JP3875922B2 - Electrolysis cell for hydrogen peroxide production - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a peroxidation that can improve the generation efficiency of hydrogen peroxide used in the treatment of water and wastewater for food, pharmaceuticals, pulp, semiconductor industry, etc. by devising the installation of electrolytic cells during operation The present invention relates to an electrolytic cell for hydrogen production.
[0002]
[Prior art]
There are concerns about the adverse effects on the environment and human bodies caused by air pollution caused by industrial and domestic waste and the deterioration of water quality in rivers and lakes, and technical measures for solving these problems are urgently needed. For example, in the treatment of drinking water, sewage and wastewater, chemicals such as chlorine have been introduced for decolorization, COD reduction and sterilization, but dangerous substances, that is, environmental hormones (exogenous endocrine disrupting substances), Chlorine injection tends to be prohibited due to the formation of carcinogenic substances.
In the incineration of waste, depending on the combustion conditions, carcinogenic substances (dioxins) are generated in the waste gas and affect the ecosystem, so safety is regarded as a problem. In order to solve this water treatment-related problem, a new water treatment method has been studied.
[0003]
The electrolysis method uses clean electrical energy to cause a desired electrochemical reaction. By controlling the chemical reaction on the cathode surface, that is, by supplying oxygen-containing gas and water to the cathode, hydrogen peroxide is generated. Conventionally, water treatment has been widely performed by decomposing a material to be treated using this. The electrolytic method makes it possible to produce hydrogen peroxide on-site, eliminates the shortcomings of hydrogen peroxide that it cannot be stored for a long time without a stabilizer, and is designed to prevent transportation risks and pollution. Is also unnecessary.
In the production of hydrogen peroxide by cathodic reduction, if waste water to be treated is used as the catholyte, the waste water directly contacts the electrode in addition to the oxidation treatment with the generated hydrogen peroxide solution, and anodizing or cathodic reduction treatment. Further, for example, the action of a superoxide anion (O ₂ ⁻ ), which is a highly active one-electron reduction product, can be expected.
[0004]
[Problems to be solved by the invention]
The Journal of Applied Electrochemistry Vol. 25, 613- (1995) shows a comparison of various electrolytic generation methods for hydrogen peroxide. Since these generation methods can be efficiently obtained in an atmosphere of an alkaline aqueous solution, it is necessary to supply an alkaline component as a raw material, and an alkaline aqueous solution such as KOH or NaOH is essential.
Journal of Electrochemical Society Vol.141, 1174- (1994) proposes a method of electrolytically producing ozone and hydrogen peroxide at the anode and cathode, respectively, using pure water as the raw material and ion exchange membrane. Is not practical. As a similar method, it has been reported that the efficiency is increased by electrolysis under high pressure, but it is still impractical from the viewpoint of safety. In addition, a method for electrolytic production of hydrogen peroxide using palladium foil has been proposed, but the concentration of the generated hydrogen peroxide is low, and there is a limit in price.
[0005]
In an electrolytic cell for producing hydrogen peroxide, an electrolytic system in which a salt such as chloride, sulfate, nitrate, acetate or the like is added to soft water or ion-exchanged water as an electrolyte may be used. There was a problem that current efficiency in the diaphragm electrolysis cell was low and running cost was high.
As described above, in the production of hydrogen peroxide water by electrolysis, an electrolytic cell for producing hydrogen peroxide that can be used at a practical level by examining electrode materials and ion exchange membranes has been proposed. Satisfactory results have not been obtained for reasons such as the concentration of hydrogen oxide, safety, or the complexity of the apparatus.
In view of the problems of the prior art, an object of the present invention is to provide an electrolytic cell for producing hydrogen peroxide that can improve the production efficiency by simply modifying the apparatus.
[0006]
[Means for Solving the Problems]
The present invention relates to a diaphragm-type electrolytic cell having an anode and a cathode and supplying hydrogen-containing gas by supplying an oxygen-containing gas and water to the cathode, and the anode and the cathode are positioned below. Thus, an electrolytic cell for producing hydrogen peroxide, which is inclined with respect to the vertical direction.
[0007]
The present invention will be described in detail below.
The present inventors have made various studies on the installation of an electrolytic cell for producing hydrogen peroxide, and found that the production efficiency of hydrogen peroxide is increased only by tilting the electrolytic cell for producing hydrogen peroxide by a predetermined angle. The invention has been reached.
The inclination angle (θ) of the electrolytic cell in the present invention is 0 ° <θ ≦ 90 ° with respect to the vertical direction, preferably 10 ° ≦ θ ≦ 90 °, more preferably 30 ° ≦ θ ≦ 90 °. In this case, the inclination angle means the angle formed by the electrode surface and the vertical direction (the electrode surface and the inclination direction are perpendicular), and the angle formed by the both ends of the electrode and the vertical direction (the direction and inclination of the electrode surface). Does not mean that the directions match. However, the electrode surface does not always have to be perpendicular to the tilt direction, and may be deviated from the right angle. Although embodiments the cathode side of the anode was the bottom as an embodiment of the tilt Ru embodiment there to the bottom,
In the present invention, the cathode side is the lower side, and it is inclined at an inclination angle in the range of 0 ° <θ ≦ 90 °.
The inclined electrolytic cell may be fixed by a general method. For example, a relatively large V-shaped groove is formed on the installation surface and fixed to the V-shaped groove, or the electrolytic cell is placed on a fixed base. It may be fixed.
[0008]
The reason why the production efficiency of hydrogen peroxide is increased only by tilting the electrolytic cell for producing hydrogen peroxide by a predetermined angle according to the present invention is not clear, but can be estimated as follows.
The hydrogen peroxide generated at the cathode moves to the anode due to the stirring effect due to the gas rise generated at the anode and decomposes there, so that the generation efficiency decreases. In addition, since the generation efficiency of hydrogen peroxide is pH-dependent and tends to decrease when acidic, the generation efficiency of hydrogen peroxide decreases when the movement of protons generated at the anode to the cathode surface is promoted. If the electrolytic cell is tilted with the cathode facing downward, the gas generated at the anode moves along the anode plate, so that the ascending speed is reduced and the stirring effect is thought to be weakened. Accordingly, it is considered that the hydrogen peroxide generated at the cathode is quickly discharged without moving to the anode and being decomposed, and the generation efficiency of hydrogen peroxide is not lowered. Moreover, since the movement of protons generated at the anode is suppressed, the efficiency increases as a result.
[0009]
The average water pressure according to the total cathode by tilting the electrolytic cell decreases, excess solution component which penetrates into the gas cathode is reduced, the supply route of the source gas from the air chamber in place sufficiently It is estimated that it is secured.
[0010]
Hydrogen peroxide is produced by the following electrolytic reaction.
Anodic reaction: 2H ₂ O → O ₂ + 4H ⁺ + 4e
3H ₂ O → O ₃ + 6H ⁺ + 6e
2H ₂ O → H ₂ O ₂ + 2H ⁺ + 2e
Cathodic reaction: O ₂ + 2H ⁺ + 2e → H ₂ O ₂
[0011]
When chloride is dissolved, hypochlorous acid is generated as shown in the following formula.
2Cl ⁻ → Cl ₂ + 2e
Cl ₂ + H ₂ O → HCl + HClO
In particular, when chloride is dissolved, gas treatment becomes indispensable, and when this oxidizing substance reaches the cathode, the cathode material is deteriorated. Therefore, it is desirable to use an electrode material that hardly generates hypochlorous acid.
When sulfate is added, persulfuric acid is generated according to the following formula depending on the electrode material.
2SO ₄ ^2- → S ₂ O ₈ ^2- + 2e
When acetate is added, carbon dioxide is generated according to the following formula in addition to oxygen depending on the electrode material.
CH ₃ COOH + 2H ₂ O → 2CO ₂ + 8H ⁺ + 8e
[0013]
In general, the anodic oxidation reaction during electrolysis of an aqueous solution is an electrolysis reaction that uses water as a raw material. However, if an electrode catalyst that is highly reactive to water discharge is used, the oxidation reaction of coexisting substances other than water Often does not progress easily. It is preferable that the decomposition product of impurities is finally converted into a low molecular weight safe substance such as carbon dioxide, water, hydrogen, oxygen, nitrogen, ammonia, and chloride ions. Care must be taken in setting the electrolysis conditions because it may be dangerous.
[0014]
The electrolytic cell used in the method of the present invention is not particularly limited as long as it is for hydrogen peroxide production. For example, the following electrolytic cell can be used.
The anode catalyst that can be used is preferably selected so that the oxygen generation reaction, which is an oxidation reaction of water, takes precedence over the generation of halogen gas or hypohalous acid by oxidation of halide ions, such as lead oxide, tin oxide, There are materials such as DSA (insoluble anode) made of noble metals such as platinum, iridium and ruthenium or oxides thereof, carbon, etc., and composite oxides including these and valve metal oxides such as titanium and tantalum can also be used. Furthermore, it is known that complex oxides such as manganese dioxide or manganese-vanadium, manganese-molybdenum, manganese-tungsten can be used, and halide ion discharge (halogen gas generation) is suppressed.
However, even if these expensive materials are used, they are consumed depending on the current density and energization time. In particular, graphite and amorphous carbon materials are significantly consumed.
[0015]
As an alternative anode material, there is conductive diamond, which is excellent in durability and is inactive against the decomposition reaction of water, from oxygen to ozone (anodic oxidation reaction) and hydrogen peroxide (cathodic reduction). Reaction). Therefore, when conductive diamond is used as the anode, a long life can be achieved, and OH radicals with oxidizing power are generated, and an electrolytic solution with high detergency can be obtained.
These electrode materials can be used as they are in the form of a plate, or on a plate having corrosion resistance such as titanium, niobium or tantalum, a wire mesh, a powder sintered body, a metal fiber sintered body, a thermal decomposition method, a resin fixing method, a composite It is formed to be 1 to 500 g / m ² by plating or the like.
As the anode power supply body, it is desirable to use a valve metal such as titanium or an alloy thereof.
[0016]
As the cathode for generating hydrogen peroxide, a conventionally used cathode such as nickel or carbon may be used. However, it is desirable to use an oxygen gas diffusion cathode, which is more efficient for reducing oxygen gas. Hydrogen peroxide can be produced.
The oxygen gas electrode preferably uses a metal such as gold or a metal oxide, or carbon such as graphite or conductive diamond as a catalyst, and an organic material such as polyaniline or thiol (—SH-containing organic compound) is used on the surface thereof. It may be coated on the surface. These catalysts can be used as they are in the form of a plate or a porous material, or they can be adhered to a plate having corrosion resistance such as stainless steel, zirconium, silver, carbon, a wire mesh, a powder sintered body, and a metal fiber sintered body by a thermal decomposition method or a resin. It is supported at 1 to 1000 g / m ² by a method, composite plating, or the like.
[0017]
As the cathode power supply, metals such as carbon, nickel, and titanium, and alloys and oxides thereof are preferably used as a porous body or a sheet, and hydrophobic so as to smoothly supply and take out the reaction product gas and electrolytic water. Alternatively, it is desirable to disperse and carry a hydrophilic material on the surface of the power feeding body.
If the conductivity of the catholyte is low, the cell voltage increases and the electrode life is shortened. In this case, an oxygen gas diffusion cathode can be used as an ion exchange membrane, including the purpose of preventing contamination by the gas electrode material. It is desirable to adopt a structure that is as close as possible (to narrow the width of the solution chamber).
The amount of oxygen supplied to the cathode should be about 1 to 2 times the theoretical amount, even if air or a commercially available cylinder is used as the oxygen source, or oxygen generated by water electrolysis in a separate electrolytic cell is used. Further, oxygen concentrated from air by a PSA (Pressure Swing Adsorption) apparatus may be used. In general, as the oxygen concentration increases, hydrogen peroxide can be produced at a higher current density.
[0018]
As an electrolytic solution to use, pure water, tap water, it can be used well water and industrial water, etc., they have small conductance, resistance loss occupying the cell voltage is not negligible. Also, if the conductivity is small, the effective electrode area is limited. In order to prevent these problems, it is desirable to impart electric conductivity to the electrolyte solution. Neutral salts such as sodium sulfate, potassium sulfate, sodium nitrate, sodium chloride and potassium chloride, or alkaline or acidic such as sodium hydroxide or sulfuric acid. A supporting electrolyte can be added.
[0019]
However, when chloride is used, hypochlorous acid is generated as described above, and this can be used as treated water in a separate line from hydrogen peroxide produced at the cathode. However effective chlorine component of the part flows to the cathode side, to oxidize the cathode catalyst and the substrate, Ru Kotogaa causing short service life of the resulting electrode.
In order to prevent this, it is preferable to use as the anode a catalyst in which electrolysis of water (oxygen generation) proceeds with priority even when chloride ions are present. Manganese dioxide (MnO ₂ , Mn—W—O _x , Mn—V—O _x , Mn—Mo—O _x ) electrodes can be used as electrode catalysts having excellent selectivity.
[0020]
On the other hand, the generation of an active oxidant can be suppressed by dissolving non-chloride salts such as sulfate, nitrate and acetate. When water such as tap water and well water is softened, hypochlorite may be generated from components such as sodium chloride and potassium chloride that are dissolved in trace amounts. When dissolved at a concentration more than twice, the production efficiency of hypochlorous acid is significantly reduced.
Since pure water does not dissolve chloride, this problem does not occur.
Carbonate is not desirable as a substance that imparts electrical conductivity as described above, because it precipitates as sodium carbonate or potassium carbonate on a cathode placed in an alkaline atmosphere. When a large amount of carbon dioxide is dissolved in the raw water, it is preferably removed in advance.
[0021]
For processing targets that contain a large amount of polyvalent metal ions such as calcium and magnesium, hydroxide may precipitate on the cathode surface and the reaction may be hindered. desirable.
The electrolysis conditions are preferably a liquid temperature of 5 to 60 ° C. and a current density of 0.1 to 100 A / dm ^{2. In} order to obtain particularly stable and high performance, a liquid temperature of 20 to 40 ° C. and a current density of 1 to 20 A / dm ² are preferable. preferable. The distance between the electrodes should be small in order to reduce the resistance loss, but is preferably 1 to 20 mm in order to reduce the pressure loss of the pump for supplying the electrolyzed water and keep the pressure distribution uniform.
As the electrolytic cell material, it is preferable to use glass lining material, carbon, titanium, stainless steel, PTFE resin, etc. having excellent corrosion resistance from the viewpoints of durability and stability of hydrogen peroxide. The concentration of the generated hydrogen peroxide can be controlled to 10 to 10,000 ppm (1% by weight) by adjusting the amount of water and the current density.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a preferred electrolytic cell that can be used for the production of hydrogen peroxide solution according to the present invention will be described with reference to FIG.
FIG. 1 is a longitudinal front view showing an embodiment of an electrolytic cell for producing hydrogen peroxide according to the present invention.
[0023]
The electrolysis cell 1 contains a porous plate-like anode 2 and an oxygen gas diffusion cathode 3, and the oxygen gas diffusion cathode 3 divides the electrolysis cell 1 into a solution chamber 4 and a gas chamber 5, and the oxygen gas A porous cathode power supply 6 is installed in close contact with the gas chamber side of the diffusion cathode 3.
An electrolyte inlet 7 and an electrolyte outlet 8 are respectively formed on the bottom plate and the top plate on the solution chamber 4 side, and an oxygen-containing gas inlet 9 and an oxygen-containing gas are respectively provided on the upper and lower portions of the back plate on the gas chamber 5 side. An outlet 10 is formed.
[0024]
The electrolysis cell 1 having such a configuration is fixed on the base 11, and the oxygen gas diffusion cathode 3 is positioned below the anode 2 at an inclination angle (θ) on the horizontal installation surface 12 together with the base 11. The back plate of the gas chamber 5 is swung on the fixed base 13 installed on the installation surface 12 and held at the inclined position.
Thus, an electrolytic solution such as tap water in which the supporting electrolyte is dissolved is supplied from the electrolytic solution inlet 7 of the electrolytic cell 1 installed at an inclination angle (θ), and air or oxygen-enriched air is supplied from the oxygen-containing gas inlet 9. When energized between the two electrodes while being introduced, oxygen is reduced at the oxygen gas diffusion cathode 3 to generate hydrogen peroxide, which is taken out from the outlet 8 as a hydrogen peroxide-containing solution.
[0025]
〔Example〕
Next, although the Example of manufacture of the hydrogen peroxide solution by this invention is described, this Example does not limit this invention.
[0026]
Example 1
An iridium oxide catalyst was supported on a titanium porous plate by a thermal decomposition method so as to be 10 g / m ² to form an anode.
Carbon powder (CABOT, Vulcan XC-72) is used as a catalyst, and this is mixed with PTFE resin, coated on a 0.5mm thick carbon sheet, and then fired at 330 ° C to form an oxygen gas diffusion cathode. The diffusion cathode was integrated with a porous SUS plate (thickness 3 mm) as a cathode power supply. A non-diaphragm electrolysis cell having a distance between the electrodes of 5 mm, a height of 20 cm, and an effective electrolysis area of 125 cm ² was constructed, and the cathode was open to the atmosphere.
The electrolytic cell was inclined at an inclination angle (θ) = 82 ° so that the cathode was positioned below the anode. Tap water was softened with an ion exchange resin, and an aqueous solution having a conductivity of 10 mS / cm dissolved in 0.056 M sodium sulfate was supplied at 10 ml / min from the electrode chamber inlet. When the liquid temperature was 20 ° C. and a current of 1.25 A was passed, the cell voltage was about 2.4 V, and about 1000 ppm of hydrogen peroxide from the outlet was obtained with a current efficiency of about 74%.
[0029]
Example 2
An electrolytic cell for producing hydrogen peroxide was constructed in the same manner as in Example 1 except that the electrolytic cell was inclined at an inclination angle (θ) = 10 ° so that the cathode was positioned below the anode, and the peroxide was oxidized. When hydrogen was produced, the cell voltage was about 2.4 V, and about 610 ppm of hydrogen peroxide was obtained from the outlet with a current efficiency of about 45%.
[0030]
Comparative Example 1
An electrolytic cell for producing hydrogen peroxide was constructed in the same manner as in Example 1 except that the electrolytic cell was made upright [inclination angle (θ) = 0 °]. Hydrogen peroxide was produced, and the cell voltage was about 2.4. V and about 560 ppm hydrogen peroxide from the outlet was obtained with a current efficiency of about 43%.
[0031]
【The invention's effect】
The present invention relates to a diaphragm-type electrolysis cell having an anode and a cathode and supplying hydrogen-containing gas by supplying an oxygen-containing gas and water to the cathode, and the anode and the cathode are positioned below. Thus, there is an electrolytic cell for producing hydrogen peroxide characterized by being inclined with respect to the vertical direction, and the inclination angle (θ) is preferably 10 ° ≦ θ ≦ 90 °, and 30 ° ≦ θ ≦. More preferably, it is 90 °.
Since the production efficiency of hydrogen peroxide is improved by a simple operation of tilting the electrolysis cell, high concentration hydrogen peroxide can be produced with high current efficiency with almost no increase in cost.
[0032]
The inclination angle is effective tends to increase as the increase, Ru remarkable effect is obtained at an inclination angle in a range of 30 ° ≦ θ ≦ 90 °.
If the cathode is a gas diffusion cathode, hydrogen generation can be suppressed and a reduction in power consumption can be achieved.
Further, when conductive diamond is used as an anode, a long life can be achieved, and OH radicals with oxidizing power are generated, and an electrolytic solution with high cleaning power can be obtained.
[Brief description of the drawings]
FIG. 1 is a longitudinal front view showing an embodiment of an electrolytic cell for producing hydrogen peroxide according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrolysis cell 2 Anode 3 Oxygen gas diffusion cathode 4 Solution chamber 5 Gas chamber 6 Cathode feeder
12 Installation surface
13 Fixed base θ Inclination angle

Claims (6)

In a non-membrane type electrolytic cell for producing hydrogen peroxide by supplying an oxygen-containing gas and water to the cathode, the anode and the cathode are arranged so that the cathode is located below. An electrolytic cell for producing hydrogen peroxide, which is inclined with respect to a vertical direction. 2. The electrolytic cell for producing hydrogen peroxide according to claim 1, wherein the inclination angle (θ) is 10 ° ≦ θ ≦ 90 °. 2. The electrolytic cell for producing hydrogen peroxide according to claim 1, wherein the inclination angle (θ) is 30 ° ≦ θ ≦ 90 °. Hydrogen peroxide-producing electrolysis cell according to any one of claims 1 cathode is a gas diffusion cathode to 3. Hydrogen peroxide-producing electrolysis cell according to any one of claims 1 positive electrode material is a conductive diamond to 4. 2. The electrolytic cell for producing hydrogen peroxide according to claim 1, wherein the electrolytic cell is a diaphragm type having a bottom plate and a top plate, and the water is supplied from the bottom plate side.

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