JP2004230251A

JP2004230251A - Distillation process

Info

Publication number: JP2004230251A
Application number: JP2003020033A
Authority: JP
Inventors: Hideaki Ueoka; 秀晃植岡; Osamu Tabata; 修田端
Original assignee: Kao Corp
Current assignee: Kao Corp
Priority date: 2003-01-29
Filing date: 2003-01-29
Publication date: 2004-08-19
Anticipated expiration: 2023-01-29
Also published as: JP4112386B2; ZA200400680B; DE102004004530A1

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distillation process by which a product of a desired composition can be stably obtained without using a complicated analytical instrument and a complicated control system and by which control to keep an operating state stable is performed to widen operational condition and range. <P>SOLUTION: When a distillation column having constitution that, when a column intermediate section partitioned into two distillation sections is used and at least one or more kinds of products are obtained from the column intermediate section, distillation is performed while adjusting a falling liquid flow rate in either of the partitioned distillation sections to a set flow rate without depending on a total amount of condensate, or distillation is performed by adjusting the falling liquid flow rate in the partitioned distillation section by detecting temperature in at least either of the partitioned distillation sections, or distillation is performed by adjusting the falling liquid flow rate in either of the partitioned distillation sections to a set flow rate without depending on the total amount of condensate and further by adjusting the falling liquid flow rate in the partitioned distillation section by detecting temperature in at least either of the partitioned distillation sections. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、２成分以上の混合物から成る原料を、蒸留により分離・精製し、所望の組成の製品を得るための改良された蒸留方法に関する。詳しくは、塔中間部が２つの蒸留部に区分された構造を有する蒸留塔を用いて上記原料の分離・精製を行うにあたり、運転状態を安定に保つ制御を行うことにより、安定して所望の組成の製品を得ることができ、かつ運転可能な条件範囲を広くすることのできる蒸留方法に関する。
【０００２】
【従来の技術】
混合品からなる原料を、蒸留により不要な成分をトップカット（低沸点成分の低減処理）あるいはボトムカット（高沸点成分の低減処理）により除去する、また所望の組成に分離・精製することは公知の技術である。一般に蒸留による分離・精製においては、ｎ個の成分を全て分離するために少なくとも（ｎ−１）本の蒸留塔が必要と考えられている。同時に装置内で加熱・冷却を繰り返す蒸留設備は、さまざまな単位操作の中でもエネルギー多消費型のプロセスである。これらのことから、蒸留プロセスの設備費やエネルギー消費量を低減するための技術開発が継続的に進められている。
【０００３】
例えば、設備費を小さくするために、１本の蒸留塔で同時に複数の製品が得られるよう、塔頂部や塔底部以外に塔中間部からも留出液を取り出すサイドカット塔等が用いられている。又、設備費を小さくするとともに、分離性能を高めかつ供給熱量の低減を図るために、蒸留塔内部に垂直分割板を設けたり、同心円柱構造物を挿入し、塔中間部の蒸留部が分割された構造を有するものが提案されている。
【０００４】
前者のサイドカット塔では、１本の蒸留塔で複数の製品が得られることから、蒸留塔の総数ならびにリボイラー、コンデンサーの総数を減らすことが可能である。しかし、基本的にサイドカット塔では、分離に必要と考えられる理論段数を縦方向に積み上げた構造となるため、機能の集約によりその塔高は大幅に大きくなる。また、サイドカット塔の場合、塔内部の原料供給段より上方には必ず原料成分のうち最も低沸成分の分布ができることから、塔頂と原料供給段の間に位置する留出口では、得られる製品への該低沸成分の混入防止には限界がある。同様の理由から、原料供給段より下方には必ず原料成分のうち最も高沸成分の分布ができることから、塔底と原料供給段の間に位置する留出口では、得られる製品への該高沸成分の混入防止には限界があるのが実状である。
【０００５】
後者の蒸留塔は一般的にはペトリューク式蒸留塔の具現化構造として知られている。例えば特許文献１及び特許文献２にこのような構造を有する蒸留塔についての記載がされている。これら文献記載の発明においては、蒸留塔内部に垂直分割板を設け、内部を２つ以上の蒸留部に分割した構造が提案されており、この構造による分離性能の向上ができることが記載されている。
【０００６】
このような構造を有する蒸留塔の運転を考えた場合、分割された各蒸留部に上部から降下させる液量、あるいは下部から上昇させる蒸気量を、供給される原料組成や製造する製品組成に応じて最適量となるよう設定する必要がある。また、安定運転を可能ならしめるための制御方法も必要となる。しかし、これらの課題に対して上記文献では、塔内部での降下液の分配あるいは上昇蒸気の分配について、さらに運転制御方法については記載されておらず、分割型構造を有する蒸留塔の運転方法としては満足の得られるものではない。
【０００７】
このような問題を解決するため、塔内分割板を有する蒸留塔の改善された運転方法が、特許文献３、特許文献４、特許文献５、特許文献６及び特許文献７に記載されている。
【０００８】
特許文献３には、垂直分割板で仕切られた２つの蒸留部に対して塔内降下液を分配する際に、分割上部に設置された液コレクターに一旦降下液を集め、この降下液の組成分析結果から一方の空間への降下液量を決定するといった、塔内降下液の組成を一定に維持する方法が記載されている。この際に降下液の組成分析は例えばオンライン形式のガスクロマトグラフィ等で実施される。他方の蒸留部への降下液量については、該液コレクターに液面レベル計が設置され、コレクター液面が常に一定となるように降下液量が調整される。
【０００９】
前記方法においては、一方の蒸留部への降下液量を決定する際にオンライン形式での組成分析を行っているが、サンプリングから分析結果が得られるまでに要する時間が長くなり、効果的な流量調整が困難になり、かえって塔内降下液の組成を乱すことが予想される。また、設備化を想定した場合においても、高価な分析機器が必要であり、分析結果からのバルブ開度調整といった複雑な制御システムを必要とする。さらに、塔内に液面レベル計を有する液コレクターが必要となるため、蒸留塔そのものの構造が大型化する可能性が考えられる。
【００１０】
又、特許文献４、特許文献５及び特許文献７には、上記に示される降下液の分配に対して、分割上部に降下液を分配させるための液ディストリビューターが設置され、予め設定された分配比となるようその孔数等が決められている。あるいは、降下液量が設定された分配比となるよう、分割板の挿入位置を塔内部で偏心させた構造を採用している。この方法によると、分割上部のコレクターで集められた降下液は、該液ディストリビューターにより、あるいは分割された空間の開口部面積に応じて常に一定の比率で分配される。これらの方法により、高価な分析機器や複雑な制御システムを用いることなく設備化が可能になると考えられる。また、液コレクター部に液面レベル計を設置する必要もないため、蒸留塔が大型化することも避けることが可能となる。また、分割部における降下液の分配を上記液ディストリビューターで調整するかわりに、降下液量を流量計等により調整して、その分配比を調整・制御する方法が特許文献６に記載されている。
【００１１】
これら文献の記載は、いずれも分割部における降下液の分配を分配比で調整・制御する方法である。このように降下液の分配を分配比で制御した場合、例えば運転中の組成変動といった外乱の影響により全降下液量が変動した場合に、それぞれの降下液流量ともに変動することになる。降下液量を流量計等により調整して、その分配比を調整する場合においても、いったん計測した流量値から分配比を計算し、さらに分配比補正のために各流量を調整しなければならないので、制御の時間遅れがかえって運転の安定化を妨げる可能性が考えられる。
【００１２】
また、塔内に分割板を有する蒸留塔は、その構造として多孔板トレイ、泡鐘式トレイ等の棚段、ラシヒリング、ポールリング等の不規則充填物、また金属板型、金網型の規則充填物のいずれを使用しても実施可能であるが、これらいずれの形態を実施する場合においても、降下液量についての制約がある。つまり、いずれの形態を実施するに対しても、その性能を発揮するための必要最小流量を確保しなければならない。例えば不規則充填物や規則充填物では、充填物の表面が降下液によって十分に濡れていないとその性能は発揮されず、所望の分離効率を得ることができない。これに対して、降下液の分配を分配比で制御した場合、先に示した外乱等の要因により、降下液流量が変動し、分離性能を満足するための必要最小流量を満足できない可能性が考えられる。とくに分割板を有する蒸留塔の場合、分割された一方の蒸留部から製品を留出させるため、製品留出側の蒸留部には少なくとも留出量に相当する量の降下液を確保する必要があり、運転条件によっては原料供給側の蒸留部への降下液量が小さくなり、原料供給側での必要最小流量を満足できない場合が考えられる。また、蒸留収率の著しく高い運転を行おうとした場合には、製品留出側の蒸留部のうち、留出部の下部に位置する棚段あるいは充填層への降下液量が極端に小さくなり、この部分での必要最小流量を満足できない場合が考えられる。即ち、これらの方法を用いた場合には、必要最小流量による運転条件の制約と、分配比との組合せから、運転条件範囲が狭くなることになる。
【００１３】
これらの現象を回避するためには、予め全降下液量が過剰になるよう、ボトムからのリボイラー加熱量を大きく設定すれば良いが、これは省エネルギーの観点から有利な方法ではない。
【００１４】
【特許文献１】
米国特許第２４７１１３４号明細書
【特許文献２】
特開昭５９−１４２８０１号公報
【特許文献３】
米国特許第４２３０５３３号明細書
【特許文献４】
特開平９−２９９７０１号公報
【特許文献５】
特開平１１−３１４００３号公報
【特許文献６】
特開２０００−１４０５０１号公報
【特許文献７】
特開２００１−７９３０２号公報
【００１５】
【発明が解決しようとする課題】
本発明の課題は、塔中間部が２つの蒸留部に区分された構造を有する蒸留塔を用い、２成分以上の混合物から成る原料を、分離・精製する方法において、複雑な分析機器や制御システムを使用することなく、安定して所望の組成の製品を得ることのできる蒸留方法、かつ運転状態を安定に保つ制御を行い、運転可能な条件範囲を広くすることのできる蒸留方法を提供することである。
【００１６】
【課題を解決するための手段】
本発明は、以下の（１）、（２）及び（３）に示す蒸留方法を提供する。
（１）塔中間部が２つの蒸留部に区分された構造を有する蒸留塔を用い、塔中間部より少なくとも１種類以上の製品を得るにあたり、何れか一方の区分された蒸留部の降下液流量を全凝縮液量によらず設定流量に調整しつつ蒸留を行うことを特徴とする蒸留方法。
（２）塔中間部が２つの蒸留部に区分された構造を有する蒸留塔を用い、塔中間部より少なくとも１種類以上の製品を得るにあたり、少なくとも何れか一方の区分された蒸留部の温度を検知することによって、区分された蒸留部の降下液流量を調整して蒸留を行うことを特徴とする蒸留方法。
（３）塔中間部が２つの蒸留部に区分された構造を有する蒸留塔を用い、塔中間部より少なくとも１種類以上の製品を得るにあたり、何れか一方の区分された蒸留部の降下液流量を全凝縮液量によらず設定流量に調整すると共に、少なくとも何れか一方の区分された蒸留部の温度を検知することによって、区分された蒸留部の降下液流量を調整して蒸留を行うことを特徴とする蒸留方法。
【００１７】
【発明の実施の形態】
［蒸留塔］
本発明において使用される蒸留塔は、塔中間部が２つの蒸留部に区分された構造を有する。蒸留部の区分は分割板や内部管を挿入すること等が簡便で一般的である。以下、分割板を用いた場合で説明する。
【００１８】
図１に本発明に用いられる蒸留塔の一例を示す。この蒸留塔１の塔中間部３は、分割板５により、２つの蒸留部６，６’に区分され、塔上部２及び塔下部４については分割板５が塔中間部３のみに設置されるため、通常の塔の構造と同じである。塔内の気液接触部の構造については、多孔板トレイ、泡鐘式トレイ等の棚段、ラシヒリング、ポールリング等の不規則充填物、また金属板型、金網型の規則充填物の使用等、いずれにおいても実施可能である。中でも、段効率に優れ、液ホールドアップが小さく、かつ圧力損失が小さいという点から、規則充填物を用いるのが好ましい。
【００１９】
蒸留原料は、分割された一方の蒸留部６に供給される。原料供給側の蒸留部６においては、原料供給口７の上下両側に棚段、充填層があっても、また上下どちらか一方にのみ棚段、充填層があってもよい。
【００２０】
塔頂及び塔中間部には製品留出口８，９、塔底には缶出液抜出口１０が設けられる。塔中間部に設けられる留出口９は、分割された他方（原料供給側とは反対）の蒸留部６’に設けられるが、留出口の数は１つ又は２つ以上あっても良い。
【００２１】
図２に本発明に用いられる蒸留塔の別の例を示す。この蒸留塔では、原料供給側とは反対側の製品留出口９の他に、原料供給側にも製品留出口９’を設けており、この製品留出口９’は複数設けても良い。
【００２２】
図１及び図２の蒸留塔において、塔頂の留出口８からの留出物は蒸気のまま塔外へ排出し、コンデンサー（凝縮器）にて冷却後、一部を製品として取出し、一部を還流として塔頂に返しても、あるいは塔頂に設けた内部コンデンサーで凝縮液すべてを内部で還流して、一部を留出液として取り出しても良い。
【００２３】
塔底の加熱部においては、リボイラーとして自然循環式（サーモサイフォン型）、液を循環させる強制循環型、蒸気のみを返すケトル型等を用いてもよい。中でも、塔底製品の熱履歴による品質劣化を防ぐという点から、流下薄膜式のものが好ましい。
【００２４】
［蒸留制御方法］
本発明の第一の態様においては、塔中間部の２つの蒸留部に降下される降下液のうちどちらか一方について、その流量が、全凝縮液量によらず設定流量に調整される。流量を調整する方法は、例えば、図３に示すように、塔中間部の上部に設けた液コレクター１１より塔中間部の２つの蒸留部６，６’に降下液ライン１２，１２’を設け、さらに一方のライン１２’に流量計１３及び流量調整弁１４を設ける。他方のライン１２については流量調整弁を設けず、液コレクター１１への降下液量と流量調整される側の降下液量の差分だけバランスした流量を降下させる。ここで、１５はディストリビューターである。
【００２５】
また、別の流量調整方法として、図４に示すように、塔中間部の上部に設けた液コレクター１１より、全ての降下液を塔外部に設置された受器１６に送り、この受器１６からポンプ１７により塔中間部の２つの蒸留部６，６’へ降下液を送ってもよい。この場合、一方のライン１２には流量計１３及び流量調整弁１４が、他方のライン１２’には流量計を設ける必要はないが、受器１６の液面レベルを調整する流量調整弁１４’を設けることが好ましい。ここで１８は液面計である。
【００２６】
流量調整を行う降下液流は、２つの蒸留部のうちの一方だけであり、原料供給側の蒸留部への降下液流か、あるいは製品留出側の蒸留部への降下液流かは、原料組成、製品組成また運転条件によって選択可能である。例えば、原料供給側の蒸留部への降下液量が小さい運転を行う場合は、原料供給側蒸留部への降下液量を調整、制御し、該蒸留部への必要降下液量を安定に確保させる。また、高収率運転を行う場合は、製品留出側蒸留部への降下液量を調整、制御し、該蒸留部への必要降下液量を安定に確保させる。
【００２７】
さらに、分割板を有する蒸留塔の運転においては、分割板を境にした２つの蒸留部のそれぞれの組成分布を精密に制御する必要がある。例えば、原料中に含まれる成分のうち、その沸点が中程度の成分について、製品中への混入組成を制御する方法として、（Ａ）原料供給側蒸留部から蒸気の形態で分割板上部を越え、凝縮後に製品留出側蒸留部へ流入する量を制御する方法と、（Ｂ）原料供給側蒸留部から蒸気の形態で分割板下部を通り製品留出側蒸留部を上昇する蒸気を制御する方法が考えられる。前者による組成調整を行う場合は、原料供給側蒸留部への降下液量制御が有効である。一方、後者の場合は、製品留出側蒸留部への降下液量制御が有効となる。
【００２８】
これら流量調整される一方の降下液量は、原料組成また製品組成に応じて、運転に必要なリボイラー加熱量とあわせ決定される。
【００２９】
このように、塔中間部の２つの蒸留部の降下液のうち一方の流量を運転条件に応じて一定に調整することにより、運転中に起こりうる各種の外乱の発生に対しても、各蒸留部への必要降下液量を安定に確保し、かつ所望の製品組成を安定に得ることができる。
【００３０】
また、本発明の第二の態様においては、塔中間部の２つの蒸留部のうち、少なくとも何れか一方の蒸留部の温度を検知することによって、区分された蒸留部の降下液流量が調整される。この方法は、蒸留塔の連続運転中に原料組成が大きく変動した場合などに特に好適である。
【００３１】
例えば、原料供給側蒸留部の温度が原料組成の変動により適正値よりも高くなった場合は、該蒸留部への降下液量不足による充填層の性能低下や、高沸成分が上昇し、分割板上部から製品留出側蒸留部へ流入する恐れがある。この為、該蒸留部の温度が適正値となるよう、原料供給側蒸留部への降下液量の微調整を行う。同様にして、製品留出側蒸留部の温度が原料組成の変動により適正値よりも高くなった場合は、該蒸留部への降下液量不足による充填層の性能低下や、塔下部から高沸成分が上昇し、製品へ高沸成分が流入する恐れがある。この為、該蒸留部の温度が適正値となるよう、製品留出側蒸留部への降下液量の微調整を行う。
【００３２】
また、他の好ましい形態として、製品組成の変化を蒸留塔内部の温度から速やかに検知し、所望の製品組成になるよう蒸留塔塔頂部での全凝縮液量の微調整を行うことが挙げられる。ここで蒸留塔塔頂部の全凝縮液とは、塔頂まで上昇した蒸気が塔頂に設置される内部あるいは外部コンデンサーにて冷却、凝縮したもの（原料成分の一部）を示す。
【００３３】
その他、本発明の別の態様は、上記第一、第二の態様を適宜、併用するものである。例えば、原料供給側蒸留部への降下液量を制御している場合、製品留出側蒸留部の温度が原料組成の変動により適正値よりも高くなった場合は、製品留出側蒸留部への降下液量不足による充填層の性能低下や、塔下部から製品留出側蒸留部への高沸成分の上昇による製品への流入が考えられる。このような現象に対して、製品留出側蒸留部の温度が適正値となるよう、蒸留塔塔頂部の全凝縮液量の微調整を行う。同様にして、製品留出側蒸留部への降下液量を制御している場合、原料供給側蒸留部の温度が原料組成の変動により適正値よりも高くなった場合は、原料供給側蒸留部への降下液量不足による充填層の性能低下や、高沸成分の上昇による分割板上部から製品留出側蒸留部への流入が考えられる。このような現象に対して、原料供給側蒸留部の温度が適正値となるよう、蒸留塔塔頂部の全凝縮液量の微調整を行う。
【００３４】
なお蒸留塔塔頂部の全凝縮液量の調整については、リボイラー加熱量を調整することにより実施すればよい。
【００３５】
［原料］
本発明による蒸留方法では、分離・精製する原料として特に限定されることはなく、例えばメタノール，エタノール，ブタノール，エチレングリコール，グリセリン等のアルコール類、蟻酸，酢酸，プロピオン酸等のカルボン酸類、酢酸メチル，酢酸エチル，プロピオン酸エチル等のエステル類、ペンタン，ヘキサン，オクタン等の炭化水素類の分離に対して実施可能である。また、一般に高真空の条件を必要とする高沸点物の分離に対しても有効であり、例えばラウリン酸，ステアリン酸等の脂肪酸類、ラウリン酸メチル，ラウリン酸エチル，ステアリン酸メチル等の脂肪酸エステル類、あるいはラウリルアルコール，ステアリルアルコール等の高級アルコール類から成る混合原料に対しても実施可能である。さらには香料，潤滑油，燃料油等の有機化合物の分離に対しても実施可能である。
【００３６】
【実施例】
以下に示す実施例及び比較例はシミュレーションにより実施した結果である。ここで、シミュレーターはＰＲＯＩＩ（ＳＩＭＳＣＩ社製）を使用した。また原料は、低沸不純物ａ、主成分ｂ〜ｅ及び高沸不純物ｆの混合物を用い、これらの各成分の蒸気圧は、下記に示すＡｎｔｏｉｎｅ式により表現され、非理想性を示す指標として、２成分系活量係数式であるＷｉｌｓｏｎ式を用いた。なお、シミュレーションに使用した各成分のＡｎｔｏｉｎｅ定数Ａ〜Ｃを表１に、Ｗｉｌｓｏｎ式の２成分パラメータを表２に、潜熱及び比熱データを表３に示す。
【００３７】
【数１】

【００３８】
【表１】

【００３９】
【表２】

【００４０】
【表３】

【００４１】
実施例１
塔頂より低沸不純物、塔底より高沸不純物を除去し、塔中間部より２つの留分（留分２及び３という）を留出させることにより、原料の分離・精製を実施する。
【００４２】
蒸留塔として図５に示す分割板５による分割型蒸留塔を使用し、また塔中間部上部からの２つの降下液のうち、原料供給側蒸留部６の降下液量を一定となるよう調整を行う。さらに、原料供給側蒸留部６の濃縮部の温度から、原料供給側蒸留部６の降下液量が調整できるよう温度制御を行う。蒸留塔のリボイラー加熱量、原料供給側蒸留部６の降下液量及び温度測定部での制御目標温度は、所望の製品組成と製品収率が得られるよう、表６の状態１に示すように予め決定する。
【００４３】
本運転条件において、表４に示す組成の原料を供給する場合、表７の状態１に示すように高純度の製品が得られる。さらに、表５に示す組成からなる原料に切換え、連続運転を継続する。この時、原料供給側蒸留部６の降下液量を塔内温度制御を行わず、当初設定する降下液量で運転を継続する場合（表６の状態２）に得られる留分２の組成を表７の状態２に示す。原料組成の大幅な変化により、当初設定する運転条件のままでは製品の純度が低下する。
【００４４】
これに対し、原料供給側蒸留部６の濃縮部の温度が、予め設定された目標値となるよう、原料供給側蒸留部６の降下液量の制御を行う。同時に、原料供給側蒸留部６の降下液量の変化量と同量だけ、塔頂凝縮液量の調整を行う（表６の状態３）。原料供給側蒸留部６の降下液量の調整により、原料供給側蒸留部６の濃縮部の温度は当初設定する温度に戻り、その結果得られる留分２の組成を表７の状態３に示す。本制御方法により、製品純度は元のレベルに改善される。
【００４５】
これは、原料組成変動により、原料供給側蒸留部６の上部から分割板５を超えて製品留出側蒸留部６’に流入する主成分ｄが増加することに対し、原料供給側蒸留部６の濃縮部の温度の上昇からこれを検知し、原料供給側蒸留部６の降下液量を増加させ、主成分ｄの流入を防止する効果による。
【００４６】
【表４】

【００４７】
【表５】

【００４８】
【表６】

【００４９】
【表７】

【００５０】
実施例２
塔頂より低沸不純物、塔底より高沸不純物を除去し、塔中間部より２つの留分（留分２及び３という）を留出させることにより、原料の分離・精製を実施する。
【００５１】
蒸留塔として図５に示す分割板５による分割型蒸留塔を使用し、また塔中間部上部からの２つの降下液のうち、製品留出側蒸留部６’の降下液量を一定となるよう調整を行う。さらに、原料供給側蒸留部６の濃縮部の温度から、塔頂での全凝縮液量が調整できるよう温度制御を行う。蒸留塔のリボイラー加熱量、製品留出側蒸留部６’の降下液量及び温度測定部での制御目標温度は、所望の製品組成と製品収率が得られるよう、表８の状態１に示すように予め決定する。
【００５２】
本運転条件において、表４に示す組成の原料を供給する場合、表９の状態１に示すように高純度の製品が得られる。さらに、表５に示す組成からなる原料に切換え、連続運転を継続する。この時、塔頂の全凝縮液量の塔内温度による制御を行わず、当初設定する塔頂全凝縮液量で運転を継続する場合（表８の状態２）に得られる留分２の組成を表９の状態２に示す。原料組成の変化により、当初設定する運転条件のままでは製品の純度が低下する。
【００５３】
これに対し、原料供給側蒸留部６の濃縮部の温度が、予め設定された目標値となるよう、塔頂での全凝縮液量の制御を行う。ここで、塔頂の全凝縮液量の調整は、リボイラー加熱量の調整を行うことにより行う（表８の状態３）。塔頂の全凝縮液量の調整により、原料供給側蒸留部６の濃縮部の温度は当初設定する温度に戻り、その結果得られる留分２の組成を表９の状態３に示す。本制御方法により、製品純度は元のレベルに改善される。
【００５４】
これは、原料組成変動により、原料供給側蒸留部６の上部から分割板５を超えて製品留出側蒸留部６’に流入する主成分ｄが増加することに対し、原料供給側蒸留部６の濃縮部の温度の上昇からこれを検知し、塔頂の全凝縮液量を増加させることで原料供給側蒸留部６への降下液量を増加させ、主成分ｄの流入を防止する効果による。
【００５５】
【表８】

【００５６】
【表９】

【００５７】
比較例１
塔中間部の２つの蒸留部の降下液量の設定を、分配比が一定となるよう調整し、その他は実施例２と同じ条件として原料の分離・精製を実施する。分割された２つの蒸留部への降下液分配比は、（原料供給側降下液量）：（製品留出側降下液量）で示し、所望の製品組成と製品収率が得られるようリボイラー加熱量、温度測定部での制御目標温度とあわせて、表１０の状態１に示すように予め決定する。
【００５８】
本条件において、表４に示す組成の原料を供給する場合、留分２の組成において不純物混入量の変動は認められるものの表１１の状態１に示す運転結果が得られる。さらに、表５に示す組成からなる原料に切換え、連続運転を継続する。この時、原料供給側蒸留部６の降下液量の塔内温度による制御を行わず、当初設定する降下液量で運転を継続する場合（表１０の状態２）に得られる留分２の組成を表１１の状態２に示す。原料組成の変化により、当初設定する運転条件のままでは製品の純度が低下する。
【００５９】
これに対し、原料供給側蒸留部６の濃縮部の温度が、予め設定された目標値となるよう、塔頂での全凝縮液量の制御を行う。ここで、塔頂の全凝縮液量の調整は、リボイラー加熱量の調整を行うことにより行う。なおこの時、２つの蒸留部における降下液量については当初設定する分配比が一定となるよう制御を継続する（表１０の状態３）。塔頂の全凝縮液量の調整にもかかわらず、原料供給側蒸留部６の濃縮部の温度は当初設定する温度に戻ることなく、留分２の組成は表１１の状態３に示すように改善されない。
【００６０】
これは、原料組成変動により、原料供給側蒸留部６の上部から分割板５を超えて製品留出側蒸留部６’に流入する主成分ｄが増加することに対し、２つの蒸留部での降下液分配比を一定にするままで、塔頂の全凝縮液量を増加すなわちリボイラー加熱量を調整するために、原料供給側、製品留出側蒸留部ともに同じ割合で上昇蒸気と降下液が変化し、両蒸留部ともに塔内組成分布を有効に調整できないことによる。
【００６１】
【表１０】

【００６２】
【表１１】

【００６３】
【発明の効果】
本発明の蒸留方法により、従来型の蒸留塔と比較して分離性に優れかつ省エネルギー型である内部分割型蒸留塔において、より安定した品質の製品を得ることができる。
【図面の簡単な説明】
【図１】本発明に用いられる蒸留塔の一例を示す略示断面図である。
【図２】本発明に用いられる蒸留塔の別の例を示す略示断面図である。
【図３】本発明の流量調整方法の一例を示す図である。
【図４】本発明の流量調整方法の別の例を示す図である。
【図５】実施例及び比較例で用いた蒸留塔の略示断面図である。
【符号の説明】
１蒸留塔
２塔上部
３塔中間部
４塔下部
５分割板
６原料供給側の蒸留部
６’ 製品留出側の蒸留部
７原料供給口
８塔頂の製品留出口
９塔中間部の製品留出口
９’ 原料供給側の製品留出口
１０缶出液抜出口
１１液コレクター
１２，１２’ 降下液ライン
１３流量計１３
１４，１４’ 流量調整弁
１５ディストリビューター
１６受器
１７ポンプ
１８液面計[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improved distillation method for separating and purifying a raw material composed of a mixture of two or more components by distillation to obtain a product having a desired composition. Specifically, in performing the separation and purification of the above-mentioned raw materials using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, by controlling the operation state to be stable, it is possible to stably perform a desired operation. The present invention relates to a distillation method capable of obtaining a product having a composition and expanding a range of operable conditions.
[0002]
[Prior art]
It is known that the raw material composed of a mixed product is removed by distillation to remove unnecessary components by top-cut (reduction processing of low-boiling components) or bottom-cut (reduction processing of high-boiling components) and to separate and purify it into a desired composition. Technology. Generally, in separation / purification by distillation, it is considered that at least (n-1) distillation columns are required to separate all n components. Distillation equipment that repeats heating and cooling in the apparatus at the same time is an energy-consuming process among various unit operations. For these reasons, technology development for reducing the equipment cost and energy consumption of the distillation process has been continuously promoted.
[0003]
For example, in order to reduce equipment costs, a side-cut column or the like is used to extract a distillate from a column middle portion in addition to a column top or a column bottom so that a plurality of products can be obtained simultaneously in one distillation column. I have. Also, in order to reduce the equipment cost, increase the separation performance and reduce the amount of heat supplied, install a vertical dividing plate inside the distillation column or insert a concentric cylindrical structure, and the distillation section in the middle of the column is divided. One having a structure described is proposed.
[0004]
In the former side-cut column, since a plurality of products can be obtained with one distillation column, it is possible to reduce the total number of distillation columns and the total number of reboilers and condensers. However, the side-cut column basically has a structure in which the number of theoretical plates considered necessary for separation are stacked in the vertical direction, and the height of the column is greatly increased due to the aggregation of functions. In the case of a side-cut column, since the lowest-boiling component among the raw material components can always be distributed above the raw material supply stage inside the column, it can be obtained at the distillate located between the top and the raw material supply stage. There is a limit in preventing the low-boiling components from being mixed into the product. For the same reason, the distribution of the highest boiling component among the raw material components is always formed below the raw material supply stage. Therefore, at the distillate located between the bottom and the raw material supply stage, the high boiling The reality is that there is a limit to the prevention of mixing of components.
[0005]
The latter distillation column is generally known as a structure embodying a Petrik-type distillation column. For example, Patent Literature 1 and Patent Literature 2 describe a distillation column having such a structure. In the inventions described in these documents, a structure in which a vertical dividing plate is provided inside the distillation column and the inside is divided into two or more distillation sections has been proposed, and it is described that the separation performance can be improved by this structure. .
[0006]
When considering the operation of a distillation column having such a structure, the amount of liquid to be dropped from the upper part or the amount of vapor to be raised from the lower part in each divided distillation part depends on the composition of the supplied raw material and the product to be manufactured. It is necessary to set the optimum amount. Also, a control method for enabling stable operation is required. However, with respect to these problems, the above-mentioned literature does not disclose the distribution of descending liquid or the distribution of ascending vapor inside the column, and further does not describe an operation control method. Is not satisfactory.
[0007]
In order to solve such a problem, improved operating methods of a distillation column having an in-column divider are described in Patent Documents 3, Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7.
[0008]
Patent Literature 3 discloses that when distributing the descending liquid in a column to two distillation sections separated by a vertical dividing plate, the descending liquid is once collected in a liquid collector provided at the upper part of the division, and the composition of the descending liquid is collected. A method is described in which the composition of the liquid falling in the tower is kept constant, such as determining the amount of liquid falling into one space from the analysis results. At this time, the composition analysis of the descending liquid is performed by, for example, online gas chromatography. With respect to the amount of liquid falling to the other distillation section, a liquid level meter is installed in the liquid collector, and the amount of liquid falling is adjusted so that the liquid level of the collector is always constant.
[0009]
In the above method, when determining the amount of liquid falling to one distillation section, the composition analysis is performed in an on-line format, but the time required from the sampling to the analysis result is increased, and the effective flow rate is increased. It is expected that the adjustment will become difficult and the composition of the liquid falling in the column will be disturbed. In addition, even when equipment is assumed, expensive analysis equipment is required, and a complicated control system such as adjusting the valve opening based on the analysis result is required. Further, since a liquid collector having a liquid level meter is required in the column, the structure of the distillation column itself may be increased in size.
[0010]
In Patent Document 4, Patent Document 5, and Patent Document 7, a liquid distributor for distributing the descending liquid is provided at the upper part of the division for the above-described distribution of the descending liquid, and a predetermined distribution is set. The number of holes and the like are determined so as to obtain a ratio. Alternatively, a structure is adopted in which the insertion position of the dividing plate is eccentric within the tower so that the liquid descending amount has a set distribution ratio. According to this method, the descending liquid collected by the collector at the upper part of the division is always distributed at a constant ratio by the liquid distributor or according to the opening area of the divided space. It is considered that these methods can be installed without using expensive analytical instruments and complicated control systems. Further, since it is not necessary to install a liquid level meter in the liquid collector, it is possible to avoid an increase in the size of the distillation column. Patent Literature 6 describes a method for adjusting and controlling a distribution ratio of a descending liquid in a dividing section by adjusting the amount of descending liquid with a flow meter or the like instead of adjusting the distribution of the descending liquid by the liquid distributor. .
[0011]
Each of these documents describes a method of adjusting and controlling the distribution of the descending liquid in the dividing section by the distribution ratio. When the distribution of the descending liquid is controlled by the distribution ratio as described above, for example, when the total descending liquid amount fluctuates due to the influence of a disturbance such as a composition fluctuation during operation, the respective descending liquid flow rates also fluctuate. Even when adjusting the distribution ratio by adjusting the descending liquid volume with a flow meter or the like, the distribution ratio must be calculated from the flow rate value once measured, and each flow rate must be adjusted to correct the distribution ratio. However, there is a possibility that the control delay may hinder the stabilization of operation.
[0012]
Distillation columns having split plates in the column are structured such as trays such as perforated plate trays and bubble-bell trays, irregular packing such as Raschig rings and pole rings, and metal plates and wire mesh type. It is possible to use any of these products, but there is a restriction on the amount of liquid fall in any of these embodiments. In other words, the minimum flow rate required to exhibit the performance of any of the embodiments must be ensured. For example, in the case of the irregular packing or the structured packing, if the surface of the packing is not sufficiently wetted by the liquid descending, the performance is not exhibited, and a desired separation efficiency cannot be obtained. On the other hand, if the distribution of the descending liquid is controlled by the distribution ratio, the flow rate of the descending liquid may fluctuate due to the above-mentioned disturbances and the like, and the possibility that the required minimum flow rate for satisfying the separation performance may not be satisfied. Conceivable. In particular, in the case of a distillation column having a dividing plate, in order to distill the product from one of the divided distillation sections, it is necessary to secure at least an amount of liquid descending in the distillation section on the product distilling side corresponding to the amount of distilling. In some cases, depending on the operating conditions, the amount of liquid falling to the distillation section on the raw material supply side becomes small, and the required minimum flow rate on the raw material supply side may not be satisfied. In addition, when an attempt is made to operate at an extremely high distillation yield, the amount of liquid falling to the tray or packed bed located below the distilling section of the distilling section on the product distilling side becomes extremely small. However, the required minimum flow rate in this part may not be satisfied. That is, when these methods are used, the operating condition range becomes narrow due to the combination of the restriction on the operating condition by the necessary minimum flow rate and the distribution ratio.
[0013]
In order to avoid these phenomena, the reboiler heating amount from the bottom may be set large so that the total liquid descending amount becomes excessive in advance, but this is not an advantageous method from the viewpoint of energy saving.
[0014]
[Patent Document 1]
U.S. Pat. No. 2,471,134
[Patent Document 2]
JP-A-59-142801
[Patent Document 3]
U.S. Pat. No. 4,230,533
[Patent Document 4]
JP-A-9-299701
[Patent Document 5]
JP-A-11-314003
[Patent Document 6]
JP-A-2000-140501
[Patent Document 7]
JP 2001-79302 A
[0015]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for separating and purifying a raw material composed of a mixture of two or more components by using a distillation column having a structure in which a column intermediate portion is divided into two distillation portions, and a complicated analytical instrument and control system. To provide a distillation method capable of stably obtaining a product of a desired composition without using the same, and a distillation method capable of controlling the operation state to be stable and widening the operable condition range. It is.
[0016]
[Means for Solving the Problems]
The present invention provides the following distillation methods (1), (2) and (3).
(1) Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, and obtaining at least one or more products from the middle section of the column, the flow rate of the descending liquid in one of the divided distillation sections. Distillation while adjusting the flow rate to a set flow rate regardless of the total amount of condensate.
(2) Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, in order to obtain at least one or more products from the middle section of the tower, the temperature of at least one of the divided distillation sections is adjusted. A distillation method, wherein the distillation is performed by adjusting the flow rate of the descending liquid in the divided distillation sections by detecting.
(3) Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, and obtaining at least one or more products from the middle section of the tower, the flow rate of the descending liquid in one of the divided distillation sections. Is adjusted to a set flow rate irrespective of the total condensate amount, and by detecting the temperature of at least one of the divided distillation sections, the flow rate of the descending liquid in the divided distillation section is adjusted to perform distillation. A distillation method characterized by the above-mentioned.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
[Distillation tower]
The distillation column used in the present invention has a structure in which the middle section of the column is divided into two distillation sections. For the division of the distillation section, it is convenient and common to insert a dividing plate or an internal tube. Hereinafter, the case where the dividing plate is used will be described.
[0018]
FIG. 1 shows an example of a distillation column used in the present invention. The middle section 3 of the distillation tower 1 is divided into two

distillation sections

6 and 6 ′ by a dividing plate 5, and the dividing plate 5 is installed only in the middle section 3 of the upper section 2 and the lower section 4. Therefore, it has the same structure as a normal tower. Regarding the structure of the gas-liquid contact part in the tower, use irregular trays such as trays such as perforated plate trays and bubble-bell trays, Raschig rings, pole rings, etc., as well as metal plates and wire mesh type regular packing. , And can be implemented in any of them. Among them, it is preferable to use the structured packing because of its excellent step efficiency, small liquid hold-up, and small pressure loss.
[0019]
The distillation raw material is supplied to one of the divided distillation units 6. In the distillation section 6 on the raw material supply side, there may be a shelf and a packed layer on both upper and lower sides of the raw material supply port 7, or a shelf and a packed layer only on one of the upper and lower sides.
[0020]

Product distilling outlets

8 and 9 are provided at the top and middle of the tower, and a bottom discharge outlet 10 is provided at the bottom of the tower. The distilling outlet 9 provided in the middle part of the column is provided in the other (different from the raw material supply side) distillation unit 6 ', but the number of distilling outlets may be one or two or more.
[0021]
FIG. 2 shows another example of the distillation column used in the present invention. In this distillation column, in addition to the product outlet 9 on the side opposite to the material supply side, a product outlet 9 ′ is provided on the material supply side, and a plurality of product outlets 9 ′ may be provided.
[0022]
In the distillation columns shown in FIGS. 1 and 2, the distillate from the outlet 8 at the top of the column is discharged as vapor to the outside of the column, and after cooling with a condenser (condenser), a part is taken out as a product. May be returned to the top of the column as reflux, or all of the condensate may be internally refluxed by an internal condenser provided at the top of the column and a part thereof may be taken out as a distillate.
[0023]
In the heating section at the bottom of the tower, a natural circulation type (thermosiphon type), a forced circulation type for circulating liquid, a kettle type for returning only steam, or the like may be used as a reboiler. Among them, a falling film type is preferred from the viewpoint of preventing quality deterioration due to heat history of the bottom product.
[0024]
[Distillation control method]
In the first aspect of the present invention, the flow rate of one of the descending liquids dropped to the two distillation sections in the middle part of the column is adjusted to the set flow rate regardless of the total condensate amount. As a method of adjusting the flow rate, for example, as shown in FIG. 3, liquid descending lines 12, 12 'are provided in two distillation sections 6, 6' in the middle of the column from a liquid collector 11 provided in the upper part of the middle of the column. Further, a flow meter 13 and a flow control valve 14 are provided on one line 12 ′. The other line 12 is not provided with a flow rate control valve, and the flow rate balanced by the difference between the flow rate of the liquid to the liquid collector 11 and the flow rate of the flow rate-controlled side is lowered. Here, 15 is a distributor.
[0025]
As another flow rate adjusting method, as shown in FIG. 4, all the descending liquid is sent from a liquid collector 11 provided at the upper part of the middle part of the tower to a receiver 16 installed outside the tower. May be sent from the pump 17 to the two distillation sections 6, 6 'in the middle section of the column by the pump 17. In this case, it is not necessary to provide a flow meter 13 and a flow control valve 14 on one line 12 and a flow meter on the other line 12 ′, but a flow control valve 14 ′ for adjusting the liquid level of the receiver 16. Is preferably provided. Here, reference numeral 18 denotes a liquid level gauge.
[0026]
The descending liquid flow for adjusting the flow rate is only one of the two distillation sections, and whether the descending liquid flow to the distillation section on the raw material supply side or the descending liquid flow to the distillation section on the product distilling side, It can be selected according to the raw material composition, product composition and operating conditions. For example, when performing an operation in which the amount of liquid descending to the distillation section on the raw material supply side is small, the amount of liquid descending to the distillation section on the raw material supply side is adjusted and controlled to stably secure the required amount of liquid descending to the distillation section. Let it. When a high-yield operation is performed, the amount of liquid falling to the distillation section on the product distilling side is adjusted and controlled to stably secure the required amount of liquid falling to the distillation section.
[0027]
Furthermore, in the operation of a distillation column having a dividing plate, it is necessary to precisely control the respective composition distributions of the two distillation sections bordering the dividing plate. For example, among the components contained in the raw material, for a component having a medium boiling point, as a method of controlling the composition mixed in the product, (A) the raw material supply side distillation section is passed over the upper part of the dividing plate in the form of steam in the form of steam. And (B) controlling the amount of vapor flowing from the raw material supply side distillation section through the lower portion of the dividing plate in the form of vapor from the raw material supply side distillation section to the product distillation side distillation section. There is a method. In the case of adjusting the composition by the former, it is effective to control the amount of the liquid descending to the distillation section on the raw material supply side. On the other hand, in the latter case, the control of the amount of liquid falling to the distillation section on the product distilling side is effective.
[0028]
The amount of one of the descending liquids whose flow rate is adjusted is determined according to the raw material composition or the product composition together with the reboiler heating amount required for operation.
[0029]
In this way, by adjusting the flow rate of one of the descending liquids of the two distillation sections in the middle part of the column to a constant value in accordance with the operating conditions, each distillation can be performed even when various disturbances that may occur during the operation are generated. It is possible to stably secure the required amount of liquid drop to the part and obtain a desired product composition stably.
[0030]
In the second aspect of the present invention, the flow rate of the descending liquid in the divided distillation sections is adjusted by detecting the temperature of at least one of the two distillation sections in the middle section of the column. You. This method is particularly suitable when the raw material composition fluctuates greatly during continuous operation of the distillation column.
[0031]
For example, when the temperature of the distillation section on the raw material supply side becomes higher than an appropriate value due to the fluctuation of the raw material composition, the performance of the packed bed deteriorates due to the insufficient amount of liquid falling into the distillation section, and the high boiling component increases, and There is a possibility that it will flow into the distillation section on the product distillate side from the top of the plate. For this reason, fine adjustment of the amount of liquid falling to the raw material supply side distillation section is performed so that the temperature of the distillation section becomes an appropriate value. Similarly, if the temperature of the distillation section on the product distillate becomes higher than an appropriate value due to the fluctuation of the raw material composition, the performance of the packed bed may be degraded due to insufficient amount of liquid falling into the distillation section, or high boiling may occur from the bottom of the column. Ingredients may rise and high boiling components may flow into the product. For this reason, the amount of the liquid descending to the product distillation side distillation section is finely adjusted so that the temperature of the distillation section becomes an appropriate value.
[0032]
Further, as another preferred embodiment, a change in the product composition is quickly detected from the temperature inside the distillation column, and fine adjustment of the total condensate amount at the top of the distillation column is performed so as to obtain a desired product composition. . Here, the total condensate at the top of the distillation column refers to a vapor that has risen to the top of the distillation column and is cooled and condensed by an internal or external condenser installed at the top (a part of the raw material components).
[0033]
In another aspect of the present invention, the above first and second aspects are appropriately used in combination. For example, when controlling the amount of liquid descending to the distillation section on the raw material supply side, when the temperature of the distillation section on the product distillation side becomes higher than an appropriate value due to fluctuation of the raw material composition, the distillation section on the product distillation side is controlled. It is conceivable that the performance of the packed bed deteriorates due to insufficient amount of the liquid falling down, or the high-boiling component flows into the product from the bottom of the column to the distillation section on the product distillate side. With respect to such a phenomenon, fine adjustment of the total amount of condensate at the top of the distillation column is performed so that the temperature of the distillation section on the product distillation side becomes an appropriate value. Similarly, when the amount of liquid falling to the product distillation side distillation section is controlled, and when the temperature of the raw material supply side distillation section becomes higher than an appropriate value due to the fluctuation of the raw material composition, the raw material supply side distillation section It is conceivable that the performance of the packed bed deteriorates due to the insufficient amount of liquid falling into the tank, and the inflow from the upper part of the dividing plate into the distillation section on the product distilling side due to the rise of high boiling components. With respect to such a phenomenon, the total amount of condensate at the top of the distillation column is finely adjusted so that the temperature of the distillation section on the raw material supply side becomes an appropriate value.
[0034]
The total amount of condensate at the top of the distillation column may be adjusted by adjusting the heating amount of the reboiler.
[0035]
[material]
In the distillation method according to the present invention, raw materials to be separated / purified are not particularly limited, and for example, alcohols such as methanol, ethanol, butanol, ethylene glycol and glycerin, carboxylic acids such as formic acid, acetic acid and propionic acid, and methyl acetate , Ethyl acetate, ethyl propionate and the like, and hydrocarbons such as pentane, hexane and octane. It is also generally effective for separating high-boiling substances requiring high vacuum conditions. For example, fatty acids such as lauric acid and stearic acid, and fatty acid esters such as methyl laurate, ethyl laurate and methyl stearate. Or a mixed raw material comprising higher alcohols such as lauryl alcohol and stearyl alcohol. Further, the present invention can be applied to separation of organic compounds such as fragrances, lubricating oils, and fuel oils.
[0036]
【Example】
The following examples and comparative examples are the results of simulations. Here, PRO II (manufactured by SIMSCI) was used as the simulator. In addition, the raw material uses a mixture of the low boiling impurities a, the main components b to e, and the high boiling impurities f, and the vapor pressure of each of these components is expressed by the following Antoine equation, and as an index indicating non-ideality, The Wilson equation, which is a two-component activity coefficient equation, was used. Table 1 shows the Antoine constants A to C of the components used in the simulation, Table 2 shows the two-component parameters of the Wilson equation, and Table 3 shows the latent heat and specific heat data.
[0037]
(Equation 1)

[0038]
[Table 1]

[0039]
[Table 2]

[0040]
[Table 3]

[0041]
Example 1
The low-boiling impurities are removed from the top of the column and the high-boiling impurities are removed from the bottom of the column, and two fractions (fractions 2 and 3) are distilled from the middle part of the column to separate and purify the raw materials.
[0042]
As the distillation column, a division type distillation column with a dividing plate 5 shown in FIG. 5 is used, and adjustment is made so that the amount of the descending liquid in the raw material supply side distillation section 6 among the two descending liquids from the upper part of the column becomes constant. Do. Further, temperature control is performed such that the amount of liquid falling in the raw material supply side distillation section 6 can be adjusted from the temperature of the enrichment section in the raw material supply side distillation section 6. The heating amount of the reboiler in the distillation column, the amount of liquid descending in the raw material supply side distillation section 6 and the control target temperature in the temperature measurement section are set as shown in State 1 in Table 6 so that a desired product composition and product yield can be obtained. Determine in advance.
[0043]
Under the present operating conditions, when a raw material having a composition shown in Table 4 is supplied, a high-purity product is obtained as shown in State 1 in Table 7. Further, the raw material having the composition shown in Table 5 is switched to continue the continuous operation. At this time, the composition of the distillate 2 obtained when the operation is continued at the initially set descending liquid amount (state 2 in Table 6) without controlling the in-column temperature of the descending liquid amount of the raw material supply-side distillation section 6 This is shown in State 2 of Table 7. Due to a significant change in the raw material composition, the purity of the product decreases under the initially set operating conditions.
[0044]
On the other hand, the descending liquid amount of the raw material supply side distillation section 6 is controlled so that the temperature of the enrichment section of the raw material supply side distillation section 6 becomes a preset target value. At the same time, the amount of condensate at the top is adjusted by the same amount as the amount of change in the amount of liquid falling in the feed-side distillation section 6 (state 3 in Table 6). By adjusting the descending liquid amount in the feed-side distillation section 6, the temperature of the enrichment section of the feed-side distillation section 6 returns to the initially set temperature, and the composition of the resulting fraction 2 is shown in State 3 in Table 7. . With this control method, the product purity is improved to the original level.
[0045]
This is because the main component d flowing from the upper portion of the raw material supply side distillation section 6 to the product distillate side distillation section 6 ′ through the dividing plate 5 increases due to the fluctuation of the raw material composition. This is detected from the rise in the temperature of the enrichment section, and the amount of liquid falling in the distillation section 6 on the raw material supply side is increased to prevent the inflow of the main component d.
[0046]
[Table 4]

[0047]
[Table 5]

[0048]
[Table 6]

[0049]
[Table 7]

[0050]
Example 2
The low-boiling impurities are removed from the top of the column and the high-boiling impurities are removed from the bottom of the column, and two fractions (fractions 2 and 3) are distilled from the middle part of the column to separate and purify the raw materials.
[0051]
As a distillation column, a division type distillation column with a dividing plate 5 shown in FIG. 5 is used, and the amount of the liquid descending from the product distilling side distillation section 6 'out of the two descending liquids from the upper part of the middle part of the column is made constant. Make adjustments. Further, temperature control is performed so that the total amount of condensate at the top of the tower can be adjusted based on the temperature of the enrichment section of the distillation section 6 on the raw material supply side. The heating amount of the reboiler in the distillation column, the amount of the liquid dropped in the distillation section 6 ′ on the product distillate side, and the control target temperature in the temperature measurement section are shown in State 1 in Table 8 so that the desired product composition and product yield can be obtained. Is determined in advance as follows.
[0052]
Under the present operating conditions, when a raw material having a composition shown in Table 4 is supplied, a high-purity product is obtained as shown in State 1 in Table 9. Further, the raw material having the composition shown in Table 5 is switched to continue the continuous operation. At this time, the composition of the fraction 2 obtained when the operation is continued with the initially set total condensate amount at the top (State 2 in Table 8) without controlling the total condensate amount at the top according to the temperature in the column. Is shown in State 2 of Table 9. Due to the change in the raw material composition, the purity of the product decreases under the initially set operating conditions.
[0053]
On the other hand, the total amount of condensed liquid at the top of the column is controlled so that the temperature of the enrichment section of the distillation section 6 on the raw material supply side becomes a preset target value. Here, the total condensate amount at the top of the column is adjusted by adjusting the reboiler heating amount (state 3 in Table 8). By adjusting the total amount of condensate at the top of the column, the temperature of the enrichment section of the distillation section 6 on the raw material supply side returns to the initially set temperature, and the composition of the resulting fraction 2 is shown in State 3 in Table 9. With this control method, the product purity is improved to the original level.
[0054]
This is because the main component d flowing from the upper portion of the raw material supply side distillation section 6 to the product distillate side distillation section 6 ′ through the dividing plate 5 increases due to the fluctuation of the raw material composition. This is detected from the rise in the temperature of the enrichment section, and the total amount of condensate at the top of the column is increased to increase the amount of liquid falling into the distillation section 6 on the raw material supply side, thereby preventing the inflow of the main component d. .
[0055]
[Table 8]

[0056]
[Table 9]

[0057]
Comparative Example 1
Separation and purification of the raw materials are carried out under the same conditions as in Example 2 except that the setting of the amount of liquid falling in the two distillation sections in the middle part of the column is adjusted so that the distribution ratio becomes constant. The distribution ratio of the falling liquid to the two divided distillation sections is shown by (raw material supply side falling liquid amount) :( product distilling side falling liquid amount), and the reboiler heating is performed so as to obtain the desired product composition and product yield. It is determined in advance as shown in State 1 of Table 10 together with the amount and the control target temperature in the temperature measuring unit.
[0058]
Under these conditions, when a raw material having the composition shown in Table 4 is supplied, the operation result shown in State 1 of Table 11 is obtained although the amount of impurities mixed in the composition of fraction 2 is changed. Further, the raw material having the composition shown in Table 5 is switched to continue the continuous operation. At this time, the composition of the distillate 2 obtained when the operation is continued at the initially set descending liquid amount (state 2 in Table 10) without controlling the descending liquid amount of the raw material supply side distillation section 6 based on the column temperature. Is shown in State 2 of Table 11. Due to the change in the raw material composition, the purity of the product decreases under the initially set operating conditions.
[0059]
On the other hand, the total amount of condensed liquid at the top of the column is controlled so that the temperature of the enrichment section of the distillation section 6 on the raw material supply side becomes a preset target value. Here, the total condensate amount at the top of the column is adjusted by adjusting the reboiler heating amount. At this time, the control is continued so that the initially set distribution ratio is constant with respect to the descending liquid amounts in the two distillation sections (state 3 in Table 10). Despite the adjustment of the total amount of condensate at the top, the temperature of the enrichment section of the feed-side distillation section 6 does not return to the initially set temperature, and the composition of the fraction 2 is as shown in State 3 in Table 11. Not improved.
[0060]
This is because the main component d flowing from the upper part of the raw material supply side distillation section 6 to the product distillate side distillation section 6 ′ through the dividing plate 5 increases due to the fluctuation of the raw material composition. In order to increase the total amount of condensate at the top of the column, that is, to adjust the heating amount of the reboiler, while keeping the falling liquid distribution ratio constant, the rising steam and the falling liquid have the same ratio on both the feed side and product distilling side distillation sections. This is due to the fact that the composition distribution in the column cannot be effectively adjusted in both distillation sections.
[0061]
[Table 10]

[0062]
[Table 11]

[0063]
【The invention's effect】
According to the distillation method of the present invention, a product of more stable quality can be obtained in an internal split type distillation column which is excellent in separability and energy saving type as compared with a conventional distillation column.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an example of a distillation column used in the present invention.
FIG. 2 is a schematic sectional view showing another example of the distillation column used in the present invention.
FIG. 3 is a diagram illustrating an example of a flow rate adjusting method according to the present invention.
FIG. 4 is a diagram showing another example of the flow rate adjusting method of the present invention.
FIG. 5 is a schematic sectional view of a distillation column used in Examples and Comparative Examples.
[Explanation of symbols]
1 Distillation tower
2 tower top
3 middle part of the tower
4 Lower part of the tower
5 Dividing plate
6 Distillation section on raw material supply side
6 'Distillation section on product distillate side
7 Raw material supply port
8 Product outlet at the top of the tower
9 Product outlet in the middle of the tower
9 'Product outlet on raw material supply side
10 Can drainage outlet
11 liquid collector
12,12 'Descending liquid line
13 Flow meter 13
14, 14 'Flow control valve
15 Distributor
16 receiver
17 Pump
18 Liquid level gauge

Claims

Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, in order to obtain at least one or more products from the middle section of the column, the total flow rate of the descending liquid in one of the divided sections is completely condensed. A distillation method characterized in that distillation is performed while adjusting to a set flow rate regardless of the liquid amount.

Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, detecting at least one of the temperatures of the divided distillation sections in obtaining at least one or more products from the middle section of the column. The distillation method is characterized in that the distillation is performed by adjusting the flow rate of the descending liquid in the divided distillation section.

Using a distillation column having a structure in which the middle section of the column is divided into two distillation sections, in order to obtain at least one or more products from the middle section of the column, the total flow rate of the descending liquid in one of the divided sections is completely condensed. Adjusting the set flow rate irrespective of the liquid amount, and detecting the temperature of at least one of the divided distillation sections, performing distillation by adjusting the descending liquid flow rate of the divided distillation sections. Distillation method.

4. The distillation method according to claim 2, wherein the total amount of condensate is adjusted by detecting the temperature, and the flow rate of the descending liquid in the divided distillation sections is adjusted.