JPS634441B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a dry semipermeable membrane, and more specifically, in a method for manufacturing a dry semipermeable membrane from a wet semipermeable membrane, even if the resulting dry membrane is stored in a dry state for a long period of time, it cannot be rewetted. The present invention relates to a method for producing a dry semipermeable membrane which, when dried, has substantially the same molecular weight cutoff and permeate volume as the initial wet membrane. Generally, semipermeable membranes such as reverse osmosis membranes and ultrafiltration membranes are manufactured as wet membranes, and in order not to change the molecular weight cutoff or permeate volume designed for the semipermeable membrane,
Until it is ready for use, it is immersed in water, alcohol, an alcohol aqueous solution, etc. and stored in a wet state. This is because when a semipermeable membrane manufactured in a wet state is once dried, the molecular weight cut off changes or the amount of permeated liquid decreases after rewetting, resulting in membrane properties that differ from those originally designed. It is from. However, storing semipermeable membranes in a wet state is associated with various disadvantages. For example, when a semipermeable membrane is stored immersed in water, microorganisms are likely to grow there. If these microorganisms attach and propagate on the membrane surface and block the micropores of the membrane, the amount of permeate will become smaller than the designed value, and the microorganisms may also decompose the membrane and change the molecular weight cutoff of the membrane. Furthermore, when the water freezes, the molecular weight cut-off of the membrane may change. On the other hand, when storing a membrane in alcohol, a sealed container must be used because the alcohol easily evaporates, which is a big disadvantage in practice. As a result of intensive research in view of the above, the present inventors found that
After drying a wet film after treating it with an aqueous solution of a specific polyhydric alcohol or its derivative under specific conditions, the dry film obtained by drying the film, when rewetted, will initially The inventors have discovered that it is possible to provide a membrane with substantially the same physical properties, particularly molecular weight cutoff and permeate volume, as the wet membrane of the present invention, leading to the present invention. The present invention provides a method for producing a dry semipermeable membrane from a wet semipermeable membrane made of a polymer selected from polyamide, polyimide, and polysulfone, in which the wet semipermeable membrane is made of a polyhydric alcohol having 2 to 16 carbon atoms and/or a derivative thereof. After treatment with an aqueous solution of at least 30% by weight of
It is characterized in that it is dried at a temperature of 5 to 70° C., and the dried membrane thus obtained, after rewetting, has substantially the same molecular weight cutoff and permeate volume as the initially wet membrane. In the present invention, the molecular weight cutoff of a semipermeable membrane refers to the molecular weight of a solute when the membrane has a 90% exclusion rate for a solute of a certain molecular weight. The wet semipermeable membrane used in the present invention is a membrane made of polyamide, polyimide, or polysulfone. The polyamide semipermeable membrane preferably has the formula Particularly preferably 70 mol% or more of the m-phenylene group among the phenylene groups,
It is a semipermeable membrane made of aromatic polyamide in which the remainder is a p-phenylene group, and such a semipermeable membrane is known (for example, in Japanese Patent Application Laid-Open No. 56-2804).
A film-forming solution is prepared by dissolving an aromatic polyamide and an inorganic salt additive such as lithium chloride in an organic solvent such as N.N-dimethylacetamide or dimethyl sulfoxide. It is obtained by casting on a material and then immersing it in water to solidify it. The polyimide that can be preferably used in the present invention has the general formula (However, R ¹ represents a divalent organic group.) It has a repeating unit represented by, preferably R ¹
is an aromatic group or _-CH2- , -C( _CH3 ) _2- , -O-,
-S-, _-SO2- ,

【formula】

[Formula] -SiA ¹ A ² - (However, A ¹ and A ² represent an alkyl group or a cycloalkyl group.) Semi-transparent polyimide which is an aromatic group bonded with a divalent bonding group such as As is already known (for example, JP-A No. 55-152507), such a semipermeable membrane is made by converting the above-mentioned aromatic Manufactured by the same method as polyamide semipermeable membranes. Particularly preferred R ¹
teeth

【Formula】Ya

An aromatic hydrocarbon group having 6 to 12 carbon atoms represented by [Formula], or an aromatic group in which these are bonded with an alkylene group, oxygen, sulfone group, sulfur, etc., such as

【formula】

[Formula] etc. Next, the polysulfone semipermeable membrane that can be preferably used in the present invention has the formula Or the expression It is a semipermeable membrane made of a polysulfone polymer having a repeating unit represented by
No. 3615024, U.S. Patent No. 4051300, Japanese Patent Application Publication No. 1973-
23183 etc.). The wet semipermeable membrane treated in the present invention is not particularly limited in its molecular weight cut-off, but has a molecular weight of 1000 to
Suitable results can be obtained when the ultrafiltration membrane has a molecular weight cut-off of about 200,000. The polyhydric alcohol having 2 to 16 carbon atoms and one of its derivatives used in the method of the present invention is water-soluble and has ^the general formula ^R3O- ( _CH2CHR2O ) _o - ^R4 () (However, , R ² , R ³ and R ⁴ are each independently hydrogen,
It represents a methyl group or an ethyl group, and n represents an integer of 1 to 5 when R ² is hydrogen, and an integer of 1 to 3 when R ² is a methyl group or an ethyl group. ) and their mono- or di-lower alkyl ethers, preferably n is an integer of 2 or 3 when R ² is hydrogen, and 1 or 3 when R ² is a methyl group or an ethyl group. 2
is an integer. Specific examples of these include (poly)ethylene glycols such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, and triethylene glycol monomethyl ether. and its methyl- or ethyl ether derivatives, (poly)propylene glycol and its methyl- or ethyl ether derivatives, such as propylene glycol, dipropylene glycol, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. Other preferred polyhydric alcohols are water-soluble and have the general formula R ⁵ -(OH) _n () (where R ⁵ represents a saturated aliphatic hydrocarbon group having 3 to 6 carbon atoms, and m represents 2 to 6 carbon atoms). It is an aliphatic polyhydric alcohol represented by (indicates an integer of 6). Specific examples include glycerin, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2,3,
Examples include 4-butanetetraol, xylitol, sorbitol, and pentaerythritol. In the present invention, particularly preferably glycerin,
At least one polyhydric alcohol selected from ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, and pentaerythritol is used. In the method of the present invention, the wet semipermeable membrane formed in water is usually treated with the polyhydric alcohol, its derivative, or an aqueous solution thereof. In the case of an aqueous solution, the concentration must be 30% by weight or more, preferably 40% by weight or more. In general, semipermeable membranes are formed from a dense layer with micropores called a skin layer on the surface, and a rough porous layer that integrally supports this layer, but in the present invention, the wet membrane is made of polyhydric alcohol. After treatment with an aqueous solution of the polyhydric alcohol or its derivative, it is dried under mild conditions, in which case the polyhydric alcohol or its derivative remains in the dense layer without being substantially volatilized, and when the wet film is dried, the film is dried. pore size shrinkage of the dense layer of the membrane, thus resulting in a molecular weight cut-off and permeate volume substantially equal to that of the originally wet membrane after rewetting. Therefore, if the concentration of the treated aqueous solution is too low, a sufficient amount of polyhydric alcohol etc. will not remain in the micropores of the dense layer to suppress the shrinkage of the pore diameter when the membrane is dried, and as a result, the pore diameter of the micropores will shrink. When the membrane is rewetted, it will have a different molecular weight cutoff and permeate volume than the original membrane. Therefore, in the present invention, the upper limit of the concentration of the treated aqueous solution is not particularly limited, but in consideration of economic efficiency, it is advantageous to use an aqueous solution of 90% by weight or less. Particularly in the present invention, it is advantageous to use an aqueous solution with a concentration of 40 to 70% by weight as the treatment liquid. For treatment of a wet semipermeable membrane with an aqueous solution, the semipermeable membrane may be immersed in a stationary or stirred aqueous solution, or the aqueous solution may be circulated and supplied to the membrane, and the aqueous solution concentration within the membrane may be brought to equilibrium. urge Usually, a treatment time of 4 to 24 hours is sufficient. When drying a semipermeable membrane after immersing it in an aqueous solution of polyhydric alcohol or its derivative, as described above, the polyhydric alcohol or its derivative should be dried to the extent that the polyhydric alcohol or its derivative does not substantially evaporate in the dense layer of the semipermeable membrane during the drying process. It is best to choose mild conditions, preferably from 5°C to 70°C, particularly preferably from 15°C to 40°C, and it may be left at such temperature or dried under ventilation. Although the drying time is not particularly limited, it is usually about 10 to 100 hours, and it is sufficient to dry the film until the moisture in the film evaporates and the film reaches a constant weight. As described above, by treating a wet semipermeable membrane manufactured to have predetermined membrane properties, particularly predetermined molecular weight cutoff and permeate amount in accordance with the method of the present invention, the dry membrane obtained can last for a long time. Even if the membrane is kept dry for a long period of time, when it is rewetted, it has essentially the same physical properties as the originally wet membrane. The problem can be solved and the presence and transport of membranes can be greatly simplified. The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. In the following, parts mean parts by weight, % of aqueous solution concentration means % by weight, and all ultra-treatments using semipermeable membranes were performed at a temperature of 25°C.
The molecular weight cutoff of the semipermeable membrane is polyethylene glycol (hereinafter referred to as PEG), which has a rejection rate of 90%.
It was evaluated based on the average molecular weight of Example 1 In the above formula (), m-phenylene group is 70
12 parts of an aromatic polyamide having a repeating unit of 30 mol% of p-phenylene groups and having an intrinsic viscosity of 1.83 in N-methyl-2-pyrrolidone solution at 30°C and 7 parts of lithium chloride were・10 parts of N-dimethylacetamide and dimethyl sulfoxide
A film forming solution was prepared by dissolving it in a mixed solvent consisting of 71 parts. Apply this film-forming solution on a glass plate at room temperature,
Immediately, it was placed in water at 20°C, immersed for 24 hours, and solidified to obtain a wet semipermeable membrane. This membrane has a pure water permeation rate of 0.69 ml/cm ² ·min under a pressure of 1 Kg/cm ² and 4 Kg/cm 2 .
of PEG with various average molecular weights under pressure of ^cm2
When a 0.2% aqueous solution was subjected to ultrafiltration, the result was shown below.
It had a high PEG exclusion rate. The molecular weight cutoff was estimated to be approximately 62,000 from the graph of the average molecular weight of PEG and the exclusion rate. PEG average molecular weight PEG exclusion rate (%) 100000 95.2 20000 33.1 7500 3.8 2000 0.5 Next, this wet membrane was immersed in a 50% glycerin aqueous solution at room temperature for 24 hours, and then at 30°C until a constant weight was reached.
and dried for 48 hours. The dried membranes were left open in an ambient atmosphere at 50% relative humidity, rewetted with water after 5, 10 and 20 days, and membrane performance was measured under the same conditions as above. The results are shown in the table. It is apparent that the dried membrane, when rewetted, has substantially the same molecular weight cutoff and permeate volume as the originally wet membrane. Example 2 In the general formula () above, R ¹ is

A film-forming solution was prepared by dissolving 27.1 parts of polyimide of the formula and 27.1 parts of diethylene glycol in 45.8 parts of N-methyl-2-pyrrolidone. A wet semipermeable membrane was obtained in the same manner as in Example 1 using this membrane forming solution. This membrane has a pure water permeation rate of 0.21 ml/cm ² ·min under a pressure of 1 Kg/cm ² , and
When a 0.2% PEG aqueous solution was subjected to ultrafiltration under a pressure of 4 Kg/cm ² , it had the following exclusion rate and the molecular weight cutoff was estimated to be about 15,000. PEG average molecular weight PEG exclusion rate (%) 100000 99.6 20000 97.8 7500 59.4 2000 9.8 After immersing this wet membrane in a 45% by weight aqueous glycerin solution in the same manner as in Example 1, it was soaked for 30 minutes until a constant weight was reached.
Dry at ℃ for 48 hours. The resulting dry film was kept at relative humidity.
50%, stored in an open environment at a temperature of 20℃, 30 days, 60 days
The membrane performance was evaluated by rewetting with water after 120 days and 120 days. The results are shown in the table. When the dried membrane is rewetted,
It is clear that the film exhibits almost the same physical properties as the original wet film. Example 3 The same film forming solution as in Example 2 was used with an inner diameter of 1.06 mm and an outer diameter of 1.9 mm.
Pressure 2Kg/cm ²・G from mm annular orifice nozzle
This was extruded into water to obtain a hollow fiber-shaped polyimide wet semipermeable membrane with an inner diameter of 1.1 mm. This hollow fiber semipermeable membrane
Pure water permeation ^rate 0.17ml/cm2 under pressure of 0.5Kg/ ^cm2 .
Furthermore, when a 0.5% PEG aqueous solution was subjected to ultrafiltration under a pressure of 2 Kg/cm ² , it had the following exclusion rate and the molecular weight cutoff was estimated to be about 25,000. PEG average molecular weight PEG exclusion rate (%) 100000 98.3 20000 84.5 7500 22.1 2000 1.8 This wet film was dried in exactly the same manner as in Example 2, and left in an open environment at 50% relative humidity and 20°C for 60 days.
After 120 and 240 days, the membrane performance was evaluated by rewetting. Again, the rewet membrane exhibited membrane physical properties that were substantially equivalent to the originally wet membrane. Example 4 Polysulfone having a repeating unit represented by the above formula (P-
A membrane forming solution was prepared by dissolving 30 parts of 1700) and 30 parts of diethylene glycol in 100 parts of N-methyl-2-pyrrolidone, and a wet semipermeable membrane was obtained in the same manner as in Example 1. This membrane produces 0.55ml/ ^cm2・min of pure water under a pressure of 1Kg/ ^cm2 .

[Table] It has a water permeability rate of 0.2 under a pressure of 4Kg/ ^cm2 .
When a %PEG aqueous solution was subjected to ultrafiltration, it showed the following membrane characteristics, and the molecular weight cutoff was estimated to be approximately 30,000. PEG average molecular weight PEG exclusion rate (%) 100000 99.9 20000 67.9 7500 0.9 This wet film was dried in exactly the same manner as in Example 1, and the obtained dry film was left in an open environment at a relative humidity of 50% and a temperature of 20°C. After 5, 10 and 20 days, the film was re-wetted with water and the physical properties of the film were evaluated. After rewetting, the film showed almost the same physical properties as the originally wet film.

Claims (1)

[Scope of Claims] 1. A method for producing a dry semipermeable membrane from a wet semipermeable membrane made of a polymer selected from polyamide, polyimide, and polysulfone, wherein the wet semipermeable membrane is mixed with a polyhydric alcohol having 2 to 16 carbon atoms and/or or a derivative thereof after treatment with an aqueous solution of 30% by weight or more, at 5 to 70°C.
1. A method for producing a dry semipermeable membrane, which comprises drying the semipermeable membrane at a temperature of 100 to 100 nm, and making the thus obtained dried membrane, after rewetting, have substantially the same molecular weight cutoff and permeate volume as the initially wet membrane. 2 Polyamide is the formula having a repeating unit represented by, and of the phenylene group, m-phenylene group is 70 mol% or more,
The method for producing a dry semipermeable membrane according to claim 1, wherein the remainder is a p-phenylene group. 3 Polyimide is a general formula (However, R ¹ represents a divalent organic group.) The method for producing a dry semipermeable membrane according to claim 1, characterized in that it has a repeating unit represented by: 4 Polysulfone is the formula Or the expression The method for producing a dry semipermeable membrane according to claim 1, characterized in that it has a repeating unit represented by: 5 Claim 1, characterized in that the original wet semipermeable membrane has a molecular weight cut-off of 1,000 to 200,000.
A method for producing a dry semipermeable membrane according to any one of Items 4 to 4. 6 Polyhydric alcohol or its derivative has the general formula R ³ O-(CH ₂ CHR ² O) _o -R ⁴ (wherein R ² , R ³ and R ⁴ are each independently hydrogen,
It represents a methyl group or an ethyl group, and n represents an integer of 1 to 5 when R ² is hydrogen, and an integer of 1 to 3 when R ² is a methyl group or an ethyl group. ) The method for producing a dry semipermeable membrane according to any one of claims 1 to 5. 7. The method for producing a dry semipermeable membrane according to claim 6, wherein the polyhydric alcohol is at least one selected from ethylene glycol, diethylene glycol, and triethylene glycol. 8. The polyhydric alcohol is represented by the general formula R ⁵ -(OH) _n (wherein R ⁵ represents a saturated aliphatic hydrocarbon group having 3 to 6 carbon atoms, and m represents an integer of 2 to 6). A method for producing a dry semipermeable membrane according to claim 1, characterized in that: 9. The method for producing a dry semipermeable membrane according to claim 8, wherein the polyhydric alcohol is glycerin.