JP4092143B2 - Method for producing maleic anhydride - Google Patents

Description

【００６２】
本発明の第二の発明は、閉塞物の発生防止とともに、蟻酸や酢酸を共沸によって除去することを目的として、上記共沸溶媒（１）と共沸溶媒（２）との混合物を共沸溶媒として使用するのであるが、この際、両者の混合比は、共沸溶媒（１）と共沸溶媒（２）との混合物質量に対して、該共沸溶媒（２）の含有割合を１〜４０質量％とすることが好ましい。より好ましくは３〜３５質量％、特に好ましくは５〜３０質量％である。１質量％を上回る混合比とすることで蟻酸や酢酸などの副生する軽沸酸分の除去効率はより向上する。一方、４０質量％を下回る混合比とすることで、親水性の有機溶媒を使用することによる析出物抑制の効果を著しく低下させることなく、かつ軽沸酸分を除去し、有効に共沸脱水蒸留による精製工程を行なうことができ好ましい。
【００６３】
具体的には、共沸溶媒（１）としてＭＩＢＫを９５質量％、共沸溶媒（２）としてｏ−キシレンを５質量％配合したもの（混合物Ａ）や、共沸溶媒（１）としてＭＩＢＫを８０質量％、共沸溶媒（２）としてｎ−オクタンを２０質量％配合したもの（混合物Ｂ）、共沸溶媒（１）として２−ヘキサノンを７５質量％、共沸溶媒（２）としてエチルベンゼンを２５質量％配合したもの（混合物Ｃ）などが例示できる。このような混合物を共沸溶媒として使用すると、例えば混合物Ａでは、留出液組成は水との共沸点８８．２℃であって、蟻酸との共沸点が９５．５℃である３成分系溶媒混合物となる。共沸蒸留塔として、濃縮部５段、回収部１０段の有堰の段塔を用いて塔底温度１７０℃で稼動した場合には、水相２０．１質量％、混合物Ａの油相７９．９質量％の共沸組成物となる。以上の方法を用いることにより、内部構造が複雑であるため閉塞が起こった場合には、洗浄作業が煩雑で困難な共沸脱水蒸留塔での、閉塞物の付着を防止し、かつ蟻酸等の軽沸酸分を簡便に除去できる。該共沸溶媒（１）と該共沸溶媒（２）との混合物は、温度２０℃の水に対する最大溶解濃度が０．１〜５質量％、好ましくは０．５〜４質量％，特に好ましくは１〜３質量％であり、温度２０℃におけるマレイン酸の最大溶解濃度が０．１〜１０．０質量％、好ましくは０．１〜８．０質量％、より好ましくは０．３〜７．０質量％、特に好ましくは１．０〜７．０質量％である。
【００６４】
上記の共沸溶媒（１）と共沸溶媒（２）との混合物は、特にベンゼンを接触気相酸化して無水マレイン酸を製造する場合には縮合物の原因物質であるアルデヒド類やキノン類の副生量が多いために効果的である。しかしながら、これらの閉塞物の発生原因物質は、原料がベンゼンの場合だけでなく、ｎ−ブタンなどの脂肪族炭化水素系や、ナフタリンやｏ−キシレンを原料とする無水フタル酸製造の副生物としての無水マレイン酸の製造の場合でも発生する。このため、本発明の方法はいずれの原料を用いた製造方法においても有用であり、例えば、ｎ−ブタンを接触気相酸化反応して得た無水マレイン酸含有ガスを水洗捕集し、上記特性を有する有機溶媒を用いて共沸脱水蒸留する工程を含む場合にも有効である。共沸脱水塔の閉塞防止に効果を発揮しかつ蟻酸等の軽沸酸分を効果的に除去して、長期運転を可能とすることができる。
【００６５】
このような共沸溶媒（１）と共沸溶媒（２）との混合物による共沸脱水工程での使用量は、使用する有機溶媒や溶媒混合物の組成比によっても異なるが、粗マレイン酸含有水溶液に含まれる水分および無水化によって発生する水分の合計量１質量部に対して、０．５〜１０質量部の範囲、特には２〜５質量部の範囲であることが好ましい。水に対する有機溶媒の使用量が少なければ、熱消費量が少なくなり工業的に有利となる。
【００６６】
以下、本発明の第二の無水マレイン酸の製造方法の好ましい態様の一例を、図１を用いて説明する。
【００６７】
本願第二の発明は、上記第一の発明に準じて行うことができる。そこで,主として第一の発明との相違について説明する。本発明では、粗マレイン酸含有水溶液を共沸蒸留によって脱水する際に、共沸溶媒（１）と共沸溶媒（２）との混合物を共沸溶媒として使用することを特徴とする。このような混合物としては、上記した各種の有機溶媒があり、共沸溶媒（１）としては特にＭＩＢＫを使用することが好ましく、共沸溶媒（２）としてはキシレンやオクタンを使用することが好ましい。共沸脱水条件は使用する共沸溶媒によって異なるため、例えば、共沸溶媒としてＭＩＢＫ７５質量％とキシレン２５質量％との混合物を使用する場合には、該共沸脱水塔（４０）には、粗マレイン酸含有水溶液１質量に対して２．２〜３．８質量のＭＩＢＫと０．８〜１．２質量のｏ−キシレンとを供給し、合計３〜５質量とする。これらは予めＭＩＢＫとトルエンとの混合物を調製した後に、共沸脱水塔（４０）に供給してよいし、それぞれ別個に供給してもよい。一般には、塔頂圧力（絶対圧）１００〜２０００ｈＰａ、より好ましくは３００〜１５００ｈＰａとする。１００ｈＰａを下回ると真空装置が大型化するばかりでなく、塔内温度が低くなり、マレイン酸やフマル酸が結晶化して蒸留できない場合がある。その一方２０００ｈＰａを越えると塔底温度が高くなりリボイラーの大型化の他に重合物が発生し易くなるばかりでなく、高耐圧装置にする必要が生じ不経済である。また、塔頂温度は５０〜１５０℃，より好ましくは６０〜１３０℃である。５０℃を下回るとコンデンサーが大型となり、その一方１５０℃を越えると塔内でマレイン酸の重合が発生しやすくなるばかりでなく無水マレイン酸の塔頂への留出が多くなり、無水マレイン酸のロスが増大することになる。
【００６８】
塔底温度は１３０〜２００℃、より好ましくは１５０〜１９５℃である。１３０℃を下回るとマレイン酸の脱水反応が遅くなり、マレイン酸の脱水不充分となり、無水マレイン酸の収率低下につながる。一方、２００℃を超えると無水マレイン酸の沸点に近くなり留出が起こり好ましくなく、また分解及び重合が発生しやすくなるからである。このような共沸脱水条件とするために、共沸溶媒の種類や添加量、粗マレイン酸含有水溶液中の水濃度、原料供給段の変更、塔頂に付属させるコンデンサーの還流比、塔段数、温度、圧力、その他の条件を調整すればよい。
【００６９】
共沸脱水に用いる共沸溶媒としては、無水マレイン酸の製造工程で回収した共沸溶媒（７１）を再使用するものであってもよい。また、図１に示すように共沸溶媒は、共沸脱水塔（４０）に直接供給する場合に限られず、供給原料に混在させて共沸脱水塔（４０）内に供給してもよい。
【００７０】
本発明の第二においても、共沸脱水の際に共沸脱水塔（４０）の塔頂部に油水分離槽（５０）を付属させ、塔頂留出液の共沸溶媒を還流させることが好ましい。また、本発明の第二においては、図１に示すように、粗製無水マレイン酸（１１）を共沸脱水塔（４０）の塔底液と共に高沸点分離装置（６０）に供給して精製を行ってもよい。
【００７１】
なお、高沸点分離装置（６０）による高沸点物質の除去工程と溶媒分離塔（７０）による共沸溶媒の除去工程とはいずれを先に行ってもよい。
【００７２】
従来は、共沸脱水塔（４０）の塔内および塔底にゲル状物質が付着した。具体的には、共沸脱水塔の塔内の内壁や棚段、あるいは、棚段部材の孔等に付着した。しかもこの付着物は水洗によっても容易に除去できず、このため無水マレイン酸の製造工程において、共沸脱水塔やその周辺設備では定期的な洗浄やアルカリ洗浄が必要であった。しかしながら、本発明では親水性の共沸溶媒とともに蟻酸および／または酢酸と共沸組成を形成する有機溶媒との混合物を使用することで、不純物によって発生するゲル状物質の付着やマレイン酸やフマル酸の析出などによる閉塞物の発生を抑制することができ、プラントの長期稼動を達成できるとともに、共沸脱水蒸留の工程で副生酸類を除去することができる。
【００７３】
また、本発明の第二の製造方法で得られる無水マレイン酸においては、無水マレイン酸中に存在する酢酸の量が１８００ｐｐｍ以下、より好ましくは１０００ｐｐｍ以下、さらには５００ｐｐｍ以下、もっとも好ましくは３００ｐｐｍ以下である事は好ましい形態である。また、蟻酸の含有量としては、０〜２００ｐｐｍの範囲、より好ましくは、０〜１００ｐｐｍの範囲である。さらに好ましくは、０〜５０ｐｐｍの範囲である。本発明の第二においては特定の共沸溶媒（２）を、共沸溶媒（１）と併用するので、共沸脱水塔の塔底液中の無水マレイン酸中に存在する軽沸分である上記の酢酸や蟻酸の量を低減することが可能となる。その結果、共沸脱水工程後の精製工程を簡略化することも可能になる。よって、本発明の第二において、共沸脱水塔の塔底液中の無水マレイン酸中に存在する酢酸および／または蟻酸が上記の範囲であることは好ましい形態である。
【００７４】
本発明の第二においても、このように共沸溶媒を除去し、および高沸点物質を除去した無水マレイン酸を更に精製塔（８０）に供給して精製し、無水マレイン酸（８１）を製品としてもよい。
【００７５】
【実施例】
以下、本発明の実施例により具体的に説明する。
【００７６】
（参考例１：水に対する有機溶媒の最大溶解濃度による、溶媒選定方法）
本発明で使用する１種の有機溶媒または２種以上の溶媒混合物の選定は以下の方法による。１００ｍｌの密閉できる蓋付のガラス容器に温度２０℃の純水８０ｇを入れ、スターラーで攪拌しながら対象とする有機溶媒または溶媒混合物を滴下し、１時間後の溶解状態を目視で観察する。溶け残りのあった場合には、１回の滴下量をさらに少なくして再度上記の溶解性を確認する。なお溶質である有機溶媒または溶媒混合物の最小滴下量は０．０２ｇとした。このようにして、とけ残りがないと認められる最大滴下量（溶質質量）を求め、水（溶媒）８０ｇへの最大溶解濃度として算出した。具体的には、
最大溶解濃度（質量％）＝（溶質／（溶質＋溶媒））×１００の式で、求めたものが、本発明における最大溶解濃度である。これらの値は本文中に記載した化学便覧やバイルシュタインに記載される当該溶媒の水への溶解性データとほぼ一致した。なお、本件の実施例は、８０ｇの溶媒に溶解する各溶質の最大溶解濃度を、上記式に従い算出したものである。最大溶解濃度は液温２０℃で測定する。なお、２種以上の有機溶媒を混合して共沸脱水蒸留で使用する場合には、上記の方法によってその混合物の最大溶解濃度を測定する。
【００７７】
上記に従って評価した、ｏ−キシレン、メチルイソブチルケトン（ＭＩＢＫ）、ジイソプロピルケトン（ＤＩＰＫ）、ジイソブチルケトン（ＤＩＢＫ）、ジブチルーテル（ＤＢＥ）およびＭＩＢＫ８５％とｏ−キシレ１５％との溶媒混合物の溶解性を表２に示す。
【００７８】
（参考例２：該溶媒に対するマレイン酸またはフマル酸の最大溶解濃度の測定）
１００ｍｌの密閉できる蓋付のガラス容器に温度２０℃の溶媒８０ｇを入れ、スターラーで攪拌しながら最大溶解濃度測定項目の試薬特級グレードのマレイン酸またはフマル酸を添加し、目視で溶解状態を確認した。１時間攪拌しても溶け残りがある時は不溶とした。溶け残りのあった場合には、１回の添加量をさらに少なくして再度上記の最大溶解濃度の確認を行なった。なお最小滴下量は０．０１ｇとした。このようにして、とけ残りがないと認められる最大滴下量（溶質質量）を求め、各溶媒８０ｇへの最大溶解濃度として算出した。具体的には、
最大溶解濃度（質量％）＝（溶質／（溶質＋溶媒））×１００の式で、最大溶解濃度として求めたものが、本発明における最大溶解濃度である。最小適下量０．０１ｇ（０．００６質量％）でもとけ残った場合、不溶とした。なお、最大溶解濃度は液温２０℃で測定する。
【００７９】
結果を表２に示す。表２から、水への最大溶解濃度や、マレイン酸やフマル酸の最大溶解濃度は、ＭＩＢＫが他の物質より比較的高い数値を示した。ＤＩＰＫ、ＤＩＢＫとケトン基がより高い分子量の置換基になるに従ってＭＩＢＫよりも最大溶解濃度は低下してゆく傾向が見られたが、ＭＩＢＫはマレイン酸やフマル酸を溶解した。しかし、ｏ−キシレンはマレイン酸やフマル酸を溶解せず、かつ水へのこれらの物質での最大溶解濃度をほとんど示さない。なお、ｏ−キシレンは、水への溶解性が低くかつマレイン酸やフマル酸を溶解しないが、ＭＩＢＫ８５％とｏ−キシレン１５％との溶媒混合物は、水への最大溶解濃度が１．５７と比較的高く、マレイン酸の最大溶解濃度３．４１、フマル酸の最大溶解濃度０．１１と、他の物質より最大溶解濃度が高かった。
【００８０】
【表２】

【００８１】
（実施例１）
１リットルガラス製フラスコに撹拌機および還流冷却器を取り付けた容器に、試験液として、表３に示す有機溶剤８２質量％、マレイン酸１２質量％、純水６質量％を混合した液５００ｇに、マレイン酸に対してホルムアルデヒド９０００質量ｐｐｍ、ベンゾキノン１５０質量ｐｐｍ、ハイドロキノン１５０質量ｐｐｍを添加して、共沸脱水蒸留の塔内推定組成液を調製した。これを、オイルバス中常圧下で加熱して析出物である縮合物の生成を試験して確認した。
【００８２】
この試験条件は、温度：内温１００℃または液が沸騰状態となる温度、熱経時テスト時間：２時間（内温９５℃となった後の時間）、縮合物生成の確認：冷却後１μｍメンブランフィルターで吸引ろ過し、メンブランフィルター上に縮合物である析出固形分が得られたかどうかを確認、とした。結果を表３に示す。なお、表中の試験時間後加熱時の油水分解状態は、２時間熱経時テスト直後の状態で観察した。
【００８３】
表３の結果から、共沸溶媒としてＭＩＢＫ、及びＭＩＢＫ８５％とｏ−キシレン１５％との溶媒混合物を使用した場合には塔内推定組成物は、油水分離せず均一の状態であった。この理由として、ＭＩＢＫ及びＭＩＢＫ８５％とｏ−キシレン１５％との溶媒混合物は水に対する最大溶解濃度が高く、また酸分であるマレイン酸やフマル酸などの溶媒混合物への溶解度も有するためと考えられた。しかしＤＢＥやｏ−キシレンを使用した場合には、油水分離して試験液は二相に別れた状態であった。また縮合物の生成についてもＭＩＢＫ溶媒を使用した場合には試験液ろ過後のメンブランフィルター上に縮合物である析出固形分は得られなかった。一方、ＤＢＥやｏ−キシレン溶媒を使用した場合では、メンブランフィルター上に析出固形分が得られ、縮合物が生成していることが確認できた。
【００８４】
【表３】

【００８５】
（実施例２）
図１に示す工程に従って無水マレイン酸を製造した。
【００８６】
まず、ベンゼンの接触気相酸化反応により排出された無水マレイン酸を含む反応ガスを、無水マレイン酸捕集器（１０）の出口ガス温度が６０℃にコントロールして無水マレイン酸を捕集した。その後、この無水マレイン酸捕集器（１０）の出口ガスを水洗捕集器（２０）に導入した。ついで、水洗捕集器（２０）で該ガスを水で洗浄し４２質量％粗マレイン酸含有水溶液を得た。なお、得られた粗マレイン酸含有水溶液にはホルムアルデヒド３２００質量ｐｐｍ、ベンゾキノン５７質量ｐｐｍ、ハイドロキノン３０質量ｐｐｍを含んでいた。この粗マレイン酸含有水溶液に対して共沸脱水溶剤としてＭＩＢＫを使用して共沸脱水を行なった。
【００８７】
共沸脱水塔（４０）として、濃縮部３２φ有堰５段、回収部５０φ有堰１０段の蒸留塔を使用した。共沸溶媒は、マレイン酸水溶液の溶解水および発生水に対し３．５質量倍を塔頂から供給し、常圧、塔底温度１７０℃で８時間共沸脱水蒸留を行なった。系内組成が一定になった時点での塔底液組成は、無水マレイン酸９０．２質量％、ＭＩＢＫ７．５質量％、マレイン酸２．２４質量％、無水フタル酸０．０６質量％、ホルムアルデヒド０．０１質量％以下、ベンゾキノン０．０１質量％以下、ハイドロキノン０．０１質量％であり、塔頂留出組成は、ＭＩＢＫ層７８質量％、水層２２質量％であった。ホルムアルデヒド、マレイン酸はほとんど水相に分配し、それぞれ０．５１質量％、０．０００１質量％であった。８時間の運転で塔内にはアルデヒド類とキノン類の縮合物およびマレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。結果を表４に示す。なお、表４における「塔内汚れ状況」の観察において、縮合物と無水マレイン酸重合体とは以下のごとく区別した。すなわち、蒸留操作後に蒸留塔を水もしくは温水で洗浄して除去できる粘着物が無水マレイン酸重合体である。またこの操作で除去することができず、０．１Ｎ水酸化ナトリウム希釈水溶液での溶解除去が必要な黒色付着物を縮合物と判断した。
【００８８】
（比較例１）
実施例２において使用した共沸溶媒ＭＩＢＫに代えて、ｏ−キシレンを使用し、共沸溶媒をマレイン酸水溶液の溶解水および発生水に対し２．５質量倍を塔頂から供給した以外は、実施例２と同様のボトム温度として８時間の共沸脱水蒸留を行なった。結果を表４に示す。
【００８９】
【表４】

【００９０】
表４から明らかなように、共沸脱水溶媒の違いにより８時間の蒸留稼動後に共沸脱水塔内に閉塞物である縮合物やマレイン酸の析出、無水マレイン酸重合体の析出物等を観察した。ＭＩＢＫを共沸脱水溶剤に使用した場合には、縮合物および無水マレイン酸重合体による塔内の汚れや析出物は全く観察されなかった。またフマル酸の析出による閉塞も観察されなかった。このため８時間以上の蒸留の長時間操作も可能であった。一方、比較例としてｏ−キシレンを共沸脱水溶剤に使用した場合には、縮合物の析出が多量に見られた。またフマル酸の析出も見られ、特に、蒸留塔回収部トレー上に固体結晶の状態で存在していた。
【００９１】
（比較例２）
実施例２において使用した共沸溶媒ＭＩＢＫに代えて、ＤＢＥを使用し、共沸溶媒をマレイン酸水溶液の溶解水および発生水に対し４．０質量倍を塔頂から供給した以外は、実施例２と同様のボトム温度として８時間の共沸脱水蒸留を行なった。その結果、比較例１と同様の塔内の汚れが発生した。結果を表５に示す。
【００９２】
（比較例３）
実施例２において使用した共沸溶媒ＭＩＢＫに代えて、ＤＩＢＫを使用し、共沸溶媒をマレイン酸水溶液の溶解水および発生水に対し１．５質量倍を塔頂から供給した以外は、実施例２と同様のボトム温度として８時間の共沸脱水蒸留を行なった。その結果、比較例１と同様の塔内の汚れが発生した。結果を表５に示す。なお、表５における「塔内汚れ状況」の評価は、表４と同じ基準を用いた。
【００９３】
【表５】

【００９４】
（１）ＭＩＢＫ等の有機溶媒と酢酸とは、Ｊ＆Ｗ Ｓｃｉｅｎｔｉｆｉｃ社製ＤＢ−５ カラムを用いたガスクロマトグラフィーで測定した。
【００９５】
（２）蟻酸、マレイン酸、フマル酸は、ＧＬサイエンス社製ＩｎｅｒｔｓｉｌＯＤＳ−３ カラムを用いた液体クロマトグラフィーで測定した。
【００９６】
（実施例３）
図１に示す工程に従って無水マレイン酸を製造した。
【００９７】
まず、ベンゼンの接触気相酸化反応により排出された無水マレイン酸を含む反応ガスを、無水マレイン酸捕集器（１０）の出口ガス温度を６０℃にコントロールして粗製無水マレイン酸（１１）を捕集した。その後、この無水マレイン酸捕集器（１０）の出口ガスを水洗捕集器（２０）に導入した。ついで、水洗捕集器（２０）で該ガスを洗浄し、次いで、粗マレイン酸含有水溶液を得た。該溶液のマレイン酸濃度は４２質量％であり、水分５８質量％、酢酸２０００質量ｐｐｍ、蟻酸７０質量ｐｐｍを含んでいた。この粗マレイン酸含有水溶液に対して共沸脱水溶媒としてＭＩＢＫ８５質量％とｏ−キシレン１５質量％を混合して使用し共沸脱水を行った。
【００９８】
共沸脱水塔（４０）として、濃縮部３２φ有堰５段、回収部５０φ有堰１０段の蒸留塔を使用した。塔底から数えて第１０段目から粗マレイン酸含有水溶液を供給した。共沸溶媒は、マレイン酸水溶液の溶解水および無水化によって発生する水分に対して３．５質量倍を塔頂から供給し、常圧、塔底温度１７０℃で８時間共沸脱水蒸留を行った。結果を表６に示す。系内組成が一定になった時点での塔底組成は、無水マレイン酸８８．４１質量％、ＭＩＢＫ０．０４質量％、ｏ−キシレン８．７０質量％、マレイン酸１．８１質量％、フマル酸１．０４質量％、蟻酸０質量ｐｐｍ、酢酸０質量ｐｐｍであり、共沸脱水塔内に供給された液中の軽沸分である副生酸類の塔底液中での存在を無くすことができた。運転で塔内にはアルデヒド類とキノン類の縮合物および無水マレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。なお、表６における「塔内汚れ状況」の評価は、表４と同じ基準を用いた。
（実施例４）
実施例３において使用した共沸溶媒の混合組成を、ＭＩＢＫ９５質量％とｏ−キシレン５質量％とした以外は、実施例３と同様の条件として８時間の共沸脱水蒸留を行った。結果を表６に示す。系内組成が一定になった時点での塔底組成は、酢酸は１７０質量ｐｐｍとわずかに残存していたが、蟻酸は０質量ｐｐｍであり塔底液に蟻酸は存在しなかった。運転で塔内にはアルデヒド類とキノン類の縮合物および無水マレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。
【００９９】
（実施例５）
実施例３において使用した共沸溶媒の混合組成を、ＭＩＢＫ８０質量％とｎ−オクタン２０質量％とし、塔底温度１９０℃とした以外は、実施例３と同様の条件として８時間の共沸脱水蒸留を行った。結果を表６に示す。系内組成が一定になった時点での塔底組成は、酢酸は５００質量ｐｐｍ残存していたが、蟻酸は０質量ｐｐｍであり塔底液に蟻酸は存在しなかった。運転で塔内にはアルデヒド類とキノン類の縮合物および無水マレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。
【０１００】
（実施例６）
実施例３において使用した共沸溶媒の混合組成を、ＭＩＢＫ１００質量％とした以外は、実施例４と同様の条件として８時間の共沸脱水蒸留を行った。結果を表６に示す。系内組成が一定になった時点での塔底組成は、酢酸は２１５０質量ｐｐｍ、蟻酸は１００質量ｐｐｍであった。酢酸、蟻酸ともに塔底液中に存在した。運転で塔内にはアルデヒド類とキノン類の縮合物および無水マレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。
【０１０１】
（実施例７）
実施例３において使用した共沸溶媒の混合組成を、ＭＩＢＫ１００質量％とし、塔底温度１９０℃とした以外は、実施例４と同様の条件として８時間の共沸脱水蒸留を行った。結果を表６に示す。系内組成が一定になった時点での塔底組成は、酢酸は１７２０質量ｐｐｍ、蟻酸は１５質量ｐｐｍであった。塔底温度を１７０℃から１９０℃に上昇させた場合でも、酢酸、蟻酸ともに塔底液中に存在した。運転で塔内にはアルデヒド類とキノン類の縮合物および無水マレイン酸重合体による塔内の汚れや析出物は観察されなかった。またフマル酸の析出による詰まりも見られなかった。
【０１０２】
【表６】

【０１０３】
【発明の効果】
無水マレイン酸製造における濃縮・脱水工程で従来析出物として現れることが問題であったマレイン酸やフマル酸は水に対しては溶解度が高く、有機溶剤への溶解度は一般的に水よりも低い。本発明では、特定の物性を有するケトン類やエステル類などの有機溶剤を共沸溶媒として使用し、該共沸溶媒が水との相溶性を有するため、共沸脱水蒸留塔内での油水分離の状態が解消され、縮合物の生成原因物質であるアルデヒド類とキノン類の水相への濃縮がなくなることで縮合反応が抑制される。また、マレイン酸、フマル酸やマレイン酸重合体の混合溶液として存在する共沸脱水工程における共沸混合物への溶解度が増加し、析出物による閉塞を防止することができる。
【０１０４】
無水マレイン酸製造での粗マレイン酸水溶液の濃縮脱水工程として共沸脱水蒸留で行う場合に、水と親和性を有する有機溶媒を用いることで析出物による塔内閉塞を防止することができるが、マレイン酸の共沸脱水に適した水と親和性を有するケトン類やエステル類などの有機溶媒は、副生物である酸類特に蟻酸や酢酸と共沸組成を持たないため、これら副生酸類の分離が困難で精製無水マレイン酸純度を低下させる原因となる。共沸溶媒として、水と親和性を有する有機溶媒と酸類特に蟻酸や酢酸と共沸組成を持つ有機溶媒との特定割合範囲での混合溶媒系を用いて共沸脱水蒸留をすることで、析出物による共沸脱水塔の閉塞を防止しつつ、共沸脱水蒸留の工程段階で副生酸類を除去できる精製プロセスとすることができる。
【図面の簡単な説明】
【図１】 図１は、本発明における無水マレイン酸の製造方法の好ましい製造方法の工程図である。
【符号の説明】
１…反応ガス、
１０…無水マレイン酸捕集器、
１１…粗製無水マレイン酸、
２０…水洗捕集器、
２１…リサイクル捕集水、
３０…濃縮装置、
４０…共沸脱水塔、
５０…油水分離槽、
５１…廃水、
６０…高沸点分離装置、
６１…残査、
７０…溶媒分離塔、
７１…共沸溶媒、
８０…精製塔、
８１…精製無水マレイン酸
９０…溶媒回収塔。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing maleic anhydride, which includes a step of azeotropically dehydrating a crude maleic acid-containing aqueous solution using an azeotropic solvent, and more specifically, in the step of azeotropic dehydration, The present invention relates to a method for producing maleic anhydride, characterized by carrying out azeotropic dehydration using an organic solvent having a dissolution concentration of 0.1 to 5% by mass as an azeotropic solvent.
[0002]
[Prior art]
Maleic anhydride has a highly reactive double bond and two carboxyl groups dehydrated to form an anhydride, so it can be used in various chemical reactions, including pharmaceuticals, polyester resins, and alkyds. It is a general-purpose compound frequently used in various fields such as resins, plasticizers, agricultural chemicals and the like. This maleic anhydride oxidizes aliphatic hydrocarbons having 4 or more carbon atoms such as n-butane, benzene and the like in a catalytic gas phase oxidation reactor, and the maleic anhydride is obtained from the resulting gas containing maleic anhydride and maleic acid. It is produced by a method of recovering and making maleic anhydride by dehydration or the like. In addition, since a considerable amount of maleic acid is contained in the cleaning water of the exhaust gas discharged when producing phthalic anhydride by the catalytic gas phase oxidation reaction of naphthalene or o-xylene, the cleaning water is recovered and recovered. Similarly, it is also produced by a method of making maleic anhydride.
[0003]
In general, when maleic anhydride is produced through a catalytic gas phase oxidation reaction, the maleic anhydride obtained by the catalytic gas phase oxidation reaction is purified as it is, and the crude product obtained by once collecting it in an aqueous solution. There is a method in which a maleic acid-containing aqueous solution is dehydrated and maleic acid is reconverted to maleic anhydride for production.
[0004]
For example, Japanese Patent Publication No. 41-3172 discloses a method for producing maleic anhydride by catalytic gas phase oxidation of a mixed gas of benzene and air, contacting a reaction gas containing maleic anhydride with water, An acid-containing aqueous solution is obtained, dissolved in molten maleic anhydride, and the mixed solution is continuously added to a maleic anhydride-aromatic hydrocarbon mixed solution at 130 to 160 ° C. to obtain maleic acid in a liquid phase. A continuous process for the dehydration of maleic anhydride is described. Aromatic hydrocarbons for dehydrating maleic anhydride include xylene, cymene, ethylbenzene, diethylbenzene, dichlorobenzene, etc., and the amount varies depending on the type of azeotropic solvent used, but usually depends on the dehydration of maleic acid. It is 2 to 5 mole times the number of moles of water to be produced.
[0005]
JP-A-50-50316 further discloses a crude maleic acid-containing aqueous solution obtained by collecting a maleic acid-containing gas obtained by catalytic oxidation of an aliphatic or aromatic hydrocarbon with a temperature of 100 to 150 ° C., pressure A method is described in which molten maleic acid is obtained by treatment with 400 to 760 mmHg, and this is evaporated and dehydrated at a temperature of 115 to 165 ° C. and a pressure of 40 to 200 mmHg to obtain maleic anhydride. The method converts a portion of maleic acid to maleic anhydride and treats the accompanying impurities with water to form a solid phase consisting of fumaric acid and other insoluble impurities and an aqueous liquid phase containing maleic acid, The solid phase is filtered out and removed from the system, and the resulting aqueous filtrate containing maleic acid is recycled and purified. The above production method is a method for suppressing the accumulation in the apparatus with the passage of time due to impurities in the continuous production method of maleic anhydride, and preventing harmful effects due to blockage due to the accumulation and a decrease in thermal conductivity.
[0006]
Further, JP-A-63-313782 discloses that maleic acid is anhydrous by azeotropic distillation of exhaust gas cleaning water containing an organic substance mainly composed of maleic acid in the range of 20 to 40% by weight with o-xylene in a dehydration tower. A method for producing maleic anhydride is disclosed, in which, when converted to maleic acid to produce maleic anhydride, the pitch accompanying maleic anhydride obtained from the lower part of the dehydration tower is removed by a vacuum evaporator.
[0007]
[Problems to be solved by the invention]
However, in the case where maleic anhydride is obtained by the catalytic gas phase oxidation reaction as described above, continuous production equipment is produced by impurities such as benzoquinone, and fumaric acid by-produced in the purification step of maleic anhydride. There are many cases where internal blockage occurs. The method described in the above Japanese Patent Application Laid-Open No. 50-50316 suppresses deposition in the apparatus over time due to impurities in such a continuous production method of maleic anhydride, and reduces clogging or thermal conductivity due to the deposition. This is a method for preventing harmful effects caused by the above, but has not yet sufficiently prevented occlusion. Further, the method described in Japanese Patent Publication No. 41-3172 is not satisfactory.
[0008]
Also, unlike the method described above, benzene and C _Four When producing maleic anhydride from a crude maleic acid-containing aqueous solution obtained by absorbing a reactive gas obtained by catalytic vapor phase oxidation of a fraction hydrocarbon into water, hydrogen peroxide is added to the crude maleic acid-containing aqueous solution. Japanese Patent Publication No. 3-76311 discloses a method for producing maleic anhydride, which is concentrated and dehydrated by adding. According to the publication, the crude maleic acid-containing aqueous solution contains various impurities, and these impurities are mixed as intermediate products and by-products when any hydrocarbon is used as a raw material. Even if the reaction catalyst is reformed, it is difficult to prevent it completely. As a result, as the above impurities, for example, when phenols and aldehydes, quinones and aldehydes coexist, resinization or gelation proceeds, and a resinous / gelled material is generated, thereby blocking the device. . Then, when hydrogen peroxide is added to the crude maleic acid-containing aqueous solution for concentration and dehydration, these impurities can be decomposed by hydrogen peroxide, so that the formation of the above resinous / gelling substances can be prevented. . However, there arises a new problem that the purifier is corroded by formic acid produced as a by-product. Furthermore, hydrogen peroxide is known to be a polymerization initiator for maleic anhydride. For this reason, particularly in an azeotropic dehydration distillation column having a high operating temperature, a maleic acid polymer that becomes a plug is newly generated. Therefore, the method disclosed in Japanese Examined Patent Publication No. 3-76311 is not sufficient as a technique for preventing the blockage of the apparatus in the industrial maleic acid production process. And when a clogging thing generate | occur | produces in an azeotropic dehydration distillation column, it will become impossible to operate continuously for a long time.
[0009]
In view of the above problems, the present invention does not cause corrosion of the apparatus, etc., and also prevents the occurrence of obstructions, and the internal structure is complicated. Therefore, when obstruction occurs, the cleaning operation is complicated and difficult. An object of the present invention is to provide a maleic anhydride production method capable of preventing clogging in a boiling dehydration distillation column and enabling continuous operation for a long period of time. It is another object of the present invention to provide a method for producing maleic anhydride that is also effective as an excellent purification step that can remove impurities produced as a by-product in the catalytic gas phase oxidation reaction.
[0010]
[Means for Solving the Problems]
The present inventors have studied in detail the types of by-products produced by catalytic gas phase oxidation reaction and clogs generated in the production process of maleic anhydride, particularly clogs in azeotropic dehydration towers. Multiple insoluble substances such as condensates of aldehydes and quinones by-produced by oxidation reaction, homopolymers of maleic acid, and fumaric acid and maleic acid precipitates of maleic acid, such as azeotropic dehydration tower It was found that it occurs in the purification apparatus. On the other hand, since maleic acid and fumaric acid have higher solubility in water than in organic solvents, when azeotropic dehydration is performed using a hydrophilic organic solvent as the azeotropic solvent, the oil-water separation state in the distillation column It has been found that by relaxing the above, blockage in the dehydration process can be prevented very efficiently, and the present invention has been completed. In addition, hydrophilic organic solvents effective in preventing clogging are less likely to form an azeotropic composition with light boiling acid components by-produced in the reaction, particularly formic acid and acetic acid, and have a low effect of distilling and removing them. Therefore, in addition to the hydrophilic organic solvent as an azeotropic solvent, it was found that formic acid and acetic acid can also be removed by using another organic solvent that forms an azeotropic composition with formic acid, acetic acid, and the like, thereby completing the present invention.
[0011]
The present invention provides a method for producing maleic anhydride comprising a step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation using an azeotropic solvent, wherein the maximum dissolution concentration in water at a temperature of 20 ° C. is 0.1 to 5% by mass. The present invention provides a method for producing maleic anhydride, which comprises using the organic solvent as azeotropic solvent (1). Maleic acid and fumaric acid, which have conventionally been problematic in the concentration / dehydration process in the maleic anhydride production process, have high solubility in water and generally low solubility in non-hydrophilic organic solvents. In the present invention, an organic solvent such as ketones and esters having a specific property of compatibility with water is used as an azeotropic solvent, thereby eliminating the state of oil-water separation in the azeotropic dehydration distillation column. It has been found that the condensation in the aqueous phase of aldehydes and quinones, which are condensate-producing substances, can be reduced, and the condensation reaction between aldehydes and quinones can be suppressed. In addition, it has also been found that the precipitation of maleic acid and fumaric acid and the solubility of the maleic anhydride polymer in an azeotropic solvent can be increased to prevent clogging by the precipitate.
[0012]
The present invention also relates to a method for producing maleic anhydride comprising a step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation using an azeotropic solvent, and forming an azeotropic composition with water to form a maximum for water having a temperature of 20 ° C. A mixture of an azeotropic solvent (1) having a dissolution concentration of 0.1 to 5% by mass and an azeotropic solvent (2) that forms an azeotropic composition with formic acid and / or acetic acid is used as an azeotropic solvent. And providing a method for producing maleic anhydride. The above-mentioned hydrophilic organic solvents such as ketones and esters do not form an azeotropic composition with by-product acids, particularly formic acid or acetic acid, and it is difficult to separate these by-product acids, so that the resulting maleic anhydride is obtained. It may cause a decrease in purity. Therefore, in the above dehydration step, a mixture of an azeotropic solvent (1) having an affinity for water and an azeotropic solvent (2) having an azeotropic composition with acids, particularly formic acid or acetic acid, is used as an azeotropic solvent. When used, it is possible to provide a purification process capable of efficiently removing by-products in the azeotropic dehydration distillation step while preventing clogging of the azeotropic dehydration tower by precipitates. Moreover, the purification process after the azeotropic dehydration distillation process can be simplified.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The first aspect of the present invention is a method for producing maleic anhydride comprising a step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation using an azeotropic solvent, wherein the maximum dissolution concentration in water at a temperature of 20 ° C. It is a manufacturing method of maleic anhydride characterized by using 0.1-5 mass% organic solvent as an azeotropic solvent (1). Examples of the azeotropic solvent (1) include ketones or esters, which relaxes the oil-water separation state that occurs between water and the azeotropic mixture during azeotropic dehydration distillation, and makes the homogeneous phase or a state close thereto. In order to form, the said azeotropic distillation can be performed on conditions with few solid precipitates. In the present specification, the “maximum dissolution concentration” means the maximum dissolution concentration defined in the Examples section. Moreover, you may refer to the solubility and solubility data described in a chemical handbook, Beilstein, etc.
[0014]
An azeotropic solvent is generally used for azeotropic dehydration of a crude maleic acid-containing aqueous solution. Conventionally, aromatic compounds such as xylene, cymene, ethylbenzene, diethylbenzene, and dichlorobenzene have been used. Therefore, azeotropic dehydration distillation was performed using an organic solvent having a relatively low solubility in water as an azeotropic solvent. However, when the above organic solvent having low solubility in water is used, there is no compatibility with water or maleic acid at the distillation tower temperature at the time of actual distillation, and water contained in the crude maleic acid-containing aqueous solution in the distillation tower. And the above azeotropic solvent are separated from each other by oil and water. Since maleic acid and impurities such as aldehydes and quinones contained in the crude maleic acid-containing aqueous solution are water-soluble and mainly present in the aqueous phase, they are concentrated in the aqueous phase separated from the oil-water and further distilled. When exposed to high temperatures for a long time, the condensation reaction of aldehydes and quinones tends to proceed, contributing to the production of solid precipitates. In addition, maleic acid and its isomers fumaric acid and maleic anhydride polymer are water-soluble and have little solubility in conventionally disclosed aromatic organic solvents, so they are likely to precipitate in organic solvents. Again, it contributes to obstruction. According to a detailed observation of the operating conditions in the azeotropic dehydration distillation column, the present inventor concentrated aldehydes and quinones on the water phase side in the region where the dehydration was insufficient and the water pressure was present. As a result, clogging with the condensate is likely to occur. It was also found that clogging due to precipitation of water-soluble maleic acid or maleic anhydride polymer is likely to occur in the tower region where dehydration proceeds and almost no water exists.
[0015]
In contrast, when azeotropic dehydration is performed using a hydrophilic organic solvent as the azeotropic solvent, the oil-water separation state in the distillation column is relaxed, and the aldehydes and quinones are localized in the aqueous phase. It has been found that the concentration in the aqueous phase can be suppressed and the condensation reaction by both can be suppressed. Examples of such hydrophilic organic solvents include maleic acid and fumaric acid, which are target products, or condensates that may be produced, or those that are not reactive with a maleic acid polymer, and have a temperature of 20 ° C. Is an organic solvent having a maximum dissolution concentration in water of 0.1 to 5% by mass, more preferably 0.5 to 4% by mass, and particularly preferably 1 to 3% by mass. When the maximum dissolved concentration in water is less than 0.1% by mass, the above-described oil / water separation state is likely to occur. On the other hand, when it exceeds 5% by mass, there is an effect of improving the oil / water separation state. When the organic solvent distilled at the top of the tower together with water is separated and recovered from water after cooling, the amount of loss to the aqueous phase increases and the amount of liquid separation recovered decreases. It will be disadvantageous. Therefore, the above organic solvent is used as the azeotropic solvent (1) in the present invention.
[0016]
Further, as the physical properties of the azeotropic solvent (1) used in the present invention, the maximum dissolution concentration of maleic acid at a temperature of 20 ° C. (normal pressure) is 0.1 to 10.0% by mass, preferably 0.1. It is preferable that it is -8.0 mass%, More preferably, it is 0.3-7.0 mass%, Especially 1.0-7.0 mass% is preferable. When the azeotropic solvent (1) used in the present invention has high solubility in maleic acid and has an affinity for maleic acid, it prevents precipitation of maleic acid and fumaric acid in the azeotropic dehydration step. As a result, precipitation of a water-soluble solid such as a maleic anhydride polymer can also be prevented. At the same time, isomerization into fumaric acid and precipitation of fumaric acid can also be prevented, which is one of the preferred embodiments of the present invention.
[0017]
The azeotropic solvent (1) used in the present invention further has a boiling point at a pressure of 1013 hPa of 80 to 190 ° C., more preferably 100 to 170 ° C., particularly 110 to 160 ° C. A boiling point higher than 190 ° C. is not preferable because it is close to the boiling point of maleic anhydride and the rate of distillation together with the organic solvent increases. On the other hand, if the boiling point is lower than 80 ° C., the dehydration reaction temperature in the distillation column is lowered, the dehydration rate is lowered, and production cannot be advantageously performed.
[0018]
Examples of the azeotropic solvent (1) used in the present invention include ketones such as methyl isobutyl ketone, diisopropyl ketone, 3-pentanone, 2-hexanone, 3-hexanone, and 2-heptanone, amyl acetate, and allyl acetate. There are alcohols such as esters, methylcyclohexanol and 2-ethyl-1-hexanol. Among these, in the present invention, ketones such as methyl isobutyl ketone, diisopropyl ketone and 2-hexanone and esters such as allyl acetate are particularly preferable. These ketones and esters are compatible with water, and the solubility of maleic acid, fumaric acid, maleic acid polymer, etc. in the azeotropic solvent (1) is increased, and the precipitation problem can be solved. It is. Although the maximum dissolution concentration varies depending on the pressure, the maximum dissolution concentration in the present invention is a value at normal pressure (1013 hPa). The maximum dissolution concentration of the azeotropic solvent (1) used in the present invention should be indicated as follows from the data described in the chemical handbook (published by Maruzen Co., Ltd.) and Beilstein Online (searched by STN International). Can do. Moreover, it can also measure by the method shown in an Example. Specifically, methyl isobutyl ketone (1.91% by mass), diisopropyl ketone (0.43% by mass), 3-pentanone (4.6% by mass), 2-hexanone (1.75% by mass), 3- Hexanone (1.57% by mass), 2-heptanone (0.44% by mass), amyl acetate (0.25% by mass), allyl acetate (2.8% by mass), 2-ethyl-1-hexanol (0 .10 mass%). In particular, ketones are preferable in that the solubility of maleic acid is excellent. Ketones satisfy the above conditions, are excellent in the effect of preventing the occurrence of clogging in the production process of maleic anhydride and the solubility of the clogging, and have no reactivity with the target maleic acid or maleic anhydride Because.
[0019]
The above azeotropic solvent (1) is one of the clogging substances in the azeotropic dehydration tower in the process when maleic anhydride is produced by catalytic gas phase oxidation using benzene as a raw material, This is particularly effective because the amount of by-products of aldehydes and quinones that are causative substances of the condensate is large. However, these aldehydes and quinones are not only produced from benzene, but also produced from maleic anhydride using aliphatic hydrocarbons such as n-butane, and from naphthalene and o-xylene. It occurs even when maleic anhydride is recovered from exhaust gas discharged during the production of phthalic anhydride. Therefore, the method of the present invention is useful in any production method using raw materials. For example, maleic anhydride-containing gas obtained by catalytic gas phase oxidation reaction of n-butane is collected by washing with water, and the above characteristics are obtained. It is also effective in the case of including a step of azeotropic dehydration distillation using an organic solvent having the above, and is effective in preventing clogging of the azeotropic dehydration tower and enables long-term operation.
[0020]
In the present invention, in the azeotropic dehydration of the crude maleic acid-containing aqueous solution, one of the azeotropic solvents (1) can be used alone, or two or more can be used in combination.
[0021]
Furthermore, even if an organic solvent having no physical property of the azeotropic solvent (1) is mixed, the obtained solvent mixture has the same physical properties as the azeotropic solvent (1), that is, an azeotropic point with a specific range of water. In the case where it has maleic acid solubility and water solubility, the same effect as that obtained when the azeotropic solvent (1) is used may be obtained.
[0022]
A case of using a mixture of a specific organic solvent, which is a solvent mixture containing the azeotropic solvent (1) as an essential component, will be described later as a second invention. Further, in the present invention, in addition to using the azeotropic solvent (1) alone or in combination with another solvent other than the azeotropic solvent (1), the solvent mixture has at least a characteristic of water at a pressure of 1013 hPa. The azeotropic point is 70 to 100 ° C., more preferably 80 to 100 ° C., particularly 85 to 100 ° C., and the maximum dissolution concentration of maleic acid at a temperature of 20 ° C. is 0.1 to 10.0% by mass, preferably 0.8. 1 to 8.0% by mass, more preferably 0.3 to 7.0% by mass, particularly 1.0 to 7.0% by mass, and the maximum dissolution concentration in water at a temperature of 20 ° C. is 0.1 to 5%. % By mass, more preferably 0.5 to 4% by mass, and particularly 1 to 3% by mass, prevents the formation of condensates of aldehydes and quinones, and also prevents maleic acid, fumaric acid, maleic acid heavy acid. Precipitation of solids such as coalescence can be prevented.
[0023]
As such a solvent mixture, the total amount of the organic solvent other than the azeotropic solvent (1) is 100% by mass with respect to methyl isobutyl ketone, 3-pentanone and 3-hexanone as the azeotropic solvent (1). The other organic solvent is blended in an amount of 1 to 40% by mass, more preferably 3 to 35% by mass, and particularly 5 to 30% by mass. If an organic solvent having low solubility in water, that is, an organic solvent other than the azeotropic solvent (1) is used in excess of 40% by mass, the effect of suppressing precipitates may be reduced, and the amount may be less than 1% by mass. This is because the effect of blending cannot be expected even if used. In addition, by using such an organic solvent having low solubility in water, the amount of the azeotropic solvent (1) used can be reduced and an economical organic solvent can be selected. As such another organic solvent, there is an advantage that any organic solvent can be used as long as it does not interfere with the azeotropic dehydration of the above-mentioned crude maleic acid-containing aqueous solution even if it is mixed. Specifically, hydrocarbons such as toluene, xylene, octane, cumene, mesitylene, ethylbenzene, and dimethylcyclohexane, sulfur-containing compounds such as isopropyl sulfide and allyl sulfide, and halides such as bromobenzene and iodopropane are preferably used. can do. When the maximum solubility of maleic acid in the solvent mixture exceeds the above range, the recovery rate of maleic acid decreases due to the high solubility. On the other hand, when the maximum solubility is below the above range, maleic acid and fumaric acid are contained in the solvent mixture. Precipitates easily.
[0024]
Furthermore, the solvent mixture may be a case where it does not contain the azeotropic solvent (1) at all as long as it has the characteristics as the solvent mixture. As described above, the present invention can relax the oil-water separation state in azeotropic dehydration distillation by using an azeotropic solvent having specific hydrophilicity, can suppress the condensation reaction between aldehydes and quinones, and is blocked. The present invention is characterized in that it can prevent the generation of substances, and the azeotropic solvent having the above-mentioned characteristics is not necessarily used to satisfy this purpose. That is, in the present invention, regardless of the type of solvent used, in the method for producing maleic anhydride including the step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation, the azeotropic point with water at a pressure of 1013 hPa is 70 to 100. And a solvent mixture in which the maximum dissolution concentration of maleic acid at a temperature of 20 ° C. is 0.1 to 10.0% by mass and the maximum dissolution concentration in water at a temperature of 20 ° C. is 0.1 to 5% by mass. Boiling dehydration is possible.
[0025]
As a solvent mixture having such a composition, there is a solvent mixture of amyl alcohol and amyl acetate. When the solvent mixture has a composition ratio of, for example, 45.9% by mass of water and 12.2% by mass of amyl alcohol and 41.9% by mass of amyl acetate, the azeotropic point with water is 94.9 ° C., The maximum dissolution concentration of maleic acid in a solvent mixture of 12.2 parts by mass of amyl alcohol and 41.9 parts by mass of amyl acetate at a temperature of 20 ° C. is 6.68% by mass, and the maximum dissolution concentration in water at a temperature of 20 ° C. is 0. 19% by mass. When the solvent mixture is used, if the clogging occurs due to the complicated internal structure, the clogging of the azeotropic dehydration distillation column, which is complicated and difficult to clean, is prevented, and the long-term apparatus Operation can be enabled.
[0026]
The amount of the azeotropic solvent (1) or solvent mixture used in the azeotropic dehydration step varies depending on the composition ratio of the azeotropic solvent (1) or solvent mixture used, but the water contained in the crude maleic acid-containing aqueous solution. It is preferably in the range of 0.5 to 10 parts by mass, particularly in the range of 2 to 5 parts by mass with respect to 1 part by mass of the total amount of moisture generated by dehydration. If the amount of the organic solvent used relative to water is small, the heat consumption is reduced, which is industrially advantageous.
[0027]
Hereinafter, an example of the preferable aspect of the manufacturing method of the 1st maleic anhydride of this invention is demonstrated using FIG. In FIG. 1, 1 is a reaction gas, 10 is a maleic anhydride collector, 11 is crude maleic anhydride, 20 is a water-washing collector, 21 is recycled collection water, 30 is a concentrating device, and 40 is azeotropic. Dehydration tower, 50 is an oil / water separation tank, 51 is waste water, 60 is a high boiling point separator, 61 is a residue, 70 is a solvent separation tower, 71 is an azeotropic solvent, 80 is a purification tower, 81 is purified maleic anhydride, 90 is It is a solvent recovery tower.
[0028]
First, a raw material gas is supplied to a catalytic gas phase oxidation reactor (not shown). The raw material gas to be supplied is not particularly limited as long as maleic acid is generated as a product by a catalytic gas phase oxidation reaction, and a known hydrocarbon used for producing maleic anhydride is used as the raw material gas. be able to. For example, hydrocarbons having 4 or more carbon atoms such as benzene, butane (n-butane), butenes (1-butene, 2-butene), butadiene (1,3-butadiene), or 1 of o-xylene and naphthalene. A seed | species or these 2 or more types of mixtures can be illustrated. In the present invention, benzene is preferably used as a raw material gas for the catalytic gas phase oxidation reaction. This is because by-products are different depending on the raw material species, and are particularly effective in suppressing occlusions, particularly condensates, generated by by-products when benzene is used as a raw material gas. Further, the production method of the present invention can be applied other than using benzene as a raw material gas.
[0029]
As the catalyst used in the reactor, a known catalyst can be used as long as it generates maleic acid or maleic anhydride, and an oxidation catalyst containing vanadium as a main component can be used. As such a catalyst, the catalysts described in JP-A-5-261292, JP-A-5-262754, JP-A-5-262755, and JP-A-6-145160 are preferably used. it can.
[0030]
Since the catalytic gas phase oxidation reaction is literally an oxidation reaction, a molecular oxygen-containing gas is supplied together with the raw material gas. As such a molecular oxygen-containing gas, air is usually used, but air diluted with an inert gas, air enriched by adding oxygen, or the like can also be used.
[0031]
Although conventionally known methods can be employed as the reaction conditions, they may be appropriately changed depending on the type of oxidation catalyst used, the concentration of the feedstock, the concentration of molecular oxygen-containing gas, and the like. For example, the reaction is performed at a temperature of 300 to 600 ° C. using a vanadium-phosphorus catalyst. The reaction gas discharged from the catalytic gas phase oxidation reactor contains reaction components by-produced with maleic anhydride and impurities contained in the raw material gas as it is, and further, oxides of the impurities and raw material compounds. These include low-boiling substances, high-boiling substances, and non-condensable gases. In the present invention, the low boiling point substance means a substance having a lower boiling point than maleic acid in the standard state, and examples include formic acid, acetic acid, acrylic acid, formaldehyde, acetaldehyde, p-benzoquinone, water and the like. The high boiling point substance means a substance having a boiling point higher than that of maleic acid in the standard state, and examples thereof include phthalic anhydride and fumaric acid. Further, the non-condensable gas refers to a gas substance in a standard state, and specific examples include nitrogen, oxygen, air, propylene, propane, carbon monoxide, carbon dioxide and the like. In addition, said standard state is a state of normal pressure 1013hPa (1 atmosphere) and temperature 0 degreeC.
[0032]
The composition of the reaction gas obtained by the catalytic vapor phase oxidation reaction of benzene is generally maleic anhydride (hereinafter, “maleic anhydride” in the composition of the reaction gas includes maleic acid converted to maleic anhydride). 2 to 5% by mass, low boiling point substances excluding water vapor, acetic acid, aldehydes and the like are 0.01 to 0.1% by mass, high boiling point substances are phthalic anhydride and the like are 0.005 to 0.03% by mass, the rest are Non-condensable gas and water vapor.
[0033]
Next, the reaction gas discharged from the reactor is supplied to the maleic anhydride collector (10). In the maleic anhydride collector (10), cooling is performed at a temperature not lower than the melting point and not higher than the boiling point of maleic anhydride, more preferably 55 to 120 ° C, particularly preferably 60 to 100 ° C, and a part of maleic anhydride is liquid. Collect. Since there is a vapor pressure residue of maleic anhydride, a large amount of maleic anhydride is also present in the reaction gas after cooling. For this reason, after performing the collection process by cooling such maleic anhydride, the exhaust gas after the process is supplied to the water washing collector (20), and a large amount of maleic anhydride present in the aqueous solution is supplied. Collect and collect as a crude maleic acid-containing aqueous solution.
[0034]
A conventionally well-known method can be employ | adopted for the collection conditions of a water-washing collector (20). Water can be used as the collection liquid, but water or a part of the aqueous solution generated in the maleic acid concentration and dehydration process can also be used as a part of the collection liquid. The tower top temperature is preferably low in order to improve the collection rate of maleic anhydride, and the tower top temperature is set to 10 using a cooler attached to the water scavenger (20). -90 degreeC, More preferably, you may be 20-60 degreeC. Below 10 ° C, the maximum dissolution concentration of maleic acid decreases and crystals are precipitated, and the efficiency of the water-washing collector (20) is increased, and the stage efficiency of the collecting tower (20) is reduced due to the deterioration of liquid dispersibility. Invite. In addition, an excessive amount of cooling energy is required. On the other hand, when the temperature exceeds 90 ° C., the collection rate of maleic anhydride decreases.
[0035]
In the water-collecting collector (20), the reaction gas collects the collected water (21) so that the maleic acid concentration in the bottom liquid is 10 to 80% by mass, more preferably 20 to 60% by mass. It is introduced into the column from the top of the column and brought into countercurrent contact with the maleic anhydride-containing gas to collect maleic anhydride. If the maleic acid concentration exceeds 80% by mass, it is necessary to raise the collection temperature to 90 ° C. or higher in order to prevent maleic acid precipitation. If the concentration is below 10% by mass, crude maleic acid is contained. It is uneconomical because more water is distilled in the concentration / dehydration process of the aqueous solution.
[0036]
In addition, unlike FIG. 1, the maleic anhydride collector (10) does not collect maleic anhydride in a liquid state, but supplies all of the reaction gas to the water-washing collector (20). Then, it may be collected as a crude maleic acid-containing aqueous solution.
[0037]
Next, the crude maleic acid-containing aqueous solution is supplied to the azeotropic dehydration tower (40). At this time, the crude maleic acid-containing aqueous solution is obtained by collecting the reaction product gas obtained by catalytic vapor phase oxidation of benzene with water. This is a more preferable embodiment because low boiling point substances such as formic acid, acetic acid, acrylic acid, formaldehyde, acetaldehyde, and p-benzoquinone can be removed by the azeotropic dehydration step of the present invention. The crude maleic acid-containing aqueous solution may be concentrated by distilling water at a stage before being supplied to the azeotropic dehydration tower (40). As such a concentrator (30), a thin film evaporator can be used in addition to known towers such as a plate tower, a wet wall tower, and a spray tower. As such a concentrating device, a thin film evaporator is preferable.
[0038]
As such an azeotropic dehydration tower (40), known towers such as a plate tower, a packed tower, a wet wall tower, and a spray tower can be used. The azeotropic dehydration tower (40) is usually preferably a plate tower or a packed tower, similar to the water scavenger (20). On the other hand, it is preferable to use a distillation column having a theoretical plate number of 3 or more, more preferably 4 to 20 plates, particularly 5 to 15 plates. If it is less than three stages, the contact time between maleic acid and the azeotropic solvent is insufficient, resulting in a decrease in the dehydration rate. Further, the distillation of maleic anhydride to the top of the column increases, and the loss of maleic anhydride increases. It is sufficient if the number of stages is sufficient and sufficient so as not to cause such an adverse effect. If there are too many stages, the equipment cost becomes high, which is uneconomical.
[0039]
In the present invention, when the crude maleic acid-containing aqueous solution is dehydrated by azeotropic distillation, an organic solvent having a maximum dissolution concentration in water of at least 20 ° C. of 0.1 to 5% by mass is used as the azeotropic solvent (1). It is characterized by that. As such an azeotropic solvent (1), there are various organic solvents described above, and it is particularly preferable to use MIBK. In addition, since the azeotropic dehydration conditions vary depending on the azeotropic solvent used, for example, when MIBK is used as the azeotropic solvent, the azeotropic dehydration tower (40) contains 1 part by mass of a crude maleic acid-containing aqueous solution. In contrast, 3 to 5 parts by mass of MIBK is supplied. Generally, the tower top pressure (absolute pressure) is 100 to 2000 hPa, more preferably 300 to 1500 hPa. If the pressure is lower than 100 hPa, not only the vacuum apparatus is increased in size, but the temperature in the column is lowered, and maleic acid or fumaric acid may be crystallized and cannot be distilled. On the other hand, if it exceeds 2000 hPa, the temperature at the bottom of the column rises, and not only the reboiler becomes larger but also a polymer is easily generated. The tower top temperature is 50 to 150 ° C, more preferably 60 to 130 ° C. When the temperature falls below 50 ° C, the condenser becomes large. On the other hand, when the temperature exceeds 150 ° C, not only the polymerization of maleic acid is likely to occur in the column, but also the distillation of maleic anhydride to the top of the column increases, Loss will increase.
[0040]
The tower bottom temperature is 130 to 200 ° C, more preferably 150 to 195 ° C. Below 130 ° C., the dehydration reaction of maleic acid becomes slow, the dehydration of maleic acid becomes insufficient, and the yield of maleic anhydride is reduced. On the other hand, when the temperature exceeds 200 ° C., it is close to the boiling point of maleic anhydride and distillation is not preferable, and decomposition and polymerization are liable to occur. In order to achieve such azeotropic dehydration conditions, the type and amount of azeotropic solvent, the water concentration in the crude maleic acid-containing aqueous solution, the change of the raw material supply stage, the reflux ratio of the condenser attached to the top of the tower, the number of tower stages, What is necessary is just to adjust temperature, pressure, and other conditions.
[0041]
As the azeotropic solvent or solvent mixture used for azeotropic dehydration, the azeotropic solvent (71) recovered in the maleic anhydride production process may be reused. Moreover, as shown in FIG. 1, an azeotropic solvent is not restricted to supplying directly to an azeotropic dehydration tower (40), You may mix with a feedstock and supply in an azeotropic dehydration tower (40). As the azeotropic solvent, a solvent mixture having the physical properties described in the present invention can also be used. Such a solvent mixture is a solvent mixture having an azeotropic point of 70 to 100 ° C. with water at a pressure of 1013 hPa, a maximum dissolution concentration of maleic acid at a temperature of 20 ° C. is 0.1 to 10.0% by mass, a temperature of 20 It is preferable that it is a solvent mixture whose maximum dissolution concentration with respect to water at 0 ° C. is 0.1 to 5% by mass, and after adjusting it to be a mixture of solvents having such physical properties, it is added to the azeotropic dehydration tower (40). What is necessary is just to supply.
[0042]
In the present invention, during the azeotropic dehydration, the oil-water separation tank (50) is attached to the top of the azeotropic dehydration tower (40), and the azeotropic solvent of the tower top distillate is refluxed. Since the organic solvent as the azeotropic solvent (1) used in the present invention is characterized by being soluble in water, the organic solvent is contained on the water phase side of the column top distillate. . In order to make the process more economical, it is advantageous to recover and use this organic solvent in an azeotropic dehydration distillation column. The aqueous phase of the column top distillate is fed to the solvent recovery column (90), whereby the dissolved organic solvent is distilled, separated from the column top and sent to the oil / water separation tank (50) for azeotropic dehydration distillation. It is recovered and used as an azeotropic solvent in the column. Further, recovered water containing no organic solvent is obtained from the tower bottom. In addition, as a solvent recovery tower (90), a conventionally well-known plate tower, a packed tower, a wet wall tower, a spray tower, etc. can be used.
[0043]
Since the bottom liquid of the azeotropic dehydration tower (40) is supplied to the high boiling point separation device (60) and the high boiling point substance is separated, the method of purifying the subsequent step can advantageously prevent the blockage of the device. Is the method. For example, phthalic anhydride, fumaric acid, high-boiling polymer, condensate and the like by-produced by the catalytic gas phase oxidation reaction are discharged as a residue (61).
[0044]
Here, the high boiling point separation device (60) may be a continuous type or a batch type, and may be a rotary residence tank type evaporator in addition to known tower columns, packed towers, wet wall towers, spray towers and the like. Or a thin film evaporator can be preferably used. Further, the above-mentioned type of device can be used in series or in parallel, alone or in combination. In the case of continuous operation, it is preferable to use a thin film evaporator in two stages in series. In addition, as shown in FIG. 1, you may refine | purify crude maleic anhydride (11) by supplying to a high boiling-point separator (60) with the bottom liquid of an azeotropic dehydration tower (40).
[0045]
When a distillation column is used, the distillation conditions of the high boiling point separation device (60) can be distilled under conventionally known distillation conditions. For example, the column top pressure (absolute pressure) is 1 to 40 kPa, more preferably 3 ~ 20kPa. The tower top temperature is 70 to 170 ° C, more preferably 90 to 140 ° C. The distillate amount can be appropriately determined according to the allowable amount of high-boiling impurities in the product. The reflux ratio is usually 0.3-3.
[0046]
When a thin film evaporator is used as the high boiling point separator (60), the temperature is generally 80 to 200 ° C, more preferably 110 to 180 ° C.
[0047]
Next, in the case where the azeotropic solvent other than maleic anhydride remains in the gas component discharged from the high boiling point separator, the azeotropic solvent is then separated by supplying it to the solvent separation tower (70). In addition, when the azeotropic dehydration distillation is performed so that the azeotropic solvent does not remain at the bottom or is in a very small amount, this step can be omitted.
[0048]
As such a solvent separation tower (70), known towers such as a plate tower, a packed tower, a wet wall tower, and a spray tower can be used. Such a solvent separation tower (70) is usually preferably a plate tower or a packed tower, like the water scavenger (20).
[0049]
The conditions for the azeotropic solvent separation tower may be conventionally known conditions, for example, a tower top temperature of 60 to 140 ° C., a reflux ratio of 1 to 30, and a tower top pressure (absolute pressure) of 10 to 60 kPa. In addition, you may perform any of the removal process of the high boiling point substance by a high boiling point separator (60), and the removal process of the azeotropic solvent by a solvent separation tower (70) previously.
[0050]
Conventionally, the gel substance adheres to the inside and the bottom of the azeotropic dehydration tower (40). Specifically, it adheres to the inner wall or shelf in the tower of the azeotropic dehydration tower, or the hole of the shelf member. In addition, this deposit cannot be easily removed by washing with water, and therefore, in the process of producing maleic anhydride, periodic washing and alkali washing are required in the azeotropic dehydration tower and its peripheral equipment. However, in the present invention, the use of a hydrophilic organic solvent as the azeotropic solvent (1) suppresses the occurrence of clogging due to adhesion of gel-like substances generated by impurities or precipitation of maleic acid or fumaric acid. And long-term operation of the plant can be achieved.
[0051]
In the present invention, the maleic anhydride from which the azeotropic solvent used in this manner has been removed and the high-boiling point material has been removed is further supplied to the purification tower (80) for purification, and the maleic anhydride (81) can be used as a product. Good. In addition, it is preferable that the refinement | purification conditions in a refinement | purification column (80) are the range of tower top absolute pressure 2-40kPa, tower top temperature 80-170 degreeC, and others can employ | adopt well-known conditions.
[0052]
A second aspect of the present invention is a method for producing maleic anhydride, which comprises a step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation using an azeotropic solvent. Use of a mixture of an azeotropic solvent (1) having a maximum dissolution concentration of 0.1 to 5% by mass and an azeotropic solvent (2) that forms an azeotropic composition with formic acid and / or acetic acid as an azeotropic solvent This is a method for producing maleic anhydride.
[0053]
When an azeotropic dehydration of a crude maleic acid-containing aqueous solution is used, if an organic solvent having low solubility in water is used, it is not compatible with water or maleic acid even at the temperature in the distillation column, and the crude maleic acid-containing aqueous solution in the distillation column The water and the azeotropic solvent contained in the oil are separated into oil and water. Since maleic acid and impurities such as aldehydes and quinones contained in the crude maleic acid-containing aqueous solution are water-soluble and mainly present in the aqueous phase, the condensation reaction of aldehydes and quinones is concentrated in the aqueous phase. It becomes easy to proceed and contributes to the production of solid precipitates. In addition, maleic acid and its isomers fumaric acid, maleic acid, and maleic anhydride polymer are water-soluble and have almost no solubility in organic solvents, so they are likely to precipitate in organic solvents and are also obstructive. It becomes a cause. On the other hand, when azeotropic dehydration is performed using a hydrophilic organic solvent, the state of oil-water separation in the distillation column is relaxed, and the presence of aldehydes and quinones in the aqueous phase is suppressed. It was found that the concentration in the phase can be reduced and the condensation reaction by both can be suppressed. As such a hydrophilic substance, an azeotropic solvent (1) having an azeotropic composition with water having a maximum dissolution concentration in water of 20 ° C. of 0.1 to 5% by mass was used. On the other hand, the azeotropic solvent (1) forms an azeotrope composition with water, but the light boiling acid content by-produced in the maleic anhydride reaction step, particularly formic acid and acetic acid as the main components thereof. Does not form an azeotropic composition. For this reason, it is difficult to remove formic acid or acetic acid by azeotropic distillation. Formic acid and acetic acid do not form an azeotropic composition with water, so formic acid or acetic acid does not azeotropically distill off with water even if water is distilled off. Therefore, in the present invention, together with the azeotropic solvent (1), the azeotropic solvent (2) that forms an azeotropic composition with formic acid and / or acetic acid is used in combination to prevent the occurrence of clogging in the azeotropic dehydration step. The light boiling acid content by-produced in the reaction process was removed by azeotropic distillation. In the present specification, the light boiling acid component means a compound of acids having a boiling point lower than that of maleic acid such as formic acid, acetic acid and acrylic acid.
[0054]
As the azeotropic solvent (1) used in the second aspect of the present invention, the azeotropic solvent (1) described in the first aspect of the present invention can be used. Specifically, the maximum dissolution concentration in water at a temperature of 20 ° C. It is 0.1-5 mass%, More preferably, it is 0.5-4 mass%, Most preferably, it is 1-3 mass%. When the maximum dissolved concentration in water is less than 0.1% by mass, the above-described oil / water separation state is likely to occur. On the other hand, when it exceeds 5% by mass, there is an effect of improving the oil / water separation state. When the organic solvent distilled off at the top of the tower together with water is separated and collected from water after being cooled, the loss to the aqueous phase increases, which is disadvantageous because the amount of separated liquid recovered decreases.
[0055]
As the physical properties of the azeotropic solvent (1) used in the second of the present invention, the maximum dissolution concentration of maleic acid at a temperature of 20 ° C. (normal pressure) is 0.1 to 10.0% by mass, preferably It is preferable that it is 0.1-8.0 mass%, More preferably, it is 0.3-7.0 mass%, Especially 1.0-7.0 mass% is preferable. When the azeotropic solvent (1) used in the present invention has a high maximum dissolution concentration in maleic acid as described above and has an affinity for maleic acid, maleic acid and fumaric acid in the azeotropic dehydration step It is a preferred form because it can prevent precipitation of water-soluble solids such as styrene and maleic anhydride polymers, and at the same time, can prevent isomerization to fumaric acid and precipitation of fumaric acid.
[0056]
The azeotropic solvent (1) used in the second of the present invention further has a boiling point at a pressure of 1013 hPa of 80 to 190 ° C., more preferably 100 to 170 ° C., particularly 110 to 160 ° C. preferable. A boiling point higher than 190 ° C. is not preferable because it is close to the boiling point of maleic anhydride and the rate of distillation together with the azeotropic solvent increases. On the other hand, if the boiling point is lower than 80 ° C., the dehydration reaction temperature in the distillation column is lowered, the dehydration rate is lowered, and production cannot be advantageously performed.
[0057]
As the azeotropic solvent (1) used in the present invention, the azeotropic solvent (1) described in the first invention can be used. Specifically, the organic solvent described in the first invention is, for example, ketones such as MIBK, diisopropyl ketone, 3-pentanone, 2-hexanone, 3-hexanone, 2-heptanone, amyl acetate, allyl acetate, etc. There are alcohols such as esters, methylcyclohexanol and 2-ethyl-1-hexanol. In the present invention, it is particularly preferable to use ketones such as MIBK, diisopropyl ketone and 2-hexanone, and esters such as allyl acetate. These ketones and esters are compatible with water, increasing the solubility of maleic acid, fumaric acid, maleic acid, and maleic anhydride polymers, etc. in azeotropic solvents, and can solve the precipitation problem. Because. In particular, ketones are preferable in that the solubility of maleic acid is excellent. This is because the above conditions are satisfied, the effect of preventing the occurrence of obstruction in the production process of maleic anhydride and the solubility are excellent, and there is no reactivity with the target maleic acid and maleic anhydride. In this invention, said 1 type can be used individually or in mixture of 2 or more types as an azeotropic solvent (1).
[0058]
In addition, as the azeotropic solvent (2) used in the second of the present invention, those which form an azeotropic composition with formic acid and / or acetic acid can be widely used. More specifically, toluene, xylene, Hydrocarbons such as octane, cumene, mesitylene, ethylbenzene, and dimethylcyclohexane, sulfur-containing compounds such as isopropyl sulfide and allyl sulfide, and halides such as bromobenzene and iodopropane can be preferably used. These boiling points, azeotropic points with formic acid, and azeotropic points with acetic acid are shown in Table 1.
[0059]
The azeotropic solvent (2) used in the second of the present invention further has a boiling point at a pressure of 1013 hPa of 80 to 190 ° C., more preferably 100 to 170 ° C., particularly 110 to 160 ° C. preferable. A boiling point higher than 190 ° C. is not preferable because it is close to the boiling point of maleic anhydride and the rate of distillation together with the azeotropic solvent increases. On the other hand, if the boiling point is lower than 80 ° C., the dehydration reaction temperature in the distillation column is lowered and the dehydration rate is lowered, so that the production cannot be advantageously performed. In this invention, 1 type of the said azeotropic solvent can be used individually or in mixture of 2 or more types as an azeotropic solvent (2).
[0060]
Further, among the above azeotropic solvents (2), hydrocarbons are particularly preferably used from the viewpoints of availability as a general-purpose product, price, stability in the use temperature range, and the like.
[0061]
[Table 1]

[0062]
The second invention of the present invention is to azeotrope a mixture of the azeotropic solvent (1) and the azeotropic solvent (2) for the purpose of preventing the occurrence of clogging and removing formic acid and acetic acid by azeotropic distillation. In this case, the mixing ratio of the two is such that the content of the azeotropic solvent (2) is 1 with respect to the amount of the mixed substance of the azeotropic solvent (1) and the azeotropic solvent (2). It is preferable to set it as -40 mass%. More preferably, it is 3-35 mass%, Most preferably, it is 5-30 mass%. By setting the mixing ratio to more than 1% by mass, the removal efficiency of light boiling acid components by-produced such as formic acid and acetic acid is further improved. On the other hand, by making the mixing ratio less than 40% by mass, the light-boiling acid content is removed and the azeotropic dehydration is effectively performed without significantly reducing the effect of suppressing precipitates by using a hydrophilic organic solvent. A purification step by distillation can be performed, which is preferable.
[0063]
Specifically, 95% by mass of MIBK as the azeotropic solvent (1), 5% by mass of o-xylene as the azeotropic solvent (2) (mixture A), and MIBK as the azeotropic solvent (1). 80% by mass, 20% by mass of n-octane blended as azeotropic solvent (2) (mixture B), 75% by mass of 2-hexanone as azeotropic solvent (1), and ethylbenzene as azeotropic solvent (2) Examples thereof include those containing 25% by mass (mixture C). When such a mixture is used as an azeotropic solvent, for example, in the mixture A, the composition of the distillate is a three-component system having an azeotropic point of 88.2 ° C with water and an azeotropic point with formic acid of 95.5 ° C. It becomes a solvent mixture. As an azeotropic distillation tower, when operated at a tower bottom temperature of 170 ° C. using a staged weir with 5 stages of concentration section and 10 stages of recovery section, the water phase is 20.1 mass% and the oil phase 79 of the mixture A It becomes an azeotropic composition of .9% by mass. By using the above method, when clogging occurs due to the complicated internal structure, the clogging of the azeotropic dehydration distillation column, which is complicated and difficult to clean, is prevented, and formic acid or the like is prevented. The light boiling acid content can be easily removed. The mixture of the azeotropic solvent (1) and the azeotropic solvent (2) has a maximum dissolution concentration in water at a temperature of 20 ° C. of 0.1 to 5% by mass, preferably 0.5 to 4% by mass, particularly preferably Is 1 to 3% by mass, and the maximum dissolution concentration of maleic acid at a temperature of 20 ° C. is 0.1 to 10.0% by mass, preferably 0.1 to 8.0% by mass, more preferably 0.3 to 7%. It is 0.0 mass%, Most preferably, it is 1.0-7.0 mass%.
[0064]
Mixtures of the azeotropic solvent (1) and the azeotropic solvent (2) described above are aldehydes and quinones that are the causative substances of the condensate, particularly when maleic anhydride is produced by catalytic vapor phase oxidation of benzene. It is effective because of the large amount of by-product. However, these clogging substances are not only produced when the raw material is benzene, but also as a by-product of phthalic anhydride production using aliphatic hydrocarbons such as n-butane, naphthalene and o-xylene as raw materials. It occurs even in the production of maleic anhydride. Therefore, the method of the present invention is useful in any production method using raw materials. For example, maleic anhydride-containing gas obtained by catalytic gas phase oxidation reaction of n-butane is collected by washing with water, and the above characteristics are obtained. It is also effective when it includes a step of azeotropic dehydration distillation using an organic solvent having It is effective in preventing clogging of the azeotropic dehydration tower, and light boiling acid components such as formic acid can be effectively removed to enable long-term operation.
[0065]
The amount used in the azeotropic dehydration step by such a mixture of the azeotropic solvent (1) and the azeotropic solvent (2) varies depending on the composition ratio of the organic solvent and the solvent mixture used, but the crude maleic acid-containing aqueous solution Is preferably in the range of 0.5 to 10 parts by mass, more preferably in the range of 2 to 5 parts by mass with respect to 1 part by mass of the total amount of moisture contained in the water and generated by dehydration. If the amount of the organic solvent used relative to water is small, the heat consumption is reduced, which is industrially advantageous.
[0066]
Hereinafter, an example of the preferable aspect of the manufacturing method of the 2nd maleic anhydride of this invention is demonstrated using FIG.
[0067]
The second invention of the present application can be performed in accordance with the first invention. Therefore, differences from the first invention will be mainly described. The present invention is characterized in that a mixture of the azeotropic solvent (1) and the azeotropic solvent (2) is used as the azeotropic solvent when the crude maleic acid-containing aqueous solution is dehydrated by azeotropic distillation. Examples of such a mixture include the above-mentioned various organic solvents. In particular, MIBK is preferably used as the azeotropic solvent (1), and xylene or octane is preferably used as the azeotropic solvent (2). . Since the azeotropic dehydration conditions differ depending on the azeotropic solvent used, for example, when a mixture of 75% by mass of MIBK and 25% by mass of xylene is used as the azeotropic solvent, the azeotropic dehydration tower (40) has a rough structure. 2.2 to 3.8 mass of MIBK and 0.8 to 1.2 mass of o-xylene are supplied to 1 mass of the maleic acid-containing aqueous solution so that the total amount is 3 to 5 mass. These may be supplied to the azeotropic dehydration tower (40) after preparing a mixture of MIBK and toluene in advance, or may be supplied separately. Generally, the tower top pressure (absolute pressure) is 100 to 2000 hPa, more preferably 300 to 1500 hPa. If the pressure is lower than 100 hPa, not only the vacuum apparatus is increased in size, but the temperature in the column is lowered, and maleic acid or fumaric acid may be crystallized and cannot be distilled. On the other hand, if it exceeds 2000 hPa, the temperature at the bottom of the column rises, and not only the reboiler becomes larger but also a polymer is easily generated. The tower top temperature is 50 to 150 ° C, more preferably 60 to 130 ° C. When the temperature falls below 50 ° C, the condenser becomes large. On the other hand, when the temperature exceeds 150 ° C, not only the polymerization of maleic acid is likely to occur in the column, but also the distillation of maleic anhydride to the top of the column increases, Loss will increase.
[0068]
The tower bottom temperature is 130 to 200 ° C, more preferably 150 to 195 ° C. Below 130 ° C., the dehydration reaction of maleic acid becomes slow, the dehydration of maleic acid becomes insufficient, and the yield of maleic anhydride is reduced. On the other hand, when the temperature exceeds 200 ° C., it is close to the boiling point of maleic anhydride and distillation is not preferable, and decomposition and polymerization are liable to occur. In order to achieve such azeotropic dehydration conditions, the type and amount of azeotropic solvent, the water concentration in the crude maleic acid-containing aqueous solution, the change of the raw material supply stage, the reflux ratio of the condenser attached to the top of the tower, the number of tower stages, What is necessary is just to adjust temperature, pressure, and other conditions.
[0069]
As the azeotropic solvent used for azeotropic dehydration, the azeotropic solvent (71) recovered in the maleic anhydride production process may be reused. Moreover, as shown in FIG. 1, an azeotropic solvent is not restricted to supplying directly to an azeotropic dehydration tower (40), You may mix with a feedstock and supply in an azeotropic dehydration tower (40).
[0070]
Also in the second aspect of the present invention, it is preferable to attach an oil / water separation tank (50) to the top of the azeotropic dehydration tower (40) during the azeotropic dehydration and to reflux the azeotropic solvent of the tower top distillate. . In the second aspect of the present invention, as shown in FIG. 1, the crude maleic anhydride (11) is supplied to the high boiling point separator (60) together with the bottom liquid of the azeotropic dehydration tower (40) for purification. You may go.
[0071]
In addition, you may perform any of the removal process of the high boiling point substance by a high boiling point separator (60), and the removal process of the azeotropic solvent by a solvent separation tower (70) previously.
[0072]
Conventionally, a gel-like substance adhered to the inside and bottom of the azeotropic dehydration tower (40). Specifically, it adhered to the inner wall and shelf in the tower of the azeotropic dehydration tower, or the hole of the shelf member. In addition, this deposit cannot be easily removed by washing with water, and therefore, in the process of producing maleic anhydride, periodic washing and alkali washing are required in the azeotropic dehydration tower and its peripheral equipment. However, in the present invention, by using a mixture of a hydrophilic azeotropic solvent and an organic solvent that forms an azeotropic composition with formic acid and / or acetic acid, adhesion of gel-like substances generated by impurities, maleic acid and fumaric acid Generation | occurrence | production of the obstruction | occlusion by precipitation of this etc. can be suppressed, long-term operation of a plant can be achieved, and by-product acids can be removed in the process of azeotropic dehydration distillation.
[0073]
In the maleic anhydride obtained by the second production method of the present invention, the amount of acetic acid present in maleic anhydride is 1800 ppm or less, more preferably 1000 ppm or less, further 500 ppm or less, and most preferably 300 ppm or less. Some are the preferred forms. Moreover, as content of formic acid, it is the range of 0-200 ppm, More preferably, it is the range of 0-100 ppm. More preferably, it is the range of 0-50 ppm. In the second of the present invention, since the specific azeotropic solvent (2) is used in combination with the azeotropic solvent (1), it is a light boiling component present in maleic anhydride in the bottom liquid of the azeotropic dehydration tower. The amount of acetic acid or formic acid can be reduced. As a result, the purification process after the azeotropic dehydration process can be simplified. Therefore, in the second aspect of the present invention, it is a preferable mode that the acetic acid and / or formic acid present in the maleic anhydride in the bottom liquid of the azeotropic dehydration tower is in the above range.
[0074]
In the second aspect of the present invention, the maleic anhydride from which the azeotropic solvent has been removed and the high-boiling point material has been removed in this way is further supplied to the purification tower (80) for purification, and the maleic anhydride (81) is obtained as a product. It is good.
[0075]
【Example】
Hereinafter, examples of the present invention will be described in detail.
[0076]
(Reference Example 1: Solvent selection method based on the maximum dissolved concentration of an organic solvent in water)
The selection of one organic solvent or a mixture of two or more solvents used in the present invention is based on the following method. 80 g of pure water at a temperature of 20 ° C. is put into a 100 ml glass container with a lid that can be sealed, and the target organic solvent or solvent mixture is dropped while stirring with a stirrer, and the dissolved state after 1 hour is visually observed. If there is any undissolved residue, the amount of one drop is further reduced and the above-mentioned solubility is confirmed again. The minimum dripping amount of the organic solvent or solvent mixture as the solute was 0.02 g. Thus, the maximum dripping amount (solute mass) recognized as having no undissolved residue was determined and calculated as the maximum dissolution concentration in 80 g of water (solvent). In particular,
The maximum dissolution concentration (mass%) = (solute / (solute + solvent)) × 100 is the maximum dissolution concentration in the present invention. These values almost coincided with the solubility data in water of the solvent described in the chemical handbook described in the text and Beilstein. In this example, the maximum dissolution concentration of each solute dissolved in 80 g of solvent is calculated according to the above formula. The maximum dissolution concentration is measured at a liquid temperature of 20 ° C. In addition, when mixing 2 or more types of organic solvents and using it by azeotropic dehydration distillation, the maximum melt | dissolution density | concentration of the mixture is measured by said method.
[0077]
The solubility of o-xylene, methyl isobutyl ketone (MIBK), diisopropyl ketone (DIPK), diisobutyl ketone (DIBK), dibutyl-teru (DBE) and a solvent mixture of 85% MIBK and 15% o-xyle, evaluated according to the above. It shows in Table 2.
[0078]
(Reference Example 2: Measurement of maximum dissolved concentration of maleic acid or fumaric acid in the solvent)
In a 100 ml glass container with a lid that can be sealed, 80 g of a solvent at a temperature of 20 ° C. was added, and while stirring with a stirrer, reagent-grade maleic acid or fumaric acid, which is the maximum dissolution concentration measurement item, was added, and the dissolution state was confirmed visually. . When there was undissolved residue even after stirring for 1 hour, it was insoluble. If there was any undissolved residue, the maximum dissolution concentration was confirmed again by further reducing the amount added once. The minimum dripping amount was 0.01 g. Thus, the maximum dripping amount (solute mass) recognized as having no residue remained was calculated and calculated as the maximum dissolution concentration in 80 g of each solvent. In particular,
The maximum dissolution concentration (mass%) = (solute / (solute + solvent)) × 100 is obtained as the maximum dissolution concentration, which is the maximum dissolution concentration in the present invention. When the minimum suitable amount 0.01 g (0.006 mass%) remained, it was considered insoluble. The maximum dissolution concentration is measured at a liquid temperature of 20 ° C.
[0079]
The results are shown in Table 2. From Table 2, the maximum dissolution concentration in water and the maximum dissolution concentration of maleic acid and fumaric acid showed numerical values that MIBK was relatively higher than other substances. Although the maximum dissolution concentration tended to be lower than MIBK as DIPK, DIBK and ketone groups became higher molecular weight substituents, MIBK dissolved maleic acid and fumaric acid. However, o-xylene does not dissolve maleic acid or fumaric acid, and shows little maximum dissolution concentration for these materials in water. Although o-xylene has low solubility in water and does not dissolve maleic acid or fumaric acid, a solvent mixture of MIBK 85% and o-xylene 15% has a maximum solubility in water of 1.57. The maximum dissolution concentration of maleic acid was 3.41, the maximum dissolution concentration of fumaric acid was 0.11, and the maximum dissolution concentration was higher than other substances.
[0080]
[Table 2]

[0081]
Example 1
In a vessel in which a stirrer and a reflux condenser are attached to a 1 liter glass flask, 500 g of a liquid obtained by mixing 82% by mass of an organic solvent shown in Table 3, 12% by mass of maleic acid, and 6% by mass of pure water as a test solution, 9000 mass ppm of formaldehyde, 150 mass ppm of benzoquinone, and 150 mass ppm of hydroquinone were added to maleic acid to prepare an estimated composition liquid in the tower for azeotropic dehydration distillation. This was confirmed by testing the formation of a condensate as a precipitate by heating in an oil bath under normal pressure.
[0082]
The test conditions were as follows: temperature: internal temperature of 100 ° C. or temperature at which the liquid reaches a boiling state, thermal aging test time: 2 hours (time after the internal temperature reaches 95 ° C.), confirmation of condensate formation: 1 μm membrane after cooling Suction filtration was performed with a filter, and it was confirmed whether or not a precipitated solid content as a condensate was obtained on the membrane filter. The results are shown in Table 3. In addition, the oil-water decomposition state at the time of heating after the test time in the table was observed in a state immediately after the 2-hour thermal aging test.
[0083]
From the results of Table 3, when MIBK and a solvent mixture of 85% MIBK and 15% o-xylene were used as the azeotropic solvent, the estimated composition in the tower was in a uniform state without oil-water separation. This is considered to be because the solvent mixture of MIBK and MIBK 85% and o-xylene 15% has a high maximum solubility in water and also has solubility in solvent mixtures such as maleic acid and fumaric acid which are acid components. It was. However, when DBE or o-xylene was used, the test liquid was separated into two phases after oil-water separation. In addition, regarding the formation of the condensate, when MIBK solvent was used, no precipitated solid content as a condensate was obtained on the membrane filter after the test solution was filtered. On the other hand, when DBE or o-xylene solvent was used, it was confirmed that a precipitated solid was obtained on the membrane filter and a condensate was formed.
[0084]
[Table 3]

[0085]
(Example 2)
Maleic anhydride was produced according to the process shown in FIG.
[0086]
First, the reaction gas containing maleic anhydride discharged by the catalytic vapor-phase oxidation reaction of benzene was collected by controlling the outlet gas temperature of the maleic anhydride collector (10) to 60 ° C. Thereafter, the outlet gas of the maleic anhydride collector (10) was introduced into the water-washing collector (20). Subsequently, the gas was washed with water in a water washing collector (20) to obtain a 42 mass% crude maleic acid-containing aqueous solution. The obtained crude maleic acid-containing aqueous solution contained formaldehyde 3200 mass ppm, benzoquinone 57 mass ppm, and hydroquinone 30 mass ppm. The crude maleic acid-containing aqueous solution was subjected to azeotropic dehydration using MIBK as an azeotropic dehydration solvent.
[0087]
As the azeotropic dehydration tower (40), a distillation tower having a concentration section 32φ weir and a recovery section 50φ weir 10 stage was used. As the azeotropic solvent, 3.5 mass times of the dissolved water and generated water of the maleic acid aqueous solution was supplied from the top of the column, and azeotropic dehydration distillation was performed at 170 ° C. at normal pressure and at the bottom temperature of 8 hours. The composition at the bottom of the system at the time when the in-system composition became constant was: maleic anhydride 90.2% by mass, MIBK 7.5% by mass, maleic acid 2.24% by mass, phthalic anhydride 0.06% by mass, formaldehyde They were 0.01 mass% or less, benzoquinone 0.01 mass% or less, and hydroquinone 0.01 mass%. The tower top distillate composition was MIBK layer 78 mass% and water layer 22 mass%. Formaldehyde and maleic acid were almost distributed in the aqueous phase, and were 0.51% by mass and 0.0001% by mass, respectively. After operation for 8 hours, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic acid polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed. The results are shown in Table 4. In addition, in the observation of “contamination status in the tower” in Table 4, the condensate and the maleic anhydride polymer were distinguished as follows. That is, a maleic anhydride polymer is an adhesive that can be removed by washing the distillation column with water or warm water after the distillation operation. Further, a black deposit that could not be removed by this operation and required to be dissolved and removed with 0.1N sodium hydroxide diluted aqueous solution was judged as a condensate.
[0088]
(Comparative Example 1)
In place of the azeotropic solvent MIBK used in Example 2, o-xylene was used, and the azeotropic solvent was supplied from the top of the column in an amount of 2.5 mass times the dissolved water and generated water of the maleic acid aqueous solution. An azeotropic dehydration distillation was performed for 8 hours at the same bottom temperature as in Example 2. The results are shown in Table 4.
[0089]
[Table 4]

[0090]
As can be seen from Table 4, due to the difference in azeotropic dehydration solvent, condensate, maleic acid precipitation, maleic anhydride polymer precipitation, etc., which are clogging substances were observed in the azeotropic dehydration tower after 8 hours of distillation. did. When MIBK was used as the azeotropic dehydration solvent, no fouling or deposits in the tower due to the condensate and maleic anhydride polymer were observed. Also, no blockage due to precipitation of fumaric acid was observed. For this reason, a long time operation of distillation for 8 hours or more was possible. On the other hand, when o-xylene was used as an azeotropic dehydration solvent as a comparative example, a large amount of condensation product was observed. In addition, precipitation of fumaric acid was also observed, and in particular, it was present in the form of solid crystals on the distillation column recovery section tray.
[0091]
(Comparative Example 2)
Instead of the azeotropic solvent MIBK used in Example 2, DBE was used, and the azeotropic solvent was supplied from the top of the column in an amount of 4.0 mass times the dissolved water and generated water of the maleic acid aqueous solution. An azeotropic dehydration distillation was carried out for 8 hours at the same bottom temperature as 2. As a result, the same dirt in the tower as in Comparative Example 1 was generated. The results are shown in Table 5.
[0092]
(Comparative Example 3)
Example 1 except that DIBK was used instead of the azeotropic solvent MIBK used in Example 2, and the azeotropic solvent was supplied from the top of the column in an amount of 1.5 times the dissolved water of the maleic acid aqueous solution and generated water. An azeotropic dehydration distillation was carried out for 8 hours at the same bottom temperature as 2. As a result, the same dirt in the tower as in Comparative Example 1 was generated. The results are shown in Table 5. Note that the same criteria as in Table 4 were used for the evaluation of the “dirt condition in the tower” in Table 5.
[0093]
[Table 5]

[0094]
(1) Organic solvents such as MIBK and acetic acid were measured by gas chromatography using a DB-5 column manufactured by J & W Scientific.
[0095]
(2) Formic acid, maleic acid, and fumaric acid were measured by liquid chromatography using an Inertsil ODS-3 column manufactured by GL Science.
[0096]
(Example 3)
Maleic anhydride was produced according to the process shown in FIG.
[0097]
First, the reaction gas containing maleic anhydride discharged by the catalytic vapor phase oxidation reaction of benzene was subjected to crude maleic anhydride (11) by controlling the outlet gas temperature of the maleic anhydride collector (10) to 60 ° C. I collected it. Thereafter, the outlet gas of the maleic anhydride collector (10) was introduced into the water-washing collector (20). Next, the gas was washed with a water washing collector (20), and then a crude maleic acid-containing aqueous solution was obtained. The maleic acid concentration of the solution was 42 mass%, and contained 58 mass% of water, 2000 mass ppm of acetic acid, and 70 mass ppm of formic acid. The crude maleic acid-containing aqueous solution was subjected to azeotropic dehydration using a mixture of 85% by mass of MIBK and 15% by mass of o-xylene as an azeotropic dehydration solvent.
[0098]
As the azeotropic dehydration tower (40), a distillation tower having a concentration section 32φ weir and a recovery section 50φ weir 10 stage was used. A crude maleic acid-containing aqueous solution was supplied from the 10th stage counting from the bottom of the tower. The azeotropic solvent is 3.5 mass times to the water generated by the dissolution of maleic acid aqueous solution and water generated from the dehydration, and is subjected to azeotropic dehydration distillation at 170 ° C for 8 hours at atmospheric pressure and bottom temperature. It was. The results are shown in Table 6. The bottom composition at the time when the in-system composition became constant was: maleic anhydride 88.41% by mass, MIBK 0.04% by mass, o-xylene 8.70% by mass, maleic acid 1.81% by mass, fumaric acid 1.04 mass%, formic acid 0 mass ppm, acetic acid 0 mass ppm, and eliminating the presence of by-products in the column bottom liquid, which is a light boiling component in the liquid supplied to the azeotropic dehydration tower did it. During the operation, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic anhydride polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed. Note that the same criteria as in Table 4 were used for the evaluation of “dirt condition in the tower” in Table 6.
Example 4
An azeotropic dehydration distillation for 8 hours was performed under the same conditions as in Example 3 except that the mixed composition of the azeotropic solvent used in Example 3 was changed to 95% by mass of MIBK and 5% by mass of o-xylene. The results are shown in Table 6. At the time when the in-system composition became constant, the composition at the bottom of the column was as little as 170 ppm by mass of acetic acid, but 0 ppm by mass of formic acid, and no formic acid was present in the column bottom liquid. During the operation, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic anhydride polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed.
[0099]
(Example 5)
The azeotropic dehydration for 8 hours was carried out under the same conditions as in Example 3 except that the mixture composition of the azeotropic solvent used in Example 3 was MIBK 80 mass% and n-octane 20 mass%, and the tower bottom temperature was 190 ° C. Distillation was performed. The results are shown in Table 6. At the time when the composition in the system became constant, 500 mass ppm of acetic acid remained in the tower bottom composition, but 0 mass ppm of formic acid, and no formic acid was present in the tower bottom liquid. During the operation, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic anhydride polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed.
[0100]
(Example 6)
An azeotropic dehydration distillation for 8 hours was performed under the same conditions as in Example 4 except that the mixed composition of the azeotropic solvent used in Example 3 was changed to 100% by mass of MIBK. The results are shown in Table 6. The tower bottom composition at the time when the in-system composition became constant was 2150 mass ppm for acetic acid and 100 mass ppm for formic acid. Both acetic acid and formic acid were present in the bottom liquid. During the operation, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic anhydride polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed.
[0101]
(Example 7)
An azeotropic dehydration distillation for 8 hours was performed under the same conditions as in Example 4 except that the mixed composition of the azeotropic solvent used in Example 3 was MIBK 100% by mass and the column bottom temperature was 190 ° C. The results are shown in Table 6. The tower bottom composition at the time when the in-system composition became constant was 1720 ppm by mass for acetic acid and 15 ppm by mass for formic acid. Even when the column bottom temperature was increased from 170 ° C. to 190 ° C., both acetic acid and formic acid were present in the column bottom liquid. During the operation, no condensation or deposits in the tower due to a condensation product of aldehydes and quinones and a maleic anhydride polymer were observed in the tower. Moreover, clogging due to precipitation of fumaric acid was not observed.
[0102]
[Table 6]

[0103]
【The invention's effect】
Maleic acid and fumaric acid, which have been problems in the conventional concentration and dehydration processes in the production of maleic anhydride, have a high solubility in water and generally have a lower solubility in organic solvents than water. In the present invention, an organic solvent such as ketones or esters having specific physical properties is used as an azeotropic solvent, and the azeotropic solvent is compatible with water, so that oil-water separation in an azeotropic dehydration distillation column is performed. The condensation reaction is suppressed by eliminating the concentration of aldehydes and quinones, which are the condensate-causing substances, into the aqueous phase. Moreover, the solubility to the azeotrope in the azeotropic dehydration process which exists as a mixed solution of maleic acid, fumaric acid, and a maleic acid polymer increases, and blockage by precipitates can be prevented.
[0104]
When performing azeotropic dehydration distillation as a concentration dehydration step of the crude maleic acid aqueous solution in maleic anhydride production, it is possible to prevent clogging in the tower due to precipitates by using an organic solvent having an affinity for water, Organic solvents such as ketones and esters with affinity for water suitable for azeotropic dehydration of maleic acid have no azeotropic composition with by-products such as formic acid and acetic acid. Is difficult, and causes a decrease in the purity of purified maleic anhydride. Precipitation by azeotropic dehydration distillation using a mixed solvent system in a specific ratio range of an organic solvent having affinity with water and an acid, especially formic acid or acetic acid, and an organic solvent having an azeotropic composition as an azeotropic solvent It is possible to provide a purification process capable of removing by-product acids in the process step of azeotropic dehydration distillation while preventing clogging of the azeotropic dehydration tower by substances.
[Brief description of the drawings]
FIG. 1 is a process diagram of a preferred production method of a method for producing maleic anhydride in the present invention.
[Explanation of symbols]
1 ... reactive gas,
10 ... maleic anhydride collector,
11 ... Crude maleic anhydride,
20 ... Water-washing collector,
21 ... Recycled collected water,
30 ... Concentrator,
40 ... azeotropic dehydration tower,
50. Oil / water separation tank,
51 ... Waste water,
60 ... High boiling point separator,
61 ...
70 ... solvent separation tower,
71 ... an azeotropic solvent,
80 ... refining tower,
81 ... Purified maleic anhydride
90 ... Solvent recovery tower.

Claims (2)

In the method for producing maleic anhydride, which comprises a step of dehydrating a crude maleic acid-containing aqueous solution by azeotropic distillation using an azeotropic solvent, methyl isobutyl ketone (MIBK ) is used as the azeotropic solvent, maleic anhydride Acid production method. The production method according to claim 1, wherein the crude maleic acid-containing aqueous solution is obtained by collecting the reaction product gas obtained by catalytic gas phase oxidation of benzene with water.

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