Intelligent nanofiltration membrane, preparation method and application thereof

Abstract

The application belongs to the technical field of nanofiltration membrane preparation, and discloses an intelligent nanofiltration membrane and a preparation method and application thereof, the preparation method comprising the following steps: S1, selecting a polyamide composite nanofiltration membrane as a raw membrane, and immersing the raw membrane in an alcohol solvent for swelling treatment; S2, preparing an alcohol solution containing a free radical initiator, a pH responsive monomer and a temperature responsive monomer, and using the alcohol solution for nanofiltration membrane modification; S3, placing the raw membrane after the swelling treatment in step S1 into the alcohol solution prepared in step S2 for modification reaction treatment; and S4, after the modification reaction treatment is completed, taking out the raw membrane and washing the raw membrane in pure water, and finally obtaining the intelligent nanofiltration membrane for high-salinity wastewater treatment. The intelligent nanofiltration membrane material prepared by the application has a temperature-pH intelligent response function, can realize efficient separation of organic matters and single / multivalent salt ions in high-salinity wastewater by adjusting temperature and pH conditions, and provides a technical path for complex high-salinity wastewater treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanofiltration membrane preparation, and relates to an intelligent nanofiltration membrane and a preparation method and application thereof, in particular to a preparation method of an intelligent nanofiltration membrane material with structural and performance response capability to temperature and pH environment, which can be suitable for efficient separation of salt ions and organic matters in high-salt wastewater. BACKGROUND

[0002] Since high-salt wastewater is widely derived from the chemical pharmaceutical, food processing, seawater desalination concentrate, petroleum refining and dyeing industries, the components thereof are complex, and high-concentration inorganic salts (such as NaCl, Na2SO4 and CaCl2), refractory organic matters (phenols, dyes and drug residues) and toxic heavy metal ions (such as Cr 3+ , Pb 2+ ) are often contained, so that the traditional treatment methods (such as physical evaporation crystallization or biochemical treatment) have problems of high energy consumption, unstable treatment effect, great risk of secondary pollution and the like.

[0003] Nanofiltration (molecular weight cutoff 200-1000 Da) is a kind of efficient membrane water treatment technology. Compared with the traditional reverse osmosis membrane material, the nanofiltration membrane can realize the selective separation of water body solutes through the pore size screening and charge effect two mechanisms, and the operation pressure is obviously reduced compared with the reverse osmosis process. With the characteristics of efficient salt separation and low energy consumption operation, the nanofiltration membrane shows great application potential in the field of high-salt wastewater treatment. At present, the nanofiltration membrane has achieved certain development in the fields of seawater refining, coal chemical wastewater and landfill leachate purification and the like. However, the types of nanofiltration membrane products on the market are various, and the commercial nanofiltration membrane is still mainly polyamide composite material. The pore size and surface charge property of this kind of membrane material are relatively fixed, and the adjustable range is limited. Due to the complex and changeable types, concentrations and acid-base environments of ions and organic matters in actual high-salt wastewater, the existing nanofiltration membrane material is difficult to adjust and control the separation performance in real time according to the water quality fluctuation of real water body, and cannot fully meet the diversified needs in the field of high-salt wastewater treatment.

[0004] Therefore, it is necessary to modify the existing nanofiltration membrane, develop a new type of intelligent nanofiltration membrane, and meet the application needs of existing high-salt wastewater treatment. SUMMARY

[0005] In view of the above problems, the application provides an intelligent nanofiltration membrane and a preparation method and application thereof. The nanofiltration membrane is an intelligent nanofiltration membrane material with a temperature and pH double-response mechanism, which realizes precise separation under different water quality conditions through a reversible regulation system, and effectively improves the adaptability and treatment efficiency of the nanofiltration membrane in real water body environment.

[0006] The application realizes precise separation of high-salt wastewater by preparing a nanofiltration membrane with a "temperature-pH" intelligent response function and reversibly regulating the separation performance thereof. Specifically, a functional molecular structure with a "temperature-pH" synergistic response capability is synthesized in situ in a polyamide nanofiltration membrane by using a temperature response monomer and a pH response monomer, thereby obtaining an intelligent response nanofiltration membrane. The membrane material can realize efficient separation of organic matter and single / multivalent salt ions in high-salt wastewater by adjusting the temperature and pH conditions, thereby providing a technical path for complex high-salt wastewater treatment.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0008] In a first aspect, the application provides a preparation method of an intelligent nanofiltration membrane, comprising the following steps:

[0009] S1: A common polyamide composite nanofiltration membrane is selected as a raw membrane, and the raw membrane is immersed in an alcohol solvent for moderate swelling treatment, so that the response monomer molecules can penetrate into the molecular chains of the nanofiltration membrane for polymerization, and is ready for use;

[0010] S2: An alcohol solution containing a free radical initiator, a pH response monomer and a temperature response monomer is configured for nanofiltration membrane modification;

[0011] S3: The raw membrane after the swelling treatment in step S1 is placed in the alcohol solution configured in step S2 for modification reaction treatment;

[0012] S4: After the modification reaction treatment is completed, the raw membrane is taken out and washed in pure water, and finally the intelligent nanofiltration membrane for high-salt wastewater treatment is obtained.

[0013] Preferably, in step S1, the core separation layer of the raw membrane nanofiltration membrane can be one of poly-piperazine amide or wholly aromatic polyamide material; the alcohol solvent is one or a mixture of methanol, ethanol, isopropyl alcohol, benzyl alcohol and n-butanol; the immersion time of the raw membrane in the alcohol solvent is 10-30 min, preferably 10-20 min.

[0014] Preferably, the temperature response monomer is one of N-isopropyl acrylamide, N-ethyl caprolactam and N,N-dimethylaminoethyl methacrylate (DMAEMA).

[0015] Preferably, the pH response monomer is one of acrylic acid, 4-vinylpyridine and vinyl imidazole.

[0016] Preferably, the free radical initiator is one of an organic peroxide, an inorganic peroxide and a free radical special initiator 2-bromoisobutyryl bromide, the organic peroxide is benzoyl peroxide, and the inorganic peroxide is potassium persulfate or ammonium persulfate.

[0017] Preferably, the mass volume fraction of the temperature-responsive monomer is 1%-20%, preferably 5%-10%; the mass volume fraction of the pH-responsive monomer is 1%-20%, preferably 5%-10%; and the mass volume fraction of the free radical initiator is 0.01%-1%, preferably 0.1%-0.5%.

[0018] Preferably, the modification reaction in step S3 is performed for 1-4h, preferably 1-2h, and the reaction solution is controlled at a temperature of 20-35℃, preferably 25-30℃; and nitrogen is injected during the reaction to deoxygenate the solution and prevent free radical deactivation.

[0019] Preferably, in step S4, the original membrane is taken out and washed in pure water three times, and the pure water used in the first two washes is at a temperature of 35-45℃ and 25-35℃, respectively, and the last time uses normal temperature pure water; wherein, the purpose of high-temperature water washing is to promote the rapid desorption and dissolution of monomers or oligomers that do not participate in the reaction, the purpose of medium-temperature water washing is to reduce the swelling and shrinking stress in the modified region, promote the preliminary stabilization and formation of the intelligent response layer, and the purpose of normal temperature water washing is to slowly restore the membrane system to the standard storage state and prevent temperature stress from disturbing the membrane pore structure. The intelligent nanofiltration membrane prepared in step S4 is stored in a 0.3% sodium sulfite solution and used as needed.

[0020] In a second aspect, the present application also provides an intelligent nanofiltration membrane prepared by the above preparation method, wherein the intelligent nanofiltration membrane has temperature and pH intelligent response functions.

[0021] In a third aspect, the present application also provides the use of the above-prepared intelligent nanofiltration membrane in high-salt wastewater treatment.

[0022] The present application introduces intelligent functional monomers with temperature responsiveness and pH responsiveness on the surface of conventional polyamide nanofiltration membranes, and uses in-situ free radical polymerization to build a controllable responsive structure layer inside the separation layer, so that the membrane material can quickly respond to changes in external environmental conditions and reversibly adjust the separation performance. The response structure can change the hydrophilicity and hydrophobicity and the charge state of the molecular chain under different temperatures and acid-base conditions, thereby adjusting the permeability of the membrane pores and the charge distribution on the membrane surface, and realizing the flux adjustment and selective retention of different types of pollutants in water. Through the "temperature-pH cooperative response" mechanism, the membrane material can dynamically adapt to the fluctuations of pollutant types and water quality conditions in high-salt wastewater, improve the separation efficiency of organic matter and single / multivalent salts, and enhance the anti-fouling performance of the membrane, which is suitable for efficient purification and resource treatment of complex high-salt wastewater in chemical, pharmaceutical, printing and dyeing industries, and the above temperature and pH response behavior has reversible characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1Figures of the response of the ion selectivity of two intelligent modified nanofiltration membranes to temperature and pH;

[0024] Figure 2 Figure of the influence of switching pH conditions on ion permeation selectivity at constant temperature (25℃);

[0025] Figure 3 Figure of the influence of switching temperature conditions on ion permeation selectivity at constant pH (9);

[0026] Figure 4 Figures of the response of the organic matter rejection selectivity of two intelligent modified nanofiltration membranes to temperature and pH;

[0027] Figure 5 Figures of the organic matter rejection selectivity under conditions of constant temperature (25℃) switching pH and constant pH (9) switching temperature. DETAILED DESCRIPTION

[0028] To make the objects, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0029] To verify the response and regulation capability of the nanofiltration membrane in the present application under temperature and pH conditions, the following performance test method is designed:

[0030] Test solution system: two representative feed liquid systems are configured in combination with the common pollution characteristics of high-salinity wastewater:

[0031] Test liquid A (inorganic salt mixed solution system): NaCl (2000 mg / L) + Na2SO4 (2000 mg / L) + MgCl2 (2000 mg / L);

[0032] Test liquid B (organic matter mixed solution system): phenol (100 mg / L, molecular weight 94 Da) + rhodamine B (50 mg / L, molecular weight 479 Da);

[0033] Response condition setting: each test liquid is tested under the following two groups of conditions

[0034] (1) Temperature: 25℃ and 40℃;

[0035] (2) pH: 4.0 and 9.0 (adjusted by NaOH or HCl);

[0036] (3) Test pressure constant 0.5 MPa;

[0037] (4) In addition to static test, in order to verify the reversible regulation function of membrane performance, the pH condition is switched at constant temperature, or the temperature is switched at constant pH, and the membrane separation performance is continuously tested.

[0038] Test index and analysis method

[0039] (1) Permeation selectivity of monovalent / multivalent ions:

[0040] Test Na + , Cl - , SO4 2- , Mg 2+ ion concentration (ion chromatography), calculate Na + / Mg 2+ , Cl - / SO4 2- separation factor α, the calculation formula is:

[0041] (1)

[0042] Among them:

[0043] C f A , C f B are the concentrations of ion A and ion B in the feed liquid, respectively;

[0044] C p A , C p B are the concentrations of ion A and ion B in the permeate, respectively;

[0045] (2) Organic matter interception selectivity K:

[0046] The separation ability of different molecular weight or polar substances is reflected by comparing the interception rate. The concentrations of phenol and rhodamine B are determined by ultraviolet-visible spectrophotometry, and the interception rate calculation formula is:

[0047] (2)

[0048] Among them:

[0049] C f and C p are the concentrations of organic matter in the feed liquid and the permeate, respectively;

[0050] The interception selectivity of nanofiltration membrane for the two is represented by the ratio K=R 罗丹明B / R 苯酚 .

[0051] The specific implementation is as follows:

[0052] Example 1

[0053] The poly-piperazine amide nanofiltration membrane was selected as the original membrane, which was placed in ethanol for swelling treatment for 15 minutes and taken out for standby. The modification solution was prepared: N-isopropyl acrylamide (mass fraction 5%) and acrylic acid (mass fraction 8%) were sequentially added to ethanol, and ammonium persulfate (mass fraction 0.3%) was added as an initiator, and the mixture was uniformly mixed.

[0054] The treated membrane was immersed in the modification solution and reacted at 28°C for 1.5 hours, and nitrogen was continuously introduced for deoxidation protection during the reaction. After the reaction was completed, the membrane was taken out and washed with three different temperatures of pure water (high temperature, medium temperature, room temperature, the same below) for three times, and finally placed in 0.3% sodium sulfite aqueous solution for standby.

[0055] Example 2

[0056] The aromatic polyamide nanofiltration membrane was selected as the original membrane, which was placed in isopropyl alcohol for swelling treatment for 20 minutes and taken out for standby. The modification solution was prepared: N-ethyl caprolactam (mass fraction 7%), 4-vinylpyridine (mass fraction 6%) and benzoyl peroxide (mass fraction 0.3%) were sequentially added to isopropyl alcohol as an initiator, and the mixture was uniformly stirred and used.

[0057] The membrane was immersed in the modification solution and reacted at 28°C for 1.5 hours, and nitrogen was continuously introduced for deoxidation. After the reaction was completed, the membrane was washed with three different temperatures of pure water for three times, and finally placed in 0.3% sodium sulfite aqueous solution for standby.

[0058] Example 3

[0059] The poly-piperazine amide nanofiltration membrane was selected as the original membrane, which was placed in benzyl alcohol for swelling treatment for 15 minutes. The modification solution was prepared: N-isopropyl acrylamide (mass fraction 6%), acrylic acid (mass fraction 6%), and 2-bromoisobutyryl bromide (mass fraction 0.2%) was added as an initiator, and the mixture was uniformly mixed and used.

[0060] The membrane was immersed in the modification solution and reacted at 30°C for 1.5 hours, and nitrogen was continuously introduced for deoxidation treatment during the reaction. After the reaction was completed, the membrane was washed with three different temperatures of pure water for three times, and finally placed in 0.3% sodium sulfite aqueous solution for standby.

[0061] Example 4

[0062] The aromatic polyamide nanofiltration membrane was selected as the original membrane, and was swelled in methanol for 10 minutes and taken out for standby. The modification solution was prepared: DMAEMA (6% by mass), acrylic acid (5% by mass), and potassium persulfate (0.4% by mass) as an initiator, and methanol as a solvent.

[0063] The membrane was immersed in the reaction solution, and reacted at 30°C for 1 hour, and nitrogen was introduced to remove dissolved oxygen in the solution. After the reaction, the membrane was washed with three kinds of pure water with different temperatures for three times, and then was stored in 0.3% sodium sulfite solution for standby.

[0064] Example 5

[0065] The poly (piperazine amide) nanofiltration membrane was selected as the original membrane, and was immersed in ethanol for 15 minutes. The modification solution was prepared: N-isopropyl acrylamide (5% by mass), ammonium persulfate (0.3% by mass), and no pH responsive monomer was added, and ethanol was used as a solvent.

[0066] The membrane was immersed in the solution, and reacted at 28°C for 1.5 hours, and nitrogen was introduced for protection. After the reaction, the membrane was washed with three kinds of pure water with different temperatures for three times, and was stored in 0.3% sodium sulfite solution.

[0067] Example 6

[0068] The aromatic polyamide nanofiltration membrane was selected as the original membrane, and was swelled in benzyl alcohol for 20 minutes. The modification solution was prepared: acrylic acid (8% by mass) and benzoyl peroxide (0.3% by mass) as an initiator were added in benzyl alcohol, and the mixture was stirred uniformly and then used.

[0069] The membrane was reacted at 30°C for 1 hour, and nitrogen was continuously introduced for deoxidation treatment during the reaction. After the reaction, the membrane was washed with three kinds of pure water with different temperatures for three times, and was stored in 0.3% sodium sulfite solution for standby.

[0070] Example 7

[0071] The poly (piperazine amide) nanofiltration membrane was swelled in a 1:1 mixture of ethanol and n-butanol for 15 minutes. The modification solution was prepared: N-ethyl caprolactam (6% by mass), vinyl imidazole (6% by mass), and potassium persulfate (0.4% by mass) were mixed uniformly and then used.

[0072] The membrane was immersed in the solution, and reacted at 30°C for 1.5 hours, and nitrogen was continuously introduced for deoxidation treatment during the reaction. After the reaction, the membrane was washed with three kinds of pure water with different temperatures for three times, and was stored in 0.3% sodium sulfite solution for standby.

[0073] Table 1: Types of intelligent response monomers and swelling solvent configurations in each example

[0074]

[0075] Experimental data results

[0076] (1) Mono- / multivalent ion permeation selectivity

[0077] Table 2 Mono- / multivalent ion permeation selectivity (poly-piperazine amide nanofiltration membrane)

[0078]

[0079] Table 3 Mono- / multivalent ion permeation selectivity (aromatic polyamide nanofiltration membrane)

[0080]

[0081] Test data description:

[0082] (1) Figure 1 are the ion selectivity response effect diagrams of two intelligent modified nanofiltration membranes to temperature and pH; it can be seen from Tables 2 and 3 that the nanofiltration membranes (Examples 1, 2, 3, 4, and 7) after double-response intelligent modification have significantly increased α (Na + / Mg 2+ ) and α (Cl - / SO4 2- ) under low temperature and alkaline pH conditions, indicating that the ion permeation selectivity is significantly improved, and the membranes have obvious response behavior to the environmental conditions of temperature and pH; (2) the single-response modified nanofiltration membranes, for example, Example 5 contains only temperature-responsive monomers, and as the temperature decreases, α (Na + / Mg 2+ ) significantly increases while the pH change has less effect; while Example 6 contains only pH-responsive monomers, and under alkaline conditions, α (Cl - / SO4 2- ) significantly increases but the temperature change has less effect, indicating that the respective membrane materials mainly respond to the environmental factors in the modification direction and mainly produce corresponding environmental response behavior; (3) as a control, the two unmodified nanofiltration membranes have less change in mono- / multivalent ion permeation selectivity under different temperatures and pH conditions, and the fluctuation of their separation performance is mainly affected by water viscosity (affected by temperature) and surface charge (affected by pH), and they do not have obvious environmental response ability;

[0083] (2) Figure 2 is the influence diagram of switching pH conditions on ion permeation selectivity at constant temperature (25℃); Figure 3Fig. 2 is a diagram of the influence of switching temperature conditions on ion permeation selectivity at constant pH (9); the continuous test results show that the response behavior of the intelligent modified nanofiltration membrane to temperature and pH can be restored to the initial performance state in the multiple condition switching process, which indicates that the response behavior has a reversible feature and can be used for long-term water treatment processes.

[0084] (2) Retention selectivity of organic matter

[0085] Table 4 Retention selectivity of organic matter with different molecular weights (poly-piperazine amide nanofiltration membrane)

[0086]

[0087] Table 5 Retention selectivity of organic matter with different molecular weights (aromatic polyamide nanofiltration membrane)

[0088]

[0089] Test data description:

[0090] (1) Figure 4 Fig. 3 is a diagram of the response effect of the organic matter retention selectivity of two intelligent modified nanofiltration membranes to temperature and pH; it can be seen from Tables 4 and 5 that the nanofiltration membranes (Examples 1, 2, 3 and 4) after double-response intelligent modification have a significant improvement in the retention selectivity of organic matter under low temperature and acidic pH conditions, and the membranes have obvious response behavior to the environmental conditions of temperature and pH; (2) the nanofiltration membranes (Examples 5 and 6) modified by single-response have mainly corresponding environmental response behavior; (3) as a control, the two unmodified nanofiltration membranes have little change in the permeation selectivity of single / multivalent ions under different temperature and pH conditions.

[0091] (2) Figure 5 Fig. 4 is a diagram of the retention selectivity of organic matter under the conditions of switching pH at constant temperature (25℃) and switching temperature at constant pH (9); the continuous test results show that the response behavior of the intelligent modified nanofiltration membrane to temperature and pH can be restored to the initial performance state in the multiple condition switching process, which indicates that the response behavior has a reversible feature and can be used for long-term water treatment processes.

[0092] The above merely describes specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a smart nanofiltration membrane, characterized in that, Includes the following steps: S1: Select a polyamide composite nanofiltration membrane as the primary membrane, immerse the primary membrane in an alcohol solvent for swelling treatment, and set it aside for use; S2: Prepare an alcohol solution containing a free radical initiator, a pH-responsive monomer, and a temperature-responsive monomer for nanofiltration membrane modification; S3: The original film after swelling treatment in step S1 is placed into the alcohol solution prepared in step S2 for modification reaction treatment; S4: After the modification reaction is completed, the original membrane is taken out and washed in pure water to finally obtain the intelligent nanofiltration membrane.

2. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, In step S1, the polyamide composite nanofiltration membrane is one of polypiperazine amide or fully aromatic polyamide material; the alcohol solvent is one or more of methanol, ethanol, isopropanol, benzyl alcohol, and n-butanol; the immersion time of the original membrane in the alcohol solvent is 10-30 min.

3. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, The temperature-responsive monomer is one of N-isopropylacrylamide, N-ethylcaprolactam, and N,N-dimethylaminoethyl methacrylate.

4. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, The pH-responsive monomer is one of acrylic acid, 4-vinylpyridine, and vinylimidazole.

5. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, The free radical initiator is one of an organic peroxidant, an inorganic peroxidant, or a free radical-specific initiator, 2-bromoisobutyryl bromide. The organic peroxidant is benzoyl peroxide; the inorganic peroxidant is potassium persulfate or ammonium persulfate.

6. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, The temperature-responsive monomer has a mass-volume fraction of 1%-20%; the pH-responsive monomer has a mass-volume fraction of 1%-20%; and the free radical initiator has a mass-volume fraction of 0.01%-1%.

7. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, The modification reaction in step S3 takes 1-4 hours; the reaction solution temperature is controlled at 20-35℃; nitrogen is injected during the reaction to deoxygenate the solution and prevent free radical deactivation.

8. The method for preparing a smart nanofiltration membrane according to claim 1, characterized in that, In step S4, the original membrane is taken out and washed three times in pure water. The temperature of the pure water used for the first two washes is 35-45℃ and 25-35℃ respectively, and the last wash is with pure water at room temperature. The intelligent nanofiltration membrane obtained in step S4 is stored in a 0.3% sodium sulfite solution for later use.

9. A smart nanofiltration membrane, characterized in that, The smart nanofiltration membrane, prepared by any one of claims 1-8, has intelligent temperature and pH response functions.

10. The application of the intelligent nanofiltration membrane as described in claim 9 in the treatment of high-salinity wastewater.

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