JP4158276B2 - Method for producing bleached pulp - Google Patents
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- JP4158276B2 JP4158276B2 JP11057499A JP11057499A JP4158276B2 JP 4158276 B2 JP4158276 B2 JP 4158276B2 JP 11057499 A JP11057499 A JP 11057499A JP 11057499 A JP11057499 A JP 11057499A JP 4158276 B2 JP4158276 B2 JP 4158276B2
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Description
【0001】
【発明の属する技術分野】
本発明は、リグノセルロース材料、特に木材或いは非木材から漂白パルプを製造する方法に関する。更に詳しく述べれば、本発明は、木材或いは非木材を蒸解した後に洗浄して得られる未晒パルプを酸素漂白した後、塩素を用いないで漂白してECF漂白パルプを製造する方法であって、初段と二段目に二酸化塩素を薬品として用い、該二酸化塩素処理の間に洗浄が有っても無くてもよく、その後、アルカリ条件下での抽出を行い、さらに必要であれば一段または多段の漂白を行う漂白パルプの製造方法に関する。
【0002】
木材パルプや非木材パルプを製紙原料として多くの用途に使用するためには、木材或いは非木材を蒸解液で蒸解し、薬品の化学作用によってパルプ化した後に得られるパルプを漂白薬品で漂白して白色度を高める必要がある。例えば、木材チップをクラフト蒸解液で蒸解して得られるクラフトパルプは包装資材のように強度を必要とする用途に使う場合を除いて、通常、酸素とアルカリにより酸素脱リグニンされた後、或いは酸素とアルカリにより酸素脱リグニンされないまま、塩素、次亜塩素酸塩、二酸化塩素、酸素、オゾン、過酸化水素、苛性ソーダ等の漂白剤及び漂白助剤からなる選ばれた漂白薬品により1段乃至は多段シーケンスで漂白され、パルプに含まれる着色原因物質であるリグニン等が除去され、白色度が70〜90%の範囲の半晒クラフトパルプ乃至完全漂白クラフトパルプとして使用されるのが一般的である。
【0003】
従来から多段漂白法においては、パルプを最初に塩素で処理し、パルプ中に含有されるリグニンを塩素化し、リグニンに可溶性を付加した後、次にアルカリで塩素化リグニンを溶解抽出して、パルプ中からリグニンを分離除去し、更に次亜塩素酸塩、二酸化塩素等を使用し、残留する少量のリグニンを分解除去し、白色度の高いパルプを得る方法が採られてきた。
【0004】
しかしながら、近年、パルプの塩素化段からの漂白排水に含まれる有機塩素化合物の環境への影響が懸念され、パルプ漂白に原子状塩素を用いない漂白シーケンスについて盛んに研究されてきている。又、次亜塩素酸塩を用いた場合もパルプの漂白時にクロロホルムが生成し、環境に悪影響を及ぼす可能性があることから、パルプ漂白に使用しない漂白シーケンス(ECF:エレメンタリークロラインフリーと省略する場合がある)漂白の模索が行われている。
【0005】
現在、塩素や次亜塩素酸塩の代替として、オゾン、酸素、過酢酸および過硫酸等の酸素系の漂白薬品が注目されている。しかしながら、これらの薬品は、酸素と過酸化水素を除いては、薬品コストが高く、又爆発性があるため取り扱いが困難である。一方二酸化塩素はコスト面、ジェネレーター容量の制限等が問題となり、現在のところ、我が国では塩素の代わりに二酸化塩素を用いることは、一般に普及するまでには至っていないが、将来的には有望な漂白方法である。塩素や次亜塩素酸塩と比較して、二酸化塩素は環境への影響が少ないが、高価であるので、なるべく添加率を少なくするための最適な漂白シーケンスや条件の探索がなされている。
【0006】
特開平4−245988号公報では、元素塩素の不在下において化学パルプを漂白する場合の二酸化塩素使用量を低減する方法として、ヘミセルロース分解酵素でパルプを処理した後、二酸化塩素で漂白すると、使用しない場合に比べ、二酸化塩素の添加率を約20%減添できる方法が開示されているが、酵素使用によるパルプ粘度低下、収率低下等の問題や、酵素処理の反応が基質特異性を有するため、顕著に効果がでないパルプなどが出てくる恐れもあり、酵素自身も安価な試薬ではないため、漂白コストは逆に増大する可能性もある。
【0007】
一方特開平4−263687号公報では二酸化塩素添加率を削減する手段として、二酸化塩素にオゾンを組み合わせて漂白することを記載しており、これによりトータルの二酸化塩素添加率は50%削減できると記載されている。しかし、パルプ粘度は27.5mPa・sから16mPa・sに低下しており、またオゾンを発生するための設備が必要となる点から、既存の工場への導入は容易ではない。
【0008】
また、特開平9−87985号公報および特開平9−87986号公報では、製紙用化学パルプの製造において、二酸化塩素の使用量を低減させる方法として、漂白前あるいは漂白後のpHを1〜3でおこない、その直後にアルカリ媒体中で過酸化物と酸素による脱リグニンおよび漂白を行うこと、あるいは二酸化塩素段にキレート剤を添加する方法が開示されている。この処理により処理後の白色度は5%程度高くなり、トータル二酸化塩素量添加率は対パルプ0.5重量%まで抑えることができたが、比較例は、塩素を含む漂白シーケンスであり、ECF漂白シーケンスの比較例を最終段まで漂白して比較していないため、ECF漂白での削減効果は定かではない。
【0009】
また、このような二酸化塩素段のpH調整やキレート剤の併用は、その後段での過酸化物と酸素の反応を効率的に行うために、重金属除去効果を主眼としており、本願発明のように、二酸化塩素漂白の効率を上げるためのものではない。また、これらの方法で処理しても、過酸化物をその直後に使用しない場合もあり、この場合には効果が見られなくなる恐れもある。
【0010】
なお、二酸化塩素段が二回続くシーケンスについてはすでに数多く述べられ、特開平4−263687号公報などにも記載されているが、これらは多段漂白の後段に設けたものであり、本発明のような、多段漂白の初段に二回続くものではない。
【0011】
【発明が解決しようとする課題】
本発明者等は、かかる背景に鑑みECFパルプ製造のために漂白性を改善する方法について種々検討を重ねた結果、未晒パルプを酸素漂白した後のパルプ繊維を、ECF漂白の初段と二段目に二酸化塩素を薬品として用い、処理温度の異なる初段と二段目の二酸化塩素処理の間に洗浄が有っても無くてもよく、次いでアルカリ条件下での抽出を行い、パルプ中のリグニン量を減少させ、使用する二酸化塩素量の減少が可能となることを見出した。このことは、有機塩素化合物の排出量をさらに低減できるので、環境負荷が少ない方法である。
本発明は、白色度が高く、安定し、高い品質を保ちつつ、排水への有機塩素化合物の排出量を低減させた経済的で低環境負荷型の漂白方法を提供することを目的とするものである。
【0012】
【課題を解決するための手段】
(1)本発明はリグノセルロース材料を蒸解して得られた未晒パルプを酸素漂白した後、元素塩素の不在下における多段漂白を行い、漂白パルプを製造する方法において、多段漂白の初段とその直後に連続した二酸化塩素段を設け、次いでアルカリ条件下での抽出処理した後、さらに漂白することを特徴とする漂白パルプの製造方法に存する。
【0013】
(2)本発明は、連続した二酸化塩素段の初段の二酸化塩素段は、処理温度70〜110℃、処理時間10〜120分の範囲で行い、その直後に連続した二段めの二酸化塩素段は処理温度40〜90℃、処理時間30〜120分の範囲で行う(1)項記載の漂白パルプの製造方法に存する。
【0014】
【発明の実施の形態】
木材を蒸解後、酸素漂白して得られるパルプを塩素や次亜塩素酸塩を含まない漂白薬品で漂白する(ECF漂白)際に、初段に二酸化塩素段を用いた直後に、アルカリ処理や酸素および過酸化物を含むアルカリ処理による抽出工程が続く従来法に比べて、二段階で二酸化塩素処理を行った後、アルカリ処理や酸素による脱リグニンを補強したアルカリで抽出する方法は、漂白全行程における二酸化塩素添加率が少なくて済む。したがって従来法より少ない二酸化塩素の使用量で済むため、二酸化塩素のジェネレーターを新規に造る場合にも、増設する場合にも、容量の小さいもので良く、経済的であり、排水中の有機塩素化合物量も少なくなり、環境保護にも役立つ方法である。
【0015】
本発明は、木材をクラフト蒸解液のような化学薬品を用いて蒸解し、得られる未漂白パルプを公知の酸素とアルカリによる酸素漂白法により脱リグニンしたパルプを、二段の二酸化塩素を、その間に洗浄することなく添加し処理する方法(初段をD1段、次段をD2段とすると、D1D2と略)あるいはその間に洗浄を行い処理する方法(D1−D2段と略する)による処理に次いでアルカリおよび/またはアルカリ条件下で酸素および/または過酸化水素で抽出するか/または該抽出後、塩素と次亜塩素酸塩を含まない漂白薬品を用いて漂白し、ハンター白色度が70〜90%の漂白パルプを製造する方法である。
【0016】
本発明で用いられるパルプは、リグノセルロース材料である針葉樹材と広葉樹材からの未漂白パルプを酸素とアルカリにより酸素漂白したパルプである。本発明に使用されるパルプを得るための蒸解法としては、クラフト蒸解、サルファイト蒸解、ポリサルファイド蒸解、ソーダ蒸解等の公知の蒸解法を用いることができるが、パルプ品質、エネルギー効率等を考慮すると、クラフト蒸解法が好適に用いられる。
【0017】
例えば、木材チップをクラフト蒸解する場合、クラフト蒸解液の硫化度は5〜75%、好ましくは15〜45%、有効アルカリ添加率は絶乾木材重量当たり5〜30重量%、好ましくは10〜25重量%、蒸解温度は140〜170℃で、蒸解方式は、連続蒸解法或いはバッチ蒸解法のどちらでもよく、連続蒸解釜を用いる場合は、蒸解液を多点で添加する修正蒸解法でもよく、その方式は特に問わない。
蒸解に際して、使用する蒸解液に蒸解助剤として、公知の環状ケト化合物を併用してもよい。
【0018】
本発明に使用される酸素漂白による脱リグニン法は、酸素とアルカリを用いる公知の中濃度法或いは高濃度法がそのまま適用できるが、現在汎用的に用いられているパルプ濃度が8〜15重量%で行われる中濃度法が好ましい。
前記中濃度法による酸素漂白による脱リグニン法で使用されるアルカリとしては苛性ソーダ或いは酸化されたクラフト白液であり、酸素ガスとアルカリは中濃度ミキサーにおいて中濃度のパルプスラリーに添加され混合が十分に行われた後、加圧下でパルプ、酸素及びアルカリの混合物を一定時間保持できる脱リグニン反応塔へ送られ、脱リグニンされるというものである。前記中濃度ミキサーは、メーカーにより異なるが500〜1000rpmで高速回転するローターを有し、高剪断力を中濃度パルプスラリーへ付与してあたかもパルプスラリーが水のような流体に変化させ、それによってパルプ、酸素及びアルカリを十分混合できる。
酸素ガスの添加率は、絶乾パルプ重量当たり0.5〜3重量%、アルカリ添加率は0.5〜4重量%、反応温度は80〜120℃、反応時間は15〜100分、パルプ濃度は8〜15重量%であり、この他の条件は公知のものが適用できる。
【0019】
本発明における分割添加あるいは連続二酸化塩素処理とは、パルプを酸性領域のpHで二酸化塩素水を添加し、或いは該水溶液を含浸させ、特定時間と温度を維持したのち、パルプの洗浄を行わず(D1D2)、あるいは行って(D1−D2)、再び二酸化塩素水をパルプに含浸させ、特定時間と温度を維持することと定義される。
【0020】
本発明のD1およびD2段におけるパルプ濃度は5〜40重量%、好ましくは8〜35重量%、更に好ましくは10〜25重量%の範囲である。パルプ濃度が5重量%未満では、処理に大容量の設備を要するので適さない。パルプ濃度が40重量%を超えると、パルプと二酸化塩素を均一に混合することが難しくなり、効果が十分得られないので適さない。
【0021】
本発明のD1段およびD2段におけるパルプ濃度は、5〜40重量%、処理温度は50〜150℃、好ましくは、D1段の場合70〜110℃、D2段は40〜90℃の範囲、保持時間は好ましくは、D1段で10〜120分、D2段は30〜120分の条件下で行われる。
処理温度が40℃未満では、二酸化塩素によるリグニンの分解反応が不十分になり、温度が150℃を超えると、多糖類の分解が顕著となり、パルプ繊維の強度低下が大きくなるので適さない。本発明の二酸化塩素処理の処理時間は10分以上であれば十分であるが、120分を超えて長くしても脱リグニンの効果は上限に到達する。
【0022】
本発明の二酸化塩素処理時の使用量は、用いる漂白前のパルプのリグニン量や後段の漂白シーケンスによっても異なるが、D1、D2段ともに絶乾パルプに対し0.1〜2.0重量%、好ましくは0.1〜1.0重量%である。
【0023】
D2段後のパルプは、アルカリ条件下でアルカリ単独および/または酸素の併用によるリグニンの抽出・漂白工程が続く(E段またはE/O段と称する)。この時アルカリ条件下にするアルカリ薬品は、苛性ソーダ、水酸化カリウム、酸化白液などが使用できるが、苛性ソーダが一般的に使用される。また過酸化物、特に過酸化水素を併用してもよい。
白色度が80%以上のパルプを得るには、アルカリ抽出段後のパルプは、さらに一段あるいは多段の漂白段を行う必要がある。薬品としては、苛性ソーダ(E)、二酸化塩素(D)、酸素(O)、過酸化水素(P)、オゾン(Z)、有機過酸等の公知の漂白剤と漂白助剤からなる漂白薬品を挙げることができ、これらの中から適宜選択されて漂白薬品として用いられる。
漂白シーケンスとして、例えばD1D2−E/O−D、D1−D2−E/O−D、D1D2−E−D、D1−D2−E−D、D1D2−E/O−D−P、D1−D2−E/O−D−P、D1D2−E/OP−D、D1−D2−E/OP−D、D1−D2−E−P、D1D2−E−P、D1D2−E/O−Z−D、D1−D2−E/O−Z−Dのような塩素を含まない漂白シーケンスを用いることができる。
【0024】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明するが、勿論本発明はこれらの実施例に限定されるものではない。
以下に示す実施例1〜4は、木材チップを蒸解して得られる未漂白パルプを酸素脱リグニンして得られたパルプを用いて、分割添加あるいは連続二酸化塩素処理した後、E/O−DまたはE/O−D−Pシーケンスで漂白を行ったものであり、比較例1、2は、一段の二酸化塩素処理したパルプをE/O−DまたはE/O−D−Pシーケンスで漂白を行ったものである。
又、特に示さない限り、D1とD2段における薬品の削減率は以下のように算出した。
【0025】
D1とD2段における合計薬品の削減率(対D段添加率)
薬品の削減率は、二段処理あるいは分割添加ありとなしにおける漂白に使用したD1とD2段の二酸化塩素の合計の薬品率から下記式(1)により算出した。D1とD2段における合計薬品の削減率、%={(D段における合計薬品添加率−本法の場合のD1とD2段における合計薬品添加率)/D段における合計薬品添加率}×100…(1)
【0026】
パルプ粘度に関してはJ.TappiNO.44に、AOX(活性炭吸着性有機ハロゲン)については米国環境庁EPA法(三菱化成製TOX−10使用)にしたがって行い、PC価については、105℃のオーブンで4時間加速度的に退色させた前後の白色度を用いて、以下の式(2)に従い評価した。
PC価=(1−退色後の白色度)2/(2×退色後の白色度))−(1−退色前の白色度)2/(2×退色前の白色度))…(2)
【0027】
実施例1
工場にてクラフト蒸解を行い酸素脱リグニンを行った広葉樹パルプ(ハンター白色度43.8%、カッパー価10.8)を用いて、以下の条件にて二段二酸化塩素処理を行った。
すなわち、この未漂白パルプをイオン交換水に濃硫酸を添加してpHを4とし、希釈して処理時のパルプ濃度が8%になるように調整した後、絶乾パルプ重量当たり二酸化塩素を0.45%添加し、ステンレス製2リットル容の間接加熱式オートクレーブに入れ、温度105℃で60分間圧力を維持しながら加熱し、パルプのD1段処理を行った。オートクレーブを冷却後、D1処理して得られたパルプを洗浄することなくプラスチック袋に移した。
【0028】
プラスチック袋中のD1処理後のパルプにD2処理時のパルプ濃度が10%になるようイオン交換水および絶乾パルプ重量当たり二酸化塩素を0.30%添加し、温度が70℃の恒温水槽に60分間浸漬してD2段の漂白を行った。得られたパルプをイオン交換水で洗浄、脱水した。
D2段後のパルプをプラスチック袋に入れ、イオン交換水を用いてパルプ濃度を10%に調整した後、苛性ソーダ゛を絶乾パルプ重量当たり1.0%添加し、D1段と同様にしてオートクレーブに入れ、酸素による1.5kg/m2の加圧を行い、温度60℃で15分処理した後、オートクレーブよりパルプを取り出しプラスチック袋に移し替え、60℃の恒温水槽にて45分間の処理を行ってE/O段の抽出を行った。得られたパルプをイオン交換水を用いて洗浄、脱水した。
【0029】
続いて、E/O段後のパルプをプラスチック袋に入れ、イオン交換水を用いてパルプ濃度10%に調整した後、絶乾パルプ重量当たり二酸化塩素を0.2%添加し、温度70℃で180分間の条件で二酸化塩素処理を行った(D3段)。得られたパルプはイオン交換水を用いて洗浄、脱水し、漂白パルプを得た。
D3段後のパルプを離解した後、Tappi試験法T205os−71(JISP 8209)に従って坪量60g/m2のシートを作製し、JIS P 8123に従ってパルプのハンター白色度を測定した結果85.0%であった。
【0030】
実施例2
実施例1と同様に添加率0.45%のD1段処理をした後、洗浄・脱水を行い、さらに二酸化塩素添加率0.25%のD2段処理を行い、以降の処理は実施例1と全く同様の処理を引き続いて行い、ハンター白色度85.0%の漂白パルプを得た。
【0031】
実施例3
実施例1と同様に添加率0.20%のD1段処理をした後、洗浄を行なわず、二酸化塩素添加率0.24%のD2段処理を行い、処理パルプをイオン交換水で洗浄後、実施例1と全く同様な条件でE/O段処理とD3段処理を行った後のパルプをプラスチック袋に入れ、イオン交換水を用いてパルプ濃度10%に調整した後、絶乾パルプ重量当たり過酸化水素を0.35%および苛性ソーダを0.5%添加し、温度70℃で120分間処理し、P段の漂白を行った。得られたパルプはイオン交換水を用いて洗浄、脱水し、ハンター白色度85.0%の漂白パルプを得た。
【0032】
実施例4
実施例3と同様に、D1−D2−E/O−D3−Pのシーケンスで漂白し、D1とD2の間に洗浄・脱水を行った。各段の薬品添加率は、D1が0.2%、D2が0.20%で、以降は実施例3と同一の添加率で行い、ハンター白色度85.0%の漂白パルプを得た。
【0033】
比較例1
実施例1と同様の未晒パルプをプラスチック袋に入れ、イオン交換水を用いて処理時のパルプ濃度が10%になるよう調整した後、絶乾パルプ重量当たり二酸化塩素を0.80%添加し、温度が70℃の恒温水槽に120分間浸漬して二酸化塩素段の漂白を行った。得られたパルプはイオン交換水で洗浄、脱水した。その後のE/O−D段処理に関しては、実施例1と全く同様に行い、ハンター白色度85.0%の漂白パルプを得た。
【0034】
比較例2
比較例1と同様のD段処理を、二酸化塩素添加率のみ0.45%に変えて行い、その後のE/O−D−P段処理は実施例2と全く同様に行い、ハンター白色度85.0%の漂白パルプを得た。
【0035】
表1に、実施例1〜4と比較例1、2の結果を示した。
【0036】
【表1】
【0037】
表1から示されるように、シーケンスによって異なるが、二段二酸化塩素処理(D1−D2)によって通常の一段処理の場合に比べて、10%〜14%の薬品が低減できることにより、有機塩素化合物は37%程度低減することができ、D1D2処理によっては5〜9%の薬品低減が可能となり、これにより有機塩素化合物は35%程度低減できた。実施例3、4では、比較例2と比べ、パルプ粘度は向上する。パルプの退色性も改善が認められた。
【0038】
【発明の効果】
本発明は、ECF漂白において、初段で二段の二酸化塩素処理することにより、パルプ粘度を低下させることなく、二酸化塩素使用量を低減でき、このために有機塩素化合物量の排出も低減できる漂白パルプの製造方法を提供するという効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing bleached pulp from lignocellulosic materials, in particular wood or non-wood. More specifically, the present invention is a method for producing ECF bleached pulp by bleaching without bleaching unbleached pulp obtained by washing after cooking wood or non-wood and then bleaching without using chlorine. Chlorine dioxide is used as a chemical in the first and second stages, and may or may not be washed during the chlorine dioxide treatment, followed by extraction under alkaline conditions, and if necessary, one or more stages The present invention relates to a method for producing bleached pulp for performing bleaching.
[0002]
In order to use wood pulp or non-wood pulp as a raw material for papermaking in many applications, the pulp obtained after cooking wood or non-wood with cooking liquor and pulping by chemical action of chemicals is bleached with bleaching chemicals. It is necessary to increase the whiteness. For example, kraft pulp obtained by cooking wood chips with kraft cooking liquor is usually oxygen delignified with oxygen and alkali, or oxygenated, except when used for applications that require strength such as packaging materials. One or more stages depending on the selected bleaching chemicals consisting of bleaching agents and bleaching aids such as chlorine, hypochlorite, chlorine dioxide, oxygen, ozone, hydrogen peroxide, caustic soda, etc. It is generally bleached in sequence to remove lignin, which is a color-causing substance contained in the pulp, and is generally used as semi-bleached kraft pulp or fully bleached kraft pulp having a whiteness in the range of 70 to 90%.
[0003]
Conventionally, in the multi-stage bleaching method, the pulp is first treated with chlorine, lignin contained in the pulp is chlorinated, soluble is added to the lignin, and then the chlorinated lignin is dissolved and extracted with an alkali. A method has been adopted in which lignin is separated and removed from the inside, and further, a hypochlorite, chlorine dioxide or the like is used to decompose and remove a small amount of residual lignin to obtain a pulp having high whiteness.
[0004]
However, in recent years, there are concerns about the environmental impact of organochlorine compounds contained in the bleaching effluent from the chlorination stage of pulp, and research has been actively conducted on bleaching sequences that do not use atomic chlorine for pulp bleaching. In addition, even when hypochlorite is used, chloroform is produced during pulp bleaching, which may adversely affect the environment. Therefore, bleaching sequences not used for pulp bleaching (ECF: Elementary Chroline Free) are omitted. There is a search for bleaching.
[0005]
At present, oxygen-based bleaching chemicals such as ozone, oxygen, peracetic acid and persulfuric acid are attracting attention as an alternative to chlorine and hypochlorite. However, with the exception of oxygen and hydrogen peroxide, these chemicals are difficult to handle because of high chemical costs and explosive properties. Chlorine dioxide, on the other hand, has problems such as cost and generator capacity limitations. At present, the use of chlorine dioxide in place of chlorine has not yet become widespread in Japan, but promising bleaching in the future. Is the method. Compared to chlorine and hypochlorite, chlorine dioxide has less influence on the environment, but is expensive, and therefore, an optimum bleaching sequence and conditions for reducing the addition rate as much as possible have been searched for.
[0006]
In JP-A-4-245588, as a method for reducing the amount of chlorine dioxide used when bleaching chemical pulp in the absence of elemental chlorine, it is not used when bleaching with chlorine dioxide after treating pulp with hemicellulose-degrading enzyme. Compared to the case, a method has been disclosed that can reduce the addition rate of chlorine dioxide by about 20%, but problems such as pulp viscosity reduction and yield reduction due to the use of enzymes, and enzyme treatment reactions have substrate specificity. In addition, there is a possibility that pulp that is not significantly effective is produced, and since the enzyme itself is not an inexpensive reagent, the bleaching cost may increase.
[0007]
On the other hand, JP-A-4-263687 describes bleaching by combining ozone with chlorine dioxide as a means for reducing the chlorine dioxide addition rate, and it is described that the total chlorine dioxide addition rate can be reduced by 50%. Has been. However, the pulp viscosity has decreased from 27.5 mPa · s to 16 mPa · s, and equipment for generating ozone is required, so introduction into an existing factory is not easy.
[0008]
In JP-A-9-87985 and JP-A-9-87986, as a method for reducing the amount of chlorine dioxide used in the manufacture of chemical pulp for papermaking, the pH before bleaching or after bleaching is 1 to 3. A method of performing delignification and bleaching with peroxide and oxygen in an alkaline medium immediately after that, or adding a chelating agent to the chlorine dioxide stage is disclosed. By this treatment, the whiteness after the treatment was increased by about 5%, and the total addition amount of chlorine dioxide could be suppressed to 0.5% by weight of the pulp. However, the comparative example is a bleaching sequence containing chlorine, and ECF. Since the comparison example of the bleaching sequence is not compared by bleaching to the final stage, the reduction effect by ECF bleaching is not certain.
[0009]
In addition, the pH adjustment of the chlorine dioxide stage and the combined use of the chelating agent mainly focus on the effect of removing heavy metals in order to efficiently perform the reaction of peroxide and oxygen in the subsequent stage, as in the present invention. It is not intended to increase the efficiency of chlorine dioxide bleaching. Moreover, even if it processes by these methods, a peroxide may not be used immediately after that, In this case, there exists a possibility that an effect may not be seen.
[0010]
A number of sequences in which the chlorine dioxide stage is repeated twice have already been described and described in Japanese Patent Application Laid-Open No. 4-263687. However, these are provided in the subsequent stage of multi-stage bleaching, as in the present invention. It does not last twice in the first stage of multistage bleaching.
[0011]
[Problems to be solved by the invention]
In view of this background, the present inventors have conducted various studies on a method for improving bleachability for the production of ECF pulp. As a result, the pulp fiber after oxygen bleaching of unbleached pulp is divided into the first and second stages of ECF bleaching. Chlorine dioxide is used as a chemical in the eyes, and there may or may not be washing between the first and second stage chlorine dioxide treatments with different treatment temperatures, followed by extraction under alkaline conditions to produce lignin in the pulp. It has been found that the amount of chlorine dioxide used can be reduced by reducing the amount. This is a method with less environmental impact because the amount of organochlorine compounds discharged can be further reduced.
An object of the present invention is to provide an economical and environmentally friendly bleaching method in which the amount of organochlorine compounds discharged into wastewater is reduced while maintaining high whiteness, stability and high quality. It is.
[0012]
[Means for Solving the Problems]
(1) The present invention relates to a method for producing bleached pulp by oxygen-bleaching unbleached pulp obtained by digesting lignocellulosic material, and then in the absence of elemental chlorine. Immediately after that, a continuous chlorine dioxide stage is provided, followed by an extraction treatment under alkaline conditions, followed by further bleaching.
[0013]
(2) In the present invention, the first chlorine dioxide stage of the continuous chlorine dioxide stage is performed at a treatment temperature of 70 to 110 ° C. and a treatment time of 10 to 120 minutes, and immediately after that, the second chlorine dioxide stage that is continuous. Exists in the manufacturing method of the bleached pulp of the (1) description performed in the range of processing temperature 40-90 degreeC and processing time 30-120 minutes.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Pulp obtained by digestion of wood and oxygen bleaching is bleached with bleaching chemicals that do not contain chlorine or hypochlorite (ECF bleaching). Immediately after using the chlorine dioxide stage in the first stage, alkali treatment and oxygen Compared with the conventional method in which the extraction process by alkali treatment containing peroxide and peroxide continues, the method of performing chlorine dioxide treatment in two steps and then extracting with alkali treatment and alkali reinforced with delignification by oxygen is the whole process of bleaching. The addition rate of chlorine dioxide in can be reduced. Therefore, the amount of chlorine dioxide used is less than that required by the conventional method. Therefore, it is possible to use a small-capacity, economical, organic chlorine compound in wastewater, regardless of whether a chlorine dioxide generator is newly built or added. It is a way to reduce the amount and help protect the environment.
[0015]
In the present invention, wood is digested with chemicals such as kraft cooking liquor, and the unbleached pulp obtained is delignified by a known oxygen and alkali oxygen bleaching method, and the two-stage chlorine dioxide, Next to the processing by the method of adding and processing without washing (abbreviated as D1D2 when the first stage is D1 stage and the next stage is D2 stage) or the method of washing and treating between them (abbreviated as D1-D2 stage) Extract with oxygen and / or hydrogen peroxide under alkaline and / or alkaline conditions and / or after the extraction, bleach with chlorine and hypochlorite-free bleaching chemicals, Hunter whiteness of 70-90 % Bleached pulp.
[0016]
The pulp used in the present invention is a pulp obtained by oxygen-bleaching unbleached pulp from softwood and hardwood, which are lignocellulosic materials, with oxygen and alkali. As the cooking method for obtaining the pulp used in the present invention, known cooking methods such as kraft cooking, sulfite cooking, polysulfide cooking, soda cooking, etc. can be used, but considering pulp quality, energy efficiency, etc. Kraft cooking is preferably used.
[0017]
For example, when kraft cooking of wood chips, the degree of sulfidation of the kraft cooking liquid is 5 to 75%, preferably 15 to 45%, and the effective alkali addition rate is 5 to 30% by weight, preferably 10 to 25% per weight of absolutely dry wood. % By weight, cooking temperature is 140-170 ° C., the cooking method may be either continuous cooking method or batch cooking method, and when using a continuous cooking kettle, it may be a modified cooking method in which a cooking solution is added at multiple points, The method is not particularly limited.
In cooking, a known cyclic keto compound may be used in combination with the cooking solution used as a cooking aid.
[0018]
As the delignification method by oxygen bleaching used in the present invention, a known medium concentration method or high concentration method using oxygen and alkali can be applied as it is, but the pulp concentration currently used for general purposes is 8 to 15% by weight. The medium concentration method carried out in is preferred.
The alkali used in the delignification method by oxygen bleaching by the medium concentration method is caustic soda or oxidized kraft white liquor, and oxygen gas and alkali are added to the medium concentration pulp slurry in the medium concentration mixer and mixed sufficiently. After being performed, the mixture of pulp, oxygen and alkali is sent to a delignification reaction tower capable of holding for a certain period of time under pressure, and delignified. The medium-concentration mixer has a rotor that rotates at a high speed of 500 to 1000 rpm, depending on the manufacturer, and imparts a high shear force to the medium-concentration pulp slurry to change the pulp slurry into a fluid such as water, thereby , Oxygen and alkali can be mixed well.
The oxygen gas addition rate is 0.5 to 3% by weight per the dry pulp weight, the alkali addition rate is 0.5 to 4% by weight, the reaction temperature is 80 to 120 ° C., the reaction time is 15 to 100 minutes, and the pulp concentration Is 8 to 15% by weight, and other known conditions can be applied.
[0019]
The split addition or continuous chlorine dioxide treatment in the present invention means that the pulp is added with chlorine dioxide water at an acidic pH, or impregnated with the aqueous solution, and the pulp is not washed after maintaining a specific time and temperature ( D1D2), or performed (D1-D2), and impregnating the pulp again with chlorine dioxide water to maintain a specific time and temperature.
[0020]
The pulp concentration in the D1 and D2 stages of the present invention is in the range of 5 to 40% by weight, preferably 8 to 35% by weight, more preferably 10 to 25% by weight. A pulp concentration of less than 5% by weight is not suitable because a large capacity of equipment is required for processing. If the pulp concentration exceeds 40% by weight, it is difficult to uniformly mix the pulp and chlorine dioxide, and the effect cannot be obtained sufficiently, so that it is not suitable.
[0021]
The pulp concentration in the D1 and D2 stages of the present invention is 5 to 40% by weight, the treatment temperature is 50 to 150 ° C., preferably 70 to 110 ° C. in the case of the D1 stage, and the D2 stage is in the range of 40 to 90 ° C. The time is preferably 10 to 120 minutes for stage D1, and 30 to 120 minutes for stage D2.
If the treatment temperature is less than 40 ° C., the decomposition reaction of lignin by chlorine dioxide becomes insufficient, and if the temperature exceeds 150 ° C., the degradation of the polysaccharide becomes significant and the strength of the pulp fiber is greatly reduced, which is not suitable. The treatment time of the chlorine dioxide treatment of the present invention is sufficient if it is 10 minutes or longer, but the effect of delignification reaches the upper limit even if it is longer than 120 minutes.
[0022]
The amount used in the chlorine dioxide treatment of the present invention varies depending on the amount of lignin of the pulp before bleaching used and the subsequent bleaching sequence, but both D1 and D2 stages are 0.1 to 2.0% by weight based on the absolutely dry pulp, Preferably it is 0.1 to 1.0 weight%.
[0023]
The pulp after stage D2 is subjected to a lignin extraction / bleaching process under alkaline conditions using alkali alone and / or oxygen in combination (referred to as stage E or E / O stage). At this time, caustic soda, potassium hydroxide, white oxide, etc. can be used as alkaline chemicals under alkaline conditions, but caustic soda is generally used. A peroxide, particularly hydrogen peroxide may be used in combination.
In order to obtain a pulp having a whiteness of 80% or more, the pulp after the alkali extraction stage needs to be further subjected to one or more bleaching stages. Examples of chemicals include caustic soda (E), chlorine dioxide (D), oxygen (O), hydrogen peroxide (P), ozone (Z), bleaching chemicals composed of known bleaching agents such as organic peracids and bleaching aids. It can be mentioned, and it selects from these suitably, and is used as a bleaching chemical | medical agent.
Examples of bleaching sequences include D1D2-E / OD, D1-D2-E / OD, D1D2-ED, D1-D2-ED, D1D2-E / ODP, D1-D2. -E / O-D-P, D1D2-E / OP-D, D1-D2-E / OP-D, D1-D2-E-P, D1D2-E-P, D1D2-E / O-Z-D A bleach-free bleaching sequence such as D1-D2-E / O-Z-D can be used.
[0024]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples.
In Examples 1 to 4 shown below, E / O-D was used after divided addition or continuous chlorine dioxide treatment using pulp obtained by oxygen delignification of unbleached pulp obtained by cooking wood chips. Alternatively, bleaching was performed using an E / O-D-P sequence. In Comparative Examples 1 and 2, bleaching was performed using one-stage chlorine dioxide treated pulp using an E / O-D or E / O-D-P sequence. It is what I did.
Moreover, unless otherwise indicated, the chemical reduction rate in the D1 and D2 stages was calculated as follows.
[0025]
Reduction rate of total chemicals in D1 and D2 stages (vs. D stage addition ratio)
The chemical reduction rate was calculated by the following formula (1) from the total chemical rate of D1 and D2 stage chlorine dioxide used for bleaching with or without two-stage treatment or with divided addition. Reduction rate of total chemicals in D1 and D2 stages,% = {(total chemical addition rate in D stages—total chemical addition ratios in D1 and D2 in this method) / total chemical addition ratio in D stages} × 100 (1)
[0026]
Regarding the pulp viscosity, J. Org. TappiNO. 44, AOX (activated carbon adsorbing organic halogen) was performed according to the US Environmental Agency EPA method (using TOX-10 manufactured by Mitsubishi Kasei), and the PC value was measured before and after fading at 105 ° C in an accelerated manner for 4 hours. Was evaluated according to the following formula (2).
PC value = (1−whiteness after fading) 2 / (2 × whiteness after fading)) − (1−whiteness before fading) 2 / (2 × whiteness before fading)) (2)
[0027]
Example 1
Two-stage chlorine dioxide treatment was performed under the following conditions using hardwood pulp (hunter whiteness 43.8%, kappa number 10.8) subjected to kraft cooking and oxygen delignification at the factory.
That is, this unbleached pulp was adjusted to pH 4 by adding concentrated sulfuric acid to ion-exchanged water and diluted so that the pulp concentration at the time of treatment was 8%. .45% was added, placed in a 2 liter indirect heating autoclave made of stainless steel, heated at a temperature of 105 ° C. while maintaining the pressure for 60 minutes, and D1 stage treatment of the pulp was performed. After cooling the autoclave, the pulp obtained by D1 treatment was transferred to a plastic bag without washing.
[0028]
To the pulp after D1 treatment in a plastic bag, 0.30% of ion-exchanged water and chlorine dioxide per bone dry pulp weight are added so that the pulp concentration at the time of D2 treatment is 10%, and the temperature is 60 ° C. in a constant temperature water bath. D2 stage bleaching was performed by dipping for a minute. The obtained pulp was washed with deionized water and dehydrated.
Place the pulp after stage D2 in a plastic bag, adjust the pulp concentration to 10% with ion-exchanged water, add 1.0% caustic soda to the dry pulp weight, and add it to the autoclave in the same way as stage D1. And pressurize 1.5kg / m 2 with oxygen, treat at 60 ° C for 15 minutes, remove the pulp from the autoclave, transfer to a plastic bag, and treat for 45 minutes in a 60 ° C constant temperature water bath. The E / O stage was extracted. The obtained pulp was washed and dehydrated using ion-exchanged water.
[0029]
Subsequently, the pulp after the E / O stage is put in a plastic bag and adjusted to a pulp concentration of 10% using ion-exchanged water, and then 0.2% of chlorine dioxide per weight of completely dried pulp is added, at a temperature of 70 ° C. Chlorine dioxide treatment was performed under conditions of 180 minutes (D3 stage). The obtained pulp was washed with deionized water and dehydrated to obtain bleached pulp.
After the pulp after D3 stage was disaggregated, a sheet having a basis weight of 60 g / m 2 was prepared according to Tappi test method T205os-71 (JISP 8209), and the hunter whiteness of the pulp was measured according to JIS P 8123. As a result, 85.0% Met.
[0030]
Example 2
As in Example 1, D1 stage treatment with an addition rate of 0.45% was performed, followed by washing and dehydration, and further D2 stage treatment with a chlorine dioxide addition rate of 0.25%. The same treatment was subsequently carried out to obtain a bleached pulp having a Hunter whiteness of 85.0%.
[0031]
Example 3
After D1 stage treatment with an addition rate of 0.20% in the same manner as in Example 1, D2 stage treatment with a chlorine dioxide addition rate of 0.24% was performed without washing, and the treated pulp was washed with ion-exchanged water. The pulp after E / O stage treatment and D3 stage treatment under exactly the same conditions as in Example 1 was placed in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, and then per dry dry pulp weight. Hydrogen peroxide 0.35% and caustic soda 0.5% were added and treated at a temperature of 70 ° C. for 120 minutes to perform P-stage bleaching. The obtained pulp was washed and dehydrated using ion-exchanged water to obtain a bleached pulp having a Hunter whiteness of 85.0%.
[0032]
Example 4
In the same manner as in Example 3, bleaching was performed with the sequence D1-D2-E / O-D3-P, and washing and dehydration were performed between D1 and D2. The chemical addition rate of each stage was 0.2% for D1 and 0.20% for D2, and thereafter the same addition rate as in Example 3 was used to obtain bleached pulp having a Hunter whiteness of 85.0%.
[0033]
Comparative Example 1
The same unbleached pulp as in Example 1 was put in a plastic bag and adjusted with ion-exchanged water so that the pulp concentration at the time of treatment was 10%, and then 0.80% of chlorine dioxide was added per absolute dry pulp weight. Then, the chlorine dioxide stage was bleached by immersing in a constant temperature water bath of 70 ° C. for 120 minutes. The obtained pulp was washed with deionized water and dehydrated. The subsequent E / O-D stage treatment was performed in exactly the same manner as in Example 1 to obtain a bleached pulp having a Hunter whiteness of 85.0%.
[0034]
Comparative Example 2
The same D stage treatment as in Comparative Example 1 was carried out by changing only the chlorine dioxide addition rate to 0.45%, and the subsequent E / O-D-P stage treatment was carried out in exactly the same manner as in Example 2, with a Hunter whiteness of 85 0.0% bleached pulp was obtained.
[0035]
Table 1 shows the results of Examples 1 to 4 and Comparative Examples 1 and 2.
[0036]
[Table 1]
[0037]
As shown in Table 1, although depending on the sequence, the chemical chlorine compound can be reduced by 10% to 14% compared to the case of the normal one-stage treatment by the two-stage chlorine dioxide treatment (D1-D2). It can be reduced by about 37%, and depending on the D1D2 treatment, it is possible to reduce the chemical by 5 to 9%, thereby reducing the organochlorine compound by about 35%. In Examples 3 and 4, the pulp viscosity is improved as compared with Comparative Example 2. The pulp fading was also improved.
[0038]
【The invention's effect】
The present invention is a bleached pulp which can reduce the amount of chlorine dioxide used without lowering the pulp viscosity by performing two-stage chlorine dioxide treatment in the first stage in ECF bleaching, and thus can reduce the discharge of organic chlorine compounds. There is an effect of providing the manufacturing method.
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