Hollow fiber composite nanofiltration membrane and preparation process thereof

Abstract

The invention relates to the technical field of membrane separation, and provides a hollow fiber composite nanofiltration membrane and a preparation process thereof.The hollow fiber composite nanofiltration membrane comprises a base membrane and a composite layer, the base membrane is a hollow fiber microporous base membrane, and the composite layer is made of modified montmorillonite and lignin; the modified montmorillonite is obtained by modifying montmorillonite with a modifier; the modifier is prepared from imidazole-4, 5-dicarboxylic acid and dimethyl sulfoxide. According to the technical scheme, the problem of low water flux of the nanofiltration membrane in related technologies is solved.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, and in particular to a hollow fiber composite nanofiltration membrane and a preparation process thereof. Background Art

[0002] With the development of social economy and the improvement of people's living standards, the demand for water resources is increasing, and the requirements for water quality are becoming more and more stringent. However, water shortage and water pollution have become severe challenges facing the world. In the field of water treatment technology, nanofiltration membrane, as a new type of membrane separation technology, has unique advantages in removing impurities, salts and harmful substances from water, and has received widespread attention. Nanofiltration membrane is a pressure-driven membrane separation process between ultrafiltration membrane and reverse osmosis. Its operating pressure is usually in the range of 0.3~2MPa, the molecular weight cutoff is 200~2000Da, and the pore size is about 1nm. Nanofiltration membrane is mainly prepared by phase inversion method, interfacial polymerization method, and layer-by-layer self-assembly method. Due to its moderate working pressure and relatively high small molecule retention rate, it has been widely used in wastewater treatment and its resource utilization, seawater desalination, drinking water purification and liquid concentration. However, compared with ultrafiltration membrane, the flux of nanofiltration membrane is relatively low, so in large-scale water treatment such as deep treatment of urban water plants or large-scale reuse of industrial wastewater, a larger membrane area or more membrane components are required to meet the treatment needs, resulting in increased equipment investment costs. Therefore, how to improve the water flux of nanofiltration membranes is a problem that needs to be solved at present. Summary of the invention

[0003] The invention provides a hollow fiber composite nanofiltration membrane and a preparation process thereof, which solves the problem of low water flux of the nanofiltration membrane in the related art.

[0004] The technical solution of the present invention is as follows: The present invention provides a hollow fiber composite nanofiltration membrane, comprising a base membrane and a composite layer, wherein the base membrane is a hollow fiber microporous base membrane, and the composite layer material comprises modified montmorillonite and lignin; the modified montmorillonite is obtained by modifying montmorillonite with a modifier; the modifier comprises imidazole-4,5-dicarboxylic acid and dimethyl sulfoxide.

[0005] As a further technical solution, the mass ratio of the modified montmorillonite to lignin is 3:1~3.

[0006] In the present invention, the water flux of the hollow fiber composite nanofiltration membrane is further improved by limiting the mass ratio of modified montmorillonite to lignin to 3:1-3.

[0007] As a further technical solution, the mass ratio of the modified montmorillonite to lignin is 3:2.

[0008] In the present invention, the water flux of the hollow fiber composite nanofiltration membrane is further improved by limiting the mass ratio of modified montmorillonite to lignin to 3:2.

[0009] As a further technical solution, the amount of the modifier added is 7% to 10% of the mass of the montmorillonite.

[0010] As a further technical solution, the mass ratio of the imidazole-4,5-dicarboxylic acid to dimethyl sulfoxide is 2-5:7.

[0011] In the present invention, the water flux of the hollow fiber composite nanofiltration membrane is further improved by limiting the mass ratio of imidazole-4,5-dicarboxylic acid to dimethyl sulfoxide to 2-5:7.

[0012] As a further technical solution, the preparation method of the modified montmorillonite comprises the following steps: S1, adding dimethyl sulfoxide and montmorillonite into a solvent and mixing to obtain a mixed solution; S2. Add imidazole-4,5-dicarboxylic acid to the mixed solution for modification, and obtain modified montmorillonite after drying.

[0013] As a further technical solution, the solvent includes one or more of methanol, ethanol, and isopropanol.

[0014] As a further technical solution, the modification temperature is 40-50°C, and the modification time is 2-3h.

[0015] As a further technical solution, the hollow fiber microporous base membrane includes one or both of a polyacrylonitrile hollow fiber microporous base membrane and a polyvinylidene fluoride hollow fiber microporous base membrane.

[0016] As a further technical solution, the method for preparing the composite layer material comprises the following steps: The modified montmorillonite and lignin are mixed by ball milling to obtain a composite layer material.

[0017] The present invention also provides a process for preparing a hollow fiber composite nanofiltration membrane, comprising the following steps: A1. dispersing the composite layer material in water to obtain a dispersion; A2. Place the dispersion on the upper layer of the hollow fiber microporous base membrane, remove water, and obtain the hollow fiber composite nanofiltration membrane after drying.

[0018] The working principle and beneficial effects of the present invention are: In the present invention, a hollow fiber composite nanofiltration membrane is composed of a hollow fiber microporous base membrane and a composite layer, wherein the hollow fiber microporous base membrane provides a stable supporting structure for the composite layer, and the composite layer composed of montmorillonite and lignin modified by imidazole-4,5-dicarboxylic acid and dimethyl sulfoxide has a higher water flux, thereby improving the water flux of the hollow fiber composite nanofiltration membrane. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Lignin, particle size: 50nm; montmorillonite, particle size: 325 mesh.

[0021] Example 1 A preparation process of a hollow fiber composite nanofiltration membrane comprises the following steps: A1, 1 g of modified montmorillonite and 0.2 g of lignin were mixed by ball milling and dispersed in 100 mL of water to obtain a dispersion; A2, pouring the dispersion into the upper layer of the polyacrylonitrile hollow fiber microporous base membrane, removing water, and drying to obtain a hollow fiber composite nanofiltration membrane; The preparation method of modified montmorillonite comprises the following steps: S1, adding 2.21 g of dimethyl sulfoxide and 36 g of montmorillonite into 400 mL of methanol to obtain a mixed solution; S2. Add 0.31 g of imidazole-4,5-dicarboxylic acid to the mixed solution, heat to 40° C. and stir for 3 h. After drying, obtain modified montmorillonite.

[0022] Example 2 A preparation process of a hollow fiber composite nanofiltration membrane comprises the following steps: A1, 1 g of modified montmorillonite and 0.2 g of lignin were mixed by ball milling and dispersed in 100 mL of water to obtain a dispersion; A2, pouring the dispersion into the upper layer of the polyacrylonitrile hollow fiber microporous base membrane, removing water, and drying to obtain a hollow fiber composite nanofiltration membrane; The preparation method of modified montmorillonite comprises the following steps: S1, adding 2.52 g of dimethyl sulfoxide and 36 g of montmorillonite into 400 mL of ethanol to obtain a mixed solution; S2. Add 0.36 g of imidazole-4,5-dicarboxylic acid to the mixed solution, heat to 50° C. and stir for 2 h. After drying, obtain modified montmorillonite.

[0023] Example 3 A preparation process of a hollow fiber composite nanofiltration membrane comprises the following steps: A1, 1 g of modified montmorillonite and 0.2 g of lignin were mixed by ball milling and dispersed in 100 mL of water to obtain a dispersion; A2, pouring the dispersion into the upper layer of the polyacrylonitrile hollow fiber microporous base membrane, removing water, and drying to obtain a hollow fiber composite nanofiltration membrane; The preparation method of modified montmorillonite comprises the following steps: S1, adding 3.15 g of dimethyl sulfoxide and 36 g of montmorillonite into 400 mL of isopropanol to obtain a mixed solution; S2. Add 0.45 g of imidazole-4,5-dicarboxylic acid to the mixed solution, heat to 50° C. and stir for 2 h. After drying, obtain modified montmorillonite.

[0024] Example 4 The difference between this embodiment and embodiment 1 is that the added amount of modified montmorillonite is 0.4 g and the added amount of lignin is 0.8 g.

[0025] Example 5 The difference between this embodiment and embodiment 1 is that the added amount of modified montmorillonite is 0.9 g and the added amount of lignin is 0.3 g.

[0026] Example 6 The difference between this embodiment and embodiment 1 is that the added amount of modified montmorillonite is 0.72 g and the added amount of lignin is 0.48 g.

[0027] Example 7 The difference between this embodiment and embodiment 1 is that the addition amount of modified montmorillonite is 0.6 g and the addition amount of lignin is 0.6 g.

[0028] Example 8 The difference between this embodiment and embodiment 6 is that the addition amount of dimethyl sulfoxide is 1.26 g and the addition amount of imidazole-4,5-dicarboxylic acid is 1.26 g.

[0029] Example 9 The difference between this embodiment and embodiment 6 is that the added amount of dimethyl sulfoxide is 1.96 g and the added amount of imidazole-4,5-dicarboxylic acid is 0.56 g.

[0030] Example 10 The only difference between this embodiment and embodiment 6 is that the added amount of dimethyl sulfoxide is 1.47 g and the added amount of imidazole-4,5-dicarboxylic acid is 1.05 g.

[0031] Comparative Example 1 The only difference between this comparative example and Example 1 is that the modified montmorillonite is replaced by an equal amount of montmorillonite.

[0032] Comparative Example 2 The only difference between this comparative example and Example 1 is that no modified montmorillonite is added.

[0033] The hollow fiber composite nanofiltration membranes prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were placed on a cross-flow separation device, with pure water as the feed liquid, and operated at a pressure of 0.3 MPa to measure the membrane flux of the hollow fiber composite nanofiltration membrane. The test results are shown in Table 1.

[0034] Table 1 Performance test results of hollow fiber composite nanofiltration membrane

[0035] Compared with Comparative Examples 1-2, the composite layer in Example 1 is composed of modified montmorillonite and lignin. As a result, the membrane flux of the hollow fiber composite nanofiltration membrane prepared in Example 1 is higher than that of Comparative Examples 1-2, indicating that the composite layer composed of modified montmorillonite and lignin can improve the water flux of the hollow fiber composite nanofiltration membrane.

[0036] Compared with Example 1, Examples 4 to 7 changed the mass ratio of modified montmorillonite and lignin. As a result, the membrane flux of the hollow fiber composite nanofiltration membrane prepared in Examples 5 to 7 was higher than that in Example 1 and Example 4, indicating that when the mass ratio of modified montmorillonite and lignin was 3:1 to 3, the water flux of the hollow fiber composite nanofiltration membrane could be further improved; by comparing Examples 5 to 7, it was found that the membrane flux of the hollow fiber composite nanofiltration membrane prepared in Example 6 was higher than that in Example 5 and Example 7, indicating that when the mass ratio of modified montmorillonite and lignin was 3:2, the water flux of the prepared hollow fiber composite nanofiltration membrane was higher.

[0037] Compared with Example 6, the mass ratio of imidazole-4,5-dicarboxylic acid and dimethyl sulfoxide was changed in Examples 8 to 10. As a result, the membrane flux of the hollow fiber composite nanofiltration membrane prepared in Examples 9 to 10 was higher than that in Examples 6 and 8, indicating that when the mass ratio of imidazole-4,5-dicarboxylic acid and dimethyl sulfoxide is 2 to 5:7, the water flux of the hollow fiber composite nanofiltration membrane can be further improved.

[0038] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A hollow fiber composite nanofiltration membrane, characterized in that: The invention comprises a base membrane and a composite layer, wherein the base membrane is a hollow fiber microporous base membrane, and the composite layer material comprises modified montmorillonite and lignin; the modified montmorillonite is obtained by modifying montmorillonite with a modifier; the modifier comprises imidazole-4,5-dicarboxylic acid and dimethyl sulfoxide.

2. A hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The mass ratio of the modified montmorillonite to lignin is 3:1-3.

3. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The amount of the modifier added is 7% to 10% of the mass of the montmorillonite.

4. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The mass ratio of the imidazole-4,5-dicarboxylic acid to dimethyl sulfoxide is 2-5:

7.

5. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The preparation method of the modified montmorillonite comprises the following steps: S1, adding dimethyl sulfoxide and montmorillonite into a solvent and mixing to obtain a mixed solution; S2. Add imidazole-4,5-dicarboxylic acid to the mixed solution for modification, and obtain modified montmorillonite after drying.

6. A hollow fiber composite nanofiltration membrane according to claim 5, characterized in that: The solvent includes one or more of methanol, ethanol and isopropanol.

7. The hollow fiber composite nanofiltration membrane according to claim 5, characterized in that: The modification temperature is 40-50° C., and the modification time is 2-3 hours.

8. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The hollow fiber microporous base membrane includes one or both of a polyacrylonitrile hollow fiber microporous base membrane and a polyvinylidene fluoride hollow fiber microporous base membrane.

9. The hollow fiber composite nanofiltration membrane according to claim 1, characterized in that: The method for preparing the composite layer material comprises the following steps: The modified montmorillonite and lignin are mixed by ball milling to obtain a composite layer material.

10. A process for preparing a hollow fiber composite nanofiltration membrane according to any one of claims 1 to 9, characterized in that: The following steps are involved: A1. dispersing the composite layer material in water to obtain a dispersion; A2. Place the dispersion on the upper layer of the hollow fiber microporous base membrane, remove water, and obtain the hollow fiber composite nanofiltration membrane after drying.

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