A preparation method of a hollow fiber water treatment membrane

Abstract

The present invention relates to a preparation method of a water treatment membrane, specifically to a preparation method of a water treatment membrane using a hollow fiber as a support and a polyamide layer as a separation layer. The present invention provides a new preparation method of a hollow fiber water treatment membrane. By designing two-stage hydrophilic modification, in the first stage, carboxymethyl cellulose is used for modification in the polyamide layer, and in the second stage, ethylene glycol containing amino groups is used for hydrophilic modification on the inner surface of the polyamide layer. The two-stage hydrophilic modification well solves the problems of progressive hydrophilicity and easy shedding of grafted substances.

Description

Technical Field

[0001] The present invention relates to a method for preparing a water treatment membrane, and particularly to a method for preparing a water treatment membrane using a hollow fiber as a support and a polyamide layer as a separation layer. Background Art

[0002] In modern water treatment technologies, membrane separation technology has been widely applied due to its advantages such as high efficiency, energy conservation, and environmental protection. As a separation medium, the membrane can effectively remove impurities, microorganisms, and harmful substances in water, improving water quality. Especially in the fields of drinking water purification, industrial wastewater treatment, and seawater desalination, membrane technology plays an irreplaceable role. With the increasing water resource tension and the continuous improvement of water quality requirements, the development of high-performance and high-efficiency membrane materials has become a current research hotspot.

[0003] As an important membrane material, polyamide composite membranes have been widely used in the water treatment field due to their excellent mechanical properties, chemical stability, and thermal stability. However, the hydrophilicity of polyamide membranes directly affects their separation efficiency and flux. Membrane materials with good hydrophilicity can more effectively adsorb and transfer water molecules, reducing the residence time of water molecules on the membrane surface, thereby improving the permeation flux and anti-fouling performance of the membrane. Therefore, improving the hydrophilicity of polyamide membranes is the key to optimizing their performance and extending their service life.

[0004] In order to improve the hydrophilicity of polyamide composite membranes, the prior art usually adopts the method of coating a hydrophilic coating or grafting a hydrophilic substance on the outer side of the membrane. Although this method can improve the hydrophilicity of the membrane to a certain extent, there are obvious problems. First, since the coating layer or hydrophilic substance is located on the outer side of the membrane, the hydrophilicity of the membrane layer gradually decreases from the outside to the inside according to the water permeation direction during the water treatment process, which is not conducive to the smooth flow of water. Second, the raw material liquid with a higher pressure directly contacts the hydrophilic coating or grafted substance, which is likely to cause the shedding of the hydrophilic coating or grafted substance. Therefore, developing a new water treatment membrane that can perform hydrophilic modification on the inner side of the polyamide membrane, with a lasting modification effect and no impact on water quality, has become an urgent problem to be solved currently. Summary of the Invention

[0005] In view of the above problems, the present invention provides a new method for preparing a hollow fiber water treatment membrane. By designing two-stage hydrophilic modification, the first stage selects to modify with carboxymethyl cellulose in the polyamide layer, and the second stage selects to perform hydrophilic modification with amino-containing ethylene glycol on the inner surface of the polyamide layer. The two-stage hydrophilic modification well solves the problems of hydrophilic progression and easy shedding of grafted substances.

[0006] Specifically, the present invention provides a method for preparing a hollow fiber water treatment membrane, which comprises the following steps: a) adding polyamine and carboxymethyl cellulose into water to form an aqueous monomer solution, wherein the mass concentration range of carboxymethyl cellulose is 0.5% - 5%; b) contacting the aqueous monomer solution formed in step a), an organic phase monomer containing acyl chloride with a hollow fiber support to carry out an interfacial polymerization reaction to form a polyamide membrane layer; c) continuously flowing a polyethylene glycol solution containing amino groups inside the hollow fiber to graft-modify the inner side of the polyamide membrane layer.

[0007] Preferably, the material of the hollow fiber support is one of polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, and polyacrylonitrile, the outer diameter of the pore membrane is 1.0 - 2.5 mm, and the wall thickness is 0.1 - 0.2 mm.

[0008] Preferably, the mass concentration range of the polyethylene glycol solution containing amino groups is 0.5% - 5%, the pH is 7.5 - 9, the flow rate range is 0.1 - 1.0 mL / min, and the modification time is 5 - 30 minutes.

[0009] Preferably, the substitution degree of NH2 in the polyethylene glycol containing amino groups is 10 - 30%.

[0010] Preferably, the solvent in the polyethylene glycol solution containing amino groups is one or more of water, methanol, and ethanol.

[0011] Preferably, the polyethylene glycol solution containing amino groups further contains a catalyst with a mass concentration of 0.1 - 3%, and the catalyst is an organotin compound, a titanate, or a zirconate catalyst.

[0012] Preferably, after step c), there is further step d). After the modification treatment, deionized water is continuously introduced into the inner side of the hollow fiber support to wash away unreacted impurities.

[0013] Preferably, the flow rate of deionized water during the washing is 0.5 - 2 mL / min, and the washing time is 2 - 12 h.

[0014] Preferably, after step d), there is further step e). The hollow fiber is placed in a drying oven and dried at 40 - 60 °C for 2 - 4 hours.

[0015] The present invention also provides a water treatment membrane prepared according to the above method. The water treatment membrane is a polyamide composite membrane, which comprises a hollow fiber support and a polyamide membrane layer; the polyamide membrane layer contains carboxymethyl cellulose, and the inner surface of the polyamide membrane layer is grafted with polyethylene glycol containing amino groups.

[0016] Compared with the prior art, the present invention designs two-stage hydrophilic modification. For the first stage, carboxymethyl cellulose is used for modification in the polyamide layer. For the second stage, ethylene glycol containing amino groups is used for hydrophilic modification on the inner surface of the polyamide layer. By optimizing the parameters, it is ensured that the inner surface of the polyamide layer has better hydrophilicity than the polyamide layer, thereby enhancing the driving force for water to pass through the polyamide layer. Secondly, the present invention grafts polyethylene glycol containing amino groups on the inner side of the polyamide layer, avoiding the direct scouring of the raw material liquid under high pressure and enhancing the stability of the water treatment membrane. Detailed implementation mode

[0017] Example 1

[0018] A preparation method of a hollow fiber water treatment membrane is as follows:

[0019] a) Add 0.5 wt% m-phenylenediamine and 2 wt% carboxymethyl cellulose (average molecular weight 20,000 Da) to water to form an aqueous monomer solution. Add 2 wt% of trimesoyl chloride in cyclohexane as an organic phase monomer.

[0020] b) Take a hollow fiber ultrafiltration membrane as a support, the material of which is polysulfone, the outer diameter of the pore membrane is 1.5 mm, and the wall thickness is 0.15 mm. Immerse the above hollow fiber support in the aqueous monomer solution and the organic phase monomer solution in sequence to form a polyamide membrane layer on the surface of the support.

[0021] c) Continuously flow PEG-NH2 with a concentration of 3 wt% inside the hollow fiber to graft-modify the inner side of the polyamide membrane layer, where the substitution degree of NH2 in PEG-NH2 is 10%, the solution uses water as a solvent, contains 1 wt% of dibutyltin dilaurate as a catalyst, the pH value is adjusted to 8, the flow rate is controlled at 0.5 mL / min, and the modification time is set to 15 minutes.

[0022] d) After the modification treatment, continuously pass deionized water into the inside of the hollow fiber support to wash away unreacted polymers and impurities. The flow rate of deionized water is set to 1 mL / min, and the washing time is set to 6 hours to ensure the purity and performance of the membrane layer.

[0023] e) After the washing is completed, place the hollow fiber in a drying oven and dry it at 50 °C for 3 hours to remove residual moisture.

[0024] Example 2

[0025] A preparation method of a hollow fiber water treatment membrane is as follows:

[0026] a) Add 0.5 wt% of m-phenylenediamine and 2 wt% of carboxymethyl cellulose to water to form an aqueous monomer solution. Add 2 wt% of trimesoyl chloride to cyclohexane as an organic phase monomer.

[0027] b) Take a hollow fiber ultrafiltration membrane as a support, which is made of polysulfone, with an outer diameter of the pore membrane of 1.5 mm and a wall thickness of 0.15 mm. Immerse the above hollow fiber support in the aqueous monomer solution and the organic phase monomer solution in sequence to form a polyamide membrane layer on the surface of the support.

[0028] c) Continuously flow PEG-NH2 with a concentration of 3 wt% inside the hollow fiber to graft-modify the inner side of the polyamide membrane layer. The substitution degree of NH2 in PEG-NH2 is 30%. The solution uses water as a solvent, contains 1 wt% of dibutyltin dilaurate as a catalyst, the pH value is adjusted to 8, the flow rate is controlled at 0.5 mL / min, and the modification time is set to 15 minutes.

[0029] d) After the modification treatment, continuously pass deionized water into the inner side of the hollow fiber support to wash away unreacted polymers and impurities. The flow rate of the deionized water is set to 1 mL / min, and the washing time is set to 6 hours to ensure the purity and performance of the membrane layer.

[0030] e) After the washing is completed, place the hollow fiber in an oven and dry it at 50 °C for 3 hours to remove residual moisture.

[0031] Comparative Example 1

[0032] A method for preparing a hollow fiber water treatment membrane, the specific steps are as follows:

[0033] a) Add 0.5 wt% of m-phenylenediamine and 2 wt% of carboxymethyl cellulose to water to form an aqueous monomer solution. Add 2 wt% of trimesoyl chloride to cyclohexane as an organic phase monomer.

[0034] b) Take a hollow fiber ultrafiltration membrane as a support, which is made of polysulfone, with an outer diameter of the pore membrane of 1.5 mm and a wall thickness of 0.15 mm. Immerse the above hollow fiber support in the aqueous monomer solution and the organic phase monomer solution in sequence to form a polyamide membrane layer on the surface of the support.

[0035] c) After the washing is completed, place the hollow fiber in an oven and dry it at 50 °C for 3 hours to remove residual moisture.

[0036] Comparative Example 2

[0037] A method for preparing a hollow fiber water treatment membrane, the specific steps are as follows:

[0038] a) Add 0.5 wt% of m-phenylenediamine and 2 wt% of carboxymethyl cellulose to water to form an aqueous monomer solution. Add 2 wt% of trimesoyl chloride to cyclohexane as an organic phase monomer.

[0039] b) Take a hollow fiber ultrafiltration membrane as a support, which is made of polysulfone, with an outer diameter of the pore membrane of 1.5 mm and a wall thickness of 0.15 mm. Immerse the above hollow fiber support in the aqueous monomer solution and the organic phase monomer solution in sequence to form a polyamide membrane layer on the surface of the support.

[0040] c) Immerse the hollow fiber support with the formed polyamide membrane layer in PEG-NH2 with a concentration of 3 wt% to graft-modify the outer side of the polyamide membrane layer, where the substitution degree of NH2 in PEG-NH2 is 10%, the solution uses water as a solvent, contains 1 wt% of dibutyltin dilaurate as a catalyst, the pH value is adjusted to 8, and the modification time is set to 15 minutes.

[0041] d) After the modification treatment, soak the modified membrane in deionized water for 6 h, and then continuously rinse the membrane with flowing water for 2 h.

[0042] e) After cleaning, place the hollow fiber in an oven and dry it at 50 °C for 3 hours to remove the residual moisture.

[0043] Comparative Example 3

[0044] A preparation method of a hollow fiber water treatment membrane, the specific steps are as follows:

[0045] a) Add 0.5 wt% of m-phenylenediamine to water to form an aqueous monomer solution. Add 2 wt% of trimesoyl chloride to cyclohexane as an organic phase monomer.

[0046] b) Take a hollow fiber ultrafiltration membrane as a support, which is made of polysulfone, with an outer diameter of the pore membrane of 1.5 mm and a wall thickness of 0.15 mm. Immerse the above hollow fiber support in the aqueous monomer solution and the organic phase monomer solution in sequence to form a polyamide membrane layer on the surface of the support.

[0047] c) Continuously flow PEG-NH2 with a concentration of 3 wt% inside the hollow fiber to graft-modify the inner side of the polyamide membrane layer, where the substitution degree of NH2 in PEG-NH2 is 10%, the solution uses water as a solvent, contains 1 wt% of dibutyltin dilaurate as a catalyst, the pH value is adjusted to 8, the flow rate is controlled at 0.5 mL / min, and the modification time is set to 15 minutes.

[0048] d) After the modification treatment, deionized water was continuously passed through the inner side of the hollow fiber support to wash away the unreacted polymers and impurities. The flow rate of the deionized water was set at 1 mL / min, and the washing time was set at 6 hours to ensure the purity and performance of the membrane layer.

[0049] e) After washing, the hollow fiber was placed in an oven and dried at 50 °C for 3 hours to remove the residual moisture.

[0050] Comparative Example 4

[0051] A method for preparing a hollow fiber water treatment membrane, the specific steps are as follows:

[0052] a) 0.5 wt% of m-phenylenediamine and 2 wt% of carboxymethyl cellulose were added to water to form an aqueous monomer solution. 2 wt% of trimesoyl chloride was added to cyclohexane as an organic phase monomer.

[0053] b) A hollow fiber ultrafiltration membrane was taken as the support, the material of which was polysulfone, the outer diameter of the pore membrane was 1.5 mm, and the wall thickness was 0.15 mm. The above-mentioned hollow fiber support was successively impregnated in the aqueous monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0054] c) A 3 wt% PEG-NH2 solution was continuously flowed through the inner side of the hollow fiber to graft-modify the inner side of the polyamide membrane layer. The substitution degree of NH2 in PEG-NH2 was 10%, the solution was solvent with water, the pH value was adjusted to 8, the flow rate was controlled at 0.5 mL / min, and the modification time was set at 15 minutes.

[0055] d) After the modification treatment, deionized water was continuously passed through the inner side of the hollow fiber support to wash away the unreacted polymers and impurities. The flow rate of the deionized water was set at 1 mL / min, and the washing time was set at 6 hours to ensure the purity and performance of the membrane layer.

[0056] e) After washing, the hollow fiber was placed in an oven and dried at 50 °C for 3 hours to remove the residual moisture.

[0057] Membrane performance characterization

[0058] Table 1 shows the results of performance tests on the above-prepared hollow fiber water treatment membranes. Test conditions: at a pressure of 0.6 MPa and room temperature, using a 2000 mg / L sodium sulfate solution as the test solution, and the test contents included the permeation performance after 1 h of testing and the permeation performance after 12 h of testing.

[0059] Table 1 Performance test results of water treatment prepared in Examples 1-2 and Comparative Examples 1-4

[0060] 1 h flux ((LMH / bar)) 1 h sodium sulfate rejection rate (%) 12 h flux ((LMH / bar)) 12 h sodium sulfate rejection rate (%) Example 1 22.6 97.3 23.3 97.2 Example 2 28.4 97.1 29.3 97.0 Comparative Example 1 7.4 97.4 8.0 97.3 Comparative Example 2 10.5 97.5 7.9 97.0 Comparative Example 3 8.8 96.9 6.8 97.0 Comparative Example 4 9.1 97.1 9.2 97.0

[0061] From the above performance tests, it can be seen that the water treatment membranes prepared in Examples 1-2 have high flux and rejection rate, and have good stability.

[0062] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a hollow fiber water treatment membrane, characterized in that The following steps are involved: a) adding polyamine and carboxymethyl cellulose to water to form an aqueous monomer solution, wherein the mass concentration of the carboxymethyl cellulose is in the range of 0.5% to 5%; b) contacting the aqueous monomer solution formed in step a) and the organic monomer solution containing acyl chloride with the hollow fiber support to carry out interfacial polymerization reaction to form a polyamide membrane layer; c) continuously flowing a polyethylene glycol solution containing amino groups inside the hollow fiber to graft-modify the inside of the polyamide membrane layer; the mass concentration range of the polyethylene glycol solution containing amino groups is 0.5%-5%, the pH is 7.5-9, the flow rate range is 0.1-1.0 mL / min, and the modification time is 5-30 minutes; the degree of substitution of NH2 in the polyethylene glycol containing amino groups is 10-30%; the polyethylene glycol solution containing amino groups contains a catalyst with a mass concentration of 0.1-3%, and the catalyst is an organic tin compound, a titanate ester or a zirconate ester catalyst; d) After the modification, deionized water is continuously passed into the inner side of the hollow fiber support to clean and remove unreacted impurities; the flow rate of the deionized water during cleaning is 0.5-2 mL / min, and the cleaning time is 2-12 h.

2. The method according to claim 1, characterized in that The hollow fiber support is made of one of polysulfone, polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene and polyacrylonitrile, the outer diameter of the pore membrane is 1.0-2.5 mm, and the wall thickness is 0.1-0.2 mm.

3. The method according to claim 1, characterized in that The solvent in the amino-containing polyethylene glycol solution is one or more of water, methanol and ethanol.

4. The method according to claim 1, characterized in that After step d), there is further step e) of placing the hollow fiber in a drying oven and drying it at 40-60° C. for 2-4 hours.

5. A water treatment membrane prepared according to the method of claim 1, characterized in that The water treatment membrane is a polyamide composite membrane, comprising a hollow fiber support and a polyamide membrane layer; the polyamide membrane layer contains carboxymethyl cellulose, and the inner surface of the polyamide membrane layer is grafted with polyethylene glycol containing amino groups.