Process method for chemically regenerating PA6 product by using waste chinlon textile

Abstract

The invention provides a process method for chemically regenerating a PA6 product by using waste chinlon textiles, and belongs to the technical field of chinlon 6 waste recovery. According to the method, the waste chinlon textile is used as a raw material, refined caprolactam is obtained through depolymerization, flash evaporation, centrifugal separation and purification, and then the refined caprolactam is subjected to two-stage polymerization including front-stage pressurization and rear-stage decompression and a devolatilization process, so that the regenerated PA6 product is directly obtained. The PA6 melt prepared by the method is low in oligomer content, low in cyclic dimer content and low in caprolactam content, the regenerated PA6 product is excellent in performance, a new method is provided for resource reutilization of waste chinlon textiles, and the method has the advantages of being low in cost and easy to popularize.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of polyamide 6 waste, and specifically relates to a process method for chemically regenerating PA6 products by using waste polyamide textiles. Background Art

[0002] In the development process of the textile industry, polyamide fibers have been favored by consumers due to their good wear resistance, resilience, fatigue resistance and other properties. However, with the continuous update of the consumer market, a large number of waste polyamide textiles face disposal problems. From the perspective of resource utilization, polyamide 6 (PA6), as an important component of polyamide textiles, is mostly derived from non-renewable resources such as petroleum. These waste fabrics contain a large amount of reusable value. Traditional treatment methods, such as landfilling or incineration, not only cause huge waste of resources, but also cause serious environmental pollution. For example, landfilling occupies land resources and is difficult to degrade, and incineration will produce harmful gases. In the field of regeneration technology, physical recycling methods are difficult to meet the requirements of high-quality regeneration, and cannot effectively separate impurities in polyamide textiles and restore the properties of polyamide. The emergence of chemical regeneration process methods provides a possibility to solve this problem. The chemical regeneration process can target waste polyamide textiles and accurately extract polyamide 6 from the polyamide textiles by chemical means, realizing the efficient recycling and reuse of resources, producing high-quality PA6 products, and promoting the green and sustainable development of the textile industry.

[0003] Patent No. CN105669969B, an invention patent named "A Nylon 6 Polymerization Method and Its Melt Direct Spinning Method", was published. It prepares a polyamide 6 prepolymer at a low temperature first, pre-controls the content of oligomers in the melt, and then completes the polymerization by a method of strengthening the polycondensation reaction kinetics before a large amount of cyclic oligomers are generated, obtaining a nylon 6 polymer melt with a certain molecular weight. However, in its process, a chain extender needs to be added to enhance the polymerization reaction before melt direct spinning. Patent No. CN114057621A, an invention patent named "A Method for Efficient Depolymerization of Waste Polyamide 6 and Its Application", was published. It discloses a process method in which the filtered waste polyamide 6 melt is fed into a depolymerization kettle containing subcritical water and mixed evenly with the subcritical water therein, depolymerization is carried out under the condition that the dynamic viscosity of the mixed system is not higher than 10 Pa·s, the depolymerized depolymerization liquid is directly fed into a rectification tower for refining to purify caprolactam, and then the purified caprolactam is fed into a polymerization kettle for ring-opening reaction, and then through polymerization, granulation, extraction and drying to obtain the finished product of recycled polyamide 6 chips. However, this patent has the following defects. First, during the process of processing waste polyamide 6 into a melt, due to the action of high heat and strong shear, the polyamide 6 melt undergoes thermal degradation and molecular chain breakage, generating impurity small molecules. Second, in this process method, after repolymerization, granulation needs to be carried out through extraction and drying to obtain the finished product of polyamide 6 chips, resulting in a long process flow, high energy consumption, low efficiency, and a large amount of water is consumed in the chip extraction process, and the caprolactam dissolved in water needs to be recovered by rectification.

[0004] Therefore, it is of great significance to study a process method for chemically recycling PA6 products from waste polyamide textiles and effectively remove impurities such as dyes, dirt, and auxiliaries in waste polyamide textiles to achieve the recycling and reuse of waste polyamide textiles. Summary of the Invention

[0005] In view of this, the present invention provides a process method for chemically recycling PA6 products from waste polyamide textiles, including the following steps:

[0006] S1. Textile crushing: Crush the waste polyamide textiles to obtain polyamide textile fragments;

[0007] S2. Pre-depolymerization: Place the polyamide textile fragments in a pre-depolymerization reaction container, and at the same time add a pre-depolymerization agent, control the reaction temperature of the pre-depolymerization at 280 - 350 °C, the reaction pressure at 8 - 15 MPa, and the reaction time at 10 - 40 min to obtain a pre-depolymerization reaction liquid;

[0008] S3. Deep depolymerization: Transfer the pre-depolymerization reaction liquid to a deep depolymerization reaction container, control the reaction temperature of the deep depolymerization at 280 - 350 °C, the reaction pressure at 8 - 15 MPa, and the reaction time at 20 - 60 min to obtain a deep depolymerization reaction liquid;

[0009] S4, Flash evaporation: The deep depolymerization reaction liquid is flash-evaporated through a pressure reducing valve until the pressure reaches 1 - 5 KPa and the temperature drops to 80 - 150 °C, obtaining a gas-phase component and a liquid-phase component;

[0010] S5, Centrifugal separation: The liquid-phase component is centrifugally separated to obtain a crude caprolactam melt solution;

[0011] S6, Purification of depolymerization products: The crude caprolactam melt solution is transferred to a purification reactor, and successively undergoes molecular enrichment purification, ion sieving purification, low-boiling component vaporization extraction, and high-boiling component fractional extraction steps to obtain a purified caprolactam melt solution;

[0012] S7, Pre-polymerization: The purified caprolactam melt solution is transferred to a pre-polymerization reaction vessel, and at the same time, a ring-opening agent, a molecular weight regulator, and a catalyst are added. The reaction temperature of the pre-polymerization is controlled at 240 - 270 °C, the reaction pressure is 0.1 - 5.5 MPa, and the reaction time is 3 - 15 h to obtain a pre-polymerization product;

[0013] S8, Post-polymerization: The pre-polymerization product is transferred to a post-polymerization reaction vessel, and at the same time, a heat stabilizer and an antioxidant are added. The reaction temperature of the post-polymerization is controlled at 230 - 270 °C, the reaction pressure is 1 - 10 KPa, and the reaction time is 2 - 8 h to obtain a post-polymerization product;

[0014] S9, Devolatilization: The post-polymerization product is transferred to a devolatilization reaction vessel, and the devolatilization reaction temperature is controlled at 230 - 255 °C, the reaction pressure is 0.1 - 10 KPa, and the reaction time is 30 - 150 min to obtain a devolatilization product;

[0015] S10, Melt filtration: The devolatilization product is filtered to obtain a polyamide 6 melt;

[0016] S11, Melt deep processing.

[0017] Preferably, the pre-depolymerizing agent described in step S2 includes water, and the mass ratio of the pre-depolymerizing agent to the nylon textile fragments is 8:1 - 15:1.

[0018] Preferably, the deep depolymerization reaction temperature in step S3 is 280 - 320 °C, the reaction pressure is 10 - 12 MPa, and the reaction time is 25 - 45 min.

[0019] Preferably, the number of flash evaporation stages described in step S4 is 2 - 4 stages.

[0020] Preferably, the centrifugal separation accuracy described in step S5 is 3 - 5 μm.

[0021] Preferably, the medium used for molecular enrichment and purification in step S6 includes one or more of bentonite, diatomite, silica gel, and activated carbon. The temperature for molecular enrichment and purification is 110 - 130°C, the reaction pressure is atmospheric pressure, and the reaction time is 30 - 90 min;

[0022] Preferably, the medium used for ion sieving and purification includes cation exchange resin and anion exchange resin. The temperature for ion sieving and purification is 70 - 80°C, the pressure is 100 KPa, and the purification time is 3 - 10 min.

[0023] Preferably, the reaction temperature for vaporization extraction of low-boiling components is 100 - 200°C, the reaction pressure is 1 - 50 KPa, and the reaction time should be less than 60 s.

[0024] Preferably, the reaction temperature for rectifying extraction of high-boiling components is 160 - 220°C, the reaction pressure is 0.3 - 5 KPa, and the reaction time should be less than 60 s.

[0025] Preferably, the addition amount of the ring-opening agent in step S7 is 1 - 5% of the mass of the purified caprolactam melt; the addition amount of the molecular weight regulator is 1 - 3% of the mass of the purified caprolactam melt; the addition amount of the catalyst is 1 - 3% of the mass of the purified caprolactam melt.

[0026] Preferably, the addition amount of the heat stabilizer in step S8 is 0.05 - 0.5% of the mass of the purified caprolactam melt; the addition amount of the antioxidant is 0.03 - 0.15% of the mass of the purified caprolactam melt.

[0027] Preferably, the reaction temperature for the post-polymerization is 235 - 255°C, the reaction pressure is 1 - 5 KPa, and the reaction time is 3 - 6 h.

[0028] Preferably, in step S9, PA6 modification monomers, polymers of non-PA6 structural units, and functional additives are selectively added according to the processing requirements of subsequent products. The addition amount of the PA6 modification monomers is 0.1 - 50% of the mass of the purified caprolactam melt; the addition amount of the polymers of non-PA6 structural units is 0.1 - 60%; the addition amount of the functional additives is 0.1 - 30% of the mass of the purified caprolactam melt.

[0029] Preferably, the filtration accuracy of the melt filtration in step S10 is 20 - 100 μm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention uses waste polyamide textiles as raw materials, and obtains pure caprolactam through depolymerization, flash evaporation, centrifugal separation, and purification. Then, the pure caprolactam is directly polymerized into recycled PA6 products through two-stage polymerization with pressure in the front stage and vacuum in the back stage and devolatilization process.

[0032] In the devolatilization process of the present invention, on-line modified polymerization such as melt copolymerization and block polymerization of PA6 is realized, and the devolatilization process of the present invention can achieve melt direct spinning, avoiding the defect of reducing the caprolactam content in the melt by the existing aqueous solution extraction method in the industry.

[0033] The PA6 melt prepared by the method of the present invention has low content of oligomers, low content of cyclic dimers, and low content of caprolactam, and the recycled polyamide textiles have excellent performance. Description of the Drawings

[0034] Figure 1 is the 1H NMR spectrum of caprolactam obtained in Example 1 of the present invention.

[0035] Figure 2 is the 13C NMR spectrum of caprolactam obtained in Example 1 of the present invention. Detailed Description of the Invention

[0036] A process for chemically recycling PA6 products using waste polyamide textiles includes the following steps:

[0037] S1. Textile fragmentation: The waste polyamide textiles are fragmented to obtain polyamide textile fragments. The waste polyamide textiles mainly contain the following components: 40-99.99% of polyamide fibers, 0-45% of non-polyamide fibers, 0-10% of inorganic / organic dyes and pigments, and 0-10% of fabric additives;

[0038] S2. Pre-depolymerization: The polyamide textile fragments are placed in a pre-depolymerization reaction vessel, and a pre-depolymerization agent is added at the same time. The reaction temperature of the pre-depolymerization is controlled at 280-350°C, the reaction pressure is 8-15 MPa, and the reaction time is 10-40 min to obtain a pre-depolymerization reaction solution;

[0039] S3. Deep depolymerization: The pre-depolymerization reaction solution is transferred to a deep depolymerization reaction vessel, and the reaction temperature of the deep depolymerization is controlled at 280-350°C, the reaction pressure is 8-15 MPa, and the reaction time is 20-60 min to obtain a deep depolymerization reaction solution;

[0040] S4. Flash evaporation: The deep depolymerization reaction solution is flash-evaporated through a pressure reducing valve until the pressure reaches 1-5 KPa and the temperature drops to 80-150°C to obtain a gas-phase component and a liquid-phase component;

[0041] S5. Centrifugal separation: The liquid-phase component is centrifugally separated to obtain a crude caprolactam melt solution;

[0042] S6, Depolymerization product purification: Transfer the crude caprolactam melt solution to a purification reactor, and successively carry out molecular enrichment purification, ion sieving purification, low-boiling component vaporization extraction, and high-boiling component fractional extraction steps to obtain a purified caprolactam melt solution;

[0043] S7, Pre-polymerization: Transfer the purified caprolactam melt solution to a pre-polymerization reaction vessel, and simultaneously add a ring-opening agent, a molecular weight regulator, and a catalyst. Control the reaction temperature of the pre-polymerization to be 240 - 270 °C, the reaction pressure to be 0.1 - 5.5 MPa, and the reaction time to be 3 - 15 h to obtain a pre-polymerization product;

[0044] S8, Post-polymerization: Transfer the pre-polymerization product to a post-polymerization reaction vessel, and simultaneously add a heat stabilizer and an antioxidant. Control the reaction temperature of the post-polymerization to be 230 - 270 °C, the reaction pressure to be 1 - 10 KPa, and the reaction time to be 2 - 8 h to obtain a post-polymerization product;

[0045] S9, Devolatilization: Transfer the post-polymerization product to a devolatilization reaction vessel, control the devolatilization reaction temperature to be 230 - 255 °C, the reaction pressure to be 0.1 - 10 KPa, and the reaction time to be 30 - 150 min to obtain a devolatilization product;

[0046] S10, Melt filtration: Filter the devolatilization product to obtain a polyamide 6 melt;

[0047] S11, Melt deep processing.

[0048] The mechanism of action of the key technical features in the present invention:

[0049] Depolymerization:

[0050] PA6 is a linear polyamide formed by the ring-opening polymerization reaction of the monomer caprolactam, and has a repeating unit structure of NH(CH 2 ) 5 CO. During the depolymerization of PA6, 6-aminocaproic acid is first generated, and 6-aminocaproic acid forms a ring to form caprolactam. Under the reaction conditions mentioned in the depolymerization process of the present invention, the depolymerizing agent is in a subcritical state, and its dielectric constant is reduced to 1, changing from a polar compound to a non-polar compound. The depolymerizing agent in the subcritical state has strong dissolving ability and decomposing ability, so that PA6 can be efficiently depolymerized into 6-aminocaproic acid, and then 6-aminocaproic acid quickly forms a ring to form caprolactam. And because the depolymerizing agent is in a subcritical state, the formation of cyclic dimers can be effectively controlled during the reaction process of 6-aminocaproic acid forming a ring to form caprolactam. In conventional technical means, due to the high molecular property of PA6, additional strong acids or strong bases need to be added to depolymerize PA6 with water.

[0051] Purification:

[0052] Molecular enrichment and purification: The raw material involved in the present invention is waste polyamide textiles. During the initial processing into products, at least one additive / auxiliary agent is inevitably added to ensure the performance of the products, and the inorganic / organic dye / pigment components contained therein are complex. In addition, during the depolymerization reaction stage, many small molecule impurities will inevitably be generated. The molecular enrichment and purification of the present invention uses a molecular enrichment and purification medium. First, the medium has a large specific surface area and a porous structure, which provides a large number of adsorption and enrichment sites and has a strong adsorption capacity. Second, during the processing of the medium, many chemical functional groups will be generated, such as ester groups, amino groups, hydroxyl groups, carboxyl groups, etc. The above chemical functional groups react with the polar impurities in the small molecule impurities generated during the depolymerization process and the impurities brought in by the raw material itself to form stable chemical bonds, enriching the impurities on the medium. In addition, the medium itself can also form van der Waals forces with the non-polar impurities in the small molecule impurities generated during the depolymerization process and the impurities brought in by the raw material itself, enriching the non-polar impurities on the medium.

[0053] Ion sieving and purification: The raw material involved in the present invention is waste polyamide textiles. During the process of caprolactam polymerization to form PA6, at least one chemical reagent such as a catalyst and a stabilizer needs to be added inevitably. The above chemical reagents form cations such as NH 4 + , Na + , Fe 2+ , Fe 3+ , Cu 2+ , Ca 2+ , Mg 2+ etc. and anions such as acetate, terephthalate, adipate, Cl - etc. The ion sieving and purification of the present invention relies on the medium used for ion sieving and purification to play a role. First, after activation, the cation exchange resin will contain a large number of hydrogen ions and negatively charged functional groups. When the depolymerization product passes through the cation resin, the cations contained therein exchange with the hydrogen ions, and then the cations form stable organic compounds with the negatively charged functional groups in the cation resin, so as to sieve and purify the cations in the depolymerization product. Second, after activation, the anion exchange resin will contain a large number of hydroxide ions and positively charged functional groups. When the depolymerization product passes through the anion resin, the anions contained therein exchange with the hydroxide ions, and then the anions form stable organic compounds with the positively charged functional groups in the anion resin, so as to sieve and purify the anions in the depolymerization product.

[0054] Low-boiling component vaporization extraction and high-boiling component fine separation extraction: This process separates caprolactam from other impurities in the depolymerization product by taking advantage of the differences in bubble points and molecular mean free paths under different pressures. First, the bubble points of the components in the depolymerization product are different. Taking caprolactam in the PA6 depolymerization product as the basis, when the depolymerization product is heated, the low-boiling components vaporize and escape from the liquid surface. Through multiple reflux extractions, the content of caprolactam in the low-boiling components escaping from the liquid surface is gradually reduced, and the low-boiling components are removed by extraction. Second, after the depolymerization product is vaporized by heating on the heating surface under the same pressure, the molecules obtain enough energy to escape from the liquid surface, and the mean free path of the vapor molecules increases. Adjacent molecules collide successively. The mean free path of light molecules is large, and the mean free path of heavy molecules is small. A fine separation extraction surface is set between the critical point of the mean free path of light molecules and the critical point of the mean free path of heavy molecules. Heavy molecules cannot reach the fine separation extraction surface due to their small mean free path and return to the heating surface to continue the processes of being heated, vaporized, and escaping from the liquid surface multiple times, so as to completely separate the light molecules. At the same time, due to their large mean free path, the light molecules come into contact with the fine separation extraction surface and quickly liquefy.

[0055] In conventional technical means, the purification of caprolactam requires benzene extraction, water back-extraction, rectification, and recrystallization. The involved process flow is cumbersome, the consumption of additional chemical reagents is large, and all the reagents used need to be recycled, resulting in high energy consumption and large pollution.

[0056] Devolatilization:

[0057] First, in conventional technical means, after the PA6 polymerization reaction ends, generally, 8-10% of caprolactam in the PA6 melt cannot react completely and needs to be back-extracted with a large amount of water to dissolve caprolactam in water, and then caprolactam is recovered by evaporation of water and reused in the polymerization process after purification. Second, conventional PA6 polymerization means cannot synthesize PA6 melt with high relative viscosity. The PA6 melt with low relative viscosity needs to be processed into slices, and then the slices are subjected to solid-phase polycondensation in a high-purity nitrogen atmosphere. The process efficiency is low, and it involves the purification and reuse of high-purity nitrogen, resulting in high energy consumption. In addition, the current modification of PA6 is all carried out by secondary melting of PA6 slices and adding modifiers to achieve PA6 modification manufacturing. However, during the secondary melting process, the molecular weight of PA6 will be broken, thermally degraded, thermally oxidized and degraded, etc., resulting in a decline in the performance of PA6. At the same time, the secondary melting of PA6 slices consumes a large amount of heat.

[0058] The devolatilization involved in the present invention can simultaneously achieve the functions of removing unreacted caprolactam in the PA6 melt, online modification, and increasing the relative viscosity. First, the devolatilization process uses a film-forming reactor to make the PA6 melt in plug flow axially and in perfect mixing flow radially. Radially, the melt interface is broken by a film-forming scraper to increase the fugacity of caprolactam under high vacuum and high temperature, enabling caprolactam to escape rapidly. After condensation, caprolactam is directly recycled to the PA6 polymerization process. Secondly, in the PA6 polymerization process, post-polymerization is mainly an exchange reaction between molecular chain segments, which belongs to polycondensation reaction. Through the devolatilization process, small molecule water generated by polycondensation can be removed in a timely manner, increasing the exchange reaction of molecular chain segments, thereby increasing the relative viscosity. When the PA6 melt stays in the devolatilization process for 15 minutes, the increase in its relative viscosity is not less than 1.0. In addition, in the devolatilization process stage, PA6 is in a melt state, and a modifier is directly added at this stage. Due to the plug flow / perfect mixing flow structure of the devolatilization reactor, the properties of the modified PA6 polymer are uniform and stable.

[0059] In some embodiments of the present invention, the pre-depolymerization agent in step S2 includes water, and the mass ratio of the pre-depolymerization agent to the nylon textile fragments is 8:1 - 15:1, preferably 10:1 - 12:1.

[0060] Considering the high temperature and high pressure of the pre-depolymerization reaction, the pre-depolymerization agent should be preheated before being added to the pre-depolymerization reactor. The preheating temperature of the pre-depolymerization agent is controlled at 300 - 320 °C, and the preheating pressure is 10 - 12 MPa.

[0061] In some embodiments of the present invention, the reaction temperature of the pre-depolymerization is 300 - 320 °C, the reaction pressure is 10 - 12 MPa, and the reaction time is 20 - 30 min.

[0062] Considering that the pre-depolymerization reaction consumes a large amount of heat, the structure of the pre-depolymerization reactor is preferably a perfect mixing flow structure.

[0063] It is advisable that there are no nylon textile fragments in the outlet stream of the pre-depolymerization reactor.

[0064] In some embodiments of the present invention, the reaction temperature of the deep depolymerization reaction in step S3 is 280 - 320 °C, the reaction pressure is 10 - 12 MPa, and the reaction time is 25 - 45 min. Considering the uniformity of the depolymerization depth, the structure of the deep depolymerization reactor is preferably a plug flow structure.

[0065] In some embodiments of the present invention, the number of flash distillation stages in step S4 is 2 - 4 stages, preferably 3 stages.

[0066] The gas-phase components obtained during the flash distillation process are a mixture of water and a small amount of low-boiling components; the liquid-phase components are mainly nylon depolymerization product caprolactam, a small amount of mechanical impurities, inorganic / organic fillers, and dyes.

[0067] A mixed liquid of the gas-phase components water and a small amount of low-boiling components is continuously fed into a distillation column. After distillation separation, the water is recycled for use in the pre-depolymerization process, and the low-boiling components are collected as solid waste as the heavy components in the water distillation process.

[0068] In some embodiments of the present invention, the centrifugal separation accuracy in step S5 is 3 - 5 μm, preferably less than 3 μm.

[0069] In some embodiments of the present invention, a small amount of mechanical impurities, inorganic / organic fillers, and dyes in the liquid-phase components are removed through a centrifugal separation process.

[0070] In some embodiments of the present invention, the medium used for molecular enrichment and purification in step S6 includes one or more of bentonite, diatomite, silica gel, and activated carbon, preferably activated carbon. The temperature for molecular enrichment and purification is 110 - 130 °C, preferably 120 °C, the reaction pressure is atmospheric pressure, and the reaction time is 30 - 90 min, preferably 45 - 60 min.

[0071] The function of molecular enrichment and purification is to enrich and purify some impurities and pigments, non-polar or weakly polar organic substances, small-diameter molecules, and strongly polar molecules in crude caprolactam.

[0072] After molecular enrichment and purification, the small molecules in crude caprolactam are reduced from 800 ppm to less than 25 ppm.

[0073] The present invention places no particular restrictions on the reactor for molecular adsorption purification extraction. Considering process selectivity and stability, a plug-flow reactor is preferred.

[0074] In some embodiments of the present invention, the medium used for ion sieving and purification includes cation exchange resin and anion exchange resin. The cation exchange resin is a strongly acidic cation exchange resin, preferably a cation exchange resin with a polystyrene structure, such as T-5213CPR, 001*7, D001, D006, and further preferably a cross-linked polystyrene structure cation exchange resin, such as T-5213CPR. The anion exchange resin is a strongly basic anion exchange resin, preferably an anion exchange resin with a polystyrene structure and a quaternary ammonium type I structure, and further preferably an anion exchange resin with a polystyrene structure, such as A-2313CPR. The anion exchange resin mainly sieves and purifies the chromogenic ions and organic substances in crude caprolactam.

[0075] In some embodiments of the present invention, the temperature for ion sieving and purification is 70 - 80 °C, the pressure is 100 KPa, and the purification time is 3 - 10 min, preferably 5 - 7 min.

[0076] After ion sieving and purification, the ionic impurities in crude caprolactam are reduced from 500 ppm to less than 5 ppm.

[0077] The reactor for ion sieving and purification of the present invention is not particularly limited. Considering process selectivity, stability, and reduction of side reactions, a plug flow reactor is preferred.

[0078] In some embodiments of the present invention, the low-boiling component vaporization extraction process mainly removes low-boiling components by means of a heat source through efficient evaporation. The low-boiling components include organic substances such as cyclohexanone oxime and cyclohexane.

[0079] The reaction temperature for the low-boiling component vaporization extraction is 100 - 200 °C, preferably 130 - 150 °C, and the reaction pressure is 1 - 50 KPa, preferably 5 - 40 KPa. During the low-boiling component vaporization extraction process, the reaction time for the low-boiling component vaporization extraction should be less than 60 s, preferably less than 30 s.

[0080] To reduce energy consumption, the gas phase from the previous multi-stage flash distillation process can be used as the heat source for the multi-effect low-boiling component vaporization extraction.

[0081] In some embodiments of the present invention, the high-boiling component fractional extraction process mainly removes high-boiling components by means of a heat source through efficient evaporation. The high-boiling components include oligomers and organic impurities. The reaction temperature for the high-boiling component fractional extraction is 160 - 220 °C, preferably 180 - 210 °C, and the reaction pressure is 0.3 - 5 KPa, preferably 0.5 - 2 KPa. During the high-boiling component fractional extraction process, the reaction time for the high-boiling component fractional extraction should be less than 60 s, preferably less than 30 s.

[0082] In some embodiments of the present invention, the ring-opening agent in step S7 includes water and organic acids, preferably water, and the addition amount of the ring-opening agent is 1 - 5% of the mass of the molten caprolactam solution, preferably 3%;

[0083] In some embodiments of the present invention, the molecular weight regulator in step S7 includes monocarboxylic acids, monoamines, dicarboxylic acids, and diamines, preferably monocarboxylic acids such as acetic acid and / or dicarboxylic acids such as adipic acid. The addition amount of the monocarboxylic acid relative to the mass of the molten caprolactam solution is 0.01 - 0.2%, preferably 0.025 - 0.15%, and the addition amount of the dicarboxylic acid relative to the mass of the molten caprolactam solution is 0.1 - 0.5%, preferably 0.15 - 0.4%.

[0084] In some embodiments of the present invention, the catalyst in step S7 includes at least one of protonic acids, Lewis acids, metal hydroxides, metal alkoxides, titanium-based catalysts, and rare earth metal catalysts, preferably protonic acids such as 6-aminocaproic acid. The addition amount of the catalyst relative to the mass of the molten caprolactam solution is 1 - 3%, preferably 2%.

[0085] In some embodiments of the present invention, the pre-polymerization reaction temperature in step S7 is 250 - 270 °C, the pre-polymerization reaction pressure is 0.1 - 5 MPa(A), and the pre-polymerization reaction time is 3 - 12 h.

[0086] It is preferable that the content of oligomers in the pre-polymerization product is less than 30%, and the content of cyclic dimers is less than 0.1%.

[0087] The pre-polymerization reactor of the present invention is a plug flow reactor, preferably a tubular reactor.

[0088] In some embodiments of the present invention, the heat stabilizer in step S8 includes at least one of cuprous iodide, copper sulfate, triphenyl phosphite, and tris(nonylphenyl) phosphite. The addition amount of the heat stabilizer is 0.05 - 0.5% of the mass of the molten caprolactam solution, preferably 0.08 - 0.12%.

[0089] In some embodiments of the present invention, the antioxidant in step S8 includes at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, tris(2,4-di-tert-butylphenyl) phosphite, and bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite. The addition amount of the antioxidant is 0.03 - 0.15% of the mass of the molten caprolactam solution, preferably 0.05 - 0.1%.

[0090] In some embodiments of the present invention, the post-polymerization reaction temperature in step S8 is 235 - 255 °C, the reaction pressure is 1 - 5 KPa, and the reaction time is 3 - 6 h.

[0091] It is preferable that the content of oligomers in the post-polymerization product is less than 5%, the content of cyclic dimers is less than 0.1%, and the content of caprolactam monomer is less than 8%.

[0092] The post-polymerization reactor is a plug flow reactor, preferably a tubular reactor.

[0093] In some embodiments of the present invention, in step S9, PA6 modification monomers, polymers of non-PA6 structural units, and functional additives are selectively added according to the processing requirements of subsequent products. The PA6 modification monomers include polyols, polyamines, other lactams, ε-caprolactone, etc.; the polymers of non-PA6 structural units include polyethers, polyolefins, etc.; the functional additives include flame retardant additives, conductive additives, reinforcing additives, etc. The addition amount of the PA6 modification monomers is 0.1-50% of the mass of the molten caprolactam solution, preferably 5-50%; the addition amount of the polymers of non-PA6 structural units is 0.1-60%, preferably 10-60%; the addition amount of the functional additives is 0.1-30% of the mass of the molten caprolactam solution, preferably 5-30%.

[0094] In some embodiments of the present invention, the devolatilization reaction temperature in step S9 is 240-250°C, the reaction pressure is 0.1-0.5 KPa(A), and the reaction time is 45-120 min.

[0095] The content of oligomers in the devolatilization product is preferably less than 1%, the content of cyclic dimers is preferably less than 0.1%, and the content of caprolactam monomers is preferably less than 0.4%.

[0096] The devolatilization reactor is a plug flow reactor, preferably a film-forming reactor.

[0097] In some embodiments of the present invention, the filtration accuracy of the melt filtration in step S10 is 20-100 μm, preferably 20-40 μm.

[0098] In some embodiments of the present invention, the melt deep processing in step S11 specifically means feeding the PA6 melt into each deep processing device and processing it into PA6 chips, nylon textile fibers, PA6 carpet filaments, industrial canvas fibers, industrial cord fabric fibers, injection molded products, etc. according to different requirements.

[0099] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0100] In the following embodiments, the test methods or testing methods, unless otherwise specified, are all conventional methods; the raw materials and auxiliaries, unless otherwise specified, are all obtained from conventional commercial channels or prepared by conventional methods.

[0101] Example 1

[0102] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and simultaneously 10000 kg / h of water at a temperature of 315 °C and a pressure of 14 MPa (A) is added. The reaction is carried out at a temperature of 310 °C and a pressure of 12 MPa (A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305 °C and a pressure of 12 MPa (A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120 °C and a pressure of 3 kPa (A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator, and after removing insoluble substances, it is continuously fed into a molecular enrichment and purification device filled with activated carbon. The enrichment and purification is carried out at 120 °C for 50 min, and then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin. The purification is carried out at 80 °C for 5 min, and then it is continuously fed into a low-boiling component vaporization extraction reactor, and the low-boiling components are removed at a temperature of 150 °C and a pressure of 25 kPa (A). Then it is continuously fed into a high-boiling component fractional extraction reactor, and caprolactam is fractionally vaporized at a temperature of 200 °C and a pressure of 800 Pa (A) to obtain 1057.3 kg / h of purified caprolactam melt solution (depolymerization product A); 1057.3 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and simultaneously 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270 °C and a pressure of 4.5 MPa (A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and simultaneously 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260 °C and a pressure of 2 kPa (A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245 °C and a pressure of 0.3 kPa (A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.4%, a cyclic dimer content of 0.06%, and a caprolactam monomer content of 0.2%.

[0103] The nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance carbon spectrum of the depolymerization product A described in Example 1 were analyzed, and the results are as Figure 1 and Figure 2 shown. No obvious impurity peaks appeared in the nuclear magnetic resonance hydrogen spectrum and nuclear magnetic resonance carbon spectrum. Thus, it shows that through the purification process of the present invention, the purity of the obtained purified caprolactam is ≥99.99%.

[0104] Example 2

[0105] 1000 kg / h of nylon textile fragments (wherein the nylon fiber content is 63%, the spandex fiber is 35%, and the inorganic / organic dyes, pigments and fabric additives are 2%) are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 315°C and a pressure of 14 MPa (A) is added. The reaction is carried out at a temperature of 310°C and a pressure of 12 MPa (A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 12 MPa (A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120°C and a pressure of 3 kPa (A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator, and after removing the insoluble substances, it is continuously fed into a molecular enrichment and purification device filled with activated carbon, and is enriched and purified at 120°C for 50 min. Then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin, and is purified at 80°C for 5 min. Then it is continuously fed into a low-boiling component vaporization extraction reactor, and the low-boiling components are removed at a temperature of 150°C and a pressure of 25 kPa (A). Then it is continuously fed into a high-boiling component fractional extraction reactor, and caprolactam is fractionally vaporized at a temperature of 200°C and a pressure of 800 Pa (A) to obtain 618 kg / h of a refined caprolactam melt solution (depolymerization product A); 618 kg / h of the refined caprolactam melt solution is continuously fed into a pre-polymerization reactor, and at the same time, 18.54 kg / h of water, 12.36 kg / h of 6-aminocaproic acid, 1.24 kg / h of adipic acid, and 0.31 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa (A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and at the same time, 0.62 Kg / h of triphenyl phosphite, 0.25 kg / h of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], and 0.25 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa (A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa (A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter, and the obtained PA6 melt (polymerization product B2) has an oligomer content of 0.5%, a cyclic dimer content of 0.1%, and a caprolactam monomer content of 0.2%.

[0106] Example 3

[0107] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and simultaneously 10000 kg / h of water at a temperature of 315°C and a pressure of 14 MPa(A) is added. The reaction is carried out at a temperature of 310°C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120°C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator, and after removing insoluble substances, it is continuously fed into a molecular enrichment purifier filled with activated carbon. The enrichment purification is carried out at 120°C for 50 min, and then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin. The purification is carried out at 80°C for 5 min, and then it is continuously fed into a low-boiling component vaporization extraction reactor. The low-boiling components are removed at a temperature of 150°C and a pressure of 25 kPa(A), and then it is continuously fed into a high-boiling component fractional extraction reactor. Caprolactam is fractionally vaporized at a temperature of 200°C and a pressure of 800 Pa(A) to obtain 1057.3 kg / h of purified caprolactam melt solution (depolymerization product A); 1057.3 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and simultaneously 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and simultaneously 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and simultaneously 150 kg / h of the flame retardant melamine is added. The reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.4%, a cyclic dimer content of 0.08%, and a caprolactam monomer content of 0.17%.

[0108] Example 4

[0109] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and simultaneously 10000 kg / h of water at a temperature of 315°C and a pressure of 14 MPa (A) is added. The reaction is carried out at a temperature of 310°C and a pressure of 12 MPa (A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 12 MPa (A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flashing, and finally a crude caprolactam melt solution at a temperature of 120°C and a pressure of 3 kPa (A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator to remove insoluble substances, and then continuously fed into a molecular enrichment and purification device filled with activated carbon. The enrichment and purification is carried out at 120°C for 50 min, and then continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin. The purification is carried out at 80°C for 5 min, and then continuously fed into a low-boiling component vaporization extraction reactor. The low-boiling components are removed at a temperature of 150°C and a pressure of 25 kPa (A), and then continuously fed into a high-boiling component fractional extraction reactor. Caprolactam is fractionally vaporized at a temperature of 200°C and a pressure of 800 Pa (A) to obtain 1057.3 kg / h of purified caprolactam melt solution (depolymerization product A); 1057.3 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and simultaneously 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa (A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and simultaneously 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa (A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and simultaneously 200 kg / h of polyethylene glycol is added. The reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa (A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 / polyethylene glycol block melt (polymerization product B2) has an oligomer content of 0.8%, a cyclic dimer content of 0.03%, and a caprolactam monomer content of 0.31%.

[0110] Example 5

[0111] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and simultaneously 10000 kg / h of water at a temperature of 315 °C and a pressure of 14 MPa(A) is added. The reaction occurs at a temperature of 310 °C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, where the reaction occurs at a temperature of 305 °C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120 °C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator to remove insoluble substances, and then continuously fed into a molecular enrichment and purification device filled with activated carbon, where it is enriched and purified at 120 °C for 50 min. Then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin, where it is purified at 80 °C for 5 min. Then it is continuously fed into a low-boiling component vaporization extraction reactor, where low-boiling components are removed at a temperature of 150 °C and a pressure of 25 kPa(A). Then it is continuously fed into a high-boiling component fractional extraction reactor, where caprolactam is fractionally vaporized at a temperature of 200 °C and a pressure of 800 Pa(A) to obtain 1057.3 kg / h of a purified caprolactam melt solution (depolymerization product A); 1057.3 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and simultaneously 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction occurs at a temperature of 270 °C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and simultaneously 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction occurs at a temperature of 260 °C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and simultaneously 300 kg / h of polyolefin elastomer is added. The reaction occurs at a temperature of 245 °C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 / polyolefin copolymer melt (polymerization product B2) has an oligomer content of 0.6%, a cyclic dimer content of 0.05%, and a caprolactam monomer content of 0.29%.

[0112] Example 6

[0113] 1000 kg / h of nylon textile fragments (where the nylon fiber content is 63%, the spandex fiber is 35%, and the inorganic / organic dyes, pigments, and fabric additives are 2%) are continuously fed into a pre-depolymerization reactor. At the same time, 10000 kg / h of water at a temperature of 315°C and a pressure of 14 MPa (A) is added, and the reaction is carried out at a temperature of 310°C and a pressure of 12 MPa (A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 12 MPa (A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120°C and a pressure of 3 kPa (A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator to remove insoluble substances, and then continuously fed into a molecular enrichment and purification device filled with activated carbon, where it is enriched and purified at 120°C for 50 min. Then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin, and purified at 80°C for 5 min. Then it is continuously fed into a low-boiling component vaporization extraction reactor, where low-boiling components are removed at a temperature of 150°C and a pressure of 25 kPa (A). Then it is continuously fed into a high-boiling component fractional extraction reactor, where caprolactam is fractionally vaporized at a temperature of 200°C and a pressure of 800 Pa (A) to obtain 618 kg / h of purified caprolactam melt solution (depolymerization product A); 618 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor. At the same time, 18.54 kg / h of water, 12.36 kg / h of 6-aminocaproic acid, 1.24 kg / h of adipic acid, and 0.31 kg / h of acetic acid are added, and the reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa (A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor. At the same time, 0.62 Kg / h of triphenyl phosphite, 0.25 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.25 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added, and the reaction is carried out at a temperature of 260°C and a pressure of 2 kPa (A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor. At the same time, 247.2 kg / h of ε-caprolactone is added, and the reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa (A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter, and the obtained PA6 / polycaprolactone block polymerization melt (polymerization product B2) has an oligomer content of 0.3%, a cyclic dimer content of 0.03%, and a caprolactam monomer content of 0.19%.

[0114] Comparative Example 1

[0115] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 315°C and a pressure of 14 MPa(A) is added. The reaction is carried out at a temperature of 310°C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally, a crude caprolactam melt solution (depolymerization product A) at a temperature of 120°C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator. After removing insoluble substances, it is continuously fed into a pre-polymerization reactor, and at the same time, 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and at the same time, 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.23%, a cyclic dimer content of 0.92%, and a caprolactam monomer content of 0.5%.

[0116] Comparative Example 2

[0117] 1000 kg / h of nylon textile fragments (where the nylon fiber content is 63%, the spandex fiber is 35%, and the inorganic / organic dyes, pigments, and fabric additives are 2%) are continuously fed into a pre-depolymerization reactor. At the same time, 10000 kg / h of water at a temperature of 315 °C and a pressure of 14 MPa (A) is added and reacted for 30 min at a temperature of 310 °C and a pressure of 12 MPa (A). The pre-depolymerization product is continuously fed into a deep-depolymerization reactor and reacted for 25 min at a temperature of 305 °C and a pressure of 12 MPa (A). The deep-depolymerization reaction liquid undergoes three-stage separation and flashing, and finally a crude caprolactam melt (depolymerization product A) at a temperature of 120 °C and a pressure of 3 kPa (A) is obtained. The melt is continuously fed into a 3-μm centrifugal separator, and after removing the insoluble matter, it is continuously fed into a pre-polymerization reactor. At the same time, 18.54 kg / h of water, 12.36 kg / h of 6-aminocaproic acid, 1.24 kg / h of adipic acid, and 0.31 kg / h of acetic acid are added and reacted for 10 h at a temperature of 270 °C and a pressure of 4.5 MPa (A). The pre-polymerization product is continuously fed into a post-polymerization reactor. At the same time, 0.62 Kg / h of triphenyl phosphite, 0.25 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.25 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. It is reacted for 5 h at a temperature of 260 °C and a pressure of 2 kPa (A). The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor and reacted for 90 min at a temperature of 245 °C and a pressure of 0.3 kPa (A). The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.43%, a cyclic dimer content of 0.92%, and a caprolactam monomer content of 0.5%.

[0118] Comparative Example 3

[0119] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 280 °C and a pressure of 14 MPa(A) is added. The reaction takes place at a temperature of 275 °C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, where the reaction occurs at a temperature of 270 °C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally, a crude caprolactam melt solution at a temperature of 120 °C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator to remove insoluble substances, and then continuously fed into a molecular enrichment and purification device filled with activated carbon for enrichment and purification at 120 °C for 50 min. It is then continuously fed into an ion mixing bed reactor filled with T-5213CPR resin and A-2313CPR resin for purification at 80 °C for 5 min. It is then continuously fed into a low-boiling component vaporization extraction reactor to remove low-boiling components at a temperature of 150 °C and a pressure of 25 kPa(A). It is then continuously fed into a high-boiling component fractional extraction reactor to fractionally vaporize caprolactam at a temperature of 200 °C and a pressure of 800 Pa(A), obtaining 974.73 kg / h of a purified caprolactam melt solution (depolymerization product A); 974.73 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and at the same time, 29.24 kg / h of water, 19.45 kg / h of 6-aminocaproic acid, 1.95 kg / h of adipic acid, and 0.48 kg / h of acetic acid are added. The reaction takes place at a temperature of 270 °C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and at the same time, 0.97 Kg / h of triphenyl phosphite, 0.39 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.39 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction takes place at a temperature of 260 °C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, where the reaction occurs at a temperature of 245 °C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter, and the obtained PA6 melt (polymerization product B2) has an oligomer content of 0.4%, a cyclic dimer content of 0.07%, and a caprolactam monomer content of 0.25%.

[0120] Comparative Example 4

[0121] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and simultaneously 10000 kg / h of water at a temperature of 315 °C and a pressure of 7.5 MPa (A) is added. The reaction is carried out at a temperature of 310 °C and a pressure of 7 MPa (A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305 °C and a pressure of 7 MPa (A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally a crude caprolactam melt solution at a temperature of 120 °C and a pressure of 3 kPa (A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator, and after removing insoluble substances, it is continuously fed into a molecular enrichment and purification device filled with activated carbon. The enrichment and purification is carried out at 120 °C for 50 min, and then it is continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin. The purification is carried out at 80 °C for 5 min, and then it is continuously fed into a low-boiling component vaporization extraction reactor. The low-boiling components are removed at a temperature of 150 °C and a pressure of 25 kPa (A), and then it is continuously fed into a high-boiling component fractional extraction reactor. Caprolactam is fractionally vaporized at a temperature of 200 °C and a pressure of 800 Pa (A) to obtain 901.16 kg / h of purified caprolactam melt solution (depolymerization product A); 901.16 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and simultaneously 27 kg / h of water, 18 kg / h of 6-aminocaproic acid, 1.8 kg / h of adipic acid, and 0.45 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270 °C and a pressure of 4.5 MPa (A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and simultaneously 0.9 kg / h of triphenyl phosphite, 0.36 kg / h of pentaerythritol tetrakis [β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], and 0.36 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260 °C and a pressure of 2 kPa (A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245 °C and a pressure of 0.3 kPa (A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.5%, a cyclic dimer content of less than 0.08%, and a caprolactam monomer content of less than 0.26%.

[0122] Comparative Example 5

[0123] 1000 kg / h of nylon textile fragments are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 280°C and a pressure of 14 MPa(A) is added. The reaction is carried out at a temperature of 275°C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 270°C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flashing, and finally, a crude caprolactam melt (depolymerization product A) at a temperature of 120°C and a pressure of 3 kPa(A) is obtained. The melt is continuously fed into a 3-μm centrifugal separator. After removing the insoluble substances, it is continuously fed into a pre-polymerization reactor. At the same time, 29.24 kg / h of water, 19.45 kg / h of 6-aminocaproic acid, 1.95 kg / h of adipic acid, and 0.48 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor. At the same time, 0.97 kg / h of triphenyl phosphite, 0.39 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.39 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.73%, a cyclic dimer content of 1.9%, and a caprolactam monomer content of 0.75%.

[0124] Comparative Example 6

[0125] 1000 kg / h of nylon textile fragments are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 315°C and a pressure of 7.5 MPa(A) is added. The reaction is carried out at a temperature of 310°C and a pressure of 7 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305°C and a pressure of 7 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation flash evaporation, and finally, a crude caprolactam melt solution (depolymerization product A) at a temperature of 120°C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator. After removing the insoluble matter, it is continuously fed into a pre-polymerization reactor. At the same time, 27 kg / h of water, 18 kg / h of 6-aminocaproic acid, 1.8 kg / h of adipic acid, and 0.45 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270°C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor. At the same time, 0.9 kg / h of triphenyl phosphite, 0.36 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.36 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260°C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product (polymerization product B1) is continuously fed into a devolatilization reactor, and the reaction is carried out at a temperature of 245°C and a pressure of 0.3 kPa(A) for 90 min. The devolatilization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B2) has an oligomer content of 0.17%, a cyclic dimer content of 2.1%, and a caprolactam monomer content of 1.3%.

[0126] Comparative Example 7

[0127] 1000 kg / h of pure polyamide textile fragments are continuously fed into a pre-depolymerization reactor, and at the same time, 10000 kg / h of water at a temperature of 315 °C and a pressure of 14 MPa(A) is added. The reaction is carried out at a temperature of 310 °C and a pressure of 12 MPa(A) for 30 min. The pre-depolymerization product is continuously fed into a deep-depolymerization reactor, and the reaction is carried out at a temperature of 305 °C and a pressure of 12 MPa(A) for 25 min. The deep-depolymerization reaction liquid undergoes three-stage separation and flash evaporation, and finally, a crude caprolactam melt solution at a temperature of 120 °C and a pressure of 3 kPa(A) is obtained. The melt solution is continuously fed into a 3-μm centrifugal separator to remove insoluble substances, and then continuously fed into a molecular enrichment and purification device filled with activated carbon. It is enriched and purified at 120 °C for 50 min, and then continuously fed into an ion mixing bed reactor filled with T-5213 CPR resin and A-2313 CPR resin. It is purified at 80 °C for 5 min, and then continuously fed into a low-boiling component vaporization extraction reactor. The low-boiling components are removed at a temperature of 150 °C and a pressure of 25 kPa(A), and then continuously fed into a high-boiling component fractional extraction reactor. Caprolactam is fractionally vaporized at a temperature of 200 °C and a pressure of 800 Pa(A) to obtain 1057.3 kg / h of purified caprolactam melt solution (depolymerization product A); 1057.3 kg / h of the purified caprolactam melt solution is continuously fed into a pre-polymerization reactor, and at the same time, 30 kg / h of water, 20 kg / h of 6-aminocaproic acid, 2 kg / h of adipic acid, and 0.5 kg / h of acetic acid are added. The reaction is carried out at a temperature of 270 °C and a pressure of 4.5 MPa(A) for 10 h. The pre-polymerization product is continuously fed into a post-polymerization reactor, and at the same time, 1 kg / h of triphenyl phosphite, 0.4 kg / h of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.4 kg / h of tris(2,4-di-tert-butylphenyl) phosphite are added. The reaction is carried out at a temperature of 260 °C and a pressure of 2 kPa(A) for 5 h. The post-polymerization product is continuously fed through a melt pump into a 30-μm melt filter. The obtained PA6 melt (polymerization product B1) has an oligomer content of 9.8%, a cyclic dimer content of 0.07%, and a caprolactam monomer content of 8.4%. The PA6 melt is pelletized to obtain pellets, and the pellets are extracted to obtain PA6 pellets (polymerization product B2).

[0128] Table 1 Comparison of Depolymerization Rate and Yield of Depolymerization Product A

[0129]

[0130] The depolymerization conditions of Example 1, Examples 3-6, Comparative Example 1, Comparative Example 2, and Comparative Example 7 are the same and all within the protection scope of the present invention. The depolymerization conditions of Example 2 are different but also within the protection scope of the present invention. The depolymerization temperatures of Comparative Example 3 and Comparative Example 5 are the same and both lower than the protection scope of the present invention. The depolymerization pressures of Comparative Example 4 and Comparative Example 6 are the same and both lower than the protection scope of the present invention. Therefore, only the depolymerization rates and the yields of depolymerization product A of Example 1, Example 2, Comparative Example 3, and Comparative Example 4 are compared.

[0131] By comparing Example 1 with Comparative Example 3, the pre-depolymerization and deep-depolymerization temperatures are lower than the protection scope of the present invention, and the depolymerization rate of PA6 is low, resulting in a low yield of caprolactam. By comparing Example 1 with Comparative Example 4, the pre-depolymerization and deep-depolymerization pressures are lower than the protection scope of the present invention, a large amount of depolymerizing agent vaporizes, 6-aminocaproic acid is not completely converted into caprolactam, and the by-products increase, all of which will lead to a low yield of caprolactam.

[0132] Table 2 Performance analysis of depolymerization product A and caprolactam

[0133]

[0134]

[0135] The raw materials used in Examples 3-6 and Comparative Example 7 and the depolymerization and purification processes are exactly the same as those in Example 1. The raw materials used in Example 2 are different. Therefore, only Example 1, Example 2, and Comparative Examples 1-6 are compared.

[0136] By comparing Example 1 with Comparative Example 1 and Example 2 with Comparative Example 2, it is known that using the depolymerization product purification process of the present invention can greatly improve the quality of caprolactam in depolymerization product A, making it reach the first-class product standard of industrial caprolactam (GB / T13254-2017).

[0137] By comparing Comparative Example 3 with Comparative Example 5 and Comparative Example 4 with Comparative Example 6, and combining the data in Table 1, it is known that although the depolymerization temperature and pressure are not within the protection scope, the quality and yield of crude caprolactam both decrease, but through the purification process of the present invention, they can both reach the first-class product standard of industrial caprolactam.

[0138] Table 3 Mechanical property analysis of polymerization product B

[0139]

[0140]

[0141] By comparing the data of Example 1, Comparative Example 1, Comparative Example 5, and Comparative Example 6, it is known that the depolymerization and purification processes of the present invention can effectively improve the quality of the recycled PA6 melt, thereby effectively enhancing the mechanical properties.

[0142] By comparing the data of Example 1, Example 2, and Comparative Example 2, it is known that spandex fibers seriously affect the mechanical properties of recycled PA6 products. Through the purification technology of the present invention, the by-products generated by spandex during the depolymerization process can be effectively removed, making the mechanical properties of recycled PA6 products of polyamide textiles containing spandex comparable to those of recycled PA6 products of pure polyamide textiles.

[0143] Table 4 Analysis of the relative viscosity and hot water extractable content of polymerization product B

[0144]

[0145] Examples 1-6 and Comparative Examples 1-6 all have a devolatilization process. Comparative Example 7 is a conventional technical means to obtain PA6 chips through hot water extraction. Therefore, only Example 1 and Comparative Example 7 are compared and analyzed.

[0146] In Example 1, polymerization product B1 is subjected to a devolatilization process to obtain polymerization product B2. Through data analysis, it is obtained that the devolatilization process can effectively reduce the content of oligomers and caprolactam monomers in the PA6 melt, and at the same time can increase the relative viscosity of the PA6 melt. In Comparative Example 7, polymerization product B1 is granulated and extracted to obtain polymerization product B2. Granulation is a conventional means for processing the PA6 melt and does not affect the performance of the PA6 melt itself. Through extraction, the content of oligomers and caprolactam monomers can be reduced, but the effect is inferior to the devolatilization process of the present invention. At the same time, due to the reduction of the content of oligomers and caprolactam monomers, its relative viscosity slightly increases. If a high-viscosity PA6 melt is required, the relative viscosity needs to be increased by solid-phase viscosity increase through conventional technical means.

[0147] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A process for chemically regenerating PA6 products using waste nylon textiles, characterized in that: The following steps are involved: S1. Textile crushing: crushing the waste nylon textiles to obtain nylon textile fragments; S2, pre-depolymerization: placing the nylon textile fragments in a pre-depolymerization reaction vessel, adding a pre-depolymerization agent, controlling the pre-depolymerization reaction temperature to 280-350° C., the reaction pressure to 8-15 MPa, and the reaction time to 10-40 min to obtain a pre-depolymerization reaction liquid; S3, deep depolymerization: transfer the pre-depolymerization reaction liquid to a deep depolymerization reaction vessel, control the deep depolymerization reaction temperature to 280-350°C, the reaction pressure to 8-15 MPa, and the reaction time to 20-60 min to obtain a deep depolymerization reaction liquid; S4, flash evaporation: flash evaporation the deep depolymerization reaction liquid through a pressure reducing valve until the pressure reaches 1-5 KPa and the temperature is reduced to 80-150° C. to obtain gas phase components and liquid phase components; S5, centrifugal separation: centrifuging the liquid phase component to obtain a crude caprolactam solution; S6, purification of depolymerization product: the crude caprolactam melt is transferred to a purification reactor, and molecular enrichment purification, ion screening purification, low-boiling component vaporization extraction, and heavy-boiling component fine extraction are sequentially performed to obtain a refined caprolactam melt; S7, pre-polymerization: the refined caprolactam melt is transferred to a pre-polymerization reaction vessel, and a ring-opening agent, a molecular weight regulator and a catalyst are added at the same time, and the reaction temperature of the pre-polymerization is controlled to be 240-270°C, the reaction pressure is 0.1-5.5MPa, and the reaction time is 3-15h to obtain a pre-polymerization product; S8, post-polymerization: transfer the pre-polymerization product to a post-polymerization reaction vessel, add a heat stabilizer and an antioxidant, control the post-polymerization reaction temperature to 230-270°C, the reaction pressure to 1-10KPa, and the reaction time to 2-8h to obtain a post-polymerization product; S9, devolatilization: transferring the post-polymerization product to a devolatilization reaction vessel, controlling the devolatilization reaction temperature to 230-255°C, the reaction pressure to 0.1-10KPa, and the reaction time to 30-150min to obtain a devolatilization product; S10, melt filtration: filtering the devolatilization product to obtain a polyamide 6 melt; S11. Melt deep processing.

2. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: In step S2, the pre-depolymerizing agent comprises water, and the mass ratio of the pre-depolymerizing agent to the nylon textile fragments is 8:1-15:

1.

3. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: The deep depolymerization reaction temperature in step S3 is 280-320° C., the reaction pressure is 10-12 MPa, and the reaction time is 25-45 min.

4. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: The flash evaporation stage number in step S4 is 2-4.

5. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: The centrifugal separation accuracy in step S5 is 3-5 μm.

6. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: The temperature of the molecular enrichment purification in step S6 is 110-130°C, the reaction pressure is normal pressure, and the reaction time is 30-90min; the temperature of the ion screening purification is 70-80°C, the pressure is 100KPa, and the purification time is 3-10min; the reaction temperature of the low-boiling component vaporization extraction is 100-200°C, the reaction pressure is 1-50KPa, and the reaction time should be less than 60s; the reaction temperature of the heavy-boiling component fine extraction is 160-220°C, the reaction pressure is 0.3-5KPa, and the reaction time should be less than 60s.

7. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: In step S7, the amount of the ring-opening agent added is 1-5% of the mass of the refined caprolactam melt; the amount of the molecular weight regulator added is 1-3% of the mass of the refined caprolactam melt; and the amount of the catalyst added is 1-3% of the mass of the refined caprolactam melt.

8. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: In step S8, the amount of the heat stabilizer added is 0.05-0.5% of the mass of the refined caprolactam melt; the amount of the antioxidant added is 0.03-0.15% of the mass of the refined caprolactam melt.

9. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: Step S9 selectively adds PA6 modified monomers, polymers of non-PA6 structural units and functional additives according to the processing requirements of subsequent products, wherein the addition amount of the PA6 modified monomers is 0.1-50% of the mass of the refined caprolactam melt; the addition amount of the polymers of non-PA6 structural units is 0.1-60%; and the addition amount of the functional additives is 0.1-30% of the mass of the refined caprolactam melt.

10. The process for chemically regenerating PA6 products from waste nylon textiles according to claim 1, characterized in that: The filtration accuracy of the melt filtration in step S10 is 20-100 μm.

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