A supported catalyst for preparing oxalic acid by PET oxidative depolymerization and a preparation method and application thereof
By using the supported catalyst Au/TiO2 to catalyze the depolymerization of PET under alkaline conditions, the problems of low catalyst activity and poor stability in existing technologies have been solved. This has enabled the efficient and selective conversion of PET to oxalic acid, reducing byproducts and resource waste, and is suitable for the high-value utilization of complex plastic waste.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING AGRICULTURAL UNIVERSITY
- Filing Date
- 2026-01-30
- Publication Date
- 2026-06-19
AI Technical Summary
Existing PET oxidative depolymerization technologies suffer from problems such as low catalyst activity, poor stability, harsh reaction conditions, insufficient target selectivity, and difficulty in being applied to actual waste plastic systems, leading to resource waste and environmental pollution.
A supported catalyst, Au/TiO2, was used to load gold nanoparticles onto TiO2 via a deposition-precipitation method for the oxidative depolymerization of PET to prepare oxalic acid. Oxygen was used as the oxidant to carry out the catalytic oxidative depolymerization reaction under alkaline conditions.
It achieves highly selective conversion of PET to oxalic acid, with an oxalic acid yield of 96%, a selectivity of 98%, few byproducts, and a carbon balance of 100%. It reduces the requirements and costs of raw material pretreatment, is suitable for complex plastic waste, and has both environmental and economic benefits.
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Figure CN122230719A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of waste plastic recycling and resource utilization, specifically relating to a supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid and its preparation method, as well as a method for the efficient conversion of waste polyethylene terephthalate (PET) into oxalic acid through depolymerization catalytic oxidation using the supported catalyst. Background Technology
[0002] Polyethylene terephthalate (PET) is one of the most widely used synthetic polyesters globally, with extensive applications in packaging and textiles. However, over 80% of waste PET is not effectively recycled, with large quantities ending up in landfills or entering the natural environment, causing severe "white pollution" and resource waste, leading to serious environmental problems and carbon resource depletion. Therefore, developing efficient, environmentally friendly, and high-value-added PET recycling technologies is of significant environmental and economic importance.
[0003] Currently, PET recycling technologies mainly include mechanical recycling and chemical recycling. Mechanical recycling involves physical melting and regeneration, a simple process but with a significant decline in product performance, and is generally used for low-value-added products. Chemical recycling, on the other hand, degrades PET into monomers or small molecule compounds through depolymerization reactions, and is a key pathway for achieving high-value recycling of PET. However, traditional chemical recycling methods such as alcoholysis and hydrolysis have limitations such as high cost, harsh conditions, and low product value. Therefore, it is necessary to develop new, high-value PET recycling strategies. In recent years, catalytic oxidative depolymerization has attracted attention as an emerging chemical recycling method for PET. This method typically involves the selective oxidation of ethylene glycol units in PET into oxygen-containing small molecules, such as oxalic acid and glycolic acid, through the action of a catalyst in the presence of oxygen or air. Compared with traditional depolymerization methods, oxidative depolymerization has potential advantages such as mild reaction conditions, no need for hydrogen, and easy product separation. However, existing PET oxidative depolymerization technologies generally suffer from disadvantages such as low target selectivity, numerous by-products, harsh reaction conditions, high energy consumption, poor economic efficiency, and complex processes. Therefore, designing efficient supported and catalytic systems is crucial for the development of PET oxidative depolymerization technology. Summary of the Invention
[0004] The purpose of this invention is to solve the problems of low catalyst activity, poor stability, harsh reaction conditions, insufficient product selectivity, and difficulty in applying to actual waste plastic systems in the prior art, and to provide an efficient and stable PET oxidative depolymerization method to achieve highly selective conversion of waste PET into high-value-added oxalic acid.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] A supported catalyst (denoted as Au / TiO2) for the oxidative depolymerization of PET to prepare oxalic acid, wherein the supported catalyst uses TiO2 as a support and supports gold nanoparticles on the support; wherein the TiO2 is commercial anatase or rutile titanium dioxide; and the loading amount of gold nanoparticles is 0.1 to 3.0 wt.%.
[0007] Preferably, the loading of the gold nanoparticles is 1.0 wt.%.
[0008] The supported catalyst for the preparation of oxalic acid by oxidative depolymerization of PET is prepared by a deposition-precipitation method, comprising: adding an aqueous solution of chloroauric acid to a TiO2 emulsion and mixing it evenly; adjusting the pH of the mixture to alkaline and aging it at 60-90°C for 2-4 hours; centrifuging or filtering, washing, and drying; and heat-treating the obtained solid under a reducing atmosphere to obtain the supported catalyst.
[0009] The concentration of the chloroauric acid solution is 1–10 mg / mL.
[0010] The chloroauric acid solution was prepared using deionized water.
[0011] The TiO2 emulsion is a uniform emulsion formed by ultrasonic dispersion at a ratio of 1g TiO2 to 100mL deionized water.
[0012] Preferably, an aqueous solution of chloroauric acid is added to the TiO2 emulsion and stirred at room temperature for 0.5 to 1 hour to ensure uniform mixing.
[0013] Preferably, sodium hydroxide solution is used to adjust the pH of the mixture to 8-10.
[0014] Preferably, the washing is performed with water until the filtrate is neutral.
[0015] The reducing atmosphere is a mixture of hydrogen and one selected from nitrogen and an inert gas, with a hydrogen volume fraction of 3-10%.
[0016] The heat treatment temperature is 300-400℃, and the heat treatment time is 2-4 hours.
[0017] Preferably, the heat treatment involves placing the solid in a tube furnace and heating it to 300°C to 400°C at a heating rate of 5 to 10°C / min under a reducing atmosphere, and then treating it at 300°C to 400°C for 2 to 4 hours.
[0018] The application of the supported catalyst (Au / TiO2) described in this invention in the oxidative depolymerization of PET to prepare oxalic acid.
[0019] A method for converting waste polyethylene terephthalate into oxalic acid by depolymerization catalytic oxidation includes: adding the supported catalyst and waste PET to an alkaline solution, using oxygen as an oxidant, and catalytically oxidizing the PET to obtain oxalic acid.
[0020] In practice, the waste PET is usually crushed first, and then depolymerized and catalytically oxidized.
[0021] The alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 0.5–3.0 M; the alkali metal hydroxide is NaOH or KOH.
[0022] The molar ratio of the alkali metal hydroxide to PET (the relative molecular mass of PET is 192) is 5:1 to 20:1.
[0023] The ratio of the supported catalyst to the alkaline solution is 5:1 to 50:1 mg / mL.
[0024] The temperature of the depolymerization catalytic oxidation is 160-200℃, preferably 180℃, the time of the depolymerization catalytic oxidation is 3-10 hours, preferably 3-8 hours, and the oxygen pressure is 0.3-1 MPa, preferably 0.1-0.5 MPa.
[0025] The waste PET mentioned above includes PET plastic products that are discarded after consumption.
[0026] This invention utilizes a wet impregnation combined with hydrogen reduction method to prepare a supported catalyst Au / TiO2. The gold nanoparticles are uniformly dispersed, exhibiting high dispersibility and structural stability. Significant electronic interactions exist between TiO2 and Au nanoparticles, leading to the gain of electrons in Au and an increase in its outer electron cloud density. This enhances the adsorption capacity for reactants (such as ethylene glycol and oxygen). The Lewis acid sites in TiO2 form local electron transfer channels with the Au nanoparticles, promoting the stabilization and directional transformation of reaction intermediates.
[0027] This invention relates to the supported catalyst Au / TiO2 for the depolymerization and catalytic oxidation of waste PET. PET is first hydrolyzed under alkaline conditions to ethylene glycol and terephthalic acid. Simultaneously, using oxygen as an oxidant, Au / TiO2 selectively catalyzes the catalytic oxidation of ethylene glycol to oxalic acid (e.g., oxalic acid). Figure 1While maintaining complete PET conversion, the yield of oxalic acid can reach 96% under optimized conditions, with a selectivity of 98%, a carbon balance of 100%, and a total amount of byproducts (formic acid, glycolic acid, etc.) of less than 5%. This invention increases the oxalic acid selectivity from less than 80% reported in the industry to 90%, achieving high selective generation of the key product and significantly reducing side reactions and resource waste. The catalyst loaded in this invention exhibits excellent stability and is more suitable for complex plastic waste, reducing raw material pretreatment requirements and costs. The target product, oxalic acid, is a high-value-added chemical with an economic value far exceeding that of low-quality recycled plastics obtained through mechanical recycling or monomers from traditional chemical recycling.
[0028] Compared with existing catalysts and PET recycling processes, this invention utilizes a supported catalyst in an oxygen-containing atmosphere and alkaline aqueous solution system to achieve highly efficient and selective oxidative depolymerization of polyethylene terephthalate (PET), directionally converting it into oxalic acid. It exhibits significant and balanced superiority in multiple core dimensions, including catalytic performance, stability, process conditions, economic benefits, and environmental benefits. It features mild reaction conditions, no need for hydrogen, safe operation, and environmental friendliness. This invention not only provides a technical pathway for the efficient resource utilization of waste PET plastics but also aligns with the development requirements of green chemistry and the circular economy, possessing broad prospects for industrial application and providing an effective technical solution for the high-value resource utilization of waste plastics. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the oxidative depolymerization of PET into oxalic acid using an Au / TiO2 catalyst.
[0030] Figure 2 This is a scanning transmission electron microscope (STEM) image of Au / TiO2.
[0031] Figure 3 The image shows the X-ray powder diffraction pattern of Au / TiO2.
[0032] Figure 4 Comparison of X-ray photoelectron spectra of Au / TiO2 and gold / carbon (Au / C).
[0033] Figure 5 The yield and selectivity of oxalic acid preparation from PET by oxidation and depolymerization using different supported noble metal catalysts. Detailed Implementation
[0034] The technical solution and its effects of the present invention are described in detail below through a series of specific experimental and comparative examples. Unless otherwise specified, all examples use the same basic reaction apparatus: a 50 mL stainless steel high-pressure reactor with a polytetrafluoroethylene liner, equipped with a magnetic stirrer, pressure gauge, and electric heating temperature control system, and oxygen is introduced using an oxygen cylinder. The air inside the reactor is replaced with oxygen before the reaction.
[0035] The product was detected by liquid chromatography (Waters 2695). The chromatographic column was an Agilent SB-Aq (5μm, 4.6mm × 250mm), the UV detector (Waters 2417) was at a wavelength of 210nm, the mobile phase (5% methanol, 95% water, 20mM NaH2PO4, pH 2.5) was used, and the flow rate was 0.8mL / min. The reaction solution was diluted with the mobile phase, centrifuged and filtered before entering the liquid chromatography system for analysis.
[0036] The formulas for calculating PET conversion rate, oxalic acid selectivity and oxalic acid yield, and carbon balance are as follows (n is the amount of substance):
[0037] PET conversion rate = n 对苯二甲酸 / n PET ×100%;
[0038] Oxalic acid selectivity = [n 草酸 / ( n 草酸 +n 乙醇酸 + n 甲酸 )]×100%;
[0039] Oxalic acid yield = n 草酸 / n PET ×100%;
[0040] Carbon balance = (n 草酸 + n 乙醇酸 +n 甲酸 + n 乙二醇 ) / n PET ×100%.
[0041] Example 1
[0042] A method for preparing a supported catalyst for the oxidative depolymerization of waste PET to oxalic acid includes the following steps:
[0043] Step (1): Weigh 1g TiO2 into 100mL of deionized water and sonicate for 30 minutes to disperse it evenly to obtain a TiO2 emulsion; then, while stirring, add 4.3mL of chloroauric acid solution with a concentration of 4mg / mL to the TiO2 emulsion. After the addition is complete, continue stirring for 0.5h to mix evenly.
[0044] Step (2): Adjust the pH of the mixture obtained in step (1) to 9 using 0.2M NaOH solution, and age it at 80℃ for 2 hours;
[0045] Step (3): Centrifuge, wash the filter cake with deionized water until the filtrate is neutral, dry, and put the obtained solid powder into a tube furnace for heat treatment in a reducing atmosphere consisting of 5% hydrogen and 95% nitrogen by volume: heat from room temperature to 350℃ at a heating rate of 10℃ / min, and maintain at 350℃ for 3 hours to obtain Au / TiO2 supported catalyst, in which the loading of Au in Au / TiO2 supported catalyst is 1.0wt.%.
[0046] Scanning transmission electron microscopy images of Au / TiO2 are as follows: Figure 2 As shown in the figure, Au nanoparticles are uniformly distributed on the TiO2 support, and the particle size of the gold nanoparticles is about 5 nm.
[0047] X-ray powder diffraction pattern of Au / TiO2 supported catalyst as follows: Figure 3 As shown. Comparison of the X-ray powder diffraction pattern with the standard card reveals that the obtained diffraction peaks are consistent with the anatase TiO2 structure. Due to the small size and low loading of gold nanoparticles, no obvious Au diffraction peaks were observed in the spectrum.
[0048] By comparing the X-ray photoelectron spectra of Au / TiO2 and Au / C (Comparative Example 1) Figure 4 It was found that there is an electron transfer between Au and TiO2, with Au gaining electrons, which enhances its adsorption capacity for reactants and improves the catalyst's reaction activity.
[0049] Comparative Example 1
[0050] In Example 1, TiO2 was replaced with conductive carbon black XC-72, and the remaining steps were the same as in Example 1 to prepare the Au / C catalyst. The Au loading in the Au / C catalyst was 1.0 wt.%.
[0051] Comparative Example 2
[0052] The 4 mg / mL chloroauric acid solution in step (1) of Example 1 was replaced with a 2 mg / mL chloroplatinic acid solution, and the amount added was 10.5 mL. The remaining steps were the same as in Example 1 to prepare the Pt / TiO2 catalyst. The Pt loading in the Pt / TiO2 catalyst was 1.0 wt.%.
[0053] Comparative Example 3
[0054] The 4 mg / mL chloroauric acid solution in step (1) of Example 1 was replaced with a 5 mg / mL chloropalladium acid solution, and the amount added was 4.7 mL. The remaining steps were the same as in Example 1 to prepare the Pd / TiO2 catalyst. The Pd loading in the Pd / TiO2 catalyst was 1.0 wt.%.
[0055] Comparative Example 4
[0056] The 4 mg / mL chloroauric acid solution in step (1) of Example 1 was replaced with a 10 mg / mL ruthenium chloride solution, and the amount added was 2 mL. The remaining steps were the same as in Example 1, and the Ru / TiO2 catalyst was prepared. The Ru loading in the Ru / TiO2 catalyst was 1.0 wt.%.
[0057] Example 2
[0058] The following steps were taken to evaluate the performance of different supported noble metal catalysts on the oxidative depolymerization of PET:
[0059] 100 mg of different supported noble metal catalysts and 192 mg of waste PET bottle powder were added to 10 mL of 2M NaOH solution. The mixture was then placed in a high-pressure reactor, oxygen was introduced to a pressure of 0.3 MPa, the reaction temperature was set to 180 °C, and the reaction was carried out for 3 h with stirring. After the reaction, the results were analyzed by liquid chromatography. The experimental performance of different catalysts on the oxidative depolymerization reaction of PET is as follows: Figure 5 As shown in Table 1, the activity of Au / TiO2 is the best among all noble metal supported catalysts.
[0060] Table 1. Results of experimental performance evaluation of different catalysts on the oxidative depolymerization reaction of PET
[0061]
Claims
1. A supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid, characterized in that: The supported catalyst uses TiO2 as a support to load gold nanoparticles onto the support; wherein the TiO2 is anatase or rutile titanium dioxide; and the loading amount of gold nanoparticles is 0.1 to 3.0 wt.%.
2. The supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid according to claim 1, characterized in that: The loading of the gold nanoparticles is 1.0 wt.%.
3. The supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid according to claim 1 or 2, characterized in that: The supported catalyst is prepared by a deposition-precipitation method, comprising: adding an aqueous chloroauric acid solution to a TiO2 emulsion and mixing thoroughly; adjusting the pH of the mixture to alkaline and aging at 60–90°C for 2–4 hours; centrifuging or filtering, washing, and drying; and subjecting the obtained solid to heat treatment under a reducing atmosphere to obtain the supported catalyst.
4. The supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid according to claim 3, characterized in that: The concentration of the chloroauric acid solution is 1–10 mg / mL; the TiO2 emulsion is a uniform emulsion formed by ultrasonic dispersion at a ratio of TiO2 to deionized water of 1 g: 100 mL.
5. The supported catalyst for the oxidative depolymerization of PET to prepare oxalic acid according to claim 3, characterized in that: The reducing atmosphere is a mixture of hydrogen and one selected from nitrogen and an inert gas, with a hydrogen volume fraction of 3-10%; the heat treatment temperature is 300-400°C, and the heat treatment time is 2-4 hours.
6. The application of the supported catalyst according to claim 1 in the preparation of oxalic acid by oxidative depolymerization of polyPET.
7. A method for converting waste PET into oxalic acid through depolymerization and catalytic oxidation, characterized in that: include: The supported catalyst described in claim 1 and waste PET are added to an alkaline solution, and oxalic acid is obtained by depolymerization catalytic oxidation of PET using oxygen as an oxidant.
8. The method for converting waste PET into oxalic acid by depolymerization catalytic oxidation according to claim 7, characterized in that: The alkaline solution is an aqueous solution of an alkali metal hydroxide with a concentration of 0.5–3.0 M; the alkali metal hydroxide is NaOH or KOH; and the molar ratio of the alkali metal hydroxide to PET is 5:1–20:
1.
9. The method for converting waste PET into oxalic acid by depolymerization catalytic oxidation according to claim 7, characterized in that: The ratio of the supported catalyst to the alkaline solution is 5:1 to 50:1 mg / mL.
10. The method for converting waste PET into oxalic acid by depolymerization catalytic oxidation according to claim 7, characterized in that: The temperature of the depolymerization catalytic oxidation is 160-200℃, preferably 180℃, the time of the depolymerization catalytic oxidation is 3-10 hours, preferably 3-8 hours, and the oxygen pressure is 0.3-1 MPa, preferably 0.1-0.5 MPa.