JP4070292B2 - Gas separation membrane with fluorine-containing polyimide resin - Google Patents

Description

【０００７】
また前記気体分離膜においては、フッ素含有ポリイミド樹脂から構成される膜が緻密膜および非対称膜から選ばれる少なくとも一つの膜であることが好ましい。ここで緻密膜とは、多孔質構造が存在せず、気体の透過性が膜への溶解性と膜中における拡散性により支配される領域の膜をいう。また非対称膜とは、膜の一方の表面が緻密層となっており、内部構造と裏面は多孔質構造になっている膜をいう。これらの概念は当業界では一般的によく知られているものである。また前記気体分離膜においては、紫外線照射が、低圧水銀ランプを用いたものであることが好ましい。
【０００８】
前記した本発明の構成によれば、繰り返し分子構造単位中に少なくとも１つの−ＣＦ₃基を有するフッ素含有ポリイミド樹脂をから構成される膜に、例えば低圧水銀ランプを用いて紫外線を照射し、これにより膜表面に活性薄層が形成された気体分離膜を用いて、混合気体から特定の成分、例えば水素ガス、炭酸ガス、酸素ガス、窒素ガス、水蒸気、有機物ガス、有機物蒸気等を高度に分離・濃縮することができる。また、取り扱う気体の物性や分離操作の圧力・分離操作によっては、浸透気化法用の分離膜としての使用が実現できる。
【０００９】
前記において、活性薄層とは特定の成分に対して分離性および分離性能安定性を十分に兼ね備えた薄層を表し、紫外線処理によりフッ素含有ポリイミド樹脂の一部が架橋して形成されたものである。
【００１０】
一般的に高分子膜の多くは酸性成分や炭化水素などの有機成分により可塑化あるいは膨潤することがよく知られている。ポリイミド樹脂などのガラス状高分子膜が一度可塑化あるいは膨潤すると、特定成分の選択的分離に寄与できるセグメント間のパッキング構造が崩れてしまい、一般的に分離性能の低下を招く傾向がある。したがって、酸性成分や有機成分などに対して高い分離性能を安定して維持できる分離膜を得るためには分離膜を構成する高分子セグメント間のパッキング構造を酸性成分や有機成分により影響されにくい構造とすることが効果的である。本発明者はこの点に着眼し、鋭意検討した結果、繰り返し分子構造単位中に少なくとも１つの−ＣＦ₃基を有するフッ素含有ポリイミド樹脂から構成される膜に、例えば低圧水銀ランプを用いて紫外線を照射し、これにより膜表面に活性薄層が形成された気体分離膜が優れた気体分離性能を有し、酸性成分や有機成分存在下でも極めて可塑化あるいは膨潤されにくく優れた耐性を有することを見出した。
【００１１】
フッ素含有ポリイミド樹脂の繰り返し分子構造単位中に−ＣＦ₃基が存在すると、低圧水銀ランプによる紫外線照射後においても含フッ素ポリイミド中に多くの−ＣＦ₃基が残存し、その結果、優れた気体分離性能を有する膜を得ることができる。また、紫外線源に例えば低圧水銀ランプを使用することにより、フッ素含有ポリイミドが局所的に架橋を起こすのに必要なエネルギーを吸収することができ、その結果、膜表面に気体分離性能、耐酸成分性、耐有機成分性に優れた架橋層から成る活性薄層を有する気体分離膜を得ることができる。
【００１２】
前記において、活性薄層の厚さが５〜１０００ｎｍ（５０〜１００００オングストローム）であるとさらに好ましい選択性を発揮する。活性薄層の厚さが５ｎｍ（５０オングストローム）未満であると形成される活性薄層にピンホール等の膜欠陥が形成され易くなり好ましくない。一方、１０００ｎｍ（１００００オングストローム）を超える厚さの場合は、形成される活性薄層における気体の透過抵抗が過大となり、実用上、透過流束が小さすぎるので好ましくない。
【００１３】
また、前記において、フッ素含有ポリイミド樹脂のフッ素含有量は６〜１２個（繰り返し分子構造単位中のフッ素原子の数）であることが、実質的に安定した高品質を有する気体分離膜を得るのに好ましい。また１２個を越えると原料コストが高くなり実用性が低下する傾向となる。
【００１４】
また前記において、フッ素含有ポリイミド樹脂が実質的に前記式（Ｉ）で表される繰り返し分子構造単位を主成分とすると、コストも低く実用的である。
【００１５】
【発明の実施の形態】
本発明者は、繰り返し分子構造単位中に少なくとも１つの−ＣＦ₃基を有するフッ素含有ポリイミド樹脂を主成分とする膜に、例えば低圧水銀ランプを用いて紫外線を照射し、これにより膜表面に活性薄層を形成させることにより、気体分離性能、耐酸成分性、耐有機成分性に優れる気体分離膜が得られることを見出し、本発明に至ったものである。
【００１６】
本発明における紫外線処理は紫外線の照射雰囲気の温度や圧力等によっても異なるが、通常波長１５０〜２７０ｎｍの紫外線を６Ｊ／ｃｍ²以上、好ましくは６〜５００Ｊ／ｃｍ²のエネルギー強度で照射するのがよい。
【００１７】
本発明に用いられるフッ素含有ポリイミド樹脂は実質的に、前記式（Ｉ）で表される繰り返し分子構造単位を主成分とする。本発明で用いられるフッ素含有ポリイミド樹脂は、テトラカルボン酸２無水物とジアミン化合物（ただし、前記酸成分またはアミン成分中の少なくとも一方の成分は−ＣＦ₃基を含む）を用いて、例えば、米国特許第３９５９３５０号明細書に記載されているような公知の重合方法で得られる。例えば、テトラカルボン酸２無水物とジアミン化合物（ただし、前記酸成分またはアミン成分中の少なくとも一方の成分は−ＣＦ₃基を含む）をほぼ等モル量を用い、極性溶媒中、約８０℃以下の温度、好ましくは、０〜６０℃で撹拌し、ポリアミック酸を重合する。ここで用いられる極性溶媒は特に限定されないが、Ｎ−メチルピロリドン、ピリジン、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキシド、テトラメチル尿素、フェノール、クレゾール、テトラハイドロフランなどが好適に用いられる。
【００１８】
得られたポリアミック酸の極性溶媒溶液にトリメチルアミン、トリエチルアミン、ピリジン等の第３級アミン化合物、無水酢酸、塩化チオニル、カルボジイミドなどのイミド化促進剤を添加し、５〜１５０℃の温度で撹拌し、イミド化する。イミド化反応を行う際、イミド化促進剤を添加することなく、上記ポリアミック酸溶液を１００〜４００℃、好ましくは、１２０〜３００℃で加熱してイミド化してもよい。
【００１９】
イミド化反応後、重合時の極性溶媒やイミド化促進剤を除去するために、多量のアセトン、アルコールまたは水等の溶液に滴下し精製することにより、膜材料として好適なポリイミド樹脂が得られる。また、イミド化促進剤を添加することなく、イミド化反応を行う場合は、ポリアミック酸溶液を多量のアセトン、またはアルコール等の溶液に滴下して得られたポリアミック酸粉末やポリアミック酸溶液から溶媒を蒸発させて得られたポリアミック酸の固体（蒸発の際、沈殿剤等を加えてポリアミック酸粉末を形成させ、濾別してもよい）を１００〜４００℃に加熱してイミド化することにより、膜材料として好適なポリイミド樹脂が得られる。
【００２０】
本発明で用いられる緻密膜の製膜法は、特に限定されないが、例えば、上述のフッ素含有ポリイミド樹脂を適当な溶媒に溶解して製膜液を調製し、製膜液をガラス、金属、プラスチック等の平滑な表面を有する平板や管に一定の厚さで流延し、次いで、加熱処理により溶媒を除去した後、紫外線処理することにより膜表面に活性薄層を形成する方法が好適に用いられる。
【００２１】
本発明で用いられる非対称膜の製造法は、特に限定されないが、生産性、コスト面から湿式相転換製膜法が好ましく用いられる。例えば、上記のフッ素含有ポリイミド樹脂を所定の有機溶媒に溶解して製膜液を調製し、製膜液をガラス、金属、プラスチック等の平板や管、あるいは、織布、不織布等の多孔質支持体上に一定の厚さで流延し、凝固液（製膜液中のフッ素含有ポリイミド樹脂は溶解しないが、製膜液中の有機溶媒と相溶性のある溶媒）に浸漬するか、または、製膜液を同心円状の２重構造のノズルから押し出し、上記凝固液に浸漬して非対称膜を調製し、その後、膜を乾燥した後、紫外線処理することにより膜表面に活性薄層を形成する方法をとることができる。
【００２２】
フッ素含有ポリイミド樹脂の溶媒としては、特に限定されないが、Ｎ−メチル−２−ピロリドン、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキシド、ジエチレングリコールジメチルエーテル、１，２−ジメトキシメタン等が挙げられる。
【００２３】
これらの有機溶媒は単独で用いる以外に、２種以上の混合溶媒としても用いられる。上記有機溶媒は極性が小さく、凝固液として用いる溶媒との親和性の弱い溶媒が好ましく、例えば、ジエチレングリコールジメチルエーテル、１，２−ジメトキシエタン等が挙げられる。凝固液として用いる溶媒との親和性の弱い溶媒を製膜液に用いた場合、湿式相転換製膜時にスキン状薄層の形成よりも製膜液中の溶媒が凝固液として用いる溶媒中へ進出する速度が十分小さくなる。その結果、広範囲にわたって、分離性能を大きく低下させるピンホールが存在しないスキン状薄層と多孔質構造層を有する非対称膜を得ることができる。
【００２４】
上記有機溶媒を浸漬し除去する際に用いられる凝固液は用いるフッ素含有ポリイミド樹脂を溶解しないが、製膜液中の溶媒と相溶性を有する溶媒であれば、特に限定されないが、水やエタノール、メタノール、イソプロピルアルコール等のアルコール類およびこれらの混合液が用いられ、特に水が好適に用いられる。製膜液中の有機溶媒を浸漬除去する際の凝固液の温度は特に限定されないが、好ましくは０〜５０℃の温度で行われる。
【００２５】
製膜液のポリイミド溶液濃度は３〜４０重量％、好ましくは１０〜３０重量％である。また、製膜液を調整する場合に必要に応じて、膨潤剤、分散剤、増粘剤等を加えてもよい。製膜液を流延する手段としては、例えば、ドクターナイフ、ドクタープレート、アプリケーター等を利用することができる。また、本発明における膜の形状は特に限定されないが、チューブ状（中空糸状を含む）、平膜状のものが好適に用いられる。
【００２６】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれら実施例に何ら限定されるものではない。
【００２７】
【実施例１】
前記式（Ｉ）で表される繰り返し単位とするフッ素含有ポリイミドを以下の方法で合成した。５，５’−２，２’−トリフルオロ−１−（トリフルオロメチル）エチリデン−ビス−１，３−イソベンゾフランジオン（６ＦＤＡ）０．１ｍｏｌと２，２−ビス（４−アミノフェニル）ヘキサフルオロプロパン（ＢＡＡＦ）０．１ｍｏｌをＮ−メチル−２−ピロリドン（ＮＭＰ）溶液中で４時間反応させポリアミック酸を得た。この後、ピリジン０．３ｍｏｌと無水酢酸０．３ｍｏｌを加え、１５時間イミド化反応を行った。反応後、更にＮＭＰを加えて８重量％に希釈し、過剰量の水中に上記ＮＭＰ溶液を滴下した後に精製し、前記式（Ｉ）で表される繰り返し単位を構造単位とするフッ素含有ポリイミド樹脂を得た。得られたフッ素含有ポリイミド樹脂の物性値は、ガラス転移温度が３０１℃で、重量平均分子量は１５９，０００であった。
【００２８】
前記式（Ｉ）で表される繰り返し単位を構造単位とするフッ素含有ポリイミド１６重量部を希釈し、有機溶媒（Ａ）としてジエチレングリコールジメチルエーテル８４重量部を加え、１００℃で６時間撹拌し溶解した。その後、濾過し、静置して十分に脱泡し、製膜液を調整した。製膜液をアプリケータを用いガラス板上に、幅２０ｃｍ、厚さ３００μｍで流延し、１１０℃で１時間、１５０℃で１時間、２００℃で３時間、さらに３００℃で５時間加熱処理を施し、厚さ３２μｍのフッ素含有ポリイミドより成る緻密膜を得た。この緻密膜に出力６５０Ｗの低圧水銀ランプ（オーク（株）製；ＶＵＶ−６５Ｂ−２２−２１、波長１８５ｎｍ、２５４ｎｍ）で１５分間照射することにより紫外線処理を施した緻密膜を得た。この紫外線処理を施した緻密膜の断面を走査型電子顕微鏡を用いて観察したところ、図１に示すように膜表面に厚さ８５０オングストローム〜２２００オングストロームの活性薄層を有していた。したがって、この膜は本発明における分離膜の条件を満足するものであった。次に、この膜について、温度２５℃、供給圧力２ａｔｍにて、ＣＯ₂ ５０ｖｏｌ．％、ＣＨ₄ ｖｏｌ．５０％の混合ガスの分離性能、及びヘキサン７日間浸漬前後の引っ張り破断強度の保持率を評価した結果を後にまとめて表１に示す。
【００２９】
【比較例１】
紫外線処理を省いた以外は実施例１と同様にして緻密膜を得た。この緻密膜の断面を走査型電子顕微鏡を用いて観察したところ、図２に示すように図１に示した紫外線処理膜の表面形態と明らかに異なっていた。次に、この膜について、実施例１と同様にして混合ガスの分離性能、及びヘキサン７日間浸漬前後の引っ張り破断強度の保持率を評価した結果を後にまとめて表１に示す。
【００３０】
【比較例２】
５，５’−２，２’−トリフルオロ−１−（トリフルオロメチル）エチリデン−ビス−１，３−イソベンゾフランジオン（６ＦＤＡ）の代わりに１，２，３，４−ブタンテトラフルオロエチレンカルボン酸２無水物を用い、また、２，２−ビス（４−アミノフェニル）ヘキサフルオロプロパン（ＢＡＡＦ）の代わりに４，４’−オキソジアニリンを用いた以外は実施例１と同様にしてフッ素非含有のポリイミド樹脂（ＢＴＣ−４，４’−ＯＤＡ）を得た。このフッ素非含有のポリイミドと有機溶媒としてＮ−メチル−２−ピロリドンを用いた以外は実施例１と同様にして厚さ３０μｍのフッ素非含有のポリイミドよりなる緻密膜を得た。この膜について、紫外線照射処理を施さなかった以外は実施例１と同様にして混合ガスの分離性能、及びヘキサン７日間浸漬前後の引っ張り破断強度の保持率を評価した結果を後にまとめて表１に示す。
【００３１】
【比較例３】
比較例２と同様にして得たフッ素非含有ポリイミドよりなる緻密膜について、実施例１と同様にして紫外線照射処理を施した後、混合ガスの分離性能を評価した結果を後にまとめて表１に示す。
【００３２】
【表１】

【００３３】
表１から明らかな通り、本発明の実施例品は酸性ガスに対して高い分離能と、有機成分に対する耐性を有することが確認できた。以上説明した通り本実施例によれば、繰り返し分子構造単位中に少なくとも１つの−ＣＦ₃基を有するフッ素含有ポリイミド樹脂から構成される膜に低圧水銀ランプを用いて紫外線を照射し、これにより膜表面に活性薄層を形成させることにより、気体分離性能、耐酸成分性、耐有機成分性に優れ、性能面、コスト面においても実用的に満足しうる気体分離膜を提供することができる。
【００３４】
【発明の効果】
以上説明した通り、本発明によれば、繰り返し分子構造単位中に少なくとも１つの−ＣＦ₃基を有するフッ素含有ポリイミド樹脂から構成される膜に例えば低圧水銀ランプを用いて紫外線を照射し、これにより膜表面に活性薄層が形成された気体分離膜とすることにより、優れた分離性能を保持しつつ、酸性成分、有機成分に対して優れた耐性を有し、性能面、コスト面共に実用的に満足できる気体分離膜を提供できる。
【図面の簡単な説明】
【図１】本発明の実施例１の紫外線処理を施した緻密膜の断面を走査型電子顕微鏡を用いて観察した写真。
【図２】比較例１で得られた紫外線処理を施さない緻密膜の断面を走査型電子顕微鏡を用いて観察した写真。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluorine-containing polyimide gas separation membrane, and in particular, separates specific components such as hydrogen gas, carbon dioxide gas, oxygen gas, nitrogen gas, water vapor, organic gas, and organic vapor from industrial mixtures. -It is related with the gas separation membrane which consists of a fluorine-containing polyimide resin used in order to concentrate.
[0002]
[Prior art]
Since polyimide has a high glass transition temperature and a rigid molecular chain structure, it is known as a membrane separation material excellent in heat resistance and chemical resistance. For example, US Pat. No. 4,378,400 and US Pat. No. 4,959,159 disclose aromatic polyimides using biphenyltetracarboxylic dianhydride. JP-A-5-7749, US Pat. No. 3,822,202, US Pat. No. 3,899,309, US Pat. No. 4,320,041, US Pat. No. 4,645,824, US Pat. No. 4838900, U.S. Pat. No. 4,899,092, U.S. Pat. No. 4,932,982, U.S. Pat.No. 4,929,405, U.S. Pat. ing.
[0003]
[Problems to be solved by the invention]
However, many of these polyimide membranes are not satisfactory in terms of separation performance and cost. On the other hand, fluorine-containing polyimide membranes that are satisfactory in terms of separation performance at the homogeneous membrane level have been obtained, but when gas mixtures containing acidic components and organic components are separated, plasticization or swelling may occur due to changes in operating conditions. As a result, there is a problem in the strength of the membrane depending on the separation application, such as a decrease in practical mechanical strength. US Pat. No. 4,717,393 discloses that a polyimide membrane synthesized using benzophenone tetracarboxylic dianhydride improves the separation performance of the membrane and the resistance to organic components by crosslinking the polyimide by ultraviolet irradiation treatment. However, with regard to polyimide membranes synthesized without using benzophenonetetracarboxylic dianhydride, the membrane separation performance and resistance to organic and acidic components have been improved to a level that can be practically satisfied by ultraviolet irradiation treatment. The membrane is still unknown.
[0004]
The present invention was made to solve these problems and has excellent resistance to acidic components and organic components while maintaining excellent separation performance, and is practical in terms of performance and cost. An object of the present invention is to provide a gas separation membrane that is satisfactory.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the gas separation membrane in the present invention is a separation for separating / concentrating a specific component such as hydrogen gas, carbon dioxide gas, oxygen gas, nitrogen gas, water vapor, organic gas, organic vapor from the mixed gas. A gas separation membrane in which an active thin layer is formed on a membrane surface by irradiating ultraviolet rays onto a membrane comprising a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit Is provided.
[0006]
In the gas separation membrane, the thickness of the active thin layer formed by the ultraviolet irradiation treatment is preferably 5 to 1000 nm (50 to 10,000 angstrom). In the gas separation membrane, the fluorine-containing polyimide resin is essentially composed of a repeating molecular structural unit represented by the formula (I) .
[Chemical 2]

[0007]
In the gas separation membrane, the membrane composed of fluorine-containing polyimide resin is preferably at least one membrane selected from a dense membrane and an asymmetric membrane. Here, the dense membrane refers to a membrane in a region where no porous structure exists and gas permeability is governed by solubility in the membrane and diffusivity in the membrane. The asymmetric membrane is a membrane in which one surface of the membrane is a dense layer and the inner structure and the back surface are porous structures. These concepts are generally well known in the art. In the gas separation membrane, it is preferable that the ultraviolet irradiation is performed using a low-pressure mercury lamp.
[0008]
According to the configuration of the present invention described above, a film composed of a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit is irradiated with ultraviolet rays using, for example, a low-pressure mercury lamp. Using a gas separation membrane with an active thin layer formed on the membrane surface, a specific component such as hydrogen gas, carbon dioxide gas, oxygen gas, nitrogen gas, water vapor, organic gas, or organic vapor is highly separated from the mixed gas.・ It can be concentrated. Further, depending on the physical properties of the gas to be handled and the pressure / separation operation of the separation operation, it can be used as a separation membrane for the pervaporation method.
[0009]
In the above, the active thin layer represents a thin layer having sufficient separation and stability for a specific component, and is formed by crosslinking a part of a fluorine-containing polyimide resin by ultraviolet treatment. is there.
[0010]
In general, it is well known that many polymer films are plasticized or swelled by organic components such as acidic components and hydrocarbons. Once a glassy polymer film such as a polyimide resin is plasticized or swollen once, the packing structure between segments that can contribute to the selective separation of a specific component is destroyed, and generally the separation performance tends to be lowered. Therefore, in order to obtain a separation membrane that can stably maintain high separation performance for acidic components and organic components, the packing structure between the polymer segments constituting the separation membrane is a structure that is not easily affected by acidic components or organic components. Is effective. The present inventor has focused on this point and, as a result of intensive studies, as a result of applying ultraviolet rays to a film composed of a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit using, for example, a low-pressure mercury lamp. Irradiation and gas separation membranes with an active thin layer formed on the membrane surface have excellent gas separation performance and are extremely resistant to plasticization or swelling even in the presence of acidic and organic components. I found it.
[0011]
If -CF ₃ groups are present in the repeating molecular structural unit of the fluorine-containing polyimide resin, many -CF ₃ groups remain in the fluorine-containing polyimide even after UV irradiation with a low-pressure mercury lamp, resulting in excellent gas separation. A membrane having performance can be obtained. In addition, by using, for example, a low-pressure mercury lamp as an ultraviolet light source, it is possible to absorb the energy necessary for the fluorine-containing polyimide to locally crosslink, resulting in gas separation performance and acid component resistance on the membrane surface. In addition, a gas separation membrane having an active thin layer composed of a crosslinked layer having excellent organic component resistance can be obtained.
[0012]
In the above, a more preferable selectivity is exhibited when the thickness of the active thin layer is 5 to 1000 nm (50 to 10,000 angstrom). If the thickness of the active thin layer is less than 5 nm (50 angstroms), film defects such as pinholes are easily formed in the formed active thin layer, which is not preferable. On the other hand, when the thickness exceeds 1000 nm (10000 angstroms), the gas permeation resistance in the formed active thin layer becomes excessive, and the permeation flux is practically too small.
[0013]
In the above, the fluorine content of the fluorine-containing polyimide resin is 6 to 12 (the number of fluorine atoms in the repeating molecular structural unit), so that a gas separation membrane having substantially stable high quality can be obtained. Is preferable. On the other hand, if the number exceeds 12, the raw material cost tends to increase and the practicality tends to decrease.
[0014]
In the above, when the fluorine-containing polyimide resin is essentially composed of the repeating molecular structural unit represented by the formula (I) , the cost is practically low .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor irradiates a film containing, as a main component, a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit, for example, using a low-pressure mercury lamp, and thereby activates the film surface. The inventors have found that a gas separation membrane excellent in gas separation performance, acid resistance, and organic resistance can be obtained by forming a thin layer, and the present invention has been achieved.
[0016]
UV treatment in the present invention varies depending on the temperature and pressure, etc. of the irradiation atmosphere of ultraviolet rays, but the ultraviolet normal wavelength 150~270nm 6J / cm ² or more, preferably that irradiation with an energy intensity of 6~500J / cm ² Good.
[0017]
Fluorine-containing polyimide resin used in the present invention is substantially composed mainly of repeating molecular unit represented by the formula (I). The fluorine-containing polyimide resin used in the present invention uses, for example, a tetracarboxylic dianhydride and a diamine compound (however, at least one of the acid component or the amine component contains a —CF ₃ group), for example, the United States It can be obtained by a known polymerization method as described in Japanese Patent No. 3959350. For example, a tetracarboxylic dianhydride and a diamine compound (however, at least one component in the acid component or amine component contains —CF ₃ group) is used in an approximately equimolar amount, and in a polar solvent, about 80 ° C. or less. The polyamic acid is polymerized by stirring at a temperature of 0, preferably 0 to 60 ° C. The polar solvent used here is not particularly limited, but N-methylpyrrolidone, pyridine, dimethylacetamide, dimethylformamide, dimethylsulfoxide, tetramethylurea, phenol, cresol, tetrahydrofuran and the like are preferably used.
[0018]
To the obtained polar solvent solution of polyamic acid, a tertiary amine compound such as trimethylamine, triethylamine and pyridine, an imidation accelerator such as acetic anhydride, thionyl chloride, carbodiimide, and the like, stirred at a temperature of 5 to 150 ° C., Imidize. When performing the imidation reaction, the polyamic acid solution may be imidized by heating at 100 to 400 ° C, preferably 120 to 300 ° C, without adding an imidization accelerator.
[0019]
After the imidation reaction, a polyimide resin suitable as a film material can be obtained by dripping and purifying a large amount of acetone, alcohol, water or the like in order to remove a polar solvent or imidization accelerator during polymerization. In addition, when an imidation reaction is performed without adding an imidization accelerator, a solvent is removed from a polyamic acid powder or a polyamic acid solution obtained by dripping a polyamic acid solution into a large amount of acetone or an alcohol solution. Membrane material is obtained by heating to 100-400 ° C. to imidize a solid of polyamic acid obtained by evaporation (a precipitant etc. may be added during evaporation to form a polyamic acid powder, which may be filtered off). A suitable polyimide resin can be obtained.
[0020]
The method for forming a dense film used in the present invention is not particularly limited. For example, a film-forming solution is prepared by dissolving the above-described fluorine-containing polyimide resin in an appropriate solvent, and the film-forming solution is made of glass, metal, or plastic. A method in which an active thin layer is formed on the surface of the film by casting it to a flat plate or tube having a smooth surface, etc. at a certain thickness, then removing the solvent by heat treatment, and then treating with ultraviolet rays is suitably used. It is done.
[0021]
Although the manufacturing method of the asymmetric membrane used in the present invention is not particularly limited, a wet phase conversion film forming method is preferably used in terms of productivity and cost. For example, a film-forming solution is prepared by dissolving the above fluorine-containing polyimide resin in a predetermined organic solvent, and the film-forming solution is a porous support such as a flat plate or tube of glass, metal, plastic, or a woven or non-woven fabric. Cast on the body at a certain thickness and immerse in a coagulation liquid (the fluorine-containing polyimide resin in the film-forming liquid does not dissolve, but is compatible with the organic solvent in the film-forming liquid), or An asymmetric membrane is prepared by extruding a membrane-forming solution from a nozzle having a concentric double structure and immersed in the coagulation solution. After that, the membrane is dried and then subjected to ultraviolet treatment to form an active thin layer on the membrane surface. Can take the way.
[0022]
The solvent for the fluorine-containing polyimide resin is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, and 1,2-dimethoxymethane.
[0023]
These organic solvents can be used as a mixed solvent of two or more, in addition to being used alone. The organic solvent has a small polarity and is preferably a solvent having a low affinity with the solvent used as the coagulating liquid. Examples thereof include diethylene glycol dimethyl ether and 1,2-dimethoxyethane. When a solvent having a weak affinity with the solvent used as the coagulation liquid is used as the film-forming liquid, the solvent in the film-forming liquid advances into the solvent used as the coagulation liquid rather than the formation of a skin-like thin layer during wet phase conversion film formation. The speed to do is small enough. As a result, it is possible to obtain an asymmetric membrane having a skin-like thin layer and a porous structure layer that do not have pinholes that greatly reduce separation performance over a wide range.
[0024]
The coagulation liquid used when immersing and removing the organic solvent does not dissolve the fluorine-containing polyimide resin to be used, but is not particularly limited as long as it is a solvent compatible with the solvent in the film forming liquid, but water, ethanol, Alcohols such as methanol and isopropyl alcohol and a mixture thereof are used, and water is particularly preferably used. Although the temperature of the coagulation liquid at the time of immersing and removing the organic solvent in the film forming liquid is not particularly limited, it is preferably performed at a temperature of 0 to 50 ° C.
[0025]
The polyimide solution concentration of the film-forming solution is 3 to 40% by weight, preferably 10 to 30% by weight. Moreover, when adjusting a film forming liquid, you may add a swelling agent, a dispersing agent, a thickener, etc. as needed. As means for casting the film-forming solution, for example, a doctor knife, a doctor plate, an applicator, or the like can be used. In addition, the shape of the membrane in the present invention is not particularly limited, but a tube shape (including a hollow fiber shape) and a flat membrane shape are preferably used.
[0026]
【Example】
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
[0027]
[Example 1]
A fluorine-containing polyimide having the repeating unit represented by the formula (I) was synthesized by the following method. 5,5′-2,2′-trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) 0.1 mol and 2,2-bis (4-aminophenyl) hexa A polyamic acid was obtained by reacting 0.1 mol of fluoropropane (BAAF) in an N-methyl-2-pyrrolidone (NMP) solution for 4 hours. Thereafter, 0.3 mol of pyridine and 0.3 mol of acetic anhydride were added, and an imidization reaction was performed for 15 hours. After the reaction, NMP is further added to dilute to 8% by weight, the NMP solution is added dropwise to an excess amount of water and purified, and the fluorine-containing polyimide resin having the repeating unit represented by the formula (I) as a structural unit Got. The physical properties of the obtained fluorine-containing polyimide resin were a glass transition temperature of 301 ° C. and a weight average molecular weight of 159,000.
[0028]
16 parts by weight of fluorine-containing polyimide having the repeating unit represented by the formula (I) as a structural unit was diluted, 84 parts by weight of diethylene glycol dimethyl ether was added as an organic solvent (A), and the mixture was stirred and dissolved at 100 ° C. for 6 hours. Then, it filtered, left still and fully degas | foamed and adjusted the film forming liquid. The film-forming solution is cast on a glass plate using an applicator with a width of 20 cm and a thickness of 300 μm, and heat-treated at 110 ° C. for 1 hour, 150 ° C. for 1 hour, 200 ° C. for 3 hours, and further at 300 ° C. for 5 hours. Thus, a dense film made of fluorine-containing polyimide having a thickness of 32 μm was obtained. The dense film was irradiated with a low-pressure mercury lamp with an output of 650 W (manufactured by Oak Co., Ltd .; VUV-65B-22-21, wavelengths 185 nm, 254 nm) for 15 minutes to obtain a dense film subjected to ultraviolet treatment. When the cross section of the dense film subjected to the ultraviolet ray treatment was observed using a scanning electron microscope, it had an active thin layer with a thickness of 850 angstroms to 2200 angstroms on the film surface as shown in FIG. Therefore, this membrane satisfied the conditions of the separation membrane in the present invention. Next, for this membrane, at a temperature of 25 ° C. and a supply pressure of 2 atm, CO ₂ 50 vol. %, CH ₄ vol. The results of evaluating the separation performance of 50% mixed gas and the tensile fracture strength retention before and after immersion for 7 days in hexane are summarized in Table 1 below.
[0029]
[Comparative Example 1]
A dense film was obtained in the same manner as in Example 1 except that the ultraviolet treatment was omitted. When the cross section of this dense film was observed using a scanning electron microscope, it was clearly different from the surface form of the ultraviolet-treated film shown in FIG. 1 as shown in FIG. Next, the results of evaluating the separation performance of the mixed gas and the retention rate of the tensile breaking strength before and after immersing in hexane for 7 days in the same manner as in Example 1 are collectively shown in Table 1.
[0030]
[Comparative Example 2]
1,2,3,4-butanetetrafluoroethylenecarboxyl instead of 5,5′-2,2′-trifluoro-1- (trifluoromethyl) ethylidene-bis-1,3-isobenzofurandione (6FDA) Fluorine in the same manner as in Example 1 except that acid dianhydride was used and 4,4′-oxodianiline was used instead of 2,2-bis (4-aminophenyl) hexafluoropropane (BAAF). A non-containing polyimide resin (BTC-4,4′-ODA) was obtained. A dense film made of 30 μm-thick fluorine-free polyimide was obtained in the same manner as in Example 1 except that this fluorine-free polyimide and N-methyl-2-pyrrolidone were used as the organic solvent. Table 1 summarizes the results of evaluating the separation performance of the mixed gas and the tensile rupture strength retention before and after immersion in hexane for 7 days in the same manner as in Example 1 except that the ultraviolet irradiation treatment was not performed. Show.
[0031]
[Comparative Example 3]
The dense film made of fluorine-free polyimide obtained in the same manner as in Comparative Example 2 was subjected to ultraviolet irradiation treatment in the same manner as in Example 1, and the results of evaluating the separation performance of the mixed gas are summarized in Table 1 later. Show.
[0032]
[Table 1]

[0033]
As is clear from Table 1, it was confirmed that the example products of the present invention have high separation ability against acid gas and resistance to organic components. As described above, according to this example, a film made of a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit is irradiated with ultraviolet rays using a low-pressure mercury lamp, whereby the film By forming an active thin layer on the surface, it is possible to provide a gas separation membrane that is excellent in gas separation performance, acid resistance, and organic component resistance and that is practically satisfactory in terms of performance and cost.
[0034]
【The invention's effect】
As described above, according to the present invention, a film composed of a fluorine-containing polyimide resin having at least one —CF ₃ group in a repeating molecular structural unit is irradiated with ultraviolet rays using, for example, a low-pressure mercury lamp. By using a gas separation membrane with an active thin layer formed on the membrane surface, it has excellent resistance to acidic and organic components while maintaining excellent separation performance, and is practical in terms of both performance and cost. Gas separation membrane satisfying the above can be provided .
[Brief description of the drawings]
FIG. 1 is a photograph of a cross-section of a dense film that has been subjected to ultraviolet treatment in Example 1 of the present invention, observed using a scanning electron microscope.
2 is a photograph of a cross section of a dense film obtained in Comparative Example 1 that is not subjected to ultraviolet treatment, observed using a scanning electron microscope. FIG.

Claims (3)

The film composed of a fluorine-containing polyimide resin having at least one —CF ₃ group in the repeating molecular structural unit is irradiated with ultraviolet rays, whereby an active thin layer is formed on the film surface, and the thickness of the active thin layer is The gas separation membrane which is 5-1000 nm (50-10000 Angstrom), and the said fluorine-containing polyimide resin has as a main component the repeating unit substantially represented by following formula (I).

  The gas separation membrane according to claim 1, wherein the membrane composed of the fluorine-containing polyimide resin is at least one membrane selected from a dense membrane and an asymmetric membrane.   The gas separation membrane according to claim 1 or 2, wherein the ultraviolet irradiation is performed by a low-pressure mercury lamp.

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