JPS5959213A - Porous support membrane and composite membrane using same - Google Patents

Abstract

PURPOSE:To provide a porous support membrane excellent in heat resistance and mechanical strength, constituted so as not to have fine pores having a pore size of 1mum or more on either one of the surfaces of a membrane mainly formed of an aromatic polyamide. CONSTITUTION:As aromatic polyamide, for example, one shown by the general formula is dissolved in an amide solvent to form a solution which is, in turn, immersed in a coagulation bath to be coagulated after discharged from a nozzle and the product is washed with water, subjected to heat treatment and dried to be preserved in water. As the amide solvent, N, N-dimethylacetamide is used and the concn. thereof is adjusted to 3-35wt%. As the coagulation bath, water is used and, as a support membrane, ones with various configurations are used according to its application. The thickness of the thin membrane is 0.01-10mum and there is no pores having a pore size of 1mum or more on either one of the surfaces thereof. The air permeation amount thereof is within a range of 1-1X 10<-6> cc(STP)/cm<2>.sec.cmHg at 20 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a porous support membrane, and more particularly to an aromatic permeable membrane used in a selectively permeable membrane which is composed of a thin membrane having selective permselectivity and a support membrane that supports the thin membrane. The present invention relates to a porous support membrane made of a group polyamide and a composite membrane using the same.

In recent years, separation methods using membranes have rapidly come into practical use from the viewpoints of resource conservation, energy conservation, and recovery of valuable materials. For example, desalination of seawater, recovery of valuables from process water, separation of liquid systems such as separation of plasma from blood, production of oxygen-enriched air with increased oxygen concentration in the air, recovery of helium gas, etc. The usefulness of membrane separation methods is being demonstrated in each field.

Selective permeable membranes used for such separation can be broadly classified into the following two types from the viewpoint of membrane structure.

That is, (G) a so-called asymmetric membrane in which the skin layer having permselectivity and a porous layer having a porous structure are continuously changed and the entire membrane is made of the same membrane material; CB) a thin membrane having permselectivity and its It basically consists of a porous support membrane for support, and is generally a so-called composite membrane in which the thin membrane and the porous support membrane are composed of different membrane layers.

The asymmetric membrane mentioned above requires a special film-forming method to form an asymmetric structure, so even if the membrane material has excellent permselectivity, there is no film-forming method and it cannot be put to practical use. It had the following drawbacks. Furthermore, since the pores are continuously changing, it also has the disadvantage that it is easily subject to mechanical deformation under usage conditions such as pressurization in practical use.

In order to improve this drawback, a composite film (B) has been proposed. Composite membranes have only recently come into practical use because they improve the above-mentioned drawbacks of asymmetric membranes and at the same time improve permeation performance by making the thickness of the membrane as thin as possible. Examples of composite membranes include composite membranes obtained by forming a thin film made of water-soluble polyethyleneimine on a porous support membrane, and subjecting the thin film to interfacial crosslinking and heat treatment (Japanese Patent Application Laid-Open No. 49-1999). 133282), composite membrane using polyepiamine instead of polyethyleneimino (see JP-A-52-40486), cross-linking of aromatic amine with aromatic polyacid no-ride on a porous support membrane. Composite membrane made of at least
-147106), composite membranes mainly for separation of liquid phase fibers, such as composite membranes in which monomers are polymerized and cross-linked by plasma irradiation on porous membranes, porous support membranes and methylpentene polymers or organopolymer Composite film made by laminating and integrating thin films made of noroxane-polycarbonate copolymer (% 1989-89564 and 1988-408)
Composite membranes using biological gas phase separation, such as (see Publication No. 68), have been proposed in the past. Porous support membranes used in such composite membranes include polysulfone, polyethersulfone, polyethylene, and polypropylene.

Cellulose ester, polycarbonate, etc. are known.

As a porous support membrane for supporting a thin membrane having permselectivity as in the above example, a substance that selectively permeates through the thin membrane does not substantially provide resistance when permeating through the porous support membrane. Conditions include having a moderately porous structure, having a moderate affinity with thin films, and being resistant to deformation due to pressure, temperature, etc. under actual usage conditions.

In the single-layer gas separation method, pervaporation method, reverse osmosis method, etc.
There is a need to develop support membranes that can operate under high temperature conditions. However, conventionally known support films do not have sufficient heat resistance, and there is a limit to their use under high temperature conditions.

In view of the above situation, the present inventors conducted research aimed at developing a support film with excellent heat resistance and mechanical strength, and as a result, they arrived at the present invention.

That is, the present invention is a membrane formed from aromatic polyamide as a layer, and one surface of the membrane has a thickness of 1 μm.
substantially free of pores with a pore diameter of more than 20°C
The amount of air permeation at 1~1×1a'6 East (ST
P )/crl See ・cyn A porous support membrane characterized in that HP is within the range of and a composite membrane formed from a thin membrane having reverse osmosis properties.

As the aromatic polyamide, for example, Japanese Patent Publication No. 35-143
Polymers produced by methods described in Japanese Patent No. 99 and *Publication No. 52-39719 can be used.

Among these, a preferable example is the following general formula (1) It has a repeating unit represented by

More preferably, Ar (and/or Ar2
Polyamide containing 20 molt or more of Todozu, straddle Ar)
and/or a polyamide containing 7.5 moles of -o-Y-Q as Ar2.

Particularly preferred aromatic polyamides include polymethaneenylene 7-thalamide and the formula (1), or these ÷
and aromatic polyamides in which Ar2 is (Y and/or a).

In general, the surface of the support membrane on which the permselective thin film is formed must be free of large pores in order to prevent the thin film from being destroyed by pressure or the like. Therefore, it is desirable that the surface is substantially free of pores having a pore diameter of 1 μm or more, preferably 0.S μm or more, particularly preferably 0.2 μm or more.

Moreover, the support membrane has an air permeation rate of 11 at 20'O.
i: 1~I X 1 (r' a: (s'rp),"
i-sec-cmHF range, preferably 0.5 to 1
x 10″Ql: (S TP)/era ・see
-cmHF range is desirable. The amount of transmission is 1 (
1) (STP) If the diameter exceeds 7d・sec・cysllP, it is difficult to obtain a membrane that does not have a pore size of 1 μm or more on any surface, and I
P) If it is smaller than 7 m·sec·cmHF, the amount of permeation will be small, and it will be difficult to fully realize the performance of the permselective thin film formed on the surface.

In order to produce the porous support membrane that is the object of the present invention, there is a method in which the aromatic polyamide is dissolved in a solvent as described below, a membrane is formed from the solution thus obtained, and the membrane is immersed in a coagulating liquid.

The concentration of aromatic polyamide in the solution is 3 to 35
1 Lii%, preferably 4 to 3+1 weights.

As the solvent for the polyamide, an amide solvent capable of dissolving 3% by weight or more, preferably 5 times, of the polyamide at 60'O is used.

Specific examples include l''i'N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethylsulfoxide, detramethylurea, and hexamethylphosphoramide.

N-Methyl-2-piperidone, N,N-dimethylethyleneurea, N-methylcaguO2cutam, N-acetylpyrrolidine, N,N-diethylacetamide, N,N
-dimethylpropionic acid amide and mixtures thereof. Particularly preferred are N,N-dimethylacetamide and N-methyl-2-pyrrolido.

Furthermore, various salts, organic substances, water, etc. may be added to the polyamide solution for the purpose of controlling the solubility of the polymer and the porosity and structure of the membrane.

Many methods have been disclosed for molding aromatic polyamides. For example, when spinning a polymer that is more popular than polymetaphenylene isophthalamide, a solution of N-methyl-2-pyrrolidone with a polymer concentration of 15 to 25% by weight is usually discharged from a nozzle, immersed in a coagulation bath, and then heat-treated and stretched. It goes through a process of crystallization. It is known that a highly concentrated inorganic salt aqueous solution is used as a coagulation bath in order to slow down the coagulation rate and achieve uniform coagulation.

Although the porous support membrane of the present invention is not limited to such a manufacturing method, after dissolving the aromatic polyamide in the solvent,
A flat membrane, hollow fiber or tubular membrane is discharged and formed by a known method. Immediately after the discharge film is formed, it is immersed in a coagulation bath, solidified, washed with water, heat treated and dried if necessary, and stored in water.

The concentration of polyamide in the solvent is 3-35% by weight, preferably 4-30% by weight. The lower the concentration of polyamide, the more porous the membrane can be obtained and the higher the air permeation rate at 20°C, but on the other hand, the maximum pore diameter will also be larger.
Since defects such as pinholes are likely to occur, it is necessary to select a material according to the purpose of use. Furthermore, a non-solvent can be added to the solvent for the purpose of enlarging the average pore diameter. For example, water, monohydric alcohol, polyhydric alcohol, acetone,
Methyl ethyl ketone.

Formamide and the like are preferably used. The amount added varies depending on the type of non-solvent, or is 10% to the total amount of dope.
40 weight ratio is preferably used.

In addition, in order to improve the solubility of the polyamide, at least one salt of monovalent or divalent cation gold can be used. As a specific example of this salt, it is possible to use 0.5 ml of salt in the amide solvent at 60°C. Substances that can dissolve more than their weight, such as alkali metal salts such as hydrologonic acid, hydrobromic acid, hydroiodic acid, nitric acid, sulfuric acid, thioanic acid, etc.

One or more of alkaline earth metal salts and ammonium salts, specifically, for example, lithium chloride, lithium nitrate, sodium iodide, carunium chloride, potassium nitrate, and sodium nitrate.

Examples include nitromagnetic acid, lithium bromide, potassium thiocyanate, ammonium bromide, ammonium nitrate, ammonium thiocyanate, and more preferably lithium chloride and lithium nitrate, which have relatively high solubility in the above-mentioned solvents.

Calcium chloride, magnesium chloride, calcium nitrate, etc. are used. These salts can be used alone or in combination of two or more.

Water is preferably used as the coagulation bath, but a small amount of inorganic salt (1 to 10% by weight),
Alternatively, an aqueous solution containing a solvent for the polyamide can also be used. A major difference from the above-mentioned spinning forming method is that water is preferably used as a coagulation bath.

The supporting membrane of the present invention may be formed in the form of a flat membrane, a tubular membrane, a hollow fiber membrane, etc. depending on the purpose of use.

1, the film may be formed on other substrates such as non-woven fabrics.

According to the present invention, since the film is made of wholly aromatic polyamide, it can be used as a support film for a composite film that has excellent heat resistance and solvent resistance.

Conventionally known methods are used to form a thin film having selective permselectivity on the polyamide support membrane, such as the above-mentioned interfacial polymerization method on the membrane surface, coating method, and coating a thin film spread on the water surface on the support membrane. Any method for forming a thin film can be used, such as a scooping method, a plasma polymerization method on the film surface, and an ultraviolet irradiation method.

In addition, the thickness of the thin film having permselectivity is usually 0.01~
10 μm, preferably 0.02 to 5 μm. 0.0
If it is less than 1 μm, it is difficult to obtain a defect-free film;
If it is more than m, the amount of permeation will be /J\, which is not preferable. The composite membrane thus obtained is preferably used for gas phase separation such as selective permeation of oxygen from a mixed gas of nitrogen and oxygen, concentration separation of rare gases such as helium, and liquid phase separation by reverse osmosis. It is also used for organic liquid mixtures and selective separation of liquids from organic liquid mixtures.

The present invention will be described in detail below using Examples, but the present invention is not limited thereto.

In the following examples, "parts" represent parts by weight.

Example 1 15 parts of polyamide (0onex manufactured by Teijin ■) were dissolved in 85 parts of dimethylacetamide. This solution was cast onto a glass plate to a thickness of 0.3 [mu]m, and then immersed in 250 ml of water to solidify, to obtain a polyamide film with a thickness of 115 μm.

The amount of air permeation through this membrane at 20°C when dry is 5.
2 X I Cf” CxO, (8TP) Shoulder secαH
9, and the maximum pore size of the surface according to the method of ASTM I"316 was 0.3 μ-. This membrane was mixed with 49.5 parts of water,
After being immersed in a mixed solution of 495 parts of ethanol and 1 part of bis(aminopropyl)tetramethyldisiloxane for 3 minutes, it was pulled out, held vertically, and drained for 10 minutes at room temperature.

Furthermore, this film was coated with one of diphenylmetane diisocyanate.
．． A composite film was obtained by immersing it in a 0% by weight n-hexane solution for 3 minutes.

When the gas permeation rate of this membrane was measured at 25°0 using a Rika Seiki Kogyo Co., Ltd. gas permeability meter, the oxygen permeation rate was 2.8 x 10-5 mm (S'l'
P) A++LseccmI92. The oxygen to nitrogen permeability ratio was 55.

Example 2 10.72 M of 3.4'-aminodiphenyl ether and 5.79 parts of paraphenylene/diamine were combined with N-methyl-2
- Dissolved in 500 parts of pyrrolidone under a nitrogen stream and heated to 0°C.
After the mixture was cooled to , 21.74 parts of terephthalyl chloride powder was immediately added with vigorous stirring. The temperature of this mixed solution increased due to heat generation, and the viscosity also increased. After about 5 hours, calcium oxide was added to neutralize the by-product hydrochloric acid. 〃・ηinh of the obtained polymer is 3.20
Met.

After dissolving 5 parts of this polymer in 95 parts of N-methyl-2-pyrrolidone, the solution was dissolved in Dacron.
A nonwoven fabric-reinforced polyamide membrane was obtained by casting on a nonwoven fabric (area weight: 13,597 m') to a thickness of 0.2 thick, and immediately immersing it in water at 25°C to coagulate it. 2 of this membrane
The amount of air permeation at 0'C is 2 x 10-3 (S
TP) lcr!・secσH9, and the maximum pore diameter is 0.
It was 15 μm. This membrane was immersed in a 1.0% by weight aqueous solution of paraphenylenediamine for 3 minutes, and then drained vertically for 10 minutes at room temperature. This membrane was immersed in n-hexane containing 0.5% by weight of trimesic acid chloride for 30 seconds to obtain a composite membrane. The performance of this membrane was measured at a pressure of 40 KGJ/m (J) using a normal reverse osmosis cell at 25'O with a 0.5% by weight NaCl aqueous solution as a stock solution.The performance of this membrane was 3117 m"hr. +Exclusion rate is 98
．． I was in Section 7.

Example 3 90.25 fl[l] of cyclohexene and 4. Poly4-methylpentene-1 (TPX D manufactured by Mitsui Petrochemical Co., Ltd.) was added to a solvent in which 5 parts of
A solution containing 5.0 parts by weight of X-810) was prepared.

This solution is held at 25゛0 and an area of about 10 m above the surface of the water is 2*! The surface of the water at 10'C from the opening of lI -
- Dropwise. This droplet expanded on the water surface and formed a film. Two of these membranes were scooped up onto the polyamide membrane used in Example 1. The oxygen permeation rate of this composite membrane when dry is 2.9 x 10”cc (S T P )/crl・
3e (F). Also, the ratio of oxygen permeability coefficient to nitrogen permeability coefficient was 3.5.

Claims (1)

[Scope of Claims] 1. A membrane made of aromatic polyamide, substantially free of pores with a pore diameter of 1 μm or more on either surface of the membrane, and having a pore diameter of 1 μm or more and Air permeation amount is 1 to 1 x 10-6 CC (STP)/*・sec
- A porous support membrane characterized by being within the range of CrnHY. 2. The porous support membrane according to item 1, wherein the aromatic polyamide can be dissolved in an amide solvent in an amount of 3% by weight or more at 60°0. 3. The porous support membrane according to item 1, wherein the aromatic polyamide is polymethanoenylene isophthalamide. 4. The aromatic polyamide is a polymer having a repeating unit represented by the following general formula (1) and in which 7.5 moles or more of all aromatic groups are -Q-Y-C5. The porous support membrane according to item 1. S, (Z) A composite membrane for gas permeation formed from the porous support membrane according to item 1 and (2) a thin film having selective gas permeability. 6(1) A composite membrane for reverse osmosis formed from the porous support membrane according to item 1 and (2) a thin membrane having reverse osmosis properties.