JPS6247053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid electrolyte membrane having oxygen permeability. More specifically, a solid electrolyte membrane made of oxides of strontium, bismuth, and iron and having ionic oxygen permeability and electronic conductivity, and a solid electrolyte membrane that uses the solid electrolyte membrane to generate oxygen from a mixed gas containing oxygen. Regarding the separation method.

In recent years, there have been remarkable advances in membrane separation technology, some of which have been put into practical use on an industrial scale. However, what has been put into practical use is liquid-liquid separation or liquid-solid separation, such as in desalination of seawater, treatment of factory waste liquid, concentration of food, etc.
Blanket separation, that is, separation of two or more types of mixed gases, is almost non-existent.

The reason why gas membrane separation is not put into practical use is that
Since there are no membranes that have low selective permselectivity, that is, they selectively allow certain gases to pass through while virtually blocking other gases, in order to obtain high-purity gases, a multi-stage membrane separation method is required in which membrane separation is repeated several times. , which would make the equipment too large;
The main reason is that a large amount of gas cannot be produced because the amount of permeation is small.

Conventionally, what is known as a gas separation membrane is mainly an organic polymer membrane. For example, there is a method of separating oxygen in the air using a carganopolysiloxane-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 sieves 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 does not require the attachment of electrodes or external circuits, has the electronic conductivity necessary for the electrode reaction to occur sufficiently, and 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 provides a solid electrolyte membrane made of oxides of strontium, bismuth, and iron that is permeable to ionic oxygen and has electronic conductivity, and a method for separating oxygen from a mixed gas containing oxygen using the solid electrolyte membrane. It is about the method.

The solid electrolyte forming the solid electrolyte membrane in the present invention is composed of oxides of strontium, bismuth, and iron, and the form of the oxide is preferably a composite form, and the composition is generally expressed by the general formula
Sr _1-x Bix FeO ₃ is suitable.
The oxide preferably includes a perovskite-type complex oxide.

In the above general formula, X is a value in the range of 0.1 to 0.9, preferably 0.1 to 0.7, particularly preferably 0.1
~0.6. If the value of

The oxide can be prepared by conventional methods. One of the methods is strontium,
Compounds containing metal atoms of bismuth and iron, especially compounds that can be converted into oxides by calcination as described below, such as oxides such as strontium oxide, bismuth oxide, and iron oxide, or preferably nitrates, carbonates, However, 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, or hydroxides and oxyhalides. There is a method of mixing in a desired ratio and firing.

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 solid electrolyte membrane of the present invention, the firing temperature is usually in the range of 500 to 1,500°C, preferably 500 to 1,300°C in an oxidizing atmosphere.

The strontium, bismuth, and iron oxides described in the present invention are solid electrolytes having ionic oxygen permeability and electronic conductivity, that is, so-called electron-oxygen ion mixed conductivity.

Ionic oxygen permeability is the ability of ionic oxygen to move from one surface to the other of a solid electrolyte membrane, and is usually expressed as oxygen ionic conductivity, while electronic conductivity is expressed as electronic conductivity. can be expressed.
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 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 solid electrolyte made of oxides of strontium, bismuth, and iron in the present invention varies depending on the mixing ratio of strontium and bismuth, but is usually 1×10 ^-4 to 5× at a temperature of 400 to 1200°C.
10 ⁻¹ Ω ⁻¹ cm ⁻¹ , and the electronic conductivity is 0.5 to 5 Ω ⁻¹ cm ⁻¹ .

In the present invention, when the solid electrolyte membrane is used for oxygen separation, the ratio of electronic conductivity to oxygen ion conductivity is preferably 1 or more.

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

In the present invention, the solid electrolyte membrane may be formed by forming an oxide obtained by the above-described preparation method, or by a method that combines oxide preparation and film formation. These films may be formed by mechanical processing such as cutting or polishing a solid material such as a pellet or sheet, or by pressure molding a powdery material, or by forming a powder into a paste. , may be coated onto a porous support and sintered.

Furthermore, film forming methods such as a vacuum evaporation method, a reactive sputtering method, a chemical vapor deposition method (CVD method), a chemical spray method, and oxidation of alloy plating can be mentioned.

In addition, during molding, fillers, reinforcing materials, etc. may be used as necessary, and when the solid electrolyte membrane is used as a gas separation membrane, it may be used alone, or as necessary. It can also be used 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 solid electrolyte membrane obtained by the above-described molding method is usually 10 ^-3 to ^{10 4} μm, and when the solid electrolyte membrane is used as an oxygen separation membrane, the separated oxygen has a particularly high purity. If it is not necessary, it may have some ventilation holes.

Since the solid electrolyte membrane of the present invention has oxygen ion conductivity and electronic conductivity, it can be used as a gas separation membrane that selectively separates oxygen in a mixed gas containing oxygen. For example, airtight chambers are provided on both sides of the solid electrolyte membrane, and one chamber is exposed to the atmosphere and the other chamber is kept under reduced pressure, or alternatively, one chamber is pressurized and the other chamber is exposed to the atmosphere. When exposed, only oxygen selectively permeates electrochemically depending on the oxygen partial pressure difference between the two chambers, and highly purified oxygen can be obtained on the low pressure side. The temperature at which the solid electrolyte membrane is used as an oxygen separation membrane is usually 400 to 1200°C, preferably 500 to 1000°C.

In addition, the solid electrolyte membrane may have a flat membrane,
It can take various forms depending on the purpose, such as a tubular membrane. Furthermore, the membrane thickness when used as an oxygen separation membrane is usually 10 ^-3 to 10 ⁴ μ, preferably 10 ⁻² to 10 ³ μ. Conventionally known solid electrolytes are mainly conductive to oxygen ions, so when used for gas separation, electrodes and external circuits are attached to both sides of the solid electrolyte to electrically short it. However, since the solid electrolyte membrane according to the present invention has a mixed conductivity of electrons and oxygen ions, it can be used as an oxygen separation membrane without any particular need for electrodes or external circuits. Can be used. Furthermore, compared to conventional organic polymer membranes, since highly purified oxygen can be obtained and it is used at high temperatures, it can be suitably used for blast furnaces and combustion aids by utilizing waste heat. As described above, the solid electrolyte membrane of the present invention is extremely useful as a gas separation membrane. The present invention will be described below with reference to Examples, but the present invention is not limited thereto. In the examples, "parts" means "parts by weight."

Example 1 2.33 parts of bismuth oxide, 1/2 strontium acetate
2.14 parts of hydrate and 1.60 parts of ferric oxide were mixed well in an agate mortar, and the mixture was placed in a crucible and thermally decomposed with a gas burner, followed by firing at 1000°C for 10 hours. The obtained sintered body was further crushed, mixed, and fired at 1150℃ for 10 hours to obtain the formula Sr0.5 Bi0.5.
A solid oxide called FeO ₃ was obtained, and the solid oxide was
Using a slicer, it was molded to a diameter of 20 mm and a thickness of 0.2 mm. The solid oxide has an oxygen ion conductivity of 2×10 ^-2 Ω ^-1 cm ^-1 and an electronic conductivity of 2.3 Ω ^-1 cm at 800°C.
It was a solid electrolyte with ^-1 .

Example 2 The solid electrolyte membrane prepared in Example 1 was used as a composite membrane using a porous support, airtight chambers were provided on both sides of the composite membrane, and the membrane was heated to a temperature of 800 ° C.
One chamber was exposed to the atmosphere, the other chamber was reduced to a pressure of 10 cmHg, and as a result of suction, oxygen gas was obtained at a rate of 0.7 cc/min on the low pressure side through the solid electrolyte membrane.

Claims (1)

[Scope of Claims] 1. A solid electrolyte membrane made of oxides of strontium, bismuth, and iron and having ionic oxygen permeability and electronic conductivity. 2 The oxide has the formula Srx Bi _1-x FeO ₃ (x is 0.1 to
0.9) The solid electrolyte membrane according to claim 1. 3 Through a solid electrolyte membrane made of oxides of strontium, bismuth, and iron that is permeable to ionic oxygen and has electronic conductivity,
A method for separating oxygen, characterized in that oxygen is separated from a mixture of oxygen and other gases at a temperature of °C.