A method for catalytic conversion of oxygen-containing waste plastics into benzoic acid monomers

Abstract

The application belongs to the technical field of high-value utilization of waste plastics, and discloses a method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers. The CeO2 catalyst supported on the Nb2O5 carrier with a special crystal form is used, and hydrogen peroxide is used as a solvent, so that the oxygen-containing waste plastics are catalytically converted into benzoic acid, terephthalic acid, o-phthalic acid and other benzoic acid monomers. The application provides a process route for directional oxidative depolymerization of oxygen-containing waste plastics into small molecular compounds, and solves the problems of difficult depolymerization, poor selectivity of depolymerization products and low added value of the oxygen-containing waste plastics in the prior art. The obtained benzoic acid monomers can be re-applied in the synthesis of plastics, so that the green cycle of the plastic synthesis process is realized.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization technology of waste plastics, and in particular to a method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers. Background Technology

[0002] Plastic materials, represented by aromatic polymers such as polyethylene terephthalate (PET), polycarbonate (PC), polyetheretherketone (PEEK), and polyphenylene oxide (PPO), possess excellent properties such as low density, ease of processing, high performance, and multifunctionality, and are widely used in various sectors of the national economy. However, with the increasing use of plastic products, oxygen-containing waste plastics have become a global environmental problem.

[0003] Currently, methods for treating oxygen-containing waste plastics include landfill, incineration, mechanical recycling, and catalytic pyrolysis. Landfill and incineration cannot fundamentally solve the environmental pollution problem, and mechanical recycling reduces the quality of recycled plastics. While catalytic pyrolysis can convert oxygen-containing waste plastics into hydrocarbon liquid fuels, it requires expensive hydrogen gas, and the catalysts often use precious metals such as ruthenium and platinum, significantly increasing processing costs. Furthermore, the resulting products have a very complex composition and low added value, making them difficult to use directly in plastic synthesis. Therefore, developing an efficient catalytic reaction process for oxygen-containing waste plastics, allowing the products to be directly applied to plastic synthesis, would not only help reduce emissions of oxygen-containing waste plastics but also reduce the plastics industry's dependence on fossil fuels.

[0004] Terephthalic acid and phthalic acid are major organic raw materials for the production of polyester fiber plastics such as PET. In modern industry, terephthalic acid and phthalic acid are mainly produced by the liquid-phase oxidation of p-xylene from the petrochemical industry. The highly selective conversion of aromatic polymers such as PET, PC, PEEK, and PPO into benzoic acid, terephthalic acid, and phthalic acid is technically challenging. This is mainly because the reaction requires a catalyst with high catalytic activity to break the CO ether bonds in these polymers, while ensuring that the resulting monomer molecules do not undergo further oxidation reactions that would affect the product selectivity. To date, there are no reports on catalytic reaction systems for the one-step catalytic conversion of plastics such as PET, PC, PEEK, and PPO into benzoic acid, terephthalic acid, and phthalic acid. Summary of the Invention

[0005] The purpose of this invention is to provide a method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers, in order to solve the problems of difficulty in depolymerization of oxygen-containing waste plastics, poor selectivity of depolymerization products, low added value, and difficulty in directly using the products obtained from the treatment of oxygen-containing waste plastics in the synthesis of plastics.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers, comprising the following steps:

[0008] The reaction of oxygen-containing waste plastics, catalysts and solvents yields benzoic acid monomers.

[0009] The catalyst is a CeO2 / Nb2O5 catalyst supported on Nb2O5.

[0010] Preferably, the oxygen-containing waste plastic includes one or more of polyethylene terephthalate, polycarbonate, polyetheretherketone, and polyphenylene ether; the solvent is hydrogen peroxide.

[0011] Preferably, the mass ratio of the oxygen-containing waste plastic to the catalyst is 1:0.05 to 1; the concentration of the oxygen-containing waste plastic in the mixture of oxygen-containing waste plastic and solvent is 1 to 50 g / L; and the mass fraction of the solvent is 1 to 10%.

[0012] Preferably, the reaction temperature is 200–300°C, the reaction time is 0.5–12 h, the reaction pressure is 6–12 MPa, and the reaction stirring rate is 200–1000 r / min.

[0013] As a preferred method, after the reaction is complete, the products obtained are sequentially filtered and rotary evaporated to obtain benzoic acid monomers.

[0014] Preferably, the benzoic acid monomers include one or more of benzoic acid, terephthalic acid, and phthalic acid.

[0015] Preferably, the preparation of the catalyst includes the following steps:

[0016] Niobium salt, ammonium oxalate, and water were mixed to obtain a mixture; the mixture was subjected to crystallization reaction and calcination in sequence to obtain Nb2O5 support; the Nb2O5 support was impregnated in Ce(NO3)3·6H2O solution, and after impregnation, it was subjected to drying and heat treatment in sequence to obtain CeO2 / Nb2O5 catalyst.

[0017] Preferably, the niobium salt is niobium oxalate; in the mixture of niobium salt and water, the concentration of niobium salt is 0.05-0.4 mol / L; the amount of ammonium oxalate used is such that the pH of the mixture is 0.5-1.

[0018] Preferably, the crystallization reaction temperature is 200–260°C, the crystallization reaction time is 2–24 h, and the crystallization reaction pressure is 5–10 MPa; the calcination temperature is 400–600°C, and the calcination time is 2–6 h.

[0019] Preferably, the concentration of the Ce(NO3)3·6H2O solution is 0.2–1 mol / L; the impregnation time is 2–12 h; the drying temperature is 80–150 °C and the drying time is 30–50 min; the heat treatment temperature is 400–600 °C and the heat treatment time is 2–6 h; and the mass fraction of Ce in the CeO2 / Nb2O5 catalyst is 1–20%.

[0020] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The CeO2 / Nb2O5 catalyst provided by the present invention is synthesized into a Nb2O5 support with a special crystal form under hydrothermal conditions; (1) the support can make the catalyst have a high specific surface area, provide more acid centers, and is beneficial to improve the depolymerization ability of CO bonds in plastics; (2) it can provide suitable coordinated unsaturated Nb centers and oxygen vacancies, which is beneficial to the directional adsorption and activation of oxygen-containing functional groups in plastics during depolymerization reaction, thereby improving the selectivity of target products; (3) the CeO2 active center has excellent oxygen storage and release capacity, which can better activate oxygen in hydrogen peroxide and improve the oxidative depolymerization ability of plastics;

[0022] 2. The method provided by this invention for catalytically converting oxygen-containing waste plastics into monomers such as benzoic acid, terephthalic acid and phthalic acid uses non-precious metal elements Nb and Ce in the catalyst, hydrogen peroxide as the solvent, no inorganic acids or bases or organic solvents are added to the reaction system, no precious metal catalysts are used, no additional H2 is consumed, and the process cost is low.

[0023] 3. The method provided by this invention for catalytically converting oxygen-containing waste plastics into monomers such as benzoic acid, terephthalic acid, and phthalic acid can be achieved in a one-step reaction by converting oxygen-containing waste plastics such as polyethylene terephthalate, polycarbonate, polyetheretherketone, and polyphenylene ether into monomers such as benzoic acid, terephthalic acid, and phthalic acid. The obtained terephthalic acid and phthalic acid can be directly used in the synthesis of plastics, thereby improving the green circular economy level of oxygen-containing waste plastics. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 The image shows the XRD pattern of the Nb2O5 support described in Example 1. Detailed Implementation

[0026] This invention provides a method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers, comprising the following steps:

[0027] The reaction of oxygen-containing waste plastics, catalysts and solvents yields benzoic acid monomers.

[0028] The catalyst is a CeO2 / Nb2O5 catalyst supported on Nb2O5.

[0029] In this invention, the oxygen-containing waste plastic is preferably one or more of polyethylene terephthalate (PET), polycarbonate (PC), polyetheretherketone (PEEK), and polyphenylene ether (PPO); the solvent is preferably hydrogen peroxide.

[0030] In this invention, the mass ratio of the oxygen-containing waste plastic to the catalyst is preferably 1:0.05 to 1, more preferably 1:0.1 to 0.9; in the mixture of oxygen-containing waste plastic and solvent, the concentration of the oxygen-containing waste plastic is preferably 1 to 50 g / L, more preferably 8 to 25 g / L; the mass fraction of the solvent is preferably 1 to 10%, more preferably 4 to 9%.

[0031] In this invention, the reaction temperature is preferably 200-300℃, more preferably 250-270℃; the reaction time is preferably 0.5-12h, more preferably 1-4h; the reaction pressure is preferably 6-12MPa, more preferably 8-10MPa; and the reaction stirring rate is preferably 200-1000r / min, more preferably 400-600r / min.

[0032] In this invention, after the reaction is completed, the product obtained from the reaction is sequentially filtered and rotary evaporated to obtain benzoic acid monomers; wherein, the filtration is performed using filter paper; the purpose of filtration is to remove the solid catalyst; the temperature of rotary evaporation is preferably 80-100℃, more preferably 90-95℃; the time of rotary evaporation is preferably 2-4h, more preferably 3-3.5h; the purpose of rotary evaporation is to remove the solvent.

[0033] In this invention, the benzoic acid monomers are preferably one or more of benzoic acid, terephthalic acid and phthalic acid.

[0034] In this invention, the preparation of the catalyst includes the following steps:

[0035] Niobium salt, ammonium oxalate, and water were mixed to obtain a mixture; the mixture was subjected to crystallization reaction and calcination in sequence to obtain Nb2O5 support; the Nb2O5 support was impregnated in Ce(NO3)3·6H2O solution, and after impregnation, it was subjected to drying and heat treatment in sequence to obtain CeO2 / Nb2O5 catalyst.

[0036] In this invention, the niobium salt is preferably niobium oxalate; in the mixture of niobium salt and water, the concentration of niobium salt is preferably 0.05-0.4 mol / L, more preferably 0.2-0.35 mol / L; the amount of ammonium oxalate is preferably such that the pH value of the mixture is 0.5-1, more preferably 0.7-0.9.

[0037] In this invention, the crystallization reaction temperature is preferably 200–260°C, more preferably 220–250°C; the crystallization reaction time is preferably 2–24 h, more preferably 6–12 h; the crystallization reaction pressure is preferably 5–10 MPa, more preferably 6–8 MPa; the calcination temperature is preferably 400–600°C, more preferably 500–550°C; and the calcination time is preferably 2–6 h, more preferably 4–5 h.

[0038] In this invention, after the crystallization reaction is completed, the product obtained from the crystallization reaction is sequentially filtered, washed and dried; the filtration is carried out using filter paper; the reagent used for washing is preferably water; the number of washings is preferably 1 to 3 times, more preferably 2 times; the drying temperature is preferably 80 to 150°C, more preferably 90 to 120°C; the drying time is preferably 30 to 50 minutes, more preferably 40 to 45 minutes.

[0039] In this invention, the concentration of the Ce(NO3)3·6H2O solution is preferably 0.2–1 mol / L, more preferably 0.4–0.7 mol / L; the impregnation time is preferably 2–12 h, more preferably 5–10 h; the drying temperature is preferably 80–150 °C, more preferably 100–120 °C; the drying time is preferably 30–50 min, more preferably 35–45 min; the heat treatment temperature is preferably 400–600 °C, more preferably 450–550 °C; the heat treatment time is preferably 2–6 h, more preferably 3–5 h; and the mass fraction of Ce in the CeO2 / Nb2O5 catalyst is preferably 1–20%, more preferably 5–12%.

[0040] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0041] Examples 1-9

[0042] The preparation methods of the CeO2 / Nb2O5 catalysts in Examples 1-9 are as follows:

[0043] (1) Niobium oxalate was dissolved in water to obtain an aqueous solution of niobium oxalate; the pH of the aqueous solution of niobium oxalate was adjusted with ammonium oxalate to obtain a mixture;

[0044] (2) The mixture was placed in a closed high-pressure reactor and crystallized under a pressure of 10 MPa. After the reaction was completed, the product was filtered with filter paper, washed with water three times, dried at 100°C for 40 min, and finally calcined at 500°C for 5 h to obtain Nb2O5 support.

[0045] (3) The Nb2O5 support was impregnated in a Ce(NO3)3·6H2O solution with a concentration of 0.5mol / L. After impregnation, it was dried at 100℃ for 40min and then heat-treated at 500℃ for 4h to obtain the CeO2 / Nb2O5 catalyst.

[0046] The preparation process parameters of the CeO2 / Nb2O5 catalysts in Examples 1-9 are shown in Table 1:

[0047] Table 1. Preparation process parameters of CeO2 / Nb2O5 catalysts in Examples 1-9

[0048]

[0049]

[0050] The CeO2 / Nb2O5 catalysts obtained in Examples 1 to 9 are respectively designated as A to I.

[0051] Examples 10-20

[0052] The methods for preparing benzoic acid monomers using oxygen-containing waste plastics in Examples 10-20 are as follows:

[0053] Oxygen-containing waste plastics and CeO2 / Nb2O5 catalyst were dispersed in 100 mL of hydrogen peroxide and then placed in a 300 mL sealed high-pressure reactor. The reaction was carried out under the conditions of 6 MPa pressure and 500 r / min stirring rate. After the reaction was completed, the product was filtered with filter paper, and the filtrate was rotary evaporated at 90 °C for 4 h to obtain benzoic acid monomers.

[0054] The method parameters for obtaining benzoic acid monomers in Examples 10-20 are shown in Table 2:

[0055] Table 2. Method parameters for obtaining benzoic acid monomers in Examples 10-20

[0056]

[0057]

[0058] Comparative Example 1

[0059] The crystallization temperature of the CeO2 / Nb2O5 catalyst prepared in Example 10, which was 220°C, was replaced with a crystallization temperature of 180°C. All other conditions were the same as in Example 10.

[0060] As can be seen from Example 10 and Comparative Example 1, when a lower crystallization temperature is used, it is impossible to obtain a CeO2 / Nb2O5 catalyst with a special crystal form, and it is impossible to catalytically convert oxygen-containing waste plastics into products such as benzoic acid, terephthalic acid and phthalic acid.

[0061] Comparative Example 2

[0062] The crystallization temperature of the CeO2 / Nb2O5 catalyst prepared in Example 10, which was 220°C, was replaced with a crystallization temperature of 280°C. All other conditions were the same as in Example 10.

[0063] As can be seen from Example 10 and Comparative Example 2, when a higher crystallization temperature is used, it is impossible to obtain CeO2 / Nb2O5 catalyst with a special crystal form, and the product yield is very low in the reaction of oxygen-containing waste plastics catalytically converted into products such as benzoic acid, terephthalic acid and phthalic acid.

[0064] Comparative Example 3

[0065] The pH value of the CeO2 / Nb2O5 catalyst prepared in Example 10 was replaced with pH value 2 instead of 1, and the rest was the same as in Example 10.

[0066] As can be seen from Example 10 and Comparative Example 3, when a higher pH value is used, it is impossible to obtain CeO2 / Nb2O5 catalyst with special crystal form, and the product yield is very low in the reaction of oxygen-containing waste plastics catalytically converted into products such as benzoic acid, terephthalic acid and phthalic acid.

[0067] Comparative Example 4

[0068] In Example 10, the concentration of niobium oxalate aqueous solution of the CeO2 / Nb2O5 catalyst prepared in Example 1 was replaced with a concentration of niobium oxalate aqueous solution of 0.02 mol / L, and the rest was the same as in Example 10.

[0069] As can be seen from Example 10 and Comparative Example 4, when a lower niobium concentration is used, it is impossible to obtain a CeO2 / Nb2O5 catalyst with a special crystal form, and the product yield is very low in the reaction of oxygen-containing waste plastics catalytically converted into products such as benzoic acid, terephthalic acid and phthalic acid.

[0070] Comparative Example 5

[0071] The crystallization time of the CeO2 / Nb2O5 catalyst prepared in Example 10 was changed from 12h to 1h, and the rest was the same as in Example 10.

[0072] As can be seen from Example 10 and Comparative Example 5, when a shorter crystallization time is used, it is impossible to obtain CeO2 / Nb2O5 catalyst with special crystal form, and the product yield is very low in the reaction of oxygen-containing waste plastics catalytically converted into products such as benzoic acid, terephthalic acid and phthalic acid.

[0073] Comparative Example 6

[0074] In Example 10, the Ce mass fraction of the CeO2 / Nb2O5 catalyst prepared in Example 1 was replaced with 0.5% Ce mass fraction instead of 5%, and the rest was the same as in Example 10.

[0075] As can be seen from Example 10 and Comparative Example 6, when a lower Ce loading is used, the CeO2 / Nb2O5 catalyst has lower activity, and its product yield is also very low in the reaction of oxygen-containing waste plastics catalytically converted into products such as benzoic acid, terephthalic acid and phthalic acid.

[0076] Comparative Example 7

[0077] The 4% hydrogen peroxide mass fraction in Example 10 was replaced with 0.5% hydrogen peroxide mass fraction, and everything else was the same as in Example 10.

[0078] As can be seen from Example 10 and Comparative Example 7, when the hydrogen peroxide concentration is too low, the yield of CeO2 / Nb2O5 catalyst in the reaction of oxygen-containing waste plastics to benzoic acid, terephthalic acid and phthalic acid is very low.

[0079] Comparative Example 8

[0080] The reaction temperature of 250°C in Example 10 was replaced with a reaction temperature of 180°C, and everything else was the same as in Example 10.

[0081] As can be seen from Example 10 and Comparative Example 8, when the reaction temperature is too low, the yield of CeO2 / Nb2O5 catalyst in the catalytic conversion of oxygen-containing waste plastics into products such as benzoic acid, terephthalic acid and phthalic acid is very low.

[0082] Comparative Example 9

[0083] The reaction time of 1 hour in Example 10 was replaced with a reaction time of 0.5 hours, and everything else was the same as in Example 10.

[0084] As can be seen from Example 10 and Comparative Example 9, when the reaction time is too short, the yield of CeO2 / Nb2O5 catalyst in the catalytic conversion of oxygen-containing waste plastics into products such as benzoic acid, terephthalic acid and phthalic acid is very low.

[0085] The benzoic acid monomers obtained in Examples 10-20 and Comparative Examples 1-9 were tested for product type and yield. The test methods are as follows:

[0086] The tests were performed using an Agilent Technologies 8890 gas chromatograph (GC). The liquid products of benzoic acid monomers obtained in Examples 10-20 and Comparative Examples 1-3 were qualitatively and quantitatively analyzed by GC. The injection port temperature was 240°C, the column temperature was 80°C for 5 min, then increased to 240°C at a rate of 10°C / min and held for 15 min. A Restek RTX-5Sil capillary column (30 m long, 0.025 mm diameter) with a film thickness of 0.25 μm was used. He was used as the carrier gas, the column flow rate was 0.5 mL / min, and an FID detector was used at a temperature of 250°C. Product yield = m (产物) / m (原料) ×100%, where m (产物) and m (原料) The values ​​are the mass (g) of the product quantified in gas chromatography and the mass (g) of the waste oxygen-containing plastic added before the reaction, respectively. The results are shown in Table 3.

[0087] Table 3. Types of benzoic acid monomers obtained in Examples 10-20 and Comparative Examples 1-9, and their corresponding product yields.

[0088]

[0089]

[0090] As shown in Table 3, this invention can convert oxygen-containing waste plastics such as PET, PC, PEEK, and PPO into benzoic acid, terephthalic acid, and phthalic acid through a one-step reaction. The benzoic acid, terephthalic acid, and phthalic acid obtained using the method described in this invention have high yields. Among them, terephthalic acid and phthalic acid can be directly used in the synthesis of plastics, improving the green circular economy level of oxygen-containing waste plastics.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers, characterized in that, Includes the following steps: The reaction of oxygen-containing waste plastics, catalysts and solvents yields benzoic acid monomers. The catalyst is a CeO2 / Nb2O5 catalyst supported on Nb2O5. The oxygen-containing waste plastic is polyethylene terephthalate; the solvent is hydrogen peroxide; and the mass fraction of the solvent is 1-10%. The reaction temperature is 200~300℃, the reaction time is 1~12h, and the reaction pressure is 6~12MPa; The preparation of the catalyst includes the following steps: Niobium salt, ammonium oxalate and water were mixed to obtain a mixture; the mixture was subjected to crystallization reaction and calcination in sequence to obtain Nb2O5 support; the Nb2O5 support was impregnated in Ce(NO3)3·6H2O solution, and after impregnation, it was subjected to drying and heat treatment in sequence to obtain CeO2 / Nb2O5 catalyst; In the mixture of niobium salt and water, the concentration of niobium salt is 0.05~0.4 mol / L; the amount of ammonium oxalate used is such that the pH of the mixture is 0.5~1; The crystallization reaction temperature is 200~260℃, the crystallization reaction time is 2~24h, and the crystallization reaction pressure is 5~10MPa; In the CeO2 / Nb2O5 catalyst, the mass fraction of Ce is 1~20%; The benzoic acid monomer is terephthalic acid.

2. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 1, characterized in that, The mass ratio of the oxygen-containing waste plastic to the catalyst is 1:0.05~1; the concentration of the oxygen-containing waste plastic in the mixture of oxygen-containing waste plastic and solvent is 1~50g / L.

3. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 1 or 2, characterized in that, The stirring rate of the reaction is 200~1000 r / min.

4. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 3, characterized in that, After the reaction was completed, the products were sequentially filtered and rotary evaporated to obtain benzoic acid monomers.

5. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 4, characterized in that, The niobium salt is niobium oxalate.

6. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 5, characterized in that, The calcination temperature is 400~600℃, and the calcination time is 2~6h.

7. The method for catalytically converting oxygen-containing waste plastics into benzoic acid monomers according to claim 6, characterized in that, The concentration of the Ce(NO3)3·6H2O solution is 0.2~1mol / L; the impregnation time is 2~12h; the drying temperature is 80~150℃ and the drying time is 30~50min; the heat treatment temperature is 400~600℃ and the heat treatment time is 2~6h.

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