JP2007069090A - Composition gradient type oxygen separation membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen separation membrane having high oxygen permeation performance and excellent reduction durability. <P>SOLUTION: Oxygen separation membranes 10, 30 have a lamination structure in which second layers 14, 34 consisting of mixed conductors such as La<SB>0.6</SB>Sr<SB>0.4</SB>Ti<SB>0.1</SB>Fe<SB>0.9</SB>O<SB>x</SB>are laminated on first layers 12, 32 consisting of mixed conductors such as La<SB>0.6</SB>Sr<SB>0.4</SB>Ti<SB>0.3</SB>Fe<SB>0.7</SB>O<SB>x</SB>. The oxygen separation membranes 10, 30 are of the composition gradient type in which the second layers 14, 34 having high reduction inflation ratio and high oxygen permeation performance are laminated on the first layers 12, 32 having low reduction inflation ratio and low oxygen permeation performance. Thus, as described above, when the first layers 12, 32 are arranged on the reduction side, the second layers 14, 34 are protected from the reducing atmosphere, and the reducing durability of the entire oxygen separation membrane can be sufficiently enhanced, accordingly. Further, the first layers 12, 32 are sufficiently thin, and high oxygen permeation performance of the entire oxygen separation membrane can be obtained even when the oxygen permeation performance of the mixed conductors is low. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an oxygen separation membrane using a mixed conductor.

  For example, a dense ceramic film having oxygen ion conductivity selectively dissociates oxygen from one side to the other side by recombining oxygen ions dissociated from the gas on one side and ionized on the other side. It is used for an oxygen separation membrane element that permeates and continuously separates oxygen from the gas. In particular, in mixed conductors that have electron conductivity in addition to oxygen ion conductivity, electrons move in the direction opposite to the direction of oxygen ion movement in the oxygen separation membrane, so the dissociation and recombination surfaces are electrically connected. There is an advantage that it is not necessary to provide an external electrode or an external circuit for returning electrons from the recombination surface to the dissociation surface. According to such an oxygen separation membrane element, since oxygen can be easily separated from a gas containing oxygen, for example, it can be used as an oxygen production method in place of a cryogenic separation method, a PSA (pressure fluctuation adsorption) method, or the like. .

The oxygen ion conductor as described above can also be used in an oxidation reaction apparatus such as a hydrocarbon partial oxidation reaction. For example, this oxygen ion conductor is formed into a film, oxygen-containing gas such as air is supplied to one surface thereof, and hydrocarbon such as methane (CH ₄ ) is supplied to the other surface, that is, the oxygen recombination side surface. If the gas containing it is supplied, the hydrocarbon can be oxidized by the permeated oxygen ions. Therefore, it can be used for GTL (Gas to Liquid: a technology for synthesizing liquid fuel from natural gas by chemical reaction), production of hydrogen gas for fuel cells, and the like.

By the way, it is known that perovskite compounds such as LaSrCoFe-based and LaGaO ₃ -based oxides are excellent as mixed conductors used for oxygen separation (see Patent Documents 1 to 8, etc.). However, since the LaSrCoFe-based oxide has a large reduction expansion coefficient, there is a problem in practical use in oxygen separation membrane applications in which the dissociation surface side is in a reducing atmosphere because cracking is likely to occur and the durability is low. The reductive expansion rate (%) is given by the following equation (1), where E _red (%) is the thermal expansion coefficient in the reducing atmosphere and E _air (%) is the _air expansion coefficient in the air atmosphere.
[{(1 + E _red / 100)-(1 + E _air / 100)} / (1 + E _air / 100)] × 100 (1)

On the other hand, LaGaO ₃ -based oxides have higher reduction durability than LaSrCoFe-based oxides, but are expensive in raw materials, and have a problem that oxygen ion conductivity is slightly inferior and mechanical strength is low. In addition, LaGaO ₃ -based oxides have a problem in water vapor resistance because the Ga component is decomposed at the water vapor contact portion. Incidentally, in the partial oxidation reaction of hydrocarbons and the like, it is desired to design a system in which water vapor is flowed to one side of the membrane in order to prevent coking (ie, carbon deposition) and thus deterioration in gas permeation performance. Even when water vapor is not flowed, water vapor is generated by the reaction between oxygen and hydrogen that has permeated through the membrane. Therefore, in applications as described above, the oxygen ion conductor is also required to have water vapor resistance.

In order to improve the strength of LaGaO ₃ -based oxides, a sintered body in which alumina powder is dispersed at the grain boundaries of LaSrGaMg-based oxide crystals, and a part of the LaGaO ₃ -based crystal structure is replaced with aluminum or the like. Sintered body, sintered body in which part of Ga of LaGaO ₃ series crystal is replaced with aluminum, magnesium, etc. (ie, aluminum, magnesium, etc. are solid solution), sintered LaGaO ₃ series oxide containing titanium or vanadium A body or the like has been proposed (see, for example, Patent Documents 9 to 12). However, these all improve the mechanical strength of the perovskite compound containing Ga to improve the reduction stability, and do not improve the water vapor resistance in the case of containing Ga.
JP 08-173776 A JP 09-161824 A Japanese Patent Laid-Open No. 11-228136 Japanese Patent Laid-Open No. 11-335164 JP 2000-251534 A JP 2000-251535 A Special Table 2000-511507 JP 2001-093325 A JP 2000-044340 A JP 2000-226260 A JP 2001-332122 A Japanese Patent Laid-Open No. 2003-112973 International Publication No. 03/040058 Pamphlet Japanese Patent Laid-Open No. 05-151918 Japanese Patent Application Laid-Open No. 07-296838 JP 09-266000 A JP 2001-052722 A JP 2002-015756 A Hitoshi Takamura et al. “Development of a new high-efficiency natural gas reforming system for the realization of household fuel cells: Development of a catalytic partial oxidation methane reformer using an oxygen permeable membrane” (Strategic Creation, Japan Science and Technology Agency) (Research Promotion Project Proceedings of the 5th Open Symposium, July 5, 2004, pp. 49-53)

Therefore, the present applicant, as LaGaO ₃ type oxide is high and inexpensive oxygen ion conductivity material compared, and LaGaO ₃ system compared to the oxide high reducing durability and water vapor resistance mixed conductor , LaSrTiFeO _x based oxide (x is 3 or slightly smaller than) proposed a like (see Patent Document 13).

Additional LaSrTiFeO _x based oxide, oxygen permeability and reducing durability varies depending on the composition ratio of the A site and B site. For example, La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O _x has a high oxygen permeation performance with an oxygen permeation rate of 10 (cc / min / cm ² ) or more when the thickness is 0.5 (mm), but the reductive expansion coefficient is low. Reduction durability is low due to the large 0.4 ~ 0.7 (%). In contrast, La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _x has an oxygen permeation rate of only 3 (cc / min / cm ² ), but its reduction expansion coefficient is as small as 0.1 (%) and its reduction durability is high. . That is, in the LaSrTiFeO _x based oxide, there oxygen permeability and reducing durability in a trade-off relationship, it is impossible to increase them together. Therefore, in current general industrial applications where reduction durability is required, oxygen permeation performance of 2 to 4 (cc / min / cm ² ) or more is required at a thickness of 0.5 (mm). A satisfactory latter composition will be used.

However, the higher the oxygen permeation performance of the mixed conductor membrane, the smaller the size of the oxygen separation membrane element required to obtain the same amount of oxygen, which in turn facilitates cost reduction and miniaturization of the device. . For example, if it has an oxygen transmission rate of about 10 (cc / min / cm ² ) comparable to La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O _x , compared with the case of using La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _x Thus, the element size can be reduced to half or less. Therefore, there has been a demand for a mixed conductor film that has high reduction durability and an oxygen transmission rate as high as possible per unit film area.

In addition, the oxygen permeation performance actually required for industrial applications is, for example, 10 (cc / min / cm ² ) or more, and the above-mentioned `` 0.5 (mm) thickness is 2 to 4 (cc / min / cm ² ) '' The values are based on the premise that the required oxygen permeation performance is secured by reducing the film thickness to about 0.1 (mm) based on the fact that the oxygen permeation performance is substantially inversely proportional to the film thickness. However, since such a thin membrane cannot stand by itself, it is necessary to adopt an asymmetric membrane structure that forms a dense membrane on the porous support. On the other hand, if an oxygen permeation performance of 0.5 (mm) thickness and 10 (cc / min / cm ² ) or more can be obtained, an oxygen separation membrane with extremely high oxygen permeation performance can be configured as an asymmetric membrane structure. Not only is it possible, but it is also possible to make the porous support useless by setting the film thickness to 0.5 (mm) which can be self-supporting. According to the latter, since the process becomes simple, the cost can be greatly reduced.

  If the reduction expansion coefficient is the same, the higher the mechanical strength, the higher the resistance to stress generated by the reduction expansion, and thus the more difficult it is to crack. For this reason, it is conceivable to increase the mechanical strength by, for example, about 2 to 3 times instead of lowering the reduction expansion coefficient, but it is actually difficult.

  The present invention has been made against the background of the above circumstances, and an object thereof is to provide an oxygen separation membrane having high oxygen permeation performance and excellent reduction durability.

The gist of the composition-graded oxygen separation membrane of the present invention for achieving such an object is as follows: (a) General formula (Ln _1-x Ae _x ) MO ₃ (where Ln is one of lanthanoids) Or two or more combinations, Ae is one or more combinations selected from Ba, Sr, and Ca, M is Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, 1 or a combination of two or more selected from Cr, Mn, Rh, Pd, Pt, and Au, 0 ≦ x ≦ 1, hereinafter referred to as general formula C)) And (b) a second layer composed of a second mixed conductor represented by the general formula C and having a reduction expansion coefficient larger than that of the first mixed conductor and stacked on the first layer. A layer.

  In this way, the oxygen separation membrane is configured in a laminated structure in which the second layer made of the second mixed conductor is laminated on the first layer made of the first mixed conductor. In this laminated structure, the second mixed conductor constituting the second layer has a characteristic that the reduction expansion coefficient is larger than that of the first mixed conductor constituting the first layer. The perovskite compound has a trade-off relationship between oxygen permeation performance and reduction durability. Therefore, the oxygen separation membrane is a laminate in which a second layer having a relatively small reduction expansion coefficient and a low oxygen permeation performance is laminated with a second layer having a relatively large reduction expansion coefficient and a high oxygen permeation performance. That is, the composition-graded oxygen separation membrane is obtained by stacking two mixed conductors having different compositions in the oxygen ion permeation direction.

  Therefore, when the oxygen separation membrane is used, if the first layer having a relatively low reduction expansion coefficient is disposed on the reducing atmosphere side, the second layer having a relatively high oxygen permeation performance is removed from the reducing atmosphere by the first layer. Protected. At this time, the gradient of the oxygen partial pressure is increased in the first layer so as to increase from the reducing atmosphere side toward the second layer depending on the film thickness and the composition of the first mixed conductor constituting the first layer. Since it is formed, the oxygen partial pressure at the interface between the first layer and the second layer becomes higher depending on the inclination. Therefore, by setting the film thickness and composition so that the reductive expansion of the first layer itself is sufficiently suppressed and the oxygen partial pressure at the interface is sufficiently low, the reductive expansion of the second layer having a large reductive expansion coefficient. As a result, the reduction durability of the entire oxygen separation membrane can be sufficiently enhanced.

  By the way, although the 1st layer is comprised with the 1st mixed conductor with low oxygen permeability, the oxygen transmission rate of a mixed conductor is substantially inversely proportional to the film thickness. That is, if the composition of the mixed conductor is the same, the oxygen permeation performance is improved as the film thickness is reduced. Therefore, by appropriately determining the film thickness, even if the oxygen permeation performance of the first mixed conductor is low, a decrease in oxygen permeation performance relative to the case where the entire oxygen separation membrane is composed of the second mixed conductor is suppressed, Therefore, sufficiently high oxygen permeation performance can be obtained. For example, if the thickness of the first layer is set so that the oxygen permeation rate in the first layer is higher than the oxygen permeation rate when the entire oxygen separation membrane is composed of the second mixed conductor, Since the decrease in the oxygen transmission rate due to the lamination of the first layer is almost negligible, it is possible to obtain the same oxygen transmission performance as when only the second layer is used.

  From the above, the required reduction durability and the desired oxygen permeation performance are weighed and the film thicknesses of the first layer and the second layer and the compositions of the first mixed conductor and the second mixed conductor are determined. By determining, an oxygen separation membrane having high oxygen permeation performance and excellent reduction durability can be obtained.

  In the present application, the perovskite compounds represented by the general formula C include those having a slightly smaller number of oxygen in addition to those having 3 oxygen, regardless of the display of the general formula C. The number of oxygen effective in the present invention varies depending on the oxygen partial pressure and cannot be uniquely determined. For example, the range of 2.4 to 3 is suitable.

  Incidentally, Patent Documents 14 to 16 describe a technique in which the composition is inclined between the solid electrolyte membrane and the electrode layer (air electrode or fuel electrode). These are intended to alleviate the difference in thermal expansion or increase the three-phase interface, and are different in configuration and purpose from the present invention in which the solid electrolyte membrane itself is compositionally graded.

  Further, Patent Document 17 discloses a technique for forming an intermediate layer (solid electrolyte) in a solid electrolyte portion to reduce a voltage drop at an air electrode. Patent Document 18 describes that a solid electrolyte portion is laminated to form an ion. Although techniques for bringing the transport number closer to 1 are described, none of them considers reduction durability, and the configuration itself is different from the present invention.

Non-patent document 1 describes a pseudo-mixed conductor obtained by mixing a ferrite compound with a CeO ₂ oxide ion conductor, and an oxygen permeable film obtained by laminating two films having different ferrite addition amounts. This is intended to improve the oxygen exchange reaction on the membrane surface, and does not consider reduction durability.

  Here, preferably, the first layer has a reductive expansion coefficient of less than 0.14 (%), and the second layer has a reductive expansion coefficient of 0.14 (%) or more. In this way, the reductive expansion coefficient of the first layer is sufficiently small and the oxygen permeation performance of the second layer is sufficiently high, so that it is more suitable for oxygen production, hydrogen production for GTL and fuel cells, and the like. . More preferably, the reduction expansion coefficient of the first layer is 0.13 (%) or less, and more preferably 0.10 (%) or less. More preferably, the reduction expansion coefficient of the second layer is 0.20 (%) or more, and more preferably 0.30 (%) or more. The reductive expansion coefficients of the first layer and the second layer are preferably different from each other by 0.10 (%), and more preferably different from each other by 0.20 (%).

Preferably, the first layer has an oxygen transmission rate of 3 (cc / min / cm ² ) or more when the thickness dimension is 0.5 (mm), and the second layer has a thickness dimension. When oxygen is 0.5 (mm), it has an oxygen transmission rate of 8 (cc / min / cm ² ) or more. In this way, since the oxygen transmission rate of the first layer is relatively high and the oxygen transmission rate of the second layer is sufficiently high, an oxygen separation membrane with higher oxygen transmission performance and better reduction durability can be obtained. can get. More preferably, the oxygen transmission rate of the first layer is 5 (cc / min / cm ² ) or more, and the oxygen transmission rate of the second layer is 10 (cc / min / cm ² ) or more.

  Preferably, the first layer and the second layer are dense. In this way, since the gas cannot pass through the oxygen separation membrane as molecules, an oxygen separation membrane with high separation performance can be obtained. In the present invention, “dense” means that the oxygen separation membrane has a structure that does not allow gas molecules in the atmosphere to which the oxygen separation membrane is exposed to permeate in the thickness direction as it is when the oxygen permeable membrane is used. Means that In other words, the preciseness mentioned here is not uniquely determined, and it is sufficient if it has the above-described characteristics in the intended use mode.

  Preferably, the thickness dimension of the first layer is 0.2 (mm) or less. In this case, since the first layer having a relatively low oxygen permeability is sufficiently thin, an oxygen separation membrane having a higher oxygen permeability can be obtained. The first layer is sufficient if it protects from the reducing atmosphere by covering the second layer. For example, it is preferable to completely cover the first layer, but there is no particular lower limit of the thickness dimension, and industrially. For example, the lower limit is about 1 (μm). Even if the first layer has such a thickness, sufficient reduction durability can be obtained.

  On the other hand, the film thickness of the second layer is preferably as thin as possible in order to obtain high oxygen permeation performance. When an oxygen separation membrane is formed on a porous support as described later, the film thickness is There is no particular lower limit for the size, but it is preferable to have a thickness that can form a dense film. On the other hand, in the case of a self-supporting membrane that does not use a porous support, the thickness of the second layer so that the entire oxygen separation membrane can be self-supporting, for example, a thickness of about 0.5 (mm) or more. Can be determined.

  Further, the oxygen separation membrane is not limited to the two-layer structure in which the first layer and the second layer are laminated, and any other layer having a different reduction expansion coefficient due to a difference in composition from any of these, It is good also as a structure of three or more layers further laminated | stacked so that the reductive expansion coefficient may become large sequentially in the lamination direction which goes to a 2nd layer from a 1st layer. As the number of layers increases, the process is disadvantageous, but the difference in coefficient of thermal expansion between the layers in contact with each other can be reduced, so that it is less likely to break even when exposed to temperature changes during the manufacturing process or use. There is.

  Preferably, the first layer and the second layer are made of the same material. In this way, since the difference in thermal expansion coefficient and the like is reduced, it is possible to easily obtain an oxygen separation membrane that is less likely to be damaged due to a temperature change during the manufacturing process or in use. That is, in order to suppress such damage, it is desirable that the difference in thermal expansion coefficient between the mixed conductors constituting the first layer and the second layer is as small as possible. Therefore, as long as these conditions are satisfied, the constituent material is not particularly limited, but it is preferable to use the same material. Examples of the material of the same family include materials having the same constituent elements but differing only in their proportions, and materials obtained by substituting one or more constituent elements with other elements. In addition, even in the case of a laminated structure of three or more layers, it is preferable that all are made of the same material, but if the difference in thermal expansion coefficient can be sufficiently reduced, it is not the same material. There is no problem.

The perovskite compound constituting the mixed conductor of the present invention contains other elements such as Zn, In, V, Sn, Ge, Ce, Mg, Sc, and Y in addition to the elements specified in the general formula C. It may be included within a range that does not substantially affect the characteristics. In addition to the perovskite compound, the first layer and the second layer may contain a trace amount of Al ₂ O ₃ , SiO ₂ , MgO, ZrO _{2 and the} like that are difficult to eliminate in production. Even if they are contained in a trace amount, they do not significantly affect the characteristics, but since any of them becomes resistance of ionic conduction, the content is desirably as small as possible.

Preferably, in the first mixed conductor, the element M is any one of Fe, Ti, Zr, Al, Co, Mn, and Ni. In this way, the (Ln _1-x Ae _x ) MO ₃ compound containing these at the B site has a relatively high reduction durability and a relatively high oxygen permeation rate. preferable. Further, it is more preferable that the B site contains Fe or Co because electron conductivity becomes high.

  Preferably, the oxygen separation membrane of the present invention is provided on the porous support so as to cover the entire surface. This porous support may be located on either the one side or the other side of the oxygen separation membrane. By configuring the oxygen separation membrane element in which the oxygen separation membrane is fixed on the porous support in this way, the porous support having a sufficiently high gas diffusion coefficient allows gas to easily pass through the inside. By configuring to an appropriate thickness, the mechanical strength of the oxygen separation membrane element can be increased without affecting the oxygen transmission rate. Moreover, since the mechanical strength of the oxygen separation membrane element is ensured by the porous support, it becomes possible to reduce the thickness dimension of the oxygen separation membrane to such an extent that the oxygen transmission rate is not limited by the film thickness, The effect of improving the permeation speed by increasing the surface area can be obtained more remarkably. In the case where such a porous support is provided, when an oxygen dissociation catalyst layer or an oxygen recombination catalyst layer is further provided, one is on the surface of the oxygen separation membrane, and the other is an oxygen separation membrane and a porous layer. Each may be provided between the support and the other, but the other may be provided on the surface of the porous support, preferably in a state of being permeated therein.

  In the above embodiment, “covering the entire surface” means that one surface of the porous support is the same as the surface of the oxygen separation membrane on the side opposite to the porous support when the oxygen separation membrane element is used. It means not being exposed to space. For example, even if one surface of a porous support provided with an oxygen separation membrane in a non-use state is partially exposed, such a mode can be used as long as that part is covered by an apparatus or the like during use. It is included in the above “covering the entire surface”.

  Preferably, the oxygen separation membrane and the porous support are made of the same material. In this way, since the thermal expansion coefficients of the two coincide with each other, even when heated or cooled during the manufacturing process or in use, damage due to the difference in thermal expansion amount is suitably suppressed.

  Preferably, the oxygen separation membrane and the porous support are made of materials having different compositions. Since the strength of the entire oxygen separation membrane element must be ensured by the support, the required properties of the support and the oxygen separation membrane are different. For example, when the required strength is relatively high, oxygen separation is required. It is desirable that the membrane and the support are made of different materials. As such a support constituent material, for example, zirconia, alumina, silicon nitride, silicon carbide and the like are suitable.

  Preferably, the porous support has an average pore diameter r in the range of 0.1 <r <20 (μm) and a porosity p in the range of 5 <p <80 (%). This range is preferable in order to suppress the decrease in the oxygen permeation rate and increase the strength of the oxygen separation membrane element as much as possible. If the pore diameter and the pore diameter are too small, the gas permeation resistance of the porous support increases, so even if the oxygen separation membrane is made thin, the porous support becomes a rate-limiting factor, so the oxygen permeation rate is remarkably high. descend. On the other hand, if the pore diameter and the pore diameter are too large, the mechanical strength is lowered and the function as a support is lost.

  Preferably, at least one of the one surface and the other surface of the oxygen separation membrane is provided with a catalyst layer for promoting dissociation or recombination of the oxygen. In this way, since the dissociation or recombination of oxygen is promoted by the catalyst layer, an oxygen separation membrane element with higher efficiency can be obtained. More preferably, one of the oxygen dissociation catalyst layer and the oxygen recombination catalyst layer is provided on one of the one surface and the other surface, and the other of the oxygen dissociation catalyst layer and the oxygen recombination catalyst layer is provided on the other of the one surface and the other surface. . The catalyst layer may be dense or porous, and an oxygen separation membrane can also serve as this.

Preferably, the oxygen dissociation catalyst layer is a La-Sr-Co-based oxide, a La-Sr-Mn-based oxide, or a platinum-based element. More preferably, it is made of La _x Sr _1-x CoO ₃ (0 ≦ x ≦ 1, preferably x = 0.6). According to such a catalyst, oxygen in the gas supplied to the one surface side of the oxygen separation membrane is suitably ionized, permeated through this, and guided to the other surface side. In addition to the above materials, the catalyst layer is composed of Sm _x SrCoO ₃ (0 ≦ x ≦ 1, preferably x = 0.5), La _1-x Sr _x MnO ₃ (0 ≦ x ≦ 1, preferably x = 0.15), La _1-x Sr _x Co _1-y Fe _y O ₃ (0 ≦ x ≦ 1, 0 <y <1, preferably x = 0.9, y = 0.1) and the like are also preferably used. The oxygen dissociation catalyst layer can be made of the same material as that of the oxygen separation membrane. In that case, the oxygen dissociation catalyst layer can be constituted by a part of the oxygen separation membrane.

  Preferably, the oxygen recombination catalyst layer includes Ni, Co, Ru, Rh, Pt, Pd, Ir, and the like. Preferably, it is made of Ni formed by reducing NiO. According to such a catalyst, oxygen ions guided to the other surface side of the oxygen separation membrane are suitably recombined, and oxygen is recovered from the other surface side. In addition, even when the oxygen dissociation catalyst layer and the oxygen recombination catalyst layer are made of any of the materials described above, oxygen can permeate through the grain boundaries or grains, so that the catalyst layer is dense as well as porous. Can also form.

  Further, the oxygen separation membrane of the present invention has a first gas supply path for supplying a gas containing oxygen to one surface side thereof, and a second gas supply path for supplying a gas containing a predetermined compound to the other surface side thereof. And a gas recovery path for recovering a gas generated by a reaction between oxygen and the predetermined compound on the other surface side. In this way, a gas containing oxygen is supplied from the first gas supply path to the one surface side, and a gas containing a predetermined compound is supplied from the second gas supply path to the other surface side. The gas generated by the reaction is recovered from the gas recovery path. Therefore, an inexpensive, highly efficient and highly durable reactor can be obtained.

Further, the oxygen separation membrane of the present invention can be used for the reduction thereof by supplying NO _x to one side in addition to the above-described oxygen production and partial oxidation reaction of hydrocarbons.

  Preferably, the oxygen separation membrane has a flat plate shape as a whole. Moreover, in the aspect provided with the catalyst layer, the oxygen dissociation catalyst layer is provided on one surface, and the oxygen recombination catalyst layer is provided on the other surface. In an aspect in which such a plate-like oxygen separation membrane is provided on a porous support and a catalyst layer is provided, after the catalyst layers are provided on both sides of the separately formed oxygen separation membrane, the porous support is provided. Alternatively, an oxygen separation membrane element is produced by sequentially forming one catalyst layer, an oxygen separation membrane, and the other catalyst layer on a porous support. Examples of the flat plate shape include a disk shape and a rectangular plate shape.

  Preferably, the oxygen separation membrane has a cylindrical shape with one end closed. In an embodiment in which a catalyst layer is provided, one of the inner peripheral surface and the outer peripheral surface is provided with the oxygen dissociation catalyst layer. The other surface corresponds to the one surface, and the other corresponds to the other surface provided with the oxygen recombination catalyst layer. The oxygen separation membrane is not limited to a flat one, and may be such a three-dimensional one. In the aspect in which the gas is supplied to the inner peripheral surface side, for example, a gas introduction tube may be inserted inside the cylindrical oxygen separation membrane and the gas may be supplied from the tip.

  Preferably, the porous support has a cylindrical shape with one end closed, and the oxygen separation membrane or the two kinds of catalyst layers and the oxygen separation membrane are sequentially laminated on the inner peripheral surface or the outer peripheral surface thereof. Is provided. In this way, the mechanical strength can be ensured by the porous support even in an aspect in which the oxygen separation membrane element has a cylindrical shape.

  The oxygen separation membrane of the present invention includes, for example, a step of mixing a predetermined binder with each of the first mixed conductor material powder and the second mixed conductor material powder and granulating them to a predetermined particle size, A step of forming the granulated powder into a predetermined shape, and a step of subjecting the formed body to a firing process at a predetermined temperature to obtain a film made of the first mixed conductor and a film made of the second mixed conductor, And a process of joining the two films together by applying a predetermined baking process. Between the molding step and the firing step, if necessary, the step of pressurizing the molded body at an isotropic pressure (for example, wet hydrostatic pressure), and the molded body in the air sufficiently more than the firing temperature And a step of decomposing and removing organic substances by heating at a low temperature. In addition, a mechanical polishing step is performed as necessary after firing.

  In addition, the predetermined forming step includes, for example, a ceramic sintered body in a first slurry containing the first mixed conductor material powder and a second slurry containing the second mixed conductor material powder. A predetermined porous support is sequentially immersed, and the first slurry and the second slurry are applied to the surface of the porous support. In this way, the composition which consists of the 1st layer and 2nd layer which were formed by the film thickness according to the coating thickness on the porous support body by baking the slurry apply | coated to the porous support body An oxygen separation membrane element to which an inclined oxygen separation membrane is fixed is obtained.

  In addition, the oxygen separation membrane of the present invention includes, for example, a step of forming a green sheet using a slurry containing the first mixed conductor material powder and the second mixed conductor material powder, and superposing the green sheets. It can also be manufactured by a process including a process of performing a baking process at the same time.

  Moreover, when forming an oxygen separation membrane on a porous support body, it can also manufacture by the process including the process of dip-coating the above slurry, and the process of performing a baking process to this. Furthermore, a first layer to a third layer, that is, an oxygen separation membrane may be formed on the porous support by sputtering or spraying.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, the drawings are appropriately simplified or modified, and the dimensional ratios, shapes, and the like of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a diagram schematically showing a cross-sectional structure for explaining the configuration of an oxygen separation membrane 10 according to an embodiment of the present invention. The oxygen separation membrane 10 has a thin disk shape having a diameter of about 20 (mm) and a thickness of about 0.5 (mm) as a whole, and includes a first layer 12, a second layer 14, and a second layer. It is configured as a laminate in which three layers 16 are laminated. The outer peripheral end faces of these three layers are hermetically sealed with a sealing member 18 made of glass or the like.

Each of the first layer 12 to the third layer 16 is a dense film made of a lanthanum perovskite compound represented by, for example, the general formula (Ln _1-x Ae _x ) MO ₃ . This perovskite compound is a mixed conductive ceramic having both oxygen ion conductivity and electronic conductivity. Therefore, while being dense, oxygen in contact with the one surface 20 or the other surface 22 can be ionized and transmitted, for example, from the other surface 22 toward the one surface 20.

The first layer 12 is made of La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _x , La _0.6 Sr _0.4 Zr _0.3 Fe _0.7 O _x or the like (however, x = about 2.4 to 3), for example, 0.1 (mm ) About thickness dimension. The second layer 14 is made of _{La 0.6 Sr 0.4 Ti 0.2 Fe 0.8} O x and _{La 0.6 Sr 0.4 Zr 0.2 Fe 0.8} O x or the like, for example, comprise a thickness of about 0.1 to 0.2 (mm) ing. The third layer 16 is made of La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O _x , La _0.6 Sr _0.4 Zr _0.1 Fe _0.9 O _x or the like, and has a thickness dimension of about 0.2 to 0.3 (mm), for example. ing. That is, the first layer 12 to the third layer 16 have different compositions, and the oxygen separation film 10 is a composition gradient film in which films having different compositions in the thickness direction are stacked.

Further, the mixed conductor (that is, the first mixed conductor) constituting the first layer 12 has a small reduction expansion coefficient of about 0.06 to 0.10 (%), for example, and about 3.3 (cc / min / cm ² ). Low oxygen permeation rate (value when thickness dimension is 0.5 (mm), hereinafter the same unless otherwise specified). Moreover, the mixed conductor (that is, the second mixed conductor) constituting the second layer 14 has a reduction expansion coefficient of about 0.08 to 0.32 (%), and about 5.9 to 6.1 (cc / min / cm ² ). Oxygen permeation rate. Further, the mixed conductor (that is, the third mixed conductor) constituting the third layer 16 has a large reduction expansion coefficient of about 0.28 to 0.7 (%) and a high of 11.0 (cc / min / cm ² ) or more. Oxygen permeation rate.

Therefore, the oxygen separation membrane 10 has a layer structure in which the reduction expansion coefficient increases and the oxygen transmission rate increases as it goes from the first layer 12 to the third layer 16. However, the first layer 12 made of the mixed conductor having a low oxygen transmission rate is a thin film of about 0.1 (mm), and the oxygen transmission rate is inversely proportional to the film thickness. Therefore, the oxygen transmission rate of each layer is 0.5 (mm). When calculated from the measured value and the film thickness when the thickness is a single layer, the first layer 12 is about 15 (cc / min / cm ² ) and the second layer 14 is about 15 to 30 (cc / min / cm ² ). The third layer 16 is about 18 to 25 (cc / min / cm ² ). Therefore, the oxygen permeation rate in the first layer 12 and the second layer 14 made of the mixed conductor having a low oxygen permeation rate is not limited by the oxygen permeation rate of the oxygen separation membrane 10 as a whole. The speed is as high as when the entire structure is composed of the mixed conductor constituting the third layer 16.

  In addition, the oxygen transmission rate calculated based on the film thickness for each of the first layer 12 to the third layer 16 is a value when each of the layers is configured as a single layer with the film thickness as described above. In the laminated structure of this example, an oxygen partial pressure gradient is formed in each layer as shown in FIG. 2 described later, but the oxygen transmission rate is a function of the ratio of the oxygen partial pressures on both sides of the membrane (described later). (See equation (2)). Therefore, the oxygen permeation rate when laminated is lower according to the oxygen partial pressure on both sides of each layer, so the thicknesses of the first layer 12 and the second layer 14 than the case where the whole is constituted by the third layer 16. The value is reduced by a value corresponding to the dimension and the constituent material.

  The oxygen separation membrane 10 configured as described above is provided with catalyst layers 24 and 26 on one surface 20 and the other surface 22, respectively, and the first layer 12 having a small reduction expansion coefficient is supplied to the reduction side, for example, fuel such as methane. The third layer 16 located on the opposite side and located on the opposite side is used on the oxidation side, for example, on the oxygen-containing gas supply side such as air. Therefore, since the second layer 14 and the third layer 16 having a large reduction expansion coefficient are protected from the reducing atmosphere by the first layer 12, the reduction durability of the oxygen separation membrane 10 and the like is improved.

The oxygen dissociation catalyst layer 26 provided on the oxidation side is provided to promote dissociation and ionization of oxygen on the other surface 22. For example, a porous layer made of La _0.6 Sr _0.4 CoO ₃ is 10 ( It is formed on substantially the entire other surface 22 with a uniform thickness dimension of about μm).

  The oxygen recombination catalyst layer 26 provided on the reduction side is provided to promote the recombination of oxygen ions on the one surface 20. For example, a porous layer made of NiO has a thickness of about 100 (μm). It is formed on substantially the entire surface 20 with such a thickness dimension.

  The oxygen separation membrane 30 schematically shown in FIG. 2 has a relatively low reductive expansion coefficient on the first layer 32 made of the first mixed conductor having a relatively low reductive expansion coefficient and a low oxygen transmission rate. The composition-graded oxygen separation membrane has a two-layer structure in which a second layer 34 made of a second mixed conductor having a large oxygen transmission rate is stacked. Although the oxygen separation membrane 10 shown in FIG. 1 has a three-layer structure, the present invention can be applied to other layers on one surface 20 or the other surface 22 of such a two-layer structure. It can also be applied to a structure having four or more layers laminated.

In the case of the two-layer structure, the first layer 32 includes La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _x , La _0.9 Sr _0.1 Ti _0.1 Fe _0.9 O _x , La _0.6 Sr _0.4 Zr _0.2 Fe _0.8 O _x , La _{It is made of 0.8} Sr _0.2 Zr _0.1 Fe _0.9 O _x or the like, and has a thickness dimension of about 0.05 to 0.1 (mm), for example. The second layer 34 is made of La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O _x , La _0.5 Sr _0.5 Ti _0.1 Fe _0.9 O _x , La _0.6 Sr _0.4 Zr _0.1 Fe _0.9 O _x , La _0.5 Sr _0.5 Zr _0.1 Fe _0.9 O consist of _x or the like, for example, a thickness of about 0.3 to 0.4 (mm). In this case, the film thickness of the entire oxygen separation membrane 30 is, for example, about 0.35 to 0.5 (mm).

In the case of the two-layer structure as described above, the mixed conductor constituting the first layer 32 has a small reduction expansion coefficient of about 0.08 to 0.10 (%) and 3.1 to 6.1 (cc / min / cm). ² ) It has a low oxygen transmission rate. Further, the mixed conductor constituting the second layer 34 has a large reduction expansion coefficient of about 0.21 to 0.7 (%) and a high oxygen transmission rate of 8.9 (cc / min / cm ² ) or more. Even in this configuration, the first layer 32 is composed of a mixed conductor having a low oxygen transmission rate. However, since the film thickness is small, the calculated oxygen transmission rate is, for example, 15 to 30 (cc / min / cm ^2). ) Is a high value. That is, in the case of the two-layer structure, as in the case of the three-layer structure, the oxygen transmission rate of the oxygen separation membrane 30 is the same as that of the second layer 34, that is, the mixed conductor having a high oxygen transmission rate. It becomes a high value.

The oxygen separation membrane 30 having such a two-layer structure is also used with the first layer 32 having a small reduction expansion coefficient positioned on the reduction side and the second layer 34 having a large reduction expansion coefficient positioned on the oxidation side. By the second layer 34 being protected from the reducing atmosphere by the first layer 32, the reduction durability of the oxygen separation membrane 30 is enhanced. The thick lines shown in FIG. 2 schematically represent oxygen partial pressures P _{1 to} P ₃ (that is, oxygen partial pressure gradients) in the atmosphere and in the film. In addition, the white arrow shown in the figure represents the movement of oxygen ions and electrons in the oxygen separation membrane 30. The principle that the second layer 34 is protected will be described with reference to FIG.

In general, the oxygen permeation rate j (O ₂ ) (mol / sec / cm ² ) of a film made of a mixed conductor is given by the following equation (2). In the following equation (2), R is a gas constant, T is an absolute temperature (K), σ _e (S / cm) is an electron conductivity, σ _i (S / cm) is an oxygen ion conductivity, F is a Faraday constant, t is the film thickness (cm), and P _h and P _l are oxygen partial pressures on both sides of the film (where P _h > P _l ).

If the above equation (2) is applied, the oxygen transmission rate j (O ₂ ) ₁ (mol / sec / cm ² ) in the first layer 32 is the following equation (3), and the oxygen transmission rate in the second layer 34: j (O ₂ ) ₂ (mol / sec / cm ² ) is represented by the following equation (4). In addition, in these formulas (3) and (4), those with the subscript 1 represent the electronic conductivity, film thickness, etc. of the first layer 32, and those with the subscript 2 are those in the second layer. 34 represents the electron conductivity, film thickness, and the like.

Therefore, if the characteristics such as the electronic conductivity of each mixed conductor, the oxygen transmission rate in the first layer 32 and the second layer 34, etc. are known, the first layer 32 and the first layer 32 can be obtained from the above equations (3) and (4). The oxygen partial pressure P ₂ at the interface 36 with the two layers 34 can be obtained. For example, oxygen partial pressure P ₁ = 1 × 10 ⁻²³ (atm), P ₃ = 2 × 10 ⁻¹ (atm), the thickness of the first layer 32 is 0.1 (mm), and the thickness of the second layer 34 is 0.4 (mm), the mixed conductor constituting the first layer 32 is La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O ₃ , and the mixed conductor constituting the second layer 34 is La _0.6 Sr _0.4 Ti _0.1 Fe _0.9 O ₃ When the above characteristic is applied, a value of about P ₂ = 10 ⁻¹⁰ to 10 ⁻⁸ (atm) is obtained. That is, as shown in FIG. 2, since the oxygen partial pressure is rapidly increased in the first layer 32 from the reducing side atmosphere toward the second layer 34, the oxygen partial pressure P _{2 at the} interface 36 is, for example, reduced side. oxygen partial becomes larger than 10 ¹⁰ times the pressure P ₁ of the. For this reason, even if the second layer 34 is composed of a mixed conductor having a large reduction expansion coefficient, the reduction force applied to the second layer 34 is 1/10 ¹⁰ or less of the reduction side. It is preferably suppressed.

Table 1 below shows the relationship between the film thickness of the first layer 32 and the second layer 34, the oxygen transmission rate of the entire film, and the oxygen partial pressure P ₂ (both calculated values) at the interface 36 in the above configuration example. Is a summary. As shown in Table 1, as the film thickness decreases, the oxygen transmission rate increases and the oxygen partial pressure P _{2 at the} interface 36 decreases. The oxygen partial pressure P ₂ is the oxygen partial pressure on the reduction side. compared to P ₁ is maintained at a value significantly higher. When the layer thickness of the first layer 32 is reduced to about 1/10, the oxygen partial pressure P ₂ is reduced by about two orders of magnitude. Therefore, even if the layer thickness is about 1 (μm), the oxygen partial pressure P _{2 at the} interface 36 is It is kept at a relatively high value of about 10 ⁻¹⁰ to 10 ⁻⁹ (atm).

  Therefore, if the second layer 34 is completely covered so as not to be exposed to the reducing atmosphere, the thickness dimension of the first layer 32 may be extremely thin. That is, according to Table 1 above, it can be said that the lower limit of the film thickness of the first layer 32 is substantially absent, but the film thickness that can be formed by a dense film is industrially 1 (μm). The degree is the limit, and this is the practical lower limit.

  In the case of the oxygen separation membrane 10 having the three-layer structure, the action of protecting the second layer 14 and the third layer 16 from the reducing atmosphere is the same as that in the case of the two-layer structure described above. That is, the oxygen partial pressure at the interface between the first layer 12 and the second layer 14 and at the interface between the second layer 14 and the third layer 16 can be obtained only by providing the first layer 12 with a film thickness of about 0.1 (mm). Each is significantly reduced.

As described above, according to the oxygen separation membranes 10 and 30 of this embodiment, the first layers 12 and 32 made of a mixed conductor such as La _0.6 Sr _0.4 Ti _0.3 Fe _0.7 O _x are formed on the La _0.6 Sr _0.4 Ti _0.1 Fe. The second layer 14, 34 made of a mixed conductor such as _0.9 O _x is laminated. Therefore, in the oxygen separation membranes 10 and 30, the second layers 14 and 34 having a large reduction expansion coefficient and a high oxygen permeation performance are laminated on the first layers 12 and 32 having a low reduction expansion coefficient and a low oxygen permeation performance. It becomes a composition gradient type. Therefore, if the first layers 12 and 32 are arranged on the reducing side as described above, the second layers 14 and 34 are protected from the reducing atmosphere, and the reduction durability of the entire oxygen separation membrane can be sufficiently enhanced. it can. In addition, since the first layers 12 and 32 are sufficiently thin, even if the oxygen transmission performance of the mixed conductor constituting the first layers 12 and 32 is low, high oxygen transmission performance of the entire oxygen separation membrane can be obtained. Based on the above, considering the required reduction durability and the desired oxygen permeation performance, the film thicknesses of the first layers 12, 32 and the second layers 14, 34, and the composition of the mixed conductor constituting them are determined. By defining, oxygen separation membranes 10 and 30 having high oxygen permeation performance and excellent reduction durability can be obtained.

FIG. 3 is a process diagram for explaining the manufacturing method of the oxygen separation membrane 10 described above. In the granulation step P1, for example, a commercially available LaSrTiFeO _x powder or LaSrZrFeO _x powder having an average particle diameter of about 1 (μm) is mixed with water, a molding aid such as an organic binder, and a dispersant to create a slurry. Then, for example, a raw material powder having an average particle diameter of about 60 (μm) is spray-granulated using a spray drier. Next, in the pressure forming step P2, the granulated raw material powder is press-molded at an appropriate pressure of, for example, about 100 (MPa), and has a diameter of, for example, about 30 (mm) and a thickness of about 3 (mm). A disk-shaped molded body is obtained. In addition, the said molded object dimension is the value determined in consideration of baking shrinkage and grinding | polishing allowance so that the 1st layer 12 grade | etc., Of the said dimension may be obtained. Further, if necessary, a pressure treatment of about 150 (MPa) can be performed by hydrostatic pressure molding (that is, CIP).

  Next, in the firing step P3, for example, after holding the molded body in the atmosphere at a temperature of about 200 to 500 (° C.) for about 10 hours to decompose and remove organic substances, further in the atmosphere about 1300 to 1600 (° C.). The molded body is fired by holding at this temperature for about 3 hours. In the thickness polishing step P4, the dense sintered body thus obtained is subjected to mechanical polishing using a surface grinder or the like, and has a predetermined thickness dimension of about 0.05 to 0.5 (mm), for example. Process into a thin film.

  Next, in the lamination / bonding step P5, two to three thin film bodies having different compositions are overlapped and fired at 1300 to 1600 (° C.) in the atmosphere. As a result, a plurality of these thin film bodies are joined to each other, and a composition gradient film, that is, oxygen separation membranes 10 and 30, in which a plurality of layers having different compositions are laminated in the thickness direction, is obtained.

Such oxygen separation membranes 10 and 30 are used by providing the catalyst layers on both surfaces 20 and 22 as described above. In the catalyst supporting step P6, for example, a commercially available La _0.6 Sr _0.4 CoO ₃ powder having an average particle diameter of about 2 (μm) is mixed with an organic solvent to prepare a slurry, which is applied to one side 20 and the catalyst is printed and supported. At the same time, for example, a commercially available NiO powder having an average particle size of about 7 (μm) is mixed with an organic solvent to prepare a slurry, which is applied to the other surface 22 to print and carry the catalyst. In the baking step P7, for example, the oxygen separation membranes 10 and 30 are obtained by holding the catalyst layers on the one surface 20 and the other surface 22 while maintaining the temperature for about 1 hour at a temperature of about 1000 (° C.), for example. It is done.

  Hereinafter, more specific examples of the present invention will be described. Table 2 below shows composition examples of the first layer 12 to the third layer 16, the first layer 32, and the second layer 34 constituting the oxygen separation membranes 10 and 30, their respective reduction expansion coefficients, and oxygen transmission rates. , And reduction durability. In the “Composition Name” column of Table 2, the abbreviations used in Tables 3 and 4 described later are shown as meaning the mixed conductor of each composition. First, the characteristics of these 16 kinds of mixed conductors constituting each layer will be described.

In Table 2 above, the reduction expansion coefficient was calculated according to the above equation (1) after measuring the thermal expansion coefficient in the atmosphere and in an atmosphere of 5% H ₂ + 95% N ₂ .

  The oxygen permeation rate was determined by manufacturing a mixed conductor thin plate having a thickness of 0.5 (mm) having the above-described composition according to the process shown in FIG. 3 and baking the catalyst on both surfaces of the thin plate. In the reactor 40 shown in FIG. 4, the measurement was performed by arranging a sample instead of the oxygen separation membrane 10.

  In the reactor 40, for example, cylindrical tubes 42 and 44 made of ceramics such as alumina whose both ends are opened are arranged above and below with the oxygen separation membrane 10 interposed therebetween, and on the inner peripheral side thereof, for example, alumina The gas introduction pipes 48 and 50 made of ceramics or the like are inserted. The oxygen separation membrane 10 has one surface 20 on which the oxygen recombination catalyst layer is provided located on the cylindrical tube 44 side, and the other surface 22 on which the oxygen dissociation catalyst layer is provided on the upper side in FIG. Arranged in the direction it is located. In addition, heaters 56 and 56 are arranged on the outer peripheral side of the cylindrical tubes 42 and 44. The cylindrical tubes 42 and 44 and the oxygen separation membrane 10 are hermetically sealed with sealing materials 58 and 58 such as glass. The gas introduction pipes 48 and 50 are arranged away from the surface of the oxygen separation membrane 10 by a distance necessary for gas supply.

  In such a reactor 40, while the inside of the apparatus is heated to a temperature of about 1000 (° C.) by the heater 56, air, that is, a gas containing oxygen, is introduced into the cylindrical tube 42 from the gas introduction tube 48, and the fuel side, A hydrocarbon such as pure methane gas is introduced from the gas introduction pipe 50. The air introduction amount is, for example, about 10 to 500 (cc / min), and the methane gas introduction amount is, for example, about 10 to 200 (cc / min). Prior to the measurement, for example, while the inside of the cylindrical tube 44 is heated to a temperature of about 1000 (° C.) by the heater 56, for example, a mixed gas of hydrogen 10 (%) and argon 90 (%) is supplied from the gas introduction tube 50 to the cylinder. It supplies in the pipe | tube 44 and heats in a reducing atmosphere. Thereby, the oxygen recombination catalyst layer, that is, the nickel oxide provided on the one surface 20 is partially or completely reduced, and the function as the oxygen recombination catalyst is exhibited.

  The air introduced from the gas introduction pipe 48 as described above passes through the exhaust path 60 formed between the gas introduction pipe 48 and the cylindrical pipe 42 while being in contact with the surface of the oxygen separation membrane 10 and the oxygen dissociation catalyst layer. It is evacuated as shown by the arrows in FIG. At this time, oxygen in the air is dissociated and ionized by the oxygen dissociation action and ionization action of the oxygen dissociation catalyst layer provided on the oxygen separation membrane 10 and the other surface 22, so that the oxygen ions have oxygen ion conductivity. 4 is transported from the other surface 22 side to the one surface 20 side as shown by the arrows in FIG.

  The oxygen ions reaching the surface 20 become oxygen molecules due to the recombination action of the oxygen separation membrane 10 made of a mixed conductor and the oxygen recombination catalyst layer provided on the surface 20, and are taken out from the surface 20. Thereby, oxygen permeate | transmits from the other surface 22 side to the one surface 20 side. However, since the oxygen separation membrane 10 made of a mixed conductor is dense and other gases cannot be ionized, gases other than oxygen do not permeate at all. That is, oxygen with extremely high purity is produced from air.

Further, the oxygen permeated in this way is in the form of ions or recombined, and then on methane gas or the like introduced from the gas introduction pipe 50 and its one side 20, in the oxygen recombination catalyst layer or in the vicinity thereof. The reaction causes a partial oxidation reaction of methane as shown in the following formula (5). The generated synthesis gas of carbon monoxide and hydrogen is recovered from a recovery path 62 formed between the gas introduction pipe 50 and the cylindrical pipe 44. The recovered synthesis gas is used, for example, for liquid fuel synthesis. As is clear from the above description, when methane gas is not introduced from the gas introduction pipe 50, oxygen can be recovered from the recovery path 62, and the reactor 40 can be used as an oxygen production apparatus.
CH ₄ + 1 / 2O ₂ → CO + 2H ₂ (5)

Further, the reduction durability shown in Table 2 was measured by measuring the amount of nitrogen in the synthesis gas recovered on the reduction side by continuously carrying out the above test, and calculating the nitrogen leak rate L _N from the change as follows ( Judgment was made according to equation 6). ◎: No increase in nitrogen leak rate in 3 to 10 hours, ○: Increase in nitrogen leak rate within 1% within 3 hours, Δ: Nitrogen leak rate in 1 hour within 1 hour An increase in the range of ˜3 (%), and × indicate an increase in the nitrogen leak rate by 3 (%) or more within 3 hours. If the nitrogen leak rate does not increase in 10 hours, it is considered that there is sufficient reduction durability for a long time.
L _N = [N ₂ amount (cc / min) / total gas amount (cc / min)] × 100 (6)

  FIG. 5 is a two-dimensional chart showing the relationship between the reduction expansion coefficient and the oxygen transmission rate of each sample measured as described above, that is, the data listed in Table 2. ◇ is the data of LSTF 1 to 8 in Table 2, and ● is the data of LSZF 1 to 8. The oxygen permeation rate is calculated from the oxygen concentration and flow rate in the syngas and the oxygen permeation area of the oxygen separation membrane 10 by performing the above test continuously for 24 hours, measuring the syngas and exhaust gas by gas chromatography. did.

As shown in Table 2 and FIG. 5, the mixed conductors constituting each layer of the oxygen separation membrane 10 have a reduction expansion coefficient and an oxygen transmission rate that are substantially proportional to each other, and the reduction expansion coefficient is reduced. If the reduction durability is increased, the oxygen permeation rate is reduced. In general applications of the oxygen separation membrane 10, it is desirable that the reduction expansion coefficient is less than 0.14 (%) in order not to cause reduction cracking. In that case, in the LSTF system, 6 (cc / min / cm ² ). Hereinafter, in the LSZF system, the material is limited to 4 (cc / min / cm ² ) or less. Therefore, it is impossible to increase both the reduction durability and the oxygen permeation rate by simply configuring the oxygen separation membrane 10 as a single layer as in the prior art and simply changing the composition.

  Examples 1 to 20 shown in Table 3 are layer configuration examples of a two-layer or three-layer stacked structure (that is, a composition gradient film) in which the first layer 12 and the like are configured with the mixed conductors listed in Table 2 above. is there. What is described as “none” in the column of the third layer means a two-layer structure. In addition, Comparative Examples 1 to 15 shown in Table 4 are layer configuration examples having a single layer using the mixed conductor listed in Table 2 or a laminated structure outside the scope of the present invention.

Examples 1 to 4, 7 to 12, and 15 to 20 are LSTF3, LSTF8, LSZF7 having a small expansion coefficient of 0.10 (%), or LSZF2 having a small 0.08 (%) (that is, those having a reduction durability of ◎). While constituting the first layer 32, LSTF1 with a reduction expansion coefficient of 0.4 (%) or more, LSTF5 with 0.36 (%), LSZF1 with 0.28 (%), or LSZF5 with 0.21 (%), that is, with a large reduction expansion coefficient Thus, the two-layer structure in which the second layer 34 is configured has a gradient composition in which the reduction expansion coefficient increases from the first layer 32 toward the second layer 34. In these configuration examples, the first layer 32 positioned on the reduction side has a reduction expansion coefficient of less than 0.14 (%) sufficient for suppressing reduction cracking, while the second layer 34 positioned on the oxidation side is 8.9 (cc / It has an extremely high oxygen transmission rate of min / cm ² ) or more.

In Examples 5, 6, 13, and 14, LSTF3 with a reduction expansion coefficient of about 0.10 (%) or LSZF3 with an extremely low degree of 0.06 (%) (that is, all of which have a reduction durability of ◎) are the first. Compare the second layer 14 with the LSTF2 or 0.08 (%) with a reductive expansion coefficient of about 0.32 (%) and a sufficiently small LSZF2 with the LSTF1 or 0.28 (%) with a large reductive expansion coefficient of 0.4 or more. By forming the third layer 16 with a relatively large LSZF1 in a three-layer structure, the graded composition has a reduction expansion coefficient that increases from the first layer 12 toward the third layer 16. Even in these structural examples, the first layer 12 positioned on the reduction side has a reduction expansion coefficient of less than 0.14 (%) sufficient for suppressing reduction cracking, while the third layer 16 positioned on the oxidation side has 11 (cc / min / cm ² ) or higher. In addition, the second layer 14 located between them has a medium oxygen transmission rate of 5.9 to 6.1 (cc / min / cm ² ).

  On the other hand, Comparative Examples 1 to 4 are configured as a single layer with the same material as the third layer 16 and the second layer 34 having a high oxygen permeation rate (that is, having a reduction durability of x to ◯). . In Comparative Examples 5 to 15, the first layers 12 and 32 are made of a material having a moderate reduction expansion coefficient of 0.14 to 0.32 (%).

  The results of evaluating the characteristics of Examples 1 to 20 are shown in Table 5, and the results of evaluating the characteristics of Comparative Examples 1 to 15 are shown in Table 6, respectively.

As shown in Table 5 above, the first layer 32 is made of a material having a reduction expansion coefficient of 0.10 (%) or less, and the second layer 34 has an oxygen transmission rate of 8.9 (cc / min / cm ² ) or more. In Examples 1 to 4, 7 to 12, and 15 to 20 made of materials, the oxygen permeation rate is 10 (cc / min / cm ² ) or more, and the reduction durability is also evaluated as ◎ (that is, the amount of nitrogen leak increases) None).

Further, as shown in Table 5 above, the first layer 12 is made of a material having a reduction expansion coefficient of 0.10 (%) or less, and the third layer 16 is oxygen permeation of 11 (cc / min / cm ² ) or more. Also in Examples 5, 6, 13, and 14 configured with the material of the speed, the oxygen permeation speed is 13 (cc / min / cm ² ) or more and the reduction durability is evaluated as ◎ (that is, there is no increase in the amount of nitrogen leak) )Met.

  In contrast, in Comparative Examples 1 to 15 in which the first layer 32 is made of a material having a reduction expansion coefficient of 0.14 (%) or more, the oxygen permeation rate is relatively high, but the reduction durability of the first layer 32 is high. Is lacking. Therefore, the reduction membrane as a whole also has a reduction durability of about x to o.

  Therefore, according to the embodiment, by using a material having a small reduction expansion coefficient for the first layers 12 and 32 and using a material having a high oxygen transmission rate on the oxidation side, oxygen having both high reduction durability and oxygen transmission performance. It is clear that the separation membranes 10 and 30 are obtained.

  In the data listed in Tables 5 and 6 above, in all of the examples and comparative examples having a laminated structure, the oxygen permeation rate of the mixed conductors constituting the plurality of layers provided in the oxygen separation membrane is The measured value of the oxygen permeation rate is higher than the value (see Table 2 above) when the entire oxygen separation membrane is constituted by the highest layer (the third layer 16 and the second layer 34). However, among the compositions shown in Table 2 above, those with insufficient reduction durability other than ◎ are measured for oxygen transmission rate in a state in which reduction cracking occurs in part. Is considered to be lower than the original value.

In the example shown in Table 5, a part of the film thickness of the oxygen separation membrane was replaced with a material having a low oxygen transmission rate, so that the oxygen separation membrane was replaced with only the material constituting the third layer 16 and the second layer 34. Since the oxygen permeation rate is low, when the original values of these constituent materials are estimated from the measured values, 18 (cc / min / cm ² ) or more for LSTF1 and LSZF1, 15 (cc / min / cm ² ) for LSTF5 and LSZF5 The above oxygen transmission rate is considered to be the original value.

  Further, reduction durability can be sufficiently obtained even when the thickness dimension of the first layers 12 and 32 is 0.1 (mm) or 0.05 (mm). That is, the first layers 12 and 32 may be formed with a very thin film thickness. In addition, the first layer 32 has a thickness of 0.1 (mm) and the second layer 34 has a thickness of 0.4 (mm). Comparing with Examples 17 to 20 in which the thickness dimension of the first layer 32 is 0.05 (mm) and the thickness dimension of the second layer 34 is 0.3 (mm), the latter has the thickness dimension of each layer and the whole. It can be seen that by making it thinner, it has a significantly higher oxygen transmission rate. Therefore, the first layers 12 and 32 are preferably thin.

In addition, apart from those listed in Tables 2 to 6, the oxygen separation membrane having a two-layer structure in which the first layer 32 is made of LSTF 3 having a thickness of 0.2 (mm) and the second layer 34 is made of LSTF 1 having a thickness of 0.3 (mm). Evaluated. As a result, the oxygen permeation rate remained at 6.2 (cc / min / cm ² ), and was the same as that of LSZF2 having the highest oxygen permeation performance among materials having a reduction expansion coefficient of less than 0.14 (%). Therefore, the effect of the present invention is remarkable when the thickness dimension of the first layer 32 positioned on the reduction side is kept to 0.2 (mm) or less.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

It is a figure which shows typically the principal part cross section of the oxygen separation membrane of one Example of this invention. It is a figure explaining the oxygen partial pressure gradient in the film | membrane in the case of a 2 layer inclination structure. It is process drawing for demonstrating the manufacturing method of the oxygen separation membrane element of FIG. It is a figure explaining the structure of the reactor using the oxygen separation membrane element of FIG. It is the graph which represented the relationship between the reductive expansion coefficient of each layer which comprises the oxygen separation membrane of FIG.

Explanation of symbols

10: oxygen separation membrane, 12: first layer, 14: second layer, 16: third layer, 18: sealing member, 20: one side, 22: other side, 24: oxygen recombination catalyst layer, 26: oxygen dissociation Catalyst layer, 30: oxygen separation membrane, 32: first layer, 34: second layer, 36: interface, 40: reactor, 42, 44: cylindrical tube, 48, 50: gas introduction tube, 56: heater, 58 : Sealing material, 60: exhaust path, 62: recovery path,

Claims (4)

General formula (Ln _1-x Ae _x ) MO ₃ (where Ln is one or more combinations of lanthanoids, Ae is one or more combinations selected from Ba, Sr, and Ca) , M is one or a combination of two or more selected from Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, Cu, Cr, Mn, Rh, Pd, Pt, and Au, 0 A first layer composed of a first mixed conductor represented by ≦ x ≦ 1);
A second layer composed of a second mixed conductor represented by the general formula and having a reduction expansion coefficient larger than that of the first mixed conductor, and laminated on the first layer. Inclined oxygen separation membrane.   2. The composition gradient oxygen according to claim 1, wherein the first layer has a reductive expansion coefficient of less than 0.14 (%), and the second layer has a reductive expansion coefficient of 0.14 (%) or more. Separation membrane. The first layer has an oxygen transmission rate of 3 (cc / min / cm ² ) or more when the thickness dimension is 0.5 (mm), and the second layer has a thickness dimension of 0.5 (mm). The composition-gradient oxygen separation membrane according to claim 1 or 2, wherein the composition gradient oxygen separation membrane has an oxygen transmission rate of 8 (cc / min / cm ² ) or more. The composition gradient oxygen separation membrane according to any one of claims 1 to 3, wherein the first layer and the second layer are dense.

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