Loose nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of dye wastewater treatment, and particularly relates to a loose nanofiltration membrane as well as a preparation method and application thereof. After the surface of the base membrane is soaked in the water phase solution and before the surface of the base membrane is soaked in the oil phase solution, deionized water is added to soak the base membrane soaked in the water phase solution. According to the loose nanofiltration membrane provided by the invention, the step of dipping with deionized water is ingeniously added, so that a water-phase solution is diluted and uniformly distributed in membrane holes, high-efficiency and high-flux separation of dye wastewater can be realized, the service life of the membrane is generally prolonged, and the sewage treatment capacity of the membrane is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of dye wastewater treatment, and particularly relates to a loose nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Dye wastewater is a major source of industrial pollution, and its typical characteristics are large wastewater volume, deep chroma, and poor biodegradability. Membrane technology has been applied to dye / salt treatment for a long time, but since it is used for dye pollution treatment, it will cause membrane surface pollution, reduce membrane processing capacity, poor separation effect, and increase energy consumption. The country has increasingly higher requirements for wastewater discharge, but there are currently no membrane materials specifically designed to address this problem. Therefore, for dye wastewater, it is very important to improve the flux of the membrane and the separation of dye / salt. Although there is currently a method of using aqueous phase additives to treat dye wastewater with membranes to achieve efficient dye / salt separation, there are still many problems: such as the poor treatment effect of the membrane on dye wastewater, low treatment flux, poor separation effect, etc. Summary of the Invention

[0003] The purpose of the present invention is to provide a loose nanofiltration membrane and a preparation method and application thereof, which can solve the current problems of low dye wastewater treatment flux and poor separation effect.

[0004] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0005] A loose nanofiltration membrane has the following preparation method: after the surface of the base membrane is immersed in an aqueous solution and before it is immersed in an oily solution, deionized water is added to immerse the membrane immersed in the aqueous solution for a period of time.

[0006] Furthermore, the immersion time in deionized water is 0-10 min and is not 0.

[0007] Furthermore, the immersion time in deionized water was 5 min.

[0008] The aqueous phase solution is a solution in which piperazine is dissolved in water, and the mass concentration of piperazine is 0.1-0.3%.

[0009] The oil phase solution is a solution of TMC dissolved in n-hexane, and the mass concentration of TMC is 0.1-0.3%.

[0010] The present invention adopts interfacial polymerization to prepare the loose nanofiltration membrane. After the aqueous phase solution is impregnated on the surface of the base membrane, deionized water is added for immersion, and then the oil phase solution is added. After the reaction, a selective layer is formed on the base membrane, and then the loose nanofiltration membrane is obtained by thermal cross-linking reaction.

[0011] Specifically, the base membrane is first fixed in the membrane assembly, an aqueous solution is poured in and allowed to stand for 5 minutes to form a water film on the surface of the base membrane, excess solution on the membrane surface is removed, deionized water is poured in and immersed for 5 minutes, and then an oil phase solution is poured in for reaction. After the reaction is completed, excess oil phase is removed and a thermal cross-linking reaction is carried out.

[0012] The diameter of the membrane assembly can range from 4 to 10 cm, and the diameter of the base membrane (such as Kevlar) can be cut to a range of 4 to 10 cm. Specifically, they can all be circular.

[0013] Furthermore, the thermal crosslinking reaction is carried out at 60-80° C. for 3-5 minutes.

[0014] The loose nanofiltration membrane has good application in dye wastewater treatment.

[0015] Specifically, when using the membrane for dye wastewater treatment, the membrane is first pressed at a pressure of 0.2-0.4 MPa, preferably for 30 minutes, to strengthen the bond between the base membrane and the selective layer. The membrane pressure is then maintained at 0.1-0.2 MPa.

[0016] The loose nanofiltration membrane of the present invention is prepared by dissolving piperazine in water to obtain an aqueous phase solution. After the base membrane surface is immersed in the aqueous phase solution, deionized water is added and immersed for different times. During the immersion process, the piperazine in the base membrane is redistributed in the deionized water, and the piperazine solution is diluted and redistributed at the same time. The deionized water is then removed and blown dry with nitrogen, and then the oil phase is added. The reaction is completed in about 1 minute. After the reaction, a thin selective layer is formed on the base membrane. Then, the excess oil phase is removed, and then a thermal cross-linking reaction is performed to obtain the loose nanofiltration membrane.

[0017] By adding the deionized water immersion step described herein, the redistributed piperazine is more uniformly distributed within the basement membrane pores, resulting in a more even distribution of piperazine molecules involved in the reaction and a reduced content. This results in a smoother and thinner selective layer. Furthermore, the diluted aqueous phase provides a more porous structure after the reaction. The membrane flux and dye / salt separation performance of the resulting membrane vary with the deionized water immersion time.

[0018] The present invention adopts the method of water-phase controlled interfacial polymerization. Traditionally, piperazine is used as a water-phase monomer to directly polymerize with TMC. The flux of the resulting membrane is relatively low, about 20 L m -2 h -1 bar -1 Below, while the flux obtained by the membrane of this application is 140L m -2 h -1 bar -1 It is about seven times that of traditional interfacial polymerization membranes. The dye / salt separation factor is also improved simultaneously, and the processing efficiency is greatly improved.

[0019] The low flux of traditional nanofiltration membranes will lead to salt retention, and dyes are more difficult to degrade and separate in the presence of salt. The membrane of the present invention can increase the separation of dyes and salts, with a dye retention rate of more than 98% and a salt retention rate of less than 12%, thereby achieving high-efficiency separation of salt and dyes.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention provides a loose nanofiltration membrane, which, by cleverly adding a deionized water impregnation step, dilutes and evenly distributes the aqueous phase solution in the membrane pores, thereby achieving high-efficiency and high-throughput separation of dye wastewater, generally extending the service life of the membrane and increasing the wastewater treatment capacity and treatment efficiency of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a scanning electron microscope photograph of the loose nanofiltration membrane obtained in Example 1;

[0023] Figure 2 The water permeability of the loose nanofiltration membranes obtained in Examples 1-5 and Comparative Example 1;

[0024] Figure 3 The permeation and separation performance data of the dye / salt (Congo red / NaCl) mixed solution of the loose nanofiltration membrane obtained in Examples 1-5 and Comparative Example 1;

[0025] Figure 4 The permeation and separation performance data of the loose nanofiltration membrane obtained in Example 1 for different dye / salt mixed solutions;

[0026] Figure 5 The figures are comparative data of water permeation, dye / salt permeation and separation performance of Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0028] Example 1

[0029] A loose nanofiltration membrane regulated by an aqueous phase, the preparation process is as follows:

[0030] 1) Preparation of a loose nanofiltration membrane: dissolving piperazine in an aqueous phase and dissolving TMC in n-hexane (oil phase), wherein the mass concentration of piperazine in the aqueous phase is 0.1% and the mass concentration of TMC in the oil phase is 0.1%;

[0031] 2) The base membrane was fixed in the membrane assembly, and the aqueous solution was poured into the membrane and allowed to stand for 5 minutes to form a water film on the membrane surface. Excess solution on the membrane surface was removed, and the membrane was immersed in deionized water for 5 minutes. Then, the oil solution was poured into the membrane and reacted for 1 minute. After the reaction, the excess oil phase was removed and thermally cross-linked in a 70°C oven for 3 minutes to obtain a loose nanofiltration composite membrane. The membrane was then removed and naturally cooled before being placed in water for testing. The membrane assembly had a diameter of 6 cm, and the Kevlar base membrane was also cut to a diameter of 6 cm.

[0032] Example 2

[0033] In step 2), the immersion time in deionized water is 1 min, and the rest is the same as in Example 1.

[0034] Example 3

[0035] In step 2), the immersion time in deionized water is 3 minutes, and the rest is the same as in Example 1.

[0036] Example 4

[0037] In step 2), the immersion time in deionized water is 7 minutes, and the rest is the same as in Example 1.

[0038] Example 5

[0039] In step 2), the immersion time in deionized water is 10 min, and the rest is the same as in Example 1.

[0040] Comparative Example 1

[0041] In step 2), deionized water immersion is not performed, and the rest is the same as in Example 1.

[0042] Comparative Example 2

[0043] In step 2), a piperazine solution with a mass concentration of 0.01% is used, and deionized water immersion is not performed. Other aspects are the same as in Example 1.

[0044] Water flux and retention performance test:

[0045] The device used in this test is the membrane evaluation instrument of Hangzhou Saifei Membrane Separation Technology Co., Ltd., model SF-SA.

[0046] The membrane was placed in a test apparatus and subjected to flux and retention tests for water and dye / salt (Congo Red / NaCl, Congo Red / Na2SO4). Flux was calculated by measuring the mass of water retained by the membrane within one minute. Retention was calculated by measuring the absorbance of the liquid before and after membrane retention using a UV spectrophotometer.

[0047] Figure 2 The water permeability of the loose nanofiltration membrane prepared by immersing in deionized water for different times is shown.

[0048] As can be seen from the figure, the membrane flux of the simple interfacial polymerization without deionized water immersion and TMC forming a polyamide layer on the surface of the base membrane is 20 L m -2 h -1 bar -1 By using deionized water for impregnation, the permeability of the membranes was improved. The flux of the membrane obtained after impregnation for 5 minutes (ie, the membrane obtained in Example 1) was increased by seven times.

[0049] Figure 3 The dye / salt (Congo red / NaCl) separation performance of loose nanofiltration membranes prepared by immersing in deionized water for different times is shown.

[0050] As shown in the figure, without deionized water immersion, the polyamide layer formed by TMC on the base membrane surface has a high retention rate for both dyes and salts, failing to achieve dye-salt separation. This leads to rapid membrane fouling, a shortened service life, and increased energy consumption. Deionized water immersion improves membrane permeability, significantly reducing salt retention, but the membrane structure remains relatively intact, maintaining a high dye retention rate. Further increasing the deionized water immersion time reduces dye retention due to excessive flux, lowering the dye / salt separation factor.

[0051] Figure 4 It shows that the loose nanofiltration membrane obtained in Example 1 can achieve dye / salt separation in different salt systems, wherein the CR / NaCl separation factor is 76 and the CR / Na2SO4 separation factor is 42.

[0052] Figure 5 The dye / salt separation (Congo red / NaCl) performance of the nanofiltration membrane prepared in comparative example 2 under low concentration of piperazine monomer is shown. -2 h -1 bar -1 , dye / salt flux 110 L m -2 h -1 bar -1 ), simply diluting the mass concentration of the piperazine solution cannot achieve high dye / salt separation performance. Therefore, the aqueous phase regulation method of the present invention not only has a dilution effect on the piperazine solution, but also realizes the redistribution of the piperazine monomer in the membrane pores and surface, effectively improving the dye / salt separation efficiency.

Claims

1. A method for preparing a loose nanofiltration membrane, characterized in that: After the surface of the base film is immersed in the aqueous solution and before being immersed in the oily solution, deionized water is added to immerse the film immersed in the aqueous solution.

2. The method for preparing a loose nanofiltration membrane according to claim 1, wherein The immersion time of deionized water is 0-10 min and is not 0.

3. The method for preparing a loose nanofiltration membrane according to claim 2, wherein: The immersion time in deionized water was 5 min.

4. The method for preparing a loose nanofiltration membrane according to claim 2, wherein: The aqueous phase solution is a solution in which piperazine is dissolved in water, and the mass concentration of piperazine is 0.1-0.3%.

5. The method for preparing a loose nanofiltration membrane according to claim 2, wherein: The oil phase solution is a solution of TMC dissolved in n-hexane, and the mass concentration of TMC is 0.1-0.3%.

6. The method for preparing a loose nanofiltration membrane according to claim 2, wherein: The loose nanofiltration membrane is prepared by interfacial polymerization. The aqueous solution is impregnated on the surface of the base membrane, deionized water is added for immersion, and then the oil phase solution is added. After the reaction, a selective layer is formed on the base membrane, and then the loose nanofiltration membrane is obtained by thermal cross-linking reaction.

7. The method for preparing a loose nanofiltration membrane according to claim 6, wherein: First, fix the base membrane in the membrane assembly, pour in the aqueous solution and let it stand for 5 minutes to form a water film on the surface of the base membrane. Remove the excess solution on the membrane surface, pour in deionized water and soak for 5 minutes, then pour in the oil phase solution to react. After the reaction is completed, remove the excess oil phase and carry out thermal cross-linking reaction.

8. The method for preparing a loose nanofiltration membrane according to claim 7, wherein: The thermal crosslinking reaction is carried out at 60-80°C for 3-5 minutes.

9. A loose nanofiltration membrane obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the loose nanofiltration membrane according to claim 9 in the treatment of dye wastewater.

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