JP4500762B2 - Oxygen separation membrane having a composition gradient structure - Google Patents

Oxygen separation membrane having a composition gradient structure Download PDF

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JP4500762B2
JP4500762B2 JP2005313381A JP2005313381A JP4500762B2 JP 4500762 B2 JP4500762 B2 JP 4500762B2 JP 2005313381 A JP2005313381 A JP 2005313381A JP 2005313381 A JP2005313381 A JP 2005313381A JP 4500762 B2 JP4500762 B2 JP 4500762B2
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洋祐 高橋
重夫 長屋
拓史 瀬尾
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Noritake Co Ltd
Chubu Electric Power Co Inc
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

本発明は、混合伝導体が用いられた酸素分離膜に関する。   The present invention relates to an oxygen separation membrane using a mixed conductor.

例えば、酸素イオン伝導性を有する緻密なセラミック膜は、その一面側において気体から解離させ且つイオン化させた酸素イオンをその他面側において再結合させることにより、酸素をその一面から他面に選択的に透過させてその気体から連続的に酸素を分離する酸素分離膜エレメントに利用される。特に、酸素イオン伝導性に加えて電子伝導性を有する混合伝導体では、酸素分離膜内を酸素イオンの移動方向とは反対方向に電子が移動するため、解離面と再結合面とを電気的に接続して電子を再結合面から解離面に戻すための外部電極や外部回路等を設ける必要がない利点がある。このような酸素分離膜エレメントによれば、酸素を含む気体から容易に酸素を分離することができるため、例えば、深冷分離法(混合ガスを冷却し、不純物を固化して取り除く方法)やＰＳＡ(圧力変動吸着)法等に代わる酸素製造法として利用できる。   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, a cryogenic separation method (a method of cooling a mixed gas to solidify and remove impurities) or PSA It can be used as an oxygen production method in place of the (pressure fluctuation adsorption) method.

また、上記のような酸素イオン伝導体は、炭化水素の部分酸化反応等の酸化用反応装置にも利用し得る。例えば、この酸素イオン伝導体を膜状に形成し、その一方の表面に空気等の酸素含有ガスを供給し、他方の表面すなわち酸素再結合側の表面にメタン(CH4)等の炭化水素を含む気体を供給すれば、透過した酸素イオンによってその炭化水素を酸化させることができる。そのため、ＧＴＬ(Gas to Liquid：天然ガスから化学反応により液体燃料を合成する技術)や、燃料電池用水素ガスの製造等に利用できるのである。 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.

ところで、酸素分離に用いる混合伝導体として、LaSrCoFe系やLaGaO3系酸化物等のペロブスカイト化合物が優れていることが知られている(特許文献１〜８参照)。しかしながら、LaSrCoFe系酸化物は還元膨張率が大きいことから、解離面側が還元雰囲気になる酸素分離膜用途では、割れが生じ易く耐久性が低いので、実用上問題がある。なお、還元膨張率(%)は、還元雰囲気下における熱膨張率をＥred(%)、空気雰囲気下における熱膨張率をＥair(%)としたとき、下記(１)式で与えられる。
[{(1＋Ｅred/100)-(1＋Ｅair/100)}/(1＋Ｅair/100)]×100 ・・・(１) 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). 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)

一方、LaGaO3系酸化物は、LaSrCoFe系酸化物に比較して還元耐久性が優るものの原料が高価であり、しかも、酸素イオン伝導性がやや劣り、機械的強度も低い問題がある。また、LaGaO3系酸化物は、水蒸気接触部でGa成分が分解することから、耐水蒸気性にも問題がある。因みに、炭化水素の部分酸化反応等においては、コーキング(すなわち炭素の析出)延いてはガス透過性能の低下を防止するために膜の一方側に水蒸気を流すシステム設計が望まれる。また、水蒸気を流さない場合にも、膜を透過した酸素と水素との反応により水蒸気が生成する。そのため、前述したような用途においては、酸素イオン伝導体に耐水蒸気性も要求されるのである。 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.

なお、LaGaO3系酸化物の強度を向上させるために、アルミナ粉末をLaSrGaMg系酸化物結晶の粒界に分散させた焼結体、LaGaO3系結晶の構造の一部をアルミニウム等で置換した焼結体、LaGaO3系結晶のGaの一部をアルミニウムやマグネシウム等で置換した(すなわちアルミニウムやマグネシウム等が固溶した)焼結体、LaGaO3系酸化物にチタンまたはバナジウムを含有させた焼結体等が提案されている(例えば特許文献９〜１２を参照)。しかしながら、これらは何れもGaを含むペロブスカイト化合物の機械的強度を向上させて還元安定性を高めることを図るものであって、Gaを含む場合における耐水蒸気性を何ら改善するものではない。
特開平０８−１７３７７６号公報 特開平０９−１６１８２４号公報 特開平１１−２２８１３６号公報 特開平１１−３３５１６４号公報 特開２０００−２５１５３４号公報 特開２０００−２５１５３５号公報 特表２０００−５１１５０７号公報 特開２００１−０９３３２５号公報 特開２０００−０４４３４０号公報 特開２０００−２２６２６０号公報 特開２００１−３３２１２２号公報 特開２００３−１１２９７３号公報 国際公開第０３／０４００５８号パンフレット 特開平０５−１５１９１８号公報 特開平０７−２９６８３８号公報 特開平０９−２６６０００号公報 特開２００１−０５２７２２号公報 特開２００２−０１５７５６号公報 高村 仁他「家庭用燃料電池実現のための新たな高効率天然ガス改質システムの構築−酸素透過膜を利用した接触部分酸化型メタン改質装置の開発−」(科学技術振興機構 戦略的創造研究推進事業 第５回公開シンポジウム予稿集、２００４年７月５日、４９〜５３頁) 特開平０７−２４０２１７号公報 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, 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 catalytic partial oxidation methane reformer using oxygen permeable membrane” (Strategic creation of Japan Science and Technology Agency) (Research Promotion Project Proceedings of the 5th Open Symposium, July 5, 2004, pp. 49-53) Japanese Patent Application Laid-Open No. 07-240217

そこで、本願出願人は、LaGaO3系酸化物に比較して原料が安価で酸素イオン伝導性が高く、且つLaGaO3系酸化物に比較して還元耐久性や耐水蒸気性の高い混合伝導体として、LaSrTiFeOx系酸化物(ｘは3またはそれよりも僅かに小さい値)等を提案した(特許文献１３を参照)。 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).

上記のLaSrTiFeOx系酸化物は、ＡサイトおよびＢサイトの組成比に応じて酸素透過性能や還元耐久性が変化する。例えば、La0.6Sr0.4Ti0.1Fe0.9Oxは、0.5(mm)厚としたときの酸素透過速度が10(cc/min/cm2)以上と高い酸素透過性能を有するが、還元膨張率が0.4〜0.7(％)と大きいため還元耐久性が低い。これに対して、La0.6Sr0.4Ti0.3Fe0.7Oxは、酸素透過速度が3(cc/min/cm2)に過ぎないが、還元膨張率が0.1(％)と小さく還元耐久性が高い。すなわち、LaSrTiFeOx系酸化物では、酸素透過性能と還元耐久性とがトレードオフの関係にあり、これらを共に高めることは不可能である。そのため、還元耐久性が要求される現在の一般的な工業用途では、0.5(mm)厚で2〜4(cc/min/cm2)以上の酸素透過性能が必要とされることから、これを満足する後者の組成が用いられることになる。 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.

しかしながら、混合伝導体膜の酸素透過性能が高いほど、同量の酸素量を得るために必要な酸素分離膜エレメントの寸法を小さくでき、延いては装置の低コスト化および小型化が容易になる。例えば、La0.6Sr0.4Ti0.1Fe0.9Ox並の10(cc/min/cm2)程度の酸素透過速度を有していれば、La0.6Sr0.4Ti0.3Fe0.7Oxを用いる場合と比較して、エレメント寸法を半分以下にできる。そのため、高い還元耐久性を有すると共に、単位膜面積当たりの酸素透過速度が可及的に高い混合伝導体膜が望まれていた。 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.

また、実際に工業用途上必要な酸素透過性能は例えば10(cc/min/cm2)以上であり、前述した「0.5(mm)厚で2〜4(cc/min/cm2)」との値は、酸素透過性能が膜厚に略反比例することに基づき、0.1(mm)程度まで膜厚を薄くして必要な酸素透過性能を確保することを前提としている。しかしながら、このような薄い膜は自立不能であるため、多孔質支持体上に混合伝導体の緻密質膜を形成する非対称膜構造を採る必要がある。これに対して、0.5(mm)厚で10(cc/min/cm2)以上の酸素透過性能が得られるのであれば、非対称膜構造として酸素透過性能の極めて高い酸素分離膜を構成することが可能であるだけでなく、膜厚を自立可能な0.5(mm)として多孔質支持体を無用とすることも可能である。後者によれば工程が簡単になるので大幅な低コスト化が可能になる。 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 film cannot be self-supporting, it is necessary to adopt an asymmetric membrane structure in which a dense membrane of a mixed conductor is formed on a 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.

なお、還元膨張率が同程度であれば、機械的強度が高いほど、還元膨張によって発生する応力に対する抵抗力が高くなり、延いては割れが生じ難くなる。そのため、還元膨張率を低くすることに代えて機械的強度を例えば２〜３倍程度に高めることも考えられるが、現実的には困難である。   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.

本発明は、以上の事情を背景として為されたものであって、その目的は、酸素透過性能が高く且つ還元耐久性の優れた酸素分離膜を提供することにある。   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.

斯かる目的を達成するための本発明の組成傾斜構造を有する酸素分離膜の要旨とするところは、(ａ)一般式(Ln1-xAex)MO3(但し、Lnはランタノイドのうちの１種または２種以上の組合せ、AeはBa、Sr、Caのうちから選ばれる１種または２種以上の組合せ、MはTi,Zr,Al,Ga,Nb,Ta,Fe,Co,Ni,Cu,Cr,Mn,Rh,Pd,Pt,およびAuのうちから選ばれる１種または２種以上の組合せ、0≦ｘ≦1。以下、一般式Ｃという。)で表される第１の混合伝導体から成る緻密質の第１層と、(ｂ)前記一般式で表され且つ前記第１の混合伝導体よりも還元膨張率が大きい第２の混合伝導体から成りその一面側に前記第１層が積層された緻密質の第２層と、(ｃ)前記一般式で表され且つ前記第２の混合伝導体よりも還元膨張率が小さい第３の混合伝導体から成り前記第２層の他面側に積層された緻密質の第３層とを、含むことにある。 In order to achieve such an object, the gist of the oxygen separation membrane having a composition gradient structure of the present invention is as follows: (a) General formula (Ln 1-x Ae x ) MO 3 (where Ln is a lanthanoid One or a combination of two or more, Ae is one or a combination of two or more selected from Ba, Sr, and Ca, M is Ti, Zr, Al, Ga, Nb, Ta, Fe, Co, Ni, 1 or a combination of two or more selected from Cu, Cr, Mn, Rh, Pd, Pt, and Au, 0 ≦ x ≦ 1, hereinafter referred to as general formula C)) A dense first layer made of a conductor, and (b) a second mixed conductor represented by the general formula and having a reduction expansion coefficient larger than that of the first mixed conductor. A dense second layer in which one layer is laminated; and (c) a third mixed conductor represented by the general formula and having a reduction expansion coefficient smaller than that of the second mixed conductor. dense stacked in the other surface And a third layer of is to contain.

また、前記目的を達成するための第２発明の要旨とするところは、前記第１発明において、前記第２層は0.14(％)以上の還元膨張率を有し、且つ前記第１層および前記第３層は0.14(％)未満の還元膨張率を有することにある。   Further, the gist of the second invention for achieving the above object is that, in the first invention, the second layer has a reduction expansion coefficient of 0.14 (%) or more, and the first layer and the The third layer is to have a reduction expansion coefficient of less than 0.14 (%).

また、前記目的を達成するための第３発明の要旨とするところは、前記第１発明または前記第２発明において、前記第１層の厚さ寸法は前記第３層の厚さ寸法の1/3倍より大きく且つ３倍未満であることにある。   Further, the gist of the third invention for achieving the above object is that, in the first invention or the second invention, the thickness dimension of the first layer is 1 / th of the thickness dimension of the third layer. It is greater than 3 times and less than 3 times.

また、前記目的を達成するための第４発明の要旨とするところは、前記第１発明乃至第３発明の何れかにおいて、前記第１層および前記第３層は同一材料から成ることにある。   The gist of the fourth invention for achieving the above object is that, in any one of the first invention to the third invention, the first layer and the third layer are made of the same material.

前記第１発明によれば、酸素分離膜は、第２の混合伝導体から成る第２層の一面に第１の混合伝導体から成る第１層が、他面に第３の混合伝導体から成る第３層がそれぞれ積層された積層構造に構成される。この積層構造において、第２層を構成する第２の混合伝導体は、第１層を構成する第１の混合伝導体および第３層を構成する第３の混合伝導体よりも還元膨張率が大きい特性を有するが、上記一般式Ｃで表されるペロブスカイト化合物は酸素透過性能と還元耐久性とがトレードオフの関係にある。そのため、上記酸素分離膜は、相対的に還元膨張率が大きく且つ酸素透過性能の高い第２層の一面および他面に、相対的に還元膨張率が小さく且つ酸素透過性能の低い第１層および第３層が積層された積層体、すなわち、組成の異なる複数の混合伝導体を酸素イオンの透過方向に積層した組成傾斜型の酸素分離膜になる。   According to the first aspect of the present invention, the oxygen separation membrane has a first layer made of the first mixed conductor on one surface of the second layer made of the second mixed conductor, and a third mixed conductor on the other surface. The third layer is formed in a stacked structure in which the third layers are stacked. In this laminated structure, the second mixed conductor constituting the second layer has a reduction expansion coefficient higher than that of the first mixed conductor constituting the first layer and the third mixed conductor constituting the third layer. Although it has large characteristics, the perovskite compound represented by the above general formula C has a trade-off relationship between oxygen permeation performance and reduction durability. Therefore, the oxygen separation membrane includes a first layer having a relatively low reduction expansion coefficient and a low oxygen permeation performance on one surface and the other surface of the second layer having a relatively large reduction expansion coefficient and a high oxygen permeation performance. A laminated body in which the third layer is laminated, that is, a composition gradient type oxygen separation membrane in which a plurality of mixed conductors having different compositions are laminated in the oxygen ion transmission direction.

したがって、酸素分離膜を使用する際には、相対的に還元膨張率が小さい第１層或いは第３層によって、相対的に酸素透過性能の高い第２層が還元雰囲気から保護される。このとき、第１層および第３層のうち、還元雰囲気側に位置するもの(以下、還元側層という)には、その膜厚やこれを構成する混合伝導体の組成に応じて、還元雰囲気側から第２層に向かうに従って高くなるように酸素分圧の傾斜が形成されるため、第２層と還元側層の界面における酸素分圧はその傾斜の程度に応じて高くなり、延いては、その第２層に負荷される還元力がその傾斜の程度に応じて低くなる。そこで、それら膜厚や組成を、還元側層自体の還元膨張が十分に抑制され且つ前記界面における酸素分圧が十分に低くなるように定めることによって、還元膨張率の大きい第２層の還元膨張を抑制し、延いては酸素分離膜全体の還元耐久性を十分に高めることができる。しかも、前記第１層、前記第２層、および前記第３層は緻密質であることから、酸素分離膜を気体が分子のまま透過し得ないため、分離性能の高い酸素分離膜が得られる。なお、本発明において「緻密質」とは、酸素透過膜の使用時において、その酸素分離膜が曝される雰囲気中の気体分子をそのまま厚み方向に透過させない組織を、酸素分離膜が有していることを意味する。すなわち、ここでいう緻密性は一義的に定められるものではなく、予定されている使用態様において上述した特性を有していれば足りる。 Therefore, when the oxygen separation membrane is used, the second layer having a relatively high oxygen permeation performance is protected from the reducing atmosphere by the first layer or the third layer having a relatively low reduction expansion coefficient. At this time, among the first layer and the third layer, the one located on the reducing atmosphere side (hereinafter referred to as the reducing side layer) has a reducing atmosphere depending on the film thickness and the composition of the mixed conductor constituting the layer. Since the gradient of oxygen partial pressure is formed so as to increase from the side toward the second layer, the oxygen partial pressure at the interface between the second layer and the reduction side layer increases according to the degree of the gradient, The reducing force applied to the second layer is lowered according to the degree of the inclination. Therefore, the reductive expansion of the second layer having a large reductive expansion rate is determined by setting the film thickness and composition such that the reductive expansion of the reducing layer itself is sufficiently suppressed and the oxygen partial pressure at the interface is sufficiently low. As a result, the reduction durability of the entire oxygen separation membrane can be sufficiently enhanced. In addition, since the first layer, the second layer, and the third layer are dense, gas cannot pass through the oxygen separation membrane as molecules, so that 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.

ところで、第１層および第３層は酸素透過速度が低い第１の混合伝導体および第３の混合伝導体でそれぞれ構成されているが、混合伝導体の酸素透過性能は膜厚に略反比例する。すなわち、混合伝導体の組成が同一であれば、膜厚を薄くするほど酸素透過性能が高められる。そのため、膜厚を適宜定めることにより、第１の混合伝導体および第３の混合伝導体の酸素透過速度が低くとも、酸素分離膜全体を第２の混合伝導体で構成した場合に対する酸素透過性能の低下を抑制し、延いては十分に高い酸素透過性能を得ることができる。例えば、酸素分離膜全体を第２の混合伝導体で構成した場合における酸素透過性能よりも、第１層および第３層の各々における酸素透過性能が高くなるようにそれら第１層および第３層の膜厚を設定すれば、それら第１層および第３層を積層することによる酸素透過性能の低下が殆ど無視できるので、第２層のみで構成する場合と同程度の酸素透過性能を得ることができる。   By the way, the first layer and the third layer are respectively composed of the first mixed conductor and the third mixed conductor having a low oxygen transmission rate, and the oxygen transmission performance of the 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 when the oxygen permeation rate of the first mixed conductor and the third mixed conductor is low, the oxygen permeation performance with respect to the case where the entire oxygen separation membrane is composed of the second mixed conductor Can be suppressed, and thus sufficiently high oxygen permeation performance can be obtained. For example, the first layer and the third layer so that the oxygen permeation performance in each of the first layer and the third layer is higher than the oxygen permeation performance when the entire oxygen separation membrane is composed of the second mixed conductor. If the film thickness is set, the decrease in oxygen permeation performance due to the lamination of the first layer and the third layer can be almost ignored, so that the oxygen permeation performance equivalent to that of the second layer is obtained. Can do.

上記により、要求される還元耐久性と所望する酸素透過性能とを比較考量して、第１層、第２層、および第３層の膜厚や、第１の混合伝導体、第２の混合伝導体、および第３の混合伝導体の組成を定めることによって、酸素透過性能が高く且つ還元耐久性に優れた酸素分離膜が得られる。   Based on the above, the required reduction durability and the desired oxygen permeation performance are compared, and the film thicknesses of the first layer, the second layer, and the third layer, the first mixed conductor, and the second mixing By defining the composition of the conductor and the third mixed conductor, an oxygen separation membrane having high oxygen permeation performance and excellent reduction durability can be obtained.

しかも、第２層の両面の各々には、それよりも還元膨張率の小さい第１層または第３層が積層されることによって厚み方向において対称的に構成されているため、第２層の一面のみにそれよりも還元膨張率の小さい層を設けた場合に比較して、酸素分離膜の両面における熱膨張係数の相違が小さくなる。そのため、酸素分離膜の製造過程における焼成時や、装置に組み付けてシールする際などに、その熱膨張係数の相違に起因して反りや割れの生ずることが抑制される利点もある。   In addition, since the first layer or the third layer having a smaller reduction expansion coefficient is laminated on each of both surfaces of the second layer, the first layer is symmetrically formed in the thickness direction. Compared with the case where only a layer having a smaller reduction expansion coefficient is provided, the difference in thermal expansion coefficient between both surfaces of the oxygen separation membrane is reduced. Therefore, there is an advantage that warpage and cracking are suppressed due to the difference in thermal expansion coefficient during firing in the manufacturing process of the oxygen separation membrane or when assembled and sealed in an apparatus.

因みに、前記のように還元膨張率の大きい第２層の還元膨張を抑制するためには、それよりも還元膨張率の小さい層を還元雰囲気側のみに設ければ足りる。しかしながら、相互に還元膨張率の異なる材料は同時に熱膨張係数も相違し、例えば、還元膨張率が大きい材料ほど熱膨張係数が大きくなる。そのため、第２層の一方の面のみに還元膨張率の小さい層を設けると、その一方の面側の熱膨張係数が小さく、且つ他方の面側の熱膨張係数が大きい積層構造、すなわち両面で熱膨張係数の著しく相違する構造となるので、焼成時やシール時に加熱したときに両面で熱膨張量が相違する問題が生じるのである。   Incidentally, as described above, in order to suppress the reductive expansion of the second layer having a large reductive expansion coefficient, it is sufficient to provide a layer having a smaller reductive expansion coefficient only on the reducing atmosphere side. However, materials having different reductive expansion coefficients also have different thermal expansion coefficients at the same time. For example, a material having a higher reductive expansion coefficient has a higher thermal expansion coefficient. Therefore, when a layer having a small reduction expansion coefficient is provided only on one surface of the second layer, a laminated structure having a small thermal expansion coefficient on one surface side and a large thermal expansion coefficient on the other surface side, that is, on both surfaces. Since the structures having remarkably different thermal expansion coefficients are used, there is a problem that the amount of thermal expansion differs between the two surfaces when heated during firing or sealing.

また、本願において、前記一般式Ｃで表されるペロブスカイト化合物には、その一般式Ｃの表示に拘らず、酸素数が３のものの他にそれよりも僅かに小さいものも含まれる。本発明において有効な酸素数は、酸素分圧によっても異なるので一義的に定めることはできないが、例えば、2.4〜3の範囲が好適である。   Further, in the present application, the perovskite compound represented by the general formula C includes a compound having a slightly smaller number of oxygen in addition to the one 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.

因みに、前記特許文献１４〜１６には、固体電解質膜と電極層(空気極または燃料極)間を組成傾斜させる技術が記載されている。これらは熱膨張差を緩和し或いは三相界面を増大することを目的とするものであって、固体電解質膜自体を組成傾斜させる本発明とは構成および目的が何れも相違する。   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.

また、前記特許文献１７には、固体電解質部に中間層(固体電解質)を形成して、空気極における電圧降下を低下させる技術が、前記特許文献１８には、固体電解質部を積層してイオン輸率を１に近づける技術が、それぞれ記載されているが、何れも還元耐久性を考慮したものではなく、本発明とは構成自体も相違する。   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.

また、前記非特許文献１には、CeO2酸化物イオン伝導体にフェライト化合物を混合した疑似混合伝導体、フェライト添加量の異なる２組成の膜を積層した酸素透過膜が記載されているが、膜表面における酸素交換反応を改善することを目的とするものであり、還元耐久性を考慮したものではない。 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.

また、前記特許文献１９には、グリーンシート製造時に生じる膜厚方向における充填状態等の違いによる収縮異方性すなわち両面における収縮率の相違に起因する反りや割れを抑制する目的で、偶数枚のグリーンシートを上下対称となるように貼り合わせる技術が記載されているが、固体電解質を組成傾斜させると共に、それに伴う熱膨張係数の相違を緩和しようとする本発明とは目的や構成が相違する。   Further, in Patent Document 19, an even number of sheets are used for the purpose of suppressing warping and cracking due to shrinkage anisotropy due to differences in the filling state in the film thickness direction and the like occurring during green sheet production, that is, differences in shrinkage rates on both sides. Although a technique for bonding green sheets so as to be vertically symmetrical is described, the object and configuration are different from the present invention in which the composition of the solid electrolyte is inclined and the difference in thermal expansion coefficient associated therewith is reduced.

また、前記第２発明によれば、第２層の酸素透過性能が十分に高く、且つ第１層および第３層の還元膨張率が十分に小さいことから、酸素製造やＧＴＬおよび燃料電池用の水素製造等に一層好適である。一層好適には、第２層の還元膨張率は0.20(％)以上であり、更に好適には、0.30(％)以上である。また、一層好適には、第１層および第３層の還元膨張率は0.13(％)以下であり、更に好適には、0.10(％)以下である。第２層と第１層および第３層の還元膨張率の相違は、0.10(％)以上であることが好ましく、0.20(％)以上相違することが更に好ましい。   Further, according to the second invention, since the oxygen permeation performance of the second layer is sufficiently high and the reductive expansion coefficients of the first layer and the third layer are sufficiently small, it is used for oxygen production, GTL and fuel cells. It is more suitable for hydrogen production and the like. More preferably, the reduction expansion coefficient of the second layer is 0.20 (%) or more, and more preferably 0.30 (%) or more. More preferably, the reduction expansion coefficients of the first layer and the third layer are 0.13 (%) or less, and more preferably 0.10 (%) or less. The difference in reduction expansion coefficient between the second layer, the first layer, and the third layer is preferably 0.10 (%) or more, and more preferably 0.20 (%) or more.

また、前記第３発明によれば、酸素分離膜の両面に備えられた第１層の厚さ寸法Ｘおよび第３層の厚さ寸法Ｙの相違が３倍未満(すなわち、1/3Ｘ＜Ｙ＜3Ｘ)に留められることから、厚さ寸法の相違に起因する熱膨張量の相違が十分に小さく留められ、延いては反りや割れの生ずる可能性が一層減じられる。すなわち、第１層および第３層の厚さ寸法は、両面における熱膨張量の相違が十分に小さくなるように定められることが好ましく、同一であることが最も好ましいが、これらの熱膨張量は材料組成すなわち材料の熱膨張係数と厚さ寸法とによって略決定される。そのため、好ましい厚さ寸法の範囲は必ずしも一義的に定め得るものではないが、熱容量等も考慮すると両層の厚さ寸法が著しく異なることは避けることが好ましい。したがって、熱膨張係数が同一或いは近似する材料を選択し、且つ厚さ寸法の相違を３倍以下に留めることが好ましいのである。   According to the third aspect of the invention, the difference between the thickness dimension X of the first layer and the thickness dimension Y of the third layer provided on both surfaces of the oxygen separation membrane is less than three times (that is, 1 / 3X <Y <3X), the difference in the amount of thermal expansion due to the difference in thickness dimension is kept sufficiently small, and the possibility of warping and cracking is further reduced. That is, the thickness dimensions of the first layer and the third layer are preferably determined so that the difference in the thermal expansion amount between both surfaces is sufficiently small, and most preferably the same, but the thermal expansion amount is It is substantially determined by the material composition, that is, the coefficient of thermal expansion and the thickness dimension of the material. For this reason, the preferable range of the thickness dimension is not necessarily uniquely defined, but it is preferable to avoid that the thickness dimension of the two layers is significantly different in consideration of the heat capacity and the like. Therefore, it is preferable to select a material having the same or similar thermal expansion coefficient and to keep the difference in thickness dimension to three times or less.

また、前記第４発明によれば、第２層の両面に設けられる第１層および第３層が同一材料で構成されることから、その両面における熱膨張係数が一致する。そのため、両面における熱膨張量が相違し、延いては反りや割れなどの生ずることが一層抑制される。すなわち、第１層および第３層の構成材料は、還元膨張率が第２層の構成材料よりも小さく且つ両面における熱膨張量の相違を十分に小さくできるのであれば特に限定されないが、両面における厚さ寸法の相違が小さいことが好ましいことから、熱膨張係数が同一或いは近似する材料で構成することが好ましく、同系材料、特に同一材料で構成することが最も好ましいのである。また、酸素分離膜全体における各層相互の熱膨張係数の相違を可及的に小さくするためには、第１層および第３層は、第２層と同系材料で構成することが好ましい。   According to the fourth aspect of the present invention, the first layer and the third layer provided on both surfaces of the second layer are made of the same material, so that the thermal expansion coefficients on both surfaces coincide. Therefore, the amount of thermal expansion on both sides is different, and further warpage and cracking are further suppressed. That is, the constituent materials of the first layer and the third layer are not particularly limited as long as the reductive expansion coefficient is smaller than that of the constituent material of the second layer and the difference in the amount of thermal expansion between both surfaces can be sufficiently reduced. Since it is preferable that the difference in thickness dimension is small, it is preferable that the material is composed of a material having the same or similar thermal expansion coefficient, and most preferably composed of a similar material, particularly the same material. In order to minimize the difference in thermal expansion coefficient between the layers in the entire oxygen separation membrane, the first layer and the third layer are preferably made of a material similar to the second layer.

なお、本願において「同系材料」とは、原則として構成元素が同一で各元素の割合のみが相違する材料を意味するものであるが、特性に著しい影響を与えない限りにおいて、一方のみに１乃至複数の元素が更に含まれていても差し支えない。また、「厚み方向において対称的」とは、材料および厚さ寸法が同一である場合に限られず、上記説明から明らかなように、第２層の両面の何れにもそれよりも低還元膨張率の層(すなわち第１層または第３層)が設けられていることを意味するものである。   In the present application, “similar materials” means materials having the same constituent elements but different only in the proportion of each element in principle. However, as long as the characteristics are not significantly affected, only 1 to A plurality of elements may be further included. Further, “symmetric in the thickness direction” is not limited to the case where the material and the thickness dimension are the same, and, as is clear from the above description, the reduction expansion coefficient lower than that on both sides of the second layer. This means that the first layer or the third layer is provided.

ここで、好適には、前記酸素分離膜は、厚み方向の中間部から前記一面および他面にそれぞれ向かうに従って還元膨張率が低下する傾斜組成を備えたものである。還元膨張に起因する不都合を抑制するためには、第２層よりも還元膨張率が十分に小さい限りにおいて、第１層および第３層よりも還元膨張率が大きい層が一面および他面に更に設けられていてもよい。しかしながら、そのような層を設ける利点が特になければ、層構成が簡単になり延いては製造工程が簡単になるように、上記のような傾斜組成とする方が好ましいのである。   Here, preferably, the oxygen separation membrane has a gradient composition in which the reduction expansion coefficient decreases from the intermediate portion in the thickness direction toward the one surface and the other surface. In order to suppress inconvenience due to reductive expansion, layers having a reductive expansion coefficient larger than those of the first layer and the third layer are further formed on one side and the other surface as long as the reductive expansion coefficient is sufficiently smaller than that of the second layer. It may be provided. However, if there is no particular advantage of providing such a layer, it is preferable to use the gradient composition as described above so that the layer structure is simplified and the manufacturing process is simplified.

すなわち、酸素分離膜は、前記第１層、第２層、および第３層が積層された３層構造に限られず、これらの何れとも組成が相違することにより還元膨張率が異なるものとされた他の層が、一面側または他面側に積層された４層以上の構成であっても良い。この場合、上記のような傾斜組成とすることが好ましいが、必須ではない。なお、積層数が多くなるほど工程的には不利であるが、接している層相互の熱膨張率の差を小さくできるため、製造過程や使用中に温度変化に曝された場合にも破損し難くなる利点がある。   That is, the oxygen separation membrane is not limited to the three-layer structure in which the first layer, the second layer, and the third layer are laminated, and the reduction expansion coefficient is different due to the difference in the composition of any of these. The other layer may have a configuration of four or more layers laminated on one side or the other side. In this case, it is preferable to use the gradient composition as described above, but it is not essential. As the number of layers increases, it is disadvantageous in terms of process, but since the difference in the coefficient of thermal expansion between the layers in contact can be reduced, it is difficult to break even when exposed to temperature changes during the manufacturing process or use. There are advantages.

また、好適には、前記第１層および前記第３層は、それぞれ50(μm)以上の厚さ寸法を備えたものである。第２層の還元膨張を抑制するための保護層としての機能を確保するためには、引掻き等による破損が生じないだけの機械的強度や、水蒸気雰囲気における長期間に亘る耐久性等が得られるように50(μm)以上の厚さ寸法を有することが好ましい。   Preferably, each of the first layer and the third layer has a thickness dimension of 50 (μm) or more. In order to ensure the function as a protective layer for suppressing the reductive expansion of the second layer, mechanical strength sufficient to prevent damage due to scratching, durability for a long period in a steam atmosphere, and the like can be obtained. Thus, it is preferable to have a thickness dimension of 50 (μm) or more.

因みに、第２層の一面のみに低還元膨張率の層を積層する場合に、その厚さ寸法が30(μm)を超えると、還元膨張率の大きい側すなわち熱膨張係数の大きい側に凹となる反りが無視できない程度まで顕著になる。すなわち、厚さ寸法が30(μm)以下であれば、両面における熱膨張量の相違によって発生する応力が極めて小さくなるため、特に高い形状精度が要求される場合を除いて反りや割れなどは殆ど問題にならないが、低還元膨張率の層を30(μm)を超える厚さ寸法で設ける場合には、本発明を適用する効果が顕著に得られる。なお、30(μm)以下の厚さ寸法で低還元膨張率の層を設けようとすると、形成方法がディップコーティング、スパッタリング、ＣＶＤ等の薄い層を形成し得るものに限定されるため、製造し得る大きさが比較的小さいものに限定されると共に、製造コストが高くなる不都合もある。本発明によれば、低還元膨張率の層の厚さ寸法が30(μm)を超えても差し支えないため、グリーンシートや焼結体を貼り合わせて焼成処理を施す等の安価で大型品(例えば、一辺が1(m)程度の矩形平板型や長さ寸法が1(m)程度の筒状等)の製造が可能な製造方法を採用し得る利点もある。   Incidentally, when a layer having a low reductive expansion coefficient is laminated on only one surface of the second layer, if the thickness dimension exceeds 30 (μm), a recess is formed on the side having a larger reductive expansion coefficient, that is, on the side having a larger thermal expansion coefficient. The warpage becomes remarkable to the extent that it cannot be ignored. In other words, if the thickness dimension is 30 (μm) or less, the stress generated by the difference in the amount of thermal expansion on both sides becomes extremely small, so there is almost no warpage or cracking unless particularly high shape accuracy is required. Although not a problem, when the layer having a low reduction expansion coefficient is provided with a thickness dimension exceeding 30 (μm), the effect of applying the present invention is remarkably obtained. If a layer with a thickness of 30 (μm) or less and a low reductive expansion coefficient is provided, the formation method is limited to those capable of forming a thin layer such as dip coating, sputtering, and CVD. In addition to being limited to a relatively small size, there are disadvantages in that the manufacturing cost increases. According to the present invention, since the thickness dimension of the layer having a low reductive expansion coefficient may exceed 30 (μm), an inexpensive and large-sized product such as a green sheet or a sintered body that is bonded and fired ( For example, there is an advantage that a manufacturing method capable of manufacturing a rectangular flat plate having a side of about 1 (m) or a cylinder having a length of about 1 (m) can be employed.

また、好適には、前記第１層および第３層は、それぞれ150(μm)未満の厚さ寸法を備えたものである。これら第１層および第３層は、第１層に比較すると酸素透過速度の低い材料で構成されることから、厚さ寸法が厚くなるほど酸素分離膜全体の酸素透過性能が低下する。そのため、酸素透過性能の十分に高い酸素分離膜を得るためには、上記厚さ寸法以下に留められることが好ましいのである。なお、第１層および第３層は、第２層を覆うことによってこれを還元雰囲気から保護するものであれば足り、例えば完全に覆うものであることが好ましいが、厚さ寸法の下限値は特になく、工業的には例えば1(μm)程度が下限値である。第１層および第３層がこの程度の厚さ寸法であっても、十分な還元耐久性を得ることができる。但し、前述したように、本発明は低還元膨張率の層の厚さ寸法が30(μm)を超えるときに特に有用性が高く、耐久性や機械的強度を考慮すると第１層および第３層が50(μm)以上であることが好ましい。   Preferably, each of the first layer and the third layer has a thickness dimension of less than 150 (μm). Since the first layer and the third layer are made of a material having a lower oxygen permeation rate than the first layer, the oxygen permeation performance of the entire oxygen separation membrane decreases as the thickness dimension increases. Therefore, in order to obtain an oxygen separation membrane having a sufficiently high oxygen permeation performance, it is preferable that the thickness is kept below the above thickness dimension. The first layer and the third layer are sufficient if they cover the second layer to protect it from the reducing atmosphere. For example, the first layer and the third layer are preferably completely covered, but the lower limit of the thickness dimension is In particular, the lower limit is industrially, for example, about 1 (μm). Even if the first layer and the third layer have such thickness dimensions, sufficient reduction durability can be obtained. However, as described above, the present invention is particularly useful when the thickness dimension of the low reductive expansion layer exceeds 30 (μm), and considering the durability and mechanical strength, the first layer and the third layer are considered. The layer is preferably 50 (μm) or more.

また、好適には、前記第２層は厚さ寸法を0.5(mm)としたときに8(cc/min/cm2)以上の酸素透過速度を有し、且つ前記第１層および前記第３層は厚さ寸法を0.5(mm)としたときに3(cc/min/cm2)以上の酸素透過速度を有するものである。このようにすれば、第２層の酸素透過速度が十分に高く且つ第１層および第３層の酸素透過速度が比較的高いことから、酸素透過性能が一層高く且つ還元耐久性に一層優れた酸素分離膜が得られる。一層好適には、第２層の酸素透過速度は10(cc/min/cm2)以上であり、第１層および第３層の酸素透過速度は5(cc/min/cm2)以上である。 Preferably, the second layer has an oxygen transmission rate of 8 (cc / min / cm 2 ) or more when the thickness dimension is 0.5 (mm), and the first layer and the third layer The layer has an oxygen transmission rate of 3 (cc / min / cm 2 ) or more when the thickness dimension is 0.5 (mm). In this way, the oxygen transmission rate of the second layer is sufficiently high and the oxygen transmission rates of the first layer and the third layer are relatively high, so that the oxygen transmission performance is higher and the reduction durability is more excellent. An oxygen separation membrane is obtained. More preferably, the oxygen transmission rate of the second layer is 10 (cc / min / cm 2 ) or more, and the oxygen transmission rate of the first layer and the third layer is 5 (cc / min / cm 2 ) or more. .

また、好適には、前記第２層の厚さ寸法は、0.4(mm)以下である。このようにすれば、第１層の厚さ寸法が十分に薄いことから、第１層および第３層の厚さ寸法を50(μm)以上にしても酸素分離膜全体の厚さ寸法が0.5(mm)以下に留められる。そのため、酸素透過性能の一層高い酸素分離膜が得られる。   Preferably, the thickness dimension of the second layer is 0.4 (mm) or less. In this case, since the thickness dimension of the first layer is sufficiently thin, even if the thickness dimension of the first layer and the third layer is 50 (μm) or more, the thickness dimension of the entire oxygen separation membrane is 0.5. (mm) or less. Therefore, an oxygen separation membrane with higher oxygen permeation performance can be obtained.

なお、第２層の膜厚は、高い酸素透過性能を得るためには可及的に薄いことが好ましく、後述するように多孔質支持体上に酸素分離膜を形成する場合には、膜厚寸法の下限値は特にないが、緻密な膜を形成できる程度の厚さ寸法とすることが好ましい。一方、多孔質支持体を用いない自立膜の場合には、酸素分離膜全体が自立可能な厚さ寸法、例えば0.5(mm)程度以上の厚さ寸法になるように第２層の厚さ寸法を定めればよい。   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 the 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.

なお、本発明の混合伝導体を構成するペロブスカイト化合物は、前記一般式Ｃに明示した元素の他に、Zn,In,V,Sn,Ge,Ce,Mg,Sc,Y等の他の元素が特性に実質的に影響を与えない程度の範囲で含まれていても差し支えない。また、第１層、第２層、および第３層は、上記ペロブスカイト化合物の他に、製造上排除することが困難な微量のAl2O3、SiO2、MgO、ZrO2等を含み得る。これらは微量が含まれていても特性に著しい影響を与えることはないが、何れもイオン伝導の抵抗になることから含有量は可及的に少ないことが望ましい。 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, the second layer, and the third layer may contain a trace amount of Al 2 O 3 , SiO 2 , MgO, ZrO 2, etc. 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.

また、好適には、前記第１の混合伝導体および前記第３の混合伝導体は、前記元素MがFe,Ti,Zr,Al,Co,Mn,Niの何れかである。このようにすれば、これらをＢサイトに含む(Ln1-xAex)MO3化合物は、還元耐久性が比較的高く且つ酸素透過速度も比較的高く、これらのバランスが良いことから、特に好ましい。また、Ｂサイトに、FeまたはCoを含むものは、電子伝導性が高くなることから一層好ましい。 Preferably, in the first mixed conductor and the third 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.

また、好適には、本発明の酸素分離膜は、多孔質支持体上にその一面全体を覆って備えられる。この多孔質支持体は、酸素分離膜の一面側および他面側の何れに位置させられても良い。このように多孔質支持体上に酸素分離膜が固定された酸素分離膜エレメントに構成すれば、ガス拡散係数の十分に高い多孔質支持体は、その内部を気体が容易に通過させられるので、適当な厚さ寸法に構成することにより、酸素透過性能に影響を与えることなく酸素分離膜エレメントの機械的強度を高め得る。しかも、酸素分離膜エレメントの機械的強度が多孔質支持体で確保されることから、酸素分離膜の厚さ寸法を酸素透過性能が膜厚で律速されない程度まで薄くすることが可能となるため、その表面積を増大させることによる透過性能向上効果が一層顕著に得られる。なお、このような多孔質支持体が備えられる場合において、更に酸素解離触媒層または酸素再結合触媒層が設けられる場合には、一方が酸素分離膜の表面に、他方が酸素分離膜と多孔質支持体との間にそれぞれ設けられてもよいが、その他方は、多孔質支持体の表面に、好適にはこれに浸透させられた状態で設けられても良い。   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 dimension, the mechanical strength of the oxygen separation membrane element can be increased without affecting the oxygen permeation performance. 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 permeation performance is not limited by the film thickness, The effect of improving the permeation performance 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.

なお、上記態様において「一面全体を覆って」とは、酸素分離膜エレメントの使用時において、多孔質支持体の一面が酸素分離膜のその多孔質支持体とは反対側に位置する面と同一空間内に曝されないことを意味するものである。例えば、非使用状態において酸素分離膜が設けられた多孔質支持体の一面が部分的に露出させられていても、その部分が使用時に装置等によって覆われるものであれば、そのような態様も上記「一面全体を覆って」に含まれる。   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”.

また、好適には、前記酸素分離膜および前記多孔質支持体は、同材料から成るものである。このようにすれば、両者の熱膨張係数が一致することから、製造工程や使用時に加熱或いは冷却された場合にも、熱膨張量の相違に起因して破損することが好適に抑制される。   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.

また、好適には、前記酸素分離膜および前記多孔質支持体は、相互に異なる組成の材料から成るものである。酸素分離膜エレメント全体の強度は支持体によって確保する必要があることから、支持体と酸素分離膜とは求められる特性が相違するため、例えば要求される強度が比較的高い場合には、酸素分離膜と支持体とを相互に異なる材料で構成することが望ましい。このような支持体構成材料としては、例えば、ジルコニア、アルミナ、窒化珪素、炭化珪素等が好適である。   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.

また、好適には、前記多孔質支持体は、平均細孔径ｒが0.1＜ｒ＜20(μm)の範囲内、気孔率ｐが5＜ｐ＜80(％)の範囲内である。酸素透過性能の低下を抑制し且つ酸素分離膜エレメントの強度を可及的に高めるためには、この範囲内が好ましい。細孔径および気孔径が小さくなり過ぎると、多孔質支持体のガス透過抵抗が大きくなることから、酸素分離膜を薄くしてもこの多孔質支持体が律速因子になるため、酸素透過性能が著しく低下する。一方、細孔径および気孔径が大きくなり過ぎると、機械的強度が低下して支持体としての機能が失われる。   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 oxygen permeation performance 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 performance 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.

また、好適には、前記酸素分離膜の一面および他面の少なくとも一方には、前記酸素の解離または再結合を促進するための触媒層が備えられる。このようにすれば、触媒層によって酸素の解離或いは再結合が促進されることから、一層効率の高い酸素分離膜エレメントが得られる。一層好適には、一面および他面の一方に酸素解離触媒層および酸素再結合触媒層の一方が、一面および他面の他方に酸素解離触媒層および酸素再結合触媒層の他方が、それぞれ設けられる。なお、触媒層は、緻密質に構成されていても、多孔質に構成されていてもよく、酸素分離膜でこれを兼ねることもできる。   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.

また、好適には、前記酸素解離触媒層は、La-Sr-Co系酸化物、La-Sr-Mn系酸化物、白金系元素である。一層好適には、LaxSr1-xCoO3(0≦x≦1、好適にはx＝0.6)から成るものである。このような触媒によれば、酸素分離膜の一面側に供給された気体中の酸素が好適にイオン化され、これを透過して他面側に導かれる。なお、触媒層は、上記材料の他、SmxSrCoO3(0≦x≦1、好適にはx＝0.5)、La1-xSrxMnO3(0≦x≦1、好適にはx＝0.15)、La1-xSrxCo1-yFeyO3(0≦x≦1、0＜y＜1、好適にはx＝0.9、y＝0.1)等も好適に用いられる。なお、酸素解離触媒層は、酸素分離膜と同じ材料で構成することもでき、その場合には、その酸素分離膜の一部で酸素解離触媒層を構成し得る。 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.

また、好適には、前記酸素再結合触媒層は、Ni、Co、Ru、Rh、Pt、Pd、Ir等を含むものである。好適には、NiOが還元されることにより形成されたNiから成るものである。このような触媒によれば、酸素分離膜の他面側に導かれた酸素イオンが好適に再結合させられ、その他面側から酸素が回収される。また、酸素解離触媒層および酸素再結合触媒層が上述したような何れの材料で構成される場合にも、酸素は粒界または粒内を透過し得るため、多孔質はもちろん緻密質の触媒層も形成し得る。   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.

また、本発明の酸素分離膜は、その一面側に酸素を含む気体を供給するための第１気体供給路と、その他面側に所定の化合物を含む気体を供給するための第２気体供給路と、その他面側において酸素と前記所定の化合物との反応により生成された気体を回収するための気体回収路とを、含む反応器にも好適に用いられる。このようにすれば、第１気体供給路からその一面側に酸素を含む気体が、第２気体供給路からその他面側に所定の化合物を含む気体がそれぞれ供給され、酸素とその所定の化合物との反応により生成された気体が気体回収路から回収される。そのため、安価且つ高効率で耐久性の高い反応器が得られる。   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.

また、本発明の酸素分離膜は、前述した酸素製造や炭化水素の部分酸化反応等の他、一面側にNOxを供給することにより、その還元にも用いることができる。 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.

また、好適には、前記酸素分離膜は全体が平坦な板状を成すものである。また、触媒層が備えられた態様においては、その一面に前記酸素解離触媒層が、他面に前記酸素再結合触媒層がそれぞれ備えられたものである。このような板状の酸素分離膜が多孔質支持体上に備えられ且つ触媒層が備えられた態様では、別途形成された酸素分離膜の両面に触媒層が設けられた後、多孔質支持体に固着され、或いは、多孔質支持体上に一方の触媒層、酸素分離膜、および他方の触媒層が順次に形成されることによって酸素分離膜エレメントが製造される。上記平坦な板状としては、円板状、矩形板状等が挙げられる。   Preferably, the oxygen separation membrane has a flat plate shape as a whole. Further, in the aspect in which the catalyst layer is provided, 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.

また、好適には、前記酸素分離膜は一端が閉じた筒状を成すものであり、触媒層が備えられる態様においては、その内周面および外周面の一方が前記酸素解離触媒層が備えられた前記一面に相当し、他方が前記酸素再結合触媒層が備えられた前記他面に相当するものである。酸素分離膜は、平坦なものに限られず、このような立体的なものであっても良い。なお、内周面側に気体の供給される態様では、例えば、筒状の酸素分離膜の内側に気体導入管を挿入し、その先端から気体を供給すればよい。   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.

また、好適には、前記多孔質支持体は一端が閉じた筒状を成し、前記酸素分離膜、または前記二種の触媒層および酸素分離膜はその内周面または外周面に順次に積層されることによって設けられたものである。このようにすれば、酸素分離膜エレメントが筒状を成す態様においても多孔質支持体によってその機械的強度を確保することができる。   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.

また、本発明の酸素分離膜は、例えば、前記第１の混合伝導体材料粉末、前記第２の混合伝導体材料粉末、および前記第３の混合伝導体材料粉末にそれぞれ所定のバインダーを混合して所定粒径に造粒する工程と、造粒粉を所定形状にそれぞれ成形する工程と、成形体に所定温度の焼成処理を施して第１の混合伝導体から成る膜、第２の混合伝導体から成る膜、および第３の混合伝導体から成る膜をそれぞれ得る工程と、それら３つの膜を重ね合わせて所定の焼成処理を施すことによって相互に接合する工程とを、含む工程によって製造される。上記成形工程と焼成工程との間には、必要に応じて、成形体を等方圧で加圧(例えば湿式静水圧加圧)する工程と、成形体を大気中で焼成温度よりも十分に低温で加熱することによって有機物を分解除去する工程とが実施される。また、焼成後には必要に応じて機械研磨工程が施される。   In the oxygen separation membrane of the present invention, for example, a predetermined binder is mixed in each of the first mixed conductor material powder, the second mixed conductor material powder, and the third mixed conductor material powder. A step of granulating to a predetermined particle size, a step of forming the granulated powder into a predetermined shape, a film made of the first mixed conductor by subjecting the formed body to a firing process at a predetermined temperature, and a second mixed conduction And a third mixed conductor film, and a step of joining the three films together by applying a predetermined baking process. The 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.

また、上記所定の成形工程は、例えば、前記第１の混合伝導体材料粉末を含む第１のスラリー、前記第２の混合伝導体材料粉末を含む第２のスラリー、および前記第３の混合伝導体材料粉末を含む第３のスラリー中にセラミック焼結体から成る所定の多孔質支持体を順次に浸漬して、その多孔質支持体の表面にそれら第１のスラリー乃至第３のスラリーを塗布するものである。このようにすれば、その多孔質支持体に塗布されたスラリーを焼成することにより、多孔質支持体上にその塗布厚みに応じた膜厚で形成された第１層乃至第３層から成る組成傾斜型酸素分離膜が固着された酸素分離膜エレメントが得られる。   Further, the predetermined forming step includes, for example, a first slurry containing the first mixed conductor material powder, a second slurry containing the second mixed conductor material powder, and the third mixed conduction. A predetermined porous support made of a ceramic sintered body is sequentially immersed in a third slurry containing body material powder, and the first to third slurries are applied to the surface of the porous support. To do. In this case, the composition comprising the first layer to the third layer formed on the porous support with a film thickness corresponding to the applied thickness by firing the slurry applied to the porous support. An oxygen separation membrane element to which an inclined oxygen separation membrane is fixed is obtained.

また、本発明の酸素分離膜は、例えば、第１の混合伝導体材料粉末、第２の混合伝導体材料粉末、および第３の混合伝導体材料粉末を含むスラリーを用いてグリーンシートを成形する工程と、それらグリーンシートを重ね合わせて同時に焼成処理を施す工程とを、含む工程によって製造することもできる。   The oxygen separation membrane of the present invention forms a green sheet using a slurry containing, for example, a first mixed conductor material powder, a second mixed conductor material powder, and a third mixed conductor material powder. It can also be manufactured by a process including a process and a process in which the green sheets are superposed and simultaneously fired.

また、多孔質支持体上に酸素分離膜を製膜する場合には、上記のようなスラリーをディップコートする工程と、これに焼成処理を施す工程とを、含む工程によって製造することもできる。更に、その多孔質支持体上にスパッタリングや溶射等によって第１層〜第３層すなわち酸素分離膜を形成してもよい。   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.

以下、本発明の一実施例を図面を参照して詳細に説明する。なお、以下の実施例において図は適宜簡略化或いは変形されており、各部の寸法比および形状等は必ずしも正確に描かれていない。   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.

図１は、本発明の一実施例の酸素分離膜１０の構成を説明するための断面構造を模式的に示す図である。酸素分離膜１０は、20(mm)程度の直径を備えて全体が0.5(mm)程度の厚さ寸法の薄板円板状を成すものであり、厚み方向において、図１における上側から、第１層１２，第２層１４，および第３層１６が積層された３層構造の積層体に構成されている。これら３層の外周端面はガラス等から成るシール部材１８で気密にシールされている。   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 in the thickness direction, from the upper side in FIG. The layer 12, the second layer 14, and the third layer 16 are stacked in a three-layer structure. The outer peripheral end faces of these three layers are hermetically sealed with a sealing member 18 made of glass or the like.

上記の第１層１２〜第３層１６は、何れも、例えば一般式(Ln1-xAex)MO3で表されるランタン系ペロブスカイト化合物で構成された緻密な膜である。このペロブスカイト化合物は、酸素イオン伝導性および電子伝導性を共に有する混合伝導性セラミックスである。そのため、緻密質でありながら、その一面２０または他面２２に接した酸素をイオン化して例えばその他面２２から一面２０に向かって透過させることができる。 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.

上記の第１層１２および第３層１６は、La0.6Sr0.4Ti0.3Fe0.7OxやLa0.6Sr0.4Zr0.3Fe0.7Ox等(但し、ｘ＝2.4〜3程度。以下、各ペロブスカイト化合物において同じ。)から成るもので、例えば、0.05〜0.1(mm)程度の厚さ寸法を備えている。また、第２層１４は、La0.6Sr0.4Ti0.1Fe0.9OxやLa0.6Sr0.4Zr0.1Fe0.9Ox等から成るもので、例えば、0.3〜0.4(mm)程度の厚さ寸法を備えている。すなわち、第２層１４と、第１層１２および第３層１６とは、互いに組成が相違し、酸素分離膜１０は、厚み方向において組成の異なる膜が積層された組成傾斜膜に構成されている。 The first layer 12 and third layer 16 of the above, La 0.6 Sr 0.4 Ti 0.3 Fe 0.7 O x and La 0.6 Sr 0.4 Zr 0.3 Fe 0.7 O x or the like (where, x = from 2.4 to 3 degrees. Hereinafter, each perovskite compound The same as the above), and has a thickness dimension of about 0.05 to 0.1 (mm), for example. The second layer 14 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 0.3 to 0.4 (mm), for example. ing. That is, the second layer 14, the first layer 12, and the third layer 16 have different compositions, and the oxygen separation film 10 is configured as a composition gradient film in which films having different compositions in the thickness direction are stacked. Yes.

また、上記の第２層１４を構成する混合伝導体(すなわち第２の混合伝導体)は、例えば0.28〜0.7(％)程度の大きい還元膨張率と、11.0(cc/min/cm2)以上の高い酸素透過速度(厚さ寸法が0.5(mm)のときの値。以下、特に断らない限り同じ。)とを有している。また、第１層１２および第３層１６を構成する混合伝導体(すなわち、第１の混合伝導体および第３の混合伝導体)は、0.06〜0.32(％)程度の比較的低い還元膨張率と、3.3〜6.1(cc/min/cm2)程度の比較的低い酸素透過速度とを有している。また、第２の混合伝導体の熱膨張係数は13.1〜14.0(×10-6/℃)程度であり、第１の混合伝導体および第３の混合伝導体の熱膨張係数は11.4〜12.9(×10-6/℃)程度である。なお、本実施例においては、第１の混合伝導体と第３の混合伝導体が同一材料で構成されており、厚さ寸法も同一である。 Further, the mixed conductor (that is, the second mixed conductor) constituting the second layer 14 has a large reduction expansion coefficient of, for example, about 0.28 to 0.7 (%) and 11.0 (cc / min / cm 2 ) or more. And a high oxygen permeation rate (value when thickness dimension is 0.5 (mm), hereinafter the same unless otherwise specified). In addition, the mixed conductor constituting the first layer 12 and the third layer 16 (that is, the first mixed conductor and the third mixed conductor) has a relatively low reduction expansion coefficient of about 0.06 to 0.32 (%). And a relatively low oxygen transmission rate of about 3.3 to 6.1 (cc / min / cm 2 ). The thermal expansion coefficient of the second mixed conductor is about 13.1 to 14.0 (× 10 −6 / ° C.), and the thermal expansion coefficients of the first mixed conductor and the third mixed conductor are 11.4 to 12.9 ( × 10 -6 / ° C) In the present embodiment, the first mixed conductor and the third mixed conductor are made of the same material, and the thickness dimension is also the same.

そのため、酸素分離膜１０は、第２層１４から第１層１２および第３層１６のそれぞれに向かうに従って還元膨張率が小さくなると共に、酸素透過速度が低くなる層構造を備えている。しかしながら、酸素透過速度の低い混合伝導体から成る第１層１２および第３層１６は、0.1(mm)以下の薄い膜であり、酸素透過性能は膜厚に反比例するため、酸素透過速度が低い混合伝導体から成る第１層１２および第３層１６における酸素透過性能は比較的高い値になる。したがって、第１層１２および第３層１６における酸素透過性能が酸素分離膜１０全体の酸素透過性能の律速にならないことから、酸素分離膜１０の酸素透過性能は、第２層１４を構成する混合伝導体で全体を構成した場合と同等の高い値になる。   Therefore, the oxygen separation membrane 10 has a layer structure in which the reduction expansion coefficient decreases and the oxygen transmission rate decreases as it goes from the second layer 14 to each of the first layer 12 and the third layer 16. However, the first layer 12 and the third layer 16 made of the mixed conductor having a low oxygen transmission rate are thin films of 0.1 (mm) or less, and the oxygen transmission performance is inversely proportional to the film thickness, so that the oxygen transmission rate is low. The oxygen permeation performance in the first layer 12 and the third layer 16 made of the mixed conductor is relatively high. Therefore, the oxygen permeation performance in the first layer 12 and the third layer 16 does not become the rate-determining function of the oxygen permeation performance of the oxygen separation membrane 10 as a whole. It becomes a high value equivalent to the case where the whole is composed of a conductor.

以上のように構成される酸素分離膜１０は、一面２０および他面２２上に触媒層２４，２６をそれぞれ設けて、例えば第１層１２を還元側、例えばメタン等の燃料供給側に位置させ、その反対側に位置する第３層１６を酸化側、例えば空気等の酸素含有ガス供給側に位置させて用いられる。そのため、還元膨張率の大きい第２層１４が、その第１層１２によって還元雰囲気から保護されるため、酸素分離膜１０の還元耐久性が高められる。   The oxygen separation membrane 10 configured as described above is provided with the catalyst layers 24 and 26 on the one surface 20 and the other surface 22, respectively, and for example, the first layer 12 is positioned on the reduction side, for example, the fuel supply side such as methane. The third layer 16 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 having a large reduction expansion coefficient is protected from the reducing atmosphere by the first layer 12, the reduction durability of the oxygen separation membrane 10 is enhanced.

なお、酸化側に設けられる酸素解離触媒層２６は、他面２２における酸素の解離およびイオン化を促進するために設けられたものであり、例えばLa0.6Sr0.4CoO3から成る多孔質層が10(μm)程度の一様な厚さ寸法を以て他面２２の略全面に形成される。 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).

また、還元側に設けられる酸素再結合触媒層２６は、一面２０における酸素イオンの再結合を促進するために設けられたものであり、例えばNiOから成る多孔質層が100(μm)程度の一様な厚さ寸法を以てその一面２０の略全面に形成される。   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.

図２は、上記酸素分離膜１０における使用時の酸素分圧を説明する模式図である。図２に示す太線は、雰囲気中および膜内における酸素分圧P1〜P4(すなわち酸素分圧勾配)を、白抜きの矢印は、酸素分離膜１０内における酸素イオンおよび電子の動きを、それぞれ表している。酸素がイオン化して空気側から還元側に向かって移動すると、酸素分離膜１０内には、その移動速度に応じた酸素分圧の勾配が形成される。酸素イオン伝導率が低い第１層１２内では、その勾配が著しく大きくなる。そのため、図２に示されるように、酸素分圧は第１層１２内を還元側雰囲気から第２層１４に向かうに従って急激に高められるので、界面３６における酸素分圧P2は、例えば還元側の酸素分圧P1の1010倍以上に大きくなる。そのため、第２層１４が還元膨張率の大きい混合伝導体で構成されていても、これに負荷される還元力は還元側の1/1010以下になるため、その還元膨張延いては破損が好適に抑制されるのである。 FIG. 2 is a schematic diagram for explaining the oxygen partial pressure during use in the oxygen separation membrane 10. The thick lines shown in FIG. 2 indicate oxygen partial pressures P 1 to P 4 (that is, oxygen partial pressure gradients) in the atmosphere and in the membrane, and the white arrows indicate the movement of oxygen ions and electrons in the oxygen separation membrane 10. Represents each. When oxygen is ionized and moves from the air side toward the reduction side, a gradient of oxygen partial pressure corresponding to the moving speed is formed in the oxygen separation membrane 10. In the first layer 12 having a low oxygen ion conductivity, the gradient becomes remarkably large. Therefore, as shown in FIG. 2, the oxygen partial pressure is rapidly increased toward the reduction side atmosphere a first layer 12 to second layer 14, the oxygen partial pressure P 2 at the interface 36, for example, reducing side oxygen partial becomes larger than 10 10 times the pressure P 1 of the. For this reason, even if the second layer 14 is composed of a mixed conductor having a large reduction expansion coefficient, the reduction force applied to the second layer 14 is 1/10 10 or less of the reduction side. It is preferably suppressed.

上述したように、本実施例の酸素分離膜１０によれば、La0.6Sr0.4Ti0.1Fe0.9Ox等の混合伝導体から成る第２層１４の両面にLa0.6Sr0.4Ti0.3Fe0.7Ox等の混合伝導体から成る第１層１２，第３層１６が積層された積層構造に構成される。そのため、酸素分離膜１０は、還元膨張率が大きく且つ酸素透過性能の高い第２層１４に、還元膨張率が小さく且つ酸素透過性能の低い第１層１２，第３層１６が積層された組成傾斜型になる。したがって、第２層１４が第１層１２によって(前記説明とは反対に第３層１６が還元雰囲気側に配置される場合には、第３層１６によって)還元雰囲気から保護され、延いては酸素分離膜全体の還元耐久性を十分に高めることができる。また、第１層１２，第３層１６は十分に薄いので、これを構成する混合伝導体の酸素透過性能が低くとも、酸素分離膜全体の高い酸素透過性能を得ることができる。上記により、要求される還元耐久性と所望する酸素透過性能とを比較考慮して、第１層１２、第２層１４、および第３層１６の膜厚や、それらを構成する混合伝導体の組成を定めることによって、酸素透過性能が高く且つ還元耐久性に優れた酸素分離膜１０が得られる。 As described above, according to the oxygen separation membrane 10 of the present embodiment, La 0.6 Sr 0.4 Ti 0.3 Fe 0.7 O is formed on both surfaces of the second layer 14 made of a mixed conductor such as La 0.6 Sr 0.4 Ti 0.1 Fe 0.9 O x. The first layer 12 and the third layer 16 made of a mixed conductor such as x are stacked to form a stacked structure. Therefore, the oxygen separation membrane 10 has a composition in which the first layer 12 and the third layer 16 having a low reduction expansion coefficient and a low oxygen permeation performance are stacked on the second layer 14 having a high reduction expansion coefficient and a high oxygen permeation performance. Be inclined. Therefore, the second layer 14 is protected from the reducing atmosphere by the first layer 12 (in the case where the third layer 16 is disposed on the reducing atmosphere side, as opposed to the above description), and thus extended. The reduction durability of the entire oxygen separation membrane can be sufficiently increased. In addition, since the first layer 12 and the third layer 16 are sufficiently thin, high oxygen permeation performance of the entire oxygen separation membrane can be obtained even if the oxygen permeation performance of the mixed conductor constituting the first layer 12 and the third layer 16 is low. Based on the above, in consideration of the required reduction durability and the desired oxygen permeation performance, the film thicknesses of the first layer 12, the second layer 14, and the third layer 16 and the mixed conductors constituting them are determined. By determining the composition, the oxygen separation membrane 10 having high oxygen permeation performance and excellent reduction durability can be obtained.

しかも、本実施例においては、還元側に設けられた第１層１２と同一の混合伝導体から成る第３層１６が酸化側にも同一の厚さ寸法で設けられていることから、使用時等において酸素分離膜１０が高温に曝された場合にも、その両面における熱膨張量の相違が生じない。そのため、受けた熱履歴に起因する酸素分離膜１０の反りや割れが好適に抑制される利点もある。   In addition, in this embodiment, the third layer 16 made of the same mixed conductor as the first layer 12 provided on the reduction side is provided on the oxidation side with the same thickness dimension. Even when the oxygen separation membrane 10 is exposed to a high temperature, etc., there is no difference in the amount of thermal expansion between the two surfaces. Therefore, there also exists an advantage by which the curvature and the crack of the oxygen separation membrane 10 resulting from the received heat history are suppressed suitably.

図３は、上記の酸素分離膜１０の製造方法を説明するための工程図である。造粒工程Ｐ１では、例えば市販の平均粒径が1(μm)程度のLaSrTiFeOx系粉末やLaSrZrFeOx系粉末に、水、有機バインダー等の成形助剤、および分散剤を混合してスラリーを作成し、例えばスプレー・ドライヤーを用いて60(μm)程度の平均粒径の原料粉末を噴霧造粒する。次いで、加圧成形工程Ｐ２では、造粒した原料粉末を例えば100(MPa)程度の適当な圧力でプレス成形して、例えば直径が30(mm)程度で、厚さ寸法が3(mm)程度の円板状の成形体を得る。なお、上記成形体寸法は前記寸法の第１層１２等が得られるように焼成収縮や研磨代を考慮して定めた値である。また、必要に応じ、静水圧加圧成形(すなわちＣＩＰ)により150(MPa)程度の加圧処理を施すことができる。 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).

次いで、焼成工程Ｐ３では、上記の成形体を例えば大気中において200〜500(℃)程度の温度で10時間程度保持して有機物を分解除去した後、更に大気中において1300〜1600(℃)程度の温度で3時間程度保持することにより、この成形体を焼成する。厚み研磨工程Ｐ４においては、このようにして得られた緻密な焼結体に平面研削盤等を用いて機械研磨加工を施し、例えば0.05〜0.5(mm)程度の予め定められた厚さ寸法の薄膜体に加工する。   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.

次いで、積層・接合工程Ｐ５では、作成した薄膜体を高還元膨張率のものが低還元膨張率のもので挟まれるように３枚重ね合わせ、大気中において1300〜1600(℃)で焼成処理を施す。これにより、それら重ね合わせた３枚の薄膜体が相互に接合され、組成の相互に異なる３層(但し、外側の２層は例えば同一組成)が厚み方向に積層された組成傾斜膜すなわち酸素分離膜１０が得られる。   Next, in the lamination / bonding step P5, three thin film bodies are stacked so that the one with a high reduction expansion coefficient is sandwiched between the ones with a low reduction expansion coefficient, and fired at 1300 to 1600 (° C) in the atmosphere. Apply. As a result, the three laminated thin film bodies are bonded to each other, and a composition gradient film in which three layers having different compositions (the outer two layers, for example, the same composition) are laminated in the thickness direction, that is, oxygen separation A membrane 10 is obtained.

このような酸素分離膜１０は、その両面２０，２２に前記のように触媒層を設けて用いられる。触媒担持工程Ｐ６では、例えば平均粒径が2(μm)程度の市販のLa0.6Sr0.4CoO3粉末を有機溶剤と混合してスラリーを調製し、これを一面２０に塗布して触媒を印刷担持すると共に、例えば平均粒径が7(μm)程度の市販のNiO粉末を有機溶剤と混合してスラリーを調製し、これを他面２２に塗布して触媒を印刷担持する。そして、焼き付け工程Ｐ７において、例えば1000(℃)程度の温度で１時間程度の時間保持して、一面２０および他面２２に触媒層をそれぞれ焼き付けることにより、前記の酸素分離膜１０が得られる。 Such an oxygen separation membrane 10 is used by providing a catalyst layer 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 membrane 10 is obtained by baking the catalyst layer 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.

以下、本発明の更に具体的な実施例を説明する。下記の表１は、前記の酸素分離膜１０を構成する第１層１２〜第３層１６の組成例と、それぞれの還元膨張率、酸素透過速度、還元耐久性、および熱膨張係数をまとめたものである。なお、表１の「組成名」欄には、各組成の混合伝導体を意味するものとして後述する表２、３において用いた略称を示した。まず、各層を構成するこれら６種類の混合伝導体の特性について説明する。   Hereinafter, more specific examples of the present invention will be described. Table 1 below summarizes the composition examples of the first layer 12 to the third layer 16 constituting the oxygen separation membrane 10 and the respective reduction expansion coefficient, oxygen permeation rate, reduction durability, and thermal expansion coefficient. Is. In the “Composition Name” column of Table 1, the abbreviations used in Tables 2 and 3 described later are shown as meaning the mixed conductor of each composition. First, the characteristics of these six kinds of mixed conductors constituting each layer will be described.

Figure 0004500762
Figure 0004500762

上記の表１において、還元膨張率は、大気中とH2５％＋N2９５％雰囲気中とで熱膨張率をそれぞれ測定し、前記(１)式に従って算出した。 In Table 1 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 .

また、酸素透過速度は、上記の各組成から成る0.5(mm)厚の混合伝導体薄板を前記図３に示される工程に従って製造し、その薄板の両面に前記触媒を焼き付けたものを試料として、図４に示される反応器４０において、酸素分離膜１０に代えて試料を配設することによって測定した。   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.

なお、上記の反応器４０は、例えば両端を開放されたアルミナ等のセラミックスから成る円筒管４２、４４が、酸素分離膜１０を挟んで上下に配置され、且つ、それらの内周側に例えばアルミナ等のセラミックスから成る気体導入管４８，５０が挿入されたものである。酸素分離膜１０は、酸素再結合触媒層が設けられている一面２０が円筒管４４側に位置し、酸素解離触媒層が設けられている他面２２が図４における上側すなわち円筒管４２側に位置する向きで配置される。また、円筒管４２，４４の外周側にはヒータ５６，５６が配置されている。また、円筒管４２，４４と酸素分離膜１０とは、例えばガラス系等の封着材５８，５８によって気密に封着されている。なお、気体導入管４８，５０は、酸素分離膜１０の表面から気体供給に必要な距離だけ離隔して配置されている。   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.

このような反応器４０において、ヒータ５６で装置内を1000(℃)程度の温度に加熱しつつ、気体導入管４８から空気すなわち酸素を含む気体を円筒管４２内に導入すると共に、燃料側すなわち気体導入管５０から純メタンガス等の炭化水素を導入する。空気導入量は例えば10〜500(cc/min)程度であり、メタンガス導入量は例えば10〜200(cc/min)程度である。なお、測定に先立ち、例えばヒータ５６によって円筒管４４内を1000(℃)程度の温度に加熱しつつ、例えば水素10(％)とアルゴン90(％)との混合ガスを気体導入管５０から円筒管４４内に供給し、還元雰囲気下で加熱する。これにより、一面２０に備えられている酸素再結合触媒層すなわちニッケル酸化物が部分的に或いは完全に還元され、酸素再結合触媒としての機能が発揮されるようになる。   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.

上記のように気体導入管４８から導入された空気は、酸素分離膜１０の表面および酸素解離触媒層に接触しつつ、気体導入管４８と円筒管４２との間に形成された排気路６０を通って図４に矢印で示されるように排気される。このとき、酸素分離膜１０およびその他面２２に設けられた酸素解離触媒層の酸素解離作用およびイオン化作用により、空気中の酸素が解離されてイオン化させられるので、その酸素イオンは、酸素イオン伝導性を有する酸素分離膜１０を通って他面２２側から一面２０側に向かって図４に矢印で示されるように輸送される。   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.

そして、一面２０に到達した酸素イオンは、混合伝導体から成る酸素分離膜１０およびその一面２０に設けられた酸素再結合触媒層の再結合作用により酸素分子となり、その一面２０から取り出される。これにより、酸素が他面２２側から一面２０側に透過することになる。しかしながら、混合伝導体から成る酸素分離膜１０は緻密質であると共に他の気体はイオン化させられないので、酸素以外の気体は全く透過しない。すなわち、空気から純度の極めて高い酸素が製造される。   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.

また、このようにして透過した酸素は、イオンのまま或いは再結合させられた後、気体導入管５０から導入されたメタンガス等とその一面２０上、酸素再結合触媒層内、或いはそれらの近傍において反応させられ、下記(２)式に示されるようなメタンの部分酸化反応が生じる。生成された一酸化炭素と水素との合成ガスは、気体導入管５０と円筒管４４との間に形成された回収路６２から回収される。回収された合成ガスは、例えば、液体燃料合成等に用いられる。なお、以上の説明から明らかなように、気体導入管５０からメタンガスを導入しない場合には、回収路６２から酸素を回収することができ、反応器４０を酸素製造装置として用いることができる。
CH4＋1/2O2 → CO＋2H2 ・・・(２) 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 (2). 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 (2)

また、前記表１に示す還元耐久性は、上記の試験を連続して実施して、還元側で回収された合成ガス中の窒素量を測定し、その変化から窒素リーク率ＬNを下記(３)式に従って求めて判断した。◎は３〜１０時間で窒素リーク率の増大が無かったもの、○は３時間以内に窒素リーク率が１(％)以下の範囲で増大したもの、△は３時間以内に窒素リーク率が１〜３(％)の範囲で増大したもの、×は３時間以内に窒素リーク率が３(％)以上増大したものである。１０時間で窒素リーク率の増大がなければ、長時間に亘る十分な還元耐久性があるものと考えられる。
ＬN ＝［N2量(cc/min)／全ガス量(cc/min)］×100 ・・・(３) In addition, the reduction durability shown in Table 1 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 ( It was determined and determined according to equation 3). ◎: 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 Increased in a range of ˜3 (%), and × indicates an increase in nitrogen leakage 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 over a long period of time.
L N = [N 2 amount (cc / min) / total gas amount (cc / min)] × 100 (3)

また、酸素透過速度は、上記の試験を２４時間連続して行って、合成ガスおよび排気ガスをガスクロマトグラフィで測定し、合成ガス中の酸素濃度と流量、および酸素分離膜１０の酸素透過部面積から算出した。   The oxygen permeation rate was determined by continuously performing the above test for 24 hours, measuring the syngas and exhaust gas by gas chromatography, the oxygen concentration and flow rate in the syngas, and the oxygen permeation area of the oxygen separation membrane 10. Calculated from

前記の表１に示されるように、酸素分離膜１０の各層を構成する混合伝導体は、何れも、還元耐久性と酸素透過速度とがトレードオフの関係にあり、還元膨張率を小さくして還元耐久性を高めようとすると、酸素透過速度が低くなる特性を有している。酸素分離膜１０の一般的な用途では、還元割れを発生させないためには、還元膨張率が0.14(％)未満であることが望ましいが、そうすると、何れの材料系でも6(cc/min/cm2)以下の材料に限定される。そのため、従来のように酸素分離膜１０を単層で構成し、単に組成を変更するだけでは、還元耐久性および酸素透過速度を共に高くすることは不可能である。 As shown in Table 1 above, all the mixed conductors constituting each layer of the oxygen separation membrane 10 have a trade-off relationship between the reduction durability and the oxygen transmission rate, 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, but in that case, any material system has 6 (cc / min / cm). 2 ) Limited to the following materials. 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.

表２に示す実施例１〜１０は、上記の表１に掲げた混合伝導体で前記第１層１２等を構成した３層の積層構造(すなわち組成傾斜膜)の層構成例である。また、表３に示す比較例１〜１０は、表１に掲げた混合伝導体を用いた２層または本発明の範囲外の積層構造とした層構成例である。   Examples 1 to 10 shown in Table 2 are layer configuration examples of a three-layer laminated 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 1 above. Further, Comparative Examples 1 to 10 shown in Table 3 are layer configuration examples having two layers using the mixed conductors listed in Table 1 or a laminated structure outside the scope of the present invention.

Figure 0004500762
Figure 0004500762

Figure 0004500762
Figure 0004500762

実施例１〜４、９は、還元膨張率が0.4(％)以上と大きいＬＳＴＦ１で第２層１４を構成すると共に、還元膨張率が0.10(％)と小さいＬＳＴＦ３(すなわち還元耐久性が◎のもの)で第１層１２および第３層１６を構成した３層構造とすることによって、第２層１４から第１層１２および第３層１６のそれぞれに向かうに従って、すなわち、厚み方向の中央側から両面に向かうに従って、還元膨張率が小さくなる傾斜組成としたものである。また、上記のうち実施例１〜３、９は、第１層１２および第３層１６の構成材料および厚さ寸法を同一にすると共に、各層の厚さ寸法を種々変更したものである。また、実施例４は、第１層１２と第３層１６を異なる厚さ寸法で設けたものである。これらの構成例では、還元側に位置させる第１層１２が還元割れの抑制に十分な0.14(％)未満の還元膨張率を有する一方、中間部に設けられた第２層１４が11.5(cc/min/cm2)もの極めて高い酸素透過速度を有する。また、第２層１４を挟む第１層１２および第３層１６は、同一材料で構成されることから同一の熱膨張係数を有する。 In Examples 1 to 4 and 9, the second layer 14 is composed of the LSTF 1 having a large reduction expansion coefficient of 0.4 (%) or more, and the LSTF 3 having a small reduction expansion coefficient of 0.10 (%) (that is, the reduction durability is ◎). The first layer 12 and the third layer 16 have a three-layer structure, so that the first layer 12 and the third layer 16 are directed from the second layer 14 to the first layer 12 and the third layer 16, respectively, that is, in the center in the thickness direction. The gradient composition is such that the reductive expansion coefficient decreases as it goes from both sides to both sides. Moreover, among Examples 1 to 3 and 9, the constituent materials and thickness dimensions of the first layer 12 and the third layer 16 are made the same, and the thickness dimensions of each layer are variously changed. In Example 4, the first layer 12 and the third layer 16 are provided with different thickness dimensions. 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 second layer 14 provided in the intermediate portion is 11.5 (cc / min / cm 2 ) with a very high oxygen transmission rate. Moreover, since the first layer 12 and the third layer 16 sandwiching the second layer 14 are made of the same material, they have the same thermal expansion coefficient.

また、実施例５〜８、１０は、還元膨張率が0.28(％)程度とやや大きいＬＳＺＦ１で第２層１４を構成すると共に、還元膨張率が0.08(％)程度と小さいＬＳＺＦ２で第１層１２および第３層１６を構成した３層構造とすることによって、第２層１４から第１層１２および第３層１６に向かうに従って還元膨張率が小さくなる傾斜組成としたものである。また、上記のうち実施例５〜７、１０は、第１層１２および第３層１６の構成材料および厚さ寸法を同一にすると共に、各層の厚さ寸法を種々変更したものである。また、実施例８は、第１層１２と第３層１６を異なる厚さ寸法で設けたものである。これらの構成例でも、還元側に位置させる第１層１２が還元割れの抑制に十分な0.14(％)未満の還元膨張率にされる一方、中間部に設けられた第２層１４が11.0(cc/min/cm2)もの極めて高い酸素透過速度とされている。また、第２層１４を挟む第１層１２および第３層１６は、同一材料で構成されることから同一の熱膨張係数を有する。 In Examples 5-8, the second layer 14 is composed of LSZF1 having a slightly large reduction expansion coefficient of about 0.28 (%), and the first layer is composed of LSZF2 having a small reduction expansion coefficient of about 0.08 (%). By adopting a three-layer structure in which 12 and the third layer 16 are configured, a gradient composition having a reduction expansion coefficient that decreases from the second layer 14 toward the first layer 12 and the third layer 16 is obtained. In addition, among the above, Examples 5 to 7 and 10 are obtained by making the constituent materials and thickness dimensions of the first layer 12 and the third layer 16 the same and variously changing the thickness dimensions of each layer. In Example 8, the first layer 12 and the third layer 16 are provided with different thickness dimensions. Also 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 second layer 14 provided in the intermediate portion is 11.0 ( cc / min / cm 2 ), which is an extremely high oxygen transmission rate. Moreover, since the first layer 12 and the third layer 16 sandwiching the second layer 14 are made of the same material, they have the same thermal expansion coefficient.

これに対して、比較例１〜８は、還元膨張率が0.28〜0.7(％)程度と大きいＬＳＴＦ１またはＬＳＺＦ１の一面のみに還元膨張率が0.08〜0.10(％)のＬＳＴＦ３またはＬＳＺＦ２を積層した２層構造としたもの、すなわち、各実施例において第３層１６を備えていないものに相当するものである。また、比較例９，１０は、実施例と同様な３層構造であるが、第３層１６の厚さ寸法が第１層１２の３倍とされたものである。   On the other hand, Comparative Examples 1 to 8 are obtained by laminating LSTF3 or LSZF2 having a reduction expansion coefficient of 0.08 to 0.10 (%) only on one surface of LSTF1 or LSZF1 having a large reduction expansion coefficient of about 0.28 to 0.7 (%). This corresponds to a layer structure, that is, one that does not include the third layer 16 in each embodiment. Comparative examples 9 and 10 have the same three-layer structure as the example, but the thickness of the third layer 16 is three times that of the first layer 12.

上記の実施例１〜１０の特性を評価した結果を、比較例１〜１０の評価結果と併せて表４に示す。   The results of evaluating the characteristics of Examples 1 to 10 are shown in Table 4 together with the evaluation results of Comparative Examples 1 to 10.

Figure 0004500762
Figure 0004500762

上記の表４に示すように、第２層１４の両面に第１層１２および第３層１６を設けた実施例１〜１０では、全て0.1(mm)以下の極めて小さな反りに留まった。また、これらのうち実施例１〜８では、13.2(cc/min/cm2)以上の特に高い酸素透過性能が得られた。なお、還元耐久性については特に表４には示さないが、実施例および比較例の全てにおいて、割れが生じることなどが無く、十分な耐久性を示した。 As shown in Table 4 above, in Examples 1 to 10 in which the first layer 12 and the third layer 16 were provided on both surfaces of the second layer 14, all remained extremely small warpages of 0.1 (mm) or less. Of these, in Examples 1 to 8, particularly high oxygen permeation performance of 13.2 (cc / min / cm 2 ) or more was obtained. Although the reduction durability is not particularly shown in Table 4, in all of the examples and comparative examples, cracks did not occur and sufficient durability was shown.

これに対して、比較例１〜８では、高還元膨張率の第２層の一方の側のみに低還元膨張率の第１層を設けた非対称構造であるため、製造過程において加熱した際に両面における熱膨張係数の相違に起因して1.4〜2.4(mm)もの大きな反りが生じた。また、比較例９，１０では第２層の両面に第１層および第３層が設けられているが、第１層に比較して第３層が著しく厚いため、非対称構造の場合ほどではないが、比較的大きな反りが生じる結果となった。   On the other hand, in Comparative Examples 1-8, since it is an asymmetrical structure which provided the 1st layer of the low reductive expansion coefficient only on one side of the 2nd layer of the high reductive expansion coefficient, when heating in a manufacture process, Due to the difference in thermal expansion coefficient on both sides, a large warp of 1.4-2.4 (mm) occurred. In Comparative Examples 9 and 10, the first layer and the third layer are provided on both sides of the second layer. However, the third layer is significantly thicker than the first layer, so that it is not as much as in the case of the asymmetric structure. However, this resulted in a relatively large warp.

上記の結果によれば、対称構造とした実施例１〜１０では、第１層１２および第３層１６の厚さ寸法が0.05(mm)または0.1(mm)程度、すなわち30(μm)以上であっても、第２層１４の特性に基づく高い酸素透過性能を保ったまま、反りが極めて小さい酸素分離膜１０が得られることが判る。   According to the above results, in Examples 1 to 10 having a symmetrical structure, the thickness dimension of the first layer 12 and the third layer 16 is about 0.05 (mm) or 0.1 (mm), that is, 30 (μm) or more. Even if it exists, it turns out that the oxygen separation membrane 10 with very small curvature is obtained, maintaining the high oxygen permeation performance based on the characteristic of the second layer 14.

また、対称構造に構成しても、第１層と第３層の厚さ寸法の相違が著しい場合、すなわち３倍以上の相違とされている場合には、一応の効果は得られるものの、反りを十分に抑制することができないことが判る。実用上求められる反りの大きさの上限は、シール方式、材料強度、膜面積等によって異なるため、一義的に定めることはできない。しかしながら、前述したような実験条件では、経験的に反りが0.2(mm)以下に留まることが必要であることが判っている。実施例１〜１０は全てこの条件を満たすが、比較例１〜１０は何れも反りが大きく、使用困難である。但し、反りがやや大きくとも許容される場合には、例えば、比較例９，１０は使用できる可能性がある。   Also, even if the symmetric structure is used, if the difference in thickness between the first layer and the third layer is significant, that is, if the difference is more than three times, a temporary effect can be obtained, but the warp. It can be seen that it cannot be sufficiently suppressed. The upper limit of the warp size required for practical use differs depending on the sealing method, material strength, film area, etc., and cannot be uniquely determined. However, under the experimental conditions as described above, it has been empirically found that the warp needs to remain below 0.2 (mm). Examples 1 to 10 all satisfy this condition, but Comparative Examples 1 to 10 are all warped and difficult to use. However, when the warpage is slightly large, for example, Comparative Examples 9 and 10 may be usable.

なお、実施例９，１０は、反りを十分に小さくできる点では他の実施例と同等の効果が得られるが、酸素透過性能は他の実施例に比較してやや劣る。これらは対称構造ではあるが、第１層１２および第３層１６がそれぞれ0.2(mm)と厚くされているため、酸素透過性能が低くなったものと考えられる。但し、これら低還元膨張率の層が厚いことから、耐久性は他の実施例に比べて高くなるため、要求される酸素透過性能や耐久性に適合する場合には、このような構成も有効である。   In Examples 9 and 10, the same effect as the other examples can be obtained in that the warpage can be sufficiently reduced, but the oxygen permeation performance is slightly inferior to the other examples. Although these are symmetric structures, the first layer 12 and the third layer 16 are each thickened to 0.2 (mm), so it is considered that the oxygen permeation performance was lowered. However, since these low reductive expansion layers are thick, durability is higher than in other examples, so such a configuration is also effective when conforming to the required oxygen permeation performance and durability. It is.

以上、本発明を図面を参照して詳細に説明したが、本発明は更に別の態様でも実施でき、その主旨を逸脱しない範囲で種々変更を加え得るものである。   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.

本発明の一実施例の酸素分離膜の要部断面構造を模式的に示す図である。It is a figure which shows typically the principal part cross-section of the oxygen separation membrane of one Example of this invention. ２層の傾斜構造の場合における膜内の酸素分圧勾配を説明する図である。It is a figure explaining the oxygen partial pressure gradient in the film | membrane in the case of a 2 layer inclination structure. 図１の酸素分離膜エレメントの製造方法を説明するための工程図である。It is process drawing for demonstrating the manufacturing method of the oxygen separation membrane element of FIG. 図１の酸素分離膜エレメントが用いられた反応器の構成を説明する図である。It is a figure explaining the structure of the reactor using the oxygen separation membrane element of FIG.

符号の説明Explanation of symbols

１０：酸素分離膜、１２：第１層、１４：第２層、１６：第３層、１８：シール部材、２０：一面、２２：他面、２４：酸素再結合触媒層、２６：酸素解離触媒層、３６：界面、４０：反応器、４２、４４：円筒管、４８、５０：気体導入管、５６：ヒータ、５８：封着材、６０：排気路、６２：回収路 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, 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)

一般式(Ln1-xAex)MO3(但し、Lnはランタノイドのうちの１種または２種以上の組合せ、AeはBa、Sr、Caのうちから選ばれる１種または２種以上の組合せ、MはTi,Zr,Al,Ga,Nb,Ta,Fe,Co,Ni,Cu,Cr,Mn,Rh,Pd,Pt,およびAuのうちから選ばれる１種または２種以上の組合せ、0≦ｘ≦1)で表される第１の混合伝導体から成る緻密質の第１層と、
前記一般式で表され且つ前記第１の混合伝導体よりも還元膨張率が大きい第２の混合伝導体から成りその一面側に前記第１層が積層された緻密質の第２層と、
前記一般式で表され且つ前記第２の混合伝導体よりも還元膨張率が小さい第３の混合伝導体から成り前記第２層の他面側に積層された緻密質の第３層と
を、含むことを特徴とする組成傾斜構造を有する酸素分離膜。 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 dense first layer comprising a first mixed conductor represented by ≦ x ≦ 1);
A dense 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, the first layer being laminated on one side thereof;
A dense third layer composed of a third mixed conductor represented by the above general formula and having a reduction expansion coefficient smaller than that of the second mixed conductor and laminated on the other surface side of the second layer; An oxygen separation membrane having a composition gradient structure. 前記第２層は0.14(％)以上の還元膨張率を有し、且つ前記第１層および前記第３層は0.14(％)未満の還元膨張率を有することを特徴とする請求項１に記載の組成傾斜構造を有する酸素分離膜。   2. The second layer according to claim 1, wherein the second layer has a reduction expansion coefficient of 0.14 (%) or more, and the first layer and the third layer have a reduction expansion coefficient of less than 0.14 (%). An oxygen separation membrane having a composition gradient structure. 前記第１層の厚さ寸法は前記第３層の厚さ寸法の1/3倍より大きく且つ３倍未満であることを特徴とする請求項１または請求項２に記載の組成傾斜構造を有する酸素分離膜。   3. The composition gradient structure according to claim 1, wherein the thickness dimension of the first layer is greater than 1/3 times and less than 3 times the thickness dimension of the third layer. 4. Oxygen separation membrane. 前記第１層および前記第３層は同一材料から成ることを特徴とする請求項１乃至請求項３の何れかに記載の組成傾斜構造を有する酸素分離膜。   The oxygen separation membrane having a composition gradient structure according to any one of claims 1 to 3, wherein the first layer and the third layer are made of the same material.
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WO2003040058A1 (en) * 2001-11-09 2003-05-15 Noritake Co.,Limited Oxygen ion conducting ceramic material and use thereof
JP2005095718A (en) * 2003-09-22 2005-04-14 Noritake Co Ltd Oxygen separation membrane element and manufacturing method therefor
JP2007073272A (en) * 2005-09-05 2007-03-22 Noritake Co Ltd Electron non-conductive composition inclination solid electrolyte membrane
JP2007069090A (en) * 2005-09-05 2007-03-22 Noritake Co Ltd Composition gradient type oxygen separation membrane

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WO2003040058A1 (en) * 2001-11-09 2003-05-15 Noritake Co.,Limited Oxygen ion conducting ceramic material and use thereof
JP2005095718A (en) * 2003-09-22 2005-04-14 Noritake Co Ltd Oxygen separation membrane element and manufacturing method therefor
JP2007073272A (en) * 2005-09-05 2007-03-22 Noritake Co Ltd Electron non-conductive composition inclination solid electrolyte membrane
JP2007069090A (en) * 2005-09-05 2007-03-22 Noritake Co Ltd Composition gradient type oxygen separation membrane

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