JP3817763B2

JP3817763B2 - Method for producing maleic anhydride

Info

Publication number: JP3817763B2
Application number: JP32707095A
Authority: JP
Inventors: 稔田中; 達也井原
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 1994-12-22
Filing date: 1995-12-15
Publication date: 2006-09-06
Anticipated expiration: 2015-12-15
Also published as: CN1061971C; KR100284064B1; KR960022434A; JP2006104204A; JPH08245610A; CN1141911A

Description

【０００１】
【発明の属する技術分野】
本発明は流動層反応器にて無水マレイン酸を製造する方法に関する。詳しくは、ｎ−ブタン、ブテン、ブタジエン等の炭素数４以上の脂肪族炭化水素からの無水マレイン酸の製造に有用な流動層酸化触媒の活性低下を抑制し、無水マレイン酸を安全に製造する方法に関するものである。
【０００２】
【従来の技術】
バナジウム−リン系複合酸化物を活性成分とする酸化触媒は、ｎ−ブタンのような炭素数４以上の脂肪族炭化水素から無水マレイン酸を製造する際に利用されてきた。それ等の例として例えば米国特許第４５２５４７１号、同第４３７４０４３号、同第４４５５４３４号、同第４３１７７７８号、同第４５１０２５８号、同第４５１１６７０号、欧州特許明細書第２２５０６２号、米国特許第４３７４７５６号、同第４５２０１２７号、同第４４７２５２７号明細書等に記載の方法を挙げることができる。
【０００３】
これらの触媒を固定床反応器で使用する場合には、経時的に活性低下が起こるため、反応を一時中断して触媒を水蒸気流と接触させて触媒活性の再生を行うのが一般的である（特開昭６０−１４３８３２号公報、米国特許第４５１５８９９号明細書参照）。また、０．２〜２容量％の低濃度炭化水素を含む空気の流れのもとで、３００〜６００℃で「コンディショニング」することも知られている（米国特許第４１７１３１６号明細書参照）。さらに混合バナジウムおよびリン酸化物触媒上に分子状酸素の排除のもとに、２〜６個の炭素原子を有するガス状炭化水素成分を通し、３００〜５００℃で触媒を活性化することも知られている（米国特許第４１７８２９８号、同第４１８１６２８号明細書参照）。
【０００４】
一方、この触媒を流動層反応器で使用する場合は反応を停止することなく、随時、反応器内部の触媒の補給および抜き出しが可能なため、反応器内に充填されている触媒と同一の新触媒を活性の低下に見合って少量ずつ随時または連続的に補給し、あるいは該反応器内の触媒量を一定に保持するため、触媒の一部を抜き出すことによって、触媒活性を概ね一定に維持することが可能になる。従って流動層反応器を使用して無水マレイン酸を製造する場合は、決められた条件下で定常状態で連続稼働する限りにおいては触媒の活性低下が起こることは少なく、例え活性低下が起こっても操業に支障をきたすような急激な低下は起こらない。
【０００５】
但し、このような流動層反応器で使用した触媒の活性再生方法も提案されている。例えば、触媒を反応器中で酸素と炭化水素等の還元性ガスの存在下（好ましくは還元性ガス＝対酸素３０モル％以上）、４００〜５５０℃の高温条件で接触させ、活性化することが開示されている（特開昭５８−１１４７３５号公報、ＵＳＰ４７４８１４０明細書参照）。
【０００６】
また反応器から外部に抜き出した触媒を水蒸気処理して再生、賦活処理し、再び反応器に戻すことも開示されている（特開平４−３１６５６７号、特開平５−４３５６７号公報等参照）。
ところで、通常工業的規模の流動層反応器で気相酸化反応により無水マレイン酸を製造する場合は、一般に、流動層反応器内にバナジウム−リン系複合酸化物を活性成分とする酸化触媒を充填し、該反応器底部のガス分散板の下方から空気を供給し、触媒を流動化させて分散板の上方に触媒の流動層を形成させ、「スタートアップヒ−タ−」と称する外部加熱装置によって空気を昇温することによって流動層の温度を気相酸化反応が起こり得る温度（２５０℃）まで昇温した後、炭素数４以上の脂肪族炭化水素を供給し、気相酸化反応を開始している。このような停止状態から定常状態への移行期間（反応開始）および定常状態から停止状態へ移行する期間（反応停止）のような非定常状態期間にも触媒の活性低下は起こり、この場合は、流動層反応器内のすべての触媒が短期間に劣化する恐れがあるので、この触媒の活性低下を抑制し、しかも安定的に非定常状態から定常状態へ移行することが望まれている。
【０００７】
しかしながら、前述のような酸素と還元性ガスの存在下に該反応器内で４００〜５５０℃で活性化する方法や、外部抜き出し触媒を再生、賦活処理する方法は、非定常状態の触媒の活性劣化を抑制するものではない。
【０００８】
【発明が解決しようとする課題】
本発明者の検討によれば、バナジウム−リン系複合酸化物を活性成分とする酸化触媒を３００℃以上に加温された空気等の酸素含有ガス雰囲気下に長時間晒した場合、著しい活性低下と流動性の悪化が認められた。従って、流動層反応器で反応を行う場合の非定常状態期間に、触媒の活性低下を抑制する方法が求められている。
【０００９】
一方、反応器出口ガスの組成は、そこでの温度と圧力の条件において可燃範囲となることを回避するよう設定すべきであるが、流動層反応器の出口ガスを直接サンプリングする場合、微細な触媒粒子によるサンプルノズルの閉塞防止用に触媒フィルタ−等の設備を設置しても安定的に連続分析することは難しい。さらに反応で生成した無水マレイン酸や水がサンプルノズル内や分析機器内で凝縮し、マレイン酸やフマル酸の析出を起こすため、定常状態期間だけでなくスタ−トアップ（反応開始）時のような非定常状態期間においては、特に流動層反応器出口ガスの正確なサンプリング・分析を行い、該ガス組成が可燃範囲外にあることを連続的に監視するのは極めて難しい。
【００１０】
尚、温度と可燃範囲との関係は、温度と限界酸素濃度との関係から明らかである。例えばブタン（９９％純度）をバナジウム−リン系複合酸化物を含有する触媒を用いたときの気相酸化反応を、反応時のブタン濃度約４％、反応温度４００〜４６０℃、ブタン変換率８０〜９８％、無水マレイン酸收率４８〜５６％の条件で実施し、反応器から抜き出した反応生成ガス（反応器を出たガスの温度は２５０〜３５０℃）中の触媒を触媒フィルターで分離した後、反応生成ガスを予熱した容積１リットルの爆発容器に導入して、１５ＫＶ交流スパーク（０．０１秒）で点火し、限界酸素濃度（＝燃焼の起こる酸素濃度の下限値、爆発容器の温度３５０〜４５０℃）を測定した結果が、特開平２−１９３７０号参考例−１に記載されている。（下記表−１参照）
【００１１】
【表１】

これにより、４００〜４６０℃で反応を行った場合での反応器出口ガスの温度が２５０〜３５０℃程度であることを考慮すると、流動層反応器出口の反応生成ガス組成のうち、可燃ガス成分（炭素数４以上の炭化水素成分、無水マレイン酸及び一酸化炭素等）とを除いたガス組成中の酸素濃度を監視し、その濃度を６ｖｏｌ％以下とすることにより、可燃範囲から外れたガス組成で安全に操業することが可能である。
【００１２】
本発明は、流動層反応器を用いた無水マレイン酸製造用触媒の活性低下を抑制した上で、反応生成ガスの安全性を確保し、かつ安定した操作で非定常状態から定常状態へ移行、及び非定常状態から定常状態へ移行することが可能な方法を提供しようとするものである。
【００１３】
【課題を解決するための手段】
本発明は、炭素数４以上の脂肪族炭化水素を流動層反応器を用いて気相酸化して無水マレイン酸を製造する方法において、バナジウム−リン系複合酸化物を活性成分とする無水マレイン酸製造用酸化触媒を充填した流動層反応器底部から
(1)不活性ガス、
又は
(2)酸素含有ガス、及び該酸素含有ガス中の酸素供給量に対して０．１〜１０モル％の供給量で、かつ触媒に対して重量比０．００１〜０．１ｈｒ^-1の割合で該炭素数４以上の脂肪族炭化水素ガスの混合ガス
を供給して該触媒の流動層を形成させつつ、該流動層の温度を少なくとも３００℃から４００℃にする昇温操作、及び／又は少なくとも４００℃から３００℃にする降温操作を行うことを特徴とする無水マレイン酸の製造法を提供するというものである。
【００１４】
【発明の実施の態様】
本発明者の検討によれば、非定常状態で、不活性ガス流通時、又は３００℃以上に加温された酸素含有ガス雰囲気下で昇温又は降温を行なう場合でも、炭素数４以上の脂肪族炭化水素の供給量を酸素供給量に対して上記の特定の範囲とした酸素含有ガスとの混合ガスを流通した時には、該触媒の活性低下は見られず、流動性も良好であることがわかった。
【００１５】
以下本発明について更に詳細に説明する。
本発明で使用する原料炭化水素としては、炭素数４以上の脂肪族炭化水素が使用される。好適な原料炭化水素はブタン（例えばｎ−ブタン）、ブテン類（例えば１−ブテン、２−ブテン）、ブタジエン（例えば１，３−ブタジエン）等の炭素数４の炭化水素であり、より好適にはｎ−ブタンである。
【００１６】
酸素含有ガスとしては通常、空気が使用されるが、不活性ガスで希釈された空気、酸素を加えて富化された空気等を使用することもできる。
また、不活性ガスとしては、窒素、二酸化炭素、水蒸気およびそれらの混合物の少なくとも一つから選ばれる不活性ガスを使用することができるが、好ましくは窒素を主体とするガスである。
【００１７】
本発明に使用される流動層反応器（１）は、例えば図１に示される、反応器底部に触媒流動層の下端を画するためのガス分散板（２）を備え、また反応器頂部に反応生成ガスから飛散した触媒を回収して触媒流動層に戻すためのサイクロン（１２）を備え、さらに流動層の下部領域であってガス分散板から上方に離れた位置に原料炭化水素供給口（７）を備え、流動層の下部領域、例えばガス分散板（２）と上記炭化水素供給口（７）との間またはその付近の位置にサイクロン（１２）で回収された触媒の実質的部分を触媒流動層に戻すためのディップレッグ（１５）の下端（１６）を備え、流動層領域には除熱のための間接熱交換装置、例えば除熱コイル（６）を備えていることが望ましい。かかる反応器としては、より具体的には特開平２−１９３７０号公報に記載の反応器等が例示される。
【００１８】
本発明で使用する触媒としては、バナジウム−リン系複合酸化物を活性成分とする酸化触媒であって、流動層反応器で使用可能なものであれば、特に限定はないが、特にバナジウムの平均原子価が約＋３．８〜＋４．８である触媒は、本発明に使用する触媒として適しており、またリン／バナジウム原子比が約０．５〜２．０を有する複合酸化物が適している。そのような触媒の活性相は、主に(VO)₂P₂O₇であり、Ｖ⁴⁺とＶ⁵⁺との間のレドックスにより反応が進行することや、Ｖ⁴⁺の存在が無水マレイン酸を生成する収率に寄与することが知られている。また触媒中には３価まで還元されたバナジウム元素も一部含むため、触媒中の全てのバナジウムを４価に換えた当量（ΣＶ値）と触媒中の４価のバナジウムとの当量比（Ｖ⁴⁺／ΣＶ値）を還元度として評価する。なお、この還元度の値を触媒活性の変化のめやすとすることができる。
【００１９】
非定常状態の触媒の活性低下抑制操作は、触媒の流動層の温度が少なくとも３００℃から４００℃に昇温する間、及び又は４００℃から３００℃に降温する間に、特には少なくとも３００℃から４００℃に昇温する間には必ず、酸化触媒を充填した流動層反応器内に、該反応器底部のガス分散板の下方から(1)不活性ガス、又は(2)酸素含有ガス、及び該酸素含有ガス中の酸素供給量に対して０．１〜１０モル％の供給量で、かつ触媒に対して重量比０．００１〜０．１ｈｒ^-1の割合で該炭素数４以上の脂肪族炭化水素ガスの混合ガスを供給するというものである。
【００２０】
さらに本発明の製造法では、定常状態では通常高生産性を得るために、反応生成ガス組成を可燃範囲の上限以上になるようにしており、逆に昇温又は降温操作を行う非定常状態時には、反応生成ガス組成を可燃範囲のガス組成の下限以下になるようにして実施する。しかし流動層の温度が昇温あるいは降温操作により反応温度の４００〜４６０℃に到達した直後に、反応生成ガス組成を可燃範囲の下限から上限へ移行させるために、単に炭化水素供給量の増減だけで組成を変化させようとすると、その過程で反応生成ガス組成は可燃範囲内を通過することにより、爆発等の危険を伴うので、通常の工業的規模の装置で実施することは殆ど不可能である。そこで本発明では、非定常状態から定常状態、あるいは定常状態から非定常状態に移行する場合には、反応器出口（図１（１４ａ））の反応生成ガス組成が可燃範囲を迂回するように調整して、該反応生成ガスが可燃範囲のガス組成を形成せずに移行させることが好ましい。
【００２１】
更に詳細に説明すると、昇温操作の後又は降温操作の前に、流動層の温度が４００〜４６０℃の範囲において、流動層反応器底部から供給する酸素含有ガスと炭素数４以上の脂肪族炭化水素ガスとの混合ガス濃度を、流動層反応器に供給する酸素含有ガス中の酸素量に対して１０モル％から１９モル％に増加させるか、又は１９モル％から１０モル％に減少させるために、
(A)該酸素含有ガスと炭化水素ガスとの混合ガス中に不活性ガスを導入するか、
(B)流動層反応器から抜き出した反応生成ガスから無水マレイン酸を回収した後の残りのガスの一部を再度流動層反応器に導入するか、又は
(C)流動層反応器に供給する前に該酸素含有ガス中で燃料を燃焼させる
ことにより、流動層反応器底部から供給される全ガス中の酸素濃度を増減させ、これにより反応生成ガスが可燃範囲のガス組成を形成せずに、非定常状態から定常状態へ、または定常状態から非定常状態へ移行することができる。
【００２２】
また、本発明における定常状態では、流動層反応器底部から供給する炭素数４以上の脂肪族炭化水素ガス濃度を、流動層反応器に供給する酸素含有ガス中の酸素量に対して１０モル％から１９モル％に増加させた後、又は１９モル％から１０モル％に減少させる前に、
流動層反応器中の炭素数４以上の脂肪族炭化水素ガス濃度を、流動層反応器に供給する酸素含有ガス中の酸素量に対して１９〜３０モル％の範囲とし、
流動層反応器から抜き出した反応生成ガス組成のうち可燃ガス（炭素数４以上の脂肪族炭化水素、無水マレイン酸及び一酸化炭素等）を除いたガス中の酸素濃度を６ｖｏｌ％以下とし、
流動層の温度を４００〜４６０℃の範囲とし、
かつ流動層反応器中の圧力を０．１〜３．０ｋｇ／ｃｍ²Ｇの範囲に維持して、本発明の気相酸化反応を行う。
【００２３】
なお流動層出口の反応生成ガスからと水を除いたガスを連続的に分析する方法としては、該反応生成ガスの一部を取り出して大量の水もしくは有機溶媒と接触させて無水マレイン酸と水を除去した後に該ガスのサンプルを常温以下まで冷却し、ガスクロマトグラフィーや酸素分析計等で分析する方法が有効であるが、特に限定されるものではない。またサイクロンで捕集されない微細な触媒粒子も通常水もしくは有機溶媒側に残るため、触媒フィルタ−の設置の有無についても特に規定するものではない。
【００２４】
また本発明では、例えば電源やユーティリティーの停止や、反応装置の定期修理等の事情により、流動層反応器中の気相酸化反応を停止して、定常状態から非定常状態へと移行させる（すなわちシャットダウン）場合にも、所定の比率の原料ガス（炭素数４以上の脂肪族炭化水素）及び酸素含有ガスの混合ガスの供給を停止して(1)不活性ガスに切り換えるか、または(2)酸素含有ガス、及び該酸素含有ガス中の酸素供給量に対して０．１〜１０モル％の供給量で、かつ触媒に対して重量比０．００１〜０．１ｈｒ^-1の割合で該炭素数４以上の脂肪族炭化水素ガスの混合ガスに切り換え、流動層の温度を少なくとも４００℃から３００℃の温度に低下させることにより、触媒の劣化を抑制する。
【００２５】
【実施例】
以下に実施例により本発明を更に具体的に説明するが、本発明は以下の実施例に限定されるものではない。
尚、例中、Ｖ⁴⁺／ΣＶ値の測定値は、２個の１００mlのビ−カ−の各々に、触媒０．１４ｇを１２Ｎ硫酸で溶解したものを入れ、１５０℃で１．５時間煮沸した後、冷却した。１方のビ−カ−中には超純水を加え、全量を８０mlとし、ＫＭｎＯ₄溶液にて滴定し、４価のバナジウム（Ｖ⁴⁺）量（meq/g)を測定した。他方のビ−カ−中には超純水を加え、全量を５０mlとし、亜硫酸水素ナトリウム溶液にて全てのバナジウム元素価を４価に換え、煮沸後、超純水を加えて全量を８０mlにし、ＫＭｎＯ₄溶液にて滴定し全バナジウム（ΣＶ）量（meq/g)を測定した。Ｖ⁴⁺／ΣＶ値（％）はＶ⁴⁺（meq/g)／ΣＶ（meq/g)×１００で求めた。
【００２６】
参考例１
特開平２−１９３７０号公報記載の参考例−１の方法で爆発容器による可燃テストを実施した。すなわち、反応器出口ガス中の触媒を分離し、容量１Ｌ（リットル）の予熱した爆発容器に導入し、１５ｋｖ交流スパーク（０．０１秒）で点火し、容器内の圧力上昇により燃焼の有無を測定した。
【００２７】
ｎ−ブタン供給量を酸素供給量に対して１９〜３０モル%の範囲内で触媒流動層の温度を４００〜４６０℃、圧力を０．１〜３．０kg/cm²-Gの範囲で無水マレイン酸を生成した結果、該流動層反応器出口の反応生成ガス可燃性については該反応生成ガスのうち可燃ガス成分と水を除いたガス中の酸素濃度が６Vol%以下であれば燃焼は起きないことがわかった。
【００２８】
参考例２
特開昭５９−９５９３３号公報の実施例２の方法、すなわち、リン酸及び五酸化バナジウムを原料として水熱合成、乾燥、焼成して得た微粉状固体を、リン酸バナジル溶液、シリカゾル溶液と混合してスラリーとし、これを乾燥、焼成して (VO)₂P₂O₇が活性成分で、リン酸バナジルをバインダーとして用いたバナジウム−リン系複合酸化物を含有する流動層触媒を製造した。
【００２９】
実施例１
参考例２で得た流動層触媒５kgを充填した内径３インチの垂直管型反応器を用い、該反応器の下部分散板の下より空気を供給し、該触媒を流動化させて該分散板の上方に触媒の流動層を形成させ、該流動層反応器の外部に設置した加熱装置により、空気を昇温することにより該流動層の温度を上昇させた。空気の供給量は空間速度（Gas Hourly Space Velocity＝ＧＨＳＶ）６５０ｈｒ^-1であった。該流動層の温度を２５０℃に到達させた後、該流動層中に純度９８ｖｏｌ％のｎ−ブタンガスを２５ｇ／ｈｒで供給（該ｎ−ブタンの供給量は触媒に対して重量比で０．００５ｈｒ^-1、酸素供給量に対して１．４モル％であった。）し、除熱コイルを使用して該流動層の温度を調整し、３００℃で５時間保持した後、該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。この結果を表−２に示した。
【００３０】
さらに該反応器にて該流動層の温度を４２１℃まで上昇させた後、塔頂圧力を１．５kg/cm²-Gに保持し、流動層反応器出口の反応生成ガス組成から無水マレイン酸と水を除いたガス組成中の酸素濃度が６ｖｏｌ％以下になるように、下部分散板の下より供給している空気を減らし、新たに窒素ガスを供給した。ｎ−ブタンの供給量は一定に保持し、その酸素供給量に対する比率は２０モル％となった。続いて該酸素とｎ−ブタン供給量の比率を維持しつつ、空気とｎ−ブタン供給量を増加し、同時に窒素ガスの供給は停止した。定常状態では、空気を３．５Ｎｍ³／ｈｒ、ｎ−ブタンを３８０ｇ／ｈｒの条件で供給し、無水マレイン酸を製造した。表−２にｎ−ブタンの転化率が８５％を示す時の流動層の温度と無水マレイン酸収率を示した。
【００３１】
実施例２
空気を加熱して流動層を２５０℃とした後、純度９８ｖｏｌ％のｎ−ブタンを５０ｇ／ｈｒで供給し、該流動層の温度を３５０℃で５時間保持した以外は実施例１と同様に流動層反応器を起動し、実施例１と同様に評価した。その結果を表−２に示した。
【００３２】
実施例３
空気を加熱して流動層を２５０℃とした後、純度９８ｖｏｌ％のｎ−ブタンを１５０ｇ／ｈｒで供給し、該流動層の温度を４００℃で５時間保持した以外は実施例１と同様に流動層反応器を起動し、実施例１と同様に評価した。その結果を表−２に示した。
【００３３】
実施例４
空気を加熱して流動層を２５０℃とした後、純度９８ｖｏｌ％のｎ−ブタンを４０ｇ／ｈｒで供給し、該流動層の温度を４００℃で５時間保持した以外は実施例１と同様に流動層反応器を起動し、実施例１と同様に評価した。その結果を表−２に示した。
【００３４】
参考例３
実施例１と同様に流動層を起動し、流動層の温度を２５０℃で４時間保持した。該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。結果を表−２に示した。
実施例５
参考例２で得た流動層触媒５kgを充填した内径３インチの垂直管型反応器を用い、反応器の下部分散板の下より純度９９ｖｏｌ％以上の窒素ガスを供給し、該触媒を流動化させて該分散板の上方に触媒の流動層を形成させ、該流動層反応器の外部に設置した加熱装置により、窒素ガスを昇温することにより該流動層の温度を上昇させた。窒素ガスの供給量はＧＨＳＶ６５０ｈｒ^-1であった。該流動層の温度を３００℃で２４時間保持した後、該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。この結果を表−２に示した。さらに該反応器にて該流動層の温度を４１７℃まで上昇させた後、塔頂圧力を１．５kg/cm²-Gに保持し下部分散板の下からの窒素ガスを空気に変更し、該流動層中には純度９８ｖｏｌ％のｎ−ブタンガスを酸素供給量に対して２０モル％の比率で供給し無水マレイン酸を製造した。尚、窒素ガスから空気への変更時は該流動層反応器出口の反応生成ガスから可燃ガス成分と水を除いたガス中の酸素濃度を常に６Vol%以下に維持し、空気は外部加熱装置で加温することなく、ＧＨＳＶを７００ｈｒ^-1で反応器に供給した。表−２にｎ−ブタンの転化率が８５％を示す時の流動層の温度と無水マレイン酸収率を示した。
【００３５】
実施例６
純度９９ｖｏｌ％以上の窒素ガスを９５ｖｏｌ％の窒素ガスと５ｖｏｌ％の水蒸気の混合ガスとし、３５０℃で４時間保持した以外は実施例５と同様に流動層反応器を起動し、実施例５と同様に評価した。その結果を表−２に示した。
比較例１
実施例１と同様に流動層を起動し、空気で流動層を昇温し、ｎ−ブタンを供給することなく、流動層の温度を３５０℃で１０時間保持した。該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。結果を表−２に示した。
【００３６】
さらに該流動層の温度を４３０℃まで空気雰囲気下で上昇させた後、該流動層中に純度９８ｖｏｌ％のｎ−ブタンガスを酸素供給量に対して２０モル％の比率で供給し無水マレイン酸を製造した。所定の反応温度に到達した後は外部加熱装置を停止した。ＧＨＳＶは７００ｈｒ^-1であった。表−２にｎ−ブタンの転化率が８５％を示す時の流動層の温度と無水マレイン酸収率を示した。
【００３７】
比較例２
比較例１と同様に空気で流動層を昇温し、流動層の温度を５００℃で１０時間保持した。該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。結果を表−２に示した。さらに該反応器にて該流動層の温度を４４５℃に設定した後、該流動層中に純度９８ｖｏｌ％のｎ−ブタンを酸素供給量に対して２０モル％の比率で供給し、無水マレイン酸を製造した。表−２にｎ−ブタンの転化率が８５％を示す時の流動層の温度と無水マレイン酸収率を示した。
【００３８】
比較例３
比較例１と同様に、空気で流動層を４００℃まで昇温し、６０時間保持した。該触媒の一部を抜き出し、Ｖ⁴⁺／ΣＶ値を測定し、触媒の色を目視で判断した。その後比較例１と同様にして活性試験を行った。結果を表−２に示した。
【００３９】
【表２】

【００４０】
【発明の効果】
活性相が (VO)₂P₂O₇であるバナジウム−リン系複合酸化物触媒を３００℃以上に加温された空気雰囲気下に５時間以上晒した場合は、空気中の過剰な酸素によって触媒が酸化され、高温になるにつれてＶ⁴⁺／ΣＶ値が初期の１００以上から８５〜４５まで低下し、更に６０時間晒した場合には３０まで低下するが、３００℃以上に加温された酸素を含まない不活性ガス、または酸素とそれに対して特定量の原料ガスを含む混合ガスの雰囲気下では、常にＶ⁴⁺／ΣＶ値が１００を越え、触媒自体の酸化傾向は認められず、その触媒活性の劣化が抑制される。
【図面の簡単な説明】
【図１】本発明の製造法を実施するのに適した流動層反応器の一例を示した図である。
【符号の説明】
１：流動層反応器、２：ガス分散板、３：酸素含有ガス供給管、４：酸素含有ガス供給管上端、５：流動層、６：流動層除熱コイル、７：原料炭化水素供給管、８：原料炭化水素供給口、９：流動層上面、１０：希薄流動層、１１：希薄流動層除熱コイル、１２，１３：サイクロン、１４：反応生成ガス抜き出し管、１４ａ：反応器出口（反応生成ガス抜き出し管出口）、１５，１７：ディップレッグ、１６，１８：ディップレッグ下端[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing maleic anhydride in a fluidized bed reactor. Specifically, the activity of a fluidized bed oxidation catalyst useful for the production of maleic anhydride from aliphatic hydrocarbons having 4 or more carbon atoms such as n-butane, butene, butadiene, etc. is suppressed, and maleic anhydride is produced safely. It is about the method.
[0002]
[Prior art]
An oxidation catalyst containing a vanadium-phosphorus composite oxide as an active component has been used in producing maleic anhydride from an aliphatic hydrocarbon having 4 or more carbon atoms such as n-butane. Examples thereof include, for example, U.S. Pat. , 4520127, 4472527, and the like.
[0003]
When these catalysts are used in a fixed bed reactor, the activity decreases with time, so it is common to suspend the reaction and bring the catalyst into contact with a steam stream to regenerate the catalyst activity. (Refer to Unexamined-Japanese-Patent No. 60-143832 and US Pat. No. 4,515,899). It is also known to “condition” at 300-600 ° C. under a stream of air containing 0.2-2% by volume low concentration hydrocarbons (see US Pat. No. 4,171,316). It is also known that a gaseous hydrocarbon component having 2 to 6 carbon atoms is passed over a mixed vanadium and phosphorous oxide catalyst with exclusion of molecular oxygen to activate the catalyst at 300 to 500 ° C. (See U.S. Pat. Nos. 4,178,298 and 4,181,628).
[0004]
On the other hand, when this catalyst is used in a fluidized bed reactor, the catalyst inside the reactor can be replenished and removed at any time without stopping the reaction. Therefore, the same new catalyst as the catalyst packed in the reactor can be used. The catalyst activity is maintained approximately constant by extracting a part of the catalyst in order to keep the catalyst amount in the reactor constant in order to keep the catalyst amount in the reactor constant or constantly in accordance with the decrease in activity. It becomes possible. Therefore, when maleic anhydride is produced using a fluidized bed reactor, the activity of the catalyst is rarely lowered as long as it is continuously operated in a steady state under the determined conditions. There will be no drastic decline that would hinder operations.
[0005]
However, a method for regenerating the activity of the catalyst used in such a fluidized bed reactor has also been proposed. For example, the catalyst is activated in a reactor in the presence of oxygen and a reducing gas such as hydrocarbon (preferably reducing gas = oxygen 30 mol% or more) at a high temperature of 400 to 550 ° C. (Refer to Japanese Patent Laid-Open No. 58-114735, USP 4748140).
[0006]
It is also disclosed that the catalyst extracted from the reactor is steamed, regenerated and activated, and returned to the reactor again (see JP-A-4-316567, JP-A-5-43567, etc.).
By the way, when producing maleic anhydride by a gas phase oxidation reaction in a fluidized bed reactor on an industrial scale, generally, an oxidation catalyst containing vanadium-phosphorous complex oxide as an active component is generally packed in the fluidized bed reactor. Then, air is supplied from below the gas dispersion plate at the bottom of the reactor, the catalyst is fluidized to form a fluidized bed of the catalyst above the dispersion plate, and an external heating device called “startup heater” is used. After raising the temperature of the fluidized bed to a temperature at which the gas phase oxidation reaction can occur (250 ° C.), an aliphatic hydrocarbon having 4 or more carbon atoms is supplied to start the gas phase oxidation reaction. ing. The catalyst activity also decreases during such non-steady state periods such as the transition period from the stop state to the steady state (reaction start) and the transition period from the steady state to the stop state (reaction stop). Since all the catalysts in the fluidized bed reactor may be deteriorated in a short time, it is desired to suppress a decrease in the activity of the catalyst and to stably shift from the unsteady state to the steady state.
[0007]
However, the method of activating at 400 to 550 ° C. in the reactor in the presence of oxygen and a reducing gas as described above, or the method of regenerating and activating the externally extracted catalyst is the activity of the unsteady state catalyst. It does not suppress deterioration.
[0008]
[Problems to be solved by the invention]
According to the study of the present inventor, when an oxidation catalyst containing a vanadium-phosphorus composite oxide as an active component is exposed to an oxygen-containing gas atmosphere such as air heated to 300 ° C. or higher for a long time, the activity decreases significantly. The fluidity was worsened. Accordingly, there is a need for a method that suppresses the decrease in catalyst activity during the unsteady state period when the reaction is carried out in a fluidized bed reactor.
[0009]
On the other hand, the composition of the reactor outlet gas should be set so as to avoid the combustible range under the temperature and pressure conditions there, but when sampling the outlet gas of the fluidized bed reactor directly, a fine catalyst Even if equipment such as a catalyst filter is installed to prevent clogging of the sample nozzle due to particles, it is difficult to perform stable continuous analysis. Furthermore, the maleic anhydride and water produced by the reaction condense in the sample nozzle and the analytical equipment, causing precipitation of maleic acid and fumaric acid, so that not only during the steady state period but also during startup (reaction start) In the non-steady state period, it is extremely difficult to perform accurate sampling / analysis of the fluidized bed reactor outlet gas and continuously monitor that the gas composition is outside the flammable range.
[0010]
The relationship between the temperature and the flammable range is clear from the relationship between the temperature and the critical oxygen concentration. For example, a gas phase oxidation reaction of butane (99% purity) using a catalyst containing a vanadium-phosphorus composite oxide is conducted at a butane concentration of about 4% during the reaction, a reaction temperature of 400 to 460 ° C., and a butane conversion rate of 80. It is carried out under the conditions of ~ 98% and maleic anhydride yield of 48 to 56%, and the catalyst in the reaction product gas extracted from the reactor (the temperature of the gas exiting the reactor is 250 to 350 ° C) is separated by a catalyst filter. After that, the reaction product gas is introduced into a preheated 1 liter explosion container and ignited with a 15 KV alternating current spark (0.01 seconds). The critical oxygen concentration (= the lower limit value of the oxygen concentration at which combustion occurs, The result of measuring the temperature 350 to 450 ° C. is described in Reference Example 1 of JP-A-2-19370. (See Table-1 below)
[0011]
[Table 1]

Thus, considering that the temperature of the reactor outlet gas when the reaction is performed at 400 to 460 ° C. is about 250 to 350 ° C., among the reaction product gas composition at the outlet of the fluidized bed reactor, the combustible gas component Gas that is out of the flammable range by monitoring the oxygen concentration in the gas composition excluding (hydrocarbon components having 4 or more carbon atoms, maleic anhydride, carbon monoxide, etc.) and setting the concentration to 6 vol% or less It is possible to operate safely with composition.
[0012]
The present invention suppresses the decrease in activity of the catalyst for producing maleic anhydride using a fluidized bed reactor, ensures the safety of the reaction product gas, and shifts from an unsteady state to a steady state with a stable operation. And a method capable of transitioning from an unsteady state to a steady state.
[0013]
[Means for Solving the Problems]
The present invention relates to a process for producing maleic anhydride by vapor-phase oxidation of an aliphatic hydrocarbon having 4 or more carbon atoms using a fluidized bed reactor, and maleic anhydride having a vanadium-phosphorus composite oxide as an active ingredient. From the bottom of a fluidized bed reactor packed with an oxidation catalyst for production
(1) inert gas,
Or
(2) Oxygen-containing gas, and a feed rate of 0.1 to 10 mol% with respect to the oxygen feed rate in the oxygen-containing gas, and a ratio by weight ratio of 0.001 to 0.1 hr ⁻¹ with respect to the catalyst And / or a temperature raising operation for raising the temperature of the fluidized bed to at least 300 ° C. to 400 ° C. while supplying a mixed gas of the aliphatic hydrocarbon gas having 4 or more carbon atoms to form a fluidized bed of the catalyst, and / or The present invention provides a method for producing maleic anhydride, which comprises performing a temperature lowering operation at least from 400 ° C to 300 ° C.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the study of the present inventor, a fat having 4 or more carbon atoms even in a non-steady state, when an inert gas flows, or when temperature is increased or decreased in an oxygen-containing gas atmosphere heated to 300 ° C. or higher. When a mixed gas with an oxygen-containing gas in which the supply amount of the group hydrocarbon is in the above specific range with respect to the oxygen supply amount is circulated, the catalyst activity is not decreased and the fluidity is good. all right.
[0015]
Hereinafter, the present invention will be described in more detail.
As the raw material hydrocarbon used in the present invention, an aliphatic hydrocarbon having 4 or more carbon atoms is used. Preferred raw material hydrocarbons are hydrocarbons having 4 carbon atoms such as butane (eg, n-butane), butenes (eg, 1-butene, 2-butene), butadiene (eg, 1,3-butadiene), and more preferably. Is n-butane.
[0016]
Usually, air is used as the oxygen-containing gas, but air diluted with an inert gas, air enriched by adding oxygen, or the like can also be used.
Further, as the inert gas, an inert gas selected from at least one of nitrogen, carbon dioxide, water vapor, and a mixture thereof can be used, but a gas mainly containing nitrogen is preferable.
[0017]
The fluidized bed reactor (1) used in the present invention is provided with a gas dispersion plate (2) for defining the lower end of the catalyst fluidized bed at the bottom of the reactor, as shown in FIG. 1, for example, and at the top of the reactor. A cyclone (12) for collecting the catalyst scattered from the reaction product gas and returning it to the catalyst fluidized bed is provided, and further, a raw material hydrocarbon feed port (in the lower region of the fluidized bed and away from the gas dispersion plate) 7), and a substantial part of the catalyst recovered by the cyclone (12) is placed in the lower region of the fluidized bed, for example, between or near the gas distribution plate (2) and the hydrocarbon feed port (7). The lower end (16) of the dipleg (15) for returning to the catalyst fluidized bed is provided, and the fluidized bed region is preferably provided with an indirect heat exchange device for heat removal, for example, a heat removal coil (6). More specifically, examples of such a reactor include a reactor described in JP-A-2-19370.
[0018]
The catalyst used in the present invention is not particularly limited as long as it is an oxidation catalyst having a vanadium-phosphorus composite oxide as an active component and can be used in a fluidized bed reactor. A catalyst having a valence of about +3.8 to +4.8 is suitable as a catalyst used in the present invention, and a composite oxide having a phosphorus / vanadium atomic ratio of about 0.5 to 2.0 is suitable. Yes. The active phase of such a catalyst is mainly (VO) ₂ P ₂ O ₇ and the reaction proceeds by redox between V ⁴⁺ and V ^5+, and the presence of V ⁴⁺ It is known to contribute to the yield of acid generation. Further, since the catalyst also contains some vanadium elements reduced to trivalent, the equivalent ratio (V value) of all vanadium in the catalyst converted to tetravalent (ΣV value) and tetravalent vanadium in the catalyst (V ^{4 +} / ΣV value) is evaluated as the degree of reduction. Note that the value of the degree of reduction can be used as an indication of a change in catalyst activity.
[0019]
The operation of suppressing the decrease in the activity of the catalyst in the unsteady state is performed while the temperature of the fluidized bed of the catalyst is increased from at least 300 ° C. to 400 ° C. and / or while the temperature is decreased from 400 ° C. to 300 ° C., in particular from at least 300 ° C. During the temperature rise to 400 ° C., in the fluidized bed reactor filled with the oxidation catalyst, (1) an inert gas or (2) an oxygen-containing gas from below the gas dispersion plate at the bottom of the reactor, and The fat having 4 or more carbon atoms in a supply amount of 0.1 to 10 mol% with respect to the oxygen supply amount in the oxygen-containing gas and in a ratio of 0.001 to 0.1 hr ⁻¹ by weight with respect to the catalyst. A mixed gas of a group hydrocarbon gas is supplied.
[0020]
Furthermore, in the production method of the present invention, in order to obtain normally high productivity in the steady state, the reaction product gas composition is set to be higher than the upper limit of the flammable range. The reaction product gas composition is set so as to be equal to or lower than the lower limit of the gas composition in the combustible range. However, immediately after the temperature of the fluidized bed reaches the reaction temperature of 400 to 460 ° C. by the temperature increase or decrease operation, in order to shift the reaction product gas composition from the lower limit to the upper limit of the flammable range, simply increase or decrease the hydrocarbon feed rate. In the process, the reaction product gas composition passes through the flammable range, and there is a risk of explosion, etc., so it is almost impossible to carry out with a normal industrial scale device. is there. Therefore, in the present invention, when transitioning from the unsteady state to the steady state or from the steady state to the unsteady state, the reaction product gas composition at the reactor outlet (FIG. 1 (14a)) is adjusted so as to bypass the combustible range. Thus, it is preferable that the reaction product gas is transferred without forming a gas composition in the combustible range.
[0021]
More specifically, after the temperature raising operation or before the temperature lowering operation, the oxygen-containing gas supplied from the bottom of the fluidized bed reactor and the aliphatic having 4 or more carbon atoms in the fluidized bed temperature range of 400 to 460 ° C. The concentration of the mixed gas with the hydrocarbon gas is increased from 10 mol% to 19 mol% or decreased from 19 mol% to 10 mol% with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor. for,
(A) introducing an inert gas into the mixed gas of the oxygen-containing gas and hydrocarbon gas,
(B) introducing a part of the remaining gas after recovering maleic anhydride from the reaction product gas extracted from the fluidized bed reactor into the fluidized bed reactor, or
(C) Combusting the fuel in the oxygen-containing gas before supplying it to the fluidized bed reactor, thereby increasing or decreasing the oxygen concentration in the total gas supplied from the bottom of the fluidized bed reactor. It is possible to transition from an unsteady state to a steady state or from a steady state to an unsteady state without forming a combustible range gas composition.
[0022]
In the steady state of the present invention, the concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms supplied from the bottom of the fluidized bed reactor is 10 mol% with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor. After increasing from 19 mol% or before decreasing from 19 mol% to 10 mol%,
The concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms in the fluidized bed reactor is in the range of 19 to 30 mol% with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor,
The oxygen concentration in the gas excluding combustible gases (aliphatic hydrocarbons having 4 or more carbon atoms, maleic anhydride, carbon monoxide, etc.) in the reaction product gas composition extracted from the fluidized bed reactor is 6 vol% or less,
The temperature of the fluidized bed is in the range of 400 to 460 ° C.
The gas phase oxidation reaction of the present invention is carried out while maintaining the pressure in the fluidized bed reactor in the range of 0.1 to 3.0 kg / cm ² G.
[0023]
In addition, as a method of continuously analyzing the gas obtained by removing water from the reaction product gas at the outlet of the fluidized bed, a part of the reaction product gas is taken out and brought into contact with a large amount of water or an organic solvent to obtain maleic anhydride and water. A method of cooling the gas sample to normal temperature or less after removing the gas and analyzing it with a gas chromatography, an oxygen analyzer or the like is effective, but is not particularly limited. Further, since fine catalyst particles that are not collected by the cyclone usually remain on the water or organic solvent side, the presence or absence of the catalyst filter is not particularly specified.
[0024]
In the present invention, the gas phase oxidation reaction in the fluidized bed reactor is stopped and shifted from the steady state to the unsteady state due to, for example, the stoppage of the power supply or utility or the periodic repair of the reaction apparatus (that is, In the case of (shutdown), the supply of the gas mixture of the specified ratio (aliphatic hydrocarbons having 4 or more carbon atoms) and oxygen-containing gas is stopped and (1) switched to inert gas or (2) The oxygen-containing gas, and the carbon in a supply amount of 0.1 to 10 mol% with respect to the oxygen supply amount in the oxygen-containing gas, and in a ratio of 0.001 to 0.1 hr ⁻¹ by weight with respect to the catalyst Switching to a mixed gas of aliphatic hydrocarbon gas of several or more and lowering the temperature of the fluidized bed from at least 400 ° C. to 300 ° C. suppresses catalyst deterioration.
[0025]
【Example】
The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.
In the examples, the measured value of V ⁴⁺ / ΣV was measured by adding 0.14 g of a catalyst dissolved in 12N sulfuric acid to each of two 100 ml beakers for 1.5 hours at 150 ° C. After boiling, it was cooled. One beaker was added with ultrapure water to make a total volume of 80 ml, titrated with a KMnO ₄ solution, and the amount of tetravalent vanadium (V ⁴⁺ ) (meq / g) was measured. In the other beaker, ultrapure water is added to make the total volume 50 ml, all vanadium element values are changed to tetravalent with sodium bisulfite solution, and after boiling, ultrapure water is added to make the total volume 80 ml. , And titrated with a KMnO ₄ solution to measure the total vanadium (ΣV) content (meq / g). V ⁴⁺ / ΣV value (%) was determined by V ⁴⁺ (meq / g) / ΣV (meq / g) × 100.
[0026]
Reference example 1
A flammability test using an explosion container was carried out by the method of Reference Example 1 described in JP-A-2-19370. That is, the catalyst in the reactor outlet gas was separated, introduced into a preheated explosion vessel with a capacity of 1 L (liter), ignited with a 15 kv AC spark (0.01 seconds), and the presence or absence of combustion was confirmed by the pressure increase in the vessel. It was measured.
[0027]
Anhydrous n-butane feed in the range of 19-30 mol% with respect to the oxygen feed rate, catalyst fluidized bed temperature at 400-460 ° C, pressure at 0.1-3.0 kg / cm ² -G As a result of the production of maleic acid, as for the combustibility of the reaction product gas at the outlet of the fluidized bed reactor, combustion occurs if the oxygen concentration in the gas excluding the combustible gas component and water in the reaction product gas is 6 Vol% or less. I knew it was n’t there.
[0028]
Reference example 2
A finely divided solid obtained by the method of Example 2 of JP-A-59-95933, that is, hydrothermal synthesis, drying, and firing using phosphoric acid and vanadium pentoxide as raw materials, is converted into a vanadyl phosphate solution, a silica sol solution, and A fluidized bed catalyst containing a vanadium-phosphorus composite oxide using (VO) ₂ P ₂ O ₇ as an active ingredient and vanadyl phosphate as a binder was prepared by mixing and making a slurry, drying and firing. .
[0029]
Example 1
Using the vertical tube reactor having an inner diameter of 3 inches filled with 5 kg of the fluidized bed catalyst obtained in Reference Example 2, air was supplied from under the lower dispersion plate of the reactor to fluidize the catalyst, and the dispersion plate A fluidized bed of the catalyst was formed above the fluidized bed, and the temperature of the fluidized bed was raised by raising the temperature of the air with a heating device installed outside the fluidized bed reactor. The amount of air supplied was space velocity (Gas Hourly Space Velocity = GHSV) 650 hr ⁻¹ . After allowing the temperature of the fluidized bed to reach 250 ° C., n-butane gas having a purity of 98 vol% was fed into the fluidized bed at 25 g / hr (the amount of n-butane fed was reduced to 0. 0 by weight with respect to the catalyst). 005 hr ⁻¹ , 1.4 mol% with respect to the oxygen supply amount)), and the temperature of the fluidized bed was adjusted using a heat removal coil and maintained at 300 ° C. for 5 hours. A part was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. The results are shown in Table 2.
[0030]
Further, after the temperature of the fluidized bed was raised to 421 ° C. in the reactor, the top pressure was maintained at 1.5 kg / cm ² -G, and maleic anhydride was determined from the reaction product gas composition at the outlet of the fluidized bed reactor. The air supplied from under the lower dispersion plate was reduced so that the oxygen concentration in the gas composition excluding water and water was 6 vol% or less, and nitrogen gas was newly supplied. The supply amount of n-butane was kept constant, and the ratio with respect to the oxygen supply amount was 20 mol%. Subsequently, while maintaining the ratio of the oxygen and n-butane supply amount, the supply amount of air and n-butane was increased, and the supply of nitrogen gas was stopped at the same time. In the steady state, maleic anhydride was produced by supplying air at 3.5 Nm ³ / hr and n-butane at 380 g / hr. Table 2 shows the fluidized bed temperature and maleic anhydride yield when the conversion of n-butane is 85%.
[0031]
Example 2
After the air was heated to 250 ° C., n-butane having a purity of 98 vol% was supplied at 50 g / hr, and the temperature of the fluidized bed was maintained at 350 ° C. for 5 hours as in Example 1. The fluidized bed reactor was started and evaluated in the same manner as in Example 1. The results are shown in Table-2.
[0032]
Example 3
After the air was heated to 250 ° C., n-butane having a purity of 98 vol% was supplied at 150 g / hr, and the temperature of the fluidized bed was maintained at 400 ° C. for 5 hours as in Example 1. The fluidized bed reactor was started and evaluated in the same manner as in Example 1. The results are shown in Table-2.
[0033]
Example 4
After the air was heated to 250 ° C., n-butane having a purity of 98 vol% was supplied at 40 g / hr, and the temperature of the fluidized bed was maintained at 400 ° C. for 5 hours as in Example 1. The fluidized bed reactor was started and evaluated in the same manner as in Example 1. The results are shown in Table-2.
[0034]
Reference example 3
The fluidized bed was started in the same manner as in Example 1, and the temperature of the fluidized bed was maintained at 250 ° C. for 4 hours. A part of the catalyst was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. The results are shown in Table-2.
Example 5
Using a vertical tube reactor having an inner diameter of 3 inches filled with 5 kg of the fluidized bed catalyst obtained in Reference Example 2, nitrogen gas having a purity of 99 vol% or more was supplied from below the lower dispersion plate of the reactor to fluidize the catalyst. Then, a fluidized bed of the catalyst was formed above the dispersion plate, and the temperature of the fluidized bed was raised by raising the temperature of the nitrogen gas with a heating device installed outside the fluidized bed reactor. The supply amount of nitrogen gas was GHSV 650 hr ⁻¹ . After maintaining the temperature of the fluidized bed at 300 ° C. for 24 hours, a part of the catalyst was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. The results are shown in Table 2. Further, after the temperature of the fluidized bed was raised to 417 ° C. in the reactor, the top pressure was maintained at 1.5 kg / cm ² -G, and the nitrogen gas from below the lower dispersion plate was changed to air, N-butane gas having a purity of 98 vol% was supplied into the fluidized bed at a ratio of 20 mol% with respect to the oxygen supply amount to produce maleic anhydride. When changing from nitrogen gas to air, the oxygen concentration in the gas excluding the combustible gas component and water from the reaction product gas at the outlet of the fluidized bed reactor is always kept below 6 Vol%. Without heating, GHSV was fed to the reactor at 700 hr ⁻¹ . Table 2 shows the fluidized bed temperature and maleic anhydride yield when the conversion of n-butane is 85%.
[0035]
Example 6
A fluidized bed reactor was started in the same manner as in Example 5 except that nitrogen gas having a purity of 99 vol% or more was mixed with 95 vol% nitrogen gas and 5 vol% water vapor, and maintained at 350 ° C. for 4 hours. Evaluation was performed in the same manner. The results are shown in Table-2.
Comparative Example 1
The fluidized bed was started in the same manner as in Example 1, the temperature of the fluidized bed was increased with air, and the temperature of the fluidized bed was maintained at 350 ° C. for 10 hours without supplying n-butane. A part of the catalyst was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. The results are shown in Table-2.
[0036]
Further, the temperature of the fluidized bed was raised to 430 ° C. in an air atmosphere, and then n-butane gas having a purity of 98 vol% was supplied into the fluidized bed at a ratio of 20 mol% with respect to the oxygen supply amount, thereby adding maleic anhydride. Manufactured. After reaching the predetermined reaction temperature, the external heating device was stopped. The GHSV was 700 hr ⁻¹ . Table 2 shows the fluidized bed temperature and maleic anhydride yield when the conversion of n-butane is 85%.
[0037]
Comparative Example 2
As in Comparative Example 1, the fluidized bed was heated with air, and the temperature of the fluidized bed was maintained at 500 ° C. for 10 hours. A part of the catalyst was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. The results are shown in Table-2. Furthermore, after the temperature of the fluidized bed was set to 445 ° C. in the reactor, n-butane having a purity of 98 vol% was fed into the fluidized bed at a ratio of 20 mol% with respect to the oxygen supply amount, and maleic anhydride was added. Manufactured. Table 2 shows the fluidized bed temperature and maleic anhydride yield when the conversion of n-butane is 85%.
[0038]
Comparative Example 3
As in Comparative Example 1, the fluidized bed was heated to 400 ° C. with air and held for 60 hours. A part of the catalyst was extracted, the V ⁴⁺ / ΣV value was measured, and the color of the catalyst was judged visually. Thereafter, an activity test was conducted in the same manner as in Comparative Example 1. The results are shown in Table-2.
[0039]
[Table 2]

[0040]
【The invention's effect】
When a vanadium-phosphorus composite oxide catalyst whose active phase is (VO) ₂ P ₂ O ₇ is exposed to an air atmosphere heated to 300 ° C. or higher for 5 hours or longer, the catalyst is caused by excess oxygen in the air. As the temperature rises, the V ⁴⁺ / ΣV value decreases from the initial 100 or more to 85 to 45, and further decreases to 30 when exposed for 60 hours, but the oxygen heated to 300 ° C. or more In an atmosphere of an inert gas not containing oxygen, or a mixed gas containing oxygen and a specific amount of a raw material gas, the V ⁴⁺ / ΣV value always exceeds 100, and the oxidation tendency of the catalyst itself is not recognized. Deterioration of catalyst activity is suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a fluidized bed reactor suitable for carrying out the production method of the present invention.
[Explanation of symbols]
1: fluidized bed reactor, 2: gas dispersion plate, 3: oxygen-containing gas supply pipe, 4: upper end of oxygen-containing gas supply pipe, 5: fluidized bed, 6: fluidized bed heat removal coil, 7: feed hydrocarbon feed pipe 8: raw material hydrocarbon feed port, 9: upper surface of fluidized bed, 10: lean fluidized bed, 11: lean fluidized bed heat removal coil, 12, 13: cyclone, 14: reaction product gas extraction pipe, 14a: reactor outlet ( Reaction product gas outlet pipe outlet), 15, 17: dipleg, 16, 18: bottom dipleg

Claims

An oxidation catalyst for producing maleic anhydride using vanadium-phosphorus composite oxide as an active component in a process for producing maleic anhydride by vapor phase oxidation of aliphatic hydrocarbons having 4 or more carbon atoms using a fluidized bed reactor From the bottom of the fluidized bed reactor packed with
(1) inert gas, or
(2) Oxygen-containing gas, and a feed rate of 0.1 to 10 mol% with respect to the oxygen feed rate in the oxygen-containing gas, and a ratio by weight ratio of 0.001 to 0.1 hr ⁻¹ with respect to the catalyst A mixed gas of the aliphatic hydrocarbon gas having 4 or more carbon atoms,
In order to form a fluidized bed of the catalyst while performing a temperature raising operation to bring the temperature of the fluidized bed to at least 300 ° C. to 400 ° C. and / or a temperature lowering operation to at least 400 ° C. to 300 ° C. A process for producing maleic anhydride.

The method for producing maleic anhydride according to claim 1, wherein the temperature raising operation and / or the temperature lowering operation is a temperature raising operation.

After the temperature raising operation or before the temperature lowering operation, the temperature of the fluidized bed is in the range of 400 to 460 ° C. (A) Introducing an inert gas into the mixed gas of the oxygen-containing gas and hydrocarbon gas, (B) A portion of the remaining gas after recovering maleic anhydride from the reaction product gas withdrawn from the fluidized bed reactor is reintroduced into the fluidized bed reactor, or (C) The method for producing maleic anhydride according to claim 1 or 2, wherein the fuel is combusted in the oxygen-containing gas before being supplied to the fluidized bed reactor.

After the temperature raising operation or before the temperature lowering operation, the concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms supplied from the bottom of the fluidized bed reactor is adjusted in the fluidized bed reaction in the temperature range of the fluidized bed from 400 to 460 ° C. To increase from 10 mol% to 19 mol% or decrease from 19 mol% to 10 mol% with respect to the amount of oxygen in the oxygen-containing gas fed to the vessel,
(A) introducing an inert gas into the mixed gas of the oxygen-containing gas and hydrocarbon gas,
(B) introducing a part of the remaining gas after recovering maleic anhydride from the reaction product gas extracted from the fluidized bed reactor into the fluidized bed reactor, or
(C) burning the fuel in the oxygen-containing gas before feeding to the fluidized bed reactor;
The method for producing maleic anhydride according to claim 1 or 2, wherein:

After the temperature raising operation or before the temperature lowering operation, the temperature of the fluidized bed is in the range of 400 to 460 ° C.
(A) Introducing an inert gas into the mixed gas of the oxygen-containing gas and hydrocarbon gas,
(B) Introducing part of the remaining gas from which the maleic anhydride has been recovered from the reaction product gas withdrawn from the fluidized bed reactor into the fluidized bed reactor, or
(C) Burning the fuel in the oxygen-containing gas before feeding it to the fluidized bed reactor;
Whether the concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms supplied from the bottom of the fluidized bed reactor is increased from 10 mol% to 19 mol% with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor Or a method for producing maleic anhydride according to claim 1, wherein the content is reduced from 19 mol% to 10 mol%.

After the concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms supplied from the bottom of the fluidized bed reactor is increased from 10 mol% to 19 mol% with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor Or the concentration of the aliphatic hydrocarbon gas having 4 or more carbon atoms in the fluidized bed reactor is reduced with respect to the amount of oxygen in the oxygen-containing gas supplied to the fluidized bed reactor before being reduced from 19 mol% to 10 mol%. The oxygen concentration in the remaining gas excluding the combustible gas in the reaction product gas composition extracted from the fluidized bed reactor is 6 vol% or less, and the temperature of the fluidized bed is 400 to 460 ° C. And maintaining the pressure in the fluidized bed reactor in the range of 0.1 to 3.0 kg / cm 2 G, the aliphatic hydrocarbon having 4 or more carbon atoms is vapor-phase oxidized. anhydrous according to any one of claim 2-5 Process for the preparation of rain acid.

Process according to any one of C 4 or more aliphatic hydrocarbons having a carbon claims 1 is n- butane 6.

Process according to any one of claims 1 to 7 oxygen-containing gas is air.

Process according to any one of claims 1 to 8 inert gas is a gas mainly composed of nitrogen.

An oxidation catalyst comprising a vanadium-phosphorus composite oxide as an active component is a composite having an average valence of vanadium of about +3.8 to +4.8 and a phosphorus / vanadium atomic ratio of about 0.5 to 2.0. The method according to any one of claims 1 to 9, which is an oxide.