JPH07100343A - Polyacrylonitrile hollow fiber membrane and production thereof - Google Patents

Abstract

PURPOSE:To product a hollow fiber membrane which suppresses heat shrinkage at high temp. and the decrease of permeant volume and mechanical characteristic being a weak point of a membrane conventionally, and low in shrinkage, large in permeant volume and excellent in mechanical characteristic even if used at a treatment of high temp. soln. to be treated or at high temp. sterilization and to provide its production method. CONSTITUTION:The polyacrylonitrile hollow fiber membrane consisting of the dense layer having <=500Angstrom pore size on one surface, forming the porous layer whose pore size is increased from the surface to the other surface and having <=10% degree of shrinkage at the time of being treated with the hot water of 85 deg.C is obtained. And the polyacrylonitrile hollow fiber membrane obtained by fiber-making using the org. solvent soln. of the acrylonitrile polymer having the superhigh degree of polymerization of intrinsic viscosity [eta] of more than 2.0 by dry.wet method is heat treated in the aq. soln. containing a surfactant or a >= bihydric alcohol and at >=70 deg.C and <=110 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyacrylonitrile hollow fiber membrane and a method for producing the same. For more details,
The present invention relates to a hollow fiber membrane having excellent dimensional stability even when it is used in hot water, having a high water permeability and high heat resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, ultrafiltration membranes such as cellulose acetate, polyacrylonitrile, polyolefin, etc. for concentration, separation / recovery, or water production of useful components in various fields such as food industry, medical field, and electronic industry field. The method of using is being studied.

The performance required for the ultrafiltration membrane is that it has a particularly high water permeability and a high solute separation ability. Further, in recent years, there is a demand for the development of a membrane that can be sterilized with hot water in consideration of contamination during use and profitability and that can be filtered as it is even if the temperature of the liquid to be treated is high.

Ultrafiltration membranes using polyacrylonitrile are characterized by superior chemical stability such as chemical resistance and solvent resistance to cellulose acetate, good mechanical properties, and hydrophobic properties as well as good water wettability. Since it has, it is often used as an ultrafiltration membrane and is described in Japanese Patent Publication No. 60-39404. However, this filtration membrane has a graded membrane structure consisting of a dense layer, a porous layer, and huge pores, and has excellent filtration capacity, but it has dimensional stability at high temperatures, especially in hot water. However, its use is limited at present due to the drawbacks such as marked deterioration of mechanical properties and a large decrease in water permeability. In order to eliminate these drawbacks, an attempt has been made and proposed to perform a constant length heat treatment or a stretching treatment in hot water in advance to eliminate the structural change of the membrane when dried and suppress the deterioration of the membrane performance (Japanese Patent Publication No. 56-3549
No. 0, Japanese Patent Publication No. 60-3844).

However, these proposals are heat treatments under a fixed length or under tension, and have the drawbacks of large thermal shrinkage when used at high temperatures, and cannot be said to sufficiently satisfy the required characteristics.

Further, Japanese Patent Laid-Open No. 3-143534 proposes a porous film containing a surfactant. this is,
The water permeability does not decrease even when the membrane is dried, and the water permeability does not deteriorate because the water wettability does not deteriorate even when the hollow fiber membrane is dried because it suppresses the foaming of the urethane or epoxy adhesive when modularized. There is an effect. However, even in this case, it is not possible to eliminate the drawback that the dimensional stability in hot water is poor.

[0007]

DISCLOSURE OF THE INVENTION The present invention suppresses the decrease in heat shrinkage at high temperature, which is a drawback of the conventional film, and has a high temperature of the solution to be treated and a small heat shrinkage even when sterilized at high temperature. It is to provide a hollow fiber membrane and a manufacturing method.

[0008]

Means for Solving the Problems The present inventors have arrived at the present invention as a result of extensive studies to solve the above problems.

The present invention has the following configuration.

"(1) One surface layer is a dense layer having a pore size of 500 angstroms or less, and a porous layer having a larger pore size from the surface layer to the other surface layer is formed and treated with hot water at 85 ° C. A polyacrylonitrile hollow fiber membrane having a shrinkage rate of 10% or less.

(2) A polyacrylinitol hollow fiber membrane produced by a dry-wet method using an organic solvent solution of an acrylonitrile polymer having an intrinsic viscosity [η] of 2.0 or more and an ultrahigh degree of polymerization is treated with a surfactant or a surfactant. 7 including dihydric or higher alcohol
A method for producing a polyacrylonitrile hollow fiber membrane, which comprises performing a heat treatment with an aqueous solution of 0 ° C or higher and 110 ° C or lower. The present invention will be described in detail below.

In the polyacrylonitrile hollow fiber membrane of the present invention, the surface layer on one side is a dense layer, and further the gradient type porous layer in which the pore size of the pores increases from the surface to the other side of the membrane. The dense layer has a pore diameter of 500 angstroms (hereinafter referred to as A) or less, but 50 to 300 A is particularly preferable in terms of filtration performance. In the present invention, a graded porous membrane layer whose pore diameter increases from one side to the other side of the membrane is formed. The range of the pore size is preferably 500 to 50000A, and particularly preferably 1000 to 20000A. Since the hollow fiber membrane of the present invention can sufficiently exhibit the effect of heat treatment, it is particularly preferable that it does not substantially contain giant pores. The huge pores referred to here are cavities having a diameter of 5 μm or more, further 10 μm or more.

The water permeability of the polyacrylonitrile hollow fiber membrane of the present invention is preferably 0.04 to 0.10 m ³ / m ² · h. The shrinkage rate when treated with hot water at 85 ° C. is required to be 10% or less. This is because if the shrinkage rate is large, there is a risk of breakage when hot water is passed through by fixing both ends with an adhesive to form a module. 7
% Or less is preferable, and 3% or less is particularly preferable. further,
When treated with hot water at 85 ° C, the rate of decrease is 20%.
The following is preferable. A decrease in the amount of water permeation tends to result in a decrease in the amount of treatment, which lowers the durability of the membrane, and inferior treatment efficiency, which leads to an increase in the size of the device.
It is particularly preferably 5% or less. In addition, the polyacrylonitrile hollow fiber membrane of the present invention has an elongation of 80 to 1 from the viewpoint of handleability in the step of forming a bijoule and durability during use.
The 50% strength is preferably in the range of 60 to 150 g / piece.

In the polyacrylonitrile of the present invention,
The intrinsic viscosity [η] is important in determining the structure of the polyacrylonitrile hollow fiber membrane, and is an acrylonitrile having an ultrahigh degree of polymerization of 2.0 or more, preferably 2.5 to 3.6, more preferably 2 Polymers with a specific degree of polymerization of 0.9 to 3.3 are used.

Further, the polymer used in the present invention is particularly preferably a polymer of 100 mol% of acrylonitrile, but 5 mol% or less of a vinyl compound having copolymerizability,
The copolymer may preferably contain 1 mol% or less.

The polyacrylonitrile hollow fiber membrane of the present invention is obtained by spinning the fiber by a generally known dry-wet method and then subjecting it to relaxation heat treatment in a specific solution.
For example, it can be manufactured by the following method.

Polyacrylonitrile 13% by weight dimethylsulfoxide (hereinafter referred to as DMSO) solution was used as a hollow fiber membrane nozzle, and 80% by weight of DMSO was used as an internal injection liquid.
A hollow fiber membrane is produced using an aqueous solution and then washed with water.
If the concentration of residual DMSO contained in the hollow fiber membrane is too high, the effect will be reduced, so 5% or less is preferable, and particularly 1
% Or less is preferable.

The obtained hollow fiber membrane is treated by immersing it in a solution containing a surfactant or a divalent or higher alcohol at 70 to 110 ° C. This is because if the temperature is lower than 70 ° C, there is no effect, and if the temperature exceeds 110 ° C, the film is damaged. More preferably, 7
It is 5 to 100 ° C.

Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, tetramethylene glycol, glycerin, pentetol and hexitol. These may be used alone or in combination of two or more.

Considering the foaming and handling of the adhesive in the modularization process, it is preferable to use a surfactant.

The surfactant may be any of an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant. For example, as the anionic surfactant, fatty acid soap, carboxylate such as N-acyl amino acid salt, sulfonate such as alkylbenzene sulfonate, alkylnaphthalene sulfonate, higher alcohol sulfate ester salt, alkyl ether sulfate salt, Examples thereof include sulfuric acid ester salts such as polyoxyethylene alkylphenyl ether sulfuric acid salts, phosphoric acid ester salts such as alkyl ether phosphoric acid ester salts and alkyl phosphoric acid ester salts. Examples of the cationic surfactant include aliphatic amines, aliphatic quaternary ammonium salts, benzalkonium salts, benzethonium chloride, pyridinium salts and imidazolinium salts. Examples of the amphoteric surfactant include carboxybetaine type, sulfobetaine type, aminocarboxylic acid salts, imidazoline derivatives and the like. Nonionic surfactants include ether types such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene block polymer, and ethers such as polyoxyethylene glycerin fatty acid ester and polyoxyethylene sorbitan fatty acid ester. Ester type,
Examples thereof include ester type such as polyethylene glycol fatty acid ester and polyglycerin fatty acid ester, and nitrogen-containing type such as aliphatic alkanolamide, polyoxyethylene fatty acid amide and polyoxyethylalkylamine. Among these, in view of ease of use and price, anionic surfactants such as sodium alkylbezene sulfonate and higher alcohol sulfate, cationic surfactants such as aliphatic quaternary ammonium salt and benzalkonium salt Is preferred, and sodium dodecyl sulfate is particularly preferred.

The concentrations of the surfactant and the polyhydric alcohol are not particularly limited, but if the concentration is too high, the flexibility of the hollow fiber membrane becomes low, resulting in a decrease in strength / elongation, which further increases the processing cost. There is a tendency that the amount of adhesion to the thread film is large and it takes time to wash when using. On the other hand, if the amount is too small, the effect will be insufficient, so the amount is preferably 2 to 90% by weight, more preferably 3 to 50% by weight, and particularly preferably 5 to 30% by weight. If the treatment time is too long, the hollow fiber membrane is deteriorated or the water permeation rate is lowered, and if the treatment time is too short, the effect cannot be sufficiently exerted.
It is preferably time, and more preferably 1 to 5 hours.

The heat treatment method may be either dry heat or wet heat as long as it is a system containing a surfactant and a polyhydric alcohol, but wet heat treatment is preferable in terms of its effect. Examples of the wet heat treatment include a batch treatment method in which a hollow fiber membrane is immersed in a solution to a predetermined temperature, and a continuous treatment method in which the hollow fiber membrane is passed through the aqueous solution at a constant rate. In case of continuous method,
It is preferable that the shrinkage ratio is a constant value. In general, the shrinkage rate changes with temperature, but once heat-treated and fixed, it will no longer shrink at temperatures below that. Therefore, in the present invention, it is particularly preferable that the heat treatment is performed by relaxing the heat treatment by an amount commensurate with the equilibrium shrinkage rate of the treatment temperature.

The water used in the aqueous solution of the present invention is not particularly limited, but water containing no impurities or foreign substances is preferred, and ultrapure water, distilled water, hollow fiber membranes, reverse osmosis membrane permeate water, etc. Is preferred.

If the outer diameter of the hollow fiber membrane of the present invention is too small, the strength tends to be poor and the water permeation rate tends to decrease, and if it is too large, the flexibility and handling properties tend to be inadequate. The thickness is preferably in the range of 1300 μm, more preferably 300 to 1000 μm. If the inner diameter is too small, the resistance of the permeate tends to increase when the treatment liquid permeates from the outside to the inside of the membrane, and the resistance of the treated liquid tends to increase when the treatment liquid permeates from the inside to the outside of the membrane. There is. On the other hand, if it is too large, the membrane pressure becomes thin and the durability tends to be poor.
The thickness is preferably 1000 μm, more preferably 150 to 700 μm. The film thickness is 2 in terms of durability etc.
The thickness is preferably 0 to 300 μm, more preferably 30 to 200 μm.

The hollow fiber membranes of the present invention include those having a dense inner surface and a larger pore diameter toward the outside, and those having a dense outer surface and a larger pore diameter toward the inner side. Can be used properly. For example, the former is suitable for internal pressure filtration, particularly internal pressure cross-flow filtration, and is used for ultrapure water production, chemical liquid purification, and the like. The latter is suitable for external pressure filtration, especially external pressure total filtration, and is used for condensate and wastewater purification of nuclear power plants.

According to an embodiment of the present invention, a hollow fiber membrane is filled in a pipe made of glass, metal, plastic or the like, and at least one end of the hollow fiber membrane is bundled and fixed with an adhesive such as a urethane-based hollow fiber. A method of using as a thread film module is preferable, but it is not particularly limited, and a known arbitrary method depending on the application can be used.

Examples will be shown below, but the present invention is not limited thereto.

[0029]

EXAMPLES In the examples of the present invention, each performance was evaluated as follows.

(1) Water permeation rate Under the conditions of a temperature of 25 ° C. and a filtration differential pressure = 0.5 kg / cm ² ,
A value obtained by passing pure water through external pressure total filtration and converting the amount of permeated water into a unit time (h) and a unit area (m ² ). (2) Intrinsic Viscosity Journal of Polymer Science
(A-1) According to the measuring method described in Volume 6, 147 to 157 (1968), dimethylformamide was used as a solvent, and the measurement was performed at 30 ° C.

(3) Strength and Elongation Using TENSILON / RTM-100 (manufactured by Toyo Baldwin Co., Ltd.), sample length 50 mm, pulling speed 50
The strength and elongation per hollow fiber membrane at the time of cutting were measured in mm / min.

(4) Shrinkage rate (ΔS) A value expressed by the following equation, where L1 is the length of a hollow fiber membrane having a length L0 after being immersed in water at 85 ° C. for 1 hour without tension. Is.

ΔS (%) = {(L0-L1) / L0} × 100 Examples 1 to 5 Acrylonitrile was polymerized in DMSO to obtain [η] = 3.
A polymer of 2 was obtained. This was diluted to obtain a spinning dope having a polymer concentration of 14% by weight. Then, using a core-sheath type hollow fiber mouthpiece having an inner diameter of 0.25 mm and a slit width of 0.1 mm, this spinning stock solution was discharged from the sheath portion at a rate of 3.2 g / min, and a DMSO 82 wt% aqueous solution was coagulated from the core portion. Injected as. The spinneret temperature is 60 ° C, and the discharged yarn is once in air (room temperature)
Of 150% by weight of DMSO, the solution was introduced into a coagulation bath consisting of a 15% by weight DMSO aqueous solution at 60 ° C. for coagulation, washed in water at 40 ° C., treated in water at 80 ° C. and wound up. The obtained hollow fiber membrane had an outer diameter of 487 μm, an inner diameter of 360 μm,
The film thickness was 65 μm, and the film structure had a dense layer with a pore size of 100 to 300 A in the outermost layer, and the pore size increased toward the inside of the film, but the size was up to 1 to 2 μm. No giant macrovoids were found.

The 2500 hollow fiber membranes thus obtained were bundled and cut into 1300 mm, and then 10% by weight of sodium dodecyl sulfate (Example 1), benzalkonium chloride (Example 2) and glycerin (Example) 3), ethylene glycol (Example 4) and propylene glycol (Example 5) were each prepared as an aqueous solution (using distilled water) and immersed in a glass tube having an inner diameter of 45 mm and a length of 1400 mm containing 1750 ml. This was put into a constant temperature water bath at 95 ° C., treated for 5 hours, and then taken out.

The membrane structure of the obtained hollow fiber membrane is 1 in the outermost layer.
It was a graded porous membrane having a dense layer with a pore size of 00 to 250 A and having a pore size increasing toward the inside of the membrane. The properties of the hollow fiber membrane at this time are shown in Table 1.

In order to evaluate the heat resistance of the polyacrylonitrile hollow fiber membrane obtained by heat treatment, 20 cm after washing with water
Disconnected. A glass tube module was made of 20 polyacrylonitrile hollow fiber membranes, treated with hot water at 85 ° C. for 1 hour, and then the water permeation amount was measured. Similarly, 2, 3, 4, 5
The amount of water permeation during the treatment was measured.

Further, the shrinkage rate was measured after the hollow fiber membrane was cut into 30 cm and immersed in hot water at 85 ° C. for 5 hours under no tension. The results are shown in Table 2.

The amount of water permeation after the heat treatment was large, and as a result of the heat resistance test, there was almost no decrease in the amount of water permeation and the shrinkage rate was extremely small. Further, the strength and elongation characteristics were also satisfactory.

Examples 6 to 8 2500 hollow fiber membranes obtained in the same manner as in Examples 1 to 5 were bundled and cut into 1300 mm, and then 10% by weight.
Adjust the sodium dodecyl sulphate of 45mm, inner diameter 45mm, length 1
The glass tube of 400 mm was immersed in 1750 ml of each. This, 70 ℃ (Example 6), 80 ℃
(Example 7) The sample was placed in a constant temperature water bath at 90 ° C (Example 8), treated for 5 hours, and then taken out.

The shrinkage at this time is 3%, 1%,
It was 0%, and it was found that both were extremely small.

Comparative Example 1 The same treatment as in Example 1 was carried out except that distilled water was used as the heat treatment liquid at 95 ° C. The properties of the hollow fiber membrane at this time are shown in Table 1. The obtained polyacrylonitrile hollow fiber membrane was evaluated in the same manner as in Examples. The results are shown in Table 2.

As a result of the heat resistance evaluation test, the water permeability decreased and the shrinkage rate was small, but the water permeability of the hollow fiber membrane itself was extremely low.

Comparative Example 2 The heat resistance was evaluated in the same manner as in Example 1 without performing the heat treatment at 95 ° C.

The results are shown in Table 2.

The water permeability of the hollow fiber membrane itself is relatively large,
Since the shrinkage rate was extremely large and both ends were adhered to form a module, some hollow fiber membranes were broken during evaluation.

Comparative Example 3 2500 hollow fiber membranes obtained in the same manner as in Examples 1 to 5 were bundled into a bundle, cut into 1300 mm, and then 10% by weight.
Adjust the sodium dodecyl sulphate of 45mm, inner diameter 45mm, length 1
The glass tube of 400 mm was immersed in 1750 ml of each. Put this in a constant temperature water bath at 50 ° C and
It was taken out after the time treatment.

At this time, the shrinkage ratio was 12.5%, and the heat treatment had almost no effect.

[0048]

[Table 1]

[Table 2]

[0049]

EFFECT OF THE INVENTION The polyacrylonitrile hollow fiber membrane of the present invention does not shrink even when a high temperature liquid to be treated is treated, and strength and water permeation amount do not decrease, so high temperature sterilization becomes possible and the treatment liquid Since it can be used without depending on the temperature, it can be applied to various applications. Further, since it is not necessary to cool the liquid to be treated once, it can be easily used and the treatment cost is low.

Claims (10)

[Claims] 1. One surface layer is a dense layer having a pore size of 500 angstroms or less, and a porous layer having a larger pore size is formed from the surface layer to the other surface layer.
A polyacrylonitrile hollow fiber membrane having a shrinkage rate of 10% or less when treated with hot water at ℃. 2. The hollow fiber membrane has an outer diameter of 200 to 1300 μm.
m, inner diameter 100 to 1000 μm, film thickness 20 to 300
The polyacrylonitrile hollow fiber membrane according to claim 1, which is in the range of μm. 3. A water permeability of 0.04 to 0.10 m ³ / m ² ·
The polyacrylonitrile hollow fiber membrane according to claim 1, which is h. 4. The polyacrylonitrile hollow fiber membrane according to claim 1, wherein the hollow fiber membrane does not substantially contain giant pores. 5. A polyacrylonitrile hollow fiber membrane having a decrease in water permeability of 20% or less when treated with hot water at 85 ° C. 6. A polyacrylonitrile hollow fiber membrane prepared by a dry-wet method using an organic solvent solution of an acrylonitrile polymer having an intrinsic viscosity [η] of 2.0 or more and an ultrahigh degree of polymerization, and a surfactant or 2 A method for producing a polyacrylonitrile hollow fiber membrane, which comprises heat-treating with an aqueous solution containing a polyhydric alcohol or higher and having a temperature of 70 ° C. or higher and 110 ° C. or lower. 7. The method for producing a polyacrylonitrile hollow fiber membrane according to claim 6, wherein the hollow fiber membrane is in a relaxed state when the heat treatment is performed. 8. The outer diameter of the hollow fiber membrane is 200 to 1300 μm.
m, inner diameter 100 to 1000 μm, film thickness 20 to 300
The method for producing a polyacrylonitrile hollow fiber membrane according to claim 6, which is in the range of μm. 9. A water permeability of 0.04 to 0.10 m ³ / m ² ·
The method for producing a polyacrylonitrile hollow fiber membrane according to claim 6, which is h. 10. The method for producing a polyacrylonitrile hollow fiber membrane according to claim 6, wherein the hollow fiber membrane does not substantially contain giant pores.