Method for decomposing polyfluorocarboxylic acid or its salt

Abstract

The present invention relates to a method for decomposing polyfluorocarboxylic acids, the method being characterized in that a mixture including polyfluorocarboxylic acids, water, and a basic compound is heated.

Description

[Technical Field]

[0001] The present invention relates to a polyfluorocarboxylic acid. or its salt This relates to a method of disassembling the above. This application claims priority based on Japanese Patent Application No. 2021-077490, filed on April 30, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, due to concerns about the environmental persistence of fluorine-containing organic compounds that have been used in surfactants, surface treatment agents, etc., there has been a movement to reduce fluorocarboxylic acids from various fluororesin products, other industrial products, drinking water, industrial wastewater, sewage, etc. These fluorine-containing organic compounds are highly stable and difficult to decompose because they are formed from carbon-fluorine bonds with large bond energy. For example, Non-Patent Document 1 describes that when heated at 307°C for 65 hours, 4% of the compounds decompose. Under these circumstances, various methods for decomposing polyfluorocarboxylic acids have been investigated, including a method of reacting them with iron powder at a high temperature of 350°C (Patent Document 1), a method of decomposing them by reaction with hydrogen peroxide (Patent Document 2), and a method of heating them together with peroxodisulfate ions (Patent Document 3). However, the method described in Patent Document 1 requires a reaction at an extremely high temperature, which places great restrictions on equipment for industrial implementation. The method described in Patent Document 2 has a low decomposition rate of polyfluorocarboxylic acid. The method described in Patent Document 3 requires an excess amount of peroxodisulfate, an oxidizing substance, to achieve a high decomposition rate, which requires costs and management. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2006-306736 [Patent Document 2] Japanese Patent Publication No. 2006-169146 [Patent Document 3] Japanese Patent Application Publication No. 2008-285449 [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of Fluorine Chemistry 126 (2005) 1510-1516 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional methods for decomposing polyfluorocarboxylic acids are insufficient in terms of decomposition power and are expensive, so there is a demand for simpler methods for decomposing polyfluorocarboxylic acids.

[0006] In view of the above circumstances, an object of the present invention is to provide a method for efficiently decomposing polyfluorocarboxylic acids in a simpler and less expensive manner. [Means for solving the problem]

[0007] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by the following configuration: Specifically, they have found that when a mixture containing polyfluorocarboxylic acids, water, and a basic compound is heated, the decomposition ability of polyfluorocarboxylic acids is improved. [1] A method for producing a polyfluorocarboxylic acid mixture comprising heating a mixture containing polyfluorocarboxylic acids, water, and a basic compound, wherein the mass ratio of the polyfluorocarboxylic acids to water (polyfluorocarboxylic acids:water) is 1:1×10 15 ~1:0.01 is preferred, and 1:1×10 12 ~1:0.1 is more preferable, and 1:1×10 9 ~1:1 is more preferred, and 1:1 x 10 6 In the method for decomposing polyfluorocarboxylic acids, a ratio of 1:10 or less is particularly preferred. [2] The decomposition method according to [1], wherein the basic compound is at least one basic compound selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, and sodium hydroxide and potassium hydroxide are preferred, and potassium hydroxide is more preferred. [3] The decomposition method according to [1] or [2], wherein the pH of the mixture is 10 or higher, preferably 10 to 14, more preferably 12 or higher, and even more preferably 12 to 14. [4] The decomposition method according to any one of [1] to [3], wherein the total content of metal powder, hydrogen peroxide, ozone, and peroxodisulfate ions relative to the total mass of the mixture is 1 mass% or less, and the mixture is preferably free of metal powder, hydrogen peroxide, ozone, and peroxodisulfate ions. [5] The decomposition method according to any one of [1] to [4], wherein the heating temperature is higher than 150°C and lower than 195°C, preferably 155 to 190°C, more preferably 160 to 185°C, and even more preferably 165 to 180°C, and the heating time is preferably 1 to 24 hours, more preferably 1 hour or longer but less than 12 hours, and even more preferably 1 hour or longer but less than 6 hours. [6] The decomposition method according to any one of [1] to [5], wherein the polyfluorocarboxylic acids have a fluorinated alkyl group having 4 to 16 carbon atoms, preferably a fluorinated alkyl group having 5 to 15 carbon atoms, and more preferably a fluorinated alkyl group having 6 to 14 carbon atoms. [7] The decomposition method according to any one of [1] to [6], wherein the polyfluorocarboxylic acids are perfluorocarboxylic acids or salts thereof, and nonafluoropentanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, or salts thereof are preferred. [8] The decomposition method according to [7], wherein the perfluorocarboxylic acid is perfluorooctanoic acid. [9] The decomposition method according to any one of [1] to [8], wherein the decomposition product of the polyfluorocarboxylic acids is a fluorinated compound represented by the following formula (D1): Rf-H (D1) In the formula (D1), Rf is a fluorinated alkyl group having 3 to 15 carbon atoms which may have an etheric oxygen atom.

[10] A method for producing a polyfluorocarboxylic acid mixture comprising heating a mixture containing polyfluorocarboxylic acids, water, and a basic compound, wherein the mass ratio of the polyfluorocarboxylic acids to water (polyfluorocarboxylic acids:water) is 1:1×10 15 ~1:0.01 is preferred, and 1:1×10 12 ~1:0.1 is more preferable, and 1:1×10 9 ~1:1 is more preferred, and 1:1 x 10 6 A particularly preferred method for producing fluorinated compounds is a ratio of 1:10.

[11] The method according to

[10] , wherein the basic compound is at least one basic compound selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate, and sodium hydroxide and potassium hydroxide are preferred, and potassium hydroxide is more preferred.

[12] The method according to

[10] or

[11] , wherein the pH of the mixture is 10 or higher, preferably 10 to 14, more preferably 12 or higher, and even more preferably 12 to 14.

[13] The method according to any one of

[10] to

[12] , wherein the total content of the metal powder, hydrogen peroxide, ozone, and peroxodisulfate ions relative to the total mass of the mixture is preferably 1 mass% or less, and the mixture is free of metal powder, hydrogen peroxide, ozone, and peroxodisulfate ions.

[14] The method according to any one of

[10] to

[13] , wherein the heating temperature is higher than 150°C and lower than 195°C, preferably 155 to 190°C, more preferably 160 to 185°C, and even more preferably 165 to 180°C, and the heating time is preferably 1 to 24 hours, more preferably 1 hour or longer but less than 12 hours, and even more preferably 1 hour or longer but less than 6 hours.

[15] The method according to any one of

[10] to

[14] , wherein the polyfluorocarboxylic acids have a fluorinated alkyl group having 6 to 16 carbon atoms, preferably a fluorinated alkyl group having 5 to 15 carbon atoms, and more preferably a fluorinated alkyl group having 6 to 14 carbon atoms.

[16] The method according to any one of

[10] to

[15] , wherein the polyfluorocarboxylic acid is a perfluorocarboxylic acid or a salt thereof, and nonafluoropentanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, or a salt thereof is preferred.

[17] The method according to

[16] , wherein the perfluorocarboxylic acid is perfluorooctanoic acid.

[18] The method according to any one of

[10] to

[17] , wherein the decomposition product of the polyfluorocarboxylic acids is a fluorinated compound represented by the following formula (D1): Rf-H (D1) In the formula (D1), Rf is a fluorinated alkyl group having 3 to 15 carbon atoms which may have an etheric oxygen atom. [Effects of the Invention]

[0008] According to the method of the present invention, polyfluorocarboxylic acids can be efficiently decomposed by a simpler and less expensive method. DETAILED DESCRIPTION OF THE INVENTION

[0009] A first aspect of the present invention is a method for decomposing perfluorocarboxylic acids, which comprises heating a mixture containing polyfluorocarboxylic acids, water, and a basic compound.

[0010] The polyfluorocarboxylic acids refer to compounds (polyfluorocarboxylic acids) in which a monovalent organic group having two or more fluorine atoms is bonded to a carboxy group, as well as salts and precursors thereof. Examples of the salt include alkali metal salts, alkaline earth metal salts, and ammonium salts of polyfluorocarboxylic acids. Lithium salts, sodium salts, potassium salts, ammonium salts, calcium salts, and magnesium salts are preferred, and lithium salts, sodium salts, potassium salts, and ammonium salts are more preferred. Examples of the precursor include fluorinated alcohols, fluorinated aldehydes, acid halides having fluorine atoms, and fluorinated carboxylic acid esters. Fluorinated alcohols are compounds in which the oxygen atom of a carbonyl group in the carboxy group of a polyfluorocarboxylic acid is substituted with two hydrogen atoms. Fluorinated aldehydes are compounds in which the hydroxyl group in the carboxy group of a polyfluorocarboxylic acid is substituted with a hydrogen atom. Fluorine-containing acid halides are compounds in which the hydroxyl group in the carboxy group of a polyfluorocarboxylic acid is substituted with a halogen atom. Fluorinated carboxylic acid esters are compounds in which the hydrogen atom of a hydroxyl group in the carboxy group of a polyfluorocarboxylic acid is substituted with a monovalent hydrocarbon group.

[0011] The polyfluorocarboxylic acids of this embodiment preferably have a fluorinated alkyl group, more preferably a perfluoroalkyl group. The fluorinated alkyl group may be a fluorinated alkyl group having an etheric oxygen atom. The fluorinated alkyl group having an etheric oxygen atom refers to a fluorinated alkyl group in which an oxygen atom is inserted between the carbon-carbon bonds of the fluorinated alkyl group. The fluorinated alkyl group is preferably bonded to the carbon atom of a carbonyl group in the polyfluorocarboxylic acids. The number of carbon atoms in the fluorinated alkyl group or perfluoroalkyl group is preferably 4 to 16, more preferably 5 to 15, and even more preferably 6 to 14. The polyfluorocarboxylic acids are preferably carboxylic acids having a perfluoroalkyl group, salts thereof, or precursors thereof, and more preferably carboxylic acids having a perfluoroalkyl group or salts thereof. The fluorinated alkyl group refers to a group having -C n H 2n+1(n is a positive integer), or a cycloalkyl group in which at least two hydrogen atoms are replaced with fluorine atoms, and may be linear or branched. n H 2n+1 (n is a positive integer), or a cycloalkyl group in which all hydrogen atoms have been replaced with fluorine atoms.

[0012] Examples of polyfluorocarboxylic acids having a fluorinated alkyl group having 4 to 16 carbon atoms include polyfluoropentanoic acid, polyfluorooctanoic acid, polyfluorononanoic acid, polyfluorodecanoic acid, polyfluoroundecanoic acid, polyfluorododecanoic acid, and polyfluorotetradecanoic acid. Examples of carboxylic acids having a perfluoroalkyl group include nonafluoropentanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, and perfluorododecanoic acid, with perfluorooctanoic acid being preferred.

[0013] The polyfluorocarboxylic acid of this embodiment is preferably a perfluorocarboxylic acid represented by the following general formula (A1) or a salt thereof. (R F COO) n1 M (A1)

[0014] R F is a perfluoroalkyl group having 4 to 16 carbon atoms which may have an etheric oxygen atom. The perfluoroalkyl group is as described above. The perfluoroalkyl group may be linear, branched, or may have a ring structure. The perfluoroalkyl group is preferably linear. The number of carbon atoms is more preferably 4 to 16, more preferably 5 to 15, and even more preferably 6 to 14. R F When the alkyl group has an etheric oxygen atom, the number of the etheric oxygen atoms is preferably 1 to 4, and more preferably 1 to 3.

[0015] M represents H, Li, Na, K, NH4, Ca, or Mg. When M is H, Li, Na, K, or NH4, n1 is 1, and when M is Ca or Mg, n1 is 2. M is preferably Li, Na, K, or NH4. These are water-soluble and easy to handle.

[0016] In this embodiment, polyfluorocarboxylic acids are heated together with water and a basic compound. The polyfluorocarboxylic acids may or may not be dissolved in water, but are preferably dissolved. The mass ratio of the polyfluorocarboxylic acids to water (polyfluorocarboxylic acids:water) is 1:1×10 15 ~1:0.01 is preferred, and 1:1×10 12 ~1:0.1 is more preferable, and 1:1 x 10 9 ~1:1 is more preferable, 1:1 x 10 6 A ratio of up to 1:10 is particularly preferred. In the method of the present embodiment, even if the concentration of polyfluorocarboxylic acids is high, efficient decomposition is possible, and even if the concentration of polyfluorocarboxylic acids is low, further reduction is possible. In particular, the REACH regulation (Registration, Evaluation, Authorization, Restriction and Chemicals) requires that the concentration of perfluorooctanoic acids be 25 ppb by mass or less. With the method of this embodiment, the concentration of perfluorooctanoic acid can be reduced to 25 ppb by mass or less, or even to about 10 ppb by mass, by adjusting the reaction time and reaction temperature.

[0017] The content of the polyfluorocarboxylic acids relative to the total mass of the mixture is preferably from 0.001 to 5 mass%, more preferably from 0.005 to 4 mass%, and even more preferably from 0.01 to 3 mass%.

[0018] The heating temperature is preferably higher than 150°C and lower than 195°C, more preferably 155 to 190°C, even more preferably 160 to 185°C, and particularly preferably 165 to 180°C. If the temperature is higher than 150°C, a sufficient decomposition rate can be ensured, which is suitable for industrial implementation. If the temperature is lower than 195°C, the temperature can be easily adjusted using heated steam or the like. The heating temperature means the temperature of the mixture during heating.

[0019] The heating time is not particularly limited and is usually 1 to 24 hours. The method of this embodiment can sufficiently decompose polyfluorocarboxylic acids in a short time of less than 12 hours, or even less than 6 hours.

[0020] Since polyfluorocarboxylic acids are acidic compounds, a basic compound is added, particularly at high concentrations, to increase the decomposition rate of polyfluorocarboxylic acids and to prevent corrosion. Examples of such basic compounds include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, and potassium bicarbonate, with sodium hydroxide and potassium hydroxide being preferred, and potassium hydroxide being more preferred.

[0021] The amount of the basic compound in the mixture is preferably equal to or greater than the amount of the polyfluorocarboxylic acids. The ratio of the number of moles of the basic compound to the number of moles of the polyfluorocarboxylic acids in the mixture is preferably 0.01 to 50,000,000, more preferably 0.1 to 500,000, and even more preferably 1 to 5,000. The content of the basic compound relative to the total mass of the mixture is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 15% by mass or less. If it is below the upper limit, it can be easily supplied to the treatment process using a solution of sodium hydroxide, potassium hydroxide, or the like. The content of the basic compound relative to the total mass of the mixture is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. That is, the content of the basic compound relative to the total mass of the mixture is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 1 to 15% by mass.

[0022] When polyfluorocarboxylic acids are decomposed by the method of this embodiment, substances other than the polyfluorocarboxylic acids, water, and basic compounds described above may be present. Examples of such substances include alcohols, carboxylic acids, and salts of inorganic and organic acids. In one aspect of the present invention, methanol is preferably contained. In another aspect of the present invention, potassium iodide is preferably contained.

[0023] When polyfluorocarboxylic acids are decomposed by the method of this embodiment, it is preferable that the mixture is substantially free of metal powder, hydrogen peroxide, ozone, and peroxodisulfate ions, and more preferably free of them. "Substantially free" means that the total content of these substances relative to the total mass of the mixture is 1% by mass or less. Examples of the metal powder include powdered iron, copper, lead, aluminum, zinc, etc.

[0024] The fluorinated compound obtained by decomposing polyfluorocarboxylic acids by the method of this embodiment is represented by the following formula (D1). Rf-H (D1) In formula (D1), Rf is a fluorinated alkyl group having 3 to 15 carbon atoms which may have an etheric oxygen atom. Here, the fluorinated alkyl group is the same as the group described above. The fluorinated alkyl group may be linear, branched, or may have a cyclic structure. The fluorinated alkyl group is preferably linear. Furthermore, the number of carbon atoms is more preferably 4 to 14, and further preferably 5 to 13. The fluorinated compound (D1) is water-insoluble and can be easily separated from the water used for decomposition by layer separation.

[0025] The method of this embodiment may be carried out in the presence of nitrogen, air, or other gases, or may be carried out in a degassed state. There are no particular limitations on the operating pressure, and either increased or reduced pressure may be used. However, by decomposing the product while reducing pressure, the generated by-products can be removed simultaneously. When reducing pressure, the absolute pressure is preferably 0.001 to 0.099 MPa, more preferably 0.01 to 0.09 MPa, and even more preferably 0.1 to 0.09 MPa. The material of the equipment for decomposition in the method of this embodiment may be any material that does not corrode, and various metals, glasses, and ceramics can be used.

[0026] By using the method of this embodiment, the decomposition rate of polyfluorocarboxylic acids, calculated by the following formula based on the mass of the polyfluorocarboxylic acids before decomposition, can be made 90.0% or more, and even 95.0% or more. The mass of polyfluorocarboxylic acids in the mixture can be calculated from measurements by liquid chromatography-mass spectrometry, which will be described later. In this way, the method of this embodiment can efficiently decompose polyfluorocarboxylic acids. Decomposition rate (%) = (mass of polyfluorocarboxylic acids before decomposition - mass of polyfluorocarboxylic acids after decomposition) / mass of polyfluorocarboxylic acids before decomposition × 100

[0027] The initial pH of the mixture containing the basic compound before decomposition is preferably 10 or higher, more preferably 12 or higher. The upper limit of the initial pH is usually 14. That is, the initial pH is preferably 10 to 14, more preferably 10 to 12. If the initial pH is within the above range, the decomposition rate of the polyfluorocarboxylic acids is further improved.

[0028] A second aspect of the present invention is a method for producing a fluorinated compound, which comprises decomposing a polyfluorocarboxylic acid to obtain the fluorinated compound. Details of each compound and its decomposition method, as well as the fluorinated compound, etc., are as described above in the first embodiment.

[0029] Using the method of this embodiment, based on the mass of polyfluorocarboxylic acids before decomposition, the recovery rate of the fluorinated compound, which is the decomposition product of polyfluorocarboxylic acid, can be made 60.0% or more, and further 70.0% or more, according to the following formula. The mass of the fluorinated compound in the mixture can be determined by methods such as calculating the number of moles and converting it to mass after identifying the structure by NMR, and calculating according to the liquid chromatography-mass spectrometry method described later. Thus, according to the method of this embodiment, the fluorinated compound, which is the decomposition product of polyfluorocarboxylic acids, can be efficiently recovered from the mixture containing polyfluorocarboxylic acids and water in a simpler and easier manner. Recovery rate (%) = (mass of the fluorinated compound generated by decomposition / molecular weight of the fluorinated compound generated by decomposition) / (mass of polyfluorocarboxylic acids before decomposition / molecular weight of polyfluorocarboxylic acids) × 100

Examples

[0030] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Decomposition rate of polyfluorocarboxylic acid] The concentration of polyfluorocarboxylic acid in the mixture obtained in each of the following examples was measured by liquid chromatography-mass spectrometry. The specific measurement conditions are as follows. A standard solution with a known concentration was prepared, and the concentration of polyfluorocarboxylic acid was calculated by the standard addition method. Using the concentration of polyfluorocarboxylic acid obtained from the mixed solution before and after decomposition, the decomposition rate of polyfluorocarboxylic acid was calculated by the following formula. In mass spectrometry (MS), C7F 15 COO - (molecular ion mass 413) was used as the primary ion, and C7F 15 - (molecular ion mass 369) was detected and monitored as the secondary ion. The decomposition rate and recovery rate were calculated by the above-mentioned formulas. <LC-MS / MS measurement conditions> Measuring device: Agilent 1260 series HPLC / 6460MS (HPLC conditions) Column: Imtakt Cadenza CD-C18, inner diameter 2mm, length 100mm Eluent: (Solution A) 0.002 mol / L ammonium acetate aqueous solution, (Solution B) HPLC-grade methanol Flow rate: 0.3mL / min Injection volume: 5μL Column oven temperature: 35°C Gradient conditions: Time from the start of measurement (minutes) and composition of the eluent (solution A / solution B (volume %)) 0 minutes (38 / 62) → 2 minutes (38 / 62) → 5 minutes (0 / 100) → 10 minutes (0 / 100) → 10.01 minutes (38 / 62) → 20 minutes (38 / 62) (MS conditions) Ionization method: ESI Nebulizer: N2 Drying gas: N2 (10 L / min) Sheath gas: N2 (10 L / min) Drying gas temperature: 300℃ Sheath gas temperature: 350℃ Detected ion: Negative Fragment voltage: 90V Collision gas: N2 Collision: 4eV Monitoring: MRM (m / z = 413 and 369)

[0031] [Comparative Example 1] A mixture was obtained by mixing 0.15 g of perfluorooctanoic acid (PFOA) and 1,500.0 g of distilled water, and this mixture was designated as test solution 1. The PFOA concentration in test solution 1 was measured and found to be 87 ppm by mass. A 1 L Hastelloy autoclave equipped with a stirrer was depressurized with a vacuum pump, and Test Liquid 1 was charged without allowing air to enter. The internal temperature was adjusted to 170°C in an oil bath and the autoclave was held under stirring for 5 hours. After cooling, the PFOA concentration in the contents was measured and found to be 5.9 ppm by mass. The PFOA decomposition rate calculated based on the charged PFOA concentration was 93.2%.

[0032] [Example 1] 1.5 g of PFOA, 1,000.2 g of distilled water, and 2.1 g of 48% potassium hydroxide aqueous solution were mixed to prepare a 1,500 mass ppm PFOA solution (hereinafter referred to as PFOA solution 1). Furthermore, 54.95 g of PFOA solution 1, 464.8 g of distilled water, and 31.35 g of 48% potassium hydroxide aqueous solution were mixed to obtain a mixture designated as test solution 2. The PFOA concentration in test solution 2 was measured and found to be 154 mass ppm. As in Comparative Example 1, the contents were held at 170°C for 5 hours and then cooled, and the PFOA concentration in the contents was measured to be 5.9 ppm by mass. The decomposition rate of PFOA calculated based on the concentration of PFOA charged was 96.2%.

[0033] [Example 2] A mixture was obtained by mixing 55.21 g of PFOA solution 1, 434.9 g of distilled water, 30.51 g of 48% potassium hydroxide aqueous solution, and 30.4 g of potassium iodide, and this mixture was designated as test solution 3. The PFOA concentration in test solution 3 was measured and found to be 170 ppm by mass. As in Comparative Example 1, the contents were held at 170°C for 5 hours and then cooled. The PFOA concentration in the contents was measured and found to be 4.2 ppm by mass. The PFOA decomposition rate calculated based on the charged PFOA concentration was 97.5%.

[0034] [Example 3] 55.04 g of PFOA solution 1, 215.2 g of distilled water, 32.56 g of 48% potassium hydroxide aqueous solution, 30.61 g of potassium iodide, and 220.08 g of methanol were mixed to obtain a mixture, which was designated as test solution 4. The PFOA concentration in test solution 4 was measured and found to be 154 ppm by mass. As in Comparative Example 1, the contents were held at 170°C for 5 hours and then cooled. The PFOA concentration in the contents was measured and found to be 0.3 ppm by mass. The PFOA decomposition rate calculated based on the charged PFOA concentration was 99.8%.

[0035] [Example 4] 15.4 g of PFOA, 449.0 g of distilled water, and 50.7 g of 48% potassium hydroxide aqueous solution were mixed to obtain Test Liquid 5, a slurry mixture. The same procedure as in Comparative Example 1 was carried out, except that the autoclave was opened before Test Liquid 5 was charged. The obtained liquid was transparent and separated into two layers, and 10.1 g of the lower layer and 494.75 g of the upper layer were recovered. The PFOA concentration in the upper layer was measured and found to be 600 ppm by mass. The decomposition rate of PFOA was calculated to be 98.1%. The lower layer was recovered and analyzed by NMR, and it was found to contain CF 15 It was confirmed that the PFOA was H, and the recovery rate based on the mass of the charged PFOA was 73.4%.

[0036] As shown in Examples 1 to 4, the method of the present invention can decompose polyfluorocarboxylic acids at a high decomposition rate, and can also efficiently recover fluorinated compounds, which are decomposition products of polyfluorocarboxylic acids. [Industrial Applicability]

[0037] The method of the present invention can easily decompose water-soluble fluorine-containing organic compounds used in surfactants, surface treatment agents, etc., and can efficiently recover fluorinated compounds having polyfluoroalkyl groups. Therefore, the method of the present invention is effective in preventing environmental pollution by fluorine-containing organic compounds.

Claims

1. A method for decomposing a polyfluorocarboxylic acid or a salt thereof, comprising heating a mixture having a pH of 12 or higher, containing a polyfluorocarboxylic acid or a salt thereof in which a linear fluorinated alkyl group having 4 to 16 carbon atoms is bonded to a carboxy group, water, and a basic compound, to a temperature higher than 150°C and lower than 195°C.

2. 2. The decomposition method according to claim 1, wherein the basic compound is at least one basic compound selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium bicarbonate, and potassium bicarbonate.

3. 3. The decomposition method according to claim 1, wherein the mixture does not contain metal powder, hydrogen peroxide, ozone, or peroxodisulfate ions.

4. The decomposition method according to claim 1 or 2, wherein the polyfluorocarboxylic acid or its salt is a perfluorocarboxylic acid or its salt.

5. The decomposition method according to claim 4, wherein the perfluorocarboxylic acid is perfluorooctanoic acid.

6. The decomposition method according to claim 1 or 2, wherein the decomposition product of the polyfluorocarboxylic acid or the salt thereof is a fluorinated compound represented by the following formula (D1): Rf-H (D1) In formula (D1), Rf is a linear fluorinated alkyl group having 3 to 15 carbon atoms.

7. A decomposition method described in claim 1 or 2, further comprising methanol.

8. A decomposition method described in claim 1 or 2, further comprising potassium iodide.

9. A decomposition method as described in claim 1 or 2, wherein the heating time is less than 12 hours.

10. A decomposition method according to claim 1 or 2, wherein the decomposition rate of the polyfluorocarboxylic acid or its salt is 95.0% or more.

11. The decomposition method described in claim 6, wherein the recovery rate of the fluorinated compound is 60.0% or more.