JP3716002B2 - Water electrolysis method - Google Patents

Water electrolysis method Download PDF

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JP3716002B2
JP3716002B2 JP01875295A JP1875295A JP3716002B2 JP 3716002 B2 JP3716002 B2 JP 3716002B2 JP 01875295 A JP01875295 A JP 01875295A JP 1875295 A JP1875295 A JP 1875295A JP 3716002 B2 JP3716002 B2 JP 3716002B2
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exchange membrane
ion exchange
ozone
water electrolysis
anode
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JPH08188895A (en
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孝之 島宗
善則 錦
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De Nora Permelec Ltd
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Permelec Electrode Ltd
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Description

【0001】
【産業上の利用分野】
本発明は、高効率で純水を電解する方法に関し、より詳細には高温においても純水を高効率で電解し、オゾンと酸素の混合ガスを得るための方法に関する。
【0002】
【従来技術とその問題点】
水電解によりオゾンを製造する工夫は古くから行われ、2種類の電解法により高濃度で高純度のオゾンが得られている。
第1の方法は、補助電解質として高電気陰性度の陰イオンを含む液を電解してオゾンを製造する溶液電解法であり、第2の方法は高分子固体電解質を使用する純粋な水電解方法である。前者の方法は電極物質、溶液(電解液)及び電解条件等の選択により極めて高い電流効率が得られるが、電解液の極めて高い腐食性のため実験室的に検討が進んでいるのみで実用装置として市販されていない。
【0003】
一方パーフルオロカーボンスルホン酸系陽イオン交換膜を固体電解質としその両側に陰極及び陽極を密着させた所謂固体電解質型又はゼロギャップ型電解である第2の方法は、構造が比較的簡単であり生成するオゾン以外には腐食性あるいは危険のある物質が存在しないため取扱いが容易であることも含めて、数種の装置が商品化されている。この装置のオゾン発生の電流効率は現在のところ最高で20%程度、通常は13〜18%であり、得られる生成ガスは13〜18重量%のオゾンを含む水が飽和した酸素ガスである。この装置を使用する電解系では液成分が脱イオン水であり腐食性は殆どないと考えてよいので、電極の消耗やその他の成分の溶出がなく、不純物が混入しないため、純粋に近い混合ガスが得られるという特徴がある。従って従前からの殺菌等の応用分野に加えて、エレクトロニクスの洗浄等の精密工学の分野にもオゾンの使用が拡大されつつある。
【0004】
この水電解によるオゾン製造方法に使用されるイオン交換膜は、多くの場合耐薬品性に優れたフッ素樹脂系イオン交換膜である。このイオン交換膜はスルホン酸型であること殆どであり、該スルホン酸型イオン交換膜は、ポリテトラフルオロエチレン(PTFE)樹脂とパーフルオロスルホニルエトキシビニルエーテルの共重合物(XR−レジン)を成膜し加水分解することにより得られる。この他にカルボン酸型イオン交換膜、該カルボン酸型イオン交換膜と前記スルホン酸型イオン交換膜との積層膜、これらの膜に強度向上のためにフッ素樹脂繊維を埋め込んだ膜、及び表面に酸化物被覆を施し親水性を改良した膜などが市販されている。
【0005】
前記イオン交換膜は各種電解に使用され、各電解用としては最適な物性のイオン交換膜が使用されるべきである。該物性としては、電流効率及び電気伝導度等があり、これらはイオン交換基の種類や濃度により決定されるが、市販されているイオン交換膜は上述の通り限定され、所定の電解に最適なイオン交換膜が入手できるとは限らない。
水を電解すると、陽極から酸素やオゾンが、又陰極から水素や過酸化水素が発生するが、特に該水電解方法では膜の特性が電解性能に決定的な影響を及ぼすことが多い。即ち、膜の抵抗が大きいと電力原単位が増加し、これを減少させるために薄い膜を使用すると生成するガスの純度が低下するといった相反する効果が現れる。
【0006】
特に電解によりオゾンを生成する純水電解系で使用する膜は、単なる隔膜や電解質としての役割のみならず、オゾンの生成効率に大きな寄与を有すると考えられている〔J. Electroanalytical. Chem. 228, p407-415 (1987)] 。
このオゾン発生装置の欠点として、オゾン生成効率が20〜40℃で最大となり、通常の運転条件ではオゾン生成に伴う熱のため液温が40℃を越えるため、十分な冷却を施さなければならないことが挙げられている。又セル電圧は陰極を水素発生反応としたときに3.0 〜3.5 Vとなり、電力原単位は他の生成方法と比較して2〜3倍に達し、又陰極に酸素還元陰極を用いた場合ではセル電圧は2.0 〜2.5 Vに低減できるが、より以上の改良が望まれている。
【0007】
【発明の目的】
本発明は、前述の従来技術の問題点を解消し、電解電圧を減少させ、特に高温領域での電流効率を維持し効率良く水電解を行なってオゾン等を製造できる水電解方法を提供することを目的とする。
【0008】
【問題点を解決するための手段】
本発明は、その両側にそれぞれ陽極及び陰極を密着配置させたパーフルオロカーボン系イオン交換膜を固体電解質とした水電解セルに脱イオン水を供給して電解し陽極生成物としてオゾンと酸素の混合物を得るための水電解方法において、前記イオン交換膜のイオン交換基の一部又は全部がリン酸基であり、陽極物質が酸化鉛又は白金であることを特徴とする水電解方法である。
【0009】
以下本発明を詳細に説明する。
本発明では、水電解による酸素及び/又はオゾン生成の際に、従来のパーフルオロカーボン系スルホン酸型又はカルボン酸型イオン交換膜に代えて、パーフルオロカーボン系リン酸型イオン交換膜を使用する。なお本発明ではイオン交換基の一部又は全部がリン酸基であるイオン交換膜をリン酸型イオン交換膜と称する。
従来のパーフルオロカーボン系スルホン酸型イオン交換膜等を使用しても低温領域では比較的高電流効率でオゾン等を生成できるが、前述の通り電解温度が高くなると徐々に電流効率が低下するという欠点があった。
【0010】
リン酸型イオン交換膜を使用して水電解を行なうと、液温が40℃程度までは前記スルホン酸型イオン交換膜を使用する電解とほぼ同じ電流効率でオゾンが発生するが、40℃を越えると急速にスルホン酸型イオン交換膜を使用する水電解の電流効率が低下し一方前記リン酸型イオン交換膜を使用する水電解では電流効率がほぼ一定に維持され、両電解における電流効率の差異が顕著になる。
従来のスルホン酸型イオン交換膜を使用する水電解特に電解オゾンの生成では、温度上昇に伴う電流効率の低下を抑制するため電解セルの冷却を行なっていたが、この冷却に必要とされる設備費は多大であり、しかも必ずしも十分に冷却されず電流効率の低下を抑制できなかった。
【0011】
これに対しパーフルオロカーボン系リン酸型イオン交換膜を使用する本発明の水電解方法では、温度上昇に伴う電流効率の低下自体が殆どないため、冷却が不要になり、付随設備を設置することなくオゾン等の生成効率をほぼ一定に維持できる。
水電解にリン酸型イオン交換膜を使用する際に高温域での電流効率の低下が生じない理由は明確ではないが、オゾン発生メカニズムが電解質成分及び濃度と深い関係にあり、本発明におけるイオン交換膜中のリン酸基と後述する酸化鉛及び白金等の陽極物質の組合せが、高温域の電流効率の維持に寄与しているものと推測できる。
【0012】
本発明の前記パーフルオロカーボン系リン酸型イオン交換膜は特に限定されず、従来公知のイオン交換膜をそのまま使用すれば良く、例えば該イオン交換膜は市販の前記スルホン酸型イオン交換膜を濃厚リン酸溶液中に高温(例えば120 〜180 ℃)で数時間から数日浸漬することにより調製できる。又カルボン酸型イオン交換膜のカルボン酸基を水素化リチウムアルミニウム等の還元剤を用いて水酸基とした後、オキシ塩化リンでリン酸化し次いで加水分解を行なうことによりリン酸エステル型に変換することもできる。更に原料成分としてのパーフルオロスルホニルエトキシビニルエーテルモノマーやパーフルオロビニルエーテルモノマーをリン酸基を有する基とした後にPTFEと共重合して成膜し所望のリン酸型イオン交換膜を得ることもできる。
本発明では、イオン交換膜のイオン交換基が全てリン酸基である必要はなく、スルホン酸基やカルボン酸基とリン酸基が共存していてもよい。
【0013】
次に本発明に係わる水電解方法で使用するイオン交換膜以外の各部材について説明する。
陽極物質としては、オゾン発生を意図してα−又はβ−二酸化鉛あるいは白金を使用する。これらの陽極物質は前記イオン交換膜に直接被覆しても、微細な多孔質電極基材に被覆しこれを前記イオン交換膜と強く接触させる所謂ゼロギャップタイプとして前記イオン交換膜と一体化しても良い。しかしながら二酸化鉛は湿潤状態のイオン交換膜との接触下で不安定であるためゼロギャップタイプとすることが望ましい。本発明では前述の直接被覆とゼロギャップタイプの両者を含めて「密着」という。
【0014】
これらの陽極物質は、チタンやタンタル等の弁金属から成る粉末あるいは繊維焼結体等の集電体(基体)上に、必要に応じて該集電体の酸化を防止しかつ電導性を保持するための貴金属や金属酸化物を含む下地層を介して、担持させる。この担持は、例えば前記陽極物質をPTFE等の樹脂と混練しペーストとして前記集電体上に担持するか、あるいは公知の電着法や熱分解法により行なえば良い。
陰極物質も同様に水電解用として汎用されている物質を使用すれば良く、水素発生を伴う場合には過電圧の小さい触媒、即ちルテニウムや白金等の貴金属又はその酸化物を好ましく使用でき、陽極物質と同様にして担持できる。又集電体としてはカーボン、ニッケル及びステンレス等の市販の材料を使用すれば良い。更に該陰極も前記陽極と同様に直接被覆又はゼロギャップタイプにより前記イオン交換膜の陽極と反対側に密着させる。
なお本発明方法では陰極としてガス拡散電極を使用することも可能である。
【0015】
このように陽極−イオン交換膜−陰極の順に積層したセル構造体を、樹脂、チタンあるいはステンレス等から成り、気液供給及び除去用の通路を有する水電解セル内に設置する。両集電体への給電部材としては気液透過用の溝や穴を有するチタンやステンレス製の多孔質板を使用することが好ましい。電極の周囲には気液シール用のガスケット材を挟み込み、全体をボルト及びナットを使用して締め付けて一体化でき、電極物質と膜との面圧は3〜50kgf/cm2 となるように調節することが望ましい。
このような構成から成るリン酸型イオン交換膜を有する水電解セルの陽極室及び陰極室に純水を入れ、電源を両極の給電端子に接続して好ましくは10〜200 A/dm2 程度の電流密度で通電する。この範囲を越える電流密度では膜内の水分が発熱により気化し膜の破壊に繋がる恐れがあり、又この範囲未満ではオゾン発生効率が著しく低下する。
【0016】
セル内温度は20〜100 ℃が好ましく特に30〜70℃が望ましい。本発明方法による電解では通常の電解条件ではこの範囲を越えることはなく、付帯設備を設置して加熱してもオゾン等の発生効率が低下し電極物質の活性も低下するため意味がない。前記範囲未満の温度にするには冷却が必要となり、かつ該冷却によりオゾン等の発生効率が低下するため無意味である。
本発明方法による電解では広い温度範囲に亘って安定し、従来の電解オゾン発生方法と異なり温度制御を行なう必要がない。
【0017】
セル内の圧力は1〜5kgf/cm2 とすることが、又陽陰極室間の差圧は0〜5kgf/cm2 とすることが望ましい。5kgf/cm2 を越えるとガスの混入及び膜の強度低下の可能性が生じる。
本発明で使用するリン酸型イオン交換膜の電導度は従来のスルホン酸型イオン交換膜より小さいため、エネルギ原単位の低減が期待され、更に特にオゾン発生の場合、オゾン発生効率が高温下でも低下せず温度変動を考慮することなく高い発生効率でオゾンを得ることができる。
【0018】
次に添付図面に基づいて本発明に係わる水電解方法で使用可能な水電解セルの一例を説明する。
図1は、本発明方法で使用可能な水電解セルの概略断面図である。
電解オゾン発生装置である電解セル1は、固体電解質であるパーフルオロカーボン系リン酸型陽イオン交換膜2により陽極室3と陰極室4とに区画されている。前記イオン交換膜2の陽極室側及び陰極室側には、それぞれ陽極物質5を被覆した陽極集電体6及び陰極物質7を被覆した陰極集電体8が密着し、ゼロギャップタイプの構造を形成している。
【0019】
前記陽極集電体6及び陰極集電体8には、それぞれ多孔性の陽極給電体9及び陰極給電体10が接続され、両給電体から両極へ通電される。両給電体と前記イオン交換膜2の間の前記電極物質及び両集電体の周囲には、1対の額縁状ガスケット11が配設され、セル内を密閉状態に維持している。12は陽極液供給口、13は陰極液供給口、14は陽極液及びガス排出口、15は陰極液及びガス排出口である。
【0020】
このような構成から成る電解セル1の陽極室3及び陰極室4にイオン交換水や蒸留水等の純水を入れ、両極間に通電すると、陽極物質5表面で水が分解されて酸素及びオゾンが発生し、前記陽極液及びガス排出口14からセル外に取り出される。この際にオゾン発生に伴って熱が生じ電解液が加熱されて昇温するが、イオン交換膜2が温度変動に対してオゾン発生効率の変動が殆どないリン酸型イオン交換膜であるため、冷却等の付帯設備を必要とすることなく、常に安定した高効率でオゾン発生を行なうことができる。
【0021】
【実施例】
次に本発明に係わる水電解方法によるオゾン製造の実施例を記載するが、該実施例は本発明を限定するものではない。
【実施例1】
デュポン社の商品名「ナフィオン117 」パーフルオロスルホン酸系陽イオン交換膜を約140 ℃の濃厚リン酸溶液中に24時間浸漬し、前記スルホン酸基をリン酸基に変換した。赤外線吸収スペクトルによる分析の結果、90%のスルホン酸基がリン酸基に変換されていた。
【0022】
このイオン交換膜を固体電解質として幅100 mm、高さ300 mmで、電解面積300 cm2 の図1に示すような脱イオン水が満たされた箱型のオゾン発生用電解セルを組み立てた。陽極触媒として酸化鉛を、陰極触媒として白金をそれぞれ使用し、熱分解法によりチタン基体上に電極被覆を形成した。
陽極室及び陰極室に空気を供給しながら電流密度100 A/dm2 となるように電解を行ない、20〜70℃の温度で10℃刻みでオゾン生成の電流効率を測定し、その結果を図2中に実線で示した。又同様の条件でセル電圧の温度変化を測定し、その結果を図3中に実線で示した。
【0023】
【比較例1】
リン酸への変性を行なっていないナフィオン117 パーフルオロスルホン酸系陽イオン交換膜を固体電解質として使用したこと以外は実施例1と同一条件でオゾン生成の電流効率を測定し、その結果を図2中に点線で示した。又同様の条件でセル電圧の温度変化を測定し、その結果を図3中に点線で示した。
図3から、実施例1のリン酸型イオン交換膜と比較例1のスルホン酸型イオン交換膜ではセル電圧の温度依存性には殆ど差異がないのに対し、図2からは、実施例1のリン酸型イオン交換膜の方が比較例1のスルホン酸型イオン交換膜より特に高温領域におけるオゾン生成の電流効率が高いことが分かる。
又同一条件での運転を行なった際の実施例1及び比較例1の消費電力量を比較したところ、実施例1の運転の方が電力量が20%少なかった。
【0024】
【実施例2】
陽極触媒として酸化イリジウム−酸化ルテニウムを、陰極触媒として酸化ルテニウムを使用したこと以外は実施例1と同一条件で水電解によるオゾン生成を行ない、その際の電流密度のセル電圧依存性を測定したところ、図4の実線で示すとおりであった。
【0025】
【比較例2】
リン酸への変性を行なっていないナフィオン117 パーフルオロスルホン酸系陽イオン交換膜を固体電解質として使用したこと以外は実施例2と同一条件で電流密度のセル電圧依存性を測定したところ、図4の点線で示すとおりであった。
図4から、実施例2のリン酸型イオン交換膜を使用するオゾン発生用電解セルと比較例1のスルホン酸型イオン交換膜を使用する電解セルとでは前者の方が200 A/dm2 において、100 mVのセル電圧の低減があったことが分かる。なお陽極酸素ガス中への陰極水素ガス混入率は、実施例2及び比較例2とも0.01%以下であった。
【0026】
【実施例3】
実施例1の電解セルで、陰極を白金と炭素粉末から成るガス拡散電極とし、酸素ボンベから酸素ガスを必要量の2倍供給しながら電流密度50〜150 A/dm2 、温度50℃で運転した結果を図5に示した。電流密度が100 A/dm2 のとき、セル電圧1.8 V及び電流効率18%となり、電力原単位として35Wh/g−O3 が得られた。
【0027】
【実施例4】
実施例1の電解セルを電流密度100 A/dm2 及び温度60℃で長期運転したところ、4000時間経過した時点でセル電圧2.6 V、オゾン生成電流効率15〜18%を得た。初期から性能変化は殆ど認められなかった。
【0028】
【発明の効果】
本発明は、その両側にそれぞれ陽極及び陰極を密着配置させたパーフルオロカーボン系イオン交換膜を固体電解質とした水電解セルに脱イオン水を供給して電解し陽極生成物としてオゾンと酸素の混合物を得るための水電解方法において、前記イオン交換膜のイオン交換基の一部又は全部がリン酸基であり、陽極物質が酸化鉛又は白金であることを特徴とする水電解方法である。
【0029】
本発明では、前記リン酸型イオン交換膜の水電解による電解オゾン発生における温度変動に対する性能変化が殆どなく、比較的高温つまり通常の電解条件で達し得る最高温度においても、低温の場合と同等のオゾン発生効率が得られる。従って従来のスルホン酸型イオン交換膜を使用する電解オゾン発生の際に行なわれているセルの冷却を行なう必要がなく、換言すると電解時の温度変動に配慮することなく水電解を行なうことができる。
これにより従来の特に電解オゾン発生における必須要素であったオゾン発生効率維持のための冷却が不要となり、付帯設備及び冷却水のコストが節約できるだけでなく、冷却が十分に行なわれないことに起因する効率低下も起こることがなくなり、安定した水電解を実施できる。
【0030】
前記リン酸型イオン交換膜は、市販のパーフルオロカーボンスルホン酸系陽イオン交換膜を濃厚リン酸溶液に浸漬して変性したり、パーフルオロカーボンカルボン酸系陽イオン交換膜のカルボン酸基の還元及びリン化合物との反応により変性したりして得ることができる。
前記リン酸型イオン交換膜を使用する際の前述の温度安定性は、使用する陽極物質との関連で生ずるものと推測され、該陽極物質としては酸化鉛又は白金が好ましく使用され、該陽極物質の使用により高濃度のオゾンを含む酸素ガスが生成する。
又陰極してガス拡散電極を使用し酸素含有ガスを供給しながら電解を行なうと陰極反応が水素発生反応から水生成反応へ変換され、消費電力が更に低減される。
【図面の簡単な説明】
【図1】本発明に係わる水電解方法に使用可能な水電解セルの概略断面図。
【図2】実施例1及び比較例1におけるオゾン生成の電流効率の温度依存性を示すグラフ。
【図3】実施例1及び比較例1におけるセル電圧の温度依存性を示すグラフ。
【図4】実施例2及び比較例2における電流密度のセル温度依存性を示すグラフ。
【図5】実施例3における電流密度のセル温度依存性を示すグラフ。
【符号の説明】
1・・・電解セル 2・・・イオン交換膜 3・・・陽極室 4・・・陰極室5・・・陽極物質 6・・・陽極集電体 7・・・陰極物質 8・・・陰極集電体 9・・・陽極給電体 10・・・陰極給電体 11・・・ガスケット 12・・・陽極液供給口 13・・・陰極液供給口 14・・・陽極液及びガス排出口 15・・・陰極液及びガス排出口
[0001]
[Industrial application fields]
The present invention relates to a method for electrolyzing pure water with high efficiency, and more particularly to a method for electrolyzing pure water with high efficiency even at a high temperature to obtain a mixed gas of ozone and oxygen.
[0002]
[Prior art and its problems]
Inventions for producing ozone by water electrolysis have been made for a long time, and high-concentration and high-purity ozone has been obtained by two kinds of electrolysis methods.
The first method is a solution electrolysis method in which ozone is produced by electrolyzing a liquid containing an anion having a high electronegativity as an auxiliary electrolyte, and the second method is a pure water electrolysis method using a polymer solid electrolyte. It is. In the former method, extremely high current efficiency can be obtained by selecting the electrode material, solution (electrolyte), electrolysis conditions, etc., but because of the extremely high corrosivity of the electrolyte, only a laboratory study has been conducted. Is not commercially available.
[0003]
On the other hand, the second method, which is a so-called solid electrolyte type or zero gap type electrolysis in which a perfluorocarbon sulfonic acid cation exchange membrane is used as a solid electrolyte and a cathode and an anode are in close contact with each other, has a relatively simple structure and is produced. Several types of equipment have been commercialized, including the fact that there is no corrosive or dangerous substance other than ozone, and that it is easy to handle. The current efficiency of ozone generation in this apparatus is currently about 20% at maximum, usually 13 to 18%, and the resulting product gas is oxygen gas saturated with water containing 13 to 18% by weight of ozone. In the electrolytic system using this device, the liquid component is deionized water and it may be considered that there is almost no corrosiveness, so there is no electrode consumption or elution of other components, and no impurities are mixed in. There is a feature that can be obtained. Therefore, in addition to conventional application fields such as sterilization, the use of ozone is expanding to the field of precision engineering such as electronics cleaning.
[0004]
In many cases, the ion exchange membrane used in the ozone production method by water electrolysis is a fluororesin ion exchange membrane having excellent chemical resistance. This ion exchange membrane is mostly a sulfonic acid type, and the sulfonic acid type ion exchange membrane is formed by forming a copolymer of polytetrafluoroethylene (PTFE) resin and perfluorosulfonylethoxyvinyl ether (XR-resin). And obtained by hydrolysis. In addition to this, a carboxylic acid type ion exchange membrane, a laminated film of the carboxylic acid type ion exchange membrane and the sulfonic acid type ion exchange membrane, a membrane in which fluororesin fibers are embedded in these membranes for strength improvement, and a surface thereof Membranes with an oxide coating and improved hydrophilicity are commercially available.
[0005]
The ion exchange membrane is used for various electrolysis, and an ion exchange membrane having optimum physical properties for each electrolysis should be used. The physical properties include current efficiency, electrical conductivity, etc., which are determined by the type and concentration of ion exchange groups, but commercially available ion exchange membranes are limited as described above and are optimal for predetermined electrolysis. Ion exchange membranes are not always available.
When water is electrolyzed, oxygen and ozone are generated from the anode, and hydrogen and hydrogen peroxide are generated from the cathode. In particular, in the water electrolysis method, the characteristics of the membrane often have a decisive influence on the electrolysis performance. That is, if the resistance of the film is large, the power consumption increases, and if a thin film is used to reduce this, there is a conflicting effect that the purity of the generated gas decreases.
[0006]
In particular, a membrane used in a pure water electrolysis system that generates ozone by electrolysis is considered to have a great contribution not only to a role as a diaphragm and an electrolyte but also to ozone generation efficiency [J. Electroanalytical. Chem. , p407-415 (1987)].
Disadvantages of this ozone generator are that ozone generation efficiency is maximum at 20-40 ° C, and the liquid temperature exceeds 40 ° C due to heat generated by ozone generation under normal operating conditions, so sufficient cooling must be applied. Is listed. The cell voltage is 3.0 to 3.5 V when the cathode is used as a hydrogen generating reaction, the power consumption is 2 to 3 times that of other production methods, and when an oxygen reduction cathode is used as the cathode, the cell Although the voltage can be reduced to 2.0 to 2.5 V, further improvement is desired.
[0007]
OBJECT OF THE INVENTION
The present invention provides a water electrolysis method that eliminates the above-mentioned problems of the prior art, reduces electrolysis voltage, maintains current efficiency particularly in a high temperature region, and efficiently performs water electrolysis to produce ozone and the like. With the goal.
[0008]
[Means for solving problems]
In the present invention, deionized water is supplied to a water electrolysis cell in which a perfluorocarbon-based ion exchange membrane in which an anode and a cathode are closely arranged on both sides thereof is used as a solid electrolyte and electrolyzed to produce a mixture of ozone and oxygen as an anode product. in water electrolysis method for obtaining, a part or the whole of the ion exchange groups of the ion exchange membrane Ri phosphate groups der a water electrolysis wherein the anode material is lead oxide or platinum.
[0009]
The present invention will be described in detail below.
In the present invention, a perfluorocarbon phosphate ion exchange membrane is used in place of the conventional perfluorocarbon sulfonic acid type or carboxylic acid type ion exchange membrane when oxygen and / or ozone are generated by water electrolysis. In the present invention, an ion exchange membrane in which some or all of the ion exchange groups are phosphate groups is referred to as a phosphate ion exchange membrane.
Even if a conventional perfluorocarbon sulfonic acid type ion exchange membrane is used, ozone can be generated with a relatively high current efficiency in the low temperature region, but as described above, the current efficiency gradually decreases as the electrolysis temperature increases. was there.
[0010]
When water electrolysis is performed using a phosphoric acid ion exchange membrane, ozone is generated with almost the same current efficiency as the electrolysis using the sulfonic acid ion exchange membrane until the liquid temperature reaches about 40 ° C. If this is exceeded, the current efficiency of water electrolysis using a sulfonic acid type ion exchange membrane will rapidly decrease, while in water electrolysis using the phosphoric acid type ion exchange membrane, the current efficiency will be maintained almost constant, The difference becomes noticeable.
In conventional water electrolysis using sulfonic acid type ion exchange membranes, especially in the production of electrolysis ozone, the electrolysis cell was cooled in order to suppress a decrease in current efficiency with temperature rise. The cost is enormous, and it is not always sufficiently cooled to prevent a decrease in current efficiency.
[0011]
On the other hand, in the water electrolysis method of the present invention using a perfluorocarbon-based phosphoric acid ion exchange membrane, there is almost no decrease in the current efficiency itself due to the temperature rise, so cooling is unnecessary and no additional equipment is installed. Generation efficiency of ozone etc. can be maintained almost constant.
The reason why current efficiency does not decrease at high temperatures when using a phosphate ion exchange membrane for water electrolysis is not clear, but the ozone generation mechanism is closely related to the electrolyte components and concentration, It can be inferred that the combination of the phosphate group in the exchange membrane and the anode material such as lead oxide and platinum described later contributes to maintaining the current efficiency in the high temperature region.
[0012]
The perfluorocarbon-based phosphate ion exchange membrane of the present invention is not particularly limited, and a conventionally known ion exchange membrane may be used as it is. For example, the ion exchange membrane may be a commercially available sulfonic acid ion exchange membrane. It can be prepared by dipping in an acid solution at a high temperature (for example, 120 to 180 ° C.) for several hours to several days. In addition, the carboxylic acid group of the carboxylic acid type ion exchange membrane is converted into a phosphate ester type by converting it to a hydroxyl group using a reducing agent such as lithium aluminum hydride, phosphorylating with phosphorus oxychloride and then hydrolyzing. You can also. Further, a desired phosphoric acid ion exchange membrane can be obtained by forming a perfluorosulfonylethoxyvinyl ether monomer or a perfluorovinyl ether monomer as a raw material component into a group having a phosphoric acid group and then copolymerizing with PTFE to form a film.
In the present invention, it is not necessary that all ion exchange groups of the ion exchange membrane are phosphoric acid groups, and sulfonic acid groups or carboxylic acid groups and phosphoric acid groups may coexist.
[0013]
Next, each member other than the ion exchange membrane used in the water electrolysis method according to the present invention will be described.
For the anode material, using the intended ozone generation α- or β- lead dioxide or platinum. These anode materials may be directly coated on the ion exchange membrane, or may be integrated with the ion exchange membrane as a so-called zero gap type in which a fine porous electrode base material is coated and strongly contacted with the ion exchange membrane. good. However, since lead dioxide is unstable under contact with a wet ion exchange membrane, it is desirable to use a zero gap type. In the present invention, both the direct coating and the zero gap type are referred to as “adhesion”.
[0014]
These anode materials, on the current collector (substrate) such as powder or fiber sintered body made of valve metal such as titanium and tantalum, prevent the current collector from being oxidized as necessary and maintain electrical conductivity. It is carried through an underlayer containing a noble metal or metal oxide. For example, the anode material may be kneaded with a resin such as PTFE and supported as a paste on the current collector, or may be performed by a known electrodeposition method or thermal decomposition method.
Similarly, the cathode material may be a material widely used for water electrolysis. When hydrogen generation is involved, a catalyst with a small overvoltage, that is, a noble metal such as ruthenium or platinum or an oxide thereof can be preferably used, and an anode material. It can be supported in the same manner. As the current collector, commercially available materials such as carbon, nickel and stainless steel may be used. Further, the cathode is also in close contact with the side opposite to the anode of the ion exchange membrane by a direct coating or a zero gap type, similarly to the anode.
In the method of the present invention, it is also possible to use a gas diffusion electrode as the cathode.
[0015]
The cell structure laminated in this order of anode-ion exchange membrane-cathode is placed in a water electrolysis cell made of resin, titanium, stainless steel, or the like and having gas-liquid supply and removal passages. As a power supply member for both current collectors, it is preferable to use a porous plate made of titanium or stainless steel having grooves and holes for gas-liquid transmission. Gasket for gas-liquid sealing is sandwiched around the electrode and the whole can be integrated by tightening with bolts and nuts, and the contact pressure between the electrode material and the membrane is adjusted to 3-50 kgf / cm 2 It is desirable to do.
Pure water is put into the anode chamber and the cathode chamber of the water electrolysis cell having the phosphoric acid ion exchange membrane having such a structure, and the power source is connected to the power supply terminals of both electrodes, preferably about 10 to 200 A / dm 2 . Energize with current density. If the current density exceeds this range, moisture in the film may vaporize due to heat generation, leading to the destruction of the film. If the current density is less than this range, the ozone generation efficiency is significantly reduced.
[0016]
The temperature in the cell is preferably 20 to 100 ° C, particularly preferably 30 to 70 ° C. In the electrolysis according to the method of the present invention, this range is not exceeded under normal electrolysis conditions, and even if ancillary equipment is installed and heated, the generation efficiency of ozone and the like is lowered, and the activity of the electrode material is also not meaningful. Cooling is required to make the temperature lower than the above range, and the generation efficiency of ozone and the like is lowered by the cooling, so that it is meaningless.
The electrolysis according to the method of the present invention is stable over a wide temperature range and does not require temperature control unlike the conventional electrolytic ozone generation method.
[0017]
It is the differential pressure between Matahi cathode chamber is desirably set at 0~5kgf / cm 2 pressure in the cell and 1~5kgf / cm 2. If it exceeds 5 kgf / cm 2 , gas may be mixed and the strength of the film may be reduced.
Since the conductivity of the phosphoric acid ion exchange membrane used in the present invention is smaller than that of the conventional sulfonic acid ion exchange membrane, a reduction in energy intensity is expected. In particular, in the case of ozone generation, the ozone generation efficiency is high even at high temperatures. Ozone can be obtained with high generation efficiency without taking into account temperature fluctuations without lowering.
[0018]
Next, an example of a water electrolysis cell that can be used in the water electrolysis method according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a water electrolysis cell that can be used in the method of the present invention.
An electrolytic cell 1 that is an electrolytic ozone generator is partitioned into an anode chamber 3 and a cathode chamber 4 by a perfluorocarbon-based phosphoric acid cation exchange membrane 2 that is a solid electrolyte. An anode current collector 6 coated with an anode material 5 and a cathode current collector 8 coated with a cathode material 7 are in close contact with the anode chamber side and the cathode chamber side of the ion exchange membrane 2, respectively. Forming.
[0019]
Porous anode feeder 9 and cathode feeder 10 are connected to anode collector 6 and cathode collector 8, respectively, and electricity is supplied from both feeders to both electrodes. A pair of frame-shaped gaskets 11 are disposed around the electrode material and the current collectors between the two power feeding bodies and the ion exchange membrane 2, and the inside of the cell is maintained in a sealed state. 12 is an anolyte supply port, 13 is a catholyte supply port, 14 is an anolyte and gas discharge port, and 15 is a catholyte and gas discharge port.
[0020]
When pure water such as ion-exchanged water or distilled water is put into the anode chamber 3 and the cathode chamber 4 of the electrolytic cell 1 having such a configuration and energized between the two electrodes, the water is decomposed on the surface of the anode material 5 to generate oxygen and ozone. And is taken out of the cell from the anolyte and gas outlet 14. At this time, heat is generated with the generation of ozone and the electrolyte is heated to raise the temperature, but the ion exchange membrane 2 is a phosphate ion exchange membrane with almost no fluctuation in ozone generation efficiency with respect to temperature fluctuations. Ozone generation can always be performed stably and with high efficiency without requiring any additional equipment such as cooling.
[0021]
【Example】
Next, examples of ozone production by the water electrolysis method according to the present invention will be described, but the examples do not limit the present invention.
[Example 1]
The product name “Nafion 117” perfluorosulfonic acid cation exchange membrane manufactured by DuPont was immersed in a concentrated phosphoric acid solution at about 140 ° C. for 24 hours to convert the sulfonic acid groups into phosphoric acid groups. As a result of analysis by infrared absorption spectrum, 90% of sulfonic acid groups were converted to phosphoric acid groups.
[0022]
Using this ion exchange membrane as a solid electrolyte, a box-type electrolytic cell for ozone generation filled with deionized water as shown in FIG. 1 having a width of 100 mm, a height of 300 mm, and an electrolytic area of 300 cm 2 was assembled. Using lead oxide as an anode catalyst and platinum as a cathode catalyst, an electrode coating was formed on a titanium substrate by a thermal decomposition method.
While supplying air to the anode chamber and cathode chamber, electrolysis was performed to obtain a current density of 100 A / dm 2, and the current efficiency of ozone generation was measured in steps of 10 ° C at a temperature of 20 to 70 ° C. Indicated by a solid line in FIG. The temperature change of the cell voltage was measured under the same conditions, and the result is shown by a solid line in FIG.
[0023]
[Comparative Example 1]
The current efficiency of ozone generation was measured under the same conditions as in Example 1 except that a Nafion 117 perfluorosulfonic acid cation exchange membrane that was not modified to phosphoric acid was used as the solid electrolyte, and the results are shown in FIG. Shown in dotted line. Further, the temperature change of the cell voltage was measured under the same conditions, and the result is shown by a dotted line in FIG.
From FIG. 3, the phosphoric acid type ion exchange membrane of Example 1 and the sulfonic acid type ion exchange membrane of Comparative Example 1 have almost no difference in the temperature dependence of the cell voltage, whereas from FIG. It can be seen that the phosphoric acid type ion exchange membrane of the present invention has higher ozone generation current efficiency than the sulfonic acid type ion exchange membrane of Comparative Example 1 particularly in the high temperature region.
Further, when the power consumption of Example 1 and Comparative Example 1 when operating under the same conditions was compared, the power consumption of Example 1 was 20% less.
[0024]
[Example 2]
Ozone generation by water electrolysis was performed under the same conditions as in Example 1 except that iridium oxide-ruthenium oxide was used as the anode catalyst and ruthenium oxide was used as the cathode catalyst, and the cell voltage dependence of the current density at that time was measured. As indicated by the solid line in FIG.
[0025]
[Comparative Example 2]
The cell voltage dependence of the current density was measured under the same conditions as in Example 2 except that a Nafion 117 perfluorosulfonic acid cation exchange membrane not modified to phosphoric acid was used as the solid electrolyte. As indicated by the dotted line.
FIG. 4 shows that the former is 200 A / dm 2 in the electrolytic cell for generating ozone using the phosphoric acid type ion exchange membrane of Example 2 and the electrolytic cell using the sulfonic acid type ion exchange membrane of Comparative Example 1. It can be seen that there was a reduction in cell voltage of 100 mV. The cathode hydrogen gas mixing rate in the anode oxygen gas was 0.01% or less in both Example 2 and Comparative Example 2.
[0026]
[Example 3]
In the electrolytic cell of Example 1, the cathode is a gas diffusion electrode made of platinum and carbon powder, and the operation is performed at a current density of 50 to 150 A / dm 2 and a temperature of 50 ° C. while supplying oxygen gas twice from the oxygen cylinder. The results are shown in FIG. When the current density was 100 A / dm 2 , the cell voltage was 1.8 V and the current efficiency was 18%, and 35 Wh / g—O 3 was obtained as the power unit.
[0027]
[Example 4]
When the electrolytic cell of Example 1 was operated for a long time at a current density of 100 A / dm 2 and a temperature of 60 ° C., a cell voltage of 2.6 V and an ozone generation current efficiency of 15 to 18% were obtained when 4000 hours passed. Almost no change in performance was observed from the beginning.
[0028]
【The invention's effect】
In the present invention, deionized water is supplied to a water electrolysis cell in which a perfluorocarbon-based ion exchange membrane in which an anode and a cathode are closely arranged on both sides thereof is used as a solid electrolyte and electrolyzed to produce a mixture of ozone and oxygen as an anode product. in water electrolysis method for obtaining, a part or the whole of the ion exchange groups of the ion exchange membrane Ri phosphate groups der a water electrolysis wherein the anode material is lead oxide or platinum.
[0029]
In the present invention, there is almost no performance change with respect to temperature fluctuation in the generation of electrolytic ozone by water electrolysis of the phosphate ion exchange membrane, and even at a relatively high temperature, that is, the highest temperature that can be reached under normal electrolysis conditions, is equivalent to the case of a low temperature. Ozone generation efficiency can be obtained. Therefore, it is not necessary to cool the cell that is used in the generation of electrolytic ozone using a conventional sulfonic acid ion exchange membrane, in other words, water electrolysis can be performed without considering temperature fluctuations during electrolysis. .
This eliminates the need for cooling for maintaining ozone generation efficiency, which is an essential element in the generation of electrolytic ozone, and saves the cost of incidental equipment and cooling water, and also results in insufficient cooling. The efficiency is not reduced and stable water electrolysis can be performed.
[0030]
The phosphoric acid ion exchange membrane may be modified by immersing a commercially available perfluorocarbon sulfonic acid cation exchange membrane in a concentrated phosphoric acid solution, reducing the carboxylic acid group of the perfluorocarbon carboxylic acid cation exchange membrane, and It can be obtained by modification with a reaction with a compound.
The aforementioned temperature stability when using the phosphoric acid ion exchange membrane is presumed to occur in relation to the anode material used, and lead oxide or platinum is preferably used as the anode material. Oxygen gas containing high-concentration ozone is generated by the use.
When electrolysis is performed while supplying an oxygen-containing gas using a gas diffusion electrode as a cathode, the cathode reaction is converted from a hydrogen generation reaction to a water generation reaction, and the power consumption is further reduced.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a water electrolysis cell that can be used in a water electrolysis method according to the present invention.
2 is a graph showing the temperature dependence of the current efficiency of ozone generation in Example 1 and Comparative Example 1. FIG.
FIG. 3 is a graph showing the temperature dependence of the cell voltage in Example 1 and Comparative Example 1.
4 is a graph showing the cell temperature dependence of the current density in Example 2 and Comparative Example 2. FIG.
5 is a graph showing the cell temperature dependence of the current density in Example 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electrolytic cell 2 ... Ion exchange membrane 3 ... Anode chamber 4 ... Cathode chamber 5 ... Anode material 6 ... Anode collector 7 ... Cathode material 8 ... Cathode Current collector 9 ... Anode feeder 10 ... Cathode feeder 11 ... Gasket 12 ... Anolyte supply port 13 ... Cathode solution supply port 14 ... Anolyte and gas outlet 15 ..Cathode solution and gas outlet

Claims (3)

その両側にそれぞれ陽極及び陰極を密着配置させたパーフルオロカーボン系イオン交換膜を固体電解質とした水電解セルに脱イオン水を供給して電解し陽極生成物としてオゾンと酸素の混合物を得るための水電解方法において、前記イオン交換膜のイオン交換基の一部又は全部がリン酸基であり、陽極物質が酸化鉛又は白金であることを特徴とする水電解方法。Water for supplying a mixture of ozone and oxygen as an anode product by supplying deionized water to a water electrolysis cell having a perfluorocarbon-based ion exchange membrane with an anode and a cathode closely arranged on both sides and using a solid electrolyte as a solid electrolyte. in the electrolytic method, water electrolysis wherein the part or all of the ion exchange groups of the ion exchange membrane Ri phosphate groups der anode material is lead oxide or platinum. イオン交換膜がパーフルオロカーボンスルホン酸系陽イオン交換膜又はパーフルオロカーボンカルボン酸系陽イオン交換膜を変性して製造した膜である請求項1に記載の水電解方法。  The water electrolysis method according to claim 1, wherein the ion exchange membrane is a membrane produced by modifying a perfluorocarbon sulfonic acid cation exchange membrane or a perfluorocarbon carboxylic acid cation exchange membrane. 陰極がガス拡散電極である請求項1に記載の水電解方法。 The water electrolysis method according to claim 1, wherein the cathode is a gas diffusion electrode.
JP01875295A 1995-01-11 1995-01-11 Water electrolysis method Expired - Fee Related JP3716002B2 (en)

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