JPS5848685A - Porous electrode for electrochemical reaction accompanied by generation of gas and electrolytic process using it - Google Patents

Abstract

PURPOSE:To drop the bath voltage in the electrolysis of an aqueous soln. of alkali metallic salt or the like accompanied by the generation of gas by providing water repellency to the inner surfaces of the pores of a porous electrode to easily remove gas generated from the electrode to the rear. CONSTITUTION:A porous electrode is used as at least one gas generating electrode between a pair of a cathode and an anode used in an electrolytic cell for electrolyzing an aqueous soln. of alkali metallic salt or the like, and water repellency is provided to at least part of the inner surfaces of the pores of the porous electrode. The water repellent porous electrode is brought close to a diaphragm, and the distance between the electrode and the diaphragm is made practically zero to bring them into contact with each other. Thus, gas generated from the surface of the porous electrode is rapidly removed to the rear, and by the rapid removal combined with the short distance between the electrodes a drop of the bath voltage can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION When a porous electrode is used as an electrode that generates gas through an electrode reaction, the present invention promptly eliminates the gas generated from the porous electrode to the back surface of the pair 1#i and III. The present invention provides a porous electrode that suppresses disturbances in current distribution and excessive increases in voltage drop due to gas and obtains a low electrolytic voltage, and a method for electrolyzing an aqueous alkali metal salt solution using the electrode.

Generally, in electrochemical cells used industrially, there are many cells in which electrochemical reactions accompanied by gas generation occur.

For example, hydrogen gas in water electrolysis or chlorine gas in salt electrolysis, etc., are used for the direct purpose of obtaining these gases, or are used separately! Some of them can be obtained as -J organisms, such as hydrogen gas produced by I-method salt electrolysis or sodium chlorate electrolysis. Well, in order to prevent the reaction products at one of the anodes from diffusing, migrating, or flowing to the other, a diaphragm is placed between the cathodes and the anodes, and specific ions can be selected. Electrochemical cells, which are divided into an electrode chamber and an anode chamber by placing an ion exchange membrane in the diaphragm to allow the electrolyte to permeate, are also widely used industrially.

In an electrochemical cell that is divided into a cathode chamber and an anode chamber by a partition 11jiifK, and in which an electrode reaction accompanied by gas generation occurs, when gas, which is an electrically insulating eyelid, stagnates between the cathode and anode, it causes a voltage drop in the electrolyte. It is well known that in such electrochemical cells, efforts have been made to use porous electrodes to facilitate gas removal to the rear surface.

In particular, the electrolysis of aqueous solutions of alkali metal salts (411) is typical of the above-mentioned type of electrochemical cell, and in particular, the electrolysis of aqueous sodium chloride solutions involves the production of chlorine and hydroxide.
Because Jum is of great industrial importance, it is carried out in large-scale industrial facilities.

As one of the electrolysis methods, among the diaphragm methods, the ion exchange membrane method, which uses an ion exchange membrane in the diaphragm, is being developed and adopted as a measure for public buildings and as an energy saving process.

However, at present, it is difficult to obtain an electrolytic voltage of less than 55 V at a current density of about 50 A/d*''.For this reason, it is difficult for the ion-exchange membrane method and salt electrolysis method to truly secure its position as an energy-saving process. In order to achieve this goal, it is necessary to consider the big problem of how to reduce the electrolytic voltage while maintaining high current efficiency.

The main elements in the electrolysis voltage in this method are the decomposition voltage, the voltage drop due to the membrane, and the voltage drop due to each electrolyte in the cathode and anode chambers, but each of these ll! The formation is not independent of each other, and the gas bubbles generated from the electrode are connected to the #! of the electrode and diaphragm. The biggest obstacle to this method is that the presence and stagnation in the vicinity of or between the surfaces affects each of these elements in a complex manner, leading to an abnormal voltage rise.

Generally speaking, the shape of the electrode is so-called a porous electrode, such as expanded metal (a) or punched metal (b) as shown in Figure 1, in order to improve degassing and liquid mixing or stirring. ), gold-shaped (C), rod-shaped (d), or other shapes are adopted. This makes it easy to quickly remove the scum generated by the electrode reaction to the back surface between the cathode and anode using a gas lift effect or forced circulation method, and at the same time, a measure is adopted to promote the stirring effect of the gas.

Furthermore, not only porous electrodes are used, but also their
# Various attempts have been made to improve the shape of the L pole, its positional relationship with the film, and the distance and position between the cathode and anode, and various proposals have been made (% 1989-109899, 1982-114, etc.). No. 571, No. 55-16371, No. 53-102874, No. 54-60278
Publication No. 54-77285, etc.).

Although the various methods shown in the above-mentioned published patents are expected to have certain effects depending on their purpose, they must use electrodes with very limited shapes and require careful attention to their installation and operation. care must be taken.

To solve these difficulties, the present inventors have developed a commonly used expanded metal and punched metal.

As a result of various studies on the shape of various porous electrodes, such as wire mesh shape and rod shape, the size of their openings, and the effect of the distance between cathode and anode on bath voltage, we unexpectedly found that the shape of the electrode There is a very specific relationship between the shortest diameter L of the opening of the porous electrode (Fig. 1) and the distance d between the cathode and anode, as shown in Fig. 2, almost unrelated to the aperture ratio etc. In other words, there is a relationship between the shortest diameter of the aperture and the bath voltage in which a minimum value of the bath voltage exists, and the shortest diameter of the aperture at which the bath voltage has a minimum value varies depending on the distance between the poles dK. , the minimum value of the bath voltage also changes. Then, if the optimal distance between poles is 4.4 and the distance between poles is *dt which is smaller than 4, and the distance between poles which is larger than 4 is 4, then the minimum value of the bath voltage is , the island vh value is higher than that when the distance between poles is 4.

In other words, a low bath voltage can be achieved by using a porous electrode with an appropriate shortest diameter of the opening (2≦L≦6■) and by maintaining an optimal interelectrode distance (5≦d≦4■). .

However, even with this method, there is a problem in that if the distance t between the poles is made too small below a certain limit, the bath voltage may increase as shown in track 1INAI in FIG.

The present inventors have developed a system in which a pair of cathodes and anodes face each other via an ion exchange membrane, in order to overcome the phenomenon that narrowing the gap between the electrodes below a certain limit would actually lead to an increase in the supply voltage.
We further investigated how the dimensional factors regarding the pores and electrode part of the porous electrode affect the bath voltage.

As a result, Il, the width of the pole M(
If a porous electrode with a diameter of 2 to 5 or more (Fig. 1) is used, it will not be possible to suppress the phenomenon of abnormal rise in bath voltage when the electrode gap is made extremely small, and the thickness of the ion exchange membrane used instead. It has been found that the above abnormal rise in bath voltage can be suppressed by using a porous electrode having an electrode portion width M corresponding to .

That is, the width M of the electrode part is 2 to 3 seconds! When using the above-mentioned normal porous electrodes, the relationship between the interelectrode distance and the bath voltage is as shown in curve A in Figure 5, whereas the relationship between the electrode distance and the bath voltage is less than 5 times the thickness of the ion exchange membrane used. If you use a porous electrode with an electrode width Mf of , the song shown in Figure 3! iB1, the abnormal increase in bath voltage when the electrode gap was made extremely small was suppressed, and a large decrease in bath voltage was achieved compared to curve M1.

As mentioned above, 1 The reason for this is not clear, but there is a unique relationship between the dimensional factors of the porous electrode and the thickness of the ion exchange membrane, and it is necessary to combine the appropriate dimensions of the two and minimize the gap between the electrodes. When narrowed, low bath voltages not obtainable with conventional methods were achieved. However, although the bath voltage decreases as the inter-electrode distance decreases, as shown by curve B in Figure 3, if the inter-electrode distance is reduced to a certain extent, the decrease in bath voltage becomes slower). However, a substantial decrease in bath voltage cannot be expected. Therefore, in addition to the dimensional factors of the electrodes and ion exchange membrane, the present inventors investigated the relationship between the conductivity of the ion exchange membrane and the bath voltage, and researched measures for lowering the bath voltage in this respect. As a result, they found that when the electrode gap was made extremely small by forming a layer with better conductivity on the surface of the ion exchange membrane used, the bath voltage was further reduced. In other words, by forming a highly conductive, low resistance layer on the film surface, we were able to change the curve A in Figure 3 to 1kA, and the -1 curve B to B2. .

Generally, when a diaphragm is placed between the cathode and the anode to cause an electrode reaction that involves gas generation at at least one of the cathode and anode, it is best to use a porous electrode for the gas generation electrode to lower the bath voltage. In order to achieve this, if the electrode gap is made as narrow as possible, this often results in an abnormal rise in bath voltage. The first possible cause is that the non-uniform current distribution occurs due to the porous a11IL pole. However, if the pores of the porous electrode are made smaller in order to prevent this, the bath voltage will actually increase as shown in FIG. This means that the generated gas is porous! This is because it does not come out smoothly from the hole in the pole to the back side. The generation of gas is expected to have the effect of stirring the liquid, but since it is an electrical insulator, it will shield the current in the liquid, and if it accumulates near the membrane or electrode surface, the shielding effect will cause This seriously disturbs the wLfIt distribution and causes an abnormal increase in voltage drop.

According to the research of the present inventors, by optimizing the dimensional factors of the electrodes and membranes and further forming a low-resistance layer on the membrane surface, the benefits of gas can be promoted and the harms thereof can be suppressed to some extent. As explained in FIG. 3, the bath voltage can be lowered. However, with these methods, when the gap between the electrodes becomes extremely narrow, the bath voltage increases (as shown by curve A in Figure 5).
, and At), the phenomenon in which the decrease in bath voltage due to decreasing the electrode gap becomes slower, if not increased (curves B and B in FIG. 3), has not been completely overcome.

Therefore, the inventors of the present invention considered that the current distribution can occur due to the porous electrode as shown in FIG. 1, #!
If L + Ml in Figure 1 is made smaller, and if a three-dimensional porous electrode with a spongy shape is used instead of the two-dimensional porous body as shown in the same figure, the current distribution attributable to the electrode structure will be Thinking that it should disappear, I used this to investigate the behavior of the bath voltage. As a result, it was found that the bath voltage rises extremely sharply where the inter-electrode distance is extremely small, as shown by curve C in FIG. The reason for this rapid rise is
This is because gas does not easily pass through the holes and gas cannot escape to the back surface. Therefore, the present inventors believe that a further reduction in bath voltage can be achieved by quickly expelling all the gas generated from the porous electrode to the back surface between the cathode and the anode, and we have proposed a method to improve the bath voltage by using the porous electrode. We continued our research with the challenge of whether it would be easier for gas to pass through the pores.

That is, as a result of intensive research into the effect of water repellent treatment on porous electrodes, the present inventors found that, for example, in the three-dimensional porous Celmet electrode introduced earlier, the relationship between the inter-electrode distance and the bath voltage was Picture song? By applying water-repellent treatment to something that would become an IMO, a large drop in bath voltage can be achieved as shown in C' in the same figure.
For the curves M1 and M in the figure, the rise of the bath voltage at the very small distances between the poles, such as A' and A/, respectively, is almost eliminated by water-repellent treatment, and furthermore, K The present invention was completed by discovering that curves B and B in FIG. 5 also exhibit substantially the same behavior as curve C' when subjected to water-repellent treatment.

The present invention will be explained in more detail below.

The water repellency treatment in the present invention refers to imparting water repellency to at least a portion of the inner surface of the pores of the porous electrode.

That is, as shown in FIG. 4, when a droplet is dropped on the surface, the gas-liquid contact angle θ is an obtuse angle (0>9♂).

As a means for imparting water repellency to porous electrodes, polyethylene and polytetraph at2 ethylene (hereinafter referred to as PTF) are used.
A hydrocarbon or fluorocarbon-based polymer material such as τ (referred to as E) is treated as described below. In the electrolysis of alkali gold chloride ll4t4 aqueous solution, the anode chamber is supersaturated with highly corrosive chlorine gas at high temperatures, and chloric acid and hypochlorous acid are also present, and the cathode chamber is filled with high [j alkali gas]. Therefore, it is necessary to select materials that are corrosion resistant and durable in these harsh environments.

In that sense, PTF'lii is the most preferable. FTP
K has a contact angle with water of 105 as measured by the present inventors.
It has a large angle of ~120° and excellent chemical stability.

However, when the present invention is applied to a system with a mild environment, it is possible to select materials that are inexpensive from an economical point of view.

One of the greatest features of the present invention is the reduction in bath voltage. By combining it with bath voltage reducing means that have been developed up to now, it is possible to achieve a synergistic effect with the effects of the bath voltage reducing means combined with the present invention without impairing the effects of the present invention in any way. , is clear from the explanation of FIG.

However, in applying the present invention, it is preferable to select the texture of the water repellent treatment that corresponds to the porous electrode to be used. For example, if the opening best diameter or hole diameter is 2.
The lifting platform to which this 8A is applied to the electrode with the shortest diameter or small pore diameter of ~3 holes or more, especially the porous 'WL electrode with α1- or less, has all the inner wall surfaces of the pores treated with water repellent treatment. do not have to. The reason for this is not clear, but if all the inner wall surfaces of the holes are treated to be water repellent, all the holes will be filled with gas, making it difficult to sufficiently supply the water bath liquid used for the electrode reaction to the electrode reaction area. The platform for such porous electrodes should be partially water-repellent treated instead of the entire inside of the pores.
Alternatively, the effects of the present invention can be exerted by separately making holes of 2 to 5 cm or more.

The porous electrode used in the present invention is an expanded metal or a) punched metal as shown in FIG.

It corresponds to the pore size, whether it is a wire mesh, rod-like or other two-dimensional shape, a three-dimensional cavernous shape, or a three-dimensional shape made by press molding or sintering powder. It can be used by applying water repellent treatment. As a special form, a two-layer structure of a porous water-repellent layer and a porous electrode layer, such as gold tII4 or carbon powder deposited on PTFKp paper, is also adopted.

The method of water repellency treatment in the present invention is not particularly limited. When using PTFKi as a water repellent material, a simple method is to immerse it in a PTFI suspension, heat treat it, and then cover it with PTIIFE.

When covering the entire inside of the hole, it is best to repeat the above method or use a suspension of Takano Shika. Furthermore, when partially injecting the inside of the hole, a low-concentration suspension can be used, or a granular or powdered electrode material and a PTFE powder or suspension can be mixed and press-molded. Alternatively, a method of sintering may also be adopted.

When using the electrode according to the present invention, the effect of reducing the bath voltage is characteristically exhibited when the distance between the cathode and the anode is made extremely small. In other words, conventional porous electricity @! If an abnormal rise in bath voltage occurs when the distance m between poles is reduced using
By imparting water repellency according to the present invention to this, the abnormal rise in bath voltage can be suppressed.

Furthermore, if the water-repellent treatment according to the present invention is applied to an electrode for which the bath voltage does not decrease further even if the distance between the electrodes is reduced beyond a certain limit, the bath voltage will further decrease as the distance between the electrodes is further reduced. As shown in No. 31, the lowest bath voltage is obtained when the diaphragm, cathode, and anode are brought close or in close contact with each other to the extent that the distance between the electrodes becomes substantially zero. In electrodes that can make the inter-electrode distance substantially zero, the effect is maximized when the inter-electrode distance is made substantially zero.

When the porous electrode according to the present invention is used in an electrolytic cell in which a diaphragm is placed between a pair of cathodes and anodes, the cathode and anodes are operated with a very narrow distance between them, or when the distance between the cathodes and the anodes becomes substantially zero. When operating the diaphragm and the cathode and/or the anode in close proximity or close contact with each other, there are no particular limitations on the method of bringing the diaphragm, cathode, and/or anode into close proximity or close contact with the vagina.

The diaphragm can be pressed against either the cathode or the anode to make a close contact using a method known so far, such as the difference in fluid pressure between the yin and yang chambers, or the mechanical Means for pressing the electrodes is also adopted. Alternatively, the diaphragm and the porous electrode according to the present invention are bonded together by a method such as pressure bonding.
A pre-integrated product can be attached to the electrolytic cell, or a method can be adopted in which the diaphragm and the porous electrode are integrated via a water- and ion-permeable layer.

From the present QIJK, for example, as the electrolytic conditions when electrolyzing an aqueous solution of an alkali metallogenide, various conditions already known can be appropriately adopted. For example, the electrolysis temperature can be from room temperature to 95°C. The current density can be operated at a current density of 10 to 80 A/mu2, but the effect is particularly great when the current density is 30 A/mu2 or more.

These conditions are desirably determined to be economically advantageous in terms of f#, such as bath voltage and current efficiency.

The present invention is not only applicable to the electrolysis of alkali metal compound bath solutions, but also applies to water electrolysis, chloric acid electrolysis production, etc., using the porous electrode according to the present invention under the respective optimum conditions. It is possible to use and apply the electrolysis method according to the invention using the porous electrode according to the invention.

The porous electrode according to the present invention and the electrolytic method according to the present invention suppress various troubles caused by the generated gas in an electrochemical cell that utilizes the IL electrode reaction accompanied by gas generation, and have a stirring effect due to the gas. It provides an extremely effective means to promote and utilize the technology, and has great significance as a true technological innovation in this field.

The present invention will be explained in more detail below using Examples and Comparative Examples, but it goes without saying that the scope of the present invention is not limited only to these Examples.

Extended band metal with the shortest opening diameter L = 3■ (Fig. 1 a)
) titanium coated with rudenium oxide at L, yt anode resistant,
An electrolytic cell was constructed by disposing a mild steel cathode in the shape of a punched metal L-4 (FIG. 1b) and an ion exchange membrane between them.

The following water repellent treatment was applied to the negative electrode.

That is, polytetrafluoroethylene, manufactured by Daikin Industries, Ltd., Polyflon Dispergylan D-1 (Polyflon average particle size approximately α3 μ, contains Polyflon particles! Ik 60%)
) was diluted with pure water to a strength of 10%. After repeating this operation five times, one side was polished with sandpaper to remove the Teflon coating.

The device was placed in an electrolytic cell so that the peeled surface faced the ion exchange membrane. If the membrane is not in a fixed position between the cathode and anode and moves due to slight pressure fluctuations during operation, or if wrinkles occur, the bath voltage will not be stable and reproducible data will not be obtained. However, since this would have a negative impact on the current efficiency, the membrane was installed in a sufficiently stretched state, and the membrane was fixed in position by pressing it against the anode side of the membrane 1r with a hydraulic pressure difference of 50 cm.

Operation was carried out under the 'tj/L solution conditions shown in Table 2 with various distances between poles. The results are shown in Table 1. First front pole distance 111d (m) 1 1.5 2
3 4 bath voltage (V) Δ48 545
A46 549 As seen in Table 1 of A51,
The bath voltage does not change much over a wide range of inter-electrode distance d=1 to 4 square meters, and even if d is narrowed to 1 square inch, the rise of the bath voltage cannot be provided.

This means that even if there is some distribution in the distance between the poles in an actual plant, it will not cause variations in the bath voltage and stable operation will be ensured, which is extremely advantageous for the operation of the actual plant.

On the other hand, when used in a shade +* that has not been subjected to water repellent treatment, as shown in Comparison 1 below, when the distance d between the electrodes is in the range of 3 to 4, it is 546 to 549 (v). The bath voltage is approximately the same as that in this example, but as d is decreased, the bath voltage becomes The phenomenon of increasing is remarkable.

Note that at times d-3 to d-4-, the bath voltage of this example shows a slightly higher value than that of Comparative Ga 1, but it is thought that this is because the current-carrying area of the electrode is small. However, as mentioned above, in this example, even if the distance between the electrodes is extremely narrow, there is no rise in the bath voltage, and the advantage that the bath voltage is stable over a wide range of distance between the electrodes is not diminished in the slightest. do not have.

2nd table anode chamber Nactp degree 280-285% cathode chamber NaOH
Concentration 27-29vrt% Bath temperature [79-81°C Current density 1[: 50 AltM' Comparative Example 1 The results of electrolysis under the same conditions as Example 1 except that the cathode was not subjected to water repellent treatment are shown below. It is shown in Table 5.

Distance between third surface poles d(w) 1.5 2 3 A5 4
Bath voltage (V) 568 358 546
549 A48 Example 2 The anode used in Example 1 was electrolyzed under the same conditions as in Example 1 except for water-resistant treated gold at the following method θ. - That is, it was coated on one side of the expanded metal anode and the inner surface of the hole using the 60% borea 0 ntais version it brush used in Experiment 1, dried and then heat treated at 550°C. After post-treatment, electrolysis was performed with the curved surface facing the opposite electrode. The results are shown in Table 4.

Distance between fourth surface poles d (m) 1 1.5 2 3
4 bath voltage (7) 539! L4G 53
8 540 543 As in Example 1, the bath voltage is stable over a wide range of inter-electrode distance IIAd, and a low bath voltage is maintained even if it is narrowed to (1-1■).Furthermore, the anode is also water repellent. By treatment, the bath voltage was 11 (V) higher than in Example 1.
It is slightly decreasing.

Implementation f1445 The anode is provided with an opening having the best diameter L-1■ as shown in FIG. 1(d).

A rod-shaped titanium electrode coated with ruthenium oxide with a width of M-1 is used vertically for the cathode, and the shortest diameter of the opening shown in Fig. 1 (a) is L = α9m1ll; the width of the pole part is M = Using CL7- expanded metal electrodes, there is a thickness of 10 mm between the cathode and anode.
An electrolytic cell is constructed by arranging a cation exchanger (approximately 125cm). Next, the anode was treated with a water repellent coating method (the same method as in Example 2) on one side of the rod, and the cathode was treated with a water repellent treatment using the dipping method as in Example 1. I installed it so that the songs that had not been treated with water were facing each other. The membrane was pressed against the anode side with a liquid pressure of about 100 cm, and electrolysis was carried out under the electrolytic conditions shown in Table 6.

Table 5 shows the results of measuring the bath voltage while changing the distance between the electrodes.

5th surface pole distance #d (m) C512 Bath voltage 1'V) A13 519
Comparative Example 2 shows the bath voltage when all the electrodes without water repellent treatment are used. When the distance between the electrodes is 2■, the bath voltage is 5 for comparison I+l12 and this example. 54(V)
, There is almost no difference from 532 (V).

However, in this example, the bath voltage decreases approximately linearly with the distance between the electrodes, and when the distance between the electrodes is @i1, Comparison 9'11
55O(V) in 2, in this example A19
A decrease in bath voltage above Cv) and CLl (to) is introduced,
Furthermore, the distance between one pole is #ll! If you change it to α5■! L13('
Bath voltages as low as V) were achieved.

In other words, when the water repellent treatment was applied, the bath voltage decreased correspondingly when the gap between the electrodes was extremely narrowed, and a decrease in the bath voltage of C1(v) or more was achieved compared to the case without the water repellent treatment.

Table 6 Anode chamber NaC1 concentration 260-270% Cathode chamber NaO
H1f degree 26-29wt% Bath temperature 1i:
79-81℃ Current density 50A/dI? Comparative Example 2 Table 7 shows the results of electrolysis performed under the same conditions as in Example 5, except that neither the cathode nor the anode was subjected to water repellent treatment.

Table 7 Distance between poles dC■) 12 Bath voltage (V) 330 34 Actual bill example 4 CF2++eC;F, and OF, =cP-o-ay,
-CF -0-(ay,)t -80,? OF.

After forming the copolymer into a 1rllll shape, it was hydrolyzed (film thickness: 7 mil, exchange capacity: 185 mθq/f). After treating the film with 11NHcj, it was thoroughly dried, and phosphorus pentachloride/oxychloride was formed. 1 with phosphorus (Juyari ratio 1/1) mixed yarn
The reaction was carried out at 20°C for 6 days to convert So and H into so and ct, and then only one side was hydrolyzed. Next section 5
4 mils of sulfonic acid base layer by treatment with 7tlb hydroiodic acid and hydrolysis.

A cation exchange membrane with a 3 mil carboxylic acid base layer was used.

On the other hand, a water permeable, ion permeable, low electrical resistance film was obtained by the following method.

CF, =CF, and CF, =C)lI-0-CF,
-CF -0- (CF, ), -80,F wound OF.

After forming a copolymer with the above into a membrane, it was hydrolyzed (film thickness: 2 mil, exchange membrane -1.1 meq/r). The iron membrane was treated in methanol at 60° C. for 1 hour and then immersed in water.

For the anode, a rod-shaped titanium electrode coated with ruthenium oxide (L = (17 ■, M-[1
Next, use the 9th extract band metal. Both the cathode and the anode were subjected to water repellent treatment in the same manner as in Example 51j3.

A low electrical resistance film is disposed between the cation exchange membrane and the cathode, and about 200-000 fluid pressure is applied from the anode chamber to the cathode, the film, and the cation exchange GL! An electrolytic cell was constructed by bringing them into close contact with each other.

#Table 8 shows the results of measuring the bath voltage under the electrolytic conditions shown in Table I9 and varying the distance m between the poles.

8th surface electrode distance d (key) 0 1 2 Bath voltage (V) s, oz 509
525 Note that even when d=00 in the same table, the thickness of the cation exchange membrane and low electrical resistance film between the cathode and anode actually exists, but in this ξ, the thickness of the cathode, the low electrical resistance film, and the anode When the ion exchange membrane and anode are in close contact with each other, 1d=
0, and in the case of d-1- and 2-2, the true distance between the cathode and the anode must be obtained by adding the thickness of the membrane and the film.

Comparative Example 5 below shows a case where both the cathode and the anode are not water-repellent treated, but compared to Comparative Example 3, when d=2■, there is a significant difference in bath voltage between this example and Comparative Example 5. However, as dt-1+o+ and Osm are made smaller, the difference between 5 and this example becomes relatively large, and (1-0111
1 and 510 (g) in Comparative Example 3, this example has 50
2 (V) and 11 (V) indicating a slightly lower bath voltage.

Table 9 Anode chamber Na0 44 degrees 210±5% Cathode chamber NaOH concentration 25±iwt% Bath temperature
85±1° C. Current density 30 A/d/ Comparative Example 5 Table 10 shows the results of electrolysis conducted under the same conditions as in Example 4, except that neither the cathode nor the anode was subjected to water repellent treatment.

40th surface pole distance *d (■) 0 1 2 Bath voltage (V) 3.10 514 523 Example 5 CTP, mcF, and CF, -cFLo-cF, -aF
-o-(ay,), -coocF.

C.F.

A cation exchange membrane was obtained by molding a copolymer with a membrane and then hydrolyzing it (membrane JIL 7 mil, exchange membrane 111-2 meq/'). The same material used in Example 4 was used for the anode, a low electrical resistance film was placed between the anode and the cation exchange membrane, and approximately 200 liquid pressure was applied to the anode from the cathode. The film and the cation exchange membrane were brought into close contact to form an electrolytic cell.

Electrolysis was carried out under the same electrolytic conditions as in Example 4 except for the following, with the NaOH concentration in the cathode chamber set to t-35 wt-, and the results are shown in Table 11.

11th surface pole distance &d(■) 0 1 2 Bath voltage (V) 512 521・529
On the other hand, as shown in Comparative Example 4 described later, when a cathode and anode without water repellent treatment are used, there is no significant difference from this example at d=2■, but as d becomes smaller, The decrease in bath voltage is larger in this example than in comparative example 4, and is relatively 4! at d=OW. Compared to L20s), the present example showed a slightly lower bath voltage of 512CV).

Table 12 shows the results of electrolysis under the same conditions as in Example 5, except that neither the gap nor the electrode was subjected to water repellent treatment.

12th surface electrode distance d (■) 0 1 2 Bath voltage (V) 520 525 530 implementation? The same IJ6 anode as used in Example 4 was used, and the same cation exchange membrane as used in Example 5 was used.

On the other hand, the spongy nickel celmet product manufactured by Sumitomo Electric Co., Ltd.
4 (26-35 cells/1nch, thickness t5) f:
After soaking in grci and drying, heat-treat at 350°C, repeat this process three times, and then polish one side with sandpaper to remove the soaked Teflon. With the side facing the opposite pole, use this as an anode.

Table 13 shows the results of electrolysis performed under the same electrolytic conditions as in Example 5 by pressing the cation exchange membrane against the anode with a liquid pressure of about 200 -.

(51) Distance between 13th front pole - d (■) 0125 Bath voltage (V) 511 522 53
4 544 On the other hand, JJi does not have water repellent treatment applied to the cathode! The results of 1@r are shown in Comparative Example 5, but d
When is 5■, ti555 (approximately a1 compared to Vl and this example)
(b) Although the bath voltage is moderately high, when d becomes smaller than 21al+, the bath voltage rises rapidly, and 582 (
It showed a commercial bath voltage of V). The effect of water repellency treatment when d is 2 or less is extremely large.

Comparative Example 5 Table 14 shows the results of electrolysis under the same conditions as Example 6 except that the cathode was not subjected to water repellent treatment.

14th surface electrode distance d (wm) 12 5 4 Bath voltage (V) 582 559 55
4 555? ! 58-48685 (9) Example 7 Titanium sponge was pulverized and sized to 100 meshes or less and 350 meshes or more using sieve I/-nK. This material was immersed in an impropatul solution of ruthenium trichloride, dried, and then heat-treated at 400 to 450° C. to coat it with ruthenium oxide. Titanium powder coated with ruthenium oxide was dispersed in methanol, and Polyflon disbarge carbon solution was added thereto to form a mixed slurry.Polyflon Paper PA-5L (average porosity 375
%.

It was precipitated to a thickness of about a5-mm by suction filtration on a forged steel with a pore diameter of 45 μm. After drying, place the extended band metal titanium with the shortest opening S (L9) covered with ruthenium oxide on top of this, and pressurize it at 100 K4/eat for 30 minutes.
This was heat treated at 0°C and used as an anode.

Table 15 shows the results of electrolysis under the same conditions as in Example 6 except that the positive & was used.

15th surface electrode distance a (sm) o 12 s bath voltage (V)! 98 512 522
35 Compared to Example 6, the parallel displacement between each pole is approximately 1
The drop in bath voltage of 1 (V) was reduced, and an unprecedentedly low bath voltage of 2.98 (V) was achieved at d-=0+w.

The pore size of the anode used in this example was measured by mercury porosimetry, and the average pore size was about 85 μm.

[Brief explanation of the drawing]

FIG. 1 defines the width M of the opening liquid and the width M of the electrode portion of various porous electrodes. FIG. 2 shows how the bath voltage is affected by L and the inter-electrode distance when a conventionally used porous electrode with a large M is rigid. FIG. 5 shows the effect on bath voltage when using a porous electrode with water repellency according to the present invention, and shows the phenomenological basis of the present invention. Figure 4 defines the meaning of water repellency in the present invention. [(V) Fig. 4 Ket θ〉9σ Fig. 3 Distance between poles (d)

Claims (1)

[Scope of Claims] t. A porous electrode for electrochemical reactions accompanied by gas generation, in which at least a portion of the surface of the porous body is treated with a water-repellent substance. 2. The porous electrode according to claim 1, wherein the electrochemical reaction accompanied by gas generation is an electrolytic reaction of an aqueous alkali metal salt solution. (5) In an electrolytic cell configured by using a porous electrode for at least one of a pair of cathodes and anodes and arranging a diaphragm between the cathodes and anodes, a porous cell in which at least a part of the surface of the porous body is treated with a water-repellent substance. 1. A method for electrolyzing an aqueous alkali metal salt solution, which comprises electrolyzing a porous electrode and the diaphragm in close proximity or close contact so that the distance between the porous electrode and the diaphragm is substantially zero.