JPS5926675B2 - Corrosion prevention method for nozzles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to diaphragm electrolysis of an aqueous alkali chloride solution, and more specifically, provides a method for preventing corrosion of a metal liquid supply/discharge nozzle attached to an electrode chamber in diaphragm electrolysis having an electrode type electrode. .

That is, the present invention provides a diaphragm electrolysis system in which a metal liquid supply/discharge nozzle attached to an electrode chamber is electrically connected to an electrode type electrode, and a plurality of cell units each containing the electrode are stacked in a filter press style. When electrolyzing an aqueous alkali chloride solution using a tank, this nozzle corrosion prevention method is characterized by installing an auxiliary electrode electrically connected to the liquid supply/discharge nozzle.

In the present invention, a cell unit consists of a pair of bipolar electrodes separated by a partition and an anode chamber and a cathode chamber.
A diaphragm electrolytic cell is constructed by stacking a plurality of cell units alternately with one or more diaphragms in a filter press manner, and providing only an anode chamber and a cathode chamber at both ends.

The general structure of each cell unit in the above-mentioned diaphragm electrolytic cell will be explained with reference to FIG. FIG. 1 is a perspective view of an example of a cell unit. Reference numeral 1 denotes a frame of the cell unit, which is usually made of metal such as iron.

Reference numeral 2 denotes an anode or a cathode (hereinafter referred to as an anode), which is fixed to the partition wall 3 by welding or the like through ribs (not shown).

The cell unit is divided into an anode chamber and a cathode chamber by a metal partition 3 provided in the middle. A nearly saturated to 3N alkali chloride aqueous solution is supplied from the salt water supply nozzle 4 to the anode chamber, and passes through the anode chamber, during which time chlorine is produced by an electrolytic reaction at the anode, and alkali metal ions are transferred to the cathode side. The remaining aqueous alkali chloride solution is discharged from the liquid discharge nozzle 5, and the chlorine gas is discharged from the gas discharge nozzle 6.
In the cathode chamber, water or a dilute aqueous caustic alkali solution is supplied from a nozzle 7, and in the cathode chamber, caustic alkali generated by the cathode is added, the aqueous caustic alkali solution is discharged from a discharge nozzle 8, and hydrogen gas is discharged from a nozzle 9. Generally, each nozzle has a shape that all penetrate the cell unit frame and are welded to the frame, as shown in an example in FIG. That is, FIG. 2 explains the structure of the anode chamber liquid discharge nozzle and its vicinity, in which the nozzle 5 penetrates the frame 1, and
The nozzle and frame are each welded at position 1. Also, on the tip side of the nozzle, there is a branch pipe 12 made of a flexible hose.
It is connected to the main pipe 13 via. The liquid supply and discharge nozzle attached to each electrode chamber of such a cell unit is as follows.
Electrolysis takes place in the anode chamber (PH adjustment was performed as necessary)
A nozzle for supplying an aqueous alkali chloride solution and a nozzle for discharging an aqueous alkali chloride solution desalinated by electrolysis.In the cathode chamber, a nozzle for supplying water or an aqueous caustic alkali solution and a nozzle for supplying an aqueous caustic alkali solution or a mixed aqueous solution of caustic alkali and alkali chloride to be produced. This is a nozzle for taking out.

In some cases, the liquid supply/discharge nozzle described above extracts a mixed phase of hydrogen gas and aqueous caustic alkali solution or chlorine gas and aqueous alkali chloride solution, and separates the gas and liquid outside the electrode chamber. Generally, the above-mentioned liquid supply and discharge nozzles are each connected to a branch pipe, and then the branch pipes are connected to a common main pipe to supply and discharge the solution. The liquid supply/discharge nozzle attached to the electrode chamber, which is the object of corrosion protection in the present invention, is made of metal, and moreover, the liquid supply/discharge nozzle is integrally constructed of a bipolar electrode and a conductive material (metal). (hereinafter referred to as electrical connection) is essential. The material of the nozzle attached to the anode chamber is generally titanium, tantalum, tungsten,
Valve metals such as zirconium and niobium are used, and ferrous materials such as iron, mild steel, stainless steel, and cast iron are used as materials for the nozzle attached to the cathode chamber. Therefore, at least a portion of the inner surface of the electrode chamber and the electrode chamber frame are also made of metal, and a metal liquid supply/discharge nozzle is generally connected to the electrode chamber frame by welding or the like. Pipe-shaped liquid supply and discharge nozzles are often used, but various other shapes can also be used. In a diaphragm electrolytic cell having bipolar electrodes as described above, even if 10 to 50 cell units, or even more in some cases, are constructed, a high voltage is applied to both ends of the electrolytic cell over a relatively short distance. Since the current is applied, leakage current tends to increase. For this reason, in the diaphragm electrolytic cell of the present invention, when the metal liquid supply and discharge nozzle is electrically connected to the bipolar electrode, the liquid supply and discharge nozzle is located close to the inside of the attached electrode chamber. The location is polarized relatively close to the polar potential, but the situation is very different at the nozzle tip. Therefore, when performing electrolysis over a long period of time, it is especially important to use the liquid supply and discharge nozzles attached to the positive and negative electrode chambers of the unit cell near the positive side of the electrolytic cell, and the anode chamber of the unit cell near the negative side of the electrolytic cell. All of the attached liquid supply and discharge nozzles undergo electrolytic corrosion from their tips and become brittle or melt, making it impossible to continue electrolysis. Compared to using a bipolar electrode or a diaphragm with a single finger shape, using a flat plate is a particular problem because the cell unit is thinner and the number of laminated layers is generally larger. be. In the above diaphragm electrolytic cell, when the number of cell units increases to 9 or more, the current density also increases to 15A/D.
As the voltage increases above m2, the leakage current also increases and the electrolytic corrosion phenomenon of the liquid supply/discharge nozzle becomes significant. The present inventors have conducted various studies on the problem of the liquid supply and discharge nozzles in diaphragm electrolytic cells becoming brittle and melting, especially due to electrolytic corrosion, and found that a portion of the current leaking from the liquid supply and discharge nozzles can be absorbed by an auxiliary electrode. The present invention was completed by discovering that the problem could be solved by dividing the flow.

However, when supplying pure water (including water with virtually no conductivity) to the cathode chamber, the leakage current through the pure water supply nozzle is generally extremely small, so corrosion of the nozzle is a particular problem. There are many cases where it is not necessary. In the present invention, the auxiliary electrode installed electrically connected to the liquid supply/discharge nozzle may be made of metal that is not significantly corrosive to the environment in which it is installed, and generally depends on the material of the liquid supply/discharge nozzle. Selected appropriately.

In particular, as the auxiliary electrode, it is advantageous to use a material that is more likely to cause an electrochemical reaction (lower overvoltage) than the nozzle material. For example, if the liquid supply/discharge nozzle attached to the anode chamber is made of titanium and leakage current flows especially on the positive side of the electrolytic cell, the auxiliary electrode may be made of a valve metal such as titanium, tantalum, or tungsten; platinum,
Platinum group metals such as palladium, iridium, ruthenium, rhodium, oxides of platinum group metals, lead oxide (PbO2),
Magnetic iron oxide, graphite, manganese dioxide, etc., and titanium, tantalum, platinum group metals, gold, etc. are also suitable when leakage current flows on the negative side of the electrolytic cell. Further, if the liquid supply/discharge nozzle attached to the cathode chamber is made of iron and leakage current flows out on the positive side of the electrolytic cell, iron, nickel, or platinum group metal is suitable for the auxiliary electrode. If the diversion of leakage current into the auxiliary electrode causes dissolution of the auxiliary electrode, the auxiliary electrode becomes a so-called sacrificial electrode. In any case, when used as an auxiliary electrode, especially platinum group metals, they are extremely useful because they have little consumption and are stable even when electrolysis is stopped, so there is no risk of contaminating the solution. The auxiliary electrode can be installed in the liquid supply/discharge nozzle by directly or indirectly electrically connecting the auxiliary electrode material within the nozzle, particularly to the tip or near the nozzle. For example, methods include directly plating the auxiliary electrode to the liquid supply/discharge nozzle to integrate it, connecting a nozzle with the auxiliary electrode material separately to the liquid supply/discharge nozzle by welding, etc. A method is adopted in which a coated nozzle mesh plate or the like is electrically connected to a liquid supply/discharge nozzle using a lead wire or the like. If the auxiliary electrode material is inert compared to the material of the liquid supply/discharge nozzle,
It is preferable that the auxiliary electrode be placed ahead of the nozzle and maintained in a state where current can easily flow therethrough. In particular, if a leakage current flows out from the liquid supply/discharge nozzle made of valve metal attached to the anode chamber, the composition of the solution in the nozzle and the saturated Kanaga electrode when anodically polarized at a current density of 100 A/Dm2 under the temperature conditions are particularly important. If a material whose reference potential does not exceed 2.0 V is used as the auxiliary electrode, the leakage current can be sufficiently shunted, and the auxiliary electrode can also be integrated with the nozzle. Such materials include platinum group metals, platinum group metal oxides, PbO2, MnO2, magnetic iron oxides, graphite, and the like. Furthermore, as the material for the auxiliary electrode for the nozzle attached to the cathode chamber on the positive side of the electrolytic cell, nickel is preferable because it has a relatively low overvoltage and relatively low consumption.
Note that the surface area required for the auxiliary electrode to be installed may be determined depending on the current value to be shunted into the auxiliary electrode, but care must be taken to ensure that the current in the auxiliary electrode is not too high.
Furthermore, as a result of many experiments on individual embodiments in which auxiliary electrodes made of various materials are installed in the liquid supply and discharge nozzle of the present invention, the present inventors have developed a book that prevents electrolytic corrosion of the liquid supply and discharge nozzle. It has been found that the effects of the invention can be achieved by adopting the following specific relationship between the leakage current and the auxiliary electrode.

That is, when the liquid supply/discharge nozzle is attached to the anode chamber and is made of titanium material, the current 1A (ampere) leaking out from the liquid supply/discharge nozzle and the electric resistance of the solution in the nozzle RA.
If the current 1A0 (ampere) passing through the auxiliary electrode (in ohms) is ]A-TAO x 1g/RA, preferably IA-
1A0<4/RA, more preferably IA-1A0<3/
Auxiliary electrodes are installed to satisfy the RAa relationship. In addition, when the liquid supply/discharge nozzle is attached to the anode chamber and is made of titanium material, the voltage o (ampere) leaking from the liquid supply/discharge nozzle and the electrical resistance of the solution inside the nozzle Rc (ohm) Current 1c0 (ampere) passing through the auxiliary electrode
is Ic-1c0<3/RO preferably IcHcO<1
・2kg0, more preferably Ic-1c0<1-0/R
The auxiliary electrode is installed so as to satisfy the relationship O. Furthermore, if the liquid supply/discharge nozzle is attached to the cathode chamber and is made of iron, stainless steel, mild steel, steel, or cast iron, the current leaking from the liquid supply/discharge nozzle is 1N.
(ampere) and the electrical resistance of the solution in the nozzle RN (ohm)
The current INO (ampere) passing through the auxiliary electrode for
・5/RN, more preferably ININO〈1・2/RN
The auxiliary electrode is installed so as to satisfy the following relationship. When the above-mentioned particularly preferable range is selected, it is possible to sufficiently prevent corrosion of the nozzle regardless of the electrolysis conditions and the liquid composition in the nozzle, and even when electrolysis is carried out for a long period of time.

In either case, the leakage current is greatest at the cell unit at the end of the electrolytic cell, so when selecting the material and location of the auxiliary electrode to be installed, it is sufficient to consider the cell unit at the end. Also, the above formula is IAO
, IcO, and INO as O, it is natural that there is no need to install an auxiliary electrode. Generally, if the liquid supply/discharge nozzle has a constant shape and the liquid composition is constant, the electrical resistance of the solution in the nozzle (RA, Rc or RN)
becomes almost constant. Therefore, in order to satisfy the above inequality, the leakage current (1A, Ic or IN) can be reduced by providing resistance in the piping connected to the liquid supply/discharge nozzle. However, in the present invention, by installing an auxiliary electrode and appropriately selecting the material and installation location to increase IAO, IcO, or INO, the above inequality can be easily satisfied without creating a large electrical resistance in the piping. I can do it. In other words, there is no need for troublesome operations such as making the piping long and thin by connecting it to a liquid supply/discharge nozzle, or installing a dropper such as a perforated plate in the piping to locally block the flowing solution, or only using it as an auxiliary method. That's fine. In the present invention, the electrical resistance R (
! :． The current 1 leaking through the liquid supply/discharge nozzle is determined by the following method.

That is, R is calculated using Ohm's law from the specific resistance of the solution in the nozzle and the shape of the solution in the nozzle (the state of filling of the solution in the nozzle). In this case, the specific resistance of the solution can be determined from literature or by conventional measuring methods. Further, when the state of the solution in the nozzle changes, the largest value among the electrical resistances of the solution in the nozzle may be taken. Furthermore, R may be estimated from measuring the voltage drop of the solution in the nozzle during electrolysis.
On the other hand, the voltage drop between two points in the supply and drainage liquid in the branch pipe during electrolysis is measured and calculated using the electrical resistance value from the geometric dimensions and specific resistance of the solution between the two points. The electrode used to measure the above voltage drop is a reversible electrode such as a Kanei electrode, a silver or silver chloride electrode in the case of a liquid supply/discharge nozzle attached to the anode chamber, or a liquid supply/discharge nozzle attached to the cathode chamber. For this purpose, a reversible electrode such as a mercury oxide electrode may be used. Alternatively, an insoluble electrode such as platinum may be used instead. The current flowing through the auxiliary electrode is determined by installing an ammeter between the liquid supply/discharge nozzle and the auxiliary electrode. The diaphragm used in the electrolytic cell of the present invention may be either a neutral membrane or an ion exchange membrane,
Generally, a two- or three-chamber cell unit is constructed by stacking one or more of them alternately with bipolar electrodes.

The present invention provides two diaphragm electrolytic cells consisting of a plurality of cell units.
The present invention can also be effectively applied to a structure in which more than one tank is electrically combined in series and/or in parallel. As a bipolar electrode, for example, a titanium-iron plate is used for the partition wall between the cathode and anode chambers, and the partition wall and the electrode are mechanically and electrically connected by a rib or a screw mechanism. The electrode may be of any conventionally known type as long as it can withstand a corrosive environment and has a sufficiently low chlorine overvoltage or hydrogen overvoltage. For example, the anode is generally made of titanium, platinum-iridium, or titanium-iridium.
A porous material coated with ruthenium mixed oxide is preferably used. Further, as the cathode, a porous material made of iron, mild steel, stainless steel, cast iron, etc., nickel-plated iron, or nickel is suitable. Example 1 The anode had a bipolar electrode consisting of a titanium lath material coated with a mixed oxide of ruthenium and titanium, and the cathode was a mild steel lath material.The main body was made of mild steel, and the inside of the anode chamber was lined with titanium. Current carrying area 30dTrI (width 50?, height 60c1
The cell unit of n) was used.

The above 49 pairs of cell units were replaced with a cation exchange membrane NafiO.
Fifty sheets of n3l5 (manufactured by Dubon) were stacked alternately in a filter press manner, and a cell unit consisting only of an anode chamber and a cathode chamber was provided at both ends to construct an electrolytic cell.

The thickness of the cell unit is 70,711 m1, and the thicknesses of the anode chamber and cathode chamber are each 30 m! 11 Also, the distance between the negative and anode is 3 degrees. In the above electrolytic cell, a titanium nozzle for removing chlorine gas is installed in the upper part of the anode chamber (gas phase part).
On the side surface of the anode chamber (liquid phase part), titanium nozzles for supplying salt water and for exiting salt water are attached by welding to a titanium lining that is electrically connected to the anode.

The above salt water supply nozzle has an inner diameter of 10.5 mm and a length of 18 mm. , the nozzle for the salt water outlet has an inner diameter of 20mm and a length of 18C.
TfL, the length of each nozzle includes the hole of the same inner diameter penetrating the anode chamber frame, and the inner surface of the hole is all lined with titanium. A mild steel nozzle is attached to the cell unit frame made of mild steel by welding.The gas phase part at the top of the cathode chamber is used for hydrogen degassing, and the liquid phase part on the side of the cathode chamber is used for supplying and exiting aqueous caustic soda solution.A mild steel nozzle is attached to the mild steel cell unit frame by welding. The supply nozzle has an inner diameter of 11.1m77! , length 12.5 (17711
The exit nozzle had an inner diameter of 12.7 mm and a length of 12 CTrL. The length of each nozzle includes the hole of the same inner diameter passing through the cathode chamber frame. In addition, salt water is supplied from a salt water supply tank that is common to each cell unit and is installed parallel to the electrolytic tank with an inner diameter of 7.7 mm. The test was carried out through a main pipe and a branch pipe with an inner diameter of 10 mm and a length of 85 cm that communicated the main pipe with each cell unit.

The outlet salt water of each unit cell has an inner diameter of 19m77! , length 8
5? branch pipe and inner diameter 10.2? The liquid was collected in a collection tank using a main tube. On the other hand, the caustic soda aqueous solution in the cathode chamber is supplied from a caustic soda aqueous solution supply tank to a main tube with an inner diameter of 5.1 cm, which is common to each unit cell and installed parallel to the electrolytic cell, and an inner diameter 8.5 mm tube that connects the main tube with each cell unit. ,
The test was carried out through a branch pipe with a length of 1 m.

Similarly, the caustic soda aqueous solution is taken out using a branch pipe with an inner diameter of 11 mm and a length of 1.1 m, and an inner diameter of 2.55 mm. The liquid was collected in a collection tank using a main tube. Note that both the branch pipe and the main pipe described above are made of heat-resistant PVC or fluorine resin. In this example, for the salt water supply nozzle attached to the anode chamber, the one in which the leakage current flows out through the nozzle on the positive side of the electrolytic cell has a thickness of about 3 cm in a range of about 2 cm from the tip of the inner surface of the nozzle.
Part of the plate was plated with 0 μm platinum. In addition, among the salt water outlet nozzles attached to the anode chamber, the leakage current flows out through the nozzle on the positive side of the electrolytic cell, from the tip of the inner surface of the nozzle to approximately 2? A mixture of ruthenium chloride and titanium chloride was applied to the area and heat treated in an electric furnace to form a coating of mixed oxide of ruthenium and titanium. On the other hand, among the salt water supply nozzle and salt water outlet nozzle attached to the anode chamber, the cell unit located on the negative side of the electrolytic cell, where the leakage current flowing in the main pipe flows into the cell unit through the nozzle, is protected against corrosion. In this case, as shown in Fig. 3, a flanged polyvinyl chloride short pipe 14 (length 5 cm) is connected to the nozzle 5, and 501 rL is drawn from the nozzle tip.
Now, the flange of the branch pipe 12 made of a flexible hose and the flange of the polyvinyl chloride pipe 14 are tightened with bolts so as to sandwich the platinum-plated disc-shaped titanium mesh (SW7TfLmXLWl3Ryu) 15. Note that the other end of the flexible hole is connected to the main pipe. Further, the tip of the nozzle and the titanium mesh are electrically connected by a titanium lead wire 16. In addition, among the cell units located on the positive side of the electrolytic cell, as a leakage current, a short Teflon tube is placed at a position 5 cm from the nozzle tip of the cell unit at a position where current flows from the cell unit through the nozzle into the main tube. (
5? ), a platinum-plated titanium mesh was installed in the same manner as above, and the titanium lead wire welded to the nozzle and the mild steel lead wire welded to the titanium mesh were tied together and electrically connected.

Using the above electrolytic cell, the current density is 45A/Ddl temperature is about 8
Electrolysis of saline solution was carried out at 0°C.

A 5.3N saline solution (approximately 67°C) containing 0.08N-HCt was supplied to the anode chamber so that the decomposition rate was 13%.
In addition, the cathode chamber contains a 14.6% caustic soda aqueous solution (approximately 35%
℃) to obtain an approximately 20% aqueous solution of caustic soda. The current efficiency for caustic soda acquisition was about 80%. Note that the voltage applied to the cathode and anode at both ends of the electrolytic cell was about 220V. After conducting electricity for 6 months, we examined the corrosion status of each nozzle, and as a result, we found that no corrosion that would pose a problem was observed at all.

Table 1 shows the electrical resistance (calculated value) of the solution in each nozzle, the leakage current value from each nozzle in the cell units at both ends of the electrolytic cell, and the measured value of the current flowing through the protective electrode.

The above leakage current is determined from the voltage drop measurement results in the solution in the branch pipe, and the current flowing through the protective electrode is determined by installing an ammeter in the lead wire that electrically connects the protective electrode and the nozzle. I asked for it. Comparative Example 1 In Example 1, the protective electrode attached to the outlet nozzle for the caustic soda aqueous solution was placed 0.5 mm from the nozzle tip. The other conditions are exactly the same for the case where the protective electrode is installed at the position of
Electrolysis was carried out for 0 days.

As a result, in the former case, corrosion was observed in the caustic soda aqueous solution outlet nozzle attached to the cell unit near the positive end of the electrolytic cell. Note that the leakage current from the caustic soda aqueous solution outlet nozzle in the terminal cell unit on the positive side of the electrolytic cell is 0.80A, and the current flowing through the protective electrode is 0.
．． It was 30A. In the latter case, significant corrosion was observed in both the salt water supply outlet nozzle of the cell unit near the positive and negative ends of the electrolytic cell, and the caustic soda aqueous solution supply nozzle and outlet nozzle of the cell unit near the positive end of the battery cell. In this case, the values of leakage current from each nozzle in the electrode chambers at both ends of the electrolytic cell were almost the same as those shown in Table 1. Example 2 In place of the metal mesh installed in the supply nozzle of the caustic soda aqueous solution in Example 1, a nickel mesh was installed in the same position and electrolysis was carried out for 6 months in the same manner.

As a result, no corrosion was observed in the nozzle. In this case, the current leaking out through the nozzle in the cell unit at the positive end of the electrolytic cell was 0.27 A, and the current flowing through the nickel auxiliary electrode was 0.25 A.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the concept of a cell unit. FIG. 2 is an explanatory diagram of the vicinity of the anode chamber liquid discharge nozzle of the cell unit. FIG. 3 is a diagram showing an example of installing the auxiliary electrode of the present invention. In the figure, 1 is a cell unit frame, 2 is an electrode, 3 is a partition wall, 4 and 7 are liquid supply nozzles, 5 and 8 are liquid discharge nozzles, 6 and 9 are gas discharge nozzles, 12 is a branch pipe made of a flexible hose, 13 14 represents a main pipe, 14 represents a short pipe, 15 represents an auxiliary electrode, and 16 represents a lead wire electrically connecting the nozzle and the auxiliary electrode.

Claims (1)

[Claims] 1. A metal liquid supply/discharge nozzle attached to the electrode chamber is electrically connected to a bipolar electrode, and a plurality of cell units each containing the electrode are stacked in a filter press style. When electrolyzing an aqueous alkali chloride solution using a diaphragm electrolytic cell,
A method for preventing corrosion of a nozzle, comprising installing an auxiliary electrode electrically connected to the liquid supply/discharge nozzle. 2. The corrosion prevention method according to claim 1, wherein the auxiliary electrode is a platinum group metal. 3. If a liquid supply/discharge nozzle is attached to the anode chamber and leakage current flows from the liquid supply/discharge nozzle, the auxiliary electrode may be made of platinum group metal oxide, manganese dioxide, lead oxide (PbO_2),
The corrosion prevention method according to claim 1, wherein the material is at least one selected from the group consisting of magnetic iron oxide and graphite. 4. The corrosion prevention method according to claim 1, wherein when a liquid supply/discharge nozzle is attached to the cathode chamber and a leakage current flows out from the liquid supply/discharge nozzle, the auxiliary electrode is made of nickel. 5. The corrosion prevention method according to claim 1, 2, or 3, wherein the liquid supply/discharge nozzle attached to the anode chamber is made of valve metal. 6. The corrosion prevention method according to claim 5, wherein the liquid supply/discharge nozzle through which leakage current flows and the auxiliary electrode are integrated. 7 Current I_A (ampere) leaking out from the titanium liquid supply/discharge nozzle attached to the anode chamber and current I_ passing through the auxiliary electrode relative to the solution resistance R_A (ohm) in the nozzle.
A_O (ampere) is I_A-I_A_O<10/R_
The corrosion prevention method according to claim 1, wherein the auxiliary electrode is installed so as to satisfy the relationship A. 8 The current I_C_O (ampere) passing through the auxiliary electrode is I_C- with respect to the current I_C (ampere) leaking in and out from the titanium liquid supply/discharge nozzle attached to the anode chamber and the electrical resistance of the solution in the nozzle R_C (ohm). I_C_O<3/
The corrosion prevention method according to claim 1, wherein the auxiliary electrode is installed so as to satisfy the relationship R_C. 9. The corrosion prevention method according to claim 1, wherein the electrode chamber is a cathode chamber and the liquid supply/discharge nozzle is made of iron. 10 Current I_ leaking out from the catholyte liquid supply and discharge nozzle
The current I_N_O passing through the auxiliary electrode is
10. The corrosion prevention method according to claim 1, wherein the auxiliary electrode is installed so that (ampere) satisfies the relationship I_N-I_N_O<3.0/R_N. 11 Claim 1 in which the diaphragm is a cation exchange membrane
Corrosion prevention method described in section.