JP4778320B2 - Electrosynthesis of perchloric acid compounds - Google Patents

Description

The present invention is an industrially important oxidant, to a manufacturing method for the purpose of obtaining explosive material, perchloric acid compounds utilized as the reaction synthesis reagents as efficiently highly pure product.

  Perchloric acid and perchlorate are one of the useful electrolytic synthetic materials for rocket fuel, explosives, and reaction catalysts. Sodium perchlorate is obtained by electrolytic oxidation of sodium chlorate, concentration and crystallization. Perchloric acid is synthesized by pyrolytic distillation of sodium perchlorate together with sulfuric acid, and is commercially available and transported as a 60-70% aqueous solution because of the risk of explosion. Potassium perchlorate is synthesized by adding potassium chloride to a solution synthesized by electrolysis, causing metathesis, cooling and separating as crystals.

Electrolysis of perchlorate uses an electrode with a platinum foil formed on the surface of a Ti substrate. However, if the chloric acid compound (chlorate) concentration of the raw material is 0.1 M or less, electrode material deterioration and electrode deterioration may occur. Accelerated, 0.01M was the lower limit. It is considered that platinum materials gradually form an oxide film on the surface under such electrolysis conditions, the performance becomes unstable due to current on / off, and consumption is accelerated by additives such as fluorine ions. It is done. Lead oxide as an alternative material has excellent decomposition characteristics and is useful, but has disadvantages such as generation of sludge, lowering product purity, and unstable performance due to unstable performance of the electrode itself. The search for an alternative electrode material that solves these problems has been a problem.
Diamond is excellent in thermal conductivity, optical transparency, high temperature and oxidation resistance, and can control electrical conductivity, especially by doping, so next generation and special semiconductor devices, energy conversion Promising as an element. Conductive diamond electrodes imparted with good electrical conductivity by doping in addition to excellent mechanical and chemical stability have recently been actively studied in application to the electrochemical field.

The following patent documents are listed.
US Pat. No. 5,399,247 discloses that organic wastewater can be decomposed using diamond as the anode material.
JP-A-9-268395: It is disclosed that diamond is useful as an electrode for functional water (including ozone).
JP 2001-192874 A discloses that conductive diamond is useful as an electrode for persulfuric acid synthesis.

JP-A-2004-211182 discloses that conductive diamond is useful as an electrode for percarbonate synthesis.
JP 2004-202283 A: When an ion exchange membrane is used when electrolytically treating wastewater containing an organic chlorine compound using a conductive diamond electrode, the movement of anions between both chambers is prevented. Thus, chlorine ions (anions) liberated at the cathode can be prevented from moving to the anode side, and the chlorine ions are oxidized from hypochlorite ions to perchlorate ions on the anode side to form organic compounds. It is disclosed to prevent degradation of the decomposition efficiency (paragraph 0023).
However, in these patent documents, for the purpose of industrial electrolytic synthesis, no examination has been made for the purpose of improving the current efficiency and purity of perchloric acid compounds.

In the present invention high purity and good power efficiency, and to consider Ru electrolytic synthesis method can synthesize perchlorate compounds such as perchloric acid.

According to the present invention, a raw material solution containing a chloric acid compound having a raw material concentration of 0.1 M or higher is electrolyzed using an anode having a conductive diamond as an anode material and a cathode until the raw material concentration is reduced to 0.01 M or lower. And a method for electrolytic synthesis of a perchloric acid compound, characterized in that a perchloric acid compound is synthesized .

The present invention will be described in detail below.
Perchloric acid compound is a target product of the present invention can be synthesized with high efficiency by electrolysis using a conductive diamond electrode salts periodate compound. Note perchloric acid compound in the present invention, perchlorates, include perchloric acid and perchlorate ions, the salt periodate compounds, chlorates, include perchloric acid and chlorate ions. Perchlorate, perchloric acid, perchlorate ions, salts periodate, each term in identifying chlorate and chlorate ion Ru is used.

When electrolytic synthesis perchlorate compounds from chlorate compound, using an anode having conductive diamond as an anode material, to obtain a high-purity target compound at high yield than when using a conventional anode it can.

Furthermore, when partitioning the anode compartment and a cathode compartment by a diaphragm, such as a cation exchange membrane, can be prevented the permeation of salt periodate ions, there is a contribution to the improvement of the efficiency and purity.
With the gas electrode suitable for the reduction of oxygen gas as the cathode, Ru can be reduced more than 0.5V power consumption rate as the cell voltage.

The present invention is an invention relating to how to synthesize a industrially important oxidant perchlorate compound in high purity, specifically the raw material solution containing chlorate compound of the raw material concentration above 0.1M The electrolyte is electrolyzed using an anode having a conductive diamond as an anode material until the concentration of the raw material is reduced to 0.01 M or less, and the target perchloric acid compound is electrolytically synthesized. is there.

When a chloric acid compound is used as a raw material, a high-purity target compound can be obtained in a higher yield than when a conventional anode is used. This technique can be applied to improve product quality by introducing an electrolytic solution containing 0.1M or less of chloric acid, which is synthesized in a conventional electrolytic cell, into an electrolytic cell having a diamond electrode. it can be said that an effective way.

When an electrolytic cell is partitioned into an anode chamber and a cathode chamber using an ion exchange membrane in the present invention, ions in each electrode chamber are prevented from moving to other electrode chambers, and a higher-purity target compound is obtained. Is possible.
When a gas electrode suitable for reduction of oxygen gas is used as the cathode, the cell voltage can be reduced and the target compound can be obtained at low cost.
In other known chemical synthesis methods, separation of a drug such as sulfuric acid is essential, whereas the present invention is advantageous in that high-purity perchloric acid can be easily synthesized. There is an environmental contribution.

  Next, the case elements of the present invention will be described in detail.

[Anode reaction]
The anodic reaction in the electrolytic cell of the present invention is represented by the formula (1) when hydrochloric acid is used as a raw material (acidic region), thereby generating perchlorate ions.
Cl ⁻ + H ₂ O = ClO ₄ ⁻ + 8H ⁺ + 8e (1)
Further, in addition to the direct electrolytic oxidation process of formula (1), the reaction of formula (2) proceeds as a side reaction, the generated chlorine reacts with water, and perchlorate ions are generated according to formula (3).
2Cl ⁻ = Cl ₂ + 2e (2)
Cl ₂ + 8H ₂ O = 2ClO ₄ ⁻ + 16H ⁺ + 14e (3)

Further, chlorate ions are by-produced according to the formula (4), and the chlorate ions react with water according to the formula (5) to synthesize the target perchlorate compound (perchlorate ion).
Cl ⁻ + 3H ₂ O = ClO ₃ ⁻ + 6H ⁺ + 6e (4)
ClO ₃ ⁻ + H ₂ O = ClO ₄ ⁻ + 2H ⁺ + 2e (5)
Another side reaction is water electrolysis represented by the formula (6).
2H ₂ O = O ₂ + 4H ⁺ + 4e (6)
As an elementary process of this reaction, generation of OH radicals can be considered, and there is also a pathway in which this radical and chlorine ions react to generate a perchloric acid compound that is a target product.

[Cathode reaction]
The cathodic reaction varies depending on whether oxygen is supplied or not.
When oxygen is not supplied, hydrogen is generated according to equation (7).
2H ⁺ + 2e = H ₂ (7)
When oxygen is supplied, water is synthesized according to formula (8) or hydrogen peroxide is synthesized according to formula (9).
O ₂ + 4H ⁺ + 4e = 2H ₂ O (8)
O ₂ + 2H ⁺ + 2e = H ₂ O ₂ (9)

[Electrode substrate of diamond electrode]
From the viewpoint of chemical stability such as consistency of thermal expansion coefficient and stability under synthetic conditions such as hydrogen atmosphere (for example, brittleness due to hydrogen absorption), the electrode substrate is generally used as a substrate. It is. However, since it is a semiconductive material, it is necessary to dope boron or the like to make it highly conductive. The surface preferably has irregularities in order to increase the mechanical strength. In order to promote the precipitation of diamond, it is desirable to perform polishing and nucleation with diamond particles. As the substrate, not only Si but also Nb, Ta, Zr, Ti (valve metal), Mo, W, graphite, and various carbides can be used.

[Diamond electrode]
A conductive diamond electrode is usually manufactured by forming a conductive diamond layer on an electrode substrate by a hot filament CVD method or a microwave plasma CVD method. Under a pressure of 1 to 100 kPa, a mixed gas having an appropriate composition made of hydrogen, carbon and boron (or nitrogen) raw materials is activated on a hot filament (1800 to 2600 ° C.) to generate carbon and hydrogen radical species. The volume ratio of hydrogen and carbon gas raw material is controlled to about 0.05 to 0.1. Although gas raw materials such as methane and diborane are usually used, it is preferable from the viewpoint of safety at the production site to use alcohols and boron oxide as carbon and boron raw materials. By maintaining the substrate temperature at 600 to 900 ° C., a carbon radical precipitation reaction is initiated on the surface thereof. At this time, since the non-diamond component is etched by the hydrogen radical, only the diamond layer grows. The deposition rate is 0.1-5 μm / H. It is presumed that a stable carbide layer formed on the substrate under the deposition conditions contributes to the improvement of the bonding strength. The doping amount is from 100 ppm to 10000 ppm, and the resistivity increases or decreases in inverse proportion to the doping amount (10 to 0.01 Ωcm). From the electrode resistance (protection of the substrate) and the manufacturing cost, the thickness is optimally 1 to 10 μm.

It has been confirmed by SIMS analysis that the B / C ratios of the supply gas and the generation layer are substantially equal. It is confirmed by Raman spectrum that the coating layer formed by the CVD method is diamond. In the SEM photograph, a polycrystalline precipitation state with a particle size of about 0.1 to 10 μm is observed.
The electrode used in the present invention is not limited to an electrode formed by the CVD method, and may be one in which powder particles are fixed to an electrode substrate.

[cathode]
In the cathode reaction involving hydrogen generation of formula (7), when chloric acid is a raw material, the cathode is used in an acidic atmosphere, and thus chemical durability is required. Base materials such as graphite and zirconium are suitable. In order to reduce the voltage, it is preferable to coat the surface with a component having excellent catalytic activity (platinum group metal, oxide thereof).
When chloride is a raw material, since the cathode is used in an alkaline atmosphere, a substrate such as graphite, stainless steel or nickel is suitable. In order to reduce the voltage, it is preferable to coat the surface with a component having excellent catalytic activity (platinum group metal, oxide thereof).
The use of a diamond electrode for the cathode is preferable because it has chemical stability.

On the other hand, when oxygen is supplied, the reduction reaction of the oxygen gas of formula (8) can proceed as a cathode reaction, and the cell voltage can be reduced. When a special catalyst is used, the oxygen gas reduction reaction preferentially proceeds as a cathode reaction, and hydrogen peroxide of formula (9) can be generated. In this case, since it can be efficiently obtained in an atmosphere of an alkaline aqueous solution, chloride is generally used as a raw material.
As an oxygen gas cathode catalyst suitable for hydrogen peroxide, platinum group metals, noble metals or oxides thereof, sulfides, or carbon such as graphite or conductive diamond are preferable. These catalysts can be used as they are in the form of plates, or on a corrosion-resistant plate such as stainless steel or carbon, a wire mesh, a powder sintered body, or a metal fiber sintered body by a thermal decomposition method, a resin fixing method, composite plating, or the like. It forms so that it may become -1000g / m < ² >.

As the cathode power supply body, metals such as carbon, nickel and stainless steel, alloys thereof and oxidation are desirable. In order to quickly supply and remove the reaction product gas and liquid, it is preferable to disperse and carry a hydrophobic or hydrophilic material. Forming a hydrophobic sheet on the back surface of the cathode opposite to the anode is effective in controlling the gas supply to the reaction surface.
The supply amount of oxygen is preferably about 1.1 to 10 times the theoretical value. As the oxygen gas that is a raw material, air, oxygen obtained by separating and concentrating it, or a commercially available cylinder may be used. If there is a gas chamber on the back of the electrode, oxygen is supplied to the oxygen, but it may be blown into the treated water and absorbed beforehand.

[Ion exchange membrane]
When a cation exchange membrane is used as the diaphragm used in the present invention and a two-chamber cell of an anode chamber and a cathode chamber is used, permeation of chloride ions and chlorate ions can be prevented, which contributes to improvement in synthesis efficiency. Moreover, it is an indispensable material for maintaining the ionic conductivity when the concentration of the electrolytic solution is reduced.
The ion exchange membrane may be either a fluororesin or a hydrocarbon resin, but the former is preferred in terms of corrosion resistance. Examples of the resin having excellent chemical resistance include a fluorinated resin having a sulfone group as an ion exchange group (Nafion as a commercial product manufactured by DuPont). Nafion is made from a copolymer of tetrafluoroethylene and perfluoro [2- (fluorosulfonylethoxy) -propyl] vinyl ether.

[Cell structure]
From the viewpoint of stability, the material of the electrolytic cell is preferably a glass lining material, carbon, titanium, stainless steel or PTFE resin having excellent corrosion resistance.
An electrolytic cell is constructed using the above materials. A diaphragm cell (FIG. 1) having two porous electrodes (anode and hydrogen cathode) to be described later, a two-chamber cell with a diaphragm sandwiched between the anode and hydrogen cathode of the cell of FIG. 1, and a porous anode and oxygen gas A two-chamber cell (FIG. 2) having a cathode and a diaphragm sandwiched between them can be used.
In the two-chamber cell, the distance between the electrodes should be as small as possible in order to reduce the resistance loss, but in order to reduce the pressure loss of the pump when supplying water and keep the pressure distribution uniform, 2 mm is preferable.

[Operating conditions]
The initial concentration of the raw material hydrochloric acid, other chlorides and chloric acid or chlorate shall be 0.1M or more. When hydrochloric acid or other chlorides are used as raw materials, chlorate ions are once generated as an intermediate by electrolysis, but thereafter the chlorate ion concentration decreases and the perchlorate ion concentration increases. By continuing the electrolysis, the raw material concentration is set to 0.01M or less. In the limit, all the raw materials can be decomposed. In that case, however, the current efficiency is lowered and excessive power is required. Therefore, after the concentration is reduced to an appropriate level, it is preferably separated by another separation method.
The higher the electrolysis conditions, the higher the reaction rate and the equilibrium value is reached in a short time, but the decomposition rate also increases, so that the appropriate temperature range is higher than room temperature and lower than 100 ° C under atmospheric pressure. It is preferable to control. Current density is preferably 1~100A / dm ^2.
When hydrochloric acid is used as a raw material, chlorine is also an intermediate for perchloric acid synthesis as shown in formula (7), and in order to increase current efficiency, it is preferable to increase the solubility as much as possible to allow the target reaction to proceed. Therefore, a larger pressure is preferable, and 0.1 to 1 MPa is preferable.
When chlorine gas remains, it can be separated and removed by a deaeration operation.

  1 and 2 show an electrolytic cell for synthesizing a perchloric acid compound according to the present invention, and FIG. 1 shows an example of a diaphragm type electrolytic cell using gas generating electrodes for both the anode and the cathode. Is an example of a diaphragm type electrolytic cell using a gas generating electrode as an anode and an oxygen gas electrode as a cathode.

The electrolytic cell 1 shown in FIG. 1 is a type that does not use a diaphragm. The electrolytic cell 1 includes a porous anode 2 in which a conductive diamond is coated on a base material such as silicon, and a platinum base material such as nickel. A porous cathode 3 coated with a cathode material such as platinum group metal oxide is disposed at intervals.
4 and 5 are raw water inlets formed on the bottom surface of the electrolysis cell, and 6 and 7 are product gas outlets formed on the top surface of the electrolysis cell.
When the electrolytic cell 1 is energized between both electrodes while supplying a chloride aqueous solution such as hydrochloric acid or sodium chloride or a chloric acid compound aqueous solution such as sodium chlorate, according to the above formulas (1), (3) and (5), etc. Perchlorate ions are electrolytically synthesized.

The electrolytic cell 11 shown in FIG. 2 is partitioned into an anode chamber 13 and a cathode gas chamber 14 by a perfluorosulfonic acid cation exchange membrane 12. A porous anode 15 coated with conductive diamond on a base material is in close contact with the anode chamber 13 side of the cation exchange membrane 12, and a gas diffusion cathode 16 is provided on the cathode gas chamber 14 side of the cation exchange membrane 12. The gas diffusion cathode 16 is in close contact with a porous cathode power supply 17 for power supply and reinforcement, in close contact.
18 is an anolyte inlet formed on the bottom of the anode chamber of the electrolytic cell, 19 is a cathode gas inlet formed on the bottom of the cathode gas chamber of the electrolytic cell, 20 is an anode gas outlet formed on the top of the electrolytic cell, 21 is a cathode gas outlet formed on the upper surface of the electrolytic cell.
When an aqueous chloride solution such as hydrochloric acid or sodium chloride or a chloric acid compound aqueous solution such as sodium chlorate is supplied to the anode chamber 13 of the electrolytic cell 11, and an oxygen-containing gas is supplied to the cathode gas chamber 14, current flows between both electrodes. As in the case of the electrolytic cell of FIG. 1, perchlorate ions are electrolytically synthesized.

  Next, although the Example and comparative example regarding the electrosynthesis of the perchloric acid compound concerning this invention are described, this invention is not limited to these.

[Example 1]
A substrate formed by forming conductive diamond doped with 5000 ppm boron on a 1 mm thick conductive silicon so as to have a thickness of 5 μm was used as an anode. As the cathode, a platinum-plated titanium plate having a thickness of 1 mm was used. The electrode area was 20 cm ² each.
In the non-diaphragm cell (volume 1000 ml) shown in FIG. 1, these electrodes were arranged facing each other so that the distance between them was 1 cm. The cell was charged with 500 ml of 0.02M sodium chlorate aqueous solution and stirred at a water temperature of 35 ° C. for 1 hour at a current of 1 A (current density: 0.05 A / cm ² ).
The analysis was performed with an ion chromatograph, and the current efficiency of perchlorate ion generation was calculated from the concentration. Sodium hypochlorite was also measured by KI titration. It was confirmed that the current efficiency of perchlorate ion generation was 20%.
When electrolysis was further continued for 4 hours, sodium chlorate as a raw material was reduced to 2 mM, and by-product hypochlorite ions were reduced to 0.1 mM.

[Comparative Example 1]
When electrolysis was performed for a total of 5 hours in the same manner as in Example 1 except that a platinum titanium plate was used instead of the diamond electrode, generation of perchlorate ions was not observed. Although results different from the conventional ones were obtained, it can be assumed that the production of perchlorate ions was less than the detection limit because the raw material concentration and current density were small.

[Comparative Example 2]
When electrolysis was performed for a total of 5 hours in the same manner as in Example 1 except that a titanium plate on which lead oxide was deposited was used instead of the diamond electrode, the current efficiency of perchlorate ion generation was about 2%. It was.

[ Reference Example 1 ]
A substrate formed by forming conductive diamond doped with 5000 ppm of boron on a niobium mesh having a base plate thickness of 2 mm as a base material was used as an anode, and a platinum-plated titanium mesh having a base plate thickness of 1 mm was used as a cathode. The electrode area is 20 cm ² each, and a two-chamber cell with an ion exchange membrane (117 Nafion) sandwiched between the anode and cathode of the diaphragm cell in FIG. 200 ml of hydrochloric acid solution was injected. When electrolysis was performed at 40 ° C. and 20 A (current density: 1 A / cm ² ) for 1 hour, perchlorate ions were obtained with a current efficiency of 12%. The hydrochloric acid concentration at this time was reduced to 0.05M. The cell voltage was 5.5V. Residual chlorine gas could be removed by deaeration.

[Comparative Example 3]
When electrolysis was carried out in the same manner as in Example 2 except that a platinum-plated titanium mesh having a thickness of 1 mm was used as the anode, the current efficiency of perchlorate ion generation was about 0.2%.

[ Reference Example 2 ]
The anode of Reference Example 1 was used, and as the cathode, graphite powder (manufactured by Tokai Carbon, TGP-2) as a catalyst was kneaded with PTFE resin, and the carbon cloth (manufactured by Zoltech, PWB-3) as the core material was mixed. It was applied and baked at 330 ° C. to prepare and use a 2 cm × 2 cm × 0.5 mm thick sheet. Using a platinum-plated titanium mesh as the cathode power supply support, a two-chamber cell with an ion exchange membrane (Nafion 117) as shown in FIG. 2 is assembled, and oxygen is supplied to the cathode chamber at 60 ° C. as in Reference Example 1. When electrolysis was performed at 20 A for 1 hour, perchlorate ions were obtained with a current efficiency of 10%. The hydrochloric acid concentration at this time was reduced to 0.05M. The cell voltage was 4.7V.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic longitudinal cross-sectional view of the diaphragm type | mold electrolysis which illustrates the electrolytic cell for the synthesis | combination of the perchloric acid compound concerning this invention. The schematic longitudinal cross-sectional view of diaphragm type | mold electrolysis similarly.

Explanation of symbols

1,11 Electrolysis cell 2,15 Anode 3,16 Cathode
12 Cation exchange membrane

Claims (3)

Electrolysis of a raw material solution containing a chloric acid compound having a raw material concentration of 0.1 M or more using an anode and a cathode having conductive diamond as an anode material until the raw material concentration is reduced to 0.01 M or less, and perchlorine A method for electrolytic synthesis of a perchloric acid compound, comprising synthesizing an acid compound. The method according to claim 1, wherein an ion exchange membrane is installed between the anode and the cathode to synthesize a perchloric acid compound . The method according to claim 1 or 2, wherein a perchloric acid compound is synthesized while electrolytically reducing oxygen at the cathode using a gas diffusion cathode.

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