JPS6353136B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal oxide composite having oxygen permeability. More specifically, the present invention relates to a metal oxide composite comprising oxides of lanthanum, bismuth, and cobalt and having electronic conductivity and oxygen ion conductivity.

In recent years, there has been remarkable progress in separation techniques using membrane methods, adsorption methods, etc., and some of them have been put into practical use on an industrial scale. However, what has been put into practical use is liquid-liquid separation or liquid-
It is a solid separation, and gas-gas separation, that is, separation of two or more types of mixed gases, has not been put into practical use very much.

The reason why it is difficult to put gas separation into practical use is, for example, in the case of membrane methods, the permselectivity is low, that is, there are no membranes that selectively allow certain gases to pass through while almost all other gases pass through. In order to obtain gas, it is necessary to adopt a multi-stage method in which membrane separation is repeated several times, which makes the equipment too large, and the amount of permeation is small, making it impossible to produce a large amount of gas. .

Conventionally, what is known as a gas separation membrane is mainly an organic polymer membrane. For example, there is a method of separating oxygen from the air using an organopolysiloxane-polycarbonate copolymer membrane.
However, the oxygen concentration that can be separated from air using such an organic polymer membrane is about 30 to 40%, which is poor selectivity. Furthermore, organic polymer membranes used for such gas separation have poor heat resistance, so in the case of oxygen, for example, they are not suitable for industrial use as separation membranes for blowing blast furnace air or combustion auxiliary membranes using waste heat. Appropriate.

In addition to separation using organic polymer membranes, oxygen enrichment methods include BaO described in U.S. Pat.
Adsorption/desorption methods using metal oxides such as Ce-Pr oxides or molecular sheep are known, but
Such an adsorption/desorption method requires steps for adsorption and desorption of oxygen, and requires complicated equipment, which is economically disadvantageous.

Furthermore, as described in U.S. Pat. No. 3,400,054, a method of separating oxygen using a solid electrolyte represented by the formula (ZrO ₂ ) _1-x (CaO) _x [X=0.05 to 0.3] is known. .

This separation method is based on the principle of electrochemically permeating oxygen in a gas mixture by utilizing the oxygen ion conductivity of a solid electrolyte. In other words, this method allows oxygen ions ionized on one side of a solid electrolyte to migrate through the solid electrolyte,
This is a method to obtain oxygen gas by discharging on the other side.
The ionization and discharge of oxygen necessary for this purpose are carried out by electrically shorted electrodes through an external circuit attached to both sides of the solid electrolyte.

In such a method, the electrode reaction does not occur only at the point where the three phases of solid electrolyte, electrode material, and oxygen gas meet, and the effective area is small, and the amount of oxygen gas and permeation is small. This method has disadvantages in that the contact deteriorates over time and is unstable, and the device is complicated, which is economically disadvantageous. The reason why the oxygen separation method described in the above-mentioned patent requires the attachment of electrodes and external circuits is that the electronic conductivity of the solid electrolyte used in the separation method is very small compared to the oxygen ion conductivity.

Therefore, the present inventors have developed a solid electrolyte that has the electronic conductivity necessary for the electrode reaction to occur sufficiently without the need for attaching electrodes or external circuits, and also has oxygen ion conductivity. The present invention was achieved as a result of intensive research aimed at developing a separation membrane that can separate high-purity oxygen, utilize waste heat, etc., and can be used industrially at high temperatures.

That is, the present invention relates to a metal oxide composite made of lanthanum, bismuth and cobalt oxides and having electronic conductivity and oxygen ion conductivity.

The metal oxide complex in the present invention consists of oxides of lanthanum, bismuth and cobalt,
The appropriate composition ratio of each atom is in the range of 0.1 to 10 g atoms of lanthanum and 0.1 to 15 g atoms of bismuth per 1 g atom of cobalt. In addition, in order for the metal oxide composite to have electronic conductivity and oxygen ion conductivity, the ratio of the sum of the number of g atoms of lanthanum and bismuth to the number of g atoms of cobalt is in the range of 0.1 to 10, preferably 0.2 to 8. is desirable, and the ratio of the number of bismuth atoms to the number of g atoms of lanthanum is
A range of 0.1 to 10, preferably 0.2 to 8 is desirable.

The metal oxide composite can be prepared by conventional methods. One method is to use compounds containing metal atoms of lanthanum, bismuth, and cobalt, especially compounds that can be converted into oxides by firing as described below, such as oxides such as lanthanum oxide, bismuth oxide, and cobalt oxide. Alternatively, nitrates and carbonates are preferred, but in addition, inorganic acid salts such as sulfates and phosphates, organic acid salts such as acetates and oxalates, halides such as chlorides, bromides, and iodides, Alternatively, there is a method in which hydroxide and oxyhalide are mixed in a desired ratio and fired.

In addition, a mixed aqueous solution of each of the metal salts described above is mixed with an alkaline aqueous solution such as aqueous ammonia,
It may be prepared by hydrolysis, a so-called co-precipitation method, and then calcined. Furthermore, methods such as oxidizing and firing a mixture or alloy of each metal can be mentioned.

In either method, when obtaining the metal oxide composite of the present invention, the firing temperature is usually in the range of 400 to 1400°C, preferably 400 to 1300°C in an oxidizing atmosphere.

The metal oxide composite made of oxides of lanthanum, bismuth, and cobalt according to the present invention is a solid electrolyte having oxygen ion conductivity and electronic conductivity, that is, so-called mixed electron-oxygen ion conductivity.

Oxygen ion conductivity is usually expressed by oxygen ion conductivity, and electronic conductivity can be expressed by electronic conductivity. These conductivities can be measured using conventional methods such as the AC bridge method described in Electrochemistry 39 665 (1971),
Measured by the four-probe method, etc. Further, the ratio between oxygen ion conductivity and electronic conductivity can be determined by measuring the oxygen ion transfer number described in the same document.

The oxygen ion conductivity of the metal oxide composite made of oxides of lanthanum, bismuth, and cobalt in the present invention varies depending on the composition ratio, but is usually 400-
1×10 ^-4 Ω ^-1 cm ^-1 or more, preferably 5×10 ^-4 Ω ^-1 cm ^-1 or more, particularly preferably 1× at a temperature of 1200°C
10 ^-3 Ω ^-1 cm ^-1 or more, electronic conductivity is 1×10 ^-2 Ω ^-1 cm ^-1
The above value is preferably 1×10 ⁻¹ Ω ⁻¹ cm ⁻¹ or more, particularly preferably 5×10 ⁻¹ Ω ⁻¹ cm ⁻¹ or more.

In the present invention, when the metal oxide composite is used for oxygen separation, the ratio of electronic conductivity to oxygen ion conductivity is preferably 0.1 or more.

Note that the solid electrolyte of the present invention may contain impurities such as metals other than lanthanum, bismuth, and cobalt as long as the mixed electron-ion conductivity of the solid electrolyte is not impaired.

When the metal oxide composite of the present invention is used for oxygen separation, it is preferable to use it in a layered form, especially as a membrane. Alternatively, a method that combines the preparation of the metal oxide composite and the film formation may be used. These films can be formed by mechanical processing such as cutting or polishing a solid material such as a pellet or sheet, or by pressure molding a powder, or by making a paste into a porous material. It may also be applied onto a solid support and sintered.

Further, film forming methods include vacuum evaporation, acetylene spraying, plasma jetting, reactive sputtering, chemical vapor deposition (CVD), chemical spraying, and oxidation of alloy plating.

In addition, during molding, fillers, reinforcing materials, etc. may be used as necessary, and the metal oxide composite may be
When used as a gas separation membrane, it may be used alone or, if necessary, as a composite membrane using a porous support.

Examples of the porous support include porous metal plates or sintered bodies such as stainless steel and bronze, and composites thereof; porous oxide sintered bodies such as porous silica alumina, porous alumina, and porous magnesia;
Examples include sintered nitrides such as boron nitride, sintered carbides such as silicon carbide, and the like.

The thickness of the metal oxide composite layer obtained by the above-described molding method is usually 10 ⁻³ to ^{10 +4} μ,
When a layer mainly composed of the metal oxide composite is used as an oxygen separation membrane, it may have some ventilation holes if the separated oxygen does not need to be of particularly high purity.

In the present invention, the metal oxide composite has oxygen ion conductivity and electronic conductivity, and therefore can be used as a gas separation layer, especially a membrane, for selectively separating oxygen in a mixed gas containing oxygen.

In the present invention, in order to separate oxygen in a mixed gas using the metal oxide composite, an airtight chamber is provided on one or both sides of the layer mainly composed of the metal oxide composite; A mixed gas containing oxygen gas is supplied, and the conditions in both chambers are set so that the oxygen partial pressure in the other chamber is lower than the oxygen partial pressure. For example, one chamber may be at normal pressure or pressurized while the other chamber is at reduced pressure, one chamber may be pressurized and the other chamber may be at normal pressure, or both chambers may be at normal pressure. Oxygen can be selectively separated to the low oxygen partial pressure side by, for example, supplying a gas having a lower oxygen partial pressure to one chamber than the other chamber. The temperature at which the metal oxide composite is used as an oxygen separation membrane is usually 300 to 1200°C, preferably 400 to 1000°C.

Further, the form of the solid electrolyte layer may be a flat film,
It can take various forms depending on the purpose, such as a tubular membrane. Furthermore, the film thickness when used as an oxygen separation membrane is usually 10 ^-3 to 10 ⁴ μ, preferably 10 ⁻² to 10 ³ μ.

As described above, the metal oxide composite of the present invention is extremely useful as a gas separation membrane.

The present invention will be described below with reference to Examples, but is not limited thereto. In the examples, "parts" means "parts by weight."

Example 1 3.26 parts of lanthanum oxide, 4.66 parts of bismuth oxide, and 9.96 parts of cobalt acetate tetrahydrate were pulverized and mixed in a mortar, the mixture was thermally decomposed at about 600°C for 1 hour, and then pulverized and mixed again to produce 500 kg. / cm ² after pressure molding,
It was fired in air at 1000°C for 8 hours.

The obtained sintered body was further pulverized and mixed, press-molded to 2t/ ^cm2 , and then fired in air at 1000℃ for 9 hours.
A metal oxide composite having an atomic composition ratio of lanthanum, bismuth, and cobalt (La:Bi:Co) of 0.5:0.5:1 was obtained. The metal oxide composite has an electronic conductivity of 9Ω ^-1 cm ^-1 and an oxygen ion conductivity of 7.5×10 ^-2 Ω ^-1 cm ^-1
It was a solid electrolyte with

Example 2 A cylindrical molded body with a bottom made of the metal oxide composite prepared in Example 1 with an outer diameter of 12.5 mm, an inner diameter of 11.5 mm, a height of 13 mm, and a thickness of 1 mm was used as a diaphragm, and one side, that is, the side surface of the cylinder. The bottom surface was exposed to air, and an airtight chamber was provided on the opposite side, and argon gas was used as a carrier gas to flow at a rate of 30 c.c./min. The amount of oxygen contained in the argon gas was measured by gas chromatography after passing through the diaphragm at 800° C. The result was 2×10 ⁻³ cc/sec·cm ² .

Example 3 Lanthanum oxide 9.77 parts, bismuth oxide 32.62 parts,
49.82 parts of cobalt acetate tetrahydrate were pulverized and mixed in a mortar, and the mixture was thermally decomposed at about 600°C for 1 hour, then pulverized and mixed again, and after pressure molding at 500 kg/cm ² ,
It was fired in air at 900°C for 8 hours. The obtained sintered body was further pulverized and mixed, pressure-formed to 2t/ ^cm2 , and then fired in air at 930℃ for 10 hours to improve the atomic composition ratio of lanthanum, bismuth, and cobalt (La:Bi:Co).
A metal oxide composite having a ratio of 0.3:0.7:1 was obtained.

The electronic conductivity and oxygen ion conductivity of the metal oxide composite at 800°C are 1.2Ω ^-1 cm ^-1 , respectively.
It was 4.3×10 ^-1 Ω ^-1 cm ^-1 .

Example 4 Lanthanum oxide 9.77 parts, bismuth oxide 32.62 parts,
99.63 parts of cobalt acetate tetrahydrate were pulverized and mixed in a mortar, the mixture was thermally decomposed at about 600°C for 1 hour, then pulverized and mixed again, and after pressure molding at 500 kg/cm ² ,
It was fired in air at 900°C for 8 hours. The obtained sintered body was further pulverized and mixed, and after pressure molding to 2t/ ^cm2 ,
Fired in the air at 910℃ for 10 hours to create a lantern,
Atomic composition ratio of bismuth and cobalt (La:Bi:
A metal oxide composite in which Co) was 0.15:0.35:1 was obtained.

The electronic conductivity and oxygen ion conductivity of the metal oxide composite at 800°C are 3.0Ω ^-1 cm ^-1 , respectively.
It was 7.3×10 ^-2 Ω ^-1 cm ^-1 .

Claims (1)

[Claims] 1. The composition ratio of each atom is 0.1 to 10 g atoms of lanthanum and 0.1 to 15 g of bismuth per 1 g atom of cobalt.
A metal oxide complex consisting of oxides of the atoms lanthanum, bismuth, and cobalt and having electronic conductivity and oxygen ion conductivity. 2 The electronic conductivity is 1×10 ^-2 Ω ^-1 cm ^-1
The metal oxide composite according to claim 1, which is the above. 3 The oxygen ion conductivity is oxygen ion conductivity 1×
The metal oxide complex according to claim 1, which has a resistance of 10 ^-4 Ω ^-1 cm ^-1 or more.