JP3960528B2 - Method for producing dimethyl carbonate and ethylene glycol - Google Patents

Description

【００１０】
（Ａ）エステル交換反応工程においては、ＥＣとＭｅＯＨとをエステル交換反応させ、ＭｅＯＨ、ＤＭＣ、ＭｅＧＥ、ＥＧ及びＥＣを含む反応混合物を得る。エステル交換反応は以下の化学反応式（１）で示され、ＭｅＧＥの副生反応は以下の化学反応式（２）で示される。
【００１１】
【化１】

【００１２】
通常、上記のエステル交換反応は触媒の存在下に行なわれる。触媒としては、カーボネート類のエステル交換触媒として一般的に使用されているものを制限なく使用するすることが出来る。具体的には、均一系触媒として、トリエチルアミン等のアミン類、ナトリウム等のアルカリ金属、クロロ酢酸ナトリウム、ナトリウムメチラート等のアルカリ金属化合物、タリウム化合物などが挙げられ、不均一系触媒として、官能基により変性したイオン交換樹脂、アルカリ金属またはアルカリ土類金属の珪酸塩を含浸した無定型シリカ類、アンモニウム交換Ｙ型ゼオライト、コバルトとニッケルとの混合酸化物などが挙げられる。
【００１３】
反応器の形式は、特に限定されないが、図示した様に、固定床式反応器（１）を使用するのが好ましい。図示した例の場合は、ＥＣ及びＭｅＯＨは反応器（１）の頂部のライン（Ｌ１）及びライン（Ｌ２）から供給され、反応液は底部のライン（Ｌ３）から取り出されている。ＥＣに対するＭｅＯＨの使用割合（モル比）は通常２〜２０であり、反応温度は通常５０〜１８０℃、反応圧力は通常１００〜２０００ＫＰａ、反応時間は通常０．５〜５時間である。
【００１４】
上記のエステル交換反応は平衡反応であり、反応液中には必ず未反応の原料成分が存在する。すなわち、反応液中には、目的生成物のＤＭＣ及びＥＧの他に、原料のＥＣ及びＭｅＯＨが含まれ、更に、副生したＭｅＧＥ等が含まれている。
【００１５】
（Ｂ）第１蒸留工程においては、上記のエステル交換反応工程の反応混合物から、ＭｅＯＨ及びＤＭＣを含み且つＭｅＧＥ含量が１０重量ｐｐｍ以下の低沸点留分を分離する。すなわち、本発明において、ＭｅＧＥの分離は高沸点留分側から行なうため、第１蒸留工程の低沸点留分側には可及的に持ち込まない様にする必要がある。
【００１６】
第１蒸留工程の蒸留塔（２）は、塔底部にリボイラー（３）、塔頂部に凝縮器（４）を備え、当該凝縮器（４）の気相部はエジェクター等の真空装置（図示せず）に連結されている。反応液はライン（Ｌ３）から蒸留塔（２）の供給段に導入され、ＭｅＯＨ及びＤＭＣを含み且つＭｅＧＥ含量が１０重量ｐｐｍ以下の低沸点留分はライン（Ｌ５）から凝縮器（４）に導入され、ＭｅＧＥ、ＥＧ及びＥＣを含む高沸点留分はライン（Ｌ４）から抜出される。
【００１７】
（Ｃ）加水分解工程においては、第１蒸留工程から回収され、且つ、ＥＣ、ＥＧ及びＭｅＧＥを含む高沸点留分に当該高沸点留分中のＥＣに対して過剰モル量の水を添加してＥＣをＥＧと二酸化炭素（ＣＯ₂）とに加水分解する。ＥＣの加水分解は以下の化学反応式（３）で示される。なお、この加水分解工程においては、生成したＥＧからＤＥＧが副生し、更に、ＴＥＧ、ＰＥＧ等が生成することもある。
【００１８】
【化２】

【００１９】
通常、上記の加水分解は触媒の存在下に行なわれる。触媒としては、活性アルミナが好適に使用される。反応器の形式は、特に限定されないが、図示した様に、固定床式反応器（５）を使用するのが好ましい。ライン（Ｌ４）から抜出された高沸点留分は、ライン（Ｌ６）から水が添加された後に、固定床式反応器（５）に供給される。ＥＣに対する水の使用割合（モル比）は通常１〜５であり、反応温度は通常１００〜２００℃、反応圧力は通常１００〜３０００ＫＰａ、反応時間は通常０．５〜５時間である。
【００２０】
（Ｄ）二酸化炭素分離工程においては、上記の加水分解工程の反応混合物から二酸化炭素を分離する。二酸化炭素の分離手段は特に制限されない。加水分解工程の反応混合物を常圧の脱炭酸タンク内に供給して加水分解工程の圧力を開放するだけで二酸化炭素を容易に分離することが出来る。
【００２１】
図示した脱炭酸タンク（気液分離器）（６）は、圧力調節器（図示せず）を備え、更に、二酸化炭素と共に留出する水蒸気を回収するために凝縮器（７）を備えている。加水分解工程の反応混合物はライン（Ｌ７）から脱炭酸タンク（６）に導入され、二酸化炭素は、凝縮器（７）の気相部のライン（Ｌ８）から抜出される。
【００２２】
（Ｅ）第２蒸留工程においては、上記の二酸化炭素分離工程から回収され、且つ、水、ＭｅＧＥ、ＥＧ及びＤＥＧを含む混合物から、水およびＭｅＧＥを含む低沸点留分と、ＤＥＧを含む高沸点留分とを分離し、ＥＧ留分を回収する。
【００２３】
第２蒸留工程の蒸留塔（８）は、塔底部にリボイラー（９）、塔頂部に二段階の凝縮器（１０）及び（１１）を備え、凝縮器（１１）の気相部はエジェクター等の真空装置（図示せず）に連結されている。すなわち、後段の凝縮器（１１）は所謂ベントコンデンサーである。二酸化炭素分離工程から回収された混合物はライン（Ｌ９）から蒸留塔（８）の供給段に導入され、水およびＭｅＧＥを含む低沸点留分は塔頂のライン（Ｌ１０）から凝縮器（１０）に導入され、ＤＥＧを含む高沸点留分は塔底のライン（Ｌ１１）から抜出される。そして、ＥＧ留分は、塔中間のライン（Ｌ１２）からサイドカットとして回収される。
【００２４】
前記の蒸留塔（２）及び（８）の形式は、棚段塔または充填塔の何れの形式であってもよい。棚段塔としては、シーブトレイ、泡鐘塔などの公知の型式を使用することが出来る。充填塔における充填物としては、スルザーパック、メラパック、ＭＣパック等の規則充填物、ＩＭＴＰ、ラシヒリング等の不規則充填物を使用することが出来る。
【００２５】
前記の蒸留塔（２）及び（８）の濃縮段および回収段の段数、操作条件（温度、圧力、還流比など）は、目的とする成分分離が行なわれる様に適宜選択される。因に、各蒸留塔の理論段数は、通常５〜３０段、好ましくは７〜２０段であり、還流比は、通常０．１〜５、好ましくは０．５〜２である。
【００２６】
なお、凝縮器（４）、（７）、（１０）及び（１１）としては一般的な多管式熱交換器を使用することが出来る。
【００２７】
本発明の好ましい実施態様においては、第２蒸留工程で分離された水およびＭｅＧＥを含む低沸点留分からＭｅＧＥを分離して水を回収し、加水分解工程の反応水として使用する。すなわち、図２に示す様に、蒸留塔（８）の二段階の凝縮器（１０）及び（１１）の内、前段のコンデンサー（１０）の温度を高め、水は凝縮するがＭｅＧＥは凝縮し難い温度（例えば６０℃）とし、コンデンサー（１０）で回収した凝縮水をライン（Ｌ１３）によって固定床式反応器（５）に供給する。
【００２８】
【実施例】
以下、本発明を実施例により更に詳細に説明するが、本発明は、その要旨を超えない限り、以下の実施例に限定されるものではない。
【００２９】
実施例１
図１に示すのと同様のプロセスにより、以下に記載した（１）エステル交換反応工程、（２）第１蒸留工程、（３）加水分解工程、（４）二酸化炭素分離工程、（５）第２蒸留工程を行なった。
【００３０】
（ａ）エステル交換反応工程：
固定床反応器（１）としては、四級アンモニウム塩構造がスペーサー基を介して架橋ポリスチレン鎖に結合したアニオン交換樹脂を充填した反応器を使用した。固定床反応器（１）に、ライン（Ｌ１）からＥＣ８８重量部、ライン（Ｌ２）からＭｅＯＨ６４重量部を供給し、反応温度：８０℃、反応圧力：２００ＫＰａ、ＬＨＳＶ：１の条件で反応させたところ、ライン（Ｌ３）から、ＭｅＯＨ２６重量％、ＤＭＣ２２重量％、ＥＧ１５重量％、ＥＣ３６重量％の反応液が得られた。反応液中には副生したＭｅＧＥが０．４重量％含まれていた。
【００３１】
（ｂ）第１蒸留工程：
蒸留塔（２）としては、三菱化学エンジニアリング（株）製「ＭＣパック２５０Ｓ」を７ｍの高さに充填した内径０．２ｍの充填塔を使用した。蒸留塔（２）にライン（Ｌ３）から上記の反応液を供給した。反応液の供給は充填部上端から２．５ｍの位置に行なった。そして、還流比０．３で蒸留分離を行なって、塔頂のライン（Ｌ５）からＭｅＯＨとＤＭＣの混合液、塔底のライン（Ｌ４）からＥＧとＥＣの混合液を得た。操作圧力は塔頂で２４ＫＰａとした。塔頂液組成は、ＭｅＯＨ５４重量％、ＤＭＣ４６重量％であり、痕跡量のＭｅＧＥが検出された。塔底液組成は、ＭｅＧＥ０．７重量％、ＥＧ３０重量％、ＥＣ６９重量％であり、ＤＭＣは１０重量ｐｐｍ未満、ＭｅＯＨ及びＤＭＥは検出されなかった。
【００３２】
（ｃ）加水分解工程：
固定床式反応器（５）としては、活性アルミナを充填した反応器を使用した。ライン（Ｌ４）から抜出れた高沸点留分にライン（Ｌ６）から水を添加して固定床式反応器（５）に供給した。水の添加量は、ＥＣに対し、１．５倍（モル）量のとした。反応温度：１８０℃、反応圧力：２５００ＫＰａ、ＬＨＳＶ：０．５で反応を行なった。加水分解後のＥＣ濃度は１０重量ｐｐｍ未満に低下した。
【００３３】
（ｄ）二酸化炭素分離工程：
ライン（Ｌ７）から上記の反応混合物を脱炭酸タンク（６）に導入し、反応混合物を常圧まで減圧し、二酸化炭素を分離した。反応混合物の液温は、減圧に伴い低下したが、１００℃を超えているため、二酸化炭素と共に水が留去する。そこで、凝縮器（７）により留出ベーパーを５０℃に冷却して凝縮し、得られた凝縮液を脱炭酸タンク（６）に戻しながら操作を行った。
【００３４】
（ｅ）第２蒸留工程：
蒸留塔（８）としては、三菱化学エンジニアリング（株）製「ＭＣパック２５０Ｓ」を９ｍの高さに充填した内径０．２ｍの充填塔を使用した。蒸留塔（８）にライン（Ｌ９）から上記の混合物を供給した。混合物の供給は充填部上端から４．５ｍの位置に行なった。そして、還流比１．２で蒸留分離を行なって、塔頂のライン（Ｌ１０）から水とＥＧの混合液、塔底のライン（Ｌ１１）からＥＧを主成分としＤＥＧ以上の高分子量エチレングリコールを含む混合液を得た。そして、充填部下端より２．３ｍの位置からＥＧベーパーを抜き出した。なお、コンデンサー（１０）における凝縮温度は４５℃、コンデンサー（１１）における凝縮温度は１０℃とした。その結果、ＭｅＧＥの９９．８重量％はコンデンサー（１０）、残りの０．２重量％はコンデンサー（１１）でそれぞれ回収された。
【００３５】
塔頂液組成は、水２７重量％、ＥＧ７０重量％であり、ＭｅＧＥ３重量％を含有していた。塔底液組成は、ＥＧ８２重量％であり、高分子量のエチレングリコール類１８重量％を含有していた。また、側流ベーパーはＤＥＧ含量３００重量ｐｐｍのＥＧであった。
【００３６】
以上の操作により、エステル交換反応において副生したＭｅＧＥの略全量が第２蒸留工程におけるＥＧ精製の際に水と共に除去された。この場合、加水分解工程の固定床式反応器（５）出口におけるＭｅＧＥ濃度は０．６重量％であった。また、蒸留塔（８）の側流ベーパーを凝縮して得られたＥＧは、ＭｅＧＥを含まず、一般的なＰＥＴ原料としての品質規格を満たすものであった。
【００３７】
実施例２
図２に示すのと同様のプロセスを採用した。すなわち、実施例１において、コンデンサー（１０）における凝縮温度は６０℃、コンデンサー（１１）における凝縮温度は１０℃とし、コンデンサー（１１）にて回収された凝縮水をライン（Ｌ１３）によって固定床式反応器（５）に供給した他は、実施例１と同様に操作した。なお、ＭｅＧＥの９１重量％はコンデンサー（１０）、残りの９重量％はコンデンサー（１１）でそれぞれ回収された。そして、この場合、固定床式反応器（５）出口におけるＭｅＧＥ濃度は０．６重量％であった。また、蒸留塔（８）の側流ベーパーを凝縮して得られたＥＧは、ＭｅＧＥを含まず、一般的なＰＥＴ原料としての品質規格を満たすものであった。
【００３８】
比較例１
図３に示すのと同様のプロセスを採用した。すなわち、実施例１において、第１蒸留工程の蒸留塔（２）において、留出量を若干増加させてＭｅＧＥを低沸点成分と共に抜き出した他は、実施例１と同様に操作した。
【００３９】
そして、蒸留塔（２）から抜き出した低沸点留分は、蒸留塔（１２）で処理した。蒸留塔（１２）としては、三菱化学エンジニアリング（株）製「ＭＣパック２５０Ｓ」を４．５ｍの高さに充填した内径０．２ｍの充填塔を使用した。蒸留塔（１２）は、塔底部にリボイラー（１３）、塔頂部に凝縮器（１４）を備え、凝縮器（１４）の気相部はエジェクター等の真空装置（図示せず）に連結されている。蒸留塔（１２）にライン（Ｌ１４）から上記の低沸点留分を供給した。低沸点留分の供給は充填部上端から１ｍの位置に行なった。そして、還流比１．０で蒸留分離を行なって、塔頂のライン（Ｌ１５）からＭｅＯＨとＤＭＣの混合液、塔底のライン（Ｌ１６）からＭｅＯＨ、ＤＭＣ及びＭｅＧＥの混合液を得た。塔頂留分中のＭｅＧＥが１０重量ｐｐｍ未満となる様に操作した。
【００４０】
エステル交換反応液の蒸留の際に低沸点側でＭｅＧＥを回収する上記の様な方法では、この蒸留分離のために必要な熱量が約２％増加する他、その後にＭｅＧＥの蒸留分離が必要となるため、消費エネルギーが実施例１の５３％増となった。
【００４１】
【発明の効果】
以上説明した本発明によれば、エチレンカーボネートとメタノールとのエステル交換反応によりジメチルカーボネート及びエチレングリコールを製造する方法であって、エステル交換反応によって副生するメチルエーテルグリコールの分離を効率的に行ない得る様に改良された上記の各化合物の製造方法が提供され、本発明の工業的価値は顕著である。
【図面の簡単な説明】
【図１】本発明の好ましい態様の一例を示すプロセス説明図
【図２】本発明の好ましい態様の他の一例を示すプロセス説明図
【図３】比較例１のプロセス説明図
【符号の説明】
１：固定床式反応器（エステル交換反応工程）
２：蒸留塔
３：リボイラー
４：凝縮器
５：固定床式反応器（加水分解工程）
６：脱炭酸タンク（気液分離器）
７：凝縮器
８：蒸留塔
９：リボイラー
１０：凝縮器
１１：凝縮器
１２：蒸留塔
１３：リボイラー
１４：凝縮器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing dimethyl carbonate and ethylene glycol. More specifically, the present invention is a method for producing each of the above compounds by an ester exchange reaction between ethylene carbonate and methanol. The present invention relates to a method for producing each of the above compounds, which is improved so that separation can be performed efficiently.
[0002]
[Prior art]
When dimethyl carbonate and ethylene glycol are produced by transesterification of ethylene carbonate and methanol, methyl ether glycol is by-produced. Dimethyl carbonate is a useful compound as a methylating agent or a carbonylating agent, and is also attracting attention as a raw material for non-phosgene polycarbonate. In addition, ethylene glycol is widely used as a raw material for polyethylene terephthalate (PET), and all require strict attention to the mixing of impurities.
[0003]
By the way, since the amount of by-produced methyl ether glycol is small, it is difficult to isolate by distillation means. However, when separating with other components, it is economically important how to provide simple equipment.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is a method for producing dimethyl carbonate and ethylene glycol by transesterification of ethylene carbonate and methanol, which is a methyl ether produced as a by-product by transesterification. It is an object of the present invention to provide a method for producing each of the above compounds which is improved so that glycol can be efficiently separated.
[0005]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has obtained the following knowledge. That is, the boiling point of methyl ether glycol is between dimethyl carbonate and ethylene glycol, and the boiling point difference between dimethyl carbonate and 34 ° C. is normal pressure. Therefore, methyl ether glycol can be extracted together with a high-boiling fraction containing ethylene glycol as a main component and containing unreacted ethylene carbonate. Furthermore, since methyl ether glycol is harder to hydrolyze than ethylene carbonate, it is recovered on the high boiling point side, then unreacted ethylene carbonate is hydrolyzed, and the resulting reaction mixture (hydrolyzed solution) is distilled and separated. By using the technology to recover ethylene glycol, it can be efficiently removed with water.
[0006]
The present invention has been completed based on the above findings, and the gist thereof is that a transesterification reaction between ethylene carbonate and methanol is performed, and a reaction mixture containing methanol, dimethyl carbonate, methyl ether glycol, ethylene glycol and ethylene carbonate is obtained. Transesterification reaction step to be obtained, a first distillation step for separating a low-boiling fraction containing methanol and dimethyl carbonate and having a methyl ether glycol content of 10 ppm by weight or less from the reaction mixture of the transesterification reaction step, the first distillation step To the high boiling fraction containing methyl ether glycol, ethylene glycol and ethylene carbonate, and adding an excess molar amount of water to the ethylene carbonate in the high boiling fraction to convert the ethylene carbonate to ethylene glycol. And a carbon dioxide separation step of separating carbon dioxide from the reaction mixture of the hydrolysis step, recovered from the carbon dioxide separation step, and water, methyl ether glycol, ethylene glycol and It includes a second distillation step in which a low-boiling fraction containing water and methyl ether glycol and a high-boiling fraction containing diethylene glycol are separated from the mixture containing diethylene glycol and the ethylene glycol fraction is recovered sequentially. In the production method of dimethyl carbonate and ethylene glycol.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a process explanatory diagram showing an example of a preferred embodiment of the present invention, and FIG. 2 is a process explanatory diagram showing another example of a preferred embodiment of the present invention.
[0008]
The production method of the present invention includes (A) a transesterification step, (B) a first distillation step, (C) a hydrolysis step, (D) a carbon dioxide separation step, and (E) a second distillation step. In the following description, the abbreviations shown in the following Table 1 may be used.
[0009]
[Table 1]

[0010]
(A) In the transesterification step, EC and MeOH are transesterified to obtain a reaction mixture containing MeOH, DMC, MeGE, EG and EC. The transesterification reaction is represented by the following chemical reaction formula (1), and the byproduct reaction of MeGE is represented by the following chemical reaction formula (2).
[0011]
[Chemical 1]

[0012]
Usually, the transesterification reaction is carried out in the presence of a catalyst. As a catalyst, what is generally used as a transesterification catalyst for carbonates can be used without limitation. Specifically, examples of the homogeneous catalyst include amines such as triethylamine, alkali metals such as sodium, alkali metal compounds such as sodium chloroacetate and sodium methylate, and thallium compounds, and heterogeneous catalysts include functional groups. Ion-exchange resin modified by the above, amorphous silica impregnated with an alkali metal or alkaline earth metal silicate, ammonium-exchanged Y-type zeolite, mixed oxide of cobalt and nickel, and the like.
[0013]
The type of the reactor is not particularly limited, but it is preferable to use a fixed bed reactor (1) as shown in the figure. In the case of the illustrated example, EC and MeOH are supplied from the top line (L1) and line (L2) of the reactor (1), and the reaction liquid is taken out from the bottom line (L3). The use ratio (molar ratio) of MeOH to EC is usually 2 to 20, the reaction temperature is usually 50 to 180 ° C., the reaction pressure is usually 100 to 2000 KPa, and the reaction time is usually 0.5 to 5 hours.
[0014]
The transesterification reaction is an equilibrium reaction, and unreacted raw material components always exist in the reaction solution. That is, the reaction liquid contains raw material EC and MeOH in addition to the target products DMC and EG, and further contains by-produced MeGE and the like.
[0015]
(B) In the first distillation step, a low-boiling fraction containing MeOH and DMC and having a MeGE content of 10 ppm by weight or less is separated from the reaction mixture of the transesterification step. That is, in the present invention, since MeGE is separated from the high boiling fraction side, it is necessary not to bring it into the low boiling fraction side of the first distillation step as much as possible.
[0016]
The distillation column (2) of the first distillation step includes a reboiler (3) at the bottom of the column and a condenser (4) at the top of the column, and the gas phase of the condenser (4) is a vacuum device (not shown) such as an ejector. Z). The reaction liquid is introduced from the line (L3) to the feed stage of the distillation column (2), and a low-boiling fraction containing MeOH and DMC and having a MeGE content of 10 ppm by weight or less is fed from the line (L5) to the condenser (4). The high-boiling fraction introduced and containing MeGE, EG and EC is withdrawn from the line (L4).
[0017]
(C) In the hydrolysis step, an excess molar amount of water is added to the high-boiling fraction recovered from the first distillation step and containing EC, EG and MeGE with respect to the EC in the high-boiling fraction. EC is hydrolyzed to EG and carbon dioxide (CO ₂ ). The hydrolysis of EC is represented by the following chemical reaction formula (3). In this hydrolysis step, DEG is produced as a by-product from the produced EG, and TEG, PEG, etc. may be produced.
[0018]
[Chemical 2]

[0019]
Usually, the hydrolysis is carried out in the presence of a catalyst. As the catalyst, activated alumina is preferably used. The type of the reactor is not particularly limited, but it is preferable to use a fixed bed reactor (5) as shown. The high-boiling fraction extracted from the line (L4) is supplied to the fixed bed reactor (5) after water is added from the line (L6). The use ratio (molar ratio) of water to EC is usually 1 to 5, the reaction temperature is usually 100 to 200 ° C., the reaction pressure is usually 100 to 3000 KPa, and the reaction time is usually 0.5 to 5 hours.
[0020]
(D) In the carbon dioxide separation step, carbon dioxide is separated from the reaction mixture in the hydrolysis step. The means for separating carbon dioxide is not particularly limited. Carbon dioxide can be easily separated simply by supplying the reaction mixture of the hydrolysis step into a decarboxylation tank under normal pressure to release the pressure of the hydrolysis step.
[0021]
The illustrated decarboxylation tank (gas-liquid separator) (6) includes a pressure regulator (not shown), and further includes a condenser (7) for recovering water vapor distilled together with carbon dioxide. . The reaction mixture in the hydrolysis step is introduced from the line (L7) into the decarboxylation tank (6), and carbon dioxide is extracted from the gas phase line (L8) of the condenser (7).
[0022]
(E) In the second distillation step, a low-boiling fraction containing water and MeGE and a high-boiling point containing DEG are recovered from a mixture containing water, MeGE, EG and DEG recovered from the carbon dioxide separation step. The fraction is separated and the EG fraction is recovered.
[0023]
The distillation column (8) of the second distillation step is equipped with a reboiler (9) at the bottom of the column and two-stage condensers (10) and (11) at the top of the column. The gas phase of the condenser (11) is an ejector or the like. Connected to a vacuum device (not shown). That is, the latter condenser (11) is a so-called vent condenser. The mixture recovered from the carbon dioxide separation step is introduced from the line (L9) to the feed stage of the distillation column (8), and the low boiling fraction containing water and MeGE is fed from the top line (L10) to the condenser (10). And the high boiling fraction containing DEG is withdrawn from the bottom line (L11). And an EG fraction is collect | recovered as a side cut from the column middle line (L12).
[0024]
The form of the distillation towers (2) and (8) may be any form of a plate tower or a packed tower. As the plate tower, a known type such as a sieve tray or a bubble bell tower can be used. As the packing in the packed tower, regular packing such as sulzer pack, mela pack and MC pack, and irregular packing such as IMTP and Raschig ring can be used.
[0025]
The number of concentration and recovery stages of the distillation columns (2) and (8) and the operating conditions (temperature, pressure, reflux ratio, etc.) are appropriately selected so that the desired component separation can be performed. Incidentally, the theoretical plate number of each distillation column is usually 5 to 30 plate, preferably 7 to 20 plate, and the reflux ratio is usually 0.1 to 5, preferably 0.5 to 2.
[0026]
In addition, as a condenser (4), (7), (10) and (11), a general multi-tube heat exchanger can be used.
[0027]
In a preferred embodiment of the present invention, MeGE is separated from the low-boiling fraction containing water and MeGE separated in the second distillation step, and water is recovered and used as reaction water in the hydrolysis step. That is, as shown in FIG. 2, among the two-stage condensers (10) and (11) of the distillation column (8), the temperature of the condenser (10) in the previous stage is increased, and water condenses but MeGE condenses. The condensate collected at the condenser (10) is supplied to the fixed bed reactor (5) through the line (L13) at a difficult temperature (for example, 60 ° C.).
[0028]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded.
[0029]
Example 1
According to a process similar to that shown in FIG. 1, the following (1) transesterification step, (2) first distillation step, (3) hydrolysis step, (4) carbon dioxide separation step, (5) no. Two distillation steps were performed.
[0030]
(A) Transesterification reaction step:
As the fixed bed reactor (1), a reactor filled with an anion exchange resin in which a quaternary ammonium salt structure was bonded to a crosslinked polystyrene chain via a spacer group was used. 88 parts by weight of EC from the line (L1) and 64 parts by weight of MeOH from the line (L2) were supplied to the fixed bed reactor (1), and reacted under the conditions of reaction temperature: 80 ° C., reaction pressure: 200 KPa, LHSV: 1. However, from the line (L3), a reaction solution of MeOH 26% by weight, DMC 22% by weight, EG 15% by weight, and EC 36% by weight was obtained. The reaction solution contained 0.4% by weight of MeGE produced as a by-product.
[0031]
(B) First distillation step:
As the distillation column (2), a packed column having an inner diameter of 0.2 m in which “MC pack 250S” manufactured by Mitsubishi Chemical Engineering Co., Ltd. was packed to a height of 7 m was used. The reaction solution was supplied from the line (L3) to the distillation column (2). The reaction solution was supplied at a position 2.5 m from the upper end of the filling portion. Then, distillation separation was performed at a reflux ratio of 0.3 to obtain a mixed solution of MeOH and DMC from a line (L5) at the top of the column, and a mixed liquid of EG and EC from a line (L4) at the bottom of the column. The operating pressure was 24 KPa at the top of the tower. The top liquid composition was MeOH 54 wt% and DMC 46 wt%, and a trace amount of MeGE was detected. The bottom liquid composition was 0.7% by weight of MeGE, 30% by weight of EG, 69% by weight of EC, DMC was less than 10 ppm by weight, and MeOH and DME were not detected.
[0032]
(C) Hydrolysis step:
As the fixed bed reactor (5), a reactor filled with activated alumina was used. Water was added from the line (L6) to the high boiling fraction withdrawn from the line (L4) and supplied to the fixed bed reactor (5). The amount of water added was 1.5 times (mol) of EC. The reaction was performed at a reaction temperature of 180 ° C., a reaction pressure of 2500 KPa, and LHSV of 0.5. The EC concentration after hydrolysis decreased to less than 10 ppm by weight.
[0033]
(D) Carbon dioxide separation step:
The above reaction mixture was introduced from the line (L7) into the decarboxylation tank (6), the reaction mixture was depressurized to normal pressure, and carbon dioxide was separated. Although the liquid temperature of the reaction mixture decreased as the pressure decreased, it exceeded 100 ° C., so water was distilled off together with carbon dioxide. Therefore, the distillation vapor was cooled to 50 ° C. by the condenser (7) and condensed, and the operation was performed while returning the obtained condensate to the decarboxylation tank (6).
[0034]
(E) Second distillation step:
As the distillation column (8), a packed column having an inner diameter of 0.2 m filled with “MC pack 250S” manufactured by Mitsubishi Chemical Engineering Co., Ltd. at a height of 9 m was used. The above mixture was fed from the line (L9) to the distillation column (8). The mixture was supplied at a position 4.5 m from the upper end of the filling part. Then, by performing distillation separation at a reflux ratio of 1.2, a mixture of water and EG is supplied from the tower top line (L10), and a high molecular weight ethylene glycol having EG as a main component and EG from the tower bottom line (L11). A liquid mixture containing was obtained. And EG vapor was extracted from the position of 2.3 m from the filling part lower end. The condensation temperature in the condenser (10) was 45 ° C., and the condensation temperature in the condenser (11) was 10 ° C. As a result, 99.8% by weight of MeGE was recovered by the condenser (10), and the remaining 0.2% by weight was recovered by the condenser (11).
[0035]
The liquid composition at the top of the column was 27% by weight of water and 70% by weight of EG, and contained 3% by weight of MeGE. The bottom liquid composition was EG 82% by weight and contained 18% by weight of high molecular weight ethylene glycols. The sidestream vapor was EG having a DEG content of 300 ppm by weight.
[0036]
As a result of the above operation, substantially the entire amount of MeGE by-produced in the transesterification reaction was removed together with water during the EG purification in the second distillation step. In this case, the MeGE concentration at the outlet of the fixed bed reactor (5) in the hydrolysis step was 0.6% by weight. Moreover, EG obtained by condensing the side stream vapor of the distillation column (8) did not contain MeGE and satisfied quality standards as a general PET raw material.
[0037]
Example 2
A process similar to that shown in FIG. 2 was employed. That is, in Example 1, the condensing temperature in the condenser (10) is 60 ° C., the condensing temperature in the condenser (11) is 10 ° C., and the condensed water recovered in the condenser (11) is fixed to the fixed bed type by the line (L13). The same operation as in Example 1 was carried out except that it was supplied to the reactor (5). In addition, 91 weight% of MeGE was collect | recovered with the capacitor | condenser (10), and the remaining 9 weight% was collect | recovered with the condenser (11), respectively. In this case, the MeGE concentration at the outlet of the fixed bed reactor (5) was 0.6% by weight. Moreover, EG obtained by condensing the side stream vapor of the distillation column (8) did not contain MeGE and satisfied quality standards as a general PET raw material.
[0038]
Comparative Example 1
A process similar to that shown in FIG. 3 was employed. That is, in Example 1, operation was performed in the same manner as in Example 1 except that in the distillation column (2) of the first distillation step, MeGE was extracted together with the low-boiling components by slightly increasing the distillate amount.
[0039]
And the low boiling-point fraction extracted from the distillation column (2) was processed with the distillation column (12). As the distillation tower (12), a packed tower having an inner diameter of 0.2 m filled with “MC pack 250S” manufactured by Mitsubishi Chemical Engineering Co., Ltd. at a height of 4.5 m was used. The distillation column (12) includes a reboiler (13) at the bottom of the column and a condenser (14) at the top of the column, and the vapor phase of the condenser (14) is connected to a vacuum device (not shown) such as an ejector. Yes. Said low boiling fraction was supplied to the distillation column (12) from the line (L14). The low-boiling fraction was supplied at a position 1 m from the upper end of the packed part. Then, distillation separation was performed at a reflux ratio of 1.0 to obtain a mixed solution of MeOH and DMC from the top line (L15) and a mixed liquid of MeOH, DMC, and MeGE from the bottom line (L16). It operated so that MeGE in a column top fraction might be less than 10 weight ppm.
[0040]
In the above-described method of recovering MeGE on the low boiling point side during the transesterification reaction distillation, the amount of heat required for this distillation separation increases by about 2%, and then MeGE distillation separation is required. Therefore, the energy consumption increased by 53% of Example 1.
[0041]
【The invention's effect】
According to the present invention described above, dimethyl carbonate and ethylene glycol are produced by transesterification of ethylene carbonate and methanol, and methyl ether glycol produced as a by-product by transesterification can be efficiently separated. Thus, an improved method for producing each of the above compounds is provided, and the industrial value of the present invention is remarkable.
[Brief description of the drawings]
FIG. 1 is a process explanatory diagram illustrating an example of a preferred embodiment of the present invention. FIG. 2 is a process explanatory diagram illustrating another example of a preferred embodiment of the present invention.
1: Fixed bed reactor (transesterification process)
2: Distillation column 3: Reboiler 4: Condenser 5: Fixed bed reactor (hydrolysis step)
6: Decarbonation tank (gas-liquid separator)
7: condenser 8: distillation tower 9: reboiler 10: condenser 11: condenser 12: distillation tower 13: reboiler 14: condenser

Claims (2)

Transesterification reaction of ethylene carbonate and methanol to obtain a reaction mixture containing methanol, dimethyl carbonate, methyl ether glycol, ethylene glycol and ethylene carbonate, from the reaction mixture of the transesterification step, methanol and dimethyl carbonate And a high-boiling fraction recovered from the first distillation step and containing methyl ether glycol, ethylene glycol and ethylene carbonate. A hydrolysis step of hydrolyzing ethylene carbonate into ethylene glycol and carbon dioxide by adding an excess molar amount of water to ethylene carbonate in the high-boiling fraction, A carbon dioxide separation step for separating carbon dioxide from the reaction mixture, a low-boiling fraction recovered from the carbon dioxide separation step and containing water and methyl ether glycol from a mixture containing water, methyl ether glycol, ethylene glycol and diethylene glycol And a second distillation step of separating the high-boiling fraction containing diethylene glycol and recovering the ethylene glycol fraction in order, and a method for producing dimethyl carbonate and ethylene glycol. The method according to claim 1, wherein methyl ether glycol is separated from the low-boiling fraction containing water and methyl ether glycol separated in the second distillation step, and water is recovered and used as reaction water in the hydrolysis step.

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