA oligomers were dissolved in formic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by adsorption resin and anion and cation exchange resin. Insoluble matter was removed by filtration. The low-boiling components were separated at 180℃ and 2000Pa for 20 min and the high-boiling components were separated at 170℃ and 500Pa for 35 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6-co-PBA oligomers.

[0098] Melt polycondensation: The above-mentioned refined PA6-co-PBA oligomer was added to a polycondensation reactor and reacted at a pressure below 100 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 230 °C for 9 hours to obtain PA6-co-PBA copolymer.

[0099] Example 3:

[0100] The waste colored nylon recycling method in this embodiment adopts a depolymerization system of terephthalic acid and ethylene glycol;

[0101] Raw material: Waste colored PA6 carpet fibers;

[0102] Recycling pretreatment: Take the recycled waste colored PA6 carpet fibers, crush them into fine powder using a shredder, treat them with industrial detergent to remove soluble impurities and oxides in the waste, and then dry them in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0103] Synthesis of depolymerizing agent: 2.28 kg of terephthalic acid, 1.35 kg of 1,6-hexanediol and 0.03 kg of zinc acetate were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 260 °C with a stirring speed of 500 r / min and the esterification reaction was carried out for 24 hours to obtain oligomers of polyethylene terephthalate as depolymerizing agent PHT.

[0104] Depolymerization of waste PA6: PA6 powder and depolymerizing agent PHT were mixed at a mass ratio of 0.32:1 and added to the depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 280°C for 20 hours to obtain crude PA6-co-PHT oligomer.

[0105] Purification of depolymerization products: The crude PA6-co-PHT oligomers were dissolved in acetic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by adsorption resin and anion and cation exchange resin. Insoluble matter was removed by filtration. The low-boiling components were then separated at 190℃ and 2500Pa for 25 min and the high-boiling components were separated at 165℃ and 1000Pa for 35 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6-co-PHT oligomers.

[0106] Melt polycondensation: The above-mentioned refined PA6-co-PHT oligomer was added to a polycondensation reactor and reacted for 30 hours at a pressure below 150 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 280 °C to obtain PA6-co-PHT copolymer.

[0107] Example 4:

[0108] The waste colored nylon recycling method in this embodiment uses a depolymerization system of sebacic acid and neopentyl glycol;

[0109] Raw materials: A mixture of waste colored PA6 carpet textiles;

[0110] Recycling pretreatment: Take the recycled waste colored PA6 carpet textile mixture, crush it into fine powder using a pulverizer, treat it with industrial detergent to remove soluble impurities and oxides in the waste, and then dry it in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0111] Synthesis of depolymerizing agent: 2 kg sebacic acid, 0.92 kg neopentyl glycol and 0.02 kg tetrabutyl titanate were mixed and added to a reactor. Under normal pressure and continuous N2 supply, the temperature was gradually increased to 200 °C with a stirring speed of 300 r / min. The esterification reaction was carried out for 5 hours to obtain polystyrene sebacic acid neopentyl glycol ester oligomer as depolymerizing agent.

[0112] Depolymerization of waste PA6: PA6 powder and depolymerizing agent were mixed at a mass ratio of 0.38:1 and added to the depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 230°C for 7 hours to obtain crude PA6-co-polypentylene glycol sebacate oligomer.

[0113] Purification of depolymerization products: The crude PA6-co-polynepentylene glycol sebacic acid ester oligomers were dissolved in m-cresol solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by silica gel and anion and cation exchange resins. Insoluble matter was removed by filtration. The low-boiling components were then separated at 200℃ and 1600Pa for 35 min and the high-boiling components were separated at 180℃ and 700Pa for 40 min to remove the low-boiling and high-boiling components, thus obtaining refined PA6-co-polynepentylene glycol sebacic acid ester oligomers.

[0114] Melt polycondensation: The above-mentioned refined PA6-co-polynepentylene glycol sebacic acid ester oligomer melt is added to the polycondensation reactor. The reaction is carried out at a pressure below 100 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 240 °C for 7 h to obtain PA6-co-polynepentylene glycol sebacic acid ester copolymer.

[0115] Example 5:

[0116] The waste colored nylon recycling method in this embodiment adopts a depolymerization system of succinic anhydride and butanediol;

[0117] Raw material: Waste colored PA6 fishing net.

[0118] Recycling pretreatment: Take the recycled waste colored PA6 fishing nets, crush them into fine powder using a shredder, treat them with industrial detergent to remove soluble impurities and oxides in the waste, and then dry them in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0119] Synthesis of depolymerizing agent: 2.7 kg succinic anhydride, 0.81 kg butanediol and 0.13 kg tetrabutyl titanate were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 180 °C with stirring at 350 r / min. The esterification reaction was carried out for 5 hours to obtain polybutylene succinate oligomer as depolymerizing agent PBS.

[0120] Depolymerization of waste PA6: PA6 powder and depolymerizing agent are mixed at a mass ratio of 5:1 and added to a depolymerization reactor. The mixture is stirred at 350 r / min and reacted at 230 °C for 20 hours to obtain crude PA6-co-PBS oligomers.

[0121] Purification of depolymerization products: The crude PA6-co-PBS oligomers were dissolved in acetic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by adsorption resin and anion and cation exchange resin. Insoluble matter was removed by filtration. The low-boiling and high-boiling components were then separated by separation at 180℃ and 2000Pa for 40 min and separation at 155℃ and 1000Pa for 40 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6-co-PBS oligomers.

[0122] Melt polycondensation: The above-mentioned refined PA6-co-PBS oligomer melt was added to the polycondensation reactor. The polycondensation reaction was carried out at a pressure below 100 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 240 °C for 10 hours to obtain PA6-co-PBS copolymer.

[0123] Example 6:

[0124] The waste colored nylon recycling method in this embodiment uses a depolymerization system of adipic acid and ethylene glycol;

[0125] Raw material: Waste colored PA6 nylon fabric;

[0126] Recycling pretreatment: Take the recycled waste colored PA6 nylon fabric, crush it into fine powder using a shredder, treat it with industrial detergent to remove soluble impurities and oxides in the waste, and then dry it in an oven at 80℃ for 8 hours to obtain colored PA6 powder.

[0127] Synthesis of depolymerizing agent: 3.04 kg adipic acid, 0.96 kg ethylene glycol and 0.12 kg p-toluenesulfonic acid were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 210 °C with a stirring speed of 450 r / min. The esterification reaction was carried out for 7 hours to obtain oligomers of polyethylene adipate as depolymerizing agents.

[0128] Depolymerization of waste PA6: PA6 powder and depolymerizing agent are mixed at a mass ratio of 0.2:1 and added to a depolymerization reactor. The mixture is stirred at 450 r / min and reacted at 250 °C for 5 hours to obtain crude PA6-co-ethylene adipate oligomer.

[0129] Purification of depolymerization products: The crude PA6-co-ethylene adipate oligomers were dissolved in m-cresol solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by bentonite and anion and cation exchange resins. Insoluble matter was removed by filtration. The low-boiling and high-boiling components were then separated by 200℃ and 2000Pa for 50 min and 180℃ and 1000Pa for 40 min to remove the low-boiling and high-boiling components, thus obtaining refined PA6-co-ethylene adipate oligomers.

[0130] Melt polycondensation: The above-mentioned refined PA6-co-polyethylene adipate oligomer was added to a polycondensation reactor. The reaction was carried out at a pressure below 200 Pa, a stirring speed of 450 r / min, and a polycondensation reaction temperature of 240 °C for 9 hours to obtain PA6-co-ethylene adipate copolymer.

[0131] Example 7:

[0132] The waste colored nylon recycling method in this embodiment adopts a depolymerization system of succinic anhydride and ethylene glycol;

[0133] Raw materials: Waste non-colored PA6 fishing nets;

[0134] Recycling pretreatment: Take the recycled waste colored PA6 fishing nets, crush them into fine powder using a shredder, remove soluble impurities using industrial detergent, and dry them in an oven at 80℃ for 9 hours to obtain colored PA6 powder.

[0135] Synthesis of depolymerizing agent: 3.47 kg succinic anhydride, 1.03 kg ethylene glycol, and 0.00045 kg zinc acetate were mixed and added to a reactor. Under normal pressure and continuous N2 purging, the temperature was gradually increased to 200 °C with a stirring speed of 300 r / min. The esterification reaction was carried out for 7 hours to obtain oligomers of polyethylene succinate, which were used as depolymerizing agents (PES).

[0136] Depolymerization of waste PA6: PA6 powder and depolymerizing agent are mixed at a mass ratio of 10:1 and added to a depolymerization reactor. The mixture is stirred at 300 r / min and reacted at 230°C for 10 hours to obtain crude PA6-co-PES oligomer.

[0137] Purification of depolymerization products: The crude PA6-co-PES oligomers were dissolved in formic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by activated carbon and anion and cation exchange resins. Insoluble matter was removed by filtration. The low-boiling components were separated at 170℃ and 2000Pa for 50 min and the high-boiling components were separated at 170℃ and 500Pa for 40 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6-co-PES oligomers.

[0138] Melt polycondensation: The above-mentioned refined PA6-co-PES oligomer was added to a polycondensation reactor and reacted at a pressure below 100 Pa, a stirring speed of 300 r / min, and a polycondensation reaction temperature of 260 °C for 9 hours to obtain PA6-co-PES copolymer.

[0139] Example 8:

[0140] The waste colored nylon recycling method in this embodiment uses a depolymerization system of sebacic acid and neopentyl glycol;

[0141] Raw materials: A mixture of waste colored PA6 carpet textiles;

[0142] Recycling pretreatment: Take the recycled waste colored PA6 carpet textile mixture, crush it into fine powder using a pulverizer, treat it with industrial detergent to remove soluble impurities and oxides in the waste, and then dry it in an oven at 80℃ for 10 hours to obtain colored PA6 powder.

[0143] Synthesis of depolymerization agent: 2.11 kg sebacic acid, 0.89 kg neopentyl glycol and 0.15 kg antimony acetate were mixed and added to the reactor. Under normal pressure and continuous N2 supply, the temperature was gradually increased to 200 °C with a stirring speed of 400 r / min. The esterification reaction was carried out for 5 hours to obtain polyneoprene glycol sebacic acid ester oligomer as depolymerization agent.

[0144] Depolymerization of waste PA6: PA6 powder (mixed with depolymerizing agent at a mass ratio of 0.45:1) was added to the depolymerization reactor and reacted at 230°C for 7 hours with a stirring speed of 400 r / min to obtain crude PA6-co-polynepentylene glycol sebacate oligomer.

[0145] Purification of depolymerization products: The crude PA6-co-polynepentylene glycol sebacic acid oligomers were dissolved in formic acid solution and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by adsorption resin and anion and cation exchange resin. Insoluble matter was removed by filtration. The low-boiling components were then separated at 200℃ and 900Pa for 50 min and the reboiling components were separated at 170℃ and 500Pa for 30 min to remove the low-boiling and reboiling components, thus obtaining purified PA6-co-polynepentylene glycol sebacic acid oligomers.

[0146] Melt polycondensation: The above-mentioned refined PA6-co-polynepentylene glycol sebacic acid oligomer was added to a polycondensation reactor and reacted for 7 hours at a pressure below 150 Pa, a stirring speed of 400 r / min, and a polycondensation reaction temperature of 240 °C to obtain PA6-co-polynepentylene glycol sebacic acid copolymer.

[0147] Comparative Example 1:

[0148] The difference between the waste colored nylon recycling method in this comparative example and Example 1 is that a one-step method is used to upgrade and regenerate PA6.

[0149] The raw materials and recycling pretreatment are the same as in Example 1;

[0150] Depolymerization of waste PA6: 1.67 kg succinic acid, 0.87 kg ethylene glycol, 0.01 kg antimony acetate and the same amount of waste colored PA6 powder as in Example 1 were mixed and added to a depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 230 °C for 6 hours to obtain crude PA6-co-PES oligomer.

[0151] The subsequent purification and melt polycondensation processes are the same as in Example 1;

[0152] The obtained purified polymer did not completely remove the color. This result proves that the one-step method, due to the extremely wide molecular weight distribution of the complex mixture system, but the impurities being wrapped in chain segments of different lengths, makes the subsequent molecular enrichment adsorption, ion exchange and distillation purification steps inefficient and incomplete. As a result, it cannot achieve efficient decolorization and the presence of dyes and other impurities is not conducive to the polycondensation reaction to obtain high molecular weight polymers, resulting in no significant improvement in their mechanical properties.

[0153] Comparative Example 2:

[0154] The difference between the waste colored nylon recycling method in this comparative example and Example 1 is that ethylene glycol is used for alcoholysis.

[0155] The raw materials and recycling pretreatment are the same as in Example 1;

[0156] Depolymerization of waste PA6: 0.87 kg of ethylene glycol, 0.01 kg of antimony acetate, and the same amount of PA6 powder as in Example 1 were mixed and added to a depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 230 °C for 6 hours. Then, 1.67 kg of succinic acid was added, and N2 was continuously introduced. The temperature was gradually increased to 230 °C while stirring at 300 r / min. The esterification reaction was carried out for 7 hours to obtain crude PA6-co-PES oligomer.

[0157] The subsequent purification and melt polycondensation processes are the same as in Example 1.

[0158] Comparative Example 3:

[0159] The difference between the waste colored nylon recycling method in this comparative example and Example 1 is that succinic acid is used for acid hydrolysis.

[0160] The raw materials and recycling pretreatment are the same as in Example 1;

[0161] Depolymerization of waste PA6: 1.67 kg of succinic acid, 0.01 kg of antimony acetate, and the same amount of PA6 powder as in Example 1 were mixed and added to a depolymerization reactor. The mixture was stirred at 300 r / min and reacted at 230 °C for 6 hours. Then, 0.87 kg of ethylene glycol was added, and N2 was continuously introduced. The temperature was gradually increased to 230 °C while stirring at 300 r / min. The esterification reaction was carried out for 7 hours to obtain crude PA6-co-PES oligomer.

[0162] The subsequent purification and melt polycondensation processes are the same as in Example 1.

[0163] Comparative Example 4:

[0164] The difference between the waste colored nylon recycling method in this comparative example and Example 1 is that the waste colored PA6 is purified, depolymerized, and then polymerized again.

[0165] The raw materials and recycling pretreatment are the same as in Example 1;

[0166] Purification of PA6: Waste colored PA6 was dissolved in formic acid solution for 3 hours and then transferred to a purification reactor. Metal ions and small molecule impurities were removed by activated carbon and anion and cation exchange resins. Insoluble matter was removed by filtration. The low-boiling components were separated at 170℃ and 2000Pa for 20 min and the high-boiling components were separated at 160℃ and 500Pa for 30 min to remove the low-boiling and high-boiling components, thus obtaining purified PA6.

[0167] The process of depolymerizing and melt polycondensing the purified PA6 is the same as in Example 1.

[0168] Comparative Example 5:

[0169] The difference between the waste colored nylon recycling method in this comparative example and Example 1 is that it uses the existing conventional melt granulation method to regenerate PA6.

[0170] The raw materials and recycling pretreatment are the same as in Example 1;

[0171] Melt granulation regeneration: PA6 powder is added to a melt reactor and N2 is continuously passed through it. The product is directly melted and regenerated at 240°C with a stirring speed of 300 r / min. The resulting product has a darker color and a lower molecular weight.

[0172] The performance of the final products of Examples 1-8 and Comparative Examples 1-5 was tested below, and the results are shown in Table 1.

[0173] Table 1 Performance parameters of the embodiments and comparative examples

[0174] .

[0175] Given that there are numerous embodiments of the present invention, and the raw materials and quantities involved can be selected within a limited range according to actual needs, and that the experimental data for each embodiment are extensive and numerous, it is not suitable to list and describe them one by one here. However, the content to be verified and the final conclusions obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be described one by one here.

[0176] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for recycling and regenerating waste colored nylon, characterized in that, Includes the following steps: (1) The waste colored nylon is sorted, impurities are removed, and it is washed and crushed to obtain polyamide 6 powder; the polyamide 6 powder is mixed with a depolymerizing agent and depolymerized at 180-280℃ for 5-20 hours under stirring conditions to obtain crude polyamide 6-co-polyester oligomer. The mass ratio of polyamide 6 powder to depolymerizing agent is (0.1-10):1, and the depolymerizing agent is a carboxyl-terminated polyester synthesized by esterification reaction of dicarboxylic acid or acid anhydride and diol. (2) The crude polyamide 6-co-polyester oligomer was dissolved in an organic solvent and purified and distilled to obtain refined polyamide 6-co-polyester oligomer; (3) The refined polyamide 6-co-polyester oligomer was subjected to melt polycondensation reaction at 180-280℃ and 0.001-500Pa pressure for 4-30 hours to obtain polyamide 6-co-polyester copolymer.

2. The method for recycling and regenerating waste colored nylon according to claim 1, characterized in that, In step (2), the organic solvent is at least one of dichloromethane, chloroform, cyclohexanone, formic acid, acetic acid, methanol, ethanol, isopropanol, m-cresol, choline ionic liquid, dimethyl sulfoxide, and carbon tetrachloride. The purification includes molecular enrichment purification and ion screening purification; The enrichment medium used in the molecular enrichment purification is selected from at least one or more of activated carbon, silica gel, adsorption resin, bentonite, and diatomaceous earth. The ion screening and purification process involves purification using ion exchange resin.

3. The method for recycling and regenerating waste colored nylon according to claim 1, characterized in that, In step (2), distillation includes the separation of low-boiling components and reboiling components; The conditions for separating the low-boiling components are: temperature of 120-180℃, pressure of 1-60kPa, and residence time of less than 60 minutes. The conditions for separating the reboiling components are: temperature 150-240℃, pressure 0.1-3kPa, and residence time less than 60 minutes.

4. The method for recycling and regenerating waste colored nylon according to claim 1, characterized in that, The waste colored nylon is selected from at least one of polyamide 6 textiles used in clothing, carpets, nylon fabrics, and fishing nets.

5. The method for recycling and regenerating waste colored nylon according to claim 1, characterized in that, It also includes the following steps: The polyamide 6-co-polyester copolymer was subjected to devolatilization treatment at 130-250℃ and pressure below 1000Pa for 30-180 minutes, and then filtered through a melt filter to obtain polyamide 6-co-polyester melt.

6. The method for recycling and regenerating waste colored nylon according to claim 1, characterized in that, The preparation process of the depolymerizing agent includes: mixing dicarboxylic acid or anhydride, diol and catalyst under inert gas protection, and carrying out esterification reaction at 180-260℃ for 5-24 hours under stirring conditions; The molar ratio of dicarboxylic acid or anhydride to diol is (1.01-3):

1.

7. The method for recycling and regenerating waste colored nylon according to claim 6, characterized in that, The dicarboxylic acid or anhydride is selected from at least one of succinic acid, adipic acid, glutaric acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, phthalic acid, isophthalic acid, terephthalic acid, malonic acid, succinic anhydride, phthalic anhydride, and adipic anhydride. The diol is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,9-nonanediol, hydroquinone, terephthalic acid diethanol, and 2,5-furandiol.

8. The method for recycling and regenerating waste colored nylon according to claim 7, characterized in that, The catalyst is added at a rate of 0.01-5% of the total mass of dicarboxylic acid or anhydride and diol. The catalyst is selected from at least one of tetrabutyl titanate, antimony acetate, zinc acetate, germanium dioxide, zinc oxide, antimony trioxide, antimony glycolate, p-benzenesulfonic acid, magnesium acetate, and magnesium succinate.

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