JP4281856B2 - Methylal manufacturing method - Google Patents

Description

【０００５】
また、反応収率を高める方法として上記特公昭４０−１５００５号公報には、メタノールとホルマリン水溶液との原料混合体を陽イオン交換体を用いて前以ってアセタール化を施し、かつ陽イオン交換体を用いた反応室から流出する液体の一部を原料混合物の供給箇所の上方から再度供給することを提案している。しかしながら、イオン交換樹脂を長期間にわたって使用していると、形状が粒状から微粉末状へと崩壊したり、金属イオンの置換等により触媒活性が低下するという問題が生じることがある。該公報の方法では、陽イオン交換体を蒸留塔内に充填する方式を採用しているために、触媒能が低下する度にメチラールの製造を中止しなければならないという不都合があった。
【０００６】
また、特開平１ー２８７０５１号公報ではメタノール、ホルムアルデヒド及び水からなる液体を蒸留塔に連結した固体酸触媒を含む反応器に強制循環させる反応蒸留塔方式によりメチラールを合成するという方法が提案されている。該公報の方法では、反応収率が向上するとともに、反応器が外部からの強制循環方式をとっているため、予備の反応器を設置すると、触媒の再生、交換、取り出しをその予備の反応器を通して行うことができるので、メチラールの製造を中止することなく長時間の連続運転を行うことができる。しかしながら、該公報の方法は、メチラールの効率的製造方法として優れた特性を有するが、副生する水の処理を考えた時、蒸留塔缶出液中のホルムアルデヒドとメタノールの濃度が高くなり、高ＣＯＤ負荷の排水が発生することになる。同時に蒸留塔を連続運転する際には蒸留塔内での泡立ちによる圧力上昇が発生し、工業的にメチラールの生産を実施するには不都合があった。
【０００７】
【課題を解決するための手段】
本発明者らは、メチラールの工業的製造方法につき鋭意検討した結果、固体酸触媒の有用性を見出すとともに、反応器の最適器数、蒸留塔の最適条件を見出し、本発明を完成するに至った。
すなわち本発明は、メタノール、ホルムアルデヒド及び水を含む液体と固体酸触媒とを接触させてメチラールに富む成分を留出成分として得るメチラールの製造方法において、蒸留塔中段で蒸留塔外部に近接してそれぞれ連結された少なくとも４基の固体酸触媒を充填した反応器を設け、最上段の反応器にメタノール、ホルムアルデヒド及び水を含む液を通液させ、蒸留塔の下方側に連結されたその他の反応器の各々と蒸留塔との間で８０℃〜１００℃の温度範囲でメタノール、ホルムアルデヒド、水及び生成したメチラールを含む液体を強制循環させ、蒸留塔の下方側に連結された反応器で固液接触しているメタノール、ホルムアルデヒド、水及び生成したメチラールを含む液体と、気液接触している蒸留塔内の蒸気が、その蒸気を生成する反応器より上方に連結された反応器で循環されたメタノール、ホルムアルデヒド、水及び生成したメチラールを含む液体と順次気液接触することにより、蒸気相中のメチラール濃度を順次高めると共に、蒸留塔の塔頂部から消泡剤を添加し、蒸留塔の缶出液の温度を１００℃〜１３０℃として副生する水を廃水として取り出すことを含むメチラールの製造方法である。
【０００８】
【発明の実施の形態】
本発明で用いられる固体酸触媒を充填した反応器の様式、及び固体酸触媒と固液接触したメタノール、ホルムアルデヒド、メチラール及び水を含む液体とメチラールを含む蒸気との気液接触の様式には特に制限はないが、その一例を図１に示す。
【０００９】
以下、本発明を、図１に示す蒸留塔を用いた場合を例として、具体的に説明する。
図１において▲１▼は蒸留塔、▲２▼はコンデンサー、▲３▼はメタノール、ホルムアルデヒド、水を含む液体の供給部、Ａ〜Ｆは固体酸触媒を充填した反応器、▲４▼は炊き上げ水蒸気の供給部、▲５▼はホルマリン水溶液又は水の供給部、▲６▼は留出液、▲７▼は塔底缶出液、及び▲８▼は消泡剤の供給部を示す。
【００１０】
本発明で用いられる蒸留塔は特に限定されることはなく、棚段塔又は充填塔のいずれでもよい。例えば、バブルキャップ、バルブトレイ、シーブトレイ等のいずれも用いることができ、また充填物についてもラシヒリング、ポールリング、ディクソンリング、テラレット等様々な形式を採用することができる。また、蒸留塔に使用される材質も特に限定されないが、ホルムアルデヒドの酸化により僅かではあるがギ酸も発生するので、ＳＵＳ３０４（ステンレス鋼）相当以上の耐食性を有する材料の使用が好ましい。
【００１１】
本発明の蒸留塔１には固体酸触媒が充填された反応器Ａ〜Ｆが蒸留塔中段部の蒸留塔の外部に連結される。本発明の原料であるメタノールとホルマリン水溶液は、供給部▲３▼からまず最上段の反応器Ａに通液され、その後蒸留塔▲１▼に供給される。本発明においては、メタノール、ホルムアルデヒド及び水を含む液体が、蒸留塔外部に連結された固体酸触媒が充填された反応器Ｂ〜Ｆに強制循環されてメチラールが合成され、蒸留塔に戻される。一方、蒸留塔の下方側に連結された反応器で固液接触したメタノール、ホルムアルデヒド、水及び生成メチラールを含む液体と蒸留塔の缶底からの蒸気とが気液接触している蒸留塔内の蒸気が、それより上方に連結された反応器中で循環させられて、固液接触した後のメタノール、ホルムアルデヒド、水及び生成メチラールを含む液体と順次気液接触することになる。これにより、蒸気相中のメチラール濃度が順次高まっていくのである。この方法により、メチラールを高収率で得ることが可能となる。
【００１２】
また、蒸留塔に連結した最上段の反応器Ａから蒸留塔塔頂までの蒸留段数は５段以上であることが好ましく、１０段〜２０段がより好ましい。最上段の反応器Ａと蒸留塔塔頂までの蒸留段数が５段未満の場合は、塔頂の留出液中のメタノール濃度が高くなり、得られるメチラールの純度が劣る。
また、蒸留塔に連結した最下段の反応器Ｆから蒸留塔塔底までの蒸留段数は５段以上であることが好ましく、１５段以上であることがより好ましい。最下段の反応器Ｆから蒸留塔塔底までの蒸留段数が５段未満の場合は、塔底の缶出液中にメタノールが混入し、その分ロスが生じると同時に廃水中のＣＯＤ負荷が高くなる。
蒸留塔の塔頂部から得られる凝縮液は、塔頂に還流される還流物と留出される留出物とに分けられるが、塔頂に還流される還流物と留出される留出物との比（モル比）は５：１から１：２であることが好ましい。
【００１３】
本発明における蒸留塔の操作は通常、常圧で行われるが、１〜２気圧の範囲で行われることが好ましい。また、この操作圧力で蒸留を行う場合、蒸留塔に連結された、強制循環のための、５基の反応器を操作するにあたり、蒸留塔の上段側から順番に、それぞれの反応器に循環する液の温度を、それぞれ８０〜９０℃、８５〜９５℃、８５〜９５℃、９０〜１００℃、及び９０〜１００℃、さらに蒸留塔の塔底液の温度を１００℃以上にすることが重要である。強制循環を行っている５基の反応器が連結されている蒸留塔中段部及び塔底部を上記温度とすることにより、メタノール、及び生成したメチラールの組成が安定し、副生した水を含む塔底の缶出液の組成がホルムアルデヒド０．１％以下及びメタノール０．０１％以下となり、ＣＯＤ負荷が５００ｐｐｍ以下の低ＣＯＤ負荷の排水として缶出液を処理することが可能となる。
以上、固体酸触媒を充填する反応器が６基の場合を例として本発明を説明したが、本発明においては、固体酸触媒を充填する反応器は少なくとも４基であり、好ましくは６基以上である。反応器数が４基未満では、メチラール合成の反応が不十分となり、蒸留塔塔底からの廃液中のホルムアルデヒド濃度が高くなり、ＣＯＤ負荷が大きくなるので好ましくない。
【００１４】
反応器に充填される固体酸触媒としては、公知の固体酸触媒であればよく、例えば、カチオン交換樹脂、フッ素化アルキレン樹脂スルホン酸基誘導体、結晶性ゼオライトなどが挙げられる。カチオン交換樹脂としてはカルボン酸基誘導体、スルホン酸基誘導体のいずれも使用し得るが、スルホン酸基誘導体が反応収率が高い点で好ましい。また、イオン交換樹脂のタイプとしては、ゲル型カチオン交換樹脂、巨大網目状カチオン交換樹脂のいずれも使用し得るが、巨大網目状カチオン交換樹脂が反応収率が高い点で好ましい。フッ素化アルキレン樹脂スルホン酸基誘導体としては、テトラフルオロエチレン樹脂スルホン酸基誘導体が好ましい。また、結晶性ゼオライト（結晶性アルミノシリケート）としては、ＳｉＯ₂ ／Ａｌ₂ Ｏ₃ のモル比が１０以上であるシリカゼオライトが好ましい。
【００１５】
また、反応器に充填される固体酸触媒の量は、蒸留塔塔頂部から１時間あたりに留出するメチラール蒸気１重量部に対して０．２〜１重量部が好ましい。充填される触媒量が少ない場合、反応が不十分となり蒸留塔塔底からの廃水のＣＯＤ負荷が高くなる。
本発明において、蒸留塔に連結した固体酸触媒を充填した５基の反応器Ｂ、Ｃ、Ｄ、Ｅ、Ｆ内に強制循環させる液の量は、固体酸触媒の触媒能及び量によって定められるが、蒸留塔の塔頂から留出するメチラール蒸気１重量部に対して、それぞれの反応器内を循環する液の量を１５〜３０重量部とすることが好ましい。
【００１６】
さらに、最上段に連結された反応器より下方に連結された強制循環のための反応器に循環させる反応液の組成は、メタノール２５〜３５重量部、ホルムアルデヒド０．００５〜５重量部、水５５〜７５重量部、及びメチラール０．０１〜５重量部である。このようにメタノール濃度を高くすることにより反応を完結させ、蒸留塔塔底のホルムアルデヒド濃度を下げることが可能となり、蒸留塔塔底からの廃水のＣＯＤ負荷を下げることができる。
【００１７】
本発明の原料であるメタノールとホルマリン水溶液は、供給部▲３▼からまず最上段の反応器Ａに通液され、その後蒸留塔▲１▼に供給される。また、本発明においては、最上段の反応器Ａよりも上部から水又はホルマリン水溶液が供給される。最上段の反応器Ａよりも上部から供給される水又はホルマリン水溶液と蒸留塔内を上昇するメチラール及びメタノールを含む蒸気とを気液接触させ、塔頂から９８％以上のメチラール及び１％以下のメタノールを留出させる。供給位置は、蒸留塔に連結した最上段の反応器と塔頂までの蒸留段数が１５〜２０段であれば、最上段の反応器から数えて１０〜１５段の範囲が好ましい。
【００１８】
供給されるメタノールの量は、ホルムアルデヒドに対してモル比で２．０〜２．２倍の量である。モル比が２倍未満の量では反応量論的にホルムアルデヒドが過剰となり、蒸留塔塔底から排出され、廃液中のホルムアルデヒド濃度が高くなり、ＣＯＤ負荷が大きくなるので好ましくない。
また、本発明においては蒸留塔塔頂部に消泡剤が添加される。消泡剤を添加しない場合、蒸留塔内で泡立が生じ、蒸留塔内の圧力が上昇し、連続的に安定した運転ができなくなるので好ましくない。消泡剤の添加方法としては還流液に添加する方法や蒸留塔に直接添加する方法等が挙げられ、いずれの方法も用いることができる。
【００１９】
消泡剤の添加量は蒸留塔塔頂部から留出するメチラール蒸気に対して０．００１ｐｐｍ〜１０００ｐｐｍであり、好ましくは０．０１ｐｐｍ〜１００ｐｐｍである。
消泡剤としては、通常の消泡剤を用いることができ、特に限定されないが、本発明において用いられる好ましい消泡剤としてはシリコンオイルが挙げられる。
シリコンオイルとしては、一般的なジメチル型シリコンオイル、変成型シリコンオイル、溶液型シリコンオイル、及びエマルジョン型シリコンオイルが挙げられるが、変成型シリコンオイルが好ましく、特にポリエーテルで変成したシリコンオイルが好ましい。シリコンオイルの粘度は５０〜１００，０００センチポイズであればよい。好ましくは１００〜２０００センチポイズの粘度を有するポリエーテルで変成したシリコンオイルが用いられる。
【００２０】
【実施例】
以下、本発明を実施例などによりさらに詳細に説明するが、これらは本発明を何ら制限するものではない。
（実施例１）
図１に示す６基の反応器を有する反応蒸留塔を使用した。最上段の反応器Ａから蒸留塔塔頂までの蒸留段数は１５段、また最下段の反応器Ｆから蒸留塔塔底までの蒸留段数は１５段とした。それぞれの反応器Ａ、Ｂ、Ｃ、Ｄ、Ｅ及びＦには、巨大網目状強カチオン交換樹脂（商品名：アンバーリスト３５）を５００ｇ充填した。供給部▲３▼から４５％ホルマリン水溶液を５６０ｇ／ｈ、メタノールを５８０ｇ／ｈで供給した。蒸留塔の中段には、それぞれ液成分を抜き出す段を設け、反応液をポンプで反応器Ｂ、Ｃ、Ｄ、Ｅ及びＦに４０リットル／ｈで循環させ、触媒と固液接触せしめるようにした。反応器Ｂ、Ｃ、Ｄ、Ｅ及びＦを出たメチラールを含有する反応液は蒸留塔の塔底から塔頂に向かってくる蒸気と気液接触し、メチラール濃度が高められる。
【００２１】
また、供給部▲５▼から２０％ホルマリン水溶液を１００ｇｒ／ｈで供給し、メチラール−メタノールの共沸蒸気からメタノールをホルマリン水溶液に選択的に吸収させた。更に蒸留塔塔頂部のガス量２１００ｇ／ｈに対して、粘度が７５０センチポイズのポリエーテルで変成したシリコンオイルを０．０１ｇ／ｈとなるようにメチラールで希釈して蒸留塔の還流ラインに供給した。蒸留塔の圧力は１．２気圧とし、塔頂に還流される還流物と留出される留出物との比（モル比）は２：１の条件でメチラールの合成を行った。７２時間後の蒸留塔の運転が安定した時の反応器Ｂ、Ｃ、Ｄ、Ｅ及びＦの各温度はそれぞれ、８５℃、９１℃、９４℃、９５℃及び９５℃であり、また、蒸留塔塔頂の温度は４７℃、蒸留塔塔底の温度は１１２℃であった。各反応器の循環液の組成はホルムアルデヒド、水、メタノール及びメチラールの各濃度が、反応器Ｂでは３．１％、６１．７％、３２．０％及び３．２％、反応器Ｃでは１．３％、６７．５％、３０．２％及び１．０％、反応器Ｄでは０．５％、７０．２％、２８．９％及び０．４％、反応器Ｅでは０．２％、７１．５％、２８．２％及び０．１％、反応器Ｆでは０．０８％、７２．６％、２７．３％及び０．０２％であり、塔頂▲６▼から７０２ｇ／ｈの留出液を抜き出した。留出液の組成は、メチラール９８％、メタノール０．３％及び水１．２％であった。塔底▲７▼から抜き出した缶出液の組成はホルムアルデヒド０．０６％及びメタノール０．００１％を含むものであった。ホルムアルデヒド基準の反応収率は９９．９％であった。また、この運転条件において、１０００時間の連続運転を行ったが蒸留等の運転は安定しており、１０００時間後の留出液及び缶出液の流量及び組成も安定していた。
【００２２】
（実施例２〜４）
固体酸触媒として、巨大網目状強酸性カチオン交換樹脂を用いる代わりに、表１に示す種々の固体酸を用いるほかは実施例１と同様の操作を行った。結果を表１に示す。
【００２３】
【表１】

【００２４】
（比較例１）
実施例１において反応器Ｄ、Ｅ及びＦを取り外し、その他は実施例１と同様の操作を行った。塔頂から６８０ｇ／ｈの留出液を抜き出した。留出物の組成は、メチラール９８％、メタノール０．８％，及び水１．２％であった。塔底▲７▼から抜き出した缶出液の組成はホルムアルデヒド０．６％及びメタノール１．３％を含むものであった。この缶出液は明らかに実施例よりＣＯＤ負荷が高く、排水処理という工業的製造の観点から大きな問題がある。
【００２５】
（比較例２）
実施例１において最上段の反応器Ａから蒸留塔塔頂までの蒸留段数を３段、また最下段の反応器Ｆから蒸留塔塔底までの蒸留段数は３段とした以外は実施例１と同様の操作を行った。塔頂から６９０ｇ／ｈの留出液を抜き出した。留出物の組成は、メチラール９４．３％、メタノール４．５％，及び水１．２％であった。塔底▲７▼から抜き出した缶出液の組成はホルムアルデヒド０．８％及びメタノール２．５％を含むものであった。留出液はメチラール純度が劣り、またこの缶出液は明らかに各実施例よりＣＯＤ負荷が高く、排水処理という工業的製造の観点から大きな問題がある。
【００２６】
（比較例３）
実施例１において反応器Ｆの温度を７９℃にまで上昇させてメチラールの合成を行った。蒸留塔の運転が安定した時の反応器Ｂ、Ｃ、Ｄ及びＥの各温度は６７℃、７３℃、７５℃及び７７℃であった。留出液の組成は、メチラール９８％、メタノール０．９％及び水０．９％であった。塔底▲７▼から抜き出した缶出液の組成はホルムアルデヒド１．３％及びメタノール０．３％を含むものであった。
【００２７】
（比較例４）
実施例１において蒸留塔塔底部の缶出液温度を９８℃にまで上昇させて実施例１と同様にメチラールの合成を行った。留出液の組成は、メチラール９８％、メタノール１．０％及び水１．０％であった。塔底▲７▼より抜き出した缶出液の組成はホルムアルデヒド１．５％及びメタノール１．５％を含むものであった。
【００２８】
（比較例５）
実施例１において蒸留塔の還流ラインに添加したポリエーテルで変成したシリコンオイルの供給を停止した以外は実施例１と同様にメチラールの合成を実施した。運転開始から６０時間後から徐々に蒸留塔内での泡立ちが確認され、さらに蒸留塔塔底部の温度が１１５℃にまで上昇した。最終的に蒸留塔塔底部の温度が１２０℃になった時点で運転を停止した。この時には蒸留塔全体での泡立ちが確認された。
【００２９】
【発明の効果】
本発明の製造方法によれば、従来技術では副生する水により反応収率に制約を受けていたメチラールの合成を高収率で行うことができる。また、本発明の方法では、副生する水の処理を容易とし、さらに泡消剤の添加により連続生産を達成させることを可能とする、工業的価値の極めて高いものである。
【図面の簡単な説明】
【図１】本発明で使用される反応器を蒸留塔外部に近接して連結された蒸留塔の概略図である。
【符号の説明】
▲１▼ 蒸留塔
▲２▼ コンデンサー
▲３▼ メタノール、ホルムアルデヒドと水を含む液体の供給部
Ａ〜Ｆ 固体酸触媒を充填した各反応器
▲４▼ 炊き上げ水蒸気
▲５▼ 水またはホルマリン水溶液の供給部
▲６▼ 留出液
▲７▼ 缶出液
▲８▼ 消泡剤の供給部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing methylal used as a plasticizer, analgesic agent, perfume and the like for a resin, and more particularly to a method for efficiently producing methylal from methanol and formaldehyde using a solid acid as a catalyst.
[0002]
[Prior art]
Methylal is synthesized by a condensation reaction between methanol and formaldehyde or paraformaldehyde in the presence of an acidic catalyst. As a method for synthesizing methylal, for example, Solvent Handbook (Kodansha version, Showa 51) discloses the use of an acidic catalyst such as hydrochloric acid, ferric chloride, and zinc chloride. Japanese Patent Publication No. 40-15005 proposes a method of increasing the reaction yield of methylal by passing a raw material mixture of methanol and a formalin aqueous solution through a distillation column packed with a cation exchanger. Although not limited to the synthesis of methylal, a reaction method using a catalyst-packed distillation column as a method for increasing the reaction yield is disclosed in JP-A-4-363132, JP-A-4-363132 and JP-A-Hei. No. 4-317701. Furthermore, Japanese Patent Laid-Open No. 1-287051 discloses a method for efficiently synthesizing methylal by a reactive distillation column system in which a liquid comprising methanol, formaldehyde and water is forcedly circulated to a reactor containing a solid acid catalyst connected to the distillation column. Is disclosed.
[0003]
[Problems to be solved by the invention]
However, in the conventionally proposed methods, when synthesizing methylal from methanol and formaldehyde, there is a problem that the reaction yield is restricted by water produced as a by-product, or production is forced to be stopped when the catalytic capacity is reduced. There may be a problem that the production of waste water is subject to large production restrictions, and industrial implementation may be complicated.
[0004]
For example, in the reaction of synthesizing methylal from methanol and formaldehyde using an acidic catalyst such as hydrochloric acid, the reaction is an equilibrium reaction as shown in the following reaction formula, so the reaction yield is improved by the presence of by-product water. There were restrictions to make it happen.
[Chemical 1]

[0005]
In addition, as a method for increasing the reaction yield, the above Japanese Patent Publication No. 40-15005 discloses that a raw material mixture of methanol and a formalin aqueous solution is acetalized in advance using a cation exchanger, and cation exchange is performed. It is proposed that a part of the liquid flowing out from the reaction chamber using the body is supplied again from above the supply point of the raw material mixture. However, when the ion exchange resin is used for a long period of time, there may be a problem that the shape collapses from a granular form to a fine powder form, or the catalytic activity decreases due to substitution of metal ions. In the method of this publication, since a system in which a cation exchanger is packed in a distillation column is employed, there is a disadvantage that the production of methylal must be stopped every time the catalytic ability is lowered.
[0006]
Japanese Patent Application Laid-Open No. 1-287051 proposes a method of synthesizing methylal by a reactive distillation column system in which a liquid consisting of methanol, formaldehyde and water is forcibly circulated through a reactor containing a solid acid catalyst connected to the distillation column. Yes. In the method of the publication, since the reaction yield is improved and the reactor adopts a forced circulation system from the outside, when a spare reactor is installed, regeneration, replacement, and removal of the catalyst are performed for the spare reactor. Therefore, continuous operation for a long time can be performed without stopping the production of methylal. However, although the method of this publication has excellent characteristics as an efficient method for producing methylal, when considering the treatment of by-product water, the concentration of formaldehyde and methanol in the distillation column can be increased. COD drainage will be generated. At the same time, when the distillation column is continuously operated, a pressure increase occurs due to foaming in the distillation column, which is inconvenient for industrially producing methylal.
[0007]
[Means for Solving the Problems]
As a result of intensive studies on the industrial production method of methylal, the present inventors have found the usefulness of the solid acid catalyst, found the optimum number of reactors and optimum conditions for the distillation column, and completed the present invention. It was.
That is, the present invention relates to a method for producing methylal by contacting a liquid containing methanol, formaldehyde, and water with a solid acid catalyst to obtain a methylal-rich component as a distilling component, and in the middle stage of the distillation column, close to the outside of the distillation column. Other reactors provided with a reactor filled with at least four connected solid acid catalysts, a liquid containing methanol, formaldehyde and water passed through the uppermost reactor and connected to the lower side of the distillation column Forcibly circulate a liquid containing methanol, formaldehyde, water and the generated methylal in the temperature range of 80 ° C. to 100 ° C. between each of them and a distillation column, and contact them with a reactor connected to the lower side of the distillation column. The vapor in the distillation column that is in gas-liquid contact with the liquid containing methanol, formaldehyde, water and methylal that is produced produces the vapor. By sequentially gas-liquid contact with the liquid containing methanol, formaldehyde, water and the generated methylal circulated in the reactor connected above the reactor, the concentration of methylal in the vapor phase is increased and the column of the distillation column is increased. An antifoaming agent is added from the top, and the temperature of the bottoms of the distillation tower is set to 100 ° C. to 130 ° C., and water produced as a by-product is taken out as waste water.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Especially for the mode of the reactor filled with the solid acid catalyst used in the present invention and the mode of gas-liquid contact between the liquid containing methanol, formaldehyde, methylal and water and the vapor containing methylal in solid-liquid contact with the solid acid catalyst. Although there is no limitation, an example is shown in FIG.
[0009]
Hereinafter, the present invention will be specifically described with reference to the case where the distillation column shown in FIG. 1 is used.
In FIG. 1, (1) is a distillation column, (2) is a condenser, (3) is a liquid supply unit containing methanol, formaldehyde and water, A to F are reactors filled with a solid acid catalyst, and (4) is cooked. A water vapor supply section, (5) a formalin aqueous solution or water supply section, (6) a distillate, (7) a bottom bottom liquid, and (8) a defoamer supply section.
[0010]
The distillation column used in the present invention is not particularly limited, and may be either a plate column or a packed column. For example, any of a bubble cap, a valve tray, a sieve tray, and the like can be used, and various forms such as a Raschig ring, a pole ring, a Dixon ring, and a terralet can be adopted for the filling. The material used for the distillation column is not particularly limited, but formic acid is also generated by oxidation of formaldehyde, but it is preferable to use a material having corrosion resistance equivalent to or higher than SUS304 (stainless steel).
[0011]
In the distillation column 1 of the present invention, reactors A to F filled with a solid acid catalyst are connected to the outside of the distillation column in the middle part of the distillation column. The methanol and formalin aqueous solution, which are raw materials of the present invention, are first fed from the supply section (3) to the uppermost reactor A and then supplied to the distillation column (1). In the present invention, a liquid containing methanol, formaldehyde, and water is forcibly circulated to reactors B to F filled with a solid acid catalyst connected to the outside of the distillation column, and methylal is synthesized and returned to the distillation column. On the other hand, in a distillation column in which a liquid containing methanol, formaldehyde, water and generated methylal in solid-liquid contact with a reactor connected to the lower side of the distillation column and vapor from the bottom of the distillation column are in gas-liquid contact. Vapor is circulated in a reactor connected above it, and comes into gas-liquid contact with a liquid containing methanol, formaldehyde, water and produced methylal after solid-liquid contact. As a result, the concentration of methylal in the vapor phase gradually increases. By this method, methylal can be obtained in high yield.
[0012]
The number of distillation stages from the uppermost reactor A connected to the distillation tower to the top of the distillation tower is preferably 5 or more, more preferably 10 to 20 stages. When the number of distillation stages from the uppermost reactor A to the top of the distillation column is less than 5, the concentration of methanol in the distillate at the top of the column becomes high and the purity of the resulting methylal is poor.
The number of distillation stages from the lowest reactor F connected to the distillation tower to the bottom of the distillation tower is preferably 5 or more, and more preferably 15 or more. When the number of distillation stages from the lowest reactor F to the bottom of the distillation column is less than 5, methanol is mixed in the bottoms of the bottom, resulting in a loss and a high COD load in the wastewater. Become.
The condensate obtained from the top of the distillation column is divided into a reflux that is refluxed to the top of the column and a distillate that is distilled, but the reflux that is refluxed to the top of the column and the distillate that is distilled. The ratio (molar ratio) to is preferably 5: 1 to 1: 2.
[0013]
The operation of the distillation column in the present invention is usually carried out at normal pressure, but is preferably carried out in the range of 1 to 2 atmospheres. When performing distillation at this operating pressure, when operating five reactors connected to the distillation column for forced circulation, the reactors are circulated in order from the upper stage side of the distillation column. It is important that the temperature of the liquid is 80 to 90 ° C, 85 to 95 ° C, 85 to 95 ° C, 90 to 100 ° C, and 90 to 100 ° C, respectively, and the temperature of the bottom liquid of the distillation column is 100 ° C or higher. It is. By setting the middle stage and the bottom of the distillation column to which the five reactors performing forced circulation are connected to the above temperature, the composition of methanol and the generated methylal is stabilized, and a column containing by-produced water The bottom bottom composition is 0.1% formaldehyde or less and 0.01% or less methanol, and the bottom discharge can be treated as low COD load wastewater with a COD load of 500 ppm or less.
The present invention has been described above by taking the case where there are six reactors filled with the solid acid catalyst as an example. However, in the present invention, there are at least four reactors filled with the solid acid catalyst, and preferably six or more reactors. It is. If the number of reactors is less than 4, the reaction for methylal synthesis becomes insufficient, the formaldehyde concentration in the waste liquid from the bottom of the distillation column increases, and the COD load increases, which is not preferable.
[0014]
The solid acid catalyst charged in the reactor may be a known solid acid catalyst, and examples thereof include a cation exchange resin, a fluorinated alkylene resin sulfonic acid group derivative, and a crystalline zeolite. As the cation exchange resin, either a carboxylic acid group derivative or a sulfonic acid group derivative can be used, but a sulfonic acid group derivative is preferable in terms of a high reaction yield. As the type of ion exchange resin, either a gel-type cation exchange resin or a giant network cation exchange resin can be used, but a giant mesh cation exchange resin is preferred because of its high reaction yield. As the fluorinated alkylene resin sulfonic acid group derivative, a tetrafluoroethylene resin sulfonic acid group derivative is preferable. Further, as the crystalline zeolite (crystalline aluminosilicate), silica zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of 10 or more is preferable.
[0015]
The amount of the solid acid catalyst charged in the reactor is preferably 0.2 to 1 part by weight with respect to 1 part by weight of methylal vapor distilled from the top of the distillation column per hour. When the amount of the catalyst to be packed is small, the reaction becomes insufficient and the COD load of waste water from the bottom of the distillation tower becomes high.
In the present invention, the amount of liquid forcedly circulated in the five reactors B, C, D, E, and F packed with the solid acid catalyst connected to the distillation column is determined by the catalytic ability and amount of the solid acid catalyst. However, it is preferable that the amount of liquid circulating in each reactor is 15 to 30 parts by weight with respect to 1 part by weight of methylal vapor distilled from the top of the distillation column.
[0016]
Furthermore, the composition of the reaction liquid to be circulated in the reactor for forced circulation connected below the reactor connected to the uppermost stage is 25 to 35 parts by weight of methanol, 0.005 to 5 parts by weight of formaldehyde, 55 of water. -75 parts by weight and 0.01-5 parts by weight of methylal. By increasing the methanol concentration in this manner, the reaction can be completed, the formaldehyde concentration at the bottom of the distillation column can be lowered, and the COD load of waste water from the bottom of the distillation column can be reduced.
[0017]
The methanol and formalin aqueous solution, which are raw materials of the present invention, are first fed from the supply section (3) to the uppermost reactor A and then supplied to the distillation column (1). In the present invention, water or a formalin aqueous solution is supplied from the upper part of the uppermost reactor A. The water or formalin aqueous solution supplied from the upper part of the uppermost reactor A is brought into gas-liquid contact with the vapor containing methylal and methanol rising in the distillation column, and 98% or more methylal and 1% or less from the top of the column. Distill off methanol. If the uppermost reactor connected to the distillation column and the number of distillation stages to the top of the column are 15 to 20, the supply position is preferably in the range of 10 to 15 from the uppermost reactor.
[0018]
The amount of methanol supplied is 2.0 to 2.2 times the molar ratio of formaldehyde. If the molar ratio is less than 2 times, formaldehyde is excessive in terms of reaction amount, and it is discharged from the bottom of the distillation column, the formaldehyde concentration in the waste liquid becomes high, and the COD load increases, which is not preferable.
In the present invention, an antifoaming agent is added to the top of the distillation column. If the antifoaming agent is not added, foaming occurs in the distillation column, the pressure in the distillation column rises, and it is not preferable because continuous and stable operation cannot be performed. Examples of the method of adding the antifoaming agent include a method of adding to the reflux liquid and a method of adding directly to the distillation column, and any method can be used.
[0019]
The amount of antifoaming agent added is 0.001 ppm to 1000 ppm, preferably 0.01 ppm to 100 ppm, based on methylal vapor distilled from the top of the distillation column.
As the antifoaming agent, a normal antifoaming agent can be used and is not particularly limited, but a preferable antifoaming agent used in the present invention includes silicone oil.
Examples of the silicone oil include general dimethyl type silicone oil, modified type silicone oil, solution type silicone oil, and emulsion type silicone oil. Modified type silicone oil is preferred, and silicone oil modified with polyether is particularly preferred. . The viscosity of the silicone oil may be 50 to 100,000 centipoise. Preferably, silicone oil modified with a polyether having a viscosity of 100 to 2000 centipoise is used.
[0020]
【Example】
EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further in detail, these do not limit this invention at all.
(Example 1)
A reactive distillation column having 6 reactors as shown in FIG. 1 was used. The number of distillation stages from the uppermost reactor A to the top of the distillation column was 15, and the number of distillation stages from the lowermost reactor F to the bottom of the distillation tower was 15. Each reactor A, B, C, D, E, and F was charged with 500 g of a giant reticulated strong cation exchange resin (trade name: Amberlyst 35). A 45% formalin aqueous solution was supplied at 560 g / h and methanol at 580 g / h from the supply section (3). In the middle column of the distillation column, a stage for extracting liquid components was provided, and the reaction liquid was circulated through the reactors B, C, D, E, and F at a rate of 40 liters / h by a pump, and brought into solid-liquid contact with the catalyst. . The reaction liquid containing methylal exiting the reactors B, C, D, E and F comes into vapor-liquid contact with the vapor coming from the bottom of the distillation column toward the top of the column, and the methylal concentration is increased.
[0021]
Further, a 20% formalin aqueous solution was supplied at 100 gr / h from the supply section (5), and methanol was selectively absorbed into the formalin aqueous solution from the azeotropic vapor of methylal-methanol. Further, with respect to the gas amount of 2100 g / h at the top of the distillation column, silicon oil modified with polyether having a viscosity of 750 centipoise was diluted with methylal so as to be 0.01 g / h and supplied to the reflux line of the distillation column. . The pressure in the distillation column was 1.2 atm. Methylal was synthesized under the condition that the ratio (molar ratio) of the refluxed product refluxed to the top of the column was 2: 1. The temperatures of the reactors B, C, D, E and F when the operation of the distillation column after 72 hours was stabilized were 85 ° C., 91 ° C., 94 ° C., 95 ° C. and 95 ° C., respectively. The temperature at the top of the column was 47 ° C., and the temperature at the bottom of the distillation column was 112 ° C. The composition of the circulating fluid in each reactor was 3.1%, 61.7%, 32.0%, and 3.2% in reactor B, and 1% in reactor C. The concentrations of formaldehyde, water, methanol, and methylal were as follows. 0.3%, 67.5%, 30.2% and 1.0%, reactor D 0.5%, 70.2%, 28.9% and 0.4%, reactor E 0.2% %, 71.5%, 28.2% and 0.1%, 0.08%, 72.6%, 27.3% and 0.02% in the reactor F, from the top (6) to 702 g / H distillate was withdrawn. The composition of the distillate was 98% methylal, 0.3% methanol and 1.2% water. The composition of the bottoms extracted from the bottom (7) contained 0.06% formaldehyde and 0.001% methanol. The reaction yield based on formaldehyde was 99.9%. Under these operating conditions, 1000 hours of continuous operation was performed, but operations such as distillation were stable, and the flow rate and composition of the distillate and bottoms after 1000 hours were also stable.
[0022]
(Examples 2 to 4)
The same operation as in Example 1 was performed except that various solid acids shown in Table 1 were used as the solid acid catalyst instead of using the giant network strongly acidic cation exchange resin. The results are shown in Table 1.
[0023]
[Table 1]

[0024]
(Comparative Example 1)
In Example 1, the reactors D, E and F were removed, and the other operations were the same as in Example 1. A distillate of 680 g / h was extracted from the top of the column. The composition of the distillate was 98% methylal, 0.8% methanol, and 1.2% water. The composition of the bottoms extracted from the bottom (7) contained 0.6% formaldehyde and 1.3% methanol. This bottoms liquid clearly has a higher COD load than the examples, and has a big problem from the viewpoint of industrial production of wastewater treatment.
[0025]
(Comparative Example 2)
Example 1 is the same as in Example 1 except that the number of distillation stages from the uppermost reactor A to the top of the distillation column is three, and the number of distillation stages from the lowermost reactor F to the bottom of the distillation tower is three. The same operation was performed. A distillate of 690 g / h was extracted from the top of the column. The composition of the distillate was 94.3% methylal, 4.5% methanol, and 1.2% water. The composition of the bottoms extracted from the bottom (7) contained 0.8% formaldehyde and 2.5% methanol. The distillate is inferior in methylal purity, and this bottom is clearly higher in COD load than in each of the examples and has a serious problem from the viewpoint of industrial production of wastewater treatment.
[0026]
(Comparative Example 3)
In Example 1, the temperature of the reactor F was raised to 79 ° C. to synthesize methylal. When the operation of the distillation column was stabilized, the temperatures of the reactors B, C, D and E were 67 ° C, 73 ° C, 75 ° C and 77 ° C. The composition of the distillate was 98% methylal, 0.9% methanol and 0.9% water. The composition of the bottoms extracted from the column bottom (7) contained 1.3% formaldehyde and 0.3% methanol.
[0027]
(Comparative Example 4)
In Example 1, methylal was synthesized in the same manner as in Example 1 by raising the bottoms temperature at the bottom of the distillation column to 98 ° C. The composition of the distillate was 98% methylal, 1.0% methanol and 1.0% water. The composition of the bottoms extracted from the column bottom (7) contained 1.5% formaldehyde and 1.5% methanol.
[0028]
(Comparative Example 5)
Methylal was synthesized in the same manner as in Example 1 except that the supply of silicone oil modified with the polyether added to the reflux line of the distillation column in Example 1 was stopped. From 60 hours after the start of operation, foaming was gradually confirmed in the distillation column, and the temperature at the bottom of the distillation column rose to 115 ° C. When the temperature at the bottom of the distillation column finally reached 120 ° C., the operation was stopped. At this time, bubbling in the entire distillation column was confirmed.
[0029]
【The invention's effect】
According to the production method of the present invention, it is possible to synthesize methylal, which is limited in reaction yield by water produced as a by-product in the prior art, in high yield. In addition, the method of the present invention has an extremely high industrial value that makes it easy to treat the by-produced water and allows continuous production to be achieved by the addition of a defoaming agent.
[Brief description of the drawings]
FIG. 1 is a schematic view of a distillation column in which a reactor used in the present invention is connected in close proximity to the outside of the distillation column.
[Explanation of symbols]
(1) Distillation tower (2) Condenser (3) Liquid supply part A to F containing methanol, formaldehyde and water Reactor filled with solid acid catalyst (4) Cooked steam (5) Supply of water or formalin aqueous solution Part (6) Distillate (7) Bottom liquid (8) Defoamer supply unit

Claims (16)

In a method for producing methylal, wherein a liquid containing methanol, formaldehyde and water is contacted with a solid acid catalyst to obtain a methylal-rich component as a distilling component, at least 4 connected in the middle of the distillation column and in close proximity to the outside of the distillation column. A reactor filled with a solid acid catalyst is provided, a liquid containing methanol, formaldehyde and water is passed through the uppermost reactor, and the reactor connected to the lower side of the distillation column is 80 ° C to 100 ° C. Forcibly circulate a liquid containing methanol, formaldehyde, water and the generated methylal in the temperature range, and a liquid and gas containing methanol, formaldehyde, water and the generated methylal in solid-liquid contact with the reactor connected to the lower side. The methanol in the distillation column in liquid contact is circulated in a reactor connected above the reactor that produces the vapor. In order to gradually increase the concentration of methylal in the vapor phase by sequentially contacting the liquid containing formaldehyde, water and the generated methylal, and adding a defoaming agent from the top of the distillation column, A method for producing methylal, comprising taking out by-produced water as waste water at a temperature of 100 ° C. to 130 ° C. The method for producing methylal according to claim 1, wherein the number of reactors filled with the solid acid catalyst is 6 or more. The methylal production according to claim 1 or 2, wherein the solid acid catalyst charged in the reactor is at least one selected from the group consisting of a cation ion exchange resin, a fluorinated alkylene resin sulfonic acid group derivative and a crystalline zeolite. Method. There are five reactors for forced circulation in the middle column of the distillation column and connected below the uppermost reactor. The temperature of the liquid circulated in each reactor is changed in order from the upper side of the distillation column. The method for producing methylal according to any one of claims 1 to 3, which is 80 to 90 ° C, 85 to 95 ° C, 85 to 95 ° C, 90 to 100 ° C, and 90 to 100 ° C, respectively. The composition of the reaction liquid to be circulated in the reactor for forced circulation connected below the reactor connected to the top is 25 to 35 parts by weight of methanol, 0.005 to 5 parts by weight of formaldehyde, 55 to 75 parts by weight of water. The method for producing methylal according to any one of claims 1 to 4, wherein the amount is 0.01 to 5 parts by weight of methylal. The method for producing methylal according to any one of claims 1 to 5, wherein the amount of methanol supplied to the distillation tower is a molar ratio of 2.0 to 2.2 times that of formaldehyde. The method for producing methylal according to any one of claims 1 to 6, wherein the operation pressure of the distillation column to which the reactor is connected is 1 to 2 atmospheres. The amount of the liquid circulated in the reactor connected below the uppermost reactor is 15 to 30 parts by weight with respect to 1 part by weight of methylal vapor distilled from the top of the distillation column. The manufacturing method of the methylal in any one of 1-7. The solid acid catalyst used per reactor is 0.2 to 1 part by weight with respect to 1 part by weight of methylal vapor distilled from the top of the distillation column per hour. A method for producing methylal as described in 1. The distillation column to which the reactor is connected has 10 to 20 distillation stages from the uppermost reactor connected to the distillation column to the top of the column, and the lowermost reactor to the column connected to the distillation column. The method for producing methylal according to any one of claims 1 to 9, wherein the number of distillation stages to the bottom is 15 or more. The ratio (molar ratio) between the refluxed product refluxed to the top of the column and the distilled product distilled out when distilling the methylal-rich component is between 5: 1 and 1: 2. The method for producing methylal according to any one of 10 above. The composition of the distillate from the top of the tower obtained by gas-liquid contact of the water or formalin aqueous solution supplied from the upper part of the uppermost reactor and the vapor containing methylal and methanol rising in the distillation tower The methylal content is 98% or more and the methanol content is 1% or less, and the composition of the bottom bottom liquid is formaldehyde 0.1% or less and methanol 0.01% or less. Method of manufacturing methylal. The method for producing methylal according to any one of claims 1 to 12, wherein an addition amount of the antifoaming agent is 0.01 ppm to 100 ppm with respect to methylal vapor distilled from the top of the distillation column. The method for producing methylal according to any one of claims 1 to 13, wherein the antifoaming agent is silicon oil. The method according to claim 14, wherein the silicone oil is a silicone oil modified with a polyether. The method according to claim 14 or 15, wherein the silicone oil has a viscosity of 100 to 20000 centipoise.

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