JP4418854B2 - Organic waste treatment methods - Google Patents

Description

【００３１】
例えば，植物性物質の主成分は一般式として(C_ｎH_2mO_m)_Nで表わされる多糖類であり，酸化反応は，(C_ｎH_2mO_m)＋ｎO₂→ｎCO₂+ｍH₂Oのように進行し，完全酸化に必要な酸素分子は炭素のモル数と1：1に近い比になると推測される。すなわち，酸素供給率100％の時に酸素は十分と予測される。
【００３２】
〔実験装置および実験手順〕
実験に用いた小型反応容器と加熱炉の概要を図1および図2にそれぞれ示す。小型反応容器１の内容積は47mlであり，反応室２の内張り３の材質はハステロイC-276である。加熱炉４は，毎分100℃の高速昇温が可能な商用電源を利用した誘導加熱方式のものである。
【００３３】
実験手順について図3に示す。実験試料には未乾燥のものを用いたが 試料量は乾燥重量で0.5ｇとした。まずこれを反応容器１に過酸化水素水と共に入れ素早く高圧バルブ５を取り付け密閉した。次に反応容器１を誘導加熱炉４に設置し，振とうさせながら昇温速度40℃／minで加熱した。所定の時間経過後，反応容器１を誘導加熱炉４からすばやく取り出し，ファンで冷却した。100℃程度にまで冷却するに要した時間は加熱に要した時間と同程度である。冷却後，まず発生ガスを採取した。ガス採取は，高圧バルブ５のガス取出し口６にチュ−ブを取り付け，水上置換により行った。炭酸ガスの水への溶解を極力避けるため，置換水に飽和食塩水を用いた。発生ガス量は1000mlメスシリンダで測定した。続いて反応容器を開けてビ−カに反応後の液を移し，この溶液の分析を行った。TOCを測定した後，その成分をGC-MSにより分析した。
【００３４】
〔実験条件〕
実験条件を表2 にまとめて示す。生ごみの種類による反応性の相違を調べるために，基準反応条件下で実験を行った。また，野菜類の人参，肉類の牛脂および魚類のトロを取り上げ，反応温度，反応時間，酸素供給率および水充填率の影響を調べるために，それぞれ表2に示すような範囲で実験を行った。
【００３５】
【表２】

【００３６】
基準条件については，酸化発熱により反応温度が変化しないようにするため試料量は乾燥重量で0.5ｇ一定とし(実験に用いた試料は乾燥させていないものである)，反応時間(所定温度到達後の保持時間)は10分とした。反応温度は植物性生ごみと動物性生ごみにおいてそれぞれ400℃と420℃とした。酸素供給率は植物性生ごみの場合100％，動物性生ごみの場合150％とした。水の充填率 (反応容器の全容積に対する蒸留水と過酸化水素との混合物（過酸化水素水）の割合) は30％とした。
【００３７】
〔実験結果（植物性生ゴミ）〕
表3に，酸素供給率を100％とした場合，反応温度400℃，反応時間10分の条件下で得られた結果を示す。液相の残存TOC測定値から求めたTOC分解率が99.5％になりほぼ完全分解が得られた。その時のガス組成もほとんどが二酸化炭素で，不完全酸化による一酸化炭素は僅か存在しているが炭化水素は検出されなかった。これらの結果から，多糖類を主成分とする植物性生ごみについては 酸素供給率が100％で酸素量は十分であると考えられる。
【００３８】
【表３】

【００３９】
〔植物性生ごみの種類による反応性の相違〕
基準反応条件下で，植物性生ごみの種類による反応性の相違を調べた結果を表4に示す。どの植物性生ごみの場合も99.6％程度のTOC分解率が得られた。
また，発生ガス組成もほとんどが二酸化炭素であった。このことから，これらの植物性生ごみは酸化されやすく，10分以内にどの試料もほぼ完全酸化分解することが分かった。また，この条件では植物性生ごみの種類による酸化分解率の相違はほとんど見られなかった。
【００４０】
各試料とも反応後の液相のpHは5.5−6.1で弱酸性を示した。GC-MSにより液相の生成物を分析した結果，どの試料においても，酢酸のピークのみが検出された。したがって，液相の酸性は残存している酢酸のためと考えられた。
【００４１】
以上の結果から，植物性生ごみは酸化され易く，種類による酸化分解のしやすさの相違はほとんどみられず，400℃では反応時間10分で99.6％程度の高TOC分解率が得られることがわかった。
【００４２】
〔反応パラメーターの影響（植物性生ゴミ）〕
表4に示したように，植物性生ごみの種類により分解率や未分解残存有機物に相違が認められなかった。そこで人参を代表として取り上げ，反応パラメーターの影響について検討した。酸素供給率が100％で酸素量はほぼ十分であることが分かったので，以下の反応温度と反応時間の検討は酸素供給率100%の条件下で行った。
【００４３】
【表４】

【００４４】
〔反応温度の影響〕
反応時間を10分とし，反応温度を380−450℃で変化させた場合の酸化分解率に及ぼす反応温度の影響を図4に示す。380℃では，TOC分解率は94.7％と比較的低いが，400℃になると急激に99％以上に上昇し，さらに温度が450℃まで上がるとこの分解率はほとんど100%になった。このことから，温度の上昇によって酸化反応が強く促進されるものの反応時間を10分とした場合に分解率が99％以上となる温度は400℃以上であることが分かった。
【００４５】
〔反応時間の影響〕
反応温度400℃において，反応時間を0−20分の範囲で変化させ，TOC分解率に及ぼす影響を調べた結果を図5に示す。 誘導加熱炉を用いて所定の温度に達するまでの昇温過程および冷却過程にそれぞれ10分程度を要するため短い反応時間での結果には誤差が大きいと考えられるが，図4に示すように，反応時間0すなわち昇温して所定の温度に到達後直ちに冷却した場合においてもTOC分解率は92−93％になった。このことから，所定の温度に達する前の昇温過程において反応はすでに開始し，かなりの程度進行していると考えられる。また，所定の温度に達した後，TOC分解率は反応時間の増加とともに増加し，10分で99.5％となるが，その後の変化は遅くなる。これらの結果から，99％以上のTOC分解率を得るためには，400℃の条件下で，約10分の反応時間が必要であるが，反応時間をさらに長くしても，分解率を上昇させる効果は小さいことが分かった。これは残存する酢酸が難分解であることによると考えられる。
【００４６】
〔酸素供給率の影響〕
図6(a)に，反応温度420℃，反応時間10分で， TOC分解率に及ぼす酸素供給率の影響を調べた結果を示す。酸素供給率が50％の時は， TOC分解率は76.3％で低い。その時のガス組成を図6(b)に示す。 酸素は残っておらずしかも不完全酸化分解で生成する一酸化炭素と炭化水素(メタン)が多量検出されている。 酸素供給率を100％にまで増加させると99.86％の分解率が得られ，さらに200％にまで増加させるとTOC分解率は99.99％になり，酸素供給率の増加によって酢酸の分解がさらに進行したことが分かる。
【００４７】
酸素供給率50％の場合に，TOC分解率は50％以上の76.3％になった。これは，図6(b)に示すように，一酸化炭素とメタンの生成によって液相中の有機炭素が減少したことによる。この場合について反応後の炭素の分布をみると，液相中に全体の約1/4が存在し，気体として約3/4が存在している。さらに，発生したガス組成をみると，CO₂:CO:CH₄≒74:22:4であった。
【００４８】
〔肉類生ごみの湿式酸化〕
〔完全分解に必要な酸素供給率〕
完全分解に要する酸素供給率を検討するために，牛脂を試料とし，反応温度を450℃と高くして，反応時間10分で，酸素供給率を100乃至150％の範囲で変化させて実験を行った。この結果を図7に示す。図7(a)に示すように，酸素供給率を100%から150％まで増加させるとTOC分解率は84.5%から99.0％に増加した。
すなわち，酸素供給率が100％と120％では牛脂を完全酸化するに必要な酸素量を満たしていない。このことは，図7(b)に示すように発生ガス中に不完全酸化分解による一酸化炭素と炭化水素(メタン)が検出されたことからも確かめられた。酸素供給率が150%になると，一酸化炭素ならびに炭化水素はほとんど検出されず，酸素量はほぼ十分になることを示している。
【００４９】
これは，酸素供給率が炭素を基準として決めたものであるためで，実際には，水素とその他の元素も酸素を消費することによる。前述したように植物性のものは主成分が多糖類であるので，元素組成として酸素と水素はH₂Oとしてほぼバランスしているから，酸素供給率が100％で十分である。しかし，牛脂の主成分である脂肪はグリセリンと高級脂肪酸が脱水して結合した化合物グリセリドであり，その炭素と水素の比はほぼ1：2であるので， (CH₂)_n+1.5O₂=nH₂O+nCO₂のように酸化されるに必要な酸素分子は炭素のモル数の約1.5倍になる。したがって，牛脂の場合，酸素供給率150％で酸素がほぼ十分になるものと考えられる。
【００５０】
また，蛋白質はポリアミドで，この単量体はα−アミノカルボン酸であるから，蛋白質を主成分とする肉類についても炭素と水素の比はほぼ1：2である。そこで， 酸素供給率を150％に設定し，反応時間10分，温度420℃の条件下で，豚もも肉について実験を行った。得られたTOC分解率は99.25％であり，蛋白質の場合も， 酸素供給率150％で酸素が十分であることが分かった。
【００５１】
酸素供給率150％の状態で酸素が十分であることが明らかとなったことから，以下の検討は酸素供給率150％の条件下で行った。
〔肉類生ごみの種類による反応性の相違〕
肉類生ごみの種類による反応性の相違を調べた結果を表5に示す。まず，TOC分解率についてみると，豚肉類と牛肉類は99％以上，鳥肉類は98%台，脂肪を主成分とするものは96.5−97.5％である。これらは，反応温度が420℃であるにもかかわらず400℃の食物性生ごみの分解率に比べて少し低い。反応後のガス組成については，酸素のほかは二酸化炭素がほとんどであった。これらの結果から，肉類生ごみも酸化されるが，植物性生ごみに比べると難分解であること，また，肉類生ごみの中で蛋白質を主成分とする蛋白質類と脂肪を主成分とする油脂類とを比較すると，後者の方がTOC分解率が低く，そのなかでも牛脂のTOC分解率が最も低いことが分かった。
【００５２】
【表５】

【００５３】
次に，反応後の液相のpHについてみると, 油脂類の反応後の溶液のpHが最も低く，3台の酸性である。また蛋白質類の反応後の溶液のpHは６前後で中性付近である。これについて，GC-MSにより液相の生成物を分析した。その結果，どの試料においても酢酸のみのピークが見られた。したがって，酸性になった理由は酢酸の残存によることがわかった。
【００５４】
〔牛脂の酸化分解性〕
上述のように，肉類生ごみ中では油脂，特に牛脂が酸化分解を受けにくいことが分かった。そこで，牛脂を対象として，反応温度，反応時間，酸素供給率および水充填率の影響を調べた。
【００５５】
〔反応温度の影響〕
図8(a)に TOC分解率に及ぼす反応温度の影響を示す。420℃以下ではTOC分解率は97％以下と比較的低いが，450℃になると99％以上に上昇し，さらに温度が470℃まで上がるとこの分解率はほとんど100％になった。このことから，牛脂の場合，温度上昇により酸化反応が強く促進されるものの，反応時間10分で分解率が99％以上となる温度は450℃以上であることが分かった。これは動物性有機物を酸化する場合大量の酢酸を生成し，酢酸は酸化を受けにくいためより高い温度が必要であることによると考えられる。
【００５６】
〔反応時間の影響〕
図9に，反応温度を450℃とした場合のTOC分解率に及ぼす反応時間の影響を示す。反応時間0分においてTOC分解率は約95％であり，5分で分解率は99%になるが，その後の変化は遅くなる。この結果を図5に示す人参の場合と比較すると，反応時間5分まではTOC分解率は牛脂の方が高く，これは，反応温度の相違によるものと考えられる。しかしそれ以降では牛脂の分解率が低くなっており，これは，TOCのほとんどを占める酢酸の生成が牛脂の場合に多く，この分解が困難であることによると考えられる。
【００５７】
〔残存TOC(酢酸)の分解〕
温度の上昇により残存TOC即ち酢酸の酸化分解が促進されることが分かったが，供給酸素量を増加させることによっても酢酸の分解を促進させることが可能と考えられる。そこで残存酢酸をさらに分解させる条件について検討を行った。
【００５８】
図10は酸素供給率が150％と200％の場合について，TOC分解率の温度依存性を調べた結果である。この結果から，温度の増加により残存TOCは減少するが，酸素供給率の増加によっても残存TOCを大幅に減少させることができることがわかる。例えば，420℃で酸素供給率が150％の場合，TOCは約1000ppm即ちTOC分解率は96％と低い。しかし，酸素供給率を200％に増加させると，約250ppm(TOC分解率99％以上)になった。さらに，温度450℃で，酸素供給率を150％から200％に増加させるとTOCは250から20ppmまで減少し，TOC分解率は99.1％から99.9％まで増加した。このように，油脂の酸化分解では多量の酢酸が生成するが，分解率をさらに上げる必要がある場合は反応温度の上昇あるいは過剰酸素の供給によって可能であることが分かった。
【００５９】
〔魚類生ごみの湿式酸化〕
〔魚の種類による反応性の相違〕
酸化分解率に及ぼす魚の種類の影響，および酸素供給率の影響を図11に示す。まず，魚の種類によるTOC分解率への影響についてみると，酸素供給率が150％以上の場合，大きな違いが見られなかった。 酸素供給率100％の場合にマグロ赤身の分解率が高いのは，難分解の脂肪分が少ないためと考えられる。
【００６０】
次に，酸素供給率によるTOC分解率への影響について見ると， 酸素供給率100％の場合はどの試料のTOC分解率も低いが，酸素供給率が150％になると約99％になる。これは魚身も蛋白質と脂肪を主体としているので肉類と同様に酸素供給率150%で酸素が十分になることを示している。このことは図12に示すガスの組成からもわかる。すなわち，酸素供給率100％の状態では一酸化炭素およびメタンガスが存在し，酸素供給率150%になるとこれらの不完全酸化分解によるガスはほとんどなくなった。酸素供給率が200％に増加すると，TOC分解率は99.6%に上昇した。この結果は，過剰の酸素の供給により残存TOCの酸化分解が促進したことを示す。
【００６１】
図13に，トロについて反応温度の影響を示す。TOC分解率は420℃では97%で比較的低く，450℃以上になると99％以上の高い分解率となる。この傾向は牛脂の場合と類似しており，これは，前述したように油脂を多量に含む動物性のものを酸化する場合難分解な酢酸を多量に生成するため，分解にはより高い温度が必要であることによると考えられる。
【００６２】
〔魚類の小骨，背骨および身と骨の混合物の酸化〕
反応時間10分，反応温度420℃，酸素供給率150％および200%で, 魚の小骨と背骨を比較したTOC分解率の結果を図14に示す。身の場合との比較を行うためトロについての結果も同時に示した。酸素供給率が150％の場合の身（トロ）のTOC分解率が多少低い傾向が認められる。脊推動物の骨は，動物の種類，年齢などで多少異なるところがあるが，大体65%の無機物（主に水酸アパタイトを主体とするリン酸カルシウム）と35%の有機物（主にコラ−ゲン蛋白）から成っている。この有機物の成分は身と同じ主に蛋白質であるため小骨と背骨ではTOC分解率の違いがみられず，トロの場合に多少分解率が低くなったものと考えられる。しかし，図15に示すように小骨と背骨の場合に発生したガス量と身の場合に発生した量を比較すると，骨の方が少ない。これは，試料量を同じにしているため，骨の場合は有機物量が少ないことによる。さらに，身と骨のそれぞれの場合の発生ガスの割合についてみると約3:1になっている。これは骨を構成する有機物の割合と一致している。
【００６３】
以上，生ごみを構成する食物の種類(植物性の野菜類，動物性の肉類と魚類)による超臨界水湿式酸化分解の難易，反応の相違(あるいは類似)および反応の特徴を明らかにするため，まず，試料として22種類の生ごみについて実験を行った。次に，野菜類の人参，肉類の牛脂および魚類のトロを取り上げ，反応パラメーターが酸化反応に及ぼす影響について検討した。その結果，
【００６４】
(1) 生ごみの完全酸化分解に必要な酸素供給率は，食物性生ごみの場合100％，動物性生ごみの場合150％であった。
【００６５】
(2) 植物性生ごみは酸化されやすく，種類による酸化分解のしやすさの相違はほとんどみられない。動物性生ごみ(魚を含む)も酸化されるが，植物性生ごみに比べると難分解である。種類による酸化分解のしやすいさに大きな相違はないが，脂肪は肉類（魚を含む）よりTOC分解率が低く，なかでも牛脂は最も酸化されにくい。
【００６６】
(3) すべての試料について，最後まで残存する中間有機生成物は酢酸であった。そこで，次に植物性生ゴミの代表として人参を，そして動物性生ゴミとしては最も分解し難かった牛脂を選択し，酢酸の利用法について検討を行った。
【００６７】
〔実験装置および実験手順〕
実験装置には，ステンレス製のバッチ式小型反応容器（内容積6cm３）を用いた。反応器の加熱は溶融塩恒温槽を用いた。
【００６８】
カルシウム剤を添加するにあたっては，反応前に添加する場合と反応後に添加する場合の2通りについて実験を行った。反応前に添加する場合には，試料と過酸化水素水ならびにカルシウム剤を一緒に反応容器に入れて反応させた。一方，反応後に添加する場合は反応後の液相中にカルシウム剤を添加・反応させた。
【００６９】
〔実験条件〕
実験条件を表6に示す。試料重量は，乾燥重量が0.067ｇとなるようにした。実験は温度400℃，反応時間10秒〜90秒，酸素供給率10〜150％の条件で行った。また，酢酸カルシウムを生成させる実験は，酢酸が多量に得られる反応条件下で行った。
【００７０】
【表６】

【００７１】
一方，酢酸除去のための反応条件については，反応温度は人参および牛脂と人参の混合系の場合400℃，420℃とし，牛脂の場合400℃〜450℃とした。反応時間は，牛脂と人参の場合30秒〜10分とし，混合系の場合30秒〜3分とした。酸素供給率は，人参の場合100％とし，牛脂の場合100〜150％とした。また，混合系の場合はその混合比により100％，あるいは110％とした。
【００７２】
〔酢酸を大量に生成させる反応条件〕
〔牛脂の酸化による酢酸の生成〕
反応温度400℃で，酸素供給率を100〜150％の範囲で変化させて酢酸濃度の経時変化を調べた。結果を図16に示す。酢酸濃度が最大になる条件は，反応温度400℃では反応時間30秒，酸素供給率100〜150％であることが分かる。また，酢酸以外の物質については，図17に示すように，酸素供給率が100%においてはC3-C5などの低級脂肪酸やアセトール，ケトン類などの不純物が残存しているが，酸素供給率が150%になるとこれらの不純物はほとんどなくなる。さらに，図18（ａ）に示したように， TOC分解率は酸素供給率が100%のとき低く，150%になると高くなる。
【００７３】
したがって，酢酸濃度が最大になる反応条件は反応温度400℃，反応時間30秒酸素供給率100〜150％であり，高濃度かつ高純度酢酸を得る反応条件は反応温度400℃，反応時間30秒，酸素供給率150％であることが分かった。
【００７４】
〔人参の酸化による酢酸の生成〕
反応温度は400℃，酸素供給率を30〜100％の範囲で変化させ，反応時間を10秒〜90秒の範囲で変化させた。結果を図19に示す。酸素供給率を低下させることにより，多量の酢酸が得られることが分かった。その中でも，反応時間30秒，酸素供給率50％の条件において最も高い酢酸濃度を得ることができた。その他で比較的高い酢酸濃度が得られる条件としては，酸素供給率30〜50％で反応時間30〜90秒の場合，ならびに酸素供給率70％で反応時間30秒の場合であった。
【００７５】
以上の結果から，牛脂と人参のいずれにおいても湿式酸化により比較的高い分解率を得ると同時に酢酸収率も高いことが示された。これは，生ごみからの酢酸の回収・利用法として本方法が高い可能性を有することを示唆する結果である。
【００７６】
〔酢酸カルシウムの生成〕
（１）牛脂の酸化により生成する酢酸を原料とした場合
〔カルシウム源として水酸化カルシウムを用いた場合〕
酢酸と水酸化カルシウムは以下のような反応により酢酸カルシウムを容易に生成することから，まず，カルシウム剤として水酸化カルシウムを用いた。
【００７７】
2CH₃COOH+Ca(OH)₂→(CH₃COO)₂Ca+2H₂O
【００７８】
この水酸化カルシウムの添加方法については，反応前ならびに反応後の二通りの実験を行った。酢酸の生成反応条件については，前述したように酢酸が比較的高純度かつ高濃度で生成した条件（反応時間30秒，反応温度400℃，酸素供給率150％）とした。図20に，同条件で生成した酢酸に水酸化カルシウムを添加して得られた物質の¹H-NMRスペクトルを示す。比較として，酢酸標準試料と酢酸カルシウム標準試料の¹H-NMRスペクトルも同図中に示す。水酸化カルシウムを添加しない場合は2.07ppmの位置に酢酸のメチル基のプロトンのシグナルが検出された。一方，水酸化カルシウムを添加した場合，反応前添加および反応後添加の両場合ともに，酢酸のメチル基のプロトンのシグナルは見られず，1.91ppmの位置に酢酸カルシウムのメチル基のプロトンのシグナルが検出された。また，図21に，水酸化カルシウムの添加前後の生成物のGC-MSクロマトグラムを示す。水酸化カルシウムを添加した場合には，添加方法に係わらず，酢酸のピークは大幅に減少している。さらに，図22に，反応後の溶液の水を蒸発させて得られた固形分をXRDにより分析した結果を示す。これにも，水酸化カルシウムの添加方法に係わらず，酢酸カルシウムの1水塩と0.5水塩のピ−クが検出された。
【００７９】
以上の分析結果から，水酸化カルシウムの添加により，反応前に添加する場合および反応後に添加する場合のいずれにおいても，酢酸カルシウムの生成を確認することが明らかとなった。
【００８０】
〔カルシウム剤添加量の影響〕
図23に，酢酸カルシウム濃度とカルシウム添加量との関係を示す。図23(a)に炭酸カルシウムを添加した場合について示す。炭酸カルシウムの添加により，「(1)炭酸カルシウムを酸化分解反応開始前に添加した場合」と，「(2)酸化分解反応終了後室温で添加した場合」とで，酢酸カルシウムの生成に大きな相違がみられる。すなわち，(1)の場合は0.05 Mの添加で最大となりそれ以上添加すると大きく減少するのに対し，(2)の場合は0.05 M以上添加してもほとんど変化がみられない。また，(1)の場合の最大生成量が(2)の場合よりも少ない。
【００８１】
酢酸カルシウムは2CH₃COOH+CaCO₃→(CH₃COO)₂Ca+CO₂＋H₂Oのように生成するので，酢酸と炭酸カルシウムの当量比は2:1である。前述のように，反応時間30秒で，酢酸の最大生成量は0.10M(6000ppm)であるので，炭酸カルシウムの当量は0.05Mであり，この添加量で酢酸カルシウムの生成量が最大となっている。 (2)の場合にこの0.05M以上炭酸カルシウムを添加しても酢酸カルシウム濃度がほぼ一定であることは炭酸カルシウムの当量が0.05Mであることの実験による証明であり，残存した酢酸はほぼ全てが酢酸カルシウムになったことを示している。それに対し(1)の場合に0.05 M以上の添加で収率が低下したことは，炭酸カルシウムが酢酸の生成反応に何らかの影響を及ぼしたことを示唆する。従って，反応前に炭酸カルシウムを添加する場合には，予想される酢酸生成モル数に対してその1/2モル数の炭酸カルシウムを添加すること，一方，反応後に炭酸カルシウムを添加する場合には，生成した酢酸モル数の1/2モル数以上の炭酸カルシウムを添加することでで最大収率の酢酸カルシウムが得られることが明らかとなった。
【００８２】
図23(b)に，水酸化カルシウムを添加した場合の結果を示す。酢酸カルシウムが最大生成量を示す時の添加量及びさらに添加量を増加させたときの酢酸カルシウム生成量の減少挙動において相違がみられている。
【００８３】
以上の結果から，酸化分解反応の前あるいは反応後に水酸化カルシウムあるいは炭酸カルシウムを添加することにより，生成した酢酸はほぼ全てが酢酸カルシウムになるが，反応前に添加する場合には最適添加量が存在することが分かった。具体的には反応前に水酸化カルシウムを添加する場合には予想される酢酸生成モル数に対してその1/2〜1モルの範囲内で水酸化カルシウムを添加すること，一方，反応後に水酸化カルシウムを添加する場合には，生成した酢酸モル数の1/2モル数以上の水酸化カルシウムを添加することでで最大収率の酢酸カルシウムが得られることが明らかとなった。
【００８４】
上述のように，反応前にカルシウムを添加する場合にある一定量以上のカルシウムを添加すると，酢酸カルシウムの生成量が急激に減少した。この理由を調べるために，GC-MSによってその生成物を分析した。図24に，炭酸カルシウムの添加量による生成物のGC-MSクロマトグラムの変化を示す。この結果から，炭酸カルシウムの添加量が0.05M(酢酸カルシウム生成量が最大になる添加量)の時，中間生成物は炭酸カルシウムを添加しない場合とほぼ同様であったが，0.07M以上になると，グリセリンやフェノ-ルなどの，炭酸カルシウムが存在しない場合にはみられなかった化合物が生成していることがわかる。さらに，0.07Mの添加量で，反応時間を10秒に短縮した実験における生成物をみると，油相(ヘキサン相)中に，ナフタレンなどの各種芳香族化合物が検出された。水酸化カルシウムを添加した場合においても図25に示すように同様の結果が得られた。
【００８５】
以上の結果から，ある量以上のカルシウム剤の添加により牛脂の酸化分解反応が抑制され，加水分解反応などの酸化反応以外の反応が顕著になることが分かった。
【００８６】
（２）人参の酸化による酢酸カルシウムの生成
牛脂の場合において，反応前にカルシウム剤を過剰に添加すると，酸化反応以外の反応が顕著になり，酢酸カルシウムの生成量が減少するという結果を得た。そこで本実験ではカルシウム剤を反応後に添加した。
【００８７】
まず，酢酸が最も高い濃度で得られる条件(反応温度400℃，反応時間30秒，酸素供給率50％)下で，カルシウム剤の添加による酢酸カルシウムの生成実験を行った。カルシウム剤の添加前後の生成物の¹H−NMRスぺクトルを図26に示す。この結果から，添加するカルシウム剤に関しては水酸化カルシウムおよび炭酸カルシウムともに，1.91ppmの位置に酢酸カルシウムのメチル基のプロトンシグナルが検出された。また，GC-MSにより分析した反応生成物を図27に示す。カルシウム剤を添加した場合においては，添加しない場合において見られる酢酸のピークが検出されないことから，反応により生成した酢酸は全て酢酸カルシウムに転換したものと考えられる。
【００８８】
〔カルシウムの添加による酢酸の除去〕
これまでの検討は酢酸を多量に生成させて酢酸カルシウムとして回収することに関してであったが，生ごみを燃料として熱エネルギ−に変換・利用することを目的とする場合には完全酸化分解が望ましい。しかし，中間生成物である酢酸は難分解であり，完全酸化分解には過剰の酸素を必要とするため，工業的にはある程度の有機物が残存することになる。そこで，酢酸濃度と回収率(あるいは除去率)の関係，酢酸の完全除去条件および酢酸以外の残存有機物と排水基準等について検討した。
【００８９】
〔残存酢酸濃度とカルシウム添加濃度が酢酸除去率に及ぼす影響〕
〔牛脂を用いた実験〕
最大酢酸濃度が得られる反応条件である反応温度400℃，反応時間30秒，酸素供給率150％の場合において酢酸の除去状况について調べた。この結果を表6（ｂ）に示す。これから，水酸化カルシウムならびに炭酸カルシウムの添加のいずれの場合においても,生成する酢酸に対して当量のカルシウム剤を添加することにより，残存酢酸濃度は6000ppmから150ppmまで大幅に減少し，この結果98％の酢酸除去率が得られることが分かった。さらに，カルシウム剤を過剰に添加すると酢酸を完全に検出限界以下に除去できることが分かった。
【００９０】
〔人参を用いた実験〕
牛脂を用いた場合の実験結果を踏まえ，残存酢酸濃度ならびにカルシウム剤の添加濃度（当量および過剰）を変化させた。その結果を表7に示す。まず，酢酸に対して当量のカルシウム剤を添加した場合についてみると，3900ppm以上と比較的高い酢酸濃度の場合には150ppmまで大幅に減少し，約97％の酢酸除去率が得られた。一方3000ppm以下の低い酢酸濃度の場合においては酢酸の除去率は残存酢酸濃度の減少とともに低下し，酢酸濃度が600ppmまで減少すると，残存酢酸の除去は20％にまで減少してしまった。しかし，カルシウム剤を過剰に添加することにより酢酸濃度に関係なくほぼ完全に除去された。
【００９１】
【表７】

【００９２】
〔牛脂と人参の混合系を用いた実験〕
表8に，反応温度420℃の場合，各条件下でカルシウム剤の添加による酢酸の変化を示す。牛脂と人参の場合と同様に，酢酸濃度が高い場合はカルシウム剤を当量添加することにより97−98％と高い除去率が得られた。酢酸濃度が低い場合は当量の添加濃度では酢酸の除去率は低い。しかし，残存酢酸濃度に関係なく，カルシウム剤を過剰に添加することにより，残存した酢酸はほぼ完全に除去されることが分かった。
【００９３】
【表８】

【００９４】
以上の結果から，牛脂，人参および牛脂と人参の混合系のいずれにおいてもカルシウム剤の添加により酢酸を完全に除去できることが分かった。
図28に，牛脂の場合について，反応温度450℃，酸素供給率120％および150％における反応後の液相中に残存する酢酸以外のTOC濃度の経時変化を示す。酸素供給率150％の場合では3分以後，酢酸以外の残存TOC濃度がほぼ０になった。この結果から，生ごみの中でも最も難分解な牛脂においても，450℃，酸素供給率150％の条件下で約3分反応させれば排水中の残存TOCをほぼ0にすることが可能であることが分かった。
以上の結果から，牛脂の場合には，排水中のTOC濃度をほぼ0にすることが可能となることが分かった。
【００９５】
人参の場合について，酸素供給率100％，420℃の条件下で，酢酸を除いた残存TOC濃度の経時変化を図29に示す。この結果から，反応時間の増加とともに，残存TOC濃度は急速に減少し，反応時間が3分では，約100ppmであり，これは排水基準以下の数値である。
【００９６】
牛脂と人参混合系の場合については，混合系における酸化分解反応性はそれぞれを単独に処理したときと大きな相違はないことから，排水中のTOC濃度は排水基準以下になる。
【００９７】
本発明は厨芥類以外にも，籾殻の処理にも適応可能である。実験結果を図30に示す。反応温度400℃，酸素供給率100%の条件では，酸素供給率50%と比較して酢酸が選択的に生成可能であることがわかる。更には，例えば道路脇の雑草などを原料としても酢酸を生成可能であり，その酢酸を原料として酢酸カルシウムを製造し，道路の融雪剤として利用することも可能である。さらには様々な有機物が処理可能と考えられる。
【００９８】
これまでは，主に超臨界水湿式酸化法による厨芥類の処理について記載したが，（亜臨界水）湿式酸化法によっても，酢酸が生成可能であることを以下に示す。試料には前記記載と同様の籾殻を使用した。実験条件は反応温度350℃，酸素供給率110%とした。結果を図31に示す。超臨界水湿式酸化法と同様に酢酸が最も多く生成していることがわかる。但し，その他の成分は超臨界水湿式酸化条件よりも多く生成しており，更なる処理が必要な場合も考えられる。しかし，酢酸以外の生成物であるシュウ酸やギ酸などもカルシウムの添加によりカルシウム化合物となって排水中から除去できるために，排水中の残存TOC濃度を低下させることが可能である。
【００９９】
また，生成した酢酸から酢酸カルシウムなどの酢酸化合物を生成する方法としては，カルシウム化合物以外にも，酸化マグネシウムなどのマグネシウム化合物の利用も可能である。結果を図32に示す。マグネシウム化合物の添加量と共に酢酸が酢酸マグネシウム化合物として回収されていることを示しており，マグネシウム化合物であってもカルシウム化合物と同様に酢酸を酢酸化合物として回収可能であることがわかる。酢酸マグネシウムは，酢酸カルシウムと同様に，道路などの融雪剤として利用することができる。
【０１００】
【発明の効果】
本発明に係る有機廃棄物の処理方法では，過剰な酸素供給，高温度の過酷な反応条件，反応時間の延長が必要となり，生ごみなどをはじめとする有機廃棄物を短時間でほぼ完全に分解するともに，中間生成物の酢酸から有価資源の酢酸カルシウムを得ることができる。処理の際，カルシウム塩として蠣殻やホタテ等の貝殻廃棄物を使用した場合には，有機廃棄物の処理と同時に貝殻廃棄物の処理も可能にする。
【図面の簡単な説明】
【図１】本発明の実施例において実験に用いた小型反応容器の縦断面図である。
【図２】本発明の実施例において実験に用いた加熱炉の正面図である。
【図３】図１の小型反応容器および図２の加熱炉を用いた実験手順を示すフローチャートである。
【図４】ＴＯＣ分解率に及ぼす反応温度の影響（人参の場合）を示すグラフである。
【図５】ＴＯＣ分解率に及ぼす反応時間の影響（人参の場合）を示すグラフである。
【図６】（ａ）ＴＯＣ分解率に及ぼす酸素供給率の影響（人参の場合）を示すグラフ，（ｂ）ガス組成に及ぼす酸素供給率の影響（人参の場合）を示すグラフである。
【図７】（ａ）ＴＯＣ分解率に及ぼす酸素供給率の影響（牛脂の場合）を示すグラフ，（ｂ）ガス組成に及ぼす酸素供給率の影響（牛脂の場合）を示すグラフである。
【図８】（ａ）ＴＯＣ分解率に及ぼす反応温度の影響（牛脂の場合）を示すグラフ，（ｂ）ガス組成に及ぼす反応温度の影響（牛脂の場合）を示すグラフである。
【図９】ＴＯＣ分解率に及ぼす反応時間の影響（牛脂の場合）を示すグラフである。
【図１０】ＴＯＣ分解率に及ぼす反応温度と酸素供給率の影響を示すグラフである。
【図１１】魚類生ごみのＴＯＣ分解率に及ぼす酸素供給率の影響を示すグラフである。
【図１２】ガス組成に及ぼす魚の種類および酸素供給率の影響を示すグラフである。
【図１３】ＴＯＣ分解率に及ぼす反応温度の影響（トロの場合）を示すグラフである。
【図１４】魚骨のＴＯＣ分解率に及ぼす酸素供給率の影響を示すグラフである。
【図１５】魚身，骨および背骨の酸化分解反応後のガス組成を示すグラフである。
【図１６】酸素供給率を変化させた場合の酢酸濃度に及ぼす反応時間の影響（牛脂の場合）を示すグラフである。
【図１７】酸素供給率１００％と１５０％の場合における牛脂の酸化中間生成物のＧＣ−ＭＳクロマトグラムである。
【図１８】牛脂のＴＯＣ分解率に及ぼす酸素供給率の影響を示すグラフである。
【図１９】酢酸濃度に及ぼす反応時間と酸素供給率の影響（人参の場合）を示すグラフである。
【図２０】生成物の ¹Ｈ−ＮＭＲスペクトル（牛脂の場合）を示すグラフである。
【図２１】水酸化カルシウムを添加した場合と添加しない場合における生成物のＧＣ−ＭＳクロマトグラムの比較（牛脂の場合）のグラフである。
【図２２】Ｃａ（ＯＨ）2 を添加した場合，水を蒸発して得られた固体のＸ線回折線図（牛脂の場合）である。
【図２３】（ａ）酢酸カルシウムの生成量に及ぼす炭酸カルシウム添加濃度の影響（牛脂の場合）を示すグラフ，（ｂ）酢酸カルシウムの生成量に及ぼす水酸化カルシウム添加濃度の影響（牛脂の場合）を示すグラフである。
【図２４】酸化分解反応前に炭酸カルシウムを添加した場合における生成物のＧＣ−ＭＳクロマトグラム（牛脂の場合）を示すグラフである。
【図２５】酸化分解反応前に水酸化カルシウムを添加した場合における生成物のＧＣ−ＭＳクロマトグラム（牛脂の場合）を示すグラフである。
【図２６】カルシウム剤の添加前後における水相中の生成物の ¹Ｈ−ＮＭＲスペクトル（人参の場合）を示すグラフである。
【図２７】水酸化カルシウムの添加前後でのＧＣ−ＭＳクロマトグラム（人参の場合）を示すグラフである。
【図２８】反応時間による酢酸以外の残存ＴＯＣ濃度の変化（牛脂の場合）を示すグラフである。
【図２９】酢酸以外の残存ＴＯＣと反応時間との関係（人参の場合）を示すグラフである。
【図３０】酢酸濃度および酢酸純度に及ぼす反応時間と酸素供給率の影響を示すグラフである。
【図３１】各種有機酸濃度に及ぼす反応時間の影響を示すグラフである。
【図３２】酢酸から酢酸カルシウム／マグネシウムへの転化率に及ぼすＣａＣＯ3 ，ＭｇＣＯ3 ／ＭｇＯ添加の影響を示すグラフである。
【符号の説明】
１ 小型反応容器
２ 反応室
３ 内張り
４ 加熱炉
５ 高圧バルブ
６ ガス取出し口[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating organic waste such as moss waste.
[0002]
[Prior art]
General waste discharged from households is about 480 million tons annually nationwide, and the main items are paper, plastics, and garbage (garbage). Among them, the proportion of moss is said to be about 30 to 40%, although there are considerable differences depending on the region, and the amount of garbage treated as general waste reaches 15 to 20 million tons per year. In addition, it is 600-1500 g per person per day (1,000 g nationwide), and is said to increase at a rate of 3-5% annually. Unlike Western countries, where garbage discharged from households is discharged into the sewage system by day-sposer treatment, it is also said that there are many droughts in Japan. The amount of moss is about 200-300g per person per day.
[0003]
For this reason, a method of converting organic substances into carbon dioxide and water by incineration was introduced, and in the past 30 years until now, incineration has become the mainstream in the treatment of general waste. However, the garbage discharged as soot has a low calorific value and contains a large amount of water (about 80%), so the combustion efficiency is poor and the heat utilization efficiency is also low. In addition, it is known that the exhaust gas discharged by incineration contains a small amount of organic substances in addition to inorganic harmful gases such as NOx and SOx.
[0004]
[Wet oxidation]
A method of oxidizing an organic substance dissolved or suspended in water under high temperature and high pressure (below the critical temperature of water) is generally called a wet oxidation method (WO). In order to incinerate organic substances in water, there are a method of solidifying through water filtration, evaporation and drying, and burning in an incinerator, or a method of evaporating and concentrating to some extent, spraying and burning in the furnace. is there. In wet oxidation, the raw material containing a large amount of water is left as it is, heated by the residual heat oxidation reaction heat, and if air is blown into it, the oxidation reaction of organic matter, that is, oxidative decomposition treatment, is performed by oxygen in the air. Is the basic principle.
[0005]
The following can be mentioned as characteristics of wet oxidation.
(1) Even garbage containing a large amount of moisture does not need to be dried, and the generated heat is directly transferred to the water phase, so high energy utilization efficiency can be expected when using it as hot water or steam.
[0006]
(2) Sulfur, nitrogen, halogen, etc. are trapped in the aqueous phase as ions, so that subsequent processing is easy. Also, no harmful substances such as dioxin, NOx, SOx are generated.
[0007]
[Conventional technology for wet oxidation]
Research on wet oxidation originated in 1944 in the United States when Zimmermann applied it to the treatment of pulp waste black liquor. In Japan, a real plant of 500m3 / d scale was constructed in 1968 in Yokohama City for sewage sludge treatment. In addition, the attempt to adapt to industrial waste treatment began with a pilot plant experiment targeting cyanide and sodium sulfide wastewater treatment at the Ministry of International Trade and Industry in 1969. Including plants and human waste / sewage treatment, about 60 plants are operating in Japan. In addition, the development of wet oxidative decomposition treatment of sludge, industrial wastewater, toxic substances and live urine has been carried out at home and abroad.
[0008]
The wet oxidation method is effective for the treatment of sludge containing a large amount of water, sewage, industrial wastewater and human waste.
However, with existing wet oxidation, the temperature is low, so organic matter is not decomposed sufficiently, and accumulation of lower carboxylic acid and residual ammonia occur. Therefore, secondary and tertiary treatment facilities such as biological treatment are required in the subsequent stage. To do. On the other hand, for the purpose of improving the decomposition rate, research on oxidation treatment using a catalyst without changing the temperature and pressure has been conducted. However, in the wet oxidation method using a catalyst, the oxidative decomposition of organic matter is not yet complete, and a post-treatment process is required. Moreover, since heavy metals such as copper ions used as a catalyst adversely affect the human body and other living organisms, it is necessary to separate the used catalyst, and it cannot be said that the completed method is still sufficient.
[0009]
(Supercritical Water Oxidation)
The supercritical water wet oxidation (SCWO) method is basically wet oxidation, and is a method of decomposing organic substances above the critical point of water. In other words, this is a method for treating organic substances in which supercritical water is used as a solvent and the organic substances are oxidized and decomposed with oxygen to convert them into carbon dioxide and water.
Supercritical water has a unique property that it dissolves many organic substances, such as homogeneously dissolving with nonpolar organic substances, and also mixes with oxygen and other gases in a single phase at an arbitrary ratio. It has very good characteristics as a place.
[0010]
Here, the characteristics of the supercritical water wet oxidation reaction are described by comparing the supercritical water wet oxidation reaction with the (subcritical water) wet oxidation reaction.
(Subcritical water) In wet oxidation, (1) Insufficient solubility of air or oxygen to oxidize organic matter in water often makes it impossible to completely oxidize organic matter. (2) Between water phase and gas phase It is necessary to mechanically stir the reaction vessel because it must take into account mass transfer, (3) Secondary processing equipment is required due to the limited decomposition of organic matter, (4) Recoverable steam There are drawbacks such as low temperature (typically 250 ° C or less) and low utility value for steam turbine power generation. On the other hand, in supercritical water wet oxidation, (1) oxygen and organic substances have a high solubility in supercritical water, and supercritical water is a single phase, so stirring is often unnecessary. (2) If the organic substance concentration in the raw material is 2% or higher, continuous operation is possible while maintaining the required reaction temperature, and if the organic substance concentration is 5% or higher, heat energy can be recovered. .
[0011]
[Conventional technology related to SCWO]
SCWO is a technology developed in the last 10-15 years, but there are many studies on this, and among them, there are many studies for complete decomposition treatment of hardly decomposed organic substances and harmful organic substances. Modell et al. Have demonstrated that chlorinated organic waste and sewage sludge can be treated to decompose starting materials on the order of 99.99%, and that they can also be applied to pulp drainage. It is intended only for the complete oxidative solution treatment of water, and there are no studies on the use of intermediate products produced by supercritical water wet oxidation of organic waste.
[0012]
[Problems to be solved by the invention]
The present invention relates to a treatment method for oxidizing and decomposing organic waste such as garbage in a supercritical region of water.
In the process of supercritical water wet oxidation of organic waste, acetic acid is produced as an intermediate product, but acetic acid is difficult to decompose.
[0013]
The present invention has been made by paying attention to such conventional problems. Organic waste that effectively uses the intermediate product acetic acid to obtain valuable resources and decomposes garbage almost completely in a short time. It aims at providing the processing method of a thing.
[0014]
[Means for Solving the Problems]
In order to achieve the above objectives, garbage is treated by oxidative decomposition under supercritical conditions, and the treatment conditions for selectively producing acetic acid for the purpose of effective utilization of acetic acid produced at that time are studied. We have invented a wastewater purification method that removes acetic acid as calcium acetate from treated water by adding a calcium agent to acetic acid, and vice versa.
[0016]
In the organic waste treatment method according to the present invention, the organic waste to be treated is garbage such as moss waste, which is domestic waste, and the garbage is beef tallow or other animal waste. Or carrots or other vegetable waste. As the calcium compound, calcium carbonate or calcium hydroxide is suitable. As calcium compounds, shellfish shells such as rice husks and scallops can be used, and it is possible to treat two birds with one stone to achieve effective use of shellfish waste. The calcium compound and / or the magnesium compound may be in an ionized state. As the magnesium compound, magnesium carbonate or magnesium oxide is suitable.
[0022]
  The present inventionIn the organic waste treatment method related toSupercritical water wet oxidation reactionA method for treating organic waste that is oxidatively decomposed byWhen the oxygen supply rate theoretically required to completely oxidize all organic carbon of the organic waste to be treated to carbon dioxide is 100%, 400 ° C. to 450 ° C. under an oxygen supply rate of 30% to 150%. Supercritical water wet oxidation reaction at a temperature of ℃, the supercritical waterIt is characterized by the presence of a calcium compound and / or a magnesium compound having a number of moles of 1/2 or more with respect to the number of moles of acetic acid produced by the reaction together with the decomposition product of the organic waste after the wet oxidation reaction.
  In the organic waste treatment method according to the present invention, the supercritical water wet oxidation reaction is preferably performed in a reaction time of 30 seconds to 180 seconds.
[0023]
  The present inventionIn the organic waste treatment method related toSupercritical water wet oxidation reactionIn the presence of calcium compound, magnesium compound or both together with organic waste, organic waste is decomposed almost completely in a short time, and acetic acid produced by the decomposition of organic waste is converted into calcium acetate, magnesium acetate or It can be changed to both.
[0025]
In the organic waste treatment method according to the present invention, when the organic waste is beef tallow or other animal organic matter, in order to increase the amount of calcium acetate produced, the reaction conditions that maximize the amount of acetic acid produced, that is, oxygen The supercritical water wet oxidation reaction is preferably performed at a supply rate of 100 to 150%, a reaction temperature of 400 ° C., and a reaction time of 30 seconds. When organic waste is ginseng or other plant organic matter, in order to increase the amount of calcium acetate produced, the reaction conditions that maximize the amount of acetic acid produced are: oxygen supply rate 50%, reaction temperature 400 ° C, reaction time It is preferable to perform the supercritical water wet oxidation reaction in 30 seconds.
[0026]
In the method for treating organic waste according to the present invention, in order to completely oxidatively decompose acetic acid, it is necessary to supply excess oxygen, severe reaction conditions at high temperature, and extension of reaction time. The supercritical water wet oxidation reaction is preferably performed at a temperature of 450 ° C. and a reaction time of 3 minutes.
[0027]
【Example】
The TOC referred to below is an abbreviation for total organic carbon, which indicates the concentration of organic substances contained in wastewater. Although the standard value varies depending on each municipality, drainage is not possible unless the TOC is below the standard value. Therefore, if the TOC cannot be lowered, additional wastewater treatment facilities are required, resulting in higher costs. The water filling rate is the volume ratio of water to the reaction container internal volume.
[0028]
30% hydrogen peroxide was used as the oxidizing agent. The amount of oxidant supplied was defined based on the amount of carbon. That is, H₂O₂1 mol to 1/2 mol O₂Suppose that all organic carbon (TOC) in the sample is completely CO.₂The theoretical amount required to oxidize the oxygen was 100%. Therefore, the amount of oxygen required for complete oxidative decomposition differs depending on the elemental composition of the sample (C: H: O, etc.), and an oxygen supply rate of 100% is not always sufficient.
[0029]
The main components of garbage are carbohydrates, fats, and proteins, and are foodstuffs of plants, meats, and fish. Each composition was measured with a CNS analyzer, and the moisture content was measured with an infrared moisture meter. Table 1 shows the elemental composition (C, N, S) of typical food products. Other elements include hydrogen and oxygen.
[0030]
[Table 1]

[0031]
For example, the main component of plant substances is expressed as a general formula (C_nH_2mO_m)_NThe oxidation reaction is (C_nH_2mO_m) + NO₂→ nCO₂+ mH₂It progresses like O, and the oxygen molecules necessary for complete oxidation are estimated to be in a ratio close to 1: 1 with the number of moles of carbon. That is, oxygen is expected to be sufficient when the oxygen supply rate is 100%.
[0032]
[Experimental equipment and experimental procedure]
The outlines of the small reaction vessel and heating furnace used in the experiment are shown in Figs. 1 and 2, respectively. The internal volume of the small reaction vessel 1 is 47 ml, and the material of the lining 3 of the reaction chamber 2 is Hastelloy C-276. The heating furnace 4 is of an induction heating type using a commercial power source capable of high-temperature heating at 100 ° C. per minute.
[0033]
The experimental procedure is shown in FIG. Although an undried sample was used as an experimental sample, the sample amount was set to 0.5 g in dry weight. First, this was put into the reaction vessel 1 together with the hydrogen peroxide solution, and the high pressure valve 5 was quickly attached and sealed. Next, the reaction vessel 1 was placed in the induction heating furnace 4 and heated at a temperature rising rate of 40 ° C./min while shaking. After a predetermined time, the reaction vessel 1 was quickly taken out from the induction heating furnace 4 and cooled with a fan. The time required for cooling to about 100 ° C. is about the same as the time required for heating. After cooling, the generated gas was first collected. The gas was collected by attaching a tube to the gas outlet 6 of the high-pressure valve 5 and replacing it with water. In order to avoid the dissolution of carbon dioxide in water as much as possible, saturated saline was used as the replacement water. The amount of gas generated was measured with a 1000 ml graduated cylinder. Subsequently, the reaction vessel was opened, the solution after the reaction was transferred to a beaker, and the solution was analyzed. After measuring TOC, the components were analyzed by GC-MS.
[0034]
[Experimental conditions]
Table 2 summarizes the experimental conditions. In order to investigate the difference in reactivity depending on the type of garbage, an experiment was conducted under standard reaction conditions. In addition, in order to examine the effects of reaction temperature, reaction time, oxygen supply rate, and water filling rate, experiments were conducted within the ranges shown in Table 2 respectively, taking vegetable ginseng, meat beef tallow and fish toro. .
[0035]
[Table 2]

[0036]
As for the reference conditions, the sample amount was fixed at 0.5 g in dry weight (the sample used in the experiment was not dried) to prevent the reaction temperature from changing due to oxidation heat generation, and the reaction time (after reaching the predetermined temperature) The retention time was 10 minutes. The reaction temperature was set to 400 ° C and 420 ° C for vegetable and animal garbage, respectively. The oxygen supply rate was set to 100% for vegetable garbage and 150% for animal garbage. The filling rate of water (ratio of the mixture of distilled water and hydrogen peroxide (hydrogen peroxide solution) to the total volume of the reaction vessel) was 30%.
[0037]
[Experimental result (vegetable garbage)]
Table 3 shows the results obtained under the conditions of a reaction temperature of 400 ° C and a reaction time of 10 minutes when the oxygen supply rate is 100%. The TOC decomposition rate determined from the residual TOC measurement value in the liquid phase was 99.5%, and almost complete decomposition was obtained. At that time, the gas composition was mostly carbon dioxide, and a small amount of carbon monoxide due to incomplete oxidation was present, but no hydrocarbon was detected. From these results, it is considered that the plant food waste mainly composed of polysaccharides has an oxygen supply rate of 100% and sufficient oxygen.
[0038]
[Table 3]

[0039]
[Difference in reactivity depending on the type of vegetable garbage]
Table 4 shows the results of examining the difference in reactivity depending on the type of vegetable waste under the standard reaction conditions. The TOC degradation rate of about 99.6% was obtained for any plant waste.
The composition of generated gas was mostly carbon dioxide. From these results, it was found that these vegetable wastes are easily oxidized, and almost all samples are oxidatively degraded within 10 minutes. Under these conditions, there was almost no difference in the rate of oxidative degradation depending on the type of vegetable waste.
[0040]
In each sample, the pH of the liquid phase after the reaction was 5.5-6.1, indicating weak acidity. As a result of analyzing liquid phase products by GC-MS, only the acetic acid peak was detected in all samples. Therefore, the acidity of the liquid phase was thought to be due to the remaining acetic acid.
[0041]
From the above results, plant garbage is easily oxidized, and there is almost no difference in oxidative degradation depending on the type, and a high TOC degradation rate of about 99.6% is obtained at 400 ° C in 10 minutes of reaction time. I understood.
[0042]
[Influence of reaction parameters (vegetable garbage)]
As shown in Table 4, there was no difference in decomposition rate or undecomposed residual organic matter depending on the type of vegetable garbage. Therefore, we took carrot as a representative and examined the effect of reaction parameters. Since it was found that the oxygen supply rate was 100% and the amount of oxygen was almost sufficient, the following reaction temperature and reaction time were examined under the conditions where the oxygen supply rate was 100%.
[0043]
[Table 4]

[0044]
[Influence of reaction temperature]
Figure 4 shows the effect of reaction temperature on the oxidative degradation rate when the reaction time is 10 minutes and the reaction temperature is changed from 380 to 450 ° C. At 380 ° C, the TOC decomposition rate is relatively low at 94.7%, but when it reached 400 ° C, it suddenly increased to over 99%, and when the temperature rose to 450 ° C, this decomposition rate almost reached 100%. From this, it was found that although the oxidation reaction is strongly accelerated by the temperature rise, the temperature at which the decomposition rate becomes 99% or more when the reaction time is 10 minutes is 400 ° C or more.
[0045]
[Influence of reaction time]
Figure 5 shows the results of examining the effect on the TOC decomposition rate by changing the reaction time from 0 to 20 minutes at a reaction temperature of 400 ° C. Although it takes about 10 minutes each for the temperature raising process and cooling process to reach a predetermined temperature using an induction heating furnace, it seems that there is a large error in the results in a short reaction time, but as shown in Fig. 4, Even when the reaction time was 0, that is, the temperature was raised and cooled immediately after reaching the predetermined temperature, the TOC decomposition rate was 92-93%. From this, it is considered that the reaction has already started in the process of raising the temperature before reaching the predetermined temperature and has progressed to a considerable extent. In addition, after reaching the prescribed temperature, the TOC decomposition rate increases with increasing reaction time, reaching 99.5% in 10 minutes, but the subsequent change is slow. From these results, in order to obtain a TOC decomposition rate of 99% or more, a reaction time of about 10 minutes is required under the condition of 400 ° C. However, even if the reaction time is further increased, the decomposition rate increases. It turned out that the effect to make was small. This is considered to be because the remaining acetic acid is hardly decomposed.
[0046]
[Effect of oxygen supply rate]
Figure 6 (a) shows the results of examining the effect of the oxygen supply rate on the TOC decomposition rate at a reaction temperature of 420 ° C and a reaction time of 10 minutes. When the oxygen supply rate is 50%, the TOC decomposition rate is 76.3%, which is low. The gas composition at that time is shown in FIG. 6 (b). A large amount of carbon monoxide and hydrocarbon (methane) produced by incomplete oxidative decomposition is detected without oxygen remaining. When the oxygen supply rate was increased to 100%, a 99.86% decomposition rate was obtained, and when it was further increased to 200%, the TOC decomposition rate became 99.99%, and the decomposition of acetic acid further progressed as the oxygen supply rate increased. I understand that.
[0047]
When the oxygen supply rate was 50%, the TOC decomposition rate became more than 50%, 76.3%. This is due to the decrease in organic carbon in the liquid phase due to the formation of carbon monoxide and methane, as shown in Fig. 6 (b). Looking at the distribution of carbon after the reaction in this case, about 1/4 of the total exists in the liquid phase and about 3/4 of the gas exists. Furthermore, looking at the generated gas composition, CO₂: CO: CH_Four≒ 74: 22: 4.
[0048]
[Wet oxidation of meat waste]
[Oxygen supply rate required for complete decomposition]
In order to examine the oxygen supply rate required for complete decomposition, experiment was conducted using beef tallow as a sample, increasing the reaction temperature to 450 ° C, changing the oxygen supply rate in the range of 100 to 150% within a reaction time of 10 minutes. went. The results are shown in FIG. As shown in Fig. 7 (a), when the oxygen supply rate was increased from 100% to 150%, the TOC decomposition rate increased from 84.5% to 99.0%.
In other words, the oxygen supply rates of 100% and 120% do not satisfy the amount of oxygen necessary for complete oxidation of beef tallow. This was confirmed by the detection of carbon monoxide and hydrocarbons (methane) due to incomplete oxidative decomposition in the generated gas as shown in Fig. 7 (b). When the oxygen supply rate reaches 150%, almost no carbon monoxide and hydrocarbons are detected, indicating that the amount of oxygen is almost sufficient.
[0049]
This is because the oxygen supply rate is determined based on carbon, and in fact, hydrogen and other elements also consume oxygen. As mentioned above, since plant-based substances are mainly composed of polysaccharides, oxygen and hydrogen are considered to be H.₂Since it is almost balanced as O, an oxygen supply rate of 100% is sufficient. However, fat, which is the main component of beef tallow, is a compound glyceride in which glycerin and higher fatty acids are dehydrated and combined, and the ratio of carbon to hydrogen is almost 1: 2.₂)_n+ 1.5O₂= nH₂O + nCO₂Thus, the number of oxygen molecules required for oxidation is about 1.5 times the number of moles of carbon. Therefore, in the case of beef tallow, the oxygen supply rate of 150% is considered to be sufficient oxygen.
[0050]
The protein is polyamide, and this monomer is α-aminocarboxylic acid. Therefore, the ratio of carbon to hydrogen is about 1: 2 for meats mainly composed of protein. Therefore, an experiment was conducted on pork thighs at an oxygen supply rate of 150%, a reaction time of 10 minutes, and a temperature of 420 ° C. The obtained TOC degradation rate was 99.25%, and in the case of protein, it was found that oxygen was sufficient at an oxygen supply rate of 150%.
[0051]
Since it became clear that oxygen was sufficient at an oxygen supply rate of 150%, the following examination was conducted under the condition of an oxygen supply rate of 150%.
[Difference in reactivity depending on the type of meat waste]
Table 5 shows the results of examining the difference in reactivity depending on the type of meat garbage. First, the TOC degradation rate is over 99% for pork and beef, 98% for poultry, and 96.5-97.5% for fat. These are slightly lower than the decomposition rate of food waste at 400 ℃ despite the reaction temperature of 420 ℃. Most of the gas composition after the reaction was carbon dioxide in addition to oxygen. From these results, meat garbage is also oxidized, but it is harder to decompose than vegetable garbage, and proteins and fats are mainly composed of protein in meat garbage. Comparing with fats and oils, it was found that the latter had a lower TOC degradation rate, and among them, the TOC degradation rate of beef tallow was the lowest.
[0052]
[Table 5]

[0053]
Next, regarding the pH of the liquid phase after the reaction, the pH of the solution after the reaction of fats and oils is the lowest, and the acidity of the three units. The pH of the solution after the reaction of the proteins is around 6 and around neutral. The liquid phase product was analyzed by GC-MS. As a result, the peak of only acetic acid was seen in any sample. Therefore, it was found that the reason for acidification was due to the remaining acetic acid.
[0054]
[Oxidative degradation of beef tallow]
As described above, it was found that fats and oils, especially beef tallow, are less susceptible to oxidative degradation in meat waste. Therefore, we investigated the effects of reaction temperature, reaction time, oxygen supply rate, and water filling rate on beef tallow.
[0055]
[Influence of reaction temperature]
Figure 8 (a) shows the effect of reaction temperature on the TOC decomposition rate. At 420 ° C or lower, the TOC decomposition rate was relatively low at 97% or lower, but when it reached 450 ° C, it increased to 99% or higher, and when the temperature rose to 470 ° C, this decomposition rate was almost 100%. From this, it was found that in the case of beef tallow, although the oxidation reaction is strongly accelerated by the temperature rise, the temperature at which the decomposition rate becomes 99% or more in 10 minutes of reaction time is 450 ° C or more. This is thought to be due to the fact that a large amount of acetic acid is produced when animal organic matter is oxidized, and acetic acid is less susceptible to oxidation, and therefore a higher temperature is required.
[0056]
[Influence of reaction time]
Figure 9 shows the effect of reaction time on the TOC decomposition rate when the reaction temperature is 450 ° C. The TOC decomposition rate is about 95% at 0 minutes and the decomposition rate is 99% at 5 minutes, but the subsequent change is slow. Comparing this result with the carrot shown in Fig. 5, the beef tallow has a higher TOC degradation rate up to a reaction time of 5 minutes, which may be due to the difference in reaction temperature. However, since then, the decomposition rate of beef tallow has decreased, and this is thought to be due to the fact that the formation of acetic acid, which accounts for most of the TOC, is more common in beef tallow and this decomposition is difficult.
[0057]
(Decomposition of residual TOC (acetic acid))
Although it was found that the oxidative decomposition of residual TOC, that is, acetic acid, was promoted by increasing the temperature, it is considered possible to promote the decomposition of acetic acid by increasing the amount of oxygen supplied. Therefore, the conditions for further decomposing residual acetic acid were examined.
[0058]
Figure 10 shows the results of examining the temperature dependence of the TOC decomposition rate when the oxygen supply rate is 150% and 200%. From this result, it can be seen that the residual TOC decreases with increasing temperature, but the residual TOC can be significantly decreased with increasing oxygen supply rate. For example, when the oxygen supply rate is 420% at 420 ° C, the TOC is about 1000ppm, that is, the TOC decomposition rate is as low as 96%. However, when the oxygen supply rate was increased to 200%, it became about 250 ppm (TOC decomposition rate of 99% or more). Furthermore, when the oxygen supply rate was increased from 150% to 200% at a temperature of 450 ° C, the TOC decreased from 250 to 20 ppm, and the TOC decomposition rate increased from 99.1% to 99.9%. In this way, a large amount of acetic acid is produced in the oxidative decomposition of fats and oils, but it was found that if the decomposition rate needs to be further increased, it can be achieved by increasing the reaction temperature or supplying excess oxygen.
[0059]
[Wet oxidation of fish garbage]
[Difference in reactivity depending on the type of fish]
Figure 11 shows the effect of fish type and oxygen supply rate on the oxidative degradation rate. First, the effect of the type of fish on the TOC degradation rate showed no significant difference when the oxygen supply rate was 150% or higher. When the oxygen supply rate is 100%, the high decomposition rate of tuna lean is considered to be due to the low fat content.
[0060]
Next, looking at the effect of the oxygen supply rate on the TOC decomposition rate, the TOC decomposition rate of any sample is low when the oxygen supply rate is 100%, but when the oxygen supply rate is 150%, it becomes about 99%. This shows that fish is mainly composed of protein and fat, so that oxygen is sufficient at an oxygen supply rate of 150%, as in meat. This can also be seen from the gas composition shown in FIG. In other words, carbon monoxide and methane gas existed when the oxygen supply rate was 100%, and when the oxygen supply rate reached 150%, these gases due to incomplete oxidative decomposition almost disappeared. When the oxygen supply rate increased to 200%, the TOC decomposition rate increased to 99.6%. This result shows that the oxidative decomposition of residual TOC was accelerated by supplying excess oxygen.
[0061]
Figure 13 shows the effect of reaction temperature on Toro. The TOC decomposition rate is relatively low at 97% at 420 ° C, and a high decomposition rate of 99% or higher at 450 ° C or higher. This tendency is similar to that of beef tallow, which, as mentioned above, produces a large amount of acetic acid that is hardly decomposed when animal products containing a large amount of fat are oxidized. It is thought that it is necessary.
[0062]
[Oxidation of fish bones, spines and mixture of body and bone]
Figure 14 shows the results of the TOC degradation rate comparing the small bones of the fish and the spine at a reaction time of 10 minutes, a reaction temperature of 420 ° C, an oxygen supply rate of 150% and 200%. The result for Toro was also shown at the same time for comparison with the body. When the oxygen supply rate is 150%, the TOC decomposition rate tends to be somewhat low. The bones of vertebrate animals vary slightly depending on the type of animal, age, etc., but roughly 65% of inorganic substances (mainly calcium phosphate mainly composed of hydroxyapatite) and 35% of organic substances (mainly collagen protein) Consists of. Since the organic components are mainly the same protein as the body, there is no difference in the TOC degradation rate between the small bones and the spine, and it is thought that the degradation rate is somewhat lower in the case of Toro. However, when the amount of gas generated in the case of the small bone and the spine is compared with the amount generated in the case of the body as shown in FIG. This is because the amount of organic matter is small in the case of bone because the sample amount is the same. Furthermore, the ratio of generated gas in the case of body and bone is about 3: 1. This is consistent with the proportion of organic matter that makes up the bone.
[0063]
To clarify the difficulty of supercritical water wet oxidative degradation, the difference in reaction (or similar), and the characteristics of the reaction, depending on the type of food composing food waste (vegetable vegetables, animal meat and fish) First, 22 types of garbage were tested as samples. Next, we examined the effects of reaction parameters on the oxidation reaction, taking vegetable ginseng, meat beef tallow and fish toro. as a result,
[0064]
(1) The oxygen supply rate required for complete oxidative decomposition of food waste was 100% for food waste and 150% for animal waste.
[0065]
(2) Vegetable waste is easily oxidized, and there is almost no difference in the oxidative degradation depending on the type. Animal food waste (including fish) is also oxidized, but it is more difficult to decompose than vegetable food waste. There is no big difference in the oxidative degradation by type, but fat has a lower TOC degradation rate than meat (including fish), and beef tallow is the least oxidized.
[0066]
  (3) For all samples, the remaining intermediate organic product was acetic acid. ThereNext, we selected carrots as representatives of vegetable garbage, and beef tallow that was the least difficult to decompose as animal garbage, and examined how to use acetic acid.
[0067]
[Experimental equipment and experimental procedure]
The experimental apparatus used was a stainless steel batch type reaction vessel (internal volume 6 cm3). The reactor was heated using a molten salt thermostat.
[0068]
When adding the calcium agent, the experiment was conducted in two ways: before and after the reaction. When added before the reaction, the sample, the hydrogen peroxide solution, and the calcium agent were put together in the reaction vessel and reacted. On the other hand, when added after the reaction, the calcium agent was added and reacted in the liquid phase after the reaction.
[0069]
[Experimental conditions]
Table 6 shows the experimental conditions. The sample weight was such that the dry weight was 0.067 g. The experiment was performed under the conditions of a temperature of 400 ° C., a reaction time of 10 to 90 seconds, and an oxygen supply rate of 10 to 150%. The experiment to produce calcium acetate was conducted under reaction conditions where a large amount of acetic acid was obtained.
[0070]
[Table 6]

[0071]
On the other hand, as for the reaction conditions for acetic acid removal, the reaction temperature was 400 ° C and 420 ° C for ginseng and beef tallow and ginseng mixed system, and 400 ° C to 450 ° C for beef tallow. The reaction time was 30 seconds to 10 minutes for beef tallow and carrots, and 30 seconds to 3 minutes for mixed systems. The oxygen supply rate was 100% for carrots and 100-150% for beef tallow. In the case of a mixed system, the mixing ratio was set to 100% or 110%.
[0072]
[Reaction conditions for producing a large amount of acetic acid]
[Production of acetic acid by oxidation of beef tallow]
Changes in acetic acid concentration over time were examined by changing the oxygen supply rate in the range of 100 to 150% at a reaction temperature of 400 ° C. The results are shown in FIG. It can be seen that the conditions for maximum acetic acid concentration are a reaction time of 30 seconds and an oxygen supply rate of 100 to 150% at a reaction temperature of 400 ° C. As for substances other than acetic acid, as shown in FIG. 17, when the oxygen supply rate is 100%, lower fatty acids such as C3-C5, impurities such as acetol and ketones remain, but the oxygen supply rate is low. At 150% these impurities are almost gone. Furthermore, as shown in Fig. 18 (a), the TOC decomposition rate is low when the oxygen supply rate is 100% and high when it is 150%.
[0073]
Therefore, the reaction conditions that maximize the acetic acid concentration are a reaction temperature of 400 ° C., a reaction time of 30 seconds, and an oxygen supply rate of 100 to 150%. The reaction conditions for obtaining high concentration and high purity acetic acid are a reaction temperature of 400 ° C. and a reaction time of 30 seconds. The oxygen supply rate was found to be 150%.
[0074]
[Production of acetic acid by carrot oxidation]
The reaction temperature was 400 ° C., the oxygen supply rate was changed in the range of 30 to 100%, and the reaction time was changed in the range of 10 to 90 seconds. The results are shown in FIG. It was found that a large amount of acetic acid can be obtained by reducing the oxygen supply rate. Among them, the highest acetic acid concentration was obtained under the conditions of a reaction time of 30 seconds and an oxygen supply rate of 50%. Other conditions under which a relatively high acetic acid concentration can be obtained were when the oxygen supply rate was 30-50% and the reaction time was 30-90 seconds, and when the oxygen supply rate was 70% and the reaction time was 30 seconds.
[0075]
From the above results, it was shown that both beef tallow and carrot have a relatively high decomposition rate by wet oxidation and at the same time a high acetic acid yield. This is a result that suggests that this method has a high possibility as a method for recovering and using acetic acid from garbage.
[0076]
[Formation of calcium acetate]
(1) When using acetic acid produced by oxidation of beef tallow as a raw material
[When calcium hydroxide is used as the calcium source]
Since acetic acid and calcium hydroxide easily generate calcium acetate by the following reaction, calcium hydroxide was first used as a calcium agent.
[0077]
2CH_ThreeCOOH + Ca (OH)₂→ (CH_ThreeCOO)₂Ca + 2H₂O
[0078]
Regarding the method of adding calcium hydroxide, two experiments were conducted before and after the reaction. As described above, the acetic acid production reaction conditions were such that acetic acid was produced with relatively high purity and high concentration (reaction time 30 seconds, reaction temperature 400 ° C., oxygen supply rate 150%). Figure 20 shows the substance obtained by adding calcium hydroxide to acetic acid produced under the same conditions.¹1 shows an H-NMR spectrum. As a comparison, acetic acid standard sample and calcium acetate standard sample¹The H-NMR spectrum is also shown in the figure. When calcium hydroxide was not added, a proton signal of the methyl group of acetic acid was detected at 2.07 ppm. On the other hand, when calcium hydroxide was added, the proton signal of the methyl group of acetic acid was not seen in both the pre-reaction and post-reaction additions, and the methyl group proton signal of calcium acetate was found at the position of 1.91 ppm. was detected. FIG. 21 shows GC-MS chromatograms of the product before and after the addition of calcium hydroxide. When calcium hydroxide is added, the acetic acid peak is greatly reduced regardless of the addition method. Further, FIG. 22 shows the result of XRD analysis of the solid content obtained by evaporating the water of the solution after the reaction. Again, calcium acetate monohydrate and 0.5 hydrate peaks were detected regardless of the method of calcium hydroxide addition.
[0079]
From the above analysis results, it was clarified that the addition of calcium hydroxide confirms the formation of calcium acetate both when added before the reaction and when added after the reaction.
[0080]
[Effect of added calcium agent]
FIG. 23 shows the relationship between the calcium acetate concentration and the amount of calcium added. FIG. 23 (a) shows the case where calcium carbonate is added. Due to the addition of calcium carbonate, there is a large difference in the formation of calcium acetate between “(1) when calcium carbonate is added before the start of oxidative decomposition reaction” and “(2) when added at room temperature after the end of the oxidative decomposition reaction”. Is seen. In other words, in case (1), the addition is maximum at 0.05 M, and when it is added more, it is greatly reduced. In case (2), there is almost no change even when 0.05 M or more is added. In addition, the maximum generation amount in (1) is smaller than in (2).
[0081]
Calcium acetate is 2CH_ThreeCOOH + CaCO_Three→ (CH_ThreeCOO)₂Ca + CO₂+ H₂Since it is formed like O, the equivalent ratio of acetic acid to calcium carbonate is 2: 1. As described above, since the maximum production amount of acetic acid is 0.10 M (6000 ppm) at a reaction time of 30 seconds, the equivalent amount of calcium carbonate is 0.05 M, and this addition amount maximizes the production amount of calcium acetate. Yes. In the case of (2), the calcium acetate concentration is almost constant even when calcium carbonate of 0.05M or more is added. This is proof by experiments that the equivalent of calcium carbonate is 0.05M. Indicates that it became calcium acetate. In contrast, in the case of (1), the yield decreased with addition of 0.05 M or more, suggesting that calcium carbonate had some influence on the acetic acid formation reaction. Therefore, when adding calcium carbonate before the reaction, add 1/2 mole of calcium carbonate to the expected number of moles of acetic acid, while when adding calcium carbonate after the reaction. It was clarified that the maximum yield of calcium acetate can be obtained by adding more than 1/2 mole of calcium carbonate.
[0082]
FIG. 23 (b) shows the results when calcium hydroxide is added. There is a difference between the amount of addition when calcium acetate shows the maximum production amount and the decrease behavior of the production amount of calcium acetate when the addition amount is further increased.
[0083]
From the above results, by adding calcium hydroxide or calcium carbonate before or after the oxidative decomposition reaction, almost all of the acetic acid produced becomes calcium acetate. I knew it existed. Specifically, when calcium hydroxide is added before the reaction, calcium hydroxide should be added within a range of 1/2 to 1 mol of the expected number of moles of acetic acid produced, while water is added after the reaction. When calcium oxide was added, it was clarified that the maximum yield of calcium acetate could be obtained by adding calcium hydroxide that was at least 1/2 mol of acetic acid.
[0084]
As mentioned above, when adding calcium beyond a certain amount when adding calcium before the reaction, the amount of calcium acetate produced decreased rapidly. To investigate the reason, the product was analyzed by GC-MS. FIG. 24 shows the change in the GC-MS chromatogram of the product depending on the amount of calcium carbonate added. From this result, when the addition amount of calcium carbonate was 0.05M (addition amount that maximizes the amount of calcium acetate production), the intermediate product was almost the same as when calcium carbonate was not added, but when it became 0.07M or more It can be seen that compounds such as glycerin and phenol, which were not seen in the absence of calcium carbonate, were formed. Furthermore, looking at the products in the experiment where the reaction time was shortened to 10 seconds with an addition amount of 0.07M, various aromatic compounds such as naphthalene were detected in the oil phase (hexane phase). Similar results were obtained when calcium hydroxide was added as shown in FIG.
[0085]
From the above results, it was found that addition of a certain amount or more of calcium agent suppresses beef tallow oxidative degradation reaction, and the reaction other than oxidation reaction such as hydrolysis reaction becomes remarkable.
[0086]
(2) Formation of calcium acetate by carrot oxidation
In the case of beef tallow, when calcium agent was added excessively before the reaction, reactions other than the oxidation reaction became prominent, and the amount of calcium acetate produced decreased. Therefore, in this experiment, a calcium agent was added after the reaction.
[0087]
First, under the conditions where acetic acid was obtained at the highest concentration (reaction temperature 400 ° C, reaction time 30 seconds, oxygen supply rate 50%), an experiment was conducted to produce calcium acetate by adding calcium agent. Of the product before and after the addition of calcium agent¹The H-NMR spectrum is shown in FIG. From these results, for the calcium agent to be added, the proton signal of the methyl group of calcium acetate was detected at the position of 1.91 ppm for both calcium hydroxide and calcium carbonate. The reaction products analyzed by GC-MS are shown in FIG. When the calcium agent is added, the acetic acid peak that is seen when the calcium agent is not added is not detected. Therefore, it is considered that all the acetic acid produced by the reaction is converted to calcium acetate.
[0088]
[Removal of acetic acid by addition of calcium]
Previous studies have been related to the production of a large amount of acetic acid and recovery as calcium acetate, but complete oxidative decomposition is desirable for the purpose of converting and using raw garbage as thermal energy. . However, acetic acid, which is an intermediate product, is difficult to decompose, and excessive oxygen is required for complete oxidative decomposition, so that some organic matter remains industrially. Therefore, the relationship between acetic acid concentration and recovery rate (or removal rate), complete removal conditions of acetic acid, residual organic substances other than acetic acid, and drainage standards were examined.
[0089]
[Effects of residual acetic acid concentration and calcium addition concentration on acetic acid removal rate]
[Experiment using beef tallow]
The removal conditions of acetic acid were investigated when the reaction temperature was 400 ° C, the reaction time was 30 seconds, and the oxygen supply rate was 150%. The results are shown in Table 6 (b). From this, in both cases of addition of calcium hydroxide and calcium carbonate, the residual acetic acid concentration was greatly reduced from 6000 ppm to 150 ppm by adding an equivalent amount of calcium agent to the acetic acid produced, resulting in 98% It was found that the acetic acid removal rate was obtained. Furthermore, it was found that acetic acid could be completely removed below the detection limit by adding an excessive amount of calcium agent.
[0090]
[Experiment using carrots]
Based on the experimental results when beef tallow was used, the residual acetic acid concentration and the calcium agent addition concentration (equivalent and excess) were varied. The results are shown in Table 7. First, when adding an equivalent amount of calcium agent to acetic acid, the acetic acid removal rate was reduced to about 97% when the acetic acid concentration was relatively high, such as 3900 ppm or higher. On the other hand, in the case of acetic acid concentration as low as 3000ppm or less, the acetic acid removal rate decreased with decreasing residual acetic acid concentration, and when the acetic acid concentration decreased to 600ppm, the removal of residual acetic acid decreased to 20%. However, it was almost completely removed regardless of the acetic acid concentration by adding an excessive amount of calcium agent.
[0091]
[Table 7]

[0092]
[Experiment using a mixed system of beef tallow and carrot]
Table 8 shows the change in acetic acid due to the addition of calcium agent under each condition when the reaction temperature is 420 ° C. As in the case of beef tallow and carrot, when the acetic acid concentration was high, a high removal rate of 97-98% was obtained by adding an equivalent amount of calcium. When the acetic acid concentration is low, the acetic acid removal rate is low at an equivalent concentration. However, it was found that the remaining acetic acid was almost completely removed by adding an excessive amount of calcium agent regardless of the residual acetic acid concentration.
[0093]
[Table 8]

[0094]
From the above results, it was found that acetic acid can be completely removed by adding calcium preparations in beef tallow, ginseng and mixed system of beef tallow and ginseng.
FIG. 28 shows the change over time of the TOC concentration other than acetic acid remaining in the liquid phase after the reaction in the case of beef tallow at a reaction temperature of 450 ° C. and an oxygen supply rate of 120% and 150%. When the oxygen supply rate was 150%, the remaining TOC concentration other than acetic acid became almost zero after 3 minutes. From this result, even in the most difficult-to-decompose beef tallow, it is possible to reduce the residual TOC in the wastewater to almost zero by reacting for about 3 minutes at 450 ℃ and oxygen supply rate of 150%. I understood that.
From the above results, it was found that in the case of beef tallow, the TOC concentration in the wastewater can be reduced to almost zero.
[0095]
For carrots, Fig. 29 shows the change over time in the residual TOC concentration excluding acetic acid under the conditions of an oxygen supply rate of 100% and 420 ° C. From this result, as the reaction time increases, the residual TOC concentration decreases rapidly, and when the reaction time is 3 minutes, it is about 100 ppm, which is below the effluent standard.
[0096]
In the case of beef tallow and ginseng mixed systems, the oxidative degradation reactivity in the mixed system is not much different from that when each was treated separately, so the TOC concentration in the wastewater is below the wastewater standard.
[0097]
The present invention can be applied to the treatment of rice husks in addition to moss. The experimental results are shown in FIG. It can be seen that acetic acid can be selectively produced under the conditions of a reaction temperature of 400 ° C. and an oxygen supply rate of 100% as compared with an oxygen supply rate of 50%. Furthermore, for example, acetic acid can be produced using weeds on the roadside as a raw material, and calcium acetate can be produced using the acetic acid as a raw material and used as a snow melting agent for roads. Furthermore, it is considered that various organic substances can be treated.
[0098]
So far, the treatment of moss by the supercritical water wet oxidation method has been mainly described, but it is shown below that acetic acid can also be produced by the (subcritical water) wet oxidation method. The sample used was the same rice husk as described above. The experimental conditions were a reaction temperature of 350 ° C and an oxygen supply rate of 110%. The results are shown in FIG. It can be seen that acetic acid is most produced as in the supercritical water wet oxidation method. However, other components are produced more than the supercritical water wet oxidation conditions, and further processing may be necessary. However, oxalic acid and formic acid, which are products other than acetic acid, can be removed from the wastewater as calcium compounds by adding calcium, so it is possible to reduce the residual TOC concentration in the wastewater.
[0099]
Further, as a method for producing an acetic acid compound such as calcium acetate from the produced acetic acid, a magnesium compound such as magnesium oxide can be used in addition to the calcium compound. The results are shown in FIG. It shows that acetic acid is recovered as a magnesium acetate compound together with the amount of magnesium compound added, and it can be understood that acetic acid can be recovered as an acetic acid compound as well as a calcium compound. Magnesium acetate can be used as a snow melting agent for roads and the like, similar to calcium acetate.
[0100]
【The invention's effect】
The organic waste treatment method according to the present invention requires excessive oxygen supply, severe reaction conditions at high temperatures, and extended reaction time, so that organic waste such as garbage is almost completely removed in a short time. While decomposing, calcium acetate as a valuable resource can be obtained from acetic acid as an intermediate product. When shellfish waste such as rice husk or scallop is used as the calcium salt during the treatment, it is possible to treat shellfish waste at the same time as organic waste.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a small reaction vessel used in an experiment in an example of the present invention.
FIG. 2 is a front view of a heating furnace used in an experiment in an example of the present invention.
3 is a flowchart showing an experimental procedure using the small reaction vessel of FIG. 1 and the heating furnace of FIG.
FIG. 4 is a graph showing the influence of reaction temperature (in the case of carrots) on the TOC decomposition rate.
FIG. 5 is a graph showing the influence of reaction time (in the case of carrot) on the TOC decomposition rate.
6A is a graph showing the effect of oxygen supply rate on TOC decomposition rate (in the case of carrots), and FIG. 6B is a graph showing the effect of oxygen supply rate on gas composition (in the case of carrots).
7A is a graph showing the effect of oxygen supply rate on TOC decomposition rate (in the case of beef tallow), and FIG. 7B is a graph showing the effect of oxygen supply rate on gas composition (in the case of beef tallow).
FIG. 8A is a graph showing the effect of reaction temperature on TOC decomposition rate (in the case of beef tallow), and FIG. 8B is a graph showing the effect of reaction temperature on gas composition (in the case of beef tallow).
FIG. 9 is a graph showing the influence of reaction time on TOC decomposition rate (in the case of beef tallow).
FIG. 10 is a graph showing the influence of reaction temperature and oxygen supply rate on the TOC decomposition rate.
FIG. 11 is a graph showing the influence of the oxygen supply rate on the TOC decomposition rate of fish garbage.
FIG. 12 is a graph showing the effect of fish type and oxygen supply rate on gas composition.
FIG. 13 is a graph showing the influence of the reaction temperature on the TOC decomposition rate (in the case of Toro).
FIG. 14 is a graph showing the influence of the oxygen supply rate on the TOC decomposition rate of fish bones.
FIG. 15 is a graph showing the gas composition after the oxidative degradation reaction of fish, bone and spine.
FIG. 16 is a graph showing the influence of reaction time (in the case of beef tallow) on the acetic acid concentration when the oxygen supply rate is changed.
FIG. 17 is a GC-MS chromatogram of an oxidation intermediate product of beef tallow when the oxygen supply rate is 100% and 150%.
FIG. 18 is a graph showing the influence of the oxygen supply rate on the TOC decomposition rate of beef tallow.
FIG. 19 is a graph showing the influence of reaction time and oxygen supply rate on acetic acid concentration (in the case of carrots).
FIG. 20: Product¹It is a graph which shows a H-NMR spectrum (in the case of tallow).
FIG. 21 is a graph of comparison of GC-MS chromatograms of products with and without calcium hydroxide (in the case of beef tallow).
FIG. 22 is an X-ray diffraction diagram (in the case of beef tallow) of a solid obtained by evaporating water when Ca (OH) 2 is added.
23A is a graph showing the effect of calcium carbonate addition concentration (in the case of beef tallow) on the calcium acetate production amount, and FIG. 23B is the effect of calcium hydroxide addition concentration on the calcium acetate production amount (in the case of beef tallow). ).
FIG. 24 is a graph showing a GC-MS chromatogram (in the case of beef tallow) of a product when calcium carbonate is added before the oxidative decomposition reaction.
FIG. 25 is a graph showing a GC-MS chromatogram (in the case of beef tallow) of a product when calcium hydroxide is added before the oxidative decomposition reaction.
FIG. 26 shows the product in the aqueous phase before and after the addition of calcium agent.¹It is a graph which shows a H-NMR spectrum (in the case of carrot).
FIG. 27 is a graph showing a GC-MS chromatogram (in the case of carrot) before and after the addition of calcium hydroxide.
FIG. 28 is a graph showing changes in residual TOC concentration other than acetic acid with reaction time (in the case of beef tallow).
FIG. 29 is a graph showing the relationship (in the case of carrot) between the remaining TOC other than acetic acid and the reaction time.
FIG. 30 is a graph showing the influence of reaction time and oxygen supply rate on acetic acid concentration and acetic acid purity.
FIG. 31 is a graph showing the effect of reaction time on various organic acid concentrations.
FIG. 32 is a graph showing the effect of addition of CaCO 3 and MgCO 3 / MgO on the conversion rate from acetic acid to calcium acetate / magnesium.
[Explanation of symbols]
1 Small reaction vessel
2 reaction chamber
3 lining
4 Heating furnace
5 High pressure valve
6 Gas outlet

Claims (2)

An organic waste treatment method that oxidizes and decomposes organic waste by supercritical water wet oxidation reaction , and the oxygen supply rate that is theoretically required to completely oxidize all organic carbon in the organic waste to be treated to carbon dioxide Is 100%, supercritical water wet oxidation reaction is performed at a temperature of 400 ° C. to 450 ° C. with an oxygen supply rate of 30% to 150%, and after the supercritical water wet oxidation reaction, A method for treating organic waste, characterized in that a calcium compound and / or a magnesium compound having a number of moles of 1/2 or more with respect to the number of moles of acetic acid produced by the reaction is present together with a decomposition product. The method for treating organic waste according to claim 1, wherein the supercritical water wet oxidation reaction is performed in a reaction time of 30 seconds to 180 seconds.

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