JP3386904B2 - Cellulose acetate hollow fiber separation membrane and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a cellulose acetate hollow fiber separation membrane used for ultrafiltration in water treatment such as water purification treatment, sewage treatment and wastewater treatment, and separation / purification and concentration operation of solution in chemical industry and pharmaceutical industry. And the manufacturing method thereof. In particular, the present invention relates to a cellulose acetate hollow fiber separation membrane having an excellent balance of mechanical properties and an improved water permeation rate, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a technique using a separation membrane in a separation operation has made remarkable progress and has been put to practical use in various applications.

As a material for such a separation membrane, for example, polysulfone-based, polyacrylonitrile-based, polyvinyl alcohol-based, polyimide-based resin, etc. are used.
In particular, polysulfone-based resins are widely used because of their excellent physical and chemical properties such as heat resistance, acid resistance, and alkali resistance, and their ease of film formation.

However, when a separation membrane made of a hydrophobic material such as a polysulfone resin is used for water treatment, polymer substances, colloids and fine particles in the water to be treated are adsorbed on the membrane surface or inside the membrane pores. However, there is a problem that the filtration rate is remarkably decreased over time due to contamination of the membrane and clogging (membrane fouling). Therefore, in order to prevent these solute substances from adsorbing on the membrane surface and the membrane pores, a hydrophilic polymer is blended with the membrane material which is a hydrophobic polymer (Japanese Patent Laid-Open No. 56-1).
55243), or coating the surface of a hydrophobic substance with a hydrophilic polymer (JP-A-61-268302).
A method for modifying the separation membrane has been proposed.

On the other hand, when a separation membrane of cellulose resin, which is a conventionally known hydrophilic polymer material, is used, adsorption of solute to the membrane is difficult to occur, so that the filtration rate in the water system with time elapses. It has the characteristic that the decrease is small. For example, a cellulose acetate or a regenerated cellulose membrane is used as a hemodialysis membrane because it has a small decrease in filtration rate with time when plasma is filtered and has little adsorption of plasma, proteins and the like. Similarly, the cellulose acetate reverse osmosis membrane is
It has been used for a long time for desalination of seawater, and it has been confirmed that the decrease in filtration rate over time is small (basic of synthetic membrane, Synthetic Polymeric Membranes, etc.).

However, even if such a cellulosic resin is used as a membrane material, in the case of a reverse osmosis membrane in which the separation active layer of the membrane is very dense and the pore size of the membrane is as small as 0.001 μm or less,
The water resistance of the membrane is high and therefore the filtration rate is significantly reduced. There is a reverse osmosis membrane disclosed in Japanese Examined Patent Publication No. 58-24164, etc., but generally, a membrane having such a dense structure is used, and in order to increase the filtration rate, the operating pressure is 10 kg.
/ Cm ² or more must be in a high pressure, not only the energy cost is increased, or result in a decrease in the water permeation speed film is compacted during filtration operation, such as or cause mechanical membrane damage The problem arises.

Further, even when the liquid to be treated is separated by an ultrafiltration membrane for polymer substances, colloidal fine particles and viruses, it is the smallest membrane, although it does not have a dense membrane structure as a reverse osmosis membrane. It may be difficult to obtain a sufficiently high filtration rate because the separation active layer having a pore size has the highest water permeation resistance.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the drawbacks of the conventional membrane structure as described above and to obtain a hollow fiber separation membrane capable of maintaining a high filtration rate for a long time even under a low filtration pressure. The present invention also provides a novel membrane structure of an ultrafiltration hollow fiber separation membrane using cellulose acetate, which is a hydrophilic polymer membrane material, as a membrane material, and a method for producing the same.

The structure of the cellulose acetate ultrafiltration hollow fiber separation membrane has hitherto been disclosed in JP-B-62-29524.
Although disclosed in Japanese Patent No. 3-5847, all of them have a uniform three-dimensional network structure in cross-section, and because of the absence of a void layer, the water permeation resistance becomes extremely large, and a high filtration rate can be obtained. I can't. Further, as disclosed in Japanese Patent Publication No. 56-58005, etc., even when voids are included in the membrane cross section, the thickness of the dense layer portion near both the inner and outer surfaces of these hollow fiber membranes is 3 μm.
Since it is larger, the filtration rate becomes smaller. Also, Japanese Patent Publication No. 58-58005 discloses a hollow fiber membrane having a porous sponge structure and circular voids coexisting with the porous sponge structure on the inner surface of the membrane.
High water permeability of (m ² · hr) / (kg / cm ² ) or more cannot be obtained. Many proposals have been made so far regarding a method for producing a cellulose acetate hollow fiber separation membrane. Particularly, as an example of adding a metal-containing additive to a membrane forming solution, Japanese Patent Publication Nos. 57-59253 and 59-4164 are disclosed. , JP-B-60-43442, etc., but all have a uniform membrane structure without a void layer, so that the pure water permeation rate is 500 liters / (m ² ·
It has not been possible to obtain a separation membrane having a high value of hr) / (kg / cm ² ) or more.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors increased the porosity of the hollow fiber membrane cross section, decreased the water permeation resistance, and increased the water permeation rate. In order to achieve this, a void portion is provided on the membrane cross section, and the porosity of the three-dimensional mesh-like porous structure portion continuous with the dense layers on both the inner and outer surfaces of the membrane is immediately measured from the vicinity of both the inner and outer surfaces of the membrane.
The porosity was increased to 40 to 80%, and the porosity was increased so as to be averaged in this range in all parts, and a separation membrane having a relatively uniform pore size distribution in the porous voids was obtained.

That is, according to the present invention, the cross section of the hollow fiber membrane having a membrane thickness of 50 to 500 μm has a three-dimensional reticulated porous portion having an average pore diameter of 0.05 to 1 μm and a size of 10 to 200 μm. The void area of the membrane is in the range of 5 to 70% with respect to the total cross-sectional area of the membrane, and the inner and outer surfaces of the hollow fiber membrane have irregular or circular micropores. The three-dimensional mesh-like porous portion of the cross section of the membrane has a substantially uniform porosity of 40 to 80% in all ranges except both the inner and outer surfaces of the hollow fiber membrane within 1/50 of the total membrane thickness. With a molecular weight cut-off in the range of 10,000 to 500,000, a tensile strength at break of the membrane of 30 kg / cm ² or more, and a transmembrane pressure difference of 1 kg / cm ² , temperature
Permeation rate of pure water at 25 ℃ is 500 liters / (m ² · h
r) A cellulose acetate hollow fiber separation membrane having the above characteristics.

Further, according to the present invention, 10 to 30% by weight of cellulose acetate having an acetylation degree of 53 to 62% and an average degree of polymerization of 100 to 500 and Group I to III of the periodic table. 0.05 to 5 mol / kg of a metal compound belonging to the above are dissolved in a water-soluble polar organic solvent having a boiling point of 100 ° C. or more to dissolve both the cellulose acetate and the additive to prepare a film-forming solution, and the film-forming solution is a double tube. Discharge from the outer tube of the mold spinneret at 80 to 140 ° C and the internal coagulation liquid at 30 to 80 ° C from the center of the spinneret.
The present invention provides a method for producing the above cellulose acetate hollow fiber separation membrane, which comprises coagulating in a coagulation bath at -80 ° C.

The three-dimensional network porous structure in the present invention means that pores having a size of 0.05 to 1 μm, which are larger than the micropore diameter of the dense layer formed on the surface of the hollow fiber membrane, are substantially inside the membrane. It refers to a structure formed as a three-dimensional network, and can give the hollow fiber separation membrane a large physical strength and elongation.

In the present invention, the three-dimensional mesh-like porous structure having a uniform pore size extends to the vicinity of both the inner and outer surfaces of the membrane, substantially within 1/50 of the total thickness from the inner and outer surfaces. It has a high porosity (40-80%) that is almost uniform in all areas except the area, so that the pore size of the three-dimensional mesh-like porous structure of the conventional membrane gradually increases from the membrane surface to the inside. The filtration resistance of the dense layers on both surface sides is extremely reduced at the same time on both surface sides, compared to the one having a continuously increasing inclined type porous layer on at least one surface side. The water permeation rate can be increased without deteriorating the strength.

The present invention is characterized in that an extreme porosity drop is formed between the inner and outer surface portions and the three-dimensional network-like porous structure portion. The presence of voids and high water permeability are characteristic. Has been achieved.

The void in the present invention is larger than the above-mentioned three-dimensional mesh-like void, and is substantially 10
It means circular or elliptical pores having a size of ˜200 μm and showing almost no filtration resistance to the permeated fluid. The void may penetrate either the outer surface side or the inner surface side, but it is preferable that it does not penetrate from the viewpoint of film strength. When the voids are present in the three-dimensional mesh-like porous structure, many voids are present inside the membrane, and the area occupied by all the voids present in the cross section of the hollow fiber membrane can be increased and the water permeation rate can be increased. On the other hand, the mechanical strength such as tensile strength and internal pressure burst pressure of the membrane is lowered.
Therefore, the area occupied by all voids present in the cross section of the hollow fiber membrane may be 5 to 70% with respect to the cross sectional area of the hollow fiber membrane, and if the balance between the water permeation rate and the mechanical strength of the membrane is considered, It is more preferably in the range of up to 50%.

Further, in the hollow fiber separation membrane of the present invention, in order to prevent suspended particles in the liquid to be treated from entering the inside of the membrane to be clogged, resulting in a decrease in the water permeation rate, the inner and outer surfaces of the membrane are not covered. It has a dense layer with regular or circular micropores, but if the average pore size of these micropores is too small, a practical water permeation rate cannot be obtained, and if the surface average pore size is too large, it will prevent suspended substances. Will be insufficient. Therefore, the surface average pore diameter of the dense layer may be substantially 0.001 to 0.05 μm, preferably
It may be in the range of 0.005 to 0.03 μm. As a comprehensive separation characteristic of the hollow fiber separation membrane of the present invention, a molecular weight cutoff of 10,000 to 500,000 is suitable.

The membrane thickness of the hollow fiber separation membrane of the present invention is adjusted in the range of 50 to 500 μm in order to obtain a larger membrane mechanical strength and a larger water permeation rate. Film thickness is 50 μm
If it is less than the above range, the mechanical strength is inferior, and there is a possibility of causing a serious trouble of causing a leak due to a mechanical impact during the filtration process. If it exceeds 500 μm, the mechanical strength of the membrane will increase, but as the membrane pressure increases, the filtration resistance will increase and the water permeability will decrease. 100 to 400 μ
The range of m is more preferable.

The mechanical strength necessary for the hollow fiber separation membrane obtained by the present invention to withstand long-term use without causing membrane damage is that the tensile strength at break is 30 kg / cm ^2.
It is desirable that the tensile elongation at break is 20% or more, and the permeation rate of pure water at a transmembrane pressure difference of 1 kg / cm ² and a temperature of 25 ° C is 500 liters / (m ² · hr). The above is desirable.

The three-dimensional network porous structure, the pore size of voids, and the occupied area% of voids per membrane cross-sectional area are evaluated by electron micrographs. The average pore diameter and thickness of the dense layer are evaluated by electron micrographs, and the thickness of the dense layer is usually in the range of 0.1 to 5 μm. .

The above-mentioned cellulose acetate hollow fiber separation membrane can be manufactured as follows. Cellulose acetate, as long as it is soluble in an ordinary organic solvent, usually has an acetylation degree of 40 to
Although it is in the range of 62%, those having an acetylation degree in the range of 53 to 62%, which are excellent in microbial decomposition resistance and chemical properties, are preferably used in the present invention. The average degree of polymerization is
The one used is 100 to 500, preferably 150 to 350.

In the present invention, as a membrane forming solution for producing a hollow fiber separation membrane, cellulose acetate is dissolved in a polar organic solvent so that the added weight thereof is 10 to 30% by weight based on the total weight of the membrane forming solution. It is preferable to obtain the desired film. Increasing the added weight of cellulose acetate increases the viscosity of the membrane forming solution, and the membrane forming solution may cause phase separation during long-term storage. In addition, since the film structure obtained in this case is generally a dense structure with a small porosity,
Its permeation rate becomes smaller. On the other hand, when the concentration of cellulose acetate added is low, the proportion of voids in the cross section of the film is large and sufficient mechanical strength of the film cannot be obtained. From the above points, the weight composition of cellulose acetate in the film forming solution is 15
It is desirable to be in the range of up to 23% by weight.

The solvent of cellulose acetate is a water-soluble polar organic solvent, and its boiling point is selected from the solvents having a boiling point of 100 ° C. or higher. For example, 1,4-dioxane, dimethyl sulfoxide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, 2-pyrrolidone, γ-butyl lactone, and the like, and mixed solutions thereof, among which the target structure is To obtain it, it is desirable to use dimethylsulfoxide and N-methyl-2-pyrrolidone, which have good solubility.

The metal compound added when the cellulose acetate is dissolved using the above-mentioned solvent is composed of a metal belonging to Group I to III of the periodic table, and includes alkali metal, alkaline earth metal, boron and aluminum. Examples include selected metal acetates, nitrates, chlorates, thiocyanates, halides and hydrates thereof. Examples of such metal compounds include calcium chloride, calcium nitrate, calcium bromide, calcium acetate, calcium iodide, potassium nitrate, potassium bromide, barium chloride,
Examples thereof include barium nitrate, aluminum chloride, lithium chloride, lithium nitrate, lithium acetate, magnesium chloride, magnesium nitrate, and magnesium acetate. Of these, lithium chloride, magnesium chloride, lithium acetate, and magnesium acetate having particularly high solubility are preferable.

When these metal compounds are present in the stock solution for film formation, cations are bonded to the hydroxyl groups or ester groups of cellulose acetate, which is nucleophilic, during microphase separation,
The spherical aggregates of cellulose acetate molecules are positively charged, and the aggregates repel each other. Such aggregates already have a fairly uniform size, and it is considered that when they are gelled by phase separation, a three-dimensional network structure having a uniform pore size is formed inside the membrane.

When the amount of the metal compound added is small, it is not possible to improve the water permeation rate by increasing the porosity. Moreover, the viscosity of the film-forming solution increases as the amount of addition increases, and film formation gradually becomes difficult. Therefore, the addition amount is 0.05 to 5 mol / kg, preferably 0.1 to 2 mol / kg, based on the total weight of the film forming solution. The latter is about 0.3-10% by weight, based on the total weight of the film-forming solution.
Equivalent to.

In producing a hollow fiber separation membrane from the above membrane forming solution, a conventionally used separation membrane production method can be adopted. That is, the hollow fiber membrane can be obtained by extruding the membrane forming solution from the outer tube of the double-tube nozzle, causing the inner coagulating liquid to flow out from the inner tube, and coagulating in a coagulating bath by dry-wet spinning or wet spinning. . The spinning temperature of the film-forming solution from the nozzle varies depending on the type of raw resin,
Usually, the temperature is 30 to 150 ° C, but the higher the degree of polymerization and the higher the degree of acetylation, the higher the viscosity, so it is necessary to spin at a relatively high temperature. Degree of polymerization is 150
In the range of to 350, 80 to 140 ° C is preferable. The internal coagulating liquid temperature or coagulating bath temperature is preferably 30 to 80 ° C,
If it is lower than 30 ° C, a dense layer is thickly formed on the surface of the membrane, and the desired filtration rate cannot be obtained. If it exceeds 80 ° C, spinning becomes difficult and the membrane-forming efficiency is deteriorated, so that a normal hollow fiber cannot be obtained. In the case of dry-wet spinning, the dry portion distance between the nozzle discharge surface and the coagulation bath surface is preferably 0.1 to 50 cm, preferably 0.5 to 30 cm, and after passing in air for 0.2 seconds or longer, it is introduced into the coagulation bath. Good.

The internal coagulation liquid or the external coagulation liquid used for film formation is a non-solvent of cellulose acetate, is compatible with the solvent of cellulose acetate, and has a function of coagulating the film formation solution. As the internal coagulation liquid, water, ethylene glycol, polyethylene glycol, glycerin, or the like and a mixed solution of two or more thereof are used. As the external coagulation liquid, in addition to the above-mentioned ones, water is particularly preferably used.

[0029]

EXAMPLES The present invention will be described in more detail based on the following examples.

The performance of the hollow fiber separation membrane of the present invention was evaluated by measuring the water permeation rate, molecular weight cutoff and tensile strength at break / elongation by the following methods.

(1) A water pressure of 1 kg / cm ² was applied from the inside to a hollow fiber membrane having an effective length of water permeation rate of 50 cm with pure water at 25 ° C., and the amount of filtered pure water was measured (based on the inner surface area).

(2) Fractionated molecular weight Various proteins having different molecular weights were used as standard solutes, the exclusion rate for each membrane was measured, and the relationship between the molecular weight and the exclusion rate was plotted in a graph. From the obtained molecular weight exclusion rate curve, ,
The molecular weight corresponding to the exclusion rate of 95% was determined and used as the molecular weight cutoff.

(3) Tensile breaking strength / elongation A hollow fiber membrane test piece with an effective sample length of 5 cm was applied to a crosshead of 10 mm.
Cross-sectional area of the sample 1
It was converted per cm ² and its elongation was measured.

Example 1 Cellulose acetate (acetylation degree: 61.3%, average degree of polymerization 280, manufactured by Daicel Chemical Industries, Ltd.) 20% by weight, lithium chloride 1% by weight
(0.32mol / kg), dimethyl sulfoxide 80% by weight at 80 ℃
After dissolving with stirring with, a membrane-forming solution was obtained by filtration. This film-forming solution was discharged from the outer tube of the double-tube type spinneret and water was discharged from the inner tube as an internal coagulating solution, and spinning was performed at a winding speed of 7 m / min. After passing through air for 1.7 seconds, it was solidified from both surfaces in a coagulating water bath at 70 ° C, then immersed in water and desolvated to obtain a hollow fiber separation membrane with an inner diameter of 0.8 mm and an outer diameter of 1.3 mm. . The obtained membrane has an inner surface average pore diameter of 0.09.
A film having a thickness of μm and a tensile strength at break of 44 kg / cm ² was obtained. The evaluation results are shown in Table 1. The average pore diameter and porosity of the obtained membrane are shown in FIGS. 1 and 2, and electron micrographs of the obtained membrane cross section at magnifications of 200 and 10,000 are shown in FIGS.

Example 2 In Example 1, 19% by weight of cellulose acetate (acetylation degree: 61.3%, average degree of polymerization 280, manufactured by Daicel Chemical Industries, Ltd.), magnesium chloride 1% by weight (0.14 mol / kg), dimethyl sulfoxide 80 A hollow fiber membrane was produced in the same manner as in Example 1 except that a weight% membrane-forming solution was used. The evaluation results of the obtained film are shown in Table 1.

Example 3 In Example 1, 19% by weight of cellulose acetate (acetylation degree: 61.3%, average degree of polymerization 280, manufactured by Daicel Chemical Industries, Ltd.), magnesium acetate 1% by weight (0.20 mol / kg), dimethyl sulfoxide 80 A hollow fiber membrane was produced in the same manner as in Example 1 except that a weight% membrane-forming solution was used. The evaluation results of the obtained film are shown in Table 1.

Comparative Example 1 Carried out in Example 1 except that cellulose acetate (acetylation degree: 61.3%, average degree of polymerization 280, manufactured by Daicel Chemical Industries, Ltd.) 19% by weight and dimethylsulfoxide 81% by weight were used. A hollow fiber separation membrane was produced in the same manner as in Example 1. The evaluation results of the obtained film are shown in Table 1. The average pore size and porosity of the obtained membrane are shown in FIGS. 1 and 2, and electron micrographs of the obtained membrane cross section at magnifications of 200 and 10,000 are shown in FIGS.

Comparative Example 2 In Example 1, 19% by weight of cellulose acetate (acetylation degree: 61.3%, average degree of polymerization: 280, manufactured by Daicel Chemical Industries, Ltd.), 1% by weight of magnesium citrate (0.02 mol / kg), dimethyl sulfoxide. Example 1 except that a film forming solution of 80% by weight was used.
A hollow fiber membrane was produced in the same manner as in. The evaluation results of the obtained film are shown in Table 1.

Comparative Example 3 Cellulose acetate (acetylation degree: 61.3%, average degree of polymerization 280, manufactured by Daicel Chemical Industries, Ltd.) 18% by weight, cellosolve acetate
A hollow fiber separation membrane with a void ratio of 44% was produced in the same manner as in Example 1 except that a membrane forming solution containing 14% by weight, 63% by weight of NMP and 5% by weight of water was used and water was used as an internal coagulating liquid. did.
The evaluation results of the obtained film are shown in Table 1.

Comparative Example 4 Cellulose acetate (acetylation degree: 56.1%, average degree of polymerization: 180) 19
%, Dimethylsulfoxide 40.5% by weight, triethyl phosphate 40.5% by weight, a coagulation bath temperature of 70 ° C. is used.
A hollow fiber separation membrane was produced in the same manner as in Example 2 except that The evaluation results of the obtained film are shown in Table 1.

[0041]

[Table 1]

[Brief description of drawings]

FIG. 1 (a) is a graph showing an average pore diameter of a cellulose acetate hollow fiber membrane of Comparative Example 1, and FIG. 1 (b) is a graph showing an average pore diameter of a cellulose acetate hollow fiber membrane of Example 1.

FIG. 2 (c) is a graph showing the porosity of the cellulose acetate hollow fiber membrane of Comparative Example 1, and FIG. 2 (d) is a graph showing the porosity of the cellulose acetate hollow fiber membrane of Example 1. is there.

FIG. 3 is an electron micrograph showing the shape of fibers on the outer surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Example 1 (1
0,000 times).

FIG. 4 is an electron micrograph (10,000 times) showing the shape of fibers in a cross section near the outer surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Example 1.

5 is an electron micrograph showing the shape of fibers on the inner surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Example 1 (1
0,000 times).

FIG. 6 is an electron micrograph (10,000 times) showing the shape of fibers in a cross section near the inner surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Example 1.

7 is an electron micrograph (200) showing the fiber shape of the cross section of the cellulose acetate hollow fiber membrane of the present invention obtained in Example 1. FIG.
Times).

8 is an electron micrograph showing the shape of fibers on the outer surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Comparative Example 1 (1
0,000 times).

FIG. 9 is an electron micrograph (10,000 times) showing the shape of fibers in a cross section near the outer surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Comparative Example 1.

10 is an electron micrograph showing the shape of fibers on the inner surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Comparative Example 1. FIG.
(10,000 times).

FIG. 11 is an electron micrograph (× 10,000) showing the shape of fibers in a cross section near the inner surface of the cellulose acetate hollow fiber membrane of the present invention obtained in Comparative Example 1.

12 is an electron micrograph (200) showing the shape of fibers in the cross section of the cellulose acetate hollow fiber membrane of the present invention obtained in Comparative Example 1.
Times).

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Claims (2)

(57) [Claims] 1. A hollow fiber membrane having a membrane thickness of 50 to 500 μm has a three-dimensional mesh-like porous portion having an average pore diameter of substantially 0.05 to 1 μm and a void portion having a size of 10 to 200 μm. The area occupied by the void portion with respect to the total cross-sectional area of the membrane is in the range of 5 to 70%, and the inner and outer surfaces of the hollow fiber membrane have irregular or circular micropores, and the cross-sectional area of the membrane is The three-dimensional mesh-like porous portion is in the entire range except both the inner and outer surfaces of the hollow fiber membrane which are within 1/50 of the total thickness.
It has a nearly uniform porosity of 40 to 80%, a molecular weight cut-off in the range of 10,000 to 500,000, and a tensile strength at break of the membrane of 30 kg / cm ²
A cellulose acetate hollow fiber separation membrane characterized by having the above, and having a transmembrane differential pressure of 1 kg / cm ² and a pure water permeation rate at a temperature of 25 ° C. of 500 liters / (m ² · hr) or more. 2. The degree of acetylation is in the range of 53 to 62%, and
Cellulose acetate with an average degree of polymerization in the range 100-500 10
.About.30% by weight and metal compounds belonging to groups I to III of the periodic table.
Dissolve 05 to 5 mol / kg in a water-soluble polar organic solvent having a boiling point of 100 ° C. or more, which dissolves both the cellulose acetate and the additive to prepare a film-forming solution, and the film-forming solution is added to a double-tube type spinneret. 2. The composition as claimed in claim 1, wherein the inner tube is discharged from the outer tube at 80 to 140 ° C. and the inner coagulating solution at 30 to 80 ° C. is discharged from the central portion of the spinneret to coagulate in a coagulating bath at 30 to 80 ° C. A method for producing a cellulose acetate hollow fiber separation membrane.