METHOD FOR RECOVERING FLUOROSURFACTANT CROSS-REFERENCE TO RELATED APPLICATION

[0001]

This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/388,810 filed on October 1, 2010, incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002]

The present invention relates to a method for recovering a fluorosurfactant .

BACKGROUND ART

[0003]

For the manufacture of fluoropolymers by aqueous emulsion polymerization, fluorosurfactants are commonly used.

[0004]

Since such fluorosurfactants used in emulsion

polymerization are expensive, reduction in the amounts of these fluorosurfactants and recovery and recycle of

fluorosurfactants used in emulsion polymerization have been proposed.

[0005]

For example, Patent Document 1 discloses a method for regenerating a basic anion-exchange resin. In this method, a basic anion-exchange resin having a fluorosurfactant adsorbed thereon is regenerated by eluting the fluorosurfactant by contacting the basic anion-exchange resin with an alkaline aqueous solution at a temperature of from 60°C to 105°C. Patent Document 1 also teaches the recovery of the eluted

fluorosurfactant . Patent Document 2 discloses a method for recovering a fluorinated emulsifier from a weakly to moderately basic anion-exchange resin with at least one ammonia-containing and water-miscible organic solvent having a boiling point lower than 110°C.

[0006]

Patent Document 3 discloses a method for recovering a fluorosurfactant , which includes: a step (X) of obtaining a fluorosurfactant-containing aqueous solution (B2) by causing the fluorosurfactant in a fluorosurfactant-containing exhaust gas mixture (A) to be absorbed in an aqueous solution (Bl) having a pH of 7 or higher and lower than 12 by contacting the fluorosurfactant-containing exhaust gas mixture (A) and the aqueous solution; a step (Y) of fixing the fluorosurfactant in the aqueous solution (B2) between layers of a laminar composite hydroxide; and a recovery step (Z) of recovering the fluorosurfactant by separating the laminar composite hydroxide (C) having the fluorosurfactant fixed between layers in the step (Y) . Patent Document 4 discloses a method for eliminating an anionic fluorosurfactant from exhaust gas streams by putting the exhaust gas streams into contact with an aqueous solution having a pH of from 3.5 to 13.8. Patent Document 5 discloses a method for recovering a highly fluorinated carbonic acid from exhaust gas streams by separating the highly fluorinated carbonic acid in a salt form into another layer by contacting the exhaust gas streams with an alkaline washing solution having a density of higher than 1.15 g/cm ³ , and also teaches the use of a potassium carbonate solution as the alkaline washing solution in this method.

[0007]

Patent Document 1 WO 2007/043278

Patent Document 2 JP 2003-512931 A

Patent Document 3 JP 2003-284921 A

Patent Document 4 US Pat. No. 2004/16343

Patent Document 5 JP 2001-506966 A SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008]

The methods of Patent Documents 1 to 5 enable recovery of fluorosurfactants separated in specific processes in the manufacture of fluoropolymers, but fail to enable

fluorosurfactants separated in each process to be collectively recovered by an easy operation.

[0009]

An object of the present invention is to provide a method for recovering a fluorosurfactant which enables collective recovery of a fluorosurfactant used in the manufacture of fluoropolymers . MEANS FOR SOLVING THE PROBLEMS

[0010]

The present invention provides a method for recovering a fluorosurfactant which includes:

obtaining a fluoropolymer aqueous dispersion by polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorosurfactant;

obtaining agglomerates (A) of the fluoropolymer by agglomerating the fluoropolymer in the fluoropolymer aqueous dispersion;

separating and separately recovering the agglomerates

(A) and a resulting solution (Bl) containing the

fluorosurfactant and the aqueous medium;

drying the agglomerates (A) into fluoropolymer particles and an exhaust gas (CI) containing the fluorosurfactant, and separately recovering the fluoropolymer particles and the exhaust gas (CI) ;

contacting the solution (Bl) with an ion-exchange resin (Dl) so as to separate them into a processed water (B2) that is obtained as a result of removal of the fluorosurfactant from the solution (Bl) , and an ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon, and separately recovering the processed water (B2) and the ion-exchange resin (D2); contacting the ion-exchange resin (D2) with an alkaline aqueous solution (El) so as to elute the fluorosurfactant from the ion-exchange resin (D2), and separating and separately recovering a regenerated ion-exchange resin (D3) removed the fluorosurfactant and an alkaline aqueous solution (E2) containing the fluorosurfactant ; and

contacting the exhaust gas (CI) with the alkaline aqueous solution (E2) so as to dissolve the fluorosurfactant contained in the exhaust gas (CI) , and recovering an alkaline aqueous solution (E3) with the fluorosurfactant dissolved therein.

[0011]

Preferably, the method for recovering a fluorosurfactant of the present invention further includes separating the alkaline solution (E3) into a fluorosurfactant solution (F) enriched in the fluorosurfactant and an alkaline aqueous solution (E4) containing the fluorosurfactant at a

concentration lower than the alkaline aqueous solution (E3) by allowing the alkaline solution (E3) to pass through a reverse osmosis membrane, and separately recovering the

fluorosurfactant solution (F) and the alkaline solution (E4) .

[0012]

Preferably, the ion-exchange resin (Dl) is a basic anion-exchange resin.

[0013]

Preferably, the ion-exchange resin (D2) is contacted with the alkaline aqueous solution (El) at a temperature of 5°C to 100°C.

EFFECTS OF THE INVENTION

[0014]

As constructed as described above, the method for recovering a fluorosurfactant of the present invention enables a fluorosurfactant separated in each process to be collectively recovered by an easy operation. An advantage other than collective recovery is that the amounts of both an alkaline aqueous solution used and a waste alkaline solution can be advantageously reduced. In addition, a solution enriched in the fluorosurfactant can be recovered, which leads to enhanced fluorosurfactant recovery efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]

Fig. 1 is a schematic view illustrating one example of the method for recovering a fluorosurfactant of the present invention .

MODES FOR CARRYING OUT THE INVENTION

[0016]

The present invention is explained in more detail below.

[0017]

The method for recovering a fluorosurfactant of the present invention includes obtaining a fluoropolymer aqueous dispersion by polymerizing a fluoromonomer in an aqueous medium in the presence of a fluorosurfactant . This polymerization process may be either an emulsion-polymerization or

suspension-polymerization process, provided that it is carried out in the presence of a fluorosurfactant .

[0018]

The polymerization process is a process for polymerizing the fluoromonomer, and the fluoromonomer may be polymerized with a monomer copolymerizable with the fluoromonomer other than fluoromonomers . The polymerization process may be carried out in the presence of two or more fluorosurfactants, and may be carried out in the presence of surfactants other than fluorosurfactants .

[0019]

In the polymerization process, additives may be used. Examples of the additives include chain transfer agents, radical scavengers, buffers, emulsification stabilizers, and dispersion stabilizers. Preferred examples of the dispersion stabilizers include paraffin.

[0020]

In the polymerization process, the polymerization conditions such as the polymerization temperature and polymerization pressure are not particularly limited, and can be appropriately selected based on factors such as the amount and type of the fluoromonomer used, and productivity. The polymerization temperature is preferably 5°C to 100°C, and more preferably 50°C to 90°C. The polymerization pressure is preferably 0.1 to 3.0 MPa.

[0021]

The polymerization process may be any of a batch, semi-batch, or continuous process and can be performed by known polymerization techniques. In the polymerization process, fluorosurfactants , chain transfer agents, polymerization initiators, stabilizers and the like can be continuously added or can be added at appropriate timings during the polymerization reaction, according to the desired yield and melt viscosity of the fluoropolymer . The polymerization process is typically carried out for 0.5 to 30 hours.

[0022]

In the case where the polymerization process is an emulsion-polymerization process, the emulsion-polymerization process can be initiated by feeding an aqueous medium, a chain transfer agent, and monomer (s) , and optionally a stabilizer and the like, to a pressure resistant reactor equipped with an agitator; adjusting the temperature and pressure; and adding a polymerization initiator. The emulsion-polymerization process can be carried out while the fluoromonomer is added to the aqueous medium.

[0023]

The amount of the fluorosurfactant used in the polymerization process is not particularly limited, but is preferably, for example, 0.0001 to 10% by mass based on 100% by mass of the aqueous medium. The more preferred lower limit is 0.001% by mass and the more preferred upper limit is 1% by mass .

[0024]

The aqueous medium is a reaction medium for the polymerization reaction and is a liquid containing water. The aqueous medium is not particularly limited, provided that it contains water. Examples thereof include a mixture containing water and a fluorine-free organic solvent (e.g. an alcohol, ether, ketone) , and a mixture containing water and a fluorine-containing organic solvent having a boiling point of not higher than 40°C.

[0025]

The method for recovering a fluorosurfactant of the present invention includes obtaining agglomerates

(coagulates) (A) of the fluoropolymer by agglomerating the fluoropolymer in the fluoropolymer aqueous dispersion. The fluoropolymer aqueous dispersion contains the fluoropolymer, the aqueous medium and the fluorosurfactant .

[0026]

The fluoropolymer is agglomerated by techniques such as adding a coagulant to the fluoropolymer aqueous dispersion; freeze coagulation; and agitating the fluoropolymer aqueous dispersion. Particularly preferred is the technique of adding a coagulant to the fluoropolymer aqueous dispersion.

[0027]

Examples of the coagulant include water-soluble organic compounds such as methanol and acetone; mineral salts such as potassium nitrate and ammonium carbonate; and inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid. Preferably, the coagulant is at least one selected from the group consisting of nitric acid, hydrochloric acid, ammonium carbonate and alcohols. Especially, nitric acid is more preferred. [0028]

In the case of freeze coagulation, the temperature and agitation speed of the fluoropolymer aqueous dispersion are not particularly limited, and may be appropriately selected, provided that the polymer is agglomerated under the selected conditions .

[0029]

The agglomerates (A) contain the fluoropolymer and the fluorosurfactant used in the emulsion-polymerization process. The agglomerates (A) may contain unreacted additives used in the polymerization process.

[0030]

The method for recovering a fluorosurfactant of the present invention includes separating and separately recovering the agglomerates (A) and a resulting solution (Bl) containing the fluorosurfactant and the aqueous medium.

[0031]

The agglomerates (A) and the solution (Bl) can be separated by performing a common solid-liquid separation process on the fluoropolymer aqueous dispersion after the agglomeration of the fluoropolymer . The solid-liquid separation process may be any of a batch, semi-batch, or continuous process, and is preferably a process using a technique such as filtration, decantation, centrifugation, and gravity settling.

[0032]

The solution (Bl) contains the fluorosurfactant and the aqueous medium used in the emulsion-polymerization process.

[0033]

The method for recovering a fluorosurfactant of the present invention includes drying the agglomerates (A) into fluoropolymer particles and an exhaust gas (CI) containing the fluorosurfactant , and separately recovering the fluoropolymer particles and the exhaust gas (CI) .

[0034] The agglomerates (A) can be dried using a thermal treatment device such as an oven, and the drying temperature should be selected so as to allow the fluorosurfactant to be separated from the fluoropolymer . For example, the drying temperature is preferably 100°C to 200°C, and more preferably 150°C to 180°C.

[0035]

The method for recovering a fluorosurfactant of the present invention includes contacting the solution (Bl) with an ion-exchange resin (Dl) so as to separate them into processed water (B2) that is obtained as a result of removal of the fluorosurfactant from the solution (Bl) , and the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon, and separately recovering the processed water (B2) and the ion-exchange resin (D2) . The fluorosurfactant is removed from the solution (Bl) by contacting the solution (Bl) with the ion-exchange resin (Dl) . As a result, the processed water (B2) removed the fluorosurfactant and the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon are obtained.

[0036]

The process of contacting the solution (Bl) and the ion-exchange resin (Dl) is not particularly limited, and may be any of a batch, semi-batch, or continuous process. For example, the contacting process may be carried out by adding the ion-exchange resin (Dl) to the solution (Bl) , and optionally agitating the resulting mixture; or by filling the ion-exchange resin (Dl) into a column, and allowing the solution (Bl) to pass through the column. Preferably, the process of contacting the ion-exchange resin (Dl) with the solution (Bl) is carried out by filling the ion-exchange resin (Dl) into a column and allowing the solution (Bl) to pass through the column.

[0037]

In the process of contacting the solution (Bl) and the ion-exchange resin (Dl), the temperature can be appropriately selected. For example, the solution (Bl) and the ion-exchange resin (Dl) may be contacted at a temperature of 0°C to 20°C. Preferably, the contact process is carried out for 10 minutes to 200 hours. The pressure during the contact process is typically atmospheric pressure but may be a reduced or elevated pressure. The process of contacting the solution (Bl) with the ion-exchange resin (Dl) may be repeated several times.

[0038]

The processed water (B2) is obtained as a result of removal of the fluorosurfactant from the solution (Bl) and has a fluorosurfactant concentration lower than the solution (Bl) . However, it is preferable that the processed water (B2) is substantially free from the fluorosurfactant .

[0039]

The process of separating the processed water (B2) and the ion-exchange resin (D2) is not particularly limited, and may be any of a batch, semi-batch, or continuous process. For example, in the case where the fluorosurfactant is adsorbed on the ion-exchange resin (Dl) by allowing the solution (Bl) to pass through a column filled with the ion-exchange resin (Dl) , the processed water (B2) and the ion-exchange resin (D2) are automatically separated because the processed water (B2) flows out of the column as a result of the passage of the solution (Bl) through the column. The ion-exchange resin (D2) may be taken out of the column and recovered, or may be recovered as it is in the column.

[0040]

The method for recovering a fluorosurfactant of the present invention includes contacting the ion-exchange resin (D2) with an alkaline aqueous solution (El) so as to elute the fluorosurfactant from the ion-exchange resin (D2), and separating and separately recovering a regenerated

ion-exchange resin (D3) removed the fluorosurfactant and an alkaline aqueous solution (E2) containing the fluorosurfactant [0041]

The method for recovering a fluorosurfactant of the present invention may further include washing the ion-exchange resin (D2) after the process of separating and recovering the processed water (B2) and the ion-exchange resin (D2) and before the process of contacting the ion-exchange resin (D2) with an alkaline aqueous solution (El) . Examples of the washing process include washing with water.

[0042]

The process of contacting the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon with an alkaline aqueous solution (El) is not particularly limited, and may be any of a batch, semi-batch, or continuous process . For example, in the case where the fluorosurfactant is adsorbed on the ion-exchange resin (Dl) by allowing the solution (Bl) to pass through a column filled with the ion-exchange resin (Dl) , this contacting process may be carried out, for example, by allowing the alkaline aqueous solution (El) to pass through the column filled with the ion-exchange resin (D2); or by taking out the ion-exchange resin (D2) from the column and adding the ion-exchange resin (D2) into the alkaline aqueous solution (El) . In the case where the ion-exchange resin (D2) is added into the alkaline aqueous solution (El) , the fluorosurfactant can be efficiently eluted from the ion-exchange resin (D2) by agitating the mixture of the ion-exchange resin (D2) and the alkaline aqueous solution (El) .

Preferably, the process of contacting the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon with the alkaline aqueous solution (El) is carried out by allowing the alkaline aqueous solution (El) to pass through the column filled with the ion-exchange resin (D2) . In order to shorten the time for recovery of the fluorosurfactant and enhance the recovery efficiency of the fluorosurfactant, the contacting process is preferably carried out by adding the ion-exchange resin (D2) into the alkaline aqueous solution (El) .

[0043]

The alkaline aqueous solution (El) is not particularly limited, but is preferably at least one selected from the group consisting of aqueous solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, calcium hydrogen carbonate, and ammonia. Especially, sodium hydroxide aqueous solution is preferred. The alkaline aqueous solution (El) may or may not contain organic solvents.

[0044]

The pH of the alkaline aqueous solution (El) is preferably

7 or higher and lower than 12, and is more preferably 8 to 11.

[0045]

The alkaline aqueous solution (El) may be heated before the contact with the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon. In the method for recovering a fluorosurfactant of the present invention, the temperature of the alkaline aqueous solution (El) that is contacted with the ion-exchange resin (D2) is preferably 40°C to 80°C. Although more fluorosurfactant is eluted at more elevated temperatures, excessively high temperatures

accelerate deterioration of the ion-exchange resin. The temperature of the alkaline aqueous solution (El) that is contacted with the ion-exchange resin (D2) is preferably 40°C to 70°C, and more preferably 50°C to 60°C.

[0046]

The pressure during the process of contacting the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon with the alkaline aqueous solution (El) is typically atmospheric pressure, but may be a reduced or elevated pressure . The process of contacting the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon with the alkaline aqueous solution (El) is preferably carried out, for example, for 20 minutes to two hours, more preferably for 30 minutes to two hours, and further more preferably for 40 minutes to two hours.

[0047] The process of contacting the ion-exchange resin (D2) having the fluorosurfactant adsorbed thereon with the alkaline aqueous solution (El) may be carried out two or more times. The contact process may be carried out only once or may be carried out two or more times, and is preferably carried out once to five times.

[0048]

The regenerated ion-exchange resin (D3) is the resin obtained as a result of the elution of the fluorosurfactant from the ion-exchange resin (D2) . The regenerated ion-exchange resin (D3) and the alkaline aqueous solution (E2) can be separated by common techniques such as filtration.

[0049]

In the method for recovering a fluorosurfactant of the present invention, the regenerated ion-exchange resin (D3) can be recycled as the ion-exchange resin (Dl) for adsorbing the fluorosurfactant in the solution (Bl) .

[0050]

The method for recovering a fluorosurfactant of the present invention includes contacting the exhaust gas (CI) with the alkaline aqueous solution (E2) so as to dissolve the fluorosurfactant contained in the exhaust gas (CI), and recovering an alkaline aqueous solution (E3) with the fluorosurfactant dissolved therein.

[0051]

The exhaust gas (CI) is gas generated by drying the agglomerates (A) of the fluoropolymer and contains the fluorosurfactant . The fluorosurfactant concentration of the exhaust gas (CI) is not particularly limited, but is typically 0.1 g/Nm ³ to 0.5 g/Nm ³ , and is preferably 0.2 g/Nm ³ to 0.5 g/Nm ³ . The exhaust gas (CI) may contain additives, such as paraffin, used in the polymerization process, in addition to the fluorosurfactant .

[0052]

The process of contacting the exhaust gas (CI) with the alkaline aqueous solution (E2) may be carried out by any of commonly known gas absorption techniques. Examples of such gas absorption techniques include techniques of a liquid falling-film type, droplet type, bubble type, and foam type.

Examples of gas absorbers used for these gas absorption techniques includes liquid falling-film type gas absorbers such as a gas absorber including a packed column, wetted-wall column, liquid-jet column, liquid-jet, connected-ball column, disc column, tourrills or cellarius tourrills, and a tyler absorber ; droplet type gas absorbers such as a gas absorber including a spay column, a disc rotation absorber, a cyclone scrubber, a venturi scrubber, a filler fluid layer absorber, and a centrifugal absorber; bubble type gas absorbers such as a gas absorber including a bubble column, a bubble agitation tank or a plate column; and foam type gas absorbers such as gas absorbers using foam separation. In terms of the absorption efficiency, device maintenance, and ease of safety check, liquid falling-film type or droplet type gas absorbers are preferable.

[0053]

In the method for recovering a fluorosurfactant of the present invention, it is preferable that the exhaust gas (CI) is contacted with the alkaline aqueous solution (E2) using a liquid falling-film type or droplet type gas absorber. In one preferred embodiment, the method of the present invention includes adding the alkaline aqueous solution (E2) to circulating water that circulates the liquid falling-film type or droplet type gas absorber, and contacting the exhaust gas (CI) with the liquid mixture of the circulating water and the alkaline water solution (E2) . The circulating water is preferably an alkaline aqueous solution. Examples of the alkaline aqueous solution include those listed for the alkaline aqueous solution (El) .

[0054]

The method for recovering a fluorosurfactant of the present invention may include separating the fluorosurfactant from the alkaline aqueous solution (E3), and recovering the fluorosurfactant .

[0055]

The method for recovering a fluorosurfactant of the present invention preferably includes separating the alkaline solution (E3) into a fluorosurfactant solution (F) enriched in the fluorosurfactant and an alkaline aqueous solution (E4) containing the fluorosurfactant at a concentration lower than the alkaline aqueous solution (E3) by allowing the alkaline solution (E3) to pass through a reverse osmosis membrane, and separately recovering the fluorosurfactant solution (F) and the alkaline aqueous solution (E4).

[0056]

The reverse osmosis membrane separates the alkaline aqueous solution (E3) into a fluorosurfactant solution (F) having a fluorosurfactant concentration higher than the alkaline aqueous solution (E3) and an alkaline aqueous solution (E4) having a fluorosurfactant concentration lower than the alkaline aqueous solution (E3) . Since the fluorosurfactant concentration of the fluorosurfactant solution (F) is increased through this condensation process, the recovery efficiency of the fluorosurfactant can be further enhanced. The method for recovering a fluorosurfactant of the present invention may further include separating and recovering the fluorosurfactant from the fluorosurfactant solution (F) .

[0057]

For example, in the case where a droplet type or liquid falling-film type gas absorber is used in the process of contacting the exhaust gas (CI) and the alkaline aqueous solution (E2) in the method for recovering a fluorosurfactant of the present invention, the recovery method of the present invention preferably includes adding the alkaline aqueous solution (E4) to circulating water that circulates the droplet type or liquid falling-film type gas absorber, and contacting the exhaust gas (CI) with the liquid mixture of the circulating water and the alkaline aqueous solution (E4) .

[0058]

As a result of the condensation through the reverse osmosis membrane, the fluorosurfactant concentration of the fluorosurfactant solution (F) is increased. Therefore, the fluorosurfactant can be efficiently recovered by recovering the fluorosurfactant from this fluorosurfactant solution (F) .

[0059]

The fluorosurfactant recovered by the recovery method of the present invention can be recycled for the manufacture of fluoropolymers .

[0060]

The method for recovering a fluorosurfactant of the present invention enables a fluorosurfactant separated in each process to be collectively recovered by an easy operation. For example, in the case where the fluorosurfactant is recovered separately from the polymer waste and the exhaust gas mixture, a larger amount of the alkaline aqueous solution is required. As a result, the fluorosurfactant concentration is not high enough and the recovery efficiency is low.

[0061]

In the emulsion-polymerization process, paraffin is preferably used as a dispersion stabilizer. However, paraffin usually remains in the agglomerates (A) of the fluoropolymer . As a result, the exhaust gas (CI) separated by drying the agglomerates (A) also contains paraffin.

If the exhaust gas (CI) contains paraffin, paraffin dissolves in circulating water in a scrubber and attaches to components such as a pipe, pump and shower through which the circulating water circulates, and therefore prevents circulation of the circulating water. Conventionally, this problem is solved by increasing the amount of circulating water that is supplied to and discharged from the scrubber, in other words, by substantially reducing the number of circulations of the circulating water. However, this conventional solution results in a low fluorosurfactant concentration of the finally recovered alkaline solution and thus results in low recovery efficiency .

In contrast, the method for recovering a fluorosurfactant of the present invention can reduce the time until the fluorosurfactant concentration reaches a predetermined level as well as the number of circulations of the circulating water, compared to the conventional technique, because the

fluorosurfactant in the exhaust gas (CI) is also recovered using the fluorosurfactant-containing solution (E2) that is separated from the fluorosurfactant aqueous dispersion obtained by the polymerization. Therefore, the paraffin concentration of the circulating water can be reduced, compared to the conventional technique. As a result, it is possible to avoid the problems caused by paraffin without reducing the fluorosurfactant concentration of the finally recovered alkaline aqueous solution (E3) .

[0062]

Hereinafter, the ion-exchange resin, fluoromonomer, and fluoropolymer according to the method for recovering a fluorosurfactant of the present invention are described in more detail .

[0063]

The ion-exchange resin (Dl) may be particles or a film of an ion-exchange resin.

[0064]

The ion-exchange resin (Dl) is preferably a basic anion-exchange resin. Examples of basic anion-exchange resins include strongly basic anion-exchange resins and weakly basic anion-exchange resins . Weakly basic anion-exchange resins are preferred .

[0065]

For example, as a basic anion-exchange resin, preferred are particles of at least one resin selected from the group consisting of a styrene/divinylbenzene cross-linked resin having amino groups as ion exchange groups, an acryl/divinylbenzene cross-linked resin having amino groups as ion exchange groups, and a cellulose resin having amino groups as ion exchange groups. Among these, resin particles of a styrene/divinylbenzene cross-linked resin having amino groups as ion exchange groups are preferred.

[0066]

A preferred example of such a basic anion-exchange resin is one having primary to tertiary amino groups or quaternary ammonium salts as exchange groups . More preferred is one having secondary or tertiary amino groups as exchange groups. Further, from the viewpoint of heat resistance, a basic anion-exchange resin having tertiary amino groups as exchange groups is particularly preferred.

[0067]

A basic anion-exchange resin having quaternary ammonium salts as exchange groups is susceptible to deposition of a fluoropolymer on the ion exchange resin surface and becomes incapable of removing a fluorosurfactant in a relatively short time, and further, the adsorption of the fluorosurfactant is strong so that the elution efficiency becomes low.

[0068]

The average particle size of the ion-exchange resin particles is preferably from 0.1 to 2 mm, more preferably from 0.2 to 1.3 mm, and particularly preferably from 0.3 to 0.8 mm. The ion-exchange resin particles are preferably uniform, whereby flow paths are hardly clogged during liquid flow. Further, the ion-exchange resin is preferably porous, and a porous type or macroporous type having a high degree of cross-linking is more preferred. The ion exchange capacity of the basic anion-exchange resin is preferably from 1.0 to 2.5 (eq/L) , and more preferably from 1.3 to 1.7 (eq/L) .

[0069]

The method for recovering a fluorosurfactant of the present invention enables recovery of any fluorosurfactants , provided that the fluorosurfactants can be adsorbed on the ion-exchange resin (Dl) and are dissolvable in the alkaline aqueous solution (El). Preferred examples of such

fluorosurfactants include anionic surfactants.

[0070]

Examples of the anionic surfactants include carboxylic acid-based surfactants and sulfonic acid-based surfactants. Specific examples of the anionic surfactants include carboxylic acid-based surfactants represented by the following formulae (i), (ii), (iii), (iv) , (v) , (vi) and (vii) .

[0071]

Carboxylic acid-based surfactants represented by the formula (i) : X-R^COOM ¹

In the formula, X is H, F or CI . Rf ¹ is a linear or branched C4-14 fluoroalkylene group, and preferably a linear or branched C5-.7 fluoroalkylene group. Rf ¹ is, for example, a linear or branched C ₇ fluoroalkylene group, and in particular, is a linear or branched perfluoroalkylene group. M ¹ is a monovalent alkali metal, NH ₄ or H.

[0072]

Specific examples of carboxylic acid-based surfactants represented by the formula (i) include C ₅ FnCO0H, C ₆ Fi ₃ COOH, C ₇ Fi ₅ COOH, and salts of these carboxylic acids.

[0073]

Carboxylic acid-based surfactants represented by the formula (ii) : X ¹ (CF ₂ ) _p -0-CX ² X ³ - (CF ₂ ) _q -0-CXX ⁵ - (CF ₂ ) _r -COOM ¹

In the formula, X ¹ , X ² , X ³ , X ⁴ and X ⁵ , which may be the same or different, independently represent H, F, or CF ₃ ; M ¹ is a monovalent alkali metal, NH ₄ or H; p is 1 or 2; q is 1 or 2; and r is 0 or 1.

Specific examples of fluoroether carboxylic acidss represented by the formula (ii) include CF ₃ OCF (CF ₃ ) CF ₂ OCF(CF ₃ ) COONH ₄ , CF ₃ CF ₂ OCF ₂ CF ₂ 0CF ₂ COONH ₄ , and CF ₃ OCF ₂ CF ₂ CF ₂ OCHFCF ₂ COONH ₄ .

[0074]

Carboxylic acid-based surfactants represented by the formula (iii) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) _n -CF (CF ₃ ) COOM ¹

In the formula, X is H, F or CI; m is an integer of 1 to 10, and is, for example, 5; n is an integer of 0 to 5, and is, for example, 1; and M ¹ is a monovalent alkali metal, NH ₄ or H.

[0075]

Preferred examples of carboxylic acid-based surfactants represented by the formula (iii) include

CF3-0-CF(CF ₃ )CF ₂ 0-CF(CF3)COOH and salts of this carboxylic acid.

[0076]

Carboxylic acid-based surfactants represented by the formula (iv) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) n-CHFCFaCOOM ¹

In the formula, X, m, n, and ¹ are the same as defined above .

[0077]

Carboxylic acid-based surfactants represented by the formula (v) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) _n -CH ₂ CF ₂ COOM ¹

In the formula, X, m, n, and M ¹ are the same as defined above .

[0078]

Carboxylic acid-based surfactants represented by the formula (vi) : Rf ³ OCF ₂ CF ₂ 0 (CF ₂ ) pCOOM ¹

In the formula, Rf ³ is a partially or fully fluorinated alkyl group; M ¹ is a monovalent alkali metal, H4 or H; and p is 1 or 2. Rf ³ is preferably a C1-3 alkyl group. Specific examples of carboxylic acid-based surfactants represented by the formula (vi) include CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COONH and

CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COOH .

[0079]

Fluoroether carboxylic acids represented by the formula

(vii) : Rf ⁴ OCHFCF ₂ COOM ¹

In the formula, Rf ⁴ is a partially or fully fluorinated linear aliphatic group or linear aliphatic group having at least one oxygen atom in the chain; and M ¹ is a monovalent alkali metal, NH ₄ or H. Rf ⁴ is preferably a C1-3 aliphatic group. Specific examples of carboxylic acid-based surfactants represented by the formula (vii) include CF30C F2C F2CF20CHFCF ₂ COONH ₄ and

C F3OC F2C F2CF2OCH FC F2COOH .

[0080]

Namely, the fluorosurfactant is preferably at least one selected from the group consisting of:

carboxylic acid-based surfactants represented by the formula (i) : X-R^COOM ¹ (X is H, F or CI; Rf ¹ is a linear or branched C4-14 fluoroalkylene group, and is preferably a linear or branched C ₅ _ ₇ fluoroalkylene group; and M ¹ is a monovalent alkali metal, NH ₄ or H) ;

carboxylic acid-based surfactants represented by the formula (ii) : X ¹ (CF ₂ ) _p -0-CX ² X ³ - (CF ₂ ) _q -0-CX ⁴ X ⁵ - (CF ₂ ) r-COO ¹ (X ¹ , X ² , X ³ , X ⁴ and X ⁵ , which may be the same or different, independently represent H, F, or CF ₃ ; ¹ is a monovalent alkali metal, NH ₄ or H; p is 1 or 2; q is 1 or 2; and r is 0 or 1) ;

carboxylic acid-based surfactants represented by the formula (iii) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) _n -CF (CF ₃ ) COOM ¹ (X is H, F or CI; m is an integer of 1 to 10; n is an integer of 0 to 5; and M ¹ is a monovalent alkali metal, NH ₄ or H) ;

carboxylic acid-based surfactants represented by the formula (iv) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) n-CHFCFzCOO ¹ (X, m, n, and M ¹ are the same as defined above) ;

carboxylic acid-based surfactants represented by the formula (v) : X- (CF ₂ ) _m -0- (CF (CF ₃ ) CF ₂ 0) _n -CH ₂ CF ₂ COOM ¹ (X, m, n, and 1 are the same as defined above) ;

carboxylic acid-based surfactants represented by the formula (vi) : Rf ³ OCF ₂ CF ₂ 0 (CF ₂ ) pCOOM ¹ (Rf ³ is a partially or fully fluorinated alkyl group; ¹ is a monovalent alkali metal, NH ₄ or H; and p is 1 or 2); and

carboxylic acid-based surfactants represented by the formula (vii) : Rf ⁴ OCHFCF ₂ COO ¹ (Rf ⁴ is a partially or fully fluorinated linear aliphatic group or a linear aliphatic group having at least one oxygen atom in the chain; and M ¹ is a monovalent alkali metal, NH ₄ or H) . In terms of high water solubility and enhanced recovery efficiency, preferred is at least one fluorosurfactant selected from the group consisting of carboxylic acid-based surfactants represented by the formula (i) in which Rf ¹ is a linear or branched C ₄ - ₆ fluoroalkylene group; and carboxylic acid-based surfactants represented by the formulae (ii) , (iii) , (iv) , (v) , (vi) and (vii) . More preferred is at least one selected from carboxylic acid-based surfactants represented by the formula

(iii) - [0081]

The fluoromonomer is not particularly limited, and is preferably, for example, at least one monomer selected from the group consisting of tetrafluoroethylene [TFE] , vinylidene fluoride [VdF] , chlorotrifluoroethylene [CTFE] , vinyl fluoride [VF] , hexafluoropropylene [HFP] , hexafluoroisobutene [HFIB] , monomers represented by the formula: CH ₂ =CX ⁶ (CF ₂ ) _n X ⁷ (X ⁶ is H or F; X ⁷ is H, F or CI; and n is an integer of 1 to 10), perfluoro (alkyl vinyl ethers) [PAVEs] represented by the formula: CF ₂ =CF-ORf ⁵ (Rf ⁵ is a Ci- ₈ perfluoroalkyl group) , alkyl perfluoro vinyl ether derivatives represented by the formula: CF ₂ =CF-OCH ₂ -Rf ⁶ (Rf ⁶ is a Ci_ ₅ perfluoro alkyl group) , trifluoroethylene, trifluoropropylene, tetrafluoropropylene, pentafluoropropylene, trifluorobutene, and

tetrafluoroisobutene .

[0082]

The monomer copolymerizable with the fluoromonomer other than fluoromonomers (fluorine-free monomer) is not

particularly limited, and is preferably, for example, at least one selected from the group consisting of ethylene [Et] , propylene [Pr] and alkyl vinyl ethers.

[0083]

The fluoropolymer is not particularly limited and examples thereof include polymers obtainable by polymerization of any of the above-mentioned fluoromonomers . The

fluoropolymer may be a resin or may be an elastomer. [0084]

If the fluoropolymer is a resin, it is preferably at least one selected from the group consisting of

polytetrafluoroethylene [PTFE] , TFE/HFP copolymer [FEP], TFE/PAVE copolymer [PFA] , Et/TFE copolymer, Et/TFE/HFP copolymer, polychlorotrifluoroethylene [PCTFE] , CTFE/TFE copolymer, Et/CTFE copolymer, polyvinylidene fluoride [PVdF] , TFE/VdF copolymer, VdF/HFP/TFE copolymer, VdF/HFP copolymer and polyvinyl fluoride [PVF] .

[0085]

The PTFE may be a TFE homopolymer or may be modified PTFE. The term "modified PTFE" herein is intended to refer to a copolymer of TFE and a small amount of a comonomer (modifying agent) which does not give melt processability to the resulting copolymer.

[0086]

The modifying agent for the modified PTFE is not particularly limited, provided that it is copolymerizable with TFE. Examples thereof include perfluoro olefins such as HFP; chlorofluoro olefins such as CTFE; hydrogen-containing fluoro olefins such as trifluoroethylene and VdF; perfluoro vinyl ether; perfluoroalkyl ethylene such as perfluorobutyl ethylene; and ethylene. Only one modifying agent may be used, or two or more modifying agents may be used.

[0087]

The perfluoro vinyl ethers used as modifying agents are not particularly limited and examples thereof include perfluoro unsaturated compounds represented by the formula (I) :

CF ₂ =CF-ORf (I)

wherein Rf is a perfluoro organic group.

The term "perfluoro organic group" herein means an organic group all of whose hydrogen atoms binding to carbon atoms are substituted with fluorine atoms. The perfluoro organic group may contain an etheric oxygen.

[0088] Preferred examples of the perfluoro vinyl ethers used as modifying agents include perfluoro (alkyl vinyl ethers) [PAVEs] represented by the above formula (I) in which Rf is a Ci-io perfluoroalkyl group. The number of carbon atoms in the perfluoroalkyl group is more preferably 1 to 5.

[0089]

Regarding the modified PTFE, typically, the ratio (% by mass) of the modifying agent to the total of the modifying agent and TFE is preferably not more than 1% by mass, and more preferably 0.001 to 1% by mass.

[0090]

The FEP preferably contains more than 2% by mass and not more than 20% by mass of HFP units. The amount of HFP units is more preferably 10 to 15 % by mass.

[0091]

The PAVE in the PFA preferably contains a Ci_ ₆ alkyl group, and is more preferably PMVE, PEVE or PPVE. The PFA preferably contains more than 2% by mass and not more than 5% by mass of PAVE units. The amount of PAVE units is more preferably 2.5 to .0% by mass .

[0092]

The FEP and PFA are not particularly limited and may be polymers obtained by polymerization with other monomer (s), provided that they have the above-mentioned compositions. Examples of other monomers usable for the FEP include PAVEs, and examples of other monomers usable for the PFA include HFP. One, or two or more of these other monomers can be used.

[0093]

Typically, the amount of the other monomer (s) polymerized in the FEP or PFA is preferably not more than 1% by mass of the fluoropolymer although it depends on the type of the monomer (s) . The upper limit thereof is more preferably 0.5% by mass, and further more preferably 0.3% by mass.

[0094]

Regarding the Et/TFE copolymer, the molar ratio (Et units) : (TFE units) is preferably (20:80) to (80:20). A ratio of Et units of less than 20:80 may result in low productivity; and a ratio of Et units of more than 80:20 may result in low corrosion resistance. The molar ratio (Et units) : (TFE units) is more preferably (35:65) to (55:45). The Et/TFE copolymer is a copolymer containing polymerized units of TFE and polymerized units of Et, and may further contain polymerized units of other fluoromonomer ( s ) .

[0095]

In one preferred embodiment, the Et/TFE copolymer contains monomer units of at least one monomer selected from the group consisting of other fluoromonomers and fluorine-free monomers, in addition to the Et and TFE units. The other fluoromonomers are not particularly limited, provided that they are copolymerizable with both ethylene and TFE. C ₃ _io

fluorovinyl monomers are suitably used and specific examples thereof include hexafluoroisobutylene, CH ₂ =CFC ₃ F ₆ H, and HFP. Particulaly, in one preferred embodiment, a fluorovinyl monomer represented by the following formula is used:

CH ₂ =CH-Rf ⁷

wherein Rf ⁷ is a C ₄ - ₈ perfluoro alkyl group.

In another preferred embodiment, the Et/TFE copolymer is an Et/TFE/HFP copolymer. In this case, the Et/TFE/HFP copolymer may contain monomer units of other fluoromonomer ( s ) (other than HFP) or monomer units of fluorine-free monomer (s) . The monomer units of monomers other than ethylene and TFE preferably constitute not more than 10 mol %, and more preferably not more than 5 mol % of all the monomer units of the copolymer of ethylene and TFE. The molar ratio (Et units) : (TFE units) : (monomer units of other fluoromonomer ( s ) or fluorine-free monomer ( s ) ) is preferably (31.5 to 54.7): (40.5 to 64.7) : (0.5 to 10) .

[0096]

The PCTFE is a polymer substantially consisted of polymerized units of CTFE. [0097]

Regarding the C FE/TFE copolymer, the molar ratio of CTFE units and TFE units CTFE : TFE is preferably (2:98) to (98:2), more preferably (5:95) to (90:10), and further more preferably (20:80) to (90: 10) .

[0098]

Alternatively, the CTFE/TFE copolymer is preferably a copolymer of CTFE, TFE and monomer ( s ) copolymerzable with CTFE and TFE. Examples of monomers copolymerizable with CTFE and TFE include ethylene, VdF, HFP, monomers represented by the formula: CH ₂ =CX ⁶ (CF ₂ ) _n X ⁷ (X ⁶ is H or F, X ⁷ is H, F or CI, and n is an integer of 1 to 10) , PAVEs and alkyl perfluoro vinyl ether derivatives represented by the formula: CF ₂ =CF-OCH ₂ -Rf ³ (Rf ³ is a Ci-5 perfluoroalkyl group) . Especially, at least one selected from the group consisting of ethylene, VdF, HFP, and PAVEs is preferred, and PAVEs is more preferred. Examples of PAVEs include those described above. The molar ratio of CTFE units and TFE units, and units of monomer (s) copolymerizable with CTFE and TFE (total monomer units of CTFE units and TFE units) : (units of monomer (s) copolymerizable with CTFE and TFE) is (90 to 99.9) : (10 to 0.1).

[0099]

Regarding the Et/CTFE copolymer, the molar ratio of Et units and CTFE units CTFE : Et is preferably (30:70) to (70:30) , and more preferably (40:60) to (60:40).

[0100]

The PVdF is a polymer substantially consisted of VdF units .

[0101]

Regarding the VdF/HFP copolymer, the molar ratio VdF/HFP is preferably (45 to 85)/ (55 to 15), more preferably (50 to 80) / (50 to 20) , and still more preferably (60 to 80) / (40 to 20) . The VdF/HFP copolymer is a copolymer containing polymerized units of VdF and polymerized units of HFP, and may further contain polymerized units of other fluoromonomer ( s ) . In one preferred embodiment, the VdF/HFP copolymer is a VdF/HFP/TFE copolymer .

[0102]

Regarding the VdF/HFP/TFE copolymer, the molar ratio VdF/HFP/TFE is preferably (40 to 80) / (10 to 35) / (10 to 25) . The VdF/HFP/TFE copolymer may be a resin or elastomer, but is normally a resin in the case where the composition of the copolymer is in the above range.

[0103]

The PVF is a polymer substantially consisted of polymerized units of VF.

[0104]

The monomer contents of each of the above-mentioned copolymers can be determined by techniques appropriately selected from NMR, FT-IR, ultimate analysis, and fluorescence X-ray analysis based on the types of monomers.

[0105]

In the case where the fluoropolymer is an elastomer, it is, for example, preferably at least one selected from the group consisting of VdF/HFP copolymer, VdF/HFP/TFE copolymer, VdF/CTFE copolymer, VdF/CTFE/TFE copolymer, VdF/PAVE copolymer, VdF/TFE/PAVE copolymer, VdF/HFP/PAVE copolymer, VdF/HFP/TFE/PAVE copolymer, VdF/TFE/Pr copolymer, and

VdF/Et/HFP copolymer. In particular, preferred is at least one selected from the group consisting of VdF/HFP copolymer, VdF/HFP/TFE copolymer, VdF/PAVE copolymer, VdF/TFE/PAVE copolymer, VdF/HFP/PAVE copolymer, and VdF/HFP/TFE/PAVE copolymer .

[0106]

In the case where the fluoropolymer is a fluoroelastomer, the PAVE is preferably, for example, at least one monomer selected from the group consisting of perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether), and is particularly preferably perfluoro (methyl vinyl ether).

[0107] Hereinafter, one example of the method for recovering a fluorosurfactant of the present invention is illustrated with reference to the figure. It should be note that the recovery method of the present invention is not limited to the embodiment illustrated in Fig. 1.

[0108]

Fig. 1 is a schematic view illustrating one example of the method for recovering a fluorosurfactant of the present invention. In Fig. 1, the black arrows indicate the flowing directions of gas or liquid and white arrows indicate separation operations using filtration or the like.

First, a fluoropolymer aqueous dispersion is obtained by emulsion polymerization of a fluoromonomer in an aqueous medium 12 in the presence of a fluorosurfactant in a polymerization device 11. Next, a coagulant is added to the obtained fluoropolymer aqueous dispersion to give coagulates of the fluoropolymer . After coagulation, the fluoropolymer aqueous dispersion including the coagulates of the fluoropolymer is taken out from the polymerization device 11, and separated into the coagulates containing the fluorosurfactant and a solution containing the fluorosurfactant and the aqueous medium by filtration. The recovered coagulates 23 are dried in a dryer 22. Through this process, fluoropolymer particles are obtained. During this drying process, an exhaust gas mixture containing the fluorosurfactant is generated from the coagulates 23, and sent into a scrubber 51 through a pipe 101.

[0109]

The solution containing the fluorosurfactant and the aqueous medium is supplied to a column 31 through a pipe 102, and contacts with an ion-exchange resin 32 in the column 31. As a result of the contact of the solution and the ion-exchange resin 32, the fluorosurfactant in the solution is adsorbed on the ion-exchange resin 32, and processed water removed the fluorosurfactant can be recovered through a pipe 103. This processed water can be recycled. Subsequently, an alkaline aqueous solution is supplied to the column 31 through a pipe 110 such that the ion-exchange resin having the fluorosurfactant absorbed thereon makes contact with this alkaline aqueous solution. As a result, the fluorosurfactant is eluted from the ion-exchange resin and the resulting alkaline solution containing the fluorosurfactant is sent through a pipe 105. This alkaline solution containing the fluorosurfactant is discharged from a liquid outlet 52 of the scrubber 51 together with circulating water that is supplied through a pipe 108 from a circulating water tank 71.

The exhaust gas mixture containing the fluorosurfactant, which is sent to the scrubber 51 through the pipe 101, makes contact with the liquid mixture 53 of the alkaline aqueous solution containing the fluorosurfactant and circulating water, which is discharged from the liquid outlet 52 of the scrubber 51. As a result, the fluorosurfactant in the exhaust gas mixture is dissolved in the liquid mixture 53. The exhaust gas mixture after removal of the fluorosurfactant is discharged through a pipe 106.

[0110]

After this process, the liquid mixture of the alkaline aqueous solution used for regeneration of the ion-exchange resin and the circulating water is sent to the circulating water tank 71 through a pipe 107.

[0111]

The above-mentioned processes are repeated until the fluorosurfactant concentration of the liquid mixture 72 in the circulating water tank 71 reaches a predetermined level. After the fluorosurfactant concentration reaches a predetermined level, a portion of the liquid mixture 72 in the circulating water tank 71 is adjusted to a pH of 6 to 8 and then supplied to a reverse osmosis membrane unit 61 provided with a reverse osmosis membrane 64 through a pipe 109. The liquid mixture supplied to the reverse osmosis membrane unit 61 is separated into a fluorosurfactant solution 63 enriched in the fluorosurfactant and an alkaline aqueous solution 62 whose fluorosurfactant concentration is reduced. Then, the fluorosurfactant solution 63 and the alkaline aqueous solution 62 are separately recovered.

[0112]

After passing through a pipe 104, the alkaline aqueous solution 62 containing a slight amount of the fluorosurfactant is mixed with fresh liquid supplied through a pipe 112, and the mixture is recycled as the alkaline aqueous solution, which is discharged from the liquid outlet 54 and contacted with the exhaust gas mixture. Since the amount of the circulating water is reduced by recovery of the fluorosurfactant solution 63, an alkaline solution may be prepared and used as part of the circulating water.

The fluorosurfactant solution 63 is recovered through a pipe 111, and the fluorosurfactant is separated from this fluorosurfactant solution. In this manner, the

fluorosurfactant can be recovered. INDUSTRIAL APPLICABILITY

[0113]

The method for recovering a fluorosurfactant of the present invention can be used for the manufacture of various fluoropolymers .

EXPLANATION OF SYMBOLS

[0114]

11: Polymerization device

12 : Aqueous medium

22: Drier

23: Agglomerate (coagulate)

31: Column

32: Ion-exchange resin

51: Scrubber

52, 54: Liquid outlet : Droplet

: Reverse osmosis membrane unit

: Alkaline aqueous solution

: Fluorosurfactant solution

: Reverse osmosis membrane

: Circulating water tank

: Liquid mixture

, 82, 83, 85, 86: Valve

1, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112: Pipe