Modified hollow fiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a modified hollow fiber membrane and a preparation method and application thereof.The preparation method comprises the steps that a PVDF hollow fiber membrane is vertically inserted into a cross-flow device, a PEI solution and a sodium lignin sulfonate solution are sequentially introduced into the cross-flow device for coordination cross-linking treatment, the surface of the membrane is washed after cross-linking, and modification of the hollow fiber membrane is achieved; a structural layer formed by sodium lignin sulfonate connected by sulfonamides and ether bonds is formed on the surface of the PVDF hollow fiber membrane, so that the anti-pollution capacity of the hollow fiber membrane and the separation performance of the hollow fiber membrane on specific substances are effectively improved, and the efficiency and the stability of the hollow fiber membrane in practical application are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface modification, and in particular relates to a modified hollow fiber membrane and a preparation method and application thereof. Background Art

[0002] Hollow fiber membranes are widely used in many fields such as water treatment, gas separation, and biomedicine due to their high specific surface area and good separation performance.

[0003] However, the original hollow fiber membranes often face some problems in practical applications, such as poor anti-pollution ability and insufficient affinity for specific substances, which limit the further improvement of their performance and the expansion of their application scope.

[0004] Currently, surface modification of hollow fiber membranes is an important means to address these issues. Traditional modification methods are either complex, requiring expensive equipment and tedious procedures; or the modified materials used are expensive, environmentally unfriendly, and the modification effect is difficult to achieve.

[0005] Therefore, it is of great practical significance to develop a simple, efficient, low-cost and environmentally friendly method for surface modification of hollow fiber membranes. Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a modified hollow fiber membrane.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: comprising:

[0010] PEI powder was added to deionized water and stirred to obtain a PEI solution;

[0011] Sodium lignin sulfonate powder is added to deionized water and stirred to obtain a sodium lignin sulfonate solution;

[0012] The PVDF hollow fiber membrane is vertically inserted into the cross-flow device, and the PEI solution and the sodium lignin sulfonate solution are successively introduced into the cross-flow device for coordination cross-linking treatment. After cross-linking, the membrane surface is rinsed to achieve the modification of the hollow fiber membrane.

[0013] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, the concentration of the PEI solution is 0.5 g / L to 2 g / L.

[0014] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, the concentration of the sodium lignin sulfonate solution is 2 g / L to 3.5 g / L.

[0015] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, PEI powder is added to deionized water and stirred at room temperature at a speed of 400 to 600 r / min for 2 to 4 hours to obtain a PEI solution.

[0016] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, sodium lignin sulfonate powder is added to deionized water and stirred at a speed of 200 to 300 r / min for 2 to 4 hours to obtain a sodium lignin sulfonate solution.

[0017] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, the flow rate of the PEI solution and the sodium lignin sulfonate solution into the cross-flow device is 50 to 100 L / h.

[0018] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, the sodium lignin sulfonate solution is introduced 5 to 15 minutes after the PEI solution is introduced.

[0019] As a preferred embodiment of the method for preparing the modified hollow fiber membrane of the present invention, the cross-linking treatment time of the sodium lignin sulfonate solution is 5 to 15 minutes.

[0020] Another object of the present invention is to provide a modified hollow fiber membrane having a structural layer formed on the surface of the PVDF hollow fiber membrane, comprising a sulfonamide and sodium lignin sulfonate connected by ether bonds, wherein the sulfonamide is generated by the reaction of the sulfonic acid groups of the sodium lignin sulfonate with the amino groups of PEI. The structural layer has a tightly entangled structure.

[0021] Another object of the present invention is to provide a modified hollow fiber membrane for use in the field of sewage treatment.

[0022] Beneficial effects of the present invention:

[0023] (1) Significant performance improvement: The anti-pollution ability and separation performance of the hollow fiber membrane for specific substances have been effectively improved, and its efficiency and stability in practical applications have been improved.

[0024] (2) The method is simple and efficient: the entire assembly process is easy to operate, the required equipment is simple and common, and the reaction time is short, which is conducive to large-scale industrial production.

[0025] (3) Low cost and environmental protection: PEI and sodium lignin sulfonate are widely available and relatively cheap, and the entire process does not use reagents harmful to the environment, which is in line with the concept of green chemistry and reduces production costs and environmental burden. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0027] Figure 1 These are test diagrams of the hollow fiber membranes of Example 1 and Comparative Example 1 for separating BSA solutions.

[0028] Figure 2 Graph showing the rejection rate and rejection flux of the hollow fiber membranes used in Example 1 and Comparative Example 1 for separating BSA solution.

[0029] Figure 3 This is a comparison diagram of the hollow fiber membranes of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0031] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0033] Unless otherwise specified, the raw materials used in the present invention are commonly available in the market.

[0034] Among them, bovine serum albumin (BSA) was purchased from Aladdin; sodium lignin sulfonate (SLS) was purchased from SigmaAldrich, PEI was purchased from Maclean, AR was analytical grade;

[0035] The PVDF hollow fiber membrane was made in the laboratory. The specific preparation method is as follows:

[0036] 14 wt% PVDF polymer was weighed and added to 86 wt% organic solvent (N,N-dimethylacetamide), stirred thoroughly, and heated at 70°C to completely dissolve the polymer to prepare a casting solution.

[0037] Then, a special spinneret is used to extrude the casting solution into a hollow shape, and at the same time, it enters a coagulation bath (water). After 24 hours of solvent and non-solvent exchange, the polymer is precipitated, and finally a PVDF hollow fiber membrane is obtained;

[0038] The present invention uses a cross-flow device (referenced in the utility model patent, "An Aeration Structure and Hollow Fiber Membrane Fiber Detection Device," publication number CN222331704U) to test the pure water permeability (PWP) of the membranes of each embodiment or comparative example at a transmembrane pressure (TMP) of 1 bar. Prior to testing, the membranes were pre-pressed with pure water at 2 bar for 20 minutes to ensure membrane stability. PWP was calculated using the following formula:

[0039] PWP=Q / (ΔP×A×t)

[0040] Where Q is the permeate volume of water (L), ΔP is the TMP (bar), and A is the effective area (m 2 ), t is the filtration time (min), where A is 12.3 cm 2 .

[0041] The retention of BSA by the membrane was tested at a transmembrane pressure (TMP) of 1 bar using a cross-flow system. The concentration of BSA was measured at 280 nm using a UV spectrophotometer. R was calculated using the following formula:

[0042]

[0043] Where R is the retention rate (%), C p is the permeate concentration (g·L -1 ), C f is the concentration of the original solution (g·L -1 ).

[0044] The membrane was tested for Cu ions at a transmembrane pressure (TMP) of 1 bar using a cross-flow system. 2+ 、Fe 3+ The concentration of CuCl2 was measured at 230 nm and the concentration of Fe was measured at 340 nm by UV spectrophotometer. 3+ The concentration, R, is calculated by the following formula:

[0045]

[0046] Where R is the retention rate (%), C p is the permeate concentration (g·L -1 ), C f is the concentration of the original solution (g·L -1 ).

[0047] Example 1

[0048] This embodiment provides a method for preparing a modified hollow fiber membrane, specifically:

[0049] 1) PEI powder was added to deionized water and stirred at 500 rpm for 3 h at room temperature to obtain a PEI solution with a concentration of 1 g / L.

[0050] 2) Sodium lignin sulfonate powder was added to deionized water and stirred at 250 r / min at room temperature for 3 h to obtain a sodium lignin sulfonate solution with a concentration of 3 g / L;

[0051] 3) A PVDF hollow fiber membrane with a length of 10 cm was vertically inserted into a cross-flow device, and 1000 ml of PEI solution and 1000 ml of sodium lignin sulfonate solution were taken. The PEI solution was first introduced at a cross-flow rate of 100 L / h for 10 minutes, and then the sodium lignin sulfonate solution was introduced at a cross-flow rate of 100 L / h for 10 minutes. After the cross-linking reaction was completed, the membrane surface was rinsed to remove the unreacted solution, thereby modifying the hollow fiber membrane to obtain the modified hollow fiber membrane of this embodiment, which was recorded as PEI-SLS membrane.

[0052] Comparative Example 1

[0053] The unmodified PVDF hollow fiber membrane is referred to as PVDF membrane.

[0054] Figure 1 The test diagram of the hollow fiber membrane separation of BSA solution in Example 1 and Comparative Example 1 is shown. Figure 2 The rejection rate and retention flux diagram of the hollow fiber membrane separation of BSA solution, Figure 3 This is a comparison chart of modified and unmodified hollow fiber membranes. It can be seen from the figure that the performance of the modified membrane is significantly improved, and the appearance color of the modified membrane has changed significantly, which proves that the modification is successful.

[0055] Comparative Example 2

[0056] Only hollow fiber membranes modified by PEI, specifically:

[0057] 1) PEI powder was added to deionized water and stirred at 500 rpm for 3 h at room temperature to obtain a PEI solution with a concentration of 1 g / L.

[0058] 2) A PVDF hollow fiber membrane with a length of 10 cm was vertically inserted into a cross-flow device, and 1000 ml of PEI solution was passed into the cross-flow device for 5 minutes at a cross-flow rate of 100 L / h. After cross-linking was completed, the membrane surface was rinsed to remove the unreacted solution, thereby modifying the hollow fiber membrane to obtain the modified hollow fiber membrane of this comparative example, which was recorded as a PEI membrane.

[0059] Comparative Example 3

[0060] The hollow fiber membrane is modified only by sodium lignin sulfonate, specifically:

[0061] 1) Sodium lignin sulfonate powder was added to deionized water and stirred at 250 r / min at room temperature for 3 h to obtain a sodium lignin sulfonate solution with a concentration of 3 g / L;

[0062] 2) A PVDF hollow fiber membrane with a length of 10 cm was vertically inserted into a cross-flow device, and 1000 ml of sodium lignin sulfonate solution was taken and passed into the cross-flow device for 5 minutes at a cross-flow rate of 100 L / h. After cross-linking was completed, the membrane surface was rinsed to remove the unreacted solution, thereby modifying the hollow fiber membrane to obtain the modified hollow fiber membrane of this example, which was recorded as SLS membrane.

[0063] The relevant properties of the films prepared in Example 1 and Comparative Examples 1 to 3 were tested, and the results are shown in Table 1.

[0064] Table 1

[0065]

[0066] As can be seen from Table 1, the PEI-SLS modified hollow fiber membrane synthesized in Example 1 of the present application has significant advantages over the unmodified PVDF hollow fiber membrane and the PEI membrane and SLS membrane modified only by PEI or SLS, especially for Cu 2+ The adsorption rate is low, which is due to the relatively simple surface chemical properties of the unmodified PVDF hollow fiber membrane, which lacks the ability to absorb Cu 2+ During the PEI-SLS modification process, PEI introduced abundant amino groups and SLS introduced sulfonic acid groups, which can interact with Cu 2+ Coordination occurs, the sulfonic acid group is negatively charged and can react with the positively charged Cu 2+ Produce electrostatic adsorption.

[0067] In addition, the hydrophilicity of the modified membrane surface is enhanced, and a hydration layer is usually formed on the hydrophilic surface. This hydration layer can not only reduce the adsorption of pollutants on the membrane surface, but also promote the adsorption of metal ions. Because metal ions exist in the form of hydrated ions in aqueous solution, the hydrophilic surface is conducive to the approach and adsorption of hydrated ions, thereby improving the adsorption rate.

[0068] Example 2

[0069] The difference between this embodiment and Example 1 is that the concentrations of the PEI solution in step 1) were adjusted to 0.5 g / L, 1 g / L, 1.5 g / L, and 2 g / L, respectively. The remaining steps and processes were similar to those in Example 1. Modified hollow fiber membranes prepared with different PEI concentrations in this embodiment were obtained, and the water flux and ink flux of the membranes were measured. The results are shown in Table 2.

[0070] Table 2

[0071] PEI concentration <![CDATA[Water flux (Lm -2 h -1 )]]> <![CDATA[Ink flux (Lm -2 h -1 )]]> 0.5g / L 134 87 1g / L 196 115 1.5g / L 136 108 2g / L 130 97

[0072] Table 2 shows that the PEI concentration significantly affects the performance of the modified hollow fiber membrane. As one of the reactants, PEI's amino groups react with the sulfonic acid groups of sodium lignin sulfonate to form sulfonamide structures, which in turn contribute to the formation of the modified structural layer. When the PEI concentration is too low, the number of amino groups in the solution is limited, reducing the probability of an effective cross-linking reaction with the sulfonic acid groups of sodium lignin sulfonate. This results in an incomplete and inconsistent structural layer formed on the surface of the PVDF hollow fiber membrane, preventing the formation of a sufficiently dense and effective functional layer. This reduces the anti-fouling ability of the modified hollow fiber membrane, making it more likely for contaminants to adhere to the membrane surface. Separation performance for specific substances also deteriorates, as the incomplete structural layer fails to provide effective selective separation channels. Furthermore, PEI not only participates in the cross-linking reaction but also influences the membrane's surface properties, such as providing active sites that facilitate material transport or anti-fouling properties. At too low a concentration, these active sites are insufficient, making it difficult to effectively improve the membrane's overall performance.

[0073] When the PEI concentration is too high, there are too many PEI molecules in the solution, which will produce a steric hindrance effect between each other. This will hinder the effective contact and reaction between the PEI molecules and the sodium lignin sulfonate molecules, so that the cross-linking reaction cannot proceed smoothly, resulting in an uneven structural layer and local defects. This uneven structural layer will affect the anti-pollution performance of the membrane, because some areas may not be able to effectively prevent the attachment of pollutants. It will also reduce the separation performance of specific substances, making the transmission and separation process of substances in the membrane chaotic. Excessive PEI may over-cover the pores of the PVDF hollow fiber membrane. Although it can change the surface properties of the membrane to a certain extent, it will also significantly increase the mass transfer resistance of the membrane. This will reduce the permeation flux of the membrane, resulting in a decrease in processing efficiency in actual applications. At the same time, the separation performance of specific substances will also be affected because the transmission of substances in the membrane is hindered, making it difficult to achieve effective separation.

[0074] Example 3

[0075] The difference between this example and Example 1 is that the concentrations of the SLS solution in step 2) were adjusted to 2 g / L, 2.5 g / L, 3 g / L, and 3.5 g / L, respectively. The remaining steps and processes were similar to those in Example 1. Modified hollow fiber membranes prepared with different SLS concentrations in this example were obtained, and the water flux and ink flux of the membranes were measured. The results are shown in Table 3.

[0076] Table 3

[0077] SLS concentration <![CDATA[Water flux (Lm -2 h -1 )]]> <![CDATA[Ink flux (Lm -2 h -1 )]]> 2g / L 132 80 2.5g / L 140 90 3g / L 196 115 3.5g / L 140 100

[0078] As can be seen from Table 3, the SLS concentration has a significant impact on the performance of the modified hollow fiber membrane. In the present invention, sodium lignin sulfonate is also one of the main components of the modified structural layer. When its concentration is too low, the number of sodium lignin sulfonate molecules in the solution is insufficient. When it is passed into the cross-flow device to react with PEI and deposited on the surface of the PVDF hollow fiber membrane, a structural layer of sufficient thickness cannot be formed. The thinner structural layer has limited blocking effect on pollutants and poor anti-pollution ability. At the same time, it is not enough to provide sufficient separation selectivity, resulting in poor separation performance for specific substances. And because the concentration of sodium lignin sulfonate is low, the intermolecular interaction in the formed structural layer is weak and the structural stability is poor. In actual application, the structural layer is easily damaged or falls off due to factors such as water flow impact and pollutant adhesion, further reducing the anti-pollution ability and separation performance of the membrane.

[0079] Excessively high sodium lignin sulfonate concentrations significantly increase solution viscosity. When introduced into a cross-flow device at a cross-flow rate of 100 L / h, the solution's flow resistance increases, potentially leading to uneven distribution of the solution across the membrane surface. This uneven solution distribution can affect the cross-linking reaction, resulting in an uneven structural layer on the membrane surface. Some areas may overreact due to excessive solution concentration, forming an overly dense structure that may even clog the membrane pores, while others may react incompletely due to insufficient solution concentration, resulting in a decrease in overall performance. Furthermore, high concentrations of sodium lignin sulfonate molecules are prone to excessive accumulation and agglomeration on the membrane surface, forming irregular, large particle structures. These large particle structures not only fail to form a compact and effective functional layer, but also become hotspots for contaminant attachment, reducing the membrane's anti-fouling ability. Furthermore, agglomeration can disrupt the uniformity of the membrane surface, affecting the separation performance of specific substances and interfering with the transport and separation processes within the membrane.

[0080] Example 4

[0081] The difference between this example and Example 1 is that the cross-flow assembly time of the two solutions in step 3) was adjusted to 5, 10, and 15 minutes, respectively. The remaining steps and processes were all based on Example 1. The modified hollow fiber membranes prepared with different cross-flow assembly times in this example were obtained, and the water flux of the membranes was measured. The results are shown in Table 4.

[0082] Table 4

[0083] Assembly time <![CDATA[Water flux (Lm -2 h -1 )]]> 5min 175 10min 196 15min 171

[0084] During the cross-flow assembly process, a PEI solution and a sodium lignin sulfonate solution sequentially come into contact with the PVDF hollow fiber membrane to undergo a cross-linking reaction. If the time is too short, the two solutions are insufficiently in contact with the membrane surface, and the amino groups of the PEI and the sulfonic acid groups of the sodium lignin sulfonate do not react completely, failing to form sufficient and strong sulfonamide chemical bonds. This results in an incomplete and discontinuous structural layer on the membrane surface, with numerous unreacted active sites and defects. Furthermore, the thin structural layer lacks sufficient separation selectivity, making it difficult to effectively separate specific substances, impacting the membrane's efficiency and stability in practical applications.

[0085] As the cross-flow assembly time increases, the cross-linking reaction continues, and the structural layer continues to thicken and densify. For membranes, an overly dense structural layer will significantly increase the membrane's mass transfer resistance and reduce the membrane's permeation flux, resulting in a significant decrease in processing efficiency in practical applications. At the same time, due to pore blockage, the separation performance of specific substances will also be affected, because the material's transmission channel within the membrane becomes narrow or even interrupted, making effective separation impossible.

[0086] Example 5

[0087] The difference between this example and Example 1 is that the cross-flow assembly flow rates of the two solutions in step 3) were adjusted to 50, 80, and 100 L / h, and the remaining steps and processes were referred to Example 1. The modified hollow fiber membranes prepared at different cross-flow assembly flow rates in this example were obtained, and the water flux of the membranes was measured. The results are shown in Table 5.

[0088] Table 5

[0089] Assembly flow rate <![CDATA[Water flux (Lm -2 h -1 )]]> 50L / h 188 80L / h 180 100L / h 196

[0090] As shown in Table 5, the cross-flow velocity also has a certain impact on membrane performance. When the cross-flow velocity is too slow, the solution flows slowly across the membrane surface, which can easily lead to concentration polarization. The concentration of the solution near the membrane surface gradually increases, while the concentration of the solution farther away from the membrane surface is relatively low, resulting in an uneven concentration distribution of the solution across the membrane surface. This uneven concentration distribution can affect the cross-linking reaction, causing the thickness and properties of the structural layer formed in different areas of the membrane surface to vary. Some areas may overreact due to excessively high solution concentration, forming an overly dense structure that may even clog the membrane pores; while other areas may react incompletely due to excessively low solution concentration, resulting in numerous defects. This uneven structural layer can reduce the membrane's anti-fouling ability and separation performance.

[0091] Further experiments have found that when the cross-flow velocity is greater than 100 L / h, the excessively fast flow rate will generate a large shear force, causing a scouring effect on the membrane surface. This scouring force may destroy the structural layer that is forming on the membrane surface, making it difficult for the membrane to adhere stably.

[0092] Comparative Example 4

[0093] The difference between this comparative example and Example 1 is that the PEI in step 1) is adjusted to PEG, and the remaining steps and processes are all based on Example 1 to obtain the modified hollow fiber membrane of this comparative example.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that the PEI in step 1) is adjusted to cellulose, and the remaining steps and processes are referred to Example 1 to obtain the modified hollow fiber membrane of this comparative example.

[0096] The water flux of the membranes prepared in Comparative Examples 4 and 5 was measured and compared with that in Example 1. The results are shown in Table 6.

[0097] Table 6

[0098]

[0099]

[0100] Comparative Example 6

[0101] The difference between this comparative example and Example 1 is that the SLS in step 1) is adjusted to sulfonated lignin SL, and the remaining steps and processes are referred to Example 1 to obtain the modified hollow fiber membrane of this comparative example.

[0102] Comparative Example 7

[0103] The difference between this comparative example and Example 1 is that the SLS in step 1) is adjusted to tannin, and the remaining steps and processes are referred to Example 1 to obtain the modified hollow fiber membrane of this comparative example.

[0104] The water flux of the membranes prepared in Comparative Examples 6 and 7 was measured and compared with that in Example 1. The results are shown in Table 7.

[0105] Table 7

[0106] <![CDATA[Water flux (Lm -2 h -1 )]]> <![CDATA[Ink flux (Lm -2 h -1 )]]> Example 1 196 115 Comparative Example 6 110 80 Comparative Example 7 120 85

[0107] From Tables 6 and 7, it can be seen that the structural layer formed by the reaction of sodium lignin sulfonate and PEI selected in this application has significant advantages on the surface of the PVDF membrane. PEI contains abundant amino groups, which can react with the sulfonic acid groups of sodium lignin sulfonate to form a sulfonamide structure, thereby constructing a tightly wound structural layer. However, the PEG molecular chain is mainly composed of ether bonds and lacks active groups that can effectively react with the sulfonic acid groups of sodium lignin sulfonate, making it difficult to form a stable chemical bond. This results in incomplete formation of the structural layer and an inability to effectively improve the membrane's anti-fouling ability and separation performance. Although cellulose contains active groups such as hydroxyl groups, its reactivity with the sulfonic acid groups of sodium lignin sulfonate is low, and the degree of reaction is limited, making it difficult to form a tight, uniform structural layer with specific functions. As a result, the performance improvement of the modified membrane is not obvious or even decreases.

[0108] In addition, the PEI molecular chain has a certain degree of flexibility and length, which can form a relatively uniform and tight coating on the membrane surface, helping to improve the stability of the structural layer and its anti-fouling ability. However, the PEG molecular chain is relatively regular and it is difficult to form a tightly wound structure similar to PEI on the membrane surface, resulting in a looser structural layer that is easily damaged by pollutants, reducing the membrane's anti-fouling performance.

[0109] The sulfonamide structure formed by the reaction of sodium lignin sulfonate and PEI, as well as the ether-linked sodium lignin sulfonate structural layer, have a tightly entangled structure and specific functional properties, effectively improving the membrane's anti-fouling ability and separation performance. While sulfonated lignin has a similar structure to sodium lignin sulfonate, the degree of sulfonation and functional group distribution may differ. As a result, the structural layer formed by the reaction with PEI is inferior to that of sodium lignin sulfonate in terms of tightness, uniformity, and functionality, affecting membrane performance.

[0110] Tannic acid is rich in reactive groups such as phenolic hydroxyl groups, but its reaction mechanism with PEI and the product structure differ from those of sodium lignin sulfonate. The resulting structural layer cannot effectively block pollutants or provide a good separation channel, resulting in a decrease in the membrane's anti-fouling ability and separation performance. Furthermore, sodium lignin sulfonate has a certain degree of hydrophilicity, which can increase the hydrophilicity of the membrane surface and synergistically reduce the adsorption and deposition of pollutants on the membrane surface.

[0111] In summary, the present invention provides a modified hollow fiber membrane, a preparation method and an application thereof. The PVDF hollow fiber membrane is vertically inserted into a cross-flow device, and a PEI solution and a sodium lignin sulfonate solution are successively introduced into the cross-flow device for coordination cross-linking treatment. After cross-linking, the membrane surface is rinsed to achieve the modification of the hollow fiber membrane. A structural layer composed of sulfonamides and sodium lignin sulfonate connected by ether bonds is formed on the surface of the PVDF hollow fiber membrane, which effectively improves the anti-pollution ability of the hollow fiber membrane and the separation performance of specific substances, thereby improving its efficiency and stability in practical applications.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a modified hollow fiber membrane, characterized in that: include, PEI powder was added to deionized water and stirred to obtain a PEI solution; Sodium lignin sulfonate powder is added to deionized water and stirred to obtain a sodium lignin sulfonate solution; The PVDF hollow fiber membrane is vertically inserted into the cross-flow device, and the PEI solution and the sodium lignin sulfonate solution are successively introduced into the cross-flow device for coordination cross-linking treatment. After cross-linking, the membrane surface is rinsed to achieve the modification of the hollow fiber membrane.

2. The method for preparing a modified hollow fiber membrane according to claim 1, wherein: The concentration of the PEI solution is 0.5 g / L to 2 g / L.

3. The method for preparing a modified hollow fiber membrane according to claim 1, wherein: The concentration of the sodium lignin sulfonate solution is 2 g / L to 3.5 g / L.

4. The method for preparing a modified hollow fiber membrane according to claim 2, wherein: PEI powder is added to deionized water and stirred at a speed of 400 to 600 r / min for 2 to 4 hours at room temperature to obtain a PEI solution.

5. The method for preparing a modified hollow fiber membrane according to claim 3, wherein: Sodium lignin sulfonate powder is added to deionized water and stirred at a speed of 200-300 r / min for 2-4 hours to obtain a sodium lignin sulfonate solution.

6. The method for preparing a modified hollow fiber membrane according to claim 1, wherein: The flow rate of the PEI solution and the sodium lignin sulfonate solution into the cross-flow device is 50 to 100 L / h.

7. The method for preparing a modified hollow fiber membrane according to claim 1, wherein: The sodium lignin sulfonate solution is then added after the PEI solution has been introduced for 5 to 15 minutes.

8. The method for preparing a modified hollow fiber membrane according to claim 7, wherein: The cross-linking treatment time of passing the sodium lignin sulfonate solution is 5 to 15 minutes.

9. The modified hollow fiber membrane prepared by the preparation method according to any one of claims 1 to 8, characterized in that: A structural layer composed of sulfonamides and sodium lignin sulfonate connected by ether bonds is formed on the surface of the PVDF hollow fiber membrane, wherein the sulfonamides are generated by the reaction of the sulfonic acid group of the sodium lignin sulfonate and the amino group of PEI.

10. The role of the modified hollow fiber membrane as claimed in claim 9 in the field of sewage treatment.

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