A method for co-catalyzing the alcoholysis of waste polyester or polycarbonate by phenol-formaldehyde resin-alkali

Abstract

This invention belongs to the field of waste polyester recycling, specifically relating to a method for the alcoholysis of waste polyester or polycarbonate using phenolic resin-alkali co-catalysis. This invention uses waste polyester or polycarbonate as raw material, methanol as solvent, and phenolic resin as an aid. Under the catalysis of an alkali, the waste polyester or polycarbonate is heated and depolymerized to obtain the alcoholysis product. This method features mild reaction conditions, rapid reaction process, and simple purification process. This depolymerization method is applicable to the recycling and upgrading of various forms of polyester or polycarbonate, solving the technical problem of efficient depolymerization of waste polyester or polycarbonate, and providing a sustainable technical path for the resource recovery of polyester or polycarbonate.

Description

Technical Field

[0001] This invention belongs to the field of waste polyester recycling, specifically relating to a method for alcoholysis of waste polyester or polycarbonate using phenolic resin-alkali co-catalysis. Background Technology

[0002] Polyester and polycarbonate, as important categories in the field of synthetic polymer materials, have become core materials in modern industrial systems due to their excellent comprehensive properties. However, their large-scale application has brought a severe environmental burden, and their waste disposal challenges exhibit both commonalities and unique characteristics. In terms of application scale, polyester, due to its good mechanical strength and processability, is widely used in packaging materials, textile fibers, disposable tableware, and other fields, with global annual production reaching tens of millions of tons. Polycarbonate, with its excellent transparency, impact resistance, and thermal stability, has achieved large-scale application in high-end fields such as electronics, automotive manufacturing, medical equipment, and optical devices. Aromatic polycarbonate, in particular, has become one of the largest-produced engineering plastics. Regarding environmental challenges, both face the problem of "difficult natural degradation and numerous drawbacks of traditional treatment methods." The stable ester bonds in the polyester molecular chain allow its natural degradation cycle to be as long as hundreds of years, while polycarbonate, due to the strong binding force between the aromatic ring and carbonate bonds in its molecular structure, has a degradation cycle of over a thousand years. Data shows that more than 400 million tons of plastic are produced globally each year, of which polyester and polycarbonate account for more than 20%, but the effective recycling rate is less than 10%. Traditional recycling methods are mainly divided into mechanical recycling, landfill and incineration, and chemical recycling. Mechanical recycling achieves material reuse through washing, crushing, and reshaping, but it has inherent drawbacks such as impurity accumulation leading to performance degradation, and it cannot handle mixed plastics or high-performance engineering plastics. In traditional landfill treatment, polyester is prone to releasing microplastics from leachate, while polycarbonate may release harmful substances such as bisphenol A (BPA) under high-temperature conditions, polluting soil and groundwater. During incineration, polyester releases carbon dioxide and small amounts of acidic gases, while polycarbonate may produce highly toxic substances such as dioxins, exacerbating air pollution. According to statistics from international environmental research institutions, as of 2024, the global cumulative amount of polyester and polycarbonate waste exceeded 500 million tons and 80 million tons, respectively, with a combined recycling rate of less than 12%, making them two key areas urgently needing breakthroughs in the control of "white pollution." Although chemical recycling can achieve closed-loop recycling by converting polymers into monomers through degradation reactions, current technologies face bottlenecks such as harsh reaction conditions (requiring high temperature and pressure), expensive catalysts, and low efficiency. More importantly, polyester and polycarbonate have a degradation cycle of decades to hundreds of years in the natural environment, making them difficult for microorganisms to decompose naturally, which has caused serious ecological crises such as soil pollution and marine plastic accumulation.

[0003] Although some progress has been made in the research on the degradation technology of polyester and polycarbonate, there are still many technical bottlenecks that need to be overcome. Specifically, they are reflected in the following aspects: (1) In terms of process optimization, although new technologies such as continuous flow reaction, microwave-assisted, and ultrasonic-assisted can improve the depolymerization efficiency, large-scale application is costly, incomplete degradation easily produces residues or harmful substances, and it is difficult to solve the problem of degradation of mixed plastics. (2) Biodegradation technology has low degradation efficiency, enzyme preparations are expensive and have poor stability, and the degradation rate is significantly affected by environmental factors such as temperature, pH value, and humidity, and its degradation capacity for commercial mixed plastics is insufficient. (3) Chemical degradation reaction (alcoholization or hydrolysis) conditions are harsh; catalyst performance is insufficient (cost is high or efficiency is low); selectivity and compatibility are poor, and when facing mixed waste of PET and commercial plastics such as PE and PP, it is impossible to accurately target the degradation of polyester or polycarbonate. The alcoholysis reaction mechanism includes two key steps: nucleophilic addition reaction to form tetrahedral intermediates, followed by elimination reaction to generate products. Previous studies (Angew. Chem. Int. Ed. 2025, 64, e202503469) have shown that phenols can significantly reduce the energy of tetrahedral intermediates and improve their stability through hydrogen bonding interactions, but often require equivalence or excess of phenols, which greatly increases costs and the difficulty of product separation.

[0004] In summary, existing polyester and polycarbonate degradation technologies suffer from common drawbacks such as low efficiency, high cost, demanding conditions, and poor environmental adaptability, failing to simultaneously meet the dual requirements of ecological protection and resource utilization. With the advancement of global "dual carbon" goals and increasingly stringent regulations for plastic pollution control, developing efficient, highly selective, and low-cost degradation technologies under mild conditions has become a critical issue urgently needing to be addressed in the field of polymer materials. Therefore, there is an urgent need to provide innovative technological solutions capable of achieving rapid degradation of polyester and polycarbonate or high-purity monomer recovery. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for the alcoholysis of waste polyester or polycarbonate using a phenolic resin-alkali co-catalytic process. Compared to small organic molecules, polymers exhibit a larger local concentration in solution. This invention leverages the ability of phenolic resin to locally increase the concentration of phenol, utilizing the hydrogen bonding interaction between phenol and tetrahedral intermediates to significantly reduce their energy and improve their stability during alcoholysis, thereby achieving the alcoholysis of waste polyester or polycarbonate using a phenolic resin-alkali co-catalytic process. This patented invention employs a phenolic resin-alkali co-catalytic system, enabling rapid alcoholysis of waste polyester or polycarbonate under mild conditions, with low catalyst dosage and easily purified products. It effectively solves the problems of harsh reaction conditions and low efficiency in traditional methods. It can selectively depolymerize polyester or polycarbonate in mixed plastics, enabling the recycling and reuse of impurity waste materials, reducing environmental pollution while conserving resources, and providing a sustainable path for the resource utilization of polymer materials.

[0006] The present invention relates to a method for alcoholysis of waste polyester or polycarbonate using phenolic resin-alkali co-catalysis. The method uses waste polyester or polycarbonate as raw material, methanol as solvent, and phenolic resin as an aid. The waste polyester or polycarbonate is depolymerized under the catalysis of alkali to obtain alcoholysis products.

[0007] The waste polyester refers to waste PET plastics (such as plastic bottles, plastic trays, films, packing straps, ropes, etc.), waste clothing containing polyester fibers or polyester, waste polylactic acid plastic bags, etc.; the waste polycarbonate refers to electronic and electrical appliance casings, car headlight covers, car interior and exterior trim parts, etc.

[0008] The amount of methanol used is 100%-500% of the mass of waste polyester or polycarbonate.

[0009] The phenolic resin includes one or more of thermoplastic phenolic resin 2123 and thermosetting phenolic resin 2130. The amount of phenolic resin used is 0.1%-20% of the mass of waste polyester or polycarbonate.

[0010] The alkali is selected from one or more of potassium carbonate, potassium bicarbonate, potassium tert-butoxide, potassium methoxide, potassium phenolate, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), tetramethylguanidine (TMG), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), triethylamine (TEA), N-methylmorpholine (NMM), and N,N-diisopropylethylamine (DIPEA). The amount of alkali used is 1%-10% of the mass of waste polyester or polycarbonate.

[0011] The alcoholysis temperature is 90-150℃, the time is 0.5-5 h, and the system pressure is controlled at 0.2-0.6 MPa.

[0012] After the alcoholysis reaction of waste PET polyester is completed, it is filtered and washed with methanol to obtain solid impurities and filtrate 1; the filtrate 1 is subjected to rotary evaporation and filtration to separate solid dimethyl terephthalate and filtrate 2; the filtrate 2 is subjected to distillation and vacuum distillation to obtain ethylene glycol product; at the same time, the methanol generated in the process can be recycled.

[0013] After the alcoholysis reaction of waste polycarbonate is completed, it is filtered and washed with methanol to obtain solid impurities and filtrate 3; the filtrate 3 is subjected to rotary evaporation and filtration to separate solid dimethyl terephthalate and filtrate 4; the filtrate 4 is subjected to distillation and vacuum distillation to obtain ethylene glycol product; at the same time, the methanol used in the process can be recycled.

[0014] The beneficial effects of this invention are reflected in:

[0015] 1. The present invention uses phenolic resin as a cocatalyst, which can locally increase the concentration of phenolic hydroxyl groups and reduce the energy of tetrahedral intermediates during alcoholysis through hydrogen bonding interactions, thereby enabling them to rapidly depolymerize under low catalyst dosage, lower temperature and pressure.

[0016] 2. The depolymerization system of the present invention uses a small amount of catalyst.

[0017] 3. The depolymerization system of this invention can selectively depolymerize polyester and polycarbonate in mixed polymers containing PVC, PA, PE, PS, cotton, etc., and has great application value.

[0018] 4. The method of this invention realizes the recycling and reuse of waste polyester and polycarbonate containing impurities, reduces the environmental pollution caused by them, saves petroleum resources, and promotes the sustainable development of economy and resources. Attached Figure Description

[0019] Figure 1 This is a flow chart of the phenolic resin-alkali co-catalytic alcoholysis process for waste PET polyester.

[0020] Figure 2 It is the dimethyl terephthalate separated after depolymerization in Example 1. 1 H NMR spectrum (d-DMSO).

[0021] Figure 3 These are dimethyl terephthalate and ethylene glycol separated after depolymerization in Example 4.

[0022] Figure 4 It is the reaction liquid after depolymerization in Example 5. 1 H NMR (d-DMSO). Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as limiting the scope of protection of the present invention, but rather as a more detailed exposition of certain aspects, features, and embodiments of the present invention. It should be clarified that the terminology used in this invention is only used to describe specific embodiments and is not intended to limit the invention. The terms "comprising," "including," "having," and "containing" as used herein are open-ended terms, meaning they cover but are not limited to the above content. The present invention is further illustrated by the following examples, which are for illustrative purposes only and not for limiting the invention; the scope of protection of the present invention is not limited thereto.

[0024] Example 1: Efficient alcoholysis recycling of waste PET plastic bottles

[0025] Remove labels and caps from discarded PET mineral water bottles, rinse the surface with water to remove dust and residual liquid, and dry in a 60 ℃ forced-air drying oven for 2 hours. After drying, crush the PET bottles using a shredder to avoid localized accumulation or excessive suspension during the reaction.

[0026] Add 0.5 g of thermoplastic phenolic resin (10% of the PET raw material mass), 150 mg of potassium carbonate (3% of the PET raw material mass), 5 g of PET plastic bottle scraps, and 20 ml of methanol sequentially to the reactor. Turn on the reactor's heating system and set the heating rate to 5 °C / min, raising the temperature from room temperature (approximately 25 °C) to 120 °C. During the heating process, activate the magnetic stirrer at a rate of 300 r / min to ensure thorough mixing of the materials and prevent localized overheating. When the reactor temperature reaches 120 °C, start timing and maintain a stable temperature of 120 ± 2 °C with the stirring rate unchanged for 2 hours. Monitor the reactor pressure in real time using a pressure monitoring device. The normal pressure range is 0.3~0.4 MPa. If abnormal pressure fluctuations occur (e.g., exceeding 0.5 MPa or falling below 0.2 MPa), adjust the heating power or stirring rate promptly to ensure stable reaction. After the reaction is complete, turn off the heating system. Cool to room temperature, filter, and wash with methanol. The filtrate was rotary evaporated to extract methanol for recycling. The remaining mixture was filtered and washed with methanol to obtain solid methyl terephthalate (yield 93%). The filtrate was then distilled and subjected to vacuum distillation to obtain ethylene glycol (yield 87%).

[0027] This embodiment also included a comparative experiment, with conditions identical to those in Example 1, except that phenolic resin was not added. After the reaction and processing procedures of Example 1, only methyl terephthalate with a yield of 55% and ethylene glycol with a yield of 50% were obtained.

[0028] Example 2: Selective alcoholysis recycling of waste polyester clothing

[0029] Wash the surface stains of waste blended clothing containing polyester (polyester fiber) (containing 5% cotton fiber impurities) with water, and dry it in a 65 ℃ forced-air drying oven for 2.5 h. Cut the dried clothing into 5 cm × 5 cm pieces and shred them with a shredder to avoid fiber agglomeration during the reaction.

[0030] Add 50 mg of thermosetting phenolic resin (1% of the polyester raw material mass), 250 mg of TEA (5% of the polyester raw material mass), 5 g of polyester fiber powder, and 40 ml of methanol sequentially to the reactor. Turn on the reactor's heating system, setting the heating rate to 5℃ / min, and raise the temperature from room temperature (approximately 25℃) to 150℃. During the heating process, activate the magnetic stirrer at a rate of 250 r / min to ensure thorough mixing of the materials and prevent localized overheating. Start timing when the reactor temperature reaches 150℃, maintaining a stable temperature of 150 ± 2℃ with the stirring rate unchanged for 1.5 hours. Monitor the reactor pressure in real-time using a pressure monitoring device. The normal pressure range is 0.4~0.5 MPa. If abnormal pressure fluctuations occur (e.g., exceeding 0.6 MPa or falling below 0.3 MPa), adjust the heating power or stirring rate promptly to ensure stable reaction. After the reaction is complete, turn off the heating system. The mixture was cooled to room temperature, filtered, and washed with methanol, with an 82% recovery rate of cotton fiber impurities. The filtrate was then rotary evaporated to remove methanol for recycling. The remaining mixture was filtered and washed with methanol to obtain a solid product, methyl terephthalate (yield 87%). The filtrate was then subjected to distillation and vacuum distillation to obtain ethylene glycol (yield 87%).

[0031] Example 3: Rapid alcoholysis recycling of waste polylactic acid plastic bags

[0032] Rinse the waste polylactic acid (PLA) plastic bags with water and dry them in a 55°C forced-air drying oven for 2 hours. Cut the dried plastic bags into 1 cm × 1 cm pieces and lightly crush them with a shredder (preserving the thin sheet shape to avoid over-crushing and clumping) to prevent uneven local suspension during the reaction.

[0033] 0.25 g of thermosetting phenolic resin (5% of the mass of polylactic acid raw material), 250 mg of potassium phenolate (5% of the mass of polylactic acid raw material), 5 g of polylactic acid fragments, and 15 ml of methanol were added sequentially to the reactor. The heating system of the reactor was turned on, and the heating rate was set to 5 °C / min, raising the temperature from room temperature (approximately 25 °C) to 110 °C. During the heating process, a magnetic stirrer was turned on, and the stirring rate was set to 350 r / min to ensure thorough mixing of the materials and prevent localized overheating. When the temperature inside the reactor reached 110 °C, the timer was started, and the temperature was maintained at 110 ± 2 °C with the stirring rate unchanged for 0.5 h. During the reaction, the pressure inside the reactor was monitored in real time using a pressure monitoring device. The normal pressure range was 0.3~0.4 MPa. If the pressure fluctuated abnormally (e.g., exceeding 0.2 MPa or falling below 0.5 MPa), the heating power or stirring rate was adjusted promptly to ensure stable reaction. After the reaction was completed, the heating system was turned off. The reactor was cooled to room temperature, filtered, and washed with methanol. The filtrate was rotary evaporated to extract methanol for recycling, and the remaining mixture was distilled to obtain methyl lactate (yield 99%).

[0034] Example 4: Selective alcoholysis recycling of PET film from mixed waste plastics

[0035] The plastics containing PET film (2 g), PE plastic (1 g), and PS foam (1 g) were rinsed with water to remove surface impurities and then dried in a 60 ℃ forced-air drying oven for 2 h. The dried plastics were then pulverized separately using a pulverizer to avoid the separation of particles of different materials during the reaction.

[0036] Add 0.2 g of thermoplastic phenolic resin (10% of the PET raw material mass), 160 mg of potassium bicarbonate (8% of the PET raw material mass), 5 g of mixed plastic granules (containing 2 g of PET, 1 g of PE plastic, and 1 g of PS foam), and 20 ml of methanol sequentially to the reactor. Turn on the reactor's heating system, setting the heating rate to 5 °C / min, and raise the temperature from room temperature (approximately 25 °C) to 130 °C. During the heating process, activate the magnetic stirrer at a rate of 300 r / min to ensure thorough mixing of the materials and prevent localized overheating. When the reactor temperature reaches 130 °C, start timing and maintain a stable temperature of 130 ± 2 °C with the stirring rate unchanged for 3 hours. Monitor the reactor pressure in real time using a pressure monitoring device. The normal pressure range is 0.4~0.5 MPa. If abnormal pressure fluctuations occur (e.g., exceeding 0.6 MPa or falling below 0.3 MPa), adjust the heating power or stirring rate promptly to ensure stable reaction. After the reaction is complete, turn off the heating system. The mixture was cooled to room temperature and filtered to separate unreacted PE and PS (94% recovery). The filtrate was rotary evaporated to extract methanol for recycling. The remaining mixture was filtered and washed with methanol to obtain solid methyl terephthalate (88% yield). The filtrate was then distilled and subjected to vacuum distillation to obtain ethylene glycol (87% yield).

[0037] Example 5: Efficient alcoholysis recycling of waste polycarbonate automotive lamp covers

[0038] Wash the surface of the waste polycarbonate automotive lamp cover (with metal fasteners removed) with water to remove dust and oil, and then dry it in a 70°C forced-air drying oven for 3 hours. Cut the dried lamp cover into 1 cm × 1 cm cubes using a cutter, and then crush it with a shredder to avoid local accumulation or excessive suspension during the reaction.

[0039] Add 4 mg of thermoplastic phenolic resin (0.1% of the polycarbonate raw material mass), 500 mg of DBN (10% of the polycarbonate raw material mass), 4 g of polycarbonate granules, and 20 ml of methanol sequentially to the reactor. Turn on the reactor's heating system, setting the heating rate to 5 °C / min, and raise the temperature from room temperature (approximately 25 °C) to 90 °C. During the heating process, activate the magnetic stirrer at a rate of 200 r / min to ensure thorough mixing of the materials and prevent localized overheating. When the reactor temperature reaches 90 °C, start timing and maintain a stable temperature of 90 ± 2 °C with the stirring rate unchanged for 5 hours. Monitor the reactor pressure in real time using a pressure monitoring device. The normal pressure range is 0.3–0.4 MPa. If abnormal pressure fluctuations occur (e.g., exceeding 0.5 MPa or falling below 0.2 MPa), adjust the heating power or stirring rate promptly to ensure stable reaction. After the reaction is complete, turn off the heating system. The mixture was cooled to room temperature, and methanol was distilled off at 80 °C for recycling. Then, dimethyl carbonate was distilled off at 110 °C (yield 58%). A small amount of cold chloroform was added to the residue after distillation to precipitate white crystalline bisphenol A (yield 90%).

Claims

1. A method for the alcoholysis of waste polyester or polycarbonate using phenolic resin-alkali co-catalysis, characterized in that: Waste polyester or polycarbonate is used as raw material and methanol is used as solvent. The waste polyester or polycarbonate is heated and depolymerized under the co-catalytic action of alkali and phenolic resin to obtain alcoholysis products.

2. The method according to claim 1, characterized in that: The waste polyester is selected from one or more of waste PET plastic, waste clothing containing polyester fiber or polyester, and waste polylactic acid plastic; the waste polycarbonate is selected from one or more of electronic and electrical appliance housings, automotive lamp covers, and automotive interior and exterior trim parts.

3. The method according to claim 1, characterized in that: The amount of methanol used is 100%-500% of the mass of waste polyester or polycarbonate.

4. The method according to claim 1, characterized in that: The phenolic resin includes one or more of thermoplastic and thermosetting phenolic resins.

5. The method according to claim 4, characterized in that: The amount of phenolic resin used is 0.1%-20% of the mass of waste polyester or polycarbonate.

6. The method according to claim 1, characterized in that: The base is selected from one or more of potassium carbonate, potassium bicarbonate, potassium tert-butoxide, potassium methoxide, potassium phenolate, 1,5-diazabicyclo[4.3.0]non-5-ene, tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, triethylamine, N-methylmorpholine, and N,N-diisopropylethylamine.

7. The method according to claim 6, characterized in that: The amount of alkali used is 1%-10% of the mass of waste polyester or polycarbonate.

8. The method according to claim 1, characterized in that: The alcoholysis temperature is 90-150℃, the time is 0.5-5 h, and the system pressure is controlled at 0.2-0.6 MPa.

9. The method according to claim 1, characterized in that: After the alcoholysis reaction of waste PET polyester is completed, it is filtered and washed with methanol to obtain solid impurities and filtrate 1; the filtrate 1 is subjected to rotary evaporation and filtration to separate solid dimethyl terephthalate and filtrate 2; the filtrate 2 is subjected to distillation and vacuum distillation to obtain ethylene glycol product; at the same time, the methanol generated in the process can be recycled.

10. The method according to claim 1, characterized in that: After the alcoholysis reaction of waste polycarbonate is completed, it is filtered and washed with methanol to obtain solid impurities and filtrate 3; the filtrate 3 is subjected to rotary evaporation and filtration to separate solid dimethyl terephthalate and filtrate 4; the filtrate 4 is subjected to distillation and vacuum distillation to obtain ethylene glycol product; at the same time, the methanol used in the process can be recycled.

Images