Recovery technology of selective electrooxidation PET plastic powder based on synergistic effect of silver and ferronickel layered double hydroxides
By loading Ag/NiFe-LDH catalyst on nickel foam, optimizing PET hydrolysis and electrocatalytic reactions, the problems of low conversion efficiency and poor selectivity of PET hydrolysis products were solved, and efficient selective oxidation recovery of formate and glycolate was achieved, which reduced energy consumption and promoted the resource utilization of PET.
Patent Information
- Application Number
- CN202510961258.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-13
- Publication Date
- 2025-10-03
AI Technical Summary
In the existing technology, the conversion efficiency and selectivity of PET hydrolysis products are low, and the traditional electrocatalysts are insufficiently stable, making it difficult to efficiently recycle PET plastic resources.
Ag/NiFe-LDH synergistic catalyst was loaded on nickel foam, and the alkaline hydrolysis conditions of PET and the electrocatalytic reaction were optimized to prepare a highly efficient selective oxidation and recovery of formate and glycolate.
Highly selective and stable electrocatalysis was achieved, increasing the selectivity of glycolic acid to 15% and the selectivity of formic acid to 80%, reducing energy consumption, promoting the generation of HER, reducing plastic pollution and realizing resource utilization.
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Figure CN120738692A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of waste plastic resource recovery, and in particular to a PET powder selective electrooxidation technology based on the synergistic effect of silver and nickel-iron layered double hydroxide. Background Art
[0002] Plastics are synthetic polymers. Due to their stable physical and chemical properties, such as oxidation resistance, low density, and good ductility, they are widely used in daily necessities, food, medicine, agriculture, construction, and chemical industries, becoming indispensable materials in human production and life. However, while plastics bring us great convenience, they also cause serious environmental pollution.
[0003] Among different types of plastics, polyethylene terephthalate (PET) has become one of the world's most important plastic materials. As of 2019, the cumulative global production of PET has exceeded one billion tons. This large amount of PET plastic needs to be properly disposed of after use to avoid any impact on the environment and ecosystem.
[0004] As a polyester material, PET can be recycled by breaking down its ester bonds through alcoholysis or hydrolysis. During alkaline hydrolysis, ethylene glycol (EG) and terephthalate (TPA) are the primary decomposition products of PET. Electrocatalytic oxidation technology, powered by renewable electricity, can convert EG into oxygenated compounds (C1 (formic acid) and C2 (glycolic acid, oxalic acid, etc.) at the positive electrode under mild conditions. EG has a low theoretical oxidation potential and can displace the oxygen evolution reaction (OER) during electrolysis while promoting hydrogen evolution reaction (HER) production at the negative electrode.
[0005] Economic analysis indicates that upcycling waste PET can generate a net profit of approximately $3,500. However, conventional electrocatalysts suffer from poor selectivity (for example, the selectivity of pure Ni-based catalysts for glycolic acid is less than 5%) and instability. Therefore, the development of efficient and highly selective electrocatalytic technologies is crucial for the recycling of waste PET. In particular, finding highly effective electrocatalysts is crucial for the resource recovery of PET. Summary of the Invention
[0006] Purpose of the present invention:
[0007] To overcome the problems of low conversion efficiency and poor selectivity of PET hydrolyzate in the existing technology, the present invention provides a PET electro-oxidation technology with Ag / NiFe-LDH synergistic catalysis supported on nickel foam (NF), which realizes a selective oxidation recovery method for the efficient preparation of formate and glycolate.
[0008] Technical solution:
[0009] This technology mainly includes three core technologies:
[0010] PET Hydrolysis: We explored optimal alkaline hydrolysis conditions for PET to maximize EM production. PET powder (0.4-1.2 g, 50 μm particle size) was added to a 1% KOH solution and stirred at 40-80°C for 12-28 hours. The optimal conditions were 60°C for 24 hours and 1.0 g PET / 100 mL KOH. HPLC analysis confirmed the production of 0.34 M ethylene glycol.
[0011] Electrocatalytic reaction: A three-electrode electrolytic cell (open type) was used, with the working electrode being an Ag / NiFe-LDH / NF composite electrode, the reference electrode being Hg / HgO, and the counter electrode being a platinum wire. The electrolyte was a PET alkaline hydrolysis solution, and the electrocatalytic reaction was carried out at a voltage of 1.5 V (vs. RHE), with a current density of up to 120 mA cm -2 .
[0012] Product analysis and detection: Qualitative and quantitative analysis of products such as formate and glycolate in the electrolyte is performed using an ion chromatograph (such as Alexlab AS2000).
[0013] Preparation of core electrode:
[0014] NF cleaning: A 2×2 cm piece of NF was cleaned in anhydrous ethanol and deionized water, respectively, and ultrasonically treated in 3 M hydrochloric acid, and then dried in a vacuum drying oven at 60°C for later use.
[0015] Preparation of NiFe-LDH / NF: The above-mentioned NF was placed in 60 mL of aqueous solution containing 1 mmol Ni(NO3)2·6H2O, 1 mmol Fe(NO3)3·9H2O, 5 mmol NH4F and 5 mmol urea, and hydrothermally reacted at 120°C for 12 hours. After drying, a nanosheet array structure was obtained.
[0016] Preparation of Ag / NiFe-LDH / NF: The above-mentioned NiFe-LDH / NF was immersed in a solution of 0.42 g AgNO3 dissolved in 100 mL deionized water and irradiated with a 500 W xenon lamp for 1 hour. Ag nanoparticles were deposited on the surface of NiFe-LDH to form a composite electrode.
[0017] Preparation of Ag / NF: The cleaned NF was immersed in a solution of 0.42 g AgNO3 dissolved in 100 mL deionized water and irradiated with a 500 W xenon lamp for 1 hour. Ag nanoparticles were deposited on the NF surface to form a composite electrode.
[0018] Beneficial effects:
[0019] Synergistic catalytic effect: The synergistic effect of Ag and NiFe-LDH improves the selectivity for glycolic acid (Faraday efficiency is about 15%) and the Faradaic efficiency for formic acid is about 80%.
[0020] Excellent stability: after 24 hours of constant current testing, the current density remains at 50% of the initial value, which is better than similar electrodes;
[0021] Low energy consumption: Compared with the traditional hydrogen production coupled with oxidation reaction by water electrolysis, EGOR reduces the overall energy consumption and promotes the generation of HER by replacing the high overpotential OER;
[0022] Environmentally friendly: Realize resource utilization of waste PET, reduce plastic pollution, and the product can be reused as chemical raw materials. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 Schematic diagram of alkaline hydrolysis and electrochemical recovery of PET plastic powder;
[0024] Figure 2 (a) HPLC curves at different temperatures, (b) different hydrolysis times, and (c) different PET powder addition amounts. (d) EG standard curve. (e) Ethylene glycol (EG) yields after PET hydrolysis under different conditions.
[0025] Figure 3 . Flowchart for the preparation of NiFe-LDH / NF and Ag / NiFe-LDH / NF;
[0026] Figure 4 XRD patterns of the prepared Ag / NF, NiFe-LDH / NF and Ag / NiFe-LDH / NF catalysts;
[0027] Figure 5 Representative SEM images and EDS elemental spectra of NiFe-LDH / NF;
[0028] Figure 6 Representative SEM images and EDS elemental spectra of Ag / NiFe-LDH / NF;
[0029] Figure 7 Representative SEM images and EDS elemental spectra of Ag / NF;
[0030] Figure 8 (a) Linear sweep voltammetry (LSV) curves of the four electrode materials in PET hydrolysate. (b) LSV curves of the Ag / NiFe-LDH / NF electrode in PET hydrolysate and 1 M KOH solution.
[0031] Figure 9 (a) 24-hour galvanostatic (CA) test of the four electrodes. (b) Ion chromatography (IC) spectra of the electrolyte after the 24-hour test. (c) Concentrations of formic acid and glycolic acid and their corresponding Faradaic efficiencies.
[0032] Text description of the attached figure
[0033] Figure 1 The patent of the present invention shows a schematic diagram of resource recovery based on the decomposition of PET plastic into terephthalic acid (TPA) and ethylene glycol (EG) in a solution containing 1M KOH and the electrocatalytic oxidation of ethylene glycol (EG).
[0034] Figure 2 Different conditions for PET hydrolysis to obtain the highest EG concentration were explored. First, the EG yield was optimized by hydrolyzing PET powder under different conditions (temperatures of 40, 50, 60, 70, and 80°C, hydrolysis times of 12, 16, 20, 24, and 28 hours, PET powder masses of 0.4, 0.6, 0.8, 1.0, and 1.2 g, and a fixed KOH volume of 100 ml). Subsequently, the hydrolyzed products were analyzed by high-performance liquid chromatography (HPLC). Figure 2 As shown in abc, it was found that the peaks under three conditions appeared at 15.8, which was consistent with the standard peak of EG. Therefore, the EG yield under different conditions can be compared with the standard curve of EG ( Figure 2 d) Compare and calculate. Figure 2 e It can be seen that the hydrolysis of 1.0 g of PET in 1 M KOH solution at 60 °C for 24 h can produce a maximum EG concentration of approximately 0.34 M. Therefore, the electrochemical performance of the catalyst was tested in this PET hydrolysate medium using a conventional three-electrode system.
[0035] Figure 3 The synthesis process of NiFe-LDH / NF, Ag / NiFe-LDH / NF and Ag / NF supported on nickel foam is demonstrated using a two-step method combined with photodeposition.
[0036] Figure 4The XRD patterns of the prepared electrodes are shown. It can be clearly seen that the diffraction peaks of NiFe-LDH / NF at 11.5°, 23.2°, 34.6° and 60.3° correspond to the (003), (006), (012) and (110) crystal planes, respectively, proving that NiFe-LDH / NF was successfully synthesized. The diffraction peaks of Ag / NF at 38.1°, 44.2°, 77.3° and 81.5°, in addition to the three diffraction peaks of the NF substrate, correspond to the (111), (200), (311) and (222) crystal planes of Ag (JCPDS No. 87 0597), indicating that the nickel foam was successfully doped with Ag. It is worth noting that among the diffraction peaks of the Ag / NiFe-LDH / NF catalyst, the diffraction peak at 38.2° is significantly prominent, which is due to the overlap of the diffraction peaks of Ag and NiFe-LDH.
[0037] Figure 5 The morphology, elemental analysis and composition of the NiFe-LDH / NF electrode were analyzed, showing the shape of nanosheet arrays.
[0038] Figure 6 The following is an SEM image and elemental composition of the Ag / NiFe-LDH / NF catalyst. It can be seen that the nanoparticles formed by Ag doping adhere to the surface of the nanosheets, but the nanosheet morphology of NiFe-LDH / NF is not changed. In addition, the SEM-EDS spectrum also shows the presence of Ni, Fe, and Ag elements, indicating that Ag is successfully doped into NiFe-LDH. Overall, the first step is to grow NiFe-LDH on a nickel foam substrate, and then stack Ag nanoparticles on the NiFe-LDH surface by photodeposition.
[0039] Figure 7 The SEM image and elemental composition of the A / NF electrode are shown. It can be seen that Ag nanoparticles are attached to the surface of the nanosheets. Furthermore, the SEM-EDS spectrum also reveals the presence of Ni and Ag.
[0040] Figure 8 a Comparison of the EGOR performance of the four electrodes (including the cleaned NF). As can be seen from the curve, Ag / NiFe-LDH / NF exhibits the best catalytic performance. From a quantitative point of view, at the same 50 and 100 mA cm -2 At the current density, Ag / NiFe-LDH / NF only requires a potential of 1.4 / 1.47 V, which is much lower than NiFe-LDH / NF (1.43 / 1.51 V), Ag / NF (1.46 / 1.59 V) and NF (1.64 / 1.66 V), which may be related to the synergistic effect of Ag and NiFe-LDH.
[0041] Figure 8b shows the linear sweep voltammetry (LSV) curve of Ag / NiFe-LDH / NF in PET hydrolyzate medium. Specifically, to achieve 100 mA cm -2 The OER current density required for the other three electrocatalysts in the PET hydrolysis medium was 1.55 V vs. RHE, which was 80 mV lower than that in the 1M KOH environment. Similarly, the other three electrocatalysts achieved the same current density in the PET hydrolysis medium with lower overpotentials compared to the 1M KOH environment, indicating that EGOR is more favorable than OER.
[0042] Figure 9 a The long-term stability of four different electrodes was evaluated by constant current (CA) test at 1.5 V for 24 h. It can be seen that Ag / NiFe-LDH / NF has the best EGOR characteristics. The initial current density of its electrode is 120 mA cm -2 , and gradually dropped to half of the initial value after 24 hours, showing better stability compared with other electrodes.
[0043] Figure 9 b is the ion chromatography (IC) spectrum of the electrolyte analyzed after the stability test, which confirmed that the reaction products were glycolic acid and formic acid.
[0044] Figure 9 c shows that the Faradaic efficiency of formic acid for all electrodes exceeds 80%, while the Faradaic efficiency of glycolic acid for the Ag / NiFe-LDH / NF electrode is approximately 15%. Comparing the four electrodes, the loading of silver nanoparticles can effectively control the amount of glycolic acid.
[0045] Overall, this finding suggests that plastic waste can be effectively converted into higher value-added products and hydrogen, demonstrating broad application prospects in the upgrading of waste plastics.
Claims
1. A selective electrooxidation technology for PET plastic powder based on the synergistic effect of silver and nickel-iron layered double hydroxide, characterized in that: include: (1) PET hydrolysis, used to hydrolyze PET powder into ethylene glycol and terephthalate under alkaline conditions, and the optimal conditions were determined by high performance liquid chromatography; (2) an electrocatalytic reaction, connected to the PET hydrolyzate, comprising a three-electrode system and an electrolytic cell, wherein the working electrode of the three-electrode system is an Ag / NiFe-LDH / NF composite electrode, the reference electrode is an Hg / HgO electrode, and the counter electrode is a platinum wire; (3) Product analysis: After the electrocatalytic reaction is completed, it is used to analyze the formate and glycolate in the electrolyte.
2. The technology according to claim 1, characterized in that The preparation method of the Ag / NiFe-LDH / NF composite electrode comprises: (1) Preparation of NiFe-LDH / NF by hydrothermal method: nickel foam was sequentially treated with ethanol, deionized water, and 3M hydrochloric acid, and then placed in a mixed solution containing Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F, and urea. The mixture was hydrothermally reacted at 120°C for 12 hours, and then washed and dried to obtain NiFe-LDH / NF. (2) Ag loading by photodeposition method: The NiFe-LDH / NF obtained in step (1) was placed in an AgNO3 aqueous solution, irradiated with a 500W xenon lamp for 1 hour, and then washed and dried to obtain an Ag / NiFe-LDH / NF composite electrode.
3. The technology according to claim 1, characterized in that The PET hydrolysis process includes various optimized conditions, such as time, temperature, amount of PET powder, etc. The optimal conditions are: 1M KOH solution and PET powder (mass to volume ratio of 10 g / L), stirring and hydrolyzing at 60°C for 24 hours.
4. The condition according to claim 1, characterized in that The electrolytic cell for the electrocatalytic reaction is an open three-electrode electrolytic cell, the electrolyte is the alkaline hydrolyzate (containing ethylene glycol) output by PET hydrolysis, and the effective area of the working electrode is 1.0 cm 2 , the operating voltage is 1.5 V relative to the reversible hydrogen electrode (RHE).
5. The technology according to claim 1, characterized in that The product separation unit includes an ion chromatograph and a crystallization device, which are used for quantitative analysis and separation of formate and glycolate in the electrolyte.
6. The technology according to claim 1, characterized in that In the NiFe-LDHNF, NiFe-LDH is a nanosheet array structure with a thickness of 50-200 nm. The Ag nanoparticles have a particle size of 10-50 nm and are evenly distributed on the surface of the NiFe-LDH nanosheets.