JPH0134947B2 - - 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 strontium, 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 seawater desalination, industrial wastewater treatment,
Liquid-liquid separation or liquid-solid separation is used, such as when concentrating foods, and vapor separation, that is, separation from a mixture of two or more gases, has not been put to 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 oxide 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.

Further, as described in US 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 is composed of oxides of strontium, bismuth, and cobalt, and the composition of each atom is 0.1 to 10 g atoms of strontium and 0.7 to 8 g atoms of bismuth per 1 g atom of cobalt.
A range of g atoms is suitable. In addition, in order for the metal oxide composite to obtain electronic conductivity and oxygen ion conductivity, the ratio of the number of g atoms of strontium and bismuth to the number of g atoms of cobalt is from 0.35 to
The number of g atoms of bismuth relative to the number of g atoms of strontium is desirably in the range of 0.2 to 15, preferably 0.4 to 10.

The metal oxide composite can be prepared by conventional methods. One method for this method is to use compounds containing metal atoms of strontium, bismuth, and cobalt, especially compounds that can be converted into oxides by firing as described below, such as strontium oxide,
Oxides such as bismuth oxide and cobalt oxide, or preferably nitrates and carbonates, but also inorganic acid salts such as sulfates and phosphates, organic acid salts such as acetates and oxalates, and chlorides. There is a method in which halides such as bromides and iodides, hydroxides, and oxyhalides 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. Further examples include methods such as oxidizing and firing a mixture or alloy of each metal.

In either method, when obtaining the metal oxide composite of the present invention, the firing temperature is usually in the range of 400 to 1300°C, preferably 400 to 1200°C in an oxidizing atmosphere.

The metal oxide complex thus obtained has a structure in which strontium, bismuth and cobalt are tightly bound together by some chemical bonding force or physical bonding force, and the three constituting the metal oxide complex are
It has been confirmed that the combination of two metal oxide components has a unique crystal structure and a unique X-ray diffraction pattern. The characteristic peaks of the X-ray diffraction pattern (CuK line) of the metal oxide composite of the present invention are as follows.

Diffraction angle (2θ) Relative intensity (2θ=28.2 peak as 100) 26.1 1~ 20 26.7 5~ 50 28.2 100 28.8 10~200 30.0 5~100 30.4 5~100 36.4 1~ 50 45.8 1~ 70 49.4 1~ 50 54.8 1 to 70 Thus, the metal oxide composite of the present invention comprising oxides of strontium, bismuth, and cobalt has oxygen ion conductivity and electronic conductivity, so-called a so-called electron-oxygen ion mixed conductive solid. It is an electrolyte.

Oxygen ion conductivity is usually expressed by oxygen ion conductivity, and electronic conductivity can be expressed by electronic conductivity. . These conductivities are measured by conventional methods such as the AC bridge method and the four-terminal method described in Electrochemistry 39 665 (1971). Further, the ratio between the oxygen ion conductivity and the 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 composed of strontium, bismuth and cobalt oxides in the present invention varies depending on the composition ratio, but is usually
1×10 ^-4 Ω ^-1 cm ^-1 or more, preferably 1×10 ^-4 Ω ^-1 cm ^{-1 or} more, particularly preferably 1 at a temperature of 400 to 1100°C
×10 ^-3 Ω ^-1 cm ^-1 or more, electronic conductivity is 1 × 10 ^-2 Ω ^-1 cm
^-1 or more, 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.

The solid electrolyte of the present invention may contain impurities such as metals other than strontium, bismuth, and cobalt as long as they do not impair the electron-ion mixed conductivity of the solid electrolyte.

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 press-molding a powder or forming a paste into a porous support. There are methods such as applying it on the body and sintering it.

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 and reinforcing materials 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 1100°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, when used as an oxygen separation membrane, the film thickness is usually
It is 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 it is not limited thereto. In the examples, "parts" means "parts by weight."

Example 1 Strontium acetate Sr (OAc) ₂ 1/2H ₂ O5.37 parts,
11.65 parts of bismuth oxide Bi ₂ O ₃ and cobalt acetate
Grind and mix 6.23 parts of Co(OAc) ₂ 4H ₂ O in a mortar to approx.
After baking at 600℃ for 1 hour, grind and mix again.
After molding at Kg/cm ² , it was sintered at 850°C for 4 hours.
This sintered body is pulverized and mixed again, pressure molded at a pressure of 2t/cm ² , and sintered at 850℃ for 4 hours to achieve an atomic composition ratio of strontium, bismuth, and cobalt of 0.5:
A metal oxide composite with a ratio of 1:0.5 was obtained.

The electronic conductivity of the metal oxide composite at 800°C is 9.0Ω ^-1 cm ^-1 and the oxygen ion conductivity is 2.8X10 ^-2 Ω ^-1
It was cm ^-1 . Furthermore, X-ray diffraction (Cu, K
-α line) The pattern was as shown in the table.

Table Diffraction angle (2 ₁ θ) Relative intensity (%) 26.1 18 26.7 33 28.2 100 28.8 66 30.0 58 30.4 46 36.4 16 45.8 32 49.4 28 54.8 32 Example 2 Thickness of the metal composite oxide obtained in Example 1 1.25
The sample was molded and sintered into a cylindrical shape with a bottom of 7.8 mm in height and 9.6 mm in inner diameter.
Argon gas was flowed at a flow rate of 30 ml/mm (converted to standard conditions) and the temperature was raised to 800°C. As a result of analyzing the oxygen concentration in argon gas using gas chromatography, it was found to be 8.94×10 ^-4 CC per unit area per second.
It was confirmed that (STP)/cm ² ·sec of oxygen passed through.

Example 3 Strontium acetate Sr (OAc) ₂ 1/2H ₂ O2.68 parts,
Bismuth oxide Bi ₂ O ₃ 11.65 parts, cobalt acetate Co
(OAc) ₂ 4H ₂ O was ground and mixed in a mortar and heated to 1 at about 600℃.
Time-fired decomposition. The mixture was pulverized and mixed again, molded at 500 kg/cm ² , and then sintered at 850° C. for 4 hours. This sintered body is pulverized and mixed again in a mortar, molded at a pressure of 2t/cm ² and sintered at 850°C for a time to obtain an atomic composition ratio of strontium, bismuth, and cobalt of 0.25:1:0.75.
A metal oxide composite was obtained.

The electronic conductivity of the metal oxide composite at 800°C is 1.9×10 ^-1 Ω ^-1 cm ^-1 , and the oxygen ion conductivity is 3.0×
It was 10 ^-2 Ω ^-1 cm ^-1 .

Example 4 The metal oxide obtained in Example 3 was coated with a thickness of 1.00 mm.
Using a sample molded and sintered into a cylindrical shape with a bottom of 9.0 mm in height, 10.4 mm in inner diameter, and 12.4 mm in outer diameter, air was applied to the outside of the cylinder, and argon gas was applied to the inside at a flow rate of 30 ml/mm (converted to standard conditions). The temperature was raised to 800°C. As a result of analyzing the oxygen concentration in argon gas using gas chromatography, it was found that the concentration of oxygen in argon gas was 1.12× per unit area per unit time.
It was confirmed that 10 ^-3 CC (STP)/cm ² , sec of oxygen passed through.

Claims (1)

[Claims] 1. The composition of each atom is 0.1 to 10 g atoms of strontium and 0.7 to 10 g atoms of bismuth per 1 g atom of cobalt.
A metal oxide composite consisting of 8g atoms of strontium, bismuth and cobalt oxides 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 composite according to claim 1, which has a resistance of 10 ^-4 Ω ^-1 cm ^-1 or more.