JP4102605B2 - Method for producing activated carbon - Google Patents
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- JP4102605B2 JP4102605B2 JP2002173145A JP2002173145A JP4102605B2 JP 4102605 B2 JP4102605 B2 JP 4102605B2 JP 2002173145 A JP2002173145 A JP 2002173145A JP 2002173145 A JP2002173145 A JP 2002173145A JP 4102605 B2 JP4102605 B2 JP 4102605B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/13—Energy storage using capacitors
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Description
【０００１】
【発明の属する技術分野】
本発明は、活性炭の製造方法に関し、さらに詳しくは、炭素前駆体にアルカリ金属化合物を添加してアルカリ賦活処理を行うに際して、アルカリ賦活反応容器の上部に賦活反応中に揮発するアルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材を充填した捕捉層を設ける、および／またはアルカリ賦活反応容器を設置した反応炉内の雰囲気ガス中に炭酸ガスを特定濃度で含有させる活性炭の製造方法に関する。本発明の活性炭は、電気二重層キャパシタ用の電極として好適である。さらに、吸着や浄水など、活性炭としての利用分野で使用することも可能である。
【０００２】
【従来の技術】
近年、携帯電話やノート型パソコンなどの新しい電子機器が次々に出現し、これら商品の小型軽量化、携帯化などの開発競争から、それに内蔵されるＩＣメモリやマイコンなども小型高性能化が進んでいる。ところが、このようなＩＣメモリなどの素子やマイコンは、電力瞬断時に電子機器のメモリ消却や機能停止などの誤作動を起こす恐れがある。実際、コンピューター機器は、適切な対策を講じなければ１０〜２０％のわずかな電圧低下であっても、電圧低下が０．００３〜０．０２秒間続くだけで、機能停止やメモリ喪失などが起こり、電子機器の機能が麻痺してしまう。
【０００３】
この対策として、Ｎｉ−Ｃｄ電池やアルミ電解コンデンサがバックアップ電源として用いられてきた。しかし、これらの電源は使用温度範囲、充放電のサイクル回数、容量、急速充放電性およびコストなどの点で充分なものではなかった。この市場ニーズに応え開発されたものが電気二重層キャパシタである。当初、電気二重層キャパシタには活性炭が電極材として用いられてきたが、最近、より高比表面積を有する活性炭素繊維を用いた電気二重層キャパシタが注目されるようになってきている。
【０００４】
さらに従来の小電力分野から電気自動車用バッテリーの補助電源などの大容量分野への応用が考えられ、一部、減速時の回生運動エネルギーをキャパシタに充電し、加速時に逆に放電してエンジンの出力の補助をさせるという目的でキャパシタを搭載した乗用車が参考出品の段階に来ている。
電気二重層の研究の歴史は古く１８７９年のHelmholtzに遡ることができる。一般に、異なる二層が接触すると、界面に正、負の電荷が短距離を隔てて配列する。この界面にできた電荷分布を電気二重層と呼ぶ。
【０００５】
電気二重層キャパシタは、この電気二重層に電圧を加えて電荷を蓄積するものである。しかし、実用化には長時間を要し、ようやく１９８０年代の初めになって、この原理を用いたファラッド単位の大容量コンデンサの出現をみた。
電気二重層キャパシタは、電極表面と電解液との界面に形成される電気二重層を利用した大容量のコンデンサであり、充放電に通常の二次電池のような化学反応を伴わない。このために、二次電池と比較して内部抵抗が格段に低く大電流放電が可能である。さらに、充放電回数の制限が無いという特徴も有している。
【０００６】
しかし、電気二重層キャパシタの最大の問題点は、二次電池に比べてエネルギー密度が低いという点であって、この点を改良すべく現在各種の検討がなされている。
電気二重層キャパシタには、プロピレンカーボネートなどの有機系極性溶媒に過塩素酸リチウムあるいは４級アンモニウム塩などの電解質を溶解させた有機溶媒系電解液を使用するものと、硫酸水溶液あるいは水酸化カリウム水溶液のような水溶液系電解液を使用するものとの、大きく分けて２種類が存在する。
【０００７】
水溶液系電解液を使用した場合には、キャパシタの容量を、有機溶媒系電解液を使用した場合の約１．３倍から２倍に上げることができ、さらに内部抵抗を１／５から１／１０に下げることができる。
水溶液系電解液を使用した場合に内部抵抗を下げることができる理由は、水溶液系電解液の電気抵抗が低いことに起因しているが、水溶液系電解液を使用する場合には、電圧を１Ｖ余りまでにしか上げることができないため体積当たりの蓄電エネルギー量は少ないという短所も併せ持っている。
【０００８】
一方、有機溶媒系電解液を使用した場合には、電気二重層キャパシタの電圧を最高３Ｖ以上まで上げることができることから、キャパシタの体積当たりの蓄電エネルギー量（蓄電エネルギー量＝１／２ＣＶ2で与えられる。Ｃ：キャパシタ容量、Ｖ：電圧）を上げることが可能であるため、容積当たりのエネルギーの高密度化という観点からは、有機溶媒系電解液の方が有利である。
【０００９】
これらの電気二重層キャパシタの電極材料としては、比表面積の大きな活性炭や活性炭素繊維が最適と考えられ、各方面で炭素材料の最適化の研究が盛んである。
活性炭の製造方法としては、ヤシ殻、石炭やフェノール樹脂などの難黒鉛系炭素材（いわゆる、ハードカーボン）を原料とし、水蒸気や二酸化炭素などによるガス賦活が一般的であるが、電気二重層キャパシタ用電極材としてより高い性能を発現する活性炭の製造方法として、炭素材をアルカリ金属化合物の共存下にて賦活する方法（以下、アルカリ賦活という）が提案されている（特開平１−１３９８６５号公報参照）。
【００１０】
この技術をピッチなどの易黒鉛系炭素材、特に、メソフェーズピッチを炭化して得た炭素材に使用する試みがなされている。例えば、特開平５−２４７７３１号公報では、メソフェーズを５０％以上含むピッチ（以下、メソフェーズピッチということがある）を紡糸して得たピッチ繊維を不融化・炭化し、得られた炭素繊維（以下、メソフェーズピッチ系炭素繊維ということがある）をアルカリ賦活する、高比表面積（特に、２０００ｍ2／ｇ以上）の活性炭素繊維の製造法が開示されている。
【００１１】
さらに、近年では、易黒鉛系炭素材をアルカリ賦活して得た活性炭素繊維を、電気二重層キャパシタ用の電極材として用いることが試みられている。例えば、特開平５−２５８９９６号公報には、メソフェーズピッチ系炭素繊維をアルカリ賦活して得た、比表面積３０００ｍ2／ｇ以上の活性炭素繊維を、水または酸類で脱灰した後、繊維の形状が残らない程度に粉砕、成形してなる電気二重層コンデンサー用電極が提案されている。
【００１２】
アルカリ賦活法で製造したこのような活性炭素繊維は、電極材として用いた場合に、従来のガス賦活で製造した活性炭や活性炭素繊維と比較して、比表面積が小さくても高い充放電特性が得られるため、単位体積当たりの充放電容量を向上させ得るという利点がある。しかしながら、アルカリ金属化合物を使用するため、賦活処理時にアルカリ金属化合物および／または賦活反応時に生成するアルカリ金属が反応容器から飛散する。
【００１３】
炭素前駆体のアルカリ賦活処理時に飛散するアルカリ金属化合物および／またはアルカリ金属は、反応炉内部の腐食を促進するとともにアルカリ金属の発火または爆発などの危険性を伴うことから、これらの問題を解消する活性炭の製造方法の出現が切望されている。
【００１４】
【発明が解決しようとする課題】
本発明は、アルカリ賦活法による活性炭の製造方法において、アルカリ賦活処理時に飛散するアルカリ金属化合物および／またはアルカリ金属による反応炉内部の腐食およびアルカリ金属の発火または爆発などの危険性を解消する活性炭の製造方法およびその製造方法にて製造された活性炭を電極として用いる電気二重層キャパシタを提供することを課題とする。
【００１５】
【課題を解決するための手段】
本発明者らは、上記課題を解決するために、種々の研究を重ねた結果、活性炭の製造方法において、炭素前駆体にアルカリ金属化合物を添加してアルカリ賦活処理を行うに際して、アルカリ賦活反応容器の上部に賦活反応時に飛散するアルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材を充填した捕捉層を設ける、および／またはアルカリ賦活反応容器を設置した反応炉内の雰囲気ガス中に炭酸ガスを特定濃度で含有させることにより、反応炉内部の腐食およびアルカリ金属の発火または爆発などの危険性を解消し得ることを見出し、本発明を完成するに至ったものである。
【００１６】
すなわち、本発明の第１の発明によれば、炭素前駆体にアルカリ金属化合物を添加してアルカリ賦活処理を行うに際して、アルカリ賦活反応容器の上部に賦活反応時に飛散するアルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材を充填した捕捉層を設け、アルカリ賦活反応容器を設置した反応炉内の雰囲気ガス中に炭酸ガスを０．０１〜２容量％の濃度で含有させる活性炭の製造方法が提供される。
また、本発明の第２の発明によれば、第１の発明において、上記アルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材として、粒状活性炭、炭素繊維マット、粒状炭、セラミックウールからなる群から選ばれる少なくとも１種を用いる活性炭の製造方法が提供される。
【００１９】
【発明の実施の形態】
以下、本発明について詳細に説明する。
（Ｉ）活性炭の製造方法
本発明に係る活性炭の製造方法では、
必要に応じて炭素前駆体を炭化処理する炭化工程、および
炭素前駆体または上記で得られた炭化物をアルカリ賦活処理して活性炭を製造するアルカリ賦活工程を含む。
【００２０】
すなわち、本発明で用いる炭素前駆体が、例えばコークスのような固体であれば、粉砕して、直接、アルカリ賦活工程にて活性炭を製造することが可能であるが、炭素前駆体が、例えばピッチのようなものであれば、通常、炭化工程およびアルカリ賦活工程を経由して活性炭を製造する。
本発明の原料として用いる炭素前駆体は、難黒鉛系炭素材および易黒鉛系炭素材のどちらでも使用可能であるが、賦活収量（歩留まり）が高く、より高い電極性能が得られるので易黒鉛系炭素材の原料としての使用が好ましい。
【００２１】
該易黒鉛系炭素材としては、石油系もしくは石炭系のピッチ類、石油系もしくは石炭系のコークスおよびそれらの炭化物などが好ましく用いられる。
また、本発明の炭素前駆体の形状としては、粒状、粉状、塊状またはメルトブロー紡糸法などにより紡糸した炭素繊維あるいはその粉砕物であってもよい。
本発明におけるアルカリ賦活工程で用いられるアルカリ金属化合物としては、水酸化カリウム、水酸化ナトリウム、炭酸カリウム、亜硝酸カリウム、硫酸カリウムおよび塩化カリウムなどを例示でき、中でも水酸化カリウムが特に好ましい。
【００２２】
このようなアルカリ金属化合物は、炭素前駆体または炭化物(以下、炭素前駆体という)に対する重量比にて１〜４（倍）、好ましくは１．５〜２．５（倍）の量で用いる。
アルカリ金属化合物の重量比が１（倍）未満では得られる活性炭の細孔形成の効率が低下する傾向があり、一方、重量比が４（倍）を超えて添加してもその効果が得られず、中和・洗浄などの後処理工程のコスト増となるので、好ましくない。
【００２３】
アルカリ賦活処理は、具体的に、このような重量比の炭素前駆体とアルカリ金属化合物とを均一に混合した後、窒素などの不活性ガス雰囲気中、６５０〜８００℃まで昇温することにより行う。
上記アルカリ賦活処理には、上部に捕捉層が設置可能なトレーなどの賦活反応容器を使用する。賦活反応容器は、加熱・昇温を行う反応炉に投入し、賦活処理を行うが、該反応炉はバッチ式、連続式の制限はない。例えば、ボックス炉、ベルト炉、トレープレッシャー炉などを使用することが可能である。
【００２４】
すなわち、アルカリ賦活処理は、通常、ニッケル製のアルカリ賦活反応容器に反応体である炭素前駆体とアルカリ金属化合物との混合物を導入し、該反応容器全体を窒素ガスなどの不活性ガス雰囲気の反応炉内にて、加熱・昇温することにより行う。
その際、未反応のアルカリ金属化合物および／または賦活反応の過程でアルカリ金属化合物が分解して生成したアルカリ金属（例えば、カリウム）が反応炉内に飛散して反応炉内部を腐食する他、飛散したアルカリ金属による発火もしくは爆発の危険性を生ずる。
【００２５】
本発明においては、アルカリ金属化合物および／またはアルカリ金属の飛散を抑制することにより賦活反応炉の腐食を防止し長期使用の可能化、および飛散したアルカリ金属による危険性を低減するために下記の（Ａ）法および／または（Ｂ）法を用いる。
（Ａ）法 賦活反応容器の上部にアルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材を充填した捕捉層を設ける。該捕捉層は、賦活反応容器の上部を覆うように直付けとしてもよく、また孔を有するニッケル板などを介して取り付けてもよい。捕捉層は、賦活反応容器に固定され、かつ着脱可能であることが好ましい。
【００２６】
該捕捉層に充填する吸着材としては、アルカリ金属化合物および／またはアルカリ金属を捕捉する吸着材であれば何ら限定されないが、粒状活性炭、粒状炭、炭素繊維マットおよびセラミックウールなどが例示できる。
（Ｂ）法 反応炉内の雰囲気ガス中に炭酸ガスを５容量％以下、好ましくは２容量％以下、より好ましくは１〜０．０１容量％の濃度で含有させる。炭酸ガス濃度が雰囲気ガス中、５容量％を超えると、アルカリ賦活処理中のアルカリ金属化合物と炭酸ガスとが反応し、賦活反応を阻害する。一方、炭酸ガス濃度が雰囲気ガス中、０．０１容量％未満であると、反応容器から飛散するアルカリ金属化合物などを十分に捕捉できない可能性がある。
【００２７】
上記の（Ａ）法および（Ｂ）法は、各々単独で用いてもよく、また組み合わせて用いてもよいが、組み合わせて用いる方がアルカリ金属化合物および／またはアルカリ金属の捕捉効率が高くなるため好ましい。
このようにして得られた活性炭は、常温に冷却した後、例えば、温水および／または温塩酸水などによる洗浄にて未反応のアルカリ金属化合物を除去し、電気二重層キャパシタの電極材として用いられる。
【００２８】
【実施例】
以下本発明を実施例によりさらに具体的に説明するが、本発明はそれに限定されるものではない。
【００２９】
【参考例１】
炭素前駆体として、平均粒径１００μｍ程度に粉砕した後、６００℃にて焼成を行った石油系コークスを用いた。該石油系コークス２．５ｋｇに水酸化カリウム５ｋｇを添加し、均一に混合した。得られた混合物を１００ｃｍ×５０ｃｍ×６ｃｍ（高さ）の純ニッケル製の上部開放角形賦活反応容器に導入し、該反応容器の上部に、１００ｃｍ×５０ｃｍ×４ｃｍ（高さ）の反応容器と同一サイズである捕捉層（上部開放形）を固定設置した。該捕捉層としては、底部に適度の大きさの穴を多数個設け、その上にニッケル製の金網を設置し、吸着材として平均粒径５ｍｍ程度の粒状ヤシ殻活性炭を５ｋｇ充填したものを用いた。
【００３０】
上記のようにして調製した賦活反応容器をバッチ式の熱風循環炉内に設置し、窒素雰囲気下にて、４００℃にて３時間保持した後、７３０℃まで昇温し、同温度にて３時間保持することによりアルカリ賦活処理を行った。
アルカリ賦活処理後のカリウム捕捉量を測定し、添加量に対して重量％に換算したところ、それぞれ、反応容器中に残留したカリウム量：８５重量％、上部捕捉層にてトラップされたカリウム量：１２重量％および反応炉内に飛散したカリウム量：３重量％であった。結果を表１に示す。
【００３１】
【参考例２】
吸着剤として上記粒状ヤシ殻活性炭に代えて、１，０００℃にて焼成を行ったマット状炭素繊維５ｋｇ充填したものを用いたこと以外は、参考例１と同様にしてアルカリ賦活処理を行った。
アルカリ賦活処理後のカリウム捕捉量を測定し、添加量に対して重量％に換算したところ、それぞれ、反応容器中に残留したカリウム量：８５重量％、上部捕捉層にてトラップされたカリウム量：１２重量％および反応炉内に飛散したカリウム量：３重量％であった。結果を表１に示す。
【００３２】
【参考例３】
賦活反応容器の上部に捕捉層を設置せず反応容器上部を開放状態とし、かつ、反応炉内の窒素ガス雰囲気中にアルカリ賦活処理の開始から終了まで、炭酸ガス濃度が２容量％となるよう炭酸ガスを導入したこと以外は、参考例１と同様にしてアルカリ賦活処理を行った。
【００３３】
アルカリ賦活処理後のカリウム捕捉量を測定し、添加量に対して重量％に換算したところ、それぞれ、反応容器中に残留したカリウム量：９０重量％および反応炉内に飛散したカリウム量：１０重量％であった。結果を表１に示す。
【００３４】
【実施例１】
参考例１と同様の捕捉層を設置し、さらに反応炉内の窒素ガス雰囲気中にアルカリ賦活処理の開始から終了まで、炭酸ガス濃度が０．４容量％となるよう炭酸ガスを導入したこと以外は、参考例１と同様にしてアルカリ賦活処理を行った。
アルカリ賦活処理後のカリウム捕捉量を測定し、添加量に対して重量％に換算したところ、それぞれ、反応容器中に残留したカリウム量：８６重量％、上部捕捉層にてトラップされたカリウム量：１３重量％および反応炉内に飛散したカリウム量：１重量％であった。結果を表１に示す。
【００３５】
【比較例１】
賦活反応容器の上部に捕捉層を設置せず反応容器上部を開放状態としたこと以外は、参考例１と同様にしてアルカリ賦活処理を行った。
アルカリ賦活処理後のカリウム捕捉量を測定し、添加量に対して重量％に換算したところ、それぞれ、反応容器中に残留したカリウム量：８５重量％および反応炉内に飛散したカリウム量：１５重量％であった。結果を表１に示す。
【００３６】
【表１】
【発明の効果】
本発明によれば、アルカリ賦活処理時に、反応炉内部の腐食を抑制し反応炉の長期使用を可能とする他、飛散するアルカリ金属に基づく危険性を解消した活性炭の製造方法、並びにその製造方法により製造された電気二重層キャパシタの電極として用いることが可能な活性炭を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing activated carbon, and more specifically, when an alkali metal compound is added to a carbon precursor to perform an alkali activation treatment, an alkali metal compound that volatilizes during the activation reaction at the top of the alkali activation reaction vessel and / or Alternatively, the present invention relates to a method for producing activated carbon in which a trapping layer filled with an adsorbent for trapping alkali metal is provided and / or carbon dioxide is contained at a specific concentration in an atmospheric gas in a reaction furnace provided with an alkali activation reaction vessel. The activated carbon of the present invention is suitable as an electrode for an electric double layer capacitor. Furthermore, it can also be used in fields of use as activated carbon, such as adsorption and water purification.
[0002]
[Prior art]
In recent years, new electronic devices such as mobile phones and notebook PCs have appeared one after another, and due to the development competition for miniaturization, weight reduction, and portability of these products, IC memories and microcomputers built into them have become smaller and higher performance. It is out. However, such an element such as an IC memory or a microcomputer may cause a malfunction such as a memory erasure or a function stop of the electronic device when power is interrupted. In fact, if computer equipment does not take appropriate measures, even if it is a slight voltage drop of 10 to 20%, the voltage drop will continue for 0.003 to 0.02 seconds, resulting in malfunction or memory loss. The function of the electronic device is paralyzed.
[0003]
As countermeasures, Ni-Cd batteries and aluminum electrolytic capacitors have been used as backup power sources. However, these power sources are not sufficient in terms of the operating temperature range, the number of charge / discharge cycles, the capacity, rapid charge / discharge characteristics, and cost. Electric double layer capacitors have been developed to meet this market need. Initially, activated carbon has been used as an electrode material for electric double layer capacitors, but recently, electric double layer capacitors using activated carbon fibers having a higher specific surface area have attracted attention.
[0004]
In addition, it can be applied from the conventional low-power field to large-capacity fields such as auxiliary power supplies for electric vehicle batteries. In part, the regenerative kinetic energy during deceleration is charged to the capacitor and discharged reversely during acceleration. Passenger cars equipped with capacitors for the purpose of assisting output are in the stage of reference exhibition.
The history of electric double layer research can be traced back to Helmholtz in 1879. In general, when two different layers come into contact, positive and negative charges are arranged at a short distance at the interface. The charge distribution formed at this interface is called an electric double layer.
[0005]
The electric double layer capacitor stores electric charges by applying a voltage to the electric double layer. However, it took a long time to put it into practical use, and at the beginning of the 1980's, we saw the emergence of large-capacity capacitors in units of farads using this principle.
An electric double layer capacitor is a large-capacity capacitor using an electric double layer formed at the interface between an electrode surface and an electrolytic solution, and does not involve a chemical reaction as in a normal secondary battery in charge and discharge. For this reason, compared with a secondary battery, internal resistance is remarkably low and a large current discharge is possible. Furthermore, there is also a feature that there is no limit on the number of charge / discharge cycles.
[0006]
However, the biggest problem of the electric double layer capacitor is that the energy density is lower than that of the secondary battery, and various studies are currently under way to improve this point.
For electric double layer capacitors, those using an organic solvent electrolyte in which an electrolyte such as lithium perchlorate or quaternary ammonium salt is dissolved in an organic polar solvent such as propylene carbonate, an aqueous sulfuric acid solution or an aqueous potassium hydroxide solution There are roughly two types, such as those using an aqueous electrolyte.
[0007]
When an aqueous electrolyte is used, the capacity of the capacitor can be increased from about 1.3 times to 2 times that when an organic solvent electrolyte is used, and the internal resistance is increased from 1/5 to 1 /. Can be lowered to 10.
The reason why the internal resistance can be lowered when the aqueous electrolyte is used is that the electrical resistance of the aqueous electrolyte is low. However, when the aqueous electrolyte is used, the voltage is 1V. Since it can only be raised too much, it has the disadvantage that the amount of energy stored per volume is small.
[0008]
On the other hand, when the organic solvent electrolyte is used, the voltage of the electric double layer capacitor can be increased up to 3 V or more, so the amount of stored energy per volume of the capacitor (the amount of stored energy = 1/2 CV 2 is given. C: Capacitor capacity, V: Voltage) can be increased, and the organic solvent electrolyte is more advantageous from the viewpoint of increasing the energy density per volume.
[0009]
As electrode materials for these electric double layer capacitors, activated carbon and activated carbon fibers having a large specific surface area are considered to be optimal, and research on optimization of carbon materials is actively conducted in various directions.
As a method for producing activated carbon, a non-graphite carbon material (so-called hard carbon) such as coconut shell, coal or phenol resin is used as a raw material, and gas activation by water vapor or carbon dioxide is generally used. As a method for producing activated carbon that exhibits higher performance as an electrode material for automobiles, a method of activating a carbon material in the presence of an alkali metal compound (hereinafter referred to as alkali activation) has been proposed (Japanese Patent Laid-Open No. 1-139865). reference).
[0010]
Attempts have been made to use this technique for easily graphite-based carbon materials such as pitch, particularly carbon materials obtained by carbonizing mesophase pitch. For example, in JP-A-5-247731, pitch fibers obtained by spinning a pitch containing 50% or more of mesophase (hereinafter sometimes referred to as mesophase pitch) are infusibilized and carbonized, and carbon fibers obtained (hereinafter referred to as “fiber fibers”) are obtained. A method for producing activated carbon fibers having a high specific surface area (particularly 2000 m 2 / g or more) that activates alkali in mesophase pitch-based carbon fibers) is disclosed.
[0011]
Furthermore, in recent years, attempts have been made to use activated carbon fibers obtained by alkali activation of an easily graphite-based carbon material as an electrode material for an electric double layer capacitor. For example, in JP-A-5-258996, activated carbon fibers having a specific surface area of 3000 m 2 / g or more obtained by alkali activation of mesophase pitch-based carbon fibers are decalcified with water or acids, and then the shape of the fibers is obtained. There has been proposed an electrode for an electric double layer capacitor that is pulverized and molded to such an extent that does not remain.
[0012]
Such activated carbon fibers produced by the alkali activation method, when used as an electrode material, have high charge / discharge characteristics even if the specific surface area is small compared to activated carbon and activated carbon fibers produced by conventional gas activation. As a result, the charge / discharge capacity per unit volume can be improved. However, since an alkali metal compound is used, the alkali metal compound and / or the alkali metal generated during the activation reaction are scattered from the reaction vessel during the activation treatment.
[0013]
Alkali metal compounds and / or alkali metals scattered during the alkali activation treatment of carbon precursors promote corrosion inside the reactor and cause dangers such as ignition or explosion of alkali metals, thus eliminating these problems. The advent of a method for producing activated carbon is eagerly desired.
[0014]
[Problems to be solved by the invention]
The present invention relates to an activated carbon that eliminates the risk of corrosion inside the reactor and alkali metal ignition or explosion caused by alkali metal compounds and / or alkali metals scattered during alkali activation treatment in the method for producing activated carbon by the alkali activation method. It is an object of the present invention to provide a manufacturing method and an electric double layer capacitor using activated carbon manufactured by the manufacturing method as an electrode.
[0015]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have made various studies and, as a result, in an activated carbon production method, an alkali activation reaction vessel is added when performing an alkali activation treatment by adding an alkali metal compound to a carbon precursor. A trapping layer filled with an alkali metal compound and / or an adsorbent that traps alkali metal that is scattered during the activation reaction is provided at the top of the catalyst, and / or carbon dioxide gas is introduced into the atmospheric gas in the reaction furnace in which the alkali activation reaction vessel is installed. It has been found that the inclusion at a specific concentration can eliminate dangers such as corrosion inside the reaction furnace and ignition or explosion of alkali metals, and the present invention has been completed.
[0016]
That is, according to the first invention of the present invention, when an alkali activation treatment is performed by adding an alkali metal compound to a carbon precursor, an alkali metal compound and / or an alkali scattered at the top of the alkali activation reaction vessel during the activation reaction. the acquisition layer filled with adsorbent to capture metal provided, method for producing activated carbon Ru is contained in a concentration of 0.01 to 2% by volume carbon dioxide in the atmosphere gas in the reactor was installed alkali activation reaction vessel Provided.
According to the second invention of the present invention, in the first invention, the adsorbent for capturing the alkali metal compound and / or alkali metal is a group consisting of granular activated carbon, carbon fiber mat, granular charcoal, and ceramic wool. A method for producing activated carbon using at least one selected from the group consisting of:
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
(I) Method for producing activated carbon In the method for producing activated carbon according to the present invention,
The carbonization process which carbonizes a carbon precursor as needed, and the alkali activation process which manufactures activated carbon by carrying out the alkali activation process of the carbon precursor or the carbide | carbonized_material obtained above are included.
[0020]
That is, if the carbon precursor used in the present invention is a solid such as coke, for example, it is possible to pulverize and directly produce activated carbon in an alkali activation process. If it is such, normally activated carbon is manufactured through a carbonization process and an alkali activation process.
The carbon precursor used as the raw material of the present invention can be either a non-graphite carbon material or a graphitizable carbon material, but has a high activation yield (yield) and higher electrode performance. Use as a carbon material is preferred.
[0021]
As the easily graphite-based carbon material, petroleum-based or coal-based pitches, petroleum-based or coal-based cokes and their carbides are preferably used.
Further, the shape of the carbon precursor of the present invention may be a carbon fiber spun by granular, powder, lump, melt blow spinning, or the like, or a pulverized product thereof.
Examples of the alkali metal compound used in the alkali activation step in the present invention include potassium hydroxide, sodium hydroxide, potassium carbonate, potassium nitrite, potassium sulfate and potassium chloride, and potassium hydroxide is particularly preferred.
[0022]
Such an alkali metal compound is used in an amount of 1 to 4 (times), preferably 1.5 to 2.5 (times) in weight ratio to the carbon precursor or carbide (hereinafter referred to as carbon precursor).
When the weight ratio of the alkali metal compound is less than 1 (times), the efficiency of pore formation of the obtained activated carbon tends to be reduced. On the other hand, even if the weight ratio exceeds 4 (times), the effect is obtained. This is not preferable because it increases the cost of post-treatment steps such as neutralization and washing.
[0023]
Specifically, the alkali activation treatment is performed by uniformly mixing the carbon precursor and the alkali metal compound in such a weight ratio and then raising the temperature to 650 to 800 ° C. in an inert gas atmosphere such as nitrogen. .
For the alkali activation treatment, an activation reaction vessel such as a tray on which a trapping layer can be installed is used. The activation reaction vessel is put into a reaction furnace that heats and heats up to perform activation treatment, but the reaction furnace is not limited to a batch type or a continuous type. For example, a box furnace, a belt furnace, a tray pressure furnace, or the like can be used.
[0024]
That is, the alkali activation treatment is usually performed by introducing a mixture of a carbon precursor as a reactant and an alkali metal compound into a nickel alkali activation reaction vessel, and reacting the entire reaction vessel in an inert gas atmosphere such as nitrogen gas. This is done by heating and raising the temperature in the furnace.
At that time, an unreacted alkali metal compound and / or an alkali metal (for example, potassium) generated by decomposition of the alkali metal compound in the course of the activation reaction scatters in the reaction furnace and corrodes the inside of the reaction furnace. There is a risk of ignition or explosion caused by alkali metal.
[0025]
In the present invention, in order to prevent corrosion of the activation reactor by suppressing the scattering of the alkali metal compound and / or alkali metal, to enable long-term use, and to reduce the danger due to the scattered alkali metal, the following ( Method A) and / or method (B) is used.
(A) Method A trapping layer filled with an adsorbent for trapping an alkali metal compound and / or alkali metal is provided at the top of the activation reaction vessel. The capture layer may be directly attached so as to cover the upper part of the activation reaction vessel, or may be attached via a nickel plate having holes. The capture layer is preferably fixed to the activation reaction vessel and detachable.
[0026]
The adsorbent filled in the trapping layer is not particularly limited as long as it is an adsorbent that traps alkali metal compounds and / or alkali metals, and examples thereof include granular activated carbon, granular charcoal, carbon fiber mat, and ceramic wool.
(B) Method Carbon dioxide gas is contained in the atmospheric gas in the reaction furnace at a concentration of 5% by volume or less, preferably 2% by volume or less, more preferably 1 to 0.01% by volume. If the carbon dioxide gas concentration exceeds 5% by volume in the atmospheric gas, the alkali metal compound and the carbon dioxide gas in the alkali activation treatment react to inhibit the activation reaction. On the other hand, when the carbon dioxide gas concentration is less than 0.01% by volume in the atmospheric gas, there is a possibility that an alkali metal compound or the like scattered from the reaction vessel cannot be sufficiently captured.
[0027]
The above methods (A) and (B) may be used singly or in combination. However, when used in combination, the trapping efficiency of the alkali metal compound and / or alkali metal becomes higher. preferable.
The activated carbon thus obtained is cooled to room temperature, and then unreacted alkali metal compound is removed by washing with warm water and / or warm hydrochloric acid, for example, and used as an electrode material for an electric double layer capacitor. .
[0028]
【Example】
The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.
[0029]
[ Reference Example 1]
As the carbon precursor, petroleum coke which was pulverized to an average particle size of about 100 μm and then baked at 600 ° C. was used. 5 kg of potassium hydroxide was added to 2.5 kg of the petroleum coke and mixed uniformly. The obtained mixture was introduced into a 100 cm × 50 cm × 6 cm (height) pure nickel upper open rectangular activation reaction vessel, and the same reaction vessel of 100 cm × 50 cm × 4 cm (height) was placed on top of the reaction vessel. The size acquisition layer (upper open type) was fixedly installed. The trapping layer is provided with a number of moderately sized holes on the bottom, a nickel wire mesh installed thereon, and an adsorbent filled with 5 kg of granular coconut shell activated carbon having an average particle size of about 5 mm. It was.
[0030]
The activation reaction vessel prepared as described above was placed in a batch-type hot-air circulating furnace, held at 400 ° C. for 3 hours in a nitrogen atmosphere, then heated to 730 ° C., and 3 at the same temperature. The alkali activation treatment was performed by holding for a period of time.
The amount of potassium trapped after the alkali activation treatment was measured and converted to wt% with respect to the added amount. The amount of potassium remaining in the reaction vessel: 85 wt%, the amount of potassium trapped in the upper trapping layer, respectively: It was 12% by weight and the amount of potassium scattered in the reactor: 3% by weight. The results are shown in Table 1.
[0031]
[ Reference Example 2]
Alkaline activation treatment was carried out in the same manner as in Reference Example 1 except that the adsorbent was replaced with the above-mentioned granular coconut shell activated carbon and filled with 5 kg of mat-like carbon fibers fired at 1,000 ° C. .
The amount of potassium trapped after the alkali activation treatment was measured and converted to wt% with respect to the added amount. The amount of potassium remaining in the reaction vessel: 85 wt%, the amount of potassium trapped in the upper trapping layer, respectively: It was 12% by weight and the amount of potassium scattered in the reactor: 3% by weight. The results are shown in Table 1.
[0032]
[ Reference Example 3]
The trapping layer is not installed on the upper part of the activation reaction vessel, the upper part of the reaction vessel is opened, and the carbon dioxide gas concentration is 2% by volume in the nitrogen gas atmosphere in the reaction furnace from the start to the end of the alkali activation process. Alkaline activation treatment was performed in the same manner as in Reference Example 1 except that carbon dioxide gas was introduced.
[0033]
The amount of potassium trapped after the alkali activation treatment was measured and converted to wt% with respect to the added amount. The amount of potassium remaining in the reaction vessel was 90 wt% and the amount of potassium scattered in the reaction furnace was 10 wt%, respectively. %Met. The results are shown in Table 1.
[0034]
[Example 1 ]
Other than installing the same trapping layer as in Reference Example 1 and introducing carbon dioxide in the nitrogen gas atmosphere in the reactor from the start to the end of the alkali activation treatment so that the carbon dioxide concentration is 0.4% by volume. The alkali activation treatment was performed in the same manner as in Reference Example 1.
The amount of potassium trapped after the alkali activation treatment was measured and converted to wt% with respect to the added amount. The amount of potassium remaining in the reaction vessel was 86 wt%, and the amount of potassium trapped in the upper trapping layer was: The amount of potassium scattered in the reaction furnace was 13% by weight and 1% by weight. The results are shown in Table 1.
[0035]
[Comparative Example 1]
Alkaline activation treatment was performed in the same manner as in Reference Example 1 except that the trapping layer was not installed on the upper part of the activation reaction vessel and the upper part of the reaction vessel was opened.
The amount of potassium captured after the alkali activation treatment was measured and converted to wt% with respect to the added amount. The amount of potassium remaining in the reaction vessel: 85 wt% and the amount of potassium scattered in the reaction furnace: 15 wt. %Met. The results are shown in Table 1.
[0036]
[Table 1]
【The invention's effect】
According to the present invention, during alkali activation treatment, in addition to suppressing corrosion inside the reaction furnace and enabling long-term use of the reaction furnace, a method for producing activated carbon that eliminates the risk based on scattered alkali metal, and a method for producing the same The activated carbon which can be used as an electrode of the electric double layer capacitor manufactured by this can be provided.
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| JP2002173145A JP4102605B2 (en) | 2002-06-13 | 2002-06-13 | Method for producing activated carbon |
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| JP2002173145A JP4102605B2 (en) | 2002-06-13 | 2002-06-13 | Method for producing activated carbon |
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| CN100337911C (en) * | 2005-01-27 | 2007-09-19 | 西北农林科技大学 | Method for producing active carbon by using straw mixed raw material |
| WO2006118204A1 (en) * | 2005-04-28 | 2006-11-09 | Mitsubishi Gas Chemical Company, Inc. | Process for producing carbon material and alkali activation apparatus |
| JP4728711B2 (en) * | 2005-07-05 | 2011-07-20 | Ｊｘ日鉱日石エネルギー株式会社 | Activated carbon production equipment |
| US8437116B2 (en) * | 2006-07-27 | 2013-05-07 | Corning Incorporated | Electric double layer capacitors, capacitor materials and methods of making the same |
| WO2008044587A1 (en) * | 2006-10-12 | 2008-04-17 | Cataler Corporation | Active carbon, and canister and intake air filter utilizing the same |
| US8809231B2 (en) | 2011-09-28 | 2014-08-19 | Corning Incorporated | Method for making alkali activated carbon |
| CN105810447A (en) * | 2016-04-29 | 2016-07-27 | 陕西科技大学 | Preparation method of porous spherical biological carbon and application |
| CN108726518B (en) * | 2018-06-28 | 2020-08-14 | 大连理工大学 | Method for preparing high-specific-surface-area activated carbon by alkali activation method |
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