JPH07163849A - Polysulfone-based hollow fiber membrane and method for producing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a polysulfone-based hollow fiber membrane which can be backwashed with gas and is excellent in stain resistance, and a method for producing the same. [Structure] A polysulfone-based hollow fiber membrane containing 1 to 10% of a hydrophilic polymer and having an air pressure of 0.3 to 5 kg / cm ↑ 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polysulfone-based hollow fiber membrane and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a technique using a membrane having a selective permeability in a separation operation has made remarkable progress and has been put to practical use in various applications. In particular, when the shape of the membrane is a hollow fiber membrane, it is advantageous because the membrane area per occupied volume can be overwhelmingly large as compared with the case of a shape such as a flat membrane or a tubular membrane.

When a liquid is filtered using a hollow fiber membrane,
As the filtration process is continued, scale, SS components and other filter residue adhere to the surface of the membrane, and the filtration rate decreases. In order to prevent such a decrease in filtration speed and perform stable filtration for a long time, the permeated liquid that has permeated the membrane is backflowed to the raw liquid side at regular intervals to peel off the filter cake adhering to the membrane surface and restore the filtration speed. Permeating liquid backwashing is performed, or gas is permeated from the permeating liquid side to the undiluted side, and the filter cake that has adhered to the membrane surface is peeled off in the same manner as above to recover the filtration rate. ing.

In order to carry out the above-mentioned permeate backwashing, a pump for backflowing the permeate (hereinafter referred to as a backwash pump) and a tank for storing the permeate (hereinafter referred to as a stock tank) are used. I need. On the other hand, the gas backwashing is advantageous in the following points as compared with the case of performing the permeate backwashing. Since the permeated liquid that has permeated the membrane is not consumed during backwashing, the filtration efficiency is good. Due to the synergistic effect of gas ejection from the hollow fiber membrane surface and the accompanying vibration of the hollow fiber membrane, the effect of removing scale and SS components adhering to the membrane surface is increased, and the backwash efficiency is high. No backwash pumps or stock tanks are required, reducing the cost of equipment. However, in order to perform gas backwashing, it is necessary that the hollow fiber membranes have good gas permeability, and not all hollow fiber membranes can be backwashed with gas. Therefore, under the present circumstances, the above-mentioned permeate backwash or gas backwash is appropriately selected and adopted according to the hollow fiber membrane used for filtration.

On the other hand, various high molecular materials such as cellulose-based polymers, polyacrylonitrile-based polymers, polyimide-based polymers, polysulfone-based polymers, polyvinyl alcohol-based polymers and fluorine-based polymers have been conventionally used as the material for the membrane. . Among these, polysulfone-based polymers are heat resistant, acid resistant, alkali resistant,
It is known as a film material with excellent resistance to oxidants.

The inventors of the present invention, as a polysulfone-based hollow fiber membrane capable of backwashing with gas, have an average pore diameter of 0.1 to 5 μm on the outer surface.
Of micropores at a porosity of 10 to 70%, the inner surface and the inside of the membrane have a fine porous structure, and the water permeability is 200.
0l / m ↑ 2 · hr · kg / cm ↑ 2 or more, the inhibition rate of polystyrene latex (particle size 3800 Å) is 90% or more, and the ventilation pressure is 0.5.
We proposed a polysulfone-based hollow fiber membrane exhibiting ˜5 kg / cm 2 (see Japanese Patent Laid-Open No. 58-91822).

[0007]

Generally, polysulfone-based hollow fiber membranes are made of a hydrophobic material, so that when the membrane is dried, the water permeability is significantly reduced, and the adsorptivity of proteins and the like is greatly contaminated. It has drawbacks such as being easily damaged. In particular, in order to recover the water permeability of the membrane once the membrane is completely dried, it is not enough to simply immerse the membrane in water, and a solvent that can mix the membrane with water such as ethanol, or a surfactant. It is necessary to once immerse the film in the aqueous solution to fully fill the fine pores in the membrane wall with water. Therefore, when the polysulfone-based hollow fiber membrane is backwashed with gas, the membrane is placed in a dry state, which may cause a decrease in water permeability.

The polysulfone-based hollow fiber membrane described in JP-A-58-91822 can be backwashed with gas, but in order to prevent the decrease in water permeability of the hollow fiber membrane, Reverse gas cleaning is performed while the hollow fiber membrane is immersed in the treatment liquid, or the relative humidity is 9% in a closed container.
In an atmosphere of 0% or more, in a relatively short time such as within 10 minutes, and in an excessive amount of gas (for example, 2,000 Nl / m ↑ 2.
It is necessary to carry out the gas backwash under the limited conditions of flowing (above hr). Further, similar to the conventional polysulfone-based hollow fiber membrane, it has a drawback that it has a large adsorptivity for proteins and the like and is easily contaminated.

The present invention has been made in view of the above problems, and it is possible to carry out backwashing with gas without reducing the water permeability of the hollow fiber membrane without providing special conditions. It is an object of the present invention to provide a polysulfone-based hollow fiber membrane excellent in stain resistance and a method for producing the same.

[0010]

According to the present invention, one of the above objects is a polysulfone type hollow fiber membrane containing a hydrophilic polymer in an amount of 1 to 10% by weight, and having a ventilation pressure of 0.3 to 10. 5k
This is achieved by providing a polysulfone-based hollow fiber membrane characterized by having g / cm ↑ 2. Another one of the above-mentioned objects is polysulfone, a hydrophilic polymer, a common solvent for both, and a fine powder that is insoluble in the common solvent. The step of extruding from a nozzle and forming a hollow fiber membrane by a dry-wet spinning method or a wet spinning method, and immersing the hollow fiber membrane after spinning in an extraction solvent that dissolves the fine powder without dissolving polysulfone. The present invention is achieved by providing a method for producing a polysulfone-based hollow fiber membrane, which comprises a step of extracting and removing a body.

The polysulfone referred to in the present invention means a polymer having the following general formula (I) or (II) as a repeating unit, but an alkyl type can be used.

[0012]

[Chemical 1]

[0013]

[Chemical 2]

Further, the hydrophilic polymer used in the present invention is a polymer which is compatible with polysulfone and has hydrophilicity, such as polyvinyl alcohol, ethylene / vinyl alcohol copolymer, ethylene / acetic acid. Examples thereof include vinyl copolymers, polyvinyl acetate, polyethylene oxide, polyvinylpyrrolidone, polyacrylic acid, and modified polymers thereof. Among them, polyvinyl alcohol and ethylene / vinyl alcohol copolymers have stain resistance of the obtained film. Is preferable, and the cross-linking structure described later is easy, which is preferable. If necessary, two or more kinds of hydrophilic polymers may be used at the same time.

The content of the hydrophilic polymer in the polysulfone hollow fiber membrane of the present invention is preferably 1 to 20% by weight, more preferably 3 to 10% by weight. When the content of the hydrophilic polymer exceeds 20% by weight, the excellent properties of polysulfone such as heat resistance and chemical resistance may be impaired, which is not preferable. On the other hand, if the content of the hydrophilic polymer is less than 1% by weight, it is difficult to impart sufficient hydrophilicity to the hollow fiber membrane.

The hydrophilic polymer is preferably present in the hollow fiber membrane in a state of being crosslinked intramolecularly and / or intermolecularly. In particular, when the hydrophilic polymer is a water-soluble polymer such as polyvinyl alcohol, it becomes insoluble in water due to such cross-linking structuring. Therefore, when the hollow fiber membrane is used, the hydrophilic polymer in the membrane is It is prevented that the hydrophilicity of the membrane is impaired due to the gradual elution.

The hydrophilic polymer may be crosslinked by a method using a so-called chemical crosslinking agent such as aldehyde or epoxide, a method of crosslinking by heat treatment,
A known method such as a method of irradiating with radiation such as γ-rays to crosslink can be mentioned, but it may be appropriately selected depending on the kind of the hydrophilic polymer.

Whether or not the hydrophilic polymer has a crosslinked structure is treated by treating the polysulfone-based hollow fiber membrane of the present invention with a solvent that dissolves the polysulfone such as dimethylformamide and the hydrophilic polymer, and then crosslinks the polymer. This can be confirmed by observing whether or not the structured hydrophilic polymer remains as an undissolved substance.

The polysulfone type hollow fiber membrane of the present invention is
It has a ventilation pressure of 3 to 5 kg / cm ↑ 2. The ventilation pressure referred to in the present invention is a measure of the gas permeation rate at the time of gas backwashing, and the polysulfone-based hollow fiber membrane is immersed in a 1% sodium lauryl sulfate aqueous solution at 25 ° C. for 24 hours, or Or 1% in 75% ethanol aqueous solution at 25 ℃
After soaking for a period of time, the hollow fiber membrane is rinsed with running water at 25 ° C. for 60 minutes or more to completely wet the so-called water in which the pores in the membrane wall and inside the membrane are sufficiently filled with water, and then When the inside of the hollow fiber membrane was pressurized with air and bubbled while the hollow fiber membrane was immersed in water, 400 Nl / m ↑ 2 · h
It refers to the air pressure required to obtain an air permeation rate of r. When the ventilation pressure of the hollow fiber membrane is less than 0.3 kg / cm ↑ 2, the hollow fiber membrane often has large voids inside the membrane, and the membrane strength is not sufficient. On the other hand, if the ventilation pressure of the hollow fiber membrane exceeds 5 kg / cm ↑ 2, it is necessary to increase the pressure of the gas during backwashing of the gas, which imposes a burden on the hollow fiber membrane and the filtration device, which is not practical. Ventilation pressure is 1-4kg / cm ↑
It is more preferable if it is in the range of 2 to 2 to 3 kg / cm ↑ 2
Within the range, it is most preferable in terms of the balance of film strength, ventilation pressure, film life, etc.

The polysulfone-based hollow fiber membrane of the present invention has micropores having an average pore diameter of 0.1 to 10 μ on at least one surface at an opening ratio of 10 to 70%. The average pore size of the fine pores referred to in the present invention is defined by the following formula (1).

[0021]

[Equation 1]

In the above formula, D (ave) means the average pore size,
D ↓ 1 means the measured diameter of the first micropore, and D ↓ n means the measured diameter of the nth micropore. Note that the measured diameters D ↓ 1 and D ↓ n indicate the diameter of a fine hole when it is close to a circle, and the diameter of a circle having the same area as the fine hole when the fine hole is not circular.

The average pore diameter of the fine pores is closely related to the ventilation pressure, and if the average pore diameter of the fine pores is less than 0.1 μ, the ventilation pressure becomes too high, which is not preferable. On the other hand, if the average pore size of the micropores exceeds 10μ, the strength of the membrane tends to be weak and a large slag will penetrate into the inside of the membrane. It is not preferable because the membrane cannot be sufficiently regenerated by washing.

In the present invention, fine pores of 0.05 μ or less are not included in the calculation of the average pore diameter. However, 0.
Micropores of 05 μm or less may be present to the extent that the objects and effects of the present invention are not impaired. Further, it is preferable that the fine pores on the surface of the membrane have a uniform pore diameter, but it is not particularly necessary that they are uniform and may be non-uniform.

The opening ratio in the present invention is expressed as a percentage by dividing the total pore area of the micropores opened on the surface of the membrane by the surface area of the membrane on the side where the micropores are present. is there. If the opening ratio is less than 10%, the water permeability of the film is low, which is not preferable. Further, if the aperture ratio exceeds 70%, the surface strength becomes small and the film is easily damaged during handling, which is not preferable. When the aperture ratio is in the range of 20 to 50%, it is more preferable in terms of the balance between the membrane permeation performance and the mechanical performance.

The polysulfone-based hollow fiber membrane of the present invention has an average pore size of 0.1 to 1 on the surface opposite to the side where the fine pores are present.
It is preferable to have fine pores of 0 μ at a ratio of the opening ratio of 10 to 70%, but it is not necessarily limited to this and may have pores of 10 μ or more.

The polysulfone type hollow fiber membrane of the present invention has a fine porous structure inside the membrane. The fine porous structure referred to here is a network structure, a honeycomb structure, a fine interstitial structure, etc., which has a function of supporting the inner surface and outer surface of the membrane, and determines the blocking rate, water permeability, ventilation pressure, etc. It also has a function to do. Further, the inside of the film may have a finger-like structure or a macrovoid structure. It should be noted that the inside of the membrane preferably has micropores of the same size as the outer surface, and the pore diameter is preferably more uniform, but it need not be particularly uniform and may be nonuniform.

The polysulfone-based hollow fiber membrane of the present invention has the above-mentioned structure on the surface and inside of the membrane.
It has a water permeability of more than 000l / m ↑ 2 ・ hr ・ kg / cm ↑ 2 and exhibits sufficiently high permeability.

The polysulfone hollow fiber membrane of the present invention has a fractional particle size in the range of 0.2 to 2 μm. Fraction particle size is 0.
If it is less than 2 μ, the ventilation pressure becomes too high, which is not preferable. Further, if the fractional particle size exceeds 2 μ, the film strength may decrease, which is not preferable.

The term "fractionated particle size" as used in the present invention means the particle size (S) of particles having a hollow fiber membrane rejection rate (R) of 90%, and at least two types of particles having different particle sizes. The blocking rate of is measured, and the value of S at which R is 90 in the following formula (2) is determined based on the measured value, and this is used as the fractional particle size.

[0031]

[Equation 2]

In the above equation, a and m are constants determined by the hollow fiber membrane, and are calculated based on the above measured values.

The polysulfone-based hollow fiber membrane of the present invention has an inner diameter of 0.2 to 3 mm and an outer diameter of 0.4 to 5 mm.

Next, a method for producing the polysulfone hollow fiber membrane of the present invention will be described.

The polysulfone-based hollow fiber membrane of the present invention comprises four components of polysulfone, a hydrophilic polymer, a common solvent for both, and a fine powder insoluble in the common solvent and having an average particle diameter of 0.01 to 5 μm. It is produced by forming a spinning stock solution in which the fine powder is uniformly dispersed by a dry-wet spinning method or a wet spinning method.

The common solvent referred to in the present invention has a solubility of 10 g (polysulfone) / 100 cc (solvent) or more in polysulfone at a temperature in the range of 0 to 120 ° C.
In addition, it has a dissolving ability of 1 g (hydrophilic polymer) / 100 cc (solvent) or more with respect to the hydrophilic polymer at a temperature in the range of 0 to 120 ° C. Examples of such a common solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, N-vinylpyrrolidone, dimethylsulfoxide, sulfolane, and the like. It may be selected according to the necessity.

Examples of the fine powder insoluble in the common solvent include metal oxides such as silicon oxide, zinc oxide and aluminum oxide, sodium chloride, sodium acetate,
Examples thereof include inorganic compounds such as sodium phosphate, calcium carbonate and calcium hydroxide. Of these, fine powder of silica (silica powder), so-called white carbon, is the best because it has a small powder particle size and various particle sizes are commercially available and can be easily dispersed in a spinning dope. The term "insoluble" in the present invention means that the solubility is 0.1 g (fine powder) / 100 cc (solvent) or less at the melting temperature of the spinning dope.

The fine powder is added for the purpose of forming fine pores in the polysulfone hollow fiber membrane. The fine powder in the present invention needs to have an average particle diameter of 0.01 to 5 μm. If the average particle size of the fine powder is less than 0.01 μ, the desired air permeability and film structure cannot be obtained, and if the average particle size of the fine powder exceeds 5 μ, it is too large and voids are formed. Only large inhomogeneous films can be obtained. It is preferable that the average particle size of the fine powder is in the range of 0.1 to 3 μ, because the obtained film structure is excellent in homogeneity and air permeability.

The concentration of polysulfone in the spinning dope needs to be within the range where it can be molded as a hollow fiber membrane, and is usually set in the range of 10 to 40% by weight, preferably 15 to 25% by weight. The concentration of polysulfone in the spinning dope is 1
If it is less than 0% by weight, the strength of the obtained hollow fiber membrane is not sufficient, and some kind of support is required for actual use, which is not preferable. On the other hand, if the concentration of polysulfone in the spinning dope exceeds 40% by weight, the viscosity of the spinning dope becomes too high and it becomes difficult to form a hollow fiber membrane, which is not preferable.

The hydrophilic polymer is 1 for polysulfone.
To 100% by weight, preferably 5 to 30% by weight. The addition amount of the hydrophilic polymer may be appropriately selected within the above range, but when a water-soluble polymer such as polyvinyl alcohol is used as the hydrophilic polymer, coagulation or washing during film formation Since a part of the hydrophilic polymer is extracted from the molded hollow fiber membrane in the step, it is preferable to add a large amount to the stock solution for spinning. Further, the addition amount of the hydrophilic polymer is appropriately adjusted depending on the molecular weight of the hydrophilic polymer.

The fine powder is 15 to 400% by weight, preferably 30 to 100% by weight, based on polysulfone.
To be added. The air permeability and pore size of the obtained polysulfone-based hollow fiber membrane can be controlled by adjusting the addition amount of these fine powders.

As the method for preparing the spinning dope in the present invention, a fine powder pre-addition method is used in which fine powder is added to and mixed with the above-mentioned common solvent, and the mixture is stirred to dissolve polysulfone and hydrophilic polymer. Simultaneous addition method in which fine powder, polysulfone and hydrophilic polymer are added to the common solvent at the same time and stirred, and further, fine powder is added and mixed after dissolving polysulfone and hydrophilic polymer in the common solvent, and then added after stirring Although any method may be used, the pre-addition method is preferable from the viewpoint of dispersibility of the fine powder.

As a method for uniformly dispersing the fine powder in the spinning dope, it is sufficient to stir with a stirrer, but in order to improve the dispersibility of the fine powder, high speed stirring, homomixer, ultrasonic dispersion, It is preferable to use a more advanced mixing / dispersing means such as a pipeline agitator or a static mixer.

The spinning stock solution thus prepared is surprisingly a spinning stock solution having a composition such that the three components of polysulfone, hydrophilic polymer and common solvent undergo phase separation to form a hollow fiber membrane. Even when present, the fine powder is dispersed in the spinning dope, so that the phase separation of the spinning dope is suppressed and the state of a homogeneous solution is maintained. In addition, it is possible to produce a polysulfone-based hollow fiber membrane which has both high water permeability and high opening ratio on the membrane surface, and is well balanced in terms of air permeability, fractionation, water permeability and hydrophilicity of the membrane. be able to. Therefore, in the method for producing a polysulfone-based hollow fiber membrane of the present invention, for example, polyvinyl alcohol
It is also possible to use hydrophilic polymers such as ethylene glycol and ethylene / vinyl alcohol copolymers, which have poor compatibility with polysulfones and which have hitherto been difficult to add to the spinning dope.

The spinning dope prepared as described above is
Usually, after defoaming, it is discharged from a nozzle having a double ring structure together with an injection liquid, and then immersed in a coagulation liquid to form a hollow fiber membrane. At the time of film formation, the spinning dope discharged from the nozzle is once passed through a fixed length of air (hereinafter referred to as the dry zone) and then introduced into the coagulating liquid, a so-called dry-wet spinning method, or discharged from the nozzle. Any of the so-called wet spinning methods in which the prepared spinning stock solution is directly introduced into the coagulation solution may be adopted, but the dry-wet spinning method makes it easy to control the outer surface structure of the hollow fiber membrane, and also the water permeability. It is more preferable because it is possible to produce a hollow fiber membrane having a high temperature.

In the dry-wet spinning method, the length of the dry zone,
The temperature and humidity determine the outer surface structure of the resulting hollow fiber membrane. When the length of the dry zone is increased or the temperature or humidity of the dry zone is increased, the pore size of the fine pores formed on the outer surface of the hollow fiber membrane tends to be generally large. Even if the dry zone length is 0.1 cm, there is a clear difference in that the outer surface structure of the obtained hollow fiber membrane is completely different from the wet spinning method in which the dry zone length is 0 cm. Show. If the dry zone is too long, the spinnability will be affected.
cm, preferably 0.1 to 50 cm.

An injection liquid is usually introduced inside the double annular nozzle for the purpose of maintaining the shape of the spinning dope discharged from the nozzle in a hollow fiber shape. Such an injection solution also has a function of controlling the inner surface structure of the obtained hollow fiber membrane. In the present invention, as the injecting liquid, water, a mixed liquid of the above-mentioned common solvent and water, a liquid incompatible with polysulfone such as alcohols and glycols, or a mixture thereof can be used. If desired, gas may be introduced inside the double annular nozzle instead of the injection liquid.

When a liquid having a good solidifying property such as water is used as the injection liquid, a dense layer is likely to be formed on the inner surface of the hollow fiber membrane. On the contrary, as the injection liquid,
For example, when a liquid having a low coagulability, such as a mixed liquid of the above-mentioned common solvent and water, is used, a hollow fiber membrane having micropores having a large pore size on the inner surface of the membrane can be produced. Also, 2
Even when gas is introduced into the inside of the heavy annular nozzle, micropores having a large pore size are formed on the inner surface of the hollow fiber membrane. In this way, the injection liquid or gas introduced into the double annular nozzle may be appropriately selected in consideration of the coagulability thereof depending on the target structure of the hollow fiber membrane, the pore size, and the like.

The coagulating liquid may be used without particular limitation as long as it is miscible with the above-mentioned common solvent and does not dissolve polysulfone. Usually, water, a mixture of the above-mentioned common solvent and water, alcohols and glycols are used. A liquid incompatible with polysulfone, or a mixture thereof is used. The outer surface structure of the obtained film can be appropriately controlled by the composition of the coagulating liquid, like the inner surface structure.

The hollow fiber membrane thus formed contains a common solvent, an excess of hydrophilic polymer, and a large amount of fine powder in the membrane. These are removed from the hollow fiber membrane by the following operations during the spinning process or after being once wound.

First, the common solvent and excess hydrophilic polymer remaining in the membrane are extracted and removed by washing with water or washing with warm water at 40 to 90 ° C. The content of the hydrophilic polymer in the hollow fiber membrane can be appropriately adjusted by controlling the amount of the hydrophilic polymer extracted and removed in the washing operation.

After the above-mentioned washing operation, the hydrophilic polymer remaining in the membrane is physically or chemically crosslinked, if necessary. As a method for forming such a crosslinked structure, a publicly known method may be appropriately selected depending on the kind of the hydrophilic polymer as described above. For example, when the hydrophilic polymer is polyvinyl alcohol or an ethylene / vinyl alcohol copolymer, a method of acetalizing with an aldehyde such as glutaraldehyde in the presence of a sulfuric acid catalyst is convenient.

Then, the fine powder remaining in the membrane is extracted and removed by an extraction solvent that dissolves the fine powder and does not dissolve polysulfone, and fine pores are formed at the traces of the powder removed. The extraction conditions for fine powder are 9 for fine powder.
It must be set so that 5% or more, preferably 100%, is extracted and removed. It depends on the type of the fine powder and the solubility of the extraction solvent, but since the fine powder is present in the polysulfone matrix, the fine powder It is set to be considerably stricter than the dissolution condition for the body alone, and it is necessary to increase the extraction temperature and the solvent concentration and to extend the extraction time. For example, in the case of extracting and removing fine silica powder, a 5-20 wt% sodium hydroxide aqueous solution is used as an extraction solvent, the extraction temperature is 60 ° C. or higher, and the extraction time is 30 minutes or longer. Need to be processed.

The above-mentioned cross-linking structure of the hydrophilic polymer does not necessarily have to be carried out prior to the extraction and removal of the fine powder, but may be carried out after the extraction and removal of the fine powder. It is also possible to perform these operations in a modular state after molding the washed hollow fiber membrane as a module.

The polysulfone-based hollow fiber membrane produced as described above is wound on a frame or a cassette and then dried. The dried hollow fiber membranes are bundled in a predetermined number, housed in a case having a predetermined shape, and then fixed at their ends with urethane resin, epoxy resin or the like to form a hollow fiber membrane module. As the hollow fiber membrane module, a type in which both ends of the hollow fiber membrane are fixed by opening, a type in which one end of the hollow fiber membrane is fixed by opening and the other end is sealed but not fixed, etc. Conventionally, various forms are known. Such a hollow fiber membrane module is attached to a conventionally known filtration device and used in separation / purification of liquid such as water purification.

When a liquid is filtered using the polysulfone-based hollow fiber membrane of the present invention, the liquid to be treated is flown outside the hollow fiber membrane and the liquid to be treated is permeated from the outside to the inside of the hollow fiber membrane. Either an external pressure system or an internal pressure system in which the liquid to be treated is caused to flow inside the hollow fiber membrane and permeate the liquid to be treated from the inside to the outside of the hollow fiber membrane may be adopted. Either a total filtration method in which the entire amount of the above is permeated through the membrane or a circulation method in which a part of the liquid to be treated permeates the membrane and the rest is circulated may be adopted. These methods may be appropriately selected according to the properties of the liquid to be treated.

Each of the above methods is appropriately selected depending on the structure, shape, etc. of the hollow fiber membrane, and the hollow fiber membrane has micropores having an average pore diameter of 0.1 to 10 .mu. In the case of having an internal pressure system in which the liquid to be treated is allowed to flow inside the hollow fiber membrane, and when the hollow fiber membrane has fine pores of the above pore size on the outer surface at the above opening ratio. Is preferably an external pressure system in which the liquid to be treated is flown outside the hollow fiber membrane. Also,
If the inner diameter of the hollow fiber membrane is 1 mm or less, the external pressure method is usually adopted, while if the inner diameter of the hollow fiber membrane is 1 mm or more,
The internal pressure method is usually adopted, but it is appropriately selected in consideration of the properties of the stock solution to be treated.

When the polysulfone-based hollow fiber membrane of the present invention is used to filter a liquid for a certain period of time, scales, SS components, and other filter residues eventually adhere to the surface of the hollow fiber membrane, and the filtration rate decreases. Come on. Therefore, gas backwashing is performed for the purpose of removing the filter residue attached to the surface of the hollow fiber membrane and recovering the filtration rate.

In the gas backwashing, the gas is permeated through the hollow fiber membrane in the direction opposite to the permeation direction of the liquid to be treated. That is, when performing the external pressure filtration, the gas is permeated from the inside to the outside of the hollow fiber membrane, and when performing the external pressure filtration, the gas is permeated from the outside to the inside of the hollow fiber membrane. .

The flow rate of the gas when performing the gas backwash is 20
~ 5,000 Nl / m ↑ 2 · hr, preferably 100 ~
It is 1,000 Nl / m ↑ 2 · hr. As a gas,
For example, air, nitrogen, etc. can be mentioned, but usually air is used. When the liquid to be treated contains a substance that is easily oxidized, it is necessary to use an inert gas such as nitrogen.

The backwashing with gas is carried out when the permeation rate of the liquid to be treated decreases to 5 to 50%, preferably 10 to 30% of the initial permeation rate at the start of filtration.

As described above, when the gas permeates the hollow fiber membrane in the direction opposite to the permeation direction of the liquid to be treated, the filter residue attached to the surface of the hollow fiber membrane is separated by the gas ejected from the membrane surface. . At this time, since the hollow fiber membrane itself also vibrates, the filter residue is removed from the hollow fiber membrane. Thus, the synergistic effect of the gas jet from the membrane surface and the vibration of the hollow fiber membrane can sufficiently remove the filter cake from the hollow fiber membrane surface.

Since the polysulfone-based hollow fiber membrane of the present invention contains a hydrophilic polymer in the membrane, it does not lose its hydrophilicity even if it is placed in a dry state and does not require any special treatment. It can be wet with water. Therefore,
In the polysulfone-based hollow fiber membrane of the present invention, the filtration rate can be recovered simply by passing water after backwashing with gas.

In addition, the polysulfone-based hollow fiber membrane of the present invention has hydrophilicity, so that it is less likely to adsorb proteins and has improved stain resistance. Furthermore, the releasability of the filter cake at the time of backwashing with gas is also improved, and together with these, it is possible to perform stable liquid filtration for a long period with less clogging.

[0065]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
The evaluation of the membrane performance in each example was performed by the following method.

A. Water permeability A bundle of 20 polysulfone-based hollow fiber membranes with an effective length of 20 cm was bundled to produce a hollow fiber membrane module with one open end.
Pure water was filtered by an external pressure method at a temperature of ℃ and a filtration pressure of 1 kg / cm ↑ 2, and the permeation amount per unit membrane area, unit time and unit pressure was measured.

B. Fractionated particle size Polystyrene latex (manufactured by Dow Chemical Co., Ltd.) having a particle size of 0.1 μm was added to water in an amount of 0.1% by weight and uniformly dispersed. The dispersion was filtered by an external pressure method with a filtration pressure of 0.5 kg / cm ↑ 2 using the hollow fiber membrane module prepared in the above A, and the concentration of polystyrene latex in the permeate was measured by a turbidimeter. The rejection rate (R) was determined. By the same operation, the blocking rate for polystyrene latex (manufactured by Dow Chemical Co., Ltd.) having particle diameters of 0.2μ, 0.5μ and 1μ was measured. Based on these measurements,
The values of the constants a and m in the above equation (2) are calculated by the method of least squares, and then R in the equation (2) is 9
The value of S at which 0 was obtained was defined as the fractionated particle size.

C. Venting pressure The hollow fiber membrane module prepared in the above A was immersed in an aqueous 75% ethanol solution for 1 hour, and then washed with running water at 25 ° C for 60 minutes to completely wet the membrane. With the wetted hollow fiber membrane immersed in water, air pressure was gradually applied from the inner surface side of the membrane, and the amount of air permeating to the outer surface side became 400 Nl / m ↑ 2 · hr. The air pressure at that time was measured.

Example 1 Polysulfone (UDEL-manufactured by Amoco Japan Co., Ltd.)
P1800, hereinafter abbreviated as PS) 20 parts by weight,
Ethylene / vinyl alcohol copolymer (EVAL-H manufactured by Kuraray Co., Ltd., hereinafter abbreviated as EVOH) 4
10 parts by weight, silica powder (manufactured by Tokuyama Soda Co., Ltd., Fineseal #B, average particle size 3 μ, hereinafter referred to as silica powder) 10 parts by weight, N, N-dimethylacetamide (hereinafter referred to as DMAc). A spinning stock solution of 66 parts by weight was prepared by the following procedure. That is,
Silica powder was uniformly dispersed in DMAc using a homogenizer, PS and EVOH were added to the obtained dispersion, and then P was obtained by stirring at 60 ° C. for 6 hours.
S and EVOH were dissolved to obtain a white slurry-like spinning stock solution in which silica powder was uniformly dispersed.

After defoaming the spinning solution obtained above, 4
Maintained at 0 ° C, discharged from a double annular nozzle having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm at 40 ° C together with an injecting liquid consisting of 80% by weight of DMAc and 20% by weight of water, to 40 ° C and a relative humidity of 100%. Extruded into conditioned air. After running in air with a dry zone length of 10 cm, it was introduced into water at 40 ° C. as a coagulating liquid to form a hollow fiber membrane.

The obtained hollow fiber membrane was washed with warm water at 60 ° C. for 30 minutes to extract and remove DMAc remaining in the membrane,
At 60 ° C., the EVOH in the film was crosslinked by immersing it in an aqueous solution containing glutaraldehyde at a rate of 1.5 g / l and sulfuric acid at a rate of 30 g / l. Next, the hollow fiber membrane after such cross-linking structuring was
The silica powder in the film was extracted and removed by immersing in a 5 wt% sodium hydroxide aqueous solution for 2 hours. Further, the hollow fiber membrane was washed with warm water at 90 ° C. for 2 hours, then at 50 ° C. for 10 hours.
By drying for an hour, a hollow fiber membrane having an outer diameter of 1 mm and an inner diameter of 0.6 mm was obtained.

The obtained hollow fiber membrane contained 2% EVOH in the membrane.
Contains 0% by weight and has a water permeability of 11,200 l / m ↑
2 · hr · kg / cm ↑ 2, fractional particle size was 1μ, and ventilation pressure was 1.2 kg / cm ↑ 2. Further, as is clear from the electron microscope photographs of 500 times shown in FIGS. 1 to 3 (hereinafter, abbreviated as SEM photographs), the outer surface of the film has fine pores having an average pore diameter of 6 μ at an aperture ratio of 20%. (FIG. 1), the inner surface of the membrane had a mesh structure with a pore size of 1 to 20 μm, and the aperture ratio was 50% (FIG. 2). The cross-sectional structure of the film was a sponge structure (Fig. 3). The water permeability of this membrane did not decrease even after the ventilation pressure was measured or in the dry state.

Example 2 20 parts by weight of PS, polyvinyl alcohol (Kuraray Co., Ltd.)
(Manufactured by PVA-217, hereinafter abbreviated as PVA)
A white slurry-like spinning solution containing 2 parts by weight, 10 parts by weight of silica powder, and 68 parts by weight of DMAc, in which silica powder was uniformly dispersed, was prepared by the same procedure as in Example 1.

After defoaming the spinning solution obtained above, 5
Maintained at 0 ° C, discharged from a double tubular nozzle with an outer diameter of 1.6 mm and an inner diameter of 0.8 mm at 50 ° C together with an injection liquid consisting of 80% by weight of DMAc and 20% by weight of water, and then at 50 ° C and a relative humidity of 100%. Extruded into conditioned air. After running in air with a dry zone length of 1 cm, it was introduced into water at 50 ° C. as a coagulating liquid to form a hollow fiber membrane.

The obtained hollow fiber membrane was washed with warm water at 60 ° C. for 30 minutes to wash DMAc and excess PVA remaining in the membrane.
Was extracted and removed, and then, at 60 ° C., it was immersed in an aqueous solution containing glutaraldehyde at a rate of 1.5 g / l and sulfuric acid at a rate of 30 g / l to cross-link PVA in the membrane. Let Next, the hollow fiber membrane after the cross-linking structure was immersed in a 15 wt% sodium hydroxide aqueous solution at 60 ° C. for 2 hours to extract and remove silica powder in the membrane. Further, the hollow fiber membrane was washed with warm water at 90 ° C. for 2 hours and then dried at 50 ° C. for 10 hours to give an outer diameter of 1
A hollow fiber membrane having a diameter of 0.6 mm and an inner diameter of 0.6 mm was obtained.

The obtained hollow fiber membrane contained 5% by weight of PVA in the membrane and had a water permeability of 6,000 l / m ↑ 2 · h.
r · kg / cm ↑ 2, fractional particle size was 0.35μ, and aeration pressure was 2.2 kg / cm ↑ 2. Further, as a result of observing the inner and outer surfaces of the film and the cross-sectional structure of the film with an electron microscope in the same manner as in Example 1, the outer surface of the film had fine pores with an average pore diameter of 3 μ at an aperture ratio of 30%. The surface had a mesh structure with a pore diameter of 1 to 20 μm, and the aperture ratio was 40%. The cross-sectional structure of the film was a sponge structure. The water permeability of this membrane did not decrease even after the ventilation pressure was measured or in the dry state.

Example 3 The same spinning dope as used in Example 2 was used. The spinning stock solution was kept at 40 ° C., and was discharged at 40 ° C. together with water as an injection liquid from a double annular nozzle having an outer diameter of 2.5 mm and an inner diameter of 1.1 mm, and the air was adjusted to 40 ° C. and a relative humidity of 100%. I pushed it out. After running in air with a dry zone length of 10 cm, it was introduced into water at 40 ° C. as a coagulating liquid to form a hollow fiber membrane.

The obtained hollow fiber membrane was washed with hot water at 60 ° C. for 80 minutes to wash DMAc and excess PVA remaining in the membrane.
Was extracted and removed, and then, at 60 ° C., it was immersed in an aqueous solution containing glutaraldehyde at a rate of 1.5 g / l and sulfuric acid at a rate of 30 g / l to cross-link PVA in the membrane. Let Next, the hollow fiber membrane after the cross-linking structure was immersed in a 15 wt% sodium hydroxide aqueous solution at 60 ° C. for 2 hours to extract and remove silica powder in the membrane. Further, the hollow fiber membrane was washed with warm water at 90 ° C. for 2 hours and then dried at 50 ° C. for 10 hours to give an outer diameter of 2
A hollow fiber membrane having a diameter of 1.2 mm and an inner diameter of 1.2 mm was obtained.

The hollow fiber membrane obtained contained 6% by weight of PVA in the membrane and had a water permeability of 4,500 l / m ↑ 2 · h.
r · kg / cm ↑ 2, fractional particle size was 0.25 μ, and aeration pressure was 3.2 kg / cm ↑ 2. As a result of observing the inner and outer surfaces of the film and the cross-sectional structure of the film with an electron microscope in the same manner as in Example 1, the inner surface of the film had fine pores with an average pore diameter of 0.5 μ at an aperture ratio of 15%. The outer surface of the has an average pore diameter of 2μ
Had micropores with an opening ratio of 20%. The cross-sectional structure of the film was a sponge structure. The water permeability of this membrane did not decrease even after the ventilation pressure was measured or in the dry state.

Comparative Example 1 20 parts by weight of PS, 2 parts by weight of PVA and 78 parts by weight of DMAc were mixed and stirred at 60 ° C. for 6 hours, but the solution was white turbid and the resulting solution remained phase separated. This solution could not be spun into a hollow fiber membrane.

Comparative Example 2 20 parts by weight of PS, 15 parts by weight of silica powder, and
A spinning dope containing 65 parts by weight of N, N-dimethylformamide (hereinafter abbreviated as DMF) was prepared by the following procedure. That is, the silica powder is uniformly dispersed in DMF using a homogenizer, PS is added to the obtained dispersion, and then PS is dissolved by stirring at 60 ° C. for 6 hours to make the silica powder uniform. A white slurry-like spinning stock solution that was dispersed was obtained.

After defoaming the spinning solution obtained above, 5
Maintained at 0 ° C, discharged from a double tubular nozzle with an outer diameter of 1.6 mm and an inner diameter of 0.8 mm at 50 ° C together with an injection liquid consisting of 80% by weight of DMF and 20% by weight of water, and at 50 ° C and a relative humidity of 100%. Extruded into conditioned air. After running in air with a dry zone length of 1 cm, it was introduced into water at 50 ° C. as a coagulating liquid to form a hollow fiber membrane.

The hollow fiber membrane thus obtained was washed with warm water at 60 ° C. for 80 minutes to extract and remove DMF remaining in the membrane, and then 6
The silica powder in the film was extracted and removed by immersing in a 15 wt% sodium hydroxide aqueous solution for 2 hours at 0 ° C. Further, the hollow fiber membrane was washed with warm water at 90 ° C. for 2 hours and then dried at 50 ° C. for 10 hours to obtain a hollow fiber membrane having an outer diameter of 1 mm and an inner diameter of 0.6 mm.

The obtained hollow fiber membrane had a water permeability of 5,500.
l / m ↑ 2 ・ hr ・ kg / cm ↑ 2, fractional particle size is 0.
The air pressure was 3μ, and the ventilation pressure was 2.4 kg / cm ↑ 2. Also,
As a result of observing the inner and outer surfaces of the film with an electron microscope in the same manner as in Example 1, the inner surface of the film had fine pores with an average pore diameter of 1 μ and an aperture ratio of 10.
%, And the outer surface of the membrane had fine pores with an average pore diameter of 3 μ at an aperture ratio of 15%. After the membrane was dried, its water permeability was measured to be 500 l / m ↑ 2 · hr ·
It was kg / cm ↑ 2, and the water permeability was reduced to about 10% as compared with the case of being in a wet state.

Test Example Using the polysulfone-based hollow fiber membranes obtained in Example 1 and Comparative Example 2, effective length 25 cm, effective membrane area 0.1 m
A hollow fiber membrane module with an open end was prepared in ↑ 2. The hollow fiber membrane module was used to filter the bacterial cell solution, and the permeation rates before and after gas backwashing were measured.

The filtration conditions and the gas backwashing conditions are as follows. Liquid to be treated: Cell (Seratia narcescens) solution, cell concentration 10 ↑ 9 cells / m ↑ 3 Filtration conditions: external pressure full filtration, filtration pressure 1 kg / cm ↑ 2 Backwash conditions: Air backwash (1000 Nl / hr ・ m ↑ 2), the permeation rate is 50l / m ↑ 2 ・ hr ・ kg / c
Performed when m ↑ 2, backwash time 30 seconds

Table 1 shows the number of backwashing and the permeation coefficient before and after gas backwashing. The permeation coefficient in this test example is a value obtained by dividing the measured permeation rate before and after gas backwashing by the initial permeation rate at the start of filtration.

[0088]

[Table 1]

As is clear from Table 1, the polysulfone-based hollow fiber membrane obtained in Example 1 has a higher permeation rate at the time of gas backwash than the polysulfone-based hollow fiber membrane obtained in Comparative Example 2. The recovery was excellent.

[0090]

EFFECTS OF THE INVENTION According to the present invention, there is provided a polysulfone-based hollow fiber membrane which can be backwashed with gas without causing a decrease in water permeability and is excellent in stain resistance, and a method for producing the same. . By using the polysulfone-based hollow fiber membrane of the present invention, it is possible to stably filter a liquid for a long time.

[Brief description of drawings]

1 is a 500X SEM photograph showing the outer surface structure of the hollow fiber membrane obtained in Example 1. FIG.

FIG. 2 is a 500 × SEM photograph showing the inner surface structure of the hollow fiber membrane obtained in Example 1.

FIG. 3 is a 500 times SEM photograph showing a cross-sectional structure of the hollow fiber membrane obtained in Example 1.

Claims (8)

[Claims] 1. A polysulfone-based hollow fiber membrane containing a hydrophilic polymer in an amount of 1 to 10% by weight, and having a ventilation pressure of 0.3 to 5.
A polysulfone-based hollow fiber membrane having a weight ratio of kg / cm ↑ 2. 2. The polysulfone-based hollow fiber membrane according to claim 1, which has a fractional particle size of 0.2 to 2 μm. 3. The polysulfone-based hollow fiber membrane according to claim 1, wherein the hydrophilic polymer is polyvinyl alcohol or an ethylene / vinyl alcohol copolymer. 4. Polysulfone, a hydrophilic polymer, a common solvent for both, and an average particle diameter of 0.01 which is insoluble in the common solvent.
A step of forming a hollow fiber membrane by a dry-wet spinning method or a wet-spinning method by extruding a spinning stock solution composed of a fine powder having a particle size of ˜5 μm and having the fine powder uniformly dispersed, through a double annular nozzle; And a step of immersing the hollow fiber membrane in an extraction solvent that dissolves the fine powder without dissolving the polysulfone to extract and remove the fine powder, the method for producing a polysulfone-based hollow fiber membrane. 5. The method for producing a polysulfone-based hollow fiber membrane according to claim 4, wherein the hydrophilic polymer in the membrane is crosslinked. 6. The method for producing a polysulfone-based hollow fiber membrane according to claim 4, wherein the hydrophilic polymer is polyvinyl alcohol or an ethylene / vinyl alcohol copolymer. 7. The fine powder is silica fine powder, as claimed in claim 4.
7. The method for producing a polysulfone-based hollow fiber membrane according to item 6. 8. The polysulfone-based hollow fiber membrane according to claim 4, wherein polysulfone, hydrophilic polymer and common solvent are present in the spinning dope in a composition that causes phase separation. Method.