JPS5829802B2 - fluoropolymer fluoropolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing an ion-exchange group-containing fluoropolymer, and more specifically, the present invention relates to an improved method for producing an ion-exchange group-containing fluoropolymer that can be effectively used as an ion-exchange membrane in electrolysis of an aqueous electrolyte solution. The present invention relates to a method for producing an improved fluorine-containing copolymer.

The fluorine-containing copolymer of the present invention has the general formula % (wherein Rf is selected from the group consisting of a fluorine atom and a perfluoroalkyl group having 1 to 10 carbon atoms, and Y is a fluorine atom and fluorovinylether and tetrafluoroethylene selected from the group consisting of trifluoromethyl group, where n is an integer from O to 3) and general formula CF2-
It is a copolymer of CFX (wherein X in the formula is selected from the group consisting of a chlorine atom, a hydrogen atom, and a trifluoromethyl group) and a fluoroolefin represented by the formula.

The fluorine-containing copolymer is hydrolyzed and converted into a copolymer having a pendant side chain containing an ion exchange group such as -8O2H group, which can be produced by electrolysis of an aqueous electrolyte solution, such as electrolysis of caustic soda and chlorine by salt electrolysis. It has been newly discovered that when used as an ion exchange membrane in manufacturing, it exhibits improved electrolytic performance, and the present invention has been completed.

For example, CF2-CFOCF2CF(CF3)OCF2CF2S included in the above formula %Formula %
O2F, perfluorovinyl ether, is a special public
As seen in Publication No. 20788 or Japanese Patent Publication No. 48-41942, tetrafluoroethylene (CF2-CF2)
Application to ion exchange membranes by copolymerizing with and further hydrolyzing has been proposed.

However, when the hydrolyzate of the copolymer of perfluorovinyl ether and tetrafluoroethylene is used as an ion exchange membrane for, for example, salt electrolysis, the current efficiency for generating caustic soda is as low as 80% or less, which poses a practical problem. It turned out that.

In addition, U.S. Pat. No. 3,282,875 and the like describe a method for synthesizing fluorovinyl ether and a method for polymerizing the fluorovinyl ether as described above. There are only examples as follows.

As a result of various studies and examinations regarding the specific copolymer of fluorovinyl ether and tetrafluoroethylene, the present inventor discovered that in addition to these, trifluorochloroethylene,
It is a new discovery that membranes can be easily formed by copolymerizing specific fluoroolefins such as trifluoroethylene and hexafluoropropylene in a specific proportion and then hydrolyzing them, and can be effectively used as ion exchange membranes. This is what I found.

Furthermore, compared to conventional copolymers of tetrafluoroethylene and specific fluorovinyl ethers, it is possible to provide an ion exchange membrane that can increase the current efficiency of producing caustic soda to 90% or more in salt electrolysis.

When used in an ion exchange membrane, the content of the specific fluorovinyl ether in the fluorine-containing copolymer is 1 to 50 mol%.
, preferably 2 to 40 mol%.

Further, the content of the specific fluoroolefins is preferably 1 to 40 mol%, preferably 2 to 30 mol%.

Fluorine copolymers containing specific fluorovinyl ethers and fluoroolefins in this range can be easily converted into copolymers having ion exchange groups such as -5O3H groups in pendant side chains by hydrolysis. , can be used as an ion exchange membrane.

Although sulfonic acid type fluoropolymer ion exchange membranes with excellent chlorine resistance, oxidation resistance, and alkali resistance have been known as diaphragms for alkaline electrolysis, the specific sulfonic acid type ion exchange membranes of the present invention In addition to these characteristics, it has the advantage of providing high current efficiency with low sliding voltage.

Thus, the present invention has been completed based on the above findings, and is based on the general formula % (wherein Rf is a group consisting of a fluorine atom and a perfluoroalkyl group having 1 to 10 carbon atoms). A group selected from
Y is a group selected from the group consisting of a fluorine atom and a trifluoromethyl group, n is an integer of O to 3), and tetrafluoroethylene and the general formula CF2-CFX (where is a group selected from the group consisting of a chlorine atom, a hydrogen atom, and a trifluoromethyl group. producing a mol% copolymer,
Furthermore, the present invention provides a new and improved method for producing a fluoropolymer containing an ion exchange group, which is characterized in that a fluoropolymer having pendant side chains containing an ion exchange group is obtained by hydrolyzing the resulting copolymer. be.

In the present invention, the content of the specific fluorovinyl ether is important, and as described above, the content in the fluoropolymer may be 1 to 50 mol%, preferably 2 to 40 mol%.

If the content is too low, the ion exchange function will not be exhibited, and if the content is too high, the mechanical strength of the ion exchange membrane will be impaired, or the ion exchange performance will decrease due to an increase in water content, which is not preferable.

Further, as described above, the content of the specific fluoroolefins may be 1 to 40 mol%, preferably 2 to 30 mol% in the fluoropolymer.

If the content of certain fluoroolefins is too small, the effect of improving current efficiency will be insufficient, and if the content is too large, the mechanical strength of the ion exchange membrane will be impaired.

In the present invention, hydrolysis of the fluorine-containing copolymer can be easily carried out by known or well-known means.

For example, by reacting with a basic aqueous solution such as NaOH, -S
The O2F group can be converted to a sulfonic acid by salting it with a sulfonic acid and then reacting with a strong inorganic acid such as H2SO4.

Copolymers with specific sulfonic acid type ion-exchange groups can be used, for example, for saline electrolysis with an anode chamber containing an aqueous sodium chloride solution and an anode instead of a porous diaphragm.
It has been newly discovered that when used as an ion exchange membrane to separate a sodium hydroxide solution and a cathode chamber containing a cathode, it provides good electrolytic performance.

For example, CF2=CFOCF2CF(CF3)OCF2CF2S
In addition to O2F and tetrafluoroethylene, a copolymer containing trifluorochloroethylene was hydrolyzed to produce 0.65 meq.
/t? An ion exchange membrane containing a polymer concentration of sulfonic acid gave a current efficiency of 91% at a low sliding voltage of 4.6 V at an 8N caustic soda concentration.

In contrast, tetrafluoroethylene containing the same concentration of sulfonic acid and CF2-CFOCF2CF(CF3)OCF2CF2S
An ion exchange membrane made of a copolymer with O3F has a sliding current of 4.6 ■.

It shows a current efficiency of only 77% in terms of voltage.

Although it is not necessarily clear why the specific fluoropolymer ion exchange membrane of the present invention provides good electrolytic performance, the following reasons may be considered, for example.

That is, the water content of the membrane immersed in an alkaline solution is a factor that regulates the electrolytic performance, and it is thought that this is based on the difference in the water content.

The water content of the hydrolyzate of the copolymer using fluoroolefins such as trifluorochloroethylene and trifluoroethylene of the present invention together with tetrafluoroethylene is different from that of the conventional copolymer using only tetrafluoroethylene. It was found to be lower than that of the combined hydrolyzate.

That is, the water content of a conventional tetrafluoroethylene copolymer hydrolyzate is, for example, an ion exchange group concentration of 0.65 meq.
/tiI-polymer membranes, when immersed in an 8N aqueous solution of caustic soda, it is approximately 10% by weight;
Iteha is a copolymer hydrolyzate containing specific fluoroolefins such as trifluorochloroethylene and trifluoroethylene with similar ion exchange group concentration together with tetrafluoroethylene, and the water content is reduced to approximately 5% by weight. That's what I'm doing.

It is believed that such a low water content can provide high current efficiency.

Incidentally, such explanation does not limit the present invention in any way.

* Wood The ion-exchange group-containing fluoropolymer of the present invention has excellent heat resistance and chemical resistance (alkali resistance, chlorine resistance, oxidation resistance, etc.), and is substantially resistant to electrolytes and electrolysis products in alkaline electrolysis, for example. and is substantially impermeable to liquids and gases,
This enables stable operation over a long period of time.

The fluorine-containing copolymer of the present invention can be produced under the action of a polymerization initiation source such as a peroxy compound, an azo compound, ultraviolet rays, or ionizing radiation, with or without the use of an inert organic solvent or an aqueous medium. It can be produced by known copolymerization means.

For example, Japanese Patent Publication No. 48-2223, Japanese Patent Publication No. 4820
Copolymerization can be carried out by methods such as those described in Japanese Patent Publication No. 788, Japanese Patent Publication No. 48-41942, and US Pat. No. 3,282,875.

Various polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization may be employed as the polymerization method.

The specific fluorovinyl ether used in the present invention can be prepared by means such as those described in US Pat. No. 3,282,875, that is, FOC-CF (OCF2
It can be easily obtained by thermally decomposing a fluorocarbon ether such as CFY) noCF2CFRfSO2FF3 or (Me is an alkali metal) at a temperature of about 200 to 600°C.

Usually, when Rf is a fluorine atom, CF2=CF(OCF2CFY)noCF2CF280
2F fluorovinyl ether is preferably employed,
In particular, CF where Y corresponds to a trifluoromethyl group and n corresponds to 1
2-CFOCF2CF(CF3)ocF2cF2so2
F is preferred.

In addition, in the fluoroolefins represented by the general formula CF2-CFX used in the present invention, X is a hydrogen atom, a chlorine atom, or a trifluoromethyl group, in consideration of ease of handling and improvement in current efficiency. Trifluoroethylene, trifluorochloroethylene selected from
Propylene hexafluoride is used.

The aforementioned specific fluorovinyl ethers and fluoroolefins can be copolymerized individually, or either one or both can be copolymerized as a mixture of two or more.

In addition to the above-mentioned specific fluorovinyl ethers and fluoroolefins, it is also possible to further copolymerize one or more kinds of other fractions.

The specific fluorine-containing copolymer of the present invention may be formed into a film by any appropriate means.

In order to make an ion exchange membrane, -SO2F groups are converted into ion exchange groups such as -8O3H groups by hydrolysis, but Σ
The hydrolysis treatment can be performed either before or after film formation.

Usually, it is preferable to perform a hydrolysis treatment after film formation.

Various methods can be used for forming the film, such as heating melt molding, casting after dissolving it in an appropriate solvent, or film forming from latex.

Since the ion exchange membrane made from the fluorine-containing copolymer of the present invention has various excellent performances, it can be widely adopted in various fields, purposes, and uses.

For example, it is suitably used in fields where corrosion resistance is particularly required, such as in diffusion dialysis, electrolytic reduction, and as diaphragms in fuel cells.

In particular, when used as a cation-selective diaphragm for alkaline electrolysis, it can exhibit high performance that cannot be obtained with conventional ion exchange membranes.

Next, embodiments of the present invention will be explained in more detail.
It goes without saying that the present invention is not limited in any way by the above description.

Example 1 37.5P C in a 200TLl stainless steel reaction vessel
F2-CFOCF2CF(CF3)OCF2CF2SO
Charge 2 F, 45.09 m of trichlorotrifluoroethane, and 200 m of azobisisobutyronitrile.

Raise the reaction vessel to 70°C and add 5.0% trifluorochloroethylene.
The reaction was carried out by charging until the concentration was 0 kg/crA, and then by charging tetrafluoroethylene until the concentration was 12.0 kg/crA.

After 20 hours, a 10.2P copolymer was obtained.

The copolymer was press-molded at 230° C. to form a film with a thickness of 130 μm, and then hydrolyzed to form an ion exchange membrane.

The ion exchange membrane is 0.65 meq/? It had a polymer functional group concentration and gave 8N caustic soda with a current efficiency of 91%.

On the other hand, tetrafluoroethylene and CF 2 =CFOCF 2 CF (CF a ) having the same functional group concentration
The QCF2CF2SO2F copolymer hydrolyzate ion exchange membrane exhibited only 77% current efficiency to provide 8N caustic soda.

Example 2 CF2-CFOCF2CF(CF3)OCF2CF2S
O□F33. ! The reaction was carried out under the same conditions as in Example 1 except that 1 was used.

After 20 hours, a copolymer of 11.5S' was obtained.

0.61meq/? An ion exchange membrane having a polymer functional group concentration was obtained.

The ion exchange membrane delivered 8N caustic soda with a current efficiency of 92%.

Example 3 The reaction was carried out under the same conditions as in Example 1 except that hexafluoropropylene was charged up to 5.0 kg/crA, and then tetrafluoroethylene was charged up to 16 kg/crA, and after 20 hours, 7.
A copolymer of 21 was obtained.

0.60meq/? An ion exchange membrane having a polymer functional group concentration was obtained.

The ion exchange membrane delivered 8N caustic soda with a current efficiency of 92%.

Example 4 33.5P CF in a 200ml stainless steel reaction vessel
2-CFOCF2CF(CF3)OCF2CF2802
F and 45.1' trichlorotrifluoroethane and 2
00rv of azobisisobutyronitrile was raised to 70°C, and then 5.5k of trifluoroethylene was added.
g/ca, then add 1 g/ca of tetrafluoroethylene.
The reaction was carried out by charging until the amount reached 1.5 p/crA.

After 20 hours, a 11.2P copolymer was obtained.

The copolymer was press-molded at 230°C to form a film and then hydrolyzed to 0.60 meq/? An ion exchange membrane having a polymer functional group concentration was obtained.

The ion exchange membrane delivered 8N caustic soda with a current efficiency of 92%.

Claims (1)

[Claims] 1 General formula % Formula % (wherein Rf is a group selected from the group consisting of a fluorine atom and a perfluoroalkyl group having 1 to 10 carbon atoms,
Y is a group selected from the group consisting of a fluorine atom and a trifluoromethyl group, n is an integer of 0 to 3) and tetrafluoroethylene, and the general formula CF2-CFX (where is a group selected from the group consisting of a chlorine atom, a hydrogen atom, and a trifluoromethyl group. producing a mol% copolymer,
An improved method for producing an ion exchange group-containing fluoropolymer, characterized in that a fluoropolymer having pendant side chains containing ion exchange groups is obtained by further hydrolyzing the resulting copolymer.