JP3804818B2 - Method for producing dialkyl oxalate - Google Patents

Description

（式中、Ａｒは、フェニル基、ナフチル基等のアリール基を表す。）
【００２１】
イオン性ハロゲン化合物を含有する一酸化炭素は、第１工程の反応で消費される一酸化炭素や、反応器、凝縮器及び再生塔を経由するガス循環系の循環ガスのパージによって系外に損失する一酸化炭素を補って、第１工程の原料ガス組成を所望の範囲に維持できるように、第３工程の再生塔の底部に導入されることが好ましい。再生塔の底部には、例えば、導管１８から、第２工程の非凝縮ガスが第３工程に供給される導管１４を経由して導入されてもよく、別途独立して導入されてもよい。
【００２２】
また、本発明では、イオン性ハロゲン化合物を含有する一酸化炭素はアルカリ処理されて第３工程の再生塔の底部に導入されることが好ましい。更に、本発明では、必要に応じて、アルカリ処理の前及び／又は後に、活性炭やアルミナ等の吸着剤による処理を行って、前記の一酸化炭素から有機物（非イオン性ハロゲン化合物など）を除去してもよい。
【００２３】
アルカリ処理は、イオン性ハロゲン化合物を含有する一酸化炭素を、アルカリ水溶液と接触させる方法やアルカリ系吸着剤と接触させる方法により行われる。これらはそれぞれ単独で行っても組み合わせて行ってもよいが、アルカリ水溶液と接触させる方法が有効である。
アルカリ水溶液としては、水酸化ナトリウム、水酸化カリウム、水酸化カルシウム、炭酸ナトリウム、炭酸カリウム、炭酸カルシウム等のアルカリ金属又はアルカリ土類金属の水酸化物や炭酸塩が使用されるが、水酸化ナトリウムが好ましい。これらアルカリ金属又はアルカリ土類金属化合物の濃度は１〜５０重量％程度であることが好ましい。また、アルカリ系吸着剤としては、ゼオライト、マグネシア、酸化亜鉛、活性炭や、それらに塩基性のアルカリ金属化合物又はアルカリ土類金属化合物（金属を含む）が担持されたものなどが使用される。
【００２４】
アルカリ処理の温度は０〜１００℃、更には１０〜５０℃であることが好ましく、圧力は常圧でも加圧でもよい。また、処理（接触）時間は一酸化炭素中に含まれるイオン性ハロゲン化合物を効果的に除去できれば特に制限されない。なお、アルカリ処理の装置としては、通常の吸収塔やスクラバーなどの簡単な装置を使用することができる。
【００２５】
なお、本発明では、前記の循環ガスのパージによって系外に損失する窒素成分を補うために、第３工程の再生塔の下部に、亜硝酸アルキル、窒素酸化物（一酸化窒素、二酸化窒素、三酸化二窒素、四酸化二窒素等）、又は硝酸が導管１６を通して導入される。このようにして、一酸化炭素が補給されると共に、必要に応じて窒素成分も補給されて、再生された亜硝酸アルキルを含有するガス（再生ガス）が第１工程に供給される。
【００２６】
前記の脱カルボニル反応は、有機リン化合物触媒の存在下、液相で行われることが好ましい。脱カルボニル反応が液相で行われる場合、触媒としては、脱カルボニル反応を比較的低温（約１００〜３５０℃）で行うことができ、かつ炭酸エステルを高選択率（少なくとも５０％以上、特に６０〜１００％）で得ることができる触媒が好ましい。
【００２７】
液相反応で使用される脱カルボニル触媒としては、例えば、有機リン化合物、好ましくは少なくとも１個の炭素−リン結合を有する有機リン化合物からなる触媒が挙げられる。このような有機リン化合物としては、式（ｗ）〜（ｚ）で示されるホスフィン（ｗ）、ホスフィンオキシド（ｘ）、ホスフィンジハライド（ｙ）及びホスホニウム塩（ｚ）から選ばれる少なくとも一種の有機リン化合物からなる触媒を好適に挙げることができる。
【００２８】
【化２】

【００２９】
〔式中、Ｒ¹ 〜Ｒ¹³は、炭素数１〜１６のアルキル基、炭素数６〜１６のアリール基及び炭素数７〜２２のアラルキル基から選ばれる少なくとも一種の基を示し、Ｘは対イオンを形成しうる原子又は原子団を示し、Ｙ¹ 及びＹ² は塩素原子、臭素原子、ヨウ素原子等のハロゲン原子をそれぞれ示す。化合物（ｗ）〜（ｚ）は少なくとも１つが前述の基を有している。〕
【００３０】
前記のＲ¹ 〜Ｒ¹³で示される基としては、例えば、炭素数１〜１６のアルキル基（メチル基、エチル基、ｎ−プロピル基、ｉ−プロピル基、ｎ−ブチル基、ｉ−ブチル基等）、炭素数６〜１６のアリール基（フェニル基、メチルフェニル基、メトキシフェニル基、クロロフェニル基、ナフチル基、メチルナフチル基、メトキシナフチル基、クロロナフチル基等）、炭素数７〜２２のアラルキル基（ベンジル基、フェネチル基、４−メチルベンジル基、４−メトキシベンジル基、ｐ−メチルフェネチル基等）が挙げられる。
【００３１】
前記のアリール基及びアラルキル基は、その芳香環を形成している炭素と直接に結合する置換基として、炭素数１〜１６のアルキル基、炭素数１〜１６のアルコキシ基、ニトロ基、及びハロゲン原子（フッ素原子、塩素原子、臭素原子等）から選ばれる少なくとも１個の置換基を有していてもよい。
【００３２】
前記の有機リン化合物（ｗ）〜（ｚ）としては、それぞれが有する基（Ｒ¹ 〜Ｒ¹³）の全てがアリール基であるものが好ましいが、その１〜２個（特に２個）がアリール基であって、残部がアルキル基又はアラルキル基であるものであってもよい。
【００３３】
式（ｗ）のＲ¹ 〜Ｒ³ の全てがアリール基であるホスフィンとしては、例えば、トリフェニルホスフィン、トリス（４−クロロフェニル）ホスフィン、トリス（４−トリル）ホスフィンが挙げられる。
【００３４】
式（ｘ）のＲ⁴ 〜Ｒ⁶ の全てがアリール基であるホスフィンオキシドとしては、例えば、トリフェニルホスフィンオキシド、トリス（４−クロロフェニル）ホスフィンオキシド、トリス（４−トリル）ホスフィンオキシドが挙げられる。
【００３５】
式（ｙ）のＲ⁷ 〜Ｒ⁹ の全てがアリール基であるホスフィンジハライドとしては、例えば、トリフェニルホスフィンジクロライド、トリフェニルホスフィンジブロマイドが挙げられる。ホスフィンジハライドの中では、トリフェニルホスフィンジクロライド等のトリアリールホスフィンジクロライドが好ましい。
【００３６】
式（ｚ）のホスホニウム塩としては、Ｒ¹⁰〜Ｒ¹³の全てがアリール基であって、しかも対イオンＸ^- がハロゲンイオン、脂肪族カルボン酸イオン、又はフルオロボレートイオンなどであるホスホニウム塩が好適であるが、Ｒ¹⁰〜Ｒ¹³の１〜３個、特に２〜３個がアリール基であって、残部がアラルキル基又はアルキル基であり、更に対イオンＸ^- がハロゲンイオン、脂肪族カルボン酸イオン、又はフルオロボレートイオンなどであるものであってもよい。
【００３７】
式（ｚ）のＲ¹⁰〜Ｒ¹³の全てがアリール基であるホスホニウム塩としては、例えば、テトラフェニルホスホニウムクロライド、テトラフェニルホスホニウムブロマイド、テトラフェニルホスホニウムヨーダイド、４−クロロフェニルトリフェニルホスホニウムクロライド、４−クロロフェニルトリフェニルホスホニウムブロマイド、４−エトキシフェニルトリフェニルホスホニウムクロライド、４−エトキシフェニルトリフェニルホスホニウムブロマイド、４−メチルフェニルトリフェニルホスホニウムクロライド、４−メチルフェニルトリフェニルホスホニウムブロマイド等の対イオンＸ^- がハロゲンイオンであるホスホニウム塩などが挙げられる。
【００３８】
前記の有機リン化合物の中では、テトラアリールホスホニウム塩が好ましい。その中ではテトラアリールホスホニウムハライドが更に好ましいが、中でもテトラフェニルホスホニウムクロライド等のテトラアリールホスホニウムクロライドが特に好ましい。
有機リン化合物からなる脱カルボニル触媒は、単独であってもまた二種以上の混合物であってもよく、更に反応液中に均一に溶解及び／又は懸濁されていてもよい。脱カルボニル反応で使用される有機リン化合物の量はシュウ酸ジエステルに対して０．００１〜５０モル％、更には０．０１〜２０モル％程度であることが好ましい。
【００３９】
前記の有機リン化合物からなる脱カルボニル触媒には、必要に応じて、無機又は有機のハロゲン化合物系添加剤が添加されることが好ましい。有機リン化合物として、ホスフィンやホスフィンオキサイドを使用する場合や、ハライド及びハイドロジェンジハライド以外のホスホニウム塩を使用する場合は、このハロゲン化合物系添加剤を添加することが好ましい。添加されるハロゲン化合物系添加剤は、有機リン化合物に対して０．０１〜１５０倍モル、更には０．０５〜１００倍モル程度であることが好ましい。
【００４０】
無機ハロゲン化合物系添加剤としては、アルミニウムのハロゲン化物（塩化アルミニウム、臭化アルミニウム等）、白金族金属のハロゲン化物（塩化白金、塩化ルテニウム、塩化パラジウム等）、リンのハロゲン化物（五塩化リン等）、硫黄のハロゲン化物（塩化チオニル等）、ハロゲン化水素（塩化水素等）、ハロゲン単体（塩素等）などが挙げられる。
【００４１】
また、有機ハロゲン化合物系添加剤としては、ハロゲン化アルキル（クロロホルム、四塩化炭素、１，２−ジクロロエタン、塩化ブチル等）、ハロゲン化アラルキル（塩化ベンジル等）、ハロゲン置換脂肪族カルボン酸（クロロ酢酸、ブロモ酢酸等）、酸ハロゲン化物（塩化オキサリル、塩化プロピオニル、塩化ベンゾイル等）などが挙げられる。有機ハロゲン化合物としては、このように、飽和炭素にハロゲン原子が結合している構造（Ｃ−Ｈａｌ）や、カルボニル炭素にハロゲン原子が結合している構造（ＣＯ−Ｈａｌ）を有するものが好適である。但し、Ｈａｌは塩素原子、臭素原子等のハロゲン原子を表す。
【００４２】
脱カルボニル反応は、例えば、シュウ酸ジアリールと有機リン化合物を主成分とする触媒（及び必要に応じてハロゲン化合物系添加剤）とを反応器に供給し、発生する一酸化炭素を除去しながら、シュウ酸ジアリールを液相で脱カルボニル反応させて炭酸ジアリールを生成させることによって行われる。このとき、反応温度は１００〜４５０℃、更には１６０〜４００℃、特に１８０〜３５０℃であることが好ましい。また、反応圧力は特に制限されるものではなく、例えば、１０ｍｍＨｇ〜１０ｋｇ／ｃｍ² Ｇの範囲であればよいが、生成する一酸化炭素を第３工程の再生塔に導入することを考慮すれば、常圧から１０ｋｇ／ｃｍ² Ｇ、更には常圧から５ｋｇ／ｃｍ² Ｇの範囲、特に２〜５ｋｇ／ｃｍ² Ｇの範囲であることが好ましい。
【００４３】
以上のようにして、他の反応（例えば、シュウ酸ジアリールの脱カルボニル反応）で生成する一酸化炭素、特にイオン性ハロゲン化合物を含有する一酸化炭素を、反応に悪影響を与えることなく（即ち、触媒活性の低下や選択率の低下を引き起こすことなく）有効に再利用しながら、シュウ酸ジアルキルを連続的に製造することができる。
【００４４】
なお、シュウ酸ジアルキルは、凝縮器２から導管１５を通して抜き出される第２工程の凝縮液から蒸留などにより分離・回収される。この操作は、凝縮液が目的物のシュウ酸ジアルキルの他に、炭酸ジアルキル、ギ酸アルキル等の副生物を少量含有するため、例えば、凝縮液を蒸留塔に導いて通常の操作で蒸留することによって行われる。
【００４５】
【実施例】
次に、実施例及び比較例を挙げて、本発明を具体的に説明する。なお、分析はガスクロマトグラフィーにより行った。また、シュウ酸ジメチル（ＤＭＯ）の空時収量（ＳＴＹ：ｇ／Ｌ・ｈｒ）及び選択率（％）は下式により求めた。但し、Ｌはリットルを示す。
【００４６】
【数１】

【００４７】
【数２】

（式中、ａはシュウ酸ジメチル、ｂは炭酸ジメチル、ｃは二酸化炭素の生成モル数をそれぞれ表す。）
【００４８】
参考例１
〔シュウ酸ジメチルの製造〕
内径２７．１ｍｍ、高さ５００ｍｍのチューブよりなるステンレス製反応器に、ペレット状α−アルミナ（直径５ｍｍ、長さ３ｍｍ）にパラジウム（金属）が０．５重量％担持された固体触媒を充填した。反応器のシェル側に熱水を通して触媒層の温度を１０３〜１１５℃に保持した後、触媒層の上部から、ダイアフラム式ガス循環ポンプにより、予め熱交換器で９０℃に予熱した原料ガス（組成：一酸化炭素２２．０容量％、亜硝酸メチル１０．０容量％、一酸化窒素４．０容量％、メタノール５．２容量％、二酸化炭素１．７容量％、窒素５７．１容量％）を、１．１５Ｎｍ³ ／ｈｒ、２ｋｇ／ｃｍ² Ｇで供給して、シュウ酸ジメチルを製造した。
【００４９】
触媒層を通過したガスを、ラシヒリングを充填した気液接触吸収塔（内径４３ｍｍ、高さ１０００ｍｍ）の塔底に導いて、その塔頂から導入したメタノール０．４２Ｌ／ｈｒと約３５℃（塔頂温度３０℃、塔底温度４０℃）で向流接触させた。そして、塔底から、凝縮液（組成：シュウ酸ジメチル４２．６重量％、炭酸ジメチル１．８重量％、ギ酸メチル０．０３重量％、メタノール４２．６重量％）０．３ｋｇ／ｈｒを得て、塔頂から、非凝縮ガス（組成：一酸化炭素１６．２容量％、亜硝酸メチル４．９容量％、一酸化窒素８．１容量％、メタノール１５．９容量％、二酸化炭素１．８容量％、窒素５３．１容量％）１．２３Ｎｍ³ ／ｈｒを得た。シュウ酸ジメチルのＳＴＹは４５０ｇ／Ｌ・ｈｒ、選択率は９６．３％であった。
【００５０】
この非凝縮ガスに酸素１３．８ＮＬ／ｈｒ及び一酸化窒素０．５ＮＬ／ｈｒを混合した混合ガスを、気液接触式再生塔（内径８３ｍｍ、高さ１０００ｍｍ）の底部に導いて、その塔頂から導入したメタノール０．３３Ｌ／ｈｒと塔頂温度３０℃、塔底温度４０℃で向流接触させ、ガス中の一酸化窒素を亜硝酸メチルに再生した。再生塔の塔頂から導出された再生ガス（組成：一酸化炭素１８．２容量％、亜硝酸メチル１０．４容量％、一酸化窒素４．２容量％、メタノール５．４容量％、二酸化炭素２．０容量％、窒素５３．０容量％）１．１Ｎｍ³ ／ｈｒは、前記循環ポンプに導いて２．１ｋｇ／ｃｍ² Ｇに昇圧し、一酸化炭素４９ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）を補給した後、前記反応器に供給した。その結果、反応成績は長時間（２００時間以上）安定していた。
再生塔の塔底から導出された、５．７重量％の水を含有するメタノール０．４８Ｌ／ｈｒは、蒸留により水を除去した後、再生塔におけるメタノール源として再使用した。
【００５１】
一方、前記の凝縮液は、その５０時間分を貯蔵して、蒸留塔（内径１５０ｍｍ、高さ７５００ｍｍ、塔底部容量１００Ｌ）でバッチ蒸留したところ（塔底温度１４０℃、圧力３５０ｍｍＨｇ）、純度９９．９重量％のシュウ酸ジメチル５．８ｋｇが得られた。
【００５２】
参考例２
〔炭酸ジフェニルの製造〕
シュウ酸ジフェニルにテトラフェニルホスホニウムクロライドを１．５モル％加え、１５０℃に加熱して溶解した。この液を、温度計、攪拌機及びオーバーフロー管を備えたガラス製反応器（内容積１Ｌ）２個を連結した装置に、定量ポンプを用いて３００ｍＬ／ｈｒで供給すると共に、２個の反応器をマントルヒーターで加熱して２３０℃に保持してシュウ酸ジフェニルの脱カルボニル反応を行った。なお、各反応器のオーバーフロー位置は６００ｍＬとした。
供給開始２０時間後、第２反応器のオーバーフロー液（脱カルボニル反応の反応液）の組成は、シュウ酸ジフェニル１４．６重量％、炭酸ジフェニル８５．１重量％であり、その量は約２７０ｍＬ／ｈｒであった。また、各反応器から発生するガスの組成は一酸化炭素約１００％であり、その量は２５ＮＬ／ｈｒであった。但し、このガスには不純物としてイオン性塩素化合物が２００容量ｐｐｍ、非イオン性塩素化合物が１２０容量ｐｐｍ含まれていた。
【００５３】
実施例１
〔シュウ酸ジメチルの製造〕
参考例２の脱カルボニル反応で発生した一酸化炭素２５ＮＬ／ｈｒをダイアフラム式圧縮機で２．１ｋｇ／ｃｍ² Ｇまで昇圧した後、５ｍｍラシヒリングを３０ｃｍ充填した充填塔（内径３２ｍｍ、高さ４５０ｍｍ）の底部に供給した。塔の上部からは５重量％水酸化ナトリウム水溶液を２００ｍｌ／ｈｒで供給してガスと接触させた。次いで、塔頂から導出された一酸化炭素２５ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）を参考例１の気液接触式再生塔の底部に供給したほかは、参考例１と同様にシュウ酸ジメチルを製造した。但し、一酸化炭素２４ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）は再生ガスに補給した。
その結果、参考例１と同様の反応成績で長時間（２００時間以上）シュウ酸ジメチルを製造することができた。
【００５４】
比較例１
〔シュウ酸ジメチルの製造〕
参考例２の脱カルボニル反応で発生した一酸化炭素２５ＮＬ／ｈｒをダイアフラム式圧縮機で２．１ｋｇ／ｃｍ² Ｇまで昇圧して、一酸化炭素２４ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）と共に再生塔から導出される再生ガスに補給したほかは、参考例１と同様にシュウ酸ジメチルを製造した。
その結果、脱カルボニル反応で発生した一酸化炭素の供給を開始して初期（５０時間程度）は実施例１と同様の反応成績であったが、それ以降徐々に活性が低下すると共に選択率も低下した。即ち、供給開始５０時間後はシュウ酸ジメチルのＳＴＹが４５０ｇ／Ｌ・ｈｒ、選択率が９６．３％であったが、２００時間後はＳＴＹが３２０ｇ／Ｌ・ｈｒ、選択率が９３．７％になった。
【００５５】
比較例２
〔シュウ酸ジメチルの製造〕
参考例２の脱カルボニル反応で発生した一酸化炭素２５ＮＬ／ｈｒをダイアフラム式圧縮機で２．１ｋｇ／ｃｍ² Ｇまで昇圧した後、５ｍｍラシヒリングを３０ｃｍ充填した充填塔（内径３２ｍｍ、高さ４５０ｍｍ）の下部に供給した。塔の上部からは５重量％水酸化ナトリウム水溶液を２００ｍｌ／ｈｒで供給してガスと接触させた。次いで、塔頂から導出された一酸化炭素２５ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）を、一酸化炭素２４ＮＬ／ｈｒ（２．１ｋｇ／ｃｍ² Ｇ）と共に再生塔から導出される再生ガスに補給したほかは、参考例１と同様にシュウ酸ジメチルを製造した。
その結果、脱カルボニル反応で発生した一酸化炭素の供給を開始した当初から二酸化炭素の副生が増え、シュウ酸ジメチルの選択率も９３．６％に低下した。シュウ酸ジメチルのＳＴＹは４３５ｇ／Ｌ・ｈｒで若干低下したが長時間維持された。
【００５６】
【発明の効果】
本発明により、他の反応で生成する一酸化炭素、特にイオン性ハロゲン化合物を含有する一酸化炭素を、反応に悪影響を与えることなく有効に利用しながら、シュウ酸ジアルキルを製造することができる。即ち、本発明により、高い空時収量を維持し、かつ選択率の低下を効果的に抑えて高い選択率を維持しながら、シュウ酸ジアルキルを連続的に製造することができる。
本発明は、例えば、シュウ酸ジアリールの脱カルボニル反応で反応系外へ除去される一酸化炭素を回収して、触媒活性の低下や選択率の低下を引き起こすことなく、シュウ酸ジアルキルの製造に再利用することができる。更に、本発明では、該一酸化炭素中のフェノールや二酸化炭素なども除去できるため、シュウ酸ジアルキルの製造工程への不純物の混入を抑えて、その反応及び分離精製における悪影響を少なくでき、不活性ガスの増加も抑えることができる。本発明の方法は工業的に非常に優れたシュウ酸ジアルキルの製造法である。
【図面の簡単な説明】
【図１】図１は本発明の一実施態様を示すフローシートである。
【符号の説明】
１は反応器、２は凝縮器、３は再生塔を示し、１１〜２１は導管を示す。[0001]
[Industrial application fields]
The present invention relates to a method for producing dialkyl oxalate by reacting carbon monoxide with alkyl nitrite, and more particularly to a method for producing dialkyl oxalate while effectively using carbon monoxide produced by other reactions.
Dialkyl oxalate is a compound useful as oxalic acid, oxamide, glycolic acid, a raw material for pharmaceutical synthesis, and the like.
[0002]
[Prior art]
Methods for producing dialkyl oxalate from carbon monoxide and alkyl nitrite are disclosed in Japanese Patent Publication No. 61-6057, Japanese Patent Publication No. 61-26977, Japanese Patent Publication No. 57-30095, and the like. However, in these known literatures, carbon monoxide produced by other reactions, in particular, carbon monoxide containing a decomposable halogen compound is effectively used without affecting the reaction to produce dialkyl oxalate. No method is disclosed.
[0003]
[Problems to be solved by the invention]
The present invention provides a novel alkyl oxalate that can be produced while effectively utilizing carbon monoxide produced in other reactions, particularly carbon monoxide containing an ionic halogen compound, without adversely affecting the reaction. It is an object to provide a method for producing dialkyl oxalate.
[0004]
[Means for Solving the Problems]
The subject of the present invention is (1) a first step in which carbon monoxide and alkyl nitrite are introduced into a reactor and reacted in the presence of a platinum group metal catalyst to produce dialkyl oxalate and nitric oxide;
(2) a second step of guiding the product of the first step to a condenser and separating it into a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
(3) The non-condensed gas in the second step is introduced into the regeneration tower, and carbon monoxide containing an ionic halogen compound is treated with alkali and introduced into the regeneration tower, and the non-condensed gas is contacted with molecular oxygen and alkyl alcohol. And regenerating nitrogen monoxide in the non-condensable gas into alkyl nitrite, and supplying each of the regenerated gas and the carbon monoxide to the first step reactor. It is solved by the production method of dialkyl oxalate.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in the first step, dialkyl oxalate and nitric oxide are produced by reacting carbon monoxide and alkyl nitrite in a reactor. This reaction can be carried out in the gas phase or in the liquid phase, but industrially it is preferably carried out in the gas phase.
Next, in the second step, the condensate containing dialkyl oxalate and the non-condensable gas containing nitric oxide are separated by condensing the product of the first step with a condenser.
[0006]
Then, in the third step, in the regeneration tower, the non-condensable gas is brought into contact with molecular oxygen and alkyl alcohol (nitrogen monoxide in the non-condensed gas is reacted with molecular oxygen and alkyl alcohol). Is played. The gas (regeneration gas) containing the alkyl nitrite is supplied to the first step as a raw material for producing the dialkyl oxalate. In the present invention, in this third step, carbon monoxide generated in another reaction, in particular, carbon monoxide containing an ionic halogen compound generated in another reaction is alkali-treated and introduced into the regeneration tower, Effectively reused in the first step as a raw material for the production of dialkyl oxalate.
[0007]
Examples of the alkyl group constituting the alkyl nitrite include, for example, carbon such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, pentyl group, and hexyl group. The lower alkyl group of number 1-6 is mentioned. The alkyl nitrite is preferably an alkyl nitrite having 1 to 4 carbon atoms such as methyl nitrite, ethyl nitrite, n-propyl nitrite, i-propyl nitrite, n-butyl nitrite, i-butyl nitrite. Of these, methyl nitrite is particularly preferable. Further, as the alkyl alcohol, alkyl alcohol which is a component of these alkyl nitrites is used.
[0008]
Next, each step of the present invention will be described in detail according to a flow sheet (FIG. 1) showing an embodiment of the present invention.
The platinum group metal catalyst used in the first step is preferably a platinum group metal or a compound thereof, but the platinum group metal compound is preferably reduced and used in the form of a platinum group metal (Japanese Patent Publication No. Sho). 61-6057, JP-B 61-26977, etc.).
Examples of the platinum group metal include platinum metal, palladium metal, rhodium metal, and iridium metal. Examples of the compound include inorganic acid salts (nitrate, sulfate, phosphate, etc.), halogens of these metals. Compounds (chlorides, bromides, etc.), organic acid salts (acetates, oxalates, benzoates, etc.), complexes, etc. are used. Of the platinum group metals or compounds thereof, palladium metals or compounds thereof are particularly preferred.
[0009]
Examples of palladium compounds include palladium inorganic acid salts (palladium nitrate, palladium sulfate, palladium phosphate, etc.), palladium halides (palladium chloride, palladium bromide, etc.), and palladium organic acid salts (palladium acetate, oxalic acid). Palladium, palladium benzoate, etc.) or palladium complexes (alkyl phosphines such as trimethylphosphine, aryl phosphines such as triphenyl phosphine, alkyl aryl phosphines such as diethyl phenyl phosphine, or aryl phosphites such as triphenyl phosphite. Etc.) as a ligand.
[0010]
The platinum group metal catalyst is preferably a solid in which the platinum group metal or a compound thereof is supported on an inert carrier in an amount of preferably 0.01 to 10% by weight, more preferably 0.2 to 2% by weight in terms of platinum group metal. It is industrially preferred to be used in the form of a catalyst. For example, it is preferable that palladium metal or a compound thereof is supported on an inert carrier such as activated carbon, alumina (α-alumina, etc.), silica, diatomaceous earth, pumice, zeolite, molecular sieve, spinel and the like in the above supported amount.
In the case of using a solid catalyst in which a platinum group metal compound is supported on a carrier, the supported platinum group metal compound is previously reduced to a platinum group metal with a reducing substance such as hydrogen or used before the reaction. It is preferable to reduce the platinum group metal with a reducing substance such as carbon monoxide in the reactor. The platinum group metal catalyst is prepared by a known method (impregnation method, evaporation to dryness method, etc.).
[0011]
The platinum group metal catalyst used in the first step can contain, for example, iron or a compound thereof (Japanese Patent Laid-Open No. 59-80630).
Examples of iron or a compound thereof include metallic iron, iron (II) compound, and iron (III) compound. As the iron (II) compound, for example, ferrous sulfate, ferrous nitrate, ferrous chloride, ferrous ammonium sulfate, ferrous lactate, ferrous hydroxide, etc. are used, and iron (III) As the compound, ferric sulfate, ferric nitrate, ferric chloride, ferric ammonium sulfate, ferric lactate, ferric hydroxide, ferric citrate and the like are used. Iron or a compound thereof is used so that the platinum group metal: iron (atomic ratio) is preferably in the range of 10,000: 1 to 1: 4, more preferably 5000: 1 to 1: 3. The catalyst containing iron or a compound thereof is prepared by a known method.
[0012]
The carbon monoxide used in the first step may be pure, but may be diluted with an inert gas such as nitrogen, or may contain a small amount of hydrogen gas or methane. Furthermore, in the present invention, carbon monoxide consumed in the first step and carbon monoxide lost in the purge of the circulating gas are supplemented, so that carbon monoxide generated in other reactions, particularly one containing an ionic halogen compound. Carbon oxide is also alkali-treated and introduced into the regeneration tower of the second step, and can be used in the first step.
[0013]
If the reaction of carbon monoxide and alkyl nitrite in the first step is a gas phase method, for example, as shown in FIG. 1, a raw material gas containing carbon monoxide and alkyl nitrite is fed into a reactor 1 through a conduit 11. And a platinum group metal catalyst in a gas phase (Japanese Patent Publication No. 61-6057, Japanese Patent Publication No. 61-26977, etc.). At this time, the contact time between the source gas and the platinum group metal catalyst is preferably 10 seconds or less, more preferably 0.2 to 5 seconds, and the reaction temperature is 50 to 200 ° C., more preferably 80 to 150 ° C. Is preferred. The reaction pressure is from normal pressure to 10 kg / cm. ² G, and further from normal pressure to 5 kg / cm ² Preferably it is in the range of G, but 2-5 kg / cm ² A range of G is more preferable. As the reactor, a single-tube or multi-tube heat exchanger type reactor is effective.
[0014]
The concentration of carbon monoxide in the source gas is selected in the range of 2 to 90% by volume. In addition, the concentration of alkyl nitrite in the raw material gas can be varied in a wide range, but in order to obtain a satisfactory reaction rate, the alkyl nitrite must be present so that the concentration in the raw material gas is 1% by volume or more. Is preferred. The concentration of alkyl nitrite in the raw material gas is selected, for example, in the range of 5 to 30% by volume.
[0015]
As described above, in the first step, a product (for example, reaction gas) containing dialkyl oxalate is obtained.
Next, in the second step, this product (for example, reaction gas) is led to the bottom of the condenser 2 (absorption tower) through the conduit 12 and cooled to a temperature at which the dialkyl oxalate is condensed, and contains the dialkyl oxalate. Separated into non-condensable gas containing condensate and nitric oxide. At this time, in order to prevent the dialkyl oxalate from being entrained in the non-condensable gas, the product is cooled and absorbed at a temperature below the boiling point of the alcohol while contacting the alkyl alcohol supplied through the conduit 13. preferable. For example, when the target product is dimethyl oxalate, it is preferable to bring 100 parts of the product into contact with 0.001 to 0.1 parts by volume of methanol at 30 to 60 ° C. The operating pressure in the second step is from normal pressure to 10 kg / cm ² G, and further from normal pressure to 5 kg / cm ² Preferably it is in the range of G, but 2-5 kg / cm ² A range of G is more preferable. In addition, as the alkyl alcohol in the second step, an alkyl alcohol which is a constituent component of alkyl nitrite is used.
[0016]
Next, since the non-condensed gas in the second step contains the nitric oxide produced in the first step in addition to the unreacted carbon monoxide and alkyl nitrite, the nitric oxide is regenerated into alkyl nitrite. Guided to the third step.
In the third step, this non-condensable gas is led to the bottom of the regeneration tower 3 through the conduit 14 and is contacted with molecular oxygen supplied through the conduit 17 and alkyl alcohol supplied through the conduit 19 (nitrogen monoxide is in the molecular form. The alkyl nitrite is regenerated by reacting with oxygen and lower alcohols. Then, the nitrite ester-containing gas (regeneration gas) derived from the regeneration tower 3 is supplied to the first step through the conduit 20 and reused. Further, the water produced by this regeneration is extracted from the regeneration tower through the conduit 21 together with the alkyl alcohol. The alkyl alcohol containing water can be purified by distillation and reused as the alkyl alcohol used in the second and third steps. As the alkyl alcohol in the third step, as described above, alkyl alcohol which is a constituent of alkyl nitrite is used. As molecular oxygen, oxygen gas or air is used.
In addition, as a regeneration tower, normal gas-liquid contact apparatuses, such as a packed tower, a bubble tower, a spray tower, a plate tower, are used.
[0017]
In the regeneration of the alkyl nitrite, the reaction is controlled so that the concentration of nitric oxide in the regeneration gas is 2 to 7% by volume.
For this reason, 0.08 to 0.2 mol of molecular oxygen is supplied to 1 mol of nitric oxide in the non-condensable gas introduced into the regeneration tower, and the boiling point of the alkyl alcohol or less at the pressure during regeneration. It is preferable to contact the non-condensable gas with molecular oxygen and the alkyl alcohol at a temperature (for example, from 0 ° C. to the boiling point of the alkyl alcohol). The supply amount of the alkyl alcohol is preferably 1 to 5 parts by volume with respect to 1 part by volume of nitric oxide in the non-condensable gas, and the contact time is preferably 0.5 to 20 seconds. The operating pressure is from normal pressure to 10 kg / cm. ² G, and further from normal pressure to 5 kg / cm ² G is preferred, but 2-5 kg / cm ² G is more preferable.
[0018]
In the present invention, the carbon monoxide produced in the other reaction, in particular, the carbon monoxide containing the ionic halogen compound produced in the other reaction is introduced into the regeneration tower in the third step through the conduit 18 after being alkali-treated. Is done. And without adversely affecting the reaction (production of oxalic acid diester), it is supplied to the reactor in the first step together with the regeneration gas and is effectively reused. Examples of the ionic halogen compound include ionic chlorine compounds such as hydrogen chloride and chlorine.
[0019]
Examples of the carbon monoxide containing the ionic halogen compound include carbon monoxide generated when decarboxylation of oxalic acid diester in the presence of an organophosphorus compound catalyst to produce a carbonate ester. . Examples of the decarbonylation reaction of the oxalic acid diester include a reaction in which diaryl carbonate and carbon monoxide are generated from diaryl oxalate in the presence of an organophosphorus compound catalyst according to the following reaction formula. Although carbon monoxide produced | generated by this reaction is highly purified, an ionic halogen compound is contained about 1 volume ppm-about 1 volume%, for example according to reaction conditions and catalyst seed | species. Furthermore, the carbon monoxide produced | generated by this reaction contains trace amount phenol and a carbon dioxide depending on the case.
[0020]
[Chemical 1]

(In the formula, Ar represents an aryl group such as a phenyl group or a naphthyl group.)
[0021]
Carbon monoxide containing ionic halogen compounds is lost outside the system due to the purging of carbon monoxide consumed in the reaction of the first step and the circulating gas in the gas circulation system that passes through the reactor, condenser and regeneration tower. It is preferable to introduce into the bottom of the regeneration tower in the third step so that the carbon monoxide to be supplemented can maintain the raw material gas composition in the first step within a desired range. For example, the non-condensed gas of the second step may be introduced into the bottom of the regeneration tower from the conduit 18 via the conduit 14 supplied to the third step, or may be introduced separately.
[0022]
In the present invention, it is preferable that carbon monoxide containing an ionic halogen compound is treated with an alkali and introduced into the bottom of the regeneration tower in the third step. Furthermore, in the present invention, if necessary, before and / or after the alkali treatment, treatment with an adsorbent such as activated carbon or alumina is performed to remove organic substances (such as nonionic halogen compounds) from the carbon monoxide. May be.
[0023]
The alkali treatment is performed by a method of contacting carbon monoxide containing an ionic halogen compound with an alkaline aqueous solution or a method of contacting with an alkaline adsorbent. These may be performed alone or in combination, but a method of contacting with an alkaline aqueous solution is effective.
As the alkaline aqueous solution, hydroxides or carbonates of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, and calcium carbonate are used. Is preferred. The concentration of the alkali metal or alkaline earth metal compound is preferably about 1 to 50% by weight. Further, as the alkaline adsorbent, zeolite, magnesia, zinc oxide, activated carbon, and those in which a basic alkali metal compound or an alkaline earth metal compound (including a metal) is supported are used.
[0024]
The temperature of the alkali treatment is preferably 0 to 100 ° C., more preferably 10 to 50 ° C. The pressure may be normal pressure or increased pressure. The treatment (contact) time is not particularly limited as long as the ionic halogen compound contained in carbon monoxide can be effectively removed. In addition, as an apparatus for alkali treatment, a simple apparatus such as a normal absorption tower or scrubber can be used.
[0025]
In the present invention, in order to compensate for the nitrogen component lost outside the system by purging the circulating gas, alkyl nitrite, nitrogen oxide (nitrogen monoxide, nitrogen dioxide, Dinitrogen trioxide, dinitrogen tetroxide, etc.) or nitric acid is introduced through conduit 16. In this way, carbon monoxide is replenished, and a nitrogen component is replenished as necessary, and the regenerated gas containing the nitrite (regenerated gas) is supplied to the first step.
[0026]
The decarbonylation reaction is preferably performed in a liquid phase in the presence of an organophosphorus compound catalyst. When the decarbonylation reaction is carried out in the liquid phase, as the catalyst, the decarbonylation reaction can be carried out at a relatively low temperature (about 100 to 350 ° C.), and the carbonate ester has a high selectivity (at least 50% or more, particularly 60 Catalysts obtainable at ˜100%) are preferred.
[0027]
Examples of the decarbonylation catalyst used in the liquid phase reaction include an organophosphorus compound, preferably a catalyst composed of an organophosphorus compound having at least one carbon-phosphorus bond. As such an organic phosphorus compound, at least one organic compound selected from phosphine (w), phosphine oxide (x), phosphine dihalide (y) and phosphonium salt (z) represented by formulas (w) to (z) is used. A catalyst comprising a phosphorus compound can be preferably mentioned.
[0028]
[Chemical 2]

[0029]
[In the formula, R ¹ ~ R ¹³ Represents at least one group selected from an alkyl group having 1 to 16 carbon atoms, an aryl group having 6 to 16 carbon atoms and an aralkyl group having 7 to 22 carbon atoms, and X is an atom or atomic group capable of forming a counter ion Y ¹ And Y ² Represents a halogen atom such as a chlorine atom, a bromine atom or an iodine atom. At least one of the compounds (w) to (z) has the aforementioned group. ]
[0030]
R above ¹ ~ R ¹³ As the group represented by, for example, an alkyl group having 1 to 16 carbon atoms (methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, etc.), 6 to 6 carbon atoms. 16 aryl groups (phenyl group, methylphenyl group, methoxyphenyl group, chlorophenyl group, naphthyl group, methylnaphthyl group, methoxynaphthyl group, chloronaphthyl group, etc.), aralkyl groups having 7 to 22 carbon atoms (benzyl group, phenethyl group) 4-methylbenzyl group, 4-methoxybenzyl group, p-methylphenethyl group, etc.).
[0031]
The aryl group and the aralkyl group have a C 1-16 alkyl group, a C 1-16 alkoxy group, a nitro group, and a halogen as a substituent directly bonded to the carbon forming the aromatic ring. It may have at least one substituent selected from atoms (fluorine atom, chlorine atom, bromine atom, etc.).
[0032]
As said organophosphorus compound (w)-(z), each group (R ¹ ~ R ¹³ ) Is preferably an aryl group, but one or two (particularly two) of them may be an aryl group and the remainder may be an alkyl group or an aralkyl group.
[0033]
R in formula (w) ¹ ~ R ^Three Examples of the phosphine in which all are aryl groups include triphenylphosphine, tris (4-chlorophenyl) phosphine, and tris (4-tolyl) phosphine.
[0034]
R in formula (x) ^Four ~ R ⁶ Examples of the phosphine oxide in which all are aryl groups include triphenylphosphine oxide, tris (4-chlorophenyl) phosphine oxide, and tris (4-tolyl) phosphine oxide.
[0035]
R in formula (y) ⁷ ~ R ⁹ Examples of the phosphine dihalide, all of which is an aryl group, include triphenylphosphine dichloride and triphenylphosphine dibromide. Among the phosphine dihalides, triarylphosphine dichlorides such as triphenylphosphine dichloride are preferable.
[0036]
As the phosphonium salt of the formula (z), R ^Ten ~ R ¹³ Are all aryl groups, and the counter ion X ^- A phosphonium salt in which is a halogen ion, an aliphatic carboxylate ion, a fluoroborate ion or the like is preferable. ^Ten ~ R ¹³ 1 to 3, particularly 2 to 3 are aryl groups, the remainder being an aralkyl group or an alkyl group, and a counter ion X ^- May be a halogen ion, an aliphatic carboxylate ion, or a fluoroborate ion.
[0037]
R in formula (z) ^Ten ~ R ¹³ Examples of phosphonium salts in which all of them are aryl groups include, for example, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium iodide, 4-chlorophenyltriphenylphosphonium chloride, 4-chlorophenyltriphenylphosphonium bromide, 4-ethoxyphenyl. Counter ions X such as triphenylphosphonium chloride, 4-ethoxyphenyltriphenylphosphonium bromide, 4-methylphenyltriphenylphosphonium chloride, 4-methylphenyltriphenylphosphonium bromide ^- A phosphonium salt in which is a halogen ion.
[0038]
Of the organic phosphorus compounds, tetraarylphosphonium salts are preferred. Among them, tetraarylphosphonium halides are more preferable, and tetraarylphosphonium chlorides such as tetraphenylphosphonium chloride are particularly preferable.
The decarbonylation catalyst composed of an organophosphorus compound may be used singly or as a mixture of two or more kinds, and may be uniformly dissolved and / or suspended in the reaction solution. The amount of the organophosphorus compound used in the decarbonylation reaction is preferably about 0.001 to 50 mol%, more preferably about 0.01 to 20 mol% with respect to the oxalic acid diester.
[0039]
It is preferable that an inorganic or organic halogen compound-based additive is added to the decarbonylation catalyst composed of the organic phosphorus compound as necessary. When phosphine or phosphine oxide is used as the organic phosphorus compound, or when a phosphonium salt other than halide and hydrogen dihalide is used, it is preferable to add this halogen compound-based additive. The halogen compound-based additive to be added is preferably about 0.01 to 150 times mol, more preferably about 0.05 to 100 times mol for the organophosphorus compound.
[0040]
Inorganic halogen compound additives include aluminum halides (aluminum chloride, aluminum bromide, etc.), platinum group metal halides (platinum chloride, ruthenium chloride, palladium chloride, etc.), phosphorus halides (phosphorus pentachloride, etc.) ), Sulfur halides (thionyl chloride and the like), hydrogen halides (hydrogen chloride and the like), halogen simple substances (chlorine and the like), and the like.
[0041]
Organic halogen compound additives include alkyl halides (chloroform, carbon tetrachloride, 1,2-dichloroethane, butyl chloride, etc.), aralkyl halides (benzyl chloride, etc.), halogen-substituted aliphatic carboxylic acids (chloroacetic acid). , Bromoacetic acid, etc.), acid halides (oxalyl chloride, propionyl chloride, benzoyl chloride, etc.) and the like. As the organic halogen compound, those having a structure in which a halogen atom is bonded to saturated carbon (C-Hal) and a structure in which a halogen atom is bonded to carbonyl carbon (CO-Hal) are suitable. is there. However, Hal represents halogen atoms, such as a chlorine atom and a bromine atom.
[0042]
In the decarbonylation reaction, for example, a catalyst comprising diaryl oxalate and an organophosphorus compound as main components (and a halogenated additive as necessary) is supplied to the reactor, and the generated carbon monoxide is removed, This is done by decarbonylating the diaryl oxalate in the liquid phase to form a diaryl carbonate. At this time, the reaction temperature is preferably 100 to 450 ° C, more preferably 160 to 400 ° C, and particularly preferably 180 to 350 ° C. The reaction pressure is not particularly limited, and for example, 10 mmHg to 10 kg / cm. ² If it is considered that the carbon monoxide to be produced is introduced into the regeneration tower of the third step, it is from the normal pressure to 10 kg / cm. ² G, and further from normal pressure to 5 kg / cm ² G range, especially 2-5kg / cm ² The range of G is preferable.
[0043]
As described above, carbon monoxide produced in other reactions (for example, decarbonylation reaction of diaryl oxalate), particularly carbon monoxide containing an ionic halogen compound, is not adversely affected (that is, The dialkyl oxalate can be continuously produced while being effectively reused (without causing a decrease in catalytic activity and a reduction in selectivity).
[0044]
The dialkyl oxalate is separated and recovered by distillation or the like from the second step condensate extracted from the condenser 2 through the conduit 15. In this operation, since the condensate contains a small amount of by-products such as dialkyl carbonate and alkyl formate in addition to the target dialkyl oxalate, for example, the condensate is introduced into a distillation column and distilled by a normal operation. Done.
[0045]
【Example】
Next, an Example and a comparative example are given and this invention is demonstrated concretely. The analysis was performed by gas chromatography. The space-time yield (STY: g / L · hr) and selectivity (%) of dimethyl oxalate (DMO) were determined by the following equations. However, L shows a liter.
[0046]
[Expression 1]

[0047]
[Expression 2]

(In the formula, a represents dimethyl oxalate, b represents dimethyl carbonate, and c represents the number of moles of carbon dioxide generated.)
[0048]
Reference example 1
[Production of dimethyl oxalate]
A stainless steel reactor composed of a tube having an inner diameter of 27.1 mm and a height of 500 mm was filled with a solid catalyst in which 0.5% by weight of palladium (metal) was supported on pellet-shaped α-alumina (diameter 5 mm, length 3 mm). . After maintaining the temperature of the catalyst layer at 103 to 115 ° C. by passing hot water through the shell side of the reactor, the raw material gas (composition) preheated to 90 ° C. with a heat exchanger by a diaphragm gas circulation pump from the upper part of the catalyst layer : Carbon monoxide 22.0% by volume, methyl nitrite 10.0% by volume, nitric oxide 4.0% by volume, methanol 5.2% by volume, carbon dioxide 1.7% by volume, nitrogen 57.1% by volume) 1.15 Nm ^Three / Hr, 2kg / cm ² G was supplied to produce dimethyl oxalate.
[0049]
The gas that passed through the catalyst layer was led to the bottom of a gas-liquid contact absorption tower (inner diameter: 43 mm, height: 1000 mm) packed with Raschig rings, and methanol introduced from the top of the tower at 0.42 L / hr and about 35 ° C. (tower Countercurrent contact was made at a top temperature of 30 ° C. and a column bottom temperature of 40 ° C.). Then, 0.3 kg / hr of condensate (composition: dimethyl oxalate 42.6% by weight, dimethyl carbonate 1.8% by weight, methyl formate 0.03% by weight, methanol 42.6% by weight) is obtained from the tower bottom. From the top of the column, non-condensable gas (composition: carbon monoxide 16.2% by volume, methyl nitrite 4.9% by volume, nitric oxide 8.1% by volume, methanol 15.9% by volume, carbon dioxide 1. 8 volume%, nitrogen 53.1 volume%) 1.23 Nm ^Three / Hr was obtained. The dimethyl oxalate had an STY of 450 g / L · hr and a selectivity of 96.3%.
[0050]
This non-condensed gas was mixed with oxygen of 13.8 NL / hr and nitrogen monoxide 0.5 NL / hr and led to the bottom of a gas-liquid contact-type regeneration tower (inner diameter 83 mm, height 1000 mm). The mixture was brought into countercurrent contact with 0.33 L / hr of methanol introduced from the above at a tower top temperature of 30 ° C. and a tower bottom temperature of 40 ° C. to regenerate nitrogen monoxide in the gas into methyl nitrite. Regeneration gas derived from the top of the regeneration tower (composition: carbon monoxide 18.2% by volume, methyl nitrite 10.4% by volume, nitric oxide 4.2% by volume, methanol 5.4% by volume, carbon dioxide 2.0% by volume, nitrogen 53.0% by volume) 1.1 Nm ^Three / Hr is 2.1 kg / cm led to the circulating pump ² Boosted to G, carbon monoxide 49NL / hr (2.1kg / cm ² G) was replenished and then fed to the reactor. As a result, the reaction results were stable for a long time (200 hours or more).
0.48 L / hr of methanol containing 5.7% by weight of water derived from the bottom of the regeneration tower was reused as a methanol source in the regeneration tower after removing water by distillation.
[0051]
On the other hand, the condensate is stored for 50 hours and batch distilled in a distillation column (inner diameter 150 mm, height 7500 mm, column bottom volume 100 L) (column bottom temperature 140 ° C., pressure 350 mmHg), purity 99 5.8 kg of 9% by weight of dimethyl oxalate was obtained.
[0052]
Reference example 2
[Production of diphenyl carbonate]
1.5 mol% of tetraphenylphosphonium chloride was added to diphenyl oxalate and dissolved by heating to 150 ° C. This liquid was supplied at a rate of 300 mL / hr using a metering pump to a device in which two glass reactors (internal volume: 1 L) equipped with a thermometer, a stirrer, and an overflow pipe were connected. The mixture was heated with a mantle heater and maintained at 230 ° C. to carry out decarbonylation of diphenyl oxalate. The overflow position of each reactor was 600 mL.
After 20 hours from the start of supply, the composition of the overflow solution (recarbonylation reaction solution) of the second reactor was 14.6% by weight of diphenyl oxalate and 85.1% by weight of diphenyl carbonate, and the amount thereof was about 270 mL / hr. The composition of the gas generated from each reactor was about 100% carbon monoxide, and the amount was 25 NL / hr. However, this gas contained 200 ppm by volume of ionic chlorine compounds and 120 ppm by volume of nonionic chlorine compounds as impurities.
[0053]
Example 1
[Production of dimethyl oxalate]
Carbon monoxide 25 NL / hr generated in the decarbonylation reaction of Reference Example 2 was 2.1 kg / cm using a diaphragm compressor. ² After the pressure was increased to G, it was supplied to the bottom of a packed tower (inner diameter: 32 mm, height: 450 mm) packed with 30 mm of 5 mm Raschig rings. From the top of the column, a 5 wt% aqueous sodium hydroxide solution was supplied at 200 ml / hr and brought into contact with the gas. Next, carbon monoxide 25 NL / hr (2.1 kg / cm ² Dimethyl oxalate was produced in the same manner as in Reference Example 1 except that G) was supplied to the bottom of the gas-liquid contact type regeneration tower of Reference Example 1. However, carbon monoxide 24 NL / hr (2.1 kg / cm ² G) was replenished with regeneration gas.
As a result, it was possible to produce dimethyl oxalate for a long time (200 hours or more) with the same reaction results as in Reference Example 1.
[0054]
Comparative Example 1
[Production of dimethyl oxalate]
Carbon monoxide 25 NL / hr generated in the decarbonylation reaction of Reference Example 2 was 2.1 kg / cm using a diaphragm compressor. ² Boosted to G, carbon monoxide 24 NL / hr (2.1 kg / cm ² Dimethyl oxalate was produced in the same manner as in Reference Example 1 except that the regeneration gas derived from the regeneration tower was supplied together with G).
As a result, the supply of carbon monoxide generated in the decarbonylation reaction was started and the initial (about 50 hours) was the same reaction results as in Example 1, but thereafter the activity gradually decreased and the selectivity was also increased. Declined. That is, STY of dimethyl oxalate was 450 g / L · hr and selectivity was 96.3% after 50 hours from the start of supply, but STY was 320 g / L · hr and selectivity was 93.7 after 200 hours. %Became.
[0055]
Comparative Example 2
[Production of dimethyl oxalate]
Carbon monoxide 25 NL / hr generated in the decarbonylation reaction of Reference Example 2 was 2.1 kg / cm using a diaphragm compressor. ² After the pressure was increased to G, it was supplied to the lower part of a packed tower (inner diameter: 32 mm, height: 450 mm) packed with 30 mm of 5 mm Raschig rings. From the upper part of the tower, a 5 wt% aqueous sodium hydroxide solution was supplied at 200 ml / hr and brought into contact with the gas. Next, carbon monoxide 25 NL / hr (2.1 kg / cm ² G), carbon monoxide 24 NL / hr (2.1 kg / cm ² Dimethyl oxalate was produced in the same manner as in Reference Example 1 except that the regeneration gas derived from the regeneration tower was supplied together with G).
As a result, carbon dioxide by-product increased from the beginning of the supply of carbon monoxide generated by the decarbonylation reaction, and the selectivity for dimethyl oxalate also decreased to 93.6%. The STY of dimethyl oxalate slightly decreased at 435 g / L · hr, but was maintained for a long time.
[0056]
【The invention's effect】
According to the present invention, dialkyl oxalate can be produced while effectively utilizing carbon monoxide produced by other reactions, particularly carbon monoxide containing an ionic halogen compound, without adversely affecting the reaction. That is, according to the present invention, dialkyl oxalate can be continuously produced while maintaining a high space-time yield and effectively suppressing a decrease in selectivity and maintaining a high selectivity.
The present invention, for example, recovers carbon monoxide that is removed from the reaction system by the decarbonylation reaction of diaryl oxalate, and regenerates the production of dialkyl oxalate without causing a decrease in catalytic activity and a decrease in selectivity. Can be used. Furthermore, in the present invention, phenol, carbon dioxide and the like in the carbon monoxide can also be removed, so that contamination of the dialkyl oxalate production process can be suppressed, and adverse effects in the reaction and separation and purification can be reduced. An increase in gas can also be suppressed. The process of the present invention is an industrially excellent process for producing dialkyl oxalate.
[Brief description of the drawings]
FIG. 1 is a flow sheet showing an embodiment of the present invention.
[Explanation of symbols]
1 represents a reactor, 2 represents a condenser, 3 represents a regeneration tower, and 11 to 21 represent conduits.

Claims (4)

(1) a first step in which carbon monoxide and alkyl nitrite are introduced into a reactor and reacted in the presence of a platinum group metal catalyst to produce dialkyl oxalate and nitric oxide;
(2) a second step of guiding the product of the first step to a condenser and separating it into a condensate containing dialkyl oxalate and a non-condensable gas containing nitric oxide;
(3) The non-condensed gas in the second step is introduced into the regeneration tower, and carbon monoxide containing an ionic halogen compound is alkali-treated and introduced into the regeneration tower, and the non-condensed gas is contacted with molecular oxygen and alkyl alcohol. And regenerating nitrogen monoxide in the non-condensable gas to alkyl nitrite, and supplying each of the regenerated gas and the carbon monoxide to the first step reactor. A method for producing dialkyl oxalate. The carbon monoxide containing an ionic halogen compound is carbon monoxide generated when a carbonic acid ester is produced by decarbonylation of an oxalic acid diester in the presence of an organophosphorus compound catalyst. A process for producing dialkyl acids. The method for producing a dialkyl oxalate according to claim 2, wherein a decarbonylation reaction is carried out by adding a halogen compound-based additive. The method for producing a dialkyl oxalate according to claim 1, 2, or 3, wherein the ionic halogen compound is an ionic chlorine compound.

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