Modified nanofiltration membrane material for advanced treatment of landfill leachate and preparation method of modified nanofiltration membrane material

Abstract

The invention discloses a modified nanofiltration membrane material and a preparation method thereof, is mainly applied to advanced treatment of landfill leachate, and belongs to the field of wastewater treatment. The preparation method comprises the following steps: carrying out interfacial polymerization reaction on piperazine and trimesoyl chloride to obtain a polyamide nanofiltration membrane, and dissolving a biquaternary ammonium salt derivative as shown in the following formula and 4-dimethylaminopyridine (DMAP) in water to obtain a mixed solution of the biquaternary ammonium salt derivative and a catalyst; the preparation method comprises the following steps: soaking the surface of a polyamide nanofiltration membrane in an aqueous solution of a biquaternary ammonium salt derivative and a catalyst, reacting for a period of time under the condition that the temperature is lower than 5 DEG C, removing the redundant solution after the reaction is finished, drying the membrane in air, and soaking the dried membrane in deionized water to obtain the modified nanofiltration membrane material. According to the nanofiltration membrane, the pure water flux and the salt rejection rate of the membrane are improved, and meanwhile, the nanofiltration membrane also shows excellent anti-pollution and antibacterial properties. # imgabs0 #

Description

Technical Field

[0001] The present invention belongs to the field of sewage and wastewater treatment, and particularly relates to a modified nanofiltration membrane material for the advanced treatment of landfill leachate and a preparation method thereof. Background Art

[0002] The total global production of municipal solid waste (MSW) in 2024 is expected to reach 2.1 billion tons, and traditional technologies such as incineration, composting, and landfilling are usually used for treatment. The landfill leachate generated by sanitary landfilling or incineration is as high as 100 million tons per year. The landfill leachate contains various toxic pollutants, such as benzene and its various derivatives, polycyclic aromatic hydrocarbons, humic acid, pesticide pathogens, etc. If untreated or improperly treated landfill leachate enters natural water bodies, it may pollute groundwater and surface water bodies, destroy the living environment of aquatic organisms, and cause persistent impacts on the ecosystem. Traditional treatment methods for landfill leachate include flocculation precipitation method, adsorption method, biological treatment method, chemical oxidation method, etc. However, with the continuous strengthening of the country's environmental pollution control efforts, the pollutant discharge standard limits of landfills are gradually decreasing, and traditional treatment methods are facing increasing challenges and are difficult to meet the treatment requirements.

[0003] Membrane separation technology has been proven to be an effective and promising treatment method, which can ensure that the final leachate meets the discharge standards. In membrane separation technology, nanofiltration membranes are widely used in sewage and wastewater treatment due to their unique pore size range and surface charge properties. They can effectively intercept multivalent ions and small organic molecules through steric hindrance and Donnan effect. These properties provide reliable technical support for the advanced treatment of landfill leachate. However, the relatively low water permeability is the main challenge for the application of ordinary nanofiltration membranes. Therefore, membrane modification is very necessary for the advanced treatment of landfill leachate. Covalent grafting, as a means of surface modification, has been proven to be an effective way to improve membrane performance and maintain long-term stability. Usually, the unreacted acyl chloride groups on the polyamide surface can be modified by monomers or polymers with amine / hydroxyl groups. Membranes with amide bonds (CONH) have poor chlorine resistance stability, which also limits some of their applications. However, the stability of the "hydroxyl-acyl chloride" esterification reaction is much better. At the same time, the introduction of new monomers can generate free volume cavities, which can serve as additional water transport channels and is beneficial to improving the hydrophilicity of the membrane and enhancing the water flux of the membrane.

[0004] Currently, the modification of nanofiltration membranes often only considers the improvement of certain aspects of their performance, such as the increase in flux, but the antibacterial property of the membrane is not good, or the flux of the membrane is sacrificed in order to improve the antibacterial property of the membrane, affecting the separation efficiency of the membrane. Therefore, in the field of advanced treatment of landfill leachate, there is an urgent need to develop a high-throughput nanofiltration membrane with high salt rejection rate, anti-pollution, and good antibacterial properties. Summary of the Invention

[0005] Aiming at the problems of small flux and the like in the advanced treatment of landfill leachate by existing nanofiltration membranes, in the present invention, grafting a bisquaternary ammonium salt derivative monomer onto a polyamide nanofiltration membrane can effectively improve the membrane flux, anti-pollution and antibacterial properties, and salt rejection rate.

[0006] To solve the above problems, the technical solution adopted in the present invention is as follows:

[0007] The present invention first provides a modified nanofiltration membrane material, which is obtained by grafting a bisquaternary ammonium salt derivative monomer onto a polyamide layer formed on the surface of a substrate membrane.

[0008] Among them, the bisquaternary ammonium salt derivative has the structure shown by the following formula:

[0009]

[0010] Furthermore, the bisquaternary ammonium salt derivative is obtained by reacting N-methyldiethanolamine with 1,2-dibromoethane. The specific preparation method is as follows: Add N-methyldiethanolamine and 1,2-dibromoethane to acetonitrile, reflux and stir for more than 12 h, stop the reaction and cool to room temperature, concentrate under reduced pressure, wash the obtained liquid with petroleum ether 3 times, and dry it in a blast dryer at 100 °C to obtain the bisquaternary ammonium salt derivative.

[0011] Secondly, the present invention provides a preparation method of the modified nanofiltration membrane material, including the following steps:

[0012] S1 Dissolve piperazine in water to obtain an aqueous piperazine solution, which is used as the aqueous phase;

[0013] S2 Dissolve trimesoyl chloride in n-hexane, which is used as the organic phase solution;

[0014] S3 Dissolve the bisquaternary ammonium salt derivative and 4-dimethylaminopyridine (DMAP) in water to obtain a mixed solution of the bisquaternary ammonium salt derivative and the catalyst;

[0015] S4 Prepare a polyamide layer on the surface of the substrate membrane to obtain a polyamide membrane: First immerse the substrate membrane in the aqueous phase prepared in step S1, then pour out the solution, remove the excess solution on the surface of the substrate membrane, and then immerse it in the organic phase solution prepared in step S2. An interfacial polymerization reaction occurs on the membrane surface to form a polyamide layer, obtaining a polyamide membrane;

[0016] S5 Immerse the polyamide layer on the surface of the polyamide membrane prepared in step S4 in the mixed solution prepared in step S3, react under the condition that the temperature is lower than 5 °C, and graft the bisquaternary ammonium salt derivative on the surface of the polyamide membrane to obtain the modified nanofiltration membrane material.

[0017] The above preparation method further includes, after the reaction is completed, removing the excess solution, placing the membrane in the air to dry, obtaining the modified nanofiltration membrane material, and soaking it in deionized water for storage.

[0018] As a further improvement of the present invention, the mass-volume concentration of piperazine in the aqueous piperazine solution is 0.5 to 1.0% w / v.

[0019] As a further improvement of the present invention, the mass-volume concentration of trimesoyl chloride in the organic phase solution is 0.2 to 0.5% w / v.

[0020] As a further improvement of the present invention, the mass-volume concentration of the bisquaternary ammonium salt derivative in the mixed solution is 0.6 to 3.0% w / v; the mass ratio of the bisquaternary ammonium salt derivative to DMAP is 1:1.

[0021] As a further improvement of the present invention, the immersion time of the substrate membrane in the aqueous phase is 5 to 10 min.

[0022] As a further improvement of the present invention, the time for the interfacial polymerization reaction of the substrate membrane in the organic phase solution is 30 s to 2 min.

[0023] As a further improvement of the present invention, the immersion time of the surface of the nanofiltration membrane in the mixed solution of the bisquaternary ammonium salt derivative and the catalyst is 5 to 15 min.

[0024] As a further improvement of the present invention, the substrate membrane comprises a polysulfone or polyethersulfone ultrafiltration membrane.

[0025] As a further improvement of the present invention, the modified nanofiltration membrane material is applied to the advanced treatment of landfill leachate.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: First, the present invention synthesizes a bisquaternary ammonium salt derivative containing multiple hydroxyl groups, and grafts the bisquaternary ammonium salt derivative monomer onto the polyamide nanofiltration membrane through an esterification reaction. The bisquaternary ammonium salt derivative is rich in a large number of hydrophilic groups, and both the hydrophilicity and electronegativity of the membrane increase after grafting. Therefore, the modified nanofiltration membrane has higher water flux and ion rejection rate. The flux of the modified nanofiltration membrane is 20 - 36.2 Lm - 2h -1 bar -1 , and the rejection rate of sodium sulfate can reach more than 96%. During the fouling test, the flux recovery rate is 90.5 - 98.2%. Second, by grafting the bisquaternary ammonium salt derivative synthesized by the present invention onto the polyamide nanofiltration membrane, the present invention also obtains an antibacterial membrane with excellent antibacterial performance. The high-flux nanofiltration membrane prepared by the present invention with high salt rejection rate, anti-fouling and good antibacterial performance is of great significance for the advanced treatment of landfill leachate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1H NMR spectrum of the bisquaternary ammonium salt derivative prepared in Example 1.

[0028] Figure 2 The surface morphology (a) and cross-sectional morphology (b) of the nanofiltration membrane prepared in Example 1. Detailed implementation manners

[0029] The present invention will be further described below in conjunction with specific examples.

[0030] Example 1

[0031] The preparation method of the modified nanofiltration membrane material in this example includes the following steps:

[0032] 1) Preparation of bisquaternary ammonium salt derivative: Add N-methyldiethanolamine (2.382 g, 20 mmol) and 1,2-dibromoethane (1.858 g, 10 mmol) to 10 mL of acetonitrile, reflux and stir for 24 h, stop the reaction and cool to room temperature, concentrate under reduced pressure, wash the obtained liquid with petroleum ether 3 times, and dry in a blast dryer at 100 °C to obtain the bisquaternary ammonium salt derivative with a yield of 99.9%. The hydrogen spectrum of the bisquaternary ammonium salt derivative is as Figure 1 shown.

[0033] 2) Preparation of aqueous phase: Dissolve 0.5 g of piperazine in 100 mL of water to prepare an aqueous solution of piperazine (0.5% w / v);

[0034] 3) Preparation of organic phase: Dissolve 0.3 g of trimesoyl chloride in 100 mL of n-hexane to prepare an organic phase solution with a mass concentration of trimesoyl chloride of 0.3% w / v;

[0035] 4) Preparation of the mixture of bisquaternary ammonium salt derivative and catalyst: Dissolve 3.0 g of bisquaternary ammonium salt derivative (3.0% w / v) and 3.0 g of DMAP (3.0% w / v) in 100 mL of water to obtain a mixture;

[0036] 5) Preparation of polyamide nanofiltration membrane: First, immerse the surface of the polyethersulfone substrate membrane (Nanjing Weihua Membrane Technology Co., Ltd., molecular weight cut-off 20 - 30 kDa) in the aqueous phase prepared in step 2) for 5 min, then pour out the solution and remove the excess water on the surface with lint-free paper, and then place the membrane surface in the organic phase solution prepared in step 3) and keep it for 1 min to initiate an interfacial polymerization reaction to obtain a polyamide membrane;

[0037] 6) Preparation of modified nanofiltration membrane: Immerse the surface of the polyamide nanofiltration membrane obtained in step 5) in the solution prepared in step 4), the reaction temperature is lower than 5 °C, the reaction time is 10 min, after the reaction, remove the excess bisquaternary ammonium salt, place the membrane to dry in air first and then soak it in deionized water. The surface of the modified nanofiltration membrane ( Figure 2 a) and cross-section ( Figure 2 b) morphologies are as Figure 2As shown, the surface has a relatively high roughness, which can provide a transmission channel for water molecules, thereby improving the permeability of the membrane. In the cross-sectional view, it can be clearly observed that there is a modified polyamide separation layer on the surface of the base membrane.

[0038] For the modified nanofiltration membrane prepared above, the water flux test was carried out. The membrane water flux was calculated according to Formula 1:

[0039]

[0040] where P is the flux of the membrane, with the unit of L m - 2h -1 bar -1 ; V is the volume of the filtrate within a certain filtration time, with the unit of L; A is the effective membrane filtration area, with the unit of m 2 ; T is the filtration time, with the unit of h; ΔP is the pressure applied during the filtration process, with the unit of bar.

[0041] For the salt separation performance experiment of the above nanofiltration membrane, the rejection rate of sodium sulfate was measured through a laboratory-scale cross-flow filtration device. The rejection rate of sodium sulfate was calculated according to the following Formula 2:

[0042]

[0043] where, C p (ppm) and C f (ppm) represent the concentrations of salt in the filtrate and the stock solution, respectively.

[0044] For the anti-fouling experiment of the above nanofiltration membrane, the anti-fouling process is mainly divided into 3 stages, namely the first stage of pure water filtration, the second stage of filtration of BSA (1000 ppm) solution, and the third stage of pure water filtration after membrane rinsing. The flux recovery rate FRR (%) and the flux decline rate FDR (%) of the membrane were calculated according to the following Formulas 3 and 4:

[0045]

[0046] where, J w1 is the pure water flux (L m - 2h -1 ), J p is the stable flux during filtration of BSA solution (Lm - 2h -1 ), J w2 is the pure water flux after membrane rinsing (Lm - 2h -1 ).

[0047] The above nanofiltration membrane was subjected to an antibacterial test. In the present invention, the common Escherichia coli was used as the bacterial strain for the antibacterial test. First, the membrane was placed in a petri dish and irradiated with ultraviolet light for 30 min to kill the existing bacteria on the membrane surface; then 200 μL of the bacterial suspension (concentration: 1×10 5 CFU / mL) was dropped on the membrane surface and placed in a constant temperature incubator at 37 °C for 2 h. 1800 μL of physiological saline was used to wash and collect the bacterial liquid; then 100 μL of the bacterial liquid was evenly dispersed on an agar plate and cultured in a constant temperature incubator at 37 °C for 12 h. The number of bacterial colonies on the plate was recorded as the number of surviving bacteria. Taking the number of bacteria (N0) in Comparative Example 1 as a reference, the calculation formula for the survival rate η of bacteria (N1) in the examples is:

[0048]

[0049] The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of the nanofiltration membrane was 34.6 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate reached 96.2%. In the anti-pollution test, the flux decline rate FDR of the membrane was 15.8%, the flux recovery rate FRR was 94.6%, and the survival rate of Escherichia coli was 0.5%.

[0050] Example 2

[0051] In this example, during the preparation process of the modified nanofiltration membrane material, piperazine was dissolved in water to prepare an aqueous solution of piperazine (1.0% w / v) as the aqueous phase, and the remaining steps were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of the nanofiltration membrane was 28.2 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate reached 97.2%, the flux decline rate FDR of the membrane was 18.3%, the flux recovery rate FRR was 93.5%, and the survival rate of Escherichia coli was 0.2%.

[0052] Example 3

[0053] In this example, during the preparation process of the modified nanofiltration membrane material, the organic phase was prepared by dissolving trimesoyl chloride in n-hexane to prepare a solution with a mass concentration of trimesoyl chloride of 0.5% w / v; the remaining steps were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of the nanofiltration membrane was 31.1 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate reached 96.5%, the flux decline rate FDR of the membrane was 17.6%, the flux recovery rate FRR was 94.0%, and the survival rate of Escherichia coli was 0.4%.

[0054] Example 4

[0055] In this example, during the preparation of the modified nanofiltration membrane material, the mixed solution was obtained by dissolving a bisquaternary ammonium salt derivative (1.5% w / v) and DMAP (1.5% w / v) in water; the remaining steps were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of this nanofiltration membrane was 20.5 Lm - 2h -1 bar -1 , the rejection rate of sodium sulfate could reach 96.8%, the flux decline rate FDR of the membrane was 19.1%, the flux recovery rate FRR was 92.0%, and the survival rate of Escherichia coli was 0.8%.

[0056] Example 5

[0057] The difference between this example and Example 1 was that the polyethersulfone substrate membrane was soaked in the aqueous phase for 10 min, and the remaining operations were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of this nanofiltration membrane was 33.8 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate could reach 96.3%, the flux decline rate FDR of the membrane was 96.3%, the flux recovery rate FRR was 95.0%, and the survival rate of Escherichia coli was 0.6%.

[0058] Example 6

[0059] The difference between this example and Example 1 was that the polyethersulfone substrate membrane was soaked in the organic phase for 2 min, and the remaining operations were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of this nanofiltration membrane was 33.0 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate could reach 96.4%, the flux decline rate FDR of the membrane was 16.5%, the flux recovery rate FRR was 94.7%, and the survival rate of Escherichia coli was 0.7%.

[0060] Example 7

[0061] The difference between this example and Example 1 was that the polyamide nanofiltration membrane was soaked in the mixed solution for 15 min, and the remaining operations were the same as in Example 1. The results showed that: under the condition that the operating pressure was 6 bar, the membrane flux of this nanofiltration membrane was 36.2 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate could reach 96.0%, the flux decline rate FDR of the membrane was 13.4%, the flux recovery rate FRR was 97.8%, and the survival rate of Escherichia coli was 0.1%.

[0062] Comparative Example 1

[0063] This comparative example is a common polyamide nanofiltration membrane prepared by the steps 1) - 5) of the example without grafting the bisquaternary ammonium salt derivative monomer. Under the condition that the operating pressure is 6 bar, the membrane flux of this nanofiltration membrane is 7.8 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate can reach 97.3%, the flux decline rate FDR of the membrane is 24.4%, the flux recovery rate FRR is 86.5%, and the survival rate of Escherichia coli is 100%.

[0064] Comparative Example 2

[0065]

[0066] This comparative example uses the hexahydroxy quaternary ammonium salt disclosed in CN 117883975 A to replace the bisquaternary ammonium salt derivative. In the preparation process of the modified nanofiltration membrane material, the mixed solution is a mixed solution obtained by dissolving the hexahydroxy quaternary ammonium salt (3.0% w / v) and DMAP (3.0% w / v) in water; the remaining steps are the same as those in Example 1. The results show that: under the condition that the operating pressure is 6 bar, the membrane flux of this nanofiltration membrane is 35.8 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate can reach 96.8%, the flux decline rate FDR of the membrane is 13.6%, the flux recovery rate FRR is 97.3%, and the survival rate of Escherichia coli is 13.8%.

[0067] Comparative Example 3

[0068]

[0069] This comparative example uses the 1,7-diaminoethyl-1,1,4,7,7-pentamethyldiethylenetriamine dibromide salt disclosed in CN 111871223 A to replace the bisquaternary ammonium salt derivative. In the preparation process of the modified nanofiltration membrane material, the mixed solution is a mixed solution obtained by dissolving the 1,7-diaminoethyl-1,1,4,7,7-pentamethyldiethylenetriamine dibromide salt (3.0% w / v) and DMAP (3.0% w / v) in water; the remaining steps are the same as those in Example 1. The results show that: under the condition that the operating pressure is 6 bar, the membrane flux of this nanofiltration membrane is 12.6 L m - 2h -1 bar -1 , the rejection rate of sodium sulfate can reach 95.2%, the flux decline rate FDR of the membrane is 21.4%, the flux recovery rate FRR is 89.3%, and the survival rate of Escherichia coli is 0.8%.

[0070] Table 1 Performance comparison of the nanofiltration membrane materials prepared in the examples and comparative examples

[0071]

[0072] The present invention and its implementation manners are schematically described above, and such description is not restrictive. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the purpose of the present invention, creatively design structural manners and embodiments similar to the technical solution, they shall fall within the protection scope of this patent.

Claims

1. A modified nanofiltration membrane material, characterized in that: The modified nanofiltration membrane material comprises a diquaternary ammonium salt layer, a polyamide layer and a base membrane from top to bottom, wherein the diquaternary ammonium salt layer is prepared by grafting a diquaternary ammonium salt derivative monomer onto the polyamide layer; the diquaternary ammonium salt derivative has a structure shown in the following formula: 。 2. The modified nanofiltration membrane material according to claim 1, characterized in that: The material of the polyamide layer is polypiperazine trimesic acid amide; the base membrane is a polysulfone membrane or a polyethersulfone membrane.

3. The method for preparing the modified nanofiltration membrane material according to claim 1 or 2, characterized in that: The following steps are involved: S1: dissolving piperazine in water to obtain a piperazine aqueous solution, which is used as the aqueous phase; S2: dissolving trimesoyl chloride in n-hexane and using it as an organic phase solution; S3 dissolving the diquaternary ammonium salt derivative and 4-dimethylaminopyridine in water to obtain a mixed solution of the diquaternary ammonium salt derivative and the catalyst; S4: immersing the substrate membrane in the aqueous phase prepared in step S1, then pouring out the solution, removing excess solution from the surface of the substrate membrane, and then immersing the substrate membrane in the organic phase solution prepared in step S2, so that an interfacial polymerization reaction occurs on the membrane surface to form a polyamide layer; S5: immersing the polyamide layer prepared in step S4 in the mixed solution prepared in step S3, and reacting at a temperature below 5° C. to obtain a modified nanofiltration membrane material.

4. The method for preparing the modified nanofiltration membrane material according to claim 3, characterized in that: The mass volume concentration of piperazine in the piperazine aqueous solution is 0.5% to 1.0%.

5. The method for preparing the modified nanofiltration membrane material according to claim 3, characterized in that: The mass volume concentration of trimesoyl chloride in the organic phase solution is 0.2% to 0.5%.

6. The method for preparing the modified nanofiltration membrane material according to claim 3, characterized in that: The mass volume concentration of the diquaternary ammonium salt derivative in the mixed solution is 0.6-3.0%.

7. The method for preparing the modified nanofiltration membrane material according to claim 3, characterized in that: The basement membrane is immersed in the water phase for 5 to 10 minutes.

8. The method for preparing a modified nanofiltration membrane material according to claim 3, characterized in that: The time for the interfacial polymerization reaction of the substrate membrane in the organic phase solution is 30 s to 2 min.

9. The method for preparing a modified nanofiltration membrane material according to claim 3, characterized in that: The surface of the nanofiltration membrane is immersed in the mixed solution of the diquaternary ammonium salt derivative and the catalyst for 5 to 15 minutes.

10. The use of the modified nanofiltration membrane material according to claim 1, characterized in that: The modified nanofiltration membrane material is applied to the deep treatment of landfill leachate.

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