JP3562983B2

JP3562983B2 - Method for producing methacrolein and methacrylic acid

Info

Publication number: JP3562983B2
Application number: JP34933998A
Authority: JP
Inventors: 聖午渡辺; 求大北
Original assignee: Mitsubishi Chemical Corp; Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Chemical Corp; Mitsubishi Rayon Co Ltd
Priority date: 1997-11-25
Filing date: 1998-11-25
Publication date: 2004-09-08
Anticipated expiration: 2018-11-25
Also published as: JPH11263739A

Description

【０００１】
【発明の属する技術分野】
本発明は、メタクロレイン及びメタクリル酸の製造方法、詳しくはイソブチレンまたは第三級ブタノールを分子状酸素により触媒の存在下気相接触酸化して、メタクロレイン及びメタクリル酸を製造する方法に関する。
【０００２】
【従来の技術】
イソブチレンまたは第三級ブタノールをモリブデン、ビスマス及び鉄を、必須成分として含有する複合酸化物からなる触媒上で接触酸化させてメタクロレイン及びメタクリル酸を製造する方法は広く知られており、工業的にも用いられている。この場合反応は触媒を固定床として用い、３００〜４００℃の温度で実施される。
【０００３】
このような気相接触酸化反応に用いられる触媒は比較的長期間使用されるが、通常、触媒の活性は経時的に低下する。特公平５−２９５０２号公報には、反応使用により触媒活性の低下したＭｏ−Ｂｉ−Ｆｅを含む多元系酸化物触媒を実質的に空気からなる雰囲気中で３８０〜５４０℃の温度で再生処理する方法が、特公平５−７０５０３号公報には、同様に触媒活性の低下した同種の触媒を酸素５〜９９．９容量％、水蒸気０．１〜９５容量％及び不活性ガスからなる酸化性ガス流通下３００〜５００℃の温度で再生処理する方法が開示されている。
【０００４】
【発明が解決しようとする課題】
しかし、本発明者らの検討によると、これら刊行物に記載されているような活性低下の進んだ触媒に対する再生処理では、処理後、一旦、触媒性能は反応使用前の水準まで回復するが、その後の活性低下速度が速く、工業的な実施の観点からは必ずしも十分に満足すべきものではない。
【０００５】
従って本発明は、触媒を長期間使用することができるイソブチレンまたは第三級ブタノールを、分子状酸素により気相接触酸化してメタクロレイン及びメタクリル酸を製造する方法を提供することを目的としている。
【０００６】
【課題を解決するための手段】
本発明は、イソブチレンまたは第三級ブタノールをモリブデン、ビスマス及び鉄を必須成分として含有する複合酸化物からなる触媒に接触酸化させメタクロレイン及びメタクリル酸を製造するに当り、該触媒を用いてイソブチレンからメタクロレイン及びメタクリル酸を得る反応の活性化エネルギーの境界温度をＴ℃とした場合に（Ｔ−３）℃以下の温度で反応を開始し、触媒の活性低下に伴い反応温度を上昇させながら反応を継続し、反応温度が該境界温度より高くなる前に触媒に対して活性化処理を行うことを特徴とするメタクロレイン及びメタクリル酸の製造方法にある。
【０００７】
【発明の実施の形態】
本発明において使用する触媒は、モリブデン、ビスマス及び鉄を必須成分として含有する複合酸化物からなり、必須成分以外の成分に特に限定はない。このような触媒は、特開昭５３−１９１８８号公報、特開昭５４−６６６１０号公報、特開昭５５−３５９号公報、特開昭５５−１９２２７号公報、特開昭５６−９５１３５号公報、特開昭６０−２８８２４号公報などに記載されているような公知の方法で得ることができる。
【０００８】
固体触媒を用いた気相接触反応において、しばしば、対象とする反応の活性化エネルギーが、ある反応温度を境界に反応温度の低い領域と高い領域で異なった値となることが知られている。例えば、ＪＯＵＲＮＡＬＯＦＣＡＴＡＬＹＳＩＳ第４１巻第１３４〜１３９ページには、１−ブテンをモリブデン及びビスマスを含む複合酸化物からなる触媒上で接触酸化させる反応において前記のような異なる活性エネルギーをもつことが報告されている。このような挙動は反応温度によって反応の律速段階が異なるために見られる現象であり、詳しくは講談社触媒講座第１巻第４節（触媒学会編）に記されている。一説によると、反応温度の低い領域では、触媒活性点上での反応分子の反応が律速段階であり、反応温度の高い領域では、反応分子の触媒活性点への拡散が律速段階であると推定されている。
【０００９】
本発明者らは、イソブチレンをモリブデン、ビスマス及び鉄を必須成分として含有する複合酸化物からなる触媒上で接触酸化させメタクロレイン及びメタクリル酸を製造する反応について活性化エネルギーを解析したところ、反応温度の低い領域と高い領域でそれぞれ異なった値となることを確認した。
【００１０】
本発明において、活性化エネルギーの境界温度は以下のようにして求められる。
まず、熱媒浴を備えた反応管に触媒を充填し、熱媒浴の温度を３１５〜３７５℃の範囲で２〜５℃間隔で変化させ、各温度におけるイソブチレンの反応率を求める。ここで反応率は以下の式により求められる。
【００１１】
【数１】
原料の反応率（％）＝Ａ／Ｂ×１００
（Ａは反応した原料のモル数、Ｂは供給した原料のモル数を表す。）
続いて、以下の式により反応速度定数を求める。
【００１２】
【数２】
Ｋ＝（ＳＶ）×（１／ρ）×ｌｎ［１００／（１００−Ｘ）］
（Ｋは反応速度定数、ＳＶは空間速度、ρは触媒の充填密度、Ｘはイソブチレンの反応率（％）を表す。）
【００１３】
続いて、横軸に１／Ｔを、縦軸にｌｎＫをとり、各データをプロットした後、２本の近似直線を引きその傾きを求める。ここで、１／Ｔは反応管の熱媒浴温度（絶対温度）の逆数、ｌｎＫは反応速度定数の自然対数を表す。近似直線は最小自乗法などの一般的な方法により求めることができる。
得られた近似直線の傾きの絶対値に気体定数を乗じた値が求める活性化エネルギーであり、２本の近似直線の交点の横座標の逆数が求める活性化エネルギーの境界温度である。
【００１４】
反応原料としてイソブチレンに代えて第三級ブタノールを用いた場合、第三級ブタノールはモリブデン、ビスマス及び鉄を必須成分として含有する触媒上で速やかにイソブチレン及び水に分解される。すなわち、反応原料として第三級ブタノールを用いた場合も、その反応形態は本質的にはイソブチレンの酸化反応と同様と考えられる。したがって、反応原料として第三級ブタノールを用いた場合も、イソブチレンからの反応の活性化エネルギーの境界温度をそのまま用いることができる。
【００１５】
一般に、触媒を工業規模で使用するに際して、一度充填された触媒について可能な限り寿命を延ばすための様々な延命策が試みられている。例えば、触媒の劣化に伴い、プロセスに許容される限界まで反応温度を徐々に上昇させて反応率を維持させる方法などである。
【００１６】
本発明者らは、イソブチレンまたは第三級ブタノールをモリブデン、ビスマス及び鉄を必須成分として含有する複合酸化物からなる触媒上で接触酸化させメタクロレイン及びメタクリル酸を製造するに際し、活性化エネルギーの境界温度をＴ℃とした場合（Ｔ−３）℃以下の温度で反応を開始し、触媒の活性低下に伴い反応温度を上昇させながら反応を継続し、反応温度が該境界温度より高くなる前に触媒に対して少なくとも１回の活性化処理を行うことにより、触媒寿命が著しく延びることを見出したのである。
【００１７】
触媒の活性低下の原因としては、触媒成分の還元、触媒成分の昇華・飛散、触媒構造中の結晶相の変化などが挙げられる。これらの原因により活性低下した触媒の活性化処理方法としては、従来技術の項で挙げた再生方法などの公知の方法が利用できるが、触媒を３００℃以上５５０℃未満の温度下に保ち、実質的に空気からなるガスを１時間以上接触させる方法が好ましい。触媒の活性化処理は、触媒を反応器から取り出して実施しても良いが、触媒が反応器に充填されたままの状態で実施した方が操作が容易であり、工業的に有利である。
【００１８】
反応温度が活性化エネルギーの境界温度より高くなるまで使用した触媒に対して前記のような活性化処理を行っても、一旦は、触媒性能が回復するが、その後の活性低下の速度が速くなり、延命の効果は乏しい。一方、本発明の方法のように活性化エネルギーの境界温度未満の反応温度でしか使用していない触媒に対して前記のような活性化処理を行った場合は、触媒性能の回復に加えて、その後の活性低下の速度も新品時と同水準となる。
【００１９】
本発明において、反応を開始する際の反応温度は、該反応の活性化エネルギーの境界温度をＴ℃とした場合に（Ｔ−３）℃以下でなければならない。この温度を超えると反応開始から再生処理実施までの期間が短くなりすぎるので工業的に不利である。なお、反応を開始する際の反応温度は、触媒活性、触媒充填量、反応ガス組成、反応ガス流速、反応圧力、反応率などで調節することができる。
【００２０】
本発明において、活性化処理を行う回数については特に制限はなく、触媒の活性が低下する度に繰り返し実施することができる。このとき目的とする生成物の選択率が許容できる範囲であれば、活性化処理を繰り返しながら反応を継続することが触媒を長期間使用できるので工業的に有利である。
【００２１】
また、本発明において触媒の活性化処理は、１回は反応温度が活性化エネルギーの境界温度より高くなる前に実施しなければならないが、その後の運転方法に特に制限はない。例えば、反応温度が活性化エネルギーの境界温度より高くなった以降も反応を継続してもよいし、そのような反応温度まで使用した触媒に対して活性化処理を行ってもよい。
【００２２】
【実施例】
以下、本発明を実施例により示す。ただし、説明中の「部」は重量部を意味する。反応生成物の分析はガスクロマトグラフィーにより行った。また、反応用原料としてのイソブチレンまたは第三級ブタノールの反応率は前記［数１］に定義した通りであり、生成されるメタクロレイン及びメタクリル酸の選択率は以下のように定義される。
【００２３】
【数３】
メタクロレインの選択率（％）＝Ｃ／Ａ×１００
（Ａは反応した原料のモル数、Ｃは生成したメタクロレインのモル数を表す。）
【００２４】
【数４】
メタクリル酸の選択率（％）＝Ｄ／Ａ×１００
（Ａは反応した原料のモル数、Ｄは生成したメタクリル酸のモル数を表す。）
【００２５】
［参考例］
水６０００部にパラモリブデン酸アンモニウム３０００部を溶解し、続いて撹拌しながら三酸化アンチモン３３０．２部を加え５０℃に加温した（Ａ液）。別に、水５５００部に硝酸鉄（ＩＩＩ）８５８．１部、硝酸コバルト３２９６．８部、硝酸亜鉛８４．３部及び硝酸セシウム１１０．４部を溶解し、そこへ水３００部に６０％硝酸１５０部及び硝酸ビスマス６８６．９部を溶解させた溶液を加え３０℃に加温した（Ｂ液）。
【００２６】
撹拌下、Ａ液にＢ液を混合しスラリー状物を得、これを９０℃で２時間熟成した後、１０３℃まで昇温し１時間濃縮した後、スプレードライヤーを用いて乾燥粉末を得た。得られた乾燥粉末を３００℃で４時間焼成し、次の組成からなる触媒前駆体粉末を得た。
【００２７】
Ｍｏ_１２Ｂｉ_１Ｆｅ_１．５Ｃｏ_８Ｚｎ_０．２Ｃｓ_０．４Ｓｂ_０．８Ｏ_ｘ
（式中Ｍｏ，Ｂｉ，Ｆｅ，Ｃｏ，Ｚｎ，Ｃｓ，Ｓｂ及びＯはそれぞれモリブデン、ビスマス、鉄、コバルト、亜鉛、セシウム、アンチモン及び酸素を表す。また元素記号右部併記の数字は各元素の原子比であり、ｘは前記各成分の原子価を満足するのに必要な酸素の原子比である。）
【００２８】
得られた触媒前駆体粉末３９２０部をグラファイト粉末８０部とよく混合した後、外径４ｍｍ、高さ４ｍｍの円柱状に成形し、成形体を５１０℃で２時間焼成し、触媒を得た。
【００２９】
得られた触媒２０００ｇを、外部に熱媒浴を有する内径２７．５ｍｍ、高さ４ｍのステンレス製反応管に充填した。続いて、イソブチレン５容量％、酸素１２容量％、水蒸気１０容量％及び窒素７３容量％からなる原料混合ガスを接触時間３．５秒で触媒層を通過させる条件下で、熱媒浴の温度を３１５〜３７５℃の範囲で２〜５℃間隔で変化させ、各温度におけるイソブチレンの反応率から活性化エネルギーを算出した。その結果、活性化エネルギーの境界温度は３３５℃であり、該境界温度より低温域での活性化エネルギーが１０２ｋＪ／ｍｏｌ、高温域での活性化エネルギーが３５ｋＪ／ｍｏｌであった。
【００３０】
［実施例１］
参考例の触媒２０００ｇを参考例と同様な反応管に充填した。続いて、熱媒浴温度を３２５℃とし、原料混合ガスの接触時間を４．５秒と変更し、反応生成物を分析した結果、イソブチレン反応率９５．５％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３であった。この反応を以下の方法で連続的に行った。すなわち、触媒活性の変化により反応率が変化した場合は熱媒浴温度を調節することで反応率をほぼ一定に保つ方法で行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ連続運転の期間は９６００時間となった。その時、イソブチレン反応率９５．４％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。
【００３１】
反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、第１回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２３℃とし、当初と同じ原料混合ガスを接触時間４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．５％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、イソブチレン反応率９５．７％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３２】
再び、反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、第２回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．３％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、イソブチレン反応率９５．５％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３３】
ここで再び、反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、第３回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．２％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、イソブチレン反応率９５．４％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３４】
［比較例１］
参考例の触媒２０００ｇを参考例と同様な反応管に充填した。続いて、熱媒浴温度を３２５℃とし、イソブチレン５容量％、酸素１２容量％、水蒸気１０容量％及び窒素７３容量％からなる原料混合ガスを接触時間４．５秒で触媒層を通過させる条件下で反応を行い、反応生成物を分析した結果、イソブチレン反応率９５．５％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を実施例１と同様の方法で連続的に行った。熱媒浴の温度が３４０℃になるまで反応を継続したところ連続運転の期間は１２０００時間となった。その時、イソブチレン反応率９５．７％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。
【００３５】
反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．１％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３４０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は６０００時間となった。その時、イソブチレン反応率９５．７％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３６】
次に、反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、再び触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．０％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３４０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は４８００時間となった。その時、イソブチレン反応率９４．８％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３７】
反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに空気を接触時間４．０秒で２４時間触媒層を通過させ、第３回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、イソブチレン反応率９５．０％、メタクロレインの選択率８７．７％、メタクリル酸の選択率５．３％であった。この反応を当初と同様の方法で連続的に行った。熱媒浴の温度が３４０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は３６００時間となった。その時、イソブチレン反応率９４．２％、メタクロレインの選択率８７．５％、メタクリル酸の選択率５．３％であった。
【００３８】
［実施例２］
参考例の触媒２０００ｇを参考例と同様な反応管に充填した。続いて、熱媒浴温度を３２５℃とし、第三級ブタノール５容量％、酸素１２容量％、水蒸気１０容量％及び窒素７３容量％からなる原料混合ガスを接触時間４．５秒で触媒層を通過させる条件下で反応を行い、反応生成物を分析した結果、第三級ブタノール反応率１００％、メタクロレインの選択率８３．４％、メタクリル酸の選択率５．１％であった。この反応を実施例１と同様の方法で連続的に行った。すなわち、触媒活性の変化により反応率が変化した場合は熱媒浴温度を調節することで反応率をほぼ一定に保つ方法で行った。ただし、この際、第三級ブタノールは該触媒に接触した際にその全量が速やかにイソブチレンと水に分解されると仮定し、反応後のガス中におけるイソブチレン濃度を分析してイソブチレンの反応率を求め、その反応率をほぼ一定に保つ方法で行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ連続運転の期間は９６００時間となった。その時、第三級ブタノール反応率１００％、メタクロレインの選択率８３．２％、メタクリル酸の選択率５．１％であった。
【００３９】
ここで反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに酸素１５容量％及び窒素８５容量％からなるガスを接触時間４．０秒で２４時間触媒層を通過させ、第１回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、第三級ブタノール反応率１００％、メタクロレインの選択率８３．４％、メタクリル酸の選択率５．１％であった。この反応を上記と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、第三級ブタノール反応率１００％、メタクロレインの選択率８３．２％、メタクリル酸の選択率５．１％であった。
【００４０】
再び反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに酸素１５容量％及び窒素８５容量％からなるガスを接触時間４．０秒で２４時間触媒層を通過させ、第２回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、第三級ブタノール反応率１００％、メタクロレインの選択率８３．３％、メタクリル酸の選択率５．１％であった。この反応を上記と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、第三級ブタノール反応率１００％、メタクロレインの選択率８３．２％、メタクリル酸の選択率５．１％であった。
【００４１】
再び反応を一旦停止し、熱媒浴温度を３８０℃に上げ、原料混合ガスの代わりに酸素１５容量％及び窒素８５容量％からなるガスを接触時間４．０秒で２４時間触媒層を通過させ、第３回目の触媒活性化処理を行った。この処理後、熱媒浴温度を３２５℃とし、上記の原料混合ガスの接触時間を４．５秒で触媒層を通過させる条件で反応を再開した。反応生成物を分析した結果、第三級ブタノール反応率１００％、メタクロレインの選択率８３．３％、メタクリル酸の選択率５．１％であった。この反応を上記と同様の方法で連続的に行った。熱媒浴の温度が３３０℃になるまで反応を継続したところ活性化処理後の連続運転の期間は８４００時間となった。その時、第三級ブタノール反応率１００％、メタクロレインの選択率８３．２％、メタクリル酸の選択率５．１％であった。
【００４２】
【発明の効果】
本発明のメタクロレイン及びメタクリル酸の製造方法によると、触媒を実質的に長期間にわたり使用することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing methacrolein and methacrylic acid, and more particularly to a method for producing methacrolein and methacrylic acid by subjecting isobutylene or tertiary butanol to gas phase catalytic oxidation with molecular oxygen in the presence of a catalyst.
[0002]
[Prior art]
A method for producing methacrolein and methacrylic acid by catalytically oxidizing isobutylene or tertiary butanol on a catalyst comprising a composite oxide containing molybdenum, bismuth and iron as essential components is widely known. Is also used. In this case, the reaction is carried out at a temperature of 300 to 400 ° C. using the catalyst as a fixed bed.
[0003]
Although the catalyst used in such a gas phase catalytic oxidation reaction is used for a relatively long time, the activity of the catalyst usually decreases with time. Japanese Patent Publication No. 5-29502 discloses that a multi-component oxide catalyst containing Mo-Bi-Fe whose catalytic activity has been reduced by use of a reaction is regenerated at a temperature of 380 to 540 ° C in an atmosphere substantially consisting of air. In the method disclosed in Japanese Patent Publication No. 5-70503, an oxidizing gas comprising 5 to 99.9% by volume of oxygen, 0.1 to 95% by volume of water vapor and an inert gas is used for the same type of catalyst having a reduced catalytic activity. A method of performing a regeneration treatment at a temperature of 300 to 500 ° C. under circulation is disclosed.
[0004]
[Problems to be solved by the invention]
However, according to the study of the present inventors, in the regeneration treatment for the catalyst whose activity has been reduced as described in these publications, after the treatment, once the catalyst performance is restored to the level before the use of the reaction, The rate of activity decrease thereafter is fast, and is not always sufficiently satisfactory from the viewpoint of industrial implementation.
[0005]
Accordingly, an object of the present invention is to provide a method for producing methacrolein and methacrylic acid by subjecting isobutylene or tertiary butanol in which a catalyst can be used for a long period of time to gas phase catalytic oxidation with molecular oxygen.
[0006]
[Means for Solving the Problems]
The present invention relates to the production of methacrolein and methacrylic acid by contact oxidation of isobutylene or tertiary butanol with a catalyst comprising a composite oxide containing molybdenum, bismuth and iron as essential components. When the boundary temperature of the activation energy of the reaction for obtaining methacrolein and methacrylic acid is T ° C., the reaction is started at a temperature of (T-3) ° C. or lower, and the reaction is performed while increasing the reaction temperature as the activity of the catalyst decreases. And performing an activation treatment on the catalyst before the reaction temperature becomes higher than the boundary temperature, in the method for producing methacrolein and methacrylic acid.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
The catalyst used in the present invention is composed of a composite oxide containing molybdenum, bismuth and iron as essential components, and there is no particular limitation on components other than the essential components. Such catalysts are disclosed in JP-A-53-19188, JP-A-54-66610, JP-A-55-359, JP-A-55-19227, and JP-A-56-95135. And a known method as described in JP-A-60-28824.
[0008]
In a gas phase catalytic reaction using a solid catalyst, it is known that the activation energy of a target reaction often has different values between a low reaction temperature region and a high reaction temperature region at a certain reaction temperature as a boundary. For example, in JOURNAL OF CATALYSIS Vol. 41, pp. 134-139, it is reported that 1-butene has a different activation energy in the reaction of catalytically oxidizing 1-butene over a catalyst comprising a composite oxide containing molybdenum and bismuth. Have been. Such behavior is a phenomenon observed because the rate-limiting step of the reaction differs depending on the reaction temperature, and is described in detail in Kodansha Catalyst Course Vol. According to one theory, it is estimated that the reaction of reactive molecules on the catalytic active site is the rate-determining step in the low reaction temperature region, and that the diffusion of the reactive molecules to the catalytic active site is the rate-limiting step in the high reaction temperature region. Have been.
[0009]
The present inventors analyzed the activation energy of the reaction for producing methacrolein and methacrylic acid by catalytically oxidizing isobutylene on a catalyst comprising a composite oxide containing molybdenum, bismuth and iron as essential components. It was confirmed that different values were obtained in a low region and a high region.
[0010]
In the present invention, the boundary temperature of the activation energy is obtained as follows.
First, a catalyst is filled in a reaction tube provided with a heat medium bath, and the temperature of the heat medium bath is changed in the range of 315 to 375 ° C. at intervals of 2 to 5 ° C., and the reaction rate of isobutylene at each temperature is determined. Here, the reaction rate is determined by the following equation.
[0011]
(Equation 1)
Raw material reaction rate (%) = A / B × 100
(A represents the number of moles of the reacted raw material, and B represents the number of moles of the supplied raw material.)
Subsequently, a reaction rate constant is determined by the following equation.
[0012]
(Equation 2)
K = (SV) × (1 / ρ) × ln [100 / (100−X)]
(K is the reaction rate constant, SV is the space velocity, ρ is the packing density of the catalyst, and X is the reaction rate (%) of isobutylene.)
[0013]
Subsequently, 1 / T is plotted on the horizontal axis, and InK is plotted on the vertical axis, and after plotting each data, two approximate straight lines are drawn to determine the slope. Here, 1 / T represents the reciprocal of the temperature (absolute temperature) of the heat medium bath of the reaction tube, and lnK represents the natural logarithm of the reaction rate constant. The approximate straight line can be obtained by a general method such as the least square method.
The value obtained by multiplying the absolute value of the slope of the obtained approximate line by the gas constant is the activation energy to be obtained, and the reciprocal of the abscissa of the intersection of the two approximate lines is the boundary temperature of the activation energy to be obtained.
[0014]
When tertiary butanol is used in place of isobutylene as a reaction raw material, tertiary butanol is rapidly decomposed into isobutylene and water on a catalyst containing molybdenum, bismuth and iron as essential components. That is, when tertiary butanol is used as a reaction raw material, the reaction form is considered to be essentially the same as the isobutylene oxidation reaction. Therefore, even when tertiary butanol is used as a reaction raw material, the boundary temperature of the activation energy of the reaction from isobutylene can be used as it is.
[0015]
In general, when a catalyst is used on an industrial scale, various life extension measures have been attempted to extend the life of a once charged catalyst as much as possible. For example, there is a method in which the reaction rate is gradually increased to a limit allowed for the process with the deterioration of the catalyst to maintain the reaction rate.
[0016]
The present inventors have found that isobutylene or tertiary butanol is catalytically oxidized on a catalyst comprising a composite oxide containing molybdenum, bismuth and iron as essential components to produce methacrolein and methacrylic acid. When the temperature is T ° C., the reaction is started at a temperature of (T-3) ° C. or lower, and the reaction is continued while increasing the reaction temperature as the activity of the catalyst decreases, before the reaction temperature becomes higher than the boundary temperature. It has been found that performing at least one activation treatment on the catalyst significantly increases the catalyst life.
[0017]
Causes of the decrease in the activity of the catalyst include reduction of the catalyst component, sublimation and scattering of the catalyst component, change in the crystal phase in the catalyst structure, and the like. As a method for activating the catalyst whose activity has been reduced due to these causes, known methods such as the regeneration method described in the section of the prior art can be used, but the catalyst is kept at a temperature of 300 ° C. or more and less than 550 ° C. A method in which a gas composed of air is brought into contact for 1 hour or more is preferable. The activation treatment of the catalyst may be carried out after removing the catalyst from the reactor, but it is easier to carry out the operation while the catalyst is filled in the reactor, which is industrially advantageous.
[0018]
Even if the above-described activation treatment is performed on the catalyst used until the reaction temperature becomes higher than the boundary temperature of the activation energy, once the catalyst performance is recovered, but the speed of the subsequent activity decrease is increased. The effect of prolonging life is poor. On the other hand, when the above-described activation treatment is performed on a catalyst that is used only at a reaction temperature lower than the boundary temperature of the activation energy as in the method of the present invention, in addition to the recovery of the catalyst performance, After that, the rate of activity decrease is also at the same level as when new.
[0019]
In the present invention, the reaction temperature at the start of the reaction must be (T-3) ° C. or lower when the boundary temperature of the activation energy of the reaction is T ° C. Exceeding this temperature is industrially disadvantageous because the period from the start of the reaction to the execution of the regeneration treatment is too short. The reaction temperature at the start of the reaction can be adjusted by the catalyst activity, the catalyst loading, the reaction gas composition, the reaction gas flow rate, the reaction pressure, the reaction rate, and the like.
[0020]
In the present invention, the number of times of the activation treatment is not particularly limited, and the activation treatment can be repeated each time the activity of the catalyst decreases. At this time, if the selectivity of the target product is within an acceptable range, continuing the reaction while repeating the activation treatment is industrially advantageous because the catalyst can be used for a long period of time.
[0021]
In the present invention, the catalyst activation treatment must be performed once before the reaction temperature becomes higher than the boundary temperature of the activation energy, but there is no particular limitation on the operation method thereafter. For example, the reaction may be continued even after the reaction temperature becomes higher than the boundary temperature of the activation energy, or the activation treatment may be performed on the catalyst used up to such a reaction temperature.
[0022]
【Example】
Hereinafter, the present invention will be described with reference to Examples. However, “parts” in the description means parts by weight. The reaction product was analyzed by gas chromatography. The reaction rate of isobutylene or tertiary butanol as a reaction raw material is as defined in the above [Equation 1], and the selectivity of methacrolein and methacrylic acid to be produced is defined as follows.
[0023]
(Equation 3)
Selectivity of methacrolein (%) = C / A × 100
(A represents the number of moles of the reacted raw material, and C represents the number of moles of generated methacrolein.)
[0024]
(Equation 4)
Methacrylic acid selectivity (%) = D / A × 100
(A represents the number of moles of the reacted raw material, and D represents the number of moles of the generated methacrylic acid.)
[0025]
[Reference example]
3000 parts of ammonium paramolybdate was dissolved in 6000 parts of water, and then 330.2 parts of antimony trioxide was added with stirring and the mixture was heated to 50 ° C. (Solution A). Separately, 858.1 parts of iron (III) nitrate, 3296.8 parts of cobalt nitrate, 84.3 parts of zinc nitrate and 110.4 parts of cesium nitrate were dissolved in 5500 parts of water, and 300 parts of water was added to 60 parts of 60% nitric acid 150 parts. And a solution in which 686.9 parts of bismuth nitrate were dissolved, and heated to 30 ° C. (Solution B).
[0026]
Under stirring, the solution A was mixed with the solution B to obtain a slurry, which was aged at 90 ° C. for 2 hours, heated to 103 ° C., concentrated for 1 hour, and then dried using a spray drier to obtain a dry powder. . The obtained dry powder was calcined at 300 ° C. for 4 hours to obtain a catalyst precursor powder having the following composition.
[0027]
Mo ₁₂ Bi ₁ Fe _1.5 Co ₈ Zn _0.2 Cs _0.4 Sb _0.8 O _x
(In the formula, Mo, Bi, Fe, Co, Zn, Cs, Sb, and O represent molybdenum, bismuth, iron, cobalt, zinc, cesium, antimony, and oxygen, respectively. And x is the atomic ratio of oxygen necessary to satisfy the valence of each component.)
[0028]
After sufficiently mixing 3920 parts of the obtained catalyst precursor powder with 80 parts of graphite powder, the mixture was molded into a column having an outer diameter of 4 mm and a height of 4 mm, and the molded body was calcined at 510 ° C. for 2 hours to obtain a catalyst.
[0029]
2000 g of the obtained catalyst was packed in a stainless steel reaction tube having an inner diameter of 27.5 mm and a height of 4 m having a heat medium bath outside. Subsequently, the temperature of the heating medium bath was changed under the condition that a raw material mixed gas consisting of 5% by volume of isobutylene, 12% by volume of oxygen, 10% by volume of steam and 73% by volume of nitrogen passed through the catalyst layer for a contact time of 3.5 seconds. The activation energy was calculated from the reaction rate of isobutylene at each temperature while changing the temperature in the range of 315 to 375 ° C at intervals of 2 to 5 ° C. As a result, the boundary temperature of the activation energy was 335 ° C., the activation energy at a temperature lower than the boundary temperature was 102 kJ / mol, and the activation energy at a high temperature was 35 kJ / mol.
[0030]
[Example 1]
2000 g of the catalyst of the reference example was packed in a reaction tube similar to that of the reference example. Subsequently, the heating medium bath temperature was set to 325 ° C., the contact time of the raw material mixed gas was changed to 4.5 seconds, and the reaction product was analyzed. As a result, the isobutylene conversion was 95.5%, and the selectivity of methacrolein was 87. The selectivity of methacrylic acid was 5.3%. This reaction was continuously performed by the following method. That is, when the reaction rate changed due to the change in the catalyst activity, the reaction rate was kept almost constant by adjusting the temperature of the heat medium bath. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the period of the continuous operation was 9,600 hours. At that time, the isobutylene conversion was 95.4%, the selectivity for methacrolein was 87.7%, and the selectivity for methacrylic acid was 5.3%.
[0031]
The reaction was temporarily stopped, the temperature of the heat medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds to perform the first catalyst activation treatment. . After this treatment, the reaction was restarted under the condition that the temperature of the heat medium bath was set to 323 ° C. and the same raw material mixed gas as in the beginning was passed through the catalyst layer for a contact time of 4.5 seconds. As a result of analyzing the reaction product, the conversion of isobutylene was 95.5%, the selectivity of methacrolein was 87.7%, and the selectivity of methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the isobutylene conversion was 95.7%, the selectivity for methacrolein was 87.5%, and the selectivity for methacrylic acid was 5.3%.
[0032]
Again, the reaction was once stopped, the temperature of the heat medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds to perform the second catalyst activation treatment. went. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the conversion of isobutylene was 95.3%, the selectivity of methacrolein was 87.7%, and the selectivity of methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the isobutylene conversion was 95.5%, the selectivity for methacrolein was 87.5%, and the selectivity for methacrylic acid was 5.3%.
[0033]
Here, the reaction was once again stopped, the temperature of the heat medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds, and the third activation of the catalyst was carried out. Processing was performed. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the isobutylene conversion was 95.2%, the selectivity for methacrolein was 87.7%, and the selectivity for methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the conversion of isobutylene was 95.4%, the selectivity of methacrolein was 87.5%, and the selectivity of methacrylic acid was 5.3%.
[0034]
[Comparative Example 1]
2000 g of the catalyst of the reference example was packed in a reaction tube similar to that of the reference example. Subsequently, the heating medium bath temperature was set to 325 ° C., and the raw material mixed gas consisting of 5% by volume of isobutylene, 12% by volume of oxygen, 10% by volume of steam and 73% by volume of nitrogen was passed through the catalyst layer for a contact time of 4.5 seconds. The reaction was carried out under the following conditions, and the reaction product was analyzed. As a result, the isobutylene conversion was 95.5%, the selectivity for methacrolein was 87.7%, and the selectivity for methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as in Example 1. When the reaction was continued until the temperature of the heating medium bath reached 340 ° C., the period of continuous operation was 12,000 hours. At that time, the conversion of isobutylene was 95.7%, the selectivity of methacrolein was 87.7%, and the selectivity of methacrylic acid was 5.3%.
[0035]
The reaction was once stopped, the temperature of the heat medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds to perform a catalyst activation treatment. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the conversion of isobutylene was 95.1%, the selectivity of methacrolein was 87.7%, and the selectivity of methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 340 ° C., the period of continuous operation after the activation treatment was 6000 hours. At that time, the isobutylene conversion was 95.7%, the selectivity for methacrolein was 87.5%, and the selectivity for methacrylic acid was 5.3%.
[0036]
Next, the reaction was temporarily stopped, the temperature of the heating medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds, and the catalyst activation treatment was performed again. . After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the isobutylene conversion was 95.0%, the selectivity for methacrolein was 87.7%, and the selectivity for methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 340 ° C., the period of continuous operation after the activation treatment was 4,800 hours. At that time, the isobutylene conversion was 94.8%, the selectivity for methacrolein was 87.5%, and the selectivity for methacrylic acid was 5.3%.
[0037]
The reaction was temporarily stopped, the temperature of the heat medium bath was raised to 380 ° C., and air instead of the raw material mixed gas was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds to perform a third catalyst activation treatment. . After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the isobutylene conversion was 95.0%, the selectivity for methacrolein was 87.7%, and the selectivity for methacrylic acid was 5.3%. This reaction was continuously performed in the same manner as at the beginning. When the reaction was continued until the temperature of the heat medium bath reached 340 ° C., the period of continuous operation after the activation treatment was 3600 hours. At that time, the conversion of isobutylene was 94.2%, the selectivity of methacrolein was 87.5%, and the selectivity of methacrylic acid was 5.3%.
[0038]
[Example 2]
2000 g of the catalyst of the reference example was packed in a reaction tube similar to that of the reference example. Subsequently, the temperature of the heat medium bath was set to 325 ° C., and the catalyst layer was contacted with a raw material mixed gas comprising 5% by volume of tertiary butanol, 12% by volume of oxygen, 10% by volume of steam and 73% by volume of nitrogen for 4.5 seconds of contact time. The reaction was carried out under the condition of passing through, and the reaction product was analyzed. As a result, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.4%, and the selectivity for methacrylic acid was 5.1%. This reaction was continuously performed in the same manner as in Example 1. That is, when the reaction rate changed due to the change in the catalyst activity, the reaction rate was kept almost constant by adjusting the temperature of the heat medium bath. However, at this time, it is assumed that the entire amount of tertiary butanol is quickly decomposed into isobutylene and water when contacted with the catalyst, and the isobutylene concentration in the gas after the reaction is analyzed to determine the reaction rate of isobutylene. The reaction was carried out in such a manner that the reaction rate was kept almost constant. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the period of the continuous operation was 9,600 hours. At that time, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.2%, and the selectivity for methacrylic acid was 5.1%.
[0039]
Here, the reaction was temporarily stopped, the temperature of the heating medium bath was raised to 380 ° C., and a gas consisting of 15% by volume of oxygen and 85% by volume of nitrogen was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds instead of the raw material mixed gas. Then, the first catalyst activation treatment was performed. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.4%, and the selectivity for methacrylic acid was 5.1%. This reaction was continuously performed in the same manner as described above. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.2%, and the selectivity for methacrylic acid was 5.1%.
[0040]
The reaction was once again stopped, the temperature of the heat medium bath was raised to 380 ° C., and a gas consisting of 15% by volume of oxygen and 85% by volume of nitrogen was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds instead of the raw material mixed gas. A second catalyst activation treatment was performed. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.3%, and the selectivity for methacrylic acid was 5.1%. This reaction was continuously performed in the same manner as described above. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.2%, and the selectivity for methacrylic acid was 5.1%.
[0041]
The reaction was once again stopped, the temperature of the heat medium bath was raised to 380 ° C., and a gas consisting of 15% by volume of oxygen and 85% by volume of nitrogen was passed through the catalyst layer for 24 hours with a contact time of 4.0 seconds instead of the raw material mixed gas. A third catalyst activation treatment was performed. After this treatment, the reaction was restarted under the conditions that the temperature of the heat medium bath was 325 ° C. and the contact time of the raw material mixed gas was 4.5 seconds to pass through the catalyst layer. As a result of analyzing the reaction product, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.3%, and the selectivity for methacrylic acid was 5.1%. This reaction was continuously performed in the same manner as described above. When the reaction was continued until the temperature of the heat medium bath reached 330 ° C., the continuous operation period after the activation treatment was 8,400 hours. At that time, the tertiary butanol conversion was 100%, the selectivity for methacrolein was 83.2%, and the selectivity for methacrylic acid was 5.1%.
[0042]
【The invention's effect】
According to the method for producing methacrolein and methacrylic acid of the present invention, the catalyst can be used for a substantially long period.

Claims

When isobutylene or tertiary butanol is oxidized in contact with a catalyst comprising a composite oxide containing molybdenum, bismuth and iron as essential components to produce methacrolein and methacrylic acid, the catalyst is used to convert methacrolein and methacrylic acid from isobutylene. When the boundary temperature of the activation energy of the reaction for obtaining the acid is T ° C., the reaction is started at a temperature of (T-3) ° C. or lower, and the reaction is continued while increasing the reaction temperature with the decrease in the activity of the catalyst; A method for producing methacrolein and methacrylic acid, wherein an activation treatment is performed on the catalyst before the reaction temperature becomes higher than the boundary temperature.