High-strength hollow fiber composite nanofiltration membrane and preparation method thereof

Abstract

The application relates to the field of membrane separation technology and discloses a high-strength hollow fiber composite nanofiltration membrane and a preparation method thereof. The high-strength hollow fiber composite nanofiltration membrane comprises a base film and a composite layer on the surface of the base film, and the preparation method of the base film comprises the following steps: extruding an outer liquid, a casting solution and a core liquid into a coagulation bath to be solidified, so as to obtain the base film; the raw materials of the casting solution comprise the following components in parts by mass: 20-25 parts of a polymer, 4-5 parts of composite carbon nanotubes, 10-12 parts of an additive and 60-70 parts of a solvent; the preparation method of the composite carbon nanotubes comprises the following steps: acidizing, washing and drying carbon nanotubes, adding water, adding palmitoyl amido propyl betaine, stirring, concentrating, drying and obtaining the composite carbon nanotubes. Through the technical scheme, the problem of low tensile strength of the hollow fiber composite nanofiltration membrane in the related art is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the field of membrane separation technology, in particular to a high-strength hollow fiber composite nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] Under the background of water resource shortage and increasing demand for industrial wastewater deep treatment, nanofiltration membrane technology has become a key support in the fields of water treatment and resource recovery due to its precise separation characteristics for ions and organic matters. The nanofiltration membrane with a hollow fiber structure gradually becomes a mainstream choice due to its high packing density, strong anti-pollution property and flexible adaptation to scenarios, and is widely used in fields such as seawater desalination, industrial wastewater reuse and complex system separation.

[0003] However, the existing hollow fiber nanofiltration membrane still faces the bottleneck of mechanical performance in actual application. In the prior art, polysulfone or polyether sulfone is used as the main material for the base film, and carbon nanotubes are additionally added to improve the breaking tensile strength of the base film. However, the carbon nanotubes tend to agglomerate, which greatly limits the improvement of the breaking tensile strength of the base film, thereby affecting the breaking tensile strength of the hollow fiber nanofiltration membrane. Not only does this lead to problems such as membrane filament rupture, deformation collapse or delamination in the process of high-pressure operation, complex medium environment or long-term service of the nanofiltration membrane, but also shortens the service life of the nanofiltration membrane, increases the maintenance cost and limits the application of the hollow fiber nanofiltration membrane in high-load working conditions. SUMMARY

[0004] The application provides a high-strength hollow fiber composite nanofiltration membrane and a preparation method thereof, and solves the problem of low breaking tensile strength of the hollow fiber composite nanofiltration membrane in the related art.

[0005] The technical scheme of the application is as follows:

[0006] The application provides a high-strength hollow fiber composite nanofiltration membrane, which comprises a base film and a composite layer on the surface of the base film, and the preparation method of the base film comprises the following steps:

[0007] extruding the outer liquid, the casting solution and the core liquid into a coagulation bath for solidification to obtain the base film;

[0008] The raw materials of the casting solution comprise the following components in parts by mass: 20-25 parts of a polymer, 4-5 parts of composite carbon nanotubes, 10-12 parts of an additive and 60-70 parts of a solvent;

[0009] The preparation method of the composite carbon nanotubes comprises the following steps:

[0010] The carbon nanotubes are acidized, washed, dried, water is added, palmitoyl amido propyl betaine is added, stirred, concentrated, and dried to obtain the composite carbon nanotubes.

[0011] As a further technical solution, the raw material of the external liquid comprises the following components by mass fraction: 5-10 parts of sodium alginate, 80-90 parts of N,N-dimethylformamide.

[0012] As a further technical solution, the core liquid is N,N-dimethylformamide.

[0013] As a further technical solution, during the extrusion, the flow rate of the external liquid is 20-40 mL / min, the flow rate of the casting liquid is 150-200 mL / min, and the flow rate of the core liquid is 100-150 mL / min.

[0014] As a further technical solution, the extrusion temperature is 30-40 DEG C.

[0015] As a further technical solution, the solidification temperature is 40-45 DEG C.

[0016] As a further technical solution, during the acidification, the carbon nanotubes are added to an acid solution and boiled;

[0017] During the acidification, the acid solution is a mixed acid solution obtained by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3-4:1;

[0018] The mass fraction of the concentrated sulfuric acid and the concentrated nitric acid is each independently 80%;

[0019] The boiling time is 1-2 h.

[0020] As a further technical solution, during the acidification, the mass-to-volume ratio of the carbon nanotubes to the mixed acid solution is 1 g:10-12 mL.

[0021] As a further technical solution, the mass-to-volume ratio of the carbon nanotubes to water is 1 g:15-20 mL.

[0022] As a further technical solution, in the preparation method of the composite carbon nanotubes, the mass ratio of the carbon nanotubes to palmitoyl amido propyl betaine is 30-35:1.

[0023] In the high-strength hollow fiber composite nanofiltration membrane, when the mass ratio of the carbon nanotubes to palmitoyl amido propyl betaine is 30-35:1, the breaking tensile strength of the hollow fiber composite nanofiltration membrane is further improved.

[0024] The mass ratio of the carbon nanotube and the palmitoyl ethyolpropanedimethylamine in the high-strength hollow fiber composite nanofiltration membrane can be 30:1, 30.5:1, 31:1, 31.5:1, 32:1, 32.5:1, 33:1, 33.5:1, 34:1, 34.5:1, 35:1, and preferably 35:1.

[0025] As a further technical solution, the polymer includes one or both of polysulfone and polyether sulfone.

[0026] As a further technical solution, the additive is polyvinylpyrrolidone.

[0027] As a further technical solution, the solvent includes one of N,N-dimethylformamide and N,N-dimethylacetamide.

[0028] As a further technical solution, the stirring temperature is 30-40 DEG C, the stirring speed is 300-400 rpm, and the stirring time is 2-3 hours.

[0029] The application further provides a preparation method of the high-strength hollow fiber composite nanofiltration membrane.

[0030] S1, injecting a first solution into a base film, maintaining pressure, removing the excess first solution, and obtaining a pretreated base film;

[0031] S2, injecting a second solution into the pretreated base film, reacting, removing the excess second solution, and obtaining the high-strength hollow fiber composite nanofiltration membrane.

[0032] As a further technical solution, the first solution is a polyvinyl alcohol aqueous solution with a mass fraction of 1-3%.

[0033] As a further technical solution, the preparation method of the second solution is as follows: uniformly mixing 5-10 parts of an additive, 5-10 parts of an acid, and 80-90 parts of water by mass to obtain the second solution.

[0034] The additive includes glutaraldehyde.

[0035] As a further technical solution, the acid includes one or both of oxalic acid and citric acid.

[0036] As a further technical solution, the additive further includes 3,5-dihydroxybenzaldehyde.

[0037] The auxiliary agent in the high-strength hollow fiber composite nanofiltration membrane further comprises 3,5-dihydroxybenzaldehyde, and the water has better compatibility with the nanofiltration membrane when the water enters the nanofiltration membrane, so that the membrane flux of the water is improved.

[0038] As a further technical solution, the mass ratio of glutaraldehyde to 3,5-dihydroxybenzaldehyde in the auxiliary agent is 5-6:1.

[0039] In the high-strength hollow fiber composite nanofiltration membrane, the mass ratio of glutaraldehyde to 3,5-dihydroxybenzaldehyde can be 5:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, 6:1, and preferably 5:1.

[0040] As a further technical solution, the pressure is 0.5-1 bar and the time is 0.5-1 h during the pressure maintaining.

[0041] As a further technical solution, the temperature of the reaction is 20-40 DEG C and the time is 0.5-1 h.

[0042] The working principle and beneficial effects of the present application are as follows:

[0043] The carbon nanotubes are first subjected to acidification treatment to introduce polar groups such as carboxyl and hydroxyl groups on the surface of the carbon nanotubes, and the surface properties of the carbon nanotubes are preliminarily changed, and the polar groups serve as active sites to create conditions for the interaction of the carbon nanotubes with other components, and then the acidified carbon nanotubes are compounded with palmitoyl amide propyl betaine to improve the dispersion stability of the carbon nanotubes, and the agglomeration of the carbon nanotubes in the system is avoided, so that the tensile strength of the hollow fiber composite nanofiltration membrane is improved. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are involved in the scope of protection of the present application.

[0045] In the following examples and comparative examples, the type of polysulfone is UDEL PSU P-1800, the type of polyethersulfone is Ultrason E PESU 2010, the type of carbon nanotube is CR2000, which is purchased from Qingdao Chao Rui Nanometer New Material Technology Co., Ltd., the type of sodium alginate is A2033-100G, which is purchased from Beijing MEG Bio-Medical Co., Ltd., the type of polyvinyl alcohol is PVA-217, which is purchased from Kuraray Co., Ltd., the mass fraction of concentrated sulfuric acid and concentrated nitric acid is 80%, and the solvent is water.

[0046] Example 1

[0047] A high-strength hollow fiber composite nanofiltration membrane comprises a base film and a composite layer located on the surface of the base film, and the preparation method of the base film comprises the following steps:

[0048] The outer liquid, the casting solution and the core liquid are extruded at 40°C, and then solidified at 45°C in a coagulation bath to obtain the base film.

[0049] During extrusion, the flow rate of the outer liquid is 40 mL / min, the flow rate of the casting solution is 200 mL / min, and the flow rate of the core liquid is 150 mL / min.

[0050] The raw materials of the outer liquid include the following components by mass fraction: sodium alginate 10 parts, N,N-dimethylformamide 90 parts.

[0051] The raw materials of the casting solution include the following components by mass fraction: polysulfone 25 parts, composite carbon nanotube 5 parts, polyvinylpyrrolidone 12 parts, N,N-dimethylformamide 70 parts.

[0052] The core liquid is N,N-dimethylformamide.

[0053] The preparation method of the composite carbon nanotube comprises the following steps:

[0054] The carbon nanotube is acidified, washed and dried, water is added (the mass-volume ratio of carbon nanotube to water is 1g:20mL), palmitoyl amide propyl betaine is added (the mass ratio of carbon nanotube to palmitoyl amide propyl betaine is 45:1), stirred at 400rpm for 2h at 40°C, concentrated and dried to obtain the composite carbon nanotube.

[0055] During acidification, the carbon nanotube is added to a mixed acid solution obtained by mixing concentrated sulfuric acid and concentrated nitric acid at a volume ratio of 4:1 (the mass-volume ratio of carbon nanotube to mixed acid solution is 1g:12mL), and boiled for 2h.

[0056] The preparation method of the high-strength hollow fiber composite nanofiltration membrane comprises the following steps:

[0057] S1, injecting polyvinyl alcohol solution (3% polyvinyl alcohol aqueous solution) into the base film, 1 bar pressure for 0.5 h, removing excess polyvinyl alcohol solution, and obtaining a pretreated base film;

[0058] S2, injecting the second solution into the pretreated base film, reacting at 40℃ for 1 h, removing excess second solution, and obtaining a nanofiltration membrane;

[0059] The preparation method of the second solution is as follows: mixing 10 parts of glutaraldehyde, 10 parts of oxalic acid and 90 parts of water by mass to obtain the second solution.

[0060] Example 2

[0061] A high-strength hollow fiber composite nanofiltration membrane includes a base film and a composite layer on the surface of the base film, and the preparation method of the base film includes the following steps:

[0062] The outer liquid, the casting solution and the core liquid are extruded at 30℃, and the base film is obtained by solidifying in a coagulation bath at 40℃.

[0063] During extrusion, the flow rate of the outer liquid is 20 mL / min, the flow rate of the casting solution is 150 mL / min, and the flow rate of the core liquid is 100 mL / min.

[0064] The raw materials of the outer liquid include the following components by mass: 5 parts of sodium alginate, 80 parts of N,N-dimethylformamide;

[0065] The raw materials of the casting solution include the following components by mass: 20 parts of polyether sulfone, 4 parts of composite carbon nanotube, 10 parts of polyvinylpyrrolidone, and 60 parts of N,N-dimethylacetamide;

[0066] The core liquid is N,N-dimethylformamide.

[0067] The preparation method of the composite carbon nanotube includes the following steps:

[0068] The carbon nanotube is acidified, washed, dried, water is added (the mass-volume ratio of carbon nanotube to water is 1g:15mL), palmitoyl amide propyl betaine is added (the mass ratio of carbon nanotube to palmitoyl amide propyl betaine is 25:1), stirred at 300rpm for 3h at 30℃, concentrated, and dried to obtain the composite carbon nanotube.

[0069] During acidification, the carbon nanotube is added to a mixed acid solution obtained by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 (the mass-volume ratio of carbon nanotube to mixed acid solution is 1g:10mL), and boiled for 1h.

[0070] The preparation method of the high-strength hollow fiber composite nanofiltration membrane includes the following steps:

[0071] S1, injecting polyvinyl alcohol solution (1% polyvinyl alcohol aqueous solution) into the base film, 0.5 bar pressure for 1 h, removing the excess polyvinyl alcohol solution, obtaining a pretreated base film;

[0072] S2, injecting the second solution into the pretreated base film, 20℃ for 1 h, removing the excess second solution, obtaining a nanofiltration membrane;

[0073] The preparation method of the second solution is as follows: mixing 5 parts of glutaraldehyde, 5 parts of citric acid and 80 parts of water by mass to obtain the second solution.

[0074] Example 3

[0075] The difference between this example and Example 2 is only that the mass ratio of carbon nanotubes to palmitoyl amido propyl betaine in this example is 40:1.

[0076] Example 4

[0077] The difference between this example and Example 2 is only that the mass ratio of carbon nanotubes to palmitoyl amido propyl betaine in this example is 30:1.

[0078] Example 5

[0079] The difference between this example and Example 2 is only that the mass ratio of carbon nanotubes to palmitoyl amido propyl betaine in this example is 35:1.

[0080] Example 6

[0081] The difference between this example and Example 5 is only that the glutaraldehyde in this example is replaced by an equal amount of an auxiliary agent;

[0082] The auxiliary agent includes glutaraldehyde and 3,5-dihydroxybenzaldehyde in a mass ratio of 6:1.

[0083] Example 7

[0084] The difference between this example and Example 5 is only that the glutaraldehyde in this example is replaced by an equal amount of an auxiliary agent;

[0085] The auxiliary agent includes glutaraldehyde and 3,5-dihydroxybenzaldehyde in a mass ratio of 5:1.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 2 is only that the composite carbon nanotubes in this comparative example are replaced by an equal amount of carbon nanotubes.

[0088] Experimental Example 1

[0089] The hollow fiber composite nanofiltration membranes prepared in Examples 1-5 and Comparative Example 1 were tested for tensile strength at break according to the method specified in HY / T 213-2016 "Determination of Tensile Strength at Break of Hollow Fiber Ultra / Microfiltration Membranes". The test results are shown in Table 1.

[0090] Table 1. Results of tensile strength test at break

[0091]

[0092] As shown in Table 1, the tensile strength at break of the high-strength hollow fiber composite nanofiltration membranes prepared in Examples 1-5 of the present invention reached more than 18.6 N. Therefore, the present invention uses palmitamide propyl betaine composite carbon nanotubes to improve the tensile strength at break of hollow fiber composite nanofiltration membranes.

[0093] Experiment Example 2

[0094] The high-strength hollow fiber composite nanofiltration membranes prepared in Examples 5-7 were placed on a cross-flow separation device, with pure water as the feed liquid, and operated at a pressure of 0.3 MPa. The membrane flux of the composite hollow fiber nanofiltration membrane was measured, and the test results are shown in Table 2.

[0095] Table 2 Membrane flux test results

[0096]

[0097] As shown in Table 2, the high-strength hollow fiber composite nanofiltration membranes prepared in Examples 6-7 of this invention achieved a membrane flux of 96.95 L·m⁻¹. -2 ·h -1 ·bar -1 Therefore, the present invention uses glutaraldehyde and 3,5-dihydroxybenzaldehyde together as additives to improve the membrane flux of high-strength hollow fiber composite nanofiltration membrane.

[0098] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength hollow fiber composite nanofiltration membrane, characterized in that, The substrate includes a base film and a composite layer located on the surface of the base film. The method for preparing the base film includes the following steps: The external liquid, casting liquid and core liquid are extruded and solidified in a coagulation bath to obtain the base film; The casting solution comprises the following components in parts by weight: 20-25 parts polymer, 4-5 parts composite carbon nanotubes, 10-12 parts additives, and 60-70 parts solvent. The method for preparing the composite carbon nanotubes includes the following steps: The carbon nanotubes were acidified, washed, dried, and then water and palmitamide propyl betaine were added. The mixture was stirred, concentrated, and dried to obtain the composite carbon nanotubes. During the acidification process, carbon nanotubes are added to an acid solution and boiled; the acid solution is a mixed acid solution obtained by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3 to 4:

1. In the preparation method of the composite carbon nanotubes, the mass ratio of carbon nanotubes to palmitamidopropyl betaine is 30~35:

1. The method for preparing the high-strength hollow fiber composite nanofiltration membrane includes the following steps: S1. Inject the first solution into the base membrane, maintain pressure, remove excess first solution, and obtain the pretreated base membrane; S2. Inject the second solution into the pretreated base membrane, react, remove the excess second solution, and obtain the high-strength hollow fiber composite nanofiltration membrane; The second solution is prepared by mixing 5-10 parts by mass of the auxiliary agent, 5-10 parts by mass of the acid, and 80-90 parts by mass of the water to obtain the second solution. The additives include glutaraldehyde and 3,5-dihydroxybenzaldehyde in a mass ratio of 5 to 6:

1.

2. The high-strength hollow fiber composite nanofiltration membrane according to claim 1, characterized in that, The polymer includes one or both of polysulfone and polyethersulfone; The additive is polyvinylpyrrolidone; The solvent includes one of N,N-dimethylformamide and N,N-dimethylacetamide.

3. The high-strength hollow fiber composite nanofiltration membrane according to claim 1, characterized in that, The stirring temperature is 30~40℃, the stirring speed is 300~400rpm, and the stirring time is 2~3h.

4. A method for preparing a high-strength hollow fiber composite nanofiltration membrane, used to prepare a high-strength hollow fiber composite nanofiltration membrane as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Inject the first solution into the base membrane, maintain pressure, remove excess first solution, and obtain the pretreated base membrane; S2. Inject the second solution into the pretreated base membrane, react, remove the excess second solution, and obtain the high-strength hollow fiber composite nanofiltration membrane.

5. The method for preparing a high-strength hollow fiber composite nanofiltration membrane according to claim 4, characterized in that, The first solution is a polyvinyl alcohol aqueous solution with a mass fraction of 1% to 3%; The second solution is prepared by mixing 5-10 parts by mass of the auxiliary agent, 5-10 parts by mass of the acid, and 80-90 parts by mass of the water to obtain the second solution. The additives include glutaraldehyde and 3,5-dihydroxybenzaldehyde in a mass ratio of 5 to 6:

1.

6. The method for preparing a high-strength hollow fiber composite nanofiltration membrane according to claim 4, characterized in that, During the pressure holding process, the pressure is 0.5~1 bar and the time is 0.5~1 h.

7. The method for preparing a high-strength hollow fiber composite nanofiltration membrane according to claim 4, characterized in that, The reaction is carried out at a temperature of 20-40°C for a time of 0.5-1 hour.

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