JPH0244903B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a nitric acid solution of ceric nitrate, which is an effective oxidizing agent and is free of ammonium ions.

The solution can be used as an oxidizing agent for the production of corresponding quinones from aromatic compounds (for example, production of 1,4-naphthoquinone from naphthalene), oxidation of aromatic side chains (for example, production of benzaldehyde from toluene),
It is widely used in the field of organic synthesis, such as oxidation of hydroxyl groups, ring opening of cycloalkanones, and carbonylation of oximes. (For example, Koichiro Oshima, Journal of the Society of Organic Synthetic Chemistry, Vol. 40, No. 12, p. 1171 (1982)) Recently, it has also been used as an etching agent in the semiconductor component manufacturing process, or as an etching agent that adheres to piping and equipment in nuclear reactor facilities. It is also known to be used as a chemical decontamination agent to dissolve and remove radioactive corrosion products.

[Prior Art] Ceric salts often used as raw materials for solutions containing ceric ions include ceric sulfate Ce(SO ₄ ) ₂ , ceric ammonium nitrate (NH ₄ ) ₂ [Ce( NO ₃ ) ₆ ], ceric perchlorate H ₂ Ce(ClO ₄ ) ₆ and the like are known.

Industrially, when an organic compound is oxidized using a ceric salt, ceric is reduced to ceric, so it is necessary to recover and oxidize it back to ceric and reuse it. Therefore, an indirect electrolysis method is often carried out in which a step of oxidizing an organic compound is combined with a step of electrochemically oxidizing and regenerating recovered cerium to ceric.

[Problems to be Solved by the Invention] However, the above-mentioned indirect electrolysis methods using ceric salts have their own drawbacks as described below.

When performing an oxidation reaction using a ceric sulfate solution, the solubility of ceric sulfate produced in the reaction is relatively low, so in order to avoid precipitation of ceric sulfate after the reaction, the concentration of ceric sulfate should be adjusted. I have no choice but to set it low. Therefore, the reaction rate of the oxidation reaction using such a low concentration ceric sulfate solution becomes slow and the reaction time becomes long. In addition, if the cerium concentration is low, when the ceric ions produced by the oxidation reaction are electrolytically oxidized and regenerated into ceric ions, the overvoltage at the anode increases, resulting in an increase in the electrolytic voltage and the decomposition of water. The oxygen-generating electrode reaction occurs more actively, leading to a decrease in the current efficiency of ceric ion generation. Furthermore, reactions using low-concentration ceric ion solutions have the disadvantage that the amount of effective ceric ions per unit volume of the solution is small, requiring large reaction vessels and incidental equipment. This makes it difficult to industrialize the oxidation reaction process using ceric sulfate. Further, among ceric salts, ceric sulfate has a relatively low oxidizing power, and may not be able to provide sufficient oxidizing power depending on the reaction.

Further, when the oxidation reaction is carried out using a ceric ammonium nitrate solution, the solubility in water is large, and the above-mentioned difficulty due to the ceric ion concentration can be overcome. However, the cerium source is a double salt of ammonium and cerium nitrate, and in a process that combines the oxidation reaction process of organic compounds and the regeneration process of ceric by electrolysis, nitrate ions and ammonium ions behave in a complicated manner due to electrolytic oxidation. However, this poses various disadvantages to industrialization. That is, depending on the conditions, nitrate ions are reduced to nitrite and ammonium ions at the cathode by electrolysis, and ammonium ions are oxidized to nitrite and nitrate ions, or nitrite ions are oxidized to nitrate ions at the anode. things happen. These redox reactions cause changes in the concentration of hydrogen ions, ammonium ions, nitrate ions, or nitrite ions, and the pH of the liquid also changes. As a result, the deterioration of the equipment and electrodes becomes complex and serious, and the ability of the ceric salt solution as an oxidizing agent also changes, making it necessary to change the settings of reaction conditions, etc. It may be necessary to analyze the liquid composition, make adjustments such as adding nitrate ions, etc., or replace the liquid in some cases.
Further, an anodic reaction such as oxidation of ammonium ions brings about a decrease in the current efficiency for producing the desired ceric ions.

When ceric perchlorate salt, which is known as another cerium source, is used, it is expensive and dangerous, and there are problems in handling from the viewpoint of corrosion, making it unsuitable for industrialization.

Furthermore, since acid solutions containing ceric ions generally have strong oxidizing power, the durability of the materials used in the electrolyzer also poses a problem.

Although salts containing ceric and their solutions are unique and excellent oxidizing agents in fields such as organic synthesis, conventional methods have the above-mentioned drawbacks and cannot be used on an industrial scale. implementation has become extremely difficult.

An object of the present invention is to produce a solution containing ceric by electrolytically oxidizing a solution containing cerous, while suppressing electrode reactions other than the oxidation of cerous ions, with high current efficiency, and relatively high current efficiency. The object of the present invention is to provide a method for producing a solution containing a concentration of ceric.

[Means for Solving the Problems] The present inventors have conducted various studies based on the belief that the drawbacks of the oxidation reaction using the above-mentioned conventional salt containing cerium and its solution are mainly due to the type of cerium salt. As a result, the present invention has been completed. That is, the present invention uses a nitric acid solution containing cerous nitrate as an anolyte, an electrolyte solution as a catholyte, and a fluorine-based anion exchange membrane and a fluorine-based cation exchange membrane are stacked as a diaphragm. This is a method of electrolytically oxidizing using a laminated fluorine-based ion exchange membrane to obtain a nitric acid solution of ceric nitrate that does not contain ammonium ions.

Hitherto, little is known about indirect electrolysis using cerous nitrate. However, as a result of research by the present inventors, the nitric acid solution of ceric nitrate obtained by the method of the present invention has a sufficient concentration as an oxidizing agent for industrial organic compounds due to the high solubility of the cerium salt. I found out that it can be done.
Furthermore, cerous nitrate has the advantage of being relatively inexpensive and easily available as a cerium salt.

The concentration of cerium in the anolyte used in the present invention is as follows:
The concentration may be lower than the solubility of cerium, ceric nitrate, or both when they coexist; however, if the concentration is too high, the viscosity of the liquid will increase, which may interfere with various operations such as electrolytic oxidation and subsequent reactions. Furthermore, the resistance during electrolysis also increases. On the other hand, if the concentration is too low, the superiority of cerium nitrate, that is, its high solubility, will not be utilized, so it is preferably within the range of 0.1 to 10 mol/(more preferably 0.2 to 5 mol/).

If the nitric acid concentration in the anolyte used in the present invention is too low, the ceric nitrate ions produced by electrolytic oxidation will be unstable and cause hydrolysis.
If the temperature is too high, decomposition of the acid itself and material corrosion will be accelerated at high temperatures;
It is desirable that the concentration be within the range of mol/molar.
Note that the nitric acid concentration here does not include the concentration of nitrate ions coming from cerium nitrate.

In the present invention, a laminated fluorine-based ion exchange membrane is used as the diaphragm. When a diaphragm is not used, nitrate ions are reduced at the cathode to generate ammonium ions, which are not only mixed into the ceric nitrate solution, but also the ceric ions generated at the anode diffuse and become ammonium ions again at the cathode. It is reduced to cerium ions, resulting in a decrease in current efficiency. Furthermore, when a conventional hydrocarbon-based ion exchange membrane is used as a diaphragm, it has poor durability and cannot provide satisfactory performance under the electrolytic conditions of the present invention. Considering the performance and durability of the ion exchange membrane, it is necessary to use a combination of a fluorine-based cation exchange membrane and a fluorine-based anion exchange membrane.

In the present invention, a laminated fluorine-based ion exchange membrane obtained by laminating a fluorine-based anion exchange membrane and a fluorine-based cation exchange membrane is used as the diaphragm. The laminated fluorine-based ion exchange membrane of the present invention has a thin layer of anion-exchange property or cation-exchange property partially introduced by modifying the surface of a fluorine-based cation exchange membrane or a fluorine-based anion exchange membrane. It is also implemented as a surface-modified fluorine-based ion exchange membrane. Generally known methods for laminating a fluorine-based anion exchange membrane and a fluorine-based cation exchange membrane include hot rolling and a method in which one membrane is polymerized on the other membrane. In particular, when a laminated fluorine-based ion exchange membrane or a surface-modified fluorine-based ion exchange membrane is used, mainly only hydrogen ions move through the membrane, and the movement of cerium ions and the like is suppressed. This is particularly preferred in practice. Furthermore, the cation exchange membrane used in the present invention may have a network of other fluorine-based polymer fibers inserted therein to reinforce its mechanical strength.

The laminated fluorine-based ion exchange membrane of the present invention may have two layers or three or more layers. For example, in the case of a three-layer structure, an anion exchange membrane, a cation exchange membrane, and an anion exchange membrane are laminated in this order. It is better to do so.

Furthermore, in the stacked fluorine-based ion exchange membrane used in the present invention, the ion exchange capacity of each fluorine-based anion exchange membrane and fluorine-based cation exchange membrane before stacking is 0.1 to 10 meq/g- A laminated layer of dry resin, preferably having an exchange capacity of 0.2 to 4 meq/g of dry resin, more preferably 0.3 to 2.5 meq/g of dry resin, is recommended. If the ion exchange capacity is too large, the mechanical strength of the resulting membrane will be low, making it difficult to manufacture the membrane, and more cerium ions will be mixed in through the membrane when used for practical electrolysis, making it difficult to operate continuously. There are disadvantages such as interference and a decrease in current efficiency. If the ion exchange capacity is too small, the electrical resistance will increase and the cell voltage will increase, leading to an increase in power consumption.

Further, as for the thickness of the film, an appropriate thickness is selected depending on the specific conductivity of the film, current efficiency, etc., and a film having a thickness of generally 0.01 to 1.5 mm, preferably 0.05 to 1.5 mm is used.

As the catholyte is independent from the anolyte through the ion exchange membrane, it is not particularly limited as long as it is an electrolyte; for example, an aqueous solution of nitric acid, sulfuric acid, etc. can be used, and the movement of cerium ions, etc. can be suppressed. For this purpose, it is also preferable to use a solution having the same composition as the anolyte before electrolysis. Furthermore, in order to prevent the movement of cerium ions from the anode chamber to the cathode chamber, it is also effective to set the cerium ion concentration in the catholyte to be higher than that in the anolyte in advance. In some cases, a bipolar reaction in which a specific reduction reaction is carried out is also possible in order to actively utilize a cathodic reaction.

The current density in electrolysis is not particularly limited, but
Generally, under high current density conditions, there is an advantage that the production amount per unit electrolytic cell increases, but on the other hand, it is disadvantageous in terms of current efficiency and electrolysis voltage. Preferably 1-70A/
dm ² , more preferably at a current density of 3 to 40 A/dm ² .

Known electrode materials are used for the electrodes used in electrolysis. For example, as the anode, oxide-coated electrodes such as iridium oxide-coated titanium, platinum-iridium oxide-coated titanium, platinum-plated titanium, graphite, and glassy carbon are used as the anode. In addition to the above-mentioned electrodes, an electrode made of stainless steel (for example, SUS-316L) is used as the cathode.

The electrolytic oxidation temperature is determined by considering the solubility of cerium nitrate in the nitric acid solution used in the present invention, the decomposition of the acid itself, the corrosion of the material, and the reaction temperature of the oxidation reaction after electrolytic oxidation. Since the concentration of cerous nitrate in the liquid can be set high even at relatively low temperatures, the temperature is relatively low compared to conventional electrolytic oxidation of acid solutions containing cerium salts, such as electrolytic oxidation of ceric sulfate in sulfuric acid aqueous solutions. Good electrolytic properties can be obtained. It is preferably carried out at a temperature of 150°C or lower, more preferably 10 to 80°C.

[Examples] Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, to check the presence or absence of ammonium ions in the anolyte after electrolytic oxidation,
ml was made basic by adding an aqueous sodium hydroxide solution, and the presence or absence of an ammonia odor was judged.

Comparative example 1 Cerous nitrate (Ce(NO) ₃・6H ₂ O) 868.4g
is dissolved in a nitric acid aqueous solution to make it 1 (nitric acid concentration: 1.5 mol/) and charged into the anolyte tank as an anolyte, and 1.5 mol/nitric acid aqueous solution is charged into a catholyte tank as a catholyte, and each solution is ion-exchanged. Electrolytic oxidation was performed under the following conditions at a temperature of 50°C while circulating in a two-chamber electrolytic cell separated by a membrane until the concentration of ceric ions in the anolyte became 1.2 mol/, and ceric nitrate was used as the anolyte. A nitric acid solution was obtained.

Anode: Pt plated Ti electrode Cathode: SUS316L Diaphragm: Fluorine-based cation exchange membrane (thickness 0.08 mm, ion exchange capacity 0.83 meq/g - dry resin) Current density: 15 A/dm ² Current efficiency at this time is 98.4% It was hot. Furthermore, no ammonium ions were detected in the anolyte after electrolytic oxidation.

Comparative Example 2 Electrolysis was carried out under the same conditions as in Comparative Example 1, except that a fluorine-based anion exchange membrane having a thickness of about 0.3 mm and having an ion exchange capacity of 0.8 meq/g-dry resin was used. The current efficiency at this time was 98.9%. Furthermore, no ammonium ions were detected in the anolyte after electrolytic oxidation.

Comparative Example 3 An anode chamber using a fluorine-based cation exchange membrane as a diaphragm between the anode chamber and the intermediate chamber, and a fluorine-based anion exchange membrane as a diaphragm between the intermediate chamber and the cathode chamber,
Using a three-chamber electrolytic cell consisting of an intermediate chamber and a cathode chamber, the anolyte contains a nitric acid solution containing 2 mol/cerium ion (nitric acid concentration: 1.5 mol/).
Electrolysis was carried out under the same conditions as Comparative Example 1, using a 1.5 mol/nitric acid aqueous solution as the catholyte and intermediate chamber solution.
A solution containing 1.2 mol/ceric ion was obtained. The current efficiency was 98.1%. No ammonium ions were detected in the anolyte after electrolysis.

Comparative Example 4 A fluorine-based cation exchange membrane 1 with an ion exchange capacity of 0.67 meq/g-dry resin was laminated with a fluorine-based cation exchange membrane 2 having an ion exchange capacity of 0.91 meq/g-dry resin. Electrolysis was carried out under the same conditions as in Comparative Example 1, except that a layered fluorine-based cation exchange membrane was used as a diaphragm and the cation exchange membrane 1 was incorporated into the electrolytic cell with the surface facing the anode side. A solution containing 2 cerium ions has a current efficiency of 98.6.
Obtained in %. No ammonium ions were detected in the anolyte after electrolysis.

Example 1 A laminated fluorine-based ion exchange membrane with a two-layer structure obtained by laminating a fluorine-based cation exchange membrane and a fluorine-based anion exchange membrane was used as a diaphragm, with the anion exchange membrane side facing the anode side. Incorporated into the electrolytic cell, anolyte before electrolysis Cerium concentration (mol/) 2 Nitric acid concentration (mol/) 4.5 Catholyte 4.5M nitric acid electrolysis temperature (℃) 50 Current density (A/dm ² ) 10 When electrolysis was carried out under the same conditions as in Comparative Example 1, a solution containing ceric ions at a concentration of 1.2 mol/l was obtained with a current efficiency of 99.5%. No ammonium ions were detected in the anolyte after electrolysis.

Example 2 Same as Example 1 except that a 3-layer laminated fluorine-based ion exchange membrane obtained by laminating a fluorine-based anion exchange membrane on both sides of a fluorine-based cation exchange membrane was used as the diaphragm. When electrolyzed under similar conditions,
A solution containing ceric ions at a concentration of 1.2 mol/l was obtained with a current efficiency of 99.6%. No ammonium ions were detected in the anode after electrolysis.

Comparative Example 5 Electrolytic oxidation was carried out under the same conditions as in Example 1 except that an unglazed diaphragm plate was used instead of the fluorine-based cation exchange membrane, and 0.94 mol/cerium ion was produced at a current efficiency of 76.8%. An anolyte containing Furthermore, ammonium ions were detected in the anolyte after electrolytic oxidation, and the presence of cerium ions due to leakage of the anolyte was observed in the anolyte. When electrolysis was further continued, the ammonium ion concentration in the anolyte further increased, and the cerium ion concentration further decreased.

Comparative Example 6 Electrolysis was carried out for two weeks under the same conditions as in Comparative Example 1, except that a hydrocarbon-based cation exchange membrane was used instead of the fluorine-based cation exchange membrane. The parts of the membrane that came into contact with the liquid were discolored, deformed and hardened, and properties such as conductivity had deteriorated, making further electrolysis virtually impossible.

Comparative Example 7 868.4g of cerous nitrate was dissolved in pure water and 1
When electrolytic oxidation was carried out under the same conditions as in Comparative Example 1, except that the above solution was used as the anolyte, a large amount of pale yellowish-white precipitate was formed at the anode due to hydrolysis of ceric ions, and the target solution was Electrolytic oxidation could not be carried out.

[Effects of the Invention] As is clear from the Examples and Comparative Examples, by carrying out the present invention, a nitric acid solution of ceric nitrate useful as an oxidizing agent can be prepared with a high ceric ion concentration and a high concentration without containing ammonium ions. Ceric ammonium nitrate can be obtained with high current efficiency, and in a process that combines an oxidation reaction process and an electrolytic oxidation process, the reaction vessel and incidental equipment are smaller than when using ceric sulfate, which has low solubility. The change in the composition of the electrolytic solution is less complicated than when using the electrolytic solution, and therefore, the solution is easier to manage and the deterioration of the device and electrodes is reduced.
Furthermore, by implementing the present invention, energy-saving and stable operation in the electrolytic oxidation process is also possible.

Claims (1)

[Claims] 1. A multilayer fluorine-based membrane obtained by laminating a fluorine-based anion exchange membrane and a fluorine-based cation exchange membrane as a diaphragm, using a nitric acid solution containing cerous nitrate as the anolyte, using an electrolyte solution as the catholyte, and as a diaphragm. A method of electrolytically oxidizing using an ion exchange membrane to obtain a nitric acid solution of ceric nitrate that does not contain ammonium ions.