Catalyst for depolymerization of polyamide containing silicon oxide, and depolymerization method using same

Abstract

The present invention relates to a method for depolymerizing a polymer having an amide functional group and, more specifically, to a method in which depolymerization is enabled even at a low temperature and monomers can be obtained at a high yield from depolymerization products by decomposing a polymer having an amide functional group using a mixed catalyst having different functions, for example, a catalyst in which an acid capable of providing protons and silicon oxide and / or a silicon-containing metal oxide are mixed as components.

Description

Polyamide depolymerization catalyst containing silicon dioxide 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 specifically, to a method for enabling the depolymerization of a polymer having an amide functional group even at low temperatures and significantly increasing the yield of the depolymerized monomer by using a mixed catalyst having different functions, such as an acid capable of providing hydrogen cations as a component; and a silicon oxide and / or a metal oxide containing silicon.

[0002] Plastic is widely used in the production of various products due to its advantages as an inexpensive, durable material that is easy to mold and process. Thanks to these benefits, plastic consumption has increased dramatically over the decades across industry and daily life. However, improperly managed plastic waste is not being properly disposed of, leading to social and international issues that extend beyond mere environmental problems. Consequently, countries are proposing various policies to address the plastic waste problem, and strong regulations are emerging in global trade markets to curb indiscriminate production and consumption. Furthermore, interest in the development of recycling technologies is also intensifying to establish a circular economy system for plastics.

[0003] Polymers with amide functional groups, such as nylon, are tough among plastics and possess excellent oil and wear resistance, so they are used as fibers for clothing, industrial, and military applications, and are also utilized as engineering plastic materials requiring high mechanical properties. Although these polymers with amide functional groups are widely used in daily life and industry due to their low cost and excellent durability, they are known to be difficult to recycle through depolymerization methods compared to other polymers (such as polyester) that can be produced by condensation or ring-opening polymerization due to their superior properties.

[0004] Reaction pathways for depolymerizing polymers having amide functional groups include hydrolysis, alkaline decomposition, alcoholysis, ammonolithism, and catalyst-based autolysis.

[0005] The most common method for depolymerizing polymers having amide functional groups is known to be to use water or steam at high temperature and high pressure, mainly reaching supercritical or subcritical states, as described in prior art patent 1 (Korean Registered Patent No. 10-1130461), as a reaction medium, and to add an inorganic acid (mainly phosphoric acid) as a catalyst or to perform depolymerization under catalyst-free conditions. Since this depolymerization method is carried out under high temperature and high pressure conditions, it has the disadvantage of requiring high initial investment costs and excessive energy consumption. Furthermore, there is a problem in that purification is difficult because not only the impurities or by-products in the depolymerization product but also the catalyst has hydrophilic characteristics similar to the monomer.

[0006] To overcome the problems associated with high-temperature heated water or steam, prior art patent 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 an aminolysis that uses free ammonia, which is difficult to handle, as a reactant. While it has the advantage of being able to decompose polymers with amide functional groups at relatively low temperatures, it has the problem of low caprolactam yield as a depolymerization monomer product and reduced product selectivity because 6-aminocaproic amide, which has an amide terminal group other than 6-aminocaproic acid, is simultaneously produced.

[0007] Prior Patent 3 (JP 4957555B2) describes a depolymerization method in which a hydrocarbon compound (aromatic and alkane compound) is added together with water to form a reaction solvent, thereby enabling the production of a high-yield monomer (caprolactam) of over 80% without the use of a catalyst within a temperature range of 300°C to 420°C. This method allows for the production of high-yield monomers by applying a relatively low depolymerization temperature, and since no catalyst is used, there may be advantages such as easy product purification after depolymerization. However, it still requires high energy, and since high-temperature hydrocarbon compounds such as toluene are used in large quantities (over 70%), it is difficult to ensure operational safety and economic feasibility.

[0008] Prior art patent 4 (International Patent Publication 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 at 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 against moisture and oxygen may decrease when in contact with air, and to produce caprolactam, a high vacuum (10 -3 Since the mmHg condition must be maintained continuously for a long time, the configuration of the process can be tricky and it may be difficult to configure large-scale facilities.

[0009] Conventional methods for depolymerizing polymers with amide functional groups all involve carrying out reactions at high temperatures above the melting point, which requires a large amount of energy. Furthermore, many of these methods involve difficulties in separating the catalyst from the product after depolymerization, or the catalyst is chemically unstable and cannot be separated or recovered. Additionally, the yield of the resulting product is very limited, side reactions are difficult to control, and purifying the monomer from the product is challenging.

[0010] In order to overcome these problems, the present invention provides a method for depolymerizing polymers having amide functional groups that is highly efficient and economical, as it utilizes multiple catalysts with different functions to overcome the performance of the depolymerization reaction and the selectivity of the product. Furthermore, it is possible to apply a low-cost catalyst consisting of silicon oxide and / or a silicon-containing metal oxide mixed with a small amount of acid without using excessive energy to increase the depolymerization reaction rate, while ensuring very high activity and selectivity even at low temperatures, and simultaneously apply a method of recovering the catalyst and purifying the monomer to a high purity after the reaction.

[0011] The present invention aims to overcome the problems of the aforementioned prior art. The objective of the present invention is to provide an efficient catalyst that enables complete depolymerization of a polymer having an amide functional group even at a temperature below the melting point of the polymer and can increase the selectivity of a desired monomer in the resulting reactant, and a composition for depolymerizing a polymer having an amide functional group comprising said catalyst.

[0012] Another objective of the present invention is to provide a method for depolymerizing a polymer having an amide functional group that can simplify the reaction and purification processes, significantly reduce energy consumption in each process, minimize material loss or waste compared to existing technologies, and produce a high yield of depolymerization monomers.

[0013] Another objective of the present invention is to provide a method for depolymerizing a polymer having an amide functional group, which suppresses the generation of by-products in the product and minimizes the inflow of by-reactants in the product, and enables obtaining a high-purity depolymerized monomer product even when using raw materials that are contaminated or contain foreign substances.

[0014] To solve the above problem, the present invention provides a composition for depolymerizing a polymer having an amide functional group, characterized by comprising (1) a monohydric alcohol, (2) an acid capable of providing a hydrogen cation (proton); and (3) a metal oxide containing silicon oxide and / or silicon.

[0015] 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 12.

[0016] In one embodiment of the present invention, the acid capable of providing the hydrogen cation may be characterized as being one or more selected from an inorganic acid having one or more hydrogen cations within the molecule, an organic acid, and a solid acid having an acidic functional group capable of donating a proton as part of the compound structure.

[0017] In one embodiment of the composition of the present invention, the silicon-containing metal oxide may further include a metal other than silicon, and may be characterized by further including one or more selected from aluminum (Al), iron (Fe), tin (Sn), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), tungsten (W), zirconium (Zr), chromium (Cr), molybdenum (Mo), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), zinc (Zn), and gallium (Ga).

[0018] In one embodiment of the composition of the present invention, the silicon oxide and / or silicon-containing metal oxide may be characterized by having a plurality of mesopores.

[0019] In one embodiment of the composition of the present invention, the silicon dioxide may be characterized as being silica gel that has not been used or has been discharged after use.

[0020] In one embodiment of the composition of the present invention, the composition may be characterized by having one or more aromatic compounds substituted with alkoxy functional groups added as a cosolvent.

[0021] In addition, the present invention provides a method for depolymerizing a polymer having an amide functional group, characterized by including the step of contacting the composition according to the present invention with a polymer having an amide functional group.

[0022] In one embodiment of the depolymerization method of the present invention, a process of filtering and separating unreacted polymer material may be additionally included.

[0023] Additionally, the depolymerization method of the present invention may include the 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 containing silicon oxide and / or silicon; and (4) an aromatic compound substituted with at least one alkoxy functional group, wherein the step of removing only the alcohol from the depolymerization reaction product to precipitate and recover (2) and / or (3) of the composition may be further added, and further include the step of adding water to the reaction product from which (2) and / or (3) of the composition have been removed to cause phase separation, and then concentrating and recovering the depolymerization monomer in a hydrophilic solvent layer.

[0024] Unlike conventional methods for depolymerizing polymers having amide functional groups and producing monomers, which could only achieve a depolymerization reaction at high temperatures above the melting point of the polymer, the present invention provides a low-temperature depolymerization method that can completely decompose a polymer having amide functional groups even below the melting point of the polymer and obtain a high yield of monomers as a product.

[0025] In addition, unlike conventional or prior research methods in which water heated to a high temperature near the critical point is added as a reaction solvent, requiring very high pressure conditions or maintaining a high vacuum to carry out depolymerization, the present invention can provide relatively mild conditions for the depolymerization of polymers having amide functional groups, and thus can help significantly reduce the initial investment cost for depolymerization reactors or equipment.

[0026] In the present invention, by using an acid and silicon oxide and / or a silicon-containing metal oxide together, which exhibit different functions when used as catalysts without causing performance degradation, interference, or structural deformation of the compound under depolymerization reaction conditions, it is possible to increase the initial depolymerization of the polymer and the decomposition reaction rate of the oligomer, while simultaneously improving selectivity for the target monomer. Through this, it is possible to construct a reaction system for the depolymerization of a polymer having an amide functional group to obtain high-performance reaction efficiency and high-purity, high-yield monomers even at low temperatures.

[0027] In addition, these catalysts can be fully recovered in their original or reusable form after the reaction, and the solid catalyst can be recovered from the reactants in the form of a liquid mixture by a simple physical separation method.

[0028] In addition, silicon oxide, which is one of the catalyst components according to the present invention, can be used as a stationary phase in a reactor, and other catalyst components, such as an acid and / or an effective metal oxide of a different type from the silicon oxide, can be supported on the silicon oxide or diluted in the reactant, and depolymerization can be performed by contacting the silicon oxide with a polymer having an amide functional group to produce a monomer therefrom. In the present invention, since part or all of the catalyst can be utilized as a fixed-bed catalyst, the process can be simplified, and there may not be many constraints in implementing scale-up and continuous processes.

[0029] In addition, in conventional methods for depolymerization of polymers having amide functional groups, separate materials such as adsorbents or neutralizing agents different from the reactants were used to remove foreign substances from the reaction products and purify the product. However, in the present invention, by controlling the thermodynamic properties of the solvent used stepwise, the solvent and catalyst used can be easily separated and recovered from the reactants according to the process flow, and a purification method for producing high-purity monomers without using the separate materials can also be provided.

[0030] The depolymerization method of a polymer having an amide functional group according to the present invention enables the polymer decomposition reaction and monomer generation to proceed at a rapid reaction rate at low temperatures, thereby allowing the operation of the process using low-cost utilities during production. Additionally, the reaction and separation processes can be combined, and the simple form of the process does not require high investment costs. Furthermore, since high yield and high-purity monomers can be produced even at low temperatures, energy consumption can be significantly reduced compared to existing methods, which can provide a solution to overcome the economic limitations of existing technologies.

[0031] In addition, the technology according to the present invention can be directly utilized for the chemical recycling of discarded waste polymer resins, thereby enabling the implementation of an eco-friendly regeneration process that significantly reduces carbon dioxide emissions. In particular, it can provide a method for recycling polymers having amide functional groups that can be repeatedly regenerated by returning them to the monomer raw material prior to synthesis through depolymerization, regardless of the form of the raw material or the type of foreign substances. This can contribute to the eco-friendly recycling of waste polymer materials that were difficult to dispose of other than through incineration or landfill.

[0032] Figure 1 is a schematic diagram of the reaction to explain the polymer depolymerization, the decomposition of the generated oligomer and the formation of the monomer, and the effects of the acid catalyst and silicon oxide catalyst on the reaction rate in the process of producing monomers from a polymer having an amide functional group through depolymerization.

[0033] Figure 2 shows the XRD spectrum measured by X-ray diffraction (XRD) analysis for a catalyst recovered during the purification process after the depolymerization reaction of a polymer having an amide functional group according to one embodiment of the present invention, compared with the XRD spectrum measured for a catalyst before use (waste silica gel as an acid catalyst and silicon oxide catalyst).

[0034] FIG. 3 shows infrared spectra measured using an total reflection infrared spectrometer (ATR-FTIR) for reaction intermediates and monomer products obtained during the process of purifying a polymer raw material having an amide functional group and a reaction product obtained by depolymerizing the same, according to one embodiment of the present invention.

[0035] FIG. 4 shows the reaction intermediate and monomer product obtained during the process of purifying a polymer raw material having an amide functional group and a reaction product obtained by depolymerizing the same according to one embodiment of the present invention, measured using nuclear magnetic resonance (NMR; solvent: trifluoroethanol(TFE)-d3). 1 This shows the H-NMR spectra.

[0036] FIG. 5 is a measurement of 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 spectrum measured against a standard substance 1 This is presented in comparison with the H-NMR spectrum.

[0037] Figure 6 shows a comparison of the XRD spectrum measured by X-ray diffraction analysis for a catalyst recovered during the purification process after the depolymerization reaction of a polymer having an amide functional group according to one embodiment of the present invention and the XRD spectrum measured for catalysts before use (phosphoric acid as an acid catalyst and SBA-15 as a silicon oxide catalyst).

[0038] Figure 7 shows a porous composite metal oxide catalyst prepared by supporting niobium oxide on silicon oxide (SBA-15), which has a large surface area due to a large number of well-developed mesopores within the structure and regular and uniformly sized pores are well aligned with each other according to one embodiment of the present invention, and the crystal structure was analyzed by X-ray diffraction analysis together with the metal oxides constituting the catalyst, and the respective XRD spectra obtained at that time are compared.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled expert in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0040] Throughout this specification, when a part is described as “comprising” a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0041] In the present invention, the silicon-containing metal oxide may be in the form where silicon oxide and the metal oxide are physically mixed or where the metal oxide is supported on silicon oxide, or it may be in the form of an oxide in which silicon and the metal are connected via oxygen or the like. Examples of the silicon-containing metal oxide include, but are not limited to, silica-alumina, zeolite beta, ferrierite, mordenite, zeolite Y, ZSM-5, Nb2O5 / SiO2, Fe2O3 / SiO2, SnO2 / SiO2, TiO2 / SiO2, V2O5 / SiO2, WO3 / SiO2, ZrO2 / SiO2, Cr2O3 / SiO2, MoO3 / SiO2, Y2O3 / SiO2, La2O3 / SiO2, CeO2 / SiO2, MgO / SiO2, CaO / SiO2, and BaO / SiO2. It may be one or more compounds selected from ZnO / SiO2.

[0042] In the present invention, the silicon oxide and / or silicon-containing metal oxide material may have a plurality of mesopores, but is not limited thereto, and may further include micropores or macropores, and preferably the total volume of pores per unit weight is 0.05 cm³ 3 ·g -1 up to 1.0 cm 3 ·g -1 It could be.

[0043] In addition, the BET specific surface area of ​​the silicon oxide and / or silicon-containing metal oxide material is 50 m² 2 / g to 3,000 m 2 It can be / g, preferably 100 m 2 / g to 2,000 m 2 / g, more preferably 200 m 2 / g to 1,000 m 2 It can be / g. BET specific surface area is 50 m² 2 If / g or less, the catalytic effect of the metal oxide material may not be prominent, and 3,000 m 2If the value is greater than 1 / g, it must be manufactured to have a complex pore structure, and it may be difficult to maintain a uniform pore structure when the reaction is performed for a long time with strong stirring.

[0044] In the present invention, the polymer having an amide functional group is a synthetic material called nylon or polyamide, and is a semicrystalline or amorphous polymer compound composed of amide bonds in its molecular structure, such as nylon 6, nylon 66, nylon 46, nylon 610, nylon 612, nylon 11, nylon 12, MXD 6 nylon, etc., and these are merely simple examples of polymers having an amide functional group and are not limited to those listed.

[0045] The method of the present invention is useful for the depolymerization of a polymer having the amide functional group, wherein the polymer having the amide functional group may not be pure but may be in a form containing various impurities. For example, it may be in a form mixed with organic or inorganic foreign substances including dyes or pigments, and / or polymers of other materials. The polymer having the amide functional group may be in a predetermined form such as powder, fiber, pellet, or ball, or may be supplied in a form that is not uniform in shape.

[0046] In the present invention, compounds initially applied for the depolymerization of a polymer having an amide functional group can be classified into three types: a polymer raw material, a solvent, and a catalyst. As a solvent for the depolymerization of a polymer having an amide functional group, (1) a monohydric alcohol is used, and as a catalyst, (2) one or more types of acids capable of providing hydrogen cations and (3) one or more types selected from silicon oxide and silicon-containing metal oxides can be used. By using mixed catalysts with different functions, the performance of the depolymerization reaction of a polymer having an amide functional group can be greatly improved even at low temperatures.

[0047] As a solvent for the depolymerization of the polymer having the above-mentioned amide functional group, the alcohol may be a mixture of one or more straight-chain or branched monohydric alcohols having 1 to 12 carbon atoms; since branched alcohols may have lower reactivity due to steric hindrance factors, straight-chain alcohols may be more advantageous. Specifically, the alcohol solvent for the depolymerization of the polymer having the above-mentioned amide functional group may be methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, or a combination thereof. As a solvent for the depolymerization of the polymer having the above-mentioned amide functional group, the alcohol may be a hydrated alcohol compound containing some water as an impurity, and since it does not directly participate in the reaction as a reactant, it is not added to or consumed by the reactant during depolymerization.

[0048] In the case of long-chain or branched monohydric alcohols with more than 12 carbon atoms, the increased hydrophobicity reduces the probability of the catalyst and nylon functional groups coming into contact, which can cause the reaction to proceed very slowly. Additionally, when polyhydric alcohols with two or more alcohol functional groups within the molecule are used as solvents, side reactions such as alcoholysis (or alcohol addition) may occur, which generate various by-products other than the regenerated monomer, making it difficult to utilize them as depolymerization solvents for the production of resynthesized monomers.

[0049] The amount of solvent for the depolymerization of the polymer having the above-mentioned amide functional group is sufficient if it allows the mixed solution prepared by adding the catalyst to 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 above-mentioned 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, sufficient contact between the catalyst solution and the raw material may not occur, and the target of depolymerization may be limited to a part or localized portion of the raw material, and if the molar ratio exceeds 5,000, it results in waste of material and energy relative to the throughput, and the concentration of the catalyst is also significantly diluted, which may slow down the reaction rate.

[0050] 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 of the components, an acid catalyst is capable of providing hydrogen cations and provides the function of increasing the rate of the initial depolymerization ((1) of FIG. 1) of the polymer having an amide functional group. The decomposition of the polymer by depolymerization produces a large amount of oligomer fractions, and the produced oligomers can be produced into monomers through a gradual depolymerization process ((2) of FIG. 1) by an acid catalyst.

[0051] When an acid providing protons as a catalyst is provided alone, the decomposition of the oligomer proceeds slowly, and if the reactants are exposed to high temperatures for a long time, a significant amount of by-products, including hydrolysis products, can be obtained through side reactions.

[0052] As another component of the catalyst for the depolymerization of polymers having monomeric amide functional groups, silicon oxide and / or silicon-containing metal oxides may be porous materials structured by numerous mesopores. Due to their structural characteristics, such materials may have a large specific surface area, which can accelerate the decomposition rate of oligomers by providing an abundance of active sites to which oligomers can make direct contact, and can also provide a function that significantly improves selectivity for monomer products. Silicon oxide or silicon-containing metal oxide catalysts having a porous structure may not have a significant effect on the decomposition rate of macromolecules initially introduced. However, since the oligomer fractions produced through polymer depolymerization mostly have a diameter of 50 nm or less, they can diffuse into the interior of the material through the mesopores ((3) in Fig. 1), thereby increasing the opportunity for contact with the metal oxides and rapidly converting them into monomers, and as they diffuse out of the pores ((4) in Fig. 1), monomers can be obtained in high yield.

[0053] As a component of the mixed catalyst intended for use in the present invention, the acid catalyst is an acidic substance according to the definition of Arrhenius or Brønsted-Lowry and represents an acid capable of donating hydrogen cations (or protons). Examples of the acid catalyst may include inorganic acids such as hydrochloric acid (HCl), hydrofluoric acid (HF), hydrobromide (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), or phenols; or solid acid catalysts in which an acidic functional group capable of donating proton ions is included in the compound structure.

[0054] Silicon oxide or a silicon-containing metal oxide may be used as another component of the mixed catalyst intended for use in the present invention, and other metals that may be included in addition to silicon may be one or more selected from aluminum (Al), iron (Fe), tin (Sn), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), tungsten (W), zirconium (Zr), chromium (Cr), molybdenum (Mo), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), zinc (Zn), and gallium (Ga). The silicon-containing metal oxide catalyst may be prepared using silicon and one or more metal precursors and may have a plurality of mesopore structures. The above silicon oxide and silicon-containing metal oxide can exhibit depolymerization performance of a polymer having an amide functional group whether silicon oxide is used alone or mixed with other metal oxides. When used in combination, it may be in a form where another metal oxide is supported on silicon oxide, or it may be used in a form where a metal oxide other than silicon oxide is supported on the pores or surface of the silicon-containing metal oxide, or simply physically added or mixed.

[0055]

[0056] Silica gel that is discarded after use can also be used as the silicon dioxide mentioned above. Although the material may be discarded in a state where it has absorbed moisture, since a small amount of moisture does not significantly affect the depolymerization performance of polymers having amide functional groups, it can be used directly without separate pretreatment such as moisture removal through drying.

[0057] The number of moles of the acid catalyst is not limited thereto, but may preferably be in a molar ratio of 0.0001 to 10 per mole of repeating monomer of the polymer having the amide functional group, and more preferably in a molar ratio of 0.001 to 0.1. If the molar ratio is less than 0.0001, the catalytic effect may not be exhibited 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 of the reactor at high temperatures for a long period.

[0058] The amount of silicon oxide and / or silicon-containing metal oxide used as a catalyst in the reactor is not limited thereto, but can preferably be adjusted to have a molar ratio of 0.001 to 1,000 relative to the molar amount of the added acid catalyst, and more preferably a molar ratio of 0.01 to 500. If the amount of silicon oxide and / or silicon-containing metal oxide used as a catalyst is less than 0.001 relative to the molar amount of the added acid catalyst, the silicon oxide and / or silicon-containing metal oxide may not function as a catalyst, and if it exceeds 1,000, the concentration of the acid catalyst is dilute, which may limit the depolymerization reaction rate.

[0059] The plurality of catalyst components mentioned above may be supplied in a form in which they are pre-mixed and in contact before being introduced into the reactants, and each may be introduced into the reactants at different times or simultaneously; if depolymerization is performed by introducing a plurality of catalysts according to the present invention, there are no restrictions on time and place.

[0060] In the present invention, as a solvent for the depolymerization reaction of a polymer having an amide functional group, a compound having an aromatic ring substituted with at least one alkoxy functional group may be added as a cosolvent in addition to a straight-chain or branched monohydric alcohol. Such a cosolvent can increase the depolymerization reaction rate of the polymer having the amide functional group and, by controlling the thermodynamic equilibrium conditions after the depolymerization reaction, can provide an efficient method for recovering most of the catalyst from the depolymerization reactant and simultaneously purifying a monomer product of high purity and high yield.

[0061] Examples of cosolvents having an aromatic ring substituted with the above alkoxy functional group are, 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 one or more compounds selected from 1-methoxy-4-prop-2-enylbenzene, 1-methoxy-4-[(E)-prop-1-enyl]benzene (cis), and 1-methoxy-4-[(E)-prop-1-enyl]benzene (trans).

[0062] The content of the above co-solvent may preferably be 5 to 98 wt% based on the total mass of all added solvents, and more preferably 20 to 95 wt%. 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%, there is a possibility that the performance of depolymerization may be reduced.

[0063] When a solvent mixed with the above straight-chain 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.

[0064] In the case of a reaction combination according to some embodiments of the present invention, all of the polymer can be decomposed within 1 hour at a reaction temperature of 200°C, which is lower than the melting point of the polymer for the depolymerization of nylon 6, and a monomer (caprolactam) yield of approximately 99.3% can be achieved within 2 hours.

[0065] In one embodiment of the present invention, a method may be used to maintain the reaction temperature for depolymerization at a temperature close to the polymer melting point (220°C or higher) in order to shorten the reaction time. In this case, the decomposition of the polymer proceeds very rapidly within 0.5 hours, all reactions are completed within 2 hours, and a monomer yield of 99.8% or higher can be achieved.

[0066] In another embodiment of the present invention, a method is provided to shorten the reaction time by controlling the concentration of the catalyst without raising the reaction temperature for depolymerization. By maintaining the reaction temperature below the polymer melting point and controlling the concentration of the acid catalyst, not only is the polymer rapidly and completely decomposed, but the oligomer is also completely decomposed to terminate the reaction, thereby allowing the monomer to be obtained in high yield.

[0067] In the present invention, the temperature during the depolymerization reaction is not limited thereto, but preferably may be 150°C to 300°C, and more preferably may be 180°C to 250°C. If the temperature is below 150°C, the depolymerization reaction may be delayed, and if it exceeds 300°C, there is a possibility that the rate of side reactions will increase along with unnecessary energy waste.

[0068] When the above depolymerization reaction is completed, if the alcohol solvent is removed by simple evaporation or distillation, the monomer product remains dissolved in the co-solvent (liquid phase), while the used catalyst can all precipitate into a solid phase, allowing most of the used catalyst to be recovered by simple physical methods such as filtration or centrifugation, and it can also be reused.

[0069] The above-mentioned recovered catalyst can be obtained in a form where an acid catalyst, one of the catalyst components, is physically introduced into or chemically adsorbed into the pores of a silicon oxide and / or silicon-containing metal oxide catalyst, which is another catalyst component.

[0070] In addition to the depolymerization monomer, catalyst residues or polar foreign substances may remain in the reaction mixture obtained after the recovery of the above catalyst, and a method of contacting with an adsorbent may be used as a means to remove them. The adsorbent may include carbon-based adsorbents such as activated carbon, silica gel, fly ash, ion exchange resin, natural clay, bentonite clay, zeolite, kaolinite, chitosan, metal-organic frameworks (MOFs), etc.

[0071] As a method to recover monomer products from reaction products from which impurities have been removed through the above adsorption process, methods such as distillation, evaporation, and drying, which separate and remove co-solvents and residual solvents by heating them into vapor, may be utilized. However, if by-products still remain in the reaction product, this method may lead to a problem where the purity of the final product is reduced.

[0072] Another method for recovering monomer products from reaction products from which impurities have been removed through the above adsorption process is to apply a liquid-liquid phase separation method by directly adding a hydrophilic solvent or water to the reaction products. When a hydrophilic solvent or water is added, phase separation occurs, and impurities or by-products can be concentrated in an organic layer (upper phase) consisting of aromatic compounds with alkoxy functional groups, while monomer products can be concentrated in a hydrophilic solvent layer (lower phase). Conditions can be provided to recover high-purity monomer products by removing the hydrophilic solvent after phase separation through methods such as evaporation, distillation, or drying.

[0073] The details of the process of the present invention will be explained below through examples, comparative examples, and experimental examples. These are representative examples related to the present invention, and it should be noted that the scope of application of the present invention cannot be limited.

[0074] [Raw Material 1] (Polymer raw material having amide functional groups)

[0075] As a polymer material having amide functional groups, a nylon 6 sample in pellet form (cylinder diameter approximately 2.2 mm, height approximately 2.6 mm) (Sigma-Aldrich, purity: 100%, density: 1.084 g / mL) was prepared as a depolymerization raw material without a separate processing step.

[0076]

[0077] Basic composition of a catalyst for low-temperature depolymerization of polymers with amide functional groups

[0078] 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 monomers by decomposing a polymer having an amide functional group at low temperature according to the present invention.

[0079]

[0080] [Example 1]

[0081] (a) Preparation process of depolymerization reactants

[0082] About 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 liner with an internal volume of 20 ml along with a magnetic stirrer, and then inserted into an autoclave vessel constituting a pressure-resistant reactor. 0.0057 g of silica gel (SiO2; Sigma-Aldrich, technical grade, 230-400 mesh, 40-63 μm) and 0.05 g of phosphoric acid (H3PO4; Alfa Aesar, 85% aq. soln.) were weighed as polymer depolymerization catalysts. Instead of adding them directly to the mixture (polymer and solvent) in the lower reaction vessel prepared for the reaction, they were transferred into a separate PTFE tube with an internal volume of 100 μl or less to prepare a small catalyst container. The gas adsorption amount of the silicon oxide (silica gel) used as a catalyst was measured using a specific surface area meter (Micromeritics, ASAP 2420), and the Brunauer-Emmett-Teller (BET) specific surface area and other pore characteristics were calculated from the results.

[0083]

[0084] (b) Preparation of the depolymerization reaction system and initiation of the reaction

[0085] An Inconel K-type thermocouple and a pressure gauge were connected to the upper head (autoclave head) of the internal pressure reactor to measure internal temperature and pressure, and a relief valve was installed with a pressure capacity set to 50 bar. A purging nitrogen tube was connected to allow the internal air to be expelled to the outside by supplying high-pressure nitrogen from the outside. A previously prepared small catalyst container was attached to the upper head and connected to a lower reaction vessel containing raw materials and solvent to prepare a sealed high-pressure reactor. Subsequently, the process of filling and discharging nitrogen from the outside through the purging nitrogen tube was repeated at least three times to completely remove the air inside the reactor.

[0086] A sealed high-pressure reactor was placed on a magnetic stirrer and transferred to a silicone oil bath heated to a high temperature beforehand. When the internal temperature of the reactor was maintained at a constant 200°C through PID control, a high-pressure nitrogen pulse was applied from the outside into the catalyst vessel to cause the catalyst to fall, thereby initiating the reaction. During the reaction process, a magnetic stirrer was used to rotate the magnetic stirrer, which was pre-positioned inside the reactor prior to the reaction, at a speed of 1,000 rpm to induce continuous mixing of the reactants.

[0087]

[0088] (c) Termination of depolymerization reaction

[0089] After 2 hours of reaction, the stirrer was stopped, the reactor was removed from the silicone oil bath maintained at a high temperature, and the reaction was terminated by rapidly transferring it to a bath filled with ice. When the internal temperature of the reaction dropped to 25°C or lower, the upper head and lower reaction vessel of the reactor were separated to open the reactor, and only the liquid phase of the moiety within the reaction product was taken to prepare a sample for quantification.

[0090]

[0091] (d) Separation and quantitative analysis of depolymerization products

[0092] By-products generated from depolymerization, including caprolactam (ε-caprolactam), caprolactam dimer, soluble oligomer, and aminocaproic acid (ε-aminocaproic acid), existed in a liquid phase 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㎛) column and UV detector (λ=214 nm)) calibrated with each standard sample, and the yield of the reaction product dissolved in the mixed solvent was calculated from this.

[0093] For HPLC analysis, a mixed solution with a water-to-methanol volume ratio of 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 trace samples taken for quantification, were filtered using PTFE filter paper (pore size: 4.5 μm). Unreacted polymers, oligomers, and trace amounts of solid catalysts may remain as solids on the filter paper; the unreacted polymers and oligomers were separated, and their reaction yields were determined by gravimetric analysis.

[0094] The conversion rate for depolymerization and the yield of products in the reactants were calculated by the following equations.

[0095] - Depolymerization conversion rate, X PA (%) = (M0-M) / M0×100

[0096] - Caprolactam yield, Y CPL (%) = N CPL / N0×100

[0097] - Yield of caprolactam dimer, Y CCD (%) = N CCD / N0×100

[0098] - Yield of soluble oligomers, Y SLO (%) = N SLO / N0×100

[0099] - Yield of insoluble oligomer, Y NSO (%) = N NSO / N0×100

[0100] - Yield of other by-products, Y Others (%) = N Others / N0×100

[0101] Here, M0 is the mass of the initial input polymer and M is the mass of the unreacted polymer. Also, N0 is the number of moles of repeating units of the initial input raw material polymer (polymer having amide functional groups), and N CPL , N CCD , N SLO and N Others represents the converted moles for caprolactam, cyclic caprolactam dimer, soluble oligomer, and other compounds produced by side reactions, respectively, as quantified by HPLC. N NSO represents the converted moles of insoluble oligomers (solids) measured by gravimetric method for the filtered solids.

[0102]

[0103] (e) Recovery of ethanol and acid catalyst from reactants

[0104] A 100 ml evaporation flask containing the liquid mixture separated as a filtrate through filtration was attached to a rotary evaporator. It was then rotated at a speed of 150 rpm while continuously contacting a constant temperature water bath maintained at 50°C, and evaporated for about 1 hour under reduced pressure conditions (40 torr) to sequentially remove ethanol and trace amounts of water. The residue remaining in the rotary evaporator was transferred to a filter, and phosphoric acid (H3PO4) was additionally recovered in solid form through filtration. The water content of unused acid catalysts can also be controlled using a similar method. Changes in crystal structure were confirmed using X-ray diffraction analysis for the recovered acid catalyst and the silicon oxide catalyst (mesoporous SiO2-based catalyst) recovered by filtration during the separation process of the depolymerization product (d) mentioned earlier, along with the catalysts before use (in the case of phosphoric acid, those from which water was removed), and the results are shown in comparison in Figure 2.

[0105]

[0106] (f) Purification and recovery of monomer (caprolactam)

[0107] In the filtrate obtained from the filtration process of (d) described above, by-products excluding the oligomer and the monomer caprolactam exist in a state where they are all dissolved in the organic solvent (anisole); therefore, the filtrate corresponds to a liquid mixture. This was passed through a column packed with approximately 20 g of silica gel, transferred to a 100 ml separatory funnel, and then mixed by adding approximately 20 g of water and shaking vigorously, followed by standing for about 20 minutes. As clear phase separation occurred, the colored by-products were concentrated in the upper organic phase, while only the clear aqueous phase in the lower layer was separated. The separated liquid phases were each placed in 100 ml evaporation flasks, and the solvents were removed from each using a rotary evaporator. By-products were obtained by removing the organic solvent from the upper liquid mixture, and high-purity caprolactam was obtained by removing water from the lower aqueous mixture through vacuum drying.

[0108]

[0109] (g) Analysis of the characteristics of the depolymerized product

[0110] In order to determine the chemical structures of the reaction intermediates and monomers obtained from the depolymerization and purification process with the raw material having the above amide functional group, a portion was taken as a sample and an infrared spectrum was obtained using an total reflection infrared spectrometer (ATR-FTIR; Bruker ALPHA II), which is shown in Figure 3.

[0111] In addition, 30 mg of each sample of the raw material and product was taken and uniformly dissolved in 0.6 ml of Trifluoroethanol-d3 solvent, and then nuclear magnetic resonance (NMR) spectroscopy (Model: Bruker AVANCE II) was performed. + For each via 500MHz 1 H-NMR spectra were obtained and compared in Figure 4. The final monomer product (caprolactam) obtained after purification was uniformly dissolved in 0.6 ml of CDCl3 together with standard samples, and nuclear magnetic resonance spectroscopy was performed on each 1 H-NMR spectra were obtained and the results were compared in Figure 5.

[0112]

[0113] [Comparative Example 1]

[0114] The depolymerization of polymers having amide functional groups, separation of products, and analysis were carried out in the same manner as in Example 1, except that no catalyst (phosphoric acid and silica gel) was used.

[0115]

[0116] [Comparative Example 2]

[0117] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that only 0.05g of phosphoric acid was used as the polymer depolymerization catalyst without using silica gel.

[0118]

[0119] [Comparative Example 3]

[0120] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that only 0.0057 g of silica gel was used as the polymer depolymerization catalyst without using phosphoric acid.

[0121]

[0122] Table 1 shows a comparison of the respective results obtained by mixing the polymer of raw material 1 into a mixed solvent composed of ethanol and anisole, adding silica gel as a catalyst that does not use a catalyst or can provide protons or / and silicon oxide, and then carrying out depolymerization at a reaction temperature of 200°C for 2 hours.

[0123] In the case of Comparative Example 1, which did not use a catalyst, the conversion rate was less than 1%, indicating that polymer decomposition hardly occurred. On the other hand, when a small amount of catalyst is added, it can be seen that most of the polymer decomposes even at a temperature lower than the melting point of the polymer.

[0124] In Comparative Example 2, which used only an acid catalyst, a large amount of polymer was decomposed at a rapid initial depolymerization rate of 73% and converted mostly into oligomers (the sum of the yields of insoluble and soluble oligomers was about 70%), and the yield of the monomer caprolactam was observed to be very low at 3% or less. In Comparative Example 3, which used only silica gel without the addition of an acid catalyst, the conversion rate was less than 2.5%, indicating that almost no decomposition of the polymer occurred.

[0125] Meanwhile, in Example 1, in which acid and silicon dioxide (silica gel) were simultaneously added as catalysts, even though the same reaction conditions were maintained and the same amount of catalyst as in Comparative Example 2 or Comparative Example 3 was added, complete decomposition of the polymer having amine functional groups occurred and the yield of the monomer (caprolactam) was also obtained at over 60%, and a very dramatic improvement in reaction performance was observed.

[0126] Unlike Comparative Examples 2 and 3, which were exposed to depolymerization conditions by applying only an acid catalyst or only silicon oxide, the performance of depolymerization was significantly improved in Example 1, in which both catalysts were applied simultaneously. This indicates that the two catalysts perform different functions and that when used together, a mutually complementary synergistic effect occurs.

[0127] By comparing the depolymerization results of Example 1 and Comparative Examples 1 to 3, the role and effect of each material applied as a catalyst can be explained. Proton-donating acid catalysts primarily have the function of increasing the rate of the initial depolymerization (reaction step 1 of FIG. 1) of polymers having amide functional groups, and can rapidly produce a large amount of oligomers.

[0128] If only an acid catalyst is present, the generated oligomer may be further decomposed to produce monomers (Figure 1 (2)), but the rate may be very limited and the time exposed to side reactions may be prolonged.

[0129] It can be seen that if silicon oxide with a large number of well-developed mesopores is added as a catalyst, a large number of oligomers generated from the depolymerization of the polymer can diffuse into the pores together with the acid catalyst, and as a result, the opportunity for contact between the oligomers and the metal oxide increases, which not only significantly accelerates the decomposition rate of the oligomers but also greatly improves the selectivity for the monomer product.

[0130] Classification Polymer (PA6) Molar conversion rate of compound applied per repeating unit mole, X PA (%) Yield of depolymerization product (%) Ethanol Anisole Catalyst Y CPL Y CCD Y SLO Y NSO Y OthersComparative Example 1 1031-0.97 0.74 0.00 0.22 0.00 0.01 Comparative Example 2 10310.12 H3PO4 7 3.06 2.9 0 0.00 6 6.6 13.5 6 0.00 Comparative Example 3 10310.021 SiO2 2.4 0 2.02 0.26 0.00 0.00 0.13 Example 1 10310.12 H3PO4 0.021 SiO2 10 0.00 6 0.25 0.79 13.85 25.11 0.00 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0131]

[0132] Changes in depolymerization performance depending on the type of silicon-containing metal oxide catalyst

[0133] The following are materials in which metal oxide compounds have the same basic phase as silicon oxide but have different geometric structures or different surface areas, and in which different metal oxides are introduced in various forms, to be applied to the depolymerization of polymers having amide functional groups using silicon-containing metal oxide catalysts for comparative evaluation of depolymerization performance.

[0134]

[0135] [Example 2]

[0136] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that silica gel beads with a diameter of 5 mm or less contained in a desiccant bag packaged together with clothing products were removed and ground into powder using a mortar and pestle, and about 0.0057 g of the powder was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0137]

[0138] [Example 3]

[0139] The depolymerization of a polymer having amide functional groups, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of silica (SiO2; Sigma-Aldrich, mesoporous SBA-15, <150 μm) having a multiple mesoporous structure arranged with pores of regular and uniform size was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid. The silicon oxide-based solid catalyst (mesoporous SiO2-based catalyst) recovered by filtration during the separation process of the depolymerization product had its crystal structure measured using X-ray diffraction analysis along with the catalyst before use (in the case of phosphoric acid, with water removed), and the results are shown for comparison in Figure 6.

[0140]

[0141] [Example 4]

[0142] A composite metal oxide material prepared by supporting niobium oxide on silica (SBA-15) having a number of well-developed mesopores within the structure, aligned into regular and uniformly sized pores through incipient wetness impregnation, was used as a catalyst. First, about 0.11 g of ammonium niobate (V) oxalate hydrate (Sigma Aldrich; 99% trace metals basis) was completely dissolved in about 5.0 g of water and absorbed by mixing and stirring with 1 g of silica, then heated in a constant temperature water bath maintained at 40°C and removed using a rotary evaporator with a vacuum of 40 mbar or less. The dried sample was placed back into a quartz container and transferred to an electric kiln. It was then dried at 120°C for more than 1 hour, heated to 450°C, and calcined for 4 hours under the condition of external airflow to produce a composite metal oxide in which niobium oxide was introduced into porous silicon oxide. The crystal structures of the prepared composite metal oxide catalyst were measured using X-ray diffraction analysis in conjunction with niobium oxide particles, which can be prepared by calcining a niobium precursor, and silicon oxide (SBA-15) used as a support, and the results were compared and shown in Figure 7. The mass of the metal (Nb) introduced into the prepared composite metal oxide (Nb2O5 / SiO2) corresponded to approximately 3% of the total mass of the metal oxide.

[0143] The depolymerization of the polymer having amide functional groups, separation of the product, and analysis were carried out in the same manner as in Example 1, except that about 0.006 g of the prepared composite metal oxide catalyst (Nb2O5 / SiO2) was used instead of silica gel.

[0144]

[0145] [Example 5]

[0146] The depolymerization of a polymer having amide functional groups, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of silica-alumina (SiO2-Al2O3; Sigma-Aldrich, grade 135, Al content ~ 6.5%), which forms a complex metal oxide structure with silicon oxide (silica) and aluminum oxide (alumina) combined through oxygen as a medium, was used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0147]

[0148] [Example 6]

[0149] Silica gel beads with a diameter of 5 mm or less contained in a spent desiccant bag were removed and vacuum dried at 120°C for at least 12 hours. 0.1 g of phosphoric acid was diluted in ethanol with an amount adjusted to allow for sufficient absorption, and then absorbed into approximately 0.2 g of the previously dried silica gel beads. Subsequently, the alcohol and water were removed by drying, thereby preparing silicon oxide with introduced phosphoric acid as a silicon-containing metal oxide catalyst. Except for using the prepared silica gel beads with phosphoric acid introduced into the pores as a polymer depolymerization catalyst, the depolymerization of a polymer having an amide functional group, the separation of the product, and the analysis were carried out in the same manner as in Example 1.

[0150]

[0151] [Example 7]

[0152] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of a beta zeolite (Zeolyst International; CP814C) with a silica and alumina molar ratio (SiO2 / Al2O3) of about 38, which was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0153]

[0154] [Example 8]

[0155] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of Ferrierite zeolite (Zeolyst International; CP814C) with a molar ratio of silica to alumina (SiO2 / Al2O3) of about 20, which was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0156]

[0157] [Example 9]

[0158] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of mordenite zeolite (Zeolyst International; CBV 21A) with a molar ratio of silica to alumina (SiO2 / Al2O3) of about 20, which was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0159]

[0160] [Example 10]

[0161] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of zeolite Y (Zeolyst International; CBV 901), which has a molar ratio of silica to alumina (SiO2 / Al2O3) of about 80 and was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0162]

[0163] [Example 11]

[0164] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of ZSM-5 (Zeolyst International; CBV 8014), which has a molar ratio of silica to alumina (SiO2 / Al2O3) of about 80 and was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0165]

[0166] [Example 12]

[0167] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.0057 g of ZSM-5 (Zeolyst International; CBV 28014), which has a molar ratio of silica to alumina (SiO2 / Al2O3) of about 280 and was activated by leaving it in a calcination furnace heated to 550°C for more than 4 hours, was taken at room temperature and used as a polymer depolymerization catalyst together with 0.05 g of phosphoric acid.

[0168]

[0169] The gas adsorption capacity of the silicon oxide and / or silicon-containing metal oxides used in the above examples and comparative examples was measured using a specific surface area analyzer (Micromeritics, ASAP 2420). From this, the Brunauer-Emmett-Teller (BET) specific surface area and other pore characteristics were calculated, and the results are presented for comparison in Table 2. Most of the measured silicon oxide and / or silicon-containing metal oxide catalysts had pore sizes of 5.0 or larger, and all were 340 m² 2 ·g -1 to 700 m 2 ·g -1It can be seen that it has a very large surface area. In the case of the waste silica gel used in Example 2, a relatively narrow pore size of 2.8 nm was observed, but 570 m 2 ·g -1 It had a large specific surface area reaching [amount].

[0170] Classification: Type of silicon oxide and / or silicon-containing metal oxide catalyst BET surface area (m 2 ·g -1 )Pore volume (cm 3 ·g -1 )Pore diameter (nm) Example 1 silica gel 4 96.6 0.7 65.18 Example 2 silica gel waste 5 69.00 18 2.76 Example 3 SBA-156 95.00 6 05.57 Example 4 Nb2O5 / SBA-156 54.3 0.5 95.56 Example 5 SiO2-Al2O3 519.00 7 74.79 Example 6 H3PO4 / silica gel waste 5 67.4 0.18 2.75 Example 7 Zeolite Beta(SiO2 / Al2O3= 38) 672.7 0.2 05.29 Example 8 Ferrierite (SiO2 / Al2O3= 20) 344.2 0.0 78.30 Example 9 Mordenite (SiO2 / Al2O3 = 20) 505.70.088.92 Example 10 Zeolite Y (SiO2 / Al2O3 = 80) 729.70.266.41 Example 11 ZSM-5 (SiO2 / Al2O3 = 80) 442.10.114.16 Example 12 ZSM-5 (SiO2 / Al2O3 = 280) 392.20.063.72

[0171]

[0172] Table 3 compares and evaluates the depolymerization performance obtained when silicon oxide or a silicon-containing metal oxide is applied to the depolymerization of a polymer having an amide functional group together with an acid catalyst.

[0173] As can be seen from the pore characteristic values ​​determined by the specific surface area measuring instrument in Table 2, silica gel is a material with a large surface area inside the particles that not only absorbs a large amount of moisture or gas but also has strong adsorption power. It is inexpensive, harmless to the human body, and simple to manufacture, so it is widely used for general and industrial purposes such as drying, storage, and moisture-proof packaging of food, clothing, and electronic products.

[0174] Small amounts of desiccant used for packaging may retain some moisture and are discarded once when the product packaged together begins to be consumed. Example 2 evaluated the depolymerization performance of a polymer having an amide functional group by applying a silicon oxide catalyst to waste silica gel that was discarded after consumption and ground into a fine powder without separate moisture removal.

[0175] In Example 2, depolymerization of all polymers occurred with only 2 hours of reaction at 200°C, and a monomer yield of over 60% was obtained. In particular, depolymerization performance very similar to that of Example 1, in which an unused silica gel of the same mass was applied as a catalyst, was observed.

[0176] It can be expected that the waste silica gel has become saturated with moisture as it has been left in the atmosphere for a long time. Nevertheless, as seen in the result of Example 2, where even a very small amount of waste silica gel is sufficient to perform as a catalyst, it can be easily inferred that the amount of moisture adsorbed to the absorbent will not affect the composition of the solvent in any embodiment of the present invention where alcohol is used as a solvent.

[0177] Example 3 is the result of applying silicon oxide with an ordered mesoporous structure, arranged into regular and uniformly sized mesopores, as a metal oxide catalyst. Although complete decomposition of the polymer occurred within 2 hours at a reaction temperature of 200°C, the monomer yield was observed to be more than 5% lower than that of Example 1 or Example 2, which had irregular pores, and in the distribution of intermediate products, a high yield of insoluble oligomers (NSO), which are expected to have a relatively large molecular size, was observed.

[0178] This can be expected to be a result of the fact that during the initial depolymerization process, random decomposition of the bonding functional groups constituting the polymer occurs, which can generate oligomer fractions with various molecular weights; and metal oxides with a mesoporous structure in which pores of relatively uniform size (diameter of 5.6 nm) are regularly arranged have a narrow pore distribution, allowing them to rapidly accommodate and process only some oligomers with a limited range of molecular sizes among oligomers with a wide molecular weight distribution.

[0179] To overcome this problem, it may be considered to additionally introduce a heterogeneous metal oxide with high reactive activity for the breakdown of amide bonds so that rapid decomposition can occur during the process of oligomers being transferred from the outside to the inside of the pore.

[0180] Example 4 is the result of applying a silicon-containing composite metal oxide catalyst in which niobium oxide was introduced at a weight ratio of approximately 3% of the metal (Nb) to silicon oxide with a mesoporous structure having a uniform pore size using an initial wet impregnation method. As compared with the pore characteristic values ​​in Table 2, the specific surface area, pore size, and volume did not change significantly despite the introduction of heterogeneous metal oxides, suggesting that niobium oxide was introduced relatively well dispersed over a wide range.

[0181] Comparing the depolymerization results of polymers with amide functional groups in Examples 3 and 4, it can be seen that the monomer yield increased by more than 32% even though only about 3% of the metal was introduced by mass ratio. This implies that optimal catalyst design and manufacturing to improve depolymerization performance is possible by appropriately combining different types of heterogeneous metal oxides or configuring them into a composite phase.

[0182] Meanwhile, in the case of Example 5, in which a silica-alumina-based metal oxide material prepared by replacing some silicon oxide phases with aluminum oxide was applied as a catalyst, somewhat low depolymerization performance was observed; however, it was observed that the selectivity for monomers and soluble oligomers increased and the yield of insoluble oligomers was very low. Since silica-alumina, like silica gel mentioned earlier, can also be designed to have a large surface area, it is expected that it can be utilized as a support material for supporting other highly active metal oxides while appropriately controlling selective depolymerization characteristics.

[0183] As another example of a variation, a composite catalyst in which an acid catalyst is pre-introduced into a silicon oxide catalyst can be considered. Example 6 is a catalyst prepared in which phosphoric acid is pre-introduced into waste silica gel beads.

[0184] The material in question may be similar to a solid catalyst that can be filled into a fixed-bed reactor or a regenerated catalyst obtained through recovery after the reaction is finished, as an example of how the present invention can be applied to commercial production. Since the waste silica gel was prepared in the form of beads without being crushed or pulverized, it was expected that there might be some limitations in mass transfer during the initial stages of the reaction. However, as a result of doubling the amount of acid catalyst introduced, the polymer was completely decomposed with only 2 hours of reaction at 200°C, and excellent reaction performance was exhibited with a monomer yield of nearly 80%.

[0185] Examples 7 to 12 are zeolites having a relatively large molar ratio of silica to alumina, applied as silicon oxide and / or silicon-containing metal oxide catalysts. Except for the beta zeolite (Example 7) having a 12-ring-channel structure in a three-dimensional structure and the ferrierite (Example 8) having a relatively low specific surface area and pore volume, very rapid decomposition rates were exhibited at the beginning of the reaction at 200°C, and complete decomposition of the polymer having amide functional groups was observed within 2 hours. In the case of Examples 9 to 11, where mordenite with a relatively large pore size, zeolite Y with a large specific surface area, and ZSM-5 with a molar ratio of silica adjusted to have a high surface area and pore volume were applied as silicon oxide and / or silicon-containing metal oxide catalysts, not only were polymers with amide functional groups decomposed very rapidly after only 2 hours of reaction at 200°C, but the caprolactam yield was also observed to be higher than 70%.

[0186] Classification, type and molar conversion rate of silicon oxide and / or silicon-containing metal oxide catalysts, X PA (%) Yield of depolymerized product (%) * Y CPL Y CCD Y SLO Y NSO Y OthersExample 1 0.12 mole H3PO4+ 0.21 mole silica gel 100.00 60.25 0.79 13.85 25.11 0.00 Example 20.12 mole H3PO4+ 0.21 mole silica gel waste, pulverized 100.00 60.76 0.76 19.48 18.9 20.08 Example 30.12 mole H3PO4+ 0.21 mole SBA-15 100.00 55.46 0.16 20.68 23.70 0.00 Example 40.12 mole H3PO4+ 0.21 mole (silica basis) Nb2O5 / SBA-15 100.00 87.88 0.44 3.52 7.07 1.09 Example 50.12 mole H3PO4+ 0.21 mole (silica basis) SiO2 / Al2O3 71.64 44.32 0.28 22.20 4.64 0.20 Example 6 0.24 mole H3PO4 loaded on silica gel waste, beads 100.00 79.36 0.32 19.98 0.00 0.34 Example 7 0.12 mole H3PO4+ 0.21 mole Zeolite Beta(SiO2 / Al2O3= 38) 84.06 27.57 0.56 6.48 48.20 1.24 Example 8 0.12 mole H3PO4+ 0.21 mole Ferrierite(SiO2 / Al2O3= 20) 50.73 31.48 0.20 3.01 15.93 0.11 Example 9 0.12 mole H3PO4+ 0.21 mole Mordenite (SiO2 / Al2O3= 20)100.0070.840.364.7622.631.40 Example 1 00.12 mole H3PO4+ 0.21 mole Zeolite Y (SiO2 / Al2O3= 80)100.0070.3117.560.009.202.94 Example 1 10.12 mole H3PO4+ 0.21 mole ZSM-5 (SiO2 / Al2O3= 80)100.0072.820.3822.534.250.03 Example 1 20.12 mole H3PO4+ 0.21 mole ZSM-5 (SiO2 / Al2O3= 280)100.0020.110.0919.0460.620.13 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h [Moles of solvent added per mole of repeating monomer] Ethanol 10 mol, Anisole 31 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers.

[0187]

[0188] Mixed metal oxide catalyst for polymer depolymerization having amide functional groups

[0189] The following are examples of various depolymerizations performed to investigate examples of various metal oxides that can be physically mixed with silicon oxide catalysts for the low-temperature depolymerization of polymers having amide functional groups.

[0190]

[0191] [Example 13]

[0192] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.5 mg of iron oxide (Fe2O3; Sigma-Aldrich, Iron(III) oxide, powder, <5 μm, ≥96%) was added as a polymer depolymerization catalyst.

[0193]

[0194] [Example 14]

[0195] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.4 mg of tin oxide (SnO2; Sigma-Aldrich, Tin(IV) oxide; 325 mesh, 99.9% trace metals basis) was added as a polymer depolymerization catalyst.

[0196]

[0197] [Example 15]

[0198] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.8 mg of titanium oxide (TiO2; Aldrich, nanopowder, 21 nm, ≥99.5% trace metals basis) was added as a polymer depolymerization catalyst.

[0199]

[0200] [Example 16]

[0201] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.7 mg of vanadium oxide (V2O5; Sigma-Aldrich, ≥99.6% trace metals basis) was added as a polymer depolymerization catalyst.

[0202]

[0203] [Example 17]

[0204] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 2.2 mg of tungsten oxide (WO3; Sigma-Aldrich, powder, ≤25 μm, ≥99% trace metals basis) was added as a polymer depolymerization catalyst.

[0205]

[0206] [Example 18]

[0207] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.2 mg of zirconium oxide (ZrO2; Sigma-Aldrich, powder, 5 μm, 99% trace metals basis) was added as a polymer depolymerization catalyst.

[0208]

[0209] [Example 19]

[0210] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.9 mg of chromium oxide (Cr2O3; Sigma-Aldrich, powder, 5 μm, 99% trace metals basis) was added as a polymer depolymerization catalyst.

[0211]

[0212] [Example 20]

[0213] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.4 mg of molybdenum oxide (MoO3; Sigma Aldrich, ACS reagent, ≥99.5%) was added as a polymer depolymerization catalyst.

[0214]

[0215] [Example 21]

[0216] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 2.1 mg of yttrium oxide (Y2O3; Sigma-Aldrich, 99.99% trace metals basis) was added as a polymer depolymerization catalyst.

[0217]

[0218] [Example 22]

[0219] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 3.1 mg of lanthanum oxide (La2O3; Sigma-Aldrich, 99.99% trace metals basis) was added as a polymer depolymerization catalyst.

[0220]

[0221] [Example 23]

[0222] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.6 mg of cerium oxide (CeO2; Sigma-Aldrich, powder, <5 μm, 99.9% trace metals basis) was added as a polymer depolymerization catalyst.

[0223]

[0224] [Example 24]

[0225] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.4 mg of magnesium oxide (MgO; Sigma-Aldrich, 97%) was added as a polymer depolymerization catalyst.

[0226]

[0227] [Example 25]

[0228] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.5 mg of calcium oxide (CaO; Samjeon Sunyak, 96.0%) was added as a polymer depolymerization catalyst.

[0229]

[0230] [Example 26]

[0231] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 1.4 mg of barium oxide (BaO; Sigma-Aldrich, 97%) was added as a polymer depolymerization catalyst.

[0232]

[0233] [Example 27]

[0234] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.8 mg of zinc oxide (ZnO; Sigma-Aldrich, powder, <5 μm, 99.9%) was added as a polymer depolymerization catalyst.

[0235]

[0236] Examples 13 to 27 investigated the sensitivity of the performance of the depolymerization reaction of polymers having amide functional groups when a small amount of a heterogeneous metal oxide catalyst was added to silicon oxide, using an acid catalyst and a silicon-containing metal oxide catalyst. The depolymerization results of polymers having amide functional groups obtained by exposing each catalyst system to the same conditions are shown for comparison in Table 4.

[0237] When depolymerization was performed by adding heterogeneous metal oxide catalysts through physical mixing, there were slight differences in performance, but it was confirmed that the catalyst performance improved slightly in all cases. Given that the increase in performance was small when simply physically mixed metal oxides were applied as catalysts, it can be seen that porous silicon oxide catalysts with a mesoporous structure have a greater influence on the depolymerization of polymers with amide functional groups and the decomposition rate of oligomers than metal oxide catalysts of metals other than silicon. Therefore, it can be presumed that catalysts with well-developed pore structures and large specific surface areas exhibit much superior catalytic functions compared to those without.

[0238] Classification Polymer (PA6) Molar conversion rate of compound applied per repeating unit mole, X PA (%) Yield of depolymerization product (%) Metal oxide / moles with added ethanol / anisole Y CPL Y CCD Y SLO Y NSO Y OthersExample 13 1031Fe2O3 / 0.0021100.0063.940.7617.1118.190.01 Example 14 1031SnO2 / 0.0021100.0064.140.7318.1516.970.00 Example 15 1031TiO2 / 0.0021100.0061.570.7723.3514.310.00 Example 16 1031V2O5 / 0.0021100.0062.460.7511.7625.010.02 Example 171031WO3 / 0.0021100.0064.040.7520.2714.930.01 Example 181031ZrO2 / 0.0021100.0061.360.8518.6519.140.00 Example 191031CrO3 / 0.0021100.0062.450.7518.1418.660.00 Example 201031MoO3 / 0.0021100.0062.320.7718.2318.670.01 Example 211031Y2O3 / 0.0021100.0063.000.7417.9618.280.01 Example 221031La2O3 / 0.0021100.0064.480.7423.1111.660.01 Example 231031CeO2 / 0.0021100.0063.270.7620.1315.850.00 Example 241031MgO / 0.0021100.0063.560.7719.2616.400.00 Example 25 1031CaO / 0.0021100.0061.990.7921.2415.970.00 Example 26 1031BaO / 0.0021100.0062.440.7624.0212.780.00 Example 27 1031ZnO / 0.0021100.0062.530.7823.2113.480.00 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h [Moles of basic catalyst added per mole of repeating unit] H3PO4 0.12 mol, Silica gel (SiO2) 0.21 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0239]

[0240] Acid catalyst for the depolymerization of polymers having amide functional groups

[0241] The following is intended to compare and observe changes in reaction characteristics or performance when different types of acid catalysts capable of providing protons are used for the low-temperature depolymerization of polymers having amide functional groups.

[0242]

[0243] [Example 28]

[0244] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 1, except that 0.075 g of sulfuric acid (H2SO4; Sigma-Aldrich, 95% aq. soln.) was used as the acid catalyst instead of phosphoric acid.

[0245]

[0246] Table 5 shows a comparison of results obtained when depolymerizing a polymer having an amide functional group by exposing it to the same reaction conditions (reaction temperature of 200°C for 2 hours), using phosphoric acid (Example 1), which is a weak acid and has 3 equivalents of protons per unit mole, or sulfuric acid (Example 28), which is a strong acid and has 2 equivalents of protons per unit mole, as the acid catalyst.

[0247] In both cases, very high initial reaction activity was exhibited, and complete polymer decomposition occurred within a short reaction time (2h). In the case of Example 1, where phosphoric acid was used as the acid catalyst, a high monomer yield of over 60% (Y) was achieved even with only a trace amount. CPL...could be obtained. In Example 28, where sulfuric acid was used, the yield of oligomers produced from incomplete polymer decomposition was observed to be over 70%, whereas in Example 1, where phosphoric acid was used, the yield of oligomers was observed to be much lower, at 40% or less. These differences in reaction performance can be controlled by varying the amount of acid, and the effect of the amount of acid on depolymerization performance will be further explained later in the comparison of depolymerization performance according to acid concentration in Table 6.

[0248] Classification Polymer (PA6) Molar conversion rate of compound applied per repeating unit mole, X PA (%) Yield of depolymerization product (%) Ethanol Anisole Catalyst Y CPL Y CCD Y SLO Y NSO Y Others Comparative Example 3 1031 No acid, 0.021 SiO2 2.40 2.02 0.26 0.00 0.00 0.13 Example 1 103 10.12 H3PO4, 0.021 SiO2 100.00 60.25 0.79 13.85 25.11 0.00 Example 28 103 10.12 H2SO4, 0.021 SiO2 100.00 28.62 0.27 21.28 49.81 0.02 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0249]

[0250] Depolymerization performance of polymers with amide functional groups according to acid catalyst concentration

[0251] The following is intended to compare and observe changes in reaction performance according to the concentration of an acid catalyst capable of providing protons for the low-temperature depolymerization of polymers having amide functional groups.

[0252]

[0253] [Example 29]

[0254] The depolymerization of the polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that the depolymerization was terminated after 4 hours of reaction.

[0255]

[0256] [Example 30]

[0257] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 0.078 g of phosphoric acid was used as the acid catalyst.

[0258]

[0259] [Example 31]

[0260] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 0.087 g of phosphoric acid was used as the acid catalyst.

[0261]

[0262] [Example 32]

[0263] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 0.104 g of phosphoric acid was used as the acid catalyst and the depolymerization was terminated after 1 hour of reaction.

[0264]

[0265] Table 6 shows the change in depolymerization performance when the same reaction conditions (reaction temperature of 200°C for 2 hours) were used, but the concentration of the added acid catalyst (phosphoric acid) was varied.

[0266] In the case of Comparative Example 3, where depolymerization was performed by adding only waste silica gel, which is silicon dioxide, without adding an acid catalyst, no depolymerization of the polymer having an amide functional group occurred at all, and consequently, almost no monomer was produced.

[0267] On the other hand, the performance of depolymerization was significantly improved even when only a small amount of phosphoric acid, an acid catalyst, was added. In particular, when the molar ratio of phosphoric acid added per mole of polymer monomer was 0.12 or higher (Examples 2, 29 to 32), complete decomposition of the polymer occurred within 2 hours. When the molar ratio of phosphoric acid added per mole of polymer monomer was maintained at 0.12 and the reaction time was maintained at 4 hours or more, the reaction was almost completed, and a very high monomer yield of 99.7% or higher was obtained.

[0268] Meanwhile, referring to the results of Example 31, in which the amount of phosphoric acid input was increased to a molar ratio of 0.20 and the reaction was carried out at 200°C for 2 hours, it can be seen that a high monomer yield of about 99.3% was obtained, as the oligomer was also mostly decomposed along with the complete decomposition of the polymer. These results clearly demonstrate that it is possible to produce a high yield of the desired monomer product by configuring the catalyst system for the depolymerization of polymers having amide functional groups according to the present invention and controlling the amount of acid catalyst input or the reaction time.

[0269] Classification Polymer (PA6) Repeating Unit Moles of compound added per mole Reaction time (h) Conversion rate, X PA (%) Yield of depolymerization product (%) Ethanol Anisole Catalyst Y CPL Y CCD Y SLO Y NSO Y OthersComparative Example 31031 No acid, 0.021 SiO222.402.020.260.000.000.13 Example 210310.12 H3PO4, 0.021 SiO22100.0060.760.7618.9219.480.08 Example 2910310.12 H3PO4, 0.021 SiO24100.0099.730.230.000.000.04 Example 3010310.18 H3PO4, 0.021 SiO22100.0090.030.475.463.970.07 Example 3110310.20 H3PO4, 0.021 SiO22100.0099.250.370.300.000.08 Example 3210310.24 H3PO4,0.021 SiO21100.0084.620.3913.721.250.02 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0270]

[0271] Depolymerization performance of polymers with amide functional groups depending on the amount of silicon oxide and / or silicon-containing metal oxide catalysts

[0272] The following is intended to compare and observe changes in reaction performance according to the amount of silicon oxide and / or silicon-containing metal oxide catalysts for the low-temperature depolymerization of polymers having amide functional groups.

[0273]

[0274] [Example 33]

[0275] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that about 0.0028 g of silica gel powder obtained by crushing a waste absorbent was used as a silicon dioxide catalyst.

[0276]

[0277] [Example 34]

[0278] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that about 0.0113 g of silica gel powder obtained by crushing a waste absorbent was used as a silicon dioxide catalyst.

[0279]

[0280] Table 7 shows the changes in performance of low-temperature depolymerization of polymers with amide functional groups when the same reaction conditions (reaction temperature of 200°C for 2 hours) were used, but the concentration of waste silica gel added as a silicon oxide catalyst was varied.

[0281] As in Example 33, when the amount of waste silica gel added relative to the number of moles of repeating units of the polymer was maintained at a low molar ratio of 0.01, only about 76% of the polymer was decomposed within 2 hours of reaction time, and the yield of the monomer was observed to be somewhat higher than 57%.

[0282] Meanwhile, in Example 2, where the amount of waste silica gel input was doubled, the conversion rate increased and complete polymer decomposition occurred, but the monomer yield was found to have increased slightly to about 60.7%. This explains that the silicon oxide catalyst, along with the acid catalyst, has some influence on the initial decomposition rate of the polymer.

[0283] In Example 34, where the amount of waste silica gel was doubled again, not only was the complete decomposition of the polymer not achieved, but the synergistic effect of the acid catalyst and silicon oxide catalyst was prominent, resulting in an increased decomposition rate of the oligomer and a relatively high monomer yield of 71.2%.

[0284] Classification Polymer (PA6) Molar conversion rate of compound applied per repeating unit mole, X PA (%) Yield of depolymerization product (%) Ethanol Anisole Catalyst Y CPL Y CCD Y SLO Y NSO Y OthersExample 33 10310.12 H3PO4,0.01 SiO2 75.945 7.44 0.58 11.48 4.56 1.88 Example 2 10310.12 H3PO4,0.02 SiO2 100.006 0.76 0.76 18.92 19.48 0.08 Example 34 10310.12 H3PO4,0.04 SiO2 100.007 1.23 0.74 7.92 20.09 0.02 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0285]

[0286] Solvents selectable for the depolymerization reaction of polymers having amide functional groups

[0287] The following examples and comparative examples are intended to explain the types, ranges, and effects of solvents that can basically be applied when performing low-temperature depolymerization of polymers having amide functional groups according to the present invention.

[0288]

[0289] [Example 35]

[0290] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that only 8.35 g of ethanol was used as the solvent for the depolymerization reaction.

[0291]

[0292] [Comparative Example 4]

[0293] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that only 19.59 g of anisole was used as the solvent for the depolymerization reaction.

[0294]

[0295] [Example 36]

[0296] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 1.42 g of methanol (Sigma-Aldrich, ≥99.8%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0297]

[0298] [Example 37]

[0299] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 3.28 g of 1-butanol (Alfa Aesar, anhydrous, 99.9%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0300]

[0301] [Example 38]

[0302] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 4.51 g of 1-hexanol (Sigma-Aldrich, ≥98%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0303]

[0304] [Example 39]

[0305] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 5.75 g of 1-octanol (Sigma-Aldrich, ≥99%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0306]

[0307] [Example 40]

[0308] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 8.23 ​​g of 1-dodecanol (Sigma-Aldrich, Lauryl alcohol ≥98%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0309]

[0310] [Comparative Example 5]

[0311] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that 8.23 ​​g of 1-octadecanol (Sigma-Aldrich, Stearyl alcohol ≥ 99%) was used instead of ethanol as the solvent for the depolymerization reaction.

[0312]

[0313] Table 8 describes the types and combinations of solvents that allow for the selective acquisition of monomer products along with effective contact between the polymer and the catalyst when performing low-temperature depolymerization of polymers having amide functional groups.

[0314] Example 35 involved using alcohol (ethanol) alone as the depolymerization solvent for a polymer having an amide functional group. By applying an acid catalyst and a silicon oxide catalyst simultaneously, complete decomposition of the polymer occurred within 2 hours at a reaction temperature of 200°C. Among the products produced from rapid depolymerization, the yield of monomers was approximately 42%, which was lower than the yield of oligomers (the total yield of oligomers was 57%, of which the fraction insoluble in alcohol accounted for more than 45%).

[0315] Comparative Example 4 is the result of carrying out the reaction by adding only anisole, which corresponds to the co-solvent of the present invention, as a solvent without using alcohol. In this case, the depolymerization rate of the polymer having an amide functional group was observed to be very slow, and the yield of the monomer was also observed to be very low.

[0316] Examples 2 and 36 to 40 observed changes in the performance of the depolymerization reaction when the number of carbon atoms in the alkyl group of the alcohol increased, in a reaction solvent composed of a mixture of alcohol and a co-solvent. In the case of Example 36, which used methanol having a relatively short alkyl group as a solvent, it showed slightly superior depolymerization performance within a shorter reaction time than Example 2, which used ethanol.

[0317] In the case of Example 37, in which butanol having 4 carbon atoms in the alkyl group bonded to the alcohol was used as a solvent, the selectivity for the monomer increased significantly along with rapid depolymerization. It can be seen that a high monomer yield of over 82% was obtained with only 2 hours of reaction at 200°C.

[0318] In the case of Example 38, in which hexanol, which has relatively hydrophobicity, was used as a solvent, it was found that the decomposition rate of the polymer slowed down, and the conversion rate after 2 hours of reaction was lowered to 82% or less. However, despite the low conversion rate, the monomer yield was observed to be about 72%, which is much higher than the oligomer yield (3% or less) generated from the incomplete decomposition of the polymer.

[0319] Meanwhile, in Example 39, in which octanol was used as a solvent, the conversion rate was reduced to approximately 56%, and the selectivity of the monomer relative to the oligomer in the depolymerized product was also reduced, resulting in a monomer yield of approximately 45%. Since a sufficient depolymerization rate was detected with only a short reaction time exposure of less than 2 hours at a temperature (200°C) lower than the melting point of the polymer having an amide functional group, it can be seen that the range of alcohols capable of forming the reaction system is effective up to dodecanol with 12 carbon atoms (Example 40).

[0320] In Comparative Example 5, in which a monohydric alcohol (octadecanol) with an alkyl group having 18 carbon atoms was applied instead, the same compositional ratio (molar ratio of compounds) was applied as a reactant under the same conditions as the previous examples (Examples 36 to 40), except for the type of alcohol, but it was observed that the depolymerization performance was significantly reduced.

[0321] In any case where monohydric alcohol was added as a solvent, the alcohol itself did not directly participate in the reaction as a reactant. However, when dihydric or polyhydric alcohols were used as reactants, the depolymerization results were not included in Table 8, but the addition reaction of alcohol proceeded along with the depolymerization, resulting in a very complex and diverse distribution of products.

[0322] Classification Polymer (PA6) Molar conversion rate of compound applied per repeating unit mole, X PA (%) Yield of depolymerized product (%) Added amount (solvent type) Anisole Y CPL Y CCD Y SLO Y NSO Y OthersExample 3541 (Ethanol)-100.0042.340.3811.8145.280.19 Comparative Example 4-417.116.490.050.110.000.45 Example 3610 (Methanol)31100.0068.210.7117.5910.972.52 Example 210 (Ethanol)31100.0060.760.7618.9219.480.08 Example 3710 (1-Butanol)31100.0082.151.0710.526.040.22 Example 3810 (1-Hexanol)318 1.5 27 1.5 26.4 4 1.2 4 1.7 3 0.60 Example 39 10 (1-Octanol)315 6.4 34 5.1 8 0.5 0 0.00 10.4 2 0.32 Example 40 10 (1-Dodecanol)315 2.4 84 5.4 7 0.1 56.8 6 0.00 0.00 Comparative Example 5 10 (1-Octadecanol)319 9 0.7 9 0.00 0.00 0.00 11 [Reaction Conditions] Reaction temperature: 200℃, Reaction time: 2h, Moles of catalyst added per mole of repeating unit: Acid catalyst (H3PO4) 0.12 mol, Silicon oxide catalyst (waste silica gel; SiO2) 0.021 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0323]

[0324] Comparison of Depolymerization Performance of Polymers with Amidation Functional Groups According to Reaction Temperature

[0325] In the preceding examples and comparative examples, performance was compared by exposing the reaction temperature to 200°C, which is lower than the melting point of the polymer having an amide functional group, for a short reaction time. In the following examples, depolymerization was performed at different temperatures to investigate the effect of reaction temperature on depolymerization performance, and the observed depolymerization performance was compared.

[0326]

[0327] [Example 41]

[0328] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that the depolymerization reaction was carried out at a temperature of 180°C and the depolymerization was terminated after 4 hours of reaction.

[0329]

[0330] [Example 42]

[0331] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that the depolymerization reaction was carried out at a temperature of 220°C and the depolymerization was terminated after 2 hours of reaction, and that the reactor was replaced with a Hastelloy C material without using a PTFE liner.

[0332]

[0333] [Example 43]

[0334] The depolymerization of a polymer having an amide functional group, separation of the product, and analysis were carried out in the same manner as in Example 2, except that the depolymerization reaction was carried out at a temperature of 240°C and the depolymerization was terminated after 2 hours of reaction, and that the reactor was replaced with a Hastelloy C material instead of using a PTFE liner.

[0335]

[0336] Table 9 shows a comparison of the observed depolymerization performance 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, but at different reaction temperatures.

[0337] As in Example 41, when depolymerization was performed at 180°C, which is much lower than the melting point of the polymer having an amide functional group, the degradation of the polymer proceeded very slowly. When exposed to depolymerization conditions at 180°C for 4 hours, only about half of the polymer (conversion rate of about 50%) was degraded, and the monomer was obtained in a relatively low yield of about 35%.

[0338] When the reaction temperature of the depolymerization was maintained at 200°C or higher (Examples 2, 42, and 43), complete polymer degradation occurred with only a short reaction time of less than 2 hours. In particular, in the case of Example 29, where the reaction was maintained at 200°C and the reaction was prolonged for 4 hours, or in Example 43, where the reaction time was maintained but the depolymerization was performed at a high temperature of 240°C, not only the polymer but also all forms of oligomers were completely degraded, and the monomer yield was obtained close to 100%, indicating that ideal depolymerization was achieved.

[0339] Classification Reaction Temperature (°C) Reaction Time (h) Conversion Rate, X PA (%)Yield of depolymerized product (%)Y CPL Y CCD Y SLO Y NSO Y Others Example 4 1180450.3635.290.407.636.690.35 Example 2 2002100.0060.760.7618.9219.480.08 Example 29 2004100.0099.730.230.000.000.04 Example 4 22202100.0081.116.484.318.100.00 Example 4 3 2402100.0099.820.180.000.000.00 [Reaction Conditions] Moles of compound added per mole of repeating unit: Ethanol 10 mol, Anisole 31 mol, Acid catalyst (H3PO4) 0.12 mol, Silicon oxide catalyst (Waste silica gel; SiO2) 0.021 mol CPL: ε-caprolactam, CCD: cyclic caprolactam dimer, SLO: soluble oligomers, NSO: Non-soluble oligomers

[0340]

[0341] Foregoing, specific parts of the present invention have been described in detail. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

[0342]

[0343] The present invention relates to a method for depolymerizing a polymer having an amide functional group, and more specifically, to a method for enabling the depolymerization of a polymer having an amide functional group even at low temperatures and significantly increasing the yield of the depolymerization monomer by using a mixed catalyst having different functions, such as an acid capable of providing hydrogen cations as a component and a silicon oxide and / or a metal oxide containing silicon. Since this can be usefully applied in technical fields such as the manufacture, recovery, and reuse of polymers containing amide functional groups, it has industrial applicability.

Claims

1. A composition for the depolymerization of a polymer having an amide functional group, (1) a monohydric alcohol; (2) an acid capable of providing a hydrogen cation; and (3) silicon oxide and / or a metal oxide containing silicon; A composition for depolymerization of a polymer having an amide functional group, characterized by including 2. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that the above monohydric alcohol is a straight-chain and / or branched monohydric alcohol.

3. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that the above monohydric alcohol solvent has 1 to 12 carbon atoms.

4. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that the acid capable of providing the above hydrogen cation is one or more selected from an inorganic acid, an organic acid having at least one hydrogen cation within the molecule, and a solid acid in which an acidic functional group capable of donating a proton ion is included as part of the compound structure.

5. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that the above silicon-containing metal oxide may further include a metal other than silicon, and is one or more selected from aluminum (Al), iron (Fe), tin (Sn), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta), tungsten (W), zirconium (Zr), chromium (Cr), molybdenum (Mo), yttrium (Y), lanthanum (La), cerium (Ce), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), barium (Ba), zinc (Zn), and gallium (Ga).

6. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that silicon oxide and / or a silicon-containing metal oxide is a material having a mesoporous structure.

7. In Paragraph 1, A composition for depolymerization of a polymer having an amide functional group, characterized in that the silicon dioxide above is silica gel that has not been used for other purposes or has been discharged after use.

8. As a composition of the depolymerization of a polymer having an amide functional group, A composition for depolymerization of a polymer having an amide functional group, characterized by further adding an aromatic compound substituted with one or more alkoxy functional groups as a cosolvent to the composition of claim 1.

9. 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 the step of contacting a polymer having an amide functional group with a composition of any one of claims 1 to 8 above.

10. In Paragraph 9, A method for depolymerizing a polymer having an amide functional group, characterized by additionally including a process of separating unreacted polymer material by filtration.

11. A method for depolymerizing a polymer having an amide functional group, A method for depolymerizing a polymer having an amide functional group, characterized by obtaining a depolymerization reaction product through the step of contacting a polymer having an amide functional group with a composition for depolymerization according to claim 8, and precipitating and recovering (2) and / or (3) of the composition for depolymerization of a polymer having an amide functional group by removing alcohol from the obtained depolymerization reaction product.

12. In Paragraph 11, A method for depolymerizing a polymer having an amide functional group, wherein water is added to a reaction product from which (2) and / or (3) have been removed to cause phase separation, and then the depolymerization monomer is concentrated in a hydrophilic solvent layer and recovered.

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