Method for decomposing polyester resin

Abstract

To provide a technique capable of inexpensively decomposing a polyester resin without using an expensive useful chemical substance as a material.SOLUTION: A method for decomposing a polyester resin brings a polyester resin into contact with a solid of an oxide or a hydroxide having a standard oxidation reduction potential in the water higher than a standard oxidation reduction potential of water in the water, and hydrolyzes the polyester resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for decomposing polyester resin. [Background technology]

[0002] Because plastics are easy to mold and can be mass-produced cheaply, they are used as materials for a wide variety of products. However, this also means that a large amount of plastic waste is generated, making the disposal of waste plastic an urgent issue. Traditionally, waste plastics have been incinerated or crushed and then landfilled. However, with the increasing volume of waste plastics, there is a shortage of facilities for incineration and crushing / grinding, and securing landfill space for the processed plastics is also becoming difficult. Therefore, instead of disposing of waste plastics, there is a growing interest in recycling them into useful materials for reuse.

[0003] One method of recycling plastics is chemical recycling. Chemical recycling is a method of reusing collected waste plastics by changing their molecular structure. Polyester resin, which is produced in large quantities among plastics, has a relatively well-established social system for separate collection, so technological development related to chemical recycling is progressing more rapidly than for other plastics.

[0004] One method for chemically regenerating polyester resins involves chemically depolymerizing the polyester resin to produce low-molecular-weight monomer components. For example, Non-Patent Literature 1 discloses hydrolysis, alcohol decomposition (methanol decomposition), amino decomposition, ammonia decomposition, and ethylene glycol decomposition as examples of methods for depolymerizing polyethylene terephthalate (PET), which is a type of polyester resin. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] U.S. Patent No. 4605762 [Non-patent literature]

[0006] [Non-Patent Document 1] Gopel Jeya, et al., "A short review on latest developments in catalytic depolymerization of Poly(ethylene terephathalate) wastes." J. of the Indian Chemical Society 99(2022)100291 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Hydrolysis is a method of recovering terephthalic acid (TPA) and ethylene glycol (EG) by hydrolyzing PET under alkaline or acidic conditions using water as a medium. Ge To achieve this, it is necessary to increase the alkaline or acidic conditions. However, under such conditions, while the recovery efficiency of TPA increases, EG is decomposed and cannot be recovered. Furthermore, increasing the acidic conditions presents the problem of corrosion of metal reactors, piping, and other equipment.

[0008] In the alcohol decomposition method, amino decomposition method, ethylene glycol decomposition method, and ammonia decomposition method, alcohol (methanol), organic amine, diol, and ammonia are used to depolymerize PET, respectively. However, since alcohol (methanol), organic amine, diol, and ammonia are all useful chemical substances, using useful chemical substances to regenerate PET goes against the purpose of recycling. Furthermore, since alcohol (methanol), organic amine, and diol are relatively expensive chemical substances, the monomer components obtained using such chemical substances are not competitive in terms of price.

[0009] The problem that this invention aims to solve is the useful and expensive chemical materialTo provide a technique capable of decomposing polyester resin at low cost without using it as a material.

Means for Solving the Problems

[0010] The method for decomposing a polyester resin according to the present invention made to solve the above problems is contacting the polyester resin with a solid of an oxide or hydroxide having a standard redox potential higher than that of water (H2O) in neutral reaction water to hydrolyze the polyester resin.

[0011] In the present invention, "neutral reaction water" is typically pure water, but may contain some impurities as long as the substance does not affect the depolymerization reaction of the polyester resin. Also, "neutral reaction water" does not necessarily have to be strictly neutral (pH = 7), and those with a pH of about 6 to 8 are also included in "neutral reaction water".

[0012] [[ID=十六]] [[ID=十七]] Examples of oxides or hydroxides having a standard redox potential higher than that of water (H2O) include lead oxide (PbO2), nickel oxide (NiO2, Ni3O4), and nickel hydroxide (Ni(OH)3). The reactions of water (H2O) with lead oxide (PbO2), nickel oxide (NiO2, Ni3O4), and nickel hydroxide (Ni(OH)3) in water, and their respective standard redox potentials (E 0 ) are as follows in (1) to (5).

[0013] (1) 2H2O (liquid) ⇔ 4H + + 4e - + О2 E 0 = 1.229V (2) PbO2 (solid) + 4H + + 2e - ⇔ Pb2 + + 2H2O E 0 = 1.468V (3) NiO2 (solid) + 4H + + 2e - ⇔ Ni2 + + 2H2O E 0 = 1.68V (4) Ni3O4 (solid) + 8H + + 2e - ⇔ 3Ni2 + + 4H2O E 0 = 1.997 V (5) Ni(OH)3 (solid) + 3H + + e - ⇔ Ni2+ + 3H2O E 0 = 2.08 V In the reaction formulas shown in (1) to (5) above, the bidirectional arrow symbol (⇔) represents equilibrium.

[0014] As can be seen from (1) to (5) above, the standard oxidation-reduction potentials (E 0 ) of lead oxide (PbO2), nickel oxides (NiO2, Ni3O4), and nickel hydroxide (Ni(OH)3) are higher than the standard oxidation-reduction potential of water (E 0 ). Therefore, on the surface of the solid of the oxide or hydroxide, water molecules come to maintain an equilibrium with the group consisting of protons (H + ), electrons (e - ), and oxygen (О2). Since this equilibrium is a phenomenon that occurs spontaneously without applying external energy, when the solids of lead oxide (PbO2), nickel oxides (NiO2, Ni3O4), and nickel hydroxide (Ni(OH)3) are placed in water, the surface of the solid (solid-liquid interface) becomes a strong acidic environment.

[0015] However, only the solid-liquid interface becomes a strong acidic environment, and the entire water (bulk) does not become an acidic environment. Therefore, in the decomposition method according to the present invention, by bringing a polyester resin into contact with the solid surface in the reaction water, the polyester resin is hydrolyzed.

[0016] The oxide or hydroxide used in the decomposition method of the present invention may be any one having a standard oxidation-reduction potential (E 0 ) higher than that of water. In addition to the above-described lead oxide (PbO2), nickel oxides (NiO2, Ni3O4), and nickel hydroxide (Ni(OH)3), for example, nickel oxyhydroxide NiO(OH) as an active material for nickel-metal hydride batteries may also be used.

[0017] The oxide or hydroxide solid used in the decomposition method of the present invention may be in any shape as long as its solid surface can be brought into contact with the polyester resin. However, since increasing the contact area between the solid surface and the polyester resin can increase the rate of polyester hydrolysis, it is preferable that the solid be in granular or powder form. Furthermore, it is preferable that the polyester resin to be treated be as small as possible. It is preferable to crush and pulverize polyester resin products such as PET bottles into small pieces (chips) and then hydrolyze them using the decomposition method of the present invention. When the polyester resin is in the form of small pieces, the oxide or hydroxide solid may be in a relatively large form other than granular or powder, such as a plate or lump. However, even in that case, if the solid is in granular or powder form, the contact area with the small pieces of polyester resin can be further increased. [Effects of the Invention]

[0018] The present invention provides a method for decomposing polyester resins, which focuses on the fact that solid oxides or hydroxides with a higher standard oxidation-reduction potential than water cause water to act as an acid at the interface with water. This mechanism is used to acid hydrolyze the polyester resin. In other words, in this invention, inexpensive and readily available neutral water is used for the hydrolysis of the polyester resin, and the solid oxide or hydroxide is used as a solid-liquid interface catalyst. Therefore, polyester resins can be depolymerized inexpensively to obtain low-molecular-weight monomers without using useful and expensive chemical substances as materials. [Brief explanation of the drawing]

[0019] [Figure 1] A schematic diagram illustrating the hydrolysis of PET in water using lead oxide (PbO2). [Figure 2] This equation represents the reaction between ethylene glycol and hydrogen at the interface between lead oxide and water. [Figure 3] Chromatogram of the components contained in the filtrate obtained in Experimental Example 1. [Figure 4]Chromatogram of the components contained in the filtrate obtained in Experimental Example 2. [Figure 5] Chromatogram of the components contained in the filtrate obtained in Experimental Example 3. [Figure 6] XRD spectrum of substances adhering to the surface of lead oxide remaining on the filter. [Figure 7] XRD spectrum of commercially available disodium terephthalate. [Figure 8] XRD spectrum of lead oxide powder remaining on the filter. [Figure 9] XRD spectrum of unused lead oxide powder. [Figure 10] SEM image of unused lead oxide. [Figure 11] Chromatogram of the components contained in the filtrate obtained in Experimental Example 4 when the reaction time was 1 hour. [Figure 12] Chromatogram of the components contained in the filtrate obtained in Experimental Example 4 when the reaction time was 3 hours. [Figure 13] Chromatogram of the components contained in the filtrate obtained in Experimental Example 4 when the reaction time was 6 hours. [Figure 14] Chromatogram of the components contained in the filtrate obtained in the comparative example. [Figure 15] XRD spectrum of substances adhering to the surface of lead oxide remaining on the filter. [Figure 16] XRD spectrum of commercially available disodium terephthalate. [Modes for carrying out the invention]

[0020] The following describes in detail the method for hydrolyzing polyester resin according to the present invention. Figure 1 is a schematic diagram illustrating the hydrolysis method for polyester resin according to the present invention. In Figure 1, granular lead oxide (PbO2) is used as the solid oxide, and small pieces (PET chips) obtained by crushing and pulverizing products such as PET bottles are used as the polyester resin. The granular lead oxide and PET chips are placed in a reaction vessel (not shown) containing water and are in contact with each other in the water.

[0021] When granular lead oxide and PET chips are in the state described above, the difference between the standard oxidation-reduction potential of lead oxide and the standard oxidation-reduction potential of water causes water to act as an acid at the interface between the solid lead oxide and water (solid-liquid interface), and the catalytic action of lead oxide spontaneously occurs. As a result, the PET in contact with the solid surface of lead oxide is hydrolyzed (depolymerized) to produce terephthalic acid and ethylene glycol. The terephthalic acid can be recovered in an insoluble state attached to the solid surface of lead oxide (PbO2), and the ethylene glycol can be recovered as an aqueous solution.

[0022] Furthermore, heating the water in the reaction vessel increases its temperature, which softens the PET chips in the water and increases the contact area with the solid lead oxide. As a result, the catalytic action of lead oxide at the solid-liquid interface is more strongly exerted, increasing the hydrolysis rate of PET.

[0023] Furthermore, if the reaction in the reaction vessel is carried out in a closed environment, when the water temperature exceeds 100°C, the vapor pressure inside the reaction vessel rises, creating a pressurized state. This disrupts the equilibrium state in equation (1) above, and the equilibrium shifts in the direction of decreasing particle numbers, as shown in equation (1') below. (1')2H2O(PbO2 surface) ⇔ 4H + +4e - +O2 ⇔ 2H2 + O2

[0024] As a result, hydrogen is generated on the solid surface of lead oxide, and at the interface between lead oxide and water, the hydrogen reacts with ethylene glycol obtained by the depolymerization of PET to produce methanol. This reaction equation is shown in Figure 2.

[0025] In other words, when the polyester resin decomposition method according to the present invention is carried out using a closed-environment reaction vessel, hydrogen can be generated within the reaction vessel without adding hydrogen from the outside, and the organic compound obtained by the depolymerization of the polyester resin can be hydrogenated. [Examples]

[0026] The following describes an example (experimental example) in which the method of the present invention is applied to a process that produces sodium terephthalate and ethylene glycol or methanol, using lead oxide (PbO2) as the solid oxide and crushed PET bottle material as the polyester resin.

[0027] Lead oxide (PbO2) is a common substance used as an electrode active material in lead-acid batteries and is widely distributed throughout the world. While lead oxide itself is not considered a safe substance, it has been proven that there are no safety issues as long as it is used in a closed reaction vessel. Therefore, in the experimental example described below, the reaction vessel was treated as being in a closed environment.

[0028] [Experimental Example 1] 1.0097 g of crushed recycled used PET bottle material (average 5 mm square, provided by Otsuka Pharmaceutical Co., Ltd., washed) was placed in a 100 mL reaction vessel (Flon Chemical NR0218). 6.5113 g of powdered lead(IV) oxide (PbO2, Kanto Chemical Co., Ltd., purity 97.0%) was added, followed by 50 mL of ultrapure water (18.2 MΩ·cm, ELGA LabWater). A 25 mm long rugby ball-shaped stirring bar (Teflon coated) was then placed in the reaction solution, and the reaction vessel was sealed with a special jig.

[0029] The above reaction vessel was heated to 190°C using a temperature control device, and then the reaction was carried out for 1 hour while maintaining the temperature at 190°C (±5°C) and rotating a stirring bar at 20 rpm.

[0030] After allowing the reaction vessel to cool naturally to room temperature, the filtrate was filtered by suction using a 0.025 μm pore size filter (47 mm in diameter, Merck Millipore), and the components of the filtrate were measured. The pH of the filtrate was 6-7. In addition, a large amount of crushed PET bottle material (hereinafter also referred to as PET crushed material) remained on the filter along with lead oxide powder.

[0031] A gas chromatograph-mass spectrometer (GCMS) (GCMS-QP2010 Ultra, Shimadzu Corporation) was used to measure the components contained in the filtrate. The measurement conditions for the gas chromatograph (GC) and mass spectrometer (MS) sections of the GCMS were set as follows.

[0032] (1)GC department Carrier gas: He. Linear velocity control was used to achieve a linear velocity of 40 cm / sec and a split ratio of 50. Column: DB-WAX UI (30m, diameter 0.250mm, film thickness 0.25μm, Agilent Technologies, Inc.) Injection temperature: 220℃ Column temperature: 50-200°C (10°C / min)

[0033] (2)MS department Interface temperature: 220℃ Ion source temperature: 200℃ Measurement mode: Scan mode (mass-to-charge ratio m / z 25-300)

[0034] Figure 3 is a chromatogram showing the GC-MS measurement results of the filtrate. As can be seen from this chromatogram, the dominant component in the filtrate was ethylene glycol (82%), with only small amounts of diethylene glycol (9%) and methanol (9%). Formic acid was also observed in small quantities.

[0035] [Experimental Example 2] The experiment was conducted using the same procedure as in Experimental Example 1, except that the amount of crushed used PET bottle material added was changed to 1.0160g, the amount of powdered lead(IV) oxide added was changed to 6.5110g, and the reaction time was changed to 3 hours. The same materials and containers used in the experiment were also used as in Experimental Example 1.

[0036] After the reaction, the reaction vessel was allowed to cool naturally to room temperature. Then, suction filtration was performed using a 0.025 μm pore size filter (47 mm diameter, Millipore), and the components of the filtrate were measured using GC-MS. The pH of the filtrate was 6-7. A small amount of PET pulverized material remained on the filter along with lead oxide powder.

[0037] The same apparatus and measurement conditions as in Experimental Example 1 were used for GC-MS. The obtained chromatogram is shown in Figure 4. As can be seen from this chromatogram, ethylene glycol (57%) was the dominant component in the filtrate. Compared to the results of Example 1, the proportion of ethylene glycol decreased, while the proportions of diethylene glycol (14%) and methanol (29%) increased. In particular, the proportion of methanol was approximately three times that of Example 1 (9%). Acetic acid and formic acid were also observed.

[0038] [Experimental Example 3] The experiment was conducted using the same procedure as in Experimental Example 1, except that the amount of crushed used PET bottle material added was changed to 1.0155 grams, the amount of powdered lead(IV) oxide added was changed to 6.5139 g, and the reaction time was changed to 6 hours. The same materials and containers used in the experiment were also used as in Experimental Example 1.

[0039] After the reaction, the reaction vessel was allowed to cool naturally to room temperature. Then, suction filtration was performed using a 0.025 μm pore size filter (47 mm diameter, Millipore), and the components of the filtrate were measured using GC-MS. The pH of the filtrate was 6-7. Furthermore, no lead oxide powder or PET pulverized material was observed on the filter. From this, it was found that when the reaction temperature is 190°C, the depolymerization of PET is completed within 6 hours.

[0040] GC-MS was performed using the same apparatus and measurement conditions as in Experimental Example 1. The obtained chromatogram is shown in Figure 5. From this chromatogram, it was found that the main component of the filtrate was methanol (88%), and ethylene glycol was below the detection limit. From this, it was considered that almost all of the ethylene glycol was converted to methanol. On the other hand, diethylene glycol (12%) remained without being converted to ethanol.

[0041] To confirm that terephthalic acid was adhering to the surface of the lead oxide powder on the filter, the lead oxide powder was placed back into the reaction vessel (Flon Chemical NR0218), to which 50 mL of ultrapure water (18.2 MΩ·cm, ELGA LabWater) and 0.44 grams of sodium hydroxide were added. A 25 mm long rugby ball-shaped stirring bar (Teflon coated) was then placed in the reaction vessel, and after sealing the reaction vessel with a special jig, the reaction was carried out at 190°C (±5°C) for 4 hours.

[0042] After allowing the reaction vessel to cool naturally to room temperature, suction filtration was performed using a 0.025 μm pore size filter (47 mm in diameter, Merck Millipore). Lead oxide powder remained on the filter. The filtrate was then placed in a 90°C drying oven and the water was completely removed over 8 hours. As a result, 0.95 grams of a slightly creamy white powder was obtained. The XRD spectrum obtained from the X-ray diffraction data of this powder is shown in Figure 6. Figure 7 shows the XRD spectrum of disodium terephthalate (Tokyo Chemical Industries, Ltd.), a commercially available experimental reagent.

[0043] Figures 6 and 7 show that the substance attached to the lead oxide powder was disodium terephthalate, and that the yield of disodium terephthalate derived from used PET was 85%.

[0044] Furthermore, to confirm that the lead oxide powder remaining on the filter was the same as the original lead oxide (PbO2), X-ray diffraction measurements were performed on this powder and the unused lead oxide powder. The XRD spectra of the lead oxide remaining on the filter and the unused lead oxide are shown in Figures 8 and 9.

[0045] A comparison of Figures 8 and 9 shows that lead oxide (PbO2) remained unchanged before and after the depolymerization reaction of PET, indicating that it acted as a solid-liquid interface catalyst. Figure 10 shows an electron microscope (SEM) image of unused lead oxide powder. From Figure 10, it can be seen that the lead oxide powder used in this experiment had a maximum length of approximately 0.1 to 3.0 μm.

[0046] [Experimental Example 4] The experiment was conducted using the same procedure as in Experimental Examples 1-3, except that the reaction temperature for PET pulverized material and water in the reaction vessel was changed to 200°C (±5°C) using lead oxide as a solid-liquid interface catalyst. In this experiment, when the reaction time was 1 hour, the amount of used PET bottles added was 1.0037 g and the amount of powdered lead oxide added was 6.5046 g. When the reaction time was 3 hours, the amount of used PET bottles added was 1.0027 g and the amount of powdered lead oxide added was 6.5103 g. When the reaction time was 6 hours, the amount of used PET bottles added was 1.0026 g and the amount of powdered lead oxide added was 6.5123 g. In all cases, the amount of ultrapure water added was 50 mL. The chromatograms of the components contained in the obtained filtrate, measured by GCMS, are shown in Figures 11-13. Figures 11, 12, and 13 show the results when the reaction time between PET pulverized material and water was 1 hour, 3 hours, and 6 hours, respectively.

[0047] As can be seen from comparing Figures 11-13 with Figures 3-5, the same results were obtained when the reaction temperature was set to 200°C as when it was set to 190°C.

[0048] [Comparative Example] As a comparative example, the same experiment as in Experimental Examples 1-3 was conducted without using powdered lead oxide. Specifically, 1.0134 grams of crushed recycled used PET bottle material (average 5 mm square, provided by Otsuka Pharmaceutical Co., Ltd., washed) was placed in a 100 mL reaction vessel (Flon Chemical NR0218). 50 mL of ultrapure water (18.2 MΩ·cm, ELGA LabWater) was added. A 25 mm long rugby ball-shaped stirring bar (Teflon coated) was then placed in the reaction vessel, and the vessel was sealed with a special jig.

[0049] The reaction vessel was heated to 200°C using a temperature control device, and then the reaction was carried out for 72 hours while maintaining the temperature at 200°C (±5°C) and rotating a stirring bar at 20 rpm.

[0050] After allowing the reaction vessel to cool naturally to room temperature, the filtrate was filtered by suction using a 0.025 μm pore filter (47 mm in diameter, Merck Millipore), and the components of the filtrate were measured. The pH of the filtrate was 4-5. A white powder remained on the filter.

[0051] To measure the components contained in the filtrate, a gas chromatograph-mass spectrometer (GCMS-QP2010 Ultra, Shimadzu Corporation) similar to that used in the experimental example was employed. The GCMS measurement conditions were the same as those in Experimental Example 1, but the column heating rate was set to 5°C / min, slower than in Experimental Example 1, in order to carefully investigate whether or not the conversion from ethylene glycol to methanol was occurring.

[0052] Figure 14 is a chromatogram showing the measurement results of the filtrate. From Figure 14, it was found that ethylene glycol can be obtained from PET by extending the reaction time, even without lead oxide (PbO2) powder. On the other hand, it was confirmed that without lead oxide powder, even with an extended reaction time, the ethylene glycol obtained from PET is hardly converted to methanol.

[0053] Furthermore, to confirm that the white powder remaining on the filter was terephthalic acid, X-ray diffraction measurements were performed on the white powder. The resulting XRD spectrum is shown in Figure 15, and the XRD spectrum of the standard substance is shown in Figure 16.

[0054] As can be seen from Figures 15 and 16, when PET was depolymerized with water alone, terephthalic acid could be recovered, but very little methanol was obtained. This result was consistent with the result in Figure 14.

[0055] Patent Document 1 reports that by using a temperature of 200°C to 300°C, PET can be hydrolyzed with water as a medium to obtain terephthalic acid and ethylene glycol. However, it is said that the temperature conditions when utilizing thermal energy (waste heat energy) discharged from chemical plants, food factories, steel mills, cement factories, etc. are at most 200°C, and at temperature conditions of 200°C to 300°C, it is not possible to cope with the situation by using only waste heat energy, and an additional heat source is required. In contrast, as shown in Experimental Examples 1 to 4, the polyester resin decomposition method according to the present invention can sufficiently hydrolyze PET to obtain terephthalic acid and ethylene glycol even at temperature conditions of 190°C to 200°C, and moreover, by extending the reaction time, it is possible to convert ethylene glycol into methanol. In other words, the polyester resin decomposition method of the present invention can utilize waste heat energy from chemical plants, food factories, etc. without adding an additional heat source, and can therefore be said to be a method that can contribute to reducing carbon dioxide emissions.

[0056] [Pattern] It will be obvious to those skilled in the art that the exemplary embodiments described above are specific examples of the following embodiments.

[0057] (Section 1) A method for decomposing polyester resin according to one aspect of the present invention is: This method involves bringing a polyester resin into contact with a solid oxide or hydroxide whose standard oxidation-reduction potential in water is higher than that of water, in water, thereby hydrolyzing the polyester resin.

[0058] According to the method for decomposing polyester resin described in paragraph 1, polyester resin can be depolymerized inexpensively to obtain low-molecular-weight monomers without using useful and expensive chemical substances as materials.

[0059] (Paragraph 2) The method for decomposing polyester resin according to Paragraph 2 is the method for decomposing polyester resin according to Paragraph 1, wherein the solid is in the form of granules, powder, or solid particles.

[0060] According to the method for decomposing polyester resin described in paragraph 2, the contact area between the solid and the polyester resin is increased, thereby increasing the rate of hydrolysis of the polyester resin.

[0061] (Article 3) The method for decomposing polyester resin according to Article 3 is the method for decomposing polyester resin according to Article 1 or Article 2, wherein the solid is one or more selected from the group consisting of lead dioxide, nickel oxide, nickel hydroxide, and nickel oxyhydroxide.

[0062] (Article 4) The method for decomposing polyester resin relating to Article 4 is the method for decomposing polyester resin relating to any of Articles 1 to 3, wherein the polyester resin is polyethylene terephthalate (PET).

[0063] (Section 5) A method for producing methanol according to another aspect of the present invention is: This method involves contacting a polyester resin with a solid oxide or hydroxide whose standard oxidation-reduction potential in water is higher than that of water, in water, and hydrolyzing the polyester resin to obtain ethanol.

[0064] In the methanol production method of paragraph 5, the solid may be in granular, powdery, or granular form, and may be one or more selected from the group consisting of lead dioxide, nickel oxide, nickel hydroxide, and nickel oxyhydroxide. Furthermore, it is preferable that the polyester resin is polyethylene terephthalate (PET).

Claims

1. A method for decomposing a polyester resin, comprising contacting the polyester resin with a solid oxide or hydroxide having a standard oxidation-reduction potential higher than that of water in neutral reaction water to hydrolyze the polyester resin, A method for decomposing polyester resin, wherein the solid is one or more selected from the group consisting of lead dioxide, nickel oxide, nickel hydroxide, and nickel oxyhydroxide.

2. The method for decomposing polyester resin according to claim 1, wherein the solid is in the form of granules, powder, or granular material.

3. The method for decomposing a polyester resin according to claim 1 or 2, wherein the polyester resin is polyethylene terephthalate (PET).

4. A method for producing methanol, comprising contacting a polyester resin with a solid oxide or hydroxide having a standard oxidation-reduction potential higher than that of water in neutral reaction water, and hydrolyzing the polyester resin to obtain methanol.

Images