JPH04349927A - Preparation of precise filter membrane - Google Patents

Abstract

PURPOSE:To enhance the total filtering quantity when a raw liquid containing a suspended substance is filtered using an anisotropic precise filter membrane. CONSTITUTION:Polysulfone and polyvinyl pyrrolidone are dissolved in N- methyl-2-pyrrolidone and water is added to the resulting solution to prepare a film forming raw solution which is, in turn, cast on a support in a dissolved state and, after humid air adjusted in its temp. is applied to the surface of the cast liquid film for 1-30sec, the liquid film is immersed in a coagulation bath to form a precise filter membrane. Thereafter, the precise filter membrane is released from the support. In this method, the temp. of the coagulation bath is changed within the range of -10 deg.C-80 deg.C to control the anisotropic ratio of the precise filter membrane to 2-1000 times.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing precision filtration membranes, and is particularly applicable to drugs in the pharmaceutical industry, alcoholic beverages in the food industry, and electronics that perform fine processing, including the aforementioned manufacturing industry and semiconductor manufacturing industry. It is used for the filtration of purified water, pure water, etc. for the production of ultrapure water used in the industrial field and laboratories of various industries, and for other precision filtration. This invention relates to a precision filtration membrane that efficiently filters water. The microfiltration membrane obtained by the production method of the present invention can be used to separate, purify, recover liquids containing or suspending various polymers, microorganisms, yeast, and fine particles.
It can be applied to concentration, etc., and particularly when it is necessary to separate fine particles from a liquid containing fine particles that requires filtration, for example, various suspensions, fermentation liquids, or liquids containing fine particles. In addition to culture fluids, it can also be used to separate fine particles from pigment suspensions, and to separate and remove crud from condensate from nuclear power plants. In addition, with the rapid development of biotechnology in recent years, cultivation, fermentation,
The production of biochemical substances through enzymatic reactions, etc. is used in pharmaceuticals, foods,
It has become popular in many fields such as chemical products. Although the added value of these produced substances increases by refining them, the current situation is that a lot of cost is incurred in this refining operation. The microfiltration membrane obtained by the production method of the present invention is particularly effective in these fields, for example, for extracellular enzyme-producing bacteria that are cultured at high density by continuously removing reaction inhibitors from the culture solution. It can be used in a wide variety of applications, including continuous recovery of enzymes when using microorganisms, recovery of enzymes from solutions obtained by crushing intracellular enzyme-producing bacteria, and removal of enzymes from culture solutions obtained in batches.

0002

[Prior Art] Conventionally, techniques for separating suspended solids from an original liquid containing suspended solids using a membrane include, for example, reverse osmosis, ultrafiltration, microfiltration, which uses pressure as a driving force,
There are electrodialysis methods that use a potential difference as a driving force, and diffusion dialysis methods that use a concentration difference as a driving force. These methods can be operated continuously, and can separate, purify, or concentrate without significantly changing the temperature or pH conditions during the separation operation, and are capable of separating, purifying, or concentrating particles,
It is possible to separate a wide range of molecules, ions, etc.
It is economical because it can maintain a large processing capacity in a small plant, requires little energy for separation operations, and can process low-concentration raw liquids that are difficult to use with other separation methods, so it has been widely implemented. There is. Furthermore, with the progress of biotechnology, higher purity, higher performance,
High precision is now required, and instead of the conventional centrifugation and diatomaceous earth filtration, it is possible to perform continuous operation and process large quantities, and there is no need to add filter aids or flocculants.
Separation efficiency is unrelated to the difference in specific gravity between the bacterial cells and the suspension, and a clear filtrate can be obtained regardless of the physical properties of the culture medium or the type of bacterial cells.A completely closed system that enables high concentration cultivation and improves production efficiency. The field of application of microfiltration or ultrafiltration technology is expanding because it allows for no leakage of bacteria, it is possible to wash the bacteria after concentration, it is easy to scale up, and it is highly economical.

[0003] Membranes used in the above separation techniques include polymer membranes mainly made of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, and polyimide.
For example, Japanese Patent Publication No. 48-40050, Japanese Patent Publication No. 58-378
No. 42, JP-A-58-91732, JP-A-56-15
4051) and porous ceramic membranes that have excellent durability such as heat resistance and chemical resistance.Ultrafiltration membranes are used when the main purpose is to filter colloids, and ultrafiltration membranes are used to filter fine particles. For precision filtration, a precision filtration membrane having micropores suitable for the purpose is used. Such precision filtration membranes are divided into so-called isotropic membranes, in which the pore diameters of the micropores existing inside the membrane do not substantially change, and pore diameters on both surfaces of the membrane do not substantially change, and pore diameters in the membrane thickness direction. It is classified as having a structure called an anisotropic membrane, in which the pore size changes continuously or discontinuously, and the pore size on one surface of the membrane is different from the pore size on the other surface. Among these, isotropic membranes are described in Japanese Patent Application Laid-Open No. 58-98015, but the entire membrane exhibits a large resistance to the flow of fluid during filtration.
Not only can only a small flow rate be obtained (that is, only a small flow rate can be obtained per unit area, per unit time, and per unit differential pressure), it also has drawbacks such as easy clogging, short filtration life, and lack of blocking resistance. Ta. On the other hand, the anisotropic film is
-6406, which has a layer with small pores called the compact layer on one surface or inside the membrane, and has relatively large pores or an extremely large finger-shaped layer, which is described in JP-A-56-154051. The void extends from the inside of the membrane to the other surface. Suspended solids are trapped on the microporous membrane surface when an isotropic membrane is used or the raw liquid is supplied to the smaller pore side of the anisotropic membrane, whereas the raw liquid is trapped on the larger pore side of the anisotropic membrane. When a liquid is supplied, suspended matter is trapped inside the microporous membrane. In other words, when suspended substances are blocked on the surface of a microfiltration membrane, the blocked suspended substances create a very large filtration resistance and the permeation flow rate decreases rapidly, resulting in a lower total filtration rate. The pore diameter changes continuously or discontinuously in the membrane thickness direction, and the pore diameter on one surface of the microfiltration membrane is different from the pore diameter on the other surface.The side with the larger surface pore diameter is placed on the raw liquid side. By using the microfiltration membrane toward the target, suspended solids can be blocked inside the microfiltration membrane, making it possible to obtain a large total filtration amount.

0004

[Problems to be Solved by the Invention] As mentioned above, a microfiltration membrane has a structure in which the pore diameter changes continuously or discontinuously in the membrane thickness direction, and the pore diameter on one surface of the microfiltration membrane is different from the pore diameter on the other surface. By using a so-called anisotropic membrane with the larger surface pore size facing toward the raw liquid side, suspended solids can be blocked inside the microfiltration membrane, making it possible to obtain a large total filtration amount. If the average pore diameter on the side with larger surface pores of the anisotropic membrane is extremely larger than the average pore diameter in the dense layer, which has the smallest pore diameter, suspended substances will be dispersed uniformly in the cross-sectional direction inside the membrane and will not be captured and will not be captured in the dense layer. Since the particles are captured in a concentrated manner, the characteristics of an anisotropic film cannot be obtained as a result, and the result is similar to that of an isotropic film where the particles are captured on the surface. On the other hand, if the average pore diameter of the anisotropic membrane on the side with larger surface pores is not much different from the average pore diameter of the dense layer with the smallest pore diameter, that is, if the membrane has a structure close to that of an isotropic membrane, suspended solids will be trapped on the surface of the filtration membrane. As a result, the total filtration rate becomes low. That is, in order to obtain the characteristics of an anisotropic membrane, an appropriate anisotropic structure is required so that suspended substances can be dispersed and captured inside the membrane. In other words, a technique is needed to change the ratio of the average pore diameter on the side of the anisotropic membrane with larger surface pores to the average pore diameter of the dense layer with the smallest pore diameter, depending on the size, type, physical properties, etc. of the suspended solids. By doing so, it is expected that a membrane structure with optimal trapping performance depending on the suspended solids will be obtained and the maximum total filtration amount will be obtained.

[0005]

[Means for Solving the Problems] The present invention has been carried out to solve the above-mentioned problems in the prior art. The purpose of the present invention is to provide a new membrane-forming technology for precision filtration membranes, in which the anisotropic structure of the membrane can be freely changed according to the properties of the object to be filtered, thereby obtaining the maximum filtration flow rate. The present invention will be explained in detail below. The anisotropic structure is defined by the ratio of the average pore diameter of the larger surface pores to the average pore diameter of the dense layer, both when the dense layer exists on one surface of the membrane and when it exists inside the membrane. That is, the anisotropy ratio of an anisotropic structure is defined as the value obtained by dividing the average pore diameter on the larger surface pore diameter by the average pore diameter in the dense layer. The average pore diameter of the membrane 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 compact layer, and b indicates the thickness of the minimum diameter layer. Side A shows the side with a smaller surface aperture, and side B shows the side with a larger surface aperture. In precision filtration membranes, the average pore size of the dense layer is usually 0.05 μm or more and 10 μm or less, as shown above.
In the case of anisotropic membranes, the average pore size on the side with larger surface pores is usually 1
It is 100 μm or more, and the ratio of the average pore diameter of the surface having a large pore size to that of the dense layer is 2 times or more and 1000 times or less. In order to obtain a high filtration rate, a preferable anisotropic structure has an average pore diameter on the larger side of the surface pores that is 2 times or more and 500 times or less, preferably 5 times or more and 50 times or less, the average pore diameter of the dense layer. Further, in the structure from the surface with large pores to the dense layer, it is preferable that the average pore size changes continuously in order to uniformly disperse suspended substances inside the membrane. In addition, in order to improve the effect of trapping suspended solids, it is preferable that the thickness of the filtration membrane is thicker, but in terms of the strength of the filtration membrane and ease of handling, it is generally 20 μm or more and 1000 μm or less, preferably 100 μm.
A thickness of 300 μm or more is used. More preferably, a thickness of 170 μm or more and 300 μm or less is used.

[0006] The precision filtration membrane of the present invention is obtained by casting a membrane-forming stock solution in which polysulfone and polyvinylpyrrolidone are dissolved in N-methyl-2-pyrrolidone and adding water in a dissolved state onto a support. By applying temperature-controlled moist air to the surface of the liquid film for a period of 1 second to 30 seconds, the evaporation of the solvent and the absorption of non-solvent vapor are controlled and the core is drawn from the surface of the liquid film to the inside. By causing cervation and then immersing the polymer in a coagulation solution containing a liquid that is a non-solvent and is compatible with the polymer's solvent, the above coacervation phase is fixed as micropores and the particles other than the micropores are fixed. Obtained by forming pores. On the other hand, in the method for controlling the anisotropy ratio of a microfiltration membrane of the present invention, the temperature of the coagulating liquid is adjusted to 80° C.
By changing the temperature below ℃, the time from the formation of the coacervation phase inside the dense layer (toward the back side) to solidification can be adjusted, and the size of the pores up to the back side can be controlled. This is possible. When the temperature of the coagulation liquid is raised, the coacervation phase is formed faster and the time required for solidification becomes longer, so the pore diameter toward the back surface becomes larger. On the other hand, when the temperature of the coagulation liquid is lowered, the formation of the coacervation phase is delayed and the time required for solidification is shortened, so that the size of the pores toward the back surface does not become so large. That is, by controlling the temperature of the coagulation liquid, the anisotropy ratio of the anisotropic film can be controlled. Further, the average pore diameter of the dense layer having micropores can be controlled by the amount of water contained in the film-forming stock solution, the water concentration contained in the temperature-controlled moist air applied after casting, and the time period during which the temperature-controlled moist air is applied.

In addition to polysulfone, the membrane-forming polymer used in the present invention can be selected depending on the use of the porous membrane and other purposes. Such polymers include cellulose acetate, nitrocellulose, sulfonated polysulfone, polyethersulfone, polyacrylonitrile, styrene-acrylonitrile copolymer,
Examples include styrene-butadiene copolymer, saponified product of ethylene-vinyl acetate copolymer polyvinyl alcohol, polycarbonate, organosiloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene oxide, polyamide, polyimide, polyamideimide, polybenzimidazole, etc. .

In addition to polyvinylpyrrolidone, inorganic electrolytes, organic electrolytes, polymers, or swelling agents called swelling agents that control the porous structure include common salt, 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. Examples of good solvents for film-forming polymers include ionic surfactants such as sodium sulfosuccinate and sodium alkylmethyltaurate, which are usually solvents for film-forming polymers and quickly coagulate when immersed in a coagulating solution. N-methyl-2-
In addition to pyrrolidone, it can be selected depending on the type of film-forming polymer. When the membrane-forming polymer is polysulfone, dioxane, tetrahydrofuran, dimethylformamide, dimethylacetamide, or a mixed solvent thereof is suitable, and when polyacrylonitrile is used, dioxane, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, Dimethyl sulfoxide etc.
In the case of polyamide, dimethylformamide, dimethylacetamide, etc. are used, and in the case of cellulose acetate, acetone, dioxane, tetrahydrofuran, N-methyl-
2-pyrrolidone and the like are suitable.

In addition to water, nonsolvents used in the present invention include cellosolves, methanol, ethanol, propanol, acetone, tetrahydrofuran, polyethylene glycol, glycerin, and the like. The polymer concentration as a membrane 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 microfiltration membrane obtained becomes so low that it has no practical meaning, and if the concentration is lower than 5% by weight, a microfiltration membrane with sufficient separation function cannot be obtained. The amount of the swelling agent added is not particularly limited as long as the addition does not impair the uniformity of the film-forming stock solution, but it is usually 0.5% by volume or more and 10% by volume or less based on the solvent. The ratio of the nonsolvent to the good solvent may be in any range as long as the mixed liquid can maintain a uniform state, but it is preferably 5% by weight or more and 50% by weight or less. Coagulation baths include water, alcohols such as methanol, ethanol, and butanol. Anything that does not dissolve the polymer can be used, 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. Preferred are water, alcohols, or a mixture of two or more of these liquids.

0010

[Examples] Examples of the present invention are shown below, but the present invention is not limited thereto. 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 membrane forming stock solution. A liquid film with a thickness of 180 μm was cast onto a glass plate through a casting coater, and air adjusted to 25°C and relative humidity of 45% was applied to the surface of the liquid film at 2 m/sec for 5 seconds, and then immediately transferred to a coagulation tank filled with water. A precision filtration membrane was obtained by immersion. Table 1 shows the average pore diameter of the dense layer of the membrane, the average pore diameter of the larger surface pore diameter, and the anisotropy ratio when the temperature of the coagulation liquid was varied from 5° C. to 25° C. to 45° C.

[0011]

[Table 1]

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

[0013]

Effects of the Invention According to the present invention, a filtration membrane is formed that has a membrane structure that has an optimal trapping performance depending on the object to be filtered, that is, the anisotropic structure of the membrane can be freely changed according to the properties of the object to be filtered. It is considered to be an extremely powerful technology in terms of system design.

[Brief explanation of the drawing]

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

Claims (2)

[Claims] Claim 1: A film-forming stock solution prepared by dissolving polysulfone and polyvinylpyrrolidone in N-methyl-2-pyrrolidone and adding water is cast on a support in a dissolved state, and a film is formed on the surface of the cast liquid film. A manufacturing method in which a precision filtration membrane is formed by immersing the liquid film in a coagulation bath after applying temperature-controlled moist air, and then peeling off the precision filtration membrane from the support, in which the temperature of the coagulation bath is changed. A membrane forming method characterized by controlling the anisotropy ratio of a precision filtration membrane. Claim 2: The temperature of the coagulation bath is -10°C or higher and 80°C.
By setting the ratio of the average pore diameter of the anisotropic membrane on the side with larger surface pores to the average pore diameter of the dense layer to 1000 or more,
2. The film forming method according to claim 1, wherein the film forming method is controlled to be less than or equal to twice as much.