JP4757396B2 - Cellulose derivative hollow fiber membrane - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、特に河川、湖沼等の天然水域の水処理用として適したセルロース誘導体中空糸膜に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
酢酸セルロース膜は、古くから海水淡水化用の非対称逆浸透膜や血液透析膜として利用されており、これらの用途に向けた中空糸膜タイプの酢酸セルロース膜が開発されている（例えば、特開昭５４−８８８８１号公報、特開昭６１−１８５３０５号公報、特開昭６０−２９７６３号公報、特開昭６３−１７９２２号公報、特開平５−２２８２０８号公報、特開平６−３４３８４２号公報）。また、酢酸セルロース膜の生体適合性や透水性を改善するために、酢酸セルロース膜以外のセルロース誘導体又はセルロースエステル膜も検討されている。例えば、特開昭５７−１３３２１１号公報、特開昭６０−４３４４２号公報、特開昭６０−５２０２号公報、特開昭６２−２９０４６８号公報、特開平１−２０２４５号公報、特開平２−１２６１１号公報、特開平２−２１１２２８号公報、特開平６−２７７４７３号公報、特開平６−３１１４４号公報等には、酢酸プロピオン酸セルロースを対象としたセルロース誘導体膜が開示されている。
【０００３】
しかし、これらの先行技術には、高い透水流束と高い強度を併せもつ中空糸膜について具体的に記載されたものはない。更に、これらの先行技術に開示された膜は透析用膜やパーベイパレーション膜で、しかも孔径の小さな膜又は非多孔膜であり、水処理用途に用いる高分画性能をもつ膜とは異なる。
【０００４】
水処理用途に用いられる酢酸セルロース中空糸膜は、例えば、特開平６−３４３８４２号公報、特開平８−１０８０５３号公報に開示されているが、これらの酢酸セルロース中空糸膜を河川水、地下水、湖沼水、海水等の天然水の浄化に用いた場合、原水中の微生物によって膜が生分解することが問題となる。そこで、酢酸セルロース中空糸膜を用いた天然水の浄化においては、通常、次亜塩素酸ナトリウムによる殺菌が常時又は間欠的に行われ、膜の生分解が阻止されている。しかし、次亜塩素酸ナトリウムが天然水中のフミン質と結合すると、発癌性のトリハロメタン等の消毒副生物を生じるという問題が生じる。
【０００５】
本発明は、上記のような酢酸セルロース膜のもつ生分解を受けやすいという問題を解決し、天然水の浄化に適用した場合にも次亜塩素酸ナトリウム水溶液等による殺菌処理を全く行わないか又は回数を大幅に減少させても生物劣化することなく、高い透水速度を維持し、かつ機械的強度に優れたセルロース誘導体中空糸膜を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者は、先に膜材料の７０質量％以上が酢酸プロピオン酸セルロース又は酢酸酪酸セルロースであるセルロース誘導体中空糸膜に係わる発明を出願している。（ＰＣＴ／ＪＰ００／０３０５６）このセルロース誘導体中空糸膜は、高い透過流束と膜強度を有している点で優れているものであるが、透過流束に関しては酢酸セルロース中空糸膜と比べると劣っているため、この点で更なる改善の余地がある。よって、本発明者は、膜強度を高く維持したまま、酢酸セルロース中空糸膜と同程度以上の透過流束を発揮できるものを得るべく研究をした結果、本発明を完成したものである。
【０００７】
本発明は、解決手段として、セルロース誘導体を膜材料とする中空糸膜であり、膜厚が５０〜５００μｍで、内外表面の少なくとも一方に０．００１〜０．０５μｍの平均孔径をもつ緻密な膜表面を有し、膜内部に平均孔径が０．５〜７μｍである空孔を有する三次元網目状多孔質構造からなり、膜内部の三次元網目状多孔質構造の孔径分布において極大値が少なくとも１つ存在し、その極大値が８μｍ以上である、膜材料の７０質量％以上が酢酸プロピオン酸セルロース又は酢酸酪酸セルロースであるセルロース誘導体中空糸膜を提供する。
【０００８】
【発明の実施の形態】
本発明のセルロース誘導体中空糸膜（以下、単に「中空糸膜」と称する）は、機械的強度と透水性をバランスよく付与するため、膜厚が５０〜５００μｍ、好ましくは１００〜４００μｍである。
【０００９】
本発明の中空糸膜は、内外表面の少なくとも一方に０．００１〜０．０５μｍ、好ましくは０．００５〜０．０３μｍの平均孔径をもつ緻密な膜表面を有している。前記平均孔径の範囲は、分画分子量に換算すると１万〜５０万、好ましくは７万〜３０万に相当する。なお、本発明の中空糸膜は、内表面、外表面又は内外表面が前記した緻密な膜表面であるが、これらの中でも内外表面が緻密な膜表面であるものが好ましい。
【００１０】
本発明の中空糸膜は、膜内部が平均孔径０．５〜７μｍ、好ましくは２〜６μｍ、より好ましくは４〜６μｍの空孔を有する三次元網目状多孔質構造からなるものである。この「三次元網目状多孔質構造」は、中空糸膜に機械的強度と伸度を付与するように作用するもので、膜表面の緻密層の孔径よりも大きな平均孔径の空孔を有するものであるが、孔径が１０μｍ以上もの巨大空孔を複数個含むものではなく、孔径が１０μｍ以上もの巨大空孔を含まないものが望ましい。
【００１１】
なお、膜内部の平均孔径は、膜断面の電子顕微鏡写真（５０００倍）を膜内表面から膜外表面にわたり等間隔に１０箇所撮影し、各箇所の写真上の５μｍ四方内に見られる孔の径を平均化し、この平均値を１０箇所の撮影部に対して平均化したものである。
【００１２】
また、膜内部の三次元網目状多孔質構造の孔径分布においては極大値が少なくとも１つ存在し、その極大値（最大孔径）は８μｍ以上、好ましくは８〜２０μｍ、より好ましくは８〜１０μｍである。この極大値を示す空孔は、中空糸膜の内表面からの距離が５０〜２００μｍの範囲に存在することが好ましく、６０〜１５０μｍの範囲に存在することがより好ましく、７５〜１２５の範囲に存在することが更に好ましい。膜内部の全空孔容積に対する孔径８μｍ以上の空孔容積の割合は、好ましくは１〜５０％、より好ましくは１〜３０％、更に好ましくは５〜２０％である。
【００１３】
本発明の中空糸膜は、セルロース誘導体を膜材料とするものであるが、膜材料の７０質量％以上、好ましくは８０質量％以上が酢酸プロピオン酸セルロース又は酢酸酪酸セルロースであり、更に好ましくは１００質量％が酢酸プロピオン酸セルロース又は酢酸酪酸セルロースである。酢酸プロピオン酸セルロース又は酢酸酪酸セルロースの含有量が７０質量％以上であると、生分解しにくくなり、他のセルロース誘導体等と混合した場合でも相溶性が良く、膜の機械的強度の低下を防止できる。
【００１４】
酢酸プロピオン酸セルロースにおける酢酸エステル基及びプロピオン酸エステル基の置換度と、酢酸酪酸セルロースにおける酢酸エステル基及び酪酸エステル基の置換度は特に制限されないが、好ましくは１．５〜２．９、より好ましくは２．０〜２．８である。また、酢酸エステル基とプロピオン酸エステル基の置換基又は酢酸エステル基と酪酸エステル基の比率は特に制限されない。更に、酢酸プロピオン酸セルロース及び酢酸酪酸セルロースの数平均分子量は、紡糸性が良いため、好ましくは１万〜５０万、より好ましくは５万〜２０万である。
【００１５】
本発明の中空糸膜において、酢酸プロピオン酸セルロース又は酢酸酪酸セルロースと他のセルロース誘導体との混合物を膜材料として用いる場合、他のセルロース誘導体としては、二酢酸セルロース、三酢酸セルロース、ブチル酸セルロース等のセルロースエステル化合物、メチルセルロース、エチルセルロース等のセルロースエーテル化合物が挙げられ、更に、ポリスルホン系ポリマー、ポリアクリロニトリル系ポリマー、ポリアミド系ポリマー、ポリビニルピロリドン、ポリビニルホルマール等を併用することができる。
【００１６】
本発明の中空糸膜は、長期にわたり耐久性を維持するため、引張破断点強度が好ましくは３ＭＰａ以上、より好ましくは４ＭＰａ以上で、かつ引張破断点伸度が好ましくは１５％以上、より好ましくは２０％以上である。
【００１７】
本発明の中空糸膜は、膜間差圧１００ｋＰａ、温度２５℃における純水の透過速度が、好ましくは４００Ｌ／（ｍ２・ｈ）以上、より好ましくは５００Ｌ／（ｍ２・ｈ）以上のものである。なお、ここで「純水」とは、電気抵抗が０．２μＳ／ｃｍ以下になるようにイオン交換した水を、分画分子量３万の膜で濾過した水をいう。
【００１８】
本発明のセルロース誘導体中空糸膜は、例えば、湿式相転換法又は乾湿式相転換法を適用して製造することができる。
【００１９】
これらの方法で用いる紡糸原液は、上記したように、膜材料として７０質量％以上の酢酸プロピオン酸セルロース又は酢酸酪酸セルロースを含むセルロース誘導体を溶剤に溶解して得る。
【００２０】
この溶剤は水と混合できるものであればよく、アセトン、ジオキサン、酢酸、ジメチルスルホキシド、ジメチルアセトアミド、Ｎ−メチル−２−ピロリドン、ジメチルホルムアミド等が挙げられる。これらの中でも、透水流束を高くするためには、１００℃以上で紡糸ができる高沸点溶剤、例えば、ジメチルスルホキシド、ジメチルアセトアミド、Ｎ−メチル−２−ピロリドンが好ましく、所定の三次元網目状多孔質構造を形成し、機械的強度を高くするため、ジメチルスルホキシドが好ましい。
【００２１】
また、これらの溶剤以外にエチレングリコール、ポリエチレングリコール等の非溶剤、塩化リチウム、塩化カルシウム、塩化マグネシウム、硝酸リチウム、硝酸バリウム、硝酸マグネシウム、酢酸リチウム、酢酸マグネシウム等の金属化合物を添加できる。
【００２２】
紡糸原液中のセルロース誘導体の濃度は、好ましくは１５〜３５質量％、より好ましくは２０〜３０質量％である。
【００２３】
内部凝固液は、濃度２０〜４０質量％、好ましくは２０〜３０質量％の極性有機溶媒水溶液を用い、この極性有機溶剤水溶液としてはジメチルスルホキシド水溶液、ジメチルホルムアミド水溶液が好ましい。このように極性有機溶媒水溶液、好ましくはジメチルスルホキシド水溶液、ジメチルホルムアミド水溶液を内部凝固液として用いることによって、上記した特定構造の中空糸膜を得ることができる。
【００２４】
凝固浴は、内部凝固液と同様のものでよいが、その他にもセルロース誘導体の非溶剤である水、エチレングリコール、ポリエチレングリコール又はこれらの非溶剤と上記した有機溶剤との混合物を用いることができる。
【００２５】
内部凝固液及び凝固浴の温度は、好ましくは３０〜９０℃、より好ましくは３０〜７０℃である。３０℃以上であると膜表面の緻密層の厚みを適度にすることができるので高い透水流束が得られ、９０℃以下であると内部凝固液及び凝固浴の沸騰が生じないので、製造操作が円滑に行える。
【００２６】
紡糸原液のノズル吐出部の温度は、好ましくは３０〜１３０℃、より好ましくは５０〜１００℃、更に好ましくは５０〜７５℃である。乾湿式紡糸の場合、ノズル吐出部と凝固浴表面との距離は、吐出後の中空糸膜が０．２秒以上空気中に留まることができるように、好ましくは１〜５０ｃｍ、より好ましくは５〜３０ｃｍの範囲で設定する。
【００２７】
本発明の中空糸膜は、特に河川水、地下水、湖沼水、海水等の天然水の浄化用に適しているが、それら以外にも、工場、家庭等の各種排水の処理にも適用することができる。
【００２８】
【実施例】
以下、実施例により本発明を更に詳しく説明するが、本発明はこれらにより限定されるものではない。なお、以下における各測定は、下記の方法により行った。
（１）純水透過流束
有効長５０ｃｍの中空糸膜に、２５℃の純水で１００ｋＰａの水圧を内側からかけ、単位時間当たりに透過した純水の量を測定し、その透水流束を内表面積基準の膜面積で割って求めた。
（２）引張破断点強度、伸度
有効長５ｃｍの中空糸膜試験片を、テンシロンを用いてクロスヘッド速度１０ｍｍ／分で引っ張り、破断点における強度及び伸度を測定した。強度は、中空糸膜断面積で割って求めた。
（３）分画分子量
分子量の異なる各種蛋白質を標準溶質とし、膜に対するそれぞれの排除率を測定して、分子量と排除率の関係をグラフにプロットし、得られた分子量排除率曲線より、排除率９０％に相当する分子量を求めた。
（４）生分解性
中空糸膜を流水状態の揖保川河川水に浸漬させ、経日的に中空糸膜をサンプリングし、その引張破断点強度を測定し、前記強度が初期強度の９０％に低下するまでの日数を求めた。
【００２９】
実施例１
酢酸プロピオン酸セルロース（置換度２．６８、数平均分子量７５０００、酢酸エステル基含有率２．５％、プロピオン酸エステル基含有率６１．２％）２２質量％、ジメチルスルホキシド７７質量％、塩化リチウム１質量％の紡糸原液を、二重管型ノズルの外管から吐出すると共に、内管から濃度３０質量％のジメチルスルホキシド水溶液（５５℃）を内部凝固液として吐出した。吐出部における紡糸原液の温度は５５℃であった。吐出した紡糸原液は、０．５秒間空気中を通過させた後、凝固浴（５０℃の温水）中で凝固させ、更に洗浄浴（５０℃の温水）中で十分に溶剤を除去して、膜厚が約２５０μｍの中空糸膜を得た。
【００３０】
図１に、得られた中空糸膜の断面構造を示す。図１（ａ）は、中空糸膜の内表面とその近傍部分を含む断面の走査型電子顕微鏡写真（５０００倍）であり、図１（ｂ）は、膜内部（膜内表面から約６０〜８５μｍの範囲）の断面の走査型電子顕微鏡写真（５０００倍）である。図１から明らかなとおり、中空糸膜は内表面に緻密な構造を有する三次元網目状多孔質構造のものであった。図２に、得られた中空糸膜の内表面からの距離と空孔径の関係を示す。図２から明らかなとおり、膜内部の空孔径は、２〜１０μｍ程度の範囲に分布しており、極大値は１０μｍを超える程度であった。実施例１で得られた中空糸膜の構造上の各数値及び試験結果を表１に示す。
【００３１】
実施例２
内部凝固液として濃度３０質量％のジメチルホルムアミド水溶液を用いた以外は実施例１と同様にして、膜厚が約２５０μｍの中空糸膜を得た。実施例２で得られた中空糸膜の構造上の各数値及び試験結果を表１に示す。
【００３２】
実施例３
酢酸酪酸セルロース（置換度２．６９、数平均分子量７５０００、酢酸基含有率１３．５％、酪酸基含有率３７．０％）２０質量％、ジメチルスルホキシド７９質量％、塩化リチウム１質量％の紡糸原液を、二重管型ノズルの外管から吐出すると共に、内管から濃度２０質量％のジメチルスルホキシド水溶液（５５℃）を内部凝固液として吐出した。吐出部における紡糸原液の温度は５５℃であった。吐出した紡糸原液は、０．５秒間空気中を通過させた後、凝固浴（５０℃の温水）中で凝固させ、更に洗浄浴（５０℃の温水）中で十分に溶剤を除去して、膜厚が約２５０μｍの中空糸膜を得た。実施例３で得られた中空糸膜の構造上の各数値及び試験結果を表１に示す。
【００３３】
実施例４
酢酸プロピオン酸セルロース（置換度２．６８、数平均分子量７５０００、酢酸エステル基含有率２．５％、プロピオン酸エステル基含有率６１．２％）と三酢酸セルロース（酢化度６０．８％、重合度１５０、ダイセル化学工業（株）製）を重量比９：１で混合した混合物２０質量％、ジメチルスルホキシド７９質量％、塩化リチウム１質量％の紡糸原液を、二重管型ノズルの外管から吐出すると共に、内管から濃度２０質量％のジメチルスルホキシド水溶液（７５℃）を内部凝固液として吐出した。吐出部における紡糸原液の温度は９０℃であった。吐出した紡糸原液は、０．５秒間空気中を通過させた後、凝固浴（７０℃の温水）中で凝固させ、更に洗浄浴（５０℃の温水）中で十分に溶剤を除去して、膜厚が約２５０μｍの中空糸膜を得た。実施例４で得られた中空糸膜の構造上の各数値及び試験結果を表１に示す。
【００３４】
比較例１
実施例１と同じ紡糸原液を二重管型ノズルの外管から吐出すると共に、内管から純水（５５℃）を内部凝固液として吐出した。吐出部における紡糸原液の温度は５５℃であった。吐出した紡糸原液は、０．５秒間空気中を通過させた後、凝固浴（５０℃の温水）中で凝固させ、更に洗浄浴（５０℃の温水）中で十分に溶剤を除去して、膜厚が約２５０μｍの中空糸膜を得た。
【００３５】
図２に、得られた中空糸膜の内表面からの距離と空孔径の関係を示す。図２から明らかなとおり、膜内部の空孔径は、２〜７μｍ程度の範囲に分布しており、極大値は７μｍを下回っていた。比較例１で得られた中空糸膜の構造上の各数値及び試験結果を表１に示す。
【００３６】
比較例２
三酢酸セルロース（酢化度６０．８％、重合度１５０、ダイセル化学工業（株）製）２０質量％、ジメチルスルホキシド７９質量％及び塩化リチウム１質量％の紡糸原液を用いた以外は実施例４と同様にして、中空糸膜を得た。この中空糸膜の断面は、三次元網目状多孔質構造内に空孔径約１５０μｍの巨大空孔が複数個存在していた。
【００３７】
比較例３
内部凝固液として純水に替えて濃度１０質量％のジメチルスルホキシド水溶液（５５℃）を用いた以外は比較例１と同様にして、膜厚が約２５０μｍの中空糸膜を得た。
【００３８】
比較例４
実施例４と組成は同じで、質量比（酢酸プロピオン酸セルロース：三酢酸セルロース＝１：９）が実施例４と異なる紡糸原液を二重管型ノズルの外管から吐出すると共に、内管から濃度３０質量％のジメチルスルホキシド水溶液（７５℃）を内部凝固液として吐出した。吐出部における紡糸原液の温度は９０℃であった。吐出した紡糸原液は、０．５秒間空気中を通過させた後、凝固浴（７０℃の温水）中で凝固させ、更に洗浄浴（５０℃の温水）中で十分に溶剤を除去して、膜厚が約２５０μｍの中空糸膜を得た。
【００３９】
【表１】
試験例１
実施例１と比較例２で得られた中空糸膜を用い、揖保川河川水を用いた濾過試験を行った。濾過は、有効膜面積０．１４ｍ2、温度９〜３７℃で、膜間差圧１０〜５０ｋＰａで行い、０．５時間ごとに６０秒間、逆圧洗浄を行った。但し、図３に示すとおり、濾過水に有効塩素濃度が１ｍｇ／Ｌになるように次亜塩素酸ナトリウムを添加したもので逆圧洗浄を行った。図３に、透過流束の経日変化を示す。
【００４１】
図３から明らかなとおり、実施例１の中空糸膜は、比較例２の酢酸セルロース膜と比べても同等の透過流束を示した。
【００４２】
【発明の効果】
本発明のセルロース誘導体中空糸膜は、機械的強度が高く、生分解もしにくいので、次亜塩素酸ナトリウム等の殺菌剤による洗浄が全く不要になるか又は大幅に減少させた場合でも、酢酸セルロース膜と同等の高い透水性能を維持することができる。
【図面の簡単な説明】
【図１】 図１（ａ）は、実施例１で得られた中空糸膜内表面を含む断面の５０００倍の走査型電子顕微鏡写真であり、図１（ｂ）は、実施例１で得られた中空糸膜内部の５０００倍の走査型電子顕微鏡写真である。
【図２】 実施例１と比較例１で得られた中空糸膜の膜内部の空孔分布を示す図である。
【図３】 実施例１と比較例２で得られた中空糸膜を用いた濾過試験における、透過流束の経日変化を示す図である、[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cellulose derivative hollow fiber membrane particularly suitable for water treatment in natural water areas such as rivers and lakes.
[0002]
[Prior art and problems to be solved by the invention]
Cellulose acetate membranes have long been used as asymmetric reverse osmosis membranes for seawater desalination and hemodialysis membranes, and hollow fiber membrane type cellulose acetate membranes for these applications have been developed (for example, JP (Showa 54-88881, JP 61-185305, JP 60-29763, JP 63-17922, JP 5-228208, JP 6-343842) . In addition, in order to improve the biocompatibility and water permeability of the cellulose acetate membrane, a cellulose derivative or cellulose ester membrane other than the cellulose acetate membrane has been studied. For example, JP 57-133211, JP 60-43442, JP 60-5202, JP 62-290468, JP 1-20245, JP No. 12611, JP-A-2-21228, JP-A-6-277473, JP-A-6-31144 and the like disclose cellulose derivative membranes intended for cellulose acetate propionate.
[0003]
However, none of these prior arts specifically describes hollow fiber membranes having both high water permeability and high strength. Furthermore, the membranes disclosed in these prior arts are dialysis membranes and pervaporation membranes, and are membranes having a small pore size or non-porous membranes, which are different from membranes having high fractionation performance used for water treatment applications. .
[0004]
Cellulose acetate hollow fiber membranes used for water treatment applications are disclosed, for example, in JP-A-6-343842 and JP-A-8-108053, and these cellulose acetate hollow fiber membranes are used in river water, groundwater, When used for purification of natural water such as lake water and seawater, the problem is that the membrane is biodegraded by microorganisms in the raw water. Therefore, in the purification of natural water using a cellulose acetate hollow fiber membrane, sterilization with sodium hypochlorite is normally or intermittently performed to prevent biodegradation of the membrane. However, when sodium hypochlorite binds to humic substances in natural water, there arises a problem that disinfection by-products such as carcinogenic trihalomethane are produced.
[0005]
The present invention solves the problem of being susceptible to biodegradation of the cellulose acetate membrane as described above, and does not perform sterilization treatment with an aqueous sodium hypochlorite solution or the like even when applied to purification of natural water or An object of the present invention is to provide a cellulose derivative hollow fiber membrane that maintains a high water permeation rate and is excellent in mechanical strength without causing biological deterioration even if the number of times is greatly reduced.
[0006]
[Means for Solving the Problems]
The present inventor has previously filed an invention relating to a cellulose derivative hollow fiber membrane in which 70% by mass or more of the membrane material is cellulose acetate propionate or cellulose acetate butyrate. (PCT / JP00 / 03056) This cellulose derivative hollow fiber membrane is excellent in that it has a high permeation flux and membrane strength, but the permeation flux is compared with that of a cellulose acetate hollow fiber membrane. Because it is inferior, there is room for further improvement in this regard. Therefore, the present inventor has completed the present invention as a result of research to obtain a permeation flux that is at least as good as that of a cellulose acetate hollow fiber membrane while maintaining high membrane strength.
[0007]
The present invention provides a hollow fiber membrane comprising a cellulose derivative as a membrane material as a solution, a dense membrane having a thickness of 50 to 500 μm and an average pore diameter of 0.001 to 0.05 μm on at least one of the inner and outer surfaces. It has a surface and a three-dimensional network porous structure having pores with an average pore diameter of 0.5 to 7 μm inside the membrane, and the maximum value in the pore size distribution of the three-dimensional network porous structure inside the membrane is at least There is provided a cellulose derivative hollow fiber membrane in which one is present and the maximum value thereof is 8 μm or more, and 70 mass% or more of the membrane material is cellulose acetate propionate or cellulose acetate butyrate.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The cellulose derivative hollow fiber membrane of the present invention (hereinafter simply referred to as “hollow fiber membrane”) has a film thickness of 50 to 500 μm, preferably 100 to 400 μm, in order to impart a good balance between mechanical strength and water permeability.
[0009]
The hollow fiber membrane of the present invention has a dense membrane surface having an average pore diameter of 0.001 to 0.05 μm, preferably 0.005 to 0.03 μm, on at least one of the inner and outer surfaces. The range of the average pore diameter corresponds to 10,000 to 500,000, preferably 70,000 to 300,000 when converted to a molecular weight cut-off. In the hollow fiber membrane of the present invention, the inner surface, the outer surface, or the inner / outer surface is the above-described dense membrane surface, and among these, the inner / outer surface is preferably a dense membrane surface.
[0010]
The hollow fiber membrane of the present invention has a three-dimensional network porous structure in which the inside of the membrane has pores having an average pore diameter of 0.5 to 7 μm, preferably 2 to 6 μm, more preferably 4 to 6 μm. This "three-dimensional network porous structure" acts to give mechanical strength and elongation to the hollow fiber membrane, and has pores with an average pore size larger than the pore size of the dense layer on the membrane surface However, it is preferable not to include a plurality of giant pores having a pore diameter of 10 μm or more, and not to contain giant pores having a pore diameter of 10 μm or more.
[0011]
The average pore diameter inside the membrane was obtained by photographing an electron micrograph (5000 times) of the membrane cross section from the inner surface of the membrane to the outer surface of the membrane at 10 equal intervals, and the pores found in 5 μm squares on the photographs at each location. The diameters are averaged, and the average value is averaged for 10 photographing units.
[0012]
In the pore size distribution of the three-dimensional network porous structure inside the membrane, there is at least one maximum value, and the maximum value (maximum pore size) is 8 μm or more, preferably 8 to 20 μm, more preferably 8 to 10 μm. is there. It is preferable that the hole which shows this maximum value exists in the range of 50-200 micrometers from the inner surface of a hollow fiber membrane, It is more preferable that it exists in the range of 60-150 micrometers, It exists in the range of 75-125. More preferably, it is present. The ratio of the pore volume having a pore diameter of 8 μm or more to the total pore volume inside the membrane is preferably 1 to 50%, more preferably 1 to 30%, and further preferably 5 to 20%.
[0013]
The hollow fiber membrane of the present invention uses a cellulose derivative as a membrane material, but 70% by mass or more, preferably 80% by mass or more of the membrane material is cellulose acetate propionate or cellulose acetate butyrate, and more preferably 100%. The mass% is cellulose acetate propionate or cellulose acetate butyrate. When the content of cellulose acetate propionate or cellulose acetate butyrate is 70% by mass or more, biodegradation is difficult, and even when mixed with other cellulose derivatives, etc., compatibility is good, and deterioration of the mechanical strength of the membrane is prevented. it can.
[0014]
The degree of substitution of acetate ester group and propionate group in cellulose acetate propionate and the degree of substitution of acetate group and butyrate group in cellulose acetate butyrate are not particularly limited, but preferably 1.5 to 2.9, more preferably Is 2.0 to 2.8. Further, the ratio of the acetate group and the propionate group or the ratio of the acetate group and the butyrate group is not particularly limited. Furthermore, the number average molecular weights of cellulose acetate propionate and cellulose acetate butyrate are preferably 10,000 to 500,000, more preferably 50,000 to 200,000 because of good spinnability.
[0015]
In the hollow fiber membrane of the present invention, when cellulose acetate propionate or a mixture of cellulose acetate butyrate and other cellulose derivatives is used as a membrane material, other cellulose derivatives include cellulose diacetate, cellulose triacetate, cellulose butyrate, etc. And cellulose ether compounds such as methyl cellulose and ethyl cellulose, and polysulfone polymers, polyacrylonitrile polymers, polyamide polymers, polyvinyl pyrrolidone, polyvinyl formal and the like can be used in combination.
[0016]
In order to maintain durability over a long period of time, the hollow fiber membrane of the present invention preferably has a tensile strength at break of 3 MPa or more, more preferably 4 MPa or more, and an elongation at break of preferably 15% or more, more preferably 20% or more.
[0017]
The hollow fiber membrane of the present invention has a transmission rate of pure water at a transmembrane pressure difference of 100 kPa and a temperature of 25 ° C. of preferably 400 L / (m 2 · h) or more, more preferably 500 L / (m 2 · h) or more. Is. Here, “pure water” refers to water obtained by filtering water ion-exchanged so as to have an electric resistance of 0.2 μS / cm or less through a membrane having a molecular weight cut off of 30,000.
[0018]
The cellulose derivative hollow fiber membrane of the present invention can be produced by applying, for example, a wet phase conversion method or a dry / wet phase conversion method.
[0019]
As described above, the spinning dope used in these methods is obtained by dissolving a cellulose derivative containing 70% by mass or more of cellulose acetate propionate or cellulose acetate butyrate as a membrane material in a solvent.
[0020]
The solvent may be any solvent that can be mixed with water, and examples thereof include acetone, dioxane, acetic acid, dimethyl sulfoxide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethylformamide and the like. Among these, in order to increase the water permeation flux, a high boiling point solvent that can be spun at 100 ° C. or higher, for example, dimethyl sulfoxide, dimethylacetamide, N-methyl-2-pyrrolidone is preferable, and a predetermined three-dimensional network porous Dimethyl sulfoxide is preferred because it forms a fine structure and increases mechanical strength.
[0021]
In addition to these solvents, non-solvents such as ethylene glycol and polyethylene glycol, and metal compounds such as lithium chloride, calcium chloride, magnesium chloride, lithium nitrate, barium nitrate, magnesium nitrate, lithium acetate, and magnesium acetate can be added.
[0022]
The concentration of the cellulose derivative in the spinning dope is preferably 15 to 35% by mass, more preferably 20 to 30% by mass.
[0023]
As the internal coagulation liquid, a polar organic solvent aqueous solution having a concentration of 20 to 40% by mass, preferably 20 to 30% by mass is used. As the polar organic solvent aqueous solution, a dimethyl sulfoxide aqueous solution and a dimethylformamide aqueous solution are preferable. As described above, by using a polar organic solvent aqueous solution, preferably a dimethyl sulfoxide aqueous solution or a dimethylformamide aqueous solution as the internal coagulation liquid, the hollow fiber membrane having the specific structure described above can be obtained.
[0024]
The coagulation bath may be the same as the internal coagulation liquid, but water, ethylene glycol, polyethylene glycol, or a mixture of these non-solvents and the above-mentioned organic solvents can also be used. .
[0025]
The temperature of the internal coagulation liquid and the coagulation bath is preferably 30 to 90 ° C, more preferably 30 to 70 ° C. When the temperature is 30 ° C. or higher, the thickness of the dense layer on the membrane surface can be made moderate, so that a high water permeability is obtained, and when it is 90 ° C. or lower, the internal coagulating liquid and the coagulation bath do not boil. Can be done smoothly.
[0026]
The temperature of the nozzle discharge part of the spinning dope is preferably 30 to 130 ° C, more preferably 50 to 100 ° C, still more preferably 50 to 75 ° C. In the case of dry and wet spinning, the distance between the nozzle discharge part and the coagulation bath surface is preferably 1 to 50 cm, more preferably 5 so that the hollow fiber membrane after discharge can remain in the air for 0.2 seconds or more. Set in the range of ~ 30 cm.
[0027]
The hollow fiber membrane of the present invention is particularly suitable for the purification of natural water such as river water, groundwater, lake water, seawater, etc. Can do.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited by these. In addition, each measurement below was performed by the following method.
(1) Pure water permeation flux An effective length of 50 cm hollow fiber membrane is subjected to a water pressure of 100 kPa with pure water at 25 ° C. from the inside to measure the amount of pure water permeated per unit time. It was obtained by dividing by the membrane area based on the inner surface area.
(2) Tensile breaking strength and elongation effective length 5 cm hollow fiber membrane test piece was pulled at a crosshead speed of 10 mm / min using Tensilon, and the strength and elongation at the breaking point were measured. The strength was determined by dividing by the cross-sectional area of the hollow fiber membrane.
(3) Proteins with different molecular weights are used as standard solutes, the respective rejection rates for the membrane are measured, the relationship between the molecular weight and the exclusion rate is plotted in a graph, and the exclusion rate is determined from the obtained molecular weight exclusion rate curve. The molecular weight corresponding to 90% was determined.
(4) The biodegradable hollow fiber membrane is immersed in flowing Hobo River water, the hollow fiber membrane is sampled over time, the tensile strength at break is measured, and the strength is reduced to 90% of the initial strength. We calculated the number of days until.
[0029]
Example 1
Cellulose acetate propionate (substitution degree 2.68, number average molecular weight 75000, acetate group content 2.5%, propionate group content 61.2%) 22% by mass, dimethyl sulfoxide 77% by mass, lithium chloride 1 A mass% spinning solution was discharged from the outer tube of a double tube type nozzle, and a 30% by mass aqueous dimethyl sulfoxide solution (55 ° C.) was discharged from the inner tube as an internal coagulating solution. The temperature of the spinning dope in the discharge part was 55 ° C. The discharged spinning solution is allowed to pass through the air for 0.5 seconds, then coagulated in a coagulation bath (50 ° C. warm water), and the solvent is sufficiently removed in a washing bath (50 ° C. hot water), A hollow fiber membrane having a thickness of about 250 μm was obtained.
[0030]
FIG. 1 shows a cross-sectional structure of the obtained hollow fiber membrane. FIG. 1 (a) is a scanning electron micrograph (5000 times) of a cross section including the inner surface of the hollow fiber membrane and the vicinity thereof, and FIG. 1 (b) shows the inside of the membrane (about 60 to It is a scanning electron micrograph (5000 times) of a cross section in a range of 85 μm. As is apparent from FIG. 1, the hollow fiber membrane had a three-dimensional network porous structure having a dense structure on the inner surface. FIG. 2 shows the relationship between the distance from the inner surface of the obtained hollow fiber membrane and the pore diameter. As apparent from FIG. 2, the pore diameter inside the film was distributed in the range of about 2 to 10 μm, and the maximum value was about 10 μm. Table 1 shows the numerical values and test results on the structure of the hollow fiber membrane obtained in Example 1.
[0031]
Example 2
A hollow fiber membrane having a film thickness of about 250 μm was obtained in the same manner as in Example 1 except that a 30% by mass dimethylformamide aqueous solution was used as the internal coagulation liquid. Table 1 shows the numerical values and test results on the structure of the hollow fiber membrane obtained in Example 2.
[0032]
Example 3
Spinning of cellulose acetate butyrate (substitution degree 2.69, number average molecular weight 75000, acetate group content 13.5%, butyrate group content 37.0%) 20% by mass, dimethyl sulfoxide 79% by mass, lithium chloride 1% by mass The stock solution was discharged from the outer tube of the double tube nozzle, and a 20% by mass dimethyl sulfoxide aqueous solution (55 ° C.) was discharged from the inner tube as an internal coagulating solution. The temperature of the spinning dope in the discharge part was 55 ° C. The discharged spinning solution is allowed to pass through the air for 0.5 seconds, then coagulated in a coagulation bath (50 ° C. warm water), and the solvent is sufficiently removed in a washing bath (50 ° C. hot water), A hollow fiber membrane having a thickness of about 250 μm was obtained. Table 1 shows the numerical values and test results on the structure of the hollow fiber membrane obtained in Example 3.
[0033]
Example 4
Cellulose acetate propionate (degree of substitution 2.68, number average molecular weight 75000, acetate group content 2.5%, propionate group content 61.2%) and cellulose triacetate (acetylation degree 60.8%, A spinning stock solution of 20% by mass of a mixture of a polymerization degree of 150 and a Daicel Chemical Industries Co., Ltd. mixture at a weight ratio of 9: 1, 79% by mass of dimethyl sulfoxide, and 1% by mass of lithium chloride is used as an outer tube of a double-tube type nozzle. From the inner tube, a 20% by mass dimethyl sulfoxide aqueous solution (75 ° C.) was discharged from the inner tube as an internal coagulating liquid. The temperature of the spinning dope in the discharge part was 90 ° C. The discharged spinning solution is allowed to pass through the air for 0.5 seconds, then coagulated in a coagulation bath (70 ° C. warm water), and the solvent is sufficiently removed in a washing bath (50 ° C. hot water). A hollow fiber membrane having a thickness of about 250 μm was obtained. Table 1 shows the numerical values and test results on the structure of the hollow fiber membrane obtained in Example 4.
[0034]
Comparative Example 1
The same spinning stock solution as in Example 1 was discharged from the outer tube of the double tube nozzle, and pure water (55 ° C.) was discharged from the inner tube as an internal coagulating solution. The temperature of the spinning dope in the discharge part was 55 ° C. The discharged spinning solution is allowed to pass through the air for 0.5 seconds, then coagulated in a coagulation bath (50 ° C. warm water), and the solvent is sufficiently removed in a washing bath (50 ° C. hot water), A hollow fiber membrane having a thickness of about 250 μm was obtained.
[0035]
FIG. 2 shows the relationship between the distance from the inner surface of the obtained hollow fiber membrane and the pore diameter. As apparent from FIG. 2, the pore diameter inside the film was distributed in the range of about 2 to 7 μm, and the maximum value was below 7 μm. Table 1 shows numerical values and test results on the structure of the hollow fiber membrane obtained in Comparative Example 1.
[0036]
Comparative Example 2
Example 4 except that a spinning stock solution of cellulose triacetate (acetylation degree 60.8%,
[0037]
Comparative Example 3
A hollow fiber membrane having a thickness of about 250 μm was obtained in the same manner as in Comparative Example 1 except that a dimethyl sulfoxide aqueous solution (55 ° C.) having a concentration of 10% by mass was used as the internal coagulation liquid instead of pure water.
[0038]
Comparative Example 4
The composition is the same as that of Example 4, and the spinning solution different in mass ratio (cellulose acetate propionate: cellulose triacetate = 1: 9) from that of Example 4 is discharged from the outer tube of the double tube type nozzle and from the inner tube. A 30% by mass dimethyl sulfoxide aqueous solution (75 ° C.) was discharged as an internal coagulation liquid. The temperature of the spinning dope in the discharge part was 90 ° C. The discharged spinning solution is allowed to pass through the air for 0.5 seconds, then coagulated in a coagulation bath (70 ° C. warm water), and the solvent is sufficiently removed in a washing bath (50 ° C. hot water). A hollow fiber membrane having a thickness of about 250 μm was obtained.
[0039]
[Table 1]
Test example 1
Using the hollow fiber membranes obtained in Example 1 and Comparative Example 2, a filtration test was conducted using Shibo River water. Filtration was performed at an effective membrane area of 0.14 m 2 , a temperature of 9 to 37 ° C., a transmembrane pressure difference of 10 to 50 kPa, and back pressure cleaning was performed every 0.5 hour for 60 seconds. However, as shown in FIG. 3, back pressure washing was performed with sodium hypochlorite added to filtered water so that the effective chlorine concentration was 1 mg / L. FIG. 3 shows changes with time in the permeation flux.
[0041]
As apparent from FIG. 3, the hollow fiber membrane of Example 1 showed the same permeation flux as compared with the cellulose acetate membrane of Comparative Example 2.
[0042]
【The invention's effect】
Since the cellulose derivative hollow fiber membrane of the present invention has high mechanical strength and is difficult to biodegrade, cellulose acetate can be used even when washing with a disinfectant such as sodium hypochlorite is completely unnecessary or greatly reduced. High water permeability equivalent to the membrane can be maintained.
[Brief description of the drawings]
FIG. 1 (a) is a scanning electron micrograph of 5000 times the cross section including the inner surface of the hollow fiber membrane obtained in Example 1, and FIG. 1 (b) is obtained in Example 1. It is a 5000 times scanning electron micrograph inside the hollow fiber membrane obtained.
FIG. 2 is a view showing the pore distribution inside the hollow fiber membranes obtained in Example 1 and Comparative Example 1.
FIG. 3 is a graph showing changes in permeation flux with time in filtration tests using the hollow fiber membranes obtained in Example 1 and Comparative Example 2.
Claims (10)
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| JP2001113063A Expired - Lifetime JP4757396B2 (en) | 2001-04-11 | 2001-04-11 | Cellulose derivative hollow fiber membrane |
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Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007245107A (en) * | 2006-03-20 | 2007-09-27 | Daicel Chem Ind Ltd | Hollow fiber porous membrane |
| EP3202486A4 (en) * | 2014-09-30 | 2018-05-23 | Toray Industries, Inc. | Separation membrane |
| CN105607272B (en) * | 2016-01-15 | 2018-02-06 | 上海玮舟微电子科技有限公司 | A kind of bearing calibration of 3D films and system |
| EP3603780A4 (en) * | 2017-03-30 | 2020-12-16 | Toray Industries, Inc. | Separation film and production method therefor |
| WO2021132399A1 (en) | 2019-12-23 | 2021-07-01 | 東レ株式会社 | Separation membrane and method for producing separation membrane |
| US20230397602A1 (en) * | 2020-10-30 | 2023-12-14 | Toyobo Co., Ltd. | Cell cryopreservation hollow fiber membrane |
| CN115245754B (en) * | 2021-04-26 | 2024-06-04 | 中国石油化工股份有限公司 | Biodegradable polymer separation membrane for adsorbing heavy metals and preparation method and application thereof |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5643417A (en) * | 1979-09-13 | 1981-04-22 | Nippon Zeon Co Ltd | Cellulosic hollow fiber |
| JP3253867B2 (en) * | 1996-10-30 | 2002-02-04 | 帝人株式会社 | Permselective hollow fiber membrane |
| US6632366B1 (en) * | 1999-05-31 | 2003-10-14 | Daicel Chemical Industries, Ltd. | Cellulose compound hollow fiber membrane |
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2001
- 2001-04-11 JP JP2001113063A patent/JP4757396B2/en not_active Expired - Lifetime
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| JP2002306937A (en) | 2002-10-22 |
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