JP3821749B2

JP3821749B2 - Cellulose acetate semipermeable membrane

Info

Publication number: JP3821749B2
Application number: JP2002129914A
Authority: JP
Inventors: 修志中塚
Original assignee: Daicel Chemical Industries Ltd
Current assignee: Daicel Corp
Priority date: 2002-05-01
Filing date: 2002-05-01
Publication date: 2006-09-13
Anticipated expiration: 2022-05-01
Also published as: JP2003320227A

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酢酸セルロース系半透膜、それを用いた濾過運転方法に関する。
【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（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）、その他、水処理用途に用いられる酢酸セルロース中空糸膜が、特開平６−３４３８４２号公報、特開平８−１０８０５３号公報等に開示されている。
【０００３】
酢酸セルロース系膜を河川水、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、膜の生分解を阻止する必要があるが、その一方で、次亜塩素酸ナトリウムによる殺菌処理によって、膜強度自体が低下していくという問題もある。
【０００４】
本発明は、上記のような酢酸セルロース膜を次亜塩素酸ナトリウム等の塩素系殺菌剤で殺菌処理した場合における膜強度の低下の問題を解決できる、次亜塩素酸ナトリウム等の塩素系殺菌剤に対する耐久性が高い酢酸セルロース系半透膜及びそれを用いた濾過運転方法を提供することを課題とする。
【０００５】
【課題を解決するための手段】
本発明者は、酢酸セルロース系半透膜の次亜塩素酸ナトリウム等の塩素系殺菌剤に対する耐久性を高めるべく研究した結果、酢酸セルロース単位中の３つのＯＨ基に置換するアセチル基の置換度を特定範囲に調整することによって、塩素系殺菌剤に対する耐久性を大幅に高められることを見出し、本発明を完成した。
【０００６】
本発明は、酢酸セルロースを含む膜材料からなる酢酸セルロース系半透膜であって、膜材料となる酢酸セルロースが、構成単位における２位、３位及び６位のアセチル置換度の合計が２．７０以上で、かつ６位のアセチル置換度が０．９０以下のものである酢酸セルロース系半透膜を提供する。
【０００７】
更に本発明は、上記の酢酸セルロース系半透膜を用いて水処理する濾過運転方法を提供する。
【０００８】
本発明において、「全構成単位における２位、３位及び６位のアセチル置換度の合計が２．７０以上で、かつ６位のアセチル置換度が０．９０以下のものである」とは、全ての構成単位が前記要件を満たすことを意味するものである。
【０００９】
本発明におけるアセチル置換度は、セルロース構成単位１個当たりの置換された平均ＯＨ基数を意味し、実施例で説明する^１３Ｃ−ＮＭＲ法により求めた。
【００１０】
【発明の実施の形態】
本発明の酢酸セルロース系半透膜は、酢酸セルロースを主成分とする膜材料からなるものであり、酢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こともできるが、酢酸セルロースの含有量が、原料基準で８０重量％以上であることが好ましく、９０重量％以上であることがより好ましい。他のセルロース誘導体としては、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を挙げることができ、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もできる。
【００１１】
膜材料となる酢酸セルロースは、全構成単位における２位、３位及び６位のアセチル置換度の合計が２．７０以上、好ましくは２．８０以上、より好ましくは２．８５以上で、かつ６位のアセチル置換度が０．９０以下、好ましくは０．８８以下のものである。
【００１２】
更に、膜材料となる酢酸セルロースは、全構成単位における２位及び３位のアセチル置換度の合計が１．９２〜２．００のものが好ましく、１．９６〜１．９９のものがより好ましく、１．９７〜１．９９のものが更に好ましい。
【００１３】
本発明の酢酸セルロース系半透膜は、中空糸膜、平膜、管状膜等の所望の形態にすることができるが、これらの中でも中空糸膜が特に好ましい。
【００１４】
中空糸膜にするときは、膜の機械的強度と透水性をバランスよく付与するため、外径は、好ましくは２００〜２０００μｍ、より好ましくは５００〜１５００μｍで、内径は、好ましくは１００〜１０００μｍ、より好ましくは４００〜１０００μｍであり、内表面と外表面を除く膜内部に存在する空孔の平均孔径は、好ましくは０．５〜５μｍ、より好ましくは０．８〜３μｍである。
【００１５】
膜内部の平均孔径は、膜断面の電子顕微鏡写真（１万倍）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。
【００１６】
中空糸膜は、機械的強度及び透水性を考慮すると、内部に孔径が１０μｍ以上の空孔を有しているものが好ましい。
【００１７】
中空糸膜は、内外表面の少なくとも一方に０．００１〜０．１μｍ、好ましくは０．００５〜０．０５μｍの平均孔径をもつ緻密な膜表面を有していることが望ましい。前記平均孔径の範囲は、分画分子量に換算すると３万〜１５０万、好ましくは５万〜５０万に相当する。
【００１８】
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。
【００１９】
本発明の酢酸セルロースの製造法は、例えば、セルロースをトリフェニルメチル化すると６位の水酸基に選択的に導入されるため、トリフェニルメチル化によりセルロース（又は低置換酢酸セルロース）の６位を保護した後、アセチル化を行い、その後、脱トリフェニルメチル化する方法が挙げられるが、特に限定されるものではない。
【００２０】
本発明の酢酸セルロース系半透膜の製造法は、例えば、酢酸セルロースを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−ピロリドン等の極性有機溶媒に溶解した製膜ドープ、或いはこの製膜ドープにエチレングリコール、ポリエチレングリコール、グリセリン等の貧溶媒、又は塩化リチウム、塩化カリウム、硝酸リチウム等の金属塩等を添加した製膜ドープを相分離させる方法が挙げられる。相分離の方法は、製膜ドープを水等の非有機溶媒に接触させる非有機溶媒誘起相分離が挙げられるが、熱誘起相分離を用いてもよい。
【００２１】
本発明の酢酸セルロース系半透膜は、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。
【００２２】
次に、本発明の酢酸セルロース系半透膜を用いた濾過運転方法について説明するが、濾過運転方法には特別なものはなく、例えば、外圧式の中空糸膜にした場合には、通常外圧式の中空糸膜を用いた場合に適用される濾過運転条件を適用することができる。
【００２３】
本発明の濾過運転方法においても、通常の濾過運転と同様にして透過水側から原水側に向けて定期的に逆圧洗浄することが望ましく、その際には、濃度３〜５ｍｇ／Ｌの次亜塩素酸ナトリウム水溶液により逆圧洗浄することができる。
【００２４】
【実施例】
以下に、実施例に基づいて本発明をより詳細に説明するが、本発明はこれらの実施例によって限定されるものではない。
【００２５】
実施例１
セルロース１００質量部に対して、硫酸７．８質量部、無水酢酸２６０質量部及び酢酸４００質量部を加え、４０℃で４０分間アセチル化を行った。その後、反応物を大過剰の水により沈殿、洗浄、乾燥し、ジメチルスルホキシド（ＤＭＳＯ）１５００質量部に溶解させた。これに、ヒドラジン１水和物２７質量部とＤＭＳＯ１００質量部の混合物を加え、５０℃で５時間、部分加水分解を行った。その後、反応物を大過剰の水により、沈殿、洗浄、乾燥し、反応物（Ａ）を得た。
【００２６】
次に、この反応物（Ａ）１００質量部をピリジン３０００質量部に１００℃で溶解し、これに塩化トリフェニルメチル８．５質量部を加え、９０℃で２５時間攪拌し、トリフェニルメチル化を行った。その後、４−ジメチルアミノピリジン９０質量部及び無水酢酸５０質量部を加え、６０℃で２０時間攪拌して、アセチル化を行った。
【００２７】
その後、反応物を大過剰の水により沈殿後、１０００質量部のメタノールによる洗浄を３回行った。反応物を乾燥後、クロロホルム３０００質量部に溶解した。これに３０質量％臭化水素酸の酢酸溶液４０質量部を加え、２５℃で５分間攪拌することにより、脱トリフェニルメチル化を行った。反応物を大過剰の水により沈殿後、１０００質量部のメタノールによる洗浄を３回行い、乾燥することで、本発明の酢酸セルロースを得た。
【００２８】
上記で得た酢酸セルロース１７質量部にＤＭＳＯ８３質量部を加え、９０℃で溶解し、これを濾過、脱泡して製膜ドープを得た。この製膜ドープを９０℃に加熱して、二重円筒管ノズルの外筒部に供給し、７０℃の水を内筒部に供給し、空中を１秒間通過させた後、７５℃の水浴中を通過させて中空糸膜を得た。
【００２９】
得られた中空糸膜のアセチル置換度は、^１３Ｃ−ＮＭＲ法により求めた。次式にグルコース環の各炭素位置を示した。
【００３０】
【化１】

【００３１】
２、３、６位のアセチル置換度は、T.Sei etal,Polymer.J.,17,1065(1985)に記載された方法で、^１３Ｃ−ＮＭＲスペクトルの測定結果により決定した。即ち、それぞれの置換度は各位の炭素シグナルのうち、アセチル基で置換されているもののシグナルの面積割合から計算した。また、全構成単位のアセチル置換度の合計は、各位の置換度を合計した。
【００３２】
得られた中空糸膜は、全構成単位における２位、３位及び６位のアセチル置換度の合計が２．８４で、かつ６位のアセチル置換度が０．８６であった。
【００３３】
この中空糸膜について、下記の方法で次亜塩素酸ナトリウム水溶液に対する耐久性を試験した。中空糸膜を有効塩素濃度１０００ｍｇ／Ｌの次亜塩素酸ナトリウム水溶液に浸漬し、浸漬された中空糸膜を経時的にサンプリングして、この中空糸膜の引張破断点強度（ＪＩＳＫ７１１３）を測定した。耐久性は、引張破断点強度の低下率として引張破断点強度の変化の傾きから求めた。即ち、この低下率が小さいほど耐久性が高いことを意味する。中空糸膜の引張破断点強度の低下率は０．９ｇ／時であった。
【００３４】
比較例１
アセチル置換度が異なるほかは実施例１と同じ性状の中空糸膜（全構成単位における２位、３位及び６位のアセチル置換度の合計が２．９０で、かつ６位のアセチル置換度が０．９３）を用い、同様にして次亜塩素酸ナトリウム水溶液に対する耐久性を試験した。中空糸膜の引張破断点強度の低下率は１．５ｇ／時であった。
【００３５】
【表１】

【００３６】
実施例２
実施例１で得られた中空糸膜を充填した膜モジュール（有効膜面積０．５ｍ^２）により、下記の方法で揖保川河川水の濾過試験を行った。
【００３７】
河川水を中空糸膜モジュールの外側に供給する外圧式のクロスフロー濾過（濾過圧力５０ｋＰａ）を行った。膜濾過水を用い、膜透過側から４５分おきに１分間の逆圧洗浄を行った。この際、逆圧洗浄水となる膜濾過水には、次亜塩素酸ナトリウム水溶液を有効塩素濃度が５０ｍｇ／Ｌとなるように注入し、膜の耐塩素性を測定した。その結果、約１年間の膜濾過運転の後も中空糸膜が切断されることなく、安定した運転ができた。
【００３８】
【発明の効果】
本発明の酢酸セルロース系半透膜は、塩素系殺菌剤に対する耐久性と生分解性され難いという性質を有しており、特に天然水の濾過処理用として適している。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cellulose acetate semipermeable membrane particularly suitable for water treatment in natural water areas such as rivers and lakes, and a filtration operation method using the same.
[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 (for example, Japanese Patent Laid-Open Nos. 54-88881, 61-185305, 60). No. -29763, JP-A 63-17922, JP-A 5-228208, JP-A 6-343842) and other cellulose acetate hollow fiber membranes used for water treatment are disclosed in No. 343842, JP-A-8-108053, and the like.
[0003]
When a cellulose acetate membrane is used for purification of natural water such as river water, groundwater, lake water, seawater, etc., there is a problem that the membrane is biodegraded by microorganisms in the raw water. Therefore, in purification of natural water using a cellulose acetate hollow fiber membrane, sterilization with sodium hypochlorite is usually performed constantly or intermittently, and it is necessary to prevent biodegradation of the membrane. There is also a problem that the film strength itself is lowered by the sterilization treatment with sodium hypochlorite.
[0004]
The present invention is a chlorine-based disinfectant such as sodium hypochlorite that can solve the problem of reduction in film strength when the cellulose acetate film as described above is sterilized with a chlorine-based disinfectant such as sodium hypochlorite. It is an object of the present invention to provide a cellulose acetate semipermeable membrane having high durability against water and a filtration operation method using the same.
[0005]
[Means for Solving the Problems]
The present inventor has studied to increase the durability of a cellulose acetate-based semipermeable membrane with respect to a chlorine-based disinfectant such as sodium hypochlorite. As a result, the substitution degree of acetyl groups substituted with three OH groups in the cellulose acetate unit It was found that the durability against a chlorine-based disinfectant can be greatly enhanced by adjusting the amount to a specific range, and the present invention has been completed.
[0006]
The present invention is a cellulose acetate-based semipermeable membrane made of a membrane material containing cellulose acetate, and the cellulose acetate as the membrane material has a total acetyl substitution degree of 2nd, 3rd and 6th positions in the structural unit of 2. A cellulose acetate-based semipermeable membrane having 70 or more and a 6-position acetyl substitution degree of 0.90 or less is provided.
[0007]
Furthermore, this invention provides the filtration driving | operation method which water-processes using said cellulose acetate type semipermeable membrane.
[0008]
In the present invention, “the total degree of acetyl substitution at the 2nd, 3rd and 6th positions in all structural units is 2.70 or more and the degree of acetyl substitution at the 6th position is 0.90 or less” It means that all the structural units satisfy the above requirements.
[0009]
The degree of acetyl substitution in the present invention means the average number of substituted OH groups per cellulose constitutional unit, and was determined by ¹³ C-NMR method described in Examples.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The cellulose acetate-based semipermeable membrane of the present invention is composed of a membrane material mainly composed of cellulose acetate, and a mixture of cellulose acetate and other cellulose derivatives can also be used as a membrane material. The amount is preferably 80% by weight or more, more preferably 90% by weight or more based on the raw material. Examples of other cellulose derivatives include cellulose ester compounds such as cellulose butyrate, and cellulose ether compounds such as methyl cellulose and ethyl cellulose. Furthermore, polysulfone polymers, polyacrylonitrile polymers, polyamide polymers, polyvinyl pyrrolidone, polyvinyl formal, etc. Can also be used together.
[0011]
The cellulose acetate used as the membrane material has a total of the acetyl substitution degree at the 2nd, 3rd and 6th positions in all the structural units of 2.70 or more, preferably 2.80 or more, more preferably 2.85 or more, and 6 The degree of acetyl substitution at the position is 0.90 or less, preferably 0.88 or less.
[0012]
Furthermore, the cellulose acetate used as the membrane material preferably has a acetyl substitution degree at the 2nd and 3rd positions of all structural units of 1.92 to 2.00, more preferably 1.96 to 1.99. Those of 1.97 to 1.99 are more preferred.
[0013]
The cellulose acetate semipermeable membrane of the present invention can be formed into a desired form such as a hollow fiber membrane, a flat membrane, a tubular membrane, etc. Among them, a hollow fiber membrane is particularly preferable.
[0014]
When making a hollow fiber membrane, the outer diameter is preferably 200 to 2000 μm, more preferably 500 to 1500 μm, and the inner diameter is preferably 100 to 1000 μm, in order to impart mechanical strength and water permeability in a balanced manner. More preferably, it is 400-1000 micrometers , The average hole diameter of the void | hole which exists in the film | membrane except an inner surface and an outer surface becomes like this. Preferably it is 0.5-5 micrometers, More preferably, it is 0.8-3 micrometers.
[0015]
The average pore size inside the membrane was taken at 10 points at equal intervals from the inner surface of the membrane to the outer surface of the membrane (10,000 magnifications), and the diameter of the pores found in a 5 μm square on each photo. Are averaged, and the average value is averaged over 10 photographing sections.
[0016]
In consideration of mechanical strength and water permeability, the hollow fiber membrane preferably has pores with a pore diameter of 10 μm or more inside.
[0017]
The hollow fiber membrane desirably has a dense membrane surface having an average pore diameter of 0.001 to 0.1 μm, preferably 0.005 to 0.05 μm, on at least one of the inner and outer surfaces. The range of the average pore diameter corresponds to 30,000 to 1,500,000, preferably 50,000 to 500,000 in terms of the molecular weight cut-off.
[0018]
In the hollow fiber membrane, 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.
[0019]
In the method for producing cellulose acetate of the present invention, for example, when cellulose is triphenylmethylated, it is selectively introduced into the hydroxyl group at the 6-position, so that the 6-position of cellulose (or low-substituted cellulose acetate) is protected by triphenylmethylation. Then, acetylation is performed, followed by detriphenylmethylation, but there is no particular limitation.
[0020]
The method for producing a cellulose acetate-based semipermeable membrane of the present invention includes, for example, a membrane dope obtained by dissolving cellulose acetate in a polar organic solvent such as dimethyl sulfoxide, dimethylacetamide, N-methyl-2-pyrrolidone, or the membrane dope. Examples thereof include a method of phase-separating a film-forming dope to which a poor solvent such as ethylene glycol, polyethylene glycol or glycerin or a metal salt such as lithium chloride, potassium chloride or lithium nitrate is added. Examples of the phase separation method include non-organic solvent-induced phase separation in which the film-forming dope is brought into contact with a non-organic solvent such as water, but heat-induced phase separation may be used.
[0021]
The cellulose acetate-based semipermeable membrane of the present invention is particularly suitable for purifying natural water such as river water, groundwater, lake water, seawater, etc. Can be applied.
[0022]
Next, the filtration operation method using the cellulose acetate-based semipermeable membrane of the present invention will be described. However, there is no special filtration operation method. For example, when an external pressure type hollow fiber membrane is used, it is usually outside. The filtration operation condition applied when using a pressure type hollow fiber membrane can be applied.
[0023]
Also in the filtration operation method of the present invention, it is desirable to perform regular back-pressure washing from the permeate side to the raw water side in the same manner as in the normal filtration operation, in which case the next concentration of 3 to 5 mg / L Back pressure washing can be performed with an aqueous sodium chlorite solution.
[0024]
【Example】
Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.
[0025]
Example 1
To 100 parts by mass of cellulose, 7.8 parts by mass of sulfuric acid, 260 parts by mass of acetic anhydride and 400 parts by mass of acetic acid were added, and acetylation was performed at 40 ° C. for 40 minutes. Thereafter, the reaction product was precipitated, washed and dried with a large excess of water, and dissolved in 1500 parts by mass of dimethyl sulfoxide (DMSO). A mixture of 27 parts by mass of hydrazine monohydrate and 100 parts by mass of DMSO was added thereto, and partial hydrolysis was performed at 50 ° C. for 5 hours. Thereafter, the reaction product was precipitated, washed and dried with a large excess of water to obtain a reaction product (A).
[0026]
Next, 100 parts by mass of this reaction product (A) is dissolved in 3000 parts by mass of pyridine at 100 ° C., 8.5 parts by mass of triphenylmethyl chloride is added thereto, and the mixture is stirred at 90 ° C. for 25 hours to triphenylmethylated. Went. Thereafter, 90 parts by mass of 4-dimethylaminopyridine and 50 parts by mass of acetic anhydride were added, and the mixture was stirred at 60 ° C. for 20 hours for acetylation.
[0027]
Thereafter, the reaction product was precipitated with a large excess of water, and then washed with 1000 parts by mass of methanol three times. The reaction product was dried and then dissolved in 3000 parts by mass of chloroform. To this, 40 parts by mass of a 30% by mass hydrobromic acid acetic acid solution was added, and the mixture was stirred at 25 ° C. for 5 minutes for detriphenylmethylation. The reaction product was precipitated with a large excess of water, washed with 1000 parts by mass of methanol three times, and dried to obtain the cellulose acetate of the present invention.
[0028]
83 parts by mass of DMSO was added to 17 parts by mass of the cellulose acetate obtained above and dissolved at 90 ° C., and this was filtered and degassed to obtain a film forming dope. The film-forming dope is heated to 90 ° C., supplied to the outer cylinder portion of the double cylindrical tube nozzle, 70 ° C. water is supplied to the inner cylinder portion, allowed to pass through the air for 1 second, and then a 75 ° C. water bath. A hollow fiber membrane was obtained by passing through the inside.
[0029]
The degree of acetyl substitution of the obtained hollow fiber membrane was determined by ¹³ C-NMR method. Each carbon position of the glucose ring is shown in the following formula.
[0030]
[Chemical 1]

[0031]
The degree of acetyl substitution at positions 2, 3, and 6 was determined by the measurement result of ¹³ C-NMR spectrum by the method described in T. Sei etal, Polymer. J., 17, 1065 (1985). That is, the degree of substitution was calculated from the area ratio of the carbon signal at each position, which was substituted with an acetyl group. Further, the total degree of acetyl substitution of all structural units was the sum of the degree of substitution at each position.
[0032]
The obtained hollow fiber membrane had a total of 2.84 acetyl substitution degrees at the 2nd, 3rd and 6th positions in all the structural units and a 6th acetyl substitution degree of 0.86.
[0033]
This hollow fiber membrane was tested for durability against an aqueous sodium hypochlorite solution by the following method. The hollow fiber membrane is immersed in an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 1000 mg / L, the immersed hollow fiber membrane is sampled over time, and the tensile strength at break (JIS K7113) of the hollow fiber membrane is measured. did. The durability was determined from the slope of the change in tensile strength at break as the rate of decrease in tensile strength at break. That is, the smaller the decrease rate, the higher the durability. The rate of decrease in tensile strength at break of the hollow fiber membrane was 0.9 g / hour.
[0034]
Comparative Example 1
A hollow fiber membrane having the same properties as in Example 1 except that the degree of acetyl substitution is different (the total degree of acetyl substitution at the 2nd, 3rd and 6th positions in all structural units is 2.90, and the degree of acetyl substitution at the 6th position is 0.93) and was similarly tested for durability against an aqueous sodium hypochlorite solution. The rate of decrease in tensile strength at break of the hollow fiber membrane was 1.5 g / hour.
[0035]
[Table 1]

[0036]
Example 2
By using the membrane module (effective membrane area 0.5 m ² ) filled with the hollow fiber membrane obtained in Example 1, a filtration test of Shibogawa river water was conducted by the following method.
[0037]
External pressure type cross flow filtration (filtration pressure 50 kPa) for supplying river water to the outside of the hollow fiber membrane module was performed. Using membrane filtered water, back pressure washing was performed for 1 minute every 45 minutes from the membrane permeation side. At this time, a sodium hypochlorite aqueous solution was injected into the membrane filtered water serving as the reverse pressure washing water so that the effective chlorine concentration was 50 mg / L, and the chlorine resistance of the membrane was measured. As a result, after the membrane filtration operation for about one year, the hollow fiber membrane was not cut and stable operation was possible.
[0038]
【The invention's effect】
The cellulose acetate semipermeable membrane of the present invention has the property of being durable against chlorinated fungicides and hardly biodegradable, and is particularly suitable for natural water filtration.

Claims

A cellulose acetate semipermeable membrane made of a membrane material containing cellulose acetate, wherein the cellulose acetate as the membrane material has a total of 2.70 or more of the degree of acetyl substitution at the 2nd, 3rd and 6th positions in all structural units And a cellulose acetate-based semipermeable membrane having a 6-position acetyl substitution degree of 0.90 or less.

The cellulose acetate-based semipermeable membrane according to claim 1, wherein the cellulose acetate as the membrane material has a total acetyl substitution degree at the 2-position and the 3-position of all structural units of 1.92 to 2.00.

The cellulose acetate semipermeable membrane according to claim 1 or 2, which is a hollow fiber membrane.

4. The acetic acid according to claim 3, wherein the hollow fiber membrane has an outer diameter of 200 to 2000 [mu] m, an inner diameter of 100 to 1000 [mu] m, and an average pore diameter of pores existing inside the membrane excluding the inner surface and the outer surface is 0.5 to 5 [mu] m. Cellulosic semipermeable membrane.

The cellulose acetate semipermeable membrane according to claim 3 or 4, wherein the hollow fiber membrane has pores having a pore diameter of 10 µm or more.

The cellulose acetate semipermeable membrane according to any one of claims 3 to 5, wherein a dense layer is provided on at least one of an inner surface and an outer surface of the hollow fiber membrane.

The cellulose acetate semipermeable membrane according to any one of claims 1 to 6, which is an ultrafiltration membrane having a fractional molecular weight of 30,000 to 1,500,000.

The cellulose acetate semipermeable membrane according to any one of claims 1 to 7, which is used for treatment of natural water.

The filtration driving | operation method which water-processes using the cellulose acetate type semipermeable membrane of any one of Claims 1-7.

The filtration operation method according to claim 9, wherein an external pressure type hollow fiber membrane module is used.

The filtration operation method according to claim 9 or 10, wherein, in the filtration operation, the backwashing is periodically performed from the permeate side to the raw water side of the cellulose acetate semipermeable membrane using permeate.

The filtration operation method according to claim 9, 10 or 11, wherein the backwashing is performed with a sodium hypochlorite aqueous solution having a concentration of 3 to 5 mg / L.