Separation membrane with excellent stain resistance and method for producing the same

Abstract

The present invention relates to a separation membrane having excellent fouling resistance, which not only has excellent fouling resistance and flow rate but also does not experience a decrease in rejection rate performance, by coating the surface of a support with a polymer solution containing a hydrophobic polymer, a hydrophilic polymer, and a sulfonated polymer, and a method for producing the same.

Description

Technical Field

[0001] The present invention relates to a separation membrane having excellent anti-fouling properties and a method for manufacturing the same.

Background Art

[0002] Conventional separation membranes can separate various dissolved substances dissociated in surface water and seawater from a solvent using various selective membranes. Such membranes include microfiltration membranes, ultrafiltration membranes, nano-separation membranes, and reverse osmosis membranes. In order to remove salts from surface water and seawater and utilize them for drinking water, agricultural water, and industrial water, research on methods for separating substances at the molecular level has been actively conducted. Among them, many studies have been conducted on the method of adding sulfonated polymers.

[0003] However, the conventional method of adding sulfonated polymers has the effect of improving the flow rate and anti-fouling properties, but there is a problem that the rejection rate of the separation membrane decreases, and research for its improvement is insufficient.

[0004] As an example of this, Korean Patent Publication No. 10-2013-0037387 manufactured a separation membrane using a sulfonated polymer membrane. However, the separation membrane manufactured in this way has a problem that the salt rejection rate greatly decreases. Therefore, it is urgent to study a separation membrane that introduces a sulfonated polymer at an appropriate ratio and has excellent flow rate while not reducing the rejection rate.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The separation membrane having excellent anti-fouling properties of the present invention for solving the above problems is to coat a sulfonated polymer solution on the separation membrane, thereby providing a separation membrane having excellent flow rate and anti-fouling properties and not causing a decrease in the rejection rate, and a method for manufacturing the same.

Means for Solving the Problems

[0006] The separation membrane with excellent anti-fouling property of the present invention for solving the above problems is a separation membrane including a support and a coating film formed on at least one surface of the support, wherein the coating film includes a hydrophobic polymer, a sulfonated polymer, and a hydrophilic polymer, the coating film contains the sulfonated polymer in an amount of 0.002 to 0.5% by weight, and when the separation membrane is operated for 50 to 70 minutes under a polyethylene glycol solution with a concentration of 100 to 5,000 ppm at a temperature of 20 to 30 °C and a pressure of 40 to 60 psi, the flow rate may be 63 gfd (gal / ft 2 ·day) or more, and the polyethylene glycol rejection rate may be 90% or more.

[0007] In a preferred embodiment of the present invention, the sulfonated polymer may include one or more selected from sulfonated polysulfone and sulfonated polyethersulfone.

[0008] In a preferred embodiment of the present invention, the hydrophobic polymer may include one or more selected from polysulfone and polyethersulfone.

[0009] In a preferred embodiment of the present invention, the hydrophilic polymer may include one or more selected from polyethylene glycol and polyvinyl pyrrolidone.

[0010] In a preferred embodiment of the present invention, the hydrophobic polymer may be included in an amount of 85 to 95% by weight based on the total weight of the mixed polymer.

[0011] In a preferred embodiment of the present invention, the separation membrane may be a nano-separation membrane, an ultrafiltration separation membrane, or a microfiltration separation membrane.

[0012] In a preferred embodiment of the present invention, the separation membrane may have an upper surface contact angle of 20° to 50°.

[0013] As another aspect of the present invention, a method for manufacturing a separation membrane excellent in antifouling property includes a step of manufacturing a polymer solution including a hydrophobic polymer, a sulfonated polymer, a mixed polymer including a hydrophilic polymer, and a solvent, a step of coating the polymer solution on at least one surface of a support and then immersing it in distilled water to form a coating film, and a step of drying the support on which the coating film is formed.

[0014] In a preferred embodiment of the present invention, the solvent may include one or more selected from dimethylacetamide, N-methyl-2-pyrrolidone, dimethylformamide, and dimethyl sulfoxide.

[0015] In a preferred embodiment of the present invention, the sulfonated polymer may have a sulfonation degree of 0.25 to 0.50.

Effects of the Invention

[0016] According to the present invention, it is possible to manufacture a separation membrane excellent in antifouling property that is not only extremely excellent in flow rate and antifouling property but also does not cause a decrease in rejection rate.

Modes for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described in more detail based on the method for manufacturing a separation membrane excellent in antifouling property of the present invention.

[0018] A method for manufacturing a separation membrane with excellent stain resistance may include a first step of manufacturing a polymer solution including a hydrophobic polymer, a sulfonated polymer, a mixed polymer including a hydrophilic polymer, and a solvent; a second step of coating the polymer solution on at least one surface of a support and then immersing it in distilled water (DI) to form a coating membrane; and a third step of drying the support on which the coating membrane is formed.

[0019] When the sum of the hydrophobic polymer, the sulfonated polymer, and the hydrophilic polymer is defined as a "mixed polymer", the polymer solution in the first step may include 20 to 36% by weight of the mixed polymer and the remaining amount of the solvent in 100% by weight, or preferably, 23 to 33% by weight of the mixed polymer and the remaining amount of the solvent in 100% by weight.

[0020] If the mixed polymer is included in less than 20% by weight, there may be a problem of low removal performance of the separation membrane. If it exceeds 36% by weight, due to the high viscosity of the polymer solution, there may be difficulties in forming the separation membrane, and due to the high content of the mixed polymer, there may be a problem that the flow rate of the separation membrane decreases rapidly.

[0021] Hereinafter, each component of the mixed polymer will be described in detail. First, the hydrophobic polymer may include one or more selected from polysulfone and polyethersulfone, and more preferably, may include polyethersulfone.

[0022] Also, the hydrophobic polymer may be included in 85 to 95% by weight of the total weight of the mixed polymer, or preferably, 86 to 94% by weight.

[0023] In addition, the sulfonated polymer may contain one or more selected from sulfonated polysulfone and sulfonated polyethersulfone, and more preferably, may contain sulfonated polyethersulfone.

[0024] Also, the sulfonated polymer may be contained in an amount of 0.002 to 0.500% by weight, preferably 0.0035 to 0.3500% by weight, based on the total weight of the mixed polymer. At this time, when the sulfonated polymer is contained in an amount less than 0.002% by weight, there may be a problem that the flow rate significantly decreases after a certain time after operation and the fouling resistance is poor. When the content exceeds 0.500% by weight, there is a problem that the rejection rate of polyethylene glycol significantly decreases. In order to maintain both the flow rate and the polyethylene rejection rate at an excellent level, it is essential to use an appropriate amount of the sulfonated polymer.

[0025] Also, the sulfonated polymer may have a sulfonation degree of 0.25 to 0.50, preferably 0.30 to 0.45. At this time, the sulfonation degree means the ratio of the sulfonation repeating unit among the total number of moles of the sulfonated polymer. When the sulfonation degree is less than 0.25, there may be a problem that the fouling resistance of the separation membrane is not improved. When it exceeds 0.50, there may be a problem that the rejection rate of polyethylene glycol significantly decreases.

[0026] Also, the sulfonated polymer may have a weight average molecular weight (Mw) of 100,000 to 180,000, preferably 110,000 to 170,000. If the weight average molecular weight is less than 100,000, there may be a problem that the synthesis of the sulfonated polymer is difficult. If it exceeds 180,000, there may be a problem that the viscosity of the polymer solution becomes high and it is difficult to form the separation membrane.

[0027] In addition, the hydrophilic polymer may contain one or more selected from polyethylene glycol and polyvinyl pyrrolidone, and more preferably, may contain polyvinyl pyrrolidone.

[0028] Also, the hydrophilic polymer may be contained in the remaining amount excluding the hydrophobic polymer and the hydrophilic polymer in the total weight of the mixed polymer.

[0029] In addition, the solvent may contain one or more selected from dimethylacetamide, N-methyl-2-pyrrolidone, dimethylformamide, and dimethyl sulfoxide, and preferably, may contain dimethylacetamide.

[0030] The polymer solution produced in the aforementioned first stage may be a mixture in which the hydrophobic polymer, the sulfonated polymer, and the hydrophilic polymer are simply mixed without cross-linking or reaction.

[0031] Next, the coating in the second stage can be performed by dipping, spraying, drop casting, self-assembly, spin coating, doctor blade, bar coating, slot die coating, microgravure coating, comma coating, printing, or casting method on at least one surface of the support.

[0032] Further, the support may contain one or more selected from a polyester-based support, a polyethylene-based support, and a polypropylene-based support, and preferably, it may be a polyester-based support.

[0033] Also, the physical properties of the membrane can be adjusted by the porosity and hydrophilicity of the support. At this time, in order to realize excellent physical properties of the membrane, the support may have an air permeability of 2 cc / cm 2 ·sec or more, preferably, it may have an air permeability of 2 to 20 cc / cm 2 ·sec. The average pore diameter of the support may be 1 to 600 μm, and preferably, it may be 5 to 300 μm. When the air permeability and the average pore diameter conditions are satisfied, smooth inflow of water and enhanced water permeability can be achieved.

[0034] Also, the thickness of the support may be 20 to 150 μm. If it is less than 20 μm, the strength of the entire membrane may decrease, and if it exceeds 150 μm, it may cause a decrease in flow rate.

[0035] Next, the formation of the coating film in the second stage can be carried out by immersing the support coated with the polymer solution in distilled water for 10 minutes to 120 minutes, and preferably, it can be carried out by immersing for 30 minutes to 60 minutes. At this time, the distilled water may be at 15 to 30 °C, and preferably, it may be at 18 to 25 °C.

[0036] Next, the drying in the third stage can be carried out at 25 to 100 °C for 0.5 minute to 5 minutes, and preferably, it can be carried out at 60 to 90 °C for 1 minute to 3 minutes. At this time, the drying can be carried out by one method selected from hot air drying and natural drying.

[0037] Hereinafter, a separation membrane excellent in anti-fouling property manufactured by the manufacturing method of a separation membrane excellent in anti-fouling property as described above will be described. The description of the separation membrane described below omits the parts described in the above manufacturing method.

[0038] The separation membrane excellent in fouling resistance of the present invention may include a support and a coating film formed on at least one surface of the support. At this time, the coating film may contain a hydrophobic polymer, a sulfonated polymer, and a hydrophilic polymer. At this time, the separation membrane may be a nano-separation membrane, an ultrafiltration separation membrane, or a microfiltration separation membrane, but preferably may be an ultrafiltration separation membrane.

[0039] Regarding the physical properties of the separation membrane, first, the upper surface contact angle of the separation membrane may be 20° to 50°, and preferably may be 30° to 40°.

[0040] If the upper surface contact angle is less than 20°, there may be a problem that the rejection rate of the separation membrane decreases, and if it exceeds 50°, there may be a problem that the flow rate of the separation membrane decreases.

[0041] In addition, the conventional separation membrane had a problem that when operated under a polyethylene glycol solution, it could not achieve excellent levels in both the flow rate and the polyethylene glycol rejection rate.

[0042] The present invention is excellent in both the flow rate and fouling resistance even under a polyethylene glycol solution. The separation membrane may have a flow rate of 63 gfd (gal / ft 2 ·day) or more when operating under the test conditions described below, preferably 65 gfd or more, and more preferably 65.5 to 120 gfd or more.

[0043] In addition, the separation membrane may have a polyethylene rejection rate of 90% or more, and preferably 95% or more. At this time, the test conditions may mean operating the separation membrane for 50 to 70 minutes in a polyethylene glycol solution with a concentration of 100 to 5,000 ppm under temperature conditions of 20°C to 30°C and pressure conditions of 40 to 60 psi. Preferably, it may mean operating for 55 to 65 minutes in a polyethylene glycol solution with a concentration of 500 to 4,000 ppm under temperature conditions of 22°C to 28°C and pressure conditions of 45 to 55 psi.

[0044] Hereinafter, the present invention will be described based on the following examples. At this time, the following examples are only presented for illustrative purposes of the invention, and the scope of the rights of the present invention is not limited by the following examples.

[0045] [Examples] Example 1: Production of a separation membrane with excellent fouling resistance A polymer solution containing 28% by weight of a mixed polymer and the balance of a solvent was prepared. At this time, the mixed polymer contains 89.2% by weight of polyethersulfone, 0.035% by weight of sulfonated polyethersulfone having a sulfonation degree of 0.35, and the balance of polyvinyl pyrrolidone.

[0046] Also, the weight average molecular weight of the sulfonated polyethersulfone is such that the weight average molecular weight (Mw) is 143,000. At this time, dimethylacetamide was used as the solvent.

[0047] Next, the polymer solution was coated on one surface of a polyester-based support with a horizontal length, vertical length, and thickness of 150 mm × 250 mm × 0.09 mm by a bar coating method so that the thickness of the coating film including the support was 0.13 mm.

[0048] Next, the support was immersed in distilled water (DI water) to form a coating film.

[0049] Next, the support with the coating film formed thereon was dried at 90°C for 2 minutes to produce a separation membrane excellent in stain resistance.

[0050] Examples 2 to 8 and Comparative Examples 1 to 8: Production of Separation Membrane Excellent in Stain Resistance Although a separation membrane excellent in stain resistance was produced in the same manner as in Example 1, Examples 2 to 8 and Comparative Examples 1 to 8 were carried out under the conditions shown in Tables 1 to 5 below.

[0051] Experimental Example 1: Evaluation of Physical Properties of Separation Membrane The separation membranes excellent in stain resistance produced in Examples 1 to 8 and Comparative Examples 1 to 8 were evaluated for their physical properties by the following methods and shown in Tables 1 to 4 below.

[0052] (1) Measurement of Top Surface Contact Angle (Wettability) To measure the wettability with respect to water, the contact angle formed between the surface of the membrane and a water droplet was measured using a contact angle measurement device (Contact angle, °). After photographing the shape of the droplet with a CCD camera, a method of calculating the interfacial tension (γ) optimized for the finally photographed droplet shape was used. The injection volume was 0.05 mL using a microsyringe, and secondary distilled water was used. Since errors can occur in the contact angle due to chemical inhomogeneity and roughness on the membrane surface, in the experiment, the experiment was carried out within a range where the error range did not exceed ±2° through more than 10 analyses.

[0053] (2) Measurement of Flow Rate and Rejection Rate When the separation membrane was operated for 60 minutes under a 1,000 ppm concentration polyethylene glycol solution at a temperature of 25°C and a pressure of 50 psi, the flow rate and the polyethylene glycol rejection rate were measured.

[0054] (3) Evaluation of Stain Resistance The initial flow rate vs. flow rate reduction rate was evaluated under the conditions of 25 °C, 50 psi, and 24-hour operation using an aqueous sodium chloride solution of 2000 ppm containing 50 ppm of dry milk, 5 ppm of dodecyltrimethylammonium bromide (DTAB), and 50 ppm of sodium dodecyl sulfate (SDS) independently for the separation membrane. At this time, the flow rate reduction rate was calculated through the following relational expression 1.

[0055] [Relational Expression 1] Flow rate reduction rate (%) = (Flow rate after 24-hour operation - Initial flow rate) / Initial flow rate × 100 (%)

[0056] [Table 1]

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] Referring to Tables 1 to 4 above, it was confirmed that Examples 1 to 8 exhibited excellent flow rates and polyethylene glycol rejection rates even in a polyethylene glycol solution, and had a low flow rate reduction rate, indicating that they were separation membranes with excellent anti-fouling properties. In addition, it was confirmed that Example 2 exhibited excellent physical properties, but showed somewhat inferior physical properties compared to Example 1.

[0061] In addition, it was confirmed that Example 2 exhibited excellent physical properties, but showed somewhat inferior physical properties compared to Example 1.

[0062] On the one hand, it can be confirmed that Comparative Example 1, which contains less than 0.002% by weight of the sulfonated polymer in the mixed polymer, has a very poor flow rate reduction rate, and contains more than 0.5% by weight. Ratio of mu In Comparative Example 3, it was confirmed that the polyethylene glycol rejection rate was very low.

[0063] Also, when the sulfonation degree of the sulfonated polymer is less than 0.25, it can be confirmed that the flow rate reduction rate increases and the anti-fouling property is poor. In Comparative Example 5 where the sulfonation degree exceeds 0.50, it was confirmed that the polyethylene glycol rejection rate was poor.

[0064] In addition, in Comparative Example 6 where the content of the mixed polymer in the mixed polymer solution is less than 20% by weight, it can be confirmed that the rejection rate is poor, the flow rate reduction rate is large, and the anti-fouling property of the separation membrane is poor. In Comparative Example 7 where the content exceeds 36% by weight, it was impossible to form the separation membrane and all physical properties were unmeasurable.

[0065] In addition, in Comparative Example 8 where the hydrophobic polymer in the mixed polymer is less than 85% by weight, it was confirmed that the flow rate was high and the physical properties such as the salt rejection rate and the anti-fouling property were poor.

[0066] As described above, one embodiment of the present invention has been described. However, the idea of the present invention is not limited to the embodiments presented in this specification. Those skilled in the art who understand the idea of the present invention can easily propose other embodiments by adding, changing, deleting, adding, etc. of components within the scope of the same idea, and it can also be said that this is within the scope of the idea of the present invention.

Claims

1. A separation membrane comprising a support and a coating film formed on at least one surface of the support, wherein the support has an air permeability of 2 to 20 cc / cm 2 ·sec, the coating film is formed by coating a polymer solution containing a mixed polymer and a solvent, the mixed polymer containing polyethersulfone (a hydrophobic polymer), sulfonated polyethersulfone (a sulfonated polymer), and polyvinyl pyrrolidone (a hydrophilic polymer), the mixed polymer contains 85 to 95% by weight of the hydrophobic polymer, 0.002 to 0.500% by weight of the sulfonated polymer, and the balance of the hydrophilic polymer in the remaining amount out of 100% by weight, the sulfonated polyethersulfone has a sulfonation degree of 0.25 to 0.50 and a weight average molecular weight of 100,000 to 180,000, and is a separation membrane excellent in anti-fouling property.

2. The separation membrane according to Claim 1, characterized in that the separation membrane is a nano-separation membrane, an ultrafiltration separation membrane or a microfiltration separation membrane.

3. The separation membrane according to Claim 1, characterized in that the upper surface contact angle of the separation membrane is 20° to 50°.

4. A step of producing a polymer solution containing a mixed polymer and a solvent, a step of forming a coating film by coating the polymer solution on at least one surface of the support and then immersing it in distilled water, and a step of drying the support on which the coating film is formed, wherein the mixed polymer contains polyethersulfone (a hydrophobic polymer), sulfonated polyethersulfone (a sulfonated polymer), and polyvinyl pyrrolidone (a hydrophilic polymer), the mixed polymer contains 85 to 95% by weight of the hydrophobic polymer, 0.002 to 0.500% by weight of the sulfonated polymer, and the balance of the hydrophilic polymer in the remaining amount out of 100% by weight, The sulfonated polyether sulfone has a sulfonation degree of 0.25 to 0.50 and a weight average molecular weight of 100,000 to 180,000, The support has an air permeability of 2 to 20 cc / cm 2 ·sec, and is a method for manufacturing a separation membrane excellent in antifouling properties.

5. The solvent contains one or more selected from dimethylacetamide (Dimethylacetamide), N-methyl-2-pyrrolidone (N-Methyl-2-pyrrolidone), dimethylformamide (Dimethylformamide), and dimethyl sulfoxide (Dimethyl sulfoxide), and is a method for manufacturing a separation membrane excellent in antifouling properties according to claim 4.

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