Preparation method of polyester nanofiltration membrane with high chlorine resistance and pollution resistance

Abstract

A preparation method of a polyester nanofiltration membrane with high chlorine resistance and pollution resistance relates to the technical field of chlorine-resistant polyester nanofiltration membranes, and comprises the following steps: sequentially dipping a polyacrylonitrile support layer in an aqueous phase solution and an oil phase solution, carrying out condensation polymerization at 25-45 DEG C to generate a polyester selection layer on the surface, and finally heating and crosslinking at 45-65 DEG C to obtain the polyester nanofiltration membrane. The aqueous phase solution is a tannic acid aqueous solution, a rhamnose aqueous solution, a vitamin C aqueous solution or a chlorogenic acid aqueous solution, the preparation method is simple and low in cost, and the formed polyester nanofiltration membrane has high chlorine resistance and pollution resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of chlorine-resistant polyester nanofiltration membranes, and specifically to a preparation method of a polyester nanofiltration membrane with high chlorine resistance and anti-pollution properties. Background Art

[0002] During the production process of the dye industry, high-salinity printing and dyeing wastewater is generated. If directly discharged, it will cause serious environmental pollution problems. Moreover, such wastewater usually contains inorganic salts (such as NaCl, Na2SO4) with a concentration as high as 5-20 wt% and high-value dye molecules (such as direct red, congo red). If the inorganic salts and dye molecules are separated and recovered, both resource reuse can be achieved and the ecological toxicity can be reduced.

[0003] Currently, polyamide membranes are mostly used to separate inorganic salts and dye molecules in printing and dyeing wastewater. However, due to their dense pore size and high surface charge density, polyamide membranes have the following problems: (1) The salt rejection rate is too high, and the rejection rate of Na2SO4 is >80%; (2) The flux is limited, and the pure water flux is generally lower than 35 L / (m 2 ·h·bar), and it is necessary to separate inorganic salts and dye molecules under high pressure (≥5 bar) conditions, resulting in high energy consumption; (3) Poor chlorine resistance, the printing and dyeing wastewater contains active chlorine, and the presence of active chlorine makes the amide bond easily break, thereby causing the rejection rate to rapidly decay; (4) Irreversible pollution, the dye molecules adsorbed on the polyamide membrane block the membrane pores through π-π stacking.

[0004] In the prior art, in order to improve the chlorine resistance of polyamide membranes, a catechol interlayer and a polyamide desalination layer are added to form a catechol self-polymerized interlayer (such as Chinese Patent CN119303455A), or a compound containing active functional groups is grafted on the membrane surface to cap the residual amino groups on the membrane surface to generate more stable groups, reducing the active sites that can react with active chlorine (such as Chinese Patent CN114504956A). However, the process of preparing nanofiltration membranes by the above methods is complex, requires multiple modifications, and has a high cost. Therefore, developing a low-cost nanofiltration membrane with high chlorine resistance and anti-pollution properties is the focus of research by researchers in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a polyester nanofiltration membrane with high chlorine resistance and anti-pollution properties. This preparation method is simple, low-cost, and the formed polyester nanofiltration membrane has high chlorine resistance and anti-pollution properties.

[0006] To achieve the above object, the specific solution adopted by the present invention is as follows: A method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane, wherein the polyacrylonitrile support layer is successively immersed in an aqueous solution and an oil-phase solution, and a polycondensation reaction is carried out at 25-45 °C to form a polyester selective layer on its surface, and finally heat cross-linking is carried out at 45-65 °C to obtain the polyester nanofiltration membrane. The aqueous solution is an aqueous solution of tannic acid, an aqueous solution of rhamnose, an aqueous solution of vitamin C, or an aqueous solution of chlorogenic acid.

[0007] As an optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: The method for preparing the polyacrylonitrile support layer is to immerse the polyacrylonitrile ultrafiltration membrane in an aqueous sodium hydroxide solution and carry out hydrolysis treatment by soaking at 50 °C for 1-2 h.

[0008] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: The concentration of the aqueous sodium hydroxide solution is 0.5-2 mol / L.

[0009] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: The oil-phase solution is a solution obtained by dissolving 1,3,5-benzenetricarbonyl chloride in a n-hexane solvent.

[0010] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: The mass fraction of 1,3,5-benzenetricarbonyl chloride in the oil-phase solution is 0.025-0.15 wt%.

[0011] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: Immerse the polyacrylonitrile support layer in the aqueous solution for 1-20 min; then immerse the polyacrylonitrile support layer in the oil-phase solution for 1-20 min.

[0012] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: The mass fraction of tannic acid in the aqueous tannic acid solution is 0.05-0.15 wt%.

[0013] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane: Immerse the polyacrylonitrile support layer successively in the aqueous tannic acid solution and the oil-phase solution, and carry out a polycondensation reaction at 30 °C to form a polyester selective layer on its surface. The mass fraction of tannic acid in the aqueous tannic acid solution is 0.10 wt%.

[0014] An application of the above polyester nanofiltration membrane in the separation of dye wastewater.

[0015] As another optimized solution of the above method for preparing a highly chlorine-resistant and anti-pollution polyester nanofiltration membrane:

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a polyester nanofiltration membrane with high chlorine resistance and anti-pollution performance. The polyacrylonitrile support layer is successively immersed in an aqueous solution and an oil phase solution. The polyphenol hydroxyl topological structures of tannic acid and chlorogenic acid provide dense cross-linking sites, enabling the precise formation of an ultrathin polyester selective layer on the surface of the polyacrylonitrile support layer. Then, heating cross-linking is carried out to obtain the polyester nanofiltration membrane. This polyester nanofiltration membrane can efficiently separate dye molecules and inorganic salts, and has high chlorine resistance and anti-pollution performance. The o-phenol specific group makes the surface of the polyester nanofiltration membrane strongly hydrophilic, improving the flux and anti-pollution performance. At the same time, the raw materials used in this preparation method are renewable and have a low cost. Description of the Drawings

[0017] Figure 1 are the pure water fluxes and dye rejection rates of the polyester nanofiltration membranes prepared in Examples 1-5;

[0018] Figure 2 are the salt rejection rates of the polyester nanofiltration membranes prepared in Examples 1-5;

[0019] Figure 3 are the water fluxes and dye rejection rates of the polyester nanofiltration membrane prepared in Example 3 after being soaked in NaClO;

[0020] Figure 4 is the normalized flux of the polyester nanofiltration membrane prepared in Example 3 after being contaminated with bovine serum albumin;

[0021] Figure 5 is the surface SEM image of the polyester nanofiltration membrane prepared in Example 3;

[0022] Figure 6 are the contact angles of the polyester nanofiltration membranes prepared in Examples 1-5. Detailed Embodiments

[0023] The following further elaborates on the technical solutions of the present invention in combination with specific embodiments. For the parts not detailedly recorded and disclosed in the following embodiments of the present invention, they should all be understood as the prior art known or should be known to those skilled in the art.

[0024] A method for preparing a polyester nanofiltration membrane with high chlorine resistance and anti-pollution performance, wherein the polyacrylonitrile support layer is successively impregnated in an aqueous solution and an oil phase solution, and a polycondensation reaction is carried out at 25-45 °C to form a polyester selective layer on its surface, and finally heating cross-linking is carried out at 45-65 °C to obtain the polyester nanofiltration membrane. The aqueous solution is an aqueous solution of tannic acid, an aqueous solution of rhamnose, an aqueous solution of vitamin C, or an aqueous solution of chlorogenic acid. Specifically, it includes the following steps:

[0025] Preparation of polyacrylonitrile support layer: Immerse the polyacrylonitrile ultrafiltration membrane in an aqueous sodium hydroxide solution and perform hydrolysis treatment by soaking at 50 °C for 1 - 2 h, where the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L. The surface of the polyacrylonitrile support layer has more carboxyl groups to increase hydrophilicity. At the same time, the increase in surface functional groups of the polyacrylonitrile ultrafiltration membrane also enhances the hydrogen bond interaction between the subsequent materials and the membrane matrix, thereby improving the adhesion between the materials and the membrane matrix.

[0026] Fix the polyacrylonitrile support layer in the membrane module, dry it with an air gun, pour the aqueous solution into the membrane module to completely immerse the polyacrylonitrile support layer, pour out the aqueous solution in the membrane module after soaking for 1 - 20 min, and air-dry it in the air.

[0027] Then pour the oil phase solution into the membrane module to completely immerse the polyacrylonitrile support layer, and carry out a polycondensation reaction at 25 - 45 °C to form a polyester selective layer on its surface. The oil phase solution is a solution obtained by dissolving 1,3,5-benzenetricarbonyl chloride in a n-hexane solvent, and the mass fraction of 1,3,5-benzenetricarbonyl chloride in the oil phase solution is 0.025 - 0.15 wt%; subsequently, drain the remaining oil phase solution, and wash the membrane surface with n-hexane to remove the unreacted monomers.

[0028] Finally, perform heat cross-linking at 45 - 65 °C to obtain a polyester nanofiltration membrane.

[0029] In this method, tannic acid and chlorogenic acid in the aqueous solution have a polyphenol hydroxyl topological structure, providing dense cross-linking sites, and can accurately generate an ultrathin polyester selective layer on the surface of the polyacrylonitrile support layer; then heat cross-linking is carried out to obtain a polyester nanofiltration membrane. This polyester nanofiltration membrane can efficiently separate dye molecules and inorganic salts, and has high chlorine resistance (chlorine resistance reaches 360000 ppm h) and anti-pollution properties; the o-phenol specific group makes the surface of the polyester nanofiltration membrane strongly hydrophilic, improving the flux and anti-pollution performance; at the same time, the raw materials used in this preparation method are renewable and have low costs.

[0030] Example 1

[0031] A preparation method of a loose polyester nanofiltration membrane with high chlorine resistance and anti-pollution properties specifically includes the following steps:

[0032] Put a 7.5×7.5 cm polyacrylonitrile ultrafiltration membrane into an aqueous sodium hydroxide solution with a concentration of 0.5 mol / L and soak it at 50 °C for 1 h to obtain a polyacrylonitrile support layer;

[0033] Weigh 5 mg of tannic acid, add 9.995 g of deionized water, and dissolve it by ultrasonic treatment to prepare an aqueous tannic acid solution with a mass fraction of 0.05 wt%;

[0034] Weigh 5 mg of 1,3,5-benzenetricarbonyl chloride and 9.995 g of n-hexane, dissolve them by ultrasonic treatment, and prepare an oil-phase solution with a mass fraction of 0.05 wt%.

[0035] Fix the alkali-treated polyacrylonitrile-based membrane in the membrane module, blow dry the deionized water on its surface with an air gun, pour 8 mL of tannic acid aqueous solution into the membrane module, let it stand for 5 min and then pour out the tannic acid aqueous solution, and air-dry it naturally.

[0036] Then slowly pour 8 mL of the oil-phase solution into the membrane module, react at 35 °C for 2 min, then drain the remaining oil-phase solution, and wash the membrane surface with n-hexane to remove the unreacted oil-phase monomers.

[0037] Immediately place the membrane module in a cross-linking condition at 60 °C for 5 min to obtain a stable loose polyester nanofiltration membrane, labeled as M-0.05, and soak it in deionized water for standby measurement.

[0038] Example 2

[0039] A preparation method of a loose polyester nanofiltration membrane with high chlorine resistance and anti-pollution performance, specifically including the following steps:

[0040] Put a 7.5×7.5 cm polyacrylonitrile ultrafiltration membrane into a sodium hydroxide aqueous solution with a concentration of 2 mol / L, soak it at 50 °C for 2 h to obtain a polyacrylonitrile support layer.

[0041] Weigh 7.5 mg of tannic acid, add 9.9925 g of deionized water, dissolve it by ultrasonic treatment, and prepare a tannic acid aqueous solution with a mass fraction of 0.075 wt%.

[0042] Weigh 5 mg of 1,3,5-benzenetricarbonyl chloride and 9.995 g of n-hexane, dissolve them by ultrasonic treatment, and prepare an oil-phase solution with a mass fraction of 0.05 wt%.

[0043] Fix the alkali-treated polyacrylonitrile-based membrane in the membrane module, blow dry the deionized water on its surface with an air gun, pour 8 mL into the membrane module, let it stand for 5 min and then pour it out, and air-dry it naturally.

[0044] Then slowly pour 8 mL of the oil-phase solution into the membrane module, react at 35 °C for 2 min, then drain the remaining oil-phase solution, and wash the membrane surface with n-hexane to remove the unreacted oil-phase monomers.

[0045] Immediately place the membrane module in a cross-linking condition at 60 °C for 5 min to obtain a stable loose polyester nanofiltration membrane, labeled as M-0.075, and soak it in deionized water for standby measurement.

[0046] Example 3

[0047] A preparation method of a loose polyester nanofiltration membrane with high chlorine resistance and anti-pollution property, specifically including the following steps:

[0048] Put a 7.5×7.5 cm polyacrylonitrile ultrafiltration membrane into an aqueous sodium hydroxide solution with a concentration of 0.5 mol / L, soak it at 50 °C for 1 h to obtain a polyacrylonitrile support layer;

[0049] Weigh 10 mg of chlorogenic acid, add 9.995 g of deionized water, and dissolve it by ultrasonic to prepare an aqueous chlorogenic acid solution with a mass fraction of 0.1 wt%;

[0050] Weigh 5 mg of 1,3,5-benzenetricarbonyl chloride and 9.995 g of n-hexane, and dissolve it by ultrasonic to prepare an oil-phase solution with a mass fraction of 0.05 wt%;

[0051] Fix the alkali-treated polyacrylonitrile-based membrane in the membrane module, blow dry the deionized water on its surface with an air gun, pour 8 mL of the chlorogenic acid aqueous solution into the membrane module, let it stand for 5 min and then pour out the chlorogenic acid aqueous solution, and air dry it naturally;

[0052] Then slowly pour 8 mL of the oil-phase solution into the membrane module, react at 35 °C for 2 min, then drain the remaining oil-phase solution, and wash the membrane surface with n-hexane to remove the unreacted oil-phase monomers;

[0053] Immediately put the membrane module into crosslinking at 60 °C for 5 min to obtain a stable loose polyester nanofiltration membrane, marked as M-0.1, soak it in deionized water, and reserve it for testing.

[0054] Example 4

[0055] A preparation method of a loose polyester nanofiltration membrane with high chlorine resistance and anti-pollution property, specifically including the following steps:

[0056] Put a 7.5×7.5 cm polyacrylonitrile ultrafiltration membrane into an aqueous sodium hydroxide solution with a concentration of 0.5 mol / L, soak it at 50 °C for 1 h to obtain a polyacrylonitrile support layer;

[0057] Weigh 12.5 mg of chlorogenic acid, add 9.995 g of deionized water, and dissolve it by ultrasonic to prepare an aqueous chlorogenic acid solution with a mass fraction of 0.125 wt%;

[0058] Weigh 5 mg of 1,3,5-benzenetricarbonyl chloride and 9.995 g of n-hexane, and dissolve it by ultrasonic to prepare an oil-phase solution with a mass fraction of 0.05 wt%;

[0059] Fix the alkali-treated polyacrylonitrile-based membrane in the membrane module, blow dry the deionized water on its surface with an air gun, pour 8 mL into it, let it stand for 5 min and then pour it out, and air dry it naturally;

[0060] Slowly pour 8 mL of the oil-phase solution into the membrane module, react at 35 °C for 2 min, then drain the remaining oil-phase solution, and wash the membrane surface with n-hexane to remove the unreacted oil-phase monomers;

[0061] Immediately place the membrane module in a crosslinking condition at 60 °C for 5 min to obtain a stable loose polyester nanofiltration membrane, labeled as M-0.125, and soak it in deionized water for standby measurement.

[0062] Example 5

[0063] A preparation method of a loose polyester nanofiltration membrane with high chlorine resistance and anti-pollution performance specifically includes the following steps:

[0064] Put a 7.5×7.5 cm polyacrylonitrile ultrafiltration membrane into an aqueous sodium hydroxide solution with a concentration of 0.5 mol / L, soak it at 50 °C for 1 h to obtain a polyacrylonitrile support layer;

[0065] Weigh 15 mg of tannic acid, add 9.985 g of deionized water, and dissolve it by ultrasonic to prepare a tannic acid aqueous solution with a mass fraction of 0.15 wt%;

[0066] Weigh 5 mg of 1,3,5-benzenetricarbonyl chloride and 9.995 g of n-hexane, and dissolve it by ultrasonic to prepare an oil-phase solution with a mass fraction of 0.05 wt%;

[0067] Fix the alkali-treated polyacrylonitrile-based membrane in the membrane module, blow dry the deionized water on its surface with an air gun, pour 8 mL of the tannic acid aqueous solution into the membrane module, pour out the tannic acid aqueous solution after standing for 5 min, and dry it naturally in the shade;

[0068] Slowly pour 8 mL of the oil-phase solution into the membrane module again, react at 35 °C for 2 min, then drain the remaining oil-phase solution, and wash the membrane surface with n-hexane to remove the unreacted oil-phase monomers;

[0069] Immediately place the membrane module in a crosslinking condition at 60 °C for 5 min to obtain a stable loose polyester nanofiltration membrane, labeled as M-0.15, and soak it in deionized water for standby measurement.

[0070] Comparative Example 1

[0071] A polyamide composite nanofiltration membrane was prepared by using a method for preparing a chlorine-resistant polyamide composite nanofiltration membrane and its preparation method disclosed in Chinese Patent CN119303455A, labeled as D-1, and reserved for standby measurement.

[0072] Comparative Example 2

[0073] A nanofiltration membrane was prepared by using a method for preparing a nanofiltration membrane with high chlorine resistance and anti-pollution performance disclosed in Chinese Patent CN 116020281A, labeled as D-2, and reserved for standby measurement.

[0074] Comparative Example 3

[0075] A nanofiltration membrane was prepared by using a chlorine-resistant nanofiltration membrane and its preparation method disclosed in Chinese Patent CN 114504956A, marked as D-3, and reserved for subsequent testing.

[0076] <Pure water flux test>

[0077] The pure water flux tests were carried out on the polyacrylonitrile ultrafiltration membrane and the polyester nanofiltration membranes prepared in Examples 1-5. The test results are as Figure 1 shown.

[0078] <Dye rejection test>

[0079] The dye rejection tests were carried out on the polyacrylonitrile ultrafiltration membrane and the polyester nanofiltration membranes prepared in Examples 1-5. The test results are as Figure 1 and Table 1 show that the dye concentration in the dye rejection test was 0.2 g / L -1 .

[0080] <Salt rejection test>

[0081] The salt rejection tests were carried out on the polyacrylonitrile ultrafiltration membrane and the polyester nanofiltration membranes prepared in Examples 1-5. The test results are as Figure 2 and Table 1 show that the salt concentration in the salt rejection test was 1 g / L -1 .

[0082] <Chlorine resistance test>

[0083] The polyester nanofiltration membrane obtained in Example 3 was immersed in 5000 ppm of NaClO for 72 h. After that, the pure water flux test and the dye rejection test were carried out on the immersed polyester nanofiltration membrane. The water flux and the Congo red dye rejection rate remained basically unchanged (as Figure 3 shown), indicating that the prepared polyester nanofiltration membrane has good chlorine resistance.

[0084] <Dynamic filtration fouling test>

[0085] The dynamic filtration fouling test was carried out on the polyester nanofiltration membrane (M-0.1) prepared in Example 3. Specifically, a 1000 ppm bovine serum albumin solution was used as the protein contaminant. After three cycles of fouling - backwashing, etc., the normalized flux of the polyester nanofiltration membrane fluctuated within a very small range (as Figure 4 shown), indicating that the prepared polyester nanofiltration membrane has excellent anti-fouling performance.

[0086] Table 1 Dye and salt rejection rates

[0087] <Comparative test>

[0088] The separation performance, chlorine resistance performance, and anti-fouling performance of M-0.1, D-1, D-2, and D-3 were tested respectively, and the results are shown in Table 2.

[0089] Table 2 Comparison table of chlorine resistance and anti-fouling performance

[0090] In summary, for the polyester nanofiltration membrane of the present invention, in a high-concentration chlorine environment, its dye rejection rate and flux can still basically remain stable, and it has excellent chlorine resistance performance and anti-fouling performance without affecting its separation effect.

[0091] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance, characterized in that: The polyacrylonitrile support layer is immersed in an aqueous solution and an oil solution in turn, and a condensation reaction is carried out at 25-45°C to form a polyester selective layer on its surface. Finally, it is heated and cross-linked at 45-65°C to obtain a polyester nanofiltration membrane. The aqueous solution is a tannic acid aqueous solution, a rhamnose aqueous solution, a vitamin C aqueous solution or a chlorogenic acid aqueous solution.

2. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 1, characterized in that: The preparation method of the polyacrylonitrile support layer is to immerse the polyacrylonitrile ultrafiltration membrane in a sodium hydroxide aqueous solution at 50° C. for 1-2 hours for hydrolysis treatment.

3. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 2, characterized in that: The concentration of the sodium hydroxide aqueous solution is 0.5-2 mol / L.

4. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 1, characterized in that: The oil phase solution is a solution obtained by dissolving 1,3,5-trimethylbenzenecarboxylic acid chloride in n-hexane solvent.

5. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 4, characterized in that: The mass fraction of 1,3,5-trimethylbenzenecarboxylic acid chloride in the oil phase solution is 0.025-0.15 wt %.

6. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 1, characterized in that: The polyacrylonitrile support layer is immersed in the aqueous phase solution for 1-20 min; and then the polyacrylonitrile support layer is immersed in the oil phase solution for 1-20 min.

7. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 1, characterized in that: The mass fraction of tannic acid in the tannic acid aqueous solution is 0.05-0.15wt%.

8. The method for preparing a polyester nanofiltration membrane with high chlorine resistance and pollution resistance as claimed in claim 1, characterized in that: The polyacrylonitrile support layer was immersed in a tannic acid aqueous solution and an oil phase solution in turn, and polycondensed at 30° C. to generate a polyester selective layer on its surface. The mass fraction of tannic acid in the tannic acid aqueous solution was 0.10 wt %.

9. A polyester nanofiltration membrane with high chlorine resistance and anti-pollution properties, characterized in that: The method is obtained by the preparation method described in any one of claims 1 to 8.

10. Use of the polyester nanofiltration membrane as claimed in claim 9 in separation of dye wastewater.

Images