KR20130078826A - Forward osmosis membrane modifided hydrophilic surface and manufacturing method thereof - Google Patents

Abstract

PURPOSE: A forward osmosis membrane and a method for manufacturing the same are provided to have an enhanced contamination resistance property and a wide utilization range because the forward osmosis membrane is stable in a wide region of pH 2-12. CONSTITUTION: A forward osmosis membrane comprises a hydrophobic polymer supporting layer which is stacked on a non-woven fabric layer with 2cc/cm^2·sec or more air permeability. The porosity of the supporting layer is distributed from the contact side to the opposite side of the non-woven fabric layer in the range of 30-80%. The outermost surface of the supporting layer is reformed to be hydrophilic by sulfonation. [Reference numerals] (AA) Non-woven fabric

Description

TECHNICAL FIELD [0001] The present invention relates to a positive osmosis membrane having a membrane surface modified to be hydrophilic,

The present invention relates to a quasi-osmotic membrane having a membrane surface modified to be hydrophilic and a method for producing the same. More particularly, the present invention relates to a quasi-osmotic membrane having a two-layer structure composed of a hydrophobic polymer support layer on a nonwoven fabric layer, The porosity is distributed to 30 to 80% to the side surface, and the outermost surface of the support layer is hydrophilically modified, thereby imparting applicable physical properties to the osmosis membrane and being applicable to a wide range of pH 2-12, And to a method for producing the same.

The cleansing membrane is separated by moving osmotic pressure generated by the concentration difference between the two solutions to the high concentration solution through the membrane using the osmotic pressure as a driving force.

Therefore, the osmosis membrane plays an important role in maintaining the high osmotic pressure while maintaining the constant concentration of the inducing solute, while allowing water to flow into the inducing solution from the raw water through the membrane well. For this purpose, it is most important that the osmosis membrane has high water permeability in the osmotic direction and that the solute of the inducing solution is not diffused in the reverse osmosis direction. In addition, the manufacture of the osmosis membrane having less membrane contamination should be preceded.

Hereinafter, the characteristics of the osmosis membrane should be summarized as follows.

First, in order to minimize the internal concentration polarization and increase the stain resistance, the porosity of the support layer in the quasi-osmosis membrane should be high and the pore bending degree should be low.

Second, in order to increase the flow rate of permeated water, the thickness of the osmosis membrane should be minimized.

Third, a hydrophilic material is used to minimize permeation resistance to water.

Fourth, in order to maintain the induction solution at a high concentration, the solute should not diffuse into the low concentration solution in the high concentration solution.

Conventionally, U.S. Patent Application Publication No. 2006-0226067 discloses a method for producing a purified osmosis membrane. A cellulose acetate triacetate, which is a hydrophilic material, is used to produce a purified osmosis membrane. More specifically, on a support layer having a thickness of 25 to 75 μm, (FO) mode by using an induction solution in the film, the flow rate of which was 11 gfd level. When the flow rate was 11 gfd A high flow rate osmosis membrane is proposed. However, it has been reported that the membrane prepared above has a disadvantage in that the induction solution of high concentration diffuses the solute in the direction of the low concentration of raw water. In the raw water condition containing a high concentration of salt such as seawater, Which is difficult to apply in practice.

Also, according to International Patent Publication No. 2008-137082, a polysulfone solution is cast on a nonwoven fabric to prepare a membrane having an ultrafiltration membrane level, and a polyfunctional amine and a polyfunctional acyl halide are interfacially polymerized on the membrane surface, Amide reverse osmosis membrane was prepared, and a membrane from which only the nonwoven fabric was removed was applied to a FO system. As a result of evaluating the physical properties of the membrane in a forward osmosis (FO) mode, a forward osmosis membrane having a salt removal rate of 0.5 gfd and a salt removal rate of 99% or more was proposed.

However, the above-mentioned osmosis membrane has a salt removal rate sufficient to separate high-concentration raw water such as seawater, but the flow rate is low, so that the use of the membrane is practically limited. Therefore, studies are being conducted to optimize the membrane structure design, thickness, and porosity that can be used as a positive osmosis membrane.

Polysulfone or polyethersulfone type polymer is utilized as a conventional membrane material, and the material has excellent chlorine resistance against chlorine as compared with a conventionally known cellulose membrane, and exhibits an equivalent salt removal rate. Further, it is advantageous in that the chemical resistance is higher than that of the film made of the conventional polyamide layer, and the energy consumption rate is low.

Accordingly, the inventors of the present invention have found that, in order to improve the physical properties of a membrane made of a polysulfone or a polyether sulfone-based hydrophobic polymer by modifying the surface of the membrane to be hydrophilic and to apply the membrane as a positive osmosis membrane, To provide a structure applicable as a positive osmosis membrane, thereby completing the present invention.

An object of the present invention is to provide a two-layer structure positive osmosis membrane in which a hydrophobic polymer support layer is laminated on a nonwoven fabric layer characterized in that the membrane surface is hydrophilically modified.

Another object of the present invention is to provide a method for producing a positive osmosis membrane in which the membrane surface is hydrophilically modified.

The present invention is characterized in that a hydrophobic polymer supporting layer is laminated on a nonwoven fabric layer having an air permeation rate of 2 cc / cm 2 sec or more, wherein the hydrophobic polymer supporting layer is distributed in a range of 30 to 80% from the nonwoven fabric contacting surface to the opposite side, The surface of which is hydrophilically modified.

In the positive osmosis membrane of the present invention, the hydrophobic polymer support layer may be a polysulfone-based polymer including polysulfone and polyether sulfone; Polyamide-based polymers; Polyimide-based polymers; Polyester-based polymers; An olefin-based polymer including polypropylene and polyethylene; A halogenated polymer comprising a polybenzimidazole polymer and polyvinylidene diprolide, or a mixed solution thereof.

At this time, the thickness of the hydrophobic polymeric support layer of the present invention is preferably 30 to 250 mu m.

In the positive osmosis membrane of the present invention, the hydrophilic modification of the outermost surface to be implemented is sulfonated and hydrophilically modified.

The thickness of the nonwoven fabric layer of the present invention is preferably 20 to 150 mu m.

The present invention can provide a film area (24cm ²⁾ in 9.0μS / cm or less, or conductivity of 0.375 (μS / cm) / min cm ² and less forward osmosis membrane having a conductivity of minute according to the above feature.

The present invention provides a method for producing a hydrotreated hygroscopic membrane.

1) a polymer solution containing 0.5 to 5% by weight of a sulfonated polysulfone-based polymer on a hydrophobic polymer is cast on a nonwoven fabric layer to form a polymer support layer having a thickness of 30 to 250 탆,

2) exposure to air at 30 to 60 DEG C for 1/6 to 60 minutes to form a surface-hardened skin layer,

3) After that, it is immersed in a coagulation bath maintained at 40 to 70 ° C, phase-transitions and dried.

In a second preferred embodiment, 1) a 0.5 to 5% sulfuric acid solution is added to a hydrophobic polymer-containing solution, and the solution is reacted at a temperature from room temperature to 60 ° C in a nitrogen atmosphere to prepare a polymer solution,

2) The polymer solution is cast on a nonwoven fabric layer to form a hydrophobic polymer support layer having a thickness of 30 to 250 탆,

3) forming a skin layer having a surface hardened by exposing it to air at 30 to 60 ° C for 1/6 to 60 minutes, and 4) immersing the skin layer in a coagulation bath maintained at 40 to 70 ° C, There is provided a method for producing a positive osmosis membrane.

In the method for producing a quasi-osmosis membrane of the present invention, the hydrophobic polymer support layer is formed with a porosity of 30 to 80% by the phase transition.

By providing a hydrophilic modified osmosis membrane on the outermost surface of the hydrophobic polymer support layer with respect to the two-layer structure of the osmosis membrane having the hydrophobic polymer support layer on the nonwoven fabric layer according to the present invention, Therefore, it is possible to provide a pure water permeable membrane having improved resistance to contamination, because the hydrophilic property of the positive osmosis membrane is improved by the surface charge.

Also, by optimizing the pore structure design, the thickness and the porosity of the membrane for a quasi-osmosis membrane having a two-layer structure in which the membrane surface is hydrophilic-modified, it is possible to provide a manufacturing method that satisfies the requirements of the osmosis membrane.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of a hydrotreated hygroscopic membrane of the present invention. Fig.

In order to accomplish the above object, the present invention provides a nonwoven fabric comprising a hydrophobic polymer supporting layer laminated on a nonwoven fabric layer having an air permeation rate of 2 cc /

The hydrophobic polymer support layer is distributed in a range of 30 to 80% from the nonwoven fabric contacting surface to the opposite side surface, and the outermost surface of the supporting layer is hydrophilically modified.

1) Nonwoven fabric layer

The nonwoven fabric layer of the present invention acts as a support for the membrane.

Preferred materials that can be used in the present invention include synthetic fibers selected from the group consisting of polyester, polypropylene, nylon and polyethylene; Or cellulose-based pulp may be used. The nonwoven fabric layer can control the physical properties of the membrane according to porosity and hydrophilicity of the material.

The porosity of the nonwoven fabric layer may be any as long as it satisfies an air permeation rate of 2 cc / cm 2 sec sec or more, more preferably 2 to 20 cc / cm 2 sec sec If the material satisfies the air permeation amount, it can be used without any particular limitation. At this time, when the average pore size of the nonwoven fabric layer of the present invention is preferably 1 to 600 μm, and more preferably 5 to 300 μm, smooth permeation of water and water permeability required for the positive osmosis membrane can be improved.

In general, the nonwoven fabric used for the reverse osmosis membrane exhibits a contact angle of 74 to 90 degrees. However, the nonwoven fabric used in the embodiment of the present invention has a high degree of absorption within 5 seconds It shows hydrophilicity. Preferably, the hydrophilic property of the material usable as the nonwoven fabric layer in the present invention is 0.1 to 74 degrees , More preferably from 0.1 to 60 degrees. By satisfying the high hydrophilicity degree of the nonwoven fabric layer of the present invention, it is possible to reduce the resistance to water and reduce the film contamination due to the internal concentration polarization (ICP). The internal concentration polarization (ICP) lowers the permeability of the membrane due to the contamination generated inside the membrane. Particularly, when the membrane is contaminated with the ICP in the osmotic membrane operated only by the osmotic pressure due to the naturally occurring concentration difference, Will decrease.

The thickness of the nonwoven fabric layer of the present invention is preferably 20 to 150 占 퐉, and if it is less than 20 占 퐉, the strength and supportability of the entire membrane is insufficient.

2) hydrophobic polymer support layer

In the embodiments of the present invention, polysulfone-based polymers including polysulfone and polyethersulfone are most preferably used as the material of the hydrophobic polymer support layer of the positive osmosis membrane.

However, hydrophobic polyamide-based polymers; Polyimide-based polymers; Polyester-based polymers; An olefin-based polymer including polypropylene and polyethylene; A halogenated polymer including a polybenzimidazole polymer and polyvinylidene diprolide, or a mixed form thereof may be applied.

Accordingly, the hydrophobic polymeric support layer of the present invention is characterized in that finger-shaped pore structures of 30 to 80% are distributed from the contact surface to the opposite side of the nonwoven fabric, and the outermost surface of the support layer is hydrophilically modified.

That is, the hydrophobic polymer support layer has a high porosity and a low porosity due to a uniform pore-like shape.

FIG. 1 is a schematic view of a quasi-osmotic membrane in which the membrane surface of the present invention is modified to be hydrophilic. In the present invention, hydrophilic modification refers to imparting sulfonated properties to the outermost surface of the membrane, It is stable in the pH 2-12 range and will have a wide range of application, and hydrophilicity can improve the stain resistance of the hydrophobic polymer support layer due to modification [ Table 1 ].

At this time, the thickness of the hydrophobic polymeric support layer of the present invention is preferably as small as possible in order to increase the flow rate, and a preferable thickness to satisfy the above is 30 to 250 탆.

The present invention can provide a film area (24cm ²⁾ in 9.0μS / cm or less, or conductivity of 0.375 (μS / cm) / min cm ² and less forward osmosis membrane having a conductivity of minute according to the above feature.

The present invention provides a method for producing a hydrotreated hygroscopic membrane.

1) a polymer solution containing 0.5 to 5% by weight of a sulfonated polysulfone-based polymer on a hydrophobic polymer is cast on a nonwoven fabric layer to form a polymer support layer having a thickness of 30 to 250 탆,

2) exposure to air at 30 to 60 DEG C for 1/6 to 60 minutes to form a surface-hardened skin layer,

3) After that, it is immersed in a coagulation bath maintained at 40 to 70 ° C, phase-transitions and dried.

In the above production method, the polymer solution of step 1) implements hydrophilicity improvement by containing a sulfonated polysulfone polymer in the hydrophobic polymer. The sulfonated polysulfone polymer preferably contains 0.5 to 5% by weight of the total polymer solution. When the content of the sulfonated polysulfone polymer is less than 0.5% by weight, the expected effect of improving the hydrophilicity of the membrane is insufficient, The viscosity of the polymer solution is lowered, and film formation is difficult, which is not preferable.

The hydrophobic polymer has a weight average molecular weight of 65,000 to 150,000 in order to take mechanical strength into consideration, and preferred examples thereof include a polysulfone-based polymer including polysulfone and polyethersulfone; Polyamide-based polymers; Polyimide-based polymers; Polyester-based polymers; An olefin-based polymer including polypropylene and polyethylene; A halogenated polymer including a polybenzimidazole polymer and polyvinylidene diprolide, or a mixed form thereof may be used. In this case, the polymer contains 10 to 25% by weight based on the total polymer solution. The polymer solution is cast on the nonwoven fabric layer to a thickness of 30 to 250 mu m to form a polymer support layer.

In step 2), the cast film is exposed to the air at 30 to 60 DEG C for 1/6 to 60 minutes to cure the surface to form the pore structure of the skin layer.

When the membrane coated with the polymer solution is exposed to the air at the air exposure temperature and time range, the organic solvent in the solution present on the surface is evaporated to dense the surface and dense pores to exclude the salt A skin layer can be formed. In this case, the air exposure time is preferably 1/6 to 60 minutes, and if it is out of the above range, the effect of forming the skin layer is insufficient or the pore shape of the whole film is affected. As the temperature and time of exposure to air become longer, the pores on the outermost surface of the polymer support layer become denser and will be asymmetrically structured with the inner pore structure of the polymer support layer.

At this time, the air exposure temperature is set to be lower than the glass transition temperature (Tg) of the applied polymer, preferably 30 to 60 DEG C, and if the air exposure temperature is less than 30 DEG C, the outermost surface pore structure effect is insufficient And if it exceeds 60 ° C, the polymer chain may be affected and the inherent properties of the polymer may be impaired.

Thereafter, in the production method, step 3) is carried out by immersing in a coagulation tank maintained at 40 to 70 캜, transforming the phase, and drying, thereby producing a positive osmosis membrane.

When the temperature of the coagulation bath is as low as 0 to 20 캜, the surface of the support layer will become dense. Thus, in the present invention, the temperature of the coagulation bath is maintained at a higher temperature than room temperature, preferably 40 to 70 캜, more preferably 40 to 60 캜, to produce a film.

Performing at such a coagulation bath temperature can optimize the pore structure of the support layer by promoting the phase transition rate.

Due to the above-described process characteristics, it is possible to form a pore-type pore structure having a porosity of 30 to 80% from the production method of the present invention.

In a second preferred embodiment, 1) a 0.5 to 5% sulfuric acid solution is added to a hydrophobic polymer-containing solution, and the solution is reacted at a temperature of 60 ° C to 60 ° C under a nitrogen atmosphere to prepare a polymer solution,

2) The polymer solution is cast on a nonwoven fabric layer to form a hydrophobic polymer support layer having a thickness of 30 to 250 탆,

3) forming a skin layer having a surface hardened by exposing it to air at 30 to 60 ° C for 1/6 to 60 minutes, and 4) immersing the skin layer in a coagulation bath maintained at 40 to 70 ° C, There is provided a method for producing a positive osmosis membrane.

In the method for producing a quasi-osmosis membrane of the present invention, the phase transition can be promoted according to the thickness control of the membrane, the air exposure time, and the temperature design of the coagulation bath, and a pore structure of 30 to 80% of the pore shape can be formed.

The method for producing a quasi-osmosis membrane of the present invention can be applied to a method for sulfonating the outermost surface of a hydrophobic polymer support layer to hydrophilically reform it. For example, the surface of the hydrophobic polymer support layer may be modified by immersing a nanofiltration membrane (NF) made of polysulfone or polyethersulfone, which is commonly used, in a sulfuric acid solution for 1 to 5 hours.

Hereinafter, the present invention will be described in more detail with reference to Examples.

The present invention is intended to more specifically illustrate the present invention, and the scope of the present invention is not limited to these embodiments.

≪ Example 1 >

Prepared by papermaking 3% sulfuric acid was added to a N-methylpyrrolidone (NMP) solution containing 17% by weight of polysulfone on a nonwoven fabric having air porosity of 6.3 cc / , The polymer solution was cast to a thickness of about 150 ± 10 μm and exposed to air at 30 ° C. for 10 minutes to control pore size formed on the cast surface (skin layer). Thereafter, the resultant was immersed in a coagulation bath consisting of non-solvent water at 40 DEG C, phase inversion was carried out, and a polymer layer composed of polysulfone was formed. At this time, 3% by weight of solvent methylpyrrolidone (NMP) was added to the coagulation bath and the temperature of the coagulation bath solution was maintained at 50 캜. After immersing and phase transitions, the formed polysulfone polymer layer was stored in ultrapure water for one day to extract the solvent.

≪ Example 2 >

A polymer solution containing 18% by weight of polysulfone and 1% by weight of a sulfonated polysulfone-based polymer in a dimethylformamide solvent was prepared and bubbles were removed. The polymer solution was cast on a nonwoven fabric having a porosity of 6.3 cc / cm < 2 > ㆍ sec air permeability prepared by a papermaking method to a thickness of about 150 +/- 10 mu m and exposed to air at 30 DEG C for 10 minutes to form a casted surface (Skin layer) was controlled. Thereafter, the resultant was immersed in a coagulation bath consisting of non-solvent water at 40 DEG C, phase inversion was carried out, and a polymer layer composed of polysulfone was formed. At this time, 3% by weight of solvent methylpyrrolidone (NMP) was added to the coagulation bath and the temperature of the coagulation bath solution was maintained at 50 캜. After immersing and phase transitions, the formed polysulfone polymer layer was stored in ultrapure water for one day to extract the solvent.

≪ Example 3 >

A polymer solution containing 17% by weight of polysulfone and 2% by weight of a sulfonated polysulfone-based polymer in a dimethylformamide solvent was used in the same manner as in Example 2 above.

≪ Comparative Example 1 &

The properties were compared using a pure osmosis membrane consisting of cellulose triacetate alone (Hydration Technology Innovation).

≪ Comparative Example 2 &

The procedure of Example 2 was repeated, except that 19 wt% of polyethersulfone was used as the polymer solution contained in the dimethylformamide solvent, without adding the sulfonated polysulfone-based polymer.

Experimental Example 1 Measurement of Membrane Flow Rate

The flow of water in the direction of the inducing solution from the raw water was induced between the membranes prepared above, and the amount of water per hour was measured by measuring the weight of the inducing solution with respect to time. At this time, 2 M NaCl was used as the induction solution, and ultrapure water (osmotic pressure of about 100 atm) was used as raw water.

≪ Experimental Example 2 >

(2M NaCl) was used as the induction solution and the electric conductivity change of the salts introduced into the raw water side (ultrapure water) in the induction solution was measured by using ultrapure water (osmotic pressure of about 100 atm) as the raw water, The conductivity of a solution between electrodes of a distance of 1 cm from a certain membrane area (24 cm ² ) was measured using a conductivity meter to evaluate the degree of despreading in terms of the change in conductivity per minute (μS / cm) The value of solids dissolved in the solution was expressed as μS / cm × 0.5-0.6 = TDS (Total Dissolved Solids, mg / L).

The results obtained by converting the conductivity values of the membrane area (24 cm ² ) to the conductivity values per minute (μS / cm) / min obtained above are shown in Table 1 below. The degree of despersion of the salt was evaluated from the result.

As shown in the above Table 1, the membrane constitution prepared in Examples 1 to 3 was compared with that of the osmosis membrane of Comparative Example 1 having a flat membrane structure composed of a single material of cellulose triacetate, which is a hydrophilic material, And the reverse diffusion of relatively low salt was confirmed.

On the other hand, as a result of the performance evaluation in the positive osmosis module, the membrane of Comparative Example 2 having the two-layer structure performed without the hydrophilic modification of the surface of the support layer was unable to measure the flow rate and salt despreading degree. From the above results, it was confirmed that the membrane of Comparative Example 2 was despensed with a large amount of salt from the inductive solution portion to the raw water in the forward osmosis module.

In addition, the membrane constitutions prepared in Examples 1 to 3 were confirmed from the contact angle results, due to the inclusion of the sulfonated polysulfone-based polymer, hydrophilicity-modifying property, from which it is possible to predict the improvement of stain resistance.

As described above, according to the present invention, the outermost surface of the hydrophobic polymer support layer is hydrophilically modified to have a two-layer structure of a hydrophilic polymer support layer on the nonwoven fabric layer, Film.

In addition, according to the manufacturing method of the present invention, a pore structure of a quasi-osmosis membrane is optimized, a thickness and a porosity are optimized, and the membrane surface is modified to be hydrophilic to provide a osmosis membrane having improved stain resistance.

While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (9)

A hydrophobic polymer supporting layer is laminated on a nonwoven fabric layer having an air permeation amount of 2 cc / cm 2 ㆍ sec or more,
Wherein the hydrophobic polymer support layer has a pore size ranging from 30% to 80% from the nonwoven fabric contacting surface to the opposite surface, and the outermost surface of the support layer is hydrophilic modified. The method of claim 1, wherein the hydrophobic polymer support layer comprises a polysulfone-based polymer including polysulfone and polyethersulfone; Polyamide-based polymers; Polyimide-based polymers; Polyester-based polymers; An olefin-based polymer including polypropylene and polyethylene; A halogenated polymer comprising a polybenzimidazole polymer and polyvinylidene diprolide, or a solution containing a mixture thereof, which is selected from the group consisting of polyvinylidene fluoride, polybenzimidazole polymer and polyvinylidene diprolide. The positive osmosis membrane according to claim 1, wherein the thickness of the hydrophobic polymer support layer is 30 to 250 탆. The positive osmosis membrane according to claim 1, wherein the outermost surface of the support layer is sulfonated and hydrophilically modified. The method of claim 1 wherein the forward osmosis membrane membrane area (24cm ²⁾ in the information, characterized in that it has a conductivity value or 0.375 (μS / cm) / min and conductivity of cm ² or less per minute 9.0μS / cm or less Osmotic membrane. The positive osmosis membrane according to claim 1, wherein the thickness of the nonwoven fabric layer is 20 to 150 mu m. A polymer solution containing 0.5 to 5% by weight of a sulfonated polysulfone-based polymer on a hydrophobic polymer is cast on a nonwoven fabric layer to form a polymer support layer having a thickness of 30 to 250 탆,
Exposed to the air for 30 minutes to 60 占 폚 for 1/6 to 60 minutes to form a surface-hardened skin layer,
And then immersing it in a coagulation bath maintained at 40 to 70 DEG C to effect phase transformation, followed by drying. A 0.5 to 5% sulfuric acid solution is added to the hydrophobic polymer-containing solution, and the solution is reacted at a temperature from room temperature to 60 캜 in a nitrogen atmosphere to prepare a polymer solution,
The polymer solution is cast on a nonwoven fabric layer to form a hydrophobic polymer support layer having a thickness of 30 to 250 탆,
Exposed to the air for 30 minutes to 60 占 폚 for 1/6 to 60 minutes to form a surface-hardened skin layer,
And then immersing it in a coagulation bath maintained at 40 to 70 DEG C to effect phase transformation, followed by drying. The method of claim 7 or 8, wherein the hydrophobic polymer support layer forms a porosity of 30 to 80% by the phase transition.

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