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

Abstract

A foam separation treatment method for separating organic fluorine compounds from water to be treated by sending a gas to the water to be treated containing organic fluorine compounds and recovering the generated foam, wherein a polymer surfactant is introduced into the water to be treated. By this, a foam separation treatment method capable of efficiently separating organic fluorine compounds from water to be treated containing organic fluorine compounds is provided.

Description

Technology Field

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

[0002] Recently, environmental pollution problems caused by perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), which are classified as organic fluorinated compounds (PFAS), have surfaced, and technologies for separating and recovering these chemical substances (Patent Document 1) and decomposing them (Patent Document 2) have been proposed. Among the technologies 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 such foam separation method. Prior art literature

[0003] Japanese Patent Publication No. JP 2023-50657, Japanese Patent Publication No. JP 2022-537895 The problem to be solved

[0004] When separating and recovering PFAS in the treated water through foam separation treatment, if the foam generation in the treated water is poor, the efficiency of foam separation may decrease.

[0005] One of the objectives of the present disclosure is to provide a foam separation treatment method capable of efficiently separating PFAS from water to be treated containing PFAS, an aqueous solution, a method of using a vinyl alcohol-based polymer, and a foam generation promoter. means of solving the problem

[0006] The above purpose is,

[0007] [1] A foam separation treatment method for separating organic fluorine compounds from water to be treated by sending gas to water to be treated containing organic fluorine compounds and recovering the generated foam, wherein a polymer surfactant is introduced into the water to be treated;

[0008] [2] Foam separation treatment method of [1] in which the above polymer surfactant is a vinyl alcohol-based polymer;

[0009] [3] A foam separation treatment method of [2] in which the viscosity average degree of polymerization of the vinyl alcohol-based polymer is 100 or more and 5,000 or less, and the degree of saponification is 30 mol% or more and 99.99 mol% or less;

[0010] [4] A foam separation treatment method of any one of [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;

[0011] [5] A foam separation treatment method of any one of [1] to [4], wherein at least one mass of a polymer surfactant is introduced relative to the amount of organic fluorine compounds contained in the water to be treated;

[0012] [6] An aqueous solution containing vinyl alcohol-based polymers and organic fluorine compounds;

[0013] [7] An aqueous solution of [6] having an average degree of polymerization of the above vinyl alcohol-based polymer 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;

[0014] [8] An aqueous solution of [6] or [7] in which the content of the vinyl alcohol-based polymer in the aqueous solution is 1 mass% or less;

[0015] [9] Any one of [6] to [8], wherein the content of vinyl alcohol-based polymer is at least 1 mass times the content of organic fluorinated compounds in the aqueous solution;

[0016]

[10] A foam separation treatment method that generates foam by sending gas into any one of [6] to [9] and recovers the foam;

[0017]

[11] In a process for separating organic fluorine compounds from water to be treated by sending a gas to the water to be treated containing organic fluorine compounds and recovering the generated foam,

[0018] A method of using a vinyl alcohol-based polymer to promote the generation of foam by mixing the vinyl alcohol-based polymer with the above-mentioned water to be treated;

[0019]

[12] Foam generation promoter composed of a vinyl alcohol-based polymer introduced into the water to be treated when separating organic fluorine compounds from the water to be treated by foam separation treatment

[0020] It is achieved by providing one of the following. Effects of the invention

[0021] According to the foam separation treatment method, aqueous solution, method of using vinyl alcohol-based polymer, and foam generation promoter of the present disclosure, the separation efficiency of PFAS can be improved. Accordingly, organic fluorinated compounds can be efficiently separated from water to be treated, and it is useful for purifying water contaminated by organic fluorinated compounds. Specific details for implementing the invention

[0022] Foam Separation Treatment Method

[0023] The foam separation treatment method of the present disclosure is a foam separation treatment method for separating an organic fluorine-based compound from a water to be treated by sending a gas to the water to be treated containing an organic fluorine-based compound and recovering the generated foam, wherein a polymer surfactant is introduced into the water to be treated.

[0024] In the foam separation treatment method of the present disclosure, a polymer surfactant is introduced into water to be treated containing an organic fluorine compound (PFAS), gas is sent to 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 recovered near the surface of the water to be treated.

[0025] As long as it does not impair the intent of the present invention, the method of introducing a polymeric surfactant into the water to be treated is not particularly limited. For example, the polymeric surfactant may be added to the water to be treated before gas is introduced into the water to be treated, or the polymeric surfactant may be added to the water to be treated while gas is introduced into the water to be treated. Additionally, for example, the water to be treated may be introduced into a treatment tank, etc., into which a polymeric surfactant has been introduced in advance, and foam separation treatment may be performed.

[0026] The gas sent to the water to be treated is not particularly limited, but for example, air, nitrogen, etc. are used, and air is preferred.

[0027] As for the means of sending gas into the water to be treated, it is not particularly limited as long as it is capable of generating foam, and for example, gas may be sent from a supply pipe installed in the water to be treated.

[0028] After foam separation treatment, the mixture of polymer surfactants and PFAS recovered may be incinerated as is, or incinerated after adsorbing it on an adsorbent such as activated carbon.

[0029] In one embodiment of the foam separation treatment method of the present disclosure, the foam separation treatment may be performed continuously, and, for example, at least one of the following processes may be performed continuously: a process of sending water to be treated to a foam separation treatment device, a process of introducing a polymer surfactant into the water to be treated, a process of sending gas to the water to be treated, and a process of recovering the generated foam.

[0030] The foam separation treatment according to the foam separation treatment method of the present disclosure may be a treatment that reduces the concentration of PFAS in the water to be treated by separating and recovering a portion of the PFAS contained in the water to be treated, or a treatment that removes PFAS from the water to be treated by separating and recovering substantially all of the PFAS contained in the water to be treated.

[0031] The amount of polymeric 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, but the content of the polymeric 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 in some cases, even more preferably 100 mass ppm or more. In addition, the content of the polymeric 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 polymeric surfactant into the water to be treated so that the content of the polymeric surfactant in the water to be treated is within the above range. Since the content of the polymeric surfactant in the water to be treated is within the above range, foaming properties are superior. Even in the case where the foam separation treatment is performed continuously in one embodiment, it is preferable to adjust the amount of polymeric surfactant introduced into the water to be treated so that the content of the polymeric surfactant in the water to be treated is within the above range.

[0032] In addition, the amount of polymeric surfactant is preferably 1 mass times or more relative to the PFAS content in the water to be treated, more preferably 10 mass times or more, even more preferably 50 mass times or more, and even more preferably 100 mass times or more. That is, in the foam separation treatment method of the present disclosure, it is preferable to introduce a polymeric surfactant at least 1 mass times relative to the amount of PFAS contained in the water to be treated. Since the amount of polymeric surfactant relative to the PFAS content in the water to be treated is within the above range, the recovery efficiency of PFAS is superior. In one embodiment, even when the 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 polymeric surfactant introduced into the water to be treated so that the amount of polymeric surfactant relative to the PFAS content in the water to be treated is within the above range.

[0033] To the extent that it does not impair the intent of the present invention, the water to be treated may contain components such as other impurities in addition to PFAS.

[0034] (Polymer surfactant)

[0035] The polymeric surfactant in the present disclosure is a compound that exhibits surface activity as a polymer. Furthermore, "is a polymer" means having a molecular weight of 1,000 or more. In the foam separation treatment method of the present disclosure, one type of polymeric surfactant may be used, or two or more types of polymeric surfactants may be used.

[0036] The molecular weight of the polymer surfactant is 1000 or more, preferably 2000 or more, more preferably 5000 or more, and even more preferably 10000 or more.

[0037] It is preferable that the HLB value of a polymeric surfactant be 3 or higher, more preferable that it be 8 or higher, and even more preferable that it be 13 or higher. The HLB value is an indicator representing the degree of affinity of a surfactant for water and oil, taking a value from 0 to 20, where the closer it is to 0, the higher the lipophilicity, and the closer it is to 20, the higher the hydrophilicity. Here, the HLB value is a value defined by the Griffin method, and HLB value = 20 × (total sum of hydrophilic portions) / (molecular weight). For example, when a certain surfactant is strongly mixed in water, if a portion of the surfactant is dispersed in water, the HLB value of the surfactant is 3 to 6; if dispersed in a milk phase, it is 6 to 8; if dispersed in a stable milk phase, it is 8 to 10; if dispersed in a translucent to transparent phase, it is 10 to 13; and if dissolved and becomes transparent, it corresponds to an HLB value of 13 or higher.

[0038] Polymeric surfactants may be polymers formed by polymerizing monomers, and are preferably polymers of nonionic monomers and / or anionic monomers. Examples of nonionic monomers include ethylene oxide, propylene oxide, (meth)acrylamide compounds, alkyl (meth)acrylate esters, styrene, acrylonitrile, vinyl acetate, etc. Examples of (meth)acrylate alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, etc. In addition, examples of anionic monomers include (meth)acrylic acid, vinylsulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, maleic acid, and salts thereof. Furthermore, in this disclosure, "(meth)acrylate" is a general term for methacrylate and acrylate. In addition, the polymeric surfactant may be a polymer formed by polymerizing one type of monomer, or a polymer formed by copolymerizing two or more types of monomers. Furthermore, the polymeric surfactant may be a polymer obtained by undergoing, for example, a process of introducing functional groups after polymerizing the monomers. Among polymeric surfactants, vinyl alcohol-based polymers (PVA) obtained using vinyl ester-based monomers such as vinyl acetate as raw materials are preferred because they have excellent water solubility, foam-forming properties, and biodegradability. That is, a preferred embodiment of the foam separation treatment method of the present disclosure is a foam separation treatment method that separates organic fluorine compounds from said water to be treated by sending gas to said water containing organic fluorine compounds and recovering the generated foam, wherein PVA is introduced into said water to be treated. In addition, the monomer serving as the raw material for PVA may be a vinyl ester-based monomer other than vinyl acetate, as described below.

[0039] PVA is a polymer having vinyl alcohol units as monomer units. PVA is obtained by saponifying a vinyl ester polymer formed by polymerizing vinyl ester monomers, which are the raw material monomers, and the PVA after saponification may contain vinyl ester units in addition to vinyl alcohol units.

[0040] In addition, PVA can be produced by saponifying a copolymer formed by copolymerizing a vinyl ester-based monomer, which is the raw material monomer, with another monomer to produce PVA containing monomer units other than vinyl alcohol units and vinyl ester units, or by reacting a specific chemical species during the polymerization process, saponification process, and / or after saponification in the manufacturing process of PVA to introduce specific functional groups to the side chains or terminals. In the present disclosure, PVA such as these may be referred to as "modified vinyl alcohol-based polymer (modified PVA)." In addition, in the present disclosure, an agent used to modify PVA may be referred to as "modified species." For example, in one embodiment, if the modified PVA has a terminal structure derived from a chain transfer agent, said chain transfer agent may be referred to as the modified species, and in one embodiment, if the modified PVA is formed by copolymerizing a “different monomer” other than a vinyl ester-based monomer, said “different monomer” may be referred to as the modified species. In addition, in the present disclosure, the ratio of units derived from the modified species to the total monomer units constituting the modified PVA may be referred to as the “modification amount.”

[0041] As a lower limit for the ratio of vinyl alcohol units to total monomer units in PVA, 35 mol% is preferred, 50 mol% is more preferred, and 65 mol% is even more preferred. Meanwhile, as an upper limit for the ratio of vinyl alcohol units, 99.95 mol% is preferred, 95 mol% is more preferred, and 90 mol% is even more preferred.

[0042] It is preferable that the viscosity average degree of polymerization of PVA be 100 or higher and 5,000 or lower. The lower limit of the viscosity average degree of polymerization of PVA is more preferably 200, and in some cases, 500 is even more preferable. Furthermore, the upper limit of the viscosity average degree of polymerization of PVA is more preferably 4,000, in some cases, 3,000 is even more preferable, and in some cases, 2,000 is even more preferable. Since the viscosity average degree of polymerization is within the above range, manufacturing tends to become easier. The viscosity average degree of polymerization is a value obtained by measuring in accordance with JIS K 6726:1994. Specifically, if the degree of saponification of PVA is less than 99.5 mol%, the viscosity average degree of polymerization is obtained by the following formula using the intrinsic viscosity [η] (liter / g) measured in water at 30°C for PVA saponified until the degree of saponification becomes 99.5 mol% or higher.

[0043] P=([η]×10 4 / 8.29) (1 / 0.62)

[0044] The lower limit of the degree of saponification of PVA is preferably 30 mol%, more preferably 50 mol%, and in some cases, even more preferably 65 mol%. Meanwhile, the upper limit of the degree of saponification of the PVA is preferably 99.99 mol%, more preferably 99 mol%, more preferably 90 mol%, and in some cases, even more preferably 80 mol%. In addition, the degree of saponification of 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 in some cases, even more preferably 65 mol% or more and 90 mol% or less. By setting the degree of saponification of PVA within the above range, the efficiency of foam separation is improved, and there is a tendency to be able to manufacture PVA more stably industrially.

[0045] A method for manufacturing PVA preferably includes a polymerization process for polymerizing vinyl ester-based monomers and a saponification process for saponifying the vinyl ester-based polymer obtained thereby.

[0046] Vinyl ester polymers can be prepared by polymerizing vinyl ester monomers using conventionally known methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, and dispersion polymerization. In order to enhance the effects of the present disclosure, a solution polymerization method using a lower alcohol is preferred. Although there are no particular limitations on the lower alcohol, alcohols with three or fewer carbon atoms, such as methanol, ethanol, propanol, and isopropanol, are preferred, and methanol is more preferred. Any polymerization method among batch, semi-batch, and continuous methods may be employed for the polymerization operation.

[0047] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versaticate, vinyl caproate, vinyl caprylate, vinyl laurylate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, etc. Among these, vinyl acetate is preferred.

[0048] In addition, as described above, regarding PVA, a modified PVA may be produced by copolymerizing a vinyl ester-based monomer with another monomer to a extent that does not impair the spirit of the present disclosure. Other monomers include, for example, α-olefins such as ethylene, propylene, n-butene, isobutylene; (meth)acrylic acid and its salts; (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, octadecyl (meth)acrylate; Acrylamide compounds such as (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamide-propanesulfonic acid and its salts, (meth)acrylamide-propyldimethylamine 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, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; Examples include 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 may be used individually or in combination of two or more. Among them, 3-(methacryloylamino)propyltrimethylammonium chloride (MAPTAC) is preferred as an acrylamide compound. The copolymerization amount (modification amount) of other monomers is preferably 10 mol% or less. Furthermore, the copolymerization amount of other monomers refers to the ratio of units derived from other monomers to the total monomer units constituting the modified PVA.

[0049] The polymerization initiator used during polymerization can be selected from known initiators (e.g., azo-based initiators, peroxide-based initiators, redox-based initiators, etc.). Examples of azo-based initiators include 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. Examples of peroxide-based initiators include percarbonate compounds such as di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, di-2-ethylhexylperoxydicarbonate, and diethoxyethylperoxydicarbonate; Examples include perester compounds such as t-butylperoxyneodecanoate, α-cumylperoxyneodecanoate, and t-butylperoxydecanoate; acetylcyclohexylsulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. may be combined with these initiators to serve as an initiator. As for redox-type initiators, for example, an initiator combining the above peroxide with a reducing agent such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, or Rongalite may be used. When polymerization is performed at high temperatures, discoloration caused by the decomposition of vinyl ester monomers may be observed. In that case, for the purpose of preventing discoloration, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of about 1 to 100 ppm by mass relative to the vinyl ester monomer.

[0050] A chain transfer agent may be co-added for purposes such as controlling the degree of polymerization of the PVA obtained during the polymerization of vinyl ester monomers or introducing 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 suitably used. The amount of chain transfer agent added is determined by the chain transfer constant of the added chain transfer agent and the degree of polymerization of the target PVA, but generally, 0.1 to 10 mass% relative to the vinyl ester used is preferred. In one embodiment, by using an alkyl mercaptan as a chain transfer agent in the polymerization process of PVA, modified PVA in which an alkyl group derived from the alkyl mercaptan is introduced at the terminal end can be obtained. The modification amount of such modified PVA, that is, the ratio of units having an alkyl group derived from the alkyl mercaptan to the total monomer units constituting the modified PVA, is preferably 0.01 mol% or more and 5 mol% or less, more preferably 0.1 mol% or more and 3 mol% or less, and even more preferably 0.3 mol% or more and 1 mol% or less. n-DDM is preferred as the alkyl mercaptan.

[0051] There are no specific limitations on the polymerization temperature, but 0 to 180°C is preferred, 20 to 160°C is more preferred, and 30 to 150°C is even more preferred. When polymerizing below the boiling point of the solvent used in the polymerization process, either reduced-pressure boiling polymerization, in which polymerization is performed while boiling the solvent under reduced pressure, or atmospheric pressure non-boiling polymerization, in which polymerization is performed under atmospheric pressure without boiling the solvent, can be selected. Additionally, when polymerizing above the boiling point of the solvent used in the polymerization process, either pressurized non-boiling polymerization, in which polymerization is performed under pressure without boiling the solvent, or pressurized boiling polymerization, in which polymerization is performed while boiling the solvent under pressure, can be selected.

[0052] As described above, PVA is obtained by saponifying vinyl ester-based polymers. As a method for the saponification reaction, examples include an alcohol decomposition reaction or a hydrolysis reaction using basic catalysts such as sodium hydroxide, potassium hydroxide, or sodium methoxide, or acidic catalysts such as p-toluenesulfonic acid. Solvents that can be used for this reaction include, for example, alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These solvents may be used individually or in combination of two or more. Among these, it is convenient and preferable to saponify using methanol or a methanol / methyl acetate mixed solution as a solvent and sodium hydroxide as a catalyst.

[0053] (Organic fluorine compounds)

[0054] The organic fluorinated compound (PFAS) may be an amphiphilic perfluoroalkane derivative, and examples of amphiphilic perfluoroalkane derivatives 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, perfluorododecanoic acid, etc. In particular, the foam separation treatment method of the present disclosure is suitable for perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, etc. 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 subject to foam separation treatment may be one type or two or more types.

[0055] Aqueous solution

[0056] One embodiment of the present invention is an aqueous solution containing PVA and PFAS. Due to the composition of such an aqueous solution, PFAS contained in said aqueous solution can be easily separated by foam separation treatment.

[0057] A preferred embodiment of the PVA and PFAS included in the aqueous solution is the same as the PVA and PFAS described above.

[0058] The content of PVA in the aqueous solution is preferably 0.1 mass ppm or more, more preferably 1 mass ppm or more, even more preferably 10 mass ppm or more, and in some cases, even more preferably 100 mass ppm or more. In addition, the content of PVA in the aqueous solution is preferably 1 mass% or less. Since the content of PVA in the aqueous solution is within the above range, the foaming properties are superior.

[0059] In addition, the content of PVA in the aqueous solution is preferably 1 mass times or more with respect to the content of PFAS, more preferably 10 mass times or more, even more preferably 50 mass times or more, and even more preferably 100 mass times or more. Since the content of PVA is within the above range, the recovery efficiency of PFAS is even better.

[0060] The aqueous solution of the present disclosure may contain various additives and impurities to the extent that it does not impair the spirit of the present invention.

[0061] In addition, one embodiment of the present invention is a foam separation treatment method that sends a gas to the aqueous solution to generate foam and recovers the foam.

[0062] <Method of using vinyl alcohol-based polymers>

[0063] One embodiment of the present invention is a method of using PVA in which, in a process of separating PFAS from water to be treated by sending gas to water to be treated containing PFAS and recovering the generated foam, the generation of foam is promoted by mixing PVA with the water to be treated.

[0064] A preferred embodiment of PVA in this method of use is the same as the PVA described above.

[0065] Foam generation promoter

[0066] One embodiment of the present invention is a foam generation promoter composed of a vinyl alcohol-based polymer that is introduced into the water to be treated when separating organic fluorine compounds from the water to be treated by foam separation treatment.

[0067] A preferred embodiment of PVA in such a foam generation promoter is the same as the PVA described above.

[0068] Examples

[0069] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to any of these examples. Furthermore, "%" and "ppm" in the examples and comparative examples represent "mass%" and "mass ppm," respectively, unless otherwise specified.

[0070] [Viscosity Average Degree of Polymerization]

[0071] The 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 average degree of polymerization of the viscosity was calculated using the following formula based on the intrinsic viscosity [η] (liter / g) measured in water at 30°C for PVA saponified until the degree of saponification was 99.5 mol% or more.

[0072] P=([η]×10 4 / 8.29) (1 / 0.62)

[0073] [Saponification]

[0074] The degree of saponification of the PVA used in the examples was measured in accordance with JIS K 6726:1994.

[0075] <Preparation Example 1>

[0076] [Manufacture of PVA1]

[0077] PVA1 was prepared as a polymeric surfactant by the following method. 640 g of vinyl acetate and 960 g of methanol were introduced into a 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, and an initiator port, and the system was nitrogen-substituted for 30 minutes while bubbling nitrogen. The reactor was heated, and when the internal temperature reached 60°C, 0.3 g of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. After polymerizing at 60°C for 5 hours, 0.3 g of hydroquinone was added, and the polymerization was stopped by cooling. The solid content concentration at the time of stopping polymerization was 20.0%, and the polymerization rate was 50%. Subsequently, the removal of unreacted vinyl acetate monomers was carried out at 50°C under reduced pressure while occasionally adding methanol, thereby obtaining a methanol solution (concentration 35%) of a vinyl ester polymer (PVAc). In addition, 3.7g of an alkaline solution (a 10% methanol solution of sodium hydroxide) was added to 457g of the methanol solution of the vinyl ester polymer (160.0g of vinyl ester polymer in the solution) prepared by adding methanol to this, and saponification was performed (the concentration of vinyl ester polymer in the saponification solution was 30%, and the molar ratio of sodium hydroxide to vinyl acetate units was 0.005). Since a gel-like substance was formed about 15 minutes after the addition of the alkaline solution, it was ground with a grinder and left at 40°C for 1 hour to proceed with saponification, after which 500g of methyl acetate was added to neutralize the remaining alkali. After confirming that neutralization was complete using a phenolphthalein indicator, a white solid was obtained by filtration fractionation, and 2,000 g of methanol was added to it and washed by leaving it at room temperature for 3 hours. After repeating the above washing operation 3 times, the white solid obtained by centrifugal dewatering was left in a dryer at 65°C for 2 days to obtain PVA1. The average degree of polymerization of PVA1 was 530, and the degree of saponification was 88.0 mol%.

[0078] <Preparation Examples 2 to 4>

[0079] [Manufacture of PVA2 to 4]

[0080] PVA2 to 4 were prepared as polymeric surfactants by the following method. PVA2 to 4 were obtained in the same manner as prepared for PVA1 in Preparation Example 1, except that the polymerization conditions (amount of vinyl acetate, amount of methanol, polymerization rate) and saponification conditions (PVAc concentration, molar ratio of sodium hydroxide to PVAc) were changed as shown in Table 1.

[0081] <Preparation Example 5>

[0082] [Manufacturing of PVA5]

[0083] PVA5 was prepared as a polymeric surfactant by the following method. In a 3L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, a delay solution dropper, and an initiator addition port, 960g of vinyl acetate, 640g of methanol, and 4.3g of 3-(methacryloylamino)propyltrimethylammonium chloride (MAPTAC) as a comonomer were added, and the system was nitrogen-substituted for 30 minutes while bubbling nitrogen. Additionally, a comonomer solution with a concentration of 20% was prepared by dissolving MAPTAC in methanol as a delay solution, and nitrogen was substituted by bubbling nitrogen gas. The temperature of the reactor was raised, and when the internal temperature reached 60°C, 0.2g of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. Polymerization was carried out at 60°C for 3 hours while maintaining a constant monomer composition (ratio of vinyl acetate to MAPTAC) in the polymerization solution by adding a delay solution dropwise. Afterward, 0.4g of hydroquinone was added, and the polymerization was stopped by cooling. The total amount of MAPTAC added until the polymerization was stopped was 13.4g. In addition, the solid content concentration at the time of polymerization cessation was 17.0%, and the polymerization rate was 30%. Subsequently, the unreacted vinyl acetate monomer was removed by adding methanol intermittently at 50°C under reduced pressure to obtain a methanol solution (concentration 35%) of the MAPTAC-modified vinyl ester-based polymer. Next, saponification was performed under the same conditions as in Preparation Example 1 described above, except that the saponification conditions (PVAc concentration, molar ratio of sodium hydroxide to PVAc) were changed as shown in Table 1, thereby obtaining PVA5. The modification amount (the ratio of MAPTAC-derived units to the total monomer units constituting PVA5) was 2.0 mol%. In addition, the modification amount of PVA5 was the MAPTAC-modified vinyl ester polymer, which is the precursor before saponification. 1 It was obtained by measuring with H-NMR.

[0084] <Preparation Example 6>

[0085] [Manufacture of PVA6]

[0086] PVA6 was prepared 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 added to a 3 L reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet, a delay solution dropper, and an initiator addition port, and the system was nitrogen-substituted for 30 minutes while bubbling nitrogen. In addition, a chain transfer agent solution was prepared by dissolving n-DDM in methanol to a concentration of 10% as a delay solution, and nitrogen was substituted by bubbling nitrogen gas. The temperature of the reactor was raised, and when the internal temperature reached 60°C, 1.0 g of 2,2'-azobisisobutyronitrile (AIBN) was added to start polymerization. Polymerization was carried out at 60°C for 3 hours while adding a delay solution dropwise to maintain a constant ratio of vinyl acetate to n-DDM in the polymerization solution. Afterward, 2.0 g of hydroquinone was added, and the polymerization was stopped by cooling. The total amount of n-DDM added until the polymerization was stopped was 6.32 g. In addition, the solid content concentration at the time of polymerization cessation was 28.9%, and the polymerization rate was 50%. Subsequently, the unreacted vinyl acetate monomer was removed by adding methanol intermittently at 50°C under reduced pressure to obtain a methanol solution (concentration 35%) of the n-DDM modified vinyl ester-based polymer. Next, saponification was performed under the same conditions as in Preparation Example 1 described above to obtain PVA6, a modified PVA having a structure derived from n-DDM at the terminals. The modification amount of PVA6 (the ratio of units having alkyl groups derived from n-DDM to the total monomer units constituting PVA6) was 0.5 mol%. In addition, the modification amount of PVA6 was the n-DDM modified vinyl ester polymer, which is the precursor before saponification. 1 It was obtained by measuring with H-NMR.

[0087]

[0088] *1) 3-(methacryloylamino)propyltrimethylammonium chloride

[0089] *2) Normal dodecyl mercaptan

[0090] <Example 1>

[0091] [PFAS Foam Separation Treatment Test]

[0092] A cylindrical ceramic air stone with a diameter of 10 mm, a length of 150 mm, and a #240 rating was set at the bottom of a 1 L beaker, and 200 ml of an aqueous solution containing 1.0 ppm of PFOA (perfluorooctanoic acid) and 100 ppm of PVA1 as PFAS was added to it as the water to be treated. Next, air was flowed through the air stone at a flow rate of 0.15 ml / min to supply air to the water to be treated, and the generated foam was collected intermittently for 30 minutes. The concentration of PFOA contained in the residual liquid after the test was analyzed using LC / MS (LC / MS-8030 manufactured by Shimadzu Corporation, column: TSKgel ODS-80Ts, detector: MS detector, ionization method: ESI mode, detection charge: negative charge), and the result was 0.08 ppm.

[0093] <Examples 2 to 10>

[0094] A separation test of PFAS was performed 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.

[0095] <Example 11>

[0096] A separation test for PFAS was performed under the same conditions as in Example 1, except that polyoxyethylene lauryl ether (Nonion K-230 manufactured by Nichiyu Co., Ltd., moles of ethylene oxide added n=30, HLB value 17.5) was used instead of PVA1. The PFOA content in the residue liquid after the test was 0.12 ppm. The results are shown in Table 2.

[0097] <Comparative Example 1>

[0098] As a result of conducting a foam separation treatment test of PFAS under the same conditions as Example 1 without the addition of a surfactant, the PFOA content in the remaining solution was 0.82 ppm.

[0099] <Comparative Example 2>

[0100] A separation test for PFAS was performed under the same conditions as in Example 1, except that lauryl dimethylaminoacetic acid betaine (Nissan Anon BL-SF manufactured by Nichiyu Co., Ltd., molecular weight 271.44) was used instead of PVA1. The PFOA content in the residue liquid after the test was 0.75 ppm. The results are shown in Table 2.

[0101]

[0102] *1) "Non-ionic K-230": Polyoxyethylene lauryl ether (n=30)

[0103] *2) "Nissanon BL-SF": Lauryldimethylamine, Betaine acetate

[0104] *3) PFOA: Perfluorooctanoic acid, PFHxS: Perfluorohexanesulfonic acid, PFBS: Perfluorobutanesulfonic acid

[0105] *4) Content of PFAS per 100 parts by mass of PVA

[0106] From the results of Table 2, it was shown that the PFAS retention rate of the example treated with foam separation using a polymer surfactant was lower than the PFAS retention rate of the comparative example treated without using a polymer surfactant, and that the example had excellent separation recovery efficiency.

Claims

Claim 1 A foam separation treatment method for separating organic fluorine compounds from water to be treated by sending gas to water to be treated containing organic fluorine compounds and recovering the generated foam, wherein a polymer surfactant is introduced into the water to be treated. Claim 2 A foam separation treatment method according to claim 1, wherein the polymer surfactant is a vinyl alcohol-based polymer. Claim 3 A foam separation treatment method according to paragraph 2, wherein the viscosity average degree of polymerization of the vinyl alcohol-based polymer is 100 or more and 5,000 or less, and the degree of saponification is 30 mol% or more and 99.99 mol% or less. Claim 4 A foam separation treatment method according to claim 1, wherein a polymer surfactant is introduced into the water to be treated such that the content of the polymer surfactant in the water to be treated is 1 mass% or less. Claim 5 A foam separation treatment method according to any one of claims 1 to 4, wherein at least one mass of a polymer surfactant is introduced relative to the amount of an organic fluorine compound contained in the water to be treated. Claim 6 An aqueous solution containing a vinyl alcohol-based polymer and an organic fluorine-based compound. Claim 7 An aqueous solution according to claim 6, wherein the viscosity average degree of polymerization of the vinyl alcohol-based polymer is 100 or more and 5,000 or less, and the degree of saponification is 30 mol% or more and 99.99 mol% or less. Claim 8 In paragraph 6, an aqueous solution having a vinyl alcohol-based polymer content of 1 mass% or less. Claim 9 In paragraph 6, an aqueous solution in which the content of a vinyl alcohol-based polymer is at least one mass times the content of an organic fluorine-based compound in the aqueous solution. Claim 10 A foam separation treatment method for generating foam by sending a gas into an aqueous solution described in any one of claims 6 to 9 and recovering said foam. Claim 11 A method of using a vinyl alcohol-based polymer in a treatment for separating organic fluorine compounds from said water to be treated by sending gas to said water containing organic fluorine compounds and recovering the generated foam, wherein the vinyl alcohol-based polymer is mixed with said water to be treated to promote the generation of foam. Claim 12 A foam generation promoter composed of a vinyl alcohol-based polymer introduced into the water to be treated when separating organic fluorine compounds from the water to be treated by foam separation treatment.

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