JP3770791B2 - High temperature type membrane reformer - Google Patents

Description

【００２６】
而して、かかるポリシラザンは、例えば、以下のように調製することができる。すなわち、ジハロシラン（Ｒ^１ＳｉＨＸ_２）或いは当該ジハロシランと他のジハロシラン（Ｒ^２Ｒ^３ＳｉＸ_２）との混合物をアンモニアと反応させることによってシラザンオリゴマーを得る。次いで、塩基性触媒の存在下で当該シラザンオリゴマーの脱水素反応を起こさせる。これにより、珪素原子に隣接する窒素原子の脱水素が行われ、結果、シラザンオリゴマーが相互に脱水素架橋して成るポリシラザンを生成することができる。なお、この生成プロセスに使用されるジハロシランの好ましいものは、上記Ｒ^１、Ｒ^２、Ｒ^３が、それぞれ、炭素数が１〜６の低級アルキル基、置換アリル基、非置換アリル基、炭素数が６〜１０の非置換アリール基、トリアルキルアミノ基、ジアルキルアミノ基のいずれかである。或いは、Ｒ^１は水素であり、Ｒ^２およびＲ^３が上記列挙した官能基のいずれかである。このときＲ^１、Ｒ^２およびＲ^３は全て同じ基でもよく、相互に異なる基でもよい。なお、上記ジハロシランの式中のＸはハロゲン基である。
なお、使用するポリシラザンの分子量に特に制限はないが、薄膜を形成する過程における粘性制御等の観点から、重量平均分子量で１０００〜２００００程度のものが好ましい。
【００２７】
而して、上述のようにしてシラザンオリゴマーから調製したポリシラザンまたは市販のポリシラザンを不活性雰囲気中で焼成することによって、微細孔を有する無機材料を形成することができる。概略すれば、典型的には予め所望する形状に成形された対称又は非対称構造を有するセラミック多孔質支持体の表面にポリシラザン溶液を所望する厚さ（例えば１〜３μｍ）で塗布する。次いで、乾燥処理を施すことによってポリシラザンから成る薄層を形成した後、不活性（非酸化性）雰囲気中で当該薄層を支持体ごと適当な温度条件下で焼成する。このことによって、微細孔が形成されたポリシラザン膜（水素分離膜）を当該支持体表面上に形成することができる。以下、より具体的に説明する。
【００２８】
上記ポリシラザン溶液の調製にあたっては、ポリシラザンを溶解するための溶媒として種々の有機溶媒を用い得る。例えば、ベンゼン、トルエン、キシレン等の芳香族系溶媒、ジオキサン、テトラヒドロフラン、ジブチルエーテル等のエーテル系溶媒が適当である。また、溶液中のポリシラザンの濃度は特に限定されないが、０．５重量％〜６０重量％程度が適当であり、１重量％〜２０重量％程度が好ましい。
【００２９】
また、かかるポリシラザン溶液を支持体の表面に塗布する方法としては、従来の薄膜形成プロセスにおいて用いられる各種の方法を採用することができる。例えば、ディップコーティング法、スピンコーティング法、スクリーン印刷法、スプレー法等が挙げられる。特にディップコーティング法では、ポリシラザン溶液の多孔質支持体内部への浸透を溶液濃度、操作条件等により制御でき、さらには不活性雰囲気中でのポリシラザンの熱分解に伴うガス発生、キャピラリー圧力、焼成収縮等による微細構造の破壊を抑制するのに寄与し得る。このため、特にディップコーティング法は、欠陥の無い多孔質セラミック膜を支持体表面に容易且つ直接的に形成するのに好適な塗布方法である。
あるいは、上記ポリシラザン溶液を支持体の表面に塗布する他の環境として製膜環境中に若干酸素を含む場合がある。この場合には、ゲル形成をプロセス中に伴う。支持体の表面部に比較的大きな細孔が分布する場合には、その細孔内部に原料溶液が奥深く浸透してしまうことによりその後のゲル化あるいは膜化が阻害されるという不具合が考えられる。さらに、膜が厚い場合では、乾燥に伴うキャピラリー圧力により、膜に欠陥を生じ易くなる。したがって、支持体の表面部に比較的大きな細孔が分布する場合にゾル−ゲル法を採用するときには、支持体の表面に予め別の平均細孔径が支持体より小さくなるセラミック層（以下「中間層」という。）を形成しておき、その滑らかな表面又は細孔内部にポリシラザン膜を積層する（即ち複数回繰返して製膜する）とよい。このことによって、支持体表面上に製膜されたポリシラザン膜の薄膜化且つ無欠陥化ができる。但し、このようにして得られる膜では、Ｓｉ−Ｏ結合を若干多く含むようになる。
【００３０】
而して、支持体表面にポリシラザン溶液を塗布（添加）して乾燥した後、当該ポリシラザン膜の付着している支持体を不活性（非酸化性）雰囲気中において焼成する。典型的には、実質的に酸素を含まない不活性ガス（窒素ガス等）中において、２００〜１３５０℃、好ましくは２００〜１０００℃（典型的には多孔質支持体の焼成温度以下及び中間層を形成する場合は当該中間層の焼成温度以下の温度とする。）の温度条件下で１〜４時間の焼成処理を行う。
かかる不活性雰囲気中における熱処理によって、耐熱性に優れる平均孔径が０．１ｎｍ〜５０ｎｍ（細孔径分布のピーク値：０．１〜５．０ｎｍ）であり、Ｓｉ−Ｎ結合の繰返し構造を基本骨格とするポリシラザン膜を形成することができる。
【００３１】
以上に説明したように、厳密で煩雑な製膜条件等を要することなく比較的簡便な手法によって、本発明の改質器に好適に用いられるポリシラザン膜を製造することができる。
ところで、多孔質支持体として窒化珪素系のものを使用した場合には、当該支持体（中間層を含む場合は当該支持体と中間層の両方）の基本骨格が、その表面に形成・積層されるポリシラザン膜と同じシラザン骨格である。このため、当該ポリシラザン膜にプロセス中に欠陥が発生するのを高度に抑制することができる。さらには、かかる欠陥発生を抑制する結果、従来のセラミック膜（例えばシリカ系の水素分離膜）よりも広範囲（典型的には５０００ｍｍ^２以上、好ましくは１５０００ｍｍ^２以上）に亘って薄く均質な水素分離膜を連続して形成することができる。このため、本発明に係るポリシラザン膜を用いると、それを採用する改質器の大型化を実現することができる。なお、このこと（作用効果）は、多孔質支持体としてアルミナ系のものを使用し、当該支持体上にアルミナ膜を形成・積層する場合にも当てはまる。
【００３２】
次に、本発明に係るシール材について説明する。本発明の改質器に用いるシール材には、６００℃又はそれ以上の高温に長時間曝された場合にも当該シール材自体が顕著に破壊・化学変化しない耐熱・耐化学性能が要求される。また、シール対象物（例えば上述の管状水素分離モジュールとジョイント部）が改質器稼働時の高温状態即ち加熱状態又は停止時の冷却状態となったことに起因して体積及び／又は形状変化（膨張、収縮変形）を起こした場合にも、そのような体積及び／又は形状変化に追随してシール状態を保持し得る柔軟性（クッション性）と高い圧縮・復元性能が要求される。
而して、これらの要求を好適に満たし得る材料として密度（嵩密度）が０．６〜１．９ｇ／ｃｍ³（特に好ましくは０．８〜１．２ｇ／ｃｍ³）の膨張黒鉛またはそれと同等の性状を有する耐熱性材料が挙げられる。以下、かかる材料について詳細に説明する。
【００３３】
天然黒鉛は炭素六員環平面が規則的に平行状態で積層した構造を持つカーボンであるところ、膨張黒鉛は、かかる天然黒鉛を濃硫酸、硝酸などの酸化剤により酸化処理することによって当該積層構造の層間距離を１００〜３００倍程度膨張させたものである。而して、かかる膨張黒鉛を上記密度範囲となるように負荷・圧縮することによって本発明に係るシール材に好適な膨張黒鉛材料を得ることができる。
かかる膨張黒鉛材料は黒鉛本来の高い耐熱性に加えて、シール性能に優れる稠密構造を有し、且つ、柔軟性並びに高い圧縮性及び弾性復元力を備えている。
かかる膨張黒鉛またはそれと同等の性質を有する耐熱性材料（典型的には膨張黒鉛と同等の熱膨張係数、酸化開始温度、圧縮率、復元率及び柔軟性（クッション性）を有する炭素質その他の無機材料）として好ましいものは、圧縮率（ＪＩＳ−Ｒ３４５３に基づく）が１０〜９０％（特に好ましくは４５〜５５％）であり、及び／又は、復元率（ＪＩＳ−Ｒ３４５３に基づく）が３〜７０％（特に好ましくは１０〜１５％）であり、及び／又は、酸化開始温度（空気中での加熱によって重量が１％減少したときの温度）が４００℃以上（特に好ましくは５００℃以上）であることを特徴とする膨張黒鉛又はその同等物である。また、窒素ガスのような不活性（非酸化性）雰囲気下において１１００℃又はそれ以上の温度（好ましくは１５００℃以上）まで所望するシール性能を維持し得る耐熱性を有するものが好適である。
かかる性状の膨張黒鉛等から形成されたシール材によると、高温稼働時においても特に優れたシール状態の保持を実現することができる。
【００３４】
なお、本発明に係るシール材の形状やタイプは、本発明の改質器の形状や水素分離モジュールの形状に対応して変動するものであり、特に限定はない。例えば、円筒形の管状水素分離モジュールを使用する場合には、当該水素分離モジュールの外壁に接する（即ち密着する）形状のシール材、典型的にはリング形状のシール材が好適に使用され得る。また、単板（モノリス）形状の水素分離モジュールを使用する場合には、当該水素分離モジュールの外縁部に接する形状のシール材、典型的にはシート形状のシール材が好適に使用され得る。特に制限するものではないが、かかる形状のシール材は、密度が０．６〜１．９ｇ／ｃｍ³（特に好ましくは０．８〜１．２ｇ／ｃｍ³）程度となるように調製された粉状膨張黒鉛を所定形状の型に充填してプレス成形したり或いはロール成形、レーザー加工することによって得ることができる。すなわち、かかる加圧成形によって当該黒鉛粉体（粒子）相互が自己接着して一体化し、結果、所望する形状（例えばＯリング様のパッキン形状）に成形され得る。あるいは、上記密度のシート（薄膜）状膨張黒鉛を積層・成形したものであってもよい。
また、構築する改質器の形状・タイプや使用条件によって適宜異なり得るが、シール性能が維持し得る限りにおいて、膨張黒鉛又はその同等物に関する他の物理的特性（熱伝導度、電気比抵抗、引っ張り強さ、熱膨張係数（但し低いものが好ましい）等）に特に制限はない。
【００３５】
本発明の改質器では、使用する改質触媒に特に制限はない。しかし、本発明の改質器は特に高温域（典型的には６００〜８００℃又は１１００℃迄の高温域）で使用することを意図したものであるから、かかる高温域で優れた触媒能を発揮し得るものが好ましい。例えば、多孔質アルミナ等の担体にパラジウム、ニッケル等の金属を担持させたものを好適に使用することができる。
また、触媒を備える部位、すなわち水素生成部の形状に特に制限はない。例えば、管状の水素分離モジュール（この場合には当該モジュール中空部が上記ガス通路となる。）を所定の反応容器（チャンバー）に収納し、そのモジュール周囲の空間に触媒を充填したものであってもよい。あるいは、かかる管状水素分離モジュールの外表面に膜状触媒層を形成（典型的にはコーティング）する形態であってもよい。なお、本発明は、基本的に吸熱反応系の改質反応を高温で動作させる場合に、上記形態を適用するものである。
【００３６】
【実施例】
本発明を以下の実施例によりさらに詳細に説明する。本発明はこれらの実施例に限定されるものではない。
【００３７】
＜実施例１＞
管状の水素分離モジュールを次のようにして作製した。すなわち、９０重量部の窒化珪素粉末（宇部興産製品：ＳＮ−Ｅ１０）と、５重量部のアルミナ粉末（住友化学工業製品：ＡＫＰ−１０）と、５重量部のイットリア粉末（三菱化学製品：Ｙ−Ｆ）と、８０重量部の水をアルミナ製ポットに投入し、直径３０ｍｍの玉石を使用して２４時間混合することによってスラリーを調製した。次いで、このスラリーに１０重量部のワックス系有機バインダーと、４重量部のワックスエマルジョンを添加して１６時間混合し、その後スプレードライにより顆粒体を作製した。
得られた顆粒体をＣＩＰ（冷間静水圧プレスによる）成形し、管形状（外径：１０ｍｍ、内径：７ｍｍ、長さ：２５０ｍｍ）に生加工した。そして、当該生加工チューブを脱脂後、１４００℃（最終焼成温度）で焼成し、管形状の窒化珪素多孔体、即ち本実施例に係る支持体を得た（図１の符号１４参照）。
【００３８】
得られた窒化珪素多孔体の細孔径（平均孔径）および孔隙率は、水銀圧入法によって測定した結果、それぞれ０．１６μｍおよび４７％であった。また、製膜面に相当する素焼き表面の８００℃における３点曲げ強度は約７０ＭＰａ以上であった。従って、かかる管（チューブ）形状の窒化珪素多孔体は、水素分離モジュールにおける支持体として充分な機械的強度を有する。なお、かかる多孔体の嵩密度は１．７７ｇ／ｃｍ^３であった。また、熱的強度の指標となる線膨張係数は２５〜８００℃の範囲でおよそ３．４×１０^−６／Ｋであった。
また、かかる多孔体はα−Ｓｉ_３Ｎ_４の結晶構造を有しており、組織は熱的に安定である。しかも、細孔径分布（孔径の変動幅）がたいへん狭く、水素分離モジュール用支持体として好ましい。すなわち、かかる性状の窒化珪素多孔体を用いると、上述したような中間層を形成することなくその表面に概ね無欠陥のセラミック膜（水素分離膜）を製膜することができる。
【００３９】
次に、上記得られた窒化珪素多孔体の外壁面（即ちチューブ円柱面の外周面）に水素分離膜としてポリシラザン膜を形成した（図１の符号１２参照）。
すなわち、ポリシラザン粉末（チッソ製品：ＮＣＰ２０１）をトルエンに溶解し（超音波攪拌処理）、ポリシラザン濃度が１０重量％であるポリシラザン溶液（コーティング溶液）を調製した。
次いで、上記窒化珪素多孔体をディップコーティング法に基づきコーティング溶液に浸漬した。なお、この浸漬処理の際には窒化珪素多孔体の外周面にのみコーティング液が付着するように、当該窒化珪素多孔体の片端開放部を合成樹脂フィルムでラップした。
浸漬後、一定の速度で窒化珪素多孔体をコーティング溶液から引き上げ、室温で乾燥した。その後、上記浸漬によってポリシラザン被膜がその外側面に形成されている窒化珪素多孔体を真空・加圧焼結炉に入れ、大気圧・窒素雰囲気中で熱処理を行った。
かかる一連の処理によって、窒化珪素多孔体の外周面にポリシラザン膜が形成された管状水素分離モジュールが得られた（図１の符号１０参照）。
【００４０】
次に、上記管状水素分離モジュール１０を利用して本実施例に係る改質器１を作製した。図１は、本実施例に係る改質器の主要部を模式的に表した説明図である。
この図に示すように、本実施例に係る改質器１は、大まかにいって、筒状のステンレス製チャンバー２と、ポリシラザン膜１２を備えた支持体（窒化珪素多孔体）１４を本体とする水素分離モジュール１０と、改質触媒１８とから構成されている。
チャンバー２には、別途、ガス供給管３と、ガス排出管４とが設けられている。また、チャンバー２の周囲にはヒーター８２（図３参照）および図示しないウォータージャケット（断熱材）が設けられており、チャンバー２内部の温度を室温〜１２００℃の範囲でコントロールすることができる。また、かかるチャンバー２の内部には、上記水素分離モジュール１０が配置されており、その周囲の空間部（水素生成部に相当する部位）２０には、触媒１８を充填することができる。
図示されるように、水素分離モジュール１０の一端は金属製キャップ５によって塞がれており、当該端部から中空部１６へのガスの流入を防止している。また、かかる水素分離モジュール１０の他端側には、本実施例に係るジョイント管３０が取り付けられている。
以下、かかるジョイント管３０について詳細に説明する。
【００４１】
図２に詳細に示すように、このジョイント管３０はいくつかの部材から構成されている。すなわち、ステンレス製の管状凸型ユニオン（フランジ）３４と、それに対応する管状凹型ユニオン（フランジ）４４と、それに付設される金属製の第１リング部材３２及び第２リング部材４２ならびに本実施例に係るシール材３８とから構成されている。なお、凸型ユニオン３４の根幹部（フラットな円盤状フランジ）中央には、水素分離モジュール１０を貫通し得るサイズの穴４６が形成されている。他方、凹型ユニオン３０の根幹部（フラットな円盤状フランジ）中央には、水素分離モジュール１０の中空部（以下「透過ガス通路１６」という。）に通じる透過ガス排出口６が形成されている。
また、シール材３８はリング状に形成された膨張黒鉛から成る部材であり、その嵩密度は１．０ｇ／ｃｍ³、ＪＩＳ−Ｒ３４５３に基づく圧縮率は約５０％であり、復元率は約１０％であった。
【００４２】
而して、図２に示すように、管状水素分離モジュール１０の一端を管状凸型ユニオン３４の穴４６に差し込む。また、管状凸型ユニオン３４の反対側（即ち突出部３６の形成されている側）から上記第１リング部材３２、シール材３８、第２リング部材４２の順に、上記穴４６を貫通してきた管状水素分離モジュール１０に嵌め入れる。このとき、図示されているように、リング形状シール材３８の内径は管状水素分離モジュール１０の外径より若干大きく形成されている。このことと膨張黒鉛特有の柔軟性により、当該モジュール１０の一端にリング形状シール材３８を嵌め入れた際には、その内壁面をモジュール１０外周面に密着させることができる。
【００４３】
次いで、上記凹型ユニオン４４を凸型ユニオン３４に締め付けることによってジョイント管３０の取付けが完了する。すなわち、図２に示すように、凹型ユニオン４４の突出部４０の内壁面及び凸型ユニオン３４の突出部３６の外壁面には、それぞれ、相互に対応する雌ねじ及び雄ねじが形成されている。さらに、凸型ユニオン３４の突出部３６は、先端部から根幹部に向けて直径が漸増するように形成されている。かかる構成の結果、凹型ユニオン４４を凸型ユニオン３４と嵌め合わせる（螺合する）ことによって、シール材３８を水素分離モジュール１０の外周面及び凹型ユニオン３４の突出部３６内壁面の双方に強く密着させることができる。すなわち、凹型ユニオン４４を凸型ユニオン３４の根元方向に螺合していくと、先端部から根幹部に向けて直径が漸増している凸型ユニオン３４の突出部３６が縮小されるに従い、上記シール材３８を水素分離モジュール１０と凹型ユニオン３４に密着させることが実現される。
このとき、図示されているように、本実施例に係るジョイント管３０では、所定のレベルまで両ユニオン３４，４４の螺合がなされた時点で、第２リング部材４２の一部４２ａが両ユニオン３４，４４の間に挟まれてストッパーの役割を果たす。このことによって、それ以上の螺合（ねじ締め）が制止され、シール材３８が必要以上に圧迫されることを防止する。従って、本実施例に係るジョイント管３０によると、上記ねじ締めが制止される時点まで両ユニオン３４，４４を螺合することによって常に最適な圧力（面圧）でシール材３８を両部材１０，３４（３６）に密着させることができる。他方、改質器１の高温稼働時における水素分離モジュール１０とジョイント管３０（即ち金属製ユニオン３４，４４）との間の体積変化量のギャップに対応させるべく、両ユニオン３４，４４と水素分離モジュール１０は接触させていない。
【００４４】
以上のようにしてジョイント管３０を取り付けた結果、水素分離モジュール１０の外部から水素分離膜１２及び支持体１４を透過して透過ガス通路１６に送出された水素リッチなガスは、ジョイント管３０の透過ガス排出口６を介して外部に排出される。このとき、図示される位置にシール部材３８を取り付けていることによって、水素生成部２０（図１参照）のガスがジョイント管３０（凹型ユニオン３４）と水素分離モジュール１０との隙間（即ち凹型ユニオン３４の穴４６）を介してリークするのを防止することができる。さらに、かかるシール材３８が上記性状の膨張黒鉛で構成されている結果、６００℃以上の高温稼働時において、ジョイント管３０（凹型ユニオン３４）と水素分離モジュール１０との隙間サイズが線膨張係数が異なる二材料間の温度変化に伴い多少変動した場合であっても、かかるシール材３８によってシール性能を維持することができる。
なお、ジョイント管３０の一部とチャンバー２の一部とは相互に溶接されており、チャンバー２内の気密状態は確保される。
【００４５】
次に、上記のようにして構築した水素分離モジュール１０を備えた改質器１（図１）を用いて、水素分離性能とシール性能を評価した。
先ず、図３に示すような水素分離モジュール（水素分離膜）を備えた膜型ガス分離システム（評価システム）を構築した。すなわち、改質器１のガス供給管３に、メタン供給装置５２、水素供給装置５４、窒素供給装置５６をガスクロマトグラフ７８、８０等を介して接続した。
図３に示すように、メタン供給装置５２は、圧力バルブを備えたメタン供給ボンベ５９、圧力計５８、流量計６４、ニードルバルブ７０等から構成されている。同様に、水素供給装置５４は、圧力バルブを備えた水素供給ボンベ６１、圧力計６０、流量計６６、ニードルバルブ７２等から構成されている。また、窒素供給装置５６は、圧力バルブを備えた窒素供給ボンベ６３、圧力計６２、流量計６８、ニードルバルブ７４等から構成されている。また、図示されているように、メタン供給装置５２と水素供給装置５４の流路はスリーウェイコック７６で連結されている。
さらに、改質器１のガス供給管３には、別途、水蒸気供給装置１００が接続されている。かかる装置は図示しない水蒸気供給源とマイクロフィーダー（水蒸気供給ポンプ）１０２とを主要構成要素としている。
他方、図４に示すように、改質器１のガス排出管４側には、圧力計１１２、ガスクロマトグラフ１１４、トラップ１１６、セッケン膜流量計１１８等を接続した。同様に、改質器１の透過ガス排出口６にも、圧力計１０４、ガスクロマトグラフ１０６、トラップ１０８、セッケン膜流量計１１０等を接続した。このようなシステムを構築することで、詳細なガス分析（改質器への供給側及び排出側の双方）を行うことができる。ガス分析では、キャリアガス（スウィープガス）はＡｒ、Ｈｅを使用し、分析対象ガスはＣＨ₄、Ｈ₂、ＣＯ、ＣＯ₂、Ｏ₂、Ｎ₂とした。
なお、本実施例に係る評価試験では、触媒１８をチャンバー２内に充填せずに行った。
【００４６】
而して、図３に示すガス分離システムを用いて水素分離性能とシール性能の評価を純ガス透過試験に基づいて行った。この試験では、水素供給装置５４および窒素供給装置５６から所定の流量で水素及び窒素をチャンバー２内に供給した。このとき、水素分離膜１２前後の差圧が２．０×１０^４Ｐａ（０．２ａｔｍ）となるようにした。
なお、かかる評価試験は、先ず室温で実施し、所定時間後、チャンバー２内の温度を７００℃に上げて同様に実施した。その後チャンバー２内の温度を再び室温に戻して同様に実施した。このように温度を変更させつつ連続的に試験することで、本実施例に係る改質器１のシール性能および高温時における水素分離特性を評価できる。
【００４７】
具体的には、適宜ヒーター８２を作動させてチャンバー２内の温度調節（室温〜７００℃〜室温）を行いつつ、上記差圧を生じさせた状態で水素及び窒素をそれぞれチャンバー２内に供給した。而して、セッケン膜流量計１０８によって透過側（即ち透過ガス排出口６と接続するガス排出側流路）の流速を測定しつつ、ＴＣＤ検出器を備えたガスクロマトグラフ１０６によって対象ガス組成を分析した。なお、水素および窒素それぞれのガス透過率は次の式「Ｑ＝Ａ／（（Ｐｒ−Ｐｐ）・Ｓ・ｔ）」から算出した。ここでＱはガス透過率（モル/m²・s・Pa）、Ａは透過量（ｍｏｌ）、Ｐｒは供給側即ちチャンバー内部空間側の圧力（Ｐａ）、Ｐｐは透過側即ち透過ガス通路側の圧力（Ｐａ）、Ｓは断面積（ｍ^２）、ｔは時間（秒：ｓ）を表す。また、水素／窒素透過係数比は、水素透過率と窒素透過率との比率すなわち式「α＝Ｑ_Ｈ２／Ｑ_Ｎ２」から算出できる。ここでαは水素／窒素透過係数比（透過率比）、Ｑ_Ｈ２は水素透過率、Ｑ_Ｎ２は窒素透過率を表す。
上記試験の結果として、水素透過流量および窒素透過流量ならびに水素／窒素透過係数比を表１に示す。
【００４８】
【表１】

【００４９】
表１から明らかなように、温度条件の推移に関わらず、水素／窒素透過係数比に顕著な差異は認められなかった。このことから、チャンバー２と水素分離モジュール１０との隙間から実質的なガスのリークは起きていないことが確認された。また、水素分離膜１２やシール材３８が加熱によって劣化していないことも確認された。すなわち、上述したシール材３８は、７００℃のような高温条件においても良好なシール性能（表中の○）を有していた。この結果は、チャンバー２内におけるシール状態をかかる高温条件下でも維持し得ることを裏付ける結果である。
また、７００℃での水素／窒素透過係数比の値から鑑みて、本実施例に係る水素分離膜では、かかる高温条件下でもクヌッセン分離程度の水素分離性能を有することが確認された。なお、本実施例の７００℃での水素透過率は、０．３×１０^-6モル/m²・ｓ・Paであった。
【００５０】
＜実施例２＞
次に、実施例１に記したのと同様の条件の処理を行って、管形状の水素分離モジュール（外径：１０ｍｍ、内径：７ｍｍ、長さ：２５０ｍｍ）を作製した。なお、本実施例においては、同様の処理によって計３つの水素分離モジュールを作製した（表２中のＮｏｓ．１〜３）。表２に示すように、これら３つの水素分離モジュールの外周面には、それぞれ、約８１００ｍｍ^２（Ｎｏ．１）、約７７６０ｍｍ^２（Ｎｏ．２）、約８２００ｍｍ^２（Ｎｏ．３）の連続したポリシラザン膜を形成した。また、表２に示すＮｏ．４のサンプルとして、所定の管状支持体（窒化珪素）表面上に、上記と同様の処理を行ってポリシラザン膜を５回繰り返し製膜したもの（膜面積：１８００ｍｍ^２）を作製した。
【００５１】
【表２】

【００５２】
而して、後述する本実施例の改質試験では、これらのサンプルを適用した。メタン改質反応を例に挙げると、改質ガスである水素又は二酸化炭素を優先的に本膜により除去できれば、平衡理論から改質反応は正反応の方向に促進される。従って、水素分離膜の選択性が高い程、同一条件での反応転化率が明らかに高くなることが推定される。本膜においても、水素分離性能を向上するためにポリシラザン膜を５回繰返し製膜をしたところ（表２のＮｏ．４）、常温で水素／窒素透過係数比１５を実現している（表２参照）。従って、この膜を適用することにより、より水素リッチな改質ガスを得ることが可能であるとともに、用途拡大が期待できる。なお、高温域での安定使用とスケールアップに対して特に構造上の問題はない。
走査型電子顕微鏡（ＳＥＭ）による測定によって、上記３つの水素分離モジュール（Ｎｏｓ．１〜３）にそれぞれ形成されたポリシラザン膜には、少なくともサブミクロンオーダーの表面欠陥は認められなかった。また、一般的なアルゴン吸着法によって各水素分離モジュール（Ｎｏｓ．１〜３）のポリシラザン膜に存在する細孔の孔径をバルク体に関して測定したところ、その細孔径のピーク値はいずれも約２ｎｍであった。また、形成された膜厚は、約５μｍであった。
【００５３】
なお、本発明を限定するものではないが、比較のために中間層を形成した窒化珪素多孔体も同時に作製した。すなわち、ポリシラザン粉末（同上）と窒化珪素粉末（同上）を原料に用いて、固形分濃度が概ね１〜１０重量％となるようにこれらにキシレンを添加することによって、中間層形成用スラリーを調製した。次いで、１時間の超音波処理による攪拌状態の中間層形成用スラリー中に、上記と同様の処理によって得られた管状の窒化珪素多孔体を浸漬した（ディップコーティング法）。なお、この浸漬処理の際には管状窒化珪素多孔体の外周面にのみ、このスラリーが付着するように、その両端開放部を合成樹脂フィルムでラップしておいた。浸漬処理後、一定の速度でかかる窒化珪素多孔体をスラリー含有容器から引き上げ、室温で４８時間乾燥した。その後、上記スラリー由来の被膜が外周面に形成されている管状窒化珪素多孔体を真空・加圧焼結炉に入れ、大気圧・窒素雰囲気中で熱処理を行った。
このことによって、管状窒化珪素多孔体の外周面に中間層が形成された。かかる処理によって得られた中間層は、ＳＥＭ観察等によって、窒化珪素をマトリックスとしてその隙間をポリシラザンが埋める微構造を有していることが明らかとなった。また、このようにして作製された中間層には、少なくともサブミクロンオーダーの表面欠陥は認められなかった。
【００５４】
次いで、実施例１と同様の処理によって、当該得られた窒化珪素多孔体の外周面（即ち中間層の表面）にポリシラザン膜（水素分離膜）を形成した。その結果、表２に記載のものと同様、中間層の表面に８０００ｍｍ^２以上に亘って連続したセラミック膜（ポリシラザン膜）が形成された。ＳＥＭによる測定によって、かかる中間層上に形成された多孔質セラミック膜には、少なくともサブミクロンオーダーの表面欠陥は認められなかった。また、このセラミック膜に存在する細孔の孔径をバルク体について測定したところ、その平均細孔はいずれも約２ｎｍ以下であった。形成された膜厚は約５μｍであった。すなわち、中間層を形成した場合も同様の性状の水素分離モジュールを形成することができた。
【００５５】
次に、上記得られたＮｏ．１〜Ｎｏ．３のモジュールについて、実施例１と同様の評価試験を行った。すなわち、上述のようにしてジョイント管３０及びキャップ５を取り付けた後、図１に示す改質器１を構築し、さらには図３に示すガス分離評価システムを用いて、７００℃の温度条件下、水素透過率および水素／窒素透過係数比を測定・算出した。なお、測定条件や算出方法は実施例１と同様である。
表２に示すように、上記３つのモジュール（水素分離膜）間で水素透過率及び水素／窒素透過係数比に顕著な差異は認められなかった。また、これらの値は、実施例１に係る水素モジュールについての結果と同様であった。このことから、本実施例で得られた水素分離モジュールについてもチャンバーと水素分離モジュールとの隙間から実質的なガスのリークは起きておらず、水素分離膜やシール材が加熱によって劣化していないことが確認された。すなわち、上述した膨張黒鉛から成るシール材とポリシラザン膜とを併用することにより、７００℃という高温域であっても常に高い水素透過能及び分離能を実現し得ることが確認された。なお、本発明は、表２中のＮｏ．４に示される高性能な高温対応型水素分離膜に対しても適用可能な技術である。膜構造上、Ｎｏ４はＮｏ．１〜３に対して製膜回数を５回に増した場合である。
【００５６】
＜実施例３＞
次に、表２に示すＮｏ．１の水素分離モジュールと所定の改質触媒とを用いて改質器を作製し、高温域における改質効率に関して詳細に評価した。
本実施例では、図４に模式的に示すように、使用する水素分離モジュール１０Ａの両端に実施例１で使用したものと同じ構造のジョイント管３０，３０Ａを各々取り付けた。次いで、かかる二つのジョイント管３０，３０Ａが取り付けられた状態の水素分離モジュール１０Ａを所定のサイズ（内部容積：約１９００ｍｌ）のチャンバー２内に配置した。
すなわち、図４に示すように、ジョイント管３０，３０Ａの各々に設けられている開口部、即ち透過ガス排出口６と透過ガス通路１６に直接ガスを供給するガス供給口６Ａとがチャンバー２外部に露出した状態となるようにして、これらジョイント管３０，３０Ａの一部とチャンバー２の一部とを相互に溶接した。
さらに、図４に示すように、水素分離モジュール１０Ａの周囲（水素生成部２０）には、粒状の多孔質アルミナ（粒径：０．５〜３ｍｍ）にニッケルを担持して成る触媒粒子（ニッケル系改質触媒）１８を約４００ｇ充填した。なお、かかる触媒１８としては、改質反応に使用していない新しいものを用いた。このようにして本実施例に係る改質器１Ａを構築した。
【００５７】
次いで、かかる改質器１Ａを用いて、改質試験を行った。すなわち、かかる改質器１Ａを組み込むことによって、図３に示すガス分離評価システム（ガス改質システム）を構築した。なお、図３に破線で示しているように、実施例１と異なる点は、水素供給装置５４等と同様の機材によって構成されたスウィープガス（ここではヘリウム）供給装置９０を別途装備し、スウィープガス供給管をガス供給口６Ａに接続していることである。このことによって、当該スウィープガス供給装置９０からガス供給口６Ａを介してスウィープガス（Ｈｅ）を水素分離モジュール１０Ａの透過ガス通路１６に直接供給することができる。
【００５８】
而して、図３及び図４に示すように、上記改質器１Ａを備えたガス分離システム（ガス改質システム）によると、ガス供給管３から非酸化条件下で供給された原料ガス（ここでは窒素とともに水蒸気を含むメタンが供給される。）がチャンバー２Ａ内の水素生成部２０に導入され、そこに充填されている触媒１８の作用即ち水蒸気改質反応（ＣＨ₄＋Ｈ₂Ｏ＝ＣＯ＋３Ｈ₂、ＣＯ＋Ｈ_２Ｏ＝ＣＯ_２＋Ｈ_２）によって水素が生成する。生成した水素の一部は、管状水素分離モジュール１０Ａの水素分離膜１２Ａ及び多孔質支持体１４Ａを透過して水素生成部２０側から管内部のガス通路１６側に分離され、当該透過ガス通路１６から透過ガス排出口６を通ってチャンバー２Ａ外部に送出される。
一方、水素生成部２０に導入されたガスであって水素分離膜１２Ａを透過しなかったものは、チャンバー２Ａ内からガス排出管４を介して外部に排出される。なお、本実施例に係る改質器１０Ａについても、ジョイント管３０，３０Ａに備えられているシール材３８（図２参照）によって水素分離モジュール１０Ａとジョイント管３０，３０Ａとの隙間がシールされている結果、原料ガスが水素分離膜１２Ａを経ずに当該隙間から透過ガス通路１６に漏出（リーク）することがない。従って、かかる構成の改質器１０Ａおよびそれを備えたガス改質システムによると、改質反応に伴って水素分離膜１２Ａを通して、反応生成物である水素が分離されることにより、水素生成部における水素濃度が減少する。これにより、反応物質側に平衡がシフトして、メタンから水素への転化反応が促進される。すなわち、本実施例に係る改質器１０Ａでは、特に６００℃以上（更には７００℃又は８００℃以上）の高温域において水素透過性能及び分離能性能に優れる高温対応タイプのポリシラザン膜と上記シール材との併用によって、かかる高温域における原料ガス（ここではメタン）から水素への高い転化率を安定して実現することができる。
次に、かかるガス改質システムによるガス転化率を以下のようにして調べた。
【００５９】
本実施例に係る改質試験では、改質反応温度条件として、６００℃、７００℃及び８００℃の３通りを設定して、以下のように行った。
すなわち、先ず、窒素を微量パージしつつ改質器１０Ａのチャンバー２Ａ内を上記いずれかの設定温度まで昇温した。続いて、メタン、水蒸気及び窒素を図３に示す各供給装置５２，１００，５６（室温で稼動）からガス供給管３を介してチャンバー２Ａ内に導入しつつ水素還元処理を約１時間行った。このとき、チャンバー２Ａ内に供給する各ガスの供給量は、次のとおりとした。すなわち、設定温度が６００℃のときは、メタン、水蒸気及び窒素の供給量（ml／min.）をそれぞれ９．０、０．０３及び１０とした。また、設定温度が７００℃のときは、メタン、水蒸気及び窒素の供給量をそれぞれ９．５、０．０３及び１０とした。さらに、設定温度が８００℃のときは、メタン、水蒸気及び窒素の供給量をそれぞれ９．５、０．０３及び１０とした。なお、スチーム比（H₂O／CH₄）は、モル比で約５とした。また、改質器（チャンバー内）の圧力は２．０×１０^５Ｐａ（２．０ａｔｍ）以内とした。さらにこの処理の間、スウィープガス（Ｎｅ）を所定の流量でガス供給口６Ａから透過ガス通路１６に導入した。
【００６０】
而して、かかる処理によって水素生成部２０において水蒸気改質反応が行われるところ、本実施例では３０分間隔で供給ガス（即ちチャンバー２Ａのガス供給管３に供給される前のもの）および改質ガス（即ちチャンバー２Ａのガス排出管４から排出された後のもの及び透過ガス排出口６から排出された後のもの）を計２回サンプリングし、ＧＣ（CHROMPAVK製：Micro-GC CP2002）を用いて分析（ＣＨ₄、Ｈ₂、ＣＯ、Ｏ₂、Ｎ₂の分析ではカラム温度１００℃で分析時間２分；ＣＯ₂の分析ではカラム温度８０℃で分析時間２分）を行った。ＧＣでの測定結果に基づいて原料ガス（メタン）から水素への転化率（％）を算出した。
【００６１】
而して、１時間の水素還元処理後、透過側ガス流（即ちスウィープガス流）を封止し、上記差圧をなくした。これにより、水素生成部２０から水素分離膜１２Ａを介する実質的なガス透過を遮断した。この状態のまま、原料メタン、水蒸気及び窒素を上記供給量でチャンバー２Ａ内に供給し続けた。そして、透過側ガス流の封止から１．５時間経過後および更に０．５時間経過後の２回（即ち３０分間隔）、供給ガスおよび改質ガスをサンプリングし、ＧＣを用いて上記と同様に分析を行った。
その後、上記差圧を設けた状態で透過側ガス流（即ちスウィープガス流）を再開した。これにより、水素生成部２０から水素分離膜１２Ａを介する実質的なガス透過が再開された。この状態のまま、原料メタン、水蒸気及び窒素を上記供給量でチャンバー２Ａ内に供給し続けた。そして、透過側ガス流の再開から１．５時間経過後および更に０．５時間経過後の２回（即ち３０分間隔）、供給ガスおよび改質ガスをサンプリングし、ＧＣを用いて同様に分析を行った。かかるサンプリング（各２回）および分析（計６回）終了後、先ずメタンガスの供給を停止し、次いで水蒸気の供給を停止した。
【００６２】
【表３】

【００６３】
上記ＧＣの分析に基づいて算出した転化率（％）を表３に示す。なお、この表における「膜透過側ガス流・有り」のものは、上記透過側ガス流再開後に測定したデータである。
表３に示す結果から明らかなように、いずれの温度条件下においても、「膜透過側ガス流・有り」のもの即ち本実施例に係る水素分離モジュールを適用した場合のほうが、「膜透過側ガス流・無し」のもの即ち本実施例に係る水素分離モジュールを実質的に使用しなかった場合（即ち水素分離膜の無い従来型の改質器に相当する。）よりも、高効率に原料ガス（ＣＨ₄）の改質反応が行われたことを実証した。このことから、本実施例に係る水素分離モジュールに形成されたポリシラザン膜の高温域における高い水素透過性能・分離性能又はシール性能の維持を実証したことになる。尚、反応に直接影響してないＮ₂ガスを省略し、改質ガスに関してＨ₂、ＣＨ₄、ＣＯ、ＣＯ₂各々の組成を検証したところ、ＣＯ、ＣＯ₂組成に対するＨ₂組成について理論反応式との整合も確認されている。
また、本実施例において使用したニッケル系改質触媒の好適温度は、操作条件にもよるが概ね８２０℃である。従って、上記ポリシラザン膜とかかる高温型の改質触媒とを併用する本実施例の改質器１Ａによると、優れた改質反応および水素分離に伴う化学平衡シフトにより、６００〜８００℃（又は６００〜１０００℃）という高温域で高効率に水素を製造することができる。なお、このことは「膜透過側ガス流・有り」のものは「膜透過側ガス流・無し」のものよりも改質反応後のメタン残存量が顕著に減少しており且つ改質ガス中の水素濃度は逆に顕著に増大している（ＧＣ分析結果）ことからも確認されている。
なお、本実施例に係る改質試験とは逆に、膜透過側ガス流を(1).無し、(2).有り、(3).無しの順番に処理を行い逐次サンプリングした改質ガスを同様に分析したところ、(1).無しのときのサンプリングと(3).無しのときのサンプリングとの間で分析結果に顕著な差異は見いだせなかった。このことより、本実施例における触媒反応の経時的変化の影響は無視できるレベルにあると判断できる。
【００６４】
また、表３に示す本実施例の結果から明らかなように、本実施例に係る改質器１Ａでは、７００℃や８００℃といった高温条件下で使用した時でも良好な化学平衡シフト（即ちポリシラザン膜を介する水素の選択的な分離による水素生成部での水素濃度の低下に基づく）を実現することができた。
このことは、実施例１に係る改質器１と同様、チャンバー２Ａと水素分離モジュール１０Ａとの隙間から実質的なガスのリークは起きていないか或いは改質反応に影響しない程度であることを示すものである。すなわち、上述したシール材３８（図２）が、８００℃のような高温条件においても良好なシール性能を維持し得ることを実証したものである。すなわち、金属製ジョイント管３０，３０Ａとセラミック製水素分離モジュール１０Ａとの隙間サイズはこれら部材の材質の相違に基づく膨張係数の違いから高温状態になるに従い徐々に拡大する傾向にあるところ、膨張黒鉛の優れた弾性変形能力（柔軟性・クッション性）によって、当該変動する隙間のシール状態を維持することができる。
また、特に、本実施例に係る水素分離モジュール１０Ａの支持体は、圧縮強度に優れる窒化珪素製である。このことによって、水素分離モジュール１０Ａの破壊を未然に防止しつつシール材３８に対する締め付け力を必然的に大きくすることができる。すなわち、比較的強く圧縮変形させることによって、膨張黒鉛製シール材３８自体の気密性及び弾性復元量の双方を向上させ、結果、高温域でのシール性能をより向上させることができる。
【００６５】
＜実施例４＞
次に、ポリシラザン膜に代えてアルミナ膜を備えた水素分離モジュールを作製した。
すなわち、３０００重量部のアルミナ粉末（５０％粒子径約３μｍ）に１００重量部の有機バインダーを添加して混合した。この混合物に６０重量部のワックスエマルジョンと６０重量部のポリエーテル系合成油（潤滑剤）と４２０重量部のイオン交換水を添加して混練し、押出し成形用坏土を得た。
次いで、その坏土を押出成形機により押出し成形した後、マイクロ波で乾燥し、空気雰囲気で熱処理して、多孔質アルミナの管状支持体を得た。
【００６６】
次いで、上記得られた多孔質管状支持体の表面を緻密化した。すなわち、１２００重量部の高純度α−アルミナ粒子（平均粒子径約０．２μｍ）に８２５重量部の蒸留水を加え、攪拌・混合しながら硝酸を添加してｐＨ調整した。そして、超音波ホモジナイザーによる撹拌後、ボールミルで混合した。
その混合物に、１４０重量部の有機バインダーに６６０重量部の蒸留水を加えて加熱スターラーで攪拌・混合した溶液と、７２重量部の可塑剤とを添加した。その後、当該調製したスラリーに約１．４規定の硝酸を添加してｐＨ調整し、ボールミルで混合して製膜用スラリーを得た。
次に、その製膜用スラリーを真空脱泡（泡抜き）した。その後、かかるスラリー中に、予め外表面研磨した上記多孔質支持体を３０秒間浸漬した。これにより、外表面に緻密層を形成した支持体を、次いで、室温大気中で乾燥し、空気雰囲気で焼成（１０３０℃）することによって、α−アルミナ層が外表面に形成された管状支持体を得た。
【００６７】
次に、かかる管状支持体のα−アルミナ層の表面及び細孔内に均質な緻密層を作製した。すなわち、１９重量部のγ−アルミナ微粒子（平均粒子径数十ｎｍ）に１９６０重量部の蒸留水を加え、それらを室温においてスターラーで２日間攪拌・混合した。その後、さらに超音波ホモジナイザーで撹拌して製膜用ゾルを調製した。その後、その製膜用ゾルに真空脱泡を施した。
次いで、その製膜用ゾル中に、上記多孔質支持体を浸漬した。それを室温大気中で乾燥し、空気雰囲気で焼成（９００℃）することによって、当該支持体の外表面の第１層（α−アルミナ層）の表面及び細孔内に、均質な緻密層である第２層（γ−アルミナ層）を形成した。
その後、当該得られた多孔管状支持体上に更に均質な緻密層（膜）を形成するため、上記製膜用ゾルの濃度を下げた低濃度製膜ゾルを用いて同様に処理することによって、第２層の外面に更に均質且つ緻密なγ−アルミナ層が形成されたアルミナ製ガス分離モジュール（外径：１０ｍｍ、内径：７ｍｍ、長さ：２５０ｍｍ、膜面積７９００ｍｍ^２）を作製した。
【００６８】
一般的な細孔分布測定法（ここでは水銀圧入法）によると、本実施例に係るガス分離モジュールの多孔質支持体部分の平均細孔径は約８μｍであり、気孔率は約３９％であった。また、本実施例に係る水素分離モジュールの膜部断面及び最表面をＳＥＭ観察した結果、上記第１層の膜厚は概ね４０μｍであった。また、第２層及びそれ以降の層を合わせたものの膜厚は第１層への含浸部分を含めて概ね１０μｍ程度であった。また、かかるＳＥＭ観察の結果から、少なくともサブミクロンオーダーの表面欠陥の発生は抑制されていることが確認された。また、製膜評価の一指標としてバブルポイントの測定を行ったところ、本作製プロセスでは、バブルポイント値は４．０以上を示すことが確認された。
【００６９】
次に、本実施例に係るアルミナ製ガス分離モジュールを使用して改質器を構築し、その評価を行った。
先ず、実施例２と同様の評価試験を行った。すなわち、上述のようにしてジョイント管３０及びキャップ５を取り付けた後、図１に示す改質器を構築し、さらには図４に示すガス分離システムを用いて、７００℃の温度条件下、水素透過率および水素／窒素透過係数比を測定・算出した。なお、測定条件や算出方法は実施例１と同様である。結果を表４に示す。
【００７０】
【表４】

【００７１】
表４に示すように、本実施例に係るアルミナ膜を有するガス分離モジュールを備えた改質器（膜型反応器）についても上記ポリシラザン膜を有する水素分離モジュールを備えた改質器（膜型反応器）と同様、高温域で高効率に改質反応を行い得ることが確認された。
実施例３と同様の処理を行って、本実施例に係るアルミナ膜ガス分離モジュールと上記ニッケル系改質触媒とを用いて膜型改質器を構築し、高温域における改質効率を評価した。而して、改質温度７００℃での結果を表５に示す。
【００７２】
【表５】

【００７３】
表５に示すように、本実施例に係るアルミナ製ガス分離モジュール及びそれを備えた膜型改質器についても、上記実施例のポリシラザン膜を有する水素分離モジュール及びそれを備えた膜型改質器と同様、７００℃の高温条件下でもアルミナ膜を通して効率よく水素を反応系外へ除去し、結果、水素生成反応側に平衡がシフトする。このため、メタンから水素への転化反応を促進させる効果が期待できる。
すなわち、本実施例に係る改質器においても、７００℃又はそれ以上の高温域において特に水素透過性能及び分離性能に優れる高温対応タイプのアルミナ膜と高温でのシール性能に優れる上記シール材との併用によって、原料ガスから水素への高い転化率を実現することができた。なお、本膜は焼結膜であるため、長時間の高温域での使用においては粒径が大きくなるとともに分離性能を低下する可能性がある。同一材質で構成されたセラミック分離膜の高温対応型膜型改質器への適用例として示したものであり、高温できわめて長時間安定して使用可能なセラミック分離膜の例ではない。
【００７４】
【発明の効果】
本発明の改質器では、６００℃以上の高温域でも優れた水素透過能及び分離能を発揮し得る水素分離膜（従来よりも高い分離性能を実現可能な高温水素分離膜：例えば水素／窒素透過係数比１５）を含む水素分離モジュールを適用しており、併せて、かかる水素分離モジュールの取付けに関して当該取付け位置からのガスリークを防止するのに膨張黒鉛から成るシール材が使用されている。
【００７５】
かかる構成の本発明の改質器によると、６００℃以上（典型的には６００〜１１００℃）の高温域においても所望のシール性能を保持することができ、さらに改質反応に伴って生成する水素を選択的に高温対応型水素分離膜を介して水素透過側に高効率且つ安定に除去することができる。このため、６００℃以上という高温且つ水蒸気雰囲気等の過酷な条件下にあっても平衡が反応物質側にシフトすることによりメタン等の原料ガスから水素への転化反応（転化率）を促進することができる。
なお、本発明の改質器は、特に高温域で高い水素製造（転化）効率が要求される高温型燃料電池（ＭＣＦＣ、ＳＯＦＣ等）用リフォーマーとして好適である。
【図面の簡単な説明】
【図１】 一実施例に係る改質器の構造を模式的に示す説明図である。
【図２】 一実施例に係るシール材を有するジョイント管を模式的に示す断面図である。
【図３】 一実施例に係る改質器を備えたガス分離システムの全体を模式的に示すブロック図である。
【図４】 一実施例に係る改質器の構造を模式的に示す説明図である。
【符号の説明】
１，１Ａ 改質器
１０，１０Ａ 水素分離モジュール
１２，１２Ａ 水素分離膜
１４，１４Ａ 多孔質支持体
１６ ガス通路
１８ 触媒
２０ 水素生成部
３０，３０Ａ ジョイント管
３８ シール材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reformer for generating hydrogen from a raw material gas. In particular, the present invention relates to a high temperature compatible membrane reformer that realizes excellent reforming efficiency even under high temperature conditions of 600 ° C. or higher.
[0002]
[Prior art]
A reformer that generates hydrogen gas by reforming a source gas such as methane or methanol (steam reforming reaction, etc.), that is, a reformer that selectively permeates hydrogen (that is, hydrogen gas is easy to permeate, etc.). Conventionally, a so-called hydrogen separation membrane having a property that gas species of this type is relatively difficult to permeate has been used to improve the conversion rate in the reformer.
In such a conventional reformer, a reaction is generated through a hydrogen separation membrane from a hydrogen generator (generally filled with a reforming catalyst) that generates hydrogen from a raw material gas introduced into the reactor from the outside. Conventionally, a part of hydrogen as a substance is separated, that is, hydrogen is selectively discharged through a hydrogen separation membrane to a gas passage provided in a state separated from a hydrogen generator. As a result, the equilibrium shifts to the reactant side in the reforming reaction performed in the hydrogen generator, and as a result, the reaction efficiency from the raw material gas to hydrogen can be improved. In this regard, for example, Japanese Patent Laid-Open No. 10-259002 discloses a membrane reactor (membrane type reformer) that improves the efficiency of the hydrogen generation reaction by separating and removing the hydrogen generated on the hydrogen generation reaction side. Yes.
[0003]
By the way, as described in the above publication, in an endothermic reforming reaction system using various reforming catalysts, the same reforming reaction is performed in the low temperature region when the reforming reaction is essentially performed in the high temperature region. The conversion rate in the reforming reaction (the conversion rate of the raw material gas to hydrogen) is higher than in the case of carrying out, and the hydrogen production efficiency is good. For example, in the dehydrogenation reaction or steam reforming reaction of cyclohexane, methane, etc., it is greatly influenced by the reaction form such as exothermic / endothermic reaction, the operating conditions such as the pressure in the reactor, the residence time of the raw material gas, and the type of catalyst. However, when the conversion rate in a relatively high temperature range such as 600 to 800 ° C. is 100, the conversion rate in a relatively low temperature range such as 300 to 500 ° C. can be approximately 50 or less. Therefore, it is desirable to use a membrane type reformer equipped with a hydrogen separation membrane in a high temperature region of 600 ° C. or higher from the viewpoint of improving the conversion rate and generating highly efficient reformed gas.
[0004]
[Problems to be solved by the invention]
However, it has been difficult to use a conventional reformer equipped with a hydrogen separation membrane as described in the above publication under a temperature condition of 600 ° C. or more for the following reason.
The first reason is a problem of an airtight structure in the reformer. That is, in order to selectively discharge hydrogen from the hydrogen generation unit side to the other gas passage side through the hydrogen separation membrane, the hydrogen gas is transmitted through a path other than the source gas passing through the hydrogen separation membrane. It is premised that the gas will not move to the gas passage side. If the raw material gas (supplied gas) leaks from the hydrogen generator side to the gas passage side, the reverse reaction related to the hydrogen generation reaction is promoted, which may lead to the effect of hindering the improvement of the conversion rate. There is. However, the seal (gas leak prevention) means / structure employed in the conventional reformer is a hydrogen separation membrane (in the case of using the reformer in the high temperature region as described above) That is, the sealing (sealing) state between the hydrogen generating part and the module including the support on which the separation membrane is formed cannot be sufficiently ensured. For this reason, it has been unavoidable to use a conventional reformer with a hydrogen separation membrane stably at a high temperature such as 600 ° C. and in a steam atmosphere.
[0005]
Further, as a second reason related to the first reason, conventionally, a hydrogen separation ability (for example, a hydrogen / nitrogen permeability coefficient ratio at 600 ° C. of at least 2.degree. 5) and hydrogen permeability (for example, hydrogen permeability at 600 ° C. is 0.1 × 10 ^-6 Mol / m ² Development and selection of a heat-resistant hydrogen separation membrane that is both inexpensive and easy to manufacture is economically suitable to maintain both, and to be applied to a reformer. It was.
[0006]
Therefore, the present invention was created to overcome the above-described reason, and the object of the present invention is to achieve high performance and high efficiency even under severe conditions (for example, 600 ° C. or higher) such as a high temperature and a steam atmosphere. The object is to provide a high temperature compatible membrane reformer capable of performing a hydrogen generation reaction.
[0007]
[Means for Solving the Problems]
The reformer of the present invention that achieves the above object is a reformer for generating a reformed gas (hydrogen, etc.) from a raw material gas (including carbon element and hydrogen element, hydrocarbon, etc.), and its interior For example, a hydrogen generation unit that generates hydrogen from a raw material gas introduced from the outside and a gas passage adjacent to the hydrogen generation unit are provided. A hydrogen separation module including a hydrogen separation membrane for allowing hydrogen to permeate from the hydrogen generation part side to the gas passage side is attached to the boundary between the hydrogen generation part and the gas passage. A seal material is provided at a position in contact with the hydrogen separation module to prevent the gas from leaking from the hydrogen generation unit side to the gas passage side without passing through the hydrogen separation membrane. Thus, the hydrogen separation membrane has a hydrogen / nitrogen permeability coefficient ratio at 600 ° C. of at least 2.5, and the hydrogen permeability at that temperature is 0.1 × 10 6. ^-6 Mol / m ² ・ S or more than Pa. Further, the sealing material has a bulk density of 0.6 to 1.9 g / cm. ^Three Is the expansion black Lead or It is composed of.
In this specification, the “hydrogen / nitrogen permeability coefficient ratio” means the ratio of hydrogen permeability to nitrogen permeability under the same condition, that is, the ratio of hydrogen gas permeability to nitrogen gas permeability under the same conditions ( Molar ratio). Here, “hydrogen permeability (mol / m ² ・ S ・ Pa) ”and“ Nitrogen permeability (mol / m ² “S · Pa)” means the unit time (1 second) and unit membrane surface area when the partial pressure of each gas (partial pressure difference between the gas supply side and the gas permeation side across the hydrogen separation membrane) is 1 Pa. (1m ² ) Hydrogen gas permeation amount (mol) and nitrogen gas permeation amount (mol) (see “Example” section below).
[0008]
In the reformer of the present invention having such a configuration, a high temperature range of typically 600 ° C. or higher is obtained by employing the sealing material having the above properties and a hydrogen separation membrane, that is, a combination of a highly heat resistant seal structure and a hydrogen separation means. Also, hydrogen is stably transferred from the hydrogen generation section (that is, the portion where the raw material gas is reformed) to the gas passage (the passage of the gas that has passed through the hydrogen separation membrane) isolated by the hydrogen separation means (membrane module). Separation can be performed selectively and efficiently. This makes it possible to effectively remove hydrogen on the hydrogen generator side, and as a result, the equilibrium of the reforming reaction shifts to the reactant side. That is, the hydrogen generation reaction (reforming reaction) can be further promoted in the direction of generating hydrogen under a high temperature condition capable of realizing an essentially high conversion rate. Therefore, according to the reformer of the present invention, a hydrogen generation reaction (reforming reaction or dehydrogenation reaction) is performed while realizing a high conversion rate under high temperature conditions, and as a result, highly efficient hydrogen production is possible.
[0009]
In one preferred reformer of the present invention, the hydrogen separation module has a porous tube shape with the hydrogen separation membrane formed on the surface, and the hydrogen generator is outside the tubular hydrogen separation module. And the hollow portion of the tubular hydrogen separation module constitutes the gas passage, and at least one end of the tubular hydrogen separation module is connected to the hollow portion so as to allow gas to flow therethrough. A tube is attached. Thus, the joint pipe and the end portion of the tubular hydrogen separation module are connected so that a part of them overlap each other, and the gap between the mutually overlapped joint pipe and the tubular hydrogen separation module is the above. The sealing material is disposed in a state of being in close contact with both sides.
[0010]
In the reformer having such a configuration, the above expansion black Lead or A gap between the tubular hydrogen separation module and the joint pipe is closed by the sealing material. As a result, in the reformer of this configuration, when the size (width) of the gap between these members fluctuates based on the difference in expansion coefficient between the hydrogen separation pipe (module) and the joint pipe (for example, at non-normal temperature) Even when the temperature is about 600 ° C. when the operation time is the standard) Lead or With the flexibility (cushioning property) and the compression / elasticity restoring property peculiar to the sealing material, it is possible to stably maintain the sealing state between the two members in response to the change in the gap.
Therefore, according to the reformer having such a configuration, it is highly efficient while preventing gas from leaking from the gap (connection part) between the two members even under high temperature operation or operating conditions that may cause a rapid temperature change. Hydrogen production can be performed.
[0011]
Further, in another preferable one as the reformer of the present invention, the expansion black constituting the sealing material is used. Lead The following properties: (1). The compression rate is 10 to 90%, and (2). The elastic recovery rate is 3 to 70%.
According to the reformer equipped with the sealing material having such properties, a sealing state related to hydrogen separation during high-temperature operation (gas leakage from the hydrogen generation part side to the gas passage side without the hydrogen separation membrane is substantially prevented. The same holds true for the following conditions).
[0012]
In another preferred one as the reformer of the present invention, the hydrogen separation membrane is Obtained by firing polysilazane in an inert atmosphere It is a ceramic film having a repeating structure mainly composed of Si-N bonds as a basic skeleton.
In the reformer having such a configuration, the hydrogen separation membrane for separating and sending out the hydrogen produced in the hydrogen production section to the gas passage side is a porous ceramic membrane having a repeating structure of Si-N bonds as a basic skeleton. As a result, the heat resistance is excellent, and the microporous structure can be kept stable even under high temperature conditions exceeding 600 ° C., for example. Therefore, according to the membrane type reformer of the present invention, hydrogen production (hydrogen generation reaction) under a high temperature condition of 600 ° C. or higher can be made more efficient by using the porous ceramic membrane and the heat-resistant sealing material. Can be done.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the reformer of the present invention is characterized by the hydrogen separation membrane (hydrogen separation module) and the seal structure / material equipped therein. Therefore, the reformer of the present invention has permeated through a hydrogen generation part (typically, an area where a predetermined reforming catalyst is disposed) and a gas passage adjacent to the hydrogen generation part (that is, a hydrogen separation membrane). The hydrogen separation module including the hydrogen separation membrane having the above performance may be disposed at the boundary with the passage through which the hydrogen-rich gas flows) in a state where the sealed state is maintained by the sealing material having the above properties, There is no particular limitation on the shape and type of the reformer itself or the shape of the hydrogen separation module.
Further, in constructing the reformer of the present invention, the addition of components other than the above-described features and auxiliary devices, deletion, modification, etc. can be performed based on methods generally used in conventional reformers. Well, this does not limit the present invention.
Hereinafter, preferred embodiments relating to the reformer of the present invention will be described.
[0014]
First, the hydrogen separation membrane applied to the reformer of the present invention will be described. The reformer of the present invention is for efficiently performing a reforming reaction under a high temperature condition, typically at a temperature of 600 ° C. or higher (preferably 700 to 800 ° C., more preferably 800 to 1000 ° C.). Is. For this reason, as the hydrogen separation membrane used in the reformer of the present invention, one having high hydrogen separation performance even in such a high temperature range is suitable. Further, the hydrogen / nitrogen permeation coefficient ratio and the hydrogen permeation rate are mentioned as indicators of such hydrogen separation performance. Thus, the hydrogen / nitrogen permeability coefficient ratio at 600 ° C. is 2.5 or more (preferably 5.0 or more, particularly preferably 10.0 or more), and the hydrogen permeability at the same temperature is 0.1. × 10 ^-6 Mol / m ² ・ S ・ Pa or more (preferably 0.3 × 10 ^-6 Mol / m ² (S · Pa or more) is suitable as a hydrogen separation membrane equipped in the reformer of the present invention.
While satisfying the above requirements at 600 ° C., the hydrogen / nitrogen permeability coefficient ratio at 700 ° C. is 2.5 or more (preferably 5.0 or more) and / or the hydrogen permeability at 700 ° C. is 0.00. 1 × 10 ^-6 Mol / m ² ・ S ・ Pa or more (preferably 0.3 × 10 ^-6 Mol / m ² (S · Pa or more) is preferable as the hydrogen separation membrane according to the present invention. While satisfying the above requirements at 600 ° C. and 700 ° C., the hydrogen / nitrogen permeability coefficient ratio at 800 ° C. is 2.5 or more (preferably 3.0 or more) and / or the hydrogen permeability at 800 ° C. Is 0.1 × 10 ^-6 Mol / m ² ・ S · Pa or more (preferably 0.2 × 10 ^-6 Mol / m ² (S · Pa or more) is particularly preferable as the hydrogen separation membrane according to the present invention.
[0015]
With regard to the high heat resistance that satisfies such conditions for the hydrogen separation membrane, little has been conventionally considered in the field, and the development of a catalyst that operates at a relatively low temperature or how efficiently the catalyst operates on the low temperature side. As the mainstream of research and development, the present inventor has created a ceramic membrane having a repeating structure mainly composed of Si—N bonds as a basic skeleton as a hydrogen separation membrane having such conditions. In addition, the present inventor has selected a ceramic membrane excellent in permeability mainly composed of α or γ-alumina as a hydrogen separation membrane having such conditions. These porous ceramic membranes have the above-mentioned conditions for the hydrogen / nitrogen permeability coefficient ratio and the hydrogen permeability, and are suitable as a hydrogen separation membrane equipped in the reformer of the present invention.
[0016]
That is, one of the suitable ceramic films provided by the present invention is specified by having a molecular structure having a repeating structure of Si—N bonds (—Si—N—Si—N—), that is, a silazane skeleton as a main skeleton. A porous ceramic film (hereinafter simply referred to as “polysilazane film”).
The polysilazane film according to the present invention may include other bonds and molecular structures as long as the basic skeleton (main skeleton) is a repeating structure of Si—N bonds (silazane skeleton). Typically, by adding a part of Si—C bond, Si—O bond, Si—H bond, etc. to the repeating structure of Si—N bond, the basic structure of the entire polysilazane film (three-dimensional network) Structure) is formed. Typically, the ratio of the number of Si atoms forming Si—N bonds to the total number of silicon (Si) atoms present in the polysilazane film is 10% or more, preferably 20% or more. If the Si-N bond formation ratio is lower than 10%, the heat resistance or the chemical stability under high temperature conditions decreases, which is not preferable for application to the reformer of the present invention. In particular, stable use in a high temperature and steam atmosphere may be impossible to achieve.
[0017]
Another suitable ceramic film provided by the present invention is a ceramic film made of α or γ-alumina. A ceramic membrane having such a structure (hereinafter abbreviated as “alumina membrane”) is also suitable as a hydrogen separation membrane having high heat resistance, like the polysilazane membrane. Alternatively, a zeolite membrane having hydrogen separation ability produced by hydrothermal synthesis or the like only in a relatively low temperature region can be used.
[0018]
Thus, the peak value of the pore size distribution of the hydrogen separation membrane suitable for the practice of the present invention including the polysilazane membrane and the alumina membrane (typically the peak value can be approximated to the average pore size) is 0.1 nm. It is preferable that it exists in the range of -10 nm. When the pore size distribution has a peak value and / or an average pore size, so-called molecular sieve or Knudsen separation occurs. Knudsen-like separation refers to separation or concentration using the difference in the permeation rate of gas molecules, and in the pores (typically about 10 nm or less), the collision with the pore wall dominates rather than the collision between the gas molecules. It is based on the nature of becoming. Furthermore, non-polar molecules having a relatively small size (dynamic molecular diameter of about 0.29 nm) such as hydrogen are mixed with those having a peak value and / or an average pore size of 0.1 to 5 nm or 1 nm or less. It is particularly effective for selective separation from gas.
[0019]
In addition, there is no particular limitation on the porosity of a hydrogen separation membrane (preferably the polysilazane membrane or alumina membrane) suitable for the practice of the present invention. Considering the balance between gas separation and transmission efficiency and mechanical strength (including thermal strength), at least 10 to 50% is considered necessary. However, in order to improve the transmission efficiency, the film thickness is reduced as follows. It is more effective to control.
Although not particularly limited, in the practice of the present invention, the thickness of the hydrogen separation membrane to be used is suitably 10 μm or less, preferably 5 μm or less, and more preferably 1 μm or less. In particular, according to the polysilazane film having such a film thickness, it is possible to efficiently perform the hydrogen separation treatment while maintaining a relatively high hydrogen separation ability (hydrogen selectivity) even under high temperature conditions.
[0020]
Next, a hydrogen separation module suitable for carrying out the present invention will be described.
The hydrogen separation module equipped in the reformer of the present invention is provided with a hydrogen separation membrane such as the above polysilazane membrane, and has such a strength that the sealing material according to the present invention is attached to maintain the sealed state. As long as there is no particular limitation, there is no particular limitation on the material and form of the module body, that is, the support (typically a porous body) on which the hydrogen separation membrane is formed.
[0021]
As the support of the hydrogen separation module according to the present invention which is preferable from the viewpoint of heat resistance, various ceramic materials such as silicon nitride, silicon carbide, silica, α-alumina, γ-alumina, zirconia, titania, calcia, various zeolites, etc. A porous ceramic body is preferred.
In particular, when the hydrogen separation membrane part and the support part are made of the same material, there is no significant difference in the thermal contraction rate / thermal expansion coefficient between them, and as a result, a hydrogen separation membrane having high thermal shock resistance is realized. be able to. That is, even in applications that are repeatedly exposed to sudden temperature changes, the frequency of thermal peeling and cracking between the membrane and the support can be significantly reduced. For example, when a polysilazane film is adopted as the hydrogen separation film, a support mainly composed of silicon nitride is preferable. Further, when an alumina membrane is employed as the hydrogen separation membrane, a support having an asymmetric membrane structure in which α-alumina, γ-alumina, or α-alumina and γ-alumina are multilayered is preferable. From the viewpoint of adhering the sealing material made of expanded graphite having the above properties, it is a porous material made of a material having high physical strength such as silicon nitride (it is difficult to break even when high surface pressure is applied to achieve high compression and elastic recovery). A quality support is preferred.
[0022]
Further, the pore diameter of the porous support is not particularly limited as long as it does not affect the permeation of hydrogen. Those having an average pore size larger than the average pore size in the separation membrane are suitable, and those having a peak value of pore size distribution of about 0.1 μm to 10 μm and / or an average pore size are preferred. The porosity is suitably 30 to 60%, preferably 35 to 50%. However, the hydrogen separation module according to the present invention typically requires a predetermined pressure when attaching (adhering) the sealing material. For this reason, a certain amount of physical strength is required for the support. Therefore, the porous support as the main body of the hydrogen separation module equipped in the reformer of the present invention has a three-point bending strength in a high temperature range (for example, 800 ° C.) of 30 MPa or more (more preferably 60 MPa or more, more preferably It is desirable to set the average pore diameter (or the peak value of the pore diameter distribution) and the porosity so that the mechanical strength is 90 MPa or more.
[0023]
The shapes that can be taken by the hydrogen separation module according to the present invention include tube shapes, membrane (thin plate) shapes, monolith shapes, honeycomb shapes, polygonal flat plate shapes, various three-dimensional shapes, and the like. In particular, a module made of a tubular porous ceramic body having a hydrogen separation membrane formed on the surface is suitable. In this case, as described in the examples described later, typically, a hydrogen generation part including a predetermined catalyst is formed outside the tubular module (porous body), and the hollow part of the tubular module receives hydrogen separated. This corresponds to the previous gas passage. The shape of the ceramic support can be obtained by a well-known molding technique such as extrusion molding, casting molding, tape molding, or press molding.
[0024]
Thus, a hydrogen separation module can be manufactured by forming a hydrogen separation membrane on a support produced based on the above molding technique or the like. For example, as a means for forming a polysilazane membrane, an alumina membrane or other hydrogen separation membrane on the surface of a porous support made of a ceramic material as described above, a general sol-gel method, thermal decomposition method, hydrothermal synthesis method can be used. And vapor phase synthesis.
Hereinafter, an example in which the polysilazane film according to the present invention is formed on the surface of a ceramic porous support will be described.
As described above, since the polysilazane film suitably employed in the reformer of the present invention has a Si—N bond repeating structure as a basic skeleton, it is manufactured from a silicon compound having the Si—N bond as a basic structure. can do. Examples of such a suitable silicon compound include polysilazane represented by the following general formula (1). Typically R in formula (1) ₁ , R ₂ , R ₃ Are hydrogen or aliphatic or aromatic hydrocarbon groups having 1 to 10 carbon atoms, respectively.
[0025]
[Chemical 1]

[0026]
Thus, such polysilazane can be prepared, for example, as follows. That is, dihalosilane (R ¹ SiHX ₂ Or other dihalosilanes (R) ² R ³ SiX ₂ The silazane oligomer is obtained by reacting the mixture with) with ammonia. Next, the silazane oligomer is dehydrogenated in the presence of a basic catalyst. Thereby, dehydrogenation of the nitrogen atom adjacent to the silicon atom is performed, and as a result, polysilazane formed by dehydrogenating and cross-linking silazane oligomers can be generated. In addition, the preferable thing of the dihalosilane used for this production | generation process is said R ¹ , R ² , R ³ Are each a lower alkyl group having 1 to 6 carbon atoms, a substituted allyl group, an unsubstituted allyl group, an unsubstituted aryl group having 6 to 10 carbon atoms, a trialkylamino group, or a dialkylamino group. Or R ¹ Is hydrogen and R ² And R ³ Is any of the functional groups listed above. At this time R ¹ , R ² And R ³ All may be the same group or different from each other. X in the formula of the dihalosilane is a halogen group.
In addition, although there is no restriction | limiting in particular in the molecular weight of polysilazane to be used, From a viewpoint of viscosity control etc. in the process of forming a thin film, a thing with a weight average molecular weight of about 1000-20000 is preferable.
[0027]
Thus, an inorganic material having fine pores can be formed by firing polysilazane prepared from a silazane oligomer as described above or commercially available polysilazane in an inert atmosphere. In summary, a polysilazane solution is typically applied to a surface of a ceramic porous support having a symmetric or asymmetric structure that has been previously formed into a desired shape at a desired thickness (eg, 1 to 3 μm). Next, after a thin layer made of polysilazane is formed by performing a drying treatment, the thin layer is fired together with the support under an appropriate temperature condition in an inert (non-oxidizing) atmosphere. As a result, a polysilazane film (hydrogen separation film) in which micropores are formed can be formed on the surface of the support. More specific description will be given below.
[0028]
In preparing the polysilazane solution, various organic solvents can be used as a solvent for dissolving the polysilazane. For example, aromatic solvents such as benzene, toluene and xylene, and ether solvents such as dioxane, tetrahydrofuran and dibutyl ether are suitable. The concentration of polysilazane in the solution is not particularly limited, but is preferably about 0.5% to 60% by weight, and preferably about 1% to 20% by weight.
[0029]
In addition, as a method for applying the polysilazane solution to the surface of the support, various methods used in conventional thin film forming processes can be employed. For example, a dip coating method, a spin coating method, a screen printing method, a spray method, etc. are mentioned. In particular, in the dip coating method, the penetration of the polysilazane solution into the porous support can be controlled by the solution concentration, operating conditions, etc., and gas generation, capillary pressure, firing shrinkage associated with the thermal decomposition of polysilazane in an inert atmosphere. This can contribute to suppressing the destruction of the fine structure due to the above. For this reason, the dip coating method is particularly a coating method suitable for easily and directly forming a defect-free porous ceramic film on the support surface.
Alternatively, as the other environment in which the polysilazane solution is applied to the surface of the support, the film forming environment may contain some oxygen. In this case, gel formation is involved in the process. In the case where relatively large pores are distributed on the surface of the support, there is a problem that the subsequent gelation or film formation is inhibited by the raw material solution penetrating deeply into the pores. Further, when the film is thick, defects are likely to occur in the film due to capillary pressure accompanying drying. Therefore, when the sol-gel method is adopted when relatively large pores are distributed on the surface of the support, a ceramic layer (hereinafter referred to as “intermediate”) in which another average pore diameter is smaller than the support in advance on the surface of the support. It is preferable that a polysilazane film is laminated on the smooth surface or inside the pores (that is, the film is repeatedly formed a plurality of times). As a result, the polysilazane film formed on the support surface can be made thinner and defect-free. However, the film obtained in this way contains a little more Si—O bonds.
[0030]
Thus, after applying (adding) the polysilazane solution to the support surface and drying, the support to which the polysilazane film is attached is fired in an inert (non-oxidizing) atmosphere. Typically, in an inert gas substantially free of oxygen (such as nitrogen gas), 200 to 1350 ° C., preferably 200 to 1000 ° C. (typically below the firing temperature of the porous support and the intermediate layer) Is formed at a temperature equal to or lower than the firing temperature of the intermediate layer.) Under a temperature condition of 1 to 4 hours.
By heat treatment in such an inert atmosphere, the average pore diameter excellent in heat resistance is 0.1 nm to 50 nm (peak value of pore diameter distribution: 0.1 to 5.0 nm), and the basic skeleton has a repeating structure of Si—N bonds. A polysilazane film can be formed.
[0031]
As described above, the polysilazane film suitably used in the reformer of the present invention can be produced by a relatively simple technique without requiring strict and complicated film forming conditions.
By the way, when a silicon nitride-based porous support is used, the basic skeleton of the support (both the support and the intermediate layer when an intermediate layer is included) is formed and laminated on the surface. It has the same silazane skeleton as the polysilazane film. For this reason, it is possible to highly suppress the occurrence of defects in the polysilazane film during the process. Furthermore, as a result of suppressing the occurrence of such defects, a wider range (typically 5000 mm) than conventional ceramic membranes (eg, silica-based hydrogen separation membranes). ² Above, preferably 15000mm ² A thin and homogeneous hydrogen separation membrane can be continuously formed over the above. For this reason, when the polysilazane film | membrane which concerns on this invention is used, the enlargement of the reformer which employ | adopts it is realizable. This (effect) is also true when an alumina-based porous support is used and an alumina film is formed and laminated on the support.
[0032]
Next, the sealing material according to the present invention will be described. The sealing material used in the reformer of the present invention is required to have heat resistance and chemical resistance performance that does not significantly destroy or chemically change the sealing material even when exposed to a high temperature of 600 ° C. or higher for a long time. . In addition, the volume and / or shape change (for example, the above-described tubular hydrogen separation module and the joint portion) is changed to a high temperature state during operation of the reformer, that is, a heating state or a cooling state when stopped ( Even when expansion or contraction deformation occurs, flexibility (cushioning property) capable of maintaining a sealed state following such volume and / or shape change and high compression / restoration performance are required.
Thus, the density (bulk density) is 0.6 to 1.9 g / cm as a material that can suitably satisfy these requirements. ^Three (Particularly preferably 0.8 to 1.2 g / cm ^Three ) Expanded graphite or a heat-resistant material having the same properties. Hereinafter, such materials will be described in detail.
[0033]
Natural graphite is carbon having a structure in which carbon six-membered ring planes are regularly laminated in parallel. Expanded graphite is obtained by oxidizing the natural graphite with an oxidizing agent such as concentrated sulfuric acid or nitric acid. The interlayer distance is expanded about 100 to 300 times. Thus, an expanded graphite material suitable for the sealing material according to the present invention can be obtained by loading and compressing the expanded graphite so as to be in the above density range.
Such an expanded graphite material has a dense structure excellent in sealing performance in addition to the high heat resistance inherent in graphite, and has flexibility, high compressibility and elastic restoring force.
Such expanded graphite or a heat-resistant material having the same properties (typically carbonaceous and other inorganic materials having the same thermal expansion coefficient, oxidation start temperature, compressibility, recovery rate and flexibility (cushioning properties) as expanded graphite. Preferred materials are those having a compression ratio (based on JIS-R3453) of 10 to 90% (particularly preferably 45 to 55%) and / or a recovery ratio (based on JIS-R3453) of 3 to 70. % (Particularly preferably 10 to 15%), and / or the oxidation start temperature (temperature when the weight is reduced by 1% by heating in air) is 400 ° C. or higher (particularly preferably 500 ° C. or higher). It is an expanded graphite or its equivalent. Further, those having heat resistance capable of maintaining a desired sealing performance up to a temperature of 1100 ° C. or higher (preferably 1500 ° C. or higher) in an inert (non-oxidizing) atmosphere such as nitrogen gas are suitable.
According to the sealing material formed from expanded graphite having such properties, it is possible to realize particularly excellent sealing state even at high temperature operation.
[0034]
In addition, the shape and type of the sealing material according to the present invention vary depending on the shape of the reformer and the shape of the hydrogen separation module of the present invention, and there is no particular limitation. For example, when a cylindrical tubular hydrogen separation module is used, a sealing material having a shape in contact with (that is, in close contact with) the outer wall of the hydrogen separation module, typically a ring-shaped sealing material, can be suitably used. In addition, when a single plate (monolith) -shaped hydrogen separation module is used, a sealing material having a shape in contact with the outer edge of the hydrogen separation module, typically a sheet-shaped sealing material, can be preferably used. Although not particularly limited, the sealing material having such a shape has a density of 0.6 to 1.9 g / cm. ^Three (Particularly preferably 0.8 to 1.2 g / cm ^Three ) Powdered expanded graphite prepared to a degree can be filled in a mold having a predetermined shape and press molded, or roll molded or laser processed. That is, the graphite powder (particles) are self-adhered and integrated by such pressure molding, and as a result, the graphite powder (particles) can be molded into a desired shape (for example, an O-ring-like packing shape). Alternatively, a sheet (thin film) expanded graphite having the above density may be laminated and molded.
In addition, it may vary depending on the shape and type of the reformer to be constructed and usage conditions. However, as long as the sealing performance can be maintained, other physical characteristics (thermal conductivity, electrical resistivity, There are no particular restrictions on the tensile strength, thermal expansion coefficient (however, a low coefficient is preferred), and the like.
[0035]
In the reformer of the present invention, the reforming catalyst to be used is not particularly limited. However, since the reformer of the present invention is intended to be used particularly in a high temperature range (typically a high temperature range of 600 to 800 ° C. or 1100 ° C.), it has excellent catalytic ability in such a high temperature range. What can be exhibited is preferable. For example, a support made of porous alumina or the like on which a metal such as palladium or nickel is supported can be preferably used.
Moreover, there is no restriction | limiting in particular in the site | part provided with a catalyst, ie, the shape of a hydrogen generation part. For example, a tubular hydrogen separation module (in this case, the module hollow portion serves as the gas passage) is stored in a predetermined reaction vessel (chamber), and a space around the module is filled with a catalyst. Also good. Or the form which forms a membrane-like catalyst layer in the outer surface of this tubular hydrogen separation module (typically coating) may be sufficient. The present invention basically applies the above-described embodiment when the reforming reaction of the endothermic reaction system is operated at a high temperature.
[0036]
【Example】
The invention is illustrated in more detail by the following examples. The present invention is not limited to these examples.
[0037]
<Example 1>
A tubular hydrogen separation module was produced as follows. That is, 90 parts by weight of silicon nitride powder (Ube Industries product: SN-E10), 5 parts by weight of alumina powder (Sumitomo Chemical product: AKP-10), and 5 parts by weight of yttria powder (Mitsubishi Chemical products: Y) -F) and 80 parts by weight of water were put into an alumina pot and mixed with a cobblestone having a diameter of 30 mm for 24 hours to prepare a slurry. Next, 10 parts by weight of a wax-based organic binder and 4 parts by weight of a wax emulsion were added to the slurry and mixed for 16 hours, and then granules were produced by spray drying.
The obtained granule was formed into a CIP (by cold isostatic pressing) and processed into a pipe shape (outer diameter: 10 mm, inner diameter: 7 mm, length: 250 mm). The raw processed tube was degreased and then fired at 1400 ° C. (final firing temperature) to obtain a tubular silicon nitride porous body, that is, a support according to this example (see reference numeral 14 in FIG. 1).
[0038]
The pore diameter (average pore diameter) and porosity of the obtained silicon nitride porous body were 0.16 μm and 47%, respectively, as measured by mercury porosimetry. Further, the three-point bending strength at 800 ° C. of the unglazed surface corresponding to the film forming surface was about 70 MPa or more. Accordingly, the tube-shaped silicon nitride porous body has sufficient mechanical strength as a support in the hydrogen separation module. The bulk density of the porous body is 1.77 g / cm. ³ Met. Further, the linear expansion coefficient serving as an index of thermal strength is approximately 3.4 × 10 in the range of 25 to 800 ° C. ^-6 / K.
Moreover, this porous body is α-Si. ₃ N ₄ The structure is thermally stable. Moreover, the pore size distribution (pore size fluctuation range) is very narrow, which is preferable as a support for a hydrogen separation module. That is, when such a porous silicon nitride material is used, a substantially defect-free ceramic membrane (hydrogen separation membrane) can be formed on the surface without forming the intermediate layer as described above.
[0039]
Next, a polysilazane film was formed as a hydrogen separation film on the outer wall surface of the obtained silicon nitride porous body (that is, the outer peripheral surface of the tube cylindrical surface) (see reference numeral 12 in FIG. 1).
That is, polysilazane powder (Chisso product: NCP201) was dissolved in toluene (ultrasonic stirring treatment) to prepare a polysilazane solution (coating solution) having a polysilazane concentration of 10% by weight.
Subsequently, the silicon nitride porous body was immersed in a coating solution based on a dip coating method. In addition, the one end open part of the silicon nitride porous body was wrapped with a synthetic resin film so that the coating liquid adhered only to the outer peripheral surface of the silicon nitride porous body during the immersion treatment.
After immersion, the silicon nitride porous body was pulled up from the coating solution at a constant speed and dried at room temperature. Thereafter, the silicon nitride porous body on which the polysilazane coating was formed on the outer surface by the immersion was placed in a vacuum / pressure sintering furnace, and heat treatment was performed in an atmospheric pressure / nitrogen atmosphere.
Through such a series of treatments, a tubular hydrogen separation module having a polysilazane film formed on the outer peripheral surface of the silicon nitride porous body was obtained (see reference numeral 10 in FIG. 1).
[0040]
Next, the reformer 1 according to this example was produced using the tubular hydrogen separation module 10. FIG. 1 is an explanatory view schematically showing the main part of the reformer according to the present embodiment.
As shown in this figure, the reformer 1 according to this example is roughly composed of a cylindrical stainless steel chamber 2 and a support (silicon nitride porous body) 14 provided with a polysilazane film 12 as a main body. The hydrogen separation module 10 and the reforming catalyst 18 are configured.
The chamber 2 is separately provided with a gas supply pipe 3 and a gas discharge pipe 4. A heater 82 (see FIG. 3) and a water jacket (insulating material) (not shown) are provided around the chamber 2 so that the temperature inside the chamber 2 can be controlled in the range of room temperature to 1200 ° C. Further, the hydrogen separation module 10 is disposed inside the chamber 2, and a space 18 (a portion corresponding to a hydrogen generation unit) 20 around the hydrogen separation module 10 can be filled with the catalyst 18.
As shown in the figure, one end of the hydrogen separation module 10 is closed with a metal cap 5 to prevent gas from flowing into the hollow portion 16 from the end. Further, the joint pipe 30 according to this embodiment is attached to the other end side of the hydrogen separation module 10.
Hereinafter, the joint pipe 30 will be described in detail.
[0041]
As shown in detail in FIG. 2, the joint pipe 30 is composed of several members. That is, the stainless steel tubular convex union (flange) 34, the corresponding tubular concave union (flange) 44, the metal first ring member 32 and the second ring member 42 attached thereto, and the present embodiment. It is comprised from the sealing material 38 which concerns. A hole 46 having a size capable of penetrating the hydrogen separation module 10 is formed at the center of the root (flat disk-shaped flange) of the convex union 34. On the other hand, a permeate gas discharge port 6 that leads to a hollow portion (hereinafter referred to as “permeate gas passage 16”) of the hydrogen separation module 10 is formed in the center of the root portion (flat disc-shaped flange) of the concave union 30.
The sealing material 38 is a member made of expanded graphite formed in a ring shape, and its bulk density is 1.0 g / cm. ^Three The compression rate based on JIS-R3453 was about 50%, and the restoration rate was about 10%.
[0042]
Thus, as shown in FIG. 2, one end of the tubular hydrogen separation module 10 is inserted into the hole 46 of the tubular convex union 34. In addition, the tubular ring that has passed through the hole 46 in the order of the first ring member 32, the sealing material 38, and the second ring member 42 from the opposite side of the tubular convex union 34 (that is, the side on which the protruding portion 36 is formed). Fit into the hydrogen separation module 10. At this time, as shown in the drawing, the inner diameter of the ring-shaped sealing material 38 is slightly larger than the outer diameter of the tubular hydrogen separation module 10. Because of this and the flexibility unique to expanded graphite, when the ring-shaped sealing material 38 is fitted into one end of the module 10, the inner wall surface thereof can be brought into close contact with the outer peripheral surface of the module 10.
[0043]
Next, the mounting of the joint pipe 30 is completed by tightening the concave union 44 to the convex union 34. That is, as shown in FIG. 2, a female screw and a male screw corresponding to each other are formed on the inner wall surface of the protruding portion 40 of the concave union 44 and the outer wall surface of the protruding portion 36 of the convex union 34, respectively. Furthermore, the protruding portion 36 of the convex union 34 is formed so that the diameter gradually increases from the tip portion toward the root portion. As a result of such a configuration, the concave union 44 is fitted (screwed) with the convex union 34, whereby the sealing material 38 is strongly adhered to both the outer peripheral surface of the hydrogen separation module 10 and the inner wall surface of the protrusion 36 of the concave union 34. Can be made. That is, when the concave union 44 is screwed in the root direction of the convex union 34, the protrusion 36 of the convex union 34 whose diameter gradually increases from the tip toward the root is reduced, Adhering the sealing material 38 to the hydrogen separation module 10 and the concave union 34 is realized.
At this time, as shown in the drawing, in the joint pipe 30 according to the present embodiment, when the unions 34 and 44 are screwed to a predetermined level, a part 42a of the second ring member 42 is unionized. It is sandwiched between 34 and 44 and serves as a stopper. This prevents further screwing (screw tightening) and prevents the sealing material 38 from being pressed more than necessary. Therefore, according to the joint pipe 30 according to the present embodiment, the seal member 38 is always brought to the both members 10 and 10 with the optimum pressure (surface pressure) by screwing the unions 34 and 44 until the screw tightening is stopped. 34 (36). On the other hand, both unions 34 and 44 are separated from the hydrogen in order to correspond to the volume change gap between the hydrogen separation module 10 and the joint pipe 30 (that is, the metal unions 34 and 44) when the reformer 1 is operated at a high temperature. Module 10 is not in contact.
[0044]
As a result of attaching the joint pipe 30 as described above, the hydrogen-rich gas transmitted from the outside of the hydrogen separation module 10 through the hydrogen separation membrane 12 and the support 14 to the permeate gas passage 16 is transferred to the joint pipe 30. It is discharged to the outside through the permeated gas discharge port 6. At this time, the seal member 38 is attached to the position shown in the figure, so that the gas in the hydrogen generation unit 20 (see FIG. 1) allows the gap between the joint pipe 30 (concave union 34) and the hydrogen separation module 10 (that is, the concave union). It is possible to prevent leakage through the 34 holes 46). Furthermore, as a result of the sealing material 38 being composed of expanded graphite having the above properties, the linear expansion coefficient of the gap size between the joint tube 30 (concave union 34) and the hydrogen separation module 10 during high-temperature operation of 600 ° C. or higher. Even when the temperature varies between two different materials, the sealing performance can be maintained by the sealing material 38.
Note that a part of the joint pipe 30 and a part of the chamber 2 are welded to each other, and an airtight state in the chamber 2 is ensured.
[0045]
Next, the hydrogen separation performance and the sealing performance were evaluated using the reformer 1 (FIG. 1) provided with the hydrogen separation module 10 constructed as described above.
First, a membrane gas separation system (evaluation system) including a hydrogen separation module (hydrogen separation membrane) as shown in FIG. 3 was constructed. That is, the methane supply device 52, the hydrogen supply device 54, and the nitrogen supply device 56 were connected to the gas supply pipe 3 of the reformer 1 via gas chromatographs 78 and 80.
As shown in FIG. 3, the methane supply device 52 includes a methane supply cylinder 59 having a pressure valve, a pressure gauge 58, a flow meter 64, a needle valve 70, and the like. Similarly, the hydrogen supply device 54 includes a hydrogen supply cylinder 61 having a pressure valve, a pressure gauge 60, a flow meter 66, a needle valve 72, and the like. The nitrogen supply device 56 includes a nitrogen supply cylinder 63 having a pressure valve, a pressure gauge 62, a flow meter 68, a needle valve 74, and the like. Further, as shown in the figure, the flow paths of the methane supply device 52 and the hydrogen supply device 54 are connected by a three-way cock 76.
Furthermore, a steam supply device 100 is separately connected to the gas supply pipe 3 of the reformer 1. This apparatus has a water vapor supply source (not shown) and a microfeeder (water vapor supply pump) 102 as main components.
On the other hand, as shown in FIG. 4, a pressure gauge 112, a gas chromatograph 114, a trap 116, a soap film flow meter 118, and the like were connected to the gas discharge pipe 4 side of the reformer 1. Similarly, a pressure gauge 104, a gas chromatograph 106, a trap 108, a soap film flow meter 110, and the like were also connected to the permeate gas discharge port 6 of the reformer 1. By constructing such a system, detailed gas analysis (both on the supply side and the discharge side to the reformer) can be performed. In gas analysis, Ar and He are used as the carrier gas (sweep gas), and the analysis target gas is CH. _Four , H ₂ , CO, CO ₂ , O ₂ , N ₂ It was.
In the evaluation test according to this example, the catalyst 18 was not filled in the chamber 2.
[0046]
Thus, the hydrogen separation performance and the sealing performance were evaluated based on the pure gas permeation test using the gas separation system shown in FIG. In this test, hydrogen and nitrogen were supplied into the chamber 2 from the hydrogen supply device 54 and the nitrogen supply device 56 at a predetermined flow rate. At this time, the differential pressure across the hydrogen separation membrane 12 is 2.0 × 10 ⁴ It was made to be Pa (0.2 atm).
This evaluation test was first performed at room temperature, and after a predetermined time, the temperature in the chamber 2 was raised to 700 ° C. and the same test was performed. Thereafter, the temperature in the chamber 2 was returned to room temperature again, and the same procedure was performed. By continuously testing while changing the temperature in this way, it is possible to evaluate the sealing performance of the reformer 1 according to the present embodiment and the hydrogen separation characteristics at high temperatures.
[0047]
Specifically, hydrogen and nitrogen were respectively supplied into the chamber 2 in a state where the above-mentioned differential pressure was generated while adjusting the temperature in the chamber 2 by appropriately operating the heater 82 (room temperature to 700 ° C. to room temperature). . Thus, the target gas composition is analyzed by the gas chromatograph 106 equipped with the TCD detector while measuring the flow rate of the permeation side (that is, the gas discharge side flow passage connected to the permeate gas discharge port 6) by the soap film flow meter 108. did. The gas permeability of each of hydrogen and nitrogen was calculated from the following equation “Q = A / ((Pr−Pp) · S · t)”. Where Q is the gas permeability (mol / m ² S · Pa), A is the permeation amount (mol), Pr is the pressure (Pa) on the supply side, that is, the chamber internal space side, Pp is the pressure (Pa) on the permeation side, that is, the permeate gas passage side, and S is the cross-sectional area (m ² ), T represents time (second: s). The hydrogen / nitrogen permeability coefficient ratio is the ratio between the hydrogen permeability and the nitrogen permeability, that is, the formula “α = Q _H2 / Q _N2 ". Where α is the hydrogen / nitrogen permeability coefficient ratio (permeability ratio), Q _H2 Is hydrogen permeability, Q _N2 Represents nitrogen permeability.
As a result of the above test, the hydrogen permeation flow rate, the nitrogen permeation flow rate, and the hydrogen / nitrogen permeation coefficient ratio are shown in Table 1.
[0048]
[Table 1]

[0049]
As is clear from Table 1, no significant difference was observed in the hydrogen / nitrogen permeability coefficient ratio regardless of the transition of the temperature condition. From this, it was confirmed that substantial gas leakage did not occur from the gap between the chamber 2 and the hydrogen separation module 10. It was also confirmed that the hydrogen separation membrane 12 and the sealing material 38 were not deteriorated by heating. That is, the sealing material 38 described above had good sealing performance (◯ in the table) even at a high temperature condition such as 700 ° C. This result confirms that the sealed state in the chamber 2 can be maintained even under such a high temperature condition.
Further, in view of the value of the hydrogen / nitrogen permeation coefficient ratio at 700 ° C., it was confirmed that the hydrogen separation membrane according to the present example has a hydrogen separation performance comparable to Knudsen separation even under such high temperature conditions. The hydrogen permeability at 700 ° C. in this example is 0.3 × 10 ^-6 Mol / m ² ・ It was s ・ Pa.
[0050]
<Example 2>
Next, processing under the same conditions as described in Example 1 was performed to produce a tubular hydrogen separation module (outer diameter: 10 mm, inner diameter: 7 mm, length: 250 mm). In this example, a total of three hydrogen separation modules were produced by the same process (Nos. 1 to 3 in Table 2). As shown in Table 2, the outer peripheral surfaces of these three hydrogen separation modules are each about 8100 mm. ² (No. 1), about 7760 mm ² (No. 2), about 8200 mm ² A continuous polysilazane film (No. 3) was formed. No. 2 shown in Table 2 As a sample of No. 4, a polysilazane film was repeatedly formed on the surface of a predetermined tubular support (silicon nitride) by performing the same treatment as above (film area: 1800 mm). ² ) Was produced.
[0051]
[Table 2]

[0052]
Thus, these samples were applied in the modification test of this example described later. Taking the methane reforming reaction as an example, if hydrogen or carbon dioxide, which is a reformed gas, can be removed preferentially by this membrane, the reforming reaction is promoted in the direction of a positive reaction from equilibrium theory. Therefore, it is estimated that the higher the selectivity of the hydrogen separation membrane, the higher the reaction conversion rate under the same conditions. Also in this membrane, when a polysilazane membrane was repeatedly formed 5 times to improve the hydrogen separation performance (No. 4 in Table 2), a hydrogen / nitrogen permeability coefficient ratio of 15 was achieved at room temperature (Table 2). reference). Therefore, by applying this film, it is possible to obtain a reformed gas richer in hydrogen and to expect an expanded use. There is no particular structural problem for stable use and scale-up in the high temperature range.
As a result of measurement with a scanning electron microscope (SEM), at least submicron-order surface defects were not observed in the polysilazane films formed on the three hydrogen separation modules (Nos. 1 to 3). Moreover, when the pore diameter of the pores existing in the polysilazane membrane of each hydrogen separation module (Nos. 1 to 3) was measured with respect to the bulk body by a general argon adsorption method, the peak value of the pore diameter was about 2 nm for all. there were. The formed film thickness was about 5 μm.
[0053]
In addition, although this invention is not limited, the silicon nitride porous body which formed the intermediate | middle layer for the comparison was also produced simultaneously. That is, by using polysilazane powder (same as above) and silicon nitride powder (same as above) as raw materials, and adding xylene to these so that the solid content concentration is approximately 1 to 10% by weight, a slurry for forming an intermediate layer is prepared. did. Next, the tubular silicon nitride porous body obtained by the same treatment as described above was immersed in a slurry for forming an intermediate layer in a stirred state by ultrasonic treatment for 1 hour (dip coating method). Note that, at the time of this dipping treatment, the open ends of the both ends were wrapped with a synthetic resin film so that the slurry adhered only to the outer peripheral surface of the tubular silicon nitride porous body. After the immersion treatment, the silicon nitride porous body was pulled up from the slurry-containing container at a constant speed and dried at room temperature for 48 hours. Thereafter, the tubular silicon nitride porous body on which the coating film derived from the slurry was formed on the outer peripheral surface was placed in a vacuum / pressure sintering furnace and heat-treated in an atmospheric pressure / nitrogen atmosphere.
As a result, an intermediate layer was formed on the outer peripheral surface of the tubular silicon nitride porous body. The intermediate layer obtained by such treatment has been revealed by SEM observation or the like to have a microstructure in which silicon nitride is used as a matrix and the gap is filled with polysilazane. Further, at least sub-micron-order surface defects were not observed in the intermediate layer thus produced.
[0054]
Next, a polysilazane film (hydrogen separation film) was formed on the outer peripheral surface (that is, the surface of the intermediate layer) of the obtained porous silicon nitride by the same treatment as in Example 1. As a result, the surface of the intermediate layer was 8000 mm as in Table 2. ² A continuous ceramic film (polysilazane film) was formed over the above. As a result of measurement by SEM, at least submicron-order surface defects were not observed in the porous ceramic film formed on the intermediate layer. Moreover, when the pore diameter of the pores present in the ceramic membrane was measured for the bulk body, the average pores were all about 2 nm or less. The formed film thickness was about 5 μm. That is, when the intermediate layer was formed, a hydrogen separation module having the same properties could be formed.
[0055]
Next, No. obtained above. 1-No. The module 3 was subjected to the same evaluation test as in Example 1. That is, after attaching the joint pipe 30 and the cap 5 as described above, the reformer 1 shown in FIG. 1 is constructed, and further, using the gas separation evaluation system shown in FIG. The hydrogen permeability and the hydrogen / nitrogen permeability coefficient ratio were measured and calculated. Measurement conditions and calculation methods are the same as those in the first embodiment.
As shown in Table 2, there was no significant difference in hydrogen permeability and hydrogen / nitrogen permeability coefficient ratio among the three modules (hydrogen separation membranes). These values were the same as the results for the hydrogen module according to Example 1. From this, also in the hydrogen separation module obtained in this example, no substantial gas leak occurred from the gap between the chamber and the hydrogen separation module, and the hydrogen separation membrane and the sealing material were not deteriorated by heating. It was confirmed. That is, it was confirmed that by using the sealing material made of expanded graphite and the polysilazane membrane in combination, a high hydrogen permeability and separation ability can always be realized even at a high temperature of 700 ° C. In addition, this invention is No.2 in Table 2. This technique can also be applied to the high-performance high-temperature compatible hydrogen separation membrane shown in FIG. In view of the film structure, No. 4 is No. This is a case where the number of film formations is increased to 5 with respect to 1-3.
[0056]
<Example 3>
Next, No. 2 shown in Table 2 was obtained. A reformer was prepared using one hydrogen separation module and a predetermined reforming catalyst, and the reforming efficiency in a high temperature region was evaluated in detail.
In this example, as schematically shown in FIG. 4, joint pipes 30 and 30A having the same structure as that used in Example 1 were attached to both ends of the hydrogen separation module 10A to be used. Next, the hydrogen separation module 10A with the two joint tubes 30 and 30A attached thereto was placed in the chamber 2 having a predetermined size (internal volume: about 1900 ml).
That is, as shown in FIG. 4, the openings provided in each of the joint pipes 30, 30 </ b> A, that is, the permeate gas discharge port 6 and the gas supply port 6 </ b> A for supplying gas directly to the permeate gas passage 16 are provided outside the chamber 2. The joint pipes 30 and 30A and a part of the chamber 2 were welded to each other so as to be exposed to each other.
Further, as shown in FIG. 4, catalyst particles (nickel formed by supporting nickel on granular porous alumina (particle size: 0.5 to 3 mm) around the hydrogen separation module 10 </ b> A (hydrogen generation unit 20). About 400 g of system reforming catalyst) 18 was filled. As the catalyst 18, a new catalyst not used for the reforming reaction was used. In this way, the reformer 1A according to this example was constructed.
[0057]
Next, a reforming test was performed using the reformer 1A. That is, the gas separation evaluation system (gas reforming system) shown in FIG. 3 was constructed by incorporating the reformer 1A. As shown by a broken line in FIG. 3, the difference from the first embodiment is that a sweep gas (here, helium) supply device 90 composed of the same equipment as the hydrogen supply device 54 and the like is separately provided, and the sweep is performed. The gas supply pipe is connected to the gas supply port 6A. Thus, the sweep gas (He) can be directly supplied from the sweep gas supply device 90 to the permeate gas passage 16 of the hydrogen separation module 10A through the gas supply port 6A.
[0058]
Thus, as shown in FIGS. 3 and 4, according to the gas separation system (gas reforming system) provided with the reformer 1A, the source gas (non-oxidizing condition) supplied from the gas supply pipe 3 ( Here, methane containing steam together with nitrogen is supplied.) Is introduced into the hydrogen generator 20 in the chamber 2A, and the action of the catalyst 18 filled therein, that is, the steam reforming reaction (CH _Four + H ₂ O = CO + 3H ₂ , CO + H ₂ O = CO ₂ + H ₂ ) Produces hydrogen. Part of the generated hydrogen permeates the hydrogen separation membrane 12A and the porous support 14A of the tubular hydrogen separation module 10A and is separated from the hydrogen generation unit 20 side to the gas passage 16 side inside the pipe, and the permeate gas passage 16 Is sent out from the chamber 2A through the permeate gas discharge port 6.
On the other hand, the gas that has been introduced into the hydrogen generator 20 and has not permeated through the hydrogen separation membrane 12A is discharged from the chamber 2A through the gas discharge pipe 4 to the outside. In the reformer 10A according to the present embodiment, the gap between the hydrogen separation module 10A and the joint pipes 30 and 30A is sealed by the sealing material 38 (see FIG. 2) provided in the joint pipes 30 and 30A. As a result, the source gas does not leak into the permeate gas passage 16 from the gap without passing through the hydrogen separation membrane 12A. Therefore, according to the reformer 10A having such a configuration and the gas reforming system including the reformer, hydrogen as a reaction product is separated through the hydrogen separation membrane 12A in accordance with the reforming reaction, so that in the hydrogen generating unit. Hydrogen concentration decreases. This shifts the equilibrium to the reactant side and promotes the conversion reaction from methane to hydrogen. That is, in the reformer 10A according to the present embodiment, the polysilazane membrane of the high temperature type and the sealing material which is excellent in hydrogen permeation performance and separation performance particularly in a high temperature range of 600 ° C. or higher (more preferably 700 ° C. or 800 ° C. or higher). By using together, it is possible to stably realize a high conversion rate from the raw material gas (here, methane) to hydrogen in such a high temperature range.
Next, the gas conversion rate by the gas reforming system was examined as follows.
[0059]
In the reforming test according to this example, three conditions of 600 ° C., 700 ° C., and 800 ° C. were set as the reforming reaction temperature conditions, and the tests were performed as follows.
That is, first, while purging a small amount of nitrogen, the temperature in the chamber 2A of the reformer 10A was raised to one of the above set temperatures. Subsequently, hydrogen reduction treatment was performed for about 1 hour while introducing methane, water vapor, and nitrogen from the supply devices 52, 100, and 56 (operating at room temperature) shown in FIG. . At this time, the supply amount of each gas supplied into the chamber 2A was as follows. That is, when the set temperature was 600 ° C., the supply amounts (ml / min.) Of methane, water vapor, and nitrogen were 9.0, 0.03, and 10, respectively. Further, when the set temperature was 700 ° C., the supply amounts of methane, water vapor and nitrogen were 9.5, 0.03 and 10, respectively. Furthermore, when the set temperature was 800 ° C., the supply amounts of methane, water vapor, and nitrogen were 9.5, 0.03, and 10, respectively. Steam ratio (H ₂ O / CH _Four ) Was about 5 in molar ratio. The pressure in the reformer (inside the chamber) is 2.0 × 10 ⁵ It was set to within Pa (2.0 atm). Further, during this process, a sweep gas (Ne) was introduced into the permeate gas passage 16 from the gas supply port 6A at a predetermined flow rate.
[0060]
Thus, when the steam reforming reaction is performed in the hydrogen generator 20 by such processing, in this embodiment, the supply gas (that is, the gas before being supplied to the gas supply pipe 3 of the chamber 2A) and the modification are changed at intervals of 30 minutes. Sampling the gas (that is, after being discharged from the gas discharge pipe 4 of the chamber 2A and after being discharged from the permeate gas discharge port 6) in total, GC (CHROMPAVK: Micro-GC CP2002) Analysis using (CH _Four , H ₂ , CO, O ₂ , N ₂ In the analysis, the column temperature is 100 ° C and the analysis time is 2 minutes; CO ₂ In this analysis, the column temperature was 80 ° C. and the analysis time was 2 minutes. The conversion rate (%) from the raw material gas (methane) to hydrogen was calculated based on the measurement result by GC.
[0061]
Thus, after one hour of hydrogen reduction treatment, the permeate side gas flow (ie sweep gas flow) was sealed to eliminate the differential pressure. As a result, substantial gas permeation from the hydrogen generator 20 via the hydrogen separation membrane 12A was blocked. In this state, raw material methane, water vapor, and nitrogen were continuously supplied into the chamber 2A at the above supply amounts. Then, after 1.5 hours have passed from the sealing of the permeate side gas flow and after 0.5 hours have passed (ie, every 30 minutes), the supply gas and the reformed gas are sampled, and the above is performed using GC. Analysis was performed in the same manner.
Thereafter, the permeate side gas flow (that is, the sweep gas flow) was restarted with the differential pressure provided. Thereby, substantial gas permeation from the hydrogen generator 20 via the hydrogen separation membrane 12A was resumed. In this state, raw material methane, water vapor, and nitrogen were continuously supplied into the chamber 2A at the above supply amount. Then, after 1.5 hours have passed since the resumption of the permeate gas flow and 0.5 hours later (ie, every 30 minutes), the supply gas and the reformed gas are sampled and analyzed in the same manner using GC Went. After completion of such sampling (2 times each) and analysis (6 times in total), the supply of methane gas was first stopped, and then the supply of water vapor was stopped.
[0062]
[Table 3]

[0063]
Table 3 shows the conversion rate (%) calculated based on the GC analysis. In the table, “membrane permeation side gas flow / present” is data measured after the permeation side gas flow is resumed.
As apparent from the results shown in Table 3, under any temperature condition, the “membrane permeation side gas flow is present”, that is, the case where the hydrogen separation module according to this example is applied is “the membrane permeation side Compared with the case where the gas separation / no gas flow module, that is, the hydrogen separation module according to this embodiment is not substantially used (that is, a conventional reformer without a hydrogen separation membrane), the raw material is more efficiently produced. Gas (CH _Four ) Demonstrated that the reforming reaction was performed. From this, it was proved that the polysilazane membrane formed in the hydrogen separation module according to the present example maintained high hydrogen permeation performance / separation performance or sealing performance in a high temperature range. N that does not directly affect the reaction ₂ Omit gas and H for reformed gas ₂ , CH _Four , CO, CO ₂ When each composition was verified, CO, CO ₂ H to composition ₂ The composition is also consistent with the theoretical reaction equation.
The preferred temperature of the nickel-based reforming catalyst used in this example is approximately 820 ° C. although it depends on the operating conditions. Therefore, according to the reformer 1A of this example that uses the polysilazane film and such a high-temperature reforming catalyst in combination, the reforming reaction and the chemical equilibrium shift associated with hydrogen separation cause 600 to 800 ° C. (or 600 ° C.). Hydrogen can be produced with high efficiency in a high temperature range of ˜1000 ° C.). This indicates that the amount of methane remaining after the reforming reaction is significantly reduced in the case of “Membrane Permeation Side Gas Flow / Without” than in the case of “Membrane Permeation Side Gas Flow / None” and in the reformed gas. On the other hand, it is confirmed that the hydrogen concentration is significantly increased (GC analysis result).
Contrary to the reforming test according to this example, the gas flow on the membrane permeate side was processed in the order of (1), none, (2), and (3). As a result of the same analysis, no significant difference was found in the analysis results between (1) sampling without (3) and sampling without (3). From this, it can be judged that the influence of the change over time of the catalytic reaction in this example is at a negligible level.
[0064]
Further, as is apparent from the results of this example shown in Table 3, the reformer 1A according to this example has a good chemical equilibrium shift (that is, polysilazane) even when used under high temperature conditions such as 700 ° C. and 800 ° C. (Based on a decrease in the hydrogen concentration in the hydrogen generator by selective separation of hydrogen through the membrane).
This means that, as in the reformer 1 according to the first embodiment, no substantial gas leaks from the gap between the chamber 2A and the hydrogen separation module 10A or does not affect the reforming reaction. It is shown. That is, it has been demonstrated that the above-described sealing material 38 (FIG. 2) can maintain good sealing performance even under high temperature conditions such as 800 ° C. That is, the gap size between the metal joint pipes 30 and 30A and the ceramic hydrogen separation module 10A tends to gradually increase as the temperature increases due to the difference in expansion coefficient based on the difference in the material of these members. With the excellent elastic deformation capability (flexibility / cushioning property), the sealing state of the fluctuating gap can be maintained.
In particular, the support of the hydrogen separation module 10A according to the present embodiment is made of silicon nitride having excellent compressive strength. As a result, it is possible to inevitably increase the clamping force against the sealing material 38 while preventing the hydrogen separation module 10A from being destroyed. That is, by compressing and deforming relatively strongly, both the airtightness and the elastic restoration amount of the expanded graphite sealing material 38 itself can be improved, and as a result, the sealing performance in a high temperature range can be further improved.
[0065]
<Example 4>
Next, a hydrogen separation module having an alumina membrane instead of the polysilazane membrane was produced.
That is, 100 parts by weight of an organic binder was added to and mixed with 3000 parts by weight of alumina powder (50% particle diameter: about 3 μm). To this mixture, 60 parts by weight of a wax emulsion, 60 parts by weight of a polyether-based synthetic oil (lubricant) and 420 parts by weight of ion-exchanged water were added and kneaded to obtain a clay for extrusion molding.
Subsequently, the kneaded material was extruded by an extruder, dried by microwaves, and heat-treated in an air atmosphere to obtain a porous alumina tubular support.
[0066]
Next, the surface of the obtained porous tubular support was densified. That is, 825 parts by weight of distilled water was added to 1200 parts by weight of high-purity α-alumina particles (average particle diameter of about 0.2 μm), and the pH was adjusted by adding nitric acid while stirring and mixing. And it stirred with the ultrasonic homogenizer, and mixed with the ball mill.
A solution obtained by adding 660 parts by weight of distilled water to 140 parts by weight of an organic binder and stirring and mixing with a heating stirrer and 72 parts by weight of a plasticizer were added to the mixture. Thereafter, about 1.4 N nitric acid was added to the prepared slurry to adjust the pH, and the mixture was mixed with a ball mill to obtain a film-forming slurry.
Next, the slurry for film formation was vacuum defoamed (foam removed). Thereafter, the porous support whose outer surface was polished in advance was immersed in the slurry for 30 seconds. Thus, the support having a dense layer formed on the outer surface is then dried in the air at room temperature and fired in an air atmosphere (1030 ° C.), whereby the tubular support having the α-alumina layer formed on the outer surface. Got.
[0067]
Next, a homogeneous dense layer was produced on the surface and pores of the α-alumina layer of the tubular support. That is, 1960 parts by weight of distilled water was added to 19 parts by weight of γ-alumina fine particles (average particle size of several tens of nm), and they were stirred and mixed at room temperature with a stirrer for 2 days. Thereafter, the mixture was further stirred with an ultrasonic homogenizer to prepare a sol for film formation. Thereafter, the film-forming sol was subjected to vacuum defoaming.
Next, the porous support was immersed in the sol for film formation. By drying it in the air at room temperature and baking (900 ° C.) in an air atmosphere, a uniform dense layer is formed on the surface and pores of the first layer (α-alumina layer) on the outer surface of the support. A certain second layer (γ-alumina layer) was formed.
Then, in order to form a more uniform dense layer (film) on the obtained porous tubular support, by similarly processing using a low concentration film-forming sol with a reduced concentration of the film-forming sol, A gas separation module made of alumina in which a more homogeneous and dense γ-alumina layer is formed on the outer surface of the second layer (outer diameter: 10 mm, inner diameter: 7 mm, length: 250 mm, membrane area: 7900 mm ² ) Was produced.
[0068]
According to a general pore distribution measurement method (here, mercury intrusion method), the average pore diameter of the porous support portion of the gas separation module according to this example is about 8 μm, and the porosity is about 39%. It was. Further, as a result of SEM observation of the cross section of the membrane part and the outermost surface of the hydrogen separation module according to this example, the film thickness of the first layer was approximately 40 μm. The film thickness of the second layer and the subsequent layers was about 10 μm including the portion impregnated in the first layer. Moreover, from the result of this SEM observation, it was confirmed that the occurrence of surface defects of at least submicron order was suppressed. Moreover, when the bubble point was measured as an index for film formation evaluation, it was confirmed that the bubble point value was 4.0 or more in this production process.
[0069]
Next, a reformer was constructed using the gas separation module made of alumina according to this example, and the evaluation was performed.
First, the same evaluation test as in Example 2 was performed. That is, after attaching the joint pipe 30 and the cap 5 as described above, the reformer shown in FIG. 1 is constructed, and further, using the gas separation system shown in FIG. The permeability and the hydrogen / nitrogen permeability coefficient ratio were measured and calculated. Measurement conditions and calculation methods are the same as those in the first embodiment. The results are shown in Table 4.
[0070]
[Table 4]

[0071]
As shown in Table 4, the reformer (membrane type reactor) provided with the gas separation module having the alumina membrane according to the present example also includes the hydrogen separation module having the polysilazane membrane (membrane type). As in the case of the reactor, it was confirmed that the reforming reaction can be performed with high efficiency in a high temperature range.
A treatment similar to that in Example 3 was performed, and a membrane type reformer was constructed using the alumina membrane gas separation module according to this example and the nickel-based reforming catalyst, and the reforming efficiency in a high temperature range was evaluated. . Thus, Table 5 shows the results at the reforming temperature of 700 ° C.
[0072]
[Table 5]

[0073]
As shown in Table 5, the alumina gas separation module according to the present example and the membrane type reformer including the same are also the hydrogen separation module having the polysilazane membrane of the above example and the membrane type reforming including the same. Similar to the reactor, hydrogen is efficiently removed from the reaction system through the alumina film even under a high temperature condition of 700 ° C., and as a result, the equilibrium shifts to the hydrogen generation reaction side. For this reason, the effect of accelerating the conversion reaction from methane to hydrogen can be expected.
That is, also in the reformer according to the present embodiment, the high temperature compatible type alumina membrane that is particularly excellent in hydrogen permeation performance and separation performance in a high temperature region of 700 ° C. or higher and the sealing material that is excellent in sealing performance at high temperatures. By using together, it was possible to achieve a high conversion rate from raw material gas to hydrogen. In addition, since this membrane is a sintered membrane, there is a possibility that the separation performance may be lowered while the particle size becomes large when used in a high temperature range for a long time. This is an example of application of a ceramic separation membrane made of the same material to a high-temperature membrane reformer, and is not an example of a ceramic separation membrane that can be used stably at a high temperature for a very long time.
[0074]
【The invention's effect】
In the reformer of the present invention, a hydrogen separation membrane capable of exhibiting excellent hydrogen permeability and separation performance even in a high temperature region of 600 ° C. or higher (high temperature hydrogen separation membrane capable of realizing higher separation performance than conventional: for example, hydrogen / nitrogen A hydrogen separation module including a permeability coefficient ratio of 15) is applied, and in addition, an expansion black is used to prevent gas leakage from the installation position with respect to the installation of the hydrogen separation module. Lead or The sealing material which consists of is used.
[0075]
According to the reformer of the present invention having such a configuration, a desired sealing performance can be maintained even in a high temperature range of 600 ° C. or higher (typically 600 to 1100 ° C.), and further, it is generated along with the reforming reaction. Hydrogen can be selectively and efficiently removed to the hydrogen permeation side through a high-temperature compatible hydrogen separation membrane. For this reason, promoting the conversion reaction (conversion rate) from source gas such as methane to hydrogen by shifting the equilibrium to the reactant side even under severe conditions such as high temperature of 600 ° C or higher and steam atmosphere Can do.
The reformer of the present invention is suitable as a reformer for high-temperature fuel cells (MCFC, SOFC, etc.) that require high hydrogen production (conversion) efficiency particularly in a high temperature range.
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing the structure of a reformer according to one embodiment.
FIG. 2 is a cross-sectional view schematically showing a joint pipe having a sealing material according to an embodiment.
FIG. 3 is a block diagram schematically showing an entire gas separation system including a reformer according to an embodiment.
FIG. 4 is an explanatory view schematically showing the structure of a reformer according to one embodiment.
[Explanation of symbols]
1,1A reformer
10,10A Hydrogen separation module
12,12A Hydrogen separation membrane
14, 14A porous support
16 Gas passage
18 Catalyst
20 Hydrogen generator
30, 30A joint pipe
38 Sealing material

Claims (3)

A reformer for generating hydrogen from a raw material gas,
Inside, a hydrogen generation unit that generates hydrogen from the source gas, and a gas passage adjacent to the hydrogen generation unit are provided,
A hydrogen separation module having a hydrogen separation membrane for permeating hydrogen from the hydrogen production unit side to the gas passage side at the boundary between the hydrogen production unit and the gas passage, the hydrogen separation membrane on the surface It is equipped with a formed porous tubular hydrogen separation module ,
The hydrogen generation part is formed outside the tubular hydrogen separation module, and the hollow part of the tubular hydrogen separation module constitutes the gas passage,
A joint pipe is attached to at least one end of the tubular hydrogen separation module in a state where gas can flow with the hollow part,
The joint tube and the end of the tubular hydrogen separation module are connected so that a part of them overlaps each other,
A sealing material for preventing gas from leaking from the hydrogen generation part side to the gas passage side without the hydrogen separation membrane interposed in the gap between the joint pipe and the tubular hydrogen separation module which are overlapped with each other is substantially provided on both sides. It is placed in close contact,
In this case, the hydrogen separation membrane is at least 2.5 hydrogen / nitrogen permeability coefficient ratio at 600 ° C., the hydrogen permeation rate at that temperature 0.1 × 10 ^-6 mol / m ² · s · Pa or more Yes,
The sealing material is expanded black lead that consists reformer bulk density of 0.6~1.9g / cm ^3. The expanded graphite constituting the sealing material has the following properties:
(1). The compression ratio is 10 to 90%;
(2). The elastic recovery rate is 3 to 70%;
The reformer according to claim 1, comprising: The reformer according to claim 1 or 2, wherein the hydrogen separation membrane is a ceramic membrane having a basic structure of a repeating structure mainly composed of Si-N bonds obtained by firing polysilazane in an inert atmosphere.

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