Search

CN-122006510-A - Neutral hollow fiber nanofiltration membrane and preparation method thereof

CN122006510ACN 122006510 ACN122006510 ACN 122006510ACN-122006510-A

Abstract

The invention discloses a neutral hydrophilic modified hollow fiber nanofiltration membrane and a preparation method thereof, the nanofiltration membrane is provided with an inner layer supporting layer and an outer layer separating layer, and is prepared by adopting an integral molding process. The inner layer support layer is of a spongy pore structure and consists of a hydrophobic polymer and a negatively charged polymer, and the outer layer separation layer is formed by the electrostatic action of a positively charged water-soluble polymer and an inner layer negatively charged substrate. The preparation adopts a double-layer spinneret plate coextrusion technology, the inner and outer layer casting film liquid is synchronously extruded, and enters a coagulating bath through an air gap to be subjected to phase inversion molding, so that the nanofiltration membrane is formed in situ. The porous sponge structure of the inner layer of the nanofiltration membrane prepared by the invention reduces mass transfer resistance, the outer separation layer ensures high interception performance, the outer surface of the membrane is electrically neutral, the anti-pollution performance of the membrane is obviously improved, the process is simple and easy to continuously produce, and the porous sponge structure has the advantages of high flux, high interception and long-acting stability.

Inventors

  • DING FANG

Assignees

  • 南通大学

Dates

Publication Date
20260512
Application Date
20260329

Claims (10)

  1. 1. The neutrality hydrophilic modified hollow fiber nanofiltration membrane is characterized by comprising an inner support layer and an outer separation layer, wherein the inner support layer and the outer separation layer are prepared through an integral molding process; the inner layer support layer is provided with a gradient spongy pore structure, and the pore diameter of the inner layer support layer is gradually dense from inside to outside; The outer separation layer comprises a positively charged water-soluble high polymer, and is formed by electrostatic interaction between the positively charged water-soluble high polymer and the negatively charged polymer of the inner support layer.
  2. 2. The neutrally charged hydrophilically modified hollow fiber nanofiltration membrane of claim 1, wherein the surface Zeta potential absolute value of the outer separation layer is less than 5 mV at pH 3-10.
  3. 3. The neutrally charged hydrophilically modified hollow fiber nanofiltration membrane of claim 1, wherein the outer separation layer has a thickness of 0.05-0.6 μm.
  4. 4. The neutrally charged hydrophilically modified hollow fiber nanofiltration membrane of claim 1, wherein the hydrophobic high molecular polymer is selected from at least one of Polyethersulfone (PES) and polysulfone (PSf), and the negatively charged polymer is selected from at least one of Sulfonated Polyethersulfone (SPES) and sulfonated polysulfone (SPSf).
  5. 5. The neutrally charged hydrophilically modified hollow fiber nanofiltration membrane of claim 4, wherein the sulfonated polyethersulfone or sulfonated polysulfone has a sulfonation degree of 0.1-0.3.
  6. 6. The neutrally charged hydrophilically-modified hollow fiber nanofiltration membrane of claim 4, wherein the positively charged water-soluble high molecular polymer is selected from at least one of chitosan, quaternized chitosan, and polyethyleneimine.
  7. 7. The preparation method of the neutrality hydrophilic modified hollow fiber nanofiltration membrane is characterized by at least comprising the following preparation steps: step 1, preparing an inner layer casting solution, namely dissolving a hydrophobic high molecular polymer, a negatively charged polymer and a pore-forming agent in a first solvent to form the inner layer casting solution; step 2, preparing an outer separation layer feed liquid, namely dissolving positively charged water-soluble polymers in a second solvent to form the outer separation layer feed liquid; step 3, double-layer spinneret coextrusion, namely extruding the inner layer casting film liquid prepared in the step 1 through an inner layer runner of a spinneret, extruding the outer layer separation layer liquid prepared in the step 2 through an outer layer runner of the spinneret, and introducing core liquid into the center of the spinneret; Step 4, forming a fiber membrane, namely enabling extruded nascent fibers to enter a coagulation bath after passing through an air gap, performing phase inversion forming, forming a loose sponge supporting structure on an inner layer, diffusing negatively charged polymers in the inner layer to the direction of an outer layer, and performing electrostatic interaction with positively charged polymers in feed liquid of the outer layer to form an electrically neutral separating layer; and 5, post-treatment, namely washing and post-treatment to obtain the neutral hydrophilic modified hollow fiber nanofiltration membrane.
  8. 8. The method for preparing the neutrally charged hydrophilic modified hollow fiber nanofiltration membrane according to claim 7, wherein the inner layer casting solution in the step 1 comprises 14-18% of hydrophobic high molecular polymer, 1-3% of negatively charged polymer, 10-30% of pore-forming agent and 60-75% of first solvent by mass percent.
  9. 9. The method for preparing a neutrally charged hydrophilically modified hollow fiber nanofiltration membrane according to claim 7, wherein the pore-forming agent in step 1 is at least one selected from polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG).
  10. 10. The method for preparing a neutrally charged hydrophilically modified hollow fiber nanofiltration membrane according to claim 7, wherein the extrusion speed ratio of the inner layer casting solution to the outer layer separation layer solution in the step 3 is 3:1 to 8:1, and the method is used for controlling the thickness of the outer layer separation layer.

Description

Neutral hollow fiber nanofiltration membrane and preparation method thereof Technical Field The invention belongs to the technical field of separation membranes, and particularly relates to an electric neutral hollow fiber nanofiltration membrane and a preparation method thereof. Background The hollow fiber membrane has the advantages of high filling density, strong self-supporting capability, capability of realizing reverse cleaning and the like, becomes a main stream product form of a membrane separation technology, and is widely applied to the fields of water treatment, biological medicine, food processing and the like. At present, a hollow fiber membrane is mainly prepared by a phase inversion method, namely, a high polymer is dissolved in a solvent to form a casting solution, the casting solution is extruded by a spinneret plate and enters a coagulating bath after air gaps, and polymer precipitation solidification is realized through solvent and non-solvent exchange, so that a porous membrane with an asymmetric structure is formed. In order to improve the hydrophilicity and anti-pollution performance of the membrane, researchers often adopt methods such as blending modification or surface coating to introduce hydrophilic components, wherein sulfonated polymers (SPES, SPSf) can not only improve the hydrophilicity of the membrane, but also introduce negatively charged groups, and the anti-pollution performance is enhanced through electrostatic repulsion. However, the prior art still has a plurality of key defects: firstly, the separation layer and the supporting layer cannot be independently regulated and controlled by the traditional single-layer spinning process, typical flux and retention rate trade-off effects exist, and high flux and high retention rate are difficult to be considered; And secondly, the single charge modification can only repel the same charge pollutant, and the different charges are easy to pollute. The complex charge component feed liquid can not be dealt with, and the comprehensive pollution resistance is difficult to realize; thirdly, the surface coating is easy to cause membrane hole blocking and flux reduction, and the coating has weak binding force with the base membrane and is easy to strip after long-term operation. The blending modified hydrophilic agent is easy to run off and has insufficient surface enrichment. The surface grafting has complex process, high cost and easy damage to the structure of the membrane body; fourthly, the existing means are difficult to accurately regulate and control the surface charge of the membrane, the electric neutral surface cannot be stably constructed, and the fine separation requirement under the conditions of high salt and wide pH range cannot be met. Therefore, developing a hollow fiber nanofiltration membrane which can achieve high flux and high retention rate, realize comprehensive pollution resistance, has lasting modification effect and simple preparation process becomes a technical problem to be solved in the field. Disclosure of Invention In order to overcome the defects, the invention designs the neutral hydrophilic modified hollow fiber nanofiltration membrane, and the cooperative promotion of membrane flux and rejection rate is realized through the structural design of double-layer integrated molding, so that the problems of incomplete pollution resistance, hydrophilic modified sacrificial flux, non-lasting modification effect and the like of a single charged membrane are solved, and meanwhile, the preparation process is simplified, and continuous production is realized. In order to achieve the technical aim, the invention provides a neutral hydrophilic modified hollow fiber nanofiltration membrane, which comprises an inner support layer and an outer separation layer, wherein the inner support layer and the outer separation layer are prepared through an integral molding process; the inner layer support layer is provided with a gradient spongy pore structure, and the pore diameter of the inner layer support layer is gradually dense from inside to outside; The outer separation layer comprises a positively charged water-soluble high polymer, and is formed by electrostatic interaction between the positively charged water-soluble high polymer and the negatively charged polymer of the inner support layer. In some technical schemes of the invention, the absolute value of the Zeta potential of the surface of the outer separation layer is less than 5 mV within the pH range of 3-10, and the outer separation layer is electrically neutral. When Zeta potential is electrically neutral, the pollution to the membrane in the filtering process can be reduced. In some embodiments of the invention, the outer separation layer has a thickness of 0.05 to 0.6 μm. The thickness of the outer separation layer is increased, so that the separation effect can be improved but the water flux can be influenced, and the balance of the separation effect and the