JP4093607B2 - Continuous process for the production of dialkyl carbonates and diols - Google Patents

Description

［ここで、Ｒ¹ は２価の基−（ＣＨ₂ ）_m −（ｍは２−６の整数）を表わしその１個以上の水素は炭素数１−１０のアルキル基やアリール基によって置換されていてもよい。また、Ｒ² は炭素数１−１２の１価の脂肪族基を表わし、その１個以上の水素は炭素数１−１０のアルキル基やアリール基で置換されていてもよい。］
【００２４】
この反応の反応率を高くするためには、反応生成物であるジアルキルカーボネートおよび／またはジオールの濃度をできるだけ低くすることが必要であり、反応蒸留法で反応を行なう場合には、通常、低沸点生成物であるジアルキルカーボネートを蒸留によって除去し、その濃度を下げることによって行なわれる。
しかしながら、純粋なメタノールを用いないで脂肪族モノアルコールとジアルキルカーボネートの混合物を用いた場合には、常にジアルキルカーボネートが供給されるために、連続蒸留塔内を流下する液相中のジアルキルカーボネートの濃度を下げることには限界があり、そのため反応率を上げることはできなかったのである。
【００２５】
例えば特開平５−２１３８３０号公報の実施例５では、高さ２５０ｃｍの塔の上部にエチレンカーボネートを供給し、塔の下部にメタノール／ジメチルカーボネート混合物（重量濃度比＝７０／３０）を気体状で供給している。その結果、エチレンカーボネートの転化率（底部組成物の組成から計算）は６２．８％であった。脂肪族モノアルコールとジアルキルカーボネートの混合物を用いないで純粋なメタノールを用いた同公報実施例２では、エチレンカーボネート転化率９８．４％が得られるのに対して、極めて低い転化率である。これは塔底部におけるジメチルカーボネートの濃度が充分に低下していないために反応がそれ以上進行しないためと推測される。実際、底部生成物中のメタノール濃度は２２．８重量％、ジメチルカーボネート濃度は９．１重量％であることから、塔底の液相のメタノール／ジメチルカーボネート重量濃度比は７１／２９であることが判る。これは、塔下部に供給されたメタノール／ジメチルカーボネート混合物（重量濃度比＝７０／３０）とほぼ同じ組成である。
【００２６】
これに対して本発明の方法においては、ジアルキルカーボネートと脂肪族モノアルコールからなる第一原料を連続多段蒸留塔へ導入する際に、第一原料の導入口と塔底の間に２段以上の蒸留段を設置し、塔底液中の脂肪族モノアルコールの重量濃度とジアルキルカーボネートの重量濃度の比ｑ（ｑ＝塔底液中の脂肪族モノアルコールの重量濃度／塔底液中のジアルキルカーボネートの重量濃度）と、導入した第一原料中の脂肪族モノアルコールの重量濃度とジアルキルカーボネートの重量濃度の比ｐ（ｐ＝第一原料中の脂肪族モノアルコールの重量濃度／第一原料中のジアルキルカーボネートの重量濃度）の比の値ｒ（ｒ＝ｑ／ｐ）を１．２以上とすることによって、純粋な脂肪族モノアルコールを使用することなく、脂肪族モノアルコールとジアルキルカーボネートとの混合物を用いて、ジアルキルカーボネートとジオールを高反応率・高収率・高選択率でしかも連続的に製造することが可能となったのである。これは、従来の技術からは予測できないことである。
【００２７】
本発明の方法が高い効果を有する理由は明確ではないがおよそ次のように考えられる。
すなわち、ガス状で供給されたジアルキルカーボネートと脂肪族モノアルコールとからなる第一原料は、塔内で環状カーボネートと反応を行ないつつ蒸留分離され、導入口より上部では蒸気相はジアルキルカーボネート濃度を増加させながら脂肪族モノアルコール／ジアルキルカーボネート最低共沸混合物を形成しつつ塔上部へ向かう。（この際、蒸気相成分の沸点が塔底液の沸点より低ければ、連続蒸留塔の操作圧力における最低共沸混合物組成よりも蒸気相のジアルキルカーボネート濃度が高くなってもよい。）
【００２８】
また、導入口より下部では、液相は流下するとともに生成するジオールの濃度を増加させつつジアルキルカーボネートも生成するが、本発明では、塔底液中の脂肪族モノアルコール／ジアルキルカーボネート重量濃度比（ｑ）を、導入した第一原料中の脂肪族モノアルコール／ジアルキルカーボネート重量濃度比（ｐ）より高く保って反応を行なう。したがって、塔底液中のジメチルカーボネート濃度は第一原料にくらべて充分低いので、塔底液と気液平衡関係にある、塔底から上昇する蒸気相中のジアルキルカーボネートも充分低い濃度となっていると推測される。この塔底から上昇するジアルキルカーボネート濃度の低い蒸気相は、流下する液相と気液接触し蒸留分離を行なう際に液相のジメチルカーボネートを効率的に蒸気相へ移動させて液相のジアルキルカーボネート濃度を減少させながら塔底へと向かわせることができるので、充分な蒸留段が存在すれば、やがて塔底における環状カーボネートの転化率を充分高くすることができるものと考えられる。
【００２９】
一方、従来行なわれていたように脂肪族アルコール導入口が塔底部にある場合には、上述したジアルキルカーボネートの蒸留分離が起こらないために、塔底液のジアルキルカーボネート濃度はほとんど低下しない。そのため、脂肪族モノアルコールとジアルキルカーボネートの混合物を導入する場合には環状カーボネートの転化率を高くすることはできないのである。
【００３０】
また、特開平５−２１３８３０号公報の実施例５では、メタノールとジメチルカーボネートの混合物を導入する位置は高さ２５０ｃｍの塔の下端から３０ｃｍ上であるが、当該実施例ではリボイラー等による塔底液の加熱は行なわれていない。すなわち、蒸留には必須である下部から上部への蒸気流がメタノール／ジメチルカーボネート供給位置から下には存在しない。したがって、流下する液相中のジメチルカーボネート濃度の低減を行なうことは全く期待できない。
【００３１】
事実、先に示したように、同実施例によれば底部生成物中のメタノール／ジメチルカーボネート重量濃度比は７１／２９であり、供給したメタノール／ジメチルカーボネート重量濃度比とほとんど同じであるので、本発明において行なわれているような、塔底部でのジメチルカーボネート濃度の低減が行なわれていないことは明らかである。
【００３２】
本発明で用いられる連続多段蒸留塔とは、蒸留の段数が４段以上の複数段を有する蒸留塔であって、連続蒸留が可能なものであるならばどのようなものであってもよい［本発明でいう段とは理論段であり、充填塔のように物理的段を有しない蒸留塔の場合には、用いる充填材のＨ．Ｅ．Ｔ．Ｐ．（１理論段あたりの高さ）で充填高さを除した数値が段数として用いられる。］。このような連続多段蒸留塔としては、例えば泡鐘トレイ、多孔板トレイ、バルブトレイ、向流トレイ等のトレイを使用した棚段塔式のものや、ラシヒリング、レッシングリング、ポールリング、ベルルサドル、インタロックスサドル、ディクソンパッキング、マクマホンパッキング、ヘリパック、スルザーパッキング、メラパック等の各種充填物を充填した充填塔式のものなど、通常、連続式の多段蒸留塔として用いられるものならばどのようなものでも使用することができる。さらには棚段部分と充填物の充填された部分とを合わせ持つ蒸留塔も好ましく用いられる。また、第１連続多段蒸留塔は、上記の蒸留塔を単独で用いてもよいし、複数の該蒸留塔を直列または並列に接続することで複数組み合わせて用いることもできる。さらにまた、固体触媒を用いる場合、この固体触媒を充填物の一部または全部とする充填塔式蒸留塔も好ましく用いられる。
【００３３】
本発明で第二原料に用いられる環状カーボネートとは、前記（Ａ）で表わされる化合物であって、例えば、エチレンカーボネート、プロピレンカーボネート等のアルキレンカーボネート類や、１，３−ジオキサシクロヘキサ−２−オン、１，３−ジオキサシクロヘプタ−２−オンなどが好ましく用いられ、エチレンカーボネート、プロピレンカーボネートが入手の容易さなどの点から特に好ましく使用される。
【００３４】
また、もう一方の第一原料における脂肪族モノアルコールとは、前記（Ｂ）で表わされる化合物であって、生成するジオールより沸点が低く、かつ、生成するジアルキルカーボネートと最低共沸混合物を形成するものであればどのような脂肪族モノアルコールでも用いることができる。例えば、メタノールなどが好ましく用いられる。
【００３５】
本発明において触媒は連続多段蒸留塔内に存在させることが必要であり、この触媒の存在する領域において、環状カーボネートと脂肪族モノアルコール類とを接触させることによって反応を進行させると同時に低沸点生成物を蒸留によって塔上部から抜き出す反応蒸留方式を用いている。
【００３６】
このような連続多段蒸留塔内に触媒を存在させる方法はどのような方法であってもよいが、例えば、反応条件下で反応液に溶解するような均一系触媒の場合、該蒸留塔に連続的に触媒を供給することにより、蒸留塔内の液相に触媒を存在させることもできるし、あるいは反応条件下で反応液に溶解しないような不均一系触媒の場合、該蒸留塔内に固体触媒を配置することにより、反応系に触媒を存在させることもできるし、これらを併用した方法であってもよい。
【００３７】
均一系触媒を該蒸留塔に連続的に供給する場合には、第二原料および／または第一原料と同時に供給してもよいし、原料とは異なる位置に供給してもよい。また、塔底から少くとも２段以上の理論段を有する位置であればどの位置に触媒を供給してもよい。しかし、該蒸留塔内で実際に反応が進行するのは触媒供給位置から下の領域であることから、塔頂から原料供給位置までの間の領域に触媒を供給することが好ましい。また、不均一系の固体触媒を用いる場合、その触媒は該蒸留塔内の任意の位置に必要量充填することができ、この触媒の存在する層の理論段が少くとも１段以上あればよく、好ましくは２段以上あればよい。蒸留塔の充填物としての効果をも併せ持つ固体触媒を用いることも好ましい。
【００３８】
本発明において用いられる触媒としては、これまでに知られている種々のものを使用することができる。例えば、リチウム、ナトリウム、カリウム、ルビジウム、セシウム、マグネシウム、カルシウム、ストロンチウム、バリウム等のアルカリ金属およびアルカリ土類金属類；アルカリ金属およびアルカリ土類金属の水素化物、水酸化物、アルコキシド化物類、アリーロキシド化物類、アミド化物類等の塩基性化合物類；アルカリ金属およびアルカリ土類金属の炭酸塩類、重炭酸塩類、有機酸塩類等の塩基性化合物類；トリエチルアミン、トリブチルアミン、トリヘキシルアミン、ベンジルジエチルアミン等の３級アミン類；Ｎ−アルキルピロール、Ｎ−アルキルインドール、オキサゾール、Ｎ−アルキルイミダゾール、Ｎ−アルキルピラゾール、オキサジアゾール、ピリジン、アルキルピリジン、キノリン、アルキルキノリン、イソキノリン、アルキルイソキノリン、アクリジン、アルキルアクリジン、フェナントロリン、アルキルフェナントロリン、ピリミジン、アルキルピリミジン、ピラジン、アルキルピラジン、トリアジン、アルキルトリアジン等の含窒素複素芳香族化合物類；ジアザビシクロウンデセン（ＤＢＵ）、ジアザビシクロノネン（ＤＢＮ）等の環状アミジン類；酸化タリウム、ハロゲン化タリウム、水酸化タリウム、炭酸タリウム、硝酸タリウム、硫酸タリウム、タリウムの有機酸塩類等のタリウム化合物類；トリブチルメトキシ錫、トリブチルエトキシ錫、ジブチルジメトキシ錫、ジエチルジエトキシ錫、ジブチルジエトキシ錫、ジブチルフェノキシ錫、ジフェニルメトキシ錫、酢酸ジブチル錫、塩化トリブチル錫、２−エチルヘキサン酸錫等の錫化合物類；ジメトキシ亜鉛、ジエトキシ亜鉛、エチレンジオキシ亜鉛、ジブトキシ亜鉛等の亜鉛化合物類；アルミニウムトリメトキシド、アルミニウムトリイソプロポキシド、アルミニウムトリブトキシド等のアルミニウム化合物類；テトラメトキシチタン、テトラエトキシチタン、テトラブトキシチタン、ジクロロジメトキシチタン、テトライソプロポキシチタン、酢酸チタン、チタンアセチルアセトナート等のチタン化合物類；トリメチルホスフィン、トリエチルホスフィン、トリブチルホスフィン、トリフェニルホスフィン、トリブチルメチルホスホニウムハライド、トリオクチルブチルホスホニウムハライド、トリフェニルメチルホスホニウムハライド等のリン化合物類；ハロゲン化ジルコニウム、ジルコニウムアセチルアセトナート、ジルコニウムアルコキシド、酢酸ジルコニウム等のジルコニウム化合物類；鉛および鉛を含む化合物類、例えば、ＰｂＯ、ＰｂＯ₂ 、Ｐｂ₃ Ｏ₄ などの酸化鉛類；ＰｂＳ、Ｐｂ₂ Ｓ₃ 、ＰｂＳ₂ などの硫化鉛類；Ｐｂ（ＯＨ）₂ 、Ｐｂ₃ Ｏ₂ （ＯＨ）₂ 、Ｐｂ₂ ［ＰｂＯ₂ （ＯＨ）₂ ］、Ｐｂ₂ Ｏ（ＯＨ）₂ などの水酸化鉛類；Ｎａ₂ ＰｂＯ₂ 、Ｋ₂ ＰｂＯ₂ 、ＮａＨＰｂＯ₂ 、ＫＨＰｂＯ₂ などの亜ナマリ酸塩類；Ｎａ₂ ＰｂＯ₃ 、Ｎａ₂ Ｈ₂ ＰｂＯ₄ 、Ｋ₂ ＰｂＯ₃ 、Ｋ₂ ［Ｐｂ（ＯＨ）₆ ］、Ｋ₄ ＰｂＯ₄ 、Ｃａ₂ ＰｂＯ₄ 、ＣａＰｂＯ₃ などの鉛酸塩類；ＰｂＣＯ₃ 、２ＰｂＣＯ₃ ・Ｐｂ（ＯＨ）₂ などの鉛の炭酸塩およびその塩基性塩類；Ｐｂ（ＯＣＨ₃ ）₂ 、（ＣＨ₃ Ｏ）Ｐｂ（ＯＰｈ）、Ｐｂ（ＯＰｈ）₂ などのアルコキシ鉛類、アリールオキシ鉛類；Ｐｂ（ＯＣＯＣＨ₃ ）₂ 、Ｐｂ（ＯＣＯＣＨ₃ ）₄ 、Ｐｂ（ＯＣＯＣＨ₃ ）₂ ・ＰｂＯ・３Ｈ₂ Ｏなどの有機酸の鉛塩およびその炭酸塩や塩基性塩類；Ｂｕ₄ Ｐｂ、Ｐｈ₄ Ｐｂ、Ｂｕ₃ ＰｂＣｌ、Ｐｈ₃ ＰｂＢｒ、Ｐｈ₃ Ｐｂ（またはＰｈ₆ Ｐｂ₂ ）、Ｂｕ₃ ＰｂＯＨ、Ｐｈ₂ ＰｂＯなどの有機鉛化合物類（Ｂｕはブチル基、Ｐｈはフエニル基を示す）；Ｐｂ−Ｎａ、Ｐｂ−Ｃａ、Ｐｂ−Ｂａ、Ｐｂ−Ｓｎ、Ｐｂ−Ｓｂなどの鉛の合金類；ホウエン鉱、センアエン鉱などの鉛鉱物類、およびこれらの鉛化合物の水和物類；３級アミノ基を有する陰イオン交換樹脂、アミド基を有するイオン交換樹脂、スルホン酸基、カルボン酸基、リン酸基のうちの少なくとも一つの交換基を有するイオン交換樹脂、第４級アンモニウム基を交換基として有する固体強塩基性アニオン交換体等のイオン交換体類；シリカ、シリカ−アルミナ、シリカーマグネシア、アルミノシリケート、ガリウムシリケート、各種ゼオライト類、各種金属交換ゼオライト類、アンモニウム交換ゼオライト類などの固体の無機化合物類等が用いられる。 固体接触として、特に好ましく用いられるのは第４級アンモニウム基を交換基として有する固体強塩基性アニオン交換体であり、このようなものとしては、例えば、第４級アンモニウム基を交換基として有する強塩基性アニオン交換樹脂、第４級アンモニウム基を交換基として有するセルロース強塩基性アニオン交換体、第４級アンモニウム基を交換基として有する無機質担体担持型強塩基性アニオン交換体などが挙げられる。
【００３９】
第４級アンモニウム基を交換基として有する強塩基性アニオン交換樹脂としては、例えば、スチレン系強塩基性アニオン交換樹脂などが好ましく用いられる。スチレン系強塩基性アニオン交換樹脂は、スチレンとジビニルベンゼンの共重合体を母体として、交換基に第４級アンモニウム（Ｉ型あるいはＩＩ型）を有する強塩基性アニオン交換樹脂であり、例えば、次の一般式で模式的に示される。
【００４０】
【化２】

【００４１】
上記式中、Ｘはアニオンを示し、通常、Ｘとしては、Ｆ^- 、Ｃｌ^- 、Ｂｒ^- 、Ｉ^- 、ＨＣＯ₃ ^- 、ＣＯ₃ ^- 、ＣＨ₃ ＣＯ₂ ^- 、ＨＣＯ₂ ^- 、ＩＯ₃ ^- 、ＢｒＯ₃ ^- 、ＣｌＯ₃ ^- の中から選ばれた少なくとも１種のアニオンが使用され、好ましくはＣｌ^- 、Ｂｒ^- 、ＨＣＯ₃ ^- 、ＣＯ₃ ^- の中から選ばれた少なくとも１種のアニオンが使用される。また、樹脂母体の構造としては、ゲル型、マクロレティキュラー型（ＭＲ型）いずれも使用できるが、耐有機溶媒性が高い点からＭＲ型が特に好ましい。
【００４２】
第４級アンモニウム基を交換基として有するセルロース強塩基性アニオン交換体としては、例えば、セルロースの−ＯＨ基の一部または全部をトリアルキルアミノエチル化して得られる、−ＯＣＨ₂ ＣＨ₂ ＮＲ₃ Ｘなる交換基を有するセルロースが挙げられる。ただし、Ｒはアルキル基を示し、通常、メチル、エチル、プロピル、ブチルなどが用いられ、好ましくはメチル、エチルが使用される。また、Ｘは前述のとおりである。
【００４３】
本発明において使用できる、第４級アンモニウム基を交換基として有する無機質担体担持型強塩基性アニオン交換体とは、無機質担体の表面水酸基−ＯＨの一部または全部を修飾することにより、４級アンモニウム基−Ｏ（ＣＨ₂ ）_n ＮＲ₃ Ｘを導入したものを意味する。ただし、Ｒ、Ｘは前述のとおりである。ｎは通常１−６の整数であり、好ましくはｎ＝２である。無機質担体としては、シリカ、アルミナ、シリカアルミナ、チタニア、ゼオライトなどを使用することができ、好ましくはシリカ、アルミナ、シリカアルミナが用いられ、特に好ましくはシリカが使用される。無機質担体の表面水酸基の修飾方法としては、任意の方法を用いることができる。例えば、無機質担体とアミノアルコールＨＯ（ＣＨ₂ ）_n ＮＲ₂ を塩基触媒存在下に脱水反応を進行させることによりアミノアルコキシ化した後に、ハロゲン化アルキルＲＸ’（Ｘ’はハロゲンを示し、通常はＣｌ、Ｂｒ、Ｉなどが使用される）と反応させて−Ｏ（ＣＨ₂ ）_n ＮＲ₃ Ｘ’基とする。さらに、アニオン交換を行なうことにより、所望のアニオンＸを有する４級アンモニウム基−Ｏ（ＣＨ₂ ）_n ＮＲ₃ Ｘとする。また、ｎ＝２の場合には、無機質担体をＮ、Ｎ−ジアルキルアジリジンで処理することにより、Ｎ、Ｎ−ジアルキルアミノエトキシ化して−ＯＣＨ₂ ＣＨ₂ ＮＲ₂ 基とした後に、上述の方法により−Ｏ（ＣＨ₂ ）_n ＮＲ₃ Ｘ基とされる。
【００４４】
第４級アンモニウム基を交換基として有する固体強塩基性アニオン交換体は、市販のものを使用することもできる。その場合には、前処理として予め所望のアニオン種でイオン交換を行なった後に、触媒として使用することもできる。
また、少くとも１個の窒素原子を含む複素環基が結合している巨大網状およびゲルタイプの有機ポリマー、または少くとも１個の窒素原子を含む複素環基が結合している無機質担体から成る固体触媒も好ましく用いられる。また、さらにはこれらの含窒素複素環基の一部または全部が４級塩化された固体触媒も同様に用いられる。
本発明で用いられる触媒の量は、使用する触媒の種類によっても異なるが、触媒を連続多段蒸留塔の反応域に連続的に供給する場合には、第一原料と第二原料の合計重量に対する割合で表わして、通常０．０００１−５０重量％で使用される。また固体触媒を連続多段蒸留塔内に設置して使用する場合には、該蒸留塔の空塔容積に対して、０．０１−７５体積％の触媒量が好ましく用いられる。
【００４５】
本発明を実施するに当り、環状カーボネートからなる第二原料を連続多段蒸留塔に供給する方法については特別な限定はなく、それらが該蒸留塔の少なくとも１段以上、好ましくは２段以上の領域において触媒と接触させることができるような供給方法であればどのような方法でもよい。すなわち、該第二原料は該連続多段蒸留塔の上記の条件を満たす段に、必要な数の導入口から連続的に供給することができる。蒸留塔内での反応量を大きくするためには、蒸留塔の上部に供給することも好ましい方法の一つである。またもう一方の原料である、ジアルキルカーボネートと脂肪族モノアルコールからなる第一原料の導入位置は、ジアルキルカーボネートを含有する脂肪族モノアルコールの組成によっても変わりうるが、その導入口と塔底との間に、通常２段以上、好ましくは４段以上の蒸留段が存在するように定められる。
【００４６】
第一原料および第二原料は液状、ガス状または液とガスとの混合物として該蒸留塔に連続的に供給される。このようにして原料を連続多段蒸留塔に供給する以外に、付加的にガス状の原料を該蒸留塔の下部から断続的または連続的に供給することも好ましい方法である。
本発明において塔底液中の脂肪族モノアルコールの重量濃度とジアルキルカーボネートの重量濃度の比ｑ（ｑ＝塔底液中の脂肪族モノアルコールの重量濃度／塔底液中のジアルキルカーボネートの重量濃度）と、導入した第一原料中の脂肪族モノアルコールの重量濃度とジアルキルカーボネートの重量濃度の比ｐ（ｐ＝第一原料中の脂肪族モノアルコールの重量濃度／第一原料中のジアルキルカーボネートの重量濃度）の比の値ｒ（ｒ＝ｑ／ｐ）は、高いほど環状カーボネートの転化率を上げられるが、あまりに高すぎると加熱に必要な熱エネルギーが大きくなる。したがって、ｒは通常１．２以上であり、好ましくは１．３−１０００、さらに好ましくは１．５−２００である。
【００４７】
なお、ｒを所望の値とするための方法は、どのような方法であっても良いが、例えば、（１）塔底に設けたリボイラー等の加熱器による塔底液の加熱、（２）第一原料の導入口と塔底の間の段に設けたリボイラー等の加熱器による当該段液相の加熱、（３）第一原料の導入口と塔底の間の段または塔底への、加熱された非凝縮性不活性ガスの導入、（４）第一原料の導入口と塔底の間の段または塔底への、炭化水素化合物等の反応に不活性な溶媒（例えば、エーテル類、脂肪族炭化水素類、芳香族炭化水素類、ハロゲン化脂肪族炭化水素類、ハロゲン化芳香族炭化水素類等）の加熱蒸気の導入、（５）第一原料の導入口と塔底の間の段または塔底への、反応に不活性な溶媒［例えば、前記（４）で例示した溶媒等］の加熱液体の導入、等により、塔底液または第一原料の導入口と塔底の間の段の液相を加熱して蒸気を発生させ、流下してくる液相との間に気液接触すなわち蒸留を行なわせることにより、液相のジアルキルカーボネート濃度を減らして所望のｒとする方法などが挙げられ、好ましい方法としては、塔底に設けたリボイラー等の加熱器による塔底液の加熱が挙げられる。
【００４８】
本発明で用いる、第一原料中のジアルキルカーボネートの濃度は、重量％で表わして、通常、０．１−５０重量％、好ましくは０．５−４０重量％、さらに好ましくは１−３０重量％である。
第二原料中に、生成物であるジアルキルカーボネートまたはジオール類が含まれていてもよい。第二原料中に含まれるジオールは、通常、０．０００１−８０重量％、好ましくは０．００１−８０重量％である。
【００４９】
連続多段蒸留塔に供給する脂肪族モノアルコールと環状カーボネートの量比は、触媒の種類や量、および反応条件によっても変わり得るが、通常、第二原料中の環状カーボネートに対して、第一原料中の脂肪族モノアルコール類はモル比で０．０１−１０００倍の範囲で供給するのが好ましい。環状カーボネートの反応率を上げるためには脂肪族モノアルコール類は２倍モル以上の過剰量供給することが好ましいが、あまり大過剰に用いると装置を大きくする必要がある。このような意味において、特に好ましいのは、２−２０倍モル量の脂肪族モノアルコール類が使用される場合である。
【００５０】
本発明においては、連続多段蒸留塔内で生成するジアルキルカーボネートを含む低沸点成分は該蒸留塔の上部から液状、ガス状または液とガスとの混合物からなる塔上部抜き出し物として連続的に抜き出される。該抜き出し物はジアルキルカーボネートと脂肪族モノアルコールの混合物であり、原料である環状カーボネートや高沸点生成物を少量含んでいてもよい。また、生成したジアルキルカーボネートは塔上部から抜き出されるので、塔上部抜出液中のジアルキルカーボネート濃度は、導入した第一原料中のジアルキルカーボネート濃度より増加するが、塔底抜出液より沸点が低ければ、どのような組成であってもよい。
【００５１】
連続多段蒸留塔から、ジアルキルカーボネートと脂肪族モノアルコールを含む低沸点成分を塔上部抜き出し物として抜き出す抜き出し口は、第二原料供給位置から塔頂の間または塔頂部にガス状物質の抜き出し口を設けることが好ましく、塔頂部に設けることがさらに好ましい。このようにして抜き出された低沸点成分の一部を該蒸留塔の上部に戻す、いわゆる還流操作を行ってもよい。しかしながら、あまりに還流比を増加させると必要な熱エネルギーが大きくなるので好ましくない。したがって、還流比は、通常０−１０が用いられ、好ましくは、０−５が用いられる。
【００５２】
本発明の方法によって生成するジオールを含む塔下部抜き出し物の抜き出し口は連続多段蒸留塔の下部に設けられ、特に好ましくは塔底部に設けられる。
本発明において連続多段蒸留塔の上部とは、該蒸留塔の塔頂から塔高の１／２の高さ迄の範囲を指し、塔頂も含まれる。また、下部とは、該蒸留塔の塔底から塔高の１／２の高さ迄の範囲を指し、塔底も含まれる。
本発明において塔下部抜き出し物とは、連続多段蒸留塔の下部から液状及び／又はガス状で連続的に抜き出される混合物であり、ジオール、脂肪族モノアルコール、ジアルキルカーボネートを含み、環状カーボネートを少量含んでいてもよい。反応条件下において反応液に溶解し得る高沸点の触媒を用いる場合は、塔下部抜き出し物中に該触媒が含まれる。
【００５３】
連続多段蒸留塔内の流下液速度および上昇蒸気速度は使用する該蒸留塔の種類により、また、充填塔をもちいる場合には充填物の種類によっても異なるが、通常フラッディングやウィーピングを起こさない範囲で実施される。
【００５４】
本発明においては、反応は主として触媒の存在する連続多段蒸留塔内の液相において起こるため、生成する反応生成物の量は、通常、該蒸留塔内のホールドアップ液量に依存している。つまり、同じ塔高、同じ塔径の蒸留塔を用いる場合にはホールドアップ液量の多い蒸留塔が反応液の滞留時間即ち反応時間を比較的長くすることができるという意味において好ましい。しかしながら、ホールドアップ液量があまりに多い場合には、滞留時間が長くなるために副反応が進行したり、フラッディングが起こりやすくなる。従つて、本発明に用いる連続多段蒸留塔のホールドアップ液量は蒸留条件や蒸留塔の種類によっても変わり得るが、連続多段蒸留塔の空塔容積に対するホールドアップ液量の容積比で表現して、通常、０．００５−０．７５で行われる。
【００５５】
また、本発明において、連続多段蒸留塔内での反応液の平均滞留時間は、反応条件や連続多段蒸留塔の種類や内部構造（例えば棚段や充填物の種類）によっても異なるが、通常０．００１−５０時間、好ましくは０．０１−１０時間、より好ましくは０．０５−５時間である。
【００５６】
反応温度は、連続多段蒸留塔内の温度であり、用いる原料の種類や反応圧力によって異なるが、通常０−３５０℃、好ましくは２０−２００℃の範囲である。また、脂肪族モノアルコールとジアルキルカーボネートが最低共沸混合物を形成する範囲内であれば、反応圧力は減圧、常圧、加圧いずれであってもよく、用いる原料の種類によっても異なるが、絶対圧力で表わして通常０．００００１−１００Ｋｇ／ｃｍ² 、好ましくは０．０００１−５０Ｋｇ／ｃｍ² 、より好ましくは０．００１−２０Ｋｇ／ｃｍ² の範囲である。
連続多段蒸留塔の塔下部抜き出し物の一部を該連続多段蒸留塔へ供給することで未反応環状カーボネートを該連続多段蒸留塔へ循環させることができる。その際、塔下部抜き出し物を該連続多段蒸留塔へ供給する導入口の位置は特に限定されないが、該蒸留塔の上部へ供給することが好ましい。
【００５７】
本発明の特に好ましい実施態様においては、第二原料としてエチレンカーボネートを用い、第一原料としてメタノールとジメチルカーボネートの混合物を用い、相当するジアルキルカーボネートであるジメチルカーボネートと、エチレングリコールを製造する場合である。この場合、原料の中で沸点の高い第二原料は、連続多段蒸留塔の触媒の存在する段から塔頂までの間に設けられた導入口から該蒸留塔内に液状で連続的に供給され、低沸点原料である第一原料は、ガス状で該蒸留塔内に連続的に供給される。そして反応によって生成した低沸点生成物であるジメチルカーボネートは未反応メタノールや、第一原料に含まれていたジメチルカーボネートとともに、該蒸留塔の塔頂部から連続的に抜き出される。高沸点生成物であるエチレングリコールは連続多段蒸留塔の塔底からメタノールおよびジメチルカーボネートとともに液状で連続的に抜き出される。
【００５８】
本発明においては、必ずしも溶媒を使用する必要はないが、反応操作を容易にする等の目的で適当な不活性溶媒、例えば、エーテル類、脂肪族炭化水素類、芳香族炭化水素類、ハロゲン化脂肪族炭化水素類、ハロゲン化芳香族炭化水素類等を反応溶媒として用いることができる。
また、反応に不活性な物質として窒素、ヘリウム、アルゴン等の不活性ガスを反応系に共存させてもよいし、生成する低沸点生成物の留去を加速する目的で連続多段蒸留塔の下部より、前記の不活性ガスや反応に不活性な低沸点有機化合物をガス伏で導入してもよい。
【００５９】
【発明の実施の形態】
以下に、本発明を実施例等を用いて具体的に説明するが、本発明は、これらの実施例等により何ら限定されるものではない。
( 実施例１)
第１図に示される装置を用いてエチレンカーボネート（ＥＣ）とメタノール（ＭｅＯＨ）から、ジメチルカーボネート（ＤＭＣ）とエチレングリコール（ＥＧ）を連続的に製造した。
充填物としてディクソンパッキング（３φ）を充填した、内径２．５cm、充填高２５０ｃｍの充填塔からなる連続多段蒸留塔１の塔頂４へ、大気圧下に第二原料であるエチレンカーボネートと水酸化ナトリウムからなる混合物（重量濃度比：エチレンカーボネート／触媒＝９９．７／０．３）を導管２から予熱器３を経て液状で連続的に供給した。また、第一原料としてメタノールとジメチルカーボネートからなる混合物［重量濃度比（ｐ）＝メタノール／ジメチルカーボネート＝８５／１５＝５．６７］を、蒸発器６’を経て塔底から１００ｃｍの位置へ設けられた導管５’からガス状で連続的に供給した。連続多段蒸留塔は大気圧で運転された。
【００６０】
塔頂４から留出するガス状成分は凝縮器７で凝縮され、その一部が環流され、他は液状で抜き出された。また、塔底８から抜き出された塔底液は、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）が２１．５を保つようにその一部がリボイラー６で加熱された。ｒ（ｒ＝ｑ／ｐ）は３．８０であった。循環する塔底液の一部は導管９から抜き出された。その他の反応条件および定常状態後の結果を第１表に示す。この結果は、エチレンカーボネートの転化率が９９％以上、ジメチルカーボネートの収率は９９％以上（エチレンカーボネート基準のジメチルカーボネートの選択率は９９％以上）、エチレングリコールの収率が９９％以上（エチレンカーボネート基準のエチレングリコール選択率は９９％以上）で得られたことを示す。
【００６１】
（比較例１）
第２図に示される、充填物としてラシッヒ・リング（６ｍｍφ）を充填した、内径３ｃｍ、充填高２５０ｃｍの、８０℃で等温的に恒温調節されている充填塔からなる蒸留塔１の塔頂４から１０ｃｍ下の位置へ、実施例１の第二原料と同様の混合物を導管２から予熱器３を経て液状で連続的に供給した。また、第一原料として実施例１の第一原料と同様の混合物を、蒸発器６’を経て塔底から３０ｃｍの位置へ設けられた導管５’からガス状で連続的に供給した。連続多段蒸留塔は大気圧で運転された。
【００６２】
塔頂４から留出するガス状成分は凝縮器７で凝縮され液状で抜き出された。また塔底液は、塔底８から導管９を経て、加熱されることなく抜き出された。抜き出された塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）は５．８９であった。ｒ（ｒ＝ｑ／ｐ）は１．０４であった。その他の反応条件および定常状態後の結果を第１表に示す。この結果はエチレンカーボネートの転化率が８４％、ジメチルカーボネートの収率は８２％（エチレンカーボネート基準のジメチルカーボネートの選択率は９８％）、エチレングリコールの収率が８２％（エチレンカーボネート基準のエチレングリコール選択率は９８％）であることを示す。
【００６３】
（実施例２）
触媒として水酸化ナトリウムの代わりにナトリウムメトキシドを用い、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）を１５．３に保ったことの他は実施例１と同様の方法で反応を行った。ｒ（ｒ＝ｑ／ｐ）は２．７０であった。反応の条件および定常状態後の結果を第１表に示す。
【００６４】
（実施例３）
触媒として水酸化ナトリウムの代わりに１，８−ジアザビシクロ（５，４，０）ウンデセン−７（ＤＢＵ）を用い、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）を８．０５に保ったことの他は実施例１と同様の方法で反応を行った。反応の条件および定常状態後の結果を第１表に示す。
【００６５】
（実施例４）
導管５’を塔底から８０ｃｍの位置へ設け、第一原料としてメタノールとジメチルカーボネート（重量濃度比：メタノール／ジメチルカーボネート＝７０／３０＝２．３３）からなる混合物を用い、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）を７．４７に保った他は実施例１と同様の方法で反応を行なった。ｒ（ｒ＝ｑ／ｐ）は３．２０であった。反応条件および定常状態後の結果を第２表に示す。
【００６６】
（実施例５）
触媒としてナトリウムメトキシドを用い、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）を３．５５に保った他は実施例４と同様の方法で反応を行なった。ｒ（ｒ＝ｑ／ｐ）は１．５２であった。反応条件および定常状態後の結果を第２表に示す。
【００６７】
（比較例２）
第一原料として実施例４で用いた第一原料と同様の混合物を用い、第二原料として実施例４で用いた第二原料と同様の混合物を用いたことの他は、比較例１と同様の方法で反応を行なった。塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）は２．４５であった。ｒ（ｒ＝ｑ／ｐ）は１．０５であった。その他の反応条件および定常状態後の結果を第２表に示す。
【００６８】
（実施例６）
第３図に示される装置を用いてエチレンカーボネートとメタノールから、ジメチルカーボネートとエチレングリコールを連続的に製造した。
開口率２％で液深５ｍｍのシーブトレイを４０段装着した塔径５０ｍｍ，塔高１６０ｃｍのオールダーショー型多段蒸留塔からなる連続多段蒸留塔１の塔頂へ、第二原料としてエチレンカーボネートと水酸化ナトリウムからなる混合物（重量濃度比：エチレンカーボネート／水酸化ナトリウム＝９９．７／０．３）を導管２から予熱器３を経て液状で連続的に供給した。また、第一原料としてメタノールとジメチルカーボネートからなる混合物［重量濃度比（ｐ）：メタノール／ジメチルカーボネート＝８５／１５＝５．６７］を、蒸発器６’を経て塔底から１０段めの位置へ設けられた導管からガス状で連続的に供給した。連続多段蒸留塔は大気圧で運転された。
【００６９】
塔頂４から留出するガス状成分は凝縮器７で凝縮され、液状で抜き出された。塔底８から抜き出された塔底液は、塔底液中のメタノール／ジメチルカーボネート重量濃度比（ｑ）が１５．９を保つようにその一部がリボイラー６で加熱された。ｒ（ｒ＝ｑ／ｐ）は２．８０であった。循環する塔底液の一部は導管９から抜き出された。その他の反応条件および定常状態後の結果を第３表に示す。
【００７０】
【表１】

【００７１】
【表２】

【００７２】
【表３】

【００７３】
【発明の効果】
本発明の方法により、工業的に入手し易い、ジアルキルカーボネートと脂肪族モノアルコールの混合物と、環状カーボネートとを用いて、高収率・高選択率で、ジアルキルカーボネートとジオールを連続的に製造できる。
【図面の簡単な説明】
【図１】第１図は、実施例１で用いた装置の模式図である。
【図２】第２図は、比較例１で用いた装置の模式図である。
【図３】第３図は、実施例６で用いた装置の模式図である。
【符号の説明】
１：連続多段蒸留塔
３：予熱器
６：リボイラー
６’：蒸発器
７：凝縮器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for continuously producing a dialkyl carbonate and a diol by reacting a cyclic carbonate and an aliphatic monoalcohol. More specifically, the present invention relates to a process for continuously producing a dialkyl carbonate and a diol by reacting with a cyclic carbonate using a mixture of a dialkyl carbonate and an aliphatic monoalcohol, which are easily available industrially, as raw materials.
[0002]
[Prior art]
Several proposals have been made regarding methods for producing dialkyl carbonates and diols from the reaction of cyclic carbonates with aliphatic monoalcohols, most of which relate to catalysts. Examples of such catalysts include alkali metals or basic compounds containing alkali metals [US Pat. No. 3,642,858, JP 54-48715 (US Pat. No. 4,181,676). )] Tertiary aliphatic amine [Japanese Patent Laid-Open No. 51-1222025 (US Pat. No. 4,062,884)], thallium compound [Japanese Patent Laid-Open No. 54-48716 (US Pat. No. 4,307) , 032 specification)], tin alkoxides (Japanese Patent Laid-Open No. 54-63023), zinc, aluminum and titanium alkoxides (Japanese Patent Laid-Open No. 54-148726), a Lewis acid and a nitrogen-containing organic base. Composite catalyst (Japanese Patent Laid-Open No. 55-64550), phosphine compound (Japanese Patent Laid-Open No. 55-64551), quaternary phosphonium salt (Japanese Patent Laid-Open No. 56-10144) ), Cyclic amidine (JP 59-106436 A), zirconium, titanium and tin compounds [JP 63-41432 A (US Pat. No. 4,661,609)], quaternary ammonium group A solid strongly basic anion exchanger having a cation (JP-A 63-238043), an ion exchange resin having a tertiary amine or quaternary ammonium group, a strong acid or weak acid ion exchange resin, impregnated in silica Solid catalysts selected from alkali metal or alkaline earth metal silicates and ammonium-exchanged zeolite [JP-A-64-31737 (US Pat. No. 4,691,041)], tertiary phosphine, 3 Homogeneous catalyst selected from quaternary arsine, tertiary stibine, divalent sulfur or selenium compound (US Pat. No. 4,734,518) ) It has been proposed.
[0003]
As a reaction method, four methods have been proposed so far. These four reaction systems are used in the most typical reaction example, a method for producing dimethyl carbonate and ethylene glycol from ethylene carbonate and methanol.
[0004]
That is, the first method is a complete batch in which ethylene carbonate, methanol and a catalyst are charged into an autoclave, which is a batch type reaction vessel, and the reaction is performed by maintaining a predetermined reaction time under pressure at a reaction temperature equal to or higher than the boiling point of methanol. [US Pat. No. 3,642,858, JP-A-54-48715 (US Pat. No. 4,181,676), JP-A-54-63023, JP-A-54-148726, JP-A-55-64550, JP-A-55-6455, JP-A-56-10144].
[0005]
The second method uses an apparatus in which a distillation column is provided in the upper part of the reaction kettle. The reaction proceeds by charging ethylene carbonate, methanol and a catalyst into a reaction vessel and heating to a predetermined temperature. In this case, the produced dimethyl carbonate and methanol form the lowest azeotrope (boiling point 63 ° C./760 mmHg), so this azeotrope can be separated from methanol (boiling point 64.6 ° C./760 mmHg). In this system, a distillation column is provided to separate the azeotropic mixture and methanol. That is, dimethyl carbonate vapor and methanol vapor evaporated from the reaction kettle are separated into azeotropic mixture vapor and liquid methanol while ascending the distillation column, and the azeotrope vapor is distilled off from the top of the distillation column to form a liquid Methanol flows down and is returned to the reaction kettle for use in the reaction. In this method, methanol is added continuously or batchwise to the reaction kettle in order to supplement methanol distilled azeotropically with the produced dimethyl carbonate. In this method, the reaction is allowed to proceed only in a batch-type reaction vessel in which a catalyst, ethylene carbonate and methanol are present. Therefore, the reaction is batch-type, and the reaction is performed under reflux over a long time of 3 to 20 hours.
[0006]
In this system, dimethyl carbonate, which is one product, is continuously extracted out of the reaction system, but ethylene glycol, which is another product, is long in combination with unreacted ethylene carbonate in the presence of a catalyst. It will stay for hours. In order to suppress the side reaction due to the long-term residence between ethylene glycol and ethylene carbonate and to prevent the decrease in selectivity, it is necessary to use a large excess of methanol with respect to ethylene carbonate charged batchwise in the reaction kettle. In fact, according to the methods proposed so far, 14 moles (US Pat. No. 3,803,201), 17 moles (Japanese Patent Laid-Open No. 1-311054) per mole of ethylene carbonate (or propylene carbonate) ), 22 mol [Japanese Patent Laid-Open No. 51-1222025 (US Pat. No. 4,062,884)], 23 mol [Japanese Patent Laid-Open No. 54-48716 (US Pat. No. 4,307,032) Note)] Much excess of methanol is used.
[0007]
In the third method, a mixed solution of ethylene carbonate and methanol is continuously supplied to a tubular reactor maintained at a predetermined reaction temperature, and unreacted ethylene carbonate, methanol, and dimethyl as a product are supplied from the other outlet. This is a continuous reaction system in which a reaction mixture containing carbonate and ethylene glycol is continuously extracted in a liquid state. There are two methods depending on the type of catalyst used. That is, a homogeneous catalyst is used to pass through a tubular reactor together with a mixed solution of ethylene carbonate and methanol, and after the reaction, the catalyst is separated from the reaction mixture [Japanese Patent Laid-Open No. 63-41432 (US Pat. No. 4,661,609), US Pat. No. 4,734,518] and a method using a heterogeneous catalyst fixed in a tubular reactor [JP 63-238043, JP 64-31737 (U.S. Pat. No. 4,691,041)].
[0008]
Since the reaction of producing dimethyl carbonate and ethylene glycol by the reaction of ethylene carbonate and methanol is an equilibrium reaction, in the continuous flow reaction method using this tubular reactor, the reaction rate of ethylene carbonate is determined by the charged composition ratio and the reaction temperature. It is impossible to increase beyond the equilibrium reaction rate. For example, according to Example 1 of JP-A-63-41432 (US Pat. No. 4,661,609), at 130 ° C. using a raw material having a feed molar ratio of methanol / ethylene carbonate = 4/1. In the flow reaction, the reaction rate of ethylene carbonate is 25%. This means that it is necessary to separate and recover a large amount of unreacted ethylene carbonate and methanol remaining in the reaction mixture and to recirculate them to the reactor. In the method of the publication (US Pat. No. 4,691,041), many facilities are used for separation, purification, recovery, and recirculation.
[0009]
The fourth method is a reactive distillation method, that is, ethylene carbonate and methanol are continuously fed into a multistage distillation column, and the reaction is carried out in the presence of a catalyst in a plurality of stages of the distillation column and at the same time, dimethyl which is a product. Continuous production method for separating carbonate and ethylene glycol [JP-A-4-198141, JP-A-4-230243, JP-A-5-213830 (German Patent 4129316), JP-A-6-9507 Publication (German Patent No. 4216121)].
[0010]
Thus, the methods proposed so far for producing dialkyl carbonates and diols from cyclic carbonates and aliphatic monoalcohols are:
(1) Complete batch reaction system
(2) Batch reaction method using a reaction kettle with a distillation column at the top
(3) Liquid flow reaction method using a tubular reactor
(4) Reactive distillation system
However, there are problems as described below.
[0011]
That is, in the case of (1) and (3), the upper limit of the reaction rate of the cyclic carbonate is determined from the charged composition and temperature, and thus the reaction cannot be completely terminated.
When the reaction rate of the cyclic carbonate is less than 100%, the cyclic carbonate and the diol coexist in the reaction solution. In order to obtain a diol from this reaction solution, a distillation separation method is usually used. For example, when producing dimethyl carbonate and ethylene glycol from ethylene carbonate and methanol, an azeotrope is not formed if the pressure is 72 torr or higher, so separation of ethylene carbonate and ethylene glycol is possible only by distillation separation. If the distillation temperature is too high, ethylene glycol will accelerate the decomposition of ethylene carbonate and usually must be distilled off under reduced pressure to form an azeotrope (McKetta, “Encyclopedia of Chemical Processing and Design”). vol. 20, p. 194, Marcel Dekker, 1984).
[0012]
Therefore, it is difficult to quantitatively obtain the raw material ethylene carbonate and the product ethylene glycol from the reaction mixture. Therefore, conventionally, a method for obtaining ethylene glycol from this azeotropic mixture has been proposed. For example, in the method described in Example 50 of JP-A No. 64-31737, a low-boiling fraction composed of methanol and dimethyl carbonate is obtained by distilling a reaction vessel distillate in a distillation column (B), and ethylene glycol. And a bottom liquid containing ethylene carbonate, and this bottom liquid is distilled in a distillation column (D) to separate into a bottom liquid composed of ethylene carbonate and an azeotropic mixture composed of ethylene glycol / ethylene carbonate. . Furthermore, the tower bottom liquid composed of ethylene carbonate is circulated again to the reaction vessel, and the diol is obtained by hydrolyzing the ethylene glycol / ethylene carbonate azeotrope and converting the cyclic carbonate to diol. However, this method has a problem that the reaction rate is low and the amount of ethylene carbonate circulated is large.
[0013]
In the case of (2), in order to increase the reaction rate of the cyclic carbonate, the dialkyl carbonate to be produced must be distilled off using an extremely large amount of aliphatic monoalcohol, which requires a long reaction time. And
In the case of (4), the reaction can proceed at a higher reaction rate than in (1), (2), and (3). In fact, an example of an ethylene carbonate reaction rate of 100% is also described. ing. However, there are no known examples of obtaining dialkyl carbonates or diols in high yield without using pure aliphatic monoalcohols.
[0014]
On the other hand, dimethyl carbonate produced by the method (4) distills together with unreacted methanol as a low-boiling component. Since dimethyl carbonate and methanol form an azeotrope, a special separation method such as distillation under pressure (Japanese Patent Laid-Open No. 51-108019) is used to obtain dimethyl carbonate from the distillate. ing. Usually, although this separation method yields dimethyl carbonate containing no methanol, it is difficult to obtain pure methanol substantially free of dimethyl carbonate because methanol is obtained as a mixture with dimethyl carbonate. For example, in the example of JP-A-51-108019, a methanol / dimethyl carbonate mixture (weight concentration ratio: 70/30) is distilled and separated to obtain pure dimethyl carbonate as a column bottom component. Only a methanol / dimethyl carbonate mixture (weight concentration ratio: 95/5) was obtained as the top fraction.
[0015]
Thus, since an extra separation step is required to obtain a pure aliphatic monoalcohol, this methanol / dimethyl carbonate mixture can be used as an industrial dimethyl carbonate production method instead of pure methanol. Is highly desirable.
However, few examples are known in which the methanol / dimethyl carbonate mixture is used as a raw material in the method (4). The only exception is Example 5 of JP-A-5-213830, but using an aliphatic monoalcohol / dialkyl carbonate mixture (weight concentration ratio = 70/30), an ethylene carbonate conversion of 62.8% was obtained. (Conversion was calculated from the bottom composition).
[0016]
Therefore, in order to substantially completely convert the cyclic carbonate in the method (4), not only a dialkyl carbonate / aliphatic monoalcohol mixture but also a pure one is used as disclosed in JP-A-6-9507. It was also necessary to supply an aliphatic monoalcohol.
However, for this purpose, a complicated process for separating methanol / dimethyl carbonate azeotrope to obtain methanol substantially free of dimethyl carbonate (for example, a method of combining two distillation columns having different operating pressures: -212456) is required separately. In fact, JP-A-6-9507 uses a pure aliphatic monoalcohol obtained by this method.
[0017]
Thus, using a mixture of an aliphatic monoalcohol and a dialkyl carbonate without using a pure aliphatic monoalcohol, the cyclic carbonate is converted at a high conversion rate, and the dialkyl carbonate and the diol are obtained at a high yield and high selectivity. Until now, no method has been proposed for the continuous production of such products.
[0018]
[Problems to be solved by the invention]
The present invention is free from the disadvantages of such previously proposed methods and uses a mixture of an aliphatic monoalcohol and a dialkyl carbonate without the use of a pure aliphatic monoalcohol. It is an object of the present invention to provide a method for continuously producing diols with high reaction rate, high yield and high selectivity.
[0019]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have conducted continuous production of dialkyl carbonates and diols by satisfying certain conditions, so that the reaction can be performed at a high reaction rate that could not be obtained by conventional methods. Based on this finding, the present invention has been completed.
[0020]
  That is, the present inventionThe concentration of dialkyl carbonate is 0.5 to 40% by weightBy continuously supplying a first raw material consisting of a dialkyl carbonate and an aliphatic monoalcohol and a second raw material consisting of a cyclic carbonate into a continuous multistage distillation column and contacting with the catalyst present in the distillation column. At the same time as performing the reaction, low-boiling components containing dialkyl carbonate to be producedBy distillationThe upper part of the distillation column is continuously withdrawn as an extract from the upper part of the tower, and the lower part of the tower containing the produced diol is continuously withdrawn from the lower part of the tower.Use reactive distillationWhen continuously producing dialkyl carbonate and diol,
[0021]
(1) The dialkyl carbonate is a dialkyl carbonate that forms a minimum azeotrope with the aliphatic monoalcohol,
(2) Between the inlet of the first raw material and the bottom of the tower4 stepsProvide the above distillation stage,
(3) r defined next is 1.2 or more
  p = weight concentration of aliphatic monoalcohol in the first raw material / weight concentration of dialkyl carbonate in the first raw material
  q = weight concentration of aliphatic monoalcohol in the bottom liquid / weight concentration of dialkyl carbonate in the bottom liquid
  r = q / p
What to do in
(4) using a mixture of an aliphatic monoalcohol and a dialkyl carbonate without using a pure aliphatic monoalcohol,
(5) The bottom liquid or the first raw material is heated by the reboiler provided at the bottom of the tower, or the stage liquid phase is heated by the reboiler provided at the stage between the inlet of the first raw material and the bottom of the tower. The liquid phase in the stage between the inlet and the bottom of the column is heated to generate steam, and gas-liquid contact, that is, distillation, is performed between the flowing liquid phase and the concentration of the dialkyl carbonate in the liquid phase. To the desired r,
(6) performing a reflux operation for returning a part of the low-boiling components continuously extracted from the upper portion of the distillation column to the upper portion of the distillation column,
A continuous production method of a dialkyl carbonate and a diol characterized by the above.
[0022]
The method of the present invention is capable of allowing the reaction to proceed at a high reaction rate as compared with the conventional method, for example, a method of supplying a mixture of an aliphatic monoalcohol and a dialkyl carbonate to the bottom of a continuous multistage distillation column. This is probably due to the following reasons.
The reaction of the present invention is a reversible equilibrium reaction represented by the following general formula (1) in which a dialkyl carbonate (C) and a diol (D) are produced from a cyclic carbonate (A) and an aliphatic monoalcohol (B). .
[0023]
[Chemical 1]

[Where R¹ Is a divalent group — (CH₂ )_m-(M is an integer of 2-6), and one or more hydrogen atoms thereof may be substituted with an alkyl group or aryl group having 1-10 carbon atoms. R² Represents a monovalent aliphatic group having 1 to 12 carbon atoms, and one or more hydrogen atoms thereof may be substituted with an alkyl group or aryl group having 1 to 10 carbon atoms. ]
[0024]
In order to increase the reaction rate of this reaction, it is necessary to reduce the concentration of dialkyl carbonate and / or diol as reaction products as much as possible. The product dialkyl carbonate is removed by distillation and the concentration is lowered.
However, when a mixture of an aliphatic monoalcohol and a dialkyl carbonate is used without using pure methanol, the dialkyl carbonate is always supplied, so that the concentration of the dialkyl carbonate in the liquid phase flowing down in the continuous distillation column. There is a limit to lowering the reaction rate, so the reaction rate could not be increased.
[0025]
For example, in Example 5 of JP-A-5-213830, ethylene carbonate is supplied to the upper part of a tower having a height of 250 cm, and a methanol / dimethyl carbonate mixture (weight concentration ratio = 70/30) is gaseous in the lower part of the tower. Supply. As a result, the conversion rate of ethylene carbonate (calculated from the composition of the bottom composition) was 62.8%. In Example 2 of the same publication using pure methanol without using a mixture of an aliphatic monoalcohol and a dialkyl carbonate, an ethylene carbonate conversion rate of 98.4% is obtained, whereas an extremely low conversion rate is obtained. This is presumably because the reaction does not proceed any further because the concentration of dimethyl carbonate at the bottom of the column is not sufficiently reduced. In fact, the methanol concentration in the bottom product is 22.8% by weight and the dimethyl carbonate concentration is 9.1% by weight, so the methanol / dimethyl carbonate weight concentration ratio of the liquid phase at the bottom of the column is 71/29. I understand. This is almost the same composition as the methanol / dimethyl carbonate mixture (weight concentration ratio = 70/30) supplied to the lower part of the tower.
[0026]
On the other hand, in the method of the present invention, when the first raw material comprising dialkyl carbonate and aliphatic monoalcohol is introduced into the continuous multistage distillation column, two or more stages are introduced between the inlet of the first raw material and the bottom of the column. A distillation stage is installed, and the ratio of the weight concentration of the aliphatic monoalcohol in the bottom liquid to the weight concentration of the dialkyl carbonate q (q = weight concentration of the aliphatic monoalcohol in the bottom liquid / dialkyl carbonate in the bottom liquid. Of the aliphatic monoalcohol in the introduced first raw material and the weight concentration of the dialkyl carbonate p (p = weight concentration of the aliphatic monoalcohol in the first raw material / in the first raw material) By making the value r (r = q / p) of the ratio of dialkyl carbonate (weight concentration) 1.2 or more, an aliphatic monoalcohol can be used without using a pure aliphatic monoalcohol. Using a mixture of dialkyl carbonate, it became possible to produce a dialkyl carbonate and a diol Moreover continuously high response rate, yield and high selectivity. This is something that cannot be predicted from the prior art.
[0027]
The reason why the method of the present invention has a high effect is not clear, but is considered as follows.
That is, the first raw material consisting of dialkyl carbonate and aliphatic monoalcohol supplied in gaseous form is distilled and separated while reacting with cyclic carbonate in the tower, and the vapor phase increases the dialkyl carbonate concentration above the inlet. To the top of the column while forming a minimum azeotrope of aliphatic monoalcohol / dialkyl carbonate. (At this time, if the boiling point of the vapor phase component is lower than the boiling point of the bottom liquid, the concentration of the dialkyl carbonate in the vapor phase may be higher than the lowest azeotrope composition at the operating pressure of the continuous distillation column.)
[0028]
Further, below the introduction port, the liquid phase flows down and dialkyl carbonate is also generated while increasing the concentration of the diol generated. In the present invention, the weight concentration ratio of aliphatic monoalcohol / dialkyl carbonate in the column bottom liquid ( The reaction is carried out while maintaining q) higher than the aliphatic monoalcohol / dialkyl carbonate weight concentration ratio (p) in the introduced first raw material. Therefore, the dimethyl carbonate concentration in the column bottom liquid is sufficiently lower than that of the first raw material, and the dialkyl carbonate in the vapor phase rising from the column bottom, which is in a gas-liquid equilibrium relationship with the column bottom liquid, is also sufficiently low. It is estimated that The vapor phase with a low dialkyl carbonate concentration rising from the bottom of the column is a gas-liquid contact with the flowing liquid phase, and the liquid phase dimethyl carbonate is efficiently transferred to the vapor phase when performing distillation separation, so that the liquid phase dialkyl carbonate is transferred. Since the concentration can be reduced toward the bottom of the column, it is considered that the conversion rate of the cyclic carbonate at the bottom of the column can be increased sufficiently if a sufficient distillation stage is present.
[0029]
On the other hand, when the aliphatic alcohol inlet is at the bottom of the column as conventionally done, the dialkyl carbonate concentration in the column bottom liquid hardly decreases because the above-mentioned distillation separation of the dialkyl carbonate does not occur. Therefore, when a mixture of an aliphatic monoalcohol and a dialkyl carbonate is introduced, the conversion rate of the cyclic carbonate cannot be increased.
[0030]
In Example 5 of JP-A-5-213830, the position where the mixture of methanol and dimethyl carbonate is introduced is 30 cm above the lower end of the 250 cm high tower. In this example, the bottom liquid by a reboiler or the like is used. Is not heated. That is, there is no bottom-to-top vapor flow that is essential for distillation, below the methanol / dimethyl carbonate feed position. Therefore, it cannot be expected to reduce the concentration of dimethyl carbonate in the flowing liquid phase.
[0031]
In fact, as indicated above, according to the example, the methanol / dimethyl carbonate weight concentration ratio in the bottom product is 71/29, which is almost the same as the supplied methanol / dimethyl carbonate weight concentration ratio. It is clear that the dimethyl carbonate concentration at the bottom of the column has not been reduced as in the present invention.
[0032]
The continuous multi-stage distillation column used in the present invention is a distillation column having a plurality of distillation stages with four or more distillation stages, and may be any type as long as continuous distillation is possible [ The stage referred to in the present invention is a theoretical stage, and in the case of a distillation column having no physical stage such as a packed column, H. E. T.A. P. A value obtained by dividing the filling height by (height per theoretical plate) is used as the number of plates. ]. Examples of such a continuous multi-stage distillation column include a tray column type using a tray such as a bubble tray, a perforated plate tray, a valve tray, and a countercurrent tray, a Raschig ring, a lessing ring, a pole ring, a Berle saddle, an interface. Any type that is normally used as a continuous multi-stage distillation column, such as a packed column type packed with various packings such as Rox Saddle, Dixon Packing, McMahon Packing, Helipak, Sulzer Packing, Mela Pack, etc. can do. Furthermore, a distillation column having both a shelf part and a part filled with packing is also preferably used. The first continuous multi-stage distillation column may be the above-mentioned distillation column alone, or a plurality of the distillation columns connected in series or in parallel may be used in combination. Furthermore, when a solid catalyst is used, a packed column type distillation column in which the solid catalyst is part or all of the packing is also preferably used.
[0033]
The cyclic carbonate used as the second raw material in the present invention is a compound represented by the above (A), and examples thereof include alkylene carbonates such as ethylene carbonate and propylene carbonate, and 1,3-dioxacyclohexa-2. -On, 1,3-dioxacyclohept-2-one and the like are preferably used, and ethylene carbonate and propylene carbonate are particularly preferably used from the viewpoint of availability.
[0034]
In addition, the aliphatic monoalcohol in the other first raw material is a compound represented by (B), which has a boiling point lower than that of the generated diol and forms the lowest azeotrope with the generated dialkyl carbonate. Any aliphatic monoalcohol can be used. For example, methanol is preferably used.
[0035]
In the present invention, the catalyst must be present in a continuous multistage distillation column. In the region where the catalyst is present, the reaction proceeds by bringing the cyclic carbonate and aliphatic monoalcohol into contact with each other, and at the same time, low boiling point production is achieved. A reactive distillation system is used in which the product is extracted from the top of the column by distillation.
[0036]
Any method may be used for allowing the catalyst to exist in the continuous multistage distillation column. For example, in the case of a homogeneous catalyst that dissolves in the reaction solution under the reaction conditions, In the case of a heterogeneous catalyst that does not dissolve in the reaction solution under the reaction conditions, it is possible to cause the catalyst to exist in the liquid phase in the distillation column. By arranging the catalyst, the catalyst can be present in the reaction system, or a method using these in combination.
[0037]
When the homogeneous catalyst is continuously supplied to the distillation column, it may be supplied simultaneously with the second raw material and / or the first raw material, or may be supplied to a position different from the raw material. Further, the catalyst may be supplied to any position as long as it has at least two theoretical plates from the tower bottom. However, since the reaction actually proceeds in the distillation column in a region below the catalyst supply position, it is preferable to supply the catalyst to a region between the top of the column and the raw material supply position. When a heterogeneous solid catalyst is used, the catalyst can be packed in a required amount in any position in the distillation column, and it is sufficient that the number of theoretical plates in the layer in which the catalyst exists is at least one. Preferably, there are two or more stages. It is also preferable to use a solid catalyst that also has an effect as a packing for a distillation column.
[0038]
Various catalysts known so far can be used as the catalyst used in the present invention. For example, alkali metals and alkaline earth metals such as lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium; alkali metal and alkaline earth metal hydrides, hydroxides, alkoxides, aryloxides Basic compounds such as amides and amidates; basic compounds such as alkali metal and alkaline earth metal carbonates, bicarbonates and organic acid salts; triethylamine, tributylamine, trihexylamine, benzyldiethylamine, etc. Tertiary amines of: N-alkylpyrrole, N-alkylindole, oxazole, N-alkylimidazole, N-alkylpyrazole, oxadiazole, pyridine, alkylpyridine, quinoline, alkylquinoline, isoquinoline, Nitrogen-containing heteroaromatic compounds such as rualkylisoquinoline, acridine, alkylacridine, phenanthroline, alkylphenanthroline, pyrimidine, alkylpyrimidine, pyrazine, alkylpyrazine, triazine, alkyltriazine; diazabicycloundecene (DBU), diazabicyclononene Cyclic amidines such as (DBN); thallium compounds such as thallium oxide, thallium halide, thallium hydroxide, thallium carbonate, thallium nitrate, thallium sulfate, organic acid salts of thallium; tributylmethoxytin, tributylethoxytin, dibutyldimethoxy Tin compounds such as tin, diethyldiethoxytin, dibutyldiethoxytin, dibutylphenoxytin, diphenylmethoxytin, dibutyltin acetate, tributyltin chloride, tin 2-ethylhexanoate; Zinc compounds such as toxizinc, diethoxyzinc, ethylenedioxyzinc and dibutoxyzinc; aluminum compounds such as aluminum trimethoxide, aluminum triisopropoxide and aluminum tributoxide; tetramethoxytitanium, tetraethoxytitanium and tetrabutoxytitanium , Titanium compounds such as dichlorodimethoxytitanium, tetraisopropoxytitanium, titanium acetate, titanium acetylacetonate; trimethylphosphine, triethylphosphine, tributylphosphine, triphenylphosphine, tributylmethylphosphonium halide, trioctylbutylphosphonium halide, triphenylmethyl Phosphorous compounds such as phosphonium halides; zirconium halide, zirconium acetylacetonate, zirconium Zirconium compounds such as mualkoxide and zirconium acetate; lead and lead-containing compounds such as PbO, PbO₂ , Pb_Three O_Four Lead oxides such as PbS, Pb₂S_Three, PbS₂ Lead sulfides such as Pb (OH)₂ , Pb_Three O₂ (OH)₂ , Pb₂ [PbO₂ (OH)₂ ], Pb₂ O (OH)₂ Lead hydroxides such as Na;₂ PbO₂ , K₂ PbO₂ NaHPbO₂ , KHPbO₂ Namariates such as Na;₂ PbO_Three , Na₂ H₂ PbO_Four , K₂ PbO_Three , K₂ [Pb (OH)₆ ], K_Four PbO_Four , Ca₂ PbO_Four , CaPbO_Three Lead salts such as PbCO_Three 2PbCO_Three ・ Pb (OH)₂ Lead carbonate and its basic salts such as Pb (OCH_Three )₂ , (CH_Three O) Pb (OPh), Pb (OPh)₂ Alkoxyleads, aryloxyleads such as Pb (OCOCH_Three )₂ , Pb (OCOCH_Three )_Four , Pb (OCOCH_Three )₂ ・ PbO ・ 3H₂ Lead salts of organic acids such as O and carbonates and basic salts thereof; Bu_Four Pb, Ph_Four Pb, Bu_Three PbCl, Ph_Three PbBr, Ph_Three Pb (or Ph₆ Pb₂ ), Bu_Three PbOH, Ph₂ Organic lead compounds such as PbO (Bu represents a butyl group, Ph represents a phenyl group); Pb-Na, Pb-Ca, Pb-Ba, Pb-Sn, Pb-Sb and other lead alloys; Lead minerals such as seneene ore, and hydrates of these lead compounds; anion exchange resins having tertiary amino groups, ion exchange resins having amide groups, sulfonic acid groups, carboxylic acid groups, phosphate groups Ion exchange resins having at least one of these exchange groups, ion exchangers such as solid strongly basic anion exchangers having a quaternary ammonium group as an exchange group; silica, silica-alumina, silica-magnesia, aluminosilicate, Solid inorganic compounds such as gallium silicate, various zeolites, various metal exchange zeolites, ammonium exchange zeolites, and the like are used. As the solid contact, a solid strongly basic anion exchanger having a quaternary ammonium group as an exchange group is particularly preferably used. Examples of such a solid contact include a strong quaternary ammonium group as an exchange group. Examples include basic anion exchange resins, cellulose strongly basic anion exchangers having quaternary ammonium groups as exchange groups, and inorganic carrier-supporting strong basic anion exchangers having quaternary ammonium groups as exchange groups.
[0039]
As the strongly basic anion exchange resin having a quaternary ammonium group as an exchange group, for example, a styrene strong basic anion exchange resin is preferably used. Styrenic strongly basic anion exchange resins are strongly basic anion exchange resins having a copolymer of styrene and divinylbenzene as a base and quaternary ammonium (type I or type II) as an exchange group. It is schematically shown by the general formula of
[0040]
[Chemical formula 2]

[0041]
In the above formula, X represents an anion, and usually X is F^-, Cl^-, Br^-, I^-, HCO_Three ^-, CO_Three ^-, CH_Three CO₂ ^-, HCO₂ ^-, IO_Three ^-, BrO_Three ^-, ClO_Three ^-At least one anion selected from the group consisting of^-, Br^-, HCO_Three ^-, CO_Three ^-At least one anion selected from among the above is used. As the structure of the resin matrix, either a gel type or a macroreticular type (MR type) can be used, but the MR type is particularly preferable because of high resistance to organic solvents.
[0042]
Examples of the cellulose strongly basic anion exchanger having a quaternary ammonium group as an exchange group include, for example, —OCH obtained by trialkylaminoethylation of a part or all of —OH groups of cellulose.₂ CH₂ NR_Three The cellulose which has the exchange group which is X is mentioned. However, R represents an alkyl group, and methyl, ethyl, propyl, butyl and the like are usually used, and methyl and ethyl are preferably used. X is as described above.
[0043]
The inorganic carrier-supporting strong basic anion exchanger having a quaternary ammonium group as an exchange group that can be used in the present invention is a quaternary ammonium by modifying a part or all of the surface hydroxyl groups -OH of the inorganic carrier. Group -O (CH₂ )_nNR_Three This means that X is introduced. However, R and X are as described above. n is usually an integer of 1-6, preferably n = 2. As the inorganic carrier, silica, alumina, silica alumina, titania, zeolite and the like can be used, preferably silica, alumina and silica alumina are used, and silica is particularly preferably used. Any method can be used as a method for modifying the surface hydroxyl group of the inorganic carrier. For example, an inorganic carrier and amino alcohol HO (CH₂ )_nNR₂ Is subjected to a dehydration reaction in the presence of a base catalyst and then reacted with an alkyl halide RX ′ (X ′ represents a halogen, and usually Cl, Br, I, etc. are used) O (CH₂ )_nNR_Three X ′ group. Furthermore, by performing anion exchange, a quaternary ammonium group having the desired anion X —O (CH₂ )_nNR_Three Let X be. When n = 2, the inorganic carrier is treated with N, N-dialkylaziridine to form N, N-dialkylaminoethoxylated —OCH.₂ CH₂ NR₂ And then converted to -O (CH₂ )_nNR_Three X group.
[0044]
A commercially available solid strong anion exchanger having a quaternary ammonium group as an exchange group can also be used. In that case, it can also be used as a catalyst after ion exchange with a desired anion species in advance as a pretreatment.
And a macro-reticular and gel-type organic polymer to which a heterocyclic group containing at least one nitrogen atom is bonded, or an inorganic carrier to which a heterocyclic group containing at least one nitrogen atom is bonded. A solid catalyst is also preferably used. Further, a solid catalyst in which part or all of these nitrogen-containing heterocyclic groups are quaternized is also used.
The amount of the catalyst used in the present invention varies depending on the type of catalyst used, but when the catalyst is continuously supplied to the reaction zone of the continuous multistage distillation column, it is based on the total weight of the first raw material and the second raw material. Expressed as a percentage, it is usually used at 0.0001-50% by weight. Moreover, when installing and using a solid catalyst in a continuous multistage distillation column, the catalyst amount of 0.01-75 volume% is preferably used with respect to the empty column volume of this distillation column.
[0045]
In carrying out the present invention, there is no particular limitation on the method for supplying the second raw material consisting of cyclic carbonate to the continuous multi-stage distillation column, and they are at least one stage, preferably two or more zones in the distillation tower. Any method may be used as long as it can be brought into contact with the catalyst. That is, the second raw material can be continuously supplied from a necessary number of inlets to the stage satisfying the above-mentioned conditions of the continuous multistage distillation column. In order to increase the amount of reaction in the distillation column, it is one of the preferable methods to supply it to the upper part of the distillation column. Further, the introduction position of the first raw material consisting of the dialkyl carbonate and the aliphatic monoalcohol, which is the other raw material, may vary depending on the composition of the aliphatic monoalcohol containing the dialkyl carbonate. There are usually two or more distillation stages, preferably four or more distillation stages.
[0046]
The first raw material and the second raw material are continuously supplied to the distillation column as a liquid, a gas, or a mixture of liquid and gas. In addition to supplying the raw material to the continuous multistage distillation column in this way, it is also a preferable method to supply the gaseous raw material intermittently or continuously from the lower part of the distillation column.
In the present invention, the ratio q of the weight concentration of the aliphatic monoalcohol in the bottom liquid and the weight concentration of the dialkyl carbonate q (q = weight concentration of the aliphatic monoalcohol in the bottom liquid / weight concentration of the dialkyl carbonate in the bottom liquid. ) And the ratio p of the weight concentration of the aliphatic monoalcohol in the introduced first raw material and the weight concentration of the dialkyl carbonate (p = weight concentration of the aliphatic monoalcohol in the first raw material / dialkyl carbonate in the first raw material) The higher the value r (r = q / p) of the ratio (weight concentration), the higher the conversion rate of the cyclic carbonate. However, if it is too high, the thermal energy required for heating increases. Therefore, r is usually 1.2 or more, preferably 1.3-1000, more preferably 1.5-200.
[0047]
Any method may be used to set r to a desired value. For example, (1) heating of the bottom liquid with a heater such as a reboiler provided at the bottom of the tower, (2) Heating of the stage liquid phase by a heater such as a reboiler provided at the stage between the inlet of the first raw material and the tower bottom, (3) to the stage between the inlet of the first raw material and the tower bottom or the tower bottom , Introduction of heated non-condensable inert gas, (4) solvent inert to reaction of hydrocarbon compound or the like to the stage between the inlet of the first raw material and the bottom of the tower or the bottom of the tower (for example, ether , Aliphatic hydrocarbons, aromatic hydrocarbons, halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons, etc.), (5) first raw material inlet and tower bottom Introducing a heated liquid of a solvent inert to the reaction [for example, the solvent exemplified in the above (4)], etc. By heating the liquid phase at the stage between the column bottom liquid or the inlet of the first raw material and the column bottom to generate steam, and causing gas-liquid contact, that is, distillation, between the flowing liquid phase A method of reducing the dialkyl carbonate concentration in the liquid phase to obtain a desired r can be mentioned, and a preferable method includes heating the column bottom liquid with a heater such as a reboiler provided at the column bottom.
[0048]
The concentration of the dialkyl carbonate in the first raw material used in the present invention is usually 0.1-50 wt%, preferably 0.5-40 wt%, more preferably 1-30 wt%, expressed as wt%. It is.
The second raw material may contain a product dialkyl carbonate or diol. The diol contained in the second raw material is usually 0.0001-80% by weight, preferably 0.001-80% by weight.
[0049]
The amount ratio of the aliphatic monoalcohol to the cyclic carbonate supplied to the continuous multistage distillation column may vary depending on the type and amount of the catalyst and the reaction conditions. It is preferable to supply the aliphatic monoalcohols in a molar ratio of 0.01 to 1000 times. In order to increase the reaction rate of the cyclic carbonate, it is preferable to supply the aliphatic monoalcohol in an excess amount of 2 moles or more, but if it is used too much, the apparatus needs to be enlarged. In this sense, particularly preferred is the case where 2 to 20 times the amount of aliphatic monoalcohol is used.
[0050]
In the present invention, the low-boiling component containing dialkyl carbonate produced in the continuous multistage distillation column is continuously extracted from the upper portion of the distillation column as a liquid extract, a gaseous state, or a column top extract composed of a mixture of liquid and gas. It is. The extracted product is a mixture of a dialkyl carbonate and an aliphatic monoalcohol, and may contain a small amount of a cyclic carbonate or a high-boiling product as a raw material. Further, since the generated dialkyl carbonate is extracted from the upper part of the tower, the dialkyl carbonate concentration in the liquid extracted from the upper part of the tower is higher than the dialkyl carbonate concentration in the introduced first raw material, but the boiling point is higher than that of the liquid extracted from the bottom of the tower. Any composition may be used as long as it is low.
[0051]
From the continuous multistage distillation column, an extraction port for extracting a low-boiling component containing dialkyl carbonate and aliphatic monoalcohol as an extract from the upper part of the column is provided between the second raw material supply position and the top of the column or a gaseous substance extraction port at the top of the column. Preferably, it is provided, and more preferably provided at the top of the column. A so-called reflux operation may be performed in which a part of the low-boiling components extracted in this manner is returned to the upper part of the distillation column. However, if the reflux ratio is increased too much, the necessary thermal energy increases, which is not preferable. Therefore, the reflux ratio is usually 0-10, preferably 0-5.
[0052]
The outlet of the bottom column extract containing the diol produced by the method of the present invention is provided at the bottom of the continuous multistage distillation column, particularly preferably at the bottom of the column.
In the present invention, the upper part of the continuous multistage distillation column refers to a range from the top of the distillation column to half the height of the column, including the top of the column. Further, the lower part refers to a range from the bottom of the distillation column to half the height of the column, and includes the bottom of the column.
In the present invention, the column bottom extract is a mixture continuously extracted in the liquid and / or gaseous form from the bottom of the continuous multistage distillation column, and contains a diol, an aliphatic monoalcohol, a dialkyl carbonate, and a small amount of cyclic carbonate. May be included. In the case of using a high boiling point catalyst that can be dissolved in the reaction solution under the reaction conditions, the catalyst is contained in the bottom extract.
[0053]
The falling liquid velocity and the rising vapor velocity in the continuous multistage distillation column vary depending on the type of the distillation column used and, depending on the type of packing when a packed column is used, but usually do not cause flooding or weeping. Implemented in a range.
[0054]
In the present invention, the reaction mainly takes place in the liquid phase in a continuous multistage distillation column in the presence of a catalyst. Therefore, the amount of reaction product produced usually depends on the amount of hold-up liquid in the distillation column. That is, in the case of using a distillation column having the same column height and the same column diameter, a distillation column having a large amount of hold-up liquid is preferable in the sense that the residence time of the reaction solution, that is, the reaction time can be made relatively long. However, when the amount of the hold-up solution is too large, the residence time becomes long, so that a side reaction proceeds or flooding is likely to occur. Accordingly, the amount of hold-up liquid in the continuous multistage distillation column used in the present invention may vary depending on the distillation conditions and the type of distillation column, but is expressed by the volume ratio of the amount of holdup liquid to the empty column volume of the continuous multistage distillation column. Usually, it is carried out at 0.005-0.75.
[0055]
In the present invention, the average residence time of the reaction liquid in the continuous multi-stage distillation column varies depending on the reaction conditions, the type of the continuous multi-stage distillation column and the internal structure (for example, the type of the shelf and the packing), but is usually 0. 0.001 to 50 hours, preferably 0.01 to 10 hours, more preferably 0.05 to 5 hours.
[0056]
The reaction temperature is the temperature in the continuous multistage distillation column, and varies depending on the type of raw material used and the reaction pressure, but is usually in the range of 0 to 350 ° C, preferably 20 to 200 ° C. In addition, the reaction pressure may be any of reduced pressure, normal pressure, and pressurized pressure as long as the aliphatic monoalcohol and dialkyl carbonate form the lowest azeotrope, and it depends on the type of raw material used. Expressed as pressure, usually 0.00001-100Kg / cm² , Preferably 0.0001-50Kg / cm² , More preferably 0.001-20 Kg / cm² Range.
An unreacted cyclic carbonate can be circulated to the continuous multistage distillation column by supplying a part of the bottom extract of the continuous multistage distillation column to the continuous multistage distillation column. At that time, the position of the inlet for supplying the extract from the lower part of the column to the continuous multistage distillation column is not particularly limited, but it is preferable to supply it to the upper part of the distillation column.
[0057]
In a particularly preferred embodiment of the present invention, ethylene carbonate is used as the second raw material, a mixture of methanol and dimethyl carbonate is used as the first raw material, and dimethyl carbonate, which is a corresponding dialkyl carbonate, and ethylene glycol are produced. . In this case, the second raw material having a high boiling point among the raw materials is continuously supplied in liquid form into the distillation tower from the inlet provided between the stage where the catalyst of the continuous multistage distillation tower is present and the top of the tower. The first raw material, which is a low boiling point raw material, is continuously supplied in the form of a gas into the distillation column. Then, dimethyl carbonate, which is a low-boiling product produced by the reaction, is continuously extracted from the top of the distillation tower together with unreacted methanol and dimethyl carbonate contained in the first raw material. Ethylene glycol, which is a high-boiling product, is continuously extracted in liquid form together with methanol and dimethyl carbonate from the bottom of a continuous multistage distillation column.
[0058]
In the present invention, it is not always necessary to use a solvent, but for the purpose of facilitating the reaction operation, a suitable inert solvent such as ethers, aliphatic hydrocarbons, aromatic hydrocarbons, halogenated compounds, etc. Aliphatic hydrocarbons, halogenated aromatic hydrocarbons and the like can be used as the reaction solvent.
In addition, an inert gas such as nitrogen, helium or argon may be present in the reaction system as a substance inert to the reaction, or the bottom of the continuous multistage distillation column for the purpose of accelerating the distillation of the low-boiling product to be produced. In addition, the above-described inert gas or a low-boiling organic compound that is inert to the reaction may be introduced in a gas.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to examples and the like, but the present invention is not limited to these examples and the like.
(Example 1)
Using the apparatus shown in FIG. 1, dimethyl carbonate (DMC) and ethylene glycol (EG) were continuously produced from ethylene carbonate (EC) and methanol (MeOH).
To the top 4 of the continuous multistage distillation column 1 consisting of a packed column having an inner diameter of 2.5 cm and a packing height of 250 cm, packed with Dixon packing (3φ) as a packing, ethylene carbonate as a second raw material and hydroxylated under atmospheric pressure A mixture of sodium (weight concentration ratio: ethylene carbonate / catalyst = 99.7 / 0.3) was continuously supplied in liquid form from the conduit 2 via the preheater 3. In addition, a mixture of methanol and dimethyl carbonate [weight concentration ratio (p) = methanol / dimethyl carbonate = 85/15 = 5.67] is provided as a first raw material at a position 100 cm from the bottom of the tower via the evaporator 6 ′. The gas was continuously supplied in the form of gas from the conduit 5 '. The continuous multistage distillation column was operated at atmospheric pressure.
[0060]
The gaseous component distilled from the top 4 was condensed in the condenser 7, a part of which was circulated, and the other was extracted in liquid form. A part of the tower bottom liquid extracted from the tower bottom 8 was heated by the reboiler 6 so that the methanol / dimethyl carbonate weight concentration ratio (q) in the tower bottom liquid was 21.5. r (r = q / p) was 3.80. A part of the circulating column bottom liquid was extracted from the conduit 9. Other reaction conditions and results after steady state are shown in Table 1. As a result, the conversion rate of ethylene carbonate was 99% or more, the yield of dimethyl carbonate was 99% or more (selectivity of dimethyl carbonate based on ethylene carbonate was 99% or more), and the yield of ethylene glycol was 99% or more (ethylene It shows that the ethylene glycol selectivity based on carbonate was 99% or more).
[0061]
(Comparative Example 1)
As shown in FIG. 2, the top 4 of the distillation column 1 is composed of a packed column packed with a Raschig ring (6 mmφ) as a packing and having an inner diameter of 3 cm, a packing height of 250 cm and isothermally controlled at 80 ° C. The mixture similar to the second raw material of Example 1 was continuously supplied in a liquid state from the conduit 2 through the preheater 3 to a position 10 cm below. Moreover, the mixture similar to the 1st raw material of Example 1 as a 1st raw material was continuously supplied in gaseous form from the conduit | pipe 5 'provided in the position of 30 cm from the tower bottom through the evaporator 6'. The continuous multistage distillation column was operated at atmospheric pressure.
[0062]
The gaseous component distilled from the top 4 was condensed by the condenser 7 and extracted in liquid form. Further, the column bottom liquid was extracted from the column bottom 8 through the conduit 9 without being heated. The methanol / dimethyl carbonate weight concentration ratio (q) in the extracted column bottom liquid was 5.89. r (r = q / p) was 1.04. Other reaction conditions and results after steady state are shown in Table 1. As a result, the conversion of ethylene carbonate was 84%, the yield of dimethyl carbonate was 82% (selectivity of dimethyl carbonate based on ethylene carbonate was 98%), and the yield of ethylene glycol was 82% (ethylene glycol based on ethylene carbonate). The selectivity is 98%).
[0063]
(Example 2)
The reaction was carried out in the same manner as in Example 1 except that sodium methoxide was used instead of sodium hydroxide as the catalyst and the methanol / dimethyl carbonate weight concentration ratio (q) in the column bottom liquid was maintained at 15.3. went. r (r = q / p) was 2.70. The reaction conditions and the results after steady state are shown in Table 1.
[0064]
(Example 3)
1,8-diazabicyclo (5,4,0) undecene-7 (DBU) was used as a catalyst instead of sodium hydroxide, and the methanol / dimethyl carbonate weight concentration ratio (q) in the column bottom liquid was kept at 8.05. The reaction was performed in the same manner as in Example 1 except that. The reaction conditions and the results after steady state are shown in Table 1.
[0065]
Example 4
A conduit 5 ′ is provided at a position 80 cm from the bottom of the tower, and a mixture of methanol and dimethyl carbonate (weight concentration ratio: methanol / dimethyl carbonate = 70/30 = 2.33) is used as the first raw material. The reaction was carried out in the same manner as in Example 1 except that the methanol / dimethyl carbonate weight concentration ratio (q) was maintained at 7.47. r (r = q / p) was 3.20. The reaction conditions and the results after steady state are shown in Table 2.
[0066]
  (Example 5)
  Sodium methoxide was used as the catalyst, and the methanol / dimethyl carbonate weight concentration ratio (q) in the tower bottom liquid was determined.3.55The reaction was carried out in the same manner as in Example 4 except that the reaction was carried out. r (r = q / p) was 1.52. The reaction conditions and the results after steady state are shown in Table 2.
[0067]
(Comparative Example 2)
Same as Comparative Example 1 except that the same mixture as the first raw material used in Example 4 was used as the first raw material, and the same mixture as the second raw material used in Example 4 was used as the second raw material. The reaction was carried out by the method. The methanol / dimethyl carbonate weight concentration ratio (q) in the column bottom liquid was 2.45. r (r = q / p) was 1.05. The other reaction conditions and the results after steady state are shown in Table 2.
[0068]
(Example 6)
Using the apparatus shown in FIG. 3, dimethyl carbonate and ethylene glycol were continuously produced from ethylene carbonate and methanol.
To the top of the continuous multi-stage distillation column 1 consisting of an old show type multi-stage distillation column having an opening ratio of 2% and a 40-stage sieve tray with a liquid depth of 5 mm and a column diameter of 50 mm and a column height of 160 cm, ethylene carbonate and water are used as the second raw materials. A mixture of sodium oxide (weight concentration ratio: ethylene carbonate / sodium hydroxide = 99.7 / 0.3) was continuously supplied in liquid form from the conduit 2 through the preheater 3. Further, a mixture of methanol and dimethyl carbonate [weight concentration ratio (p): methanol / dimethyl carbonate = 85/15 = 5.67] as the first raw material is positioned at the 10th stage from the tower bottom via the evaporator 6 ′. The gas was continuously supplied in the form of gas from a conduit provided in The continuous multistage distillation column was operated at atmospheric pressure.
[0069]
The gaseous component distilled from the top 4 was condensed by the condenser 7 and extracted in liquid form. A part of the column bottom liquid extracted from the column bottom 8 was heated by the reboiler 6 so that the methanol / dimethyl carbonate weight concentration ratio (q) in the column bottom liquid was maintained at 15.9. r (r = q / p) was 2.80. A part of the circulating column bottom liquid was extracted from the conduit 9. The other reaction conditions and the results after steady state are shown in Table 3.
[0070]
[Table 1]

[0071]
[Table 2]

[0072]
[Table 3]

[0073]
【The invention's effect】
By the method of the present invention, a dialkyl carbonate and a diol can be continuously produced with a high yield and a high selectivity by using a mixture of a dialkyl carbonate and an aliphatic monoalcohol, which are easily available industrially, and a cyclic carbonate. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an apparatus used in Example 1. FIG.
FIG. 2 is a schematic diagram of an apparatus used in Comparative Example 1. FIG.
FIG. 3 is a schematic diagram of an apparatus used in Example 6.
[Explanation of symbols]
1: Continuous multistage distillation column
3: Preheater
6: Reboiler
6 ': Evaporator
7: Condenser

Claims (2)

A first raw material consisting of a dialkyl carbonate having a concentration of dialkyl carbonate of 0.5 to 40% by weight and an aliphatic monoalcohol and a second raw material consisting of a cyclic carbonate are continuously fed into a continuous multistage distillation column, and the distillation at the same time carry out the reaction by contacting with a catalyst which is present in the column, continuously withdrawing a low boiling point component as a column top extracted product from the top of the distillation column by distillation containing the product dialkyl carbonates to produce a diol In the continuous production of dialkyl carbonate and diol by using a reactive distillation system in which the bottom extract containing the column is continuously extracted from the bottom of the column,
(1) The dialkyl carbonate is a dialkyl carbonate that forms a minimum azeotrope with the aliphatic monoalcohol,
(2) Four or more distillation stages are provided between the inlet of the first raw material and the tower bottom,
(3) r defined as follows is 1.2 or more p = weight concentration of aliphatic monoalcohol in the first raw material / weight concentration of dialkyl carbonate in the first raw material q = aliphatic monoalcohol in the bottom liquid Weight concentration / weight concentration of dialkyl carbonate in the bottom liquid r = q / p
What to do in
(4) using a mixture of an aliphatic monoalcohol and a dialkyl carbonate without using a pure aliphatic monoalcohol,
(5) The bottom liquid or the first raw material is heated by the reboiler provided at the bottom of the tower, or the stage liquid phase is heated by the reboiler provided at the stage between the inlet of the first raw material and the bottom of the tower. The liquid phase in the stage between the inlet and the bottom of the column is heated to generate steam, and gas-liquid contact, that is, distillation, is performed between the flowing liquid phase and the concentration of the dialkyl carbonate in the liquid phase. To the desired r,
(6) performing a reflux operation for returning a part of the low-boiling components continuously extracted from the upper portion of the distillation column to the upper portion of the distillation column,
A continuous process for producing a dialkyl carbonate and a diol. Aliphatic monoalcohol is methanol, continuous process for preparing dialkyl carbonate and diol 請 Motomeko 1 wherein the dialkyl carbonate is Ru dimethyl carbonate der.

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