JP4065935B2

JP4065935B2 - Method for producing charcoal for adsorption

Info

Publication number: JP4065935B2
Application number: JP2001251336A
Authority: JP
Inventors: 寿宏北村; 裕之片山
Original assignee: National University Corp Shimane University
Current assignee: National University Corp Shimane University
Priority date: 2001-08-22
Filing date: 2001-08-22
Publication date: 2008-03-26
Anticipated expiration: 2021-08-22
Also published as: JP2003054926A

Description

【０００１】
【発明の属する技術分野】
この発明は，廃木材等の木材から吸着性の大きい木炭を製造する吸着用木炭の製造方法に関する。
【０００２】
【従来の技術】
従来，吸着剤としては活性炭が広く利用されてきた。活性炭は，椰子殻等の特殊の植物系材料を原料として一度炭化した後に，これを再度加熱し，水蒸気や二酸化炭素等を含む特定の雰囲気中で賦活を行い製造されている。この場合，原料が特定の原料に限定され，しかも，製造に炭化と賦活の２段階のプロセスを必要とする等の要因があり，木炭の歩留まりが低く，価格が高いものになっている。即ち，活性炭の製造方法は，一般的に，炭化と比表面積を大きくする処理の賦活から成る２段のプロセスで製造しているものである。
【０００３】
また，特開平９−２４１０１４号公報に開示された活性炭の製造方法は，植物系又は鉱物系原料から一段焼成するだけで活性炭を製造するものであり，０．５〜５容量％の酸素を含むガスとの接触の下で，植物系原料を４００℃以上で焼成するものであり，また，鉱物系原料を５００℃以上で焼成するものである。
【０００４】
【発明が解決しようとする課題】
前掲特開平９−２４１０１４号公報に開示された活性炭の製造方法は，酸素と原料との反応が複雑になり，活性炭の歩留まりが必要以上に低下するという間題があり，該公報の明細書中では，炭酸ガスが使用されることが記載されているが，炭酸ガスが不活性ガスとして使用されるものである。上記活性炭の製造方法は，炭化処理する雰囲気が不活性ガスと酸素とからなる雰囲気で，木材の炭化処理が行われているものである。
【０００５】
本発明に係る吸着用木炭の製造方法は、酸素を含有させずに、窒素ガス、アルゴンガス、ヘリウムガス、水素ガス及び一酸化炭素ガスの群からから選択されるガスの少なくとも１種を含む不活性ガスの雰囲気中に，反応ガスとしての二酸化炭素を供給して木材を予め決められた炭化温度に制御し，木材を炭化させると同時に，ＣとＣＯ₂とによる２ＣＯの反応を生じさせて賦活を行わせ，比表面積を増大させるようにした。
【０００６】
この発明は，窒素ガス等の不活性ガスの雰囲気中に，酸素を供給することなく，反応ガスとしての二酸化炭素を供給して木材を予め決められて炭化温度に制御し，前記木材を炭化させると同時に，ＣとＣＯ₂とによる２ＣＯの反応を生じさせて賦活を行わせ，比表面積を増大させることから成る吸着用木炭の製造方法に関する。
【０００７】
この吸着用木炭の製造方法は，前記木材の炭化温度を７００〜１０００℃の範囲内に温度調整して比表面積を増大させる制御を行うものである。
【０００８】
この吸着用木炭の製造方法は，前記不活性ガスとして窒素ガスを使用し，前記窒素ガスに供給される前記反応ガスの前記二酸化炭素の供給量は，１〜１０容量％に制御して前記二酸化炭素を炭化炉内に流通させるものである。
【０００９】
この吸着用木炭の製造方法は，製鋼炉，スクラップ溶解炉，精錬炉，焼却炉，溶融炉等の炉からの排ガスを木材炭化炉へ導き，その熱エネルギーによって前記木材の炭化処理を行うものである。
【００１０】
この吸着用木炭の製造方法は，前記木材として間伐材，端材等の廃木材をサイジングし，前記木材の炭化処理を行って前記木炭及び木酢液を製造するものである。
【００１１】
この吸着用木炭の製造方法は，上記のように構成されているので，窒素ガス等の不活性ガスの雰囲気に反応ガスとしての二酸化炭素を混合し，炭化と賦活を同時に行ったので，活性炭並みの比表面積を持つ木炭を製造することができる。また，この吸着用木炭の製造方法は，木炭の収率を制御することにより，比表面積を制御することが可能である。また，廃木材の有効利用と製鉄炉や焼却炉での排ガス浄化を同時に行うことを着眼し，排ガス吸着用の木炭を廃木材から安価に効率的に製造することが可能になった。その結果，二酸化炭素を利用して炭化を行うことで，吸着用に利用できる比表面積の大きな木炭を製造することができるようになった。
【００１２】
【発明の実施の形態】
以下，図面を参照して，この発明による吸着用木炭の製造方法の実施例を説明する。この発明による吸着用木炭の製造方法は，木材を炭化して木炭を製造し，その木炭を吸着剤として活用するものである。この吸着用木炭の製造方法は，特に，従来の炭化処理と異なって不活性ガスの雰囲気に二酸化炭素を供給して炭化と賦活とを同時に行うという一段階のプロセスで製造することを特徴としています。
【００１３】
この吸着用木炭の製造方法では，スギ材を用いて炭化実験を行い，木炭の比表面積について調査を行ったところ，図３に示すように，木炭の比表面積は，７００−９００℃の炭化温度では，木炭の歩留まりと比表面積が一次の正の相関関係になることが分かった。また，この吸着用木炭の製造方法は，作製した木炭について，従来の活性炭の製造時の３％程度の歩留まりと比較すると，同程度の比表面積を持つ木炭が歩留まり良く製造でき，また，比表面積が木炭の歩留まりで制御することが可能であることが分かった。
【００１４】
この吸着用木炭の製造方法は，主として，窒素ガス等の不活性ガスの雰囲気中に，反応ガスとしての二酸化炭素を供給して木材を予め決められて炭化温度に制御し，前記木材を炭化させると同時に，ＣとＣＯ₂とによる２ＣＯの反応を生じさせて賦活を行わせ，比表面積を増大させるものである。不活性ガスとしては，窒素ガスのほかに，アルゴンガス，ヘリウムガス，水素ガス，一酸化炭素ガスやこれらの混合したガスを利用することができる。また，反応ガスとしては，二酸化炭素のほかに，水蒸気（スチーム）や二酸化炭素と水蒸気を混合したガスを利用することができる。水蒸気の場合，水蒸気（Ｈ₂Ｏ）と木炭中の炭素ＣとによりＨ₂とＣＯが生成する反応が進行し，木炭の賦活が進行する。さらに，焼却炉の燃焼排ガスや金属精錬炉からの排ガスを利用することもできる。
【００１５】
この吸着用木炭の製造方法について，吸着性能の目安として比表面積に着目して，木炭の比表面積に及ぼす二酸化炭素の影響を明らかにするため，スギ材を原料とし窒素＋二酸化炭素の混合ガス気流中で炭化を行い，木炭の比表面積と細孔径分布に及ぼす炭化温度と二酸化炭素濃度の影響について調査した。その結果，木炭の比表面積は，４００〜７００℃の炭化温度では小さく，炭化温度や雰囲気中酸素濃度の影響をほとんど受けないが，炭化温度が７００℃を超えると，木炭の比表面積は，炭化温度の上昇と共に増大し，９００℃で最大となり，１０００℃では減少した。さらに，図３に示すようにこの吸着用木炭の製造方法では，７００〜９００℃の温度範囲内では，木炭の歩留まりと比表面積とは同一の良好な一次の負の相関関係があり，回帰直線の傾きの絶対値は１０００℃の炭化で低下することが分かった。そこで，これを熱力学的な検討から，木炭の比表面積の増大には，Ｃ＋ＣＯ₂＝２ＣＯの反応が関与していると推定されたので，この吸着用木炭の製造方法では，木材の炭化温度を７００〜１０００℃の範囲内に温度調整して比表面積を増大させる制御を行うことにした。
【００１６】
また，この吸着用木炭の製造方法は，具体的には，木材として廃木材を使用し，不活性ガスとして窒素ガスが使用し，窒素ガスに供給される二酸化炭素の供給量を１〜１０容量％に制御して二酸化炭素を炭化炉内に流通させることが有効であった。製鉄炉からの排ガスの熱によって木材の炭化処理を行うことができることも分かった。
【００１７】
この吸着用木炭の製造方法を確立するために，次のようなデータを得た。この吸着用木炭の製造方法によって，木材としてスギ材を使用し，炭化と賦活を同時に行って木炭を製造したところ，窒素と二酸化炭素の混合ガス気流中でスギ材の炭化では，木炭の比表面積に及ぼす炭化温度と二酸化炭素の影響について調査した結果，以下のことが明らかになった。
【００１８】
この吸着用木炭の製造方法で作製した木炭の比表面積は，図２示すように，７００〜９００℃の温度範囲では温度の上昇と共に増大し，炭化温度が９００℃から１０００℃に上昇すると減少する。この傾向は，二酸化炭素の濃度が高いほど顕著であった。また，図３に示すように，７００〜９００℃の温度範囲と，１０００℃の温度での炭化の場合に，木炭の歩留まりが低下するほど，比表面積が増大するという負の相関関係があることが分かった。７００〜９００℃の温度範囲で得られた回帰直線の傾きの絶対値は，窒素と酸素雰囲気での炭化で得られた回帰直線の傾きの絶対値より大きい。木炭の増大には，酸素よりも二酸化炭素が有効である。また，炭化温度７００〜９００℃の温度範囲での木材の炭化では，図３に示すグラフを参照すると，木炭の比表面積は，炭化温度，二酸化炭素の濃度や保持時間の影響を受けず，木炭の歩留まりのみで決定されることが分かった。
【００１９】
図１には，この発明による吸着用木炭の製造方法の一実施例を達成する木炭利用排ガス浄化システムのブロック図が示されている。この木炭利用排ガス浄化システム１は，製鋼炉，スクラップ溶解炉，精錬炉，焼却炉，溶融炉等の炉５の廃熱を利用し，間伐材，端材等の廃木材３を利用するので，極めて安価に木炭を製造し，副産物として木酢液を製造するものである。また，製造された木炭や木酢液は，工業，林業や農業等に利用されるものであり，例えば，木炭は，ガス吸着剤，汚水浄化材等の吸着剤，土壌改良剤等に利用され，また，木酢液は，土壌改良剤，有機農業利用，消毒剤等に利用され，発生した灰は肥料等に利用することができる。
【００２０】
この木炭利用排ガス浄化システム１は，例えば，廃木材３をサイジング４の処理をし，炉５からの排ガス熱をダスト分離機６等を通して木材炭化炉２へ導き，その熱エネルギーによって木材の炭化処理を行って木炭を製造するものであり，副産物として木酢液が製造される。木材炭化炉２からのガスは，ガス冷却・ダスト分離機７を通して木炭吸着塔８へ導き，木炭吸着塔８でダイオキシン，硫化物等の有害物を木炭で吸着浄化処理し，クリーンな排ガスとして煙突等の放出手段９から外部へ排出する。炉５には．スクラップ等の原料１０が投入され，炉５によって溶鋼１１に生成され，発生したスラグ１２やダスト１３は，廃棄又は種々の処理が行われ，含まれている重金属等は回収される。
【００２１】
この吸着用木炭の製造方法によって木材を炭化して木炭を作製するにあたって，木炭炭化炉に窒素と二酸化炭素とのガス気流を作り，コントローラで温度と雰囲気を制御しながら，大容量型の熱天秤装置を用いて木材の重量変化を連続的に測定した。木材としては，十分に乾燥させた市販のスギの心材から一辺が約１０ｍｍの角材を切り出し，炭化用の試料にした。木材の含水率を試験毎に測定した結果１１．０〜１３．６％の範囲であり，試験毎の大きな変化はなかった。主な試験の結果を，表１と表２に示す。この時の炭化温度は４００〜１０００℃とし，雰囲気中の二酸化炭素濃度は１〜１０％とした。
【表１】

【表２】

【００２２】
試料の重量を測定した後，試料をアルミナ製のルツボに入れ，内容積が約９００ｃｍ³の木炭炭化炉内でルツボを天秤で吊るし，外気と遮断した。木炭炭化炉内の雰囲気を一定に保つため，反応によって消費される二酸化炭素を，所定の濃度に保つために木炭炭化炉内に流通した。ガスを流通したまま，１００℃／ｍｉｎの速度で所定の温度まで加熱昇温して所定の時間保持した後，急冷した。この間の試料の重量変化を温度と共に連続的に記録した。また，ガス流量は，炭化が木材中の水分や熱分解物の影響を受けないように１０００ｃｍ³／ｍｉｎに設定した。所定の二酸化炭素濃度のガスは，窒素ガスおよび二酸化炭素ガスを，流量計を用いて所定の割合で流通させ，流量計の出口で混合し，調製した。用いた窒素ガス，二酸化炭素ガスとも，主要な成分の純度が９９．９９％以上であり，露点は−７０℃以下である。窒素ガスは，酸素含有量が１０ｐｐｍ以下の純度を有する。また，試験後に得られた木炭の重量を，水分等の吸着，吸収を受けないように冷却後，直ちに測定した。
【００２３】
また，炭化前試料の重量Ｗ₀（ｇ），含水率μ（％）と木炭の重量Ｗ₀（ｇ）から，下記の式に従って木炭の歩留まりＹ（％）を算出した。
Ｙ＝Ｗｃ／｛Ｗ₀・（１−μ／１００）｝×１００
得られた木炭について，比表面積及び細孔径分布，細孔容積の測定を行なった。木炭をカッターにて３ｍｍ以下に粗粉砕した後，これを相対圧０．２９４で比表面積を測定した。測定した木炭の比表面積と細孔容積の結果と．上記の式から算出した木炭の歩留まりを表１と表２に示した。
【００２４】
表１と表２から分かるように，木炭の歩留まりは，窒素ガスと二酸化炭素との混合ガス雰囲気中での炭化では炭化温度が高くなるほど低下する傾向があることが分かる。また，木炭の歩留まりは，主に，木材の熱分解による揮発分の放出と，炭化雰囲気中の二酸化炭素と木炭との反応による木炭中の炭素の消費とにより決定される。炭化温度の上昇に伴う木炭の歩留まりの低下は，木炭と二酸化炭素との反応の進行に伴う炭素の消費が主な原因と考えられる。
【００２５】
窒素と二酸化炭素の混合ガス雰囲気中で炭化した木炭の比表面積に及ぼす炭化温度の影響は，窒素雰囲気中で炭化した木炭と比較して図２に示す。図２に示すように，４００〜６００℃の温度範囲で炭化した場合には，得られた木炭の比表面積は小さく，また，温度や雰囲気中の二酸化炭素濃度に依存しない傾向が見られた。更に，７００〜１０００℃の温度範囲での炭化では，木炭の比表面積は，炭化温度の上昇と共に増大し９００℃で最大となり，１０００℃で減少する傾向が見られた。この傾向は，二酸化炭素濃度が高くなるほど顕著になる。一方，窒素雰囲気での炭化では，炭化温度の上昇に伴い木炭の比表面積が増大する傾向は見られない。
【００２６】
木炭の比表面積を増大できる炭化条件を，７００〜１０００℃の温度範囲での炭化の場合について検討する。木炭の比表面積と木炭の歩留まり（木炭と雰囲気中の酸素との反応量）との間に相関関係があり，相関関係が炭化温度で異なることが明らかになった。炭化温度において得られた木炭の比表面積と木炭の歩留まりとの関係を図３に示した。図３には，窒素と５％二酸化炭素との雰囲気中で，７００℃で３００分炭化を行った木炭の比表面積の結果も併せて示した。図３に示すように，木炭の歩留まりと比表面積の間には相関関係があることが分かる。特に，７００〜９００℃での炭化では，炭化濃度，雰囲気中の二酸化炭素濃度，保持時間に依存せず，木炭の歩留まりと比表面積とは良好な相関関係があることが分かる。そこで，７００〜９００℃の温度範囲の炭化と１０００℃での炭化結果を分けて，最小二乗法によって求めた回帰直線を図示した。この時の相関係数は，７００〜９００℃での炭化の結果では−０．９２，１０００℃での炭化の結果では−０．８２の値であり，木炭の歩留まりと比表面積とは高い負の相関関係がある。従って，７００〜９００℃の温度範囲の炭化では，木炭の比表面積は，炭化温度，雰囲気中の二酸化炭素濃度，保持時間に依存せず，炭化温度と木炭の歩留まり（木炭と雰囲気中の二酸化炭素との反応量）とで決定されることが分かる。
【００２７】
表１と表２に示すように，同一の炭化温度では，二酸化炭素濃度が高いほど木炭の歩留まりが低下する傾向がある。また，図３に示すように，同一の炭化温度では，木炭の歩留まりと比表面積とは高い負の相関関係にあることが認められた。以上の結果から，図２に示した，７００〜１０００℃の温度範囲での炭化において，木炭の比表面積が炭化温度の上昇と共に増大し，９００℃で最大となり，１２７３Ｋで減少する傾向が見られ，この傾向が二酸化炭素濃度が高くなるほど顕著になるという結果は，雰囲気中の二酸化炭素濃度そのものの影響ではなく，二酸化炭素と木炭との反応量による影響であることが分かる。言い換えると，同一の炭化温度では雰囲気中の二酸化炭素濃度が高いほど，二酸化炭素と木炭との反応速度が速く，保持時間内での反応量が増大（木炭の歩留まりが減少）し，比表面積が大きくなったとことが分かる。
【００２８】
図３に示すように，木炭の歩留まりと比表面積は，負の相関関係を持ち，回帰直線の傾きの絶対値は，炭化温度７００〜９００℃での炭化に比べ，１０００℃では大幅に小さくなる。従って，スギ材を原料にして大きな比表面積を持つ木炭を製造するためには，７００〜９００℃での炭化が有効であり，９００℃以上の高い温度での炭化を避ける温度制御が必要であることが分かる。
【００２９】
次に，木炭の比表面積に及ぼす炭化雰囲気の影響を考察すると次のとおりである。ここで，窒素と酸素雰囲気中で炭化を行った場合を参考にするため，図３に，窒素と酸素との雰囲気中で，９００℃で炭化を行った場合の結果を示している。また，窒素と二酸化炭素との雰囲気中で７００〜９００℃の温度範囲での炭化では，木炭の歩留まりと比表面積との相関関係は，炭化温度の影響を受けない。また，木炭の歩留まりと比表面積との相関関係を示す回帰直線の傾きの絶対値は，窒素と酸素との雰囲気での炭化の結果と比較すると，窒素と二酸化炭素との雰囲気での炭化の場合の方が大きいことが分かる。従って，木炭の比表面積を増大させるためには，窒素と二酸化炭素との雰囲気中での炭化が有効であると言える。
【００３０】
また，木炭の細孔分布と細孔容積に及ぼす炭化温度の影響を考察すると次のとおりである。木炭の細孔容積に及ぼす炭化温度の影響を図４に示す。図４に示すように，細孔容積は炭化温度の上昇と共に緩やかに増大し，７００℃で最大となり，温度の上昇と共に緩やかに低下し，１０００℃で急激に低下する傾向が見られる。また，窒素と５％二酸化炭素との雰囲気中で炭化した木炭の細孔径分布を図５に示す。全ての条件において０．５〜３μｍの細孔が発達していることがわかる。４００〜８００℃の範囲での炭化では，細孔径分布に及ぼす炭化温度の明確な影響は見られない。９００℃の炭化では１〜２μｍでのピークが低下し，１０〜２０μｍのピークが増大する傾向がある。また，１０００℃での炭化では，両方のピークが低下し，１０〜２０μｍのピークが径の小さい方向に移行していることが分かる。１０００℃の炭化では，細孔分布が径の小さい方向に移行し，細孔容積が急激に低下することから，木炭の熱収縮が生じていると考えられる。一方，４００℃の炭化での細孔容積の低下の原因は，表１と表２に示すように，高温での炭化に比べ木炭の歩留まりが高く未炭化物が残留したためと考えられる。
【００３１】
この吸着用木炭の製造方法について，上記の試験より次のことが分かった。
１．４００〜６００℃の温度範囲では，木炭の比表面積は小さく，また，炭化温度や雰囲気中の二酸化炭素濃度に依存しない傾向が見られる。
２．木炭の比表面積は，７００〜９００℃の温度範囲では温度の上昇と共に増大し，炭化温度が９００℃から１０００℃に上昇すると減少する。この傾向は，二酸化炭素濃度が高いほど顕著である。
３．７００〜９００℃の温度範囲で，及び，１０００℃の温度での炭化の場合，それぞれ，木炭の歩留まりが低下するほど比表面積が増大するという負の相関関係がある。７００〜９００℃の温度範囲で得られた回帰直線の傾きの絶対値は，窒素と酸素との雰囲気での炭化の結果と比較すると，窒素と二酸化炭素との雰囲気での炭化結果の方が大きい。即ち，木炭の比表面積の増大には，酸素よりも二酸化炭素が有効である。
４．７００〜９００℃の温度範囲での炭化では，木炭の比表面積は，炭化温度，二酸化炭素濃度，保持時間の影響を受けず，木炭の歩留まりのみで決定される。
５．１０００℃での炭化では，木炭の歩留まりと比表面積の相関関係において，回帰直線の傾きの絶対値が小さくなる傾向が見られる。これは，細孔容積や細孔径分布の結果から，炭化温度の上昇により木炭の熱収縮が生じ，比表面積が低下したことによると考えられる。
６．炭化温度が７００℃を境にして木炭の比表面積が増大する主な原因は，熱力学的な検討から，７００℃より高い温度ではＣ＋ＣＯ₂＝２ＣＯの反応が進行し細孔の生成に関与していることである。
【００３２】
この発明による吸着用木炭の製造方法によって作製した木炭による吸着性能を試験するため，木炭によるブタンガスの吸着性能を試験したところ，図６に示す結果を得た。図６から分かるように，この吸着用木炭の製造方法で製造した木炭は，活性炭のブタンガスの吸着より優れていることが分かる。また，窒素ガスと二酸化炭素とから成る炭化雰囲気は，二酸化炭素が１〜１０％の含有で十分であることが分かる。
【００３３】
【発明の効果】
この発明による吸着用木炭の製造方法は，上記のように構成されているので，木材の炭化処理において，炭化温度を７００℃〜９００℃の温度範囲に制御すれば，二酸化炭素（ＣＯ₂）と木材（Ｃ）とによって一酸化炭素（２ＣＯ）への反応が生じて比表面積の大きい木炭が製造される。
【図面の簡単な説明】
【図１】この発明による吸着用木炭の製造方法の一実施例を達成する木炭利用排ガス浄化システムを説明するブロック図である。
【図２】木炭の比表面積と炭化温度との関係を示すグラフである。
【図３】木炭の比表面積と歩留りとの関係を示すグラフである。
【図４】炭化温度とポア容積との関係を示すグラフである。
【図５】木炭の細孔径分布図である。
【図６】炭化雰囲気における二酸化炭素の濃度と比表面積及び吸着量との関係を示すグラフである。
【符号の説明】
１木炭利用排ガス浄化システム
２木材炭化炉
３廃木材
４サイジング
５製鋼炉，スクラップ溶解炉等の炉
６ダスト分離機
７ガス冷却・ダスト分離機
８木炭吸着塔
９クリーン排ガス放出手段
１０スクラップ原料
１１溶鋼
１２スラグ
１３ダスト[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing charcoal for adsorption, which produces charcoal having high adsorptivity from wood such as waste wood.
[0002]
[Prior art]
Conventionally, activated carbon has been widely used as an adsorbent. Activated carbon is manufactured by carbonizing once a special plant-based material such as coconut shell as a raw material, then heating it again and activating it in a specific atmosphere containing water vapor, carbon dioxide and the like. In this case, the raw material is limited to a specific raw material, and there are factors such as the need for a two-stage process of carbonization and activation for production, and the yield of charcoal is low and the price is high. That is, the method for producing activated carbon is generally produced by a two-stage process consisting of carbonization and activation of treatment for increasing the specific surface area.
[0003]
Moreover, the manufacturing method of the activated carbon disclosed by Unexamined-Japanese-Patent No. 9-241414 manufactures activated carbon only by one-step baking from a plant-type or mineral-type raw material, and contains 0.5-5 volume% oxygen. A plant-based raw material is fired at 400 ° C. or higher under contact with gas, and a mineral-based raw material is fired at 500 ° C. or higher.
[0004]
[Problems to be solved by the invention]
The method for producing activated carbon disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-241414 has the problem that the reaction between oxygen and the raw material becomes complicated, and the yield of activated carbon is unnecessarily lowered. Describes that carbon dioxide is used, but carbon dioxide is used as an inert gas. In the method for producing activated carbon, the carbonization treatment is performed in an atmosphere in which the carbonization treatment includes an inert gas and oxygen.
[0005]
The method for producing charcoal for adsorption according to the present invention does not contain oxygen and contains at least one gas selected from the group consisting of nitrogen gas, argon gas, helium gas, hydrogen gas, and carbon monoxide gas. In the active gas atmosphere, carbon dioxide as a reactive gas is supplied to control the wood to a predetermined carbonization temperature, and the wood is carbonized. At the same time, a 2CO reaction between C and CO ₂ is caused to activate the wood. The specific surface area was increased.
[0006]
The present invention supplies carbon dioxide as a reaction gas without supplying oxygen in an atmosphere of an inert gas such as nitrogen gas to control the wood to a predetermined carbonization temperature and carbonize the wood. At the same time, the present invention relates to a method for producing charcoal for adsorption comprising causing a reaction of 2CO by C and CO ₂ to activate and increasing the specific surface area.
[0007]
In this method for producing charcoal for adsorption, the carbonization temperature of the wood is adjusted within the range of 700 to 1000 ° C. to control to increase the specific surface area.
[0008]
In this method for producing charcoal for adsorption, nitrogen gas is used as the inert gas, and the supply amount of the carbon dioxide of the reaction gas supplied to the nitrogen gas is controlled to 1 to 10% by volume and the carbon dioxide is supplied. Carbon is circulated in the carbonization furnace.
[0009]
This method of producing charcoal for adsorption is a method in which exhaust gas from furnaces such as steel making furnaces, scrap melting furnaces, refining furnaces, incinerators, melting furnaces, etc. is led to a wood carbonization furnace, and the wood is carbonized by its thermal energy. is there.
[0010]
In this method for producing charcoal for adsorption, the wood is sized from waste wood such as thinned wood and milled wood, and the wood is carbonized to produce the charcoal and charcoal vinegar.
[0011]
Since this method for producing charcoal for adsorption is configured as described above, carbon dioxide as a reactive gas is mixed in an inert gas atmosphere such as nitrogen gas, and carbonization and activation are performed simultaneously. A charcoal having a specific surface area can be produced. In addition, in this method for producing adsorption charcoal, the specific surface area can be controlled by controlling the yield of charcoal. In addition, by focusing on the effective use of waste wood and the purification of exhaust gas in iron and incinerators at the same time, it has become possible to produce charcoal for exhaust gas adsorption at low cost and efficiently from waste wood. As a result, charcoal using carbon dioxide can be used to produce charcoal with a large specific surface area that can be used for adsorption.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, with reference to the drawings, an embodiment of the method for producing adsorption charcoal according to the present invention will be described. The method for producing charcoal for adsorption according to the present invention is to charcoal wood to produce charcoal and to use the charcoal as an adsorbent. This method for producing charcoal for adsorption is particularly characterized in that it is produced by a one-step process in which carbon dioxide is supplied to an inert gas atmosphere and carbonization and activation are performed simultaneously, unlike conventional carbonization treatment. The
[0013]
In this method for producing charcoal for adsorption, carbonization experiments were conducted using cedar wood, and the specific surface area of charcoal was investigated. As shown in FIG. 3, the specific surface area of charcoal was measured at a carbonization temperature of 700-900 ° C. Then, it was found that the yield of charcoal and the specific surface area had a first-order positive correlation. In addition, this method of producing charcoal for adsorption can produce charcoal with the same specific surface area with a good yield compared to the yield of about 3% of the conventional activated charcoal. However, it was found that it can be controlled by the yield of charcoal.
[0014]
This method of producing charcoal for adsorption mainly supplies carbon dioxide as a reaction gas in an atmosphere of an inert gas such as nitrogen gas, and wood is carbonized in advance by controlling the wood to a predetermined carbonization temperature. At the same time, a reaction of 2CO with C and CO ₂ is caused to activate and increase the specific surface area. As the inert gas, in addition to nitrogen gas, argon gas, helium gas, hydrogen gas, carbon monoxide gas, or a mixed gas thereof can be used. As the reactive gas, in addition to carbon dioxide, steam (steam) or a gas in which carbon dioxide and water vapor are mixed can be used. In the case of steam, the reaction in which H ₂ and CO are generated by steam (H ₂ O) and carbon C in the charcoal proceeds, and the activation of charcoal proceeds. In addition, exhaust gas from incinerators and exhaust gas from metal refining furnaces can be used.
[0015]
In order to clarify the effect of carbon dioxide on the specific surface area of charcoal, focusing on the specific surface area as a measure of the adsorption performance for this method of producing charcoal for adsorption, a mixed gas stream of nitrogen + carbon dioxide using cedar wood as a raw material The effect of carbonization temperature and carbon dioxide concentration on the specific surface area and pore size distribution of charcoal was investigated. As a result, the specific surface area of charcoal is small at the carbonization temperature of 400 to 700 ° C. and is hardly affected by the carbonization temperature and the oxygen concentration in the atmosphere, but when the carbonization temperature exceeds 700 ° C., the specific surface area of charcoal is It increased with increasing temperature, reached a maximum at 900 ° C, and decreased at 1000 ° C. Furthermore, as shown in FIG. 3, in this method for producing charcoal for adsorption, within the temperature range of 700 to 900 ° C., the yield of charcoal and the specific surface area have the same good first-order negative correlation, and the regression line It was found that the absolute value of the slope decreased with carbonization at 1000 ° C. Therefore, it was estimated from the thermodynamic investigation that the reaction of C + CO ₂ = 2CO was involved in the increase of the specific surface area of charcoal. In this method of producing charcoal for adsorption, the carbonization temperature of wood Was controlled to increase the specific surface area by adjusting the temperature within the range of 700 to 1000 ° C.
[0016]
In addition, the method for producing the charcoal for adsorption specifically uses waste wood as wood, uses nitrogen gas as an inert gas, and adjusts the supply amount of carbon dioxide supplied to the nitrogen gas to 1 to 10 volumes. It was effective to circulate carbon dioxide in the carbonization furnace while controlling it to%. It was also found that wood can be carbonized by the heat of the exhaust gas from the iron making furnace.
[0017]
The following data were obtained in order to establish a method for manufacturing this charcoal for adsorption. By this method of producing charcoal for adsorption, cedar wood was used as wood, and charcoal was activated and activated simultaneously to produce charcoal. The carbonization of cedar wood in a mixed gas stream of nitrogen and carbon dioxide resulted in the specific surface area of charcoal. As a result of investigating the effects of carbonization temperature and carbon dioxide on the following, the following was clarified.
[0018]
As shown in FIG. 2, the specific surface area of the charcoal produced by this adsorption charcoal manufacturing method increases with increasing temperature in the temperature range of 700 to 900 ° C., and decreases when the carbonizing temperature increases from 900 ° C. to 1000 ° C. . This tendency was more prominent as the concentration of carbon dioxide was higher. Further, as shown in FIG. 3, in the case of carbonization at a temperature range of 700 to 900 ° C. and carbonization at a temperature of 1000 ° C., there is a negative correlation that the specific surface area increases as the yield of charcoal decreases. I understood. The absolute value of the slope of the regression line obtained in the temperature range of 700 to 900 ° C. is larger than the absolute value of the slope of the regression line obtained by carbonization in a nitrogen and oxygen atmosphere. Carbon dioxide is more effective than oxygen for increasing charcoal. In the case of carbonization of wood at a carbonization temperature range of 700 to 900 ° C., referring to the graph shown in FIG. 3, the specific surface area of charcoal is not affected by the carbonization temperature, the concentration of carbon dioxide or the holding time. It was found that it was determined only by the yield.
[0019]
FIG. 1 shows a block diagram of an exhaust gas purification system using charcoal that achieves an embodiment of a method for producing adsorption charcoal according to the present invention. This exhaust gas purification system 1 using charcoal uses waste heat from a furnace 5 such as a steelmaking furnace, scrap melting furnace, refining furnace, incinerator, melting furnace, etc., and uses waste wood 3 such as thinned wood, scraps, etc. Charcoal is produced at a very low cost, and wood vinegar is produced as a by-product. The manufactured charcoal and vinegar are used in industry, forestry, agriculture, etc. For example, charcoal is used in gas adsorbents, adsorbents such as sewage purification materials, soil conditioners, etc. In addition, wood vinegar is used as a soil conditioner, organic agricultural use, disinfectant, etc., and the generated ash can be used as a fertilizer.
[0020]
In this charcoal exhaust gas purification system 1, for example, waste wood 3 is treated with sizing 4 and exhaust gas heat from the furnace 5 is guided to a wood carbonization furnace 2 through a dust separator 6 or the like, and the wood is carbonized by the thermal energy. The charcoal is produced as a by-product. The gas from the wood carbonization furnace 2 is guided to the charcoal adsorption tower 8 through the gas cooling / dust separator 7, and the charcoal adsorption tower 8 adsorbs and purifies harmful substances such as dioxins and sulfides with the charcoal to obtain a chimney as a clean exhaust gas. Or the like from the discharge means 9 such as In the furnace 5. Raw material 10 such as scrap is charged, and the slag 12 and dust 13 generated in the molten steel 11 by the furnace 5 are discarded or subjected to various treatments, and the contained heavy metals are recovered.
[0021]
When producing charcoal by carbonizing wood using this method of producing charcoal for adsorption, a gas flow of nitrogen and carbon dioxide is created in the charcoal carbonization furnace, and the temperature and atmosphere are controlled by the controller, and a large-capacity thermobalance The weight change of the wood was continuously measured using the apparatus. As wood, a square material having a side of about 10 mm was cut out from a commercially available cedar core material which had been sufficiently dried, and used as a sample for carbonization. As a result of measuring the moisture content of wood for each test, it was in the range of 11.0 to 13.6%, and there was no significant change from test to test. Tables 1 and 2 show the results of the main tests. The carbonization temperature at this time was 400 to 1000 ° C., and the carbon dioxide concentration in the atmosphere was 1 to 10%.
[Table 1]

[Table 2]

[0022]
After measuring the weight of the sample, the sample was placed in an alumina crucible, and the crucible was hung with a balance in a charcoal carbonization furnace having an internal volume of about 900 cm ³ to block it from the outside air. In order to keep the atmosphere inside the charcoal carbonization furnace constant, the carbon dioxide consumed by the reaction was circulated in the charcoal carbonization furnace in order to maintain a predetermined concentration. With the gas flowing, the temperature was raised to a predetermined temperature at a rate of 100 ° C./min and held for a predetermined time, followed by rapid cooling. During this time, the weight change of the sample was recorded continuously with temperature. The gas flow rate was set to 1000 cm ³ / min so that carbonization would not be affected by moisture or pyrolysis products in the wood. A gas having a predetermined carbon dioxide concentration was prepared by circulating nitrogen gas and carbon dioxide gas at a predetermined ratio using a flow meter and mixing them at the outlet of the flow meter. Both the nitrogen gas and carbon dioxide gas used have a purity of 99.99% or more and a dew point of −70 ° C. or less. Nitrogen gas has a purity with an oxygen content of 10 ppm or less. In addition, the weight of charcoal obtained after the test was measured immediately after cooling so as not to absorb or absorb moisture.
[0023]
Further, the yield Y (%) of charcoal was calculated from the weight W ₀ (g) of the sample before carbonization, the moisture content μ (%) and the weight W ₀ (g) of charcoal according to the following formula.
Y = Wc / {W _0. (1-μ / 100)} × 100
The obtained charcoal was measured for specific surface area, pore size distribution, and pore volume. After the charcoal was coarsely pulverized to 3 mm or less with a cutter, the specific surface area was measured at a relative pressure of 0.294. Results of specific surface area and pore volume of charcoal measured. Tables 1 and 2 show the charcoal yield calculated from the above formula.
[0024]
As can be seen from Tables 1 and 2, the yield of charcoal tends to decrease as the carbonization temperature increases in carbonization in a mixed gas atmosphere of nitrogen gas and carbon dioxide. Moreover, the yield of charcoal is mainly determined by the release of volatiles by pyrolysis of wood and the consumption of carbon in charcoal by the reaction of carbon dioxide and charcoal in a carbonizing atmosphere. The decrease in the yield of charcoal due to the increase in the carbonization temperature is thought to be mainly due to the consumption of carbon as the reaction between charcoal and carbon dioxide proceeds.
[0025]
The effect of carbonization temperature on the specific surface area of charcoal carbonized in a mixed gas atmosphere of nitrogen and carbon dioxide is shown in FIG. 2 in comparison with charcoal carbonized in nitrogen atmosphere. As shown in FIG. 2, when carbonized in a temperature range of 400 to 600 ° C., the obtained charcoal had a small specific surface area, and a tendency not to depend on the temperature and the carbon dioxide concentration in the atmosphere was observed. Furthermore, in the carbonization in the temperature range of 700 to 1000 ° C., the specific surface area of charcoal increased with the increase of the carbonization temperature, reached a maximum at 900 ° C. and decreased at 1000 ° C. This tendency becomes more prominent as the carbon dioxide concentration increases. On the other hand, in carbonization in a nitrogen atmosphere, there is no tendency for the specific surface area of charcoal to increase as the carbonization temperature increases.
[0026]
The carbonization conditions that can increase the specific surface area of charcoal will be examined in the case of carbonization in the temperature range of 700 to 1000 ° C. It was found that there is a correlation between the specific surface area of charcoal and the yield of charcoal (the amount of reaction between charcoal and atmospheric oxygen), and the correlation varies with the carbonization temperature. The relationship between the specific surface area of charcoal obtained at the carbonization temperature and the yield of charcoal is shown in FIG. FIG. 3 also shows the results of the specific surface area of charcoal that was carbonized at 700 ° C. for 300 minutes in an atmosphere of nitrogen and 5% carbon dioxide. As shown in FIG. 3, it can be seen that there is a correlation between the yield of charcoal and the specific surface area. In particular, carbonization at 700 to 900 ° C. does not depend on the carbonization concentration, the carbon dioxide concentration in the atmosphere, and the retention time, and it can be seen that there is a good correlation between the yield of charcoal and the specific surface area. Therefore, the regression line obtained by the least square method is illustrated by separating the carbonization in the temperature range of 700 to 900 ° C and the carbonization result at 1000 ° C. The correlation coefficient at this time is -0.92 for the result of carbonization at 700 to 900 ° C and -0.82 for the result of carbonization at 1000 ° C, and the charcoal yield and specific surface area are negative. There is a correlation. Therefore, in carbonization in the temperature range of 700 to 900 ° C., the specific surface area of charcoal does not depend on the carbonization temperature, the carbon dioxide concentration in the atmosphere, and the holding time, and the carbonization temperature and the yield of charcoal (carbon dioxide in the charcoal and atmosphere). The amount of reaction with
[0027]
As shown in Tables 1 and 2, at the same carbonization temperature, the yield of charcoal tends to decrease as the carbon dioxide concentration increases. In addition, as shown in FIG. 3, it was recognized that the yield of charcoal and the specific surface area had a high negative correlation at the same carbonization temperature. From the above results, in the carbonization in the temperature range of 700 to 1000 ° C. shown in FIG. 2, the specific surface area of charcoal increases with increasing carbonization temperature, reaches a maximum at 900 ° C., and decreases at 1273K. , It can be seen that the result that this tendency becomes more prominent as the carbon dioxide concentration becomes higher is not the influence of the carbon dioxide concentration itself in the atmosphere, but the influence of the reaction amount of carbon dioxide and charcoal. In other words, at the same carbonization temperature, the higher the carbon dioxide concentration in the atmosphere, the faster the reaction rate between carbon dioxide and charcoal, and the amount of reaction within the holding time increases (the yield of charcoal decreases), and the specific surface area increases. You can see that it has grown.
[0028]
As shown in FIG. 3, the yield and specific surface area of charcoal have a negative correlation, and the absolute value of the slope of the regression line is significantly smaller at 1000 ° C. than at carbonization temperature of 700 to 900 ° C. . Therefore, in order to produce charcoal with a large specific surface area using cedar as a raw material, carbonization at 700 to 900 ° C. is effective, and temperature control to avoid carbonization at a high temperature of 900 ° C. or higher is necessary. I understand that.
[0029]
Next, the effect of the carbonization atmosphere on the specific surface area of charcoal is considered as follows. Here, in order to refer to the case where carbonization is performed in a nitrogen and oxygen atmosphere, FIG. 3 shows the result when carbonization is performed at 900 ° C. in an atmosphere of nitrogen and oxygen. Further, in carbonization in a temperature range of 700 to 900 ° C. in an atmosphere of nitrogen and carbon dioxide, the correlation between the yield of charcoal and the specific surface area is not affected by the carbonization temperature. In addition, the absolute value of the slope of the regression line indicating the correlation between the charcoal yield and the specific surface area is compared with the result of carbonization in an atmosphere of nitrogen and oxygen in the case of carbonization in an atmosphere of nitrogen and carbon dioxide. It can be seen that is larger. Therefore, it can be said that carbonization in an atmosphere of nitrogen and carbon dioxide is effective for increasing the specific surface area of charcoal.
[0030]
The effect of carbonization temperature on the pore distribution and pore volume of charcoal is considered as follows. The effect of carbonization temperature on the pore volume of charcoal is shown in FIG. As shown in FIG. 4, the pore volume gradually increases with increasing carbonization temperature, reaches a maximum at 700 ° C., gradually decreases with increasing temperature, and rapidly decreases at 1000 ° C. FIG. 5 shows the pore size distribution of charcoal carbonized in an atmosphere of nitrogen and 5% carbon dioxide. It can be seen that 0.5 to 3 μm pores are developed under all conditions. In the carbonization in the range of 400 to 800 ° C., no clear influence of the carbonization temperature on the pore size distribution is observed. Carbonization at 900 ° C. tends to decrease the peak at 1 to 2 μm and increase the peak at 10 to 20 μm. Moreover, in carbonization at 1000 degreeC, it turns out that both peaks fall and the peak of 10-20 micrometers has shifted to the direction where a diameter is small. In carbonization at 1000 ° C., the pore distribution shifts in the direction of decreasing diameter, and the pore volume rapidly decreases, so it is considered that thermal contraction of charcoal has occurred. On the other hand, as shown in Tables 1 and 2, the cause of the decrease in pore volume due to carbonization at 400 ° C. is considered to be that the yield of charcoal is higher than that at high temperature and uncarburized remains.
[0031]
About the manufacturing method of this charcoal for adsorption | suction, the following thing was understood from said test.
1. In the temperature range of 400 to 600 ° C., the specific surface area of charcoal is small, and a tendency not to depend on the carbonization temperature or the carbon dioxide concentration in the atmosphere is observed.
2. The specific surface area of charcoal increases with increasing temperature in the temperature range of 700-900 ° C, and decreases when the carbonizing temperature increases from 900 ° C to 1000 ° C. This tendency becomes more remarkable as the carbon dioxide concentration increases.
3. In the case of carbonization at a temperature range of 700 to 900 ° C. and 1000 ° C., there is a negative correlation that the specific surface area increases as the yield of charcoal decreases. The absolute value of the slope of the regression line obtained in the temperature range of 700 to 900 ° C. is larger in the carbonization result in the atmosphere of nitrogen and carbon dioxide than in the result of carbonization in the atmosphere of nitrogen and oxygen. . That is, carbon dioxide is more effective than oxygen for increasing the specific surface area of charcoal.
4. In carbonization in the temperature range of 700 to 900 ° C., the specific surface area of charcoal is not affected by the carbonization temperature, carbon dioxide concentration, and holding time, and is determined only by the yield of charcoal.
5. In carbonization at 1000 ° C., the absolute value of the slope of the regression line tends to decrease in the correlation between the charcoal yield and the specific surface area. From the results of pore volume and pore size distribution, this is thought to be due to the thermal shrinkage of charcoal caused by the increase in carbonization temperature and the reduction in specific surface area.
6). The main reason for the increase in the specific surface area of charcoal when the carbonization temperature reaches 700 ° C is that the reaction of C + CO ₂ = 2CO proceeds at a temperature higher than 700 ° C and participates in pore formation from a thermodynamic study. It is that.
[0032]
In order to test the adsorption performance of charcoal produced by the method for producing charcoal for adsorption according to the present invention, the adsorption performance of butane gas by charcoal was tested, and the results shown in FIG. 6 were obtained. As can be seen from FIG. 6, the charcoal produced by this method for producing charcoal for adsorption is superior to the adsorption of activated carbon butane gas. Moreover, it turns out that the carbonization atmosphere consisting of nitrogen gas and carbon dioxide is sufficient if the carbon dioxide content is 1 to 10%.
[0033]
【The invention's effect】
Since the method for producing the charcoal for adsorption according to the present invention is configured as described above, if the carbonization temperature is controlled in a temperature range of 700 ° C. to 900 ° C. in the carbonization treatment of wood, carbon dioxide (CO ₂ ) and The wood (C) reacts with carbon monoxide (2CO) to produce charcoal having a large specific surface area.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a block diagram for explaining an exhaust gas purification system using charcoal that achieves one embodiment of a method for producing charcoal for adsorption according to the present invention.
FIG. 2 is a graph showing the relationship between the specific surface area of charcoal and the carbonization temperature.
FIG. 3 is a graph showing the relationship between the specific surface area of charcoal and the yield.
FIG. 4 is a graph showing the relationship between carbonization temperature and pore volume.
FIG. 5 is a pore size distribution chart of charcoal.
FIG. 6 is a graph showing the relationship between the concentration of carbon dioxide, the specific surface area, and the amount of adsorption in a carbonized atmosphere.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Charcoal use exhaust gas purification system 2 Wood carbonization furnace 3 Waste wood 4 Sizing 5 Steelmaking furnace, scrap melting furnace, etc. 6 Dust separator 7 Gas cooling / dust separator 8 Charcoal adsorption tower 9 Clean exhaust gas discharge means 10 Scrap raw material 11 Molten steel 12 Slag 13 Dust

Claims

Carbon dioxide as a reactive gas in an inert gas atmosphere containing at least one gas selected from the group consisting of nitrogen gas, argon gas, helium gas, hydrogen gas, and carbon monoxide gas without containing oxygen the timber to supply, and the temperature adjusted to the range of 800 to 900 ° C., the wood and at the same time carbonized, to perform the activation by causing reaction of 2CO by the C and CO _2, increasing the specific surface area A method for producing charcoal for adsorption, which comprises increasing the specific surface area by performing control.

Nitrogen gas is used as the inert gas, and the supply amount of the carbon dioxide of the reaction gas supplied to the nitrogen gas is controlled to 1 to 10% by volume, and the carbon dioxide is circulated in the carbonization furnace. The method for producing charcoal for adsorption according to claim 1 , comprising:

The method for producing charcoal for adsorption according to claim 1 or 2 , wherein the exhaust gas from the furnace is guided to a wood carbonization furnace, and the wood is carbonized by its thermal energy.

The method for producing charcoal for adsorption according to any one of claims 1 to 3 , wherein the wood is obtained by sizing waste wood and carbonizing the wood to produce the charcoal and charcoal vinegar. .