High-strength polyamide composite film and method for producing the same

Abstract

The application discloses a high-strength polyamide composite membrane and a preparation method thereof. The composite membrane comprises a porous support layer and a polyamide selection layer formed on the porous support layer. The selection layer has a double-network structure, a loose first polyamide network formed by first interfacial polymerization, and a second polyamide network containing covalently connected sulfonimide groups formed by second interfacial polymerization on the basis of the first polyamide network. The interpenetrating reinforced network significantly improves the mechanical strength of the membrane, and the sulfonimide groups endow the membrane with good hydrophilicity, chemical resistance and anti-pollution property. The preparation process is simple and controllable, and is easy for large-scale production. The application is suitable for the fields of seawater desalination, industrial wastewater treatment and food concentration.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a high-strength polyamide composite membrane and its preparation method, which is suitable for pressure-driven membrane separation processes such as reverse osmosis and nanofiltration. Background Technology

[0002] Polyamide composite membranes, due to their excellent separation performance and high water flux, have become the most widely used membrane materials in reverse osmosis and nanofiltration, and are widely used in seawater desalination, brackish water desalination, industrial wastewater treatment, food and pharmaceutical concentration, and other fields. Traditional polyamide composite membranes are usually prepared using a single-stage interfacial polymerization process, in which a porous support layer is first immersed in a polyamine aqueous solution, drained, and then immersed in a polyacrylamide organic solution, where a polymerization reaction occurs at the two-phase interface to form a polyamide selective layer.

[0003] However, polyamide films prepared using this traditional process have the following inherent defects:

[0004] Insufficient mechanical strength: The polyamide layer formed by single interfacial polymerization is relatively thin (usually 100-200nm) and has a single network structure. Under high pressure operation, frequent cleaning and highly polluted water conditions, the membrane layer is prone to damage and peeling, resulting in a significant reduction in the membrane's service life.

[0005] Poor chemical resistance: The amide bonds in the polyamide molecular chain are easily degraded by oxidants (such as sodium hypochlorite), strong acids and alkalis, which limits the application of the membrane in the treatment of highly oxidizing and corrosive water.

[0006] Weak antifouling properties: Traditional polyamide membranes have poor hydrophilicity and carry a certain charge, making them prone to adsorbing pollutants such as organic matter and microorganisms in the water, resulting in membrane flux decay and increased operating costs.

[0007] To address the aforementioned issues, various improvement methods have been proposed in existing technologies. For example, doping the polyamide layer with inorganic nanoparticles (such as silica and graphene oxide) can enhance mechanical strength, or introducing hydrophilic groups through chemical grafting modification can improve antifouling properties. However, these methods have significant limitations: inorganic nanoparticles are prone to aggregation in the organic phase, leading to uneven membrane performance; and the interfacial bonding between nanoparticles and the polyamide matrix is ​​weak, making them prone to detachment over long-term operation. Chemical grafting modification typically requires complex reaction steps and can easily damage the original structure of the polyamide layer, resulting in decreased membrane separation performance. Furthermore, some studies have employed multiple interfacial polymerization processes to thicken the polyamide layer and improve strength. However, due to the lack of effective chemical bonding between the multiple polymerizations, delamination easily occurs between the two layers, and without introducing functional groups, it is impossible to simultaneously improve the membrane's chemical resistance and antifouling properties.

[0008] Therefore, developing a polyamide composite membrane with high mechanical strength, excellent chemical resistance and anti-fouling properties, and its simple and easy preparation method, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-strength polyamide composite membrane and its preparation method. The composite membrane forms an interpenetrating reinforced polyamide network structure through two interfacial polymerizations, and at the same time introduces sulfonylimide functional groups, which significantly improves the mechanical strength of the membrane while effectively improving the chemical resistance and antifouling properties of the membrane.

[0010] The specific solution of this invention is as follows:

[0011] A high-strength polyamide composite membrane includes a porous support layer and a polyamide selective layer located on the porous support layer. The polyamide selective layer comprises: a first polyamide network formed by a first interfacial polymerization, the first polyamide network having a loose structure and containing unreacted residual active groups on its surface and in its shallow layer; and a second polyamide network formed on the first polyamide network by a second interfacial polymerization, the second polyamide network containing covalently linked sulfonylimide groups.

[0012] The sulfonylimide group has the structure shown in formula (I):

[0013] -SO2-NR1-SO2-R2(I); In formula (I), R1 is selected from hydrogen, alkali metal ions, ammonium ions, or C1-C4 alkyl groups; R2 is selected from C1-C4 alkyl groups. 10 Alkyl, C1-C 10 The R2 group is a perfluoroalkyl, phenyl, halophenyl, naphthyl, biphenyl, or heteroaryl group, and the R2 group is optionally substituted by one or more substituents selected from halogen, nitro, C1-C4 alkyl, or C1-C4 alkoxy groups.

[0014] The second polyamide network is formed by interfacial polymerization of a second polyamine monomer containing a sulfonylimide side group and a second polyacrylamide chloride monomer; the polyamine monomer containing the sulfonylimide side group has the structure shown in formula (II):

[0015] (NH2) n -Ar-(SO2-NR1-SO2-R2) m (II);

[0016] In equation (II), Ar is C6-C 20 Aromatic groups or C1-C 10Aliphatic group; n is 2 or 3, representing the number of amino groups directly attached to Ar; m is 1 or 2, representing the number of sulfonylimide side groups attached to Ar; R1 and R2 are defined as in claim 2; the second polyacrylamide chloride monomer is selected from one or more of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, and adipoyl chloride.

[0017] The polyamine monomer containing the sulfonylimide side group is selected from one or more of 3,5-diamino-4'-(trifluoromethylbenzenesulfonylimide)benzene, 4,4'-diamino-2-(benzenesulfonylimide)biphenyl, 2,4-diaminobenzenesulfonylimide, N,N'-bis(3-aminophenyl)benzene-1,3-disulfonylimide, and 1,3-diaminopropane-2-sulfonylimide.

[0018] The first polyamide network is formed by a first polyamine monomer and a first polyacrylamide chloride monomer through a first interfacial polymerization; the first polyamine monomer is selected from one or more of m-phenylenediamine, p-phenylenediamine, piperazine, and triaminobenzene, and the first polyacrylamide chloride monomer is selected from one or more of pyromellitic tricarboxylic acid chloride, terephthaloyl chloride, and adipoyl chloride.

[0019] A method for preparing a high-strength polyamide composite film includes the following steps:

[0020] (1) Provide a porous support layer; (2) Contact the porous support layer with a first aqueous solution containing a first polyamine monomer for 10s-5min, and then contact it with a first organic solution containing a first polyacrylamide monomer for 5s-3min to perform the first interfacial polymerization, forming a first polyamide network rich in unreacted acrylamide groups on the porous support membrane to obtain a nascent composite membrane; (3) Immediately contact the nascent composite membrane obtained in step (2) directly with a second aqueous solution containing a second polyamine monomer for 30s-10min without washing and drying, the second polyamine monomer containing sulfonylimide side groups; (4) Then contact it with a second organic solution containing a second polyacrylamide monomer for 10s-5min to perform the second interfacial polymerization, and place the membrane after the second polymerization in an oven for heat treatment at 40℃ to 80℃ for 2 to 10min to finally obtain the polyamide composite membrane.

[0021] The porous support layer is selected from one or more of polysulfone, polyethersulfone, polyimide, and polyacrylonitrile, with an average pore size of 0.01μm-1μm and a thickness of 50μm-200μm.

[0022] In step (2): the mass concentration of the first polyamine monomer in the first aqueous phase solution is 0.5%-3.0%; the mass concentration of the first polyacrylamide chloride monomer in the first organic phase solution is 0.05%-0.15%; and the solvent is selected from one or more of n-hexane, cyclohexane, and n-heptane.

[0023] In step (3), the mass concentration of the second polyamine monomer in the second aqueous phase solution is 0.1%-2.0%, and the pH value of the solution is 7.5-9.5; in step (4), the mass concentration of the second polyacrylamide chloride monomer in the second organic phase solution is 0.08%-0.2%.

[0024] The nascent composite membrane enters the second aqueous phase solution within 30 seconds after the first interfacial polymerization reaction is completed.

[0025] This invention discloses a high-strength polyamide composite membrane and its preparation method. The composite membrane includes a porous support layer and a polyamide selective layer formed thereon. The selective layer has a dual-network structure, consisting of a loose first polyamide network formed by a first interfacial polymerization and a second polyamide network containing covalently linked sulfonylimide groups formed by a second interfacial polymerization. This interpenetrating reinforced network significantly improves the mechanical strength of the membrane, while the sulfonylimide groups endow the membrane with good hydrophilicity, chemical resistance, and antifouling properties. The preparation process is simple and controllable, easy to scale up, and suitable for seawater desalination, industrial wastewater treatment, and food concentration.

[0026] This invention employs two interfacial polymerization processes to construct an interpenetrating reinforcement network, significantly improving the mechanical strength of the membrane. Furthermore, it introduces covalently linked sulfonylimide functional groups, utilizing their strong electron-withdrawing effect to enhance the antioxidant properties and acid and alkali resistance of the amide bonds, while simultaneously leveraging their strong hydrophilicity and negative charge properties to enhance the membrane's antifouling ability.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The first interfacial polymerization forms a loose first polyamide network and retains a large number of unreacted acyl chloride active groups; during the second interfacial polymerization, the polyamine containing sulfonylimide side groups not only reacts with the acyl chloride monomer in the second organic phase to form a second polyamide network, but also covalently bonds with the residual acyl chloride groups on the first polyamide network to form an interpenetrating reinforced bilayer polyamide network structure, effectively avoiding the problem of membrane layer delamination, increasing the tensile strength of the membrane by more than 30% compared with traditional single-polymerization membranes, and significantly extending the service life.

[0029] 2. The sulfonimide group introduced into the second polyamide network has a strong electron-withdrawing effect, which can reduce the electron cloud density of nitrogen atoms on the amide bond, thereby improving the antioxidant and acid and alkali resistance of the amide bond. After the membrane is soaked in sodium hypochlorite solution with an effective chlorine concentration of 2000 ppm for 24 hours, the salt rejection rate is still above 95%.

[0030] 3. The sulfonylimide group is a strongly hydrophilic group, which can significantly improve the hydrophilicity of the membrane surface and reduce the hydrophobic interaction between the membrane and pollutants. At the same time, the sulfonylimide group carries a negative charge, which can reduce the adsorption of negatively charged pollutants through electrostatic repulsion, thereby increasing the membrane flux recovery rate to over 90%. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 This is an electron microscope image of the surface of a high-strength polyamide composite film in Embodiment 2 of the present invention;

[0033] Figure 2 The separation performance of the polyamide composite membranes in Examples 1-5 and Comparative Examples 1-3 of this invention;

[0034] Figure 3 The polyamide composite films in Examples 1-5 and Comparative Examples 1-3 of this invention exhibit chlorine resistance and antifouling properties.

[0035] Figure 4 The mechanical strength properties of the polyamide composite films in Examples 1-5 and Comparative Examples 1-3 of this invention are described. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0037] Example 1

[0038] This embodiment provides a method for preparing a high-strength polyamide composite film, the specific steps of which are as follows:

[0039] (1) Provide a porous support layer: a polysulfone ultrafiltration membrane is used as a porous support layer with an average pore size of 0.05 μm and a thickness of 120 μm;

[0040] (2) First interfacial polymerization: The polysulfone support layer was immersed in a 1.5% m-phenylenediamine aqueous solution for 30s. After removal, excess solution was drained from the surface with a rubber roller. Then, it was immersed in a 0.1% trimesoyl chloride hexane solution for 10s to carry out the first interfacial polymerization, forming a first polyamide network rich in unreacted acyl chloride groups, and obtaining the nascent composite film.

[0041] (3) Second interfacial polymerization: Within 15 seconds after the first interfacial polymerization, the nascent composite membrane is directly immersed in a 0.5% (w / w) aqueous solution of 3,5-diamino-4'-(trifluoromethylbenzenesulfonylimide)benzene without washing or drying. The pH of the solution is adjusted to 8.5 with sodium hydroxide and the contact time is 2 min. After being taken out and drained, it is immersed in a 0.12% (w / w) solution of trimesoyl chloride and hexane for 20 seconds to carry out the second interfacial polymerization.

[0042] (4) Heat treatment: The membrane after secondary polymerization is placed in a 60°C oven for 5 minutes for heat treatment. After taking it out, it is rinsed with deionized water to obtain the high-strength polyamide composite membrane, which is marked as M1.

[0043] Example 2

[0044] The only difference between this embodiment and Example 1 is that in step (3), the polyamine monomer containing sulfonylimide side group is 4,4'-diamino-2-(benzenesulfonylimide)biphenyl with a mass concentration of 0.8%, a solution pH of 9.0, and a contact time of 3 min; the remaining steps and parameters are the same as in Example 1, and the polyamide composite film prepared is marked as M2.

[0045] Example 3

[0046] The only difference between this embodiment and Example 1 is that in step (2), the first polyamine monomer is piperazine with a mass concentration of 2.0% and a contact time of 1 min; the first polyacrylamide chloride monomer is terephthaloyl chloride with a mass concentration of 0.08% and a contact time of 15 s; the remaining steps and parameters are the same as in Example 1, and the polyamide composite film prepared is marked as M3.

[0047] Example 4

[0048] The only difference between this embodiment and embodiment 1 is that in step (4), the heat treatment temperature is 70°C and the heat treatment time is 3 min; the remaining steps and parameters are the same as in embodiment 1, and the polyamide composite film prepared is marked as M4.

[0049] Example 5

[0050] The only difference between this embodiment and Example 1 is that in step (3), the nascent composite membrane enters the second aqueous phase solution within 25 seconds after the first interfacial polymerization is completed; the remaining steps and parameters are the same as in Example 1, and the polyamide composite membrane prepared is marked as M5.

[0051] Comparative Example 1

[0052] This comparative example uses a traditional single-step interfacial polymerization process to prepare polyamide composite films. The specific steps are as follows:

[0053] (1) Provide the same polysulfone porous support layer as in Example 1;

[0054] (2) Immerse the support layer in a 1.5% m-phenylenediamine aqueous solution for 30s, drain it, and then immerse it in a 0.1% pyromellitic chloride hexane solution for 10s.

[0055] (3) The polymerized membrane was placed in a 60°C oven for 5 minutes for heat treatment. After taking it out, it was rinsed with deionized water to obtain a traditional polyamide composite membrane, which was labeled as D1.

[0056] Comparative Example 2

[0057] The only difference between this comparative example and Example 1 is that in step (3), the second aqueous solution does not contain polyamine monomers with sulfonamide side groups, and only uses an aqueous solution of m-phenylenediamine with a mass concentration of 0.5%; the remaining steps and parameters are the same as in Example 1, and the polyamide composite film prepared is labeled as D2.

[0058] Comparative Example 3

[0059] The only difference between this comparative example and Example 1 is that in step (3), the nascent composite membrane is first rinsed with deionized water and dried after the first interfacial polymerization, and then enters the second aqueous phase solution; the remaining steps and parameters are the same as in Example 1, and the polyamide composite membrane prepared is labeled as D3.

[0060] Performance testing

[0061] The following performance tests were performed on the polyamide composite films prepared in the above embodiments and comparative examples:

[0062] Separation performance test: The water flux and salt rejection rate of the membrane were tested using a cross-flow membrane test device under the conditions of operating pressure of 1.55 MPa, temperature of 25℃ and feed liquid of 2000 ppm sodium chloride aqueous solution.

[0063] Mechanical strength test: The tensile strength of the membrane was tested using a universal testing machine in accordance with the standard GB / T1040.3-2006. The sample size was 50mm×10mm and the tensile rate was 50mm / min.

[0064] Chlorine resistance test: The membrane sample was immersed in a sodium hypochlorite solution with an effective chlorine concentration of 2000 ppm and soaked at room temperature for 24 h. The salt rejection rate and retention rate were then tested.

[0065] Antifouling test: Bovine serum albumin (BSA, 1 g / L) was used as a model pollutant. Under the conditions of operating pressure of 1.55 MPa and temperature of 25℃, the initial water flux J0 of the membrane was first tested. Then, the membrane was continuously filtered with BSA solution for 2 h, and the water flux J1 after fouling was tested. The membrane surface was then rinsed with deionized water for 30 min, and the water flux J2 after cleaning was tested. The flux recovery rate FRR was calculated as FRR = J2 / J0 × 100%.

[0066] The test results are shown in the table below:

[0067]

[0068] Results Analysis

[0069] Compared with the traditional single-polymerization membrane D1, the membranes M1-M5 prepared in the embodiments of the present invention have significantly improved performance in all aspects, including tensile strength increased by 27%-39%, salt rejection rate and retention rate increased by 23%-25%, and flux recovery rate increased by 22%-25%. Example M2 has the best comprehensive advantages, which proves the effectiveness of the technical solution of the present invention.

[0070] Compared with the secondary polymerized membrane D2 without the introduction of sulfonylimide groups, the chlorine resistance and antifouling properties of Examples M1-M5 are significantly better, indicating that the introduction of sulfonylimide groups is a key factor in improving the chemical resistance and antifouling properties of the membrane.

[0071] Compared with membrane D3, which underwent secondary polymerization after washing and drying following the first polymerization, the tensile strength of Examples M1-M5 was higher, indicating that secondary polymerization without washing and drying can retain more residual active groups, resulting in stronger covalent bonds between the two polyamide networks.

[0072] The performance differences between different embodiments indicate that by adjusting parameters such as the type of polyamine monomer, reaction time, and heat treatment conditions, the membrane performance can be flexibly controlled to meet the needs of different application scenarios.

[0073] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

[0074] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A high-strength polyamide composite membrane, comprising a porous support layer and a polyamide selective layer located on the porous support layer, characterized in that, The polyamide selective layer comprises: a first polyamide network formed by a first interfacial polymerization, the first polyamide network having a loose structure with a volume porosity of 15% to 30%, and containing unreacted residual active groups on its surface and in its shallow layer; and a second polyamide network formed on the first polyamide network by a second interfacial polymerization, the second polyamide network containing covalently linked sulfonylimide groups.

2. The high-strength polyamide composite film as described in claim 1, characterized in that: The sulfonylimide group has the structure shown in formula (I): -SO2-NR1-SO2-R2(I); In formula (I), R1 is selected from hydrogen, alkali metal ions, ammonium ions, or C1-C4 alkyl groups; R2 is selected from C1-C4 alkyl groups. 10 Alkyl, C1-C 10 The R2 group is a perfluoroalkyl, phenyl, halophenyl, naphthyl, biphenyl, or heteroaryl group, and the R2 group is optionally substituted by one or more substituents selected from halogen, nitro, C1-C4 alkyl, or C1-C4 alkoxy groups.

3. The high-strength polyamide composite film as described in claim 1, characterized in that: The second polyamide network is formed by interfacial polymerization of a second polyamine monomer containing a sulfonylimide side group and a second polyacrylamide chloride monomer; the polyamine monomer containing the sulfonylimide side group has the structure shown in formula (II): (NH2) n -Ar-(SO2-NR1-SO2-R2) m (II); In formula (II), Ar is C6-C 20 Aromatic groups or C1-C 10 Aliphatic group; n is 2 or 3, representing the number of amino groups directly attached to Ar; m is 1 or 2, representing the number of sulfonylimide side groups attached to Ar; R1 and R2 are defined as in claim 2; the second polyacrylamide monomer is selected from one or more of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, and adipoyl chloride.

4. The high-strength polyamide composite film as described in claim 3, characterized in that: The polyamine monomer containing the sulfonylimide side group is selected from one or more of 3,5-diamino-4'-(trifluoromethylbenzenesulfonylimide)benzene, 4,4'-diamino-2-(benzenesulfonylimide)biphenyl, 2,4-diaminobenzenesulfonylimide, N,N'-bis(3-aminophenyl)benzene-1,3-disulfonylimide, and 1,3-diaminopropane-2-sulfonylimide.

5. The high-strength polyamide composite film as described in claim 1, characterized in that: The first polyamide network is formed by a first polyamine monomer and a first polyacrylamide chloride monomer through a first interfacial polymerization; the first polyamine monomer is selected from one or more of m-phenylenediamine, p-phenylenediamine, piperazine, and triaminobenzene, and the first polyacrylamide chloride monomer is selected from one or more of pyromellitic tricarboxylic acid chloride, terephthaloyl chloride, and adipoyl chloride.

6. A method for preparing a high-strength polyamide composite film as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Provide a porous support layer; (2) Contact the porous support layer with a first aqueous solution containing a first polyamine monomer for 10s-5min, and then contact it with a first organic solution containing a first polyacrylamide monomer for 5s-3min to perform the first interfacial polymerization, forming a first polyamide network rich in unreacted acrylamide groups on the porous support membrane to obtain a nascent composite membrane; (3) Immediately contact the nascent composite membrane obtained in step (2) directly with a second aqueous solution containing a second polyamine monomer for 30s-10min without washing and drying, the second polyamine monomer containing sulfonylimide side groups; (4) Then contact it with a second organic solution containing a second polyacrylamide monomer for 10s-5min to perform the second interfacial polymerization, and place the membrane after the second polymerization in an oven for heat treatment at 40℃ to 80℃ for 2 to 10min to finally obtain the polyamide composite membrane.

7. The method for preparing a high-strength polyamide composite film as described in claim 6, characterized in that: The porous support layer is selected from one or more of polysulfone, polyethersulfone, polyimide, and polyacrylonitrile, with an average pore size of 0.01μm-1μm and a thickness of 50μm-200μm.

8. The method for preparing a high-strength polyamide composite film as described in claim 6, characterized in that, In step (2): the mass concentration of the first polyamine monomer in the first aqueous phase solution is 0.5%-3.0%; the mass concentration of the first polyacrylamide chloride monomer in the first organic phase solution is 0.05%-0.15%; and the solvent is selected from one or more of n-hexane, cyclohexane, and n-heptane.

9. The method for preparing a high-strength polyamide composite film as described in claim 6, characterized in that: In step (3), the mass concentration of the second polyamine monomer in the second aqueous phase solution is 0.1%-2.0%, and the pH value of the solution is 7.5-9.5; in step (4), the mass concentration of the second polyacrylamide chloride monomer in the second organic phase solution is 0.08%-0.2%.

10. The method for preparing a high-strength polyamide composite film as described in claim 6, characterized in that: The nascent composite membrane enters the second aqueous phase solution within 30 seconds after the first interfacial polymerization reaction is completed.

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