Method for producing monomers for forming chemically recycled resins and method for producing chemically recycled resins

Abstract

To provide a monomer for forming a chemically recycled resin and a method for producing a chemically recycled resin, which can produce a monomer for forming a chemically recycled resin that can produce a high-quality chemically recycled resin. [Solution] A method for producing a monomer for forming a chemically recycled resin, comprising a laminate having a first resin layer containing a hydrolyzable resin and a second resin layer containing a polyolefin resin, the method comprising: a hydrolysis step of immersing the laminate in a liquid phase containing water and performing hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer to obtain a solid-liquid mixture having a liquid phase containing water and hydrolyzed products of the hydrolyzable resin, and a solid phase containing a polyolefin resin; a separation step of separating the polyolefin resin from the solid-liquid mixture; and a decomposition step of decomposing the polyolefin resin to obtain a monomer for forming a chemically recycled resin.

Description

Technical Field

[0001] The present disclosure relates to a method for producing a monomer for forming a chemically recycled resin and a method for producing a chemically recycled resin.

Background Art

[0002] As recycling methods for mixed waste plastics such as PE / PP / PS, a material recycling method, a chemical recycling method, etc. are known. Among them, in recent years, the chemical recycling method has been attracting attention. The reasons are as follows. That is, in the chemical recycling method in which mixed waste plastics are chemically decomposed and reused, since packaging containers and the like are chemically decomposed, recycling is possible even if foreign substances are mixed in, and plastics that are difficult to process by the material recycling method can be reused. Also, in the chemical recycling method, by performing chemical treatment, a high-quality recycled resin similar to virgin resin can be obtained, and the quality of the recycled resin can be improved. Furthermore, in the chemical recycling method, since the monomers obtained from mixed waste plastics are used as chemical raw materials, the amount of fossil resources used is reduced, and this also contributes to the reduction of CO2 emissions. As a method for chemically recycling mixed waste plastics to obtain a chemically recycled resin, a method is known in which mixed waste plastics are pyrolyzed, the pyrolysis oil such as naphtha obtained is naphtha cracked to obtain monomers such as ethylene and propylene, and then this monomer is polymerized using it as a raw material to obtain a chemically recycled resin such as polyethylene and polypropylene (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

[0004] Incidentally, used packaging containers included in mixed waste plastics are sometimes composed of laminates consisting of a layer containing polyolefin resin and a layer containing polyester resin or polyamide resin. However, the method described in Non-Patent Document 1 above sometimes results in a low average molecular weight of the resulting chemically recycled resin, or a highly branched chemically recycled resin is obtained even when the goal is to obtain a linear chemically recycled resin. Therefore, the above method had room for improvement in terms of the quality of the chemically recycled resin.

[0005] Therefore, the object of this disclosure is to provide a method for producing monomers for forming chemically recycled resins, which can produce monomers for forming chemically recycled resins that can be used to produce high-quality chemically recycled resins, and a method for producing chemically recycled resins. [Means for solving the problem]

[0006] The inventors of this disclosure investigated the reasons why the average molecular weight of the chemically recycled resin obtained by the method described in Patent Document 1 was small, or why a chemically recycled resin with many branches was obtained even when an attempt was made to obtain a linear chemically recycled resin. They noticed that when nitrogen atoms or oxygen atoms were mixed in the obtained monomer, these nitrogen atoms and oxygen atoms tended to inhibit polymerization during the process of polymerizing the monomer to obtain the chemically recycled resin, which led to this disclosure.

[0007] One aspect of this disclosure provides a method for producing a monomer for forming a chemically recycled resin using a laminate comprising a first resin layer containing a hydrolyzable resin and a second resin layer containing a polyolefin resin, comprising: a hydrolysis step of immersing the laminate in a liquid phase containing water and performing hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer to obtain a solid-liquid mixture having a liquid phase containing water and the hydrolyzed product of the hydrolyzable resin and a solid phase containing the polyolefin resin; a separation step of separating the polyolefin resin from the solid-liquid mixture; and a decomposition step of decomposing the polyolefin resin to obtain a monomer for forming a chemically recycled resin. According to this manufacturing method, in the hydrolysis step, the laminate is immersed in a liquid phase containing water and subjected to hydrothermal treatment. When the hydrolyzable resin in the first resin layer is hydrolyzed, the hydrolyzates of the hydrolyzable resin can migrate to the liquid phase. At this time, if the hydrolyzable resin contains nitrogen atoms or oxygen atoms, the hydrolyzates will also contain nitrogen atoms or oxygen atoms, and these hydrolyzates will migrate to the liquid phase. On the other hand, the polyolefin resin is not hydrolyzed. As a result, the hydrolysis step yields a solid-liquid mixture containing a liquid phase with water and hydrolyzates of the hydrolyzable resin, and a solid phase with polyolefin resin. Therefore, when the polyolefin resin is separated from the solid-liquid mixture in the separation step, the polyolefin resin is separated from the hydrolyzates containing nitrogen atoms and oxygen atoms. Thus, even if the polyolefin resin is decomposed in the decomposition step, monomers for forming chemically recycled resins with a low amount of nitrogen atoms and oxygen atoms can be obtained. As a result, when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins, the formation of chemically recycled resins by nitrogen atoms and oxygen atoms is less likely to be inhibited. In other words, it becomes more difficult to obtain chemically recycled resins with a low average molecular weight or chemically recycled resins with many branches. Therefore, according to the manufacturing method of this disclosure, it is possible to produce monomers for forming chemically recycled resins that can be used to produce high-quality chemically recycled resins. Furthermore, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins with low levels of nitrogen and oxygen atoms can be obtained. Therefore, when polymerizing such monomers to produce chemically recycled resins, the step of removing nitrogen and oxygen atoms by hydrogenation can be omitted. In addition, according to the manufacturing method of this disclosure, the step of removing the first resin layer can be omitted by pre-selecting the laminate to contain the first resin layer using an optical method (a method of selecting the first resin layer using infrared light). Accordingly, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins that can efficiently produce chemically recycled resins can also be manufactured.

[0008] The above-described method for producing monomers for forming chemically recycled resins is useful when the hydrolyzable resin includes at least one of a hydrolyzable resin containing nitrogen atoms and a hydrolyzable resin containing oxygen atoms. In this case, hydrolyzed products of hydrolyzable resins containing nitrogen atoms and hydrolyzed products of hydrolyzable resins containing oxygen atoms readily migrate to the liquid phase during the hydrolysis process, and the hydrolyzed products containing nitrogen atoms or oxygen atoms can be easily separated from the polyolefin resin during the separation process, thereby obtaining monomers for forming chemically recycled resins with a low amount of nitrogen or oxygen atom contamination.

[0009] In the above-described method for producing monomers for forming chemically recycled resins, the laminate may be a laminate obtained by crushing a molded body or a laminated film. When the laminate is obtained by crushing a molded body or laminated film, the cross-sectional area of ​​the first resin layer of the laminate can be increased compared to the molded body or laminated film before crushing, and the contact area between the first resin layer and water can be increased. Therefore, compared to directly hydrothermally treating the molded body or laminated film, the hydrothermal treatment can be performed more efficiently, and the efficiency of hydrolysis product generation can be improved. As a result, the amount of nitrogen atoms or oxygen atoms mixed in the solid phase can be reduced, and even when the polyolefin resin is decomposed in the decomposition process, monomers for forming chemically recycled resins with less nitrogen and oxygen atoms mixed in can be obtained.

[0010] In the above-described method for producing monomers for forming chemically recycled resins, the laminate may have a base material and a sealant layer, and one of the base material and the sealant may include the first resin layer and the other may include the second resin layer. In this case, during the hydrolysis process, the hydrolyzable resin in the first resin layer, which is contained in either the substrate or the sealant layer of the laminate, is hydrolyzed, and the hydrolyzed product can migrate to the liquid phase. Furthermore, the polyolefin resin in the second resin layer, which is contained in the other of the sealant layer and the substrate, is not hydrolyzed and therefore remains in the solid phase.

[0011] In the above-described method for producing monomers for forming chemically recycled resins, the laminate comprises a base material, an adhesive resin layer, and a sealant layer, wherein the adhesive resin layer includes the first resin layer, and at least one of the base material and the sealant layer includes the second resin layer. In this case, during the hydrolysis process, the hydrolyzable resin in the first resin layer contained within the adhesive resin layer of the laminate is hydrolyzed, allowing the hydrolyzed product to migrate to the liquid phase. Furthermore, the polyolefin resin in the second resin layer, contained within at least one of the substrate and sealant layers of the laminate, is not hydrolyzed and therefore remains in the solid phase.

[0012] In the above-described method for producing monomers for forming chemically recycled resins, the hydrolyzable resin may include a polyester resin, and in the separation step, the polyolefin resin may be separated from the solid-liquid mixture while adjusting the temperature of the liquid phase of the solid-liquid mixture to maintain the temperature of the liquid phase at the end of the hydrolysis step. When a hydrolyzable resin contains polyester resin, if the temperature of the liquid phase drops below the precipitation temperature of the hydrolyzable resin hydrolysates in the liquid phase, the hydrolyzates will precipitate as solids in the liquid phase. In contrast, in the separation process, by adjusting the temperature of the liquid phase of the solid-liquid mixture to be maintained at the temperature of the liquid phase at the end of the hydrolysis process, the precipitation of hydrolyzates as solids in the liquid phase is suppressed, and the hydrolyzates can be left in the liquid phase. Therefore, it becomes possible to eliminate the process of separating the polyolefin resin and the solid hydrolyzates in the solid phase, and monomers for chemical recycling resin formation can be produced efficiently.

[0013] The above-described method for producing monomers for forming chemically recycled resins may further include an alkaline treatment step between the hydrolysis step and the separation step, in which the hydrolyzable resin contains a polyester resin, and the alkaline treatment step is performed to lower the temperature of the liquid phase of the solid-liquid mixture and treat the solid phase with an alkaline solution. When a hydrolyzable resin contains polyester resin, if the temperature of the liquid phase of the solid-liquid mixture decreases, the hydrolyzates of the hydrolyzable resin precipitate as solids in the liquid phase. In contrast, in the alkaline treatment process, even if the temperature of the liquid phase of the solid-liquid mixture decreases and the hydrolyzates in the liquid phase precipitate as solids, these solid hydrolyzates can be dissolved in the alkaline solution, allowing the hydrolyzates to remain in the liquid phase. Therefore, it becomes possible to eliminate the process of separating the polyolefin resin from the solid hydrolyzates in the solid phase, enabling the efficient production of monomers for chemical recycling resin formation.

[0014] Another aspect of this disclosure is the provision of a method for producing a chemically recycled resin, which involves polymerizing the monomers for forming a chemically recycled resin produced by the above-described method for producing monomers for forming a chemically recycled resin to produce a chemically recycled resin. According to this manufacturing method, monomers for forming chemical recycled resins with a low amount of nitrogen and oxygen atoms can be obtained. As a result, when polymerizing such monomers to produce chemical recycled resins, the formation of the chemical recycled resin by nitrogen and oxygen atoms is less likely to be inhibited. In other words, it becomes more difficult to obtain chemical recycled resins with a low average molecular weight or chemical recycled resins with many branches. Therefore, according to the manufacturing method of this disclosure, high-quality chemical recycled resins can be produced. Furthermore, according to the manufacturing method of the present disclosure, a monomer for forming a chemically recycled resin with a low amount of nitrogen and oxygen atoms can be obtained by the above-mentioned method for manufacturing monomers for forming chemically recycled resins. Therefore, when polymerizing such monomers for forming chemically recycled resins to produce a chemically recycled resin, the step of removing nitrogen and oxygen atoms by hydrogenation can be omitted. In addition, according to the above-mentioned method for manufacturing monomers for forming chemically recycled resins, the step of pre-selecting whether the laminate contains a first resin layer using an optical method (a method of selecting the first resin layer using infrared rays) and removing the first resin layer can also be omitted. Accordingly, according to the manufacturing method of the present disclosure, a high-quality chemically recycled resin can be efficiently produced. [Effects of the Invention]

[0015] This disclosure provides a method for producing a monomer for forming a chemically recycled resin, which can produce a high-quality chemically recycled resin, and a method for producing a chemically recycled resin. [Brief explanation of the drawing]

[0016] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a laminate used in a method for producing a monomer for forming a chemical recycling resin according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a state in which the laminate is hydrolyzed in a hydrolysis step of a method for producing a monomer for forming a chemical recycling resin. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of a laminated film. [Figure 4] FIG. 4 is a cross-sectional view schematically showing another example of the laminated film. [Figure 5] FIG. 5 is a cross-sectional view schematically showing a sealant layer having a three-layer structure of a laminated film. [Figure 6] FIG. 6 is a cross-sectional view schematically showing a sealant layer having a five-layer structure of a laminated film.

MODE FOR CARRYING OUT THE INVENTION

[0017] <<METHOD FOR PRODUCING MONOMER FOR FORMING CHEMICAL RECYCLING RESIN>> Hereinafter, embodiments of a method for producing a monomer for forming a chemical recycling resin according to the present disclosure will be described with reference to FIGS. 1 to 6.

[0018] The method for producing a monomer for forming a chemical recycling resin according to the present disclosure is a method for producing a monomer for forming a chemical recycling resin using a laminate 100. The laminate 100 shown in FIG. 1 includes a first resin layer 10 containing a hydrolyzable resin and a second resin layer 20 containing a polyolefin resin. The method for producing a monomer for forming a chemical recycling resin according to the present disclosure includes a hydrolysis step (see FIG. 2) of immersing the laminate 100 in a liquid phase 31 containing water and performing hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer 10 to obtain a solid-liquid mixture 30 having a liquid phase 31 containing water and a hydrolyzate of the hydrolyzable resin and a solid phase 32 containing the second resin layer 20, a separation step of separating the polyolefin resin from the solid-liquid mixture 30, and a decomposition step of decomposing the polyolefin resin to obtain a monomer for forming a chemical recycling resin. Furthermore, if the hydrolyzable resin of the present disclosure is a polyester resin, the method for producing a monomer for forming a chemically recycled resin may further include an alkaline treatment step between the hydrolysis step and the separation step, in which the temperature of the liquid phase 31 of the solid-liquid mixture 30 is lowered and the solid phase 32 is treated with an alkaline solution.

[0019] According to this manufacturing method, in the hydrolysis step, the laminate 100 is immersed in a liquid phase 31 containing water and subjected to hydrothermal treatment. When the hydrolyzable resin in the first resin layer 10 is hydrolyzed, the hydrolyzed products of the hydrolyzable resin can migrate to the liquid phase 31. At this time, if the hydrolyzable resin contains nitrogen atoms or oxygen atoms, the hydrolyzed products will also contain nitrogen atoms or oxygen atoms, and these hydrolyzed products will migrate to the liquid phase 31. On the other hand, the polyolefin resin is not hydrolyzed. As a result, in the hydrolysis step, a solid-liquid mixture 30 is obtained, which includes a liquid phase 31 containing water and hydrolyzed products of the hydrolyzable resin, and a solid phase 32 containing polyolefin resin. Therefore, when the polyolefin resin is separated from the solid-liquid mixture 30 in the separation step, the polyolefin resin contained in the solid phase 32 is separated from the hydrolyzed products containing nitrogen atoms or oxygen atoms. Therefore, even if the polyolefin resin is decomposed in the decomposition step, monomers for forming chemically recycled resins with a low amount of nitrogen atoms or oxygen atoms can be obtained. As a result, when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins, the formation of chemically recycled resins by nitrogen atoms and oxygen atoms is less likely to be inhibited. In other words, it becomes more difficult to obtain chemically recycled resins with a small average molecular weight or chemically recycled resins with many branches. Therefore, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured. Furthermore, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins with low levels of nitrogen and oxygen atoms can be obtained. Therefore, when polymerizing such monomers to produce chemically recycled resins, the step of removing nitrogen and oxygen atoms by hydrogenation can be omitted. In addition, according to the manufacturing method of this disclosure, the laminate 100 can be pre-selected to contain the first resin layer 10 using an optical method (a method of selecting the first resin layer 10 using infrared light) and the step of removing the first resin layer 10 can be omitted. Accordingly, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins that enable the efficient production of high-quality chemically recycled resins can be manufactured.

[0020] The hydrolysis process, alkali treatment process, separation process, and decomposition process will be described in detail below.

[0021] (1) Hydrolysis process The laminate 100 that is subjected to hydrolysis in the hydrolysis process comprises a first resin layer 10 containing a hydrolyzable resin and a second resin layer 20 containing a polyolefin resin.

[0022] (1st resin layer) The hydrolyzable resin contained in the first resin layer 10 refers to a resin that reacts with water and decomposes into its constituent units. Examples of hydrolyzable resins include polyester resins, polyamide resins, ester-based polyurethane resins, and ether-based polyurethane resins. In particular, the method for producing monomers for forming chemically recycled resins according to this disclosure is useful when the hydrolyzable resin is at least one of a hydrolyzable resin containing nitrogen atoms (at least one of polyamide resin and polyurethane resin) and a hydrolyzable resin containing oxygen atoms (e.g., polyester resin). In this case, the hydrolysates of the hydrolyzable resin readily migrate to the liquid phase 31 in the hydrolysis step, and the hydrolysates containing nitrogen atoms or oxygen atoms can be easily separated from the polyolefin resin in the separation step, making it possible to obtain monomers for forming chemically recycled resins with low levels of nitrogen or oxygen atom contamination.

[0023] Examples of polyester resins include oxygen-containing polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN).

[0024] Examples of polyamide resins include nylon 6, nylon 66, nylon 6 / 66, nylon 12, polyamide resins mainly composed of aliphatic diamines such as hexamethylenediamine and aromatic dicarboxylic acids such as phthalates (terephthalic acid or isophthalic acid), and polyamide resins mainly composed of aromatic diamines such as metaxylenediamine and aliphatic dicarboxylic acids such as adipic acid.

[0025] The content of hydrolyzable resin in the first resin layer 10 is not particularly limited and is 100% by mass or less, but may be 1% by mass or more, or 5% by mass or more.

[0026] (2nd resin layer) The polyolefin resin contained in the second resin layer 20 is a resin that is not hydrolyzed by water. Examples of polyolefin resins include polyethylene (PE) and polypropylene (PP). The content of polyolefin resin in the second resin layer 20 is not particularly limited and is 100% by mass or less, but may be 20% by mass or more, or 50% by mass or more.

[0027] (Laminated structure) The laminate 100 may consist of only one first resin layer 10, or it may consist of multiple first resin layers 10. The laminate 100 may contain only one second resin layer 20, or it may contain multiple second resin layers 20. The laminate 100 may be a packaging laminate or a non-packaging laminate.

[0028] The laminate 100 may contain components such as fibers and inorganic materials, but if the laminate 100 is a packaging laminate, the laminate 100 does not need to contain fibers and inorganic materials. The laminate 100 may be a molded body or a laminated film, but it is preferable that it be a laminate obtained by crushing a molded body or a laminated film. When the laminate 100 is a laminate obtained by crushing a molded body or a laminated film, the cross-sectional area of ​​the first resin layer 10 of the laminate 100 can be increased compared to a molded body or a laminated film, and the contact area between the first resin layer 10 and water can be increased. Therefore, compared to the case where a molded body or a laminated film is subjected to hydrothermal treatment as is, the hydrothermal treatment can be performed more efficiently, and the efficiency of hydrolysis product generation can be improved, so the amount of nitrogen atoms or oxygen atoms mixed in the solid phase 32 can be reduced, and even if the polyolefin resin is decomposed in the decomposition step, monomers for forming chemically recycled resins with less nitrogen atoms or oxygen atoms can be obtained.

[0029] (Molded body) A molded body refers to a structure formed by molding that is not in the form of a film. Examples of molded bodies include bottles, caps, stoppers, cups, containers, and pallets.

[0030] (Laminated film) The laminated film may be composed of the laminated film 100A shown in Figure 3. The laminated film 100A comprises a base material 110 and a sealant layer 120. Here, the base material 110 may include a first resin layer 10, and the sealant layer 120 may include a second resin layer 20. In this case, during the hydrolysis process, the hydrolyzable resin in the first resin layer 10 contained in the base material 110 of the laminated film 100A is hydrolyzed, and the hydrolyzed product can migrate to the liquid phase 31. Also, the polyolefin resin in the sealant layer 120 is not hydrolyzed and is therefore included in the solid phase 32. In the laminated film 100A, the base material 110 may consist only of the first resin layer 10, or it may include both the first resin layer 10 and the second resin layer 20. In this case, the number of the first resin layer 10 and the second resin layer 20 is not limited to one, but may be multiple. Furthermore, the sealant layer 120 may consist only of the second resin layer 20, or it may include both the second resin layer 20 and the first resin layer 10. In this case, the number of the first resin layer 10 and the second resin layer 20 is not limited to one, but may be multiple. Furthermore, in the laminated film 100A, the base material 110 may include a second resin layer 20, and the sealant layer 120 may include a first resin layer 10.

[0031] The laminated film may be composed of the laminated film 100B shown in Figure 4. The laminated film 100B comprises a base material 110, an adhesive resin layer 130, and a sealant layer 120 in this order. Here, the adhesive resin layer 130 includes a first resin layer 10, and at least one of the base material 110 and the sealant layer 120 includes a second resin layer 20. In this case, during the hydrolysis process, the hydrolyzable resin in the first resin layer 10 contained in the adhesive resin layer 130 of the laminated film 100B is hydrolyzed, and the hydrolyzed product can migrate to the liquid phase 31. Also, the polyolefin resin in the second resin layer 20 contained in at least one of the base material 110 and the sealant layer 120 is not hydrolyzed and is therefore contained in the solid phase 32. In the laminated film 100B, the adhesive resin layer 130 may consist only of the first resin layer 10, or it may consist of the first resin layer 10 and the second resin layer 20. In this case, the number of the first resin layer 10 and the second resin layer 20 is not limited to one, but may be multiple. Furthermore, it is sufficient if at least one of the base material 110 and the sealant layer 120 has the second resin layer 20. Therefore, the base material 110 alone may contain the second resin layer 20, the sealant layer 120 alone may contain the second resin layer 20, or both the base material 110 and the sealant layer 120 may contain the second resin layer 20. In at least one of the substrate 110 and the sealant layer 120, the number of second resin layers 20 is not limited to one, but may be multiple.

[0032] In laminated films 100A and 100B, if the resin contained in the base material 110 is a hydrolyzable resin, examples of hydrolyzable resins include polyester resins, polyamide resins, and ester-based polyurethane resins. In the laminated film 100B, the adhesive resin layer 130 is a layer containing an adhesive resin that adheres the substrate 110 and the sealant layer 120, and may be an anchor layer or an adhesive layer. If the adhesive resin is a hydrolyzable resin, for example, an ester-based polyurethane resin is used as the hydrolyzable resin. In laminated films 100A and 100B, examples of polyolefin resins included in the sealant layer 120 include polyethylene and polypropylene.

[0033] The sealant layer 120 may be composed of a three-layer structure of a second resin layer 20 / first resin layer 10 / second resin layer 20, as shown in Figure 5, for example, as shown in sealant layer 120A, or it may be composed of a five-layer structure of a second resin layer 20 / first resin layer 10 / third resin layer 40 / first resin layer 10 / second resin layer 20, as shown in Figure 6, as shown in sealant layer 120B. In the three-layer sealant layer 120A, the second resin layer 20 may contain polyethylene or polypropylene as a polyolefin resin, and the first resin layer 10 may contain a polyamide resin (for example, nylon). In this case, the three-layer sealant layer 120A can have excellent lamination suitability, high puncture strength, sealing properties, and bag breakage strength, and can be suitably used as a sealant layer for lamination and the like. In the three-layer sealant layer 120A, an ethylene vinyl alcohol copolymer (EVOH) layer may be used instead of the first resin layer 10. In this case, the three-layer sealant layer 120A has excellent gas barrier properties and can therefore be suitably used as a barrier sealant layer or a sealant layer for contents-resistant packaging materials. In the five-layer sealant layer 120B, the second resin layer 20 may contain polyethylene or polypropylene as a polyolefin resin, the first resin layer 10 in contact with the second resin layer 20 may contain a polyamide resin (e.g., nylon), and the third resin layer 40 provided between the two first resin layers 10 may contain ethylene vinyl alcohol copolymer (EVOH). In this case, the five-layer sealant layer 120B has high gas barrier properties, excellent lamination suitability, and high puncture strength, making it suitable for use as a laminate sealant layer or a barrier sealant layer.

[0034] The laminated film 100A and the laminated film 100B may further comprise a barrier layer. The barrier layer may be, for example, a metal foil or a resin film with a vapor-deposited layer. If the vapor-deposited layer is provided on a resin film, the vapor-deposited layer may be provided on the surface of the substrate 110 on the side of the sealant layer 120, on the surface of the substrate 110 opposite to the sealant layer 120, or on both the surface on the side of the sealant layer 120 and the surface opposite to the sealant layer 120. Examples of metal foils include aluminum foil. Examples of vapor-deposited layers include metal vapor-deposited layers such as aluminum vapor-deposited layers, and inorganic metal oxide vapor-deposited layers such as alumina vapor-deposited layers and silica vapor-deposited layers. Examples of resin films include polyester resin layers (e.g., PET layers).

[0035] The size of the laminate 100 is not particularly limited, but when viewed from above, the maximum length is preferably 8 mm or less, and more preferably 5 mm or less. The size of the laminate 100 may be greater than 0 mm, may be 2 mm or larger, or may be 3 mm or larger.

[0036] <Liquid phase> The liquid phase 31 is stored in the container 33 and contains water. The water can be deionized water, reverse osmosis water, distilled water, purified water, well water, tap water, industrial water, etc. Before hydrothermal treatment, the liquid phase 31 mainly contains water, but after hydrothermal treatment, the liquid phase 31 contains water and hydrolyzed products of hydrolyzable resin.

[0037] <Hydrothermal treatment> The hydrothermal treatment is carried out under a pressure of 101 kPa (1 atm) or higher, and the temperature of the liquid phase 31 is set to a temperature above the temperature at which the hydrolysis reaction of the hydrolyzable resin proceeds. When the hydrolyzable resin is, for example, polyethylene terephthalate as a polyester resin, the temperature of the liquid phase 31 is preferably 250 to 380°C, and more preferably 325 to 365°C. When the hydrolyzable resin is, for example, nylon as a polyamide resin, the temperature of the liquid phase 31 is preferably 300°C or higher. The temperature of the liquid phase 31 may be 380°C or lower, or 365°C or lower. The temperature of the liquid phase 31 may be below the decomposition temperature of the polyolefin resin, or it may be above the decomposition temperature. If the temperature of the liquid phase 31 is above the decomposition temperature of the polyolefin resin, the polyolefin resin will be reduced in molecular weight, which reduces the amount of polyolefin resin decomposed in the decomposition process and allows the decomposition process to be carried out efficiently.

[0038] The time for hydrothermal treatment (treatment time) is not particularly limited, but from the viewpoint of effectively promoting the hydrolysis of the hydrolyzable resin, it is preferably 1 minute or more, and may be 3 minutes or more, 8 minutes or more, 10 minutes or more, or 15 minutes or more. From the viewpoint of improving the production efficiency of monomers for chemical recycling resin formation, the processing time should be as short as possible, preferably 90 minutes or less. The processing time may also be 60 minutes or less, 40 minutes or less, or 30 minutes or less.

[0039] During hydrothermal treatment, the pressure should be greater than or equal to the water vapor pressure at the temperature of the liquid phase 31 up to the critical temperature of water, and is usually sufficient at a pressure of 101 kPa or higher. If the temperature of the liquid phase 31 during hydrothermal treatment is above the critical temperature, there is no particular limit to the pressure, and it may be, for example, "critical pressure + 40 MPa" or less.

[0040] The atmosphere used in hydrothermal treatment may be, for example, an atmospheric atmosphere or an inert gas atmosphere. Examples of inert gas atmospheres include argon gas atmospheres, helium gas atmospheres, nitrogen gas atmospheres, and mixtures thereof.

[0041] Hydrothermal treatment is usually carried out in a sealed state, but it may also be carried out in an open state. When hydrothermal treatment is carried out in an open state, it is preferable to provide a pressure regulating valve in the flow path leading to the reaction field to adjust the pressure.

[0042] <Solid-liquid mixture> The solid-liquid mixture 30 comprises a liquid phase 31 and a solid phase 32. The liquid phase 31 comprises water and a water-soluble hydrolysate of a hydrolyzable resin. The water-soluble hydrolysates are determined by the hydrolyzable resin. When the hydrolyzable resin is a polyamide resin, examples of water-soluble hydrolysates include nitrogen-containing compounds such as ε-caprolactam, hexamethylenediamine, adipic acid, and aminocaproic acid. When the hydrolyzable resin is a polyester resin, examples of water-soluble hydrolysates include dicarboxylic acids such as terephthalic acid and 1,4-dicarboxylic acid naltalene, and oxygen-containing compounds such as diols such as ethylene glycol and butylene glycol. In the case of ester-based polyurethane resins, examples of water-soluble hydrolysates include nitrogen-containing compounds such as isocyanates.

[0043] The solid phase 32 contains a polyolefin resin. If a portion of the polyolefin resin decomposes during the hydrothermal treatment of the laminate 100, the solid phase 32 also contains the decomposed products of the polyolefin resin. Furthermore, if the hydrolyzable resin's hydrolyzates include water-insoluble hydrolyzates, the solid phase 32 also includes those water-insoluble hydrolyzates.

[0044] (2) Alkali treatment process The alkali treatment step is a step included between the hydrolysis step and the separation step when the hydrolyzable resin contains a polyester resin, and is a step in which the temperature of the liquid phase 31 of the solid-liquid mixture 30 is lowered and the solid phase 32 is treated with an alkaline solution. When the hydrolyzable resin contains polyester resin, lowering the temperature of the liquid phase 31 of the solid-liquid mixture 30 tends to cause the hydrolyzates of the hydrolyzable resin to precipitate as solids in the liquid phase 31. For example, if the polyester resin is polyethylene terephthalate, lowering the temperature of the liquid phase 31 of the solid-liquid mixture 30 causes terephthalic acid to precipitate as a solid in the liquid phase 31. Even in this case, the solid hydrolyzates can be dissolved in the alkaline solution during the alkali treatment process, leaving the hydrolyzates in the liquid phase 31. Therefore, the process of separating the polyolefin resin and the solid hydrolyzates in the solid phase 32 can be omitted, and monomers for chemical recycling resin formation can be produced efficiently. Furthermore, since the separation process is performed after lowering the temperature of the liquid phase 31 of the solid-liquid mixture 30, there is no need to use a highly heat-resistant filter material when separating the polyolefin resin by filtration during the separation process. The temperature of the liquid phase 31 of the solid-liquid mixture 30 should be lowered to a temperature lower than the temperature during hydrothermal treatment, but it may be lowered to 100°C or below, 80°C or below, 60°C or below, or 40°C or below. The temperature of the liquid phase 31 of the solid-liquid mixture 30 is preferably 20°C or higher, and more preferably 30°C or higher. By setting the temperature of the liquid phase 31 of the solid-liquid mixture 30 to 20°C or higher, the amount of solid hydrolysates can be reduced, and therefore the amount of alkaline solution added corresponding to that amount can be further reduced. Examples of alkalis contained in alkaline solutions include sodium hydroxide, potassium hydroxide, and ammonia.

[0045] (3) Separation process The separation step is a step of separating the polyolefin resin from the solid-liquid mixture 30. One method for separating polyolefin resin from the solid-liquid mixture 30 is filtration. However, polyolefin resin can also be separated from the solid-liquid mixture 30 by making the specific gravity of the liquid phase 31 containing water greater than the specific gravity of the polyolefin resin, thereby floating the polyolefin resin on the liquid phase 31 and recovering it. To make the specific gravity of the liquid phase 31 containing water greater than the specific gravity of the polyolefin resin, the water content in the liquid phase 31 should be increased. Even if the liquid phase 31 contains water-soluble hydrolysates in addition to water, the specific gravity of the water-soluble hydrolysates is usually greater than 1, so the specific gravity of the liquid phase 31 will be greater than 1. On the other hand, the specific gravity of the polyolefin resin is usually less than 1. Therefore, in the solid-liquid mixture 30, the polyolefin resin will float on the surface of the liquid phase 31. If the hydrolyzable resin contains a polyester resin, the polyolefin resin may be separated from the solid-liquid mixture 30 during the separation process while adjusting the temperature of the liquid phase 31 of the solid-liquid mixture 30 to maintain the temperature of the liquid phase 31 at the end of the hydrolysis process. When the hydrolyzable resin contains polyester resin, if the temperature of the liquid phase 31 of the solid-liquid mixture 30 decreases and the hydrolyzates of the hydrolyzable resin fall below the precipitation temperature of the hydrolyzates in the liquid phase 31, they precipitate as solids in the liquid phase 31. For example, if the polyester resin is polyethylene terephthalate, if the temperature of the liquid phase 31 of the solid-liquid mixture 30 decreases and the terephthalic acid, which is a hydrolyzable resin, falls below the precipitation temperature of terephthalic acid in the liquid phase 31, terephthalic acid precipitates as a solid in the liquid phase 31. In contrast, in the separation process, by adjusting the temperature of the liquid phase 31 of the solid-liquid mixture 30 to be maintained at the temperature of the liquid phase 31 at the end of the hydrolysis process, the precipitation of hydrolyzates in the liquid phase 31 as solids is suppressed, and the hydrolyzates can be left in the liquid phase 31. Therefore, it becomes possible to omit the process of separating the polyolefin resin and the solid hydrolyzates in the solid phase 32, and monomers for chemical recycling resin formation can be produced efficiently. Furthermore, the temperature of the liquid phase 31 at the end of the hydrolysis process is preferably 250 to 350°C when the hydrolyzable resin is a polyester resin.

[0046] (4) Decomposition process The decomposition process involves decomposing polyolefin resin to obtain monomers for forming chemically recycled resins. The decomposition of polyolefin resin can be carried out by thermal decomposition. Thermal decomposition can be performed by placing the polyolefin resin in a container and heating it, then heating the polyolefin resin to a temperature above its thermal decomposition temperature. The temperature in the decomposition process is not particularly limited, as long as it is above the thermal decomposition temperature of the polyolefin resin, but it is preferably 350°C or higher, and more preferably 365°C or higher. The temperature during the decomposition process may be 550°C or lower, 500°C or lower, or 450°C or lower. Furthermore, a catalyst that accelerates the decomposition of the polyolefin resin may be used during the decomposition process.

[0047] Furthermore, the pressure inside the container during the decomposition process is not particularly limited, but is preferably 100 kPa (atmospheric pressure) or less.

[0048] The atmosphere during the decomposition process is typically an oxygen-free atmosphere. Examples of oxygen-free atmospheres include inert gas atmospheres. Examples of inert gas atmospheres include argon gas atmospheres, helium gas atmospheres, nitrogen gas atmospheres, and mixtures thereof. The resulting decomposition products become pyrolysis oils such as naphtha, and by naphtha cracking these pyrolysis oils, monomers for forming chemically recycled resins can be obtained. The monomer obtained for chemical recycling resin formation varies depending on the polyolefin resin. If the polyolefin resin is polyethylene, the monomer for chemical recycling resin formation is ethylene; if the polyolefin resin is polypropylene, the monomer for chemical recycling resin formation is propylene.

[0049] <<Methods for Chemical Recycling>> The method for producing a chemically recycled resin described herein is a method for producing a chemically recycled resin by polymerizing the monomer for forming a chemically recycled resin produced by the method for producing a monomer for forming a chemically recycled resin described above.

[0050] According to this manufacturing method, monomers for forming chemical recycled resins with a low amount of nitrogen and oxygen atoms can be obtained. As a result, when polymerizing such monomers to produce chemical recycled resins, the formation of the chemical recycled resin is less likely to be inhibited by nitrogen and oxygen atoms. In other words, it becomes more difficult to obtain chemical recycled resins with a low average molecular weight or chemical recycled resins with many branches. Therefore, according to the manufacturing method of this disclosure, high-quality chemical recycled resins can be produced.

[0051] If the chemically recycled resin is, for example, low-density polyethylene, the chemically recycled resin can be obtained by polymerizing a monomer for chemical recycling resin formation (ethylene monomer) under high pressure of, for example, 10 to 20 MPa. When the chemically recycled resin is, for example, high-density polyethylene, it can be obtained by polymerizing a monomer for forming the chemically recycled resin (ethylene monomer) at atmospheric pressure. In this case, a catalyst is usually used to promote polymerization. Examples of catalysts include Ziegler-Natta catalysts and metallocene catalysts. From the viewpoint of narrowing the molecular weight distribution of the chemically recycled resin, metallocene catalysts are preferred as the catalyst.

[0052] When the chemically recycled resin is, for example, polypropylene, it can be obtained by polymerizing a monomer for chemical recycling resin formation (propylene monomer) at a pressure of 1.5 to 6 MPa and a temperature of 60 to 100°C. A catalyst is usually used to promote polymerization. Examples of catalysts include Ziegler-Natta catalysts and metallocene catalysts. From the viewpoint of narrowing the molecular weight distribution of the chemically recycled resin, metallocene catalysts are preferred.

[0053] This disclosure relates to the following invention. [1] A method for producing monomers for forming chemically recycled resins using a laminate comprising a first resin layer containing a hydrolyzable resin and a second resin layer containing a polyolefin resin, A hydrolysis step is performed by immersing the laminate in a liquid phase containing water and performing hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer, thereby obtaining a solid-liquid mixture having a liquid phase containing water and the hydrolyzed product of the hydrolyzable resin, and a solid phase containing the polyolefin resin. A separation step of separating the polyolefin resin from the solid-liquid mixture, A decomposition step of decomposing the aforementioned polyolefin resin to obtain monomers for forming chemically recycled resins, A method for producing monomers for forming chemically recycled resins, including [the specified element]. [2] The method for producing a monomer for forming a chemical recycling resin according to [1], wherein the hydrolyzable resin comprises at least one of a hydrolyzable resin containing nitrogen atoms and a hydrolyzable resin containing oxygen atoms. [3] The method for producing a monomer for forming a chemically recycled resin according to [1] or [2], wherein the laminate is a laminate obtained by crushing a molded body or a laminated film. [4] The laminate comprises a base material and a sealant layer, The substrate and the sealant include the first resin layer, A method for producing a monomer for forming a chemically recycled resin according to any one of [1] to [3], wherein the other party comprises the second resin layer. [5] The laminate comprises a base material, an adhesive resin layer, and a sealant layer, The adhesive resin layer includes the first resin layer, A method for producing a monomer for forming a chemically recycled resin according to any one of [1] to [3], wherein at least one of the substrate and the sealant layer comprises the second resin layer. [6] The hydrolyzable resin contains a polyester resin, A method for producing a monomer for forming a chemically recycled resin according to any one of [1] to [5], wherein in the separation step, the polyolefin resin is separated from the solid-liquid mixture while adjusting the temperature of the liquid phase of the solid-liquid mixture to maintain the temperature of the liquid phase at the end of the hydrolysis step. [7] The hydrolyzable resin includes a polyester resin, A method for producing a monomer for forming a chemically recycled resin according to any one of [1] to [5], further comprising an alkaline treatment step between the hydrolysis step and the separation step, wherein the alkaline treatment step is performed to lower the temperature of the liquid phase of the solid-liquid mixture and treat the solid phase with an alkaline solution. A method for producing a chemically recycled resin, comprising polymerizing a monomer for forming a chemically recycled resin, which is produced by a method for producing a monomer for forming a chemically recycled resin described in any of [8][1] to [7]. [Explanation of Symbols]

[0054] 10...First resin layer, 20...Second resin layer, 30...Solid-liquid mixture, 31...Liquid phase, 32...Solid phase, 100...Laminate, 110...Substrate, 120, 120A, 120B...Sealant layer, 130...Adhesive resin layer.

Claims

1. A method for producing monomers for forming chemically recycled resins, using a laminate comprising a first resin layer containing a hydrolyzable resin and a second resin layer containing a polyolefin resin, A hydrolysis step is performed by immersing the laminate in a liquid phase containing water and performing hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer, thereby obtaining a solid-liquid mixture having a liquid phase containing water and the hydrolyzed product of the hydrolyzable resin, and a solid phase containing the polyolefin resin. A separation step of separating the polyolefin resin from the solid-liquid mixture, A decomposition step of decomposing the aforementioned polyolefin resin to obtain monomers for forming chemically recycled resins, A method for producing monomers for forming chemically recycled resins, including [the specified element].

2. The method for producing a monomer for forming a chemically recycled resin according to claim 1, wherein the hydrolyzable resin comprises at least one of a hydrolyzable resin containing nitrogen atoms and a hydrolyzable resin containing oxygen atoms.

3. The method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, wherein the laminate is a laminate obtained by crushing a molded body or a laminated film.

4. The laminate has a substrate and a sealant layer, The substrate and the sealant include the first resin layer, The method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, wherein the other party includes the second resin layer.

5. The laminate comprises a base material, an adhesive resin layer, and a sealant layer. The adhesive resin layer includes the first resin layer, A method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, wherein at least one of the substrate and the sealant layer includes the second resin layer.

6. The hydrolyzable resin includes a polyester resin, A method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, wherein in the separation step, the polyolefin resin is separated from the solid-liquid mixture while adjusting the temperature of the liquid phase of the solid-liquid mixture to be higher than the precipitation temperature of the hydrolysate in the liquid phase.

7. The hydrolyzable resin includes a polyester resin, A method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, further comprising an alkaline treatment step between the hydrolysis step and the separation step, in which the temperature of the liquid phase of the solid-liquid mixture is lowered and the solid phase is treated with an alkaline solution.

8. A method for producing a chemically recycled resin, comprising polymerizing a monomer for forming a chemically recycled resin, produced by the method for producing a monomer for forming a chemically recycled resin according to claim 1 or 2, to produce a chemically recycled resin.

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