Technological method for preparing glycollic acid by utilizing PET (Polyethylene Terephthalate) waste through one-pot method

Abstract

The invention discloses a process method for preparing glycollic acid by utilizing PET (Polyethylene Terephthalate) waste through a one-pot method. The technological method comprises the following steps: adding alkali liquor, PET waste and a monatomic catalyst into a high-pressure reaction kettle, oxygenating to 1.2-1.5 MPa, heating to a target temperature, reacting, and separating and purifying after the reaction is finished to obtain glycollic acid, wherein the monatomic catalyst is selected from Pd1 / TiO2. According to the method, high-yield and high-selectivity glycollic acid is successfully prepared by using Pd1 / TiO2 as a catalyst and adopting a one-pot method, and the method for catalyzing by using the monatomic catalyst Pd1 / TiO2 has the advantages that the adsorption mode of EG can be accurately limited, a side reaction path caused by multi-point adsorption is avoided, the selective generation of * CHO-CHO * intermediates is ensured, the product selectivity is further improved, and meanwhile, the method is suitable for industrial production. The strong metal-carrier interaction between the TiO2 carrier and Pd monatomic regulates and controls the electronic structure of Pd, weakens the adsorption strength of carbonyl-containing intermediates, relieves catalyst poisoning, accelerates glycollic acid desorption, and further improves the reaction efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thermal catalytic synthesis. More particularly, it relates to a process for the one-pot preparation of glycolic acid from PET waste. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a dominant thermoplastic polyester with a global annual production of over 700 million tons, which is widely used in food packaging and textile industries. Despite its wide application, more than 80% of PET is incinerated or accumulated in natural ecosystems after consumption without recycling, which causes serious environmental pollution and consumption of carbon resources. Current PET recycling mainly relies on thermal melting mechanical processing reorganization. However, this method is often affected by additives and pollutants, and the recycled materials face problems such as quality decline and functional weakening. For complex PET-based products, including dyed textiles, polymer mixtures and multi-layer packaging, mechanical recycling is economically and technically infeasible due to their complex ingredient combinations. In contrast, chemical recycling strategies, such as hydrolysis, alcoholysis, hydrogenation, pyrolysis, etc., can effectively decompose PET into its constituent monomers, thereby realizing the regeneration of the original equivalent polymer. Among them, alkaline hydrolysis is a very promising approach, which can completely decompose PET into terephthalic acid (TPA) and ethylene glycol (EG) monomers. However, its industrial application faces some key challenges: (1) the energy-intensive pretreatment and product separation processes increase operating costs; (2) the market price of EG (about 5 yuan / kg) is too low compared to TPA (about 8 yuan / kg), resulting in economic imbalance in monomer valorization; (3) under mild conditions, the rate of decomposition reaction is not ideal, and the temperature needs to be raised or the reaction time needs to be prolonged, and these interrelated limitations together limit the efficiency and economic competitiveness of the process.

[0003] Ethylene glycol (EG), a hydrolysis product of polyethylene terephthalate (PET), is widely studied as a potential upgrade strategy by converting it into glycolic acid (GA, 20 $ / kg) through thermal, photocatalytic and electrocatalytic methods. As a chemical intermediate, GA has a wide range of industrial applications, especially as a monomer for the synthesis of biodegradable polyglycolic acid (PGA) plastics. Although photocatalytic / electrocatalytic methods can achieve a GA yield of up to 90%, PET needs to be first pre-depolymerized in strong base for a long time (more than about 10 hours) and the corresponding EG solution needs to be separated before the subsequent photocatalytic / electrocatalytic process. In contrast, thermal catalytic methods can provide higher GA yields without pre-depolymerization. However, thermal catalysis still has two problems: poor selectivity for GA and easy deactivation of the catalyst, which is due to two basic reaction characteristics: (1) there are parallel competitive pathways in the oxidation of ethylene glycol, including selective single-point adsorption (selective dehydrogenation of the terminal CH2OH group to form a *CHO-CH2OH intermediate) and non-selective multi-point adsorption (simultaneous dehydrogenation of both CH2OH groups to form a *CHO-CHO* intermediate); (2) strong adsorption of the carbonyl-containing intermediate (*CO-CH2OH) on the surface of noble metals, leading to irreversible poisoning of the catalyst. Therefore, developing a more efficient and selective thermal catalytic PET-to-glycolic acid system is crucial for realizing scalable PET value utilization. SUMMARY

[0004] To solve the problems in the prior art, the purpose of the present application is to provide a process for preparing glycolic acid from PET waste by one-pot method. The process uses a single-atom catalyst Pd1 / TiO2 to efficiently convert PET waste into TPA and GA by one-pot method. The entire process is green, environmentally friendly, simple to operate, short in time required and low in energy consumption.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The present application provides a process for preparing glycolic acid from PET waste by one-pot method, comprising the following steps:

[0007] The alkali solution, PET waste and single-atom catalyst are added to a high-pressure reaction kettle, oxygen is charged to 1.2-1.5 MPa, heated to the target temperature, and reacted. After the reaction is completed, glycolic acid is obtained after separation and purification.

[0008] The single-atom catalyst is selected from Pd1 / TiO2.

[0009] It should be noted that the raw material PET waste used in the present application is derived from industrial waste or post-consumer recycled material from different sources. In addition, Pd1 represents a single-atom Pd.

[0010] Furthermore, the mass ratio of the PET waste to the single-atom catalyst is 1:3% to 1:10%; for example, the mass ratio of the PET waste to the single-atom catalyst can be 1:3%, 1:4%, 1:5%, 1:6%, 1:7%, 1:8%, 1:9%, 1:10%, etc.

[0011] Furthermore, the single-atom catalyst is prepared according to the following steps:

[0012] TiO2 nanosheets were dispersed in an aqueous solution, and a palladium salt solution was added while stirring. After irradiation with a xenon lamp, the mixture was centrifuged, washed with water, and vacuum dried to obtain the final product.

[0013] TiO2 nanosheets can be obtained by methods commonly used in the art, such as the solvothermal method. The following is an exemplary preparation process for TiO2 nanosheets:

[0014] TiCl4 was added dropwise to ethylene glycol, with the volume of ethylene glycol being approximately 20–30 times that of TiCl4, and the mixture was stirred continuously until no more gas was emitted. Next, an equal volume of water to TiCl4 was added to the mixture, and the mixture was ultrasonically dispersed to obtain a clear solution. The clear solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene (PTFE) and heated at 140–160 °C for 3–5 hours. After cooling, the white product was collected and further washed with water and ethanol. The product was then dried in a vacuum oven to obtain bronze-phase TiO2 ultrathin nanosheets (TiO2).

[0015] Furthermore, TiO2 nanosheets will wrinkle and shrink into nanoflower-like shapes, with diameters ranging from 10 to 100 nanometers.

[0016] Furthermore, the xenon lamp irradiation time is 20–40 minutes.

[0017] Furthermore, the palladium salt solution is selected from one or more salt solutions containing chloropalladium acid, sodium chloropalladium, potassium chloropalladium, palladium nitrate, and palladium acetate, and the Pd content in the palladium salt solution is 3 to 20 mg / mL; for example, the Pd content in the palladium salt solution can be 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL, 20 mg / mL, etc.

[0018] Furthermore, the mass percentage of Pd1 in the single-atom catalyst is 0.3% to 2.0%; exemplaryly, its mass percentage can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0019] Furthermore, the reaction temperature is 130–150°C, and the reaction time is 2–3 hours.

[0020] Furthermore, the alkaline solution is selected from potassium hydroxide solution and / or sodium hydroxide solution, with a concentration of 1 to 5 mol / L.

[0021] Furthermore, the mass-to-volume ratio of PET waste to alkaline solution is 1:5 to 1:20.

[0022] Furthermore, the separation and purification includes the following steps:

[0023] The reaction solution obtained after the reaction is filtered, and the pH of the filtrate is adjusted to 4-5 until no new white flocculent precipitate is formed. After filtration, the solid is terephthalic acid. The pigment impurities in the filtrate are adsorbed with activated carbon. The filtrate is concentrated to dryness under reduced pressure to obtain solid crystals, the main components of which are neutral salt and glycolic acid. The solid is redispersed with acetone, which can extract the glycolic acid in the solid. After filtration, a filtrate rich in glycolic acid is obtained. After evaporation, glycolic acid is obtained.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention uses the single-atom catalyst Pd 1 / Using TiO2 as a catalyst, a one-pot process successfully converted PET waste into high-value-added glycolic acid. The entire process is fast, requiring only 2-3 hours of reaction time, and yields glycolic acid with high selectivity (over 85%). Compared to the two-step "hydrolysis-oxidation" method required by photo / electrocatalysis, this process is simpler, eliminating the need for lengthy strong-base pre-depolymerization and reducing the required time. Compared to traditional precious metal thermocatalysis methods, the use of a single-atom catalyst restricts the single adsorption configuration of ethylene glycol / glycolic acid, which helps suppress the formation of *CHO-CHO*, reduces byproducts from polyhydroxy oxidation, and further improves selectivity for obtaining the single glycolic acid product. Furthermore, the process for obtaining glycolic acid is more environmentally friendly, producing no harmful substances and consuming less energy than traditional processes. Attached Figure Description

[0026] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0027] Figure 1 The XRD pattern of the single-atom catalyst Pd1 / TiO2 prepared in Example 1 of this invention is shown.

[0028] Figure 2 The image shows a TEM image of the single-atom catalyst Pd1 / TiO2 prepared in Example 1 of the present invention.

[0029] Figure 3 The image shows a HADDF-STEM image of the single-atom catalyst Pd1 / TiO2 prepared in Example 1 of the present invention.

[0030] Figure 4 The elemental mapping diagram of the single-atom catalyst Pd1 / TiO2 prepared in Example 1 of the present invention is shown.

[0031] Figure 5 The carbon NMR spectrum of the filtrate after reaction at 140°C for 2.5 h in Example 1 of this invention is shown.

[0032] Figure 6 The changes in the main components of the reaction solution during the one-pot conversion of PET at 140℃ for 0-3.5h are shown.

[0033] Figure 7 Pd1 / TiO2 and Pd are shown NP / FTIR spectrum of ethylene glycol and glycolic acid after adsorption by TiO2 Figure 7 In the diagram, 'a' represents the adsorption of ethylene glycol. Figure 7 In the diagram, b represents the adsorption of glycolic acid.

[0034] Figure 8 Pd1 / TiO2 and Pd are shown NP CO-stripping test graph of / TiO2. Detailed Implementation

[0035] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0036] In addition, unless otherwise specified, all raw materials used in this invention can be obtained commercially available. Any range described in this invention includes the end value and any value between the end values, as well as any subrange formed by the end value or any value between the end values.

[0037] Example 1

[0038] 1. Preparation of single-atom catalyst Pd1 / TiO2

[0039] 1 mL of TiCl4 was added dropwise to 30 mL of ethylene glycol, stirring continuously until no more gas was emitted. Next, 1 mL of deionized water was added to the mixture and dispersed under sonication until a clear yellow solution was formed. The homogeneous solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and heated at 150 °C for 4 h using a solvothermal method. After cooling, the white product was collected and further washed with water and ethanol. It was then dried in a vacuum oven to obtain bronze-phase titanium dioxide ultrathin nanosheets (TiO2).

[0040] 300 mg TiO2 was dispersed in 100 mL of water and stirred continuously. Then, 2 mL of palladium chloride solution (H2PdCl4, Pd content: 3 mg / mL) was added to the solution, and the mixture was immediately irradiated with a xenon lamp for 20 min. After treatment, the sample was centrifuged and rinsed twice with deionized water, and finally dried overnight in a vacuum oven to obtain the single-atom catalyst Pd1 / TiO2.

[0041] Figure 1 The XRD pattern of the single-atom catalyst Pd1 / TiO2 shows that the present invention successfully synthesized bronze phase titanium dioxide (TiO2) without the formation of Pd nanoparticles. Figure 2 The image shows a TEM image of the single-atom catalyst Pd1 / TiO2, which demonstrates the morphology of the ultrathin nanosheets of TiO2 and indicates that no Pd nanoparticles were formed. Figure 3 The image shows the HADDF-STEM image of the single-atom catalyst Pd1 / TiO2, revealing that single-atom Pd is dispersed on the TiO2 surface. Figure 4 The elemental mapping diagram of the single-atom catalyst Pd1 / TiO2 shows the uniform distribution of Pd, with a mass percentage of approximately 0.5%.

[0042] 2. One-pot conversion of PET

[0043] A 1 mol / L alkaline solution was prepared by dissolving 2.4 g of sodium hydroxide in water. Then, 3 g of PET particles and 300 mg of Pd1 / TiO2 were added to the alkaline solution, and the mixture was stirred evenly within a polytetrafluoroethylene (PTFE) liner. The liner was then placed in a high-pressure reactor, oxygen was introduced at 1.2 MPa, and the reactor was heated to 140 °C for 2.5 h. After the reaction, the catalyst was filtered to separate the catalyst; the filtrate was a solution of sodium terephthalate and sodium glycolate.

[0044] Figure 5 The nuclear magnetic resonance carbon spectrum of the filtrate shows that the products in the solution after the reaction are only glycolic acid and terephthalic acid. Figure 6To monitor the changes in the main components of the reaction solution from 0 to 3.5 h, it was found that PET could complete depolymerization within 1.5 h, and the generated ethylene glycol was gradually converted into glycolic acid within 2.5 h, reaching a yield of 92.2% and a glycolic acid selectivity of 95.1%.

[0045] 3. Product purification.

[0046] Dilute sulfuric acid (2 mol / L) was gradually added dropwise to the filtered reaction solution until the solution pH ≈ 5 and no new white flocculent precipitate formed. The solution was filtered to separate the precipitate, which was then washed three times with water and dried to obtain terephthalic acid with a yield of 97.6%. Pigment impurities in the filtrate were adsorbed with activated carbon, and the filtrate was evaporated to dryness to obtain solid crystals, the main components of which were sodium sulfate and glycolic acid. Glycolic acid was extracted from the crystals with acetone, and after evaporation, a solid glycolic acid powder was obtained with a yield of 84.2%.

[0047] Example 2

[0048] The catalyst preparation and one-pot conversion process for PET are the same as in Example 1, except that the reaction temperature in the one-pot conversion of PET is adjusted to 120°C.

[0049] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 95.4%, glycolic acid in a yield of 55.5%, and glycolic acid selectivity was 97.6%.

[0050] Example 3

[0051] The catalyst preparation and one-pot conversion process for PET are the same as in Example 1, except that the reaction temperature in the one-pot conversion of PET is adjusted to 130°C.

[0052] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 97.9%, glycolic acid in a yield of 80.0%, and the selectivity of glycolic acid was 96.9%.

[0053] Example 4

[0054] The catalyst preparation and one-pot conversion process for PET are the same as in Example 1, except that the reaction temperature in the one-pot conversion of PET is adjusted to 150°C.

[0055] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 98.3%, glycolic acid in a yield of 87.56%, and the selectivity for glycolic acid was 88.41%.

[0056] Example 5

[0057] 1. Preparation of single-atom catalyst Pd1 / TiO2

[0058] The preparation method is the same as in Example 1.

[0059] 2. One-pot conversion of PET

[0060] 2.4 g of sodium hydroxide was dissolved in water to prepare an alkaline solution with a concentration of 1 mol / L. Then, 300 mg of Pd1 / TiO2 and 3 g of waste PET plastic products (such as non-woven fabrics, plastic bottles, trays, textiles, etc.) were added to the solution and mixed thoroughly within a polytetrafluoroethylene (PTFE) liner. The liner was then placed in a high-pressure reactor, oxygen was introduced at 1.2 MPa, and the mixture was heated to 140 °C for 2.5 h. After the reaction, the catalyst was filtered to separate the catalyst; the filtrate was a solution of sodium terephthalate and sodium glycolate.

[0061] 3. Product purification

[0062] Activated carbon was added to the filtered reaction solution and allowed to stand for several hours to adsorb impurities such as pigments, removing them from the solution. After filtering and separating the activated carbon, dilute sulfuric acid (2 mol / L) was gradually added dropwise to the solution until the pH of the solution was approximately 5 and no new white flocculent precipitate formed. The precipitate was filtered, separated, washed three times with water, and dried to obtain terephthalic acid. The pigment impurities in the filtrate were adsorbed with activated carbon, and the filtrate was evaporated to dryness to obtain solid crystals, the main components of which were sodium sulfate and glycolic acid. The glycolic acid in the crystals was extracted and separated with acetone, and after evaporation, a solid glycolic acid powder was obtained.

[0063] Table 1 shows that various PET plastic processed products can be used as raw materials to separate terephthalic acid and glycolic acid, with terephthalic acid yield >90% and glycolic acid yield >75%. This indicates that the process method of this invention has high yields for the production of terephthalic acid and glycolic acid from PET products of different sources.

[0064] Table 1

[0065] Waste PET articles Terephthalic acid yield Glycolic acid yield Nonwoven fabric 83.8％ 97.4％ Clear plastic bottle 84.9％ 97.8％ Colored plastic bottle 78.5％ 94.9％ Clear tray 83.7％ 97.4％ Black tray 77.5％ 91.1％ Polyester 86.4％ 98.4％ Black polyester 75.6％ 90.9％

[0066] Comparative Example 1

[0067] The catalyst preparation and one-pot conversion process for PET are the same as in Example 1, except that the reaction temperature in the one-pot conversion of PET is adjusted to 160°C.

[0068] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 98.2%, glycolic acid in a yield of 74.36%, and the selectivity of glycolic acid was 74.4%.

[0069] Comparative Example 2

[0070] The process of catalyst preparation and one-pot PET conversion is the same as in Example 1, except that TiO2 is replaced with ZnO to prepare a single-atom catalyst Pd1 / ZnO, and the single-atom catalyst Pd1 / ZnO is used for one-pot PET conversion.

[0071] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 98.7%, glycolic acid in a yield of 75.9%, and glycolic acid selectivity was 78.6%.

[0072] Comparative Example 3

[0073] The process of catalyst preparation and one-pot PET conversion is the same as in Example 1, except that TiO2 is replaced with CeO2 to prepare a single-atom catalyst Pd1 / CeO2, and the single-atom catalyst Pd1 / CeO2 is used for one-pot PET conversion.

[0074] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 95.6%, glycolic acid in a yield of 66.5%, and the selectivity for glycolic acid was 52.1%.

[0075] Comparative Example 4

[0076] The catalyst preparation and one-pot PET conversion process are the same as in Example 1, except that TiO2 is replaced with ZrO2 to prepare a single-atom catalyst Pd1 / ZrO2, and the single-atom catalyst Pd1 / ZrO2 is used for one-pot PET conversion.

[0077] After the same product purification process as in Example 1, terephthalic acid was obtained in a yield of 96.1%, glycolic acid in a yield of 75.0%, and the selectivity for glycolic acid was 78.9%.

[0078] Comparative Example 5

[0079] The PET conversion and purification process in this comparative example is the same as in Example 1, except that Pd nanoparticles supported on TiO2 are used as a catalyst.

[0080] 1. Pd nanoparticles supporting TiO2 (Pd NP Preparation of / TiO2)

[0081] The synthesis of TiO2 was the same as in Example 1.

[0082] 300 mg of synthesized TiO2 was dispersed in 40 mL of water and stirred continuously. Then, 2 mL of chloropalladium acid solution (H2PdCl4, Pd content: 3 mg / mL) was added to the solution and stirred until homogeneous. 1 mL of freshly prepared sodium borohydride solution (1 mg / mL) was added, and reduction was carried out for 2–3 h. After treatment, the sample was centrifuged and washed twice with deionized water, and finally dried overnight in a vacuum oven to obtain Pd.NP / TiO2.

[0083] 2. One-pot conversion of PET

[0084] A 1 mol / L alkaline solution was prepared by dissolving 2.4 g of sodium hydroxide in water. Then, 3 g of PET particles and 300 mg of Pd were added to the solution. NP / TiO2 was mixed with a polytetrafluoroethylene liner and stirred evenly. The liner was then placed in a high-pressure reactor, oxygen was introduced at 1.2 MPa, and the mixture was heated to 140°C for 2.5 h. After the reaction was completed, the catalyst was filtered and separated, and the filtrate was a solution of sodium terephthalate and sodium glycolate.

[0085] 3. Product purification

[0086] The purification process was the same as in Example 1, yielding terephthalic acid in 97.4% and glycolic acid in 78.6%, with a selectivity of 79.7%. This indicates that Pd... NP Pd1 / TiO2 also has the ability to convert to glycolic acid, but the yield and selectivity of glycolic acid are still lower than those of Pd1 / TiO2.

[0087] To explain why Pd1 / TiO2 exhibits superior selectivity, the adsorption configurations of ethylene glycol and glycolic acid on the catalyst surface were investigated. Figure 7 Infrared results indicate that the single-atom structure of Pd1 / TiO2 restricts the single adsorption configuration of ethylene glycol / glycolic acid, which is beneficial for suppressing the formation of *CHO-CHO* and reducing the byproducts of polyhydroxyl oxidation. Furthermore, the oxidative desorption behavior of the carbonyl intermediate was also characterized by electrochemical CO-stripping. Figure 8 The lower CO oxidation potential on Pd1 / TiO2 indicates that the carbonyl intermediate is more conducive to desorption on the surface, which alleviates catalyst poisoning and increases the yield of glycolic acid.

[0088] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A process for preparing glycolic acid from PET waste in a one-pot process, characterized in that, Includes the following steps: Alkali solution, PET waste and single-atom catalyst are added to a high-pressure reactor, oxygen is introduced to 1.2-1.5 MPa, and the reactor is heated to the target temperature to carry out the reaction. After the reaction is completed, glycolic acid is obtained by separation and purification. The single-atom catalyst is selected from Pd1 / TiO2.

2. The process method according to claim 1, characterized in that, The mass ratio of the PET waste to the single-atom catalyst is 1:3% to 1:10%.

3. The process method according to claim 1, characterized in that, The single-atom catalyst was prepared according to the following steps: TiO2 nanosheets were dispersed in an aqueous solution, and a palladium salt solution was added while stirring. After irradiation with a xenon lamp, the mixture was centrifuged, washed with water, and dried under vacuum to obtain the final product.

4. The process method according to claim 3, characterized in that, The xenon lamp irradiation time is 20–40 minutes.

5. The process method according to claim 3, characterized in that, The palladium salt solution is selected from one or more salt solutions of chloropalladium acid, sodium chloropalladium, potassium chloropalladium, palladium nitrate, and palladium acetate, and the Pd content in the palladium salt solution is 3 to 20 mg / mL.

6. The process method according to claim 1, characterized in that, The mass percentage of Pd1 in single-atom catalysts ranges from 0.3% to 2.0%.

7. The process method according to claim 1, characterized in that, The reaction temperature is 130–150℃, and the reaction time is 2–3 hours.

8. The process method according to claim 1, characterized in that, The alkaline solution is selected from potassium hydroxide solution and / or sodium hydroxide solution, with a concentration of 1 to 5 mol / L.

9. The process method according to claim 1, characterized in that, The mass-to-volume ratio of PET waste to alkaline solution is 1:5 to 1:

20.

10. The process method according to claim 1, characterized in that, The separation and purification process includes the following steps: The reaction solution obtained after the reaction was filtered, the pH of the filtrate was adjusted to 4-5, filtered again, the pigment impurities in the filtrate were adsorbed with activated carbon, the filtrate was concentrated to dryness under reduced pressure, the solid was redispersed with acetone, filtered again, and a filtrate rich in glycolic acid was obtained, which was then evaporated to obtain glycolic acid.

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