JP3545199B2

JP3545199B2 - Activated carbon catalyst and flue gas desulfurization method

Info

Publication number: JP3545199B2
Application number: JP09458498A
Authority: JP
Inventors: 洋一梅原; 大武田; 和茂川村; 脩戸河里
Original assignee: Chiyoda Corp
Current assignee: Chiyoda Corp
Priority date: 1998-04-07
Filing date: 1998-04-07
Publication date: 2004-07-21
Anticipated expiration: 2018-04-07
Also published as: JPH11290688A

Description

【０００１】
【発明の属する技術分野】
本発明は、排ガス中に含まれる硫黄酸化物を接触硫酸化反応によって硫酸として回収除去するための活性炭触媒、およびそれを用いた当該排煙脱硫方法に関するものである。
【０００２】
【従来の技術】
従来より、排ガス中に含まれる亜硫酸ガス等の硫黄酸化物を触媒及び酸素の共存下に低温で気相酸化し、最終的に硫酸として回収する方法が、接触硫酸化反応として知られている。この方法において、上記触媒としては活性炭が最も好んで用いられるが、これは、上記触媒として例えばアルミナ、シリカ、チタニア、ゼオライト等のセラミックス系担体からなるものを用いた場合には、それだけでは活性が不足するために触媒種として金属または金属酸化物を担持させる必要があり、そうした触媒種が反応により生成する硫酸の攻撃を受けて溶解ないし変質してしまうために、長時間にわたって安定した活性を維持することが困難であるという問題があるからである。これに対し活性炭には、金属や金属酸化物等の触媒種を担持しなくても相当な活性を有し、かつその活性が長時間にわたって劣化することなく持続するため、上記問題を生ずることがないという特長がある。
【０００３】
しかしながら、排煙脱硫装置において工業的に用いるには、市販の活性炭そのままでは常に高活性が安定して得られるとはいえず、所望の脱硫効果を安定して得るには触媒充填量を十分に大きくしなければならないため、湿式排煙脱硫プロセス等の他の脱硫プロセスと比較して割高となることが多い。常に高活性が安定して得られない原因は、次のように考えられている。すなわち、活性炭の亜硫酸ガス吸着・酸化活性（以下、単に「活性」と称す。）は本来は非常に大きいのであるが、低温かつ水蒸気の存在下において亜硫酸ガスが活性炭表面に吸着・酸化されるとそこで水分を吸収して希硫酸を生成し、これが活性炭の細孔を被覆・閉塞して亜硫酸ガスの拡散や活性点との接触を妨害する結果、活性炭内部の活性点が十分に利用されなくなるのである。このため、活性炭に撥水性を付与して、生成した希硫酸を速やかに活性炭の細孔から排出することにより、当該活性炭の高活性を維持しようとする各種の試みが提案されている。
【０００４】
例えば、Ｃｈｅｍ．Ｅｎｇ．Ｃｏｍｍ．Ｖｏｌ．６０（１９８７），ｐ．２５３には、平均直径０．７８ｍｍの活性炭にポリテトラフルオロエチレン（ＰＴＦＥ）の分散液を吹きかけることにより、ＰＴＦＥの添加量８〜２０％の領域において亜硫酸ガスの吸着・酸化反応の速度定数が３倍に上昇したとの事例が報告されている。また、特開昭５９−３６５３１号公報には、活性炭に撥水化処理を施すことで亜硫酸ガスの吸着・酸化活性が上昇すること、具体的には５〜１０ｍｍの粒状活性炭にＰＴＦＥ分散液を含浸させ、２００℃で２時間加熱処理することにより、活性炭単味の触媒に比べてはるかに高い活性を示すことが開示されている。
【０００５】
【発明が解決しようとする課題】
本発明者等は、活性炭の触媒活性を高める上記のような従来の方法の有効性を検証するため、以下の確認実験を行った。まず、上述した従来の撥水化技術に基づき、直径２．８〜４．０ｍｍの粒径範囲にある各種市販の活性炭にスプレー法或いは浸漬法によってＰＴＦＥを含浸担持させてその活性を測定したところ、活性炭単味の場合と比較してある程度の活性の向上とその長時間にわたる持続性が認められた。しかしながら、大規模な工業的実施を考慮して他の競合するプロセスと比較すると、依然としてこの程度の活性の向上では十分とはいえず、より一層の触媒活性の向上が必要であるとの認識に達した。
【０００６】
本発明者等は、更に検討を行った結果、触媒活性の向上には活性炭のマクロポア（５ｎｍを超える細孔直径を有する孔）のみを撥水化することが有効であることを見出した。すなわち、１０〜１００ｎｍの球相当直径を有するポリスチレン（ＰＳ）粒子を撥水性物質として粒状活性炭に含浸担持させることにより、当該活性炭の触媒活性が大幅に向上することを確認した。しかしながら、ＰＳよりも撥水性が大きいＰＴＦＥ等のフッ素樹脂粒子を用いようとすると、そのようなフッ素樹脂粒子の市販品は平均球相当直径が１００ｎｍ以上であるため、スプレー法や浸漬法等の含浸担持方法では原料活性炭のマクロポアを撥水化できない。この点を確認するため、本発明者等は、市販の粒状活性炭にＰＴＦＥ分散液をスプレー法あるいは浸漬法で含浸担持して活性炭触媒を作製し、このものについてフッ素の分布をＥＰＭＡで面分析した。それによると、ＰＴＦＥ粒子は活性炭粒子の内部には全く侵入しておらず、すべて粒子の外表面に付着していることが判明した。すなわち、市販の粒状活性炭には直径１μｍ以上の細孔がほとんど存在しないため、直径が０．２〜０．４μｍの範囲にあるＰＴＦＥ粒子が上記細孔内に侵入するには抵抗が大きすぎるのである。因みに、ＰＴＦＥ分散液に代えて、平均粒径が０．３μｍのＰＳ粒子の分散液を用いた場合についても、同様の実験結果を得た。そして、これら２種類の撥水性粒子を担持した活性炭触媒について活性試験を行ったところ、ＰＴＦＥを担持したものの方がＰＳ粒子を担持したものよりも僅かに活性が高かったものの、いずれも期待するほどの高活性を発現することはなかった。
【０００７】
更に本発明者等は、原料活性炭におけるマクロポアのうち、どの程度の細孔径のものを撥水化することが最も活性向上に寄与するのかについて調べた。まず、それぞれ平均直径が１０、２８、５５、１０２、３００ｎｍである５種類のラテックス（サイズが比較的均一なＰＳ球状粒子を１０重量％程度水に分散させたもの）を準備し、これらを０．１〜５重量％の各種濃度に希釈して、各々に粒状の原料活性炭を減圧下で浸漬して減圧乾燥することにより活性炭触媒を調製し、それぞれについて活性を評価した。その結果、いずれの活性炭触媒においても最高の活性を発現するＰＳの添加量は１重量％付近にあること、平均直径が２８ｎｍ及び５５ｎｍのものが最も高い活性を示し、平均直径が１０ｎｍ及び１０２ｎｍのものはそれよりも若干活性が低くなり、さらに平均直径３００ｎｍのものは未処理の活性炭と比べてわずかに活性が高いにすぎないことが判明した。この５種類の活性炭触媒について粒子破断面をＳＥＭ観察したところ、平均直径が５５ｎｍ以下のＰＳ粒子は満遍なく活性炭粒子の内部にまで侵入しているのに対し、１０２ｎｍのＰＳ粒子は活性炭粒子の表面近傍に多く存在しており、さらに３００ｎｍのＰＳ粒子は活性炭粒子の外表面にのみ付着していることがわかった。平均直径１０ｎｍのＰＳ粒子を含浸した活性炭触媒が平均直径２８ｎｍ及び５５ｎｍのＰＳ粒子を含浸したものより活性が低くなった理由については推定の域を出ないが、ＰＳ粒子が微細になるほど原料活性炭のポアを閉塞しやすくなるためではないかと考えられる。すなわち上記実験結果から、平均粒径２８ｎｍのＰＳ粒子が侵入できる最小の細孔径以上のマクロポアを撥水化することが有効であることが示唆されたことになる。
【０００８】
かくして、触媒粒子を構成する原料活性炭、特にそのマクロポアを撥水化することが活性の向上に大きく寄与すること、また触媒粒子の内部まで満遍なく撥水化することが有効なこと、そしてＰＳと比較するとＰＴＦＥ等のフッ素樹脂の方が撥水化作用が大きい分だけ活性向上効果も大きいことが確認された。そこで本発明者等は、市販のフッ素樹脂粒子の平均粒径が比較的大きく粒状活性炭への含浸担持では有効に撥水化できないことに鑑み、粒状活性炭を微粉砕してフッ素樹脂粒子とともに混合して成形することとし、かくして成形体を構成する活性炭粉末粒子間の間隙（これは「大きなマクロポア」ということもできる。）並びに原料活性炭自体のマクロポアの一部をフッ素樹脂粒子により撥水化することを試みた。こうして得られた活性炭触媒の活性は、原料活性炭自体はもとより、原料活性炭にＰＳ粒子を含浸担持させて製造した活性炭触媒に比べても大きく向上していた。
【０００９】
本発明者等は、活性炭粉末をフッ素樹脂とともに混合して成形する際の粉砕条件については、活性炭をできる限り細かい粒子にまで粉砕してＰＴＦＥ分散液と混合すれば、ＰＴＦＥによる活性炭粉末粒子間の間隙の修飾率が高くなってより高い活性が得られるものと考えていたので、市販の活性炭を平均粒子径１０μｍまで粉砕してＰＴＦＥ分散液と混合することにより活性炭触媒を調製し、これについて触媒活性を評価した。しかしながら、ＰＴＦＥの添加量を２〜３０重量％の範囲で種々に変えても、期待したほどの活性の向上が認められなかった。これは、原料活性炭をあまりに細かく粉砕してしまうと、本来生成硫酸の排出経路となるべき活性炭粉末粒子間の間隙が極端に狭くなり、さらにはそのような間隙がＰＴＦＥによって閉塞されてしまうからではないかと考えられる。そこで、粉砕するに際して活性炭粉末の粒子サイズには最適値があるのではないかと考え、ＰＴＦＥの添加量を一定にして活性炭粉末の平均粒子径を１０〜３０００μｍまで種々に変えて成形してみたところ、後述するように１２〜６００μｍの範囲において比較的に高活性の活性炭触媒を得ることができた。
【００１０】
更に本発明者等は、少量のＰＴＦＥの添加で高活性な触媒を得るため、マクロポアの撥水性を効果的に向上させる方法について検討した。具体的には、同一量のＰＴＦＥの添加でもその投影面積を大きくすることにより、活性炭粉末の表面及び内部マクロポアをＰＴＦＥとより広く接触させることができ、それらをより強く撥水化することができると考えた。すなわち、活性炭粉末とＰＴＦＥ粒子とを混合する際に剪断力をかけ、ＰＴＦＥ粒子を変形させるとともに活性炭粉末と広く密着させることにより、活性炭粉末の表面及び内部マクロポアに強い撥水性を発現させることを考えたのである。そこで、活性炭粉末に対して０．５〜３０重量％のＰＴＦＥ粒子を粉末もしくは分散液として加え、ニーダ、ロール混練機、カレンダーロール、ロール式ミル等を用いて混練後、成形して活性炭触媒を得た。これを用いて脱硫試験を行ったところ、単に活性炭粉末とＰＴＦＥ粒子を混合して成形しただけのものと比べ、活性炭粉末に加えるＰＴＦＥ粉末の量を少なくしても同等の活性が得られることがわかった。
【００１１】
【課題を解決するための手段】
本発明は、以上の知見に基づいてなされたものであり、所望のサイズ範囲の細孔が効果的に撥水化され高い触媒活性を発現する活性炭触媒を提供するものである。本発明はまた、上記活性炭触媒を用いることにより脱硫効率および経済性にすぐれた排煙脱硫方法を提供するものである。
【００１２】
本発明は、硫黄酸化物を含む排ガスと接触させ、上記硫黄酸化物を吸着し酸化して硫酸として回収除去するための活性炭触媒であって、平均粒子径が１２〜６００μｍ、好ましくは２０〜２００μｍの活性炭粉末と、上記活性炭粉末に対して０．５〜２５重量％、好ましくは１〜２０重量％のフッ素樹脂とを含み、上記活性炭粉末に上記フッ素樹脂の粒子または粒子分散液を加え、これに剪断力をかけて混練し、所定形状に成形してなるものを提供する。
【００１３】
本発明はまた、上記で得られた活性炭触媒を、硫黄酸化物を含む排ガスと接触させ、排ガス中の硫黄酸化物を上記活性炭触媒に吸着し酸化して硫酸として回収除去する排煙脱硫方法を提供するものでもある。この場合、活性炭触媒を水、アルカリ水、希硫酸などで連続的に洗浄して脱硫性能を向上させたり、あるいは間欠洗浄して生成硫酸を洗い出したり中和することにより再生してもよい。
【００１４】
【発明の実施の形態】
本発明に係る活性炭触媒は、排ガス中の亜硫酸ガスを共存する酸素により酸化して硫酸として回収除去するためのものであって、撥水性の強いフッ素樹脂の粒子と適切な粒径範囲を有する活性炭粉末とを剪断力をかけて十分に混練してから成形することにより得られる。
【００１５】
ここで、撥水化による活性の向上に大きな影響を与える第１の重要な点は、活性炭粉末とフッ素樹脂粒子とを剪断力をかけて混練することにある。本発明では、撥水性物質であるフッ素樹脂を活性炭粉末に付着させて撥水化を行っているので、撥水化させるべき表面をフッ素樹脂で広く覆うことが効果的な撥水化につながる要素となる。このため、同一量のフッ素樹脂であっても、粒状のものを大きく変形させて投影面積を大きくし、これにより撥水化させるべき表面を広く覆うようにすると、活性炭触媒全体をより強く撥水化することができる。本発明では、活性炭粉末とフッ素樹脂粒子とをよく混合してから剪断力をかけて練り込むことが、フッ素樹脂粒子を投影面積の大きな形に変形させ、これを活性炭粉末の表面に広く密着させたりマクロポア内に圧入したりする作用をなす。従って、活性炭粉末とフッ素樹脂粒子との混合物に十分な剪断力を与えることが本発明では本質的な要素である。一般に当該混合物１ｇ当たり０．５Ｗ以上、好ましくは１Ｗ以上の仕事率で１０分以上混練すれば所望の効果が得られるが、必要な混練エネルギーの量は他の条件によって異なるため、混練エネルギーの量だけで混練条件を一義的に特定できるわけではない。要するに、粒状のフッ素樹脂が変形して活性炭表面に広く密着したりマクロポア内に圧入したりするのに十分な混練エネルギーが与えられればよい。混練による剪断力付与の効果により、本発明の活性炭触媒では、触媒粒子を構成する活性炭粉末間の間隙が、触媒粒子表面部から内部にわたって満遍なく撥水化された大きなマクロポアを形成し、また個々の活性炭粉末自体に存在するマクロポアの一部も撥水化されている。さらに、混練によっても変形されずに残った一部のフッ素樹脂粒子は、やはり活性炭粉末のマクロポア内に侵入してその撥水化に寄与することになる。
【００１６】
本発明の活性炭触媒を製造するのに使用する活性炭は、原料活性炭の炭種による活性の差異が本発明により緩和されるので、比較的自由に選択することができるが、好ましくはそれ自体の触媒活性が高いものを選ぶべきである。本発明者等が行った活性の比較試験によれば、石炭を主原料とする活性炭を用いたものは、他の椰子殻、ビート、石油ピッチなどを主原料とする活性炭を用いたものより高活性を示す傾向があった。石炭を主原料とする活性炭を用いたものが高活性を示す理由は、必ずしも定かではないが、もともと石炭系の活性炭は他の原料からなる活性炭と比較して亜硫酸ガスの吸着・酸化活性点の数が多いにも拘わらず、疎水性の程度が低いために所望の高活性が安定して得られないという難点があり、これが撥水化処理により克服されたことで、その本来の優れた活性が顕著に現れたからであろうと推察される。ただし、本発明の活性炭触媒は、その原料活性炭の炭種に拘わらず、原料活性炭自体あるいはそれとフッ素樹脂粒子とを単に混合して成形したものに比べて大幅な活性の向上が期待されるものである。なお、焼成などの前処理を行った活性炭を用いてもよい。
【００１７】
ここで、撥水化による活性の向上に大きな影響を与える第２の重要な点は、原料となる活性炭粉末の粒度の調整にある。当該活性炭粉末の粒度が粗すぎると、どのようにフッ素樹脂の添加量を選択しても高活性は発現しない。また逆に、上記粒度が細かすぎても、生成した硫酸の排出流路となるべき活性炭粉末間の間隙が極端に狭くなり、さらにはそうした間隙がフッ素樹脂によって閉塞されてしまう結果、使用の際の急激な活性の低下を招来する。本発明者等の知見によれば、高活性を得るための活性炭粉末の粒度範囲は、平均粒子径が１２〜６００μｍ、好ましくは２０〜２００μｍの範囲である。なお、活性炭粉末は粒状活性炭を粉砕して調製するのが一般的であるが、未だ賦活されていない石炭などを粉砕し、これをフッ素樹脂粒子と混練して成形した後に賦活してもよい。
【００１８】
活性炭粉末と混練するためのフッ素樹脂としては、一般に市販されている各種フッ素樹脂粒子の粉末あるいは分散液（ラテックス）を使用することができる。フッ素の含有率の高いものが撥水性に優れるため好ましく、そのようなフッ素樹脂としてはポリテトラフルオロエチレン（ＰＴＦＥ）、パーフルオロアルコキシ樹脂（ＰＦＡ）、四フッ化エチレン六フッ化プロピレン共重合体（ＦＥＰ）、三フッ化塩化エチレン樹脂（ＰＣＴＥＦ）等がある。これらのフッ素樹脂はポリスチレンやポリエチレン等よりも撥水性が大きく、しかも市販されている分散液中におけるこれらのフッ素樹脂の平均粒子径は０．２〜０．４μｍと比較的大きいために活性炭粉末のミクロポア内に侵入することがなく、よってこれらと活性炭粉末とを混合し混練して成形することにより、活性炭粉末間の間隙（大きなマクロポア）及び活性炭粉末の内部マクロポアが撥水化された所望の活性炭触媒を得ることができる。
【００１９】
ここで、撥水化による活性向上に大きな影響を与える第３の重要な点は、フッ素樹脂粒子の添加量にある。本発明の活性炭触媒は、活性炭粉末の平均粒子径の如何に拘わらず、活性炭粉末に対して０．５〜２５重量％、好ましくは１〜２０重量％のフッ素樹脂を含むことにより所望の高活性を示す。フッ素樹脂は成形に際してバインダーとしても働くので、そうしたバインダー効果をも考慮して添加量を決めることが好ましい。なお、フッ素樹脂の添加量が少ない場合には、成形のために別途バインダーを使用することができる。
【００２０】
活性炭粉末とフッ素樹脂との混練物を成形するには、押出成形、打錠成形、転動造粒法などの種々の成形法が適用可能である。例えば、強度の大きな活性炭触媒を得たい場合には、混合粉末を押圧して一定形状に成形する打錠成形が好ましい。また、排ガス中の煤塵等の蓄積による差圧の発生を抑えたい場合には、混合粉末をプレート状あるいはハニカム状に成形することもできる。以上のように、本発明の活性炭触媒にあっては、活性炭粉末を原料として任意形状のものを作ることができ、活性の向上と併せて製造コストの観点からも有利である。
【００２１】
なお、得られた成形物には、必要ならば粉砕して適当な粒度に調整した後、続いて撥水化処理を施してもよい。これにより、活性炭触媒の外表面部をより強く撥水化し、表面における水膜の形成を妨げ、マクロポア入口部の液による閉塞を防止し、外部から内部への水蒸気や水溶液の侵入を強く阻害する。従って、触媒内部の活性点が有効に利用され、高い触媒性能が得られることになる。この撥水化処理の方法としては、撥水性物質の微粒子の分散液、あるいは撥水性物質をトルエン等の有機溶媒に溶解した溶液を、スプレー法或いは浸漬法等により成形物に含浸させればよい。この場合、撥水性物質としては、フッ素樹脂が高密着性、高撥水性を発現する点で好ましい。一方、有機溶媒溶液を用いる場合には、分子量が１万以上の高分子撥水性物質を溶解して用いることが好ましい。分子量がこれより小さいものを用いると、活性点が必要以上に撥水性物質で覆われて有効な活性点の数が低下する。撥水性物質は、０．１〜３．５重量％、好ましくは０．２〜３重量％含浸させることが好ましい。
【００２２】
【実施例】
以下、本発明を実施例により更に具体的に説明する。
実施例１
市販されている石炭系活性炭を、窒素気流中、８００℃で１時間焼成した。得られた活性炭５００ｇを市販されている粉砕器にて粉砕した後、ステンレス製の篩（１５０μｍ）を用いて篩振盪機での２時間の分級操作にかけ、１５０μｍ以下の微粉活性炭を得た。次に、市販のＰＴＦＥ分散液（直径０．２〜０．４μｍのＰＴＦＥ粒子を６０重量％含む）に水を加えて６倍に希釈し、この希釈したＰＴＦＥ分散液１１１ｇと上記微粉活性炭１００ｇとを直径３００ｍｍの磁製乳鉢にて１０分混練した後、圧縮成形機にて５００ｋｇｆ／ｃｍ^２で成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。更に、この活性炭触媒を４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。
【００２３】
このようにして得られた本発明の活性炭触媒につき、接触硫酸化反応試験装置を用いて５％希硫酸水溶液２００ｍＬ／ｈｒを触媒層に流しながら活性試験を行った。具体的には、内径１６ｍｍのジャケット付き硝子製反応器に活性炭触媒を４０ｍＬ充填し、
ＳＯ_２：８００容量ｐｐｍ
Ｏ_２：４容量％
ＣＯ_２：１０容量％
Ｎ_２：残部
相対湿度：１００％
の組成のガスを、５０℃、６００ｄｍ^３／ｈｒ（ＳＶ＝１５０００ｈｒ^ー１）で流し、出口ＳＯ_２濃度をＳＯ_２計（紫外式、赤外式）で測定して触媒活性を評価したところ、試験開始後１００ｈｒ後における脱硫率４２％を得た。
【００２４】
実施例２
実施例１と同様にして得た微粉活性炭１００ｇに実施例１と同じ希釈ＰＴＦＥ分散液１１１ｇを加えたものを、ニーダー（容量４００ｍＬ、ゼット型ブレード、回転数４３ｒｐｍ、仕事率２５０Ｗ）で３０分混練した後、５００ｋｇｆ／ｃｍ^２で圧縮成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率４７％を得た。
【００２５】
実施例３
実施例１と同様にして得た微粉活性炭１００ｇに実施例１と同じ希釈ＰＴＦＥ分散液１１１ｇを加えたものを、ニーダー（容量４００ｍＬ、ゼット型ブレード、回転数４３ｒｐｍ、仕事率２５０Ｗ）で３０分混練し、次いでプレスロール機で圧延（ロール間隙３ｍｍ、２ｍｍ、１．５ｍｍ、１ｍｍで順次圧延）し、これを粗砕した後、５００ｋｇｆ／ｃｍ^２で圧縮成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率５４％を得た。
【００２６】
実施例４
実施例１と同様にして得た微粉活性炭１００ｇに実施例１と同じ希釈ＰＴＦＥ分散液１１１ｇを加えたものを、ニーダー（容量４００ｍＬ、ゼット型ブレード、回転数４３ｒｐｍ、仕事率２５０Ｗ）で３０分混練した後、さらに３本ロール式ミル（ロール寸法６３．５Φ×１５０Ｌ、ロール回転数８４ｒｐｍ、２０５ｒｐｍ、５００ｒｐｍ、仕事率４００Ｗ）で１５分混練し、５００ｋｇｆ／ｃｍ^２で圧縮成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率６６％を得た。
【００２７】
実施例５
実施例１と同様にして得た微粉活性炭２００ｇに実施例１と同じ希釈ＰＴＦＥ分散液２２２ｇを加えたものを、ロール型加圧ニーダー（容量５００ｍＬ、回転数２０ｒｐｍ、仕事率２０００Ｗ）で１５分混練した後、５００ｋｇｆ／ｃｍ^２で圧縮成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率６８％を得た。
【００２８】
実施例６
実施例１と同様にして粉砕した活性炭を実施例１と同様な方法で分級した。このとき、メッシュの異なる篩の組合せ（０〜２５μｍ、２０〜５３μｍ、５３〜１０６μｍ、１０６〜２１２μｍ、２１２〜３００μｍ、２８００〜４０００μｍ）を用いることにより、平均粒子径の異なる６種の微粉活性炭を得た。これら６種の微粉活性炭各１００ｇに実施例１と同じ希釈ＰＴＦＥ分散液各１１１ｇを加えたものに対して、それぞれ実施例３と同様な操作（混練、成形、乾燥、粗砕、分級）を行うことにより、ＰＴＦＥを１０重量％含有する直径２．８〜４．０ｍｍの粒状活性炭をそれぞれ得た。
【００２９】
このようにして得られた各活性炭触媒につき、実施例１と同様な方法で活性試験を行った。表１および図１は試験開始後１００ｈｒ後における各触媒の脱硫性能を示すものである。これらの結果より、微粉活性炭の平均粒子径の範囲が１２〜６００μｍ、好ましくは２０〜２００μｍのときに、高い脱硫率が得られることがわかる。
【表１】

【００３０】
実施例７
実施例１と同様にして粉砕した活性炭を実施例１と同様な方法で分級して微粉活性炭を得た。次に、市販のＰＴＦＥ分散液（６０重量％）に水を加えて１．５〜２０倍に希釈し、３〜４０重量％の各種濃度の希釈ＰＴＦＥ分散液を得た。これらの希釈ＰＴＦＥ分散液各１１１ｇに対してそれぞれ上記微粉活性炭１００ｇを加えたものに対し、実施例３と同様な操作（混練、成形、乾燥、粗砕、分級）を行うことにより、ＰＴＦＥを０〜３０重量％の各種割合で含有する直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。
【００３１】
このようにして得られた各活性炭触媒につき、実施例１と同様な方法で活性試験を行った。表２および図２は試験開始後１００ｈｒ後における各触媒の脱硫性能を示すものである。これらの結果より、微粉活性炭と混練するＰＴＦＥの添加量が０．５〜２５重量％、好ましくは１〜２０重量％ときに、高い脱硫率が得られることがわかる。
【表２】

【００３２】
実施例８
実施例１と同様にして得た微粉活性炭１００ｇに実施例１と同じ希釈ＰＴＦＥ分散液１１１ｇを加えたものを、小型擂壊機（鉢外径１７８ｍｍ、回転数１００ｒｐｍ、仕事率１００Ｗ）で１０分混練した後、５００ｋｇｆ／ｃｍ^２で加圧成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率４３％を得た。
【００３３】
実施例９
実施例１と同様にして得た微粉活性炭５００ｇに実施例１と同じ希釈ＰＴＦＥ分散液５５５ｇを加えたものを、Ｖ字双子円筒型混合機（容量１０００ｍＬ、回転数３０ｒｐｍ）で６０分間混合し、次いで得られた混合物１００ｇを小型擂壊機（鉢外径１７８ｍｍ、回転数１００ｒｐｍ、仕事率１００Ｗ）で１０分混練した後、５００ｋｇｆ／ｃｍ^２で加圧成形してＰＴＦＥを１０重量％含有する活性炭触媒を得た。これを４５〜５０℃で１２時間乾燥した後、粗砕・分級して直径２．８〜４．０ｍｍの粒状活性炭触媒を得た。こうして得られた本発明の活性炭触媒につき、実施例１と同様な方法で活性試験を行ったところ、脱硫率４３％を得た。
【００３４】
比較例
乳鉢で手混練する代わりに、Ｖ字双子円筒型混合機にて６０分間混合して目視にて十分混合されたことを確認した以外は、実施例１と同様の操作を行った。得られた活性炭触媒を用いて活性試験を行った結果は、脱硫率１８％であった。
【図面の簡単な説明】
【図１】微粉活性炭の平均粒子径とそれを用いて得られる本発明の触媒の脱硫性能との関係を示す。
【図２】微粉活性炭と混練するＰＴＦＥの含有量と本発明の触媒の脱硫性能との関係を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an activated carbon catalyst for recovering and removing sulfur oxides contained in exhaust gas as sulfuric acid by a catalytic sulfation reaction, and to a flue gas desulfurization method using the same.
[0002]
[Prior art]
BACKGROUND ART Conventionally, a method of subjecting a sulfur oxide such as a sulfurous acid gas contained in an exhaust gas to gas phase oxidation at a low temperature in the presence of a catalyst and oxygen and finally recovering it as sulfuric acid is known as a catalytic sulfation reaction. In this method, activated carbon is most preferably used as the above-mentioned catalyst. However, when a catalyst comprising a ceramic-based carrier such as alumina, silica, titania, or zeolite is used as the above-mentioned catalyst, the activity alone is not sufficient. It is necessary to carry a metal or metal oxide as a catalyst species because of the shortage, and since such a catalyst species is attacked by sulfuric acid generated by the reaction, it dissolves or deteriorates, and maintains a stable activity for a long time. This is because there is a problem that it is difficult to do so. On the other hand, activated carbon has considerable activity even without supporting a catalyst species such as a metal or a metal oxide, and its activity is maintained for a long time without deterioration. There is a feature that there is no.
[0003]
However, for industrial use in a flue gas desulfurization apparatus, it cannot be said that a commercially available activated carbon as it is is not always possible to obtain a high activity stably, and a sufficient catalyst loading is required to stably obtain a desired desulfurization effect. Because it must be large, it is often expensive compared to other desulfurization processes such as wet flue gas desulfurization processes. The reason why high activity cannot always be obtained stably is considered as follows. In other words, the sulfur dioxide adsorption / oxidation activity (hereinafter simply referred to as "activity") of activated carbon is originally very large, but when sulfur dioxide is adsorbed and oxidized on the activated carbon surface at low temperature and in the presence of steam. Then, it absorbs water to generate dilute sulfuric acid, which covers and closes the pores of the activated carbon and prevents the diffusion of sulfurous acid gas and the contact with the active points.As a result, the active points inside the activated carbon are not fully utilized. is there. For this reason, various attempts have been made to maintain the high activity of the activated carbon by imparting water repellency to the activated carbon and promptly discharging the generated dilute sulfuric acid from the pores of the activated carbon.
[0004]
For example, Chem. Eng. Comm. Vol. 60 (1987), p. 253, a dispersion of polytetrafluoroethylene (PTFE) is sprayed on activated carbon having an average diameter of 0.78 mm, so that the rate constant of the adsorption and oxidation reaction of sulfurous acid gas is 3 in the range of 8 to 20% of the PTFE addition amount. Cases have been reported to have doubled. Japanese Unexamined Patent Publication (Kokai) No. 59-36531 discloses that a water-repellent treatment is applied to activated carbon to increase the adsorption and oxidation activity of sulfurous acid gas. Specifically, a PTFE dispersion liquid is applied to granular activated carbon of 5 to 10 mm. It is disclosed that by impregnating and heat-treating at 200 ° C. for 2 hours, the catalyst shows much higher activity than the activated carbon-only catalyst.
[0005]
[Problems to be solved by the invention]
The present inventors conducted the following confirmation experiments in order to verify the effectiveness of the above-described conventional method for increasing the catalytic activity of activated carbon. First, based on the above-mentioned conventional water-repellent technology, PTFE was impregnated and supported on various types of commercially available activated carbon having a particle size range of 2.8 to 4.0 mm by a spray method or an immersion method, and the activity was measured. However, compared to the case of using only activated carbon, an improvement in the activity to some extent and its long-lasting activity were observed. However, when compared to other competing processes in view of large-scale industrial implementation, this level of activity improvement is still not sufficient, and it has been recognized that further improvement in catalyst activity is necessary. Reached.
[0006]
As a result of further studies, the present inventors have found that it is effective to make only the macropores (pores having a pore diameter exceeding 5 nm) of activated carbon water-repellent to improve the catalytic activity. That is, it was confirmed that the catalytic activity of the activated carbon was significantly improved by impregnating and supporting polystyrene (PS) particles having a sphere equivalent diameter of 10 to 100 nm as a water-repellent substance on the granular activated carbon. However, when attempting to use fluororesin particles such as PTFE having higher water repellency than PS, commercially available products of such fluororesin particles have an average equivalent spherical diameter of 100 nm or more. With the loading method, the macropores of the raw activated carbon cannot be made water-repellent. To confirm this point, the present inventors prepared an activated carbon catalyst by impregnating a commercially available granular activated carbon with a PTFE dispersion by a spray method or an immersion method, and analyzed the distribution of fluorine with respect to this by EPMA. . According to this, it was found that the PTFE particles did not penetrate into the activated carbon particles at all, but were all attached to the outer surfaces of the particles. That is, since commercially available granular activated carbon hardly has pores having a diameter of 1 μm or more, the resistance is too large for PTFE particles having a diameter in the range of 0.2 to 0.4 μm to penetrate into the pores. is there. Incidentally, similar experimental results were obtained when a dispersion of PS particles having an average particle diameter of 0.3 μm was used instead of the PTFE dispersion. Then, when an activity test was performed on the activated carbon catalyst supporting these two types of water-repellent particles, the PTFE-supported one was slightly higher in activity than the PS-particle-supported one, but both were as expected. Did not express high activity.
[0007]
Furthermore, the present inventors investigated how much the pore size of the macropores in the raw material activated carbon contributes to the activity improvement most. First, five types of latexes (average diameters of 10, 28, 55, 102, and 300 nm, respectively, in which PS spherical particles having a relatively uniform size are dispersed in water at about 10% by weight) are prepared. The active carbon catalyst was prepared by diluting the raw material activated carbon into various concentrations of 0.1 to 5% by weight, immersing the raw activated carbon under reduced pressure, and drying under reduced pressure. As a result, the addition amount of PS exhibiting the highest activity in any of the activated carbon catalysts was around 1% by weight, those having an average diameter of 28 nm and 55 nm showed the highest activity, and those having an average diameter of 10 nm and 102 nm. Those with a slightly lower activity were found, and those with an average diameter of 300 nm were found to be only slightly more active than the untreated activated carbon. SEM observation of the particle fracture surfaces of these five types of activated carbon catalysts revealed that PS particles having an average diameter of 55 nm or less penetrated evenly into the interior of the activated carbon particles, whereas PS particles having an average diameter of 102 nm were near the surface of the activated carbon particles. It was found that PS particles of 300 nm were attached only to the outer surface of the activated carbon particles. The reason why the activated carbon catalyst impregnated with PS particles having an average diameter of 10 nm is lower in activity than those impregnated with PS particles having an average diameter of 28 nm and 55 nm does not fall out of speculation. It is thought that the pores are likely to be closed. In other words, the above experimental results suggest that it is effective to make water repellent macropores having a minimum pore diameter that allows PS particles having an average particle diameter of 28 nm to enter.
[0008]
Thus, the water repellency of the raw activated carbon constituting the catalyst particles, especially its macropores, greatly contributes to the improvement of the activity, the fact that it is effective to uniformly water repellent even inside the catalyst particles, and a comparison with PS As a result, it was confirmed that a fluororesin such as PTFE has a greater activity improving effect as much as a water repellent effect. In view of the fact that the average particle size of commercially available fluororesin particles is relatively large and cannot be effectively made water-repellent by impregnation on granular activated carbon, the present inventors have finely pulverized the granular activated carbon and mixed it with the fluororesin particles. The gap between the activated carbon powder particles constituting the molded body (this can also be called “large macropores”) and part of the macropores of the raw material activated carbon itself are made water-repellent by fluororesin particles. Tried. The activity of the activated carbon catalyst thus obtained was greatly improved as compared to the activated carbon catalyst produced by impregnating and supporting PS particles on the activated carbon raw material as well as the activated carbon raw material itself.
[0009]
The inventors of the present invention have considered that the grinding conditions for mixing activated carbon powder with a fluororesin and molding them are as follows: if activated carbon is pulverized to the finest possible particles and mixed with a PTFE dispersion, Since it was considered that the modification rate of the gap was increased and higher activity was obtained, a commercially available activated carbon was pulverized to an average particle diameter of 10 μm and mixed with a PTFE dispersion to prepare an activated carbon catalyst. Activity was evaluated. However, even if the addition amount of PTFE was variously changed in the range of 2 to 30% by weight, the expected improvement in activity was not observed. This is because if the raw material activated carbon is pulverized too finely, the gap between the activated carbon powder particles, which should be a discharge path for the generated sulfuric acid, becomes extremely narrow, and furthermore, such a gap is closed by PTFE. It is thought that there is not. Therefore, when pulverizing, it was thought that there was an optimum value for the particle size of the activated carbon powder, and when the amount of PTFE added was kept constant, the average particle diameter of the activated carbon powder was variously changed from 10 to 3000 μm. As described later, an activated carbon catalyst having a relatively high activity could be obtained in the range of 12 to 600 μm.
[0010]
Furthermore, the present inventors have studied a method for effectively improving the water repellency of macropores in order to obtain a highly active catalyst by adding a small amount of PTFE. Specifically, even if the same amount of PTFE is added, by increasing the projected area, the surface and the internal macropores of the activated carbon powder can be brought into broader contact with PTFE, and they can be made more water-repellent. I thought. That is, it is considered that a shearing force is applied when mixing the activated carbon powder and the PTFE particles to deform the PTFE particles and to make the PTFE particles adhere to the activated carbon powder widely, thereby exhibiting strong water repellency on the surface and the internal macropores of the activated carbon powder. It was. Therefore, PTFE particles of 0.5 to 30% by weight with respect to the activated carbon powder are added as a powder or a dispersion, kneaded using a kneader, a roll kneader, a calender roll, a roll mill or the like, and then molded to form an activated carbon catalyst. Obtained. When a desulfurization test was performed using this, it was found that the same activity could be obtained even when the amount of PTFE powder added to the activated carbon powder was reduced, as compared with the case where activated carbon powder and PTFE particles were simply mixed and molded. all right.
[0011]
[Means for Solving the Problems]
The present invention has been made based on the above findings, and provides an activated carbon catalyst in which pores in a desired size range are effectively made water-repellent and exhibit high catalytic activity. The present invention also provides a flue gas desulfurization method excellent in desulfurization efficiency and economy by using the above activated carbon catalyst.
[0012]
The present invention is an activated carbon catalyst for contacting with an exhaust gas containing a sulfur oxide, adsorbing and oxidizing the sulfur oxide to recover and remove it as sulfuric acid, having an average particle diameter of 12 to 600 μm, preferably 20 to 200 μm. Activated carbon powder, and 0.5 to 25% by weight, preferably 1 to 20% by weight, of the fluorocarbon resin based on the activated carbon powder, and the fluorocarbon resin particles or the particle dispersion are added to the activated carbon powder. And kneaded by applying a shearing force to the mixture to form a predetermined shape.
[0013]
The present invention also provides a flue gas desulfurization method in which the activated carbon catalyst obtained above is brought into contact with an exhaust gas containing sulfur oxide, and the sulfur oxide in the exhaust gas is adsorbed on the activated carbon catalyst, oxidized, and recovered and removed as sulfuric acid. It also provides. In this case, the activated carbon catalyst may be continuously washed with water, alkaline water, dilute sulfuric acid or the like to improve the desulfurization performance, or may be intermittently washed to regenerate by washing out and neutralizing the sulfuric acid produced.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The activated carbon catalyst according to the present invention is for oxidizing sulfur dioxide gas in exhaust gas with coexisting oxygen to recover and remove it as sulfuric acid, and has activated carbon having strong water-repellent fluororesin particles and an appropriate particle size range. It is obtained by sufficiently kneading the powder with a shearing force and then molding.
[0015]
Here, the first important point that greatly affects the improvement of the activity by water repellency is that the activated carbon powder and the fluororesin particles are kneaded by applying a shearing force. In the present invention, since the water-repellent substance is attached to the activated carbon powder by applying the fluorocarbon resin as the water-repellent substance, the surface to be water-repellent is widely covered with the fluorocarbon resin. It becomes. For this reason, even if the same amount of fluororesin is used, if the granular material is greatly deformed to increase the projected area and thereby widely cover the surface to be made water-repellent, the entire activated carbon catalyst becomes more strongly water-repellent. Can be In the present invention, the active carbon powder and the fluorocarbon resin particles are mixed well and then kneaded by applying a shearing force, thereby deforming the fluorocarbon resin particles into a shape having a large projected area and causing the fluorocarbon resin particles to adhere widely to the surface of the activated carbon powder. Or presses into the macropore. Therefore, it is an essential element in the present invention to apply a sufficient shearing force to the mixture of the activated carbon powder and the fluororesin particles. Generally, a desired effect can be obtained by kneading at a power of 0.5 W or more, preferably 1 W or more per 1 g of the mixture, for at least 10 minutes. However, the required amount of kneading energy varies depending on other conditions. The kneading conditions cannot be uniquely specified by itself. In short, it suffices if sufficient kneading energy is applied so that the granular fluororesin is deformed and adheres widely to the activated carbon surface or is pressed into the macropore. Due to the effect of imparting shearing force by kneading, in the activated carbon catalyst of the present invention, the gaps between the activated carbon powders constituting the catalyst particles form large macropores that are uniformly water-repellent from the surface to the inside of the catalyst particles. Some of the macropores present in the activated carbon powder itself are also water-repellent. Further, some of the fluororesin particles that remain without being deformed by the kneading also enter the macropores of the activated carbon powder and contribute to the water repellency.
[0016]
The activated carbon used for producing the activated carbon catalyst of the present invention can be selected relatively freely, because the difference in the activity of the raw activated carbon depending on the type of charcoal is mitigated by the present invention. You should choose one with high activity. According to a comparative test of the activity performed by the present inventors, those using activated carbon based on coal are higher than those using activated carbon based on other coconut shells, beets, oil pitch and the like. There was a tendency to show activity. The reason why activated carbon using coal as a main raw material shows high activity is not always clear, but originally activated carbon based on coal has a higher sulfur dioxide adsorption / oxidation active point than activated carbon composed of other raw materials. Despite the large number, there is a drawback that the desired high activity cannot be stably obtained due to the low degree of hydrophobicity. It is presumed that this was due to the remarkable appearance. However, the activated carbon catalyst of the present invention is expected to have a significant improvement in activity compared to the raw activated carbon itself or a mixture obtained by simply mixing the raw activated carbon with fluorocarbon resin particles, regardless of the type of the raw activated carbon. is there. Note that activated carbon that has been subjected to pretreatment such as firing may be used.
[0017]
Here, the second important point that greatly affects the improvement of the activity by water repellency is the adjustment of the particle size of the activated carbon powder as a raw material. If the particle size of the activated carbon powder is too coarse, high activity will not be exhibited regardless of the amount of the fluororesin to be added. Conversely, if the particle size is too small, the gap between the activated carbon powders that should serve as a discharge channel for the generated sulfuric acid becomes extremely narrow, and furthermore, such a gap is closed by the fluororesin, resulting in a problem during use. Causes a rapid decrease in activity. According to the findings of the present inventors, the average particle diameter of the activated carbon powder for obtaining high activity is in the range of 12 to 600 μm, preferably 20 to 200 μm. The activated carbon powder is generally prepared by pulverizing granular activated carbon, but may be activated after pulverizing coal or the like that has not yet been activated, kneading it with fluororesin particles, and molding.
[0018]
As the fluororesin to be kneaded with the activated carbon powder, generally commercially available powders or dispersions (latex) of various fluororesin particles can be used. Those having a high fluorine content are preferable because of their excellent water repellency. Examples of such fluororesins include polytetrafluoroethylene (PTFE), perfluoroalkoxy resin (PFA), and tetrafluoroethylene hexafluoropropylene copolymer ( FEP) and ethylene trifluoride ethylene resin (PCTEF). These fluororesins have higher water repellency than polystyrene, polyethylene, etc., and the average particle diameter of these fluororesins in commercially available dispersions is relatively large, 0.2 to 0.4 μm. The desired activated carbon in which the gaps between the activated carbon powders (large macropores) and the internal macropores of the activated carbon powder are made water-repellent is obtained by mixing, kneading and molding the activated carbon powder without invading the inside of the micropores. A catalyst can be obtained.
[0019]
Here, the third important point that greatly affects the activity improvement by water repellency is the amount of fluororesin particles added. The activated carbon catalyst of the present invention contains 0.5 to 25% by weight, preferably 1 to 20% by weight, of a fluororesin, based on the activated carbon powder, irrespective of the average particle size of the activated carbon powder. Is shown. Since the fluororesin also functions as a binder at the time of molding, it is preferable to determine the addition amount in consideration of such a binder effect. When the addition amount of the fluororesin is small, a binder can be separately used for molding.
[0020]
In order to form a kneaded product of activated carbon powder and a fluororesin, various molding methods such as extrusion molding, tablet molding, and rolling granulation can be applied. For example, when it is desired to obtain an activated carbon catalyst having a high strength, tablet molding in which the mixed powder is pressed to form a predetermined shape is preferable. When it is desired to suppress the generation of a differential pressure due to accumulation of dust and the like in exhaust gas, the mixed powder can be formed into a plate shape or a honeycomb shape. As described above, in the activated carbon catalyst of the present invention, an activated carbon powder can be made into an arbitrary shape using activated carbon powder as a raw material, which is advantageous from the viewpoint of production cost as well as improvement of activity.
[0021]
If necessary, the obtained molded product may be pulverized to adjust the particle size to an appropriate particle size, and then subjected to a water-repellent treatment. This makes the outer surface of the activated carbon catalyst more water repellent, prevents the formation of a water film on the surface, prevents blockage of the macropore inlet by liquid, and strongly inhibits the invasion of water vapor and aqueous solution from the outside to the inside. . Therefore, active points inside the catalyst are effectively used, and high catalyst performance is obtained. As a method of the water-repellent treatment, a molded product may be impregnated with a dispersion of fine particles of a water-repellent substance or a solution in which the water-repellent substance is dissolved in an organic solvent such as toluene by a spray method or an immersion method. . In this case, as the water repellent substance, a fluororesin is preferable in that it exhibits high adhesion and high water repellency. On the other hand, when an organic solvent solution is used, it is preferable to dissolve a polymer water-repellent substance having a molecular weight of 10,000 or more before use. If the molecular weight is smaller than this, the active sites are unnecessarily covered with the water-repellent substance, and the number of effective active sites decreases. It is preferable that the water-repellent substance is impregnated with 0.1 to 3.5% by weight, preferably 0.2 to 3% by weight.
[0022]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
A commercially available coal-based activated carbon was calcined at 800 ° C. for 1 hour in a nitrogen stream. After 500 g of the obtained activated carbon was pulverized with a commercially available pulverizer, it was subjected to a classification operation for 2 hours with a sieve shaker using a stainless steel sieve (150 μm) to obtain fine powdered activated carbon of 150 μm or less. Next, water was added to a commercially available PTFE dispersion (containing 60% by weight of PTFE particles having a diameter of 0.2 to 0.4 μm) to dilute it 6-fold, and 111 g of the diluted PTFE dispersion and 100 g of the fine powdered activated carbon were added. Is kneaded in a porcelain mortar with a diameter of 300 mm for 10 minutes, and then 500 kgf / cm in a compression molding machine.²  To obtain an activated carbon catalyst containing 10% by weight of PTFE. Further, after drying this activated carbon catalyst at 45 to 50 ° C. for 12 hours, it was roughly crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm.
[0023]
With respect to the activated carbon catalyst of the present invention thus obtained, an activity test was performed using a catalytic sulfation reaction test apparatus while flowing 200 mL / hr of a 5% dilute sulfuric acid aqueous solution through the catalyst layer. Specifically, 40 mL of activated carbon catalyst was charged into a jacketed glass reactor having an inner diameter of 16 mm,
SO₂: 800 ppm by volume
O₂: 4% by volume
CO₂: 10% by volume
N₂: The rest
Relative humidity: 100%
Gas at a temperature of 50 ° C. and 600 dm³/ Hr (SV = 15000 hr^-1) And exit SO₂  SO concentration₂  When the catalytic activity was evaluated by measuring with a meter (ultraviolet or infrared), a desulfurization rate of 42% was obtained 100 hours after the start of the test.
[0024]
Example 2
A mixture of 100 g of fine powdered activated carbon obtained in the same manner as in Example 1 and 111 g of the same diluted PTFE dispersion as in Example 1 was kneaded for 30 minutes in a kneader (capacity: 400 mL, Z-type blade, rotation speed: 43 rpm, power: 250 W). After doing, 500kgf / cm²  To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. The activated carbon catalyst of the present invention thus obtained was subjected to an activity test in the same manner as in Example 1. As a result, a desulfurization rate of 47% was obtained.
[0025]
Example 3
A mixture of 100 g of fine powdered activated carbon obtained in the same manner as in Example 1 and 111 g of the same diluted PTFE dispersion as in Example 1 was kneaded for 30 minutes in a kneader (capacity: 400 mL, Z-type blade, rotation speed: 43 rpm, power: 250 W). Then, it was rolled by a press roll machine (rolls were sequentially rolled at a roll gap of 3 mm, 2 mm, 1.5 mm, and 1 mm), crushed, and then 500 kgf / cm²  To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. The activated carbon catalyst of the present invention thus obtained was subjected to an activity test in the same manner as in Example 1. As a result, a desulfurization rate of 54% was obtained.
[0026]
Example 4
A mixture of 100 g of fine powdered activated carbon obtained in the same manner as in Example 1 and 111 g of the same diluted PTFE dispersion as in Example 1 was kneaded for 30 minutes in a kneader (capacity: 400 mL, Z-type blade, rotation speed: 43 rpm, power: 250 W). After that, the mixture was further kneaded with a three-roll mill (roll size: 63.5 Φ × 150 L, roll rotation speed: 84 rpm, 205 rpm, 500 rpm, power 400 W) for 15 minutes, and 500 kgf / cm.²  To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. The activated carbon catalyst of the present invention thus obtained was subjected to an activity test in the same manner as in Example 1. As a result, a desulfurization rate of 66% was obtained.
[0027]
Example 5
A mixture of 200 g of fine powdered activated carbon obtained in the same manner as in Example 1 and 222 g of the same diluted PTFE dispersion as in Example 1 was kneaded with a roll-type pressure kneader (capacity: 500 mL, rotation speed: 20 rpm, power: 2,000 W) for 15 minutes. After doing, 500kgf / cm²  To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. An activity test was carried out on the thus obtained activated carbon catalyst of the present invention in the same manner as in Example 1. As a result, a desulfurization rate of 68% was obtained.
[0028]
Example 6
Activated carbon ground in the same manner as in Example 1 was classified in the same manner as in Example 1. At this time, by using a combination of sieves having different meshes (0 to 25 μm, 20 to 53 μm, 53 to 106 μm, 106 to 212 μm, 212 to 300 μm, 2800 to 4000 μm), six types of fine powder activated carbon having different average particle diameters can be obtained. Obtained. The same operation (kneading, molding, drying, crushing, and classification) as in Example 3 is performed on each of the six kinds of fine powdered activated carbon and 100 g of each of the same diluted PTFE dispersion liquid as in Example 1 and 111 g of each. As a result, granular activated carbon having a diameter of 2.8 to 4.0 mm and containing 10% by weight of PTFE was obtained.
[0029]
An activity test was performed on each of the thus obtained activated carbon catalysts in the same manner as in Example 1. Table 1 and FIG. 1 show the desulfurization performance of each catalyst 100 hours after the start of the test. From these results, it can be seen that a high desulfurization rate can be obtained when the range of the average particle diameter of the finely powdered activated carbon is 12 to 600 µm, preferably 20 to 200 µm.
[Table 1]

[0030]
Example 7
Activated carbon ground in the same manner as in Example 1 was classified in the same manner as in Example 1 to obtain fine powdered activated carbon. Next, water was added to a commercially available PTFE dispersion (60% by weight) to dilute it 1.5 to 20 times to obtain diluted PTFE dispersions having various concentrations of 3 to 40% by weight. The same operation (mixing, molding, drying, crushing, and classification) as in Example 3 was performed on each of 111 g of each of the diluted PTFE dispersions and 100 g of the above-mentioned fine powdered activated carbon, to reduce the PTFE to 0. Granular activated carbon catalysts having a diameter of 2.8 to 4.0 mm containing various ratios of up to 30% by weight were obtained.
[0031]
An activity test was performed on each of the thus obtained activated carbon catalysts in the same manner as in Example 1. Table 2 and FIG. 2 show the desulfurization performance of each catalyst 100 hours after the start of the test. From these results, it is understood that a high desulfurization rate can be obtained when the addition amount of PTFE kneaded with the fine powder activated carbon is 0.5 to 25% by weight, preferably 1 to 20% by weight.
[Table 2]

[0032]
Example 8
What added 111 g of the same diluted PTFE dispersion liquid as in Example 1 to 100 g of fine powdered activated carbon obtained in the same manner as in Example 1 was used for 10 minutes with a small grinding machine (pot outer diameter: 178 mm, rotation speed: 100 rpm, power: 100 W). After kneading, 500kgf / cm² To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. The activated carbon catalyst of the present invention thus obtained was subjected to an activity test in the same manner as in Example 1, and as a result, a desulfurization rate of 43% was obtained.
[0033]
Example 9
A mixture of 500 g of fine powdered activated carbon obtained in the same manner as in Example 1 and 555 g of the same diluted PTFE dispersion as in Example 1 was mixed for 60 minutes by a V-shaped twin cylindrical mixer (capacity: 1000 mL, rotation speed: 30 rpm). Next, 100 g of the obtained mixture was kneaded for 10 minutes with a small mortar (pot outer diameter 178 mm, rotation number 100 rpm, power 100 W), and then 500 kgf / cm.² To obtain an activated carbon catalyst containing 10% by weight of PTFE. This was dried at 45 to 50 ° C. for 12 hours, crushed and classified to obtain a granular activated carbon catalyst having a diameter of 2.8 to 4.0 mm. The activated carbon catalyst of the present invention thus obtained was subjected to an activity test in the same manner as in Example 1, and as a result, a desulfurization rate of 43% was obtained.
[0034]
Comparative example
The same operation as in Example 1 was performed, except that the mixture was mixed with a V-shaped twin cylindrical mixer for 60 minutes and visually confirmed that the mixture was sufficiently mixed, instead of manually kneading with a mortar. As a result of performing an activity test using the obtained activated carbon catalyst, the desulfurization rate was 18%.
[Brief description of the drawings]
FIG. 1 shows the relationship between the average particle size of fine powdered activated carbon and the desulfurization performance of a catalyst of the present invention obtained using the same.
FIG. 2 shows the relationship between the content of PTFE kneaded with fine powdered activated carbon and the desulfurization performance of the catalyst of the present invention.

Claims

An activated carbon catalyst for bringing into contact with an exhaust gas containing sulfur oxides, adsorbing and oxidizing the sulfur oxides to recover and remove them as sulfuric acid, and having an average particle diameter of 20 to 200 μm, and an activated carbon powder, 1 to 20% by weight of a fluororesin, and the particles or the particle dispersion of the fluororesin are added to the activated carbon powder, and the mixture is kneaded with a shearing force to deform the fluororesin particles. are those obtained by molding into a predetermined shape, is gap formed between the particles of the activated carbon powder, the peripheral wall surface of the gap, so produced sulfuric acid is easily discharged from the gap, the deformed fluororesin particles Activated carbon catalyst characterized by being water repellent.

The fluorine resin is polytetrafluoroethylene, perfluoroalkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer, or trifluoride claim 1, wherein the activated carbon catalyst is ethylene chloride resin.

3. The activated carbon catalyst according to claim 1 , wherein the activated carbon catalyst is subjected to a water-repellent treatment after being formed into a predetermined shape.

The activated carbon catalyst according to any one of claims 1 to 3, is brought into contact with an exhaust gas containing sulfur oxide, and the sulfur oxide in the exhaust gas is adsorbed to the activated carbon catalyst, oxidized, and recovered and removed as sulfuric acid. Flue gas desulfurization method.