KR101334924B1 - Polyester reverse osmosis composite membrane and preparation method thereof - Google Patents

Abstract

The reverse osmosis composite membrane comprising a porous support and a crosslinked polyester active layer formed on the surface of the pores of the porous support has high permeability and salt removal rate and is excellent in chlorine resistance, and thus can be used in a seawater desalination process to exhibit excellent performance. have.

Description

Polyester Reverse Osmosis Composite Membrane and Manufacturing Method Thereof {POLYESTER REVERSE OSMOSIS COMPOSITE MEMBRANE AND PREPARATION METHOD THEREOF}

The present invention relates to a polyester-based reverse osmosis composite membrane used in the field of water treatment and a method for producing the same.

Reverse osmosis membranes are used for seawater desalination, and since there are various kinds of organisms in seawater, they are treated with a powerful oxidant such as NaOCl to remove microorganisms before applying seawater to reverse osmosis membranes. All NaOCl is not removed but remains in some seawater.

Reverse osmosis composite membranes for water treatment, which are widely used in the current market, are mostly polyamide based composite membranes, and are manufactured by forming a crosslinked polyamide layer on a porous support surface. Such a conventional polyamide reverse osmosis composite membrane shows excellent permeability and salt rejection rate, but since amide bonds are very susceptible to attack of chlorine ions, they are easily decomposed to strong oxidizing agents such as NaOCl, resulting in poor chlorine resistance. In use, it has a problem that the permeation performance of the membrane sharply drops.

Therefore, in order to increase the utilization of the membrane and further increase the economic efficiency, it is necessary to develop a reverse osmosis membrane having excellent chlorine resistance, particularly in the case of a reverse osmosis membrane for seawater desalination.

 Kim, Young-Kil et al., A Study on Improving Chlorine Resistance by Surface Modification of Reverse Osmosis Membranes, Membrane, Vol. 15, No. 4, 2005, 320-329.

Accordingly, it is an object of the present invention to provide a reverse osmosis composite membrane having excellent chlorine resistance and a preparation method thereof.

In accordance with the above object, the present invention provides a reverse osmosis composite membrane comprising a porous support and a crosslinked polyester active layer formed on the surface of the pores of the porous support.

In addition, the present invention comprises the step of interfacial polymerization of the aromatic polyhydric alcohol solution and aromatic polyhydric acyl halide solution on the porous support to form a crosslinked polyester active layer on the surface of the porous support, the reverse osmosis composite membrane It provides a manufacturing method.

The reverse osmosis composite membrane of the present invention has high permeability and salt removal rate and is excellent in chlorine resistance, and thus can be used in a seawater desalination process to exhibit excellent performance.

1 is a SEM image of the surface of the active layer of the reverse osmosis composite membrane prepared in Example 1 of the present invention.

Hereinafter, the present invention will be described in more detail.

Reverse osmosis composite membrane of the present invention is characterized in that it comprises a porous support and a crosslinked polyester active layer formed on the surface of the pores of the porous support.

In the reverse osmosis composite membrane of the present invention, the polyester active layer may be a polyester active layer formed by crosslinking polymerization of an aromatic polyhydric alcohol and an aromatic polyvalent acyl halide, and preferably, the monomers are formed by interfacial polymerization on a porous support. It may be a polyester active layer.

The aromatic polyhydric alcohol is preferably selected from the group consisting of resorcinol, hydroquinone, benzenedimethanol, dihydroxybiphenyl, benzenedithiol, and mixtures thereof, of which resorcinol or hydroquinone is more preferable. Do.

The aromatic polyvalent acyl halide is preferably selected from the group consisting of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, and mixtures thereof, of which trimesoyl chloride is more preferable.

In addition, the cross-polymerized polyester in the reverse osmosis membrane may include additional unit components such as aliphatic polyhydric alcohols and / or aliphatic polyhydric carboxylic acids in addition to aromatic polyhydric alcohols and aromatic polyhydric acyl halides. For example, aliphatic polyhydric alcohol components, such as 1,2-hexanediol, 1,6-hexanediol, and 2-ethyl-1,3-hexanediol (EHD), succinic acid, adipic acid, suberic acid, etc. Aliphatic polyhydric carboxylic acid is possible.

The porous support used in the reverse osmosis composite membrane of the present invention is a porous structure suitable for providing the mechanical strength required by the separator and minimizing the permeation resistance when the permeate is permeated, preferably having a ground structure and a sponge structure. . These porous supports are polysulfones, polyesulfones, polyacrylonitriles, polyimides, polyimides, polypropylenes, polyethylenes, polyamides, polymethylmethacrylates, polyvinylidene fluorides, and mixtures thereof on porous substrates. It can be obtained by casting a solution of a polymer selected from the resin and then forming fine pores using a phase transfer method. The porous support obtained can preferably be an ultrafiltration membrane.

In addition, the porous support used in the present invention preferably has pores having a molecular weight of 1,000 to 300,000 g / mol, more preferably 1,000 to 100,000 g / mol. In addition, the porosity of the porous support may be 60 to 90%. If the pore size and porosity of the porous support is within the above range, it may exhibit better performance in terms of permeability and salt removal rate.

In addition, the porous substrate may be a nonwoven fabric, for example, may be a nonwoven fabric made of a material such as polyester, polypropylene, nylon, among which a polyester-based nonwoven fabric is most preferable, and nanofibers may be included.

The reverse osmosis composite membrane of the present invention may have a pore size having a molecular weight of 400 g / mol or less, and may have a porosity of 20 to 60%. In addition, the thickness of the polyester active layer in the reverse osmosis composite membrane of the present invention may be 5 to 500 nm.

The reverse osmosis composite membrane of the present invention is excellent in chlorine resistance compared to the reverse osmosis membrane having a polyamide-based polymer active layer by providing a non-polyamide-based polymer active layer. In addition, as the operating pressure increases, the driving force increases and the permeation rate increases, while the permeability of the solute is constant regardless of the pressure, while as the permeation rate increases, the solute content in the permeate decreases as the operating pressure increases. Increasingly, it exhibits high permeability and salt rejection rate, making it well suited for efficient seawater desalination membrane systems. In addition, the reverse osmosis composite membrane of the present invention can be produced using the interfacial polymerization method, thereby reducing the production time.

Hereinafter, an example of a method of manufacturing the reverse osmosis composite membrane of the present invention will be described in detail step by step.

(1) Preparation of Porous Support

The porous support used in the present invention may be prepared by casting a polymer solution on a porous substrate and then forming fine pores using a phase transition method.

At this time, the polymer solution, polysulfone, polyisulfone, polyacrylonitrile, polyimide, polyimide, polypropylene, polyethylene, polyamide, polymethyl methacrylate, polyvinylidene fluoride and It may be a solution of the polymer selected from the mixed resin, it is preferable to contain the polymer in an amount of 5 to 30% by weight based on the total weight of the polymer solution. As the solvent, N, N-dimethylacetamide, N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide or a mixture thereof can be used. In addition to the polymer and the solvent, the polymer solution may further include a surfactant, a pore-forming agent, a hydrophilic polymer, and the like in an amount of 5 to 30 wt% based on the total weight of the polymer solution. When the composition of the polymer solution is within the above preferred range, the porous support to be prepared may have pores of a suitable size.

In addition, a casting process and a phase change method for preparing a porous support may be performed by a commonly known method, respectively.

The prepared porous support should be stored in an undried state until it is used to prevent the shrinkage of pores, and it is preferable to wash with sufficient distilled water before use again.

(2) Formation of Polyester Active Layer

Next, the porous support is immersed in an aromatic polyhydric alcohol solution to fill the pores of the porous support with an aromatic polyhydric alcohol solution to remove the aromatic polyhydric alcohol solution present on the surface of the porous support, and then the resulting porous support is converted into an aromatic polyvalent acyl halide solution. It is possible to form a polyester active layer by interfacial polymerization of the aromatic polyhydric alcohol and the aromatic polyhydric acyl halide by immersion in.

Here, the aromatic polyhydric alcohol solution is preferably in a concentration of 0.5 to 10.0% by weight, water may be used as a solvent, NaOH, glycerol, alcohol may be added.

In addition, the aromatic polyhydric acyl halide solution is preferably in a concentration of 0.1 to 5.0% by weight, and hydrocarbons containing 8 to 12 carbon alkanes, normal hexane, and the like may be used as the solvent, and among them, 8 to 12 carbon atoms. It is preferable to use hydrocarbons containing two alkanes as a solvent in order to consider environmental problems and to prevent fires due to boiling points.

When the aromatic polyhydric alcohol solution and aromatic polyhydric acyl halide solution have the above preferred composition, the polyester active layer synthesized by the interfacial polymerization method may have a ridge and valley structure.

In addition, the aromatic polyhydric alcohol solution and / or the aromatic polyhydric acyl halide solution may further include an aliphatic polyhydric alcohol and / or an aliphatic polyhydric carboxylic acid component, and an alkyl alcohol compound such as glycerol may be added as an interfacial polymerization aid. And also additives for facilitating film formation and improving the permeation performance of the resulting reverse osmosis membrane, for example camphorsulfonic acid, sodium lauryl sulfate, hexanediol, tetrabutylammonium bromide or mixtures thereof It is preferably added at 0.1 to 50% by weight based on the total weight.

In this step, an immersion method can be used as a method of filling the pores of the porous support with an aromatic polyhydric alcohol. In addition, as a method of removing the aromatic polyhydric alcohol solution from the porous support surface, it is possible to remove excess aromatic polyhydric alcohol solution present on the surface, for example, by pressing the roller at an appropriate pressure.

An example of the reaction in which the aromatic polyhydric alcohol and the aromatic polyhydric acyl halide interfacially polymerize in this step is shown in Scheme 1 below.

Scheme 1

The interfacial polymerization reaction may be performed for 5 seconds to 10 minutes, more preferably for 10 seconds to 2 minutes. When in the above range, the thickness of the polyester active layer to be synthesized can be formed more appropriately.

By using the interfacial polymerization method in the present invention, it is possible to easily form a cross-linked polymer layer having a thickness of less than micrometer, and the prepared polymer layer may have a high crosslinking degree, thereby exhibiting very high permeability and salt rejection rate. In addition, it is possible to easily prepare a polymer having a high molecular weight without accurately matching the equivalent ratio of the monomers used, and because the formation rate of the polymer is very fast, it is possible to increase the productivity of the separation membrane by shortening the production time of the composite membrane.

(3) post-processing steps

The porous support on which the polyester active layer is formed can be heat treated as a post-treatment process, for example, it is preferably carried out for 1 to 30 minutes at a temperature of 30 to 150 ℃. Through this heat treatment process, all of the reaction solvent can be removed and the formed polyester active layer can be well adhered to the surface of the porous support by hydrophobic-hydrophobic interaction, thereby providing physical stability of the reverse osmosis composite membrane. .

In addition, it is preferable to store the finally prepared reverse osmosis composite membrane soaked in distilled water again.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by these examples.

Preparation Example 1 Preparation of Porous Support with Polyesulfone Coating Layer

Based on the total weight of the solution, 18% by weight of polyesulfone (PES, Solvay), 10% by weight of polyethylene glycol 600 (PEG600, three thousand), and 20% by weight of ethoxyethanol (Aldrich) were N, N-dimethyl It was dissolved in acetamide (DMAc, Junsei) to prepare a polymer solution. The prepared solution was cast on the porous nonwoven fabric having a thickness of 150 μm, and then immersed in distilled water to prepare a porous support having a molecular weight of about 50,000 g / mol at the ultrafiltration membrane level using a phase transfer method.

After completion of the phase transition, the ultrafiltration membrane was heat treated at 40 ° C. for 2 hours to completely remove the remaining solvent, and then immersed in 50% ethanol solution for 2 hours to increase hydrophilicity, and then washed with distilled water to completely remove the remaining solution. .

Preparation Example 2 Preparation of Porous Support with Polyacrylonitrile Coating Layer

A polymer solution was prepared by dissolving 18% by weight of polyisulfone based on the total weight of the solution in a solvent of N-methylpyrrolidone (NMP, Junsei). The prepared solution was cast on the porous nonwoven fabric having a thickness of 150 μm, and then immersed in distilled water to prepare a porous support having a molecular weight of about 50,000 g / mol at the ultrafiltration membrane level using a phase transfer method.

After completion of the phase transition, the ultrafiltration membrane was heat treated at 40 ° C. for 2 hours to completely remove the remaining solvent, and then immersed in 0.1 M sodium hydroxide solution at 40 ° C. for 1 hour in order to increase hydrophilicity, and then in 1 M hydrochloric acid solution. It was immersed in time and washed with distilled water to completely remove the remaining solution.

Example 1 Preparation of Reverse Osmosis Composite Membrane

For preparing the polyester active layer, after preparing an aqueous solution of resorcinol comprising 3.0% by weight of resorcinol (Aldrich) and 1.2% by weight of sodium hydroxide (NaOH, Junsei) based on the total weight of the aqueous solution, Before dipping the porous support prepared in Preparation Example 1 for 1 minute and removed to remove the remaining solution on the surface with a rubber roller.

Thereafter, the porous support was immersed in a solution in which trimethoyl chloride (TMC, Aldrich) was dissolved in an organic solvent (Isol-C, SK Chem) at 0.2% by weight for 1 minute, followed by interfacial polymerization, and then taken out to 42 ° C. It dried in the oven of 5 minutes and obtained the reverse osmosis composite membrane.

Example 2: Preparation of Reverse Osmosis Composite Membrane

Perform the same procedure as in Example 1, except that 0.15% by weight of sodium lauryl sulfate (Aldrich), 5.0% by weight of isopropyl alcohol (Aldrich), and 0.11% by weight of tetrabutylammonium bromide (Aldrich) in the aqueous solution of resorcinol % Was further added to prepare a reverse osmosis composite membrane.

Example 3: Preparation of Reverse Osmosis Composite Membrane

The same procedure as in Example 1 was carried out, in addition to the resorcinol aqueous solution, 1,2-hexanediol (Aldrich), 1,6-hexanediol (Aldrich), and 2-ethyl-1,3-hexane An aliphatic diol such as diol (EHD, Aldrich) was added each 0.3 wt% to prepare a reverse osmosis composite membrane.

Example 4: Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared by the same procedure as in Example 1 except that 0.3 wt% of succinic acid, adipic acid, and suveric acid were additionally added to the aqueous solution of resorcinol.

Example 5: Preparation of Reverse Osmosis Composite Membrane

In the same procedure as in Example 1, but using hydroquinone instead of resorcinol, a reverse osmosis composite membrane was prepared.

Example 6: Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared in the same manner as in Example 3, using hydroquinone instead of resorcinol.

Example 7: Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared in the same manner as in Example 2, using the porous support prepared in Preparation Example 2 as the porous support.

Example 8: Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared in the same manner as in Example 3, using the porous support prepared in Preparation Example 2 as the porous support.

Example 9 Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared in the same manner as in Example 6, using the porous support prepared in Preparation Example 2 as the porous support.

Example 10 Preparation of Reverse Osmosis Composite Membrane

The reverse osmosis composite membrane was prepared in the same manner as in Example 6, using the porous support prepared in Preparation Example 2 as the porous support.

Test Example 1: SEM observation of the surface

The surface of the active layer of the reverse osmosis composite membrane prepared in Example 1 was observed in a scanning electron microscope (SEM) and is shown in FIG. 1.

As shown in FIG. 1, the surface of the active layer has a ridge and valley structure, thereby increasing the roughness of the surface and increasing the hydrophilicity of the membrane surface, thereby improving the permeation performance of the reverse osmosis composite membrane.

Test Example 2: Evaluation of Transmission Performance

The reverse osmosis composite membrane prepared in Example 1 was evaluated by permeation of 1,000 ppm NaCl aqueous solution at room temperature, and the permeate flow rate was 1.4LPM, after consolidation at 800 psi for 2 hours, the pressure was lowered at 30 at each pressure. Measured after running for minutes. The test results showed that the permeability and rejection rate increased with increasing operating pressure, indicating the characteristics of reverse osmosis membrane.

In addition, 1,000 ppm NaCl aqueous solution was separated by permeation at room temperature and 400 psi using the reverse osmosis composite membranes obtained in Examples 1 to 9, and the results are shown in Table 1 below.

Example Permeability (㎥ / ㎡day) NaCl exclusion rate (%) One 1.5 95.9 2 1.7 96.7 3 1.8 99.5 4 1.6 96.9 5 1.6 97.3 6 1.7 98.4 7 1.8 97.9 8 1.9 99.8 9 1.7 97.1

As shown in Table 1, the reverse osmosis composite membrane prepared in the embodiment of the present invention can be seen that the excellent permeability and salt rejection.

Test Example 3: Evaluation of Chlorine Resistance

In order to examine the chlorine resistance and chemical stability of the reverse osmosis composite membrane, 500 mg of the polyester active layers of the reverse osmosis composite membranes of Examples 1 and 5 were added to a 1% sodium hypochlorite aqueous solution and reacted at room temperature for 48 hours, and then filtered. After washing with distilled water and dried in vacuo. The change in Tg value of the polyester before and after exposure to chlorine ions was measured by differential scanning calorimetry (DSC), and the results are shown in Table 2 below.

division Tg (℃) before treatment Tg (℃) after treatment Polyester active layer of Example 1 176.95 175.79 Polyester active layer of Example 5 146.04 145.67

As shown in Table 2, almost no change in Tg value before and after chlorine exposure showed very good chemical stability against chlorine.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, It is to be understood that the invention may be practiced within the scope of the appended claims.

Claims (10)

A reverse osmosis composite membrane comprising a porous support and a crosslinked polyester active layer formed on a surface of pores of the porous support,
The crosslinked polyester active layer comprises a polyester in which an aromatic polyhydric alcohol and an aromatic polyhydric acyl halide are cross-polymerized,
The cross-polymerized polyester further comprises an aliphatic polyhydric alcohol, an aliphatic polyhydric carboxylic acid, or both as unit components, reverse osmosis composite membrane.
delete The method of claim 1,
And the aromatic polyhydric alcohol is selected from the group consisting of resorcinol, hydroquinone, benzenedimethanol, dihydroxybiphenyl, benzenedithiol, and mixtures thereof.
The method of claim 1,
And said aromatic polyvalent acyl halide is selected from the group consisting of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride and mixtures thereof.
The method of claim 1,
The porous support is selected from polysulfone, polyesulfone, polyacrylonitrile, polyimide, polyimide, polypropylene, polyethylene, polyamide, polymethyl methacrylate, polyvinylidene fluoride and mixed resins thereof. Reverse osmosis composite membrane, characterized in that the selected polymer layer is coated on a porous substrate.
Interfacial polymerization of the aromatic polyhydric alcohol solution and the aromatic polyhydric acyl halide solution on the porous support to form a crosslinked polyester active layer on the surface of the porous support,
The reverse osmosis of claim 1, comprising adding an aliphatic polyhydric alcohol, an aliphatic polyhydric carboxylic acid, or both to at least one of the aromatic polyhydric alcohol solution and the aromatic polyhydric acyl halide solution before the interfacial polymerization reaction. Method for producing a composite membrane.
The method according to claim 6,
The interfacial polymerization reaction,
The porous support is immersed in an aromatic polyhydric alcohol solution to fill the pores of the porous support with an aromatic polyhydric alcohol solution, and then the aromatic polyhydric alcohol solution present on the surface of the porous support is removed. Method for producing a reverse osmosis composite membrane, characterized in that carried out by reacting the polyhydric alcohol and aromatic polyhydric acyl halide for 5 seconds to 10 minutes.
The method according to claim 6,
A method for producing a reverse osmosis composite membrane, wherein an alkyl alcohol compound is added to at least one of the aromatic polyhydric alcohol solution and the aromatic polyhydric acyl halide solution as a polymerization aid.
The method according to claim 6,
The aromatic polyhydric alcohol solution has a concentration of 0.5 to 10.0% by weight, uses water as a solvent, further comprises NaOH, glycerol or alcohol,
The aromatic polyvalent acyl halide solution has a concentration of 0.1 to 5.0% by weight, and comprises a hydrocarbon or a normal hexane containing 8 to 12 carbon alkanes as a solvent, a method for producing a reverse osmosis composite membrane.
The method according to claim 6,
The porous support is a polysulfone, polyisulfone, polyacrylonitrile, polyimide, polyimide, polypropylene, polyethylene, polyamide, polymethylmethacrylate, polyvinylidene fluoride and the like on a porous substrate After casting the solution of the polymer selected from the mixed resin of the method characterized in that it is prepared by forming a fine pores by using a phase transfer method, the reverse osmosis composite membrane manufacturing method.

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