Foam separation treatment method, aqueous solution, method for using vinyl alcohol-based polymer, and foam generation promoter

Abstract

This foam separation treatment method is for separating an organic fluorine-based compound from water to be treated containing the organic fluorine-based compound, by recovering foam generated by feeding a gas into the water to be treated, and involves introducing a polymer surfactant into the water to be treated. Accordingly, provided is a foam separation treatment method capable of efficiently separating an organic fluorine-based compound from water to be treated containing the organic fluorine-based compound.

Description

Foam separation treatment method, aqueous solution, method of using vinyl alcohol polymer, and foam generation promoter

[0001] The present disclosure relates to a foam separation treatment method, an aqueous solution, a method for using a vinyl alcohol-based polymer, and a foam production promoter.

[0002] In recent years, environmental pollution problems caused by perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), which are classified as organic fluorine-based compounds (PFAS), have become apparent, and techniques for separating and recovering these chemical substances (Patent Document 1) and decomposing them (Patent Document 2) have been proposed. Among the techniques for separating and recovering chemical substances, a water treatment method called foam separation is known, and Patent Document 1 discloses a foam separation treatment device used in this foam separation method.

[0003] JP 2023-50657 A JP 2022-537895 A

[0004] When PFAS in water to be treated is separated and recovered by foam separation, if the water to be treated does not foam well, the efficiency of foam separation may be poor.

[0005] An object of the present disclosure is to provide a foam separation treatment method, an aqueous solution, a method for using a vinyl alcohol polymer, and a foam production promoter that can efficiently separate PFAS from PFAS-containing water to be treated.

[0006] The above object is achieved by providing: [1] a foam separation method for separating organic fluorine-based compounds from water to be treated by feeding a gas into the water to be treated containing the organic fluorine-based compounds and recovering the generated foam, the foam separation method comprising introducing a polymer surfactant into the water to be treated; [2] the foam separation method according to claim 1, wherein the polymer surfactant is a vinyl alcohol polymer; [3] the foam separation method according to [2], wherein the vinyl alcohol polymer has a viscosity-average degree of polymerization of 100 to 5,000 and a degree of saponification of 30 mol % to 99.99 mol %; [4] any of the foam separation methods [1] to [3], wherein a polymer surfactant is introduced into the water to be treated so that the content of the polymer surfactant in the water to be treated is 1 mass % or less; [5] any of the foam separation methods [1] to [4], wherein a polymer surfactant is introduced in an amount equal to or greater than 1 mass % relative to the amount of the organic fluorine-based compounds contained in the water to be treated; [6] an aqueous solution containing a vinyl alcohol polymer and an organic fluorine-based compound; [7] The aqueous solution of [6], wherein the viscosity-average degree of polymerization of the vinyl alcohol polymer is 100 to 5,000 and the degree of saponification is 30 mol% to 99.99 mol%; [8] The aqueous solution of [6] or [7], wherein the content of the vinyl alcohol polymer in the aqueous solution is 1 mass% or less; [9] The aqueous solution of any one of [6] to [8], wherein the content of the vinyl alcohol polymer is 1 mass% or more relative to the content of the organic fluorine-based compound in the aqueous solution;

[10] A foam separation treatment method, which comprises feeding a gas into the aqueous solution of any one of [6] to [9] to generate foam and recovering the foam;

[11] A method of using a vinyl alcohol polymer in a treatment for separating organic fluorine-based compounds from water to be treated, which contains organic fluorine-based compounds, by feeding a gas into the water to be treated and recovering the generated foam, wherein the vinyl alcohol polymer is mixed with the water to be treated to promote foam generation;

[12] A foam production promoter comprising a vinyl alcohol polymer, which is introduced into the water to be treated when an organic fluorine-based compound is separated from the water by foam separation treatment.

[0007] The foam separation method, aqueous solution, method of using a vinyl alcohol polymer, and foam production promoter of the present disclosure can improve the separation efficiency of PFAS, thereby enabling efficient separation of organic fluorine compounds from water to be treated, and is useful for purifying water contaminated with organic fluorine compounds.

[0008] <Foam separation treatment method> The foam separation treatment method of the present disclosure is a foam separation treatment method that separates organic fluorine-based compounds from water to be treated by injecting gas into the water to be treated, which contains the organic fluorine-based compounds, and recovering the foam that is generated, and that introduces a polymer surfactant into the water to be treated.

[0009] In the foam separation treatment method of the present disclosure, a polymer surfactant is introduced into water to be treated that contains an organic fluorine-based compound (PFAS), a gas is fed into the water to be treated to generate bubbles, the polymer surfactant and PFAS are concentrated at the air-water interface of the bubbles to generate foam, and the foam may be collected near the surface of the water to be treated.

[0010] The method of introducing the polymer surfactant into the water to be treated is not particularly limited as long as it does not impair the spirit of the present invention, and for example, the polymer surfactant may be added to the water to be treated before feeding a gas into the water to be treated, or the polymer surfactant may be added to the water to be treated while feeding a gas into the water to be treated.Furthermore, for example, the water to be treated may be introduced into a treatment tank or the like that has previously been charged with the polymer surfactant, and then foam separation treatment may be performed.

[0011] The gas to be fed into the water to be treated is not particularly limited, but may be, for example, air or nitrogen, with air being preferred.

[0012] The means for feeding gas into the water to be treated is not particularly limited as long as it is capable of generating bubbles. For example, gas may be fed from an air pipe installed in the water to be treated.

[0013] After the foam separation treatment, the recovered mixture of polymer surfactant and PFAS may be incinerated as it is, or may be incinerated after being adsorbed onto an adsorbent such as activated carbon.

[0014] In one embodiment of the foam separation treatment method of the present disclosure, the foam separation treatment may be carried out continuously, for example, by continuously performing at least one of the steps of feeding the water to be treated into a foam separation treatment device, introducing a polymer surfactant into the water to be treated, feeding gas into the water to be treated, and collecting the generated foam.

[0015] The foam separation treatment according to the foam separation treatment method of the present disclosure may be a treatment for reducing the concentration of PFAS in the treated water by separating and recovering a portion of the PFAS contained in the treated water, or may be a treatment for removing PFAS from the treated water by separating and recovering substantially the entire amount of PFAS contained in the treated water.

[0016] The amount of polymer surfactant introduced into the water to be treated is not particularly limited as long as it does not impair the spirit of the present invention. However, the content of polymer surfactant in the water to be treated is preferably 0.1 mass ppm or more, more preferably 1 mass ppm or more, even more preferably 10 mass ppm or more, and even more preferably 100 mass ppm or more. Furthermore, the content of polymer surfactant in the water to be treated is preferably 1 mass% or less. That is, in the foam separation treatment method of the present disclosure, it is preferable to introduce the polymer surfactant into the water to be treated so that the content of polymer surfactant in the water to be treated is within the above range. By having the content of polymer surfactant in the water to be treated within the above range, the foaming properties are more excellent. In one embodiment, even when the foam separation treatment is performed continuously, it is preferable to adjust the amount of polymer surfactant introduced into the water to be treated so that the content of polymer surfactant in the water to be treated is within the above range.

[0017] Furthermore, the amount of polymer surfactant is preferably 1 mass or more, more preferably 10 mass or more, even more preferably 50 mass or more, and even more preferably 100 mass or more relative to the PFAS content in the water to be treated. That is, in the foam separation treatment method of the present disclosure, it is preferable to introduce a polymer surfactant in an amount 1 mass or more relative to the amount of PFAS contained in the water to be treated. When the amount of polymer surfactant relative to the PFAS content in the water to be treated is within the above range, the PFAS recovery efficiency is more excellent. In one embodiment, even when foam separation treatment is performed continuously, it is preferable to adjust the amount of water to be treated introduced into the treatment system and / or the amount of polymer surfactant introduced into the water to be treated so that the amount of polymer surfactant relative to the PFAS content in the water to be treated is within the above range.

[0018] The water to be treated may contain other components such as impurities in addition to PFAS, as long as the gist of the present invention is not impaired.

[0019] (Polymer surfactant) The polymer surfactant in the present disclosure is a polymer compound that exhibits surface activity. The term "polymer" means that the molecular weight is 1000 or more. In the foam separation treatment method of the present disclosure, one type of polymer surfactant may be used, or two or more types of polymer surfactants may be used.

[0020] The molecular weight of the polymer surfactant is 1,000 or more, preferably 2,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more.

[0021] The HLB value of the polymer surfactant is preferably 3 or more, more preferably 8 or more, and even more preferably 13 or more. The HLB value is an index that represents the degree of affinity of a surfactant for water and oil, and ranges from 0 to 20, with values ​​closer to 0 indicating higher lipophilicity and values ​​closer to 20 indicating higher hydrophilicity. Here, the HLB value is a value defined by the Griffin method, and is given by HLB value = 20 x (sum of formula weights of hydrophilic moieties) / (molecular weight). For example, when a certain surfactant is vigorously mixed in water, if a portion of the surfactant disperses in water, the HLB value of the surfactant corresponds to 3 to 6; if a dispersion becomes milky, the HLB value corresponds to 6 to 8; if a stable milky dispersion, the HLB value corresponds to 8 to 10; if a translucent or transparent dispersion, the HLB value corresponds to 10 to 13; and if the surfactant dissolves and becomes transparent, the HLB value corresponds to 13 or more.

[0022] The polymer surfactant may be a polymer obtained by polymerizing a monomer, and is preferably a polymer of a nonionic monomer and / or an anionic monomer. Examples of nonionic monomers include ethylene oxide, propylene oxide, (meth)acrylamide compounds, (meth)acrylic acid alkyl esters, styrene, acrylonitrile, and vinyl acetate. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and hydroxyethyl (meth)acrylate. Examples of anionic monomers include (meth)acrylic acid, vinyl sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic acid, and salts thereof. In the present disclosure, "(meth)acrylic" refers collectively to methacrylic and acrylic. The polymer surfactant may be a polymer obtained by polymerizing one type of monomer, or may be a polymer obtained by copolymerizing two or more types of monomers. The polymer surfactant may also be a polymer obtained by polymerizing the monomer and then, for example, introducing a functional group. Among polymer surfactants, vinyl alcohol polymers (PVA) obtained from vinyl ester monomers such as vinyl acetate are preferred because of their excellent water solubility, foam-forming properties, and biodegradability. That is, a preferred embodiment of the foam separation method of the present disclosure is a foam separation method for separating organic fluorine compounds from water to be treated by injecting gas into the water to be treated containing the organic fluorine compounds and recovering the generated foam, in which PVA is introduced into the water to be treated. Note that the monomer used as the raw material for PVA may be a vinyl ester monomer other than vinyl acetate, as described below.

[0023] PVA is a polymer containing vinyl alcohol units as monomer units. PVA is obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer, which is a raw material monomer for PVA. The saponified PVA may contain vinyl ester units in addition to vinyl alcohol units.

[0024] PVA can also be produced by saponifying a copolymer obtained by copolymerizing a vinyl ester monomer, which is a raw material monomer, with other monomers to produce a PVA containing monomer units other than vinyl alcohol units and vinyl ester units, or by reacting a specific chemical species with the PVA during the polymerization process, the saponification process, and / or after saponification to introduce specific functional groups into the side chains or terminals of the PVA. In this disclosure, such PVAs may be referred to as "modified vinyl alcohol polymers (modified PVAs)." In this disclosure, the agent used to modify PVA may be referred to as the "modified species." For example, in one embodiment, if the modified PVA has a terminal structure derived from a chain transfer agent, the chain transfer agent may be referred to as the modified species. In another embodiment, if the modified PVA is produced by copolymerizing "other monomers" other than vinyl ester monomers, the "other monomers" may be referred to as the modified species. In the present disclosure, the ratio of units derived from modified species to all monomer units constituting the modified PVA may be referred to as the "modification amount."

[0025] The lower limit of the proportion of vinyl alcohol units to all monomer units in PVA is preferably 35 mol%, more preferably 50 mol%, and even more preferably 65 mol% in some cases, while the upper limit of the proportion of vinyl alcohol units is preferably 99.95 mol%, more preferably 95 mol%, and even more preferably 90 mol% in some cases.

[0026] The viscosity-average degree of polymerization of the PVA is preferably 100 or more and 5,000 or less. The lower limit of the viscosity-average degree of polymerization of the PVA is more preferably 200, and sometimes even more preferably 500. The upper limit of the viscosity-average degree of polymerization of the PVA is more preferably 4,000, more preferably 3,000, and sometimes even more preferably 2,000. When the viscosity-average degree of polymerization is within the above range, production tends to be easier. The viscosity-average degree of polymerization is a value obtained by measurement in accordance with JIS K 6726:1994. Specifically, when the saponification degree of the PVA is less than 99.5 mol%, the viscosity-average degree of polymerization can be calculated by the following formula using the intrinsic viscosity [η] (liters / g) measured in water at 30°C for PVA saponified to a saponification degree of 99.5 mol% or more. P = ([η] x 10 ４ / 8.29) （１／０．６２）

[0027] The lower limit of the saponification degree of the PVA is preferably 30 mol%, more preferably 50 mol%, and even more preferably 65 mol%. On the other hand, the upper limit of the saponification degree of the PVA is preferably 99.99 mol%, more preferably 99 mol%, even more preferably 90 mol%, and even more preferably 80 mol%. The saponification degree of the PVA is preferably 30 mol% or more and 99.99 mol% or less, more preferably 50 mol% or more and 99.99 mol% or less, and even more preferably 65 mol% or more and 90 mol% or less. By setting the saponification degree of the PVA within the above range, the efficiency of foam separation improves and the PVA tends to be produced more stably industrially.

[0028] The method for producing PVA preferably includes a polymerization step of polymerizing a vinyl ester monomer and a saponification step of saponifying the vinyl ester polymer obtained thereby.

[0029] Vinyl ester polymers can be produced by polymerizing vinyl ester monomers using conventional methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization. To enhance the effects of the present disclosure, solution polymerization, in which polymerization is carried out using a lower alcohol, is preferred. While the lower alcohol is not particularly limited, alcohols having 3 or fewer carbon atoms, such as methanol, ethanol, propanol, and isopropanol, are preferred, with methanol being more preferred. The polymerization process can be carried out in any of batch, semi-batch, and continuous modes.

[0030] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. Of these, vinyl acetate is preferred.

[0031] As described above, PVA may be modified by copolymerizing a vinyl ester monomer with other monomers within the scope of the present disclosure. Examples of other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; (meth)acrylic acid and salts thereof; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidopropanesulfonic ... and (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate. Examples of suitable acrylamide compounds include amidopropyldimethylamine and its salts or quaternary salts, N-methylol(meth)acrylamide and its derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; and isopropenyl acetate. These compounds may be used alone or in combination of two or more. Among these, 3-(methacryloylamino)propyltrimethylammonium chloride (MAPTAC) is preferred as the acrylamide compound. The amount of copolymerization (modification) of other monomers is preferably 10 mol% or less. The copolymerization amount of the other monomer means the ratio of units derived from the other monomer to the total monomer units constituting the modified PVA.

[0032] The polymerization initiator used in the polymerization can be selected from known initiators (e.g., azo initiators, peroxide initiators, redox initiators, etc.). Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide initiators include percarbonate compounds such as di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxydecanate; acetylcyclohexylsulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. These initiators may be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like to form an initiator. Examples of redox initiators include initiators that combine the above-mentioned peroxides with reducing agents such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and Rongalite. When polymerization is carried out at high temperatures, coloration due to decomposition of the vinyl ester monomer may be observed. In such cases, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of approximately 1 to 100 ppm by mass relative to the vinyl ester monomer to prevent coloration.

[0033] During polymerization of vinyl ester monomers, a chain transfer agent may be present to adjust the degree of polymerization of the resulting PVA or to introduce functional groups into the PVA. Examples of chain transfer agents include aldehydes such as acetaldehyde, propionaldehyde, butylaldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol; thiocarboxylic acids such as thioacetic acid; halogenated hydrocarbons such as trichloroethylene and perchloroethylene; and alkyl mercaptans such as normal dodecyl mercaptan (n-DDM). Among these, aldehydes and alkyl mercaptans are preferred. The amount of chain transfer agent added is determined depending on the chain transfer constant of the chain transfer agent and the desired degree of polymerization of the PVA, but is generally 0.1 to 10% by mass based on the vinyl ester used. In one embodiment, by using an alkyl mercaptan as a chain transfer agent in the polymerization process of PVA, a modified PVA can be obtained in which an alkyl group derived from the alkyl mercaptan is introduced at the terminal. The degree of modification of such a modified PVA, i.e., the ratio of units having an alkyl group derived from the alkyl mercaptan to all monomer units constituting the modified PVA, is preferably 0.01 mol% to 5 mol%, more preferably 0.1 mol% to 3 mol%, and even more preferably 0.3 mol% to 1 mol%. As the alkyl mercaptan, n-DDM is preferred.

[0034] The polymerization temperature is not particularly limited, and is preferably 0 to 180°C, more preferably 20 to 160°C, and even more preferably 30 to 150°C. When polymerization is carried out at a temperature below the boiling point of the solvent used in the polymerization step, either reduced-pressure boiling polymerization, in which polymerization is carried out while boiling the solvent under reduced pressure, or atmospheric non-boiling polymerization, in which polymerization is carried out under conditions where the solvent is not boiled under atmospheric pressure, can be selected. Furthermore, when polymerization is carried out at a temperature above the boiling point of the solvent used in the polymerization step, either pressurized non-boiling polymerization, in which polymerization is carried out under conditions where the solvent is not boiled under pressure, or pressurized boiling polymerization, in which polymerization is carried out while boiling the solvent under pressure, can be selected.

[0035] As described above, PVA can be obtained by saponifying a vinyl ester polymer. Examples of methods for the saponification reaction include alcoholysis or hydrolysis using a basic catalyst such as sodium hydroxide, potassium hydroxide, or sodium methoxide, or an acidic catalyst such as p-toluenesulfonic acid. Examples of solvents that can be used in this reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone-methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These solvents can be used alone or in combination of two or more. Among these, saponification using methanol or a methanol / methyl acetate mixed solution as the solvent and sodium hydroxide as the catalyst is preferred for its simplicity.

[0036] (Organic Fluorine-Based Compound) The organic fluorine-based compound (PFAS) may be an amphiphilic perfluoroalkane derivative, and examples of the amphiphilic perfluoroalkane derivative include perfluoroalkanecarboxylic acids, perfluoroalkylsulfonic acids, and 1H,1H,2H,2H-perfluoroalkyl alcohols. Examples of perfluoroalkanecarboxylic acids include perfluorobutanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, and perfluorododecanoic acid. In particular, the foam separation treatment method of the present disclosure is suitable for perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, and perfluorooctanoic acid. Examples of perfluoroalkylsulfonic acids include perfluorobutanesulfonic acid, perfluorohexanesulfonic acid, perfluorooctanesulfonic acid, and salts thereof. Examples of 1H,1H,2H,2H-perfluoroalkyl alcohols include 1H,1H,2H,2H-perfluoro-1-hexanol, 1H,1H,2H,2H-perfluoro-1-octanol, 1H,1H,2H,2H-perfluoro-1-decanol, etc. The PFAS to be subjected to the foam separation treatment may be one type or two or more types.

[0037] <Aqueous Solution> One embodiment of the present invention is an aqueous solution containing PVA and PFAS. Due to the composition of such an aqueous solution, the PFAS contained in the aqueous solution can be easily separated by foam separation treatment.

[0038] The preferred embodiments of the PVA and PFAS contained in the aqueous solution are the same as those of the PVA and PFAS described above.

[0039] The content of PVA in the aqueous solution is preferably 0.1 ppm by mass or more, more preferably 1 ppm by mass or more, even more preferably 10 ppm by mass or more, and in some cases even more preferably 100 ppm by mass or more. The content of PVA in the aqueous solution is preferably 1% by mass or less. When the content of PVA in the aqueous solution is in the above range, the foaming property is more excellent.

[0040] The content of PVA in the aqueous solution is preferably 1 time by mass or more, more preferably 10 times by mass or more, even more preferably 50 times by mass or more, and even more preferably 100 times by mass or more, relative to the content of PFAS. When the PVA content is within the above range, the recovery efficiency of PFAS is more excellent.

[0041] The aqueous solution of the present disclosure may contain various additives and impurities within the scope of the present invention.

[0042] Another embodiment of the present invention is a foam separation treatment method, which comprises feeding a gas into the aqueous solution to generate foam, and recovering the foam.

[0043] <Method of Using Vinyl Alcohol-Based Polymer> One embodiment of the present invention is a method of using PVA in a process of separating PFAS from PFAS-containing water to be treated by feeding a gas into the water to be treated and collecting the generated foam, in which PVA is mixed with the water to be treated to promote foam generation.

[0044] The preferred embodiment of the PVA in such a method of use is the same as the PVA described above.

[0045] <Foam Production Promoter> One embodiment of the present invention is a foam production promoter made of a vinyl alcohol polymer that is introduced into water to be treated when organofluorine-based compounds are separated from the water by foam separation treatment.

[0046] The preferred embodiment of the PVA in the foam production promoter is the same as the PVA described above.

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "%" and "ppm" represent "% by mass" and "ppm by mass", respectively, unless otherwise specified.

[0048] [Viscosity Average Degree of Polymerization] The viscosity average degree of polymerization of the PVA used in the examples was measured in accordance with JIS K 6726:1994. Specifically, when the degree of saponification was less than 99.5 mol%, the PVA was saponified to a degree of saponification of 99.5 mol% or more, and the viscosity average degree of polymerization was calculated by the following formula using the intrinsic viscosity [η] (liters / g) measured in water at 30°C: P = ([η] x 10 ４ / 8.29) （１／０．６２）

[0049] [Saponification Degree] The saponification degree of the PVA used in the examples was measured in accordance with JIS K 6726:1994.

[0050] <Production Example 1> [Production of PVA1] PVA1 was produced as a polymeric surfactant by the following method. 640 g of vinyl acetate and 960 g of methanol were charged into a 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, and an initiator addition port. The system was purged with nitrogen for 30 minutes while nitrogen bubbling was performed. The reactor was heated, and when the internal temperature reached 60°C, 0.3 g of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. After 5 hours of polymerization at 60°C, 0.3 g of hydroquinone was added and the mixture was cooled to terminate the polymerization. The solids concentration at the time of termination of the polymerization was 20.0%, and the polymerization rate was 50%. Subsequently, unreacted vinyl acetate monomer was removed at 50°C under reduced pressure with occasional addition of methanol, yielding a methanol solution of vinyl ester polymer (PVAc) (concentration 35%). Methanol was then added to the resulting solution to prepare 457 g of a methanol solution of vinyl ester polymer (160.0 g of vinyl ester polymer in the solution). To this solution, 3.7 g of an alkaline solution (10% sodium hydroxide in methanol) was added for saponification (the vinyl ester polymer concentration in the saponification solution was 30%, and the molar ratio of sodium hydroxide to vinyl acetate units was 0.005). Approximately 15 minutes after the addition of the alkaline solution, a gel-like substance was formed. This was crushed in a grinder and left at 40°C for 1 hour to allow saponification to proceed. Then, 500 g of methyl acetate was added to neutralize the remaining alkali. After confirming completion of neutralization using a phenolphthalein indicator, the solution was filtered to obtain a white solid. 2,000 g of methanol was added to the solid and the solid was left to wash at room temperature for 3 hours. This washing procedure was repeated three times, and the resulting white solid was centrifuged and left to dry at 65°C for 2 days to obtain PVA1. The viscosity-average degree of polymerization of PVA1 was 530, and the degree of saponification was 88.0 mol%.

[0051] <Production Examples 2 to 4> [Production of PVAs 2 to 4] PVAs 2 to 4 were produced as polymer surfactants by the following method. PVAs 2 to 4 were obtained in the same manner as PVA1 in Production Example 1, except that the polymerization conditions (amount of vinyl acetate used, amount of methanol used, polymerization rate) and saponification conditions (PVAc concentration, molar ratio of sodium hydroxide to PVAc) were changed as shown in Table 1.

[0052] <Production Example 5> [Production of PVA5] PVA5 was produced as a polymeric surfactant by the following method. 960 g of vinyl acetate, 640 g of methanol, and 4.3 g of 3-(methacryloylamino)propyltrimethylammonium chloride (MAPTAC) as a comonomer were charged into a 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, a delay solution drip inlet, and an initiator addition inlet. The system was then purged with nitrogen for 30 minutes while bubbling with nitrogen. A 20% comonomer solution was prepared as a delay solution by dissolving MAPTAC in methanol, and the system was then purged with nitrogen by bubbling with nitrogen gas. The reactor was then heated, and when the internal temperature reached 60°C, 0.2 g of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The delay solution was added dropwise to maintain a constant monomer composition (ratio of vinyl acetate to MAPTAC) in the polymerization solution. Polymerization was then carried out at 60°C for 3 hours, followed by the addition of 0.4 g of hydroquinone and cooling to terminate the polymerization. The total amount of MAPTAC added until the polymerization was terminated was 13.4 g. The solids concentration at the time of polymerization termination was 17.0%, and the polymerization rate was 30%. Subsequently, unreacted vinyl acetate monomer was removed at 50°C under reduced pressure with occasional addition of methanol, yielding a methanol solution of MAPTAC-modified vinyl ester polymer (concentration: 35%). Next, saponification was carried out under the same conditions as in Production Example 1, except that the saponification conditions (PVAc concentration, molar ratio of sodium hydroxide to PVAc) were changed as shown in Table 1, yielding PVA5. The modification amount (ratio of MAPTAC-derived units to all monomer units constituting PVA5) was 2.0 mol%. The modification amount of PVA5 was determined by the MAPTAC-modified vinyl ester polymer (pre-saponification precursor) before saponification. １ It was determined by H-NMR measurement.

[0053] <Production Example 6> [Production of PVA6] PVA6 was produced as a polymeric surfactant by the following method. 960 g of vinyl acetate, 640 g of methanol, and 0.36 g of normal dodecyl mercaptan (n-DDM) were charged into a 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, a delay solution drip inlet, and an initiator addition inlet. The system was then purged with nitrogen for 30 minutes while bubbling with nitrogen. A chain transfer agent solution with a concentration of 10% was prepared as a delay solution by dissolving n-DDM in methanol, and the atmosphere was purged with nitrogen by bubbling with nitrogen gas. The reactor was then heated, and when the internal temperature reached 60°C, 1.0 g of 2,2'-azobisisobutyronitrile (AIBN) was added to initiate polymerization. The delay solution was added dropwise to maintain a constant ratio of vinyl acetate to n-DDM in the polymerization solution. Polymerization was continued for 3 hours at 60°C, after which 2.0 g of hydroquinone was added and the solution was cooled to terminate the polymerization. The total amount of n-DDM added until the polymerization was terminated was 6.32 g. The solids concentration at the time of polymerization termination was 28.9%, and the conversion was 50%. Subsequently, unreacted vinyl acetate monomer was removed at 50°C under reduced pressure with occasional addition of methanol, yielding a methanol solution (concentration: 35%) of an n-DDM-modified vinyl ester polymer. Next, saponification was carried out under the same conditions as in Production Example 1 above, yielding PVA6, a modified PVA having an n-DDM-derived terminal structure. The modification level of PVA6 (the ratio of units having an n-DDM-derived alkyl group to all monomer units constituting PVA6) was 0.5 mol %. The modification level of PVA6 was determined by comparing the n-DDM-modified vinyl ester polymer, which was the precursor, with the n-DDM-modified vinyl ester polymer before saponification. １ It was determined by H-NMR measurement.

[0054]

[0055] <Example 1> [PFAS foam separation treatment test] A ceramic cylindrical air stone with a diameter of 10 mm, a length of 150 mm, and #240 was set at the bottom of a 1 L beaker, and 200 ml of an aqueous solution containing 1.0 ppm PFOA (perfluorooctanoic acid) and 100 ppm PVA1 as PFAS was added as the water to be treated. Next, air was passed through the air stone at a flow rate of 0.15 ml / min, and the air was sent into the water to be treated, and the generated foam was collected at regular intervals for 30 minutes. The concentration of PFOA contained in the residual liquid after the test was analyzed using LC / MS (Shimadzu Corporation LC / MS-8030, column: TSKgel ODS-80Ts, detector: MS detector, ionization method: ESI mode, detection charge: Negative charge), and it was 0.08 ppm.

[0056] Examples 2 to 10 A PFAS separation test was carried out under the same conditions as in Example 1, except that the types and concentrations of PVA and PFAS were changed as shown in Table 2. The results are shown in Table 2.

[0057] Example 11 A PFAS separation test was carried out under the same conditions as in Example 1, except that polyoxyethylene lauryl ether (NOF Corporation, "Nonion K-230," ethylene oxide addition mole number n = 30, HLB value 17.5) was used instead of PVA1. The PFOA content in the residual liquid after the test was 0.12 ppm. The results are shown in Table 2.

[0058] Comparative Example 1 When a foam separation treatment test for PFAS was carried out under the same conditions as in Example 1, but without adding a surfactant, the PFOA content in the remaining solution was 0.82 ppm.

[0059] <Comparative Example 2> A PFAS separation test was carried out under the same conditions as in Example 1, except that lauryl dimethylaminoacetic acid betaine ("Nissan Anon BL-SF" manufactured by NOF Corporation, molecular weight 271.44) was used instead of PVA1. The PFOA content in the residual liquid after the test was 0.75 ppm. The results are shown in Table 2.

[0060]

[0061] The results in Table 2 show that the PFAS residual rate in the Examples in which foam separation treatment was carried out using a polymer surfactant was lower than the PFAS residual rate in the Comparative Examples in which treatment was carried out without using a polymer surfactant, and that the Examples were superior in separation and recovery efficiency.

Claims

1. A foam separation treatment method for separating organic fluorine-based compounds from water to be treated by pumping gas into the water to be treated containing the organic fluorine-based compounds and recovering the foam generated, the foam separation treatment method comprising introducing a polymeric surfactant into the water to be treated.

2. The foam separation treatment method according to claim 1, wherein the polymer surfactant is a vinyl alcohol polymer.

3. The foam separation treatment method according to claim 2, wherein the vinyl alcohol polymer has a viscosity average degree of polymerization of 100 or more and 5,000 or less, and a degree of saponification of 30 mol % or more and 99.99 mol % or less.

4. A foam separation treatment method as described in claim 1, in which a polymer surfactant is introduced into the water to be treated so that the content of the polymer surfactant in the water to be treated is 1 mass% or less.

5. A foam separation treatment method according to any one of claims 1 to 4, wherein a polymer surfactant is introduced in an amount at least 1 times by mass relative to the amount of the organofluorine-based compound contained in the water to be treated.

6. An aqueous solution containing a vinyl alcohol polymer and an organic fluorine compound.

7. The aqueous solution according to claim 6, wherein the vinyl alcohol polymer has a viscosity average degree of polymerization of 100 or more and 5,000 or less, and a degree of saponification of 30 mol % or more and 99.99 mol % or less.

8. The aqueous solution according to claim 6, wherein the content of the vinyl alcohol polymer in the aqueous solution is 1% by mass or less.

9. The aqueous solution according to claim 6, wherein the content of the vinyl alcohol polymer in the aqueous solution is 1 time by mass or more relative to the content of the organic fluorine-based compound in the aqueous solution.

10. A foam separation treatment method, which comprises feeding a gas into the aqueous solution according to any one of claims 6 to 9 to generate foam, and recovering the foam.

11. A method for using a vinyl alcohol-based polymer in a process for separating organic fluorine-based compounds from water to be treated by pumping gas into the water to be treated containing the organic fluorine-based compounds and recovering the foam generated, the method comprising mixing the vinyl alcohol-based polymer with the water to be treated to promote foam generation.

12. A foam production promoter comprising a vinyl alcohol polymer which is introduced into water to be treated when organofluorine-based compounds are separated from the water by foam separation treatment.

Images