JP4885159B2 - Oxygen separation membrane element - Google Patents

Description

  The present invention relates to an oxygen separation membrane made of a perovskite oxide, which is an oxygen ion conductor, and its use, and more specifically, an oxidation catalyst made of a perovskite oxide, an oxygen separation membrane comprising the oxidation catalyst, and the The present invention relates to an oxygen separation membrane element including an oxidation separation membrane and use thereof.

For example, an oxide ceramic body having a perovskite structure as an oxygen ion conductor having a property of selectively transmitting oxygen ions (typically also called O ²⁻ ; oxide ions) at a high temperature of 500 ° C. or higher. It has been known. In particular, some oxygen ion conductors exhibit electronic conductivity (including hole conductivity) and are called oxygen ion-electron mixed conductors (hereinafter simply referred to as “mixed conductors”). A dense ceramic material made of a perovskite oxide of such a mixed conductor, typically a ceramic material formed in a film shape, can be used from one surface without using an external electrode or an external circuit for short-circuiting both surfaces. Oxygen ions can be continuously transmitted through the other surface. For this reason, in particular, the operating temperature is 800 to 1000 ° C. as an oxygen separation material (oxygen separation membrane element) that selectively permeates oxygen from the oxygen-containing gas (such as air) supplied to one surface to the other surface. It can be suitably used in a high temperature range.
For example, the oxygen separation membrane element having such a structure is an oxidation reaction apparatus for separating oxygen-containing gas (air) and hydrocarbon gas and selectively permeating oxygen to perform a partial oxidation reaction of hydrocarbon, so-called diaphragm. It can be suitably used as a component of the reactor. That is, when an oxygen-containing gas is brought into contact with the surface on one side of the oxygen separation membrane and a hydrocarbon gas (for example, methane) is brought into contact with the surface on the other side, oxygen ions supplied through the oxygen separation membrane from one surface are supplied. The hydrocarbon is partially oxidized on the other side.
Thus, the technique of partially oxidizing hydrocarbons using an oxygen separation membrane is suitably used in the GTL (Gas To Liquid) technique for producing a synthetic liquid fuel (such as methanol) or the fuel cell field.
As this type of prior art, Patent Documents 1 to 4 describe some perovskite oxides that are mixed conductors. Patent Documents 5 to 9 exemplify oxygen separation materials (membrane elements) including an oxygen separation membrane composed of a perovskite oxide.

In order to increase the efficiency of the above-mentioned partial oxidation reaction of hydrocarbons, a catalyst that promotes the oxidation reaction is usually formed (attached) on the surface of the oxygen separation membrane on the side that comes into contact with hydrocarbons as an oxidizable gas. As the catalyst for promoting the oxidation reaction (oxidation catalyst), typically, a platinum group metal such as nickel (Ni) or rhodium (Rh) or a metal catalyst such as cobalt (Co) is used.
On the other hand, as a conventional method for supporting a catalyst metal on a carrier, an impregnation method in which a carrier is impregnated with a solution containing a catalyst metal and dried, or a metal fine particle dispersion is applied to the carrier, so that the metal fine particles are directly applied to the carrier. There is a method of carrying. Patent Document 10 discloses that a carrier whose Al ₂ O ₃ particles are covered with CeO ₂ is supported by Ni by impregnation as a hydrocarbon partial oxidation catalyst. However, when the catalyst metal is attached to the surface of the oxygen separation membrane by such a method, there is a possibility that the constituent element of the oxygen separation membrane reacts with the catalytic metal element to destroy the oxygen separation membrane. In addition, during the preparation of the catalyst and during the reaction, the catalyst metal particles spread inside the oxygen separation membrane and become isolated, or agglomerate and localize inside the membrane, thereby reducing the catalytic activity and reducing the oxygen separation membrane. There was a problem that performance deteriorated. In addition, Patent Documents 11 to 13 describe conventional examples of catalysts having a perovskite structure.

JP 2000-251534 A JP 2000-251535 A Special Table 2000-511507 JP 2001-93325 A International Publication No. WO2003 / 040058 Pamphlet JP 2006-82040 A JP 2007-51032 A JP 2007-51034 A JP 2007-51035 A JP 2007-237084 A JP 2004-167485 A Japanese translation of PCT publication No. 2004-511893 JP 2001-224963 A

  It is considered that the reaction between the oxygen separation membrane and the metal catalyst body is caused by the fact that the oxygen separation membrane has a perovskite type crystal structure that easily incorporates the catalytic metal element. On the other hand, because of the perovskite crystal structure, the oxygen separation membrane has high oxygen permeability and reduction durability. Therefore, there is a demand for an oxygen separation membrane element in which a catalyst body capable of maintaining high catalytic activity for a long time while maintaining the crystal structure of the oxygen separation membrane.

  Accordingly, an object of the present invention is to provide an oxygen separation membrane in which an oxidation catalyst body capable of maintaining high catalytic activity (for example, catalytic activity for partially oxidizing hydrocarbons) over a long period of time and a membrane element including the membrane. Another object is to provide an oxidation catalyst suitable for such purpose (for example, suitable for partial oxidation of carbonaceous materials such as hydrocarbons).

  The inventor forms a composite oxide in which a catalytic metal element is introduced into a perovskite crystal structure on at least one surface of an oxygen separation membrane made of an oxygen ion conductive ceramic body, thereby forming an in-film catalytic metal element film. Tried to suppress movement. As a result, the catalytic metal element does not move through the oxygen separation membrane, and as a result, the perovskite complex oxide into which the catalytic metal element is introduced is suitable as an oxidation catalyst body, and the oxidation catalyst body is placed on the oxygen separation membrane surface. It was found that the attached oxygen separation membrane element has an excellent catalytic activity.

That is, an oxygen separation membrane element provided by the present invention includes an oxygen separation membrane made of an oxygen ion conductive ceramic body (preferably an oxygen ion-electron mixed conductive ceramic body) that is a perovskite oxide, and the oxygen separation membrane. an oxygen separation membrane element comprising at least one of formed on a surface oxidation catalyst body, the oxide catalyst has the general formula ABB'O _{3-δ (δ} is determined in the charge neutrality condition is satisfied A perovskite oxide, wherein A is one or more elements selected from the group consisting of lanthanoids, ie Ln (typically La), Ba, Sr and Ca. , B is a plurality of metal elements that can constitute a perovskite structure including at least Ti and Fe, and B ′ is composed of nickel, cobalt, and a platinum group element. Characterized in that one or more elements selected from the group (a metal element capable of constituting the catalytic metal element, i.e. an oxidation catalyst).

In the oxidation catalyst body having the above structure, any catalytic metal element (typically Ni) is introduced as B ′ in the general formula (that is, part of the B site of the perovskite oxide). That is, a catalytic metal element such as Ni is incorporated into a part of the perovskite crystal structure (that is, B site). Therefore, when the oxidation catalyst body is formed on at least one surface of an oxygen separation membrane made of a dense ceramic body having oxygen ion conductivity, the catalytic metal element (for example, Ni) in the oxidation catalyst body is The metal particles may exist in a state of being uniformly dispersed in the oxidation catalyst body without being diffused, aggregated and unevenly distributed in the oxygen separation membrane, or ionized and moved into the membrane.
With such a configuration, when the oxygen separation membrane element of the present invention is used for an application for partial oxidation of hydrocarbons (for example, the GTL treatment), oxidation of carbon proceeds during the partial oxidation reaction of the supplied hydrocarbon gas (ie, The occurrence of defects such as carbon deposition (coking) due to substantial carbonization reaction is prevented. Therefore, according to the oxygen separation membrane element provided with the oxidation catalyst body, high catalytic activity can be stably maintained over a long period of time, and for example, hydrocarbons can be partially oxidized with high efficiency.

Moreover, the strength of the perovskite crystal structure is improved by including Ti as an essential constituent element in the B site. For this reason, the oxygen separation membrane element exhibits good durability even on the side where the oxidation catalyst body is formed (attached), and the occurrence of cracks and the like is suppressed.
In addition, by including Fe element as an essential constituent element at the B site, the oxygen ion-electron mixed conductivity of the oxidation catalyst body, which is lowered by the presence of Ti, can be recovered.

  Further, in a preferred embodiment of the oxygen separation membrane element disclosed herein, the oxygen ion conductive ceramic body (preferably an oxygen ion-electron mixed conductive ceramic body) constituting the oxygen separation membrane is formed of the oxygen separation membrane. The oxidation catalyst body formed on the surface is a perovskite oxide having a composition containing all of the elements constituting A and B.

  In this way, the ceramic body constituting the oxygen separation membrane is a perovskite oxide having the same composition as the oxidation catalyst body on the surface thereof, so that the oxygen separation membrane and the surface of the oxygen separation membrane are formed (attached). D) The thermal expansion coefficient (thermal expansion coefficient) with the catalyst layer made of the oxidation catalyst body can be made substantially uniform. Thereby, the physical stability (adhesive strength, etc.) at the interface between the membrane and the catalyst layer can be improved, and a high-strength membrane element can be provided.

Further, by forming the B site of the perovskite structure (that is, the site consisting of B and B ′) with Ni, Ti and Fe, for example, the oxidation of carbon proceeds during the partial oxidation reaction of hydrocarbons (substantially) It is possible to prevent the phenomenon of carbon deposition (coking) from occurring due to the occurrence of a carbonization reaction.
Further, by changing the content (molar ratio) of Ni, Ti and Fe elements in the B site, the oxygen ion conductivity (preferably oxygen ion-electron mixed conductivity), catalytic activity, stability, Durability etc. can be adjusted with good balance. In a preferred embodiment as the oxidation catalyst body disclosed herein,
Formula _{A (Ni x Ti y Fe z} ) O 3-δ
(Here, A is one or more elements selected from the group consisting of Ln, Ba, Sr and Ca, x + y + z = 1, 0.05 ≦ x ≦ 0.3, 0 .Ltoreq.y.ltoreq.0.3, 0.4.ltoreq.z.ltoreq.0.85, and .delta. Is a value determined to satisfy the charge neutrality condition). And

  An oxygen separation membrane element comprising an oxygen separation membrane having an oxidation catalyst body having such a composition range formed (attached) on its surface has catalytic activity and oxygen ion conductivity (preferably oxygen ion-electron mixed conductivity). , Stability and durability (strength) are well-balanced, and can be suitably used for, for example, a partial oxidation reaction of hydrocarbons.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than the matters specifically mentioned in the present specification (for example, the oxidation catalyst body) and matters necessary for the implementation of the present invention (for example, the raw material powder mixing method) are the conventional techniques in this field. It can be grasped as a design matter of those skilled in the art based on the above. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

The oxygen separation membrane element of the present invention includes an oxygen separation membrane in which an oxygen ion-electron mixed conductive ceramic body is formed in a film shape, and an oxidation catalyst body formed on (attached to) at least one surface of the oxygen separation membrane. It is the structure provided with.
First, an oxidation catalyst body suitable for applications such as hydrocarbon partial oxidation will be described.
The oxidation catalyst is a perovskite oxide represented by the general formula ABB′O _3-δ (δ is a value determined so as to satisfy the charge neutrality condition, hereinafter referred to as “general formula (C)”). Since the number of oxygen atoms in the general formula (C) varies depending on the kind of atoms substituting a part of the perovskite structure, the substitution ratio, and other conditions, it is difficult to display accurately. Therefore, a positive number δ (0 <δ <1) not exceeding 1 is adopted as a value that is determined so as to satisfy the charge neutrality condition, and the number of oxygen atoms is expressed as 3-δ in this specification. . In this field, the number of oxygen atoms may be indicated as 3 for convenience, but it does not represent a different compound.
A in the general formula (C) is a combination of one or more elements selected from the group consisting of Ln (typically La), Ba, Sr and Ca. La and / or Sr are preferred. By selecting two or more elements as A in the general formula (C) and substituting some atoms of the perovskite structure, lattice defects are introduced into the A site. The lattice defects at the A site contribute to the improvement of oxygen mobility in the crystal structure. The amount of substitution at the A site may be adjusted in consideration of the balance between the amount of lattice defects and the stabilization of the structure.

The B element constituting the B site of the oxidation catalyst body may be a plurality of metal elements that can constitute a perovskite structure including at least Ti and Fe. Typically, it is composed of Ti and Fe. In addition, for example, Cr, Mn, Zr, Ga, Al, Zn, Mg and the like may be included.
The element B ′ may be one or more elements selected from the group consisting of nickel, cobalt, and platinum group elements. Ni is preferred. Here, nickel, cobalt, and a platinum group element are preferable as a catalytic metal element that functions as a catalyst for promoting a partial oxidation reaction of hydrocarbons. When an oxidation catalyst body in which a catalyst metal such as Ni is taken into the B site is attached to at least one surface of an oxygen separation membrane described later, the metal element such as Ni is fixed in the crystal structure of the catalyst body. Therefore, the metal particles are not dispersed or aggregated from the catalyst body into the oxygen separation membrane or ionized to move into the membrane. For this reason, the oxidation catalyst body disclosed here can maintain high catalytic activity stably over a long period of time. In addition, although Co, or platinum group elements, such as Pt, Pd, and Rh, can be used as a catalyst metal, compared with these metals, Ni is more easily available and is more economical. Further, high catalytic activity can be obtained.
Moreover, the strength of the crystal structure is improved by including Ti as an essential constituent element in the B site. For this reason, the oxygen separation membrane according to the present invention exhibits good durability by suppressing the occurrence of cracks and the like without decreasing the strength even on the side where the catalyst body is formed (attached).
Furthermore, by including Fe as an essential constituent element in the B site, the electron conductivity is improved together with the oxygen ion conductivity. Therefore, the inclusion of Ti at the B site may reduce the mixed conductivity of the oxidation catalyst itself, but it is possible to recover the reduced oxygen ion-electron mixed conductivity due to the introduction of Fe. For this reason, the oxygen ion-electron mixed conductivity, catalytic activity, stability, durability, etc. of the oxidation catalyst body can be adjusted in a well-balanced manner by changing the content (molar ratio) of catalytic metals such as Ni and Ti and Fe. .

Suitable perovskite oxide as such an oxidation _{catalyst: A (Ni x Ti y Fe} z) Ni in _{O 3-[delta],} the molar ratio of Ti and Fe x: y: z (where, x + y + z = 1 ) and when, The possible ranges of x, y, and z are preferably 0.05 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.3, and 0.4 ≦ z ≦ 0.85. If the value of x is smaller than 0.05, the catalytic activity of this catalytic body is too low, and if it is larger than 0.3, the catalytic activity is improved, but the strength of the catalytic body may be lowered too much. Further, when the value of y is less than 0.1 or the value of z is greater than 0.85, the oxygen ion-electron mixed conductivity of the catalyst body is improved, but the strength is reduced and crack resistance is reduced. Decreases. On the other hand, when the value of y is larger than 0.3 or the value of z is smaller than 0.4, the strength of the catalyst body is improved, but the oxygen ion-electron mixed conductivity is lowered.

Further, a part of Fe as an essential constituent element may be substituted with Mg. By introducing Mg, the strength of the oxidation catalyst can be increased. For example, in the formula: A (Ni _x Ti _y Fe _z Mg _{z ′} ) O _3-δ (A in the formula is the same as the above general formula), the balance between oxygen ion-electron mixed conductivity and strength of the catalyst body When the molar ratio of Mg is z ′ (where x + y + z + z ′ = 1), the possible range of z and z ′ is preferably 0.4 ≦ z + z ′ ≦ 0.85. It is preferable that 0.3 ≦ z ≦ 0.8 and 0.05 ≦ z ′ ≦ 0.1.

Next, the oxygen separation membrane will be described.
First, in the present specification, the “membrane” is not limited to a specific thickness, and refers to a membrane-like or layer-like portion that functions as an “oxygen ion conductor (preferably a mixed conductor)” in the oxygen separation membrane element. .
The ceramic body constituting the oxygen separation membrane is not limited to a specific constituent element as long as it has a perovskite structure that is an oxygen ion conductor, but it has both oxygen ion conductivity and electron conductivity. In the case of a mixed conductor having one, the other side without using an external electrode or an external circuit for short-circuiting one side (oxygen supply side) and the other side (oxygen permeation side) of the oxygen separation membrane. This is preferable because oxygen ions can be continuously permeated to the surface and the permeation rate of oxygen ions can be increased.
Typically, this type of ceramic body includes a composite oxide having a composition represented by the general formula Ln _1-p Ae _p MO _3-δ (hereinafter referred to as “general formula (D)”). Here, Ln in the formula is at least one selected from lanthanoids (typically La), Ae is at least one selected from the group consisting of Sr, Ca and Ba, and M is Mg, Mn, At least one selected from the group consisting of Ga, Ti, Co, Ni, Al, Fe, Cu, In, Sn, Zr, V, Cr, Zn, Ge, Sc and Y, and 0 ≦ p ≦ 1 . For example, as a suitable mixed conductor, a composite oxidation represented by the formula: (La _1-p Sr _p ) (Ti _1-q Fe _q ) O _3-δ (where 0 <p <1, 0 <q <1) (Hereinafter also referred to as “LSTF oxide”), and specific examples include La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O _3-δ , La _0.6 Sr _0.4 Ti. _Examples include _0.3 Fe _0.7 O _3-δ .

  Such a mixed conductive ceramic body is preferably a perovskite oxide having a composition similar to that of the oxidation catalyst. That is, it is preferable that M in the general formula (D) contains Ti and Fe other than the catalyst metal Ni. By making the composition of the oxygen separation membrane and the oxidation catalyst similar, the thermal expansion coefficient (thermal expansion coefficient) of the oxygen separation membrane and the catalyst layer made of the oxidation catalyst attached to the oxygen separation membrane can be made substantially uniform. it can. Thereby, the physical stability (adhesive strength etc.) in the interface of a film | membrane and a catalyst layer can be improved. That is, even if such an oxygen separation membrane element is composed of two layers of an oxygen separation membrane and the catalyst layer, the catalyst metal is only in a depth range near the lower surface pole corresponding to the thickness of the catalyst layer. It can be regarded as an integral oxygen separation membrane having the same crystal structure in which Ni is distributed. For this reason, the oxygen separation membrane element is less likely to react with the constituent elements of the oxidation catalyst body and the constituent elements of the oxygen separation membrane. Therefore, a perovskite oxide suitable as such an oxidation catalyst includes, for example, one in which Ni is introduced into the B site (corresponding to B ′ in the above general formula) of the above LSTF oxide.

  Regarding the thickness dimension of the oxygen separation membrane, as will be described later, when the oxygen separation membrane is not supported by the porous base material, it is preferably within the range of 50 to 5000 μm, and is supported by the porous base material. If it is, it is preferably within the range of 1000 μm or less. Within these ranges, the film thickness of the oxygen separation membrane is sufficiently thin as long as the mechanical strength of the oxygen separation membrane element can be ensured, so that the above film thickness does not become the rate limiting rate of the oxygen transmission rate. . In particular, when a porous substrate is provided, mechanical strength is not required for the oxygen separation membrane itself, so if the density of the oxygen separation membrane is maintained, the above-mentioned film thickness dimension lower limit is There is no particular limitation.

  Further, if the oxidation catalyst body is formed on one surface of the oxygen separation membrane and the catalyst body for promoting the dissociation of oxygen is formed on the other surface, oxygen ions can be transmitted more efficiently. Since an oxygen separation membrane element is obtained, it is preferable. As a dissociation catalyst for promoting oxygen dissociation, La-Sr-Co-based oxides, La-Sr-Mn-based oxides, and platinum-based elements are preferable. For example, perovskite oxides containing La, Sr, Co, and Fe as constituent elements as described in the examples described later can be given. If such a catalyst body is attached to the oxygen separation membrane, oxygen in the gas (air) supplied to one surface side (air electrode side) of the oxygen separation membrane is suitably ionized and permeated through the oxygen separation membrane. Thus, it can efficiently move to the other surface side (fuel electrode side) to which the oxidation catalyst body is attached.

Next, the porous substrate will be described.
The oxygen separation membrane element of the present invention may have a configuration in which the porous substrate is not provided, but preferably has a configuration in which the oxygen separation membrane is provided on the surface of the porous substrate. At this time, part or all of the surface of the oxygen separation membrane is supported by the porous substrate. Even if a porous substrate is provided, gas can easily pass through the porous substrate, so that the mechanical strength of the entire oxygen separation membrane element can be increased without lowering the oxygen transmission rate.
As the porous substrate, ceramic porous bodies having various properties that are employed in this type of conventional membrane element can be used. A material made of a material having stable heat resistance in the use temperature range of the membrane element (usually 500 ° C. or higher, typically 800 to 1000 ° C.) is preferably used. For example, a ceramic porous body having the same composition as the oxygen separation membrane having a perovskite structure, or a ceramic porous body mainly composed of magnesia, zirconia, silicon nitride, silicon carbide, or the like can be used. Alternatively, a metallic porous body mainly composed of a metallic material may be used. Although not particularly limited, the average pore diameter based on the mercury intrusion method of the porous substrate used is suitably about 0.1 μm to 20 μm, and the porosity based on the mercury intrusion method is suitably about 5 to 60%.

  An oxygen separation membrane element comprising a porous substrate, an oxygen separation membrane supported by the porous substrate, and a catalyst body formed on (attached to) the surface of the oxygen separation membrane. The shape is substantially determined by the shape of the porous substrate. For example, a porous base formed into a plate shape (including a flat shape, a spherical shape, etc.) or a tubular shape (including an open tube with both ends open, a closed tube with one end open and the other closed). There is a material in which one catalyst body (for example, an oxygen dissociation catalyst body), an oxygen separation membrane, and the other catalyst body (for example, an oxidation catalyst body) are stacked in this order.

Next, a method for manufacturing the oxygen separation membrane element will be described.
First, a method for producing a ceramic body (porous substrate) to be produced will be described. Compound powder (raw material powder) containing metal atoms constituting the ceramic body is mixed at a desired ceramic body composition ratio, the mixture is formed, and fired in an oxidizing atmosphere (for example, in the air) or an inert gas atmosphere. Thus, a ceramic body having a desired shape is obtained. The raw material powder includes an oxide containing a metal atom constituting the ceramic body or a compound that can be converted into an oxide by heating (a carbonate, nitrate, sulfate, phosphate, acetate, oxalate, halide of the metal atom) , Hydroxides, oxyhalides, and the like) may be used. The raw material powder may contain a compound (a composite metal oxide, a composite metal carbonate, or the like) containing two or more metal atoms among the metal atoms constituting the ceramic body.

The appropriate firing temperature is typically 1000 to 1800 ° C. (preferably 1200 to 1600 ° C.), although it varies depending on the composition of the ceramic body. Moreover, the firing step can include one or more calcination steps and a main firing step performed thereafter. In this case, the main baking step is preferably performed at the baking temperature as described above, and the calcining step is preferably performed at a lower baking temperature (for example, 800 to 1500 ° C.) than the main baking step.
For example, by calcining the raw material powder and pulverizing the calcined raw material using a wet ball mill or the like, a calcined powder (main firing raw material powder) can be obtained. Furthermore, a raw material powder (or calcined powder) is mixed with water, a molding aid such as an organic binder, and a dispersant to prepare a slurry, and a desired particle size (using a granulator such as a spray dryer) For example, it can granulate to an average particle diameter of 10-100 micrometers.
It should be noted that a conventionally known molding method such as uniaxial compression molding, isostatic pressing, extrusion molding or the like should be adopted for molding the calcined powder obtained by pulverizing the raw material powder or calcined material (the raw powder for main firing). Can do. For such molding, conventionally known binders, dispersants and the like can be used.

  A technique for forming an oxygen separation membrane of perovskite oxide on the surface of the porous substrate made by the above method is not particularly limited, and various conventionally known techniques can be employed. For example, a mixed powder obtained by mixing a raw material powder containing metal atoms constituting the perovskite oxide (for example, LSTF oxide) at a desired composition ratio of the perovskite oxide is mixed with a suitable binder, dispersant, A slurry is prepared by mixing with a plasticizer, a solvent and the like, and the slurry is applied (applied) to the surface of the porous substrate by a general technique such as dip coating. The coating (film) on the porous substrate thus obtained is dried at an appropriate temperature (typically 60 to 100 ° C.) and then baked in the temperature range as described above. An oxygen separation membrane made of a perovskite oxide can be formed on the surface of the substrate. Instead of the above mixed powder, a commercially available perovskite oxide powder having a predetermined composition ratio may be used.

  The method for forming (attaching) the catalyst body on the surface of the oxygen separation membrane is not particularly limited. For example, a target catalyst body can be formed (attached) on the membrane surface by preparing a slurry containing catalyst powder, applying the slurry to the surface of the oxygen separation membrane, and drying the slurry. Thereafter, the formed catalyst body may be further calcined. Moreover, it can be made to adhere to the whole surface or one part area | region to the one or both surfaces of an oxygen separation membrane. The catalyst body is preferably attached (coated) so as to cover the entire surface of the oxygen separation membrane, but may be formed only in a partial region, for example, in a dot shape, a stripe shape, a lattice shape, or the like. When an oxygen dissociation catalyst body is provided on one side of the oxygen separation membrane and an oxidation catalyst body is provided on the other side, it is not necessary to form each catalyst body directly on the surface of the oxygen separation membrane. If it is, each catalyst function is suitably exhibited. Therefore, when one catalyst body, the oxygen separation membrane, and the other catalyst body are sequentially formed and laminated on the porous base material, one catalyst body may be attached on the porous base material. The method of forming (attaching) one catalyst body on the porous substrate may be the same as in the case of the oxygen separation membrane.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the following examples.

<Preparation of porous substrate made of MgO>
A molding aid such as a binder was mixed with commercially available magnesia (MgO) powder and kneaded with a ball mill or the like. Thereafter, it was press-molded under a pressure of 100 MPa to obtain a cylindrical molded body having a diameter of 18 mm and a thickness (wall thickness) of about 2 mm. Next, the molded body was pre-baked at 350 ° C. for about 2 hours in the air to remove the binder, and further subjected to main baking at 1400 ° C. for about 6 hours in the air to obtain a sintered body ( A porous substrate) was obtained.

<Formation of Catalyst Layer Consisting of Oxygen Dissociation Catalyst La _0.6 Sr _0.4 Co _0.8 Fe _0.2 O _3-δ >
La ₂ O ₃ , SrCO ₃ , Co ₂ O ₃ and Fe ₂ O ₃ as raw material powders were mixed at a stoichiometric ratio of the composition of the sintered body (oxygen dissociation catalyst body) obtained after firing. That is, mixing was performed so that La was 0.6, Sr was 0.4, Co was 0.8, and Fe was 0.2 mol. After this mixture is fired at 1250 ° C. in the air, the fired body is pulverized and mixed with an organic solvent to prepare a film-forming slurry (average particle size of about 2 μm) and applied to the surface of the porous substrate. The oxygen dissociation catalyst layer (see reference numeral 12 in FIG. 1 described later) was baked on the outer peripheral surface of the porous substrate at about 1000 ° C.

<Preparation of oxygen separation membrane made of LSTF oxide>
An appropriate amount of a general binder and water are added to and mixed with La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _3-δ (LSTF oxide) powder having an average particle diameter of about 1 μm. Thus, a slurry for film formation was prepared.
Next, the slurry was applied to the surface of the porous substrate to which the oxygen dissociation catalyst body was adhered. After drying at 80 ° C., the temperature was raised to a temperature range of 1000 to 1600 ° C. (here, firing temperature: about 1400 ° C.), and firing was carried out at the maximum firing temperature for 3 hours. As a result, an oxygen separation membrane (average film thickness 100 μm) made of LSTF oxide was formed on the surface of the oxygen dissociation catalyst layer on the outer peripheral surface of the porous substrate.

<Formation of the catalyst layer made of an oxide catalyst _{La 0.6 Sr 0.4 Ni x Ti y} Fe z O 3-δ>
La ₂ O ₃ , SrCO ₃ , NiCO ₃ , TiO ₂ and Fe ₂ O ₃ as raw material powders were mixed at a stoichiometric ratio of the composition of the sintered body (oxidation catalyst body) obtained after firing. That is, mixing was performed so that La was 0.6, Sr was 0.4, Ni was x, Ti was y, and Fe was z mole (where x + y + z = 1). The mixture was first heated to a temperature range of 200 to 500 ° C. (here, about 500 ° C.) in the atmosphere and held for 10 hours. This decomposed and removed the organic matter. Thereafter, the temperature is raised to a temperature range of 1300 to 1600 ° C. in the atmosphere (here, maximum firing temperature: about 1400 ° C.), and then fired by holding at the maximum firing temperature for 3 hours to form a perovskite oxide. La was obtained _{0.6 Sr 0.4 Ni x Ti y Fe} z O 3-δ. Next, this fired body was pulverized, and appropriate amounts of a general binder and water were added and mixed to prepare a film-forming slurry (average particle size of about 1 μm). The slurry is applied to the surface of the oxygen separation membrane, dried at 80 ° C., and then heated to a temperature range of 1000 to 1600 ° C. (here, maximum firing temperature: about 1400 ° C.) in the atmosphere to obtain the maximum firing temperature. And the oxidation catalyst layer was baked on the surface of the oxygen separation membrane.
Here, the oxidation catalyst bodies in which the combinations of x, y, and z were changed as shown below were designated as Experimental Examples 1 to 4, respectively.
Experimental Example 1: x = 0.15, y = 0.15, z = 0.7
Experimental Example 2: x = 0.3, y = 0.3, z = 0.4
Experimental Example 3: x = 0, y = 0.3, z = 0.7
Experimental Example 4: x = 0.3, y = 0, z = 0.7
As described above, as schematically shown in FIG. 1, the oxygen separation membrane element 10 in which the oxygen dissociation catalyst layer 12, the oxygen separation membrane 13, and the oxidation catalyst layer 14 were sequentially laminated on the porous substrate 11 was produced. . In FIG. 1, the thicknesses of the oxygen dissociation catalyst layer 12 and the oxidation catalyst layer 14 are drawn larger than the actual thickness considering the thickness of the porous base material 11 and the oxygen separation membrane 13. Yes.

<Comparative Example 1>
An appropriate amount of a general binder and water were added to commercially available nickel oxide (NiO) powder to prepare a slurry. The slurry was applied to the surface of the MgO porous substrate prepared by the above method, and then heated at 1000 ° C. in a hydrogen atmosphere to reduce NiO to Ni. As a result, a porous substrate on which the catalytic metal particles Ni were directly applied to the surface and supported was prepared.

<Comparative example 2>
A commercially available La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _3-δ powder (LSTF oxide) and Ni powder were mixed, and a general binder was added to prepare a slurry. This slurry was coated on the surface of the porous substrate on the oxygen separation membrane formed by the above method, and heated at 1000 ° C. to carry Ni on the carrier. Thereby, the LSTF oxide carrying the catalyst metal Ni was obtained.

<Construction of hydrocarbon oxidation reactor>
Using the cylindrical oxygen separation membrane element 10 to which the catalyst layer 14 obtained by the above method was attached, an oxidation reaction module 2 having the configuration shown in FIG. 2 was produced. Furthermore, using these modules 2, a hydrocarbon oxidation reaction apparatus 1 as shown in FIG. Although the oxygen dissociation catalyst layer (see reference numeral 12 in FIG. 1) is formed between the porous substrate 11 and the oxygen separation membrane 13, it is not shown in FIG. Further, the thickness dimensions of the oxidation catalyst layer 14, the porous substrate 11 and the oxygen separation membrane 13 do not reflect the actual dimensional relationship.
The oxidation reaction module 2 is inserted into a metal chamber 31, an oxygen separation membrane element 10 accommodated in the metal chamber 31, a metal holder 32 for fixing the oxygen separation membrane element 10, and a cylinder inside the oxygen separation membrane element 10. The oxygen inlet tube 21 is made up of. The metal chamber 31 is provided with an inlet 31a through which a gas containing hydrocarbon (CH _{4 in} this embodiment) flows into the chamber 31 and an outlet 31b through which the gas flows out. In the oxygen separation membrane element 10, one opening end in the axial direction is closed, and the other opening end is fixed to the metal holder 32 in a state of being airtightly joined with a sealant 41. The metal holder 32 includes a pedestal portion 32a that fixes the oxygen separation membrane element 10 and a support portion 32b that supports the pedestal portion. An opening having the same diameter as the inner diameter of the oxygen separation membrane element 10 is formed in the central portion of the pedestal portion 32 a and the support portion 32 b so as to penetrate the metal holder 32. An opening end portion of the support portion 32b opposite to the pedestal portion 32a protrudes from the metal chamber 31 and faces the outside. Therefore, a tubular cavity is formed from the projecting open end to the end of the oxygen separation membrane element 10 on the closed side. The oxygen introduction tube 21 is inserted into the cavity. That is, the oxygen introduction tube 21 is inserted from the open end of the metal holder 32 protruding from the metal chamber 31, inserted into the metal holder 32, and inserted to the vicinity of the closed end of the oxygen separation membrane element 10. .
Air (a gas containing oxygen) flows through the oxygen introduction pipe 21 and is introduced into the oxygen separation membrane element 10, and the air flowing out of the oxygen introduction pipe 21 flows between the outer peripheral surface of the oxygen introduction pipe 21 and the oxygen separation membrane element 10. Flows in the space 20 (oxygen source supply space 20) formed between the inner peripheral surface 10a (the inner wall surface of the porous base material 11) and flows out from the metal chamber 31 (the opening end of the support portion). To do. On the other hand, CH ₄ (gas containing hydrocarbon) flows in a space 30 (oxidation reaction space 30) formed by the inner wall surface of the metal chamber 31 and the outer peripheral surface of the oxygen separation membrane element 10. Accordingly, the cylindrical oxygen separation membrane element 10, the oxidation catalyst layer 14 in the outer peripheral surface 10b is in contact with the CH _4, while its inner peripheral surface 10a (inner wall surface of the porous substrate 11) is air (Air) Contact with.

FIG. 3 is a schematic diagram showing a hydrocarbon oxidation reaction apparatus 1 constructed using the module 2 having such a configuration. The apparatus 1 includes a module 2, an oxygen source supply unit 52, and a hydrocarbon gas supply unit 53. In the hydrocarbon oxidation reaction apparatus 1, an oxygen source supply means 52 is connected to the oxygen introduction pipe 21 of the module 2. On the other hand, a hydrocarbon gas supply means 53 is connected to the metal chamber 31 at its inlet 31a. For this reason, the hydrocarbon oxidation reaction apparatus 1 is configured to be supplied with air (Air) and CH ₄ to the module 2. FIG. 3 does not show inflow and outflow paths between the oxygen source supply means 52 and the hydrocarbon gas supply means 53 and the module 2. The hydrocarbon oxidation reaction apparatus 1 shown in FIG. 3 includes a heating means (such as a heater) 54 for heating the oxygen separation element 10 (particularly the oxygen separation membrane 13) to a desired temperature.
While maintaining the oxygen separation membrane 13 at a predetermined use temperature (for example, 500 ° C. or more) by the heating means 54, air (Air) and CH ₄ are circulated to the module 2 by the oxygen source supply means 52 and the hydrocarbon gas supply means 53. Let Thereby, oxygen in the air that has contacted the inner peripheral surface 10a of the oxygen separation membrane element 10 (inner wall surface of the porous base material 11) permeates the inside of the porous base material 11 and the surface 13a of the oxygen separation membrane 13 On the (surface on the porous base material 11 side), electrons are received and become oxygen ions. The oxygen ions permeate through the oxygen separation membrane 13 and the other surface 13b (the surface on the outer peripheral surface 10b side of the oxygen separation membrane element 10). ), It oxidizes in contact with CH ₄ , thereby producing reactants such as CO, CO ₂ , H ₂ . In this way, the hydrocarbon oxidation reaction (here, the partial oxidation reaction of CH ₄ ) is performed.

<Evaluation of oxygen permeation performance of oxygen separation membrane element>
In the hydrocarbon oxidation reaction apparatus 1, the oxygen separation element 10 (oxygen separation membrane 13) is heated to 1000 ° C., the oxygen source supply space 20 is 4000 mL / min of air, and the oxidation reaction space 30 is 1000 mL of CH ₄ gas. Each was supplied at a flow rate of / min.
300 hours of continuous operation was performed under the above conditions, and the composition of the gas discharged from the outlet 31b of the metal chamber 31 (oxygen reaction space 30) during that time was measured by a gas chromatograph. The conversion rate of methane (CH ₄ ) was calculated from the composition of the exhaust gas. Here, the methane conversion is a ratio with respect to the total supply amount of the difference obtained by subtracting the CH ₄ content in the exhaust gas from the total supply amount of CH ₄ (percentage).
Further, it was also examined whether or not coking occurred on the surface 13b of the oxygen separation membrane element 10 on the oxidation reaction space 30 side.
For Comparative Example 1 and Comparative Example 2, the same MgO porous substrate 11 supporting Ni particles and the LSTF oxide supporting Ni particles were used in place of the above-described oxidation separation membrane element 10, respectively. Evaluation was performed.
Table 1 shows the results of the methane conversion rates of Experimental Examples 1 to 4 and Comparative Examples 1 and 2 and the presence or absence of coking.

<Electrical conductivity evaluation of oxygen separation membrane element>
The electrical conductivity of the oxygen separation membrane element 10 was measured for Experimental Examples 1 to 4. First, after applying a platinum paste as an electrode on the surface of each oxygen separation membrane element 10, a platinum wire is connected and baked at 850 to 1100 ° C. for 10 to 60 minutes to adjust to an arbitrary oxygen partial pressure and temperature. The electric conductivity was determined by measuring the resistance value by the DC four-terminal method or the AC two-terminal method.
Table 2 shows the measurement results of the electrical conductivities of Experimental Examples 1 to 4 under a constant temperature condition (800 ° C.).

As shown in Table 1, in the oxygen separation membrane element 10 using an oxidation catalyst body made of a perovskite oxide represented by La _0.6 Sr _0.4 Ni _x Ti _y Fe _z O _{3 -δ} , Ni Is contained in the B site at a predetermined ratio, the methane oxidation reaction is promoted and the methane conversion rate is large. On the other hand, when Ti is not contained in the B site at a predetermined ratio, it was confirmed by this example that the strength of the perovskite oxide is reduced and cracks are likely to occur.
Further, the oxidation catalyst body composed of the perovskite oxide containing Ni at a predetermined molar ratio has improved catalytic activity as compared with the conventional oxidation catalyst body supporting Ni, and the methane conversion rate is increased. Coking can be effectively prevented. Furthermore, in Experimental Examples 1 and 2, such an oxidation catalyst body was not deactivated even when 300 hours of continuous operation was performed, and exhibited stable catalytic activity.

As shown in Table 2, in the oxygen separation membrane element 10 using an oxidation catalyst body made of a perovskite oxide represented by La _0.6 Sr _0.4 Ni _x Ti _y Fe _z O _3-δ In Experimental Examples 1 to 3, an electrical conductivity of about 20 S / cm was obtained. Therefore, it was confirmed that the oxygen separation membrane element disclosed here has sufficient electron conductivity.
As described above, the oxidation catalyst body having the above composition has crack resistance, exhibits sufficient electron conductivity, stably maintains high catalytic activity over a long period of time even when continuously used at high temperature, and has an efficiency. It is a catalyst that can oxidize methane well. Accordingly, the oxygen separation membrane element disclosed herein is a membrane material particularly suitable for such applications.
Although the present invention has been described in detail above, these are merely examples, and the present invention can be implemented in other modes, and various modifications can be made without departing from the spirit of the present invention.

It is a disassembled perspective view which shows typically the structure of the oxygen separation membrane element which concerns on one Example. It is sectional drawing which showed typically the oxidation reaction module which comprises the hydrocarbon oxidation reaction apparatus for evaluating the oxygen permeation performance of an oxygen separation membrane element. It is the schematic diagram which showed schematic structure of the hydrocarbon oxidation reaction apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hydrocarbon oxidation reaction apparatus 2 Oxidation reaction module 10 Oxygen separation membrane element 11 Porous base material 13 Oxygen separation membrane 14 Oxidation catalyst layer

Claims (3)

An oxygen separation membrane element comprising an oxygen separation membrane made of an oxygen ion conductive ceramic body that is a perovskite oxide and an oxidation catalyst body formed on at least one surface of the oxygen separation membrane,
The oxidation catalyst is a perovskite oxide represented by the general formula ABB′O _3-δ (δ is a value determined so as to satisfy the charge neutrality condition),
Here, A is one or more elements selected from the group consisting of Ln (lanthanoid), Ba, Sr and Ca, and B forms a perovskite structure including at least Ti and Fe. An oxygen separation membrane element, which is a plurality of metal elements to be obtained, and B ′ is one or more elements selected from the group consisting of nickel, cobalt, and platinum group elements.   The oxygen ion conductive ceramic body constituting the oxygen separation membrane is a perovskite type composition having a composition containing all of the elements constituting the A and B of the oxidation catalyst body formed on the surface of the oxygen separation membrane. The oxygen separation membrane element according to claim 1, wherein the oxygen separation membrane element is an oxide. The oxidation catalyst has the general formula _{A (Ni x Ti y Fe z} ) O 3-δ
Here, A is one or more elements selected from the group consisting of Ln (lanthanoid), Ba, Sr and Ca, x + y + z = 1, and 0.05 ≦ x ≦ 0.3. 0.1 ≦ y ≦ 0.3, 0.4 ≦ z ≦ 0.85, and δ is a value determined to satisfy the charge neutrality condition;
The oxygen separation membrane element according to claim 1, wherein the oxygen separation membrane element is a perovskite oxide represented by the formula:

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