Method for preparing formate from PET waste plastics
Through hydrothermal pretreatment and electrocatalytic oxidation combined with centrifugal separation and purification, the high energy consumption and complex product separation problems in the PET waste plastic treatment process are solved, and efficient preparation of formate and terephthalate is achieved, with high Faraday efficiency and low energy consumption.
Patent Information
- Application Number
- CN202510518268.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-24
- Publication Date
- 2025-08-08
AI Technical Summary
When processing PET waste plastics, the prior art has problems such as high energy consumption, complex operation, low product selectivity and yield, and complex separation and purification processes.
The PET powder was pretreated by hydrothermal reaction, and then the PET hydrolyzed was electrolyzed in an H-type electrolytic cell, and electrocatalytic oxidation was performed using a foamed nickel electrode loaded with tin dioxide, and combined with centrifugation and pH adjustment separation and purification to prepare formic acid and terephthalate.
The efficient conversion of PET waste plastic into high value-added chemicals has been achieved, with a Faraday efficiency of up to 99.8%, a productivity of 3.24mmol cm-2h-1, and the electrode preparation is simple, the material cost is low, the energy consumption is low, and the product purification is simple.
Smart Images
Figure CN120443198A_ABST
Abstract
Description
Technical field:
[0001] The invention belongs to the technical field of electrochemical synthesis, and particularly relates to a method for preparing formate by utilizing PET waste plastics. Background technology:
[0002] The continued production and use of plastics worldwide has caused serious environmental pollution and ecosystem damage. As one of the most commonly used plastic materials, polyethylene terephthalate (PET) has become an indispensable part of modern society due to its excellent properties, with an annual production of nearly 70 million tons for packaging and textiles. However, these plastics are inherently resistant to degradation, and most PET is disposed of through downstream recycling routes such as landfill, incineration, and mechanical recycling, which is not only harmful to the environment but also seriously wastes carbon resources and causes huge economic losses. In recent years, electrocatalytic technology has become a promising method for plastic waste treatment due to its mild reaction conditions, high selectivity, and low carbon emissions. Through electrocatalytic conversion of PET waste plastics, it can be converted into valuable carbon-containing fuels and chemicals, such as formates. However, this method often requires high energy consumption or complex operating conditions, such as high temperature, high pressure, or the use of expensive electrode materials, which increases processing costs and energy consumption. At the same time, existing technologies have low selectivity and yield for formate, and the product separation and purification processes are complex, increasing the economic and operational difficulty of the process. Summary of the invention:
[0003] In view of the above problems, the present invention provides a method for preparing formate from PET waste plastics, so as to achieve efficient conversion of polyethylene terephthalate (PET) waste plastics into high value-added chemicals such as formate and terephthalate.
[0004] A method for preparing formate using PET waste plastics, the method specifically comprising:
[0005] Step 1: dissolving PET powder in an alkaline solution, and filling the alkaline solution into a polytetrafluoroethylene-lined hydrothermal reactor for hydrothermal reaction to obtain a PET hydrolyzate, wherein the PET hydrolyzate comprises ethylene glycol and terephthalic acid;
[0006] Step 2: electrolyzing the PET hydrolyzate in an H-type electrolytic cell to obtain formate and terephthalate, wherein the anolyte of the electrolytic cell is the PET hydrolyzate, the catholyte is an alkaline solution, and the working electrode is one of tin dioxide-loaded nickel foam, SnO2 / CP (carbon cloth), and nickel foam;
[0007] Step 3: Centrifuge the electrolyzed PET hydrolyzate to obtain a filtrate, adjust the pH of the filtrate to separate terephthalic acid, and then condense and recrystallize the filtrate to obtain a crude formate product, and vacuum dry the crude formate product to obtain formate.
[0008] Preferably, the diaphragm of the H-type electrolytic cell is a perfluorosulfonic acid ion membrane Nafion 117, the reference electrode is a Hg / HgO electrode, and the counter electrode is a platinum electrode.
[0009] Preferably, the potential of the working electrode is 0.2-0.8 V relative to the reference electrode.
[0010] Preferably, the preparation method of the tin dioxide-loaded nickel foam electrode is:
[0011] Pretreatment of nickel foam: The nickel foam was ultrasonically washed with 3 M HCl, anhydrous ethanol, and deionized water for 5 min, respectively, and dried in a vacuum oven for 3 h;
[0012] Preparation of a SnO2-loaded nickel foam electrode: urea, anhydrous ethanol, and deionized water were mixed and stirred to completely dissolve the urea, followed by addition of SnCl4·5H2O and stirring for 30 minutes to obtain a precursor solution, and the precursor solution and pretreated nickel foam were placed in a polytetrafluoroethylene-lined hydrothermal reactor for a hydrothermal reaction to obtain a SnO2-loaded nickel foam electrode;
[0013] The tin dioxide electrode is prepared by mixing urea, anhydrous ethanol, and deionized water, stirring to completely dissolve the urea, adding SnCl4·5H2O, and stirring for 30 minutes to obtain a precursor solution, loading the precursor solution into a polytetrafluoroethylene-lined hydrothermal reactor for a hydrothermal reaction to obtain tin dioxide nanoparticles; uniformly drop-coating the tin dioxide nanoparticles on CP, and vacuum drying to obtain a SnO2 / CP electrode;
[0014] The nickel foam electrode was prepared by ultrasonically washing the nickel foam with 3M HCl, anhydrous ethanol, and deionized water for 5 minutes, respectively, and drying the nickel foam in a vacuum oven for 3 hours.
[0015] Preferably, the hydrothermal reaction conditions during electrode preparation are 180° C. for 12 h.
[0016] Preferably, in step three, the pH of the filtrate is adjusted by formic acid, and the recrystallization temperature is 75°C.
[0017] Preferably, in the step 2, when electrolyzing the PET hydrolyzate, a magnetic stirrer is turned on to stir the PET hydrolyzate at a speed of 600 rpm, a temperature of 25° C., and an electrolysis time of 1 to 6 hours.
[0018] Preferably, the alkali solution is sodium hydroxide solution.
[0019] Preferably, the hydrothermal reaction temperature in step 1 is 60° C., and the hydrothermal reaction time is 18 h.
[0020] The present invention designs a method for preparing formate from PET waste plastics. Through an integrated process of "pretreatment hydrolysis-electrocatalytic oxidation-separation and purification", the efficient conversion of polyethylene terephthalate (PET) waste plastics into high-value-added chemicals, formate and terephthalate, is achieved through electric reforming technology. An open-loop process chain of "PET waste plastics → monomers → high-value-added chemicals" is constructed, thereby achieving efficient recovery of carbon resources in PET waste plastics. At the same time, the electrode preparation process is simple. SnO2 nanosheets are grown in situ on a nickel foam substrate by a hydrothermal method, without the need for complex binders or precious metals. The material cost is low and the mechanical stability is strong. The tin dioxide-loaded nickel foam (SnO2 / NF) electrode has a flower-like nanosheet structure, which significantly increases the specific surface area and exposes more active sites. It has a formate FE of up to 99.8% and a carbon content of 3.24 mmol / cm -2 h -1 The product has excellent productivity, achieving relatively high Faradaic efficiency and low energy consumption. Product purification can be achieved by simple centrifugation, adjusting pH, precipitating TPA and recrystallizing. Description of the drawings:
[0021] Attachment Figure 1 It is a schematic diagram of the PET electrical reforming process and product separation disclosed in the present invention.
[0022] Attachment Figure 2 This is the XRD pattern of the SnO2 / NF electrode prepared in Example 1 of the present invention.
[0023] Attachment Figure 3 This is a SEM image of the SnO2 / NF electrode prepared in Example 1 of the present invention.
[0024] Attachment Figure 4 The PET hydrolyzate in the application example of the present invention is 1 H NMR spectrum.
[0025] Attachment Figure 5 2 is the LSV diagram of the electrodes of Example 1 to Example 3 in the application examples of the present invention.
[0026] Attachment Figure 6 The PET electrolyte after SnO2 / NF electrode was electrolyzed at 1.48V vs. RHE potential for 6h in the application embodiment of the present invention is 1 H NMR spectrum.
[0027] Attachment Figure 7 It is the Faradaic efficiency (FE) and yield of formate after electrolysis of SnO2 / NF electrode at a potential of 1.48V vs. RHE for 6h in the application example of the present invention. Specific implementation method:
[0028] In order to make the technical solution of the present invention easier to understand, a method for preparing formate from PET waste plastic disclosed in the present invention is now clearly and completely described in combination with embodiments and drawings.
[0029] Example 1: Preparation of SnO2-loaded nickel foam electrode:
[0030] Pretreatment of nickel foam (NF): Nickel foam NF (1 cm × 1 cm) was sonicated in an ultrasonic water bath with 3 M HCl, anhydrous ethanol, and deionized water for 5 min each, and then dried in a vacuum oven at 60 °C for 3 h to remove the surface oxide layer.
[0031] Preparation of SnO2-loaded nickel foam electrode: 0.3123 g of urea was weighed and dissolved in 10 mL of ethanol and 10 mL of deionized water. 1.6 mmol of SnCl4·5H2O was then added and stirred for 30 min. The prepared solution and pretreated NF were transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and maintained at 180°C for approximately 12 h. After cooling naturally to room temperature, the mixture was rinsed several times with anhydrous ethanol and deionized water and dried in a vacuum oven at 60°C for 12 h to obtain a SnO2-loaded nickel foam electrode, designated as SnO2 / NF electrode.
[0032] Figure 2 The XRD pattern of the SnO2 / NF electrode prepared in this example shows that the obvious characteristic peaks at 29.92°, 42.61°, and 47.12° are attributed to the (111), (112), and (022) crystal planes of SnO2, indicating the formation of SnO2 (PDF#00-029-1484). The three strong signal peaks at 44.5°, 51.8°, and 76.4° correspond to the (111), (200), and (220) crystal planes of the metal support NF (PDF#04-004-8492). In particular, a characteristic peak at 43.09° (PDF#97-064-6096) belonging to the (200) crystal plane of NiO was observed (PDF#97-064-6096). This can be attributed to the partial oxidation of the NF substrate during the in-situ growth of SnO2 under hydrothermal conditions, resulting in the formation of high-valent nickel species.
[0033] Figure 3 This is a SEM image of the SnO2 / NF electrode prepared in this example. Scanning electron microscopy (SEM) analysis of the SnO2 / NF electrode revealed a flower-like morphology composed of aggregated nanosheets on the surface. This may promote the exposure of catalytically active sites, potentially improving electrode performance in electrocatalytic applications.
[0034] Example 2:
[0035] Preparation of the tin dioxide electrode: 0.3123 g of urea was dissolved in 10 mL of ethanol and 10 mL of deionized water. 1.6 mmol of SnCl₄·5H₂O was then added and stirred for 30 minutes. The resulting solution was transferred to a 50 mL / 50 mL Teflon-lined stainless steel autoclave and maintained at 180°C for approximately 12 hours. After cooling to room temperature, the mixture was rinsed several times with anhydrous ethanol and deionized water and dried in a vacuum oven at 60°C for 12 hours to obtain SnO₂ nanoparticles. 5 mg of the prepared SnO₂ NPs was added to 500 μL of ethanol and 10 μL of Nafion. After sonication for two hours, 100 μL of the solution was evenly applied to a 1 × 0.5 cm CP plate using a pipette and then dried in a vacuum oven to obtain a SnO₂ / CP electrode.
[0036] Example 3:
[0037] Preparation of pure nickel foam electrode: Commercial nickel foam NF (1 cm × 1 cm) was ultrasonicated in an ultrasonic water bath with 3 M HCl, anhydrous ethanol and deionized water for 5 min each, and dried in a vacuum oven at 60 °C for 3 h to obtain a pure nickel foam (NF) electrode.
[0038] Application examples:
[0039] Step 1: PET pretreatment
[0040] 6.3 g of PET powder was hydrolyzed in 100 mL of 2.0 M NaOH solution at 60 °C for 18 h. Figure 4 As shown, through 1 HNMR spectroscopy identified that the main hydrolysis products were TPA and EG.
[0041] Step 2: Electrocatalytic PET oxidation upgrading
[0042] Platinum was used as the counter electrode, Hg / HgO electrode was used as the reference electrode, and the electrodes prepared in Examples 1 to 3 were selected as working electrodes in an electrolytic cell containing PET hydrolyzate. The scanning speed of the LSV test was 100 mV s -1 , voltage range is 1.15-1.7V vs.RHE, test temperature is room temperature. Figure 5 As shown, the linear sweep voltammetry (LSV) curves show that the SnO2 / NF electrode exhibits a low onset potential (1.3 V vs. RHE) and a high current density, and has excellent ethylene glycol oxidation reaction (EGOR) activity.
[0043] like Figure 1As shown, the SnO2 / NF electrode prepared in Example 1 was used as the working electrode to electrolyze the PET hydrolyzate at a constant potential of 1.48 V vs. RHE. 100 μL of the anolyte was removed every 0.5 hours and quantitatively and qualitatively analyzed by ion chromatography and H-NMR spectroscopy. An equal amount of PET hydrolyzate was then added to continue the reaction. Figure 6 As shown in Figure 2, formate was identified as the only oxidation product after 6 h of electrolysis and showed the highest formate FE (99.8%) and excellent productivity (3.24 mmol cm -2 h -1 )(like Figure 7 shown).
[0044] Step 3: Separation and purification of formate products
[0045] Solid impurities in the electrolyte after the reaction were removed by centrifugation, and formic acid was added dropwise to adjust the solution's pH to approximately 3. Approximately 5.52 g of terephthalate (TPA) was extracted by filtration, yielding 87.62%. The filtrate was then evaporated and crystallized at 60°C, cooled, and vacuum-dried at 60°C for 8 hours to yield approximately 5.61 g of sodium formate crystals, with a yield of 89.05%. This impressive yield provides a reliable pathway for the resourceful utilization of PET waste plastics.
[0046] It should be pointed out that for ordinary technicians in this technical field, they can make several improvements, replacements, modifications and embellishments without departing from the principles and purpose of the present invention. These improvements, replacements, modifications and embellishments should also be regarded as the scope of protection of the present invention.
Claims
1. A method for preparing formate using PET waste plastics, characterized in that: The method is specifically as follows: Step 1: dissolving PET powder in an alkaline solution, and filling the alkaline solution into a polytetrafluoroethylene-lined hydrothermal reactor for hydrothermal reaction to obtain a PET hydrolyzate, wherein the PET hydrolyzate comprises ethylene glycol and terephthalic acid; Step 2: electrolyzing the PET hydrolyzate in an H-type electrolytic cell to obtain formate and terephthalate, wherein the anolyte of the electrolytic cell is the PET hydrolyzate, the catholyte is an alkaline solution, and the working electrode is one of tin dioxide-loaded nickel foam, SnO2 / CP, and nickel foam; Step 3: Centrifuge the electrolyzed PET hydrolyzate to obtain a filtrate, adjust the pH of the filtrate to separate terephthalic acid, and then condense and recrystallize the filtrate to obtain a crude formate product, and vacuum dry the crude formate product to obtain formate.
2. The method for preparing formate from PET waste plastics according to claim 1, wherein: The diaphragm of the H-type electrolytic cell is a perfluorosulfonic acid ion membrane Nafion 117, the reference electrode is a Hg / HgO electrode, and the counter electrode is a platinum sheet electrode.
3. The method for preparing formate from PET waste plastics according to claim 2, wherein: The potential of the working electrode was 0.2-0.8 V relative to the reference electrode.
4. The method for preparing formate from PET waste plastics according to claim 1, wherein: The preparation method of the tin dioxide-loaded nickel foam electrode is as follows: Pretreatment of nickel foam: The nickel foam was ultrasonically washed with 3 M HCl, anhydrous ethanol, and deionized water for 5 min, respectively, and dried in a vacuum oven for 3 h; Preparation of a SnO2-loaded nickel foam electrode: urea, anhydrous ethanol, and deionized water were mixed and stirred to completely dissolve the urea, followed by addition of SnCl4·5H2O and stirring for 30 minutes to obtain a precursor solution, and the precursor solution and pretreated nickel foam were placed in a polytetrafluoroethylene-lined hydrothermal reactor for a hydrothermal reaction to obtain a SnO2-loaded nickel foam electrode; The tin dioxide electrode is prepared by mixing urea, anhydrous ethanol, and deionized water, stirring to completely dissolve the urea, adding SnCl4·5H2O, and stirring for 30 minutes to obtain a precursor solution, loading the precursor solution into a polytetrafluoroethylene-lined hydrothermal reactor for a hydrothermal reaction to obtain tin dioxide nanoparticles; uniformly drop-coating the tin dioxide nanoparticles on CP, and vacuum drying to obtain a SnO2 / CP electrode; The nickel foam electrode was prepared by ultrasonically washing the nickel foam with 3M HCl, anhydrous ethanol, and deionized water for 5 minutes, respectively, and drying the nickel foam in a vacuum oven for 3 hours.
5. The method for preparing formate from PET waste plastics according to claim 4, wherein: The hydrothermal reaction was carried out at 180° C. for 12 h.
6. The method for preparing formate from PET waste plastics according to claim 1, wherein: In the step 3, the pH of the filtrate is adjusted by formic acid, and the recrystallization temperature is 75°C.
7. The method for preparing formate from PET waste plastics according to claim 1, wherein: In the step 2, when electrolyzing the PET hydrolyzate, a magnetic stirrer is turned on to stir the PET hydrolyzate at a speed of 600 rpm, a temperature of 25° C., and an electrolysis time of 1 to 6 hours.
8. The method for preparing formate from PET waste plastics according to claim 1, wherein: The alkali solution is sodium hydroxide solution.
9. The method for preparing formate from PET waste plastics according to claim 1, wherein: The hydrothermal reaction temperature in step 1 is 60° C., and the hydrothermal reaction time is 18 h.