KR19990032690A - Method for producing a composite membrane having a hydrophilic coating layer of a thin film on a hydrophobic support membrane - Google Patents

Abstract

The present invention relates to a method for manufacturing a composite membrane having a thin hydrophilic coating layer on a hydrophobic support membrane, and more specifically, a material reactive with a hydrophilic polymer (hereinafter referred to as a "reactive agent") is a surface of the hydrophobic support membrane and internal pores. When impregnated with hydrophilic polymer solution by dispersing in the inside, hydrophilic polymer can be applied on hydrophobic support membrane thinly by reaction between hydrophilic polymer and reactant on the surface of hydrophobic support membrane. The present invention relates to a method for producing a composite membrane, which is improved as much as possible.

Description

Method for producing a composite membrane having a thin hydrophilic coating layer on a hydrophobic support membrane

The present invention relates to a method for manufacturing a composite membrane having a thin hydrophilic coating layer on a hydrophobic support membrane, and more specifically, a material reactive with a hydrophilic polymer (hereinafter referred to as a "reactive agent") is a surface of the hydrophobic support membrane and internal pores. When impregnated with hydrophilic polymer solution by dispersing in the inside, hydrophilic polymer can be applied on hydrophobic support membrane thinly by reaction between hydrophilic polymer and reactant on the surface of hydrophobic support membrane. The present invention relates to a method for producing a composite membrane, which is improved as much as possible.

In order to improve permeation rate and productivity in membrane separation, thinning of the membrane may be essential. In general, the permeation rate is inversely proportional to the thickness of the membrane, but if the thickness of the membrane is too thin to increase the permeation rate, the mechanical strength of the membrane decreases and the fracture easily occurs. Therefore, when the membrane is thinned, a support membrane capable of supporting the membrane is required.

Here, the support membrane should simply support the non-porous active layer of the thin film, but should not affect the permeate flow through the active layer of the thin film. This type of membrane is called a composite membrane, which is mainly used for reverse osmosis, pervaporation and gas separation.

Usually, an asymmetric ultrafiltration membrane is mainly used as a supporting membrane, and hydrophobic polysulfone membranes and polyimide membranes are commercially available. A composite film coated with a hydrophilic polymer having a weak hydrophilic property in a thin film form by surface polymerization and coating (J. Macromol. Sci. Chem., A15 (1981) 727 to 755, J. Membr. Sci., 48. (1990) 203), but the active layer of the hydrophilic polymer is required to separate the aqueous mixture containing the ionic organic material.

These hydrophobic support membranes have good conditions for their mechanical strength, chemical resistance, and heat resistance, but they are hydrophobic and thus have limitations in applying hydrophilic polymers. Hydrophobic polymers have a relatively low surface tension compared to hydrophilic polymers, resulting in hydrophilic coating. Because it is difficult. In other words, when the hydrophilic polymer is applied thinly, the wettability is not good and it is agglomerated with each other to obtain a uniform layer. If the thickness of the hydrophilic polymer layer is applied too thick, the permeation rate of the permeate is reduced, resulting in a decrease in productivity.

Physical and chemical treatment of the surface of the hydrophobic support membrane can increase the surface area of the support membrane or activate the surface of the hydrophobic support membrane to increase the adhesion to the hydrophilic polymer to some extent, but the physical and chemical properties between the hydrophobic support membrane and the hydrophilic polymer to be applied can be increased. If the properties are very different, this treatment is not the ultimate method for applying the hydrophilic polymer of the thin film. Therefore, the application of the hydrophilic polymer using a hydrophilic support membrane may be relatively easy to apply due to the increase in adhesion at the interface and the similarity of physicochemical properties. However, the hydrophilic support membrane to be used should be excellent in mechanical, thermal and chemical properties, so that the types of polymers in this category are very limited. Representative hydrophilic support membranes include cellulose acetate and polyacrylonitrile (German Patent DE 3,220,570 A1 (1983), European Patent 0,096,339 (1983)). However, cellulose acetate has a problem in chemical and biochemical properties, and polyacrylonitrile has a problem in that its use is limited because its price is very high and its price is very high even though it is sold in the form of a membrane. . In addition, even in the case of a hydrophilic support film, the mechanical, heat resistance, and chemical resistance mentioned above should be good in order to satisfy the requirements as a support film, so that the hydrophilicity may not be very large. Can represent the same problem.

Therefore, there is an urgent need to use a polysulfone or polyimide support membrane which is easy to purchase commercially, is inexpensive, and has excellent properties to be provided as a support membrane.

In the present invention, to improve the above problems by applying a hydrophilic thin film on the hydrophobic support membrane to prepare a composite membrane by impregnating a hydrophobic support membrane in the aqueous solution of the hydrophilic polymer to improve the wettability of the hydrophilic polymer on the hydrophobic support membrane and thereby In addition to facilitating the application of hydrophilic polymers, the affinity between hydrophobic support membranes and polymers can be increased, and the chemical reactions of the reactants distributed between hydrophilic polymers and hydrophobic support membranes can overcome the limitations of affinity and surface tension at the interface. It is an object of the present invention to provide a method for producing a composite membrane having a hydrophilic coating layer of a thin film on a hydrophobic support membrane.

The present invention is a method for producing a composite membrane by applying a hydrophilic polymer on the hydrophobic support membrane, the hydrophobic support membrane is immersed in an aqueous solution of a reactive agent that is reactive with the hydrophilic polymer to distribute the reactant on the surface of the hydrophobic support membrane and the internal pores And at the same time, a method of producing a composite membrane in which the hydrophilic polymer is thinly coated on the hydrophobic support membrane by a reaction between the hydrophilic polymer and the reactant on the surface of the hydrophobic support membrane.

The present invention will be described in more detail as follows.

When the hydrophobic support membrane is immersed in the aqueous solution in which the hydrophilic polymer reactant is dissolved for a predetermined time, the reactant penetrates into the pores existing on the surface and inside of the hydrophobic support membrane. Can be. That is, regardless of whether the reactant has affinity with the hydrophobic support membrane, the process may uniformly distribute the reactant on the surface and inside the hydrophobic support membrane.

In the present invention, it is preferable to use a polysulfone or polyetherimide ultrafiltration membrane as the hydrophobic support membrane in view of price and mechanical properties. Such hydrophobic support membrane may have a flat or hollow fiber membrane.

According to the present invention, before applying the hydrophilic polymer to the hydrophobic support membrane, it is preferable to remove the swelling agent filled in the pores of the support membrane by a pretreatment process.

Because the swelling agent is mainly made of glycerin, if the hydrophilic polymer is applied without removing the swelling agent, the desired composite membrane cannot be prepared and the polymer cannot be effectively applied because the reactive agent does not penetrate into the pores. to be.

In order to remove such a swelling agent, the hydrophobic support membrane may be immersed in an aqueous solution in which isopropyl alcohol and water are mixed at a weight ratio of 1: 1 for 1 to 5 hours to remove the swelling agent.

As described above, the reactive agent of the hydrophilic polymer is distributed on the hydrophobic support membrane surface and the inside of which the swelling agent is removed.

Since the hydrophilic polymer used in the present invention should have excellent film forming and mechanical properties, sodium alginate, chitosan or polyvinyl alcohol may be preferably used. The same effects can be obtained by using other hydrophilic polymers other than the hydrophilic polymers exemplified above.

In addition, a crosslinking agent, a coagulant, a reaction modifier, or the like of a hydrophilic polymer may be used as the reactant used in the present invention. Preferably, when sodium alginate is used as the hydrophilic polymer, calcium chloride, aluminum nitrate, aluminum sulfate, copper sulfate or hydrochloric acid may be used, sulfuric acid may be used when chitosan is used, and glutaraldehyde may be used when polyvinyl is used. have.

According to the present invention, first, the hydrophobic support membrane from which the swelling agent is removed is immersed for 5 minutes or more in an aqueous solution in which the concentration of the reactant is adjusted to 0.5 to 20%. When the concentration of the aqueous solution of the reactant is less than 0.5%, the hydrophobic support membrane may not be sufficiently dispersed in the pores on the surface and the hydrophilic polymer is difficult to be applied. When the concentration exceeds 20%, a large amount penetrates into the surface of the membrane so that the reactive layer is applied. Is formed. In addition, when the time for immersion is less than 5 minutes, the reactant cannot sufficiently penetrate into the hydrophobic support membrane, and usually, about 5 to 10 minutes, the desired degree of penetration is achieved.

As such, after dispersing the reactant, the support membrane is taken out of the aqueous solution and immersed in an aqueous hydrophilic polymer solution without a drying step, or completely dried, and then immersed in an aqueous hydrophilic polymer solution to form a chemical reaction between the reactive agent and the hydrophilic polymer on the surface of the hydrophobic support membrane. Hydrophilic polymer is uniformly applied on the hydrophobic support membrane. The concentration of the hydrophilic polymer aqueous solution is adjusted to 0.1 to 1%. If less than 0.1%, the hydrophilic thin film cannot be coated on the hydrophobic support membrane, and if it exceeds 1%, the thickness of the coating layer of the hydrophilic thin film becomes too thick. Immersion time is more than 5 minutes, if the immersion time is less than 5 minutes, the reaction time is not enough, it is difficult to apply the polymer sufficiently.

In the present invention, it is important to control the thickness of the coating layer of the hydrophilic thin film when the hydrophilic thin film is coated on the hydrophobic support membrane. The coating thickness is controlled by the concentration of the reactant in the aqueous solution of the reactant and the concentration of the hydrophilic polymer in the hydrophilic polymer solution. The higher the concentration of reactant and hydrophilic polymer, the thicker it is. It is preferable to adjust the thickness so that it becomes 0.1-1.5 micrometer, but if it is less than 0.1 micrometer, it will be difficult to form an application layer without defect, and when it exceeds 1.5 micrometer, the application layer will be too thick and the permeation | transmission rate of a material will become small.

After immersion in an aqueous hydrophilic polymer solution, the support membrane can be taken out, dried in air and further reacted at high temperature in an oven if necessary. Through this process, a composite membrane having excellent adhesion between the hydrophobic support membrane and the thin film layer of the hydrophilic polymer can be prepared.

The cross section of the film was observed using an electron microscope to examine the state of the coating on the thus prepared composite films. It was observed that a coating layer without thickness defects of 0.1 to 1.5 μm was formed. In addition, in order to test the performance of the membrane in the present invention, the aqueous solution of the anionic emulsifier was separated using reverse osmosis, and the membrane separation was measured using a membrane cell designed to minimize concentration polarization in the reverse osmosis system.

Although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example.

Example 1

The polyetherimide ultrafiltration membrane was immersed in a mixture of isopropanol and water in a weight ratio of 1: 1 for 5 hours to remove glycerin in the pores of the membrane, washed with distilled water, and then immersed in 0.5% aqueous calcium chloride solution for 10 minutes. It was then immediately immersed in an aqueous solution of 0.2% sodium alginate. The membrane was prepared by immersion in 1.5% calcium chloride solution for 5 minutes, dried in air, and then subjected to reverse osmosis membrane separation experiment in which a small amount of anionic emulsifier was dissolved. The results are shown in Table 1 below.

Examples 2-4

In the same manner as in Example 1, the membrane was prepared by immersing the polysulfone ultrafiltration membrane from which glycerin was removed in 1.0, 1.5, and 2.0% calcium chloride aqueous solution, respectively, and the reverse osmosis results of the anionic emulsifier aqueous solution are shown in Table 1 below. It was.

Example Calcium chloride concentration (%) Coating film thickness (㎛) Permeation experiment Penetration rate (㎏ / ㎡h) % Rejection One 0.5 0.1 81.9 95.4 2 1.0 0.2 78.6 97.8 3 1.5 0.2 74.1 98.1 4 2.0 1.0 40.4 98.9

In Table 1, when the concentration of calcium chloride, which is a crosslinking agent of sodium alginate, was used in different concentrations, the coating thickness and permeation characteristics of the prepared composite membrane were shown.

As the concentration of the polyvalent crosslinking agent increases, the thickness of the coating film increases, but a coating film of less than 1 μm is obtained in the use concentration range, and shows a relatively excellent permeability. Also, the composite membrane prepared during the membrane separation process does not separate the coating film from the support membrane. Excellent adhesive strength is shown. In particular, the high rejection rate means that the coating layer is free of defects and can be confirmed by an electron microscope.

Examples 5-7

In the same manner as in Example 3, the membrane was prepared by immersing in an aqueous solution of sodium alginate at 0.1, 0.3, 0.5%, and the reverse osmosis results of the anionic emulsifier aqueous solution are shown in Table 2 below.

Example Sodium alginate aqueous solution concentration (%) Coating film thickness (㎛) Permeation experiment Penetration rate (㎏ / ㎡h) % Rejection 5 0.1 0.1 81.9 95.4 6 0.3 0.5 47.5 98.8 7 0.5 1.3 26.6 99.1

In Table 2, it can be seen that the greater the concentration of the aqueous sodium alginate solution is, the thicker the coating thickness of the prepared composite membrane can be obtained. At a polymer concentration of less than 0.3%, a coating thickness of less than 1 μm can be obtained. You can see the high.

Example 8

In the same manner as in Example 3, the membrane was prepared by immersing the polysulfone membrane from which glycerin was removed in a 1% hydrochloric acid aqueous solution as a coagulant. The results of reverse osmosis of the anionic emulsifier aqueous solution are shown in Table 3 below.

Examples 9-10

In the same manner as in Example 3, the polysulfone membrane from which glycerin was removed was immersed in 5% glutaraldehyde as a polyvinyl alcohol crosslinking agent and 0.15% hydrochloric acid solution as a catalyst for 10 minutes, and then 0.5% and 1.0% polyvinyl alcohol was dissolved. It was immersed in the aqueous solution for 5 minutes. Then, the resultant was dried in air and further crosslinked at 100 ° C. for 10 minutes, and the reverse osmosis results of the anionic emulsifier aqueous solution are shown in Table 3 below.

Example 11

In the same manner as in Example 3, the polysulfone membrane from which glycerin was removed was immersed in 2% sulfuric acid aqueous solution, which is a crosslinking agent of chitosan, for 10 minutes, and then immersed in 0.3% aqueous chitosan solution for 5 minutes. Subsequently, the mixture was immersed again in 0.5% sulfuric acid solution, followed by further crosslinking reaction, and dried in air to prepare a composite membrane. The results of reverse osmosis for anionic emulsifier aqueous solution are shown in Table 3 below.

Example Coating polymer Coating film thickness (㎛) Permeation experiment Penetration rate (㎏ / ㎡h) % Rejection 8 Sodium alginate 0.3 78.7 94.3 9 Polyvinyl alcohol 0.1 63.5 93.9 10 Polyvinyl alcohol 0.2 49.1 97.5 11 Chitosan 0.3 26.3 89.4

In Table 3, when the coagulant is used as the reactant or when other hydrophilic polymers other than sodium alginate are used as the coating polymer and the crosslinking agent is used as the reactive material, the thickness and permeation characteristics of the coating film of the prepared composite membrane are shown.

In these cases, the coating layer of the thin film was also formed, but in the case of chitosan, the low permeation rate and rejection rate were chitosan, which is a typical cationic polymer, so that the solute of the anion adheres to the membrane surface and fouling occurs on the surface of the support membrane. Therefore, since the degree becomes more severe, the permeation rate is worsened and the exclusion rate is also accompanied.

Comparative Examples 1 to 4

In the same manner as in Example 1, the polysulfone ultrafiltration membrane was immersed in an aqueous solution of calcium chloride which is a reactant having the concentration shown in the following Table 4 and each polymer was applied to prepare a membrane and then reverse osmosis pressure separation result for an anionic emulsifier aqueous solution. Is shown in Table 4 below.

Comparative example % Of reactant Coating polymer Coating film thickness (㎛) Permeation experiment Penetration rate (㎏ / ㎡h) % Rejection One 0.2 Sodium alginate - 326.5 4.8 2 0.3 Chitosan - 301.0 4.1 3 25 Sodium alginate 5.2 2.3 99.7 4 30 Chitosan 5.7 2.4 99.5

As shown in Table 4, when the polysulfone ultrafiltration membrane was immersed in an aqueous solution of a reactant having a concentration of 0.2% and 0.3% and coated with a coating polymer to prepare a separation membrane, a permeation experiment was carried out to react the ultrafiltration membrane of the present invention. Compared to the separator prepared by applying the coated polymer after immersing in the aqueous solution, the permeation rate is high, but the exclusion rate is low because the coated polymer is not applied, and the concentration of the reactive solution is 25%. And 30%, the thickness of the coating film is higher than that of the separator of the present invention, so that the rejection rate is high, but the permeation rate is very low.

As described above, the present invention not only can produce a composite membrane having a coating layer of a thin hydrophilic polymer on a hydrophobic support membrane due to a chemical reaction between the reactive agent distributed on the hydrophobic support membrane and the hydrophilic polymer which is a coated polymer. By controlling the concentration of the aqueous solution or the concentration of the hydrophilic polymer aqueous solution it is possible to control the thickness of the coating layer, it can be seen that it is very effective in producing a composite membrane having a hydrophilic coating layer of a thin film with good separation productivity.

Claims (10)

A method of manufacturing a composite membrane by applying a hydrophilic polymer on a hydrophobic support membrane, wherein the hydrophobic support membrane is immersed in an aqueous solution of a reactive agent that is reactive with the hydrophilic polymer to distribute the reactant on the surface of the hydrophobic support membrane and in the pores. And the hydrophilic polymer is thinly coated on the hydrophobic support membrane by a reaction between the hydrophilic polymer and the reactive agent on the surface of the hydrophobic support membrane. The method of manufacturing a composite membrane having a thin hydrophilic coating layer on a hydrophobic support membrane according to claim 1, wherein the hydrophobic support membrane is made of polysulfone or polyetherimide. The method for producing a composite membrane having a hydrophilic coating layer of a thin film on a hydrophobic support membrane according to claim 1 or 2, wherein the hydrophobic support membrane is a flat membrane or a hollow fiber membrane. The method according to claim 1, wherein the hydrophilic polymer is sodium alginate, chitosan or polyvinyl alcohol. The method for producing a composite film having a hydrophilic coating layer of a thin film on a hydrophobic support film according to claim 1 or 4, wherein the concentration of the hydrophilic polymer is 0.1 to 1%. The method of claim 1, wherein the reactive agent which is reactive with the hydrophilic polymer is calcium chloride, aluminum nitrate, aluminum sulfate, copper sulfate, or hydrochloric acid when sodium alginate is used as the hydrophilic polymer, and sulfuric acid, polyvinyl alcohol when chitosan is used. A method for producing a composite membrane having a thin film coating layer on a hydrophobic support membrane, characterized in that it is glutaraldehyde when used. The method for producing a composite membrane having a coating layer of a thin film on a hydrophobic support membrane according to claim 1 or 6, wherein the concentration of the reactive agent is 0.5 to 20%. The method of claim 1, wherein the hydrophobic support membrane is immersed for 5 minutes or more in an aqueous solution of a reactive agent, and soaked for 5 minutes or more in an aqueous solution of a hydrophilic polymer so that the hydrophilic polymer is applied to the surface of the hydrophobic support membrane by a chemical reaction between the reactant and the hydrophilic polymer. A method for producing a composite membrane having a coating layer of a thin film on a hydrophobic support membrane. The hydrophobic support membrane according to claim 1 or 8, wherein the hydrophobic support membrane is immersed in a hydrophilic polymer solution immediately after being immersed in a reactant or without drying, or completely dried and then immersed in the polymer solution. The manufacturing method of the composite film which has a coating layer of a thin film. The hydrophobic support membrane according to claim 1, wherein the hydrophobic support membrane is prepared by applying a hydrophilic polymer thereon to adjust the concentration of the reactant solution and the concentration of the hydrophilic polymer aqueous solution to produce a coating thickness of 0.1 to 1.5 µm. The manufacturing method of the composite film which has a thin hydrophilic coating layer on it.