1-(2-aminoethyl) bromopyridine quaternized nanofiltration membrane as well as preparation method and application thereof in lithium-magnesium separation

Abstract

The invention relates to a 1-(2-aminoethyl) bromopyridine quaternized nanofiltration membrane as well as a preparation method and application thereof in lithium-magnesium separation. The method comprises the following steps: measuring pyridine and 2-bromoethylamine hydrobromide, and heating in acetonitrile in a nitrogen atmosphere; and carrying out centrifugation and vacuum drying to obtain the 1-(2-aminoethyl) bromopyridine. The preparation method comprises the following steps: soaking a polyacrylonitrile (PAN) substrate for 30 seconds by using a piperazine aqueous solution, removing redundant liquid, soaking a membrane for 30 seconds by using a normal hexane solution of triformyl chloride, removing redundant solution, and heating and crosslinking the obtained membrane to obtain the polyamide membrane. And finally, soaking the PA membrane in the solution, removing the redundant solution, and heating and cross-linking the obtained membrane to obtain x-ABP-PA (x is the mass percent of ABP in the solution). The prepared nanofiltration membrane can be used for separating lithium and magnesium in brine, and the separation factor reaches 7.7 (SLi < + > / Mg < 2 + > = 7.7). The material has the characteristics of high separation factor, simplicity in operation, pollution resistance, high stability and the like, and has very high practical application value.

Description

Technical Field

[0001] This invention belongs to the field of preparation of quaternized nanofiltration membranes and separation of lithium and magnesium, specifically involving quaternized nanofiltration membranes of 1-(2-aminoethyl)bromopyridine, their preparation methods, and their application in lithium and magnesium separation. Background Technology

[0002] With the rapid growth of global demand for lithium resources, lithium extraction from salt lakes has become an important method for developing lithium resources and has attracted widespread attention.

[0003] Salt lakes contain abundant lithium resources, but their brine suffers from problems such as a high magnesium-to-lithium ratio, low lithium concentration, interference from impurity ions, and low technological maturity. Therefore, developing an efficient lithium extraction method is urgently needed. Current methods for lithium extraction from salt lakes mainly include precipitation, adsorption, membrane separation, solvent extraction, electrodialysis, and ion exchange. Considering the actual conditions of salt lake brine, membrane separation offers advantages such as high separation efficiency, simple operation, strong adaptability, low long-term operating costs, and high product quality. Nanofiltration membranes, based on pressure-driven separation, utilize the pore size and surface charge characteristics of nanofiltration membranes to remove large molecular impurities and highly charged ions. In salt lake brine, due to the diagonal regularity, magnesium ions and lithium ions are similar, making lithium-magnesium separation a challenge in salt lake lithium extraction. To achieve efficient lithium-magnesium separation, a nanofiltration membrane capable of effectively separating lithium and magnesium needs to be developed.

[0004] The quaternized nanofiltration membrane with 1-(2-aminoethyl)bromopyridine uses polyamide as its backbone, containing numerous angstrom-level pores and acyl chloride groups, which provide grafting sites for quaternary ammonium salts. The 1-(2-aminoethyl)bromopyridine modified on the polyamide membrane surface exhibits a stronger electrostatic repulsion effect on magnesium ions. The presence of angstrom-level pores requires magnesium ions to overcome a greater dehydration energy barrier when passing through the membrane. The synergistic effect of electrostatic repulsion and size sieving enables the separation of lithium and magnesium in brine, solving the application limitation problem of polyamide membranes due to excessive negative charge and enhancing their lithium and magnesium separation performance. A novel quaternized nanofiltration membrane, x-ABP-PA, was prepared by grafting 1-(2-aminoethyl)bromopyridine onto a polyamide membrane. This nanofiltration membrane features high separation efficiency, environmental friendliness, simple operation, and recyclability, showing promising application prospects. Summary of the Invention

[0005] This invention mainly grafts 1-(2-aminoethyl)bromopyridine onto a polyamide membrane. The angstrom-level pores on the main polyamide membrane have a size sieving effect on magnesium ions. The positively charged 1-(2-aminoethyl)bromopyridine has a stronger electrostatic repulsion effect on magnesium ions. The synergistic effect of size sieving and electrostatic repulsion achieves lithium-magnesium separation, which can effectively separate lithium from brine.

[0006] Pyridine and 2-bromoethylamine hydrobromide were measured and heated in acetonitrile under a nitrogen atmosphere. After centrifugation and vacuum drying, 1-(2-aminoethyl)bromopyridine (ABP) was obtained. A polyacrylonitrile (PAN) substrate was immersed in a piperazine (PIP) aqueous solution for 30 s. After removing excess liquid, the membrane was immersed in a triformyl chloride (TMC) n-hexane solution for 30 s. After removing excess solution, the resulting membrane was heated for crosslinking to obtain a polyamide (PA) membrane. Finally, the PA membrane was immersed in an ABP solution, and after removing excess solution, the resulting membrane was heated for crosslinking to obtain x-ABP-PA (x is the mass percentage of ABP in the solution).

[0007] The present invention is achieved through the following technical solution: a quaternized nanofiltration membrane of 1-(2-aminoethyl)bromopyridine, wherein 1-(2-aminoethyl)bromopyridine is grafted onto a polyamide membrane and named x-ABP-PA, wherein x is 0.5-4.

[0008] The above-mentioned method for preparing a quaternized nanofiltration membrane of 1-(2-aminoethyl)bromopyridine includes the following steps:

[0009] 1) Measure appropriate amounts of pyridine and acetonitrile, and heat them under nitrogen atmosphere at a certain temperature under reflux.

[0010] 2) Weigh an appropriate amount of 2-bromoethylamine hydrobromide and slowly add it to the above solution, then heat for a period of time;

[0011] 3) After the reaction was completed, the solid obtained was separated by centrifugation and dried under vacuum to obtain 1-(2-aminoethyl)bromopyridine;

[0012] 4) The polyacrylonitrile substrate should be soaked in an ethanol solution for a period of time;

[0013] 5) Soak the polyacrylonitrile substrate in piperazine aqueous solution, remove excess liquid, and then soak the membrane in a triformyl chloride n-hexane solution with a certain mass fraction.

[0014] 6) Remove excess triformyl chloride hexane solution, and dry the resulting membrane to obtain a polyamide membrane;

[0015] 7) Weigh a certain mass of 1-(2-aminoethyl)bromopyridine and dissolve it in ultrapure water of different pH to prepare an aqueous solution of 1-(2-aminoethyl)bromopyridine.

[0016] 8) Immerse the polyamide membrane in a 1-(2-aminoethyl)bromopyridine solution for a period of time, remove the excess solution, and then dry the resulting membrane to obtain a 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane.

[0017] In the above-mentioned method for preparing 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane, in steps 1) and 2), the ratio of 2-bromoethylamine hydrobromide:pyridine:acetonitrile is 4.0-4.5 g: 1.0-1.5 mL: 25.0-30.0 mL.

[0018] In the above-mentioned method for preparing quaternized 1-(2-aminoethyl)bromopyridine nanofiltration membrane, in step 1), the reflux temperature is 75-85 °C, and in step 2), the heating time is 20-26 h.

[0019] In the above-mentioned method for preparing 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane, in step 4), the polyacrylonitrile substrate is immersed in a 30% ethanol solution for 3-5 h.

[0020] In the above-mentioned method for preparing 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane, in step 5), the concentration of piperazine aqueous solution is 0.8-1.2 wt%, and the concentration of triformyl chloride / n-hexane solution is 0.1-0.3 wt%.

[0021] In the above-mentioned method for preparing quaternized 1-(2-aminoethyl)bromopyridine nanofiltration membrane, in step 7), the pH range of the ultrapure water is 9-13, and the concentration of the 1-(2-aminoethyl)bromopyridine aqueous solution is 0.5-4.0 wt%.

[0022] In the above-mentioned method for preparing quaternized 1-(2-aminoethyl)bromopyridine nanofiltration membrane, in step 3), the drying temperature is 45-65℃ and the drying time is 10-14 h; in step 6), the drying temperature is 50-70℃ and the drying time is 8-12 min; in step 8), the soaking time is 8-16 min, the drying temperature is 40-60℃ and the drying time is 8-12 min.

[0023] The above-mentioned quaternized 1-(2-aminoethyl)bromopyridine nanofiltration membrane is used in the separation of lithium and magnesium in brine.

[0024] The above-described application is performed as follows: In a mixed solution containing lithium and magnesium, the pH is adjusted to 7, and the above-described 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane is used for retention at room temperature.

[0025] The beneficial effects of this invention are:

[0026] 1) The synthesis of this invention is simple. By grafting the quaternary ammonium salt 1-(2-aminoethyl)bromopyridine onto a polyamide membrane, a nanofiltration membrane that is easy to operate and achieves separation can be obtained, which can effectively separate lithium and magnesium and is suitable for practical applications.

[0027] 2) The nanofiltration membrane x-ABP-PA prepared by this invention exhibits excellent separation performance, with a separation factor (S) for lithium and magnesium in simulated brine. Li + / Mg 2+ The value is 7.7.

[0028] 3) The nanofiltration membrane x-ABP-PA prepared by this invention has good antifouling ability against sodium alginate and bovine serum albumin. After three cycles, the water flux recovery rate of x-ABP-PA membrane is as high as 97.0% and 81.4%, respectively.

[0029] 4) The nanofiltration membrane x-ABP-PA prepared in this invention is susceptible to impurity ions Na+. + K + Ca 2+ and SO4 2- It has little impact and strong application prospects. Attached Figure Description

[0030] Figure 1 (a) Fourier transform infrared spectra of PA membrane and 1-ABP-PA membrane; (b) Retention rates of PA membrane and 1-ABP-PA membrane for PEG of different molecular weights (inset: pore size distribution).

[0031] Figure 2 SEM images of the PA membrane (a) in plan and (b) in cross section; SEM images of the 1-ABP-PA membrane (c) in plan and (d) in cross section.

[0032] Figure 3 The effects of operating pressure on (a) rejection rate and (b) water flux of PA membrane and 1-ABP-PA membrane when using 1000 ppm MgCl2 as feed liquid; the effects of operating pressure on (c) rejection rate and (d) water flux of PA membrane and 1-ABP-PA membrane when using 1000 ppm LiCl as feed liquid.

[0033] Figure 4 The effects of horizontal flow rate on (a) rejection rate and (b) water flux of PA membrane and 1-ABP-PA membrane when using 1000 ppm MgCl2 as feed liquid; the effects of horizontal flow rate on (c) rejection rate and (d) water flux of PA membrane and 1-ABP-PA membrane when using 1000 ppm LiCl as feed liquid.

[0034] Figure 5 The x-ABP-PA membrane was used to evaluate (a) lithium and magnesium rejection rate and water flux of a lithium-magnesium mixture, and (b) separation factor (total feed concentration 2000 ppm, Mg...). 2+ / Li + =20).

[0035] Figure 6 The effects of MgCl2 concentration and LiCl concentration on (a) magnesium or lithium rejection rate and (b) water flux of PA membrane and 1-ABP-PA membrane.

[0036] Figure 7 (a) Rejection rate and (b) water flux of PA membrane and 1-ABP-PA membrane for different inorganic salts.

[0037] Figure 8 The effect of different magnesium-to-lithium ratio feed solutions (1:1, 5:1, 10:1, 20:1, 50:1, 100:1) on the nanofiltration performance of (a) PA membrane and (b) 1-ABP-PA membrane (total feed solution concentration was 2000 ppm).

[0038] Figure 9 For different concentrations of (a) Na + (b)K + (c)Ca 2+ and (d)SO4 2- The effect on the performance of 1-ABP-PA membrane in separating lithium and magnesium.

[0039] Figure 10 Stability testing of 1-ABP-PA membrane.

[0040] Figure 11 The antifouling properties of 1-ABP-PA membranes were determined by: (a) 1 mM sodium alginate; (b) 1 mM bovine serum albumin.

[0041] Figure 12 Synthetic route for x-ABP-PA nanofiltration membrane, which is quaternized from 1-(2-aminoethyl)bromopyridine. Detailed Implementation

[0042] Example 1: Preparation and characterization of quaternized 1-(2-aminoethyl)bromopyridine nanofiltration membrane

[0043] (I) Preparation method

[0044] The synthetic route for the quaternized nanofiltration membrane x-ABP-PA of 1-(2-aminoethyl)bromopyridine is as follows: Figure 12 As shown:

[0045] 1) Measure 1.2 mL of pyridine and 30 mL of acetonitrile into a three-necked flask and heat under nitrogen atmosphere in an oil bath at 80 °C under reflux.

[0046] 2) Weigh 4.3 g of 2-bromoethylamine hydrobromide and slowly add it to the three-necked flask mentioned above, then heat for 24 h;

[0047] 3) After the reaction was completed, the solid obtained was separated and dried under vacuum at 50 °C for 12 h to obtain 1-(2-aminoethyl)bromopyridine;

[0048] 4) The polyacrylonitrile substrate was first soaked in a 30% (v / v) ethanol solution for 4 hours;

[0049] 5) Soak the polyacrylonitrile substrate in a 1.0 wt% piperazine aqueous solution, remove excess liquid, and then soak the membrane in a 0.2 wt% triformyl chloride n-hexane solution;

[0050] 6) Remove excess triformyl chloride hexane solution, and dry the resulting membrane at 60 °C for 10 min to obtain a polyamide membrane;

[0051] 7) Weigh a certain mass of 1-(2-aminoethyl)bromopyridine and dissolve it in ultrapure water with a pH of 9-13 (using 1.0 mol L⁻¹). -1 NaOH solution and 1.0 mol L -1 The pH was adjusted with HCl to prepare a 0.5-4.0 wt% aqueous solution of 1-(2-aminoethyl)bromopyridine.

[0052] 8) Immerse the polyamide membrane in a 1-(2-aminoethyl)bromopyridine solution for 8-16 min. After removing excess solution, dry the resulting membrane at 40-60 °C for 8-12 min to obtain the 1-(2-aminoethyl)bromopyridine quaternized nanofiltration membrane x-ABP-PA. (x in x-ABP-PA represents the mass percentage of ABP in the solution). Experiments determined that the 1-ABP-PA membrane exhibited the best lithium-magnesium separation performance (see Example 3), therefore, the 1-ABP-PA membrane was used for subsequent characterization and experiments.

[0053] (ii) Characterization

[0054] The prepared PA membrane and 1-ABP-PA membrane were subjected to Fourier transform infrared spectroscopy, molecular weight cutoff, and scanning electron microscopy. Figure 1 and Figure 2 As shown. The chemical structures of the PA membrane and the 1-ABP-PA membrane were analyzed by FTIR. Figure 1 (a) PA membrane and 1-ABP-PA membrane at 1627 cm -1 The peak at 3053 cm⁻¹ can be attributed to the stretching vibration peak of the C=O group in the amide group, indicating that the film has a polyamide structure. Compared with PA film, 1-ABP-PA film shows a higher peak at 3053 cm⁻¹. -1 CN appears on ABP. + The stretching vibration peak indicates that the PA membrane was successfully quaternized by ABP. The molecular weight cutoff (MWCO) of the PA membrane and the 1-ABP-PA membrane was tested using polyethylene glycol (PEG) of different molecular weights, and the pore size of the membrane was calculated. Figure 1 (b) Compared to the PA membrane, the MWCO of the 1-ABP-PA membrane decreased from 383.38 Da to 336.93 Da, and the pore size decreased from 2.2 Å to 2.0 Å, indicating that the pore size of the PA membrane decreased after being quaternized with ABP. Scanning electron microscopy analysis was performed on the planar and cross-sectional areas of the PA and 1-ABP-PA membranes. Figure 2 (a) It can be seen that the PA film surface has a striped morphology, and the film thickness is approximately 2.0 μm. Figure 2 (b)). From Figure 2 As shown in (c), the surface of the 1-ABP-PA membrane is granular, and compared with the PA membrane, the thickness of the 1-ABP-PA membrane is approximately 2.1 μm thicker. Figure 2 (d)).

[0055] Example 2: Effects of pressure and horizontal flow rate on the nanofiltration performance of 1-ABP-PA membrane

[0056] Methods: A single solution of 1000 ppm MgCl2 and a single solution of 1000 ppm LiCl were used as feed solutions. The effects of varying the operating pressure or the horizontal flow rate of the feed solution on the nanofiltration performance of PA and 1-ABP-PA membranes were investigated. The pressure ranged from 1 to 5 bar, and the horizontal flow rate ranged from 10 to 50 L / m. -2 h -1 (LPH).

[0057] like Figure 3 As shown in (ab), when using a 1000 ppm MgCl2 solution as the feed liquid, the rejection rate of MgCl2 and the water flux of both the PA membrane and the 1-ABP-PA membrane generally showed an increasing trend with increasing pressure. When the pressure reached 5 bar, the 1-ABP-PA membrane achieved a MgCl2 rejection rate as high as 90% while maintaining a flux of 54.5 L / m. -2 h -1 The water flux. From Figure 3 As shown in (cd), with increasing pressure, the rejection rate of 1000 ppm LiCl by the PA membrane and the 1-ABP-PA membrane did not change significantly; however, the water flux generally showed an increasing trend. The water flux of the 1-ABP-PA membrane was 63.3 L / m² at a pressure of 5 bar. -2 h -1 To ensure both a high MgCl2 rejection rate and a large water flux, a pressure of 5 bar was selected as the operating pressure for the cross-flow nanofiltration unit. Figure 4As can be seen, when the horizontal flow rate increases from 10 LPH to 50 LPH, the rejection rates of both PA membrane and 1-ABP-PA membrane for 1000 ppm MgCl2 single feed solution and 1000 ppm LiCl single feed solution remain basically stable, and the water flux does not change significantly. Therefore, a horizontal flow rate of 50 LPH was selected for subsequent experiments.

[0058] Example 3: 2000 ppm Mg 2+ and Li + Mixed liquid (Mg) 2+ / Li + =20) Effect of on the nanofiltration performance of x-ABP-PA membrane

[0059] Method: Using 2000 ppm Mg 2+ and Li + Mixed liquid (Mg) 2+ / Li + =20) was used as the feed liquid, with pressure controlled at 5 bar and horizontal flow rate at 50 LPH, for the Mg of the x-ABP-PA membrane. 2+ Retention rate, Li + Retention rate and water flux were tested, and magnesium-lithium separation factor was calculated.

[0060] PA membranes were quaternized by using 0.5, 1.0, 2.0, 3.0, and 4.0 wt% ABP aqueous solutions, respectively, to obtain 0.5-ABP-PA, 1-ABP-PA, 2-ABP-PA, 3-ABP-PA, and 4-ABP-PA membranes, respectively. Figure 5 As shown in (a), the experimental data results of this series of materials indicate that the 1-ABP-PA film has a positive effect on Mg 2+ The retention rate was as high as 87%, while for Li + The retention rate is only 17%, and the water flux can reach 51.5 L / m³. -2 h -1 Among this series of materials, the magnesium-lithium separation factor of the 1-ABP-PA membrane is 7.7 (S). Li + / Mg 2+ =7.7), far exceeding other proportions of membrane materials ( Figure 5 (b)).

[0061] Example 4: Effects of different concentrations of MgCl2 and LiCl single feed solutions on the nanofiltration performance of 1-ABP-PA membranes

[0062] Methods: Single solutions of MgCl2 and LiCl at concentrations of 1000, 2000, 3000, 4000, and 5000 ppm were used as feed solutions. The pressure was controlled at 5 bar and the horizontal flow rate was 50 LPH. The effects of different concentrations of MgCl2 and LiCl on the nanofiltration performance of the 1-ABP-PA membrane were investigated. The results are shown in Figure 6.

[0063] like Figure 6 As shown, after the concentration of MgCl2 solution increased from 1000 ppm to 5000 ppm, the rejection rate of MgCl2 by the 1-ABP-PA membrane decreased from 90.3% to 81.4%, and the water flux decreased from 55.1 L / m³. -2 h -1 Reduced to 33.4 L m -2 h -1 After the concentration of LiCl solution increased from 1000 ppm to 5000 ppm, the LiCl rejection rate of the 1-ABP-PA membrane remained basically at 20%, while the water flux increased from 62.5 L / m³. -2 h -1 Reduced to 43.4 L m -2 h -1 The above results indicate that the performance of the 1-ABP-PA membrane is affected to some extent by the feed concentration, with the rejection rate being less affected and the water flux being more significantly affected.

[0064] Example 5: Effect of different salt solutions on the nanofiltration performance of 1-ABP-PA membrane

[0065] Methods: In this section, a single solution of MgCl2, MgSO4, NaCl, Na2SO4, CaCl2, CaSO4, and LiCl at 1000 ppm was selected as the feed liquid. The pressure was controlled at 5 bar and the horizontal flow rate was 50 LPH. The effects of different salt solutions on the nanofiltration performance of the 1-ABP-PA membrane were investigated. The results are shown in Figure 7.

[0066] Depend on Figure 7 It can be seen that when different salt solutions are used as feed liquids, the water flux of the PA membrane ranges from 28 to 49 L / m. -2 h -1 The water flux of the 1-ABP-PA membrane is between 52 and 71 L / m³. -2 h -1 The retention capacities of PA membranes and 1-ABP-PA membranes for different salt solutions follow the order MgSO4 > CaSO4 > MgCl2 > CaCl2 > Na2SO4 > LiCl > NaCl, because SO42-... 2- Electronegativity is greater than Cl - Its distribution capacity on the membrane surface is less than that of Cl.- Therefore, Ca, which belongs to the same divalent ion, 2+ With Mg 2+ Sulfates are more readily retained by the membrane than chlorides; and because Mg 2+ The hydrated ionic radius (4.28 Å) is greater than that of Ca. 2+ (4.12 Å), therefore, when the anion is SO4 2- or Cl - At that time, Mg 2+ The retention rate is greater than that of Ca 2+ Similarly, when the cations are both positive monovalent Na + With Li + At that time, SO4 2- The partition coefficient of Cl on the membrane surface is less than that of Cl. - Therefore, the PA membrane and 1-ABP-PA membrane have a higher rejection rate for Na2SO4 than LiCl and NaCl. Furthermore, because Li... + The hydrated ionic radius of (3.82 Å) is greater than that of Na. + (3.58 Å), therefore, when the anion is Cl... - At that time, Li + The retention rate is greater than that of Na + .

[0067] Example 6 Effect of different magnesium-to-lithium ratio feed solutions on the nanofiltration performance of 1-ABP-PA membrane

[0068] Method: In the test, Mg 2+ and Li + The total concentration was maintained at 2000 ppm, and Mg was prepared separately. 2+ / Li + Solutions of 1, 5, 10, 20, 50, and 100 were used as feed solutions, with the pressure controlled at 5 bar and the horizontal flow rate at 50 LPH. The effects of different magnesium-to-lithium ratio feed solutions on the nanofiltration performance of PA membranes and 1-ABP-PA membranes were investigated. The results are shown in Figure 8.

[0069] from Figure 8 As can be seen in (a), the lowest water flux of the PA membrane was 42.0 L / m³ in the tests of different magnesium-to-lithium ratio feed solutions. -2 h -1 After nanofiltration through the PA membrane, the magnesium-to-lithium ratio of the feed solution can be reduced from the initial 1, 5, 10, 20, 50, and 100 to 0.54, 2.40, 4.26, 9.41, 23.57, and 50.61, respectively. The test results of the 1-ABP-PA membrane for feed solutions with different magnesium-to-lithium ratios are shown below. Figure 8 As shown in (b), the lowest water flux of the 1-ABP-PA membrane is 51.5 L / m². -2 h -1The magnesium-to-lithium ratio of the feed liquid can be reduced from the initial 1, 5, 10, 20, 50, and 100 to 0.16, 1.09, 1.70, 4.54, 13.39, and 30.69, respectively, far exceeding that of the PA membrane. This indicates that the 1-ABP-PA membrane has better magnesium-to-lithium separation performance than the PA membrane.

[0070] Example 7: Effect of coexisting ions in the mixed solution on the nanofiltration performance of the 1-ABP-PA membrane.

[0071] Methods: To more accurately simulate actual salt lake brine, different concentrations of NaCl, KCl, CaCl2, MgSO4 up to 2000 ppm of Mg were added to the study. 2+ and Li + Mixed liquid (Mg) 2+ / Li + =20) to analyze the effect of these coexisting ions on lithium-magnesium separation. The pressure was controlled at 5 bar, and the horizontal flow rate was 50 LPH. The results are as follows. Figure 9 .

[0072] from Figure 9 As can be seen from (ab), the introduction of Na + and K + It will cause Mg 2+ Retention rate and Li + The retention rates all showed an increasing trend, possibly because Na+ has a smaller hydrated ionic radius. + (3.58 Å) and K + (3.31 Å) and Li + There is competition between (3.82 Å) and Na + and K + It has a higher diffusion rate and can therefore pass through the membrane faster, thus Li + Intercepted, Mg 2+ Retention rate and Li + Retention rates all increased. Ca 2+ The results of the effect on lithium-magnesium separation are as follows Figure 9 As shown in (c), because Ca 2+ With Mg 2+ The hydrated ionic radii are not significantly different (Ca 2+ With Mg 2+ The hydrated ionic radii are 4.12 Å and 4.28 Å, respectively, so the competition between the two is relatively weak. When the concentration of CaCl2 introduced increases to 2 g / L... -1 At that time, Ca, with its relatively small hydrated ionic radius, 2+ Only then can a competitive advantage be generated, Mg 2+ The retention rate began to decline; with the introduction of more and more Ca... 2+In order to maintain the electroneutrality of the solution, more and more Li + Through membrane materials, Li + The retention rate shows a decreasing trend, which is beneficial for lithium-magnesium separation. SO4 2- The results of the effect on lithium-magnesium separation are as follows Figure 9 As shown in (d), SO4 2- Compared to Cl - It has stronger electronegativity and a smaller distribution capacity on the membrane surface than Cl. - , making Cl - Li can preferentially pass through the membrane in order to maintain the electroneutrality of the solution. + The Li content was further reduced through membrane materials. + The retention rate of Mg 2+ The retention rate remained essentially unchanged, ultimately leading to an increase in the separation factor.

[0073] Example 8: Stability test of 1-ABP-PA membrane

[0074] Method: Using 2000 ppm Mg 2+ and Li + Mixed solution (Mg) 2+ / Li + =20) was used as the feed liquid. The cross-flow nanofiltration unit pressure was controlled at 5 bar, the horizontal flow rate was controlled at 50 LPH, and it was run continuously for a period of time. The stability of the 1-ABP-PA membrane in the lithium-magnesium separation process was tested, and the results are as follows: Figure 10 .

[0075] from Figure 10 As can be seen, in the first 24 hours, the 1-ABP-PA membrane maintained a MgCl2 rejection rate of over 80% and a LiCl rejection rate of around 20%, while also possessing approximately 55 L m -2 h -1 The water flux indicates that the 1-ABP-PA membrane can maintain high separation performance for 24 h under continuous nanofiltration conditions. After 24 h, the MgCl2 rejection rate begins to gradually decrease, and the separation performance of the 1-ABP-PA membrane begins to become unstable.

[0076] Example 9: Antifouling properties of 1-ABP-PA membrane

[0077] Methods: To investigate the antifouling ability of the 1-ABP-PA membrane, 1 mM sodium alginate solution and 1 mM bovine serum albumin solution were prepared as feed solutions. The cross-flow nanofiltration apparatus was operated at a pressure of 5 bar and a horizontal flow rate of 50 LPH. Ultrapure water was first passed through the membrane for 1 h, followed by either 1 mM sodium alginate solution or 1 mM bovine serum albumin solution for 2 h. The membrane was then rinsed with ultrapure water for 15 min. This experimental procedure was repeated for three cycles before the water flux was measured. The changes in water flux after the initial flow rate and after three cycles were compared. The results are shown below. Figure 11 As shown.

[0078] from Figure 11 As shown in (a), when using 1 mM sodium alginate solution as the feed solution, the water flux recovery rate of the 1-ABP-PA membrane reached 97.0% after three cycles. When the feed solution was 1 mM bovine serum albumin solution, the water flux recovery rate of the 1-ABP-PA membrane was 81.4% after three cycles. The above experimental results indicate that the 1-ABP-PA membrane is only slightly affected by microorganisms, while proteins have a certain influence on the 1-ABP-PA membrane.

Claims

1. A nanofiltration membrane of 1-(2-aminoethyl) bromopyridinium quaternized, characterized in that, 1-(2-aminoethyl) bromopyridine is grafted onto polyamide membrane, named x-ABP-PA, wherein x is 0.5-4.

2. A process for the preparation of a 1-(2-aminoethyl) bromopyridinium quaternary ammonium nanofiltration membrane according to claim 1, characterized in that, The method comprises the following steps: 1) a certain amount of pyridine and acetonitrile are weighed and heated to reflux at a certain temperature under nitrogen atmosphere; 2) a certain amount of 2-bromoethylamine hydrobromide is slowly added into the above solution and heated for a period of time; 3) after the reaction is completed, the obtained solid is centrifuged and separated, and vacuum drying is performed to obtain 1-(2-aminoethyl) bromopyridine; 4) the polyacrylonitrile substrate is soaked in ethanol solution for a period of time; 5) the polyacrylonitrile substrate is soaked in piperazine aqueous solution, and after the excess liquid is removed, the membrane is soaked in a certain mass fraction of trimesoyl chloride / n-hexane solution; 6) the excess trimesoyl chloride / n-hexane solution is removed, and the obtained membrane is dried to obtain a polyamide membrane; 7) a certain amount of 1-(2-aminoethyl) bromopyridine is dissolved in ultrapure water of different pH to prepare a 1-(2-aminoethyl) bromopyridine aqueous solution; 8) the polyamide membrane is soaked in the 1-(2-aminoethyl) bromopyridine solution for a period of time, the excess solution is removed, and the obtained membrane is dried again to obtain a 1-(2-aminoethyl) bromopyridine quaternized nanofiltration membrane.

3. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In steps 1) and 2), 2-bromoethylamine hydrobromide: pyridine: acetonitrile = 4.0-4.5 g: 1.0-1.5 mL: 25.0-30.0 mL.

4. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In step 1), the temperature for heating to reflux is 75-85 ℃, and in step 2), the heating time is 20-26 h.

5. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In step 4), the polyacrylonitrile substrate is soaked in a 30% ethanol solution, and the soaking time is 3-5 h.

6. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In step 5), the concentration of the piperazine aqueous solution is 0.8-1.2 wt%, and the concentration of the trimesoyl chloride / n-hexane solution is 0.1-0.3 wt%.

7. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In step 7), the pH of the ultrapure water is 9-13, and the concentration of the 1-(2-aminoethyl) bromopyridine aqueous solution is 0.5-4.0 wt%.

8. The method for preparing a 1 -(2-aminoethyl) bromopyridinium quaternized nanofiltration membrane according to claim 2, characterized by: In step 3), the drying temperature is 45-65 ℃, and the drying time is 10-14 h; in step 6), the drying temperature is 50-70 ℃, and the drying time is 8-12 min; in step 8), the soaking time is 8-16 min, the drying temperature is 40-60 ℃, and the drying time is 8-12 min.

9. The 1-(2-aminoethyl) bromopyridine quaternized nanofiltration membrane of claim 1 is used for separating lithium and magnesium in brine.

10. Use according to claim 9, characterized in that, The method is as follows: in a mixed solution containing lithium and magnesium, the pH is adjusted to 7, and the 1-(2-aminoethyl) bromopyridine quaternized nanofiltration membrane of claim 1 is used for interception at room temperature.

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