Side chain ion pair modified polyether sulphone hollow fiber ultrafiltration membrane and preparation method thereof

Abstract

The invention relates to the field of high-molecular polymer materials, and discloses a side chain ion pair modified polyarylether sulfone hollow fiber ultrafiltration membrane and a preparation method thereof, and the preparation method comprises the following steps: (1) preparing polyarylether sulfone; (2) preparing side chain ion pair modified polyether sulphone; (3) preparing a membrane casting solution; and (4) preparing the hollow fiber ultrafiltration membrane. According to the hollow fiber ultrafiltration membrane disclosed by the invention, polyarylether sulfone prepared by a condensation polymerization method is used as a base material, the number of active sites is controlled by adjusting the molar ratio of amino-containing monomers on a polymer main chain, and finally controllable adjustment of ion pairs and charge capacity on the surface of the hollow fiber membrane is realized; the side chain ion pair modified polyarylether sulfone is adopted as a main body structure of the ultrafiltration membrane, after the membrane is formed, the membrane has permanent ion pair charge property, the surface is endowed with permanent hydrophilicity, and the anti-pollution capacity of the ultrafiltration membrane can be improved.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and particularly relates to a side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane and a preparation method thereof, belonging to the field of membrane technology. Background Art

[0002] During the ultrafiltration process, a common phenomenon is that the permeation rate of the membrane decreases with the prolongation of the operation time. For ultrafiltration, once the feed liquid comes into contact with the membrane, membrane fouling begins. If the membrane material is not selected appropriately, it will have a significant impact on the separation and permeation performance of the membrane. Compared with the initial pure water permeation rate, the flux of the membrane after intercepting the feed liquid for a period of time can be reduced by 20%-40%. When the fouling is severe, the membrane flux can decrease by more than 80%. Membrane fouling of ultrafiltration membranes refers to the phenomenon that particles, colloidal particles or solute macromolecules in the feed liquid are adsorbed, deposited on the membrane surface or in the membrane pores through physical adsorption, chemical action or mechanical interception, resulting in the reduction of the membrane pore size or blockage, and causing irreversible changes in the permeation rate and separation characteristics of the membrane. Membrane fouling will lead to a series of serious consequences, such as the decrease of the permeation rate; due to membrane fouling, it is required to increase the membrane area and the membrane cleaning system, resulting in an increase in equipment costs (the cleaning cost is about 5%-20% of the operating cost); the frequent cleaning of the membrane reduces the membrane life and increases the production cost; membrane fouling may also affect the separation ability of the membrane, thus affecting the product quality.

[0003] Increasing the hydrophilicity of the separation membrane can enhance the anti-fouling performance of the membrane. The main reason for the easy fouling of hydrophobic membranes is that there is almost no hydrogen bond interaction between the membrane interface and water. The repulsion between water molecules and the hydrophobic membrane surface is a spontaneous process with increasing entropy. Therefore, pollutant molecules tend to adsorb on the membrane surface and control the boundary layer. In contrast, a membrane with a hydrophilic layer has a higher surface tension and can form hydrogen bonds with surrounding water molecules, thereby reconstructing a thin water boundary between the membrane and the bulk solution. This boundary layer can prevent the adsorption and deposition of hydrophobic pollutants on the membrane surface, thus reducing fouling.

[0004] Charged polymer materials can endow ultrafiltration membranes with special properties. For example, a positively charged surface can effectively reduce the adsorption of positively charged pollutants (such as bacteria, proteins, certain colloids) through electrostatic repulsion, reducing the risk of membrane fouling; charged polymers often have hydrophilic groups (such as amino groups), which can improve the hydrophilicity of the membrane surface, reduce the adhesion of hydrophobic pollutants (such as oils and fats), and extend the membrane life; during the ultrafiltration process, the charge effect can make up for the pore size limitation and improve the separation efficiency of small molecule charged substances; some positively charged polymers can still maintain charge stability in a wide pH range (such as pH 2-12) and are suitable for harsh chemical environments. Summary of the Invention

[0005] To solve the above technical problems existing in the prior art, the technical problem to be solved by the present invention is to provide a side-chain ion pair modified polyarylether sulfone hollow fiber ultrafiltration membrane and a preparation method thereof.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a side-chain ion pair modified polyarylether sulfone hollow fiber ultrafiltration membrane, comprising the following steps:

[0008] (1) Preparation of polyarylether sulfone

[0009] The polyarylether sulfone PAES-NH2 (IV) containing an amino-phenolphthalein structure is obtained by solvent co-polycondensation of 2-(3-(dimethylamine)propyl)-3,3-bis(4-hydroxyphenyl)isoindolinone monomer (I), 4,4'-difluorodiphenyl sulfone monomer (II), and 2,2'-bis(4-hydroxyphenyl)hexafluoropropane monomer (III), wherein the molar ratio of monomer (I) to the sum of monomer (III) and monomer (II) is 1:1, and the molar ratio of monomer (III) to monomer (II) is m:100 - m = 100% - 11%:1% - 90%; the number average molecular weight Mn of the PAES-NH2 is 20,000 - 200,000;

[0010]

[0011] (2) Preparation of side-chain ion pair modified polyarylether sulfone

[0012] The prepared PAES-NH2 is dissolved in an organic solvent and cooled to below 0 °C, and then sodium 3-bromopropanesulfonate shown in formula (IV) is added in a mass ratio of 10:1.50 - 3.00, stirred for a certain period of time, precipitated in methanol, ethanol or isopropanol, and vacuum dried to obtain side-chain ion pair modified polyarylether sulfone PAES-N-S, the structural formula of which is shown in formula (V);

[0013]

[0014] (3) Preparation of the casting solution

[0015] A certain amount of side-chain ion pair modified polyarylether sulfone PAES-N-S, polyvinylpyrrolidone PVP or / and polyethylene glycol PEG and other additives are dissolved in a solvent, and at room temperature, stirred and dissolved for 3 - 5 hours until a homogeneous solution is formed, and after ultrasonic treatment or vacuum or static defoaming for several hours, a casting solution with a certain concentration is prepared;

[0016] (4) Preparation of the hollow fiber ultrafiltration membrane

[0017] 1) The casting solution prepared in step (3) is extruded through a spinneret by a metering pump. After passing through an air gap of 1 - 10 cm, it is vertically immersed in a gel bath at 45 - 75 °C for phase separation and curing, and then introduced into a wire collecting tank through a winding wheel with a winding speed of 4 - 10 m / min to form a hollow fiber ultrafiltration membrane;

[0018] 2) At room temperature, the hollow fiber ultrafiltration membrane prepared in step 1) is soaked in deionized water for shaping and rinsed with clear water to remove residual solvents and additives, forming a shaped hollow fiber ultrafiltration membrane.

[0019] Further, in step (1), the molar ratio of the monomer (III) to the monomer (II) is m:100 - m, preferably 20%:80%.

[0020] Further, in step (3), the raw materials are weighed according to the following weight ratio: 14 - 24 parts of PAES - N - S, 14 - 25 parts of PVP / PEG, 1 - 2 parts of other additives, and 49 - 72 parts of organic solvent.

[0021] Further, the intrinsic viscosity range of the casting solution is 0.5 - 1.0, and the preferred intrinsic viscosity range is 0.7 - 0.9.

[0022] Further, the grade of the PVP is one or any combination of K85, K90, or K120; the grade of the PEG is one or any combination of PEG200, PEG400, PEG600, PEG800, or PEG1000.

[0023] Further, the solvent used in step (1) is one or more of N,N'-dimethylacetamide (DMAc), N,N'-dimethylformamide (DMF), and N-methylpyrrolidone (NMP).

[0024] Further, the other additives in step (3) are one or more of pure water, polyethylene glycol, oxalic acid, and water-soluble inorganic salts; the water-soluble inorganic salts are at least one of lithium chloride (LiCl) and lithium nitrate (LiNO3).

[0025] A side-chain ion pair modified poly(arylene ether sulfone) hollow fiber ultrafiltration membrane is prepared by using the described preparation method.

[0026] Compared with the prior art, the advantages of the side-chain ion pair modified poly(arylene ether sulfone) hollow fiber ultrafiltration membrane and its preparation method of the present invention are as follows:

[0027] 1) The hollow fiber ultrafiltration membrane of the present invention uses poly(arylene ether sulfone) prepared by polycondensation polymerization as the base material, and controls the number of active sites by adjusting the molar ratio of the amine group-containing monomer on the polymer main chain, and finally realizes the controllable adjustment of the ion pair and the charge amount on the surface of the hollow fiber membrane.

[0028] 2) The hollow fiber ultrafiltration membrane of the present invention uses polyarylethersulfone modified with side-chain ion pairs as the main structure of the ultrafiltration membrane. After film formation, it has permanent ion pair chargeability and also imparts permanent hydrophilicity to the surface, which can improve the anti-fouling ability of the ultrafiltration membrane. Detailed implementation mode

[0029] To further illustrate the technical solution of the present invention, the following describes the preferred implementation modes of the present invention in combination with specific embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] Example 1

[0031] 1) Preparation of polymer:

[0032] 50.8041 g (200 mmol) of 4,4'-difluorodiphenylsulfone monomer, 6.7246 g (20 mmol) of 2,2'-bis(4-hydroxyphenyl)hexafluoropropane monomer, and 72.4482 g (180 mmol) of 2-(3-(dimethylamine)propyl)-3,3-bis(4-hydroxyphenyl)isoindolinone monomer were successively added to a 250 mL three-necked round-bottom flask equipped with a water separator. Using DMAc (500 mL) as the solvent, 56 g of K2CO3 and 200 mL of toluene were added as a catalyst and a water carrier, respectively. Under a N2 atmosphere, the reaction was carried out at 155 °C for 12 hours, and then at 165 °C for 12 hours. After the solution was cooled to room temperature, it was poured into 400 mL of ethanol, and a precipitate was obtained by high-speed stirring. After filtration and separation, a white solid was obtained, which was washed repeatedly with ethanol and water, and dried in vacuo at 80 °C for 20 hours to obtain 208.1 g of amino-containing polyarylethersulfone PAES-NH2 with a number average molecular weight Mn = 129000.

[0033] 200.0 g of PAES-NH2 was dissolved in 1.0 L of the organic solvent NMP and cooled to below 0 °C. Then, 50.0 g of sodium 3-bromopropanesulfonate was added according to a mass ratio of 10:2, and the mixture was stirred at room temperature for 12 hours, and then precipitated in isopropanol and dried in vacuo at 60 °C to obtain 210.0 g of polyarylethersulfone modified with side-chain ion pairs (PAES-N-S).

[0034] 2) Preparation of casting solution:

[0035] Weigh 160 g (16 wt%) of PAES-N-S, 160 g (8 wt% / 8 wt%) of PVPK90 / PEG900, and 10 g (1 wt%) of LiNO3 into a dosing container containing 680 g (67 wt%) of DMAc, and stir at room temperature for 5 hours to form a homogeneous casting solution. After ultrasonic treatment of the casting solution for 1 hour, it is sealed and reserved. The intrinsic viscosity is measured to be 0.77.

[0036] 3) Preparation of hollow fiber ultrafiltration membrane:

[0037] The casting solution is extruded through a spinneret by a metering pump. After passing through an air gap of 4.5 cm, it is vertically immersed in a gel bath at 60 °C for phase separation and curing, and then introduced into a wire collecting tank by a winding wheel with a speed of 7 m / min to form a nascent hollow fiber ultrafiltration membrane. The nascent hollow fiber ultrafiltration membrane is immersed in deionized water at 25 °C for 48 hours for sizing, and is washed with clear water to remove residual solvents and additives to form a sized hollow fiber ultrafiltration membrane.

[0038] 4) Performance of hollow fiber ultrafiltration membrane:

[0039] The cross-sectional morphology of the membrane is observed by SEM, showing a sponge-like structure with dense inner and outer skins; the inner diameter of the membrane is about 850 μm; the outer diameter of the membrane is about 2400 μm, and the average porosity is 21.5%. The contact angle of the outer surface is 82.5°.

[0040] Under the test conditions of a temperature of 25 °C, a solution pH of 4.0, and a transmembrane pressure difference of 0.1 MPa, the pure water flux of the membrane is measured to be 364.3 L / (m 2 ·h), and the membrane flux after filtering in a bovine serum albumin (BSA, pollution simulation object: 500 mg / L) solution for 4 hours is 320.1 L / (m 2 ·h), and the rejection rate of BSA is 93.4%. (The test method refers to the literature report Journal of Membrane Science 659 (2022) 120779).

[0041] Example 2

[0042] 1) Preparation of polymer: The same preparation process as in Example 1 is adopted.

[0043] 2) Preparation of casting solution: The same preparation process as in Example 1 is adopted, except that the feeding ratio is different, as shown in Table 1.

[0044] 3) Preparation of hollow fiber ultrafiltration membrane: The same preparation process as in Example 1 is adopted.

[0045] 4) Performance of hollow fiber ultrafiltration membrane:

[0046] Using the same characterization conditions as in Example 1, the difference lies in the observed cross-sectional morphology, presenting a sponge-like structure with dense inner and outer cortices, an average porosity of 22.9%; the inner diameter of the membrane is about 830 μm; the outer diameter of the membrane is about 2340 μm. The contact angle of the outer surface is 84.0°.

[0047] Using the same test conditions as in Example 1, the difference is that the pure water flux of the membrane is measured to be 382.5 L / (m 2 ·h), and the membrane flux after filtering in BSA solution for 4 hours is 335.8 L / (m 2 ·h), and the rejection rate of BSA is 95.1%.

[0048] The preparation methods and test conditions of Example 3, Example 4, Example 5, and Example 6 are the same as those of Example 1 and Example 2, and the test results are listed in Table 1.

[0049]

[0050]

[0051] Table 1.

Claims

1. A preparation method of a side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane, characterized in that It includes the following steps: (1) Preparation of polyarylethersulfone 2-(3-(Dimethylamino)propyl)-3,3-bis(4-hydroxyphenyl)isoindolinone monomer (I), 4,4'-difluorodiphenylsulfone monomer (II) and 2,2'-bis(4-hydroxyphenyl)hexafluoropropane monomer (III) are subjected to solvent co-polycondensation to obtain polyarylethersulfone PAES-NH2 (IV) containing an amino-phenolphthalein structure, where the molar ratio of monomer (I) to the sum of monomer (III) and monomer (II) is 1:1, and the molar ratio of monomer (III) to monomer (II) is m:100 - m = 100% - 11%:1% - 90%; the number-average molecular weight Mn of the PAES-NH2 is 20000 - 200000; (2) Preparation of side-chain ion-pair modified polyarylethersulfone The prepared PAES-NH2 is dissolved in an organic solvent and cooled to below 0 °C, and then sodium 3-bromopropanesulfonate shown in formula (IV) is added in a mass ratio of 10:1.50 - 3.00, stirred for a certain period of time, precipitated out in methanol, ethanol or isopropanol, and vacuum dried to obtain side-chain ion-pair modified polyarylethersulfone PAES-N-S, the structural formula of which is shown in formula (V); (3) Preparation of casting solution A certain amount of side-chain ion-pair modified polyarylethersulfone PAES-N-S, polyvinylpyrrolidone PVP or / and polyethylene glycol PEG and other additives are dissolved in a solvent, and at room temperature, stirred and dissolved for 3 - 5 hours until a homogeneous solution is formed. After ultrasonic treatment or vacuum or static defoaming for several hours, a casting solution with a certain concentration is prepared; (4) Preparation of hollow fiber ultrafiltration membrane 1) The casting solution prepared in step (3) is extruded through a spinneret by a metering pump, after passing through an air gap of 1 - 10 cm, vertically immersed in a gel bath at 45 - 75 °C for phase separation and curing, and then introduced into a wire collecting tank by a winding wheel with a winding speed of 4 - 10 m / min to form a hollow fiber ultrafiltration membrane; 2) At room temperature, the hollow fiber ultrafiltration membrane prepared in step 1) is soaked in deionized water for shaping and rinsed with clear water to remove residual solvents and additives to form a shaped hollow fiber ultrafiltration membrane.

2. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: In step (1), the molar ratio of monomer (III) to monomer (II) of m:100 - m is preferably: 20%:80%.

3. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: In step (3), the raw materials are weighed according to the following weight parts ratio: 14 - 24 parts of PAES-N-S, 14 - 25 parts of PVP / PEG, 1 - 2 parts of other additives, and 49 - 72 parts of organic solvent.

4. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: The intrinsic viscosity range of the casting solution is 0.5 - 1.0, and the preferred intrinsic viscosity range is 0.7 - 0.

9.

5. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: The grade of the PVP is one of K85, K90 or K120 or any combination thereof; the grade of the PEG is one of PEG200, PEG400, PEG600, PEG800 or PEG1000 or any combination thereof.

6. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: The solvent used in step (1) is one or more of N,N'-dimethylacetamide DMAc, N,N'-dimethylformamide DMF, N-methylpyrrolidone NMP.

7. The preparation method of the side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane according to claim 1, characterized in that: In step (3), the other additives are one or more of pure water, polyethylene glycol, oxalic acid, and water-soluble inorganic salts; the water-soluble inorganic salts are at least one of lithium chloride (LiCl) and lithium nitrate (LiNO3).

8. A side-chain ion pair modified polyarylethersulfone hollow fiber ultrafiltration membrane, characterized in that Prepared by using the preparation method according to any one of claims 1-7.

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