Recycled monomers, recycled monomer production method, and recycled monomer production equipment

Abstract

To provide recycled monomers and a production method thereof, which method suppresses excessive reactions of products obtained by depolymerization, while taking advantage of merits of high-temperature and high-pressure water, and can generate recycled monomers such as a dicarboxylic acid and a diol in high yields.SOLUTION: In a preferable embodiment of the production method of recycled monomers of the present invention, when the polymer is a thermoplastic polyester (A) and when the melting point of the thermoplastic polyester as measured by a differential scanning calorimeter is represented by Mp°C, the reaction temperature by X°C, the reaction time by Y minutes, and the mass ratio of water and the thermoplastic polyester (A) by Z:1, X and X*Y*Z, the product of X, Y and Z, satisfy the following (I) and (II) simultaneously: (I) Mp≤X<300; and (II) 2000≤X*Y*Z≤20000.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a chemical recycling technology for polymers that achieves both resource recycling and reduction of greenhouse gas emissions. [Background technology]

[0002] In recent years, interest in global environmental issues has increased, triggered by the marine plastic problem, and awareness of the need to build a sustainable society is spreading. Global environmental issues include global warming, resource depletion, and water shortages, many of which are caused by the increase in resource consumption and greenhouse gas emissions due to the use of fossil fuels and rapid industrial development since the Industrial Revolution. Therefore, in order to build a sustainable society, technologies for recycling fossil resources such as plastics and reducing greenhouse gas emissions are becoming increasingly important.

[0003] Thermoplastic polyesters are used in large quantities in various fields, such as fibers, films, bottles, molded products, and engineering plastics. Known technologies for depolymerizing thermoplastic polyesters and returning them to monomers for recycling include the methanolysis method, in which methanol is reacted with thermoplastic polyester in the presence of a catalyst such as zinc acetate to recover methyl ester monomers, and the glucolysis method, in which ethylene glycol is reacted with thermoplastic polyester in the presence of a catalyst such as sodium carbonate to recover oligomers. Commercial facilities that use these technologies to depolymerize polyesters are already in operation.

[0004] Furthermore, as a method for depolymerizing thermoplastic polyester without using an organic solvent such as methanol or ethylene glycol, a method for recovering diol and dicarboxylic acid, which are raw material monomers, by contacting polyester with high-temperature, high-pressure water has been disclosed (see, for example, Patent Documents 1 to 3). The method for depolymerizing using only water has the advantage of being a green recycling method since it does not require a catalyst and does not use petroleum-derived organic solvents.

[0005] In the depolymerization using high-temperature, high-pressure water, a method has been disclosed in which an alkali is added to the water to improve the recovery rate of the dicarboxylic acid, which is the raw material monomer (e.g., Patent Documents 4 to 7). However, the depolymerization requires a long time or requires an extremely high depolymerization temperature.

[0006] Furthermore, plastics are often made of multiple polymers to give them the properties required for their intended use, and there are only a limited number of materials made of a single polymer. In order to recycle materials made of multiple polymers, studies have been conducted on the method of separating them into single polymers before depolymerization, and then depolymerizing each polymer to regenerate the monomers. However, there has been a need to develop recycling technology for materials that are difficult to separate.

[0007] In light of the above, if a method for simultaneously depolymerizing multiple polymers could be established, not only would the pretreatment step be unnecessary, but it would also be possible to develop a recycling process for materials composed of multiple polymers that could not previously be separated into single polymers.

[0008] Patent Document 8 describes a depolymerization method for hydrolyzing a material selected from polyester, polyamide, and polycarbonate. However, there is no mention of simultaneously depolymerizing multiple polymers.

[0009] Non-Patent Document 1 mentions the hydrolysis of PC (polycarbonate) / PBT (polybutylene terephthalate), PC / PET (polyethylene terephthalate), and PBT / PET, but the reaction temperature is high and it is difficult to obtain recycled monomers in high yields.

[0010] On the other hand, as a plastic recycling apparatus, for example, an apparatus has been disclosed in which unsaturated polyester resin molded products and subcritical water are contacted by batch processing in a weight ratio of the unsaturated polyester resin molded products to the subcritical water in the range of 1:6 to 1:9 at a temperature of 180°C to 250°C to produce a monomer (see Patent Document 9).

[0011] Also disclosed is an apparatus and method for continuously hydrolyzing waste polyethylene terephthalate (PET) by contacting it with high-temperature, high-pressure water in a molten state, and recovering the raw material monomer (see Patent Document 10). [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2000-309663 A [Patent Document 2] JP 2007-332361 A [Patent Document 3] Japanese Patent Application Publication No. 6-72922 [Patent Document 4] Special Publication No. 11-502870 [Patent Document 5] Japanese Patent Application Publication No. 8-302061 [Patent Document 6] International Publication No. 2007 / 148353 [Patent Document 7] International Publication No. 2004 / 041917 [Patent Document 8] U.S. Pat. No. 4,605,762 [Patent Document 9] JP 2012-106244 A [Patent Document 10] Japanese Patent Application Publication No. 9-77905 [Non-patent literature]

[0013] [Non-Patent Document 1] Waste Management,68(2017)24-31 Summary of the Invention [Problem to be solved by the invention]

[0014] According to the method for depolymerizing thermoplastic polyester disclosed in Patent Document 1, high yields of ethylene glycol and terephthalic acid can be obtained, such as 92% and 96%, respectively. However, the disclosed method for depolymerizing polyester performs the reaction at a high temperature of 300°C to 350°C, using about six times the amount of water, which has a very high specific heat capacity of 4.2 kJ / kg·K and a heat of vaporization of 2,250 kJ / kg, relative to the amount of thermoplastic polyester, and the energy costs for the depolymerization reaction and for recovering ethylene glycol from a low-concentration aqueous ethylene glycol solution are high.

[0015] In addition, in Patent Document 2, terephthalic acid is added during hydrolysis of polyethylene terephthalate, and ethylene glycol and terephthalic acid are obtained with a 100% yield at 300°C for 10 minutes. However, when the reaction temperature is changed to 265°C, the yield of ethylene glycol and terephthalic acid falls to 56%, and the yield falls further without the addition of terephthalic acid. Furthermore, water is used in a large amount, about 9 times the amount of thermoplastic polyester, which causes the problem of high energy costs.

[0016] On the other hand, the depolymerization method of polyethylene terephthalate disclosed in Patent Document 3 uses only water and has a relatively low reaction temperature of 280°C, and yet can obtain depolymerized products at high yields of 90% ethylene glycol and 96% terephthalic acid. However, the depolymerization reaction takes 6 hours, which is not efficient. Furthermore, in Patent Document 3, in order to improve the deterioration of color tone caused by coloring impurities having unsaturated bonds that are difficult to remove through purification, the waste PET is subjected to a hydrogenation treatment using 1% by weight of a palladium / carbon catalyst. In fact, when the present inventors performed a depolymerization experiment using polyethylene terephthalate as a raw material under the same or similar conditions as the method described in Patent Document 3, except that the hydrogenation treatment was not performed, the reaction mixture was colored light orange.

[0017] In view of the above-mentioned conventional techniques, the recycled monomer of the present invention, the method for producing the recycled monomer, and the first and second preferred aspects of the present invention described below aim to provide a method capable of producing recycled monomers such as dicarboxylic acids and diols in high yields by suppressing over-reaction of the product obtained by depolymerization while taking advantage of the advantages of high-temperature, high-pressure water.

[0018] In addition, a third preferred embodiment of the present invention described below aims to provide a method capable of producing recycled monomers, particularly dicarboxylic acids and diols, in high yields from materials composed of multiple polymers that have been difficult to chemically recycle until now.

[0019] On the other hand, the depolymerization apparatus disclosed in Patent Document 9 as a plastic recycling apparatus has a batch type reactor, so when treating a large amount, the reactor volume increases due to the influence of the cycle time of charging and discharging, which leads to an increase in the cost of the apparatus for producing recycled monomers and insufficient efficiency. On the other hand, when the amount of subcritical water added to the resin molded article is reduced, the amount of resin molded article treated increases, improving efficiency, but a sufficient yield of recycled monomers cannot be obtained.

[0020] In addition, the method and device for hydrolyzing waste PET disclosed in Patent Document 10 is a continuous type, which can prevent an increase in reactor volume as in the batch type, and can produce recycled monomer more efficiently than in the batch type. However, as in the above, when the amount of high-temperature, high-pressure water added to the waste PET is reduced, a sufficient recycled monomer yield cannot be obtained.

[0021] Therefore, an object of the present invention is to provide an apparatus for producing recycled monomers that can produce recycled monomers with high efficiency and high yield using a continuous reactor. [Means for solving the problem]

[0022] In order to solve the above problems, the present invention has the following configuration. 1. A recycled monomer produced by contacting a composition containing a polymer with subcritical water, wherein, in the composition containing the polymer, the melting point of the polymer measured with a differential scanning calorimeter is Mp℃, the reaction temperature is X℃, the reaction time is Y minutes, and the mass ratio of water to polymer is Z:1, and the product X·Y·Z of X, Y, and Z simultaneously satisfies the following (I) and (II): (I) Mp≦X<300 (II) 2000≦X·Y·Z≦20000 2. The recycled monomer according to claim 1, wherein the polymer is a thermoplastic polyester or a thermoplastic polyamide. 3. A recycled polymer obtained by repolymerizing the recycled monomer described in 1 above. 4. Clothing fibers, industrial fibers, films, sheets, automotive parts, or electric / electronic parts made using the recycled polymers described in 3 above. 5. A method for producing a recycled monomer, comprising the step of contacting a composition containing a polymer with subcritical water. 6. A method for producing a recycled monomer according to 5 above, wherein the polymer is a thermoplastic polyester (A), the melting point of the thermoplastic polyester (A) measured by a differential scanning calorimeter is Mp°C, the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to the thermoplastic polyester (A) is Z:1, and the product X·Y·Z of X, Y, and Z simultaneously satisfies the following (I) and (II): (I) Mp≦X<300 (II) 2000≦X·Y·Z≦20000 7. The method for producing a recycled monomer according to the above item 6, wherein a concentration of diol derived from the thermoplastic polyester (A) in the reaction mixture obtained by contacting a composition containing the thermoplastic polyester (A) with subcritical water and hydrolyzing the thermoplastic polyester (A) is 4.9 mass% or more. 8. The method for producing a recycled monomer according to the above item 6, wherein a concentration of cyclic ether derived from the thermoplastic polyester (A) in the reaction mixture obtained by contacting a composition containing the thermoplastic polyester (A) with subcritical water and hydrolyzing the thermoplastic polyester (A) is 3.0 mass% or more. 9. The method for producing a recycled monomer according to 6 above, wherein the mass ratio Z of the subcritical water to the thermoplastic polyester (A) is less than 6. 10. The method for producing a recycled monomer according to 6 above, wherein the thermoplastic polyester (A) is primarily at least one selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof. 11. The method for producing a recycled monomer according to the above 6, wherein the thermoplastic polyester (A) is a waste material containing at least a polyester. 12. The method for producing a recycled monomer according to the above item 6, wherein the recycled monomer is a dicarboxylic acid and / or a diol. 13. A method for producing a thermoplastic polyester using a dicarboxylic acid and / or a diol obtained by the method according to 12 above as a raw material. 14. A method for producing a thermoplastic polyester product, comprising using the thermoplastic polyester obtained by the method according to 12 above as a raw material to produce a product containing the thermoplastic polyester, such as a fiber, film or molded article. 15. A method for producing a product of a composition containing thermoplastic polyester, comprising using the composition containing thermoplastic polyester obtained by the method described in 12 above as a raw material to produce a product of the composition containing thermoplastic polyester, such as a fiber, a film or a molded article. 16. The method for producing a recycled monomer according to 5 above, wherein the polymer is a thermoplastic polyester (A) and 0.01 to 4.0 parts by weight of an alkali metal salt and / or an alkaline earth metal salt is blended with 100 parts by weight of the thermoplastic polyester (A). 17. The method for producing a recycled monomer according to the above 16, wherein 100 to 1,000 parts by weight of subcritical water is mixed with 100 parts by weight of the thermoplastic polyester (A). 18. The method for producing a recycled monomer according to the above 16, wherein the temperature in the step of contacting with subcritical water is 250 to 350°C. 19. The method for producing a recycled monomer according to the above 16, wherein the pressure in the step of contacting with subcritical water is 3 to 30 MPa. 20. The method for producing recycled monomers according to claim 16, wherein the alkali metal salt and / or alkaline earth metal salt is a metal hydroxide and / or a metal carbonate. 21. The method for producing a recycled monomer according to the above item 16, wherein the thermoplastic polyester (A) is at least one selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof. 22. The method for producing a recycled monomer according to the above item 16, wherein the composition containing the thermoplastic polyester (A) contains at least one selected from the group consisting of an antioxidant, a heat resistance agent, a weather resistance agent, a release agent and a crystal nucleating agent. 23. The method for producing a recycled monomer according to claim 16, wherein the composition containing the thermoplastic polyester (A) is a waste product. 24. The method for producing a recycled monomer according to claim 16, wherein the recycled monomer is a dicarboxylic acid and / or a diol. 25. A method for producing a thermoplastic polyester using a dicarboxylic acid and / or a diol obtained by the method according to 24 above as a raw material. 26. A method for producing a composition containing a thermoplastic polyester, comprising blending at least one selected from an antioxidant, a weather resistance agent, a release agent and a crystal nucleating agent with the thermoplastic polyester obtained by the production method described in 25 above. 27. A method for producing a thermoplastic polyester product, comprising using the thermoplastic polyester obtained by the method described in 25 above as a raw material to produce a product containing thermoplastic polyester such as fiber, film or molded article. 28. A method for producing a product of a composition containing thermoplastic polyester, comprising using the composition containing thermoplastic polyester obtained by the method described in 26 above as a raw material to produce a product of the composition containing thermoplastic polyester, such as a fiber, a film or a molded article. 29. A composition comprising a polymer, comprising polymer I and polymer II; Polymer I is a thermoplastic polyester (A), Polymer II is one polymer selected from the group consisting of thermoplastic polyester (B) having a melting point different from that of thermoplastic polyester (A), polycarbonate and polyurethane, or a combination of these polymers; the content of polymer II in the composition (the total content of thermoplastic polyester (B), polycarbonate, and polyurethane) is 1 to 100 parts by weight based on 100 parts by weight of polymer I; 6. The method for producing a recycled monomer according to 5 above, comprising the step of simultaneously contacting polymer I and polymer II in the composition with subcritical water at 250 to 350°C. 30. A composition comprising a polymer, comprising polymer I and polymer II; Polymer I is a thermoplastic polyester (A), Polymer II is one polymer selected from the group consisting of thermoplastic polyester (B) having a melting point different from that of thermoplastic polyester (A), polycarbonate and polyurethane, or a combination of these polymers; the content of polymer II in the composition (the total content of thermoplastic polyester (B), polycarbonate, and polyurethane) is 1 to 100 parts by weight based on 100 parts by weight of polymer I; 6. The method for producing a recycled monomer according to 5 above, comprising the step of simultaneously hydrolyzing polymer I and polymer II in the composition by contacting them with subcritical water at 200 to 350° C. in the presence of an alkaline component. 31. A method for producing a recycled monomer described in claim 29 or 30, wherein the composition containing the polymer comprises a mixture of a composition containing polymer I and a composition containing polymer II, and / or a mixture of a composition containing polymer I and a composition containing polymer II. 32. The method for producing a recycled monomer according to 29 or 30 above, wherein 100 to 900 parts by weight of water are mixed with respect to 100 parts by weight of the polymer component in the composition containing the polymer. 33. The method for producing a recycled monomer according to 29 or 30 above, wherein the pressure in the step of contacting with subcritical water is 4.0 MPa to 30 MPa. 34. A method for producing a recycled monomer according to claim 29, further comprising blending an alkaline component into the composition containing the polymer. 35. The method for producing a recycled monomer according to claim 29 or 30, wherein the thermoplastic polyester (A) is selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate and copolymers thereof. 36. A method for producing a recycled monomer described in 29 or 30 above, wherein the thermoplastic polyester (B) is at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate and copolymers thereof, and is a thermoplastic polyester having a melting point different from that of the polyester (A). 37. A method for producing a recycled monomer according to claim 29 or 30, wherein the difference in melting point between the thermoplastic polyester (A) and the thermoplastic polyester (B) is 10°C or more. 38. The method for producing a recycled monomer according to claim 29 or 30, wherein the composition containing the polymer is a waste product. 39. The method for producing a recycled monomer according to claim 29 or 30, wherein the recycled monomer is terephthalic acid and / or a diol. 40. A method for producing a thermoplastic polyester, comprising using a dicarboxylic acid and / or a diol obtained by the method according to 29 or 30 above as a polymerization raw material to produce a thermoplastic polyester. 41. A method for producing a thermoplastic polyester product, comprising using the thermoplastic polyester obtained by the method described in 40 above as a raw material to produce a thermoplastic polyester product such as a fiber, film or molded article. 42. A method for producing a product of a composition containing a thermoplastic polyester, comprising using the composition containing a thermoplastic polyester obtained by the method described in 40 above as a raw material to produce a product of the composition containing a thermoplastic polyester, such as a fiber, a film or a molded article. 43. A thermoplastic polymer-containing composition supplying apparatus comprising: a means (L) for heating and pressurizing a composition containing a polymer and supplying the same; a means (M) for generating and supplying subcritical water; a means (N) for mixing the composition containing a thermoplastic polymer supplied from the means (L) with the subcritical water supplied from the means (M); and a continuous reactor (O) for hydrolyzing the polymer. Recycled monomer manufacturing equipment. 44. A system comprising a device (P) for monitoring the internal temperatures of the upstream and downstream parts of the continuous reactor (O) and a temperature control mechanism (Q) for heating and / or cooling the continuous reactor (O); The temperature control mechanism (Q) is operated based on the device (P) to control the internal temperature of the continuous reactor (O). 44. The apparatus for producing recycled monomers as described in 43 above. 45. A plurality of the temperature control mechanisms (Q) are installed; Operate a plurality of the temperature adjustment mechanisms (Q) based on the device (P); 44. The apparatus for producing recycled monomers as described in 43 above. 46. ​​The temperature control mechanism (Q) is controlled so that the internal temperature of the downstream portion of the continuous reactor (O) is 10°C or more lower than the internal temperature of the upstream portion. 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. 47. The continuous reactor (O) is a tubular continuous reactor. 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. 48. The means (L) is an extruder; 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. 49. The means (N) is a static mixer. 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. 50. The composition containing the polymer is a waste of a resin molded product. 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. 51. The polymer is a thermoplastic polyamide or a thermoplastic polyester; 46. ​​The apparatus for producing recycled monomers according to 44 or 45 above. Effect of the Invention

[0023] The recycled monomer of the present invention, the method for producing the recycled monomer, and the first preferred embodiment of the present invention described below can depolymerize a composition containing a thermoplastic polyester with high efficiency even by treating the composition with a small amount of water for a short period of time, and can provide a reaction mixture containing diols and dicarboxylic acids at high concentrations, thereby providing a method that consumes less energy for the depolymerization reaction and distillative purification. Furthermore, the depolymerization reaction conditions of low temperature and short time suppress secondary reactions of diols and dicarboxylic acids, and colorless diols and dicarboxylic acids can be obtained in high yields.

[0024] In addition, in a second preferred embodiment of the present invention described below, a specific amount of an alkali metal salt and / or an alkaline earth metal salt is added to hydrolyze a composition containing a thermoplastic polyester, thereby suppressing over-reaction of the product and producing a dicarboxylic acid and / or a diol in high yield.

[0025] Furthermore, a third preferred embodiment of the present invention described later can provide a method for simultaneously hydrolyzing a material composed of multiple polymers that has been difficult to chemically recycle, and producing recycled monomers in high yields. In particular, by having a step of simultaneously hydrolyzing a composition containing specific amounts of polymer I composed of thermoplastic polyester (A) and polymer II composed of at least one selected from thermoplastic polyester (B) having a melting point different from that of thermoplastic polyester (A), polycarbonate, and polyurethane, using subcritical water in a specific temperature range, dicarboxylic acid and / or diol can be produced in high yields.

[0026] In addition, the recycled monomer production apparatus of the present invention uses a continuous reactor and precisely controls the reaction temperatures in the upstream and downstream of the continuous reactor, thereby enabling the production of recycled monomer with high efficiency and high yield. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a production apparatus for recycled monomers according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing another embodiment of the recycling monomer production apparatus of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will now be described in further detail.

[0029] [1] Recycled monomers, recycled polymers, and various products made from recycled monomers The recycled monomer of the present invention is a recycled monomer produced by contacting a composition containing a polymer with subcritical water, and is produced under conditions where, in the composition containing a polymer, the melting point of the polymer measured with a differential scanning calorimeter is Mp°C, the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to polymer is Z:1, the product X·Y·Z of X, Y, and Z simultaneously satisfies the following (I) and (II): (I) Mp≦X<300 (II) 2000≦X·Y·Z≦20000.

[0030] The recycled monomer is preferably a monomer obtained by depolymerizing a polymer that is produced in large quantities and has a high need for recycling. Specifically, a monomer of a thermoplastic polyester or a monomer of a thermoplastic polyamide is preferable. Examples of the former monomer include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, 1,4-anthracenedicarboxylic acid, 1,5-anthracenedicarboxylic acid, 1,8-anthracenedicarboxylic acid, 2,6-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, and dimer acid; and 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid. Examples of the suitable dicarboxylic acids include alicyclic dicarboxylic acids and their ester-forming derivatives; aliphatic or alicyclic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol; long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol; and aromatic dioxy compounds, such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, and bisphenol F, and their ester-forming derivatives.

[0031] Examples of the latter monomers include amino acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, 12-aminododecanoic acid, and para-aminomethylbenzoic acid, lactams such as ε-caprolactam and ω-laurolactam, ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, and tetradecanediamine. Examples of the dicarboxylic acids include aliphatic diamines such as amines, pentadecanediamine, hexadecanediamine, heptadecanediamine, octadecanediamine, nonadecanediamine, eicosanediamine, 2-methyl-1,5-diaminopentane, and 2-methyl-1,8-diaminooctane; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid; and dialkyl esters and dichlorides of these dicarboxylic acids.

[0032] In the recycled monomer of the present invention, the polymer is preferably a thermoplastic polyester or a thermoplastic polyamide. As the thermoplastic polyester, a homopolymer or copolymer obtained by polycondensation of a dicarboxylic acid or its ester-forming derivative with a diol or its ester-forming derivative is preferable, and specifically, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polypropylene isophthalate, polybutylene isophthalate, polybutylene naphthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / naphthalate, polybutylene terephthalate / decane dicarboxylate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / poly Examples of aromatic polyester resins include ethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / succinate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polypropylene terephthalate / sebacate, polybutylene terephthalate / sebacate, polypropylene terephthalate / isophthalate / adipate, polybutylene terephthalate / isophthalate / succinate, polybutylene terephthalate / isophthalate / adipate, and polybutylene terephthalate / isophthalate / sebacate, and may be a mixture of two or more kinds.

[0033] On the other hand, the thermoplastic polyamide is preferably a homopolymer or copolymer obtained by polycondensation of an amino acid, lactam or dicarboxylic acid with a diamine, and specifically includes polycaproamide (polyamide 6), polyhexamethylene adipamide (polyamide 66), polytetramethylene adipamide (polyamide 46), polypentamethylene adipamide (polyamide 56), polytetramethylene sebacamide (polyamide 410), polypentamethylene sebacamide (polyamide 510), polyhexamethylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), and copolymers thereof, and may be a mixture of two or more kinds. From the viewpoint of large production amount and securing a large amount of recycling resources, it is more preferable that the polymer is a thermoplastic polyester.

[0034] The recycled polymer of the present invention can be obtained by repolymerizing the recycled monomer of the present invention. By repolymerizing the recycled monomer of the present invention to obtain a recycled polymer, the polymer can be used as a plastic material, thereby contributing to resource circulation.

[0035] The textile fibers for clothing, the textile fibers for industrial use, the films, the sheets, the automobile parts, or the electric / electronic parts of the present invention are made using the recycled polymers of the present invention. The products have the added value of being environmentally friendly.

[0036] [2] Method for producing recycled monomers The method for producing a recycled monomer of the present invention includes a step of contacting a composition containing a polymer with subcritical water. The method for producing a recycled monomer of the present invention includes the following four preferred aspects. In this specification, the three preferred aspects of the method for producing a recycled monomer of the present invention may be simply referred to as the "first preferred aspect of the present invention," the "second preferred aspect of the present invention," and the "third preferred aspect of the present invention," respectively. In addition, the method for producing a recycled monomer described in the section "(3) Apparatus for producing a recycled monomer" below may be simply referred to as the "fourth preferred aspect of the present invention."

[0037] [2-1] First Preferred Aspect of the Invention A first preferred embodiment is a method for producing a recycled monomer, which includes a step of contacting a composition containing a thermoplastic polyester (A) with subcritical water, in which, when the melting point of the thermoplastic polyester (A) measured with a differential scanning calorimeter is Mp°C, the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to thermoplastic polyester (A) is Z:1, the product X·Y·Z of X, Y, and Z simultaneously satisfies the following (I) and (II): (I) Mp≦X<300 (II) 2000≦X·Y·Z≦20000.

[0038] By bringing the thermoplastic polyester (A) into contact with subcritical water and hydrolyzing it, it is possible to depolymerize it into the diol and / or dicarboxylic acid that constitute the thermoplastic polyester (A).

[0039] The thermoplastic polyester (A) used in the present invention is a homopolymer or copolymer obtained by polycondensation of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as main raw materials. Here, the main raw material means that the constituent units of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative in the polymer are 50 mol % or more, preferably 80 mol % or more, and more preferably 90 mol % or more.

[0040] Examples of the dicarboxylic acid or its ester-forming derivative include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, 1,4-anthracenedicarboxylic acid, 1,5-anthracenedicarboxylic acid, 1,8-anthracenedicarboxylic acid, 2,6-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, and dimer acid; alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, and their ester-forming derivatives. Two or more of these may be used.

[0041] The ester-forming derivatives referred to here are the lower alkyl esters, acid anhydrides, acid halides, etc. of the dicarboxylic acids mentioned above. As the lower alkyl esters of dicarboxylic acids, methyl esters, ethyl esters, hydroxyethyl esters, hydroxybutyl esters, etc. are preferably used. As the acid anhydrides of dicarboxylic acids, anhydrides of dicarboxylic acids and anhydrides of dicarboxylic acids and acetic acid, etc. are preferably used. As the halides of dicarboxylic acids, acid chlorides, acid bromides, acid iodides, etc. are preferably used.

[0042] Examples of the diol or its ester-forming derivative include aliphatic or alicyclic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol, long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol, and aromatic dioxy compounds, such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, and bisphenol F, and ester-forming derivatives thereof. Two or more of these may be used.

[0043] Examples of homopolymers or copolymers having a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as structural units include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polypropylene isophthalate, polybutylene isophthalate, polybutylene naphthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / naphthalate, polybutylene terephthalate / decane dicarboxylate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene Examples of aromatic polyester resins include aromatic polyester resins such as ethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / succinate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polypropylene terephthalate / sebacate, polybutylene terephthalate / sebacate, polypropylene terephthalate / isophthalate / adipate, polybutylene terephthalate / isophthalate / succinate, polybutylene terephthalate / isophthalate / adipate, and polybutylene terephthalate / isophthalate / sebacate.

[0044] Here, " / " represents a copolymer. These homopolymers and copolymers may be used alone or in a mixture of two or more at any content. Among them, for the purpose of recycling the thermoplastic polyester (A) and promoting the cyclical use of fossil resources, homopolymers or copolymers made mainly from residues of aromatic dicarboxylic acids or their ester-forming derivatives, which are produced and consumed in large quantities, and aliphatic diols or their ester-forming derivatives are preferred. Examples of the preferred polymers include homopolymers or copolymers obtained by polycondensation of at least one selected from terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and their ester-forming derivatives, and at least one selected from ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol or their ester-forming derivatives, among which at least one selected from the group consisting of polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof are particularly preferably used.

[0045] The thermoplastic polyester (A) of the present invention may be blended with a polymerization catalyst, a thermoplastic resin other than the thermoplastic polyester, a dye, various additives, a fibrous filler, a filler other than the fibrous filler, etc., within the scope of the present invention. The fibrous filler here may be any filler having a fibrous shape. The filler other than the fibrous filler may be either an organic filler or an inorganic filler, and may be, for example, a non-fibrous filler. Two or more of these may be blended.

[0046] The thermoplastic polyester (A) of the present invention may be waste of a resin molded article containing at least a thermoplastic polyester. The waste of a resin molded article containing a thermoplastic polyester includes thermoplastic polyester products, industrial waste generated in the manufacturing process of a thermoplastic polyester product, or used waste of a thermoplastic polyester product. Examples of thermoplastic polyester products include containers such as beverage bottles and seasoning bottles, sheet products such as food trays, blister packs, food dividers, and industrial trays, film products such as packaging films, optical functional films, magnetic tapes, and insulating materials, textile structures for clothing such as used clothes, uniforms, sportswear, and innerwear, industrial textile structures such as curtains, carpets, nets, belts, and sheets, molded articles such as automobile parts, electric and electronic parts, building materials, daily necessities, household goods, and sanitary goods. Furthermore, waste products, pellet waste, and lump waste generated in the production process of these products are also subject to waste. Waste of a resin molded article containing a thermoplastic polyester may be subjected to the depolymerization method of the present invention together with products other than the thermoplastic polyester (A) to the extent that the effect of the present invention is not impaired.

[0047] A method for depolymerizing a thermoplastic polyester (A) in a first preferred embodiment of the present invention includes a step of contacting a thermoplastic polyester with subcritical water, and is characterized in that, when at least the thermoplastic polyester (A) and water are heated and mixed, when the melting point of the thermoplastic polyester is Mp°C, the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to thermoplastic polyester is Z:1, the product X·Y·Z of X, X, Y and Z simultaneously satisfies (i) Mp≦X<300 and (ii) 2000≦X·Y·Z≦20000.

[0048] The melting point of the thermoplastic polyester (A) in the present invention is the temperature of an endothermic peak that appears when the thermoplastic polyester (A) is cooled from a molten state to 30°C at a rate of 20°C / min under an inert gas atmosphere using a differential scanning calorimeter manufactured by TA Instruments, and then heated to the melting point + 40°C at a rate of 20°C / min. However, when two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is taken as the melting point. There is no particular restriction on the melting point of the thermoplastic polyester, but a preferred melting point range is more than 50°C and less than 300°C. If the melting point is more than 50°C, the thermoplastic polyester becomes solid at room temperature, and therefore has excellent handleability. In addition, if the melting point is less than 300°C, the melted state can be mixed with water in a temperature range where the conversion reaction of the depolymerization product can be suppressed, and therefore the reaction efficiency can be improved, which is preferable.

[0049] There are no particular limitations on the water used here, and any type of water may be used, such as tap water, ion-exchanged water, distilled water, or well water. From the viewpoint of suppressing side reactions due to the influence of coexisting salts, however, ion-exchanged water or distilled water is preferably used.

[0050] The water may be heated to a temperature between the melting point Mp℃ of the thermoplastic polyester (A) and less than 300℃ when reacting with the thermoplastic polyester (A). When the pressure is increased to 22.1MPa and the temperature to 374.2℃, the water is in a state that is neither liquid nor gas. This point is called the critical point of water, and hot water in the vicinity of the critical point at a temperature and pressure slightly lower than the critical point is called subcritical water. The water used in the present invention is subcritical water at a temperature lower than 300℃. Although this subcritical water is water, it has the characteristics of (i) a low dielectric constant and (ii) a high ionic product, and the dielectric constant and ionic product of subcritical water depend on the temperature and partial pressure of water and can be controlled. The low dielectric constant makes it an excellent solvent for organic compounds despite being water, and the high ionic product makes it have high hydrogen ion and hydroxide ion concentrations, resulting in excellent hydrolysis action.

[0051] In addition, the water pressure is preferably higher than the saturated vapor pressure. The water may be in a liquid state or a gaseous state such as water vapor, or both may be used. However, since the reaction proceeds more easily in a liquid state than in a gaseous state as a reaction field, the water pressure is preferably higher than the saturated vapor pressure. In addition, the upper limit of the water pressure is not particularly limited, but it is preferably 30 MPa. The upper limit of the water pressure is more preferably 25 MPa, and even more preferably 22 MPa. By being in such a pressure range, the ionic product of the water tends to be high, which is preferable. As a method of making the water pressure range like this, there is a method of pressurizing the inside of the pressure vessel and sealing it. To pressurize the inside of the pressure vessel, there is a method of sealing in a gas in addition to the water. Examples of such gases include air, argon, and nitrogen. From the viewpoint of suppressing side reactions such as oxidation reactions, it is preferable to use nitrogen or argon as the gas to be sealed. In addition, the inside of the pressure vessel can be pressurized by introducing high-pressure water. When using high-pressure water, it is also possible to make the pressure vessel gas-free. The degree of pressurization by gas or high pressure water is not particularly limited since it is set to the desired pressure, but is preferably 0.3 MPa or more.

[0052] In the method for depolymerizing a thermoplastic polyester resin (A) in the first preferred embodiment of the present invention, the reaction temperature is M°C or more and less than 300°C when the melting point of the thermoplastic polyester (A) is Mp°C. The reaction temperature here refers to the temperature during which the thermoplastic polyester (A) is reacted with water for a certain period of time in a temperature-controlled reaction vessel, and may be a constant temperature or a temperature that varies with time. There is no particular restriction on the temperature during the temperature increase process until the reaction temperature is reached or the cooling process after the reaction at the reaction temperature, as long as it does not exceed the reaction temperature. By setting the reaction temperature at or above the melting point of the thermoplastic polyester, the thermoplastic polyester (A) becomes molten during the reaction, and when mixed with water, it disperses in the form of droplets, increasing the interfacial area, thereby improving the reaction efficiency. On the other hand, by setting the reaction temperature to less than 300°C, the hot water solubility of the dicarboxylic acid that acts catalytically on the diol conversion reaction (overreaction) can be adjusted, and the diol conversion reaction can be suppressed. For the purpose of reducing coloration, the reaction temperature is preferably 290° C. or lower, and for the purpose of increasing the diol yield, the reaction temperature is particularly preferably 280° C. or lower.

[0053] When the reaction temperature X is in the above-mentioned preferred range, when the mass ratio of water to the thermoplastic polyester is Z:1, Z is preferably less than 6. Diols have high water solubility and are well mixed with water in a temperature range from room temperature to the reaction temperature X, while it is known that the water solubility of dicarboxylic acids tends to be low at room temperature and high in hot water. For example, terephthalic acid, which is a dicarboxylic acid produced by hydrolysis of polyethylene terephthalate and polybutylene terephthalate, is almost insoluble in water at room temperature (20°C) at 15 mg / L, but the higher the temperature, the higher the water solubility becomes, and the terephthalic acid aqueous solution becomes 10 mass% at 250°C and 44 mass% at 300°C. By adjusting the hot water solubility of the dicarboxylic acid in the temperature range where the reaction temperature X can be preferably taken and making Z less than 6, the concentration of the dicarboxylic acid relative to the diol can be relatively low, and diol and dicarboxylic acid can be obtained in high yield. From the advantages of improving the processing efficiency and avoiding the enlargement of the equipment, Z is more preferably 5 or less, and particularly preferably 4 or less.

[0054] The method for depolymerizing thermoplastic polyester (A) in the first preferred embodiment of the present invention is characterized in that, when the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to thermoplastic polyester is Z:1, the product X·Y·Z of X, Y, and Z is 2000≦X·Y·Z≦20000. The reaction time Y here refers to the time for mixing thermoplastic polyester (A) and water in a reaction vessel controlled at reaction temperature X. Y does not include the heating time until the reaction temperature X is reached or the cooling time after the reaction at reaction temperature X. The value of Y is not particularly limited as long as it satisfies the range of the product of X, Y, and Z, and can be set according to X and Z. The product of X, Y, and Z is preferably 17,500 or less, more preferably 15,000 or less, and particularly preferably 12,500 or less. In addition, the product of X, Y, and Z is preferably 2,200 or more, more preferably 2,400 or more, and particularly preferably 2,600 or more, for example. The reaction may be carried out at multiple temperatures, in which case the product X·Y·Z is the sum of the products X·Y·Z at each reaction temperature. The present invention relates to an energy-saving depolymerization method that aims to achieve both the recycling of fossil resources and the reduction of greenhouse gas emissions. Since the specific heat capacity of water is 4.3 kJ / kg·K and the heat of vaporization is 2,250 kJ / kg, which are very high compared to other organic solvents, it is important to reduce the amount of water used, and by setting the product of X, Y, and Z within these condition ranges, it is possible to achieve both efficient production of dicarboxylic acids and diols and energy conservation.

[0055] Furthermore, in order to achieve energy saving during diol recovery and purification, the concentration of the diol derived from the thermoplastic polyester (A) contained in the reaction mixture is preferably 4.9% by mass or more. The concentration of the diol is more preferably 6.0% by weight or more, and even more preferably 7.0% by weight or more. When the concentration of the diol contained in the reaction mixture is in the above-mentioned preferred range, the amount of the reaction mixture to be treated to recover 1 kg of diol can be reduced, so that the equipment can be made smaller, and the energy required for heating water during recovery can be reduced. The concentration of the diol derived from the thermoplastic polyester (A) contained in the reaction mixture can be determined by an absolute calibration curve method using a gas chromatography GC-2010 manufactured by Shimadzu Corporation. Note that the diol referred to here is a diol produced by depolymerization of the thermoplastic polyester (A), and is not one added before and / or after the reaction. As a method for adjusting the concentration of the diol derived from the thermoplastic polyester (A) contained in the reaction mixture to the above-mentioned preferred range, an example can be given of depolymerizing the thermoplastic polyester (A) according to the present invention, with the mass ratio Z of water to the thermoplastic polyester (A) being in the above-mentioned preferred range.

[0056] When polybutylene terephthalate is used as the thermoplastic polyester (A), the depolymerization produces butanediol, which is the raw material, and cyclic ether (tetrahydrofuran) produced by dehydration reaction of butanediol, and the amount of the latter cyclic ether produced increases. When polybutylene terephthalate is used as the thermoplastic polyester (A), the concentration of the cyclic ether derived from the thermoplastic polyester (A) in the reaction mixture is preferably 3.0 mass% or more. More preferably, it is 5.0 weight% or more, and even more preferably, it is 6.0 weight% or more. By being in the above-mentioned preferred range, energy consumption during recovery and purification of the cyclic ether can be suppressed.

[0057] As a result of investigating the reaction of a thermoplastic polyester with water to produce diols and dicarboxylic acids, the solubility of dicarboxylic acids in hot water, and the conversion reaction of diols, it has been found that for thermoplastic polyesters other than the above-mentioned polybutylene terephthalate, by setting X, the product of X, Y, and Z, and further setting Z within the above-mentioned ranges, the conversion reaction of diols can be suppressed, and the yield of dicarboxylic acids and diols constituting the thermoplastic polyester, particularly the yield of diols, can be significantly improved.

[0058] Further, by adding an alkaline component, the yield of the generated monomer can be improved. Examples of the alkaline component include alkali metals such as lithium, sodium, and potassium, alkaline earth metals such as calcium, hydroxides such as ammonium, carbonates, bicarbonates, and amines. In particular, at least one selected from sodium hydroxide, potassium hydroxide, and calcium hydroxide is preferable. The amount of the alkaline component is preferably 0.01 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the thermoplastic polyester (A). More preferably, it is 20 parts by weight or more, and even more preferably, it is 30 parts by weight or more. On the other hand, it is more preferably 45 parts by weight or less, and even more preferably, it is 42 parts by weight or less. When the alkaline component is added, a dicarboxylate is generated by hydrolysis of the thermoplastic polyester. The dicarboxylate can be converted into a dicarboxylic acid, which is a raw material for the thermoplastic polyester, by treating it with an acidic aqueous solution.

[0059] In the first preferred embodiment of the present invention, the depolymerization of the thermoplastic polyester can be carried out by various known reaction methods such as a batch method and a continuous method. For example, in the case of a batch method, an autoclave equipped with a stirrer and a heating function, a vertical or horizontal reactor, a vertical or horizontal reactor equipped with a compression mechanism such as a cylinder in addition to a stirrer and a heating function, and the like can be used. In the case of a continuous method, an extruder equipped with a heating function, a tubular reactor, a tubular reactor equipped with a mixing mechanism such as a baffle, a line mixer, a vertical or horizontal reactor, a vertical or horizontal reactor equipped with a stirrer, a tower, and the like can be used. In addition, the atmosphere in the production is preferably a non-oxidizing atmosphere, and is preferably carried out under an inert atmosphere such as nitrogen, helium, or argon, and is preferably a nitrogen atmosphere from the viewpoints of economy and ease of handling.

[0060] The method for recovering the diol and dicarboxylic acid produced by the depolymerization method for thermoplastic polyester in the first preferred embodiment of the present invention is not particularly limited, and any method can be adopted. For example, when the depolymerization reaction is carried out in a batch manner, the reaction mixture (C) can be obtained as a diol aqueous solution in which the solid dicarboxylic acid is dispersed and / or precipitated by distillation together with water after the depolymerization reaction is completed. When the depolymerization reaction is carried out in a continuous manner, the reaction mixture (C) can be obtained as a diol aqueous solution in which the solid dicarboxylic acid is dispersed as the reaction proceeds. The solid dicarboxylic acid is separated from the obtained reaction mixture (C) by a known method such as solid-liquid separation, and the diol is separated from water by distillation separation, whereby the diol and dicarboxylic acid with high purity can be recovered. In addition, if there is a component insoluble in water in the reaction mixture, it can be separated by a known method such as solid-liquid separation under conditions in which the dicarboxylic acid dissolves, and can be subjected to a diol and dicarboxylic acid recovery process.

[0061] To obtain a diol with a higher purity, the recovered diol can be combined with other purification methods such as precision distillation of the diol, distillation under reduced pressure with the addition of a small amount of sodium hydroxide, treatment with activated carbon, ion exchange treatment, recrystallization, etc. By these methods, impurities that are difficult to separate by distillation separation can be efficiently removed.

[0062] In the method for depolymerizing a thermoplastic polyester according to the first preferred embodiment of the present invention, a diol and a dicarboxylic acid with high purity can be obtained, and therefore, they can be used as polymerization raw materials for a thermoplastic polyester, similar to diols and carboxylic acids produced from petroleum-derived raw materials. Thermoplastic polyesters (recycled polymers) can be produced by subjecting diols and dicarboxylic acids or their ester-forming derivatives to a commonly known polycondensation reaction.

[0063] The thermoplastic polyester thus obtained, like the thermoplastic polyester produced from petroleum-derived raw materials, can be processed and used into various products such as clothing fibers, industrial fibers, films, sheets, bottles, injection molded products, etc. These products are useful as agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical supplies, automotive parts, electric and electronic parts, and other applications.

[0064] [2-2] Second Preferred Aspect of the Invention A second preferred embodiment of the present invention is a method for producing a recycled monomer, which comprises a step of contacting a composition containing a thermoplastic polyester (A) with subcritical water, and blending 0.01 to 4.0 parts by weight of an alkali metal salt and / or an alkaline earth metal salt with respect to 100 parts by weight of the thermoplastic polyester (A) in the composition containing the thermoplastic polyester (A). In the composition containing the thermoplastic polyester (A), other components such as additives affect the depolymerization of the thermoplastic polyester (A). In the second preferred embodiment of the present invention, blending an alkali metal salt and / or an alkaline earth metal salt can improve the yield of the recycled monomer obtained by depolymerization, and by keeping the blending amount to a small amount, an increase in the emission of greenhouse gases derived from the alkali metal salt and / or the alkaline earth metal salt can be suppressed.

[0065] The thermoplastic polyester (A) used in the second preferred embodiment of the present invention is a homopolymer or copolymer obtained by polycondensation of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as main raw materials. Here, the main raw material means that the constituent units of dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative in the polymer are 50 mol % or more, more preferably 80 mol % or more, and even more preferably 90 mol % or more.

[0066] Examples of the dicarboxylic acid or an ester-forming derivative thereof include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, 1,4-anthracenedicarboxylic acid, 1,5-anthracenedicarboxylic acid, 1,8-anthracenedicarboxylic acid, 2,6-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, and dimer acid; alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; and ester-forming derivatives thereof.

[0067] The ester-forming derivatives referred to here are the lower alkyl esters, acid anhydrides, acid halides, etc. of the dicarboxylic acids mentioned above. As the lower alkyl esters of dicarboxylic acids, methyl esters, ethyl esters, hydroxyethyl esters, hydroxybutyl esters, etc. are preferably used. As the acid anhydrides of dicarboxylic acids, anhydrides of dicarboxylic acids and anhydrides of dicarboxylic acids and acetic acid, etc. are preferably used. As the halides of dicarboxylic acids, acid chlorides, acid bromides, acid iodides, etc. are preferably used.

[0068] Examples of the diol or its ester-forming derivative include aliphatic or alicyclic glycols having 2 to 20 carbon atoms, such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, cyclohexanedimethanol, cyclohexanediol, and dimer diol; long-chain glycols having a molecular weight of 200 to 100,000, such as polyethylene glycol, poly-1,3-propylene glycol, and polytetramethylene glycol; aromatic dioxy compounds, such as 4,4'-dihydroxybiphenyl, hydroquinone, t-butylhydroquinone, bisphenol A, bisphenol S, and bisphenol F, and ester-forming derivatives thereof.

[0069] Examples of homopolymers or copolymers having a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as structural units include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene isophthalate, polypropylene isophthalate, polybutylene isophthalate, polyethylene naphthalate, polypropylene naphthalate, polybutylene naphthalate, polyethylene isophthalate / terephthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polyethylene terephthalate / naphthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / naphthalate, polybutylene terephthalate / decane dicarboxylate, polyethylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, polyethylene terephthalate / polyethylene Examples of aromatic polyester resins include aromatic polyester resins such as polyethylene glycol, polypropylene terephthalate / polyethylene glycol, polybutylene terephthalate / polyethylene glycol, polyethylene terephthalate / polytetramethylene glycol, polypropylene terephthalate / polytetramethylene glycol, polybutylene terephthalate / polytetramethylene glycol, polyethylene terephthalate / isophthalate / polytetramethylene glycol, polypropylene terephthalate / isophthalate / polytetramethylene glycol, polybutylene terephthalate / isophthalate / polytetramethylene glycol, polyethylene terephthalate / succinate, polypropylene terephthalate / succinate, polybutylene terephthalate / succinate, polyethylene terephthalate / adipate, polypropylene terephthalate / adipate, polybutylene terephthalate / adipate, polyethylene terephthalate / sebacate, polypropylene terephthalate / sebacate, and polybutylene terephthalate / sebacate.

[0070] Here, " / " represents a copolymer. These homopolymers and copolymers may be used alone or in a mixture of two or more at any content. Among them, for the purpose of recycling thermoplastic polyester and promoting the cyclical use of fossil resources, homopolymers or copolymers made mainly of aromatic dicarboxylic acid or its ester-forming derivative and aliphatic diol or its ester-forming derivative, which are produced and consumed in large quantities, are preferred. Examples of the preferred polymers include homopolymers or copolymers obtained by polycondensing at least one selected from terephthalic acid, naphthalenedicarboxylic acid, and their ester-forming derivatives with at least one selected from ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol or their ester-forming derivatives, and among them, the thermoplastic polyester (A) in the composition containing the thermoplastic polyester (A) is particularly preferably at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof.

[0071] Examples of the alkali metal salt include lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, cesium hydrogen carbonate, lithium phosphate, sodium phosphate, potassium phosphate, cesium phosphate, dilithium hydrogen phosphate, dipotassium hydrogen phosphate, dicesium hydrogen phosphate, lithium monohydrogen phosphate, sodium monohydrogen phosphate, potassium monohydrogen phosphate, cesium monohydrogen phosphate, lithium borate, sodium borate, potassium borate, cesium borate, lithium citrate, sodium citrate, potassium citrate, cesium citrate, lithium formate, sodium formate, potassium formate, cesium formate, lithium acetate, sodium acetate, potassium acetate, cesium acetate, lithium oxalate, sodium oxalate, potassium oxalate, cesium oxalate, lithium maleate, potassium maleate, and cesium maleate. Among these, lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and cesium hydrogen carbonate are more preferable.

[0072] Examples of alkaline earth metal salts include magnesium hydroxide, calcium hydroxide, barium hydroxide, magnesium carbonate, calcium carbonate, barium carbonate, magnesium phosphate, calcium phosphate, barium phosphate, magnesium hydrogen phosphate, calcium hydrogen phosphate, barium hydrogen phosphate, dimagnesium hydrogen phosphate, dicalcium hydrogen phosphate, dibarium hydrogen phosphate, magnesium borate, calcium borate, barium borate, magnesium citrate, calcium citrate, barium citrate, magnesium formate, calcium formate, barium formate, magnesium acetate, calcium acetate, barium acetate, magnesium borate, calcium borate, barium borate, magnesium oxalate, calcium oxalate, barium oxalate, magnesium maleate, calcium maleate, barium maleate, etc. Among these, magnesium hydroxide, calcium hydroxide, barium hydroxide, magnesium carbonate, calcium carbonate, and barium carbonate are more preferable.

[0073] By blending 0.01 to 4.0 parts by weight of an alkali metal salt and / or an alkaline earth metal salt with respect to 100 parts by weight of the thermoplastic polyester (A), the over-reaction of the product due to depolymerization can be suppressed, and the polyester monomer can be obtained in high yield. The blending amount of the alkali metal salt and / or the alkaline earth metal salt is more preferably 0.05 parts by weight or more, and even more preferably 0.25 parts by weight or more. On the other hand, it is more preferably 2.5 parts by weight or less, and even more preferably 1.0 parts by weight or less.

[0074] In a second preferred embodiment of the present invention, it is preferable to blend 100 to 1000 parts by weight of water per 100 parts by weight of the thermoplastic polyester (A) in the composition containing the thermoplastic polyester (A). By blending 100 to 1000 parts by weight of water, it is possible to obtain a polyester monomer in a high yield while suppressing the environmental load by suppressing the consumption of energy for heating the water. The blending amount of water is more preferably 150 parts by weight or more, and even more preferably 200 parts by weight or more. On the other hand, it is more preferably 800 parts by weight or less, and even more preferably 600 parts by weight or less.

[0075] In a second preferred embodiment of the present invention, the temperature in the step (step 1) of blending an alkali metal salt and / or an alkaline earth metal salt with the thermoplastic polyester (A) and depolymerizing it is preferably set to 250 to 350°C. By setting the temperature within this range, depolymerization is promoted and over-reaction of the product is suppressed, making it possible to obtain the polyester monomer in a high yield. The temperature is more preferably 260°C or higher, and even more preferably 270°C or higher. On the other hand, the temperature is more preferably 320°C or lower, and even more preferably 300°C or lower.

[0076] In a second preferred embodiment of the present invention, the pressure in the step (step 1) of blending an alkali metal salt and / or an alkaline earth metal salt with the thermoplastic polyester (A) and depolymerizing it is preferably 3 to 30 MPa. By setting the pressure within this range, the ion concentration of water increases, so that there is a possibility that the thermoplastic polyester (A) can be efficiently depolymerized. The pressure is more preferably 4.5 MPa or more, and even more preferably 6.0 MPa or more. On the other hand, the pressure is more preferably 25 MPa or less, and even more preferably 20 MPa or less.

[0077] In a second preferred embodiment of the present invention, a composition containing a thermoplastic polyester (A) may be used in which a dye, various additives, a fibrous filler, an organic filler other than a fibrous filler, an inorganic filler, etc. are blended with the thermoplastic polyester (A). Examples of the additives include an antioxidant, a weathering agent, a mold release agent, a crystal nucleating agent, etc.

[0078] Examples of the antioxidant include hindered phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants.

[0079] Phenol-based antioxidants include 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-ethylphenol, 4,4'-butylidenebis(6-t-butyl-3-methylphenol), 2,2'-methylene-bis(4-methyl-6-t-butylphenol), 2,2'-methylene-bis(4-ethyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, and octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate. nate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-di-t-butylphenyl)butane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 1,6-hexanediol bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] ], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamide), 3,5-di-t-butyl-4-hydroxybenzylphosph isoctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 2,4-bis[(octylthio)methyl]-o-cresol, or isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate.

[0080] Examples of phosphorus-based antioxidants include triphenyl phosphite, triisodecyl phosphite, isodecyl diphenyl phosphite, 2-ethylhexyl diphenyl phosphite, 4,4'-isopropylidenediphenol alkyl (C12 to C15) phosphite, tris(nonylphenyl) phosphite (ADEKA STAB 1178), tris(2,4-di-t-butylphenyl) phosphite, 2,2'-methylenebis(4,6-di-t-butylphenyl) 2-ethylhexyl phosphite, 3,9-bis(2,6-di-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane.

[0081] Examples of sulfur-based antioxidants include dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, ditridecyl thiodipropionate, pentaerythritol (3-lauryl thiopropionate), and 2-mercaptobenzimidazole.

[0082] These antioxidants may be used alone, or two or more of them may be used in combination since a synergistic effect may be obtained by combining two or more of them.

[0083] Examples of weather resistance agents include ultraviolet absorbers and light stabilizers. Specific examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers such as 2-hydroxy-4-octyloxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, and 2,2',4,4'-tetrahydroxybenzophenone, 4,6-bis(1-methyl-1-phenylethyl)-2-(2H-benzotriazol-2-yl)phenol, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, 2-[2'-hydroxy-3',5'-bis(α,α'-dimethylbenzyl)phenyl]benzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol], 2-( Benzotriazole-based ultraviolet absorbers represented by 2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2-(2H-benzotriazol-2-yl)-p-cresol, 2-(5-chloro-2H-benzotriazol-2-yl)-6-t-butyl-4-methylphenol, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]phenol, and methyl-3-[3-tert-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionate-polyethylene glycol condensates, and triazine-based ultraviolet absorbers represented by 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine, and the like can be mentioned.

[0084] Specific examples of the light stabilizer include bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, and tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarbo xylates, poly{[6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidyl)imino]hexamethylene[(2,2,6,6-tetramethylpiperidyl)imino]}, polymethylpropyl 3-oxy-[4-(2,2,6,6-tetramethyl)piperidinyl]siloxane, 1,2,3,4-butanetetracarboxylic acid and Examples of hindered amine light stabilizers include a mixed ester of 1,2,2,6,6-pentamethyl-4-piperidinol and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, a mixed ester of 1,2,3,4-butanetetracarboxylic acid and 2,2,6,6-tetramethyl-4-piperidinol and 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, bis(1-undecaneoxy-2,2,6,6-tetramethylpiperidin-4-yl)carbonate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, and 2,2,6,6-tetramethyl-4-piperidyl methacrylate.

[0085] Specific examples of the release agent include fatty acids, fatty acid metal salts, oxyfatty acids, fatty acid esters, partially saponified aliphatic esters, paraffin, low molecular weight polyolefins, fatty acid amides, alkylene bis fatty acid amides, aliphatic ketones, and modified silicones.

[0086] Among them, the fatty acid ester-based release agent is composed of a tri- to hexahydric aliphatic alcohol and a fatty acid, and examples of the tri- to hexahydric aliphatic alcohol include glycerol, diglycerol, erythritol, pentaerythritol, sorbitol, triglycerol, dipentaerythritol, and tetraglycerol.

[0087] Furthermore, examples of the fatty acid-based release agent include linear or branched saturated fatty acids having 5 to 30 carbon atoms, such as pentanoic acid, hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid. Specific examples of the nucleating agent include inorganic nucleating agents such as synthetic mica, talc (such as Hitron), clay, zeolite, magnesium oxide, calcium sulfide, boron nitride, and neodymium oxide.

[0088] Examples of organic crystal nucleating agents include metal salts of organic carboxylates such as sodium benzoate, potassium benzoate, lithium benzoate, calcium benzoate, magnesium benzoate, barium benzoate, lithium terephthalate, sodium terephthalate, potassium terephthalate, sodium toluate, sodium salicylate, potassium salicylate, zinc salicylate, aluminum dibenzoate, potassium dibenzoate, lithium dibenzoate, sodium β-naphthalate, and sodium cyclohexanecarboxylate; organic sulfonates such as sodium p-toluenesulfonate and sodium sulfoisophthalate; sorbitol compounds; metal salts of phenylphosphonates; and metal salts of phosphorus compounds such as sodium-2,2′-methylenebis(4,6-di-t-butylphenyl)phosphate.

[0089] The amount of the additive is preferably 0.01 to 3.0 parts by weight relative to 100 parts by weight of the thermoplastic polyester (A) in the composition containing the thermoplastic polyester (A). By setting the amount within this range, the effect of the additive can be maintained and the thermal decomposition of the additive can be suppressed when melt-kneaded with the thermoplastic polyester (A). The amount of the additive is more preferably 0.05 parts by weight or more, and even more preferably 0.1 parts by weight or more. On the other hand, it is more preferably 2.0 parts by weight or less, and even more preferably 1.0 parts by weight or less.

[0090] When a composition containing the thermoplastic polyester (A) containing the above additive is depolymerized, there is a problem that the over-reaction of the product tends to proceed, resulting in a decrease in the production yield of the polyester monomer. In a second preferred embodiment of the present invention, an alkali metal salt and / or an alkaline earth metal salt is added to suppress the over-reaction, thereby enabling the polyester monomer to be produced in a high yield.

[0091] In the second preferred embodiment of the present invention, the composition containing the thermoplastic polyester (A) can be depolymerized by various known reaction methods such as a batch method and a continuous method. For example, in the case of a batch method, an autoclave equipped with a stirrer and a heating function, a vertical or horizontal reactor, a vertical or horizontal reactor equipped with a compression mechanism such as a cylinder in addition to a stirrer and a heating function, and the like can be used. In the case of a continuous method, an extruder equipped with a heating function, a tubular reactor, a tubular reactor equipped with a mixing mechanism such as a baffle, a line mixer, a vertical or horizontal reactor, a vertical or horizontal reactor equipped with a stirrer, a tower, and the like can be used. In addition, the atmosphere in the production is preferably a non-oxidizing atmosphere, and is preferably an inert atmosphere such as nitrogen, helium, or argon, and is preferably a nitrogen atmosphere from the viewpoints of economy and ease of handling.

[0092] There is no particular limitation on the method for recovering the diol and dicarboxylic acid produced by the depolymerization method of the composition containing the thermoplastic polyester (A) in the second preferred embodiment of the present invention. For example, when the depolymerization reaction is carried out in a batchwise manner, the reaction mixture can be obtained as an aqueous diol solution in which the solid dicarboxylic acid is dispersed and / or precipitated by distillation together with water after the depolymerization reaction is completed. When the depolymerization reaction is carried out in a continuous manner, the reaction mixture can be obtained as an aqueous diol solution in which the solid dicarboxylic acid is dispersed as the reaction proceeds. The solid dicarboxylic acid can be separated from the obtained reaction mixture by a known method such as solid-liquid separation, and the diol can be separated from the water by distillation separation to recover diol and dicarboxylic acid with high purity. In addition, if there is a component insoluble in water in the reaction mixture, it can be separated by a known method such as solid-liquid separation under conditions in which the dicarboxylic acid dissolves, and can be subjected to a diol and dicarboxylic acid recovery process.

[0093] To obtain a diol with a higher purity, the recovered diol can be combined with other purification methods such as precision distillation of the diol, distillation under reduced pressure with the addition of a small amount of sodium hydroxide, treatment with activated carbon, ion exchange treatment, recrystallization, etc. By these methods, impurities that are difficult to separate by distillation separation can be efficiently removed.

[0094] Examples of methods for obtaining a dicarboxylic acid with a higher purity include a method in which the dicarboxylic acid is dissolved in a solvent in which the dicarboxylic acid is soluble and then recrystallized, and a method in which the dicarboxylic acid is esterified to convert it into a dialkyl dicarboxylate, which is then purified by distillation, and then converted back into the dicarboxylic acid.

[0095] In the method for depolymerizing a composition containing a thermoplastic polyester (A) in the second preferred embodiment of the present invention, the diol and carboxylic acid produced from a petroleum-derived raw material can be used as the polymerization raw material for the thermoplastic polyester (A). The thermoplastic polyester (A) can be produced by subjecting a diol and / or a dicarboxylic acid directly or an ester-forming derivative thereof to a polycondensation reaction via a commonly known esterification reaction or transesterification reaction. According to the second preferred embodiment of the present invention, a composition containing a used and discarded thermoplastic polyester (A) can be chemically recycled.

[0096] The polyester thus obtained can be processed and used in various products such as fibers, films, bottles, injection molded products, etc., in the same manner as the thermoplastic polyester (A) produced from petroleum-derived raw materials. These products are useful as agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical supplies, automotive parts, electric and electronic parts, and other applications.

[0097] [2-3] Third Preferred Aspect of the Invention A third preferred embodiment of the present invention is a method for producing a recycled monomer, comprising: a polymer I and a polymer II, wherein the polymer I is a thermoplastic polyester (A); the polymer II is one polymer selected from the group consisting of a thermoplastic polyester (B) having a melting point different from that of the thermoplastic polyester (A), a polycarbonate, and a polyurethane, or a combination of these polymers; the content of the polymer II in the composition (the total content of the thermoplastic polyester (B), the polycarbonate, and the polyurethane) is 1 to 100 parts by weight per 100 parts by weight of the polymer I; and the method comprises a step of contacting the polymer I and the polymer II in the composition with subcritical water at 250 to 350°C to simultaneously hydrolyze them.

[0098] In the method for producing a recycled monomer according to the third preferred embodiment of the present invention, the recycled monomer is preferably terephthalic acid and / or a diol. By using terephthalic acid and / or a diol as the recycled monomer, polyester, which is produced in large quantities as a plastic, can be recycled, which contributes greatly to resource circulation.

[0099] The thermoplastic polyester (A) and thermoplastic polyester (B) used in the third preferred embodiment of the present invention are obtained by polycondensation of dicarboxylic acid or its ester-forming derivative, and diol as main raw materials. Here, the main raw material means that the structural units of dicarboxylic acid, its ester-forming derivative, and diol in the polymer are 80 mol% or more in total. The total of these structural units is more preferably 90 mol% or more, even more preferably 95 mol% or more, and most preferably 100 mol%.

[0100] Examples of dicarboxylic acids or ester-forming derivatives thereof include, but are not limited to, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenylether-4,4'-dicarboxylic acid, diphenylthioether-4,4'-dicarboxylic acid, 5-tetrabutylphosphonium isophthalic acid, and 5-sodium sulfoisophthalic acid; and aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, azelaic acid, undecanedioic acid, and dodecanedioic acid, or ester-forming derivatives thereof.

[0101] The ester-forming derivatives referred to here are the lower alkyl esters, acid anhydrides, acid halides, etc. of the dicarboxylic acids mentioned above. As the lower alkyl esters of dicarboxylic acids, methyl esters, ethyl esters, hydroxyethyl esters, hydroxybutyl esters, etc. are preferably used. As the acid anhydrides of dicarboxylic acids, anhydrides of dicarboxylic acids and anhydrides of dicarboxylic acids and acetic acid, etc. are preferably used. As the halides of dicarboxylic acids, acid chlorides, acid bromides, acid iodides, etc. are preferably used.

[0102] As the dicarboxylic acid or its ester-forming derivative, an aromatic dicarboxylic acid or its ester-forming derivative, which is used in large amounts as a thermoplastic polyester raw material for fibers, resins, and films, is preferred. As the aromatic dicarboxylic acid or its ester-forming derivative, terephthalic acid, 2,6-naphthalenedicarboxylic acid, or their dimethyl esters are more preferred.

[0103] Examples of diols include ethylene glycol, 1,3-propanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, decamethylene glycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, cyclohexanedimethanol, xylylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and bisphenol A-ethylene oxide adducts. Among these, ethylene glycol, 1,3-propanediol, and 1,4-butanediol are more preferred in that the resulting thermoplastic polyester has high versatility.

[0104] The dicarboxylic acid, the ester-forming derivative of the dicarboxylic acid, and the diol may each be used alone or in combination of two or more kinds.

[0105] Examples of the thermoplastic polyester used in the third preferred embodiment of the present invention include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexane dimethylene terephthalate, polyethylene isophthalate, polypropylene isophthalate, polybutylene isophthalate, polycyclohexane dimethylene isophthalate, polyethylene naphthalate, polypropylene naphthalate, polybutylene naphthalate, polycyclohexane dimethylene terephthalate / polyethylene terephthalate, polyethylene isophthalate / terephthalate, polypropylene isophthalate / terephthalate, polybutylene isophthalate / terephthalate, polyethylene terephthalate / naphthalate, polypropylene terephthalate / naphthalate, polybutylene terephthalate / naphthalate, polyethylene terephthalate / 5-sodium sulfoisophthalate, polypropylene terephthalate / 5-sodium sulfoisophthalate, polybutylene terephthalate / 5-sodium sulfoisophthalate, etc. Here, " / " represents a copolymer. Among these, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are preferred, and polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate are more preferred because they are highly versatile and can be recovered in large amounts as recycling resources.

[0106] In the method for producing a recycled monomer according to the third preferred embodiment of the present invention, the thermoplastic polyester (A) is preferably selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof. These thermoplastic polyesters are produced in large quantities, and there is a high need for recycling them.

[0107] In the method for producing a recycled monomer according to the third preferred embodiment of the present invention, the thermoplastic polyester (B) is preferably at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof, and is a thermoplastic polyester having a melting point different from that of the thermoplastic polyester (A). These thermoplastic polyesters are produced in large quantities, and there is a high demand for recycling them.

[0108] In the method for producing a recycled monomer according to the third preferred embodiment of the present invention, it is more preferable that both the thermoplastic polyester (A) and the thermoplastic polyester (B) are at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof. By using the above-mentioned thermoplastic polyesters as both the thermoplastic polyester (A) and the thermoplastic polyester (B), separation and purification of the recycled monomer after simultaneous depolymerization becomes easy.

[0109] The intrinsic viscosity of each of the thermoplastic polyester (A) and the thermoplastic polyester (B) used in the third preferred embodiment of the present invention is preferably 0.4 to 2.0 dl / g. Here, the intrinsic viscosity of the thermoplastic polyester (A) and the thermoplastic polyester (B) is a value measured at 25°C using o-chlorophenol as a solvent. When the thermoplastic polyester used in the third preferred embodiment of the present invention is polyethylene terephthalate, the intrinsic viscosity IV is preferably 0.4 to 1.5 dl / g, more preferably 0.6 to 1.3 dl / g. When the thermoplastic polyester used in the third preferred embodiment of the present invention is polypropylene terephthalate, the intrinsic viscosity is more preferably 0.6 to 2.0 dl / g, more preferably 0.7 to 1.6 dl / g. When the thermoplastic polyester used in the third preferred embodiment of the present invention is polybutylene terephthalate, the intrinsic viscosity is more preferably 0.6 to 2.0 dl / g, more preferably 0.8 to 1.8 dl / g.

[0110] In the third preferred embodiment of the present invention, when the composition contains thermoplastic polyester (A) and thermoplastic polyester (B), the thermoplastic polyester with a larger content is defined as thermoplastic polyester (A). When the content of thermoplastic polyester (A) and the content of thermoplastic polyester (B) are the same, the thermoplastic polyester with a higher melting point is defined as thermoplastic polyester (A).

[0111] The polycarbonate used in the third preferred embodiment of the present invention may be one obtained by interfacial polymerization of a dihydroxy compound and phosgene, one obtained by polymerizing a dihydroxy compound and diphenyl carbonate by melt transesterification, one obtained by polymerizing a carbonate prepolymer by solid-phase transesterification, or one obtained by ring-opening polymerization of a cyclic carbonate compound. The dihydroxy compound used here may be one or more selected from 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A), 4,4'-dihydroxydiphenylalkane, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylether, 2,2'-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1'-bis(4-hydroxyphenyl)cyclohexane, and isosorbide (1,4:3,6-dianhydro-D-sorbitol). Among them, 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A) is preferred.

[0112] In addition, other dihydroxy compounds other than bisphenol A, such as 4,4'-dihydroxydiphenylalkanes, 4,4'-dihydroxydiphenyl sulfones, 4,4'-dihydroxydiphenyl ethers, or isosorbide (1,4:3,6-dianhydro-D-sorbitol), can be used simultaneously with bisphenol A, and the amount of the other dihydroxy compounds used is preferably 10 mol % or less based on the total amount of the dihydroxy compounds.

[0113] The degree of polymerization of these polycarbonates is not particularly limited, but from the viewpoints of excellent practical strength and easy hydrolysis, the viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 10,000 to 50,000, more preferably 15,000 or more, and even more preferably 18,000 or more. On the other hand, it is more preferably 40,000 or less, and even more preferably 35,000 or less.

[0114] Here, the viscosity average molecular weight (Mv) means a value calculated by measuring the intrinsic viscosity [η] (unit: dl / g) at 20°C using dichloromethane as a solvent and an Ubbelohde viscometer, and then calculating from Schnell's viscosity formula, i.e., [η] = 1.23 × 10-4 × (Mv)0.83. Here, the intrinsic viscosity [η] is a value calculated by measuring the specific viscosity [ηsp] at each solution concentration [c] (g / dl) and using the following formula. [η] = lim ηsp / c(c→0)

[0115] The polyurethane used in the third preferred embodiment of the present invention is not particularly limited, and may be any polyurethane that uses polymer diol and diisocyanate as starting materials. It may also be polyurethane urea made of polymer diol, diisocyanate, and low molecular weight diamine as a chain extender, polyurethane urethane made of polymer diol, diisocyanate, and low molecular weight diol as a chain extender, or polyurethane urea using a compound having a hydroxyl group and an amino group in the molecule as a chain extender.

[0116] The polymer diol used in the third preferred embodiment of the present invention is preferably at least one selected from polyether diols, polyester diols, and polycarbonate diols. In particular, it is preferable to use polyether diols from the viewpoint of easy separation after hydrolysis.

[0117] As the polyether diol, for example, polyethylene oxide, polyethylene glycol, a derivative of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol (hereinafter abbreviated as PTMG), modified PTMG which is a copolymer of tetrahydrofuran (hereinafter abbreviated as THF) and 3-methyltetrahydrofuran, modified PTMG which is a copolymer of THF and 2,3-dimethylTHF, polyol having side chains on both sides as disclosed in Japanese Patent No. 2615131, random copolymer in which THF and ethylene oxide and / or propylene oxide are irregularly arranged, etc. may be preferably used. These polyether diols may be used alone or in a mixture or copolymer of two or more kinds.

[0118] In addition, polyester diols such as butylene adipate, polycaprolactone diol, and polyester polyols having side chains as disclosed in JP-A-61-26612 and polycarbonate diols as disclosed in JP-B-2-289516 can also be used.

[0119] The above polymer diols may be used alone, or two or more kinds may be mixed or copolymerized for use.

[0120] The molecular weight of the polymer diol used in the third preferred embodiment of the present invention is preferably a number average molecular weight of 1,000 or more and 8,000 or less, more preferably 1,800 or more and 6,000 or less, from the viewpoint of maintaining practical strength.

[0121] The diisocyanate used in the third preferred embodiment of the present invention includes aromatic diisocyanates such as diphenylmethane diisocyanate, tolylene diisocyanate, 1,4-diisocyanate benzene, xylylene diisocyanate, and 2,6-naphthalene diisocyanate, and alicyclic diisocyanates such as methylene bis(cyclohexyl isocyanate), isophorone diisocyanate, methylcyclohexane 2,4-diisocyanate, methylcyclohexane 2,6-diisocyanate, cyclohexane 1,4-diisocyanate, hexahydroxylylene diisocyanate, hexahydrotolylene diisocyanate, and octahydro-1,5-naphthalene diisocyanate. Alicyclic diisocyanates can be effectively used, particularly when suppressing yellowing of polyurethane yarn. These diisocyanates may be used alone or in combination of two or more.

[0122] In a third preferred embodiment of the present invention, the molecular weight of the polyurethane is preferably in the range of 30,000 to 150,000 in terms of number average molecular weight, from the viewpoints of maintaining practical strength and facilitating depolymerization. The molecular weight is measured by GPC (gel permeation chromatography) and converted into polystyrene.

[0123] In a third preferred embodiment of the present invention, a polymer I made of a thermoplastic polyester (A) and a polymer II made of at least one selected from a thermoplastic polyester (B) having a melting point different from that of the thermoplastic polyester (A), polycarbonate, and polyurethane are simultaneously depolymerized, which has the effect of increasing the yield of the dicarboxylic acid produced compared to depolymerizing only the thermoplastic polyester (A). In order to achieve this effect, it is necessary that at least one polymer selected from the thermoplastic polyester (B), polycarbonate, and polyurethane is contained in an amount of 1 part by weight or more per 100 parts by weight of the thermoplastic polyester (A). The amount is more preferably 5 parts by weight or more, even more preferably 10 parts by weight or more, and most preferably 20 parts by weight or more.

[0124] In the hydrolysis of a polymer, it is presumed that the hydrolysis is promoted by melting the polymer or dissolving the polymer in water. By simultaneously heating a thermoplastic polyester (A) and at least one selected from a thermoplastic polyester (B) having a melting point different from that of the thermoplastic polyester (A), polycarbonate, and polyurethane in the presence of water, the polymer with a high melting point dissolves in the melt or solution of the polymer with a low melting point (for polymers that do not show a melting point, the melting point is defined as the glass transition temperature), and the hydrolysis of the polymer with a high melting point is also promoted, and / or the depolymerized product of one polymer promotes the depolymerization of the other polymer, it is considered that the yield of the produced monomer is increased by simultaneous hydrolysis.

[0125] Here, the melting point is the temperature of an endothermic peak that appears when a polymer is cooled from a molten state to 0°C at a temperature drop rate of 20°C / min under a nitrogen gas atmosphere using a differential scanning calorimeter (DSC), and then heated to melting point + 40°C at a temperature rise rate of 20°C / min. However, when two or more endothermic peaks are detected, the temperature of the endothermic peak with the greatest peak intensity is taken as the melting point. In addition, for polymers that do not show a melting point, the glass transition temperature (melting point in the third preferred embodiment of the present invention) is the temperature of the midpoint of a step-like endothermic peak that appears when a polymer is cooled from a molten state to 0°C at a temperature drop rate of 20°C / min under a nitrogen gas atmosphere, and then heated at a temperature rise rate of 20°C / min. Furthermore, in the case of polyurethane urea, since its melting point is higher than the thermal decomposition temperature of the polymer, it is difficult to measure the melting point accurately using DSC. In this case, in a TGA curve obtained by heating at a heating rate of 20°C / min in a nitrogen gas atmosphere using a thermogravimetric analyzer (TGA), the intersection point between the baseline of the initiation weight and the tangent to the maximum gradient point of the TGA curve after weight loss due to thermal decomposition is defined as the decomposition onset temperature (melting point in a third preferred embodiment of the present invention).

[0126] In a third preferred embodiment of the present invention, the difference between the melting point of the thermoplastic polyester (A) and the melting point of the thermoplastic polyester (B), polycarbonate or polyurethane is preferably 10° C. or more, and more preferably the difference between the melting points of the thermoplastic polyester (A) and the thermoplastic polyester (B) is 10° C. or more. By combining polymers with a large difference in melting point, the polymer with the higher melting point becomes more easily dissolved, and hydrolysis can be promoted. The difference in melting point is more preferably 20° C. or more, more preferably 30° C. or more.

[0127] The polymer used in the third preferred embodiment of the present invention may include polymers other than thermoplastic polyesters, polycarbonates, and polyurethanes. For example, polyamides, polyolefins, modified polyphenylene ethers, polysulfones, polyketones, polyetherimides, polyarylates, polyethersulfones, polyetherketones, polythioetherketones, polyetheretherketones, polyimides, polyamideimides, polyethylene tetrafluoride, and polyphenylene sulfides may be included. The amount of the polymer other than thermoplastic polyesters, polycarbonates, and polyurethanes is preferably less than 50 parts by weight relative to 100 parts by weight of the polymer component in the composition in the third preferred embodiment of the present invention. More preferably, it is 40 parts by weight or less, and even more preferably 30 parts by weight or less.

[0128] The composition used in the third preferred embodiment of the present invention may contain additives other than the polymer, such as a filler, a nucleating agent, a plasticizer, an ultraviolet resistant agent, a release agent, a flame retardant, a colorant (e.g., a pigment or a dye), a lubricant, an antistatic agent, and an antioxidant.

[0129] Examples of the filler include glass fibers, carbon fibers, potassium titanate whiskers, zinc oxide whiskers, aluminum borate whiskers, aramid fibers, alumina fibers, silicon carbide fibers, ceramic fibers, asbestos fibers, gypsum fibers, metal fibers, glass sheets, wollastonite, zeolite, sericite, kaolin, mica, talc, clay, pyrophyllite, bentonite, montmorillonite, hectorite, synthetic mica, asbestos, graphite, aluminosilicate, alumina, silica, magnesium oxide, zirconium oxide, titanium oxide, iron oxide, calcium carbonate, magnesium carbonate, dolomite, calcium sulfate, barium sulfate, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, glass beads, hollow glass beads, ceramic beads, boron nitride, silicon carbide, and wollastonite.

[0130] From the viewpoint of separation property after hydrolysis by contact with subcritical water, the fibrous filler is preferably glass fiber or carbon fiber. The cross-sectional shape of the fibrous filler is not particularly limited, and may be either a circular or flat fiber. In a third preferred embodiment of the present invention, the content of the fibrous filler in the polymer composition is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less in the composition.

[0131] In a third preferred embodiment of the present invention, polymer I and polymer II in the composition are simultaneously hydrolyzed by contacting them with subcritical water at 250 to 350°C. When water is heated to a pressure of 22.1 MPa and a temperature of 374.2°C, it is in a state that is neither liquid nor gas. Water in this state is called supercritical water. Hot water in a region near the critical point of water at a temperature and pressure slightly lower than the critical point of water is called subcritical water. Although subcritical water is water, it has the characteristics of (i) a low dielectric constant and (ii) a high ionic product. The dielectric constant and ionic product of subcritical water depend on the temperature and partial pressure of water and can be controlled. The low dielectric constant makes it an excellent solvent for organic compounds, even though it is water. Furthermore, the high ionic product increases the hydrogen ion and hydroxide ion concentrations. Therefore, subcritical water has an excellent hydrolysis action.

[0132] There is no particular limitation on the water used as the raw material for the subcritical water, and any type of water may be used, such as tap water, deionized water, distilled water, well water, etc. From the viewpoint of suppressing side reactions due to the influence of coexisting salts, deionized water and distilled water are preferably used.

[0133] The hydrolysis in the third preferred embodiment of the present invention must have a step of being carried out at 250°C or higher and 350°C or lower. This temperature range promotes hydrolysis, inhibits over-reaction of the product, and improves the polyester monomer yield. The third preferred embodiment of the present invention does not include a step of hydrolysis at a temperature higher than 350°C. 260°C or higher is preferred, 270°C or higher is more preferred, and 280°C or higher is even more preferred. On the other hand, 320°C or lower is preferred, 310°C or lower is more preferred, and 300°C or lower is even more preferred.

[0134] Another embodiment of the method for producing a recycled monomer in the third preferred embodiment of the present invention is a method for producing a recycled monomer, comprising: a composition containing a polymer, comprising polymer I and polymer II, polymer I being a thermoplastic polyester (A), polymer II being a thermoplastic polyester (B) having a melting point different from that of the thermoplastic polyester (A), a polymer selected from the group consisting of polycarbonate and polyurethane, or a combination of these polymers; the content of polymer II in the composition (total content of thermoplastic polyester (B), polycarbonate and polyurethane) is 1 to 100 parts by weight per 100 parts by weight of polymer I; and a step of simultaneously hydrolyzing polymer I and polymer II in the composition by contacting them with subcritical water at 200 to 350°C under conditions in which an alkaline component is blended. In another embodiment of the method for producing a recycled monomer in the third preferred embodiment of the present invention, the temperature of the hydrolysis reaction can be expanded to 200 to 350°C by further blending an alkaline component. That is, by blending an alkaline component, hydrolysis can be promoted even at a lower temperature. The temperature of the hydrolysis reaction when an alkaline component is blended is preferably 210° C. or higher, more preferably 220° C. or higher. On the other hand, the temperature of the hydrolysis reaction when an alkaline component is blended is preferably 300° C. or lower, more preferably 290° C. or lower.

[0135] In the method for producing a recycled monomer in the third preferred embodiment of the present invention, the composition may include a composition containing polymer I and polymer II, and / or a mixture of a composition containing polymer I and a composition containing polymer II. That is, in the third preferred embodiment of the present invention, the composition to be hydrolyzed may be a composition containing either a composition containing polymer I and polymer II, or a mixture of a composition containing polymer I and a composition containing polymer II, or may be a composition containing both of them. Here, "a composition containing polymer I and polymer II" refers to, for example, a composition obtained by kneading polymer I and polymer II (including the case where polymer I and / or polymer II contain any other component) at or above the melting point of either polymer (or above the glass transition temperature for a polymer that does not have a melting point). In addition, "a mixture of a composition containing polymer I and a composition containing polymer II" refers to, for example, a composition obtained by mixing a composition (e.g., pellets) containing polymer I (including the case where it contains any other component) and a composition (e.g., pellets) containing polymer II (including the case where it contains any other component) in a solid state below the melting points of both polymers (below the glass transition temperature for a polymer that does not have a melting point).

[0136] In the hydrolysis in the third preferred embodiment of the present invention, it is preferable to mix 100 parts by weight or more and 900 parts by weight or less of water per 100 parts by weight of the polymer component in the composition. By adjusting the amount within this range, the hydrolysis is promoted and the energy consumption for heating the water can be suppressed. The amount of water is more preferably 150 parts by weight or more, and even more preferably 200 parts by weight or more. On the other hand, the amount of water is more preferably 500 parts by weight or less, and even more preferably 350 parts by weight or less.

[0137] Further, in a third preferred embodiment of the present invention, the pressure in the step of contacting with subcritical water at 250 to 350°C and simultaneously hydrolyzing is preferably equal to or higher than the saturated vapor pressure of water, specifically, 4.0 MPa to 30 MPa. By setting the pressure in this range, the ion concentration of water can be increased and hydrolysis can be promoted. It is more preferably 5.0 MPa or higher, and even more preferably 6.0 MPa or higher. On the other hand, it is more preferably 25 MPa or lower, and even more preferably 22 MPa or lower. In order to set the pressure in the above pressure range, a method of pressurizing the inside of a pressure vessel can be mentioned. To pressurize the inside of a pressure vessel, a method of sealing a gas in addition to water, and a method of introducing high-pressure water can be mentioned. Such gases include air, argon, nitrogen, etc., but from the viewpoint of suppressing side reactions such as oxidation reactions, it is preferable to use an inert gas such as nitrogen or argon. The degree of pressurization by gas or high-pressure water is not particularly limited because it is set to the desired pressure, but 0.3 MPa or higher is preferable. When pressurizing with high-pressure water, it is also possible to make the inside of the pressure vessel gas-free.

[0138] In a third preferred embodiment of the present invention, it is preferable to further add an alkaline component in the above step. By adding an alkaline component, it is possible to suppress over-reaction of the product due to hydrolysis and improve the monomer yield. Examples of the alkaline component include alkali metals such as lithium, sodium, and potassium, alkaline earth metals such as calcium, hydroxides such as ammonium, carbonates, bicarbonates, and amines. In particular, at least one selected from sodium hydroxide, potassium hydroxide, and calcium hydroxide is preferable. The amount of the alkaline component to be added is preferably 0.01 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the polymer component in the composition. More preferably, it is 20 parts by weight or more, and even more preferably, it is 30 parts by weight or more. On the other hand, it is more preferably 45 parts by weight or less, and even more preferably, it is 40 parts by weight or less. When an alkaline component is added, a dicarboxylate is generated by hydrolysis of the thermoplastic polyester. The dicarboxylate can be converted to a dicarboxylic acid, which is a raw material for the thermoplastic polyester, by treating it with an acidic aqueous solution.

[0139] In the third preferred embodiment of the present invention, the hydrolysis of the composition containing the polymer can be carried out in various known reaction methods such as a batch method and a continuous method. For example, in the case of a batch method, autoclaves, vertical or horizontal reactors, and vertical or horizontal reactors equipped with a compression mechanism such as a cylinder in addition to a stirrer and a heating function can be used. In the case of a continuous method, extruders, tubular reactors, tubular reactors equipped with a mixing mechanism such as a baffle, line mixers, vertical or horizontal reactors, vertical or horizontal reactors equipped with a stirrer, towers, and the like can be used. In addition, the production atmosphere is preferably a non-oxidizing atmosphere, and is preferably carried out under an inert atmosphere such as nitrogen, helium, or argon, and is preferably carried out under a nitrogen atmosphere from the viewpoints of economy and ease of handling.

[0140] There is no particular limitation on the method for recovering the diol and dicarboxylic acid produced by hydrolysis of the composition in the third preferred embodiment of the present invention. For example, when terephthalic acid is used as a raw material for thermoplastic polyester, after the hydrolysis reaction, solid terephthalic acid can be obtained as a reaction mixture in which it is dispersed and / or precipitated in water. The solid terephthalic acid can be separated by solid-liquid separation of the resulting reaction mixture. As a method for obtaining terephthalic acid of higher purity, there can be mentioned a method of dissolving terephthalic acid in a solvent in which terephthalic acid is soluble and recrystallizing it, a method of esterifying terephthalic acid to convert it to dialkyl terephthalate, purifying it by distillation, and then converting it back to terephthalic acid, and the like. In addition, when a water-soluble diol is used as a raw material for thermoplastic polyester, after the hydrolysis reaction, the diol and water can be separated by distilling and separating the aqueous solution. As a method for obtaining a diol of higher purity, the recovered diol can be combined with a purification method such as a method of precision distilling the diol, a method of distilling under reduced pressure by adding a small amount of sodium hydroxide, a method of treating with activated carbon, a method of treating with ion exchange, or a method of recrystallization. By these methods, impurities that are difficult to separate by distillation separation can be efficiently removed.

[0141] In a third preferred embodiment of the present invention, in addition to the hydrolyzate of the thermoplastic polyester, the hydrolyzate of polycarbonate and polyurethane may also be produced. Specifically, the hydrolysis of thermoplastic polyester and polycarbonate produces diol, dicarboxylic acid, and dihydroxy compound, respectively, which can be reused as polymer raw materials. On the other hand, the hydrolysis of polyurethane produces diamine, polymer diol, etc. Diamine can be reused as a raw material for polyurethane by converting it to isocyanate. Also, polymer diol can be reused as a raw material for polyurethane.

[0142] In the method for producing a thermoplastic polyester according to the third preferred embodiment of the present invention, a dicarboxylic acid and / or a diol obtained by the method for producing a recycled monomer according to the third preferred embodiment of the present invention is used as a polymerization raw material to produce a thermoplastic polyester. The dicarboxylic acid and / or a diol obtained by the method for producing a recycled monomer according to the third preferred embodiment of the present invention is preferably a dicarboxylic acid and / or a diol obtained by hydrolysis of a thermoplastic polyester (A) and / or a thermoplastic polyester (B). For example, a thermoplastic polyester can be produced through a first step consisting of an esterification reaction between a dicarboxylic acid and a diol, followed by a second step of a polycondensation reaction. Alternatively, a thermoplastic polyester can be produced through a first step consisting of an ester exchange reaction between a dialkyl dicarboxylate obtained by chemically converting a dicarboxylic acid and a diol, followed by a second step of a polycondensation reaction.

[0143] In the method for producing a recycled monomer according to the third preferred embodiment of the present invention, the composition is preferably a waste material. The waste material is hydrolyzed under specific conditions to regenerate the monomer, which can then be repolymerized to be reused as a thermoplastic polyester.

[0144] Furthermore, it is possible to produce a composition containing a thermoplastic polyester by blending the recycled thermoplastic polyester with dyes, various additives, fibrous fillers, non-fibrous fillers, other polymers, etc. Examples of additives include antioxidants, weathering agents, mold release agents, crystal nucleating agents, etc.

[0145] The thermoplastic polyester obtained by the method for producing a thermoplastic polyester in the third preferred embodiment of the present invention and the composition containing the thermoplastic polyester can be used to produce various thermoplastic polyester products such as fibers, films, and bottles obtained by melt spinning, melt film formation, melt extrusion molding, etc., and molded products obtained by injection molding, blow molding, extrusion molding, etc., and products of compositions containing various thermoplastic polyesters. These products are useful as agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, industrial films, sheets, stationery, medical supplies, clothing, automotive parts, electric and electronic parts, and other applications.

[0146] In the method for producing a thermoplastic polyester product according to the third preferred embodiment of the present invention, a thermoplastic polyester product such as a fiber, a film or a molded product is produced using the thermoplastic polyester obtained by the method for producing a thermoplastic polyester according to the third preferred embodiment of the present invention as a raw material. In the method for producing a product of a composition containing a thermoplastic polyester according to the third preferred embodiment of the present invention, a product of a composition containing a thermoplastic polyester obtained by the method for producing a thermoplastic polyester according to the third preferred embodiment of the present invention is produced. Examples of the thermoplastic polyester product and the product containing a thermoplastic polyester, and examples of the method for producing the thermoplastic polyester product and the product containing a thermoplastic polyester are as described above.

[0147] [3] Recycled monomer manufacturing equipment The apparatus for producing recycled monomers of the present invention comprises a means (L) for heating and pressurizing a composition containing a thermoplastic polymer and supplying the same, a means (M) for generating and supplying subcritical water, a means (N) for mixing the composition containing the thermoplastic polymer supplied from the means (L) with the subcritical water supplied from the means (M), and a continuous reactor (O) for hydrolyzing the thermoplastic polymer. Each component will be described below.

[0148] (1) Composition containing a thermoplastic polymer The composition containing a thermoplastic polymer in the recycling monomer production apparatus of the present invention may be of any type as long as it contains a hydrolyzable polymer. Examples of the hydrolyzable polymer include thermoplastic polyamide and thermoplastic polyester. Examples of the thermoplastic polyamide include polyamide 6 and polyamide 66. Examples of the thermoplastic polyester include polyethylene terephthalate and polybutylene terephthalate. Thermoplastic polyamide is widely used as an engineering plastic and a textile product. Thermoplastic polyester is also widely used as a general-purpose plastic, a bottle, and a textile product. Therefore, these hydrolyzable polymers are preferable in terms of ease of resource recovery and ease of hydrolysis.

[0149] In the recycled monomer production apparatus of the present invention, the composition containing a thermoplastic polymer may be a waste resin molded article.

[0150] When the thermoplastic polymer is a thermoplastic polyamide, wastes of resin molded articles containing the thermoplastic polyamide include polyamide products, industrial wastes generated in the process of manufacturing polyamide products, or used wastes of polyamide products. Examples of polyamide products include textile structures for clothing such as used clothes, uniforms, sportswear, and innerwear, industrial textile structures such as curtains, carpets, ropes, nets, belts, sheets, and airbags, automobile parts, molded parts for housing construction materials, electrical and electronic molded parts, aircraft parts, industrial machine parts, film products, extrusion molded products, on-site polymerization molded products, and RIM molded products. In addition, wastes include product scraps, pellet scraps, lump scraps, and cutting scraps generated during cutting processes.

[0151] When the thermoplastic polymer is a thermoplastic polyester, waste of resin molded articles containing the thermoplastic polyester may include thermoplastic polyester products, industrial waste generated during the manufacturing process of thermoplastic polyester products, or used waste of thermoplastic polyester products. Examples of thermoplastic polyester products include containers such as beverage bottles and seasoning bottles, sheet products such as food trays, blister packs, food dividers, and industrial trays, film products such as packaging films, optical functional films, magnetic tapes, and insulating materials, textile structures for clothing such as used clothing, uniforms, sportswear, and innerwear, industrial textile structures such as curtains, carpets, nets, belts, and sheets, molded products such as automobile parts, electrical and electronic parts, building materials, daily necessities, household goods, and sanitary goods. In addition, product scraps, pellet scraps, and lump scraps generated during the production process are also subject to waste.

[0152] The composition containing the thermoplastic polymer in the recycling monomer production apparatus of the present invention may contain a fibrous filler. The fibrous filler may be any filler having a fibrous shape. Specifically, the filler may be glass fiber, polyacrylonitrile (PAN)-based or pitch-based carbon fiber, stainless steel fiber, metal fiber such as aluminum fiber or brass fiber, organic fiber such as polyester fiber or aromatic polyamide fiber, gypsum fiber, ceramic fiber, asbestos fiber, zirconia fiber, alumina fiber, silica fiber, titanium oxide fiber, silicon carbide fiber, rock wool, potassium titanate whisker, silicon nitride whisker, wollastonite, alumina silicate, or other fibrous or whisker-like filler, glass fiber, carbon fiber, aromatic polyamide fiber, polyester fiber, etc., coated with one or more metals selected from the group consisting of nickel, copper, cobalt, silver, aluminum, iron, and alloys thereof. Two or more of these may be contained. The content of the fibrous filler is preferably 1 to 200 parts by mass with respect to 100 parts by mass of the thermoplastic polymer as the main component.

[0153] The composition containing a thermoplastic polymer in the recycled monomer production apparatus of the present invention may further contain fillers other than the fibrous fillers, various additives, etc., within the scope of not impairing the object of the invention of the recycled monomer production apparatus of the present invention. The fillers other than the fibrous fillers, i.e., the non-fibrous fillers, may be either organic fillers or inorganic fillers, or may contain two or more of these. Examples of non-fibrous fillers include non-swelling silicates such as talc, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite, bentonite, asbestos, alumina silicate, and calcium silicate; swellable layered silicates such as Li-type fluorine taeniolite, Na-type fluorine taeniolite, Na-type tetrasilicic fluorine mica, and Li-type tetrasilicic fluorine mica; metal oxides such as silicon oxide, magnesium oxide, alumina, silica, diatomaceous earth, zirconium oxide, titanium oxide, iron oxide, zinc oxide, calcium oxide, tin oxide, and antimony oxide; calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dolomite, and the like. Examples of the swellable layered silicate include metal carbonates such as mites and hydrotalcites, metal sulfates such as calcium sulfate and barium sulfate, metal hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide, and alkaline magnesium carbonate, smectite clay minerals such as montmorillonite, beidellite, nontronite, saponite, hectorite, and sauconite, and various clay minerals such as vermiculite, halloysite, kanemite, kenyaite, zirconium phosphate, and titanium phosphate, glass beads, glass flakes, ceramic beads, boron nitride, aluminum nitride, silicon carbide, calcium phosphate, carbon black, and graphite. The above-mentioned swellable layered silicate may have an exchangeable cation present between layers exchanged with an organic onium ion. Examples of the organic onium ion include ammonium ion, phosphonium ion, and sulfonium ion.

[0154] Specific examples of various additives include antioxidants and heat stabilizers (hindered phenols, hydroquinones, phosphites and their substitutes, copper halides, iodine compounds, etc.), weathering agents (resorcinols, salicylates, benzotriazoles, benzophenones, hindered amines, etc.), release agents and lubricants (aliphatic alcohols, aliphatic amides, aliphatic bisamides, bisureas, polyethylene waxes, etc.), pigments (cadmium sulfide, phthalocyanine, carbon black, etc.), dyes (nigrosine, aniline black, etc.), plasticizers (octyl p-oxybenzoate, N-butylbenzenesulfonamide, etc.), and band-forming agents. Examples of the additives include antistatic agents (alkyl sulfate-type anionic antistatic agents, quaternary ammonium salt-type cationic antistatic agents, nonionic antistatic agents such as polyoxyethylene sorbitan monostearate, betaine-type amphoteric antistatic agents, etc.), flame retardants (hydroxides such as melamine cyanurate, magnesium hydroxide, and aluminum hydroxide, phosphorus-based flame retardants such as ammonium polyphosphate, melamine polyphosphate, and metal phosphinate salts, brominated polystyrene, brominated polyphenylene oxide, brominated polycarbonate, brominated epoxy resin, and combinations of these brominated flame retardants with antimony trioxide, etc.). When these additives are contained, the content is preferably 10 parts by mass or less, and more preferably 1 part by mass or less, based on 100 parts by mass of the thermoplastic polymer component that is the main component.

[0155] (2) Means for heating, pressurizing and supplying a composition containing a thermoplastic polymer (L) The recycled monomer production apparatus in the recycled monomer production apparatus of the present invention has a means (L) (sometimes simply referred to as "means (L)" in the present invention) for heating and pressurizing a composition containing a thermoplastic polymer and supplying it. Examples of the means (L) include a device that heats and melts the composition using an electric heater and pressurizes the composition using a gear pump, a device that simultaneously heats and pressurizes the composition using an extruder, a device that combines an extruder and a gear pump, and a device that further heats the thermoplastic polymer discharged from the extruder using an electric heater. Among these, it is preferable that the means (L) is a device that uses an extruder. When the means (L) is a device that uses an extruder, the pressure at which the thermoplastic polymer is extruded becomes more stable.

[0156] The temperature to which the composition containing the thermoplastic polymer is heated is preferably a temperature at which the composition containing the thermoplastic polymer melts. By heating the composition containing the thermoplastic polymer to a temperature at which the composition containing the thermoplastic polymer melts, the contact area with the subcritical water can be increased, and the reaction can be carried out quickly.

[0157] (3) A means for generating and supplying subcritical water (M) The recycling monomer manufacturing apparatus of the present invention has a means (M) for generating and supplying subcritical water (sometimes simply referred to as "means (M)" in the recycling monomer manufacturing apparatus of the present invention). When water is heated to a pressure of 22.1 MPa and a temperature of 374.2°C, it is in a state that is neither liquid nor gas. Water in this state is called supercritical water. Hot water in a region near the critical point of water, at a temperature and pressure slightly lower than the critical point of water, is called subcritical water. Although subcritical water is water, it has the characteristics of (i) a low dielectric constant and (ii) a high ionic product. The dielectric constant and ionic product of subcritical water depend on the temperature and partial pressure of water, and can be controlled. The low dielectric constant makes it an excellent solvent for organic compounds, despite being water. Furthermore, the high ionic product increases the hydrogen ion and hydroxide ion concentrations. Therefore, subcritical water has an excellent hydrolysis effect.

[0158] There is no particular limitation on the water used as the raw material for the subcritical water, and any type of water may be used, such as tap water, deionized water, distilled water, well water, etc. From the viewpoint of suppressing side reactions due to the influence of coexisting salts, deionized water and distilled water are preferably used.

[0159] Examples of the means (M) include a device that introduces water under pressure into a high-pressure facility using a diaphragm pump, mono pump, gear pump, plunger pump, or the like, and then heats it to a predetermined temperature using a heat exchanger, electric heater, heating furnace, or the like, but devices not exemplified here may also be used.

[0160] The subcritical water in the recycled monomer production apparatus of the present invention is preferably heated to a temperature equal to or higher than the melting point of the composition containing a thermoplastic polymer. By heating the subcritical water to a temperature equal to or higher than the melting point of the composition containing a thermoplastic polymer, the composition containing a thermoplastic polymer is dispersed in droplets, and the interfacial area is increased, thereby improving the reaction efficiency. After the subcritical water comes into contact with the composition containing a thermoplastic polymer, the temperature of the reaction system rises and falls due to the endothermic heat of the hydrolysis reaction, so it is preferable to control the temperature of the subcritical water according to the composition containing a thermoplastic polymer used. If the temperature of the reaction system is low, the hydrolysis reaction becomes insufficient, and if the temperature of the reaction system is high, an overreaction is likely to proceed, both of which lead to a decrease in the yield of the recycled monomer. Considering the degree of endothermic heat generation during the hydrolysis reaction, the supply temperature of the subcritical water is preferably less than ±20°C, more preferably less than ±10°C, and even more preferably less than ±5°C, relative to the temperature at the inlet of the continuous reactor (O).

[0161] As for the supply pressure of the subcritical water, since it is preferable that the subcritical water is maintained as a liquid in the continuous reactor (O), a preferable example of the supply pressure of the subcritical water is a pressure higher than the saturated vapor pressure of water at the maximum temperature of the subcritical water. For example, the vapor pressure of water is 6.4 MPa at 280° C., 8.6 MPa at 300° C., 11.3 MPa at 320° C., and 16.5 MPa at 350° C., and therefore, a pressure higher than this must be applied in order to maintain the water as a liquid.

[0162] (4) Means for mixing a composition containing a thermoplastic polymer with subcritical water (N) The recycled monomer production apparatus of the present invention has a means (N) (sometimes simply referred to as "means (N)" in the recycled monomer production apparatus of the present invention) for mixing the composition containing the thermoplastic polymer supplied from the means (L) with the subcritical water supplied from the means (M). Examples of the means (N) include a mixing tank, a channel with a screw, a jet mixer, a homogenizer, and a static mixer. In particular, it is preferable that the means (N) is a static mixer, since it has no moving parts and has a small pressure loss.

[0163] The recycled monomer production apparatus of the present invention is characterized by the rapid mixing of pre-pressurized and heated subcritical water and a composition containing a thermoplastic polymer. Conventional recycled monomer production apparatuses equipped with a batch reactor in which a reaction tank containing water and a composition containing a thermoplastic polymer is heated while reacting, and continuous recycled monomer production apparatuses in which a slurry of a composition containing a thermoplastic polymer dispersed in water is pressurized and heated while reacting, can precisely control the reaction initiation temperature in the recycled monomer production apparatus of the present invention, since the temperature at the time of contact between the composition containing a thermoplastic polymer and the subcritical water can be controlled. As a result, the depolymerization reaction of the thermoplastic polymer can be progressed in a short time while suppressing overdecomposition of the monomer, and the monomer yield can be increased. In addition, the reaction can be started instantly, so the residence time in the continuous reactor (O) can be reduced. As a result, the volume of the continuous reactor (O) can be reduced, leading to a reduction in the cost of the apparatus.

[0164] (5) A continuous reactor (O), a device (P) for monitoring the internal temperatures upstream and downstream of the continuous reactor (O), and a temperature control mechanism (Q) for heating and / or cooling the continuous reactor (O) The recycled monomer production apparatus of the present invention has a device (P) for monitoring the internal temperature upstream and downstream of the continuous reactor (O) (in the recycled monomer production apparatus of the present invention, this may be simply referred to as the "device (P)"), and a temperature control mechanism (Q) for heating and / or cooling the continuous reactor (O) (in the recycled monomer production apparatus of the present invention, this may be simply referred to as the "temperature control mechanism (Q)"), and it is preferable that the temperature control mechanism (Q) is operated based on the device (P) to control the internal temperature of the continuous reactor (O).

[0165] The recycled monomer production apparatus of the present invention has a continuous reactor (O) for hydrolysis of a thermoplastic polymer. The continuous reactor (O) can continuously process a composition containing a thermoplastic polymer, so that the time for charging and unloading required in batch processing can be reduced, and the volume of the continuous reactor (O) can be reduced.

[0166] Examples of the continuous reactor (O) include a tubular type, a tower type, and a multi-stage mixing tank type. An agitator may be provided in the continuous reactor (O). The continuous reactor (O) may be a multi-stage arrangement of multiple containers, or a multi-tubular continuous reactor may be a multi-stage arrangement of multiple flow paths. Among these, it is preferable that the continuous reactor (O) is a tubular continuous reactor. A tubular continuous reactor is simple and has no moving parts, and it is easy to control the reaction temperature, which is important in the depolymerization treatment of a composition containing a thermoplastic polymer with subcritical water.

[0167] In one embodiment of the recycling monomer production apparatus of the present invention, it is preferable to have a device (P) for monitoring the internal temperature of the upstream and downstream parts of the continuous reactor (O). Examples of devices for monitoring the internal temperature include a thermocouple, a platinum resistance thermometer, a bimetal thermometer, a radiation thermometer, a thermograph, a thermistor, and the like. The upstream part of the continuous reactor (O) means a position of 1 / 2 or less on the upstream side of the total reaction volume of the continuous reactor (O). The upstream part of the continuous reactor (O) is preferably a position of 1 / 3 or less on the upstream side of the total reaction volume of the continuous reactor (O), more preferably a position of 1 / 4 or less on the upstream side, and even more preferably a position of 1 / 5 or less on the upstream side. In addition, the downstream part of the continuous reactor (O) means a position of 1 / 2 or less on the downstream side of the total reaction volume of the continuous reactor. The downstream part of the continuous reactor (O) is preferably a position of 1 / 3 or less on the downstream side of the total reaction volume of the continuous reactor, more preferably a position of 1 / 4 or less on the downstream side, and even more preferably a position of 1 / 5 or less on the downstream side. A plurality of devices for monitoring the internal temperature may be installed in the reactor. The total reaction volume means the total reaction volume from the inlet to the outlet of the continuous reactor (O). When a plurality of vessels are arranged in multiple stages as the continuous reactor (O), the total reaction volume is the total volume of the plurality of vessels.

[0168] The temperatures of the means (L) and the means (M) may be controlled based on the internal temperature of the upstream part of the continuous reactor (O). By controlling the feeder based on the internal temperature of the upstream part of the continuous reactor (O), the temperature of the upstream part of the continuous reactor can be precisely controlled. Therefore, it is possible to prevent overdecomposition of the monomer due to an excessive rise in temperature at the beginning of the reaction and a decrease in the depolymerization reaction rate due to insufficient temperature rise.

[0169] The recycling monomer production apparatus of the present invention preferably has a temperature control mechanism (Q) for heating and / or cooling the continuous reactor (O), and the temperature control mechanism (Q) is operated based on the device (P) to control the internal temperature of the continuous reactor (O). By controlling the temperature of the continuous reactor (O) based on the internal temperatures of the upstream and downstream parts of the continuous reactor (O) in this manner, the temperature of the continuous reactor (O) can be precisely controlled. Therefore, it is possible to prevent overdecomposition of monomers due to overheating, generation of oligomers due to repolymerization, and a decrease in the depolymerization reaction rate due to insufficient heating, particularly in the later stage of the reaction.

[0170] In the recycling monomer production apparatus of the present invention, it is preferable that a plurality of the temperature control mechanisms (Q) are installed and the plurality of the temperature control mechanisms (Q) are operated based on the device (P). By installing a plurality of the temperature control mechanisms (Q), more precise temperature control can be realized according to the progress of the hydrolysis reaction in the upstream and downstream parts of the continuous reactor (O).

[0171] In the recycling monomer production apparatus of the present invention, it is preferable to control the temperature control mechanism (Q) so that the internal temperature of the downstream part of the continuous reactor (O) is 10°C or more lower than the internal temperature of the upstream part. By adopting such a configuration, in the reaction of hydrolyzing a thermoplastic polymer, the temperature in the early stage of the reaction is made higher than that in the later stage of the reaction, which makes it easier to promote hydrolysis of the thermoplastic polymer contained in a large amount in the reaction solution in the early stage of the reaction. On the other hand, since the reaction solution in the later stage of the reaction contains a large amount of hydrolyzed recycled monomer, it is easier to suppress repolymerization of the recycled monomer by making the temperature lower than that in the early stage of the reaction. In other words, by adopting such a configuration, it is easier to achieve both highly efficient hydrolysis of the thermoplastic polymer and high yield of the recycled monomer. It is more preferable that the internal temperature of the downstream part of the continuous reactor (O) is 20°C or more lower than the internal temperature of the upstream part, and even more preferable that it is 30°C or more lower. In addition, the internal temperature of the downstream part of the continuous reactor (O) relative to the internal temperature of the upstream part is not particularly limited, but from the viewpoint of maintaining the reaction rate of the hydrolysis reaction of the thermoplastic polymer, it is usually 100° C. or less lower, preferably 80° C. or less lower, and more preferably 60° C. or less lower.

[0172] When the composition containing the thermoplastic polymer to be depolymerized is a waste, it is usually difficult to keep the quality of the waste constant. Furthermore, a change in the composition of the waste may cause disturbance and affect the temperature inside the reactor. Even in such a case, as described in the present invention, the reaction temperature can be controlled instantly even if disturbance such as a change in the composition of the thermoplastic polymer occurs by heating and / or cooling the continuous reactor (O) based on the internal temperature of the continuous reactor (O).

[0173] The means for heating the continuous reactor (O) is not particularly limited, but examples thereof include a method of attaching a jacket or shell to the continuous reactor (O) and heating with a heat medium such as steam, a method of heating with an electric heater, etc. The method for cooling the continuous reactor (O) is not particularly limited, but examples thereof include a method of attaching a jacket or shell to the continuous reactor (O) and cooling with a heat medium / coolant having a temperature lower than the internal temperature of the continuous reactor (O), and a method of cooling by blowing air over the surface of the continuous reactor (O).

[0174] When the continuous reactor (O) is a tubular continuous reactor, the larger the inner diameter of the tubular continuous reactor, the more the flow rate that can be processed per surface area of ​​the tubular continuous reactor can be increased, but the heat transfer area decreases, which makes it easier for temperature distribution to occur in the axial and radial directions. Therefore, it becomes more important to install a device for monitoring the internal temperature of the continuous reactor described in the present invention and a temperature control device for heating and / or cooling the continuous reactor (O). The inner diameter of the tubular continuous reactor is preferably 1 cm or more, more preferably 2 cm or more.

[0175] When the mass flow ratio of the subcritical water and the thermoplastic polymer component in the composition containing a thermoplastic polymer is X:1, X is preferably less than 6. Since the specific heat capacity of water is 4.3 kJ / kg·K and the heat of vaporization is 2250 kJ / kg, which are very high compared to other organic solvents, it is preferable to set X to less than 6 and reduce the amount of water used from the viewpoint of energy saving. In addition, by setting X to less than 6, the temperature change in the continuous reactor (O) due to the reaction heat of the depolymerization reaction of the composition containing a thermoplastic polymer becomes large, and therefore, as described in the present invention, the importance of performing temperature control based on the internal temperature of the continuous reactor (O) is increased, which is preferable. Furthermore, by setting X to less than 6, the processing amount of the composition containing a thermoplastic polymer per unit volume of the continuous reactor (O) can be increased, which also leads to a reduction in the equipment cost. In addition, by setting X to less than 6, the concentration of the recycled monomer increases in the downstream part of the continuous reactor (O), which promotes the repolymerization of the recycled monomer, and therefore, as described in the present invention, the importance of performing temperature control based on the internal temperature of the continuous reactor (O) is increased, which is preferable.

[0176] When the maximum temperature indicated by the device (P) for monitoring the internal temperatures of the upstream and downstream parts of the continuous reactor (O) performing hydrolysis is Y ° C., it is preferable to control the product of X and Y to be 2000 or less. The maximum temperature Y ° C. refers to the higher of the maximum temperature indicated by the internal temperature indicated by the upstream part and the maximum temperature indicated by the internal temperature indicated by the downstream part. The product of X and Y is more preferably 1600 or less, even more preferably 1300 or less, and particularly preferably 1200 or less. There is no particular restriction on the lower limit of the product of X and Y, but it is preferably 300, more preferably 320, and particularly preferably 340. By setting the product of X and Y within these condition ranges, it is possible to easily achieve both the efficiency of the depolymerization treatment of the composition containing the thermoplastic polymer and energy saving.

[0177] In addition, when the average residence time of the mixture of the composition containing a thermoplastic polymer and the subcritical water in the continuous reactor (O) is Z minutes, it is preferable to control the product of X, Y, and Z to be 60,000 or less. The average residence time is the value obtained by dividing the "volume of the continuous reactor (O)" by the "volumetric flow rate of the mixture of the composition containing a thermoplastic polymer and the subcritical water". The product of X, Y, and Z is more preferably 40,000 or less, and even more preferably 30,000 or less. In addition, there is no particular restriction on the lower limit of the product of X, Y, and Z, but 5,000 is preferable, 8,000 is more preferable, and 9,000 is particularly preferable. By setting the product of X, Y, and Z to such a preferable condition range, it is possible to easily achieve both the efficiency of the depolymerization treatment of the composition containing a thermoplastic polymer and energy saving.

[0178] (6) Cooler, back pressure valve The reaction solution discharged from the continuous reactor (O) is preferably introduced into an apparatus for terminating the hydrolysis reaction. Examples of the apparatus for terminating the hydrolysis reaction include a cooler and a flash tank. Of these, the apparatus for terminating the hydrolysis reaction is preferably a cooler. Examples of the cooler include known means such as a heat exchanger. Since the reaction solution after leaving the cooler is usually under high pressure, it is preferable to release the pressure by known means such as a back pressure valve.

[0179] (7) Monomer purification equipment After the reaction has been stopped, the reaction solution is preferably purified by known methods such as distillation and crystallization.

[0180] The purified monomer is preferably repolymerized and reused as a composition containing a thermoplastic polymer. As the repolymerization method, a known polymerization method can be used.

[0181] (8) Method for Producing Recycled Monomer (Fourth Preferred Aspect of the Invention) A fourth preferred embodiment of the present invention is a method for producing a recycled monomer, comprising the step of contacting a composition containing a thermoplastic polymer with subcritical water to hydrolyze the thermoplastic polymer. The definitions, examples, and preferred embodiments of the composition containing a thermoplastic polymer and the subcritical water are as described above. The reaction conditions for the hydrolysis step, i.e., the preferred mixing ratio, temperature, pressure, etc., are as described above.

[0182] In a fourth preferred embodiment of the present invention, the thermoplastic polymer is preferably a thermoplastic polyester or a thermoplastic polyamide. When the thermoplastic polymer is a thermoplastic polyester or a thermoplastic polyamide, it becomes easy to recover the monomer before polymerization by hydrolysis.

[0183] In the fourth preferred embodiment of the present invention, in the step of hydrolyzing the thermoplastic polymer, the reaction temperature in the later stage of the hydrolysis reaction is preferably 10° C. or more lower than the reaction temperature in the early stage of the hydrolysis reaction. By making the temperature in the early stage of the hydrolysis reaction higher than the late stage of the hydrolysis reaction, it is easy to promote the hydrolysis of the thermoplastic polymer contained in a large amount in the reaction solution in the early stage of the reaction. On the other hand, since the reaction solution in the late stage of the reaction contains a large amount of hydrolyzed recycled monomer, it is easy to suppress the repolymerization of the recycled monomer by making the temperature lower than the early stage of the reaction. That is, it is easy to achieve both highly efficient hydrolysis of the thermoplastic polymer and high yield of the recycled monomer. The reaction temperature in the later stage of the hydrolysis reaction is more preferably 20° C. or more lower than the reaction temperature in the early stage of the hydrolysis reaction, and even more preferably 30° C. or more lower. In addition, the reaction temperature in the later stage of the hydrolysis reaction is not particularly limited to the reaction temperature in the early stage of the hydrolysis reaction, but from the viewpoint of maintaining the reaction rate of the reaction of hydrolyzing the thermoplastic polymer, it is usually 100° C. or less lower, preferably 80° C. or less lower, and more preferably 60° C. or less lower. EXAMPLES

[0184] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0185] In the first to fourth preferred embodiments of the present invention and the examples of the recycled monomer production apparatus, the following raw materials were used.

[0186] [Raw materials used in the description of the first preferred embodiment] Thermoplastic polyester (A-1): Commercially available polyethylene terephthalate resin pellets, melting point 254°C Thermoplastic polyester (A-2): Washed and dried PET bottle flakes, melting point 255℃ Thermoplastic polyester (A-3): Commercially available polybutylene terephthalate resin pellets, melting point 224°C

[0187] Here, the melting point was determined as the temperature of the endothermic peak that appeared when each resin molded body was cooled from a molten state to 30° C. at a temperature drop rate of 20° C. / min in a nitrogen gas atmosphere using a differential scanning calorimeter, and then heated to the melting point + 40° C. at a temperature rise rate of 20° C. / min. However, when two or more endothermic peaks were detected, the temperature of the endothermic peak with the greatest peak intensity was determined as the melting point.

[0188] [Raw materials used in the description of the second preferred embodiment] PET: Polyethylene terephthalate resin (intrinsic viscosity 0.62 dl / g) manufactured by Toray Industries, Inc. PBT1: Polybutylene terephthalate resin (intrinsic viscosity 0.85 dl / g) manufactured by Toray Industries, Inc. PBT2: A polyester resin composition obtained by blending PBT1 (100 parts by weight) with pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (Irganox 1010 [product name] manufactured by BASF) (0.5 parts by weight) and melt-kneading the mixture at 250°C. PBT3: A polyester resin composition obtained by blending 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol] (Adekastab LA-31G) (0.5 parts by weight) with PBT1 (100 parts by weight) and melt-kneading at 250°C. PBT4: A polyester resin composition obtained by blending 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (Adekastab PEP-36) (0.5 parts by weight) with PBT1 (100 parts by weight) and melt-kneading at 250°C. PBT5: A polyester resin composition obtained by blending PBT1 (100 parts by weight) with BASF's Irganox 1010 (trade name) (0.5 parts by weight), Adeka STAB LA-31G (0.5 parts by weight), and Adeka STAB PEP-36 (0.5 parts by weight), and melt-kneading the mixture at 250°C.

[0189] [Raw materials used in the description of the third preferred embodiment] Polyethylene terephthalate [PET] (manufactured by Toray Industries, Inc., intrinsic viscosity 0.62 dl / g, melting point 254°C) Polybutylene terephthalate [PBT] (manufactured by Toray Industries, Inc., intrinsic viscosity 0.85 dl / g, melting point 224°C) Polycarbonate [PC] (Idemitsu Kosan Co., Ltd. "Toughlon" (registered trademark) A2200, viscosity average molecular weight 22000, no melting point, glass transition temperature 150°C) Polyurethane [PU] (polyurethane urea consisting of PTMG with a molecular weight of 1,800, diphenylmethane diisocyanate, ethylenediamine and diethylamine as an end-blocking agent, with a thermal decomposition starting temperature of 277°C).

[0190] [Apparatus for producing recycled monomer and raw materials used in the description of the fourth preferred embodiment] Polyethylene terephthalate (PET-A)] Commercially available polyethylene terephthalate resin pellets (PET-A): Melting point 254°C Polyethylene terephthalate resin waste (PET-B): Washed and dried PET bottle flakes, melting point 255°C.

[0191] Here, the melting point was determined as the temperature of an endothermic peak that appeared when a thermoplastic polyester was cooled from a molten state to 30° C. at a rate of 20° C. / min in a nitrogen gas atmosphere using a differential scanning calorimeter, and then heated to the melting point + 40° C. at a rate of 20° C. / min. However, when two or more endothermic peaks were detected, the temperature of the endothermic peak with the greatest peak intensity was determined as the melting point.

[0192] Evaluation method [Diol yield (GC)] The diol yield (GC) of the present invention was calculated by gas chromatography under the following measurement conditions. Equipment: Shimadzu GC-2010 Column: Agilent Technologies DB-5 0.32mm x 30m (0.25μm) Carrier gas: Helium Detector: Flame ionization detector (FID) Sample: Approximately 1.2 g of the reaction mixture was taken, diluted with approximately 5 g of methanol, and filtered to separate and remove components insoluble in methanol, thereby preparing a sample for gas chromatography measurement. Quantitative determination of diol: The amount of diol was quantified by the absolute calibration curve method.

[0193] [Dicarboxylic acid yield (HPLC)] The dicarboxylic acid yield (HPLC) of the present invention was calculated by high performance liquid chromatography under the following measurement conditions. Equipment: Shimadzu LC-10Avp series Column: Mightysil RP-18GP150-4.6 Detector: Photodiode array detector (UV=254nm) Flow rate: 1mL / min Column temperature: 40℃ Mobile phase: 0.1% acetic acid aqueous solution / acetonitrile Sample: Approximately 0.1 g of the reaction mixture was taken, diluted with approximately 10 g of dimethylformamide, and filtered to separate and remove components insoluble in dimethylformamide, thereby preparing a sample for high performance liquid chromatography measurement. Quantitative determination of dicarboxylic acid: The amount of dicarboxylic acid was quantified by the absolute calibration curve method (however, in Examples 9, 12 to 25, 35, and 36 and Comparative Examples 8 to 10, disodium terephthalate or diammonium terephthalate was produced, but was converted to terephthalic acid by the acid contained in the mobile phase).

[0194] [Examples of the first preferred embodiment and comparative examples] [Example 1] Into a SUS316L autoclave equipped with a stirrer, 20.0 g of thermoplastic polyester (A-1) and 60.0 g of deionized water were charged. The mass ratio of water to thermoplastic polyester (Z:1) was 3:1.

[0195] The reaction vessel was replaced with nitrogen, and after sealing under a nitrogen pressure of 0.5 MPa, the reaction was carried out by holding at 260°C for 15 minutes while stirring at 200 rpm. During the reaction, the pressure in the system was 4.5 MPa. After the reaction was completed, the reaction mixture was cooled to room temperature and collected. The reaction temperature X°C was 260°C, and the residence time at the reaction temperature of 260°C was 15 minutes, so the product of X, Y, and Z is 11,700.

[0196] The diol yield calculated by gas chromatography of the recovered reaction mixture was 95%, the dicarboxylic acid yield calculated by high performance liquid chromatography was 83%, and the diol concentration in the reaction mixture was 7.63 mass%. The reaction mixture was white in color.

[0197] [Examples 2 to 7, Comparative Examples 1 to 5] Using thermoplastic polyester (A-1) as the raw material, depolymerization was carried out in the same manner as in Example 1, except for changing the amount of water relative to the thermoplastic polyester, the reaction temperature, and the reaction time. The reaction conditions, diol yield, dicarboxylic acid yield, and color tone of the reaction mixture are shown in Tables 1 and 2.

[0198] [Example 8] Except for using the thermoplastic polyester (A-2) as the raw material, depolymerization was carried out in the same manner as in Example 1. The diol yield, dicarboxylic acid yield, and color tone of the reaction mixture are shown in Table 1.

[0199] [Example 9] Except for further adding sodium hydroxide, depolymerization was carried out in the same manner as in Example 1. The diol yield, dicarboxylic acid yield, and color tone of the reaction mixture are shown in Table 1.

[0200] [Example 10] Except for using the thermoplastic polyester (A-3) as the raw material, depolymerization was carried out in the same manner as in Example 2. The diol yield, cyclic ether yield, dicarboxylic acid yield, and color tone of the reaction mixture are shown in Table 1.

[0201] [Table 1]

[0202] [Table 2]

[0203] From Examples 1 to 8, it is understood that by setting X to be equal to or higher than the melting point of the thermoplastic polyester (A-1) and the thermoplastic polyester waste (A-2) and lower than 300°C, and setting the product of X, Y, and Z to be equal to or higher than 2,000 and equal to or lower than 20,000, it is possible to obtain diol and dicarboxylic acid in high yield while greatly suppressing the amount of energy required for depolymerization of the thermoplastic polyester, and further obtain a reaction mixture with an increased concentration of diol and no coloring.

[0204] In Comparative Example 1, in which the reaction was carried out at 240°C, which is lower than the melting point of the thermoplastic polyester (A-1), 254°C, the diol and dicarboxylic acid yields were significantly reduced to less than half that of Example 1, which was carried out under the same conditions except for the reaction temperature. This is believed to be because the depolymerization reaction was limited to the surface of the solid thermoplastic polyester (A-1), resulting in insufficient reaction. In Comparative Example 3, in which X and Z were within the preferred ranges but the product of X, Y, and Z was less than 2,000 due to the short reaction time, the reaction also proceeded insufficiently, resulting in a reduction in the diol and dicarboxylic acid yields compared to Example 1. In this way, when at least one of X or the product of X, Y, and Z does not meet the preferred range, the thermoplastic polyester and / or oligomer remains, and the amount discarded as residue increases, which is not preferable.

[0205] In Comparative Example 2, in which the reaction was carried out at 300°C, a large amount of energy was required to heat water with a large specific heat capacity, but the diol yield was lower than that of Example 1, and the reaction mixture contained a large amount of over-reactants such as coloring impurities. In Comparative Example 4, in which the product of X, Y, and Z exceeds 20,000, X and Z are within the preferred range, but the reaction mixture was heated for a long time, and a decrease in the diol yield and coloring of the reaction mixture were observed as in Comparative Example 2. In this way, when at least one of X or the product of X, Y, and Z exceeds the preferred range, the diol produced changes into an over-reactant (for example, in the case of ethylene glycol, acetaldehyde, diethylene glycol, coloring impurities, etc.), and the yield decreases. In particular, acetaldehyde, which is a type of over-reactant, cannot be removed by removing heavy components by distillation alone, and additional treatment such as hydrogenation is required, which complicates the equipment in the recovery process and requires additional energy for treatment, so it is desirable to carry out the depolymerization reaction under conditions that suppress over-reaction.

[0206] In Comparative Example 5, in which the amount of water relative to the thermoplastic polyester (A-1) exceeds the preferred range, the yield is lower than that of Example 1. When the amount of water relative to the thermoplastic polyester exceeds the preferred range, the amount of energy required to heat water having a large specific heat capacity during the depolymerization reaction increases, and the equipment used for the depolymerization reaction becomes large, which is not preferred.

[0207] A comparison between Example 1 and Example 9 shows that when the reaction temperature is 260° C., the yield is improved by adding an alkaline component.

[0208] From Example 10, it is evident that terephthalic acid can be obtained in high yield even when polybutylene terephthalate is used as the thermoplastic polyester.

[0209] [Reference example 1] 123 parts by mass of bis(hydroxyethyl) terephthalate, which had been produced in advance by the transesterification reaction of dimethyl terephthalate (manufactured by Kanto Chemical Co., Ltd.) and ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.), was charged at a temperature of 250°C and a pressure of 1.2 x 105 A slurry of 100 parts by mass of high-purity terephthalic acid (manufactured by Mitsui Chemicals, Inc.) and 45 parts by mass of ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) was sequentially supplied over a period of 4 hours to an esterification reactor maintained at a pressure of 1 Pa. After completion of the supply, the esterification reaction was continued for another hour to obtain an esterification reaction product.

[0210] 100 parts by mass of the obtained esterification reaction product was weighed and charged into a polycondensation reactor, melted and stirred at a temperature of 250°C, and tetraisopropyltitanium was added so that the titanium atom amount was 15 ppm relative to the theoretical yield of polyester obtained after polycondensation. While stirring at 30 rpm, the reaction system was gradually heated from 250°C to 285°C and the pressure was reduced to 40 Pa. The time to reach the final temperature and the final pressure was both 60 minutes. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen to return to normal pressure and the polycondensation reaction was stopped, and the mixture was discharged into cold water in the form of a strand, which was immediately cut to obtain polymer pellets.

[0211] [Example 11] The reaction mixture obtained in the same manner as in Example 1 was cooled to room temperature, and the precipitated recycled terephthalic acid was filtered off. Meanwhile, water was removed from the filtrate after filtering off the recycled terephthalic acid under reduced pressure, and then the filtrate was distilled to obtain recycled ethylene glycol. Polyethylene terephthalate containing 55% by mass of recycled monomer was produced in the same manner as in Reference Example 1, except that the recycled ethylene glycol and recycled terephthalic acid obtained in this manner were used as esterification reaction raw materials. The melting point of the recycled polyethylene terephthalate was 256°C, and the color tone was similar to that of the polyethylene terephthalate obtained in Reference Example 1.

[0212] [Comparative Example 6] Recycled polyethylene terephthalate was produced in the same manner as in Reference Example 1, except that recycled terephthalic acid and recycled ethylene glycol obtained in the same manner as in Comparative Example 2 were used. The melting point of the resulting recycled polyethylene terephthalate was 256°C and it was pale orange in color.

[0213] Therefore, as can be seen from Example 9 and Comparative Example 6, the depolymerization reaction of the present invention can produce high-purity diols and dicarboxylic acids that are free of color, and therefore it is possible to produce thermoplastic polyesters equivalent to those produced by using commercially available diols and dicarboxylic acids as raw materials.

[0214] [Examples of the second preferred embodiment and comparative examples] [Example 12] 20.0 g of polyethylene terephthalate resin (PET), 40.0 g of deionized water, and 0.01 g of sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a SUS316L autoclave equipped with a stirrer. The atmosphere in the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm for 15 minutes at 300°C under a nitrogen pressure of 0.5 MPa and sealed. The pressure in the system during the reaction was 8.0 MPa. After the reaction, the mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 16.2 g of terephthalic acid (yield 94%) and 0.1 g of benzoic acid (yield 0.8%) were obtained. The results are shown in Table 3.

[0215] [Examples 13 and 14, Comparative Examples 7 and 8] Except for changing the amount of sodium hydroxide added, the polyethylene terephthalate resin was depolymerized in the same manner as in Example 12. The results are shown in Table 3.

[0216] [Table 3]

[0217] Comparing Examples 12 to 14 with Comparative Examples 7 and 8, it can be seen that by adding a specific amount of sodium hydroxide to depolymerize PET, the production of benzoic acid (an over-reacted product of terephthalic acid) is suppressed, and terephthalic acid can be obtained in high yield.

[0218] [Comparative Example 9] 20.0 g of polyethylene terephthalate resin (PET), 40.0 g of deionized water, and 0.36 mL of 28% ammonia water (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a SUS316L autoclave equipped with a stirrer. The inside of the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm for 15 minutes at 300°C under a nitrogen pressure of 0.5 MPa and sealed. The pressure in the system during the reaction was 8.0 MPa. After the reaction, the reaction mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 10.7 g of terephthalic acid (62% yield) and 2.3 g of benzoic acid (18% yield) were obtained. On the other hand, when the filtrate was analyzed by GC, the yield of ethylene glycol was 78%. The results are shown in Table 4 together with the results of Example 2.

[0219] [Comparative Example 10] 20.0g of polyethylene terephthalate resin (PET), 40.0g of deionized water, and 10.0g of sodium hydroxide were added to a SUS316L autoclave equipped with a stirrer. The inside of the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm for 15 minutes at 300°C under a nitrogen pressure of 0.5MPa while sealed. The pressure in the system during the reaction was 8.0MPa. After the reaction, the reaction mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 15.6g of terephthalic acid (yield 90%) and 0.11g of benzoic acid (yield 0.9%) were obtained. On the other hand, when the filtrate was analyzed by GC, the yield of ethylene glycol was 52%. The results are shown in Table 4.

[0220] [Table 4]

[0221] It can be seen from Example 13 and Comparative Example 9 that the sodium hydroxide-added formulation has a lower yield of benzoic acid and a higher yield of terephthalic acid and ethylene glycol than the ammonia-added formulation. Also, it can be seen from Example 13 and Comparative Example 10 that the yield of terephthalic acid and ethylene glycol is low when the amount of sodium hydroxide added is large.

[0222] [Example 15] 20.0 g of polybutylene terephthalate resin (PBT1), 60.0 g of deionized water, and 0.1 g of sodium hydroxide were added to a SUS316L autoclave equipped with a stirrer. The atmosphere in the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm at 280°C for 15 minutes under a nitrogen pressure of 0.5 MPa while sealed. The pressure in the system during the reaction was 6.3 MPa. After the reaction, the mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 16.9 g of terephthalic acid (yield 98%) and 0.03 g of benzoic acid (yield 0.2%) were obtained. The results are shown in Table 5.

[0223] [Examples 16 to 21, Comparative Examples 11 to 15] Except for changing the type of polybutylene terephthalate resin composition and the amount of sodium hydroxide added, the polybutylene terephthalate resin composition was depolymerized in the same manner as in Example 15. The results are shown in Table 5.

[0224] [Table 5]

[0225] It can be seen from Comparative Example 11 and Comparative Examples 12 to 15 that the yield of benzoic acid increases and the yield of terephthalic acid decreases by blending an antioxidant and a weathering agent into PBT. Also, it can be seen from Comparative Examples 12 to 15 and Examples 16 to 21 that even in the case of PBT blended with additives, the yield of benzoic acid decreases and the yield of terephthalic acid increases by adding sodium hydroxide.

[0226] [Example 22] 20.0 g of polybutylene terephthalate resin composition (PBT5), 60.0 g of deionized water, and 0.1 g of sodium hydroxide were added to a SUS316L autoclave equipped with a stirrer. The inside of the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm for 15 minutes at 260°C under a sealed condition with nitrogen pressure of 0.5 MPa. During the reaction, the pressure in the system was 5.0 MPa. After the reaction, the reaction mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 15.6 g of terephthalic acid (yield 90%) and 0.03 g of benzoic acid (yield 0.2%) were obtained. The results are shown in Table 6 together with the results of Example 20.

[0227] [Example 23] Except for changing the temperature, the polybutylene terephthalate resin composition was depolymerized in exactly the same manner as in Example 22. The results are shown in Table 6.

[0228] [Table 6]

[0229] Comparison of Example 22 with Example 20 shows that the yield of terephthalic acid is improved by increasing the temperature from 260° C. to 280° C. Comparison of Example 20 with Example 23 shows that the yield of benzoic acid is increased and the yield of terephthalic acid is decreased by increasing the temperature from 280° C. to 300° C. Therefore, it can be seen that the yield of terephthalic acid is highest when the temperature is 280° C.

[0230] [Example 24] 20.0 g of polybutylene terephthalate resin (PBT5), 40.0 g of deionized water, and 0.1 g of sodium hydroxide were added to a SUS316L autoclave equipped with a stirrer. The inside of the reaction vessel was replaced with nitrogen, and the mixture was stirred at 200 rpm for 15 minutes at 280°C under a nitrogen pressure of 0.5 MPa and sealed. The pressure in the system during the reaction was 6.3 MPa. After the reaction, the mixture was cooled to room temperature and the reaction product was recovered. After filtering the reaction product, the solid matter was dried using a vacuum pump (80°C). 14.3 g of terephthalic acid (yield 83%) and 0.01 g of benzoic acid (yield 0.1%) were obtained. The results are shown in Table 7 together with the results of Example 20.

[0231] [Example 25] A polybutylene terephthalate resin composition was obtained in the same manner as in Example 24, except that the blending amount of the polybutylene terephthalate resin composition and the blending amount of water were changed. The results are shown in Table 7.

[0232] [Table 7]

[0233] A comparison between Example 24 and Example 20 shows that the yield of terephthalic acid is improved by increasing the amount of water from 200 parts by weight to 300 parts by weight. A comparison between Example 20 and Example 25 shows that the yield of terephthalic acid is reduced by increasing the amount of water from 300 parts by weight to 800 parts by weight. Thus, it can be seen that the yield of terephthalic acid is highest when the amount of water is 300 parts by weight.

[0234] [Examples of the third preferred embodiment and comparative examples] [Example 26] A polyester mixture containing 10.0 g of polyethylene terephthalate and 10.0 g of polybutylene terephthalate and 50.0 g of deionized water were charged into a SUS316L autoclave equipped with a stirrer. The reactor was replaced with nitrogen, sealed under a nitrogen pressure of 0.3 MPa, and then the reaction was carried out by holding at 260°C for 15 minutes while stirring at 200 rpm. The pressure in the system during the reaction was 4.8 MPa. After the reaction was completed, the mixture was cooled to room temperature, and the white precipitate was collected by filtration. The terephthalic acid yield calculated by high performance liquid chromatography measurement of the collected precipitate is shown in Table 8. The terephthalic acid yield was 90% and the ethylene glycol yield was 83%.

[0235] [Example 27] Except for changing the amount of deionized water to 30.0 g, hydrolysis of the polyester mixture was carried out in exactly the same manner as in Example 26. The results are shown in Table 8. The yield of terephthalic acid was 88%, and the yield of ethylene glycol was 82%.

[0236] [Example 28] Except for changing the amount of deionized water to 100 g, hydrolysis of the polyester mixture was carried out in exactly the same manner as in Example 26. The results are shown in Table 8. The yield of terephthalic acid was 95%, and the yield of ethylene glycol was 88%.

[0237] [Example 29] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer-containing composition was changed to a polyester mixture containing 19.0 g of polyethylene terephthalate and 1.0 g of polybutylene terephthalate. The results are shown in Table 8. The yield of terephthalic acid was 85%, and the yield of ethylene glycol was 78%.

[0238] [Example 30] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer-containing composition was changed to a polyester mixture containing 19.8 g of polyethylene terephthalate and 0.2 g of polybutylene terephthalate. The results are shown in Table 8. The yield of terephthalic acid was 82%, and the yield of ethylene glycol was 76%.

[0239] [Example 31] Hydrolysis of the polyester mixture was carried out in exactly the same manner as in Example 26, except that the reaction temperature was changed to 290° C. The results are shown in Table 8. The yield of terephthalic acid was 98%, and the yield of ethylene glycol was 90%.

[0240] [Example 32] Except for changing the nitrogen pressure to 8.5 MPa, hydrolysis of the polyester mixture was carried out in exactly the same manner as in Example 26. The results are shown in Table 8. The yield of terephthalic acid was 97%, and the yield of ethylene glycol was 90%.

[0241] [Example 33] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer-containing composition was changed to a mixture containing 16.0 g of polybutylene terephthalate and 4.0 g of polycarbonate, and the reaction temperature was changed to 250° C. The results are shown in Table 8. The yield of terephthalic acid was 85%.

[0242] [Example 34] Hydrolysis was carried out in the same manner as in Example 26, except that the polymer-containing composition was changed to a mixture containing 18.0 g of polyethylene terephthalate and 2.0 g of polyurethane urea. The results are shown in Table 8. The yield of terephthalic acid was 84%, and the yield of ethylene glycol was 74%.

[0243] [Example 35] Hydrolysis was carried out in exactly the same manner as in Example 34, except that 7.7 g of sodium hydroxide was further added. 100 g of deionized water was added to the obtained hydrolyzate, and the entire amount of the generated disodium terephthalate was dissolved. After filtering, hydrochloric acid was added to the aqueous solution, and the precipitated terephthalic acid was collected. The results are shown in Table 8. The yield of terephthalic acid was 95%, and the yield of ethylene glycol was 93%.

[0244] [Example 36] Hydrolysis was carried out in exactly the same manner as in Example 35, except that the reaction temperature was changed to 230° C. The results are shown in Table 8. The yield of terephthalic acid was 92%, and the yield of ethylene glycol was 90%.

[0245] [Comparative Example 16] Hydrolysis of the polyester mixture was carried out in exactly the same manner as in Example 26, except that the reaction temperature was changed to 240° C. The results are shown in Table 9. The yield of terephthalic acid was 10%, and the yield of ethylene glycol was 8%.

[0246] [Comparative Example 17] Except for changing the polymer-containing composition to 20.0 g of polyethylene terephthalate only, hydrolysis was carried out in exactly the same manner as in Example 26. The results are shown in Table 9. The yield of terephthalic acid was 78%, and the yield of ethylene glycol was 72%.

[0247] [Comparative Example 18] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer was changed to 20.0 g of polyethylene terephthalate and 30 g of deionized water. The results are shown in Table 9. The yield of terephthalic acid was 73%, and the yield of ethylene glycol was 68%.

[0248] [Comparative Example 19] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer was 20.0 g of polybutylene terephthalate only, and the reaction temperature was changed to 250° C. The results are shown in Table 9. The yield of terephthalic acid was 75%.

[0249] [Comparative Example 20] Hydrolysis was carried out in exactly the same manner as in Example 26, except that the polymer-containing composition was changed to a polyester mixture containing 19.92 g of polyethylene terephthalate and 0.08 g of polybutylene terephthalate. The results are shown in Table 9. The yield of terephthalic acid was 79%, and the yield of ethylene glycol was 72%.

[0250] [Table 8]

[0251] [Table 9]

[0252] Comparisons of Examples 26, 29, and 30 with Comparative Example 17, and comparisons of Example 27 with Comparative Example 18 show that simultaneous hydrolysis of PET and PBT improves the yield of recycled monomers.

[0253] A comparison between Example 33 and Comparative Example 19 shows that the yield of terephthalic acid is improved by simultaneously hydrolyzing PBT and PC.

[0254] A comparison of Examples 26 and 31 with Comparative Example 16 shows that the yield of recycled monomer is improved by increasing the reaction temperature.

[0255] A comparison of Examples 26 and 28 shows that the yield of recycled monomer can be improved by appropriately increasing the amount of water used in hydrolysis.

[0256] A comparison of Examples 26 and 32 shows that the yield of recycled monomer can be improved by appropriately increasing the pressure in hydrolysis.

[0257] A comparison of Comparative Example 17 and Comparative Example 20 shows that the yield of recycled monomers when a polymer mixture of 100 parts by weight of PET and 0.4 parts by weight of PBT was simultaneously hydrolyzed was almost the same as when PET alone was hydrolyzed.

[0258] A comparison between Example 34 and Comparative Example 17 shows that the yield of recycled monomers is improved by simultaneously hydrolyzing PET and PU.

[0259] A comparison between Example 34 and Example 35 shows that the addition of sodium hydroxide for hydrolysis makes it possible to obtain recycled monomer in high yield.

[0260] A comparison between Example 35 and Example 36 shows that when an alkaline component is added, recycled monomer can be obtained in high yield even if the reaction temperature is lowered.

[0261] [Reference example 2] 123 parts by weight of bis(hydroxyethyl)terephthalate, which had been produced in advance by the transesterification reaction of dimethyl terephthalate (manufactured by Kanto Chemical Co., Ltd.) and ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.), was charged. A slurry of 100 parts by weight of high-purity terephthalic acid (manufactured by Mitsui Chemicals, Inc.) and 45 parts by weight of ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) was sequentially fed over 4 hours into an esterification reactor maintained at a temperature of 250°C and a pressure of 1.2 x 105 Pa. After the end of the feeding, the esterification reaction was continued for another hour to obtain an esterification reaction product.

[0262] 100 parts by weight of the obtained esterification reaction product was weighed and charged into a polycondensation reactor, melted and stirred at a temperature of 250°C, and tetraisopropyltitanium was added so that the titanium atom equivalent was 15 ppm relative to the theoretical yield of polyester obtained after polycondensation. While stirring at 30 rpm, the reaction system was gradually heated from 250°C to 285°C and the pressure was reduced to 40 Pa. The time to reach the final temperature and final pressure was both 60 minutes. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in the form of a strand, and immediately cut to obtain polymer pellets. The melting point of this polymer was 254°C.

[0263] [Example 37] After the hydrolysis in Example 1, terephthalic acid, monohydroxyethyl terephthalate, and benzoic acid were detected as components precipitated at room temperature. Monohydroxyethyl terephthalate is a polymerization precursor of polyethylene terephthalate, and can be used as a polymerization raw material. On the other hand, benzoic acid may inhibit polymerization as an end-capping agent during polymerization, so the precipitated components were washed three times in hot ethanol to remove benzoic acid. With this method, a mixture of terephthalic acid and monohydroxyethyl terephthalate (weight ratio 89:11) was recovered.

[0264] Furthermore, the water-soluble component obtained by the hydrolysis in Example 26 was distilled to recover ethylene glycol.

[0265] 123 parts by weight of bis(hydroxyethyl)terephthalate, which had been produced in advance by the transesterification reaction of dimethyl terephthalate (manufactured by Kanto Chemical Co., Ltd.) and ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.), was charged. A slurry of 102 parts by weight of the mixture of terephthalic acid and monohydroxyethyl terephthalate (recycled monomer) recovered by the above method and 42 parts by weight of ethylene glycol (recycled monomer) was sequentially fed into the esterification reactor, which was kept at a temperature of 250°C and a pressure of 1.2×105 Pa, over a period of 4 hours. After the end of the feeding, the esterification reaction was continued for another hour to obtain an esterification reaction product.

[0266] 100 parts by weight of the obtained esterification reaction product was weighed and charged into a polycondensation reactor, melted and stirred at a temperature of 250°C, and tetraisopropyltitanium was added so that the titanium atom amount was 15 ppm relative to the theoretical yield of polyester obtained after polycondensation. While stirring at 30 rpm, the reaction system was gradually heated from 250°C to 285°C and the pressure was reduced to 40 Pa. The time to reach the final temperature and the final pressure was both 60 minutes. When the predetermined stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in the form of a strand, and immediately cut to obtain polymer pellets. The melting point of this polymer was 254°C, the same as in Reference Example 2.

[0267] [Apparatus for producing recycled monomer, and examples and comparative examples of the fourth preferred embodiment] [Example 38] The recycled monomer production apparatus shown in FIG. 1 was used. An extruder 2 was used as the means (L) for heating and pressurizing the composition containing a thermoplastic polymer and supplying it. A high-pressure pump 4 and an electric heater 5 were used as the means (M) for generating and supplying subcritical water. The heating temperatures of the extruder 2 and the electric heater 5 were controlled to the set temperatures using an extruder / electric heater temperature control device 14. A static mixer 6 was used as the means (N) for mixing the composition containing the thermoplastic polymer supplied from the means (L) and the subcritical water supplied from the means (M). A tubular continuous reactor 7 and a tubular continuous reactor 8, which can flow a heat medium countercurrently through the external jacket, were used in series as the continuous reactor (O) for hydrolysis connected to the means (N).

[0268] As a composition containing a thermoplastic polymer as a raw material, polyethylene terephthalate (PET-A) was charged into a raw material hopper 1, and PET-A was melted and pressurized using an extruder 2. The temperature of PET-A was 281°C, the pressure was 20 MPa, and the supply rate was 13.0 g / min. Deionized water was stored in a water tank 3, and pressurized using a high-pressure pump 4 and heated using an electric heater 5 to obtain subcritical water. The temperature of the subcritical water was 281°C, the pressure was 20 MPa, and the supply rate was 39.0 g / min. The mass flow ratio (X:1) of the thermoplastic polymer component in the composition containing subcritical water and a thermoplastic polymer was 3:1. The composition containing a thermoplastic polymer that was heated, melted, and pressurized was merged with the flow of subcritical water and supplied to a static mixer 6 having 24 elements. The solution discharged from the static mixer 6 was supplied to a tubular continuous reactor 7 having an inner diameter of 2.3 cm and a length of 250 cm, and the solution discharged from the tubular continuous reactor 7 was supplied to a tubular continuous reactor 8 having an inner diameter of 2.3 cm and a length of 250 cm.

[0269] A continuous reactor upstream temperature monitoring device 12 for monitoring the temperature in the upstream part of the continuous reactor (O) was inserted at a position 5 cm from the inlet of the tubular continuous reactor 7, and a continuous reactor downstream temperature monitoring device 13 for monitoring the temperature in the downstream part of the continuous reactor (O) was inserted at a position 5 cm from the outlet of the tubular continuous reactor 8. Based on the signal from the continuous reactor upstream temperature monitoring device 12, the flow rate and temperature of the heat medium supplied to the jacket of the tubular continuous reactor 7 were adjusted by the continuous reactor temperature adjustment mechanism 15 of the tubular continuous reactor 7. Based on the signals from the continuous reactor upstream temperature monitoring device 12 and the continuous reactor downstream temperature monitoring device 13, the flow rate and temperature of the heat medium supplied to the jacket of the tubular continuous reactor 8 were adjusted by the continuous reactor temperature adjustment mechanism 16 of the tubular continuous reactor 8. The temperature of the continuous reactor upstream temperature monitoring device 12 was 280°C, and the temperature of the continuous reactor downstream temperature monitoring device 13 was 240°C.

[0270] The average residence time Z in the continuous reactor (O) was 30 minutes. The product of X and Y, and the product of X, Y, and Z are shown in Table 10.

[0271] The reaction solution discharged from the tubular continuous reactor 8 was heat exchanged with cooling water in the heat exchanger 9 and cooled to 40° C. Thereafter, the pressure of the reaction solution was released from 20 MPa to atmospheric pressure by the back pressure valve 10 and the reaction solution was stored in the reaction solution tank 11.

[0272] The reaction solution stored in the reaction solution tank 11 was cooled to room temperature, and the solid matter (terephthalic acid) was collected by suction filtration and separated from the solution (aqueous ethylene glycol solution). From the weight of the solid matter and the results of HPLC analysis, the molar yield of terephthalic acid was 98%. Meanwhile, from the weight of the solution and the results of GC analysis, the molar yield of ethylene glycol was 80%.

[0273] [Table 10]

[0274] [Example 39] The recycling monomer production apparatus was operated in the same manner as in Example 38 except for the setting of the temperature of the temperature monitoring device 13 downstream of the continuous reactor. The results are shown in Table 10.

[0275] [Example 40] The recycling monomer production apparatus was operated in the same manner as in Example 38 except for the setting of the temperature of the temperature monitoring device 13 downstream of the continuous reactor. The results are shown in Table 10.

[0276] [Example 41] The recycled monomer production apparatus shown in FIG. 2 was used. The apparatus shown in FIG. 2 is characterized by having one tubular continuous reactor 7 and one continuous reactor temperature control mechanism 15 compared to the apparatus shown in FIG. 1. A continuous reactor upstream temperature monitoring device 12 for monitoring the temperature in the upstream part of the continuous reactor (O) was inserted at a position 5 cm from the inlet of the tubular continuous reactor 7, and a continuous reactor downstream temperature monitoring device 13 for monitoring the temperature in the downstream part of the continuous reactor (O) was inserted at a position 5 cm from the outlet of the tubular continuous reactor 7. The continuous reactor temperature control mechanism 15 was set so that both the internal temperatures in the upstream and downstream parts of the tubular continuous reactor 7 in the apparatus shown in FIG. 2 were kept at 280° C., and the flow rate and temperature of the heat medium flowing through the tubular continuous reactor 8 were controlled. The other conditions were as shown in Table 10, and the recycled monomer production apparatus shown in FIG. 2 was operated, and the results were as shown in Table 10. By operating the reactor at a temperature of 280°C, the hydrolysis reaction proceeds quickly, making it possible to treat the reactor with a shorter residence time than in Example 38. However, it is presumed that the molar yield of terephthalic acid decreased because it is difficult to inhibit the repolymerization reaction of terephthalic acid, especially in the later stage of the reaction. The molar yield of ethylene glycol was comparable to that of the other Examples.

[0277] [Example 42] The recycled monomer production apparatus shown in FIG. 2 was used. In the apparatus shown in FIG. 2, the temperature of the upstream part of the tubular continuous reactor 7 was kept close to 280° C., and the temperature of the downstream part of the tubular continuous reactor was set to 240° C. by the continuous reactor temperature control mechanism 15. At this time, the flow rate of the heat medium was controlled to be reduced so that a temperature gradient was generated in the tubular continuous reactor 8. The other conditions were as shown in Table 10, and the recycled monomer production apparatus shown in FIG. 2 was operated, and the results were as shown in Table 10. It is presumed that the molar yield of terephthalic acid was reduced compared to Example 38 because the time for maintaining the maximum temperature was shortened due to the single temperature control mechanism.

[0278] [Example 43] The recycled monomer production apparatus was operated in the same manner as in Example 38, except that the composition containing the thermoplastic polymer was changed to PET-B, and the results are shown in Table 10. It was shown that recycled monomers can be produced in the same manner as in Example 38, even if the composition containing the target thermoplastic polymer is a polyethylene terephthalate resin waste. [Explanation of symbols]

[0279] 1 Raw material hopper 2. Extruder 3. Water tank 4. High pressure pump 5 Electric heater 6. Static Mixer 7. Continuous tubular reactor 8. Continuous tubular reactor 9 Heat exchanger 10 Backpressure valve 11 Reaction solution tank 12. Temperature monitoring device upstream of continuous reactor 13. Temperature monitoring device downstream of continuous reactor 14 Extruder / Electric heater temperature control device 15 Continuous reactor temperature control mechanism 16 Continuous reactor temperature control mechanism

Claims

1. A method for producing recycled monomers, comprising the step of contacting a composition containing a polymer with subcritical water, wherein the polymer is a thermoplastic polyester (A), and when the melting point of the thermoplastic polyester (A) measured by differential scanning calorimeter is Mp°C, the reaction temperature is X°C, the reaction time is Y minutes, and the mass ratio of water to thermoplastic polyester (A) is Z:1, X and the product X・Y・Z of X, Y, and Z simultaneously satisfy the following conditions (I) and (II). (I) Mp≦X≦290 (II) 2000≦X・Y・Z≦20000

2. A method for producing a recycled monomer according to claim 1, wherein the concentration of a diol derived from thermoplastic polyester (A) in the reaction mixture obtained by contacting a composition containing thermoplastic polyester (A) with subcritical water and hydrolyzing the thermoplastic polyester (A) is 4.9% by mass or more.

3. A method for producing a recycled monomer according to claim 1, wherein the concentration of a cyclic ether derived from the thermoplastic polyester (A) in the reaction mixture obtained by contacting a composition containing thermoplastic polyester (A) with subcritical water and hydrolyzing the thermoplastic polyester (A) is 3.0% by mass or more.

4. A method for producing recycled monomer according to claim 1, wherein the mass ratio Z of subcritical water to thermoplastic polyester (A) is less than 6.

5. A method for producing a recycled monomer according to claim 1, wherein the thermoplastic polyester (A) is mainly composed of at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof.

6. The method for producing a recycled monomer according to Claim 1, wherein an alkaline component is blended in an amount of 0.01 parts by weight or more and 50 parts by weight or less per 100 parts by weight of thermoplastic polyester (A).

7. The method for producing a recycled monomer according to claim 6, wherein the alkaline component is at least one selected from hydroxides, carbonates, and bicarbonates of alkali metals and / or alkaline earth metals.

8. A method for producing a recycled monomer according to claim 1, wherein the thermoplastic polyester (A) is waste containing at least polyester.

9. A method for producing a recycled monomer according to claim 1, wherein the recycled monomer is a dicarboxylic acid and / or a diol.

10. A method for producing a thermoplastic polyester using a dicarboxylic acid and / or diol obtained by the production method of claim 9 as a raw material.

11. A method for producing thermoplastic polyester products, comprising using thermoplastic polyester obtained by the manufacturing method described in claim 10 as a raw material to produce products containing thermoplastic polyester in the form of fibers, films, or molded articles.

12. A method for producing a product of a thermoplastic polyester composition, comprising using a composition containing a thermoplastic polyester obtained by the manufacturing method described in claim 10 as a raw material to produce a product of a thermoplastic polyester composition in the form of fibers, films, or molded articles.

13. A method for producing a recycled monomer, comprising the step of contacting a composition containing a polymer with subcritical water, wherein the polymer is a thermoplastic polyester (A), and 0.01 to 4.0 parts by weight of an alkali metal salt and / or alkaline earth metal salt are blended with 100 parts by weight of thermoplastic polyester (A).

14. A method for producing a recycled monomer according to claim 13, comprising blending 100 to 1,000 parts by weight of subcritical water with 100 parts by weight of thermoplastic polyester (A).

15. A method for producing recycled monomer according to claim 13, wherein the temperature of the step in contacting with subcritical water is 250 to 350°C.

16. A method for producing recycled monomer according to claim 13, wherein the pressure in the step of contacting with subcritical water is 3 to 30 MPa.

17. The method for producing a recycled monomer according to claim 13, wherein the alkali metal salt and / or alkaline earth metal salt is a metal hydroxide and / or metal carbonate.

18. The method for producing a recycled monomer according to claim 13, wherein the thermoplastic polyester (A) is at least one selected from polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and copolymers thereof.

19. A method for producing a recycled monomer according to claim 13, wherein the composition containing thermoplastic polyester (A) comprises at least one selected from antioxidants, heat resistant agents, weather resistant agents, mold release agents, and crystal nucleating agents.

20. A method for producing a recycled monomer according to claim 13, wherein the composition containing thermoplastic polyester (A) is waste.

21. A method for producing a recycled monomer according to claim 13, wherein the recycled monomer is a dicarboxylic acid and / or a diol.

22. A method for producing a thermoplastic polyester using a dicarboxylic acid and / or diol obtained by the manufacturing method described in claim 21 as a raw material.

23. A method for producing a composition containing a thermoplastic polyester, comprising blending at least one selected from an antioxidant, a weathering agent, a mold release agent, and a crystal nucleating agent with the thermoplastic polyester obtained by the manufacturing method described in claim 22.

24. A method for producing thermoplastic polyester products, comprising using thermoplastic polyester obtained by the manufacturing method described in claim 22 as a raw material to produce products containing thermoplastic polyester in the form of fibers, films, or molded articles.

25. A method for producing a product of a thermoplastic polyester composition, comprising using a composition containing a thermoplastic polyester obtained by the manufacturing method described in claim 23 as a raw material to produce a product of a thermoplastic polyester composition in the form of fibers, films, or molded articles.

26. The system comprises means (L) for heating and pressurizing and supplying a composition containing a polymer; means (M) for generating and supplying subcritical water; means (N) for mixing the composition containing the thermoplastic polymer supplied from means (L) with the subcritical water supplied from means (M); a continuous reactor (O) for hydrolyzing the polymer; an apparatus (P) for monitoring the internal temperature of the upstream and downstream sections of the continuous reactor (O); and a temperature control mechanism (Q) for heating and / or cooling the continuous reactor (O) based on the internal temperature monitored by the apparatus (P) to control the internal temperature of the continuous reactor (O). A manufacturing device for recycled monomers.

27. Multiple temperature control mechanisms (Q) are installed, Multiple temperature control mechanisms (Q) are operated based on the aforementioned device (P). The apparatus for producing recycled monomer according to claim 26.

28. The temperature control mechanism (Q) controls the internal temperature of the downstream part of the continuous reactor (O) to be 10°C or more lower than the internal temperature of the upstream part. The apparatus for producing recycled monomer according to claim 26 or 27.

29. The continuous reactor (O) is a tubular continuous reactor. The apparatus for producing recycled monomer according to claim 26 or 27.

30. The means (L) is an extruder. The apparatus for producing recycled monomer according to claim 26 or 27.

31. The means (N) is a static mixer. The apparatus for producing recycled monomer according to claim 26 or 27.

32. The composition containing the aforementioned polymer is waste from a resin molded product. The apparatus for producing recycled monomer according to claim 26 or 27.

33. The polymer is a thermoplastic polyamide or thermoplastic polyester. The apparatus for producing recycled monomer according to claim 26 or 27.

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