A method for solvent-induced catalyst-free polyester depolymerization and its application

Abstract

The invention discloses a method for solvent-induced catalyst-free polyester depolymerization and its application, belonging to the technical field of depolymerization and recovery of polymer materials. The method of the invention constructs a reaction system including polyester, alkylating agent and solvent; the polyester includes polyethylene terephthalate, polyethylene succinate, polyethylene adipate or polyethylene 2,5-furandicarboxylate; the alkylating agent is a carbonate alkylating agent; the solvent is an organic solvent with an amide bond; the reaction system is placed in a reactor under air conditions at a temperature of 170 to 200 ° C for 1 to 12 h of depolymerization reaction, and the reaction is cooled to room temperature after completion to obtain product dicarboxylic acid ester and ethylene carbonate. The method has high depolymerization efficiency and rapid reaction time, and has higher environmental friendliness, resource utilization efficiency and operational safety.

Description

Technical Field

[0001] The invention relates to the technical field of depolymerization and recovery of polymer materials, and in particular to a solvent-induced catalyst-free polyester depolymerization method and application thereof. Background Art

[0002] Chemical depolymerization of polyethylene terephthalate (PET) is an important method to achieve green and sustainable development. The chemical depolymerization method can retain the chemical composition of plastics and convert them into stable monomer molecules. Dimethyl terephthalate (DMT) is one of the key monomers for synthesizing new polymers or other chemical products, and has high recycling value. Generally, the depolymerization process of PET plastic to DMT is carried out by methanolysis (such as the Chinese patent document with publication number CN101565374A, etc.), where methanol acts as a nucleophilic agent to attack the C=O bond in the polyester, thereby achieving depolymerization and producing DMT and ethylene glycol (EG). However, this process is often reversible and requires a high temperature environment and excess methanol and catalyst to promote the reaction. At the same time, due to the high boiling point of ethylene glycol, the product is difficult to separate, thereby limiting the high yield of the depolymerization product. Therefore, it is necessary to develop a simpler and more efficient directional preparation route from PET to DMT. In addition, the ethylene glycol unit of PET also has great potential for conversion into high value-added chemicals. By selecting a suitable EG capture agent, the equilibrium of the PET depolymerization reaction can also be promoted to move toward the positive direction, thereby overcoming the bottleneck problem of incomplete PET depolymerization.

[0003] A Chinese patent document with publication number CN113801621A discloses a method for alcoholysis of waste PET. In a protective atmosphere, waste PET and an alcoholysis agent react at 170 to 200° C. for 3 to 5 hours under the action of a catalyst, and then undergo subsequent treatment to obtain an alcoholysis product, diethylene glycol terephthalate; the alcoholysis agent is ethylene glycol; and the catalyst includes one or more of zinc acetate, magnesium acetate, and sodium carbonate.

[0004] A Chinese patent document with publication number CN118290287A discloses a depolymerization method for achieving directional recovery of PET fibers. The method utilizes the interaction between ethylenediamine and a composite metal catalyst composed of a titanium compound and a zinc compound to achieve directional depolymerization of polyethylene terephthalate, thereby depolymerizing polyethylene terephthalate waste into diethylenediamine terephthalate.

[0005] In the prior art including the above invention, catalysts are widely used in PET depolymerization reactions. However, the high cost of catalysts, catalyst deactivation, increased side reactions, and reaction condition restrictions increase the complexity of their use. In this context, a reaction in which the raw materials in the absence of a catalyst or in a reaction system can be converted into a catalyst is particularly important because it has higher environmental friendliness, resource utilization efficiency, and operational safety, and has a very high application value. At present, there is no PET depolymerization path in which the raw materials in the absence of a catalyst or in a reaction system can be converted into a catalyst to achieve directional preparation of DMT.

[0006] Ethylene carbonate (EC) is an organic solvent with excellent performance and can also be used as an organic intermediate to synthesize chemicals. If the PET depolymerization process can further synthesize EC, it can not only solve the problem of ethylene glycol separation while achieving high value-added conversion, but also promote the equilibrium of the PET depolymerization reaction to proceed in the forward direction. Summary of the invention

[0007] In view of the deficiencies in the above-mentioned prior art, the present invention provides a method for solvent-induced catalyst-free polyester depolymerization. The method does not add an additional catalyst, but utilizes solvent ring-opening catalysis to depolymerize polyester and further upgrade it to carboxylic acid ester and vinyl carbonate. The method has a wide substrate applicability and is suitable for the depolymerization and upgrading of various polyesters including polyethylene terephthalate, polyethylene succinate, etc. The method has higher environmental friendliness, resource utilization efficiency and operational safety, and has high application value.

[0008] The specific technical solutions adopted are as follows:

[0009] A method for solvent-induced catalyst-free polyester depolymerization, comprising the following steps:

[0010] Constructing a reaction system including polyester, alkylating agent and solvent; the polyester includes polyethylene terephthalate, polyethylene succinate, polyethylene adipate or polyethylene 2,5-furandicarboxylate; the alkylating agent is a carbonate alkylating agent; the solvent is an organic solvent having an amide bond;

[0011] The reaction system is placed in a reactor under air conditions at a temperature of 170 to 200° C. for 1 to 12 hours for depolymerization reaction. After the reaction is completed, the temperature is cooled to room temperature to obtain product dicarboxylic acid esters and ethylene carbonate.

[0012] The inventors found in the experimental process that the polyester depolymerization reaction can be achieved by using an organic solvent having an amide bond without adding an additional catalyst. N-methylpyrrolidone NMP is used as an example to illustrate the depolymerization reaction of the present invention. First, there is inevitably a trace amount of water in the raw materials of the corresponding reaction system. NMP reacts with the trace amount of water in the system during the heating process to generate 4-(methylamino)butyric acid. 4-(methylamino)butyric acid has a carboxyl group and an imino group, which can form hydrogen bonds with the polyester and the alkylating agent respectively, and play an acid-base synergistic catalytic role in the reaction. The alkylating agent, as a nucleophilic agent, attacks the carbonyl carbon in the polyester to form a tetrahedral intermediate, and gradually decomposes into oligomers. The oligomers continue to decompose to produce carboxylic acid esters and ethylene glycol. Further, the alkylating agent and ethylene glycol are activated by 4-(methylamino)butyric acid in a similar manner, and the hydroxyl group of ethylene glycol forms an oxidized alkane ion, which nucleophilically attacks the carbonyl carbon of the alkylating agent to form an intermediate and release a methanol molecule. The intermediate undergoes intramolecular rearrangement to generate ethylene carbonate and release another molecule of methanol. N , N -Dimethylformamide and the like do not have a ring structure, but they also have an amide bond and can also be used to prepare dicarboxylic acid esters and ethylene carbonate without a catalyst.

[0013] Preferably, the solvent is N -methylpyrrolidone, N -Ethylpyrrolidone, N -Butylpyrrolidone, N -Hydroxyethylpyrrolidone, N -Benzylpyrrolidone, N -methylcaprolactam, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, N,N -dimethylformamide or N,N - at least one of dimethylacetamide.

[0014] Preferably, the alkylating agent is dimethyl carbonate, diethyl carbonate or dimethyl pyrocarbonate.

[0015] Preferably, the molar ratio of the polyester (based on the molar number of polyester structural units) to the alkylating agent is 1:1-10.

[0016] Preferably, the amount of the solvent added is 0.1 to 5 mL / mmol of polyester, further 0.5 to 2 mL / mmol of polyester.

[0017] Preferably, the depolymerization temperature is 180° C. and the depolymerization time is 3 hours.

[0018] Specifically, the dicarboxylic acid ester includes dimethyl terephthalate, diethyl terephthalate, dimethyl succinate, dimethyl adipate or dimethyl 2,5-furandicarboxylate.

[0019] The present invention also provides application of the solvent-induced catalyst-free polyester depolymerization method in the treatment of waste polyester products.

[0020] The present invention also provides a method for treating waste polyester products, which utilizes the solvent-induced catalyst-free polyester depolymerization method to treat the waste polyester products.

[0021] Optionally, the waste polyester is waste made of polyethylene terephthalate, polyethylene succinate, polyethylene adipate or polyethylene 2,5-furandicarboxylate.

[0022] Specifically, a reaction system including waste polyester, an alkylating agent and a solvent is constructed; the alkylating agent is a carbonate alkylating agent; the solvent is an organic solvent having an amide bond; the reaction system is placed in a reactor under air conditions at a temperature of 180 to 200° C. for 1 to 12 hours for depolymerization reaction, and after the reaction is completed, the temperature is cooled to room temperature to obtain product dicarboxylic acid esters and vinyl carbonate.

[0023] Waste polyester products are in the form of waste bottles, waste films, colored strapping ropes, non-woven fabrics, etc.

[0024] The waste polyester products need to be broken into centimeter-sized flakes, particles or powders before processing. The breaking process can ensure the resource utilization effect of the waste polyester products and improve the yield.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The polyester depolymerization strategy developed in the present invention is carried out under catalyst-free conditions. The organic solvent with amide bonds is transformed during the reaction, and the intermediates after the transformation play an acid-base synergistic catalytic role in the reaction. The depolymerization efficiency is high and the reaction time is fast. It has higher environmental friendliness, resource utilization efficiency and operational safety.

[0027] (2) The polyester depolymerization strategy developed in the present invention has the advantages of simple conditions and short reaction time. It can achieve complete depolymerization of polyester under standard reaction conditions. The method has a wide range of applications and has excellent effects on a variety of polyesters including polyethylene terephthalate, polyethylene succinate, polyethylene adipate, and polyethylene 2,5-furandicarboxylate. It can also efficiently complete targeted upgrading and conversion of waste polyesters in various product forms in a relatively short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 To verify N -High-resolution mass spectrometry results of the presence of methylpyrrolidone conversion products.

[0029] Figure 2To verify N -NMR hydrogen spectrum results of the transformation products of methylpyrrolidone. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the examples and accompanying drawings. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods of the following examples that do not specify specific conditions are usually performed under normal conditions or under conditions recommended by the manufacturer. The content that is not described in detail in this specification sheet belongs to the prior art known to professionals in the field. The experimental materials used in the following examples, if not otherwise specified, can be purchased by conventional biochemical reagent companies.

[0031] Example 1

[0032] In a high pressure reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N- Methyl pyrrolidone (8 mL) was placed in the reactor, and stirring and heating were started. The reaction system was heated to 180°C and reacted at this temperature for 3 h. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution. The obtained mixed solution was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate DMT was 99%, and the yield of ethylene carbonate was 89%.

[0033] Specifically, in the actual production process, the process of separating the mixed solution to obtain the product dicarboxylic acid ester and ethylene carbonate is as follows: 30 ml of water is added to the mixed solution to precipitate DMT, and the precipitated DMT is dried; the remaining mixed solution is subjected to stepwise rotary evaporation according to the boiling point (the boiling point of dimethyl carbonate DMC is 91°C, N- Methylpyrrolidone NMP has a boiling point of 202°C and ethylene carbonate has a boiling point of 248°C), and the product ethylene carbonate is obtained.

[0034] Example 2

[0035] In a high-pressure reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.84 g of diethyl carbonate (24 mmol) and N- Methyl pyrrolidone (8 mL) was placed in the reactor, and stirring and heating were started. The reaction system was heated to 200°C and reacted at this temperature for 12 h. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution, which was the product. The obtained mixed solution was passed through 1The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the PET decomposition rate of this example was 100%, the yield of diethyl terephthalate was 93%, and the yield of ethylene carbonate was 58%.

[0036] Example 3

[0037] In a high pressure reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 3.22 g of dimethyl pyrocarbonate (24 mmol) and N- Methyl pyrrolidone (8 mL) was placed in the reactor, and stirring and heating were started. The reaction system was heated to 200°C and reacted at this temperature for 12 h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixture was the product. The resulting mixture was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the PET decomposition rate of this example was 100%, and the yield of dimethyl terephthalate was 94%.

[0038] Example 4

[0039] In a high-pressure reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol), and different organic solvents with amide bonds ( N -Ethylpyrrolidone, N -Butylpyrrolidone, N -Hydroxyethylpyrrolidone, N -Benzylpyrrolidone, cyclohexylpyrrolidone, N -methylcaprolactam, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, N,N -dimethylformamide, N,N -dimethylacetamide) (8 mL), after placing the reactor, start stirring and heating. The reaction system is heated to 180°C and reacted at this temperature for 3 h. After the reaction is completed, the temperature is lowered to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results are shown in Table 1.

[0040] Table 1 Statistical results of product yields corresponding to different solvents

[0041]

[0042] Example 5

[0043] Discarded PET plastic bottles (common commercially available brand plastic bottles) were crushed to centimeter level in advance, and then 0.768 g of centimeter-level crushed PET plastic bottles (about 4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N -Methyl pyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system is heated to 180 ° C and reacted at this temperature for 3 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the PET decomposition rate of this example was 100%, the yield of dimethyl terephthalate was 97%, and the yield of ethylene carbonate was 83%.

[0044] Example 6

[0045] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.576 g of polyethylene succinate (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N -Methyl pyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system is heated to 180 ° C and reacted at this temperature for 3 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene succinate in this example was 100%, the yield of dimethyl succinate was 84%, and the yield of ethylene carbonate was 74%.

[0046] Example 7

[0047] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.688 g of polyethylene adipate (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N -Methyl pyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system is heated to 180 ° C and reacted at this temperature for 3 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene adipate in this example was 100%, the yield of dimethyl adipate was 75%, and the yield of ethylene carbonate was 75%.

[0048] Example 8

[0049] In a pressure tube reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.728 g of polyethylene 2,5-furandicarboxylate (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N -Methyl pyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system is heated to 180 ° C and reacted at this temperature for 3 h. After the reaction is completed, the temperature is cooled to room temperature, and the resulting mixed solution is the product. The resulting mixed solution is passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of polyethylene 2,5-furandicarboxylate in this example was 100%, the yield of dimethyl 2,5-furandicarboxylate was 91%, and the yield of ethylene carbonate was 75%.

[0050] Example 9

[0051] In a high-pressure reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and different volumes of N- Methyl pyrrolidone (2 mL, 4 mL, 8 mL, 12 mL) was placed in the reactor, and stirring and heating were started. The reaction system was heated to 180°C and reacted at this temperature for 3 h. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution, and the obtained mixed solution was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the decomposition rate of PET in this embodiment was 100%, the yields of dimethyl terephthalate (DMT) were 81%, 84%, 99%, 99%, and the yields of ethylene carbonate were 81%, 83%, 89%, 80%, respectively.

[0052] Example 10

[0053] In a high pressure reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N- Methyl pyrrolidone (8 mL) was placed in the reactor, and stirring and heating were started. The reaction system was heated to 170°C, 180°C, and 190°C respectively, and reacted at this temperature for 3 h. After the reaction was completed, the temperature was lowered to room temperature to obtain a mixed solution, and the obtained mixed solution was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results showed that the PET decomposition rate of the present embodiment was 100%, the dimethyl terephthalate DMT yields were 91%, 99%, 92%, and the ethylene carbonate yields were 87%, 89%, 92%, respectively.

[0054] Comparative Example 1

[0055] In a high pressure reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and N -Methyl pyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system was heated to 150 ° C and reacted at this temperature for 3 h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixture was passed through 1 The yields were determined by H NMR with mesitylene as the internal standard. The yield of dimethyl terephthalate was 0% and the yield of ethylene carbonate was 0%.

[0056] Comparative Example 2

[0057] In a high-pressure reactor equipped with an electromagnetic stirrer, a thermocouple, and a programmable temperature controller, 0.768 g of CR-pure PET powder (4 mmol), 2.84 g of diethyl carbonate (24 mmol) and N -methylpyrrolidone (8 mL), after placing the reactor, start stirring and heating. The reaction system was heated to 160 ° C and reacted at this temperature for 3 h. After the reaction was completed, the temperature was lowered to room temperature, and the resulting mixture was passed through 1 The yields were determined by H NMR with mesitylene as the internal standard. The yield of diethyl terephthalate was 0% and the yield of ethylene carbonate was 0%.

[0058] Comparative Example 3

[0059] 0.768 g of CR-pure PET powder (4 mmol), 2.16 g of dimethyl carbonate (24 mmol) and different organic solvents (1,4-dioxane, acetonitrile, toluene, cyclohexane, tetrahydrofuran, dichloromethane) (8 mL) were added to a high-pressure reactor equipped with an electromagnetic stirrer, a thermocouple and a programmable temperature controller. A solvent-free comparative experiment was also set up. After placing the reactor, stirring and heating were turned on. The reaction system was heated to 180°C and reacted at this temperature for 3 h. After the reaction was completed, the temperature was cooled to room temperature and the resulting mixture was passed through 1 The yield was determined by H NMR with mesitylene as the internal standard. The results are shown in Table 2.

[0060] Table 2 Statistical results of product yields corresponding to different solvents

[0061]

[0062] Sample analysis

[0063] The present invention has been verified by high-resolution mass spectrometry and nuclear magnetic resonance hydrogen spectrum. N -Methylpyrrolidone conversion products do exist, and the results are as follows Figure 1 and Figure 2 As shown, Figure 1 Figure 1 is a high-resolution mass spectrum of a representative solution after reaction. In positive ion mode, the main peaks of mass scanning are the protonated molecule [M + H] peak (m / z 118.0871) and the M + 1 isotope [M + 1 + H] peak (m / z 119.0498) of 4-(methylamino)butyric acid, while no corresponding characteristic peaks were detected in the original NMP solution. 1 H NMR Figure 2 Compared with the standard spectrum of 4-(methylamino)butyric acid, its characteristic peaks were detected at 2.3 ppm and 1.9 ppm, and its content was about 1.5 mmol% of the total NMP.

[0064] At the same time, the present invention also uses acetonitrile as a solvent and adds an exogenous acid catalyst / base catalyst, proving that the solvent conversion product does have an acid-base synergistic catalytic effect.

[0065] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for solvent-induced catalyst-free polyester depolymerization, characterized in that: The following methods are included: A reaction system comprising a polyester, an alkylating agent and a solvent is constructed; the polyester is polyethylene terephthalate, polyethylene succinate, polyethylene adipate or polyethylene 2,5-furandicarboxylate; the alkylating agent is a carbonate alkylating agent; The reaction system is placed in a reactor under air conditions at a temperature of 170 to 200° C. for 1 to 12 hours for depolymerization reaction, and after the reaction is completed, the temperature is cooled to room temperature to obtain dicarboxylic acid ester and ethylene carbonate as products; The solvent is N -methylpyrrolidone, N -Ethylpyrrolidone, N -Butylpyrrolidone, N -Hydroxyethylpyrrolidone, N -Benzylpyrrolidone, N -methylcaprolactam, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethylpropyleneurea, N,N -dimethylformamide or N,N - at least one of dimethylacetamide.

2. The method for solvent-induced catalyst-free polyester depolymerization according to claim 1, characterized in that: The alkylating agent is dimethyl carbonate, diethyl carbonate or dimethyl pyrocarbonate.

3. The method for solvent-induced catalyst-free polyester depolymerization according to claim 1, characterized in that: The molar ratio of the polyester to the alkylating agent is 1:1-10.

4. The method for solvent-induced catalyst-free polyester depolymerization according to claim 1, characterized in that: The amount of the solvent added is 0.1-5 mL / mmol polyester.

5. Use of the method for solvent-induced catalyst-free polyester depolymerization according to any one of claims 1 to 4 in the treatment of waste polyester products.

6. A method for treating waste polyester products, characterized in that: The waste polyester product is treated by the method for solvent-induced catalyst-free polyester depolymerization as described in any one of claims 1 to 4.

7. The method for treating waste polyester products according to claim 6, characterized in that: The waste polyester is waste made of polyethylene terephthalate, polyethylene succinate, polyethylene adipate or polyethylene 2,5-furandicarboxylate.

8. The method for treating waste polyester products according to claim 6, characterized in that: Waste polyester products come in the form of waste bottles, waste films, colored twine or non-woven fabrics, which are broken into centimeter-sized flakes, granules or powders before processing.

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