JP4476367B2

JP4476367B2 - Purification method of acrylamide aqueous solution

Info

Publication number: JP4476367B2
Application number: JP26981496A
Authority: JP
Inventors: 重夫金山; 和也片山; 秀也高橋; 芳彦神原
Original assignee: Mitsui Chemicals Inc
Current assignee: Mitsui Chemicals Inc
Priority date: 1996-10-11
Filing date: 1996-10-11
Publication date: 2010-06-09
Anticipated expiration: 2016-10-11
Also published as: JPH10114731A

Description

【０００１】
【発明の属する技術分野】
本発明は、アクリロニトリルの接触水和によって得られる粗アクリルアミド水溶液（以下、粗ＡＡＭと略する）の精製方法に関する。さらに詳しくは、分子量が十分に高く水溶性も良好なポリマーの原料となりうる、高品位なアクリルアミドまたはアクリルアミド水溶液を効率的に製造するための、粗ＡＡＭの精製方法に関する。
【０００２】
【従来の技術】
粗ＡＡＭは、通常、重金属イオンやアミン性物質などのカチオン性不純物を含有している。このため、粗ＡＡＭは陽イオン交換樹脂やキレート樹脂への通液により、また必要に応じてさらに陰イオン交換樹脂に通液することにより精製される。特公昭５７−３２０４８にはキレート樹脂への通液による粗ＡＡＭの精製により、重金属イオンを重合トラブルなく除去できる旨記載されているが、この方法ではアミン性物質など金属イオン以外の不純物の除去が困難であるため、製品として得られるアクリルアミドまたはアクリルアミド水溶液（以下、ＡＡＭ製品と略する）を重合体とした場合の水溶性や分子量などで評価される品質（以下、重合品質と略する）は良好とは言いがたい。
【０００３】
また特公昭５６−３９３０３、特開昭５２−９３７１２、および特開平４−２７０２５３には、粗ＡＡＭ精製用の強酸性陽イオン交換樹脂はアルカリ塩型での使用が望ましいことが記載されている。しかしながら、この他に特公昭５５−３５３７６や特開昭５０−８３３２３の記載によれば、アミン性物質など金属塩以外のカチオン性物質を十分に吸着除去でき、しかも金属塩の吸着効率も高く、イオン交換樹脂量を少なくすることができるという点で遊離酸型での使用のほうが優れており、ＡＡＭ製品の重合品質も遊離酸型の樹脂で処理したもののほうが良好である。ところが、遊離酸型で使用する場合には処理液のｐＨの低下等により、アルカリ塩型での使用に比べて格段にアクリルアミド（以下、ＡＡＭと記す）の重合トラブルが起こりやすい。したがって、前者の出願でアルカリ塩型が望ましいとしている記述は主に精製時の重合トラブル防止の観点からなされたものと考えられる。
【０００４】
また、強酸性陽イオン交換樹脂を用いる粗ＡＡＭの精製においては、一般にゲル型樹脂を使用するほうがＡＡＭ重合のトラブルが発生しにくい。しかしながら、「ダイヤイオン」第７版（平成６年、三菱化成社刊）などに記載されている如く、ゲル型樹脂は使用時の破砕劣化が起こりやすく長期間の使用が困難であるという問題があり、マクロポーラス型（以下、ＭＰ型と記す）樹脂のほうが有利である。
【０００５】
前述の特公昭５５−３５３７６では、強酸性陽イオン交換樹脂として、架橋度１ないし４％の低架橋度のＭＰ型樹脂の使用が、樹脂の破砕劣化が少ない点で望ましいとされている。しかしながら、本発明者らの実験によれば、実施例２および比較例３に示す如く、ＭＰ型樹脂による粗ＡＡＭの精製において架橋度が大きい樹脂を用いるほうが破砕劣化が起こりにくかった。一方、遊離酸型で使用する場合には架橋度が大きい樹脂のほうがＡＡＭの重合を生起しやすいという結果が得られた。これらの結果から、ＭＰ型強酸性陽イオン交換樹脂を用いる粗ＡＡＭの精製で低架橋度の樹脂を使用することは、イオン交換樹脂の破砕を減少させ長期間使用するというよりも、むしろ重合トラブルを抑制するという点で効果があると考えるべきである。したがって、他の方法で重合トラブルを抑制できる場合には、高架橋度のイオン交換樹脂を用いるほうが長期間使用できるという点で有利である。
【０００６】
特開平４−３１２５６２には、陽イオン交換樹脂による粗ＡＡＭの精製に際して、精製処理前の粗ＡＡＭに空気と酸素ガスとの混合ガスを導入することなどで樹脂塔出口液の溶存酸素濃度を２ｐｐｍ以上に保持することにより、粗ＡＡＭの精製処理中のＡＡＭの重合トラブルを抑制できることが記載されている。この方法においても、陽イオン交換樹脂をアルカリ塩型で用いる場合にはＡＡＭの重合をある程度まで抑制することができるが、遊離酸型で用いる場合、とりわけＭＰ型陽イオン交換樹脂を遊離酸型で用いる場合には重合防止効果が不十分である。また、粗ＡＡＭ通液終了後に塔内に残存するＡＡＭ水溶液を排出する際の重合トラブルに対しても十分な対策とはなり得ない。さらに、粗ＡＡＭに酸素濃度の高いガスを導入することは、過酸化物の生成等によりＡＡＭ製品の重合品質に影響を与える可能性がある。
【０００７】
【発明が解決しようとする課題】
本発明の目的は、従来困難であった高架橋度ＭＰ型強酸性陽イオン交換樹脂、とりわけ遊離酸型のものの安定な使用を可能とし、粗ＡＡＭの効果的な精製を可能とすることで不純物が少なく重合品質が良好なＡＡＭ製品を効率よく製造することにある。
【０００８】
【課題を解決するための手段】
高架橋度ＭＰ型強酸性陽イオン交換樹脂、とりわけ遊離酸型のものの粗ＡＡＭ精製における安定な使用を可能とし、重合品質が良好なＡＡＭ製品を効率よく製造するため、本発明者らは、該イオン交換樹脂使用の際のＡＡＭ重合トラブルの防止方法について鋭意検討を重ねた結果、重合トラブルの発生頻度を大幅に低減する方法を見いだした。
【０００９】
粗ＡＡＭ精製のための陽イオン交換樹脂塔におけるＡＡＭ重合トラブルは、粗ＡＡＭ通液中のものと粗ＡＡＭ通液終了後、置換水洗などにより塔内のＡＡＭ水溶液を排出する際のものとに大別される。粗ＡＡＭ通液中の重合トラブルについては、溶存酸素濃度の低下、微小な吸着熱の蓄積、液の偏流など様々な原因が考えられるが、意外にもイオン交換樹脂から溶出する不純物が重合の主原因となっていることが判明した。また、置換水洗時のＡＡＭ重合トラブルについて検討したところ、驚くべきことに置換水洗時、塔出口液のＡＡＭ濃度低下と前後して同液の溶存酸素濃度が急激に低下し、これがイオン交換樹脂からの溶出不純物とともに重合発生の主原因となることが判明した。
【００１０】
これらの結果をもとに、本発明者らは架橋度８％以上のＭＰ型強酸性陽イオン交換樹脂にアルカリ通液及び酸通液による交互処理を施しイオン交換樹脂由来の溶出不純物の量を低減し、また粗ＡＡＭ精製処理後の樹脂塔からのＡＡＭ水溶液の排出を酸素含有水による置換水洗または酸素含有ガスによる押し出しにより行い、ＡＡＭ水溶液排出時の塔内液の溶存酸素濃度を十分な値に保つことによって、ＡＡＭ製品の重合品質に全く影響を与えることなく重合トラブルを防止できることを見いだし本発明を完成した。
【００１１】
すなわち本発明のアクリルアミド水溶液の精製方法は、アクリロニトリルの接触水和により得られる粗アクリルアミド水溶液を陽イオン交換樹脂を用いて精製するにあたり、架橋度８％以上のマクロポーラス型強酸性陽イオン交換樹脂を、アルカリ及び酸の交互通液による前処理を施した後に使用するとともに、精製終了後、イオン交換樹脂塔内部に残留したアクリルアミド水溶液を酸素含有水による置換水洗および／または酸素含有ガスによる押し出しにより排出することを特徴とするものである。
【００１２】
【発明の実施の形態】
本発明における粗ＡＡＭは、銅系の触媒を用いるアクリロニトリルの接触水和により得られる反応液に濃縮操作を施すことにより、未反応のアクリロニトリルを除去するとともにＡＡＭ濃度を希望する値としたもので、通常、ＡＡＭ濃度は１０〜５５重量％、銅イオン濃度は１０〜１００重量ｐｐｍである。
【００１３】
本発明において使用する強酸性陽イオン交換樹脂はスチレンとジビニルベンゼンとの共重合体にスルホン基を付加したものである。このようなイオン交換樹脂には、透明でゲル構造を有するゲル型樹脂と多孔性のＭＰ型樹脂とがあるが、ゲル型樹脂はＭＰ型樹脂に比べて破砕劣化が著しく、長期間使用するには不適当である。ＭＰ型イオン交換樹脂の架橋度は原料モノマーの全量に対するジビニルベンゼンモノマー量の重量比によって定義されるが、イオン交換樹脂を長期間安定に使用するためには、耐酸化性および耐破砕性などの点で優れた、架橋度８％以上の高架橋度品の使用が必要である。
【００１４】
このような高架橋度ＭＰ型強酸性イオン交換樹脂は市販品として入手可能であり、たとえばレバチットＳＰ１１２やレバチットＳＰ１２０（共にバイエル社製）、アンバーライト２００Ｃ（東京有機化学社製）、ダイヤイオンＰＫ−２２８（三菱化学社製）等がある。なお、強酸性陽イオン交換樹脂はその末端スルホン基の状態により遊離酸型とナトリウム塩型（以下、Ｎａ型と記す）等のアルカリ塩型とに分類できるが、市販品は通常Ｎａ型で供給されるので、これを遊離酸酸型で使用するためには事前に塩酸等の酸で処理し酸型に変換する必要がある。
【００１５】
本発明のイオン交換樹脂の前処理は、イオン交換樹脂を充填した樹脂塔にアルカリ水溶液の通液と塩酸や硫酸などの酸の通液とを交互に繰り返し行う。ここで、アルカリ水溶液および酸は通常、規定濃度で０．５〜１０、好ましくは１〜３のものを、空塔速度毎時１〜１０で下降流で通液する。通液量は通常、樹脂交換容量の１．５〜１０倍当量で、２〜４倍当量がより好ましい。アルカリ水溶液の通液は加温下で行うほうが効果的であり、通液温度は樹脂中不純物の除去効果と樹脂の耐熱性との両面から４０℃以上１３０℃以下が好ましく、５０℃以上１００℃以下がさらに好ましい。酸の通液温度は常温でよい。酸とアルカリの交互通液の反復回数はコストが許容する範囲で多いほどよいが、通常は２〜５回程度である。酸およびアルカリ水溶液を通液した後は、酸およびアルカリ通液の１〜５倍程度の流速で塔出口液のｐＨが５．５〜８になるまで十分に水洗を行う。
【００１６】
これらのイオン交換樹脂の前処理は樹脂塔の代わりに樹脂槽を用いてバッチ方式にて行うこともできるが、一般には樹脂塔による通液で行うほうが効率がよい。本発明における重合防止方法は強酸性陽イオン交換樹脂を遊離酸型、アルカリ塩型のいずれで用いる場合にも効果があるが、遊離酸型で使用するほうがアミン性物質を十分に除去し、かつ処理効率を上げることが出来る。
【００１７】
本発明において、イオン交換樹脂による粗ＡＡＭの精製は樹脂槽を用いて行うこともできるが、一般的には、イオン交換樹脂を充填した樹脂塔に粗ＡＡＭを下降流で通液することにより行われる。粗ＡＡＭの通液速度には特に制限はないが処理効率と不純物の十分な除去とを両立させるためには空塔速度は毎時０．５〜１０が望ましい。
【００１８】
本発明の精製終了後のイオン交換樹脂塔からのＡＡＭ水溶液の排出とは、粗ＡＡＭの通液により樹脂の交換容量または運転操作上の必要から樹脂塔の切り替えが必要となった際に、塔内に残存しているＡＡＭ水溶液を排出するために行なうものである。イオン交換樹脂塔からのＡＡＭ水溶液の排出は、通常、置換水洗、すなわち水を粗ＡＡＭ通液の１〜４倍程度の空塔速度で下降流にて通液することにより行われる。また置換水洗のほかに、ガスを樹脂塔上部から導入して加圧により、あるいは自然流下によりＡＡＭ水溶液を排出する。
【００１９】
本発明においては、置換水洗によるイオン交換樹脂塔からのＡＡＭ水溶液の排出に使用する酸素含有水の溶存酸素濃度は１０重量ｐｐｍ以上とするのがよく、１０ｐｐｍより酸素濃度が低すぎると重合トラブルが発生し易い。また、ガスによる押し出しによりイオン交換樹脂塔からＡＡＭ水溶液を排出する際に使用する酸素含有ガスは、酸素濃度が１０容量％以上のものがよく、ガスの導入量は樹脂塔出口液の流量が目標値通りになるように調節すればよい。
【００２０】
【実施例】
以下、実施例により本発明を具体的に説明するが、ＡＡＭおよびアミン性物質の分析は液体クロマトグラフィーにより、ポリアクリルアミドの分析はゲル浸透クロマトグラフィーにより行った。また、ＡＡＭ水溶液中の銅の定量は、過剰のＥＤＴＡによるキレート化物を四塩化炭素により抽出した後、これを原子吸光法により分析することで行った。さらに、ＡＡＭ水溶液および水中の溶存酸素濃度の測定においては、市販のガルバニ電池式溶存酸素計を脱気水および空気飽和水で衡正して用いた。
【００２１】
実施例１
以下の処理条件で、強酸性陽イオン交換樹脂による粗ＡＡＭの精製テストを行った。
［粗ＡＡＭ］ラネー銅を触媒として接触水和法により製造したＡＡＭ濃度約４９重量％、銅含有量約６０重量ｐｐｍの粗ＡＡＭ水溶液を用いた。
［イオン交換樹脂］東京有機化学社製のＭＰ型強酸性陽イオン交換樹脂、アンバーライト２００ＣＴ（架橋度２０％）を用いた。
［樹脂塔］内径５２ｍｍ、高さ７５０ｍｍ（内容積約１６００ｍｌ）のポリ塩化ビニル製の樹脂塔に、湿潤状態で８００ｍｌ（充填層高約３８０ｍｍ）のイオン交換樹脂を充填した。
［樹脂の前処理］Ｎａ型のアンバーライト２００ＣＴに対し、塩酸およびＮａＯＨ水溶液の通薬を交互にそれぞれ２回ずつ施した後、さらに塩酸の通薬により遊離酸型とした。ここで、塩酸ないしＮａＯＨ水溶液は規定濃度２．０のものを用いた。通薬は下降流、流量は毎時２４００ｍｌで、一回あたり６０分間行った。各通薬の間には塔出口液のｐＨが５．５〜８の範囲内となるまで十分な水洗を行った。なお、通薬温度は塩酸が常温、ＮａＯＨ水溶液が７０℃である。
［精製］樹脂塔に粗ＡＡＭを下降流で流量毎時２４００ｍｌ（空塔速度毎時３．０）にて４８時間通液し精製を行った後、溶存酸素濃度約８０ｐｐｍの蒸留水を用いて、温度１７℃、流量毎時２４００ｍｌの下降流で約１２０分間置換水洗を行なった。樹脂塔出口液の溶存酸素濃度は１．４〜２．０ｐｐｍでほぼ一定に保たれた。塔内ＡＡＭの低下を確認して水洗を終了したのち、樹脂塔を解体して塔内樹脂の目視点検を行った。同様のテストを１０系列の樹脂塔で並行して行ったが、粗ＡＡＭ通液中の重合は１例も見られなく、置換水洗中の樹脂塔出口液のポリアクリルアミド濃度は１０ｐｐｍ程度で安定しており、塔内樹脂の目視点検においてもポリマーは全く認められなかった。尚、置換水洗水は水１ｍ³当たり標準状態換算で５６リットルの酸素ガスを１７℃で導入した蒸留水（水圧３．２気圧）を用いた。
【００２２】
比較例１
塩酸およびＮａＯＨ水溶液の交互通液による前処理を行わずに、単に塩酸通液によりＮａ型から遊離酸型に変換したアンバーライト２００ＣＴを用いた以外は実施例１と同様にして、粗ＡＡＭの精製を１０系列の樹脂塔による並行テストを行った。結果は１０系列の樹脂塔のすべてにおいて粗ＡＡＭ通液中に重合物が生成した。
【００２３】
比較例２
置換水洗用に酸素ガス導入を行わない蒸留水（溶存酸素５〜６ｐｐｍ）を使用して置換水洗を実施した以外は実施例１と同様にして粗ＡＡＭの精製を行った。テストは５系列の樹脂塔による並行テストを行ったが、このいずれにおいても置換水洗開始の約３５分後、樹脂塔内のＡＡＭ濃度が低下する直前に樹脂塔出口液の溶存酸素濃度が急激に０となり、溶存酸素濃度の低下と同じタイミングで樹脂塔出口液のポリアクリルアミド濃度が８０〜３００ｐｐｍまで増大した。また、五系列の並行テスト中２系列では、これと同じタイミングで樹脂塔下部でのゲル状重合物の生成により塔の差圧が上昇し、通液継続が不可能となった。
【００２４】
実施例２
実施例１と同様の前処理を施したアンバーライト２００ＣＴ（架橋度２０％）およびダイヤイオンＰＫ−２１６（架橋度８％）を用いて、それぞれについて粗ＡＡＭ精製、置換水洗、イオン交換樹脂再生の反復テストを実施し、樹脂の破砕による樹脂塔差圧の上昇を調べた。
［粗ＡＡＭの精製］イオン交換樹脂塔、粗ＡＡＭ、通液条件とも、実施例１と同様に行った。
［置換水洗］粗ＡＡＭの精製終了後、実施例１と同様の条件で８時間以上置換水洗を実施し、樹脂塔出口液のＡＡＭ濃度が０．０１重量％以下であることを確認して終了とした。
［再生］規定濃度２．０の塩酸を用いて実施例１における塩酸通液と同じ条件で再生を行い、その後、樹脂塔出口液のｐＨが５．５以上となるまで水洗した。
［結果］精製、置換水洗、再生を反復して５回行い、粗ＡＡＭ精製前と５回目の置換水洗が終了した後との樹脂塔の差圧を比較した結果、差圧上昇はアンバーライト２００ＣＴで約５ｋＰａ、ダイヤイオンＰＫ−２１６で約７ｋＰａであった。なお、実験終了後、樹脂塔を解体して塔内部を点検したが、重合物生成などの異常は見られなく、差圧上昇は破砕等の樹脂形態変化による影響と考えられるが軽微である。
【００２５】
比較例３
実施例１と同様の前処理を施したダイヤイオンＰＫ−２０８（架橋度４％、三菱化学社製）を用いて、実施例２と同様のテストを行ったところ、差圧上昇は約１７ｋＰａあった。なお、実験終了後、樹脂塔を解体点検したが、重合物生成やその他の異常は無く、差圧上昇は樹脂の破砕による影響と考えられる。
【００２６】
実施例３
実施例１と同様の前処理を施し遊離酸型に変換したイオン交換樹脂アンバーライト２００ＣＴを用いて、実施例１と同様の条件で粗ＡＡＭ精製開始の１２時間後の樹脂塔出口液（ＡＡＭ製品）を約２００ｍＬ採取して不純物の分析を行い、表１の結果が得られた。ＡＡＭ中の不純物は極めて少なかった。
【００２７】
参考例１
Ｎａ型のアンバーライト２００ＣＴに塩酸およびＮａＯＨ水溶液を交互にそれぞれ２回通薬前処理し、Ｎａ型で用いた以外は実施例３と同様にして、粗ＡＡＭ精製開始の１２時間後の樹脂塔出口液（ＡＡＭ製品）を約２００ｍＬ採取し、不純物の分析を行った。結果は表１に示す。ＡＡＭ製品中の不純物は実施例３に比しては多いが、しかし許容レベルであった。
【００２８】
実施例５
実施例１と同条件で粗ＡＡＭの精製を樹脂塔５系列の並行テストで行い、精製終了後、塔内に残存するＡＡＭ水溶液の排出を空気（酸素濃度約２１容量％）による加圧、押し出しで行うとともに、樹脂塔出口液の溶存酸素濃度を測定した。ここで、樹脂塔への空気の導入量は、塔出口液の流量が毎時２４００ｍＬとなるように調整した。塔内液排出中、出口液の溶存酸素濃度は１．７〜３．０ｐｐｍで安定しており、重合トラブルは５系列の樹脂塔の何れにおいても全く発生しなかった。
【００２９】
【表１】

【００３０】
【発明の効果】
粗ＡＡＭ中のカチオン性不純物を、重合などのトラブルなく効率的かつ効果的に除去することができ、分子量が十分大きく水溶性が良好な高分子凝集剤の製造原料として有用なアクリルアミドが効率よく製造できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying a crude acrylamide aqueous solution (hereinafter abbreviated as crude AAM) obtained by catalytic hydration of acrylonitrile. More specifically, the present invention relates to a method for purifying crude AAM for efficiently producing high-grade acrylamide or an aqueous acrylamide solution that can be a raw material for a polymer having a sufficiently high molecular weight and good water solubility.
[0002]
[Prior art]
Crude AAM usually contains cationic impurities such as heavy metal ions and amine substances. For this reason, the crude AAM is purified by passing through a cation exchange resin or a chelate resin and, if necessary, further passing through an anion exchange resin. Japanese Examined Patent Publication No. 57-32048 describes that heavy metal ions can be removed without polymerization trouble by purification of crude AAM by passing through a chelate resin. However, this method can remove impurities other than metal ions such as amine substances. Because it is difficult, the quality (hereinafter abbreviated as polymerization quality) evaluated by the water solubility and molecular weight when polymerized as the product acrylamide or acrylamide aqueous solution (hereinafter abbreviated as AAM product) is good. It's hard to say.
[0003]
JP-B-56-39303, JP-A-52-93712, and JP-A-4-270253 describe that strongly acidic cation exchange resins for purification of crude AAM are preferably used in an alkali salt form. However, according to the description of JP-B-55-35376 and JP-A-50-83323, cationic substances other than metal salts such as amine substances can be sufficiently adsorbed and removed, and the adsorption efficiency of metal salts is high. The use of the free acid type is superior in that the amount of the ion exchange resin can be reduced, and the polymerization quality of the AAM product is better when it is treated with the free acid type resin. However, when the free acid type is used, the polymerization trouble of acrylamide (hereinafter referred to as AAM) is much more likely to occur than the alkaline salt type due to a decrease in pH of the treatment solution. Therefore, the description that the alkali salt type is desirable in the former application is considered to have been made mainly from the viewpoint of preventing polymerization troubles during purification.
[0004]
Further, in the purification of crude AAM using a strongly acidic cation exchange resin, it is generally less likely that AAM polymerization troubles occur when a gel type resin is used. However, as described in “Diaion” 7th edition (1994, published by Mitsubishi Kasei Co., Ltd.) and the like, gel-type resins are prone to crushing deterioration during use and are difficult to use for a long time. Yes, a macroporous type (hereinafter referred to as MP type) resin is more advantageous.
[0005]
In the above-mentioned Japanese Patent Publication No. 55-35376, the use of an MP type resin having a low crosslinking degree of 1 to 4% as a strong acidic cation exchange resin is desirable in that the resin is less crushed and deteriorated. However, according to the experiments by the present inventors, as shown in Example 2 and Comparative Example 3, crushing degradation was less likely to occur when a resin having a higher degree of crosslinking was used in the purification of crude AAM using an MP type resin. On the other hand, when used in the free acid form, it was found that a resin having a higher degree of crosslinking is more likely to cause AAM polymerization. From these results, it can be seen that the use of a low cross-linking resin in the purification of crude AAM using an MP type strongly acidic cation exchange resin reduces the crushing of the ion exchange resin and causes a polymerization trouble rather than using it for a long time. It should be considered effective in terms of suppressing Therefore, when polymerization troubles can be suppressed by other methods, it is advantageous in that an ion exchange resin having a high degree of crosslinking can be used for a long period of time.
[0006]
In Japanese Patent Laid-Open No. 4-312562, when the crude AAM is purified with a cation exchange resin, the dissolved oxygen concentration of the resin tower outlet liquid is reduced to 2 ppm by introducing a mixed gas of air and oxygen gas into the crude AAM before the purification treatment. It is described that by maintaining the above, AAM polymerization troubles during purification of crude AAM can be suppressed. Also in this method, when the cation exchange resin is used in the alkali salt form, the polymerization of AAM can be suppressed to some extent. However, when used in the free acid form, in particular, the MP cation exchange resin is used in the free acid form. When used, the polymerization preventing effect is insufficient. In addition, it cannot be a sufficient countermeasure against a polymerization trouble when discharging the AAM aqueous solution remaining in the tower after completion of the crude AAM flow. Furthermore, introduction of a gas having a high oxygen concentration into the crude AAM may affect the polymerization quality of the AAM product due to the formation of peroxides.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to enable stable use of a highly cross-linked MP type strongly acidic cation exchange resin, in particular, a free acid type, which has been difficult in the prior art, and enables effective purification of crude AAM. The object is to efficiently produce an AAM product having a small polymerization quality and good quality.
[0008]
[Means for Solving the Problems]
In order to efficiently produce an AAM product having a high degree of polymerization and enabling stable use of a highly cross-linked MP type strongly acidic cation exchange resin, particularly a free acid type, in crude AAM purification, the present inventors As a result of intensive studies on a method for preventing AAM polymerization trouble when using an exchange resin, a method for greatly reducing the frequency of occurrence of polymerization trouble has been found.
[0009]
AAM polymerization troubles in the cation exchange resin tower for the purification of crude AAM are largely classified into those during the passage of the crude AAM and those when the AAM aqueous solution in the tower is discharged by washing with replacement water after the passage of the crude AAM. Separated. There are various possible causes for polymerization troubles during the passage of crude AAM, such as a decrease in dissolved oxygen concentration, accumulation of minute adsorption heat, and liquid drift, but unexpectedly impurities eluted from the ion exchange resin are the main causes of polymerization. It turned out to be the cause. In addition, when AAM polymerization trouble at the time of replacement water washing was examined, surprisingly, at the time of replacement water washing, the dissolved oxygen concentration of the same liquid suddenly decreased before and after the decrease of the AAM concentration of the tower outlet liquid. It became clear that it became the main cause of polymerization generation together with the elution impurities.
[0010]
Based on these results, the present inventors performed an alternate treatment with an alkaline solution and an acid solution on an MP-type strongly acidic cation exchange resin having a crosslinking degree of 8% or more to determine the amount of impurities eluted from the ion exchange resin. The AAM aqueous solution is discharged from the resin tower after the crude AAM refining treatment by washing with oxygen-containing water or by extrusion with an oxygen-containing gas, and the dissolved oxygen concentration in the tower at the time of discharging the AAM aqueous solution is a sufficient value. Thus, the inventors have found that polymerization trouble can be prevented without affecting the polymerization quality of AAM products at all, and the present invention has been completed.
[0011]
That is, the method for purifying an aqueous acrylamide solution of the present invention uses a macroporous strongly acidic cation exchange resin having a crosslinking degree of 8% or more when purifying a crude acrylamide aqueous solution obtained by catalytic hydration of acrylonitrile using a cation exchange resin. The acrylamide aqueous solution remaining inside the ion-exchange resin tower is exhausted by substituting with oxygen-containing water and / or extruding with oxygen-containing gas. It is characterized by doing.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The crude AAM in the present invention is a reaction solution obtained by catalytic hydration of acrylonitrile using a copper-based catalyst to remove unreacted acrylonitrile and a desired AAM concentration by performing a concentration operation. Usually, the AAM concentration is 10 to 55% by weight, and the copper ion concentration is 10 to 100 ppm by weight.
[0013]
The strongly acidic cation exchange resin used in the present invention is obtained by adding a sulfone group to a copolymer of styrene and divinylbenzene. Such ion exchange resins include a gel-type resin having a transparent gel structure and a porous MP-type resin, but the gel-type resin is significantly crushed and deteriorated compared to the MP-type resin, and is used for a long time. Is inappropriate. The degree of cross-linking of the MP type ion exchange resin is defined by the weight ratio of the amount of divinylbenzene monomer to the total amount of raw material monomers. In order to use the ion exchange resin stably for a long period of time, the oxidation resistance and crush resistance, etc. It is necessary to use a highly crosslinked product having a crosslinking degree of 8% or more, which is excellent in terms of the point.
[0014]
Such a highly crosslinked MP type strongly acidic ion exchange resin is commercially available, for example, Levatit SP112, Levachit SP120 (both manufactured by Bayer), Amberlite 200C (manufactured by Tokyo Organic Chemical Co., Ltd.), Diaion PK-228. (Mitsubishi Chemical Corporation). Strong acid cation exchange resins can be classified into free acid type and alkali salt type such as sodium salt type (hereinafter referred to as Na type) depending on the state of the terminal sulfone group, but commercially available products are usually supplied in Na type. Therefore, in order to use it in the free acid form, it is necessary to treat it with an acid such as hydrochloric acid in advance and convert it to the acid form.
[0015]
In the pretreatment of the ion exchange resin of the present invention, an alkaline aqueous solution and an acid such as hydrochloric acid or sulfuric acid are alternately and repeatedly passed through a resin tower filled with the ion exchange resin. Here, the alkaline aqueous solution and the acid are normally passed in a downward flow at a prescribed concentration of 0.5 to 10, preferably 1 to 3, at a superficial velocity of 1 to 10 per hour. The amount of liquid passing is usually 1.5 to 10 times equivalent of the resin exchange capacity, and more preferably 2 to 4 times equivalent. It is more effective to pass the alkaline aqueous solution under heating, and the passing temperature is preferably 40 ° C. or higher and 130 ° C. or lower, and 50 ° C. or higher and 100 ° C. from the viewpoints of the effect of removing impurities in the resin and the heat resistance of the resin. The following is more preferable. The acid passing temperature may be room temperature. The number of repetitions of alternating acid and alkali flow is better as long as the cost allows, but it is usually about 2 to 5 times. After passing the acid and alkali aqueous solution, the solution is sufficiently washed with water at a flow rate of about 1 to 5 times that of the acid and alkali solution until the pH of the tower outlet liquid becomes 5.5 to 8.
[0016]
The pretreatment of these ion exchange resins can be carried out in a batch system using a resin tank instead of the resin tower, but in general, it is more efficient to carry out the liquid flow through the resin tower. The method for preventing polymerization in the present invention is effective when the strong acid cation exchange resin is used in either a free acid type or an alkali salt type, but the use of the free acid type sufficiently removes the amine substance, and Processing efficiency can be increased.
[0017]
In the present invention, the purification of the crude AAM with the ion exchange resin can be performed using a resin tank. However, in general, the crude AAM is conducted by passing the crude AAM in a downward flow through a resin tower filled with the ion exchange resin. Is called. The flow rate of the crude AAM is not particularly limited, but the superficial velocity is preferably 0.5 to 10 per hour in order to achieve both processing efficiency and sufficient removal of impurities.
[0018]
The discharge of the AAM aqueous solution from the ion exchange resin tower after the completion of the purification of the present invention means that when the resin tower needs to be switched due to the exchange capacity of the resin or the operational operation due to the passage of the crude AAM, This is performed to discharge the remaining AAM aqueous solution. The discharge of the AAM aqueous solution from the ion exchange resin tower is usually performed by washing with substitution water, that is, by passing water in a downward flow at a superficial velocity of about 1 to 4 times that of the crude AAM. In addition to washing with replacement water, gas is introduced from the upper part of the resin tower and the AAM aqueous solution is discharged by pressurization or natural flow.
[0019]
In the present invention, the dissolved oxygen concentration of the oxygen-containing water used for discharging the AAM aqueous solution from the ion exchange resin tower by substitution water washing should be 10 ppm by weight or more, and if the oxygen concentration is too low than 10 ppm, polymerization trouble will occur. It is easy to generate. In addition, the oxygen-containing gas used for discharging the AAM aqueous solution from the ion exchange resin tower by gas extrusion should have an oxygen concentration of 10% by volume or more, and the gas introduction amount is targeted at the flow rate of the resin tower outlet liquid. You just have to adjust it to get the value.
[0020]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. Analysis of AAM and amine substances was performed by liquid chromatography, and analysis of polyacrylamide was performed by gel permeation chromatography. In addition, copper in the AAM aqueous solution was quantified by extracting an excess of EDTA chelate with carbon tetrachloride and then analyzing it by atomic absorption spectrometry. Furthermore, in the measurement of the dissolved oxygen concentration in the AAM aqueous solution and water, a commercially available galvanic cell type dissolved oxygen meter was used with deaerated water and air saturated water.
[0021]
Example 1
A purification test of crude AAM with a strongly acidic cation exchange resin was performed under the following treatment conditions.
[Rough AAM] A crude AAM aqueous solution prepared by catalytic hydration using Raney copper as a catalyst and having an AAM concentration of about 49% by weight and a copper content of about 60 ppm by weight was used.
[Ion Exchange Resin] MP type strongly acidic cation exchange resin, Amberlite 200CT (crosslinking degree 20%) manufactured by Tokyo Organic Chemical Co., Ltd. was used.
[Resin Tower] A polyvinyl chloride resin tower having an inner diameter of 52 mm and a height of 750 mm (inner volume of about 1600 ml) was filled with 800 ml of ion exchange resin (packed bed height of about 380 mm) in a wet state.
[Pretreatment of Resin] Na-type Amberlite 200CT was applied with hydrochloric acid and NaOH aqueous solution alternately twice, respectively, and then made into a free acid type by passing hydrochloric acid. Here, hydrochloric acid or NaOH aqueous solution having a specified concentration of 2.0 was used. The medicine was flowed downward, the flow rate was 2400 ml / hour, and it was performed for 60 minutes at a time. Sufficient water washing was performed between each medicine until the pH of the tower outlet liquid was in the range of 5.5-8. The drug delivery temperature is normal temperature for hydrochloric acid and 70 ° C. for NaOH aqueous solution.
[Purification] After purifying the resin tower by flowing crude AAM in a downward flow at a flow rate of 2400 ml / hour (superficial velocity 3.0 / hour) for 48 hours, using distilled water having a dissolved oxygen concentration of about 80 ppm, The replacement water was washed for about 120 minutes at a descending flow of 2400 ml per hour at 17 ° C. The dissolved oxygen concentration of the resin tower outlet liquid was kept almost constant at 1.4 to 2.0 ppm. After confirming the drop of AAM in the tower and finishing the water washing, the resin tower was disassembled and the resin in the tower was visually inspected. A similar test was conducted in parallel with 10 series resin towers, but no polymerization was observed in the crude AAM liquid passage, and the polyacrylamide concentration in the resin tower outlet liquid during replacement water washing was stable at about 10 ppm. In the visual inspection of the resin in the tower, no polymer was observed. The replacement flush water used was distilled water (water pressure: 3.2 atmospheres) into which 56 liters of oxygen gas was introduced at 17 ° C. per 1 m ³ of water.
[0022]
Comparative Example 1
Purification of crude AAM was carried out in the same manner as in Example 1 except that Amberlite 200CT converted from Na type to free acid type by simply passing hydrochloric acid was used without pretreatment by alternately passing hydrochloric acid and NaOH aqueous solution. A parallel test using 10 series resin towers was conducted. As a result, a polymer was generated during the passage of crude AAM in all 10 series resin towers.
[0023]
Comparative Example 2
The crude AAM was purified in the same manner as in Example 1 except that the replacement water was washed using distilled water (dissolved oxygen 5 to 6 ppm) without introducing oxygen gas for the replacement water. The test was conducted in parallel with five series of resin towers. In either case, about 35 minutes after the start of the replacement water washing, the dissolved oxygen concentration in the resin tower outlet liquid suddenly increased immediately before the AAM concentration in the resin tower decreased. The polyacrylamide concentration in the resin tower outlet liquid increased to 80 to 300 ppm at the same timing as the decrease in dissolved oxygen concentration. Further, in the two series in the five series of parallel tests, the differential pressure of the tower increased due to the formation of a gel polymer in the lower part of the resin tower at the same timing, and it was impossible to continue liquid flow.
[0024]
Example 2
Using Amberlite 200CT (crosslinking degree 20%) and Diaion PK-216 (crosslinking degree 8%) subjected to the same pretreatment as in Example 1, the crude AAM purification, the replacement water washing, and the ion exchange resin regeneration were performed. Repeated tests were conducted to investigate the increase in resin tower differential pressure due to resin crushing.
[Purification of Crude AAM] The ion exchange resin tower, crude AAM, and liquid flow conditions were the same as in Example 1.
[Substitutional water washing] After completion of purification of the crude AAM, substitution water washing was carried out for 8 hours or more under the same conditions as in Example 1, and it was confirmed that the AAM concentration in the resin tower outlet liquid was 0.01% by weight or less. It was.
[Regeneration] Regeneration was performed using hydrochloric acid having a specified concentration of 2.0 under the same conditions as in the case of passing hydrochloric acid in Example 1, and then washed with water until the pH of the resin tower outlet liquid reached 5.5 or higher.
[Result] The purification, replacement water washing, and regeneration were repeated 5 times, and the differential pressure of the resin tower was compared before the crude AAM purification and after the fifth replacement water washing was completed. And about 7 kPa with Diaion PK-216. After the experiment was completed, the resin tower was disassembled and the inside of the tower was inspected. Abnormalities such as the formation of polymer were not observed, and the increase in the differential pressure is considered to be the effect of changes in the resin form such as crushing, but is minor.
[0025]
Comparative Example 3
The same test as in Example 2 was performed using Diaion PK-208 (crosslinking degree 4%, manufactured by Mitsubishi Chemical Corporation) that had been subjected to the same pretreatment as in Example 1. As a result, the increase in the differential pressure was about 17 kPa. It was. After the experiment was completed, the resin tower was disassembled and inspected, but there was no polymer formation and other abnormalities, and the increase in the differential pressure is considered to be the effect of crushing the resin.
[0026]
Example 3
Resin tower outlet liquid (AAM product) 12 hours after the start of crude AAM purification under the same conditions as in Example 1, using ion-exchange resin Amberlite 200CT that was subjected to the same pretreatment as in Example 1 and converted to the free acid type. ) Was collected and analyzed for impurities, and the results shown in Table 1 were obtained. There were very few impurities in AAM.
[0027]
Reference example 1
Resin tower outlet 12 hours after the start of crude AAM purification, except that Na-type Amberlite 200CT was pretreated with hydrochloric acid and NaOH aqueous solution twice each alternately and used in Na-type. About 200 mL of the liquid (AAM product) was collected and analyzed for impurities. The results are shown in Table 1. Impurities in the AAM product were higher than in Example 3, but at an acceptable level.
[0028]
Example 5
The crude AAM was purified by the parallel test of the resin tower 5 series under the same conditions as in Example 1. After the purification was completed, the AAM aqueous solution remaining in the tower was discharged and pressurized with air (oxygen concentration of about 21% by volume) and extruded. And the dissolved oxygen concentration of the resin tower outlet liquid was measured. Here, the amount of air introduced into the resin tower was adjusted so that the flow rate of the tower outlet liquid was 2400 mL per hour. During discharge of the liquid in the tower, the dissolved oxygen concentration in the outlet liquid was stable at 1.7 to 3.0 ppm, and no polymerization trouble occurred in any of the five series of resin towers.
[0029]
[Table 1]

[0030]
【The invention's effect】
Cationic impurities in crude AAM can be efficiently and effectively removed without problems such as polymerization, and acrylamide useful as a raw material for producing polymer flocculants with sufficiently high molecular weight and good water solubility can be produced efficiently. it can.

Claims

When purifying a crude acrylamide aqueous solution obtained by catalytic hydration of acrylonitrile using a cation exchange resin, a macroporous strongly acidic cation exchange resin having a crosslinking degree of 8% or more is pretreated with an alternating solution of alkali and acid. In addition, the cation exchange resin is treated with an acid to make it a free acid form, followed by washing with water until the pH becomes 5.5 to 8, and after the purification is completed, the ion exchange resin tower A method for purifying an aqueous acrylamide solution, characterized in that the aqueous acrylamide solution remaining inside is drained by washing with oxygen-containing water and / or extruding with an oxygen-containing gas.

The method for purifying an acrylamide aqueous solution according to claim 1, wherein the treatment temperature in the alkali flow is 40 ° C. to 130 ° C.

The method for purifying an acrylamide aqueous solution according to claim 1, wherein the dissolved oxygen concentration of the oxygen-containing water is 10 ppm by weight or more.

The method for purifying an acrylamide aqueous solution according to claim 1, wherein the oxygen concentration in the oxygen-containing gas is 10% by volume or more.