JP2004263103A - Polymerization inhibitor of aromatic vinyl compound, and polymerization-inhibiting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymerization inhibitor exhibiting effects on an aromatic vinyl compound in an amount smaller than that of a conventionally used polymerization inhibitor; and to provide a method for inhibiting the polymerization of the aromatic vinyl compound by using the inhibitor. <P>SOLUTION: The polymerization inhibitor of the aromatic vinyl compound contains an N-nitroso compound having sterically hindering tertiary hydrocarbon group or alicyclic hydrocarbon group such as N-nitroso-N-cyclohexylaniline and N-nitroso-N-(tert-butyl)aniline as an active ingredient. Preferably, an N-oxyl compound such as 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol and 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one is used in combination with the N-nitroso compound. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

（式中、Ｒ^１は立体障害性の三級炭化水素基又は脂環炭化水素基、Ａｒは炭素原子数６ないし１４の芳香族炭化水素基を示す）
【００１１】
請求項２に係る発明は、請求項１記載の芳香族ビニル化合物の重合抑制剤に係り、前記Ｎ−ニトロソ化合物が、Ｎ−ニトロソ−Ｎ−シクロヘキシルアニリン及び／又はＮ−ニトロソ−Ｎ−（ｔｅｒｔ−ブチル）アニリンである。
【００１２】
請求項３に係る発明は、請求項１記載の芳香族ビニル化合物の重合抑制剤に係り、さらに下記一般式（２）で表されるＮ−オキシル化合物を含有する。
【化４】

（式中、Ｒ^２は水素原子、酸素原子、水酸基、炭素数１〜３のアルキル基、炭素数１〜３のアルコキシ基、炭素数１〜３のカルボン酸又は炭素数１〜３のアミドである）
【００１３】
請求項４に係る発明は、請求項３記載の芳香族ビニル化合物の重合抑制剤に係り、前記Ｎ−オキシル化合物が２，２，６，６−テトラメチルピペリジン−１−オキシル、４−ヒドロキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル及び４−オキソ−２，２，６，６−テトラメチルピペリジン−１−オキシルのうちの少なくとの１種である。
【００１４】
請求項５に係る発明は、請求項３又は４記載の芳香族ビニル化合物の重合抑制剤に係り、前記Ｎ−ニトロソ化合物と前記Ｎ−オキシル化合物を重量比で９５：５〜１：２で含有する。
【００１５】
請求項６に係る発明は、芳香族ビニル化合物の重合抑制剤方法に係り、芳香族ビニル化合物の製造、精製、貯蔵或いは輸送工程において、請求項１乃至５のうちのいずれか記載の重合抑制剤を添加することである。
【００１６】
【発明の実施の形態】
以下、本発明について詳細に説明する。
本発明の重合抑制剤の対象とする芳香族ビニル化合物は、スチレン、メチルスチレン、エチルスチレン、ジビニルベンゼンなどである。
【００１７】
重合抑制剤であるＮ−ニトロソ化合物は前記一般式（１）で表されものであり、式中、Ｒは立体障害性の三級炭化水素基又は脂環炭化水素基であり、具体的にはｔｅｒｔ−ブチル基、１，１−ジメチルプロピル基、１，１−ジメチルブチル基、シクロペンチル基、２−メチルシクロペンチル基、２−エチルシクロペンチル基、シクロヘキシル基、２−メチルシクロヘキシル基、２−エチルシクロヘキシル基、シクロヘプチル基、２−メチルシクロヘプチル基、２−エチルシクロヘプチル基、シクロオクチル基、２−メチルシクロオクチル基、２−エチルシクロオクチル基であり、好ましくはｔｅｒｔ−ブチル基、シクロヘキシル基である。Ａｒは炭素原子数６ないし１４のアリール基を表し、具体的にはフェニル基、トリル基、エチルフェニル基、プロピルフェニル基、クメニル基、ブチルフェニル基、オクチルフェニル基、ナフチル基、メチルナフチル基等であり、これらのＮ−ニトロソ化合物はプロセスの状況に合わせてその１種類をあるいは２種類以上を組み合わせて使用する。
【００１８】
本発明の重合抑制方法を実施する対象は、芳香族ビニル化合物を製造、精製、貯蔵、あるいは輸送する工程などである。
【００１９】
重合抑制剤は、基本的に重合の進行速度を遅くする重合抑制タイプと、重合が開始する迄の時間を遅らせる重合禁止するタイプがある。実際の重合抑制剤を、厳密に区分することはできないが、本発明のＮ−ニトロソ化合物は、重合抑制タイプの傾向が強いものである。芳香族ビニル化合物を扱う工程では、滞留時間が長い個所がしばしば存在するので、一般的には禁止剤タイプよりも抑制剤タイプがより好ましく選ばれるが、重合禁止機能をさらに付与することでより効果的に使用できることがある。
【００２０】
芳香族ビニル化合物を扱う工程における重合抑制は、上記Ｎ−ニトロソ化合物に、重合禁止タイプのＮ−オキシル化合物を組合せることで、さらに効果を上げることができる。
【００２１】
本発明において、Ｎ−ニトロソ化合物と組合せて用いるＮ−オキシル化合物は、前記一般式（２）で表されるピペリジン−１−オキシルである。一般式（２）においてＲ^２は水素原子、酸素原子、水酸基、炭素数１〜３のアルキル基、炭素数１〜３のアルコキシ基、炭素数１〜３のカルボン酸基又は炭素数１〜３のアミド基である。炭素数１〜３のアルキル基としては、メチル基、エチル基、プロピル基、イソプロピル基があり、炭素数１〜３のアルコキシ基としてはメトキシ基、エトキシ基、プロポキシ基、イソプロポキシ基があり、炭素数１〜３のカルボン酸基としては蟻酸基、酢酸基、プロピオン酸基があり、炭素数１〜３のアミド基としては蟻酸アミド基、酢酸アミド基、プロピオン酸アミド基がある。具体的には、２，２，６，６−テトラメチルピペリジン−１−オキシル、４−ヒドロキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−オキソ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−メトキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−エトキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−カルボキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−カルバモイル−２，２，６，６−テトラメチルピペリジン−１−オキシル等が挙げられ、好ましくは２，２，６，６−テトラメチルピペリジン−１−オキシル、４−ヒドロキシ−２，２，６，６−テトラメチルピペリジン−１−オキシル、４−オキソ−２，２，６，６−テトラメチルピペリジン−１−オキシルである。これらのＮ−オキシル化合物はプロセスの状況に合わせてその１種類をあるいは２種類以上を組み合わせて使用する。
【００２２】
本発明の重合抑制剤は、Ｎ−ニトロソ化合物、あるいはＮ−ニトロソ化合物とＮ−オキシル化合物を含む重合抑制剤で有り、通常、Ｎ−ニトロソ化合物、Ｎ−オキシル化合物を溶解し得る有機溶剤、例えば芳香族系有機溶剤に溶解して使用される。具体的な有機溶剤としては、ベンゼン、トルエン、キシレン、エチルベンゼン等が有り、これらの１種以上が用いられる。重合抑制剤中のＮ−ニトロソ化合物、Ｎ−オキシル化合物の濃度は、一律に決められるものではなく、適宜決定されれば良いが、一般にはそれぞれ１〜２０重量％である。また、Ｎ−ニトロソ化合物、Ｎ−オキシル化合物の溶解度や溶解安定性を改善するためにアルコール類［例えば、エチレングリコール、ブチルグリコール等］を配合しても何ら差し支えない。本発明の効果を妨げない範囲において、従来から使用されてきた重合抑制剤を配合してもよい。
【００２３】
Ｎ−ニトロソ化合物とＮ−オキシル化合物を含む重合抑制剤の場合、Ｎ−ニトロソ化合物とＮ−オキシル化合物の配合比は、目的とする芳香族ビニル化合物の種類、量、運転状況および重合抑制効果の要求の程度により一律に決められるものでなく適宜決定されれば良いが、通常、重量比でＮ−ニトロソ化合物とＮ−オキシル化合物を９５：５〜１：２であり、好ましくは９：１〜１：１である。
【００２４】
本発明の重合抑制剤の調製方法は、特に限定されるものではなく、Ｎ−ニトロソ化合物、あるいはＮ−ニトロソ化合物とＮ−オキシル化合物を撹拌下、芳香族系有機溶剤に溶解することによって行われる。
【００２５】
本発明の重合抑制剤の添加量についても、芳香族ビニル化合物の種類や量はもちろん、工程の運転状況、要求度、経済的観点などを加味して決められるべきものであり、一律に決めることはできないが、一般的にはＮ−ニトロソ化合物を、芳香族ビニル化合物に基づいて１〜２０００ｐｐｍ、好ましくは１０〜１０００ｐｐｍである。この範囲よりも少ないと効果が十分でないことが多く、またこの範囲より多くとも工程上は大きな問題はないが、添加量の増加に見合う効果の増大が得られず、むしろ経済的に好ましくないことが多い。
【００２６】
また、Ｎ−オキシル化合物を組み合わせて用いる場合に、Ｎ−オキシル化合物の量は限定するものではなく、工程の運転状況や経済的観点から任意に決められるものであるが、一般的には、芳香族ビニル化合物に基づいて１〜２０００ｐｐｍ、好ましくは５〜５００ｐｐｍである。この範囲よりも少ないと組合せて用いることの意義が十分大きくないことがあり、またこの範囲を超えて多くすると、効果は充分あるが添加量の割に効果が大きくならず、経済的にみて不利となることがある。
【００２７】
本発明のＮ−ニトロソ化合物とＮ−オキシル化合物は、上記のように重合抑制の機能が少し異なっており、本発明のＮ−ニトロソ化合物は、初期の重合抑制は安定Ｎ−オキシル化合物に比べ劣るものの、比較的長時間にわたり重合を抑制することができ、Ｎ−オキシル化合物は、初期の重合抑制に優れるが、時間を経て系内のラジカルと反応して消耗するとそれ以後は実質的に重合抑制効果がなくなる。従って、工程の要求に応じて両者の最適配合を設定して添加することが望ましい。例えば、工程の状況から長期間にわたり、重合を抑制したい場合にはＮ−ニトロソ化合物を多く、初期の重合を抑制したい場合はＮ−オキシル化合物を多くするなど、任意に添加量、および組合せ比率を変えて最適化を図ることができる。
【００２８】
本発明において、Ｎ−ニトロソ化合物単独に、あるいはＮ−ニトロソ化合物とＮ−オキシル化合物を組み合わせて該工程に添加する場所は特に限定されるものではないが、通常、芳香族ビニル化合物が重合し、汚れとして問題化する箇所より上流のプロセスに添加する。例えば、スチレンは一般にエチルベンゼンの脱水素反応によって製造され、生成したスチレンと未反応エチルベンゼンを連続的に蒸留分離していることから、そのエチルベンゼン脱水素後の蒸留塔群に供給するのがよい。
【００２９】
工程への添加方法は特に限定されるものではないが、通常、ある特定箇所に一括添加するか、あるいはいくつかの箇所に分けて添加するなどの方法が適宜選択される。この際、Ｎ−ニトロソ化合物とＮ−オキシル化合物はそれぞれ別々にまた添加場所を変えて添加することも出来るが、予め両者を所望する比率で混合し、そのプロセス流体と同じ液体、例えばスチレンの場合にはエチルベンゼンや粗スチレンに溶解して添加するのが実際上便利である。
【００３０】
上記で説明したように、ニトロソ基に隣接して立体的に大きな立体障害基を有するＮ−ニトロソ化合物を用いることにその特徴がある。立体的に大きな基の導入により、重合抑制特性が変化する理由は明らかでないが、重合抑制を担う活性点であるニトロソ基とラジカルとの反応により生じたニトロキサイドが立体的に大きい基で挟まれ、安定化されたものと考えられる。また、後記実施例で示すように、本発明のＮ−ニトロソ化合物は、芳香族ビニル化合物を扱う工程で一般的に使用されている２，４−ジニトロ−６−ｓｅｃ−ブチルフェノール（ＤＮＢＰ）よりも抑制効果が高いという利点を有する。
【００３１】
【実施例】
実施例によって、本発明をさらに詳細に説明するが、本発明は以下の実施例になんら限定されるものではない。
【００３２】
〔評価に用いた重合抑制剤〕
（本発明のＮ−ニトロソ化合物）
Ｎ−１：Ｎ−ニトロソ−Ｎ−シクロヘキシルアニリン〔「Ｈ−２」（商品名）、大内新興（株）製〕
Ｎ−２：Ｎ−ニトロソ−Ｎ−（ｔｅｒｔ−ブチル）アニリン（Ｎ−２）
米国特許第２，６９２，２８７号記載の方法に準じて以下の方法でＮ−（ｔｅｒｔ−ブチル）アニリン合成し、次に亜硝酸と反応させてＮ−ニトロソ−Ｎ−（ｔｅｒｔ−ブチル）アニリンを得た。１００ｍｌのガラス製耐圧容器にアニリン塩酸塩１．３ｇ（１０ミリモル）、ｔｅｒｔ−ブチルアルコール３．７ｇ（５０ミリモル）、ヨウ素０．００５ｇを入れ、１４０℃で５時間加熱した。加熱後、反応混合物を水に溶解させ、次いで水酸化アンモニウム溶液を加え、ジエチルエーテルにより抽出した。減圧下で溶媒を留去し、残留物を得、シリカゲルを用いたクロマトグラフィーにより該残留物を精製し、Ｎ−ｔｅｒｔ−ブチルアニリンを得た。合成したＮ−ｔｅｒｔ−ブチルアニリン１．４９ｇ（１０ミリモル）を２００ｍｌフラスコに入れ、０℃に冷却しながら１：１濃塩酸４０ｍｌ（濃塩酸２０ｍｌと水２０ｍｌの混合液）を加え、次に亜硝酸ナトリウム溶液〔亜硝酸ナトリウム０．７６ｇ（１１ミリモル）を水１５ｍｌに溶解した溶液〕を２０分間かけて滴下した。滴下終了後、過剰の酸を水酸化ナトリウム溶液で中和し、反応混合物を分液ロートに注ぎ、１００ｍｌのジエチルエーテルで抽出した。水層と有機層を分離し、有機層を硫酸ナトリウムで乾燥した後、減圧下で溶媒を留去し、Ｎ−ニトロソ−Ｎ−ｔｅｒｔ−ブチルアニリンを得た。反応は、ほぼ定量的に進行し、精製することなしに重合抑制剤の試験に供した。
Ｎ−３：Ｎ−ニトロソ−１−（ｔｅｒｔ−ブチル）アミノナフタレン
「Ｎ−２」において、アニリン塩酸塩の代わりに１−アミノナフタレン塩酸塩を使用してＮ−ニトロソ−１−（ｔｅｒｔ−ブチル）アミノナフタレンを合成した。
【００３３】
〔比較で用いたＮ−ニトロソ化合物〕
Ｎ−４：Ｎ−ニトロソ−Ｎ−メチルアニリン〔「Ｈ−１」（商品名）、大内新興（株）製〕を使用した。
Ｎ−５：Ｎ−ニトロソ−Ｎ−フェニルアニリン〔「スコノック」（商品名）、大内新興（株）〕を使用した。
【００３４】
〔比較で用いたその他の重合抑制剤〕
ＤＮＢＰ：２，４−ジニトロ−６−ｓｅｃ−ブチルフェノール（ＳＮＰＥ社製）
【００３５】
〔Ｎ−オキシル化合物〕
ＴＥＭＰＯ：１−オキシル−２，２，６，６−テトラメチルピペリジ
Ｈ−ＴＥＭＰＯ：１−オキシル−２，２，６，６−テトラメチルピペリジン−４−オール（Ａｌｄｒｉｃｈ社製）
Ｏ−ＴＥＭＰＯ：１−オキシル−２，２，６，６−テトラメチルピペリジン−４−オン（Ａｌｄｒｉｃｈ社製）
【００３６】
〔重合抑制試験１〕
還流冷却器を備えた４つ口セパラブルフラスコにスチレンモノマー（予めアルカリ洗浄してモノマー中に含まれる重合抑制剤を除き、水洗、乾燥した）１００ｇを入れ、所定量の重合抑制剤を加え、高純度窒素ガスを８０ｍＬ／分の流量で通気しながら１２０℃に加熱、保持した。一定時間毎に内容物の一部を取り出し、９倍容量のメタノールを加えて生成したポリマーを液中に懸濁状態で析出させ、濾過してポリマー重量を秤量した。ポリマー量から、モノマー中のポリマー生成量％を計算で求めた。結果を表１にまとめた。
【００３７】
【表１】

【００３８】
この結果から、本発明の立体障害性置換基のあるＮ−ニトロソ化合物は、長期にわたって重合を抑制していることが分かる。置換基がメチル基、フェニル基の場合には極く初期の重合は抑制しうるが、その後は速い速度で重合が進行しているに対して、本発明のＮ−ニトロソ化合物は試験開始後１２０分後であってもポリマー濃度は約１％程度であり本発明の重合抑制剤が従来使用のＮ−ニトロソアニリン誘導体と比較して極めて優れた重合抑制剤であることが容易に理解される。さらに比較例（４，５）には現在実工程で一般的に使用されている２，４−ジニトロ−６−ｓｅｃ−ブチルフェノール（ＤＮＢＰ）について行ったが、重合抑制効果を比較すると本発明の重合抑制剤がこの重合抑制剤より優れた重合抑制効果を有していることを明瞭に示している。
【００３９】
〔重合抑制試験２〕
重合抑制試験１と同様な試験方法により、Ｎ−ニトロソ化合物とＮ−オキシル化合物を組合せて重合抑制効果を評価した。結果を表２に示す。
【００４０】
【表２】

【００４１】
本発明のＮ−ニトロソ化合物とＮ−オキシル化合物を組合せて添加することにより、初期の重合はもちろんのこと、長期にわたり重合が抑制され相乗効果が発揮されることが理解される。
【００４２】
【発明の効果】
本発明のＮ−ニトロソ化合物を使用することにより、芳香族ビニル化合物を製造、精製、貯蔵するプロセスにおける初期の重合はもちろんのこと、長期にわたり重合を抑制することが可能になる。本発明のＮ−ニトロソ化合物は、従来使用のＮ−ニトロソ化合物に比べて少量で効果が発現することから、使用量を減らすことができ、経済効果とともに、取扱い上の煩雑さも軽減される。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polymerization inhibitor for an aromatic vinyl compound containing a specific N-nitroso compound as an active ingredient, and to suppress the polymerization that occurs in the production, purification, storage, or transport process of the aromatic vinyl compound using the polymerization inhibitor. Also, the present invention relates to a method for suppressing generation of dirt in a process in which dirt is generated by polymerization of an aromatic vinyl compound in a petroleum refining plant or the like.
[0002]
[Prior art]
Aromatic vinyl compounds, especially styrene, are industrially very important compounds as raw materials for producing polystyrene, synthetic rubber, ABS resin, and the like, and are industrially produced in large quantities.
[0003]
In general, aromatic vinyl compounds are extremely easy to polymerize, and are easily polymerized due to factors such as heat in the production or purification process, lowering the yield of the aromatic vinyl compound monomer, and causing contamination (fouling) in related equipment. Ring), which causes problems in operation of the equipment. In addition to the process of producing and refining an aromatic vinyl compound, in a petroleum refining plant and the like, there is a problem that the presence of the aromatic vinyl compound causes stains resulting from polymerization of the compound. To avoid these problems, polymerization inhibitors are generally used.
[0004]
As the polymerization inhibitor, various compounds are known. Among the nitroso compounds, N, N-nitrosomethylaniline (for example, see Patent Document 1), a combination of N-nitrosodiphenylamine and dinitro-o-cresol [for example, Patent Document 2], a combination of N-nitrosodiphenylamine and dinitro-p-cresol [for example, see Patent Document 3], nitrosophenol [for example, see Patent Document 4], N-nitroso-N, N'-di-3. -Pentyl-p-phenylenediamine (for example, see Patent Document 5).
[0005]
[Patent Document 1]
US Patent No. 288,138 [Patent Document 2]
US Patent No. 3,988,212 [Patent Document 3]
US Patent No. 4,341,600 [Patent Document 4]
JP-A-5-156233 [Patent Document 5]
JP-A-11-140001
Further, as a polymerization inhibitor for an aromatic vinyl compound containing styrenes, a stable N-oxyl compound (for example, see Patent Document 6) has been proposed. However, the stable N-oxyl compound is extremely effective in suppressing the polymerization at the initial stage, but when the compound itself disappears by the reaction with the radical, the polymerization occurs at the same rate as the absence of the drug, and the aromatic vinyl compound is particularly separated and purified. When the residence time of the process liquid is relatively long at the bottom of the distillation column, or in a separation process equipped with a plurality of distillation columns, a stable N-oxyl compound is Has been consumed and there has been a problem that polymerization inhibition cannot be expected. In addition, a combination of a stable N-oxyl compound and p-nitrosophenol (for example, see Patent Document 7), a combination of a stable N-oxyl compound and p-nitrophenol (for example, see Patent Document 8), nitrophenol and sulfonic acids There is a proposal to use a combination [for example, see Patent Document 9].
[0007]
[Patent Document 6]
JP-A-1-165534 [Patent Document 7]
JP-A-8-59524 [Patent Document 8]
Japanese Patent Application Laid-Open No. 9-268138 [Patent Document 9]
JP 2003-12708 A
[Problems to be solved by the invention]
In general, polymerization inhibitors such as nitroso compounds and nitrophenols are highly toxic, and it is desired that the desired effects can be exhibited with as little as possible. In view of the above, an object of the present invention is to provide a polymerization inhibitor exhibiting an effect with respect to an aromatic vinyl compound in a smaller amount than before, and a method for suppressing polymerization of an aromatic vinyl compound using the same.
[0009]
[Means for Solving the Problems]
The present inventors have studied in detail the polymerization reaction characteristics of an aromatic vinyl compound and the polymerization inhibition characteristics of various nitroso compounds, and have found that a tertiary hydrocarbon group having a sterically large sterically hindered group adjacent to the nitroso group. Introducing an alicyclic hydrocarbon group not only enhances the polymerization inhibitory effect than the conventionally known N-nitroso-N-methylaniline and N-nitroso-N-phenylaniline (N-nitrosodiphenylamine), but also increases the aromaticity. The present inventors have found that the inhibitory effect is higher than that of 2,4-dinitro-6-sec-butylphenol (DNBP) which is generally used in a process for treating an aromatic vinyl compound, and have accomplished the present invention.
[0010]
That is, the invention according to claim 1 relates to a polymerization inhibitor for an aromatic vinyl compound, and contains an N-nitroso compound represented by the following general formula (1) as an active ingredient.
Embedded image

(In the formula, R ¹ represents a sterically hindered tertiary hydrocarbon group or an alicyclic hydrocarbon group, and Ar represents an aromatic hydrocarbon group having 6 to 14 carbon atoms.)
[0011]
The invention according to claim 2 relates to the polymerization inhibitor for an aromatic vinyl compound according to claim 1, wherein the N-nitroso compound is N-nitroso-N-cyclohexylaniline and / or N-nitroso-N- (tert) -Butyl) aniline.
[0012]
The invention according to claim 3 relates to the polymerization inhibitor for an aromatic vinyl compound according to claim 1, and further contains an N-oxyl compound represented by the following general formula (2).
Embedded image

(In the formula, R ² is a hydrogen atom, an oxygen atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a carboxylic acid having 1 to 3 carbon atoms, or an amide having 1 to 3 carbon atoms. is there)
[0013]
The invention according to claim 4 relates to the polymerization inhibitor for an aromatic vinyl compound according to claim 3, wherein the N-oxyl compound is 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy- It is at least one of 2,2,6,6-tetramethylpiperidine-1-oxyl and 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl.
[0014]
The invention according to claim 5 relates to a polymerization inhibitor for an aromatic vinyl compound according to claim 3 or 4, wherein the N-nitroso compound and the N-oxyl compound are contained in a weight ratio of 95: 5 to 1: 2. I do.
[0015]
The invention according to claim 6 relates to a method for inhibiting polymerization of an aromatic vinyl compound, and in the step of producing, purifying, storing or transporting the aromatic vinyl compound, the polymerization inhibitor according to any one of claims 1 to 5. Is to be added.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
Aromatic vinyl compounds targeted by the polymerization inhibitors of the present invention include styrene, methylstyrene, ethylstyrene, divinylbenzene, and the like.
[0017]
The N-nitroso compound which is a polymerization inhibitor is represented by the general formula (1), wherein R is a sterically hindered tertiary hydrocarbon group or an alicyclic hydrocarbon group. tert-butyl group, 1,1-dimethylpropyl group, 1,1-dimethylbutyl group, cyclopentyl group, 2-methylcyclopentyl group, 2-ethylcyclopentyl group, cyclohexyl group, 2-methylcyclohexyl group, 2-ethylcyclohexyl group , Cycloheptyl group, 2-methylcycloheptyl group, 2-ethylcycloheptyl group, cyclooctyl group, 2-methylcyclooctyl group, 2-ethylcyclooctyl group, and preferably tert-butyl group and cyclohexyl group. . Ar represents an aryl group having 6 to 14 carbon atoms, specifically, phenyl, tolyl, ethylphenyl, propylphenyl, cumenyl, butylphenyl, octylphenyl, naphthyl, methylnaphthyl, etc. These N-nitroso compounds are used alone or in combination of two or more according to the situation of the process.
[0018]
The target for carrying out the polymerization inhibiting method of the present invention is a process for producing, purifying, storing, or transporting an aromatic vinyl compound.
[0019]
The polymerization inhibitors include a polymerization inhibition type which basically slows down the progress of the polymerization and a polymerization inhibition type which delays the time until the start of the polymerization. Although an actual polymerization inhibitor cannot be strictly classified, the N-nitroso compound of the present invention has a strong tendency of a polymerization inhibition type. In the process of handling an aromatic vinyl compound, there are often places where the residence time is long, so in general, the inhibitor type is more preferably selected than the inhibitor type, but more effective by further imparting a polymerization inhibiting function. May be used in some cases.
[0020]
The effect of suppressing polymerization in the step of treating an aromatic vinyl compound can be further enhanced by combining a polymerization-inhibited N-oxyl compound with the N-nitroso compound.
[0021]
In the present invention, the N-oxyl compound used in combination with the N-nitroso compound is piperidine-1-oxyl represented by the general formula (2). In the general formula (2), R ² represents a hydrogen atom, an oxygen atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a carboxylic acid group having 1 to 3 carbon atoms, or 1 to 3 carbon atoms. Is an amide group of Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group, and examples of the alkoxy group having 1 to 3 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, and an isopropoxy group. Carboxylic acid groups having 1 to 3 carbon atoms include formic acid groups, acetic acid groups, and propionic acid groups, and amide groups having 1 to 3 carbon atoms include formic acid amide groups, acetic acid amide groups, and propionic acid amide groups. Specifically, 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6 , 6-Tetramethylpiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-1-oxyl And 4-carboxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-carbamoyl-2,2,6,6-tetramethylpiperidine-1-oxyl, and the like. , 6,6-Tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-oxo-2,2,6,6-tetramethyl It is a Perijin-1-oxyl. These N-oxyl compounds are used alone or in combination of two or more according to the process conditions.
[0022]
The polymerization inhibitor of the present invention is an N-nitroso compound, or a polymerization inhibitor containing an N-nitroso compound and an N-oxyl compound, and is usually an N-nitroso compound, an organic solvent capable of dissolving the N-oxyl compound, for example, It is used after being dissolved in an aromatic organic solvent. Specific examples of the organic solvent include benzene, toluene, xylene, and ethylbenzene, and one or more of these are used. The concentrations of the N-nitroso compound and the N-oxyl compound in the polymerization inhibitor are not determined uniformly, but may be determined appropriately, but are generally 1 to 20% by weight. Further, in order to improve the solubility and dissolution stability of the N-nitroso compound and the N-oxyl compound, alcohols (for example, ethylene glycol, butyl glycol, etc.) may be blended. As long as the effects of the present invention are not impaired, conventionally used polymerization inhibitors may be blended.
[0023]
In the case of a polymerization inhibitor containing an N-nitroso compound and an N-oxyl compound, the compounding ratio of the N-nitroso compound and the N-oxyl compound depends on the type, amount, operation status and polymerization suppression effect of the target aromatic vinyl compound. It is not necessarily determined uniformly according to the degree of demand, but may be determined as appropriate. Usually, the N-nitroso compound and the N-oxyl compound are in a weight ratio of 95: 5 to 1: 2, preferably 9: 1 to 1: 1. 1: 1.
[0024]
The method for preparing the polymerization inhibitor of the present invention is not particularly limited, and is carried out by dissolving an N-nitroso compound or an N-nitroso compound and an N-oxyl compound in an aromatic organic solvent with stirring. .
[0025]
The addition amount of the polymerization inhibitor of the present invention should be determined in consideration of the type and amount of the aromatic vinyl compound, as well as the operation status of the process, the degree of demand, and the economic viewpoint, and should be determined uniformly. In general, the amount of the N-nitroso compound is 1 to 2000 ppm, preferably 10 to 1000 ppm based on the aromatic vinyl compound. If the amount is less than this range, the effect is often not sufficient, and if it is more than this range, there is no major problem in the process, but the effect corresponding to the increase in the added amount cannot be obtained, and it is economically unfavorable. There are many.
[0026]
When the N-oxyl compound is used in combination, the amount of the N-oxyl compound is not limited, and can be arbitrarily determined from the operating conditions of the process and economical viewpoint. 1 to 2000 ppm, preferably 5 to 500 ppm, based on the aromatic vinyl compound. If the amount is less than this range, the significance of the combined use may not be sufficiently large, and if the amount exceeds this range, the effect is sufficient but the effect is not large for the added amount, which is economically disadvantageous. It may be.
[0027]
The N-nitroso compound and the N-oxyl compound of the present invention have a slightly different function of inhibiting polymerization as described above, and the N-nitroso compound of the present invention has an initial polymerization inhibition that is inferior to a stable N-oxyl compound. However, the polymerization can be suppressed for a relatively long time, and the N-oxyl compound is excellent in suppressing the polymerization at the initial stage. However, when the N-oxyl compound is consumed by reacting with the radicals in the system over time, the polymerization is substantially suppressed thereafter. Ineffective. Therefore, it is desirable to set and add the optimum combination of the two according to the requirements of the process. For example, over a long period of time from the state of the process, if the polymerization is desired to be suppressed, the N-nitroso compound is increased, and if the initial polymerization is suppressed, the N-oxyl compound is increased. It can be changed to optimize.
[0028]
In the present invention, the place where the N-nitroso compound alone or the N-nitroso compound and the N-oxyl compound are added to the step in combination is not particularly limited, but usually, the aromatic vinyl compound is polymerized, It is added to the process upstream from the point where it becomes a problem as dirt. For example, styrene is generally produced by a dehydrogenation reaction of ethylbenzene, and since the produced styrene and unreacted ethylbenzene are continuously separated by distillation, it is preferable to supply the styrene to a distillation column group after the ethylbenzene is dehydrogenated.
[0029]
The method of addition to the process is not particularly limited, but usually, a method of adding all at once to a specific location, or adding to several locations separately is appropriately selected. At this time, the N-nitroso compound and the N-oxyl compound can be added separately or in different places, but they can be added in a desired ratio in advance and mixed with the same liquid as the process fluid, for example, styrene. It is practically convenient to add the compound dissolved in ethylbenzene or crude styrene.
[0030]
As described above, the feature is that an N-nitroso compound having a sterically large sterically hindering group adjacent to the nitroso group is used. It is not clear why the polymerization inhibitory properties change due to the introduction of a sterically large group, but the nitroxide generated by the reaction between the nitroso group, which is the active site responsible for the polymerization, and the radical is sandwiched between the sterically large groups, It is considered stabilized. Further, as shown in the examples below, the N-nitroso compound of the present invention is more effective than 2,4-dinitro-6-sec-butylphenol (DNBP) generally used in a process for handling an aromatic vinyl compound. It has the advantage that the suppression effect is high.
[0031]
【Example】
The present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.
[0032]
(Polymerization inhibitor used for evaluation)
(N-nitroso compound of the present invention)
N-1: N-nitroso-N-cyclohexylaniline [“H-2” (trade name), manufactured by Ouchi Shinko Co., Ltd.]
N-2: N-nitroso-N- (tert-butyl) aniline (N-2)
According to the method described in U.S. Pat. No. 2,692,287, N- (tert-butyl) aniline is synthesized by the following method and then reacted with nitrous acid to give N-nitroso-N- (tert-butyl) aniline. Got. 1.3 g (10 mmol) of aniline hydrochloride, 3.7 g (50 mmol) of tert-butyl alcohol and 0.005 g of iodine were placed in a 100 ml glass pressure vessel, and heated at 140 ° C. for 5 hours. After heating, the reaction mixture was dissolved in water, then ammonium hydroxide solution was added and extracted with diethyl ether. The solvent was distilled off under reduced pressure to obtain a residue, which was purified by chromatography on silica gel to obtain N-tert-butylaniline. 1.49 g (10 mmol) of the synthesized N-tert-butylaniline was placed in a 200 ml flask, and while cooling to 0 ° C., 40 ml of 1: 1 concentrated hydrochloric acid (a mixture of 20 ml of concentrated hydrochloric acid and 20 ml of water) was added. A sodium nitrate solution (a solution of 0.76 g (11 mmol) of sodium nitrite dissolved in 15 ml of water) was added dropwise over 20 minutes. After completion of the dropwise addition, the excess acid was neutralized with a sodium hydroxide solution, and the reaction mixture was poured into a separating funnel and extracted with 100 ml of diethyl ether. After separating the aqueous layer and the organic layer and drying the organic layer with sodium sulfate, the solvent was distilled off under reduced pressure to obtain N-nitroso-N-tert-butylaniline. The reaction proceeded almost quantitatively and was subjected to a test for a polymerization inhibitor without purification.
N-3: N-nitroso-1- (tert-butyl) in N-nitroso-1- (tert-butyl) aminonaphthalene “N-2” using 1-aminonaphthalene hydrochloride instead of aniline hydrochloride. ) Amino naphthalene was synthesized.
[0033]
[N-nitroso compound used for comparison]
N-4: N-nitroso-N-methylaniline [“H-1” (trade name), manufactured by Ouchi Shinko Co., Ltd.] was used.
N-5: N-nitroso-N-phenylaniline [“Sconock” (trade name), Ouchi Shinko Co., Ltd.] was used.
[0034]
[Other polymerization inhibitors used for comparison]
DNBP: 2,4-dinitro-6-sec-butylphenol (manufactured by SNPE)
[0035]
[N-oxyl compound]
TEMPO: 1-oxyl-2,2,6,6-tetramethylpiperidi H-TEMPO: 1-oxyl-2,2,6,6-tetramethylpiperidin-4-ol (manufactured by Aldrich)
O-TEMPO: 1-oxyl-2,2,6,6-tetramethylpiperidin-4-one (manufactured by Aldrich)
[0036]
[Polymerization inhibition test 1]
A 4-neck separable flask equipped with a reflux condenser is charged with 100 g of styrene monomer (preliminarily washed with alkali to remove the polymerization inhibitor contained in the monomer, washed with water and dried), and a predetermined amount of the polymerization inhibitor is added. The mixture was heated and maintained at 120 ° C. while passing high-purity nitrogen gas at a flow rate of 80 mL / min. At regular intervals, a part of the content was taken out, and a polymer produced by adding 9 times the volume of methanol was precipitated in a liquid in a suspended state, filtered and weighed. From the amount of the polymer, the amount of the polymer generated in the monomer was calculated. The results are summarized in Table 1.
[0037]
[Table 1]

[0038]
These results show that the N-nitroso compound having a sterically hindered substituent of the present invention suppresses polymerization for a long period of time. When the substituent is a methyl group or a phenyl group, the polymerization at the very beginning can be suppressed, but thereafter the polymerization proceeds at a high rate, whereas the N-nitroso compound of the present invention is 120 minutes after the start of the test. Even after a minute, the polymer concentration is about 1%, and it is easily understood that the polymerization inhibitor of the present invention is a very excellent polymerization inhibitor as compared with a conventionally used N-nitrosoaniline derivative. In Comparative Examples (4, 5), 2,4-dinitro-6-sec-butylphenol (DNBP), which is currently generally used in actual processes, was used. It clearly shows that the inhibitor has a better polymerization inhibitory effect than this polymerization inhibitor.
[0039]
[Polymerization inhibition test 2]
According to the same test method as in the polymerization inhibition test 1, the polymerization inhibition effect was evaluated by combining the N-nitroso compound and the N-oxyl compound. Table 2 shows the results.
[0040]
[Table 2]

[0041]
It is understood that the combination of the N-nitroso compound and the N-oxyl compound of the present invention suppresses not only the initial polymerization but also the polymerization for a long period of time, thereby exhibiting a synergistic effect.
[0042]
【The invention's effect】
By using the N-nitroso compound of the present invention, it is possible to suppress the polymerization for a long time as well as the initial polymerization in the process of producing, purifying and storing the aromatic vinyl compound. The N-nitroso compound of the present invention exerts its effect in a smaller amount than the conventionally used N-nitroso compound, so that the amount of use can be reduced, and the economical effect and the complexity of handling are reduced.

Claims (6)

A polymerization inhibitor for an aromatic vinyl compound containing an N-nitroso compound represented by the following general formula (1) as an active ingredient.

(In the formula, R ¹ represents a sterically hindered tertiary hydrocarbon group or an alicyclic hydrocarbon group, and Ar represents an aromatic hydrocarbon group having 6 to 14 carbon atoms.) The polymerization inhibitor for an aromatic vinyl compound according to claim 1, wherein the N-nitroso compound is N-nitroso-N-cyclohexylaniline and / or N-nitroso-N- (tert-butyl) aniline. The polymerization inhibitor for an aromatic vinyl compound according to claim 1, further comprising an N-oxyl compound represented by the following general formula (2).

(Wherein, R ² is a hydrogen atom, an oxygen atom, a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a carboxylic acid having 1 to 3 carbon atoms, or an amide having 1 to 3 carbon atoms. is there) The N-oxyl compound is 2,2,6,6-tetramethylpiperidine-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and 4-oxo-2,2, The polymerization inhibitor for an aromatic vinyl compound according to claim 3, which is at least one kind of 6,6-tetramethylpiperidine-1-oxyl. The polymerization inhibitor for an aromatic vinyl compound according to claim 3 or 4, wherein the N-nitroso compound and the N-oxyl compound are in a weight ratio of 95: 5 to 1: 2. A method for inhibiting polymerization of an aromatic vinyl compound, comprising adding the polymerization inhibitor according to any one of claims 1 to 5 in a process of producing, purifying, storing, or transporting the aromatic vinyl compound.