Method for producing monomer for forming chemically recycled resin and method for producing chemically recycled resin

Abstract

This method for producing a monomer for forming a chemically recycled resin is a production method in which a laminate including a polyolefin resin is used. This production method comprises: a treatment step in which a laminate is subjected to a treatment for making the laminate separable into a polyolefin resin and a non-polyolefin resin component, which is not a polyolefin resin, thereby obtaining a treated object; a separation step in which the polyolefin resin is separated from the treated object; and a decomposition step in which the polyolefin resin is decomposed to obtain a monomer for forming a chemically recycled resin.

Description

Method for Producing Monomer for Chemical Recycling Resin and Method for Producing Chemical Recycling Resin

[0001] The present disclosure relates to a method for producing a monomer for chemical recycling resin and a method for producing a chemical recycling resin.

[0002] As recycling methods for mixed waste plastics such as PE / PP / PS, a material recycling method and a chemical recycling method 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 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 in the material recycling method can be reused. In addition, 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 monomer obtained from mixed waste plastics is used as a chemical raw material, the amount of fossil resources used is reduced, which also contributes to the reduction of CO ２ 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).

[0003] Isaburo Fuchikawa, "Chemical Recycling of Plastics and Its Technology Development (Part 1)", Asahi Research Center, Ltd., May 2020, p. 5, lines 4-8

[0004] By the way, used packaging containers contained in mixed waste plastics may be composed of a laminate of a layer containing a polyolefin resin and a layer containing a polyester resin or a polyamide resin.

[0005] Furthermore, used packaging containers included in mixed waste plastics may consist of laminates comprising a base layer, an adhesive resin layer, and a sealant layer, and the base layer and sealant layer may also contain polyolefin resin. However, the method described in Non-Patent Document 1 above may result in a small average molecular weight of the resulting chemically recycled resin, or a chemically recycled resin with many branches may be obtained even when attempting 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.

[0006] 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.

[0007] The inventors of this disclosure investigated the reasons why the average molecular weight of the chemically recycled resin obtained by the method described in Non-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 if at least one of nitrogen atoms, oxygen atoms, and chlorine atoms was mixed in the obtained monomer, at least one of these nitrogen atoms, oxygen atoms, and chlorine atoms tended to inhibit polymerization during the process of polymerizing the monomer to obtain a chemically recycled resin, which led to this disclosure.

[0008] One aspect of this disclosure provides a method for producing a monomer for forming a chemically recycled resin using a laminate containing a polyolefin resin, comprising: a processing step of obtaining a processed product by processing the laminate so that it can be separated into the polyolefin resin and a non-polyolefin resin component different from the polyolefin resin; a separation step of separating the polyolefin resin from the processed product; 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 processing step, a processed product is obtained by processing the laminate so that it can be separated into the polyolefin resin and a non-polyolefin resin component different from the polyolefin resin. Here, if the non-polyolefin resin component contains at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, then when the polyolefin resin is separated from the processed product in the separation step, the polyolefin resin will be separated from the non-polyolefin resin component containing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms. For this reason, even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming a chemically recycled resin with a small amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms can be obtained. As a result, when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins, the formation of the chemically recycled resin is less likely to be inhibited by at least one of nitrogen atoms, oxygen atoms, and chlorine atoms. 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 the present disclosure, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured. Furthermore, since the manufacturing method of the present disclosure can produce monomers for forming chemically recycled resins with a small amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, the step of removing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms by hydrogenation when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins can be omitted.

[0009] In the above-described method for producing monomers for forming chemically recycled resins, the laminate comprises a first resin layer containing a hydrolyzable resin and a second resin layer containing a polyolefin resin, and the processing step may include a hydrolysis step in which the laminate is immersed in a liquid phase containing water and subjected to hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer, and a solid-liquid mixture having a liquid phase containing water and the hydrolyzed product of the hydrolyzable resin as the non-polyolefin resin component, and a solid phase containing the polyolefin resin, is obtained as the processed product. According to this manufacturing method, in the hydrolysis step, the laminate is immersed in a liquid phase containing water and subjected to hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer, allowing the hydrolyzed product of the hydrolyzable resin to migrate to the liquid phase. At this time, if the hydrolyzable resin contains at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, the hydrolyzed product will also contain at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, and this hydrolyzed product will migrate to the liquid phase. Furthermore, if the polyolefin resin contained in the second resin layer contains impurities (particularly nitrogen atoms or chlorine atoms), these impurities are removed from the polyolefin resin and migrated to the liquid phase. On the other hand, the polyolefin resin from which the impurities have been removed is not hydrolyzed. As a result, the hydrolysis step yields a solid-liquid mixture containing a liquid phase with water and hydrolyzable resin hydrolysates, and a solid phase with polyolefin resin from which the impurities have been removed. Therefore, when the polyolefin resin is separated from the solid-liquid mixture in the separation step, the polyolefin resin from which the impurities have been removed is separated from hydrolysates containing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms. Thus, even when the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin can be obtained with a low amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms. As a result, when polymerizing such a monomer for forming chemically recycled resin to produce chemically recycled resin, the formation of the chemically recycled resin by at least one of nitrogen atoms, oxygen atoms, and chlorine 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, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured. Furthermore, since a solid-liquid mixture is obtained in the hydrolysis step, which includes a liquid phase containing water and hydrolyzed products of a hydrolyzable resin and a solid phase containing a polyolefin resin from which impurities have been removed, the separation of the polyolefin resin and the removal of impurities can be performed in fewer steps (preferably simultaneously). As a result, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured efficiently. Moreover, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins with a low amount of at least one of nitrogen, oxygen, and chlorine atoms can be obtained, so when polymerizing such monomers for forming chemically recycled resins to produce a chemically recycled resin, the step of removing at least one of nitrogen, oxygen, and chlorine atoms by hydrogenation can be omitted. Furthermore, according to the manufacturing method of this disclosure, 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 light) and removing the first resin layer can be omitted. Therefore, according to the manufacturing method of this disclosure, it is also possible to produce monomers for forming chemically recycled resins that can efficiently produce chemically recycled resins.

[0010] The above method for producing monomers for forming chemically recycled resins is useful when the hydrolyzable resin contains at least one of a hydrolyzable resin containing nitrogen atoms, a hydrolyzable resin containing oxygen atoms, and a hydrolyzable resin containing chlorine atoms. In this case, at least one of the hydrolyzates of the hydrolyzable resin containing nitrogen atoms, the hydrolyzates of the hydrolyzable resin containing oxygen atoms, and the hydrolyzable resin containing chlorine atoms easily migrate to the liquid phase in the hydrolysis step, and the hydrolyzates containing nitrogen atoms, the hydrolyzates containing oxygen atoms, or the hydrolyzates containing chlorine 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 a low amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in.

[0011] The above method for producing a monomer for forming a chemically recycled resin may further include a step of crushing a molded body or laminated film to obtain a laminate before the processing step. If the above processing step is further included, 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. As a result, compared to hydrothermally treating the molded body or laminated film as is, the hydrothermal treatment can be performed more efficiently, and the efficiency of hydrolysis product generation can be improved, so that the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in the solid phase can be reduced, and even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming a chemically recycled resin with a smaller amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in can be obtained.

[0012] In the above-described method for producing monomers for forming chemically recycled resins, the laminate may have a base material and a sealant layer, where one of the base material and the sealant layer contains the first resin layer and the other contains the second resin layer. In this case, during the hydrolysis step, the hydrolyzable resin in the first resin layer contained in one of the base material and 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 contained in the other of the sealant layer and the base material is not hydrolyzed and is therefore contained in the solid phase.

[0013] 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 step, the hydrolyzable resin in the first resin layer contained in the adhesive resin 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 contained in at least one of the base material and the sealant layer of the laminate is not hydrolyzed and is therefore contained in the solid phase.

[0014] 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 the hydrolyzable resin includes a polyester resin, if the temperature of the liquid phase drops below the precipitation temperature of the hydrolyzable resin hydrolysates in the liquid phase, they will precipitate as solids in the liquid phase. In contrast, by adjusting the temperature of the liquid phase of the solid-liquid mixture in the separation step to maintain the temperature of the liquid phase at the end of the hydrolysis step, the precipitation of hydrolysates in the liquid phase as solids is suppressed, and the hydrolysates can be left in the liquid phase. Therefore, it becomes possible to omit the process of separating the polyolefin resin and the solid hydrolysates in the solid phase, and monomers for forming chemically recycled resins can be produced efficiently.

[0015] 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 treatment step is to lower the temperature of the liquid phase of the solid-liquid mixture and treat the solid phase with an alkaline solution. When the hydrolyzable resin contains a polyester resin, when the temperature of the liquid phase of the solid-liquid mixture is lowered, the hydrolyzates of the hydrolyzable resin precipitate as solids in the liquid phase. In contrast, in the alkaline treatment step, even if the temperature of the liquid phase of the solid-liquid mixture is lowered and the hydrolyzates in the liquid phase precipitate as solids, these solid hydrolyzates can be dissolved in the alkaline solution, making it possible to leave the hydrolyzates in the liquid phase. Therefore, it becomes possible to omit the process of separating the polyolefin resin and the solid hydrolyzates in the solid phase, and monomers for forming chemically recycled resins can be produced efficiently.

[0016] In the above-described method for producing monomers for forming chemically recycled resins, the laminate comprises 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, and the processing step includes an alkaline processing step of alkaline processing the laminate with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the base layer and the sealant layer to obtain the processed product, and the separation step is a step of separating the polyolefin resin contained in at least one of the base layer and the sealant layer from the adhesive resin as the non-polyolefin resin component in the processed product. According to this manufacturing method, in the alkaline processing step, the laminate is alkaline processed with an alkaline solution, and the adhesive resin layer is dissolved or swelled and peeled off from the base layer and the sealant layer. Furthermore, if the polyolefin resin contained in at least one of the base layer and the sealant layer contains impurities (especially nitrogen atoms or chlorine atoms), these impurities are removed and transferred to the alkaline solution. Then, in the separation step, the polyolefin resin, from which impurities have been removed, is separated from the adhesive resin, from at least one of the substrate layer and the sealant layer. Therefore, even if the adhesive resin or polyolefin resin is a resin containing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, a polyolefin resin with a low amount of at least one of nitrogen atoms, oxygen atoms, and chlorine 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 at least one of nitrogen atoms, oxygen atoms, and chlorine 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 at least one of nitrogen atoms, oxygen atoms, and chlorine 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, a monomer for forming chemically recycled resin that can produce a high-quality chemically recycled resin can be manufactured.Furthermore, in the alkali treatment step, if the polyolefin resin contained in at least one of the substrate layer and sealant layer contains impurities (particularly nitrogen atoms or chlorine atoms), these impurities are removed and transferred to the alkaline solution. Therefore, the separation of the polyolefin resin and the removal of impurities can be performed in fewer steps (preferably simultaneously). As a result, monomers for forming chemically recycled resins, which can produce high-quality chemically recycled resins, can be efficiently manufactured. Moreover, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins with low levels of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms can be obtained. Therefore, when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins, the step of removing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms by hydrogenation can be omitted. Furthermore, 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. Therefore, according to the manufacturing method of this disclosure, it is also possible to produce monomers for forming chemically recycled resins that can efficiently produce chemically recycled resins.

[0017] 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, a resin containing oxygen atoms, and a resin containing chlorine atoms. This is because, generally, when the adhesive resin contains at least one of a resin containing nitrogen atoms, a resin containing oxygen atoms, and a resin containing chlorine atoms, it is easier to obtain a polyolefin resin with a high amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms.

[0018] The above method for producing monomers for forming chemically recycled resins may further include a step of crushing a molded body or laminated film to obtain a laminate before the processing step. Including a step of crushing a molded body or laminated film to obtain a laminate before the processing step allows for an increase in the cross-sectional area of ​​the adhesive resin layer of the laminate compared to the molded body or laminated film before crushing, thereby increasing the contact area between the adhesive resin layer and the alkaline solution. As a result, 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, improving the efficiency of the dissolution or swelling of the adhesive resin. This reduces the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed into the polyolefin resin, and even when the polyolefin resin is decomposed in the decomposition step, monomers for forming chemically recycled resins with a smaller amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in can be obtained.

[0019] 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 their specific gravity difference. In this case, the polyolefin resin can be easily recovered by separating the polyolefin resin and the adhesive resin by their specific gravity difference.

[0020] 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 solution. If the adhesive resin layer remains undissolved or swollen after the alkali treatment step, the polyolefin resin can be easily recovered by removing the adhesive resin as a high-density component using a specific gravity separation solution, leaving the polyolefin resin behind.

[0021] 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 by a specific gravity separation liquid. In this case, since the polyolefin resin floats as a low-density component by the specific gravity separation liquid, the polyolefin resin can be easily recovered.

[0022] The above-described method for producing monomers for forming chemically recycled resin may include an impurity removal step, prior to the decomposition step, in which at least one impurity, consisting of nitrogen atoms, oxygen atoms, and chlorine atoms, is removed from the polyolefin resin.

[0023] In the above-described method for producing monomers for forming chemically recycled resins, the impurity removal step may be performed in the processing step. In this case, since the impurity removal step and the processing step are performed simultaneously, monomers for forming chemically recycled resins can be produced efficiently.

[0024] Another aspect of this disclosure provides a method for producing a chemically recycled resin, which involves polymerizing the monomer for forming a chemically recycled resin, produced by the above-described method for producing a monomer for forming a chemically recycled resin. According to this method, a monomer for forming a chemically recycled resin can be obtained in which the amount of at least one of nitrogen, oxygen, and chlorine atoms is reduced. As a result, when polymerizing such a monomer to produce a chemically recycled resin, the formation of the chemically recycled resin by at least one of nitrogen, oxygen, and chlorine 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 highly branched chemically recycled resin. Therefore, the method of this disclosure makes it possible to produce a high-quality chemically recycled resin. Furthermore, according to the manufacturing method of the present disclosure, a monomer for forming a chemically recycled resin can be obtained in which the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms is reduced. Therefore, when polymerizing such a monomer for forming a chemically recycled resin to produce a chemically recycled resin, the step of removing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms by hydrogenation can be omitted. In addition, according to the manufacturing method of the monomer for forming a chemically recycled resin, 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 light) and removing the first resin layer can also be omitted. Therefore, according to the manufacturing method of the present disclosure, a high-quality chemically recycled resin can be efficiently produced.

[0025] 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.

[0026] Figure 1 is a schematic cross-sectional view showing a laminate used in the first embodiment of the method for producing a monomer for forming a chemically recycled resin according to the present disclosure. Figure 2 is a schematic cross-sectional view showing the laminate being hydrolyzed in the hydrolysis step of the first embodiment of the method for producing a monomer for forming a chemically recycled resin. Figure 3 is a schematic cross-sectional view showing an example of a laminated film. Figure 4 is a schematic cross-sectional view showing another example of a laminated film. Figure 5 is a schematic cross-sectional view showing a three-layer sealant layer of a laminated film. Figure 6 is a schematic cross-sectional view showing a five-layer sealant layer of a laminated film. Figure 7 is a schematic cross-sectional view showing a laminate used in the second embodiment of the method for producing a monomer for forming a chemically recycled resin according to the present disclosure. Figure 8 is a schematic cross-sectional view showing the laminate in contact with an alkaline solution in the peeling step of the second embodiment of the method for producing a monomer for forming a chemically recycled resin. Figure 9 is a schematic cross-sectional view showing a three-layer sealant layer of a laminate. Figure 10 is a schematic cross-sectional view showing a five-layer sealant layer of a laminate.

[0027] <<Method for producing monomers for forming chemically recycled resins>> The method for producing monomers for forming chemically recycled resins according to this disclosure is a method using a laminate containing a polyolefin resin. This manufacturing method includes a processing step of obtaining a processed product by processing the laminate so that it can be separated into a polyolefin resin and a non-polyolefin resin component different from the polyolefin resin; a separation step of separating the polyolefin resin from the processed product; and a decomposition step of decomposing the polyolefin resin to obtain monomers for forming chemically recycled resins. Here, the non-polyolefin resin component is a component different from the polyolefin resin and includes not only resins different from the polyolefin resin (non-polyolefin resins) but also decomposition products of the non-polyolefin resin (low molecular weight compounds), etc.

[0028] According to this manufacturing method, a processed product is obtained by performing a treatment in the processing step that allows the laminate to be separated into a polyolefin resin and a non-polyolefin resin component different from the polyolefin resin. Here, if the non-polyolefin resin component contains at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, when the polyolefin resin is separated from the processed product in the separation step, the polyolefin resin will be separated from the non-polyolefin resin component containing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms. Therefore, even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with a low amount of at least one of nitrogen atoms, oxygen atoms, and chlorine 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 at least one of nitrogen atoms, oxygen atoms, and chlorine 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, it is possible to produce a monomer for forming chemically recycled resin that can produce a high-quality chemically recycled resin.

[0029] Furthermore, according to the manufacturing method of this disclosure, a monomer for forming chemical recycling resins can be obtained in which the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms is low. Therefore, when polymerizing such a monomer for forming chemical recycling resins to produce a chemical recycling resin, the step of removing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms by hydrogenation can be omitted.

[0030] (First Embodiment) Hereinafter, a first embodiment of the method for producing a monomer for forming a chemically recycled resin according to the present disclosure will be described with reference to Figures 1 to 6.

[0031] The method for producing a monomer for forming a chemically recycled resin according to the first embodiment is a method for producing a monomer for forming a chemically recycled resin using a laminate 100. The laminate 100 shown in Figure 1 comprises 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 chemically recycled resin according to the first embodiment includes a hydrolysis step (see Figure 2) in which the laminate 100 is immersed in a liquid phase 31 containing water and subjected to hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer 10 and a solid-liquid mixture 30 is obtained as a processed product having a liquid phase 31 containing water and hydrolyzed products of the hydrolyzable resin as the non-polyolefin resin component, and a solid phase 32 containing the second resin layer 20; a separation step for separating the polyolefin resin from the solid-liquid mixture 30; and a decomposition step for decomposing the polyolefin resin to obtain a monomer for forming a chemically recycled resin. The hydrolysis step described above is a step in which a processed product is obtained by performing a treatment that makes the laminate 100 separable into a polyolefin resin and a hydrolyzate as a non-polyolefin resin component. In the method for producing a monomer for forming a chemically recycled resin according to the first embodiment, if the hydrolyzable resin contains a polyester resin, the above treatment step may further include an alkali 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. Furthermore, the method for producing a monomer for forming a chemically recycled resin according to the first embodiment may include an impurity removal step before the decomposition step, in which at least one impurity of nitrogen atoms, oxygen atoms, and chlorine atoms is removed from the polyolefin resin.

[0032] 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 to hydrolyze the hydrolyzable resin in the first resin layer 10, allowing the hydrolyzed product of the hydrolyzable resin to migrate to the liquid phase 31. At this time, if the hydrolyzable resin contains at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, the hydrolyzed product will also contain at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, and this hydrolyzed product will migrate to the liquid phase 31. Furthermore, if the polyolefin resin contained in the second resin layer 20 contains impurities (especially nitrogen atoms or chlorine atoms), these impurities are removed, and these impurities also migrate to the liquid phase. On the other hand, the polyolefin resin from which impurities have been removed 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 product of the hydrolyzable resin, and a solid phase 32 containing the polyolefin resin from which impurities have been removed. 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 a hydrolysate containing at least one of nitrogen, oxygen, and chlorine atoms, in addition to having impurities removed. As a result, even when the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin can be obtained that contains a small amount of at least one of nitrogen, oxygen, and chlorine atoms. Consequently, when such a monomer for forming chemically recycled resin is polymerized to produce a chemically recycled resin, the formation of the chemically recycled resin by at least one of nitrogen, oxygen, and chlorine atoms is less likely to be inhibited. In other words, it becomes more difficult to obtain, for example, 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. Furthermore, since the hydrolysis process yields a solid-liquid mixture 30 comprising a liquid phase 31 containing water and hydrolyzable resin hydrolysates, and a solid phase 32 containing polyolefin resin from which impurities have been removed, the separation of the polyolefin resin and the removal of impurities can be carried out in fewer steps (preferably simultaneously).As a result, monomers for forming chemically recycled resins, which are capable of producing high-quality chemically recycled resins, can be efficiently manufactured. Furthermore, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins with a low amount of at least one of nitrogen, oxygen, and chlorine atoms can be obtained. Therefore, when polymerizing such monomers to produce chemically recycled resins, the step of removing at least one of nitrogen, oxygen, and chlorine atoms by hydrogenation can be omitted. In addition, according to the manufacturing method of this disclosure, the step of pre-selecting the laminate 100 to contain the first resin layer 10 using an optical method (a method of selecting the first resin layer 10 using infrared light) and removing the first resin layer 10 can be omitted. Accordingly, according to the manufacturing method of this disclosure, monomers for forming chemically recycled resins, which are capable of efficiently producing high-quality chemically recycled resins, can be manufactured.

[0033] The hydrolysis process, alkali treatment process, separation process, impurity removal process, and decomposition process will be described in detail below.

[0034] (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.

[0035] (First Resin Layer) The hydrolyzable resin contained in the first resin layer 10 is 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 a monomer for forming a chemically recycled resin according to the first embodiment 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 easily migrate to the liquid phase 31 in the hydrolysis step, and the hydrolysates containing nitrogen atoms, hydrolysates containing oxygen atoms, or hydrolysates containing chlorine atoms can be easily separated from the polyolefin resin in the separation step, making it possible to obtain a monomer for forming a chemically recycled resin with a small amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in.

[0036] Examples of polyester resins include oxygen-containing polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN).

[0037] 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.

[0038] The content of hydrolyzable resin in the first resin layer 10 is not particularly limited, but is 100% by mass or less. The content of hydrolyzable resin in the first resin layer 10 may be 95% by mass or less, 90% by mass or less, or 80% by mass or less. The content of hydrolyzable resin in the first resin layer 10 may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 80% by mass or more.

[0039] The first resin layer 10 may be, for example, a base material, an intermediate base material layer, a sealant layer, a surface protection layer, an overcoat layer, or a printing layer.

[0040] (Second 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, but is 100% by mass or less. The content of polyolefin resin in the second resin layer 20 may be 95% by mass or less, 90% by mass or less, or 80% by mass or less. The content of polyolefin resin in the second resin layer 20 may be 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0041] (Laminate) 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 consist of only one second resin layer 20, or it may consist of multiple second resin layers 20. The laminate 100 may be a packaging laminate or a non-packaging laminate.

[0042] 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 is a laminate obtained by crushing a molded body or a laminated film. If 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 that the amount of at least one of nitrogen atoms, oxygen atoms and chlorine atoms mixed in the solid phase 32 can be reduced, and even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with a smaller amount of at least one of nitrogen atoms, oxygen atoms and chlorine atoms mixed in can be obtained. A laminate obtained by crushing a molded body or laminated film can be obtained by a step of crushing a molded body or laminated film to obtain a laminate, prior to the above processing step.

[0043] (Molded body) A molded body is 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.

[0044] (Laminated Film) The laminated film may be composed of the laminated film 100A shown in FIG. 3. The laminated film 100A includes 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, in the hydrolysis step, the hydrolyzable resin in the first resin layer 10 contained in the base material 110 of the laminated film 100A is hydrolyzed, and the hydrolysis product can migrate to the liquid phase 31. Further, since the polyolefin resin in the sealant layer 120 is not hydrolyzed, it is contained in the solid phase 32. In the laminated film 100A, the base material 110 may be composed only of the first resin layer 10, or may include 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 each, and may be plural. Also, the sealant layer 120 may be composed only of the second resin layer 20, or may include 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 each, and may be plural. Furthermore, in the laminated film 100A, the base material 110 may include the second resin layer 20, and the sealant layer 120 may include the first resin layer 10.

[0045] 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 included 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 first resin layers 10 and second resin layers 20 is not limited to one, but may be multiple. Also, it is sufficient that at least one of the substrate 110 and the sealant layer 120 has the second resin layer 20. Therefore, only the substrate 110 may contain the second resin layer 20, only the sealant layer 120 may contain the second resin layer 20, or both the substrate 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.

[0046] 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 resin, polyamide resin, and ester-based polyurethane resin. In laminated film 100B, the adhesive resin layer 130 is a layer containing an adhesive resin that adheres the base material 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 contained in the sealant layer 120 include polyethylene and polypropylene.

[0047] The sealant layer 120 may be configured in a three-layer structure of the second resin layer 20 / the first resin layer 10 / the second resin layer 20, such as the sealant layer 120A shown in FIG. 5, or may be configured in a five-layer structure of the second resin layer 20 / the first resin layer 10 / the third resin layer 40 / the first resin layer 10 / the second resin layer 20, such as the sealant layer 120B shown in FIG. 6. 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 has excellent lamination suitability and can have high piercing strength, sealing property, and bag-breaking strength, and can be suitably used for a sealant layer for lamination or 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, since the three-layer sealant layer 120A has excellent gas barrier properties, it can be suitably used for a barrier sealant layer or a sealant layer for a container resistant to the contents. In the five-layer sealant layer 120B, the second resin layer 20 contains polyethylene or polypropylene as a polyolefin resin, the first resin layer 10 in contact with the second resin layer 20 contains a polyamide resin (for example, nylon), and the third resin layer 40 provided between the two first resin layers 10 may contain an ethylene-vinyl alcohol copolymer (EVOH). In this case, the five-layer sealant layer 120B has high gas barrier properties, excellent lamination suitability, and high piercing strength, and can be suitably used for a sealant layer for lamination or a barrier sealant layer or the like.

[0048] Laminated films 100A and 100B may further comprise a barrier layer. The barrier layer may be, for example, a metal foil, a vapor-deposited layer, a resin film with a vapor-deposited layer, or a coating layer formed by coating with a barrier resin. When 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 foil include aluminum foil. Examples of vapor-deposited layers include metal vapor-deposited layers such as aluminum vapor-deposited layers, 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) and polyolefin resin layers (e.g., stretched polypropylene (OPP) layers, unstretched polypropylene (CPP) layers, polyethylene (PE) layers). Examples of coating layers include ethylene vinyl alcohol copolymer resin (EVOH) layers and polyvinyl alcohol-based resin layers.

[0049] 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 more, or may be 3 mm or more.

[0050] <Liquid Phase> The liquid phase 31 is stored in the container 33 and contains water. As water, deionized water, reverse osmosis water, distilled water, purified water, well water, tap water, industrial water, etc. can be used. 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.

[0051] <Hydrothermal Treatment> The hydrothermal treatment is carried out under a pressure of 101 kPa (1 atm) or higher, by setting the temperature of the liquid phase 31 to a temperature above the temperature at which the hydrolysis reaction of the hydrolyzable resin proceeds. When the hydrolyzable resin is polyethylene terephthalate as a polyester resin, for example, 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 nylon as a polyamide resin, for example, 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 above the decomposition temperature. When the temperature of the liquid phase 31 is above the decomposition temperature of the polyolefin resin, the polyolefin resin becomes low molecular weight, so the amount of polyolefin resin decomposed in the decomposition process can be reduced, and the decomposition process can be carried out efficiently.

[0052] 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 forming chemically recycled resins, the shorter the treatment time, the better, and it is preferably 90 minutes or less. The treatment time may be 60 minutes or less, 40 minutes or less, or 30 minutes or less.

[0053] During hydrothermal treatment, the pressure must be equal to or greater than 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 upper limit on the pressure, and it may be, for example, less than or equal to "critical pressure + 40 MPa".

[0054] 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.

[0055] 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.

[0056] <Solid-Liquid Mixture> The solid-liquid mixture 30 includes a liquid phase 31 and a solid phase 32. The liquid phase 31 includes water and a water-soluble hydrolysate of the hydrolyzable resin. The water-soluble hydrolysate is 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 naphthalene, and oxygen-containing compounds such as diols such as ethylene glycol and butylene glycol. When the hydrolyzable resin is an ester-based polyurethane resin, examples of water-soluble hydrolysates include nitrogen-containing compounds such as isocyanates.

[0057] 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 contains water-insoluble hydrolysates, the solid phase 32 also contains those water-insoluble hydrolysates.

[0058] (2) Alkali treatment step The alkali treatment step is a step included between the hydrolysis step and the separation step when the hydrolyzable resin contains 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, when 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 are dissolved in the alkaline solution during the alkali treatment step, making it possible to leave the hydrolyzates 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, since the separation process is carried out after lowering the temperature of the liquid phase 31 of the solid-liquid mixture 30, it becomes unnecessary to use a highly heat-resistant filter material when separating polyolefin resin by filtration in the separation process. The temperature of the liquid phase 31 of the solid-liquid mixture 30 only needs to be 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 included in the alkaline solution include sodium hydroxide, potassium hydroxide, and ammonia.

[0059] (3) Separation process The separation process is a process of separating the polyolefin resin from the solid-liquid mixture 30. One method for separating the polyolefin resin from the solid-liquid mixture 30 is filtration, but the 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, causing the polyolefin resin to float on the liquid phase 31 and recovering the polyolefin resin. 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 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. If the hydrolyzable resin contains polyester resin, when the temperature of the liquid phase 31 of the solid-liquid mixture 30 decreases and the hydrolyzed product of the hydrolyzable resin falls below the precipitation temperature of the hydrolyzed product in the liquid phase 31, it precipitates as a solid in the liquid phase 31. For example, if the polyester resin is polyethylene terephthalate, when the temperature of the liquid phase 31 of the solid-liquid mixture 30 decreases and the terephthalic acid, which is a hydrolyzed product of the 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, the temperature of the liquid phase 31 of the solid-liquid mixture 30 is adjusted to be maintained at the temperature of the liquid phase 31 at the end of the hydrolysis process. This suppresses the precipitation of hydrolyzed products in the liquid phase 31 as solids, making it possible to retain the hydrolyzed products in the liquid phase 31. Therefore, the process of separating the polyolefin resin from the solid hydrolyzed products in the solid phase 32 can be omitted, and monomers for chemical recycling resin formation can be produced efficiently. 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.

[0060] (4) Impurity Removal Step The impurity removal step is a step of removing at least one impurity from the polyolefin resin, consisting of nitrogen atoms, oxygen atoms, and chlorine atoms. In this case, the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed into the polyolefin resin that is decomposed in the decomposition step can be further reduced, and even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with an even lower amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in can be obtained. The removal of impurities from the polyolefin resin can be carried out, for example, by the same treatment as the hydrolysis step described above. The impurity removal step may be carried out before the decomposition step, between the hydrolysis step and the separation step, between the separation step and the decomposition step, or in the hydrolysis step. When the impurity removal step is carried out in the hydrolysis step, the impurity removal step and the separation step are carried out simultaneously, so monomers for forming chemically recycled resin can be produced efficiently.

[0061] (5) Decomposition process The decomposition process is a process of decomposing the polyolefin resin to obtain monomers for forming chemically recycled resin. The decomposition of the polyolefin resin can be carried out by thermal decomposition. Thermal decomposition can be carried out by placing the polyolefin resin in a container and heating it, and then heating the polyolefin resin to a temperature above the thermal decomposition temperature of the polyolefin resin. 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 in the decomposition process may be 550°C or lower, 500°C or lower, or 450°C or lower. In addition, a catalyst that promotes the decomposition of the polyolefin resin may be used in the decomposition process.

[0062] Furthermore, the pressure inside the container during the decomposition process is not particularly limited, but is preferably, for example, 100 kPa (atmospheric pressure) or less.

[0063] 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 are pyrolysis oils such as naphtha, and by naphtha cracking this pyrolysis oil, monomers for chemical recycling resin formation are obtained. The monomers obtained for chemical recycling resin formation vary depending on the polyolefin resin. If the polyolefin resin is polyethylene, the monomer for chemical recycling resin formation is ethylene, and if the polyolefin resin is polypropylene, the monomer for chemical recycling resin formation is propylene.

[0064] In the first embodiment, a laminate 100 in which the resin contained in the first resin layer 10 is a hydrolyzable resin is described, but this laminate is just one example, and the method for producing a monomer for forming a chemically recycled resin of this disclosure can also be applied to a laminate in which the resin contained in the first resin layer 10 is a polyolefin resin, and can also be applied to a laminate in which all layers other than the adhesive resin layer are polyolefin resins.

[0065] (Second Embodiment) A second embodiment of the method for producing the monomer for forming chemically recycled resins of the present disclosure will be described below with reference to Figures 7 to 10.

[0066] The method for producing monomers for forming chemically recycled resins according to the second embodiment is a method for producing monomers for forming chemically recycled resins using the laminate 100P shown in Figure 7. The laminate 100P comprises a base layer 10P, an adhesive resin layer 30P, and a sealant layer 20P in this order. Here, the adhesive resin layer 30P contains an adhesive resin, and at least one of the base layer 10P and the sealant layer 20P contains a polyolefin resin. Both the base layer 10P and the sealant layer 20P may contain a polyolefin resin. In the method for producing a monomer for forming a chemically recycled resin according to the second embodiment, the above processing steps include: an alkaline treatment step in which the laminate 100P is alkaline-treated with an alkaline solution 40P to dissolve or swell the adhesive resin layer 30P and peel it off from the base layer 10P and the sealant layer 20P to obtain a processed product; a separation step in which the polyolefin resin contained in at least one of the base layer 10P and the sealant layer 20P is separated from the adhesive resin as a non-polyolefin resin component in the processed product; and a decomposition step in which the polyolefin resin separated in the separation step is decomposed to obtain a monomer for forming a chemically recycled resin (see Figure 8). The alkaline treatment step is a step in which a processed product is obtained by performing a treatment on the laminate 100P that makes it separable into a polyolefin resin and an adhesive resin as a non-polyolefin resin component. The method for producing a monomer for forming a chemically recycled resin according to the second embodiment may include an impurity removal step in which at least one impurity of nitrogen atoms, oxygen atoms and chlorine atoms is removed from the polyolefin resin before the decomposition step.

[0067] According to this manufacturing method, in the alkali treatment step, the laminate 100P is alkali-treated with an alkaline solution 40P to dissolve or swell the adhesive resin layer 30P and peel it off from the base layer 10P and the sealant layer 20P. Furthermore, if the polyolefin resin contained in at least one of the base layer 10P and the sealant layer 20P contains impurities (particularly nitrogen atoms or chlorine atoms), these impurities are removed and transferred to the alkaline solution 40P. Then, in the separation step, the polyolefin resin from which impurities have been removed, contained in at least one of the base layer 10P and the sealant layer 20P, is separated from the adhesive resin. Therefore, even if the adhesive resin or polyolefin resin is a resin containing at least one of nitrogen atoms, oxygen atoms, and chlorine atoms, a polyolefin resin with a low amount of at least one of nitrogen atoms, oxygen atoms, and chlorine 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 at least one of nitrogen atoms, oxygen atoms, and chlorine atoms can be obtained. As a result, when polymerizing such monomers for forming chemically recycled resins to produce chemically recycled resins, the formation of the chemically recycled resin by at least one of nitrogen atoms, oxygen atoms, and chlorine 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 the second embodiment, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured. Furthermore, in the alkali treatment step, if the polyolefin resin contained in at least one of the base layer 10P and the sealant layer 20P contains impurities (especially nitrogen atoms or chlorine atoms), these impurities are removed and transferred to the alkaline solution 40P. For this reason, the separation of the polyolefin resin and the removal of impurities can be performed in fewer steps (preferably simultaneously). As a result, monomers for forming chemically recycled resins that can produce high-quality chemically recycled resins can be manufactured efficiently.

[0068] Furthermore, according to the manufacturing method of the second embodiment, a monomer for forming chemical recycled resin with a low amount of at least one of nitrogen, oxygen, and chlorine atoms can be obtained. Therefore, when polymerizing such a monomer for forming chemical recycled resin to produce a chemical recycled resin, the step of removing at least one of nitrogen, oxygen, and chlorine atoms by hydrogenation can be omitted. In addition, according to the manufacturing method of the second embodiment, the laminate 100P can be pre-selected using an optical method (a method of selecting layers containing non-polyolefin resin using infrared light) to remove layers containing non-polyolefin resin, and the step of removing layers containing non-polyolefin resin can be omitted. Accordingly, according to the manufacturing method of the second embodiment, it is also possible to produce a monomer for forming chemical recycled resin that can efficiently produce high-quality chemical recycled resin.

[0069] The alkali treatment process, separation process, impurity removal process, and decomposition process will be described in detail below.

[0070] (1) Alkali treatment process The alkali treatment process involves alkali treatment of the laminate 100P with an alkaline solution 40P to dissolve or swell the adhesive resin layer 30P and peel off the base layer 10P and the sealant layer 20P. The laminate 100P to be alkali treated comprises a base layer 10P, an adhesive resin layer 30P, and a sealant layer 20P in this order.

[0071] <Base Layer and Sealant Layer> Examples of polyolefin resins included in at least one of the base layer 10P and the sealant layer 20P 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 copolymer. Examples of polypropylene include homopolypropylene, block polypropylene, random polypropylene, and propylene-α-olefin copolymer. Examples of α-olefins include ethylene and 1-butene. The polyolefin resin may be included only in the base layer 10P, only in the sealant layer 20P, or in both the base layer 10P and the sealant layer 20P. At least one of the base layer 10P and the sealant layer 20P may contain a resin other than polyolefin resin (hereinafter also referred to as "non-polyolefin resin"). Examples of non-polyolefin resins include polyester resin, polyamide resin, and urethane resin.

[0072] Examples of polyester resins include oxygen-containing polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN).

[0073] 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.

[0074] The polyolefin resin content in the base layer 10P or the sealant layer 20P containing the polyolefin resin is not particularly limited, but is 100% by mass or less. The polyolefin resin content in the base layer 10P or the sealant layer 20P containing the polyolefin resin may be 95% by mass or less, 90% by mass or less, or 80% by mass or less. The polyolefin resin content in the base layer 10P or the sealant layer 20P containing the polyolefin resin may be 20% by mass or more, 30% by mass or more, 50% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0075] The sealant layer 20P 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 9, for example, as the sealant layer 120AP, 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 10, as the sealant layer 120BP.

[0076] In the three-layer sealant layer 120AP, 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 120AP has excellent lamination suitability and can be provided with high puncture strength, sealing properties, and bag breakage strength, making it suitable for use as a sealant layer for lamination and the like. In the three-layer sealant layer 120AP, the first resin layer 20B may contain ethylene vinyl alcohol copolymer (EVOH) instead of polyamide resin. In this case, the three-layer sealant layer 120AP has excellent gas barrier properties and can be suitable for use as a barrier sealant layer or a sealant layer for contents-resistant packaging materials.

[0077] In the five-layer sealant layer 120BP, 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 an 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.

[0078] <Adhesive Resin Layer> The adhesive resin layer 30P may be an anchor layer or an adhesive layer. The adhesive resin contained in the adhesive resin layer 30P is a resin capable of bonding the base layer 10P and the sealant layer 20P. 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. Among these, because they are easily dissolved or swelled in alkaline solutions, it is preferable that the adhesive resin be a resin obtained by curing ester resins, urethane resins, or ether resins using isocyanate. The method for producing a monomer for forming a chemically recycled resin according to the second embodiment is useful when the adhesive resin contains at least one of a resin having nitrogen atoms, a resin having oxygen atoms, and a resin having chlorine atoms. This is because, generally, when an adhesive resin contains at least one of a nitrogen atom-containing resin, an oxygen atom-containing resin, and a chlorine atom-containing resin, it is easier to obtain a polyolefin resin with a high amount of at least one of the nitrogen, oxygen, and chlorine atoms. Examples of adhesive resins containing nitrogen atoms include urethane adhesives. Examples of adhesive resins containing oxygen atoms include acrylic adhesives, epoxy adhesives, silicone adhesives, and polyvinyl ether adhesives.

[0079] <Barrier Layer> The laminate 100P may further comprise a barrier layer. The barrier layer may be, for example, a metal foil, a vapor-deposited layer, a resin film on which a vapor-deposited layer is provided, or a coating layer formed by coating with a barrier resin. When the vapor-deposited layer is provided on a resin film, the vapor-deposited layer may be provided on the surface of the base layer 10P on the side of the sealant layer 20P, on the surface of the base layer 10P opposite to the sealant layer 20P, or on the surface on the side of the sealant layer 20P and on the surface opposite to the sealant layer 20P. Examples of metal foil include aluminum foil. Examples of vapor-deposited layers include metal vapor-deposited layers such as aluminum vapor-deposited layers, 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). Examples of coating layers include ethylene vinyl alcohol copolymer resin (EVOH) layers and polyvinyl alcohol-based resin layers.

[0080] <Laminate> The laminate 100P may be a packaging laminate or a non-packaging laminate.

[0081] The laminate 100P may contain components such as fibers and inorganic materials, but if the laminate 100P is a packaging laminate, the laminate 100P does not need to contain fibers and inorganic materials.

[0082] The laminate 100P 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 30P of the laminate 100P can be increased compared to a molded body or a laminated film, and the contact area between the adhesive resin layer 30P 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 at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed into the polyolefin resin can be reduced, and even when the polyolefin resin is decomposed in the decomposition step, a monomer for forming a chemically recycled resin with a smaller amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in can be obtained. The laminate obtained by crushing a molded body or a laminated film can be obtained by a step of crushing a molded body or a laminated film to obtain a laminate before the above treatment step.

[0083] (Molded body) A molded body is 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.

[0084] The size of the laminate 100P 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 100P may be greater than 0 mm, may be 2 mm or more, or may be 3 mm or more.

[0085] <Alkali Treatment> The alkaline solution 40P 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 30P 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 alone or in mixtures. As water, deionized water, reverse osmosis water, distilled water, purified water, well water, tap water, industrial water, etc., can be used. As alcohol, methanol, ethanol, propanol, isopropanol, etc., can be used. As glycol ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, etc., can be used.

[0086] The temperature of the alkaline solution 40P is not particularly limited, but from the viewpoint of promoting the dissolution or swelling of the adhesive resin layer 30P, it is preferably 40°C or higher, and more preferably 65°C or higher.

[0087] The temperature of the alkaline solution 40P may be 90°C or lower, 85°C or lower, or 80°C or lower. The concentration of alkali in the alkaline solution 40P 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 40P may be 5% by mass or more. Examples of alkalis contained in the alkaline solution 40P include sodium hydroxide, dimethylbis(2-hydroxyethyl)ammonium hydroxide, monomethyltris(2-hydroxyethyl)ammonium hydroxide, and trimethyl-2-hydroxyethylammonium hydroxide.

[0088] The alkali treatment time is not particularly limited, but from the viewpoint of promoting the dissolution or swelling of the adhesive resin layer 30P, it is preferably 30 minutes or more, and more preferably 60 minutes or more. The alkali treatment time may be 240 minutes or less, or 180 minutes or less.

[0089] The pressure during alkaline treatment is not particularly limited and may be atmospheric pressure.

[0090] 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.

[0091] The alkaline treatment may be carried out in a sealed state or in an open state.

[0092] In the alkali treatment step, if the adhesive resin layer 30P is swollen but at least one of the substrate layer 10P and the sealant layer 20P does not peel off from the adhesive resin layer 30P and the laminate 100P remains, stress is applied to the laminate 100P to peel off the substrate layer 10P and the sealant layer 20P from the adhesive resin layer 30P. A method for applying stress to the laminate 100P is, for example, to generate a flow in the alkaline solution 40P (for example, by stirring the alkaline solution 40P).

[0093] (2) Separation process The separation process is a process of separating the polyolefin resin contained in at least one of the base layer 10P and the sealant layer 20P from the adhesive resin.

[0094] If the adhesive resin layer 30P is dissolved in the alkaline solution during the alkali treatment step, the separation step includes a first step of removing the base layer 10P and the sealant layer 20P from the alkaline solution 40P. In this case, since the adhesive resin is dissolved in the alkaline solution 40P and at least one of the base layer 10P and the sealant layer 20P contains polyolefin resin, the polyolefin resin is separated from the adhesive resin. At this time, since the base layer 10 and the sealant layer 20P have been peeled off from the adhesive resin during the alkali treatment step, the base layer 10P and the sealant layer 20P are separated from each other. The first step can be carried out, for example, by filtering the solid-liquid mixture 42 containing the alkaline solution 40P, the base layer 10P and the sealant layer 20P.

[0095] 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") if one of the base layer 10P and the sealant layer 20P does not contain polyolefin resin. The second step may be, for example, a step of separating the non-polyolefin resin-containing layer and the polyolefin resin-containing layer by 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 the specific gravity separation liquid, if the polyolefin resin is to float as a low specific gravity component, a liquid having a specific gravity less than or equal to the specific gravity of the non-polyolefin resin and greater than the specific gravity 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 specific gravity component, so the polyolefin resin can be easily recovered. 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.

[0096] If the adhesive resin layer 30P swells in the alkaline solution 40P during the alkali treatment step, the separation step includes a third step (fractionation step) in which the adhesive resin layer 30P, the base layer 10P, and the sealant layer 20P are removed from the alkaline solution 40P, and then the base layer 10P and the sealant layer 20P are separated from the adhesive resin layer 30P. At this time, since the base layer 10P and the sealant layer 20P have been peeled off from the adhesive resin layer 30P during the alkali treatment step, the adhesive resin layer 30P, the base layer 10P, and the sealant layer 20P are separated from each other. The third step may be, for example, a step of filtering the solid-liquid mixture 42 containing the alkaline solution 40P, the adhesive resin layer 30P, the base layer 10P, and the sealant layer 20P.

[0097] Furthermore, the third step may be a step of separating the adhesive resin layer 30P containing the adhesive resin from the polyolefin resin contained in at least one of the base layer 10P and the sealant layer 20P based on the difference in specific gravity. In this case, a specific gravity separation liquid can be used. As the specific gravity separation liquid, if the polyolefin resin is to be floated as a low specific gravity component, a liquid having a specific gravity less than or equal to the specific gravity of the adhesive resin and greater than the specific gravity 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 specific gravity component, so the polyolefin resin can be easily recovered. Also, as the specific gravity separation liquid, if the adhesive resin is to be removed as a high specific gravity component, a liquid having a specific gravity less than the specific gravity of the adhesive resin and greater than or equal to the specific gravity 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 specific gravity component. Therefore, since the polyolefin resin remains after the adhesive resin is removed, the polyolefin resin can be easily recovered.

[0098] 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 10P and the sealant layer 20P does not contain polyolefin resin. The fourth step may be a step of separating the non-polyolefin resin-containing layer and the polyolefin resin-containing layer by, for example, a difference in specific gravity. In this case, a specific gravity separation liquid can be used. As the specific gravity separation liquid, if the polyolefin resin is to be floated as a low specific gravity component, a liquid having a specific gravity less than or equal to the specific gravity of the non-polyolefin resin and greater than the specific gravity 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 specific gravity component, so the polyolefin resin can be easily recovered. Also, as the specific gravity separation liquid, if the non-polyolefin resin is to be removed as a high specific gravity component, a liquid having a specific gravity less than the specific gravity of the non-polyolefin resin and greater than or equal to the specific gravity of the polyolefin resin is preferred. When this specific gravity separation liquid is used, the non-polyolefin resin settles in the specific gravity separation liquid as a high specific gravity component. Therefore, by removing the non-polyolefin resin, the polyolefin resin remains, making it easy to recover.

[0099] Examples of the specific gravity separation liquid include water, ethanol, and chloroform. Water is preferred among these. Since polyolefin resin has a lower specific gravity than water, the polyolefin resin can be made to float on the water surface, and thus easily separated. The specific gravity separation liquid may be the same as or different from the solvent contained in the alkaline solution 40P. When using the specific gravity separation liquid in the separation process, the temperature of the specific gravity separation liquid is not particularly limited and may be at room temperature.

[0100] (3) Impurity Removal Step The impurity removal step is a step of removing at least one impurity from the polyolefin resin, consisting of nitrogen atoms, oxygen atoms, and chlorine atoms. In this case, the amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed into the polyolefin resin that is decomposed in the decomposition step can be further reduced, and even if the polyolefin resin is decomposed in the decomposition step, a monomer for forming chemically recycled resin with an even lower amount of at least one of nitrogen atoms, oxygen atoms, and chlorine atoms mixed in can be obtained. The removal of impurities from the polyolefin resin can be carried out, for example, by a process similar to the alkali treatment step described above. The impurity removal step may be carried out before the decomposition step, between the alkali treatment step and the separation step, between the separation step and the decomposition step, or in the alkali treatment step. When the impurity removal step is carried out in the alkali treatment step, the impurity removal step and the separation step are carried out simultaneously, so monomers for forming chemically recycled resin can be produced efficiently.

[0101] (4) Decomposition step The decomposition step is a step of decomposing the polyolefin resin separated in the separation step to obtain monomers for forming chemically recycled resin. The decomposition of the polyolefin resin can be carried out by thermal decomposition. Thermal decomposition can be carried out by heating the polyolefin resin after placing it in a container. The temperature in the decomposition step 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 in the decomposition step may be 550°C or lower, 500°C or lower, or 450°C or lower. In addition, a catalyst that promotes the decomposition of the polyolefin resin may be used in the decomposition step.

[0102] Furthermore, the pressure inside the container during the decomposition process is not particularly limited, but is preferably, for example, 100 kPa (atmospheric pressure) or less.

[0103] 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 monomers for chemical recycling resin formation are obtained by naphtha cracking of these pyrolysis oils.

[0104] 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.

[0105] <<Method for Manufacturing Chemical Recycling>> The method for manufacturing chemical recycling resin according to this disclosure is a method for manufacturing chemical recycling resin by polymerizing the monomer for forming chemical recycling resin produced by the above-described method for manufacturing monomer for forming chemical recycling resin.

[0106] According to this manufacturing method, a monomer for forming a chemically recycled resin can be obtained in which the amount of at least one of nitrogen, oxygen, and chlorine atoms is reduced. As a result, when polymerizing such a monomer for forming a chemically recycled resin to produce a chemically recycled resin, the formation of the chemically recycled resin by at least one of nitrogen, oxygen, and chlorine atoms is less likely to be inhibited. In other words, 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 high-quality chemically recycled resin can be produced.

[0107] When the chemically recycled resin is, for example, low-density polyethylene, it can be obtained by polymerizing a monomer for chemical recycling resin formation (ethylene monomer) under high pressure, 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 chemical recycling resin formation (ethylene monomer) at atmospheric pressure, for example. 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, a metallocene catalyst is preferred as the catalyst.

[0108] 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.

[0109] 10...First resin layer, 20...Second resin layer, 30...Solid-liquid mixture, 31...Liquid phase, 32...Solid phase, 100...Laminate, 110...Base material, 120, 120A, 120B...Sealant layer, 130...Adhesive resin layer, 10P...Base material layer, 20P, 120AP, 120BP...Sealant layer, 30P...Adhesive resin layer, 40P...Alkaline solution, 100P...Laminate.

Claims

1. A method for producing a monomer for forming a chemically recycled resin using a laminate containing a polyolefin resin, comprising: a processing step of obtaining a processed product by performing a treatment on the laminate so that it can be separated into the polyolefin resin and a non-polyolefin resin component different from the polyolefin resin; a separation step of separating the polyolefin resin from the processed product; and a decomposition step of decomposing the polyolefin resin to obtain a monomer for forming a chemically recycled resin.

2. The method for producing a monomer for forming a chemically recycled resin according to claim 1, wherein the laminate comprises a first resin layer containing a hydrolyzable resin and a second resin layer containing the polyolefin resin, and the processing step includes a hydrolysis step in which the laminate is immersed in a liquid phase containing water and subjected to hydrothermal treatment to hydrolyze the hydrolyzable resin in the first resin layer, and a solid-liquid mixture having a liquid phase containing water and the hydrolyzed product of the hydrolyzable resin as the non-polyolefin resin component, and a solid phase containing the polyolefin resin, is obtained as the processed product.

3. The method for producing a monomer for forming a chemical recycling resin according to claim 2, wherein the hydrolyzable resin comprises at least one of a hydrolyzable resin containing a nitrogen atom, a hydrolyzable resin containing an oxygen atom, and a hydrolyzable resin containing a chlorine atom.

4. A method for producing a monomer for forming a chemically recycled resin according to claim 2 or 3, further comprising a step of crushing a molded body or laminated film to obtain the laminate before the processing step.

5. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 2 to 4, wherein the laminate has a base material and a sealant layer, and one of the base material and the sealant layer includes the first resin layer and the other includes the second resin layer.

6. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 2 to 5, wherein the laminate comprises a base material, an adhesive resin layer, and a sealant layer, 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.

7. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 2 to 6, wherein the hydrolyzable resin includes a polyester resin, and 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.

8. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 2 to 6, wherein the hydrolyzable resin comprises a polyester resin, and the processing step further includes an alkaline processing 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.

9. The method for producing a monomer for forming a chemically recycled resin according to claim 1, wherein the laminate comprises a base layer, an adhesive resin layer, and a sealant layer in this order, 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 processing step includes an alkaline processing step of alkaline processing the laminate with an alkaline solution to dissolve or swell the adhesive resin layer and peel off the base layer and the sealant layer to obtain the processed product, and the separation step is a step of separating the polyolefin resin contained in at least one of the base layer and the sealant layer from the adhesive resin as the non-polyolefin resin component in the processed product.

10. The method for producing a monomer for forming a chemically recycled resin according to claim 9, wherein the adhesive resin comprises at least one of a resin containing nitrogen atoms, a resin containing oxygen atoms, and a resin containing chlorine atoms.

11. A method for producing a monomer for forming a chemically recycled resin according to claim 9 or 10, further comprising a step of crushing a molded body or laminated film to obtain the laminate before the processing step.

12. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 9 to 11, wherein the separation step includes a separation step of separating the polyolefin resin and the adhesive resin based on the difference in specific gravity.

13. The method for producing a monomer for forming a chemically recycled resin according to claim 12, wherein the separation step is a step of removing the adhesive resin as a high-density component with a specific gravity separation liquid.

14. The method for producing a monomer for forming a chemically recycled resin according to claim 12, wherein the separation step is a step of floating the polyolefin resin as a low-density component with a specific gravity separation liquid.

15. A method for producing a monomer for forming a chemically recycled resin according to any one of claims 1 to 14, comprising an impurity removal step of removing at least one impurity, consisting of a nitrogen atom, an oxygen atom, and a chlorine atom, from the polyolefin resin before the decomposition step.

16. The method for producing a monomer for forming a chemically recycled resin according to claim 15, wherein the impurity removal step is performed in the processing step.

17. A method for producing a chemically recycled resin, comprising polymerizing a monomer for forming a chemically recycled resin, produced by a method for producing a monomer for forming a chemically recycled resin according to any one of claims 1 to 16, to produce a chemically recycled resin.

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