JPH0479685B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a composite membrane for liquid separation for separating at least one type of liquid molecule from a liquid mixture. [Prior art and its problems] Microfilter ultrafiltration membranes, reverse osmosis membranes, alcohol separation membranes, etc. have been developed using various membrane manufacturing methods, but as the molecular weight cutoff of the membranes becomes smaller, Also, the more precise the filtration, the more inconvenient the large pore diameter portion, especially at the base of the pore size distribution. The question of why such large holes exist and how the number of such holes can be reduced has become a major problem. When the thickness of the layer that contributes to separation on the membrane surface becomes less than 10 μm or even less than 1 μm, the dust present there can no longer be ignored, and the part with the dust becomes a pinhole, and this pinhole causes separation. It is a major cause of bad sex. However, the number of dust and impurities contained in the polymer is extremely large, for example, from spinning from a single stock solution to forming a flat membrane to melt spinning. When forming a film from a polymer containing these dusts and impurities,
Ideally, the polymer solution should not contain dirt or impurities that are larger than the average pore size of the membrane to be formed. However, as a practical matter, 1μm
It is difficult to remove the following dirt because the viscosity of the polymer solution is high and the filtration pressure actually increases. However, when it comes to particles of 0.1 μm, there is no easy way to remove them. The present invention was developed as a result of intensive research into these problems.
By using a support porous hollow fiber with an average pore diameter of 0.5 μm or less, dust of a desired size contained in the coating liquid is removed, concentrated to a desired concentration, and then a composite having a desired molecular weight cut-off is formed. It was possible to obtain membrane hollow fibers, and the present invention was completed. [Means for Solving the Problems] That is, the present invention provides the following steps: (1) One surface of a porous hollow fiber support is coated with a dilute polymer solution containing a non-solvent, and the coating liquid is introduced into the porous membrane support. After holding
A method for forming a composite membrane, which comprises concentrating a coating liquid in a heated inert air stream and then coagulating the coating material by bringing it into contact with a coagulation liquid. (2) After coating one surface of the porous hollow fiber support with a dilute polymer solution containing a non-solvent and retaining the coating liquid in the porous membrane support,
A composite membrane forming method characterized by evaporating a solvent using heated inert gas. It is related to. The present invention will be explained in detail below. The hollow fiber support in the present invention may have an average pore diameter of 0.5 μm or less, preferably 0.1 μm or less, as observed by a scanning electron microscope, a molecular weight cut-off of 8000 or more, and a porosity of 10 to 80%. Any of these can be used. Support hollow fibers with a pore size exceeding 0.5 μm generally have weak pressure resistance, and during coating, a large amount of dust contained in the coating solution
This is not preferable because it is difficult to create a defect-free coating film because it incorporates the following: On the other hand, a molecular weight cut-off of 1000 or less is not preferred because the permeation resistance of the support is high and the permeability of the resulting composite membrane is low. The hollow fiber support may be made of any material that satisfies the above conditions, and includes polymers, inorganic materials such as alumina, glass, other metals, and sintered porous ceramics. Among these, polymeric materials are preferred. Polymer materials are generally known as porous membrane materials, and preferred examples include polysulfone, polyethersulfone, polyacrylonitrile, polystyrene, polymethyl methacrylate, polymethyl acrylate, vinyl chloride, vinylidene chloride, Chlorinated polyethylene, polycarbonate, cellulose acetate esters such as cellulose acetate and cellulose acetate butyrate, polyamides such as nylon 6, nylon 66, nylon 4, and nylon 11, polyimides such as polybenzimidazole, polyamideimide, polyacetal, polyphenylene oxide , polyxylene oxide, polyurethane, polyethylene terephthalate, polyalkyl methacrylate, polyalkyl acrylate, polyphenylene terephthalate, polysulfide, polyvinyl fluoride, polyvinylidene fluoride, polytri- or tetrafluoroethylene, and other fluorine-based polymers, polysulfide, Polyacetylene derivatives with trimethylsilyl groups such as polyphosphazene, polyvinyl alcohol, polyvinyl ester, polyvinyl acetate, polypropion vinyl, polyvinylpyridine, polycarbodiimide, polyacetylene, polytrimethylsilylpropylene, etc., with the following chemical formula:

[Formula] (where R ₁ and R ₂ are trimethylsilyl group (Si(CH ₃ ) ₃ ), phenyl group,
Polymers having repeating units of aliphatic substituents such as methyl, ethyl, and propyl groups, and
This and ditrimethylsilyldiethynylbenzene,
Copolymer with dimethylphenylethylsilane, etc.
and those containing some of these crosslinks. Further, block polymers having the above polymers as repeating units, block polymers having the above polymers as main backbone chains, all of the above polymers and polymers have halogen groups (-F, -Cl, -Br, -I), methyl,
It also includes derivatives into which substituents such as ethyl, propyl, -COOH, _-SO3H , and _-NH4 ⁺ have been introduced, and crosslinked products with divinylbenzene. Also included are mixtures of different combinations of the above polymers. More preferable examples include a method in which inorganic fine particles are mixed and formed into hollow fibers using a known polymer melt molding method, and then stretched to a certain extent under appropriate temperature conditions, or a method in which a polymer and an inorganic It is manufactured by mixing the fine particles and an appropriate organic liquid, molding the mixture into a hollow state using a known polymer solvent molding technique, and then extracting the organic liquid from the molded product. Examples of these products and their manufacturing methods are disclosed in publications such as JP-A-52-70988 and JP-A-52-156776. In these porous polymer membranes containing inorganic fine particles, the amount of inorganic fine particles is preferably 10% to 80% by weight. If it is less than 10% by weight, the amount of plasticizer is large and even if it is uniformly dispersed in the polymer, it is difficult to form continuous pores, and a practical porous membrane cannot be obtained. If it exceeds 80% by weight, the strength of the membrane will be low and it will not be possible to obtain a practical porous membrane. Examples of inorganic fine particles include carbon black,
silicon oxide, calcium silicate, aluminum silicate,
Examples include aluminum oxide, titanium oxide, kaolin clay, calcium carbonate, magnesium carbonate, diatomaceous earth, talc, barium sulfate, mica, and asbestos, and these may be used alone or in a mixture of two or more thereof. Further, the particle shape of the inorganic fine particles used in the present invention is not particularly limited, but may be fine particles with an average particle size of 0.005 to 1 μm and a specific surface area of 30 to 800 m ² /g, or porous particles. This is preferable when obtaining a porous polymer membrane containing inorganic fine particles with uniform properties and excellent performance. The polymer constituting the porous polymer membrane containing inorganic fine particles is not particularly limited, but for example, polymers such as ethylene, propylene, butene-1, etc., or one or more of these as the main Consisting of a group of polyolefin resins such as copolymers contained as components, polymers such as vinyl fluoride, vinylidene fluoride, trifluoroethylene, or tetrafluoroethylene, or copolymers containing these as constituent components. Fluorocarbon resins, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyamide resins, polystyrene resins, polyvinyl chloride, and many other thermoplastic resins that can be extruded, either alone or in combination. You can choose from a mixture of resins. Furthermore, after molding, these resins are processed to produce fluorine,
halogens and hydroxyl groups such as chlorine and bromine,
It is also possible to add functional groups such as alkoxy groups, acyl groups, amide groups, and sulfone groups. Examples of particularly preferable polymers for producing a porous polymer membrane containing inorganic fine particles include polyolefin resins and fluorine resins. Various polyethylenes, polypropylenes, and copolymers thereof, ranging from low-density polyethylene to high-density polyethylene, have excellent strength, chemical resistance, flexibility, etc., and are easy to mix and knead with inorganic fine particles. Sheets, films, hollow fibers, etc. can be formed very easily from the resulting mixture by ordinary forming processing means. Fluorine-based resins are superior to polyolefin-based resins in terms of chemical resistance, strength, and heat resistance. Examples of fluorocarbon resins include tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkoxyethylene copolymer, polytrifluoroethylene resin, and tetrafluoroethylene-ethylene copolymer. There are polymerized and polyvinylidene resins. The porous polymer membrane containing inorganic fine particles in the present invention has an average pore diameter of 0.5 μm or less, preferably at the interface between the polymer and inorganic fine particles in the membrane and/or between the inorganic fine particles.
The porosity of the network structure is imparted by fine voids of 0.1 μm, more preferably 0.07 μm or less.
In the present invention, it is extremely desirable to use a porous membrane having such a fine average pore system. The usefulness of using such a porous polymer membrane containing inorganic fine particles can also be seen in the following coating film formation process. A method for forming a thin layer of a polymer on a porous support membrane is to thinly coat (laminate) a solution of the polymer dissolved in an appropriate solvent on the porous membrane using known means, and then It is practical to remove it by evaporation. The presence of inorganic fine particles makes the porous film containing inorganic fine particles extremely wettable by the polymer solution, making it possible to coat the polymer solution in a thin and relatively constant thickness. . Furthermore, since the pores of the porous polymer membrane containing inorganic fine particles form a fine network structure consisting mainly of gaps between the inorganic fine particles, the solvent in the coated polymer solution not only evaporates from the surface; It penetrates extremely quickly through the network structure of the gaps between the inorganic particles and is evaporated from the back side. The resulting thin polymer film is an extremely thin film that has a relatively uniform thickness with little penetration into the pores and is also homogeneous in the thickness direction. Furthermore, the anchor effect between the inorganic fine particles and the coating layer improves the adhesion between the support membrane and the gas separation active thin membrane, or the porous membrane used as the support membrane can withstand compression under severe operating conditions such as temperature and pressure. This results in important practical improvements for gas separation membranes, such as improved properties. In this sense, the blending of inorganic fine particles is an important requirement for extremely high effectiveness. Alternatively, a porous polymer membrane containing inorganic fine particles may be immersed in an alkaline aqueous solution to dissolve and remove the inorganic matter, thereby increasing the porosity and may be used in the same manner. The coating material in the present invention is limited to a polymer and a solvent that does not dissolve the hollow fibers of the porous support. Various resins are used, and representative examples include polysulfone resins, cellulose acetate, polyvinyl fluoride, polyester resins represented by polyethylene terephthalate, polyamideimide resins, aliphatic or aromatic polyamide resins, and polycarbonates. resins, polyimide resins, polyphenylene ether resins, butadiene-acrylonitrile copolymers, and the like. Among these, polysulfone resins and polyphenylene ether resins are preferred because they are easy to form a thin film during solution coating. Some of the polysulfones that can be used include repeating structural units. (wherein R and R′ may be the same or different aliphatic or aromatic hydrocarbyl-containing moieties,
For example, some have polymeric backbones containing from 1 to about 40 carbon atoms, with the sulfur in the sulfonyl group attached to an aliphatic or aromatic carbon atom. This polysulfone preferably has an average molecular weight of 10,000 or more, which is suitable for forming a thin film. When the polysulfone is not cross-linked, the molecular weight of the polysulfone is generally less than about 500,000. R and R may be linked by carbon-carbon bonds or by various linking groups, e.g.

【formula】 【formula】

【formula】

It can be bonded by a group of [Formula] or the like. Particularly advantageous polysulfones are R and
At least one of R' includes an aromatic hydrocarbyl-containing moiety and the sulfonyl moiety is bonded to at least one aromatic carbon atom. Common aromatic hydrocarbyl-containing moieties include phenylene and substituted phenylene moieties, bisphenyl and substituted bisphenyl moieties, formula Bisphenylmethane and substituted bisphenylmethane moieties with a nucleus of, formula Substituted and unsubstituted bisphenyl ethers (wherein X is oxygen or sulfur) and others are included. In the above bisphenylmethane and bisphenyl ether moieties, R ₁ to _{R 10} may be the same or different, and the structure [In the formula, X ₁ and X ₂ are the same or different hydrogen or halogen (fluorine, chlorine, bromine), p is 0 or an integer from 1 to about 6, and Z is hydrogen, halogen (fluorine, chlorine, Bromine), (-Y) _-q R ₁₁ (where q is 0
or 1, and Y is -O-, -S-, -SS-,

[Formula] or

[Formula] and R ₁₁ is hydrogen, e.g. substituted or unsubstituted alkyl containing from 1 to about 8 carbon atoms, or monocyclic or bicyclic substitution containing e.g. about 6 to 15 carbon atoms. or unsubstituted aryl groups), monocyclic or bicyclic heterocycles having a heteroatom of at least one of nitrogen, oxygen and sulfur and having about 5 to 15 ring atoms, sulfate and Sulfono, especially those containing lower alkyl or containing monocyclic or bicyclic aryls, and sulfono, phosphorus-containing moieties such as phosphino and phosphonates and phosphono, especially containing lower alkyl or containing monocyclic or bicyclic aryls. Phosphates and phosphonos containing
Primary, secondary, tertiary and quaternary amines (secondary, tertiary and quaternary amines often contain lower alkyl or monocyclic or bicyclic aryl moieties) ) containing amines, isothioureyls,
thiouryl, guanidyl, trialkylsilyl, trialkylstannyl, dialkylstivinyl, etc.
Substituents on the phenyl group of bisphenylmethane and bisphenyl ether moieties are often in the ortho position. That is, _R7 to _R10 are hydrogen. Polysulfones with aromatic hydrocarbyl-containing moieties are
They generally have good thermal stability, are resistant to attack by chemical reagents, and have an excellent combination of toughness and flexibility. Useful polysulfones are commercially available from Union Carbide, such as "Udel P-
1700" and "Udel P-3500." Both of these products have the general formula (In the formula, n representing the degree of polymerization is about 50 to 80.) Poly(arylene ether)
Sulfones are also advantageous. structure Also useful is polyether sulfone, available under the trade name "100P" from ICI Corporation. Still other useful polysulfones can be prepared by modification of the polymers, such as by cross-linking, grafting, quaternization, and the like. As polyphelene ether, the following general formula is used. (In the formula, R ₁ and R ₃ independently represent an alkyl group having 1 to 4 carbon atoms or a halogen atom, R ₂ represents hydrogen, an alkyl group having 1 to 4 carbon atoms, or a halogen atom, and n is 50 to 300 , preferably 6 to 280,
More preferably, it is an integer in the range of 70 to 250. ) may be preferably used. Typical examples of polyphenylene ether represented by the above general formula include poly(2,6-dimethylphenylene-1,4-ether), poly(2,6-diethylphenylene-1,4-ether), Poly(2-methyl-6-ethylphenylene-1,4-
ether), poly(2-methyl-6-chlorophenylene-1,4-ether), poly(2,6-dichlorophenylene-1,4-ether), poly(2,6-di-n-propylphenylene) -1,4
-ether), poly(2-methyl-6-n-butylphenylene-1,4-ether), poly(2-
methyl-6-bromophenylene-1,4-ether), poly(2,3,6-trimethylphenol)
Examples include. More preferred are polyacetylene resins. For polyacetylene resin, the following general formula is used:

〔Example〕

Examples are shown below. Example 1 23% by weight of silicon oxide (Aerosil #200 (trade name), specific surface area 175m ² /g, average particle size 16mμ) and 54% by weight dioctyl phthalate (DOP) were mixed in a Henshil mixer, and this was mixed with high density Polyethylene resin [Suntec S-360 (registered trademark) manufactured by Asahi Kasei Corporation]
23% by weight was added and mixed again in the Henschel mixer. Nitrogen gas was mixed into the mixture through a hollow fiber spinning nozzle to spin hollow fibers. The formed hollow fibers were immersed in 1,1,1-trichloroethane (chlorocene) for 5 minutes to extract DOP. The inner and outer diameters of the obtained hollow fibers were 0.75 mm and 1.35 mm, respectively, and the composition of the porous membrane was polyethylene resin 50.
Weight%, fine silicic acid 50% by weight, average pore diameter of porous membrane
It was 0.02 μm and the porosity was 58%. Next, the following coating operation was performed on this hollow fiber. Polysulfone (UCC Cordel P-3500,
(trade name), N-methylpyrrolidone as a solvent,
Tetraethylene glycol as a non-solvent,
They were mixed at a ratio of 5.90% and 5% by weight, respectively, to form a uniform solution. After setting the solvent temperature to 25°C, sealing one end of the porous hollow fiber support by fusion and immersing it in the solution,
From the other end of the hollow fiber, a vacuum pump was used to create a pressure gradient of 150 mmHg from the inside to the outside of the hollow fiber, and the dilute polymer solution was sucked into the outer surface of the hollow fiber and into the cells of the porous body. After shaking off the excess polymer solution with nitrogen gas, a nitrogen stream heated to 120°C was introduced onto the hollow fiber for 30 minutes to evaporate the solvent, and then water at 30°C was introduced onto the hollow fiber. , the polymer on the hollow fiber was coagulated by microphase separation. The molecular weight cutoff of this composite membrane is 3000, and the water permeability is 30.
(m ³ /m ² Kg/cm ² Day). Note that the above operation was performed under a nitrogen atmosphere because water is disliked. Example 2 Using a porous membrane support similar to Example 1, polyether sulfone (manufactured by ICI), solvent N-methylpyrrolidone, and non-solvent tetraethylene glycol were mixed in proportions of 5, 90, and 5% by weight, respectively. A homogeneous solution was obtained. Thereafter, in the same manner as in Example 1, polyether sulfone was coated on the polyethylene porous hollow fiber support. The resulting composite membrane has a molecular weight cutoff of 2000 and a water permeability of
40 (m ³ /m ² Kg/m ² Day). Example 3 A polyethylene porous hollow fiber support similar to that used in Example 1 was used, and the porosity was increased by eluting the fine powdered silicic acid contained in the membrane with a hot alkali. I coated the soil. The resulting porous membrane had an average pore diameter of 0.05 μm and a porosity of 65%. Polysulfone (P-3500) as a polymer, dichloromethane as a solvent, and methanol as a non-solvent were mixed in proportions of 5, 90, and 5% by weight, respectively, to form a homogeneous solution, and then applied onto a hollow fiber in the same manner as in Example 1. Infiltrated. Thereafter, the insoluble polymer solution was removed using nitrogen gas, and the solvent was completely evaporated by continuing to flow nitrogen gas heated to 60°C. The average pore diameter of the obtained hollow fibers was 0.02 μm, and the water permeability was 200 (m ³ /m ² Kg/cm ² Day). Example 4 A homogeneous solvent obtained by mixing polytrimethylsilylpropylene, solvent dimethylacetamide, and non-solvent tetraethylene glycol in proportions of 8, 84, and 8% by weight, respectively, was prepared in the same manner as in Example 1 to form a porous polyethylene hollow fiber. The membrane was infiltrated into the cell. After removing excess polymer with nitrogen gas, nitrogen gas at 120°C was introduced for 30 minutes to evaporate the solvent, and then water was introduced onto the hollow fibers to solidify the polymer. The resulting composite membrane has a molecular weight cutoff of 100 and a water permeability of
50 (m ² /m ² Kg/cm ² Day). Example 5 Di(trimethylsilylethynyl)benzene, cyclohexane solution, and non-solvent methanol were each mixed with 8:
A homogeneous solution mixed at a ratio of 84:8% by weight was infiltrated into the outer surface of the ultrafiltration membrane hollow fiber SI-1 (trade name) manufactured by Asahi Kasei Industries, Ltd. in the same manner as in Example 1. Afterwards, excess polymer solution was removed using nitrogen gas, and heated nitrogen gas at 60°C was introduced onto the surface of the ultrafiltration membrane to evaporate the solvent. After 30 minutes, methanol was introduced onto the membrane to completely solidify the polymer. The resulting composite membrane has a molecular weight cutoff of 1000 and a water permeability of
10 (m ³ /m ² Kg/cm ² Day). [Effects of the Invention] The effects of the present invention can be summarized as follows. (1) There is no need to filter the hollow fiber spinning stock solution in advance. (2) The coating solution can be used to form a film without any impurity contamination while keeping it clean. (3) Therefore, there are fewer pinholes in the composite membrane. (4) The coating layer is located in the porous pores of the support and is firmly anchored, so even if the coating layer is made thin, it has high strength. (5) Therefore, a large flux can be obtained. (6) Even if the surface skin layer is scratched, there is little damage because the surface skin layer exists within the porous cells. (7) Since any dilute solution can be used, even polymers with low solubility can be used in coating solutions. (8) Polymers that tend to crack easily when made into films can also be used. Also, those with a small molecular weight,
Polymers that are difficult to form into films and that are easily crystallized can also be used. (9) Porous membrane supports with various pore sizes can be selected to control the cleanliness of the coating solution. In addition, a porous membrane support that has good affinity with the coating material can be selected.

Claims (1)

[Scope of Claims] 1 One surface of a porous hollow fiber support is coated with a dilute polymer solution containing a non-solvent, and the coating solution is retained in the porous support membrane, and then heated in a heated inert air stream. A method for forming a composite membrane, characterized in that the coating material is solidified by concentrating the coating liquid and then bringing the coating material into contact with a coagulation liquid. 2. One surface of the porous hollow fiber support is coated with a dilute polymer solution containing a non-solvent, and after the coating liquid is retained in the porous support membrane, the solvent is evaporated using heated inert gas. Composite membrane manufacturing method.