A nanofiltration membrane for efficient separation of dye salts, its preparation method and application

Abstract

The present invention belongs to the technical field of membrane separation, and in particular relates to a nanofiltration membrane for efficient separation of dye salts, its preparation method and application. The preparation method includes the following steps: Step 1 is to mix an ionic liquid and water to obtain a mixed solution, dissolve cyclen in the mixed solution to obtain an aqueous solution, and pour the aqueous solution onto the surface of the base membrane and completely wet it; Step 2 is to dissolve isophthaloyl chloride in n-hexane to obtain an organic solution, and pour the organic solution onto the surface of the membrane treated in Step 1 for interfacial polymerization reaction to obtain the nanofiltration membrane for efficient separation of dye salts. The nanofiltration membrane prepared by the preparation method of the present invention using cyclen and isophthaloyl chloride as monomers through interfacial polymerization has a highly ordered honeycomb-like nanoporous structure, the membrane surface charge is close to neutral, and the ionic liquid added to the aqueous solution further improves the hydrophilicity of the membrane surface, which can effectively improve the permeation flux and selectivity of the membrane.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a nanofiltration membrane for efficient separation of dye and salt, a preparation method thereof, and an application thereof. Background Art

[0002] Printing and dyeing wastewater has the characteristics of high salinity (NaCl: 1 - 5 wt%, Na 2 SO 4 : 0.5 - 3 wt%), high COD, high chromaticity, etc. If it is discharged without proper treatment, it will cause great environmental hazards. However, the efficient treatment of printing and dyeing wastewater and the recycling of dyes and salts have always been challenging problems. On the one hand, the high salinity in the wastewater can have an adverse effect on the removal of dyes by conventional biological, physical or chemical methods; on the other hand, many printing and dyeing wastewater treatment processes (biodegradation, oxidation, etc.) mainly remove dyes or destroy the dye structure, which may produce toxic and harmful by-products and it is difficult to achieve the recycling of dyes and inorganic salts. Therefore, dye / salt separation is the key step to achieve the efficient treatment of printing and dyeing wastewater and resource recycling.

[0003] Nanofiltration membrane is between ultrafiltration and reverse osmosis, and it is a membrane mainly composed of a polyamide selective layer with a molecular weight cut-off of 200 - 1000 Da, which is widely used in the separation of dyes and salts. However, due to its significant steric hindrance (small membrane pore size) and Donnan exclusion effect (negatively charged membrane surface), the existing commercial nanofiltration membranes have a medium retention capacity for monovalent salts and a higher retention capacity for divalent salts. The ideal nanofiltration membrane for dye / salt separation should have a high dye retention rate and a low salt retention rate. Therefore, in order to achieve efficient dye / salt separation, it is urgent to develop a loose nanofiltration membrane with near-neutral surface charge and larger pore size. Summary of the Invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a nanofiltration membrane for efficient separation of dye and salt, a preparation method thereof, and an application thereof, which is suitable for the efficient separation of dyes and salts in a high-salinity dye / salt mixed solution.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows:

[0006] The present invention provides a preparation method of a nanofiltration membrane for efficient separation of dye and salt, comprising the following steps:

[0007] Step 1 is to mix an ionic liquid and water to obtain a mixed solution, dissolve cyclen in the mixed solution to obtain an aqueous solution, pour the aqueous solution onto the surface of a support membrane and completely wet it, and remove the excess aqueous solution on the surface of the support membrane;

[0008] Step 2 is to dissolve isophthaloyl chloride in n-hexane to obtain an organic phase solution, pour the organic phase solution onto the surface of the membrane treated in Step 1 for interfacial polymerization reaction, remove the excess organic phase solution on the membrane surface after the reaction is completed, and perform rinsing after the organic solvent has completely volatilized to obtain the nanofiltration membrane for efficient dye-salt separation.

[0009] Further, the ionic liquid in Step 1 is [Bmin][BF4].

[0010] Further, the mass concentration of cyclen in the aqueous solution in Step 1 is 0.1 - 0.7 wt%.

[0011] Further, the volume ratio of the ionic liquid to water in the aqueous solution in Step 1 is 95 - 99 v / v%.

[0012] Further, the base membrane in Step 1 is a polyethersulfone ultrafiltration membrane or a polysulfone ultrafiltration membrane.

[0013] Further, the contact time between the aqueous solution in Step 1 and the base membrane is 20 - 60 s.

[0014] Further, the mass concentration of isophthaloyl chloride in the organic phase solution in Step 2 is 0.15 wt%.

[0015] Further, the time of the interfacial polymerization reaction in Step 2 is 40 - 120 s.

[0016] The present invention also provides a nanofiltration membrane for efficient dye-salt separation prepared by the above preparation method.

[0017] The present invention also provides an application of the nanofiltration membrane for efficient dye-salt separation, which is applied in the field of printing and dyeing wastewater treatment; the nanofiltration membrane is applied in the separation of dyes and salts in printing and dyeing wastewater treatment.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] In the preparation method of the nanofiltration membrane for efficient dye-salt separation of the present invention, the nanofiltration membrane prepared by interfacial polymerization using cyclen and isophthaloyl chloride as monomers has a highly ordered honeycomb-like nanoporous structure, the membrane surface charge is close to neutral, and the ionic liquid ([Bmin][BF4]) added to the aqueous solution further improves the hydrophilicity of the membrane surface, thereby effectively improving the permeation flux and dye-salt separation selectivity of the membrane.

[0020] The nanofiltration membrane for efficient separation of dye salts described in the present invention is applied in the process of treating printing and dyeing wastewater. Compared with traditional nanofiltration membranes, this membrane has a surface charge close to neutral and a relatively large pore size, reducing the Donnan exclusion effect. Therefore, the retention of mono / di-salts is low, and it has a high dye / salt separation factor. In addition, this membrane has high separation stability for dye / salt mixed solutions.

[0021] The preparation method of the nanofiltration membrane provided by the present invention is simple and can achieve large-scale production, opening up a new way for efficient treatment of printing and dyeing wastewater. Brief Description of the Drawings

[0022] Figure 1 Scanning electron microscope images of the nanofiltration membrane described in Example 1 of the present invention: Among them, (a) is the surface of the nanofiltration membrane, and (b) is the cross-section of the nanofiltration membrane;

[0023] Figure 2 Pore size comparison diagram of the nanofiltration membranes described in Example 1 of the present invention and Comparative Examples 1-2;

[0024] Figure 3 Surface zeta potential comparison diagram of the nanofiltration membranes described in Example 1 of the present invention and Comparative Examples 1-2;

[0025] Figure 4 Surface contact angle comparison diagram of the nanofiltration membranes described in Example 1 of the present invention and Comparative Examples 1-2;

[0026] Figure 5 Permeation flux and retention effect diagrams of the nanofiltration membrane described in Example 1 of the present invention for sodium chloride or sodium sulfate at a concentration of 1 g / L and different dye concentrations of 0.2 g / L;

[0027] Figure 6 Retention effect diagrams of the nanofiltration membrane described in Example 1 of the present invention for dyes and salts in dye / salt mixed solutions with different NaCl concentrations (5, 10, 20, 40 g / L) and an active yellow 145 concentration of 0.2 g / L;

[0028] Figure 7 For the nanofiltration membrane described in Example 1 of the present invention for different Na 2 SO 4 Concentrations (5, 10, 20, 40 g / L) and retention effect diagrams of dyes and salts in dye / salt mixed solutions with an active yellow 145 concentration of 0.2 g / L. Detailed Description of the Invention

[0029] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0030] The present invention will be described in detail below in conjunction with embodiments.

[0031] Embodiment 1

[0032] A method for preparing a nanofiltration membrane for efficient separation of dye salts, comprising the following steps:

[0033] (1) Dissolve cyclen in a mixed solution of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as the aqueous phase solution. The mass concentration of cyclen in the aqueous phase solution is 0.6 wt%. Pour the aqueous phase solution onto the surface of the substrate membrane. After contacting for 30 s, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0034] (2) Prepare a 0.15 wt% solution of isophthaloyl chloride in n-hexane as the organic phase solution. Pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction. After reacting for 1 min, remove the excess organic phase solution on the surface of the membrane. After the organic solvent has completely evaporated, wash with n-hexane 3 times. Place the prepared nanofiltration membrane in an oven at 60 °C for 30 min, then thoroughly rinse with deionized water and store in water. The morphology of the nanofiltration membrane is as Figure 1 shown in (a). There are protrusions on the membrane surface, and from the cross-sectional scanning electron microscope Figure 1 (b), it can be clearly seen that there is a relatively thin surface layer on the surface of the substrate membrane, indicating that a nanofiltration membrane with a polyamide selective layer has been successfully prepared.

[0035] Embodiment 2

[0036] A method for preparing a nanofiltration membrane for efficient separation of dye salts, comprising the following steps:

[0037] (1) Dissolve cyclen in a mixed solution of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as the aqueous phase solution. The concentration of cyclen in the aqueous phase solution is 0.3 wt%. Pour the aqueous phase solution onto the surface of the substrate membrane. After contacting for 30 s, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0038] (2) Prepare a 0.15 wt% solution of isophthaloyl chloride in n-hexane as the organic phase solution. Pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction. After reacting for 1 min, remove the excess organic phase solution on the surface of the membrane. After the organic solvent has completely evaporated, wash with n-hexane 3 times. Place the prepared nanofiltration membrane in an oven at 60 °C for 30 min, then thoroughly rinse with deionized water and store in water.

[0039] Comparative Example 1

[0040] The nanofiltration membrane uses a commercial nanofiltration NF270, and the manufacturer is VONTRON.

[0041] Comparative Example 2

[0042] A preparation method of a nanofiltration membrane for dye-salt separation, comprising the following steps:

[0043] (1) Prepare an aqueous solution of cyclanoline at 0.6 wt% as the aqueous phase solution, pour the aqueous phase solution onto the surface of the substrate membrane, after contacting for 5 min, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0044] (2) Prepare a n-hexane solution of isophthaloyl chloride at 0.15 wt% as the organic phase solution, pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction, after reacting for 10 min, remove the excess organic phase solution on the surface of the membrane, after the organic solvent has completely evaporated, wash with n-hexane 3 times, put the prepared nanofiltration membrane into an oven at 60 °C for 30 min, thoroughly rinse with deionized water, and then store it in water.

[0045] Comparative Example 3

[0046] A preparation method of a nanofiltration membrane for dye-salt separation, comprising the following steps:

[0047] (1) Prepare an aqueous solution of cyclanoline at 0.6 wt% as the aqueous phase solution, pour the aqueous phase solution onto the surface of the substrate membrane, after contacting for 30 s, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0048] (2) Prepare a n-hexane solution of isophthaloyl chloride at 0.15 wt% as the organic phase solution, pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction, after reacting for 1 min, remove the excess organic phase solution on the surface of the membrane, after the organic solvent has completely evaporated, wash with n-hexane 3 times, put the prepared nanofiltration membrane into an oven at 60 °C for 30 min, thoroughly rinse with deionized water, and then store it in water.

[0049] Comparative Example 4

[0050] A preparation method of a nanofiltration membrane for dye-salt separation, comprising the following steps:

[0051] (1) Dissolve cyclanoline in a mixed solution of ionic liquid ([Bmin][BF4]) and water (75 v / v%) as the aqueous phase solution with a mass concentration of 0.6 wt%, pour the aqueous phase solution onto the surface of the substrate membrane, after contacting for 30 s, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0052] (2) Prepare a n-hexane solution of isophthaloyl chloride at 0.15 wt% as the organic phase solution, pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction, after reacting for 1 min, remove the excess organic phase solution on the surface of the membrane, after the organic solvent has completely evaporated, wash with n-hexane 3 times, put the prepared nanofiltration membrane into an oven at 60 °C for 30 min, thoroughly rinse with deionized water, and then store it in water.

[0053] Comparative Example 5

[0054] A method for preparing a nanofiltration membrane for efficient separation of dye salts, comprising the following steps:

[0055] (1) Dissolve cyclen in a mixed solution of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as the aqueous phase solution. The mass concentration of cyclen in the aqueous phase solution is 0.8 wt%. Pour the aqueous phase solution onto the surface of the substrate membrane. After contacting for 30 s, remove the excess aqueous phase solution on the surface of the substrate membrane;

[0056] (2) Prepare a hexane solution of 0.15 wt% isophthaloyl chloride as the organic phase solution. Pour the organic phase solution onto the surface of the above-mentioned membrane for interfacial polymerization reaction. After reacting for 1 min, remove the excess organic phase solution on the membrane surface. After the organic solvent has completely volatilized, wash it 3 times with hexane. Put the prepared nanofiltration membrane into an oven at 60 °C for 30 min, then thoroughly rinse it with deionized water and store it in water.

[0057] The test is carried out in a constant temperature cross-flow filtration device at 25 ± 1 °C, and the operating pressure is 4 bar. The pure water flux of the membrane is measured during the test. Additionally, 1 g / L of NaCl, Na 2 SO 4 and 0.2 g / L of reactive dye are used to measure the salt rejection rate and decolorization rate of the membrane. The test results are shown in Table 1.

[0058] Table 1 Pure water flux, salt rejection rate and decolorization rate of the membrane

[0059]

[0060] As shown in Table 1, the nanofiltration membrane provided by the present invention, which uses cyclen and isophthaloyl chloride as interfacial polymerization monomers and ionic liquid ([Bmin][BF4]) as the aqueous phase co-solvent, has a higher water flux and better retention and separation effects of dyes and salts. And the addition of ionic liquid also shortens the interfacial reaction time.

[0061] As Figure 2 shown, it is a pore size comparison diagram of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 in Comparative Example 1, and the nanofiltration membrane with no ionic liquid in the aqueous phase solution prepared in Comparative Example 2, indicating that the average pore size of the nanofiltration membrane prepared using cyclen and isophthaloyl chloride as interfacial polymerization monomers is larger than that of the commercial nanofiltration membrane NF270, enabling the nanofiltration membrane to have a higher water flux, being more conducive to the permeation of small molecule salts, and improving the selective separation of dyes and salts. As Figure 3As shown, it is a comparison chart of the surface zeta potential of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 in Comparative Example 1, and the nanofiltration membrane with an ionic liquid-free aqueous solution prepared in Comparative Example 2, indicating that the surface charge of the nanofiltration membrane prepared using cyclen and isophthaloyl chloride as interfacial polymerization monomers is close to neutral, reducing the Donnan exclusion effect. Therefore, the rejection of mono / di salts is low, further improving the selective separation of dyes and salts. As Figure 4 shown, it is a comparison chart of the surface contact angle of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 in Comparative Example 1, and the nanofiltration membrane with an ionic liquid-free aqueous solution prepared in Comparative Example 2, indicating that the introduction of the ionic liquid ([Bmin][BF4]) in the aqueous solution enhances the hydrophilicity of the nanofiltration membrane surface, further improving the membrane permeation flux and selectivity.

[0062] As Figure 5 shown, it is a graph of the permeation flux and rejection effect of the nanofiltration membrane prepared in Example 1 on different salts and different dyes. It can be seen that the nanofiltration membrane prepared by the present invention has a high permeation flux, decolorization rate, and a low salt rejection rate.

[0063] As Figure 6 and Figure 7 shown, it is a graph of the rejection effect of the nanofiltration membrane prepared in Example 1 on dyes and salts in dye / salt mixed solutions with different salts and different salt concentrations. It shows that the nanofiltration membrane prepared in this study has a low salt rejection rate for different concentrations of NaCl, Na 2 SO 4 and a high rejection rate for the reactive yellow 145 dye, and the change is small with the increase of salt concentration, indicating that the membrane has high separation stability for dye / salt mixed solutions and is suitable for the efficient separation of dyes and salts in high-salt printing and dyeing wastewater.

[0064] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a nanofiltration membrane for efficient dye-salt separation, characterized in that: The steps include: Step 1 is to mix the ionic liquid and water to obtain a mixed solution, dissolve cyclopentane in the mixed solution to obtain an aqueous solution, pour the aqueous solution onto the surface of the basement membrane and completely infiltrate it, and remove excess aqueous solution from the surface of the basement membrane; Step 2 is to dissolve isophthaloyl chloride in n-hexane to obtain an organic phase solution, pour the organic phase solution onto the membrane surface treated in step 1 to carry out an interfacial polymerization reaction, remove excess organic phase solution from the membrane surface after the reaction is completed, and rinse after the organic solvent is completely evaporated to obtain the nanofiltration membrane for efficient dye-salt separation; The ionic liquid in step 1 is [Bmin][BF4]; The mass concentration of cyclopentane in the aqueous solution in step 1 is 0.1-0.7 wt %; The volume ratio of the ionic liquid to water in the aqueous solution in step 1 is 95-99 v / v%.

2. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The base membrane in step 1 is a polyethersulfone ultrafiltration membrane or a polysulfone ultrafiltration membrane.

3. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The contact time between the aqueous solution in step 1 and the basement membrane is 20-60 s.

4. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The mass concentration of phthaloyl chloride in the organic phase solution in step 2 is 0.15wt%.

5. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The interfacial polymerization reaction time in step 2 is 40-120 s.

6. A nanofiltration membrane for efficient dye-salt separation prepared by the preparation method according to any one of claims 1 to 5.

7. The use of the nanofiltration membrane for efficient dye-salt separation according to claim 6, characterized in that: The nanofiltration membrane is used in the field of printing and dyeing wastewater treatment; the nanofiltration membrane is used in the separation of dyes and salts in printing and dyeing wastewater treatment.

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