Preparation method of hollow fiber water treatment membrane

Abstract

The invention relates to a preparation method of a water treatment membrane, in particular to a preparation method of a water treatment membrane adopting hollow fibers as a support body and a polyamide layer as a separation layer. According to the novel preparation method of the hollow fiber water treatment membrane, two-stage hydrophilic modification is designed, in the first stage, carboxymethyl cellulose is selected to be used for modification in a polyamide layer, and in the second stage, amino-containing ethylene glycol is selected to be used for hydrophilic modification on the inner surface of the polyamide layer. The two-stage hydrophilic modification well solves the problems of hydrophilic progression and easy falling of grafted substances.

Description

Technical Field

[0001] The invention relates to a method for preparing a water treatment membrane, in particular 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 technology, membrane separation technology is widely used due to its advantages such as high efficiency, energy saving and environmental protection. As a separation medium, membrane can effectively remove impurities, microorganisms and harmful substances in water and improve 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 shortage of water resources and the continuous improvement of water quality requirements, the development of high-performance and high-efficiency membrane materials has become a hot topic in current research.

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

[0004] In order to improve the hydrophilicity of polyamide composite membranes, the prior art generally adopts a method of coating a hydrophilic coating or grafting a hydrophilic substance on the outside 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 the hydrophilic substance is located on the outside of the membrane, the hydrophilicity of the membrane layer gradually decreases from the outside to the inside according to the penetration direction of water during the water treatment process, which is not conducive to the smooth flow of water. Secondly, the raw material liquid with a higher pressure directly contacts the hydrophilic coating or the graft, which easily causes the hydrophilic coating or the graft to fall off. Therefore, the development of a new water treatment membrane, which can be hydrophilically modified on the inside of the polyamide membrane, and the new method of modification effect is long-lasting and does not affect the water quality, has become a problem to be solved at present. Summary of the invention

[0005] In view of the above problems, the present invention provides a novel method for preparing a hollow fiber water treatment membrane, which is designed with two-stage hydrophilic modification, wherein the first stage is to modify the polyamide layer with carboxymethyl cellulose, and the second stage is to modify the inner surface of the polyamide layer with amino-containing ethylene glycol. The two-stage hydrophilic modification solves the problems of hydrophilic progression and easy shedding of grafted materials.

[0006] Specifically, the present invention provides a method for preparing a hollow fiber water treatment membrane, which comprises the following steps: a) adding a 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%-5%; b) contacting the aqueous monomer solution formed in step a) and an organic 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 an amino group inside the hollow fiber to graft-modify the inside of the polyamide membrane layer.

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

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

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

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

[0011] Preferably, the amino group-containing polyethylene glycol solution further comprises a catalyst with a mass concentration of 0.1-3%, wherein the catalyst is an organic tin compound, a titanate ester or a zirconate ester catalyst.

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

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

[0014] Preferably, 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.

[0015] The present invention also provides a water treatment membrane prepared according to the above method, wherein 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.

[0016] Compared with the prior art, the present invention designs a two-stage hydrophilic modification, the first stage is to use carboxymethyl cellulose for modification in the polyamide layer, and the second stage is to use amino-containing ethylene glycol 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 improving the power of water passing through the polyamide layer. Secondly, the present invention grafts the amino-containing polyethylene glycol on the inner side of the polyamide layer, avoiding the direct scouring of the high-pressure raw material liquid and improving the stability of the water treatment membrane. DETAILED DESCRIPTION

[0017] Example 1

[0018] A method for preparing a hollow fiber water treatment membrane, the specific steps are as follows:

[0019] a) 0.5 wt% m-phenylenediamine and 2 wt% carboxymethyl cellulose (average molecular weight 20,000 Da) were added to water to form an aqueous monomer solution. 2 wt% isophthalic acid chloride was added to cyclohexane as an organic monomer.

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

[0021] c) PEG-NH with a concentration of 3 wt% was continuously flowed inside the hollow fiber. 2 , in order to graft the inner side of the polyamide membrane layer, where PEG-NH 2 NH 2 The degree of substitution is 10%, the solution uses water as solvent, contains 1wt% dibutyltin dilaurate as 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, deionized water was continuously passed through the inner side of the hollow fiber support to clean and remove unreacted polymer and impurities. The flow rate of deionized water was set to 1 mL / min and the cleaning time was set to 6 hours to ensure the purity and performance of the membrane layer.

[0023] e) After cleaning, the hollow fiber was placed in a drying oven at 50°C for 3 hours to remove residual moisture.

[0024] Example 2

[0025] A method for preparing a hollow fiber water treatment membrane, the specific steps are as follows:

[0026] a) 0.5 wt% m-phenylenediamine and 2 wt% carboxymethyl cellulose were added to water to form an aqueous monomer solution. 2 wt% isophthalic acid chloride was added to cyclohexane as an organic monomer.

[0027] b) A hollow fiber ultrafiltration membrane is used as a support, the material of which is polysulfone, the outer diameter of the pore size membrane is 1.5 mm, and the wall thickness is 0.15 mm. The above hollow fiber support is sequentially immersed in the aqueous phase monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0028] c) PEG-NH with a concentration of 3 wt% was continuously flowed inside the hollow fiber. 2 , in order to graft the inner side of the polyamide membrane layer, where PEG-NH 2 NH 2 The degree of substitution is 30%, the solution uses water as solvent, contains 1wt% dibutyltin dilaurate as 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, deionized water was continuously passed through the inner side of the hollow fiber support to clean and remove unreacted polymer and impurities. The flow rate of deionized water was set to 1 mL / min and the cleaning time was set to 6 hours to ensure the purity and performance of the membrane layer.

[0030] e) After cleaning, the hollow fiber was placed in a drying oven 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) 0.5 wt% m-phenylenediamine and 2 wt% carboxymethyl cellulose were added to water to form an aqueous monomer solution. 2 wt% isophthalic acid chloride was added to cyclohexane as an organic monomer.

[0034] b) A hollow fiber ultrafiltration membrane is used as a support, the material of which is polysulfone, the outer diameter of the pore size membrane is 1.5 mm, and the wall thickness is 0.15 mm. The above hollow fiber support is sequentially immersed in the aqueous phase monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0035] c) After cleaning, the hollow fiber was placed in a drying oven 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) 0.5 wt% m-phenylenediamine and 2 wt% carboxymethyl cellulose were added to water to form an aqueous monomer solution. 2 wt% isophthalic acid chloride was added to cyclohexane as an organic monomer.

[0039] b) A hollow fiber ultrafiltration membrane is used as a support, the material of which is polysulfone, the outer diameter of the pore size membrane is 1.5 mm, and the wall thickness is 0.15 mm. The above hollow fiber support is sequentially immersed in the aqueous phase monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0040] c) The hollow fiber support body formed with the polyamide membrane layer is immersed in PEG-NH 2 , in order to graft the outer side of the polyamide membrane layer, where PEG-NH 2 NH 2 The degree of substitution is 10%, the solution uses water as solvent, contains 1wt% dibutyltin dilaurate as catalyst, the pH value is adjusted to 8, and the modification time is set to 15 minutes.

[0041] d) After the modification treatment, the modified membrane was soaked in deionized water for 6 h and then rinsed continuously with running water for 2 h.

[0042] e) After cleaning, the hollow fiber was placed in a drying oven at 50°C for 3 hours to remove residual moisture.

[0043] Comparative Example 3

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

[0045] a) 0.5 wt% of m-phenylenediamine was added to water to form an aqueous monomer solution. 2 wt% of isophthalic acid chloride was added to cyclohexane as an organic monomer.

[0046] b) A hollow fiber ultrafiltration membrane is used as a support, the material of which is polysulfone, the outer diameter of the pore size membrane is 1.5 mm, and the wall thickness is 0.15 mm. The above hollow fiber support is sequentially immersed in the aqueous phase monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0047] c) PEG-NH3 with a concentration of 3 wt% was continuously flowed inside the hollow fiber. 2 , in order to graft the inner side of the polyamide membrane layer, where PEG-NH 2 NH 2 The degree of substitution is 10%, the solution uses water as solvent, contains 1wt% dibutyltin dilaurate as 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, deionized water was continuously passed through the inner side of the hollow fiber support to clean and remove unreacted polymer and impurities. The flow rate of deionized water was set to 1 mL / min and the cleaning time was set to 6 hours to ensure the purity and performance of the membrane layer.

[0049] e) After cleaning, the hollow fiber was placed in a drying oven at 50°C for 3 hours to remove 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% m-phenylenediamine and 2 wt% carboxymethyl cellulose were added to water to form an aqueous monomer solution. 2 wt% isophthalic acid chloride was added to cyclohexane as an organic monomer.

[0053] b) A hollow fiber ultrafiltration membrane is used as a support, the material of which is polysulfone, the outer diameter of the pore size membrane is 1.5 mm, and the wall thickness is 0.15 mm. The above hollow fiber support is sequentially immersed in the aqueous phase monomer solution and the organic phase monomer solution to form a polyamide membrane layer on the surface of the support.

[0054] c) PEG-NH3 with a concentration of 3 wt% was continuously flowed inside the hollow fiber. 2 , in order to graft the inner side of the polyamide membrane layer, where PEG-NH 2 NH 2 The degree of substitution was 10%, water was used as the solvent, the pH value was adjusted to 8, the flow rate was controlled at 0.5 mL / min, and the modification time was set to 15 minutes.

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

[0056] e) After cleaning, the hollow fiber was placed in a drying oven at 50°C for 3 hours to remove residual moisture.

[0057] Membrane performance characterization

[0058] Table 1 shows the results of the performance test of the prepared hollow fiber water treatment membrane. Test conditions: at a pressure of 0.6 MPa and room temperature, with a 2000 mg / L sodium sulfate solution as the test solution, the test contents include the permeability after testing for 1 hour and the permeability after testing for 12 hours.

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

[0060] 1h flux (LMH / bar) 1h Sodium sulfate retention rate (%) 12h flux (LMH / bar) 12h Sodium sulfate retention 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] It can be seen from the above performance tests that the water treatment membrane prepared in Examples 1-2 has a higher flux and rejection rate, and has good stability.

[0062] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that 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 containing acyl chloride with the hollow fiber support to carry out interfacial polymerization reaction to form a polyamide membrane layer; c) A polyethylene glycol solution containing amino groups is continuously flowed inside the hollow fiber to graft-modify the inside of the polyamide membrane layer.

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 mass concentration range of the amino-containing polyethylene glycol solution 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.

4. The method according to claim 1, characterized in that The degree of substitution of NH2 in the amino-containing polyethylene glycol is 10-30%.

5. 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.

6. The method according to claim 1, characterized in that The amino-containing polyethylene glycol solution also 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.

7. The method according to claim 1, characterized in that After step c), there is also step d) after the modification treatment, deionized water is continuously passed into the inner side of the hollow fiber support body to wash and remove unreacted impurities.

8. The method according to claim 6, characterized in that The flow rate of deionized water during the cleaning is 0.5-2 mL / min, and the cleaning time is 2-12 h.

9. The method according to claim 6, 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.

10. A water treatment membrane prepared by the method according to 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.