JPS6289735A - Regeneration of fluorine-containing cation-exchange membrane for alkali chloride electrolysis - Google Patents

Abstract

PURPOSE:The cation-exchange membrane is heat-pressed in the state where the ion-exchange groups are converted into ester type and a new porous layer containing particles which have gas and liquid permeability, but not electrode activity is heat-pressed on the membrane surface to fully restore the current efficiency of the membrane. CONSTITUTION:In the regeneration of a fluorine-containing cation-exchange membrane which is lowered in its electrolytic performance after being used in electrolysis of aqueous alkali chloride where the ion-exchange groups are alkali metal salt and gas and liquid-permeable, but electrolytically inactive particles are included on the surface on the cathode side and/or anode side. The ion-exchange groups are converted into ester, then, the membrane is heat- pressed and a new porous layer containing gas and liquid-permeable, but electrolytically inactive particles is heat-laminated on the anode and/or cathode surfaces.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fluorine-containing cation exchange membrane for electrolysis, and furthermore, an i'F
L<ha,ll! This invention relates to a +TF production method for membranes used for electrolysis of aqueous alkaline solutions and the like.

[Prior art] Rumor has it that by electrolyzing the upper n-ionized sodium 1
4 J:.

As a method for manufacturing ♂, the ion exchange model using a fluororesin cation/exchange membrane as a barrier is the conventional mercury 71
:1 Asbestos separation + 1'2 I), it has been attracting attention in recent years because it is advantageous from the viewpoint of public safety and energy saving, and it can produce highly concentrated caustic soda with extremely low sodium chloride content. There is.

As for the cation exchange membranes used in the ion exchange membrane method, carboxylic acid type membranes have a higher current efficiency than sulfonic acid type membranes. (
It is said that he is right-handed because he is capable of manufacturing i+f. Furthermore, when comparing a carboxylic acid type fluororesin film and a sulfonate type fluororesin film, it has been pointed out that the latter has a problem of higher electrical resistance than the latter.

Up to now, various proposals have been made regarding fluororesin cation/exchange membranes as diaphragms for sodium lithide electrolysis, with the aim of solving the problem described in item 1ii. For example, JP-A-II/150-120492 discloses cation exchange 119 consisting of a perfluorocarbon polymer sharing carboxylic acid) and sulfonic acid groups! In addition, a method based on copolymerization of a carboxylic acid type monomer and a sulfonic acid type monomer, and a method obtained by impregnating and bonding a carboxylic acid type monomer to a sulfonic acid ηJ fluororesin membrane have been reported. These are said to have both high current efficiency -V and high electrical conductivity due to the contribution of sulfonic acid groups having high electrical conductivity in addition to the characteristics of carboxylic acid groups. Further, JP-A-52-313589 describes a blend film of a carboxylic acid type perfluorocarbon polymer and a sulfonic acid type perfluorocarbon polymer, and a laminated film of a carboxylic acid type film and a sulfonic acid type membrane. There is. In these cases, the difficulty of producing highly concentrated caustic soda with high current efficiency in sulfonic acid membranes can be overcome by laminating carboxylic acid membranes or blending carboxylic acid polymers. has been done.

Therefore, a number of various proposals have been made to date to improve the insufficient electrolytic performance of the sulfo/acid type 10. For example, by subjecting the surface of a membrane made of a perfluorocarbon polymer having sulfonic acid groups to binary treatment and/or oxidation treatment, the sulfonic acid groups are chemically converted to carboxylic acid groups, and the surface of the sulfonic acid type membrane is converted into carboxylic acid groups. Method of forming acid type thin layer ('llF opening/closing 52-24175
．． 1i-f+ 52-2417 et al., 52-24177
) etc. are known.

= On the other hand, various methods have been proposed for performance recovery υ in iono-removal salt electrolysis.

(Unexamined Japanese Patent Publication No. 53-39H, No. 53-57199, No. 54-
29892, 54-+55!119tll, 55
-22311, 55-4N858, 55-8174
5) For these, the film with Ga and Mg deposited and low current efficiency is treated with acid and alkali to remove Ca and Mg, and if necessary, converted into ester form and heated, or anode It is described that the pH of the room should be lowered and then the temperature should be energized, and that the heat treatment should be carried out after using a heat exchanger. It has been reported that the seven-day effect-V can be recovered by these (natural treatment methods).

[Problems to be solved by the invention] Positive, f-off, and exchange 11! ,! In alkaline chloride electrolysis, in order to lower the power source level, the anode chamber is usually filled with a 2.5 to 5.0 normal (N) nickel, which excludes heavy metal ions such as calcium and magnesium as much as possible. Alkali chloride is supplied and electrolysis is carried out at 80-85°C. Furthermore, in order to lower the electrolysis rate, the cation exchange membrane is provided with a porous layer containing corrosion-resistant particles that have no electrode activity on the membrane surface and used for electrolysis. (Unexamined Japanese Patent Publication No. 58-7558
3, No. 56-108888, etc.) In this electrolysis, due to electrolysis operation trouble, the electrolyte C degree becomes extremely pale for a temporary or long period of time, or the temperature measurement becomes 7.
The temperature may drop below 0℃.

'lb: If the solution temperature is extremely low and continues for a long period of time, cation exchange IIA will be affected? This causes many cracks on the membrane surface, where the scum produced by electrolysis accumulates, increasing the gas resistance loss and increasing the decomposition pressure. Even if the concentration of the solution solution is increased, the wrinkles that have once formed do not completely disappear during electrolysis, and as a result, the electrolysis voltage is maintained high.

On the other hand, as mentioned above, the temperature of the seed water may drop to 70° C. or lower for a temporary or long period of time due to load fluctuations or the reasons for the dissolution system. Even if electrolysis is performed at around 90° C. after such low-temperature electrolysis, the current efficiency may not completely recover to its original value. Such a decrease in current efficiency tends to occur more easily as the obtained caustic soda concentration is higher and the current density is higher. On the other hand, such a decrease in current efficiency also depends on the structure of the membrane, such as reinforcement method, ion exchange capacity, membrane n, etc.

Although the causes of these phenomena are not yet clear, they are thought to be as follows. That is, in order to obtain highly concentrated caustic soda with high efficiency, it is necessary that the concentration of ions fixed on the cathode side of the membrane be high. When the fixed ion concentration is high, as a result of the small number of water molecules around the fixed ions, the mobility of Ha counter ions is easily constrained by the fixed ions, and the activation energy of Ha ion mobility in the membrane becomes high. When the temperature drops, the mobility of Na ions decreases. If electrolysis is performed in such a state, the water-containing structure around the fixed ions will change, and even if the temperature is raised again, it will not return to its original structure, so it is thought that the current efficiency will not recover.

Such a phenomenon is undesirable because it causes an increase in electrolytic power.

It is an object of the present invention to provide a new method for restoring the performance of membranes with increased voltage and/or reduced IE flow efficiency as described above.

[Means for solving the problem] Unreleased 1!11 was made to solve the above-mentioned problem, and was developed to improve the performance of perfluorocation membranes that were used in the electrolysis of aqueous alkali chloride solutions. A fluorine-containing membrane having an ion exchange group of an alkali metal salt type, and having a porous layer containing gas- and liquid-permeable particles having no electrode activity on at least one surface of the anode side or the cathode side of the membrane. In order to restore the performance of the cation exchange membrane, the ion exchange membrane is converted into an ester type and subjected to heat press treatment, and at least one surface of the anode side and the cathode side of the membrane is coated with a gas- and liquid-permeable electrode active. The present invention provides a method for regenerating a fluorine-containing cation exchange membrane for alkaline electrolysis, which comprises newly heat-pressing a porous layer containing particles that do not contain particles.

According to the present invention, the performance of a membrane whose electrolytic voltage has increased and whose current efficiency has decreased due to use in electrolysis can be restored. In the present invention, the ion exchange group undergoes a heat pressing treatment under a specific form and a step of reinstalling a new porous layer containing gas- and liquid-permeable particles with no electrode activity on the membrane surface. This is achieved by

If any of the above steps is missing, the purpose of the present invention cannot be achieved.1 For example, if there is little re-establishment of the porous layer on the membrane surface, not only will the electrolytic voltage not decrease, but the theoretical efficiency will also decrease. It is not possible to restore the electrolytic voltage and current efficiency, and heating presses with ester-type ion-exchange groups are also necessary; for example, heating presses with acid-type ion-exchange groups cannot achieve sufficient recovery of electrolytic voltage and current efficiency. .

In the present invention, in order to convert the ion exchange group of the ion exchange membrane from an alkali metal salt type to an ester type, one or more of the ion exchange groups is brought into contact with an aqueous solution of an inorganic acid or an organic acid, preferably in the presence of a polar organic compound. More preferably, the alkali metal salt is first converted into the acid form. Preferred examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and preferred examples of the organic acid include acetic acid, propionic acid, and perfluoroacetic acid. These inorganic or organic acids are preferably used as a 0.5 to 80% aqueous solution. This contact treatment is preferably carried out at a reaction temperature of 10 to 120° C. for 30 minutes to 20 hours, whereby the conversion of the exchange group is easily carried out.

Next, in order to convert it into an ester form, it is converted into the acid form and then reacted with alcohol to form an ester.

”, Preferably, the alcohol is )ノ, mokin1
~5 alcohols are used, such as methanol, ethanol, propatool, butanol, and the soaking process is
Preferably temperature 1O~+20°C1 reaction time 30 minutes~4
This will be done at 0 hours. Through the swelling phenomenon in these processes, the porous layer on the membrane surface falls off except for a part.

The membrane thus converted to the ester type preferably has a concentration of 70
°C~250℃, especially 100~230℃, time 30 seconds~
Pressing is carried out for 30 minutes at a pressure of 0.5 to 100 kg/crrr' or 0.5 to 100 kg/am in the case of a roll press.

Furthermore, a porous layer consisting of particles having no electrode activity is placed on one or both sides of the shaft at a temperature of 80 to 220°C and a pressure of 1 to 200°C.
Reinstall at 150 kg/ctn'. This can be done by separately forming a porous layer in advance and heat-pressing it onto the membrane surface, or by forming the porous particles preferably with ethanol,
It can be formed by spraying or the like onto the membrane surface using a dispersion medium such as water. The formation of these pores is described, for example, in Japanese Patent Application Laid-Open No. 57-1F3181 Gin. The thickness of the formed porous layer is smaller than that of the ion exchanger itself, preferably from 0.01 to 200 mm thick, especially from 0.1 to 100 mm thick. The particles constituting the porous layer include Group 1, iron group, Cr, Mn, B, etc. on the periodic table, and their oxides, pyrolyl acetides, nitrides, and carbides.

Next, the ion exchange membrane used in the present invention is made of a polymer containing, for example, a carpoquinyl group, a sulfonic acid group, a phosphonic acid group, a phenolic lactic acid group, and 9 cation exchange groups. It is particularly preferable to use a fluorine-containing polymer for the coalescence. Examples of the ion-exchange group-containing fluorine-containing polymer include a vinyl monomer such as tetrafluoroethylene or chlorotrifluoroethylene and a sulfonic acid, carboxylic acid, or phosphoric acid group. A co-polymerization with a perfluorinated vinyl monomer having an ion exchange group, such as, is preferably used. Further, a film-like polymer of trifluorostyrene with ion exchange groups such as sulfonic acid groups added thereto can also be used.

When one of these C1 combinations having the structure F is used, it is possible to obtain a highly purified r/Y alkali with a relatively high 'market efficiency -4' and at a low electrolytic voltage. Therefore, it is particularly preferable as a cation exchange membrane used in the present invention.

4CF2-CXX'>M4cFz-CX'tx■ Here, X is F, CI, H or -CFJ, and X' is
or CFJ(CF2)s and m is 1 to 5,
Y is selected from the following:

4CF: *x^, -0(CFz)X A,
(O-CF2-CFhA.

Z Rf Z Rf x, y, z are all 0-1 (Ill', Z, l1l
f is -F or C1-10 perfluoroalternate, (
It is chosen from scratch. Also, A is -503M, -GOON or -SOF, which can be converted into these groups by hydrolysis, -
CN, -COF or -○○OR, M represents water or an alkali metal, and R represents an alkyl group of Cl-10.

The cation exchange capacity used in this study is 0.5~
4.0 meq/g dry blast resin, especially 0.8-2.0
It is preferred to have a dry resin of milli'I/l/g dry resin.

An ion exchange table that takes! - In order to reduce
In particular, a content of 3 to 25 mol% is suitable.

Furthermore, the cation exchange membrane used in the present invention does not necessarily need to be formed from one type of aggregation, nor does it need to have only one type of ion exchange group. For example, as an ion exchange membrane S, the cathode side is smaller than the anode side, and the cathode side is a laminated membrane of two types of polymers, the cathode side is a weakly acidic exchange group such as a carboxylic acid group cap, and the anode side is a strong acid exchange group made of a sulfonic acid group cap. , (Ion exchange membranes with () are also used.

These ion exchange membranes are manufactured by various known methods. In addition, these ion exchangers may be preferably made of a fluorine-containing polymer of polytetrafluoroethylene T, woven fabrics such as nets, non-aluminum cloth or metal meshes, depending on safety.
It can be reinforced with porous material etc.

Further, the thickness of the ion exchange membrane is 20 to 500 #L, preferably 50 to 400 JL. A porous layer that is permeable to gases and liquids and does not affect electrode activity is formed on at least the surface of the anode side or cathode side of the ion exchange membrane of the present invention. Regarding the formation of a porous layer, see JP-A-57-
This is as described in Publication No. 113181 and the like.

[Function] In the present invention, it is not necessarily clear that the electrolytic moat can be recovered by converting the ion exchange group from an alkali salt type to an ester type, then hot pressing, and then providing a porous layer on the membrane surface. 5 By using the method of the present invention, the recurrence of wrinkles on the membrane surface is prevented, and furthermore, the cathode side of the membrane, which is thought to mainly control the expression of current efficiency, swells, and the metal beads deposited within the membrane are swollen. It is thought that after the elution of the polymer chains, the polymer chains are easily rearranged, and the electrolytic f& is recovered by returning to the initial structure in which h is easily mobile.

[Example] Example 1 Tetrafluoroethylene and CFz = CFO(GF
r) By catalytic polymerization of 3COOCH3 and varying the polymerization pressure and temperature, copolymers with ion exchange capacities of 1.44 meq/g dry resin and 1.20 meq/ga dry resin were obtained. The former copolymer is referred to as A, and the latter copolymer is referred to as B. Copolymer A was extruded to a thickness of 250 mm.
I got a film of Le. This film is designated as A-1. Further, copolymer B was similarly extruded to obtain a film having a thickness of 20 ml. This film was designated as B-1.Then, both films were superimposed and laminated at 200°C using a hot roll to obtain a composite film.

- 10 parts of zirconium oxide powder with a grain size of 5, methyl cellulose (viscosity of 2% aqueous solution 1500 centipoise)
o, 491. A paste was obtained by kneading a mixture containing 18 parts of water, 2 parts of cyclohexanol, and 1 part of cyclohexanone. The paste has a mesh number of 200 and a thickness of 75.
A-1 of the ion exchange membrane prepared by laminating the above using a Tetron screen, a printing plate with a 30μ thick screen mask on the screen, and a polyurethane squeegee.
Screen printed on the side. The adhesive layer obtained on the membrane surface was dried in air. On the other hand, on the other side of the membrane having the porous layer obtained in this manner, β
Silicon carbide particles were deposited. After that, the temperature was 40℃.
At a pressure of 30 kg/cm', each 119 particle layer was placed on the ion exchange membrane surface at a pressure of 7. By doing so, there are 11!2 1crn' grains of zirconium butyride and silicon carbide particles on the anode side and cathode side of the membrane, respectively.
．． Ion exchange membranes with 0 mg and 0.7 mg attached were created.

The membrane was soaked in a 25% aqueous solution of caustic soda at 70°C for te hours.
Hydrolysis was performed to obtain a sodium-type ion exchange membrane.

The film thus obtained had a low chlorine overvoltage on the A-1 layer side, which was coated with a solid body of ruthenium oxide, iridium oxide, and titanium oxide on punched titanium metal (2 liters in short axis, 5 liters in major axis). 5US30 for the anode and B-1 layer.
Raney nickel containing ruthenium (5% ruthenium, 50% nickel, 45% aluminum) is electrodeposited on 4-piece punched metal (short diameter 2 mm, long diameter 5 layers) to have a low hydrogen overvoltage. While supplying a 300 g/l sodium chloride aqueous solution to the anode chamber and water to the cathode side, the sodium concentration of the brine in the anode chamber was kept at 200 g/liter, and the caustic soda concentration in the cathode chamber was kept at 35% by weight. Electrolysis was carried out under the conditions of 30A/dm'' and 90°C.The initial performance was a current efficiency of 98.0%, and a voltage of 3.
1OV, but electrolysis trouble occurred during the process, and 350
The performance after 1-1ffl conversion decreased and the current efficiency was 94.5%,
The voltage was 3.25V. Disassemble the battery case and take out the membrane.
As a result of the investigation, many wrinkles with a width of 5 ml 11 to 10 mff 1 had occurred.

The membrane with poor performance was treated in IN hydrochloric acid containing 20% dimethyl sulfoxide at 70°C for 16 hours to convert the ion exchange groups into acid form, and then in methanol at 25°C for 16 hours.
By soaking for a period of time, the ion exchange group was converted into a methyl ester type.

9, which had been converted from the sodium form to the methyl ester film, was pressed at 120° C. and a pressure of 10 kg/c for 3 minutes, and the wrinkles that appeared when the film was taken out of the container completely disappeared. Furthermore, zirconium oxide and β-silicon carbide particles were coated on both sides of the film at 140°C using the same method as described above.
After reheat pressing at a pressure of 30 kg/crn' and hydrolyzing it in the same manner as before, electrolysis was carried out under exactly the same conditions as described above.

゛The electrolytic performance is current efficiency 96.0%, voltage 3. It was lOV. After 10 days, the electrolysis was stopped and the membrane was taken out from the tank and its appearance was examined, but the membrane did not appear.

Comparative Example 1 An ion exchange membrane obtained in the same manner as in Example 1 was hydrolyzed and electrolyzed under the same conditions. Initial performance is current efficiency 95
．． 8%, voltage 3. It was IOV.

After 320-n operation, the current efficiency is 95.0% and the voltage is 3.
It was 26■. When the ion exchange membrane was taken out from the container and observed, there were quite a lot of cracks with a width of 5 to 10 mm.

11!2 with reduced performance at 150℃, pressure crab] OK
After pressing for 5 minutes under the condition of g/cm' to smooth out the wrinkles, the sample was again subjected to electrolysis using an aqueous sodium chloride solution. The current efficiency was 95.0% and the voltage was 3.25V. After stopping the electrolysis and inspecting the ion exchange membrane, we found that many wrinkles had regenerated.

Comparative Example 2 An ion exchange membrane obtained in the same manner as in Example 1 was treated under the same conditions.
Hydrolyzed and electrolyzed. Initial performance is current efficiency 85
．． 7%, voltage 3. After operation at 1OV and 320FJ, the current efficiency was 94.0% and the voltage was 3.24V. When the ion exchange membrane was taken out of the container and observed, many wrinkles were found. , said IIIA! was ion-exchanged in IN hydrochloric acid containing 0% dimethyl sulfochloride (converted from sodium form to acid form at 120°C, pressure 20 kg/ctn').
The sample was pressed for 5 minutes, hydrolyzed in the same manner as before, and then subjected to sodium chloride aqueous solution electrolysis again.

The electrolysis performance was a current efficiency of 95.0% and a voltage of 3.20V, and wrinkles were observed in the ion exchange membrane after the electrolysis was stopped.

Comparative Example 3 An ion exchange membrane whose performance was degraded (current efficiency 34.0%, voltage 3.24 V) after electrolyzing 300r + sodium chloride aqueous solution was treated in 1 munic acid containing 20% dimethyl sulfoxide to remove ion exchange groups. The ion exchange membrane was converted into acid form and then immersed in methanol at 25°C for 16 hours to convert the ion exchange groups to methyl ester form.The ion exchange membrane was then hydrolyzed in the same manner as before, and it was used for Itf degree sodium chloride and aqueous electrolysis. As a result, the current efficiency was 94.5%, 1t! :The pressure was 3.20V.

After the electrolysis was stopped, wrinkles appeared on the ion exchange membrane, and drop-off of the particle layer that had been pressed onto both sides was observed.

Comparative Example 4 An ion exchange membrane whose conversion performance was reduced to 34ooa by electrolysis of an aqueous sodium chloride solution, a current efficiency of 94.0%, and a voltage of 3.24 V was converted into a methyl ester type in the same manner as in Example 1, Then the temperature was 120°C and the pressure was 10kg/cr.
n', press flattened for 23 minutes.

The membrane was hydrolyzed with a 25% aqueous sodium hydroxide solution at 70° C. for 6 hours to obtain a sodium type ion exchange membrane, which was then subjected to electrolysis of a brine sodium aqueous solution.

The electrolytic performance was a current efficiency of 95.0% and a voltage of 3.14V.

After stopping the electrolysis, we took out the ion exchange membrane and examined its appearance. Although there were relatively few particles, the layer of particles that had been crimped on both sides had fallen off.

Example 2 Tetrafluoroethylene and CF2=CFO(CFz
) 3coocn: catalytic polymerization of +, ion exchange capacity! 1.44 mm/g dry resin and 1.20
A copolymer having a milliequivalent weight of 7 g dry resin was obtained. The former copolymer is designated as A, and the latter copolymer is designated as B. On the other hand, tedrafluoroethylene and CF2 = CFOCF2CF (CF
:+)O(CF?hSO2F was also added as a catalyst to obtain a copolymer of dry resin with ion exchange capacity of ¥1.1 mttz and +l knee/g. This polymer is referred to as C.

Copolymer A and copolymer C were blended in a ratio of 1:1 and then kneaded with a hot roll. By extrusion molding, the film thickness is 180 mm from A, and the film thickness is 20 mm from #L film E and B.
Film G with a film thickness of 20 was obtained from the pot films F and C, and film H with a film thickness of 15 μL was obtained from D. Next, each film was stacked together in the order of G, H, E, and F using a hot roll. 2
Lamination was carried out at 00°C. The laminated film was coated with G in the same manner as in Example 1.
Zirconium oxide particles were attached to the layer side, and β silicon carbide was attached to the F layer side.

The soaked membrane was hydrolyzed in the same manner as in Example 1 and used in an aqueous sodium chloride solution. Current density 30A/cm",
While maintaining the sodium chloride concentration in the anode chamber at 200 g 1 liter,
When electrolysis was performed at 0° C., the current efficiency after IO [1] was 96.0% and the voltage was 3.02V. After that, while keeping the current density at 30A/d, the temperature measurement was lowered to 60℃ and electrolysis was performed for 30 minutes, and then the temperature measurement was raised to 90℃ again, and the current efficiency after 1 El was 93.
0%, and the current efficiency after 5 days was 93.5%,
The voltage was 3.02V.

Stop the electrolysis, take out the ion exchange membrane whose current efficiency has decreased, and add it to IN hydrochloric acid containing 10% dimethyl sulfoxide.
The sample was treated at 50 DEG C. for 16 hours to convert the ion exchange group into an acid form, and then immersed in methanol at 15 DEG C. for 5 hours to convert the ion exchange group into a methyl ester type. The membrane thus converted to the ester type was heated at 125°C and at a pressure of 25 kg/cr.
A flattening treatment was carried out by pressing at 140° C. for 5 minutes at a pressure of 30 kg/cm. was hydrolyzed in the same manner as before, and the sodium chloride aqueous solution was electrolyzed again. After 20 days of re-electrolysis,
30A/drn', 90℃, 200g/41 Mai
1. Under the advancing conditions of 35% NaOH, the current efficiency recovered to almost its original value of 96.0%, and when electrolysis was continued for an additional 35 days, the current efficiency remained at 96%, and the voltage was 3. It was .02V.

[9. Bright effect] The present invention has an excellent effect of almost completely recovering the performance of a membrane degraded by electrolysis through a relatively easy treatment, and furthermore, the recovery treatment according to the present invention can improve Since it can be applied multiple times, it can have the effect of substantially extending the life of the membrane. Furthermore, by sufficiently carrying out the acid treatment and esterification treatment of the present invention, it is also possible to remove impurities within the membrane that adversely affect current efficiency.

Claims (5)

[Claims] (1) The ion exchange group of the fluorine-containing cation exchange membrane whose performance has deteriorated due to electrolysis of an aqueous alkali chloride solution is of the alkali metal salt type, and at least one surface of the anode side and the cathode side of the membrane contains gas. In order to restore the performance of a fluorine-containing cation exchange membrane having a porous layer containing liquid-permeable particles with no electrode activity, the membrane is heated and pressed in a state where the ion exchange group is converted to an ester type. A fluorine-containing product for alkaline electrolysis, characterized in that a porous layer containing gas- and liquid-permeable particles having no electrode activity is newly bonded under heat and pressure on the anode side, or on the surface or both surfaces of the anode side or cathode side. Method for regenerating cation exchange membranes. (2) The method according to claim 1, characterized in that the alkali metal salt type ion exchange group is brought into contact with an acid or an acid and then an alcohol having 1 to 5 carbon atoms to convert it into an ester type. (3) The method according to claim 1, wherein the hot press treatment temperature is 70° C. to 250° C. or less, and the pressure is 0.5 to 100 kg/cm^2 or kg/cm. (4) The cation exchange capacity of the fluorine-containing cation exchange membrane is 0
．． 5-2.5 meq/g dry resin. The method of claim 1. (5) Particles with no electrode activity are group IV of the periodic table, V-
2. The method according to claim 1, comprising oxides, hydroxides, nitrides or carbides of B group, iron group, Cr, Mn, B.