JP2961629B2 - Manufacturing method of microfiltration membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a microfiltration membrane, and more particularly, to a drug in the pharmaceutical industry, an alcoholic beverage in the food industry, and an electronic device which performs fine processing including the manufacturing industry and the semiconductor manufacturing industry. It is used for filtration of purified water and pure water for the production of ultrapure water and other microfiltration used in the industrial field and also in laboratories of various industries, and fine particles and microorganisms of submicron order of 10 μm or less, especially 1 μm or less. And a microfiltration membrane for efficiently filtering the same. Microfiltration membrane obtained by the production method of the present invention, various polymers, microorganisms, yeast,
It is applied to separation, purification, recovery, concentration, etc. of liquids containing or suspending fine particles, and can be applied particularly when it is necessary to separate the fine particles from a liquid containing fine fine particles that require filtration. For example, in addition to various kinds of suspensions containing fine particles, fermentation liquid or culture liquid, etc., it is also applied to the case of separating fine particles from a pigment suspension or the like, and separating and removing clad from condensate of nuclear power generation. . With the rapid development of biotechnology in recent years, production of biochemical substances by cultivation, fermentation, enzymatic reaction, and the like has been actively performed in many fields such as pharmaceuticals, foods, and chemical products. Purification of these products increases their added value, but the purification operation is currently costly. The microfiltration membrane obtained by the production method of the present invention is particularly effective in these fields, for example, an extracellular enzyme-producing bacterium that performs high-density culture by continuously removing a reaction inhibitor from a culture solution. The method can be applied to a wide variety of applications, such as continuous recovery of enzyme when is used, recovery of enzyme from a solution obtained by crushing intracellular enzyme-producing bacteria, and removal from a culture solution obtained by a batch method.

[0002]

2. Description of the Related Art Conventionally, techniques for separating a suspended substance from a raw liquid containing the suspended substance using a membrane include, for example, a reverse osmosis method using pressure as a driving force, an ultrafiltration method, a microfiltration method, and the like.
There are an electrodialysis method using a potential difference as a driving force and a diffusion dialysis method using a concentration difference as a driving force. These methods can be operated continuously, and can be separated, purified or concentrated without greatly changing the conditions of temperature and pH during the separation operation, and can be used for particles,
It is possible to separate a wide range of molecules, ions, etc.
It is economical because the processing capacity of a small plant can be kept large, the energy required for the separation operation is small, and it is possible to process low-concentration raw liquid which is difficult with other separation methods. I have. Furthermore, with the advancement of biotechnology, higher purity, higher performance,
High precision is required, and continuous operation is possible instead of conventional centrifugation and diatomaceous earth filtration, and large-scale processing can be performed.Addition of filter aids and flocculants is not required.
Separation efficiency is independent of the specific gravity difference between the cells and the suspension, and a clear filtrate can be obtained regardless of the properties of the culture solution and the type of cells. The application field of microfiltration or ultrafiltration technology is expanding because of the fact that cell filtration is possible, there is no leakage of bacteria, cells can be washed after concentration, scale-up is easy, and economic efficiency is high.

As the membrane used for the above-mentioned separation technique, a polymer membrane mainly composed of an organic polymer such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, polyimide, etc. No. 48-40050, JP-A-58-37
842, JP-A-58-91732, JP-A-56-1
No. 54051) and porous ceramic membranes having excellent durability such as heat resistance and chemical resistance. When mainly used for filtering colloids, an ultrafiltration membrane is used, and fine particles are used. In microfiltration for filtration, a microfiltration membrane having micropores suitable for the filtration is used. Such a microfiltration membrane has a so-called isotropic membrane in which the pore size of the micropores present therein does not substantially change and the pore sizes of both surfaces of the membrane do not substantially change, and a pore size in the thickness direction. The film is classified as having a structure called a so-called anisotropic film, which changes continuously or discontinuously and has a different pore size on one surface and the other surface. Of these, isotropic membranes
As described in Japanese Patent Application Laid-Open No. 58-98015, the entire membrane shows a large resistance to the flow of the fluid during filtration, and only a small flow rate can be obtained (that is, per unit area,
(A small flow rate can be obtained per unit time and per unit differential pressure.) In addition, there are drawbacks such as easy clogging, short filtration life, and no blocking resistance. On the other hand, the anisotropic film has a layer having a small pore diameter called a dense layer described in JP-B-55-6406 and JP-A-56-154051 on one surface of the film or inside the film. It has large holes or extremely large finger-shaped voids from the inside of the membrane to the other surface. Suspended substances are trapped on the microporous membrane surface when an isotropic membrane is used or when the raw liquid is supplied to the small pore side of the anisotropic membrane, while the original liquid is trapped on the large pore side of the anisotropic membrane. When supplying a liquid, the suspended matter is trapped inside the microporous membrane. In other words, when suspended substances are blocked on the surface of the microfiltration membrane, the suspended substances that have been blocked have an extremely large filtration resistance and the permeation flow rate drops rapidly, resulting in a low total filtration rate. The pore size changes continuously or discontinuously in the film thickness direction and the pore size of one surface of the microfiltration membrane is different from that of the other. When used in this manner, suspended substances can be prevented inside the microfiltration membrane, so that a large total filtration amount can be obtained.

[0004]

As described above, the microfiltration membrane has a structure in which the pore size changes continuously or discontinuously in the film thickness direction and the pore size on one surface of the microfiltration membrane differs from the other. By using the so-called anisotropic membrane having a large surface pore diameter toward the raw liquid side, suspended substances can be prevented inside the microfiltration membrane, so that a large total filtration amount can be obtained. If the average pore size on the side with the larger surface pore size of the anisotropic film is extremely larger than the average pore size on the dense layer with the smallest pore size, the suspended substance is uniformly dispersed in the Since the particles are intensively captured at the portion, the characteristics of the anisotropic film cannot be obtained as a result, and the same result as in the case of being captured on the surface like an isotropic film is obtained. On the other hand, in the case where the average pore size on the side where the surface pore size of the anisotropic membrane is large is not so different from the average pore size of the dense layer having the smallest pore size, that is, in the case of a structure close to an isotropic membrane, suspended substances are trapped on the filtration membrane surface. As a result, the total filtration amount is low. That is, in order to obtain the properties of the anisotropic film, an appropriate anisotropic structure is necessary for the suspended substance to be dispersed and trapped inside the film. That is, a technique for changing the ratio of the average pore diameter on the side with the larger surface pore diameter of the anisotropic film to the average pore diameter on the dense layer with the smallest pore diameter depending on the size, type, physical properties, and the like of the suspended substance is required. By doing so, it is expected that a membrane structure having an optimum trapping performance according to the suspended substance will be obtained, and the maximum total filtration amount will be obtained.

[0005]

SUMMARY OF THE INVENTION According to the present invention, there is provided a film-forming stock solution obtained by dissolving polysulfone and polyvinylpyrrolidone in N-methyl-2-pyrrolidone and adding water thereto, dispersing the solution on a support in a dissolved state, In a manufacturing method, a microfiltration membrane is formed by immersing the liquid membrane in a coagulation bath after applying a temperature-controlled wet air to the surface of the extended liquid membrane, and then the microfiltration membrane is peeled off from the support. Controlling the anisotropy ratio of the microfiltration membrane by setting the temperature of the coagulation bath to one temperature of -10 ° C or more and 80 ° C or less and setting the average surface pore diameter of the back surface to 1 µm or more and 100 µm or less. Was achieved by the following film forming method. Hereinafter, the present invention will be described in detail. The anisotropic structure is defined by the ratio of the average pore diameter on the side with the larger surface pore diameter to the average pore diameter of the dense layer both when the dense layer exists on one surface of the film and when it exists inside the film. That is, the anisotropy ratio of the anisotropic structure is defined as a value obtained by dividing the average pore diameter on the side having the larger surface pore diameter by the average pore diameter of the dense layer. The average pore diameter of the film surface shown here was calculated from a photograph obtained by an electron microscope, and the average pore diameter of the dense layer was measured by the ASTM-316-80 method as shown in FIG. In FIG. 1, a indicates the average diameter of the measured minimum diameter layer of the dense layer, and b indicates the minimum diameter layer thickness.
A side shows the side with a small surface diameter, and B side shows the side with a large surface diameter. In a microfiltration membrane, the average pore diameter of the dense layer is usually 0.05 μm or more and 10 μm or less as described above. In the case of an anisotropic membrane, the average pore diameter on the side with a large surface pore diameter is usually 1 μm or more and 100 μm or less. The ratio of the average pore diameter of the surface having a large pore diameter to the average pore diameter of the dense layer is 2 times or more and 1000 times or less. A preferable anisotropic structure for obtaining a high filtration amount is such that the average pore size on the side with the larger surface pore size is 2 times or more and 500 times or less, preferably 5 times or more and 50 times or less of the average pore size of the dense layer. Further, in the structure from the surface having a large surface pore size to the dense layer, it is preferable that the average pore size is continuously changed in order to uniformly disperse the suspended substance inside the film. In order to improve the effect of trapping suspended substances, it is preferable that the thickness of the filtration membrane is large, but from the viewpoint of the strength of the filtration membrane and handleability, it is generally 20 μm or more and 1000 μm or less, preferably 100 μm or less.
Those having a size of not less than μm and not more than 300 μm are used. More preferably, those having a size of 170 μm or more and 300 μm or less are used.

[0006] The microfiltration membrane of the present invention is prepared by dissolving polysulfone and polyvinylpyrrolidone in N-methyl-2-pyrrolidone and adding water, and then casting the solution on a support in a dissolved state. By applying a controlled temperature and humid air to the surface of the liquid film for 1 second or more and 30 seconds or less, the evaporation of the solvent and the absorption of the non-solvent vapor are controlled to the liquid film, and the core is formed from the surface of the liquid film toward the inside. The celvation is caused, and thereafter, the coacervation phase is fixed as micropores by immersing in a coagulation liquid containing a liquid that is non-solvent for the polymer and is compatible with the solvent of the polymer. Obtained by forming pores. On the other hand, the method for controlling an anisotropic ratio of a microfiltration membrane of the present invention is characterized in that the temperature of the coagulation liquid is in the range of −10 ° C. to 80
Adjusting the time from formation of the coacervation phase to solidification inside the dense layer (toward the back side) by controlling the temperature below ℃, and controlling the size of the pore diameter up to the back side Is possible. When the temperature of the coagulation liquid is increased, the formation of the coacervation phase is accelerated, and the time until solidification is increased, so that the pore diameter toward the back surface increases. On the other hand, when the temperature of the coagulation liquid is lowered, the formation of the coacervation phase is delayed and the time until solidification is shortened, so that the size of the pore diameter toward the back surface is not so large. That is, the anisotropic ratio of the anisotropic film can be controlled by controlling the temperature of the coagulating liquid. The average pore size of the dense layer having fine pores can be controlled by the amount of water contained in the stock solution for film formation, the concentration of water contained in the temperature-adjusted moist air after casting, and the time for applying the temperature-adjusted moist air.

[0007] In addition to polysulfone, the polymer for forming a membrane used in the present invention can be selected according to the purpose of the porous membrane or other purposes. Such polymers include cellulose acetate, nitrocellulose, sulfonated polysulfone, polyethersulfone, polyacrylonitrile, styrene-acrylonitrile copolymer,
Styrene-butadiene copolymer, saponified ethylene-vinyl acetate copolymer polyvinyl alcohol, polycarbonate, organosiloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene oxide, polyamide, polyimide, polyamideimide, polybenzimidazole, etc. .

An inorganic electrolyte, an organic electrolyte, a polymer, or an electrolyte called a swelling agent for controlling the porous structure is not limited to polyvinylpyrrolidone, but may be sodium chloride, lithium chloride, sodium nitrate, potassium nitrate, sodium sulfate, Metal salts of inorganic acids such as zinc chloride; metal salts of organic acids such as sodium acetate and sodium formate; polymers such as polyethylene glycol and polyvinylpyrrolidone; polymer electrolytes such as sodium polystyrene sulfonate and polyvinylbenzyltrimethylammonium chloride; dioctyl As a good solvent for a film-forming polymer, which can be mentioned as an ionic surfactant such as sodium sulfosuccinate and sodium alkylmethyltaurate, it is usually a solvent for a film-forming polymer and rapidly solidifies when immersed in a coagulating liquid. Replaced with liquid One is used, N- methyl-2
In addition to pyrrolidone, it can be selected depending on the type of the film-forming polymer. When the polymer for forming a membrane is polysulfone, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide or a mixed solvent thereof is suitable.For polyacrylonitrile, dioxane, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, When dimethyl sulfoxide and the like are polyamides, dimethylformamide and dimethylacetamide are suitable, and when cellulose acetate is used, acetone, dioxane, tetrahydrofuran, N-methyl-2-pyrrolidone and the like are suitable.

The non-solvent in the present invention includes, in addition to water, cellosolves, methanol, ethanol, propanol, acetone, tetrahydrofuran, polyethylene glycol, glycerin and the like. The polymer concentration as a film forming stock solution is 5% by weight or more and 35% by weight or less, preferably 10% by weight or more and 30% by weight or less. If it exceeds 35% by weight, the water permeability of the obtained microfiltration membrane becomes so small as to have no practical significance, and if it is lower than 5% by weight, a microfiltration membrane having a sufficient separation function cannot be obtained. The addition amount of the swelling agent is not particularly limited as long as the uniformity of the film forming stock solution is not lost by the addition, but is usually 0.5% by volume or more and 10% by volume or less based on the solvent. The ratio of the non-solvent to the good solvent may be in any range as long as the mixed solution can maintain a uniform state, but is preferably 5% by weight or more and 50% by weight or less. Coagulation baths include water, alcohols such as methanol, ethanol, and butanol. Any material can be used as long as it does not dissolve the polymer, such as glycol ethers such as ethylene glycol and diethylene glycol, aliphatic hydrocarbons such as n-hexane and n-heptane, and glycerols such as glycerin. Preference is given to water, alcohols or a mixture of two or more of these.

[0010]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. Example 15 parts of polysulfone (P3500, manufactured by Amoco), 15 parts of polyvinylpyrrolidone, and 3 parts of water are dissolved in 67 parts of N-methyl-2-pyrrolidone to obtain a stock solution. A glass plate is cast through a casting coater with a liquid film thickness of 180 μm, and the surface of the liquid film is exposed to air adjusted to 25 ° C. and a relative humidity of 45% at 2 m / sec for 5 seconds, and then immediately into a coagulating liquid tank filled with water. It was immersed to obtain a microfiltration membrane. Table 1 shows the average pore diameter of the dense layer, the average pore diameter on the side with the larger surface pore diameter, and the anisotropy ratio when the temperature of the coagulating liquid was changed to 5 ° C., 25 ° C., and 45 ° C.

[0011]

[Table 1]

The average pore size of the film surface shown here was calculated from a photograph obtained by an electron microscope, and the average pore size of the dense layer was measured by the ASTM-316-80 method.

[0013]

According to the present invention, it is possible to form a membrane structure having an optimum trapping performance according to an object to be filtered, that is, to freely change the anisotropic structure of the membrane according to the properties of the object to be filtered. It is considered to be a very powerful technology in system design.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of a cross section of a microfiltration membrane.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-139930 (JP, A) JP-A-63-141607 (JP, A) JP-A-63-93309 (JP, A) JP-A-60-1985 206416 (JP, A) JP-A-61-38603 (JP, A) JP-A-61-232860 (JP, A) JP-A-61-238306 (JP, A) JP-A-55-35969 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 71/68 B01D 71/44

Claims (3)

(57) [Claims] 1. A film-forming stock solution obtained by dissolving polysulfone and polyvinylpyrrolidone in N-methyl-2-pyrrolidone and adding water is cast on a support in a dissolved state, and is applied to the surface of the cast liquid film. In a production method of forming a microfiltration membrane by immersing the liquid membrane in a coagulation bath after applying a controlled temperature humid air, and then peeling the microfiltration membrane from the support.
The temperature of the coagulation bath is set to one temperature of -10 ° C or more and 80 ° C or less, and the average surface pore diameter of the back surface is 1 µm or more and 100 µm or less.
A membrane production method comprising controlling the anisotropy ratio of a microfiltration membrane by: 2. An average surface pore size of not less than 5.0 μm and not more than 50.
2. The method according to claim 1, wherein the thickness is set to 0 μm or less. 3. The film forming method according to claim 1, wherein the fine pores of the dense layer are fixed by immersion in a coagulating liquid.