JPH06238140A - Filter membrane - Google Patents

Abstract

PURPOSE:To provide a filter membrane capable of easily removing clogging caused by filtering operation in the filter membrane to be used for solid-liquid separation of dispersion liquid containing particles and polymer component such as fungus-fermentation liquid, crushed cell liquid, biologically processed waste water, and enzym fermentation liquid. CONSTITUTION:The membrane base material of this filter membrane consists of an inorg, membrane having narrow pores. Polymers are graft-polymerized on the surface of the membrane and on the inner surface of narrow pores.

Description

Detailed Description of the Invention

[Background of the Invention]

TECHNICAL FIELD The present invention relates to a filtration membrane used in an ultrafiltration method or a microfiltration method.

[0002]

2. Description of the Related Art In recent years, a separation technique using a porous membrane has been remarkably developed. For example, a technique for separating a solvent and ions by a reverse osmosis method, a technique for separating a solvent and a solute by an ultrafiltration method,
Furthermore, it has been put to practical use as a technique for separating particle components in a solvent by a microfiltration method.

Membrane materials conventionally used in such separation techniques include organic materials such as cellulose acetate, polyacrylonitrile, polyamide, polysulfone, and polyethylene, and aluminum oxide, zirconium oxide, silicon oxide, and the like. Inorganic materials are known.

A film made of an organic material (organic film) is formed by an evaporation method, a coacervation method, a stretching method or the like, while a film made of an inorganic material (an inorganic film) is formed by sintering inorganic fine particles.
The film is formed by a method utilizing the phase separation phenomenon.

These membranes are used as membranes for so-called bioindustry substance production, solid-liquid separation in wastewater treatment, and polymer component separation. In the liquid supplied to the membrane in such treatment, particle components,
It is general that various polymer components are mixed. Further, both the particle component and the polymer component have a large particle size distribution and a large molecular weight distribution. for that reason,
Even if the pore size of the membrane or the molecular weight cutoff that indicates the size of the polymer that can be separated by the membrane is adjusted to the size of the component to be separated, other components present in the liquid may cause clogging of the membrane. I will end up. Such clogging of the membrane deteriorates the filtration performance of the membrane over time.

The clogged membrane can be recovered in membrane performance by washing operations such as back pressure washing, flush washing, sponge ball washing and chemical washing. Here, the back pressure cleaning is a method of removing the clogging layer of the membrane by pumping the membrane permeate from the permeate side to the membrane feed side, and the flush cleaning is a method in which the membrane feed solution is temporarily moved at a high speed. Surface cleaning method, and the sponge ball cleaning method is a method in which small particles of sponge are poured onto the film surface together with the film supply solution to clean the film surface. These physical cleaning methods are simple and do not use chemicals, so there is no risk of contamination by foreign substances during cleaning. Therefore, the washing operation is incorporated into the filtering operation,
It is possible to recover the membrane performance without substantially stopping the filtration operation.

However, the membrane performance may not be sufficiently recovered by these physical cleaning methods. In such a case, it is necessary to stop the filtration operation and clean the membrane with an acid, an alkali, an oxidizing agent or the like. Chemical washing is an excellent method in that the recovery performance (cleaning recovery) of the filtration performance of the membrane is high, but it is necessary to substantially stop the filtration operation,
Post-processing of cleaning chemicals is complicated.

[0008] Many of the conventionally known membranes have not been able to efficiently recover the membrane performance by physical cleaning, so chemical cleaning has been frequently used.

[Outline of the Invention]

Therefore, when a filter membrane capable of efficiently recovering its membrane performance by physical washing was studied, it was found that a polymer could be grafted on the membrane surface and the pore inner surface. It has been found that it is effective for improving the wash recoverability of.

The present invention is based on the above findings,
It is an object of the present invention to provide a filtration membrane which can easily recover the filtration performance of the membrane by physical washing, that is, which has a high wash recovery property.

The present invention is a filtration membrane used for solid-liquid separation of a dispersion liquid containing particles and a polymer component, such as a bacterial cell fermentation liquid, a cell lysate, a biological treatment wastewater, and an enzyme fermentation liquid. It is therefore an object of the present invention to provide a filtration membrane capable of easily removing clogging due to filtration operation.

Another object of the present invention is to provide an efficient physical cleaning method for the filtration membrane.

[0013]

The filtration membrane according to the present invention comprises:
A filtration membrane having a membrane base material made of an inorganic material having pores, in which a polymer is grafted on the surface and the inner surface of the pores.

Further, the method for cleaning a filtration membrane according to the present invention comprises pumping a solution having a high salt concentration from the permeate side of the filtration membrane with a solution of urea or a grafted polymer having an isoelectric point pH. The one.

[Detailed Description of the Invention] The filtration membrane according to the present invention uses a membrane made of an inorganic material as a membrane substrate. This membrane substrate has pores set between the size of the component that is desired to pass through the membrane and the size of the component that is not desired to pass through. For example, the size of the microorganism is about 1/10 μm to 10 μm, and the size of the crushed material particles in the solution obtained by crushing the culture of the microorganism is 10 nm or more. On the other hand, a polymer component produced by a microorganism generally has a size of about several to several tens of nm and a molecular weight of about 10 ³ to 10 ⁵ . Therefore, the desired polymer component is separated from the culture of the microorganism or its crushed product by filtration using a membrane in which the average pore size or the molecular weight cut-off is set according to the polymer component produced by the microorganism. can do. That is, in order to separate a target polymer component from such a culture of microorganisms or a crushed product thereof, pores having an average pore diameter of 5 nm to 50 μm, preferably 50 nm to 5 μm.
The following pores, or the molecular weight cutoff is 1 × 10 ³ or more 1 ×
A film having pores represented by 10 ⁸ or less, preferably 1 × 10 ⁴ or more and 1 × 10 ⁸ or less may be used.

The membrane substrate is preferably made of an inorganic material from the viewpoint of its strength. Specific examples of preferable inorganic materials include aluminum, zirconium, iron, silicon, tin, titanium, nickel, cobalt, carbon, aluminum oxide, zirconium oxide, silicon oxide, tin oxide, titanium oxide, silicon carbide, aluminum carbide, silicon nitride. , Aluminum nitride, magnesium oxide, nickel oxide, and composite oxides thereof. In particular, aluminum oxide, zirconium oxide, silicon oxide, tin oxide, titanium oxide and composite oxides thereof, carbon, silicon carbide and aluminum nitride are preferable.

Further, the film base material is not limited to the one made of only the inorganic material, but may be made of the inorganic material as a base and formed as a composite with the organic material. For example, there is one in which a thin film made of an organic material is formed on the surface of a filtration film made of an inorganic material. A specific example is a composite membrane formed by coating a surface of an aluminum oxide film with a cellulose acetate solution, immersing it in water, and causing a JP cervation reaction in the cellulose acetate solution.

Such a membrane substrate can be manufactured by a known method or a method similar thereto while adjusting the pores to be set in a predetermined range. For example,
The inorganic material particles are molded with a binder and then fired to obtain porosity, which can be used as a membrane substrate. In this case, the pore diameter or the molecular weight cutoff can be determined by appropriately selecting the size of the particles of the inorganic material that is the starting material. Specific production can be carried out according to the methods described in, for example, JP-A-59-48646, JP-A-3-143535, and JP-A-4-100505.

The filtration membrane according to the present invention is formed by grafting a polymer chain on the membrane surface of the membrane base material and the pore inner surface of the membrane as described above.

Specific examples of the polymer grafted on the surface of the membrane substrate and the surface inside the pores include, for example, methyl methacrylate, styrene, ethyl methacrylate, acrylic acid,
Vinyl acetate, vinyl alcohol, vinyl chloride, butadiene, cellulose, acrylonitrile, acryloamide,
Examples thereof include polymers of monomers such as methacrylonitrile. That is, the polymer to be grafted may be a homopolymer or a copolymer. When it is a copolymer, it may be a block polymer or a random polymer thereof. The polymer to be grafted may be linear or branched.

Specific examples of preferable polymers include polymethylmethacrylate, polystyrene, polymethylmethacrylate, polyvinyl acetate, polyvinyl alcohol, polystyrene and the like.

These polymers are reacted with the functional groups present on the surface of the membrane material to form a graft membrane made of the polymer. The polymer to be grafted may be already grafted as a polymer when reacted with a functional group present on the surface of the membrane material, or may be brought into contact with a functional group on the surface of the membrane material as a monomer to simultaneously graft. The monomer may be polymerized by a polymerization reaction.

For example, the film is brought into contact with the monomer, and then the polymerization is initiated by the polymerization initiator. In this polymerization reaction, the initiator, the reaction conditions therefor, and the like can be appropriately determined in consideration of the types of monomers and functional groups on the film surface, the thickness of the graft film to be formed, and the like. A specific reaction is, for example, S. Yamashita et al. App
l. Polymer Sci. , 17, 2935 (19
73) and the like.

The grafting may be carried out by utilizing the functional group originally possessed by the membrane surface, but the functional group on the membrane surface may be replaced with another functional group to modify the membrane surface. Good. As such a modification method, a silane coupling agent such as trimethylchlorosilane or octadecyldimethylchlorosilane is used to provide an alkylsilane group on the surface, a method for providing a phenyl group using dimethylphenylchlorosilane, and γ-aminopropyltrisilane. Examples thereof include a method of providing an amino group using ethoxysilane.

The thickness of the polymer to be grafted is preferably 500 μm or less, more preferably 1 nm or more and 100 μm or less, and most preferably 20 on the surface of the membrane substrate.
It is not less than nm and not more than 100 μm. The graft membrane is also formed on the inner surface of the pores of the membrane, and its thickness is 1/2 of the pore diameter.
The thickness of the graft film is preferably in the range of 1/3 to 2/3 of the pore diameter.

Filtration with the filtration membrane of the present invention may be carried out in the same manner as conventional filtration membranes. That is, it can be used as a filtration membrane in a filtration method such as a cross-flow filtration method or a total filtration method. Also, the filtration conditions may be appropriately determined depending on the filtration method and the substance to be filtered.

And, in the filtration membrane according to the present invention,
Extremely efficient filtration by conventional physical cleaning, namely back pressure cleaning, flush cleaning, sponge ball cleaning, backflow cleaning, cleaning by pulsing the flow of the membrane feed solution, and method of periodically opening and closing the membrane permeate valve. It is possible to recover the performance. Back pressure washing is particularly preferable.

The excellent washing recovery property of the filtration membrane according to the present invention is presumed to be due to the following reasons. It is generally said that the substance that clogs the pores of the filtration membrane has a size equal to the pore size and about 1/10 of the size. The membrane and the graft membrane formed on the surface inside the pores are
It does not prevent the solvent from penetrating the membrane, and on the other hand, it traps the particles, which are said to be the cause of the clogging of the pores, on the upper part of the comb-like polymer chain. The particles thus supplemented are only physically supplemented by the graft polymer,
Further, since the comb-shaped graft polymer has a certain flexibility, it is easily desorbed by applying a physical force such as back pressure washing. It is believed that this allows the membrane to easily restore its filtration performance.

The filtration membrane according to the present invention is excellent in mechanical strength because the membrane material is made of an inorganic material.
Therefore, when backwashing, a higher pressure, for example 50
The solution can be pressure-fed from the permeation side at a pressure of 0 KPa or higher. Thereby, more efficient back pressure cleaning can be performed.

Even more surprisingly, the use of a high salt concentration solution, a solution of urea or a grafted polymer at the isoelectric point pH as the solution pumped from the permeate side results in more efficient back pressure washing. It was found that it could be done. Although not restricted by the following theory, it is considered that such back pressure cleaning is advantageous for the following reason. That is, when the grafted polymer chains in the membrane and the membrane pores come into contact with a high salt concentration solution or a solution of the grafted polymer at the isoelectric point pH, the electrostatic repulsion between the polymer chains decreases. As a result, the polymer chain contracts. As a result, it is presumed that the particles trapped in the polymer chains will be easily detached and the backwashing will be performed more efficiently.

Specific examples of the high-salt-concentration solution include an aqueous solution of a salt composed of a combination of a cation selected from lithium, sodium, potassium, ammonium and guanidine and an anion selected from chlorine, sulfuric acid and tannic acid. However, more preferable examples include sodium chloride solution, ammonium sulfate solution, guanidine hydrochloride, tannate and the like. The concentration is preferably 10 mmol / l or more, more preferably 100 m to 10 mol / l. The composition of the solution of the grafted polymer at the isoelectric point pH is not particularly limited, but it is preferable that it does not affect the membrane material and the graft polymer.

In the case of back pressure washing using a high salt concentration solution, urea or a solution of a grafted polymer having an isoelectric point pH, the volume ratio of the back pressure washing solution and the liquid to be filtered should be sufficiently small. Therefore, it can be said that there is little effect on the filtering operation again, which is advantageous.

[0033]

The present invention will be explained in more detail by the following examples, but the present invention is not limited to these examples.

Example 1 Production of filtration membrane Inner diameter 7 mm, outer diameter 10 mm, length 200 mm, pore diameter 0.2 μ
m or 0.5 μm tubular internal pressure type alumina ceramic membrane is disclosed in JP-A-3-143535 and JP-A-4-1005.
Prepared as described in No. 05. The film was dehydrated by heating at 500 ° C. and then refluxed in a 5% toluene solution of trimethylchlorosilane for 8 hours to replace the hydroxyl group on the alumina film surface with trimethylsilane. Next, using benzoyl peroxide as a polymerization initiator, methyl methacrylate was graft-polymerized at 50 ° C. on the methyl group of trimethylsilane on the film surface. By controlling the reaction time, a filtration membrane grafted with poly (methyl methacrylate) having a thickness of 0.1 μm to 500 μm as shown in Table 1 below was obtained.

Example 2 Production of Filtration Membrane In the same manner as in Example 1 except that styrene was used in place of methyl methacrylate as a monomer, a particle size of 0.1 μm to 500 μm as shown in Table 1 below was used. A polystyrene-grafted filtration membrane having a thickness was obtained.

Example 3 Evaluation of Wash Recovery Property The wash recovery property of the filtration membrane produced in Example 1 was evaluated by repeating solid-liquid filtration and washing of the fermentation broth. For comparison, the cleaning recovery of the tubular internal pressure type alumina ceramic membrane whose surface was not graft-treated was also evaluated in the same manner.

As a fermentation broth, a fermentation broth of Bacillus macerans (IFO-3940) which secretes β-galactosidase outside the body was reported by Miyazaki et al. (Agric. Biol. Chem., 5
2, 625 (1988)).

The filtration operation was performed as follows. That is,
Fermentation liquid with a membrane surface velocity of 1.0 m · s ⁻¹ and filtration pressure of 50 kPa
Was filtered for 30 minutes under the cross-flow conditions, and then the permeated liquid was back-pressure washed at 200 kPa for 60 seconds.
This cycle of filtration-backwashing operation was repeated 10 times.

The membrane permeation flow rate after repeating the filtration-back pressure washing operation 10 times was measured, and the loss of permeate due to back pressure washing was corrected to obtain the average membrane permeation flow rate. In addition, the initial membrane permeation flow rate (Jφ) of the filtration membrane and the filtration-back pressure washing operation were performed at 10
Membrane permeation flow rates (J ₁₀ ) after repetition were compared. The results are shown in the following table.

[0040]

[Table 1] Example 4 Back Pressure Washing with High Salt Concentration Solution Instead of back pressure washing to repel permeate, 0.2 mol / l N 2 was used.
The washing recoverability of the membrane was evaluated in the same manner as in Example 3 except that back pressure washing was performed in which the aCl aqueous solution was pressure-fed from the permeate side. The results are shown in the table below.

[0041]

[Table 2]

[0042]

EFFECTS OF THE INVENTION According to the present invention, a filtration membrane having a high wash recovery property can be obtained by grafting a polymer on the membrane surface and the pore inner surface. Also, by using a high salt concentration solution or a solution of urea or a grafted polymer having an isoelectric point pH as the solution pumped from the permeate side, efficient back pressure washing can be performed.

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Claims (7)

[Claims] 1. A filtration membrane having a membrane base material of a membrane made of an inorganic material having pores, wherein the surface and inner surfaces of the pores are grafted with a polymer. 2. The membrane substrate has an average pore diameter of 5 nm or more and 50 μm.
Pore or molecular weight cut off below 1 × 10 ³ or more 1 × 10 ⁸
The filtration membrane according to claim 1, which has pores represented below. 3. The thickness of the grafted polymer is 500 μm
The filtration membrane according to claim 1, wherein: 4. The polymer is methyl methacrylate, styrene,
The filtration according to claim 1, which is a polymer or copolymer of one or more monomers selected from ethyl methacrylate, acrylic acid, vinyl acetate, vinyl alcohol, vinyl chloride, butadiene, cellulose, acrylonitrile, acryloamide, and methacrylonitrile. film. 5. The filtration membrane according to claim 1, wherein the membrane substrate is made of a composite of an inorganic material and an organic material. 6. The method for cleaning a filtration membrane according to claim 1, wherein a solution having a high salt concentration, a solution of urea or a grafted polymer having an isoelectric point pH is used from the permeation side. A method comprising pumping. 7. A solution having a high salt concentration is lithium, sodium,
7. An aqueous solution of a salt comprising a combination of a cation selected from potassium, ammonium and guanidine and an anion selected from chlorine, sulfuric acid and tannic acid, the concentration of which is 10 mmol / l or more. How to wash the filtration membrane.