Method for decomposing fluorine-containing compound, and system for decomposing fluorine-containing compound

Abstract

The present disclosure provides a method for decomposing a fluorine-containing compound and a system for decomposing a fluorine-containing compound which make it possible to efficiently decompose a fluorine-containing compound. The present disclosure relates to a method for decomposing a fluorine-containing compound, the method including a step for irradiating the fluorine-containing compound with ionizing radiation under conditions of a pH of 4 or less.

Description

Method for decomposing fluorine-containing compounds, and system for decomposing fluorine-containing compounds

[0001] This disclosure relates to a method for decomposing fluorine-containing compounds and a system for decomposing fluorine-containing compounds.

[0002] Non-patent document 1 describes a method for decomposing perfluorooctanoic acid (PFOA) and the like by irradiating them with gamma rays in water under neutral and alkaline conditions.

[0003] David Patch, 8 others, “Elucidating degradation mechanisms for a range of per- and polyfluoroalkyl substances (PFAS) via “controlled irradiation studies”, Science of The Total Environment, Volume 832, 1 August 2022, 154941

[0004] This disclosure aims to provide a method for decomposing fluorine-containing compounds and a system for decomposing fluorine-containing compounds that can efficiently decompose fluorine-containing compounds.

[0005] (1) of this disclosure is a method for decomposing a fluorine-containing compound, which includes the step of irradiating the fluorine-containing compound with ionizing radiation under conditions of pH 4 or lower.

[0006] Disclosure (2) is the decomposition method according to Disclosure (1), wherein the fluorine-containing compound is a fluorine-containing organic compound.

[0007] Disclosure (3) is a decomposition method according to Disclosure (1) or (2), wherein the fluorine-containing compound is a fluorine-containing organic compound having 2 to 21 carbon atoms.

[0008] Disclosure (4) is a method for decomposing any combination of the fluorine-containing compound with any of Disclosures (1) to (3), which are fluorine-containing organic compounds having 8 to 21 carbon atoms.

[0009] Disclosure (5) is a method for decomposing any combination of the fluorine-containing compound with any of Disclosures (1) to (3), which are fluorine-containing organic compounds having 4 to 8 carbon atoms.

[0010] Disclosure (6) is a method for decomposing any combination of the fluorine-containing compound with any of Disclosures (1) to (3), wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 2 to 21 carbon atoms and salts thereof, and fluorine-containing sulfonic acids having 2 to 21 carbon atoms and salts thereof.

[0011] Disclosure (7) is a method for decomposing any combination of the fluorine-containing compound with any of Disclosures (1) to (3), wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 8 to 21 carbon atoms and salts thereof, and fluorine-containing sulfonic acids having 8 to 21 carbon atoms and salts thereof.

[0012] Disclosure (8) is a method for decomposing any combination of the fluorine-containing compound with any of Disclosures (1) to (3), wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 4 to 8 carbon atoms and salts thereof.

[0013] Disclosure (9) is a method for decomposing a fluorine-containing compound, which is contained in at least one selected from the group consisting of gaseous substances, mist-like substances, liquid substances, and solid substances, in any combination with any of Disclosures (1) to (8), wherein the fluorine-containing compound is irradiated with the ionizing radiation.

[0014] Disclosure (10) is a method for decomposing a fluorine-containing compound in water in any combination of any of Disclosures (1) to (9), wherein the fluorine-containing compound is irradiated with the ionizing radiation.

[0015] Disclosure (11) is a decomposition method in any combination of any of Disclosures (1) to (10) in which the ionizing radiation is irradiated in an atmosphere with an oxygen concentration of less than 30 volume percent.

[0016] Disclosure (12) is a decomposition method in any combination of any of Disclosures (1) to (11) in which the ionizing radiation is irradiated in an atmosphere of -20°C or higher and less than 100°C.

[0017] Disclosure (13) is a decomposition method in any combination of any of Disclosures (1) to (12) in which the ionizing radiation is irradiated in an atmosphere of -20°C or higher and 40°C or lower.

[0018] Disclosure (14) is a decomposition method in any combination of any of Disclosures (1) to (13) in which the ionizing radiation is irradiated in the substantially absence of oxygen.

[0019] Disclosure (15) is a decomposition method in any combination of any of Disclosures (1) to (14) for irradiating a substantially closed space with ionizing radiation.

[0020] This disclosure (16) is a decomposition method in any combination of any of the disclosures (1) to (15) in which the ionizing radiation is irradiated in an atmosphere of 1 atm or more.

[0021] Disclosure (17) is a method for decomposing any combination of the ionizing radiation with any of Disclosures (1) to (16), wherein the ionizing radiation is ionizable light or electron beam.

[0022] Disclosure (18) is a method for decomposing any combination of any of Disclosures (1) to (17), wherein the ionizing radiation is at least one selected from the group consisting of gamma rays, electron beams, X-rays, and ion beams.

[0023] Disclosure (19) is a method for decomposing any combination of the ionizing radiation being gamma rays or electron beams as described in Disclosures (1) to (18).

[0024] Disclosure (20) is a decomposition method for any combination of any of Disclosures (1) to (19) wherein the absorbed dose of the ionizing radiation is 1 kGy or more.

[0025] Disclosure (21) is a decomposition method for any combination of any of Disclosures (1) to (20) wherein the absorbed dose of the ionizing radiation is 10 kGy or more.

[0026] Disclosure (22) is a decomposition method for any combination of any of Disclosures (1) to (21) wherein the absorbed dose of the ionizing radiation is 10 kGy to 10 MGy.

[0027] Disclosure (23) is a decomposition method for any combination of any of Disclosures (1) to (22) wherein the dose rate of the ionizing radiation is 10 Gy / h or more.

[0028] The present disclosure (24) is a decomposition method in any combination of any of the present disclosures (1) to (23) for maintaining the pH in the system at 4 or less during the period from the start to the end of irradiation with ionizing radiation.

[0029] This disclosure (25) is a decomposition method in any combination of any of the disclosures (1) to (24) wherein the concentration of the fluorine-containing compound in the system is 0.5 mM or more.

[0030] The present disclosure (26) is a decomposition method in any combination of any of the present disclosures (1) to (24), wherein the concentration of the fluorine-containing compound in the system is 0.1 to 12 mM.

[0031] Disclosure (27) is a decomposition method in which 15% or more of the fluorine-containing compound is decomposed in any combination with any of Disclosures (1) to (26).

[0032] This disclosure (28) is a decomposition method in any combination of any of the disclosures (1) to (27) for continuously irradiating with the ionizing radiation.

[0033] Disclosure (29) is a method for decomposing a composition comprising the fluorine-containing compound and a liquid medium, in any combination of the above disclosures (1) to (28), wherein the composition is irradiated with the ionizing radiation.

[0034] Disclosure (30) is a method of decomposition in any combination of any of Disclosures (1) to (29) wherein an aqueous solution containing the fluorine-containing compound is irradiated with the ionizing radiation.

[0035] The present disclosure (31) is a decomposition method in any combination of any of the present disclosures (1) to (30), wherein the material of the irradiation surface for ionizing radiation in the channel through which the composition containing the fluorine compound passes is at least one selected from the group consisting of metals, ceramics, and polymer materials.

[0036] The present disclosure (32) is a decomposition method for any combination of the irradiation surface with any of the present disclosures (1) to (31), wherein the energy decay rate is 30% or less.

[0037] The present disclosure (33) is a decomposition method in any combination of the present disclosures (1) to (32), wherein the thickness of the irradiation surface is 10 to 1000 μm.

[0038] The present disclosure (34) is a decomposition method of any combination of any one of the present disclosures (1) to (33) by irradiating the ionizing radiation in an atmosphere of 15 to 50 °C.

[0039] The present disclosure (35) is a decomposition method of any combination of any one of the present disclosures (1) to (34) by irradiating the ionizing radiation in an atmosphere of 1 to 20 atm.

[0040] The present disclosure (36) is a decomposition method of any combination of any one of the present disclosures (1) to (35) in which the absorbed dose of the ionizing radiation is 50 to 400 kGy.

[0041] The present disclosure (37) is a decomposition method of any combination of any one of the present disclosures (1) to (36) in which the material of the irradiation surface of the ionizing radiation in the flow path through which the composition containing the fluorine-containing compound passes is metal.

[0042] The present disclosure (38) is a decomposition method of any combination of any one of the present disclosures (1) to (37), further including a step of irradiating the fluorine-containing compound with ionizing radiation under basic conditions.

[0043] The present disclosure (39) is a decomposition method of any combination of any one of the present disclosures (1) to (38), further including a step of concentrating the fluorine-containing compound.

[0044] The present disclosure (40) is a decomposition system for a fluorine-containing compound, comprising irradiation means for irradiating the fluorine-containing compound with ionizing radiation and adjustment means for adjusting the pH in the system to 4 or less.

[0045] According to the present disclosure, it is possible to provide a decomposition method for a fluorine-containing compound and a decomposition system for a fluorine-containing compound that can efficiently decompose the fluorine-containing compound.

[0046] Schematic diagram showing a specific example of the configuration of a flow path through which a composition containing a fluorine-containing compound passes in a form of continuously irradiating ionizing radiation. Diagram showing the relationship between the absorbed dose of gamma rays and the decomposition rate in Example 2. Diagram showing the relationship between the dose of electron beam (low energy) and the decomposition rate in Example 6. Diagram showing the relationship between the dose of electron beam (high energy) and the decomposition rate in Example 7.

[0047] Hereinafter, the present disclosure will be specifically described.

[0048] This disclosure relates to a method for decomposing a fluorine-containing compound, which includes a step of irradiating the fluorine-containing compound with ionizing radiation under conditions of pH 4 or lower (hereinafter also referred to as step (1)). According to the decomposition method of this disclosure, fluorine-containing compounds can be efficiently decomposed.

[0049] Under acidic conditions, such as in systems containing hydrochloric acid, hydrated electrons and hydroxyl radicals are mainly released from chloride ions (Cl) in the solution. － They are captured by ) and respectively as a chloride radical anion and a hydroxyl ion (OH － ) is generated, and it is thought that under alkaline conditions the hydrated electrons that contribute to the reaction cannot react with the fluorine-containing compound. This is because when the aqueous solution of the fluorine-containing compound is strongly acidic, the hydrated electrons are unable to react with the oxonium ion (H) in the solution. ３ O ＋ ) reacts with proton ions (H ＋ This is thought to be because it induces hydroxyl radicals, inhibiting the reaction between hydrated electrons and fluorine-containing compounds. In other words, under acidic conditions, hydrated electrons and hydroxyl radicals are inactivated, so it is thought that something other than hydrated electrons triggers the reaction. Here, according to research on the radiolysis of water [J. W. T. Spinks. R. J. Woods: An Introduction to Radiation Chemistry, Third Edition, John-Wiley and Sons, Inc., New York, Toronto 1990. ISBN 0-471-61403-3. 574 Seiten, Preis: DM 91, 45. https: / / doi.org / 10.1002 / bbpc.19910950346], under strongly acidic conditions, hydrated electrons are converted into hydrogen atoms (hydrogen radicals) by reaction with protons. Hydrogen atoms are one of the simplest radicals and can react with other radicals, add to double bonds, and extract side chain atoms from organic compounds to induce organic radicals. In other words, in the acidic region below pH 4, the trigger for the reaction is thought to be a hydrogen atom (hydrogen radical).

[0050] In the decomposition process of fluorine-containing compounds under acidic conditions, first, the hydrated electrons generated by ionizing radiation irradiation are captured by proton ions or chloride ions from hydrochloric acid, generating hydrogen atoms and chloride radical anions. Next, the hydrogen atoms extract fluorine atoms from the fluorine-containing compounds, inducing free radicals on the fluorine-containing compound molecules and initiating decomposition. Alternatively, although the possibility is low, radicals can also be induced on the fluorine-containing compound chain by direct radiation reaction, resulting in decomposition. Note that the reactivity of hydrogen atoms is high and affected by temperature, becoming hydrogen molecules, vaporizing, and diffusing into the atmosphere. This decomposition mechanism was considered based on experimental data from pulse radiolysis and product analysis.

[0051] According to the research on the radiation decomposition of water mentioned above, under acidic conditions such as in a system containing hydrochloric acid, hydrated electrons and hydroxyl radicals are mainly captured by chloride ions (Cl － ) in the solution, generating chloride radical anions and hydroxyl ions (OH － ) respectively, and the hydroxyl radicals are deactivated. On the strong alkaline side, hydrogen atoms are converted into hydrated electrons and protons, and hydroxyl radicals are converted into oxygen ions (O － ) and proton ions. Furthermore, the influence of oxygen is that in the strongly acidic region with a pH of 8 or lower, hydrogen peroxide (H ２ O ２ ) and hydrogen molecules (H ２ ) increase significantly at the expense of hydroxyl radicals and hydrated electrons. Under alkaline conditions, hydroxyl radicals react with dissolved oxygen to form superoxide radical anions. From the above, different from the ultraviolet method, in the decomposition of fluorine-containing compounds by the radiation method, hydroxyl radicals hardly contribute to the decomposition reaction regardless of the pH. Therefore, in the radiation method, the decomposition reaction can be induced even in a system containing inorganic salts and other impurities.

[0052] The fluorine-containing compound used in the decomposition method of this disclosure may be any compound having a fluorine atom, but it is preferably a fluorine-containing low molecular weight compound with a molecular weight of 1000 or less, more preferably a fluorine-containing low molecular weight compound with a molecular weight of 800 or less, and even more preferably a fluorine-containing low molecular weight compound with a molecular weight of 500 or less. Furthermore, the above fluorine-containing compound may be a fluorine-containing organic compound or a fluorine-containing inorganic compound, but it is preferably a fluorine-containing organic compound.

[0053] The carbon number of the above fluorine-containing compound is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, even more preferably 5 or more, even more preferably 6 or more, even more preferably 7 or more, and particularly preferably 8 or more. In fluorine-containing compounds with relatively long chain lengths, such as those with 7 or more carbon atoms or 8 or more, ionizing radiation, and hydrogen atoms / molecules and hydrogen radicals generated in aqueous solutions by irradiation with ionizing radiation, readily extract fluorine from the molecular chain, so the decomposition rate can be particularly improved by carrying out step (1). The carbon number of the above fluorine-containing compound is also preferably 21 or less, more preferably 15 or less, even more preferably 14 or less, even more preferably 13 or less, particularly preferably 10 or less, and most preferably 8 or less.

[0054] The above fluorine-containing compound may have hydrophilic groups. The hydrophilic groups may be carboxyl groups (-COOH) and their salt forms, and sulfo groups (-SO). ３ Examples include H) and its salt forms. In particular, carboxyl groups (-COOH) and its salt forms, and sulfo groups (-SO) ３ At least one selected from the group consisting of H) and its salt form group is preferred, and at least one selected from the group consisting of a carboxyl group (-COOH) and its salt form group is more preferred.

[0055] Examples of the fluorine-containing compounds mentioned above include fluorine-containing carboxylic acids and their salts, fluorine-containing sulfonic acids and their salts, and one or more of these can be used. In particular, at least one selected from the group consisting of fluorine-containing carboxylic acids and their salts, and fluorine-containing sulfonic acids and their salts is preferred, and at least one selected from the group consisting of perfluorocarboxylic acids and their salts, and perfluorosulfonic acids and their salts is more preferred. All of these may have an ether linkage (-O-).

[0056] Among the above fluorine-containing compounds, fluorine-containing organic compounds having 2 to 21 carbon atoms are preferred, and fluorine-containing organic compounds having 8 to 21 carbon atoms are more preferred. As the above fluorine-containing compound, at least one selected from the group consisting of fluorine-containing carboxylic acids and salts having 2 to 21 carbon atoms, and fluorine-containing sulfonic acids and salts having 2 to 21 carbon atoms is preferred, and at least one selected from the group consisting of fluorine-containing carboxylic acids and salts having 8 to 21 carbon atoms, and fluorine-containing sulfonic acids and salts having 8 to 21 carbon atoms is more preferred. As the above fluorine-containing compound, at least one selected from the group consisting of fluorine-containing carboxylic acids and salts having 4 to 8 carbon atoms, and fluorine-containing sulfonic acids and salts having 4 to 8 carbon atoms is also preferred, and at least one selected from the group consisting of fluorine-containing carboxylic acids and salts having 4 to 8 carbon atoms is also preferred.

[0057] In the decomposition method of this disclosure, it is also preferable to irradiate the composition containing the fluorine-containing compound with ionizing radiation. The form of the above composition is not limited and may be a gaseous substance, a mist, a liquid, a solid, or a combination thereof. The above composition may be at least one selected from the group consisting of a gaseous substance, a mist, a liquid, and a solid containing a fluorine-containing compound, and may be an aqueous solution, an aqueous dispersion, a slurry, soil, an adsorbent, etc., containing a fluorine-containing compound. Among these, an aqueous solution is preferred. In the decomposition method of this disclosure, it is preferable to irradiate the fluorine-containing compound contained in at least one selected from the group consisting of a gaseous substance, a mist, a liquid, and a solid with ionizing radiation.

[0058] Furthermore, one preferred form of the composition is one in which the composition contains a fluorine-containing compound and a liquid medium. In the above composition, the fluorine-containing compound may be dissolved in the liquid medium or dispersed in it, but it is preferable that it be dissolved. That is, one preferred form of the composition is one in which the composition is a solution containing a fluorine-containing compound. Examples of the above liquid medium include water, methanol, acetone, and other polar solvents. One of these liquid media may be used alone, or two or more may be used in combination. Among these, methanol, acetone, and water are preferred, and water is more preferred.

[0059] The above composition preferably contains at least water in addition to the fluorine-containing compound. In this case, the decomposition of the fluorine-containing compound is promoted by the direct action of ionizing radiation and hydrogen radicals generated by irradiation with ionizing radiation on the molecular chains of the fluorine-containing compound, thereby enabling more efficient decomposition of the fluorine-containing compound. In the decomposition method of this disclosure, it is preferable to irradiate the fluorine-containing compound in water with ionizing radiation, and more preferably to irradiate an aqueous solution containing the fluorine-containing compound with ionizing radiation.

[0060] If the above composition contains water, the water content is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 50% by mass or more, and even more preferably 100% by mass or more, relative to the fluorine-containing compound.

[0061] The ionizing radiation in the decomposition method of this disclosure is not limited to any radiation capable of ionizing a substance, but it is preferably ionizing light or an electron beam. Examples of the above-mentioned ionizing radiation include gamma rays, X-rays, electron beams, neutron beams, particle beams, plasma rays, high-energy ions, and ion beams, but ion beams, gamma rays, X-rays, or electron beams are preferred, and X-rays or electron beams are more preferred. Alternatively, from the viewpoint of industrial use, gamma rays or electron beams are more preferred. X-rays or electron beams generated from an electron accelerator are preferred because the apparatus configuration is simple and it is possible to process large quantities of fluorine-containing compounds. Furthermore, X-rays or electron beams from an electron accelerator are also preferred because they allow for small-scale apparatus configurations, such as for processing small amounts of fluorine-containing compounds.

[0062] Gamma rays can be generated, for example, from radioisotopes. X-rays can be generated, for example, as bremsstrahlung X-rays by irradiating a target such as a metal with a particle beam from a particle accelerator. Alternatively, quasi-monochromatic X-rays can be generated by colliding a laser beam with a high-energy electron beam and causing inverse Compton scattering (laser-Compton scattering). Furthermore, X-rays can be generated by synchrotron radiation, or by installing an undulator or wiggler in the lower stage of a particle accelerator. Electron beams can be generated, for example, from an electron accelerator. When using electron beams, it is preferable that the energy of the electron beam generated from the electron accelerator is 50 keV or higher, but it is more preferable that the energy of the electron beam generated from the electron accelerator is 1 MeV or higher, and even more preferable that it is 2 MeV or higher, in order to enable the processing of large quantities of fluorine-containing compounds. There is no particular upper limit to the energy. The energy of the electron beam generated from the electron accelerator may be 10 MeV or less, and preferably 7 MeV or less, in order to avoid the activation of materials by photo-nuclear reactions. Furthermore, the electron flow is preferably 0.1 mA or more, more preferably 1 mA or more, even more preferably 5 mA or more, and may be 100 mA or less. In addition to irradiation with a continuous electron flow, electrons may be irradiated repeatedly in a pulsed manner. There may also be multiple irradiation sources. For example, irradiation may be performed not only from one direction from one electron accelerator, but also from two or more directions from two or more electron accelerators. Of course, the beam may be distributed from one accelerator and irradiated from multiple directions.

[0063] The absorbed dose of ionizing radiation in step (1) is preferably, for example, 1 kGy or more, more preferably 10 kGy or more, even more preferably 50 kGy or more, even more preferably 100 kGy or more, even more preferably 150 kGy or more, even more preferably 200 kGy or more, even more preferably 250 kGy or more, especially preferably 300 kGy or more, and also preferably 10 MGy or less, more preferably 5 MGy or less, even more preferably 1 MGy or less, even more preferably 750 kGy or less, even more preferably 500 kGy or less, and even more preferably 400 kGy or less. The irradiation with the above ionizing radiation may be carried out continuously until the desired absorbed dose is reached, or it may be carried out intermittently and repeatedly until the cumulative absorbed dose reaches the desired dose.

[0064] The dose rate of ionizing radiation in step (1) is preferably 10 Gy / h or more, more preferably 0.1 kGy / h or more, even more preferably 1 kGy / h or more, even more preferably 3 kGy / h or more, even more preferably 10 kGy / h or more, even more preferably 200 kGy / h or more, even more preferably 2 MGy / h or more, even more preferably 10 MGy / h or more, and especially preferably 200 MGy / h or more, and may also be 10 GGy / h or less.

[0065] The irradiation temperature of the ionizing radiation in step (1) is preferably -20°C or higher, more preferably -10°C or higher, even more preferably 0°C or higher, even more preferably 1°C or higher, even more preferably 5°C or higher, even more preferably 10°C or higher, and even more preferably 15°C or higher, and may also be 200°C or lower, 150°C or lower, 100°C or lower, or even less than 100°C. It may even be 50°C or lower. Economically, it is preferable to irradiate in a temperature range from room temperature to about 50°C. In order to increase the decomposition efficiency by radiation, the irradiation method may be controlled by external temperature control to prevent hydrogen radicals from being deactivated by excessive temperature rise due to beam heating, or by controlling the irradiation method by intermittently repeating irradiation to suppress the rise in temperature or promote cooling.

[0066] In step (1), the irradiation temperature of the ionizing radiation is preferably between -20°C and 40°C. Under conditions of pH 4 or lower, the ionizing radiation generates heat, which can deactivate hydrogen radicals and reduce the reaction efficiency of the decomposition reaction of fluorine-containing compounds. By setting the irradiation temperature during ionizing radiation within the above range, fluorine-containing compounds can be decomposed more efficiently.

[0067] In step (1), the irradiation with ionizing radiation is preferably carried out in an atmosphere with an oxygen concentration of less than 30 volume percent. More preferably, it is 25 volume percent or less, even more preferably 15 volume percent or less, even more preferably 10 volume percent or less, and even more preferably 5 volume percent or less. By setting the oxygen concentration during irradiation with ionizing radiation within the above range, fluorine-containing compounds can be decomposed more efficiently.

[0068] The dissolved oxygen concentration in the solution containing the fluorine-containing compound in step (1) is preferably 15 mg / L or less. More preferably 12 mg / L or less, even more preferably 10 mg / L or less, and may also be 0 mg / L or more. By setting the dissolved oxygen concentration in the solution containing the fluorine-containing compound within the above range when irradiating with ionizing radiation, the fluorine-containing compound can be decomposed more efficiently. Active measures may or may not be taken to reduce the dissolved oxygen concentration in the solution containing the fluorine-containing compound. The irradiation may be carried out in a container with a closed bubbling vent using nitrogen gas or argon gas to actively reduce the dissolved oxygen concentration to a value lower than the saturated dissolved oxygen concentration. More preferably, a dissolved oxygen concentration close to zero is preferred. The dissolved oxygen concentration is measured using a dissolved oxygen meter (DO meter) or the like.

[0069] The irradiation with ionizing radiation in step (1) may be carried out substantially in the absence of oxygen or in the presence of oxygen, but it is preferable to carry it out substantially in the absence of oxygen and / or in a substantially closed space as described later, and more preferably substantially in the absence of oxygen, in order to decompose fluorine-containing compounds more efficiently. In particular, when decomposing fluorine-containing compounds in liquid substances such as water, it is preferable to carry out the irradiation substantially in the absence of oxygen and / or in a substantially closed space as described later, and more preferably substantially in the absence of oxygen.

[0070] In this specification, "substantially oxygen-free" means that the oxygen concentration in the atmosphere in which the process is carried out is less than 2.0 volume%. In order to more efficiently decompose fluorine-containing compounds, the oxygen concentration is preferably 1.0 volume% or less, more preferably less than 1.0 volume%, even more preferably 0.5 volume% or less, even more preferably 0.1 volume% or less, and particularly preferably 0.01 volume% or less. The lower limit of the oxygen concentration may be below the detection limit. The main component gas at this time may be an inert gas. Examples of inert gases include nitrogen gas, argon gas, helium gas, and mixtures thereof. For industrial use, nitrogen gas is preferred. In a substantially closed space, as described later, the oxygen concentration in the atmosphere in which the process is carried out is preferably less than 20 volume% before the process is carried out. In a substantially closed space, as described later, the oxygen concentration decreases as oxygen in the space is consumed in the initial stages of the reaction. Therefore, if the oxygen concentration is less than 20 volume% before the process is carried out, the substantially oxygen-free state described above can be maintained during the process. The above oxygen concentration can be easily measured by methods such as analyzing the atmosphere in which the process is carried out, for example, by analyzing the gas phase portion in the container in which the above fluorine-containing compound is placed using gas chromatography, by using an oxygen concentration measuring instrument, or by examining the color of an oxygen indicator placed in the container.

[0071] When irradiating a fluorine-containing compound contained in a liquid such as an aqueous solution, the absence of substantially no oxygen means that the oxygen concentration in the liquid is less than 2.0% by volume. In order to decompose the fluorine-containing compound more efficiently, the oxygen concentration is preferably 1.0% by volume or less, more preferably less than 1.0% by volume, even more preferably 0.5% by volume or less, even more preferably 0.1% by volume or less, and particularly preferably 0.01% by volume or less. The lower limit of the oxygen concentration may be below the detection limit. The oxygen concentration in the liquid can be measured using a dissolved oxygen meter or the like. Even if the liquid contains more oxygen than the above range at the start of irradiation, the fluorine-containing compound can be efficiently decomposed by performing the irradiation in a substantially closed space, as described later.

[0072] Furthermore, the irradiation environment may be under pressure, atmospheric pressure, or reduced pressure. In terms of the working environment, a reduced pressure environment is preferred. Here, a reduced pressure environment means an environment in which the vacuum level is reduced to 100 Pa or less using a vacuum pump such as a diaphragm pump, oil rotary pump, or scroll pump. In order to decompose fluorine-containing compounds more efficiently, a vacuum level of 10 Pa or less is preferred, and 1 Pa or less is more preferred. As a method of maintaining the reduced pressure environment during irradiation, a sealed container for reduced pressure may be used, or the reduced pressure environment may be maintained by constantly evacuating the container with a vacuum pump, or the reduced pressure environment inside the container may be maintained by repeatedly turning the vacuum pump on and off intermittently. To remove oxygen present in the environment and create an environment that is virtually oxygen-free, an oxygen adsorbent may be used. An oxygen adsorbent is also called an oxygen scavenger, and the terms are synonymous. Of course, an oxygen adsorbent may be used in combination with the above methods. As a method of combination, an oxygen adsorbent may be placed in the sealed container together with the fluorine-containing compound, or the inside of the sealed container may be uniformly or unevenly coated with an oxygen adsorbent.

[0073] One method for carrying out irradiation in the substantially absence of oxygen is to carry out irradiation in a space where there is substantially no oxygen present.

[0074] The above-mentioned space, which is substantially free of oxygen, refers to a space in which the oxygen concentration within the space can be locally adjusted to the range described above during irradiation. For example, a container that can be sealed to allow adjustment of the oxygen concentration inside the space (hereinafter referred to as a sealed container) can be used. Alternatively, the space in which irradiation is performed may be locally made substantially free of oxygen by gas showers with inert gas or differential exhaust using a vacuum pump system. Furthermore, as a method of maintaining the substantially oxygen-free state during irradiation using inert gas, a sealed container may be used, or the state may be maintained by continuously circulating inert gas, or by repeatedly switching the circulation of inert gas on and off intermittently.

[0075] The above-mentioned sealed container may be connected to piping for drawing in or exhausting inert gases, etc., as described later, or for exhausting gases inside the sealed container, and may also be connected to other piping, lids, valves, flanges, etc. Furthermore, its shape is not particularly limited and may be cylindrical, prismatic, spherical, etc., and may be a bag with a variable internal volume. Furthermore, its material is not particularly limited and may be metal, glass, polymer, composite material made by laminating these, etc. The above-mentioned sealed container is preferably made of a material and structure that allows radiation to pass through and does not deteriorate by radiation irradiation, but is not limited thereto. Furthermore, the above-mentioned sealed container is not limited to a pressure-resistant container.

[0076] The above-mentioned sealed container is preferably made of a material that has corrosion resistance, particularly resistance to acids and bases. Preferred materials for the above-mentioned sealed container include ceramics; metals such as aluminum and its alloys, and stainless steel; rubber materials that can be sealed by physical stress, such as ethylene-propylene rubber, tetrafluoroethylene-propylene rubber, chloroprene rubber, and polyester elastomer; and materials that can be sealed by heat fusion or epoxy adhesives. Among these, thermoplastic organic materials that can be sealed by heat fusion are particularly preferred. In terms of resistance to ionizing radiation irradiation, among the thermoplastic organic materials mentioned above, polyesters such as polyethylene terephthalate (PET), polyamide (PA), polyethylene (PE), polyamide-imide (PAI), nylon, polyvinyl chloride (PVC), thermoplastic polyimide (TPI), polyphenylene sulfide (PPS), polyetherimide (PEI), cyclic polyolefin (COP), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), hexafluoropropylene-tetrafluoroethylene copolymer (FEP), and perfluoroalkoxyalkane (PFA) are preferred. Furthermore, these materials may be multilayer films with two or three layers, or even composite multilayer films of organic and inorganic materials combined with aluminum foil or the like.

[0077] The state in which the sealed container is substantially free of oxygen can be achieved, for example, by creating a substantially vacuum inside the sealed container or by filling it with an inert gas. Here, substantially vacuum means that the pressure inside the container is 100 Pa or less, preferably 50 Pa or less, and more preferably 10 Pa or less. Alternatively, the state in which the sealed container is substantially free of oxygen can also be achieved, for example, by performing irradiation when the oxygen concentration inside the sealed container is less than 20 volume percent before the process is carried out, thereby chemically reacting the organic material or fluorine-containing compound constituting the sealed container with oxygen and consuming the oxygen, thereby reducing the oxygen concentration.

[0078] The inert gas mentioned above must be inert to the decomposition reaction of fluorine-containing compounds caused by radiation irradiation. Examples of such inert gases include nitrogen, helium, argon, and neon. Among these, nitrogen is preferred.

[0079] The above inert gas preferably has an oxygen content of less than 2.0 volume%, more preferably 1.0 volume% or less, even more preferably less than 1.0 volume%, even more preferably 0.5 volume% or less, even more preferably 0.1 volume% or less, and particularly preferably 0.01 volume% or less. The lower limit is not particularly limited and may be an amount below the detection limit. When the oxygen content in the above inert gas is within the above range, fluorine-containing compounds can be decomposed more efficiently. The oxygen content can be confirmed by gas chromatography analysis, as well as by a galvanic cell type oxygen concentration meter, a zirconia type oxygen concentration meter, oxygen detection paper, etc.

[0080] In step (1), irradiation with ionizing radiation may be carried out under an atmosphere of 1 atm or higher. More preferably, it may be 5 atm or higher, even more preferably 10 atm or higher, and also preferably 100 atm or lower, more preferably 50 atm or lower, and even more preferably 20 atm or lower. By setting the pressure during irradiation with ionizing radiation within the above range, fluorine-containing compounds can be decomposed more efficiently.

[0081] Furthermore, hydrogen gas may be present in the atmosphere to efficiently decompose the fluorine-containing compound by reacting it with hydrogen. While there are no particular restrictions on the hydrogen concentration in the atmosphere at this time, it is preferable to have a concentration of less than 3% by volume from the viewpoint of ease of handling.

[0082] The oxygen adsorbent described above is not particularly limited as long as it has the function of adsorbing oxygen, and known adsorbents that exhibit oxygen adsorption effects can be used, such as inorganic oxygen adsorbents such as iron-based, zinc-based, and hydrosulfite-based, and organic oxygen adsorbents such as ascorbic acid-based, polyhydric alcohol-based, and activated carbon-based. The oxygen adsorbent described above may be a water-dependent type that requires water when reacting with oxygen, or a self-reacting type that does not require water, but a self-reacting type is preferred. As the oxygen adsorbent described above, iron-based self-reacting oxygen adsorbents and quicklime are preferred, and among these, iron-based self-reacting oxygen adsorbents are preferred.

[0083] The decomposition method of this disclosure preferably further includes the steps of placing the material to be processed (the fluorine-containing compound or a composition containing the fluorine-containing compound) into a sealed container in the substantially absence of oxygen, and / or removing oxygen from the material to be processed. This step may be performed before step (1).

[0084] Methods for placing the material to be treated into a sealed container in the substantially absence of oxygen include, for example, a method in which the material to be treated is placed in the sealed container, and then, if necessary, an oxygen adsorbent is added to the sealed container and the inside of the sealed container is degassed under reduced pressure; a method in which the material to be treated and at least one selected from the group consisting of an inert gas and an oxygen adsorbent are placed in the sealed container; and a combination of these methods.

[0085] Methods for removing oxygen from a material to be treated include placing the material in a sealed container and repeatedly performing degassing under reduced pressure and replacement with an inert gas, or gradually reducing the oxygen concentration by circulating an inert gas through the material, such as through bubbling.

[0086] It is also preferable to carry out the irradiation with the above-mentioned ionizing radiation in a substantially enclosed space. Here, a substantially enclosed space means a space in which no additional oxygen is supplied. In a substantially enclosed space, oxygen may be present in the space (including in the object being treated) at the start of irradiation, for example, 2.0 volume percent or more of oxygen, or an amount of oxygen equivalent to that of the atmosphere. Even if oxygen is present in the space at the start of irradiation, since no additional oxygen is supplied, the oxygen in the space is consumed in the initial stages of the reaction, and thereafter oxygen becomes substantially absent, so it is thought that fluorine-containing compounds can be decomposed. Therefore, there is an advantage that it is not necessary to remove oxygen from the space or the object being treated beforehand. As a substantially enclosed space, for example, the sealed container described above can be used.

[0087] In a configuration in which irradiation is carried out in a substantially closed space, if oxygen is present in the space at the start of irradiation, the fluorine-containing compound can be decomposed more efficiently by setting the absorbed dose to 50 kGy or more, preferably 100 kGy or more, and more preferably 150 kGy or more. Furthermore, the fluorine-containing compound can be decomposed more efficiently by setting the volume filling rate of the material to be treated in the above space to 70% or more, preferably 75% or more, and more preferably 80% or more.

[0088] The irradiation with ionizing radiation in step (1) must be carried out at a pH of 4 or less in the system. In order to decompose fluorine-containing compounds more efficiently, the pH is preferably less than 4, more preferably 3 or less, even more preferably 2.5 or less, and even more preferably 2 or less. It may also be 0 or more, 0.5 or more, or 1 or more. The pH in the system can be measured using a pH meter.

[0089] In step (1), it is preferable to maintain the pH in the system within the above-mentioned range during the period from the start to the end of the ionizing radiation irradiation. This allows for more efficient decomposition of fluorine-containing compounds.

[0090] In step (1), the pH of the system can be adjusted, for example, by adding an acidic substance and, if necessary, a basic substance to the reaction system. Examples of the acidic substance include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and sulfonic acid; and organic acids such as formic acid, acetic acid, and lactic acid. One or more of these can be used. Hydrochloric acid is preferred. Examples of the basic substance include inorganic bases such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia; and organic bases such as amines. One or more of these can be used. Sodium hydroxide is preferred.

[0091] In step (1), methods for maintaining the pH of the system within the above-mentioned range include, for example, adding an acidic substance (and a basic substance if necessary) in response to changes in pH during irradiation, or introducing an excess amount of acidic substance into the system beforehand. If necessary, the pH of the system may be continuously measured during irradiation. Furthermore, the addition of acidic substances (and basic substances if necessary) may be done all at once, intermittently, or continuously.

[0092] In step (1), the concentration of the fluorine-containing compound in the system (initial concentration) may be, for example, 0.01 mM (molecular / L) or higher, but it is preferable that it be 0.1 mM or higher, more preferably 0.5 mM or higher, even more preferably 0.8 mM or higher, and may also be 15 mM or lower, or 12 mM or lower, in order to decompose the fluorine-containing compound more efficiently. When the number of carbon atoms in the fluorine-containing compound is 5 or less, the concentration is preferably 3 mM or higher, more preferably 5 mM or higher, and even more preferably 8 mM or higher. When the number of carbon atoms in the fluorine-containing compound is 6 or more, the concentration is preferably 8 mM or lower, more preferably 5 mM or lower, and even more preferably 3 mM or lower.

[0093] Step (1) can be carried out in either a batch or continuous manner. Continuous processing is preferable because it facilitates the large-scale processing of fluorine-containing compounds. Multiple batch processing steps are also possible.

[0094] Thus, in step (1), continuous irradiation with ionizing radiation is also a preferred configuration. Continuous processing makes it easy to process large quantities. Furthermore, compared to batch processing, a higher decomposition effect can be achieved even at low doses. In this specification, continuous irradiation with ionizing radiation means irradiating with ionizing radiation while supplying (adding) and discharging (removing) the contents of the irradiation container (composition containing fluorine compounds). Therefore, in this specification, the configuration of continuous irradiation with ionizing radiation does not include configurations in which ionizing radiation is irradiated without supplying and discharging the contents of the irradiation container. However, configurations in which ionizing radiation is continuously irradiated while moving a container such as a container containing the contents to the irradiation section on a conveyor or the like are included.

[0095] In step (1), in a configuration in which ionizing radiation is continuously irradiated, it is preferable that the flow path through which the composition containing the fluorine-containing compound passes has at least one flow path configuration within the ionizing radiation irradiation area. A specific example of a flow path configuration is shown in Figure 1. Examples include the folded flow path configuration shown in Figure 1(a), the parallel flow path configuration shown in Figure 1(b), and the water tank type flow path configuration shown in Figure 1(c). Furthermore, in a vertical irradiation method, if the irradiation surface is left open and covered with a film or the like to prevent the scattering of the composition and protect the accelerator's exit window, it is also possible to form a concave flow path.

[0096] In step (1), when ionizing radiation is continuously irradiated, it is preferable to irradiate the composition containing the fluorine-containing compound in a uniform manner. Methods for doing so include stirring and narrowing the channel diameter. Stirring methods include introducing a line mixer, creating rifling grooves in the irradiation area, and thermal convection.

[0097] The material of the irradiation surface for ionizing radiation in the above-mentioned flow path is preferably at least one selected from the group consisting of metals (including alloys), ceramics, and polymer materials, from the viewpoint of being able to irradiate with ionizing radiation continuously, with metals being particularly preferred. As the above-mentioned metal, a metal with a specific gravity of 9 or less is preferred, and for example, a single metal composition of aluminum, titanium, or iron, or an alloy composition containing one or more of these is more preferred. Alternatively, a laminated material in which these metals are coated with a polymer film may also be used. As the above-mentioned polymer material, a radiation-resistant polymer or fiber-reinforced plastic (FRP) is more preferred, and among fiber-reinforced plastics, glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (ArFRP), and carbon fiber reinforced plastic (CFRP) containing a resin having a polymer structure with a benzene ring are more preferred. As the above-mentioned ceramic material, fine ceramics such as silicon-based, aluminum-based, and titanium-based ceramics are preferred, as well as hybrid ceramics mixed with polymers, and metal-bonded ceramics and ceramic fiber reinforced ceramics (CRC) composited with metals are preferred. Furthermore, in cases where the container is moved to the irradiation area by a conveyor belt or the like while being continuously irradiated with ionizing radiation, polyethylene or other materials can be used for the irradiation surface of the ionizing radiation.

[0098] Furthermore, slits may be provided in the irradiation surface, and the material of the slit portion may include a titanium thin film, conductive glass, or tempered glass with a metal wire inside that serves as a substitute for grounding. In addition, polymer films such as polyimide, polyethylene, polyvinyl chloride, or nylon may be used, provided that they are replaced periodically.

[0099] The thickness of the irradiation surface can be appropriately set depending on the material and irradiation conditions, but for example, it is preferably 1000 μm or less, more preferably 700 μm or less, and even more preferably 500 μm or less. The lower limit is not particularly limited, but for example, it is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more. As an example, when irradiating with an electron beam of several MeV, it is preferable to use an aluminum or titanium tube with a thickness of 300 μm or less, and when irradiating with an electron beam of 5 to 10 MeV, it is preferable to use a stainless steel tube with a thickness of 500 μm or less.

[0100] The irradiation surface is preferably irradiated with an energy decay rate of 30% or less. More preferably, it is 20% or less, and even more preferably, 10% or less. The lower limit is not particularly limited and may be, for example, 1% or more. By having the energy decay rate of the irradiation surface within the above range, the irradiation energy can be sufficiently utilized for the decomposition reaction of fluorine-containing compounds, and the fluorine-containing compounds can be decomposed more efficiently. The energy decay rate can be determined by the Monte Carlo method, for example, by the EGS code developed at KEK or the PHITS (Particle and Heavy Ion Transport code System) code developed at JAEA. Furthermore, in practical measurements, a layer of CTA (cellulose triacetate) film and a Gafchromic dosimeter is irradiated, and the absorption spectrum of each layer is measured using a spectrophotometer to calculate the absorbed dose and measure the energy distribution. In addition, the attenuation rate can be measured by irradiating a polyethylene block and then analyzing the absorption of double bonds using micro-FT-IR (Reference: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Vol 265, pp. 312-317, 2007).

[0101] The decomposition method of this disclosure may further preferably include a step of irradiating the fluorine-containing compound with ionizing radiation under basic conditions (hereinafter also referred to as step (2)). This allows for more efficient decomposition of the fluorine-containing compound, and in particular, allows for more efficient decomposition of fluorine-containing compounds with relatively short chain lengths, such as those with 6 or fewer carbon atoms or 5 or fewer carbon atoms.

[0102] The order in which steps (1) and (2) are performed is not particularly limited; step (2) may be performed before step (1), step (2) may be performed after step (1), or steps (1) and (2) may be repeated alternately. It is preferable to perform step (2) after step (1) in order to decompose fluorine-containing compounds more efficiently. As described above, step (1) can accelerate the decomposition of fluorine-containing compounds with relatively long chains, so by decomposing fluorine-containing compounds with relatively long chains in step (1) and then decomposing relatively short-chain fluorine-containing compounds in step (2), the decomposition efficiency of fluorine-containing compounds can be further increased.

[0103] The ionizing radiation and absorbed doses that can be used in process (2) are the same as in process (1). However, in process (2), fluorine-containing compounds can be efficiently decomposed even at low doses such as 150 kGy or less, 100 kGy or less, and 80 kGy or less.

[0104] The pH of the system in step (2) is preferably 8 or higher, more preferably 9 or higher, even more preferably 10 or higher, even more preferably 11 or higher, particularly preferably 12 or higher, and may also be 14 or lower. When the pH is within the above range, hydrogen fluoride generated by irradiation can be efficiently removed, and the decomposition reaction of fluorine-containing compounds can be promoted, so that fluorine-containing compounds can be decomposed even more efficiently.

[0105] In step (2), it is preferable to maintain the pH in the system within the above-mentioned range during the period from the start to the end of the ionizing radiation irradiation. This is because the irradiation generates acid, and as the pH changes to the neutral side, the proportion of hydrated electrons generated in the aqueous solution by radiation irradiation that react with substances other than fluorine-containing compounds increases, thereby suppressing the decomposition of fluorine-containing compounds. By maintaining the pH in the system within the above-mentioned range, fluorine-containing compounds can be decomposed even more efficiently.

[0106] In step (2), hydroxide ions (OH) in the system － The hydroxide ion concentration is preferably 0.1 mM (mol / L) or higher, more preferably 1 mM or higher, even more preferably 10 mM or higher, even more preferably 30 mM or higher, even more preferably 50 mM or higher, even more preferably 70 mM or higher, particularly preferably 90 mM or higher, and may be 1 M or less, preferably 300 mM or less, more preferably 200 mM or less, and even more preferably 150 mM or less. When the hydroxide ion concentration is within the above range, hydrogen fluoride generated by irradiation can be efficiently removed, and the decomposition reaction of fluorine-containing compounds can be promoted, so that fluorine-containing compounds can be decomposed even more efficiently. The hydroxide ion concentration in the system is measured using a pH meter or the like.

[0107] In step (2), it is preferable to maintain the concentration of hydroxide ions in the system within the above-mentioned range during the period from the start to the end of the ionizing radiation irradiation. This allows for more efficient decomposition of fluorine-containing compounds.

[0108] The pH or hydroxide ion concentration in the system in step (2) can be adjusted, for example, by adding a basic substance and, if necessary, an acidic substance to the reaction system. Examples of basic and acidic substances that can be used in step (2) are the same as those that can be used in step (1).

[0109] In step (2), methods for maintaining the pH or hydroxide ion concentration in the system within the above-mentioned range include, for example, adding a basic substance (and an acidic substance if necessary) in response to changes in pH or hydroxide ion concentration during irradiation, or introducing an excess amount of basic substance into the system beforehand. If necessary, the pH or hydroxide ion concentration in the system may be continuously measured during irradiation. Furthermore, the addition of basic substances (and acidic substances if necessary) may be done all at once, intermittently, or continuously.

[0110] In step (2), the concentration of the fluorine-containing compound in the system (initial concentration) may be, for example, 0.001 mM or more, but it is preferable that it be 0.01 mM or more, more preferably 0.05 mM or more, even more preferably 0.1 mM or more, and may be 200 mM or less, preferably 100 mM or less, more preferably 10 mM or less, even more preferably 8 mM or less, and even more preferably 5 mM or less.

[0111] Step (2) may include step (2a) of removing hydrogen fluoride generated by irradiation with ionizing radiation. Hydrogen fluoride generated by irradiation may consume hydroxide ions in the system, inhibiting the decomposition reaction of fluorine-containing compounds. By removing hydrogen fluoride, the hydroxide ion concentration in the system can be maintained within a predetermined range, and the decomposition reaction of fluorine-containing compounds can be promoted, thus enabling more efficient decomposition of fluorine-containing compounds. It is preferable to carry out step (2) while removing hydrogen fluoride generated by irradiation with ionizing radiation.

[0112] Methods for removing hydrogen fluoride include methods using a basic substance (reacting with a basic substance) and methods for separating and removing hydrogen fluoride. These methods can be used individually or in combination.

[0113] Basic substances used to remove hydrogen fluoride include the basic substances mentioned above that can be used to adjust pH and hydroxide ion concentration. Removal of hydrogen fluoride using basic substances can be carried out, for example, by adding the basic substance so that the pH and hydroxide ion concentration remain within the ranges described above. As mentioned above, the basic substance may be added in response to changes in pH and hydroxide ion concentration, or an excess amount may be added beforehand. Hydrogen fluoride, which is sequentially generated by irradiation with ionizing radiation, is removed by being added to the system or by reacting with pre-existing basic substances.

[0114] The separation and removal of hydrogen fluoride can be carried out using separation techniques such as coagulation and sedimentation, or adsorption, and can also be carried out using separation and removal equipment that utilizes these separation techniques.

[0115] Step (2) can be carried out in either a batch or continuous manner. Continuous processing is preferable because it facilitates the large-scale processing of fluorine-containing compounds. Multiple batch processing steps are also possible.

[0116] The decomposition method of this disclosure may further preferably include a step of concentrating the fluorine-containing compound. This concentration step may be performed before irradiation with ionizing radiation. More specifically, it may be performed before step (1) or before step (2). If both steps (1) and (2) are performed, it may be performed between step (1) and step (2). In the concentration step, it is preferable to concentrate the compound so that the concentration of the fluorine-containing compound in the system falls within the range described above. The method of concentration is not particularly limited, and known methods may be employed.

[0117] The decomposition method of this disclosure can decompose the above-mentioned fluorine-containing compound. Examples of decomposition products include hydrogen fluoride, a fluorine-containing compound with a reduced number of carbon atoms compared to before treatment, and carbon dioxide.

[0118] The decomposition rate of the fluorine-containing compound in the decomposition method of this disclosure may be 5% or more, preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, even more preferably 30% or more, even more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, and especially preferably 90% or more. It may also be 100% or less, or 99.9% or less. The decomposition rate can be determined from the mass of the fluorine-containing compound to be treated before and after treatment.

[0119] This disclosure also relates to a decomposition system for fluorine-containing compounds, comprising an irradiation means for irradiating a fluorine-containing compound with ionizing radiation and an adjustment means (hereinafter also referred to as adjustment means (1)) for adjusting the pH in the system to 4 or less.

[0120] Since the decomposition system of this disclosure is equipped with the above-described means, it can be used in the decomposition method of this disclosure described above and can efficiently decompose fluorine-containing compounds.

[0121] Examples of fluorine-containing compounds and ionizing radiation in the decomposition system of this disclosure include those similar to those in the decomposition method of this disclosure.

[0122] The above-mentioned irradiation means is, for example, a device or facility for irradiating with ionizing radiation, which can irradiate a fluorine-containing compound with the above-mentioned dose of ionizing radiation.

[0123] The adjusting means (1) includes, for example, an acidic substance and, optionally, a basic substance. Preferably, the adjusting means (1) is capable of maintaining the pH of the system at 4 or below. The adjusting means (1) may also include an adding means (1) for adding an acidic substance (and, optionally, a basic substance) to the system.

[0124] The decomposition system of this disclosure may include adjustment means (2) for adjusting the pH in the system to the basic range. This allows for the step of irradiating the fluorine-containing compound with ionizing radiation under basic conditions, thereby enabling more efficient decomposition of the fluorine-containing compound.

[0125] The adjusting means (2) may be capable of adjusting the pH of the system to 8 or higher, and may include, for example, a basic substance and, if necessary, an acidic substance. Preferably, the adjusting means (2) is capable of maintaining the pH of the system at 8 or higher. The adjusting means (2) may also include an adding means (2) for adding a basic substance (and, if necessary, an acidic substance) to the system. Preferably, the adjusting means (2) is capable of adjusting the concentration of hydroxide ions in the system to 0.1 mM or higher, and more preferably, is capable of maintaining the concentration of hydroxide ions in the system at 0.1 mM or higher. The adjusting means (1) may also serve as the adjusting means (2).

[0126] The decomposition system of this disclosure preferably also includes a removal means for removing hydrogen fluoride generated by irradiation with the ionizing radiation. This can accelerate the decomposition reaction of the fluorine-containing compound when irradiating it with ionizing radiation under basic conditions, thereby enabling more efficient decomposition of the fluorine-containing compound. The removal means is, for example, the basic substance or separation and removal device described above.

[0127] The decomposition system of this disclosure preferably includes a storage means for storing the fluorine-containing compound. The storage means is, for example, a sealed container capable of storing the fluorine-containing compound. The sealed container is as described above.

[0128] The decomposition system of this disclosure may include adjustment means (3) for adjusting the oxygen concentration of the reaction system.

[0129] The decomposition method and decomposition system of this disclosure can be used for the decomposition treatment of fluorine-containing compounds, and can be suitably used, for example, for the treatment of water, soil, adsorbents, etc., containing fluorine-containing compounds. Furthermore, the decomposition method and decomposition system of this disclosure can be scaled up or down, allowing for the large-scale treatment of fluorine-containing compounds if scaled up, and enabling their introduction into public facilities, etc., if scaled down.

[0130] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0131] The present disclosure will now be further described with reference to examples, but the present disclosure is not limited to these examples.

[0132] Each value was determined using the following method.

[0133] <Decomposition Rate of Fluorine-Containing Compounds> The amount (mass) of fluorine-containing compounds in the sample before and after treatment was measured using liquid chromatography (Waters Acquity UPLC, detector: UV), and the decomposition rate was calculated based on the following formula: Decomposition rate (%) = (Amount of fluorine-containing compound before treatment - Amount of fluorine-containing compound after treatment) / (Amount of fluorine-containing compound before treatment)

[0134] The reagents used in each experimental example are as follows: (Fluorine-containing compounds) C4: Perfluoro-n-butanoic acid (PFBA) C6: Perfluoro-n-hexanoic acid (PFHxA) C8: Perfluorooctanoic acid (PFOA) (Acidic substances, basic substances) 1N hydrochloric acid: Manufactured by Kishida Chemical Co., Ltd. 1N sodium hydroxide aqueous solution: Manufactured by Kishida Chemical Co., Ltd. (Others) Calcium chloride: Manufactured by Kishida Chemical Co., Ltd., for U-tubes

[0135] Example 1 The initial concentration of the fluorine-containing compound was set to 0.1 mM. Aqueous solutions of C8 and C6, adjusted to pH 3 with 1N hydrochloric acid, were placed in 20 cc glass ampoules and sealed with silicone W caps. Then, nitrogen bubbling was performed at room temperature for 30 minutes to create an oxygen-free (virtually oxygen-free) environment. Next, gamma rays from cobalt-60 were irradiated at 100.8 kGy. The irradiation conditions at this time were an average dose rate of 2.4 kGy / h at the center of the sample and an irradiation temperature of 25°C. After irradiation, the ampoules were opened, transferred to screw tubes, and LC-UV analysis was performed. The results are shown in Table 1.

[0136]

[0137] Example 2 The initial concentration of the fluorine-containing compound was set to 10 mM. Aqueous solutions of C8, C6, and C4, adjusted to pH 2 with 1N hydrochloric acid, were placed in 20 cc glass ampoules and sealed with silicone W caps. Subsequently, some samples were subjected to nitrogen bubbling at room temperature for 30 minutes to create an oxygen-free environment, and samples were prepared under atmospheric conditions and under oxygen-free conditions. Next, gamma rays from cobalt-60 were irradiated up to a maximum of 168 kGy. The irradiation conditions at this time were an average dose rate of 2.4 kGy / h at the center of the sample and an irradiation temperature of 25°C. After irradiation, the ampoules were opened, transferred to screw tubes, and LC-UV analysis was performed. Figure 2 shows the relationship between absorbed dose and decomposition rate for each sample at room temperature, in an oxygen-free environment, and under atmospheric conditions, and under gamma ray irradiation. In Figure 2, "O2" indicates irradiation in an atmospheric environment, and "O2-free" indicates irradiation in an oxygen-free environment.

[0138] The results from Example 2 showed that fluorine-containing compounds can be decomposed even in an oxygen-free environment or in a sealed atmosphere.

[0139] Example 3 The initial concentrations of aqueous solutions of various fluorine-containing compounds, C8 and C4, were varied to 0.1 mM, 1 mM, and 10 mM. Each aqueous solution was adjusted to pH 2 with 1N hydrochloric acid, placed in a 20 cc glass ampoule, and sealed with a silicone W cap. Then, nitrogen bubbling was performed at room temperature for 30 minutes to create an oxygen-free environment for each sample. Next, gamma rays from cobalt-60 were irradiated at 100.8 kGy. The irradiation conditions at this time were an average dose rate of 2.4 kGy / h at the center of the sample and an irradiation temperature of 25°C. After irradiation, the ampoules were opened, transferred to screw tubes, and LC-UV analysis was performed. The results are shown in Table 2.

[0140]

[0141] Example 4 A 0.1 mM aqueous solution of C4, either without calcium chloride or with 0.1 mM to 1 mM added, was adjusted to pH 2 with 1N hydrochloric acid and placed in a 20 cc glass ampoule, sealed with a silicone W cap. Then, nitrogen bubbling was performed at room temperature for 30 minutes to prepare a sample in an oxygen-free environment. Next, gamma rays from cobalt-60 were irradiated at 100.8 kGy. The irradiation conditions at this time were an average dose rate of 2.4 kGy / h at the center of the sample and an irradiation temperature of 25°C. After irradiation, the ampoule was opened, transferred to a screw tube, and LC-UV analysis was performed. The results are shown in Table 3.

[0142]

[0143] The results from Example 4 showed that the presence of inorganic salts does not significantly affect the decomposition rate of fluorine-containing compounds.

[0144] Example 5-1 Initial concentrations of fluorine-containing compounds C8 and C6 were set to 0.1 mM, and aqueous solutions were prepared by adjusting the hydrogen chloride concentration to 100 mM (pH 2) using 1N hydrochloric acid. Each aqueous solution was placed in a 20 cc glass ampoule and sealed with a silicone W cap. Next, gamma rays from cobalt-60 were irradiated at 100.8 kGy. The irradiation conditions at this time were an average dose rate of 2.4 kGy / h at the center of the sample and an irradiation temperature of 25°C. After irradiation, the ampoules were opened, transferred to screw tubes, and LC-UV analysis was performed. The results are shown in Table 4.

[0145] Example 5-2 Each aqueous solution from Example 5-1 was placed in an Asahi Kasei Pax Hiryu™ HN-102 poly bag (250 mm x 150 mm, 75 μm thick) and sealed in air using a heat sealer. Next, an electron beam of 300 kGy was irradiated from an Iwasaki Electric low-energy electron accelerator (rated 250 kV, 10 mA). The irradiation conditions at this time were an acceleration voltage of 250 keV, a current of 3 mA, a transport speed of 20 m / min, and a temperature of 25°C. The dose rate per pass was 25 kGy / pass, as measured by a CTA film dosimeter. After irradiation, the bag was opened, the contents were transferred to a screw tube, and LC-UV analysis was performed. The results are shown in Table 4.

[0146]

[0147] Example 6 Each aqueous solution from Example 5-1 was placed in an Asahi Kasei Pax Hiryu™ HN-102 poly bag (250 mm x 150 mm, 75 μm thick) and then sealed by heat sealing. Next, electron beam irradiation was performed up to a maximum of 500 kGy using an Iwasaki Electric low-energy electron accelerator (rated 250 kV, 10 mA). The irradiation conditions at this time were an acceleration voltage of 250 keV, a current of 3 mA, a transport speed of 20 m / min, and a temperature of 25°C. The dose rate per pass was 25 kGy / pass, as measured by a CTA film dosimeter. After irradiation, the bags were opened, transferred to screw tubes, and LC-UV analysis was performed. Figure 3 shows the relationship between the dose of the electron beam (low energy) and the decomposition rate of each fluorine-containing compound.

[0148] Example 7 Initial concentrations of the fluorine-containing compounds C8 and C4 were set to 0.1 mM, and aqueous solutions were prepared by adjusting the hydrogen chloride concentration to 100 mM (pH 2) using 1N hydrochloric acid. The aqueous solutions were then placed in a plastic bag (250 mm x 150 mm, 75 μm thick) and sealed under air using a heat sealer. Next, irradiation was performed using a 2 MV high-energy electron accelerator (NHV Corporation). To avoid damage to the plastic bag due to beam heating, the irradiation conditions were set to an absorbed dose of 10 kGy per pass (acceleration voltage: 2 MeV, current: 2 mA, transport speed: 2.45 m / min, exit window-sample position distance: 20 cm). The sample was attached to a pallet (conveyor irradiation tray) for irradiation. The desired absorbed dose was achieved by changing the number of passes. After irradiation, the bag was opened, transferred to a screw-cap tube, and LC-UV analysis was performed. Figure 4 shows the relationship between the dose of electron beams (high energy) and the decomposition rate of each fluorine-containing compound.

[0149] Example 8: Irradiation in a flow state was simulated. The initial concentration of each fluorine-containing compound, C8, C6, and C4, was set to 0.1 mM, and aqueous solutions were prepared by adjusting the hydrogen chloride concentration to 100 mM (pH 2) using 1N hydrochloric acid. 10 cc of the sample was placed in a nylon tube with an outer diameter of 6 mm and an inner diameter of 4 mm and sealed. Next, irradiation was performed using a 2 MV high-energy electron accelerator (manufactured by NHV Corporation). The irradiation conditions at this time were an absorbed dose of 10 kGy per pass (acceleration voltage: 2 MeV, current value: 2 mA, transport speed: 2.45 m / min, exit window-sample position distance: 20 cm), and the sample was attached to a conveyor pallet and irradiated with 500 kGy. The absorbed dose was adjusted to the desired dose by changing the number of passes. After irradiation, the tube was opened, transferred to a screw tube, and LC-UV analysis was performed. The results are shown in Table 5. The pH of the aqueous solution after irradiation was 2.

[0150]

[0151] The results from Example 8 showed that a good decomposition rate can be obtained in a flow state (a state in which the sample is circulated in the tube).

[0152] Example 9 Initial concentrations of C8, C6, and C4 fluorine-containing compounds were set to 0.1 mM. 1 mM calcium chloride was added, and aqueous solutions were prepared by adjusting the hydrogen chloride concentration to 100 mM (pH 2) using 1N hydrochloric acid. The prepared samples were then placed in a plastic bag (250 mm x 150 mm, 75 μm thick) and sealed under air using a heat sealer. Next, the samples were irradiated using a 2 MV high-energy electron accelerator (NHV Corporation) at varying doses. To avoid damage to the plastic bag due to beam heating, the absorbed dose per pass was set to 10 kGy (acceleration voltage: 2 MeV, current: 2 mA, transport speed: 2.45 m / min, exit window-sample position distance: 20 cm). The desired absorbed dose was achieved by changing the number of passes. After irradiation, the bags were opened, transferred to screw-cap tubes, and LC-UV analysis was performed. The results are shown in Table 6.

[0153]

[0154] Example 10 Continuous irradiation was simulated. An aqueous solution was prepared by adjusting the concentration of hydrogen chloride to 100 mM (pH 2) using 1N hydrochloric acid, with an initial concentration of 0.1 mM of the fluorine-containing compound C8. The aqueous solution was pumped into the flow path. Continuous irradiation was performed under the following conditions: <Electron beam generator> Cockcroft-Walton electrostatic accelerator manufactured by NHV Corporation (rated: 40 kW, 2 MV, 20 mA) <Flow path> Material: Aluminum Outer diameter / Inner diameter: 3 mm / 2.4 mm Flow path length in irradiation area: 500 mm <Irradiation conditions> Temperature: 25°C Pressure: 1 atm Oxygen concentration: 21 vol% Flow rate: 5 mL / min Dose rate: Shown in Table 7 (Table 7 shows the relationship between current and dose when the flow rate is 5 mL / min.) Dose: Dose rate × Residence time (27.132 seconds)

[0155]

[0156] The results are shown in Table 8.

[0157]

Claims

1. A method for decomposing a fluorine-containing compound, comprising the step of irradiating the fluorine-containing compound with ionizing radiation under conditions of pH 4 or lower.

2. The decomposition method according to claim 1, wherein the fluorine-containing compound is a fluorine-containing organic compound.

3. The decomposition method according to claim 1 or 2, wherein the fluorine-containing compound is a fluorine-containing organic compound having 2 to 21 carbon atoms.

4. The decomposition method according to any one of claims 1 to 3, wherein the fluorine-containing compound is a fluorine-containing organic compound having 8 to 21 carbon atoms.

5. The decomposition method according to any one of claims 1 to 3, wherein the fluorine-containing compound is a fluorine-containing organic compound having 4 to 8 carbon atoms.

6. The decomposition method according to any one of claims 1 to 3, wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 2 to 21 carbon atoms and salts thereof, and fluorine-containing sulfonic acids having 2 to 21 carbon atoms and salts thereof.

7. The decomposition method according to any one of claims 1 to 3, wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 8 to 21 carbon atoms and salts thereof, and fluorine-containing sulfonic acids having 8 to 21 carbon atoms and salts thereof.

8. The decomposition method according to any one of claims 1 to 3, wherein the fluorine-containing compound is at least one selected from the group consisting of fluorine-containing carboxylic acids having 4 to 8 carbon atoms and salts thereof.

9. A decomposition method according to any one of claims 1 to 8, wherein the fluorine-containing compound is irradiated with the ionizing radiation, the fluorine-containing compound being contained in at least one selected from the group consisting of gaseous substances, mist-like substances, liquid substances, and solid substances.

10. A decomposition method according to any one of claims 1 to 9, wherein the fluorine-containing compound in water is irradiated with the ionizing radiation.

11. The decomposition method according to any one of claims 1 to 10, wherein the ionizing radiation is irradiated in an atmosphere in which the oxygen concentration is less than 30 volume percent.

12. The decomposition method according to any one of claims 1 to 11, wherein the ionizing radiation is irradiated in an atmosphere of -20°C or higher and less than 100°C.

13. The decomposition method according to any one of claims 1 to 12, wherein the ionizing radiation is irradiated in an atmosphere of -20°C or higher and 40°C or lower.

14. The decomposition method according to any one of claims 1 to 13, wherein the ionizing radiation is irradiated in substantially the absence of oxygen.

15. The decomposition method according to any one of claims 1 to 14, wherein the ionizing radiation is irradiated in a substantially enclosed space.

16. The decomposition method according to any one of claims 1 to 15, wherein the ionizing radiation is irradiated in an atmosphere of 1 atm or higher.

17. The decomposition method according to any one of claims 1 to 16, wherein the ionizing radiation is ionizable light or electron beam.

18. The decomposition method according to any one of claims 1 to 17, wherein the ionizing radiation is at least one selected from the group consisting of gamma rays, electron beams, X-rays, and ion beams.

19. The decomposition method according to any one of claims 1 to 18, wherein the ionizing radiation is gamma rays or electron beams.

20. The decomposition method according to any one of claims 1 to 19, wherein the absorbed dose of the ionizing radiation is 1 kGy or more.

21. The decomposition method according to any one of claims 1 to 20, wherein the absorbed dose of the ionizing radiation is 10 kGy or more.

22. The decomposition method according to any one of claims 1 to 21, wherein the absorbed dose of the ionizing radiation is 10 kGy to 10 mgy.

23. The decomposition method according to any one of claims 1 to 22, wherein the dose rate of the ionizing radiation is 10 Gy / h or more.

24. The decomposition method according to any one of claims 1 to 23, wherein the pH of the system is maintained at 4 or less during the period from the start to the end of irradiation with the ionizing radiation.

25. The decomposition method according to any one of claims 1 to 24, wherein the concentration of the fluorine-containing compound in the system is 0.5 mM or more.

26. The decomposition method according to any one of claims 1 to 24, wherein the concentration of the fluorine-containing compound in the system is 0.1 to 12 mM.

27. The decomposition method according to any one of claims 1 to 26, wherein 15% or more of the fluorine-containing compound is decomposed.

28. The decomposition method according to any one of claims 1 to 27, wherein the ionizing radiation is irradiated continuously.

29. A decomposition method according to any one of claims 1 to 28, wherein the composition comprising the fluorine-containing compound and the liquid medium is irradiated with the ionizing radiation.

30. The decomposition method according to any one of claims 1 to 29, wherein an aqueous solution containing the fluorine-containing compound is irradiated with the ionizing radiation.

31. The decomposition method according to any one of claims 1 to 30, wherein the material of the irradiation surface for ionizing radiation in the channel through which the composition containing the fluorine compound passes is at least one selected from the group consisting of metals, ceramics, and polymer materials.

32. The decomposition method according to any one of claims 1 to 31, wherein the irradiation surface has an energy decay rate of 30% or less.

33. The decomposition method according to any one of claims 1 to 32, wherein the thickness of the irradiated surface is 10 to 1000 μm.

34. The decomposition method according to any one of claims 1 to 33, wherein the ionizing radiation is irradiated in an atmosphere of 15 to 50°C.

35. The decomposition method according to any one of claims 1 to 34, wherein the ionizing radiation is irradiated in an atmosphere of 1 to 20 atm.

36. The decomposition method according to any one of claims 1 to 35, wherein the absorbed dose of the ionizing radiation is 50 to 400 kGy.

37. The decomposition method according to any one of claims 1 to 36, wherein the material of the irradiated surface for ionizing radiation in the channel through which the composition containing the fluorine compound passes is a metal.

38. The decomposition method according to any one of claims 1 to 37, further comprising the step of irradiating the fluorine-containing compound with ionizing radiation under basic conditions.

39. The decomposition method according to any one of claims 1 to 38, further comprising the step of concentrating the fluorine-containing compound.

40. A system for decomposing fluorine-containing compounds, comprising an irradiation means for irradiating fluorine-containing compounds with ionizing radiation, and an adjustment means for adjusting the pH of the system to 4 or less.

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