JPH051048B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a gas separation composite membrane for separating at least one type of gas from a gas mixture. [Prior Art] Separating specific component gases from a gas mixture is an industrially important operation. For example, hydrogen recovery from purge gas generated in swimming plants in the oil refining industry, separation and purification of hydrogen from a mixture of hydrogen and carbon monoxide generated in reformers, hydrogen recovery from purge gas in ammonia synthesis plants, methanol synthesis plants, etc. , separation of hydrogen in adjusting the molar ratio of hydrogen and carbon monoxide in oxo synthesis gas, etc. Recently, attempts have been made to use polymer membranes for these gas separations. If successful, this is because it is an easy-to-handle, energy-saving, and industrially valuable method. Regarding the application of polymer membranes to gas separation, research is being conducted on various membranes such as homogeneous membranes, porous membranes, and composite membranes, but proposals for gas separation membranes can be broadly divided into the following two types. One method is to form a polymer having a desired separation coefficient as an ultrathin film on a suitable porous support membrane. In order to increase the gas permeation rate to a practically useful extent, ultrathin membranes must be
The film thickness must be 1 μm or less, preferably 0.5 μm or less. In order to form such an ultra-thin film uniformly and firmly adhered to a porous support without defects such as pinholes, it is necessary to clean the stock solution with high precision,
Even if we introduce an advanced cleaning system using a clean bench in the workplace, or take measures to prevent vibrations, the potential defects cannot be covered, and coating is required to form a defect-free film in 2 to 3 layers. This would be extremely difficult, the manufacturing process would be complicated, and the cost would be high, making it unsuitable for industrial implementation. Another method is, for example, Japanese Patent Application Laid-Open No. 53-86684.
This is the method disclosed in No. This method uses a polymer that has a high separation coefficient for a certain gas to form a porous membrane that has a gas permeation rate comparable to that of a dense, homogeneous, ultrathin membrane of the polymer,
The micropores on at least one surface of the porous membrane are coated with another polymer having a low separation coefficient but a higher gas permeability so as to be occluded. [Problems to be solved by the invention] However, the polymer solution used for porous membrane hollow fiber spinning contains many impurities such as dust and catalysts, and these impurities must be removed by a filter before spinning. However, it is nearly impossible to filter out dust of 0.1 μm or less because the amount of stock solution to be filtered is large and the filtration pressure increases due to clogging of the filter cloth. Therefore, it is inevitable that a porous membrane obtained by spinning a stock solution containing impurities will have many defects. Therefore, coating the film with silicone or the like is essential in order to cover the defects formed on the film. However, this method is not suitable for producing a thin, stable and defect-free skin layer on hollow fibers, and coating membrane formation has the disadvantage that the process is complicated and operation is difficult. It is something. The present inventors have made earnest efforts to overcome these difficulties, and as a result, have achieved the present invention. [Means for Solving the Problems] That is, the present invention coats one surface of a porous hollow fiber support with a monomer or a monomer solution, retains the coating liquid in the porous support membrane, and then removes the monomer. The present invention relates to a method for forming a composite membrane for gas separation, which is characterized by polymerization. The present invention will be explained in detail below. The porous hollow fiber support in the present invention has an average pore diameter of 0.5 μm or less, preferably 0.1 μm or less, as observed by a scanning electron microscope, preferably a molecular weight cut-off of 1000 or more, and a porosity of 10 to 80. % can be used. Support hollow fibers with a membrane pore size exceeding 0.5 μm generally have weak pressure resistance, and during coating, a large amount of dust contained in the coating solution is removed.
Since it is difficult to create a defect-free coating film because it incorporates particles with a diameter of 0.5 μm or less, it is not preferable.
Furthermore, a molecular weight cut-off of less than 1000 is not preferred because the permeation resistance of the support membrane is high and the permeability of the resulting composite membrane is low. The porous hollow fiber support may be made of any material as long as it satisfies the above conditions, but generally 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, Fluorine-based polymers such as polyxylene oxide, polyurethane, polyethylene terephthalate, polyalkyl methacrylate, polyalkyl acrylate, polyphenylene terephthalate, polysulfide, polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, or polytetrafluoroethylene; Polyacetylene derivatives with trimethylsilyl groups such as phosphazene, 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 a repeating unit of aliphatic substituents such as methyl, ethyl, and propyl groups, and
This and ditrimethylsilyldiethynylbenzene,
Also included are copolymers with dimethyldiphenylethylsilane and the like, and those partially containing crosslinking with these. Further, a block polymer having the above polymer as a repeating unit, a block polymer having the above polymer as a main backbone chain, a halogen group (-F, -Cl, -Br, -I) in all of the above polymers,
Methyl, ethyl, propyl, -COOH, _-SO3H ,
It also includes derivatives into which substituents such as -NH ₄ ⁺ 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 produced by mixing fine particles and a suitable organic liquid, molding the mixture into a hollow shape using known polymer melt molding technology, and then extracting the organic liquid from the molded product. Examples of these products and their manufacturing methods are:
It is 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, even if a large amount of plasticizer is used and it is uniformly dispersed in the polymer, it will be difficult to form continuous pores, and a practical porous membrane will not 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. Furthermore, 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 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. thermoplastic 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 of two or more. 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.
It is easy to mix and knead with inorganic fine particles, and the resulting mixture can be extremely easily molded into sheets, films, hollow fibers, etc. by ordinary molding 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. and polyfluorinated vinylidene resin. 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 the 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 or less, 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 diameter. The importance of blending inorganic fine particles can also be seen in the subsequent formation of the coating film. A method for forming a thin layer of a polymer on a porous membrane support 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 porous membrane containing inorganic fine particles is extremely easily wetted by the polymer solution due to the presence of the inorganic fine particles, so it is possible to coat the polymer solution in a thin and relatively constant thickness. Become. 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 also evaporated and removed from the back surface. As a result, the thin polymer film that is formed is an extremely thin film that is less likely to penetrate into the pores of the porous support film, has a relatively uniform thickness, 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 film and the coated gas separation active thin film, or the porous film as a support film can be used under harsh conditions such as temperature and pressure. Important improvements have been made in practical use as gas separation membranes, such as improved compaction resistance. In this sense, the blending of inorganic fine particles is an important requirement for extremely high effectiveness. Furthermore, a porous polymer membrane containing inorganic fine particles may be immersed in an alkaline aqueous solution to dissolve and remove inorganic substances to increase the porosity and may be used in the same manner. The coating material in the present invention is a monomer that forms a polymer after polymerization, a catalyst,
Polymerization can be easily initiated using an initiator, heat, or light. These monomers include epoxy and amine combinations, methyl methacrylate, methyl acrylate, butyl acrylate, etc., silicones, room temperature polymerizable RTV silicones, and other monomers alone or in mixtures. More preferred are polyacetylene monomers. The general formula for polyacetylene monomers is

〔Example〕

Examples are shown below. Example 1 23% by weight of silicon oxide [Aerosil #200 (trade name), specific surface area 175 m ² /g, average particle size 16 μm] and 54% by weight of dioctyl phthalate (DOP) were mixed in a Henshil mixer, and this was mixed with high density 23% by weight of polyethylene (Suntec S-360 (registered trademark)) resin was added and mixed again using a Henshil 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. As monomers, ) trimethylsilylpropylene, ) di(trimethylsilylethynyl)benzene, and ) dimethyl(phenylethynyl)silane were each dissolved in n-hexane, and a 2% by weight solution was prepared on the outer surface of the hollow fiber under a nitrogen atmosphere. Above, the inside of the hollow fiber was vacuumed under a reduced pressure of 150 mmHg compared to the outside to infiltrate into the porous membrane, and then a 1.2% by weight solution of methoxyphenylcarbenepentacarbonyltungsten in n-hexane was prepared as a polymerization catalyst. , the hollow fibers were further coated under a nitrogen atmosphere. After that, nitrogen gas at 60°C was flowed to gradually evaporate n-hexane, and then at 60°C for 2 hours.
The polymerization was completed by continuously supplying nitrogen gas for an hour. When the permeability of the obtained composite membrane was measured, it was found that: (monomer): P _O2 = 5×10 ^-4 α ^O2 _N2 = 3.0; (monomer): P _O2 = 4×10 ^-4 α ^O2 _N2 = 4.0; ) was P _O2 = 1×10 ^-4 α ^O2 _N2 = 5.0 (the unit of P is cm ² (STP)/cm ²・sec・cm
Hg). [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) Coating monomers or monomer solutions can be used to form films without impurity contamination while being cleaned. (3) Therefore, there are fewer pinholes in the composite membrane. (4) the coating layer is in the porous support;
Because it is firmly anchored, it has great strength even if the coating layer is made thinner. (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 the coating solution. (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)

[Claims] 1. Film production of a composite membrane for gas separation, characterized by coating one surface of a porous hollow fiber support with a monomer or a monomer solution, retaining the coating liquid in the porous support membrane, and then polymerizing the monomer. Method.