Anion exchange fibres derived from chloromethylstyrene grafted POLYOLEIN FIBRES for rapid column-mode removal of nitrate in water

水中硝酸イオンのカラム法による迅速除去を目的としてクロロメチルスチレングラフトポリオレフィン繊維から誘導した陰イオン交換繊維

郷 康弘*; 吉田 裕美*; 城 昭典*; 玉田 正男; 片貝 秋雄

Go, Yasuhiro*; Yoshida, Hiromi*; Jo, Akinori*; Tamada, Masao; Katakai, Akio

工業的規模のカラムで利用される樹脂の直径は、圧損を軽減するため0.5mm程度と大きく、この樹脂を充填したカラムに硝酸で汚染された水を空間速度(SV)1000h以上の高速で通液しても効率よく硝酸イオンを除去できない。そこで、SV3000h程度の高速通液条件下でも硝酸イオンを迅速に補足可能な陰イオン交換繊維(FBDA)をクロロメチルスチレン(CMS)をグラフトした繊維にn-ブチルジメチルアミン(BDA)を導入して合成した。得られたFBDAの陰イオン交換容量は2.2meq/gであった。この湿潤FBDAを充填したカラムに、1mMの硝酸ナトリウム溶液をSV1000から3000hで通液したところ、硝酸イオンの破過曲線はSVに依存せず良い一致を示した。そのときの破過容量は1.1mmol/gと一定であった。共存陰イオンとしての塩化物イオンと硫酸イオンの影響をSV1000hで検討した。等モル並びに5倍モル濃度の塩化物イオンの共存下では、硝酸イオンの破過容量はそれぞれ0.83並びに0.48mmol/gとなった。一方、等モル濃度の硫酸イオンの共存下では0.43mmol/gとなった。以上の結果から、共存陰イオン濃度が河川水の平均濃度以下の場合には、14ppm程度の低濃度の硝酸イオン含有水を極めて迅速に浄化できることがわかった。

Although granular anion exchange resins are useful for column-mode removal of nitrate in water, sizes of granular resins used in industrial scale columns are ca. 0.5 mm to reduce pressure loss in column operations. Since large granular resins bring down adsorption kinetics, it is difficult to supply water polluted with nitrate to granular resin packed columns at extremely high flow rates more than 1000 h in space velocity (SV). In this work, we have prepared an anion exchange fiber named FBDA, which rapidly takes up nitrate in column-mode even at the flow rate of feed of 3000 h in SV. FBDA was prepared by electron beam irradiation induced liquid phase graft polymerization of chloromethylstyrene (CMS) onto polyethylene-coated polypropylene fiber (PPPE; 1.5 denier) and the subsequent quaternization of the CMS-grafted fiber with n-butyldimethylamine (BDA). The resulting BDA-fixed fiber (FBDA) has anion exchange capacity of 2.2 meq/g. To the column (i.d. 1.3 cm) containing 2.0 mL wet FBDA, 1 mM nitrate feeding solutions in the absence and presence of a competing anion was fed to the column at given flow rates. In the absence of a competing anion, shapes of breakthrough profiles of nitrate are independent of the flow rates from 1000 to 3000 h in SV, giving the constant breakthrough capacity for nitrate as high as 1.1 mmol/g. Effect of chloride and sulfate was tested at the flow rate of 1000 h. In the presence of 1 mM and 5 mM chloride, breakthrough capacities for nitrate were reduced to 0.83 and 0.48 mmol/g, respectively. However, equimolar sulfate reduced the breakthrough capacity down to 0.43 mmol/g. Thus, the presented FBDA is useful for rapid purification of water contaminated with low concentration levels of nitrate, so long as concentrations of chloride and sulfate are nearly equal orders as those in most river waters. Almost the same results were also obtained in case of the triethylamine-fixed fiber named FTEA.