JPH0331093B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a separation membrane with excellent heat resistance and mechanical strength. More specifically, it is a separation membrane with excellent heat resistance and mechanical strength that is mainly made of aromatic condensed ring polyamide.The wet membrane is suitable for use in hot fluids and high pressure steam sterilization. In addition, the dry membrane is a gas separation membrane that enriches a specific gas from a high-temperature gas mixture, and in particular, a dry membrane that enriches a specific gas from a high-temperature gas mixture. It is suitable for film formation. Conventional technology In recent years, there has been remarkable progress in separation technologies that use organic polymers as membrane materials, such as microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, and gas separation membranes, and some of them have been used industrially. It has been put into practical use on a large scale. For example, precision filtration membranes or ultrafiltration membranes are used to treat industrial wastewater, convert building wastewater into gray water, and concentrate liquid foods, and reverse osmosis membranes are used to desalinate seawater. However, these separation membranes have poor heat resistance, and separation membranes for high-temperature fluids remain at the research stage, and a separation membrane that enables high-pressure steam sterilization treatment, which requires even higher heat resistance, has not yet been proposed. Regarding gas separation membranes, that is, separation membranes that enrich a specific gas from a mixed gas, membrane separation of gases with significantly different molecular weights, such as hydrogen gas and methane gas, is at the practical stage, but Practical use of chemical membranes is limited to the medical field. There are many industrial uses of oxygen-enriched air that do not necessarily require high oxygen concentrations, such as blast furnaces, high-temperature gas furnaces, etc.
Oxygen-enriched air containing 25-30% oxygen will accomplish that purpose, but for such applications,
A stable, large-volume supply of oxygen-enriched air and low cost are required. The technical problem in obtaining oxygen-enriched air using gas separation membranes is to increase the permeation flow rate per unit area of the membrane without reducing the membrane separation capacity. The purpose is to increase the membrane area per module unit volume when put into practical use. Furthermore, there is an inversely proportional relationship between the thickness of the separation membrane and the permeation flow rate per membrane unit, and in order to increase the permeation flow rate, it is necessary to reduce the thickness of the separation membrane. As a method for forming such an oxygen-enriched membrane, a combination of a thin membrane having a separation function and a supporting porous membrane has been proposed. For example, organopolysiloxane
By dropping a polycarbonate copolymer solution onto the surface of a liquid casting support, an extremely thin gas separation membrane of about 0.1 μm is made (see Japanese Patent Application Laid-open No. 1983-40868), and then composited with a porous support. is being attempted. However, it is difficult to produce such a composite membrane with an extremely thin separation membrane on its surface without defects such as pinholes and cracks, and there are also many problems such as the difficulty of handling during module production. In addition, such siloxane-based separation membranes have poor heat resistance, with the optimum separation temperature being 20°C, which has the disadvantage that the separation rate decreases as the temperature rises and does not function properly as an oxygen-enriching membrane at temperatures above 40°C. . On the other hand, an example of an attempt to fabricate an extremely thin gas separation membrane on a porous support by low-temperature plasma polymerization is an oxygen enrichment membrane made by plasma polymerizing an organosilicon compound (see Japanese Patent Laid-Open No. 59-55309). It will be done. However, although the plasma polymerization method has the advantage of being able to use a wide range of organic substances as membrane materials and being easy in principle to produce thin films, it is extremely difficult to completely fill the pores of a porous support with a plasma polymerized membrane. Moreover, since plasma polymerized film formation requires a vacuum device, the film size is limited, and film formation takes several minutes or more, making it difficult to say that it is a practical method for producing oxygen-enriched films. . Problems to be Solved by the Invention An object of the present invention is to provide an ultrafiltration membrane which is a separation membrane with excellent heat resistance and mechanical strength, and which enables, for example, separation of hot fluids or high-pressure steam sterilization treatment. Another object of the present invention is to provide a gas separation membrane that is easy to manufacture and easy to handle, and in particular, an oxygen-enriched membrane that can supply oxygen-enriched air even under high-temperature conditions. Means for Solving the Problems The present invention is a polyamide represented by the general formula (-NH-X-NH-Y) _-o (n is the average degree of polymerization),
is the formula (However, R represents either H, CH ₃ or C ₂ H ₅ ), and Y is the formula or Y consists of both formula (a) and formula -CO-(CH ₂ ) ₄ -CO- (b), and the molar ratio of formula (a) in the Y component is 5% or more This is a polyamide separation membrane whose membrane material is a copolymer. Among the polyamides used as membrane materials for the separation membrane of the present invention, polyamides in which X in the general formula is the formula (1) and Y is the formula (a) are of the formula (However, R represents any one of H, CH ₃ and C ₂ H ₅ ). 9,9-bis(4-aminophenyl)fluorenes represented by the formula It can be obtained by reacting terephthalic acid chloride, isophthalic acid chloride, or an acid chloride of a derivative thereof represented by the following in a solvent such as dimethylacetamide or N-methylpyridone under cooling for several hours. In the following description of the invention, such polyamides have the general formula: (However, R is any one of H, CH ₃ and C ₂ H _5. ) Refers to a polymer consisting of the repeating unit (A) represented by: On the other hand, a copolyamide in which X in the general formula is formula (1) and Y includes both formula (a) and formula (b) is the above-mentioned 9,9-bis(4-aminophenyl)fluorene. Similarly, the above-mentioned terephthalic acid chloride, isophthalic acid chloride, etc. and adipic acid chloride represented by the formula ClCO-(CH ₂ ) ₄ -COCl or a derivative thereof, etc. are mixed at a molar ratio of formula (a) of 5% or more. A copolymerized polyamide is obtained by reacting in the same manner as for obtaining a polymer from repeating unit (A). In the following description of the present invention, such copolyamides are defined by the repeating unit (A) and the general formula (However, R represents any one of H, CH ₃ and C ₂ H _5. ) Refers to a copolymer having a repeating unit (B) represented by: Furthermore, in order to prevent discoloration of the above-mentioned polyamide used as a membrane material in the present invention due to contact with air or to improve the durability of mechanical strength, it is desirable to stabilize the polymer terminal with a benzoyl group or the like. Any such polyamide of the present invention can be dissolved in an organic solvent such as dimethylacetamide, N-methylpyrrolidone, or cresol;
The amount dissolved can be increased by adding inorganic salts such as lithium chloride or calcium chloride. The polyamide used as the membrane material of the separation membrane of the present invention is
It is a polymer of repeating unit (A) alone or a copolymer of repeating unit (A) and repeating unit (B), and both polymers have excellent heat resistance and mechanical strength. For example, the decomposition temperature and glass transition point of a polyamide containing a single repeating unit (A-1) in which the dibasic acid residue in general formula (A) is a terephthalic acid residue and R is H are 455°C and 380°C, respectively. ℃, and R in general formula (B) is H
A repeating unit (B-1) which is a repeating unit (A
-1): The decomposition temperature and glass transition point of the copolyamide in which the repeating unit (B-1) is in a molar ratio of 10:90 are 415°C and 230°C, respectively. The tensile strength of such polyamides is 10 to 12.
It is a membrane material with excellent mechanical strength, in the Kg/mm ² range. Furthermore, even if the dibasic acid residue in general formula (A) is an isophthalic acid residue, R in general formulas (A) and (B)
Even if it is H, CH ₃ or C ₂ H ₅ , there is no significant change in heat resistance and mechanical strength. The separation membrane of the present invention is formed using the above-mentioned polyamide as a membrane material, for example, by a wet method, but the membrane forming method is not particularly limited.
It is manufactured into tubular membranes or hollow fiber membranes. For example, a film-forming stock solution prepared by dissolving a polyamide consisting of a single repeating unit (A) or a copolymer polyamide having repeating units (A) and repeating units (B) in a suitable solvent containing lithium chloride is used as it is on a smooth glass plate. After a part of the solvent is evaporated for a certain period of time, it is immersed in a non-solvent that mixes with the solvent in the film-forming stock solution, and the solvent is removed to form a flat film. Further, a hollow fiber membrane is formed by simultaneously extruding the above-mentioned membrane-forming stock solution from the annular opening of the double-tube structured hollow fiber spinning nozzle and extruding the non-solvent into the coagulation liquid from the circular opening. A polyamide membrane formed by such a wet method can be used as an ultrafiltration membrane in a wet membrane state. Furthermore, by increasing the molar ratio of the repeating unit (B) in the copolyamide, the molecular weight cutoff of the ultrafiltration membrane can be increased. However, repeating unit (B)
Since the wet membrane of a polyamide separation membrane consisting solely of polyamide has poor mechanical strength, it is necessary to make it into a copolymer with the repeating unit (A) in order to make it suitable for practical use as an ultrafiltration membrane. , a repeating unit in a copolymer
The proportion of (A) shall be 5 mol% or more. That is, the proportion of formula (a) in the polyamide Y component represented by the general formula is 5 mol % or more. On the other hand, by drying the polyamide wet membrane of the present invention, it can be suitably used as a gas separation membrane. The drying method may be a conventional method, for example, air drying at room temperature and then vacuum drying or heating drying at about 100°C. The polyamide membrane of the present invention is a separation membrane with excellent heat resistance and mechanical strength, and its wet membrane has performance as an ultrafiltration membrane and enables separation of high-temperature fluids and high-pressure steam sterilization treatment. It has excellent features not found in conventional ultrafiltration membranes, and is widely used in separation processes of industrial high-temperature fluids such as the production of high-temperature pure water, and separation processes in the medical industry that require sterilization. Available. Furthermore, the dry membrane of the separation membrane of the present invention has a gas separation function, a simple membrane manufacturing method, excellent heat resistance and mechanical strength, and ease of handling. It can be used in many fields for the purpose of enriching gases, and has particularly excellent performance as an oxygen-enriching membrane for producing oxygen-enriched air to be blown into combustion furnaces. Examples Examples of the present invention are shown below, but the present invention is not limited thereto. In addition, in the following examples, the permeation rate of pure water was an operating pressure of 1.0 Kg/cm ² , a flow rate of 1.5 cm/sec, and a temperature of 25 to
Measurement was performed at 83°C. In addition, the dextran rejection rates of monodisperse dextran aqueous solutions with average molecular weights of 70,000, 40,000, and 10,000 were measured under the same conditions as above, and the dextran molecular weight at which the rejection rate was 50% was defined as the molecular weight cutoff at the temperature. In the example of a gas separation membrane, the permeation rate of a mixed gas or pure gas is measured by a pressurization method at 25 to 160°C, the composition of the permeated mixed gas is determined by a gas chromatograph, and the separation rate a at that temperature is determined. was determined from the permeated mixed gas composition ratio/raw material mixed gas composition ratio. Example 1 100 parts by weight of N,N-dimethylacetamide and 5 parts by weight of lithium chloride A hollow fiber membrane having an outer diameter of 1.0 mm and an inner diameter of 0.65 mm was obtained by a known hollow fiber manufacturing method by dissolving 20 parts by weight of polyamide having the repeating unit (A-1) represented by: Table 1 shows the pure water permeation rate, molecular weight cutoff, and bursting strength at the temperature of the obtained wet hollow fiber membrane. Here, the bursting strength is expressed as the bursting pressure when pure water is pressurized inside a hollow fiber whose one end is sealed. Table 1 shows that the polyamide hollow fiber wet membrane composed of the repeating unit (A-1) has excellent heat resistance, and the molecular weight cutoff and bursting strength are almost the same at 83°C and 25°C. Furthermore, the reason why the permeation rate of pure water increases with temperature is because the viscosity of water decreases. Example 2 The same hollow fiber membrane as in Example 1 was subjected to high-pressure steam sterilization treatment at 121°C and approximately 1.2 atm, and the pure water permeation rate measured at 25°C was 30/m ² hr. kg・cm
^-2 , the molecular weight cut-off was 6000, and the bursting strength was 25 Kg·cm ^-2 , which were almost the same as the results at 25°C shown in Example 1. Example 3 Formula A polyamide consisting of a single repeating unit (A-2) represented by was formed into a hollow fiber membrane in the same manner as in Example 1, and the water permeation rate at 25°C measured in the same manner as in Example 1 was 80/m ²・hour・Kg・cm ^-2 , molecular weight cut off is
8000, and the bursting strength was 24Kg・cm ^-2 . Example 4 Formula A polyamide hollow fiber membrane consisting of a single repeating unit (A-1') represented by was formed in the same manner as in Example 1, and the pure water permeation rate at 25°C was 40/m ² hr.
Kg・cm ^-2 , molecular weight cut off 7000, bursting strength 27Kg・cm ^-2
I got it. Example 5 Formula A polyamide hollow fiber membrane consisting of a single repeating unit (A-1'') represented by was formed in the same manner as in Example 1, and the pure water permeation rate at 25°C was 38/m ² hr.
Kg・cm ^-2 , molecular weight cut off is 7000, bursting strength is 28Kg・
cm ^-2 was obtained. Example 6 Repeating unit (A-1) and formula shown in Example 1 A copolymer with a repeating unit (B-1) represented by repeating unit (A-1): repeating unit (B-1)
A hollow fiber membrane was obtained in the same manner as in Example 1 using a copolymerized polyamide having a molar ratio of 50:50 as the membrane material. The pure water permeation rate, molecular weight cutoff, and bursting strength of the obtained wet hollow fiber membrane at the relevant temperature were determined by the second method.
Shown in the table. Example 7 In Example 6, a copolyamide in which the repeating unit (A-1): repeating unit (B-1) was in a molar ratio of 10:90 and 5:95 was used as a membrane material, and in the same manner as in Example 1. A hollow fiber was obtained. The pure water permeation rate at the temperature of the obtained wet hollow fiber membrane, the molecular weight cut off,
and bursting strength are shown in Table 3. Example 8 The wet hollow fiber membrane obtained in Example 1 was air-dried at room temperature and then sufficiently dried at 100° C. to obtain a dry hollow fiber membrane.
After sealing one end of the obtained dry hollow fiber membrane, it was assembled into a gas separation membrane module, containing 79% nitrogen and 21% oxygen.
The permeation rate and separation rate a using artificial air with
(O/N) was determined. The results are shown in Table 4. Also,
The ratio of pure oxygen permeation rate to nitrogen permeation rate is 120℃
It was 2.6. This example is a repeating unit (A
The dried polyamide hollow fiber membrane made of -1) has been shown to have heat resistance not seen in conventional oxygen enrichment membranes. Example 9 A wet flat membrane was formed by casting the same film-forming stock solution in Example 1 onto a glass plate and then immersing it in a coagulating solution, and then drying it in the same manner as in Example 7 to reduce the thickness. 0.1mm
A dry flat membrane was obtained. The obtained dry flat membrane was assembled into a flat membrane type gas separation module, and the permeation rate and separation rate a (O/N) were measured using the same artificial air as in Example 8.
I asked for In addition, the permeation rate of a mixed gas of 50% argon and 50% nitrogen and the separation rate of argon/nitrogen a
(Ar/N) was determined. The obtained results are also shown in Table 5. Example 10 Table 6 shows the artificial air permeation rate and separation rate a (O/N) obtained with a dry flat membrane formed using 15 parts by weight of polyamide contained in the membrane forming stock solution in Example 9.

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[Table] Effects of the invention Among separation membranes made of organic polymers, the polyamide separation membrane of the present invention enables the separation of fluids heated at 83°C, and is also capable of high-pressure steam sterilization at 121°C and approximately 1.2 atm. The purpose of the present invention is to provide an ultrafiltration membrane that can maintain its separation performance even when the membrane is wet.Furthermore, the dry membrane of the polyamide separation membrane of the present invention has a gas separation function without the need for compositing, and has heat resistance and It is suitable for practical gas separation membranes that have excellent mechanical strength, are simple to form, and are easy to handle, particularly oxygen enrichment membranes.

Claims (1)

[Claims] 1. A polyamide separation membrane using a polyamide represented by the general formula (-NH-X-NH-Y) _-o (n indicates the number of repeating units) as a membrane material. However, X is the formula (R represents either H, CH ₃ or C ₂ H _5. ) Y is the formula Let it be expressed as . 2 formulas The polyamide separation membrane according to claim 1, wherein the dibasic acid residue is a terephthalic acid residue or an isophthalic acid residue. 3. A polyamide separation membrane whose membrane material is polyamide represented by the general formula (-NH-X-NH-Y) _-o (n indicates the number of repeating units). However, X is the formula (R represents either H, CH ₃ or C ₂ H _5. ) Y is the formula and the formula -CO-(CH ₂ ) ₄ -CO- ...(b), and the proportion of formula (a) in the Y component is 5.
It shall be mol% or more. 4 formula 4. The polyamide separation membrane according to claim 3, wherein the dibasic acid residue is a terephthalic acid residue or an isophthalic acid residue.