1331145 (1) 玖、發明說明 【發明所屬之技術領域】 本發明係有關碳酸烷二醇脂之製造方法，詳細的說， 係有關由乙烯氣相氧化之氧化反應氣體中之碳酸氣爲原料 製造高品質的碳酸烷二醇酯之方法。 【先前技術】 碳酸烷二醇酯係作爲有機溶劑及作爲反應試藥有用之 化合物。特別是使用於鋰之二次電池等之溶劑外，使用作 爲碳酸烷酯之原料。 作爲碳酸烷二醇酯之製造方法，一般以環氧乙烷（氧 化乙烯）與碳酸氣反應，向來已有很多報告有關其催化劑 、製程。 作爲原料之碳酸氣，一般工業用之碳酸氣係得自氨製 造用氫氣製造程序之副產碳酸氣，或於醱酵製程生成之碳 酸氣’此等經回收及精製之各步驟，通常具9 9.5體積％ 以上之純度。或因應必要可用市售之高純度碳酸氣。 另一方面’環氣乙烷之製造步驟亦副產碳酸氣。即， 環氧乙烷之製造法，通常，使乙烯以銀催化劑進行部份氧 化之方法，此時，產生之副反應爲乙烯之完全氧化反應， 生成碳酸氣。碳酸氣有害於乙烯之部份氧化反應，一般須 要除去之碳酸氣’通常排出至大氣中，假若，此排出之副 產碳酸氣可作爲碳酸烷二醇酯製造原料時，不僅有利於經 濟’在環境面上不會排出溫暖化氣體之碳酸氣而固定化， -4 - (2) (2)1331145 亦可謂有益之方法。特別是，目的製品爲碳酸乙二醇酯時 ，同一工場能得到二種原料，可簡略化原料之貯存，運輸 有關之設備，在經濟上可謂極爲有效率。 使用有關環氣乙烷之製造步驟之副產碳酸氣作爲碳酸 烷二醇酯之製造原料，已揭示於日本特開平9-67365號公 報。 又，有關環氧乙烷之製造步驟副產之碳酸氣之分離回 收方法，已揭示於日本特開昭50-4〇508號公報。 使用回收此環氧乙烷製造步驟副產之碳酸氣製造碳酸 烷二醇酯，具很多利點。但是回收之碳酸氣，通常較上述 一般工業用碳酸氣純度低，一般含大量碳化氫，通常爲1 體積％以上。相關於碳酸烷二醇酯之製造程序，因爲原料 之碳酸氣以過量供應反應器，使未反應之碳酸氣循環使用 ’使用此等低純度之碳酸氣時，於上述碳酸氣循環步驟反 應系產生碳化氫蓄積，降低反應器中之碳酸氣分壓，阻礙 碳酸烷二醇酯之生成反應，同時促進不期望之副反應，有 影響製品碳酸乙二醇酯之品質問題。 爲迴避上述不相宜，通常，含原料環氧烷烴之碳酸氣 需要較多之排放，成爲原料碳酸氣之損失，及原料環氧烷 烴之損失’加上排出氣體之除害設備等大型化而在經濟面 上無利益。 碳酸氣體高純度化之方法，雖然有例如極冷分離等已 存在的方法’但因爲需要大能源之故，作爲得到大量之原 料碳酸氣之方法並不適當。 -5- (3) (3)1331145 因此，本發明之課題爲提供由乙烯之氧化反應製造環 氧乙烷時副產之碳酸氣作爲原料之製造高品質碳酸烷二醇 酯之方法。 【發明內容】 〔發明之揭示〕 本發明者，爲解決上述課題，經深入硏究結果，發現 藉由限制由環氧乙烷之製造程序回收碳酸氣中之雜質濃度 於某一水準以下，可迴避上述問題，有效率的製造碳酸乙 二醇酯，而完成本發明。 即本發明之要旨爲環氧烷烴與碳酸氣反應製造碳酸烷 二醇酯時，使用由乙烯之氣相氧化反應之氧化反應氣體經 回收環氧乙烷後之氧化反應廢氣體至少一部份回收且純度 爲99.5體積％以上之碳酸氣作爲原料之碳酸氣爲特徵之 碳酸烷二醇酯之製造方法。 〔用以實施發明之最佳型態〕 以下詳細明本發明之實施型態。 〔環氧乙烷之製造〕 環氧乙烷之製造，通常使用由銀催化劑進行乙烯之接 觸氣相氧化。有關此方法，Ullmanns Encyclopedia of Industrial Chemistry， 5th Ed.，vol A 10，pll7 如以下 記載，原料之乙烯及氧氣及作爲稀釋氣體之甲烷爲主成分 -6 - (4) (4)1331145 之氣體，通過塡充銀催化劑之多管式反應器進行反應。乙 烯之環氧乙烷之選擇率爲80%程度，殘餘20%程度由完 全氧化反應而成爲碳酸氣及水。由反應器流出之氧化反應 氣體，由生成之環氧乙烷及未反應乙烯、及碳酸氣、氧氣 、稀釋氣體等所構成。生成之環氧乙烷於以水爲吸收液的 吸收塔吸收於液相中。被吸收於吸收液中之環氧乙烷於環 氧乙烷解吸塔中解吸，由塔頂回收高濃度之水溶液，再於 蒸餾塔脫水精製，成爲製品。製品之環氧乙烷可作爲依本 發明方法之碳酸乙二醇酯製造方法之原料使用。 〔碳酸氣之回收〕 吸收環氧乙烷後之氧化反應廢氣之全量或一部份送至 碳酸氣去除系統（碳酸氣回收裝置）。 雖然氧化反應廢氣之組成依工廠之運轉條件多少有差 異，但依 Ullmanns Encyclopedia of Industrial Chemistry ，5th Ed.，vol A 10，p 124，大約含 15 〜40 體積 ％ 之乙 烯，1〜60體積％之甲烷及5〜15體積％之碳酸氣。 碳酸氣去除系統（碳酸氣回收裝置），含碳酸氣吸收 塔、預備解吸裝置及碳酸氣解吸塔所構成。 送至碳酸氣去除系統之氧化反應廢氣，首先導入碳酸 氣吸收塔之底部，經由塔頂導入之含有碳酸氣吸收劑之水 溶液所成之碳酸氣吸收液洗淨，將氣體中之大部份碳酸氣 除去。碳酸氣吸收劑可列舉如碳酸鉀等之鹼金屬碳酸鹽， 二異丙醇胺等之烷醇胺類，氨基酸之鹼金屬鹽等，特以碳 (5) (5)1331145 酸鉀爲合適。由上述之洗淨處理，與碳酸氣同爲原料之乙 烯及稀釋氣體之甲烷亦微量溶解於吸收液中。由塔頂排出 之減少碳酸氣之氧化反應廢氣，與未送至碳酸氣去除系統 之氧化反應廢氣合流，追加已消耗之氧氣及乙烯後，再次 作爲氧化反應原料送至氧化反應器。 碳酸氣吸收塔通常以1.0〜2.5 MPa，理想爲1.5〜2.2 MPa之高壓操作。溫度通常爲30〜150 °C，理想爲60〜 120 °C。碳酸氣吸收塔之形式無特別限制，板式塔、塡充 塔之任一者均宜。由碳酸氣吸收塔之塔底所得之碳酸氣吸 收液中之碳酸氣濃度，因爲與吸收液之種類、吸收塔之操 作溫度有關，故不能一槪而論，但通常爲3〜20重量％。 吸收碳酸氣之碳酸氣吸收液送至預備解吸裝置。如上 述因爲吸收液中溶解微量之乙烯及甲烷等，故直接進行碳 酸氣之解吸時，乙烯及甲烷等混入回收碳酸氣中而降低純 度。預備解吸裝置係於解吸碳酸氣吸收液中所吸收的氣體 成分之全量前將其一部份解吸，由此降低碳酸氣吸收液中 溶存之碳化氫等之低沸點的雜質氣體成分之濃度。預備解 吸裝置之構造可使用塡充塔或板式塔，由於甲烷及乙烯之 溶解度較碳酸氣爲低，不需要設置特別之蒸餾塔，通常單 純之減壓閃蒸罐即已充分。又，爲促進解吸亦可具有再沸 器。因爲藉由預備解吸裝置解吸之氣體含乙烯及甲烷，適 合再循環於環氧乙烷之回收系（吸收塔）或乙烯之氣相氧 化步驟。 預備解吸裝置之操作溫度通常爲50〜150 °C，理想爲 (6) (6)1331145 95〜120°C，操作壓力通常爲〇·1〜丨.〇 MPa，理想爲0.1〜 0.5 MPa。此時，解吸之氣體量不充分時，不能充分進行 去除碳化氫，由碳酸氣解吸塔回收之碳酸氣之純度不足以 供給碳酸烷二醇酯之製造。另一方面’因爲徒然增加解吸 量關聯製程之非效率，故不甚理想。 ♦ 有關本發明最後於碳酸氣解吸塔所回收之碳酸氣之純 度必要爲99.5體積％以上’較理想爲99.6體積％以上’ 更理想爲99.7體積％以上，該純度事實上依預備解吸裝 置之解吸處理相關之碳化氫去除程度而決定。通常，預備 解吸裝置相關之解吸量（A)，與該預備解吸裝置解吸量 及由碳酸氣解吸塔之頂所回收之碳酸氣量之和（B)(此 約略相當於碳酸氣解吸塔之吸收氣體量）之比（B/A) (以下以預備解吸裝置之解吸率稱之）通常控制成爲2% 以上，理想爲2.5 %以上，更理想爲3 %以上。可得到適 宜之效果。但是，解吸率過份提升時，碳酸氣之純度提高 但碳酸氣回收程序之效率下降。因此，解吸率之上限通常 爲 10%。 由解吸裝置所排出之碳酸氣吸收液送至碳酸氣解吸塔 。碳酸氣解吸塔係爲解吸碳酸氣吸收液中溶存之約全量碳 酸氣。碳酸氣解吸塔之構造依解吸率之觀點以塡充塔或板 式塔爲理想。解吸之方式係於碳酸氣解吸塔之底部設置再 沸器，或吹入水蒸氣，或者其兩方均進行之加熱汽提爲理 想。 碳酸氣解吸塔之解吸處理，通常以低於預備解吸裝置 -9- (7) (7)1331145 低或同一程度之壓力，理想爲0.3 MPa以下實施。又，解 吸溫度通常爲50〜150°C，理想爲80〜120°C，碳酸氣吸 收液係由碳酸氣解吸塔之塔頂導入，底部由熱交換器加熱 ，解吸所吸收之碳酸氣體。因應必要吹入水蒸氣汽提，可 促進解吸。 碳酸氣吸收液以碳酸氣解吸塔解吸處理，由排放所吸 收之碳酸氣而再生，再度作爲碳酸氣吸收液循環供給於碳 酸氣吸收塔。 如此由環氣乙烷之製造程序所回收之高純度碳酸氣， 具有充分碳酸烷二醇酯製造之原料純度，可適合於該用途 〔碳酸烷二醇酯之製造〕 環氧烷羥與由如上述之環氧乙烷製造程序所回收之碳 酸氣反應而製造碳酸烷二醇酯。 碳酸烷二醇酯生成反應之催化劑可使用公知者，可列 舉如鹼金屬之溴化物或碘化物（日本特公昭38-23175號 公報）、鹼土金屬之鹵化物（美國專利第2667497號公報 )、烷基胺、第4級銨鹽（美國專利第2773070號公報） 、有機錫或鍺或碲化合物（日本特開昭57-183784號公報 )、鹵化有機銹鹽（日本特開昭58_126884號公報）等， 其中依活性及選擇性以溴化鉀、碘化鉀等之鹼金屬鹼化物 及幽化有機銹鹽爲理想。 已有提案使用複數之管型反應器與冷卻器之直列配置 -10- (8) (8)1331145 (Springmann, F ette sei fen anstrichemittl " , vo 1. 73, p 396— 399 ,( 1971))，迴管型反應器（pepp el, Industrial and Engineering，vo 1. 50，p767 — p770, ( 1958)) > 氣泡 塔（日本特開平6-345699號公報）作爲製造碳酸烷二醇 酯之反應器。上述之任一之方法均可使用，其中以外部循 環型之氣泡塔，因對液相之碳酸氣之擴散供給與迴避由除 熱而引起之失控反應優，故理想。 因上述反應爲發熱反應，反應溫度以除熱量控制。反 應溫度亦依使用之催化劑而異，通常爲80〜200°C，理想 爲 1 0 0 〜1 8 0 °C。 碳酸烷二醇酯生成之反應速度由原料之碳酸氣之分壓 所支配，壓力以高者爲理想。但是壓力高時反應器及週邊 機器亦要求耐高壓，機器費用連帶增加。壓力較隹範圍一 般爲l~10Mpa、更佳爲l~5MPa。 碳酸氣相對於供應反應器之環氧乙烷之量，通常供應 1〜20莫耳倍，碳酸氣不僅爲原料，亦具有攪拌作用以防 止反應器內之液體因組成分佈，熱分佈而產生副反應之效 果，比反應必要量過剩供給。未反應及過剩之碳酸氣爲防 止副產輕沸物與原料碳酸氣中雜質之蓄積需排放一部份， 再度循環至反應器使用》此處之排放量由監視雜質之蓄積 量而控制。因此，排放量相對於再循環碳酸氣流量，通常 爲0.1〜8%，理想爲0.2〜5%。 帶入碳酸烷二醇酯之製造步驟之雜質多時，此等產生 之蓄積造成反應之不適宜。雜質之蓄積其本身對反應之影 -11 - (9) (9)1331145 響亦不能否定，與其相比，因碳酸氣分壓之下降對主反應 速度之下降效果更大。依此所要之反應時間延長，造成生 產性下降，品質下降。 對於碳酸氣分壓之下降，增加上述排放量亦可維持分 壓，其造成原料碳酸氣之損失，原料環氧乙烷之損失，排 放氣體之除害設備等之大型化造成經濟上之不利益。催化 劑因應基於所望生產性之溶解度之範圍可使用催化劑的活 性之必要之濃度。催化劑通常與溶劑同時供給反應器，反 應後與生成之碳酸烷二醇酯分離，因應必要追加其不足量 後循環使用。.使用目的物之碳酸烷二醇酯作爲溶劑因爲簡 便故理想。 與催化劑分離後之碳酸烷二醇酯，即已具充分之純度 ，因應必要通常可再以減壓蒸餾設備等精製爲高純度。 【實施方式】 其次由實施例詳細的說明具體的實施型態，在不超越 本發明之要旨不限定於以下實施例。 實施例1 使用如圖1所示程序構成之製造裝置實施反應。 (1)由環氧乙烷（E0)製造步驟回收C02 以下各物質之流量以導入C02吸收塔1之氧化反應廢 氣之重量速度爲1重量份，以其爲標準表示之。 -12- (10) 1331145 由使用銀催化劑之乙烯接觸氣相氧化步驟所得之 氧化反應氣經回收環氧乙烷後之氧化反應廢氣（C02 6體積％ ’ CH4濃度57體積％，C2H4濃度24體積分 重量份，由管線L1導入理論段數3段，以110 °C溫 1.7 MPa壓力操作之碳酸氣（C02)吸收塔1之底部，由 吸收塔1之頂部經管線L4導入作爲吸收液之碳酸 K2C03 )水溶液7重量份。 吸收C02之吸收液經由管線L3導入以107°C溫 0.15 MPa壓力操作之預備解吸裝置（閃蒸器）2，由 處理減低液中碳化氫之濃度後，由管線L7供給理論 5段以溫度1 l〇°C溫度，0.1 MPa壓力操作之碳酸氣（ )解吸塔3之塔頂，解吸回收C02。此時，由閃蒸器 管線L6解吸之氣體量，相對於由該閃蒸器2所解吸 體量與由C02解吸塔3經管線L8回收C02量之合計 當於5.0% (解吸率5.0% )。 回收之C02以氣壓機（圖上無顯示）昇壓，經 L8供給碳酸酯化反應器4 » 測定回收C〇2中所含之烴類之濃度時’存在之 爲0.03體積％，C2H4爲0.06體積％ (任一者均爲水 外計算）。由其結果，經計算C02之純度爲99.91體 (2 )碳酸乙二醇酯（EC )化反應 以下各物質之流量以環氧乙烷之重量速度爲1重 乙烯 濃度 6)1 度， C〇2 鉀（ 度， 解吸 段數 C〇2 2經 之氣 ，相 管線 ch4 分除 積％ 量份 -13- (11) (11)1331145 ，以其爲標準表示之。 使用上述回收之C〇2進行EC化反應。氣泡塔型式之 碳酸酯化反應器4之底部導入由乙烯之氧化反應所得之環 氧乙烷1重量份（由管線L9)及上述C02 8.2重量份（ 由管線L8)，供給作爲催化劑之溶解於〇.1重量份碳酸 乙二醇酯之〇.〇1重量份碘化鉀（由管線L10)，反應液 經氣泡塔4之塔頂經管線L 1 1與氣體同時排出，以氣液分 離器5氣液分離。已氣液分離之氣體（L12)經管線L13 排放全體之0.5%至系統外經氣壓機（圖上無顯示）與上 述解吸之C02 ( L8 )合流後，再度循環至EC化反應器4 。已氣液分離後之之液體（L15)之一部份由管線L14排 出作爲製品，殘餘者以熱交換器6除熱後再循環至EC反 應器4之底部。反應器控制於1 80 °C，2 MPa。 依以上之條件連續運轉時，反應器4內之碳化氫濃度 固定於4體積％程度，可安定的運轉。由管線L14回收之 反應液，以4 kPa壓力，138°C溫度蒸發碳酸乙二醇酯分 離催化劑得到碳酸乙二醇酯。 〔比較例1〕 調製純度98.9體積％之C02(含CH4: 0.37體積％ ，C2H4 : 0.74體積％作爲雜質）作爲原料。 除了利用上述調製之C02以外與實施例1同樣操作進 行EC化反應。繼續連續運轉，循環氣體中之碳化氫濃度 上升，相對的C〇2之濃度下降，最後碳化氫之濃度成爲 -14 - (12) (12)1331145 24體積％。E0之轉化率出現下降，須調整原料供給速度 維持一定。由反應液分離催化劑所得之碳酸乙二醇酯發現 副產之醛化合物爲起因之著色。 〔比較例2〕 相關之連續運轉，爲維持C02之分壓，循環氣體之排 放率由0.5%變更爲10%以外，與比較例1作同樣的操作 。維持C02濃度爲96體積％，EC之品質約略與實施例1 同等，排放之EO量約爲10倍。 〔商業上之可利用性〕 依本發明有效的活用碳酸氣，減低原料碳酸氣及原料 氧化乙烷之排出，且可得到製造高品質之碳酸烷二醇酯之 效果。 【圖式簡單說明】 圖1係顯示構成使用於本發明製造裝置之程序流程圖 主要元件對照表 1 C02吸收塔 2 預備解吸裝置（閃蒸器） 3 碳酸氣（C02 )解吸塔 4 碳酸酯化反應器 -15- (13)1331145 5 氣液分離器 6 熱交換器1331145 (1) Field of the Invention The present invention relates to a method for producing an alkylene glycol glycol, and more particularly to a method for producing carbonic acid gas from an oxidation reaction gas of ethylene gas phase oxidation. A method of high quality alkylene carbonate. [Prior Art] The alkylene carbonate is an organic solvent and a compound useful as a reaction reagent. In particular, it is used as a raw material of an alkyl carbonate in addition to a solvent such as a lithium secondary battery. As a method for producing an alkylene carbonate, ethylene oxide (ethylene oxide) is generally reacted with carbonic acid gas, and many catalysts and processes have been reported. As the carbon dioxide gas as a raw material, the carbonic acid gas for industrial use is obtained from the carbonic acid gas produced by the hydrogen production process for ammonia production, or the carbonic acid gas produced in the fermentation process, which is usually recovered and refined. 9.5 vol% or more of purity. Or commercially available high purity carbonic acid gas may be used as necessary. On the other hand, the manufacturing process of cyclohexane is also a by-product of carbonation. Namely, in the method for producing ethylene oxide, a method in which ethylene is partially oxidized by a silver catalyst is usually used. In this case, a side reaction occurs as a complete oxidation reaction of ethylene to form carbonic acid gas. Carbonic acid gas is harmful to the partial oxidation of ethylene, and the carbonic acid gas that is generally required to be removed is usually discharged to the atmosphere. If this by-product carbonation gas can be used as a raw material for the production of alkylene carbonate, it is not only beneficial to the economy. The environmental surface does not emit carbon dioxide gas from the warming gas and is fixed. -4 - (2) (2) 1331145 can also be described as a beneficial method. In particular, when the intended product is ethylene carbonate, two materials can be obtained in the same workshop, which can simplify the storage of raw materials and transport related equipment, which is economically efficient. The use of a carbonic acid gas as a by-product of the production process of the cyclohexane as a raw material for the alkylene carbonate is disclosed in Japanese Laid-Open Patent Publication No. Hei 9-67365. Further, a method for separating and recovering carbonic acid gas which is a by-product of the production process of ethylene oxide is disclosed in Japanese Laid-Open Patent Publication No. SHO-50-4. The use of carbonic acid gas which is a by-product of the recovery of this ethylene oxide production step to produce alkylene carbonate has many advantages. However, the recovered carbonic acid gas is generally less pure than the above-mentioned general industrial carbonic acid gas, and generally contains a large amount of hydrocarbon, usually 1% by volume or more. Related to the manufacturing procedure of the alkylene carbonate, since the carbonation gas of the raw material is supplied to the reactor in excess, and the unreacted carbonic acid gas is recycled. When the low-purity carbonic acid gas is used, the reaction system is produced in the above-described carbonic acid gas circulation step. The accumulation of carbon dioxide reduces the partial pressure of carbonic acid gas in the reactor, hinders the formation reaction of the alkylene carbonate, and promotes undesirable side reactions, which affects the quality of the product ethylene carbonate. In order to avoid the above-mentioned inconvenience, in general, the carbonic acid gas containing the raw material alkylene oxide requires a large amount of emissions, which is a loss of the raw material carbonic acid gas, and the loss of the raw material alkylene oxide, plus the large-scale detoxification equipment of the exhaust gas. There is no interest in the economy. Although the method of purifying carbonic acid gas has an existing method such as extremely cold separation, it is not suitable as a method of obtaining a large amount of raw carbonic acid gas because of a large energy source. -5- (3) (3) 1331145 Therefore, an object of the present invention is to provide a method for producing a high-quality alkylene glycolate as a raw material by a by-product carbonation gas produced by producing an ethylene oxide by an oxidation reaction of ethylene. [Disclosure of the Invention] The present inventors have found that, by solving the above problems, it has been found that by limiting the concentration of impurities in the carbon dioxide gas recovered by the manufacturing process of ethylene oxide to a certain level or lower, The present invention has been accomplished by avoiding the above problems and efficiently producing ethylene carbonate. That is, the gist of the present invention is that when an alkylene oxide is reacted with carbonic acid gas to produce an alkylene carbonate, at least a part of the oxidation reaction waste gas after recovery of the ethylene oxide by the oxidation reaction gas of ethylene gas phase is recovered. A method for producing an alkylene carbonate which is characterized by a carbonation gas having a purity of 99.5% by volume or more as a raw material. [Best Mode for Carrying Out the Invention] The embodiments of the present invention will be described in detail below. [Production of Ethylene Oxide] For the production of ethylene oxide, contact gas phase oxidation of ethylene by a silver catalyst is usually used. In this method, Ullmanns Encyclopedia of Industrial Chemistry, 5th Ed., vol A 10, pll7, as described below, the raw material of ethylene and oxygen and methane as a diluent gas as a main component -6 - (4) (4) 1331145 gas, The reaction was carried out by a multitubular reactor packed with a silver catalyst. The selectivity of ethylene oxide of ethylene is about 80%, and the residual 20% is converted into carbonic acid gas and water by a complete oxidation reaction. The oxidizing reaction gas flowing out of the reactor is composed of produced ethylene oxide and unreacted ethylene, carbonic acid gas, oxygen gas, diluent gas, and the like. The resulting ethylene oxide is absorbed in the liquid phase in an absorption tower in which water is used as an absorption liquid. The ethylene oxide absorbed in the absorption liquid is desorbed in the ethylene oxide desorption column, and a high-concentration aqueous solution is recovered from the top of the column, and then dehydrated and purified in a distillation column to obtain a product. The ethylene oxide of the product can be used as a raw material for the ethylene carbonate production method according to the method of the present invention. [Recovery of Carbonation Gas] The entire amount or part of the oxidation reaction waste gas after absorbing ethylene oxide is sent to a carbonation gas removal system (carbonation gas recovery unit). Although the composition of the oxidation reaction off-gas varies depending on the operating conditions of the plant, according to Ullmanns Encyclopedia of Industrial Chemistry, 5th Ed., vol A 10, p 124, approximately 15 to 40% by volume of ethylene, 1 to 60% by volume Methane and 5 to 15% by volume of carbonic acid gas. A carbon dioxide gas removal system (carbonation gas recovery unit) comprising a carbon dioxide gas absorption tower, a preliminary desorption unit, and a carbon dioxide desorption tower. The oxidation reaction waste gas sent to the carbonation gas removal system is first introduced into the bottom of the carbon dioxide gas absorption tower, and is washed by the carbon dioxide gas absorption liquid formed by the aqueous solution containing the carbonation gas absorbent introduced from the top of the tower to remove most of the carbonic acid in the gas. Gas removal. Examples of the carbon dioxide gas absorbent include an alkali metal carbonate such as potassium carbonate, an alkanolamine such as diisopropanolamine, an alkali metal salt of an amino acid, and the like, and carbon (5) (5) 1331145 potassium is particularly suitable. By the above-described washing treatment, methane which is a raw material of ethylene carbonate and a diluent gas is also slightly dissolved in the absorbing liquid. The carbon dioxide-reduced oxidation reaction off-gas discharged from the top of the column is combined with the oxidation reaction off-gas which is not sent to the carbon dioxide removal system, and the consumed oxygen and ethylene are added, and then sent to the oxidation reactor as an oxidation reaction raw material. The carbon dioxide gas absorption tower is usually operated at a high pressure of 1.0 to 2.5 MPa, preferably 1.5 to 2.2 MPa. The temperature is usually 30 to 150 ° C, preferably 60 to 120 ° C. The form of the carbon dioxide gas absorption tower is not particularly limited, and any of the plate tower and the crucible column is suitable. The concentration of carbonic acid gas in the carbon dioxide gas absorption liquid obtained from the bottom of the carbon dioxide gas absorption tower is not related to the type of the absorption liquid and the operating temperature of the absorption tower, but is usually 3 to 20% by weight. The carbon dioxide gas absorption liquid that absorbs the carbon dioxide gas is sent to the preliminary desorption device. As described above, since a small amount of ethylene and methane are dissolved in the absorption liquid, when carbonic acid gas is directly desorbed, ethylene and methane are mixed into the recovered carbonic acid gas to lower the purity. The preliminary desorbing device desorbs a part of the gas component absorbed in the carbon dioxide absorbing liquid before desorption, thereby reducing the concentration of the low-boiling impurity gas component such as hydrocarbons dissolved in the carbon dioxide absorbing liquid. The structure of the preliminary desorption device can be used as a pylon or a plate column. Since the solubility of methane and ethylene is lower than that of carbonic acid gas, it is not necessary to provide a special distillation column, and a simple vacuum depressurization tank is usually sufficient. Further, a reboiler may be provided to promote desorption. Since the gas desorbed by the preliminary desorbing device contains ethylene and methane, it is suitable for recycling to a recovery system (absorption column) of ethylene oxide or a gas phase oxidation step of ethylene. The operating temperature of the preliminary desorbing device is usually 50 to 150 ° C, preferably (6) (6) 1331145 95 to 120 ° C, and the operating pressure is usually 〇·1 to 丨.〇 MPa, preferably 0.1 to 0.5 MPa. At this time, when the amount of desorbed gas is insufficient, the removal of hydrocarbons is not sufficiently performed, and the purity of the carbonic acid gas recovered by the carbon dioxide desorption column is insufficient to supply the production of the alkylene carbonate. On the other hand, it is not ideal because it increases the efficiency of the desorption-related process. ♦ The purity of the carbonic acid gas recovered in the carbon dioxide desorption column of the present invention is required to be 99.5 vol% or more, more preferably 99.6% vol% or more, more preferably 99.7 vol% or more, which is in fact desorbed by a preliminary desorption device. It is determined by the degree of treatment related to the removal of hydrocarbons. Usually, the desorption amount (A) associated with the preliminary desorption device, the sum of the desorption amount of the preliminary desorption device and the amount of carbon dioxide recovered from the top of the carbon dioxide desorption column (B) (this approximately corresponds to the absorption gas of the carbon dioxide desorption column) The ratio (B/A) (hereinafter referred to as the desorption rate of the preliminary desorption device) is usually controlled to 2% or more, preferably 2.5% or more, and more preferably 3% or more. Appropriate results can be obtained. However, when the desorption rate is excessively increased, the purity of the carbonic acid gas is increased but the efficiency of the carbonation gas recovery process is lowered. Therefore, the upper limit of the desorption rate is usually 10%. The carbon dioxide gas absorbing liquid discharged from the desorbing device is sent to the carbon dioxide desorbing tower. The carbon dioxide desorption column is about depleted the total amount of carbonic acid gas dissolved in the carbon dioxide absorption liquid. The structure of the carbon dioxide desorption column is ideal for the desorption column or the plate column depending on the desorption rate. The desorption method is based on the fact that a reboiler is placed at the bottom of the carbon dioxide desorption column, or water vapor is blown in, or both of them are heated and stripped. The desorption treatment of the carbon dioxide desorption column is usually carried out at a pressure lower than the preliminary desorption device -9-(7) (7) 1331145 or the same degree, preferably 0.3 MPa or less. Further, the desorption temperature is usually 50 to 150 ° C, preferably 80 to 120 ° C, and the carbon dioxide gas is introduced from the top of the carbon dioxide desorption column, and the bottom is heated by a heat exchanger to desorb the absorbed carbonic acid gas. Desorption can be promoted by blowing water vapor stripping as necessary. The carbon dioxide gas absorption liquid is desorbed by a carbon dioxide gas desorption column, regenerated by discharging the carbon dioxide gas absorbed, and is again supplied as a carbon dioxide gas absorption liquid to the carbonic acid gas absorption tower. The high-purity carbonic acid gas thus recovered by the production process of the cyclohexane has a purity of a raw material produced by a sufficient alkylene carbonate, and is suitable for the purpose [manufacture of an alkylene carbonate). The carbonic acid gas recovered by the above-described ethylene oxide production process is reacted to produce an alkylene carbonate. The catalyst for the alkylene carbonate formation reaction can be a known one, and examples thereof include a bromide or an iodide of an alkali metal (Japanese Patent Publication No. Sho 38-23175), and an alkaline earth metal halide (U.S. Patent No. 2667497). Alkylamine, a fourth-order ammonium salt (U.S. Patent No. 2,773,070), an organotin or a ruthenium or a ruthenium compound (Japanese Unexamined Patent Publication No. SHO-57-183784), or a halogenated organic rust salt (JP-A-58-126884) Etc., among them, alkali metal alkalizides such as potassium bromide and potassium iodide and a clarified organic rust salt are preferred depending on the activity and selectivity. It has been proposed to use an inline configuration of a plurality of tubular reactors and coolers -10- (8) (8) 1331145 (Springmann, Fette sei fen anstrichemittl ", vo 1. 73, p 396-399, (1971) ), a reductive reactor (pepp el, Industrial and Engineering, vo 1. 50, p767 - p770, (1958)) > a bubble column (JP-A-6-345699) as a production of alkylene carbonate reactor. Any of the above methods can be used. Among them, an externally-circulating bubble column is preferred because it provides excellent diffusion control due to diffusion of carbonic acid gas in the liquid phase and avoidance by heat removal. Since the above reaction is an exothermic reaction, the reaction temperature is controlled by heat removal. The reaction temperature also varies depending on the catalyst to be used, and is usually 80 to 200 ° C, preferably 1 0 0 to 1 80 ° C. The reaction rate of the formation of the alkylene carbonate is governed by the partial pressure of the carbonic acid gas of the raw material, and the pressure is preferably as high as possible. However, when the pressure is high, the reactor and the peripheral equipment are also required to withstand high pressure, and the machine cost is increased. The pressure range is generally l~10Mpa, more preferably l~5MPa. The carbonic acid gas phase is usually supplied in an amount of 1 to 20 moles for the amount of ethylene oxide supplied to the reactor. The carbonic acid gas is not only a raw material but also has a stirring action to prevent the liquid in the reactor from being distributed due to composition distribution and heat distribution. The effect of the reaction is excessively supplied than the amount necessary for the reaction. The unreacted and excess carbonation gas is controlled to prevent the accumulation of impurities in the by-product light boiler and the raw material carbon dioxide, and is recycled to the reactor. The emission here is controlled by the accumulation of monitored impurities. Therefore, the discharge amount is usually 0.1 to 8%, preferably 0.2 to 5%, based on the recycled carbon dioxide gas flow rate. When a large amount of impurities are introduced into the production step of the alkylene carbonate, the accumulation of these causes an unfavorable reaction. The accumulation of impurities itself affects the reaction. -11 - (9) (9) 1331145 The sound can not be denied. In contrast, the decrease in the partial pressure of carbonic acid is more effective in reducing the main reaction rate. The reaction time required for this is prolonged, resulting in a decline in productivity and a decline in quality. For the decrease of the partial pressure of carbonic acid gas, it is also possible to maintain the partial pressure by increasing the above-mentioned emissions, which causes the loss of the raw material carbonic acid gas, the loss of the raw material ethylene oxide, and the large-scale detoxification equipment of the exhaust gas, which is economically disadvantageous. . The catalyst can be used at the concentration necessary to use the activity of the catalyst based on the range of solubility that is expected to be productive. The catalyst is usually supplied to the reactor at the same time as the solvent, and is separated from the produced alkylene carbonate by the reaction, and is recycled after it is necessary to add an insufficient amount. It is convenient to use the alkyl carbonate carbonate of the target as a solvent. The alkylene carbonate which has been separated from the catalyst is sufficiently pure, and if necessary, it can be purified to a high purity by a vacuum distillation apparatus or the like. [Embodiment] The specific embodiments are described in detail below with reference to the embodiments, and the present invention is not limited to the following examples. Example 1 A reaction was carried out using a manufacturing apparatus having a procedure as shown in Fig. 1. (1) The flow rate of each of the following substances in the production of CO 2 by the ethylene oxide (E0) production step is 1 part by weight based on the weight of the oxidation reaction waste gas introduced into the CO 2 absorption tower 1, which is represented by the standard. -12- (10) 1331145 Oxidation reaction waste gas obtained by contacting ethylene oxide with a silver catalyst in a gas phase oxidation step after recovering ethylene oxide (C02 6 vol% 'CH4 concentration 57 vol%, C2H4 concentration 24 vol. Divided by weight, introduced into the theoretical section number 3 by the line L1, the bottom of the carbon dioxide gas (C02) absorption tower 1 operated at a pressure of 1.7 MPa at 110 ° C, and introduced into the bottom of the absorption tower 1 via the line L4 as carbonic acid. K2C03) 7 parts by weight of an aqueous solution. The absorption liquid absorbing CO 2 is introduced into a preliminary desorption device (flash evaporator) 2 operated at a pressure of 0.15 MPa at a temperature of 107 ° C via a line L3. After the concentration of the hydrocarbon in the liquid is reduced by the treatment, the theoretical 5 stages are supplied from the line L7 at a temperature of 1 l. 〇 ° C temperature, 0.1 MPa pressure operated carbon dioxide ( ) desorption tower 3 top, desorption recovery of CO 2 . At this time, the amount of gas desorbed by the flasher line L6 was 5.0% (desorption rate 5.0%) with respect to the total amount of desorbed by the flasher 2 and the amount of CO 2 recovered by the CO 2 desorber 3 via the line L8. The recovered C02 is pressurized by a pneumatic machine (not shown) and supplied to the carbonation reactor 4 via L8. » The concentration of hydrocarbons contained in the recovered C〇2 is determined to be 0.03 vol% and C2H4 is 0.06. % by volume (either is calculated outside of water). As a result, it was calculated that the purity of CO 2 was 99.91 (2) ethylene carbonate (EC) reaction. The flow rate of each of the following materials was 1 weight ethylene oxide at a weight rate of ethylene oxide 6) 1 degree, C〇 2 Potassium (degree, number of desorption stages C〇2 2 gas, phase line ch4 points divided by % of parts -13- (11) (11) 1331145, which is expressed by the standard. C 使用2 using the above recovery The acetylation reaction is carried out, and 1 part by weight of ethylene oxide obtained by the oxidation reaction of ethylene (from line L9) and 8.2 parts by weight of the above CO 2 (by line L8) are supplied to the bottom of the bubble column type carbonation reactor 4. As a catalyst, it is dissolved in 1 part by weight of ethylene carbonate, 1 part by weight of potassium iodide (from line L10), and the reaction liquid is simultaneously discharged through the line L 1 1 and the gas through the top of the bubble column 4 to the gas. The liquid separator 5 is gas-liquid separated. The gas-liquid separation gas (L12) is discharged through 0.5% of the entire line through the line L13 to the outside of the system through the air press (not shown) and merged with the above-mentioned desorbed C02 (L8), and then circulated again. To the EC reactor 4. One of the liquid (L15) after the gas-liquid separation is partially connected to the line L14 The product is discharged as a product, and the remainder is recycled to the bottom of the EC reactor 4 by heat removal in the heat exchanger 6. The reactor is controlled at 1 80 ° C, 2 MPa. Carbonization in the reactor 4 when continuously operated under the above conditions The hydrogen concentration was fixed at about 4% by volume, and the operation was stable. The reaction liquid recovered from the line L14 was evaporated at a temperature of 138 ° C at a temperature of 138 ° C to obtain ethylene carbonate. [Comparative Example 1 The CO 2 (containing CH4: 0.37 vol%, C2H4: 0.74 vol% as an impurity) having a purity of 98.9 vol. was prepared as a raw material. The EC reaction was carried out in the same manner as in Example 1 except for the above-mentioned prepared CO 2 . The concentration of hydrocarbon in the gas rises, and the concentration of C〇2 decreases. Finally, the concentration of hydrocarbon becomes -14 - (12) (12) 1331145 24% by volume. The conversion rate of E0 decreases, and the feed rate of raw materials must be adjusted. Certainly, the ethylene carbonate obtained by separating the catalyst from the reaction liquid found that the by-produced aldehyde compound was the cause of coloring. [Comparative Example 2] In order to maintain the partial pressure of CO 2 , the circulating gas was continuously operated. The same operation as in Comparative Example 1 was carried out except that the emission rate was changed from 0.5% to 10%. The CO 2 concentration was maintained at 96% by volume, and the quality of the EC was approximately the same as that of Example 1, and the amount of EO discharged was about 10 times. The above-mentioned usability is effective according to the present invention, and the use of carbonic acid gas is effectively utilized, and the discharge of the raw material carbonic acid gas and the raw material oxidized ethane is reduced, and the effect of producing a high-quality alkylene carbonate is obtained. [Simplified illustration] FIG. The main components of the flow chart showing the composition used in the manufacturing apparatus of the present invention are shown in Table 1. C02 absorption tower 2 preliminary desorption device (flash evaporator) 3 carbon dioxide gas (C02) desorption column 4 carbonation reactor -15- (13) 1331145 5 gas-liquid separator 6 heat exchanger
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