Method for removing organofluorine compounds

Abstract

This invention provides a method for removing organofluorine compounds that can remove PFAS from treated water in the presence of high concentrations of chloride ions. [Solution] A method for removing organofluorine compounds, comprising bringing water to be treated, which has a pH of 1.0 or less, a chloride ion concentration of 10,000 mg / L or more, and contains PFAS having 4 to 8 carbon atoms, into contact with an ion exchange resin to adsorb and remove the PFAS.

Description

Technical Field

[0001] The present invention relates to a method for removing an organic fluorine compound from treated water containing the organic fluorine compound.

Background Art

[0002] Per- and polyfluoroalkyl substances (hereinafter, "PFAS") are widely used in various industrial and chemical applications such as surface treatment agents, packaging materials, and liquid fire extinguishing agents. Since PFAS is a highly stable chemical substance, it is difficult to decompose under natural conditions after being released into the environment. Therefore, it has been found to have long-term persistence and bioaccumulation in the environment, and various toxicity possibilities have been suggested.

[0003] In recent years, the presence of PFAS in environmental water has been confirmed and has become a problem. In particular, in industrial fields such as semiconductor manufacturing, metal surface treatment, and chemical manufacturing, cases have been reported where PFAS is mixed into strongly acidic waste liquids containing hydrochloric acid or wastewater containing high concentrations of inorganic ions. As a means for removing PFAS from environmental water, Patent Document 1 discloses activated carbon having a high collection rate of PFAS in a water sample and a filter body using the same. Further, Patent Document 2 discloses a treatment system for an organic fluorine compound that can detoxify the organic fluorine compound in the treated water at a low cost.

[0004] Furthermore, Patent Document 3 describes a method for removing an organic fluorine compound from treated water containing interfering ions such as high-concentration sulfate ions and the organic fluorine compound. In this method, a step of adsorbing and removing PFAS by bringing the treated water containing PFAS into contact with an ion exchange resin in a system in which inorganic ions mainly composed of sulfate ions coexist is included.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-171711 [Patent Document 2] Japanese Patent Publication No. 2010-131478 [Patent Document 3] Special Publication No. 2013-542844 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, methods for removing PFAS from environmental water include using activated carbon and using ion exchange resins. However, it has been pointed out that activated carbon does not have sufficient adsorption capacity for short-chain PFAS (especially those with 6 or fewer carbon atoms), making it difficult to obtain a practical removal rate. Furthermore, although Patent Document 3 describes a technique for adsorbing and removing PFAS using ion exchange resins, it does not target systems with strongly acidic conditions (e.g., pH 1.0 or lower) and high concentrations of chloride ions (e.g., 10,000 mg / L or higher). Thus, in reality, there has been little practical consideration given to the removal of PFAS from treated water such as industrial wastewater that is strongly acidic and has high concentrations of chloride ions.

[0007] Under these circumstances, the object of the present invention is to provide a method for removing organofluorine compounds that can remove PFAS from water to be treated even when high concentrations of chloride ions are present under strongly acidic conditions. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to solve the above problems and have found that the following invention is suitable for the above purpose, leading to the present invention.

[0009] In other words, the present invention relates to the following invention. <1> A method for removing organofluorine compounds, comprising bringing treated water containing PFAS having a pH of 1.0 or less, a chloride ion concentration of 10,000 mg / L or more, and 4 to 8 carbon atoms into contact with an ion exchange resin to adsorb and remove the PFAS. <2> The treated water is a wastewater containing hydrochloric acid, with a chloride ion concentration of 100,000 mg / L or more and a fluoride ion concentration of 1,000 mg / L or more. <1> A method for removing organofluorine compounds as described above. <3> The PFAS is at least one selected from perfluorocarboxylic acids having 4 to 8 carbon atoms. <1> or <2> A method for removing organofluorine compounds as described above. <4> The removal rate of PFAS with 4 carbon atoms is over 90%. <1> from <3> A method for removing organofluorine compounds as described in any of the following. <5> The removal rate of PFAS with 5 to 8 carbon atoms is over 95% for each. <1> from <4> A method for removing organofluorine compounds as described in any of the following. <6> The ion exchange resin is an anion exchange resin having an amine group. <1> from <5> A method for removing organofluorine compounds as described in any of the following. <7> The ion exchange resin is made of a styrene-based resin having a quaternary amine group and is a gel-type strongly basic anion exchange resin. <6> A method for removing organofluorine compounds as described above. <8> The process includes, before bringing the water to be treated into contact with the ion exchange resin, a step of bringing the water to be treated into contact with an adsorbent different from the ion exchange resin. <1> from <7> A method for removing organofluorine compounds as described in any of the following. <9> The adsorbent is activated carbon. <8> A method for removing organofluorine compounds as described above. [Effects of the Invention]

[0010] According to the present invention, organofluorine compounds can be removed from treated water containing contaminating ions and organofluorine compounds. In particular, even under strongly acidic conditions with a pH of 1.0 or less and a chloride ion concentration of 10,000 mg / L or more, where high concentrations of chloride ions are present, PFAS with 4 to 8 carbon atoms can be removed with a high removal rate. [Brief explanation of the drawing]

[0011] [Figure 1] This is a conceptual diagram of the apparatus used in the method (1) for removing organofluorine compounds of the present invention. [Figure 2] This is a conceptual diagram of the apparatus used in the method (2) for removing organofluorine compounds of the present invention. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and can be modified and implemented as appropriate without departing from the spirit of the invention. In this specification, "~" is used to indicate an expression that includes the numerical value or physical quantity before and after it. In this specification, the expression "A and / or B" includes "A only," "B only," and "both A and B."

[0013] The present invention relates to a method for removing organofluorine compounds from water to be treated that contains high concentrations of contaminating ions and organofluorine compounds, wherein the water to be treated contains PFAS as the organofluorine compound, and the method includes the step of contacting the water to be treated with an ion exchange resin to adsorb and remove the PFAS. More particularly, the present invention relates to a method for removing organofluorine compounds in which PFAS is adsorbed and removed by contacting water to be treated, which has a pH of 1.0 or less, a chloride ion concentration of 10,000 mg / L or more, and contains PFAS having 4 to 8 carbon atoms, with an ion exchange resin.

[0014] The method for removing organic fluorine compounds of the present invention can selectively adsorb and remove PFAS (PFAS having 4 to 8 carbon atoms, particularly short-chain PFAS having 6 or less carbon atoms) in the water to be treated even under conditions where high-concentration impurity ions coexist, particularly under conditions where the chloride ion concentration is 10,000 mg / L or more (about 1 wt% or more). For example, according to the method for removing organic fluorine compounds of the present invention, a removal rate of more than 90% for PFAS having 4 carbon atoms and more than 95% for PFAS having 5 to 8 carbon atoms can be achieved respectively. In addition, in this specification, "removing PFAS" does not only mean completely removing PFAS from the water to be treated, but also includes removing a part of PFAS from the water to be treated.

[0015] Hereinafter, the method for removing organic fluorine compounds of the present invention will be described in more detail.

[0016] (Water to be treated) The water to be treated is the water to be treated in the present invention, and is water containing at least an organic fluorine compound containing PFAS and impurity ions. Note that the water to be treated may contain a liquid other than water (for example, ethanol, etc.) as long as the object of the present invention is not impaired.

[0017] There is no particular limitation on the type of the water to be treated, and any of environmental water, domestic sewage, agricultural drainage, and industrial wastewater can be targeted.

[0018] In this specification, "environmental water" refers to water existing in nature and includes rivers, lakes, seas, groundwater, etc. In addition, "domestic sewage" is the water discharged from households and includes drainage from kitchens, baths, washing machines, toilets, etc. "Agricultural drainage" is the drainage generated by agricultural activities and includes the remaining water after irrigation and the effluent water due to the use of agricultural chemicals and chemical fertilizers. "Industrial wastewater" is the water discharged from factories and business establishments due to production activities and includes the water used in manufacturing processes, washing water, cooling water, etc.

[0019] As the water to be treated containing high-concentration impurity ions, industrial wastewater is one of the preferred targets. The water to be treated may be wastewater containing hydrochloric acid, in which case it may contain chloride ions at a concentration of 100,000 mg / L or more and fluoride ions at a concentration of 1,000 mg / L or more.

[0020] (Interfering ions) Contaminating ions are ions other than organofluorine compounds present in the treated water. A key feature of the present invention is that, in the method for removing organofluorine compounds of the present invention, the interfering ions include at least chloride ions, and PFAS can be removed even under conditions where chloride ions are present at high concentrations. On the other hand, the interfering ions other than chloride ions are not particularly limited, and typically include one or more selected from the group consisting of sulfate ions, nitrate ions, phosphate ions, sulfite ions, hypochlorite ions, fluoride ions, acetate ions, humic acid ions, carbonate ions, and bicarbonate ions.

[0021] In the method for removing organofluorine compounds of the present invention, the concentration of contaminating ions is not limited, but water to be treated with a concentration of contaminating ions of about 0.01% by weight or more and 30% by weight or less is preferred. In particular, the method for removing organofluorine compounds of the present invention is applicable to water to be treated with a chloride ion concentration of 10,000 mg / L or more (about 1% by weight or more), but its technical feature is that it can adsorb and remove PFAS with a high removal rate even in water to be treated with a chloride ion concentration of 100,000 mg / L or more, and even 120,000 mg / L or more. Under conditions in which such high concentrations of chloride ions coexist, it is generally expected that the adsorption of organic acidic substances by anion exchange resins will be inhibited, but according to the present invention, PFAS can be selectively removed without such inhibition. Furthermore, while there is no upper limit to the chloride ion concentration as long as it does not impair the purpose of the present invention, it is limited to 300,000 mg / L or less (approximately 30% by weight or less) and 200,000 mg / L or less (approximately 20% by weight or less).

[0022] The content of each contaminating ion in the treated water can be measured by liquid chromatography-mass spectrometry (LC-MS / MS), inductively coupled plasma mass spectrometry (ICP-MS), etc.

[0023] The present invention's method for removing organofluorine compounds is suitable for strongly acidic water to be treated, with a pH of 2.0 or lower, and particularly a pH of 1.0 or lower. The pH of the water to be treated can be measured, for example, with a pH meter.

[0024] (Organofluorine compounds) In the method for removing organofluorine compounds of the present invention, the organofluorine compounds contained in the treated water are organic compounds having a carbon (C)-fluorine (F) bond, and include at least PFAS.

[0025] PFAS (Per- and Polyfluoroalkyl Substances) is a general term for "perfluoroalkyl compounds" and "polyfluoroalkyl compounds." Furthermore, "perfluoroalkyl compounds" are organic compounds in which the hydrogen atoms bonded to carbon are completely replaced by fluorine atoms. "Polyfluoroalkyl compounds," on the other hand, are organic compounds in which the hydrogen atoms bonded to carbon are partially replaced by fluorine atoms.

[0026] In this specification, when "PFAS" is used, it refers not only to perfluoroalkyl compounds and polyfluoroalkyl compounds, but also to perfluoroalkyl compounds and polyfluoroalkyl compounds that contain atoms other than carbon, such as etheric oxygen atoms, between carbon atoms.

[0027] In the method for removing organofluorine compounds of the present invention, PFAS having polar groups is a suitable target for removal. Examples of polar groups include anionic functional groups such as hydroxyl groups, sulfonic acid groups (sulfo groups), and carboxylic acid groups (carboxyl groups), and cationic functional groups such as amino groups.

[0028] PFAS having a sulfonic acid group or a carboxylic acid group are particularly preferred targets, specifically including perfluoroalkyl sulfonic acid, polyfluoroalkyl sulfonic acid, perfluoroalkyl carboxylic acid, and polyfluoroalkyl carboxylic acid.

[0029] The carbon number of PFAS targeted by the method for removing organofluorine compounds of the present invention is not limited as long as it can be dissolved or dispersed in water and removed by adsorption using an ion exchange resin as described later. The method for removing organofluorine compounds of the present invention targets PFAS having 4 to 8 carbon atoms. In particular, at least one PFAS selected from perfluorocarboxylic acids having 4 to 8 carbon atoms is a suitable target for removal. However, the present invention is not limited thereto, and depending on the composition of the water to be treated, the type of functional group of the PFAS, etc., PFAS having 1 to 21 carbon atoms may also be targeted for removal. In particular, the presence of short-chain PFAS having 1 to 3 carbon atoms does not hinder the adsorption removal in the present invention.

[0030] In particular, sulfonic acid groups or carboxylic acid groups have high polarity, which increases their adsorption capacity to ion exchange resins. Therefore, if a PFAS has sulfonic acid groups or carboxylic acid groups, short-chain PFAS with 6 or fewer carbon atoms are also targets for removal.

[0031] In the method for removing organofluorine compounds of the present invention, the content of PFAS in the treated water is not particularly limited and may be, for example, 1 ng / L to 2000 mg / L.

[0032] In particular, water to be treated containing PFAS with 4 to 8 carbon atoms at concentrations of 1 μg / L to 200 mg / L is a suitable target. As shown in the examples described later, the method for removing organofluorine compounds of the present invention can achieve a removal rate of over 90% (preferably over 95%, more preferably over 97%) for PFAS with 4 carbon atoms, and over 95% (preferably over 98%, more preferably over 99%) for PFAS with 5 to 8 carbon atoms.

[0033] In the method for removing organofluorine compounds of the present invention, the treated water may contain organofluorine compounds other than PFAS, as long as the adsorption and removal of PFAS is not significantly impaired. Examples of organofluorine compounds other than PFAS include aromatic fluorine compounds such as fluorobenzene, and fluorine-based polymers such as polytetrafluoroethylene (PTFE).

[0034] In the method for removing organofluorine compounds of the present invention, the treated water may contain organic compounds other than organofluorine compounds, as long as the adsorption removal of PFAS by the ion exchange resin is not significantly impaired. Examples of organic compounds other than organofluorine compounds include oils and fats (fatty acids), organic acids (acetic acid, citric acid, etc.), aldehydes (acetaldehyde, etc.), phenols (phenol, cresol, etc.), and organic solvents (benzene, toluene, etc.). If the water to be treated contains organic compounds other than organofluorine compounds, it is preferable to remove these other organic compounds from the water using other adsorbents (such as activated carbon) before it is subjected to ion exchange resin.

[0035] (Ion exchange resin with PFAS adsorption capacity) The ion exchange resin selected according to the present invention is one that has adsorption capacity for PFAS (particularly PFAS having 4 to 8 carbon atoms) even in the presence of contaminating ions at high concentrations (for example, chloride ion concentration of 10,000 mg / L or more (approximately 1% by weight or more)).

[0036] The ion exchange resin according to the present invention can be either a cation exchange resin or an anion exchange resin, as long as it achieves the objective of the present invention. However, in embodiments where the PFAS has an anionic functional group such as a carboxylic acid group or a sulfonic acid group, an anion exchange resin is preferred, and an anion exchange resin having an amine group is particularly preferred.

[0037] An anion exchange resin having PFAS adsorption capacity includes a resin in which a functional group having PFAS adsorption capacity is bonded to a substrate polymer.

[0038] The functional group having the ability to adsorb PFAS is arbitrary as long as it achieves the objective of the present invention. As an anion exchange resin having PFAS adsorption capacity, an anion exchange resin containing one or more selected from the group consisting of primary amine groups, secondary amine groups, tertiary amine groups, quaternary amine groups, polyamine groups, and bispicolylamine groups can be used. Among these, primary amine groups, secondary amine groups, tertiary amine groups, and quaternary amine groups are preferred, with tertiary and quaternary amine groups being particularly preferred due to their excellent PFAS adsorption capacity.

[0039] As the base polymer in the anion exchange resin having PFAS adsorption capacity, any polymer can be used as long as it does not impair the objective of the present invention, and examples include styrene-based crosslinked copolymers and (meth)acrylic-based crosslinked copolymers. In this invention, "(meth)acrylic" refers to a combination of "acrylic" and "methacrylic."

[0040] In the present invention, "styrene-based crosslinked copolymer" means a crosslinked copolymer obtained by copolymerizing a monovinyl aromatic monomer with a crosslinkable aromatic monomer, and "(meth)acrylic-based crosslinked copolymer" means a crosslinked copolymer obtained by copolymerizing a (meth)acrylic monomer with a crosslinkable (meth)acrylic monomer.

[0041] Examples of monovinyl aromatic monomers include alkyl-substituted styrenes such as styrene, methylstyrene, and ethylstyrene, and halogen-substituted styrenes such as bromostyrene. These may be used individually or in mixtures of two or more. Among the monovinyl aromatic monomers, styrene or monomers mainly composed of styrene are preferred.

[0042] Examples of crosslinkable aromatic monomers include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, divinylxylene, divinylbiphenyl, bis(vinylphenyl)methane, bis(vinylphenyl)ethane, bis(vinylphenyl)propane, and bis(vinylphenyl)butane. These may be used individually or in combination of two or more.

[0043] Examples of (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, iso-(meth)acrylate, iso-butyl (meth)acrylate, t-butyl (meth)acrylate, n-butyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, butyl (meth)acrylate, benzyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, glycidyl (meth)acrylate, 2-hydroxy-3-chloropropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, etc. These may be used individually or in combination of two or more.

[0044] Examples of crosslinkable (meth)acrylic monomers include polymethylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. These may be used individually or in combination of two or more.

[0045] Furthermore, the structure of the resin portion of these anion exchange resins may be gel-type or porous-type (MP type (macroporous type) or MR type (macroretic type)).

[0046] The ion exchange resin used in the present invention may have a high or low uniformity of particle size, as long as it does not impair the objective of the present invention.

[0047] The average particle size of ion exchange resin can be measured using known methods. For example, it can be measured using an image processing method (spread the ion exchange resin in a petri dish, take an image of the resin with a microscope connected to a digital camera, and then process the outline of the image to determine the particle size).

[0048] Suitable commercially available anion exchange resins with PFAS adsorption capacity include Muromac WMT-718B (Muromachi Chemical Co., Ltd.) and Lewatit TP108 DW (LANXESS Corporation).

[0049] "Muromac WMT-718B" (Muromachi Chemical Co., Ltd.) is a macroporous, strongly basic anion exchange resin made of a styrene-based resin having a tertiary amine group. "Muromac WMT-718B" is characterized by its excellent PFAS adsorption performance and large adsorption capacity under strong acid conditions containing high concentrations of interfering ions. Furthermore, "Lewatit TP108 DW" (LANXESS Corporation) is a gel-type strongly basic anion exchange resin made of a styrene-based resin having a quaternary amine group. As shown in the examples, "Lewatit TP108 DW" can selectively adsorb and remove PFAS under conditions of a strong acid containing a high concentration of interfering ions.

[0050] The method of using ion exchange resins with PFAS adsorption capacity is simply to bring them into contact with the water to be treated, which contains PFAS. For example, ion exchange resins with PFAS adsorption capacity may be used by installing a new, dedicated resin tower and filling it, or they may be used by stacking them at the bottom of other adsorbents, such as activated carbon, in treatment equipment that already uses other adsorbents.

[0051] (Method and apparatus for removing organic fluorine compounds) Hereinafter, in the method for removing organofluorine compounds of the present invention, the method using only an ion exchange resin having PFAS adsorption capacity will be referred to as "method for removing organofluorine compounds of the present invention (1)," and the method using an ion exchange resin having PFAS adsorption capacity and other adsorbents will be referred to as "method for removing organofluorine compounds of the present invention (2)," and collectively referred to as "method for removing organofluorine compounds of the present invention."

[0052] The present invention's method for removing organofluorine compounds (1) involves using an ion exchange resin having PFAS adsorption capacity to remove PFAS from water to be treated. Since the present invention's method for removing organofluorine compounds (1) uses only an ion exchange resin having PFAS adsorption capacity, the process can be simplified.

[0053] Furthermore, the method for removing organofluorine compounds of the present invention may include any additional processing steps, as long as the objective of removing PFAS is achieved.

[0054] Figure 1 shows a conceptual diagram of the apparatus (organofluorine compound removal apparatus 1) used in the method (1) for removing organofluorine compounds of the present invention. The organofluorine compound removal apparatus 1 includes a packed column 10 filled with an ion exchange resin having PFAS adsorption capacity. By supplying the water to be treated, which contains PFAS, to the packed column 10, the water to be treated is brought into contact with the ion exchange resin to adsorb and remove the PFAS, and the treated water from which the PFAS has been removed is discharged.

[0055] Although Figure 1 shows one packed column 10, two or more packed columns 10 may be arranged in series or parallel (or a combination of series and parallel). For example, two types of ion exchange resins with different PFAS adsorption capacities may be used, with a packed column filled with ion exchange resin A, which has PFAS adsorption capacity and a large adsorption capacity, placed in the front stage, and a packed column filled with ion exchange resin B, which has superior PFAS adsorption capacity, placed in the rear stage in a series configuration.

[0056] The treatment conditions in the method for removing organofluorine compounds (1) of the present invention are any conditions that can remove the target PFAS, and can be appropriately determined by the type and amount of ion exchange resin having PFAS adsorption capacity used, the type and content (concentration) of interfering ions, the type and content (concentration) of PFAS, etc. The flow rate SV of the water to be treated is, for example, 0.1 to 50 h -1 Preferably 1 to 10 hours -1 This can be done. The temperature of the water to be treated can be, for example, 0 to 50°C.

[0057] The present invention provides a method (2) for removing organofluorine compounds, which involves using an ion exchange resin having PFAS adsorption capacity and another adsorbent, and includes a step of contacting the water to be treated with an adsorbent different from the ion exchange resin having PFAS adsorption capacity (hereinafter referred to as "other adsorbent") before contacting the water to be treated with the ion exchange resin having PFAS adsorption capacity.

[0058] The present invention's method for removing organofluorine compounds (2) involves using another adsorbent before the ion exchange resin having PFAS adsorption capacity, thereby effectively removing impurities in the treated water that cannot be sufficiently removed by the ion exchange resin having PFAS adsorption capacity alone, particularly organic substances other than PFAS.

[0059] Figure 2 shows a conceptual diagram of the apparatus (organofluorine compound removal apparatus 1A) used in the method for removing organofluorine compounds (2) of the present invention. The organofluorine compound removal apparatus 1A comprises a packed column 20 filled with other adsorbents in the front stage and a packed column 10 filled with an ion exchange resin having PFAS adsorption capacity in the rear stage. The water to be treated is supplied to the packed column 20, where it comes into contact with other adsorbents to remove impurities (especially organic substances other than PFAS). Then, it is supplied to the packed column 10, where it comes into contact with an ion exchange resin that has PFAS adsorption capacity to adsorb PFAS, and the treated water from which PFAS has been removed is discharged.

[0060] Although Figure 2 shows an example where one packed tower 10 and one packed tower 20 are arranged in series, the packed tower 20 only needs to be in front of the packed tower 10, and a combination of one or more packed towers 20 and one or more packed towers 10 is also acceptable.

[0061] The treatment conditions in the method for removing organofluorine compounds (2) of the present invention are any conditions that can remove the target PFAS, and can be appropriately determined by the type and amount of ion exchange resin and other adsorbents having PFAS adsorption capacity, the type and content (concentration) of PFAS contained in the water to be treated, the type and content (concentration) of impurities other than PFAS, etc. The flow rate SV of the water to be treated is, for example, 0.1 to 50 h -1 Preferably 1 to 10 hours -1 This can be done. The temperature of the water to be treated can be, for example, 0 to 50°C.

[0062] In the method for removing organofluorine compounds (2) of the present invention, other adsorbents are optional as long as they do not impair the purpose of the present invention, and may be appropriately selected depending on impurities other than PFAS contained in the water to be treated.

[0063] As other adsorbents, carbon-based adsorbents, inorganic adsorbents, and organic adsorbents can be used, as long as they do not impair the objectives of the present invention. The other adsorbents may be used individually or in any mixture of two or more in any proportion.

[0064] Activated carbon is a specific example of a carbon-based adsorbent. The shape (powder, granules, fibers, etc.) and size of activated carbon are arbitrary and can be appropriately selected according to the type and amount of water to be treated. Activated carbon is suitable as an adsorbent because of its cost-effectiveness and excellent adsorption capacity for organic compounds other than PFAS.

[0065] Examples of inorganic adsorbents include natural zeolites, synthetic zeolites, acid clay, molecular sieves, silica gel, silica alumina gel, and porous glass. The shape (powder, granules, fibers, etc.) and size of these inorganic adsorbents are arbitrary and can be appropriately selected according to the type and amount of water to be treated.

[0066] Specifically, as the organic adsorbent, an ion exchange resin that does not fall under the category of ion exchange resins having the above-mentioned PFAS adsorption capacity (other ion exchange resins) can be used. The structure of the ion exchange resin included in the other ion exchange resin may be gel type or porous type (MP type (macroporous type) or MR type (macroretic type)), and it is preferable to use ion exchange resins such as styrene-based or acrylic-based resins.

[0067] The method for removing organofluorine compounds according to the present invention has been described above, but the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention. Furthermore, matters not explicitly disclosed in the above embodiments do not deviate from what is normally practiced by those skilled in the art, and values ​​that can be easily anticipated by those skilled in the art can be adopted. [Examples]

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Furthermore, in the solutions of the examples, the "%" indicates "weight percent" unless otherwise specified. Also, when the extraction solvent is a mixed solvent, the balance of water is omitted. For example, "50% ethanol" means a mixed solvent of 50% ethanol by volume and 50% water by volume.

[0069] [Example 1] The adsorption characteristics of PFAS adsorption ion exchange resin for perfluorobutanoic acid (PFBA, 4 carbon atoms) in simulated wastewater containing high concentrations of hydrochloric acid were confirmed using the test method described below.

[0070] The ion exchange resins used are as follows: • Ion exchange resin (a): Lewatit TP108 DW (anion exchange resin for PFAS adsorption, manufactured by Lanxess)

[0071] The following fluid flow tests were conducted. Four types of raw water (raw water 1-4) for PFAS adsorption evaluation were prepared by adding PFBA to HCl aqueous solutions with HCl concentrations of 0%, 0.1%, 1%, or 10% to a concentration of 100 mg / L (based on the amount charged). The calculated pH values ​​for raw water 2 (HCl: 0.1%), raw water 3 (HCl: 1%), and raw water 4 (HCl: 10%) were pH 1.6 for raw water 2, pH 0.6 for raw water 3, and pH -0.5 for raw water 4.

[0072] A column (Muromac Mini Column L (φ10mm)) packed with 10 mL of ion exchange resin (a) for PFAS adsorption was passed through the resin at SV5 (50 mL / h). After passing 4 BV (four times the volume of the packed ion exchange resin) of the evaluation raw water through the column and discarding it, 100 mL of the evaluation raw water that had passed through the column (hereinafter referred to as the processed solution) was recovered.

[0073] The raw water and treated water used for evaluation were analyzed using LC-MS / MS (Waters Xevo-TQ) to measure PFBA concentration and determine the PFBA removal rate. The evaluation results are shown in Table 1.

[0074] [Table 1]

[0075] As shown in Table 1, it was confirmed that the removal rate of PFBA, a PFAS with 4 carbon atoms, was 99% or higher even at HCl concentrations of 0.1% to 10%.

[0076] [Example 2] Using the test method described below, the adsorption characteristics of two types of ion exchange resins (ion exchange resins (a) and (b)) for PFBA at a lower concentration than in Example 1 were confirmed in an aqueous system containing a high concentration of hydrochloric acid.

[0077] The ion exchange resins used are as follows: • Ion exchange resin (a): Lewatit TP108 DW (manufactured by Lanxess) • Ion exchange resin (b): Muromac WMT-718B-FB (manufactured by Muromachi Chemical Co., Ltd.)

[0078] [Example 2-1] Two types of raw water samples (raw water 5 and 6) with different HCl concentrations were prepared for PFAS adsorption evaluation by adding PFBA to 100 μg / L (based on the amount charged) of HCl aqueous solutions with HCl concentrations of 1% or 10%. The calculated pH values ​​for raw water 5 (HCl: 1%) and raw water 6 (HCl: 10%) were pH 0.6 and pH -0.5, respectively. Next, the experiment was carried out in the same manner as in Example 1, except that the raw water for evaluation obtained was used (ion exchange resin (a)). The results are shown in Table 2.

[0079] [Table 2]

[0080] [Example 2-2] The experiment was conducted in the same manner as in Experimental Example 1, except that ion exchange resin (b) was used. The results are shown in Table 3.

[0081] [Table 3]

[0082] As shown in Tables 2 and 3, with the raw water used for evaluation at an HCl concentration of 1%, both ion exchange resin (a) and ion exchange resin (b) showed a PFBA removal rate of 95% or higher. In the evaluation raw water with an HCl concentration of 10%, the PFBA removal rate of ion exchange resin (a) was 95% or higher, confirming that ion exchange resin (a) exhibits PFBA adsorption capacity even under high HCl and low PFBA concentration conditions. Ion exchange resin (b) also exhibits PFBA adsorption capacity, but it was confirmed that its PFBA adsorption capacity was smaller compared to ion exchange resin (a).

[0083] [Example 3] Using highly acidic wastewater containing hydrochloric acid (hereinafter referred to as "raw water 7") as a real-world sample, we conducted an experiment to remove PFAS with 4 to 8 carbon atoms (C4 to C8) using an ion exchange resin. The undiluted solution 7 contains the following PFAS to be removed: <Undiluted Solution 7> • Wastewater containing hydrochloric acid (pH approximately 0.5) Chloride ions: 120,000 mg / L • Fluoride ions: 1,300 mg / L <PFAS to be removed> • Perfluorobutanoic acid (PFBA, C4) • Perfluoropentanoic acid (PFPeA, C5) • Perfluorohexanoic acid (PFHxA, C6) • Perfluoroheptanoic acid (PFHpA, C7) • Perfluorooctanoic acid (PFOA, C8)

[0084] [Example 3-1] A column packed with 10 mL of ion exchange resin (a) (Lewatit TP108 DW) was subjected to a flow of raw water 7 through the resin at SV10 (100 mL / h) for 1 hour, after which the treated water was collected. The PFAS concentrations in the raw water 7 and the recovered treated water were measured, and the removal rate for each PFAS was determined. Table 4 shows the PFAS concentrations (μg / L) and PFAS removal rates (%) in the raw water 7.

[0085] [Table 4]

[0086] As shown in Table 4, it was confirmed that the ion exchange resin (a) achieved high removal rates for all PFAS (C4: 90% or higher, C5-C8: 99.9% or higher).

[0087] [Example 3-2] Using a real sample of highly acidic wastewater (raw water 7) containing hydrochloric acid (pH approximately 0.5), we conducted an experiment to remove C4-C8 PFAS using activated carbon in the pre-stage and ion exchange resin in the post-stage.

[0088] First, the wastewater obtained by passing raw water 7 through a predetermined amount of activated carbon was designated as "raw water 8," and the raw water 8 was passed through an ion exchange resin (a) under the same conditions as in [Example 3-1] to recover the treated water. The concentrations of PFAS in raw water 8 and the recovered treated water were measured, and the removal rate for each PFAS was determined. Table 5 shows the concentrations (μg / L) and removal rates (%) of each PFAS contained in raw water 8. The concentrations of chloride ions and fluoride ions in raw water 8 were also measured and were the same as those in raw water 7 (chloride ions: 120,000 mg / L, fluoride ions: 1,300 mg / L).

[0089] [Table 5]

[0090] As shown in Table 5, the PFAS C6-C8 in raw water 8 was less than 0.01 μg / L and was substantially removed by the preceding activated carbon treatment. However, PFBA (C4) and PFPeA (C5) were not completely adsorbed by the activated carbon and remained in raw water 8. Nevertheless, the removal rates calculated from the treated water recovered by passing raw water 8 through the subsequent ion exchange resin (a) were over 90% for PFBA (C4) and over 99% for PFPeA (C5).

[0091] As described above, in highly acidic wastewater containing hydrochloric acid, C6-C8 PFAS can be adsorbed by activated carbon, while it was confirmed that ion exchange resin (a) can also remove shorter carbon chain PFBA (C4) and PFPeA (C5), which cannot be completely removed by activated carbon. Due to its high PFAS removal rate, ion exchange resin (a) can be said to be particularly effective for wastewater containing short-chain PFAS. [Industrial applicability]

[0092] According to the present invention's method for removing organofluorine compounds, it is possible to effectively remove organofluorine compounds (PFAS) from equipment such as factories that use them, or from PFAS contained in externally supplied water used in such equipment, even if high concentrations of chloride ions are present.

Claims

1. A method for removing organofluorine compounds, comprising bringing treated water containing PFAS having 4 to 8 carbon atoms, with a pH of 1.0 or less and a chloride ion concentration of 10,000 mg / L or more, into contact with an ion exchange resin to adsorb and remove the PFAS.

2. The method for removing organofluorine compounds according to claim 1, wherein the treated water is a waste liquid containing hydrochloric acid, and contains a chloride ion concentration of 100,000 mg / L or more and a fluoride ion concentration of 1,000 mg / L or more.

3. The method for removing an organofluorine compound according to claim 1, wherein the PFAS is at least one selected from perfluorocarboxylic acids having 4 to 8 carbon atoms.

4. The method for removing organofluorine compounds according to claim 1, wherein the removal rate of PFAS having 4 carbon atoms is more than 90%.

5. The method for removing organofluorine compounds according to claim 1, wherein the removal rate of PFAS having 5 to 8 carbon atoms is more than 95% for each.

6. The method for removing an organofluorine compound according to claim 1, wherein the ion exchange resin is an anion exchange resin having an amine group.

7. The method for removing organofluorine compounds according to claim 6, wherein the ion exchange resin is made of a styrene-based resin having a quaternary amine group and is a gel-type strongly basic anion exchange resin.

8. A method for removing an organofluorine compound according to any one of claims 1 to 7, comprising the step of contacting the water to be treated with an adsorbent different from the ion exchange resin before the step of contacting the water to be treated with the ion exchange resin.

9. The method for removing an organofluorine compound according to claim 8, wherein the adsorbent is activated carbon.

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