JP2014091838A - Reverse current prevention method for ion exchange membrane electrolytic cell - Google Patents

Abstract

A reverse current prevention method for an ion exchange membrane electrolytic cell capable of preventing a reverse current generated after the operation of the ion exchange membrane electrolytic cell is stopped is provided.
An anode chamber containing an anode, a cathode chamber containing a cathode, an anolyte supply manifold for supplying an anolyte to the anode chamber, and a catholyte for supplying the catholyte to the cathode chamber. A reverse current prevention method for the ion exchange membrane electrolytic cell 100 having a supply manifold 124. After the operation of the ion exchange membrane electrolytic cell 100 is stopped, the anolyte supply pipe 127 that supplies the anolyte from the anolyte tank 123 to the anolyte supply manifold 121, and the catholyte from the catholyte tank 123 to the catholyte supply manifold 124. Is injected into at least one of the catholyte supply pipe 128 for supplying the anolyte or a low-conductivity substance having a lower electrical conductivity than the catholyte.
[Selection] Figure 1

Description

  The present invention relates to a method for preventing reverse current of an ion exchange membrane electrolytic cell (hereinafter also simply referred to as “electrolytic cell”), and more specifically, ion exchange capable of preventing reverse current generated after the operation of the ion exchange membrane electrolytic cell is stopped. The present invention relates to a method for preventing reverse current of a membrane electrolytic cell.

  Today, as an ion exchange membrane electrolytic cell, a bipolar ion exchange membrane electrolytic cell in which a bipolar element in which an anode chamber having an anode on one side and a cathode chamber having a cathode on one side is integrated is arranged with an ion exchange membrane interposed therebetween. It has been known. In this type of electrolytic cell, several tens of bipolar elements are arranged in series across an ion exchange membrane to constitute an electrolytic cell, and a plurality of electrolytic cells are electrically connected to operate.

When the electrolytic solution is circulated through the positive / catholyte supply pipe and the positive / catholyte discharge pipe during the operation of the electrolytic cell, a leakage current flows through the piping of each bipolar element. For example, in the electrolysis of salt water, when the operation of the electrolytic cell is stopped, chlorine (Cl ₂ ) that is an active substance in the anolyte in the anode chamber and hydrogen (H ₂ ) that is an active substance in the catholyte in the cathode chamber As a result, an electromotive force is generated in the unit cell via the ion exchange membrane, and a leakage current flows through the piping even during the stop as in the case of operation. Therefore, a current (reverse current) in the direction opposite to the normal electrolysis direction flows inside the electrolytic cell. Since these reverse currents lead to electrolytic cell performance deterioration such as cathode deterioration, various measures have been taken for the purpose of reducing the reverse current.

As a general technique for preventing a reverse current, for example, in Patent Document 1, a saline solution is injected into the anode chamber after the operation of the saline electrolyzer is stopped, and chlorine (Cl ₂ ) which is an active substance existing in the anode chamber is used. Techniques for removal have been proposed. According to this operation, since the concentration of the active substance in the electrolytic solution is lowered, the electromotive force of the reverse current can be reduced. Furthermore, the temperature of the electrolytic solution is also related as a cause of increasing the electromotive force of the reverse current. If the temperature of the electrolytic solution is lowered, specifically, if the temperature of the electrolytic solution is close to room temperature, the electromotive force of the reverse current is reduced. Therefore, the temperature of the electrolytic cell is preferably low, and the saline solution is injected into the anode chamber. Also plays the role of lowering the temperature of the electrolyte. Further, in Patent Document 2, as a method for removing a residual voltage of a water electrolysis cell, oxygen (O ₂ ) remaining in the anode chamber, the cathode chamber is continuously supplied with pure water as an electrolytic solution to both the anode chamber and the cathode chamber. A technique for removing hydrogen (H ₂ ) remaining in the electrolytic cell from the electrolytic cell has been proposed.

  As another technique for reducing the reverse current of the electrolytic cell, Patent Document 3 discloses that after the operation of the electrolytic cell is stopped, a direct current voltage is applied between the anode and the cathode so that a minute amount is generated from the anode to the cathode. There has been proposed a technique for preventing the generation of a reverse current by passing a current (anticorrosive current). In addition, the development of electrodes that are less susceptible to the influence of reverse current is also underway. For example, in Patent Document 4, a mixed layer containing metallic nickel, nickel oxide, and carbon atoms is formed on the surface of a conductive substrate having a nickel surface, and a platinum group metal or platinum group metal is formed on the mixed layer. An aqueous electrolysis cathode provided with an electrode catalyst layer containing a metal compound has been proposed. Furthermore, Patent Document 5 proposes a method for reducing the reverse current that optimizes the length and the bent position of the hose connecting the catholyte outlet and the catholyte recovery tube.

JP-A-55-58383 JP-A-8-144079 Japanese Patent Laid-Open No. 62-13589 JP2011-190534A (Patent No. 5006456) JP 2012-158775 A

Although the techniques proposed in Patent Document 1 and Patent Document 2 provide a certain effect as a countermeasure against the reverse current generated when the electrolytic cell is stopped, they are not always satisfactory and leave room for further improvement. ing. Moreover, when there are many elements which comprise an electrolytic cell, the reverse current larger than a perfect short circuit may flow through an element by superposition | conversion of a reverse current. In this case, the cathode potential may reach an oxygen (O ₂ ) generation region. In such a situation, when a technique described in Patent Document 3 is applied and an anticorrosion current is passed from the anode to the cathode, hydrogen (H ₂ ) diffuses from the cathode chamber through the ion exchange membrane to the anode chamber, An explosion of (H ₂ ) -oxygen (O ₂ ) may occur. On the other hand, there is a problem that chlorine (Cl ₂ ) is generated when a high-current anticorrosive current is applied so as not to cause hydrogen (H ₂ ) -oxygen (O ₂ ).

  Further, the aqueous solution electrolysis cathode described in Patent Document 4 is excellent as a countermeasure against the reverse current that has been generated, but the effect of preventing the generation of the reverse current cannot be obtained. Furthermore, as in Patent Document 5, even if the length and the bent position of the hose connecting the catholyte outlet and the catholyte recovery tube are optimized, the reverse current cannot be sufficiently prevented. .

  Therefore, an object of the present invention is to provide a reverse current prevention method for an ion exchange membrane electrolytic cell that can prevent a reverse current generated after the operation of the ion exchange membrane electrolytic cell is stopped.

  As a result of intensive studies to solve the above problems, the present inventor has obtained the following idea. That is, Patent Documents 1 and 2 disclose that an electromotive force of a reverse current is obtained by continuously supplying an electrolytic solution to the anode chamber and the cathode chamber to remove the active substance in the anode chamber and the cathode chamber even after the operation of the electrolytic cell is stopped. It is to reduce. However, in addition to reducing the electromotive force of the reverse current, it is possible to prevent the reverse current by increasing the electrical resistance of the liquid in the pipe. Based on such an idea, the present inventor has further intensively studied. As a result, when the operation of the electrolytic cell is stopped, it has been found that the above-mentioned problems can be solved by following the following procedure, and the present invention has been completed. It was.

That is, the reverse current prevention method for an ion exchange membrane electrolytic cell according to the present invention includes an anode chamber for housing an anode, a cathode chamber for housing a cathode, an anolyte supply manifold for supplying an anolyte to the anode chamber, In a method for preventing reverse current of an ion exchange membrane electrolytic cell having a catholyte supply manifold for supplying catholyte to a cathode chamber,
After the operation of the ion exchange membrane electrolytic cell is stopped, an anolyte supply pipe for supplying anolyte from the anolyte tank to the anolyte supply manifold, and a catholyte from the catholyte tank to the catholyte supply manifold The anolyte or a low-conductivity substance having a lower electrical conductivity than the catholyte is injected into at least one of the catholyte supply tubes.

  In the reverse current prevention method for an ion exchange membrane electrolytic cell of the present invention, the low-conductivity substance is preferably water. Moreover, in the reverse current prevention method of the ion exchange membrane electrolytic cell of this invention, it is preferable to stop the circulation of the catholyte after the operation of the ion exchange membrane electrolytic cell is stopped. Furthermore, in the method for preventing reverse current of the ion exchange membrane electrolytic cell of the present invention, after the operation of the ion exchange membrane electrolytic cell is stopped, at least one of the anolyte supply tube and the catholyte supply tube is made of an inert gas. Substitution is preferred. Furthermore, in the reverse current prevention method for an ion exchange membrane electrolytic cell according to the present invention, the ion exchange membrane electrolytic cell has at least two catholyte circulation paths each having a catholyte discharge manifold and a catholyte supply manifold. In this case, it is preferable that after the operation of the ion exchange membrane electrolytic cell is stopped, at least one of the catholyte circulation paths is electrically disconnected from other catholyte circulation paths.

  ADVANTAGE OF THE INVENTION According to this invention, the reverse current prevention method of the ion exchange membrane electrolytic cell which can prevent the reverse current which arises after the operation stop of an ion exchange membrane electrolytic cell can be provided.

It is a schematic block diagram of an example of the ion exchange membrane electrolyzer which electrically connected two bipolar ion exchange membrane electrolyzers. It is a schematic block diagram of an example of a bipolar element. It is a schematic block diagram of an example of the ion exchange membrane electrolytic cell which electrically connected the 2 single electrode type ion exchange membrane electrolytic cell. (A) is a schematic block diagram of an example of an anode element, (b) is a schematic block diagram of an example of a cathode element. It is a schematic block diagram of an electric current measurement apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an example of an ion exchange membrane electrolytic cell in which two bipolar ion exchange membrane electrolytic cells are electrically connected, and FIG. 2 is a schematic configuration diagram of an example of a bipolar element. Hereinafter, the method for preventing reverse current in the electrolytic cell of the present invention will be described by taking electrolysis of salt as an example. An ion exchange membrane electrolytic cell 100 shown in FIG. 1 is configured by electrically connecting an electrolytic cell A and an electrolytic cell B surrounded by a dotted line. In each illustrated electrolytic cell A, B, a plurality of bipolar elements 101 are laminated via an ion exchange membrane 102, and an end anode element 103 and an end cathode element are arranged at both ends of the plurality of bipolar elements 101 arranged in series. 104 are arranged.

  As shown in FIG. 2, the bipolar element 101 includes an anode chamber 107 in which an anode 105 is spaced from an anode partition wall 106, and a cathode chamber 110 in which a cathode 108 is spaced from a cathode partition wall 109, Are integrally formed, and the anode 105 and the cathode 108 are held by the anode rib 111 provided on the anode partition wall 106 and the cathode rib 112 provided on the cathode partition wall 109, respectively. In addition, an anode chamber side gas-liquid separation means 113 and a cathode chamber side gas-liquid separation means 114 are provided above the anode chamber 107 and the cathode chamber 110, respectively. In the illustrated example, an anolyte supply unit 115 is provided in the lower part of the anode chamber 107, and the anode chamber side gas-liquid separation means 113 discharges anolyte (salt water) having a reduced concentration to the anolyte discharge unit. 116 is provided. Further, a catholyte supply unit 117 is provided below the cathode chamber 110, and the cathode chamber side gas-liquid separation means 114 discharges the catholyte (sodium hydroxide aqueous solution) having an increased concentration to the cathode chamber. A portion 118 is provided.

According to the example shown in FIG. 1, the anolyte discharge portion 116 and the catholyte discharge portion 118 of the plurality of bipolar elements 101 are connected to the anolyte discharge manifold 119 and the catholyte discharge manifold 120, respectively. An anolyte supply manifold 121 for supplying anolyte to the anolyte chamber 107 is connected to a supply salt water tank 123, which is an anolyte supply tank, via an anolyte supply valve 122. The catholyte supply manifold 124 is connected to a circulating caustic tank 126 that is a catholyte tank via a catholyte supply valve 125. Note that the anolyte recovered in the anolyte discharge manifold 119 is removed from the dissolved chlorine gas (Cl ₂ ) by a dechlorination tower, sent to the supply salt water tank 123 through adjustment of the salt concentration and the like. Further, the catholyte collected by the catholyte discharge manifold 120 is sent to the circulation caustic tank 126, a part is circulated to the electrolytic cell, and a part of the caustic soda (NaOH) is taken out as a product.

  When the saline solution is electrolyzed using the ion exchange membrane electrolytic cell 100 having a configuration in which two bipolar ion exchange membrane electrolytic cells as shown in FIG. 1 are electrically connected, the operation of the electrolytic cell 100 is stopped. Then, as described above, the dissolved chlorine in the anode chamber 107 and the hydrogen in the cathode chamber 110 serve as a driving force, and a reverse current is generated in the piping of the bipolar element 101 and each manifold. Therefore, in the reverse current prevention method of the present invention, after the operation of the electrolytic cell 100 is stopped, the anolyte supply pipe 127 that supplies the anolyte from the supply saltwater tank 123 to the anolyte supply manifold 121 and the circulation caustic tank 126 are used. An anolyte or a low-conductivity substance having a lower electrical conductivity than the catholyte is injected into at least one of the catholyte supply pipes 128 that supply the catholyte to the catholyte supply manifold 124.

  By injecting the anolyte supply pipe 127 or the catholyte supply pipe 128 into the anolyte or the low conductivity material having a lower electrical conductivity than the catholyte, the electric resistance of the liquid in the pipe is increased. Thereby, after the operation of the electrolytic cell 100 is stopped, the reverse current flowing in the electric circuit formed between each bipolar element 101 having internal electromotive force and piping such as a manifold can be reduced. Note that the reverse current is conspicuous because the electromotive force is high and high while the liquid temperature after the operation of the electrolytic cell 100 is high and the active substance concentration in the electrolytic solution is high, and therefore the anolyte supply pipe 127 and the catholyte supply pipe. It is desirable that the low-conductivity substance is injected into 128 immediately after the operation is stopped.

As described above, conventionally, in the technique for preventing reverse current in the electrolytic bath of saline solution, the anode chamber 107 and the cathode chamber 110 are electrolyzed after the operation of the electrolytic bath 100 is stopped mainly for the purpose of removing the active substance in the electrolytic solution. The liquid has been injected. On the other hand, in the reverse current prevention method of the present invention, a low-conductivity substance having lower electrical conductivity than the anolyte or catholyte is injected into at least one of the anolyte supply tube 127 and the catholyte supply tube 128. In addition, the electrical resistance of the electrolyte in the pipe is increased to reduce the reverse current. Moreover, injecting a low-conductivity substance leads to removal of the active substance (Cl ₂ , H ₂ ), and furthermore, by injecting a low-conductivity substance, the electrolytic cell temperature can be lowered. But it ’s excellent.

In the reverse current prevention method of the present invention, the low-conductivity substance is not particularly limited as long as it has a lower electrical conductivity than anolyte or catholyte and can prevent reverse current. For example, water is preferably used. Can be used. When water is used as the low-conductivity substance, one having an electrical conductivity of 10 ⁻⁵ Ω ⁻¹ cm ⁻¹ or less is particularly suitable, and it is from pure water, ion exchange water, boiler steam drain, caustic / salt water evaporation equipment. Condensed water or the like can be suitably used. In addition, when an inert gas is used as the low-conductivity substance, nitrogen gas (N ₂ ), helium gas (He), argon (Ar), or the like can be preferably used. In the example shown in FIG. 1, pure water tanks 129a and 129b are arranged, and pure water is injected into the anolyte supply pipe 127 and the catholyte supply pipe 128, respectively.

In the reverse current prevention method of the present invention, it is preferable to inject a low-conductivity substance into both the anolyte supply pipe 127 and the catholyte supply pipe 128, but a low-conductivity substance may be injected into either one. For example, the low conductivity material may be injected only into the catholyte supply tube 128, and the anolyte supply tube 127 may supply the anolyte (salt water) as before to remove the active material (Cl ₂ ). Further, sodium sulfite having a molar amount of 2 to 20 times that of the active substance (Cl ₂ ) is supplied to the anolyte to the anolyte supply pipe 127 to remove the active substance (Cl ₂ ) by oxidation-reduction reaction. Is also effective.

  In the reverse current prevention method of the present invention, it is preferable to stop the circulation of the catholyte after the operation of the electrolytic cell 100 is stopped. During operation of the electrolytic cell 100, the anolyte overflows from the anolyte discharge part 116 and the catholyte overflows from the catholyte discharge part 118. The overflowed anolyte is removed from the system to adjust the salt concentration, etc., but most of the catholyte is collected in the circulation caustic tank 126 and circulates through the catholyte supply manifold 124 to the cathode chamber 110. And used. Therefore, an electric circuit is formed between each bipolar element 101 and each manifold pipe, and a leakage current flows. This causes a reverse current when the electrolytic cell 100 stops operating. Therefore, by stopping the circulation of the catholyte after the operation of the electrolytic cell 100 is stopped, the electric circuit formed between each element 101 and the catholyte discharge manifold 120 is disconnected, and the reverse current caused by the leakage current To prevent.

Furthermore, in the reverse current prevention method of the present invention, after the operation of the electrolytic cell 100 is stopped, the anolyte supply pipe 127 that supplies the anolyte from the supply saltwater tank 123 to the anolyte supply manifold 121 and the cathode from the circulation caustic tank 126 are provided. It is also preferable to replace at least one of the catholyte supply pipes 128 that supply the catholyte to the liquid supply manifold 124 with an inert gas such as N ₂ gas. By replacing the anolyte supply pipe 127 and the catholyte supply pipe 128 with an inert gas, the electrical circuit formed between each bipolar element 101 and the piping of each manifold, etc. is disconnected, resulting in leakage current. The reverse current can be prevented.

  Furthermore, in the reverse current prevention method of the present invention, when a plurality of electrolytic cells (two electrolytic cells A and B in the example shown in FIG. 1) are incorporated in one electric circuit, the electrolytic cell 100 is After the operation is stopped, it is preferable to electrically disconnect the catholyte circulation path of at least one electrolytic cell from the catholyte circulation path of another electrolytic cell. Specifically, for example, the catholyte supply valves 125a and 125b of the line for supplying the catholyte from the external circulating caustic tank 126 are closed between the catholyte supply manifolds 124a and 124b shown in FIG. The electrical connection between the catholyte circulation path of the tank A and the catholyte circulation path of the electrolytic tank B is disconnected. This is particularly effective when the number of elements 101 constituting the electrolytic cell 100 is large. In the illustrated example, the potential difference formed between the electrolytic cells A and B and pipes such as the manifolds is electrolysis. Since the potential difference between the tank A and piping such as the manifold is divided into the potential difference between the electrolytic tank B and piping such as the manifold, the reverse current can be reduced to about ½.

  FIG. 3 is a schematic configuration diagram of an example of an ion exchange membrane electrolytic cell in which two monopolar ion exchange membrane electrolytic cells are electrically connected. FIG. 4A is a schematic configuration of an example of an anode element. It is a figure, (b) is a schematic block diagram of an example of a cathode element. The ion exchange membrane electrolytic cell 200 shown in FIG. 3 is configured by electrically connecting an electrolytic cell C and an electrolytic cell D surrounded by a dotted line in the drawing. In each illustrated electrolytic cell C, D, anode elements 201 and cathode elements 202 are alternately arranged with an ion exchange membrane 203 interposed therebetween, and half cathode elements 204 are arranged at both ends.

  As shown in FIG. 4, the anode element 201 has anodes 205 on both sides, and the cathode element 202 has cathodes 206 on both sides, each of the anode chambers 207 and cathodes of the electrolytic cells C and D shown in FIG. 3. A chamber 208 is formed. In addition, an anode chamber side gas / liquid separation means 209 and a cathode chamber side gas / liquid separation means 210 are provided above the anode chamber 207 and the cathode chamber 208, respectively. In the illustrated example, an anolyte supply unit 211 is provided below the anode chamber 207, and the anode chamber side gas-liquid separation means 209 discharges anolyte (salt water) having a reduced concentration to the anode chamber side gas-liquid separation means 209. A discharge unit 212 is provided. The cathode chamber 208 is provided with a catholyte supply unit 213, and the cathode chamber side gas-liquid separation means 210 is provided with a catholyte discharge unit 214 that discharges the concentrated catholyte (sodium hydroxide aqueous solution). It has been.

Further, according to the example shown in FIG. 3, the anolyte discharge part 212 of the anode element 201 and the catholyte discharge part 214 of the cathode element 202 are connected to the anolyte discharge manifold 215 and the catholyte discharge manifold 216, respectively. ing. Further, the anolyte supply manifold 217 for supplying the anolyte to the anolyte chamber 207 is connected to the supply salt water tank 219 via the anolyte supply valve 218, and for supplying the catholyte to the cathode chamber 208. The manifold 220 is connected to the circulating caustic tank 222 via the catholyte supply valve 221. Note that the anolyte recovered in the anolyte discharge manifold 215 is removed from the dissolved chlorine gas (Cl ₂ ) by a dechlorination tower, and sent to the supply salt water tank 219 after adjusting the salt concentration or the like. Further, the catholyte collected by the catholyte discharge manifold 216 is sent to the circulating caustic tank 222, a part is circulated to the electrolytic cell, and a part of the caustic soda (NaOH) is taken out as a product.

When the saline is electrolyzed using an ion exchange membrane electrolytic cell 200 having a configuration in which two monopolar ion exchange membrane electrolytic cells are electrically connected as shown in FIG. Similarly to the membrane electrolytic cell, dissolved chlorine (Cl ₂ ) in the anode chamber 207 and hydrogen (H ₂ ) in the cathode chamber 208 serve as driving forces, and each piping of the anode element 201, the cathode element 202, the manifold, and the like. A reverse current is generated. Therefore, in the reverse current prevention method of the present invention, after the operation of the electrolytic cell 200 is stopped, the anolyte supply pipe 223 for supplying the anolyte from the supply saltwater tank 219 to the anolyte supply manifold 217 and the circulation caustic tank 222 are used. An anolyte or a low-conductivity substance having a lower electrical conductivity than the catholyte is injected into at least one of the catholyte supply pipes 224 that supply the catholyte to the catholyte supply manifold 220.

By injecting into the anolyte supply pipe 223 or the catholyte supply pipe 224, a low-conductivity substance having a lower electrical conductivity than the anolyte or the catholyte, the electric resistance of the liquid in the pipe is increased and the reverse current is reduced. can do. Note that the generation of the reverse current is significant because the electromotive force is high and high while the liquid temperature after the operation of the electrolytic cell 200 is high and the active substance concentration in the electrolytic solution is high. It is desirable to inject the low-conductivity substance into the liquid supply pipe 223 and the catholyte supply pipe 224 immediately after the operation is stopped. Also in this embodiment, injecting a low-conductivity substance also leads to removal of the active substance (Cl ₂ , H ₂ ), and by injecting a low-conductivity substance, the electrolytic cell The temperature can be lowered.

Also in this embodiment, the low-conductivity substance is not particularly limited as long as it has a lower electrical conductivity than anolyte or catholyte and can prevent reverse current. For example, water is preferably used. it can. When water is used as the low-conductivity substance, it is preferable that the electrical conductivity is 10 ⁻⁵ Ω ⁻¹ cm ⁻¹ or less, and it is condensed from pure water, ion exchange water, boiler steam drain, caustic / salt water evaporation equipment. Water or the like can be suitably used. In addition, when an inert gas is used as the low-conductivity substance, nitrogen gas (N ₂ ), helium gas (He), argon (Ar), or the like can be preferably used. In the example shown in FIG. 3 as well, pure water tanks 225a and 225b are disposed, and pure water is supplied to the anolyte supply pipe 223 and the catholyte supply pipe 224, respectively.

Also in this embodiment, it is preferable to inject a low conductivity material into both the anolyte supply tube 223 and the catholyte supply tube 224, but a low conductivity material may be injected into either one. For example, the low conductivity material may be injected only into the catholyte supply tube 224, and the anolyte supply tube 223 may supply the anolyte (salt water) to remove the active material (Cl ₂ ). It is also effective to supply sodium sulfite in an amount of 2 to 20 times the molar amount of the active substance (Cl ₂ ) to the anolyte and remove the active substance (Cl ₂ ) by oxidation-reduction reaction.

  Also in the present embodiment, it is preferable to stop the circulation of the catholyte after the operation of the electrolytic cell 200 is stopped. During the operation of the electrolytic cell 200, the anolyte overflows from the anolyte discharge part 212 and the catholyte overflows from the catholyte discharge part 214. The overflowed anolyte is discharged out of the system for adjusting the salt concentration, etc., but most of the catholyte is collected in the circulating caustic tank 222 and passes through the catholyte supply manifold 220 to the cathode chamber 208. Used in circulation. Therefore, an electric circuit is formed between the cathode element 202 and each manifold and other piping, and a leakage current flows. This causes a reverse current when the electrolytic cell 200 stops operating. Therefore, by stopping the circulation of the catholyte after the operation of the electrolytic cell 200 is stopped, the electric circuit formed between each cathode element 202 and the catholyte discharge manifold 216 is disconnected, and the reverse caused by the leakage current Prevent current.

Further, also in the present embodiment, after the operation of the electrolytic cell 200 is stopped, the anolyte supply pipe 223 for supplying the anolyte from the supply salt water tank 219 to the anolyte supply manifold 217 and the catholyte supply from the circulating caustic tank 222 are performed. At least one of the catholyte supply pipes 224 that supply the catholyte to the manifold 220 may be replaced with an inert gas such as N ₂ gas. By replacing the anolyte supply pipe 223 and the catholyte supply pipe 224 with an inert gas, the electric circuit formed between the pipes of the anode element 201, the cathode element 202, each manifold, and the like is disconnected, and the leakage current It is possible to prevent the reverse current caused by.

  Furthermore, also in this embodiment, when a plurality of electrolytic cells (in the example shown in FIG. 3, two electrolytic cells C and D) are incorporated in one electric circuit, the cathode of at least one electrolytic cell. It is preferable to electrically disconnect the liquid circulation path from the catholyte circulation path of another electrolytic cell. Specifically, for example, the catholyte supply valves 221a and 221b of the line for supplying the catholyte from the external circulating caustic tank 222 are closed between the catholyte supply manifolds 220a and 220b shown in FIG. The electrical connection between the catholyte circulation path of the tank C and the catholyte circulation path of the electrolytic cell D is disconnected. This is particularly effective when the number of the elements 201 and 202 constituting the electrolytic cell 200 is large, and the potential difference formed between the electrolytic cells C and D and piping such as the manifolds is the electrolytic cell C. Therefore, the reverse current can be reduced to about ½.

  Up to this point, in the reverse current prevention method of the present invention, the electrolytic cell 100 electrically connected to the two bipolar ion exchange membrane electrolytic cells and the two monopolar ion exchange membrane electrolytic cells are electrically connected. However, in the reverse current prevention method of the present invention, after the operation of the ion exchange membrane electrolytic cell is stopped, at least one of the anode chamber and the cathode chamber has low conductivity. It is only important to inject a substance, and there are no particular restrictions on other configurations. For example, as the anode and the cathode, known electrodes that are conventionally used can be adopted. Moreover, there is no restriction | limiting in particular also about the operating condition of an electrolytic cell, The general condition currently performed can be applied.

In the reverse current prevention method of the present invention, when pure water is injected into the anode chambers 107 and 207 and the cathode chambers 110 and 208 as a low-conductivity substance, the ion exchange membranes 102 and 203 are swollen. There is a concern that the exchange membranes 102 and 203 are wrinkled and mechanically damaged. However, the durability of perfluoro cation exchange membranes that use carboxylic acid or sulfonic acid, which is generally used in current ion exchange membrane type salt electrolysis, etc., or an acid that is a combination of both, has improved day by day. Concerns are also eliminated and it can be used without problems. For example, F8020, F8020SP and F8080 manufactured by Asahi Glass Co., Ltd., N2010, N2030 and N2040 manufactured by DuPont Co., Ltd., and F4401, F4403 and F6801 manufactured by Asahi Kasei Co., Ltd. can be suitably used. Furthermore, after the operation is stopped, it is also effective to press the membrane against the anode chamber by applying a pressure of 400-600 mmH ₂ O to the cathode chamber to prevent wrinkling of the membrane.

  Further, when the operation of the electrolytic cell is stopped using the reverse current prevention method of the present invention, the low conductive material is injected into the anode chambers 107 and 207 and the cathode chambers 110 and 208 for a time when the influence of the reverse current is large. Only need. This is because it may be difficult to adjust the concentration of the anolyte or catholyte when the electrolytic cell is started up again. Therefore, when storing the electrolytic cell, after the operation of the electrolytic cell is stopped, the reverse current prevention method of the present invention is applied. The chamber is preferably replaced and stored.

Hereafter, the reverse current prevention method of the ion exchange membrane electrolytic cell of this invention is demonstrated in detail using an Example.
In each case of the conventional example and the example, the voltage and the reverse current value of each manifold were measured. As an electrolytic cell having a configuration of the type shown in FIG. 1, an electrolytic cell in which n-BiTAC 896 (manufactured by Chlorine Engineers Co., Ltd.) is arranged in series was used.

  The reverse current was measured by incorporating the current measuring apparatus 300 having the configuration shown in FIG. 5 into the anolyte discharge manifold 119, the catholyte discharge manifold 120, the anolyte supply manifold 121, and the catholyte supply manifold 124. After the anolyte and catholyte discharged from each element 101 in the electrolytic cell 100 merge in the anolyte discharge manifold 119 and the catholyte discharge manifold 120, respectively, and the anolyte and catholyte are respectively anolyte. Before being dispersed in the supply manifold 121 and the catholyte supply manifold 124, two mesh-shaped platinum electrodes 301 are installed where the anolyte and the catholyte pass, and an ammeter 302 is connected to these electrodes. The current value was measured. The piping 303 between the platinum electrodes 301 was made of PVC for insulation. The pipes 304 on both sides of the current measuring device 301 were made of titanium for anode measurement and made of nickel for cathode measurement. Moreover, the arrow in a figure shows the flow of an anolyte and a catholyte.

<Conventional example>
As a treatment after the operation of the electrolytic cell 100 was stopped, salt water having a temperature of 60 ° C. and a concentration of 300 g / L was supplied to the anode chamber 107 through the anolyte supply manifold 121 at a flow rate of 0.25 m ³ / h / element. . A sodium hydroxide (NaOH) aqueous solution having a temperature of 85 ° C. and a concentration of 30% by mass was supplied to the cathode chamber 110 through the catholyte supply manifold 124 at a flow rate of 0.25 m ³ / h / element.

  3 hours and 6 hours after the operation was stopped, the potential and reverse current in the anolyte supply manifold 121, the anolyte discharge manifold 119, the catholyte supply manifold 124, and the catholyte discharge manifold 120 were measured. The obtained results are shown in Table 1 together with the conditions after the operation of the electrolytic cell 100 was stopped. Here, the value of the reverse current is the sum of the currents measured in each manifold, and indicates the maximum value. The cell voltage after 3 hours of shutdown is 1.6 V, the anolyte discharged from the anode chamber 107 is salt water having a temperature of 65 ° C. and a concentration of 300 g / L, and the catholyte discharged from the cathode chamber 110. Was a sodium hydroxide aqueous solution having a temperature of 65 ° C. and a concentration of 28% by mass. Further, the cell voltage after 6 hours of shutdown is 1.6 V, the anolyte discharged from the anode chamber 107 is salt water having a temperature of 40 ° C. and a concentration of 300 g / L, and the catholyte discharged from the cathode chamber 110. Was a sodium hydroxide aqueous solution having a temperature of 40 ° C. and a concentration of 28% by mass.

<Example>
As a treatment after the operation of the electrolytic cell 100 is stopped, pure water (electric conductivity: 10 ⁻⁵ Ω ⁻¹ cm ⁻¹ or less) at a temperature of 25 ° C. is used at a flow rate of 0.25 m ³ / h / element. The solution was injected from the supply pipe 127 into the anode chamber 107 through the anolyte supply manifold 121. Also, pure water (electric conductivity: 10 ⁻⁵ Ω ⁻¹ cm ⁻¹ or less) at a temperature of 25 ° C. is supplied from the catholyte supply pipe 128 to the catholyte supply manifold 124 at a flow rate of 0.25 m ³ / h / element. Injected. The supply of pure water to the catholyte supply manifold 124 was stopped after the catholyte supply manifold 124 was replaced with pure water.

  Similar to the conventional example, the potential and reverse current in the anolyte supply manifold 121, the anolyte discharge manifold 119, the catholyte supply manifold 124, and the catholyte discharge manifold 120 are measured 3 hours and 6 hours after the shutdown. did. The obtained results are shown in Table 1 together with the conditions after the operation of the electrolytic cell 100 was stopped. The cell voltage after 3 hours of shutdown is 1.3 V, the anolyte discharged from the anode chamber 107 is salt water having a temperature of 40 ° C. and a concentration of 14 g / L, and almost no catholyte is discharged from the cathode chamber 110. It was not being done. Furthermore, the cell voltage after 6 hours of shutdown is 1.3 V, the anolyte discharged from the anode chamber 107 is salt water having a temperature of 30 ° C. and a concentration of 1 g / L, and the catholyte is almost discharged from the cathode chamber 110. It was not being done. Here, since the pure water was supplied to the anolyte supply manifold and the catholyte supply manifold, and almost no liquid was flowing to the catholyte discharge manifold, these manifold potentials could not be measured. It was.

  From Table 1, it can be seen that according to the reverse current prevention method of the present invention, the reverse current after the electrolytic cell is stopped can be greatly reduced.

DESCRIPTION OF SYMBOLS 100 Bipolar ion exchange membrane electrolytic cell 101 Bipolar element 102 Ion exchange membrane 103 End anode element 104 End cathode element 105 Anode 106 Anode partition 107 Anode chamber 108 Cathode 109 Cathode partition 110 Cathode chamber 111 Anode rib 112 Cathode rib 113 Anode chamber side Gas-liquid separation means 114 Cathode chamber side gas-liquid separation means 115 Anolyte supply part 116 Anolyte discharge part 117 Catholyte supply part 118 Catholyte discharge part 119 Anolyte discharge manifold 120 Catholyte discharge manifold 121 Anolyte supply manifold 122 Anolyte Supply Valve 123 Supply Salt Water Tank 124 Catholyte Supply Manifold 125 Catholyte Supply Valve 126 Circulating Caustic Tank 127 Anolyte Supply Pipe 128 Catholyte Supply Pipe 129 Pure Water Tank 200 Monopolar Type Ion exchange membrane electrolytic cell 201 Anode element 202 Cathode element 203 Ion exchange membrane 204 Half cathode element 205 Anode 206 Cathode 207 Anode chamber 208 Cathode chamber 209 Anode chamber side gas-liquid separation means 210 Cathode chamber side gas-liquid separation means 211 Anode solution supply section 212 Anolyte Discharge Portion 213 Catholyte Supply Portion 214 Catholyte Discharge Portion 215 Anolyte Discharge Manifold 216 Catholyte Discharge Manifold 217 Anolyte Supply Manifold 218 Anolyte Supply Valve 219 Supply Salt Water Tank 220 Catholyte Supply Manifold 221 Cathode Liquid supply valve 222 Circulating caustic tank 223 Anolyte supply pipe 224 Catholyte supply pipe 225 Pure water tank 300 Current measuring device 301 Platinum electrode 302 Ammeter 303, 304 Piping

Claims (5)

An anode chamber containing an anode; a cathode chamber containing a cathode; an anolyte supply manifold for supplying an anolyte to the anode chamber; and a catholyte supply manifold for supplying a catholyte to the cathode chamber. In the method for preventing reverse current of the ion exchange membrane electrolytic cell,
After the operation of the ion exchange membrane electrolytic cell is stopped, an anolyte supply pipe for supplying anolyte from the anolyte tank to the anolyte supply manifold, and a catholyte from the catholyte tank to the catholyte supply manifold A method for preventing reverse current in an ion exchange membrane electrolytic cell, wherein the anolyte or a low-conductivity substance having a lower electrical conductivity than the catholyte is injected into at least one of the catholyte supply tubes.   The method for preventing reverse current of an ion exchange membrane electrolytic cell according to claim 1, wherein the low-conductivity substance is pure water.   The method for preventing reverse current of an ion exchange membrane electrolytic cell according to claim 1 or 2, wherein the circulation of the catholyte is stopped after the operation of the ion exchange membrane electrolytic cell is stopped.   The ion exchange membrane according to any one of claims 1 to 3, wherein at least one of the anolyte supply pipe and the catholyte supply pipe is replaced with an inert gas after the operation of the ion exchange membrane electrolytic cell is stopped. Method for preventing reverse current of electrolytic cell.   The ion exchange membrane electrolyzer has at least two catholyte circulation paths having a catholyte discharge manifold and a catholyte supply manifold, and after stopping the operation of the ion exchange membrane electrolyzer, at least one of the above The method for preventing reverse current in an ion exchange membrane electrolytic cell according to any one of claims 1 to 4, wherein the catholyte circulation path is electrically disconnected from other catholyte circulation paths.

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