JP4770802B2 - Wastewater treatment method - Google Patents

Description

The present invention relates to a wastewater treatment method.

In the production of a fluorine-containing polymer, generally, a polymerization reaction is carried out in an aqueous medium in the presence of a fluorine-containing surfactant, so that wastewater containing the fluorine-containing surfactant is generated. Methods for removing the fluorine-containing surfactant from this waste water have been studied conventionally.

As a method for recovering the fluorine-containing surfactant from wastewater generated in the production process of the fluorine-containing polymer, a removal technique using complex formation of the fluorine-containing surfactant has been proposed.

Patent Documents 1 and 2 disclose a method of removing a fluorine surfactant by forming a layered double hydroxide by dropping a mixed aqueous solution containing divalent metal ions and trivalent metal ions into waste water. Is described. However, in these methods, the fluorine-containing surfactant is removed, but the nonionic surfactant is not removed. Therefore, a separate step of removing the nonionic surfactant is necessary.

Patent Document 3 and Patent Document 4 include a method for removing a water-insoluble salt by adding a metal salt of a polyvalent metal such as aluminum, calcium or magnesium to remove an organic acid compound such as a fluorine-containing alkylcarboxylic acid. Are listed. However, in these methods, the fluorine-containing surfactant is removed, but the nonionic surfactant is not removed. Therefore, a separate step of removing the nonionic surfactant is necessary.

Regarding the production of a fluoropolymer, a product having a low content of a fluorosurfactant is required. As a means for reducing the content of the fluorosurfactant in the aqueous fluoropolymer dispersion, for example, by a polymerization reaction It is known that the obtained aqueous dispersion is subjected to phase separation concentration, electric concentration or the like (for example, see Patent Document 5). When such an operation is performed, since a nonionic surfactant is added, wastewater containing not only the fluorine-containing surfactant but also the nonionic surfactant is generated. However, a method for removing these surfactants from the waste water simultaneously has not been proposed.
JP 2003-285075 A JP 2003-285076 A JP 2006-206866 A JP 2007-002072 A International Publication No. 2004/050179 Pamphlet

In view of the above-mentioned present situation, the present invention is to provide a method for easily removing a fluorine-containing surfactant and a nonionic surfactant in waste water.

The present invention includes a step (i) of adding an electrolyte to a liquid to be treated containing water, a fluorine-containing surfactant and a nonionic surfactant and having a fluorine-containing polymer concentration of 0.5% by mass or less, and the above By heating the liquid to be treated after step (i), the phase (1) substantially free of the fluorine-containing surfactant and the nonionic surfactant, the fluorine-containing surfactant and the nonionic surfactant are added. A wastewater treatment method comprising a step (ii) of phase separation into a phase (2) to be contained.
Conventionally, an aqueous solution containing a nonionic surfactant is heated above the cloud point of the nonionic surfactant to phase separate into a phase containing substantially no nonionic surfactant and a phase containing nonionic surfactant. It was known to do. However, when the fluorine-containing surfactant coexists, this phase separation is difficult to proceed, and it has been found that the phase separation proceeds by further heating by adding an electrolyte. The present invention has been completed by finding that the fluorine-containing emulsifier to be selectively transferred to a phase containing a nonionic surfactant.
The present invention is described in detail below.

In the present invention, the liquid to be treated contains water, a fluorine-containing surfactant, and a nonionic surfactant.
As the liquid to be treated, for example, drainage generated in preparing the fluoropolymer aqueous dispersion can be considered. That is, when reducing the content of the fluorine-containing surfactant in the fluorine-containing polymer aqueous dispersion, as described above, the fluorine-containing surfactant used for the polymerization and the operation for performing the reduction (phase separation concentration) And wastewater containing nonionic surfactant used for electric concentration, etc.).
On the other hand, in the conventional wastewater treatment method, only a method for removing the fluorine-containing surfactant has been proposed, and a method for simultaneously removing the fluorine-containing surfactant and the nonionic surfactant has not been studied. .
On the other hand, the waste water treatment method of the present invention is a method capable of simultaneously removing the fluorine-containing surfactant and the nonionic surfactant from the waste water in a short time.

The liquid to be treated may contain only one type of fluorine-containing surfactant and nonionic surfactant, or may contain two or more types, or only one of them. It may contain more than seeds.

Examples of the fluorine-containing surfactant include compounds having a fluorine-substituted hydrocarbon group as a hydrophobic group and a carboxylic acid, sulfonic acid and / or salt thereof as a hydrophilic group.
Examples of the fluorine-substituted hydrocarbon group include fluorinated alkyl groups and fluorinated alkoxy groups having 4 to 10 carbon atoms, preferably 5 to 7 carbon atoms, to which fluorine atoms are bonded. More specifically, examples thereof include perfluoroalkyl groups and perfluoroalkoxy groups having 4 to 10 carbon atoms, preferably 5 to 7 carbon atoms, to which fluorine atoms are bonded. The fluorine-substituted hydrocarbon group may contain ether bondable oxygen in the structure.
Typical examples of the fluorine-containing surfactant include perfluoroalkyl carboxylic acids, perfluoroether carboxylic acids, and salts thereof.

In the liquid to be treated, the content of the fluorine-containing surfactant is generally 0.01 to 2% by mass.
The content is preferably 0.05% by mass or more, more preferably 1% by mass or less, based on the removal efficiency, from the viewpoint of removal efficiency.

In the present specification, the content of the fluorine-containing surfactant is a value determined from ¹⁹ F-NMR (measuring instrument AC300P, manufactured by Bruker Biospin).

The nonionic surfactant is not particularly limited as long as it is a known one, and examples thereof include ether type nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkylene alkyl ether, and ethylene oxide. / Ester-type nonionic surfactants such as polyoxyethylene derivatives such as propylene oxide block copolymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, Examples include amine-based nonionic surfactants such as polyoxyethylene alkylamine and alkylalkanolamide.

The nonionic surfactant preferably does not have an alkylphenol in the structure, and a polyoxyethylene nonionic surfactant is more preferable. Furthermore, what has a cloud point of 50-90 degreeC is preferable.
In the present specification, the cloud point is determined according to ISO 1065 (Method A) when 15 ml of a measurement diluted sample is placed in a test tube and heated until it becomes completely opaque, and then gradually cooled with stirring. Is a value measured as the temperature at which becomes transparent.

In the liquid to be treated, the content of the nonionic surfactant is generally 1% by mass or more and 30% by mass or less. In terms of removal efficiency, the preferable lower limit is 2.5% by mass, and the preferable upper limit is 25% by mass.

In this specification, the content (N) of the nonionic surfactant is about 1 g (Xg) of a sample taken in an aluminum cup having a diameter of 5 cm and heated at 100 ° C. for 1 hour. The heating residue (Yg) obtained was calculated from the formula: N = [(Y−Z) / X] × 100 (%) from the heating residue (Zg) heated at 300 ° C. for 1 hour.

The liquid to be treated may contain a fluorine-containing polymer as long as its concentration is 0.5% by mass or less. The above-mentioned fluoropolymer is, for example, mixed in wastewater generated during the preparation of the fluoropolymer aqueous dispersion, and should be removed by the wastewater treatment method of the present invention.
If the concentration of the fluorine-containing polymer exceeds 0.5% by mass, the removal efficiency of the fluorine-containing surfactant and the nonionic surfactant is decreased, which is not preferable.

In this specification, the fluorine-containing polymer concentration (P) is determined by measuring about 1 g (Xg) of a sample in an aluminum cup having a diameter of 5 cm, heating at 100 ° C. for 1 hour, and further heating at 300 ° C. for 1 hour. From the minute (Zg), it is calculated from the formula: P = (Z / X) × 100 (%).

The fluorine-containing polymer is not particularly limited, but is polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / hexafluoropropylene [HFP] copolymer [FEP], TFE / perfluoro (alkyl vinyl ether) [PAVE]. ] Copolymer [PFA], Ethylene / TFE copolymer [ETFE], Polyvinylidene fluoride [PVDF], Polychlorotrifluoroethylene [PCTFE] and the like.

The PTFE may be a tetrafluoroethylene [TFE] homopolymer or a modified polytetrafluoroethylene [modified PTFE].
In the present specification, the modified PTFE means a non-melt processable fluorine-containing polymer obtained by polymerizing TFE and a small amount of monomer. Examples of the trace monomer include fluoroolefins such as HFP and chlorotrifluoroethylene [CTFE], fluoro (alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; Fluorodioxole; perfluoroalkylethylene; ω-hydroperfluoroolefin and the like.

Typical examples of the fluorine-containing polymer in the liquid to be treated include TFE homopolymer and modified PTFE.

The liquid to be treated may be produced by any method as long as it contains the fluorine-containing surfactant and the nonionic surfactant described above.
Examples of the liquid to be treated include waste water generated when the fluoropolymer aqueous dispersion obtained by polymerization is concentrated.

The wastewater treatment method of the present invention includes a step (i) of adding an electrolyte to the liquid to be treated and a step (ii) of phase separation by heating the liquid to be treated after the above step (i). .

Examples of the electrolyte include inorganic acids, metal hydrates, and salts thereof. In the case of inorganic acids, sulfuric acid is preferable. The salt of the inorganic acid is preferably a chloride or sulfate of a 1 to 3 metal. Examples of the metal include Na, K, Ca, Mg, and Al. The inorganic salt is preferably a sodium salt or an aluminum salt, and more preferably a sodium salt. More specifically, Na ₂ SO ₄ , NaCl, Al ₂ (SO ₄ ) ₃ may be mentioned. Examples of the metal hydrate include metal hydrates such as Na, K, Ca, Mg, and Al.

The addition amount of the electrolyte is preferably 0.01 to 5% by mass with respect to the liquid to be treated, and a more preferable range is 0.1 to 1% by mass. If the amount added is small, the amount of nonionic surfactant remaining in the phase (1) substantially free of fluorine-containing surfactant and nonionic surfactant increases, and if the amount added is excessive, the effect is improved. Therefore, economic efficiency is impaired.

It is preferable to perform the said process (i) under the temperature of 5-60 degreeC. It is preferable to stir when adding the electrolyte.

The step (ii) is preferably performed in the presence of 1 to 30 parts by mass of a nonionic surfactant with respect to 100 parts by mass of the liquid to be treated in terms of removal efficiency.
The amount of the nonionic surfactant is more preferably 3 parts by mass and more preferably 25 parts by mass with respect to 100 parts by mass of the liquid to be treated.
When the content of the nonionic surfactant in the liquid to be treated is within the range, it is not necessary to add the nonionic surfactant in the step (ii). The content is an amount corresponding to the total amount of the nonionic surfactant when there are two or more nonionic surfactants in the liquid to be treated.

The nonionic surfactant in the step (ii) is preferably the same type as that contained in the liquid to be treated.

The step (ii) can be carried out by heating and standing at a temperature higher than the cloud point of the nonionic surfactant, preferably higher by 5 ° C. or higher, but 60 to 95 ° C. in terms of good separation efficiency. More preferably.
The step (ii) may be generally performed in 20 minutes to 24 hours.

In the present invention, by carrying out the steps (i) and (ii) described above, the phase (1) substantially free of the fluorinated surfactant and the nonionic surfactant, the fluorinated surfactant and the nonionic surfactant The phase can be separated into phase (2) containing the agent.
The phase (1) and the phase (2) can be separated by performing a known method such as decantation.

In the present specification, “substantially free of fluorine-containing surfactant and nonionic surfactant” means that the content of fluorine-containing surfactant and nonionic surfactant is less than 25 ppm, respectively, and 2.3 mass %, Preferably less than 1.0% by weight.

In the wastewater treatment method of the present invention, when the fluorine-containing polymer concentration of the liquid to be treated is 0.01 to 0.5% by mass, in addition to the above step (i) and step (ii), the phase (1) A step of phase separation into a phase (3) containing substantially no fluorine-containing polymer and a phase (4) containing a fluorine-containing polymer by adding a flocculant and / or an electrolyte and further heating (hereinafter, this step) May also be referred to as “step (iii)”).

In the present specification, “substantially no fluorine-containing polymer” means that the content of the fluorine-containing polymer is less than 0.01% by mass.

In the present invention, the step (iii) comprises adding a flocculant and / or an electrolyte to the phase (1) to agglomerate the fluoropolymer, and further heating to contain the surfactant in the fluoropolymer. Phase (4) to be selectively transferred.
The step (iii) may not be particularly performed when the concentration of the fluoropolymer in the liquid to be treated is less than 0.01% by mass.

In the step (iii), as the flocculant, for example, anionic, cationic and amphoteric known polymer flocculants can be used. As the anionic, acrylamide / acrylic acid polymer and cationic N, N-dimethylaminoethyl acrylate / acrylamide polymer, polyaluminum chloride (PAC), and the like. The said electrolyte can use the thing similar to what was illustrated about the above-mentioned process (i).

In the said process (iii), it is preferable to add a total of 0.5-10 mass% of a flocculant and / or electrolyte with respect to the total amount of surfactant in a phase (1).
The addition amount is more preferably 1 to 6% by mass.

The flocculant and / or electrolyte is preferably added with stirring. The above addition may be generally performed at a temperature of 5 to 40 ° C.

The heating in the step (iii) is preferably performed at a temperature of 60 to 95 ° C., more preferably 70 to 85 ° C. in terms of good separation efficiency. The main heating may be performed for a certain period of time from the start of heating, but is preferably performed by standing until the phases are separated after the stirring.

The phase (3) and the phase (4) generated by the phase separation can be separated by performing a conventionally known operation such as filtration and decantation.

The treated water obtained by the wastewater treatment method of the present invention has a very low surfactant content, and can be reused for applications such as industrial water.

Since the waste water treatment method of the present invention is configured as described above, the fluorine-containing surfactant and the nonionic surfactant can be easily removed.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

“Part” and “%” in each example and comparative example mean “part by mass” and “% by mass”, respectively, unless otherwise specified.
In each example and comparative example, each physical property was measured by the following method.

Content of fluorine-containing surfactant
^{It was determined by 19} F-NMR (measuring instrument AC300P, manufactured by Bruker Biospin).

Nonionic surfactant content (N)
About 1 g (Xg) of the sample was put in an aluminum cup having a diameter of 5 cm, and the heating residue (Yg) heated at 100 ° C. for 1 hour, and the obtained heating residue (Yg) was further heated at 300 ° C. for 1 hour. From the heating residue (Zg), it was calculated from the formula: N = [(Y−Z) / X] × 100 (%).

Examples 1-6
Nonionic surfactant having a tridecyl ethoxylate structure (cloud point 60 ° C.) 7.5%, perfluorooctanoic acid ammonium salt [PFOA] 5000 ppm and polytetrafluoroethylene [PTFE] (average particle size 240 nm) 0.1% An aqueous solution containing was prepared as a liquid to be treated.
500 g of this liquid to be treated was placed in a 1 L glass graduated cylinder, and 10 g of a 25% aqueous solution of the compound shown in Table 1 was added. did. The upper phase and the lower phase of the phase-separated liquid were separated by decantation, and the amount of nonionic surfactant and the PFOA concentration contained in each phase were measured.

The results of Examples 1 to 6 are shown in Table 1.

Example 7
Based on 40 g of the upper phase obtained in Example 1, 1.2 g of Hakutron SX (Hakuto Chemical) as a flocculant, 1.7 g of A15B (Hakuto Chemical) 0.1% aqueous solution, and polyaluminum chloride [PAC] 0 .83 g was added, and the mixture was stirred at 80 ° C. for 1 hour and allowed to stand. Since it separated into a supernatant phase and a precipitation phase in about 1 hour, it was 35 g when the supernatant phase was recovered after cooling. The concentration of PFOA contained in the supernatant phase was less than 1 ppm, and the amount of nonionic surfactant was very low at 0.05%.

The treated water obtained by the wastewater treatment method of the present invention does not substantially contain a fluorine-containing surfactant and a nonionic surfactant, and can be reused for applications such as industrial water.

Claims (9)

Adding an electrolyte to a liquid to be treated containing water, a fluorine-containing surfactant and a nonionic surfactant and having a fluorine-containing polymer concentration of 0.5% by mass or less; and the step (i) A phase (1) substantially free of the fluorine-containing surfactant and the nonionic surfactant and a phase containing the fluorine-containing surfactant and the nonionic surfactant (2) by heating the liquid to be treated And a step (ii) of phase separation into a wastewater treatment method. The wastewater treatment method according to claim 1, wherein the concentration of the fluorine-containing surfactant contained in the liquid to be treated is 0.05% by mass or more. The wastewater treatment method according to claim 1 or 2, wherein the nonionic surfactant concentration contained in the liquid to be treated is 1% by mass or more. The liquid to be treated has a fluorine-containing polymer concentration of 0.01 to 0.5% by mass,
A phase (3) substantially free of fluorine-containing polymer by adding a flocculant and / or an electrolyte to the phase (1) substantially free of the fluorine-containing surfactant and nonionic surfactant; The wastewater treatment method according to claim 1, 2 or 3, further comprising a step of phase separation into the phase (4) containing the fluoropolymer. The wastewater treatment method according to claim 1, wherein the electrolyte added in step (i) is a sodium salt. The wastewater treatment method according to claim 1, 2, 3, 4 or 5, wherein the amount of electrolyte added in step (i) is 1 to 20 moles per mole of fluorine-containing surfactant. The wastewater treatment method according to claim 1, 2, 3, 4, 5, or 6, wherein heating is performed at a temperature of 60 to 95 ° C in the step (ii). The waste water treatment method according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the fluorine-containing surfactant is perfluoroalkyl carboxylic acid, perfluoroether carboxylic acid or a salt thereof. The wastewater treatment method according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the nonionic surfactant has a cloud point of 50 to 90 ° C.