KR20070071832A - Method for preparation of hydrophilic asymmetric utrafiltration and microfiltration membranes containing silvernano particles - Google Patents

Abstract

A method for manufacturing ultrafiltration and microfiltration membranes which can be hydrophilized simply and economically and are excellent in permeation rate, contamination resistance and microorganism resistance is provided, wherein the membranes can provide an effect of substantially reducing membrane fouling in the case where the membranes are applied to a membrane coupled activated sludge process. A method for manufacturing asymmetric ultrafiltration and microfiltration membranes comprises the steps of: dissolving a polymer into a solvent to prepare a polymer solution; and adding silver nitrate to the polymer solution, and manufacturing a flat membrane from the mixed solution(1) by a phase inversion process. The step of manufacturing the flat membrane by the phase inversion process comprises the steps of: adding silver nitrate into the polymer solution; negatively charging the silver nitrate added polymer solution to cast the negatively charged polymer solution onto a non-woven fabric(3) while ionizing silver nitrate; passing the cast polymer solution through positively charged rolls(2) to impregnate and adhere silver nanoparticles onto a surface of the flat membrane; and impregnating the silver nanoparticle impregnated and adhered cast polymer solution with a non-solvent to form a filtration membrane.

Description

METHODS FOR PREPARATION OF HYDROPHILIC ASYMMETRIC UTRAFILTRATION AND MICROFILTRATION MEMBRANES CONTAINING SILVERNANO PARTICLES}

1 is a schematic diagram of a method for producing an ultrafiltration membrane and a microfiltration membrane of the present invention.

2 is a graph showing a change in permeation flow rate in a membrane-bound microbial reactor for checking the fouling resistance of the ultrafiltration membrane and the microfiltration membrane prepared according to Examples 1 to 3 and Comparative Examples 1 to 2 of the present invention. will be.

* Explanation of symbols for the main parts of the drawings

1: Polymer solution containing silver nitrate 2: Roll

3: nonwoven fabric 4: knife

The present invention relates to a method for manufacturing asymmetric ultrafiltration membranes and microfiltration membranes excellent in fouling resistance, and more specifically, impregnating and fixing silver nanoparticles in a polymer on the surface of a separator for permanent hydrophilicization of membranes in a flat membrane manufacturing step by phase inversion. The present invention relates to a method for producing an asymmetric ultrafiltration membrane and a microfiltration membrane having excellent water permeability, fouling resistance and microbial resistance.

Generally, the asymmetric ultrafiltration membrane is prepared by a phase inversion method using polysulfone, polyether sulfone, cellulose acetate, or the like as a polymer material. This asymmetric membrane has a structure consisting of an integrated asymmetric structure consisting of a porous material and a skin layer that enables selective separation.

On the other hand, since most membrane materials except for cellulose acetate are hydrophobic, ultrafiltration membranes made from these materials are generally superior to cellulose acetate membranes in terms of chemical resistance and strength of the membrane itself, but have low filtration performance and severe membrane contamination. Has its drawbacks.

In order to overcome this drawback, techniques for hydrophilizing hydrophobic membrane materials have been tried in various ways. Representative methods include (1) adsorbing nonvolatile water-soluble polyhydric alcohols such as glycerin to a hydrophobic membrane, and (2) adsorbing water-soluble polymer substances such as polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol to the hydrophobic membrane. (JP-A-63-31501, etc.), (3) A method of immobilizing a hydrophilic polymer on a hydrophobic membrane, and a method of chemically bonding a hydrophilic monomer such as acrylamide to the surface of a hydrophobic membrane. 59032, etc.), (4) a method of immobilizing a hydrophilic polymer by irradiating the membrane with water in the presence of water to immobilize the hydrophilic polymer (Japanese Patent Laid-Open No. Hei 4-300636, etc.), and the membrane in a dry state. A method of insolubilizing a hydrophilic polymer and immobilizing it by heat treatment (Japanese Patent Laid-Open No. 9-103664, etc.), (5) A method of sulfonating a surface of a hydrophobic membrane (Japanese Patent Laid-Open Publication No. 9-103664). BOS63-54452, etc.), (6) a method of making a film from a mixture of hydrophilic polymer materials such as polyethylene glycol and polyvinylpyrrolidone and hydrophobic polymer dope (Japanese Patent Laid-Open No. 61-93801, etc.), (7) A method of imparting a hydrophilic group to the surface of the membrane by treating with an aqueous alkali solution (NaOH, KOH, etc.) (JP-A-58-93734, etc.), (8) After the hydrophobic porous membrane is immersed in alcohol, treated with a water-soluble polymer aqueous solution, After drying, a method of insolubilizing with heat treatment, radiation or the like (Japanese Patent Publication No. 54-17978, etc.) is known.

Of these, the methods (1) to (3) have generally been used for a long time as a method of hydrophilizing hydrophobic membranes, but the hydrophilicity imparting agent used in each method is detached from the hydrophobic membrane once contacted with water. The problem is that the hydrophilicity is lost. Moreover, depending on the use, it may be avoided that these hydrophilicity imparting agents are mixed in the filtrate. As an improved method of (2), a method of making the hydrophilic impurity difficult to dissolve in water by performing radiation or heat treatment again after performing the method of (2) has been proposed. However, there is a problem that a decrease in the film strength is caused or that the effect is not sufficiently satisfactory.

In addition, the method of (4) and (5) has the advantage that the hydrophilicity of the hydrophobic membrane is maintained almost permanently and the hydrophilicity-imparting agent is not eluted in the filtrate, but the treatment method is relatively complicated and uneconomical. .

In addition, although the method of (6) has been known for a long time, it is difficult to adjust the residual state of the hydrophilic polymer material in the hydrophobic membrane, and the problems such as the change in filtration characteristics over time or the elution of the hydrophilic polymer material gradually eludes. have. Also regarding the method of said (7), there exists a problem that film | membrane intensity | strength falls by alkali aqueous solution process in which the raw material to process is limited. Also in the method (8), there is a problem that the film strength is lowered due to drying, heat treatment, irradiation or the like during insolubilization treatment.

As described above, the hydrophilicity-imparting agent is usually eluted into the filtrate, and in order to prevent this, a complicated and inexpensive treatment method has to be adopted, and it is difficult to obtain a membrane having excellent hydrophilic performance. Therefore, there is a need for development of a method and a hydrophilic membrane capable of carrying out a hydrophilic treatment easily and economically without incurring deterioration and strength reduction of a membrane material accompanying hydrophilization treatment.

The present invention has been made to overcome the above problems of the prior art,

It is an object of the present invention to add silver nitrate to a polymer solution, and then to impregnate and fix the silver nanoparticles in the polymer on the surface of the separator by a phase inversion method. It is to provide a method for producing an ultrafiltration membrane and a microfiltration membrane.

One aspect of the present invention for solving the above technical problem is to prepare a polymer solution by dissolving the polymer in a solvent; And adding the silver nitrate to the polymer solution and then preparing the same in a flat membrane form by a phase inversion method.

Another aspect of the present invention relates to a method for producing an ultrafiltration membrane and a microfiltration membrane further comprising a pore control agent to adjust the pore size of the filtration membrane in the polymer solution.

Hereinafter, the present invention will be described in more detail.

The present invention is added to the polymer solution consisting of a polymer selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile and polyimide 0.01 to 5% by weight of silver nitrate to the polymer, and then The method is cast on a nonwoven fabric by the conversion method and the silver nanoparticles are impregnated and fixed on the surface of the separator to prevent elution of the silver nanoparticles and to be easily hydrophilized.

The asymmetric ultrafiltration membrane and the method of manufacturing the microfiltration membrane of the present invention will be described in more detail with reference to the accompanying drawings.

1 is a schematic diagram of a method for producing an ultrafiltration membrane and a microfiltration membrane of the present invention.

Referring to Figure 1, after adding the silver nitrate 0.01 to 5% by weight of the polymer solution to the polymer, by applying a (-) electricity to the polymer solution (1), after transferring the prepared polymer solution to the front end of the knife (4), It is cast while applying to the surface of the nonwoven fabric 3 to produce a flat film. At this time, (+) electricity is applied to the roll 2, which is a conductor in contact with the back surface of the nonwoven fabric, to induce silver ions in the polymer solution to be distributed on the surface side of the nonwoven fabric. In the above process, silver nitrate in the polymer solution is ionized with (+) silver ions and (-) nitrate ions, cast on a nonwoven fabric, and then passed through a (+) charged roll. It is located on the outer side of the coating by impregnation, and is impregnated and fixed in the polymer as silver nanoparticles, and the nitrate ions are dissolved in the non-solvent to solidify the polymer solution.

The non-solvent process refers to a process of removing the remaining solvent by coagulating in water of 25 ~ 60 ℃, the prepared ultrafiltration membrane and the microfiltration membrane with hot water of 50 ~ 90 ℃ for 10 to 30 hours, After that, the asymmetric ultrafiltration and microfiltration membranes according to the present invention are completed.

The polymer solution used in the present invention is used by dissolving a polymer selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile and polyimide in a solvent so as to have a concentration of 10 to 25% by weight. . If the content of the polymer in the polymer solution is less than 10% by weight, there is a problem that the physical properties of the asymmetric membrane is weak, and if it exceeds 25% by weight, the solution viscosity is too large to be difficult to cast and the porosity is too small.

Examples of the solvent include, but are not limited to, dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide, dimethylsulfoxide, and the like. Can be used.

In addition, the present invention can be used by adding additional additives to adjust the pore size of the filtration membrane is prepared, which is well known in the art to select a known pore control agent to suit the desired pore size It is added to the appropriate amount. As pore regulators, poly (ethylene glycol), poly (vinylpyrrolidone), and poly (vinyl alcohol) of various molecular weights can be selected to increase pore size, and 1,4-dioxane and diethylene can be used to reduce pore size. Glycol dimethyl ether etc. can be selected and used.

The silver nitrate used in the present invention can be used as long as it can be commonly obtained. Since the silver nanoparticles in which silver ions generated by ionization in the polymer solution charged with silver nitrate are fixed to the separator are hydrophilic, the hydrophobic membrane is hydrophilized and is firmly fixed to the membrane composed of the polymer and is not eluted. It has excellent microbial resistance. This effect is due to the excellent antimicrobial and antimicrobial functions of silver, so that the antimicrobial and antimicrobial effects are increased in proportion to the surface area of the nano-sized particles.

When the asymmetric ultrafiltration membrane and the microfiltration membrane prepared according to the present invention are applied to the membrane-bound activated sludge method, the reduction of the permeated water due to the attachment of microorganisms is remarkably reduced compared to the conventional separation membrane. Therefore, it can be used for the manufacture of a flat separator for the purpose of use as a membrane bio-reactor for inhibiting the attachment of microorganisms.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example 1

After preparing a polymer solution made by mixing 15% by weight of polyvinylidene fluoride, 10% by weight of polyvinylpyrrolidone and 75% by weight of dimethylacetamide in which 0.05% by weight of silver nitrate was dispersed relative to the weight of polyvinylidene fluoride, Defoaming and cooling were applied on a nonwoven fabric with a thickness of 300 占 퐉 and solidified in 50 占 폚 water. The prepared microfiltration membrane was dried after removing the remaining solvent in water at 60 ℃ for 24 hours.

Example 2

An asymmetric microfiltration membrane was prepared in the same manner as in Example 1 except that silver nitrate was used in an amount of 0.1 wt% based on the weight of polyvinylidene fluoride.

Example 3

Asymmetric microfiltration membranes were prepared in the same manner as in Example 1, except that silver nitrate was used in an amount of 0.5 wt% based on the weight of polyvinylidene fluoride.

Comparative Example 1

Asymmetric filtration membranes were prepared in the same manner as in Example 1 except that silver nitrate was not added.

Comparative Example 2

Asymmetric filtration membranes were prepared in the same manner as in Example 1, except that the microfiltration membrane prepared by the method of Comparative Example 1 was dried after removing the solvent remaining in a 3% by weight aqueous solution of glycerin at 60 ° C. for 24 hours.

[Property evaluation]

(1) Hydrophilicity and Hydrophilic Performance

In order to measure the degree of hydrophilization and hydrophilic performance of the membrane surface prepared by Examples 1 to 3 and Comparative Examples 1 to 2, the contact angle was measured by using a contact angle measuring instrument (S300, Phoenix 300 plus). Table 1 shows. The contact angle refers to the angle formed by the droplet surface and the object surface when a certain amount of fine water droplets are placed on a horizontal object surface, and the more hydrophilic, the smaller the contact angle is. The contact angle was measured by measuring the hydrophilicity of the prepared membrane in a dry state, and filtering it with ultrapure water for 48 hours under 0.1 atm, and then drying and re-measuring to compare how the hydrophilic performance is maintained.

As can be seen in Table 1 above, in the case of the initial contact angle, Comparative Example 2 to which glycerin, which is a nonvolatile water-soluble polyhydric alcohol, is added, has a smaller contact angle than that of Comparative Example 1 to which silver nanoparticles and glycerin are not added. You can see that it is hydrated.

On the other hand, Examples 1 to 3 in which silver nitrate (silver nanoparticles) were added were not different from Comparative Example 1. This is because polyvinylpyrrolidone added as a pore-forming agent in the preparation of the separator is a hydrophilic water-soluble polymer having higher hydrophilicity than that of silver nanoparticles. It is believed that the contribution to hydrophilization was greater.

However, at the contact angle after water flow for 48 hours, the numerical values of Examples 1 to 3 were lower than those of Comparative Examples 1 and 2, and although the hydrophilicity was relatively lower than that of polyhydric alcohols or hydrophilic polymers, silver nanoparticles were immobilized on the membrane and eluted. Rather, it can be seen that high hydrophilicity can be imparted when the membrane is actually operated.

(2) Filtration performance

Polystyrene beads (Sigma) having an average particle diameter of 0.05 μm in ultrapure water and ultrapure water to measure pure permeation rate and solute rejection of the membranes prepared in Examples 1 to 3 and Comparative Examples 1 and 2 with ultrapure water for 48 hours. The filtering performance was measured using a solution of 1000 ppm dispersed as raw water. The membrane was mounted in a pressurized cell having a contact area with raw water of 75 cm 2 and passed through at 20 ° C and 1 atmosphere. The permeation performance was ultra pure water as raw water, and the pure permeation rate was calculated by Equation 1 below by measuring the volume of the filtered water and is shown in Table 2 below.

In addition, the filtration performance was measured using a polystyrene bead dispersion as raw water, using a UV meter (Optizen 2120UV) to measure the polystyrene bead concentration of the filtered water to calculate the solute exclusion ratio according to Equation 2 below Table 2 Shown in

As can be seen in Table 2, the solute excretion was almost no difference, but the pure permeation rate is slightly higher in Examples 1 to 3 with the addition of silver nitrate (silver nanoparticles). Showed performance.

(3) pollution resistance

The membranes prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were manufactured by immersion type modules having a membrane area of 0.2 m 2, and then introduced into a membrane-bound microbial reactor to observe a decrease in permeation flow rate due to membrane contamination. The microbial concentration (MLSS) of the microbial reactor was maintained at 10,000 ppm and the membrane modules prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were simultaneously installed and compared to remove deviations caused by raw water. 2 is shown.

As shown in FIG. 2, in Comparative Examples 1 and 2, the decrease in permeation flux due to membrane fouling proceeds rapidly, whereas in Examples 1 to 3 in which silver nitrate (silver nanoparticles) is added, the decrease in permeate flow rate is considerably delayed. It can be confirmed that this excellent.

According to the present invention as described above, when impregnating silver nitrate in a polymer solution and then preparing asymmetric ultrafiltration and microfiltration membranes by the phase inversion method, the hydrophilic silver nanoparticles are impregnated and fixed on the surface of the membrane, compared to membranes having the same pore size. Membrane of the present invention having a high permeate flow rate and excellent membrane fouling resistance, and the membrane having the excellent permeate flow rate, fouling resistance and microbial resistance, in particular when applied to the membrane-bound activated sludge method It can provide a reducing effect.

Claims (5)

Dissolving the polymer in a solvent to prepare a polymer solution; and Adding silver nitrate to the polymer solution and preparing the same in a flat membrane form by a phase inversion method; Method for producing an asymmetric ultrafiltration membrane and microfiltration membrane comprising a. According to claim 1, wherein the polymer constituting the polymer solution is selected from the group consisting of polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile and polyimide, the content of which is 10 Method for producing an asymmetric ultrafiltration membrane and microfiltration membrane, characterized in that in the range of ~ 25% by weight. The method of claim 1 or 2, wherein the polymer solution further comprises a pore control agent to adjust the pore size of the filtration membrane. According to claim 1, wherein the step of preparing a flat membrane by the phase inversion method Adding silver nitrate to the polymer solution; Negatively charging the polymer solution to which the silver nitrate is added to cast the non-woven fabric while ionizing the silver nitrate; Impregnating and fixing silver nanoparticles on the surface of the flat membrane while passing the cast polymer solution through a positively charged roll; And Impregnating the cast polymer solution having the silver nanoparticles impregnated therein with a non-solvent to form a filtration membrane; Method for producing an asymmetric ultrafiltration membrane and microfiltration membrane comprising a. The method of claim 1 or 4, wherein the silver nitrate is added in an amount of 0.01 to 5% by weight based on the polymer.

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