Chitosan composite nanofiltration membrane and preparation method thereof

Abstract

According to the novel preparation method of the MOFs particle doped chitosan nanofiltration membrane, crystallization of MOFs particles is concentrated in the subsequent membrane preparation process, the MOFs particles doped on a support body are used as nucleation centers, and nutrients in a membrane casting solution are attracted to the surface of the support body to grow into the MOFs particles. The content of MOFs particles on the surface of the membrane is reduced, the loss probability of MOFs is reduced, the movement process of nutrition is also beneficial to formation of a loose pore channel structure, and application of the chitosan membrane in nanofiltration is facilitated.

Description

Technical Field

[0001] The invention relates to a nanofiltration membrane and a preparation method thereof, and in particular to a composite nanofiltration membrane made of chitosan material and a preparation method thereof. Background Art

[0002] Nanofiltration is a common membrane separation technology with a retention range of 200-2000. Its operating pressure is lower than that of reverse osmosis. The retention rate of monovalent ions is much lower than that of divalent ions, and it has a better separation effect on organic pollutants.

[0003] Chitosan is obtained by deacetylation of chitin, which is widely present in nature. It has good biofunctionality and compatibility, blood compatibility, safety, and microbial degradability. Therefore, it has attracted wide attention from all walks of life and has made significant progress in its application research in many fields. Its above advantages also make it an ideal separation membrane material. Because chitosan has a large number of hydrophilic groups, the prior art already has chitosan mixed with other components to prepare nanofiltration membranes for application.

[0004] For nanofiltration membranes, the higher the water flux, the better. In order to continue to improve the water flux and pollution resistance, other materials are often added to the nanofiltration membrane. MOFs material is a common hydrophilic additive because of its regular molecular sieve structure. However, during the MOFs addition process, it is easy to cause membrane performance loss due to particle agglomeration. To improve this situation, the CN117018888A patent chooses to dope the MOFs particles in the chitosan pervaporation separation membrane layer in the in-situ preparation method. According to its description, it actually realizes the in-situ polymerization of MOFs particles during the aging of the casting liquid. Moreover, some MOFs particles will also be embedded on the membrane surface, so it is very easy to remove the inorganic particles on the membrane surface during the pervaporation vacuum suction process, resulting in contamination of the separation process. Moreover, the doping of MOFs and chitosan generally results in a denser membrane layer, so that the membrane is generally used for more refined pervaporation, and less for nanofiltration processes.

[0005] Therefore, it is necessary to optimize the doping method of the prior art so that it can be used in the nanofiltration process. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention optimizes the existing doping method, thereby enabling MOFs-doped chitosan membrane to be applied to the nanofiltration process and solving the problem of easy detachment of particles on the membrane surface.

[0007] The present invention provides a method for preparing a chitosan composite nanofiltration membrane, comprising the following steps: (1) Preparation of ultrafiltration membrane support doped with MOFs nanoparticles; (2) pouring a casting solution containing fumaric acid, ZrOCl2·8H2O, chitosan, and acetic acid on the surface of the support to form a chitosan film containing MOFs particles; (3) The chitosan membrane is further placed in an organic solution of trimesoyl chloride for cross-linking, thereby obtaining a nanofiltration membrane.

[0008] Preferably, the ultrafiltration membrane is prepared by the following steps: (1-1) mixing a membrane-forming polymer, an additive, MOFs nanoparticles and a solvent, and performing degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then immersed in a coagulation bath for phase inversion; (1-3) Drying to form a film.

[0009] Preferably, the mass contents of the film-forming polymer, additive and MOFs nanoparticles in the ultrafiltration membrane casting solution are 15-35wt%, 0.5-3wt% and 0.5-10wt% respectively.

[0010] Preferably, the MOFs particles are MOF-81, the film-forming polymer is one or more of polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polytetrafluoroethylene, and polyvinylidene fluoride; the additive is one of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and lithium chloride; Preferably, the casting solution in step (2) is prepared by the following steps: (2-1) Dissolve chitosan in acetic acid solution, and add fumaric acid and ZrOCl2·8H2O in sequence, react at 60-80°C for 1-2h, and stand for degassing to form a casting solution; (2-2) Lay the support body flat on the bottom of the container, pour the casting liquid evenly on the surface of the support body, and place it at 40-60°C to continue reacting for 2-5 hours to form a film.

[0011] Preferably, in the casting solution, the concentration of chitosan is 2-5wt%, the concentration of acetic acid is 2-5wt%, the concentration of fumaric acid is 0.05-0.5wt%, and the concentration of ZrOCl2·8H2O is 0.1-1.5wt%.

[0012] Preferably, in step (3), the concentration of trimesoyl chloride is 0.05-0.5 wt %, and the cross-linking time is 5-20 min.

[0013] The present invention also provides a chitosan composite nanofiltration membrane prepared according to the above method, which comprises an ultrafiltration membrane support and a chitosan nanofiltration layer, wherein MOFs particles are mixed and doped inside the ultrafiltration membrane support and inside the chitosan nanofiltration layer respectively.

[0014] The chitosan composite nanofiltration membrane prepared by the invention is applied in the field of water treatment.

[0015] Beneficial effects: The present invention focuses the crystallization of MOFs particles in the subsequent membrane preparation process, and uses the MOFs particles doped on the support as the nucleation center to attract the "nutrients" in the casting solution to the surface of the support to grow into MOFs particles, thereby reducing the content of MOFs particles on the membrane surface and the probability of MOFs loss. The movement of "nutrients" is also conducive to the formation of a loose pore structure, which is conducive to the application of chitosan membranes in nanofiltration. Moreover, the MOFs particles in the support can increase the water flux of the entire membrane. DETAILED DESCRIPTION

[0016] The present invention is further described below with reference to examples, but the protection scope of the present invention is not limited thereto.

[0017] Example 1 (1-1) 20 wt% polyethersulfone, 0.5 wt% polyvinylpyrrolidone, MOFs nanoparticles (average particle size of 87 nm) and NN-dimethylacetamide were mixed and allowed to stand for degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then placed in a coagulation bath of pure water for immersion to achieve phase inversion; (1-3) drying at 60°C to form a support; (2-1) Chitosan was dissolved in acetic acid solution, and fumaric acid and ZrOCl2·8H2O were added in sequence, reacted at 70°C for 2 h, and allowed to stand for degassing to form a casting solution, wherein the concentration of chitosan in the casting solution was 3 wt%, the concentration of acetic acid was 2.5 wt%, the concentration of fumaric acid was 0.2 wt%, and the concentration of ZrOCl2 was 0.55 wt%; (2-2) Laying the support body flat on the bottom of the container, pouring the casting liquid evenly on the surface of the support body, and placing it at 50°C to continue the closed reaction for 4 hours to form a chitosan film; (3) The chitosan membrane is further placed in a 0.2 wt % organic solution of trimesoyl chloride for cross-linking for 10 min to obtain a nanofiltration membrane.

[0018] Comparative Example 1 (1-1) 20 wt% polyethersulfone, 0.5 wt% polyvinylpyrrolidone and NN dimethylacetamide were mixed and allowed to stand for degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then placed in a coagulation bath of pure water for immersion to achieve phase inversion; (1-3) drying at 60°C to form a support; (2-1) Chitosan was dissolved in acetic acid solution, and fumaric acid and ZrOCl2·8H2O were added in sequence, reacted at 70°C for 2 h, and allowed to stand for degassing to form a casting solution, wherein the concentration of chitosan in the casting solution was 3 wt%, the concentration of acetic acid was 2.5 wt%, the concentration of fumaric acid was 0.2 wt%, and the concentration of ZrOCl2 was 0.55 wt%; (2-2) Laying the support body flat on the bottom of the container, pouring the casting liquid evenly on the surface of the support body, and placing it at 50°C to continue the closed reaction for 4 hours to form a chitosan film; (3) The chitosan membrane is further placed in a 0.2 wt % organic solution of trimesoyl chloride for cross-linking for 10 min to obtain a nanofiltration membrane.

[0019] Comparative Example 2 (1-1) 20 wt% polyethersulfone, 0.5 wt% polyvinylpyrrolidone, MOFs nanoparticles (average particle size of 87 nm) and NN-dimethylacetamide were mixed and allowed to stand for degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then placed in a coagulation bath of pure water for immersion to achieve phase inversion; (1-3) drying at 60°C to form a support; (2-1) Chitosan was dissolved in acetic acid solution, and fumaric acid and ZrOCl2·8H2O were added in sequence, and the mixture was reacted at 70°C for 6 h. The mixture was allowed to stand for degassing to form a casting solution, in which the concentration of chitosan was 3 wt%, the concentration of acetic acid was 2.5 wt%, the concentration of fumaric acid was 0.2 wt%, and the concentration of ZrOCl2 was 0.55 wt%; (2-2) pouring the casting solution evenly on the surface of the support, and drying it at room temperature to form a chitosan film; (3) The chitosan membrane is further placed in a 0.2 wt % organic solution of trimesoyl chloride for cross-linking for 10 min to obtain a nanofiltration membrane.

[0020] Comparative Example 3 (1-1) 20 wt% polyethersulfone, 0.5 wt% polyvinylpyrrolidone, MOFs nanoparticles (average particle size of 87 nm) and NN-dimethylacetamide were mixed and allowed to stand for degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then placed in a coagulation bath of pure water for immersion to achieve phase inversion; (1-3) drying at 60°C to form a support; (2-1) Chitosan was dissolved in acetic acid solution, and fumaric acid and ZrOCl2·8H2O were added in sequence, reacted at 70°C for 4 h, and allowed to stand for degassing to form a casting solution, in which the concentration of chitosan was 3wt%, the concentration of acetic acid was 2.5wt%, the concentration of fumaric acid was 0.2wt%, and the concentration of ZrOCl2 was 0.55wt%; (2-2) Laying the support body flat on the bottom of the container, pouring the casting liquid evenly on the surface of the support body, and placing it at 50°C to continue the closed reaction for 2 hours to form a chitosan film; (3) The chitosan membrane is further placed in a 0.2 wt % organic solution of trimesoyl chloride for cross-linking for 10 min to obtain a nanofiltration membrane.

[0021] The nanofiltration membranes prepared in the above examples and comparative examples were subjected to separation experiments at 25°C and 0.6MPa with 1g / L magnesium chloride. (1) The separation data of the nanofiltration membranes were tested after 1 hour of testing. (2) The nanofiltration membranes were flushed under a water flow pressure of 10MPa for 12 hours, and then the separation performance of the nanofiltration membranes was continuously tested. The characterization results are shown in the following table: Table 1 Characterization results of different embodiments and comparative examples The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a chitosan composite nanofiltration membrane, characterized in that The steps include: (1) Preparation of ultrafiltration membrane support doped with MOFs nanoparticles; (2) pouring a casting solution containing fumaric acid, ZrOCl2·8H2O, chitosan, and acetic acid on the surface of the support to form a chitosan film containing MOFs particles; (3) The chitosan membrane is further placed in an organic solution of trimesoyl chloride for cross-linking, thereby obtaining a nanofiltration membrane.

2. The method according to claim 1, characterized in that The ultrafiltration membrane is prepared by the following steps: (1-1) mixing a membrane-forming polymer, an additive, MOFs nanoparticles and a solvent, and performing degassing to form an ultrafiltration membrane casting solution; (1-2) The ultrafiltration membrane casting solution is evenly scraped onto a glass plate and then immersed in a coagulation bath for phase inversion; (1-3) Drying to form a film.

3. The method according to claim 2, characterized in that The mass contents of the film-forming polymer, the additive and the MOFs nanoparticles in the ultrafiltration membrane casting solution are 15-35wt%, 0.5-3wt% and 0.5-10wt% respectively.

4. The method according to claim 2, characterized in that The MOFs particles are MOF-81, the film-forming polymer is one or more of polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polytetrafluoroethylene, and polyvinylidene fluoride; and the additive is one of polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and lithium chloride.

5. The method according to claim 1, characterized in that The casting solution in step (2) is prepared by the following steps: (2-1) Dissolve chitosan in acetic acid solution, and add fumaric acid and ZrOCl2·8H2O in sequence, react at 60-80°C for 1-2h, and stand for degassing to form a casting solution; (2-2) Lay the support body flat on the bottom of the container, pour the casting liquid evenly on the surface of the support body, and place it at 40-60°C to continue reacting for 2-5 hours to form a film.

6. The method according to claim 5, characterized in that The concentration of chitosan in the casting solution is 2-5wt%, the concentration of acetic acid is 2-5wt%, the concentration of fumaric acid is 0.05-0.5wt%, and the concentration of ZrOCl2·8H2O is 0.1-1.5wt%.

7. The method according to claim 1, characterized in that In step (3), the concentration of trimesoyl chloride is 0.05-0.5wt%, and the cross-linking time is 5-20min.

8. A chitosan composite nanofiltration membrane prepared according to the method of claim 1, characterized in that The invention comprises an ultrafiltration membrane support and a chitosan nanofiltration layer, wherein MOFs particles are mixed and doped inside the ultrafiltration membrane support and inside the chitosan nanofiltration layer respectively.

9. Use of the chitosan composite nanofiltration membrane according to claim 1 in the field of water treatment.

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