REVERSE OSMOSIS MEMBRANE

Abstract

Provided is a reverse osmosis membrane using a hydrophilized polyolefin-based microporous membrane.

A reverse osmosis membrane according to the present invention may provide a large treatment area per unit volume by using a thin film type support, thereby improving water treatment performance.

Claims

1. A reverse osmosis membrane comprising: a polyamide active layer formed on a hydrophilized polyolefin-based microporous membrane, wherein, the polyolefin-based microporous membrane has a space ratio of 20 to 70%, a maximum pore size measured by a bubble point method of 0.1 m or less, and a product of a tensile strength and a thickness in at least one of a transverse direction and a longitudinal direction of 0.3 kgf/cm or more.

2. The reverse osmosis membrane of claim 1, wherein the polyolefin-based microporous membrane has a contact angle of water of 90 degrees or less.

3. The reverse osmosis membrane of claim 1, wherein the polyolefin-based microporous membrane is a film or a sheet.

4. The reverse osmosis membrane of claim 1, wherein the polyolefin-based microporous membrane is selected from a single layer microporous membrane formed of any one selected from a polyethylene, a polypropylene, and a mixture thereof; a composite microporous membrane having two or more layers in which the polyethylene and the polypropylene are alternately stacked in two or more layers; and a multilayer microporous membrane in which the polyethylene or the polypropylene is stacked in two or more layers.

5. The reverse osmosis membrane of claim 1, wherein the hydrophilization is performed by any one method selected from formation of a coating layer by applying any one selected from a surfactant, a surface active agent, a wetting agent, a polymer solution containing inorganic particles, and a hydrophilic polymer, plasma treatment, UV-ozone treatment, corona discharge, surface foaming, and grafting with a hydrophilic polymer by plasma treatment.

6. The reverse osmosis membrane of claim 1, wherein the polyamide active layer is formed by interfacial polymerization of an aqueous solution containing a polyfunctional amine and an organic solution containing a polyfunctional acyl halide.

7. The reverse osmosis membrane of claim 1, wherein the reverse osmosis membrane has a salt rejection of 97% or more and a permeate flux of 35 L/m.sup.2hr or more.

Description

EXAMPLE 1

[0088] 1) Manufacture of Microporous Membrane 35 wt % of high-density polyethylene having a weight average molecular weight of 3.810.sup.5 g/mole and 65 wt % of a diluent in which dibutyl phthalate and a paraffin oil having a kinematic viscosity of 160 cSt at 40 C. are mixed at a weight ratio of 1:1 were mixed. The composition was extruded using a biaxial compounder equipped with a T-die at 245 C., and passed a section set at 175 C. to induce phase separation of a polyethylene and the diluent as a single phase, thereby manufacturing a sheet using a casting roll. The sheet manufactured using a sequential biaxial stretching machine was stretched 7.0 times in a longitudinal direction and a transverse direction at a stretching temperature of 127 C., respectively. Following stretching, a heat setting temperature was 130 C., a heat setting width was 1 times in a preheating section, 1.3 times in a hot stretching section, and 1.2 times in a final heat setting section. Physical properties of the manufactured polyethylene macroporous membrane were measured and shown in Table 1 below.

[0089] 2) Hydrophilization of Microporous Membrane

[0090] A surface of the manufactured microporous membrane was corona-treated so as to have 59 degrees of the contact angle of water.

[0091] The corona treatment was carried out with a gap of 2 mm between the electrodes and the membrane at a speed of 0.5 m/min under a voltage of 250 V by using a CTW0212 from Wedge, and the results were shown in Table 2.

[0092] 3) Manufacture of Reverse Osmosis Membrane

[0093] Metaphenylenediamine (MPD, 99%) was dissolved in deionized water (Mili-Q water, 18 M.Math.cm) to produce 2 wt % of an aqueous MPD solution. Next, the hydrophilized microporous membrane was immersed in the aqueous MPD solution for 1 minute, and removed, and then the residual solution was removed using a rubber roller.

[0094] Then, trimesoyl chloride (TMC, 98%) was dissolved in n-hexane (98%) produce 0.1 wt % of a TMC organic solution, the reverse osmosis membrane support from which the residual solution was removed was immersed in the TMC organic solution for 1 minute, removed, washed with n-hexane, and dried at ambient temperature for 5 minutes.

[0095] The reverse osmosis membrane support was washed with an aqueous solution containing 0.2 wt % of sodium carbonate for 30 minutes, followed by washing with pure water again at ambient temperature, thereby producing a reverse osmosis membrane.

[0096] Physical properties of the manufactured reverse osmosis membrane were evaluated and shown in Table 1 below.

EXAMPLES 2 to 6

[0097] Examples 2 to 6 were performed in the same manner as in Example 1, except that the thickness, the space ratio, the maximum pore size, the product of the thickness and the tensile strength, and the contact angle of water were changed by varying the production conditions of the polyolefin microporous membrane and the conditions of the corona treatment, as shown in Table 1 below.

[0098] Physical properties of the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below. The respective corona treatment conditions were separately shown in Table 2.

EXAMPLE 7

[0099] 1) Manufacture of Microporous Membrane

[0100] A casting film made of a homopolypropylene having a melt flow index of 2.0 g/10 minutes at 230 C. was heat-treated, followed by 10% stretching at 50 C. and stretching 150% stretching at 130 C. in a uniaxial direction to obtain a polypropylene microporous membrane.

[0101] The manufactured polypropylene microporous membrane was corona treated and hydrophilized in the same process as in Example 1 to manufacture a reverse osmosis membrane.

[0102] Physical properties the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below. The corona treatment conditions were separately shown in Table 2.

Comparative Examples 1 to 3

[0103] Comparative Examples 1 to 3 were performed using the same raw materials as in Example 1, and the thickness, the space ratio, the maximum pore size, the product of the thickness and the tensile strength, and the contact angle of water were changed as shown in Table 1 below by varying the production conditions of the polyolefin membrane and the conditions of the corona treatment.

[0104] Physical properties of the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below. The corona treatment conditions were separately shown in Table 2.

Comparative Example 4

[0105] Comparative Examples 4 was performed using the same raw materials as in Example 7, and the thickness, the space ratio, the maximum pore size, the product of the thickness and the tensile strength, and the contact angle of water were changed as shown in Table 1 below by varying the production conditions of the polyolefin microporous membrane and the conditions of the corona treatment.

[0106] Physical properties of the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below. The corona treatment conditions were separately shown in Table 2.

Comparative Example 5

[0107] Comparative Example 5 was performed in the same manner as in Example 1, except that the polyolefin microporous membrane was not corona treated to manufacture a reverse osmosis membrane.

[0108] The physical properties of the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below.

Comparative Example 6

[0109] Comparative Example 6 was performed in the same manner as in Example 3, except that the polyolefin microporous membrane was not corona treated to manufacture a reverse osmosis membrane.

[0110] Physical properties of the manufactured polyethylene microporous membrane and the reverse osmosis membrane were evaluated and shown in Table 1 below.

TABLE-US-00001 TABLE 1 Polyolefin Microporous Memebrane Properties Thickness Contact Maximum Tensile strength Angle Space Pore (kgf/cm) of Salt Permeate Thickness Ratio Size Longitudinal Transverse Water Rejection Flux (m) (%) (nm) Direction Direction () (%) (L/m2hr) Remake Example 1 20 46 50 3.9 3.5 59 99.2 41.9 Example 2 20 46 50 13.9 3.5 87 98.4 40.1 Example 3 20 62 74 3.2 1.3 63 97.1 37.6 Example 4 30 70 88 2.4 1.3 60 97.5 38.1 Example 5 5 21 28 1.5 1.2 53 99.3 42.5 Example 6 25 66 99 2.6 1.0 72 97.8 39.8 Example 7 25 39 51 5.5 0.3 75 99.0 40.3 Comparative 35 72 92 2.2 0.4 62 75.2 36.2 Example 1 Comparative 20 64 103 2.0 1.2 63 36.8 44.2 Pinhole Example 2 Generation Comparativc 5 19 24 1.6 1.4 57 99.4 17.6 Example 3 Comparative 16 43 58 2.6 0.24 77 Not Not Fracture Example 4 Measurable Measurable Generation Comparative 20 46 50 3.9 3.5 120 7.0 13.6 Example 5 Comparative 20 62 74 3.2 1.5 119 26.3 0.7 Example

TABLE-US-00002 TABLE 2 Gap Between Voltage electrode and Throughput rate (V) Membrane (mm) (m/min) Example 1 250 2 0.5 Example 2 170 5 2.0 Example 3 170 2 2.0 Example 4 250 2 1.5 Example 5 250 2 0.2 Example 6 250 2 2.5 Example 7 250 2 3.0 Comparative Example 1 170 2 1.3 Comparative Example 2 170 2 2.0 Comparative Example 3 230 2 0.3 Comparative Example 4 250 2 3.0

[0111] As shown in Table 1 above, it was found that the salt rejection was as high as 97% or more and the permeate flux was as high as 35 L/m.sup.2hr or more in the range satisfying all conditions that the thin film type polyolefin-based microporous membrane as a support, the space ratio of the polyolefin-based microporous membrane was 20 to 70%, the maximum pore size measured by the bubble point method was 0.1 l or less, and the product of the tensile strength and the thickness in at least one of the transverse direction and the longitudinal direction was 0.3 kgf/cm or more.

[0112] As shown in Comparative Examples 5 and 6, it was found that when the hydrophilization was not performed, the salt rejection and the permeate flux were very low even if physical properties of the microporous membrane were same.