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

Abstract

To provide a method for producing monomers for forming chemically recycled resins, which can be used to produce high-quality chemically recycled resins. [Solution] A method for producing a monomer for forming a chemically recycled resin, using a laminate comprising a base layer, an adhesive resin layer, and a sealant layer in this order, wherein at least one of the base layer and the sealant layer contains a polyolefin resin, and the adhesive resin contains an adhesive resin, comprising: an alkali treatment step of alkali treating the laminate with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the base layer and the sealant layer; a separation step of separating the polyolefin resin contained in at least one of the base layer and the sealant layer from the adhesive resin; and a decomposition step of decomposing the polyolefin resin separated in the separation step 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 chemical recycling resin and a method for producing a chemical recycling 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 attracted attention. The reasons are as follows. That is, in the chemical recycling method of chemically decomposing and recycling mixed waste plastics, 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 recycled. 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, which also contributes to the reduction of CO2 emissions. As a method for chemically recycling mixed waste plastics to obtain a chemical recycling resin, a method is known in which mixed waste plastics are thermally decomposed, the obtained pyrolysis oil such as naphtha is naphtha cracked to obtain monomers such as ethylene and propylene, and then this monomer is polymerized as a raw material to obtain a chemical recycling 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 may consist of a laminate comprising a base layer, an adhesive resin layer, and a sealant layer, and the base layer and sealant layer may contain polyolefin 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 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 base layer, an adhesive resin layer, and a sealant layer in this order, wherein at least one of the base layer and the sealant layer contains a polyolefin resin, and the adhesive resin layer contains an adhesive resin, comprising: an alkali treatment step of alkali treatment of the laminate with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the base layer and the sealant layer; a separation step of separating the polyolefin resin contained in at least one of the base layer and the sealant layer from the adhesive resin; and a decomposition step of decomposing the polyolefin resin separated in the separation step to obtain a monomer for forming a chemically recycled resin. According to this manufacturing method, in the peeling step, the laminate is treated with an alkaline solution, and the adhesive resin layer is dissolved or swollen and peeled off from the substrate layer and sealant layer. In the separation step, the polyolefin resin contained in at least one of the substrate layer and sealant layer is separated from the adhesive resin. Therefore, even if the adhesive resin is a resin containing nitrogen atoms and oxygen atoms, a polyolefin resin with a low amount of nitrogen and oxygen atoms can be obtained. Consequently, even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with a low amount of nitrogen and oxygen atoms can be obtained. As a result, when polymerizing such a monomer for forming chemically recycled resin to produce a chemically recycled resin, the formation of the chemically recycled resin by nitrogen and oxygen atoms is less likely to be inhibited. In other words, for example, it becomes more difficult to obtain a chemically recycled resin with a small average molecular weight or a chemically recycled resin with many branches. Therefore, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins that can be used to 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 step of pre-selecting the laminate to include a layer containing a non-polyolefin resin using an optical method (a method of selecting non-polyolefin resins using infrared light) and removing the layer containing the non-polyolefin resin can be omitted. 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 method for producing monomers for forming chemically recycled resins is useful when the adhesive resin contains at least one of a resin containing nitrogen atoms and a resin containing oxygen atoms. This is because, generally, when an adhesive resin contains at least one of a resin containing nitrogen atoms and a resin containing oxygen atoms, it tends to yield a polyolefin resin with a high concentration of either nitrogen or oxygen atoms.

[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 adhesive resin layer of the laminate can be increased compared to the molded body or laminated film before crushing, and the contact area between the adhesive resin layer and the alkaline solution can be increased. Therefore, compared to treating the molded body or laminated film directly with an alkaline solution, the dissolution or swelling of the adhesive resin can be performed more efficiently, improving the efficiency of the dissolution or swelling of the adhesive resin. As a result, the amount of nitrogen atoms or oxygen atoms mixed into the polyolefin resin 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 can be obtained.

[0010] In the above-described method for producing monomers for forming chemically recycled resins, the separation step may include a separation step in which the polyolefin resin and the adhesive resin are separated by the difference in specific gravity. In this case, the polyolefin resin can be easily recovered by separating it from the adhesive resin based on the difference in specific gravity.

[0011] In the above-described method for producing monomers for forming chemically recycled resins, the separation step may be a step in which the adhesive resin is removed as a high-density component using a specific gravity separation liquid. If the adhesive resin layer remains undissolved or swollen during the alkaline treatment process, the adhesive resin can be removed as a high-density component using a specific gravity separation solution, leaving the polyolefin resin behind, which can then be easily recovered.

[0012] In the above-described method for producing monomers for forming chemically recycled resins, the separation step may be a step in which the polyolefin resin is floated as a low-density component using a specific gravity separation liquid. In this case, the polyolefin resin floats as a low-density component due to the specific gravity separation liquid, allowing for easy recovery of the polyolefin resin.

[0013] 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 by the above-mentioned method for producing monomers for forming chemical recycled resins. As a result, when polymerizing such monomers for forming chemical recycled resins to produce chemical recycled resins, the formation of chemical recycled resins 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 manufacturing method for 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 manufacturing method for monomers for forming chemically recycled resins, the step of pre-selecting the laminate to include a layer containing a non-polyolefin resin using an optical method (a method of selecting the layer containing a non-polyolefin resin using infrared light) and removing the layer containing the non-polyolefin resin can also be omitted. Therefore, according to the manufacturing method of the present disclosure, a high-quality chemically recycled resin can be produced efficiently. [Effects of the Invention]

[0014] This disclosure provides a method for producing monomers for forming chemically recycled resins, which can be used to produce high-quality chemically recycled resins, and a method for producing chemically recycled resins. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a cross-sectional view schematically showing a laminate used in a method for producing a monomer for forming a chemical recycling resin of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view schematically showing a state in which the laminate is in contact with an alkaline solution in a peeling step of a method for producing a monomer for forming a chemical recycling resin. <0000​​​​​​​​​​​​​​​​​​​​​​​According to this manufacturing method, in the alkali treatment step, the laminate 100 is alkali-treated with an alkaline solution 40 to dissolve or swell the adhesive resin layer 30 and peel it off from the base layer 10 and the sealant layer 20. In the separation step, the polyolefin resin contained in at least one of the base layer 10 and the sealant layer 20 is separated from the adhesive resin. Therefore, even if the adhesive resin is a resin containing nitrogen atoms and oxygen atoms, a polyolefin resin with a low amount of nitrogen atoms and oxygen atoms can be obtained. Consequently, even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with a low amount of nitrogen atoms and oxygen atoms can be obtained. As a result, when polymerizing such a monomer for forming chemically recycled resin to produce a chemically recycled resin, the formation of the chemically recycled resin by nitrogen atoms and oxygen atoms is less likely to be inhibited. That is, for example, it becomes more difficult to obtain a chemically recycled resin with a small average molecular weight or a chemically recycled resin with many branches. Therefore, according to the manufacturing method of this disclosure, a monomer for forming chemically recycled resin that can produce a high-quality chemically recycled resin can be manufactured.

[0019] 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 using an optical method (a method of selecting layers containing non-polyolefin resins using infrared light) to remove layers containing non-polyolefin resins, and the step of removing such layers 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 alkali treatment process, separation process, and decomposition process will be described in detail below.

[0021] (1) Alkali treatment process The alkali treatment process involves alkali treatment of the laminate 100 with an alkaline solution 40 to dissolve or swell the adhesive resin layer 30 and peel off the substrate layer 10 and the sealant layer 20. The laminate 100 to be subjected to alkaline treatment comprises a base layer 10, an adhesive resin layer 30, and a sealant layer 20 in this order.

[0022] <Substrate layer and sealant layer> Examples of polyolefin resins included in at least one of the base layer 10 and the sealant layer 20 include polyethylene (PE) and polypropylene (PP). Examples of polyethylene include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), and ethylene-α-olefin copolymers. Examples of polypropylene include homopolypropylene, block polypropylene, random polypropylene, and propylene-α-olefin copolymers. Examples of α-olefins include ethylene and 1-butene. The polyolefin resin may be contained only in the base layer 10, only in the sealant layer 20, or in both the base layer 10 and the sealant layer 20. At least one of the base layer 10 and the sealant layer 20 may contain a resin other than polyolefin resin (hereinafter also referred to as "non-polyolefin resin"). Examples of non-polyolefin resins include polyester resins, polyamide resins, and urethane resins.

[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 polyolefin resin content in the base layer 10 containing polyolefin resin, or the sealant layer 20 containing polyolefin resin, is not particularly limited and may be 100% by mass or less, but may be 20% by mass or more, or 50% by mass or more.

[0026] The sealant layer 20 may be composed of a three-layer structure of polyolefin resin layer 20A / first resin layer 20B / polyolefin resin layer 20A, as shown in Figure 3, for example, or it may be composed of a five-layer structure of polyolefin resin layer 20A / first resin layer 20B / second resin layer 20C / first resin layer 20B / polyolefin resin layer 20A, as shown in Figure 4, for example, the sealant layer 120B.

[0027] In the three-layer sealant layer 120A, the polyolefin resin layer 20A may contain polyethylene or polypropylene as the polyolefin resin, and the first resin layer 20B 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. In the three-layer sealant layer 120A, the first resin layer 20B may contain ethylene vinyl alcohol copolymer (EVOH) instead of polyamide resin. 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.

[0028] In a five-layer sealant layer 120B, the polyolefin resin layer 20A may contain polyethylene or polypropylene as the polyolefin resin, the first resin layer 20B in contact with the polyolefin resin layer 20A may contain a polyamide resin (e.g., nylon), and the second resin layer 20C provided between the two first resin layers 20B 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.

[0029] <Adhesive resin layer> The adhesive resin 30 may be an anchor layer or an adhesive layer. The adhesive resin contained in the adhesive resin layer 30 is a resin capable of bonding the substrate layer 10 and the sealant layer 20. Examples of adhesive resins include resins obtained by curing adhesives, polyester resins, and polypropylene resins. Examples of adhesives include acrylic adhesives, ester adhesives, epoxy adhesives, silicone adhesives, polyolefin adhesives, urethane adhesives, and polyvinyl ether adhesives. In particular, because they readily dissolve or swell in alkaline solutions, the adhesive resin is preferably an ester-based resin, a urethane-based resin, or an ether-based resin cured with isocyanate. The method for producing monomers for forming chemically recycled resins described herein is useful when the adhesive resin contains at least one of a resin having nitrogen atoms and a resin having oxygen atoms. This is because, generally, when the adhesive resin contains at least one of a resin having nitrogen atoms and a resin having oxygen atoms, it is easier to obtain a polyolefin resin with a high amount of nitrogen atoms or oxygen atoms. Examples of adhesive resins containing nitrogen atoms include urethane-based adhesives. Examples of adhesive resins containing oxygen atoms include acrylic-based adhesives, epoxy-based adhesives, silicone-based adhesives, and polyvinyl ether-based adhesives.

[0030] <Barrier layer> The laminate 100 may further comprise a barrier layer. The barrier layer may be, for example, a metal foil or a resin film on which a vapor-deposited layer is provided. If the vapor-deposited layer is provided on a resin film, the vapor-deposited layer may be provided on the surface of the base layer 10 on the side of the sealant layer 20, on the surface of the base layer 10 opposite to the sealant layer 20, or on both the surface on the side of the sealant layer 20 and the surface opposite to the sealant layer 20. 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), polyamide resin layers (e.g., NY layers), and polyolefin resin layers (e.g., OPP layers, CPP layers, PE layers).

[0031] <Laminate> The laminate 100 may be a packaging laminate or a non-packaging laminate.

[0032] 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.

[0033] 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 adhesive resin layer 30 of the laminate 100 can be increased compared to a molded body or a laminated film, and the contact area between the adhesive resin layer 30 and water can be increased. Therefore, compared to the case where the molded body or laminated film is directly treated with an alkaline solution, the dissolution or swelling of the adhesive resin can be performed more efficiently, and the efficiency of the dissolution or swelling of the adhesive resin can be improved, so the amount of nitrogen atoms or oxygen atoms mixed into the polyolefin resin can be reduced, and even when the polyolefin resin is decomposed in the decomposition process, monomers for forming chemically recycled resins with less nitrogen atoms or oxygen atoms can be obtained.

[0034] (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.

[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] <Alkaline treatment> The alkaline solution 40 is stored in container 41 and contains alkali and solvent. Examples of alkalis include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, sodium ethylate, potassium ethylate, and lithium methylate, but are not particularly limited. If the adhesive resin contained in the adhesive resin layer 30 has hydroxyl groups, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and ammonium salts are preferred. Examples of solvents include water, alcohol, glycol ether, and polar solvents such as N-methyl-2-pyrrolidone, which may be used individually or in combination. As for water, deionized water, reverse osmosis water, distilled water, purified water, well water, tap water, industrial water, etc., can be used. As for alcohol, methanol, ethanol, propanol, isopropanol, etc., can be used. As for glycol ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, etc., can be used.

[0037] The temperature of the alkaline solution 40 is not particularly limited, but from the viewpoint of promoting the dissolution or swelling of the adhesive resin layer 30, it is preferably 40°C or higher, and more preferably 65°C or higher.

[0038] The temperature of the alkaline solution 40 may be 90°C or lower, 85°C or lower, or 80°C or lower. The concentration of alkali in the alkaline solution 40 is not particularly limited, but is preferably 1% by mass or more, more preferably 3% by mass or more. The concentration of alkali in the alkaline solution 40 may be 5% by mass or more. Examples of alkalis contained in alkaline solution 40 include sodium hydroxide, dimethylbis(2-hydroxyethyl)ammonium hydroxide, monomethyltris(2-hydroxyethyl)ammonium hydroxide, and trimethyl-2-hydroxyethylammonium hydroxide.

[0039] The alkali treatment time is not particularly limited, but from the viewpoint of promoting the dissolution or swelling of the adhesive resin layer 30, it is preferably 30 minutes or more, and more preferably 60 minutes or more. The alkaline treatment time may be 240 minutes or less, or 180 minutes or less.

[0040] The pressure during alkaline treatment is not particularly limited and may be atmospheric pressure.

[0041] The atmosphere used in alkaline treatment may be an atmospheric atmosphere or an inert gas atmosphere. Examples of inert gas atmospheres include argon gas atmosphere, helium gas atmosphere, nitrogen gas atmosphere, and mixed gas atmospheres thereof.

[0042] The alkaline treatment may be carried out in a sealed state or in an open state.

[0043] In the alkali treatment step, if the adhesive resin layer 30 swells but at least one of the substrate layer 10 and the sealant layer 20 does not peel off from the adhesive resin layer 30 and the laminate 100 remains intact, stress is applied to the laminate 100 to cause the substrate layer 10 and the sealant layer 20 to peel off from the adhesive resin layer 30. A method for applying stress to the laminate 100 is, for example, to generate a flow in the alkaline solution 40 (for example, by stirring the alkaline solution 40).

[0044] (2) Separation process The separation step is a step of separating the polyolefin resin contained in at least one of the substrate layer 10 and the sealant layer 20 from the adhesive resin.

[0045] If the adhesive resin layer 30 is dissolved in the alkaline solution during the alkali treatment step, the separation step includes a first step of removing the base layer 10 and the sealant layer 20 from the alkaline solution 40. In this case, since the adhesive resin is dissolved in the alkaline solution 40 and at least one of the base layer 10 and the sealant layer 20 contains polyolefin resin, the polyolefin resin is separated from the adhesive resin. At this time, since the base layer 10 and the sealant layer 20 have been peeled off from the adhesive resin during the alkali treatment step, the base layer 10 and the sealant layer 20 are separated from each other. The first step can be carried out, for example, by filtering a solid-liquid mixture 42 containing an alkaline solution 40, a substrate layer 10, and a sealant layer 20.

[0046] If one of the base layer 10 and the sealant layer 20 does not contain polyolefin resin, the separation step may further include a second step of separating the layer containing polyolefin resin (hereinafter also referred to as the "polyolefin resin-containing layer") from the layer containing non-polyolefin resin (hereinafter also referred to as the "non-polyolefin resin-containing layer"). The second step may be, for example, a step of separating the non-polyolefin resin-containing layer from the polyolefin resin-containing layer based on the difference in specific gravity. In this case, a specific gravity separation liquid can be used. As the specific gravity separation liquid, a liquid having a specific gravity between the specific gravity of the non-polyolefin resin and the specific gravity of the polyolefin resin can be used. As a specific gravity separation liquid, when the polyolefin resin is to be floated as a low-density component, a liquid with a specific gravity less than or equal to that of the non-polyolefin resin but greater than that of the polyolefin resin can be used. When this specific gravity separation liquid is used, the polyolefin resin floats on the surface of the specific gravity separation liquid as a low-density component, making it easy to recover the polyolefin resin. Furthermore, when removing non-polyolefin resin as a high-density component, a specific gravity separation liquid with a specific gravity lower than that of the non-polyolefin resin and higher than that of the polyolefin resin is preferable. When this specific gravity separation liquid is used, the non-polyolefin resin settles in the specific gravity separation liquid as a high-density component. Therefore, since the polyolefin resin remains after the removal of the non-polyolefin resin, the polyolefin resin can be easily recovered.

[0047] If the adhesive resin layer 30 swells in the alkaline solution during the alkali treatment process, the separation process includes a third step (fractionation step) in which the adhesive resin layer 30, the base layer 10, and the sealant layer 20 are removed from the alkaline solution 40, and then the base layer 10 and the sealant layer 20 are separated from the adhesive resin layer 30. At this point, since the base layer 10 and the sealant layer 20 have been peeled off from the adhesive resin layer 30 during the alkali treatment process, the adhesive resin layer 30, the base layer 10, and the sealant layer 20 are separated from each other. The third step may be, for example, filtering the solid-liquid mixture 42 containing the alkaline solution 40, adhesive resin layer 30, substrate layer 10, and sealant layer 20.

[0048] Furthermore, the third step may be a step of separating the adhesive resin layer 30 containing the adhesive resin from the polyolefin resin contained in at least one of the base layer 10 and the sealant layer 20 based on the difference in specific gravity. In this case, a specific gravity separation liquid can be used. As a specific gravity separation liquid, when the polyolefin resin is to be floated as a low-density component, a liquid with a specific gravity less than or equal to that of the adhesive resin but greater than that of the polyolefin resin can be used. When this specific gravity separation liquid is used, the polyolefin resin floats on the surface of the specific gravity separation liquid as a low-density component, making it easy to recover the polyolefin resin. Furthermore, when removing the adhesive resin as a high-density component, a specific gravity separation liquid with a specific gravity lower than that of the adhesive resin and higher than that of the polyolefin resin is preferable. When this specific gravity separation liquid is used, the adhesive resin settles in the specific gravity separation liquid as a high-density component. Therefore, since the polyolefin resin remains after the removal of the adhesive resin, the polyolefin resin can be easily recovered.

[0049] The separation step may further include a fourth step of separating the polyolefin resin-containing layer from the non-polyolefin resin-containing layer if one of the base layer 10 and the sealant layer 20 does not contain a polyolefin resin. The fourth step may be, for example, a step to separate the non-polyolefin resin-containing layer from the polyolefin resin-containing layer based on the difference in specific gravity. In this case, a specific gravity separation solution can be used. As a specific gravity separation liquid, when the polyolefin resin is to be floated as a low-density component, a liquid with a specific gravity less than or equal to that of the non-polyolefin resin but greater than that of the polyolefin resin can be used. When this specific gravity separation liquid is used, the polyolefin resin floats on the surface of the specific gravity separation liquid as a low-density component, making it easy to recover the polyolefin resin. Furthermore, when removing non-polyolefin resin as a high-density component, a specific gravity separation liquid with a specific gravity lower than that of the non-polyolefin resin and higher than that of the polyolefin resin is preferable. When this specific gravity separation liquid is used, the non-polyolefin resin settles in the specific gravity separation liquid as a high-density component. Therefore, since the polyolefin resin remains after the removal of the non-polyolefin resin, the polyolefin resin can be easily recovered.

[0050] Examples of the specific gravity separation liquids mentioned above include water, ethanol, and chloroform. Of these, water is preferred. Since polyolefin resin has a lower specific gravity than water, the polyolefin resin can be made to float on the water surface, and thus the polyolefin resin can be easily separated. The specific gravity separation solution may or may not be the same as the solvent contained in the alkaline solution 40. When using a specific gravity separation solution in the separation process, the temperature of the specific gravity separation solution is not particularly restricted and can be at room temperature.

[0051] (3) Decomposition process The decomposition process involves decomposing the polyolefin resin separated in the separation process 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.

[0052] Furthermore, the pressure inside the container during the decomposition process is not particularly limited, but is preferably 100 kPa (atmospheric pressure) or less.

[0053] 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.

[0054] 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.

[0055] <<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.

[0056] 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.

[0057] 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 manufacturing method for 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 manufacturing method for monomers for forming chemically recycled resins, the step of pre-selecting the laminate 100 to include a layer containing a non-polyolefin resin using an optical method (a method of selecting the layer containing a non-polyolefin resin using infrared light) and removing the layer containing the non-polyolefin resin can also be omitted. Therefore, according to the manufacturing method of the present disclosure, a high-quality chemically recycled resin can be efficiently produced.

[0058] 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.

[0059] 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.

[0060] This disclosure relates to the following invention. [1] A method for producing a monomer for forming a chemically recycled resin, comprising a base layer, an adhesive resin layer and a sealant layer in this order, wherein at least one of the base layer and the sealant layer contains a polyolefin resin and the adhesive resin layer contains an adhesive resin, The laminate is subjected to an alkaline treatment step in which the laminate is treated with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the substrate layer and the sealant layer. A separation step of separating the polyolefin resin contained in at least one of the substrate layer and the sealant layer from the adhesive resin, A decomposition step is performed to decompose the polyolefin resin separated in the separation step 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 [1], wherein the adhesive resin comprises at least one of a resin containing nitrogen atoms and a 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] A method for producing a monomer for forming a chemically recycled resin according to any one of [1] to [3], wherein the separation step includes a separation step of separating the polyolefin resin and the adhesive resin based on the difference in specific gravity. [5] The method for producing a monomer for forming a chemically recycled resin according to [4], wherein the separation step is a step of removing the adhesive resin as a high-density component with a specific gravity separation liquid. [6] The method for producing a monomer for forming a chemically recycled resin according to [4], wherein the separation step is a step of floating the polyolefin resin as a low-density component with a specific gravity separation liquid. 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 [7][1] to [6], to produce a chemically recycled resin. [Explanation of symbols]

[0061] 10...Base layer, 20, 120A, 120B...Sealant layer, 30...Adhesive resin layer, 40...Alkaline solution, 100...Laminate.

Claims

1. A method for producing monomers for forming chemically recycled resins, comprising a substrate layer, an adhesive resin layer, and a sealant layer in this order, wherein at least one of the substrate layer and the sealant layer contains a polyolefin resin, and the adhesive resin layer contains an adhesive resin, The laminate is subjected to an alkaline treatment step in which the laminate is treated with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the substrate layer and the sealant layer. A separation step of separating the polyolefin resin contained in at least one of the substrate layer and the sealant layer from the adhesive resin, A decomposition step is performed to decompose the polyolefin resin separated in the separation step 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 adhesive resin comprises at least one of a resin containing nitrogen atoms and a resin containing oxygen atoms.

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

4. The method for producing a monomer for forming a chemically recycled resin according to claim 1, wherein the separation step includes a separation step of separating the polyolefin resin and the adhesive resin based on the difference in specific gravity.

5. The method for producing a monomer for forming a chemically recycled resin according to claim 4, wherein the separation step is a step of removing the adhesive resin as a high-density component with a specific gravity separation liquid.

6. The method for producing a monomer for forming a chemically recycled resin according to claim 4, wherein the separation step is a step of floating the polyolefin resin as a low-density component with a specific gravity separation liquid.

7. 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 any one of claims 1 to 6, to produce a chemically recycled resin.

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