JP4080126B2

JP4080126B2 - Method for producing polylactic acid

Info

Publication number: JP4080126B2
Application number: JP2000028280A
Authority: JP
Inventors: 徹矢野; 渉一佐川
Original assignee: Nishikawa Rubber Co Ltd
Current assignee: Nishikawa Rubber Co Ltd
Priority date: 2000-02-04
Filing date: 2000-02-04
Publication date: 2008-04-23
Anticipated expiration: 2020-02-04
Also published as: JP2001213949A

Description

【０００１】
【発明の属する技術分野】
本発明は、乳酸モノマーを直接脱水重縮合反応によって高分子量のポリ乳酸を製造する装置及びその製造方法に関するものである。
【０００２】
【従来の技術】
生分解プラスチックとして広く用いられるポリ乳酸は、乳酸を原料として加水分解及び熱分解で容易にオリゴマーになる性質を有し、且つ透明性と剛性に富み、他の生分解性物質と共重合して、フィルム、繊維、一般成形品等に適している。
上述したポリ乳酸を直接脱水重縮合反応によって製造するために特開平１０−１３０３７６号公報に開示された従来の代表的な装置の要部は、図３に示したように構成されていた。
【０００３】
即ち、従来のポリ乳酸の直接脱水重縮合反応製造装置１の要部は、重縮合反応部２と、攪拌機付還流部７を具備して成り、前記重縮合反応部２は、外周面が加熱用ジャケット（図示せず）で覆われた重縮合反応槽３の内部に、後述する一方のスクリュ１０の回転軸の延伸部にリボン状の攪拌翼を巻回して成る攪拌機４を旋回自在に装着すると共に、該重縮合反応槽３の逆円錐状底面部から外部にポリ乳酸を排出させる開閉弁５とギアポンプ６を有する排出流路を配設して成っていた。なお、導入口３ａから前記加熱用ジャケット内に供給された加熱媒体が放出口３ｂから放出される。
【０００４】
一方、前記攪拌機付還流部７は、中空状内部に各フライトを絡み合うように二本のスクリュ１０，１１を軸着した晶析還流シリンダ９の下方開口部を前記重縮合反応槽３の上方蓋中心部に気密に貫入させると共に、該晶析還流シリンダ９の上方端部に連結部を介してスクリュ駆動モータ８を配設して成っていた。
なお、前記晶析還流シリンダ９の外周面は冷却用ジャケット（図示せず）で覆われ、導入口９ａから該冷却用ジャケット内に供給された冷却媒体が放出口９ｂから放出される。
【０００５】
更に、前記晶析還流シリンダ９の上方側面に吸引口１２が配設され、該吸引口１２はノックアウトドラム１３、冷却トラップ１５及び真空ポンプ１７に順次気密に接続されていた。前記ノックアウトドラム１３及び前記冷却トラップ１５の底部に各開閉弁１４，１６が夫々配設されていた。
【０００６】
以上のように要部が構成された従来のポリ乳酸の直接脱水重縮合反応製造装置１は、前記真空ポンプ１７を起動して前記冷却トラップ１５、前記ノックアウトドラム１３、前記晶析還流シリンダ９及び前記重縮合反応槽３の系内を減圧して、乳酸モノマー、溶媒、触媒等を前記重縮合反応槽３内に投入し、前記加熱用ジャケットの導入口３ａから前記加熱媒体を循環供給することによって、前記重縮合反応槽３の内部温度を所定の温度に維持しながら、前記攪拌機４により反応溶液を攪拌し、前記乳酸モノマーを直接脱水重縮合反応させることによって、所望するポリ乳酸を生成させる一方、副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気を前記晶析還流シリンダ９の中空状内部に吸引させていた。
【０００７】
前記冷却用ジャケットの導入口９ａから前記冷却媒体を循環供給することによって、前記晶析還流シリンダ９の内部温度を前記ラクチド及び一部の前記乳酸低分子化合物が晶析する温度に維持しながら、前記二本のスクリュ１０，１１を所望する方向に回転させて、晶析した前記ラクチド及び一部の前記乳酸低分子化合物と液化した残りの前記乳酸低分子化合物が前記重縮合反応槽３内に強制的に還流させることによって、前記乳酸モノマーを直接脱水重縮合反応速度を高めると共に重縮合反応を高分子側に移行させて、高分子量のポリ乳酸を効率良く製造することを可能にするものであった。なお、前記副生水の蒸気は、前記ノックアウトドラム１３を経て前記冷却トラップ１５で液化された後、系外に排出されていた。
【０００８】
【発明が解決しようとする課題】
しかしながら、前述した従来のポリ乳酸の直接脱水重縮合反応製造装置及び方法は、反応溶液に対する溶媒の使用が避けられず、その残留分によってポリ乳酸の分離精製や循環コストの大幅な低減が困難であった。一方、前記溶媒を含まないでヒドロキシカルボン酸を直接脱水重縮合反応させてポリヒドロキシカルボン酸を生成させると、前記ヒドロキシカルボン酸中に大量に含まれる水によって重縮合触媒、例えば、オクチル酸スズが加水分解して重縮合反応速度が著しく低下してしまった。
【０００９】
更に、従来のポリ乳酸の直接脱水重縮合反応製造装置及び方法は、重縮合反応が進行して樹脂の溶融粘度が増加すると、重縮合反応速度が低下して通常の加工に耐える機械強度を有する樹脂ペレットが得難く、その対策として重縮合反応時間を長くすると、樹脂ペレットのラセミ化が進行してその融点が低下し易い欠点があった。
樹脂ペレットの融点の低下を防ぐためには、反応溶液の気液接触面や表面更新性を良くして脱水重縮合反応を促進させることが望まれるが、従来の単なるリボン状攪拌翼を有する攪拌機では、前記気液接触面や表面更新性を良くし、且つ攪拌翼によるポリマー鎖の物理的な切断を抑制して高分子量のポリ乳酸を効率良く製造することが困難であった。
【００１０】
本発明は、前述した従来技術の問題点を解消し、無溶媒直接脱水重縮合反応を比較的簡略化された構造で効率良く、且つ高分子量のポリ乳酸を生成する装置及び方法を提供することを目的とするものである。
【００１１】
【課題を解決するための手段】
本発明のかかる目的は、重縮合反応部に乳酸モノマーを主成分とする反応溶液を投入して減圧下で無溶媒直接脱水重縮合反応によりポリ乳酸を生成する一方、前記無溶媒直接脱水重縮合反応により副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気をラクチド還流部に吸引し、液化したラクチド及び乳酸低分子化合物を前記重縮合反応部に還流させ、前記副生水を大気圧系に排出させるポリ乳酸の製造装置において；前記重縮合反応部が、外周面を温度調節用ジャケットで覆い、逆円錐状に形成された内部底面を有する重縮合反応槽と、前記重縮合反応槽の逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する逆円錐状ダブルヘリカル攪拌機とを具備して成り；前記ラクチド還流部が、外周面を温度調節用ジャケットで覆い、中空状内部の下方を前記重縮合反応槽の内部に気密に連通する一方、中空状内部の上方を減圧源に気密に連通する還流シリンダを具備して成ることを特徴とするポリ乳酸の製造装置によって達成される。
【００１２】
更に、本発明のかかる目的は、重縮合反応部における重縮合反応槽内に、主成分として乳酸モノマーと副成分としてコーンスターチと触媒としてモノブチルスズオキサイドとを含有する反応溶液を投入し、９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して前記反応溶液を、逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する逆円錐状ダブルヘリカル攪拌機で攪拌しながら無溶媒直接脱水重縮合反応によりポリ乳酸を生成する一方、前記無溶媒直接脱水重縮合反応により副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気を、ラクチド還流部において９ｋＰａ〜0.01ｋＰａの減圧下にある還流シリンダ内に吸引し、３０℃〜８０℃の範囲で冷却されて液化したラクチド及び乳酸低分子化合物を前記重縮合反応槽内に還流させると共に、前記副生水を大気圧系に排出させることを特徴とするポリ乳酸の製造方法によって達成される。
【００１３】
更に、本発明のかかる目的は、前記重縮合反応槽内における前記反応溶液の反応時間を16〜30時間の範囲内に設定することを特徴とするポリ乳酸の製造方法によって達成される。
【００１４】
【作用】
本発明のポリ乳酸の製造装置は、前記重縮合反応部における前記重縮合反応槽が逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する前記逆円錐状ダブルヘリカル攪拌機を具備して成るので、前記逆円錐状ダブルヘリカル攪拌機が乳酸モノマーを主成分とする前記反応溶液を広い気液接触面と高い表面更新性でポリマー鎖の物理的な切断を招くことなく攪拌し、無溶媒直接脱水重縮合反応により高分子量のポリ乳酸を効率良く製造する。
【００１５】
更に、本発明のポリ乳酸の製造方法は、前記重縮合反応槽内に、主成分として乳酸モノマーと副成分としてコーンスターチと触媒としてモノブチルスズオキサイドとを含有する前記反応溶液を投入し、９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して前記反応溶液を、逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する前記逆円錐状ダブルヘリカル攪拌機で攪拌しながら無溶媒直接脱水重縮合反応によりポリ乳酸を生成する一方、前記無溶媒直接脱水重縮合反応により副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気を、９ｋＰａ〜0.01ｋＰａの減圧下にある前記還流シリンダ内に吸引し、３０℃〜８０℃の範囲で冷却されて液化したラクチド及び乳酸低分子化合物を前記重縮合反応槽内に還流させると共に、前記副生水を大気圧系に排出させるので、溶媒を全く含まない前記反応溶液であっても前記触媒としてのモノブチルスズオキサイドが乳酸モノマーによって加水分解して重縮合反応速度が著しく低下させることがなく、溶媒の残留分によるポリ乳酸の分離精製や循環コストの上昇を抑制する。
【００１６】
更に、本発明のポリ乳酸の製造方法は、前記重縮合反応槽内の無溶媒直接脱水重縮合反応を９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して行うことによって、ポリ乳酸の高分子量化する時間を短縮できる一方、高温による乳酸ポリマーの解重合反応でラクチドに分解することが避けられる。
また、前記重縮合反応槽内における前記反応溶液の反応時間を16〜30時間の範囲内に設定することによって、高分子量化及び高耐熱性を有するポリ乳酸樹脂ペレットが生成される。
【００１７】
【発明の実施の形態】
本発明のポリ乳酸の製造装置及び製造方法の一実施態様について、添付した図面に基づき以下に詳述する。図１は本発明のポリ乳酸の製造装置の要部を示すフローシート図であり、図２は本発明のポリ乳酸の製造装置における重縮合反応槽を一部破断して示した斜視図である。図１に示した本発明のポリ乳酸の製造装置２０の要部は、重縮合反応部２２、ラクチド還流部２９及び減圧源４０に大別される。
【００１８】
先ず、前記重縮合反応部２２は、図２からより明らかなように、外周面を温度調節用ジャケット２４で覆い、逆円錐状に形成された内部底面を有する重縮合反応槽２３と、前記重縮合反応槽２３の逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼２７を有し、槽外の駆動モータ２５によって回転駆動される逆円錐状ダブルヘリカル攪拌機２６とを具備して成る。
更に、前記重縮合反応槽２３の前記温度調節用ジャケット２４は、加熱媒体及び冷却媒体が循環供給可能なように各導入口２４ａと放出口２４ｂが適宜配設される。前記加熱媒体及び冷却媒体は、図示していない加熱媒体ヒータ及び冷却媒体クーラから循環供給される。
【００１９】
次に、前記ラクチド還流部２９は、外周面を温度調節用ジャケット３１で覆い、中空状内部の下方を前記重縮合反応槽２３の内部に吸引路３２と還流路３３を介して気密に連通する一方、中空状内部の上方を吸引口３４を介して例えば真空ポンプから成る減圧源４０に気密に連通する還流シリンダ３０を具備して成る。前記吸引路３２，３４及び前記還流路３３の各外周面は、前記還流シリンダ３０の温度調節用ジャケット３１の延長部分で覆われ、該温度調節用ジャケット３１に加熱媒体及び冷却媒体が循環供給可能なように各導入口３１ａと放出口３１ｂが適宜配設される。前記加熱媒体及び冷却媒体は、図示していない加熱媒体ヒータ及び冷却媒体クーラから循環供給される。
【００２０】
また、前記還流シリンダ３０の上方に配設した前記吸引口３４から、凝縮水コンデンサ３５、凝縮水ポット３７及びコールドトラップ３８の順で前記減圧源４０まで気密に接続され、前記重縮合反応槽２３から前記減圧源４０までの減圧系が形成される。
前記凝縮水コンデンサ３５は外周面を冷却用ジャケット３６で覆い、該冷却用ジャケット３６に図示していない冷却媒体クーラから冷却媒体が循環供給される。前記コールドトラップ３８も外周面を冷却用ジャケット３９で覆い、該冷却用ジャケット３９に図示していない冷却媒体クーラから冷却媒体が循環供給される。なお、前記加熱媒体の各循環経路は、その分岐配管を加熱媒体膨張タンク２１に接続されて、昇温に伴う前記加熱媒体の体積膨張分の吸収を図る。
【００２１】
以上、記述したように構成される本発明のポリ乳酸の製造装置２０の要部は、次に記すようにポリ乳酸を生成する。先ず、前記重縮合反応部２２における前記重縮合反応槽２３内に、主成分として乳酸モノマー（例えば、10％の水分を含むＬ−乳酸）と副成分としてコーンスターチと触媒としてモノブチルスズオキサイドとを含有する反応溶液を投入し、９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して前記反応溶液を、逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能な前記リボン翼２７を有する前記逆円錐状ダブルヘリカル攪拌機２６で攪拌しながら16〜30時間にわたる無溶媒直接脱水重縮合反応によりポリ乳酸を生成し、前記重縮合反応槽２３の逆円錐状の内部底面から排出流路２８を経て大気系に該ポリ乳酸を排出する。
【００２２】
一方、前記無溶媒直接脱水重縮合反応により副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気を、前記ラクチド還流部２９において９ｋＰａ〜0.01ｋＰａの減圧下にある前記還流シリンダ３０内に吸引し、３０℃〜８０℃の範囲で冷却されて液化したラクチド及び乳酸低分子化合物を前記重縮合反応槽２３内に還流させると共に、前記副生水を前記吸引口３４から、前記凝縮水コンデンサ３５に送り、約５℃程度に冷却、凝縮させて、前記凝縮水ポット３７から大気圧系に排出させ、更に未凝縮分の微量な前記副生水を前記コールドトラップ３８で約−65℃程度に冷却、凝縮させて大気圧系に排出させる。
【００２３】
【発明の効果】
以上、記述した本発明のポリ乳酸の製造装置及び製造方法は、次に記すような新規な効果を奏するものである。即ち、本発明のポリ乳酸の製造装置は、前記重縮合反応部における前記重縮合反応槽が逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する前記逆円錐状ダブルヘリカル攪拌機を具備して成るので、前記逆円錐状ダブルヘリカル攪拌機が乳酸モノマーを主成分とする前記反応溶液を広い気液接触面と高い表面更新性でポリマー鎖の物理的な切断を招くことなく攪拌し、その結果、無溶媒直接脱水重縮合反応により高分子量のポリ乳酸を効率良く製造することが可能になった。
【００２４】
更に、本発明のポリ乳酸の製造方法は、前記重縮合反応槽内に、主成分として乳酸モノマーと副成分としてコーンスターチと触媒としてモノブチルスズオキサイドとを含有する前記反応溶液を投入し、９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して前記反応溶液を、逆円錐状の内部底面から直胴内面に沿って複式螺旋状に旋回可能なリボン翼を有する前記逆円錐状ダブルヘリカル攪拌機で攪拌しながら無溶媒直接脱水重縮合反応によりポリ乳酸を生成する一方、前記無溶媒直接脱水重縮合反応により副生されたラクチド、乳酸低分子化合物、副生水等を含む各蒸気を、９ｋＰａ〜0.01ｋＰａの減圧下にある前記還流シリンダ内に吸引し、３０℃〜８０℃の範囲で冷却されて液化したラクチド及び乳酸低分子化合物を前記重縮合反応槽内に還流させると共に、前記副生水を大気圧系に排出させるので、溶媒を全く含まない前記反応溶液であっても前記触媒としてのモノブチルスズオキサイドが乳酸モノマーによって加水分解して重縮合反応速度が著しく低下させることがなく、溶媒の残留分によるポリ乳酸の分離精製や循環コストの上昇を抑制することが可能になった。
【００２５】
更に、本発明のポリ乳酸の製造方法は、前記重縮合反応槽内の無溶媒直接脱水重縮合反応を９ｋＰａ〜0.01ｋＰａの減圧下で反応温度を160 ℃〜220 ℃の範囲に維持して行うことによって、ポリ乳酸の高分子量化する時間を短縮できる一方、高温による乳酸ポリマーの解重合反応でラクチドに分解することが避けられ、また、前記重縮合反応槽内における前記反応溶液の反応時間を16〜30時間の範囲内に設定することによって、高分子量化及び高耐熱性を有するポリ乳酸樹脂ペレットを生成することが可能になった。
【００２６】
前述した本発明のポリ乳酸の製造装置及び製造方法による新規な効果を、実施例及び比較例によって一層明確にする。
［実施例及び比較例の諸条件］；
−１．製造装置 …… 実施例及び比較例ともに重縮合反応槽の攪拌機を除く他の装置は、図１に示した装置を使用した。重縮合反応槽の攪拌機の仕様は、表１の通りである。
−２．製造方法 …… 表１の通りである。
【００２７】
【表１】

【００２８】
［実施例及び比較例の結果］；
−１．ポリ乳酸の重量平均分子量 …… 実施例のポリ乳酸は480,000 、比較例１のポリ乳酸は60,000、比較例２のポリ乳酸は40,000であった。
−２．生分解性 …… 比較例１及び比較例２のポリ乳酸は、機械的強度が劣り、ＪＩＳＫ7113 で規定される１号試験片の形状に射出成形し、土中埋没試験ができなかった。
実施例のポリ乳酸から成る１号試験片を、真砂土を主成分とする畑土中に４ヶ月埋没させた後、重量測定した結果、８％の減少が認められ、且つ樹脂表面の白濁も認められた。
以上の結果から、実施例は22時間と言う比較的短時間の無溶媒直接脱水重縮合反応により、高分子量で生分解性に富むポリ乳酸を効率良く生成できることが確認できた。
【図面の簡単な説明】
【図１】本発明のポリ乳酸の製造装置の要部を示すフローシート図である。
【図２】本発明のポリ乳酸の製造装置における重縮合反応槽を一部破断して示した斜視図である。
【図３】従来のポリ乳酸の製造装置の要部を示すフローシート図である。
【符号の説明】
１従来のポリ乳酸の直接脱水重縮合反応製造装置
２重縮合反応部
３重縮合反応槽
４攪拌機
５開閉弁
６ギアポンプ
７攪拌機付還流部
８スクリュ駆動モータ
９晶析還流シリンダ
１０スクリュ
１１スクリュ
２０本発明のポリ乳酸の製造装置
２１加熱媒体膨張タンク
２２重縮合反応部
２３重縮合反応槽
２４温度調節用ジャケット
２５駆動モータ
２６逆円錐状ダブルヘリカル攪拌機
２７リボン翼
２８排出流路
２９ラクチド還流部
３０還流シリンダ
３１温度調節用ジャケット
３２吸引路
３３還流路
３４吸引口
３５凝縮水コンデンサ
３６冷却用ジャケット
３７凝縮水ポット
３８コールドトラップ
３９冷却用ジャケット
４０減圧源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for producing high molecular weight polylactic acid by direct dehydration polycondensation reaction of a lactic acid monomer and a method for producing the same.
[0002]
[Prior art]
Polylactic acid widely used as a biodegradable plastic has the property of easily becoming an oligomer by hydrolysis and thermal decomposition using lactic acid as a raw material, and has high transparency and rigidity, and is copolymerized with other biodegradable substances. Suitable for films, fibers, general molded products, etc.
In order to produce the above-mentioned polylactic acid by direct dehydration polycondensation reaction, the main part of a conventional representative apparatus disclosed in Japanese Patent Application Laid-Open No. 10-130376 has been configured as shown in FIG.
[0003]
That is, the main part of the conventional polylactic acid direct dehydration polycondensation reaction production apparatus 1 comprises a polycondensation reaction unit 2 and a reflux unit 7 with a stirrer, and the polycondensation reaction unit 2 is heated on the outer peripheral surface. A stirrer 4 in which a ribbon-shaped stirring blade is wound around the extending portion of the rotating shaft of one screw 10 to be described later is rotatably mounted inside the polycondensation reaction tank 3 covered with a jacket (not shown). In addition, the polycondensation reaction tank 3 is provided with a discharge flow path having an on-off valve 5 and a gear pump 6 for discharging polylactic acid to the outside from the inverted conical bottom. Note that the heating medium supplied into the heating jacket from the introduction port 3a is discharged from the discharge port 3b.
[0004]
On the other hand, the reflux unit 7 with a stirrer has a lower opening of a crystallization reflux cylinder 9 in which two

screws

10 and 11 are axially attached so that each flight is entangled with each other inside a hollow shape, and an upper lid of the polycondensation reaction tank 3. The screw driving motor 8 was disposed at the upper end portion of the crystallization reflux cylinder 9 via a connecting portion while being airtightly penetrated into the center portion.
The outer peripheral surface of the crystallization reflux cylinder 9 is covered with a cooling jacket (not shown), and the cooling medium supplied into the cooling jacket from the introduction port 9a is discharged from the discharge port 9b.
[0005]
Further, a suction port 12 is disposed on the upper side surface of the crystallization reflux cylinder 9, and the suction port 12 is sequentially connected to a knockout drum 13, a cooling trap 15 and a vacuum pump 17 in an airtight manner. On-off valves 14 and 16 are disposed at the bottoms of the knockout drum 13 and the cooling trap 15, respectively.
[0006]
In the conventional polylactic acid direct dehydration polycondensation reaction production apparatus 1 having the main parts as described above, the vacuum pump 17 is activated and the cooling trap 15, the knockout drum 13, the crystallization reflux cylinder 9 and The pressure in the system of the polycondensation reaction tank 3 is reduced, lactic acid monomers, a solvent, a catalyst, and the like are introduced into the polycondensation reaction tank 3, and the heating medium is circulated and supplied from the inlet 3a of the heating jacket. Thus, while maintaining the internal temperature of the polycondensation reaction tank 3 at a predetermined temperature, the reaction solution is stirred by the stirrer 4, and the lactic acid monomer is directly subjected to dehydration polycondensation reaction, thereby producing the desired polylactic acid. On the other hand, each vapor containing by-produced lactide, lactic acid low molecular weight compound, by-product water and the like was sucked into the hollow inside of the crystallization reflux cylinder 9.
[0007]
By circulating and supplying the cooling medium from the inlet 9a of the cooling jacket, while maintaining the internal temperature of the crystallization reflux cylinder 9 at a temperature at which the lactide and some of the lactic acid low molecular compounds are crystallized, The two

screws

10 and 11 are rotated in a desired direction so that the crystallized lactide and a part of the lactic acid low molecular weight compound and the remaining lactic acid low molecular weight compound are liquefied in the polycondensation reaction tank 3. By forcibly refluxing, it is possible to increase the rate of dehydration polycondensation reaction of the lactic acid monomer directly and shift the polycondensation reaction to the polymer side, thereby making it possible to efficiently produce high molecular weight polylactic acid. there were. The vapor of by-product water was liquefied by the cooling trap 15 via the knockout drum 13 and then discharged out of the system.
[0008]
[Problems to be solved by the invention]
However, in the conventional polylactic acid direct dehydration polycondensation reaction production apparatus and method described above, the use of a solvent for the reaction solution is inevitable, and it is difficult to significantly reduce polylactic acid separation and purification and the circulation cost due to the residue. there were. On the other hand, when polyhydroxycarboxylic acid is produced by directly dehydrating polycondensation reaction of hydroxycarboxylic acid without containing the solvent, a polycondensation catalyst such as tin octylate is formed by water contained in a large amount in the hydroxycarboxylic acid. Hydrolysis resulted in a significant decrease in the polycondensation reaction rate.
[0009]
Furthermore, the conventional polylactic acid direct dehydration polycondensation reaction production apparatus and method have a mechanical strength that can withstand normal processing by reducing the polycondensation reaction rate when the polycondensation reaction proceeds and the melt viscosity of the resin increases. When resin pellets are difficult to obtain and the polycondensation reaction time is increased as a countermeasure, there is a drawback that racemization of the resin pellets proceeds and the melting point tends to decrease.
In order to prevent the melting point of the resin pellets from decreasing, it is desirable to improve the gas-liquid contact surface and surface renewability of the reaction solution to promote the dehydration polycondensation reaction. However, in a conventional stirrer having a simple ribbon-shaped stirring blade, It has been difficult to efficiently produce high molecular weight polylactic acid by improving the gas-liquid contact surface and surface renewability and suppressing physical breakage of the polymer chain by the stirring blade.
[0010]
The present invention provides an apparatus and method for solving the above-mentioned problems of the prior art and efficiently producing a high molecular weight polylactic acid with a relatively simplified structure in a solvent-free direct dehydration polycondensation reaction. It is intended.
[0011]
[Means for Solving the Problems]
The object of the present invention is to add a reaction solution containing a lactic acid monomer as a main component to the polycondensation reaction part to produce polylactic acid by a solventless direct dehydration polycondensation reaction under reduced pressure, while the solventless direct dehydration polycondensation is performed. Each vapor containing lactide, lactic acid low molecular compound, by-product water, etc. produced as a by-product in the reaction is sucked into the lactide reflux part, and the liquefied lactide and lactic acid low molecular compound are refluxed to the polycondensation reaction part, In the polylactic acid production apparatus for discharging water to an atmospheric pressure system; the polycondensation reaction section has a polycondensation reaction tank having an inner bottom surface formed in an inverted conical shape with an outer peripheral surface covered with a temperature control jacket; A reverse conical double-helical stirrer having a ribbon blade that can be spirally swiveled from the reverse conical inner bottom surface of the polycondensation reaction tank along the inner surface of the straight cylinder; The warm It is covered with an adjustment jacket, and comprises a reflux cylinder that communicates the lower part of the hollow interior in an airtight manner with the interior of the polycondensation reaction tank, while the upper part of the hollow interior communicates in an airtight manner with a reduced pressure source. This is achieved by an apparatus for producing polylactic acid.
[0012]
Further, the object of the present invention is to charge a reaction solution containing lactic acid monomer as a main component, corn starch as a subcomponent and monobutyltin oxide as a catalyst into a polycondensation reaction tank in the polycondensation reaction section, An inverted cone having ribbon blades capable of swirling the reaction solution in a double spiral form along the inner surface of the straight cylinder from the inverted conical inner bottom surface while maintaining the reaction temperature in the range of 160 ° C. to 220 ° C. under a reduced pressure of kPa Each containing polylactic acid by solventless direct dehydration polycondensation reaction while stirring with a cylindrical double helical stirrer, while containing lactide, lactic acid low molecular weight compound, byproduct water, etc. produced by the solventless direct dehydration polycondensation reaction Vapor is sucked into a reflux cylinder under reduced pressure of 9 kPa to 0.01 kPa in the lactide reflux section, and cooled and liquefied in the range of 30 ° C. to 80 ° C., lactide and milk This is achieved by a method for producing polylactic acid, characterized in that an acid low molecular weight compound is refluxed into the polycondensation reaction tank and the by-product water is discharged to an atmospheric pressure system.
[0013]
Furthermore, this object of the present invention is achieved by a method for producing polylactic acid, characterized in that the reaction time of the reaction solution in the polycondensation reaction tank is set within a range of 16 to 30 hours.
[0014]
[Action]
In the polylactic acid production apparatus of the present invention, the polycondensation reaction tank in the polycondensation reaction section has the inverted conical shape having a ribbon blade that can swivel in a double spiral shape from the inner bottom surface of the inverted conical shape along the inner surface of the straight cylinder. Since the double helical stirrer is provided, the inverted conical double helical stirrer causes the reaction solution mainly composed of lactic acid monomer to physically break the polymer chain with a wide gas-liquid contact surface and high surface renewability. Without stirring, high molecular weight polylactic acid is efficiently produced by solvent-free direct dehydration polycondensation reaction.
[0015]
Furthermore, in the polylactic acid production method of the present invention, the reaction solution containing lactic acid monomer as a main component, corn starch as a subcomponent and monobutyltin oxide as a catalyst is charged into the polycondensation reaction tank, and 9 kPa to 0.01 Maintaining the reaction temperature in the range of 160 ° C. to 220 ° C. under a reduced pressure of kPa, the reaction solution has a ribbon blade capable of swirling in a double spiral form along the inner surface of the straight cylinder from the inner bottom surface of the inverted cone. Polylactic acid is produced by solvent-free direct dehydration polycondensation reaction while stirring with a conical double helical stirrer, and contains lactide, lactic acid low molecular weight compound, by-product water, etc. produced as a by-product by the solvent-free direct dehydration polycondensation reaction. Each vapor is sucked into the reflux cylinder under a reduced pressure of 9 kPa to 0.01 kPa, and cooled and liquefied in a range of 30 ° C. to 80 ° C., the lactide and the lactic acid low molecular weight compound are preliminarily obtained. While refluxing the polycondensation reaction tank and discharging the by-product water to the atmospheric pressure system, monobutyltin oxide as the catalyst is hydrolyzed by the lactic acid monomer even in the reaction solution containing no solvent. Thus, the polycondensation reaction rate is not significantly reduced, and the separation and purification of polylactic acid and the increase in the circulation cost due to the residual solvent are suppressed.
[0016]
Furthermore, in the method for producing polylactic acid according to the present invention, the solvent-free direct dehydration polycondensation reaction in the polycondensation reaction tank is performed under a reduced pressure of 9 kPa to 0.01 kPa while maintaining the reaction temperature in the range of 160 ° C to 220 ° C. As a result, the time for increasing the molecular weight of the polylactic acid can be shortened, while the decomposition of the lactic acid polymer at a high temperature by the depolymerization reaction can be avoided.
Moreover, the polylactic acid resin pellet which has high molecular weight and high heat resistance is produced | generated by setting the reaction time of the said reaction solution in the said polycondensation reaction tank in the range of 16-30 hours.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the polylactic acid production apparatus and production method of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a flow sheet showing the main part of the polylactic acid production apparatus of the present invention, and FIG. 2 is a perspective view showing a partially broken polycondensation reaction tank in the polylactic acid production apparatus of the present invention. . 1 is roughly divided into a polycondensation reaction unit 22, a lactide reflux unit 29, and a reduced pressure source 40.
[0018]
First, as is clear from FIG. 2, the polycondensation reaction section 22 has a polycondensation reaction tank 23 having an inner bottom surface formed by covering the outer peripheral surface with a temperature adjusting jacket 24 and having an inverted conical shape, A reverse-conical double-helical stirrer 26 having a ribbon blade 27 that can be swirled in a double spiral shape from the reverse conical inner bottom surface of the condensation reaction tank 23 along the inner surface of the straight cylinder and rotated by a drive motor 25 outside the tank. And comprising.
Further, the temperature adjusting jacket 24 of the polycondensation reaction tank 23 is appropriately provided with inlets 24a and outlets 24b so that a heating medium and a cooling medium can be circulated and supplied. The heating medium and the cooling medium are circulated and supplied from a heating medium heater and a cooling medium cooler (not shown).
[0019]
Next, the lactide recirculation part 29 covers the outer peripheral surface with a temperature adjusting jacket 31, and the lower part of the hollow interior communicates with the inside of the polycondensation reaction tank 23 in an airtight manner via the suction path 32 and the recirculation path 33. On the other hand, a reflux cylinder 30 is provided that communicates airtightly with a decompression source 40 such as a vacuum pump through a suction port 34 above the hollow interior. The outer peripheral surfaces of the

suction paths

32 and 34 and the reflux path 33 are covered with an extension portion of the temperature adjustment jacket 31 of the reflux cylinder 30, and a heating medium and a cooling medium can be circulated and supplied to the temperature adjustment jacket 31. In this way, each inlet 31a and outlet 31b are appropriately arranged. The heating medium and the cooling medium are circulated and supplied from a heating medium heater and a cooling medium cooler (not shown).
[0020]
Further, from the suction port 34 disposed above the reflux cylinder 30, a condensed water condenser 35, a condensed water pot 37, and a cold trap 38 are connected in an airtight manner to the decompression source 40 in this order, and the polycondensation reaction tank 23. To a reduced pressure source 40 is formed.
The condensed water condenser 35 has an outer peripheral surface covered with a cooling jacket 36, and a cooling medium is circulated and supplied to the cooling jacket 36 from a cooling medium cooler (not shown). The cold trap 38 also has an outer peripheral surface covered with a cooling jacket 39, and a cooling medium is circulated and supplied to the cooling jacket 39 from a cooling medium cooler (not shown). Each circulation path of the heating medium has a branch pipe connected to the heating medium expansion tank 21 so as to absorb the volume expansion of the heating medium as the temperature rises.
[0021]
The main part of the polylactic acid production apparatus 20 of the present invention configured as described above generates polylactic acid as described below. First, the polycondensation reaction tank 23 in the polycondensation reaction unit 22 contains a lactic acid monomer (for example, L-lactic acid containing 10% water) as a main component, corn starch as a subcomponent, and monobutyltin oxide as a catalyst. The reaction solution is charged and the reaction temperature is maintained in a range of 160 ° C. to 220 ° C. under a reduced pressure of 9 kPa to 0.01 kPa. Polylactic acid is produced by solvent-free direct dehydration polycondensation reaction over 16 to 30 hours while stirring with the inverted conical double helical stirrer 26 having the ribbon blades 27 that can swivel in the reverse direction. The polylactic acid is discharged from the internal bottom surface to the atmospheric system through the discharge channel 28.
[0022]
Meanwhile, the reflux cylinder in which each vapor containing lactide, lactic acid low molecular weight compound, by-product water and the like by-produced by the solventless direct dehydration polycondensation reaction is reduced in pressure in the lactide reflux section 29 from 9 kPa to 0.01 kPa. The lactide and the lactic acid low molecular weight compound sucked into 30 and cooled and liquefied in the range of 30 ° C. to 80 ° C. are refluxed into the polycondensation reaction tank 23, and the by-product water is supplied from the suction port 34. It is sent to the condensed water condenser 35, cooled to about 5 ° C., condensed, discharged from the condensed water pot 37 to the atmospheric pressure system, and a small amount of uncondensed by-product water is about − Cool to about 65 ℃, condense and discharge to atmospheric pressure system.
[0023]
【The invention's effect】
As described above, the polylactic acid production apparatus and production method of the present invention have the following novel effects. That is, in the polylactic acid production apparatus of the present invention, the polycondensation reaction tank in the polycondensation reaction section has a ribbon blade that can swivel in a double spiral shape from the inner bottom surface of the inverted cone to the inner surface of the straight cylinder. Since it has a conical double helical stirrer, the reverse conical double helical stirrer can physically break the polymer chain with a wide gas-liquid contact surface and high surface renewability of the reaction solution mainly composed of lactic acid monomer. As a result, it was possible to efficiently produce high molecular weight polylactic acid by solvent-free direct dehydration polycondensation reaction.
[0024]
Furthermore, in the polylactic acid production method of the present invention, the reaction solution containing lactic acid monomer as a main component, corn starch as a subcomponent and monobutyltin oxide as a catalyst is charged into the polycondensation reaction tank, and 9 kPa to 0.01 Maintaining the reaction temperature in the range of 160 ° C. to 220 ° C. under a reduced pressure of kPa, the reaction solution has a ribbon blade capable of swirling in a double spiral form along the inner surface of the straight cylinder from the inner bottom surface of the inverted cone. Polylactic acid is produced by solvent-free direct dehydration polycondensation reaction while stirring with a conical double helical stirrer, and contains lactide, lactic acid low molecular weight compound, by-product water, etc. produced as a by-product by the solvent-free direct dehydration polycondensation reaction. Each vapor is sucked into the reflux cylinder under a reduced pressure of 9 kPa to 0.01 kPa, and cooled and liquefied in a range of 30 ° C. to 80 ° C., the lactide and the lactic acid low molecular weight compound are preliminarily obtained. While refluxing the polycondensation reaction tank and discharging the by-product water to the atmospheric pressure system, monobutyltin oxide as the catalyst is hydrolyzed by the lactic acid monomer even in the reaction solution containing no solvent. Thus, the polycondensation reaction rate is not significantly reduced, and it is possible to suppress the separation and purification of polylactic acid and the increase in the circulation cost due to the residual solvent.
[0025]
Furthermore, in the method for producing polylactic acid according to the present invention, the solvent-free direct dehydration polycondensation reaction in the polycondensation reaction tank is performed under a reduced pressure of 9 kPa to 0.01 kPa while maintaining the reaction temperature in the range of 160 ° C to 220 ° C. This can shorten the time to increase the molecular weight of polylactic acid, while avoiding decomposition to lactide in the depolymerization reaction of the lactic acid polymer at a high temperature, and reducing the reaction time of the reaction solution in the polycondensation reaction tank. By setting within the range of 16 to 30 hours, it became possible to produce polylactic acid resin pellets having high molecular weight and high heat resistance.
[0026]
The novel effect of the polylactic acid production apparatus and production method of the present invention described above will be further clarified by Examples and Comparative Examples.
[Conditions of Examples and Comparative Examples];
-1. Production apparatus: The apparatus shown in FIG. 1 was used as an apparatus other than the stirrer in the polycondensation reaction tank in both Examples and Comparative Examples. The specifications of the stirrer of the polycondensation reaction tank are as shown in Table 1.
-2. Manufacturing method: as shown in Table 1.
[0027]
[Table 1]

[0028]
[Results of Examples and Comparative Examples];
-1. Weight average molecular weight of polylactic acid: The polylactic acid in the example was 480,000, the polylactic acid in Comparative Example 1 was 60,000, and the polylactic acid in Comparative Example 2 was 40,000.
-2. Biodegradability: The polylactic acid of Comparative Example 1 and Comparative Example 2 was inferior in mechanical strength, injection-molded into the shape of No. 1 test piece defined in JIS K7113, and could not be subjected to the soil burying test.
As a result of weight measurement of No. 1 test piece made of polylactic acid of the example in a field soil mainly composed of pure sand soil for 4 months, an 8% reduction was observed, and the cloudiness of the resin surface was also observed. Admitted.
From the above results, it was confirmed that polylactic acid having a high molecular weight and high biodegradability can be efficiently produced by a relatively short solvent-free direct dehydration polycondensation reaction of 22 hours in Examples.
[Brief description of the drawings]
FIG. 1 is a flow sheet diagram showing a main part of a polylactic acid production apparatus of the present invention.
FIG. 2 is a perspective view showing a partially broken polycondensation reaction tank in the polylactic acid production apparatus of the present invention.
FIG. 3 is a flow sheet diagram showing a main part of a conventional polylactic acid production apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Conventional polylactic acid direct dehydration polycondensation reaction production apparatus 2 Polycondensation reaction part 3 Polycondensation reaction tank 4 Stirrer 5 On-off valve 6 Gear pump 7 Recirculation part with agitator 8 Screw drive motor 9 Crystallization reflux cylinder 10 Screw 11 Screw 20 Inventive Polylactic Acid Production Device 21 Heating Medium Expansion Tank 22 Polycondensation Reaction Unit 23 Polycondensation Reaction Tank 24 Temperature Control Jacket 25 Drive Motor 26 Reverse Conical Double Helical Stirrer 27 Ribbon Blade 28 Discharge Flow Path 29 Lactide Recirculation Unit 30 Reflux Cylinder 31 Temperature control jacket 32 Suction path 33 Reflux path 34 Suction port 35 Condensate condenser 36 Cooling jacket 37 Condensate pot 38 Cold trap 39 Cooling jacket 40 Depressurization source

Claims

A polylactic acid is produced by a solvent-free direct dehydration polycondensation reaction under reduced pressure while a reaction solution containing a lactic acid monomer as a main component is introduced into the polycondensation reaction part (22). Each vapor containing lactide, lactic acid low molecular weight compound, by-product water, etc. is sucked into the lactide reflux part (29), and the liquefied lactide and lactic acid low molecular weight compound are refluxed to the polycondensation reaction part (22), In the polylactic acid production apparatus (20) for discharging by-product water to the atmospheric pressure system; the polycondensation reaction part (22) is formed in an inverted conical shape with the outer peripheral surface covered with a temperature control jacket (24). A reverse side having a polycondensation reaction tank (23) having an inner bottom surface and a ribbon blade (27) capable of swiveling in a double spiral shape from the reverse conical inner bottom surface of the polycondensation reaction tank (23) along the inner surface of the straight cylinder. Conical double helical stirrer 26); the lactide reflux part (29) covers the outer peripheral surface with a temperature control jacket (31), and the lower part of the hollow interior is sealed inside the polycondensation reaction tank (23). Using the polylactic acid production apparatus comprising a reflux cylinder (30) that communicates airtightly with the reduced pressure source (40) above the hollow interior, the polycondensation reaction section (22) Into the polycondensation reaction tank (23), a reaction solution containing lactic acid monomer as a main component, corn starch as a subcomponent and monobutyltin oxide as a catalyst is charged , and the reaction temperature is reduced from 160 ° C. to 9 kPa to 0.01 kPa under reduced pressure. the reaction solution was maintained in the range of 220 ° C., the reverse conical double helical agitator having a ribbon blade (27) pivotable into the double spiral from the inverse conical inner bottom along the straight body inner surface 26) While producing polylactic acid by solvent-free direct dehydration polycondensation reaction while stirring in 26), each vapor containing lactide, lactic acid low molecular weight compound, by-product water, etc. by-produced by the solvent-free direct dehydration polycondensation reaction is produced. The lactide refluxing part (29) is sucked into the reflux cylinder (30) under a reduced pressure of 9 kPa to 0.01 kPa, and cooled and liquefied in a range of 30 ° C to 80 ° C, the liquefied lactide and lactic acid low molecular weight compound are A method for producing polylactic acid, comprising refluxing into a polycondensation reaction tank (23) and discharging the by-product water to an atmospheric pressure system .

The method for producing polylactic acid according to claim 1, wherein the reaction time of the reaction solution in the polycondensation reaction tank (23) is set within a range of 16 to 30 hours .