JPS59170280A - Method for preventing corrosion of alkali chloride electrolytic cell - Google Patents

Abstract

PURPOSE:To prevent perfectly the corrosion of an alkali chloride electrolytic cell by placing an auxiliary electrode in a pipe for feeding a catholyte, a pipe for drawing a soln. produced in a cathode chamber or a common path in the electrolytic cell and by making the voltage of the auxiliary electrode higher than the anode voltage by >=0.1V. CONSTITUTION:A plurality of unit metallic electrolytic cells are electrically connected in series to install a double electrode type electrolytic cell 1. Auxiliary electrodes 6 are placed in one or more parts selected among pipes 2 for feeding a catholyte, pipes 3 for drawing a soln. produced in cathode chambers, and common paths 4, 5 in the cell 1. Voltage to be applied to the electrodes 6 is made higher than the voltage of the anode terminal of the cell 1 by >=0.1V. Thus, the corrosion of the electrolytic cell can be perfectly prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ion exchange de-electrolysis of aqueous alkali chloride solutions, and more specifically provides a method for completely preventing corrosion occurring in each unit electrolytic cell in a plurality of electrolytic cells electrically connected in series. It is something.

As a method for producing caustic alkali and chlorine by electrolyzing an aqueous alkali chloride solution, a negative and anode are provided with an ion exchange membrane sandwiched between them, forming a negative and anode chamber, and the alkali chloride is electrolyzed to obtain a caustic alkaline solution. There is an ion exchange membrane method for alkaline earth metal chloride. An electrolytic cell plant using this method is a monopolar electrolytic cell that is constructed by electrically connecting several frames of a single monopolar cell equipped with a J4-pole cathode and anode across an ion exchange membrane. Alternatively, a single bipolar cell with an ion-exchange membrane and a negative and anode can be connected electrically in series as a unit electrolytic cell. It is formed by electrically connecting several bipolar electrolytic cells in parallel and in series.

An aqueous caustic alkali solution produced by electrolyzing alkali chloride using such an electrolyzer plant is collected in a tank or the like through one common passage provided between several units. Also, the liquid is supplied to the first several unit electrolytic cells through one common passage. However, since the unit electrolytic cells are electrically connected in series, the potential at each unit +1 is different γ
Therefore, during electrolysis, the liquid is supplied to the cathode chamber of the unit electrolytic cell, and the monoalkaline aqueous solution M generated in the cathode chamber is
When the liquid is extracted into a common passage, it is decomposed through the liquid.
Part of the DC leaks. Due to this current leakage, the electrolytic cell cathode chamber body, especially the vicinity of the liquid supply nozzle 2 and the produced liquid extraction nozzle of the cathode chamber body, act as so-called electrodes, and electrolysis occurs in these parts, and anodic oxidation occurs in the parts that act as anodes. This phenomenon results in corrosion.

Conventionally, in order to prevent corrosion of the electrolytic cell body, it has been proposed to install an auxiliary electrode in the trough and electrically parallel it to the cell at the anode end of a bipolar electrolytic cell as a method to prevent electrolytic corrosion. (Special Publication No. 56-44951).

However, if such a method is adopted.

Corrosion can be suppressed to some extent only if the cathode chamber is made of a high-grade material such as pure Ni, but it is not economical or
If the material of the cathode chamber and its attached nozzles are made of iron or stainless steel in consideration of manufacturability and operability, the corrosion and dissolution reaction will still proceed in a natural corrosion state in the single electrolytic cell on the high potential side, and the cathode The chamber liquid supply nozzle, produced liquid extraction nozzle, and part of the cathode chamber main body were damaged by corrosion, so after a certain period of electrolytic operation, it would be necessary to replace them, clean them, or repair the weld overlay to completely eliminate corrosion. There is nothing you can do to prevent it.

Here, the natural corrosion state means a state where no external voltage is applied, and means a state where electrolytic corrosion has completely stopped. In addition, a single electrolytic cell on the high potential side means 0 single electrolytic cells near the anode end if it is a bipolar electrolytic cell, and if it is a monopolar electrolytic cell, it means the single electrolytic cell near the anode end. means a single electrolytic cell that is electrically connected in series to form a monopolar electrolytic cell located on the high potential side of a circuit of electrolytic cells.

In recent years, the hydrogen overvoltage of the cathode has been reduced to reduce the electrolyzer bath voltage. The so-called active cathode has been developed and some reports have been made (Soda and Chlorine, 1981 No. 8, P.
427-449).

According to this, if eluted ions such as heavy metals are present in the catholyte, they will electrochemically precipitate on the active cathode, resulting in the loss of the original low hydrogen overvoltage characteristics. In other words, in order to install an active cathode in the electrolytic cell unit and maintain the low hydrogen overvoltage characteristics of the cathode for a long period of time, it is necessary to completely prevent corrosion that occurs in the cathode chamber body and the nozzles attached to the cathode chamber body. It is.

Similarly, with respect to ion exchange membranes used in ion exchange membrane electrolysis, if metal ions are present in the catholyte, they will form a layer or precipitate on the surface of the ion exchange membrane, reducing the withdrawal voltage characteristics.

Therefore, this also creates a need to completely prevent corrosion of the cathode chamber body.

In light of the above points, the present inventor has completed the present invention as a result of repeated research.

That is, the present invention is constructed by electrically connecting a number of unit electrolytic cells made of metal in series, and each unit electrolytic cell body is provided with an electrically insulating cathode chamber liquid supply pipe and a cathode chamber produced liquid extraction pipe. In an electrolytic cell plant configured such that the cathode chamber liquid supply pipe and/or the cathode chamber product liquid withdrawal pipe are configured to collect the feed liquid clam and/or the withdrawn liquid through a common passage, the cathode chamber An auxiliary electric conductor is provided in at least one of the liquid supply pipe, the cathode chamber generation/extraction pipe, and the common pipe, so that the voltage applied to the auxiliary electrode is 0.0 or less than the anode terminal voltage of the intermediate electrode electrolyzer. The present invention provides a method for preventing corrosion of a hedged Alka IJ i group tank, which is characterized by increasing the stiffness by 1v or more.

In the present invention, the electrolytic cell main body is a member that constitutes the cell, and for example, in the case of an electrode pool type electrolytic cell, the box body corresponds to this; in the case of a filter press type electrolytic cell, the chamber frame corresponds to this. Titanium, titanium alloy, tantalum, zirconium, niobium, etc. are generally used as materials for the anode chamber and the nozzle attached to the anode chamber, which are the members constituting the cathode chamber.

Iron, mild steel% cast iron, stainless steel, Ni-based alloy, N1, etc. are used. The nozzles attached to the anode and cathode chambers are generally connected by welding or the like. Pipe-shaped nozzles are often used for liquid supply and liquid discharge nozzles, but
Other various shapes can also be used.

The cathode chamber liquid supply pipe and cathode chamber generated liquid pipe of the present invention are desirable. This is because there is a risk of corrosion current flowing through the liquid supply pipe, the produced liquid extraction pipe, and the common passage if they are electrically conductive. The piping material may be used as long as it can withstand caustic sorter liquid, hydrogen gas, etc. at electrolytic temperatures and is electrically insulating.

Examples include Teflon, asbestos% vinyl chloride, acrylic resin, E, P, D, M, rubber, and other rubbers.

Since the auxiliary electrode of the present invention operates as an anode, the I! Electrodes such as graphite blocks, so-called contact metal electrodes in which platinum group metals are coated on titanium or tantalum,
Also pure Ni, Zr.

Ag or the like is used as the electrode.

Oxygen gas is often generated on the surface of the auxiliary electrode, so if you want to prevent oxygen gas from entering the room, a method is used to install a gas Mf membrane around the auxiliary electrode and extract it outside the thread. Ru.

Is the voltage applied to the auxiliary electrode in the present invention a nuclear polar type? It is 0.1 V or more than the anode terminal voltage of the No. 11 solution device. 0.
If it is less than 1V, the effect of preventing corrosion of the cathode chamber main body, the nozzle attached to the cathode chamber, etc. is small. Therefore, 0.1V or more is desirable. Preferably it is 2V or more.

The method of applying voltage to the auxiliary electrode is to connect a battery or fuel cell, etc. electrically in series to the anode chanter of the bipolar electrolysis device, or to connect it to the auxiliary electrode.
Alternatively, various methods may be adopted, such as inserting an auxiliary rectifying path between the anode terminal and the auxiliary electrode circuit. As the auxiliary rectifying path, an element such as a silicon thyristor or a silicon diode is used.

The locations where the auxiliary electrode of the present invention is installed are not limited to 1%, but are effective from an operational point of view, and from the viewpoint of efficiency in preventing corrosion, inside the cathode religious supply pipe, inside the cathode chamber generation sludge extraction pipe, and inside the common passage. It is preferable to provide at least one of the following.

When using the present invention, especially when the electrolytically produced liquid is caustic, current leaks through the liquid in the form of droplets between the supply pipe and/or the extraction pipe and the connection position with the common passage of the pipe. It is preferable to provide a drip breaker to prevent this. By installing a drip breaker, corrosion protection can be achieved with a small amount of current, energy loss can be reduced, and corrosion protection of the electrolytic cell can be achieved efficiently.

According to the present invention, an auxiliary electrode is installed in at least one of the cathode chamber liquid supply tube, the cathode chamber generated sludge extraction tube, and the common passage, and the voltage applied to the auxiliary electrode is applied to the anode terminal of the polarized electrolyzer. Corrosion of the electrolytic cell body and the metal nozzle attached to the electrolytic cell body can be prevented by increasing the voltage by 0.1 V or more.

It can be completely prevented. For this reason, the life of the electrolytic cell is significantly extended, and it is also economically advantageous, especially when expensive metals are used as the material for the electrolytic cell. Furthermore, maintenance can be reduced compared to conventional methods.

When the method of the present invention is used, the amount of metal ions eluted into the cathode chamber supply liquid and the cathode chamber extraction liquid is quite large, so even when an active cathode with low hydrogen overvoltage characteristics is used, metal ions on the active cathode are Stable electrolytic operation can be maintained for a long period of time without deterioration due to adsorption and precipitation reactions of metal ions released from the bath.

In addition, since there are no metal ions released from the bath, an amazing lifespan can be maintained without causing any adverse effects on the ion exchange membrane, that is, deterioration of the performance of the ion exchange membrane.

Next, examples of the present invention will be described.

(Example 1) The anode has a middle electrode type electrode made of expanded metal of titanium coated with ruthenium oxide and titanium oxide, and the cathode is made of expanded metal of Ni.The main body has an anode chamber made of titanium and an electrode chamber made of titanium. is Sυ530
A cell unit made of 4 stainless steel and having a current carrying area of 200 d+n (width 2 rn x height em) was used.

The cation exchange membrane Nafio was added to the 25 pairs of nocell units mentioned above.
An image electrode type electrolytic cell 1 as shown in FIG. 1 was prepared by sandwiching a diaphragm of N 901 (trade name, manufactured by DuPont).

A liquid supply pipe 22 and a production pumping outlet pipe 3 made of fluorine Jugetsu were installed in the cathode chamber body of the electrolytic cell. In addition, one common passage 4.5 is connected to each of the cell supply pipe 2 and extraction pipe 3 provided in each cell unit, and one Ni auxiliary plate is connected to each of the common passages. 'A pole 6 is provided.

The auxiliary 'tlf, @i, 6 was electrically connected to the anode terminal of the scoop electrode type electrolytic pot electrolyzer, and a silicon rectifier 7 was installed in each of the circuits. Further, as shown in FIG. 2, a Teflon gas separation membrane 8 and a gas vent pipe 9 were installed near the auxiliary electrode. Next, electrolyze the salt at a current density of 30A/d.
m', the electrolysis temperature was 90°C. At that time, a test piece made of 8U19304 stainless steel was attached near the cathode chamber produced liquid extraction nozzle, the auxiliary electrode circuit rectifier voltage was varied, and the corrosion rate of 8US304 with respect to the rectifier voltage was measured. The results obtained are shown in Table 1.

As is clear from Table 1, when the voltage applied to the auxiliary electrode was Ov, the 8U 5304 attached to the A1 cell nozzle was severely corroded. If the voltage applied to the auxiliary electrode is made 0.1V or more lower than the anode terminal voltage by an uninvented method, it will be 5U.
Corrosion of S304 was significantly reduced, and complete corrosion protection was achieved especially at 1 V or more. The attachment inside the excavated pipe was changed. Since it is difficult to install a plate-shaped auxiliary box electrode 6, a N''m cylindrical one was used to investigate the relationship between the corrosion rate of 5US304 and the auxiliary electrode circuit rectifier voltage.

The results were exactly the same as the values shown in Table 1, proving that the method of the present invention is an amazing method for completely preventing corrosion of electrolytic cells.

(Example 3) In Example 1, the cathode was replaced with an electroplated expanded metal as described below, and electrolytic operation was performed.

(Electroplating conditions) 1. Plating bath composition Nickel sulfate 1. OM Zρthiourea
0.2 M/boric acid 0.3
M/I12, plating condition bath temperature 40℃aL flow density
0.5 A/dm' plating time: 1 hour As a result, as shown in Table 2, the cell voltage showed a constant value of about 3.10 V with almost no change over time. 1
After one year of electrolytic operation, the electrolytic cell was dismantled and the corrosion was investigated, but no corrosion was observed inside the x*t 441, and no deposits were detected on the cathode.

Table 2 (Comparative Example 1) Back In Example 3, the auxiliary electrode was removed and electrolysis operation was performed. As a result, the initial bath voltage during electrolysis operation was 3.10 V. However, after a few days had passed, an increase in bath voltage was observed, and after 20 days, it was about 3
．． A bath voltage of 50 V was achieved. After 30 days of electrolytic operation, ■ When we dismantled the group tank, we found severe corrosion not only inside the electrolytic tank's liquid supply nozzle and liquid discharge nozzle, but also inside the electrolytic cell near these nozzles, and on the cathode. A considerable amount of Fe was also precipitated.

(Comparative Example 2) In Example 2, the auxiliary electrode and the anode terminal of the power source for electrolytic sliding electrolysis were electrically connected without any connection between them, and
Electrolytic operation was performed.

As a result, although the rate of increase in bath voltage was slower than in Comparative Example 1, it reached a bath voltage of about 3.40 V after about 60 days.

From this, it is clear that the method of the present invention is not only a very effective method for completely preventing corrosion in a single tank, but also a method that can maintain excellent electrolytic performance from the viewpoint of energy conservation. .

[Brief explanation of the drawing]

FIGS. 1 to 3 are explanatory views schematically showing various aspects of an electrolysis device for an alkali chloride bath provided with an auxiliary electrode and an auxiliary rectifier circuit according to the present invention. In each figure, ] is a polarized electrolytic cell, 2 is a cathode chamber liquid supply pipe, 3 is a cathode chamber liquid extraction pipe, 4 is a common passage for the cathode chamber liquid supply pipe, and 5 is an anode chamber liquid extraction pipe. Common passage of the tube, 6 is an auxiliary electrode, 7 is a silicon rectifier, 8 is a gas separation membrane, 9 is a gas venting tube Patent applicant: Toyo Soda Kogyo Co., Ltd. 405 6 δ Figure 1 Figure 2 Completed, Figure 3

Claims (1)

[Scope of Claims] 1) It is constructed by electrically connecting several metallic unit electrolytic cells in series, and each unit electrolytic cell body is equipped with an electrically insulating cathode chamber liquid supply pipe and a cathode chamber generated liquid drain. An exit pipe is provided, and the electrode chamber liquid supply pipe and the cathode chamber product liquid withdrawal pipe are configured to collect the supply liquid and the liquid discharged through a common passage. In an electrolytic cell plant, an auxiliary electrode is provided in at least one of the gap electrode chamber liquid supply pipe, the cathode chamber generated sludge extraction pipe, and the common passage, so that the voltage applied to the auxiliary electrode is 0 from the anode terminal voltage
．． A method for preventing corrosion of an alkali chloride electrolytic cell, characterized by making the voltage higher than 1V. 2) An auxiliary rectifier is provided between the pole of the auxiliary pole and the anode prong of the power source for electrolysis of the collar-pole type electrolysis device, and these are electrically connected in series. Method according to item 1. 3) A batch I no-tube fuel cell is provided between the auxiliary electrode and the anode terminal of the bipolar electrolyzer power supply. 4) A patent characterized in that the unit electrolytic cell is an alkali chloride electrolytic cell using an ion exchange membrane as a diaphragm. The method described in any one of claims 1 to 3