JPH0565595B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention uses an existing bipolar diaphragm electrolytic cell that produces caustic alkali using asbestos as a diaphragm, and replaces the asbestos diaphragm with a cation exchange membrane. The present invention relates to a method for producing highly concentrated and highly purified caustic alkali at low cell voltage.

(Background of the Invention and Prior Art) The method for obtaining caustic alkali by electrolyzing alkali chloride was changed from the mercury method using mercury to the diaphragm method using asbestos membranes from the viewpoint of pollution prevention.Currently, this diaphragm method has become the mainstream method for producing caustic alkali.

The following rigid bipolar diaphragm electrolytic cell is known as one of the typical existing diaphragm electrolytic cells for producing caustic alkali using such an asbestos diaphragm.

In other words, a large number of electrolytic cells are sequentially arranged side by side using partition walls as partitions, and apart from the partition walls at the ends of the large number of electrolytic cells arranged side by side, the middle partition wall has an extension end closed on one side in horizontal section. A large number of approximately U-shaped finger anodes are extended, and a cathode back screen is installed on the opposite side of the partition wall at a distance of a few thousand feet from the partition wall. The finger cathode is extended from the cathode back screen, and the anode and cathode fingers on both sides of the partition are supported using a power supply rod that penetrates the partition.
Each electrolytic cell is structured so that it can be electrically connected and conductive, and is partitioned by partition walls like this.
A finger anode extending from one partition wall and a finger cathode extending from the other partition wall, which are adjacent to each other, are inserted into each other in a staggered manner to maintain a small gap between the two, and The asbestos diaphragm is a bipolar diaphragm electrolytic cell in which asbestos slurry is preliminarily deposited in a layered manner on a mesh-like finger cathode.

In addition, the power supply method for such electrolytic cells is such that the anode side of the electrolytic cells at one end of a large number of electrolytic cells arranged side by side is connected to the positive electrode of the power supply device, and the cathode side of the cell at the other end is connected to the negative pole of the power supply device. be configured.

The inside of each electrolytic cell is divided into an anode chamber and a cathode chamber by an asbestos diaphragm. Specifically, the surrounding area of the cathode back screen is joined to the flange on the cathode chamber side of the electrolytic cell, so that the flange of the electrolytic cell is closed. A cathode chamber is formed within the swinger cathode and between the partition wall and the cathode back screen. In electrolysis of alkali chloride using an asbestos diaphragm formed by depositing asbestos slurry on a bag-shaped finger cathode as described above,
Caustic alkali is obtained from the cathode chamber by performing electrolysis while maintaining a high level of alkali chloride solution supplied to the anode chamber.

However, in the diaphragm electrolytic cell using an asbestos diaphragm as described above, the concentration of caustic alkali obtained from the cathode chamber is extremely low due to the liquid permeability of the asbestos diaphragm, and it also contains a large amount of alkali chloride. There are some difficulties. For example, in salt water electrolysis, the caustic soda concentration is 10 to 13 wt%, and 15 to 13 wt%.
Contains 18wt% salt. Therefore, for industrial use, it is further concentrated and the salt that precipitates during the concentration process is separated, but the approximately 50wt% caustic soda that becomes the product still contains approximately
Since it contains 1wt% of salt, it is difficult to use it directly in fields such as the rayon industry.

Incidentally, recently, an ion exchange membrane method using a cation exchange membrane as a diaphragm has been developed as an electrolytic method belonging to the same diaphragm method that does not contain alkali chloride and can produce caustic alkali at a high concentration.

Therefore, in a broad sense, taking advantage of the common features of both of the above, which belong to the same diaphragm method, electrolysis of alkali chloride is carried out by replacing and installing a cation exchange membrane as a diaphragm in an asbestos diaphragm electrolytic cell with existing equipment. ,
If high-purity and high-concentration caustic alkali can be obtained by this method, it will be possible to replace it with the ion-exchange membrane method without making large capital investments in electrolyzers, which would have great industrial merits. It is a big one.

(Problems to be Solved by the Invention) In view of this, the present inventors installed a cation exchange membrane in place of the conventional asbestos in the above-mentioned bipolar diaphragm electrolytic cell to electrolyze alkali chloride. We conducted a study on a method for producing caustic alkali.

However, in the application of simple replacement of the diaphragm mentioned above,
It has become clear that there are several problems described below.

That is, a large number of bag-shaped membranes made of cation exchange membranes are placed over the finger cathodes one by one, and the individual finger cathodes and bag-shaped cation exchange membranes are sealed to assemble the electrolytic cell. In this electrolytic cell, electrolysis is carried out in the same manner as before, while the level of the saline solution supplied to the anode chamber is kept higher than the level of the caustic soda solution in the cathode chamber, and the generated hydrogen gas is extracted from the upper part of the cathode chamber. When electrolysis was carried out, the cell voltage was very high, and the caustic soda obtained contained more iron than the caustic soda obtained by the conventional electrolytic method using an asbestos diaphragm. Even more unfavorably, we have experienced several times that the salt content in the caustic soda gradually increases as the operation continues, and the current efficiency of the caustic soda in the cathode chamber decreases.

The inventors also attempted to conduct electrolysis by making the hydrogen gas pressure in the cathode chamber higher than the chlorine gas pressure in the anode chamber, but in this case too, the cell voltage was high, and in addition, Several serious problems were encountered, including the low current efficiency of the resulting caustic soda.

As mentioned above, the present invention was made in order to overcome the problems that occur when converting existing electrolytic cell equipment that used asbestos diaphragms to electrolytic cell equipment that uses ion exchange membranes as diaphragms. be.

That is, the first object of the present invention is that when a cation exchange membrane is installed as a diaphragm in a rigid bipolar diaphragm electrolytic cell that produces caustic alkali using existing asbestos as a diaphragm, The object of the present invention is to provide a method capable of obtaining highly concentrated caustic soda with an extremely lower cell voltage than when an asbestos diaphragm is used.

A second object of the present invention is to provide a high-purity product with extremely low iron and alkali chloride contents when an electrolytic cell is constructed using a cation exchange membrane as a diaphragm in the conventional electrolytic cell equipment. The object of the present invention is to provide a method capable of producing caustic alkali.

A third object of the present invention is to provide an electrolytic cell using the cation exchange membrane as a diaphragm, in which the cation exchange membrane has excellent durability and maintains stable and high current efficiency over a long period of time. The object of the present invention is to provide a method capable of producing high purity caustic alkali.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have investigated the causes of the problems described above and conducted various studies and examinations on methods of solving them. As a result, each problem has been solved. It was clarified that these are related to the method of installing the cation exchange membrane, the method of extracting electrolytic products, that is, caustic alkali and hydrogen gas, from the cathode chamber, and the structure itself of the finger anode installed in the anode chamber. , which led to the completion of the present invention.

The method of the present invention for achieving the above object is characterized by a large number of finger anodes extending from one of the opposing partition walls of the electrolytic cell and a large number of finger anodes extending from the other opposing partition wall. A finger cathode and a finger cathode are assembled in such a way that the fingers are inserted into each other in a staggered manner to maintain a small distance between the electrodes, and then a continuous bag-shaped cation exchange membrane is placed over the finger cathode and the finger cathode is A bipolar electrolytic cell is used, in which the inside of the tank is divided into an anode chamber and a cathode chamber by attaching and sealing the peripheral part of the ion exchange membrane to the flange on the cathode chamber side near the base of the finger cathode of the electrolytic cell. A method for producing caustic alkali, comprising performing electrolysis while supplying alkali chloride to an anode chamber to generate caustic alkali in a cathode chamber,
Water or low concentration caustic alkali is supplied from the lower part of the cathode chamber, and while electrolysis is performed in the absence of a gas phase in the cathode chamber, the caustic alkali and hydrogen gas generated in the cathode chamber are transferred to the upper part of the cathode chamber. Extract the gas-liquid mixture from the upper nozzle provided,
Furthermore, the level of the liquid in the anode chamber during electrolysis is kept below the level of the liquid in the cathode chamber.

Hereinafter, the present invention will be explained in more detail based on the drawings.

Figure 1 is a partial sectional view of one example of an existing bipolar diaphragm method electrolytic cell used in the asbestos diaphragm method, viewed from above with a horizontal cross section of one of the electrolytic cell portions. FIG. 2 is a perspective view showing one of the many finger anodes installed in the anode chamber.

In the figure, reference numeral 1 indicates a partition wall, and a power supply rod 4 is attached to the partition wall 1 by penetrating the partition wall 1 and joining it. A power supply body 3 is connected to the end of the power supply rod 4 that protrudes from the partition wall 1 toward the anode chamber, and an anode plate made of expanded metal based on titanium coated with an anode active material such as ruthenium oxide is attached to the center. A large number of finger anodes 2 which are bent to form a U-shape in horizontal cross section are joined to this power supply body 3.

On the cathode chamber side of one of the partition walls 1, a cathode back screen 5 is provided at a distance from the partition wall 1, and a finger-shaped hollow whose end is connected to the power supply rod 4 of the next stage through the cathode back screen 5 is provided. The cathode back screen 5 has a cathode, and the periphery of the cathode back screen 5 is joined to the cathode chamber side flange 7 of the electrolytic chamber, so that the inside of the finger cathode 6 and between the partition wall 1 and the cathode back screen 5 form a cathode chamber. is forming.

Inside the individual finger anodes 2,
An anode support is attached over the entire length of the finger anode 2 in order to limit inward deflection of the finger anode.

3 and 4 are perspective views showing an example of a finger anode in which an anode support 8 is attached inside the U-shaped finger anode 2 shown in FIGS. 1 and 2. FIG.

It is preferable that at least one anode support 8 is attached within 200 mm of the tip 9 of the finger anode 2 and the joint between the finger anode 2 and the power supply body 4, respectively. Furthermore, the finger anode may be attached at two or three locations so as to divide its length equally. The installation method is not particularly limited, but each finger anode is taken out from the anode chamber, and the upper
An anode support 8 that matches the width and length of the finger in the vertical direction may be inserted through the lower finger opening 10 and the upper and lower ends may be joined and fixed, or the finger anode tip 9 may be inserted in the vertical direction. Cut the finger anode into two anode plates,
A method may be used in which each anode plate is pushed apart, the anode support 8 is bonded and fixed to one of the anode plates, and after the anode support is attached, the tip of the finger is bonded and fixed again. When performing this cutting process, there is an advantage that the distance from the cathode, which is the opposite electrode, can be arbitrarily adjusted by widening the fingers and width of the anode support.

In addition, when using an electrolytic cell in which the finger anode is attached with the tip of the finger anode cut off and the two anode plates expanded toward the finger anode side in order to narrow the distance from the cathode, It is extremely easy to attach and process the anode support 8 as described above without the complicated operation of attaching and detaching individual finger anodes, and to join and fix the cut finger tips to each other via the bridging plate 11. be.

Any material can be used for the anode support as long as it has chlorine resistance, but titanium, which is the same as the anode base material, is easy to bond and install.
Among them, preferred. Further, a material coated with an anode active material may be used as the anode support. The shape of the anode support can be any shape, such as a prismatic column, a hollow pipe, or a perforated plate. Among these, it is preferable to use a hollow pipe because it functions as a downcomer that promotes circulation of the anolyte. Further, when a pipe is used, it is preferable to attach the pipe to the finger anode so that it is a point joint rather than a surface joint. Next, the cation exchange membrane is attached to a bipolar diaphragm electrolytic cell containing the anode finger having the anode support described above.

In the present invention, the cation exchange membrane is constructed by covering each finger anode with a bag-like cation exchange membrane, and instead of sealing them individually, the open ends of adjacent bag-like cation exchange membranes are A continuous bag-shaped cation exchange membrane is manufactured by joining the membranes with a sheet for the outer flange by joining them together using heat and pressure, or by splicing them together with a sheet that is easily heat-sealed. The bag-like membrane is placed over the finger cathode and sealed around the finger cathode at the flange of the electrolytic cell.

When performing electrolysis using a bipolar electrolytic cell, the voltage applied between the electrolytic cells is usually very high, 200 to 800 volts, and the so-called leakage current that flows in and out through the common header is larger than in the case of a monopolar electrolytic cell. Therefore, if the individual finger cathodes and cation exchange membranes are sealed using a so-called internal mechanical seal method using a metal that is resistant to electrolyte, the durability of the sealing material itself will be reduced over a long period of time. Regardless of the nature of the problem, there is a great risk of problems such as seal failure due to local corrosion of the sealing material due to leakage current, as well as contamination of impurities into the electrolytic product and reduction in current efficiency.

On the other hand, when the present invention employs a method in which the cation exchange membrane is sealed at the flange portion of the electrolytic cell, the above-mentioned concerns about contamination with impurities and reduction in current efficiency can be eliminated.

Furthermore, according to the configuration of the present invention in which the finger cathode is covered with a cation exchange membrane, the anode chamber becomes an open system in which the gas generated inside can freely escape, so that the chlorine generated in the anode chamber becomes This has the advantage that gas does not remain in the anode chamber and the cation exchange membrane is not damaged.

As the ion exchange membrane used in the present invention, any membrane made of a polymer containing a cation exchange group such as a carboxylic acid group, a sulfonic acid group, or a phosphonic acid group can be used. It is preferable to use a fluorine-containing polymer from the viewpoint of durability, heat resistance, etc.

Further, the ion exchange membrane does not necessarily need to have only one type of exchange group. Of course, it is also possible to use membranes with different ion exchange groups on one side and the other side, or membranes with a mixture of two or more types of exchange groups.

The cation exchange membrane having a continuous bag shape, which is one of the elements constituting the electrolytic cell of the present invention, can be manufactured using, for example, the method proposed in Japanese Patent Application No. 125849/1984 by the present applicant. Figure 5a
to e show examples of the manufacturing process.

To explain this process, first, a tetrafluoroethylene-hexafluoroallopicin copolymer (hereinafter referred to as "allopicin hexafluoride") is coated on the outer periphery of the cation exchange membrane sheet 12 (see Figure 5a).
(hereinafter referred to as FEP) and tetrafluoroethylene-perfluorovinyl ether copolymer (hereinafter referred to as PFA)
Frame sheet 13 such as
℃, a pressure of 0 to 40 kg/cm ² , and a time of 10 to 20 seconds (see Fig. 5b, the joined areas are indicated by dotted shading), and after roughly folding it in half. , side frame sheet 13 such as FEP
By joining them together, a bag-like cation exchange membrane unit having a rectangular parallelepiped shape with one side open is made (see FIG. 5c).

Next, the frame sheet 13 such as FEP on the edge of the bag-shaped opening is heated at a temperature of 150 to 300°C and a pressure of 1 to 20 kg/kg.
cm ² (see Figure 5 d), and then a continuous bag-like membrane is made by joining the flared parts of adjacent bag-like membranes under the above-mentioned bonding conditions (see Figure 5 e). ).

Separately, as shown in examples of manufacturing process diagrams in FIGS. 6a to 6c, each unit of bag-shaped cations as shown in FIG. 6a is placed on a separately prepared flare sheet 13 such as FEP. Openings suitable for fitting the exchange membrane 14 (corresponding to the one shown in FIG. 5d) are sequentially made (see FIG. 6b), and the bag-shaped membrane 14 is inserted into these openings. A continuous bag-shaped cation exchange membrane may be manufactured by joining the periphery of the membrane (the joints are indicated by dotted shading in FIG. 6c).

The bag-shaped membrane created in this way can withstand electrolysis for a long time because FEP and PFA sheets with extremely excellent adhesion and strength are used in the flared and bent parts. .

Also, polytetrafluoroethylene CF ₂ = CFO
(CF ₂ ) ₃ When using a cation exchange membrane in which the exchange group is a carboxylic acid group, typically a copolymer of COOCH ₃ , a continuous bag-like membrane is created with the exchange group in the form of an ester such as COOCH ₃ . In some cases, the sheet-shaped cation exchange membrane is folded in half and the ends of two of the three overlapping sides are the temperature
A bag-like membrane is produced by bonding at 130-300℃, a pressure of 1-30Kg/ ^cm2 , and a time of 10-20 seconds, and the open end of the bag-like membrane is bonded at 200-300℃, 1- 5Kg/
A bag-shaped cation exchange membrane having a flared flange portion is provided under conditions of cm ² , and the open peripheral flanges of adjacent bag-shaped cation exchange membranes are further bonded together under the above bonding conditions. The method can also create a continuous bag-like cation exchange membrane, which is a series of bag-like membranes.

The cation exchange membrane formed into a continuous bag shape as described above must be treated with sufficient care to avoid damage to the membrane due to rubbing between the finger cathode and finger anode and the bag-like ion exchange membrane. Attached to the electrolytic cell.

There are no particular restrictions on how to wear it, but
For example, a continuous bag-shaped ion exchange membrane is placed over the finger cathode, the cathode chamber is kept under reduced pressure, and the ion exchange membrane is tightly attached and integrated with the finger cathode, and then the finger anode in the anode chamber is The method of inserting and assembling the continuous bag-shaped ion-exchange membrane between the membranes is one of the preferred methods since there is no fear of damage to the continuous bag-shaped ion exchange membrane.

The cation exchange membrane installed in this way is attached to the cathode chamber flange when the electrolytic cell is finally tightened.
Completely sealed between the anode chamber flanges.

The bipolar electrolytic cell equipped with the continuous bag-like cation exchange membrane assembled as described above can generate caustic alkali in the cathode chamber by electrolyzing while supplying alkali chloride to the anode chamber.

Next, regarding the electrolytic conditions of the present invention, Figs.
The production of caustic soda by electrolysis of salt water will be explained as an example using the schematic diagram shown in the figure.

The saline solution to be supplied is supplied to the lower part of the anode chamber as shown in FIG. In this case, a feed nozzle 15 is provided on the lower flange of the electrolytic cell anode side,
It may be supplied from this nozzle, or an internal tube 17 with chlorine resistance may be supplied from the nozzle 16 provided at the upper corner.
The saline solution may be supplied to the lower part of the anode chamber using a
The generated chlorine gas 18 and fresh salt water 19 are extracted from the opposite upper corner.

By adopting such a method for supplying and extracting saline water in the anode chamber, the concentration of saline water in the anode chamber can be made uniform.

On the other hand, as shown in FIGS. 8 and 9, water or a dilute aqueous solution of caustic soda is supplied to the lower part of the cathode chamber. It is confirmed that by supplying the caustic soda aqueous solution from the lower part of the cathode chamber, the current efficiency of the resulting caustic soda becomes higher than when supplying it from the upper part. This is thought to be because the concentration of caustic soda in the cathode chamber becomes uniform and the current efficiency increases.

The method of supplying water or a dilute aqueous solution of caustic soda to the lower part of the cathode chamber using the nozzle 20 at the bottom of the side, which is installed as a nozzle for drawing out caustic soda in the case of the existing asbestos electrolysis method, is a modification of the electrolytic cell. This is preferable because it does not require . In this case, a method of supplying by attaching an internal supply pipe provided with a dispersion hole to the nozzle portion is more effective in making the concentration of caustic soda uniform in the cathode chamber.

Then, the generated hydrogen gas and caustic soda are sent to the upper nozzle 21 in a state where no gas phase exists in the cathode chamber.
One of the major features of the present invention is that the gas is extracted from the gas in a mixed state of gas and liquid.

The reason why hydrogen gas and caustic soda are extracted in a gas-liquid mixed state is as follows. That is, according to the studies of the present inventors, when hydrogen gas and caustic soda are extracted from the cathode chamber, they are extracted by gas-liquid separation, unlike the above method (specifically, hydrogen gas is extracted from the upper nozzle, and caustic soda is extracted from the cathode chamber). If a method is used in which iron is extracted separately from above the side of the cathode chamber, the concentration of iron in the caustic product is extremely high. This fact indicates that the gas-liquid separation method has been considered as an effective means for reducing pressure fluctuations within the cathode chamber, and furthermore, when the cathode and cathode chamber are made of mild steel, This is surprising considering that in order to prevent corrosion of mild steel by highly concentrated caustic soda, the preferred method was to reduce the area of the cathode chamber that comes in contact with the caustic soda aqueous solution, or in other words, to increase the gas phase area within the cathode chamber. It is the right thing to do. According to the findings of the present inventors, this is completely different from such conventional understanding, and rather, extracting the hydrogen gas and caustic soda generated in the cathode chamber from the upper nozzle of the cathode chamber in a gas-liquid mixture state is the best way to remove the hydrogen gas and caustic soda from the caustic soda. It has become clear that it is effective in lowering the concentration of iron, and based on this knowledge, the above configuration, which cannot be adopted in common sense from the conventional technology, is adopted.
This led to the adoption of the characteristic configuration of the present invention, in which the mixture of gas and liquid is extracted from 1.

The present invention also maintains the liquid level in the cathode chamber during electrolysis at the level of the gas-liquid separator 22 connected to the nozzle shown in FIG. 9, while keeping the liquid level in the anode chamber lower than the liquid level in the cathode chamber. There is another major feature in keeping the temperature low.

As a result, the cation exchange membrane is pushed toward the anode chamber due to the difference in specific gravity between the liquid in the cathode chamber and the liquid in the anode chamber, and this satisfies the conditions for lowering the cell voltage. It is.

In addition, in response to this, for example, as explained in FIGS. 3 and 4, it is recommended to attach an anode support to the finger anode to eliminate the risk of the finger anode being dented by pressure from the cathode chamber side. . As a result, saline solution is stably supplied to the anode chamber inside each finger anode,
Furthermore, since a narrow distance between electrodes is maintained, it is possible to electrolyze saline water with high current efficiency and low cell voltage.

In addition, regarding the electrolytic conditions other than the conditions described above, the conditions when using a cation exchange membrane known so far can be applied. For example, the electrolysis temperature is 50
~95°C, current density is 10~30A/ ^dm2 , and caustic soda concentration is 20~40wt%, but the preferred conditions are 85~95°C, 15~25A/ ^dm2 , and 30~95°C, respectively.
It is 38wt%.

(Effects of the invention) As explained above, by using a bipolar diaphragm electrolytic cell that used an existing asbestos diaphragm, instead of asbestos as the diaphragm, cations formed into a continuous bag shape were used. An exchange membrane is placed over the finger cathode, and the area around this cation exchange membrane is
In an electrolytic cell assembled by tightening and sealing the surrounding flange of the electrolytic cell, alkali chloride is supplied to the lower part of the anode chamber, water or caustic alkali is supplied to the lower part of the cathode chamber, and the generated caustic alkali and hydrogen gas are supplied from the upper part of the cathode chamber. By extracting gas and liquid in a mixed state and performing electrolysis by keeping the liquid level in the anode chamber lower than the liquid level in the cathode chamber during electrode operation, electrolysis can be achieved with extremely low cell voltage. The caustic alkali obtained from the cathode chamber becomes highly pure with extremely low iron and alkali chloride contents, and this has the excellent effect of being able to achieve this while maintaining stable current efficiency over a long period of time. In addition, since a cation exchange membrane is placed over the finger cathode, the anode chamber is an open system for generated chlorine gas, so chlorine gas does not accumulate in the anode chamber or bag-like membrane. Therefore, the durability of the film is also excellent.

The production method of the present invention is particularly effective for the production of potassium hydroxide from potassium chloride and the production of caustic soda from saline solution, and is especially useful as an invention that provides excellent effects on the production of caustic soda from saline solution.

(Example) Hereinafter, more specific configurations and effects of the present invention will be explained using examples.

Example: This is a finger anode for an existing bipolar diaphragm electrolyzer, and the sides are made of 1/2 mesh titanium expanded metal coated with ruthenium oxide, with a height of 1220 mm, a length of 335 mm, and a U-shaped cross section. The tip of the finger anode is cut with a gas cutter, and the anode plate is welded to the power supply body.
The position of mm was bent outward. Then, the distance between the anode plates is widened so that the distance from the U-shaped bag-like finger cathode, which has a cross-sectional size of 335 mm in length, a width at the tip of 16 mm, and a width at the base of 25 mm, is 2.5 mm. did. Then, a titanium pipe of 1220 mm, inner diameter 28 mm, and outer diameter 31 mm was attached to the inside of the center of this anode plate by TIG welding, and then cut into two pieces.
The tips of the two anode plates are coated with ruthenium oxide, which has a smooth surface and has a thickness of 1.5 mm.
It was fixed by TIG welding via a bridge plate with a length of 1220 mm, which was manufactured by bending an expanded rolled mesh made of titanium with a diameter of 1 mm.

44 of the finger anode modified in this way
A continuous bag-shaped cation exchange membrane having carboxylic acid groups prepared by the following method was attached to a bipolar electrolytic cell equipped with a single finger cathode and a finger cathode.

Polytetrafluoroethylene CF ₂ = CFO
A cation exchange membrane made of a copolymer of (CF ₂ ) ₃ COOCH ₃ is formed into a bag shape using a heat fusion method, and then a flare is attached around the opening under heat and pressure, making the bag depth 340 mm. , length 1230mm, width at the tip of the bag 25mm
A bag-like membrane with a bag opening width of 45 mm was prepared.

Next, the adjacent flare parts of these 44 bag-like membranes were joined together using a heat fusion method to produce 44 continuous bag-like membranes with a pitch of 65 mm at the tips of the bag-like membranes. The flange portion was attached by heat-sealing the same copolymer sheet as the membrane.

The bag portion of the 44 continuous bag-shaped ion exchange membrane thus manufactured was previously smoothed with a file to remove protrusions and edges around the tip of the finger cathode. It was placed over the finger cathodes of a bipolar electrolytic cell equipped with 44 finger cathodes each having a finger root width of 45 mm and a tip width of 16 mm.

After covering the finger cathode with the ion exchange membrane, the ion exchange membrane flange was sealed between the cathode chamber flange and the degree of vacuum in the cathode chamber was reduced to −50 mmH ₂ O.
I aspirated it so that it was. The degree of vacuum in the cathode chamber was maintained at -50 mmH ₂ O, and the ion exchange membrane was kept in close contact with the finger cathode at a height of 1200 mm.
mm, length 330 mm, finger part maximum width 35 mm, and a bipolar electrolytic cell was assembled by incorporating a finger anode with an internal anode support into the anode chamber. After this, reduce the pressure inside the cathode chamber by +100mm.
The change in pressure inside the anode chamber was examined under a pressurized state of H ₂ O, but no increase in pressure inside the anode chamber was observed even after being left for 20 minutes, confirming that there was no damage to the ion exchange membrane.

27wt% in the cathode chamber of the electrolytic cell assembled in this way.
of caustic soda was supplied, 305 g of saline solution was supplied to the anode chamber, and the cation exchange membrane was hydrolyzed at 70° C. for 40 hours under the following conditions.

305 g of saline solution was supplied to the lower part of the anode through a nozzle provided in the upper corner of the anode chamber using an internal tube, and chlorine gas and fresh salt water were extracted from the nozzle in the upper corner on the opposite side. On the other hand, 31wt% caustic soda was supplied from a nozzle installed at the bottom of the side of the cathode chamber, and hydrogen gas and caustic soda were extracted in a gas-liquid mixture from a nozzle at the upper corner. At this time, a gas-liquid separator was installed above the upper outlet nozzles of the anode chamber and the cathode chamber, respectively, so that the cathode chamber liquid level was 100 mm higher than the anode chamber liquid level.

When electrolysis was carried out at 90℃ by applying a current of 72kA, on the 10th day, the cell voltage was 3.37V and the voltage from the cathode chamber was
32.3wt% caustic soda was obtained with a current efficiency of 95.7%, and the salt concentration in the caustic soda was 12ppm.
Also, the iron concentration was very low at 0.65ppm.

These electrolytic performance values were stable even after 6 months of long-term operation, with a cell voltage of 3.38 volts and a current efficiency of 95.4% for 32.1% caustic soda. The salt concentration in the caustic soda was 10 ppm, and the iron concentration was 0.60 ppm.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an existing bipolar diaphragm electrolyzer;
Fig. 2 is a perspective view of a finger anode of an existing bipolar diaphragm electrolytic cell, Figs. 3 and 4 are perspective views showing examples of finger anodes used in the present invention, and Figs. 5 a to e. and FIGS. 6 a to 6 c are explanatory diagrams showing an example of the manufacturing process of the continuous bag-shaped ion exchange membrane in the present invention, FIG. 7 is a diagram showing the liquid level on the anode side of the present invention, and FIGS. FIG. 9 is a diagram showing the liquid level on the cathode side of the present invention. 1... Bulkhead, 2... Finger anode, 3...
...power supply body, 4 ... power supply rod, 5 ... cathode back screen, 6 ... finger cathode, 7 ...
Cathode chamber side flange part, 8... Anode support, 9...
...Finger anode tip, 10...Finger anode opening, 11...Bridging plate, 12...
... Cation exchange membrane sheet, 13 ... Frame sheet, 14 ... Bag-shaped ion exchange membrane, 15 ... Anode chamber lower feed nozzle, 16 ... Anode chamber upper nozzle, 17 ... Internal intubation tube, 18 ... Produced chlorine gas, 1
9... Fresh salt water, 20... Cathode chamber lower nozzle, 21
... Cathode chamber upper nozzle, 22 ... Gas-liquid separator.

Claims (1)

[Claims] 1. A large number of finger anodes extending from one of the opposing partition walls of an electrolytic cell and a large number of finger cathodes extending from the other opposing partition wall are inserted into each other in a staggered manner. Furthermore, a continuous bag-shaped cation exchange membrane is placed over the finger cathode, and the periphery of the cation exchange membrane is placed near the base of the finger cathode of the electrolytic cell. A multi-electrode electrolytic cell is used, in which the inside of the tank is divided into an anode chamber and a cathode chamber by attaching and sealing the flange on the cathode chamber side, and electrolysis is carried out while supplying alkali chloride to the anode chamber. A method for producing caustic alkali in which a caustic alkali is produced, wherein water or low concentration caustic alkali is supplied from the lower part of the cathode chamber, and electrolysis is performed in a state where no gas phase exists in the cathode chamber. The caustic alkali and hydrogen gas generated are extracted in a gas-liquid mixture from an upper nozzle provided in the upper part of the cathode chamber, and the level of the liquid in the anode chamber during electrolysis is maintained below the level of the liquid in the cathode chamber. A method for producing caustic alkali.