A positively charged nanofiltration membrane based on quaternized monomer and its preparation method and application

Abstract

The present invention discloses a positively charged nanofiltration membrane based on a quaternized monomer and a preparation method and application thereof, belonging to the technical field of nanofiltration membrane preparation and ion separation. The method comprises the following steps: providing a quaternized 1,4-diazabicyclo[2.2.2]octane dissolved in water to obtain an aqueous phase monomer solution; and an organic phase monomer solution containing trimesoyl chloride and n-hexane; immersing a porous base nanofiltration membrane in the aqueous phase monomer solution, taking out and removing the residual solution on the membrane surface, immersing it in the organic phase monomer solution to undergo interfacial polymerization to form a polyamide layer, then heat-treating it, and cooling it to obtain the positively charged nanofiltration membrane. The present invention can effectively regulate the thickness of the polyamide layer of the nanofiltration membrane according to the monomer concentration and the condensation time, and prepare a positively charged nanofiltration membrane, which can improve water flux and lithium / magnesium selectivity.

Description

Technical Field

[0001] The invention relates to the technical field of water pollution control and sewage treatment, and in particular to a positively charged nanofiltration membrane based on a quaternary ammonium monomer and a preparation method and application thereof. Background Art

[0002] As a scarce metal, the rapid development of new energy vehicles and electronic products industries will increase the demand for lithium resources. Based on the concept of green and sustainable development, it is urgent to develop process technologies that can optimize the extraction of lithium to meet the demand for lithium in the new energy industry in various countries around the world. Salt lake brine has become an important source of lithium extraction because lithium accounts for >58%. Technical methods such as adsorption, reverse osmosis and evaporation / precipitation are more suitable for reducing the lithium-magnesium ratio of influent and concentrating lithium. Nanofiltration has become an effective way to extract lithium from salt lakes due to its simple operation and economic efficiency. It can better meet the selective separation of lithium ions and interfering ions (sodium ions, potassium ions and calcium ions, etc.), thereby improving the purity of lithium. However, due to the close radius of lithium ions (0.76Å) and magnesium ions (0.72Å), it is usually difficult to selectively separate them according to size screening. At the same time, because lithium ions (1+) and magnesium ions (2+) are both positively charged, and the polyamide selective layer of most nanofiltration membranes is negatively charged, there is an electrostatic attraction between the polyamide nanofiltration membrane and lithium / magnesium ions, resulting in a low selective separation efficiency between the two.

[0003] Therefore, in view of the differences in radius and charge of lithium / magnesium ions, on the one hand, it is necessary to precisely control the average pore size of the nanofiltration membrane between 0.72Å and 0.76Å; on the other hand, it is necessary to enhance the electrostatic repulsion between the membrane surface and magnesium ions by enhancing the positive charge on the surface of the nanofiltration membrane, thereby promoting the highly selective separation of lithium / magnesium ions. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a positively charged nanofiltration membrane based on quaternized monomers and a preparation method and application thereof. The present invention uses 2-bromobenzylamine, 3-bromobenzylamine and 4-bromobenzylamine to quaternize 1,4-diazabicyclo[2.2.2]octane (Dabco) to obtain a positively charged new monomer with a symmetrical structure, and adopts an interfacial polymerization method to prepare a positively charged polyamide nanofiltration membrane, which not only has excellent water permeation flux, but also can achieve high selective separation of lithium ions and magnesium ions. Compared with conventional piperazine and m-phenylenediamine monomers, the present invention selects amine monomers with symmetrical cage structures and cyclic twisted structures as raw materials to effectively improve the porosity and hydrophilicity of the nanofiltration membrane. Quaternizing the amine monomers is a key way to give the new monomers a positive charge. The positively charged polyamide nanofiltration membrane based on the quaternized monomer can improve the permeability and lithium / magnesium selectivity of the membrane.

[0005] The first object of the present invention is to provide a method for preparing a positively charged nanofiltration membrane based on a quaternized monomer, comprising the following steps:

[0006] A quaternized 1,4-diazabicyclo[2.2.2]octane is dissolved in water to obtain an aqueous monomer solution; and an organic monomer solution containing trimesoyl chloride and n-hexane;

[0007] The porous base nanofiltration membrane is immersed in an aqueous monomer solution, the residual solution on the membrane surface is taken out and removed, and then immersed in an organic monomer solution to undergo interfacial polymerization to form a polyamide layer, followed by heat treatment and cooling to obtain the positively charged nanofiltration membrane.

[0008] In some embodiments of the present invention, the quaternized 1,4-diazabicyclo[2.2.2]octane is prepared by the following method:

[0009] S1, dissolving the brombenzylamine compound in an organic solvent to obtain a brombenzylamine compound solution;

[0010] S2. Add the 1,4-diazabicyclo[2.2.2]octane solution to the bromobenzylamine compound solution, heat to reflux, separate the reaction solution into solid and liquid, take the solid phase, and vacuum dry to obtain the quaternized 1,4-diazabicyclo[2.2.2]octane.

[0011] In some embodiments of the present invention, in step S1, the bromobenzylamine compound is selected from one or more of 2-bromobenzylamine, 3-bromobenzylamine, and 4-bromobenzylamine;

[0012] The organic solvent is selected from one or more of ethanol, acetonitrile, N,N-dimethylformamide, isopropanol, and ethyl acetate.

[0013] In some embodiments of the present invention, in step S2, the molar ratio of the brombenzylamine compound to 1,4-diazabicyclo[2.2.2]octane is 2:1 to 2.5:1;

[0014] The heating reflux temperature is 50~100℃, and the heating reflux time is 8~24h;

[0015] The vacuum drying temperature is 30-70° C., and the vacuum drying time is 6-24 hours.

[0016] In some embodiments of the present invention, the porous base nanofiltration membrane is selected from one or more of a polysulfone membrane, a polyethersulfone membrane, and a polyvinylidene fluoride membrane;

[0017] The solvent of the organic phase monomer solution is selected from one or more of ethanol, acetonitrile, N,N-dimethylformamide, isopropanol, and ethyl acetate.

[0018] In some embodiments of the present invention, the concentration of the aqueous monomer solution is 0.1-2.0 wt %;

[0019] The concentration of trimesoyl chloride in the organic phase monomer solution is 0.1-1.0 wt %.

[0020] In some embodiments of the present invention, the immersion time of the aqueous monomer solution is 0.5 to 3 min, and the immersion time of the organic monomer solution is 0.5 to 3 min;

[0021] The temperature of the heat treatment is 40-80° C., and the time of the heat treatment is 2-10 min.

[0022] The second object of the present invention is to provide a positively charged nanofiltration membrane based on quaternized monomers.

[0023] The third object of the present invention is to provide the use of the positively charged nanofiltration membrane in the separation of lithium ions and magnesium ions.

[0024] Furthermore, the positively charged nanofiltration membrane is used for separation of LiCl and MgCl2.

[0025] Furthermore, the Li + The concentration is 500~1000 ppm, Mg 2+ The concentration is 500~1000ppm.

[0026] The positively charged nanofiltration membrane is subjected to Li + / Mg 2+ Separation.

[0027] The above technical solution of the present invention has the following advantages compared with the prior art:

[0028] (1) The present invention uses 2-bromobenzylamine, 3-bromobenzylamine and 4-bromobenzylamine to quaternize 1,4-diazabicyclo[2.2.2]octane with a symmetrical cage structure, and synthesizes three new positively charged monomers D1, D2 and D3 with symmetrical structures. Then, an interfacial polymerization method is used, with D1, D2 and D3 as aqueous monomers and TMC as an organic phase monomer. By adjusting the mass concentration and condensation time of the aqueous phase monomer and the organic phase monomer, a positive charge layer is constructed on the surface of the polyamide nanofiltration membrane to increase the Li + / Mg 2+ This can be attributed to the following: (1) the twisted structures of D1, D2, and D3 can enhance the microporosity and connectivity of the polyamide nanofiltration membrane, allowing water molecules to quickly pass through the nanofiltration membrane, thereby improving the membrane permeability; (2) the two symmetrical quaternary amine groups contained in D1, D2, and D3 can increase the positive charge on the surface of the polyamide nanofiltration membrane, promoting the membrane's selectivity to Mg 2+The electrostatic repulsion is greater than that of Li + Stronger, thus enhancing Li + / Mg 2+ Selective.

[0029] (2) The present invention uses a two-component mixed liquid with a total concentration of 1000 ppm as the simulated brine (Li + / Mg 2+ The mass ratio is 1:40 to 1:100), and the separation performance of the positively charged nanofiltration membrane of the present invention is tested. + The retention rate is 34%~42%, Mg 2+ The interception rate is 96%~96.5%, Li + / Mg 2+ The selectivity is 15~18, and the water flux is 10~16 (L / m 2 ·h·bar). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 This is a schematic diagram of the synthesis of monomer D1 in Example 1 of the present invention;

[0032] Figure 2 This is a schematic diagram of the synthesis of monomer D2 in Example 2 of the present invention;

[0033] Figure 3 This is a schematic diagram of the synthesis of monomer D3 in Example 3 of the present invention;

[0034] Figure 4 The water flux, retention rate and separation factor of the positively charged nanofiltration membranes obtained in Examples 1 to 3 of the present invention and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0036] Example 1

[0037] This embodiment provides a method for preparing a positively charged nanofiltration membrane, the steps are as follows:

[0038] (1) Preparation of aqueous monomer solution:

[0039] The quaternization reaction was carried out according to the molar ratio of 2-bromobenzylamine to 1,4-diazabicyclo[2.2.2]octane of 2:1:

[0040] (i) Dissolve 0.118 mol of 2-bromobenzylamine in 100 mL of ethanol in a flask, and simultaneously dissolve 0.054 mol of 1,4-diazabicyclo[2.2.2]octane in ethanol and drip into the flask. Reflux at 70°C for 12 h, filter the precipitate, wash the precipitate with ethanol several times, dry it in a vacuum oven, and grind the product and record it as D1.

[0041] (ii) Dissolve 1.0 g of D1 monomer in 99 g of deionized water to obtain a D1 solution with a mass concentration of 1.0 wt%.

[0042] (2) Preparation of organic phase monomer solution: 0.015 g of TMC was dissolved in 9.985 g of n-hexane to obtain a TMC n-hexane solution with a mass concentration of 0.15 wt%.

[0043] (3) Preparation of polyamide layer by interfacial polymerization: First, the surface of the cleaned PSF membrane substrate was immersed in 1.0 wt% D1 solution for 120 s, and the residual solution was gently removed with a rubber roller. Then, the membrane substrate was mounted on a customized plastic mold and then contacted with 0.15 wt% TMC n-hexane solution for 60 s. The residual solution on the membrane surface was poured off and the resulting positively charged nanofiltration membrane was heat treated at 50 °C for 10 min. Finally, after the membrane was cooled to room temperature, it was stored in deionized water and soaked to remove the residual solution to obtain a positively charged nanofiltration membrane, which was named D1-TMC.

[0044] Example 2

[0045] This embodiment provides a method for preparing a positively charged nanofiltration membrane, the steps are as follows:

[0046] (1) Preparation of aqueous monomer solution: Quaternization reaction was carried out according to the molar ratio of 3-bromobenzylamine to 1,4-diazabicyclo[2.2.2]octane being 2:1:

[0047] (i) Dissolve 0.118 mol of 2-bromobenzylamine in 100 mL of ethanol in a flask. Dissolve 0.054 mol of 1,4-diazabicyclo[2.2.2]octane in ethanol and drip into the flask. Reflux at 70°C for 12 h, filter the precipitate, wash the precipitate with ethanol several times, dry it in a vacuum oven, grind the product and record it as D2.

[0048] (ii) Dissolve 1.0 g of D2 monomer in 99 g of deionized water to obtain a D2 solution with a mass concentration of 1.0 wt%.

[0049] (2) Preparation of organic phase monomer solution: 0.015 g of TMC was dissolved in 9.985 g of n-hexane to obtain a TMC n-hexane solution with a mass concentration of 0.15 wt%.

[0050] (3) Preparation of polyamide layer by interfacial polymerization: First, the surface of the cleaned PSF membrane substrate was immersed in 1.0 wt% D2 solution for 120 s, and the residual solution was gently removed with a rubber roller. Then, the membrane substrate was mounted on a customized plastic mold and then contacted with 0.15 wt% TMC n-hexane solution for 60 s. The residual solution on the membrane surface was poured off and the resulting positively charged nanofiltration membrane was heat treated at 50 °C for 10 min. Finally, after the membrane was cooled to room temperature, it was stored in deionized water and soaked to remove the residual solution to obtain a positively charged nanofiltration membrane, which was named D2-TMC.

[0051] Example 3

[0052] This embodiment provides a method for preparing a positively charged nanofiltration membrane, the steps are as follows:

[0053] (1) Preparation of aqueous monomer solution:

[0054] The quaternization reaction was carried out according to the molar ratio of 4-bromobenzylamine to 1,4-diazabicyclo[2.2.2]octane of 2:1:

[0055] (i) Dissolve 0.118 mol of 2-bromobenzylamine in 100 mL of ethanol in a flask, and at the same time, dissolve 0.054 mol of 1,4-diazabicyclo[2.2.2]octane in ethanol and drip into the flask. Reflux at 70°C for 12 h, filter the precipitate, wash the precipitate with ethanol several times, dry it in a vacuum oven, grind the product and record it as D3.

[0056] (ii) Dissolve 1.0 g of D3 monomer in 99 g of deionized water to obtain a D3 solution with a mass concentration of 1.0 wt%.

[0057] (2) Preparation of organic phase monomer solution: 0.015 g of TMC was dissolved in 9.985 g of n-hexane to obtain a TMC n-hexane solution with a mass concentration of 0.15 wt%.

[0058] (3) Preparation of polyamide layer by interfacial polymerization: First, the surface of the cleaned PSF membrane substrate was immersed in 1.0 wt% D3 solution for 120 s, and the residual solution was gently removed with a rubber roller. Then, the membrane substrate was mounted on a customized plastic mold and then contacted with 0.15 wt% TMC n-hexane solution for 60 s. The residual solution on the membrane surface was poured off and the resulting positively charged nanofiltration membrane was heat treated at 50 °C for 10 min. Finally, after the membrane was cooled to room temperature, it was stored in deionized water and soaked to remove the residual solution to obtain a positively charged nanofiltration membrane, which was named D3-TMC.

[0059] Comparative Example 1

[0060] This comparative example provides a method for preparing a nanofiltration membrane, comprising the following steps:

[0061] (1) Preparation of aqueous monomer solution: 0.5 g of PIP monomer was dissolved in 99.5 g of deionized water to obtain a PIP solution with a mass concentration of 0.5 wt%.

[0062] (2) Preparation of organic phase monomer solution: 0.015 g of TMC was dissolved in 9.985 g of n-hexane to obtain a TMC n-hexane solution with a mass concentration of 0.15 wt%.

[0063] (3) Preparation of polyamide layer by interfacial polymerization: First, the surface of the cleaned PSF membrane substrate was immersed in 0.5 wt% PIP solution for 120 s, and the residual solution was gently removed with a rubber roller. Then, the membrane substrate was mounted on a customized plastic mold and then contacted with 0.15 wt% TMC n-hexane solution for 60 s. The residual solution on the membrane surface was poured off and the resulting positively charged nanofiltration membrane was heat treated at 50 °C for 10 min. Finally, after the membrane was cooled to room temperature, it was stored in deionized water and soaked to remove the residual solution to obtain a positively charged nanofiltration membrane, which was named PIP-TMC.

[0064] Effect verification

[0065] The nanofiltration membranes prepared in Examples 1 to 3 and Comparative Example 1 were used to test the separation performance of LiCl and MgCl2. The nanofiltration membranes were tested for separation performance using a cross-flow filtration device at a transmembrane pressure of 10 bar and an operating temperature of 25°C to 30°C. The membrane flux (J) was tested using pure water as the feed solution. A two-component mixed solution (LiCl) (1000 ppm) and MgCl2 (1000 ppm) was added to the mixture. + / Mg 2+ The inorganic salt rejection rate (R) and separation factor (S) of the membrane were tested by using the feed solution of 1:100. Mg,Li ). The test results are as follows Figure 4 shown.

[0066] (1) The permeation flux is calculated using the formula J = V / (A × t × P), where J (L / m 2 ·h·bar) is the permeation flux of the membrane, V(L) is the total volume of liquid passing through the membrane, A(m 2 ) is the effective filtration area, t(h) is the filtration time, and P(bar) is the filtration pressure.

[0067] (2) The inorganic salt retention rate is calculated using the formula R = (C0-C1) / C0, where R represents the inorganic salt retention rate, C0 and C1 represent the conductivity of the feed solution and the permeate solution, respectively.

[0068] (3) The separation factor of LiCl and MgCl2 is calculated using the formula S Mg,Li =(C Mg,p / C Li,p ) / (C Mg,f / C Li,f ), where C Mg,p and C Li,p Represents Mg in the infiltration solution 2+ and Li + The concentration, C Mg,f and C Li,f Represents the Mg content in the feed solution 2+ and Li + concentration.

[0069] Depend on Figure 4 It can be seen that the positively charged polyamide nanofiltration membrane prepared with D1, D2 and D3 as aqueous phase monomers and TMC as organic phase monomer effectively improved the Li + / Mg 2+ Separation performance.

[0070] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a positively charged nanofiltration membrane based on a quaternized monomer, characterized in that: The following steps are involved: A quaternized 1,4-diazabicyclo[2.2.2]octane is provided and dissolved in water to obtain an aqueous monomer solution; and an organic monomer solution containing trimesoyl chloride and n-hexane; The porous base nanofiltration membrane is immersed in an aqueous monomer solution, the residual solution on the membrane surface is taken out and removed, and then immersed in an organic monomer solution to undergo interfacial polymerization to form a polyamide layer, followed by heat treatment and cooling to obtain the positively charged nanofiltration membrane; the quaternized 1,4-diazabicyclo[2.2.2]octane is prepared by the following method: S1, dissolving the brombenzylamine compound in an organic solvent to obtain a brombenzylamine compound solution; S2, adding the 1,4-diazabicyclo[2.2.2]octane solution to the bromobenzylamine compound solution, heating to reflux, performing solid-liquid separation on the reaction solution, taking the solid phase, and vacuum drying to obtain the quaternized 1,4-diazabicyclo[2.2.2]octane; The bromobenzylamine compound is selected from one or more of 2-bromobenzylamine, 3-bromobenzylamine and 4-bromobenzylamine.

2. The preparation method according to claim 1, characterized in that: In step S1, the organic solvent is selected from one or more of ethanol, acetonitrile, N,N-dimethylformamide, isopropanol, and ethyl acetate.

3. The preparation method according to claim 1, characterized in that: In step S2, the molar ratio of the brombenzylamine compound to 1,4-diazabicyclo[2.2.2]octane is 2:1 to 2.5:1; The heating reflux temperature is 50~100℃, and the heating reflux time is 8~24h; The vacuum drying temperature is 30-70° C., and the vacuum drying time is 6-24 hours.

4. The preparation method according to claim 1, characterized in that: The porous base nanofiltration membrane is selected from one or more of a polysulfone membrane, a polyethersulfone membrane, and a polyvinylidene fluoride membrane.

5. The preparation method according to claim 1, characterized in that: The concentration of the aqueous monomer solution is 0.1-2.0 wt %.

6. The preparation method according to claim 1, characterized in that: The concentration of trimesoyl chloride in the organic phase monomer solution is 0.1-1.0 wt %.

7. The preparation method according to claim 1, characterized in that: The immersion time of the aqueous monomer solution is 0.5 to 3 minutes, and the immersion time of the organic monomer solution is 0.5 to 3 minutes; The temperature of the heat treatment is 40-80° C., and the time of the heat treatment is 2-10 min.

8. A positively charged nanofiltration membrane based on a quaternized monomer, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the positively charged nanofiltration membrane described in claim 8 in the separation of lithium ions and magnesium ions.

Images