JP2550543B2 - Polyacrylonitrile-based hollow fiber membrane and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-performance polyacrylonitrile-based ultrafiltration hollow fiber membrane, more specifically, high-performance polyacrylonitrile having high water permeability, a small pore size, and a narrow pore size distribution. TECHNICAL FIELD The present invention relates to a hollow fiber membrane for ultrafiltration and a method for producing the same.

(Prior Art) Conventionally, a method using an ultra-permeation membrane such as cellulose acetate, polyacrylonitrile, or polyolefin for concentration or recovery of active ingredients or water production in various fields such as food industry, medical field, and electronic industry field. Is being considered. The performance required for the ultrafiltration membrane is particularly high water permeability and high solute separation ability. Among them, polyacrylonitrile-based ultrapermeability membrane has superior chemical stability than cellulose acetate, has good mechanical properties, is a hydrophobic material, and has the characteristic of being easily wet with water. The formation is described in, for example, Japanese Patent Publication Nos. 52-15072 and 53-31106.

The former has a so-called dense layer and is composed of a graded porous layer and a reticulated porous structure, and the latter is a production method using a solution having a relatively high polymer concentration. However, neither membrane has sufficient separation or overcapacity,
Further improvement is required.

The inventors of the present invention have completed the present invention as a result of earnest researches in view of the present situation.

(Problems to be Solved by the Invention) That is, the object of the present invention is a hollow fiber having a high separation capacity and a high capacity as compared with a conventional polyacrylonitrile-based ultra-use hollow fiber membrane, and a well-balanced hollow fiber. To provide a membrane.

(Means for Solving Problems) The present invention has the following configurations.

(1) A polyacrylonitrile-based hollow fiber membrane comprising a blend of an acrylonitrile-based polymer having an ultrahigh degree of polymerization and an acrylonitrile-based copolymer containing a hydrophilic group.

(2) The polyacrylonitrile-based hollow fiber membrane according to claim (1), wherein the acrylonitrile-based polymer having an ultrahigh degree of polymerization has an intrinsic viscosity of 2.0 or more.

(3) Spinning using an organic solvent solution consisting of a blend of an acrylonitrile-based polymer having an ultrahigh degree of polymerization and an acrylonitrile-based copolymer containing a hydrophilic group and having a total polymer concentration of 5 to 15% by weight A method for producing a polyacrylonitrile-based hollow fiber membrane, which comprises:

(4) The method for producing a polyacrylonitrile-based hollow fiber membrane according to claim (3), wherein the spinning is performed by a dry-wet method.

A feature of the present invention is that an acrylonitrile-based polymer (hereinafter, abbreviated as AN-based polymer) having an ultra-high degree of polymerization is used and yarn is formed at a low polymer concentration.

An organic solvent solution of an AN polymer with an ultra-high degree of polymerization easily forms a dense layer when solidifying, and if the polymer concentration of the solution is low, the dense layer becomes thin and the inside is relatively large. It has a porous or network structure with a pore size.
Those with such a membrane structure have an ultra fast velocity (UFR)
Is large, the solvent permeability is high, and the presence of the dense layer also provides excellent separation ability, and maintains sufficient mechanical strength.

The hollow fiber membrane of the present invention has a structure as shown in FIGS. That is, the membrane surface has a dense layer (skin layer) of 0.1 to 0.3 μm, a few μm inside is a porous structure, and the inside is a network structure with huge voids, and therefore high separation ability and overcapacity. And has sufficient mechanical strength.

The AN-based polymer having an ultra-high degree of polymerization as a main component in the present invention has an intrinsic viscosity of 2.0 or more, preferably 2.5 to 3.6,
More preferably, it has a specific degree of polymerization of 2.9 to 3.3. Further, the polymer contains at least 90 mol% of AN, preferably 95 to 100 mol% and not more than 5 mol% of a vinyl compound having copolymerizability with the AN, preferably 0 to 5 mol%.
It is an AN homopolymer or AN-based copolymer composed of 1 mol%.

The vinyl compound may be any known compound having copolymerizability with various ANs, and is not particularly limited, but preferable copolymerization components include acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, Examples thereof include vinyl acetate, sodium allyl sulfonate, sodium methallyl sulfonate, and sodium P-styrene sulfonate.

In the present invention, the organic solvent that dissolves the AN polymer is
Any solvent can be used as long as it is used for AN, and dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAC), ethylene carbonate, butyl lactone and the like can be exemplified, but DMSO can be particularly preferably selected. The obtained polymer solution is used as a spinning dope.

However, the total polymer concentration of this spinning dope is about 5
-15% by weight, preferably 8-13%, and if the total polymer concentration is lower than 5%, not only will it be difficult to form a dense layer, but the mechanical strength will be insufficient. Can not stand. On the other hand, if the total polymer concentration exceeds 15%, the dense layer becomes too thick, or the pore diameter of the porous layer / mesh structure layer becomes small, resulting in a marked decrease in overcapacity and an increase in viscosity. Therefore, the spinnability is deteriorated, which is not preferable.

In the present invention, the purpose of blending an AN-based copolymer containing a hydrophilic group with an AN-based polymer having an ultra-high degree of polymerization is to improve the spinnability and control the separation ability by changing the coagulability, For example, it can be used in a field requiring high hydrophilicity. The AN
The system copolymer is a polymer composed of 50% by weight or more of acrylonitrile and one or more known monomers of 0 to 50% by weight which are copolymerizable with acrylonitrile. Examples of the method of imparting the hydrophilic group to the acrylonitrile-based copolymer containing a hydrophilic group in the present invention include a method of copolymerizing with a vinyl monomer containing another hydrophilic group to be copolymerized with acrylonitrile. Vinyl monomers containing such hydrophilic groups include hydroxyethyl methacrylate, acrylamide, methacrylamide, N-methylol acrylamide, N-vinyl-2-oxazolidone, vinylpyrrolidone, dimethylaminoethyl methacrylate, and acrylic acid, methacrylic acid, and itacone. Examples of the acid include acrylic acid, acrylic sulfonic acid, methallyl sulfonic acid, vinylbenzene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and salts thereof, but the invention is not limited thereto. Furthermore, after adding vinyl monomers containing such a hydrophilic group, ethyl acrylate, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, styrene for adjusting other polymer properties. There is no problem in adding components that do not have great hydrophilicity, such as butadiene, butadiene, and isoprene. The blending ratio of the AN copolymer is 80% by weight or less, preferably 60% or less, more preferably 40% or less. However, if the total polymer concentration is increased in order to increase the mechanical strength, the supercapacity decreases, which is not preferable.

In addition, water, alcohols, inorganic salts, or other polymers such as polyethylene glycol and polyvinylpyrrolidone may be added to the polymer solution in order to increase the water permeability.

Hereinafter, the method for producing the polyacrylonitrile-based hollow fiber membrane of the present invention will be described.

The polyacrylonitrile-based hollow fiber membrane in the present invention is an acrylonitrile-based polymer containing acrylonitrile having an intrinsic viscosity of 2.0 or more and an ultra-high degree of polymerization, and the total polymer concentration using the organic solvent is within the range of 5 to 15% by weight. It can be produced by preparing a spinning dope in (1) and spinning it by a dry-wet method.

That is, specifically, the solution is discharged from the sheath using a sheath-core type hollow fiber die, and a gas or coagulating liquid is discharged from the core to evaporate the organic solvent in the gas phase for 0 to 20 minutes. Then, this is immersed in a mixed solution of water and an organic solvent, and then treated in water or a mixed solution of water and a non-solvent at a temperature of less than 40 ° C. to manufacture. The mixing ratio of water and the organic solvent is selected from 40:60 to 100: 0, because if the amount of the organic solvent is too large, coagulation is slowed down and the inside of the film is densified and the supercapacity is lowered. If the temperature of the mixed solution is too high, the shrinkage of the film will occur and the supercapacity will be lowered, so that the temperature is selected from 0 ° C to 70 ° C.

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

The water permeability (UFR) in the examples means the amount of water flowing out through the hollow fiber membrane to the outside when the water or the aqueous solution is flown through the hollow portion of the hollow fiber membrane in units of effective area, time and pressure of the membrane. It is converted. Where water-UFR is pure water,
Alb-UFR represents the amount of water permeation when a bovine serum albumin (Fraction V) aqueous solution was used. Furthermore, the rejection rate (abbreviated as R _j )
Is an aqueous solution containing a solute such as bovine serum albumin (concentration C
It is a value calculated by the following equation by flowing i) into the hollow fiber membrane and measuring the concentration (Cd) of the solution flowing out through the membrane.

In addition, the intrinsic viscosity of the polymer is
ence (A-1) Vol. 6, pp. 147-157 (1968), according to the measuring method described in dimethylformamide (DM
It is a value measured at 30 ° C using F) as a solvent.

(Example) Example 1 A polymer of acrylonitrile 100 mol% [η] = 3.2 was DMSO.
Polymerized in DMSO with a polymer having a polymer concentration of 15.5% by weight and a copolymer of acrylonitrile 97 mol%, methyl acrylate 2 mol%, sodium allylsulfonate 1 mol% and [η] = 1.2. 22.4 wt% concentration was mixed so that the ratio of polymer to copolymer was 8: 2, and D
It was diluted with MSO to obtain a spinning dope having a total polymer concentration of 11.5% by weight. The stock solution was spun at 1.3 cc / mi from the sheath using a sheath-core type hollow fiber spinneret with an inner diameter of 0.25 mm and a slit width of 0.075 mm.
Water was injected into the core and spinning was performed in the same manner as in Example 1 except that the liquid was discharged at a speed of n.

The dimensions of the obtained hollow fiber are: inner diameter 220μm, film thickness 55μm
The microstructure was the same as in Example 1. Water-UFR is 540
ml / h ・ mmHg ・ m ² , R _j 99.4% and 5% Alb-UFR is 84 ml / h ・ mm
It was very good with Hg · m ² .

Comparative Example 1 A copolymer containing 97 mol% of acrylonitrile, 2 mol% of methyl acrylate, 1 mol% of allyl sulfonate and [η] = 1.18 was polymerized in DMSO to obtain a spinning dope having a polymer concentration of 22.6%. This stock solution was discharged at a rate of 0.8 cc / min from the sheath portion using a sheath-core type hollow fiber spinneret with an inner diameter of 1.6 mm and a slit width of 0.2 mm, and nitrogen was introduced into the core portion at a water column pressure of 25 mm to produce a spinning temperature.
Discharge at 60 ° C, pass 5 mm in air (room temperature), then 30
It was introduced into water at 0 ° C to solidify, then washed with water and wound up.

The obtained hollow fiber membrane had an inner diameter of 225 μm and a membrane thickness of 32 μm.
The microstructure is a uniform porous structure without a dense layer, and water-UFR is 105 ml / h · mmHg · m ² , R _j 99.5% and 5% Alb.
-UFR was 27 ml / h · mmHg · m ² and overperformance was not very good.

Comparative Example 2 A copolymer of acrylonitrile 97 mol%, methyl acrylate 2 mol%, sodium allyl sulfonate 1 mol%, [η] = 1.16 was polymerized in DMSO and diluted to obtain a spinning stock solution having a polymer concentration of 16.0%. It was Using this stock solution, spinning was carried out in the same manner as in Example 1. The dimensions of the obtained hollow fiber membrane are 215
μm, with a thick dense layer, water-UFR 208 ml / h ・ mmHg ・
With m ² and R _j = 99.8%, 5% Alb-UFR was 17 ml / h · mmHg · m ² and the overperformance was not very good.

(Effects of the Invention) The polyacrylonitrile-based hollow fiber membrane of the present invention has excellent separation performance and supercapacity, and also has a well-balanced ultraperformance.

In particular, it can be applied to various industrial fields more than conventional hollow fiber membranes. Examples include water treatment fields such as medical fields, food fields, pharmaceutical fields, microbial fields, electronics industry, and nuclear power generation.

[Brief description of drawings]

1 to 3 show the hollow fiber membrane fibers obtained in Example 1, which were sample-adjusted by the ultrathin section method, and the shape of the hollow fiber membrane fibers was observed by a transmission electron microscope. These images were taken at 10,000x, 20,000x, and 40,000x, respectively. The innermost dense layer has a thickness of 0.1-0.3 μm and a thickness of 200-300
There are Å fine holes. Further, there is a porous structure layer having relatively large pores over several μm, the outside thereof is a network structure layer containing giant voids, and the innermost layer has a different structure from other parts.

Claims (4)

(57) [Claims] 1. A polyacrylonitrile-based hollow fiber membrane comprising a blend of an acrylonitrile-based polymer having an ultrahigh degree of polymerization and an acrylonitrile-based copolymer containing a hydrophilic group. 2. A polyacrylonitrile-based hollow fiber membrane according to claim 1, wherein the acrylonitrile-based polymer having an ultrahigh degree of polymerization has an intrinsic viscosity of 2.0 or more. 3. An organic solvent solution comprising a blend of an acrylonitrile polymer having an ultrahigh degree of polymerization and an acrylonitrile copolymer having a hydrophilic group and having a total polymer concentration of 5 to 15% by weight is used. A method for producing a polyacrylonitrile-based hollow fiber membrane, which comprises: 4. The method for producing a polyacrylonitrile-based hollow fiber membrane according to claim 3, wherein the spinning is carried out by a dry-wet method.