Depolymerization catalyst for polymer having amide functional group and depolymerization method using same

Abstract

The present invention relates to a depolymerization method for a polymer having an amide functional group and, more specifically, to a method capable of achieving depolymerization even at low temperatures and obtaining monomers from depolymerization products in high yield by decomposing a polymer having an amide functional group using a mixed catalyst with different functions, for example, a mixed catalyst in which an acid catalyst capable of providing protons and a metal oxide catalyst are mixed as components.

Description

Depolymerization catalyst for polymers having amide functional groups and depolymerization method using the same

[0001] The present invention relates to a method for depolymerizing a polymer having an amide functional group, and more particularly, to a method for enabling depolymerization of a polymer having an amide functional group even at a low temperature by using a mixed catalyst having different functions, for example, a mixed catalyst comprising an acid catalyst capable of providing hydrogen cations as a component and a metal oxide catalyst, and also significantly increasing the yield of a depolymerized monomer.

[0002] Plastics are inexpensive, durable, and easy to mold and process, making them a versatile material used in the production of a wide range of products. These advantages have led to a dramatic increase in plastic consumption across industries and daily life for decades. However, improperly managed plastic waste, if not properly disposed of, is causing not only environmental problems but also various social and international issues. Due to these issues, each country is proposing various policies to address the issue of plastic waste, and strict regulations are emerging in global trade markets to curb indiscriminate production and consumption. Furthermore, interest in developing recycling technologies to establish a circular economy for plastics is also growing.

[0003] Polymers with amide functional groups, such as nylon, are among the toughest plastics, and boast excellent oil and abrasion resistance. These polymers are used as fibers for clothing, industrial applications, and military applications, and are also utilized as engineering plastics that require high mechanical properties. These polymers with amide functional groups are inexpensive yet highly durable, making them widely used in daily life and industry. However, due to their superior properties, they are known to be difficult to recycle through depolymerization methods compared to other polymers (a representative example is polyester) that can be manufactured through condensation polymerization or ring-opening polymerization.

[0004] Known reaction pathways for depolymerizing polymers with amide functional groups include hydrolysis, alkaline decomposition, alcoholysis, ammonolysis, and catalyst-based autolysis.

[0005] The most common method for depolymerizing a polymer with an amide functional group is to use water or steam at a high temperature and high pressure, mainly reaching supercritical or subcritical temperatures, as a reaction medium, and to add an inorganic acid (mainly phosphoric acid) as a catalyst or to perform depolymerization under non-catalytic conditions, as in Prior Art Patent 1 (Korean Patent No. 10-1130461). This depolymerization method requires a high initial investment cost and excessive energy consumption because it is carried out under high temperature and high pressure conditions, and there is a problem that purification is difficult because not only foreign substances or by-products in the depolymerization product but also the catalyst has hydrophilic properties similar to the monomer.

[0006] To overcome the problems of water or steam heated to high temperatures, Prior Art 2 (US 6,011,153) describes a method for decomposing nylon 6 at a low temperature of 280°C to 330°C using ammonia water. This method is aminolysis that uses free ammonia, which is difficult to handle, as a reactant, and has the advantage of being able to decompose polymers with amide functional groups at relatively low temperatures. However, it has the problem that the yield of caprolactam as a depolymerized monomer product is low, and 6-aminocaproic amide having an amide terminal group other than 6-aminocaproic acid is simultaneously produced, so the selectivity of the product is low.

[0007] Prior art patent 3 (JP 4957555B2) describes a depolymerization method that uses hydrocarbon compounds (aromatic and alkane compounds) and water as a reaction solvent to produce a high yield of monomer (caprolactam) of 80% or more without the use of a catalyst at a temperature range of 300°C to 420°C. This method can produce a high yield of monomer using a relatively low depolymerization temperature, and because it does not use a catalyst, it may have the advantage of easy product purification after depolymerization. However, it still requires a lot of energy and uses a large amount of high-temperature hydrocarbon compounds, such as toluene, exceeding 70%, making it difficult to ensure operational safety and economic feasibility.

[0008] Prior patent 4 (International Publication No. PCT / US2023 / 072354) reported a method for producing caprolactam with a yield of up to 90% by depolymerizing nylon 6 using a lanthanide-based organometallic catalyst under relatively low reaction conditions (240°C) close to the melting point of nylon 6 without using a solvent. However, in this method, the stability of the applied catalyst to moisture and oxygen may be reduced when in contact with air, and a high vacuum (10) is required to produce caprolactam. -3 Because the conditions must be maintained continuously for long periods of time, the process configuration can be difficult and it may be difficult to construct large-scale facilities.

[0009] Conventional methods for depolymerizing polymers with amide functionalities all require high temperatures above the melting point (or melting point), requiring significant energy consumption. Furthermore, many of these methods are difficult to separate the catalyst from the product after depolymerization, or are chemically unstable, making them impossible to separate or recover. Furthermore, the yield of the resulting product is extremely limited, controlling side reactions is challenging, and purifying the monomer from the resulting product is challenging.

[0010] In order to overcome these problems, the present invention proposes a method for improving the performance of the depolymerization reaction and the selectivity of the product by using multiple catalysts with different functions, and provides a method for depolymerizing a polymer having an amide functional group that is highly efficient and economical, as it not only does not use excessive energy to increase the depolymerization reaction rate, but also allows all the catalysts to be recovered in their original form without loss, and at the same time, the monomers can be purified to a high purity.

[0011] [Prior Art Literature]

[0012] (Patent Document 0001) Korean Patent No. 10-1130461 (registered on March 9, 2012)

[0013] (Patent Document 0002) U.S. Patent No. 6,011,153 (registered on January 4, 2000)

[0014] (Patent Document 0003) Japanese Patent No. 4957555 (registered on March 30, 2012)

[0015] (Patent Document 0004) International Patent Publication No. PCT / US2023 / 072354 (Published on February 22, 2024)

[0016] The present invention is intended to overcome the problems of the prior art described above, and the purpose of the present invention is to provide an efficient catalyst form and composition capable of completely depolymerizing a polymer having an amide functional group even at a temperature below the melting point and increasing the selectivity of a desired monomer in the resulting reactant.

[0017] Another object of the present invention is to provide a method for depolymerizing a polymer having an amide functional group, which can simplify the reaction and purification process, significantly reduce energy consumption in each process, minimize loss or waste of materials compared to existing technologies, and produce a high yield of depolymerized monomer.

[0018] Another object of the present invention is to provide a method for depolymerizing a polymer having an amide functional group, which suppresses the production of by-products in a product while minimizing the introduction of by-products into the product, and obtains a high-purity depolymerized monomer product even when using a raw material that is contaminated or contains foreign substances.

[0019] In order to solve the above problem, the present invention provides a composition for depolymerization of a polymer having an amide functional group, characterized by including (1) a monohydric alcohol; (2) an acid capable of providing a hydrogen cation (proton); and (3) a metal oxide.

[0020] In one embodiment of the composition of the present invention, the monohydric alcohol may be a straight-chain and / or branched monohydric alcohol, and the number of carbon atoms of the alcohol may be 1 to 8.

[0021] In one embodiment of the present invention, the acid capable of providing the hydrogen cation may be characterized by being at least one selected from among an inorganic acid, an organic acid, and a solid acid having an acidic functional group capable of donating a proton ion as part of the compound structure, each having at least one hydrogen cation in the molecule.

[0022] In one embodiment of the composition of the present invention, the metal oxide is an oxide of a metal selected from vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), aluminum (Al), gallium (Ga), tin (Sn), and iron (Fe), and may be a single metal oxide composed of one metal or a composite metal oxide of two or more metals, and may be supported on a support or used as a metal oxide itself without being supported on a support.

[0023] In one embodiment of the composition of the present invention, the composition may be characterized in that an aromatic compound substituted with one or more alkoxy functional groups is added as a cosolvent.

[0024] In addition, the present invention provides a method for depolymerizing a polymer having an amide functional group, characterized in that it comprises a step of contacting the composition according to the present invention with a polymer having an amide functional group.

[0025] In one embodiment of the depolymerization method of the present invention, a process of filtering and separating unreacted polymer material may be additionally included.

[0026] In addition, the depolymerization method of the present invention may include a step of contacting a polymer having an amide functional group with a composition comprising (1) a monohydric alcohol; (2) an acid capable of providing a hydrogen cation; (3) a metal oxide; and (4) an aromatic compound substituted with at least one alkoxy functional group; wherein a step of removing only the alcohol from the depolymerization reaction product to precipitate and recover the acid and / or metal oxide used as a catalyst may be further added, and a step of adding water to the reaction product from which the acid and / or metal oxide used as a catalyst has been removed to cause phase separation and then concentrating the depolymerization monomer in a hydrophilic solvent layer to recover it may be further included.

[0027] Unlike existing methods that could only achieve a depolymerization reaction at a high temperature higher than the melting point of a polymer for depolymerization of a polymer having an amide functional group and production of a monomer, the present invention provides a low-temperature depolymerization method that can completely decompose a polymer having an amide functional group even at a temperature lower than the melting point of the polymer and obtain a high-yield monomer as a product therefrom.

[0028] In addition, unlike existing or prior research methods that require very high pressure conditions or that depolymerize while maintaining a high vacuum by adding water heated to a high temperature near the critical point as a reaction solvent, the present invention can provide relatively mild conditions for depolymerization of a polymer having an amide functional group, and thereby can help significantly reduce the initial investment cost for a depolymerization reactor or equipment.

[0029] In the present invention, by using two or more types of catalysts, namely, an acid and a metal oxide, which exhibit different functions, without causing performance degradation, interference, or structural modification of the compound under depolymerization reaction conditions, the reaction rate for the depolymerization of a polymer and the decomposition reaction of an oligomer can be increased while simultaneously improving the selectivity for the desired monomer, and through this, it is possible to configure a reaction system for the depolymerization of a polymer having an amide functional group to obtain a monomer with high reaction efficiency, high purity, and high yield even at low temperatures.

[0030] In addition, these catalysts can be fully recovered in their original or reusable form after the reaction, and solid catalysts can be recovered from the reactants in the form of a liquid mixture by a simple physical separation method.

[0031] In addition, since some or all of the effective catalyst components can be supported on a support and utilized as a fixed-bed catalyst, the process can be simplified, and there may not be many restrictions in implementing scale-up and continuous processes.

[0032] In addition, in the existing method for depolymerizing a polymer having an amide functional group, separate materials, such as adsorbents or neutralizing agents, are used to remove foreign substances from the reaction products and purify the products. However, in the present invention, by controlling the thermodynamic characteristics of the solvent used in stages, the solvent and catalyst used can be easily separated and recovered from the reactants according to the flow of the process, and a purification method for producing a high-purity monomer without using the separate materials can be provided.

[0033] The method for depolymerizing a polymer having an amide functional group according to the present invention allows for polymer decomposition and monomer production at a rapid rate at low temperatures, enabling operation of the process using low-cost utilities during the production process. Furthermore, the reaction and separation processes can be combined, and the process structure is simple, eliminating the need for high investment costs. Furthermore, since high yields and high-purity monomers can be produced even at low temperatures, energy consumption can be significantly reduced compared to existing methods. This can offer a solution that overcomes the economic limitations of existing technologies.

[0034] Furthermore, the technology according to the present invention can be directly applied to the chemical recycling of discarded polymer resins, enabling the implementation of an eco-friendly recycling process that significantly reduces carbon dioxide emissions. Specifically, regardless of the raw material type or the type of foreign matter present, the technology can be used to revert the polymer to its pre-synthetic monomer through depolymerization, thereby providing a method for recycling polymers with amide functional groups that can be repeatedly regenerated. This can contribute to the eco-friendly recycling of waste polymer materials that were previously difficult to treat except through incineration or landfill.

[0035] Figure 1 is a reaction schematic diagram for explaining the influence of multiple catalysts used in the present invention on the reaction rates of the steps of polymer decomposition, oligomer decomposition, and direct production of monomers from the polymer during the depolymerization process of a polymer having an amide functional group.

[0036] FIG. 2 shows an XRD spectrum measured by X-ray diffraction (XRD) analysis for an acid catalyst and a metal oxide catalyst recovered from a purification process after depolymerization of a polymer having an amide functional group according to one embodiment of the present invention, compared with an XRD spectrum measured for the catalyst before use.

[0037] FIG. 3 shows infrared spectra measured using an atomic reflection infrared spectroscopy (ATR-FTIR) for a polymer raw material having an amide functional group and a reaction intermediate and monomer product obtained in the process of purifying a reaction product obtained by decomposing the polymer raw material through depolymerization according to one embodiment of the present invention.

[0038] Figure 4 is a graph of the results obtained by measuring the reaction intermediate and monomer products obtained in the process of purifying a polymer raw material having an amide functional group and a reaction product obtained by depolymerizing the polymer raw material according to one embodiment of the present invention using nuclear magnetic resonance spectroscopy (NMR; solvent: Trifluoroethanol (TFE)-d3). 1 H-NMR spectra are shown.

[0039] Figure 5 is a graph showing the results obtained by measuring the final product obtained through the depolymerization and purification process of a polymer having an amide functional group according to one embodiment of the present invention. 1 H-NMR spectra measured against standard substances 1 It is shown in comparison with the H-NMR spectrum.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0041] Throughout this specification, whenever a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0042] In the present invention, metal does not include metalloids, and means alkali metals, alkaline earth metals, transition metals, post-transition metals, and lactanides and actinides.

[0043] In the present invention, the polymer having the amide functional group is a synthetic material called nylon or polyamide, and is a semi-crystalline or amorphous polymer compound composed of amide bonds in its molecular structure, and examples thereof include nylon 6, nylon 66, nylon 46, nylon 610, nylon 612, nylon 11, nylon 12, MXD 6 nylon, etc., and these are merely examples of polymers having the amide functional group and are not limited to those listed.

[0044] The method of the present invention is useful for depolymerizing a polymer having an amide functional group, wherein the polymer having an amide functional group may not be pure but may contain various impurities. For example, it may be mixed with organic and inorganic foreign substances including dyes or pigments, and / or polymers of other materials. The polymer having an amide functional group may be in a predetermined form, such as a powder, fiber, pellet, or ball, or may be supplied in an irregular form.

[0045] In the present invention, the compounds initially added for depolymerization of a polymer having an amide functional group can be divided into three types: a polymer raw material, a solvent, and a catalyst. The solvent for depolymerization of a polymer having an amide functional group may be (1) a monohydric alcohol, and the catalyst may be composed of (2) at least one type of acid capable of providing hydrogen cations and (3) at least one type of metal oxide. By using a mixed catalyst having different functions, the performance of the depolymerization reaction of a polymer having an amide functional group can be significantly improved even at low temperatures.

[0046] As a solvent for depolymerizing the polymer having the above amide functional group, the alcohol may be a mixture of one or more straight-chain or branched monohydric alcohols having 1 to 8 carbon atoms. Since branched alcohols may have lower reactivity due to steric hindrance, straight-chain alcohols may be more advantageous. More specifically, the alcohol solvent for depolymerizing the polymer having the above amide functional group may be methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, or a combination thereof. The alcohol as a solvent for depolymerizing the polymer having the above amide functional group may be a hydrous alcohol compound that partially contains moisture as an impurity, and does not directly participate in the reaction as a reactant, and is neither added to nor consumed in the reactant during depolymerization.

[0047] Long-chain monohydric alcohols with more than eight carbon atoms increase hydrophobicity, reducing the likelihood of the catalyst and nylon functional groups coming into contact with each other, which can significantly slow down the reaction. Furthermore, when dihydric or polyhydric alcohols with two or more intramolecular alcohol functionalities are used as solvents, side reactions such as alcoholysis (or alcohol addition) can occur, generating various byproducts in addition to the regenerated monomer. Therefore, they may be difficult to utilize as depolymerization solvents for the production of regenerated monomers.

[0048] The content of the solvent for depolymerization of the polymer having the amide functional group is sufficient so that the mixed solution prepared by adding the catalyst can come into contact with the polymer, and preferably, the molar ratio may be 0.1 to 5,000 per mole of repeating unit of the polymer having the amide functional group, and more preferably, the molar ratio may be 1 to 500 per mole of repeating unit. If the molar ratio of the solvent per mole of repeating unit of the polymer is less than 0.1, contact between the catalyst solution and the raw material may not sufficiently occur, and thus the target of depolymerization may be limited to a part or local area of ​​the raw material, and if the molar ratio exceeds 5,000, this may result in waste of materials and energy relative to the throughput, and the concentration of the catalyst may also be greatly diluted, which may slow down the reaction rate.

[0049] In the method for depolymerizing a polymer having an amide functional group according to the present invention, a plurality of catalysts are used, and as one component of these, an acid catalyst can provide hydrogen cations, and provides a function of increasing the speed of the initial depolymerization of the polymer having an amide functional group (reaction step 1 of FIG. 1). The polymer decomposition by depolymerization produces a large amount of oligomer fractions, and monomers can be produced through a gradual depolymerization reaction (reaction step 2 of FIG. 1). Another component of the catalyst for depolymerizing a polymer having an amide functional group may be a metal oxide, and provides a function of improving the selectivity of the depolymerized monomer product. That is, the acid catalyst and the metal oxide are applied differently in stages, and ultimately have the effect of increasing the speed of the reaction (reaction step 3 of FIG. 1) for directly producing a monomer from the decomposition of the polymer having an amide functional group.

[0050] As a component of the mixed catalyst to be used in the present invention, the acid catalyst is an acidic substance according to the definition of Arrhenius or Brønstedt-Lowry, and represents an acid capable of donating hydrogen cations (or protons). Examples of the acid catalyst include inorganic acids such as hydrochloric acid (HCl), hydrofluoric acid (HF), hydrobromic acid (HBr), nitric acid (HNO3), sulfuric acid (H2SO4), phosphoric acid (H3PO4), or boric acid (H3BO3); organic acids such as carboxylic acid (RCOOH), sulfinic acid (RSO2H), sulfonic acid (RSO3H), and phenols; or solid acid catalysts in which an acidic functional group capable of donating a proton ion is included in the compound structure.

[0051] As another component of the mixed catalyst to be used in the present invention, the metal oxide catalyst is an oxide of a metal selected from among metal elements such as vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), aluminum (Al), gallium (Ga), tin (Sn), iron (Fe), etc., and is a single metal oxide composed of one metal or a composite metal oxide composed of two or more metals.

[0052] The above metal oxide catalyst may be supplied to the reactant in a state in which it is not supported on a support or in a form in which the metal oxide is supported on a porous support with well-developed pores. Examples of the porous support include alumina (Al2O3), silica-alumina, zeolite, carbon body, etc.

[0053] The molar number of the acid catalyst is not limited thereto, but may preferably be a molar ratio of 0.0001 to 10 per mole of repeating unit of the polymer having the amide functional group, and more preferably a molar ratio of 0.001 to 0.1. If the molar ratio is less than 0.0001, the catalytic effect may not be expressed or may be insufficient, and if the molar ratio exceeds 10, side reactions may be promoted and there is a possibility of causing corrosion problems in the reactor at high temperatures for a long period of time.

[0054] The amount of the metal oxide catalyst in the reactor is not limited thereto, but may preferably be adjusted to have a molar ratio of 0.001 to 1,000 relative to the molar number of the acid catalyst introduced, and more preferably, a molar ratio of 0.01 to 500. If the amount of the metal oxide catalyst is less than 0.001 relative to the molar number of the acid catalyst introduced, the function of the metal oxide catalyst may not be expressed, and if it exceeds 1,000, the concentration of the acid catalyst may be diluted, which may limit the depolymerization reaction rate.

[0055] In the present invention, a cosolvent, in addition to a straight-chain or branched monohydric alcohol, may be added as a solvent for a depolymerization reaction of a polymer having an amide functional group. This cosolvent increases the depolymerization reaction rate of the polymer having the amide functional group, and by controlling the thermodynamic equilibrium conditions after the depolymerization reaction, it can provide an efficient method for recovering most of the catalyst from the depolymerization reaction product while simultaneously purifying a high-purity, high-yield monomer product.

[0056] Examples of co-solvents which are compounds having an aromatic ring substituted with the above alkoxy functional group include, but are not limited to, methoxybenzene, ethoxybenzene, butoxybenzene, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2-diethoxybenzene, 1,3-diethoxybenzene, 1,4-diethoxybenzene, 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 1,3,5-trimethoxybenzene, 1,2,3-triethoxybenzene, 1,2,4-triethoxybenzene, 1,3,5-triethoxybenzene, 1,2,3,4-tetramethoxybenzene, 1,2,3,5-tetramethoxybenzene, 1,2,4,5-Tetramethoxybenzene, 1-methoxy-2-methylbenzene, 1-methoxy-3-methylbenzene, 1-methoxy-4-methylbenzene, 1-ethyl-2-methoxybenzene, 1-ethyl-3-methoxybenzene, 1-ethyl-4-methoxybenzene, 1-ethoxy-2-methylbenzene, 1-ethoxy-3-methylbenzene, 1-ethoxy-4-methylbenzene, 1-ethoxy-2-ethylbenzene, 1-ethoxy-3-ethylbenzene, 1-ethoxy-4-ethylbenzene, 1-methoxy-2-prop-2-enylbenzene, 1-methoxy-3-prop-1-enylbenzene, 1-methoxy-3-prop- 2-enylbenzene, It may be at least one compound selected from among 1-methoxy-4-prop-2-enylbenzene, 1-methoxy-4-[(E)-prop-1-enyl]benzene(cis), 1-methoxy-4-[(E)-prop-1-enyl]benzene(trans).

[0057] The content of the above co-solvent may be preferably 5 to 98 wt%, and more preferably 20 to 95 wt%, based on the total mass of all solvents introduced. If the content of the above co-solvent is less than 5 wt%, the effect of the co-solvent may be weak, and if it exceeds 98 wt%, the depolymerization performance may be reduced.

[0058] When a solvent containing a mixture of the linear or branched monohydric alcohol and a compound having an aromatic ring substituted with an alkoxy functional group is applied to the depolymerization of a polymer having an amide functional group, the reaction temperature can be further lowered and the time required for the decomposition of the polymer can also be significantly reduced.

[0059] In the case of the reaction combination according to some examples of the present invention, when the reaction temperature for depolymerizing nylon 6 is 200°C, which is lower than the melting point of the polymer, all polymers can be decomposed within 2 hours, and a monomer (caprolactam) yield of approximately 98% can be achieved within 4 hours.

[0060] In one embodiment of the present invention, a method of maintaining the reaction temperature for depolymerization at a temperature close to the polymer melting point (220°C or higher) to shorten the reaction time can be used, in which case, the decomposition of the polymer proceeds very quickly within 0.5 hours, all reactions are completed within 2 hours, and a monomer yield of 97% or more can be achieved.

[0061] In another embodiment of the present invention, a method is provided for shortening the reaction time by adjusting the concentration of the catalyst without increasing the reaction temperature for depolymerization. Maintaining the reaction temperature below the polymer melting point while adjusting the concentration of the acid catalyst not only results in rapid and complete polymer decomposition, but also complete decomposition of the oligomer, thereby completing the reaction and yielding monomers in high yields.

[0062] In the present invention, the temperature during the depolymerization reaction is not limited thereto, but may preferably be 150°C to 300°C, and more preferably 180°C to 250°C. If the temperature is less than 150°C, the depolymerization reaction may be delayed, and if it exceeds 300°C, there is a possibility that the speed of side reactions may increase along with unnecessary energy waste.

[0063] When the above depolymerization reaction is completed, the alcohol solvent is removed through a simple evaporation or distillation method, and the monomer product exists in a state (liquid phase) dissolved in the co-solvent, but both types of catalysts used are precipitated in a solid phase, so most of the catalyst can be recovered and reused through a simple physical method such as filtration or centrifugation.

[0064] In addition to the depolymerized monomer, the reaction mixture obtained after recovery of the catalyst may contain catalyst residues or polar foreign substances. A method of contacting the reaction mixture with an adsorbent may be used as a means of removing these substances. Examples of the adsorbent include carbon-based adsorbents such as activated carbon, silica gel, fly ash, ion exchange resins, natural clay, bentonite clay, zeolite, kaolinite, chitosan, and metal-organic frameworks (MOFs).

[0065] One method for recovering monomer products from reaction products from which foreign substances have been removed through the above adsorption process may involve methods such as distillation, evaporation, and drying, which heat the co-solvent and residual solvent to separate and remove them as vapor. However, these methods may have the problem of reducing the purity of the final product if by-products still remain in the reaction products.

[0066] Another method for recovering monomer products from reaction products from which foreign substances have been removed through the above adsorption process may involve applying a liquid-liquid phase separation method by directly adding a hydrophilic solvent or water to the reaction product. When a hydrophilic solvent or water is added, phase separation occurs, and foreign substances or side products can be concentrated in the organic layer (upper phase) consisting entirely of aromatic compounds with alkyl groups, while the monomer products can be concentrated in the hydrophilic solvent layer (lower phase). After phase separation, conditions for recovering high-purity monomer products can be provided by removing the hydrophilic solvent through a method such as evaporation, distillation, or drying.

[0067] Below, the details of the process of the present invention will be explained through examples, comparative examples, and experimental examples. These are representative examples related to the present invention and should not be construed as limiting the scope of application of the present invention.

[0068]

[0069] [Raw Material 1] (Polymer raw material with amide functional group)

[0070] A nylon 6 sample (Sigma-Aldrich, purity: 100%, density: 1.084 g / mL) in pellet form (cylinder diameter: approximately 2.2 mm, height: approximately 2.6 mm) as a polymer material having an amide functional group was prepared as a depolymerization raw material without any separate treatment process.

[0071] [Raw Material 2] (Polymer raw material with amide functional group)

[0072] A polymer having an amide functional group was prepared as a depolymerization raw material by extracting the polymer (nylon 6) having an amide functional group and a polyurethane elastic fiber from a colored (lavender) blended waste fiber in a weight ratio of 3:1 through a selective separation process (method known in Korean Patent No. 10-2664279).

[0073]

[0074] Basic composition of a catalyst for low-temperature depolymerization of polymers with amide functional groups

[0075] The following examples and comparative examples are intended to explain the basic composition and combination of a depolymerization catalyst that must be provided to produce a monomer by decomposing a polymer having an amide functional group at low temperature according to the present invention.

[0076] [Example 1]

[0077] (a) Preparation process of depolymerization reactants

[0078] Approximately 0.5 g of a polymer sample having an amide functional group of raw material 1, 2.04 g of ethanol (Sigma Aldrich, Pure, 200 proof, anhydrous, ≥99.5%), and 14.81 g of anisole (Sigma-Aldrich; ≥99.7%) were weighed and placed in a PEEK material vessel (liner) with an internal volume of 20 ml together with a magnetic stirrer, and then inserted into a lower reactor (autoclave vessel) constituting a pressure-resistant reactor. As a polymer depolymerization catalyst, 0.025 g of niobium oxide (Nb2O5; Sigma-Aldrich; ≥99.9%) and 0.05 g of phosphoric acid (H3PO4; Alfa Aesar, 85% aq. soln.) were weighed and, instead of being added directly to the mixture (polymer and solvent) in the lower reactor prepared for the reaction, transferred to a separate PTFE tube with an internal volume of 100 μL or less to prepare a small catalyst vessel.

[0079] (b) Preparation of the depolymerization reaction system and initiation of the reaction

[0080] The upper head (autoclave head) of the pressure reactor is equipped with a K-type thermocouple and a pressure gauge made of Inconel to measure the internal temperature and pressure, a relief valve with an acceptable pressure of 50 bar, and a purging nitrogen pipe to exhaust the air inside by supplying high-pressure nitrogen from the outside. After attaching the small catalyst container prepared in advance to the upper head, it is connected to the lower reactor containing the raw material and solvent to prepare a sealed high-pressure reactor. Afterwards, the process of charging and discharging nitrogen from the outside through the purging nitrogen pipe was repeated at least three times to completely remove the air inside the reactor.

[0081] The sealed high-pressure reactor was placed on a magnetic stirrer and transferred to a preheated silicone oil bath. When the temperature inside the reactor was maintained at a constant 200°C through PID control, a high-pressure nitrogen pulse was applied from the outside to the inside of the catalyst vessel to cause the catalyst to fall, thereby initiating the reaction. During the reaction, a magnetic stirrer was used to rotate the magnetic stirrer pre-positioned inside the reactor at a speed of 1,000 rpm to induce continuous mixing of the reactants.

[0082] (c) Termination of depolymerization reaction

[0083] After 2 hours of reaction, the stirrer was stopped, the reactor was removed from the high-temperature silicone oil bath, and quickly placed in an ice bath to terminate the reaction. When the internal temperature of the reaction chamber dropped below 25°C, the upper head and lower reactor were separated, the reactor was opened, and only a trace amount (moiety) of the liquid phase within the reactant was collected to prepare a sample for quantitative analysis.

[0084] (d) Separation and quantitative analysis of depolymerized products

[0085] Byproducts including caprolactam (ε-caprolactam), caprolactam dimer, soluble oligomer, and aminocaproic acid generated from depolymerization existed as liquids completely dissolved in the reaction solvent. The concentrations of these components were quantified using high-performance liquid chromatography (Dionex Thermo UltiMate 3000 with Agilent Zorbax SB-C8, 4.6 × 250 mm (5 μm) column and UV detector (λ = 214 nm)) calibrated with each standard sample, and the yield of the reaction products dissolved in the mixed solvent was calculated from this.

[0086] For HPLC analysis, a mixed solution of water and methanol (volume ratio 70:30) was used as the mobile phase, and the total flow rate was maintained at 0.7 ml / min. All reaction mixtures, except for a small amount of sample taken for quantification, were filtered using PTFE filter paper (pore size: 4.5 μm). Unreacted polymers, oligomers, and trace amounts of solid catalyst (Nb2O5) may remain as solids on the filter paper. The unreacted polymers and oligomers were separated individually, and the reaction yields for them were determined gravimetrically.

[0087] The conversion rate for depolymerization and the yield of products in the reactants were calculated by the following equations.

[0088] - Depolymerization conversion rate, X PA (%) = (M0-M) / M0×100

[0089] - Yield of caprolactam, Y CPL (%) = N CPL / N0×100

[0090] - Yield of caprolactam dimer, Y CCD (%) = N CCD / N0×100

[0091] - Yield of available oligomers, Y SLO (%) = N SLO / N0×100

[0092] - Yield of insoluble oligomers, Y NSO (%) = N NSO / N0×100

[0093] - Yield of other by-products, Y Others (%) = N Others / N0×100

[0094] Here, M0 is the mass of the initial input polymer and M is the mass of the unreacted polymer. In addition, N0 is the number of moles of repeating units of the initial input raw polymer (polymer with amide functional groups), and N CPL , N CCD , N SLO and N OthersThe converted moles for caprolactam, cyclic caprolactam dimer, soluble oligomer, and other compounds produced by side reactions, respectively, as determined by HPLC, are shown in Table 1. N NSO represents the converted mole number of insoluble oligomers (solids) measured gravimetrically for the filtered solids.

[0095] (e) Recovery of ethanol and acid catalyst from the reactants.

[0096] A 100 ml evaporation flask containing the liquid mixture separated as a filtrate through filtration was attached to a rotary evaporator, and then continuously contacted with a constant temperature water bath maintained at 50℃ while rotating at a speed of 150 rpm, evaporating for about 1 hour under reduced pressure (40 torr) to sequentially remove ethanol and a trace of moisture. The residue remaining in the rotary evaporator was transferred to a filter, and the acid catalyst phosphoric acid (H3PO4) was recovered as a solid powder through filtration. The water content of unused acid catalysts can also be controlled in a similar manner. The recovered acid catalyst and the metal oxide catalyst (Nb2O5) recovered by filtration in the separation process of the depolymerization product (d) were analyzed by X-ray diffraction together with the catalysts before use (in the case of phosphoric acid, moisture was removed). The results are compared and shown in Fig. 2.

[0097] (f) Purification and recovery of monomer (caprolactam)

[0098] In the filtrate obtained from the filtration process of (d) above, by-products and monomeric caprolactam, excluding oligomers, are all dissolved in the organic solvent (anisole), so the filtrate corresponds to a liquid mixture. This was passed through a column filled with about 20 g of silica gel, then transferred to a 100 ml separatory funnel, and about 20 g of water was added. After vigorously shaking and mixing, it was left for about 20 minutes. As clear phase separation occurred, the colored by-products were concentrated in the upper organic phase, and only the transparent aqueous phase in the lower layer was separated. The separated liquid phases were each placed in a 100 ml evaporation flask, and the solvent was removed separately using a rotary evaporator. By-products could be obtained by removing the organic solvent from the upper liquid mixture, and high-purity caprolactam could be obtained by removing water from the lower aqueous mixture.

[0099] (g) Characteristics of depolymerized products

[0100] In order to determine the chemical structure of the raw material having the above amide functional group and the reaction intermediates and monomers obtained during the depolymerization and purification process, some of the samples were taken and an infrared spectrum was obtained using an atomic reflection infrared spectroscopy (ATR-FTIR; Bruker ALPHA II), which is shown in Fig. 3.

[0101] In addition, 30 mg of each sample for raw materials and products was taken and uniformly dissolved in 0.6 ml of Trifluoroethanol-d3 solvent, and then nuclear magnetic resonance spectroscopy (NMR, model name: Bruker AVANCE Ⅱ) was performed. + 500MHz) for each 1 H-NMR spectra were obtained and compared and presented in Fig. 4. The monomer product (caprolactam) finally obtained after purification was uniformly dissolved in 30.6 ml of CDCl together with the standard sample, and each was analyzed using nuclear magnetic resonance spectroscopy.1 H-NMR spectra were obtained and the results are compared in Fig. 5.

[0102] [Comparative Example 1]

[0103] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that niobium oxide and phosphoric acid were not used as catalysts.

[0104] [Comparative Example 2]

[0105] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that only 0.05 g of phosphoric acid was used as a polymer depolymerization catalyst without using niobium oxide.

[0106] [Comparative Example 3]

[0107] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that only 0.025 g of niobium oxide was used as a polymer depolymerization catalyst without using phosphoric acid.

[0108] Table 1 shows the results obtained by mixing the polymer of raw material 1 in a mixed solvent consisting of ethanol and anisole, adding an acid or / and a metal oxide capable of providing a proton without using a catalyst, and then performing depolymerization at a reaction temperature of 200℃ for 2 hours. In the case of Comparative Example 1 where no catalyst was used, the conversion rate was less than 1%, indicating that the polymer decomposition hardly progressed. On the other hand, when a trace amount of catalyst was added, it was seen that most of the polymer was decomposed even at a temperature lower than the melting point of the polymer. When comparing the results of Comparative Example 2 using only an acid catalyst and Comparative Example 3 using only a metal oxide catalyst, 73% and 76% of the initial polymer were decomposed and converted into low-molecular-weight substances, respectively, but there was a very large difference in the distribution of the obtained products. In Comparative Example 2, which used a proton-donating acid as a catalyst, the yield of the monomer caprolactam was observed to be very low at less than 3%, but the production yield of oligomers (sum of insoluble and soluble oligomers) was observed to be very high at over 70%. This clearly demonstrates that the proton-donating acid has the function of increasing the rate of the initial depolymerization (reaction step 1 in Fig. 1) of polymers with amide functional groups. On the other hand, when niobium oxide, a metal oxide, was added as a sole catalyst as in Comparative Example 3, the amount of oligomers produced was observed to be less than half of that in Comparative Example 2, which used an acid catalyst, but the yield of monomers was observed to be very high at over 45%. This can be assumed to be the result of the metal oxide catalyst (niobium oxide) accelerating the decomposition of the oligomer (reaction step 2 in Fig. 1) or promoting the reaction in which the monomer is directly produced simultaneously with the decomposition of the polymer (reaction step 3 in Fig. 1). In order to find out which of these two assumptions is correct, it is expected that it will be possible to find out through experiments in which oligomers are used as raw materials instead of polymers under the same conditions and then each catalyst is applied to compare the reaction rates. This will be explained in more detail in the results in Table 9.

[0109] Meanwhile, in Example 1, where the two catalysts were used together, all polymers were decomposed within 2 hours, and the yield of caprolactam was also observed to be very high, at over 65%. Unlike when only a single catalyst was used (Comparative Examples 2 and 3), the performance was improved and the monomer yield was greatly increased, indicating that the two catalysts exhibit different functions and that their combined use produces a complementary synergistic effect.

[0110] Changes in depolymerization performance according to the composition of the catalyst Number of moles of compound added per mole of repeating polymer (PA6) Conversion rate, X PA (%) Yield of depolymerized product (%) Ethanol-anisole catalyst Y CPL Y CCD Y SLO Y NSO Y Others Comparative Example 11031-0.970.740.000.220.000.01 Comparative Example 210310.12 H3PO473.062.900.0066.613.560.00 Comparative Example 310310.021 Nb2O576.2345.300.1920.659.970.12 Example 110310.12 H3PO4,0.021 Nb2O5100.0065.400.1617.1117.320.01 [Reaction Conditions] Reaction Temperature: 200℃, Reaction Time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0111] Selection of oxidation catalysts for depolymerization of polymers with amide functional groups

[0112] The following is a comparative explanation of the types of metal oxides that can be selected for low-temperature depolymerization of polymers having amide functional groups and their corresponding depolymerization performances.

[0113] [Example 2]

[0114] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.012 g of zirconium oxide (ZrO2; Sigma Aldrich, powder, 5 μm, 99% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0115] [Example 3]

[0116] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0075 g of titanium oxide (TiO2; Aldrich, nanopowder (21 nm), ≥99.5% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0117] [Example 4]

[0118] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.014 g of molybdenum oxide (MoO3; Sigma-Aldrich, ≥99.5%) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0119] [Example 5]

[0120] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were performed in the same manner as in Example 1, except that 0.014 g of tungsten oxide (WO3; Sigma-Aldrich, powder (≤25 μm), ≥99% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0121] [Example 6]

[0122] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were performed in the same manner as in Example 1, except that 0.017 g of yttrium oxide (Y2O3; Sigma-Aldrich, 99.99% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0123] [Example 7]

[0124] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0038 g of lanthanum oxide (La2O3; Sigma-Aldrich, 99.99% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0125] [Example 8]

[0126] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were performed in the same manner as in Example 1, except that 0.0077 g of cerium oxide (CeO2; Sigma-Aldrich, powder (<5 μm), 99.9% trace metals basis) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0127] [Example 9]

[0128] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0053 g of magnesium oxide (MgO; Sigma-Aldrich, 97%) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0129] [Example 10]

[0130] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0095 g of calcium oxide (CaO; Samchun Pure Chemicals, 96.0%) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0131] [Example 11]

[0132] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.021 g of barium oxide (BaO; Sigma-Aldrich, 97%) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0133] [Example 12]

[0134] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0057 g of zinc oxide (ZnO; Sigma-Aldrich, powder (<5 μm), 99.9%) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0135] [Example 13]

[0136] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.016 g of aluminum oxide (Al2O3; Sigma-Aldrich, activated, basic, Brockmann I) was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid instead of niobium oxide.

[0137] Table 2 shows a comparison of the characteristics and performance of the depolymerization reaction of polymers having amide functional groups when the metal oxide catalysts were changed according to Examples 1 to 13. In order to clearly distinguish the difference in performance according to the catalyst composition, conditions were used in which the reaction time was limited to 2 hours at 200°C, similar to Table 1. When niobium oxide and zirconium oxide metal oxide catalysts were used as in Examples 1 and 2, all polymers were decomposed within 2 hours of reaction, and when calcium oxide (Example 10), titanium oxide (Example 3), and cerium oxide (Example 8) were used, very high initial reaction activities were observed with conversions of 97%, 85%, and 84% or more, respectively, within 2 hours of reaction. These metal oxide catalysts not only accelerated the depolymerization reaction rate of the polymer, but also observed a high monomer yield of 49% or more after only 2 hours of reaction. When other types of metal oxides were used (Examples 4 to 7, Example 9, and Examples 11 to 13), the effect of improving the initial depolymerization rate was not observed, but it was found that the selectivity for monomers was also greatly improved compared to when only an acid catalyst was used. In Comparative Example 2, where only an acid catalyst was used, the monomer yield was less than 3%, whereas in all examples where the metal oxide catalyst was simultaneously applied, a yield higher than 20% was observed.

[0138] PA depolymerization performance classification by metal oxide catalyst type Number of moles of compound added per mole of repeating polymer (PA6) unit Conversion rate, X PA (%) Yield of depolymerized product (%) Ethanol-anisole catalyst Y CPL Y CCD Y SLO Y NSO Y OthersExample 1 10310.12 H3PO4, 0.021 Nb2O5 100.006 5.400.16 17.1117.320.01 Example 2 10310.12 H3PO4, 0.021 ZrO2 100.004 9.970.99 21.342 7.700.00 Example 3 10310.12 H3PO4, 0.021 TiO2 85.154 9.130.10 29.336.580.00 Example 4 10310.12 H3PO4, 0.021 MoO3 33.95 21.720.06 5.266.9 10.00 Example 5 10310.12 H3PO4, 0.021 WO343.9221.540.0616.975.350.00Example 610310.12 H3PO4,0.021 Y2O336.5724.020.095.047.420.00Example 710310.12 H3PO4,0.021 La2O367.6226.420.0340.220.940.00Example 810310.12 H3PO4,0.021 CeO284.1555.510.2221.337.090.00Example 910310.12 H3PO4,0.021 MgO48.8432.810.1111.424.500.00Example 1010310.12 H3PO4, 0.021 CaO97.4949.350.1836.3111.640.00Example 1110310.12 H3PO4, 0.021 BaO45.8822.950.0718.064.810.00Example 1210310.12 H3PO4, 0.021 ZnO44.9923.170.0518.093.670.00Example 1310310.12 H3PO4, 0.021 Al2O358.4044.710.178.095.430.00[Reaction conditions] Reaction temperature: 200℃, Reaction time: 2hCPL: ε-caprolactam, CCD: cyclic caprolactam dimer,SLO: soluble oligomers,NSO: Non-soluble oligomers

[0139] Acid catalyst for depolymerization of polymers with amide functional groups

[0140] The following is to compare and observe the changes in reaction characteristics and performance when the type of acid catalyst that can provide protons for low-temperature depolymerization of a polymer having an amide functional group is changed.

[0141] [Example 14]

[0142] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.08 g of sulfuric acid (H2SO4; Sigma-Aldrich, 95% aq. soln.) was used as an acid catalyst instead of phosphoric acid.

[0143] Table 3 shows the results obtained by comparing the results obtained by using phosphoric acid (Example 1), which is a weak acid with 3 equivalents of protons per unit mol, as an acid catalyst, and sulfuric acid (Example 14), which is a strong acid with 2 equivalents of protons per unit mol, as an acid catalyst in performing the depolymerization of a polymer having an amide functional group under the same reaction conditions (reaction temperature 200°C for 2 hours). In both cases, complete polymer decomposition occurred within a short reaction time (2 h), and monomers were produced in a yield more than 50% higher. In the case of Example 1, which used phosphoric acid as an acid catalyst, the yield (Y) was higher than that of Example 14, which used sulfuric acid. CPL ) was observed to be somewhat advantageous in obtaining the polymer, but the polymer decomposition occurred incompletely, and the amount of insoluble oligomers produced was observed to be relatively high. On the other hand, when sulfuric acid was used as an acid catalyst, the rate of hydrolysis and side reactions also increased, and the concentration of by-products in the product including aminocaproic acid (Y Others) was observed to be somewhat higher. These subtle differences in performance can be controlled by varying the reaction conditions, and although acid catalysts with different characteristics were used, very high initial reaction activities were observed in both cases regardless of acid strength or equivalent weight, and high monomer yields were obtained despite the application of low-temperature reaction conditions. This clearly demonstrates that both catalysts can be utilized as effective acid catalysts for the depolymerization of polymers with amide functional groups.

[0144] Changes in depolymerization performance according to the type of acid catalyst Number of moles of compound added per mole of repeating polymer (PA6) Conversion rate, X PA (%) Yield of depolymerized product (%) Ethanol-anisole catalyst Y CPL Y CCD Y SLO Y NSO Y Others Example 110310.12 H3PO4, 0.021 Nb2O5 100.0065.400.1617.1117.320.01 Example 1410310.12 H2SO4, 0.021 Nb2O5 100.0050.950.1434.1712.112.63 [Reaction conditions] Reaction temperature: 200℃, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0145] Changes in the depolymerization performance of polymers with amide functional groups according to the concentration of acid catalyst.

[0146] The following is to compare and observe the change in reaction performance according to the concentration of an acid catalyst capable of providing protons for low-temperature depolymerization of a polymer having an amide functional group.

[0147] [Example 15]

[0148] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.0043 g of phosphoric acid was used as an acid catalyst.

[0149] [Example 16]

[0150] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.026 g of phosphoric acid was used as an acid catalyst.

[0151] [Example 17]

[0152] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.039 g of phosphoric acid was used as an acid catalyst.

[0153] [Example 18]

[0154] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 0.065 g of phosphoric acid was used as an acid catalyst.

[0155] [Example 19]

[0156] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that 0.078 g of phosphoric acid was used as an acid catalyst.

[0157] Table 4 shows the changes in depolymerization performance observed when the same reaction conditions (reaction temperature 200℃ for 2 hours) were used but the concentration of the introduced acid catalyst (phosphoric acid) was changed. In Comparative Example 3, where depolymerization was performed by adding only a metal oxide catalyst without adding an acid catalyst, a high conversion rate of over 76% was observed, but the monomer yield was relatively low at about 45%. On the other hand, as in Example 15, even when only a very small amount of 0.01 moles of phosphoric acid was introduced per mole of repeating unit of the polymer having an amide functional group, the amount of oligomer produced decreased, and it was found that the monomer yield increased by about 7% or more. As the amount of phosphoric acid used increased, the synergistic effect with the metal oxide catalyst became prominent, and when the mole ratio of phosphoric acid introduced per mole of polymer unit was 0.12 or more (Examples 1, 18, and 19), complete decomposition of the polymer occurred within 2 hours. Meanwhile, referring to the results of Example 19, where the amount of phosphoric acid added was increased to a molar ratio of 0.18, it can be seen that not only the polymer but also the oligomer was mostly decomposed, resulting in a high monomer yield of approximately 96%. These results imply that the amount of acid catalyst added can also be utilized as a process control variable to rapidly produce a high yield of monomer from the depolymerization of polymers with amide functional groups.

[0158] Changes in depolymerization performance according to acid catalyst concentration Number of moles of compound added per mole of repeating polymer (PA6) Conversion rate, X PA (%) Yield of depolymerized product (%) Ethanol-anisole catalyst Y CPL Y CCD Y SLO Y NSO Y OthersComparative Example 310310.021 Nb2O5 76.2345.300.1920.659.970.12Example 1510310.01 H3PO4,0.021 Nb2O5 72.8352.710.4012.167.560.01Example 1610310.06 H3PO4,0.021 Nb2O5 71.9259.870.404.766.860.02Example 1710310.09 H3PO4,0.021 Nb2O5 87.8463.920.3913.789.730.02Example 110310.12 H3PO4,0.021 Nb2O5 100.006 5.40 0.16 17.11 17.32 0.01 Example 18 103 10.15 H3PO4, 0.02 1 Nb2O5 100.007 8.24 0.25 4.70 16.8 10.01 Example 19 103 10.18 H2SO4, 0.02 1 Nb2O5 100.009 5.58 2.85 0.001.57 0.00 [Reaction conditions] Reaction temperature: 200°C, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0159] Solvents that can be selected for depolymerization of polymers with amide functional groups

[0160] The following examples and comparative examples are intended to explain the types, ranges, and effects of solvents that can be basically applied when performing low-temperature depolymerization of a polymer having an amide functional group according to the present invention.

[0161] [Comparative Example 4]

[0162] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that only 19.59 g of anisole was used as a solvent for the depolymerization reaction.

[0163] [Example 20]

[0164] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that only 8.35 g of ethanol was used as a solvent for the depolymerization reaction.

[0165] [Example 21]

[0166] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 1.42 g of methanol (Sigma-Aldrich, ≥99.8%) was used instead of ethanol as a solvent for the depolymerization reaction.

[0167] [Example 22]

[0168] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 2.66 g of 1-propanol (Sigma-Aldrich, ≥99.5%) was used instead of ethanol as a solvent for the depolymerization reaction.

[0169] [Example 23]

[0170] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 2.66 g of isopropanol (Sigma-Aldrich, ≥99.5%) was used instead of ethanol as a solvent for the depolymerization reaction.

[0171] [Example 24]

[0172] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 4.51 g of 1-hexanol (Sigma-Aldrich, ≥98%) was used instead of ethanol as a solvent for the depolymerization reaction.

[0173] [Example 25]

[0174] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that 5.75 g of 1-octanol (Sigma-Aldrich, ≥99%) was used instead of ethanol as a solvent for the depolymerization reaction.

[0175] Table 5 shows the types of basic solvents that can be used to form reactants while ensuring effective contact between the polymer and catalyst during low-temperature depolymerization of amide-functionalized polymers. Example 20 used alcohol (ethanol) alone as a depolymerization solvent for a polymer with amide functionalities. When both acid and metal oxide catalysts were applied simultaneously, complete polymer decomposition occurred within 2 hours at a reaction temperature of 200°C. The monomer yield of the resulting product was over 30%, but the yield of alcohol-insoluble oligomers was observed to be higher, over 50%. In this case, the decomposition rate of the oligomer was observed to be relatively slow, but it can be expected that further monomer yields can be increased by exposure to depolymerization conditions for a long period of time. Comparative Example 4 shows the results of a reaction performed using only anisole, which can be used as a cosolvent, as a solvent without adding alcohol. In this case, the depolymerization rate of the polymer with amide functionalities was observed to be very slow, and the monomer yield was also very low.

[0176] Example 1 and Examples 21 to 25 observed changes in the performance of the depolymerization reaction when the number of carbon atoms in the alkyl group of the alcohol increased. Monohydric alcohols with short alkyl groups (e.g., methanol) showed superior depolymerization performance within a shorter reaction time than monohydric alcohols with long chains. When octanol, which has a relatively hydrophobic alkyl group with 8 carbon atoms bonded to the alcohol, was used as a solvent (Example 25), the conversion rate was only about 30%, and the monomer yield was also low at 22%. Monohydric alcohols with an alkyl group bonded with more than 8 carbon atoms showed significantly reduced depolymerization performance. When monohydric alcohols were added as solvents, the alcohol itself did not directly participate in the reaction as a reactant, but when dihydric or polyhydric alcohols were used as reactants, addition reactions of the alcohols occurred together with depolymerization, resulting in a very complex and diverse product distribution.

[0177] Selection of solvent for depolymerization of polymers with amide functional groups Number of moles of compound added per mole of repeating polymer (PA6) Conversion rate, X PA (%)Yield of depolymerized product (%)Addition amount (solvent type)Anisole Y CPL Y CCD Y SLO Y NSO Y OthersExample 2041 (Ethanol) -100.0032.440.1216.1151.300.03 Comparative Example 4-417.576.930.060.120.000.46 Example 2110 (Methanol) 31100.0072.250.5219.887.200.15 Example 110 (Ethanol) 31100.0065.400.1617.1117.320.01 Example 2210 (1-Propanol) 3159.2022.080.0532.144.910.02 Example 2310 (2-Propanol) 3132.37 32.130.210.000.000.03 Example 2410 (1-Hexanol) 3146.23 36.34 0.156.84 2.85 0.05 Example 2510 (1-Octanol) 3130.56 22.130.07 2.77 5.20 0.38 [Reaction conditions] Reaction temperature: 200°C, Reaction time: 2 h, Number of moles of catalyst added per mole of repeating unit: Acid catalyst (H3PO4) 0.12 mole, Metal oxide catalyst (Nb2O5) 0.021 mole CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0178] Changes in the depolymerization performance of polymers with amide functional groups according to the solvent ratio

[0179] The following are for observing the change in the depolymerization performance of a polymer having an amide functional group according to the ratio of alcohol and cosolvent (alkyl benzene) in forming a mixed solvent according to the method of the present invention.

[0180] [Example 26]

[0181] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis of the product were performed in the same manner as in Example 1, except that a mixture of 4.17 g of ethanol and 9.79 g of anisole was used as a solvent for the depolymerization reaction.

[0182] [Example 27]

[0183] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis of the product were performed in the same manner as in Example 1, except that a mixture of 6.31 g of ethanol and 4.78 g of anisole was used as a solvent for the depolymerization reaction.

[0184] Table 6 shows a comparison of the change in the depolymerization performance of a polymer having an amide functional group by controlling the concentration ratio of the cosolvent of alcohol (or water) and alkoxybenzene while adding the same molar number of mixed solvents for the depolymerization reaction. In Comparative Example 4, where depolymerization was performed after mixing only anisole as a cosolvent with the catalyst without adding alcohol, the polymer conversion was less than 8% and the monomer yield was also less than 7%, which was very poor depolymerization performance. On the other hand, as in Example 1, complete depolymerization of the polymer was achieved even with the addition of a very small amount of alcohol, and it can be seen that the monomer yield significantly increased by more than 65% even with only a short low-temperature depolymerization of 2 hours. Meanwhile, in Example 26, where the molar ratio of alcohol and cosolvent was the same, no decrease in depolymerization performance was observed, but when the amount of cosolvent added was lowered as in Example 27 or no cosolvent was added at all as in Example 20, the depolymerization rate was not significantly affected, but the monomer yield was observed to be somewhat lower. By summarizing the results in Table 6, it can be easily inferred that the addition of a cosolvent not only accelerates the depolymerization rate of the polymer but also promotes the decomposition of oligomers, which can help increase the monomer yield within a short reaction time.

[0185] Changes in depolymerization performance according to the ratio of solvents Number of moles of compound added per mole of repeating polymer (PA6) Conversion rate, X PA (%)Yield of depolymerized product (%)Ethanol Anisole Y CPL Y CCD Y SLO Y NSO Y OthersComparative Example 4-4 17.5 76.9 30.06 0.12 0.00 0.46 Example 1 10 3 110 0.00 6 5.40 0.16 17.11 17.3 20.01 Example 2 6 20.5 20.5 100.00 6 2.35 0.19 19.36 17.9 6 0.14 Example 2 7 3 110 100.00 5 4.6 10.23 27.09 18.05 0.02 Example 2 0 4 1-100.00 3 2.4 4 0.12 16.11 5 1.30 0.03 [Reaction Conditions] Reaction temperature: 200°C, Reaction time: 2 h, Number of moles of catalyst added per mole of repeating unit: Acid catalyst (H3PO4) 0.12 mole, Metal oxide Catalyst (Nb2O5) 0.021 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0186] Comparison of depolymerization performance of polymers with amide functional groups according to reaction temperature.

[0187] In the previous examples and comparative examples, the performance was compared by exposing the polymer to a reaction temperature of 200°C, which is lower than the melting point of the polymer with an amide functional group, for a short reaction time. The following examples are intended to investigate the effect of reaction temperature on depolymerization performance by performing depolymerization at different temperatures and comparing the observed depolymerization performance.

[0188] [Example 28]

[0189] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that the depolymerization reaction was carried out at a temperature of 160°C.

[0190] [Example 29]

[0191] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that the depolymerization reaction was carried out at a temperature of 160°C and the reaction time was 12 hours.

[0192] [Example 30]

[0193] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that the depolymerization reaction was carried out at a temperature of 180°C.

[0194] [Example 31]

[0195] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that the depolymerization reaction was carried out at a temperature of 220°C and the reactor was replaced with a Hastelloy C material instead of a PTFE liner.

[0196] [Example 32]

[0197] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that the depolymerization reaction was carried out at a temperature of 240°C and the reactor was replaced with a Hastelloy C material instead of a PTFE liner.

[0198] Table 7 shows the comparison of the depolymerization performance observed when the same depolymerization composition was prepared according to the present invention and the depolymerization of a polymer having an amide functional group was repeatedly performed at different reaction temperatures. When the depolymerization was performed at 160°C, which is much lower than the melting point of the polymer having an amide functional group, the decomposition of the polymer proceeded very slowly. When exposed to the depolymerization conditions at 160°C for 2 hours (Example 28), the polymer conversion was observed to be less than 5%, which is a very slow decomposition rate. However, when left under the same conditions for more than 12 hours (Example 29), gradual polymer decomposition occurred, and the conversion was observed to be higher than 73%, and the monomer yield also reached approximately 39%. When left under the same conditions for more than 24 hours, decomposition of all polymers was observed. Meanwhile, when the depolymerization reaction temperature was maintained at 200°C or higher (Examples 1, 31, and 32), complete polymer decomposition occurred in a short reaction time of less than 2 hours. In Examples 31 and 32, which were maintained near or above the melting point of the polymer, not only the depolymerization of the polymer but also the complete decomposition of the oligomer occurred within 2 hours, resulting in a monomer yield of 97% or higher, and it can be seen that the concentration of the oligomer at which further decomposition can occur was greatly reduced, reaching the end point of the reaction.

[0199] Changes in depolymerization performance according to reaction temperature. Classification. Reaction temperature (℃) Reaction time (h) Conversion rate, X PA (%)Yield of depolymerized product (%)Y CPL Y CCD Y SLO Y NSO Y OthersExample 28 16 0 2 4.75 0.86 0.00 0.37 3.50 0.02 Example 29 16 0 1 2 7 3.49 38 90 0.08 8.99 25 51 0.01 Example 30 18 0 2 3 0.79 16 95 0.01 8 04 5.73 0.06 Example 1 2 0 0 2 1 0 0.00 6 5.40 0.16 17 1 1 7 3 2 0.01 Example 3 1 2 2 0 2 1 0 0.00 9 6.69 0.55 2.63 0.00 0.14 Example 3 2 2 4 0 2 1 0 0.00 9 6.60 0.63 2.56 0.00 0.20 [Reaction conditions] Number of moles of compound added per mole of repeating unit: 10 moles of ethanol, anisole 31 mol, acid catalyst (H3PO4) 0.12 mol, metal oxide catalyst (Nb2O5) 0.021 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: non-soluble oligomers

[0200] Changes in the depolymerization performance of polymers with amide functional groups according to reaction time

[0201] In the following examples, depolymerization reactions were performed at different reaction times to determine the time required for all oligomers produced by decomposition of polymers with amide functional groups to be converted into monomers, and the distribution of the resulting depolymerization products was compared and observed.

[0202] [Example 33]

[0203] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that the reaction time was 3 hours.

[0204] [Example 34]

[0205] Depolymerization of a polymer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that the reaction time was 4 hours.

[0206] [Example 35]

[0207] Depolymerization of a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that raw material 2 extracted from waste fiber was used instead of raw material 1 as the depolymerization raw material and the reaction time was 4 hours.

[0208] Examples 33 and 34 were performed to depolymerize a polymer having an amide functional group by maintaining the same composition of reactants and reaction conditions as in Example 1 and maintaining the reaction time for 3 hours and 4 hours, respectively. As shown in the results of Example 1, complete decomposition of the polymer occurred within 2 hours of the reaction time, but the yields of soluble and insoluble oligomers were each more than 17%, and continuous contact with the acid catalyst and the metal oxide catalyst, i.e., extension of the reaction time, was required for these to be completely converted into monomers. In Example 33, where the reaction time was maintained for 3 hours, the yield of the monomer significantly increased to more than 85%, and in Example 34, where the reaction time was extended to 4 hours, a high monomer yield of more than 97% was obtained. In Example 35, where nylon 6 (raw material 2) separated and purified through a pretreatment process from nylon-span blend waste fibers was used as a reactant instead of raw material 1 and exposed to depolymerization conditions for 4 hours, a similar result to Example 34 was observed, with a final yield of monomers of 97% or more.

[0209] Changes in depolymerization performance according to reaction time and applied raw materials. Category. Raw material. Reaction time (h). Conversion rate, X. PA (%)Yield of depolymerized product (%)Y CPL Y CCD Y SLO Y NSO Y OthersExample 1 Raw material 12100.0065.400.1617.1117.320.01 Example 33 Raw material 13100.0085.580.4512.721.230.02 Example 34 Raw material 14100.0097.550.541.820.000.09 Example 35 Raw material 24100.0097.250.422.290.000.05 [Reaction conditions] Reaction temperature: 200°C, Reaction time: 2 h, Number of moles of compound added per mole of repeating unit: 10 moles of ethanol, 31 moles of anisole, 0.12 moles of acid catalyst (H3PO4), 0.021 moles of metal oxide catalyst (Nb2O5) CPL: ε-caprolactam, CCD: cyclic caprolactam dimer,SLO: soluble oligomers,NSO: Non-soluble oligomers

[0210] Comparison of the decomposition performance of depolymerization intermediates (oligomers)

[0211] As described in the comparative description of the depolymerization reaction results with different catalyst configurations as various examples shown in Table 1 above, it was confirmed that the acid catalyst and metal oxide catalyst applied for depolymerization of polymers having amide functional groups exhibit different functions.

[0212] The polymers with amide functional groups and the oligomers produced through partial depolymerization were observed to exhibit different decomposition behaviors by acid catalysts and metal oxide catalysts. To investigate this, the insoluble oligomers, which are intermediates produced during the depolymerization reaction, were separated and purified to prepare the raw material for depolymerization (raw material 3). As shown in Table 1, the depolymerization reaction characteristics of the insoluble oligomers were identified by applying different catalysts under the same reaction conditions, and from this, the acid catalyst and metal oxide catalyst were investigated to determine which reaction step each mainly affected.

[0213] [Raw Material 3] (Insoluble oligomer in the product produced from depolymerization)

[0214] 10 g of a polymer raw material (Material 1) having an amide functional group was depolymerized according to the method of Example 1 or Example 2, and unreacted substances and insoluble oligomers were separated from the depolymerized product through filtration. The insoluble oligomer obtained as a powder contained a trace amount of the metal oxide catalyst used in the depolymerization. To remove the catalyst, about 1.7 g of the powder obtained through filtration was added to about 50 ml of formic acid (Sigma-Aldrich, 98-100%) to dissolve the oligomer, and then the solid containing the catalyst was removed through filtration. Most of the formic acid in the obtained filtrate was removed using a rotary evaporator, and the powder obtained through evaporation was washed with ethanol and dried three times to obtain more than 1.5 g of a sample containing no metal oxide. The obtained white powder sample was prepared as Material 3.

[0215] [Comparative Example 5]

[0216] Depolymerization of an insoluble oligomer derived from a polymer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that about 0.5 g of the oligomer prepared as raw material 3 was used instead of raw material 1 as a depolymerization raw material and only 0.05 g of phosphoric acid was used instead of niobium oxide as a depolymerization catalyst.

[0217] [Comparative Example 6]

[0218] Depolymerization of a polymer oligomer having an amide functional group, separation and analysis of the product were carried out in the same manner as in Example 1, except that approximately 0.5 g of the oligomer prepared as raw material 3 was used instead of raw material 1 as the depolymerization raw material and only 0.025 g of niobium oxide was used instead of phosphoric acid as the depolymerization catalyst.

[0219] [Example 36]

[0220] Depolymerization of a polymer oligomer having an amide functional group, separation of the product, and analysis were performed in the same manner as in Example 1, except that approximately 0.5 g of the oligomer prepared as raw material 3 instead of raw material 1 was used as the raw material for depolymerization.

[0221] Table 9 presents the experimental results to determine how acid catalysts (phosphoric acid) and metal oxide catalysts (niobium oxide) affect the decomposition of oligomers, which are reaction intermediates generated during the depolymerization process of polymers with amide functional groups (reaction step 2 in Fig. 1). To compare the decomposition performance of oligomers and monomer yields, the conversion rate for the decomposition process (or depolymerization) of insoluble oligomers was considered here instead of polymers with amide functional groups, and this was calculated from the following equation.

[0222] - Conversion rate of insoluble oligomers, X NSO (%) = (M NSO,0 -M NSO ) / M NSO,0 ×100

[0223] Here, M NSO,0 is the mass of the initial insoluble oligomer and M NSO is the mass of unreacted insoluble oligomer.

[0224] In contrast to the reaction behavior of Comparative Examples 2 and 3 in Table 1, in Comparative Example 5, which used only an acid catalyst, the monomer yield reached 70%, but in Comparative Example 6, which used only a metal oxide as a catalyst, the monomer yield was observed to be low at 40%. This can be inferred to be a result that occurs because the acid catalyst has a greater effect on the speed of the step (reaction steps 1 and 2 in Fig. 1) in which polymers or oligomers are decomposed into small molecules. On the other hand, in Example 36, which used both an acid catalyst and a metal oxide catalyst, the synergistic effect due to the use of a mixed catalyst was expressed, as in Example 1, and it can be seen that most of the oligomers were converted into monomers with only 2 hours of reaction time, approaching the end point of the reaction.

[0225] Decomposition performance of oligomers by acid catalyst and metal oxide catalyst Classification Number of moles of compound added per mole of repeating unit of PA6 oligomer Conversion rate, X NSO (%) Yield of depolymerized product (%) Ethanol-anisole catalyst Y CPL Y CCD Y SLO Y Others Comparative Example 5 10310.12 H3PO4 100.006 9.84 0.19 28.73 1.24 Comparative Example 6 10310.021 Nb2O5 100.003 9.92 0.14 59.21 0.73 Example 36 10310.12 H3PO4, 0.021 Nb2O5 100.009 6.43 0.56 1.80 1.21 [Reaction Conditions] Reaction Temperature: 200°C, Reaction Time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0226] While specific aspects of the present invention have been described in detail above, it will be apparent to those skilled in the art that these specific descriptions merely represent preferred embodiments and are not intended to limit the scope of the present invention. Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

[0227]

[0228] The method for depolymerizing a polymer having an amide functional group according to the present invention provides a low-temperature depolymerization method capable of completely decomposing a polymer having an amide functional group even at a temperature below the melting point of the polymer and obtaining a high yield of monomer as a product therefrom, unlike existing methods that could only achieve a depolymerization reaction at a high temperature above the melting point of the polymer, and furthermore, the yield of the depolymerized monomer can be greatly increased, and thus its industrial applicability is recognized.

Claims

A composition for depolymerization of a polymer having an amide functional group, (1) a monohydric alcohol; (2) an acid capable of donating hydrogen cations; and (3) a metal oxide; A composition for depolymerization of a polymer having an amide functional group, characterized by including the above. In paragraph 1, A composition for depolymerizing a polymer having an amide functional group, characterized in that the monohydric alcohol is a straight-chain and / or branched monohydric alcohol. In paragraph 1, A composition for depolymerizing a polymer having an amide functional group, characterized in that the above monohydric alcohol solvent has 1 to 8 carbon atoms. In paragraph 1, A composition for depolymerizing a polymer having an amide functional group, characterized in that the acid capable of providing the hydrogen cation is at least one selected from among an inorganic acid, an organic acid, and a solid acid having an acidic functional group capable of donating a proton as part of the compound structure, each having at least one hydrogen cation in the molecule. In paragraph 1, The above metal oxide is an oxide of a metal selected from among vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), aluminum (Al), gallium (Ga), tin (Sn), and iron (Fe), and is a composition for depolymerizing a polymer having an amide functional group, characterized in that it is a single metal oxide composed of one metal or a composite metal oxide of two or more metals. In paragraph 5, A composition for depolymerizing a polymer having an amide functional group, characterized in that the metal oxide is supported on a porous support. As a composition for depolymerization of a polymer having an amide functional group, A composition for depolymerizing a polymer having an amide functional group, characterized in that an aromatic compound substituted with one or more alkoxy functional groups is further added as a cosolvent to the composition of claim 1. In a method for depolymerizing a polymer having an amide functional group, A method for depolymerizing a polymer having an amide functional group, characterized by comprising a step of contacting a polymer having an amide functional group with a composition of any one of claims 1 to 7. In paragraph 8, A method for depolymerizing a polymer having an amide functional group, characterized in that it additionally includes a process of filtering and separating unreacted polymer material. In a method for depolymerizing a polymer having an amide functional group, A method for depolymerizing a polymer having an amide functional group, characterized in that a depolymerization reaction product is obtained through a step of contacting a depolymerization composition according to claim 7 with a polymer having an amide functional group, and an acid and / or metal oxide used as a catalyst is precipitated and recovered by removing alcohol from the obtained depolymerization reaction product. In paragraph 10, A method for depolymerizing a polymer having an amide functional group, which comprises adding water to a reactant from which an acid and / or metal oxide used as a catalyst has been removed to cause phase separation, and then concentrating the depolymerized monomer in a hydrophilic solvent layer and then recovering the monomer.

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