KR101447268B1 - Thin film composite membrane and method for preparing the same - Google Patents

Abstract

The thin film composite separator of the present invention comprises a support layer containing a fluorine-based polymer; And an active layer comprising polyamide formed on the surface of the support layer, wherein the support layer has a nanofiber web shape.

Description

TECHNICAL FIELD [0001] The present invention relates to a thin film composite separator,

The present invention relates to a thin film composite separator and a method of manufacturing the same. More particularly, the present invention relates to a method for producing an aqueous solution having a high salt rejection rate, a good water permeability, an excellent chemical resistance and a mechanical strength, and an osmotic pressure such as forward osmosis (FO) To a thin film composite separator suitable for a membrane separation process and a method for producing the same.

Membrane technology has been applied to recent water treatment. For example, microfiltration (MF) membranes and ultrafiltration (UF) membranes are used for water treatment in water purification plants, and reverse osmosis membranes are used for desalination of seawater. Reverse osmosis membranes and nanofiltration membranes are also used for processing semiconductor water, boiler water, medical water, and laboratory pure water. Water treatment technologies using these membranes are attracting attention due to their excellent processing capacity compared to installation space and low processing cost.

In recent years, unlike existing membrane processes that produce water permeation by applying pressure such as microfiltration, ultrafiltration, reverse osmosis, and nanofiltration, the osmotic pressure difference between the membranes is used as a driving force to cause water permeation. A forward osmosis (FO) process has attracted attention as a new area of water treatment. This is because the osmotic pressure is used as a driving force in contrast to the conventional separation membrane process, which enables water treatment to be performed at a lower energy than the conventional process requiring pressurization.

Currently, HTI is the only company that has a single-membrane structure made of cellulose triacetate with a thinner thickness compared to conventional reverse osmosis (RO) composite membranes. However, it has a low rejection rate for salts such as sodium chloride and it is not applicable to various purification processes such as desalination process.

HTI cellulosic triacetate monolayer, which is the only commercially available purified osmosis membrane, has a thinner thickness than conventional membranes applied to conventional reverse osmosis (RO) and nanofiltration (NF) membranes, and has relatively good water permeability However, the application of sewage treatment, desalination, etc. is limited due to the low rejection ratio (draw solute back diffusion has a similar physical meaning) to salts such as sodium chloride.

In the case of composite membrane with polyamide thin film active layer, unlike HTI 's cellulose triaceate monolayer, the structural excellence of the polyamide thin film constituting the active layer can achieve a good rejection rate for sodium chloride and the like. As a result, application of a composite membrane having a polyamide thin film active layer as a quasi-osmosis membrane applicable to sewage treatment, desalination and the like has been attempted. However, in the case of conventional RO or NF composite membranes with a polyamide thin film active layer, the water permeability is low due to the structural limitations of the support ( J. Membr . Sci . 281 (2006), 70-87).

When the porous body having high porosity is used as a support to solve this problem, there is a disadvantage that relatively low mechanical strength is exhibited due to high porosity. However, unlike conventional membrane processes that pressurize and permeate water, such as reverse osmosis (RO) or nanofiltration (NF) membranes, the mechanical properties required for membrane materials in membrane separation processes, such as osmosis using osmotic pressure, The performance of the positive osmosis membrane may be degraded if the thickness of the support layer is increased.

In addition, unlike conventional membrane processes such as RO and NF which pressurize and form water permeation in a complex type polymer membrane, surface hydrophilicity of the membrane support in the passive osmosis process has a significant influence on the water permeation performance of the polymer membrane ( J. Membr . Sci . 318 (2008) 458-466). It is important to ensure the surface hydrophilicity of the support in the polymer membrane for positive osmosis.

Therefore, it is necessary to develop a polymer membrane capable of maintaining the mechanical strength for a long period of time, maintaining excellent mechanical strength, excellent water permeability, excellent durability due to high chemical resistance, and maintaining the mechanical strength for a long period of time It is true.

One object of the present invention is to provide a thin film composite separator having excellent water permeability and chemical resistance while securing mechanical strength and a method for producing the same.

Another object of the present invention is to provide a thin film composite separator excellent in strength and durability and a method of manufacturing the same.

Another object of the present invention is to provide a thin film composite membrane having excellent performance in the membrane separation process due to its ability to increase the surface hydrophilicity while maintaining the original strength even when hydrophilic functional groups are introduced into the surface of the membrane support, .

It is another object of the present invention to provide a membrane separation method and a membrane separation method which can be widely applied to membrane separation using a variety of osmotic pressure such as brackish water or sea water desalination, And to provide a method for producing the same.

One aspect of the present invention relates to a thin film composite membrane. Wherein the thin film composite separator comprises a support layer containing a fluorine-based polymer; And an active layer comprising polyamide formed on the surface of the support layer, wherein the support layer has a nanofiber web shape.

In an embodiment, the fluoropolymer is a polymer containing fluorine in the polymer repeating unit or a copolymer containing repeating units constituting the fluoropolymer in an amount of 50% or more based on the number of repeating units in the polymer chain, And a polymer blend blended at least 50% by weight of the polymer blend. For example, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyethylene (ETFE), polyethylenechlorotrifluoroethylene (ECTFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer (PFA), perfluoroalkoxy And perfluoropolyoxetane may be used.

In an embodiment, the active layer including the polyamide is formed by interfacial polymerization with a support layer containing the fluorine-based polymer.

In a specific example, a hydrophilic functional group may be introduced into the surface of the support layer containing the fluorine-based polymer.

In an embodiment, the thickness of the support layer is 10 to 500 탆, and the thickness of the active layer is 0.01 to 2 탆.

In an embodiment, the nanofibers constituting the support layer may have a diameter of 1 to 1000 nm.

In an embodiment, the support layer is made of nanofibers and has an open pore structure in which pores between the nanofibers are connected to each other, and the porosity may be 40 to 90%.

Another aspect of the present invention relates to a method for producing the thin film composite separator. The method comprises contacting a fluorine-based polymeric support having a nanofiber web form with an amine aqueous solution; And contacting the fluorine-containing polymer scaffold containing the amine aqueous solution with a polyfunctional acyl halide solution to form an active layer comprising polyamide on the surface of the support.

In an embodiment, the fluorine-based polymer scaffold having the nanofiber web form may be contacted with the amine aqueous solution after the hydrophilization treatment.

In an embodiment, the fluorine-based polymer scaffold having the nanofiber web form is formed by electrospinning. The electrospinning can be conducted under the conditions of a radiation voltage of 2 to 30 kV, a radiation distance of 1 to 25 cm, and a radiation rate of 0.1 to 5.0 ml / hr.

The present invention has excellent water permeability and chemical resistance, and is excellent in strength and durability while securing mechanical strength, and can increase surface hydrophilicity while maintaining original strength even when hydrophilic functional groups are introduced, Thin film composite membranes which have excellent performance and have a high rejection rate against salts and can be widely applied to segregation of various osmosis membranes such as brackish water or sea water desalination, The present invention has the effect of providing the method.

FIG. 1 is an FE-SEM image of the nanofiber web support prepared in Production Examples 1 to 3 of the present invention.
FIG. 2 is an FE-SEM image of the upper part of the thin film composite separator prepared in Example 1. FIG.
3 is an FE-SEM image of a cross-section of the thin film composite membrane produced in Example 1. Fig.
FIG. 4 is a graph showing the ATR-FT-IR measurement of the support of the thin film composite membrane produced in Example 4. FIG.
FIG. 5 is a graph showing the ATR-FT-IR measurement of the support of the thin film composite membrane produced in Example 5. FIG.
6 is an FE-SEM image of the nanofiber web prepared in Comparative Example 1. FIG.
FIG. 7 is an FE-SEM image of the nanofiber web prepared in Comparative Example 2. FIG.

The thin film composite separator of the present invention comprises a support layer containing a fluorine-based polymer; And an active layer including polyamide formed on the upper surface of the support layer.

Support layer

As the support layer of the present invention, a fluorine-based polymer having a nanofiber web form is used. By applying such a fluorine-based polymer, it has high endurance and can maintain strength and durability in the use of various inducing solutions and treating agents. Especially, it can exhibit excellent strength compared with polymer materials other than fluoropolymer materials, which are relatively different from each other in manufacturing nanofiber. That is, since the web-shaped support having a one-dimensional structure made of nanofibers can realize high porosity with an open pore structure, it is possible to exhibit excellent water permeability when applied as a support for a composite membrane for positive osmosis However, since it exhibits a relatively low mechanical strength due to high porosity, there is a problem in applying the nanofiber web form as a support. In the present invention, by using a fluorine-based polymer as a support material, not only a high strength can be exhibited even after being made into nanofibers, but also a support excellent in chemical resistance can be manufactured.

The fluorine-based polymer used as the polymer scaffold may be selected from the group consisting of polyvinylfluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyethylenetetrafluoroethylene (ETFE), polyethylenechlorotrifluoroethylene (ECTFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer , PFA) Perfluoropolyoxetane or the like, or a polymer containing fluorine in the polymer repeating unit or a copolymer containing repeating units constituting these fluoropolymers in an amount of 50% or more based on the number of repeating units in the polymer chain Can be used. These may be used alone or in combination of two or more. Of these, polyvinylidene fluoride is preferable. These fluorinated polymers may be blended with other polymers or additives. In this case, these fluorinated polymers may be used in an amount of 50% or more by weight.

The support layer having the nanofiber web form may be prepared by electrospinning, jet blowing, or the like. For example, it can be produced by electrospinning at a radiation voltage of 2 to 30 kV, a radiation distance of 1 to 25 cm, and a radiation rate of 0.1 to 5.0 ml / hr. In the case of spinning under the above conditions, there is an advantage that the spinning area can be easily controlled and the productivity of the support can be optimized by controlling the number and spacing of the nozzle nozzles.

In the embodiment, the diameter of the nanofibers constituting the support layer can be controlled by controlling the concentration of the polymer, the type of additives, the type of solvent, and the combination of different solvents during spinning. Preferably, the nanofibers constituting the support layer may have a diameter of 1 to 1000 nm. In this range, the gap between the nanofibers may be small enough to support the active layer, while the pores may have open pores sized to transmit water. Preferably 10 to 600 nm.

In embodiments, the thickness of the support layer may be between 10 and 500 microns. A mechanical strength and a sufficient water permeability that are usable in the above range can be achieved. And preferably 20 to 200 mu m.

In the specific example, the support layer is made of nanofibers and has pore structure, which is a so-called open pore structure in which pores between nanofibers are connected to each other, and can have a porosity of 40 to 90% higher than that of the conventional support structure. In this range, a high water permeability in the normal osmosis separation process can be achieved.

In one embodiment, the support layer may have a tensile strength of 5 to 25 MPa as measured by the ASTM D638 standard. In this range, since the conventional non-fluorine separation membrane support material has a higher strength than the same structure or other structure of the same material, a thinner support can be manufactured while maintaining mechanical strength, and water permeability is high.

In another embodiment, the support layer may have an elongation of from 20% to 100% as measured by the ASTM D638 standard. In the above range, the support has a high resistance to damage because of the high maximum deformation against mechanical impact or expansion and contraction externally applied, and high energy absorption.

The conventional porous support has a tortuosity of 0.6 or less as measured by a CFP-1500AEL capillary flow porometer manufactured by PMI. In contrast, since the support layer of the present invention has a nanofiber web shape, the tortuosity measured by a CFP-1500AEL capillary flow porometer manufactured by PMI Co. has a value of 0.65 to 0.9.

Preferably, a hydrophilic functional group may be introduced into the surface of the support layer containing the fluorine-based polymer. In particular, since the support layer containing the fluorine-based polymer of the present invention has a nanofiber web shape, the surface modification treatment is easy. That is, the support layer containing the fluorine-based polymer in the nanofiber web form can more uniformly introduce the hydrophilic functional group onto the surface thereof than the single membrane or the support of the TFC separation membrane applied to the conventional RO or NF process.

In addition, the nanofiber web composed of the fluorine-based polymer material may have enhanced surface hydrophilicity while maintaining the original strength inherent in the nanofiber due to the high-endochemical properties of the material even after the modification treatment for surface-introducing hydrophilic functional groups.

The hydrophilic functional group may be introduced into the surface of the support layer by a conventional method. In a specific example, hydrophilic functional groups can be introduced by treatment with ultraviolet rays of 180 to 350 nm in a state where hydrazine vapor is distributed in an inert gas. Ultraviolet rays, X-rays, gamma rays or the like in the presence of at least one active gas such as hydrazine, nitrogen (N ₂ ), oxygen (O ₂ ), ammonia (NH ₃ ) or the like or by using an oxidizing agent such as potassium permanganate Chemical treatment, atom transfer radical polymerization (ATRP), and the like.

Active layer

The active layer is formed on the surface of the support layer and includes a polyamide-based resin. By including the polyamide resin in this manner, a high salt rejection rate can be secured as compared with the conventional single membrane made of cellulose triacetate having a low salt rejection ratio.

On the other hand, when a polyamide resin is used as an active layer, existing RO or NF composite membranes can exhibit low water permeability when used in the osmotic filtration. However, in the present invention, since the support is made into a nanofiber web, can do.

In an embodiment, the active layer including the polyamide is formed by interfacial polymerization with a support layer containing the fluorine-based polymer.

For example, after a fluorine-based polymer scaffold having a nanofiber web form is brought into contact with an amine aqueous solution, the fluorine-based polymer scaffold containing the amine aqueous solution is brought into contact with a polyfunctional acyl halide solution and subjected to interfacial polymerization to form a polyamide May be formed. The contact may be carried out by dipping, spraying or the like, preferably by dipping.

The fluorine-based polymer scaffold having the nanofiber web may be hydrophilized.

The amine aqueous solution includes a polyamine and water. Examples of the polyamine include phenylene diamine, cyclohexanediamine, piperazine, and the like, but are not limited thereto. The polyamine may be contained in an amount of 0.1 to 15% by weight based on the total weight of the aqueous solution. The amine aqueous solution may further include a polar solvent. The polar solvent may be an ethylene glycol derivative, a propylene glycol derivative, a 1,3-propanediol derivative, a sulfoxide derivative, a sulfone derivative, a nitrile derivative, a ketone derivative or a urea derivative.

The polyfunctional acyl halide solution includes a polyfunctional acyl halide and an organic solvent. Examples of the polyfunctional acyl halide include trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, 1,3,5-cyclohexanetricarbonyl chloride, 1,2,3,4-cyclohexanetetracarbonyl chloride and the like Can be used. These may be used alone or in combination of two or more. The double trimethoyl chloride is most preferable in terms of the salt removal ratio. The polyfunctional acyl halide may be used in an amount of 0.01 to 5% by weight in the whole solution. As the organic solvent, aliphatic hydrocarbons having 5 to 12 carbon atoms may be preferably used.

The reaction time in the interfacial polymerization may be 30 seconds to 20 minutes.

The active layer formed in such a manner as to be interfacial can have a thickness of 0.01 to 2 탆. It is advantageous in that the water rejection rate is not lowered while achieving a salt rejection rate of 90% or more necessary for effective membrane separation in the above range. Preferably 0.05 to 0.5 mu m.

Hereinafter, the present invention will be described in more detail by way of examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Example

Production Examples 1 to 3 : Preparation of PVDF nanofiber web webs

PVDF (Solvay SOLEF PVDF-1015) was subjected to electrospinning at a collecting distance of 10 cm under the conditions of Table 1 under conditions of 12 kV and 1.0 mL / h using No.23 nozzles to prepare a PVDF nanofiber web support .

Solution composition Nanofiber
diameter The tensile strength
(MPa) Elongation
(%) PVDF menstruum additive Production Example 1 5.00 g DMF
25 mL - 500 nm 8.9 ± 0.7 32 Production Example 2 4.00 g NaCl powder
10 mg 150 nm 10.1 ± 1.1 39 Production Example 3 LiCl
10 mg 200 nm 11.8 ± 1.7 35

FE-SEM images of the nanofiber web supporters of Preparation Examples 1 to 3 were measured and shown in Fig. 1, respectively.

Examples 1 to 3 : Preparation of thin film composite membrane

The PVDF nanofiber web supporters prepared in Preparation Examples 1 to 3 were immersed in a 1 wt% aqueous solution of m-phenylene diamine (MPD) for 2 minutes, squeezed with a rubber roller on a glass plate, Respectively. The PVDF nanofiber web support with MPD aqueous solution was immersed in a solution prepared by dissolving 0.05 w / v% trimesoly chloride (TMC) in n-hexane for 1 minute to interfacially polymerize MPD and TMC on the PVDF nanofiber web support surface ) To form a polyamide active layer. The polyimide active layer was introduced on the surface of the PVDF nanofiber web support, and the prepared osmotic membrane was taken out of the TMC / n-hexane solution, washed with deionized water, and immersed in deionized water. Analytical samples were vacuum dried in an oven. FE-SEM photographs of the top and cross sections of the membrane composite membrane prepared in Example 1 are shown in FIGS. 2 and 3, respectively. Also, for the support prepared in Example 2, the contact angle of ultrapure water was measured by dropping 5.0 μL of ultrapure water on the surface of the nanofiber web by setting the tilt to 0 in the dynamic ultrapure water contact angle measuring instrument. The program used for the contact angle analysis is the DSA Registered Version, the operating program of the device. The measurement results are shown in Table 2 below.

Example  4

The PVDF nanofiber web support prepared in Preparation Example 2 was irradiated with ultraviolet light of 254 nm at an illuminance of about 100,000 lux with a SANKYO DENKI G25T8 UV lamp in a state where hydrazine vapor was distributed in an inert gas at 60 to 80 ° C for 12 to 48 hours. The surface-treated support was formed into a thin film composite membrane in the same manner as in Examples 1 to 3 above. ATR-FT-IR was measured on the support of the prepared thin film composite membrane, which is shown in FIG.

Example  5

The procedure of Example 4 was repeated except that PTFE (Millipore FHLP 04700) was used without using a PVDF nanofiber web support. ATR-FT-IR was measured on the support of the prepared thin film composite membrane, which is shown in Fig.

Comparative Example  One

Thin film composite membranes were prepared in the same manner as in Example 2, except that a nanofiber web support prepared using the polysulfone (BASF Ultrason 6010) as the material of the nanofiber web supporter was used. The FE-SEM photograph of the fabricated nanofiber web is shown in FIG.

Comparative Example  2

The procedure of Example 2 was repeated except that the nanofiber web supporter was prepared using cellulose acetate (Sigma Aldrich, number average molecular weight: 30,000) as the material of the nanofiber web support, A separator was prepared. An FE-SEM photograph of the fabricated nanofiber web is shown in FIG.

Solution composition Radiation condition Materials used menstruum additive nozzle type Voltage Injection speed Collection distance Example 2 PVDF: 4.00 g DMF
25 mL NaCl powder
10 mg No.23 12 kV 1.0 mL / h 10 cm Comparative Example 1 Polysulfone: 5.00 g DMAc / Acetone (9: 1 v / v)
20 mL NaCl powder
10 mg No.23 12 kV 1.0 mL / h 10 cm Comparative Example 2 Cellulose acetate: 4.00 g Acetone / DMAc (7: 3 v / v)
16 g NH ₄ OH
2 wt% No.23 10-16 kV 1.0 mL / h 12 cm

The physical properties of the web support prepared in Example 2 and Comparative Examples 1 and 2 are shown in Table 3.

Material Tensile Strength (MPa) Elongation (%) Contact angle (degree) Ultrapure water contact picture Example 2 10.1 ± 1.1 39 11.8 ± 3.5

Comparative Example 1 2.57 + - 0.23 14 15.2 + 0.14

Comparative Example 2 0.80 + 0.15 <5 0 Distilled water droplets spread out sideways so photos can not be measured

Comparative Example  3

The procedure of Example 1 was repeated except that a PVDF porous support was used instead of the nanofiber web type as the support layer. The PVDF porous support was dissolved in 16% by weight of dimethylacetamide using PVDF (Solvay SOLEF PVDF-1015), which was the same as the product used for preparing the nanofiber web support, and the solvent was cast on a glass plate using an applicator Then immersed in deionized water at room temperature together with the next glass plate to prepare a nonwoven fabric.

Table 4 shows the water permeability of the individual membranes in the cleansing osmosis membrane separation using the custom-made water permeability test apparatus customized for the membrane composite membranes prepared in Example 1 and Comparative Example 3. Specifically, using a draw solution consisting of a mixture of 2 L of deionized water, 2 L of deionized water and 500 mL of a 5 M aqueous NaCl solution, each solution was sprayed at a rate of 100 CCM In the form of cross flow.

Time (min) 3 6 9 12 15 Average Water Transmission (LMH) Example 1 12.5 13.8 12.7 13.2 11.9 12.8 Comparative Example 3 5.04 5.84 4.15 5.04 4.75 4.96

As shown in Table 4, it can be seen that the water permeability of Example 1 in which the support of the nanofiber web type is applied to the support layer is significantly higher than that of Comparative Example 3 in which the porous support is applied.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (11)

A support layer containing a fluorine-based polymer; And an active layer comprising polyamide formed on the surface of the support layer;
Wherein the support layer has a nanofiber web form,
The fluorinated polymer may be at least one selected from the group consisting of polyvinylfluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE) (ETFE), polyethylenechlorotrifluoroethylene (ECTFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer (PFA), and purple At least one fluorinated polymer selected from the group consisting of perfluoropolyoxetane; A copolymer comprising repeating units constituting these fluorinated polymers in an amount of 50% or more based on the number of repeating units in the polymer chain; Or a polymer blend in which the fluorinated polymer is mixed in an amount of 50% or more by weight.
delete The thin film composite separator according to claim 1, wherein the active layer comprising polyamide is formed by interfacial polymerization with a support layer containing the fluorine-based polymer.
The thin film composite separator according to claim 1, wherein a hydrophilic functional group is introduced on a surface of the support layer containing the fluorine-based polymer.
The thin film composite separator according to claim 1, wherein the thickness of the support layer is 10 to 500 탆, and the thickness of the active layer is 0.01 to 2 탆.
The thin film composite separator according to claim 1, wherein the nanofibers constituting the support layer have a diameter of 1 to 1000 nm.
The thin film composite separator according to claim 1, wherein the support layer is made of nanofibers so that the pores between the nanofibers are connected to each other and have a porosity of 40 to 90%.
Contacting a fluorine-based polymer scaffold having a nanofiber web form with an amine aqueous solution; And
Contacting the fluorine-containing polymer scaffold containing the amine aqueous solution with a polyfunctional acyl halide solution to form an active layer comprising polyamide on the surface of the support;
&Lt; / RTI &gt;
The fluorinated polymer may be at least one selected from the group consisting of polyvinylfluoride (PVF), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE) (ETFE), polyethylenechlorotrifluoroethylene (ECTFE), fluorinated ethylene-propylene (FEP), perfluoroalkoxy polymer (PFA), and purple At least one fluorinated polymer selected from the group consisting of perfluoropolyoxetane; A copolymer comprising repeating units constituting these fluorinated polymers in an amount of 50% or more based on the number of repeating units in the polymer chain; Or a blend of these fluoropolymers blended in an amount of 50% or more by weight based on the weight of the polymer blend.
9. The method according to claim 8, wherein the fluorine-based polymer scaffold having the nanofiber web form is contacted with an aqueous amine solution after the hydrophilizing treatment.
The method of claim 8, wherein the fluorine-based polymer scaffold having the nanofiber web is electrospun.
11. The method according to claim 10, wherein the electrospinning is conducted under conditions of a radiation voltage of 2 to 30 kV, a radiation distance of 1 to 25 cm, and a radiation rate of 0.1 to 5.0 ml / hr.

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