JP2004148138A - Hydrogen separation membrane and hydrogen production apparatus using the same - Google Patents

Abstract

Provided is a hydrogen separation membrane in which the number of pinholes generated in the separation membrane is small and the amount of CO mixed into hydrogen gas is small.
The catalyst is formed on a support, a catalyst portion including a CO conversion catalyst disposed on at least one surface of the support, and a surface on which the catalyst portion is disposed. The above problem is solved by a hydrogen separation membrane having a separation membrane for selectively passing hydrogen.
[Selection diagram] Fig. 1

Description

【００２５】
で表される反応によって、ＣＯを除去する反応を促進する触媒である。ルテニウム系またはニッケル系の触媒が一般に用いられている。ルテニウム系およびニッケル系は、ＣＯのメタン化能に優れるため好ましい。ただし、メタン化触媒が、これらに限定されるわけではない。
【００２６】
シフト触媒とは、下記式（２）：
【００２７】
【化２】

【００２８】
で表される反応によって、ＣＯを除去する反応を促進する触媒である。ＣｕＯ−ＺｎＯ触媒、Ｆｅ系触媒などが、シフト触媒として知られている。ＣｕＯ−ＺｎＯ触媒およびＦｅ系触媒は、シフト反応を効果的に促進させうる。ただし、シフト触媒が、これらに限定されるわけではない。
【００２９】
ＣＯ選択酸化触媒とは、ガス中に含まれる成分のうち、ＣＯを選択的に酸化する反応を促進する触媒である。ＣＯ選択酸化触媒によって、ＣＯが二酸化炭素（ＣＯ_２）に転化される反応が促進される。ＣＯ選択酸化触媒としては、白金やルテニウムなどの貴金属を担持した触媒が用いられる。白金やルテニウムからなる触媒は、ＣＯ選択酸化能に優れるため好適である。ただし、ＣＯ選択酸化触媒が、これらに限定されるわけではない。
【００３０】
触媒部は、ＣＯ変成触媒のみから形成されてもよいし、必要に応じてＣＯ変成触媒以外の成分を含んでも良い。また、２種以上のＣＯ変成触媒を組み合わせて用いても良い。
【００３１】
触媒部は、支持体表面の凹凸を緩和するように配置されることが好ましい。支持体表面の凹凸が少ないと、触媒部が支持体上に配置された後に形成される分離膜における、ピンホールの発生が抑制される。触媒部は、図１に示すように、支持体表面の凹部にのみ配置して、支持体表面の凹凸を緩和してもよい。また、支持体表面が触媒部からなる触媒部によって被覆される程度に、多量の触媒部が配置されてもよい。ただし、配置される触媒部の量が多すぎると、水素分離膜が大型化する、触媒使用量が増加して水素分離膜の製造コストが増大する、水素分離膜の圧力損失が増大して水素分離膜の水素透過性能が低下する、といった弊害が生じる。このため、配置される触媒部は少ないことが好ましい。具体的には、触媒部は、支持体の厚さより薄く、かつ、分離膜の厚さより薄いことが好ましい。ここで触媒部の厚さとは、支持体上に配置されてなる触媒部の平均の厚さをいう。触媒部の平均の厚さは、支持体に配置された触媒部の体積をａ、触媒部が配置されてなる支持体の表面積をｂとすると、ａ／ｂで求められる量である。ただし、かような算出方法に限定されるものではなく、触媒部が触媒層として存在する場合には、触媒層の任意の９点を測定してその平均を触媒部の平均の厚さとしてもよい。
【００３２】
分離膜は、混合ガスから、水素を選択的に通過させる機能を有する膜を意味する。分離膜は、触媒部が形成された支持体上に、製膜される。分離膜は、パラジウム（Ｐｄ）、バナジウム（Ｖ）、ニオブ（Ｎｂ）、タンタル（Ｔａ）、もしくはジルコニウム（Ｚｒ）の単体から形成されうる。分離膜は、前記元素の複合体から形成されてもよい。また、分離膜は、前記単体または前記複合体と銀（Ａｇ）または銅（Ｃｕ）との合金から形成されてもよい。これらの材料から形成される分離膜は、水素をプロトン化して金属結晶格子間を拡散させ、透過させる性質が高い。分離膜の作用によって、複数成分からなる混合ガスから水素ガスのみが選択して取り出される。
【００３３】
分離膜は、厚すぎると分離膜に用いられる金属使用量の増加に伴い、製造コストが上昇する。また、分離膜が厚すぎると水素透過性能が低下する恐れがある。一方、分離膜が薄すぎると、選択的に水素を通過させる性能が不十分になる恐れがある。これらを考慮すると、分離膜の厚さは、好ましくは２μｍ以下であり、より好ましくは１〜２μｍである。分離膜の厚さは走査型電子顕微鏡によって測定されうる。
【００３４】
続いて、本発明の水素分離膜の製造方法について簡単に説明する。ただし、以下の説明は、水素分離膜の製造方法の一態様に過ぎず、本発明の水素分離膜は、これ以外の方法によっても製造されうる。
【００３５】
まず、所望する大きさの支持体を準備する。粒子の集合体を支持体として用いる場合には、粒子を必要に応じてバインダーなどを用いて固まらせた材料が用いられ得る。支持体の材質や製造方法は特に限定されず、上述した方法のほか、各種公知技術を用い得る。
【００３６】
次に、載置された支持体の表面にＣＯ変成触媒を含む水溶液を供給して、支持体の凹部に分布させる。ＣＯ変成触媒を含む水溶液の濃度は、使用するＣＯ変成触媒に応じて調整する必要があり、特に限定されるべきものではない。効率を優先するのであれば、高濃度の水溶液を調製するとよい。ＣＯ変成触媒を含む水溶液を供給する際には、支持体は撥水性を有することが好ましい。撥水性を有していると、ＣＯ変成触媒を含む水溶液が、支持体表面の凹部に分布されやすい。これを焼成し、ＣＯ変成触媒を固着させる。これが触媒部となる。
【００３７】
触媒部を形成した後に、分離膜を製膜する。分離膜は、無電解メッキ、ＣＶＤ、ゾル−ゲル法、スプレー熱分解法などを用いて製膜されうる。製膜方法に関しては公知の知見を適宜参照できる。例えば、無電解メッキに関しては、Ｓ． Ｉｌｉａｓ， Ｎ． Ｓｕ， Ｕ．Ｉ． Ｕｄｏ−Ａｋａ， Ｆ．Ｇ． Ｋｉｎｇ： Ｓｅｐａｒａｔｉｏｎ Ｓｃｉｅｎｃｅ ａｎｄ Ｔｅｃｈｎｏｌｏｇｙ， ３２，４８７−５０４（１９９７）を、ＣＶＤに関しては、Ｓ． Ｙａｎ， Ｈ． Ｍａｅｄａ， Ｋ． Ｋｕｓａｋａｂｅ， Ｓ． Ｍｏｒｏｏｋａ： Ｉｎｄ． Ｅｎｇ． Ｃｈｅｍ． Ｒｅｓ．， ３３， ．２０９６−２１０１ （１９９４）を、ゾル−ゲル法に関しては、Ｍ． Ｃｈａｉ， Ｙ． Ｙａｍａｓｈｉｔａ， Ｍ． Ｍａｃｈｉｄａ， Ｋ． Ｅｇｕｃｈｉ， Ｈ． Ａｒａｉ： Ｊ． ＭｅｍｂｒａｎｅＳｃｉ．， ９７， １９９−２０７ （１９９４）を、スプレー熱分解法に関しては、Ｚ．Ｙ． Ｌｉ， Ｈ． Ｍａｅｄａ， Ｋ． Ｋｕｓａｋａｂｅ， Ｓ． Ｍｏｒｏｏｋａ， Ｈ． Ａｎｚａｉ， Ｓ． Ａｋｉｙａｍａ： Ｊ． Ｍｅｍｂｒａｎｅ Ｓｃｉ．， ７８，
２４７−２５４（１９９３）などの文献や刊行物を参照しうる。
【００３８】
本発明の水素分離膜は、水素製造装置に用いられ得る。水素製造装置は、燃料電池システムにおける、水素製造源として用いられる。以下、本発明の水素分離膜が適用されてなる燃料電池システムについて、図面を参照しながら説明する。図３は、燃料電池システムの第一の実施形態を説明するための概略図である。
【００３９】
高純度の水素ガス（改質ガス）を生成するための炭化水素系燃料と水とが、コントロールユニット（Ｃ／Ｕ）２１１からの信号によって制御される第一燃料噴射弁２１２と水噴射弁２１３により蒸発器２１４に供給される。蒸発器２１４には、別途、改質器２１５に隣接して設けられてなる燃焼器２１６から、燃焼ガスが供給される。蒸発器２１４における、炭化水素系燃料および水と燃焼ガスとの間での熱交換によって、炭化水素系燃料および水が、蒸発器２１４において気化する。
【００４０】
気化した炭化水素系燃料および水は、燃料ガスとして改質器２１５に導入される。改質器２１５に導入された燃料ガスは、燃焼室２１６から発生する熱量を利用して、改質される。燃焼室２１６には、第二燃料噴射弁２１７が設けられており、熱量が不足した場合、コントロールユニット２１１からの信号によって燃料が追加供給される。
【００４１】
ここで、Ｃ_ｎＨ_ｍで表される炭化水素系燃料と水との改質反応について説明する。燃料は、まず下記式（３）で表される反応によって、一酸化炭素および水素に変換される。さらに、下記式（４）で表されるシフト反応によって、白金の触媒毒である一酸化炭素が二酸化炭素および水素に変換される。式（４）のシフト反応は、一般的に低温では水素、高温ではＣＯの生成する方向に進行する。改質器２１５では、下記式（３）を主体として式（４）の反応が行われるが、高級炭化水素の改質反応では、通常改質温度が高いため、式（４）の反応はＣＯの生成する方向に進行し易い。
【００４２】
【化３】

【００４３】
改質器２１５で生成した改質ガスは、水素分離膜ユニット２１８の一次側通路２１９に供給される。改質ガスは水素分離膜ユニット２１８内の水素分離膜２２０によって水素が単離され、高純度の水素ガスとして、二次側通路２２１へ供給される。水素分離膜２２０を透過しえないガスおよび燃料電池２２２から排出される余剰水素は、燃焼器２１６に供給され、改質器２１５を加熱するために用いられる。水素分離膜ユニット２１８には、本発明の水素分離膜２２０が設けられる。このため、水素分離膜ユニット２１８によって、ＣＯ濃度を著しく低減させうる。また、ＣＯ変成触媒の使用量削減による製造コストの抑制、水素分離膜の薄型化による水素分離膜ユニットの小型化、ひいては燃料電池システムの小型化といった効果が得られる。
【００４４】
二次側通路２２１へ供給された水素ガスは、燃料電池２２２に供給され、燃料電池２２２の燃料として使用される。別途、酸化剤として空気が、コントロールユニット２１１からの信号を受けた空気制御バルブ２２３の動作によって、燃料電池２２２に供給される。燃料電池では、下記式（５）〜（７）で表される電気化学反応によって、起電力が生じる。
【００４５】
【化４】

【００４６】
ここで、前記式（５）は陰極側における反応、前記式（６）は陽極側における反応を表す。燃料電池２２２全体としては、前記式（７）に示す反応が進行する。自動車の動力源としては、固体高分子型燃料電池（ＰＥＦＣ）の使用が検討されているが、ＰＥＦＣは白金等の触媒を具備する。ＣＯは白金触媒に吸着して、触媒の機能を低下させ、前記式（６）に示したアノードにおける反応を阻害して燃料電池２２２の性能を低下させる。このため、ＣＯが膜を透過することを効果的に防止する本発明の水素分離膜は、ＰＥＦＣに適用されると特に有益である。なお、燃料電池システムは、必要に応じて、ＣＯ除去器やＣＯ選択酸化装置などのＣＯ除去装置をさらに具備しても構わない。しかしながら、本発明の水素分離膜を用いれば、これらの装置を必要とせずとも、ＰＥＦＣを稼動させることが可能である。この場合、燃料電池システムの小型化が達成される。したがって、自動車のような、動力装置の小型化および軽量化が強く求められる分野において、本発明の水素分離膜は特に有益であるといえる。なお、最終的に燃料電池２２２に供給される燃料ガス中のＣＯ濃度は、数十ｐｐｍ以下にまで低減させることが一般的である。
【００４７】
さらに、本発明の水素分離膜が適用されてなる燃料電池システムの第二の実施形態について、図面を参照しながら説明する。図４は、燃料電池システムの他の実施形態を説明するための概略図である。燃料電池システムの第二の実施形態は、（ｉ）炭化水素系燃料ガスから水素リッチガスへの改質反応が進行する改質部、（ｉｉ）前記改質反応に必要な熱量を供給するための燃焼部、（ｉｉｉ）改質部で生じた水素ガスを選択的に通過させる水素分離膜、および（ｉｖ）前記水素分離膜を通過した水素ガス用の水素通路が、一体化されてなる水素製造装置を有する燃料電池システムである。ここでいう「一体化されてなる」とは、一の装置内部に、（ｉ）改質部、（ｉｉ）燃焼部、（ｉｉｉ）水素分離膜、および（ｉｖ）水素通路が含まれており、改質反応により生じた水素ガスが改質部から直接的に水素分離膜を用いて分離される態様を意味する。したがって、配管を通じて、改質された水素リッチガスを水素分離膜が設けられてなるような実施態様は、本願でいう「一体化」には該当しない。
【００４８】
改質部とは、炭化水素系燃料ガスから水素リッチガスへの改質反応が進行する部位を意味する。燃焼部とは、水素分離膜によって水素が分離された残りの燃料の全部もしくは一部、および／または、燃料電池の余剰水素を用いて燃焼を行い、改質部で行われる改質反応に必要な熱量を発生させる部位を意味する。水素分離膜としては、本発明の水素分離膜が用いられる。水素通路とは、水素分離膜によって分離された水素ガスが供給される部位を意味する。水素分離膜を通過した水素ガスが供給される部位であれば、特にその形状は限定されない。
【００４９】
前記（ｉ）〜（ｉｖ）が一体されてなる水素製造装置においては、改質反応が促進され、燃料電池システムの小型化が達成されうる。かような水素製造装置の効果を、該水素製造装置を有する燃料電池システムを用いて、説明する。
【００５０】
高純度の水素ガス（改質ガス）を生成するための炭化水素系燃料と水とが、コントロールユニット（Ｃ／Ｕ）３１１からの信号によって制御される第一燃料噴射弁３１２と水噴射弁３１３により蒸発器３１４に供給される。蒸発器３１４には、別途、水素製造装置３２４における燃焼部３２５から、燃焼ガスが供給される。蒸発器３１４における、炭化水素系燃料および水と燃焼ガスとの間での熱交換によって、炭化水素系燃料および水が、蒸発器３１４において気化する。
【００５１】
気化した炭化水素系燃料および水は、燃料ガスとして水素製造装置３２４における改質部３２６に導入される。改質部３２６に導入された燃料ガスは、燃焼部３２５から発生する熱量を利用して、改質される。燃焼室３１６には、第二燃料噴射弁３１７が設けられており、熱量が不足した場合、コントロールユニット３１１からの信号によって燃料が追加供給される。
【００５２】
改質部３２６で生成した改質ガスは、水素製造装置３２４に設けられてなる水素分離膜３２０によって水素が単離され、高純度の水素ガスとして、水素通路３２７を経て、燃料電池３２２へ供給される。水素分離膜３２０を透過しえないガスおよび燃料電池３２２から排出される余剰水素は、燃焼部３２５に供給され、改質部３２６を加熱するために用いられる。水素製造装置３２４には、本発明の水素分離膜３２０が設けられる。このため、水素製造装置３２４によって、ＣＯ濃度を著しく低減させうる。また、ＣＯ変成触媒の使用量削減による製造コストの抑制、水素分離膜の薄型化による燃料電池システムの小型化といった効果が得られる。
【００５３】
燃料電池３２２には、酸化剤として空気が、コントロールユニット３１１からの信号を受けた空気制御バルブ３２３の動作によって、供給される。燃料電池では、前記式（５）〜（７）で表される電気化学反応によって、起電力が生じる。燃料電池システムの第二の実施形態においては、前記燃料電池システムの第一の実施形態と同様の電気化学反応が起きる。
【００５４】
第二の実施形態の水素製造装置においては、改質部３２６で生成した水素ガスが、水素分離膜３２０によって改質反応と同時に選択的に単離される。そして、水素通路３２７を経て燃料電池３２２へと供給される。このため、前記第一の実施形態と比較して、改質反応をより効果的に促進することが可能である。つまり、改質反応によって生成した水素が、速やかに水素分離膜によって分離される。その結果、改質反応が生じる部位での水素濃度を効果的に減少させることができ、水素が改質される方向へ化学平衡が促進される。改質反応が促進される結果、必要となる改質触媒容量を削減することができ、燃料電池システムの小型化が達成されうる。
【図面の簡単な説明】
【図１】本発明の水素分離膜の断面模式図である。
【図２】分離膜の膜厚と分離膜を通過する気体におけるＣＯ濃度との関係を示すグラフである。
【図３】燃料電池システムの第一の実施形態を説明するための概略図である。
【図４】燃料電池システムの他の実施形態を説明するための概略図である。
【符号の説明】
１０１…支持体、１０２…触媒部、１０３…分離膜、１０４…ピンホール、２１１…コントロールユニット（Ｃ／Ｕ）、２１２…第一燃料噴射弁、２１３…水噴射弁、２１４…蒸発器、２１５…改質器、２１６…燃焼器、２１７…第二燃料噴射弁、２１８…水素分離膜ユニット、２１９…一次側通路、２２０…水素分離膜、２２１…二次側通路、２２２…燃料電池、２２３…空気制御バルブ、３１１…コントロールユニット（Ｃ／Ｕ）、３１２…第一燃料噴射弁、３１３…水噴射弁、３１４…蒸発器、３１６…燃焼室、３１７…第二燃料噴射弁、３２０…水素分離膜、３２２…燃料電池、３２３…空気制御バルブ、３２４…水素製造装置、３２５…燃焼部、３２６…改質部、３２７…水素通路。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen separation membrane used for selectively extracting hydrogen gas from a gas containing hydrogen gas.
[0002]
[Prior art]
As public interest in fuel cells has increased, it has been desired to develop means for supplying hydrogen as a fuel. The hydrogen gas supplied to the fuel cell is preferably of high purity. In particular, when the fuel cell is a polymer electrolyte fuel cell (PEFC), carbon monoxide (CO) acts as a catalyst poison for the electrode with respect to platinum used as a catalyst. For this reason, the CO concentration in the hydrogen gas needs to be reduced to several tens ppm or less.
[0003]
One of means for supplying high-purity hydrogen gas is a hydrogen separation membrane. The hydrogen separation membrane is used to separate hydrogen gas from a mixed gas containing hydrogen. In general, high-purity hydrogen gas is separated using a hydrogen production apparatus including a mixed gas flow path, a separation layer provided with a hydrogen separation membrane, and a high-purity hydrogen gas flow path. In such a hydrogen production apparatus, only the hydrogen gas in the mixed gas passes through the separation layer and is supplied to the flow path for the hydrogen gas.
[0004]
In the hydrogen separation membrane, a separation membrane that functions to selectively separate hydrogen is formed on the surface of a support using a chemical vapor deposition method (CVD) or a physical vapor deposition method (PVD). However, it is difficult to manufacture a completely defect-free separation film, and some pinholes are formed in the separation film. Then, the mixed gas is mixed into the hydrogen gas flowing through the flow path for the hydrogen gas through the pinhole. As described above, CO adversely affects a fuel cell as a catalyst poison of platinum. It is known that CO mixed in such hydrogen gas can be removed by supporting a catalyst for methanizing CO in a high-purity hydrogen gas flow path (for example, see Patent Document 1). .).
[0005]
[Patent Document 1]
JP-A-2002-128506
[0006]
[Problems to be solved by the invention]
However, the method of supporting the methanation catalyst in the flow path for hydrogen gas does not fundamentally solve the problem of pinholes in the separation membrane.
[0007]
Therefore, an object of the present invention is to provide a hydrogen separation membrane in which the number of pinholes generated in the separation membrane is small and the amount of CO mixed into the hydrogen gas is small.
[0008]
[Means for Solving the Problems]
The present invention is formed on a support, a catalyst portion including a CO conversion catalyst, which is disposed on at least one surface of the support, and formed on one surface on which the catalyst portion is disposed. And a separation membrane through which hydrogen can be selectively passed.
[0009]
【The invention's effect】
In the hydrogen separation membrane of the present invention, a catalyst section containing a CO shift catalyst is formed on the surface of a support. Irregularities on the surface of the support can be mitigated by the catalyst portion. When the catalyst part is formed on the surface of the support, when forming the separation membrane on the surface on which the catalyst part is formed, pinholes are not easily generated in the separation membrane. Therefore, a hydrogen separation membrane having a separation membrane with a small number of pinholes is obtained. Thus, the hydrogen separation membrane of the present invention can fundamentally solve the problem of pinholes occurring in the separation membrane. Further, the catalyst section includes a CO conversion catalyst that converts CO into another compound. For this reason, CO that has penetrated the separation membrane through the slightly generated pinhole is also transformed into a compound other than CO.
[0010]
As described above, the hydrogen separation membrane of the present invention effectively removes CO that passes through the hydrogen separation membrane and enters the flow path for hydrogen gas, and greatly contributes to poisoning of the fuel cell.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is formed on a support, a catalyst portion including a CO conversion catalyst, which is disposed on at least one surface of the support, and formed on one surface on which the catalyst portion is disposed. And a separation membrane through which hydrogen can be selectively passed.
[0012]
The configuration and operation of the hydrogen separation membrane of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of the hydrogen separation membrane of the present invention. It can be composed mainly of ceramics and metals. For example, an aggregate of particles having an average particle diameter of about several tens μm is used as the support 101. On at least one surface of the support 101, a catalyst unit 102 containing a CO shift catalyst is disposed. Normally, the support 101 has a flat plate shape, and the catalyst unit 102 is disposed on the main surface (the surface having the largest area) of the flat support. The catalyst unit 102 is preferably arranged so as to flatten the irregularities on the surface of the support 101. In FIG. 1, the catalyst unit 102 is disposed only in the concave portion on the surface of the support 101, but the catalyst unit 102 may be disposed so as to cover the entire surface of the support 101. In that case, the catalyst unit 102 forms a catalyst layer, and the hydrogen separation membrane has a structure in which the support 101, the catalyst layer, and the separation membrane 103 are stacked in this order. The catalyst unit 102 can be composed of particles having an average particle diameter of several μm. The CO shift catalyst contained in the catalyst unit 102 promotes a CO methanation reaction, a shift reaction, a CO selective oxidation reaction, and the like, and converts a CO entering through the pinhole 104 generated in the separation membrane 103 into a harmless compound. Metamorphoses into On the surface side where the catalyst unit 102 is formed, a separation membrane 103 for selectively passing hydrogen is formed. The separation membrane may be formed using a film formation method such as electroless plating, CVD, a sol-gel method, and a spray pyrolysis method. However, the embodiment shown in FIG. 1 is merely an embodiment of the hydrogen separation membrane of the present invention, and the hydrogen separation membrane of the present invention is not limited to such an embodiment. In some cases, the separation film 103 may have a two-layer structure, or another layer may be stacked. However, it should be noted that as the number of layers increases, the thickness of the hydrogen separation membrane increases.
[0013]
In the film formation stage, if there are large irregularities on the surface of the support 101, pinholes 104 are likely to occur. Then, CO in the reformed gas is mixed into the flow path for hydrogen gas through the pinhole 104. As a result, the downstream fuel cell is poisoned, and the power generation efficiency is reduced. On the other hand, in the hydrogen separation membrane of the present invention, the surface of the support 101 is flattened by the catalyst unit 102. If the surface of the support 101 is flattened by the catalyst part 102, it is difficult to form the pinhole 104. Further, even when the pinhole 104 is formed, the CO that has passed through the pinhole 104 can be removed by the CO conversion catalyst included in the catalyst unit 102. For this reason, it is possible to reduce the amount of CO supplied to the fuel cell to an extremely low concentration. That is, the hydrogen separation membrane of the present invention can suppress the generation of pinholes that cause CO to enter the flow path for hydrogen gas, and can also effectively remove the CO that has passed through the pinholes. Therefore, it is very excellent as a means for supplying high-purity hydrogen gas to a fuel cell or the like. In order to enhance the effect of effectively removing the CO that has passed through the pinhole by the catalyst portion including the CO shift catalyst, the catalyst portion may be disposed at a portion of the separation membrane where the pinhole exists. preferable. In order to ensure that the catalyst portion is disposed at the site where the pinhole exists, the catalyst portion may be present as a layer between the support and the separation membrane. That is, the support, the catalyst layer containing the CO shift catalyst, and the separation membrane are preferably laminated in this order.
[0014]
When a methanation catalyst for converting CO into methane is separately supported in the hydrogen gas flow path in order to remove CO that has passed through the pinhole, a large amount of methanation catalyst is required. For this reason, the production cost of the hydrogen production apparatus increases. Further, when a methanation catalyst is carried in the flow path for hydrogen gas, the pressure loss increases, and the hydrogen permeation performance of the hydrogen separation membrane may decrease. In this regard, the hydrogen separation membrane of the present invention has a configuration in which the catalyst section containing the CO shift catalyst is disposed between the support and the separation membrane. In the hydrogen separation membrane of the present invention having such a configuration, it is possible to sufficiently remove CO mixed into the flow path for hydrogen gas without arranging a large number of catalyst units. If the amount of the CO conversion catalyst used for the hydrogen separation membrane is small, the production cost of the hydrogen separation membrane naturally decreases.
[0015]
Further, in the hydrogen separation membrane of the present invention, the separation membrane 103 can be thinned. When the thickness of the separation film 103 is reduced, the number of pinholes tends to increase. FIG. 2 is a graph showing the relationship between the thickness of the separation membrane and the CO concentration in the gas passing through the separation membrane. As shown in FIG. 2, as the thickness of the separation membrane decreases, the amount of CO penetrating through the separation membrane tends to increase. To reduce the size of the apparatus, it is preferable to make the separation membrane thinner, but if the separation membrane is made thinner, the CO separation ability will decrease. Since the hydrogen separation membrane of the present invention includes the CO conversion catalyst disposed between the separation membrane and the support, it is possible to effectively remove CO penetrating the separation membrane. Therefore, even if the separation membrane is thinned, the amount of CO supplied downstream can be effectively reduced. By reducing the thickness of the separation membrane, the amount of metal used for the separation membrane can be reduced, and the production cost of the entire hydrogen separation membrane can be suppressed. Further, by reducing the thickness of the hydrogen separation membrane, the size of the hydrogen production apparatus provided with the hydrogen separation membrane can be reduced.
[0016]
Next, each component of the hydrogen separation membrane of the present invention will be described in detail.
[0017]
The support is preferably made of alumina, silica, or cordierite, or a composite ceramic body thereof. These supports have low pressure losses. There is no particular limitation on the specific structure and manufacturing method of the support. A known material may be used, or a newly developed material may be used as long as the material functions as a support of the hydrogen separation membrane.
[0018]
The support may be formed from a hydrogen resistant metal having high corrosion resistance to hydrogen. The term “hydrogen resistance” means a property that there is substantially no risk of hydrogen embrittlement and destruction due to contact with hydrogen. A metal having such characteristics is excellent in hydrogen resistance, and thus is excellent as a hydrogen separation membrane. The metal having hydrogen resistance may be SUS (stainless steel) or pure iron. These may be used as a single substance or as a composite of two or more materials. When a support made of these materials is used, a hydrogen separation membrane having excellent durability and thermal shock resistance can be obtained. In the case where SUS or pure iron is used, unlike a structure composed of a large number of particles as shown in FIG. 1, the support becomes a support having a flat plate surface.
[0019]
The size of the support is not particularly limited. The size may be appropriately determined according to the site where the hydrogen separation membrane is installed. The thickness of the support is preferably equal to or greater than the thickness of the hydrogen separation membrane. This is to ensure that the separation membrane is supported by the support.
[0020]
The support and the catalyst part may use a material that is an aggregate of particles. In this case, the average particle diameter of the particles constituting the support is five times the average particle diameter of the particles constituting the catalyst part. It is preferable that it is above. As shown in FIG. 1, when the particle diameter of the particles constituting the catalyst portion is smaller than the particle diameter of the particles constituting the support, the concave portions on the surface of the support can be effectively flattened. For this reason, it is preferable that the average particle diameter of the particles constituting the support is at least 5 times the average particle diameter of the particles constituting the catalyst portion. Although the upper limit is not particularly limited, according to a normal manufacturing process, the average particle diameter of the particles constituting the support is 10 times or less the average particle diameter of the particles constituting the catalyst portion. The average particle size of the particles constituting the support and the average particle size of the particles constituting the catalyst portion can be measured using a scanning electron microscope or the like.
[0021]
In addition, about the shape, kind, manufacturing method, etc. of a support body, JP-A-2002-128512, JP-A-2002-126474, JP-A-11-286785, and the like can be appropriately referred to.
[0022]
The CO conversion catalyst contained in the catalyst section is not particularly limited as long as it promotes the reaction for removing CO. For example, a methanation catalyst for converting CO to methane, ₂ And H ₂ A shift catalyst that converts to O or a CO selective oxidation catalyst that selectively oxidizes CO can be used as the CO conversion catalyst.
[0023]
The methanation catalyst is represented by the following formula (1):
[0024]
Embedded image

[0025]
Is a catalyst that promotes the reaction for removing CO by the reaction represented by Ruthenium-based or nickel-based catalysts are commonly used. Ruthenium-based and nickel-based are preferred because they have excellent CO methanation ability. However, the methanation catalyst is not limited to these.
[0026]
The shift catalyst is represented by the following formula (2):
[0027]
Embedded image

[0028]
Is a catalyst that promotes the reaction for removing CO by the reaction represented by CuO—ZnO catalysts, Fe-based catalysts, and the like are known as shift catalysts. The CuO—ZnO catalyst and the Fe-based catalyst can effectively promote the shift reaction. However, the shift catalyst is not limited to these.
[0029]
The CO selective oxidation catalyst is a catalyst that promotes a reaction of selectively oxidizing CO among components contained in the gas. The CO selective oxidation catalyst converts CO into carbon dioxide (CO ₂ ) Is promoted. As the CO selective oxidation catalyst, a catalyst supporting a noble metal such as platinum or ruthenium is used. A catalyst made of platinum or ruthenium is preferable because of its excellent CO selective oxidation ability. However, the CO selective oxidation catalyst is not limited to these.
[0030]
The catalyst section may be formed only of the CO shift catalyst, or may include components other than the CO shift catalyst as needed. Further, two or more types of CO shift catalysts may be used in combination.
[0031]
The catalyst section is preferably arranged so as to reduce unevenness on the surface of the support. When there are few irregularities on the surface of the support, the generation of pinholes in the separation membrane formed after the catalyst portion is disposed on the support is suppressed. As shown in FIG. 1, the catalyst portion may be arranged only in the concave portion on the surface of the support to reduce the unevenness on the surface of the support. Further, a large number of catalyst parts may be arranged to such an extent that the surface of the support is covered with the catalyst part composed of the catalyst part. However, if the amount of the catalyst unit to be disposed is too large, the hydrogen separation membrane becomes large, the amount of catalyst used increases, the production cost of the hydrogen separation membrane increases, and the pressure loss of the hydrogen separation membrane increases, and There is an adverse effect that the hydrogen permeability of the separation membrane is reduced. For this reason, it is preferable that the number of the catalyst parts arranged is small. Specifically, the catalyst portion is preferably thinner than the thickness of the support and thinner than the thickness of the separation membrane. Here, the thickness of the catalyst portion refers to the average thickness of the catalyst portion disposed on the support. The average thickness of the catalyst unit is an amount determined by a / b, where a is the volume of the catalyst unit disposed on the support, and b is the surface area of the support on which the catalyst unit is disposed. However, the present invention is not limited to such a calculation method. In the case where the catalyst portion is present as a catalyst layer, any nine points of the catalyst layer are measured, and the average is taken as the average thickness of the catalyst portion. Good.
[0032]
The separation membrane means a membrane having a function of selectively passing hydrogen from a mixed gas. The separation membrane is formed on a support on which the catalyst unit is formed. The separation membrane may be formed of a simple substance of palladium (Pd), vanadium (V), niobium (Nb), tantalum (Ta), or zirconium (Zr). The separation membrane may be formed from a composite of the above elements. Further, the separation membrane may be formed from an alloy of the simple substance or the composite and silver (Ag) or copper (Cu). Separation membranes formed from these materials have a high property of protonating hydrogen to diffuse and permeate between metal crystal lattices. By the action of the separation membrane, only hydrogen gas is selectively extracted from the mixed gas composed of a plurality of components.
[0033]
If the separation membrane is too thick, the production cost increases with an increase in the amount of metal used for the separation membrane. Further, if the separation membrane is too thick, the hydrogen permeability may be reduced. On the other hand, if the separation membrane is too thin, the ability to selectively pass hydrogen may be insufficient. In consideration of these, the thickness of the separation membrane is preferably 2 μm or less, more preferably 1-2 μm. The thickness of the separation membrane can be measured by a scanning electron microscope.
[0034]
Subsequently, the method for producing a hydrogen separation membrane of the present invention will be briefly described. However, the following description is merely one embodiment of the method for producing a hydrogen separation membrane, and the hydrogen separation membrane of the present invention can be produced by other methods.
[0035]
First, a support having a desired size is prepared. When an aggregate of particles is used as a support, a material obtained by solidifying particles with a binder or the like as necessary can be used. The material and manufacturing method of the support are not particularly limited, and various known techniques can be used in addition to the above-described methods.
[0036]
Next, an aqueous solution containing a CO conversion catalyst is supplied to the surface of the placed support to distribute the solution in the concave portions of the support. The concentration of the aqueous solution containing the CO shift catalyst needs to be adjusted according to the CO shift catalyst to be used, and is not particularly limited. If priority is given to efficiency, a high-concentration aqueous solution may be prepared. When supplying the aqueous solution containing the CO shift catalyst, the support preferably has water repellency. When it has water repellency, the aqueous solution containing the CO shift catalyst is easily distributed to the concave portions on the surface of the support. This is calcined to fix the CO shift catalyst. This is the catalyst section.
[0037]
After forming the catalyst part, a separation membrane is formed. The separation membrane may be formed using electroless plating, CVD, a sol-gel method, a spray pyrolysis method, or the like. Known knowledge can be appropriately referred to for the film forming method. For example, regarding electroless plating, S.A. Ilias, N.M. Su, U.S.A. I. Udo-Aka, F .; G. FIG. King: Separation Science and Technology, 32, 487-504 (1997); Yan, H .; Maeda, K .; Kusakabe, S .; Morooka: Ind. Eng. Chem. Res. , 33,. 2096-1101 (1994) is described by M.M. Chai, Y .; Yamashita, M .; Machida, K .; Eguchi, H .; Arai: J. Membrane Sci. , 97, 199-207 (1994); Y. Li, H .; Maeda, K .; Kusakabe, S .; Morooka, H .; Anzai, S .; Akiyama: J.A. Membrane Sci. , 78,
247-254 (1993).
[0038]
The hydrogen separation membrane of the present invention can be used for a hydrogen production device. The hydrogen production device is used as a hydrogen production source in a fuel cell system. Hereinafter, a fuel cell system to which the hydrogen separation membrane of the present invention is applied will be described with reference to the drawings. FIG. 3 is a schematic diagram for explaining the first embodiment of the fuel cell system.
[0039]
A first fuel injection valve 212 and a water injection valve 213, which are controlled by a signal from a control unit (C / U) 211, to supply a hydrocarbon-based fuel and water for producing high-purity hydrogen gas (reformed gas). Is supplied to the evaporator 214. Combustion gas is separately supplied to the evaporator 214 from a combustor 216 provided adjacent to the reformer 215. The heat exchange between the hydrocarbon-based fuel and water and the combustion gas in the evaporator 214 causes the hydrocarbon-based fuel and water to evaporate in the evaporator 214.
[0040]
The vaporized hydrocarbon-based fuel and water are introduced into the reformer 215 as fuel gas. The fuel gas introduced into the reformer 215 is reformed using heat generated from the combustion chamber 216. The combustion chamber 216 is provided with a second fuel injection valve 217, and when the amount of heat is insufficient, additional fuel is supplied by a signal from the control unit 211.
[0041]
Where C _n H _m The reforming reaction between the hydrocarbon-based fuel and water represented by the following formula will be described. The fuel is first converted to carbon monoxide and hydrogen by a reaction represented by the following formula (3). Further, carbon monoxide, which is a catalyst poison of platinum, is converted into carbon dioxide and hydrogen by a shift reaction represented by the following formula (4). The shift reaction of the formula (4) generally proceeds in a direction of generating hydrogen at a low temperature and generating CO at a high temperature. In the reformer 215, the reaction of the formula (4) is carried out mainly by the following formula (3). However, in the reforming reaction of higher hydrocarbons, the reaction of the formula (4) is generally carried out at a high reforming temperature. Easily progresses in the direction in which is generated.
[0042]
Embedded image

[0043]
The reformed gas generated in the reformer 215 is supplied to the primary side passage 219 of the hydrogen separation membrane unit 218. Hydrogen is isolated from the reformed gas by the hydrogen separation membrane 220 in the hydrogen separation membrane unit 218 and is supplied to the secondary side passage 221 as high-purity hydrogen gas. The gas that cannot pass through the hydrogen separation membrane 220 and the surplus hydrogen discharged from the fuel cell 222 are supplied to the combustor 216 and used to heat the reformer 215. The hydrogen separation membrane unit 218 is provided with the hydrogen separation membrane 220 of the present invention. For this reason, the CO concentration can be significantly reduced by the hydrogen separation membrane unit 218. In addition, the effects of reducing the production cost by reducing the amount of CO conversion catalyst used, reducing the size of the hydrogen separation membrane unit by reducing the thickness of the hydrogen separation membrane, and further reducing the size of the fuel cell system can be obtained.
[0044]
The hydrogen gas supplied to the secondary passage 221 is supplied to the fuel cell 222 and used as fuel for the fuel cell 222. Separately, air as an oxidant is supplied to the fuel cell 222 by the operation of the air control valve 223 receiving a signal from the control unit 211. In a fuel cell, an electromotive force is generated by an electrochemical reaction represented by the following equations (5) to (7).
[0045]
Embedded image

[0046]
Here, equation (5) represents the reaction on the cathode side, and equation (6) represents the reaction on the anode side. The reaction represented by the formula (7) proceeds as a whole of the fuel cell 222. The use of a polymer electrolyte fuel cell (PEFC) as a power source for an automobile has been studied, but the PEFC includes a catalyst such as platinum. The CO is adsorbed on the platinum catalyst and lowers the function of the catalyst, and inhibits the reaction at the anode shown in the above formula (6) to lower the performance of the fuel cell 222. For this reason, the hydrogen separation membrane of the present invention, which effectively prevents CO from permeating the membrane, is particularly advantageous when applied to PEFC. Note that the fuel cell system may further include a CO removing device such as a CO remover or a CO selective oxidizing device as necessary. However, if the hydrogen separation membrane of the present invention is used, it is possible to operate PEFC without requiring these devices. In this case, downsizing of the fuel cell system is achieved. Therefore, it can be said that the hydrogen separation membrane of the present invention is particularly useful in a field in which miniaturization and weight reduction of a power unit are strongly required, such as an automobile. It is general that the CO concentration in the fuel gas finally supplied to the fuel cell 222 is reduced to several tens ppm or less.
[0047]
Further, a second embodiment of the fuel cell system to which the hydrogen separation membrane of the present invention is applied will be described with reference to the drawings. FIG. 4 is a schematic diagram for explaining another embodiment of the fuel cell system. The second embodiment of the fuel cell system includes (i) a reforming section in which a reforming reaction from a hydrocarbon-based fuel gas to a hydrogen-rich gas proceeds, and (ii) a heat source for supplying heat required for the reforming reaction. Hydrogen production in which a combustion section, (iii) a hydrogen separation membrane for selectively passing hydrogen gas generated in a reforming section, and (iv) a hydrogen passage for hydrogen gas passing through the hydrogen separation membrane are integrated. It is a fuel cell system having a device. Here, “integrated” means that (i) a reforming section, (ii) a combustion section, (iii) a hydrogen separation membrane, and (iv) a hydrogen passage are included in one device. Means that hydrogen gas generated by the reforming reaction is separated directly from the reforming section by using a hydrogen separation membrane. Therefore, an embodiment in which a reformed hydrogen-rich gas is provided with a hydrogen separation membrane through a pipe does not correspond to “integration” in the present application.
[0048]
The reforming section means a portion where a reforming reaction from a hydrocarbon-based fuel gas to a hydrogen-rich gas proceeds. The combustion part is a part that burns using all or part of the remaining fuel from which hydrogen has been separated by the hydrogen separation membrane and / or excess hydrogen from the fuel cell, and is necessary for the reforming reaction performed in the reforming part. Means a site that generates a large amount of heat. As the hydrogen separation membrane, the hydrogen separation membrane of the present invention is used. The hydrogen passage means a portion to which the hydrogen gas separated by the hydrogen separation membrane is supplied. The shape is not particularly limited as long as the portion is supplied with hydrogen gas that has passed through the hydrogen separation membrane.
[0049]
In the hydrogen production apparatus in which the above (i) to (iv) are integrated, the reforming reaction is promoted, and downsizing of the fuel cell system can be achieved. The effect of such a hydrogen production device will be described using a fuel cell system having the hydrogen production device.
[0050]
A first fuel injection valve 312 and a water injection valve 313 in which a hydrocarbon fuel and water for generating high-purity hydrogen gas (reformed gas) are controlled by a signal from a control unit (C / U) 311 Is supplied to the evaporator 314. A combustion gas is separately supplied to the evaporator 314 from a combustion unit 325 in the hydrogen production device 324. The heat exchange between the hydrocarbon fuel and water and the combustion gas in the evaporator 314 causes the hydrocarbon fuel and water to evaporate in the evaporator 314.
[0051]
The vaporized hydrocarbon-based fuel and water are introduced into the reforming section 326 of the hydrogen production device 324 as fuel gas. The fuel gas introduced into the reforming section 326 is reformed using the heat generated from the combustion section 325. The combustion chamber 316 is provided with a second fuel injection valve 317, and when the amount of heat is insufficient, additional fuel is supplied by a signal from the control unit 311.
[0052]
In the reformed gas generated in the reforming section 326, hydrogen is isolated by the hydrogen separation membrane 320 provided in the hydrogen production device 324, and supplied to the fuel cell 322 through the hydrogen passage 327 as high-purity hydrogen gas. Is done. The gas that cannot pass through the hydrogen separation membrane 320 and the surplus hydrogen discharged from the fuel cell 322 are supplied to the combustion unit 325 and used to heat the reforming unit 326. The hydrogen production apparatus 324 is provided with the hydrogen separation membrane 320 of the present invention. For this reason, the hydrogen concentration can be significantly reduced by the hydrogen production device 324. In addition, effects such as suppression of manufacturing cost by reducing the amount of CO conversion catalyst used and downsizing of the fuel cell system by thinning the hydrogen separation membrane can be obtained.
[0053]
Air as an oxidant is supplied to the fuel cell 322 by the operation of the air control valve 323 receiving a signal from the control unit 311. In the fuel cell, an electromotive force is generated by the electrochemical reaction represented by the above formulas (5) to (7). In the second embodiment of the fuel cell system, the same electrochemical reaction occurs as in the first embodiment of the fuel cell system.
[0054]
In the hydrogen production apparatus according to the second embodiment, the hydrogen gas generated in the reforming section 326 is selectively isolated by the hydrogen separation membrane 320 simultaneously with the reforming reaction. Then, the fuel is supplied to the fuel cell 322 through the hydrogen passage 327. For this reason, the reforming reaction can be more effectively promoted as compared with the first embodiment. That is, hydrogen generated by the reforming reaction is quickly separated by the hydrogen separation membrane. As a result, the hydrogen concentration at the site where the reforming reaction occurs can be effectively reduced, and the chemical equilibrium is promoted in the direction in which the hydrogen is reformed. As a result of promoting the reforming reaction, the required capacity of the reforming catalyst can be reduced, and downsizing of the fuel cell system can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a hydrogen separation membrane of the present invention.
FIG. 2 is a graph showing the relationship between the thickness of a separation membrane and the concentration of CO in a gas passing through the separation membrane.
FIG. 3 is a schematic diagram illustrating a first embodiment of a fuel cell system.
FIG. 4 is a schematic diagram for explaining another embodiment of the fuel cell system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Support body, 102 ... Catalyst part, 103 ... Separation membrane, 104 ... Pinhole, 211 ... Control unit (C / U), 212 ... First fuel injection valve, 213 ... Water injection valve, 214 ... Evaporator, 215 ... reformer, 216 ... combustor, 217 ... second fuel injection valve, 218 ... hydrogen separation membrane unit, 219 ... primary side passage, 220 ... hydrogen separation membrane, 221 ... secondary side passage, 222 ... fuel cell, 223 ... air control valve, 311 ... control unit (C / U), 312 ... first fuel injection valve, 313 ... water injection valve, 314 ... evaporator, 316 ... combustion chamber, 317 ... second fuel injection valve, 320 ... hydrogen Separation membrane, 322: fuel cell, 323: air control valve, 324: hydrogen production device, 325: combustion unit, 326: reforming unit, 327: hydrogen passage.

Claims (16)

A support,
A catalyst portion comprising a CO conversion catalyst, which is disposed on at least one surface of the support;
A separation membrane formed on one surface on which the catalyst unit is arranged, and through which hydrogen is selectively passed;
A hydrogen separation membrane having: 2. The hydrogen separation membrane according to claim 1, wherein unevenness on the surface of the support is flattened by the catalyst portion. 3. 3. The hydrogen separation membrane according to claim 1, wherein the catalyst portion is disposed at a portion of the separation membrane where a pinhole exists. 4. The hydrogen separation membrane according to any one of claims 1 to 3, wherein the support is made of alumina, silica, or cordierite, or is made of a composite ceramic body thereof. The hydrogen separation membrane according to any one of claims 1 to 3, wherein the support is made of a hydrogen-resistant metal. The hydrogen separation membrane according to claim 5, wherein the hydrogen-resistant metal is SUS, pure iron, or a composite thereof. The hydrogen separation according to any one of claims 1 to 4, wherein the average particle diameter of the particles constituting the support is at least 5 times the average particle diameter of the particles constituting the catalyst portion. film. The hydrogen separation membrane according to any one of claims 1 to 7, wherein a thickness of the support is equal to or greater than a thickness of the separation membrane. The hydrogen separation membrane according to any one of claims 1 to 8, wherein the CO shift catalyst contained in the catalyst unit is a methanation catalyst that shifts CO to methane. CO shifting catalyst contained in the catalyst unit, hydrogen separation membrane according to any one of claims 1-9, characterized in that a shift catalyst for transforming CO to CO ₂ and H _{2 O.} The hydrogen separation membrane according to any one of claims 1 to 10, wherein the CO shift catalyst contained in the catalyst unit is a CO selective oxidation catalyst that selectively oxidizes CO. The hydrogen separation membrane according to any one of claims 1 to 11, wherein the catalyst portion is thinner than the thickness of the support and thinner than the thickness of the separation membrane. The separation membrane may be a simple substance of palladium (Pd), vanadium (V), niobium (Nb), tantalum (Ta), or zirconium (Zr), or a composite thereof, or the simplex or the composite and silver (Ag) 13. The hydrogen separation membrane according to claim 1, wherein the hydrogen separation membrane is an alloy with copper (Cu). The hydrogen separation membrane according to claim 1, wherein the thickness of the separation membrane is 2 μm or less. A hydrogen production apparatus comprising the hydrogen separation membrane according to claim 1. (I) a reforming section in which a reforming reaction from a hydrocarbon-based fuel gas to a hydrogen-rich gas proceeds; (ii) a combustion section for supplying heat required for the reforming reaction; and (iii) a reforming section. The hydrogen production apparatus according to claim 15, wherein the hydrogen separation membrane for selectively passing the hydrogen gas and (iv) a hydrogen passage for the hydrogen gas that has passed through the hydrogen separation membrane are integrated.

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