JPS59120211A - Preparation of composite membrane - Google Patents

Abstract

PURPOSE:To prepare an oxygen enriching membrane free from a defect and having a uniform thickness, by a method wherein a porous support having specific oxygen gas permeation speed and an asymmetric structure is impregnated with a specific liquid and the surface of the impregnated support is coated with a polymer solution to form a membrane. CONSTITUTION:As a porous support, for example, a polysulfone support wherein the permeation speed of oxygen gas permeating through the sectional area of the support is 10m<3>/m<2>.hr.atm or more, the average pore size of the front surface thereof to be coated with a polymer is 5-500Angstrom , the average pore size of the back surface thereof is larger than that of the front surface and the structure thereof is asymmetric is used. This support is preliminarily impregnated with a film forming polymer and a liquid not substantially swelling or dissolving the support, for example, water or ethanol. Subsequently, the surface of this porous support is coated with a polymer solution to form a membrane. In this case, as the polymer, one of which the permeation coefficient ratio of oxygen/nitrogen is 1.8 or more is used and nitrogen-containing polysiloxane is pref.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composite membrane, particularly for the separation of gaseous bodies, especially for enriching oxygen from the atmosphere.

Oxygen-enriched air with an oxygen concentration of 25 to 50% is indispensable for, for example, blowing air to open furnaces, assisting combustion, petroleum protein processing, waste liquid treatment, and breathing in medical care. Conventionally, as a method for obtaining oxygen-enriched air, high-purity oxygen was produced by cryogenic liquefaction distillation, and then air was mixed to obtain professional oxygen ha.

However, in this method, since high-purity oxygen is generally contained in a pressure vessel, there are risks in handling the pressure vessel, or the necessity and operation of a pressure regulator to keep the mixed gas level constant. There were various problems such as complexity.

On the other hand, as a method for obtaining 25 to 50% oxygen-enriched nitrogen,
A membrane blocking method has been proposed. This method directly obtains oxygen-electrified air, is operationally simple, and is economical.
It is advantageous.

Oxygen-containing membranes used for such purposes must not only have excellent oxygen selective separation and permeation rate, but also have mechanical strength and other durability to withstand long-term use. is required.

In order to meet such requirements, a permselective material is usually made as thin as possible without causing defects, and a composite membrane is put into practical use by covering it with a porous support for reinforcement. Conventionally, various methods of forming a composite film by bending have been studied and proposals have been made. For example, the so-called water casting method in which a dilute polymer solution is spread on the water surface and then deposited on a porous support (Japanese Patent Application Laid-Open No. 40868/1986, etc.)
, a coating method in which a cylindrical molecule solution is directly cast or coated onto a porous support R and then dried (Japanese Patent Laid-Open No. 1022-1989)
92 et al.) are known. However, in addition to the difficulty in forming a defect-free thin film in the former method, it is also extremely difficult to attach the obtained thin film to a porous support without causing defects. On the other hand,
In the latter method, problems such as film breakage, non-uniformity of film thickness, and increase in film thickness may occur due to the influence of the affinity between the solution and the support or the penetration of the solution into the pores of the support. Easy to occur.

Although several methods have been proposed to solve these I\+1 problems, it has not yet been possible to obtain a uniform thin film composite film free of defects.

The present inventors have conducted various studies and examinations to solve these problems, and have found that using a porous support membrane having a specific physical structure, impregnating it with a specific liquid in advance, and then applying a polymer solution or The above problems can be solved by casting and drying, and it has a thin film with a uniform thickness and no defects.It has excellent permeation rate and separation ability for dust and debris, and also has excellent mechanical strength and durability. It was discovered that a composite membrane could be obtained.

In other words, the permeation rate of oxygen gas passing through its cross section as a porous support should be at least [o m'/m''・danger・at)I], preferably at least 50 m"7m"・left・atm. It is also important that the average pore size of the surface on which the polymer thin film is formed is 5 to 500X, preferably 10 to 300X.
X, more preferably 20 to 100 days, and it is essential that the back surface has a slightly asymmetric structure with a larger pore diameter than the front surface. The above-mentioned properties can be achieved only when a support film that satisfies both of these properties at the same time is used.

In a normal porous support membrane, the gas permeation rate decreases as the porosity becomes less than 100X.
rr? /n?・It is known that when the permeability is less than round/atm, it becomes unstable. Although it is difficult to accurately measure the diameter of such micropores, it is possible to evaluate by the exclusion rate of a solute of an appropriate size (for example, lysozyme), or by a bubbling method. Additionally, when obtaining a composite membrane with excellent mechanical strength and durability, it is generally advantageous to use a porous support with a smaller pore diameter, but in this case, the permeation resistance of the porous support membrane itself increases. This results in a decrease in the permeation rate as a composite membrane, or a decrease in dispersion ability as a composite membrane due to the influence of Knudsen diffusion.

Therefore, if the oxygen permeation rate of the porous support membrane itself is less than the above range, the dregs permeation rate as a composite membrane with the polymer thin film serving as the separation membrane will be insufficient. Furthermore, if the average pore diameter is too large, the thin membrane may be damaged and the pores may collapse, resulting in insufficient separation ability and durability as a composite membrane. On the other hand, if the pore size is too small, the influence of Knudsen diffusion will become stronger, which is inappropriate. Furthermore, when a porous support without an asymmetric structure is used, the resistance of the pores is high and the influence of Knudsen diffusion tends to be strong, resulting in a decrease in the separation performance of the composite membrane. Furthermore, in this case, it is difficult to control the amount of liquid impregnated into the porous support and its position from the surface of the support, so that the uniformity and reproducibility of the film thickness of the polymer thin film becomes opaque.

There are no particular restrictions on the material of such a porous η support membrane as long as it is a cylindrical material, but it should be considered from the viewpoints of providing the above-mentioned physical structure, mechanical strength, heat resistance, properties, etc. Polysulfone is suitable for use in men.Others,
Acrylonitrile, polyethylene, polyamide, polyvinyl alcohol, cellulose, white) 7
Examples include fluoroenalene, N-vinyl-2-pyrrolidone, polypropylene, and copolymers or mixtures of two or more of these components.

Although there are no restrictions on the thin film-forming polymer material, materials that have a waste separation function can be advantageously used. In particular, the membrane according to the present invention (-1) can be advantageously used in the production of oxygen-enriched air. In this case, the thin film-forming polymer material is preferably a material with excellent oxygen permselectivity; The ratio of gas permeability coefficients must be at least 1.8 and freeze-friendly (2.0. , polycarbonate, polyvinyl acetate, cellulose acetate, vinyl polymers such as POIJ (4-methylpentene-1), copolymers of fluoroolefins and olefin vinyl ethers, vinyl esters, etc., such as chlorotrifluroethylene/isobutyl vinyl Examples include Niful/vinyl vivalate copolymer and Chlorotrifle loethylene/vinyl vivalate copolymer, but nitrogen-containing polysiloxane is preferable from the viewpoint of sludge permeation rate and separation performance. An example of the non-containing polysiloxane is OHs CHa CHs CH3CH3.

Before attaching these thin film-forming polymeric materials to the surface of the porous support on the micropore side, a liquid that does not dissolve or swell the polymeric material and the porous support membrane is injected into the pores of the porous support in advance. It is necessary to impregnate it. In this case, the liquid need not be miscible with the solvent in which the thin film-forming polymer is dissolved, but this is not an essential requirement. What is important is that the liquid does not dissolve or swell the art dealer molecules, and the liquid and the solvent may be compatible. Such liquids depend on the types of polymers forming the thin film and the porous support, but generally include water,
Methane-quaternary and the like are preferably used. In particular, water can be suitably used in connection with the manufacturing process of porous support membranes.

In order to further control the performance of the resulting composite membrane,
It is important to control the amount of liquid with which the porous support membrane is impregnated, more precisely the depth from the surface in contact with the membrane being coated to the liquid level. It is difficult to uniquely quantify and express such a percentage because it depends on the microstructure of the porous support, but it is difficult to express it quantitatively because it depends on the microstructure of the porous support.
? It is desirable to control it.

As such operations and treatments, methods such as wiping the surface of the porous support using a sponge roll or the like, applying pressure with a roll, and evaporating the liquid can be adopted. In particular, a method using roll pressure can be suitably employed.

For example, specifically, a porous support is immersed in a liquid such as sweet potato, water, or methanol, and the pores are sufficiently filled with the liquid.

When the porous support is dry or impregnated with a solvent that is incompatible with water or methanol! d II Step If necessary, the porous support may be sufficiently impregnated with a liquid such as water or methanol by evaporating the solvent or by irradiating the porous support with ultrasonic waves. After that, the porous support is pulled out of the liquid, and after the liquid is drained, the nip air pressure of o1 to 5 Kq/crA-a, preferably 1 to 3 Kr/(-dG and 0.1 to
It is possible to control the impregnation of the liquid in the porous support by nipping the liquid-impregnated porous support using nip rolls driven at a roll surface speed of 1 om/m, preferably 1-5 m/m. I can do it.

A polymer solution is supported on the liquid-impregnated membrane thus obtained,
Examples of the method for forming a composite film include a coating method, a dipping method, etc., but the method is not particularly limited to these methods.

In addition, the porous support to which these solutions are attached is dried using an appropriate method such as air drying, blow drying, reduced pressure drying, freeze drying, critical point drying, etc., but preferably air drying or blow drying is used. It is thoroughly dried.

The thus obtained composite membrane can also be subjected to secondary treatments such as crosslinking and grafting. In that case, the crosslinking agent may be dispersed or dissolved in the polymer solution in advance, or once a thin film is formed, a solution containing a curing agent is applied to the surface of the thin film to perform crosslinking and grafting. You can also do the following. It is also possible to further laminate another separation membrane on the NFC composite membrane obtained in this manner to form a Tokoura multilayer laminated composite membrane. In this case, it is also preferable to use a membrane with excellent selectivity as the layer binding 1 to be placed, rather than a membrane supported directly on a porous support.

Next, the present invention will be explained using examples.

Example 1 Polydimethylsiloxane is dissolved in trichlorotrifluoroethane to prepare a 0.5% (W/V) solution. Asymmetric porous membrane made of folysulfone containing sufficient methanol (
Surface active layer bore diameter line 3oX, cumulative acid permeation rate Qo 2-1
00yt? /m''-fyp・film thickness 240μ including atm lining non-woven fabric) using a two-roll crimping machine,
Nip air pressure 1.7 Kr/i-G, roll surface speed 1
Nip at m/m. The silicone solution was applied to the surface of the methanol-impregnated water sulfone asymmetric porous membrane at a film forming rate of 3 m.
/mix twice and dry it to obtain the desired composite membrane. As a result of measuring the scum permeability of this composite membrane, the acid violet permeation rate Qox-1,2n? /'mF ・-/y
The l-atm oxygen/nitrogen separation coefficient α was 2.0.

Example 2 Example except that an amine group-containing polyorganosiloxane having a composition of approximately 5000 in number average degree of offsetting was used as the silicone liquid, and water was used instead of methanol as the liquid to be impregnated into the porous support. ] A composite membrane was prepared according to the method and its sludge permeability was measured, and it was found to be QO2''. O
(The same applies hereinafter where units are omitted) α=2.0 was obtained.

Example 3 Amine group-containing polyorganosiloxane 51 that disrupts the composition of number average S: degree of about 5000 as a silicone solution and crosslinking agent β-(3,4-ethoxycyclohexyl)ethyltrimethoxysilane 0.2F'& trichloro A composite membrane was prepared according to Example 1 except that the membrane dissolved in 1 t of trifluoroethane was used, and its permeability was measured, and Q, 02 = 4.81α-2,0 was obtained.

Example 4 Two rolls of a polysulfone porous support made of polyolkanosiloxane, which was used in Example 2 instead of polydimethylsiloxane in Example 1, and further filled with methanol. k4'l nig air pressure 3
f/' crA -G, roll surface speed 3 m/
A composite membrane was prepared according to Example 1 except for 'mrn', and its sludge permeability was measured, and it was found that Qo2-13
．． α=21.

Example 5 In Example 1, a chlorotrifluoroethylene/isobutyl vinyl ether/vinyl hybarate terpolymer (
Solid viscosity at 30°C in tetrahydrofuran: 0.4
6. Oxygen permeability coefficient PO2-7x], 0-10al
(STP) -cm/'ad -S-cmHgα-48
) was prepared in accordance with Example 1, and its scum permeability was measured.
15, α=4.8.

Example 6 Amino group-containing crosslinked polyornononosiloxane/polysulfone k produced in Example 3 A chlorotrifluoroethylene/vinyl vivalate binary copolymer (in tetrahydrofuran) having a composition of δ was applied to the surface of the porous membrane. 30℃
Intrinsic viscosity i1.45°PO2-lXl0', α=
4.6) into an ultra-thin film (thickness 4
00^) were laminated. The scum permeability of the obtained composite membrane was Q02-0.6. It was rare with α=4.1.

Comparative Example 1 Composite was carried out in the same manner as in Example 2, except that in Example 2, a cellumous porous membrane with an asymmetrical structure (Siliboa Filter MFVS, hore diameter 250X) was used instead of the asymmetric porous layer membrane made of polysulfone. When a membrane was prepared and its gas permeability was measured, it was found that Qo 2 ''' 1.5 +α
-1.3.

Comparative Example 2 In Example 1, the roll nip operation of the polysulfone asymmetric porous membrane containing sufficient methanol was omitted, and other i1: A composite membrane was prepared according to Example 1, and its gas permeability was measured, and Qo2'= 2.3-55. α engineering 1
．． There were large differences between 5 and 2.0 depending on the location.

Comparative Example 3 Instead of the polysulfone asymmetric porous membrane with fine pores @ l + surface bore diameter of 30X in Example 2, bore diameter]000^
A composite membrane was prepared in the same manner as in Example 3, except for using a nitrocellulose symmetrically structured porous membrane (Toyo Kouchi Membrane Filter-8/TM-s)2, and its scum permeability was measured. Qoz=88+α-1.2.

Ratio Example 4 Q+ of the asymmetric porous membrane made of polysulfone in Example 2
A composite membrane was prepared according to Example 2 except that 12 was 5, and its scum permeability was measured.
7+α=2.0.

Comparative Example 5 A composite membrane was prepared according to Example 2 except that instead of using a water-impregnated polysulfone asymmetric porous membrane in Example 2, a dried one was used, and the gas permeability of the membrane was measured. Q ox ” ” rα−2,
It was 0.

Among the sub-agents: 1) Akira Sub-agent Ryo Hagi Hara - 79

Claims (1)

[Scope of Claims] (1) When forming a thin film of a polymer on the surface of a porous support by coating or coating the surface of a porous support with a polymer solution, the porous quality support l
l; The permeation rate of oxygen force passing through the Ir surface is 10 ze/m
''・Left・A porous polymer support with an asymmetric structure having an average pore diameter of 5 to 500 mm on the surface on which a polymer thin film is formed and a larger average pore diameter on the back surface is used at ATM or higher, and the support is prepared in advance. A method for producing a composite membrane, characterized in that the thin film-forming polymer and the porous support are impregnated with a liquid that does not substantially swell or dissolve the thin film-forming polymer. Transmission coefficient ratio 1
．． The method according to claim (1), wherein the method is a monomer having a selective gas permeability of 8 or more. (8) The method according to claim (1) or (2), wherein the thin film-forming polymer is an organic polysiloxane. (4) The method according to claim (8), wherein the polysiloxane is a siloxane-containing polysiloxane. (5) The method according to claim (1), wherein the material of the porous support is polysulfone.