JPS602909B2 - Performance recovery method of cation exchange membrane for alkali chloride electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for restoring the performance of intestinal ion exchange membranes for alkali chloride electrolysis.

More specifically, the present invention relates to a method for restoring the performance of an ion exchange membrane which is used to electrolyze an aqueous alkali chloride solution to produce chlorine and alkali hydroxide, and whose performance has deteriorated during the process. There is a method of separating the cathode and anode of an electrolytic cell with a diaphragm, and supplying an aqueous alkali chloride solution to the anode chamber for electrolysis, thereby producing chlorine in the anode chamber and alkali hydroxide in the cathode chamber.

As this diaphragm, an asbestos diaphragm has been used as a secondary diaphragm. However, this method has drawbacks such as alkali chloride being mixed into the alkali hydroxide obtained, resulting in poor purity and inability to obtain a highly concentrated alkali hydroxide. In order to solve these drawbacks, the use of intestinal ion exchange membranes as this diaphragm has recently been proposed and is attracting attention. However, if this intestinal ion exchange membrane, which can overcome the drawbacks of asbestos diaphragms, is used continuously, the current efficiency of the tympanic membrane will gradually decrease, and the voltage will increase, causing problems that are completely inconvenient economically. It became clear.

On the other hand, cation exchange membranes for alkali chloride electrolysis are generally expensive, and membrane-related costs account for a considerable portion of the alkali hydroxide production cost.

Considering this point, it is economically advantageous to restore the performance of a membrane whose performance has deteriorated and use it repeatedly3.
It is. In fact, based on these points, methods for restoring the performance of intestinal ion exchange membranes have been proposed.

For example, a method in which a perfluorocarbon cation exchange membrane is swollen with an organic solvent and then the solvent is removed from the membrane (Japanese Patent Application Laid-Open No. 52-130491), a fluorine-containing carboxylic acid cation exchange membrane is A method of heat treatment (Mochiseki Shokyu-3999), a method of contacting a perfluorocarbon-based ion exchange membrane with an acid solution having oxidizing power (Samurai Sekisho 53)
-375 jobs).

4. Various methods are being considered to make it even better.

Therefore, the inventors of the present invention have continued to conduct intensive research while paying attention to these points, and as a result, we have discovered that the performance of cation exchange membranes for alkali chloride electrolysis can be restored using a new method that has never been proposed before. It was a success.

That is, after soaking the perfluorocarbon-based cation-exchange pus used for electrolysis of an aqueous alkali chloride solution in polyethylene glycol, the membrane was sandwiched between smooth plates and 40 qo~
This is a method for restoring the performance of a cation exchange membrane, which consists of further treating an intestinal ion exchange membrane that has been heat-treated in a range of 180°C with hydrochloric acid, and then immersing the membrane in an aqueous solution of caustic soda.

Although it is unclear why performance is restored by the process of the present invention, it is thought to be as follows.

This is thought to be due to the fact that the exchange groups in the cation exchange membrane whose performance has deteriorated are rearranged to their original state by the action of polyethylene glycol and heating.

Furthermore, in the present invention, we have experienced that by applying the treatment of the present invention, the fly flow efficiency is improved more than the original performance. This is thought to be due to the fact that, depending on the treatment, the intestinal ion exchange groups are arranged in positions that are convenient for effectively blocking hydroxyl ions. This can be understood from the fact that general cross-linked ion exchange membranes, such as cation exchange membranes based on copolymers of styrene and dipinylbenzene, are ineffective. However, in this state, it is thought that some strain has occurred in the film.

It is thought that the distortion was eliminated by this hydrochloric acid treatment. It should be noted that this explanation has been made for the purpose of explaining the mechanism of the present invention, and does not limit the present invention in any way.

Preferred cation exchange membranes used in the present invention include:
1 The exchange group on one surface layer of the cation exchange membrane is -SQN
MR, [where M is day, alkali metal salt, R is -C
Elbow 2M (n = integer from 0 to 6), 1Cn ratio nCO
OM (however, n and M are the same as above) (however, p = an integer of 0 to 6, q = an integer of 2 or more), phenyl group or R2MN02S- {however, M is the same as above, R2 is or - CmH2m (However, these are two R2MN0
2S- group, common R2, m: an integer of 1 to 6)}]
, an intestinal ion exchange membrane in which the remaining exchange group is -S08M (M is the same as above).

To obtain this type of intestinal ion exchange membrane, a copolymer having the following general formula (wherein x=-CF3, -CF2-○-CF3; n=0 or 1 to 5; m=0 or 1; k / evening = 3-1 Isoko or 5-13) Specifically, use an example.

Of course, it is not limited to only these structures.

In these copolymers, the weight of the resin containing 1 equivalent of sulfonyl halide group is 700 to 2800 m (hereinafter referred to as
It is written as EW=700-2800. ) is preferable. The most preferred structure is that represented by formula {1}.

Next, the polymer having the above structure is made into a film, and one side of this film is mixed with ammonia gas, methylamine, ethylamine, n-bropylamine, aminoacetic acid, 2-aminopropanoic acid, 7-amino/hebutanoic acid, and aniline. , aminostyrene addition polymer, ethylenediamine, 1,3-diaminopropane, 1,6-diaminohexane, etc. are reacted.

When reacted with a diamine, a cross-linked form between -S02F groups in the polymer, for example -S02NM-Cm ratio m-NMS
02-1, and in the case of aminostyrene addition polymer,
Take Z. Although the depth of the reaction layer is effective in the range of 0.01 to 80% of the film thickness, it is preferably 0.1 to 30%. It is obtained by subjecting the film-like material thus obtained to high temperature treatment and hydrolysis, if necessary.

2 The exchange group on one surface layer of the intestinal ion exchange membrane is -COO
M (however, M is the same as above), and the remaining exchange group is -SQM (however, M is the same as above) In order to obtain this type of intestinal ion exchange membrane, for example, the above formula 1
It can be obtained by a method such as treating one side of a film-like product of a copolymer having a structure of 5 to 5 with a reducing agent.

3. A cation exchange membrane in which all of the exchange groups of the cation exchange membrane are -COOM (M is the same as above). To obtain this type of intestinal ion exchange membrane, a copolymer having the following general formula is used. Or a=an integer of 2 to 4, b=an integer of 0 or 1 to 5, C=
Integer A of 1 to 5 = COF, COOC is (p1q)/r = 0.5 to 1
9, preferably 1 to 10, for example, can be obtained by forming into a film-like material and then hydrolyzing it.

The above cation exchange membrane may also be appropriately reinforced with polyester fiber cloth, rayon fiber cloth, Teflon fiber cloth, etc. for the purpose of improving the functional properties of the membrane.

The intestinal ion exchange membrane described above is thus subjected to alkaline chloride electrolysis.

However, when the membrane is used for long-term electrolysis, the current efficiency of the membrane decreases and the cell voltage increases. Although this decrease in performance is not necessarily clear, we believe that it is due to the inability of the exchange group to remain in its original state, as described above. Based on this point, in the present invention, the above-mentioned cation exchange membrane whose performance has deteriorated as it is used is subjected to a performance recovery treatment as follows.

That is, a cation exchange membrane whose performance has deteriorated due to electrolysis of an aqueous alkali chloride solution is immersed in polyethylene glycol, and then the membrane is sandwiched between smooth plates and 40 qo to 1803
This is achieved by heat-treating the film in the range of 0.0 and further treating with hydrochloric acid, and then immersing the film in an aqueous solution of caustic soda.

The time required for immersion in polyethylene glycol may be about 5 to 5 field hours. The polyethylene glycol is an oligomer having a molecular weight of 200 to 700, preferably 200 to 600. The soaking treatment can be carried out by removing the membrane of the intestinal ion exchange membrane whose performance has deteriorated from the electrolytic cell and soaking it in the above-mentioned polyethylene glycol. In this case, the exchange group in the ion exchange membrane may be either an acid type or a salt type. Polyethylene glycol may be heated if necessary.
The time for heat treatment by sandwiching between smooth plates is in the range of 1 to 5 q hours. Smooth plates include glass plates, stainless steel plates,
Alternatively, a Teflon plate or the like can be used. Next, the intestinal ion exchange membrane treated as described above is treated with hydrochloric acid.

The concentration of hydrochloric acid used is in the range of 0.0 to 1 sail.
Preferably 0. The range is from the mark to the fence.

The treatment temperature ranges from 4 to 95°C, preferably from 60 to 860°C. Treatment times range from 30 minutes to 5 hours. The cation exchange membrane treated as described above is soaked in a caustic soda aqueous solution. EXAMPLES The effects of the present invention will be explained in detail below using Examples, but it goes without saying that the present invention is not limited to these Examples.

Example 1 Only one side of a film (EW=1200, film thickness=7 mils) consisting of a copolymer of CF2=CF2 and the formula was brought into contact with ethylenediamine,
After thoroughly cleaning the surface, it was dried.

A color test on a cross section of the two films showed that the reaction occurred to a depth of 1.5 mils.

After introducing Teflon fiber into the film, 18 pi 0 ~
A cation exchange membrane was obtained by heat treatment at a temperature of 200°C and further hydrolysis. A two-chamber electrolytic cell was assembled using the obtained cation exchange membrane as an ant belly.

The energized area was the first. While saline was supplied to the anode chamber, electricity was applied at a current density of 3 m/dm2 to electrolyze the saline. During the electrolysis operation, water was continuously poured so that the concentration of caustic soda in the cathode chamber was always in the range of 2% to 29%.
At the initial stage of energization, the current efficiency is 90% and the voltage is 4.32.
The fin flow efficiency was 82 after the 3rd month of energization.
%, the cell voltage was 4.52 volts.

At this point, the turtle tank was disassembled and the membrane was removed. In order to examine the performance recovery of the membrane, it was divided into 3 ratios x 3 ratios. One of the membranes was soaked in polyethylene glycol with a molecular weight of 200 at room temperature for one day, and then the membrane was placed on a glass plate.
After being sandwiched between smooth plates made of chloroprene rubber and polyester sheets and heat-treated at 120 qo for 8 hours,
Furthermore, it was treated in hydrochloric acid at 65°C for 2 hours.

After being left at room temperature for 1 day, it was soaked in carp NaOH for 2 days. Next, a two-chamber electrolytic cell with a current-carrying area of 20 arcs x 2 runs was assembled, and current was applied under the same conditions as before.

At this time, the current efficiency was 91% and the voltage was 4.35 volts. Example 2 One sheet from Example 1 was treated in IN hydrochloric acid to convert the exchange group to the acid form.

After soaking the membrane in polyethylene glycol having a molecular weight of 300 at room temperature for one day, it was sandwiched between smooth plates made of a glass plate, chloroprene rubber and a polyester sheet.
Heat treatment was performed at 0°C for 10 hours. Further 2. egg in hydrochloric acid 65
qo, treated for 2 hours. After leaving it at room temperature for a day.
It was soaked in Iso NaOH for 2 weeks. Next, the energized area is 20 skins
A two-chamber electrolytic cell with 20 cells was assembled and energized under the same conditions as before.

At this time, the current efficiency is 92% and the cell voltage is 4. It was a powder bolt. Example 3 One sheet from Example 1 was treated in IN hydrochloric acid to convert the exchange group to the acid form.

50% of the eardrum in polyethylene glycol with a molecular weight of 600.
After soaking at ℃ for 1 day, sandwiched between smooth plates made of glass plate, chloroprene rubber and polyester sheet,
Heat treatment was performed for 3 hours at Further, in hydrochloric acid at 65℃, 2
Time processed. After leaving at room temperature for one day, carp NaOH
It was soaked in water for two weeks. Next, the energized area is 2 ratios x 2 mountains.
A chamber type electrolytic cell was assembled and energized under the same conditions as before. At this time, the current efficiency was 90% and the voltage was 4.21 volts.
Comparative Example 1 *The cation exchange membrane divided in Example 1 was treated in IN hydrochloric acid to convert the exchange groups to acid form.

The membrane was sandwiched between smooth plates made of a glass plate, a chloroprene rubber sheet, and a polyester sheet, and heat-treated at 120° C. for 8 hours. Further, the sample was treated in hydrochloric acid at 65° C. for 2 hours, and then soaked in NaOH for 2 weeks. Next, a two-chamber electrolytic cell with a current-carrying area of 2 squares x 2 squares was assembled and energized under the same conditions as before. Current efficiency at this time is 88%, cell voltage 4.61
It was a bolt. Example 4 A film of a copolymer of the formula CF2 = CF2 (EW = 120, film thickness = 7 mils) was hydrolyzed and then treated in IN hydrochloric acid to convert the exchange groups into acid form.

The membrane was mixed with phosphorus oxychloride and phosphorus pentoxide (weighted = 1/1)
was processed to form the sulfonyl chloride form.

After the reaction was completed, the mixture was thoroughly washed in carbon tetrachloride and then dried. Confirmation of the conversion of sulfonyl chloride groups was obtained by surface infrared spectroscopy. After combining the two membranes and setting them in a cell, they were immersed in a 57% aqueous hydrobrodic acid solution to convert only one side into carboxylic acid groups. Carboxylic acid groups were confirmed by surface infrared spectroscopy.
As a result of the color test, the carboxylic acid base layer of the membrane was 1.3 mil. The sulfonyl chloride groups present in the membrane were converted to sulfonic acid groups by hydrolysis. A two-chamber electrolytic cell was assembled using the obtained cation exchange membrane as a diaphragm.

The area of the electrostatic discharge was 2 melons x 20 enemies. Salt water was energized in the anode chamber at a current density of 3 d to perform electrolysis of the salt water. During the electrolysis operation, water was continuously poured so that the caustic soda concentration in the cathode chamber was always in the range of 24 M% to 25 wt%. At the initial stage of energization, the current efficiency was 90% and the voltage was 3.75 volts.

After 3 months of electricity, the current efficiency was 3.93 volts and the voltage was 3.93 volts. At this point, disassemble the crab tank, remove the membrane, and
The exchange group was converted into acid form by treatment in N-hydrochloric acid. After soaking the membrane in polyethylene glycol having a molecular weight of 300 at room temperature for one day, it was sandwiched between smooth plates made of a glass plate, chloroprene rubber and a polyester sheet, and heat-treated at 130°C for 8 hours. The mixture was treated in hydrochloric acid at 65° C. for 2 hours. After treatment, after being immersed in NaOH for two weeks, when electricity was started under the same electrolysis conditions as before, the current efficiency was %% and the voltage was 3.61 volts.

Example 5 CF2=CF2, CF2=CF-0-CF3 and formula C
A ternary copolymer of F2iCF-○1←CF2Na3-COOCH3 is molded into a film-like material and hydrolyzed to form an ion exchange membrane (exchange group capacity, 1.2 heq/g・dhi・resin film thickness). , 0.2 sail).

A two-chamber electrolytic cell with a current-carrying area of 20 m x 2 mounds was assembled, and while saline was supplied to the anode chamber, electricity was applied at a current density of 3 M/d to perform electrolysis of the saline. During the electrolysis operation, water was continuously poured so that the concentration of caustic soda in the cathode chamber was always in the range of 2% to 3%. At the initial stage of energization, the current efficiency is 91
%, and the voltage was 4.68 volts.

Claims (1)

[Claims] 1. A perfluorocarbon cation exchange membrane used for electrolysis of an aqueous alkali chloride solution is immersed in polyethylene glycol, then sandwiched between smooth slopes, heated in a range of 40°C to 180°C, and further treated with hydrochloric acid. A method for restoring the performance of a cation exchange membrane, which is then immersed in a caustic soda aqueous solution. 2. The method according to claim 1, which uses a cation exchange membrane in which the cation exchange groups contained in the cation exchange membrane are free acid groups and/or alkali metal salts. 3 The exchange group on one surface layer of the cation exchange membrane is -SO_
2NMR_1 [However, M is H, alkali metal salt, R_
1 is -CnH_2_n_+_1 (however, n = an integer from 0 to 6), -CnH_2COOM (however, n and M are the same as above), ▲Mathematical formula, chemical formula, table, etc.▼ (however, p = an integer from 0 to 6) , q=an integer of 2 or more), phenyl group, or R_2MNO_2S- {however, M is the same as above, R_2 is ▲ there is a numerical formula, chemical formula, table, etc. ▼ or -CmH_2m- (however, these are two
A patent claim using a cation exchange membrane in which the common R_2 of the MNO_2S- group is m = an integer of 1 to 6), and the remaining part of the exchanger is -SO_3M (however, M is the same as above) The method according to item 1 or 2. 4 The exchange group on one surface layer of the cation exchange membrane is -COO
M (however, M is the same as above), and the exchange group of the remaining part is -SO_3M (however, M is the same as above) using a cation exchange membrane according to claim 1 or 2 Method. 5 All of the exchange groups in the cation exchange membrane are -COOM(
The method according to claim 1 or 2, wherein a cation exchange membrane (M is the same as above) is used. 6. The method according to claim 1, 2, 3, 4 or 5, wherein polyethylene glycol having a molecular weight of 200 to 700 is used. 7. The method according to claim 1, 2, 3, 4, 5 or 6, wherein the hydrochloric acid treatment is carried out in a range of 0.05N to 10N. 8. The method according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the hydrochloric acid treatment is carried out at a temperature in the range of 40°C to 95°C.