JP2002128508A - Oxygen production method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen production method and a production apparatus capable of producing oxygen efficiently and safely with a small amount of electric power when required on-site. SOLUTION: Hydrogen peroxide is generated from an oxygen-containing raw material gas by electrolysis, and the hydrogen peroxide is continuously decomposed in the presence of a metal oxide to generate oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for selectively separating oxygen from a raw material gas containing oxygen such as air, that is, a method and an apparatus for producing oxygen.

[0002]

2. Description of the Related Art Oxygen is used for oxygen masks for emergency medical treatment and sports such as mountain climbing, oxygen burners using oxygen and fuel gas such as hydrogen and city gas, oxygen-enriched combustion equipment, fish farming, and tropical fish. It is used as an oxidizing agent for transportation and fuel cells, and is in great demand.

As methods for producing oxygen, (1) a method of liquefying air for fractional distillation, (2) a method of electrolyzing water,
(3) A method of decomposing a peroxide such as hydrogen peroxide in the presence of a catalyst such as MnO ₂ , and (4) a method of decomposing a permanganate with an aqueous alkali solution are conventionally known.

[0004]

The above-mentioned conventional method for producing oxygen has the following problems. The method (1) requires a large-sized device such as a cooling device for liquefying air and a distillation device for fractional distillation, and it is difficult to produce oxygen at a place of use (on-site).

The method (2) requires a large amount of electric power because it is necessary to electrolyze water at a voltage of 1.23 V or more.
In addition, since explosive hydrogen is generated as a by-product, a device for safely collecting and storing this or a device for safely dissipating it is necessary, which also makes the manufacturing device large. There is.

According to the methods (3) and (4), on-site production of oxygen is possible, but a chemical substance such as a chemically unstable peroxide or potassium manganate having a strong oxidizing power is used. There is a drawback that equipment for safe storage is required.

The present invention solves these problems and provides a simple and safe on-site production of oxygen with little power and without the need for equipment for storing unstable chemicals. It is an object to provide a method and a device enabling this.

[0008]

According to the present invention, there is provided a process for producing hydrogen peroxide from an oxygen-containing raw material gas by electrolysis and decomposing the hydrogen peroxide in the presence of a metal oxide to produce oxygen. The present invention relates to a method for producing oxygen. The metal oxide is preferably a manganese oxide.

The present invention also provides (1) an electrolyte solution flow path,
(2) an oxygen supply unit installed upstream of the electrolyte solution flow path to take in oxygen from the outside and come into contact with the electrolyte solution; and (3) oxygen installed in the electrolyte solution and installed adjacent to the oxygen supply unit. (Cathode) for electrolytic reduction of hydrogen to generate hydrogen peroxide, (4) a counter electrode (anode) of the electrode, (5) a power supply for applying a voltage between the electrode and the counter electrode,
(6) a metal oxide that is provided downstream of the electrode in the electrolyte flow path and decomposes hydrogen peroxide contained in the electrolyte to generate oxygen; and (6) the metal oxide in the electrolyte flow path The present invention relates to an oxygen production apparatus which is provided downstream of a metal oxide and has an oxygen separation unit for extracting oxygen contained in an electrolytic solution. The electrolyte is preferably an alkaline aqueous solution. The electrode is preferably made of glassy carbon. The metal oxide is preferably a manganese oxide.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method for producing oxygen of the present invention, a gas containing oxygen such as air is used as a raw material. When electrolysis is carried out by including such a source gas in the electrolyte, on the cathode side, 2H ₂ O + O ₂ (in the source gas) + 2e ⁻ → H ₂ O ₂ +2
OH ^- hydrogen peroxide (H ₂ O ₂₎ generated by oxygen reduction reactions. On the other hand, on the anode side, an oxidation reaction of 2OH ⁻ → H ₂ O ₂ + 2e ⁻ occurs to generate hydrogen peroxide. That is, when a gas containing oxygen is electrolyzed in the electrolytic solution, the reaction represented by the following formula (1): H ₂ O + ／ O ₂ → H ₂ O ₂ (1) proceeds as a whole, and hydrogen peroxide is generated. When the generated hydrogen peroxide is brought into contact with the metal oxide, a reaction of the formula (2): 2H ₂ O ₂ + (metal oxide) → O ₂ + 2H ₂ O (2) occurs, and the hydrogen peroxide is decomposed. Oxygen is produced.

In the method for producing oxygen of the present invention, the reactions of the above formulas (1) and (2) are allowed to proceed continuously. That is, hydrogen peroxide is generated from a raw material gas containing oxygen such as air, and then the generated hydrogen peroxide is immediately decomposed by the catalytic action of a metal oxide, and the oxygen generated at that time is recovered. Therefore, it is possible to safely and stably produce oxygen when needed.

The reaction on the cathode side is, for example, 0.1 N
Ag / Ag in an alkaline aqueous solution (N: normality)
It can be performed at a potential of about minus 0.2 V with respect to the Cl reference electrode. On the other hand, the reaction on the anode side can be performed at a potential of about plus 0.2 V with respect to the reference electrode. Therefore, a voltage of at least 0.5 V only needs to be applied to the electrode pair consisting of the cathode and the anode, and electrolysis can be performed at a voltage that is about one third as compared with electrolysis of water.

A cathode and an anode for electrolysis may be made of a conductive material. Examples of the conductive material include metals, metal oxides, metal hydroxides, metal sulfides, carbon materials, and conductive polymers. Among these, carbon materials and metals that are not oxidized or reduced by themselves at a voltage of about 0.5 V are preferable in consideration of a potential region where electrolysis is performed. Among them, the carbon material is preferably glassy carbon, activated carbon, and the like, and the metal is platinum, gold, ruthenium, titanium,
Stainless steel is preferred.

Examples of metal oxides that decompose hydrogen peroxide include manganese oxides such as MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and Mn ₅ O ₈ , platinum oxide, ruthenium oxide, SrTiO 2.
₃ , a perovskite oxide such as Sr _x Cu _1-x TiO ₃ (x = 0 to 0.5) can be used. Among them, manganese oxide is preferable because it has a high catalytic activity for decomposing hydrogen peroxide, hardly deteriorates, and is inexpensive. As the manganese oxide, the MnO ₂ positive electrode of the used manganese dry battery can be used as it is or after baking, and thus is particularly preferable from the viewpoint of resource recycling.

As the electrolytic solution used for the electrolysis, an aqueous solution containing a solute or a non-aqueous solution is preferable. Among them, a low-concentration alkaline aqueous solution of 1 N or less is preferable because the solubility of oxygen is high and the diffusion of oxygen is fast, so that an electrode reaction can be efficiently caused.

Next, an example of an apparatus for producing oxygen suitable for carrying out the method for producing oxygen of the present invention will be described with reference to FIG. In the case of the apparatus for producing oxygen shown in FIG. 1, the closed electrolyte flow path 3 around which the electrolyte is circulated by the pump 10.
An oxygen supply unit is installed on the upstream side of. The arrow 4 in FIG. 1 indicates the traveling direction of the electrolytic solution. The oxygen supply unit includes an intake 6 for taking in a source gas containing oxygen from the outside, and an oxygen permeable membrane 7 interposed between the intake and the electrolyte flow path.

Since the oxygen-permeable film has a property of selectively passing a gas such as oxygen, the electrolyte does not leak out of the electrolyte flow path through the membrane. Oxygen in the source gas passes through the oxygen permeable membrane, diffuses into the electrode adjacent to the membrane, and contacts the electrolyte.

An electrode pair consisting of an electrode 1a and a counter electrode 1b for promoting the reaction of the above formula (1) is provided at a position adjacent to the oxygen supply section of the electrolyte solution flow path. Electrode 1
a and the counter electrode 1b are connected to the power source 5, respectively.
A voltage of about 0.5 V can be applied between the electrode pairs.

As shown in FIG. 1, it is preferable that the oxygen permeable membrane 7 is integrated with the electrode 1a that performs the oxygen reduction reaction, because the electrolyte and the oxygen can be efficiently brought into contact with each other. As the oxygen permeable film, for example, a water-repellent porous film made of a fluorine resin, a film made of a silicone resin having a property of selectively transmitting oxygen, or the like can be used.

The hydrogen peroxide generated by the reaction of the above formula (1) moves to the downstream side where the reaction bed 2 made of metal oxide is installed while being contained in the electrolytic solution. Reaction bed 2
It is preferable that the electrolyte solution flow path be installed in as wide a range as possible so that hydrogen peroxide is efficiently decomposed and oxygen is efficiently generated.

The electrolyte passed through the reaction bed contains a large amount of oxygen generated by decomposition of hydrogen peroxide. Therefore, when this electrolytic solution comes into contact with the gas-liquid separation membrane 8 provided at the most downstream of the electrolytic solution flow path, oxygen passes through this membrane and is taken out to the outside through the oxygen take-out port 9. The electrolyte from which oxygen has been removed is transported upstream of the electrolyte flow path by the pump 10 and comes into contact with oxygen again. According to such an apparatus, oxygen can be continuously and efficiently produced.

The electrolyte from which oxygen has been removed at the most downstream side of the electrolyte flow path may be stored as it is on the downstream side or may be discharged to the outside. In that case, the electrolyte containing oxygen may be supplied continuously or intermittently from the upstream side of the electrolyte flow path.

In the oxygen production apparatus of the present invention, as long as the oxygen production method of the present invention is used, it is not always necessary to provide an electrolytic solution flow path as shown in FIG. It is not necessary to dispose the electrode pair for electrolytic reduction and the metal oxide for decomposing the generated hydrogen peroxide to generate oxygen separately. For example, a metal oxide for decomposing hydrogen peroxide may be dispersed in an electrolytic solution, or a metal oxide may be contained in an electrode. However, FIG.
By using such an apparatus, it is possible to prevent the generated hydrogen peroxide from being further reduced at the electrode pair and to be reduced to hydroxide ions (OH ⁻ ), thereby increasing the oxygen generation efficiency.

[0024]

Next, the present invention will be specifically described based on examples. Example 1 Oxygen reduction effect obtained by molding a mixture of glassy carbon powder, acetylene black powder and fluororesin (weight ratio: 30: 5: 5) into a plate shape with nickel net as the center. An electrode, a counter electrode made of a platinum network, and Mn ₃
A porous hydrogen peroxide decomposition reaction bed obtained by molding a mixture (weight ratio: 30: 5: 5) of O ₄ powder, acetylene black and fluororesin into a plate shape around a nickel net. Got ready. Then, a concentration of 0.2 M (M: mol /
The working electrode, counter electrode and reaction bed were immersed in a beaker containing 1 liter of an aqueous KOH solution.

When a voltage of 0.5 V was applied between the working electrode and the counter electrode while stirring the aqueous solution, oxygen bubbles were generated from the reaction bed. Even when the stirring of the aqueous solution was stopped, bubbles continued to be generated. In this case, the air in the atmosphere dissolves into the aqueous KOH solution from the surface of the water, and the above formulas (1) and (2)
It is considered that oxygen was purified through the reaction to produce high-purity oxygen, and the bubbles were generated.

Example 2 A mixture (weight ratio: 30: 5: 20: 5) of activated carbon powder, acetylene black powder, Mn ₅ O ₈ powder, and fluororesin was formed into a plate shape with nickel net as the center. The obtained working electrode for oxygen reduction containing manganese oxide for hydrogen peroxide decomposition and a counter electrode made of a platinum net were prepared. The working electrode and the counter electrode were immersed in a beaker containing a 0.5 M KOH aqueous solution.

When a voltage of 0.7 V was applied between the working electrode and the counter electrode while stirring the aqueous solution, oxygen bubbles were generated from the working electrode. Even when the stirring of the aqueous solution was stopped, bubbles continued to be generated. When the applied voltage was higher than 0.7 V, the generation of bubbles became gentle but did not stop.

Example 3 An oxygen producing apparatus shown in FIG. 1 was assembled. Porous electrode 1 for oxygen reduction forming an electrode pair
a is a mixture of glassy carbon powder, activated carbon powder, acetylene black and fluororesin (weight ratio 10: 30: 5:
5) is obtained by forming a plate around a nickel net. On one side of the electrode 1a, a porous and water-repellent oxygen-permeable film 7 having a thickness of 0.5 mm obtained by sintering fluororesin particles was disposed, and both were brought into close contact with a hot roll. Nickel net was used as the counter electrode 1b of the electrode 1a. The reaction bed 2 is obtained by molding a mixture (weight ratio: 30: 5: 5) of Mn ₂ O ₃ powder, acetylene black, and a fluororesin into a plate shape around a nickel net. The same gas-liquid separation membrane 8 as the oxygen permeable membrane 7 was used.

After a voltage of 0.6 V is applied to the electrode pair by the power supply 5, a concentration of 0.1 is applied to the electrolyte passage 3 made of stainless steel.
M KOH aqueous solution was filled, and the electrolyte was circulated by the pump 10 so that the electrode pair was on the downstream side and the reaction bed was on the upstream side. As a result, high purity (purity 99
% Or more) of oxygen. When this device was continuously operated, the amount of electricity consumed was 90%.
% Of oxygen could be produced.

When the applied voltage was set to 1.0 V, the amount of generated oxygen was reduced to an amount corresponding to 58% of the amount of consumed electricity, but oxygen could be continuously produced. When the pump is stopped to stop the flow of the electrolyte, the value of the current flowing from the power supply to the electrode is reduced, and the amount of generated oxygen is reduced. Could be manufactured continuously.
When the application of the voltage was stopped, generation of oxygen disappeared after a while.

Instead of a 0.1 M KOH aqueous solution, a 0.5 M sodium acetate aqueous solution or 0.2 M
When a phosphoric acid aqueous solution of M was used, oxygen could be efficiently produced.

[0032]

According to the present invention, when necessary on-site, oxygen can be produced safely and simply and efficiently with a small amount of electric power.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an internal configuration of an example of an oxygen production apparatus according to the present invention as viewed from above.

[Explanation of symbols]

 1a Electrode 1b Counter electrode 2 Reaction bed 3 Electrolyte flow path 4 Electrolyte flow direction 5 Power supply 6 Intake port 7 Oxygen permeable membrane 8 Gas-liquid separation membrane 9 Oxygen outlet 10 Pump

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G042 BA08 BB06 4K011 AA10 AA22 AA23 AA31 BA03 CA04 DA07 4K021 AA01 AB15 BA02 BB01 BB03 DB53 DC01

Claims (6)

[Claims] 1. A method for producing oxygen, comprising: generating hydrogen peroxide from an oxygen-containing raw material gas by electrolysis, and decomposing the hydrogen peroxide in the presence of a metal oxide to generate oxygen. 2. The method according to claim 1, wherein the metal oxide is a manganese oxide. And (3) an oxygen supply unit provided upstream of the electrolyte solution flow path and adapted to take in oxygen from the outside and come into contact with the electrolyte solution, and (3) an oxygen supply unit. An electrode which is installed adjacently and which electrolytically reduces oxygen contained in the electrolyte to generate hydrogen peroxide; (4) a counter electrode of the electrode;
(5) a power supply for applying a voltage between the electrode and the counter electrode; and (6) a power supply installed downstream of the electrode in the electrolyte flow path to decompose hydrogen peroxide contained in the electrolyte. And (6) an oxygen production apparatus having an oxygen separator installed downstream of the metal oxide in the electrolytic solution flow path to extract oxygen contained in the electrolytic solution. 4. The oxygen producing apparatus according to claim 3, wherein the electrolytic solution is an alkaline aqueous solution. 5. The oxygen producing apparatus according to claim 3, wherein the electrode is made of glassy carbon. 6. The oxygen producing apparatus according to claim 3, wherein the metal oxide is a manganese oxide.