Nanofiltration membrane preparation method based on spinning nozzle chemistry

Abstract

The invention provides a nanofiltration membrane preparation method based on spinning nozzle chemistry, belongs to the technical field of nanofiltration membrane manufacturing and processing, and aims at solving the technical problems that a nanofiltration membrane preparation technology is tedious, the reproducibility is poor, a separation layer is thick and the like. The method comprises the following steps: adding a cationic polyelectrolyte polymer, polyether sulfone (PES), a solvent and an additive into a stirring kettle, stirring, and heating to 60-70 DEG C to obtain a functional membrane casting solution; the preparation method comprises the following steps: adding an anionic polyelectrolyte polymer containing an amino group, an amine crosslinking agent, a solvent and an additive into a stirring kettle, and uniformly stirring and mixing to obtain functional core liquid; co-extruding the obtained functional casting membrane solution and the functional core solution through a spinning nozzle, and simultaneously carrying out phase inversion, polyelectrolyte and amino crosslinking to form a hollow fiber membrane with a compact nano-pore separation layer; according to the invention, synchronous molding of the base membrane and the functional separation layer of the nanofiltration membrane is realized by using an integrated membrane forming technology, and the preparation method has the advantages of simple preparation process, low cost, good separation performance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofilter membrane manufacturing and processing, and specifically to a method for preparing a nanofilter membrane based on spinneret chemistry. Background Art

[0002] As an emerging membrane separation technology, nanofiltration has the advantages of high selective separation efficiency, low energy consumption, environmental protection, etc., and is gradually replacing some traditional separation technologies with high energy consumption, high pollution, and complex processes. Nanofiltration is a pressure-driven membrane separation technology between ultrafiltration and reverse osmosis. The effective pore size of the nanofilter membrane is ≤2 nm, and the molecular cut-off is 200 - 1000 Da. The surface of the nanofilter membrane generally has a charge property, and it separates salts and organic substances with different valences through charge effect and pore size screening effect. With its unique separation characteristics, the nanofiltration separation technology has now been widely used in fields such as petrochemical industry, biopharmaceuticals, printing and dyeing wastewater treatment, brackish water desalination, and heavy metal removal.

[0003] Traditional zwitterionic nanofilter membranes have low flux, and it is not easy to prepare an ultrathin, uniform, and dense active layer on the hollow fiber substrate membrane. To solve the problems existing in the prior art, the invention with the publication number CN114471181B discloses a method for preparing a highly permeable zwitterionic hollow fiber nanofilter membrane (hereinafter referred to as the prior art 1), and its preparation steps include: ① soaking the hollow fiber substrate membrane with an aqueous solution containing inorganic salts and polyamines, ② removing the residual aqueous solution by gas blowing or solvent flushing, ③ soaking the hollow fiber substrate membrane in an organic phase solution containing polyacyl chloride to carry out an interfacial polymerization reaction;

[0004] The zwitterionic hollow fiber nanofilter membrane prepared in the prior art 1 has high flux, rejection rate, and excellent anti-fouling performance; however, the hollow fiber nanofilter membrane in the prior art 1 requires multiple impregnation and cleaning steps during the preparation process, with poor efficiency; the bonding strength between the hollow fiber substrate and the nanofilter layer is low, and interfacial peeling is likely to occur; and a large amount of organic solvents are used for soaking or injecting into the hollow fiber tube, resulting in high costs and other problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a nanofilter membrane based on spinneret chemistry, which can realize the synchronous formation of the spinning substrate membrane and the functional layer during actual use, and solve the problems of cumbersome traditional process steps and high costs.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for preparing a nanofilter membrane based on spinneret chemistry, comprising the following steps:

[0008] Step 1: Preparation of casting solution. A basic casting solution is prepared and a cationic polyelectrolyte polymer and a functional modification additive are added thereto to form a casting solution.

[0009] Step 2: Preparation of core solution. A basic core solution is prepared and an anionic polyelectrolyte polymer containing an amino group, an amine crosslinking agent and other functional additives are added thereto to form a core solution.

[0010] Step 3: Crosslinking and integrated film formation. The casting solution and the core solution in Steps 1 and 2 are co-extruded through the casting solution chamber (103) and the core solution chamber (104) of a spinneret, and polyelectrolyte and amine crosslinking occur in the inner cavity of the formed hollow fiber membrane to form a dense nanoporous separation layer.

[0011] Step 4: Curing and forming. The hollow structure extruded in Step 3 passes through an air gap and is solidified to form a nascent hollow fiber membrane, and then through cleaning, soaking, drying and winding, etc., the target nanofiltration membrane can be obtained.

[0012] Wherein, the basic casting solution is composed of a polymer and a solvent, and the basic core solution is composed of water and a solvent.

[0013] Preferably, in Step 1, the polymer is PES and the solvent is one of DMAc, DMF and DMSO.

[0014] Preferably, in Step 1, the cationic polyelectrolyte polymer is PAH or PEI.

[0015] Preferably, in Step 1, the functional modification additive includes a hydrophilic additive, a pore size regulator and a viscosity regulator.

[0016] Preferably, in Step 2, the anionic polyelectrolyte polymer is PSS and PVS, and the amine crosslinking agent is GA.

[0017] Preferably, in Step 1, the mass fraction of the polymer is 15-20 wt%, the mass fraction of the solvent is 60-80 wt%, the mass fraction of the cationic polyelectrolyte polymer is 1-10 wt%, and the mass fraction of the functional modification additive is 10-12 wt%.

[0018] Preferably, in Step 2, the mass percentage of the solvent is 40-50 wt%, the mass percentage of water is 30-50 wt%, the mass percentage of glycerol is 0-30 wt%, the mass percentage of GA is 1-10 wt%, and the mass percentage of PSS is 1-10 wt%.

[0019] Preferably, the curing and forming in step 4 includes that the temperature of the casting solution is 60°C - 70°C, the vacuum degassing time is 10h - 16h, the pressures of the casting solution and the core solution are 0.1 - 0.3 MPa, the winding speed is 10 - 30 m / min, and the air gap is 1 - 5 cm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] In this embodiment, the core solution contains a negatively charged polyelectrolyte PSS and an amine crosslinking agent GA, and the functional modification additive added to the casting solution contains PEI, and the PEI is a positively charged amino-containing weak electrolyte; the ionic crosslinking between the polyelectrolytes with opposite charges is superimposed with the covalent crosslinking for the first time, and at the same time, the phase inversion of the inert film to form a polymer occurs, so that the composite nanofiltration hollow fiber membrane with crosslinked polyelectrolytes can be manufactured in a one-step process;

[0022] The ionic crosslinking between the PSS and the PEI is combined with the covalent crosslinking of the PEI, and then a required polymer selective layer is formed on the surface of the lumen channel in the hollow fiber tube formed by the spinneret; by precisely controlling the flow rates of the casting solution and the inner layer core solution, precise polymerization is carried out to avoid material waste; in actual use, the polymer selective layer can separate different valence salts and organic substances in the liquid entering the hollow fiber, and has a high rejection rate for salts, a high burst pressure, and a molecular cut-off amount lower than 350 Da;

[0023] Moreover, by synchronously extruding the substrate and the functional layer through the spinneret, the use of organic solvents is reduced by about 40 - 60% compared with the interfacial polymerization in the later stage of the prior art; among them, on the one hand, the precise use of polymer monomers in the spinneret chemistry reduces the solvent by about 30 - 40%, and on the other hand, the regulation of the functional modification additive and other functional additives reduces the solvent by about 10 - 15%; and multiple impregnation and cleaning treatment steps are omitted. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a three-dimensional view of the spinneret in the present invention.

[0026] Figure 2 It is a structural schematic diagram of the spinneret in the present invention.

[0027] In the drawings, the list of components represented by each reference numeral is as follows:

[0028] 101 - outer shell, 102 - inner shell, 103 - casting solution chamber, 104 - core liquid chamber, 105 - casting solution pipe, 106 - core liquid pipe. Specific Embodiments

[0029] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the embodiments of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than restrictive.

[0030] In the description of the embodiments of the present invention, it should be understood that the orientation or positional relationships indicated by terms such as "length", "vertical", "horizontal", "top", "bottom", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the embodiments of the present invention.

[0031] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0032] In the embodiments of the present invention, unless otherwise clearly specified and limited, terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, an electrical connection, or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0033] In the embodiments of the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may include direct contact between the first and second features, or may include indirect contact between the first and second features through additional features therebetween. Moreover, the first feature being "above", "over" and "on top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is lower than that of the second feature.

[0034] The following disclosure provides many different embodiments or examples for implementing different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the embodiments of the present invention. In addition, the embodiments of the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed.

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] Embodiment 1

[0037] Refer to Figure 1 - Figure 2 , this embodiment discloses a method for preparing a nanofiltration membrane, specifically a method for preparing a nanofiltration membrane based on spinneret chemistry, including the following steps:

[0038] Step 1: Preparation of the casting solution, preparing a basic casting solution, and adding a cationic polyelectrolyte polymer and a functional modification additive thereto;

[0039] Step 2: Preparation of the core solution, preparing a basic core solution, and adding an anionic polyelectrolyte polymer containing an amino group, an amine crosslinking agent and other functional additives thereto to form a core solution;

[0040] Step 3: Crosslinking and integrated film formation, co-extruding the casting solution and the core solution in steps 1 and 2 through the casting solution chamber (103) and the core solution chamber (104) of the spinneret, and forming a dense nanoporous separation layer by polyelectrolyte and amine crosslinking in the inner cavity of the formed hollow fiber membrane;

[0041] Step 4: Curing and forming, subjecting the hollow structure extruded in step 3 to an air gap and solidification to form a primary hollow fiber membrane, and then obtaining the target nanofiltration membrane through washing, soaking, drying and winding the fiber, etc.;

[0042] Among them, the basic casting solution is composed of a polymer and a solvent, and the basic core solution is composed of water and a solvent.

[0043] In this embodiment, the core solution includes an anionic polyelectrolyte polymer containing an amino group and a crosslinking agent, and the casting solution includes a cationic polyelectrolyte polymer; the ionic crosslinking between the anionic polyelectrolyte polymer and the cationic polyelectrolyte polymer with opposite charges is superimposed on the covalent crosslinking for the first time, and at the same time, the phase inversion of the inert membrane-forming polymer occurs, so that the composite nanofiltration hollow fiber membrane with crosslinked polyelectrolytes can be manufactured in a one-step process; the polymer precipitates in the form of an inversed-induced porous support structure during the reaction; after the cationic polyelectrolyte polymer diffuses out of the casting solution, it can form a polyelectrolyte complex with the anionic polyelectrolyte polymer in the core solution on the membrane surface. At the same time, the amine crosslinking agent in the core solution crosslinks the amino groups of the cationic polyelectrolyte polymer molecules; the ionic crosslinking between the anionic polyelectrolyte polymer and the cationic polyelectrolyte polymer is combined with the covalent crosslinking of the cationic polyelectrolyte polymer to form the required selective layer on the surface of the lumen channel in the hollow fiber tube formed by the spinneret; by precisely controlling the flow rates of the casting solution and the inner core solution and precisely polymerizing, material waste is avoided; in actual use, the selective layer can separate different valence salts and organic substances in the liquid entering the hollow fiber, has a high salt rejection rate, a high burst pressure, and a molecular cut-off of less than 350 Da; and by extruding through the spinneret, the support layer and the separation layer are formed synchronously, and online crosslinking and polymerization can be realized to enhance the bonding strength; the materials for interfacial polymerization are precisely dispersed in the casting solution and the core solution, reducing the use of organic solvents by about 40-60% compared with the later interfacial polymerization in the prior art; among them, on the one hand, the precise use of polymer monomers in the spinneret chemistry reduces the solvent by about 30-40%, and on the other hand, the regulation of functional modification additives and other functional additives reduces the solvent by about 10-15%; and multiple impregnation and cleaning treatment steps are omitted, and there are no volatile by-products during the curing process; in this embodiment, the other functional additives are water, PEG, EG, etc.

[0044] Among them, in step 1, the polymer is PES, and the solvent is one of DMAc, DMF, and DMSO. The PES is polyethersulfone, the DMAc is N,N-dimethylacetamide, the DMF is N-methylpyrrolidone, and the DMSO is dimethyl sulfoxide; in this embodiment, the solvent is DMF (N-methylpyrrolidone).

[0045] Further optimized, in step 1, the cationic polyelectrolyte polymer is PAH or PEI. The PAH is polyallylamine hydrochloride, and the PEI is polyethyleneimine; in this embodiment, the cationic polyelectrolyte polymer is polyethyleneimine (PEI).

[0046] For further optimization, the functional modification additives described in step 1 include hydrophilic additives, pore size regulators, and viscosity regulators. In this embodiment, the hydrophilic additive is polyethylene glycol PEG400 or Tween 80, the pore size regulator is lithium chloride LiCl, and the viscosity regulator is glycerol; among them, the PEG400 is polyethylene glycol with a molecular weight of 400 (Da); in step 1, the ratio of glycerol, PEG, and PEI is 5:1:2.

[0047] Among them, the anionic polyelectrolyte polymer described in step 2 is sodium polystyrene sulfonate (PSS) and potassium polyvinyl sulfonate (PVS); the amine crosslinking agent is glutaraldehyde (GA). The PSS is sodium polystyrene sulfonate, the PVS is potassium polyvinyl sulfonate, and the GA is glutaraldehyde.

[0048] For further optimization, in step 1, the mass fraction of the polymer is 15 - 20 wt%, the mass fraction of the solvent is 60 - 80 wt%, the mass fraction of the cationic polyelectrolyte polymer is 1 - 10 wt%, and the mass fraction of the functional modification additive is 10 - 12 wt%.

[0049] Among them, in step 2, the mass percentage of the solvent is 40 - 50 wt%, the mass percentage of water is 30 - 50 wt%, the mass percentage of glycerol is 0 - 30 wt%, the mass percentage of GA is 1 - 10 wt%, and the mass percentage of PSS is 1 - 10 wt%.

[0050] For further optimization, the curing and forming in step 4 includes that the temperature of the casting solution is 60°C - 70°C, the vacuum degassing time is 10 h - 16 h, the pressure of the casting solution and the core liquid is 0.1 - 0.3 MPa, the winding speed is 10 - 30 m / min, and the air gap is 1 - 5 cm. Pressurizing the casting solution and the core liquid can greatly improve the production efficiency of the hollow fiber filaments. By adjusting the length of the air gap, the evaporation rate of the solvent can be controlled;

[0051] Among them, in step 1, before preparing the casting solution, PES is vacuum dried at 30°C for 24 h to remove the moisture in the polymer and improve the quality of the membrane product; the casting solution after vacuum degassing needs to be filtered through a casting solution filter before being injected into the spinneret to remove the dust, uncompletely dissolved polymer particles, and additive agglomerates that may be mixed in the casting solution, and to avoid the appearance of pinholes, defects, or uneven structures on the surface of the generated hollow fiber tube, and to improve the separation efficiency, mechanical strength, and service life of the hollow fiber tube; in this embodiment, the casting solution filter is a 40 μm filtering device in the prior art, and the structure and function of the filter will not be elaborated one by one here.

[0052] For further optimization, in step 4, after the hollow fiber tube enters the coagulation bath, it is washed with water at 60°C for 24 h, stabilized with 5% glycerol for 24 h, and then air-dried at room temperature. Washing the hollow fiber tube with water at 60°C for 24 h at a high temperature is to elute the solvent in the hollow fiber membrane, and soaking it in glycerol is to prevent the membrane pores in the hollow fiber membrane from collapsing.

[0053] Example 2

[0054] In this example, the casting solution includes a polymer (PES) with a mass fraction of 18 wt%, a solvent (NMP) with a mass fraction of 66 wt%, a cationic polyelectrolyte polymer (PEI) with a mass fraction of 4 wt%, glycerol with a mass fraction of 10 wt%, and PEG400 with a mass fraction of 2 wt%; the core liquid includes water with a mass fraction of 30 wt%, a solvent with a mass fraction of 40 wt%, and glycerol with a mass fraction of 30 wt%; wherein, the flow rate of the casting solution pumped into the casting solution chamber is 4.5 mL / min, the flow rate of the core liquid pumped into the core liquid chamber is 2 mL / min, the wire drawing speed is 5 m / min, and the air gap is 1 cm.

[0055] Example 3

[0056] In this example, the casting solution includes a polymer (PES) with a mass fraction of 18 wt%, a solvent (NMP) with a mass fraction of 66 wt%, a cationic polyelectrolyte polymer (PEI) with a mass fraction of 4 wt%, glycerol with a mass fraction of 10 wt%, and PEG400 with a mass fraction of 2 wt%; the core liquid includes water with a mass fraction of 40 wt%, a solvent with a mass fraction of 50 wt%, and an amine cross-linking agent (GA) with a mass fraction of 10 wt%; wherein, the flow rate of the casting solution pumped into the casting solution chamber is 4.5 mL / min, the flow rate of the core liquid pumped into the core liquid chamber is 2 mL / min, the wire drawing speed is 5 m / min, and the air gap is 1 cm; wherein, the flow rate of the casting solution pumped into the casting solution chamber is 4.5 mL / min, the flow rate of the core liquid pumped into the core liquid chamber is 2 mL / min, the wire drawing speed is 5 m / min, and the air gap is 1 cm.

[0057] Example 4

[0058] In this example, the casting solution includes a polymer (PES) with a mass fraction of 18 wt%, a solvent (NMP) with a mass fraction of 66 wt%, a cationic polyelectrolyte polymer (PEI) with a mass fraction of 4 wt%, glycerol with a mass fraction of 10 wt%, and PEG400 with a mass fraction of 2 wt%; the core liquid includes water with a mass fraction of 40 wt%, a solvent with a mass fraction of 45 wt%, an amine crosslinking agent (GA) with a mass fraction of 5 wt%, and sodium polystyrene sulfonate (PSS) with a mass fraction of 10 wt%. Among them, the flow rate of the casting solution pumped into the casting solution chamber is 4.5 mL / min, the flow rate of the core liquid pumped into the core liquid chamber is 2 mL / min, the wire drawing speed is 5 m / min, and the air gap is 1 cm.

[0059] Example Five

[0060] In this example, the casting solution includes a polymer (PES) with a mass fraction of 18 wt%, a solvent (NMP) with a mass fraction of 66 wt%, a cationic polyelectrolyte polymer (PEI) with a mass fraction of 4 wt%, glycerol with a mass fraction of 10 wt%, and PEG400 with a mass fraction of 2 wt%; the core liquid includes water with a mass fraction of 50 wt%, a solvent with a mass fraction of 45 wt%, an amine crosslinking agent (GA) with a mass fraction of 2 wt%, and sodium polystyrene sulfonate (PSS) with a mass fraction of 3 wt%. Among them, the flow rate of the casting solution pumped into the casting solution chamber is 2.5 mL / min, the flow rate of the core liquid pumped into the core liquid chamber is 2 mL / min, the wire drawing speed is 3 m / min, and the air gap is 1 cm.

[0061] Among them, Table 1 shows the effect comparison of Examples 2 to 5:

[0062]

[0063] Table 2 shows the performance comparison between Example 4 and the products of foreign manufacturers:

[0064]

[0065]

[0066] As shown in Table 1, by comparing Examples 2 to 5 above, it can be seen that under the condition that the components of the casting solution and the air gap remain unchanged; in Example 4, when the mass fraction of water in the core liquid is 40 wt%, the mass fraction of the solvent is 45 wt%, the mass fraction of glycerol is 0 wt%, the mass fraction of GA is 5 wt%, and the mass fraction of PSS is 10 wt%; the flux of the prepared nanofiltration membrane is 24, the molecular weight cut-off is 320 Da, the CaCl2 rejection rate > 95%, the MgSO4 rejection rate > 95%, and the NaCl rejection rate > 80%; thus, it can be known that the molecular weight cut-off and rejection rate of the nanofiltration membrane prepared by the technical solution described in Example 4 are the highest, which is the preferred solution.

[0067] As shown in Table 2, compared with the nanofiltration membranes produced in the European and American environments (such as NX Filtration, etc.), the flux, molecular weight cut-off, and rejection rate of the nanofiltration membrane prepared by the technical solution described in Example 4 are the highest, which is the preferred solution.

[0068] Example 6

[0069] See Figure 1 - Figure 2 , this example is a further optimization based on Example 1. Based on the above-described method for preparing a nanofiltration membrane based on spinneret chemistry, this example also describes a spinneret, which includes an outer shell 101 and an inner shell 102 coaxially arranged with the outer shell 101. A casting solution chamber 103 is formed between the outer shell 101 and the inner shell 102, and the casting solution chamber 103 is used to extrude the casting solution. A core liquid chamber 104 is arranged in the inner shell 102, and the core liquid chamber 104 is used to extrude the core liquid; the core liquid in the core liquid chamber 104 and the casting solution in the casting solution chamber 103 each contain substances to be polymerized. By precisely controlling the flow rates of the casting solution and the inner layer core liquid, precise polymerization can be achieved, avoiding material waste; a casting solution pipe 105 communicating with the casting solution chamber 103 is connected to the outer shell 101, and a core liquid pipe 106 communicating with the core liquid chamber 104 is connected to the inner shell 102.

[0070] Among them, the outer shell 101 gradually converges in the direction towards the inner shell 102 at the discharge port end, so that the flow direction of the outer layer casting solution can converge inward under the guidance of the outer shell 101. The inclined extrusion can enable the casting layer to preferentially contract inward in the air gap, forming a denser skin layer; at the same time, the inner layer core liquid forms a stable laminar flow contact interface, increasing the contact area and fitting pressure between the casting solution and the core liquid, and promoting the reaction of the polymer at the interface.

[0071] For further optimization, the bottom end of the outer shell 101 is located below the bottom end of the inner shell 102, and the casting solution cavity 103 extends 0.5 - 1 mm more than the core liquid cavity 104, so as to form a delayed contact area between the discharge port of the casting solution cavity 103 and the discharge port of the core liquid cavity 104, avoiding the premature mixing of the casting solution and the core liquid during extrusion.

[0072] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0073] The above description is only for the preferred embodiments of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nanofiltration membrane based on spinneret chemistry, characterized in that: The following steps are involved: Step 1: preparing a casting solution, preparing a basic casting solution, and adding a cationic polyelectrolyte polymer and a functional modification additive to the basic casting solution; Step 2: core liquid preparation, preparing a basic core liquid, and adding an anionic polyelectrolyte polymer containing an amino group, an amine cross-linking agent and other functional additives into the basic core liquid to prepare the core liquid; Step 3: cross-linking and integrated membrane formation, the casting liquid and the core liquid of step 1 and step 2 are co-extruded through the casting liquid cavity (103) and the core liquid cavity (104) of the spinneret, and polyelectrolyte and amine cross-linking occur in the inner cavity of the hollow fiber membrane to form a dense nanoporous separation layer; Step 4: solidification and molding, the hollow structure extruded in step 3 is solidified through air gap to form a primary hollow fiber membrane, and then the target nanofiltration membrane is obtained by washing, soaking, drying and winding; Among them, the basic casting liquid is composed of a high molecular polymer and a solvent, and the basic core liquid is composed of water and a solvent.

2. A method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 1, characterized in that: The high molecular polymer in step 1 is PES, and the solvent is one of DMAc, DMF and DMSO.

3. A method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 2, characterized in that: The cationic polyelectrolyte polymer in step 1 is PAH or PEI.

4. A method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 3, characterized in that: The functional modification additives in step 1 include hydrophilic additives, pore size regulators and viscosity regulators.

5. The method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 1, characterized in that: The anionic polyelectrolyte polymers in step 2 are PSS and PVS, and the amine cross-linking agent is GA.

6. A method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 4, characterized in that: In step 1, the mass fraction of the polymer is 15-20 wt %, the mass fraction of the solvent is 60-80 wt %, the mass fraction of the cationic polyelectrolyte polymer is 1-10 wt %, and the mass fraction of the functional modification additive is 10-12 wt %.

7. A method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 5, characterized in that: In step 2, the mass percentage of the solvent is 40-50wt%, the mass percentage of water is 30-50wt%, the mass percentage of glycerol is 0-30wt%, the mass percentage of GA is 1-10wt%, and the mass percentage of PSS is 1-10wt%.

8. The method for preparing a nanofiltration membrane based on spinneret chemistry according to claim 1, characterized in that: The curing molding in step 4 includes a casting liquid temperature of 60°C-70°C, a vacuum degassing time of 10h-16h, a casting liquid and core liquid pressure of 0.1-0.3MPa, a winding speed of 10-30m / min, and an air gap of 1-5cm.

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