Fluorine-containing organic solid waste rapid degradation and recovery method

Abstract

The invention relates to the field of waste polymer material recovery and resource utilization, and particularly discloses a method for realizing ultra-fast recovery of fluorine-containing organic waste through a self-propagating reaction. According to the method, liquid sodium-potassium alloy (NaK) is used as a reaction medium, under the protection of inert atmosphere, fluorine-containing organic solid waste is in contact with NaK, electron transfer is induced through mechanical friction, C-F bond breakage is catalyzed and induced, a defluorination reaction is triggered, reaction heat is released, a self-propagating combustion reaction is initiated, and finally, carbon materials and metal fluoride products are recycled. The method is rapid in reaction, does not need external heating, can efficiently recover fluorine-containing waste and prepare high-added-value materials, and is suitable for green large-scale treatment of waste fluoropolymers and preparation of functional materials.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste recycling, and particularly relates to a method for rapidly degrading and recycling fluorine-containing organic solid waste. Background Art

[0002] Fluorine-containing organic compounds, especially polytetrafluoroethylene (PTFE), are widely used in sealing materials, insulating layers, anti-corrosion linings, etc. due to their excellent heat resistance, chemical corrosion resistance, and low friction coefficient. Although these applications improve the performance of products, they also bring difficulties in waste treatment. Due to the highly stable carbon-fluorine bond (C–F bond) in the PTFE molecular structure, its thermal stability and chemical inertness make it almost impossible to decompose in the natural environment, resulting in the long-term accumulation of solid waste and becoming a type of "difficult-to-treat" waste.

[0003] Traditional treatment methods for PTFE waste mainly include physical treatment, pyrolysis, incineration, etc., but there are many limitations. Physical treatment usually only changes the form of PTFE waste, such as crushing and grinding. The performance of the products obtained by physical recycling is far inferior to that of the original PTFE, and it is impossible to realize its resource recycling. For example, CN104175421A discloses a method for recycling polytetrafluoroethylene waste, which recovers polytetrafluoroethylene particles by means of cleaning → drying → crushing → three-stage temperature-controlled forming. The quality of the polytetrafluoroethylene recovered by this method is low, and its application scenarios are limited. Although pyrolysis and incineration methods can partially degrade PTFE, they will produce harmful fluorides and highly toxic gases (such as carbon difluoride and carbon tetrafluoride, etc.), which not only pose safety hazards but also cause serious environmental pollution. Therefore, there is an urgent need to develop a method that can decompose the PTFE molecular chain under mild conditions and realize the green recycling of carbon and fluorine sources in the polymer.

[0004] In addition to PTFE, other types of fluorine-containing organic solid waste, such as fluorinated ethylene propylene (FEP) and perfluorooctanoic acid substances (such as PFOA, PFOS), also face treatment difficulties. As a copolymer of PTFE, FEP retains a high-strength C–F bond, and its thermal decomposition temperature is slightly lower than that of PTFE, but it still has extremely strong chemical inertness. Small molecule fluorine-containing organic compounds such as PFOA and PFOS are widely used in surfactants, anti-fouling coatings and other fields, and have characteristics of biological non-degradability, environmental mobility and bioaccumulation, and have been listed as persistent organic pollutants (POPs). Currently, the mainstream treatment methods include high-temperature incineration, plasma decomposition, supercritical water oxidation, etc., but they generally have problems such as high treatment cost, low efficiency, and difficulty in controlling by-products. Therefore, developing a mild degradation method with strong versatility and applicable to various types of fluorine-containing solid waste is of great significance not only for PTFE but also for the treatment of FEP and PFOA pollutants.

[0005] In recent years, the molecular-level degradation and component recycling of plastic waste by breaking the molecular structure of plastics through chemical reactions have gradually attracted the attention of researchers. Compared with physical and pyrolysis treatment methods, chemical recycling not only has the characteristics of high treatment efficiency and high resource recovery rate, but also can achieve the directional recovery of specific components, thus providing new ideas for the resource utilization of waste plastics. For fluorinated organic compounds, due to the extremely high bond energy of the C–F bond, traditional chemical recycling methods cannot achieve atomic-level recycling of the structure of fluorinated organic compounds, and there are still problems such as harsh reaction conditions, long treatment time, and many by-products. For example, Patent CN114058074A discloses a method for recycling waste polytetrafluoroethylene. By using microwave radiation technology for the regeneration of waste polytetrafluoroethylene, the main principle is to destroy the stable crystalline state of polytetrafluoroethylene and convert it into an amorphous colloid, and then prepare various forms of polytetrafluoroethylene products. Although this technology uses a high-energy radiation light source to break the crystalline state of PTFE, it can only partially break the C–F bond and has poor selectivity. In addition, this method has cumbersome steps and high costs and cannot be applied on a large scale. Summary of the Invention

[0006] In view of the above problems, the present invention proposes a method for ultra-fast chemical recycling of fluorinated organic compound waste by contact electrocatalytic induced self-propagating reaction. The technical solution of the present invention is as follows:

[0007] A method for rapid degradation and recycling of fluorinated organic solid waste, characterized in that liquid sodium-potassium alloy is used as a reaction medium, and the C–F bond in the fluorinated compound molecules in the fluorinated organic solid waste is excited by friction-induced electron transfer to trigger the Wurtz-type defluorination reaction, release reaction heat and form a self-sustaining combustion wave, realizing complete breakage and transformation inside the polymer, and finally generating porous carbon and metal fluoride products.

[0008] Furthermore, the method includes the following steps:

[0009] (1) Material preparation: Dry the fluorinated organic solid waste to remove moisture and crush it into powder.

[0010] (2) Under an inert atmosphere, lay the powder obtained in step (1) in a reaction vessel and drop liquid sodium-potassium alloy.

[0011] (3) Induce electron transfer through mechanical perturbation to activate the carbon-fluorine bond in the fluorinated compound waste powder molecules, trigger the defluorination self-propagating combustion reaction, promote the breakage and transformation of the internal structure of the fluorinated compound, and generate porous carbon materials and metal fluorides.

[0012] (4) Cool, filter and centrifuge to collect the product.

[0013] The method of removing moisture described in step (1) includes one or more of baking, drying, or other methods that can reduce the water content of the sample, and the treatment temperature range is 60°C to 300°C.

[0014] The comminution method described in step (1) includes one or more of ball milling, shearing, grinding, or other methods that can reduce the particle size of the sample.

[0015] The inert atmosphere described in step (2) is one or more of argon and nitrogen.

[0016] The fluorine-containing organic solid waste is polytetrafluoroethylene, perfluoroethylene-propylene, perfluorooctanoic acid, perfluorooctane sulfonate, perfluorooctane, perfluorodecalin, perfluorodecanoic acid, octafluoronaphthalene, perfluorocarboxylic acid, tetrafluoroethylene, perfluorobutane sulfonic acid, hexafluoropropylene, hexafluoroethane, octafluoropropane, octafluorocyclobutane, perfluorohexyl sulfonic acid and its salts, and their isomers that contain fluorine compounds.

[0017] The composition of the liquid sodium-potassium alloy described in step (2) meets the requirement of maintaining a liquid state under room temperature reaction conditions, and the mass ratio of sodium to potassium is 60:40 to 10:90, preferably 22:78.

[0018] The dosage of the liquid sodium-potassium alloy added dropwise in step (2) is calculated according to the stoichiometric ratio based on the chemical composition of the fluorine-containing organic solid waste to be degraded and the molar ratio of the selected sodium-potassium alloy to ensure complete reaction.

[0019] The mechanical perturbation method described in step (3) includes one or more of slight scratching, vibration, stirring, or other physical perturbation methods that can trigger the electron transfer process.

[0020] Compared with the traditional method, the present invention has the advantages of low energy consumption, high reaction efficiency, environmental friendliness, etc. It not only improves the treatment efficiency of fluorine-containing organic compound solid waste, but also can effectively reduce the risk of generating harmful substances in the traditional treatment method. Therefore, while realizing the harmless treatment of fluorine-containing organic compound solid waste, the present invention has the advantages of resource utilization and environmental friendliness, and provides a new technical approach for the resource utilization of fluorine-containing organic compound waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a schematic diagram of the reaction process and reaction device of the present invention;

[0023] Figure 2 Optical diagram of carbon material and metal fluoride generated by the reaction of sodium-potassium alloy with fluorinated organic compound in the present invention;

[0024] Figure 3 Structure characterization diagram of carbon material generated by the reaction of sodium-potassium alloy with polytetrafluoroethylene (PTFE) in the present invention;

[0025] Figure 4 Structure characterization diagram of carbon material generated by the reaction of sodium-potassium alloy with perfluoroethylenepropylene (FEP) in the present invention;

[0026] Figure 5 Structure characterization diagram of carbon material generated by the reaction of sodium-potassium alloy with perfluorooctanoic acid (PFOA) in the present invention; Detailed implementation mode

[0027] For the convenience of understanding the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0028] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. The preferred implementation methods and materials described herein are only for demonstration purposes. Without departing from the principles of the embodiments of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0029] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0030] In this embodiment, the complete breakage of the C–F bond in PTFE is achieved by using a self-propagating reaction of liquid sodium-potassium alloy with fluorinated organic compound powder, and then high-value carbon materials and metal fluorides are obtained. The specific steps are as follows:

[0031] (1) Material preparation: Take waste fluorinated organic compound powder and dry it to remove surface moisture; prepare liquid sodium-potassium alloy (liquid at room temperature, with a molar ratio of sodium to potassium of 22:78).

[0032] (2) Reaction device: Under the protection of an inert atmosphere (such as argon), evenly lay the fluorinated organic compound powder in a stainless steel reaction container.

[0033] (3) Reaction initiation: A small amount of liquid sodium-potassium alloy is dropped onto the surface of the fluorinated organic compound. Through mechanical stirring and friction, the delocalized electrons of the liquid alloy are induced to transfer to the fluorinated organic compound material, activating the cleavage of the C–F bonds on the surface of the fluorinated compound material.

[0034] (4) Self-propagating reaction: The cleavage of the C–F bond is an exothermic reaction that releases heat and forms a combustion center. The heat released by the combustion center spreads rapidly, triggering the cleavage and transformation within the entire fluorinated compound sample. The whole process is completed within a few seconds.

[0035] (5) Product collection and treatment: After cooling, the reaction products are collected. The main product is a porous carbon material with a high specific surface area, and the by-products are stable metal fluorides (such as NaF, KF), which can be separated and purified by simple suction filtration.

[0036] Example 1: Ultra-rapid recovery of PTFE waste

[0037] Take the waste PTFE powder and dry it in an oven at 80 °C for 6 hours to remove moisture. The dried PTFE is evenly spread in a stainless-steel reactor and operated under argon gas filling. Use a dropper to drop about the stoichiometric ratio of liquid sodium-potassium alloy onto the surface of the PTFE powder, and stimulate the defluorination reaction through magnetic stirring. The PTFE quickly catches fire and completes the cleavage and transformation in the self-propagating mode. The whole process lasts for about a few seconds. After cooling, the products are collected. Confirmed by XRD, Raman, BET, and SEM characterization, the main product is a porous carbon material with a spherical structure ( Figure 3 ), and the separated products are NaF and KF. This method realizes the efficient and green recovery of PTFE waste.

[0038] Example 2: Ultra-rapid recovery of FEP waste

[0039] Take the waste perfluoroethylene-propylene (FEP) film, cut it into small pieces (side length < 5 mm), and treat it in a vacuum drying oven at 80 °C for 6 hours to remove residual moisture. Weigh the treated FEP sample and place it in a stainless-steel reactor under argon gas atmosphere protection. Use a dropper to drop liquid sodium-potassium alloy onto the surface of the FEP, and stimulate the defluorination reaction through magnetic stirring to quickly activate the self-propagating reaction. Local ignition occurs on the surface of the FEP, and the combustion wave spreads along the film, and the reaction is completed within a few seconds. The reaction products are characterized by XRD and Raman as typical hierarchical carbon materials ( Figure 4 ).

[0040] Example 3: Ultra-rapid recovery of PFOA waste

[0041] Take the solid powder of standard-grade perfluorooctanoic acid (PFOA) and place it in a stainless-steel reactor. Use a dropper to add liquid sodium-potassium alloy to cover the surface of PFOA, and start the reaction by magnetic stirring. It is observed that PFOA reacts rapidly with NaK and generates local heat release, forming a slight spark, and the conversion is completed within 3 seconds. The product is cooled and recovered. XRD and Raman analyses show that a porous carbon material ( Figure 5 ) is formed. This result indicates that the method of the present invention can be effectively applied to the rapid degradation and harmless treatment of small-molecule fluorinated organic compounds (such as PFOA).

[0042] In summary, the recovery method of the present invention does not require continuous input of external energy, the initial reaction conditions are relatively mild, and it can be carried out at a relatively low temperature, thereby reducing energy consumption and production costs. Secondly, the reaction of the present invention has a high reaction rate and reaction efficiency, and can break and degrade the molecular structure of fluorinated organic compounds (such as PTFE, FEP, PFOA, etc.) within a few seconds, improving the recovery efficiency of waste fluorinated organic compounds. In conclusion, compared with traditional methods, the chemical recovery of fluorinated organic compound waste using self-propagating reaction has lower energy consumption, higher reaction efficiency and better applicability, and is a more promising technical solution.

[0043] The above is only the preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for rapid degradation and recovery of fluorine-containing organic solid waste, characterized in that: Using liquid sodium-potassium alloy as the reaction medium, friction-induced electron transfer is used to excite the C–F bonds in the fluorine-containing compound molecules, triggering a Waltz-type defluorination reaction, releasing reaction heat and forming a self-sustaining combustion wave, achieving complete breakage and transformation of the polymer, and ultimately generating porous carbon and metal fluoride products.

2. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 1, Its characteristics include the following steps: (1) Material preparation: Dry the fluorine-containing organic solid waste to remove moisture and crush it into powder; (2) under an inert atmosphere, placing the powder obtained in step (1) in a reaction vessel, and adding dropwise liquid sodium-potassium alloy; (3) Inducing electron transfer through mechanical disturbance, activating the carbon-fluorine bonds in the molecules of the fluorine-containing compound waste powder, triggering the defluorination self-propagating combustion reaction, promoting the fracture and transformation of the internal structure of the fluorine-containing compound, and generating porous carbon materials and metal fluorides; (4) Cool, filter, centrifuge and collect the product.

3. The method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2, characterized in that: The method of removing moisture in step (1) includes baking, drying or other methods capable of reducing the moisture content of the sample, and the processing temperature ranges from 60°C to 300°C.

4. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The comminution method in step (1) includes one or more of ball milling, shearing, grinding or other methods for reducing the particle size of sample particles.

5. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The inert atmosphere in step (2) is one or more of argon and nitrogen.

6. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The fluorine-containing organic solid waste is polytetrafluoroethylene, polyperfluoroethylene propylene, perfluorooctanoic acid, perfluorooctane sulfonate, perfluorooctane, perfluorodecalin, perfluorodecanoic acid, octafluoronaphthalene, perfluorocarboxylic acid, tetrafluoroethylene, perfluorobutane sulfonic acid, hexafluoropropylene, hexafluoroethane, octafluoropropane, octafluorocyclobutane, perfluorohexyl sulfonic acid and its salts and their isomers having fluorine-containing compounds.

7. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The composition of the liquid sodium-potassium alloy in step (2) meets the requirement of maintaining a liquid state under room temperature reaction conditions, and the mass ratio of sodium to potassium is 60:40 to 10:

90.

8. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The mass ratio of sodium to potassium in the liquid sodium-potassium alloy in step (2) is 22:

78.

9. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The amount of the liquid sodium-potassium alloy added dropwise in step (2) is calculated according to the stoichiometric ratio based on the chemical composition of the fluorine-containing organic solid waste to be degraded and the molar ratio of the selected sodium-potassium alloy to ensure complete reaction.

10. A method for rapid degradation and recovery of fluorine-containing organic solid waste according to claim 2 or 3, characterized in that: The mechanical disturbance method in step (3) includes slight scraping, vibration, stirring, or one or more other physical disturbance methods that can trigger the electron transfer process.

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