Process for realizing efficient cascade depolymerization of pet by using an extremely low load organic amine catalyst

Abstract

The application discloses a process for realizing efficient cascade depolymerization of PET by using an extremely low-load organic amine catalyst, and belongs to the field of recycling of polyester plastics. By adding an additional nucleophilic auxiliary, the catalytic performance of a binary organic amine can be greatly improved, PET depolymerization can be realized under extremely low load (250 ppm-500 ppm), dimethyl terephthalate and ethylene carbonate can be prepared, and the use cost of the catalyst is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of polyester plastic recycling, specifically involving a process for achieving efficient tandem depolymerization of PET using an extremely low-load organic amine catalyst. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in clothing, food packaging, and other fields, providing great convenience for daily life. However, these materials degrade very slowly in nature after being discarded, causing significant environmental problems. Currently, commercial physical recycling methods can only recycle high-quality transparent bottle flakes and can only achieve a single cycle. Chemical methods, on the other hand, are receiving increasing attention because they can be re-degraded into high-purity monomers that can then be repolymerized into high-quality polyesters. Among these methods, methanol hydrolysis has been extensively studied due to its low dissolution cost and the fact that the product, dimethyl terephthalate (DMT), is easily purified through decolorization and recrystallization. However, the inability to effectively remove the byproduct ethylene glycol (EG) prevents a reduction in solvent consumption. Therefore, capturing and converting ethylene glycol fragments is crucial for improving efficiency. In recent years, the use of dimethyl carbonate (DMC) as a solvent and EG capture agent has shown advantages. It is environmentally friendly, low in toxicity, and the ethylene carbonate (EC) produced after transesterification with EG is also an important component of the electrolyte in lithium batteries. Mei Qingqing et al. used ionic liquid catalysts to achieve the depolymerization of PET in DMC (CN117603043B), and Liu Zhimin et al. also achieved the depolymerization of PET in DMC using inorganic metal salts with halide anions (CN119118826B). However, although DMC showed the above advantages, the amount of catalyst used was relatively high: compared with the amount of PET repeating units added, the proportion of catalyst was generally 5 mol% or more, which posed a considerable challenge to the subsequent separation and recovery of catalyst. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a process for achieving efficient tandem depolymerization of PET using an extremely low-load organic amine catalyst. This invention utilizes a bifunctional organic amine catalyst to achieve efficient depolymerization of PET under DMC solvent and added nucleophilic auxiliary conditions. Through the special synergistic effect of the bifunctional organic amine catalyst and the added nucleophilic auxiliary, PET depolymerization and the preparation of dimethyl terephthalate and ethylene carbonate can be achieved under extremely low catalyst loading (250 ppm ~ 500 ppm), significantly reducing the cost of catalyst use.

[0004] The present invention provides a process for achieving efficient tandem depolymerization of PET using an extremely low-load organic amine catalyst, comprising the following steps:

[0005] PET waste (bottle flakes, cloth, film, etc.) is placed in a reactor, and dimethyl carbonate, nucleophilic additives, and bifunctional organic amine catalysts are added. The reactor is heated to 140℃~200℃ and stirred for 1~8 hours to complete the depolymerization reaction, obtaining dimethyl terephthalate (DMT) and ethylene carbonate (EC) as a byproduct.

[0006] The nucleophilic auxiliary is methanol or ethylene glycol.

[0007] The bifunctional organic amine catalyst is a multi-substituted chain or cyclic diorganic amine, selected from compounds with the following structures:

[0008]

[0009] R1, R2, R3, and R4 are each independently selected from hydrogen, alkyl, cycloalkyl, alkenyl, halogen, etc., preferably alkyl, and more preferably methyl.

[0010] In the reaction system:

[0011] The molar ratio of dimethyl carbonate to PET is 6:1 to 16:1, preferably 8:1, which is approximately 0.72 mL DMC / mmol PET repeating unit by volume.

[0012] The molar ratio of the nucleophilic auxiliary agent to PET is 0.2:1 to 1:1, preferably 0.5:1.

[0013] The molar ratio of the bifunctional organic amine catalyst to PET is 0.00025:1 to 0.001:1, preferably 0.0005:1.

[0014] The preferred reaction temperature is 180 ℃, and the preferred reaction time is 3 h.

[0015] This invention utilizes a bifunctional organic amine catalyst to catalyze the depolymerization of polyethylene terephthalate (PET) to prepare dimethyl terephthalate (DMT) with ethylene carbonate (EC) as a byproduct. Ethylene glycol (EG) fragments are captured and released in situ in a dimethyl carbonate solvent system for reuse in the depolymerization of polyester. With the addition of certain auxiliary agents (methanol or ethylene glycol) before the reaction, the system can achieve highly efficient depolymerization of polyester at extremely low catalyst loading (250 ppm ~ 500 ppm), significantly reducing the cost of catalyst use. Attached Figure Description

[0016] Figure 1 It is the product DMT 1 H NMR spectrum.

[0017] Figure 2 It is the product EC.1 H NMR spectrum. Detailed Implementation

[0018] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0019] Example 1:

[0020] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.54 μL N,N′-dimethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 88.5%, EC 87.7%.

[0021] Example 2:

[0022] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.65 μL N,N,N′-trimethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 91.1%, EC 87.7%.

[0023] Example 3:

[0024] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.74 μL N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 90.5%, EC 81.7%.

[0025] Example 4:

[0026] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.83 μL N,N,N′,N′-tetramethylpropanediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 90.5%, EC 85.2%.

[0027] Example 5:

[0028] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.91 μL N,N,N′,N′-tetramethylbutanediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 92.3%, EC 84.7%.

[0029] Example 6:

[0030] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.96 μL N,N,N′,N′-tetramethyl-1,2-cyclohexanediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 92.2%, EC 86.0%.

[0031] Example 7:

[0032] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.74 μL N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 180 °C and stirred for 3 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 95.0%, EC 83.7%.

[0033] Example 8:

[0034] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.74 μL N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 200 °C and stirred for 2 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 93.8%, EC 86.5%.

[0035] Example 9:

[0036] 1.92 g of PET chips (10 mmol), 7.2 mL of dimethyl carbonate, and 0.74 μL of N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 10.2%, EC 32.2%.

[0037] Example 10:

[0038] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.31 g ethylene glycol (5 mmol), and 0.74 μL N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 76.6%, EC 80.9%.

[0039] Example 11:

[0040] 1.92 g of PET chips, 7.2 mL of dimethyl carbonate, 0.64 g of methanol (20 mmol), and 0.74 μL of N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel high-pressure reactor. The mixture was heated to 160 °C and stirred for 3 h. After the reaction was complete, the reactor was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 90.6%, EC 83.9%.

[0041] Example 12:

[0042] 1.92 g of PET chips, 7.2 mL of dimethyl carbonate, 0.32 g of methanol (10 mmol), and 0.74 μL of N,N,N′,N′-tetramethylethylenediamine (0.005 mmol) were added to a 30 mL stainless steel high-pressure reactor. The mixture was heated to 160 °C and stirred for 3 h. After the reaction was complete, the reactor was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography, using propylene carbonate (PC) as an internal standard. Yield: DMT 88.8%, EC 85.9%.

[0043] Example 13:

[0044] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.69 μL triethylamine (0.005 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography. Propylene carbonate (PC) was used as an internal standard. Yield: DMT 0%, EC 0.02%.

[0045] Example 14:

[0046] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 0.75 μL 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 0.005 mmol) were added to a 30 mL stainless steel high-pressure reactor. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the reactor was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography. Propylene carbonate (PC) was used as an internal standard. Yield: DMT 10.2%, EC 22.3%.

[0047] Example 15:

[0048] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 9.24 μL 2-azhexane (0.1 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography. Propylene carbonate (PC) was used as an internal standard. Yield: DMT 0%, EC 0.01%.

[0049] Example 16:

[0050] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 7.71 μL N,N′-dimethylacetamide (0.1 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography. Propylene carbonate (PC) was used as an internal standard. Yield: DMT 0%, EC 0.02%.

[0051] Example 17:

[0052] 1.92 g PET chips (10 mmol), 7.2 mL dimethyl carbonate, 0.62 g ethylene glycol (10 mmol), and 9.90 μL N,N′-dimethylformamide (0.1 mmol) were added to a 30 mL stainless steel autoclave. The mixture was heated to 160 °C and stirred for 4 h. After the reaction was complete, the autoclave was rapidly cooled in a water bath. After cooling, the mixture was dissolved and diluted with dioxane, and the yield was determined by gas chromatography. Propylene carbonate (PC) was used as an internal standard. Yield: DMT 0%, EC 0.02%.

[0053] Examples 1-8, compared with Comparative Examples 9-10 and 13-17, demonstrate that not all organic amine catalysts can achieve the depolymerization of PET; long-chain, multi-substituted diamines exhibit superior catalytic performance. Furthermore, additional nucleophilic auxiliaries can significantly increase the reaction rate, with methanol showing better performance than ethylene glycol.

Claims

1. A process for achieving efficient tandem depolymerization of PET using an extremely low-loaded organic amine catalyst, characterized in that... Includes the following steps: PET waste is placed in a reactor, and dimethyl carbonate, nucleophilic additives, and bifunctional organic amine catalysts are added. The reactor is heated to 140°C to 200°C and stirred for 1 to 8 hours to complete the depolymerization reaction, obtaining dimethyl terephthalate and ethylene carbonate as a byproduct. The bifunctional organic amine catalyst is a multi-substituted chain or cyclic diorganic amine, selected from compounds with the following structures: ； R1, R2, R3, and R4 are each independently selected from hydrogen or methyl; The molar ratio of the bifunctional organic amine catalyst to PET is 0.00025:1 to 0.001:1; The nucleophilic auxiliary is methanol or ethylene glycol.

2. The process according to claim 1, characterized in that: The molar ratio of the nucleophilic auxiliary agent to PET is 0.2:1 to 1:

1.

3. The process according to claim 1, characterized in that: The molar ratio of dimethyl carbonate to PET is 6:1 to 16:1.

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