JPH0450057B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a hollow fiber separation membrane for precision filtration and ultrafiltration used for concentration, separation, and purification of liquid foods and pharmaceutical manufacturing processes, and a method for producing the same. The present invention relates to a hollow fiber separation membrane that uses polyamide with excellent properties as a membrane material and whose separation performance does not deteriorate even when subjected to high-pressure steam sterilization, and a method for manufacturing the same. [Prior art] Separation membranes such as reverse osmosis membranes, ultrafiltration membranes, and precision filtration membranes are used for seawater desalination, pure water production, wastewater treatment and gray water recovery, concentration of liquid foods, and separation and purification in pharmaceutical manufacturing processes. It is used in a wide range of industrial fields, and its range of applications is also expanding. These separation membranes are broadly classified into flat membranes, tubular membranes, and hollow fiber membranes depending on their shape, and all of them are used in the form of modules built into a case. Among these separation membrane modules, hollow fiber membrane modules do not require an auxiliary porous carrier to improve membrane strength, so the membrane area per unit volume of the module can be increased, making it suitable for industrial membrane separation processes. hollow fiber membrane modules are often used. Among the above-mentioned fields of application of separation membranes, when used in liquid food concentration and separation/purification processes in the pharmaceutical manufacturing field, the separation membrane module must be kept in a clean state by sterilization. Generally, methods for sterilizing equipment include treatment with liquid chemicals such as hypochlorite aqueous solution and gaseous chemicals such as ethylene oxide, but after treatment with liquid chemicals, sufficient cleaning must be performed to remove residual chemicals. Moreover, it is necessary to take measures against the exhaust gas after gaseous chemical treatment. The quickest, simplest, and safest sterilization method for humans is high-pressure steam treatment. By treating with high-pressure steam heated to 123 to 127 degrees Celsius, it can quickly destroy bacteria, viruses, and even the most heat-resistant spores. It can be killed in time.
However, in separation membranes that have already been put into practical use, the membrane material softens in such high-temperature environments, the pore structure that determines separation performance disappears, and the separation membrane no longer functions as intended. For example, cellulose-based or polyolefin-based separation membranes lose their functionality at 40°C, and even polysulfone-based separation membranes, which have relatively excellent heat resistance, lose their separation performance when treated with high-temperature water of 100°C or higher. Aromatic polyamides and polyimides are known as polymers with excellent heat resistance, and many polymers having high glass transition temperatures or decomposition temperatures of 300° C. or higher have been reported. However, because aromatic polyamides and polyimides have high heat resistance, it is practically difficult to use a melt manufacturing method to produce hollow fibers by heating and melting them, and wet manufacturing methods are possible because they are difficult to dissolve in organic solvents. The types of polymers that can be used are also limited. Due to such limitations in materials and manufacturing methods, membrane materials for ultrafiltration membranes and precision filtration membranes with large pore diameters in the range of 0.01 to 1 μm have been developed using polyamide or polyimide, which are solvent soluble and have excellent heat resistance. A hollow fiber separation membrane and its manufacturing method have not yet been proposed. The general manufacturing process of the wet manufacturing method for hollow fiber membranes is as follows:
A membrane forming stock solution production process in which the polymer of the membrane material is dissolved in a solvent, a coagulation core solution production process, and a process of extruding the membrane forming stock solution and coagulation core solution from the annular opening and the circular opening of a spinning nozzle having a double tubular structure, respectively. The process consists of an aerial traveling process in which the membrane forming stock solution and coagulation core liquid reach the coagulation bath from the spinning nozzle, and a coagulation process in which solvent removal and coagulation are completed in the coagulation bath. The cross-sectional structure of a separation membrane obtained by such a manufacturing process is composed of a microporous layer called a surface dense layer, which determines the molecular weight cutoff for separation in many cases, and a porous layer supporting the microporous layer. Attempts have been made to manufacture ultrafiltration membranes and hollow fiber separation membranes for precision filtration with micropore diameters of 0.01 μm or more by appropriately selecting this manufacturing process. There is still room for improvement in the mechanical strength of the hollow fibers. For example, Tokukai Akira
As described in Japanese Patent No. 55-106243, there is a method in which polyethylene oxide is added to the membrane forming stock solution and eluted and removed after membrane forming, but it is difficult to obtain a hollow fiber separation membrane having a uniform pore size of 0.01 μm or more. Also, Tokukai Akira
In Publication No. 60-222112, a hollow fiber membrane made of polysulfone and having a pore diameter of 0.01 μm is manufactured using the phase separation effect of a membrane-forming stock solution. however,
The viscosity of the membrane-forming stock solution is low, making it difficult to obtain a hollow fiber separation membrane with sufficient membrane pressure. Moreover, such hollow fiber separation membranes do not have the heat resistance to withstand high pressure steam sterilization conditions. The present inventors disclosed in Japanese Patent Application No. 62-18237 that a condensed ring polyamide having a fluorene skeleton has excellent heat resistance and is soluble in organic solvents, so wet spinning of hollow fibers is possible. proposed that it is possible to provide an ultrafiltration membrane with an estimated pore size of 1 to 2 nm and whose separation performance does not deteriorate even when subjected to high-pressure steam sterilization. The present inventors investigated a method for producing ultrafiltration membranes and hollow fiber separation membranes for precision filtration with pore diameters larger than 0.01 μm using the above heat-resistant polyamide, and found that the thickness from the inner surface to the outer surface of the hollow fibers was It consists of a network structure throughout the body, and the inner and outer surfaces have pores with a maximum diameter of 0.01 to 1 μm that are continuous to the network structure.
The present invention has been achieved in which a hollow fiber separation membrane having holes of [Problems to be Solved by the Invention] The purpose of the present invention is to have heat resistance that can withstand high-pressure steam sterilization conditions, and to have a maximum pore size of 0.01 on the outer and inner surfaces.
A hollow fiber separation membrane having pores of ~1 μm and a method for manufacturing the same are provided. [Means for solving the problem] The hollow fiber is composed of a network structure over the entire thickness from the inner surface to the outer surface, and pores with a maximum diameter of 0.05 to 1 μm are formed continuously in the network structure on the inner and outer surfaces. This is a hollow fiber separation membrane characterized by being made of a polyamide represented by the general formula (a). However, l indicates the number of repeating units, R is H,
Indicates either CH ₃ or C ₂ H ₅ . In addition, the hollow fiber is composed of a network structure over the entire thickness from the inner surface to the outer surface, and the inner and outer surfaces have pores of 0.01 to 0.05 μm continuous to the network structure. A hollow fiber separation membrane comprising a mixture of a polyamide represented by the following formula (b) and a polyamide represented by the following general formula (b). However, m and n indicate repeating units, R is H,
Indicates either CH ₃ or C ₂ H ₅ . General formula (b) in a hollow fiber separation membrane made of a polyamide mixture represented by the above general formulas (a) and (b)
The weight percentage of polyamide represented by is 50%
and the molar ratio n/m of the polyamide repeating unit represented by general formula (b) is 0.05 to
1. The hollow fiber separation membrane described above is manufactured by a wet manufacturing method. That is, the polyamide and its good solvent,
At least one kind selected from the electrolyte group consisting of monovalent and divalent cations, and monohydric alcohols such as ethyl alcohol and propyl alcohol, and polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin. The composition of the film-forming stock solution containing at least one kind of alcohol is such that it has a phase transition temperature at which it transitions from a homogeneous phase state to a phase-separated state. At least one of the temperature of the coagulated core liquid extruded from the annular opening of the hollow fiber spinning nozzle and simultaneously extruded from the circular opening, the atmospheric temperature during air travel from the nozzle to the external coagulating liquid, and the temperature of the external coagulating liquid, preferably is a method for manufacturing a hollow separation membrane, characterized in that coagulation and solvent removal are performed while causing a phase transition of a membrane forming stock solution from a homogeneous phase state to a phase separation state by lowering two or more temperatures below the phase transition temperature. be. Further, it is characterized in that the phase transition temperature of the membrane forming stock solution used is in the range of 10 to 80°C. Among the polyamides used as the material for the hollow fiber separation membrane of the present invention, the polyamide represented by the general formula (a) is (However, R represents either H, CH ₃ or C ₂ H _5. ) 9,9'-bis(4-aminophenyl)fluorenes represented by the formula It can be obtained by reacting isophthalic acid chloride or terephthalic acid chloride represented by the formula in a solvent such as N,N'-dimethylacetamide or N-methyl-2-pyrrolidone under cooling for several hours. In addition, the polyamide represented by the general formula (b) is
The above-mentioned 9,9'-bis(4-aminophenyl)fluorene is mixed with an acid chloride mixture in which adipic acid chloride and isophthalic acid chloride or terephthalic acid chloride are in a molar ratio of n:m to obtain a compound represented by general formula (a). It can be obtained by reacting in the same manner as polyamide. The polyamides represented by general formulas (a) and (b), which are the raw materials for the hollow fiber separation membrane of the present invention, both have excellent heat resistance. For example, in general formula (a), R is H
The glass transition temperature of polyamide is 380℃, and the decomposition temperature is 455℃. Also, in general formula (b), R is H
The glass transition temperature of polyamide with a repeating unit molar ratio n/m of 0.05 is 265°C and the decomposition temperature is 440°C, and the glass transition temperature of polyamide with a molar ratio n/m of 0.11 is 230°C and decomposition temperature. is 415
It is ℃. Among the hollow fiber separation membranes of the present invention, the general formula
In the case of a mixture of (a) and (b), general formula (b)
The weight percentage of polyamide represented by is 50%
Hereinafter, it is preferably 5 to 35%, and the molar ratio n/m of the repeating unit is 0.05 to 1, preferably
By setting it to 0.05 to 0.3, high heat resistance of the obtained hollow fiber separation membrane is maintained. The hollow fiber separation membrane of the present invention consists of a network structure over the entire thickness from the inner surface to the outer surface of the hollow fiber,
Its outer and inner surfaces have pores with a maximum diameter of 0.01 to 1 μm formed continuously in a network structure,
Among these, hollow fiber separation membranes with pores with a maximum pore diameter of 0.05 to 1 μm are made only of polyamide represented by the general formula (a), and hollow fiber separation membranes with pores with a maximum pore diameter of 0.01 to 0.05 μm are made with the general formula ( It is characterized by being made of a polyamide mixture represented by a) and (b). Here, the polyamide represented by the general formula (b) has the effect of reducing the diameter of the surface pores of the hollow fiber separation membrane obtained. Figure 1 is an example of a cross-sectional micrograph of a hollow fiber separation membrane made of polyamide in which R is H in the general formula (a), and it can be confirmed that it consists of a network structure over the entire thickness from the inner surface to the outer surface. On the other hand, Figure 2 is a microscopic photograph of the outer surface, and the maximum pore diameter is approximately 0.2 μm.
It can be confirmed that The range of this maximum pore diameter is adjusted during the manufacturing process of the hollow fiber membrane made of the polyamide. The hollow fiber separation membrane of the present invention can be obtained by a wet manufacturing method, the details of which will be described below. The film-forming stock solution of the present invention comprises a polyamide represented by the general formula (a) or a mixture of polyamides represented by the general formulas (a) and (b), a good solvent for the polyamide, an inorganic electrolyte, and a monovalent or polyhydric polyamide. It is a mixed solution of alcohols. Here, examples of good solvents for polyamide include polar solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethylsulfoxide. LiCl, LiNO ₃ and CaCl ₂ as inorganic electrolytes are dissolved in these polar solvents alone or in a mixture thereof to increase the solubility of the polyamide in the solvent. Monohydric or polyhydric alcohols are added for the purpose of inducing a transition to a phase separation state by cooling the membrane forming stock solution in a homogeneous phase state, and monohydric alcohols such as ethyl alcohol, propyl alcohol, cyclohexanol, etc. At least one type of polyhydric alcohol such as ethylene glycol, propylene glycol, and glycerin. The composition of such a membrane-forming stock solution varies depending on the maximum pore diameters of the outer and inner surfaces of the target hollow fiber separation membrane, but it generally contains 100 parts by weight of solvent, 10 to 50 parts by weight of polyamide, and 0.5 parts by weight of inorganic electrolyte. ~10 parts by weight, and 20 to 200 parts by weight of monohydric or polyhydric alcohol. The spinning core liquid and external coagulation liquid used to coagulate and remove solvent from the above film-forming stock solution include water alone, or water and monohydric alcohol such as methyl alcohol, polyhydric alcohol such as ethylene glycol, and N,N-dimethylacetamide. A mixed solution of a good solvent such as N-methyl-2-pyrrolidone is used. In a wet manufacturing method in which a membrane forming stock solution and a spinning core solution are extruded from an annular opening and a circular opening of a double-tubular spinning nozzle, respectively, and are introduced into an external coagulating liquid through an air travel process to manufacture a hollow fiber, the present invention In this case, at least one, preferably two or more of the spinning core liquid temperature, the atmospheric temperature during air travel, and the external coagulation liquid temperature are sufficiently low to cause a phase transition of the membrane forming stock solution from a homogeneous phase state to a phase separated state. is set to especially,
Setting the temperatures of the spinning core liquid and the external coagulating liquid to below the phase transition temperature is effective in increasing the pore size on the surface of the resulting hollow fiber separation membrane. This phase transition temperature can be determined by separately measuring the temperature change in the viscosity of the membrane forming stock solution. For example, for 100 parts by weight of N-methyl-2-pyrrolidone, 20 parts by weight of polyamide in which R is H in general formula (a) (hereinafter referred to as polyamide having repeating unit (a-1)),
The viscosity of a film-forming stock solution containing 5 parts by weight of LiCl and 58 parts by weight of ethylene glycol was measured using an E-type viscometer, and the results are shown in FIG. In FIG. 3, the viscosity of the film-forming stock solution differs greatly at 32° C., indicating that it is in a homogeneous phase state with high viscosity at the high temperature side and a phase separated state with low viscosity at the low temperature side. However, even in a phase-separated state, the viscosity is sufficiently high for spinning hollow fibers, and in this state, it is possible to obtain hollow fibers with superior strength compared to polysulfone resins, which have a lower viscosity. In the hollow fiber separation membrane of the present invention, the membrane forming stock solution extruded from the spinning nozzle is coagulated and desolvated below the phase transition temperature, but in order to practically obtain a low temperature below the phase transition temperature, the phase transition temperature is The temperature is preferably 10°C or higher. On the other hand, the membrane-forming stock solution introduced into the spinning nozzle is maintained in a homogeneous phase state by heating, and the phase transition temperature of the film-forming stock solution is preferably 80° C. or lower in order to suppress the generation of steam due to heating. The preferred phase transition temperature range of the membrane forming stock solution is 10 to 80℃.
It is. The phase transition temperature is optimized depending on the type of good solvent and the type and amount of monohydric and polyhydric alcohols to be added. By using N-methyl-2-pyrrolidone and at least one of polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin as the added alcohol, the phase transition temperature can be suitably adjusted to 10
Can be adjusted to ~80℃. [Function] The hollow fiber separation membrane obtained by the present invention is made of polyamide with a high glass transition temperature and high decomposition temperature as a membrane material, so it has excellent heat resistance and can be manufactured using the phase separation phenomenon of the membrane forming solution. Because it is a membrane method, it has large pore diameters and excellent water permeability, making it possible to perform high-pressure steam sterilization in fields where membranes are used, such as concentration of liquid foods, purification in pharmaceutical manufacturing processes, and separation, which require sterilization operations. It can be used as an ultrafiltration membrane and a microfiltration membrane. [Example] Examples of the present invention are listed below, but the present invention is not limited thereto. In the following examples, an E-type viscometer with a cooling rate of 0.5°C/min was used to measure the phase transition temperature of the film-forming stock solution. The pore sizes on the inner and outer surfaces of the hollow fiber separation membrane were determined from scanning electron micrographs. In addition, the pure water permeation rate of the hollow fiber separation membrane is at an operating pressure of 1.0 Kg/cm ² and a flow rate of 1.5 cm/cm 2 .
Measurements were made at a temperature of 25°C. Example 1 N-methyl-2-pyrrolidone (hereinafter referred to as NMP)
100 parts by weight and 5 parts by weight of lithium chloride 20 parts by weight of polyamide having a repeating unit (a-1) represented by ethylene glycol (hereinafter referred to as
EG) 58 parts by weight to prepare a membrane forming stock solution,
From the change in viscosity with temperature (Figure 3), the phase transition temperature
Obtained 32°C. This film-forming stock solution was heated to 40°C and extruded through the annular opening of the spinning nozzle (outer diameter 1.0 mm, inner diameter 0.8 mm), and at the same time, a spinning core solution of 185 parts by weight of NMP dissolved in 100 parts by weight of water at 5°C was added. After extrusion, the temperature during air travel was 25℃, and the external coagulation liquid was water alone, and the temperature was 5℃ for coagulation and desolvation.
A hollow fiber separation membrane with a diameter of 1.0 mm and an inner diameter of 0.7 mm was obtained. The obtained hollow fiber separation membrane consists of a network structure from the inner surface to the outer surface (Fig. 1), and the inner and outer surfaces have pores that are continuous to the network structure.
Its maximum pore diameter is 0.1 μm on the inner surface and on the outer surface.
It was 0.2 μm (Figure 2). In addition, the water permeation rate is
It was 1050/ ^m2・hour・atmospheric pressure. These membrane forming conditions and hollow fiber performance are summarized in Table 1. Examples 2 to 6 5 parts by weight of lithium chloride was dissolved in 100 parts by weight of NMP, 15 to 20 parts by weight of polyamide having the same repeating unit (a-1) as in Example 1, EG as a polyhydric alcohol, and propylene glycol (hereinafter PG). ) or glycerin (hereinafter referred to as Gly) to prepare a film-forming stock solution, and prepared using the same method as in Example 1 with an outer diameter of 1.0 mm.
A hollow fiber separation membrane with an inner diameter of 0.7 mm was obtained under the membrane forming conditions shown in Table 1. Table 1 also shows the characteristics of the hollow fiber separation membrane. The pore diameters of the inner and outer surfaces of the hollow fiber separation membrane can be controlled to 0.05 to 1 μm by adjusting the type and concentration of the polyhydric alcohol added to the membrane forming stock solution. Examples 7 and 8 Dissolve 5 parts by weight of lithium chloride in 100 parts by weight of NMP, and add 20 parts by weight of membrane material polyamide to the same repeating unit (a-1) and formula as in Example 1. A mixture with a polyamide having a repeating unit (b-1) represented by and having n/m of 0.11,
A hollow fiber separation membrane having an outer diameter of 1.0 mm and an inner diameter of 0.7 mm was obtained in the same manner as in Example 1 from a membrane forming stock solution containing EG as an added polyhydric alcohol. Table 1 summarizes the membrane forming conditions and characteristics of the hollow fiber separation membrane. Repeating unit (a-
By using the polyamide mixture of 1) and (b-1), the pore sizes on the inner and outer surfaces of the hollow fiber separation membrane can be controlled to 0.01 to 0.05 μm. Example 9 The hollow fiber separation membranes shown in Examples 1 and 8 were treated with pressurized steam at 123° C. for 30 minutes, and then the characteristics of the hollow fiber separation membranes were examined. As a result, the maximum pore diameters of the inner and outer surfaces of the hollow fibers of Example 1 remained unchanged at 0.1 and 0.2 μm, and the water permeation rate was 1020/m ² ·hr·atm. Furthermore, the maximum pore diameters on the inner and outer surfaces of the hollow fiber separation membrane of Example 8 remained unchanged, and the water permeation rate was 300/m ² .
It was hot at the time and atmospheric pressure. That is, the characteristics of the hollow fiber separation membrane of the present invention do not deteriorate even when subjected to pressurized steam sterilization.

【table】

[Table] [Effects of the Invention] The hollow fiber separation membrane obtained by the present invention is made of polyamide, which has a high glass transition temperature and decomposition temperature, as a membrane material, so it has excellent heat resistance and also has excellent phase separation of the membrane forming solution. Because it is a membrane-forming method that utilizes this phenomenon, it has large pores and excellent water permeability, making it suitable for concentration of liquid foods, purification in pharmaceutical manufacturing processes,
In the field of membrane application requiring sterilization operations such as separation, ultrafiltration membranes and microfiltration membranes capable of high-pressure steam sterilization can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional scanning electron micrograph of the hollow fiber separation membrane of the present invention, and FIG. 2 is a scanning electron micrograph of its outer surface. Figure 3 shows an example of the temperature change in the viscosity (η) of the film-forming stock solution, and the phase transition temperature is 32℃.
It shows that.

Claims (1)

[Scope of Claims] 1. The hollow fiber is composed of a network structure over the entire thickness from the inner surface to the outer surface, and has pores with a maximum diameter of 0.05 to 1 μm that are continuous to the network structure on the inner and outer surfaces. A hollow fiber separation membrane comprising a polyamide represented by the general formula (a). However, l indicates the number of repeating units, R is H,
Indicates either CH ₃ or C ₂ H ₅ . 2 The hollow fiber is composed of a network structure over the entire thickness from the inner surface to the outer surface, and the inner and outer surfaces have pores with a maximum diameter of 0.01 to 0.05 μm that are continuous to the network structure.
A hollow fiber separation membrane comprising a polyamide mixture represented by at least one of general formula (a) or (b) having pores. However, l, m, and n represent repeating units, and R represents any one of H, CH ₃ , and C ₂ H ₅ . 3. The hollow fiber separation membrane according to claim 2, wherein the weight percent of the polyamide represented by the general formula (b) in the polyamide mixture is 50% or less. 4. The hollow fiber separation membrane according to claim 2 or 3, wherein the molar ratio n/m of the repeating units of the polyamide represented by the general formula (b) is from 0.05 to 1. 5 Polyamide, a good solvent for the polyamide, at least one kind selected from the electrolyte group consisting of monovalent and divalent cations, and monohydric alcohols such as ethyl alcohol, propyl alcohol, and cyclohexanol, ethylene glycol,
The composition of the membrane forming stock solution containing at least one kind selected from polyhydric alcohols such as propylene glycol and glycerin has a phase transition temperature at which the composition changes from a homogeneous phase state to a phase separation state, and The heated homogeneous phase membrane forming stock solution is pushed out from the annular opening of the double-tubular hollow fiber spinning nozzle, and the temperature of the coagulating core liquid that is simultaneously pushed out from the circular opening and the atmosphere during air travel from the nozzle to the external coagulating liquid. By setting at least one, preferably two or more of the temperature and the temperature of the external coagulating liquid below the phase transition temperature, coagulation and desolvation can be carried out while causing the membrane forming stock solution to undergo a phase transition from a homogeneous phase state to a phase separated state. A method for producing a hollow fiber separation membrane, characterized in that the hollow fiber separation membrane according to any one of claims 1 to 4 is obtained by carrying out the following steps. 6 The phase transition temperature of the hollow fiber membrane forming stock solution is 10℃ to 80℃
The method for producing a hollow fiber separation membrane according to claim 5.