JPS633956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane.

In general, vertical electrolytic cells using cation exchange membranes are often used, but a special example is a horizontal electrolytic cell with the anode at the top, a water retainer placed below the membrane, and the cathode. Types that replenish water to the tank, and three-chamber electrolyzers with a cathode chamber at the top are known.

However, these known horizontal electrolytic cells require special means for holding the electrodes and membrane horizontally, or special methods for replenishing the liquid.
The cell voltage, current efficiency, etc. could not be said to be satisfactory either.

The inventors of the present invention have conducted intensive studies on a method of electrolyzing a cell with a simple structure while ensuring an extremely low cell voltage, and as a result, have completed the present invention as outlined below.

That is, the present invention provides a method for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane, which includes a porous cathode, a cation exchange membrane, and at least a substantially flat portion on the surface facing the cation exchange membrane. Using an electrolytic cell with a structure in which three porous anodes are kept parallel and tilted toward the anode side from the vertical direction,
This is an ion exchange membrane method for electrolyzing an aqueous alkali chloride solution, characterized in that electrolysis is carried out with at least a cation exchange membrane brought close to the flat portion of the anode.

Although the present invention is an electrolysis method using an electrolytic cell having a special internal structure, it is applicable to both monopolar and bipolar electrolytic cell types.

The electrolytic cell used in the present invention first has an anode,
The three surfaces of the membrane and the cathode remain parallel, and at least these three surfaces are tilted as they are, and the tilted state is always tilted toward the anode side from the vertical direction.

In this case, the electrolytic cell itself may be tilted, and the anode-membrane-cathode tilt may be measured as described above.
Alternatively, the anode-membrane-cathode inside may be simply tilted without tilting the electrolytic cell itself. When the electrolytic cell or the electrodes and membranes inside it are tilted in this way, when the direction of the tilt is toward the anode side,
Cell voltage decreases. In particular, a remarkable phenomenon of cell voltage drop is observed in a certain range of tilt angles, and the preferred angle is 85° to 30°, and the more preferred range is 75° to 45° (90° is Vertical, assuming 0° is horizontal). On the other hand, if it is tilted toward the cathode, on the other hand, an increase in cell voltage is observed, making it impossible to achieve the desired effect.

Both the cathode and anode used in such an electrolytic cell with a tilted structure are porous, and among these, the porous anode having the structure described below is particularly suitable.

That is, it has holes uniformly large enough for gas bubbles to escape easily, with a porosity ranging from 20 to 70%, and at least a substantially flat portion on the porous surface facing the membrane. . Of course, the surface opposite to the membrane may also have such a flat portion. An electrode having such a flat part is preferably one in which when the cation exchange membrane is brought into contact with the anode during electrolytic operation, the area of the contact part is about 20% or more of the apparent inside of the electrode. Usually, this is a product made by rolling an expander net with a roll or press, or a punching plate. In addition to this, it is also possible to use a net with a fine mesh made of thin wires. For example, a 100 to 10 mesh net with a wire diameter of about 0.2 mmφ is used to prevent the contact part of each thin wire with the cation exchange membrane. The area ratio corresponds to the above ratio.

On the other hand, the cathode used in the present invention may be a porous cathode having a flat portion at least on the surface facing the cation exchange membrane, similar to the above-mentioned anode, or a porous cathode having no such flat portion. It may be a normal porous cathode.

The anode, membrane, and cathode, which maintain the above-mentioned inclined state, are arranged in parallel, and at least when the electrolytic cell is operated, the cation exchange membrane is brought close to the flat part of the anode.
That is, it is located near or in contact with the anode.

In this case, the internal structure of the electrolytic cell may be such that the anode and the membrane are in contact with each other, or the anode and the membrane may have a structure that maintains a small distance so that the internal pressure of the cathode is lower than the internal pressure of the anode during operation of the electrolytic cell. The membrane may be held high to press it against the flat part of the anode, or both may be used in combination.

On the other hand, the cathode and the membrane may be in contact with each other, or they may be arranged so as to maintain a slight distance therebetween.

In general, bubbles generated at the cathode and bubbles generated at the anode differ in their size and amount; fine bubbles are observed at the cathode, and it is easier for the bubbles at the anode to separate and rise from the site where they are generated.

According to the method of the present invention, since the cathode is tilted and substantially located at the top, air bubbles can freely rise in the liquid without any obstructions, and therefore air bubbles are removed more effectively than in a vertical electrolytic cell. will be held. On the other hand, at the anode, there is a cation exchange membrane and a cathode at the top, and the bubbles are obstructed by this, but since the anode with a flat part is close to the membrane, they are interposed between the membrane and the anode and stagnate. There are almost no bubbles, and they rise along the back surface of the anode as relatively large bubbles, making it possible to perform degassing that is comparable to the bubble separation effect of conventional rigid electrolytic cells.

Therefore, in combination with the bubble separation effect at the cathode, the cell voltage can be significantly reduced.

In addition, the presence of a flat portion, especially in the anode, is effective in ensuring effective current flow by shortening the current flow path due to contact with the membrane.

In the electrolysis method of the present invention, it is desirable to operate the cathode chamber pressure at a higher pressure than the anode chamber pressure.

By doing so, the contact of the membrane with the anode becomes excellent, and the increase in bubble separation in the cathode chamber becomes more effective, thereby making it possible to further effectively reduce the cell voltage.

The pressure difference is more than 100mmH ₂ O, especially 300mmH ₂ O
The above is preferable, and furthermore, the pressure in both the anode chamber and the cathode chamber of the electrolytic cell is increased to about 0.6 Kg/cm ² or more, and the cathode chamber pressure is maintained higher than the anode chamber pressure as described above. It will be even more effective if you do so.

The exchange membrane used in the present invention is preferably a fluorine-containing one that has corrosion resistance against the anolyte, chlorine gas, catholyte, and hydrogen gas,
Ion exchange groups include those containing sulfonic acid groups, carboxylic acid groups, amide groups, phosphoric acid groups, and other groups, as long as they can be used for alkali chloride electrolysis.
There are no restrictions.

The anode contains at least a platinum group metal or a platinum group oxide, and further contains a valve metal oxide, antimony,
Any material can be used, even if it contains a cobalt-based oxide, as long as it has corrosion resistance against alkali chloride electrolysis and has a low chlorine overvoltage.

In addition, as the cathode, iron, alloys mainly composed of iron, nickel alloys mainly composed of nickel, etc. can be used, and on top of these, electroplating, electroless plating, pyrolytic baking, suitable binder and low-temperature coating can be used. It is possible to use a so-called low hydrogen overvoltage cathode, such as a combination with particles that exhibit hydrogen overpressure.The shape of the cathode is so-called porous, such as a punched plate, expander glass, mesh, etc. .

Further, a preferable shape is a flat shape similar to the above-mentioned anode.

The present invention will be described below with reference to the drawings, and in each drawing, parts with common figure numbers indicate the names of the same members.

FIG. 1 is a schematic longitudinal cross-sectional view showing the simplest structure of an ion exchange membrane electrolytic cell used in the method of the present invention, in which a cation exchange membrane 1 is used to form an anode chamber 3 and a cathode chamber 2.
It is divided into. The cathode chamber 2 has a catholyte inlet 6
Water or dilute alkali is supplied to the cathode chamber, and caustic alkali and hydrogen gas are produced here. The anode chamber 3 has an anolyte inlet 8
An aqueous alkali chloride solution is supplied to the anode chamber, chlorine gas is generated at the anode 5, and is discharged from the outlet 9 together with the dilute aqueous alkali chloride solution. The cathode 4, cation exchange membrane 1, and anode 5 in this electrolytic cell are arranged parallel to each other, and the structure is such that the cathode 4 is located above the anode 5 due to the inclination of the electrolytic cell itself. At least the anode 5 has a flat shape and is in contact with the cation exchange membrane 1.

The preferred angle α between the horizontal line of the electrolytic cell and the electrode surface is in the range of 85 to 30°.

It is also desirable that the pressure difference between the upper part of the cathode chamber (outlet nozzle attachment part) and the upper part of the anode chamber be at least 100 mmH ₂ O higher in the cathode chamber than in the anode chamber during electrolysis operation. When gas and liquid are discharged from one nozzle as shown in this figure, the pressure is at the part where the gas and liquid are mixed,
In cases where gas and liquid are discharged separately, this is the pressure at the top of the liquid.

FIG. 2 shows a schematic vertical cross-sectional view, partially cut away, of a bipolar electrolytic cell tilted. Current is supplied from the anode side at the bottom of the slope and is sent to the anode 5 through the conductor 11. Further, it is sent through the membrane 1 to the cathode 4, then through the conductor 11 to the anode, and finally from the cathode at the end through the conductor 11 to the rectifier or the next electrolytic cell. The conductor 11 is made of a catholyte corrosion-resistant material in the cathode chamber 2, and is made of an anolyte corrosion-resistant material in the anode chamber 3. Although this figure shows a type in which the anode and cathode penetrate through the partition wall and are electrically connected, the present invention is not limited to this. For example, a lead rod is inserted from the anode and cathode. The electrical connection may be made outside the battery case, or a Clyde plate made of titanium/copper/iron may be used, and the electrical connection may be made directly using ribs or the like.

FIG. 3 is a schematic vertical cross-sectional view, partially cut away, showing an example of a monopolar electrolytic cell. In this figure, both ends are anode chambers 3, and the anode chamber 3 and the cathode chamber 2 are arranged sequentially from the end, and finally ends with the anode chamber 3.
In the cathode chamber 2, one set of cathodes 4 are arranged for each membrane 1, and the cathode chamber has a V-shape. The cathode chamber is electrically connected to the cathode 4 from a cathode lead rod 13 via a cathode conductor 15.

In the anode chamber 3, one set of anodes 5 is arranged for each membrane 1, the terminal anode chamber has one set of anodes 5, and the intermediate anode chamber 5 has two sets of anodes 5. The shape of the anode chamber is inverted V-shaped in the middle, and at the end,
It has an inverted V shape cut near the center. The anode chamber is electrically connected to the anode 5 from an anode lead rod 12 via an anode conductor 14 . The inclination 2 of this container is shown as the angle of the V-shaped part with respect to the horizontal plane.

Examples will be described below.

Example 1 Multipolar electrolytic cell 5 with an effective height of 1 m and an effective area of 1 m ²
It consists of a cell (5 membranes), and the anode chamber has a pH≒9.
Approximately 300g/KCl is supplied, and approximately 200-210g/KCl is discharged from the anode chamber. Approximately 25% of KOH at 0.5 m ³ /h is circulated to the cathode chamber.
By heating this circulating fluid, the temperature is maintained at 85°. The electrolytic cell used in this example is based on the tilted electrolytic cell having the structure shown in FIG. 2, but the upper part of the anode chamber is a mold, so that the liquid and gas are discharged separately. The upper part of the cathode chamber has a similar structure, but the gas and liquid are mixed and extracted. By adjusting the pressure on the gas phase side, the pressure in the upper part of the cathode chamber can be changed. The anode is titanium expander SV6 x LW12 x t1.5 x S1.5
Pt/ A material coated with 0.6μ of Ir (7/3wt%) was used. The cathode was made of stainless steel and had similar dimensions and shape. The connection between the anode and the cathode is of the type that passes through the partition plate, and the anode side and the cathode side are made of materials that are corrosion resistant to each liquid, and the structure is such that there is no leakage of both liquids.

Fluorine-containing grease was applied to the anode side without using a gasket, and a 2.5m/m neoprene gasket was used on the cathode side, so that the distance between the poles was approximately 2m/m. As the cation exchange membrane, Nafyon 415 manufactured by DuPont was used. The pressure in the cathode chamber is lower than that in the anode chamber.
Operation was carried out at 2.5KA with a high temperature of 500H ₂ O. Figure 4 shows the results of a test conducted by changing the inclination of the container every day from 3 weeks after energization. However, the voltage indicates the voltage for 5 cells.

Example 2 Using the battery case of Example 1, only one cell on the anode side was made into a lath net without being rolled, and the battery was operated at an inclination of 60°.

The voltage of 4 cells rolled is 3.28~
Those in the 3.32V range and not rolled are
It showed 3.46V.

Furthermore, when I changed the cathode side to one that does not have a roll, the voltage was 3.51V.

Example 3 Using the same equipment as in Example-1, tilt the battery case.
Figure 5 shows the results of examining the change in cell voltage due to the difference in pressure between the cathode and anode chambers at an angle of 80°.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic vertical cross-sectional views explaining each aspect of the electrolytic cell used in the present invention. Figure 1 shows the basic structure, Figure 2 shows the bipolar electrolytic cell, The figure shows a monopolar electrolytic cell. FIG. 4 is a graph showing changes in cell voltage with respect to changes in the inclination angle of the electrolytic cell used in the method of the present invention, and FIG. 5 is a graph showing cell voltage due to the pressure difference between the cathode chamber pressure and anode chamber pressure in the electrolytic cell. It is a graph showing changes in. 1...Cation exchange membrane, 2...Cathode chamber, 3...Anode chamber, 4...Cathode, 5...Anode, α...Inclination angle.

Claims (1)

[Claims] 1. A method for electrolyzing an aqueous alkali chloride solution using a cation exchange membrane, including a porous cathode, a cation exchange membrane, and a porous cathode having a substantially flat portion at least on the surface facing the cation exchange membrane. Using an electrolytic cell with a structure in which the three anodes are kept parallel and tilted toward the anode from the vertical direction,
1. A method for electrolyzing an aqueous alkali chloride solution using an ion exchange membrane method, characterized in that electrolysis is carried out with at least a cation exchange membrane brought close to the flat portion of the anode.