JPH0692616A - Method and apparatus for carbon monoxide oxidation reaction - Google Patents

Abstract

PURPOSE:To efficiently oxidize CO at lower temperatures by such a method that an O2 feed chamber and a CO oxidation chamber are provided by partitioning with a specific solid electrolyte bearing electrodes, followed by applying voltage between the electrodes to convert O2 to O ions, which are passed through the solid electrolyte to effect CO oxidation. CONSTITUTION:Firstly, a solid electrolyte 1 is prepared, which is characterized by converting O2 to O ions, penetrating the O ions, and changing the O ions into active O species. Both surfaces of this electrolyte are then covered with electrode materials (anode and cathode) 4; cathode surface is fed with O2, and anode surface with CO. Next, direct current voltage 5 is applied between the electrodes 4 to convert the O2 to O ions, and the O ions are made to penetrate to the other side of the solid electrolyte. The CO is then oxidized at <=300 deg.C by the active O species produced from the O ions penetrated through the electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide oxidation reaction method and apparatus using a solid electrolyte.

[0002]

2. Description of the Related Art Carbon monoxide is contained in combustion gas such as exhaust gas of automobiles.
Since it is harmful to the human body, detoxification by oxidation of carbon monoxide is important in terms of air purification. Conventionally, the oxidation of carbon monoxide has been carried out in the presence of a catalyst, but more recently, using a solid electrolyte having the property of allowing oxygen ions to permeate,
A method for carrying out an oxidation reaction of carbon monoxide has been proposed.

For example, an electrochemical purification device for exhaust gas having catalyst electrodes on both sides of a solid electrolyte (Japanese Patent Publication No. 55-397).
No. 4), water vapor is supplied to one side of an oxygen ion conductive solid electrolyte membrane having electrodes on both sides and carbon monoxide is circulated to the other side, and electric power is obtained by connecting both electrodes at the same time.
Carbon monoxide shift reaction method (Japanese Patent Laid-Open No. 62-278288) in which high-purity hydrogen gas is obtained from an outlet on the side of supplying steam, platinum electrodes are formed on both sides of a solid electrolyte, and air is formed on one side and the other side is formed. A method to oxidize carbon monoxide on the platinum electrode surface by flowing a gas containing carbon monoxide into the surface (JOURNAL OF CAT
ALYSIS. VOL82. P322-331 1983) etc.

However, in all of these methods, the reaction temperature is 3
The reaction is performed at a temperature of 00 ° C. or higher and an applied voltage of about 1.5 V per 1 mm of the thickness of the solid electrolyte, and no reaction is disclosed in a low temperature region from room temperature to less than 300 ° C. As described above, in the conventional method, the applicable temperature range is a high temperature of 300 ° C. or higher. For example, when applied to the treatment of exhaust gas of an automobile, the exhaust temperature at the time of engine start is 300 ° C.
If it is less than the above, there is a problem that carbon monoxide cannot be sufficiently oxidized as it is, and means for separately heating the solid electrolyte is required.

The reasons why the carbon monoxide oxidation reaction using the solid electrolyte is not carried out below 300 ° C. are as follows. That is, in the above method, under low temperature conditions such as a temperature of less than 300 ° C., the oxygen ion permeability of the solid electrolyte becomes small, and it is difficult for the solid electrolyte to permeate oxygen ions in an amount sufficient to oxidize carbon monoxide. Because it has been generally considered. Therefore, development of a carbon monoxide oxidation reaction method using a solid electrolyte at less than 300 ° C. is desired.

The object of the present invention, in order to solve the above problems, has hitherto been considered to be difficult to carry out an efficient reaction.
It is an object of the present invention to provide an oxidation reaction method and an apparatus for efficiently performing the oxidation reaction in the carbon monoxide oxidation reaction using a solid electrolyte at a temperature lower than ° C.

[0007]

The summary of the present invention is as follows.
(1) Both surfaces of a solid electrolyte having a property of converting oxygen into oxygen ions, a property of transmitting oxygen ions and a property of converting oxygen ions into active oxygen species are coated with electrode materials, and a voltage is applied between the electrodes. In the method of carrying out the oxidation reaction by supplying oxygen to the electrode surface on one side of the solid electrolyte and carbon monoxide to the electrode surface on the other side or in the vicinity thereof, oxygen is converted to oxygen ions on the oxygen supply side. After that, oxygen ions are permeated to the other side of the solid electrolyte, and the carbon monoxide is oxidized at a temperature of less than 300 ° C. by active oxygen species converted from the oxygen ions permeated on the carbon monoxide supply side. Oxidation reaction method, and (2) solid electrolyte having properties of converting oxygen into oxygen ions, properties of transmitting oxygen ions and properties of converting oxygen ions into active oxygen species Surface and the electrode material coated with the electrode with the solid electrolyte, and means for supplying and means for applying a voltage between the electrodes, the oxygen on one side of the electrode surface of the solid electrolyte,
An oxidation reaction device comprising means for supplying carbon monoxide to the surface of the electrode on the other side or in the vicinity thereof, wherein carbon monoxide is oxidized at a temperature of less than 300 ° C. It relates to a reactor. Hereinafter, the present invention will be described in detail.

First, the carbon monoxide reactor of the present invention will be described. The solid electrolyte that can be used in the present invention is not particularly limited, but is preferably a metal oxide composed of one kind or two or more kinds, and a crystal structure having a fluorite structure. In the fluorite type structure of the metal oxide, the arrangement of oxygen ions is far from the closest packing, and there is an empty site with eight coordinations of oxygen ions. It is considered that a large amount of lattice defects are likely to occur due to such a loose structure. In other words, it is said that the fluorite structure retains its basic crystal structure even if some heteroatoms enter due to its looseness and various defects occur (Tetsuichi Kudo and Kazuo Fueki, "Solid Eye"). Onyx] Kodansha Scientific 1
Issued the first printing on May 20, 986). By utilizing the lattice defects of oxygen ions in such a fluorite structure, a property of transmitting oxygen ions is generated.

Examples of the above-mentioned metal oxide having a fluorite structure include cerium oxide, thorium oxide, zirconium oxide, hafnium oxide, bismuth oxide and magnesium oxide, calcium oxide, scandium oxide, yttrium oxide in addition to these metal oxides. , Lanthanum oxide, niobium oxide, tungsten oxide, neodymium oxide, samarium oxide, gadnium oxide, erbium oxide, and ytterbium oxide are solid-solved. Among these, zirconium oxide in which yttrium oxide is dissolved in solid solution, zirconium oxide in which calcium oxide is dissolved in solid solution, and cerium oxide in which scandium oxide is dissolved in solid solution are preferably used from the viewpoints of wide application temperature range and easy availability.

The shape of the solid electrolyte is not particularly limited, but may be any shape having a substantially constant thickness such as a plate shape or a tube shape. Further, as long as it has a substantially constant thickness, it is also preferable that the structure is not flat but has an uneven structure and a large surface area so that a reaction field can be efficiently provided.

Here, the thickness of the solid electrolyte is 1.0 mm.
Is preferably less than 1 μm, more preferably 1 μm to 0.5 mm,
Particularly preferably, it is 10 μm to 0.5 mm. 1.0 m
If the temperature is less than 300 ° C., it is difficult for oxygen ions having good permeability to pass through oxygen ions. Those having a thickness of less than 1 μm are difficult to manufacture, and are likely to have many holes through which molecular oxygen can pass. Further, there is a problem in strength because it is easily cracked due to a sudden temperature change. However, the thinner the thickness of the solid electrolyte, the larger the applied voltage per unit thickness for the same applied voltage, which increases the permeation amount of oxygen ions,
The oxidation reaction method of the present invention can be suitably performed.

Since the mechanical strength decreases as the solid electrolyte becomes thinner (for example, 0.1 mm or less), the solid electrolyte is made of a porous material (for example, porous alumina, porous zirconia, etc.) having a low diffusion resistance of oxygen molecules. You may mount and use a solid electrolyte on the surface of a support body.

Examples of the method for producing the solid electrolyte include, but are not limited to, firing method, plasma spraying, sol-gel method, vacuum deposition and sputtering. The solid electrolyte as described above has the property of converting oxygen into oxygen ions, the property of transmitting oxygen ions, and the property of converting oxygen ions into active oxygen species. In the present invention, these properties are less than 300 ° C. It can be expressed at low temperature.

In the present invention, both surfaces of the solid electrolyte are coated with electrode materials. This electrode efficiently donates electrons to convert oxygen supplied to one side into oxygen ions and accepts electrons to convert oxygen ions permeating the solid electrolyte into active oxygen species on the other side. It is provided for. The electrode material may be one having sufficient conductivity, for example, metals such as gold, platinum, silver, copper, iron, aluminum, nickel, zinc, tin, alloys composed of two or more metals, or carbon. Etc. Such an electrode is formed by a method of applying an electrode material in a paste form, a method of coating the solid electrolyte surface by a sputtering method or a vacuum deposition method, a method of adhering a metal mesh to the solid electrolyte surface, and the like. It is not limited.

The oxidation reaction apparatus of the present invention comprises such a solid electrolyte with electrodes, means for applying a voltage between the electrodes, and means for supplying oxygen to the electrode surface on one side of the solid electrolyte.
A means for supplying carbon monoxide to the electrode surface of the solid electrolyte or the vicinity thereof is provided so that carbon monoxide is oxidized by the active oxygen species generated on the other side of the solid electrolyte.

In the present invention, in order to permeate oxygen ions in the solid electrolyte, it is necessary to generate a potential difference between both electrodes. In order to generate a potential difference, a means for applying a voltage between the electrodes is required, and it is not particularly limited as long as it can apply a DC voltage, but for example, a stabilizing power source, a dry battery, a lead acid battery or the like can be used. it can.

The means for supplying oxygen include, for example, a method of supplying oxygen or a mixture of oxygen such as air with a high-pressure gas cylinder, a method of supplying with an air pump or an air compressor, or a method of exposing to the atmosphere. However, it is not particularly limited. Oxygen is supplied to the electrode surface on one side of the solid electrolyte by this oxygen supply means, and oxygen is converted to oxygen ions.

As means for supplying carbon monoxide, a method of supplying a carbon monoxide-containing gas (for example, automobile exhaust gas) by a pump or the like, and a method of supplying carbon monoxide with an inert gas (helium,
For example, it may be diluted with nitrogen or the like and supplied. Note that it is desirable to supply carbon monoxide to the surface of the electrode or the vicinity thereof.

In the carbon monoxide oxidation reaction apparatus of the present invention, it is possible to use a reactor as shown in FIG. 1 for supplying oxygen and carbon monoxide. That is, it is possible to adopt a method of supplying the respective substances to the oxygen supply chamber and the oxidation reaction chamber by using a reactor partitioned by the solid electrolyte with electrodes into the oxygen supply chamber and the oxidation reaction chamber. In addition to such a reactor, for example, a reactor in which the inside or outside of a tubular solid electrolyte with an electrode is an oxygen supply chamber or an oxidation reaction chamber, one side of the solid electrolyte with an electrode is exposed to the atmosphere to form an open system. Various types of reactors such as existing reactors can be used. However, in the present invention,
It is not always necessary to use a reactor with such a closed system geometry.

In the present invention, auxiliary means for producing a pressure gradient or a concentration gradient may be provided if necessary. As means for producing the pressure gradient, means for pressurizing the oxygen supply chamber side with a pressurizing pump, means for depressurizing the oxygen reaction chamber side with a vacuum pump, and the like can be mentioned. As a means for producing a concentration gradient, a means for supplying an oxygen-containing gas having a high oxygen concentration to the oxygen supply chamber side, a means for increasing the pressure of the oxygen-containing gas by a pressure pump to supply a gas having a high oxygen concentration, a reaction Examples include means for supplying carbon monoxide mixed with an inert gas (nitrogen, helium, etc.) to the chamber side.

Next, the carbon monoxide oxidation reaction method of the present invention will be described. The oxidation reaction method of the present invention can be suitably performed using the above-mentioned oxidation reaction device. The oxygen used may be a pure component oxygen molecule gas, air, or a gas in which oxygen is mixed with another gas (for example, nitrogen, helium, etc.), and such a substance is supplied by the above-mentioned supply means. . The carbon monoxide used may be a pure component carbon monoxide molecular gas or a carbon monoxide-containing gas such as automobile exhaust gas.

In the present invention, specific conditions for permeating oxygen ions in the solid electrolyte include a temperature of 300.
The potential difference may be generated through the solid electrolyte so that carbon monoxide can be efficiently oxidized at a temperature lower than ° C. By appropriately adjusting the potential difference in this manner, carbon monoxide can be oxidized by 60 mol% or more, preferably 80 mol% or more. A pressure gradient or a concentration gradient may be generated in order to improve the oxygen ion permeability in the solid electrolyte. To generate a potential difference, a voltage is applied between the electrodes by the voltage applying means. The applied voltage per 1 mm thickness of the solid electrolyte is usually 20-0.04T V / mm or more, preferably 20-0.04T V / mm to 200-0.4T.
V / mm. Here, T represents a temperature [° C.].
If it is less than 20-0.04 TV / mm, the oxygen ion permeability of the solid electrolyte becomes small and the oxidation of carbon monoxide cannot be efficiently performed at a temperature of less than 300 ° C. When a pressure gradient is generated, a method of pressurizing the oxygen supply side, a method of depressurizing the carbon monoxide supply side, and the like can be mentioned. At this time, the differential pressure for causing the permeation of oxygen ions is usually 10 mmHg or more, preferably 50 mmHg or more as the oxygen partial pressure. When generating a concentration gradient, a method of supplying a gas having a high oxygen concentration to the oxygen supply side,
The oxygen-containing gas may be pressurized to supply a gas having a high oxygen concentration, or carbon monoxide mixed with an inert gas may be supplied to the reaction substrate supply side. At this time, the difference in oxygen concentration for causing the permeation of oxygen ions is usually 5 mol% or more, preferably 10 mol% or more.

The reaction temperature of the carbon monoxide oxidation reaction is 300.
Below 50 ° C, usually 50-300 ° C, preferably 100
~ 300 ° C. If the temperature is lower than 50 ° C, the permeation rate of oxygen ions in the solid electrolyte is low, which is not preferable. The pressure on the oxidation reaction side may be normal pressure, but when a pressure gradient is generated through the solid electrolyte as described above, it may be performed under reduced pressure. The decompression condition in this case is 500 m
It is preferably mHg or less, more preferably 200 mmHg or less. The pressure on the oxidation supply side may be normal pressure, but may be increased when a pressure gradient is generated through the solid electrolyte as described above. The pressurizing condition in this case is 0.1 k.
gf / cm ² or more, preferably 1 kgf / cm ² or more. The carbon monoxide oxidation reaction method and apparatus using a solid electrolyte have been described above.

By using the present invention, it is possible to remove carbon monoxide contained in exhaust gas from various combustion furnaces such as incinerators in general and internal combustion engines. The use of the present invention is not limited to the above, and carbon monoxide can be efficiently oxidized by using the active oxygen species obtained by the present invention.

The mechanism of the oxidation reaction method of the present invention is considered as follows. A solid electrolyte composed of one or more kinds of metal oxides having a fluorite type crystal structure has a property of transmitting oxygen ions through lattice defects of oxygen ions. When both sides of this solid electrolyte are covered with electrodes and oxygen is brought into contact with one side of the solid electrolyte, 1 / 2O ₂ + 2e ^{− on the} electrode surface.
→ O ^{2 −} reaction occurs and oxygen ions enter into lattice defects in the solid electrolyte. Oxygen ions that have entered the lattice defects are transported to the other side due to the potential difference due to the voltage applied between the electrodes. On the surface of the electrode on the other side, a reaction of O ^2- → O ^* + 2e ⁻ occurs and active oxygen species are generated. The carbon monoxide introduced by this reactive oxygen species is presumed to be oxidized.

The permeability of oxygen ions in the solid electrolyte increases as the temperature rises and as the thickness of the solid electrolyte decreases. That is, the thinner the thickness, the larger the applied voltage can be, and the applied voltage per unit thickness of the solid electrolyte can be increased. Oxygen ions permeate well even at a low temperature of less than 300 ° C., and a sufficient amount of active oxygen species can be obtained. Can be generated, and carbon monoxide can be oxidized at a low temperature.

[0027]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 FIG. 1 schematically shows an example of a reactor portion of a carbon monoxide oxidation reaction apparatus according to the present invention, in which two spaces partitioned by a solid electrolyte with electrodes are respectively oxygenated. Supply room,
It is used as an oxidation reaction chamber. Reference numeral 1 is a zirconium oxide disc (manufactured by Japan Fine Ceramics Co., Ltd., thickness 0.1 mm, diameter 80 mm) in which solid electrolyte having oxygen ion permeability and 8 mol% concentration of yttrium oxide was solid-dissolved. Reference numeral 2 is an oxygen supply chamber for supplying oxygen into the solid electrolyte. 3 is an oxidation reaction chamber that supplies carbon monoxide and reacts with the active oxygen species. 4 is a gold electrode (thickness 10 to 2) produced by applying paste gold (manufactured by Nippon Kin Liquid Co., Ltd.)
0 μm) on both sides of the solid electrolyte. Reference numeral 5 is a stabilized DC power supply for applying a voltage between the solid electrolytes. 6 is an ammeter for measuring the current flowing in the system when a voltage is applied.

Example 2 An oxidation reaction of carbon monoxide was carried out using the apparatus shown in FIG. The reaction method and the result are shown below. Two
Air was supplied at a flow rate of 50 ml / min to the oxygen supply chamber. On the other hand, in the oxidation reaction chamber of 3, carbon monoxide 822pp
Helium gas containing 20 mol% of oxygen and 20 mol% of oxygen was passed through the high pressure gas cylinder at a flow rate of 20 ml / min. The reaction was carried out by heating with a heater so that the reaction temperature was 150 ° C., and applying a voltage of +35 V / mm to the 4th electrode on the anode side by the power supply device of 5 under normal pressure. To quantify the reaction product, the amount of carbon dioxide as a product in the outlet gas was measured by gas chromatography (GC-8A manufactured by Shimadzu). As the analysis conditions, WG-100 (manufactured by GL Sciences) was used as a column, column temperature: 50 ° C., carrier gas: helium, carrier pressure: 0.8 kg / cm ² , detector: T
It was done by CD. As a result, carbon dioxide was not detected in the inlet gas, but carbon dioxide was detected in the outlet gas.
95 ppm was present, and it was confirmed that 97 mol% of the supplied carbon monoxide was oxidized.

[0030]

EFFECTS OF THE INVENTION According to the present invention, it has become possible to efficiently oxidize carbon monoxide at a temperature of less than 300 ° C., which has hitherto been considered difficult to perform an efficient reaction. Therefore, it is possible to provide a method for oxidizing carbon monoxide at a low temperature of less than 300 ° C., and the present invention can be widely applied.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a reactor portion of a carbon monoxide oxidation reaction apparatus of the present invention.

[Explanation of symbols]

 1 Solid Electrolyte 2 Oxygen Supply Chamber 3 Oxidation Reaction Chamber 4 Electrode 5 Power Supply Device 6 Ammeter 7 Reactor

Claims (4)

[Claims] 1. A solid electrolyte having the characteristics of converting oxygen into oxygen ions, the characteristics of allowing oxygen ions to permeate, and the characteristics of converting oxygen ions into active oxygen species, is coated with electrode materials to apply a voltage between the electrodes. In the method of performing an oxidation reaction by applying, oxygen is supplied to the electrode surface on one side of the solid electrolyte and carbon monoxide is supplied to the electrode surface on the other side or in the vicinity thereof, and oxygen is converted into oxygen ions on the oxygen supply side. After conversion, the oxygen ions are permeated to the other side of the solid electrolyte, and the active carbon species converted from the oxygen ions permeated on the carbon monoxide supply side oxidize the carbon monoxide at a temperature of less than 300 ° C. And the oxidation reaction method. 2. The oxidation reaction method according to claim 1, wherein the applied voltage per 1 mm thickness of the solid electrolyte is 20-0.04 TV / mm (where T represents temperature [° C.]) or more. 3. A solid electrolyte with electrodes in which both surfaces of a solid electrolyte having a property of converting oxygen into oxygen ions, a property of transmitting oxygen ions and a property of converting oxygen ions into active oxygen species are coated with electrode materials. An oxidation reaction comprising means for applying a voltage between the electrodes, means for supplying oxygen to the electrode surface on one side of the solid electrolyte, and means for supplying carbon monoxide to the electrode surface on the other side or in the vicinity thereof. In the device,
A carbon monoxide oxidation reactor characterized by being configured to oxidize carbon monoxide at a temperature of less than 300 ° C. 4. The carbon monoxide oxidation reactor according to claim 3, wherein the applied voltage per 1 mm thickness of the solid electrolyte is 20-0.04 TV / mm (where T represents temperature [° C.]) or more.