Method for recycling waste nylon textile

Abstract

The present application belongs to the technical field of recycling of waste textiles, and particularly relates to a method for recycling waste nylon textiles, comprising: mechanically crushing the waste nylon textiles to obtain nylon fragments; mixing the nylon fragments, polyacrylic acid, metal or its compound, and then, under inert atmosphere and stirring, heating to 60-120 DEG C for 0.5-2 hours, and then, continuously heating to 220-300 DEG C, and catalytically depolymerizing under 1-5 MPa to obtain depolymerate; wherein the metal element of the metal or its compound is a metal having coordination ability with carbonyl; purifying the depolymerate to obtain caprolactam. The present application uses one-step mixing and two-step heating process, and the catalyst exists in the form of coexistence of metal coordination sites and carboxyl, so that the catalyst simultaneously plays the metal coordination activation role and the amide bond breaking and exchange reaction participated by carboxylic acid in the depolymerization process, forming a synergistically promoted efficient depolymerization mechanism, and effectively improving the efficiency of catalytic depolymerization.

Description

Technical Field

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

[0002] Nylon, also known as polycaprolactam or PA6, is an important synthetic fiber material used in engineering and textiles, and is widely used in clothing, home textiles and industrial textiles.

[0003] The existing methods for recycling waste nylon are mainly chemical depolymerization, which realizes the monomer recovery of nylon. However, most of them rely on strong acid, strong alkali or metal-supported catalytic systems, which generally have problems such as harsh reaction conditions, long depolymerization time, severe equipment corrosion and difficulty in catalyst recovery. Summary of the Invention

[0004] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a method for recycling and regenerating waste nylon textiles that meets one or more of the aforementioned needs.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for recycling and regenerating waste nylon textiles includes the following steps:

[0007] S1. Mechanically crush waste nylon textiles to obtain nylon fragments;

[0008] S2. After mixing nylon fragments, polyacrylic acid, metal or its compound, the mixture is heated to 60-120 °C and held for 0.5-2 h under an inert atmosphere and with stirring. Then, the temperature is further increased to 220-300 °C and catalytic depolymerization is carried out at 1-5 MPa to obtain the depolymerized product. The metal element of the metal or its compound is a metal with the ability to coordinate with carbonyl groups.

[0009] S3. The depolymerized product is purified to obtain caprolactam.

[0010] As a preferred embodiment, the metal element of the metal or its compound is a divalent metal, and the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.1~0.3).

[0011] As a preferred embodiment, the metal element of the metal or its compound is a trivalent metal, and the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.07~0.2).

[0012] As a preferred embodiment, the metal element of the metal or its compound is a tetravalent metal, and the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.05~0.15).

[0013] As a preferred embodiment, the metal element is Zn, Sn, Fe, Al, or Ti.

[0014] As a preferred embodiment, in step S2, the mass ratio of nylon fragments to polyacrylic acid is (5-50):1.

[0015] As a preferred embodiment, in step S2, the reaction time for catalytic depolymerization is 2 to 8 hours.

[0016] As a preferred embodiment, if the waste nylon textile is dyed textile, then chemical decolorization is performed after mechanical crushing in step S1.

[0017] As a preferred embodiment, step S3 includes the following purification steps:

[0018] S31. Flash evaporation is performed on the depolymerized product. The concentrated organic phase after flash evaporation enters a falling film evaporator and is evaporated under reduced pressure at an absolute pressure of 0.05–5 kPa and a temperature of 80–150 °C. The resulting gaseous caprolactam is condensed and collected to obtain crude caprolactam.

[0019] S32. Crude caprolactam is dissolved in an organic solvent and decolorized by adsorption or chemical means. After decolorization, the solvent is recovered by vacuum distillation to obtain concentrated crude caprolactam.

[0020] S33. Under reduced pressure, crude caprolactam is distilled at a pressure of 50–300 Pa at the top of the column, a temperature of 160–200 ℃ at the bottom of the column, and a temperature of 110–140 ℃ at the top of the column to obtain caprolactam.

[0021] As a preferred embodiment, the solid residue after flash evaporation is dispersed in water or an organic solvent, then filtered to remove impurities, and the filtrate is subjected to rotary evaporation and drying to obtain a regenerated catalyst.

[0022] Compared with the prior art, the beneficial effects of this invention are:

[0023] This invention anchors the metal active center to the main chain side group of polyacrylic acid, constructing a polymeric catalyst containing side-chain metal and carboxyl groups. While maintaining high activation capacity for PA6 amide bonds, it achieves stable existence and reusability of the catalyst. Furthermore, the side-chain carboxyl groups in the catalyst are not completely replaced by metal ions, but exist as metal coordination sites coexisting with the carboxyl groups. This allows the catalyst to simultaneously exert metal coordination activation and amide bond breaking and exchange reactions involving carboxylic acids during depolymerization, forming a synergistically promoted and highly efficient depolymerization mechanism.

[0024] In this synergistic system, the metal active center effectively reduces the activation energy for PA6 amide bond breaking, while the ortho-carboxyl group accelerates the depolymerization and rearrangement of the molecular chain. This significantly improves the depolymerization rate and monomer generation efficiency under milder conditions, while shortening the depolymerization time. Compared with existing technologies, this method exhibits significant advantages in depolymerization efficiency, reaction kinetics, and catalyst cycle stability. It is suitable for the efficient and green chemical recycling of waste nylon textiles and has promising industrial application prospects. Attached Figure Description

[0025] Figure 1 This is the infrared spectrum of the catalyst and zinc oxide in Example 1 of the present invention;

[0026] Figure 2 This is the X-ray photoelectron spectrum of the catalyst in Example 1 of the present invention. Detailed Implementation

[0027] The following provides a detailed description of the method for recycling and regenerating waste nylon textiles according to the present invention.

[0028] The present invention discloses a method for recycling and regenerating waste nylon textiles, employing a polymeric catalyst containing metal and carboxyl groups to depolymerize nylon. The polymeric chains containing side-chain metal and carboxyl groups simultaneously act as catalysts and participate in the reaction during depolymerization. The unsubstituted carboxyl groups in the side chains provide an acidic environment and exchange with the nylon molecular chains. The active centers of the side-chain metal synergistically promote the breaking of amide bonds through coordination, thereby achieving efficient depolymerization of nylon. Furthermore, simple separation is achieved based on the solid-phase characteristics of the polymeric catalyst.

[0029] Specifically, the method for recycling and regenerating waste nylon textiles of the present invention includes the following steps:

[0030] (1) Pretreatment;

[0031] Waste nylon textiles are sorted and mechanically crushed to obtain textile fragments;

[0032] If the waste nylon textiles are dyed textiles, the textile fragments will be put into a chemical decolorizing solution and chemically decolorized at 40–120 °C for 0.5–10 h. After decolorization, the textiles will be separated into solid and liquid, washed with water until neutral, and then dried at 80–120 °C. The specific temperature and time of the treatment can be selected according to the actual application.

[0033] The chemical decolorization treatment described above is preferably carried out at 60–90 °C for 1.5–3 h.

[0034] The above decolorization solution is an aqueous solution containing 0.5–2 wt% hydrogen peroxide and a pH of 9–11 or an aqueous solution containing 1–2 wt% sodium dithionite and a pH of 7–10; the specific choice can be made according to actual application requirements.

[0035] (2) Catalytic depolymerization;

[0036] After mixing the pretreated textile fragments from step (1) with polyacrylic acid, metal, or their compounds, the mixture is heated to 60–120 °C and held for 0.5–2 h under an inert atmosphere and stirring conditions of 100–300 r / min to obtain a polymer catalyst. Then, the temperature is further increased to 220–300 °C and catalytic depolymerization is carried out at 1–5 MPa for 2–8 h to obtain the depolymerized product. The specific processing parameters such as temperature, time, pressure, and stirring conditions can be selected according to the actual application.

[0037] The mass ratio of textile fragments to polyacrylic acid is (5-50):1; more preferably (10-25):1, and the specific mass ratio can be determined according to actual application requirements.

[0038] The metal elements of the aforementioned metals or their compounds are metals that have the ability to coordinate with carbonyl groups, such as Zn, Sn, Fe, Al, Ti, etc., and the specific elements are determined according to the actual application requirements.

[0039] More specifically, if the metal element of the metal or its compound is a divalent metal, the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.1~0.3), ensuring that the polymer catalyst contains side-chain metal and carboxyl groups;

[0040] If the metal element in the metal or its compound is a trivalent metal, the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.07~0.2) to ensure that the polymer catalyst contains side-chain metal and carboxyl groups;

[0041] If the metal element in the metal or its compound is a tetravalent metal, the molar ratio of the carboxylic acid group to the metal element in polyacrylic acid is 1:(0.05~0.15) to ensure that the polymer catalyst contains side-chain metal and carboxyl groups;

[0042] The synthesis temperature of the above catalyst is further preferably 80–100 °C, and the synthesis time is further preferably 0.8–1.5 h;

[0043] The temperature for the above-mentioned catalytic depolymerization is further preferably 220–250 °C, the pressure is further preferably 1–3 MPa, and the time is further preferably 4–10 h.

[0044] The aforementioned inert atmosphere is nitrogen with a purity ≥ 99.99%;

[0045] (3) Product separation and preliminary purification;

[0046] The depolymerized product obtained in step (2) is transferred to a flash evaporator and flashed at a pressure of 50–200 kPa to separate and recover more than 85% of the water. The concentrated organic phase after flashing enters a falling film evaporator and is evaporated under reduced pressure at an absolute pressure of 0.05–5 kPa and a temperature of 80–150 °C. The evaporated caprolactam gas phase is completely condensed and collected by a condenser at 20–40 °C to obtain crude caprolactam.

[0047] The operating pressure of the aforementioned flash tank is further preferably 80–150 kPa;

[0048] The above-mentioned reduced pressure evaporation conditions are further preferably 100-800 Pa absolute pressure and 100-130 ℃ temperature;

[0049] (4) Decolorization and distillation again;

[0050] The crude caprolactam obtained in step (3) is dissolved in an organic solvent of 2 to 10 times its mass to obtain a decolorized solution; the decolorized solution is subjected to dynamic adsorption decolorization through an adsorption column packed with activated carbon and / or diatomaceous earth, or 1 to 5% of the crude caprolactam mass of decolorizing agent is added and statically decolorized at 50 to 80 °C for 0.5 to 1.5 h, followed by filtration; the decolorized solution is subjected to vacuum distillation to recover the solvent and obtain concentrated crude caprolactam; the crude caprolactam is fed into a distillation column and subjected to vacuum distillation under the conditions of an absolute pressure of 50 to 300 Pa at the top of the column, a bottom temperature of 160 to 200 °C, and a top temperature of 110 to 140 °C, and the vapor fraction is collected at the top of the column and condensed to obtain the caprolactam product;

[0051] The above-mentioned reduced pressure distillation conditions are further optimized as follows: top pressure 120-150 Pa, bottom temperature 185-195 ℃, and top temperature 132-136 ℃;

[0052] (5) Catalyst recovery and regeneration;

[0053] The solid slurry remaining after flash evaporation in step (3) is filtered by pressure or centrifugation to obtain a wet catalyst filter cake; the filter cake is washed 2 to 3 times with water or organic solvent at 50 to 80 ℃, and the amount of solvent used each time is 2 to 5 times the mass of the filter cake; the washed catalyst is dried in a vacuum drying oven at 100 to 120 ℃ for 2 to 4 h.

[0054] The organic solvents mentioned above are selected from one or more of methanol, ethanol, isopropanol, and ethyl acetate.

[0055] The following specific embodiments and comparative examples further explain the recycling and regeneration method of waste nylon textiles of the present invention.

[0056] Example 1:

[0057] The recycling method for waste nylon textiles in this embodiment is used for recycling waste navy blue pure nylon products, and specifically includes the following steps:

[0058] (1) Pretreatment;

[0059] Take 2 kg of waste dark blue 100% nylon, sort and crush it into fragments, weigh 500.0 g of fragments, place them in a stirred reactor, add a decolorizing solution containing 2 wt% hydrogen peroxide (adjust pH to 10.5 with NaOH), solid-liquid ratio 1:15, stir at 85 ℃ for 2.5 h. After treatment, the color of the fabric fades from dark blue to light grayish white. After pressure filtration, wash thoroughly with 60 ℃ hot water until neutral, and then dry in a 105 ℃ forced-air drying oven for 6 h to obtain light gray clean nylon fragments.

[0060] (2) Catalytic depolymerization;

[0061] Accurately weigh 100 g of the above-mentioned clean fragments and add them together with 7.8 g of polyacrylic acid and 2.2 g of zinc oxide into a high-pressure reactor. After replacing the air with nitrogen, the reaction system is heated to 80 °C and maintained at a stirring speed of 250 r / min for 1 h to synthesize the catalyst. Then, the temperature is increased to 230 °C at a rate of 8 °C / min, and the catalyst is depolymerized under a pressure of 1.8 MPa for 4 h.

[0062] Among them, Zn 2+ The molar ratio of the polyacrylic acid side chain carboxyl group to the polyacrylic acid side chain carboxyl group is 0.25:1;

[0063] (3) Product separation and preliminary purification;

[0064] The depolymerized liquid was transferred to a flash tank for dehydration at 80 kPa pressure. The organic phase was evaporated under reduced pressure in a falling film evaporator at 1.5 kPa and 125 °C. Finally, it was condensed to obtain light yellow transparent crude caprolactam.

[0065] (4) Decolorization and distillation again;

[0066] Crude caprolactam was dissolved in 400.0 g of methanol and decolorized by passing it through an activated carbon fixed bed adsorption column. The decolorized solution was concentrated by rotary evaporation and then subjected to vacuum distillation. The fractions were collected to obtain caprolactam.

[0067] The vacuum distillation column has a top pressure of 150 Pa, a top temperature of 135 ℃, a bottom temperature of 190 ℃, and a reflux ratio of 3:1.

[0068] (5) Product analysis and catalyst recovery and regeneration;

[0069] like Figure 1As shown, infrared spectroscopy was performed on ZnO and the catalyst PAA-ZnO. The pure ZnO sample showed no obvious characteristic absorption peaks of organic functional groups, consistent with the structural characteristics of its inorganic oxide. For the catalyst PAA-ZnO, at 3500 cm⁻¹... -1 Near the 1667.56 cm⁻¹, a stretching vibration peak of the carboxyhydroxyl group (-OH) is observed. -1 1616.18 cm -1 1562.64 cm -1 New peaks appeared nearby, corresponding to carboxyl groups and Zn. 2+ The carboxylate salt -COO formed after the reaction - -Zn 2+ The stretching vibration peaks indicate that the carboxyl group of PAA interacts with Zn. 2 + Chemical bonding occurred, rather than simple physical mixing; for example... Figure 2 As shown, X-ray photoelectron spectroscopy results indicate the presence of three elements—Zn, O, and C—in the catalyst, corresponding to the composition of the PAA-ZnO composite structure. The results from the infrared and X-ray photoelectron spectroscopy analyses corroborate each other, confirming that the PAA-ZnO catalyst is formed by the interaction of the PAA carboxyl group and Zn... 2+ The stable composite system formed by chemical bonding provides structural support for its catalytic performance and recovery stability;

[0070] This embodiment ultimately yielded a colorless and transparent caprolactam product, with a caprolactam yield of 91.9% based on the recovered crude caprolactam.

[0071] The solid slurry remaining after flash dehydration in step (3) was separated by pressure filtration to obtain a wet filter cake containing the catalyst. Methanol was added to the wet filter cake and stirred and washed twice at 60 °C. The mass of methanol used in each wash was 3 times the mass of the wet filter cake to remove residual caprolactam and low molecular weight byproducts. After washing, the obtained catalyst was placed in a vacuum drying oven at 110 °C and dried for 3 h to obtain the recovered PAA-ZnO catalyst. The recovered catalyst maintained good structural stability and could be directly used for subsequent cyclic depolymerization reactions.

[0072] Example 2:

[0073] The recycling method for waste nylon textiles in this embodiment is used for the recycling of black pure nylon waste, and specifically includes the following steps:

[0074] (1) Pretreatment;

[0075] Take 2 kg of black waste nylon with a lot of stains on the surface. After crushing, wash it with hot water at 60 ℃ for 15 minutes, and then perform chemical decolorization. The decolorization solution is a strong oxidizing system containing 2 wt% hydrogen peroxide aqueous solution with a pH of 9. It is treated at 90 ℃ for 3 h. After treatment, the fragments are dark gray. The subsequent pressure filtration separation, water washing and drying are the same as in Example 1 to obtain clean fragments for later use.

[0076] (2) Catalytic depolymerization;

[0077] Accurately weigh 100 g of the above-mentioned clean fragments, add 8.76 g of polyacrylic acid and 1.24 g of alumina to a high-pressure reactor, replace the air with nitrogen, heat the reaction system to 100 °C and maintain it for 1.5 h under a stirring speed of 300 r / min to synthesize the catalyst; then increase the temperature to 250 °C at 8 °C / min and catalytically depolymerize under a pressure of 1.0 MPa for 6 h.

[0078] Subsequent product separation and preliminary purification, recoloring and distillation, catalyst recovery and regeneration operations are the same as in Example 1;

[0079] In this embodiment, the caprolactam yield is 95.6% based on the recovered crude caprolactam.

[0080] Example 3:

[0081] The recycling method for waste nylon textiles in this embodiment is used for recycling fluorescent yellow-green pure nylon waste, and specifically includes the following steps:

[0082] (1) Pretreatment;

[0083] Take 2 kg of fluorescent yellow-green nylon waste, crush it and then chemically decolorize it. The decolorizing solution is an aqueous solution of 2 wt% sodium dithionite with a pH of 10 and a solid-liquid ratio of 1:10. Stir at 70 °C for 2 h. After treatment, the fluorescence is basically eliminated and the fragments are very light beige. Subsequent pressure filtration, washing and drying are the same as in Example 1 to obtain clean fragments for later use.

[0084] (2) Catalytic depolymerization;

[0085] Accurately weigh 100 g of the above-mentioned clean fragments and add them together with 4.1 g of polyacrylic acid and 0.4 g of iron oxide into a high-pressure reactor. After replacing the air with nitrogen, the reaction system is heated to 90 °C for 1 h under a stirring speed of 300 r / min to synthesize the catalyst. Then, the temperature is increased to 240 °C at 8 °C / min and the catalyst is depolymerized under a pressure of 1.5 MPa for 8 h.

[0086] Subsequent product separation and preliminary purification, recoloring and distillation, catalyst recovery and regeneration operations are the same as in Example 1;

[0087] In this embodiment, the caprolactam yield was 89.4% based on the recovered crude caprolactam.

[0088] Example 4:

[0089] The recycling method for waste nylon textiles in this embodiment is used for the recycling of military green camouflage pure nylon waste, and specifically includes the following steps:

[0090] (1) Pretreatment;

[0091] Two kilograms of military green camouflage nylon waste, composed of multiple colors including green, brown, and black, were first treated with a 2 wt% hydrogen peroxide solution at pH 11 at 70 ℃ for 2 hours. After washing with water, it was then treated with a 2 wt% sodium dithionite solution at pH 7 at 80 ℃ for 1.5 hours. After treatment, the color was basically uniformly light yellowish-brown. Subsequent pressure filtration, washing, and drying were the same as in Example 1 to obtain clean fragments for later use.

[0092] (2) Catalytic depolymerization;

[0093] Accurately weigh 100 g of the above-mentioned clean fragments and add them together with 3.54 g of polyacrylic acid and 0.46 g of zinc oxide into a high-pressure reactor. After replacing the air with nitrogen, the reaction system is heated to 120 °C and reacted for 0.5 h under a stirring speed of 100 r / min. Then, the temperature is raised to 300 °C and catalytic depolymerization is carried out under a pressure of 3.0 MPa for 2 h.

[0094] Subsequent product separation and preliminary purification, recoloring and distillation, catalyst recovery and regeneration operations are the same as in Example 1;

[0095] In this embodiment, the caprolactam yield was 90.7% based on the recovered crude caprolactam.

[0096] Example 5:

[0097] The recycling method for waste nylon textiles in this embodiment is used for the recycling of light gray pure nylon waste yarn, and specifically includes the following steps:

[0098] (1) Pretreatment and deep decolorization;

[0099] Take 2 kg of light gray nylon waste yarn, which is light in color, and use a 1 wt% sodium dithionite washing and decolorizing solution with pH 7 to treat it at 60 ℃ for 1.5 h. Then wash and dry it with water to obtain clean fragments for later use.

[0100] (2) Catalytic depolymerization;

[0101] Accurately weigh 100 g of the above clean fragments, add 3.75 g of polyacrylic acid and 0.25 g of alumina to a high-pressure reactor, replace the air with nitrogen, and heat the reaction system to 80 °C for 0.8 h under a stirring speed of 250 r / min to synthesize the catalyst. Then, raise the temperature to 230 °C and catalytically depolymerize under a pressure of 1.5 MPa for 5 h.

[0102] Subsequent product separation and preliminary purification, recoloring and distillation, catalyst recovery and regeneration operations are the same as in Example 1;

[0103] In this embodiment, the caprolactam yield is 93.5% based on the recovered crude caprolactam.

[0104] Example 6:

[0105] The recycling method for waste nylon textiles in this embodiment is used for the recycling of white pure nylon waste, and specifically includes the following steps:

[0106] (1) Pretreatment;

[0107] Take 2 kg of pure nylon filament waste without added pigments, sort it and break it into fragments, wash it with deionized water at 60℃ for 1.0 h, wash it until neutral and then dry it.

[0108] (2) Catalytic depolymerization;

[0109] Accurately weigh 100 g of the above-mentioned clean fragments and add them together with 4.9 g of polyacrylic acid and 1.1 g of zinc oxide into a high-pressure reactor. After replacing the air with nitrogen, the reaction system is heated to 60 °C and maintained at a stirring speed of 250 r / min for 2 h to synthesize the catalyst. Then, the temperature is increased to 220 °C at a rate of 8 °C / min, and the catalyst is depolymerized under a pressure of 1.0 MPa for 4 h.

[0110] Subsequent product separation and preliminary purification, recoloring and distillation, catalyst recovery and regeneration operations are the same as in Example 1;

[0111] In this embodiment, the caprolactam yield was 94.1% based on the recovered crude caprolactam.

[0112] Example 7:

[0113] The difference between the waste nylon textile recycling method in this embodiment and that in embodiment 1 is:

[0114] During the catalytic depolymerization process, accurately weigh 100 g of the above-mentioned clean fragments, 20 g of polyacrylic acid, and titanium hydroxide according to the molar ratio of polyacrylic acid to titanium ions of 1:0.05; other steps and conditions are the same as in Example 1;

[0115] In this embodiment, the caprolactam yield was 90.8% based on the recovered crude caprolactam.

[0116] Example 8:

[0117] The difference between the waste nylon textile recycling method in this embodiment and that in embodiment 1 is:

[0118] During the catalytic depolymerization process, accurately weigh 100 g of the above-mentioned clean fragments, 2 g of polyacrylic acid, and titanium hydroxide according to the molar ratio of polyacrylic acid to titanium ions of 1:0.1; other steps and conditions are the same as in Example 1;

[0119] In this embodiment, the caprolactam yield was 91.3% based on the recovered crude caprolactam.

[0120] Example 9:

[0121] The difference between the waste nylon textile recycling method in this embodiment and that in embodiment 1 is:

[0122] During the catalytic depolymerization process, accurately weigh 100 g of the above-mentioned clean fragments, 10 g of polyacrylic acid, and titanium hydroxide according to the molar ratio of polyacrylic acid to titanium ions of 1:0.15; other steps and conditions are the same as in Example 1;

[0123] In this embodiment, the caprolactam yield was 92.7% based on the recovered crude caprolactam.

[0124] Example 10:

[0125] The difference between the waste nylon textile recycling method in this embodiment and that in embodiment 1 is:

[0126] During the catalytic depolymerization process, accurately weigh 100 g of the above-mentioned clean fragments and 10 g of polyacrylic acid, and mix the polyacrylic acid with Sn... 2+ Stannous oxide was weighed with an ion molar ratio of 1:0.1; other steps and conditions were the same as in Example 1.

[0127] In this embodiment, the caprolactam yield was 93.7% based on the recovered crude caprolactam.

[0128] Comparative Example 1:

[0129] The difference between the waste nylon textile recycling method in this comparative example and Example 1 is that the synthesis time of the catalyst was not guaranteed.

[0130] Specifically, during the catalytic depolymerization process, the reaction system was directly heated to 230°C at a heating rate of 8°C / min, and catalytic depolymerization was carried out for 5 h under a pressure of 1.8 MPa. Other steps and conditions were the same as in Example 1.

[0131] In this comparative example, based on the recovered crude caprolactam, the caprolactam yield was 83.0%, which was significantly lower than that of Example 1. Under the same reaction temperature conditions, it took longer to reach a stable depolymerization state, and the depolymerization rate was significantly reduced. At the same time, some metal oxides that did not fully participate in the reaction were observed to be physically mixed with polyacrylic acid in the reaction residue, resulting in insufficient homogeneity of the catalytic system. The activity of the recovered catalyst was significantly lower than that of Example 1, and the depolymerization efficiency further decreased after multiple cycles.

[0132] The results show that without low-temperature in-situ reaction to form a polymer catalyst containing side-chain metals and carboxyl groups, the metal source and the carboxyl-containing polymer are difficult to form stable and uniformly distributed active centers, which leads to a significant reduction in the initiation efficiency and overall rate of polyamide depolymerization.

[0133] Comparative Example 2:

[0134] The difference between the waste nylon textile recycling method in this comparative example and Example 1 is that the metal completely replaces the carboxyl groups of polyacrylic acid.

[0135] Specifically, adjust Zn 2+ The molar ratio of polyacrylic acid to the carboxyl group of the side chain is 0.55:1; other steps and conditions are the same as in Example 1;

[0136] The synthesized polymeric catalyst does not contain carboxylic acid groups in its polymeric side chains; it exists only as a zinc carboxylic acid structure.

[0137] In this embodiment, the caprolactam yield was 70.6% based on the recovered crude caprolactam, which was significantly lower than 91.9% in Example 1. At the same time, within the same reaction time, the proportion of incompletely depolymerized oligomers in the reaction system was higher, indicating that the depolymerization rate was lower than that in Example 1.

[0138] The results showed that when the carboxyl group was replaced by Zn 2+ Under conditions of complete substitution, the catalytic system struggles to achieve efficient and rapid depolymerization of nylon.

[0139] Comparative Example 3:

[0140] The difference between the waste nylon textile recycling method in this comparative example and Example 1 is that only polyacrylic acid is used for catalytic depolymerization.

[0141] Specifically, accurately weigh 100.0 g of the above-mentioned clean fragments and add them to a high-pressure reactor along with 10.0 g of polyacrylic acid. The remaining steps and conditions are the same as in Example 1.

[0142] In this embodiment, the caprolactam yield was 78.4% based on the recovered crude caprolactam, which is significantly lower than the 91.9% in Example 1. Within the same reaction time, there were many oligomers that were not completely depolymerized in the reaction system, indicating that the depolymerization rate and depth were both insufficient.

[0143] The depolymerization process of polycaprolactam PA6 by the polymer chain catalytic system containing side-chain carboxylic acids and metals in this invention is as follows:

[0144] In this reaction system, metal ion M + First, it reacts with the carboxyl groups on the polyacrylic acid (PAA) chain to form a stable carboxylic acid metal salt structure, thereby constructing a metal active center with strong polarization ability on the PAA chain segment. This carboxylic acid metal salt structure achieves stable anchoring of metal ions on the polymer backbone and significantly enhances the amide bond reactivity of PA6, transforming it from a structural group into a reaction site with actual catalytic function. Under the synergistic effect of metal and carboxyl groups, the PAA carboxyl groups located near the metal coordination sites can directly participate in the depolymerization reaction of the amide bonds in the PA6 molecular chain, while the metal ions simultaneously further activate the carbonyl groups through coordination, thereby significantly reducing the energy barrier required for amide bond cleavage. This synergistic effect causes the amide bonds to preferentially break near the carboxyl-metal active center, achieving efficient depolymerization of the PA6 main chain. As the main chain cleavage continues, the resulting oligomeric segments containing terminal carboxyl groups undergo further intramolecular cyclization under the induction of metal coordination, ultimately generating a stable six-membered ring lactam product, caprolactam, achieving efficient depolymerization of PA6 in the synergistic catalytic system.

[0145] 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.

[0146] 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 nylon textiles, characterized in that, Includes the following steps: S1. Mechanically crush waste nylon textiles to obtain nylon fragments; S2. After mixing nylon fragments, polyacrylic acid, and a metal compound, the mixture is heated to 60–120 °C and held for 0.5–2 h under an inert atmosphere and with stirring. Then, the temperature is further increased to 220–300 °C, and catalytic depolymerization is carried out at 1–5 MPa to obtain the depolymerized product. The metal element in the metal compound is a metal with the ability to coordinate with carbonyl groups. S3. Purify the depolymerized product to obtain caprolactam; The metal compound is zinc oxide, aluminum oxide, iron oxide, titanium hydroxide, or stannous oxide; When the metal element in the metal compound is a divalent metal, the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.1~0.3). When the metal element in the metal compound is a trivalent metal, the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.07~0.2). When the metal element of the metal compound is a tetravalent metal, the molar ratio of the carboxylic acid group of polyacrylic acid to the metal element is 1:(0.05~0.15).

2. The method for recycling and regenerating waste nylon textiles according to claim 1, characterized in that, In step S2, the mass ratio of nylon fragments to polyacrylic acid is (5-50):

1.

3. The method for recycling and regenerating waste nylon textiles according to claim 1, characterized in that, In step S2, the reaction time for catalytic depolymerization is 2 to 8 hours.

4. The method for recycling and regenerating waste nylon textiles according to claim 1, characterized in that, If the waste nylon textiles are dyed textiles, then chemical decolorization will be carried out after mechanical crushing in step S1.

5. The method for recycling and regenerating waste nylon textiles according to claim 1, characterized in that, In step S3, purification includes the following steps: S31. Flash evaporation is performed on the depolymerized product. The concentrated organic phase after flash evaporation enters a falling film evaporator and is evaporated under reduced pressure at an absolute pressure of 0.05–5 kPa and a temperature of 80–150 °C. The resulting gaseous caprolactam is condensed and collected to obtain crude caprolactam. S32. Crude caprolactam is dissolved in an organic solvent and decolorized by adsorption or chemical means. After decolorization, the solvent is recovered by vacuum distillation to obtain concentrated crude caprolactam. S33. Under reduced pressure, crude caprolactam is distilled at a pressure of 50–300 Pa at the top of the column, a temperature of 160–200 ℃ at the bottom of the column, and a temperature of 110–140 ℃ at the top of the column to obtain caprolactam.

6. The method for recycling and regenerating waste nylon textiles according to claim 5, characterized in that, The solid residue after flash evaporation is dispersed in water or an organic solvent, then filtered to remove impurities, and the filtrate is subjected to rotary evaporation and drying to obtain a regenerated catalyst.

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