A method for recovering nylon from waste nylon and cotton blended textiles

Abstract

The present application relates to a kind of methods for recycling nylon from waste nylon and cotton blended textiles, comprising: waste nylon and cotton blended textiles are sheared and broken, impurity is removed, washing and drying, and sample fragments are obtained;Hydrogen ion of part of sulfonic acid group in polystyrene sulfonic acid is replaced by metal ion to obtain catalyst;Wherein, metal ion is the metal ion capable of coordinating with amide bond;Sample fragments are mixed with catalyst and then depolymerization is carried out, and the depolymerization product obtained is purified to obtain caprolactam.The present application can realize the directional catalytic depolymerization effect of nylon, while separating cotton component;Using the synergistic effect of polystyrene sulfonic acid and polystyrene sulfonic acid metal salt coexisting in the structure of catalyst, the newly exposed amide bond is continuously activated by proton, and the metal ion synchronously stabilizes the intermediate, so that the molecular chain is uniformly broken from the end to the inside, rather than locally broken, to avoid the generation of oligomer, directly generate caprolactam monomer, and improve the yield of caprolactam.

Description

Technical Field

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

[0002] Currently, recycling technologies for waste single-component textiles are relatively mature. However, for nylon and cotton blended textiles, due to the significant differences in the chemical structures and properties of the two polymers, it is difficult to achieve effective separation and efficient recycling.

[0003] Therefore, there is an urgent need in this field to develop a method for the targeted recycling of nylon in blended textiles, so as to achieve the effective separation and recycling of nylon from cotton. Summary of the Invention

[0004] Based on the aforementioned shortcomings and deficiencies in the existing technology, the purpose of this invention is to provide a method for recovering nylon from waste nylon and cotton blended textiles.

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

[0006] A method for recovering nylon from waste nylon-cotton blended textiles includes the following steps:

[0007] S1. Waste nylon-cotton blended textiles are sheared, crushed, cleaned, and dried to obtain sample fragments; the mass percentage of nylon in the waste nylon-cotton blended textiles is 50-90%.

[0008] A catalyst is obtained by replacing some of the hydrogen ions of the sulfonic acid groups in polystyrene sulfonic acid with metal ions; wherein the metal ions are metal ions that can coordinate with amide bonds.

[0009] S2. After mixing the sample fragments with the catalyst, a depolymerization reaction is carried out. The resulting depolymerization product is purified to obtain caprolactam.

[0010] As a preferred embodiment, in step S1, the catalyst preparation process includes:

[0011] Polystyrene sulfonic acid, a metal or its compound are mixed in water and stirred to react. After the reaction, the solution is filtered, and the filtrate is collected, rotary evaporated and dried to obtain the catalyst.

[0012] As a preferred embodiment, the metal ion is a divalent ion, and the molar ratio of the sulfonic acid group of polystyrene sulfonic acid to the metal ion is 1:(0.05~0.45).

[0013] Alternatively, the metal ion is a trivalent ion, and the molar ratio of the sulfonic acid group of polystyrene sulfonic acid to the metal ion is 1:(0.05-0.3).

[0014] As a preferred embodiment, the metal ion is Mg. 2+ Zn 2+ Ca 2+ Al 3+ Fe 3+ Mn 3+ or Sb 3+ .

[0015] As a preferred embodiment, in step S2, the mass ratio of sample fragments to catalyst is (20-1000):1.

[0016] As a preferred embodiment, in step S2, the depolymerization reaction is carried out in an inert gas environment at a temperature of 220–300°C for a reaction time of at least 2 hours.

[0017] As a preferred embodiment, the purification is carried out by vacuum distillation, with a pressure of -101 to -95 kPa, an internal temperature of 120 to 140°C, and a top temperature of 100°C to 120°C.

[0018] As a preferred embodiment, in step S3, the solid residual components are dispersed in water or an organic solvent, then filtered to remove impurities, and the filtrate is subjected to rotary evaporation and drying to obtain the regenerated catalyst.

[0019] As a preferred embodiment, the organic solvent is methanol, ethanol, N,N-dimethylformamide, formic acid, or acetic acid.

[0020] Compared with the prior art, the beneficial effects of this invention are:

[0021] (1) The catalyst used in the method of recovering nylon from waste nylon and cotton blended textiles of the present invention utilizes the synergistic effect of the coexistence of polystyrene sulfonic acid and polystyrene sulfonic acid metal salt in its structure. The protons (i.e. hydrogen ions) of the sulfonic acid group attack the carbonyl oxygen of the amide bond in the nylon molecular chain, thereby enhancing the polarity of the amide bond (increasing the positive charge of the carbonyl carbon), providing reaction sites for the coordination of metal ions; the metal ions coordinate with the nitrogen atom of the amide bond to form a cyclic intermediate, reducing the activation energy of amide bond breaking and promoting the rapid breaking of CN bonds; the protons continuously activate the newly exposed amide bonds, and the metal ions simultaneously stabilize the intermediate, so that the molecular chain breaks uniformly from the end to the inside, rather than breaking locally, avoiding the formation of oligomers, directly generating caprolactam monomer, and improving the yield of caprolactam;

[0022] (2) Since there are amide bonds in the nylon molecular chain, while there are no amide bonds in the cotton molecular chain, and the catalyst of the present invention can efficiently depolymerize amide bonds, it can achieve the directional catalytic depolymerization effect of nylon, thereby separating cotton and other impurities that do not participate in the reaction. Attached Figure Description

[0023] Figure 1 This is the infrared spectrum of the catalyst in Example 1 of the present invention;

[0024] Figure 2 This is the X-ray photoelectron spectrum of the S element in the catalyst of Example 1 of the present invention;

[0025] Figure 3 This is the X-ray photoelectron spectrum of Zn element in the catalyst of Example 1 of the present invention;

[0026] Figure 4 This is the full spectrum of the catalyst of Example 1 of the present invention. Detailed Implementation

[0027] The following is a detailed description of the method for recovering nylon from waste nylon and cotton blended textiles according to the present invention.

[0028] This invention adopts the core concept of directional catalysis-solid phase impurity separation-stepwise purification. It utilizes the directional catalytic activity of a polymer chain catalyst containing Lewis acid side chains on the amide bonds of nylon to achieve precise separation of nylon and cotton. Specifically, it includes four core steps: pretreatment, directional depolymerization of nylon and purification of caprolactam, and catalyst regeneration and recycling.

[0029] Specifically, the method for recovering nylon from waste nylon-cotton blended textiles of the present invention includes the following steps:

[0030] 1) Pretreatment: A drum-type magnetic separator is used to sort nylon and cotton blended fabrics (nylon content 50-90%). Metal impurities are adsorbed on the drum surface and detached from the fabric as the drum rotates, thus removing the metal impurities. A twin-shaft shearing shredder is used to cut the fabric into uniform-sized fragments to prevent the fabric from tangling with subsequent equipment, while also breaking the seams between the fabrics and separating adhered parts. The fabric is then conveyed to a vibrating screen to further remove impurities and fiber debris. Finally, the fabric sample fragments are immersed in a neutral cleaning solution for ultrasonic cleaning for 10-60 minutes to remove surface stains. After cleaning, the sample fragments are rinsed with deionized water until neutral and then transferred to an oven at 80-120℃ to dry, obtaining the sample fragments.

[0031] The above-mentioned neutral cleaning solution needs to meet the following requirements: pH 6.5-7.5, strong detergency, easy rinsing and removal, and no damage to the fabric.

[0032] 2) Catalyst preparation: Accurately weigh polystyrene sulfonic acid and metal oxide powder according to the target ratio (molar ratio), dissolve them in water, turn on the stirring and constant temperature water bath, and the reaction ends when the metal ions replace the hydrogen of the sulfonic acid group to form a complex; filter the reaction solution, collect the filtrate, and then rotary evaporate and dry it to obtain the final polymer chain catalyst containing Lewis acid side chain.

[0033] Specifically, by controlling the target ratio, the hydrogen ions (i.e., protons) of some sulfonic acid groups in polystyrene sulfonic acid are replaced by metal ions, but not all of them, thus achieving the coexistence of polystyrene sulfonic acid and polystyrene sulfonic acid metal salt in the catalyst. Specifically, the metal ions are those capable of coordinating with amide bonds, selected from Mg... 2+ Zn 2+ Ca 2+ Al 3+ Fe 3+ Mn 3+ Sb 3+ The specific options can be selected based on actual application needs;

[0034] If the metal ion is a divalent ion, the molar ratio of the sulfonic acid group of polystyrene sulfonic acid to the metal ion is 1:(0.05~0.45). The specific molar ratio can be determined according to the actual application requirements.

[0035] If the metal ion is a trivalent ion, the molar ratio of the sulfonic acid group of polystyrene sulfonic acid to the metal ion is 1:(0.05~0.3). The specific molar ratio can be determined according to the actual application requirements.

[0036] 3) Directional depolymerization: Weigh the sample fragments and the catalyst containing Lewis acid side chain, and add them sequentially to the reaction vessel. Inert gas is introduced into the vessel for 10 minutes to completely remove air and oxidize under high temperature conditions. Start the stirring and heating system, control the stirring speed to 100-500 r / min, and heat the reaction system to 220-300℃ at a rate of 5-10℃ / min. React for at least 2 hours. Under these conditions, the active center of Lewis acid on the catalyst side chain (i.e., metal ions) activates the amide bond of nylon molecules through coordination, causing it to depolymerize into caprolactam. Cotton does not participate in the reaction due to its molecular structure difference and remains in the solid residue.

[0037] The mass ratio of the above-mentioned catalyst containing Lewis acid polymer chain with side chain to sample fragments is 1:(20-1000). Too little catalyst will result in insufficient catalytic efficiency and prolong the reaction time; too much catalyst will increase the recovery cost. Therefore, the above range is more appropriate.

[0038] 4) Caprolactam purification: The depolymerization product is fed into a continuous distillation column, and the pressure (i.e., gauge pressure) is controlled to -101 to -95 kPa, the temperature inside the column is 120 to 140℃, and the temperature at the top of the column is 100℃ to 120℃. Caprolactam can be obtained by collecting the fraction from this stage.

[0039] 5) Catalyst regeneration and recycling: The solid residue from step 4) is dispersed in water or an organic solvent, then filtered to remove impurities. The filtrate is then subjected to rotary evaporation and drying to obtain the regenerated catalyst. The regenerated catalyst can be reused 5 to 8 times, and each reuse only requires the addition of 5 to 10 wt% of the initial amount of fresh catalyst to maintain the original catalytic efficiency.

[0040] In the above process, the parameter control of each step needs to be flexibly adjusted according to the actual composition ratio of waste textiles: when the mass ratio of nylon in blended textiles is higher than 50%, the depolymerization reaction temperature can be appropriately increased and the reaction time extended to ensure that the nylon is fully depolymerized; when the cotton ratio is higher than 70%, the amount of catalyst can be reduced to reduce process costs.

[0041] The method for recovering nylon from waste nylon and cotton blended textiles of the present invention will be further explained and illustrated below through specific embodiments and comparative examples.

[0042] Example 1:

[0043] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0044] (1) Pretreatment: 50g of waste nylon / cotton blended textiles (nylon accounts for 50% of the mass), after removing impurities, crushed and put into an aqueous solution of sodium dodecylbenzenesulfonate, ultrasonically cleaned at 50℃ for 30 minutes, rinsed with water, and dried at 100℃ for 2 hours to obtain sample fragments.

[0045] (2) Catalyst preparation: Weigh 5g of polystyrene sulfonic acid and 0.663g of zinc oxide at a molar ratio of 1:0.3 for the sulfonic acid groups of polystyrene sulfonic acid and zinc oxide, add them to 15mL of water, stir and heat for 2 hours at 60℃ and 250r / min. After the reaction is completed, filter the solution, collect the filtrate and rotary evaporate it to obtain a solid catalyst, dry it and collect it for later use.

[0046] The following is a characterization analysis of the catalyst:

[0047] like Figure 1 As shown, comparison of infrared spectra reveals that the 3700–3000 cm⁻¹ range... -1 The yellow area represents the OH stretching vibration peak of -SO3H in polystyrene sulfonic acid, due to Zn 2+ The H in the group was replaced + This weakens the stretching vibration of the OH group in -SO3H; at the same time, the peak here does not completely disappear, which proves that Zn 2+ Sulfonate was successfully formed, which then formed a stable complex with the remaining polystyrene sulfonic acid;

[0048] like Figures 2 to 4As shown, XPS analysis can prove that Zn 2+ The sulfonate group that has entered the polystyrene sulfonic acid, but has not completely reacted, can form a complex that can have a synergistic effect.

[0049] (3) Directional depolymerization: 50g of sample fragments and 2.5g of catalyst were sent to the reactor and nitrogen gas flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged. The reactor was heated to 220°C at a rate of 10°C / min and the stirring speed was controlled at 100r / min. The reaction was carried out for 10 hours and the depolymerization product was obtained after the reaction was completed.

[0050] (4) Purification: The depolymerization product is fed into a continuous distillation column. The system gauge pressure is controlled to -100 kPa, the temperature inside the vessel is 125°C, and the temperature at the top of the column is 115°C. At this time, the caprolactam component vaporizes. The fraction collected at this stage is cooled by a condenser and converted into liquid to obtain caprolactam. The actual yield of caprolactam after distillation is 92.7%. Other remaining components will remain at the bottom of the column.

[0051] (5) Catalyst regeneration: The residue at the bottom of the tower is dispersed in water, filtered to remove impurities, and the filtrate is collected for rotary evaporation and drying to obtain a regenerated catalyst, which can be directly used for the directional depolymerization of nylon.

[0052] Example 2:

[0053] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0054] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon content 60%), and remove impurities in the same way as in Example 1;

[0055] (2) Catalyst preparation: The molar ratio of sulfonic acid groups in polystyrene sulfonic acid to calcium oxide was adjusted to 1:0.35, and the other steps were the same as in Example 1;

[0056] (3) Directional depolymerization: 50g of sample fragments and 1g of catalyst were fed into a 50mL reactor and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged. Compared with Example 1, the nylon in this example was in excess, the reaction temperature was appropriately increased to 230℃ and the reaction time was extended to 3 hours, while other parameters remained unchanged.

[0057] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 92.9%;

[0058] (5) The catalyst regeneration is the same as in Example 1. When the regenerated catalyst is reused for the second time, 8wt% of new catalyst is added and the catalytic efficiency still meets the process requirements.

[0059] Example 3:

[0060] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0061] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon accounts for 70% of the mass), and remove impurities in the same way as in Example 1;

[0062] (2) Catalyst preparation: The molar ratio of sulfonic acid groups in polystyrene sulfonic acid to magnesium oxide was adjusted to 1:0.45, and the other steps were the same as in Example 1;

[0063] (3) Directional depolymerization: 50g of sample fragments and 0.5g of catalyst were fed into a 50mL reactor, and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged; Compared with Example 1, the nylon content was increased in this example, the reaction temperature was increased to 240℃ and the reaction time was extended to 4 hours, while other parameters remained unchanged;

[0064] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 93.1%;

[0065] (5) Catalyst regeneration is the same as in Example 1. When the regenerated catalyst is reused for the second time, 8wt% new catalyst is added, and the catalytic efficiency still meets the process requirements.

[0066] Example 4:

[0067] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0068] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon content 80%), and remove impurities in the same way as in Example 1;

[0069] (2) Catalyst preparation: Same as in Example 1;

[0070] (3) Directional depolymerization: 50g of sample fragments and 0.1g of catalyst were fed into a 50mL reactor, and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged; compared with Example 1, in this example, nylon was in excess, the reaction temperature was increased to 250℃ and the reaction time was extended to 5 hours, while other parameters remained unchanged;

[0071] (4) The enrichment and purification operation was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 93.6%;

[0072] (5) Catalyst regeneration is the same as in Example 1. When the regenerated catalyst is reused for the second time, 8wt% new catalyst is added, and the catalytic efficiency still meets the process requirements.

[0073] Example 5:

[0074] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0075] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon content 90%), and remove impurities in the same way as in Example 1;

[0076] (2) Catalyst preparation: Same as in Example 2;

[0077] (3) Directional depolymerization: 50g of sample fragments and 0.05g of catalyst were fed into a 50mL reactor and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged. Compared with Example 1, this example has an excess of nylon, increases the reaction temperature to 300℃ and extends the reaction time to 4 hours, while other parameters remain unchanged.

[0078] (4) The purification procedure was the same as in Example 1; the yield of caprolactam after distillation was 94.0%;

[0079] (5) Catalyst regeneration is the same as in Example 1. When the regenerated catalyst is reused for the third time, 10wt% new catalyst is added, and the catalytic efficiency still meets the process requirements.

[0080] Example 6:

[0081] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0082] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon accounts for 70% of the mass), and remove impurities in the same way as in Example 1;

[0083] (2) Catalyst preparation: Polystyrene sulfonic acid and iron oxide Fe2O3 were weighed at a molar ratio of 1:0.2 between the sulfonic acid groups of polystyrene sulfonic acid and the iron ions of iron oxide. Other steps were the same as in Example 1.

[0084] (3) Directional depolymerization: 50g of sample fragments and 0.5g of catalyst were fed into a 50mL reactor and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged. Compared with Example 1, the nylon content was increased in this example, the reaction temperature was increased to 230℃ and the reaction time was extended to 4 hours, while other parameters remained unchanged.

[0085] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 90.1%;

[0086] (5) The catalyst regeneration is the same as in Example 1, with 8wt% new catalyst added, and the catalytic efficiency still meets the process requirements.

[0087] Example 7:

[0088] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0089] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon accounts for 70% of the mass), and remove impurities in the same way as in Example 1;

[0090] (2) Catalyst preparation: Polystyrene sulfonic acid and manganese oxide Mn2O3 were weighed at a molar ratio of 1:0.05 between the sulfonic acid groups of polystyrene sulfonic acid and the manganese ions of manganese oxide. Other steps were the same as in Example 1.

[0091] (3) Directional depolymerization: 50g of sample fragments and 0.5g of catalyst were fed into a 50mL reactor and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged. Compared with Example 1, the nylon content was increased in this example, the reaction temperature was increased to 230℃ and the reaction time was extended to 4 hours, while other parameters remained unchanged.

[0092] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 93.2%;

[0093] (5) The catalyst regeneration is the same as in Example 1, with 8wt% new catalyst added, and the catalytic efficiency still meets the process requirements.

[0094] Example 8:

[0095] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0096] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon content 80%), and remove impurities in the same way as in Example 1;

[0097] (2) Catalyst preparation: Polystyrene sulfonic acid and aluminum oxide Al2O3 were weighed at a molar ratio of 1:0.15 between the sulfonic acid groups of polystyrene sulfonic acid and the aluminum ions of alumina. Other steps were the same as in Example 1.

[0098] (3) Directional depolymerization: 50g of sample fragments and 0.1g of catalyst were fed into a 50mL reactor, and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged; Compared with Example 1, the nylon content was increased in this example, the reaction temperature was increased to 230℃ and the reaction time was extended to 5 hours, while other parameters remained unchanged;

[0099] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 95.1%;

[0100] (5) The catalyst regeneration is the same as in Example 1, with 8wt% new catalyst added, and the catalytic efficiency still meets the process requirements.

[0101] Example 9:

[0102] The method for recovering nylon from waste nylon-cotton blended textiles in this embodiment includes the following steps:

[0103] (1) Pretreatment: Sort 50g of waste nylon / cotton blended textiles (nylon content 80%), and remove impurities in the same way as in Example 1;

[0104] (2) Catalyst preparation: Polystyrene sulfonic acid and antimony trioxide were weighed at a molar ratio of 1:0.3 for the sulfonic acid groups of polystyrene sulfonic acid and the antimony ions of antimony trioxide. Other steps were the same as in Example 1.

[0105] (3) Directional depolymerization: 50g of sample fragments and 0.1g of catalyst were fed into a 50mL reactor, and nitrogen flow was continuously introduced for 10 minutes to ensure that the air in the reactor was completely discharged; Compared with Example 1, the nylon content was increased in this example, the reaction temperature was increased to 230℃ and the reaction time was extended to 5 hours, while other parameters remained unchanged;

[0106] (4) The purification procedure was the same as in Example 1; after distillation, caprolactam was obtained in a yield of 95.0%;

[0107] (5) The catalyst regeneration is the same as in Example 1, with 8wt% new catalyst added, and the catalytic efficiency still meets the process requirements.

[0108] Comparative Example 1:

[0109] The difference between the recovery method in this comparative example and that in Example 5 is that only polystyrene sulfonic acid is used as a catalyst;

[0110] During the directional depolymerization process, 50g of sample fragments and 0.2g of polystyrene sulfonic acid were fed into a 50mL reactor, and the remaining steps were the same as in Example 5.

[0111] The final caprolactam yield was only 32.5%;

[0112] The protons of polystyrene sulfonate continuously activate newly exposed amide bonds. Due to the lack of metal ions, the intermediate cannot be stabilized synchronously, the molecular chain breaks randomly, and the side reactions cannot be prevented, resulting in a low yield.

[0113] Comparative Example 2:

[0114] The difference between the recovery method in this comparative example and that in Example 5 is that only zinc oxide is used as a catalyst;

[0115] During the directional depolymerization process, 50g of sample fragments and 0.2g of zinc oxide were fed into a 50mL reactor, and the remaining steps were the same as in Example 5.

[0116] The final caprolactam yield was 48.7%;

[0117] Although ZnO, as a small-molecule Lewis acid, can partially activate amide bonds, it does not have the continuous activation of amide bonds by protons like polystyrene sulfonate. Therefore, it cannot achieve the directional depolymerization of nylon and cannot prevent side reactions. In addition, cotton will undergo partial degradation at high temperatures, producing impurities and reducing the yield.

[0118] Comparative Example 3:

[0119] The difference between the recovery method in this comparative example and that in Example 5 is that a physical mixture of polystyrene sulfonic acid and zinc oxide is used as a catalyst.

[0120] During the directional depolymerization process, 50g of sample fragments were physically mixed with 0.134g of polystyrene sulfonic acid and 0.066g of zinc oxide and then directly added to the reactor. The remaining steps were the same as in Example 5.

[0121] The final caprolactam yield was 51.3%;

[0122] Simple physical blending cannot form a synergistic effect; ZnO is not converted into active centers, and only a small amount undergoes hydrolysis to generate Zn. 2+ Limited catalytic activity, and polystyrene sulfonic acid and Zn 2+ There was no synergistic effect between them, making it impossible to depolymerize nylon in a targeted and efficient manner, resulting in more side reactions and lower yield.

[0123] Comparative Example 4:

[0124] The difference between the recovery method in this comparative example and that in Example 5 is that Zn is used. 2+ The sulfonate group completely replaces polystyrene sulfonic acid as a catalyst;

[0125] Specifically, the molar ratio of the feed was adjusted to 1:1 during the preparation of the catalyst to ensure that the sulfonate ions were completely replaced, and the preparation process was the same as in Example 1.

[0126] The remaining steps are the same as in Example 5;

[0127] The final caprolactam yield was 67.2%.

[0128] Although fully salted zinc polystyrene sulfonate forms a solid-phase catalyst, it loses the synergistic effect of the -SO3H group and the sulfonic acid metal salt, resulting in decreased stability of the intermediate and weakened coordination activation ability for amide bonds. Due to the absence of sulfonic acid groups, it cannot form hydrogen bonds with nylon, which reduces the contact energy between the catalyst and the nylon amide bonds, ultimately leading to a decrease in yield.

[0129] Comparative Example 5:

[0130] The difference between the recovery method in this comparative example and that in Example 5 is that zinc acetate is used as a catalyst.

[0131] During the directional depolymerization process, 50g of sample fragments and 0.2g of zinc acetate were fed into a 50mL reactor, and the remaining steps were the same as in Example 5;

[0132] The remaining steps are the same as in Example 5;

[0133] The final caprolactam yield was 53.6%.

[0134] Although zinc acetate is a Lewis acid that can activate nylon amide bonds, it lacks co-catalysis and cannot directionally depolymerize nylon, resulting in a low yield.

[0135] 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.

[0136] 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 recovering nylon from waste nylon-cotton blended textiles, characterized in that, Includes the following steps: S1. Waste nylon-cotton blended textiles are sheared, crushed, cleaned, and dried to obtain sample fragments; the mass percentage of nylon in the waste nylon-cotton blended textiles is 50-90%. A catalyst is obtained by replacing some of the hydrogen ions of the sulfonic acid groups in polystyrene sulfonic acid with metal ions; wherein the metal ion is Mg. 2+ Zn 2+ Ca 2+ Al 3+ Fe 3+ Mn 3+ or Sb 3+ ; When the metal ion is a divalent ion, the molar ratio of the sulfonic acid group to the metal ion in polystyrene sulfonic acid is 1:(0.05~0.45); when the metal ion is a trivalent ion, the molar ratio of the sulfonic acid group to the metal ion in polystyrene sulfonic acid is 1:(0.05~0.3). S2. After mixing the sample fragments with the catalyst, a depolymerization reaction is carried out. The resulting depolymerization product is purified to obtain caprolactam.

2. The method according to claim 1, characterized in that, In step S1, the catalyst preparation process includes: Polystyrene sulfonic acid and a metal compound were mixed in water and stirred to react. After the reaction, the solution was filtered, and the filtrate was collected, rotary evaporated, and dried to obtain the catalyst.

3. The method according to claim 1, characterized in that, In step S2, the mass ratio of sample fragments to catalyst is (20-1000):

1.

4. The method according to claim 1, characterized in that, In step S2, the depolymerization reaction is carried out in an inert gas environment at a temperature of 220–300°C for at least 2 hours.

5. The method according to claim 1, characterized in that, The purification process is vacuum distillation, with a pressure of -101 to -95 kPa, an internal temperature of 120 to 140°C, and a top temperature of 100°C to 120°C.

6. The method according to claim 1, characterized in that, It also includes the following steps: S3. Remove impurities from the purified solid residue components to recover the regenerated catalyst.

7. The method according to claim 6, characterized in that, In step S3, the solid residual components are dispersed in water or organic solvent, then filtered to remove impurities, and the filtrate is subjected to rotary evaporation and drying to obtain the regenerated catalyst.

8. The method according to claim 7, characterized in that, The organic solvent is methanol, ethanol, N,N-dimethylformamide, formic acid, or acetic acid.

Images