JP4671493B2 - Gas separation membrane and method of using the same - Google Patents
Gas separation membrane and method of using the same Download PDFInfo
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- JP4671493B2 JP4671493B2 JP2000370031A JP2000370031A JP4671493B2 JP 4671493 B2 JP4671493 B2 JP 4671493B2 JP 2000370031 A JP2000370031 A JP 2000370031A JP 2000370031 A JP2000370031 A JP 2000370031A JP 4671493 B2 JP4671493 B2 JP 4671493B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Description
【０００１】
【発明の属する技術分野】
本発明は、スキン層と多孔質層とから構成される非対称構造を有するガス分離膜であって、膜透過成分（ガス）が多孔質層を透過するときの抵抗を小さくすることによって膜透過成分の膜透過速度を大きくしていること、且つ、中空糸ガス分離膜として実用レベル以上の機械的強度を持っていること、且つ、優れた耐水性及び耐熱水性を有していることを特徴とするガス分離膜に関する。また、前記のガス分離膜を用いたことを特徴とする除湿方法及び加湿方法に関する。
【０００２】
【従来の技術】
種々のガス分離方法においてガス分離膜が使用されている。これらの多くは、ガス選択透過性が高いガラス状ポリマーで形成されたガス分離膜である。概して、ガラス状ポリマーはガス選択透過性（分離度）は高いけれども、ガス透過係数が小さいという短所がある。このため、多くのガラス状ポリマーで形成されたガス分離膜は、多孔質層（支持層）と薄いスキン層（分離層）とから構成される非対称構造、すなわち、ガスの透過抵抗を生じる分離層を薄くしてガス透過速度が小さくなりすぎないようにして用いられている。
【０００３】
ガス分離膜は、通常、中空糸膜の多数本（例えば、百本から数十万本）を集束して中空糸束とし、その中空糸束の少なくとも一方の端部をエポキシ樹脂のような硬化性樹脂やホットメルト型熱可塑性樹脂などで前記端部において中空糸膜が開口状態となるように固着して中空糸分離膜エレメントを構成し、更に、単数又は複数の前記中空糸分離膜エレメントを少なくとも混合ガスの導入口、透過ガスの排出口、非透過ガスの排出口を有する容器内に、中空糸膜の内側へ通じる空間と中空糸膜の外側へ通じる空間が隔絶するように装着されて構成される中空糸ガス分離膜モジュールとして用いられる。中空糸ガス分離膜モジュールにおいては、混合ガスは中空糸膜の内側あるいは外側に接する空間へ供給され、中空糸膜に接して流る間に混合ガス中の特定成分（膜透過成分）が選択的に膜を透過して透過ガスの排出口から回収され、特定成分（膜透過成分）が除かれたガスが非透過ガスの排出口から回収されることによって、ガス分離がおこなわれる。
【０００４】
ポリマーの混合物からなるガス分離膜については、米国特許第５０５５１１６号公報は、特定構造を持つ２種以上のポリイミドの混合物からなるガス分離膜を開示し、ポリイミドのブレンド比によって酸素や窒素の透過速度を直線的にコントロールできることを示している。また、米国特許第５２４８３１９号公報はフェニルインダン残基を含有するポリイミドと特定のポリイミド、ポリアミド、ポリアミドイミドとの混合物からなるガス分離膜を開示している。また、米国特許第５６０８０１４号公報は特定のポリエーテルスルホンと特定の芳香族ポリイミドと特定の芳香族ポリイミド又はポリアミド又はポリアミドイミドとの混合物からなるガス分離膜を、米国特許第５９１７１３７号公報は特定のポリエーテルスルホンと特定の芳香族ポリイミドとの混合物からなるガス分離膜を開示している。しかしながら、これらの公報では、水蒸気透過速度や多孔質層のガス透過抵抗については言及していない。また、極めて高い水蒸気透過速度を持ち、且つ、非対称中空糸膜として工業的にモジュール化して実際に用いることができるレベルの機械的強度を併せ持ったガス分離膜については開示も示唆もなかった。
【０００５】
水蒸気が膜透過成分である除湿膜や加湿膜では、耐水性及び耐熱水性が重要である。しかしながら、水蒸気を含むガスの透過速度を改良した膜においては、しばしば耐水性及び耐熱水性が劣るものがあった。特開平２−２２２７１７号公報では、耐水性及び耐熱水性が優れたポリイミド分離膜を開示しているが、有機蒸気の脱水に用いられるものであって、水蒸気の透過速度は小さいものであった。
【０００６】
【発明が解決しようとする課題】
非対称構造の膜では、膜透過成分（ガス）が膜を透過する透過速度の律速過程は、膜透過成分が膜のスキン層を透過する過程である。膜透過成分が膜の多孔質層を透過する過程は透過抵抗が比較的小さい。このため、多くの場合、膜透過成分が膜の多孔質層を透過する過程の膜透過成分が膜を透過する透過速度に対する影響は、実際上は無視できる。
【０００７】
ところが、スキン層を極めて薄くして膜透過成分が膜を透過する透過速度を極めて大きくする場合や、膜透過成分が膜を極めて透過し易いガスである場合には、膜透過成分が膜を透過する透過速度は、膜透過成分がスキン層を透過する過程のみならず多孔質層を透過する過程によっても無視できない影響を受ける場合がある。この場合には、非対称構造の膜であっても膜透過成分が膜を透過する透過速度を改良する余地があり、これを改良したより高効率でよりコンパクトな高性能ガス分離膜の開発が求められていた。特に、膜を透過する成分が水蒸気の場合は、水蒸気が膜を透過する透過速度が他の無機ガスに比べて極めて大きい（数百倍から数千倍に達することもある）ので、膜を透過する水蒸気の透過速度は多孔質層の透過抵抗によって影響を受ける。このため、水蒸気が多孔質層を透過するときの透過抵抗を小さくすれば水蒸気が膜を透過する透過速度を大きくすることができると考えられ、そのような改良をおこなって水蒸気が膜を透過する透過速度を大きくした高効率でコンパクトな高性能の除湿膜及び／又は加湿膜の開発が求められていた。
【０００８】
しかしながら、非対称構造を有する膜において、単に多孔質層を薄くしたり多孔質層の多孔性を高めることによって、膜透過成分が膜を透過するときの透過抵抗をより小さくして膜透過成分が膜を透過する透過速度を大きくしようとすると、透過速度は大きくできるが多孔質層が担うべき膜の支持機能即ち機械的強度が低下する。このために、向上された膜透過成分が膜を透過する透過速度と、非対称中空糸膜として工業的にモジュール化して実際に用いることができるレベルの機械的強度、言い換えれば、実用レベルの機械的強度との両方を併せ持った実用的な高性能ガス分離膜を得ることは困難であった。
【０００９】
更に、ガス分離膜を除湿や加湿のために用いる時に、膜の耐水性及び耐熱水性が劣ると長期間安定して使用ができなかったり用途が限定されるという問題が生じた。このため、耐水性及び耐熱水性が優れた除湿膜及び／又は加湿膜の開発が求められていた。
【００１０】
【課題を解決するための手段】
本発明は、このような状況に鑑みてなされたものであり、本発明者らは、少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物で非対称膜を形成することによって、多孔質層の膜透過成分が膜を透過するときの透過抵抗を小さく（透過速度を大きく）しながら、膜の機械的強度を実用レベル以上に保持し得ること、更に、優れた耐水性及び耐熱水性を有するガス分離膜を製造することができることを見出して本発明に到達した。
【００１１】
すなわち、本発明は、スキン層（分離層）と多孔質層（支持層）とから構成される非対称構造を有し、水蒸気透過速度（Ｐ’H2O）が２．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、水蒸気と窒素の透過速度比（Ｐ’H20／Ｐ’N2）が５０以上である膜において、前記膜の多孔質層（支持層）のヘリウムガスの透過速度（Ｐ’He）が２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ2以上、破断伸度が１０％以上であり、１００℃の熱水中で５０時間熱水処理した後の中空糸膜の破断伸度が熱水処理前の８０％以上保持することを特徴とするガス分離膜に関する。
また、スキン層（分離層）と多孔質層（支持層）とから構成される非対称構造を有し、水蒸気透過速度（Ｐ’H2O）が２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、水蒸気と窒素の透過速度比（Ｐ’H2O／Ｐ’N2）が５０以上である膜において、前記膜の多孔質層（支持層）のヘリウムガスの透過速度（Ｐ’He）が３．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ2以上、破断伸度が１０％以上であり、１００℃の熱水中で５０時間熱水処理した後の中空糸膜の破断伸度が熱水処理前の８０％以上保持することを特徴とするガス分離膜に関する。
更に、少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物で形成されたことを特徴とする前記ガス分離膜に関する。
更に、中空糸膜での引張強度が３．０ｋｇｆ／ｍｍ2以上、破断伸度が１５％以上であることを特徴とする前記ガス分離膜に関する。
更に、１００℃の熱水中で５０時間熱水処理した後、中空糸膜の破断伸度が熱水処理前の９０％以上を保持することを特徴とする前記ガス分離膜に関する。
更に、前記ガス分離膜を用いることを特徴とする除湿方法、前記ガス分離膜を用いることを特徴とする加湿方法、又、前記ガス分離膜を用いて、燃料電池の供給ガスを除湿及び／又は加湿することを特徴とする除湿及び／又は加湿方法に関する。
【００１２】
本発明において、膜の水蒸気透過速度（Ｐ’H2O）、水蒸気と窒素の透過速度比（Ｐ’H2O／Ｐ’N2）、膜の多孔質層（支持層）のヘリウム透過速度（Ｐ’He）は５０℃におけるものである。
また、本発明において、前記膜の多孔質層（支持層）のヘリウム透過速度（Ｐ’He）は膜の多孔質層（支持層）のガス透過抵抗を示すもの（但し、値が大きい方が抵抗が小さい）として用いており、次のような測定方法で測定した値として規定されるものである。即ち、非対称中空糸膜を酸素プラズマ処理によって表面のスキン層を削り、ヘリウムガスと窒素ガスとの透過速度比が実質的に均質膜の透過速度比とは認められない領域に到達したときのヘリウムガスの透過速度（Ｐ’He）である。具体的には、プラズマ処理前のヘリウムと窒素の透過速度比（Ｐ’He／Ｐ’N2）が２０以上の膜をプラズマ処理して、前記透過速度比（Ｐ’He／Ｐ’N2）が１．２以下になったときのヘリウムガスの透過速度である。このヘリウムガスの透過速度（Ｐ’He）の値が大きいと、その膜の多孔質層のガス透過抵抗が小さいことを意味し、ヘリウムガスの透過速度（Ｐ’He）の値が小さいと、その膜の多孔質層のガス透過抵抗が大きいことを意味する。
【００１３】
また、本発明における機械的強度は、膜を中空糸としたときの引張試験における引張強度と破断伸度で表わしている。これらは温度２３℃にて引張試験機を用いて試料の有効長２０ｍｍ、引張速度１０ｍｍ／分で測定した値である。引張り強度は中空糸膜の引張破断時の応力を中空糸の膜断面積で除した値［単位：ｋｇｆ／ｍｍ2］であり、破断伸度は中空糸の元の長さをＬ0、引張破断時の長さをＬとしたときの（Ｌ−Ｌ0）／Ｌ0×１００［単位：％］である。
【００１４】
また、本発明では、中空糸膜の耐水性及び耐熱水性を示す指標として、温度１００℃の熱水中で５０時間熱水処理をおこなった後の引張試験における破断伸度の保持率［単位：％］を用いた。
【００１５】
【発明の実施の形態】
本発明の非対称ガス分離膜は、多孔質層のガス透過抵抗を小さく（ガス透過速度を大きく）して膜透過成分（特に、水蒸気）の膜の透過速度を改良し、且つ、非対称中空糸膜として工業的にモジュール化して実際に用いることができるレベルの機械的強度、言い換えれば、実用レベルの機械的強度を持ち、且つ、優れた耐水性及び耐熱水性を持っている。
【００１６】
すなわち、本発明は、多孔質層のガス透過速度がヘリウムガスの透過速度（Ｐ’He）で２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上となるようにし、且つ、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ２以上、破断伸度が１０％以上とすることによって、水蒸気透過速度（Ｐ’H2O）が２．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上の高い透過速度を持ち、且つ、中空糸膜として優れた耐圧性と工業的にガス分離膜モジュールへの加工が可能な実用レベルの機械的強度を持ち、且つ、優れた耐水性及び耐熱水性を持った非対称ガス分離膜である。
【００１７】
また、本発明は、多孔質層のガス透過速度がヘリウムガスの透過速度（Ｐ’He）で３．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上となるようにし、且つ、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ２以上、破断伸度が１０％以上とすることによって、水蒸気透過速度（Ｐ’H2O）が２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上の高い透過速度を持ち、且つ、中空糸膜として優れた耐圧性と工業的にガス分離膜モジュールへの加工が可能な実用レベルの機械的強度を持ち、且つ、優れた耐水性及び耐熱水性を持った非対称ガス分離膜である。
【００１８】
膜の多孔質層のガス透過速度が、ヘリウムガスの透過速度（Ｐ’He）で２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上、好ましくは３．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上、より好ましくは３．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であれば、多孔質層のガス透過抵抗は小さくなって膜のガス透過性能への影響は少なくなるか又は実質的に無視できるようになり、膜の水蒸気透過速度（Ｐ’H2O）が２．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上、更に、２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上のガス分離膜を得ることが可能になる。逆に、膜の多孔質層のガス透過速度がヘリウムガスの透過速度（Ｐ’He）で３．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以下、特に、２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以下であると、多孔質層のガス透過抵抗が大きいので、膜のガス透過速度を大きくすることが難しくなり、改良された水蒸気透過速度を持つ高性能ガス分離膜を得ることは難しい。
【００１９】
また、本発明は、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ2以上、好ましくは３．０ｋｇｆ／ｍｍ2以上であり、且つ、破断伸度が１０％以上、好ましくは１５％以上の非対称構造を有するガス分離膜である。このような機械的強度を持った中空糸膜は、容易に破損や破断することなく取扱うことができるので、工業的にモジュール化（ガス分離膜モジュールへの組立て及び加工）をすることができる。更に、このような機械的強度を持った中空糸膜を用いたガス分離膜モジュールは、優れた耐圧性や耐久性を持つので特に有用である。一方、引張強度が２．５ｋｇｆ／ｍｍ2以下、又は、破断伸度が１０％以下であると、ガス分離膜モジュールへの組立て及び加工時に中空糸膜が破損や破断を起こし易いので工業的に分離膜モジュールへ組立て及び加工することが困難になり、更に、分離膜モジュールとしても、耐圧性が低くなり用途や使用条件が限定される。また、分離膜モジュール内の中空糸膜は供給され中空糸の内側や外側を流れて排出されるガスの流量、流速、圧力、温度、及び、それらの変動によって、連続的又は断続的に変形応力を受けるので、引張強度が２．５ｋｇｆ／ｍｍ2以下、又は、破断伸度が１０％以下であると、容易に破損や破断が発生するので問題が生じ易い。
【００２０】
また、本発明は、水蒸気と窒素との透過速度比（Ｐ’H2O／Ｐ’N2）が５０以上のガス分離膜である。水蒸気と窒素との透過速度比（Ｐ’H2O／Ｐ’N2）が５０以上であると、ガス選択性が実用以上であることを意味し、特に、水蒸気を選択的に透過して、−１５℃以下の露点を持つ乾燥空気を容易に得ることができるので除湿膜として有用であるし、又、優れた加湿膜としても有用である。
【００２１】
更に、本発明のガス分離膜は、改良されたガス透過速度と実用レベル以上の機械的強度を有することに加えて、優れた耐水性及び耐熱水性を有する。本発明のガス分離膜は、温度１００℃の熱水中で５０時間熱水処理した後でも、中空糸膜の破断伸度が熱水処理前の８０％以上、特に好ましくは９０％以上を保持することができる耐水性及び耐熱水性を有する。このため、本発明のガス分離膜は、加湿膜及び／又は除湿膜として広範囲な用途に使用することができ、且つ、長期間使用しても高性能を維持することができる。
【００２２】
本発明のガス分離膜は、少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物で膜を形成することで得ることが可能であり、好ましくは、２種類以上のポリイミドの混合物で膜を形成することで得ることが可能である。１種類のポリイミドで多孔質層の多孔性を高めるとガス透過速度は改良できるが、機械的強度は低下するので、本発明のガス分離膜を得ることはできない。尚、前記の１種類のポリイミドとは、一定のモノマー組成が繰返し単位として重合しているポリイミドであり、いわゆるホモポリイミドも、共重合ポリイミドも、１種類のポリマーである。また、本発明において、少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物を形成することができるポリイミド以外のポリマーは、特に限定しないが、芳香族ポリアミド、芳香族ポリアミドイミド、芳香族ポリエーテルイミド、芳香族ポリスルホン、芳香族ポリカーボネートなどを挙げることができる。
【００２３】
本発明で用いる少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物は、少なくとも１種類の高いガス選択透過性（分離度が高く透過速度が大きい）を持つポリイミドと、少なくとも１種類の優れた機械的強度を持つポリイミドあるいはポリイミド以外のポリマーを含むポリマー混合物である。これらのポリマー混合物は同一の溶媒に溶解し得るものである。また、これらのポリマー混合物を溶媒に溶解した溶液は外観上濁りが生じないものが好ましい。外観上明らかに不均一なポリマー混合物溶液を用いると本発明のガス分離膜を得ることはできない。本発明のガス分離膜は、前記のポリマー混合物が溶解したポリマー溶液を用いて、Ｌｏｅｂらが提案（例えば、米国特許３，１３３，１３２号）した方法、即ち、ポリマー混合物溶液をノズルから押し出して目的形状物とし空気又は窒素雰囲気空間を通過させた後で凝固浴に浸漬する、いわゆる乾湿式法により製造することができる。前記乾湿式法では凝固過程において、目的形状をしたポリマー溶液の溶媒と凝固液中のポリマーに対する貧溶媒との置換によってポリマー相と溶媒相の相分離が進行し、ポリマーが多孔質構造を形成するが、本発明のポリマー混合物溶液の凝固過程の場合には、前記のポリマー相と溶媒相の相分離の進行に加えて、少なくとも１種類のポリイミドを含む２種類以上のポりマー間で少なくとも分子鎖レベルの不均一化又は相分離が進行して、より多孔性を高めながら機械的強度の低下は抑制される多孔質構造を形成するものと推定される。ポリマー混合物でなくポリマー混合物と同一のモノマー組成からなる１種類の共重合ポリマーを用いて膜を形成しても、改良されたガス透過速度と実用レベルの機械的強度を併せ持つ高性能ガス分離膜を得ることはできない。
【００２４】
本発明のガス分離膜の製造方法は、より詳しくは次のとおりである。即ち、１種類のポリイミドを含む２種類以上のポリマーを同一溶媒に溶解したポリマー混合物溶液を調製し、これをノズルから中空糸状などの目的とする形状に吐出させ、吐出直後に空気又は窒素雰囲気中を通したあと、ポリマー混合物を実質的には溶解せず且つポリマー混合物溶液の溶媒とは相溶性を有する凝固液に浸漬して非対称構造を形成し、その後乾燥、加熱処理を経て分離膜を製造する。ポリマー混合物溶液は、１種類のポリイミドを含む２種類以上のポリマーの溶液を別々に調製後それらを混合してもよいし、１種類のポリイミドを含む２種類以上のポリマーを順次同一溶媒に溶解してもよい。ポリマー混合物溶液の濃度は１０〜２５重量％が製膜上好ましい。また、ノズルから吐出させるポリマー混合物溶液の溶液粘度（回転粘度）は、吐出温度で５０〜１５０００ポイズ、特に１００〜１００００ポイズが中空糸状などの吐出後の形状を安定に得ることができるので好ましい。凝固液への浸漬は、一次凝固液に浸漬して中空糸状などの膜の形状が保持できる程度に凝固した後、案内ロールに巻き取られ、次いで二次凝固液に浸漬して膜全体を十分に凝固させることが好ましい。凝固した膜の乾燥は炭化水素などの溶媒を用いて凝固液と置換した後乾燥する方法が効率的である。加熱処理は用いられている１種類のポリイミドを含む２種類以上のポリマーの軟化点又は二次転移点よりも低い温度で実施されることが好ましい。
【００２５】
本発明のガス分離膜のスキン層の厚さは１０〜２００ｎｍであり、好ましくは２０〜１００ｎｍである。また、本発明のガス分離膜の多孔質層の厚さは２０〜２００μｍであり、好ましくは３０〜１００μｍである。スキン層の厚さが１０ｎｍ以下は製造することが困難であり、２００ｎｍ以上にするとガス透過速度が小さくなって本発明のガス分離膜を得ることができなくなる。また、多孔質層が２０μｍ以下では機械的強度が小さくなって支持機能が果たせなくなり、２００μｍ以上になると多孔質層のガス透過抵抗が大きくなり改良されたガス透過速度をもったガス分離膜を得ることができなくなる。
【００２６】
本発明のガス分離膜は、中空糸膜として好適に用いられるが、中空糸膜の内径は３０〜５００μｍのものが好適である。また、本発明の中空糸膜は通常のガス分離膜モジュールに組み込んで好適に用いることができる。例えば、中空糸膜は適当な長さで１００〜２０００００本程度が束ねられる。束ね方は、平行配列、交叉配列、織物状でもよく、束の略中心部に芯管があってもよく、束の外周部をプラスチック製のフィルムで取巻かれたものでも構わない。この中空糸束は少なくとも一方の端部において中空糸膜が開口状態を保持した状態で管板によって固着され、少なくとも混合ガスの導入口、透過ガスの排出口、非透過ガスの排出口とを備える容器内に収納され、管板は容器内の空間を隔絶するように容器に密閉して取り付けられる。供給される混合ガスは、中空糸膜の内側又は外側に接する空間へ供給され、中空糸膜に接して流れる間に混合ガス中の特定成分が選択的に膜を透過して透過ガス排出口から回収され、透過されなかった非透過ガスは非透過ガス排出口から排出することによって回収され、ガス分離がおこなわれる。また、透過ガス側の空間に例えば供給された混合ガスと向流になる方向にキャリアガスを流して透過ガスの回収を促進してもよく、その際、キャリアガスとして非透過ガスを用いてもよい。
【００２７】
本発明のガス分離膜は水蒸気透過速度が極めて大きいので、本発明のガス分離膜を用いることによって除湿及び／又は加湿を極めて効率よく好適におこなうことができる。除湿をおこなう場合、本発明のガス分離膜からなるガス分離膜モジュールに、水蒸気を含有する混合ガスを中空糸膜の内側あるいは外側に接する空間へ供給することによって、水蒸気を選択的に膜の透過側へ透過して非透過ガスとして除湿されたガスを極めて効率よく得ることができる。特に、水蒸気を含有する混合ガスは中空糸膜の内側へ供給し、中空糸膜の外側の空間へ乾燥したキャリアーガスを混合ガスと向流になるように導入することがより高効率で除湿ができるので好ましく、更に、キャリアーガスとしてガス分離膜の非透過側で得られる除湿されたガスの一部をリサイクルして用いることが簡便なキャリアガスの導入方法として好ましい。加湿する場合には、水蒸気をより多量に含有する（水蒸気分圧が高い）混合ガスを中空糸膜の内側あるいは外側に接する空間へ供給し、中空糸膜の反対側の空間へ水蒸気をより少量含有する（水蒸気分圧が低い）ガスを供給することによって、水蒸気が膜を選択的に透過して、水蒸気をより少量含有するガスを容易に加湿することができる。特に、水蒸気をより多量に含有する混合ガスと水蒸気をより少量含有するガスは中空糸膜を挟んで向流となるように供給することが高効率になるので望ましい。
【００２８】
更に、本発明のガス分離膜を用いることによって、燃料電池用の供給ガスの除湿及び／又は加湿を極めて効率よく好適におこなうことができる。固体高分子型燃料電池は、一般に水素イオン伝導性の固体高分子電解質膜の両側を白金触媒を担持したカーボン電極で挟み込んで積層した発電素子と、それらの各電極に水素等の燃料ガスあるいは酸素等の酸化性ガスを供給したり電極からの排出ガスを排出するための配流機能を備えたセパレータや更にその外側に配置した集電体などを積層して構成されている。この電池では、固体高分子電解質膜が乾燥すると、イオン伝導度が低下するとともに、固体高分子電解質膜と電極との接触不良をおこして出力の急激な低下をきたすため、固体高分子電解質膜が一定の湿度を保つように制御することが重要である。このため、供給ガス（燃料ガス及び／又は酸化性ガス）の加湿（水分が多すぎる場合は加湿の代わりに除湿）をおこなうことが必要である。前記供給ガスの加湿方法として分離膜を用いることは既に提案されている。特開平３−２６９９５８号公報にはテトラフルオロエチレン樹脂からなる多孔質膜を用いることが開示されている。中空糸状多孔質膜を用いることによって単位面積当たりの透過膜面積を大きくし、加湿性能を高めることが特開平８−２７３６８７号公報や特開平８−３１５８３８号公報に開示されている。しかしながら、これらの加湿膜では加湿性能が十分でないとうい問題を有していたし、長時間水と膜が接触していると膜の燃料電池の供給ガス側に水がしみ出て液滴が生成するという不都合があった。更に、自動車用などの燃料電池では、燃料電池の排出ガス中の水分を分離膜によって選択的に透過させて燃料電池の供給ガスへリサイクルして使用する方法が検討されているが、前記の多孔質膜では燃料電池の排出ガス中の水分以外の成分を燃料電池の供給ガスへ混入させるなどの問題もあった。
【００２９】
本発明のガス分離膜は、水蒸気透過速度が極めて高いので加湿及び／又は除湿を効率よくおこなうことができる。また、本発明のガス分離膜は少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物で形成された膜であり、好ましくは、２種類以上のポリイミドの混合物で形成された膜であるので燃料電池用に用いる時に要求される耐熱性、耐薬品性などが優れている。更に、固体高分子型燃料電池が運転される１００℃前後の耐熱水性も極めて良好である。しかも、本発明のガス分離膜は、スキン層（分離層）と多孔質層（支持層）とから構成される非対称構造を有しているので、燃料電池で長時間使用したとき燃料電池の供給ガス側の膜面に水がしみ出て液滴が生成するという不都合や、燃料電池の排出ガス中の水分以外の成分を燃料電池の供給ガスへ混入させるといった問題は生じ難い。本発明のガス分離膜を用いれば、燃料電池の供給ガスを除湿及び／又は加湿を極めて好適におこなうことができる。
【００３０】
【実施例】
次に、本発明における中空糸ガス分離膜の製造とその特性について具体的に説明する。尚、本発明は実施例に限定されるものではない。
【００３１】
（ポリイミド（ａ）溶液の調製）
３，３’，４，４’−ビフェニルテトラカルボン酸二無水物（以下、ｓ−ＢＰＤＡと略記することもある）２９．４２２ｇと、２，２’−ビス（３，４−ジカルボキシフェニル）ヘキサフルオロプロパン二無水物（以下、６ＦＤＡと略記することもある）４４．４２４ｇと、４，４’−ジアミノジフェニルエーテル（以下、ＤＡＤＥと略記することもある）１６．１７９ｇと、１，４−ビス（４−アミノフェノキシ）ベンゼン（以下、ＴＰＥＱと略記することもある）３５．４３２ｇとを、溶媒のパラクロロフェノール（以下、ＰＣＰと略記することもある）７２６．４４ｇと共にセパラブルフラスコ中にて重合温度１８０℃で１７時間重合し、回転粘度が１７４８ポイズ、ポリマー濃度が１４重量％のポリイミド（ａ）溶液を得た。
【００３２】
（ポリイミド（ｂ）溶液の調製）
ｓ−ＢＰＤＡ８８．２６６ｇと、ＤＡＤＥ６０．９７３ｇとを、溶媒のＰＣＰ８５０．４１ｇと共にセパラブルフラスコ中にて重合温度１８０℃で１０時間重合し、回転粘度１７３０ポイズ、ポリマー濃度１４重量％のポリイミド（ｂ）溶液を得た。
【００３３】
（ポリイミド（ｃ）溶液の調製）
ｓ−ＢＰＤＡ４４．１３３ｇと、６ＦＤＡ６６．６３６ｇと、ＤＡＤＥ６０．４３２ｇとを、溶媒のＰＣＰ９８５．３２ｇと共にセパラブルフラスコ中にて重合温度１８０℃で１２時間重合し、回転粘度１６７４ポイズ、ポリマー濃度１４重量％のポリイミド（ｃ）溶液を得た。
【００３４】
（非対称中空糸膜の製造方法）
ポリイミド溶液、又は、ポリイミド混合物溶液を、４００メッシュの金網で濾過したあと、中空糸紡糸ノズル（円形開口部外径１０００μｍ、円形開口部スリット幅２００μｍ、芯部開口部外径４００μｍ）から吐出させ、吐出した中空糸状体を窒素雰囲気中に通した後、温度０℃の所定濃度（７０〜８０重量％）のエタノール水溶液からなる凝固液に浸漬し湿潤糸とした。これを温度５０℃のエタノール中に２時間浸漬し脱溶媒処理を完了し、更に、温度７０℃のイソオクタン中に３時間浸漬洗浄して溶媒を置換後、温度１００℃で絶乾状態まで乾燥し、その後所定温度（２００〜３００℃）で１時間の熱処理をおこなった。得られた中空糸膜はいずれも、外径寸法約４７０μｍ、内径寸法約３２０μｍ、膜厚約７５μｍのものであった。
【００３５】
（中空糸膜の水蒸気透過性能の測定方法）
約１０本の中空糸膜と、ステンレスパイプと、エポキシ樹脂系接着剤とを使用して有効長が２０ｍｍの透過性能評価用のエレメントを作成し、これをステンレス容器に装着してペンシルモジュールとした。このペンシルモジュールの中空糸の外側へ水蒸気量１５００ｐｐｍの窒素ガスを一定量供給し、透過側へは一定量のキャリアガス（Ａｒガス）を流しながら水蒸気分離をおこない、非透過ガス及び透過ガスの水蒸気量を鏡面式の露点計で検出した。測定した水蒸気量（水蒸気分圧）と供給ガス量及び有効膜面積から膜の水蒸気透過速度を算出した。尚、これらの測定は５０℃でおこなった。
【００３６】
（中空糸膜の窒素ガス透過性能の測定方法）
約１５本の中空糸膜と、ステンレスパイプと、エポキシ樹脂系接着剤とを使用して有効長が１０ｃｍの透過性能評価用のエレメントを作成し、これをステンレス容器に装着してペンシルモジュールとした。それに一定圧力の窒素純ガスを供給して透過流量を測定した。測定した透過窒素ガス量と供給圧力及び有効膜面積から窒素ガスの透過速度を算出した。尚、これらの測定は５０℃でおこなった。
【００３７】
（中空糸膜の多孔質層のヘリウムガス透過性能の測定方法）
プラズマ処理装置に多数本の中空糸膜を均一にひろげて設置し、印加電圧２０Ｖで酸素プラズマ処理をおこなった。酸素プラズマ処理を５分間おこなう毎に中空糸の一部（数本）を取り出して、プラスマ処理時間の異なった中空糸膜を得た。これらの中空糸膜を用いて前記と同様の方法でガス透過測定用ペンシルモジュール（有効長１０ｍｍ）を作成し、これに窒素純ガスあるいはヘリウム純ガスを一定量圧力で供給してそれぞれの透過流量を測定し、測定した透過流量と供給圧力及び有効膜面積から窒素あるいはヘリウムの透過速度を算出した。２０分間以上プラズマ処理した中空糸膜のこれらの値の比即ちＰ’He／Ｐ’N2は１．２以下になったので、２０分間処理した中空糸膜のヘリウムの透過速度（Ｐ’He）を、本発明で用いる膜の多孔質層のヘリウムの透過速度とした。尚、これらの測定は５０℃でおこなった。
【００３８】
（中空糸膜の引張強度と破断伸度の測定）
引張試験機を用いて有効長２０ｍｍ、引張速度１０ｍｍ／分で測定した。破断面積は破断面を光学顕微鏡を用いて寸法を測定して算出した。
【００３９】
（回転粘度の測定方法）
ポリイミド溶液の回転粘度は、回転粘度計（ローターのずり速度１．７５／ｓｅｃ）を用い温度１００℃で測定した。
【００４０】
（中空糸膜の耐水性及び耐熱水性の測定）
破断伸度が既知の中空糸膜を試料として、ステンレス容器内にイオン交換水と前記中空糸膜を入れて密封し、前記容器を１００℃のオーブン中に入れ５０時間保持して中空糸膜を熱水処理した。熱水処理後の中空糸膜は容器から取り出され１００℃のオーブン中で乾燥した。乾燥後の中空糸膜は前記の引張試験方法に従って破断伸度を測定した。耐水性及び耐熱水性は、破断伸度の保持率［％］を指標として表わした。
【００４１】
〔実施例１〕
前記ポリイミド（ａ）溶液２８０ｇと、前記ポリイミド（ｂ）溶液１２０ｇとを、セパラブルフラスコにて温度１３０℃で３時間攪拌してポリイミド混合物溶液を得た。この混合物溶液のポリマー濃度は１４重量％であり、回転粘度は１７８６ポイズであった。このポリイミド混合物溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的特性を前記の方法によって測定した。結果は表−１のとおりであった。
【００４２】
〔実施例２〕
前記ポリイミド（ａ）溶液３６０ｇと、前記ポリイミド（ｂ）溶液４０ｇとを、セパラブルフラスコにて温度１３０℃で３時間攪拌してポリイミド混合物溶液を得た。この混合物溶液のポリマー濃度は１４重量％であり、回転粘度は１８０４ポイズであった。このポリイミド混合物溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的特性を前記の方法によって測定した。結果は表−１のとおりであった。
【００４３】
〔比較例１〕
前記ポリイミド（ａ）溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的強度を前記の方法によって測定した。結果は表−１のとおりであった。
【００４４】
〔比較例２〕
前記ポリイミド（ｂ）溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的強度を前記の方法によって測定した。結果は表−１のとおりであった。
【００４５】
〔実施例３〕
前記ポリイミド（ｃ）溶液２４０ｇと、前記ポリイミド（ｂ）溶液１６０ｇとを、セパラブルフラスコにて温度１３０℃で３時間攪拌してポリイミド混合物溶液を得た。この混合物溶液のポリマー濃度は１４重量％であり、回転粘度は１７４８ポイズであった。このポリイミド混合物溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的特性を前記の方法によって測定した。結果は表−１のとおりであった。
【００４６】
〔実施例４〕
前記ポリイミド（ｃ）溶液２８０ｇと、前記ポリイミド（ｂ）溶液１２０ｇとを、セパラブルフラスコにて温度１３０℃で３時間攪拌してポリイミド混合物溶液を得た。この混合物溶液のポリマー濃度は１４重量％であり、回転粘度は１７８６ポイズであった。このポリイミド混合物溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的特性を前記の方法によって測定した。結果は表−１のとおりであった。
【００４７】
〔実施例５〕
前記ポリイミド（ｃ）溶液３６０ｇと、前記ポリイミド（ｂ）溶液４０ｇとを、セパラブルフラスコにて温度１３０℃で３時間攪拌してポリイミド混合物溶液を得た。この混合物溶液のポリマー濃度は１４重量％であり、回転粘度は１６９３ポイズであった。このポリイミド混合物溶液を用いて、前記の非対称中空糸膜の製造方法に基づいて、中空糸膜を製造した。この中空糸膜のガス透過性能と機械的特性を前記の方法によって測定した。結果は表−１のとおりであった。
【００４８】
実施例と比較例で得られた中空糸膜の、水蒸気透過速度、水蒸気と窒素の透過速度比、中空糸膜の機械的強度、多孔質層のヘリウム透過速度の測定結果は表−１に示すとおりであった。実施例１〜５の膜は、水蒸気透過速度（Ｐ’H2O）が２．０×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、水蒸気と窒素の透過速度比（Ｐ’H2O／Ｐ’He）が５０以上であり、多孔質層のヘリウム透過速度（Ｐ’He）が２．５×１０-3ｃｍ3（ＳＴＰ）／ｃｍ2・ｓｅｃ・ｃｍＨｇ以上であり、中空糸膜での引張強度が２．５ｋｇｆ／ｍｍ2以上であり、破断伸度が１０％以上である。これらの分離膜は、改良された優れた水蒸気透過速度を持ち、かつ、実用レベルの機械的強度を持つので分離膜モジュールへの加工が容易におこなうことが出来る高性能中空糸ガス分離膜である。しかしながら、比較例１の膜は多孔質層のヘリウム透過速度や膜の水蒸気透過速度は優れているが中空糸膜の引張強度が２．５ｋｇｆ／ｍｍ2以下で破断伸度が１０％以下であり、実用レベルの機械的強度がなく分離膜モジュールへの加工、組立てが工業的に困難なものである。また、比較例２は、中空糸膜としての機械的強度は実用レベル以上であるが、多孔質層のヘリウム透過速度や膜の水蒸気透過速度が低いものである。更に、実施例１〜５は、耐水性及び耐熱水性が非常に優れたものであった。
【表１】
【発明の効果】
本発明は、以上説明したようなものであるから、以下に記載されるような効果を有する。
【００５０】
本発明のガス分離膜は、改良されたガス透過速度を持つ非対称膜であり、しかも、非対称膜として工業的にモジュール化して実際に用いることができるレベルの機械的強度、言い換えれば、実用レベルの機械的強度をも併せ持ち、更に、優れた耐水性及び耐熱水特性を持つ高性能ガス分離膜である。このため、本発明のガス分離膜を用いれば、ガス分離速度が向上したより高効率でよりコンパクトな高性能中空糸ガス分離膜モジュールを提供することができ、高効率のガス分離を実現することができる。また、本発明のガス分離膜は、少なくとも１種類のポリイミドを含む２種類以上のポリマーの混合物で非対称構造を有する膜を形成することで得ることができる。
【００５１】
特に、本発明のガス分離膜を用いることによって、極めて高効率に除湿及び／又は加湿をおこなうことができる。更に、本発明のガス分離膜を用いることによって、固体高分子型燃料電池の供給ガスを、極めて好適に除湿及び／又は加湿することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas separation membrane having an asymmetric structure composed of a skin layer and a porous layer, wherein the membrane permeation component is reduced by reducing the resistance when the membrane permeation component (gas) permeates the porous layer. The membrane permeation rate is increased, the hollow fiber gas separation membrane has mechanical strength higher than the practical level, and has excellent water resistance and hot water resistance. The present invention relates to a gas separation membrane. The present invention also relates to a dehumidification method and a humidification method using the gas separation membrane.
[0002]
[Prior art]
Gas separation membranes are used in various gas separation methods. Many of these are gas separation membranes formed of a glassy polymer with high gas selective permeability. In general, glassy polymers have a high gas selective permeability (separation) but a small gas permeability coefficient. For this reason, a gas separation membrane formed of many glassy polymers has an asymmetric structure composed of a porous layer (support layer) and a thin skin layer (separation layer), that is, a separation layer that generates a gas permeation resistance. Is used so that the gas permeation rate does not become too small.
[0003]
A gas separation membrane is usually formed by concentrating many hollow fiber membranes (for example, hundreds to hundreds of thousands) into a hollow fiber bundle, and at least one end of the hollow fiber bundle is cured like an epoxy resin. A hollow fiber separation membrane element is formed by adhering the hollow fiber membrane in an open state at the end with an adhesive resin or a hot-melt type thermoplastic resin, and further, one or more hollow fiber separation membrane elements are In a container having at least a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet, the space leading to the inside of the hollow fiber membrane and the space leading to the outside of the hollow fiber membrane are separated from each other. Used as a configured hollow fiber gas separation membrane module. In the hollow fiber gas separation membrane module, the mixed gas is supplied to a space in contact with the inside or outside of the hollow fiber membrane, and a specific component (membrane permeable component) in the mixed gas is selectively selected while flowing in contact with the hollow fiber membrane. Gas is separated from the permeated gas through the membrane and collected from the permeate gas outlet, and the gas from which the specific component (membrane permeate component) is removed is collected from the non-permeate gas outlet.
[0004]
Regarding a gas separation membrane made of a mixture of polymers, US Pat. No. 5,055,116 discloses a gas separation membrane made of a mixture of two or more types of polyimides having a specific structure, and the permeation rate of oxygen and nitrogen depending on the polyimide blend ratio. It is shown that can be controlled linearly. US Pat. No. 5,248,319 discloses a gas separation membrane comprising a mixture of a polyimide containing a phenylindane residue and a specific polyimide, polyamide, or polyamideimide. US Pat. No. 5,608,014 discloses a gas separation membrane made of a mixture of a specific polyethersulfone, a specific aromatic polyimide, and a specific aromatic polyimide or polyamide or polyamideimide, while US Pat. No. 5,917,137 discloses a specific A gas separation membrane made of a mixture of polyethersulfone and a specific aromatic polyimide is disclosed. However, these publications do not mention the water vapor transmission rate and the gas transmission resistance of the porous layer. Further, there was no disclosure or suggestion of a gas separation membrane having a very high water vapor transmission rate and having a mechanical strength of a level that can be industrially modularized and actually used as an asymmetric hollow fiber membrane.
[0005]
Water resistance and hot water resistance are important for a dehumidification film or a humidification film in which water vapor is a membrane permeation component. However, membranes with improved permeation rate of gas containing water vapor often have poor water resistance and hot water resistance. JP-A-2-222717 discloses a polyimide separation membrane having excellent water resistance and hot water resistance, but is used for dehydration of organic vapor and has a low water vapor transmission rate.
[0006]
[Problems to be solved by the invention]
In a film having an asymmetric structure, the rate-limiting process of the permeation rate through which the membrane permeation component (gas) permeates the membrane is a process in which the membrane permeation component permeates the skin layer of the membrane. The process in which the membrane permeation component permeates through the porous layer of the membrane has a relatively small permeation resistance. For this reason, in many cases, the influence on the permeation speed at which the membrane permeation component permeates the porous layer of the membrane is negligible in practice.
[0007]
However, when the skin layer is extremely thin and the permeation rate of the membrane permeation component through the membrane is extremely large, or when the membrane permeation component is a gas that is very easy to permeate the membrane, the membrane permeation component permeates the membrane. The permeation rate to be transmitted may be influenced not only by the process of the membrane permeation component permeating the skin layer but also by the process of permeation through the porous layer. In this case, even if the membrane has an asymmetric structure, there is room for improving the permeation rate at which the membrane permeation component permeates through the membrane, and the development of a higher efficiency and more compact high performance gas separation membrane that has improved this is required. It was done. In particular, when the component that permeates the membrane is water vapor, the permeation rate through which the water vapor permeates the membrane is much higher than that of other inorganic gases (may reach several hundred to several thousand times). The permeation rate of water vapor is affected by the permeation resistance of the porous layer. For this reason, it is considered that if the permeation resistance when water vapor passes through the porous layer is reduced, the permeation speed at which water vapor permeates the membrane can be increased. Development of a highly efficient and compact high-performance dehumidifying membrane and / or humidifying membrane with a high permeation rate has been demanded.
[0008]
However, in a membrane having an asymmetric structure, by simply thinning the porous layer or increasing the porosity of the porous layer, the permeation resistance when the membrane permeation component permeates the membrane is reduced, and the membrane permeation component becomes a membrane. When trying to increase the permeation rate through the film, the permeation rate can be increased, but the supporting function of the membrane, that is, the mechanical strength that the porous layer should bear, is lowered. For this reason, the improved membrane permeation rate permeates through the membrane and the mechanical strength at a level that can be practically used as an asymmetric hollow fiber membrane industrially, in other words, at a practical level of mechanical strength. It was difficult to obtain a practical high-performance gas separation membrane having both strength and strength.
[0009]
Furthermore, when the gas separation membrane is used for dehumidification or humidification, if the water resistance and hot water resistance of the membrane are inferior, there is a problem that it cannot be used stably for a long period of time or its use is limited. For this reason, development of the dehumidification film | membrane and / or humidification film | membrane which was excellent in water resistance and hot water resistance was calculated | required.
[0010]
[Means for Solving the Problems]
The present invention has been made in view of such a situation, and the present inventors have formed a porous film by forming an asymmetric membrane with a mixture of two or more kinds of polymers including at least one kind of polyimide. A gas having excellent water resistance and hot water resistance while maintaining the mechanical strength of the membrane at a practical level or more while reducing the permeation resistance when the membrane permeation component permeates the membrane (increasing the permeation rate). The inventors have found that a separation membrane can be produced and have reached the present invention.
[0011]
That is, the present invention has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor transmission rate (P ′ H2O ) Is 2.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, Permeation rate ratio of water vapor and nitrogen (P ′ H20 / P ' N2 ) Is 50 or more, the transmission rate of helium gas (P ′) through the porous layer (support layer) of the membrane He ) Is 2.5 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, and the tensile strength at the hollow fiber membrane is 2.5 kgf / mm 2 As described above, the breaking elongation is 10% or more, and the breaking elongation of the hollow fiber membrane after hydrothermal treatment for 50 hours in hot water at 100 ° C. is maintained at 80% or more before the hot water treatment. The present invention relates to a gas separation membrane.
Further, it has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), and has a water vapor transmission rate (P ′ H2O ) Is 2.5 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, Permeation rate ratio of water vapor and nitrogen (P ′ H2O / P ' N2 ) Is 50 or more, the transmission rate of helium gas (P ′) through the porous layer (support layer) of the membrane He ) Is 3.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, and the tensile strength at the hollow fiber membrane is 2.5 kgf / mm 2 As described above, the breaking elongation is 10% or more, and the breaking elongation of the hollow fiber membrane after hot water treatment in hot water at 100 ° C. for 50 hours is maintained at 80% or more before the hot water treatment. The present invention relates to a gas separation membrane.
Furthermore, the present invention relates to the gas separation membrane, wherein the gas separation membrane is formed of a mixture of two or more types of polymers including at least one type of polyimide.
Furthermore, the tensile strength at the hollow fiber membrane is 3.0 kgf / mm 2 As described above, the present invention relates to the gas separation membrane having a breaking elongation of 15% or more.
Furthermore, the present invention relates to the gas separation membrane, wherein after the hydrothermal treatment in hot water at 100 ° C. for 50 hours, the breaking elongation of the hollow fiber membrane is maintained at 90% or more before the hydrothermal treatment.
Further, a dehumidification method using the gas separation membrane, a humidification method using the gas separation membrane, and / or dehumidifying and / or depleting the gas supplied to the fuel cell using the gas separation membrane The present invention relates to a dehumidification and / or humidification method characterized by humidification.
[0012]
In the present invention, the water vapor transmission rate (P ′ of the membrane) H2O ), Water vapor and nitrogen permeation rate ratio (P ') H2O / P ' N2 ), Helium permeation rate (P ′) of the porous layer (support layer) of the membrane He ) Is at 50 ° C.
In the present invention, the helium permeation rate (P ′) of the porous layer (support layer) of the membrane He ) Is used to indicate the gas permeation resistance of the porous layer (support layer) of the membrane (however, the larger the value, the smaller the resistance), which is specified as a value measured by the following measurement method It is. That is, helium when the skin layer on the surface of the asymmetric hollow fiber membrane is scraped by oxygen plasma treatment and reaches a region where the transmission rate ratio of helium gas and nitrogen gas is not substantially recognized as the transmission rate ratio of the homogeneous membrane. Gas permeation rate (P ' He ). Specifically, the transmission rate ratio of helium and nitrogen (P ′ before plasma treatment) He / P ' N2 ) Is processed by plasma treatment, and the transmission rate ratio (P ′ He / P ' N2 ) Is the permeation rate of helium gas when it becomes 1.2 or less. The transmission speed of this helium gas (P ′ He ) Is large, it means that the gas permeation resistance of the porous layer of the membrane is small, and the permeation rate of helium gas (P ′ He A small value of) means that the gas permeation resistance of the porous layer of the membrane is large.
[0013]
Further, the mechanical strength in the present invention is represented by the tensile strength and elongation at break in a tensile test when the membrane is a hollow fiber. These are values measured at a temperature of 23 ° C. using a tensile tester at an effective length of the sample of 20 mm and a tensile speed of 10 mm / min. The tensile strength is a value obtained by dividing the stress at the time of tensile breaking of the hollow fiber membrane by the membrane cross-sectional area of the hollow fiber [unit: kgf / mm 2 And the elongation at break is the original length of the hollow fiber L 0 , When the length at the time of tensile fracture is L (LL 0 ) / L 0 × 100 [unit:%].
[0014]
Further, in the present invention, as an index indicating the water resistance and hot water resistance of the hollow fiber membrane, retention rate of breaking elongation in a tensile test after performing hydrothermal treatment for 50 hours in hot water at a temperature of 100 ° C. [unit: %] Was used.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The asymmetric gas separation membrane of the present invention improves the permeation rate of the membrane permeation component (especially water vapor) by reducing the gas permeation resistance of the porous layer (increasing the gas permeation rate), and the asymmetric hollow fiber membrane As such, it has a mechanical strength of a level that can be industrially modularized and actually used, in other words, has a practical level of mechanical strength, and has excellent water resistance and hot water resistance.
[0016]
That is, according to the present invention, the gas permeation rate of the porous layer is the helium gas permeation rate (P ′ He ) 2.5 × 10 -3 cm Three (STP) / cm 2 The water vapor permeation rate (P ′) is set to be sec · cmHg or more, the tensile strength at the hollow fiber membrane is 2.5 kgf / mm 2 or more, and the elongation at break is 10% or more. H2O ) Is 2.0 × 10 -3 cm Three (STP) / cm 2 · High permeation rate of sec · cmHg or more, excellent pressure resistance as a hollow fiber membrane, and mechanical strength at a practical level that can be industrially processed into a gas separation membrane module, and excellent water resistance It is an asymmetric gas separation membrane with heat resistance and hot water resistance.
[0017]
Further, according to the present invention, the gas permeation rate of the porous layer is the helium gas permeation rate (P ′ He ) 3.0 × 10 -3 cm Three (STP) / cm 2 The water vapor permeation rate (P ′) is set to be sec · cmHg or more, the tensile strength at the hollow fiber membrane is 2.5 kgf / mm 2 or more, and the elongation at break is 10% or more. H2O ) Is 2.5 × 10 -3 cm Three (STP) / cm 2 · High permeation rate of sec · cmHg or more, excellent pressure resistance as a hollow fiber membrane, and mechanical strength at a practical level that can be industrially processed into a gas separation membrane module, and excellent water resistance It is an asymmetric gas separation membrane with heat resistance and hot water resistance.
[0018]
The gas permeation rate of the porous layer of the membrane is the helium gas permeation rate (P ′ He ) 2.5 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, preferably 3.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, more preferably 3.5 × 10 -3 cm Three (STP) / cm 2 If it is sec · cmHg or more, the gas permeation resistance of the porous layer is reduced, and the influence on the gas permeation performance of the membrane is reduced or substantially negligible. H2O ) Is 2.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, and 2.5 × 10 -3 cm Three (STP) / cm 2 A gas separation membrane of sec · cmHg or higher can be obtained. Conversely, the gas permeation rate of the porous layer of the membrane is equal to the helium gas permeation rate (P ′ He ) 3.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or less, especially 2.5 × 10 -3 cm Three (STP) / cm 2 -Since the gas permeation resistance of the porous layer is large when it is less than sec · cmHg, it becomes difficult to increase the gas permeation rate of the membrane, and obtaining a high-performance gas separation membrane having an improved water vapor permeation rate is difficult.
[0019]
In the present invention, the tensile strength at the hollow fiber membrane is 2.5 kgf / mm. 2 Or more, preferably 3.0 kgf / mm 2 This is a gas separation membrane having an asymmetric structure with a breaking elongation of 10% or more, preferably 15% or more. Since the hollow fiber membrane having such mechanical strength can be easily handled without being damaged or broken, it can be industrially modularized (assembled into a gas separation membrane module and processed). Furthermore, a gas separation membrane module using such a hollow fiber membrane having mechanical strength is particularly useful because it has excellent pressure resistance and durability. On the other hand, the tensile strength is 2.5 kgf / mm 2 If the breaking elongation is 10% or less or below, the hollow fiber membrane is likely to break or break during assembly and processing into the gas separation membrane module, making it difficult to industrially assemble and process into the separation membrane module. Furthermore, as a separation membrane module, the pressure resistance is lowered and the usage and use conditions are limited. In addition, the hollow fiber membrane in the separation membrane module is continuously or intermittently deformed depending on the flow rate, flow velocity, pressure, temperature, and variations of the gas supplied and flowing inside and outside the hollow fiber. The tensile strength is 2.5kgf / mm 2 If the elongation at break is 10% or less, breakage or breakage easily occurs, and a problem is likely to occur.
[0020]
Further, the present invention provides a permeation rate ratio of water vapor and nitrogen (P ′ H2O / P ' N2 ) Is a gas separation membrane of 50 or more. Permeation rate ratio of water vapor and nitrogen (P ' H2O / P ' N2 ) Of 50 or more means that gas selectivity is more than practical, and in particular, dry water having a dew point of −15 ° C. or less can be easily obtained by selectively permeating water vapor. It is useful as a dehumidifying film and also as an excellent humidifying film.
[0021]
Furthermore, the gas separation membrane of the present invention has excellent water resistance and hot water resistance in addition to having an improved gas permeation rate and a mechanical strength exceeding a practical level. The gas separation membrane of the present invention maintains the elongation at break of the hollow fiber membrane of 80% or more, particularly preferably 90% or more before the hydrothermal treatment even after hydrothermal treatment in hot water at a temperature of 100 ° C. for 50 hours. It has water resistance and hot water resistance. Therefore, the gas separation membrane of the present invention can be used in a wide range of applications as a humidifying membrane and / or a dehumidifying membrane, and can maintain high performance even when used for a long period of time.
[0022]
The gas separation membrane of the present invention can be obtained by forming a membrane with a mixture of two or more types of polymers containing at least one type of polyimide, and preferably forms a membrane with a mixture of two or more types of polyimides. Can be obtained. Increasing the porosity of the porous layer with one kind of polyimide can improve the gas permeation rate, but the mechanical strength decreases, so the gas separation membrane of the present invention cannot be obtained. The one kind of polyimide is a polyimide in which a certain monomer composition is polymerized as a repeating unit, and so-called homopolyimide and copolymerized polyimide are one kind of polymer. In the present invention, polymers other than polyimide that can form a mixture of two or more kinds of polymers including at least one kind of polyimide are not particularly limited, but aromatic polyamide, aromatic polyamideimide, aromatic polyether Examples thereof include imide, aromatic polysulfone, and aromatic polycarbonate.
[0023]
A mixture of two or more kinds of polymers including at least one kind of polyimide used in the present invention is at least one kind of polyimide having high gas selective permeability (high separation degree and high permeation rate) and at least one kind of excellent It is a polymer mixture containing a polyimide having mechanical strength or a polymer other than polyimide. These polymer mixtures can be dissolved in the same solvent. Moreover, the solution which melt | dissolved these polymer mixtures in the solvent has a preferable thing which does not produce turbidity in appearance. If a polymer mixture solution that is clearly non-uniform in appearance is used, the gas separation membrane of the present invention cannot be obtained. The gas separation membrane of the present invention is a method proposed by Loeb et al. (For example, US Pat. No. 3,133,132) using a polymer solution in which the polymer mixture is dissolved, that is, the polymer mixture solution is extruded from a nozzle. It can be produced by a so-called dry-wet method in which the target shape is made to pass through an air or nitrogen atmosphere space and then immersed in a coagulation bath. In the dry-wet method, in the solidification process, phase separation of the polymer phase and the solvent phase proceeds by substitution of the solvent of the polymer solution having the desired shape with the poor solvent for the polymer in the coagulation liquid, and the polymer forms a porous structure. However, in the solidification process of the polymer mixture solution of the present invention, in addition to the progress of phase separation of the polymer phase and the solvent phase, at least molecules between two or more kinds of polymers including at least one type of polyimide are used. It is presumed that chain level heterogeneity or phase separation proceeds to form a porous structure in which a decrease in mechanical strength is suppressed while increasing porosity. A high-performance gas separation membrane that combines an improved gas permeation rate and a practical level of mechanical strength even when the membrane is formed using a copolymer of the same monomer composition as the polymer mixture instead of the polymer mixture. I can't get it.
[0024]
The manufacturing method of the gas separation membrane of the present invention is as follows in more detail. That is, a polymer mixture solution in which two or more kinds of polymers including one kind of polyimide are dissolved in the same solvent is prepared, and this is discharged from a nozzle into a desired shape such as a hollow fiber shape. After passing, the polymer mixture is not substantially dissolved and is immersed in a coagulation liquid that is compatible with the solvent of the polymer mixture solution to form an asymmetric structure, followed by drying and heat treatment to produce a separation membrane To do. The polymer mixture solution may be prepared by separately preparing two or more types of polymer solutions containing one type of polyimide, or by dissolving two or more types of polymers containing one type of polyimide sequentially in the same solvent. May be. The concentration of the polymer mixture solution is preferably 10 to 25% by weight for film formation. Further, the solution viscosity (rotational viscosity) of the polymer mixture solution discharged from the nozzle is preferably 50 to 15000 poise, particularly 100 to 10000 poise at the discharge temperature, because a shape after discharge such as a hollow fiber shape can be stably obtained. For immersion in the coagulation liquid, the film is immersed in the primary coagulation liquid and solidified to such an extent that the shape of the membrane such as a hollow fiber can be maintained, wound on a guide roll, and then immersed in the secondary coagulation liquid to fully saturate the entire film. It is preferable to solidify. For drying the coagulated film, a method of drying after replacing the coagulating liquid with a solvent such as hydrocarbon is effective. The heat treatment is preferably performed at a temperature lower than the softening point or the second order transition point of two or more kinds of polymers including one kind of polyimide used.
[0025]
The thickness of the skin layer of the gas separation membrane of the present invention is 10 to 200 nm, preferably 20 to 100 nm. The thickness of the porous layer of the gas separation membrane of the present invention is 20 to 200 μm, preferably 30 to 100 μm. If the thickness of the skin layer is 10 nm or less, it is difficult to produce, and if it is 200 nm or more, the gas permeation rate decreases and the gas separation membrane of the present invention cannot be obtained. Further, when the porous layer is 20 μm or less, the mechanical strength becomes small and the supporting function cannot be achieved. When the porous layer is 200 μm or more, the gas permeation resistance of the porous layer increases and a gas separation membrane having an improved gas permeation rate is obtained. I can't do that.
[0026]
The gas separation membrane of the present invention is suitably used as a hollow fiber membrane, and the hollow fiber membrane preferably has an inner diameter of 30 to 500 μm. Further, the hollow fiber membrane of the present invention can be suitably used by being incorporated in a normal gas separation membrane module. For example, about 100 to 200,000 hollow fiber membranes are bundled with an appropriate length. The method of bundling may be a parallel arrangement, a cross arrangement, or a woven shape, and a core tube may be provided at a substantially central portion of the bundle, or the outer peripheral portion of the bundle may be surrounded by a plastic film. The hollow fiber bundle is fixed by a tube plate with the hollow fiber membrane kept open at at least one end, and includes at least a mixed gas inlet, a permeate gas outlet, and a non-permeate gas outlet. The tube plate is housed in the container, and the tube sheet is hermetically attached to the container so as to isolate the space in the container. The supplied mixed gas is supplied to a space in contact with the inside or outside of the hollow fiber membrane, and a specific component in the mixed gas selectively permeates through the membrane while flowing in contact with the hollow fiber membrane from the permeated gas discharge port. The non-permeated gas recovered and not permeated is recovered by discharging from the non-permeate gas outlet, and gas separation is performed. Further, for example, a carrier gas may be allowed to flow in a direction countercurrent to the supplied mixed gas in the space on the permeate gas side to facilitate recovery of the permeate gas. In this case, a non-permeate gas may be used as the carrier gas. Good.
[0027]
Since the gas separation membrane of the present invention has a very high water vapor transmission rate, dehumidification and / or humidification can be performed very efficiently and suitably by using the gas separation membrane of the present invention. When dehumidification is performed, water vapor is selectively permeated through the membrane by supplying the gas separation membrane module comprising the gas separation membrane of the present invention with a mixed gas containing water vapor to a space in contact with the inside or outside of the hollow fiber membrane. A gas that permeates to the side and is dehumidified as a non-permeating gas can be obtained very efficiently. In particular, it is more efficient and dehumidified to supply a mixed gas containing water vapor to the inside of the hollow fiber membrane and introduce the dried carrier gas into the space outside the hollow fiber membrane so as to counter flow with the mixed gas. In addition, it is preferable to recycle and use a part of the dehumidified gas obtained on the non-permeating side of the gas separation membrane as the carrier gas as a simple carrier gas introduction method. When humidifying, supply a mixed gas containing a larger amount of water vapor (high water vapor partial pressure) to the space in contact with the inside or outside of the hollow fiber membrane, and a smaller amount of water vapor into the space on the opposite side of the hollow fiber membrane. By supplying a gas containing (low water vapor partial pressure), the water vapor selectively permeates the membrane, and the gas containing a smaller amount of water vapor can be easily humidified. In particular, a mixed gas containing a larger amount of water vapor and a gas containing a smaller amount of water vapor are desirable because it is highly efficient to supply the mixed gas so as to counter flow across the hollow fiber membrane.
[0028]
Furthermore, by using the gas separation membrane of the present invention, dehumidification and / or humidification of the supply gas for the fuel cell can be performed extremely efficiently and suitably. A polymer electrolyte fuel cell generally includes a power generation element in which both sides of a hydrogen ion conductive solid polymer electrolyte membrane are sandwiched by carbon electrodes carrying a platinum catalyst, and a fuel gas such as hydrogen or oxygen on each of these electrodes. A separator having a flow distribution function for supplying an oxidizing gas such as gas or discharging exhaust gas from an electrode, and a current collector disposed on the outer side of the separator are stacked. In this battery, when the solid polymer electrolyte membrane is dried, the ionic conductivity is lowered, and the solid polymer electrolyte membrane and the electrode are poorly contacted to cause a sudden drop in output. It is important to control to maintain a constant humidity. For this reason, it is necessary to humidify the supply gas (fuel gas and / or oxidizing gas) (dehumidification instead of humidification if there is too much water). It has already been proposed to use a separation membrane as a method for humidifying the supply gas. JP-A-3-269958 discloses the use of a porous film made of tetrafluoroethylene resin. JP-A-8-273687 and JP-A-8-315838 disclose that the permeation membrane area per unit area is increased by using a hollow fiber-like porous membrane and the humidification performance is improved. However, these humidifying membranes have a problem that the humidifying performance is not sufficient, and when water and the membrane are in contact with each other for a long time, water oozes out to the supply gas side of the fuel cell of the membrane and droplets are generated. There was an inconvenience of doing. Further, in fuel cells for automobiles and the like, a method of selectively permeating moisture in the exhaust gas of the fuel cell through the separation membrane and recycling it to the supply gas of the fuel cell has been studied. In the membrane, there is a problem that components other than moisture in the exhaust gas of the fuel cell are mixed into the supply gas of the fuel cell.
[0029]
Since the gas separation membrane of the present invention has an extremely high water vapor transmission rate, humidification and / or dehumidification can be performed efficiently. The gas separation membrane of the present invention is a membrane formed of a mixture of two or more types of polymers including at least one type of polyimide, and preferably a membrane formed of a mixture of two or more types of polyimide. Excellent heat resistance and chemical resistance required for use in batteries. Furthermore, the hot water resistance around 100 ° C. at which the polymer electrolyte fuel cell is operated is very good. Moreover, since the gas separation membrane of the present invention has an asymmetric structure composed of a skin layer (separation layer) and a porous layer (support layer), the fuel cell supply when used for a long time in a fuel cell Problems such as inconvenience that water oozes out to the gas side membrane surface and droplets are generated, and that components other than moisture in the exhaust gas of the fuel cell are mixed into the supply gas of the fuel cell hardly occur. By using the gas separation membrane of the present invention, it is possible to dehumidify and / or humidify the supply gas of the fuel cell very suitably.
[0030]
【Example】
Next, the production and characteristics of the hollow fiber gas separation membrane in the present invention will be specifically described. In addition, this invention is not limited to an Example.
[0031]
(Preparation of polyimide (a) solution)
29.422 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes abbreviated as s-BPDA) and 2,2′-bis (3,4-dicarboxyphenyl) 44.424 g of hexafluoropropane dianhydride (hereinafter sometimes abbreviated as 6FDA), 16.179 g of 4,4′-diaminodiphenyl ether (hereinafter also abbreviated as DADE), and 1,4-bis 35.432 g of (4-aminophenoxy) benzene (hereinafter also abbreviated as TPEQ) and 726.44 g of parachlorophenol (hereinafter also abbreviated as PCP) as a solvent in a separable flask Polymerization was carried out at a polymerization temperature of 180 ° C. for 17 hours to obtain a polyimide (a) solution having a rotational viscosity of 1748 poise and a polymer concentration of 14% by weight.
[0032]
(Preparation of polyimide (b) solution)
88.266 g of s-BPDA and 60.733 of DADE were polymerized in a separable flask for 10 hours at a polymerization temperature of 180 ° C. together with PCP850.41 g of a solvent, and a polyimide (b) having a rotational viscosity of 1730 poise and a polymer concentration of 14% by weight A solution was obtained.
[0033]
(Preparation of polyimide (c) solution)
44.133 g of s-BPDA, 66.636 g of 6FDA, and 60.432 g of DADE were polymerized in a separable flask at a polymerization temperature of 180 ° C. for 12 hours together with a solvent PCP of 98.32 g, a rotational viscosity of 1654 poise, and a polymer concentration of 14% by weight. A polyimide (c) solution was obtained.
[0034]
(Method for producing asymmetric hollow fiber membrane)
After the polyimide solution or the polyimide mixture solution is filtered through a 400 mesh wire mesh, it is discharged from a hollow fiber spinning nozzle (circular opening outer diameter 1000 μm, circular opening slit width 200 μm, core opening outer diameter 400 μm), The discharged hollow fiber-like body was passed through a nitrogen atmosphere, and then immersed in a coagulation liquid composed of an aqueous ethanol solution having a predetermined concentration (70 to 80% by weight) at a temperature of 0 ° C. to obtain a wet yarn. This was immersed in ethanol at a temperature of 50 ° C. for 2 hours to complete the solvent removal treatment, and further washed by immersion in isooctane at a temperature of 70 ° C. for 3 hours to replace the solvent. Thereafter, heat treatment was performed at a predetermined temperature (200 to 300 ° C.) for 1 hour. Each of the obtained hollow fiber membranes had an outer diameter of about 470 μm, an inner diameter of about 320 μm, and a film thickness of about 75 μm.
[0035]
(Measurement method of water vapor permeability of hollow fiber membrane)
Using about 10 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluating permeation performance having an effective length of 20 mm was prepared, and this was attached to a stainless steel container to form a pencil module. . A fixed amount of 1500 ppm of nitrogen gas is supplied to the outside of the hollow fiber of the pencil module, and water vapor is separated while flowing a fixed amount of carrier gas (Ar gas) to the permeate side. The amount was detected with a specular dew point meter. The water vapor transmission rate of the membrane was calculated from the measured amount of water vapor (water vapor partial pressure), the amount of supplied gas, and the effective membrane area. These measurements were made at 50 ° C.
[0036]
(Measurement method of nitrogen gas permeation performance of hollow fiber membrane)
Using about 15 hollow fiber membranes, a stainless steel pipe, and an epoxy resin adhesive, an element for evaluating permeation performance having an effective length of 10 cm was prepared, and this was attached to a stainless steel container to form a pencil module. . Nitrogen pure gas at a constant pressure was supplied thereto, and the permeation flow rate was measured. The permeation rate of nitrogen gas was calculated from the measured amount of permeated nitrogen gas, supply pressure, and effective membrane area. These measurements were made at 50 ° C.
[0037]
(Measurement method of helium gas permeation performance of porous layer of hollow fiber membrane)
A large number of hollow fiber membranes were uniformly spread and installed in the plasma processing apparatus, and oxygen plasma processing was performed at an applied voltage of 20V. Every time oxygen plasma treatment was performed for 5 minutes, some (several) hollow fibers were taken out to obtain hollow fiber membranes with different plasma treatment times. Using these hollow fiber membranes, a gas permeation measuring pencil module (effective length 10 mm) is prepared by the same method as described above, and nitrogen permeation gas or helium pure gas is supplied at a constant pressure to each permeate flow rate. The permeation rate of nitrogen or helium was calculated from the measured permeation flow rate, supply pressure, and effective membrane area. The ratio of these values for hollow fiber membranes plasma treated for more than 20 minutes, ie P ′ He / P ' N2 Was 1.2 or less, so the permeation rate of helium (P ′ He ) Was defined as the helium permeation rate of the porous layer of the membrane used in the present invention. These measurements were made at 50 ° C.
[0038]
(Measurement of tensile strength and breaking elongation of hollow fiber membrane)
Using a tensile tester, measurement was performed at an effective length of 20 mm and a tensile speed of 10 mm / min. The fracture area was calculated by measuring the dimensions of the fractured surface using an optical microscope.
[0039]
(Method for measuring rotational viscosity)
The rotational viscosity of the polyimide solution was measured at a temperature of 100 ° C. using a rotational viscometer (rotor shear rate of 1.75 / sec).
[0040]
(Measurement of water resistance and hot water resistance of hollow fiber membranes)
Using a hollow fiber membrane having a known breaking elongation as a sample, ion-exchanged water and the hollow fiber membrane are placed in a stainless steel container and sealed, and the container is placed in an oven at 100 ° C. and held for 50 hours to form a hollow fiber membrane. It was treated with hot water. The hollow fiber membrane after the hot water treatment was taken out of the container and dried in an oven at 100 ° C. The hollow fiber membrane after drying was measured for elongation at break according to the tensile test method described above. Water resistance and hot water resistance were expressed using the retention rate [%] of elongation at break as an index.
[0041]
[Example 1]
280 g of the polyimide (a) solution and 120 g of the polyimide (b) solution were stirred in a separable flask at a temperature of 130 ° C. for 3 hours to obtain a polyimide mixture solution. The polymer concentration of this mixture solution was 14% by weight, and the rotational viscosity was 1786 poise. Using this polyimide mixture solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical properties of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0042]
[Example 2]
360 g of the polyimide (a) solution and 40 g of the polyimide (b) solution were stirred at a temperature of 130 ° C. for 3 hours in a separable flask to obtain a polyimide mixture solution. The polymer concentration of this mixture solution was 14% by weight, and the rotational viscosity was 1804 poise. Using this polyimide mixture solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical properties of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0043]
[Comparative Example 1]
Using the polyimide (a) solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical strength of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0044]
[Comparative Example 2]
Using the polyimide (b) solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical strength of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0045]
Example 3
240 g of the polyimide (c) solution and 160 g of the polyimide (b) solution were stirred in a separable flask at a temperature of 130 ° C. for 3 hours to obtain a polyimide mixture solution. The polymer concentration of this mixture solution was 14% by weight, and the rotational viscosity was 1748 poise. Using this polyimide mixture solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical properties of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0046]
Example 4
280 g of the polyimide (c) solution and 120 g of the polyimide (b) solution were stirred in a separable flask at a temperature of 130 ° C. for 3 hours to obtain a polyimide mixture solution. The polymer concentration of this mixture solution was 14% by weight, and the rotational viscosity was 1786 poise. Using this polyimide mixture solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical properties of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0047]
Example 5
360 g of the polyimide (c) solution and 40 g of the polyimide (b) solution were stirred in a separable flask at a temperature of 130 ° C. for 3 hours to obtain a polyimide mixture solution. The polymer concentration of this mixture solution was 14% by weight, and the rotational viscosity was 1693 poise. Using this polyimide mixture solution, a hollow fiber membrane was produced based on the method for producing an asymmetric hollow fiber membrane. The gas permeation performance and mechanical properties of this hollow fiber membrane were measured by the above methods. The results are shown in Table 1.
[0048]
Table 1 shows the measurement results of the water vapor transmission rate, the water vapor and nitrogen transmission rate ratio, the mechanical strength of the hollow fiber membrane, and the helium transmission rate of the porous layer of the hollow fiber membranes obtained in Examples and Comparative Examples. It was as follows. The membranes of Examples 1-5 have a water vapor transmission rate (P ′ H2O ) Is 2.0 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, Permeation rate ratio of water vapor and nitrogen (P ′ H2O / P ' He ) Is 50 or more and the helium permeation rate (P ′) of the porous layer He ) Is 2.5 × 10 -3 cm Three (STP) / cm 2 ・ Sec · cmHg or more, and the tensile strength at the hollow fiber membrane is 2.5 kgf / mm 2 Thus, the elongation at break is 10% or more. These separation membranes are high-performance hollow fiber gas separation membranes that have improved and excellent water vapor transmission rate and mechanical strength at a practical level, so that they can be easily processed into separation membrane modules. . However, the membrane of Comparative Example 1 is excellent in the helium permeation rate of the porous layer and the water vapor permeation rate of the membrane, but the tensile strength of the hollow fiber membrane is 2.5 kgf / mm. 2 In the following, the elongation at break is 10% or less, and there is no mechanical strength at a practical level, and it is industrially difficult to process and assemble the separation membrane module. In Comparative Example 2, the mechanical strength of the hollow fiber membrane is not less than a practical level, but the helium permeation rate of the porous layer and the water vapor permeation rate of the membrane are low. Further, Examples 1 to 5 were very excellent in water resistance and hot water resistance.
[Table 1]
【The invention's effect】
Since the present invention is as described above, the present invention has the effects described below.
[0050]
The gas separation membrane of the present invention is an asymmetric membrane having an improved gas permeation rate, and furthermore, mechanical strength at a level that can be industrially modularized and used as an asymmetric membrane, in other words, at a practical level. It is a high-performance gas separation membrane that has both mechanical strength and excellent water resistance and hot water resistance. For this reason, by using the gas separation membrane of the present invention, it is possible to provide a more efficient and more compact high-performance hollow fiber gas separation membrane module with improved gas separation speed, and to realize highly efficient gas separation. Can do. In addition, the gas separation membrane of the present invention can be obtained by forming a membrane having an asymmetric structure with a mixture of two or more types of polymers including at least one type of polyimide.
[0051]
In particular, dehumidification and / or humidification can be performed with extremely high efficiency by using the gas separation membrane of the present invention. Furthermore, by using the gas separation membrane of the present invention, the supply gas of the polymer electrolyte fuel cell can be dehumidified and / or humidified very suitably.
Claims (7)
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000370031A JP4671493B2 (en) | 2000-12-05 | 2000-12-05 | Gas separation membrane and method of using the same |
| EP01100017A EP1118371B1 (en) | 2000-01-19 | 2001-01-04 | Gas separation membrane and its use |
| DE60127734T DE60127734T2 (en) | 2000-01-19 | 2001-01-04 | Gas separation membrane and its use |
| US09/766,116 US6464755B2 (en) | 2000-01-19 | 2001-01-19 | Gas separation membrane and method for its use |
| CNB011162392A CN1202902C (en) | 2000-01-19 | 2001-01-19 | Gas separating membrane and its utilizing method |
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| JP2000370031A JP4671493B2 (en) | 2000-12-05 | 2000-12-05 | Gas separation membrane and method of using the same |
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| JP2006348692A Division JP4858160B2 (en) | 2006-12-25 | 2006-12-25 | Gas separation membrane and method of using the same |
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| JP2002172311A JP2002172311A (en) | 2002-06-18 |
| JP4671493B2 true JP4671493B2 (en) | 2011-04-20 |
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| JP2000370031A Expired - Lifetime JP4671493B2 (en) | 2000-01-19 | 2000-12-05 | Gas separation membrane and method of using the same |
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| JP2002289228A (en) * | 2001-03-22 | 2002-10-04 | Nok Corp | Humidifier and its use |
| JP5358903B2 (en) * | 2006-07-21 | 2013-12-04 | 宇部興産株式会社 | Asymmetric hollow fiber gas separation membrane, gas separation method, and gas separation membrane module |
| JP5114912B2 (en) * | 2006-10-02 | 2013-01-09 | 宇部興産株式会社 | Asymmetric membrane, gas separation membrane, and gas separation method formed of Si atom-containing polyimide |
| US8561812B2 (en) * | 2009-03-27 | 2013-10-22 | Uop Llc | Blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups |
| US7810652B2 (en) * | 2009-09-25 | 2010-10-12 | Uop Llc | Method to improve the selectivity of polybenzoxazole membranes |
| EP3112493B1 (en) * | 2014-02-25 | 2022-12-14 | JFE Steel Corporation | Method for controlling dew point of reduction furnace, and reduction furnace |
| JP6548562B2 (en) * | 2015-12-08 | 2019-07-24 | Ａｇｃエンジニアリング株式会社 | Dehumidifying module and gas analyzer equipped with the dehumidifying module |
| JP6866730B2 (en) * | 2017-03-31 | 2021-04-28 | 宇部興産株式会社 | Gas separation membrane |
| JP2019193918A (en) * | 2018-05-01 | 2019-11-07 | 宇部興産株式会社 | Composite membrane for gas separation |
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