Method for producing residue for recycling

Abstract

A method for producing a recyclable residue from a resin mixture containing a polymer having an ester bond, in which generation of carboxylic acid during decomposition is sufficiently reduced. [Solution] A method for producing residue for recycling, in which a resin mixture containing a polymer having an ester bond (polymer E) is treated with a polymer E depolymerization accelerator to produce a depolymerized product, and the depolymerized product is removed to obtain a residue with a reduced polymer E content.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a residue for recycling. The present invention also relates to a method for producing a depolymerized product, a method for producing terephthalic acid crystals, a method for producing bis(2-hydroxyethyl) terephthalate crystals, and a method for producing a raw material for recycling. [Background technology]

[0002] Various resin products (e.g., plastic products) are used, and resin mixtures (e.g., plastic composite materials) that combine multiple different polymer materials are often used to meet requirements such as product performance and design. In addition, household waste usually contains a mixture of multiple types of resins (e.g., plastics).

[0003] On the other hand, from the perspective of reuse and recycling, separation by polymer material is preferable. However, it is difficult to mechanically or physically separate resin mixtures (e.g., plastic composite materials) and resin waste (plastic waste) by polymer material, and a method for separating them according to chemical reactivity is required.

[0004] Non-Patent Document 1 states that pyrolysis can convert waste plastics that cannot be processed by mechanical recycling into oil and gas, but that polyvinyl chloride (PVC) and polyethylene terephthalate (PET) produce corrosive gases and sublimated substances during pyrolysis, which can reduce the quality of the pyrolysis products and damage the processing plant. Non-Patent Document 2 states that a synergistic effect on the dechlorination of plastics was observed by combining acidic β-zeolite and alkaline hydrotalcite in a 1:1 ratio.

[0005] The group to which the present inventors belong recently reported that terephthalic acid derivatives can be extracted from used PET and PVC, and PET can be repolymerized (Non-Patent Document 3). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of the Japan Petroleum Institute, 59, (6),243-253(2016),Toshiaki Yoshioka et al. “Feedstock Recycling via waste PlasticPyrolysis” [Non-patent document 2] Fuel Processing Technology 248 (2023) 107823, Petr Koutnik et al. “Dechlorination during pyrolysis of plastics: Effect of municipal plastic wastecomposition” [Non-patent document 3] Abstracts of the 33rd Japan Society of Material Cycles and Waste Management Online Lecture, "Mechanism of Terephthalic Acid Derivative Formation in PET-PVC Co-thermal Reaction and Repolymerization of the Derivative to PET," by Akihiro Yoshida et al., published August 29, 2022, https: / / www.jstage.jst.go.jp / article / jsmcwm / 33 / 0 / 33_327 / _article / -char / ja Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide: (1) a method for producing a recyclable residue from a resin mixture containing a polymer having an ester bond (hereinafter also referred to as "Polymer E") in which the generation of carboxylic acid during decomposition is sufficiently reduced; (2) a method for producing a depolymerized product containing carboxylic acid or a derivative thereof from a resin containing a polymer having an ester bond (hereinafter also referred to as "Polymer E") or its residue in such a way that the depolymerized product can be easily separated and recovered; (3) a method for producing crystals of terephthalic acid (TPA) or bis(2-hydroxyethyl) terephthalate (BHET) from a resin mixture containing a reaction product of a diol and terephthalic acid; or (4) a method for producing a recyclable raw material containing TPA, mono(2-chloroethyl) terephthalate (MCET), or bis(2-chloroethyl) terephthalate (BCET) from a resin containing PET. [Means for solving the problem]

[0008] The present disclosure provides, for example, the inventions described in the following [1] to

[36] .

[0009] [1] A method for producing a residue for recycling, which comprises treating a resin mixture containing a polymer having an ester bond (polymer E) with a depolymerization accelerator for polymer E to produce a depolymerized product, removing the depolymerized product, and obtaining a residue with a reduced content of polymer E.

[0010] The recyclable residue produced by the method [1] has a sufficiently reduced amount of carboxylic acid generated during decomposition, as will be described later. Carboxylic acid is an acidic substance that corrodes manufacturing equipment, etc. However, even if the recyclable residue is subjected to processes such as heating and chemical reaction for recycling, the generation of carboxylic acid is suppressed as described above, so that corrosion of manufacturing equipment, etc. is suppressed.

[0011] The above-mentioned residue for recycling is a residue with a reduced content of polymer E. "The content of polymer E is reduced" means that the content of polymer E in the above-mentioned residue is reduced compared to the content of polymer E in a resin mixture containing the same mass of polymer E as the residue. The content of polymer E is reduced by applying a polymer E depolymerization accelerator to a resin mixture containing polymer E.

[0012] [2] The method according to [1], wherein the depolymerization accelerator is at least one selected from the group consisting of hydrogen chloride and chlorine.

[0013] In the case of [2], the depolymerization of polymer E can be carried out more efficiently.

[0014] [3] The resin mixture contains a polymer having a chlorine atom (hereinafter also referred to as “polymer C”), The method according to [2], wherein the depolymerization accelerator contains hydrogen chloride produced by thermal decomposition of polymer C.

[0015] In [3], for example, polymer C is thermally decomposed by a predetermined operation such as heating to generate hydrogen chloride derived from polymer C, and the hydrogen chloride can function as a depolymerization accelerator for polymer E.

[0016] [4] The method according to any one of [1] to [3], wherein the depolymerized product is a carboxylic acid or a derivative thereof.

[0017] [5] The method according to any one of [1] to [4], wherein the depolymerized product is removed in a gaseous state.

[0018] [6] The method according to any one of [1] to [5], wherein the polymer E is a polyester.

[0019] [7] The method according to any one of [1] to [6], wherein the depolymerization accelerator for polymer E is allowed to act on the resin mixture in a heated state.

[0020] [8] The manufacturing method according to [7], wherein the heating temperature is 600°C or less.

[0021] In the cases of [4] and [5], the above-mentioned residue for recycling can be produced more efficiently.

[0022] [9] A method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin containing a polymer having an ester bond (polymer E), comprising the steps of: The production method comprises the steps of: causing a depolymerization accelerator for polymer E to act on the resin, thereby producing a gaseous depolymerized product; isolating the gaseous depolymerized product from the depolymerization reaction system and condensing or sublimating the depolymerized product.

[0023] "Isolated from the depolymerization reaction system" means irreversibly separated to a region that cannot participate in the depolymerization reaction. The "region that cannot participate in the depolymerization reaction" means a region that cannot be converted into a reactant and a product by the depolymerization reaction.

[0024] The depolymerized product produced by the method [9] can be easily separated and recovered from the resin or its residue. For example, if the depolymerized product aggregates or sublimes in the depolymerization reaction system, the depolymerized product may scatter or otherwise come into contact with the resin during recovery, making separation difficult. However, the method [9] allows the depolymerized product to be recovered separated from the depolymerization reaction system, making it easy to separate and recover the depolymerized product from the resin mixture.

[0025] In addition, since the depolymerized product produced by the method [9] is separated from the depolymerization reaction system, the depolymerized product can be recovered without stopping the depolymerization reaction, thereby enabling the depolymerized product to be produced efficiently.

[0026] In addition, the depolymerized product produced by the method [9] has high whiteness and low yellowness. This is believed to be because the depolymerized product is isolated from the depolymerization reaction system and is therefore not or is less susceptible to the influence of the depolymerization reaction system. For example, the depolymerized product may become discolored under high-temperature conditions, but because the depolymerized product is isolated from the depolymerization reaction system, it is not or is less likely to become discolored even when the depolymerization reaction system is at a high temperature.

[0027]

[10] allowing the depolymerization accelerator to act on the resin in a first container containing the resin; The production method according to [9], wherein the gaseous depolymerized product is introduced into a second vessel to be separated from the depolymerization reaction system.

[0028] In the case of

[10] , it is easier to separate and recover the depolymerized product from the resin or its residue.

[0029]

[11] The production method according to

[10] , wherein the polymerization accelerator is introduced into a second vessel together with the depolymerized product, and at least a portion of the depolymerization accelerator introduced into the second vessel is introduced into the first vessel in a gaseous state.

[0030] In the case of

[11] , it is possible to suppress a decrease in the amount of the depolymerization accelerator in the depolymerization reaction system in the first vessel due to the transfer of the depolymerization accelerator to the second vessel, and therefore the depolymerization reaction can be carried out more efficiently. Specifically, the depolymerization reaction can be carried out with a smaller amount of the depolymerization accelerator, and the depolymerization reaction can be carried out at a faster reaction rate.

[0031]

[12] The method according to any one of [9] to

[12] , wherein the depolymerization accelerator is at least one selected from the group consisting of hydrogen chloride and hydrogen.

[0032]

[13] The resin is a resin mixture containing a polymer having a chlorine atom (polymer C), The method according to any one of [9] to

[11] , wherein the depolymerization accelerator is generated by thermal decomposition of polymer C.

[0033] In

[13] , for example, polymer C is thermally decomposed by a predetermined operation such as heating to generate hydrogen chloride derived from polymer C, and the hydrogen chloride can function as a depolymerization accelerator for polymer E.

[0034]

[14] The method according to any one of [9] to

[13] , wherein the polymer E is a polyester.

[0035]

[15] The method according to any one of [9] to

[14] , wherein the depolymerization accelerator for polymer E is allowed to act on the resin in a heated state.

[0036]

[16] The manufacturing method according to

[15] , wherein the heating is performed at a temperature of 600°C or less.

[0037] In the cases of

[13] to

[16] , the depolymerized product can be produced more efficiently.

[0038]

[17] A method for producing crystals of terephthalic acid, the method comprising: allowing hydrogen chloride to act on a resin containing a reaction product of a diol and terephthalic acid, to produce a depolymerized product containing terephthalic acid and an ester of terephthalic acid and a chloroalcohol in which one hydroxyl group of the diol is substituted with a chlorine atom; hydrolyzing the ester to increase the content of terephthalic acid in the depolymerized product; and crystallizing the terephthalic acid during and / or after the hydrolysis.

[0039] The manufacturing method

[17] can produce TPA crystals with a purity of 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, or 100 mol%. Furthermore, the manufacturing method

[17] can produce TPA crystals with a whiteness index (WI) of 50 or more, 60 or more, 70 or more, or 80 or more. Furthermore, the manufacturing method

[17] can produce TPA crystals with a yellowness index (YI) of 50 or less, 40 or less, 30 or less, or 20 or less. Purity refers to the percentage (%) of the amount of TPA contained in the crystals as determined by HPLC relative to the mass of the crystals divided by the molecular weight of TPA. Unless otherwise specified, purity in the following description refers to a similarly determined value.

[0040] In this specification, WI and YI were measured using a spectrophotometer SQ7700 manufactured by Nippon Denshoku Industries Co., Ltd. Specifically, the object to be measured was tightly packed in a glass container made of optical glass, and the SQ7700 was used to irradiate the bottom of the container with white light having a diameter of 6 mm. WI and YI were calculated using the SQ7700 based on the wavelength spectrum of the reflected light. Prior to measuring the object to be measured, the SQ7700 was calibrated so that the WI and YI calculated using a white board as a reference were 100 and 0, respectively.

[0041] The production method

[17] can produce TPA crystals with a yield of 10% or more, 30% or more, 60% or more, or 80% or more. The yield refers to the percentage of the amount of TPA in the crystals relative to the amount of TPA in the depolymerized product when the depolymerized product is hydrolyzed to convert BCET and MCET in the depolymerized product to TPA.

[0042]

[18] The reactant is polyethylene terephthalate; The method according to

[17] , wherein the esters are mono(2-chloroethyl) terephthalate and bis(2-chloroethyl) terephthalate.

[0043]

[19] The method according to

[17] or

[18] , wherein the depolymerized product is hydrolyzed in a heated solvent containing water.

[0044]

[20] The method according to

[19] , wherein the solvent is an aprotic polar solvent.

[0045]

[18] ~

[20] , TPA crystals can be produced more efficiently.

[0046]

[21] A method for producing crystals of bis(2-hydroxyethyl) terephthalate, which comprises the steps of: reacting hydrogen chloride with a resin mixture containing a reaction product of a diol and terephthalic acid; esterifying or transesterifying a depolymerized product containing terephthalic acid and an ester of terephthalic acid and a chloroalcohol (an alcohol substituted with a chlorine atom) in which one hydroxyl group of the diol is substituted with a chlorine atom; and producing and crystallizing bis(2-hydroxyethyl) terephthalate.

[0047] The depolymerized product contains little or no BHET, but the ratio of the amount of BHET to the total amount of TPA, terephthalic acid, a chloroalcohol ester in which one hydroxyl group of the diol is substituted with a chlorine atom, and BHET in the BHET crystals obtained by the production method

[21] can be 20 mol% or more, 50 mol% or more, or 90 mol% or more. The amounts of TPA, terephthalic acid, a chloroalcohol ester in which one hydroxyl group of the diol is substituted with a chlorine atom, and BHET refer to values ​​determined by HPLC. Unless otherwise specified, in the following description, the amounts of TPA, terephthalic acid, a chloroalcohol ester in which one hydroxyl group of the diol is substituted with a chlorine atom, and BHET refer to values ​​determined similarly.

[0048]

[22] The reactant is polyethylene terephthalate, The method according to

[21] , wherein the esters are mono(2-chloroethyl) terephthalate and bis(2-chloroethyl) terephthalate.

[0049]

[23] The method according to

[21] or

[22] , wherein the depolymerized product is esterified or transesterified with ethylene glycol.

[0050]

[24] The production method according to

[23] , wherein the depolymerized product is esterified or transesterified in the ethylene glycol in a heated state.

[0051] In the cases of

[22] -

[24] , BHET crystals can be produced more efficiently.

[0052]

[25] A method for producing a raw material for recycling containing bis(2-chloroethyl) terephthalate, comprising contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, with a solvent, removing a matter insoluble in the solvent, including the terephthalic acid and the mono(2-chloroethyl) terephthalate, and obtaining the bis(2-chloroethyl) terephthalate dissolved in the solvent, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0053] The manufacturing method of

[25] makes it possible to produce a raw material for recycling that contains no or little TPA and MCET, but contains BCET.

[0054]

[26] The method according to

[25] , wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

[0055]

[27] A depolymerization product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, is brought into contact with a first solvent, and the bis(2-chloroethyl) terephthalate dissolved in the first solvent is separated from a matter insoluble in the first solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate; a method for producing a recycle raw material containing mono(2-chloroethyl) terephthalate, the method comprising contacting the insoluble matter with a second solvent to remove the insoluble matter in the second solvent containing the terephthalic acid, and obtaining the mono(2-chloroethyl) terephthalate dissolved in the second solvent, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively; The production method, wherein the solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

[0056] The manufacturing method of

[27] makes it possible to produce a raw material for recycling that contains no or little TPA and BCET, but contains MCET.

[0057]

[28] The production method according to

[27] , wherein the first solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

[0058]

[29] The production method according to

[27] or

[28] , wherein the second solvent is at least one solvent selected from the group consisting of ether solvents, ketone solvents, ester solvents, and alcohol solvents.

[0059]

[30] A depolymerization product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, is brought into contact with a first solvent, and the bis(2-chloroethyl) terephthalate dissolved in the first solvent is separated from a matter insoluble in the first solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate; A method for producing a recycling raw material containing terephthalic acid, comprising contacting the insoluble matter with a second solvent to obtain a matter insoluble in the second solvent containing the terephthalic acid, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively; The production method, wherein the solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

[0060] The manufacturing method of

[30] makes it possible to produce a raw material for recycling that contains no or little BCET and MCET and contains TPA.

[0061]

[31] The production method according to

[30] , wherein the first solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

[0062]

[32] The production method according to

[30] or

[31] , wherein the second solvent is at least one solvent selected from the group consisting of ether solvents, ketone solvents, ester solvents, and alcohol solvents.

[0063]

[33] A method for producing terephthalic acid crystals, comprising: contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, with a solvent; removing insoluble matter in the solvent, including the terephthalic acid and the mono(2-chloroethyl) terephthalate, to obtain bis(2-chloroethyl) terephthalate dissolved in the solvent; and hydrolyzing the obtained bis(2-chloroethyl) terephthalate to produce terephthalic acid and crystallize the same, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0064] The production method

[33] can produce TPA crystals with a purity of 80 mol% or more, 90 mol% or more, or 95 mol% or more. The production method

[33] can produce TPA crystals with a yield of 50% or more, 60% or more, or 70% or more. The yield refers to the percentage of the amount of TPA contained in the crystals relative to the amount of BCET.

[0065]

[34] The method according to

[33] , wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

[0066] The production method

[34] can further improve the purity and yield.

[0067]

[35] A depolymerization product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, which is produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, is brought into contact with a solvent, and the bis(2-chloroethyl) terephthalate dissolved in the solvent is separated from a matter insoluble in the solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate; A method for producing terephthalic acid crystals, comprising hydrolyzing the insoluble matter to increase the content of terephthalic acid in the insoluble matter, and crystallizing the terephthalic acid during and / or after the hydrolysis, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0068] The production method

[35] can produce TPA crystals with a purity of 80 mol% or more, 90 mol% or more, or 95 mol% or more. The production method

[35] can also produce TPA crystals with a WI of 50 or more, 60 or more, 70 or more, or 80 or more. The production method

[35] can also produce TPA crystals with a YI of 30 or less, 20 or less, or 10 or less.

[0069] The production method

[35] can produce TPA crystals with a yield of 70% or more, 80% or more, or 90% or more, where the yield is the percentage of the amount of TPA contained in the crystals relative to the total amount of TPA and MCET contained in the toluene-insoluble matter.

[0070]

[36] The method according to

[35] , wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

[0071] The production method

[36] can further improve the yield.

[0072] The present disclosure also provides the inventions described in [1A] to [10A] below. [1A]: A plastic containing a polymer having an ester bond (hereinafter referred to as polymer (E)) and a polymer having a chlorine atom (hereinafter referred to as polymer (C)) is thermally decomposed at a temperature equal to or higher than the temperature at which a thermal decomposition product is generated from polymer (C), Separating the carboxylic acid compound and its derivatives derived from the polymer (E) from the plastic using the pyrolysis product; The method for recycling plastics includes obtaining a secondary reuse material from the plastics, in which the content of the carboxylic acid compound and its derivatives derived from the polymer (E) is reduced. [2A]: The method for recycling plastics according to [1A], wherein the pyrolysis product is a chlorine-containing pyrolysis product. [3A]: The method for recycling plastics according to [1] or [2], wherein the reduction rate of the carboxylic acid compound and its derivatives is 40 mol % or more. [4A]: The method for recycling plastics according to any one of [1A] to [3A], further comprising the step of reducing the chlorine atoms by 85 mol % or more. [5A]: The method for recycling plastics according to any one of [1A] to [4A], wherein the secondary reuse material contains charcoal and / or hydrocarbon compounds as a main component. [6A]: The method for recycling plastics according to any one of [1A] to [5A], wherein the thermal decomposition temperature is 600°C or lower. [7A]: The method for recycling plastics according to any one of [1A] to [6A], wherein the carboxylic acid compound and its derivatives are sublimated, and then cooled and separated. [8A]: The method for recycling plastics according to any one of [1A] to [7A], wherein the carboxylic acid compound and its derivative are at least one selected from the group consisting of terephthalic acid, mono(2-chloroethyl) terephthalate, bis(2-chloroethyl) terephthalate, mono(2-chloroethyl) 2,6-naphthalenedicarboxylate, bis(2-chloroethyl) 2,6-naphthalenedicarboxylate, bis(4-chlorobutyl) terephthalate, bis(3-chloropropyl) terephthalate, isophthalic acid, 2,5-furandicarboxylic acid, and derivatives thereof. [9A]: The method for recycling plastics according to any one of [1A] to [8A], wherein the carboxylic acid compound, a derivative thereof, or a compound derived therefrom is used to repolymerize a polyester resin. [10A]: A method for obtaining a pyrolysis residue with a reduced content of acidic substances by heating a polymer having chlorine atoms (hereinafter referred to as polymer (C)) and a polymer having an ester bond (hereinafter referred to as polymer (E)) and separating acidic substances derived from polymer (C) and polymer (E) while suppressing the generation of chlorine-containing gas.

[0073] As described above, the present invention provides a method for recycling plastics containing a polymer (E) having an ester bond, in which the plastics have reduced carboxylic acid compounds and their derivatives derived from the polymer (E) are extracted as secondary use materials (e.g., solid fuel, oil-recycled raw material, recycled plastic raw material), and a method for obtaining pyrolysis residues.

[0074] That is, the embodiments [1A] to [10A] have the excellent effect of providing a method for recycling plastics, in which a plastic containing a polymer (E) having an ester bond has reduced carboxylic acid compounds and their derivatives derived from the polymer (E) is extracted as a secondary use material (e.g., solid fuel, oil-recycled raw material, recycled plastic raw material), and a method for obtaining a pyrolysis residue. [Effects of the Invention]

[0075] The present invention can provide: (1) a production method for producing a recyclable residue from a resin mixture containing a polymer having an ester bond (hereinafter also referred to as "polymer E") in which the generation of carboxylic acid during decomposition is sufficiently reduced; (2) a production method for producing a depolymerized product containing carboxylic acid or a derivative thereof from a resin containing a polymer having an ester bond (hereinafter also referred to as "polymer E") or its residue in such a way that the depolymerized product can be easily separated and recovered; (3) a production method for producing crystals of terephthalic acid (TPA) or bis(2-hydroxyethyl) terephthalate (BHET) from a resin mixture containing a reaction product of a diol and terephthalic acid; or (4) a production method for producing a recyclable raw material containing TPA, mono(2-chloroethyl) terephthalate (MCET), or bis(2-chloroethyl) terephthalate (BCET) from a resin containing PET. [Brief explanation of the drawings]

[0076] [Figure 1] FIG. 1 is a flowchart showing an example of a method for recycling plastics according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a plastic processing device used in the method for recycling plastics according to the present embodiment. It can also be said to be a schematic diagram illustrating an example of an apparatus used in the method for producing recyclable residue according to the present embodiment. [Figure 3] 1 is a schematic diagram illustrating an example of a plastic processing device used in a plastic recycling method according to a modified example. It can also be said to be a schematic diagram illustrating an example of an apparatus used in a method for producing recyclable residue according to a modified example. [Figure 4] 1 is a graph plotting the pressure and temperature in the vessel over time in the thermal decomposition test of Test Example 19. [Figure 5] 1 is a graph plotting the pressure and temperature inside the vessel over time in the thermal decomposition test of Test Example 20. [Figure 6] FIG. 2 shows a molecular weight curve of the polyethylene and a recycle residue according to the present embodiment obtained from a resin mixture containing a polymer (polymer E) and polyethylene. [Figure 7] FIG. 1 is a schematic diagram illustrating an example of an apparatus used in a production method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin mixture containing a polymer having an ester bond (polymer E) according to the present embodiment. [Figure 8] FIG. 2 is a schematic diagram illustrating an example of an apparatus used in the method for producing a recyclable residue according to the present embodiment. [Figure 9] 1 shows HPLC chromatograms of the depolymerized product and the crystals obtained by the method for producing TPA crystals (part 1) according to the present embodiment. [Figure 10] 1H-NMR spectrum of commercially available TPA. [Figure 11] 1 is a 1H-NMR spectrum of a crystal obtained by the method for producing a TPA crystal (part 1) according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0077] The present disclosure will be described in detail below. Needless to say, other embodiments are also included within the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure. Furthermore, in this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range. Unless otherwise noted, each component may be used independently, either alone or in combination of two or more types. The numerical values ​​described in this specification refer to values ​​obtained by the method described in the Examples below.

[0078] [Method for producing residue for recycling] In the method for producing a residue for recycling according to this embodiment, a depolymerization accelerator for polymer E is applied to a resin mixture containing polymer E to produce a depolymerized product, and the depolymerized product is then removed to obtain a residue with a reduced content of polymer E.

[0079] The recyclable residue produced from a resin mixture containing polymer E by the method for producing a recyclable residue according to this embodiment has a sufficiently reduced amount of carboxylic acid generated during decomposition. The phrase "the amount of carboxylic acid generated during decomposition is sufficiently reduced" in relation to the recyclable residue means that when the resin mixture containing polymer E and an equal mass of the recyclable residue are decomposed using the decomposition method described below, the total amount of carboxylic acid generated from the recyclable residue is smaller than that of the resin mixture containing polymer E. For example, when the total amount of carboxylic acid generated from the resin mixture containing polymer E is taken as 100%, the percentage (%) of the total amount of carboxylic acid generated from the recyclable residue is subtracted from 100 (hereinafter referred to as the "reduction rate (%) of the amount of carboxylic acid generated during decomposition"), which is 1% or more, 10% or more, 20% or more, 40% or more, 60% or more, 80% or more, 90% or more, 95% or more, or 99% or more. This means that the recyclable residue has a "sufficiently reduced amount of carboxylic acid generated during decomposition." Furthermore, when polymer E is a polyester, the "amount of substance of TPA" can be treated as the "total amount of substance of carboxylic acids." The total amount of substance of carboxylic acids can be measured using HPLC in a conventional manner. The HPLC conditions may be the same as those used in the examples described below.

[0080] The "decomposition method" described above involves adding 0.1 g of the target substance (a resin mixture or recycle residue containing polymer E) to 15 mL of methanol, adding 2 mL of a 35% by mass aqueous solution of tetrapropylammonium hydroxide, and then heating at 75°C for 7 days. This decomposition method can hydrolyze ester bonds.

[0081] The resin mixture containing polymer E may contain two or more types of polymer E, or may contain one or more types of polymer E and one or more types of resin other than polymer E.

[0082] The resin mixture containing polymer E may be, for example, one contained in household waste, clothing, industrial waste, or the like.

[0083] Polymer E is a polymer having an ester bond, which is a chemical bond represented by the structural formula R-COO-R' (R and R' are monovalent organic groups). Examples of Polymer E include polymers having an ester bond in the main chain, such as polyester, and polymers having an ester bond in the side chain, with polymers having an ester bond in the main chain being preferred, and polyester being more preferred.

[0084] Examples of polyesters that are polymer E include reaction products of dicarboxylic acids and diols. Examples of such reaction products include polyethylene terephthalate (PET) in which the dicarboxylic acid is terephthalic acid and the diol is ethylene glycol, PET-G in which the dicarboxylic acid is terephthalic acid and the diol is a mixture of ethylene glycol and cyclohexane 1,4-dimethanol, polyethylene naphthalate (PEN) in which the dicarboxylic acid is 2,6-naphthalenedicarboxylic acid and the diol is ethylene glycol, polyethylene furanoate (PEF) in which the dicarboxylic acid is 2,5-furandicarboxylic acid and the diol is ethylene glycol, polybutylene terephthalate, and polyethylene succinate. The reaction product of terephthalic acid and diol is preferred, and PET is more preferred.

[0085] In addition to the above, examples of the dicarboxylic acid in the reaction product of the dicarboxylic acid and the diol include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorene acid.

[0086] The diol in the reaction product of the dicarboxylic acid and the diol may be an alkylene diol, for example, an alkylene diol having 2 to 5, 2 to 4, or 2 to 3 carbon atoms.

[0087] In addition to the above, examples of the diol in the reaction product of the dicarboxylic acid and the diol include 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecaneethanol, tetracyclododecanedimethanol, tetracyclododecanediethanol, decalindimethanol, decahydronaphthalenedi ... Examples of suitable hydroxyethyl ethers include carlindiethanol, 5-methylol-5-ethyl-2-(1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, and bis-β-hydroxyethyl terephthalate (BHET).

[0088] The polyester that is the polymer E may be a reaction product of an ester of a dicarboxylic acid, a dicarboxylic acid chloride or a dicarboxylic acid anhydride with a diol.

[0089] The upper limit of the content of polymer E in the resin mixture containing polymer E may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the resin mixture. The lower limit of the content of polymer E in the resin mixture containing polymer E may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, based on the total amount of the resin mixture. These upper and lower limits can be freely combined as long as the upper limit is greater than the lower limit.

[0090] Resins other than the above-mentioned polymer E include polymer C; olefin-based resins such as polyethylene and polypropylene (which refer to homopolymers of olefins, copolymers of different olefins, and copolymers of olefins and compounds other than olefins having ethylenically unsaturated groups); polystyrene; polyurethane; polymethyl methacrylate; vinyl acetate resin; polycarbonate; ABS resin; polyphenol; polyamide; polyacetal; fluororesin; melamine resin; epoxy resin; polyimide; polyvinyl alcohol, etc., with polymer C or olefin-based resins being preferred, and polymer C or polyethylene being more preferred. Naturally, the resin mixture containing the above-mentioned polymer E does not necessarily have to contain polymer C.

[0091] Polymer C is a polymer having chlorine atoms, and typically has chlorine atoms in its side chains. Examples of polymer C include polyvinyl chloride (PVC), polyvinylidene chloride, chlorinated polyethylene, polychloroprene, and chlorinated natural rubber, with PVC being preferred from the viewpoint of efficient generation of hydrogen chloride.

[0092] Polymer C may also be a reaction product of vinyl chloride (CH═CHCl) with a compound having an ethylenically unsaturated group. Examples of the compound having an ethylenically unsaturated group include vinyl esters such as vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate and butyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; maleic esters such as butyl maleate and diethyl maleate; vinyl ethers such as vinyl methyl ether, vinyl butyl ether, and vinyl octyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; α-olefins such as ethylene and propylene; styrenes and their substitution products such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, and chlorostyrene; vinylidene halides other than vinyl chloride, such as vinylidene chloride and vinyl bromide; and vinyl halides.

[0093] When the resin mixture containing polymer E contains polymer C, the upper limit of the content of polymer C in the resin mixture containing polymer E may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the resin mixture. When the resin mixture containing polymer E contains polymer C, the lower limit of the content of polymer C in the resin mixture containing polymer E may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, based on the total amount of the resin mixture. These upper and lower limits can be freely combined as long as the upper limit is greater than the lower limit.

[0094] When the resin mixture containing polymer E contains polymer C, the mass ratio of polymer E to polymer C in the resin mixture containing polymer E may be 1:8 to 16:1, 1:8 to 8:1, 1:4 to 12:1, 1:2 to 8:1, 1:1 to 7:1, 2:1 to 6:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, or 7:1. When polymer E is PET and polymer C is PVC, the mass ratio of PET to PVC in the resin mixture containing polymer E may be 1:1 to 6:1 or 2:1 to 3:1. Furthermore, the mass ratio of carboxylic acid-derived groups in polymer E to chlorine atoms in the resin mixture containing polymer E may be 2:1 to 1:6 or 1:1 to 1:2.

[0095] The upper limit of the olefin resin content in the resin mixture containing polymer E may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more, based on the total amount of the resin mixture. The lower limit of the olefin resin content in the resin mixture containing polymer E may be 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, based on the total amount of the resin mixture. These upper and lower limits can be freely combined as long as the upper limit is greater than the lower limit.

[0096] In addition to the resins described above, the resin mixture containing polymer E may also contain other components such as components used in the synthesis of the resin, such as catalysts and initiators; additives for imparting specific functions to the resin (e.g., flame retardants, antistatic agents, plasticizers, UV protection agents, fillers, etc.); and, if the resin mixture is contained in household waste, clothing, industrial waste, etc., materials derived from these sources (e.g., blended fibers, cellulose, nylon fibers, metals, concrete, wood, building materials, water, organic solvents, dyes, paints, etc.). The total content of the other components in the resin mixture containing polymer E may be 10% by mass or less, 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total amount of the resin mixture.

[0097] An example of the depolymerization accelerator for polymer E is a depolymerization accelerator capable of decomposing (e.g., hydrolyzing) the ester bond of polymer E. Examples of the depolymerization accelerator include hydrogen chloride (hydrogen chloride gas), chlorine (chlorine gas), and radicals. At least one selected from the group consisting of hydrogen chloride and chlorine is preferred, and hydrogen chloride is more preferred.

[0098] When the resin mixture containing polymer E contains polymer C, at least a portion of the depolymerization accelerator for polymer E may be generated by thermal decomposition of polymer C. Examples of substances generated by thermal decomposition of polymer C include hydrogen chloride (hydrogen chloride gas), chlorine (chlorine gas), and radicals, with hydrogen chloride being preferred. Examples of the radical species include radical species generated by cleavage of the C-Cl bond in polymer C.

[0099] The thermal decomposition of polymer C can be carried out, for example, by heating a resin mixture containing polymer E. The heating temperature can be appropriately set depending on the type of polymer E, etc., but the lower limit may be 170°C or more, 200°C or more, 250°C or more, or 300°C or more, and the upper limit may be 600°C or less, 500°C or less, or 450°C or less. These conditions and lower limits can be freely combined. When polymer E is PVC, the heating temperature may be 170 to 180°C.

[0100] The method for treating a resin mixture containing polymer E with a depolymerization accelerator for polymer E is not particularly limited, as long as it is performed in a manner that produces a depolymerized product. For example, from the viewpoint of efficiently producing a depolymerized product, the depolymerization accelerator for polymer E may be treated with a resin mixture containing polymer E in a heated state. The heating state may be, for example, 600°C or less, 500°C or less, or 450°C or less. These heating states may be 170°C or more, 200°C or more, 250°C or more, or 300°C or more. The time for treating a resin mixture containing polymer E in a heated state with the depolymerization accelerator for polymer E may be 1 to 60 hours, 2 to 55 hours, 5 to 50 hours, 10 to 45 hours, 15 to 40 hours, 20 to 35 hours, or 25 to 30 hours.

[0101] Furthermore, the action of the depolymerization accelerator for polymer E on the resin mixture containing polymer E may be carried out in a vacuum. For example, the resin mixture containing polymer E may be placed in a vacuum container, and the depolymerization accelerator for polymer E may be supplied to the container. In this specification, a pressure of 1 kPa or less can be considered a vacuum.

[0102] The depolymerization accelerator for polymer E is not particularly limited as long as it can depolymerize polymer E, and may be a commercially available depolymerization accelerator (for example, a depolymerization accelerator contained in a gas cylinder) or a depolymerization accelerator such as hydrogen chloride generated by thermal decomposition of polymer C.

[0103] Furthermore, when the resin mixture containing polymer E contains a resin other than polymer E, the heating condition may be set to a temperature at which the resin undergoes no or little thermal decomposition. In this case, it is possible to produce a residue for recycling containing the resin in which thermal decomposition has not progressed or has hardly progressed (the molecular weight has not been reduced or has hardly been reduced).

[0104] When a depolymerization accelerator capable of decomposing the ester bonds of polymer E acts on polymer E, the decomposition of the ester bonds can produce alcohols and carboxylic acids or carboxylic acid derivatives. When heated, the alcohols can decompose into hydrogen gas, alkenes, water, etc.

[0105] The depolymerized product varies depending on the composition of the resin mixture containing polymer E. The depolymerized product typically contains a carboxylic acid or a derivative thereof derived from polymer E, and in this case can be referred to as a "depolymerized product containing a carboxylic acid or a derivative thereof." For example, when the resin mixture contains PET as polymer E, the depolymerized product typically contains terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate. When the resin mixture contains PEN as polymer E, the depolymerized product typically contains naphthalene dicarboxylic acid, mono(2-chloroethyl) 2,6-naphthalene dicarboxylate, and bis(2-chloroethyl) 2,6-naphthalene dicarboxylate. When the resin mixture contains polybutylene terephthalate as polymer E, the depolymerized product typically contains terephthalic acid and bis(4-chlorobutyl) terephthalate. When the resin mixture contains polypropylene terephthalate as polymer E, the depolymerized product typically contains terephthalic acid and bis(3-chloropropyl) terephthalate.

[0106] As described above, the carboxylic acid contained in the depolymerized product may be at least one selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, mono(2-chloroethyl) terephthalate, and mono(2-chloroethyl) 2,6-naphthalenedicarboxylic acid.

[0107] The derivative of carboxylic acid contained in the depolymerized product includes an ester of carboxylic acid and halogenated alcohol, which is a compound having no carboxy group. The halogenated alcohol includes chlorinated alcohol. The halogenated alcohol may have 2 to 10 or 2 to 4 carbon atoms. The halogenated alcohol may have 1 to 2 or 1 halogen atom. Examples of the halogenated alcohol include 2-chloroethanol, 3-chloropropanol, and 4-chlorobutanol. The carboxylic acid may be the same as the carboxylic acid contained in the depolymerized product described above.

[0108] As described above, the carboxylic acid derivative contained in the depolymerized product may be at least one selected from the group consisting of bis(2-chloroethyl) terephthalate, bis(2-chloroethyl) 2,6-naphthalenedicarboxylate, bis(4-chlorobutyl) terephthalate, and bis(3-chloropropyl) terephthalate.

[0109] The depolymerized product can be removed, for example, by removing the depolymerized product in a gaseous state. For example, the depolymerized product generated by the depolymerization reaction may be separated from the depolymerization reaction system in a gaseous state, condensed or sublimated, and the resulting solid or liquid depolymerized product may be discarded. Examples of such a separation method include a method in which the depolymerized product is transported in a gaseous state by an air current.

[0110] When heated during the manufacturing process, the residue for recycling contains charcoal, hydrocarbon compounds, etc. Furthermore, when the resin mixture containing polymer E contains a resin other than polymer E as described above, the residue for recycling may contain the resin or a depolymerized product of the resin.

[0111] As described above, the generation of carboxylic acids during decomposition of the residue for recycling is sufficiently reduced, and therefore the residue for recycling can be suitably used as a solid fuel, a raw material for oils and fats, a liquefied fuel, etc.

[0112] Next, an example of a method for producing a recyclable residue according to this embodiment will be described with reference to Fig. 2. The method for producing a recyclable residue described below is merely one aspect of this embodiment, and naturally, this embodiment is not limited to the following content.

[0113] Fig. 2 shows an example of an apparatus for producing a residue for recycling. The apparatus 101 shown in Fig. 2 includes a pyrolysis furnace 1, a plastic (which can also be called a resin mixture) supply port 2 connected to the pyrolysis furnace 1, a sublimate (which can also be called a depolymerized product) capture section 3, and pipes 4, 5, and 8 that connect the pyrolysis furnace 1 and the capture section 3. In the apparatus 101, gas is circulated in the direction of the arrows in the figure (from pyrolysis furnace 1, pipe 4, pipe 5, sublimate capture section 3, pipe 8, to pyrolysis furnace 1 in that order) by a gas suction means such as a pump.

[0114] The supply port 2 can be freely opened and closed, and a resin mixture containing polymer E can be introduced into the pyrolysis furnace 1 from the outside through the supply port 2 as needed.

[0115] The resin mixture is placed in the pyrolysis furnace 1, and a depolymerization accelerator is supplied thereto, allowing the depolymerization accelerator to act on the resin mixture, thereby producing a depolymerized product and a residue. At this time, by externally heating the first container, it is possible to accelerate the depolymerization reaction and maintain the depolymerized product in a gaseous state. The depolymerization accelerator may be supplied to the pyrolysis furnace 1 from an external source. In this case, the supply source may be a gas cylinder containing the depolymerization accelerator, a container containing polymer C, or the like. By heating the container containing polymer C, a depolymerization accelerator such as hydrogen chloride can be produced.

[0116] Furthermore, when the resin mixture contains polymer C, the pyrolysis furnace 1 may be heated from the outside to thermally decompose the polymer C, and the depolymerization reaction may be advanced by the depolymerization accelerator such as hydrogen chloride thus generated. In this case, the depolymerization accelerator may or may not be supplied from the outside of the first vessel.

[0117] When the resulting depolymerized product is in a gaseous state, the depolymerized product is guided by the airflow produced by the gas suction means to the capture unit 3 via the pipes 4 and 5. In this case, in order to maintain the depolymerized product in a gaseous state, the pipes 4 and 5 can be heated from the outside, the circulation flow rate can be increased, or the like.

[0118] The depolymerized products in a gaseous state introduced into the capture unit 3 are cooled in the capture unit 3, and condense or sublimate into a liquid or solid, which accumulates in the capture unit 3. By collecting the depolymerized products accumulated in this manner, the depolymerized products can be removed from the residue.

[0119] Next, an example of a method for producing a recyclable residue according to this embodiment will be described with reference to Fig. 3. The method for producing a recyclable residue described below is merely one aspect of this embodiment, and naturally, this embodiment is not limited to the following content.

[0120] FIG. 3 shows an example of an apparatus for producing a residue for recycling. The apparatus 102 shown in FIG. 3 includes a horizontal processing furnace 10, a plastic (which can also be called a resin mixture) supply inlet 2 connected to the horizontal processing furnace 10, and a pyrolysis residue outlet 13 and exhaust outlet 14 connected to the horizontal processing furnace 10 on the longitudinal opposite side of the supply inlet. The exhaust outlet 14 is connected to the top of the processing furnace 10, and the outlet 13 is connected to the bottom of the processing furnace 10. The horizontal processing furnace 10 has a heating section (heating zone) 11 and a cooling section (cooling zone) 12, and the heating section 11 is located between the cooling section 12 and the supply inlet 2. In the apparatus 102, the exhaust outlet 14 draws in gas, so that the gas flows from the supply inlet 2 to the exhaust outlet 14.

[0121] The supply port 2 can be freely opened and closed, and a resin mixture containing polymer E can be introduced into the pyrolysis furnace 10 from the outside through the supply port 2 as needed. A depolymerization accelerator can also be introduced into the horizontal treatment furnace 10. The depolymerization accelerator can act on the resin mixture in the heating section 11, for example, thereby generating a depolymerized product and a residue. At this time, the depolymerized product can be maintained in a gaseous state by being heated in the heating section 11. The depolymerized product in a gaseous state is solidified or sublimated in the cooling section. This allows the depolymerized product to be removed from the residue.

[0122] Next, an example of a method for producing a recyclable residue according to this embodiment will be described with reference to Fig. 8. The method for producing a recyclable residue described below is merely one aspect of this embodiment, and naturally, this embodiment is not limited to the following content.

[0123] Fig. 8 shows an example of an apparatus for producing a residue for recycling. The apparatus 106 shown in Fig. 8 includes a third container 24, a fourth container 26, a fifth container 28, a third connecting pipe 34 connecting the third container 24 and the fourth container 26, and a fourth connecting pipe 36 connecting the fourth container 26 and the fifth container 28.

[0124] The third communication pipe 34 is provided with a cock 34a. By operating the cock 34a, communication between the third container 24 and the fourth container 26 can be opened or closed.

[0125] The fourth communicating pipe 36 includes a pump 36a, a cock 36b, and a cock 36c. By operating the pump 36a, gas can be introduced from the cock 36b to the fifth container 28. By operating the cocks 36b and 36c, communication between the fourth container 26 and the pump 36a, between the fourth container 26 and the fifth container 28, and between the pump 36a and the fifth container 28 can be independently opened or closed.

[0126] The apparatus 106 is evacuated, polymer C is placed in the third container 24, and the third container 24 is heated with the cock 34a open and the cock 36b closed. This causes the polymer C to thermally decompose, generating hydrogen chloride, and the third container 24 and the fourth container 26 are filled with hydrogen chloride. By cooling the fourth container 26 to −40 to −80°C, impurities other than hydrogen chloride generated by the thermal decomposition of the polymer C in the fourth container 26 can be solidified, sublimated, or the like, and remain in the fourth container 26. Then, the cock 36b is operated to open communication between the fourth container 26, the pump 36a, and the fifth container 28, and the hydrogen chloride in the fourth container 26 can be introduced into the fifth container 28 by operating the pump 36a. By storing a resin mixture containing polymer E in the fifth container 28 in advance, the hydrogen chloride introduced into the fifth container 28 as described above can be allowed to act on the resin mixture containing polymer E to produce a depolymerized product and a residue. When the hydrogen chloride is allowed to act on the resin mixture containing polymer E, the cock 36b can be closed, and the fifth container 28 can be heated from the outside. The produced depolymerized product and residue can be recovered.

[0127] The following Aspect A can be cited as one aspect of the method for producing a recyclable residue according to this embodiment. The content described in Aspect A can be freely incorporated into the method for producing a recyclable residue according to this embodiment described above, and the content described in the method for producing a recyclable residue according to this embodiment described above can be freely incorporated into Aspect A. In the following Aspect A, "plastic" can be read as "resin."

[0128] [Aspect A] FIG. 1 shows an example of a flowchart for the plastic recycling method of this embodiment. In this plastic recycling method, a plastic containing a polymer having chlorine atoms (hereinafter referred to as polymer (C)) and a polymer having ester bonds (hereinafter referred to as polymer (E)) is thermally decomposed at a temperature equal to or higher than the temperature at which thermal decomposition products are generated from polymer (C) (Step 1). Furthermore, the thermal decomposition products generated from polymer (C) are used to decompose polymer (E), and carboxylic acid compounds and their derivatives (hereinafter simply referred to as "acidic substances") derived from polymer (E) are separated from the plastic (Step 2). It is then confirmed whether the acidic substances derived from polymer (E) have been sufficiently reduced from the plastic (Step 3). If the reduction in the acidic substances is not sufficient, Steps 1 and 2 are continued. Once the reduction in the acidic substances is sufficient, the plastic residue is extracted as a secondary reuse material (Step 4). Note that Step 3 is not required; at least Steps 1, 2, and 4 are sufficient.

[0129] In addition to reducing carboxylic acid compounds and their derivatives, which are acidic substances derived from polymer (E), from the residual plastics, it is more preferable to reduce chlorine-containing compounds derived from polymer (C) from the residual plastics. Examples of compounds containing chlorine atoms include acidic substances such as hydrogen chloride, chlorine gas, and chlorine-containing organic compounds. Chlorine gas dissolves in water to produce hydrochloric acid, and is therefore classified as an acidic substance in this specification. Furthermore, most chlorine-containing organic compounds generate hydrogen chloride upon combustion, and therefore chlorine-containing organic compounds are classified as acidic substances in this specification. In this specification, the content of chlorine atoms derived from polymer (C) may be referred to as the content of acidic substances derived from polymer (C). Each step is described in detail below.

[0130] <Step 1> Step 1 is a process of thermally decomposing a plastic containing polymer (C) and polymer (E) at a temperature equal to or higher than the temperature at which pyrolysis products are generated from polymer (C). The plastic may be any plastic containing polymer (C) and polymer (E). Examples include plastic waste such as household waste and industrial waste. The plastic may also contain other materials besides plastic, such as metal, concrete, wood, building materials, liquids such as water and organic solvents, dyes, paints, fibers such as cellulose, etc., without departing from the spirit of the present disclosure.

[0131] Polymer (C) is a polymer having a chlorine atom. Polymer (E) is a polymer having an ester bond. An ester bond is a chemical bond represented by the structural formula R-COO-R' (R and R' are monovalent organic groups). Examples of polymer (E) include polyesters having an ester bond in the main chain and polymers having an ester bond in the side chain. Polymers (C) and (E) may each independently be one type or two or more types.

[0132] The pyrolysis products of polymer (C) include not only decomposition products of polymer (C) but also substances in the process of decomposition. Examples of pyrolysis products of polymer (C) include chlorine-containing pyrolysis products. Specific examples of chlorine-containing pyrolysis products include chlorine-containing gases such as hydrogen chloride gas and chlorine gas, and radical species generated by cleavage of C-Cl bonds on polymer chains. Radical species generated by cleavage of C-C or C-H bonds in polymer (C) can also be generated from radical species generated by cleavage of C-C bonds or C-H bonds. The chemical species that actually promote the decomposition of polymer (E) may be hydrogen ions (H+) generated by dissociation of hydrogen chloride gas in the pyrolysis products or cleavage of C-H bonds.

[0133] Because polymer (C) has chlorine in its side groups or side chains, it is prone to dechlorination or radical generation at relatively low temperatures. These chlorine-containing pyrolysis products promote the decomposition of the ester bonds of polymer (E) even at temperatures where polymer (E) alone does not undergo thermal decomposition. In other words, the pyrolysis products from polymer (C) can promote the decomposition of the ester bonds of polymer (E) even at temperatures where polymer (E) alone does not undergo thermal decomposition.

[0134] The pyrolysis of the plastic can be carried out in an airtight or open container. From the viewpoint of scale-up, it is preferable to carry out the pyrolysis in an open container, while an airtight container is preferable from the viewpoint of reliable recovery of chlorine-containing pyrolysis products. The atmosphere in the airtight container may be an inert atmosphere such as nitrogen or argon, or air. Furthermore, it may be carried out at normal pressure, or under increased, reduced, or vacuum pressure.

[0135] The temperature at which pyrolysis products are generated varies depending on conditions such as the type of polymer (C) and pressure, but typically, chlorine-containing pyrolysis products are generated by heating to 200°C or higher. Since polyvinyl chloride, a general-purpose plastic, generates chlorine-containing pyrolysis products at 170 to 180°C, the lower limit of the pyrolysis temperature is preferably 170°C. The lower limit of the pyrolysis temperature is more preferably 250°C, and even more preferably 300°C. Chlorine-free pyrolysis products are also generated, mainly derived from chlorine-containing pyrolysis products, and it is believed that these also contribute to the decomposition of polymer (E).

[0136] The position of the ester bond in the polymer (E) may be in the main chain, side chain, or side group. From the viewpoint of more effectively achieving the effects of the present disclosure, the polymer (E) is preferably a polyester resin having an ester bond in the main chain. The polymer (E) having an ester bond in the main chain does not decompose when used alone, unless heated at a temperature exceeding 400°C. On the other hand, in the presence of chlorine-containing thermal decomposition products of the polymer (C), decomposition due to main chain scission of the polymer (E) may occur even at temperatures below 400°C.

[0137] The upper limit of the thermal decomposition temperature may be set appropriately depending on the components of the plastic and the equipment. From the viewpoint of efficiently extracting the thermal decomposition residue of the plastic as a secondary reuse material, the upper limit is preferably 600°C, more preferably 500°C, and even more preferably 450°C.

[0138] The thermal decomposition time for this plastic can be set as desired. Typically, the heating time at a temperature of 200 to 600°C is about 1 to 60 hours. Specific examples of the heating time include 2 hours, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, and 55 hours. By setting the heating time to 1 to 60 hours, the decomposition of polymer (C) in the plastic proceeds sufficiently, generating a sufficient amount of chlorine-containing thermal decomposition products and promoting the decomposition of the ester bonds in polymer (E).

[0139] Specific examples of the polymer (C) include polyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene, polychloroprene, and chlorinated natural rubber. Other examples include copolymers of vinyl chloride monomer with one or more monomers copolymerizable with the above-mentioned monomer, and chlorine-added polymers in which chlorine is added to a polymer.

[0140] Monomers copolymerizable with vinyl chloride monomer include vinyl esters such as vinyl acetate and vinyl propionate; acrylic esters such as methyl acrylate and butyl acrylate; methacrylic esters such as methyl methacrylate and ethyl methacrylate; fumarates such as butyl maleate and diethyl maleate; vinyl ethers such as vinyl methyl ether, vinyl butyl ether, and vinyl octyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; α-olefins such as ethylene and propylene; styrenes and their substituted derivatives such as styrene, α-methylstyrene, vinyltoluene, t-butylstyrene, and chlorostyrene; vinylidene halides and vinyl halides other than vinyl chloride, such as vinylidene chloride and vinyl bromide; and phthalates such as diallyl phthalate. From the viewpoint of efficiently promoting the decomposition of polymer (E), polymer (C) is preferably polyvinyl chloride.

[0141] Specific examples of the polymer (E) include polyethylene terephthalate (PET), in which the dicarboxylic acid component is terephthalic acid and the diol component is ethylene glycol, polyethylene naphthalate (PEN), in which the dicarboxylic acid component is 2,6-naphthalenedicarboxylic acid and the diol component is ethylene glycol, and polyethylene furanoate (PEF), in which the dicarboxylic acid component is 2,5-furandicarboxylic acid and the diol component is ethylene glycol. Further examples include polybutylene terephthalate and polyethylene succinate.

[0142] Other dicarboxylic acid components include, for example, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, decalindicarboxylic acid, terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodiumsulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenanthrenedicarboxylic acid, 9,9'-bis(4-carboxyphenyl)fluorene acid, and ester-forming derivatives thereof. Examples of ester-forming derivatives include esters of dicarboxylic acids, dicarboxylic acid chlorides, and dicarboxylic acid anhydrides.

[0143] Examples of diol components other than those mentioned above include 1,2-propanediol, 1,3-propanediol, butanediol, 2-methyl-1,3-propanediol, hexanediol, neopentyl glycol, cyclohexanedimethanol, cyclohexanediethanol, decahydronaphthalenedimethanol, decahydronaphthalenediethanol, norbornanedimethanol, norbornanediethanol, tricyclodecanedimethanol, tricyclodecaneethanol, tetracyclododecanedimethanol, tetracyclododecanediethanol, decalindimethanol, decalindimethanol, 5-methylol-5-ethyl-2-( 1,1-dimethyl-2-hydroxyethyl)-1,3-dioxane, cyclohexanediol, bicyclohexyl-4,4'-diol, 2,2-bis(4-hydroxycyclohexylpropane), 2,2-bis(4-(2-hydroxyethoxy)cyclohexyl)propane, cyclopentanediol, 3-methyl-1,2-cyclopentadiol, 4-cyclopentene-1,3-diol, adamantanediol, paraxylene glycol, bisphenol A, bisphenol S, styrene glycol, trimethylolpropane, pentaerythritol, and bis-β-hydroxyethyl terephthalate (BHET) may also be used.

[0144] The majority of commonly used resins found in household waste are polyester resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, and PET. Therefore, the majority of polymer (C) in plastics found in household waste is polyvinyl chloride, and the majority of polymer (E) is polyester resins such as PET. Olefin-based plastics such as polyethylene and polypropylene, as well as polystyrene, undergo main chain scission during thermal decomposition. Their thermal decomposition onset temperature is typically around 400°C, higher than that of polymer (C). Therefore, when thermal decomposition is performed near the temperature at which chlorine-containing pyrolysis products are generated from polymer (C), olefin-based plastics and polystyrene do not substantially decompose. For example, when the thermal decomposition temperature is set above 500°C, olefin-based plastics and polystyrene also undergo thermal decomposition, but since they do not substantially react with the chlorine-containing pyrolysis products, the main chains of these plastics, such as olefin-based plastics with low molecular weights, remain in the secondary recycling material.

[0145] The plastic may include plastics other than those listed above without departing from the spirit of the present disclosure. Examples of the plastic include polyurethane, polymethyl methacrylate, vinyl acetate resin, polycarbonate, ABS resin, polyphenol, polyamide, polyacetal, fluororesin, melamine resin, epoxy resin, polyimide, and polyvinyl alcohol. As mentioned above, other materials besides plastic may also be included without departing from the spirit of the present disclosure.

[0146] It is not necessary for the polymer (E) and polymer (C) to be in contact with each other during pyrolysis. In other words, it is sufficient that the chlorine-containing pyrolysis products dechlorinated from polymer (C) can come into contact with polymer (E). For example, this plastic may also include a case where the container containing polymer (E) and the container containing polymer (C) are separate, and the chlorine-containing pyrolysis products of polymer (C) are supplied to polymer (E) through a connecting pipe.

[0147] Plastics can be subjected to Step 1 in the same state as they are collected as waste. Eliminating the pretreatment step simplifies the process. On the other hand, from the perspective of improving the efficiency of the heat treatment process, pulverization as a pretreatment is preferable. Pulverization significantly increases the surface area of ​​the plastic, significantly increasing the decomposition rate of polymer (E) by chlorine-containing pyrolysis products generated from polymer (C). From a cost perspective, relatively large-sized pulverized plastics, such as granules, are preferable, while powder-sized pulverized plastics are preferable from the perspective of shortening the heat treatment time. Furthermore, if the heating temperature in Step 1 is above the melting temperature of polymer (E), pulverization as a pretreatment significantly improves the mixing and kneading efficiency. As a result, a significant reduction in the heat treatment time can be expected.

[0148] As a preliminary step to step 1, a process of separating out different materials contained in the plastic before the crushing process may be performed. For example, magnetic materials may be collected by magnetic force, or concrete may be collected by specific gravity. Furthermore, after crushing, centrifugal separation may be performed to remove different materials by specific gravity.

[0149] The plastic may contain catalysts, initiators, or additives (e.g., flame retardants, antistatic agents, plasticizers, UV protection agents, and fillers) used in the synthesis of the plastic material to impart specific functions to the plastic material. For example, metal particles, metal oxide particles, ceramic particles, etc. may be contained in the plastic. These may be removed in advance using magnetic force or specific gravity, or they may be removed at the pyrolysis residue stage, or they may be used directly as solid fuel without being removed.

[0150] From the viewpoint of promoting effective decomposition of polymer (E), the mass ratio of polymer (E) to polymer (C) in the plastic is preferably 1:8 to 8:1. Specific examples of the mass ratio include 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, and 7:1. From the viewpoint of efficiently utilizing chlorine-containing pyrolysis products in the decomposition reaction of the ester bonds of polymer (E) and preventing excessive amounts of chlorine-containing pyrolysis products, when polyvinyl chloride is selected as polymer (E) and polyethylene terephthalate is selected as polymer (C), the mass ratio is preferably 3:1 to 2:1. In other combinations, the molar ratio of the carboxylic acid-derived structure in the dicarboxylic acid-derived structural unit constituting polymer (E) to the chlorine atoms constituting polymer (C) is preferably 1:1 to 1:2. It is preferable that polymer (C) be primarily composed of polyvinyl chloride, and polymer (E) be primarily composed of PET. The term "major component" as used herein refers to the component that is most abundant in each of polymers (C) and (E). The main component is preferably 40% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0151] The plastic may be sampled to monitor the chlorine concentration and ester bond concentration in the plastic, and any missing components may be replenished using off-cuts from the production line at the factory.

[0152] <Step 2> Step 2 is a process in which polymer (E) is decomposed using pyrolysis products generated from polymer (C) by pyrolysis, and acidic substances (carboxylic acid compounds and their derivatives) containing structures derived from polymer (E) are separated from the plastic. Examples of derivatives of carboxylic acid compounds include chlorine-containing carboxylic acid compound derivatives consisting of carboxylic acid components obtained by decomposing the ester bonds of polymer (E).

[0153] Figure 2 shows a schematic diagram illustrating an example of a plastic processing device used in this plastic recycling method. As shown in the figure, the plastic processing device 101 has a pyrolysis furnace 1, a plastic supply port 2, and a sublimate capture unit 3. The pyrolysis furnace 1 and the capture unit 3 are connected by pipes 4, 5, and 8. Gas is sucked in the direction of the arrow in the figure by a gas suction means (not shown).

[0154] Above the pyrolysis furnace 1, there is a plastic supply port 2 that can be opened and closed freely, and, in response to instructions from a control unit (not shown), for example, crushed plastic is supplied from the plastic supply port 2 at appropriate times.

[0155] The pyrolysis furnace 1 is heated to a temperature above the temperature at which pyrolysis products are generated from the polymer (C). The heating softens the plastic, and in some cases, it may even melt. The heating promotes the decomposition of the polymer (E) in the pyrolysis furnace 1. Specifically, pyrolysis products are generated from the polymer (C), which promotes the decomposition of the ester bonds in the polymer (E), resulting in the production of carboxylic acid compounds and their derivatives, which are acidic substances containing structures derived from the polymer (E). The ester bonds in the polymer (E) are preferably decomposed into carboxylic acid compounds or their derivatives and alcohols or their derivatives. The alcohols or their derivatives may be recovered by solvent extraction, sublimation, or other means. This makes it possible to recycle the raw materials for the polymer (E). The plastic recycling method disclosed herein allows for efficient removal of acidic substances derived from the polymer (E), which is advantageous in avoiding equipment deterioration.

[0156] It is preferable that the pipe 4 is kept warm to prevent the precipitation of the sublimate, while it is preferable that the pipe 5 has a cooling mechanism. A specific example of a cooling structure is to provide a flow path through which a cooling medium passes inside or outside the pipe 5. Any gas such as air or any liquid such as water can be used as the cooling medium. The temperature of the cooling medium may be any temperature at which the sublimate solidifies, for example, room temperature.

[0157] According to this method, by heating the polymer (C) at a temperature or higher at which chlorine-containing pyrolysis products are produced, the decomposition of the polymer (E) can be promoted even at temperatures below the decomposition temperature of the polymer (E), and the decomposition of the ester bonds of the polymer (E) has the excellent effect of enabling the recovery and recycling of raw materials derived from the polymer (E).

[0158] When PET is used as polymer (E), decomposition of the ester bonds in polymer (E) produces acidic substances such as terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate. When PEN is used as polymer (E), naphthalene dicarboxylic acid, mono(2-chloroethyl) 2,6-naphthalene dicarboxylic acid, and bis(2-chloroethyl) 2,6-naphthalene dicarboxylic acid are obtained. When polybutylene terephthalate is used as polymer (E), terephthalic acid, bis(4-chlorobutyl) terephthalate, and the like are obtained. When polypropylene terephthalate is used as polymer (E), terephthalic acid and bis(3-chloropropyl) terephthalate are obtained.

[0159] Examples of methods for recovering the acidic substance generated in step 2 include recovering it as a sublimate and dissolving it in a solvent and separating it. If the acidic substance can be extracted as a sublimate at the pyrolysis temperature, a simple method is to gasify it, separate it, and then separate it as a solid. Figure 2 shows an example of recovery as a sublimate. The carboxylic acid compound and its derivatives that have become gaseous as sublimates are cooled in cooling section 9 via pipes 4 and 5 and recovered as a solid from the sublimate in capture section 3. The cooling temperature in capture section 3 is arbitrary and can be set to, for example, 20 to 150°C. On the other hand, hydrogen chloride gas and chlorine gas, which are chlorine-containing pyrolysis products, remain gaseous even after cooling, so they are returned to pyrolysis furnace 1 and used to promote the decomposition of polymer (E).

[0160] If the amount of polymer (C) in the plastic is insufficient relative to the amount of polymer (E), the amount of carboxylic acid compounds containing structures derived from polymer (E) and their derivatives will not be sufficiently reduced. Prior to supplying the plastic, the ratio of polymer (E) to polymer (C) in the plastic may be sampled, and the insufficient component may be added as necessary to ensure that the amount of carboxylic acid compounds containing structures derived from polymer (E) and their derivatives is sufficiently reduced. Alternatively, a chlorine-containing pyrolysis product supply port (not shown) may be provided in the pyrolysis furnace 1, and the required amount of chlorine-containing pyrolysis product may be supplied.

[0161] Figure 3 is a schematic diagram illustrating another example of a plastic processing device used in the modified plastic recycling method. As shown in the figure, the plastic processing device 102 has a heating section 11 and a plastic supply port 2 on the left side of a horizontal processing furnace 10, and a cooling section 12, a pyrolysis residue outlet 13, and an exhaust port 14 on the right side. Acidic substances can be recovered in the cooling section 12. The device may be tilted as needed to prevent molten raw plastic from reaching the cooling section 12 without reacting.

[0162] In terms of downsizing, it is advantageous to collect gases sublimated in the heating section of a plastics processing device above the device. However, if a cooling section is provided above the heating section, there is a risk that the acidic substances collected in the capture section will fall into the heating section due to gravity or that they will clog a filter or the like provided between the heating section and the cooling section. In this modified plastic processing device, the cooling section, which captures acidic substances, and the heating section, which performs thermal decomposition, are arranged horizontally. This allows the acidic substances pyrolyzed in the heating section to be efficiently separated, effectively preventing the acidic substances from being mixed back into the pyrolysis residue and the filter installed between the heating section and the cooling section from being clogged.

[0163] <Step 3> Step 3 is a process for confirming that the acidic substances (carboxylic acid compounds and their derivatives) derived from the polymer (E) have been sufficiently reduced from the plastic. The reduction rate of the plastic may be appropriately set depending on the application and purpose. For example, the reduction rate of the acidic substances can be confirmed by sampling the plastic.

[0164] The secondary reuse material is, for example, solid fuel or oil and fat raw material. The reduction rate of acidic substances in the plastic extracted as the secondary reuse material is preferably 40 mol% or more. According to the plastic recycling method disclosed herein, acidic substances derived from polymer (E) can be reduced from plastic, thereby effectively alleviating the problems of corrosion of equipment when solid fuel is used for thermal recycling and release of acidic substances derived from polymer (E) into the atmosphere.

[0165] When the polymer (E) is a polyester resin, the ester bond is decomposed to decompose the polymer into an alcohol and a carboxylic acid or its derivative. In this case, the carboxylic acid or its derivative becomes an acidic substance. Therefore, when the polymer (E) is a polyester resin, it is desirable that the ester bond is decomposed and that the acidic carboxylic acid or its derivative does not remain in the thermal decomposition residue of the plastic. That is, it is preferable that the acidic carboxylic acid or its derivative does not remain in the thermal decomposition residue of the plastic, and it is more preferable that the ester bond does not remain in the polymer (E). The reduction rate of the acidic substance derived from the polymer (E) can be determined, for example, by the method described in the Examples below. The reduction rate of the acidic substance is preferably 40 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more.

[0166] <Step 3-2> An optional step may be included to confirm that the chlorine content of the plastic has been sufficiently reduced (hereinafter also referred to as step 3-2). This can be confirmed by sampling the plastic and measuring the chlorine content. Alternatively, the chlorine content of the plastic in the pyrolysis furnace 1 may be measured at appropriate times using a sensor installed in the pyrolysis furnace 1.

[0167] The chlorine reduction rate of the polymer (C) is determined, for example, as in the Examples described later. The chlorine reduction rate is preferably 30 mol% or more, more preferably 45 mol% or more, even more preferably 85 mol% or more, and particularly preferably 99 mol% or more.

[0168] The plastic recycling method disclosed herein has the excellent effect of reducing not only acidic substances derived from polymer (E) but also acidic substances (chlorine-containing compounds) derived from polymer (C) from plastics. Because the acidic substances derived from polymer (E) and polymer (C) can be significantly reduced, excellent secondary reuse materials can be extracted. For example, this method can effectively alleviate the problems of equipment corrosion when using solid fuel for thermal recycling and the release of acidic substances derived from polymer (E) and polymer (C) into the atmosphere.

[0169] <Step 4> Step 4 is the process of extracting plastics as secondary reuse materials. Secondary reuse materials include solid fuels, oil and fat raw materials, and liquefied fuels. Secondary reuse materials are primarily composed of charcoal and / or hydrocarbon compounds. Here, the term "major component" refers to the component with the largest mass in the secondary reuse material. If the secondary reuse material contains charcoal and hydrocarbon compounds, the combined amount of these components may be the component with the largest mass ratio.

[0170] Acidic substances such as carboxylic acids and their derivatives pose problems of corrosion and pipe blockage. Furthermore, the residues generated during chemical recycling are primarily composed of hydrocarbons. If these residues contain acidic substances such as carboxylic acids and their derivatives, they produce acidic gases during combustion, resulting in corrosion of equipment and the need for flue gas treatment. Similar issues can arise in thermal recycling, which involves directly burning plastics. To address this issue, adding hydrated lime to plastic raw materials has been proposed (Eiichi Ono et al., "Development of Dechlorination Technology for Recycling Used Plastic Containers and Packaging into Oil," Journal of the Japan Society of Material Cycles and Waste Management, Vol. 22, No. 3, pp. 178-189, 2011). However, the use of hydrated lime leaves calcium residues in the residues, which can lead to serious problems when reusing the residues, especially when using them as fuel, such as increased ash content requiring industrial waste disposal and calcium adhesion to the incinerator.

[0171] This method can promote the thermal decomposition of polymer (E) at low temperatures. The carboxylic acid compounds and their derivatives, which are generated from the ester bonds of polymer (E), can then be obtained. As a result, acidic substances (carboxylic acid compounds and their derivatives derived from polymer (E) and chlorine-containing compounds derived from polymer (C)) can be efficiently removed from residual plastics at temperatures lower than the thermal decomposition temperature of polymer (E).

[0172] According to this method for recycling plastics, acidic substances derived from polymer (E) can be removed from multiple plastics that are difficult to separate into single plastic materials, and a secondary reuse material suitable as a solid fuel for thermal recycling or a raw material for chemical recycling by liquefaction can be obtained. Therefore, the secondary reuse material is suitable as a solid fuel or a raw material for liquefaction, which have become increasingly important in recent years due to the recent tight energy demand and rising prices of resource fuels.

[0173] Furthermore, this method allows for easy separation of carboxylic acid compounds containing structures derived from polymer (E), their derivatives, and compounds derived therefrom from the pyrolysis residue by methods such as sublimation. By subjecting these carboxylic acid compounds, their derivatives, or compounds derived therefrom, such as sublimates, purified sublimates, or sublimates to a specific treatment, it is possible to isolate, for example, monocarboxylic acids or polycarboxylic acids with two or more carboxy groups as monomers and use them as raw materials for polyester resins, which can then be repolymerized. Furthermore, these compounds can be used as monomers for products other than polyester resins, or as various additives such as plasticizers and flame retardants, or as reaction reagents.

[0174] The present disclosure further provides a method for significantly reducing the content of acidic substances in a pyrolysis residue that can be reused as a fat or oil raw material, by heating polymer (C) and polymer (E) and separating acidic substances derived from polymer (C) and polymer (E) while suppressing the generation of chlorine-containing gas. The mixing ratio of polymer (C) to polymer (E) is preferably the above-mentioned ratio. Since the content of acidic substances can be significantly reduced, the resulting product is also suitable for use as a solid fuel or liquid fuel.

[0175] The above is aspect A.

[0176] [Method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin mixture containing a polymer having an ester bond (polymer E)] The method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin containing a polymer having an ester bond (polymer E) according to the present embodiment includes allowing a depolymerization accelerator for polymer E to act on the resin, thereby generating the gaseous depolymerized product, and separating the gaseous depolymerized product from the depolymerization reaction system and condensing or sublimating it.

[0177] In the production method, the "polymer E," the "depolymerized product containing a carboxylic acid or a derivative thereof," the "depolymerization accelerator for polymer E," and the "acting on a resin mixture with the depolymerization accelerator for polymer E" may be the same as those in the above-mentioned [Method for producing a residue for recycling].

[0178] The resin containing polymer E may be a resin containing only polymer E (single resin), or a resin (resin mixture) containing polymer E and a resin other than polymer E. The resin mixture may be the same as the "resin mixture containing polymer E" in the above [Method for producing residue for recycling].

[0179] That is, for example, the resin may contain polymer C and the depolymerization accelerator may be one produced by thermal decomposition of polymer C, the depolymerization accelerator may be at least one selected from the group consisting of hydrogen chloride and chlorine, polymer E may be polyester, and the depolymerization accelerator for polymer E may be allowed to act on the resin in a heated state (for example, at 600°C or lower).

[0180] The single resin containing polymer E may contain one or more types of polymer E. The single resin containing polymer E may be a resin consisting of polymer E, or may be a resin containing, in addition to polymer E, the "other components" in the above-mentioned [Method for producing recyclable residue]. When the single resin containing polymer E contains the other components, the total content of the other components may be 10% by mass or less, 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total amount of the resin.

[0181] The gaseous depolymerization product may be separated from the depolymerization reaction system by, for example, allowing the depolymerization accelerator to act on a resin containing the polymer E in a first container containing the resin, and then guiding the gaseous depolymerization product to a second container (Aspect 1). In another aspect, the gaseous depolymerization product may be separated from the depolymerization reaction system by, for example, allowing the depolymerization accelerator to act on a resin containing the polymer E in a first container containing the resin, and then guiding the gaseous depolymerization product to a region in the first container that is at least a certain distance horizontally from the polymerization reaction system.

[0182] In the first embodiment, the depolymerization reaction may be advanced by supplying a depolymerization accelerator to the first container from outside the first container. Furthermore, when the resin containing polymer E also contains polymer C, the first container may be heated from the outside to thermally decompose the polymer C, and the depolymerization reaction may be advanced by the depolymerization accelerator, such as hydrogen chloride, thus generated. In this case, the depolymerization accelerator may or may not be supplied from the outside of the first container.

[0183] The depolymerized product in a gaseous state may be introduced into the second container by conveying a gas from the first container to the second container by a pump, etc. For example, the first container and the second container may be connected to each other by a first connecting pipe, and in this case, the depolymerized product in a gaseous state in the first container may be introduced into the second container by conveying a gas from the first container to the second container through the first connecting pipe by a pump, etc.

[0184] When the gaseous depolymerized product is introduced into the second container, it is preferable to maintain the gaseous state at a sufficiently high temperature. Such a temperature can be appropriately set depending on the type of depolymerized product. For example, when the resin containing polymer E contains PET (i.e., when the depolymerized product contains TPA, BCET, and MCET), it is preferable to maintain the depolymerized product at 180°C or higher, or 350°C or higher. Examples of a method for maintaining the gaseous depolymerized product at a sufficiently high temperature include sufficiently increasing the temperature of the first container and, if used, the first connecting pipe.

[0185] In Aspect 1, the depolymerization accelerator may be introduced into a second container together with the depolymerized product, and at least a portion of the depolymerization accelerator introduced into the second container may be introduced in a gaseous state into the first container. For example, the first container and the second container may be connected to each other via a first connecting pipe and a second connecting pipe (Aspect 1-1). Alternatively, the depolymerized product and the gaseous depolymerization accelerator may be introduced from the first container to the second container through the first connecting pipe, and then the gaseous depolymerization accelerator may be introduced from the second container to the first container through the second connecting pipe. This can reduce the amount of depolymerization accelerator supplied from outside to the first container.

[0186] Condensation or sublimation of the depolymerized product may be achieved by cooling the depolymerized product or by pressurizing the depolymerized product. Cooling the depolymerized product means lowering the temperature of the depolymerized product (e.g., lowering the temperature of the depolymerized product by 0.1°C or more, 1°C or more, 5°C or more, 10°C or more, 25°C or more, 50°C or more, 100°C or more, 200°C or more, or 300°C or more). For example, in Aspect 1-1, if the temperature of the second container is lower than the temperature of the first communicating conduit, the depolymerized product can be cooled by guiding the depolymerized product from the first communicating conduit to the second container. For example, if the temperature of the first communicating conduit is 180 to 350°C, the depolymerized product can be cooled by adjusting the temperature of the second container to -100 to 180°C and guiding the depolymerized product from the first communicating conduit to the second container. Furthermore, when the temperature of the gas in the first communicating pipe is 180 to 350° C., the depolymerized product can be cooled by guiding the depolymerized product from the first communicating pipe to the second container by setting the temperature of the gas in the second container to −100 to 180° C. When the depolymerized product is guided to a container such as the second container, the depolymerized product may be cooled by cooling the container.

[0187] Next, an example of Aspect 1-1 will be described below with reference to Fig. 7. The production method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin containing polymer E described below is merely one aspect of this embodiment, and naturally, this embodiment is not limited to the content described below.

[0188] Fig. 7 shows an apparatus for carrying out a production method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin containing polymer E. The apparatus 104 shown in Fig. 7 includes a first container 20, a second container 22, and a first communicating pipe 30 and a second communicating pipe 32 that communicate between the first container 20 and the second container 22.

[0189] The second communicating pipe 32 is equipped with a pressure gauge 32a, a circulation pump 32b, and a flow meter 32c. The pressure gauge 32a can measure the consumption rate of the depolymerization accelerator in the apparatus 104, thereby enabling evaluation of the reaction rate of the depolymerization reaction. The circulation pump 32b can circulate the gas in the apparatus 104. Specifically, the gas in the apparatus 104 can be circulated from the first container 20, through the first communicating pipe 30, the second container 22, the second communicating pipe 32, and the first container 20, in that order. The flow meter 32c can measure the flow rate of the gas flow in the apparatus 104 created by the circulation pump 32b. It is possible to omit the pressure gauge 32a and the flow meter 32c from the above-described apparatus 104.

[0190] A resin containing the polymer E is placed in a first container, and a depolymerization accelerator is supplied thereto, whereby the depolymerization accelerator acts on the resin, thereby producing a depolymerized product. In this case, by externally heating the first container, it is possible to accelerate the depolymerization reaction and maintain the depolymerized product in a gaseous state.

[0191] The resulting gaseous depolymerized product is guided through the first communicating pipe 30 to the second container 22 by the airflow created by the circulation pump 32b. At this time, in order to maintain the gaseous state of the depolymerized product, the first communicating pipe 30 can be heated from the outside, the circulation flow rate can be increased, or the like.

[0192] The depolymerized material in a gaseous state introduced into the second container 22 can be cooled in the second container 22. This can be done, for example, by cooling the second container 22. By being cooled, the depolymerized material condenses or sublimes to become a liquid or solid, and can be accumulated in the second container 22. The depolymerized material accumulated in this manner can be recovered.

[0193] Here, by setting the second container 22 or the second communicating pipe 32 at a temperature equal to or lower than a certain temperature (for example, room temperature), the gaseous depolymerized products introduced into the second container 22 can be separated from the depolymerization reaction system. That is, the airflow created by the circulation pump 32b prevents the depolymerized products from passing through the first communicating pipe 30 to reach the first container 20. On the other hand, the depolymerized products condense or sublimate in the second container 22 or the second communicating pipe 30, and therefore cannot pass through the second communicating pipe 30 to reach the first container 20.

[0194] Furthermore, the depolymerization accelerator can be introduced into the second container 22 together with the depolymerized product, and at least a portion of the depolymerization accelerator introduced into the second container 22 can be introduced in a gaseous state into the first container 20. Such movement of the depolymerization accelerator can be achieved by an airflow created by the circulation pump 32b. By introducing at least a portion of the depolymerization accelerator introduced into the second container 22 into the first container 20 in a gaseous state, a reduction in the amount of the depolymerization accelerator in the first container 20 can be suppressed.

[0195] [Method for producing TPA crystals (part 1)] The method (1) for producing terephthalic acid crystals according to the present embodiment includes: causing hydrogen chloride to act on a resin containing a reaction product of a diol and terephthalic acid, to produce a depolymerized product containing terephthalic acid and an ester of terephthalic acid and a chloroalcohol in which one hydroxyl group of the diol is substituted with a chlorine atom; hydrolyzing the ester to increase the content of terephthalic acid in the depolymerized product; and crystallizing the terephthalic acid during and / or after the hydrolysis.

[0196] The resin containing the reaction product of a diol and terephthalic acid may be a resin (single resin) containing only the reaction product as a resin, or a resin (resin mixture) containing the reaction product and a resin other than the reaction product as a resin. The resin mixture may be the same as the "resin mixture containing polymer E" in the above [Method for producing residue for recycling], in which polymer E is a reaction product of a diol and terephthalic acid.

[0197] The single resin containing a reaction product of a diol and terephthalic acid may contain one or more reaction products of a diol and terephthalic acid. The single resin containing a reaction product of a diol and terephthalic acid may be a resin consisting of a reaction product of a diol and terephthalic acid, or may be a resin containing, in addition to the reaction product of a diol and terephthalic acid, the "other components" in the above-mentioned [Method for producing recyclable residue]. When the single resin containing a reaction product of a diol and terephthalic acid contains the other components, the total content of the other components may be 10% by mass or less, 5% by mass or less, 1% by mass or less, or 0.1% by mass or less, based on the total amount of the resin.

[0198] The reaction product of a diol and terephthalic acid may be at least one selected from the group consisting of PET, polybutylene terephthalate, and polytrimethylene terephthalate, and is preferably PET.

[0199] When hydrogen chloride acts on a resin containing a reaction product of a diol and terephthalic acid, the reaction product is depolymerized to produce at least terephthalic acid and an ester of a chloroalcohol in which one hydroxyl group of the diol is substituted with a chlorine atom. When the reaction product of a diol and terephthalic acid is PET, the ester includes mono(2-chloroethyl)terephthalate and bis(2-chloroethyl)terephthalate. When the reaction product of a diol and terephthalic acid is polybutylene terephthalate, the ester includes bis(4-chlorobutyl)terephthalate. When the reaction product of a diol and terephthalic acid is polytrimethylene terephthalate, the ester includes bis(3-chloropropyl)terephthalate.

[0200] The hydrolysis of the depolymerized product can be carried out, for example, in a water-containing solvent. Examples of water-containing solvents include water and aprotic polar solvents containing water. The aprotic polar solvent is preferably at least one selected from the group consisting of 1,3-dimethyl-2-imidazolidinone (DMI), N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). From the viewpoints of improving the purity of TPA in the crystals and improving the yield of TPA, it is more preferably at least one selected from the group consisting of DMI and NMP. From the viewpoints of further improving the purity of TPA in the crystals, further improving the yield of TPA, increasing WI, and reducing YI, it is even more preferably DMI. The water is preferably distilled water.

[0201] The hydrolysis may be carried out under heating conditions. For example, when the hydrolysis of the depolymerized product is carried out in water, the product may be heated at 170 to 250°C or 190 to 230°C for 2 to 8 hours or 3 to 5 hours. Although the depolymerized product usually has low solubility in water, the depolymerized product can be sufficiently dissolved in water by applying high temperature and high pressure conditions. When the hydrolysis of the depolymerized product is carried out in water, the product may be heated at 100 to 160°C or 120 to 140°C for 18 to 30 hours or 20 to 26 hours.

[0202] To promote hydrolysis, an appropriate base can be added to the water used as the water-containing solvent. An example of the base is sodium hydroxide. When a base is added to the water, the hydrolysis can be promoted, for example, by heating the water at 100°C or less. Depending on the amount and type of base added, the product after hydrolysis may become a water-soluble salt of terephthalic acid and remain dissolved in water without precipitating. In this case, the addition of an appropriate acid can liberate terephthalic acid, which can then be isolated as crystals.

[0203] Crystal formation is usually observed during the hydrolysis, and further crystal formation occurs upon cooling after completion of the hydrolysis.

[0204] During or after the hydrolysis, the crystals or TPA solids may be adsorbed onto activated carbon. For example, activated carbon can be added to a system in which the hydrolysis is or has been progressing, and mixed to adsorb the crystals or TPA solids onto activated carbon. The activated carbon may be crushed. The particle size of the activated carbon may be 0.05 to 3 mm or 0.2 to 1 mm.

[0205] The obtained crystals may be washed, dried, etc. Methanol may be used for washing. Drying may be performed overnight at 60 to 80°C in a vacuum oven.

[0206] The resulting TPA crystals can be used as a raw material for PET. PET can be produced using conventional methods, but it is preferable to produce PET by subjecting the TPA crystals to melt polymerization followed by solid-state polymerization. The PET obtained in this manner can have a number-average molecular weight, crystallization temperature, and melting point comparable to those of the PET used in the PET bottles of Ilohasu (registered trademark) Tennensui (manufactured by Coca-Cola).

[0207] [Method for producing BHET crystals] The method for producing bis(2-hydroxyethyl) terephthalate crystals according to this embodiment includes producing bis(2-hydroxyethyl) terephthalate and crystallizing it by esterification or transesterification of a depolymerized product containing terephthalic acid and an ester of terephthalic acid and a chloroalcohol in which one hydroxyl group of the diol is substituted with a chlorine atom, the depolymerized product being produced by allowing hydrogen chloride to act on a resin containing a reaction product of a diol and terephthalic acid.

[0208] The resin containing the reaction product of a diol and terephthalic acid may be the same as that in the above-mentioned [Production Method of TPA Crystals (Part 1)]. The reaction product of a diol and terephthalic acid, and the chloroalcohol ester in which one hydroxyl group of the diol is substituted with a chlorine atom, may also be the same as those in the above-mentioned [Production Method of TPA Crystals (Part 1)].

[0209] The depolymerized product can be esterified or transesterified using, for example, ethylene glycol. TPA is esterified with ethylene glycol to produce BHET, MCET is esterified and transesterified to produce BHET, and BCET is transesterified to produce BHET. Esterification or transesterification with ethylene glycol may be carried out at 80 to 120°C or 90 to 110°C for 10 to 30 hours or 20 to 28 hours. For example, when esterification or transesterification is carried out at 90 to 110°C for 20 to 28 hours, the percentage of the amount of BHET relative to the total amount of TPA, MCET, BCET, and BHET after the reaction can be 90% or more, 95% or more, or 97% or more.

[0210] The esterification or transesterification of the depolymerized product may be carried out in ethylene glycol, which allows the esterification or transesterification to proceed efficiently. The depolymerized product usually exhibits sufficient solubility in ethylene glycol.

[0211] [Method for producing recycled raw materials containing BCET, MCET, or TPA] A method for producing a recyclable material containing bis(2-chloroethyl) terephthalate according to this embodiment includes contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by treating a resin containing polyethylene terephthalate with hydrogen chloride, with a solvent (first solvent), removing insoluble matter in the solvent (first solvent) containing the terephthalic acid and mono(2-chloroethyl) terephthalate, and obtaining the bis(2-chloroethyl) terephthalate dissolved in the solvent (first solvent). The solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent (first solvent) are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0212] A method for producing a recyclable material containing mono(2-chloroethyl) terephthalate according to this embodiment includes contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by treating a resin containing polyethylene terephthalate with hydrogen chloride, with a first solvent to separate the bis(2-chloroethyl) terephthalate dissolved in the first solvent from a material insoluble in the first solvent containing the terephthalic acid and mono(2-chloroethyl) terephthalate, and then contacting the insoluble material with a second solvent to remove the material insoluble in the second solvent containing the terephthalic acid, thereby obtaining the mono(2-chloroethyl) terephthalate dissolved in the second solvent. The solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively. The solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

[0213] A method for producing a terephthalic acid-containing recyclable material according to this embodiment includes contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by treating a polyethylene terephthalate-containing resin with hydrogen chloride, with a first solvent to separate the bis(2-chloroethyl) terephthalate dissolved in the first solvent from a first solvent-insoluble material containing the terephthalic acid and mono(2-chloroethyl) terephthalate, and then contacting the insoluble material with a second solvent to obtain an ethyl acetate-insoluble material containing the terephthalic acid. The solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively. The solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

[0214] As used herein, solubility refers to the solubility (mass%) obtained by the method described in "Solubility Measurement Method <G2-6-190>" (https: / / www.pmda.go.jp / files / 000270159.pdf, accessed December 24, 2024) at a solvent temperature of 25°C.

[0215] The method for producing a raw material for recycling containing BCET according to the present embodiment, the method for producing a raw material for recycling containing MCET according to the present embodiment, and the method for producing a raw material for recycling containing TPA according to the present embodiment can also be considered as a series of operations constituting solvent separation of the depolymerized product using toluene and ethyl acetate.

[0216] In the method for producing a recyclable material containing BCET according to the present embodiment, the method for producing a recyclable material containing MCET according to the present embodiment, and the method for producing a recyclable material containing TPA according to the present embodiment, the resin containing PET may be the same as the resin containing a reaction product of a diol and terephthalic acid in the above-mentioned [Method for producing TPA crystals (part 1)], in which the reaction product is PET.

[0217] In the method for producing a recycling material containing BCET according to this embodiment, the method for producing a recycling material containing MCET according to this embodiment, and the method for producing a recycling material containing TPA according to this embodiment, the first solvent is not particularly limited as long as its solubility is within the above-mentioned range, and may be at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents. Examples of the aromatic hydrocarbon solvent include toluene, benzene, xylene, mesitylene, and tetralin. Examples of the aliphatic hydrocarbon solvent include pentane, hexane, cyclohexane, and petroleum ether. Examples of the ether solvent include diethyl ether, diisopropyl ether, and methyl t-butyl ether. The first solvent is preferably an aromatic hydrocarbon solvent, and more preferably toluene.

[0218] The solubility of terephthalic acid in the first solvent is 1% by mass or less, i.e., the upper limit is 1% by mass, but the upper limit may be 0.9%, 0.7%, or 0.5% by mass. The lower limit of the solubility may be 0.01%, 0.1%, or 0.2% by mass. These upper and lower limits may be freely combined.

[0219] The solubility of mono(2-chloroethyl) terephthalate in the first solvent is 3% by mass or less, i.e., the upper limit is 3% by mass, but the upper limit may be 2.5%, 2%, 1.5%, or 1% by mass. The lower limit of the solubility may be 0.01%, 0.1%, or 0.2% by mass. These upper and lower limits may be freely combined.

[0220] The solubility of bis(2-chloroethyl) terephthalate in the first solvent is 3% by mass or more, i.e., the lower limit is 3% by mass, but the lower limit may be 3.5%, 4%, 4.5%, or 5% by mass. The upper limit of the solubility may be 20%, 15%, or 10% by mass. These upper and lower limits may be freely combined.

[0221] The second solvent is not particularly limited as long as its solubility is within the above-mentioned range, and may be at least one solvent selected from the group consisting of ether solvents, ketone solvents, ester solvents, and alcohol solvents. Examples of the ether solvent include tetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane. Examples of the ketone solvent include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of the ester solvent include ethyl acetate, methyl acetate, isopropyl acetate, n-butyl acetate, and methyl propionate. Examples of the alcohol solvent include methanol, ethanol, and 2-propanol. As the second solvent, an ester solvent is preferred, and ethyl acetate is more preferred.

[0222] The solubility of terephthalic acid in the second solvent is 1% by mass or less, i.e., the upper limit is 1% by mass, but the upper limit may be 0.9%, 0.7%, or 0.5% by mass. The lower limit of the solubility may be 0.01%, 0.1%, or 0.2% by mass. These upper and lower limits may be freely combined.

[0223] The solubility of mono(2-chloroethyl) terephthalate in the second solvent is 1% by mass or more, i.e., the lower limit is 1% by mass, but the lower limit may be 1.2%, 1.5%, 2%, or 3% by mass. The upper limit of the solubility may be 20%, 15%, or 10% by mass. These upper and lower limits may be freely combined.

[0224] The contacting of the depolymerized product with the first solvent may be carried out by adding the depolymerized product to the first solvent. The first solvent may then be stirred. By such an operation, BCET dissolved in the first solvent can be efficiently separated from the matter insoluble in the first solvent, including TPA and MCET.

[0225] The contacting of the first solvent-insoluble material with the second solvent may be carried out by adding the first solvent-insoluble material to the second solvent. The second solvent may then be stirred. This procedure allows for efficient separation of the MCET dissolved in the second solvent from the second solvent-insoluble material, including TPA.

[0226] Recycled raw materials containing BCET, MCET, or TPA can be used as resin raw materials, etc. Crystals of BCET, MCET, or TPA can also be obtained from recycled raw materials containing BCET, MCET, or TPA. For example, BCET can be crystallized by cooling in a mixed solvent of ethanol:hexane = 15:85 by volume. MCET can also be crystallized by cooling in a mixed solvent of ethyl acetate:ethanol = 60:10 by volume.

[0227] [Method for producing TPA crystals (part 2)] The second method for producing terephthalic acid crystals according to this embodiment involves contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by treating a resin containing polyethylene terephthalate with hydrogen chloride, with a solvent (first solvent), removing insoluble materials in the solvent (first solvent) containing the terephthalic acid and mono(2-chloroethyl) terephthalate, obtaining bis(2-chloroethyl) terephthalate dissolved in the solvent (first solvent), and hydrolyzing the resulting bis(2-chloroethyl) terephthalate to produce and crystallize terephthalic acid. The solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0228] The first solvent may be the same as that in the above-mentioned [Method for producing a recyclable material containing BCET, MCET, or TPA]. The PET-containing resin may be the same as that in the above-mentioned [Method for producing TPA crystals (part 1)], in which the reaction product is PET, in the resin containing the reaction product of a diol and terephthalic acid.

[0229] Hydrolysis may be carried out, for example, by heating under alkaline conditions. For example, sodium hydroxide may be added to a solvent such as toluene containing the bis(2-chloroethyl) terephthalate, and the mixture may be stirred at 60 to 90°C for 20 to 28 hours to allow hydrolysis to proceed. After hydrolysis, terephthalic acid dissolves in an aqueous sodium hydroxide solution as an anion (terephthalate). Terephthalic acid can be recovered by neutralizing this solution with an appropriate acid. The resulting powder may be washed, dried, or the like.

[0230] [Method for producing TPA crystals (part 3)] A third method for producing terephthalic acid crystals according to this embodiment includes contacting a depolymerized product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, produced by treating a resin containing polyethylene terephthalate with hydrogen chloride, with a solvent (first solvent), separating the bis(2-chloroethyl) terephthalate dissolved in the solvent (first solvent) from a solvent-insoluble material containing the terephthalic acid and mono(2-chloroethyl) terephthalate, and hydrolyzing the insoluble material to increase the terephthalic acid content in the insoluble material, and crystallizing the terephthalic acid during and / or after the hydrolysis. The solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

[0231] The first solvent may be the same as that in the above-mentioned [Method for producing a recyclable material containing BCET, MCET, or TPA]. The PET-containing resin may be the same as that in the above-mentioned [Method for producing TPA crystals (part 1)], in which the reaction product is PET, in the resin containing the reaction product of a diol and terephthalic acid.

[0232] Hydrolysis may be carried out, for example, by adding water to the insoluble matter in the first solvent and boiling the mixture, which may be continued for 20 to 28 hours. Crystallization is usually observed during hydrolysis. After that, cooling can further confirm crystallization. The obtained crystals may be washed, dried, etc.

[0233] The "diol," "resin mixture containing polyethylene terephthalate," and "depolymerized product containing terephthalic acid, mono(2-chloroethyl)terephthalate, and bis(2-chloroethyl)terephthalate" in the above-mentioned [Method for producing TPA crystals (1)], [Method for producing BHET crystals], [Method for producing recycled raw materials containing BCET, MCET, or TPA], [Method for producing TPA crystals (2)], and [Method for producing TPA crystals (3)] may be the same as those in the above-mentioned [Method for producing recycled residue].

[0234] Furthermore, in the above-mentioned [Method for producing TPA crystals (Part 1)], [Method for producing BHET crystals], [Method for producing raw materials for recycling containing BCET, MCET, or TPA], [Method for producing TPA crystals (Part 2)], and [Method for producing TPA crystals (Part 3)], the act of reacting the resin with hydrogen chloride may be carried out in the same manner as in the "acting on a resin mixture containing polyethylene terephthalate with hydrogen chloride" in the above-mentioned [Method for producing residue for recycling]. [Example]

[0235] The present invention will be described in detail below with reference to examples. Note that the following examples are provided for illustrative purposes only, and the present invention is not limited to the examples described below. Unless otherwise specified, the units and measurement methods described herein are in accordance with the provisions of JIS (Japanese Industrial Standards).

[0236] Example A Hereinafter, the present invention will be described in more detail with reference to Example A, but the present invention is not limited to Example A. In the description of Example A (including Table 2, Table 3, and Figure 1), "Terms in Example A" and similar terms in Table 1 below can be read as "replaceable terms." This reinterpretation is natural in light of the description of Example A.

[0237] [Table 1]

[0238] <Method for measuring the reduction rate of acidic substances in plastics> A plastic mixture was prepared by blending PET as polymer (E) and PVC as polymer (C) in the blending ratio shown in Table 2 below. A portion of this mixture was taken out, and the content of carboxylic acid compounds and their derivatives in the plastic mixture was determined by the following method, and this was taken as the content of acidic substances derived from polymer (E). Specifically, 0.1 g of the plastic mixture was added to 15 mL of methanol, 2 mL of 35% tetrapropylammonium hydroxide aqueous solution was added, and the mixture was heated at 75°C for 7 days to decompose the ester bonds of the PET and hydrolyze it into soluble dialcohols and dicarboxylates. The soluble dicarboxylates produced by hydrolysis were then neutralized in an organic solvent and quantified by HPLC to determine the content (mass%) of acidic substances derived from polymer (E) in 100% by mass of the plastic mixture before Step 1 (α). The amount of acidic substances derived from polymer (E) in the plastic mixture (β, dicarboxylic acid content) was calculated by multiplying this content (α) by the mass of the plastic mixture subjected to Step 1.

[0239] The content of chlorine derived from polymer (C) in the plastic mixture before step 1 was determined by the following method. Specifically, the plastic mixture was measured using combustion-ion chromatography (IEC62321-3-2AnnexC:2020 (quartz tube combustion-IC method)), and the chlorine content (mass%) in the plastic before the test, γ, was determined. The amount of acidic substance (chlorine) derived from polymer (C) in the plastic mixture, δ, was determined by multiplying this content, γ, by the mass of the plastic mixture before step 1.

[0240] Because dicarboxylic acids are divalent acids, they have twice the acidic capacity of chlorine in terms of the amount of substance. Therefore, the amount of acidic substance ε in a plastic mixture was calculated by multiplying the amount of acidic substance β (dicarboxylic acid content) derived from polymer (E) in the plastic mixture by 2 and adding this value to the amount of acidic substance (chlorine) δ in the plastic mixture, as shown in the following formula. (Amount of acidic substance in plastic mixture ε) = (Amount of acidic substance (chlorine) in plastic mixture δ) + (Content of dicarboxylic acid in plastic mixture (amount of acidic substance) β) × 2

[0241] On the other hand, after the plastic mixture was reacted in a glass reaction tube under the conditions shown in Table 2 below, the mass of the solid pyrolysis residue remaining in the heating section of the glass tube was measured, and then the amount of acidic substance ζ (dicarboxylic acid content) and the amount of acidic substance (chlorine) η were measured in the same manner as above, and the amount of acidic substance θ in the solid pyrolysis residue was calculated using the same formula. Furthermore, the reduction rate of acidic substances was calculated using the following formula. {1 - (amount of acidic substance θ in the solid pyrolysis residue after step 4) / (amount of acidic substance ε in the plastic mixture before step 1)} x 100

[0242] The chlorine reduction rate was calculated using the following formula: {1 - (amount of acidic substance (chlorine) in pyrolysis residue η) / (amount of acidic substance (chlorine) in plastic mixture δ)} x 100 The reduction rate of the amount of acidic substances (carboxylic acid compounds and their derivatives) derived from the polymer (E) was calculated using the following formula. {1 - (amount of acidic substances in the pyrolysis residue (dicarboxylic acid content) ζ) / (amount of acidic substances in the plastic mixture (dicarboxylic acid content) β)} x 100

[0243] <Test Examples 1-18> A plastic mixture was prepared at the blending ratio shown in Table 2 below. In the table, PET stands for polyethylene terephthalate, PVC stands for polyvinyl chloride, PS stands for polystyrene, PE stands for polyethylene, and PP stands for polypropylene. The blending amounts, the volume of the reaction vessel, and the reaction time were as shown in Table 2. The reaction temperature was 350°C for Test Examples 13 to 15, and 330°C for the others. A glass reaction tube was used as the reaction vessel. The plastic mixture was sealed in the reaction tube and placed under vacuum, and a thermal decomposition test was carried out. The reaction tube was thermally decomposed for the time shown in Table 2.

[0244] [Table 2]

[0245] In Test Examples 1 to 18, brown to black pyrolysis residues were formed at the bottom of the reaction tube. Furthermore, in Test Example 2, where PVC and PET were mixed in the plastic, deposition of white sublimates was confirmed in the cooling area.

[0246] <Analysis of sublimated products> The structure of the sublimates attached to the cold part was analyzed by gas chromatography-mass spectrometry (GC / MS) and 1 Analysis by H NMR confirmed the formation of terephthalic acid and its derivatives (mono(2-chloroethyl) terephthalate (MCET), bis(2-chloroethyl) terephthalate (BCET), and terephthalic acid (TPA)).

[0247] <Production of terephthalic acid> Terephthalic acid was obtained by alkaline hydrolysis of the sublimate. Specifically, 0.1 g of the sublimate was added to 15 mL of methanol, 2 mL of 35% tetrapropylammonium hydroxide solution was added, and the mixture was heated at 75 °C for 7 days to hydrolyze it into a soluble terephthalate salt. Further, the resulting terephthalate salt was reacted with any strong acid, such as hydrochloric acid or sulfuric acid, to produce terephthalic acid.

[0248] <Polymerization of terephthalic acid> 1.0 g of terephthalic acid obtained by the above method and 0.54 g of reagent terephthalate (2-hydroxyethyl) were placed in a glass container, and 0.98 mL of ethylene glycol was added. After replacing the atmosphere in the glass container with argon gas, the container was heated at 255°C for 6 hours until the contents were completely dissolved. The temperature was then gradually increased to 285°C, while the pressure inside the glass tube was gradually reduced over 2 hours to prevent the ethylene glycol from bumping. Finally, the container was heated at 285°C under a pressure of 0.3 kPa for 30 minutes. After cooling, the solidified PET resin was crushed and extracted (yield: 1.45 g, 94%).

[0249] Table 3 shows the content and amount of acidic substances in the plastic before thermal decomposition. It also shows the mass of the bottom solid, the content and amount of acidic substances in the residual plastic (bottom solid) after the thermal decomposition test. It also shows the reduction rate of acidic substances due to the thermal decomposition test. The upper column of the table shows the actual measured value for the reduction rate in each test example, and the lower column shows the total reduction rate (Test Example 1, Test Example 6) when PET and PVC were heated separately at the blending amounts of each test example, as a reference value.

[0250] [Table 3]

[0251] In Test Example 1, in which only PET was heated, it was confirmed that heating did not reduce acidic substances. On the other hand, in Test Example 7, in which only PVC was heated, a high reduction rate of acidic substances was achieved. When PET and PVC are mixed and heated, if no reaction occurs between the two, the acidic substance removal rate should be the arithmetic mean value obtained by multiplying the acidic substance removal rate when PET and PVC are heated separately by the PET / PVC blend ratio and adding the results. However, in Test Examples 2 to 5, in which PET and PVC were actually mixed and heated, a significantly higher acidic substance removal rate was observed than the expected removal rate when heated individually. In particular, when PET and PVC were mixed at mass ratios of 4:1, 3:1, and 2:1, a remarkable effect was observed, with an acidic substance removal rate of over 90%. Focusing on the individual reduction rates of chlorine and terephthalic acid in Test Examples 1 to 6, the chlorine reduction rate in Test Examples 2 to 5, in which PET and PVC were mixed and heated, was comparable to that in Test Example 6, in which PVC was heated separately, whereas the terephthalic acid reduction rate in Test Examples 2 to 5 was clearly higher than that in Test Example 1. In particular, Test Examples 3 to 5, in which a sufficient amount of PVC was added to PET, showed particularly high terephthalic acid reduction rates. From these results, it is believed that dicarboxylic acids derived from the plastic polymer (E) react with the thermal decomposition products of PVC and sublimate as dicarboxylic acid chlorides, thereby removing chlorine from the plastic material. Furthermore, as shown in Test Examples 8, 11, and 14, the acidic substance removal effect of this method is also observed in the presence of general-purpose plastic materials such as PE, PP, and PS. Furthermore, as shown in Test Examples 16 to 18, even when PET was added to industrial waste materials such as mesh sheets and leather sheets containing PET and PVC as components, and wallpaper containing PVC and cellulose as components, a high acid substance removal rate of 75 to 94% was achieved, confirming the high industrial usefulness of this method.

[0252] According to this method, by mixing and heating polymer (E) and polymer (C), not only can the acidic substances in the pyrolysis residue be reduced, but also the amount of acidic gas generated in the gas phase from polymer (C) can be reduced. Pyrolyzing only polymer (C) to remove acidic substances is a common practice, as described in Non-Patent Documents 1 and 2. However, according to this method, the step of removing acidic substances and extracting pyrolysis residue can be carried out in a reactor with reduced corrosion resistance, and industrially beneficial effects can be expected, such as simplifying the treatment equipment for the generated exhaust gas.

[0253] Next, an example of the results of examining the amount of gas generated in a thermal decomposition test will be described with reference to Test Examples 19 and 20. <Test Example 19> PET + PVC (PET 6g, PVC 2g) was prepared as the plastic. Next, the plastic was sealed in a glass reaction tube (1265mL) and evacuated, and a thermal decomposition test was performed. The reaction tube was maintained at 330°C, and the pressure and temperature inside the container were measured over time (initial pressure: 57kPa, final pressure: 12kPa).

[0254] <Test Example 20> A thermal decomposition test was carried out in the same manner as in Test Example 20, except that 2 g of PVC was used instead of plastic (initial pressure: 83 kPa, final pressure: 80 kPa).

[0255] Figure 4 shows a graph plotting the pressure and temperature changes versus the thermal decomposition test time for Test Example 19. Figure 5 shows a graph plotting the pressure and temperature changes versus the thermal decomposition test time for Test Example 20. As shown in these figures, it was confirmed that the gas pressure in the gas phase was significantly lower in Test Example 19 than in Test Example 20. This is thought to be because in Test Example 19, in which PET and PVC were thermally decomposed, hydrogen chloride gas was consumed due to the production of terephthalic acid derivatives, etc.

[0256] The above is Example A.

[0257] The present invention will be described in more detail below with reference to Examples B to E, but the present invention is not limited to Examples B to E. In Examples B to E, unless otherwise specified, the WI and YI of the depolymerized products were measured by the following methods. Furthermore, in Examples B to E, unless otherwise specified, the content of TPA, MCET, BCET, or BHET in the measurement target was measured by HPLC.

[0258] (Measurement of WI and YI of depolymerized products) The WI and YI of the measurement object (depolymerized product, etc.) were measured using a spectrophotometer SQ7700 (manufactured by Nippon Denshoku Industries Co., Ltd.). Specifically, the measurement object was tightly packed in a glass container made of optical glass, and the SQ7700 irradiated the bottom of the container with white light having a diameter of 6 mm. The WI and YI were calculated using the SQ7700 based on the wavelength spectrum of the reflected light. Before measuring the measurement object, the SQ7700 was calibrated so that the WI and YI calculated using a white board as a reference were 100 and 0, respectively.

[0259] Example B In Example B, using the apparatus 106 shown in FIG. 8, evaluations were performed on the depolymerized products and residues of PET obtained under the following conditions: contacting PET with hydrogen chloride gas (Test Example B1), contacting a mixture of PET and PE with hydrogen chloride gas (Test Example B2), heating a mixture of PET and PVC (Test Example B3), and heating PET (Test Example B4).

[0260] (HPLC conditions) In Example B, the TPA content of the target was measured by HPLC as follows. First, 0.100 g of the target solid was weighed out, and 2 ml of TPAOH solution and 10 ml of methanol were added dropwise to the solid. The mixture was then stirred at 800 rpm at 75°C for one week. The resulting solution was diluted with 50 ml of pure water, and 0.300 ml was added dropwise to 40 ml of mobile phase. The resulting solution was subjected to HPLC analysis for TPA content. The HPLC method was set as follows: Temperature: 40°C, Pressure: 50.0 MPa, Column flow rate: 0.30 mL / min, Column type: AQ-C18 1.9 μm, Mobile phase: 0.05 vol% aqueous phosphoric acid:methanol = 65:35 mixed solution, Analysis wavelength: 236 nm (wavelength 1), 254 nm (wavelength 2)

[0261] (High temperature GPC analysis) In Example B, the weight-average molecular weight of the target was determined by high-temperature GPC analysis as follows. First, a sample was weighed to 1 mg / mL, and a solvent (tetrachlorobenzene with 0.1 wt% butylated hydroxytoluene added) was added and the mixture was dissolved by shaking at 140°C for 1 hour. The resulting solution was analyzed using a Tosoh HLC-8321GPC / HT (detector: RI, Tosoh Corporation), and the weight-average molecular weight (Mw) was obtained from the resulting molecular weight curve. Polystyrene was used as a molecular weight standard.

[0262] The fifth container 28 and the third container 24 in FIG. 8 used in Example B were equipped with separable flasks (1 L), and the pump 36a was equipped with a gas bag.

[0263] (Test Example B1) 5.0035 g of an empty PET bottle of Ilohas® Tennensui (manufactured by Coca-Cola Company) was placed in the fifth container 28, and 7.0072 g of PVC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., n: approximately 1050) was placed in the third container 24. The entire apparatus 106 was then evacuated (1 kPa). The fourth container 26 was cooled to and maintained at -60°C. The third container 24 was then heated to 330°C and maintained at 330°C for one hour to thermally decompose the PVC and generate hydrogen chloride gas. During heating, the stopcock 34a was open, the stopcock 36b was open between the fourth container 26 and the pump 36a, the fourth container 26 and the fifth container 28 were closed, and the pump 36a and the fifth container 28 were closed. The hydrogen chloride gas generated as described above was passed through the fourth container 26, where impurities other than hydrogen chloride were removed by solidification, sublimation, etc., and the resulting high-purity hydrogen chloride gas was collected in the pump 36a. Then, the valves 36b and 36c were operated to open the passage between the pump 36a and the fifth container 28, and the hydrogen chloride gas was introduced into the fifth container 28. Then, the valve 36c was closed, and the fifth container 28 was heated to 330°C and maintained at 330°C for 8 hours to generate a depolymerized product. The fifth container 28 was then cooled, air was introduced, and the depolymerized product precipitated inside was scraped and recovered. The mass (g) of the recovered depolymerized product, WI, YI, and terephthalic acid recovery rates (%) were measured. Furthermore, the fifth container 28 was checked for the presence or absence of residue after the hydrogen chloride gas had reacted with the PET. If such residue was found, the mass (g) and TPA residual rate (%) were measured. Here, the solid remaining at the bottom of the fifth vessel 28 after the reaction was completed was defined as the residue.

[0264] (Test Example B2) The same procedure as in Test Example B1 was performed, except that instead of placing 5.0035 g of an empty PET bottle of "Ilohas® Tennensui (manufactured by Coca-Cola Company)" in the fifth container 28 and 7.0072 g of PVC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., n: approximately 1050) in the third container 24, 1.0785 g of an empty PET bottle of Ilohas® Tennensui (manufactured by Coca-Cola Company) and 5.0074 g of PE (Hi-Zex 6200 BPU, HDPE, molecular weight 150,000) were placed in the fifth container 28, and 7.0073 g of PVC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., n: approximately 1050) was placed in the third container 24. Additionally, the weight-average molecular weight of the residue was measured. At this time, for comparison, the weight average molecular weight of the PE used as the raw material (Hi-Zex 6200BPU, HDPE, molecular weight 150,000, hereinafter also referred to as "raw material PE") was also measured.

[0265] (Test Example B3) A 5.0046 g empty PET bottle of Ilohas® Tennensui (manufactured by Coca-Cola Company) and 7.0195 g of PVC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., n: approximately 1050) were placed in the fifth container 28. The fifth container 28 was then evacuated, and the stopcock 36c was closed. The fifth container 28 was then heated to 330°C and maintained at 330°C for 8 hours to generate a depolymerized product. The fifth container 28 was then cooled, air was introduced, and the depolymerized product precipitated inside was scraped and recovered. The mass (g) of the recovered depolymerized product, WI, YI, and TPA recovery rate (%) were measured. Furthermore, the fifth container 28 was checked for the presence or absence of residue after the hydrogen chloride gas was applied to the PET. If such residue was found, the mass (g) and TPA residual rate (%) were measured. Here, the solid remaining at the bottom of the fifth vessel 28 after the reaction was completed was defined as the residue.

[0266] (Test Example B4) The same procedure as above (Test Example B3) was carried out, except that instead of "putting 5.0046 g of an empty PET bottle of Ilohas (registered trademark) Tennensui (manufactured by Coca-Cola Company) and 7.0195 g of PVC (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., n: about 1050) into the fifth container 28," a 5.0232 g empty PET bottle of Ilohas (registered trademark) Tennensui (manufactured by Coca-Cola Company) was put into the fifth container 28.

[0267] The results of Test Examples B1 to B4 are shown in Table 4. In Table 4, "TPA residual rate (%)" indicates the ratio of the amount of terephthalic acid obtained by hydrolysis of the residue to the amount of terephthalic acid obtained by hydrolyzing the same amount of PET as the input PET. In Table 4, "TPA recovery rate (%)" indicates the ratio of the amount of terephthalic acid obtained by hydrolysis of the depolymerized product to the amount of terephthalic acid obtained by hydrolyzing the same amount of PET as the input PET. Since "TPA residual rate (%)" and "TPA recovery rate (%)" are calculated as described above, the amount of terephthalic acid derivatives in the residue and depolymerized product was converted into terephthalic acid amounts.

[0268] [Table 4]

[0269] As shown in Table 4, the TPA recovery rate in Test Example B4 was 4.0%, while Test Examples B1 and B3 showed higher TPA recoveries of 91.6% and 88.1%, respectively. This indicates that PET can be depolymerized efficiently by either exposing PET to hydrogen chloride gas or by exposing PET to hydrogen chloride gas generated by thermal decomposition of PVC. Furthermore, in Test Example B1, only a trace amount of brown colored material was observed as residue, indicating that all or almost all of the PET can be depolymerized by exposing PET to hydrogen chloride. Based on this, the residues in Test Examples B2 and B3 are likely derived from PE and PVC, respectively. Furthermore, the WI of Test Example B1 was larger than that of Test Example B3, and the YI of Test Example B1 was smaller than that of Test Example B3, indicating that depolymerizing PET by exposing PET to hydrogen chloride gas produces a more colorless depolymerized product than by heating PET in the presence of both PET and PVC. Furthermore, in Test Example B2, the amount of PE added was 5.0074 g, while the residue was 4.9935 g, indicating that by reacting hydrogen chloride with a mixture of PET and PE, PE from which PET has been removed can be obtained in high yield.

[0270] Figure 6 shows the molecular weight curves of the residue and feed PE obtained in Test Example B2. The weight-average molecular weights (Mw) of the residue and feed PE were 371,000 and 265,000, respectively. As mentioned above, the residue in Test Example B2 is believed to be derived from PE. According to Table 4, the "mass" of the "residue" was 4.9935 g, which is almost no decrease from the "PE input amount" of 5.0074 g. Considering this, it is believed that the thermal decomposition of PE in Test Example B2 was barely progressing, and that PE accounted for the majority of the residue. Furthermore, Figure 6 shows that the molecular weight curves of the residue and feed PE obtained in Test Example B2 were almost identical. These results demonstrate that applying hydrogen chloride to a mixture of PET and PE produces a residue primarily composed of PE, with a molecular weight curve that is almost identical to that of the PE.

[0271] Example C In Example C, a depolymerized product containing a carboxylic acid or a derivative thereof was produced from a resin mixture containing polymer E using the apparatus 104 shown in FIG.

[0272] (HPLC conditions) In Example C, the TPA content of the target was measured by the following HPLC. 0.100 g of the target solid was weighed out, to which 2 ml of TPAOH solution and 10 ml of methanol were added dropwise, followed by stirring at 800 rpm at 75°C for one week. The resulting solution was diluted with 50 ml of pure water, and 0.300 ml was added dropwise to 40 ml of mobile phase (a 4:1 mixture of 0.05% by volume aqueous H3PO4 phosphoric acid solution and methanol). The resulting solution was subjected to HPLC analysis for terephthalic acid content. The HPLC method was set as follows: Temperature: 40°C, Pressure: 50.0 MPa, Column flow rate: 0.30 mL / min, Column type: AQ-C18 1.9 μm (Lot. No.: RAQ2-6366), Solvent: 0.05% by volume phosphoric acid aqueous solution: methanol = 65:35 mixed solution, Measurement wavelength: 236 nm (wavelength 1), 254 nm (wavelength 2), Time: 10 min

[0273] Using the apparatus 104 shown in FIG. 7, depolymerized materials containing carboxylic acids or derivatives thereof were produced from empty PET bottles of Ilohasu (registered trademark) Tennensui (manufactured by Coca-Cola Company) and PVC (JAN: 4987481347557, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (Test Examples C1 to C6).

[0274] 7 used in Example C were as follows: It was confirmed that the gas inside the apparatus 104 circulated through the apparatus 104 in the order of the first container, the first connecting pipe, the second container, the second connecting pipe, and the first container. In addition, a vacuum was created inside the apparatus 104 using a vacuum rotary pump, and the presence of leaks was confirmed using the pressure gauge 32a described below. The first container 20 and the second container 22 were each equipped with a separable flask (1 L), a fluororubber O-ring attached to a recess in the upper part of the separable flask, and a two-neck separable cover attached to the separable flask via the O-ring. An electric furnace was installed outside the first container 20 to heat the separable flask and the two-neck separable cover. First communicating tube 30: A U-shaped glass tube with an outer diameter of 20 mm was used. Fluorine grease was applied to the ground portion of this U-shaped glass tube, thereby tightly adhering it to the first container 20 and the second container 22. The outlet of the U-shaped glass tube to the second container 22 was located near the bottom of the second container 22 so that the discharged gas would reach the bottom of the second container 22. A heater was installed outside the first communicating tube 30 to heat the first communicating tube 30. Second communicating tube 32...It was equipped with a glass tube for connecting a Toyoron hose connected to second container 22, a pressure gauge 32a with a range of approximately 0.5 kPa to atmospheric pressure, a circulation diaphragm pump 32b, a flow meter 32c, a glass tube for connecting a Toyoron hose connected to first container 20, and a Toyoron hose with an outer diameter of 9 mm connecting these in this order. A data logger was connected to pressure gauge 32a.

[0275] In Test Examples C1 to C6, 6.6 g of an empty PET bottle of Ilohasu (registered trademark) Tennensui (manufactured by Coca-Cola Company) and 3.3 g of PVC (JAN: 4987481347557, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in the first container 20 in a weight ratio of PET:PVC = 2:1. The inside of the device 104 was evacuated using the vacuum rotary pump. The electric furnace installed outside the first container 20 was then heated to 330°C at a heating rate of 5°C / min, thereby heating the separable flask of the first container to 330°C. The separable flask was then maintained at 330°C for 8 hours to allow the reaction to proceed. During this process, the separable cover of the first container was either heated to the temperature shown in Table 5 or not. When the electric furnace was heated to 330°C as described above, a heater installed outside the first connecting pipe 30 was used to heat the center of the U-shaped glass tube of the first connecting pipe and the end of the U-shaped glass tube on the second container side to the temperatures shown in Table 5 below. During the reaction, the gas in the apparatus 104 was circulated through the apparatus 104 by the circulation diaphragm pump 32b at the circulation flow rate shown in Table 5 below, in the order of the first container, the first connecting pipe, the second container, the second connecting pipe, and the first container. During the reaction, a pressure gauge was used to check for leakage of gas outside the apparatus 104 and to measure the reaction rate. The reaction rate was evaluated based on the consumption of hydrogen chloride gas.

[0276] [Table 5]

[0277] The reaction produced a solid depolymerized product. After completion of the reaction, the apparatus 104 was disassembled, and the depolymerized product accumulated in the separable flask and two-neck separable cover of the first container 20, the first connecting pipe 30, and the second container 22 was collected, and its mass, WI, and YI were measured. The results are shown in Table 6. In Table 2, the "percentage (%)" indicates the proportion of the depolymerized product (g) at each location, with the collected depolymerized product (g) being taken as 100%. Table 7 also shows the percentages of the amounts of TPA, MCET, and BCET in the depolymerized product collected from each location in Test Example C6, based on the total amount of the depolymerized product.

[0278] [Table 6]

[0279] [Table 7]

[0280] As shown in Table 6, at least in Test Examples C1 and 3 to 6, a depolymerized product containing BCET, MCET, and TPA accumulated in second vessel 22. This is thought to be because hydrogen chloride generated by the thermal decomposition of PVC reacted with PET, thereby producing a depolymerized product containing BCET, MCET, and TPA, and at least a portion of the depolymerized product was introduced into second vessel 22 in a gaseous state, where it became a solid. The amount of depolymerized product (g) in second vessel 22 was greater in Test Example C3 (circulation flow rate: 1.5 L / min) than in Test Example C1 (no circulation), and the amount of depolymerized product (g) in second vessel 22 was greater in Test Example C6 (circulation flow rate: 1.5 L / min) than in Test Example C5 (circulation flow rate: 0.4 L / min). These results indicate that increasing the circulation flow rate can increase the amount of depolymerized product introduced into second vessel 22 in a gaseous state. Furthermore, the amount of depolymerized material (g) in the second vessel 22 was greater in Test Example C5 (high heating temperature conditions) than in Test Example C2 (weakest heating conditions) and Test Example C4 (moderate heating temperature conditions), and the amount of depolymerized material (g) in the second vessel 22 was greater in Test Example C6 (high heating temperature conditions) than in Test Example C3 (weakest heating conditions). This indicates that, at least within the temperature range shown in Table 6, increasing the temperatures of the first vessel and the first communicating pipe can increase the amount of depolymerized material introduced into the second vessel 22 in a gaseous state. Furthermore, the values ​​shown in Table 7 indicate that mono(2-chloroethyl) terephthalate and bis(2-chloroethyl) terephthalate in particular were efficiently transferred to the second vessel 22.

[0281] Furthermore, when the WI and YI of the depolymerized product of Test Example C6 were compared with those of Test Example B3, the WI of Test Example C6 was larger than that of Test Example B3, and the YI of Test Example C6 was smaller than that of Test Example B3. This indicates that coloration of the depolymerized product can be suppressed by separating the depolymerized product from the depolymerization reaction system and guiding it to second container 22.

[0282] Example D In Example D, BCET (Test Example D1), MCET (Test Example D2), and TPA (Test Example D2) were obtained from the depolymerized product obtained in Test Example 19 of Example A by solvent separation.

[0283] (Test Example D1) 20.39 g of the depolymerized product was weighed out into an Erlenmeyer flask, and 100 ml of toluene was added and stirred. The resulting insoluble solid, which is a substance insoluble in toluene, and the supernatant liquid were separated by filtration or centrifugation, and the supernatant liquid was collected in a separate container. Thereafter, 100 mL of toluene was similarly added to the insoluble solid, and the mixture was stirred, and the insoluble solid, which is a substance insoluble in toluene, and the supernatant liquid were separated and collected. This procedure was repeated three times. All of the insoluble solids obtained in this manner were combined and used in the following (Test Example D2). All of the supernatants obtained in this manner were combined and the toluene was removed, yielding toluene-dissolved product 1. The yield of toluene-dissolved product 1 was 7.85 g. Toluene-dissolved product 1 was 1 The toluene solution 1 was further dissolved in 26 mL of a mixed solvent of 15% by volume of ethanol and 85% by volume of hexane, and the solution was cooled to recrystallize BCET, yielding 7.05 g of pure BCET.

[0284] (Test Example D2) 12.05 g of the insoluble solid was placed in an Erlenmeyer flask, 100 ml of ethyl acetate was added, and the mixture was stirred. The insoluble solid, which is a substance insoluble in ethyl acetate, and the supernatant liquid were separated by filtration or centrifugation, and the supernatant liquid was collected in a separate container. Thereafter, 100 ml of ethyl acetate was added to the insoluble solid, and the mixture was stirred, and the insoluble solid, which is a substance insoluble in ethyl acetate, and the supernatant liquid were separated and collected. This procedure was repeated seven times. The insoluble solid, which is a substance insoluble in ethyl acetate obtained in this manner, was collected to obtain Insoluble Solid 1. Insoluble Solid 1 was 1 The product was confirmed to be TPA by HNMR. All of the supernatants obtained in the above operations using ethyl acetate were combined, and the ethyl acetate was removed to obtain ethyl acetate dissolved product 1. The yield of ethyl acetate dissolved product 1 was 12.86 g. 1HNMR confirmed that the product was MCET. Furthermore, the ethyl acetate solution 1 was dissolved in a mixed solvent of 60 mL of ethyl acetate and 10 mL of ethanol, and the solution was cooled to recrystallize MCET, yielding 5.43 g of pure MCET.

[0285] The results of the above (Test Example D1) and (Test Example D2) showed that the depolymerized products produced by treating a resin mixture containing PET with a depolymerization accelerator such as hydrogen chloride can be fractionated into BCET, MCET, and TPA by solvent separation using toluene and ethyl acetate.

[0286] Example E In Example E, TPA (Test Examples E1 and E3) or BHET (Test Example E2) was obtained from the depolymerized product obtained in Test Example 19 of Example A, as will be described later. In addition, in Test Example E1, PET was obtained from the obtained TPA. 1 HNMR analysis showed that the depolymerized product contained TPA, BCET, and MCET.

[0287] (HPLC conditions: Test Examples E1 and E2) The TPA content of the target substance in Test Example E1 and the TPA, MCET, BCET, and BHET contents of the target substances in Test Example E2 were measured by HPLC as follows. First, 20 mg of the target substance was weighed and placed into weighed, empty screw bottle 1, and screw bottle 1 was then weighed. Next, 10 mL of DMF was placed into screw bottle 1, stirred thoroughly, and then weighed. Next, screw bottle 2 was prepared, weighed empty, and then 9 mL of DMF was placed into screw bottle 2 and weighed. Next, empty screw bottle 3 was prepared, weighed, and then 10 mL of mobile phase was placed into screw bottle 2 and weighed. Next, 300 μL of the solution in screw bottle 1 was taken and placed into screw bottle 3 and weighed. The solution in screw bottle 3 was then transferred to a 1.5 mL vial and subjected to HPLC analysis for the TPA content. The HPLC method was set as follows. Temperature: 40°C, Pressure: 50.0 MPa, Column flow rate: 0.30 mL / min, Column type: AQ-C18 1.9 μm (Lot. No.: RAQ2-6366), Solvent: 0.05% by volume aqueous phosphoric acid:methanol = 60:40 mixed solution, Detection wavelength: 236 nm (wavelength 1), 254 nm (wavelength 2), Time: 20 min (alkali hydrolyzed sublimate)

[0288] (HPLC conditions: Test Example E3) In Test Example E3, the TPA content of the target substance was measured by HPLC as follows. First, 0.100 g of the target substance was weighed and dissolved in 40 ml of DMF. Then, 0.300 ml of the resulting solution was added dropwise to 40 ml of mobile phase. The resulting solution was subjected to HPLC analysis for the TPA content. The HPLC method was set as follows: Temperature: 40°C, Pressure: 50.0 MPa, Column flow rate: 0.30 mL / min, Column type: AQ-C18 1.9 μm, Mobile phase: 0.05% by volume phosphoric acid aqueous solution: methanol = 65:35 mixed solution, Analysis wavelength: 236 nm (wavelength 1), 254 nm (wavelength 2)

[0289] In Test Examples E1 to E3, the TPA yield refers to the ratio (%) of the amount of terephthalic acid to the amount of terephthalic acid obtained by subjecting the same amount of depolymerized product to hydrolysis. The hydrolysis was performed by first weighing a centrifuge tube containing a stirrer, and then adding 0.1 g of the depolymerized product to the centrifuge tube and weighing it. Next, 2 mL of tetrapropylammonium hydroxide and 10 mL of methanol were added to the centrifuge tube. The mixture was then reacted for 7 days at 75°C and 800 rpm with stirring in a personal organic synthesis apparatus. During this process, tetrapropylammonium hydroxide and methanol were added as needed to prevent the solvent in the centrifuge tube from drying up. The depolymerized product was hydrolyzed by the above procedure.

[0290] ( 1 H-NMR analysis) In Test Example E1, 1H-NMR analysis was performed according to the following procedure. First, an empty screw bottle was weighed. 8 mg of the object to be measured was weighed and placed in the screw bottle, and the screw bottle was weighed. Then, 500 μL of DMSO-d6 was placed in the screw bottle, and the screw bottle was weighed. Then, an NMR tube was prepared and weighed empty, and then 50 μL of the solution in the screw bottle was taken and placed in the NMR tube. Then, the NMR tube was weighed. 600 μL of DMSO-d6 was placed in the NMR tube, and the NMR tube was weighed. Then, analysis was performed using a JNM-ECX500 (manufactured by JEOL).

[0291] (GPC analysis) In Test Example E1, the molecular weight of PET was measured by GPC analysis. Specifically, an empty test tube was first weighed, and 25 mg of the PET to be measured was placed in the tube. The test tube was then weighed. 0.5 mL of o-chlorophenol was then placed in the test tube and weighed. The test tube was then heated to 130°C without stirring to dissolve the PET in the o-chlorophenol. After dissolution, 9.5 mL of chloroform was placed in the test tube, gently shaken, and weighed. An empty screw bottle was then prepared and weighed, and 2 mL of the solution from the test tube was placed in the screw bottle. The screw bottle was then weighed again. 3 mL of chloroform was then placed in the screw bottle and weighed. The solution from the screw bottle was then transferred to a 1.5 mL vial and subjected to GPC analysis. The GPC analysis conditions were as follows. Temperature: 40°C, Column flow rate: 0.80 mL / min, Column type: TSKgel SuperHM-M (Part No.: 0018000, Column No.: 901KA00077K), Solvent: Chloroform, Wavelength: 254 nm, Analysis time: 25 min

[0292] (DSC measurement) In Test Example E1, the crystallization temperature and melting point of PET were determined by DSC measurement. Specifically, approximately 10 mg of PET to be measured was placed in an aluminum capsule, and then pretreated by heating the sample to 300°C, holding it for 10 minutes to melt it, and then rapidly cooling it to make it amorphous. The sample was then heated from room temperature to 300°C at a heating rate of 10°C / min using a DSC6200 (Seiko Instruments Inc.), and the heat absorption and heat generation in the sample were measured.

[0293] (Test Example E1) In Test Example E1, the depolymerized product was hydrolyzed in water to obtain TPA crystals (Test Example E1-1), and the depolymerized product was hydrolyzed in an organic solvent containing water to obtain TPA crystals (Test Example E1-2).

[0294] (Test Example E1-1) 5.00 g of the depolymerized product was weighed and placed in an autoclave (TAS-100 pressure-resistant glass) with a Teflon inner tube. 50 mL of distilled water was then added and weighed. The mixture was then heated in an oven at 210 °C for 4 hours. After heating, the autoclave was removed and left overnight at room temperature. The autoclave was then opened. Crystals were observed inside the autoclave. The crystals were filtered under reduced pressure using a membrane filter. The crystals were washed with methanol during the vacuum filtration, and the washings were collected along with the filtrate. The crystals were dried overnight at 70 °C under vacuum. The crystals obtained after drying were weighed and the recovery amount calculated was 3.03 g. The chromatogram obtained by subjecting the crystals and the depolymerized product to HPLC under the above conditions is shown in Figure 9. The purity, yield, WI, YI, and visually observed color of the TPA in the crystals are shown in Table 8 below. Hereinafter, the crystals will also be referred to as "crystals (distilled water)."

[0295] Although the depolymerized product had extremely low solubility in water, it was demonstrated that MCET and BCET contained in the depolymerized product could be converted to TPA by carrying out the reaction under high temperature or high temperature and pressure conditions as described above.

[0296] As shown in Figure 9, in addition to TPA, peaks for MCET and BCET were detected in the depolymerized product, but in the crystals (distilled water), only a TPA peak was detected, but no MCET or BCET peaks were detected, indicating that the crystals (distilled water) had a high TPA purity.

[0297] (Test Example E1-2) In Test Example E1-2, the depolymerized product was hydrolyzed in a solvent containing DMI, NMP, or DMAc. Specifically, the depolymerized product was weighed out in the amount (g) shown in Table 8 below and placed in a glass test tube containing a stirrer. Each organic solvent was then added to the glass test tube in the amount shown in Table 8 below. The glass test tube was then stirred at 130°C and 600 rpm using a heated stirrer to completely dissolve the depolymerized product in the solvent. After confirming complete dissolution, distilled water was added in an amount 1 / 5 by weight of the depolymerized product. The mixture was then stirred at 130°C and 600 rpm using a heated stirrer for 24 hours. Crystal formation was observed during the reaction. The glass test tube was then removed from the heated stirrer and allowed to cool at room temperature overnight, during which time further crystals formed. The liquid portion was filtered under reduced pressure using a membrane filter and collected in a centrifuge tube. During filtration, the crystals were washed with methanol, and the washings were collected in the centrifuge tube along with the filtrate. The collected crystals were dried overnight at 70°C under vacuum. The dried crystals were weighed and the amount recovered was calculated. The TPA purity, TPA yield, WI, YI, and visually observed color of the crystals are shown in Table 9 below. Hereinafter, the crystals obtained as described above using a solvent containing DMI, NMP, or DMAc will be referred to as "crystals (DMI)," "crystals (NMP)," and "crystals (DMAc)," respectively.

[0298] [Table 8]

[0299] [Table 9]

[0300] As shown in Table 9, hydrolysis of the depolymerized product using distilled water or a mixed solvent of DMI and distilled water resulted in a high yield of TPA and a high purity of TPA. It was also shown that white TPA could be obtained by hydrolyzing the depolymerized product using a mixed solvent of DMI and distilled water. The molar ratio of BCET, MCET, and TPA in the depolymerized product was approximately BCET:MCET:TPA = 1:2:1, and the purity of TPA in the depolymerized product was approximately 20-30%. Therefore, it can be said that the purity of TPA in the crystals of Test Examples E1-1 and E1-2 was increased from that of the depolymerized product.

[0301] Next, TPA (Tokyo Chemical Industry Co., Ltd.) 1 The H-NMR spectrum of the crystal (NMP) is shown in Figure 10. 1 The H-NMR spectrum is shown in Figure 11. As shown in Figures 10 and 11, these 1 The H-NMR spectra were similar, suggesting that the purity of the crystals (NMP) was as high as that of TPA (Tokyo Chemical Industry Co., Ltd.).

[0302] Next, PET was synthesized by melt polymerization or solid-state polymerization using crystals (NMP), crystals (DMI), or TPA (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter also referred to as "TPA (commercially available)") as a raw material.

[0303] (PET synthesis by melt polymerization method) An empty glass tube (internal volume approximately 20 mL) was weighed, and crystals (NMP), crystals (DMI), or commercially available TPA were added and weighed. BHET (Tokyo Chemical Industry Co., Ltd.) was added to the glass tube in a ratio of approximately 1 / 4 of the amount of TPA added. Furthermore, dehydrated ethylene glycol containing an SbO compound dissolved therein as a catalyst was added to the glass tube so that the Sb content was 300 ppm. The atmosphere inside the tube was then purged with Ar, and heating commenced. The temperature was raised to 255°C at a rate of 5°C / min. The glass tube was maintained at 255°C while being appropriately shaken until all of the TPA was dissolved. Once the contents of the glass tube had turned into a transparent liquid, the temperature was raised from 255°C to 265°C at a rate of 2°C / min and maintained at 265°C for 30 to 45 minutes. During this time, the pressure inside the sealed tube was gradually reduced from atmospheric pressure to 25 kPa. After holding at 265°C, the temperature was increased from 265°C to 275°C at a rate of 2°C / min and held at 275°C for 30 to 45 minutes. During this time, the pressure inside the sealed tube was gradually reduced from 25 kPa to 5 kPa. After holding at 275°C, the temperature was increased from 275°C to 280°C at a rate of 2°C / min and held at 280°C for 30 to 45 minutes. During this time, the pressure inside the sealed tube was gradually reduced from 5 kPa to 1 kPa. After holding at 280°C, the temperature was increased from 280°C to 285°C at a rate of 2°C / min and held at 285°C for 30 to 45 minutes. During this time, the pressure inside the sealed tube was gradually reduced from 1 kPa to the lowest vacuum level achievable by the device. After holding at 285°C, the sealed tube was filled with Ar to approximately atmospheric pressure, allowed to cool, and the solidified PET was removed. Hereinafter, the above PET obtained using crystalline (NMP), crystalline (DMI), and commercially available TPA as raw materials will also be referred to as melt-polymerized PET (NMP), melt-polymerized PET (DMI), and melt-polymerized PET (commercially available), respectively.

[0304] (PET synthesis by solid-state polymerization) The melt-polymerized PET (NMP), melt-polymerized PET (DMI), or commercially available melt-polymerized PET obtained in the above (PET synthesis by melt polymerization method) was subjected to solid-state polymerization, which involves polymerization below the melting point, to obtain high-molecular-weight PET. Specifically, an empty sealed glass tube was first weighed, and the PET obtained in the above (PET synthesis by melt polymerization method) was cut into approximately 5 mm square pieces and placed in the sealed glass tube and weighed. The pressure inside the sealed glass tube was then reduced to 0.5 kPa or less using a vacuum pump. The temperature was then increased to 140°C at a rate of 5°C / min to dry out any remaining moisture in the polymer chains of the PET, and the temperature was maintained at 140°C for 2-3 hours. The temperature was then immediately increased to 220°C at a rate of 5°C / min and maintained at 220°C for 4 hours. All heating was performed by continuously applying a vacuum pump to maintain a low pressure inside the sealed glass tube. After heating at 220°C, the sealed glass tube was cooled to room temperature under reduced pressure. The sealed glass tube was then filled with Ar gas up to atmospheric pressure, and the PET was then removed from the sealed glass tube. Hereinafter, the low molecular weight PET (NMP), low molecular weight PET (DMI), and PET obtained from the low molecular weight PET (commercially available) will also be referred to as solid-state polymerized PET (NMP), solid-state polymerized PET (DMI), and solid-state polymerized PET (commercially available), respectively.

[0305] DSC measurements were performed on melt-polymerized PET (NMP), solid-state polymerized PET (NMP), and an empty PET bottle of Ilohas® Tennensui (manufactured by The Coca-Cola Company). The crystallization temperatures were 108°C, 133°C, and 131°C, respectively, and the melting points were 225°C, 230°C, and 254°C, respectively. The crystallization temperature of melt-polymerized PET (NMP) was lower than that of the above-mentioned PET bottles, but the crystallization temperature of solid-state polymerized PET (NMP) was similar to that of the above-mentioned PET bottles. Therefore, it is believed that the degree of polymerization was sufficiently improved by solid-state polymerization.

[0306] GPC analysis of melt-polymerized PET (DMI), commercially available melt-polymerized PET, solid-state polymerized PET (DMI), and an empty PET bottle containing ILOHASU (registered trademark) Tennensui (manufactured by The Coca-Cola Company) revealed that their number-average molecular weights were 9,400, 7,800, 24,500, and 29,300, respectively. The number-average molecular weights of the melt-polymerized PET (DMI) and commercially available melt-polymerized PET were smaller than those of the PET bottles, but the number-average molecular weight of the solid-state polymerized PET (DMI) was comparable to that of the PET bottles. Therefore, it is believed that the number-average molecular weight was sufficiently improved by solid-state polymerization.

[0307] DSC measurements were performed on melt-polymerized PET (DMI), commercially available melt-polymerized PET, solid-state polymerized PET (DMI), and an empty PET bottle containing Ilohas® Tennensui (registered trademark) (manufactured by The Coca-Cola Company). The crystallization temperatures were 90°C, 107°C, 129°C, and 131°C, respectively, and the melting points were 242°C, 254°C, 249°C, and 255°C, respectively. The crystallization temperatures of the melt-polymerized PET (DMI) and commercially available melt-polymerized PET were lower than those of the PET bottles, but the crystallization temperature of the solid-state polymerized PET (DMI) was comparable to that of the PET bottles. Therefore, it is believed that the degree of polymerization was sufficiently improved by solid-state polymerization. Furthermore, the melting points of the melt-polymerized PET (DMI), commercially available melt-polymerized PET, and solid-state polymerized PET (DMI) were comparable to those of the PET bottles. From the above results, it is considered that the solid-state polymerized PET (DMI) has properties similar to those of empty PET bottles of Ilohasu (registered trademark) Tennensui (manufactured by Coca-Cola Company).

[0308] (Test Example E2) In Test Example E2, the production of BHET by esterification or transesterification of the above-mentioned depolymerized product will be described in detail with specific examples.

[0309] 1.0 g of the depolymerized product was added to a glass test tube along with a magnetic stirrer, and 3.0 mL of ethylene glycol reagent was then added. The glass test tube was heated and stirred at 100°C. One hour and 24 hours after the start of heating, a portion of the contents was removed and cooled to room temperature, resulting in the formation of crystals. The crystals were subjected to HPLC analysis using the method described above to confirm their composition. The results are shown in Table 10 below. The values ​​in Table 10 indicate the proportion (mol%) of the amount of each component relative to the total amount of TPA, MCET, BCET, and BHET.

[0310] [Table 10]

[0311] As can be seen from Table 10, TPA, MCET, and BCET contained in the depolymerized product were esterified or transesterified to BHET by heating in ethylene glycol at 100°C. Furthermore, most of the TPA, MCET, and BCET contained in the depolymerized product were converted to BHET by esterification or transesterification after 24 hours.

[0312] (Test Example E3) In Test Example 3, the depolymerized product was subjected to solvent separation using toluene (Test Example E3-0), and the resulting toluene-insoluble matter (Test Example E3-1) and toluene-soluble matter (Test Example E3-2) were each hydrolyzed to obtain TPA.

[0313] (Test Example E3-0) Empty PET bottle fragments of Ilohas® Tennensui (manufactured by The Coca-Cola Company) and PVC (JAN: 4987481347557, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed out in a mass ratio of 3:1 and heated in a vacuum glass chamber at 330°C to obtain a depolymerized PET. 10 mL of toluene was added to 4.0 g of the depolymerized product and the mixture was shaken. This mixture was centrifuged, and the upper toluene phase containing toluene-soluble matter was transferred to a separate container. Then, 10 mL of toluene was added to the remaining toluene-insoluble solid, and the mixture was shaken. The toluene phase was transferred to the same container. This procedure was repeated five times. This yielded a toluene phase containing toluene-soluble matter and toluene-insoluble matter.

[0314] In addition, based on the results of Example D, it can be said that the toluene phase containing the toluene-soluble matter contains BCET, and the toluene-insoluble matter contains MCET and TPA.

[0315] (Test Example E3-1) The toluene-insoluble matter obtained in Test Example E3-0 was dried under vacuum to remove the toluene, yielding 2.0 g of toluene-insoluble matter. 20 mL of water was added to 2.0 g of the toluene-insoluble matter, and the mixture was boiled in a test tube while stirring. After boiling for 24 hours, the resulting powder was separated by filtration and dried under vacuum. The mass of the resulting powder was measured, and the purity, WI, and YI of TPA were then measured. The yield of TPA was calculated by evaluating the total amount (mol) of MCET and TPA in the toluene-insoluble matter and then calculating the formula: (the amount of TPA in the crystals) / (the total amount of MCET and TPA in the toluene-insoluble matter) × 100 (%). The results are shown in Table 11 below.

[0316] (Test Example E3-2) To the toluene phase containing the toluene-soluble matter obtained in (Test Example E3-0), 9 mL of 0.6 M aqueous NaOH solution was added, and the mixture was sealed in a glass container and heated and stirred at 75°C for 24 hours. The lower aqueous phase was then separated and collected, and 2 M aqueous HCl solution was added until crystal precipitation stopped. The precipitated crystals were collected by vacuum filtration and dried under vacuum. The mass of the obtained crystals was measured, and the TPA purity, WI, and YI were then measured. The TPA yield was calculated by evaluating the amount of BCET (mol) in the toluene phase and then calculating the formula: (the amount of TPA in the crystals) / (the amount of BCET in the toluene phase) × 100 (%). The results are shown in Table 11 below.

[0317] [Table 11]

[0318] As shown in Table 11, high-purity TPA crystals were obtained by hydrolysis of both the toluene-insoluble and toluene-soluble fractions. As mentioned above, the hydrolysis of the toluene-insoluble fraction proceeded by boiling in water, eliminating the need for alkaline components such as NaOH. Therefore, by separating the depolymerized product with toluene and then hydrolyzing the toluene-insoluble and toluene-soluble fractions, respectively, it was possible to reduce the amount of alkaline components such as NaOH used compared to directly hydrolyzing the depolymerized product. Furthermore, the WI of the crystals obtained by hydrolysis of the toluene-insoluble fraction was high, but the YI was low. This is likely due to the separation of impurities, such as PVC plasticizers, that cause coloration in the depolymerized product as toluene-soluble matter.

[0319] Example F In Example F, TPA was obtained by hydrolysis of the depolymerized product obtained in Test Example 19 of Example A, purification with activated carbon, etc., as described below. 1 HNMR analysis showed that the depolymerized product contained TPA, BCET, and MCET.

[0320] (HPLC conditions) The content of TPA to be measured in Example F was measured by the following HPLC. First, 0.100 g of the solid to be measured was weighed and dissolved in 40 mL of DMF. 0.300 mL of the resulting solution was added dropwise to 40 mL of the mobile phase described below. The resulting solution was subjected to HPLC analysis to determine the TPA content. The HPLC method was set as follows: Temperature: 40°C, Pressure: 50.0 MPa, Column flow rate: 0.30 mL / min, Column type: AQ-C18 1.9 μm, Mobile phase: 0.05% by volume phosphoric acid aqueous solution: methanol = 65:35 mixed solution, Detection wavelength: 236 nm (wavelength 1), 254 nm (wavelength 2)

[0321] Here, the yield of TPA was determined in the same manner as in Test Examples E1 to E3 above.

[0322] To 1.0 g of the depolymerized product, 10 mL of 1.3 M NaOH aqueous solution was added, and 1.0 g of activated carbon (Fujifilm Wako, activated carbon, crushed, 0.2-1 mm) was added. The mixture was heated and stirred at 90°C for 5 hours. The activated carbon was then removed by vacuum filtration to obtain a filtrate. 10 mL of 2.0 M diluted hydrochloric acid was added to the filtrate, and the resulting TPA was recovered by vacuum filtration and dried in vacuo to remove water. The mass of the resulting TPA was measured, followed by measurements of the yield, purity, WI, and YI. For comparison, the WI and YI of the depolymerized product and a commercially available TPA reagent (Tokyo Chemical Industry Co., Ltd.) were also measured. These results are shown in Table 12. In Table 12, "Test Example F" refers to the TPA obtained as described above.

[0323] [Table 12]

[0324] As shown in Table 12, the WI of the TPA obtained as described above was higher than that of commercially available TPA. Furthermore, the YI of the TPA obtained as described above was lower than that of commercially available TPA. These results demonstrate that the use of activated carbon significantly increases the purity of TPA obtained from the depolymerized product as a recycled raw material, significantly increases the WI, and significantly reduces the YI. [Explanation of symbols]

[0325] 1...pyrolysis furnace, 2...plastic supply inlet, 3...capture section, 4,5,8...piping, 9...cooling section, 10...treatment furnace, 11...heating section, 12...cooling section, 13...exit, 14...exhaust outlet, 20...first container, 22...second container, 24...third container, 26...fourth container, 28...fifth container, 30...first connecting pipe, 32...second connecting pipe, 32a...pressure gauge, 32b...circulating pump, 32c...flow meter, 34...third connecting pipe, 34a...cock, 36...fourth connecting pipe, 36a...pump, 36b...cock, 36c...cock, 101...plastic processing device, 102...plastic processing device, 104...apparatus used in a production method or the like for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin mixture containing polymer E, 106...apparatus used in a production method or the like for producing a residue for recycling.

Claims

1. A method for producing a residue for recycling, comprising the steps of: treating a resin mixture containing a polymer having an ester bond (polymer E) with a depolymerization accelerator for polymer E to produce a depolymerized product; and removing the depolymerized product to obtain a residue with a reduced content of polymer E.

2. The method according to claim 1 , wherein the depolymerization accelerator is at least one selected from the group consisting of hydrogen chloride and chlorine.

3. the resin mixture includes a polymer having a chlorine atom (polymer C), The method according to claim 1 or 2, wherein the depolymerization accelerator contains hydrogen chloride generated by thermal decomposition of the polymer C.

4. The method according to any one of claims 1 to 3, wherein the depolymerized product is a carboxylic acid or a derivative thereof.

5. The method according to any one of claims 1 to 4, wherein the depolymerized product is removed in a gaseous state.

6. The method according to any one of claims 1 to 5, wherein the polymer E is a polyester.

7. The method according to any one of claims 1 to 6, wherein the depolymerization accelerator for polymer E is allowed to act on the resin mixture in a heated state.

8. The method according to claim 7, wherein the heating is carried out at 600°C or less.

9. A method for producing a depolymerized product containing a carboxylic acid or a derivative thereof from a resin containing a polymer having an ester bond (polymer E), comprising the steps of: The depolymerization product in a gaseous state produced by reacting a depolymerization accelerator for polymer E with the resin is separated from the depolymerization reaction system and condensed or sublimated.

10. allowing the depolymerization accelerator to act on the resin in a first container containing the resin; The method according to claim 9 , wherein the gaseous depolymerized product is separated from the depolymerization reaction system by being introduced into a second container.

11. The production method according to claim 10, wherein the depolymerization accelerator is introduced into a second vessel together with the depolymerized product, and at least a portion of the depolymerization accelerator introduced into the second vessel is introduced in a gaseous state into the first vessel.

12. The method according to any one of claims 9 to 11, wherein the depolymerization accelerator is at least one selected from the group consisting of hydrogen chloride and chlorine.

13. the resin is a resin mixture containing a polymer having a chlorine atom (polymer C), The method according to any one of claims 9 to 11, wherein the depolymerization accelerator contains hydrogen chloride generated by thermal decomposition of polymer C.

14. The method according to any one of claims 9 to 13, wherein the polymer E is a polyester.

15. The method according to any one of claims 9 to 14, wherein the depolymerization accelerator for polymer E is allowed to act on the resin in a heated state.

16. The method according to claim 15, wherein the heating is carried out at 600°C or less.

17. A method for producing terephthalic acid crystals, comprising: allowing hydrogen chloride to act on a resin containing a reaction product of a diol and terephthalic acid, to produce a depolymerized product containing terephthalic acid and an ester of terephthalic acid and a chloroalcohol in which one hydroxyl group of the diol is substituted with a chlorine atom; hydrolyzing the ester to increase the content of terephthalic acid in the depolymerized product; and crystallizing the terephthalic acid during and / or after the hydrolysis.

18. the reactant is polyethylene terephthalate; The process according to claim 17, wherein the esters are mono(2-chloroethyl) terephthalate and bis(2-chloroethyl) terephthalate.

19. The method according to claim 17 or 18, wherein the depolymerized product is hydrolyzed in a solvent containing water under heating.

20. The method of claim 19, wherein the solvent is an aprotic polar solvent.

21. A method for producing crystals of bis(2-hydroxyethyl) terephthalate, comprising: allowing hydrogen chloride to act on a resin containing a reaction product of a diol and terephthalic acid; producing a depolymerized product containing terephthalic acid; and an ester of terephthalic acid and a chloroalcohol in which one hydroxyl group of the diol has been substituted with a chlorine atom; and then producing bis(2-hydroxyethyl) terephthalate by esterification or transesterification; and crystallizing the resulting product.

22. the reactant is polyethylene terephthalate; The process of claim 21, wherein the esters are mono(2-chloroethyl) terephthalate and bis(2-chloroethyl) terephthalate.

23. The method according to claim 21 or 22, wherein the depolymerization product is esterified or transesterified with ethylene glycol.

24. The method according to claim 23, wherein the depolymerization product is subjected to esterification or transesterification in the ethylene glycol in a heated state.

25. A method for producing a raw material for recycling containing bis(2-chloroethyl) terephthalate, the method comprising contacting a depolymerized product, which is produced by allowing hydrogen chloride to act on a resin containing polyethylene terephthalate, and which contains terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, with a solvent, removing matter insoluble in the solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate, and obtaining the bis(2-chloroethyl) terephthalate dissolved in the solvent, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

26. The method according to claim 25, wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

27. a depolymerization product, which is produced by allowing hydrogen chloride to act on a resin containing polyethylene terephthalate and which contains terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, is brought into contact with a first solvent, and the bis(2-chloroethyl) terephthalate dissolved in the first solvent is separated from a matter insoluble in the first solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate; a method for producing a recycle raw material containing mono(2-chloroethyl) terephthalate, the method comprising contacting the insoluble matter with a second solvent to remove the insoluble matter in the second solvent containing the terephthalic acid, and obtaining the mono(2-chloroethyl) terephthalate dissolved in the second solvent, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively; the solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

28. 28. The method according to claim 27, wherein the first solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

29. 29. The method according to claim 27 or 28, wherein the second solvent is at least one solvent selected from the group consisting of an ether solvent, a ketone solvent, an ester solvent, and an alcohol solvent.

30. a depolymerization product, which is produced by allowing hydrogen chloride to act on a resin containing polyethylene terephthalate and which contains terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, is brought into contact with a first solvent, and the bis(2-chloroethyl) terephthalate dissolved in the first solvent is separated from a matter insoluble in the first solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate; A method for producing a recycle raw material containing terephthalic acid, comprising contacting the insoluble matter with a second solvent to obtain a matter insoluble in the second solvent, the matter containing the terephthalic acid, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the first solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively; the solubilities of terephthalic acid and mono(2-chloroethyl) terephthalate in the second solvent are 1% by mass or less and 1% by mass or more, respectively.

31. 31. The method according to claim 30, wherein the first solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

32. 32. The method according to claim 30 or 31, wherein the second solvent is at least one solvent selected from the group consisting of an ether solvent, a ketone solvent, an ester solvent, and an alcohol solvent.

33. A method for producing terephthalic acid crystals, comprising contacting a depolymerized product, which is produced by reacting hydrogen chloride with a resin containing polyethylene terephthalate, and which contains terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, with a solvent to remove insoluble matter in the solvent, which contains the terephthalic acid and the mono(2-chloroethyl) terephthalate, to obtain bis(2-chloroethyl) terephthalate dissolved in the solvent, and hydrolyzing the obtained bis(2-chloroethyl) terephthalate to produce terephthalic acid and crystallize the same, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

34. The method according to claim 33, wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

35. a depolymerization product produced by allowing hydrogen chloride to act on a resin containing polyethylene terephthalate, the depolymerization product containing terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate, is brought into contact with a solvent, and the bis(2-chloroethyl) terephthalate dissolved in the solvent is separated from a matter insoluble in the solvent, the matter containing the terephthalic acid and the mono(2-chloroethyl) terephthalate; A method for producing terephthalic acid crystals, comprising hydrolyzing the insoluble matter to increase the content of terephthalic acid in the insoluble matter, and crystallizing the terephthalic acid during and / or after the hydrolysis, the solubilities of terephthalic acid, mono(2-chloroethyl) terephthalate, and bis(2-chloroethyl) terephthalate in the solvent are 1% by mass or less, 3% by mass or less, and 3% by mass or more, respectively.

36. The method according to claim 35, wherein the solvent is at least one solvent selected from the group consisting of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and ether solvents.

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