Method for decomposing polytetrafluoroethylene and derivatives thereof

Abstract

To provide a practical decomposition method for converting polytetrafluoroethylene (PTFE) and a derivative thereof into inorganic fluorides under mild conditions, the decomposition method being safe and industrially applicable.SOLUTION: A method for decomposing polytetrafluoroethylene or a derivative thereof is provided, wherein, polytetrafluoroethylene represented by the general formula (1) (where A and B each independently represent a hydrogen atom, a fluorine atom, a carboxyl group, an amide group, a trifluorovinyl group, a sulfo group, or a phenyl group, and n represents an integer of 2 or more) and / or a derivative thereof is reacted with a sodium metal dispersion in a solvent to produce an inorganic fluoride.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for decomposing polytetrafluoroethylene (hereinafter abbreviated as "PTFE") and its derivatives. PTFE has excellent heat resistance, chemical resistance, and sliding properties, and is used in a variety of applications, such as sealing materials, coating materials, and sliding components. However, due to its high stability, PTFE decomposes very slowly in the environment, and its environmental persistence has been noted. By carrying out a PTFE decomposition process, reducing PTFE emissions into the environment and recovering the fluorine source, it is possible to contribute to the realization of a sustainable society. [Background technology]

[0002] PTFE decomposes at temperatures above 500°C, which requires a lot of energy and is costly. In addition, hydrogen fluoride, which is generated during incineration, is a corrosive gas and is expected to accelerate the deterioration of incinerators.

[0003] In recent years, methods have been reported for defluorinating and decomposing PTFE by reacting it with an alkali metal or an alkali metal-naphthalene complex (e.g., Non-Patent Document 1). However, defluorinating PTFE using an alkali metal requires a high temperature of 200°C, and alkali metals are highly reactive, which poses a risk of fire. Furthermore, although defluorinating PTFE using an alkali metal-naphthalene complex proceeds at room temperature, the complex itself is unstable, and therefore must be prepared each time from naphthalene and the alkali metal. Therefore, a method for decomposing PTFE using safer, more readily available reagents is desired.

[0004] Meanwhile, defluorination of perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids using metallic sodium dispersions has been reported (e.g., Patent Document 1). Metallic sodium dispersions are in the form of a paste in which metallic sodium particles are dispersed in mineral oil, and are characterized by their ability to be handled in air and their ease of supply to a reactor. Metallic sodium dispersions are safer and easier to operate than metallic sodium alone, but no reports have been made on the decomposition of PTFE. In addition, the fluorocarbon chains of PTFE are generally longer than those of perfluoroalkyl compounds, and the longer the fluorocarbon chain, the more difficult it is to decompose. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0107291. [Non-patent literature]

[0006] [Non-Patent Document 1] Y.Yamada, O.Tanaike, S.Shiraishi,TANSO,2004,215,285-294. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a practical method for decomposing PTFE into inorganic fluorides under mild conditions, that is, a method for decomposing PTFE that is safe and can be carried out industrially. [Means for solving the problem]

[0008] As a result of extensive research into methods for decomposing PTFE, the present inventors discovered a method for decomposing PTFE into inorganic fluorides under mild conditions by reacting PTFE with a dispersion of metallic sodium in a solvent, thereby completing the present invention.

[0009] That is, the present invention relates to the following inventions. [1] Formula (1) [ka] (In formula (1), A and B each independently represent a hydrogen atom, a fluorine atom, a carboxyl group, an amide group, a trifluorovinyl group, a sulfo group, or a phenyl group; and n represents an integer of 2 or greater.) A method for decomposing polytetrafluoroethylene and its derivatives, comprising reacting polytetrafluoroethylene represented by the formula (I) with a dispersion of metallic sodium in a solvent to produce an inorganic fluoride. [2] The method for decomposing polytetrafluoroethylene and its derivatives according to item [1], wherein the amount of metallic sodium used in the reaction is 1.0 molar equivalent to 10 molar equivalents relative to the total molar amount of fluorine atoms contained in polytetrafluoroethylene and its derivatives. [3] The method for decomposing polytetrafluoroethylene and its derivatives according to item [1] or [2], wherein the solvent is one or more organic solvents selected from the group consisting of tetrahydrofuran, 1,4-dioxane, diglyme, triglyme, and tetraglyme. [4] The method for decomposing polytetrafluoroethylene and its derivatives according to item [1] or [2], wherein the reaction temperature is 0°C to 100°C. [Effects of the Invention]

[0010] The present invention provides a method capable of decomposing polytetrafluoroethylene and / or its derivatives into inorganic fluorides under mild conditions, i.e., at a relatively low temperature and in a short time. DETAILED DESCRIPTION OF THE INVENTION

[0011] In a method for decomposing polytetrafluoroethylene and its derivatives according to one embodiment of the present invention, polytetrafluoroethylene and / or its derivatives can be decomposed into inorganic fluorides by reacting the polytetrafluoroethylene and / or its derivatives with a metallic sodium dispersion in a solvent. The present invention will be described in detail below.

[0012] Polytetrafluoroethylene and its derivatives applicable to the present invention are represented by the following formula (1).

[0013] [ka]

[0014] In formula (1), A and B each independently represent a hydrogen atom, a fluorine atom, a carboxyl group, an amide group, a trifluorovinyl group, a sulfo group, or a phenyl group, and n represents an integer of 2 or greater.

[0015] The polymer terminals of PTFE vary depending on the reaction initiator and post-treatment method used during polymer production, and the terminal structure can be analyzed by infrared absorption spectroscopy as described in J. Fluorine Chem. 1999, 95, 71, for example.

[0016] The PTFE applicable to the present invention is not particularly limited, but may be a PTFE having an average molecular weight of 10 2 ~10 8 The method for analyzing the average molecular weight of PTFE is, for example, to calculate the average molecular weight distribution from the elastic modulus measurement when the resin is molten, as described in Polymer Engineering & Science, 1988, 28, 538.

[0017] Examples of solvents that can be used in the present invention include tetrahydrofuran, 1,4-dioxane, diglyme, triglyme, and tetraglyme, and these can be used either alone or in any combination of two or more solvents. The amount of the solvent used is preferably 2 to 200 times the weight of the PTFE to be subjected to the reaction. The above solvent is preferably anhydrous, and if necessary, a solvent that has been purified by distillation or dehydrated using a drying agent such as a molecular sieve may be used.

[0018] Dispersions of metallic sodium are made by pulverizing metallic sodium to increase the surface area and dispersing it in a non-polar solvent such as mineral oil, which prevents the reaction caused by metallic sodium from quenching (stopping the reaction) and prevents it from self-decomposing during storage (these are called metallic sodium dispersions or sodium dispersions). The average particle size of metallic sodium is preferably 1 μm to 30 μm. If the average particle size is smaller than 1 μm, the reactivity will be high but handling may be difficult, whereas if the average particle size exceeds 30 μm, the reactivity may be low.

[0019] The amount of metallic sodium dispersion used is preferably 1.0 to 10 molar equivalents, more preferably 1.1 to 5.0 molar equivalents, of metallic sodium relative to the total molar amount of fluorine atoms contained in PTFE. That is, the amount of metallic sodium dispersion used can be determined by calculating the total molar amount of fluorine atoms contained from the weight of PTFE to be subjected to the reaction and the repeating structural unit (-C2F4-) of PTFE.

[0020] The reaction temperature applicable to the present invention varies depending on the type of solvent used, but is usually in the range of 0°C to 100°C, and from the viewpoint of energy saving, it is preferably 10°C to 80°C, and more preferably 10°C to 30°C.

[0021] The reaction conditions applicable to the present invention include an inert gas atmosphere such as nitrogen gas or argon gas, or an atmosphere open to the air. An inert gas atmosphere is preferred because it provides a high fluorine recovery rate.

[0022] The solvent used to quench unreacted metallic sodium during post-reaction treatment may be a protic solvent such as water, methanol, ethanol, propanol, etc. The amount used varies depending on the amount of unreacted metallic sodium, and it is preferable to add the solvent until hydrogen generation ceases.

[0023] When the PTFE and / or its derivatives to be decomposed are in a liquid state, metallic sodium can be substantially uniformly dispersed by adding a metallic sodium dispersion and stirring, and the stirring speed etc. may be adjusted as necessary. When the PTFE and / or its derivatives to be decomposed are in a solid state, it is advisable to set the conditions for adding the metallic sodium dispersion according to their size, shape, density, etc. For example, in mixing with a stirrer etc., the PTFE can be physically crushed somewhat. Also, with a stirring rod etc., a material with a large surface area can be decomposed while being crushed, and the shape, size, and stirring speed of the stirring rod may also be adjusted as appropriate. In addition to these, it is also possible to generate bubbles with an inert gas etc. and stir.

[0024] The inorganic fluoride generated by the above decomposition method may be converted into calcium fluoride and recovered by, for example, the method described in Green Chem., 2022, 24, 6255 - 6263.

Examples

[0025] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited only to these examples.

[0026] The following equipment was used for analysis. 19 F-NMR (282 MHz): Varian Mercury 300 manufactured by Varian and Bruker Avance 500 manufactured by Bruker. Ion chromatography apparatus: Ion Chromatograph IC-8100ST manufactured by Tosoh Corporation (conductivity detector).

[0027] Example 1 <Decomposition of PTFE> After drying in an oven, 60.0 mg of PTFE powder (Kitamura Corporation, Grade: KTL-2N) (total fluorine atomic weight 2.4 mmol) and 2.5 mL of anhydrous 1,4-dioxane were added to a nitrogen-purged glass reaction vessel equipped with a glass stirrer. Next, 1.10 g of metallic sodium dispersion (TCI SD Super Fine®: Sodium 25 wt% dispersion in mineral oil) (12 mmol metallic sodium, 5 equivalents relative to the number of fluorine atoms) was added dropwise, and the mixture was stirred at 80°C for 24 hours under a nitrogen atmosphere. After stirring, the mixture was cooled to 0°C, and water was added dropwise while stirring until hydrogen generation ceased. After stirring at room temperature for 5 minutes, the mixture was subjected to suction filtration, and the solid was washed with diethyl ether and water. The aqueous layer of the filtrate was separated, and the organic phase was extracted three times with water. The solvent was removed from the organic phase by distillation under reduced pressure, and the organic phase was dried. 1 H-NMR and 19 F-NMR was measured. The combined aqueous layers were freeze-dried to obtain a solid. A portion of the precipitated solid was used to quantify fluoride ions using ion chromatography. The remaining solid was added with DO until it was completely dissolved, and a portion of the solution was used to 19 F-NMR was measured.

[0028] <Ion chromatography measurement method> The aqueous layer of the reaction solution in Example 1 was freeze-dried, and 5.0 mg of the resulting solid was weighed and placed in a 50 mL polypropylene volumetric flask. Distilled water was then added to prepare a sample solution with a total volume of 50 mL. Next, 250 μL of this sample solution was added to a 10 mL polypropylene volumetric flask, and distilled water was added to prepare a 20-fold diluted sample solution with a total volume of 10 mL, which was used for ion chromatography measurement. 1.0 mL of the 20-fold diluted sample solution was taken using a syringe (barrel: polypropylene), and fluoride ions were quantified using an ion chromatography device (ion chromatograph IC-8100ST (electrical conductivity detector)). The measurements were performed using a column (TSKgel® SuperIC-Anion HS), an eluent (TSKgel® eluent Conc. IC-A HS-10 (75 mmol / L, NaHCO3 + 8.0 mmol / L Na2CO3) diluted 10-fold with distilled water), and an anion suppressor gel (TSKgel® suppress IC-A). The measurements were performed using an automatic exchange gel suppressor system, an oven temperature of 40°C, a flow rate of 1.5 mL / min, and a loop volume of 30 μL. The retention time of fluoride anions was approximately 1.75 min, and the amount of fluoride anions was quantified from the calibration curve, resulting in a fluoride recovery of 69%.

[0029] Examples 2 to 18 <PTFE decomposition under various conditions> Using the same reaction apparatus, the same PTFE powder (60.0 mg, total fluorine atomic weight 2.4 mmol), and the same metallic sodium dispersion as in Example 1, the reaction was carried out in the metallic sodium equivalent amount relative to the total molar amount of fluorine atoms, solvent, temperature, and time shown in Table 1. After carrying out the reaction using the same procedures as in Example 1, the aqueous layer was freeze-dried to obtain a solid, which was subjected to quantitative measurement of fluoride ions by ion chromatography. The fluorine recovery rate was calculated and the results are shown in Table 1.

[0030] Table 1 [Table 1]

[0031] Examples 19-20 <Decomposition of PTFE (Scale-up)> Using the same reactor as in Example 1 and the same PTFE powder, the amount used was increased to 600 mg (total fluorine atomic weight 24 mmol), and the same sodium metal dispersion was used. The reaction was carried out with the sodium metal equivalent, solvent, temperature, and time with respect to the total molar amount of fluorine atoms shown in Table 2. After carrying out the reaction in the same manner as in Example 1, quantitative measurement of fluoride ions by ion chromatography was performed on the solid obtained by freeze-drying the aqueous layer, and the results of calculating the fluorine recovery rate are shown in Table 2.

[0032] Table 2

Table 2

[0033] Examples 21 - 38 <Decomposition of 1,4-diphenyloctadecafluorobutane> Using the same reactor as in Example 1 and the same sodium metal dispersion, instead of PTFE, 0.2 mmol (total fluorine atomic weight 1.6 mmol) of 1,4-diphenyloctadecafluorobutane was used, and the reaction was carried out with the solvent, Na equivalent, temperature, and time shown in Table 3. After carrying out the reaction in the same manner as in Example 1, quantitative measurement of fluoride ions by ion chromatography was performed on the solid obtained by freeze-drying the aqueous layer, and the results of calculating the fluorine recovery rate are shown in Table 3.

[0034]

Chemical formula

[0035] Table 3

Table 3

[0036] In the above Examples 21 to 38, compounds with short tetrafluoroethylene chains were used, and a higher fluorine recovery rate was achieved when compared with the case where PTFE powder was used under the same conditions of metal sodium equivalent, reaction temperature, and reaction time. This shows that the shorter the tetrafluoroethylene chain, the shorter the time for completion of decomposition, and treatment efficiency can be optimized by controlling the reaction time depending on the chain length of the tetrafluoroethylene to be decomposed.

[0037] Examples 39 to 41 <Decomposition under atmospheric conditions> Using the same reaction apparatus and the same metallic sodium dispersion as in Example 1, and using PTFE or 1,4-diphenyloctafluorobutane as the decomposition target, the nitrogen atmosphere condition was changed to an open-to-air condition, and the reaction was carried out with the solvent, Na equivalent, temperature, and time shown in Table 4. After carrying out the reaction using the same procedures as in Example 1, the aqueous layer was freeze-dried and the resulting solid was subjected to quantitative measurement of fluoride ions by ion chromatography, and the fluorine recovery rate was calculated. The results are shown in Table 4.

[0038] Table 4 [Table 4] [Industrial Applicability]

[0039] The present invention can provide a safe and industrially viable decomposition method for decomposing polytetrafluoroethylene and / or its derivatives into inorganic fluorides under mild conditions.

Claims

1. The following general formula (1) 【Chemistry 4】 (In formula (1), A and B each independently represent a hydrogen atom, a fluorine atom, a carboxyl group, an amide group, a trifluorovinyl group, a sulfo group, or a phenyl group; and n represents an integer of 2 or greater.) 1. A method for decomposing polytetrafluoroethylene and its derivatives, comprising reacting polytetrafluoroethylene and / or its derivatives represented by the formula (I) with a dispersion of metallic sodium in a solvent to produce an inorganic fluoride.

2. 2. The method for decomposing polytetrafluoroethylene and its derivatives according to claim 1, wherein the amount of metallic sodium subjected to the reaction is 1.0 to 10 molar equivalents relative to the total molar amount of fluorine atoms contained in polytetrafluoroethylene and its derivatives.

3. 3. The method for decomposing polytetrafluoroethylene and its derivatives according to claim 1, wherein the solvent is one or more organic solvents selected from the group consisting of tetrahydrofuran, 1,4-dioxane, diglyme, triglyme, and tetraglyme.

4. 3. The method for decomposing polytetrafluoroethylene and its derivatives according to claim 1, wherein the reaction temperature is 0°C to 100°C.

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