Polyester plastic degradation method

Abstract

The invention provides a polyester plastic degradation method which comprises the following steps: (1) reacting polyester plastic, an alcoholysis reagent and alkali under the action of a Ru / C catalyst to obtain a reaction mixed solution and hydrogen; carrying out acidification separation on the reaction mixed solution to obtain terephthalic acid and lactic acid; the polyester plastic is selected from polyethylene glycol terephthalate; and (2) reacting terephthalic acid with hydrogen under the action of a Ru / C catalyst to obtain the 1, 4-cyclohexanedicarboxylic acid. When the method provided by the invention is used for degrading the polyester plastics, the degradation and conversion of the polyester plastics can be realized by only using one commercial catalyst under the condition that external hydrogen is not needed, so that the polyester plastics are directionally converted into high-value chemicals. Furthermore, the polyester plastic has excellent conversion rate, and the lactic acid and the 1, 4-cyclohexanedicarboxylic acid in the degraded and converted product have higher yield and purity.

Description

Technical Field

[0001] The present application relates to the technical field of organic intermediate synthesis, and in particular to a method for degrading polyester plastics. Background Art

[0002] The indiscriminate disposal and incineration of plastic waste has resulted in massive resource waste and environmental pollution, contradicting the contemporary emphasis on energy conservation and emission reduction. Polyethylene terephthalate (PET) is the most widely used polyester plastic, with an annual production exceeding 70 million tons, primarily used in textiles, packaging, and beverage bottles. Currently, post-consumer PET waste is primarily recycled mechanically, but this inevitably leads to recycling degradation. Chemical recycling can recover terephthalic acid (TPA) and ethylene glycol (EG) monomers through the depolymerization of PET using acids, bases, metals, or enzymes. In addition to recovering TPA and EG monomers, other reagents can be used to upcycle the monomers or plastics into value-added chemicals or materials. For example, the resulting TPA can be catalytically hydrogenated to 1,4-cyclohexanedicarboxylic acid (CHDA) or 1,4-cyclohexanedimethanol (CHDM). EG is also considered a crucial platform molecule, capable of being oxidized to formic or glycolic acid or reformed with H2O to produce H2. Furthermore, EG can undergo dehydrogenative cross-coupling with methanol to produce lactic acid (LA) and H2. Unfortunately, the strategies reported to date have not yet simultaneously upcycled both components, EG and TPA, into value-added chemicals. Summary of the Invention

[0003] The purpose of this application is to provide a polyester plastic degradation method to address the degradation and conversion issues of polyethylene terephthalate (PET), enabling the simultaneous and targeted conversion of PET monomers ethylene glycol and terephthalic acid into high-value chemicals. The specific technical solution is as follows:

[0004] The first aspect of the present application provides a method for degrading polyester plastics, which comprises:

[0005] (1) reacting the polyester plastic, an alcoholysis agent, and a base under the action of a Ru / C catalyst to obtain a reaction mixture and hydrogen; acidifying and separating the reaction mixture to obtain terephthalic acid and lactic acid;

[0006] The mass ratio of the polyester plastic, the base and the Ru / C catalyst is 20-40:50-100:1; the mass volume ratio of the polyester plastic to the alcoholysis reagent is 50-100 g:1 L; the polyester plastic is selected from polyethylene terephthalate;

[0007] (2) reacting the generated terephthalic acid and the hydrogen under the action of the Ru / C catalyst to obtain 1,4-cyclohexanedicarboxylic acid;

[0008] The mass ratio of the terephthalic acid, the hydrogen and the Ru / C catalyst is 2-5:0.1-0.3:0.1-0.5.

[0009] In one embodiment of the present application, the alcoholysis reagent is selected from at least one of methanol and ethylene glycol.

[0010] In one embodiment of the present application, the base is selected from at least one of NaOH, KOH, CaOH and CsOH.

[0011] In one embodiment of the present application, the Ru / C catalyst is a 5-15 wt% Ru / C catalyst.

[0012] In one embodiment of the present application, the reaction temperature of step (1) is 140-180° C., and the reaction time is 8-12 hours.

[0013] In one embodiment of the present application, the reaction temperature of step (2) is 140-180° C., and the reaction time is 25-35 hours.

[0014] In one embodiment of the present application, the acidification separation comprises: adding acid to the reaction mixture, adjusting the pH to less than 7, and separating terephthalic acid and lactic acid.

[0015] In one embodiment of the present application, the acid is selected from at least one of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0016] In one embodiment of the present application, a solvent is further added in step (2), and the mass volume ratio of the terephthalic acid to the solvent is 0.01-0.05 g:1 mL.

[0017] In one embodiment of the present application, the solvent is selected from at least one of water and methanol.

[0018] Beneficial effects of this application:

[0019] This application provides a method for degrading polyester plastics, achieving the degradation and conversion of polyester plastics using only a commercial catalyst without the need for external hydrogen. This method allows the simultaneous and targeted conversion of the monomers ethylene glycol and terephthalic acid of polyethylene terephthalate into high-value chemicals. Furthermore, the polyethylene terephthalate has an excellent conversion rate, and the lactic acid and 1,4-cyclohexanedicarboxylic acid in the degradation and conversion products have high yields and purities.

[0020] In addition, this application effectively collects and recovers the hydrogen generated by lactic acid formation and dehydrogenation of alcoholysis reagents, and applies it to the complete hydrogenation of terephthalic acid to 1,4-cyclohexanedicarboxylic acid, successfully coupling the two reactions, making the entire process atom-economical, and fully utilizing the carbon, hydrogen, and oxygen atoms stored in polyethylene terephthalate, providing a new idea for the co-conversion of carbon and hydrogen sources.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0023] Figure 1 is the product lactic acid in Example 1 1 H NMR (D O) spectrum;

[0024] Figure 2 The product 1,4-cyclohexanedicarboxylic acid in Example 1 1 H NMR (D O) spectrum;

[0025] Figure 3 This is the reaction process of upgrading the polyethylene terephthalate in Example 1 to lactic acid and 1,4-cyclohexanedicarboxylic acid. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] The first aspect of the present application provides a method for degrading polyester plastics, which comprises:

[0028] (1) reacting the polyester plastic, an alcoholysis agent, and a base under the action of a Ru / C catalyst to obtain a reaction mixture and hydrogen; acidifying and separating the reaction mixture to obtain terephthalic acid and lactic acid;

[0029] The mass ratio of the polyester plastic, the base and the Ru / C catalyst is 20-40:50-100:1; the mass volume ratio of the polyester plastic to the alcoholysis reagent is 50-100 g:1 L; the polyester plastic is selected from polyethylene terephthalate;

[0030] (2) reacting the generated terephthalic acid and the hydrogen under the action of the Ru / C catalyst to obtain 1,4-cyclohexanedicarboxylic acid;

[0031] The mass ratio of the terephthalic acid, the hydrogen and the Ru / C catalyst is 2-5:0.1-0.3:0.1-0.5.

[0032] The inventors discovered that by effectively collecting and recovering the hydrogen generated by lactic acid formation and dehydrogenation of the alcoholysis reagent, and applying it to the complete hydrogenation of terephthalic acid to 1,4-cyclohexanedicarboxylic acid, they successfully coupled these two reactions, making the entire process atom-economical and fully utilizing the carbon, hydrogen, and oxygen atoms stored in polyethylene terephthalate. This method, used to degrade polyethylene terephthalate, achieves both degradation and conversion of polyethylene terephthalate using only a Ru / C catalyst without the need for external hydrogen, enabling the simultaneous, targeted conversion of the polyethylene terephthalate monomers, ethylene glycol, and terephthalic acid, into high-value chemicals.

[0033] Furthermore, the above method was used to degrade polyethylene terephthalate, resulting in an excellent conversion rate of polyethylene terephthalate. The lactic acid and 1,4-cyclohexanedicarboxylic acid in the degradation and conversion products had high yields and purities. The inventors discovered that excessive amounts of polyester plastics inhibit dehydrogenation and coupling reactions. As the amount of polyester plastic increases, the production of terephthalic acid and ethylene glycol increases. However, when the amount of polyester plastic is too large, while the production of terephthalic acid and ethylene glycol increases, the production of lactic acid and hydrogen decreases. By controlling the amount of polyester plastic within the range of this application, a molar ratio of hydrogen to terephthalic acid of approximately 3 to 5 can be achieved, ensuring smooth hydrogenation of terephthalic acid. In addition, without the addition of alkali, polyester plastics will depolymerize into ethylene glycol and dimethyl terephthalate. As the amount of alkali increases to within the range of this application, the dehydrogenation reaction of the alcoholysis reagent is accelerated, and the generation of lactic acid and hydrogen also gradually increases, and a molar ratio of hydrogen to terephthalic acid of about 3 to 5 can be achieved, ensuring that the hydrogenation reaction of terephthalic acid proceeds smoothly; when the amount of alkali used is too large, it is not conducive to the hydrogenation of terephthalic acid.

[0034] In the present application, there is no particular limitation on the weight average molecular weight of polyethylene terephthalate, as long as the purpose of the present application can be achieved. For example, the weight average molecular weight of polyethylene terephthalate can be 20 to 100 kDa.

[0035] In this application, there is no particular limitation on the size of the polyester plastic during the degradation process, as long as the purpose of this application can be achieved. For example, when the mass of the polyester plastic to be degraded is greater than 1g, the polyester plastic is cut into 0.5cm×0.5cm pieces to facilitate the reaction.

[0036] In one embodiment of the present application, the mass ratio of the polyester plastic, the base, and the Ru / C catalyst in step (1) is 20-40:70-90:1; and the mass-volume ratio of the polyester plastic to the alcoholysis reagent is 70-80 g:1 L. The inventors have found that when the amounts of the polyester plastic, base, Ru / C catalyst, and alcoholysis reagent are within the ranges of the present application, the lactic acid and 1,4-cyclohexanedicarboxylic acid in the products of polyethylene terephthalate degradation and conversion have higher yields and purities.

[0037] In one embodiment of the present application, the alcoholysis reagent is selected from at least one of methanol and ethylene glycol. The inventors have discovered that selecting the above alcoholysis reagent can better generate hydrogen, thereby meeting the requirements of subsequent terephthalic acid hydrogenation, and thereby achieving higher yields and purities of lactic acid and 1,4-cyclohexanedicarboxylic acid in the products of polyethylene terephthalate degradation and conversion.

[0038] In one embodiment of the present application, the base is selected from at least one of NaOH, KOH, CaOH, and CsOH. The inventors have discovered that selecting the above bases can better achieve the coupling of ethylene glycol monomer generated by depolymerization of polyethylene terephthalate with an alcoholysis reagent to produce lactic acid, as well as the dehydrogenation of the alcoholysis reagent to produce sufficient hydrogen. This, in turn, results in higher yields and higher purities of lactic acid and 1,4-cyclohexanedicarboxylic acid in the products of polyethylene terephthalate degradation and conversion.

[0039] In one embodiment of the present application, the Ru / C catalyst comprises 5-15 wt% Ru / C. The inventors have discovered that selecting the above catalyst can better achieve the coupling of ethylene glycol monomer generated by depolymerization of polyethylene terephthalate with an alcoholysis reagent to produce lactic acid, thereby achieving higher yields and higher purities of lactic acid and 1,4-cyclohexanedicarboxylic acid in the products of polyethylene terephthalate degradation and conversion.

[0040] In one embodiment of the present application, the reaction temperature of step (1) is 140-180°C, and the reaction time is 8-12 hours; preferably, the reaction temperature is 150-170°C, and the reaction time is 9-11 hours. The inventors have found that when the reaction temperature and reaction time of step (1) are within the above ranges, the polyethylene terephthalate can have a higher conversion rate, and the lactic acid and 1,4-cyclohexanedicarboxylic acid in the degradation and conversion products have a higher yield and purity.

[0041] In one embodiment of the present application, the reaction temperature of step (2) is 140-180°C, and the reaction time is 25-35 hours; preferably, the reaction temperature is 150-170°C, and the reaction time is 28-32 hours. The inventors have found that when the reaction temperature and reaction time of step (2) are within the above ranges, the polyethylene terephthalate can have a higher conversion rate, and the lactic acid and 1,4-cyclohexanedicarboxylic acid in the degradation and conversion products have a higher yield and purity.

[0042] In one embodiment of the present application, the reactions of step (1) and step (2) are carried out under stirring. The present application does not particularly limit the stirring method and speed, as long as the purpose of the present application can be achieved. For example, mechanical stirring can be used, and the stirring speed can be 500-700 rpm.

[0043] In one embodiment of the present application, the acidification separation comprises: adding acid to the reaction mixture, adjusting the pH to less than 7, and separating terephthalic acid and lactic acid.

[0044] In one embodiment of the present application, the acid is selected from at least one of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0045] In the present application, the concentration of the hydrochloric acid, sulfuric acid, formic acid or acetic acid is not particularly limited, as long as the purpose of the present application can be achieved. For example, the concentration of the hydrochloric acid, sulfuric acid, formic acid or acetic acid can be 2 to 5 mol / L.

[0046] In one embodiment of the present application, a solvent is further added in step (2), and the mass volume ratio of the terephthalic acid to the solvent is 0.01-0.05 g:1 mL.

[0047] In one embodiment of the present application, the solvent is selected from at least one of water and methanol.

[0048] The method of the present application is used to degrade polyester plastics. The degradation and conversion of polyester plastics is achieved using only a commercial catalyst without the need for external hydrogen, enabling the targeted conversion of polyester plastics into high-value chemicals. The method of the present application not only demonstrates the atomic economy of waste resource conversion, but also expands the potential for upcycling polyethylene terephthalate by combining plastic upgrading with one-carbon chemistry. Furthermore, polyethylene terephthalate has an excellent conversion rate, and the lactic acid and 1,4-cyclohexanedicarboxylic acid in the products after degradation and conversion have high yields and purities.

[0049] Example

[0050] The following examples and comparative examples further illustrate the embodiments of the present application. Various tests and evaluations were performed according to the following methods. Unless otherwise specified, "parts" and "%" are by mass, "room temperature" refers to 25±5°C, and "about" or "~" refers to ±0.5.

[0051] Yield calculation: Yield = actual mass of synthesized product / theoretical mass of synthesized product × 100%.

[0052] Test methods and equipment

[0053] Qualitative and quantitative analysis of gas-phase products: Detected by online gas chromatograph (Agilent 8890) equipped with a thermal conductivity detector (TCD) and a hydrogen flame ionization (FID) detector;

[0054] Qualitative and quantitative analysis of liquid products: using maleic acid as internal standard, nuclear magnetic resonance ( 1 H NMR) analysis (Bruker AVANCE III 500 MHz NMR).

[0055] Example 1

[0056] (1) In a 250 mL stainless steel autoclave, 3 g of polyethylene terephthalate (PET) plastic bottle (weight-average molecular weight 50 kDa, cut into 0.5 cm × 0.5 cm dimensions), 8 g of NaOH, 100 mg of 5 wt% Ru / C catalyst (purchased from AlfaAesar), and 40 mL of methanol were added. The autoclave was heated to 160°C with constant stirring at 600 rpm for 10 hours.

[0057] When the system gauge pressure rose from 0 MPa to 1.2 MPa, it indicated that hydrogen was formed, and the hydrogen yield was approximately 103 mmol. After the temperature was cooled to room temperature, water was added to the reactor, and all the gas generated in the reactor was collected in another vacuum tank. At this stage, 1.1 g of sodium lactate (yield 63%) and 2.47 g of disodium terephthalate (yield 100%) were obtained.

[0058] (2) Open the reactor, add 100 mL of water and stir thoroughly, then separate the Ru / C catalyst by suction filtration. The catalyst is dried at 70°C and prepared for next use. Then, add 5 mol / L HCl aqueous solution to the reactor until the pH is less than 7, at which time terephthalic acid will precipitate. Centrifuge to obtain 2.38 g of terephthalic acid (purity of about 100%, yield of 97%). The supernatant is evaporated by vacuum rotary evaporation to remove water, and further separated and purified by ether extraction three times to obtain 0.74 g of lactic acid (purity of about 91%, yield of 55%). 1 H NMR (D2O) spectrum Figure 1 As shown;

[0059] The terephthalic acid and Ru / C catalyst separated above were washed three times with deionized water and then transferred back to the reactor together with 180 mL of water. The reactor was sealed and evacuated to remove the remaining air. The hydrogen stored in the vacuum tank was reintroduced into the reactor and reacted at 160° C. for 30 hours to complete the hydrogenation of the terephthalic acid.

[0060] After the temperature was cooled to room temperature, the system pressure dropped from 2.4 MPa to 0.3 MPa, and the Ru / C catalyst was further separated to finally obtain 2.16 g of 1,4-cyclohexanedicarboxylic acid (purity of about 100%, yield of 84%). 1 H NMR (D2O) spectrum Figure 2 shown.

[0061] Figure 3 The reaction process of upgrading the polyethylene terephthalate plastic bottle of Example 1 to lactic acid and 1,4-cyclohexanedicarboxylic acid is shown.

[0062] Combined with the results of Example 1 above, it can be seen that the method of the present application can simultaneously and directionally convert the monomers ethylene glycol and terephthalic acid of polyethylene terephthalate into lactic acid and 1,4-cyclohexanedicarboxylic acid, achieving a lactic acid yield of up to 55% and a purity of approximately 91% in the product after degradation and conversion; and a 1,4-cyclohexanedicarboxylic acid yield of up to 84% and a purity close to 100%.

[0063] Based on the above analysis, the method of the present application is used to degrade polyester plastics, achieving the degradation and conversion of polyester plastics using only a commercial catalyst without the need for external hydrogen, so that the monomers ethylene glycol and terephthalic acid of polyethylene terephthalate are simultaneously and directionally converted into high-value chemicals. Furthermore, polyethylene terephthalate has an excellent conversion rate, and the lactic acid and 1,4-cyclohexanedicarboxylic acid in the products after degradation and conversion have a high yield and purity. The method of the present application not only embodies the atomic economy of waste resource conversion, but also expands the possibility of recycling polyester plastics by combining plastic upgrading with one-carbon chemistry.

[0064] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for degrading polyester plastics, comprising: (1) reacting the polyester plastic, an alcoholysis agent, and a base under the action of a Ru / C catalyst to obtain a reaction mixture and hydrogen; Acidifying and separating the reaction mixture to obtain terephthalic acid and lactic acid; The mass ratio of the polyester plastic, the base and the Ru / C catalyst is 20-40:50-100:1; the mass volume ratio of the polyester plastic to the alcoholysis reagent is 50-100 g:1 L; the polyester plastic is selected from polyethylene terephthalate; (2) reacting the generated terephthalic acid and the hydrogen under the action of the Ru / C catalyst to obtain 1,4-cyclohexanedicarboxylic acid; The mass ratio of the terephthalic acid, the hydrogen and the Ru / C catalyst is 2-5:0.1-0.3:0.1-0.

5.

2. The method according to claim 1, wherein The alcoholysis reagent is selected from at least one of methanol and ethylene glycol.

3. The method according to claim 1, wherein The base is selected from at least one of NaOH, KOH, CaOH and CsOH.

4. The method according to claim 1, wherein The Ru / C catalyst is a 5-15 wt% Ru / C catalyst.

5. The method according to claim 1, wherein The reaction temperature of step (1) is 140-180° C., and the reaction time is 8-12 hours.

6. The method according to claim 1, wherein The reaction temperature of step (2) is 140-180° C., and the reaction time is 25-35 hours.

7. The method according to claim 1, wherein The acidification separation comprises: adding acid to the reaction mixture, adjusting the pH to less than 7, and separating to obtain terephthalic acid and lactic acid.

8. The method according to claim 7, wherein: The acid is selected from at least one of hydrochloric acid, sulfuric acid, formic acid and acetic acid.

9. The method according to claim 1, wherein: In step (2), a solvent is further added, and the mass volume ratio of the terephthalic acid to the solvent is 0.01-0.05 g:1 mL.

10. The method according to claim 9, wherein: The solvent is selected from at least one of water and methanol.

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