JP2006052434A - Method for recovering capability of salt solution electrolysis cell, and method for producing raw caustic soda solution and chlorine using fluorine-containing cation-exchange membrane treated by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering the capability of a fluorine-containing cation-exchange membrane, and to provide a method for producing a raw caustic soda solution and chlorine using the fluorine-containing cation-exchange membrane treated by the method. <P>SOLUTION: The method for recovering the capability of the fluorine-containing cation-exchange membrane comprises the steps of: supplying an acidified salt solution having a pH of 1.5 to 3.5, to an anode chamber of a salt solution electrolytic cell which is partitioned by the fluorine-containing cation-exchange membrane; supplying a dilute caustic soda solution with a concentration of 20 to 30 wt.%, to a cathode chamber; and a step of holding the acidified salt solution and the dilute caustic soda solution in the electrolytic cell, in the state of having stopped energization. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for recovering the performance of a saline electrolyzer, a production caustic soda solution using a fluorine-containing cation exchange membrane treated by the method, and a method for producing chlorine.

  A method of producing a produced caustic soda solution and chlorine by electrolyzing saline using an electrolytic cell having a fluorine-containing cation exchange membrane as a diaphragm is generally widely known. In this salt water electrolysis, when operating for a long period of time or when the impurity concentration in the salt water is high, deposition of impurities occurs in the ion exchange membrane, and the electrolytic voltage increases and / or current efficiency decreases. There was a problem that the film performance was lowered. The impurities in the saline are substances that are included in the raw salt used for saline electrolysis, such as calcium, magnesium, silicon, and strontium, and affect the membrane performance. These impurities are fluorine-containing cation exchange membranes. Therefore, a much more rigorous salt water refining method is required as compared with the asbestos diaphragm method and the mercury method. As one of such purification methods, there is known a method in which purification by a chelate resin is further added to a normal saline purification step to remove calcium, magnesium and the like. However, even if purification with a chelate resin is performed, it is difficult to completely remove impurities in the saline solution, and impurities of about 10 ppb remain in the saline solution. Even such a very small amount of impurities is gradually deposited in the membrane over a long period of operation, and the membrane performance is lowered. The fluorine-containing cation exchange membrane having such a lowered performance is Usually, it can be replaced with a new fluorine-containing cation exchange membrane. However, since a fluorine-containing cation exchange membrane used for saline electrolysis is considerably expensive, a technique for recovering the performance of the membrane whose membrane performance has deteriorated is desired from the viewpoint of economy.

  As such a recovery process, when the membrane is once removed from the electrolytic cell and processed, it is practically difficult to reattach the electrolytic cell after the treatment, and the membrane is attached to the electrolytic cell. It is desired to process as it is. In addition, even when the treatment is performed while attached to the electrolytic cell, depending on the treatment solution and treatment temperature conditions, the membrane may swell, wrinkles may occur, or the membrane may come into contact with the electrode and scratches may be generated. Because of the problems, it is desirable to process without damaging the film. Furthermore, depending on the treatment liquid, when the treatment is performed with current applied, water blisters may be generated on the membrane and the electrolysis voltage may increase. Therefore, it is desirable to perform a recovery treatment with the current supply stopped. ing.

As such a recovery treatment method, for example, an acid having a pH of 1 or less is installed in an anode chamber of an electrolytic cell in which a perfluorocarbon-based cation exchange membrane with an increased electrolysis voltage and a reduced current efficiency is attached in a state where energization is stopped. A method of restoring membrane performance by supplying a solution and bringing the ion exchange membrane into contact with the acid solution is disclosed (for example, see Patent Document 1). However, in this method, since the pH of the acid solution is extremely low, the exchange group of the ion exchange membrane is protonated (H ⁺ ) and the ion exchange capability is lost. As a result, the electric resistance of the ion exchange membrane is reduced. Titanium that is generally used as an anode chamber material of an electrolytic cell has a problem of damaging the anode chamber material because the corrosion rate increases at pH 1 or lower. In addition, by disassembling the electrolytic cell having a fluorine-containing ion exchange membrane with reduced current efficiency due to I and / or Ba contained in the saline solution, the energization is interrupted and hot water is supplied to the cathode chamber and held. A method for restoring current efficiency (for example, see Patent Document 2) is disclosed. However, this method has a problem that the membrane is swollen and wrinkles are generated, or scratches are generated by contact with the electrode and the electric resistance is increased, so that the electrolysis voltage cannot be lowered.

  In this way, impurities deposited on the fluorine-containing cation exchange membrane can be efficiently removed without removing the ion exchange membrane from the electrolytic cell in a state where current is stopped, and the membrane and the electrolytic cell material are deteriorated. However, there is currently no method for recovering electrolysis voltage and current efficiency.

JP 53-37598 A JP 2000-1794 A

  The present invention provides a method for recovering the performance of a fluorine-containing cation exchange membrane. Also provided are a production caustic soda solution and a chlorine production method using a fluorine-containing cation exchange membrane treated by the method.

  That is, the present invention provides a step of supplying acidic saline having a pH of 1.5 to 3.5 to the anode chamber of a saline electrolysis cell partitioned by a fluorine-containing cation exchange membrane, and a caustic soda concentration of 20 to 30 wt. The present invention relates to a method for recovering the performance of a fluorine-containing cation exchange membrane, comprising a step of supplying a diluted caustic soda solution of 25% and a step of holding the acidic saline solution and the diluted caustic soda solution in the electrolytic cell in a state where current supply is stopped.

  It is preferable that the salt concentration of the acidic saline supplied to the anode chamber is 150 to 300 g / L.

  It is preferable that the temperature in the anode chamber is 60 to 80 ° C.

  Further, the present invention provides a production caustic soda solution comprising a step of supplying saline to an anode chamber of an electrolytic cell having a fluorine-containing cation exchange membrane treated by the performance recovery method, and a step of electrolyzing the saline Regarding the method.

  Furthermore, this invention relates to the manufacturing method of chlorine including the process of supplying salt solution to the anode chamber of the electrolytic cell which has the fluorine-containing cation exchange membrane processed by the said performance recovery method, and the process of electrolyzing this salt solution .

  In the performance recovery method of the present invention, acidic saline having a pH of 1.5 to 3.5 was supplied to the anode chamber, a diluted caustic soda solution having a caustic soda concentration of 20 to 30% by weight was supplied to the cathode chamber, and energization was stopped. By holding the acidic saline solution and diluted caustic soda solution in the electrolytic cell in a state, it is possible to recover performances such as electrolysis voltage and current efficiency of the ion exchange membrane whose performance has been lowered.

  The present invention includes a step of supplying acidic saline having a pH of 1.5 to 3.5 to an anode chamber of a saline electrolysis cell partitioned by a fluorine-containing cation exchange membrane, and a caustic soda concentration of 20 to 30% by weight to the cathode chamber. The present invention relates to a method for recovering the performance of a fluorine-containing cation exchange membrane, comprising a step of supplying a diluted caustic soda solution, and a step of holding the acidic saline solution and the diluted caustic soda solution in the electrolytic cell in a state where energization is stopped.

The performance recovery method of the present invention can remove impurities deposited in an ion exchange membrane in saline electrolysis. In the saline used in the saline electrolysis, calcium, magnesium, silicon, strontium and the like contained in the raw material salt are present as impurities, but such impurities, together with sodium ions during the saline electrolysis, When they move through the ion exchange membranes and reach their saturation solubility, they are converted into Ca (OH) ₂ , Mg (OH) ₂ , SiO ₂ , Sr (OH) · 8H ₂ O, etc. This increases the film resistance.

  In addition, the resistance component of the electrolytic cell includes membrane resistance, electrode resistance, liquid resistance, bubble resistance, etc. When these resistance values increase, the value of the electrolysis voltage when a constant current is passed increases, The value (product of current value and voltage value) increases. As a result, the power consumption (the power value necessary to produce 1 ton of caustic soda) increases, resulting in an increase in product cost. Therefore, as described above, if impurities adhere to the surface and the inside of the ion exchange membrane, the membrane resistance increases and the product cost also increases. However, according to the performance recovery method of the present invention, the impurities attached to the film can be removed to reduce the film resistance and the electrolysis voltage. As a result, the power unit is reduced and the product cost is reduced. is there. Furthermore, since the membrane resistance is reduced, the amount of electrolysis power can be effectively used for the electrolysis reaction, and the current efficiency can be recovered.

  The fluorine-containing cation exchange membrane used in the present invention is not particularly limited as long as it is generally used for saline electrolysis, and the polymer structure and film thickness of the ion exchange membrane are not limited. There is no particular limitation as long as the object can be achieved. As an ion exchange membrane, what is an ion exchange membrane comprised from a reinforcing material, a high moisture content layer, and a low moisture content layer is mention | raise | lifted, for example. Examples of the reinforcing material include PTFE fibers, and the high water content layer and the low water content layer include those made of a fluorine-based polymer having a sulfonic acid group or a carboxylic acid group. The high water content layer is a sulfonic acid layer. It is preferably made of a fluorine-based polymer having a group, and the low water content layer is preferably made of a fluorine-based polymer having a carboxylic acid group. Examples of the fluorine-based polymer having a sulfonic acid group and the fluorine-based polymer having a carboxylic acid group include, for example, general formula (1) and general formula (2):

(In the formula, X is a fluorine atom or —CF ₃ , and Y is

A is —SO ₃ M, —COOM, M is an alkali metal, m is an integer of 0-2, and n is an integer of 1-4)
Examples thereof include a polymer having a repeating unit represented by: Examples of the alkali metal include sodium (Na) and potassium (K).

Moreover, as a film thickness of the whole fluorine-containing cation exchange membrane, it is preferable that it is 50-500 micrometers, and it is more preferable that it is 100-300 micrometers. Furthermore, a gas adhesion preventing layer may be provided on the anode and cathode surfaces in order to prevent electrical resistance from increasing due to bubbles adhering to the film surface. As the commercially available fluorine-containing cation exchange membrane, Nafion ^(R) (Nafion ^(R) manufactured by DuPont), Flemion ^(R) (Flemion ^(R) manufactured by Asahi Glass Co., Ltd.), Aciplex ^(R) (Aciplex ^(R) Asahi Kasei Chemicals Corporation).

  The acidic saline solution used in the performance recovery method of the present invention is acidified by adding an acid.

The acid solution for acidification, hydrochloric, mineral acids such as sulfuric acid, in the like organic acids such as acetic acid, which also is again electrolyzed remained in the membrane Among these, ClO ^- decomposition Then, hydrochloric acid is preferable because it is not converted into Cl ₂ and does not deteriorate the performance of the fluorinated cation exchange membrane (hereinafter referred to as membrane performance). Furthermore, hydrochloric acid is preferred because it is less likely to react with an alkali metal present in the ion-exchange membrane to precipitate precipitates than other acid solutions such as mineral acids such as sulfuric acid and organic acids such as acetic acid.

  The pH of the acidic saline is 1.5 to 3.5, preferably 1.5 to 2.5, and more preferably 1.7 to 2.0. When the pH is 1.5 to 3.5, protonation of the ion exchange groups in the ion exchange membrane can be suppressed, so that the ion exchange ability of the ion exchange groups can be maintained, and as a result, the electrical resistance of the membrane Can be prevented from rising. Furthermore, since calcium and / or other impurities deposited in the film can be sufficiently dissolved, a sufficient performance recovery effect can be obtained.

  Moreover, as acidic salt solution, what has little content of an impurity is preferable. The content of impurities is preferably comparable or less than that generally used for saline electrolysis, specifically, the total of impurities calcium and magnesium in acidic saline. The concentration is preferably 20 ppb or less, and more preferably 10 ppb or less. When the total concentration of calcium and magnesium is 20 ppb or less, an increase in electrolytic voltage and / or a decrease in current efficiency can be suppressed.

  Further, as impurities, in addition to calcium and magnesium as described above, silicon, strontium and the like are included in the raw salt used for acidic saline, and substances that affect membrane performance are also included. It is preferable that the content of impurities is also small so as not to affect the film performance.

  The production method of the acidic saline solution is not particularly limited. For example, an acid saline solution can be prepared by adding an acid to a saline solution generally used for saline electrolysis.

  The salt concentration of the acidic saline is preferably 150 to 300 g / L, more preferably 150 to 250 g / L, and still more preferably 190 to 230 g / L. When the concentration is 150 to 300 g / L, it is possible to suppress swelling of the ion exchange membrane. Therefore, it is possible to prevent the membrane from coming into contact with the electrode and causing scratches on the membrane or wrinkles on the membrane. Further, since the ion exchange membrane can be prevented from shrinking, the impurities deposited in the membrane can be sufficiently brought into contact with the acidic saline solution, and as a result, a sufficient performance recovery effect can be obtained.

  The diluted caustic soda solution used in the performance recovery method of the present invention preferably has a small impurity content in the diluted caustic soda solution. The content of impurities is preferably comparable or less than that generally used for saline electrolysis, specifically, the total of calcium and magnesium as impurities in dilute caustic soda solution The concentration of is preferably 20 ppb or less, and more preferably 10 ppb or less. When the total concentration of calcium and magnesium is 20 ppb or less, an increase in electrolytic voltage and / or a decrease in current efficiency can be suppressed. Furthermore, iron, which is an impurity in the diluted caustic soda solution, has a great influence on the cathode. When the iron content increases, it adheres to the electrode and affects the electrode overvoltage. Specifically, it is preferably 0.1 ppm or less, and more preferably 0.05 ppm or less. When the iron concentration is 0.1 ppm or less, it is possible to suppress an increase in the overvoltage of the electrode, and thus it is possible to prevent the electrolytic voltage from increasing.

  Here, the impurities include silicon and sulfur in addition to the calcium, magnesium and iron, but the content of these is preferably small enough not to affect the film performance.

  The manufacturing method of the diluted caustic soda solution used in the performance recovery method of the present invention is not particularly limited, and for example, a product obtained by diluting a production caustic soda solution generally manufactured by brine electrolysis can be used.

  Here, the produced caustic soda solution is a caustic soda solution having a caustic soda concentration of 31 to 35% by weight generated in the cathode chamber by electrolysis. The produced caustic soda solution is mixed with the caustic soda solution or pure water supplied to the electrolytic cell. A diluted caustic soda solution may be prepared.

  The caustic soda concentration of the diluted caustic soda solution used in the performance recovery method of the present invention is preferably 20 to 30% by weight, more preferably 20 to 25% by weight, and more preferably 20 to 23% by weight. When the caustic soda concentration is 20 to 30% by weight, it is possible to suppress the ion exchange membrane from expanding, and thus it is possible to suppress the membrane from coming into contact with the electrode and causing damage to the membrane, or the membrane from being wrinkled. . In addition, by suppressing the expansion of the ion exchange membrane, the amount of the diluted caustic soda solution penetrating into the anode chamber can be suppressed, so that the pH of the acidic saline solution in the anode chamber can be kept low and the impurities can be sufficiently dissolved. Sufficient performance recovery can be obtained. Furthermore, since the shrinkage of the ion exchange membrane can also be suppressed, the amount of water transferred from the polymer layer having a sulfonic acid group and the amount of water transferred from the polymer layer having a carboxylic acid group in the ion exchange membrane are reduced. As a result, a sufficient performance recovery can be obtained.

  The performance recovery method of the present invention is characterized by the pH of the acidic saline solution in the anode chamber, the salt concentration, and the caustic soda concentration of the diluted caustic soda solution in the cathode chamber.

  The pH of the acidic saline solution in the anode chamber is in the range of 1.5 to 3.5. The pH of the diluted caustic soda solution in the cathode chamber is in the pH range corresponding to a caustic soda concentration of 20 to 30% by weight. When the pH of the bipolar chamber is in such a range, an environment in which impurities deposited on the ion exchange membrane can be more easily eluted can be created.

  When the salt concentration of the acidic saline solution in the anode chamber is low or the sodium hydroxide concentration of the diluted caustic soda solution in the cathode chamber is low, it acts to loosen the ion exchange membrane, and the acidic saline solution, diluted caustic soda solution, and eluted impurities are removed. Since it can be made to flow more freely, performance recovery by elution of impurities can be promoted, which is preferable.

  The performance recovery method of the present invention will be described with reference to FIG. In the performance recovery method of the present invention, after the energization is stopped, the anode chamber 2 of the electrolytic cell 10 is divided into the anode chamber 2 having the anode 3 and the cathode chamber 7 having the cathode 8 by the fluorine-containing cation exchange membrane 5. The acidic saline solution 1 is supplied, the diluted caustic soda solution 6 is supplied to the cathode chamber, and then the acidic saline solution 1 and the diluted caustic soda solution 6 are held in the electrolytic cell 10 in a state where power supply is stopped. After the completion, the acidic chamber and the eluted impurities 4 are discharged from the anode chamber 2, and the diluted caustic soda solution 9 containing NaCl is discharged from the cathode chamber 7.

  In the performance recovery method of the present invention, the method for supplying the treatment solution to the anode chamber and the cathode chamber is not particularly limited, and may be supplied continuously and intermittently. Preferably, the anode chamber and the cathode chamber are supplied so as to completely replace the solution supplied during the salt electrolysis. More preferably, after the solution is completely replaced, the supply of the diluted caustic soda solution to the cathode chamber is stopped and the supply of the acidic saline solution to the anode chamber is continued. By stopping the supply of the diluted caustic soda solution, the permeation amount of the diluted caustic soda solution penetrating from the cathode chamber to the anode chamber can be reduced, and the pH increase of the anode chamber can be prevented. In addition, by continuing to supply acidic saline to the anode chamber, it is possible to prevent a pH increase due to the diluted caustic soda solution that has permeated from the cathode chamber, to maintain the pH in the anode chamber low, and to elute impurities in the membrane. Easy to do.

  The temperature of the electrolytic cell in the performance recovery treatment is preferably 60 to 80 ° C, more preferably 60 to 70 ° C, and still more preferably 60 to 65 ° C. Since the shrinkage of the ion exchange membrane can be suppressed when the temperature is 60 to 80 ° C., the amount of water transferred from the layer comprising a polymer having a sulfonic acid group and the water migration of a layer comprising a polymer having a carboxylic acid group The amount does not decrease and as a result a sufficient performance recovery is obtained. Furthermore, since the swelling of the ion exchange membrane can also be suppressed, the amount of the diluted caustic soda solution penetrating into the anode chamber can be suppressed, the pH of the acidic saline solution in the anode chamber can be kept low to dissolve impurities, and a sufficient performance recovery effect can be obtained. can get.

  The time required for the performance recovery treatment is preferably 1 hour or more, more preferably 1 to 16 hours, and further preferably 1 to 8 hours.

  Moreover, in the performance recovery method of this invention, a solution is hold | maintained in the state which stopped electricity supply. If the treatment is performed while the current is applied, water blisters are generated in the membrane and the electrolysis voltage may increase, which is not preferable. However, it is not impeded that anticorrosion of the electrolytic cell and other maintenance minute currents flow to such an extent that the above-described effects are not generated.

  The performance recovery method of the present invention recovers the performance of an ion exchange membrane in which impurities accumulate due to long-term use. However, due to the increase of impurities in saline, the electrolysis voltage is greatly increased and / or the current efficiency is decreased. It is also possible to implement on an ion exchange membrane. In addition, the number of times of performing the performance recovery method of the present invention before replacing the ion exchange membrane is not limited, and can be performed any number of times.

  Further, the present invention provides a production caustic soda solution comprising a step of supplying saline to an anode chamber of an electrolytic cell having a fluorine-containing cation exchange membrane treated by the performance recovery method, and a step of electrolyzing the saline The present invention relates to a method and a method for producing chlorine including the same steps.

  As shown in FIG. 2, the production method of the production caustic soda solution of the present invention uses the electrolytic cell 10 having the fluorine-containing ion exchange membrane 14 treated by the above performance recovery method to produce the production caustic soda by usual salt electrolysis. Solution 16 can be produced. Specifically, when electrolysis is performed by supplying the saline solution 11 to the anode chamber 2 of the electrolytic cell 10 and supplying the caustic soda solution 15 to the cathode chamber 7, chlorine gas 13 is generated from the anode chamber 2, and the cathode chamber 7 produces a production caustic soda solution 16 and hydrogen gas 17. Moreover, the fresh salt water 12 which is undecomposed salt solution is discharged | emitted from the anode chamber 2 after electrolysis. Further, the caustic soda solution 16 having a concentration of 31 to 35% by weight produced in the cathode chamber 7 is extracted from the cathode chamber 7 as a part of the product, and diluted by adding pure water 18 to the remaining produced caustic soda solution 16 after the extraction. The produced caustic soda solution 16 that has been or has not been diluted can be further supplied to the cathode chamber 7 as a caustic soda solution 15 to perform brine electrolysis.

  The saline solution is preferably prepared by dissolving the raw material salt and removing impurities in the primary purification and secondary purification steps. The salt concentration of the saline is preferably 270 to 320 g / L, and more preferably 300 to 310 g / L. Since the salt concentration of the saline is 270 to 320 g / L, the shrinkage of the ion exchange membrane can be suppressed, so that the solution can sufficiently penetrate into the membrane. Further, the salt concentration of undecomposed saline (fresh salt water) discharged from the anode chamber after electrolysis is preferably 150 to 230 g / L, and more preferably 190 to 210 g / L. When the salt concentration of undecomposed saline (fresh salt water) is 150 to 230 g / L, expansion of the ion exchange membrane can be suppressed, and generation of wrinkles and scratches can be prevented.

As the caustic soda solution supplied to the cathode chamber, a part of the produced caustic soda solution produced by electrolysis is extracted as a product and diluted with pure water added to the remaining produced caustic soda solution, or left undiluted. Production caustic soda solution can be used. When the current density is 1 to 7 kA / m ² , the caustic soda concentration is preferably 30 to 34% by weight, and more preferably 31 to 32% by weight. When the caustic soda concentration is 30 to 34% by weight, shrinkage of the ion exchange membrane can be suppressed, so that the solution can sufficiently penetrate into the membrane. Furthermore, since the expansion of the ion exchange membrane can also be suppressed, it is possible to prevent an increase in the amount of NaCl transferred from the anode and increase the salt concentration in the produced caustic soda solution, thereby improving the quality of the product. Can do.

The temperature of the anode chamber and the cathode chamber during electrolysis is not particularly limited and may be any temperature that is usually used. However, in order to maximize the film performance, the temperature range should be set according to the current density. Is preferred. The temperature range is slightly different depending on the type of film. For example, when the current density is 1.0 kA / m ² or more and less than 2.0 kA / m ² , 68 to 82 ° C. is preferable, and 2.0 kA / m ^2. above, it is less than 3.0 kA / m ^2, preferably from 77 to 85 ° C., 3.0 kA / m ² or more, is less than 4 kA / m ^2, preferably 80-88 ° C.. Also, the ion exchange membrane tends to physically expand and contract as the temperature of the electrolytic cell rises or falls, affecting the performance of the membrane. For example, the membrane expands as the temperature rises, and the membrane resistance tends to decrease and the electrolysis voltage decreases, but at an excessively high temperature, the membrane and the electrode expand due to generation of wrinkles or expansion of the membrane. There is a tendency for the film to come into contact and become scratched. As a result, the film resistance tends to increase and the electrolysis voltage tends to increase. Moreover, when it exceeds 90 degreeC, there exists a tendency which affects the lifetime of a film | membrane and a gasket. On the contrary, when the temperature is lowered, the film contracts as the temperature is lowered, and the current efficiency is once increased. However, when the temperature is further lowered, the current efficiency tends to be greatly lowered. Further, at an excessively low temperature, the solution tends to be prevented from penetrating into the membrane and damaged.

During electrolysis, hydrogen (H ₂ ) is generated on the cathode surface and hydroxide ions (OH ⁻ ) are generated. On the other hand, chlorine (Cl ₂ ) is generated and sodium ions (Na ⁺ ) are generated on the anode surface. This sodium ion moves from the anode chamber to the cathode chamber through the fluorine-containing cation exchange membrane, and is combined with the hydroxide ion in the cathode chamber. In the cathode chamber, a caustic soda solution having a caustic soda concentration of 31 to 35% by weight is produced. It is manufactured.

  The electrolytic cell is not particularly limited as long as it is normally used for saline electrolysis, and may be a monopolar type or a bipolar type.

Also, the electrode is not particularly limited as long as it is usually used for saline electrolysis, but as the anode, a RuO ₂ material (ruthenium oxide of about 20 g · m ^{−2 on a} titanium substrate is heated. The cathode is preferably a Ni chemical-coated film cathode, a porous Ni cathode, a Raney Ni alloy cathode, or the like.

  Next, the present invention will be described with reference to examples, but the present invention is not limited to such examples.

<Method for measuring pH of acidic saline solution>
For pH measurement of acidic saline, a pH meter (PH82 manufactured by Yokogawa Electric Co., Ltd.) employing a measurement range of pH 0 to 14, a measured value automatically corrected and displayed at 25 ° C., and a glass electrode method as a measurement principle is used. After the pH meter is calibrated with standard solutions of pH 4 and pH 7, the pH of the acidic saline solution is measured by the following method.

  15 L of acidic saline is placed in a 20 L container made of polypropylene, and the pH is measured under the condition of 25 ° C.

<Method for measuring pH of diluted caustic soda solution, caustic soda solution, and produced caustic soda solution>
For pH measurement of dilute caustic soda solution, caustic soda solution, and production caustic soda solution, pH range adopting glass electrode method for measuring range pH 0-14, measured value automatically corrected display at 25 ° C, and measuring principle (Yokogawa Electric Corporation) Use PH82). After the pH meter is calibrated with standard solutions of pH 7 and pH 9, the pH of the diluted caustic soda solution, the caustic soda solution, and the produced caustic soda solution is measured by the following method.

  When pH becomes 14.0 or more, the value calculated by the following formula is judged as pH value.

<Test piece production>
Actual electrolytic loaded ion exchange membrane tank removed (DuPont Co., Nafion ^(R) 981 (Nafion ^(R) 981)), was cut into 10 × 10 cm as a film for the test piece. One of the test pieces was immersed in 1.0 mol / L hydrochloric acid for 16 hours, and the composition of the hydrochloric acid was analyzed by ICP. As a result, accumulation of calcium and other impurities was detected.

Example 1
The prepared test piece membrane is placed in a clamping type electrolytic cell (effective membrane area: 1.0 dm ² , anode: RuO ₂ coated Ti expanded metal, cathode: active nickel coated nickel expanded metal, 0.5 mm gap) The electrolytic bath temperature is 82 ° C., the current density is 30 A / dm ² , a salt solution of 310 g / L is supplied to the anode chamber as an electrolysis solution, and Cl ₂ and a salt concentration of 200 g are supplied at the outlet of the anode chamber by electrolysis. The flow rate is adjusted so as to discharge / L undecomposed saline solution, a caustic soda solution having a caustic soda concentration of 32 wt% is supplied to the cathode chamber, and a production caustic soda solution having an caustic soda concentration of 33 wt% is discharged by electrolysis. The flow rate was adjusted and electrolysis was performed. Electrolysis was performed for 10 days until the voltage and current efficiency transitions were stabilized under the above conditions, and after confirming that the voltage was 3.410 V and the current efficiency was 94.10%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 60 ° C., and an acidic saline solution having a pH of 2.0 and a salt concentration of 300 g / L was supplied as a performance recovery treatment solution and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 60 ° C., a diluted caustic soda solution having a caustic soda concentration of 30% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance is restored for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out the electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. As a result of conducting electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the voltage was reduced by 40 mV, the current efficiency was increased by 0.5%, and the effect of restoring the performance of the film was observed. The results are shown in Table 1.

Example 2
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution (fresh salt solution) with a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and caustic soda concentration of 32 wt. % Caustic soda solution was supplied, and electrolysis was performed by adjusting the flow rate so as to discharge the produced caustic soda solution having a caustic soda concentration of 33 wt% by electrolysis. Electrolysis was performed for 10 days until the voltage and current efficiency transitions were stabilized under the above conditions, and after confirming that the voltage was 3.412 V and the current efficiency was 94.12%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 60 ° C., and an acidic saline solution having a pH of 2.0 and a salt concentration of 200 g / L was supplied as a performance recovery treatment solution, and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 60 ° C., a diluted caustic soda solution having a caustic soda concentration of 23% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance is restored for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. As a result of performing electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the voltage was reduced by 50 mV, the current efficiency was increased by 1.2%, and the effect of restoring the performance of the film was observed. The results are shown in Table 1.

Example 3
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution (fresh salt solution) with a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and caustic soda concentration of 32 wt. % Caustic soda solution was supplied, and electrolysis was performed by adjusting the flow rate so as to discharge the produced caustic soda solution having a caustic soda concentration of 33 wt% by electrolysis. Electrolysis was performed for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, and after confirming that the voltage was 3.408 V and the current efficiency was 94.11%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 60 ° C., and an acidic saline solution having a pH of 1.7 and a salt concentration of 200 g / L was supplied as a performance recovery treatment solution and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 60 ° C., a diluted caustic soda solution having a caustic soda concentration of 23% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance is restored for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out the electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline solution having Cl ₂ and a salt concentration of 200 g / L at the outlet of the anode chamber. The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathode chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis, and electrolysis was performed. As a result of electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the voltage was reduced by 56 mV, the current efficiency was increased by 1.6%, and the effect of restoring the performance of the film was observed. The results are shown in Table 1.

Example 4
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution (fresh salt solution) with a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and caustic soda concentration of 32 wt. % Caustic soda solution was supplied, and electrolysis was performed by adjusting the flow rate so as to discharge the produced caustic soda solution having a caustic soda concentration of 33 wt% by electrolysis. Electrolysis was carried out for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions. After confirming that the voltage was 3.414 V and the current efficiency was 94.11%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 60 ° C., and an acidic saline solution having a pH of 1.7 and a salt concentration of 200 g / L was supplied as a performance recovery treatment solution and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 60 ° C., a diluted caustic soda solution having a caustic soda concentration of 30% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance is restored for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. As a result of performing electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the voltage was decreased by 48 mV, the current efficiency was increased by 0.8%, and the performance recovery effect of the film was recognized. The results are shown in Table 1.

Comparative Example 1
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution (fresh salt solution) with a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and caustic soda concentration of 32 wt. % Caustic soda solution was supplied, and electrolysis was performed by adjusting the flow rate so as to discharge the produced caustic soda solution having a caustic soda concentration of 33 wt% by electrolysis. Electrolysis was performed for 10 days until the voltage and current efficiency transitions were stabilized under the above conditions, and after confirming that the voltage was 3.410 V and the current efficiency was 94.10%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 80 ° C., and a saline solution having a pH of 9.0 and a salt concentration of 320 g / L was supplied as a performance recovery treatment solution and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 80 ° C., a caustic soda solution having a caustic soda concentration of 34% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance recovery treatment is performed for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out the electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. As a result of conducting electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the performance of the film was not recovered as before. The results are shown in Table 1.

Comparative Example 2
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, and the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution having a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and a caustic soda solution having a caustic soda concentration of 32% by weight in the cathode chamber. Then, the flow rate was adjusted so as to discharge the produced caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis, and electrolysis was performed. Electrolysis was performed for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, and after confirming that the voltage was 3.408 V and the current efficiency was 94.15%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 60 ° C., hot water was supplied and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 60 ° C., a caustic soda solution having a caustic soda concentration of 32% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance recovery treatment is performed for 8 hours. Carried out.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. Immediately after the electrolysis, the voltage increased, the electrolysis was stopped, and the state of the membrane was confirmed. As a result, wrinkles were generated on the membrane. The results are shown in Table 1.

Comparative Example 3
In the same manner as in Example 1, the prepared test piece membrane was placed in a clamping type electrolytic cell, and the electrolytic cell temperature was 82 ° C., the current density was 30 A / dm ² , and the salt concentration in the anode chamber as an electrolytic solution was 310 g / L salt solution is supplied, the flow rate is adjusted to discharge Cl ₂ and undecomposed saline solution (fresh salt solution) with a salt concentration of 200 g / L at the outlet of the anode chamber by electrolysis, and caustic soda concentration of 32 wt. % Caustic soda solution was supplied, and electrolysis was performed by adjusting the flow rate so as to discharge the produced caustic soda solution having a caustic soda concentration of 33 wt% by electrolysis. Electrolysis was performed for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, and after confirming that the voltage was 3.413 V and the current efficiency was 94.11%, the electrolysis was stopped.

  After the electrolysis was stopped, the anode chamber was kept at 45 ° C., and a solution with a pH of 9.0 and a sodium chloride concentration of 20 g / L was supplied as a performance recovery treatment solution and circulated for 8 hours. On the other hand, the cathode chamber is maintained at 45 ° C., a solution having a caustic soda concentration of 2% by weight is supplied as a performance recovery treatment solution, the supply is stopped after the cathode chamber is completely replaced, and the performance recovery treatment is carried out for 8 hours. did.

After the performance recovery process was completed, electrolysis was performed again to confirm the performance recovery effect, and voltage and current efficiency transitions were confirmed. In order to carry out electrolysis, the treatment solution and the solution for electrolysis were exchanged. As an electrolysis solution, a saline solution having a salt concentration of 310 g / L was supplied to the anode chamber, and a caustic soda solution having a caustic soda concentration of 32% by weight was supplied to the cathode chamber. After the solution in the electrolytic cell is completely replaced, the electrolytic cell temperature is 82 ° C., the current density is 30 A / dm ² , and the anode chamber solution is electrolyzed and undecomposed saline (Cl ₂ and sodium chloride concentration 200 g / L at the outlet of the anode chamber). The flow rate was adjusted so as to discharge (fresh salt water), and the flow rate was adjusted so that the cathodic chamber solution discharged a caustic soda solution having a caustic soda concentration of 33% by weight by electrolysis. As a result of performing electrolysis for 10 days until the transition of voltage and current efficiency was stabilized under the above conditions, the voltage increased by 27 mV, the current efficiency increased by 1.5%, the voltage increased, and only the current efficiency was recovered. . The results are shown in Table 1.

It is a figure which shows the structure of the electrolytic cell at the time of a performance recovery process. It is a figure which shows the structure of the electrolytic vessel at the time of electrolysis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acidic salt solution 2 Anode chamber 3 Anode 4 Acidic salt solution and elution impurities 5 Fluorine-containing cation exchange membrane 6 Diluted caustic soda solution 7 Cathode chamber 8 Cathode 9 Diluted caustic soda solution containing NaCl 10 Electrolytic cell 11 Saline 12 Fresh salt 13 Chlorine Gas 14 Fluorine-containing ion exchange membrane treated by the performance recovery method of the present invention 15 Caustic soda solution 16 Production caustic soda solution 17 Hydrogen gas 18 Pure water

Claims (5)

A step of supplying an acidic saline solution having a pH of 1.5 to 3.5 to an anode chamber of a saline electrolytic cell partitioned with a fluorine-containing cation exchange membrane, and a diluted caustic soda solution having a caustic soda concentration of 20 to 30% by weight to the cathode chamber. A method for recovering the performance of a fluorinated cation exchange membrane, comprising a step of supplying, and a step of holding the acidic saline solution and diluted caustic soda solution in the electrolytic cell in a state in which energization is stopped. The performance recovery method according to claim 1, wherein the salt concentration of the acidic saline supplied to the anode chamber is 150 to 300 g / L. The performance recovery method according to claim 1 or 2, wherein the temperature in the anode chamber is 60 to 80 ° C. A production caustic soda solution comprising a step of supplying saline to an anode chamber of an electrolytic cell having a fluorine-containing cation exchange membrane treated by the performance recovery method according to claim 1, 2 and 3, and a step of electrolyzing the saline Manufacturing method. A process for supplying chlorine to an anode chamber of an electrolytic cell having a fluorine-containing cation exchange membrane treated by the method for recovering performance according to claim 1, 2 or 3, and a process for producing chlorine comprising the step of electrolyzing the saline Method.

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