JP2006225693A - Method for producing periodate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing periodates with improved current efficiency for periodic acid and great productivity, by removing insoluble iodates or periodates precipitating on the surface of a lead dioxide anode during electrolysis when producing them through an electrolytic process of electrolytically oxidizing iodine and/or iodates contained in an aqueous solution, with a simple method. <P>SOLUTION: The electrolytic process comprises the steps of: electrolytically oxidizing iodine and/or iodates contained in the aqueous solution into periodic acid by anodically polarizing the lead dioxide electrode; and electrolytically activating the surface of the electrode in the electrolytic solution. The electrolytic activation step employs electrolysis at higher voltage than average voltage in the oxidation electrolysis by at least 1.0 V, or electrolysis in the aqueous solution containing iodine and/or iodic acid of less than 30 g/L. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid in an electrolysis step, and more specifically, insoluble iodate or The present invention relates to a method for producing periodic acids while activating deterioration of electrode activity due to periodate adhesion by a simple method.

  As a method for producing periodate (hereinafter referred to as one containing periodate and its salts), a method for producing periodate by electrolytically oxidizing iodine is known.

  As the above method, Patent Document 1 discloses a method for producing periodic acid or a salt thereof by electrolytically oxidizing an aqueous solution of iodic acid and a salt thereof with a lead dioxide electrode. According to this production method, it is possible to produce periodate salts of relatively high purity that do not contain impurities such as chlorine and sulfuric acid. However, as shown in, for example, Patent Document 2 or Patent Document 3, a lead dioxide electrode has an insoluble periodate (for example, sodium periodate, lead periodate, etc.) on the electrode surface along with the progress of electrolysis. ) Is deposited, and the consumption of lead dioxide, which is an electrode catalyst, increases locally due to high current density, or the iodic acid of the raw material is not supplied to the electrode surface, and the catalytic activity of the lead dioxide electrode, ie periodic acid It is known that the current efficiency is reduced and the electrode is inactivated.

  Conventionally, such an inactivated electrode is removed from the electrolytic cell and immersed or electrolyzed in an aqueous solution of sulfuric acid or the like to wash and remove deposits on the electrode surface, or physically polish the electrode surface. Thus, the regeneration of the electrode has been attempted, but the labor involved in the cleaning work is complicated, the cost of cleaning chemicals is increased, and the problem to be solved remains that the manufacturing cost increases.

Japanese Patent Publication No. 38-5255 Japanese Patent Publication No. 36-10312 Japanese Patent Laid-Open No. 56-23286

  The object of the present invention is to solve the above-mentioned problems and to produce periodate by electrolytic oxidation of an aqueous solution containing iodine and / or iodate by an electrolysis process. By removing the precipitated insoluble iodate or periodate by a simple method and electrolyzing while activating the lead dioxide anode surface, the current efficiency is improved and periodate with excellent productivity is produced. It is to provide a way to do.

  As a result of intensive research, the present inventors removed insoluble iodate or periodate deposited on the surface of the lead dioxide anode during the electrolysis process by a simple method, and electrolyzed while activating the lead dioxide anode surface. As a result, it has been found that the current efficiency can be improved and the periodate can be produced with high productivity, and the present invention has been completed.

  That is, the present invention relates to a method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid by an electrolysis step, wherein the electrolysis step is performed in an aqueous solution containing iodine and / or iodate. The production of periodates, comprising oxidation electrolysis in which a lead dioxide electrode is positively polarized and electrolytically oxidized to periodate, and electrode activation electrolysis in which the electrode surface is activated in the electrolytic solution Is the method.

  Further, the present invention provides the above-described periodate production method, wherein the electrode activated electrolysis is electrolyzed at a voltage at least 1.0 V higher than the average voltage in the oxidation electrolysis. Is the method.

  In addition, the present invention is a method for producing periodate, wherein the electrode activation electrolysis is electrolyzed in an aqueous solution containing less than 30 g / L of iodine and / or iodic acid.

Further, according to the present invention, in any one of the methods for producing periodates, the oxidation electrolysis has a current density of more than 3 A / dm ² and less than 20 A / dm ² and the electrode activation electrolysis has a current density of more than 20 A / dm ^{2 and} more than 50 A / dm. This is a method for producing periodate, which is performed at ² or less.

  The lead dioxide electrode is an electrode in which a lead dioxide layer is formed on a titanium substrate.

  The periodate is at least one selected from the group consisting of periodic acid, lithium periodate, sodium periodate, potassium periodate and ammonium periodate. This is a method for producing iodates.

  According to the present invention, in the method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid by an electrolysis step, the electrolysis step is carried out in an aqueous solution containing iodine and / or iodate. By combining the oxidation electrolysis that positively polarizes the lead dioxide electrode and electrolytically oxidizes it to periodic acid, and the electrode activation electrolysis that activates the electrode surface in the electrolyte, the insoluble matter adhering to the lead dioxide electrode surface is obtained. Iodate or periodate can be easily removed, the deterioration of current efficiency due to the adhesion is improved, and there is no need to remove and regenerate the electrode as in the past. It is possible to manufacture.

  The present invention relates to a method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid by an electrolysis step, wherein the electrolysis step is carried out in an aqueous solution containing iodine and / or iodate. A method for producing periodates, comprising oxidation electrolysis in which a lead electrode is positively polarized and electrolytically oxidized to periodate, and electrode activation electrolysis in which the electrode surface is activated in the electrolytic solution. is there.

  In the electrolysis process of the present invention, for example, the electrolytic cell shown in FIG. 1 (schematic diagram showing the configuration of the diaphragm electrolytic cell) can be used. In FIG. 1, the diaphragm electrolytic cell 1 is an ion exchange membrane, made of magnetic material. Or, it is divided into an anode chamber 3 and a cathode chamber 4 through a diaphragm 2 such as a resin porous membrane, and the anode 5 is provided with a lead dioxide electrode, and the cathode 6 is provided with stainless steel, titanium or the like.

  The lead dioxide electrode is not particularly limited as long as it is an electrode in which an electrode catalyst layer is coated with lead dioxide. Specifically, a lead dioxide layer is coated on a titanium substrate described in JP-A-56-166384. The electrode made to be preferable is preferable.

  As the anolyte of the diaphragm type electrolytic cell, an aqueous solution containing iodine and / or iodic acid (hereinafter abbreviated as “iodine raw material”) can be used. Specifically, the salt containing the iodine raw material is water, What melt | dissolved in the aqueous solution of an alkali metal hydroxide or various acids is mentioned. The concentration of the iodine raw material contained in the anolyte is preferably at least 50 g / L. When the iodine raw material is less than 50 g / L, the cell voltage is high, and the concentration of the periodate obtained is low, resulting in poor productivity.

  Moreover, as a catholyte, aqueous solution, such as a sulfuric acid, sodium hydroxide, sodium sulfate, can be used, and it does not specifically limit.

  The electrolysis step of the present invention uses the diaphragm-type electrolytic cell configured as described above, and in the aqueous solution containing the iodine raw material, the oxidation electrolysis in which the lead dioxide electrode is positively polarized and electrolytically oxidized to periodate, Electrode activation electrolysis that activates the electrode surface in the electrolytic solution is included.

  The electrolysis process in the present invention comprises oxidation electrolysis and electrode activation electrolysis, and the oxidation electrolysis is mainly a reaction in which iodine raw material in the electrolytic solution is electrolytically oxidized to periodic acid, and oxygen is generated as a side reaction. In this case, the oxidation electrolysis refers to an electrolysis state in which the current efficiency of periodate generation is 40% or more and the current consumed for oxygen generation is less than 60%.

  On the other hand, electrode activation electrolysis increases the generation of oxygen gas on the electrode surface by electrolyzing a lead dioxide anode on which insoluble salts are deposited in an electrolyte containing a high current density or a small amount of iodine raw material. The electrode is activated by peeling off these precipitates by this gas generation pressure, and the conditions for electrode activation electrolysis are preferably in a range where the current consumed for oxygen generation is at least 70%. .

  In general, when electrolysis is performed in a low current density region in an electrolytic solution containing a large amount of iodine raw material, oxidation electrolysis tends to proceed. Conversely, in an electrolytic solution containing a small amount of iodine raw material, electrolysis is performed in a high current density region. Is easy to progress.

  In practicing the present invention, it is preferable that the electrolysis step is appropriately performed electrode activation electrolysis when the current efficiency of periodate generation is reduced to less than about 40%. For example, by increasing the current density and performing electrolysis for a certain period of time, or by performing electrolysis for a certain period of time in an aqueous solution containing less than 30 g / L of iodine raw material, so that the voltage becomes at least 1.0 V higher than the average voltage in The generation of gas from the electrode is promoted, the deposit on the electrode surface can be removed by the gas generation pressure, and the electrode can be regenerated and activated. Moreover, the same effect can be obtained even when electrolysis is performed by increasing the current density in an aqueous solution containing less than 30 g / L of the iodine raw material.

  Electrode activation electrolysis may be performed for a certain period of time by increasing the current density so that the electrolysis voltage increases by at least 1.0 V during the electrolysis process during the electrolysis process, or at the end of electrolysis, the concentration of the iodine raw material Electrolysis may be performed for a certain period of time at a point of time of less than 30 g / L.

  The electrolysis time required for electrode activation is determined by conditions such as the scale of the electrolytic cell, the type of electrolytic solution, and the current density, and is not particularly limited, but the effect of electrode activation can be obtained by performing electrolysis for at least 1 hour. .

The current density of oxidation electrolysis and electrode activation electrolysis in the electrolysis process is usually in the range of oxidation electrolysis over 3 A / dm ^{2 over} 20 A / dm ² and electrode activation electrolysis over 20 A / dm ^{2 over} 50 A / dm ² It is. When the current density of electrode activation electrolysis exceeds 50 A / dm ² , the electrode may be adversely affected.

  Under the above electrolysis conditions, the iodine raw material is electrolytically oxidized to periodic acid to obtain the desired periodate. Specifically, when an iodic acid aqueous solution is used as the anolyte, a periodic acid aqueous solution is generated by the electrolysis step shown in the present invention, and after the obtained anolyte is filtered, it is appropriately concentrated to a predetermined concentration. To obtain the desired periodic acid.

  When a sodium iodate aqueous solution is used as the anolyte, a sodium periodate aqueous solution is produced by electrolytic oxidation. The obtained anolyte is concentrated, cooled, and filtered to obtain sodium periodate crystals. In addition, when an aqueous hydrochloric acid solution in which iodine is suspended and dissolved is used as the anolyte, a periodic acid aqueous solution is similarly produced. After neutralizing this with an alkali, the solution is concentrated to dryness and the corresponding lithium periodate is prepared. , Sodium periodate, potassium periodate, and ammonium periodate can be obtained.

  According to the present invention, in the method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid in an electrolysis step, the electrolysis step comprises positively polarizing a lead dioxide electrode in the electrolyte solution. Insoluble iodate or periodate adhering to the electrode surface can be obtained by combining oxidative electrolysis that performs electrolytic oxidation to periodate and electrode activation electrolysis that activates the electrode surface in the electrolytic solution. Periodic acid salt can be produced with high productivity because it can be easily removed, the current efficiency deteriorates due to adhesion, and the local consumption of the electrode is improved, and it is not necessary to remove and regenerate the electrode as in the past. It is possible.

  The embodiment of the present invention will be specifically described based on examples. In addition, this invention is not limited at all by the Example.

Example 1
Fluororesin cation exchange membrane to membrane (registered trademark of Du Pont Nafion NE424), anode PbO ₂ coated titanium electrodes (active surface: 0.45dm ^2), titanium electrodes (active surface: 0.45dm ²⁾ to the cathode, respectively Using the provided diaphragm electrolytic cell (FIG. 1), supplying 1 L of 100 g / L sodium iodate aqueous solution to the anode chamber and 1 L of 40 g / L sodium hydroxide aqueous solution to the cathode chamber, respectively, the current density was 10 A / dm. Periodic acid oxidation electrolysis was carried out at ² (current 4.5 A) for 6 hours. The average voltage at this time was about 5 V, and the current efficiency of periodic acid (indicating the percentage of current consumed to generate periodic acid with respect to the total applied current) was 80%.

  As a result of repeating the same electrolysis operation a plurality of times using a newly prepared electrolytic solution, the current efficiency of periodic acid showed a tendency to gradually decrease, and after 6 batches, about 40 %, And it was confirmed that black lead iodate was deposited on the electrode surface.

After electrolysis of the 6th batch, in the same electrolytic solution in which the iodic acid concentration was reduced to about 60 g / L by oxidation electrolysis, current was passed for 1 hour under conditions of a current density of 50 A / dm ² (22.5 A) and a cell voltage of about 10 V. Electrode activation electrolysis was performed.

  After the activation electrolysis, the seventh batch of electrolysis was performed using the newly prepared electrolyte. As a result, the periodic acid current efficiency was recovered to 78%, and it was confirmed that the electrode surface was activated. did.

Comparative Example 1
In Example 1, after completion of electrolysis in the sixth batch, electrolysis in the seventh batch was performed in the same manner as in Example 1 except that electrode activation electrolysis was not performed. As a result, the current efficiency of periodic acid was 40%, and the electrode surface could not be activated.

  The results of Example 1 and Comparative Example 1 are shown in Table 1.

Table 1

Example 2
The same diaphragm electrolytic cell as in Example 1 was used, and 1 L of 200 g / L iodic acid aqueous solution was supplied to the anode chamber, and 1 L of 40 g / L sodium hydroxide solution was supplied to the cathode chamber, respectively, and the current density was 20 A / dm ^2. Periodic acid was oxidized and electrolyzed at (current 9A) for 8 hours. The average voltage at this time was about 9 V, and the current efficiency of periodic acid was 72%.

  In the electrolytic solution in which the iodic acid concentration was reduced to about 30 g / L by the oxidation electrolysis, current activation was performed for 1 hour at the same current density as that in the oxidation electrolysis to perform electrode activation electrolysis. After the electrode activation electrolysis, the concentration of iodic acid in the anolyte was less than 10 g / L.

  The above electrolysis operation including oxidation electrolysis and electrode activation electrolysis in each electrolysis step was made into one batch, and the same electrolysis operation was repeated several times using a newly prepared electrolytic solution, but no decrease in current efficiency was observed, As a result of conducting the sixth batch of electrolysis, the current efficiency of periodic acid was 70%.

Comparative Example 2
In Example 2, the sixth batch of electrolysis was performed in the same manner as in Example 2 except that electrode activation electrolysis was not performed for each batch. As a result, the current efficiency of periodic acid was reduced to 45%.

  The results of Example 2 and Comparative Example 2 are shown in Table 2.

Table 2

  From the results of Tables 1 and 2, insoluble iodate or periodate attached to the electrode surface can be easily removed by performing electrode activation electrolysis after oxidation electrolysis, and the current efficiency due to these adhesions. The deterioration of the electrode and the local consumption of the electrode are improved, and it is not necessary to remove and regenerate the electrode as in the prior art. Therefore, it is possible to produce periodate with high productivity.

It is a schematic diagram which shows the structure of a diaphragm electrolytic cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diaphragm electrolytic cell 2 Diaphragm 3 Anode chamber 4 Cathode chamber 5 Anode 6 Cathode

Claims (6)

In a method for producing periodate by electrolytically oxidizing an aqueous solution containing iodine and / or iodic acid in an electrolysis step, the electrolysis step comprises positively treating a lead dioxide electrode in an aqueous solution containing iodine and / or iodate. A method for producing periodate, comprising oxidation electrolysis that is polarized and electrolytically oxidized to periodic acid, and electrode activation electrolysis that activates an electrode surface in the electrolytic solution. The method for producing periodates according to claim 1, wherein the electrode activated electrolysis is electrolyzed at a voltage at least 1.0 V higher than the average voltage in the oxidation electrolysis. . The method for producing periodates according to claim 1, wherein the electrode activated electrolysis is electrolyzed in an aqueous solution containing less than 30 g / L of iodine and / or iodic acid. Production method. The method of manufacturing a periodate salt according to claim 1, oxide electrolysis current density 3A / dm ² super 20A / dm ² or less and the electrode activation electrolyte current density 20A / dm ² super 50A / dm ² rows below A method for producing periodates, characterized in that The method for producing periodate according to any one of claims 1 to 4, wherein the lead dioxide electrode is an electrode in which a lead dioxide layer is formed on a titanium substrate. The periodate is at least one selected from the group consisting of periodic acid, lithium periodate, sodium periodate, potassium periodate and ammonium periodate. Item 6. The method for producing periodate according to any one of Items 5 to 6.

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