Method for preparing modified base film, method for preparing composite nanofiltration membrane, and composite nanofiltration membrane

Abstract

The application designs a preparation method of a modified base film, a preparation method of a composite nanofiltration membrane using the modified base film and a composite nanofiltration membrane prepared by the method in order to solve the problems of low water flux and poor firmness of a desalination layer of the composite nanofiltration membrane. The preparation method of the modified base film comprises the following steps: step one, dissolving aramid polymer and imidazole additives in an organic solvent to prepare casting solution; step two, placing the base film reinforced layer coated with the casting solution in a gel solution to prepare the modified base film. The preparation method of the composite nanofiltration membrane comprises the steps of immersing the modified base film in an aqueous solution and an oil phase solution for reaction, and preparing the composite nanofiltration membrane after the reaction. The modified base film prepared by the application has good water flux, and in the process of being used for the preparation and molding of the composite nanofiltration membrane, the water flux of the composite nanofiltration membrane and the firmness between the desalination layer and the modified base film are improved, and the desalination stability of the composite nanofiltration membrane is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a polymer film, in particular, the present application relates to a preparation method of a modified base film, a preparation method of a composite nanofiltration membrane using the modified base film and the composite nanofiltration membrane. BACKGROUND

[0002] Nanofiltration is a membrane separation technology between ultrafiltration and reverse osmosis. The composite nanofiltration membrane has good separation performance for high-valence, divalent salt and small-molecule organic matter, and also has the advantages of low operating pressure, large pure water flux and low cost, and has wide application prospect in the fields of water softening, desalination, wastewater treatment and the like.

[0003] The composite nanofiltration membrane is usually composed of a base film and a desalination layer, wherein the base film is usually composed of a reinforcing layer, a supporting layer and the like, and the performance of the composite nanofiltration membrane not only depends on the desalination layer with high selectivity, but also is closely related to the surface properties and pore structure of the supporting layer of the base film. As the generation place of the desalination layer, the material and chemical properties (hydrophilicity or hydrophobicity) of the supporting layer affect the thickness, roughness and cross-linking structure of the desalination layer, and further affect the overall performance of the composite nanofiltration membrane. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of a modified base film, comprising the following steps: step one, dissolving aramid polymer and imidazole additive in an organic solvent to obtain casting solution; step two, coating the casting solution on the reinforcing layer of the base film, and then placing the base film reinforcing layer coated with the casting solution in a gel solution to obtain the modified base film.

[0005] In the present application, the imidazole additive is directly added to the organic solution containing aramid polymer to form the casting solution. When the casting solution is coated on the reinforcing layer of the base film, the supporting layer is formed on the reinforcing layer of the base film, and then the modified base film is obtained. After the reaction of the imidazole additive and the aramid polymer, the supporting layer formed has hydrophilic groups such as carboxyl and sulfonic acid groups through hydrogen bonding, which on one hand helps to improve the porosity of the supporting layer of the modified base film, so that the pores of the supporting layer of the modified base film are more, thereby having good water flux; on the other hand, in the process of preparing the composite nanofiltration membrane, the modified base film with large porosity can improve the adsorption of the water phase solution in the subsequent preparation of the desalination layer, thereby improving the firmness between the desalination layer and the supporting layer of the base film. Finally, the present application has simple manufacturing process and low cost.

[0006] The reaction of the aramid polymer and the imidazole additive is as follows (taking para-aramid and imidazole-1-acetic acid as an example):

[0007]

[0008] The molecular formula of the para-aramid is The molecular formula of the imidazole-1-acetic acid is The aramid polymer is dissolved in an organic solvent, and then interacts with the imidazole additive through hydrogen bonding to form a base film support layer with hydrophilic groups such as carboxyl and sulfonic acid groups.

[0009] In an embodiment, the aramid polymer in step one comprises one or more of meta-aramid, para-aramid, modified meta-aramid, and modified para-aramid, wherein the modified meta-aramid and modified para-aramid are obtained by conventional modification methods.

[0010] In an embodiment, the imidazole additive in step one is imidazole-1-acetic acid (CAS: 22884-10-2) and / or 2-methylimidazole-4-sulfonic acid (CAS: 34916-84-2).

[0011] In an embodiment, the organic solvent in step one is selected from one or more of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0012] In an embodiment, the mass fraction of the aramid polymer in the casting solution in step one is 10.00%-25.00%, and the mass fraction of the imidazole additive is 5.00%-30.00%; the mass ratio of the aramid polymer to the imidazole additive can be (1:3)-(5:1). Alternatively, the mass fraction of the aramid polymer is 15.00%-20.00%, and the mass fraction of the imidazole additive is 10.00%-20.00%; the mass ratio of the aramid polymer to the imidazole additive can be (3:4)-(2:1).

[0013] In an embodiment, the casting solution in step one further comprises an inorganic additive; the mass fraction of the inorganic additive is 2.00%-5.00%; the inorganic additive is selected from one or more of LiCl, LiNO3, CH3COONa, NaNO3, and CaCl2. Thus, the inorganic additive can improve the porosity of the base film.

[0014] In an embodiment, the gel solution in step two comprises an organic solvent and water; the mass fraction of the organic solvent in the gel solution is 0.00%-30.00%, or 10.00%-20.00%, or the gel solution only contains deionized water; the organic solvent is selected from one or more of N-methylpyrrolidone, dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0015] In an embodiment, the temperature of the gel solution in step two is 10-80°C, or the temperature of the gel solution is 20-60°C.

[0016] As an embodiment, the thickness of the base film reinforcing layer in step two is 50-150 μm (microns) ; the casting solution is coated on the base film reinforcing layer to form a coating layer, and the thickness of the coating layer is 50-100 μm.

[0017] As an embodiment, the base film reinforcing layer in step two is a non-woven fabric.

[0018] The second object of the present application is to provide a preparation method of a composite nanofiltration membrane, which comprises sequentially immersing the modified base film in an aqueous phase solution and an oil phase solution for reaction (interfacial polymerization reaction), and obtaining the composite nanofiltration membrane after the reaction.

[0019] Thus, the modified base film is first immersed in the aqueous phase solution to enable the support layer of the modified base film to be adsorbed with the aqueous phase solution, and then the modified base film adsorbed with the aqueous phase solution is immersed in the oil phase solution for interfacial polymerization reaction, and a desalination layer is formed on the support layer after the reaction. Since the support layer with a large porosity improves the adsorption with the aqueous phase solution, the firmness of the support layer and the desalination layer is improved, thereby improving the desalination stability of the composite nanofiltration membrane, and the composite nanofiltration membrane has a good water flux.

[0020] The interfacial polymerization reaction is as follows:

[0021]

[0022] wherein, PIP is piperazine TMC is trimesoyl chloride

[0023] As an embodiment, the aqueous phase solution is prepared by dissolving one or more of piperazine (PIP), m-phenylenediamine (MPD) and polyethyleneimine (PEI) in water. The total mass of the piperazine (PIP), m-phenylenediamine (MPD) and polyethyleneimine (PEI) accounts for 0.10%-1.00% of the mass of the aqueous phase solution. The aqueous phase solution can also include a surfactant with a total mass of 0.02%-0.10% of the mass of the aqueous phase solution, and the surfactant is, for example, sodium lauryl sulfate.

[0024] As an embodiment, the modified base film is immersed in the aqueous phase solution for 1-10 minutes and then taken out.

[0025] As an embodiment, the oil phase solution is prepared by dissolving one or more of trimesoyl chloride (TMC), terephthaloyl chloride and isophthaloyl chloride in an oil phase solvent. The total mass of the trimesoyl chloride (TMC), terephthaloyl chloride and isophthaloyl chloride accounts for 0.01%-0.50% of the mass of the oil phase solution.

[0026] As an implementation form, the oil phase solvent comprises one or more of hexane, cyclohexane and isoparaffin.

[0027] As an implementation form, the isoparaffin is one or more of Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M and Isopar V.

[0028] As an implementation form, after the modified base film is taken out from the water phase solution, the modified base film is immersed in the oil phase solution for 0.5-5 minutes and then taken out, and the modified base film is dried at a temperature of 70-120℃ for 1-10 minutes.

[0029] A third object of the present application is to prepare a composite nanofiltration membrane.

[0030] The present application has the following beneficial effects:

[0031] The modified base film prepared by the casting solution prepared from the aramid polymer and the imidazole additive has hydrophilic groups such as carboxyl and sulfonic acid groups on the support layer formed on the base film reinforcing layer after the reaction of the imidazole additive with the aramid polymer, which on one hand helps to improve the porosity of the support layer of the modified base film, so that the support layer has more pores, thereby having a good water flux, and on the other hand, in the preparation process of the composite nanofiltration membrane, the modified base film with a larger porosity can improve the adsorption of the water phase solution in the subsequent preparation of the desalination layer, thereby improving the firmness between the desalination layer and the base film support layer. Thus, the prepared composite nanofiltration membrane has a good water flux and high desalination stability. The preparation process of the present application is simple, easy to implement, and has low cost, mild reaction conditions, stable performance, and great industrial application prospect. DETAILED DESCRIPTION

[0032] The following specific examples will describe the present application in detail, however, the present application is not limited to the following examples.

[0033] In the present application, the following methods are used to test the water flux of the prepared modified base film, the water flux of the composite nanofiltration membrane, the desalination rate and the desalination stability:

[0034] The prepared modified base film (at 0.1Mpa) and the composite nanofiltration membrane (at 0.3MPa) are pre-pressed with pure water for half an hour, and the pure water flux of the membrane is tested with pure water, and the rejection performance (desalination rate) of the composite nanofiltration membrane is tested with an electrolyte solution of 2g / L MgSO4, and the recovery rate of pure water is controlled to be 15%.

[0035] The calculation formula of the water flux of the modified base film and the composite nanofiltration membrane is shown in (1):

[0036]

[0037] Wherein, A = effective membrane area, m 2 ; t - time required to collect the volume of produced liquid, h; Q - volume of produced liquid collected in t, L.

[0038] When calculating the water flux of the modified base membrane and the composite nanofiltration membrane, the modified base membrane and the composite nanofiltration membrane are repeatedly measured 3 times, and the average value is taken to obtain the water flux of the modified base membrane and the composite nanofiltration membrane.

[0039] The rejection performance calculation method of the composite nanofiltration membrane is shown in (2):

[0040]

[0041] Wherein, R - rejection rate of the membrane, C f - conductivity of the stock solution, μS / cm; C p - conductivity of the produced water, μS / cm.

[0042] When calculating the rejection performance of the composite nanofiltration membrane, the composite nanofiltration membrane is repeatedly measured 3 times, and the average value is taken to obtain the rejection rate of the composite nanofiltration membrane.

[0043] In order to test the firmness of the desalination layer of the composite nanofiltration membrane, the water flux and rejection rate of the composite nanofiltration membrane are tested after running test for 24 hours, and the firmness of the desalination layer of the composite nanofiltration membrane can be directly reflected by the degree of attenuation of the water flux.

[0044] Comparative Example 1

[0045] (1) Para-aramid and CaCl2 are added to dimethylacetamide to dissolve and prepare a casting solution. The mass fraction of meta-aramid in the casting solution is 15.00%, and the mass fraction of CaCl2 is 2.00%.

[0046] (2) The casting solution is transported to a coating head and coated on a non-woven fabric with a thickness of 100 μm, wherein the coating layer thickness is 100 μm.

[0047] (3) Dimethylacetamide with a mass fraction of 10.00% is dissolved in water to prepare a gel solution, and the non-woven fabric of step (2) is immersed in the gel solution at 30°C to phase invert into a film, and then rinsed to obtain a modified base membrane.

[0048] (4) Remove the excess water on the surface of the modified base membrane, and then immerse it in an aqueous solution of piperazine with a mass fraction of 0.50% and sodium lauryl sulfate with a mass fraction of 0.02% for 2 minutes.

[0049] (5) remove the excess water phase solution on the surface of the modified base membrane, then immerse the modified base membrane into the hexane solution of trimesoyl chloride (0.15% by mass) (oil phase solution), take it out after 0.5 minutes, and dry it in an oven at 100°C for 10 minutes to obtain the composite nanofiltration membrane.

[0050] Test results: the pure water flux of the modified base membrane at 0.1 MPa is 420 L / (m 2 ·h). The pure water flux of the prepared composite nanofiltration membrane is 38.6 L / (m 2 ·h), and the rejection rate to MgSO4 with a concentration of 0.2% is 94.00%. After continuous operation for 24 hours, the pure water flux of the composite nanofiltration membrane is 29.3 L / (m 2 ·h), and the rejection rate to MgSO4 with a concentration of 0.20% is 96.00%.

[0051] Example 1

[0052] (1) Dissolve p-aramid, CaCl2, and imidazole-1-acetic acid in dimethylacetamide to prepare a casting solution. The mass fraction of p-aramid in the casting solution is 15.00%, the mass fraction of CaCl2 is 2.00%, and the mass fraction of imidazole-1-acetic acid is 5.00%.

[0053] (2) Deliver the casting solution to a coating head and coat it on a non-woven fabric with a thickness of 100 μm, wherein the coating layer has a thickness of 100 μm.

[0054] (3) Dissolve dimethylacetamide with a mass fraction of 10.00% in water to prepare a gel solution, immerse the non-woven fabric of step (2) in the gel solution at 30°C to phase invert into a film, and then rinse to obtain a modified base membrane.

[0055] (4) Remove the excess water on the surface of the modified base membrane, and then immerse it in an aqueous phase solution of piperazine with a mass fraction of 0.50% and sodium lauryl sulfate with a mass fraction of 0.02% for 2 minutes.

[0056] (5) Remove the excess water phase solution on the surface of the modified base membrane, then immerse the modified base membrane into the hexane solution of trimesoyl chloride (0.15% by mass) (oil phase solution), take it out after 0.5 minutes, and dry it in an oven at 100°C for 10 minutes to obtain the composite nanofiltration membrane.

[0057] Test results: the pure water flux of the modified base membrane at 0.1 MPa is 530 L / (m 2 ·h). The pure water flux of the prepared composite nanofiltration membrane is 50.7 L / (m 2 ·h), and the rejection rate to MgSO4 with a concentration of 0.20% is 98.80%. After continuous operation for 24 hours, the pure water flux of the composite nanofiltration membrane is 48 L / (m2 • h) was 99.60% for MgSO4with a concentration of 0.20%.

[0058] Example 2

[0059] (1) A casting solution was prepared by dissolving meta-aramid, LiCl2, and imidazole-1-acetic acid in N-methylpyrrolidone. The mass fraction of meta-aramid in the casting solution was 10.00%, the mass fraction of LiCl2was 2.00%, and the mass fraction of imidazole-1-acetic acid was 30.00%.

[0060] (2) The casting solution was delivered to a coating head and coated on a non-woven fabric with a thickness of 50 μm, and the coating layer had a thickness of 80 μm.

[0061] (3) A gel solution was prepared by dissolving N-methylpyrrolidone with a mass fraction of 20.00% in water, and the non-woven fabric of step (2) was immersed in the gel solution at 10°C to phase invert into a film, and after rinsing, a modified base film was obtained.

[0062] (4) The modified base film was immersed in an aqueous solution of m-phenylenediamine with a mass fraction of 1.00% and sodium lauryl sulfate with a mass fraction of 0.10% for 1 minute.

[0063] (5) The modified base film was immersed in a cyclohexane solution (oil phase solution) of terephthaloyl chloride with a mass fraction of 0.10% for 1 minute, and then taken out and dried in an oven at a temperature of 100°C for 8 minutes to obtain a composite nanofiltration membrane.

[0064] Test results: the pure water flux of the modified base film was 590 L / (m 2 · h) at 0.1 MPa. The pure water flux of the composite nanofiltration membrane obtained was 44 L / (m 2 · h), and the rejection rate for MgSO4with a concentration of 0.20% was 97.10%. After 24 hours of continuous operation, the pure water flux of the composite nanofiltration membrane was 52.7 L / (m 2 · h), and the rejection rate for MgSO4with a concentration of 0.20% was 98.50%.

[0065] Example 3

[0066] (1) A casting solution was prepared by dissolving modified meta-aramid, NaNO3, and 2-methylimidazole-4-sulfonic acid in N,N-dimethylformamide. The mass fraction of modified meta-aramid in the casting solution was 20.00%, the mass fraction of NaNO3was 5.00%, and the mass fraction of 2-methylimidazole-4-sulfonic acid was 10.00%.

[0067] (2) The casting solution is delivered to a coating head and coated on a nonwoven fabric having a thickness of 150 μm, wherein the coating layer has a thickness of 50 μm.

[0068] (3) A gel solution is prepared by dissolving pure ionized water, and the nonwoven fabric of step (2) is immersed in the gel solution at 30°C to phase invert into a film, and then rinsed to obtain a modified base film.

[0069] (4) The excess water on the surface of the modified base film is removed, and then the modified base film is immersed in an aqueous solution of 0.50% by mass of polyethyleneimine and 0.05% by mass of sodium lauryl sulfate for 2 minutes.

[0070] (5) The excess aqueous solution on the surface of the modified base film is removed, and then the modified base film is immersed in an isoparaffin solution (an oil phase solution) of 0.01% by mass of isophthaloyl chloride, taken out after 5 minutes, and dried in an oven at 70°C for 10 minutes to obtain a composite nanofiltration membrane.

[0071] Test results: The pure water flux of the modified base film at 0.1 MPa is 555 L / (m 2 ·h). The pure water flux of the obtained composite nanofiltration membrane is 52.2 L / (m 2 ·h), and the rejection rate for 0.20% by mass of MgSO4 is 96.70%. After 24 hours of continuous operation, the pure water flux of the composite nanofiltration membrane is 47 L / (m 2 ·h), and the rejection rate for 0.20% by mass of MgSO4 is 97.40%.

[0072] Example 4

[0073] (1) A casting solution is prepared by adding a modified para-aramid, CH3COONa, and 2-methylimidazole-4-sulfonic acid to dimethyl sulfoxide. The mass fraction of the modified para-aramid in the casting solution is 25.00%, the mass fraction of CH3COONa is 3.00%, and the mass fraction of 2-methylimidazole sulfonic acid is 20.00%.

[0074] (2) The casting solution is delivered to a coating head and coated on a nonwoven fabric having a thickness of 100 μm, wherein the coating layer has a thickness of 100 μm.

[0075] (3) A gel solution is prepared by dissolving dimethyl sulfoxide having a mass fraction of 30.00% in water, and the nonwoven fabric of step (2) is immersed in the gel solution at 10°C to phase invert into a film, and then rinsed with pure water to obtain a modified base film.

[0076] (4) The excess water on the surface of the modified base film is removed, and then the modified base film is immersed in an aqueous solution of 0.10% by mass of piperazine and 0.10% by mass of sodium lauryl sulfate for 10 minutes.

[0077] (5) The excess aqueous solution on the surface of the modified base membrane was removed, and then the modified base membrane was immersed in a cyclohexane solution (an oil phase solution) of terephthaloyl chloride with a mass fraction of 0.50%. After 1 minute, the modified base membrane was taken out and dried in an oven at a temperature of 120°C for 1 minute to obtain a composite nanofiltration membrane.

[0078] Test results: The pure water flux of the modified base membrane at 0.1 MPa was 490 L / (m 2 ·h). The pure water flux of the prepared composite nanofiltration membrane was 43 L / (m 2 ·h), and the rejection rate for MgSO4 with a concentration of 0.20% was 96.40%. After 24 hours of continuous operation, the pure water flux of the composite nanofiltration membrane was 41 L / (m 2 ·h), and the rejection rate for MgSO4 with a concentration of 0.20% was 97.50%.

[0079] Table 1: Water flux and rejection rate of Comparative Example 1 and Examples 1-4

[0080]

[0081]

[0082] Table 2: Degree of attenuation of water flux of Comparative Example 1 and Examples 1-4

[0083] Water flux decay rate / % Comparative Example 1 24.09 Example 1 5.33 Example 2 2.95 Example 3 9.96 Example 4 4.65

[0084] From the results of Table 1 and Table 2, it can be seen that the modified base membrane prepared by using aramid polymer and imidazole additive to prepare a casting solution has a good pure water flux; the composite nanofiltration membrane prepared by using the modified base membrane has a good pure water flux and a good desalination rate; and the degree of attenuation of water flux after 24 hours of operation test can intuitively reflect the firmness of the desalination layer and the base membrane of the composite nanofiltration membrane. From the test results for 24 hours, it can be seen that the desalination layer and the base membrane of the composite nanofiltration membrane have good firmness.

Claims

1. A method for producing a modified base film, characterized by, The method comprises the following steps: Step one, dissolving aramid polymer and imidazole additive in organic solvent to prepare casting solution; Step two, coating the casting solution on the base film reinforcing layer, and then placing the base film reinforcing layer coated with the casting solution in a gel solution to prepare the modified base film; The imidazole additive in step one is imidazole-1-acetic acid and / or 2-methyl imidazole-4-sulfonic acid.

2. The method for preparing a modified base film as described in claim 1, characterized in that, The aramid polymer in step one comprises one or more of meta-aramid, para-aramid, modified meta-aramid and modified para-aramid.

3. The method for preparing a modified base film as described in claim 1, characterized in that, The organic solvent in step one is selected from one or more of N-methyl pyrrolidone, dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide.

4. The method for preparing a modified base film as described in claim 1, characterized in that, The mass fraction of the aramid polymer in step one is 10.00%-25.00%, and the mass fraction of the imidazole additive is 5.00%-30.00%.

5. The method for preparing a modified base film as described in claim 1, characterized in that, The casting solution in step one further comprises an inorganic additive; the mass fraction of the inorganic additive is 2.00%-5.00%; the inorganic additive is selected from one or more of LiCl, LiNO3, CH3COONa, NaNO3 and CaCl2.

6. The method for preparing a modified base film as described in claim 1, characterized in that, The gel solution in step two comprises an organic solvent and water; the mass fraction of the organic solvent in the gel solution is 0.00%-30.00%; the organic solvent is selected from one or more of N-methyl pyrrolidone, dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide.

7. The method for preparing a modified base film according to claim 1, characterized in that, The base film reinforcing layer in step two is a non-woven fabric.

8. A method for preparing a composite nanofiltration membrane, characterized by, The modified base film prepared by the method of any one of claims 1 to 7 is sequentially immersed in an aqueous solution and an oil phase solution for reaction, and a composite nanofiltration membrane is prepared after the reaction.

9. The method of claim 8, wherein the composite nanofiltration membrane is prepared by the steps of: The aqueous solution is prepared by dissolving one or more of piperazine, m-phenylenediamine and polyethyleneimine in water.

10. The method for preparing a composite nanofiltration membrane as described in claim 8, characterized in that, The oil phase solution is prepared by dissolving one or more of trimesoyl chloride, terephthaloyl chloride and isophthaloyl chloride in an oil phase solvent.

11. The method of claim 10, wherein the composite nanofiltration membrane is prepared by the steps of: The oil phase solvent comprises one or more of hexane, cyclohexane and isomeric alkanes.

12. A composite nanofiltration membrane prepared by the method of any one of claims 8 to 11.

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