Nanofiltration membrane for efficiently separating dyed salt as well as preparation method and application of nanofiltration membrane

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to a nanofiltration membrane for efficient salt dyeing separation and a preparation method and application thereof.The preparation method comprises the following steps that 1, ionic liquid and water are mixed to obtain a mixed solution, cycleanine is dissolved in the mixed solution to obtain a water-phase solution, and the water-phase solution is filtered to obtain a filtrate; pouring the water-phase solution to the surface of the base membrane and completely infiltrating the water-phase solution; and 2, dissolving isophthaloyl dichloride in normal hexane to obtain an organic phase solution, pouring the organic phase solution to the surface of the membrane treated in the step 1, and carrying out an interfacial polymerization reaction to obtain the nanofiltration membrane for efficient salt dyeing separation. According to the preparation method disclosed by the invention, the nanofiltration membrane prepared by taking cycleanine and isophthaloyl dichloride as monomers through interfacial polymerization has a highly-ordered honeycomb nanopore structure, charges on the surface of the membrane are close to neutral, and the ionic liquid added into a water-phase solution further improves the hydrophilicity of the surface of the membrane; the permeation flux and selectivity of the membrane can be effectively improved.

Description

Technical Field

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

[0002] Printing and dyeing wastewater has the characteristics of high salinity (NaCl: 1-5wt%, Na2SO4: 0.5-3wt%), high COD, high chroma, etc. If it is discharged without proper treatment, it will cause great environmental harm. However, the efficient treatment of printing and dyeing wastewater and the recycling of dyes and salts have always been challenging issues. On the one hand, the high salinity in the wastewater can easily 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 recovery and reuse of dyes and inorganic salts. Therefore, dye / salt separation is a key step to achieve efficient treatment of printing and dyeing wastewater and resource recycling and reuse.

[0003] Nanofiltration membrane is a membrane mainly composed of polyamide selective layer, which is between ultrafiltration and reverse osmosis and has a molecular weight cutoff of 200-1000Da. It 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 (negative charge on the membrane surface), the existing commercial nanofiltration membrane has a moderate 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 a near-neutral surface charge and a 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 dye-salt separation and a preparation method and application thereof, which is suitable for efficient separation of dye and salt in a dye / salt mixture with high salinity.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows: The present invention provides a method for preparing a nanofiltration membrane for efficient dye-salt separation, comprising the following steps: 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, and pour the organic phase solution onto the membrane surface treated in step 1 to perform an interfacial polymerization reaction. After the reaction is completed, the excess organic phase solution on the membrane surface is removed, and the membrane is rinsed after the organic solvent is completely evaporated to obtain the nanofiltration membrane for efficient dye-salt separation.

[0006] Furthermore, the ionic liquid in step 1 is [Bmin][BF4].

[0007] Furthermore, the mass concentration of cyclamen in the aqueous solution in step 1 is 0.1-0.7 wt %.

[0008] Furthermore, the volume ratio of the ionic liquid to water in the aqueous solution in step 1 is 95-99 v / v%.

[0009] Furthermore, the base membrane in step 1 is a polyethersulfone ultrafiltration membrane or a polysulfone ultrafiltration membrane.

[0010] Furthermore, the contact time between the aqueous solution in step 1 and the basement membrane is 20-60 s.

[0011] Furthermore, the mass concentration of phthaloyl chloride in the organic phase solution in step 2 is 0.15 wt %.

[0012] Furthermore, the interfacial polymerization reaction time in step 2 is 40-120 s.

[0013] The invention also proposes a nanofiltration membrane prepared by the preparation method and used for efficient dye-salt separation.

[0014] The present invention also proposes an application of a nanofiltration membrane for efficient dye-salt separation, wherein the nanofiltration membrane 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.

[0015] Compared with the prior art, the present invention has the following advantages: In the preparation method of the nanofiltration membrane for efficient dye-salt separation described in the present invention, the nanofiltration membrane prepared by interfacial polymerization using cyclopentane and isophthaloyl chloride as monomers has a highly ordered honeycomb nanopore structure, and the charge on the membrane surface is close to neutral. The ionic liquid ([Bmin][BF4]) added to the aqueous solution further improves the hydrophilicity of the membrane surface, thereby effectively improving the membrane's permeation flux and dye-salt separation selectivity.

[0016] The nanofiltration membrane for efficient dye-salt separation of the present invention is applied to the treatment of printing and dyeing wastewater. Compared with the conventional nanofiltration membrane, the membrane has a surface charge close to neutrality and a larger pore size, which reduces the Donnan exclusion effect, so the retention of mono- / di-salt is lower, thereby having a higher dye / salt separation factor. In addition, the membrane has a higher separation stability for the dye / salt mixture.

[0017] The preparation method of the nanofiltration membrane provided by the invention is simple and can realize large-scale production, thus opening up a new way for efficiently treating printing and dyeing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The scanning electron microscope images of the nanofiltration membrane described in Example 1 of the present invention are as follows: (a) is the surface of the nanofiltration membrane, and (b) is the cross-section of the nanofiltration membrane; Figure 2 This is a comparison diagram of the pore sizes of the nanofiltration membranes described in Example 1 of the present invention and Comparative Examples 1-2; Figure 3 This is a comparison diagram of the surface zeta potential of the nanofiltration membrane described in Example 1 of the present invention and Comparative Examples 1-2; Figure 4 This is a comparison diagram of the surface contact angles of the nanofiltration membranes described in Example 1 of the present invention and Comparative Examples 1-2; Figure 5 The permeation flux and interception effect diagram of the nanofiltration membrane described in Example 1 of the present invention for a sodium chloride or sodium sulfate concentration of 1 g / L and a different dye concentration of 0.2 g / L; Figure 6 This is a diagram showing the interception effect of the nanofiltration membrane described in Example 1 of the present invention on dyes and salts in a dye / salt mixture with different NaCl concentrations (5, 10, 20, 40 g / L) and an Active Yellow 145 concentration of 0.2 g / L; Figure 7 This is a diagram showing the retention effect of the nanofiltration membrane described in Example 1 of the present invention on dyes and salts in a dye / salt mixture with different Na2SO4 concentrations (5, 10, 20, 40 g / L) and an Active Yellow 145 concentration of 0.2 g / L. DETAILED DESCRIPTION

[0019] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0020] The present invention will be described in detail below with reference to the embodiments.

[0021] Example 1

[0022] A method for preparing a nanofiltration membrane for efficient dye-salt separation comprises the following steps: (1) dissolving cyclopentane in a mixture of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as an aqueous solution, wherein the mass concentration of cyclopentane in the aqueous solution is 0.6 wt %. The aqueous solution is poured onto the surface of the basement membrane. After contacting for 30 s, the excess aqueous solution on the surface of the basement membrane is removed. (2) Prepare a 0.15 wt% isophthaloyl chloride n-hexane solution as the organic phase solution, pour the organic phase solution onto the surface of the above membrane for interfacial polymerization reaction, and after 1 min of reaction, remove the excess organic phase solution on the membrane surface. After the organic solvent evaporates completely, wash it with n-hexane three times, put the prepared nanofiltration membrane into a 60°C oven for 30 min, rinse it thoroughly with deionized water, and store it in water. The morphology of the nanofiltration membrane is as follows Figure 1 As shown in (a), there are protrusions on the membrane surface, and 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 base membrane, indicating that the nanofiltration membrane with a polyamide selective layer was successfully prepared.

[0023] Example 2

[0024] A method for preparing a nanofiltration membrane for efficient dye-salt separation comprises the following steps: (1) dissolving cyclopentane in a mixture of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as an aqueous solution, wherein the concentration of cyclopentane in the aqueous solution is 0.3 wt %. The aqueous solution is poured onto the surface of the basement membrane. After contacting for 30 s, the excess aqueous solution on the surface of the basement membrane is removed. (2) A 0.15 wt% isophthaloyl chloride n-hexane solution was prepared as the organic phase solution, and the organic phase solution was poured onto the surface of the above membrane for interfacial polymerization reaction. After the reaction for 1 min, the excess organic phase solution on the membrane surface was removed. After the organic solvent was completely evaporated, the membrane was washed with n-hexane for 3 times. The prepared nanofiltration membrane was placed in a 60°C oven for 30 min, and then thoroughly rinsed with deionized water and stored in water.

[0025] Comparative Example 1 The nanofiltration membrane used was commercial nanofiltration NF270, produced by VONTRON.

[0026] Comparative Example 2 A method for preparing a nanofiltration membrane for dye-salt separation comprises the following steps: (1) preparing a 0.6 wt % aqueous solution of cyclopentane as an aqueous phase solution, pouring the aqueous phase solution onto the surface of the basement membrane, and removing excess aqueous phase solution from the surface of the basement membrane after contacting for 5 minutes; (2) A 0.15 wt% isophthaloyl chloride n-hexane solution was prepared as the organic phase solution, and the organic phase solution was poured onto the surface of the membrane for interfacial polymerization reaction. After the reaction for 10 min, the excess organic phase solution on the membrane surface was removed. After the organic solvent was completely evaporated, the membrane was washed with n-hexane for 3 times. The prepared nanofiltration membrane was placed in a 60°C oven for 30 min, and then rinsed thoroughly with deionized water and stored in water.

[0027] Comparative Example 3 A method for preparing a nanofiltration membrane for dye-salt separation comprises the following steps: (1) preparing a 0.6 wt % aqueous solution of cyclopentane as an aqueous phase solution, pouring the aqueous phase solution onto the surface of the basement membrane, and removing excess aqueous phase solution from the surface of the basement membrane after contacting for 30 seconds; (2) A 0.15 wt% isophthaloyl chloride n-hexane solution was prepared as the organic phase solution, and the organic phase solution was poured onto the surface of the membrane for interfacial polymerization reaction. After the reaction for 1 min, the excess organic phase solution on the membrane surface was removed. After the organic solvent was completely evaporated, the membrane was washed with n-hexane for 3 times. The prepared nanofiltration membrane was placed in a 60°C oven for 30 min, and then thoroughly rinsed with deionized water and stored in water.

[0028] Comparative Example 4 A method for preparing a nanofiltration membrane for dye-salt separation comprises the following steps: (1) Cyclotrimethylenetetramine was dissolved in a mixture of ionic liquid ([Bmin][BF4]) and water (75 v / v%) to obtain an aqueous solution with a mass concentration of 0.6 wt %. The aqueous solution was poured onto the surface of the basement membrane. After contacting for 30 s, the excess aqueous solution on the surface of the basement membrane was removed. (2) A 0.15 wt% isophthaloyl chloride n-hexane solution was prepared as the organic phase solution, and the organic phase solution was poured onto the surface of the membrane for interfacial polymerization reaction. After the reaction for 1 min, the excess organic phase solution on the membrane surface was removed. After the organic solvent was completely evaporated, the membrane was washed with n-hexane for 3 times. The prepared nanofiltration membrane was placed in a 60°C oven for 30 min, and then thoroughly rinsed with deionized water and stored in water.

[0029] Comparative Example 5 A method for preparing a nanofiltration membrane for efficient dye-salt separation comprises the following steps: (1) dissolving cyclopentane in a mixture of ionic liquid ([Bmin][BF4]) and water (95 v / v%) as an aqueous solution, wherein the mass concentration of cyclopentane in the aqueous solution is 0.8 wt %. The aqueous solution is poured onto the surface of the basement membrane. After contacting for 30 s, the excess aqueous solution on the surface of the basement membrane is removed. (2) A 0.15 wt% isophthaloyl chloride n-hexane solution was prepared as the organic phase solution, and the organic phase solution was poured onto the surface of the above membrane for interfacial polymerization reaction. After the reaction for 1 min, the excess organic phase solution on the membrane surface was removed. After the organic solvent was completely evaporated, the membrane was washed with n-hexane for 3 times. The prepared nanofiltration membrane was placed in a 60°C oven for 30 min, and then thoroughly rinsed with deionized water and stored in water.

[0030] The test was carried out in a constant temperature cross-flow filtration device at 25±1℃ and an operating pressure of 4 bar. The pure water flux of the membrane was measured during the test, and the salt rejection rate and decolorization rate of the membrane were measured using 1 g / L NaCl, Na2SO4 and 0.2 g / L active dye. The test results are shown in Table 1.

[0031] Table 1 Membrane pure water flux, salt rejection rate and decolorization rate

[0032] As shown in Table 1, the nanofiltration membrane prepared by the present invention using cyclopentane and isophthaloyl chloride as interfacial polymerization monomers and ionic liquid ([Bmin][BF4]) as an aqueous phase co-solvent has a higher water flux and a better retention and separation effect of dyes and salts, and the addition of the ionic liquid also shortens the interfacial reaction time.

[0033] like Figure 2 As shown, it is a pore size comparison diagram of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 of Comparative Example 1, and the nanofiltration membrane prepared in Comparative Example 2 whose aqueous phase solution does not contain ionic liquid, indicating that the average pore size of the nanofiltration membrane prepared using cyclopentane and isophthaloyl chloride as interfacial polymerization monomers is larger than that of the commercial nanofiltration membrane NF270, so that the nanofiltration membrane has a higher water flux, is more conducive to the penetration of small molecule salts, and improves the selective separation of dyes and salts. Figure 3 As shown, the surface zeta potential comparison diagram of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 in Comparative Example 1, and the nanofiltration membrane prepared in Comparative Example 2 whose aqueous solution does not contain ionic liquid shows that the surface charge of the nanofiltration membrane prepared by using cyclopentane and isophthaloyl chloride as interfacial polymerization monomers is close to neutral, which reduces the Donnan exclusion effect, and thus has a lower retention of mono / di-salts, further improving the selective separation of dyes and salts. Figure 4 As shown, it is a comparison diagram of the surface contact angles of the nanofiltration membrane prepared in Example 1, the commercial nanofiltration membrane NF270 in Comparative Example 1, and the nanofiltration membrane prepared in Comparative Example 2 whose aqueous solution does not contain ionic liquid, indicating that the introduction of ionic liquid ([Bmin][BF4]) in the aqueous solution improves the hydrophilicity of the nanofiltration membrane surface, and further improves the permeation flux and selectivity of the membrane.

[0034] like Figure 5As shown, it is a diagram of the permeation flux and retention effect of the nanofiltration membrane prepared in Example 1 for different salts and different dyes. It can be seen that the nanofiltration membrane prepared by the present invention has a higher permeation flux, decolorization rate and lower salt rejection rate.

[0035] like Figure 6 and Figure 7 The figure shows the interception effect of the nanofiltration membrane prepared in Example 1 on dyes and salts in dye / salt mixtures with different salts and different salt concentrations. It shows that the nanofiltration membrane prepared in this study has low salt interception rates for different concentrations of NaCl and Na2SO4, but has a high interception rate for Reactive Yellow 145 dye and changes less with the increase of salt concentration, indicating that the membrane has high separation stability for dye / salt mixtures and is suitable for efficient separation of dyes and salts in high-salt printing and dyeing wastewater.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should 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, and pour the organic phase solution onto the membrane surface treated in step 1 to perform an interfacial polymerization reaction. After the reaction is completed, the excess organic phase solution on the membrane surface is removed, and the membrane is rinsed after the organic solvent is completely evaporated to obtain the nanofiltration membrane for efficient dye-salt separation.

2. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The ionic liquid in step 1 is [Bmin][BF4].

3. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The mass concentration of cyclamen in the aqueous solution in step 1 is 0.1-0.7 wt %.

4. The method for preparing a nanofiltration membrane for efficient dye-salt separation according to claim 1, characterized in that: The volume ratio of the ionic liquid to water in the aqueous solution in step 1 is 95-99 v / v%.

5. 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.

6. 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.

7. 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%.

8. 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.

9. A nanofiltration membrane for efficient dye-salt separation prepared by the preparation method according to any one of claims 1 to 8.

10. The use of the nanofiltration membrane for efficient dye-salt separation according to claim 9, 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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