JPH04277023A - Production of heat-resistant porous hollow fiber membrane - Google Patents

Abstract

PURPOSE:To produce a heat-resistant porous hollow fiber membrane characterized by that the max. value of a pore radius is sharply present within the range of 10-1000nm and showing high separation capacity and chemical stability and excellent in heat resistance. CONSTITUTION:A polymer mixture solution of a cross-linkable polymer and a non-cross-linkable polymer is prepared and spun to form a hollow fiber membrane. This hollow fiber membrane is immersed in a cross-linking treatment solution and heat-treated in pressurized steam to cross-link the cross-linkable polymer in the hollow fiber membrane. After a non-cross-linkable polymer is extracted and removed from the hollow fiber membrame by a solvent, the hollow fiber membrane is thermally oxidized at 200-300 deg.C in an oxidizable atmosphere to form a heat-resistace porous hollow fiber membrane.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing porous hollow fiber membranes having excellent heat resistance.

0002

[Prior Art] There are a wide variety of membrane materials, including synthetic polymers such as polyamide, polyester, polyacrylonitrile, polypropylene, and tetrafluoroethylene; cellulose;
There are membranes made of natural polymers such as collagen; and inorganic polymers such as glass and ceramics, and are used in the right place as reverse osmosis membranes, ultrafiltration membranes, precision filtration membranes, etc. depending on the purpose.

Several types of activated carbon fibers for adsorption separation are already known. Examples include those made from recycled cellulose fibers, acrylonitrile fibers, phenol fibers, and pitch fibers. Fibrous activated carbon has many advantages over granular activated carbon, such as a significantly larger contact area and faster adsorption and desorption rates. Furthermore, by using hollow fibers, complicated processes such as adsorption and desorption are freed, and the fluid can be separated from the fluid by simply passing it through the hollow fibers under pressure, making an energy-saving process possible. Regarding hollow activated carbon fibers, Japanese Patent Application Laid-Open No. 48-87121 describes that voids are formed in a carbon material with a hollow ratio of 10 to 80% and a specific surface area of 400 m2/g or more to adsorb trace substances in gases and liquids. A hollow fiber is disclosed that has the function of The manufacturing method for this hollow fiber is to crosslink the skin part of a fiber made from phenol, elute the uncrosslinked core part with a solvent, carbonize the obtained hollow fiber, and then activate it with an oxidizing gas such as water vapor. This method makes the material porous. Therefore, the pore radius is micropores of 1 to 2 nm, and the hollow portions of the obtained hollow fibers lack uniformity, have a large fluid resistance, and have a low permeation rate.

[0004] JP-A-58-91826 discloses a pitch-based hollow carbon fiber, but the hollow inner diameter is 10
It is small, less than μm, has no pores in the membrane wall, and is not intended as a separation membrane.

[0005] Also, Japanese Patent Laid-Open No. 179102/1982 and Japanese Patent Laid-open No. 202703/1987 disclose carbon membranes with a multilayer structure, but the former carbon membrane has at least one microporous dense layer. At least one layer has large pores to increase the permeation rate, and the orientation coefficient of the multilayer structure as a whole is as small as 0.7. Furthermore, the latter carbon membrane also has an extremely fragile membrane structure, consisting of a porous layer that has separation ability and a porous layer with a sponge structure that has voids with a maximum pore diameter of 5 μm or more to accelerate the permeation rate. It is impractical.

Furthermore, Japanese Patent Application Laid-Open No. 61-47827 discloses carbonized hollow fibers made from polyvinyl alcohol fibers;
The core part, which is made infusible during the carbonization process and has not been penetrated by the dehydrating agent, is melted and removed to make it hollow, and it is activated with steam to produce porous hollow carbon fibers.

[0007] Also, Japanese Patent Application Laid-Open No. 63-4812 (=E
No. P252339) proposes a method for producing a carbon membrane having pores, in which a hollow fiber membrane in which pores have been previously provided by an extraction method is treated with an aqueous hydrazine solution, and then made flame resistant and carbonized.

[0008] However, the activated carbon fibers and porous hollow carbon fibers according to the prior art have small average radii of pores of 1 to 5 nm, so it is difficult to adsorb substances with relatively small molecular weights from the gas phase. Although it is suitable for separation, it is not suitable for the adsorption separation of a substance having a relatively large molecular weight from the gas phase or liquid phase, which is the intention of the present invention. In addition, most of these fibers lack physical properties such as strength and elongation, and lack flexibility.

[0009]

[Problem to be solved by the invention] Films made from organic polymer materials are easy to process, and excellent technologies have been developed for thinning films and controlling microstructures, making it easy to mold hollow fiber membranes and modules. It has advantages such as heat resistance, chemical resistance,
There are drawbacks such as corrosion resistance. Therefore, the current situation is that the field of application is limited. On the other hand, those made from inorganic materials such as glass and ceramics have excellent heat resistance and chemical resistance, but are difficult to process into hollow fiber membranes.
Even if processed, only hollow fibers with large inner diameters, thick membranes, and rigidity could be obtained, making it difficult to form them into modules and the like.

[0010] The object of the present invention is to form a hollow fiber membrane using an organic polymer with good processability, crosslink the fiber structure, heat set it, form a porous structure, and then thermally oxidize it to form a heat-resistant porous membrane. An object of the present invention is to provide a method for manufacturing a quality hollow fiber membrane.

[0011]

[Means for Solving the Problems] That is, the present invention provides a polymer in which 40 to 80% by weight of a crosslinkable polymer (A) and 20 to 60% by weight of a non-crosslinkable polymer (B) are dissolved in a solvent (C). A step of preparing a combined solution, a step of spinning the polymer solution using a nozzle for producing hollow fibers and shaping it into a hollow fiber membrane, and a step of immersing the hollow fiber membrane in a crosslinking treatment solution at a weight of 0.2 kg/cm2G.
A step of crosslinking the crosslinkable polymer (A) by heating in the above pressurized steam, a step of eluting and removing the non-crosslinkable polymer (B) from the hollow fiber membrane with an extractant (E), and a step of eluting and removing the non-crosslinkable polymer (B) from the hollow fiber membrane. 2 membranes
This is a method for producing a heat-resistant porous hollow fiber membrane, which includes thermal oxidation in an oxidizing atmosphere of 00 to 300°C, and further heat treatment at 300°C or higher in an inert gas atmosphere as necessary.

0012

[Action] The crosslinkable polymer (A) used in the present invention is a polymer that can form a crosslinked structure by thermal oxidation treatment in an oxidizing atmosphere and immersion treatment in a chemical solution, and includes polyacrylonitrile, polyvinyl Among these, polyacrylonitrile and acrylonitrile copolymers (hereinafter referred to as acrylonitrile polymers) are preferred due to their ease of shaping and the porous structure that can be obtained. Preferable from the viewpoint of stability etc.

The above-mentioned acrylonitrile-based polymer according to the present invention includes 90 to 100 mol % of acrylonitrile units and 0 to 10 mol % of other monomers copolymerizable with acrylonitrile.
It is an acrylonitrile homopolymer or copolymer composed of mol%. Examples of copolymerizable monomers include acrylic acid, methacrylic acid, itaconic acid and derivatives thereof, such as methyl acrylate, ethyl acrylate, benzyl acrylate, methyl methacrylate,
Ethyl methacrylate; amide derivatives such as acrylamide and methacrylamide; halogenated vinyl monomers such as vinyl acetate, vinyl chloride, and vinylidene chloride; sulfonic acid derivatives such as sodium methacrylsulfonate and sodium styrene sulfonate; It is not necessarily limited to these. As the acrylonitrile polymer, polyacrylonitrile, acrylonitrile-methacrylic acid copolymer, acrylonitrile-methyl acrylate-itaconic acid copolymer, acrylonitrile-methyl acrylate-methacrylic acid copolymer, etc. are particularly preferred.

The degree of polymerization indicated by the specific viscosity of an acrylonitrile polymer is determined by dissolving 0.1 g of the polymer in 100 ml of dimethylformamide containing 0.1 N of rhodan soda.
The specific viscosity measured at °C is preferably in the range of 0.1 to 0.4, more preferably in the range of 0.2 to 0.3. If it is outside this range, the spinning operation tends to become difficult and the performance of the hollow fiber membrane obtained tends to be poor.

The non-crosslinkable polymer (B) used in the present invention is:
Those that do not form a crosslinked structure by heat treatment or immersion treatment in a chemical solution, or even if they do, the degree of crosslinking is relatively small and can be practically ignored, and is soluble in the solvent of the crosslinkable polymer (A) It is something. Examples of such non-crosslinkable polymers (B) include aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene; methyl methacrylate, ethyl methacrylate, n-
Homopolymers such as methacrylate monomers such as butyl methacrylate, or copolymers consisting of 51 mol% or more of these monomers and 49 mol% or less of other copolymerizable monomer units other than acrylonitrile, etc. Can be mentioned. Particularly preferred are styrene polymers and methyl methacrylate polymers. Examples of other monomers that can be copolymerized here include acrylate monomers such as methyl methacrylate, ethyl acrylate, and n-butyl acrylate; and acrylic acid and methacrylic acid.

The degree of polymerization indicated by the specific viscosity of the non-crosslinkable polymer (B) is as follows, in order to facilitate the adjustment of the viscosity when preparing a mixed polymer solution with the crosslinkable polymer (A). The specific viscosity is preferably in the range of 0.1 to 0.4, and 0.2
A value in the range of ˜0.3 is more preferable.

The solvent (C) used in the present invention can be a common solvent for the crosslinkable polymer (A), the non-crosslinkable polymer (B), and the compatibilizer (D) used as an optional component described below. It is something. Examples of this solvent (C) include dimethylformamide, dimethylacetamide, dimethylsulfoxide, and the like.

The compatibilizer (D), which is optionally used in carrying out the present invention, exhibits a compatibilizing effect on both the crosslinkable polymer (A) and the non-crosslinkable polymer (B). Various materials can be used, from low molecular weight ones such as oligomers to high molecular weight ones, as long as they exhibit a compatibility effect. Specifically, the segment (a) is compatible with the crosslinkable polymer (A) or is composed of the same monomer as the polymer (A), and the segment (a) is compatible with the non-crosslinkable polymer (B). Examples include polymers that are soluble or have a segment (b) composed of the same monomer as the polymer (B) in the same polymer chain, such as block polymers and graft polymers. Such block polymers and graft polymers can be produced by known methods, for example, as described in Japanese Patent Publication No. 39978/1983.

The crosslinkable polymer (A) and non-crosslinkable polymer (B) used in the present invention often have poor compatibility. The compatibilizer (D) is used to mix and dissolve the crosslinkable polymer (A) and the non-crosslinkable polymer (B) together with the solvent (C). It has the function of making the solution B) into uniform small dispersed particles and keeping the resulting mixed solution in a stable state. Due to the effect of the compatibilizer, the polymers (A) and (B) form a sea-island structure, and by spinning and drawing, each polymer is oriented in the fiber axis direction, and the fibrils are entangled with each other independently.
Forms a network structure. Therefore, the non-crosslinkable polymer (B
) Even if the components are eluted and removed, the fibril structure made of the crosslinkable polymer (A) remains as it is as a network structure, preventing a decrease in film strength, and the compatibilizer (D) It also plays the role of controlling the size of the dispersed phase and controls the pore size of the hollow fiber membrane finally obtained.

Specific examples of the compatibilizer (D) include block copolymers composed of 30 mol% or more of acrylonitrile, 10 mol% or more of methyl methacrylate, and 10 mol% or less of other monomers copolymerizable with these. and graft copolymers.

In the present invention, the preferred mixing ratio of the crosslinkable polymer (A), the non-crosslinkable polymer (B) and the compatibilizer (D) is 40 to 80% by weight of the crosslinkable polymer (A) and 40 to 80% by weight of the non-crosslinkable polymer (A), The content of the polymer (B) is 20 to 60% by weight, and the compatibilizer (D) is
is 0 to 10% by weight, more preferably 0 to 5% by weight [provided that the total amount of components (A), (B) and (D) is 100% by weight].

If the amount of the non-crosslinkable polymer (B) used is less than 20% by weight, it will be difficult to obtain pores communicating from the inner wall surface to the outer wall surface of the finally obtained porous hollow fiber membrane. In addition, as the amount of non-crosslinkable polymer (B) used increases, the number of communicating pores increases and the pore volume also increases, and the amount used increases.
If it exceeds 0% by weight, the total pore volume will increase, resulting in a decrease in the strength of the porous hollow fiber membrane finally obtained.

As the mixing amount of the compatibilizer (D) increases, the size of the dispersed particles decreases, and as a result, the stability of the polymer solution increases. This contributes to reducing the radius of the pores and the distribution of pore sizes in the porous hollow fiber membrane that is finally obtained, but if the mixing amount exceeds 10% by weight, Since the effect of addition is saturated, a mixing amount of up to 10% by weight is sufficient.

[0024] The polymer in the polymer solution [component (A), (B)
The concentration of the total amount of component ) and component (D) is 10 to 3.
5% by weight, preferably 15-30% by weight. Mixing may be performed simultaneously during dissolution. Alternatively, each may be dissolved individually and the polymer solution may be mixed immediately before spinning using a known static kneading element that does not require a driving part. In this case, the compatibilizer (D) is not necessarily required. The effectiveness of the mixing is controlled by the number of elements in the static kneading element. That is,
As the number of elements increases, the radius of the pores of the finally obtained porous hollow fiber membrane becomes smaller.

[0025] The concentration of the polymer in the polymer solution is 10% by weight.
If the amount is less, the strength characteristics of the porous hollow fiber membrane finally obtained will deteriorate, which is not preferable. Moreover, if it exceeds 35% by weight, the viscosity of the mixed solution increases, the stability of the polymer solution decreases, and it becomes a cause of troubles such as difficulty in filtration, which is not preferable.

The polymer solution is spun into hollow fibers using a hollow fiber manufacturing nozzle such as an annular slit or sheath-core type nozzle. The spinning method may be wet spinning, wet-dry spinning, or dry spinning, but wet spinning or wet-dry spinning is preferred, and wet-dry spinning is particularly preferred.

[0027] To explain the case of spinning using a dry-wet spinning method, for example, a polymer solution discharged from a sheath-core nozzle once travels in the air, and then is introduced into a coagulation bath and coagulated. . Coagulants that have a relatively gentle coagulating power are
This is preferable because phase separation proceeds gently and a tough film is easily obtained. Usually, an aqueous solution of the solvent (C) is used, with a solvent concentration of 40 to 85% by weight, preferably 60 to 80% by weight, 80% by weight, preferably 60 to 80% by weight,
It is preferable to solidify at a temperature of 0.degree. C. or less, preferably 70.degree. C. or less. Outside this range, fragile hollow fiber membranes are likely to be formed.

[0028] Next, it is washed in warm or hot water and stretched. The stretching is preferably carried out in two or more stages, and the total stretching ratio is 3 times or more, preferably 5 times or more. It is preferable that the stretching is as high as possible without causing destruction of the fiber structure, but the upper limit of the total stretching ratio varies depending on the stretching method and the stretching medium, but the guideline is approximately 80% of the stretching ratio at which stretch breakage occurs.

Next, the obtained hollow fiber membrane is immersed in a crosslinking treatment solution, usually in a water-swollen state, and then 0.2 kg/c
The crosslinkable polymer (A) in the hollow fiber membrane is chemically crosslinked and heat set by heating in pressurized steam at a temperature of m2G (105° C.) or higher.

As the crosslinking treatment liquid, the crosslinkable polymer (A)
When is an acrylic polymer, an aqueous solution of hydroxylamine, hydrazine, etc. can be used. It is known to modify acrylic fibers using hydroxylamine or hydrazine, and various methods have been proposed. Examples include treatment with an aqueous solution containing 80% or less hydroxylamine, an inorganic or organic salt of hydroxylamine, and treatment with an aqueous solution in the presence of a strong inorganic acid salt of hydroxylamine and an alkaline substance. An example of hydrazine treatment is
Examples include treatment with an aqueous solution containing 80% or less hydrazine, treatment with an inorganic salt or organic acid salt of hydrazine, and the like. The aspects of each reaction are complex and cannot be uniformly defined, but as a guideline for crosslinking reactions, the solubility of the crosslinkable polymer (A) in dimethylformamide (hereinafter abbreviated as DMF) is 50% by weight or less, preferably 20% by weight or less. It is desirable that the treatment be carried out so that the amount is less than % by weight. The concentration of the treatment solution when immersed in a hydroxylamine or hydrazine aqueous solution is
It is not possible to define it unconditionally as it is affected by the soaking treatment time, the amount of squeezing, etc., but the amount of squeezing should be 80 to 1% of the weight of the fiber.
In the case of 20%, the treatment liquid concentration is in the range of 2 to 80% by weight, preferably 5 to 70% by weight. If the treatment liquid concentration is less than 2% by weight, the solubility in DMF is large and the effect of the crosslinking reaction is small. If the concentration of the treatment liquid exceeds 80% by weight, the solubility of the crosslinkable polymer (A) in DMF will decrease, but the fibers will become brittle, which is not preferable. The fiber weighs 0.2 kg after being immersed in a treatment solution with an appropriate concentration to adjust the squeezing rate.
The reaction treatment is carried out in pressurized steam at a temperature of /cm2G (105°C) or higher. When the processing pressure is high (high temperature), the processing time may be short, and when the processing pressure is low (low temperature), the reaction processing time needs to be lengthened. Processing pressure is 0
．． 2 to 5.0 kg/cm2G, preferably 0.2 to 3.
0 kg/cm2G. The treatment time is preferably 1 to 300 seconds, more preferably 5 to 120 seconds. Processing pressure is 0
．． If the weight is less than 2 kg/cm2G and the treatment time is short, the crosslinking treatment cannot be carried out sufficiently. Processing pressure is 5.0kg/cm2
If G is exceeded and the reaction treatment time exceeds 300 seconds, the fibers become brittle, which is not preferable. Then, it is dried to obtain a hollow fiber membrane consisting of a blend of the crosslinkable polymer (A) and the non-crosslinkable polymer (B).

[0031] The dimensions of the hollow fiber membrane include the nozzle, solution discharge amount,
Although it can be adjusted depending on the stretching conditions, etc., the inner diameter is 20 μm to 100 μm.
It is easy to manufacture a film having a thickness of 0 μm and a film thickness in the range of 1/4 to 1/10 of the inner diameter.

Thereafter, only the non-crosslinkable polymer (B) was extracted from the obtained hollow fiber membrane using an extractant (E) capable of dissolving the non-crosslinkable polymer (B) using a Soxhlet type extractor. It is removed by elution and made porous. In order to improve the heat resistance performance of the final porous hollow fiber membrane and sharpen the pore size distribution, non-crosslinkable polymer (B)
It is preferable to remove it as completely as possible. As the extractant (E), benzene, toluene, acetone, methyl ethyl ketone, methylene chloride, acetic acid esters, halogenated aliphatic hydrocarbons, etc. can be preferably used. By making the fiber porous in this manner, it is possible to increase the diffusion rate of the oxidizing agent into the interior of the fiber of the hollow fiber membrane in the next thermal oxidation step.

[0033] In the thermal oxidation treatment step, the hollow fiber membrane is
Oxidizing gas (e.g. O2, O3,
Thermal oxidation treatment is performed in an atmosphere (gas containing S, NO, SO2, etc.), usually in air. Note that when performing the thermal oxidation treatment, it is desirable to control the hollow fiber membrane so that it does not shrink in the length direction. Excessive shrinkage during the thermal oxidation treatment step is undesirable because it reduces the mechanical strength of the hollow fiber membrane. Excessive elongation is also undesirable as it may cause the hollow fiber membrane to break. Therefore, it is preferable to perform the thermal oxidation treatment while controlling the elongation in the range of 0 to 15%. Thermal oxidation temperature is 200
If the thermal oxidation temperature is lower than 300° C., it will take a long time to obtain the target heat resistance, and if the thermal oxidation temperature exceeds 300° C., thermal decomposition will occur due to an exothermic reaction, and the decomposed gas may ignite and cause combustion. The treatment time is 10 to 60 minutes, preferably 20 to 30 minutes. If necessary, 300°C or higher, preferably 40°C
Inert gas (e.g. N2, A
r, He) Heat resistance treatment is performed in an atmosphere, usually nitrogen gas, while controlling the tension. At this time, the non-crosslinkable polymer that was not completely eluted with the eluent completely thermally decomposes and disappears. A part of the solvent-soluble portion of the crosslinkable polymer also thermally decomposes and disappears, making it possible to produce a heat-resistant porous hollow fiber membrane.

Unlike a sponge structure, the porous structure of the heat-resistant porous hollow fiber membrane produced by the present invention is composed of countless pores parallel to the fiber axis, and these pores are These are pores that are continuously connected from the inner wall surface to the outer wall surface. This can be observed using small-angle X-ray scattering intensity or a scanning electron microscope. It is thought that such a unique porous structure is formed for the following reasons. That is, during spinning from a mixed solution, the dispersed particles of each polymer are subjected to shear stress and stretching, and are arranged in parallel to the fiber axis, and the fibrils of each polymer phase separate from each other, forming an entangled network structure. Form. Then, the fibrils arranged in parallel to the fiber axis of the non-crosslinkable polymer (B) are extracted and removed with a solvent, resulting in a porous structure. On the other hand, in the crosslinkable polymer (A) remaining in the hollow fiber membrane, the fibrils are firmly crosslinked and fixed by a crosslinking agent such as hydroxylamine or hydrazine, thereby preventing shrinkage of pore volume in the subsequent thermal oxidation treatment step. . However, the microstructure of the crosslinkable polymer (A) consisting of fibrils is also a structure in which thin fibers are connected in parallel to the fiber axis, which makes the hollow fiber membrane of the present invention tough.

Another feature of the heat-resistant porous hollow fiber membrane according to the present invention is that the pore size distribution of the pore radius determined from the pore volume differential curve is very sharp, and the maximum value of the pore radius is usually 10. Since it exists in the range of ~1000 nm, it exhibits high separation performance when used as a separation membrane. In addition, the total pore volume is usually as large as 1 to 3 cm3/g, and the number of pores per unit membrane thickness is large, making the water permeation rate high. Furthermore, the hollow fiber membrane according to the present invention has high chemical stability and exhibits strong resistance to all pH ranges and most chemical solutions. The LOI value, which is a measure of heat resistance, is usually as high as 40 or more, making it possible to provide a module that can be used at high temperatures.

[0036]

Effects of the Invention The porous hollow fiber membrane according to the present invention having such excellent characteristics can be used for various purposes, such as separation and purification of pyrodiene, polymeric substances, etc. in the pharmaceutical industry, gas separation in the chemical industry, In particular, it can be used for separation of organic gases and purification of organic chemicals. In addition, in the food industry, alcoholic beverages, soft drinks, soy sauce,
It can be effectively used to clarify vinegar, etc.

Furthermore, it can be used for purification of products from enzymes, separation of proteins, enzymes, etc. in the bioindustry field. It is also particularly useful in the medical field, where proteins, viruses, and bacteria are separated, and in fields that require sterilization and sterilization at high temperatures.

[0038]

[Examples] The present invention will be specifically explained below with reference to Examples. Note that "parts" in the following description indicate parts by weight. In addition, various physical property evaluations were performed in accordance with the following. 1) The specific viscosity of the polymer was measured at 25°C by dissolving 0.1 g of the polymer in 100 ml of dimethylformamide containing 0.1N rhodan soda. 2) The pore distribution structure of the heat-resistant porous hollow fiber membrane is CARL
It was measured by the mercury intrusion method using a porosimeter 200 manufactured by ERBA, and the pore radius was determined as the equivalent radius of a cylinder. 3) Specific surface area is measured by methanol isothermal adsorption curve, BE
It was calculated by applying the formula of T. 4) Single fiber strength and elongation were determined using Tensilon UTM-II type (manufactured by Toyo Sokki Co., Ltd.) at a tensile rate of 100%/min.
It was measured with 5) Limiting oxygen index (LOI) is JIS K 7201
It was measured according to the method of The sample was fixed in a bundle of about 1 g with a length of 100 mm and placed in a combustion cylinder, and then a mixed gas of oxygen and nitrogen was poured into the cylinder at 11.4 l/g.
After flowing for about 30 seconds at a flow rate of The nitrogen flow rate was measured and calculated according to the formula below.

[0039]

[Equation 1] Synthesis Example 1: Preparation of compatibilizer (D1) 1 part of cyclohexanone peroxide (Peroxa H, trade name, manufactured by NOF Corporation) was dissolved in 100 parts of MMA,
800 parts of pure water and 1 part of Pellex OTP (trade name, manufactured by NOF Corporation) as an emulsifier were added to the reaction vessel, and after sufficient substitution with inert gas, it was kept at 40°C and 0.76 parts of Rongalit was added. After adjusting the pH to 3 with an aqueous sulfuric acid solution, polymerization was started. Stirring was continued to complete the first stage emulsion polymerization in 150 minutes. Then, in the second stage, A is added to this emulsion.
After adding 72 parts of N, the temperature was raised to 70°C and 1 part was added again.
Stirring was continued for 50 minutes, and 4 parts of Glauber's salt was further added and stirred for 30 minutes to complete polymerization. The polymer was taken out, filtered, washed with water and dried to obtain a block copolymer compatibilizer (D1) with a polymerization rate of 65.7% and a specific viscosity of 0.19. Synthesis Example 2: Preparation of compatibilizer (D2) 1 part of cyclohexanone peroxide (Peroxa H) was dissolved in 100 parts of MMA, 800 parts of pure water and 1 part of Pellex OTP as an emulsifier were added to the reaction vessel, and the mixture was sufficiently replaced with inert gas. After that, it was kept at 40°C and Rongalit 0.
After adjusting the pH to 3 with 76 parts and an aqueous sulfuric acid solution, polymerization was started. Stirring was continued to complete the first stage emulsion polymerization in 120 minutes. Then, in the second stage, AN6 was added to this emulsion.
After adding 0 parts and 10 parts of VAc, the temperature was raised to 70°C, stirring was continued for 150 minutes, and 4 parts of Glauber's salt was added.
The polymerization was completed by stirring for 0 minutes. The polymer was taken out, filtered, washed with water, and dried to a specific viscosity of 0.18 with a polymerization rate of 65%.
A block polymer compatibilizer (D2) having a composition of 30 mol % AN/65 mol % MMA/5 mol % VAc was obtained. Examples 1 to 4 An AN/MAA copolymer with a specific viscosity of 0.24 ( A1) 60 parts and methyl methacrylate (hereinafter referred to as M
It is abbreviated as MA. ) 99% mol%, methyl acrylate (
Hereinafter, it will be abbreviated as MA. ) 35 to 40 parts of a non-crosslinked copolymer (B1), which is an MMA/MA copolymer with a specific viscosity of 0.21, consisting of 1 mol% and the mixing amount of the compatibilizer (D1) prepared in Synthesis Example 1. Four types of polymer solutions were prepared by mixing 0 to 5 parts of the following in the proportions shown in Table 1. Note that dimethylformamide (hereinafter abbreviated as DMF) was used as the solvent (C), the polymer concentration was 26% by weight, and the mixed solution was kept at a temperature of 60° C. to defoam.

A sheath-core type nozzle consisting of a sheath with an outer diameter of 2.0 mmφ, an inner diameter of 1.5 mmφ, and a core with a diameter of 1.0 mm was used, and the above-mentioned four types of polymer solutions were applied one by one through the sheath. A 60% by weight aqueous solution of DMF was discharged from the core, and after traveling 10cm in the air, 70% by weight of DMF was released.
The aqueous solution was introduced into a coagulation bath at a temperature of 70° C. for spinning and coagulation, and then washed in warm water at 60° C. and stretched 3.0 times. Then, it was stretched twice in hot water at 98°C. This hollow fiber membrane in a water-swollen state with a total stretching ratio of 6 times was immersed in an aqueous solution containing 10% by weight of hydroxylamine sulfate and 10% by weight of dibasic sodium phosphate, and was taken out at a squeezing rate of about 90% to 1.0 k
g/cm2G (120°C) and subjected to crosslinking reaction treatment. Next, they were washed in hot water at 98°C, dried in a dryer at 140°C, and wound up into perforated bobbins for cheese dyeing. Then, the non-crosslinkable polymer (B1) was extracted with acetone using a Soxhlet type extractor.
The mixture was eluted and removed for ~12 hours to obtain a porous hollow fiber membrane precursor. These four types of precursors were oxidized for 90 minutes in an air atmosphere at 240°C. The membrane was then treated in a nitrogen gas atmosphere at 400° C. for 2 minutes to produce a heat-resistant porous hollow fiber membrane of the present invention.

The inner diameter of the four types of hollow fiber membranes obtained was 350
The film thickness was in the range of ±10 μm and 40±5 μm. Table 1 shows the evaluation results of these hollow fiber membranes. Further, the pore volume differential curves of these hollow fiber membranes are shown in Figure 1.

[0042]

[Table 1] Table 1 and FIG. 1 show that the pore radius can be controlled by changing the amount of the block copolymer as a compatibilizer mixed. That is, by increasing the blending amount of the compatibilizer, the radius of the pores can be made smaller. Examples 5 to 7, Comparative Examples 1 and 2 AN95 mol%, MA 4 mol%, itaconic acid (hereinafter referred to as I
Specific viscosity 0.21 composed of 1 mol% (abbreviated as A)
AN/MA/IA copolymer (A2) and MMA87
Specific viscosity 0.19 composed of mol%, MA13 mol%
A non-crosslinkable polymer (B2) which is an MMA/MA copolymer of
), AN30 mol%, MMA6 prepared by the following method
A compatibilizer (D2), which is a block polymer with a specific viscosity of 0.18, consisting of 5 mol% of vinyl acetate (hereinafter abbreviated as VAc) and 5 mol% of dimethyl Acetamide (hereinafter abbreviated as DMAc),
It was dissolved at a polymer concentration of 24% by weight.

[0043] Using the same nozzle as in Example 1, discharge was carried out in the same manner as in Example 1, and after traveling 5 cm in the air, DMAc
A 72% by weight aqueous solution was introduced into a coagulation bath at a temperature of 70° C. and spun to coagulate. The film was then washed in warm water at 60°C and stretched twice. Furthermore, it was stretched 3.0 times in hot water at 98°C. On the other hand, as Comparative Example 2, a hollow fiber membrane in a water-swollen state was obtained by processing under the same conditions as in Example 5 except that the film was not stretched in hot water and was passed through the film at a constant length. These hollow fiber membranes were immersed in an aqueous solution of 12% by weight of hydrazine hydrochloride and 10% by weight of sodium tripophosphate, pH 6, taken out at a squeezing rate of 110%, and treated in saturated steam at 2.0 kg/cm2 (134°C), The fiber microstructure was cross-linked with a chemical solution and heat-set. Next, they were washed in hot water at 98°C, dried at 160°C, and wound up onto porous bobbins. Next, using methyl ethyl ketone as an extractant, only the non-crosslinkable polymer mixed in the hollow fiber membrane was eluted to obtain five types of heat-resistant porous hollow fiber membrane precursors. These precursors were prepared in the same manner as in Example 1 in an air atmosphere at a temperature of 240°C.
Oxidation treatment was performed for 20 minutes. Then, under a nitrogen gas atmosphere, 400
C. for 2 minutes to produce a heat-resistant porous hollow fiber membrane of the present invention.

Table 2 shows various performances of the hollow fiber membranes obtained.

[0045]

[Table 2] From the results in Table 2, it can be seen that as the blend amount of the non-crosslinkable polymer increases, the total pore volume increases. Comparative Example 1 had closed pores (pores not communicating with either the hollow fiber membrane surface or the hollow part). The material of Comparative Example 2 was inferior in flexibility and could not be used.

Incidentally, FIG. 2 shows the pore volume cumulative distribution curves of these five types of hollow fiber membranes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a pore volume differential curve of a hollow fiber membrane obtained by the production method of the present invention.

FIG. 2 is a diagram showing cumulative pore volume distribution curves of hollow fiber membranes obtained by the production method of the present invention and a comparative example.

Claims (4)

[Claims] Claim 1: Crosslinkable polymer (A) 40-80% by weight
and 20 to 60% by weight of the non-crosslinkable polymer (B) in a solvent (C
), a step of spinning the polymer solution using a hollow fiber production nozzle to form a hollow fiber membrane, and after immersing the hollow fiber membrane in a crosslinking treatment solution. 0.
A step of crosslinking the crosslinkable polymer (A) by heating in pressurized steam of 2 kg/cm2G or more, a step of eluting and removing the non-crosslinkable polymer (B) from the hollow fiber membrane with an extractant (E), and The hollow fiber membrane is thermally oxidized in an oxidizing atmosphere at 200 to 300°C, and if necessary, oxidized in an inert gas atmosphere for 3
A method for producing a heat-resistant porous hollow fiber membrane, comprising a step of heat treatment at 00°C or higher. 2. The heat-resistant polymer solution according to claim 1, wherein the crosslinkable polymer (A), the non-crosslinkable polymer (B) and the solvent (C) are further mixed with a compatibilizer (D) to prepare a polymer solution. A method for producing a porous hollow fiber membrane. 3. The crosslinkable polymer (A) is polyacrylonitrile, acrylonitrile-methacrylic acid copolymer,
Acrylonitrile-methyl acrylate-itaconic acid copolymer and acrylonitrile-methyl acrylate-
The method for producing a heat-resistant porous hollow fiber membrane according to claim 1 or 2, wherein the membrane is one or more selected from the group consisting of methacrylic acid copolymers. 4. The non-crosslinkable polymer (B) is a homopolymer of an aromatic vinyl monomer, an aliphatic vinyl monomer, or a methacrylate monomer, or contains 51 mol% or more of these monomers. The method for producing a heat-resistant porous hollow fiber membrane according to claim 1, 2 or 3, wherein the copolymer is a copolymer comprising 49 mol% or less of a copolymerizable monomer other than acrylonitrile.