JP3596997B2 - Electrode feeder, method for producing the same, and electrolytic cell for producing hydrogen peroxide - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electrode power supply having good production efficiency and little elution of electrode components, in particular, an electrode power supply for hydrogen peroxide production, a method for producing the same, and an electrolytic cell, and more particularly to a conventional carbon simple substance, metal or alloy. The present invention relates to an electrode power supply for producing hydrogen peroxide, which can almost completely prevent a reduction in yield due to decomposition of generated hydrogen peroxide and elution of an electrode material as compared with an electrode power supply to be used, a method for producing the same, and an electrolytic cell.
[0002]
[Prior art and its problems]
Hydrogen peroxide is an essential and essential basic chemical in the food, pharmaceutical, pulp, textile and semiconductor industries. Conventionally, hydrogen peroxide has been industrially obtained by autoxidizing 2-alkylanthraquinol, and mass synthesis has been continuously performed by simultaneously reducing the resulting anthraquinone by hydrogen and returning it to the original anthraquinone. . For the purification, complicated operations such as repeated rectification are required. In addition, hydrogen peroxide is unstable and cannot be stored for a long period of time. Therefore, demand for an on-site type hydrogen peroxide production apparatus is increasing.
[0003]
Conventionally, the production of hydrogen peroxide using a reduction reaction of oxygen gas has been proposed. U.S. Pat. No. 3,592,749 discloses an apparatus for producing several types of hydrogen peroxide, and U.S. Pat. No. 4,384,931. Disclose a method for producing an alkaline hydrogen peroxide solution using an ion exchange membrane. U.S. Pat. No. 3,969,201 proposes an apparatus for producing hydrogen peroxide comprising a three-dimensionally structured carbon cathode and an ion exchange membrane. However, in these methods, the amount of alkali essential for the production of hydrogen peroxide increases almost in proportion to the produced hydrogen peroxide, so that the alkali concentration relative to the concentration of hydrogen peroxide obtained becomes too high and the application is limited. Would.
U.S. Pat. Nos. 4,406,758, 4,891,107 and 4,457,953 disclose methods for producing hydrogen peroxide using a porous membrane and a hydrophobic carbon cathode. Thus, an alkaline aqueous hydrogen peroxide solution having a small weight ratio (sodium hydroxide / hydrogen peroxide) has been obtained. However, these methods have the drawback that it is difficult to control the amount and speed of the transfer of the electrolyte solution from the anode chamber to the cathode chamber, the operation conditions are complicated to manage, and the ratio of particularly generated hydrogen peroxide is not constant.
[0004]
Further, Journal of Electrochemical Society, vol. 130, 1117 to (1983) propose a method of using an anion-exchange membrane and supplying sulfuric acid to an intermediate chamber to stably obtain an acidic hydrogen peroxide solution. Further, in Vol. 57 of Electrochemistry, p. 1073 (1989), a method for improving performance by using a membrane electrode assembly as an anode is reported. However, these methods have a problem in terms of economical efficiency due to the consumption of electric power, and furthermore have a drawback that the use and mixing of sulfuric acid are inevitable. To date, a sufficiently satisfactory method for producing hydrogen peroxide has been obtained. Absent.
JP-A-6-88273, JP-A-6-336687 and JP-A-6-200389 disclose a hydrogen peroxide production apparatus including a carbon cathode having a three-dimensional structure and an ion exchange membrane, and a method for producing hydrogen peroxide using the apparatus. Yield production and electrode materials are disclosed. However, it has been found that this device has a problem in increasing its size. That is, when a carbon plate is used as a cathode power supply, since carbon is porous, oxygen, which is a reaction raw material, and an alkaline aqueous solution to be generated are easily transmitted and weakened. Although it is possible to impregnate with a phenolic resin impregnant as a seal, it cannot be an effective measure because the impregnant does not have resistance to the alkaline aqueous solution. Also, when a metal or alloy is used as a power supply, catalytic decomposition of hydrogen peroxide often occurs. Gold is relatively unlikely to undergo the catalytic decomposition, but is expensive and difficult to put into practical use.
[0005]
[Object of the invention]
The present invention is intended to solve the above-mentioned problems of the prior art, that is, the weakening of the electrode and the power supply and the peroxidation generated by the conventional method using carbon alone, a metal or an alloy as the electrode power supply. An object of the present invention is to provide an electrode power supply which can prevent hydrogen decomposition almost completely and can operate efficiently, a method for producing the same, and an electrolytic cell for producing hydrogen peroxide.
[0006]
[Means for solving the problem]
The electrode feeder according to the present invention is an electrolytic cell for producing hydrogen peroxide, characterized in that a dense film containing a carbon component is formed on at least a portion of the surface of the electrode feeder made of a metal or an alloy that comes into contact with the electrolytic solution. An electrode power supply , and a power supply for electrolysis characterized in that a film containing a carbon component is formed on at least a portion of the surface of the electrode power supply made of a metal or an alloy that comes into contact with the electrolytic solution, wherein the power supply is made of graphite or the like. The carbon component is kneaded with a fluororesin, molded into a sheet-like film, and the film is adhered and fixed to at least a portion of the surface of the plate-like electrode substrate which comes into contact with the electrolytic solution. The electrode feeder can be used as a cathode feeder for a two-chamber method and a three-chamber method electrolytic cell to constitute an electrolytic cell.
[0007]
Hereinafter, the present invention will be described in detail.
The conventional anodic reaction in the production of hydrogen peroxide by electrolysis is a reaction of generating oxygen gas by oxidizing hydroxyl ions present in the anode chamber, and is represented by the following chemical formula (1).
^{_{4OH - → O 2 + 2H 2}} 0 + 4e ▲ 1 ▼
On the other hand, the cathodic reaction for the production of hydrogen peroxide is a reduction reaction of oxygen gas, and is represented by the following formula (2) when represented by a chemical formula.
O ₂ + H ₂₀ + 2e → OH ⁻ + HO ₂ ^{− (} 2)
The decomposition of hydrogen peroxide by conventional electrolysis is represented by equations (3) to (5).
OH ⁻ + HO ₂ ⁻ → O ₂ + H ₂₀ + 2e (3)
^{_{H 2 0 + HO 2 - +}} 2e → 3OH - ▲ 4 ▼
2HO ₂ ⁻ → 2OH ⁻ + O ₂ ▲ 5 ▼
[0008]
The hydrogen peroxide decomposition reaction represented by the formulas (3) to (5) proceeds when the generated hydrogen peroxide ion comes into contact with a metal or an alloy having catalytic activity for catalytic cracking. In the present invention, since the cathode having a catalytic ability for hydrogen peroxide decomposition is covered with a dense film containing a carbon component, the catholyte containing hydrogen peroxide does not come into contact with the cathode through the film. Therefore, the generated hydrogen peroxide is hardly decomposed (the current efficiency of hydrogen peroxide generation is maintained at a high level), and the hydrogen peroxide is directly taken out of the tank from the catholyte outlet to be used for a predetermined purpose.
Conversely, from the viewpoint of protection of the cathode, the cathode does not come into contact with hydrogen peroxide, which is liable to cause electrode deterioration. Therefore, the cathode is not weakened and its life is not shortened, and a stable electrolysis operation can be performed for a long time. . This means that the electrode material does not elute into the generated aqueous hydrogen peroxide solution, and the obtained hydrogen peroxide can be obtained as a high-purity product free of impurities.
[0009]
The electrode feeder, in particular, the cathode feeder in the present invention, is formed by coating an electrode base made of a metal such as iron, aluminum, copper and nickel or an alloy mainly containing the metal such as stainless steel with a coating mainly containing carbon. Configure. As described above, this coating is to prevent the electrode substrate from substantially contacting the electrode solution, and its thickness may be any thickness sufficient to prevent contact with the electrode solution. Usually, it is 0.1 to 5 mm. The shape of the film may be determined as appropriate according to the power supply.When the power supply is plate-shaped, it covers one side of the power supply as a sheet, and when it is a mesh, the entire mesh is covered. What is necessary is just to be the shape made.
As the carbon component, untreated carbonaceous material cannot be used from the viewpoint of corrosion resistance, and conductive diamond doped with 100 to 10,000 ppm of graphite, glassy carbon, boron, or the like, fluorine-treated carbon, or the like is used. This carbon component is kneaded with a fluororesin powder such as polytetrafluoroethylene (PTFE) that functions as a binder, processed into, for example, a sheet shape, and is tightly fixed and coated on the electrode substrate by a pressure treatment or an adhesive. The amount of the fluororesin to be added is appropriately selected within a range where the conductivity is not impaired, and the mixing ratio is desirably 5: 1 to 1: 1 by volume. The pressure of the pressure treatment is set to about 1 to 100 kgf / cm ² . It is preferable to use a conductive adhesive, and when the adhesive is not conductive, the adhesive area is set to be half or less of the whole.
[0010]
The electrode feeder of the present invention having such a configuration is used as an electrode feeder of a two-chamber method and a three-chamber method electrolyzer for producing hydrogen peroxide, particularly as a cathode feeder. Used in a state of being electrically connected to the anode or the cathode. The feeders for both electrodes may be constituted by the same feeder, and a supply port or an outlet for the electrode solution or gas may be opened in each feeder.
The shape of the anode and the cathode is not particularly limited, but is preferably a shape having good contact efficiency with the electrode solution such as a wire mesh, a sponge, a felt, and a shape having porosity by powder sintering. The thickness of the electrode is preferably as small as possible because the conductivity of the supplied alkaline aqueous solution or the generated alkaline aqueous solution containing hydrogen peroxide is often low. However, if the electrode thickness is too small, the flow of the electrode solution and the flow of gas are hindered. In some cases, the optimum range is 0.5 to 5 mm.
The anode catalyst is preferably a metal such as platinum, iridium or their oxides or carbon when supplying an acidic aqueous solution to the anode chamber to generate oxygen, and these catalysts are preferably titanium, niobium, tantalum having the above-mentioned shape, It is supported on a corrosion-resistant anode substrate such as stainless steel, zirconium, or carbon by a thermal decomposition method, a resin fixing method, a composite plating method, or the like so as to have a weight of about 10 to 500 g / m ² .
[0011]
On the other hand, oxygen and water are supplied to the cathode to generate hydrogen peroxide, but from the viewpoint of reaction efficiency, it is desirable to be more alkaline than neutral, and as the catalyst and the cathode material, use gold or carbon with little hydrogen peroxide decomposition. It is preferable that the support be carried on a cathode substrate having an appropriate shape by a thermal decomposition method or the like so as to have a weight of about 10 to 500 g / m ² , as in the case of the above-described anode substrate. In order to smoothly supply and remove the oxygen-containing gas, the reaction product gas, and the liquid as the raw materials, a hydrophobic or hydrophilic material may be dispersed and supported on the cathode.
A porous fluororesin or an ion-exchange membrane is used as a diaphragm for partitioning the anode chamber and the cathode chamber, or the anode chamber, and the intermediate chamber and the cathode chamber. The ion exchange membrane may be either a fluororesin type or a hydrocarbon type, but the former is preferred from the viewpoint of corrosion resistance. Examples of the former include Nafion 117, Nafion 350, Nafion 902 and Nafion 961 (both manufactured by DuPont) having a sulfonic acid group or a carboxylic acid group. The ion exchange membrane has a function of preventing each ion generated at the anode and the cathode from being consumed at the counter electrode, and promptly performing electrolysis even when the conductivity of the electrode solution is low as in the present invention. .
[0012]
The structure of the electrolytic cell of the present invention is not particularly limited except that it is divided into an anode chamber and a cathode chamber (including an anode gas chamber-an intermediate chamber-a cathode chamber) by a cation exchange membrane. In a two-chamber electrolytic cell, the cation exchange membrane separates the anode chamber and the cathode chamber, and the anode or cathode partitions the anode or cathode chamber into a gas chamber on the opposite side of the solution chamber on the cation exchange membrane side. May be. However, with such a structure, if the conductivity of the electrode solution is low, the cell voltage increases, the structure becomes complicated, and there are many disadvantages such as the necessity of gas-liquid separation. Therefore, it is desirable that the anode and the cathode are in close contact with or bonded to the ion exchange membrane. When they are brought into close contact with each other, it is sufficient to mechanically combine them in advance or apply pressure during electrolysis, and the applied pressure is preferably about 0.1 to 30 kgf / cm ² .
From the viewpoint of durability and stabilization of hydrogen peroxide, the electrolytic cell itself is preferably formed using glass, a resin lining material, carbon, titanium, stainless steel, nickel, PTFE resin, etc. having excellent corrosion resistance. In the case of a material which may cause decomposition of hydrogen peroxide, it is preferable to form a film containing the above-mentioned carbon component or a film made of another corrosion-resistant material on the surface, that is, the inner wall of the electrolytic cell.
[0013]
The oxygen-containing gas as a raw material may be air obtained by previously removing carbon dioxide, oxygen gas in a commercially available oxygen cylinder, or oxygen gas produced by electrolysis using a separately installed electrolytic cell. Alternatively, oxygen-enriched air obtained by concentrating air using a PSA (Pressure Swing Adsorption) device may be used.
The supply amount of oxygen is preferably about 1.5 to 30 times the stoichiometric amount, and it is desirable that the oxygen is wetted by contact with water before the supply in order to make the concentration uniform and protect the membrane.
The concentration of the alkali produced in the cathode chamber can be set so as to be suitable for the production of hydrogen peroxide in the preceding stage. When the concentration of the alkali, for example, sodium hydroxide is 2 to 15%, the peroxide solution of the produced aqueous alkaline hydrogen peroxide solution is dissolved. The hydrogen concentration becomes 1 to 5% by weight. The amount of recovery depends on the application, but 1-5% by weight of hydrogen peroxide and 1-10% by weight of sodium hydroxide.
As the electrolysis conditions, the temperature is preferably 30 to 60 ° C., and the current density is preferably 1 to 50 A / dm ² .
[0014]
FIG. 1 is a schematic longitudinal sectional view showing an example of an electrolytic cell for producing hydrogen peroxide having a power supply for electrolysis according to the present invention.
The two-chamber electrolytic cell 1 is divided into an anode chamber 3 and a cathode chamber 4 by a cation exchange membrane 2 such as a perfluorocarbon sulfonic acid type, and a fibrous, sponge-like or felt-like inside is formed in the anode chamber 3. An anode 5 made of a metal is accommodated so as to form a space for supplying and removing an electrolytic solution above and below. An anode feeder 8 having an anolyte supply port 6 near the upper part and an anolyte outlet 7 near the lower part is electrically connected to the anode 5, and the anode 5 is supplied with power through the anode feeder 8.
[0015]
On the other hand, in the cathode chamber 4, a fibrous, sponge-like or felt-like cathode 9 made of a carbon-based material such as graphite is accommodated so as to form a space above and below for supplying and removing an electrolytic solution. The cathode 9 has a catholyte supply port 10 near the upper portion and a catholyte outlet 11 near the lower portion, and further has a carbon-based material such as graphite and PTFE powder as a binder on the surface in contact with the cathode 9. Are electrically connected to each other, and the cathode 9 is supplied with power through the cathode power supply 13.
The periphery of the anode chamber 3 and the cathode chamber are sealed by an anode gasket 14 and a cathode gasket 15, respectively. An anode chamber frame 16 and a cathode chamber frame 17 are located outside the anode power supply 8 and the cathode power supply 13, respectively. By pressing both chamber frames inward, the ion exchange membrane 2, the electrodes 5 and 9, and the electrode feeders 8 and 13 are integrated.
[0016]
The catholyte containing pure gas containing oxygen-containing gas is supplied from the catholyte supply port 10 to the catholyte chamber 4 of the electrolytic cell 1 having such a configuration, and the sodium hydroxide aqueous solution and the like are supplied from the anolyte supply port 6 to the anode chamber 3. When a current is passed between the electrodes, the catholyte in which oxygen is dissolved comes into contact with the cathode 9, and the oxygen is reduced according to the formula (2) to generate hydrogen peroxide ions. Since a dense film made of carbon and PTFE is formed on the cathode side surface of the cathode power supply 13 for supplying power to the cathode 9, the hydrogen peroxide ions do not pass through the film 12 and reach the surface of the cathode power supply 13. There is no. Therefore, the hydrogen peroxide does not decompose, the cathode power supply 13 does not deteriorate, and the cathode material does not elute into the catholyte.
Therefore, the aqueous solution of hydrogen peroxide taken out from the catholyte outlet 11 contains almost the same amount of hydrogen peroxide as that produced by electrolysis without decomposition, and there is no decrease in purity due to the mixing of electrode materials. Furthermore, the cathode power supply 13 does not come into direct contact with the catholyte, and stable operation can be performed for a long period of time.
[0017]
【Example】
Next, an example regarding the production of hydrogen peroxide using the electrode power supply of the present invention will be described, but the example does not limit the present invention.
[0018]
Embodiment 1
An anode prepared by weaving stainless steel fibers and a cathode made of graphite felt (each having an electrode area of 0.5 dm ² ) were brought into close contact with both surfaces of a cation exchange membrane Nafion 350 (manufactured by DuPont). A 1 mm thick dense sheet prepared by mixing and firing graphite powder (TGP-7, manufactured by Tokai Carbon Co., Ltd.) and fluororesin powder (30J, manufactured by Mitsui Fluorochemicals Co., Ltd.) is attached to the surface of a stainless steel plate. A cathode feeder was connected to the cathode.
[0019]
400 ml / min of oxygen gas and 2.5 ml / min of pure water are supplied to the cathode chamber from a commercially available oxygen gas cylinder, and a sufficient amount of sodium hydroxide having a concentration of 40 g / l is supplied to the anode chamber. Supplied. When the temperature was 30 ° C. and a current of 2.5 A was passed between the two electrodes, the cell voltage was 1.8 V, and water having a concentration of 40 g / l containing 15 g / l hydrogen peroxide was supplied from the catholyte outlet. An aqueous sodium oxide solution was obtained.
The weight ratio (alkali hydroxide / hydrogen peroxide) was 2.6, and the current efficiency of hydrogen peroxide generation was 95%. In addition, no dissolved component of stainless steel was detected in the product obtained at the catholyte outlet after 48 hours.
[0020]
[Comparative Example 1]
The operation was performed under the same conditions as in Example 1 using an electrolytic cell manufactured under the same conditions as in Example 1 except that the film was not stuck on the surface of the stainless steel plate. The cell voltage was 1.7 V, and the cathode voltage was 1.7 V. An aqueous solution of sodium hydroxide having a concentration of 45 g / l containing 12 g / l of hydrogen peroxide was obtained from the liquid outlet.
The weight ratio was 3.8, and the current efficiency for producing hydrogen peroxide was 80%. A small amount of dissolved stainless steel was detected in the obtained aqueous hydrogen peroxide solution.
[0021]
【The invention's effect】
The electrode feeder according to the present invention is an electrolytic cell for producing hydrogen peroxide, characterized in that a dense film containing a carbon component is formed on at least a portion of the surface of the electrode feeder made of a metal or an alloy that comes into contact with the electrolytic solution. It is an electrode feeder.
In conventional electrode feeders using simple carbon, metals or alloys, in the case of simple carbon, the electrode solution such as an aqueous solution of hydrogen peroxide generated in the porous simple carbon penetrates, weakening the electrode and shortening its life. There is a disadvantage that the electrode material is eluted and the aqueous hydrogen peroxide solution is contaminated. Further, a metal electrode such as stainless steel has a disadvantage that decomposition of hydrogen peroxide occurs to reduce current efficiency, and a gold electrode has a disadvantage that decomposition of hydrogen peroxide hardly occurs but is too expensive.
On the other hand, in an electrode feeder in which a dense film containing a carbon component is formed on the surface in contact with the electrode solution, such as the electrode feeder according to the present invention, the film does not allow the electrode solution to pass through, so that the electrode solution is not generated. There is no decrease in current efficiency due to decomposition of hydrogen oxide, deterioration of the electrode and the accompanying contamination of the aqueous hydrogen peroxide solution. Pollution can be effectively prevented. Further, by using the electrode power supply of the present invention, it is possible to easily cope with an increase in the size of the electrolytic cell, and to configure an electrolytic cell suitable for the production of a large amount of hydrogen peroxide.
[0022]
Further, the method for manufacturing an electrode power feeder according to the present invention is a method for manufacturing a sheet made of metal or alloy after kneading a carbon component selected from graphite, glassy carbon, diamond and fluorinated carbon with a fluororesin to form a sheet-like film. A method for producing an electrode power feeder for an electrolytic cell for producing hydrogen peroxide, comprising: fixing the film to at least a portion of the surface of the electrode power feeder in contact with the electrolytic solution. The electrode feeder manufactured by this manufacturing method also produces the same effect.
[0023]
The above-described electrode feeder can be used by being incorporated in an electrolytic cell for producing hydrogen peroxide in a two-chamber method or a three-chamber method. In order to reliably exert the effects of the present invention, the electrolytic cell is made of glass, resin lining material, or the like. It is desirable to use a material which has corrosion resistance and does not cause decomposition of hydrogen peroxide. If the electrolytic cell is made of a metal or an alloy that has corrosion resistance but decomposes hydrogen peroxide, a material that has corrosion resistance and does not cause hydrogen peroxide decomposition, such as a coating containing a carbon component, is formed on the cathode chamber inner wall. It is desirable to coat with.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing an example of an electrolytic cell according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... 2-chamber electrolytic cell 2 ... Cation exchange membrane 3 ... Anode chamber 4 ... Cathode chamber 5 ... Anode 6 ... Anolyte supply port 7 ... Anolyte outlet 8 Anode Power Supply 9 Cathode 10 Catholyte Supply Port 11 Catholyte Outlet 12 Coating 13 Cathode Power Supply 14 Anode Gasket 15 Cathode gasket 16 ・ ・ ・ Anode chamber frame 17 ・ ・ ・ Cathode chamber frame

Claims (4)

An electrode feeder for an electrolytic cell for producing hydrogen peroxide, wherein a dense film containing a carbon component is formed on at least a portion of a surface of the electrode feeder made of a metal or an alloy which comes into contact with an electrolytic solution. After kneading a carbon component selected from graphite, glassy carbon, conductive diamond and fluorinated carbon with a fluororesin and forming it into a sheet-like dense film, at least the surface of the plate-like electrode power feeder made of metal or alloy A method for producing an electrode feeder for an electrolytic cell for producing hydrogen peroxide, comprising coating the above-mentioned film on a portion that comes into contact with an electrolytic solution. Oxygen-containing gas and water are supplied to the cathode chamber of an electrolytic cell partitioned into an anode chamber containing an anode and a cathode chamber containing a cathode by a cation exchange membrane, and electrolysis is performed to obtain an aqueous solution containing hydrogen peroxide. In a hydrogen production electrolytic cell, a cathode feeder in which a dense film containing a carbon component is formed on at least a portion of a surface of an electrode feeder made of a metal or an alloy which is in contact with an electrolyte as a cathode feeder for feeding power to the cathode. An electrolytic cell characterized by using: The electrolytic cell according to claim 3, wherein the cathode chamber inner wall is coated with a film containing a carbon component.

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